PB81-112757
A Manual for the Use of Electrostatic Precipitators to Collect Fly Ash
Particles
Southern Research Inst.
Birmingham, AL
Prepared for
Industrial Environmental Research Lab.
Research Triangle Park, NC
May 1980
U.S. DEPARTMENT OF COMMERCE
National Technical Information Service
r®
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United States Industrial Environmental Research EPA-600/8-80-025
Environmental Protection Laboratory May 1980
Agency Research Triangle Park NC 27711
Research and Development PUR I—1127 ...7
c/EFA A Manual for the Use of
Electrostatic Precipitators
to Collect Fly Ash Particles
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, havtf been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the SPECIAL REPORTS series. This series is
reserved for reports which are intended to meet the technical information needs
of specifically targeted user groups. Reports in this series include Problem Orient-
ed Reports, Research Application Reports, and Executive Summary Documents.
Typical of these reports include state-of-the-art analyses, technology assess-
ments, reports on the results of major research and development efforts, design
manuals, and user manuals.
EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental Protection Agency, and
approved for publication. Approval does not signify that the contents necessarily
reflect the views and policy of the Agency, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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NOTICE
THIS DOCUMENT HAS BEEN REPRODUCED
FROM THE BEST COPY FURNISHED US BY
THE SPONSORING AGENCY. ALTHOUGH IT
IS RECOGNIZED THAT CERTAIN PORTIONS
ARE ILLEGIBLE, IT IS BEING RELEASED
IN THE INTEREST OF MAKING AVAILABLE
AS MUCH INFORMATION AS POSSIBLE.
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TECHNICAL REPORT DATA
f/'l, we read Inunctions on the re\ em be Jon' completing!
EPA--600/8-80-025
: TlTLf AND SUOTITLE
A Manual for tho Use of Electrostatic Precipitators
to Collect Fly Ash Particles
b. Ht I'OHT DATC
May 1980
7 AUTKORIS)
Jack R. McDonald and Alan H. Dean
8. PERFORMING ORGANIZATION REPORT NO.
SORI-EAS-80-066 (3540-7)
7PcH-ORMfNG ORGANIZATION NAME AND ADDRESS
Southern Research Institute
2000 Ninth Avenue, South
Birmingham, Alabama 35205
12 SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
3. F
ENT'S ACCESSION NO.
JLL27JU-
5. PERFORMING ORGAMl/AT ION CODE
10. PROGRAM ELEMENT NO.
E HE 62 4
11. CONTRACT/GRANT NO.
68-02-2114, Task 7
13. TYPE OF REPORT AND PERIOD COVERED
Task Final; 12/78-2/80
14. SPONSORING AGENCY CODE
EPA/600/13
15.SUPPLEMENTARY NOTES jjERL-RTP project officer is Leslie E. Sparks, Mail Drop 61,
919/541-2925.
6. ABSTRACT
The report incorporates the results of many studies into a manual oriented
toward the collection of fly ash particles (produced by the combustion of pulverized
coal) by electrostatic precipitation (ESP). It presents concepts, measurement tech-
niques, factors influencing ESP performance, data, and data analysis from a prac-
tical standpoint. Extensive use of data from full-size ESPs should familiarize the
user with what to expect in actual field operation. The manual covers fundamentals
of ESP, mechanical and electrical components of ESPs, factors influencing ESP per-
formance, measurement of important parameters, advantages and disadvantages of
:old-side, hot-side, and flue-gas-conditioned ESPs, safety aspects, maintenance,
roubles hooting, the use of a computer model for ESP, and features of a well-
equipped ESP. Studies considered in this report include those, by various individ-
uals and organizations, on comprehensive performance evaluations of full-scale
ESPs, in situ and laboratory measurement of fly ash resistivity, rapping reentrain-
ment, evaluations of the effects of flue gas conditioning agents on ESP performance,
fundamental operation of hot-side ESPs, basic laboratory experiments, and develop-
ment of a 'mathematical model of ESP. information from these studies can be used
by power plant personnel to select, size, maintain, and troubleshoot ESPs.
KEY WORDS AND DOCUMENT ANALYSIS
1 DESCRIPTORS
Pollution " ~~
Electrostatic Precipitation
Fly Ash
Measurement
Maintenance
Mathematical Models
^Electrical Resistivity
-STATEMENT
Release to Public
b.IDENTIFIERS/OPEN ENDED TERMS
Pollution Control
Stationary Sources
Operation
Troubleshooting
19. SECURITY CLASS (This Report)
Unclassified
20. SECURITY CLASS (This pagej
Unclassified
E'PA Form 22.J3-1 (")-7.Ti
c. COSATI HicUl/Groap
13B
13H
21B
14 B
15E
12A
20C
21. NO. OF PAGES
22. PRICE
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EPA-600/8-80-025
May 1980
A Manual for the Use of
Electrostatic Precipitators to
Collect Fly Ash Particles
by
Jack R. McDonald and Alan H Dean
Southern Research Institute
2000 Ninth Avenue, South
Birmingham, Alabama 35205
Contract No. 68-02-2114
Task No. 7
Program Element No EHE624
EPA Project Officer Leslie E. Sparks
Industrial Environmental Research Laboratory
Office of Environmental Engineering and Technology
Research Triangle Park, NC 27711
Prepared for
U S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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DISCLAIMER
This report has been reviewed by the Industrial Environmental
Research Laboratory, U.S. Environmental Protection Agency, and
approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the U.S.
Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation
for use.
11
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ABSTRACT
Recent studies performed by various individuals and organi-
zations have been directed toward obtaining a fuller and better
understanding of the application of electrostatic precipitators
to collect fly ash particles produced in the combustion of pul-
verized coal. These studies include comprehensive performance
evaluations of full-scale precipitators, in situ and laboratory
measurement of fly ash resistivity, rapping reentrainment in-
vestigations, tests to evaluate the effects of flue gas con-
ditioning agents on precipitator performance, investigations
into the fundamental operation of hot-side precipitators, basic
laboratory experiments, and development of a mathematical model
of electrostatic precipitation. As a result of these studies,
new sources of information are available that can be used by
power plant personnel as an aid in selecting, sizing, maintaining,
and troubleshooting electrostatic precipitators.
This manual brings together the results of these and previous
studies and incorporates them into a document which is oriented
toward the collection of fly ash particles by electrostatic pre-
cipitation. An attempt has been made to present concepts, mea-
surement techniques, factors influencing precipitator performance,
data, and data analysis from a practical standpoint. Extensive
use of data from full-scale precipitators should familiarize the
user with what to expect in actual field applications.
The manual covers fundamentals of electrostatic precipitation,
mechanical and electrical components of electrostatic precipitators,
factors influencing precipitator performance, measurement of im-
portant parameters, advantages and disadvantages of cold-side,
hot-side, and flue gas conditioned electrostatic precipitators,
safety aspects, maintenance procedures, troubleshooting procedures,
the usage of a computer model for electrostatic precipitation,
and features of a well-equipped electrostatic precipitator.
This manual was submitted in partial fulfillment of Task VII
of Contract No. 68-02-2114 by Southern Research Institute under
the sponsorship of the U.S. Environmental Protection Agency.
111
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CONTENTS
Disclaimer.
Abstract
Figures
Tables
Acknowledgment,
1. Introduction * 1
2. Terminology and General Design Features Associated
with Electrostatic Precipitators Used to Collect Fly
Ash Particles 4
3. Fundamental Principles of Electrostatic Precipitation. 8
General Considerations 8
Creation of an Electric Field and Corona Current.... 8
Particle Charging 12
Particle Collection 16
Removal of Collected Material. 22
4. Limiting Factors Affecting Precipitator Performance... 24
Allowable Voltage and Current Density 24
Nonideal Effects 26
Nonuniform Gas Velocity Distribution 26
Gas Sneakage 26
Particle Reentrainment 27
5. Use of Electrostatic Precipitators for the Collection
of Fly Ash 28
Reasons for Using Electrostatic Precipitators to
Collect Fly Ash 28
Design of Precipitators Used to Collect Fly Ash 29
General Description 29
Precipitator Shell 29
Electrical Sections 30
Electrical energization 30
Historical development 30
Power supplies 33
High voltage rectifiers 33
Spark-rate 33
Design and operating requirements 33
Sources of high voltage electrical equipment.. 37
Discharge electrode system 37
Geometries of discharge elctrodes 37
Types of discharge electrodes 39
New designs 47
Discharge electrode support. 47
Collecting electrode system 47
Geometries of collecting electrodes 51
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Ash Removal Designs 54
General 54
Rappers 54
New technology in rapper control 59
Hoppers 59
Removal from hoppers 67
Dust removal systems 72
Container removal 72
Dry vacuum systems 72
Wet vacuum systems 72
Screw conveyors 72
Scraper bottom 72
Gas Flow Devices 73
General 73
Straighteners 73
Splitters 76
Transformation splitters 76
Vanes 78
Diffusion plates 80
Types of Precipitators Used to Collect Fly Ash 81
Cold-side 81
Hot-side 82
Compilation of Installations Using Electrostatic
Precipitators to Collect Fly Ash 88
6. Analysis of Factors Influencing ESP Performance 89
Particle Size Distribution 89
General Discussion 89
Characterization of Particle Size Distribution.... 90
Field Methods for Measuring Particle Size
Distributions 100
General considerations in making field
measurements 100
Inertial (Aerodynamic) methods 101
Optical methods 120
Diffusional and condensation nuclei methods 124
Electrical mobility method 134
Other Specialized Particle Sizing Systems for
Field Use " 138
Respirable particle classifier (RPC) impactor... 138
Large particle sizing system (LPSS) 139
Laboratory Methods for Measuring Particle Size
Distributions 146
Sedimentation and elutriation 149
Centrifuges 151
Microscopy 156
Sieves 156
Coulter counter 158
Effect of Particle Size Distribution on ESP
Performance 158
Measured Size Distributions from Various
Installations 164
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Plant number one ..... 164
Plant, number, two. .-. • • 164
Plant number three. .. 17.7
Plant, number four* »-•;.>.... I"77
Plant" number - five.''.";. ....^ . *.....'."... .•'.". 177
Plant number .six. • • • I85
Plant number seven..., 185
Plant number eight. 185
Plant number nine. , 185
Plant number ten. 195
Plant number eleven. 195
Plant number twelve 195
Plant number thirteen 203
Plant number fourteen.. 203
Plant number fifteen... 203
Summary of Inlet Particle Size Distributions...... 203
Specific Collection Area. 213
Voltage-Current Characteristics . . • 218
Electrical Circuitry for a Precipitator 218
Measurement of Voltage-Current Characteristics.... 222
Effect of Electrode Geometry 226
Effect Due to Gas Properties 239
Effects Due to Particle-s 254
Effects Due to Chemical Conditioning Agents....... 267
Effect of Voltage-Current Characteristics on
Precipitator Performance 277
Measured Secondary Voltage-Current Data from
Full-Scale Precipitators Collecting Fly Ash 282
Measured cold-side curves 282
Plant 1 - cold-side ESPs collecting ash from
low sulfur Western coal 282
Plant 2 - cold-side ESPs collecting ash from
high sulfur Eastern coal 289
Plant 3 - cold-side ESPs collecting ash from
high sulfur Eastern coal 294
Plant 4 - cold-side ESPs collecting ash from
low sulfur Western coal 294
Plant 5 - cold-side ESP collecting ash from
medium sulfur Southeastern coal 306
Plant 6 - cold-side ESP collecting ash from
Midwestern coal 311
Plant 7 - cold-side ESP collecting ash from
low sulfur Western coal 311
Measured hot-side curves 311
Plant 8 - hot-side ESP collecting ash from
low sulfur Eastern coal 311
Plant 9 - hot-side ESP collecting ash from
low sulfur Western coal 318
Plant 10 - hot-side ESP collecting ash from
a Western power plant burning low sulfur coal. 323
vi
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Resistivity of Collected Fly Ash 323
Effect of Ash Resistivity on Precipitator
Performance 323
Measured Voltage-Current Curves Demonstrating
Back Corona 338
Factors Influencing Ash Resistivity 340
Volume and surface conduction 340
Factors influencing volume resistivity 343
Factors influencing surface resistivity 345
Combined effects of volume and surface
conduction 353
Prediction of Fly Ash Resistivity 356
Measurement of Ash Resistivity 361
Factors influencing measurement of resistivity.. 361
Particle size distribution and porosity 362
Electric field. . 362
Method of depositing ash layer 363
Thickness of ash layer 363
Time of current flow 363
Source variability 364
Methods for measuring ash resistivity 364
General considerations 364
Laboratory versus in situ measurements 365
Laboratory measurements - standard technique.. 366
Apparatus for standard technique 366
Experimental procedure for standard technique. 368
Variations for the standard technique used
in laboratory studies 370
Laboratory studies simulating flue gases
containing SOx - experimental apparatus
utilizing ASME, PTC-28, test cells 371
Experimental procedure 375
Problems encountered using SOx 375
Experiments to develop apparatus and procedure
to utilize environments containing SOx 376
Development of a radial flow test cell and
procedure - equipment 379
Test procedure 383
In situ measurements 384
In situ resistivity probes - point-to-plane
probe 386
Description of SoRI point-plane probe 390
General maintenance of SoRI point-plane
probe 392
Operation of the SoRI point-plane probe - pre-
field trip preparation 393
Operating instructions 394
Operating outline. 398
Calculations 398
Cyclone resistivity probes 404
Kevatron electrostatic precipitator analyzer.. 406
Lurgi electrostatic collection resistivity
device 409
Comparison of in situ resistivity probes 409
vii
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Limitations Due to Non-Ideal Effects 411
Gas Velocity Distribution 414
General discussion 414
Criteria for a good gas flow distribution 414
Field experience with gas flow distribution 415
Correlation of collection efficiency with gas
velocity distribution 441
Gas sneakage 446
Air flow model studies.... - 452
Basis for model studies 452
Similarity of fluid flows 454
Flow model construction f57
Instrumentation 458
Particle Reentrainment 459
Rapping reentrainment 459
Background 459
Emissions due to rapping • • 465
Summary of the results of rapping studies 493
Reentrainment from factors other than rapping... 496
Nonuniform Temperature and Dust Concentration 497
7. Emissions from Electrostatic Precipitators 499
Particulate Emissions. 499
Methods for Determination of Overall Mass
Efficiency 499
EPA Test Method 5 499
Description of Components 500
ASTM - Test Method 502
ASTM Performance Test Code 27 505
Status of Rules and Regulations Governing Par-
ticulate Matter, Sulfur Oxide, Nitrogen Oxide, and
Opacity for Coal-Fired Power Boilers in the United
States 506
Background 506
Current Status of Emission Regulations 507
Performance Evaluation 507
Discussion and Definition of Opacity 508
Relationship Between Opacity and Mass Concentra-
tion and Particle Size 511
Theoretical relationship 511
Observed relationship 513
Example of Modeling of Opacity Versus Mass at the
Exit of an Electrostatic Precipitator.... 518
Measurement of Relative Stack Emission Levels
and Opacity 518
8. Choosing an Electrostatic Precipitator: Cold-Side
Versus Hot-Side Versus Conditioning Agents 526
Advantages and Disadvantages of the Different
Precipitator Options 526
V11.1
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General Discussion 526
Cold-Side Electrostatic Precipitator 526
Hot-Side Electrostatic Precipitator 527
Cold-Side Electrostatic Precipitator with
Chemical Flue Gas Conditioning 529
Possible advantages of chemical flue gas
conditioning 529
Properties and utilization of well-known con-
ditioning agents 530
Utility utilization and capital and operating
costs of conditioning systems 534
Possible disadvantages of chemical flue gas
conditioning 535
Precipitator requirements and economic com-
parisons 536
9. Safety Aspects of Working with Electrostatic Pre-
cipitators , 543
Rules and Regulations 543
Hazards 543
Fire and Explosion Hazards 543
Electrical Shock Hazards 544
Toxic Gas Hazard 545
Other More Minor Hazards 545
10. Maintenance Procedures. 547
11. Troubleshooting 557
Diagnosis of ESP Problems 557
Available Instrumentation for Electrostatic Pre-
cipitators 559
Spark Rate Meters 559
Secondary Voltage and Current Meters 567
Opacity Meters '.,-• 573
Hopper Level Meters...... 573
12. An Electrostatic Precipitator Computer Model 575
Introduction 575
Capabilities of the Model 576
Basic Framework of the Model 577
Latest Improvements to the Model 579
Calculation of Voltage-Current Characteristics.... 579
Method for Predicting Trends Due to Particulate
Space Charge 580
Method for Estimating Effects Due to Rapping
Reentrainment 581
Empirical Corrections to No-Rap Migration
Velocities 582
User-Oriented Improvements 582
Applications and Usefulness of the Model 585
Use of the Model for Troubleshooting 585
Use of the Model for Sizing of Precipitators 591
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13. Features of a Well-Equipped Electrostatic
Precipitator 597
References ......... 599
Appendices
A. Power plant and air quality data for those plants
with electrostatic precipitators 625
B. Cascade impactor stage parameters - - Andersen
Mark III stack sampler, Modified Brink Model B,
MRI Model 1502, Sierra Model 226, and University
of Washington Mark III 680
C. Particulate matter, sulfur oxide, and nitrogen
oxide emission limits for coal-fired power boilers
in the United States. Regulations applicable to
visible emission allowed for fuel-fired boilers.... 686
D. Low temperature corrosion and fouling... 702-703
Introduction 703
Sulfuric acid occurence in flue gas..... 703
SOX, HaO, and H2SCh* equilibria.. 703
Determination of the sulfuric acid dew point... 705
Condensation characteristics 712
Factors influencing corrosion rates 715
Acid strength 715
Acid deposition rate. 720
Fly ash alkalinity 723
Hydrochloric acid 725
Fouling of low temperature surfaces 730
Laboratory corrosion studies 731
Summary of field experience and plant data 737
Methods of assessing corrosion tendencies of
flue gases 742
Introduction 742
Corrosion probes 743
Acid deposition probes 743
Gas and ash analysis 743
Summary and conclusions 744
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FIGURES
Number Page
1 General precipitator layout and nomenclature1 5
2 Typical precipitator electrical arrangements and
terminology 6
3a Region near small-radius electrode3 10
3b Electric field configuration for wire-plate
geometry 3 10
4 Experimental data showing the dependence of the
current density and electric field at the plate1*. 11
5 Electric field configuration during field
charging3 13
6a Electric field configuration and ion distribution
for particle charging with no applied field3 14
6b Electric field configuration and ion distribution
for particle charging in an applied field after
saturation charge is reached3 14
7 Particle charge vs. dia. for DOP aerosols. The
open symbols are Hewitt's (1957) data8'9 17
8 Number of charges per particle vs. the charging
field strength for PSL and PVTL particles, with
Nt = 1.5 x 1013 sec/m3.8'9 18
9 Number of charges per particle vs. the Nt product
for a 1.4 um dia. DOP aerosol. Four different
values of the charging field strength were
used8'9 19
10 Illustration of thermal expansion bearing surface
for precipitator installation2 ** 31
11 Power supply system for modern precipitators27 34
XI
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Number Page
12
13
14a
14b
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Schematic diagram - modern HV rectifier set with
SCR type automatic control for electrostatic
precipitators 2 6
Typical forms of discharge or corona electrodes27..
Rigid discharge electrode star wire3 1
Rigid discharge electrode isodyn wire3 l .
Example of weighted wire electrode system3 3
"European" discharge wire system with rigid dis-
charge' wires on a two dimensional frame3 l
"European" discharge wire system with discharge
wires strung between horizontal supports on a
three dimensional frame 31
"European" discharge wire system with discharge
wires supported off a mast3 :
"European" discharge wire system with self-
supporting rigid discharge electrodes3 1
Unitized Dura-trade rigid-type electrode3 **
Example of high-temperature support bushings35.....
Example of high- temperature support bushings3 5
Various types of collection electrodes2 3
Exclusive Wheelabrator Lurgi collecting electrodes.
The CSW, with single overlap, and the double over-
lap CSH design3 6
Typical electromagnetic rapper assembly38
Typical vibratory rapper3 9 ' u °
Mechanical-type rapper1* l
KAY-RAY fly ash control system
Level source housing - Model 7063P
Flyash level detector - Model 7316P
36
38
40
40
41
42
43
44
45
46
48
49
50
52
53
55
57
58
61
62
63
Xll
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Number Page
32 Typical hopper installation, Texas Nuclear
Division, Ramsey Engineering Co 65
33 Typical installation of detector Type CL-10DJ 68
34 Hopper level detector No. 3-3404-26 70
35 Computation of gas velocity distribution 74
36 Flow devices 75
37 Elbow loss as a function of radius ratio2 3 77
' ~\
38 Streamlined turning vane elbow2 3 79
39 Liquid S02 system1*8 83
40 Sulfur burning SC>2 system1*8 84
41 Schematic of an ESP system when a hot-side pre-
cipitator has been retrofitted to supplement the
existing cold-side precipitator2 7 85
42 Illustration of the effects of fly ash resistivity
on precipitator size for 99.5% collection effi-
ciency. Curves are plotted on the basis of actual
cubic feet per minute of gas flow. For 700°F hot-
side and 300°F cold-side temperature, the ratio of
gas flow for the same size boiler would be about
1.5. Hot-side resistivity is assumed to be not
limiting1*9 86
43 Examples of frequency or particle size distribu-
tions. D is the particle diameter50 91
44 A single particle size distribution presented in
four ways. The measurements were made in the
effluence from a coal-fired power boiler52 95
45 Size distributions plotted on log probability
paper5 3 97
46 Schematic diagram, operation of cascade impactor515. 102
47 Approximate relationship among jet diameter, number
of jets per stage, jet velocity, and stage cut
point for circular jet impactors. From Smith and
McCain51 105
48 Design chart for round impactors. (Dso = aero-
dynamic diameter at 50% cut point.) After Marple58. 106
xiii
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Number Page
49 Schematics of five commercial cascade impactors7°.. 108-109
50 Calibration of an Anderson Mark III impactor.
Collection efficieney,vs. particle size for stages
1 through 8. After Gushing, et'al6'8 110
51 Hypothetical flow through typical reverse flow
cyclone7 7.. .. 112
52 Comparison of cascade impactor stage with cyclone
collection efficiency curve78 113
53 Series cyclone used in the U.S.S.R. for sizing flue
gas aerosol particles. From Rusanov6 l 115
54 Schematic of the Southern Research Institute three
series cyclone system8 2 ,, 11-7
55 The EPA/Southern Research Institute five series
cyclone system8 ° 118
56 Laboratory calibration of the EPA/Southern Research
Institute five series cyclone system. (Flow rate
of 28.3 £/min, temperature of 20°C, and particle
density of 1 g/cm3".) 8 ° 119
57 Schematic of the Acurex-Aerotherm source assess-
ment sampling system (SASS) 8 ** 121
58 Schematic of an optical single particle counter85.. 122
59 Experimental calibration curves for two optical
particle counters. After Willeke and Liu8 7 123
60 Optical configuration for six commercial particle
counters8 8 125
61a Parallel plate diffusion battery9 2 127
61b Parallel plate diffusion battery penetration curves
for monodisperse aerosols (12 channels, 0.1 x 10 x
48 cm)92 127
62 Screen-type diffusion battery. The battery is 21
cm long, 4 cm in diameter, and contains 55, 635
mesh stainless steel screens. After Sinclair9".... 129
63 Diagram of a condensation nuclei counter. After
Haberl and Fusco9 6 131
64 Diffusion battery and condensation nuclei counter
layout for fine particle sizing106 132
xiv
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Number Page
65 Theoretical parallel plate diffusion battery
penetration curvesl °6 133
66 Particle mobility as a function of diameter for
shellac aerosol particles charged in a positive
ion field (after Cochet and Trillat3). K is the
dielectric constant of the aerosol1 °7 135
67 The electric mobility principle11 2 136
68 Flow schematic and electronic block diagram of
the Electrical Aerosol Analyser1 x " 137
69 Respirable particle classifying (RPC) impactor1:s.. 140
70 Cumulative mass loading versus particle diameter,
March 11, 1975IIS 141
71 Cumulative mass loading versus particle diameter,
March 12, 1975ll6 142
72 Cumulative mass loading versus particle diameter,
March 13, 1975116 143
73 Cumulative grain loading versus particle size116... 144
74 Large particle sizing system117 145
75 Extractive sampling system117 147
76 Block diagram of large particle sizing system117... 148
77 The Roller elutriator. After Allen119 150
78 The Banco microparticle classifier12 ° 152
79 A cut-away sketch, of the Goetz Aerosol Spectro-
meter spiral.centrifuge. In assembled form the
vertical axes (1) coincide and the horizontal
•arrows (2) coincide. After Gerber122':2 3'l2* 153
80 Cross-sectional sketch of the Stober Centrifuge.
After Stober and Flachsbart12 5 154
81 Cross-sectional sketch of a conifuge129 155
82 Three diameters used to estimate particle size in
microscopic analyses13l , 157
83 Operating principle of the Coulter Counter.
Courtesy of Coulter Electronics13 5 160
xv
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Number Page
84 Typical data for effective migration velocity
and collection efficiency as a function;:of
particle diameter13 6 .- 162
85 Effect of particle size distribution on overall
mass collection efficiency187 • 163
86 Plant 1 cumulative inlet distribution between 0.25
ym and 10.0 ym particle diameter for a cold-side
electrostatic precipitator collecting ash from a
low sulfur Western coal. 165
87 Plant 1 cumulative outlet distribution, rappers on,
for a cold-side electrostatic precipitator col-
lecting ash from a low sulfur Western coal 166
88 Plant 1 cumulative outlet distribution, rappers
off, for a cold-side electrostatic precipitator
collecting ash from a low sulfur Western coal 167
89 Plant 1, rap/no-rap fractional efficiency including
ultrafine and impactor measurements for a cold-
side electrostatic precipitator collecting ash
from a low sulfur Western coal . 168
90 Plant 2 inlet cumulative size distribution for a
cold-side electrostatic precipitator collecting
ash from a high sulfur Eastern coal 169
91 Plant 2 average inlet cumulative size distribution
for a cold-side electrostatic precipitator col-
lecting ash from a high sulfur Eastern coal 170
92 Plant 2 outlet group 1 size distribution at reduced
load and normal precipitator operation for a cold-
side electrostatic precipitator collecting ash
from a high sulfur Eastern coal ^ . .. 171
93 Plant 2 outlet group 2 size distribution with
normal operation of a cold-side electrostatic
precipitator collecting ash from a high sulfur
Eastern coal 172
94 Plant 2 outlet group 5 size distribution for a
cold-side precipitator operating at one-half
current density collecting ash from a high sulfur
Eastern coal 173
95 Plant 2 fractional efficieny, outlet group 1 for
reduced load and normal operation of a cold-side
electrostatic precipitator collecting ash from a
high sulfur Eastern coal 174
xvi
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Number Page
96 Plant 2 fractional efficiency, outlet group 2
with normal operation of a cold-side electro-
static precipitator collecting ash from a high
sulfur Eastern coal 175
97 Plant 2 fractional efficiency, outlet group 5
for a cold-side electrostatic precipitator
operating at one-half current density collecting
ash from a high sulfur Eastern coal 176
98 Plant 3 inlet cumulative size distribution for a
cold-side electrostatic precipitator collecting
ash from a high sulfur Eastern coal 178
99 Plant 3 outlet cumulative size distribution for a
cold-side electrostatic precipitator collecting ash
from a high sulfur Eastern coal 179
100 Plant 3 fractional efficiency for normal operation
of a cold-side electrostatic precipitator col-
lecting ash from a high sulfur Eastern coal 180
101 Plant 3 fractional efficiency data for normal
operating conditions obtained from both the
ultra fine system and impactors for a cold-side
electrostatic precipitator collecting ash from
a high sulfur Eastern coal 181
102 Plant 4 inlet cumulative size distribution re-
sulting from impactor measurements made on ducts
Bl and B2 of a hot-side precipitator collecting
ash from a low sulfur Eastern coal 182
103 Plant 4 outlet cumulative size distribution re-
sulting from impactor measurements made on ducts
Bl and B2 of a hot-side precipitator collecting
ash from a low sulfur Eastern coal 183
104 Plant 4 fractional efficiency data obtained with
the ultrafine sizing system and impactors for
duct Bl of a hot-side precipitator collecting
ash from a low sulfur Eastern coal, with and
without rapping 184
105 Plant 5 inlet cumulative size distribution re-
sulting from impactor measurements on a cold-
side precipitator collecting ash from a low
sulfur Western coal. 186
xvii
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Number Page
106 Plant 5 outlet cumulative size distribution re-
sulting from impactor measurements on a cold-
side precipitator collecting ash from a'-low
sulfur Western coal ,.;. . 187
107 Plant 5 fractional efficiency data obtained
with the ultrafine sizing system and impactors
under normal conditions on a cold-side precipita-
tor collecting ash from a low sulfur Western coal., 188
108 Plant 6 inlet cumulative size distribution re-
sulting from impactor measurements on a hot-side
precipitator collecting ash from a low sulfur
Western coal -. • 189
109 Plant 6 outlet cumulative size distribution re-
sulting from impactor measurements on a hot-
side precipitator collecting ash from a low sulfur
Western coal 190
110 Plant 6 fractional efficiency data obtained with
the ultrafine sizing system and impactors under
normal conditions on a hot-side precipitator
collecting ash from a low sulfur Western coal 191
111 Plant 7 inlet cumulative size distribution re-
sulting from impactor measurements on a cold-side
precipitator collecting ash from a high sulfur
coal 192
112 Plant 7 outlet cumulative size distribution re-
sulting from impactor measurements on a cold-
side precipitator collecting ash from a high
sulfur coal 193
113 Plant 8 fractional collection efficiencies for
small particle fraction obtained with Brink
impactors on a cold-side precipitator collecting
ash from a low sulfur Western coal 194
1.14 Plant 9 inlet cumulative size distribution re-
sulting from measurements with a modified Brink
impactor on a cold-side precipitator collecting
ash from a medium sulfur (1.0-1.5%) Southeastern
coal (0 and + represent different sampling
conditions) 196
115 Plant 9 outlet cumulative size distribution ob-
tained from an Anderson impactor on a cold-side
precipitator collecting ash from a medium sulfur
(1.0-1.5%) Southeastern coal 197
xviii
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Number Page
116 Plant 9 fractional efficiency measurements on
a cold-side precipitator collecting ash from a
medium sulfur (1,0-1.5%) Southeastern coal 198
117 Plant 10 fractional efficiency measurements on
a hot-side precipitator collecting ash from a
low-medium sulfur (1.0%) Western coal 199
118 Plant 11 fractional efficiency measurements on
a cold-side precipitator collecting ash from a
plant burning Midwestern coal and refuse 200
119 Plant 12 inlet cumulative size distribution ob-
tained with modified impactors on a cold-side
precipitator collecting ash from a plant burning
a high sulfur (^2.0%) Eastern coal 201
120 Plant 12 outlet cumulative size distribution ob-
tained with modified impactors on a cold-side
precipitator collecting ash from a plant burning
a high sulfur Eastern coal 202
121 Plant 13 fractional efficiency data measured by
optical and diffusional methods on a cold-side
electrostatic precipitator collecting ash from a
high sulfur (3.6%) Midwestern coal 204
122 Plant 14 fractional efficiency data obtained by
using optical, diffusional, and impactor mea-
surements performed on a pilot-scale precipitator
collecting ash from a low sulfur Western coal 205
123 Plant 15 inlet cumulative size distribution at
the conditions indicated obtained by using Brink
impactors with precollector cyclones and back-up
filters on a pilot precipitator collecting ash
from a low sulfur Western coal 206
124 Plant 15 outlet cumulative particle size dis-
tribution at the conditions indicated obtained
by using an Andersen impactor with a back-up
filter on a pilot precipitator collecting ash
from a low sulfur Western coal 207
125 Plant 15 outlet cumulative particle size dis-
tribution at the conditions indicated obtained
by using, an Andersen impactor •with a .back-up
filter on ~ pilot precipitator collecting ash
from a low sulfur Western coal 208
xix
-------
Number • Page
126 Plant 15 outlet cumulative particle size dis-
tribution at the conditions indicated obtained
by using an Andersen impactor with a back-up
filter on a pilot precipitator collecting ash
from a low sulfur Western coal.......,-.: 209
127 Plant 15 outlet cumulative particle size dis-
tribution at the conditions indicated obtained
by using an Andersen impactor with a back-up
filter on a pilot precipitator collecting ash
from a low sulfur Western coal « 210
128 Plant 15 outlet cumulative particle size dis-
tribution at the conditions indicated obtained
by using an Andersen impactor with a back-up
filter on a pilot precipitator collecting ash
from a low sulfur Western coal 211
129 Inlet size distributions of cold-side ESPs pre-
ceded by mechanical collectors 212
130 Inlet size distributions of hot-side ESP in-
stallations 214
131 Inlet size distributions of cold-side ESPs col-
lecting ashes from high sulfur and low sulfur
coals 215
132 Experimental fraction efficiency data obtained
from a laboratory precipitator collecting
dioctylphthalate (DOP) droplets under essentially
idealized conditions at two different SCAs at
two different current densities13 8 ., 216
133 Effects of SCA on overall mass collection
efficiency 217
134 Measured efficiency as a function of specific
collection area 219
135 Electrical equivalent circuit of a precipitator
electrode system with a dust layer. After
Oglesby and Nichols139 220
136 Voltage-current relationship in an ideal capacitor/
resistor parallel combination 221
137 Voltage divider network for measuring precipitator
secondary voltages and currents 223
138 Sample V-I curve data sheet 225
xx
-------
Number Page
139 Typical voltage-current curve derived experi-
mentally in a laboratory wire-duct precipitator.
After McDonald1 " 2 227
140 Theoretical curves showing the effect of wire size
on voltage-current characteristics 229
141 Theoretical curves showing the effect of plate-
to-plate spacing on voltage-current characteristics 230
142 Theoretical curves showing the effect of wire-to-
wire spacing on voltage-current characteristics.... 231
143 Theoretical curves showing the effect of wire size
on the electric field and current density 232
144 Theoretical curves showing the effect of plate-to-
plate spacing on the electric field and current
density 233
145 Theoretical curves showing the effect of wire-to-
wire spacing on the electric field and current
density 234
146 Secondary voltage-current curves obtained from the
inlet sections of several cold-side full-scale
precipitators having different electrode
geometries 236
147 Secondary voltage-current curves obtained from the
outlet sections of several cold-side full-scale
precipitators having different electrode
geometries 237
148 Sparking voltage as a. function of number of
corona wires 238
149 Effect of air pressure on sparkoyer voltage and
voltage-current characteristics 241
150 Effect of air pressure on sparkover voltage 242
151 Effect of temperature on sparkover voltage and
voltage-current characteristics1 "*6 243
152 Voltage-current curves obtained from outlet
electrical fields in several cold-side electro-
static precipitators , 245
153 Voltage-current curves obtained from outlet
electrical fields in several hot-side electro-
static precipitators 246
xxi
-------
Number
154 Influence of gas composition on the voZtage-
current characteristicsl ** 7 , 247
155 Influence of gas composition on the voltage-
current characteristics and sparkover voltages1"7.. 248
156 Influence of gas composition on the voltage-
current characteristics and sparkover voltages11*7.. 249
157a Schematic diagram of mobility tube1 **8. 251
157b Ion-current waveform obtained for E/N = 3.1 x
10~18 V'cm2, N = 8.0 x 1018 cm"3, and T = 300°K.
The waveform obtained at the second is smaller in
peak height and broader than that obtained at the
first grid because of diffusion effects. The loss
of ions to the grids under these conditions was
negligible1 " 8 251
158a Cylindrical corona discharge system for determining
effective mobility15 ° 252
158b Negative corona voltage-current characteristics for
simulated flue gas with H20 volume concentration of
1) 0,6%, 2) 8.4%, and 3) 17.8%. Solid line theory,
circles data15 ° 252
159 Schematic diagram of an in situ "ion mobility
probe" 253
160 Theoretical curves showing the effect of effective
mobility on volt age-cur rent characteristics'* 256
161 Theoretical curves showing the effect of effective
mobility on the electric field,and current
density 257
162 Collection efficiency as a function of reduced
effective ion mobility for several particle sizes.. 258
163 Secondary voltage-current curves demonstrating the
particulate space charge effect in a full-scale,
cold-side precipitator collecting fly ash 260
164 Theoretical voltage-current curves for a specific
collection area of 19.7 m2/(in3/sec) : 52 261
165 Theoretical voltage-current curves for a specific
collection area of 59.1 m2/(m3/sec):52 262
166 Theoretical voltage-current curves for a specific
collection area of 98.4 m2/(m3/sec):52 263
xxii
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Number Page
167 Comparison of theoretical voltage-current curves
for different specific collection area132 264
168 Voltage vs. current characteristic for second
field clean electrode and 1 cm layer of 1 x 10:1
ohm-cm dust 266
169 Effect on the voltage-current characteristics of
adding SO3 in the vapor state to the gas stream
at a location prior to the precipitator 268
170 Effect on the voltage-current characteristics of
adding SO3 in the vapor state to the gas stream
at a location prior to the precipitator 269
171 Current density vs. voltage for a full-scale, cold-
side precipitator without and with SO3 conditioning 271
172 Current density vs. voltage for a full-scale, cold-
side precipitator without and with NHs conditioning
low sulfur coal 273
173 Current density vs. voltage for a full-scale, cold-
side precipitator without and with NHs conditioning
high sulfur coal 274
174 Rapidity of the effect of ammonia injection on the
voltage supplied to the inlet electrical field of
a full-scale, cold-side precipitator (high-sulfur
coal) 275
175 Current density vs. voltage for a full-scale, cold-
side precipitator without and with NH3 conditioning
. (high sulfur coal) 276
176 Reduction of rapping reen.trainment by ammonia 278
177 Experimental voltage-current curves from a wire-
plate laboratory precipitator16 7 279
178 Theoretically calculated effect of current density
on overall mass collection efficiency187 281
179 Experimental fractional efficiencies and migration
velocities for negative corona with a wire of
radius 0.119 cm and gas velocity of l.."49 m/sec138.. 283
180 Measured, overall mass collection efficiencies ob-
tg--f«M frcnr fiiM-scale, cold-side precipitators
collecting fly ash plotted as a function of
specific collection area for various average
current densities. 284
xxiii
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Number Page
181 Precipitator layout for Plant 1, Unit 1... 288
182 Voltage vs. current density for left or north side
of Unit 1 precipitator of Plant 1... 290
183 Voltage vs. current density for right or south
side of Unit 1 precipitator, of Plant 1 291
184 Precipitator layout for Plant 2, Unit 4. 293
185 Voltage vs. current relationship for transformer
rectifier #3A, Plant 2 296
186 Voltaae vs. current for transformer rectifier
#1A, Plant 2 297
187 Voltage vs. current for transformer rectifier
#2A, Plant 2 298
188 Plant 3, Unit 5 precipitator layout 299
189 Secondary V-I curve for TR ABl of Unit 5 of
Plant 3 301
190 Secondary V-I curve for TR AB2 of Unit 5 of
Plant 3 302
191 Secondary V-I curve for TR B3 of Unit 5 of Plant 3. 303
192 Secondary V-I curve for TR B4 of Unit 5 of Plant 3. 304
193 Plant 4, Unit 1 precipitator layout 305
194 Secondary current-voltage relationship, Plant 4,
Unit 1, Chamber 5 308
195 Precipitator layout at Plant 5, Unit 10„ 309
196 Voltage-current relationships obtained on precipi-
tator "B", Plant 5, Unit 10 310
197 Secondary voltage vs. current curves from Plant 6.. 312
198 Voltage-current characteristics of Section IB inlet
Plant 7 314
199 Plant 8, Unit 3 precipitator configuration 315
200 V-I curves for Unit 3, Plant 8 317
xx iv
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Number Page
201 Ductwork arrangement for Plant 9, Unit 3 319
202 Chamber arrangement for Plant 9, Unit 3 320
203 Inlet voltage-current curves for Plants 9 and 8.... 321
204 Outlet voltage-current curves for Plants 9 and 8... 322
205 Voltage current-curve, Unit 3, Chambers 7 and 8,
Plant 9 (solid symbols are operating points) 324
206 Precipitator information and layout for the hot-
side Plant 10 collector 328
207 Typical secondary voltage-current curves obtained
from a hot-side ESP collecting ash from a Western
power plant burning low sulfur coal 331
208 Experimentally determined effect of resistivity
on allowable current density in a precipitator^68.. 333
209 Effect of resistivity on overall mass collection
efficiency 334
210 Measured overall mass collection efficiencies as
a function of specific collection area for cold-
side, full-scale precipitators collecting fly
ashes of various values of measured resistivity.... 335
211 Electrostatic force on the dust layer as a function
of current density for several values of re-
sistivity. . 337
212 Voltage-current curves which demonstrate the be-
havior resulting from the occurrence of back
corona 339
213 Typical temperature-resistivity relationship for
fly ash ". 341
214 Resistivity as a function of combined lithium and
sodium concentrations for a specific set of test
conditionsllz 344
215 Resistivity vs. temperature for two fly ash samples
illustrating influence of sodium content17 3 346
216 Fly,: ash resistivity as a function of environmental
water concentration for various test tempera-
tures l 7 2 348
XXV
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Number Page
217 Typical resistivity-temperature data showing the
influence of environmental water concentration172.. 349
218 Effect of S03 on resistivity172............. ....... 351
219 Resistivity as a function of environmental sulfur.
trioxide concentration for eight fly ashes172 352
220 Variation in particulate in situ resistivity with
electric field . .... 354
221 Typical resistivity values as a function of applied
ash layer electric field172 355
222 Bulk electrical resistivity apparatusf general
arrangement179 367
223 Schematic of apparatus setup for standard resis-
tivity measurements18 ° 369
224 316 stainless steel environmental resistivity
chamber181 374
225 Weight percent soluble sulfate1e 3 378
226 Combination parallel plate-radial flow resistivity
test cell and electrical circuit1 e 6 380
227 Glass environmental resistivity chamber18 7 381
228 Resistivity vs. time of environmental exposure 382
229 Point-to-plane resistivity probe189 387
230 Typical voltage-current density relationships for
point-to-plane resistivity probe19 ° 389
231 Schematic diagram of SoRI probe system191 391
232 Sample data sheet for point-plane resistivity
probe , 399
233 V-I data obtained from point-plane resistivity
probe 400
234 Two possible types of "dirty" V-I curves obtainable
with a point-plane probe 402
235 Resistivity apparatus using mechanical cyclone dust
collector (from Cohen and Dickinson) 19 2 405
xxvi
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Number Page
236 Cyclone probe inserted in duct19 3 407
237 Kevatron resistivity probe (from Tassicker,
et at) 19lt 408
238 Lurgi in situ resistivity probel9 5 410
239 Comparison of Kevatron and cyclone resistivities
with point-plane resistivities at an electric
field of 2.5 kV/cm. Settled values for cyclone
peak values for Kevatron19 6 412
240 Comparison of Kevatron and cyclone resistivities
with point-plane resistivities at an electric
field of 2.5 kV/cm. Peak current values used
for Cyclone and Kevatron19 6 413
241 Side elevation of electrostatic precipitator198.... 416
242 Gas-flow imbalance, outlet flues and i.d. fans
(Unit A) 19 8 417
243 Side elevation of i.d. fans (Unit A)198 419
244 Gas-flow patterns, plane view of outlet flues
(Unit A) 19 8 420
245 Lower precipitator inlet velocity profile duct 68
, as measured with.continuous traverse (Unit B)198... 422
246 Typical measured velocity profile, as installed—
lower precipitator inlet (Unit B) 19 8 423
247 Average inlet velocity side elevation profiles —
as installed (Unit B)1" 424
248 Average outlet velocity side elevation profiles —
as installed (Unit B) l18 426
249 Histogram analysis of upper precipitator inlet
velocity measurements (Unit B) 19 8 427
250 Histogram analysis of lower precipitator inlet
velocity measurements (Unit B) : 9 8 428
251 Vertical gas flow distribution lower precipitator
inlet — model corrected19 8 430
252 Vertical gas flow distribution lower precipitator
outlet — model corrected198 431
xxv ii
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Number Page
253 Precipitator layout for installation with -
chevron arrangement138 433
254 Precipitator layout for third gas velocity dis-
tribution analysis201 ........... .---- 439
255 Gas velocity distribution2 °: - 440
256 Precipitator layout for the fourth gas velocity
distribution analysis202.. 442
257 Gas velocity distribution (ft/min) 20* 443
258 "F" as a function of ideal efficiency and gas flow
standard deviation. • 447
259 Degradation from 99.9% efficiency with sneakage.... 450
260 Correction factor for gas- sneakage when N = 5 451
s
261 Velocity profile in hopper202 ' 453
262 Shear (parallel) rapping efficiency for various
precipitated dust layers having about 0.2 grams of
dust per square inch as a function of maximum
acceleration in multiples of "g". Curve (1) fly
ash, 70° to 300°F, power off. Curve (2) fly ash,
300°F, power on. Curve (3) cement kiln feed, 70°F,
power off. Curve (4) cement kiln feed, 200 or 300°F,
power on. Curve (5) fly ash, 70°F, power on. Curve
(6) cement kiln feed, 70°F, power on*08 462
263 Rapping efficiency for a precipitated layer of
copper ore reverberatory furnace dust, rapped with
a ballistic pendulum having an energy of 0.11 foot-
pound, at various temperatures2 °8 463
264 Block diagram of experimental layout for a rapping
reentrainment study ° 466
265 Near full-scale pilot precipitator at FluiDyne
Engineering2 ° 471
266 FluiDyne pilot precipitator2 ° 472
267 Average efficiencies for FluiDyne pilot precipita-
tor for various rapping intervals20 474
268 Dust removal efficiency versus the time interval
between raps2 ° 475
xxviii
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Number Page
269 Cumulative percent distribution for rapping
puffs, rapping intervals of 12, 32, and 52
minutes, pilot test20 477
270 Spatial distribution of particles in rapping puff20 478
271 Rapping puffs at the exit plane of the pilot
precipitator, upstream and downstream raps20. 479
272 Events for test period Plant I217 485
273 Particles per minute vs. time for large particle
system on August 6, 1975 — rappers on (Plant
I)217 486
274 Particles per minute vs. time for large particle
system on August 7, 1975 — rappers off (Plant
1) 217 487
275 Plant 1 rap-no-rap fractional efficiency including
ultrafine and impactor measurements2 17 488
276 Rap-no-rap ultrafine and impactor fractional
efficiency. Normal current density, Plant 2215.... 489
277 Ultrafine and impactor rap-no-rap fractional
efficiencies, Duct Bl, Plant No. 4, with 50%
confidence intervals2 1 7 491
278 Measured rapping emissions versus calculated par-
ticulate removal by last field19 492
279 Apparent rapping puff size distribution for six
full-scale precipitators19 494
280 Average rapping puff size distribution for six
full-scale precipitatorsl 9. 495
281 The EPA Method 5 particulate sampling train222 501
282 ASTM-type particulate sampling train2 2 7 504
283 Schematic of a transmissometer showing projection
and view angles which must be no greater than 5°
. for EPA compliance2 3 3. . 510
284 Effluent transmittance vs. in stack transmittance
for varying ratios of stack exit diameter to in
stack path length: A = 1/4, B = 1/2, C = 3/4,
D = 1, E = 4/3, F = 2, G = 4237 512
xx ix
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Number Page
285 Parameter K as a function of the log-normal
size distribution parameters for a white aerosol
after Ensor and Pilat2 3 9 514
286 Parameter K as a function of the log-normal
size distribution parameters for a black aerosol
after Ensor and Pilat239.................. 515 -
287 Correlation data between opacity and mass measure-
ments of particulate matter in emissions from a
coal-burning power plant. After Nader21*7 517
288 Optical assembly diagram of a nephelometer used in
stack monitoring. The scattering angle 6, for any
light ray from the source,, is the angle between the
ray and the horizontal line a. From Ensor and
Sevan2 k 8 520
289 Optical diagram of the PILLS V instrument. From
Schmitt, et al2 5 2 521
290 Schematic of Laser-TV monitor. After Tipton253.... 523
291 Dewpoint curve for suIfuric acid in the presence
of 10% water vapor 533
292 Effect of specific collection area on overall mass
collection efficiency (curves based on a fractional
gas sneakage of 0.05 and a normalized standard of
deviation of gas velocity distribution of 0.25).... 537
293 Schematic of Enviornecs Automatic Voltage Control
Unit2 8 3 564
294 Typical response to spark2 8 3 - 565
295 Diagram of a Wahlco automatic voltage control
unit2 e 3 , 566
296 Connection diagram for the external connections to
A.V.C. self-contained spark rate meter283 568
297 Block diagram saturable core reactor-type system283 569
298 Block diagram Thyristor-type system283 570
299 Average rapping puff size distribution and log-
normal approximation for six full-scale precipi-
tators. These data are a result of work sponsored
by the Electric Power Research Institute19 583
XXX
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Number Page
300 Empirical correction factors for the "no-rap"
migration velocities calculated from the mathe-
matical model. This work was sponsored by the
Electric Power Research Institute19 584
301 Equilibrium conversion of S02 to S03 704
302 Equilibrium conversion of S03 to HaSOi* at 8.0
volume % H20 in flue gas 706
303 Dew point and condensate composition for vapor
mixtures of H20 and H2SOi» at 760 mm Hg total
pressure (Abel and Greenewalt) 2" 708
304 H2SOtf dew points for typical flue gas moisture
concentrations 709
305 H2SOi» dew points obtained by various investi-
gators 713
306 Percent H2SO^ available for condensation for flue
gas of 100 ppm H2SO.» and 10% H20 vapor (calculated
from Figure 303) 714
307 Variation in condensation rate with surface
temperature (From H. D. Taylor)311* 716
308 Equilibrium sulfuric acid condensate composition... 718
309 Corrosion of steel in flue gas as a function of
calculated H^Oi* condensate strength (corrosion
data from Piper and Van Vliet; H2SOi, data from
Greenewalt) 3ls/299 719
310 Corrosion of steel as a function of H2SOi( concen-
tration at 23.4°C (75°F)91S 721
311 Variation of condensation and corrosion with
surface temperature (data from Thurlow)317 722
312 Variation in rate of acid buildup (RBU) and excess
cation content of fly ash as a function of surface
temperature. Coal contains 7% sulfur with 3%
excess 02 (data from Lee) 3 °7 724
313 Consumption of the available base on fly ash as a
function of the concentration of neutralizing acid
in flue gas with 5 gr/scf fly ash...... 726
xxx i
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Number Page
314 The effect of chlorine addition on corrosion of
mild steel in a synthetic flue gas (fr.om R. W.
Rear) 321 y 729
315 Schematic diagram of apparatus us6 734
xxxii
-------
TABLES
Number Page
1
2
3
4
5
6
7
8
9
10.
11
12
13
14
15
Design and Operation Requirements for Modern HV
Electrical Equipment in Electrostatic Precipi-
tation26
Specifications for Texas Nuclear Detector and
Source and Source Heads
Specifications for United Conveyor Corporation
Hopper Level Detector
Electrical Specifications for Point Control and
Continuous Control Models of PRTMCO
Hot-Side Precipitation Installations'* 9
Summary of Nomenclature Used to Describe Particle
Size Distributions Si
Commercial Cascade Impactor Sampling Systems89
Characteristics of Commercial, Optical, Particle
Counters 8 9
Comparison Table of Common Sieve Series : 3 2
Reduced Effective Negative Ion Mobilities for
Various Gas Compositions
As Received, Proximate Chemical Analyses of Coal
Samples from Cold-Side and Hot-Side Units
Chemical Analyses of Ash Samples from Cold-Side
and Hot-Side Units
Gas Analyses, from Cold-Side and Hot-Side Units
Average Electrical Readings, Plant 1
Average Electrical Operating Conditions during
Sampling Periods
•"
35
66
69
71
87
93-94
107
126
159
255
285
286
287
292
295
XXXlll
-------
Number Page
16 Averages of Hourly Electrical Readings Plant 3,
"B" Side of Precipitator 5 . . 3°°
17 Operating Secondary Voltages and Currents Daily
Averages, Unit 1, Chamber 5 307
18 Voltage-Current Operating Data 313
19 Average Electrical Operating Conditions (Plant 8).. 316
20 Averages of Hourly Meter Readings, Chambers 7
and 8 325-327
21 Hot-Side, Plant 10, Secondary Voltage-Current
Readings 329-330
22 Coal and Flue Analyses Obtained from Utilities
Industry Survey 342
23 As-received, Ultimate Coal Analysis and Coal Ash
Analysis Used in Prediction of Fly Ash Resis-
tivity 358
24 Calculation of Stoichiometric Flue Gas from Coal
Analysis177 359
25 Conversion of Weight Percent Analysis of Coal Ash
to Molecular Percent as Oxides 360
26 Resistivity Test Procedures Comparison of Certain
Features Used by Various Laboratories » . 372-373
27 Resistivity Probe - Pre-field Trip Inspection
Check List 395
28 Velocity Distribution from Unit A of Chevron
Arrangement » 435-436
29 Statistical Evaluation of Velocity Distribution
from Unit A of Chevron Arrangement. 437
30 Particle Properties and Precipitator Design Factors
which Affect Reentrainment2°9 464
31 Result from Pilot-Scale Rapping Experiments 473
32 Summary of Results from EPRI Tests217 481
33 Summary of Reentrainment Results217 482
xxxiv
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Number Page
34 Typical Flue Gas and Ash Compositions2: 7 484
35 Sampling Systems for Testing by EPA Method 5226 503
36 Physical Properties of Conditioning Agents 531
37 Design Parameters for Different Precipitator
Options and Operating Conditions on an 800 MW
Unit 540
38 Total Fixed Investment of Precipitator Options
Under Different Operating Conditions for an
800 MW Unit ($1000) 542
39 Initial Electrostatic Precipitator Start-Up Pro-
cedure and Inspection2 7 "* 548-549
40 Typical Maintenance Schedule27If'275'27S 550-552
41 Most Common Maintenance Problems279 553
42 Power Plant Electrostatic. Precipitator Maintenance
Problems 279 554
43 Trouble Shooting Chart277 560-562
44 Power Plant and Air Quality Data for Those Plants
with Electrostatic Precipitators 626-643
45 Power Plant and Air Quality Data for Those Plants
with Electrostatic Precipitators 644-661
46 Power Plant and Air Quality Data for Those Plants
with Electrostatic Precipitators 662-679
47 Cascade Impactor Stage Parameters Anderson Mark III
Stack Sampler 681-685
48 Particulate Matter, Sulfur Oxide, and Nitrogen
Oxide Emission Limits for Coal-fired Power
Boilers in the United. States '' 2 687-692
48a Counties of California-Emission Regulations for
Power Plants 693-696
49 Regulations Applicable to Visible Emissions Allowed
for Fuel-Fired Boilers 697-701
50 Composition,, Percent by Weight, Spectrographic
Analysis of Specimens Tested (from Piper and
Van Vliet) 3:5 717
XXXV
-------
Number Page
51 Sulfur and Chlorine Concentrations in Flue Gas
(from Halstead) 3 2 ° 728
52 Fly Ash Properties 732
53 Corrosion Rate Experiments 735
54 Properties of Flue Gas and Fly Ash for Various
Coal-Fired Boilers "738
XXXVI
-------
SECTION 1
INTRODUCTION
Recent studies performed by various individuals and organi-
zations have been directed toward obtaining a fuller and better
understanding of the application of electrostatic precipitators
to collect fly ash particles produced in the combustion of pul-
verized coal. These studies include comprehensive performance
evaluations of full-scale precipitators, in situ and laboratory
measurement of fly ash resistivity, rapping reentrainment in-
vestigations, tests to evaluate the effects of flue gas con-
ditioning agents on precipitator performance, investigations
into the fundamental operation of hot-side precipitators, basic
laboratory experiments/ and development of a mathematical model
of electrostatic precipitation. As a result of these studies,
new sources of information are available that can be used by
power plant personnel as an aid in selecting, sizing, maintaining,
and troubleshooting electrostatic precipitators.
The purpose of the present work is to bring together the
results of these and previous studies and to incorporate them
into a document which is oriented toward the collection of fly
ash particles by electrostatic precipitation. Since the scope
and detail of this document are rather extensive, an expanded
table of contents has been provided for use in retrieving in-
formation on specific topics contained in the text. It is
suggested that the user familiarize himself with the table of
contents so that he can use the text in the most effective
manner when addressing specific needs. An attempt has been
made to present concepts, measurement techniques, factors in-
fluencing precipitator performance, data, and data analysis from
a practical standpoint. Theoretical developments and equations
have been avoided where possible. Therefore, discussions, de-
scriptions, and data from small-scale and full-scale precipitators
have been stressed in illustrating many of the important con-
siderations associated with electrostatic precipitators. The
extensive use of data from full-scale precipitators should
familarize the user with.what no expect in actual field appli-
cations.
In the text, Sections 2-5 deal primarily with the basic
components of electrostatic precipitators and with the funda-
mental principles of electrostatic precipitation in order to
-------
establish the framework for ensuing discussions. The basic
mechanical and electrical components associated with electro-
static precipitators are discussed with respect to their functions
and various designs. The fundamental steps in electrostatic pre-
cipitation involving the maintainence of an electric field and
corona current, particle charging, particle transport to the
collection electrodes, and removal of particles from the collec-
tion electrodes are discussed in:sufficient detail to provide
an understanding of the importance of the various physical
mechanisms and of the factors affecting these mechanisms.
Limiting factors affecting electrostatic precipitator perfor-
mance are discussed in order to familiarize the reader with
effects that result in less than optimal performance. The types
of electrostatic precipitators presently used to collect fly ash
particles are described briefly. These include cold-side, hot-
side, and flue gas conditioned electrostatic precipitators. A
compilation of installations in the U<,S. using electrostatic
precipitators to collect fly ash particles has been prepared.
This compilation includes coal, boiler, and electrostatic pre-
cipitator data for each installation. .
In Section 6, factors influencing electrostatic precipitator
performance, along with measurement techniques and .-experimental
data, are discussed extensively. These factors include particle
size distribution, specific collection area, voltage-current
characteristics, resistivity of the collected fly ash, and non-
ideal effects such as nonuniform gas velocity distribution, gas
bypassage of electrified regions (sneakage), and particle reentrain-
ment. Methods and instrumentation for measuring particle size dis-
tributions, voltage-current characteristics, fly ash resistivity,
gas velocity distribution, gas sneakage, and rapping reentrainment
are described in detail. Methods of interpretation and analysis
of the data obtained from the various types of measurements are
discussed.
Since the particulate emissions from an electrostatic pre-
cipitator must meet mass and opacity standards, it is important
to be familiar with methods for measuring these quantities.
Section 7 deals with the different methods for measuring mass
and opacity. The dependence of opacity on mass and particle
size distribution is discussed.'
The material in Section 8 is intended to be used as a guide
in selecting the type of electrostatic precipitator which is
best suited from a cost and reliability standpoint for a parti-
cular application. The advantages and disadvantages of cold-side,
hot-side, and flue gas conditioned electrostatic precipitators
are discussed. Estimates are made of the costs for the different
options when treating ashes with low, moderate, and high resis-
tivities.
-------
Sections 9, 10, and 11 deal with effective utilization of
electrostatic precipitators by discussing safety considerations,
maintenance procedures, and troubleshooting of problems, respec-
tively. Since serious accidents can occur when working with
electrostatic precipitators, it is important to be aware of the
hazards involved and to take the proper precautions. Following
proper maintenance procedures will result in better precipitator
performance over the long term, fewer operating problems, less
down time, and longer life of certain components. Many electro-
static precipitator problems can be diagnosed and corrected by
using appropriate troubleshooting procedures. The equipping of
an electrostatic precipitator with instrumentation which is
helpful in troubleshooting of problems is discussed.
Since it has been shown that a computer model, which has
been developed under the sponsorship of the U.S. Environmental
Protection Agency, can be used to advantage in predicting elec-
trostatic precipitator performance as a function of the operating
parameters, Section 12 discusses this approach. The capabilities
of the modeling approach are stressed. The applications and
usefulness of the model are discussed extensively. Applications
include predictions of efficiency as a function of particle size
distribution, specific collection area, electrical operating con-
ditions, and nonideal conditions. These applications are in-
corporated into useful procedures for troubleshooting and sizing
electrostatic precipitators.
Section 13 points out features that a well-equipped elec-
trostatic precipitator should possess. These features are a
natural consequence of the preceding material in the manual.
These features are intended to yield flexibility, reliability,
ease in analysis of precipitator performance, and, ultimately,
the best possible precipitator performance.
-------
SECTION 2
TERMINOLOGY AND GENERAL DESIGN FEATURES ASSOCIATED
WITH ELECTROSTATIC PRECIPITATORS USED TO
COLLECT FLY ASH PARTICLES
An electrostatic precipitator (ESP) is a device which is
used to remove suspended particulate matter from industrial pro-
cess streams. Dry electrode, parallel ;plate electrostatic
precipitators are used by the electric utility industry to
remove fly ash particles from the effluent -gas produced in the
combustion of coal. Figure 1 shows a schematic diagram of a
wire-plate electrostatic precipitator.1 Although the details
of construction will vary from one manufacturer to another,
the basic features are the same. ,
Since uniform, low turbulence gas flow is desirable in the
collection regions of a precipitator, several devices may be em-
ployed to achieve good gas flow quality before the gas is treated.
Turning or guide vanes are used in the duct work prior to the pre-
cipitator in order to preserve gas-flow patterns following a sharp
turn or sudden transition. This prevents the introduction of un-
due turbulence into the gas flow. Plenum chambers and/or diffusion
screens (plates) are used to achieve reduced turbulence and im-
proved uniformity of the gas flow in expansion turns or transitions
prior to the gas treatment regions of the precipitator.
The gas entering the treatment regions of the precipitator
flows through several passage ways (gas passages) formed by plates
(collection electrodes) which are parallel to one another. A
series of discharge electrodes is located midway between the
plates in each gas passage. High voltage electrical power supplies
provide the voltage and current which are needed to separate the
particles from the gas stream. The discharge electrodes are held
at a high negative potential with the collection electrodes grounded.
A precipitator may be both physically and electrically section-
alized. Figure 2 shows two possible precipitator layouts with the
terminology concerning sectionalization.2 A chamber is a gas-
tight longitudinal subdivision of a precipitator. A precipitator
without any internal dividing wall is a single chamber precipitator.
A precipitator with one dividing wall is a two-chamber precipitator,
etc. An electrical field is a physical portion of a'precipitator
that is energized by a single power supply. A bus section is the
-------
RAPPER INSULATOR
Ul
BUS DUCT
TRANSFORMER
RECTIFIER
INSULATOR COMPARTMENT
GAS FLOW
DIFFUSOR
PERFORATED
PLATES
GAS
DISTRIBUTION
DEVICE
COLLECTING SURFACE
X.
GAS PASSAGE
DISCHARGE ELECTRODE
HOPPER
HIGH VOLTAGE SYSTEM
SUPPORT INSULATOR
COLLECTING SURFACE
RAPPER
DISCHARGE ELECTRODE
RAPPER
TURNING VANES
TURNING VANES
3646-001
Figure 1. General precipitator layout and nomenclature.1
-------
TRANSFORMER/RECTIFIER
. BUS SECTIONS
INTERNAL PARTITION
BUS SECTIONS
CHAMBERS
GAS FLOW
CHAMBERS
FIELDS
CASE 1: 1 PRECIPITATOR, 2 CHAMBERS, 12 BUS SECTIONS, 6 POWER SUPPLIES, 3 FIELDS
TRANSFORMER/RECTIFIER
B'US SECTIONS
INTERNAL PARTITION
BUS SECTIONS
CHAMBERS
GAS FLOW
FIELDS
CHAMBERS
3540-00:
CASE II: 1 PRECIPITATOR, 2 CHAMBERS, 12 BUS SECTIONS, 12 POWER SUPPLIES, 3 FIELDS
Figure 2. Typical precipitator electrical arrangements
and terminology.2
-------
smallest portion of an electrostatic precipitator which can be
deenergized independently. An electrical field may contain two
or more bus sections. Electrical fields in the direction of gas
flow may be physically separated in order to provide internal
access to the precipitator.
The material which is collected on the collection and discharge
electrodes is removed by mechanical jarring (or rapping). Devices
called rappers are used to provide the force necessary to dislodge
the collected material from the electrode surfaces. Rappers may
provide the rapping force through impact or vibration of the elec-
trodes. The material which is dislodged during rapping falls under
the influence of gravity. A certain amount of the material dislodged
during rapping falls into hoppers which are located below the
electrified regions. Material collected in the hoppers is trans-
ported away from the precipitator in some type of disposal process.
Portions of the gas flowing through a precipitator may pass
through regions below and above the collection electrodes where
treatment will not occur. Normally, baffles are located in the
region below the collection electrodes. These baffles redirect
the gas flow back into the treatment region and prevent the dis-
turbance of the material collected in the hoppers.
-------
SECTION 3
FUNDAMENTAL PRINCIPLES OF ELECTROSTATIC PRECIPITATION
GENERAL CONSIDERATIONS
The electrostatic precipitation process involves several com-
plicated and interrelated physical mechanisms: the creation of a
nonuniform electric field and ionic current in a corona discharge;
the ionic and electronic charging-' of particles moving in combined
electro- and hydro-dynamic fields; and, the turbulent transport of
charged particles to a collection surface. In many practical appli-
cations, the removal of the collected particulate layer from the
collection surface presents a serious problem since the removal, pro-
cedures introduce collected material back into the gas stream and
cause a reduction in collection efficiency. Other practical con-
siderations which reduce the collection efficiency are nonuniform
gas velocity distribution, bypassage of the electrified regions by
particle-laden gas, and particle reentrainment during periods when
no attempt is being made to remove the collected material. In
certain applications, the flue gas environment and fly ash com-
position are such that the collected particulate layer limits the
maximum values of useful voltage and current.
CREATION OF AN ELECTRIC FIELD AND CORONA CURRENT
The first step in the precipitation process is the creation
of an electric field and corona current. This is accomplished by
applying a large potential difference between a small-radius elec-
trode and a much larger radius electrode, where the two electrodes
are separated by a region of space containing an insulating gas.
For industrial applications, a large negative potential is applied
at the small-radius electrode and the large-radius electrode is
grounded.
At any applied voltage, an electric field exists in the inter-
electrode space. For applied voltages less than a value referred to
as the "corona starting voltage", a purely electrostatic field is
present. At applied voltages above the corona starting voltage,
the electric field in the vicinity of the small-radius electrode
is large enough to produce ionization by electron impact. Between
collisions with neutral molecules, free electrons are accelerated
to high velocities and, upon collision with a neutral molecule,
their energies are sufficiently high to cause an electron to be
8
-------
separated from a neutral molecule. Then, as the increased number
of electrons moves out from the vicinity of the small-radius elec-
trode, further collisions between electrons and neutral molecules
occur. In a limited high electric field region near the small-
radius electrode, each collision between an electron and a neutral
molecule has a certain probability of forming a positive molecular
ion and another electron, and an electron avalanche is established.
The positive ions migrate to the small-radius electrode,,,and the
electrons migrate into the lower electric field regions toward the
large-radius electrode. These electrons quickly lose much of their
energy and, when one of them collides with a neutral electro-
negative molecule, there is a probability that attachment will
occur and a negative ion will be formed. Thus, negative ions,
along with any electrons which do not attach to a neutral mole-
cule, migrate under the influence of the electric field to the
large-radius electrode and provide the current necessary for the
precipitation process.
Figure 3-a is a schematic diagram showing the region very
near the small-radius electrode where the current-carrying nega-
tive ions are formed.3 As these negative ions migrate to the
large-radius electrode, they constitute a steady-state charge
distribution in the interelectrode space which is referred to as
an "ionic space charge". This "ionic space charge" establishes
an electric field which adds to the electrostatic field to give
the total electric field. As the applied voltage is increased,
more ionizing sequences result and the "ionic space charge" in-
creases. This leads to a higher average electric field and cur-
rent density in the interelectrode space.
Figure 3-b gives a qualitative representation of the electric
field distribution, and equipotential surfaces in a wire-plate
geometry which is commonly used',:5 Although the electric field
is very nonuniform near the wire, it becomes essentially uniform
near the collection plates. The current density is very nonuni-
form throughout the interelectrode space and is maximum along a
line from the wire to the plate. Figure 4 contains experimental
data showing the positional dependence of the current density and
electric field at the plate.1* The data were taken under laboratory
conditions with positive corona in ambient air at an applied volt-
age of 26 kV. The geometry consisted of a wire radius of 0.15 mm,
plate-to-plate spacing of 23 cm, and a wire-to-wire spacing of
10 cm. In Figure 4, corona wires are located directly across
from the points X = -0.1, 0, and 0.1 m at the plate. Positions
x = -0.05 and 0.05 m correspond to positions at the plate, midway
between corona wires. The data show both the current density and
electric field at the plate to be maximum directly across from a
corona wire. Although the degree of uniformity of the electric
field and current density distributions will vary for different
electode geometries, the general features will be the same as
those of a wire-plate geometry-
-------
SMALL-RADIUS ELECTRODE AT
HIGH NEGATIVE POTENTIAL
REGION Of ELECTRON AVALANCHE
WHERE POSITIVE IONS AND ELECTRONS
ARE PRODUCED
REGION OF IONIZATION WHERE ELECTRONS
ATTACH TO NEUTRAL MOLECULES TO
FORM NEGATIVE IONS
Figure 3-a. Region near small-radius electrode.
SMALL-RADIUS ELECTRODE AT
HIGH NEGATIVE POTENTIAL
ELECTRIC FIELD
LINES
V
EQUIPOTENTIAL
SURFACES
IONS WHICH CONSTITUTE A CURRENT
AND A SPACE CHARGE FIELD
\
GROUNDED LARGE-
RADIUS ELECTRODE
3640-OOS
Figure 3-b. Electric field configuration for wire-plate
geometry.3
10
-------
0.07
0.06
0.05
I
< 0.04
O 0.03
Ul
X
tc.
0.02
0.01
THEORETICAL
i TASSICKER MEASURED
•0.06
0.0
DISPLACEMENT,
3.0
2.0
1.0
X
<
Q
OC
0.05
3540-305
Figure 4. Experimental data showing the dependence of the
current density and electric field at the plate.1*
11
-------
In order to maximize the collection efficiency obtainable
from the electrostatic precipitation process, the highest possible
values of applied voltage and current density should be employed.
In practice, the highest useful values of.applied voltage and
current density are limited by either electr.ical breakdown of the
gas throughout the interelectrode space, or of the gas in the col-
lected particulate layer. High values of applied voltage and
current density are desirable because o.f their beneficial effect
on particle charging and particle transport to the collection
electrode. In general, the voltage-current characteristics of
a precipitator depend on the geometry of the electrodes, the
composition, temperature, and pressure of the gas, the particu-
late mass loading and size distribution, and the resistivity of
the collected particulate layer. Thus, maximum values of voltage
and current can vary widely from one precipitator to another and
from one application to another.
PARTICLE CHARGING
Once an electric field and current density are established,
particle charging can take place. Particle charging is essential
to the precipitation process because the electrical force which
causes a particle to migrate toward the collection electrode is
directly proportional to the charge on the particle. The most
significant factors influencing particle charging are particle
diameter, applied electric field, current density, and exposure
time.
The particle charging process can be attributed mainly to two
physical mechanisms, field charging and thermal charging:5'6'7
(1) At any instant in time and location in"space near a par-
ticle, the total electric field is the sum of the electric field
due to the charge on the particle and the applied electric field.
In the field charging mechanism, molecular ions are visualized
as drifting along electric field lines. Those ions moving toward
the particle along electric field lines which intersect the par-
ticle surface impinge upon the particle surface and place charge
on the particle.
Figure 5 depicts the field charging mechanism during the
time it is effective in charging a particle.3 In this mechanism,
only a limited portion of the particle surface (0<6<]I) can suffer
— 2
an impact with an ion and collisions of ions with other portions
of the particle surface are neglected. Field charging takes place
very rapidly and terminates when sufficient charge (the saturation
charge) is accumulated to repel additional ions. Figure 6-b
depicts the electric field configuration once the particle has
attained the saturation charge.3 In this case, the electric
field lines are such that the ions move along'them around the
particle.
12
-------
X, Z, e • SPHERICAL COORDINATE SYSTEM
NEGATIVELY CHARGED PARTICLE
ELECTRIC FIELD LINES
3640-004
Figure 5. Electric field configuration during field charging.
13
-------
NEGATIVE IONS
X, 2 - COORDINATE AXES
NEGATIVELY CHARGED
PARTICLE
ELECTRIC FIELD LINES
Figure 6-a. Electric field configuration and ion distribution
for particle charging with no applied field.3
X, Z - COORDINATE AXES
PARTICLE HAS SATURATION CHARGE
©-
3640-005
Figure 6-b.
Electric field configuration and ion distribution
for particle charging in an applied field after
saturation charge is reached.
14
-------
Theories based on the mechanism of field charging agree rea-
sonably well with experiments whenever particle diameters exceed
about 0.5 ym and the applied electric field is moderate to high.
In these theories, the amount of charge accumulated by a particle
depends on the particle diameter, applied electric field, ion
density, exposure time, ion mobility, and dielectric constant of
the particle.
(2) The thermal charging mechanism depends on collisions
between particles and ions which have random motion due to their
thermal kinetic energy. In this mechanism, the particle charging
rate is determined by the probability of collisions between a
particle and ions. If a supply of ions is available, particle
charging occurs even in the absence of an applied electric field.
Although the charging rate becomes negligible after a long period
of time, it never has a zero value as is the case with the field
charging mechanism. Charging by this mechanism takes place over
the entire surface of the particle and requires a relatively long
time to produce a limiting value of charge.
Figure 6-a depicts the thermal charging process in the absence
of an applied electric field.J In this case, the ion distribution
is uniform around the surface of the particle and each element of
surface area has an equal probability of experiencing an ion col-
lision. Thermal charging theories which neglect the effect of
the applied electric field adequately describe the charging rate
over a fairly broad range of particle sizes where the applied
electric field is low or equal to zero. In addition, they work
well for particles less than 0.1 um in diameter regardless of
the magnitude of the applied electric field.
Figure 6-b depicts the thermal charging process in the pre-
sence of an applied electric field after the particle has attained
the saturation charge determined from field charging theory.3 The
effect of the applied electric field is to cause a large increase
in ion concentration on one side of the particle while causing
only a relatively small decrease on the other side. Although the
ion concentration near the surface of the particle becomes very
nonuniform, the net effect is to increase the average ion con-
centration, the probability of collisions between ions and the
particle, and the particle charging rate.
In thermal charging theories, the amount of charge accumu-
lated by a particle depends on the particle diameter, ion density,
mean thermal velocity of the ions, absolute temperature of the gas,
particle dielectric constant,, residence time, and the applied elec-
tric field. The effect of the applied electric field on the thermal
charging process must be taken into account for fine particles
having diameters between 0.1 and 2.0 ym. Depending most importantly
on the applied electric,field and to a lesser extent on certain
other variables, particles in this size range can acquire values
of charge which are 2-3 times larger than that prediced from either
15
-------
the field or the thermal charging theories. For these particles,
neither field nor thermal charging predominates and both mechanisms
must be taken into account simultaneously.
Figures 7, 8, and 9 contain experimental data8'9 showing the
dependence of particle charge on the variables which are most im-
portant in the charging process. These variables are the particle
diameter (d), charging electric field strength (E), and ion density-
residence time product (Nt) . The data were obtained under laboratory
conditions using dioctyl phthalate (DQP), polyvinyltoluene latex
(PVTL), and polystyrene latex (PSL) particles ranging in diameter
from 0.109 to 7 ym. In the data shown here, the particles were
charged by positive ions formed in a corona discharge in ambient
air. In electrostatic precipitators used to collect fly ash par-
ticles, the average values of E and Nt are approximately in the
ranges of 1.5-4.5 kV/cm and 0.1-1.0 x 1011* sec/m3, respectively.
The data clearly show that particle charge can be increased by in-
creasing d, E, and Nt. However, for a fixed value of E, increasing
Nt beyond a certain value will not result in a significant increase
in charge on a particle with a given diameter.
In most cases, particle charging has a noticeable effect on
the electrical conditions in a precipitator. The introduction of
a significant number of fine particles or a heavy concentration of
large particles into an electrostatic precipitator significantly
influences the voltage-current characteristic. Qualitatively, the
effect is seen by an increased voltage for a given current compared
to the particle-free situation. As the particles acquire charge,
they must carry part of the current but they are much less mobile
than the ions. This results in a lower "effective mobility" for
the charge carriers and, in order to obtain a given particle-free
current, higher voltages must be applied to increase the drift
velocities of the charge carriers and the ion densities.
The charged particles, which move very slowly, establish a
particulate space charge in the interelectrode space. The distri-
bution of the particulate space charge results in an electric field
distribution which adds to the electric fields due to the electro-
static field and the ionic field to give the total electric field
distribution. It is important to consider the space charge re-
sulting from particles because of its influence on the electric
field distribution, especially the electric field near the collec-
tion plate, The electric field at the plate for a given current
is higher in the particle containing case than in the particle-
free case. The particulate space charge is a function of position
along the length of the precipitator since particle charging and
collection are a function of length.
PARTICLE COLLECTION
As the particle-laden gas moves through a precipitator, each
charged particle has a component of velocity directed towards the
collection electrode. This component of velocity is called the
16
-------
UJ
O
cc
y
i—
c:
• O0.6 kV/cm
AA3.6 kV/cm
• Q7.5 kV/cm
0.1
PARTICLE DIAMETER, jum
Figure 7. Particle charge vs. dia. for OOP aerosols. The
open symbols are Hewitt's (1957) data.8'9
17
-------
500
200
to
"c
3
£ 50
c
1
"o>
LU 20
-------
800
600
« 500
400
emen
w
0
o
LJ
O 200
I
O
u
o
I 100
80
60
i i
° — Q-
,
E» 2.0X10* V/m
a"
E»6.0XI0V/m
O—-O" 0 O—O
11
10
Fig:ur.e\9. Number-o-f. charges per particle vs. the Nt product
for a 1.4 Tim dia. DOP aerosol.. Four different
values of the charging field strength were used.8'9
19
-------
electrical drift velocity, or electrical migration velocity, and
results from the electrical and viscous drag forces acting upon a
suspended charged particle. For particle sizes of practical in-
terest, the time required for a particle to achieve a steady-state
value of electrical migration velocity is negligible. Near the
collection electrode,1
(1)
where w_ = electrical migration velocity near the collection elec-
trode of a particle of radius a (m/sec),
P
q
charge on particle (coul),
£_ = electric field near the collection electrode (volt/m),
= particle radius (m),
= gas viscosity (kg/m'-sec) ,
P
a
C = Cunningham correction factor, or slip correction factor11 =
(1 + AX/a),
where A = 1.257 + 0.400 exp (-1.10 a/X) , and
X = mean free path of gas molecules (in) .
If the gas flow in a precipitator were laminar, then each charged
particle would have a trajectory which could be determined from the
velocity of the gas and the electrical migration velocity. In this
case, the collection length required for 100% collection of particles
with a known migration velocity can be calculated.. For cases where
turbulence exists, a laminar flow calculation is of interest only
from the standpoint that it establishes the best possible collection
efficiency for a given collection length.
In industrial precipitators, laminar flow never occurs and, in
any collection mechanism, the effect of turbulent gas flow must be
considered. The turbulence is due to the complex motion of the gas
itself, electric wind effects of the corona, and transfer of momentum
to the gas by the movement of the particles. Average gas flow ve-
locities in most cases of practical interest are between 0.6 and
2.0 m/sec. Due to eddy formation, electric wind, and other possible
effects, the instantaneous velocity of a .small volume of gas sur-
rounding a particle may reach peak values which are much higher than
the average gas velocity- In contrast, migration velocities for
particles smaller than 0.6 ym in diameter are usually less than 0.3
m/sec. Therefore, the motion of these smaller particles tends to
be dominated by the turbulent motion of the gas stream. Under these
conditions, the paths taken by the particles are random and the de-
termination of the collection efficiency of a given' particle becomes,
20
-------
in effect, the problem of determining the probability that a par-
ticle will enter a laminar boundary zone adjacent to the collection
electrode in which capture is assured.
Using probability Concepts and the statistical nature of the
large number of particles in a precipitator, White12 derived an
expression for the collection efficiency in the form
n = 1 - exp (-ApWp/Q), (2)
where n = collection fraction for a monodisperse aerosol,
A = collection area (m2),
w = electrical migration velocity near the collection elec-
p trode of the particles in the monodisperse aerosol (m/sec) ,
and
Q = gas volume flow rate (m3/sec) .
The simplifying assumptions on which the derivation of equa-
tion (2) is based are:
(1) The gas is flowing in a turbulent pattern at a constant,
mean foward-velocity.
(.2) Turbulence is small scale (eddies are small compared to
the dimensions of the duct) , fully developed, and completely random.
(3) The particle electrical migration velocity near the col-
lecting surface is constant for all particles and is small compared
with the average gas velocity.
(4) There is an absence of disturbing effects, such as particle
reentrainment, back corona, particle agglomeration, or uneven corona.
Experimental data1 3 under conditions which are consistent with the
above assumptions demonstrate that equation (2) adequately describes
the collection of monodisperse aerosols in an electrostatic pre-
cipitator under certain idealized conditions.
In industrial precipitators, the above assumptions are never
completely satisfied but they can be approached closely for fine
particles. With proper design, the ratio of the standard deviation
of the gas velocity distribution to the average gas velocity can be
made to be 0.25 or less so that an essentially uniform, mean forward-
velocity would exist. Although turbulence is not generally a com-
pletely random process, a theoretical determination of the degree
of correlation between successive states of flow and between adja-
cent regions of the flow pattern is a difficult problem and simple
descriptive equations do, not presently exist for typical precipitator
: geometries. At the present, for purposes of discussion, it appears
practical and plausible to assume that the turbulence is highly
21
-------
random. The turbulence does not dominate the motion of parti-
cles larger than about 10 yin diameter due to their relatively
high electrical migration velocities. Under these conditions,
equation (2) would be expected to underpredict collection
efficiencies. The practical effect in determining precipitator
performance will be slight, however, since even equation (2)
predicts collection efficiencies greater than 99.6% for 10 ym
diameter particles at relatively low values of current density
and collection area [i.e., a current density of 10 nA/cm2 and a
collection area to volume flow ratio of 39.4 m2/(m3/sec)].
It should be kept in mind that in the real situation the par-
ticles inside a precipitator are not uniformly mixed in cross-
sections perpendicular to the direction of gas flow and that
particle concentration gradients do exist. These concentration
gradients are not predicted from equation (2). The concentration
profiles for the finer particles will deviate only slightly from
a uniform distribution with the deviation increasing with in-
creasing particle diameter. Thus, although equation (2) repre-
sents a simple and most times adequate calculational tool for
practical purposes, it does not provide for all particle di-
ameters a faithful representation of the physical mechanisms
which occur in the precipitation process.
According to equation (2), the collection efficiency for a
given particle diameter can be increased by increasing A and/or
w or by decreasing Q. Increasing w involves increasing q and/or
E . In order to increase w , the applied voltage and current
P P
density must be increased. This increases both q and E .
REMOVAL OF COLLECTED MATERIAL
In dry collection, the removal of the precipitated material
from the collection plates and subsequent conveyance of the mate-
rial away from the precipitator represent fundamental steps in
the collection process. These steps are fundamental because col-
lected material must be removed from the precipitator and because
the buildup of excessively thick layers on the plates must be
prevented in order to ensure optimum electrical operating con-
ditions. Material which has been precipitated on the collection
plates is usually dislodged by mechanical jarring or vibration of
the plates, a process called rapping. The dislodged material
falls under the influence of gravity into hoppers located below
the plates and is subsequently removed from the precipitator.
The effect of rapping on the collection process is deter-
mined primarily by the intensity and frequency of the force
applied to the plates. Ideally, the rapping intensity must be
large enough to remove a significant fraction of the collected
material but not so large as to propel material back into the
22
-------
main gas stream. The rapping frequency must be adjusted so that
a larger thickness which is easy to remove and does not signifi-
cantly degrade the electrical conditions is reached between raps.
In practice, the optimum rapping intensity and frequency must be
determined by experimentation. With perfect rapping, the sheet
of collected material would not reentrain, but would migrate down
the collection plate in a stick-slip mode, sticking by the elec-
trical holding forces and slipping when released by the rapping
forces.
23
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SECTION 4
LIMITING FACTORS AFFECTING .PRECIPITATOR PERFORMANCE
ALLOWABLE VOLTAGE AND CURRENT DENSITY
The performance of a precipitator which has good mechanical
and structural features will be determined primarily by the elec-
trical operating conditions. Any limitations on applied voltage
and current density will be reflected in the optimum collection
efficiency which can be obtained. A precipitator should be operated
at the highest useful values of applied voltage and current density
for the following reasons: (!)• high applied voltages produce high
electric fields; (2) high electric fields produce high values of
the saturation and limiting charge that a particle may obtain; (3)
high current densities produce high rates at which particles charge
to the saturation or limiting values of charge; (4) high current
densities produce an increased electric field near the collection
electrode due to the "ionic space charge" contribution to the field;
and (5) high values of electric field and particle charge produce
high migration velocities and increased transport of particles to
the collection electrode.
Electrical conditions in a precipitator are limited by either
electrical breakdown of the gas in the interelectrode space or by
electrical breakdown of the gas in the collected particulate layer.
In a clean-gas, clean-plate environment, gas breakdown can originate
at the collection electrode due to surface irregularities and edge
effects which result in localized regions of high electric field.
If the electric field in the interelectrode space is high enough,
the gas breakdown will be evidenced by a spark which propagates
across the interelectrode space. The operating applied voltage
and current density will be limited by these sparking conditions.
If a particulate layer is deposited on the collection electrode,
then the corona current must pass through the particulate layer to
the grounded, collection electrode. The voltage drop (V ) across
the particulate layer is
VL = jpt, (3)
where j = current density (A/cm2),
p = resistivity of particulate layer (ohm-cm), and
24
-------
t = thickness of the layer (cm).
The average electric field in the particulate layer (ET) is given
by L
EL = jp. (4)
The average electric field in the particulate layer can be
increased to the point that the gas in the interstitial space
breaks down electrically. This breakdown results from the accel-
eration of free electrons to ionization velocity to produce an
avalanche condition similar to that at the corona electrode. When
this breakdown occurs, one of two possible situations will ensue.
If the electrical resistivity of the particulate layer is moderate
(^Q.1-1.0 x 1011 ohm-cm), then the applied voltage may be suffi-
ciently high so that a spark will propagate across the interelec-
trode space. The rate of sparking for a given precipitator geometry
.will determine the operating electrical conditions in such a cir-
cumstance. If the electrical resistivity of the particulate layer
is high (>1011 ohm-cm), then the applied voltage may not be high
enough to cause a spark to propagate across the interelectrode
space. In this case, the particulate layer will be continuously
broken down electrically and will discharge positive ions into
the interelectrode space. This condition is called back corona.
The effect of these positive ions is to reduce the amount of
negative charge on a particle due to bipolar charging and reduce
the electric field associated with the "ionic space charge". Both
the magnitude of particle charge and rate of particle charging are
affected by back corona. Useful precipitator current is therefore
limited to values which occur .prior to electrical breakdown whether
the breakdown occurs as sparkover or back corona.
Field experience shows that current densities for cold side
precipitators are limited to approximately 50^70 nA/cm2 due to
electrical breakdown of the gases in the interelectrode space.
Consequently, this constitutes a current limit under conditions
where breakdown of the particulate layer does not occur.
Electrical breakdown of the particulate layer has been studied
extensively by Penney and Craigl ** and Pottinger s and can be in-
fluenced by many factors. Experimental measurements show that par-
ticulate layers experience electrical breakdown at average electric
field strengths across the layers of approximately 5 kV/cm. Since
it takes an electric field strength of approximately 30 kV/cm to
cause electrical breakdown of air, this suggests that high localized
fields exist in the particulate layer and produce the breakdown of
the. gas in the layer. The presence of dielectric or conducting
particles can cause localized regions of high electric field which
constitute a negligible contribution,to the average electric field
across the layer. The size distribution of the collected particles
also influences the electrical breakdown strength by changing the
volume of interstices.16 It has also been found that breakdown
25
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strength varies with particulate resistivity with the higher break-
down strength being associated with the higher resistivity-
NONIDEAL EFFECTS
The nonidealities which exist in full-scale electrostatic pre-
cipitators will reduce the ideal collection efficiency that may be
achieved with a given specific collection area. The nonideal ef-
fects of major importance are (1) nonuniform gas velocity distri-
bution, (2) gas sneakage, and (3) particle reentrainment. These
nonideal effects must be minimized by proper design and optimization
of a precipitator in order to avoid serious degradation in per-
formance.
Nonuniform Gas Velocity Distribution
Uniform, low-turbulence gas flow is essential for optimum
precipitator performance. Nonuniform gas flow through a precipi-
tator lowers performance due to two effects. First, due to the
exponential nature of the collection mechanism, it can be shown
mathematically that uneven treatment of the gas lowers collection
efficiency in the high velocity zones to an extent not compensated
for in the low velocity zones. Secondly, high velocity regions
near collection plates and in hopper areas can sweep particles
back into the main gas stream.
Although it is known that a poor gas velocity distribution
results in reduced collection efficiency, it is difficult to formu-
late a mathematical description for gas flow quality. White17
discusses nonuniform gas flow and suggests corrective actions.
Preszler and Lajos18 assign a figure-of-merit based upon the rela-
tive kinetic energy of the actual velocity distribution compared
to the kinetic energy of the average velocity- This figure-of-
merit provides a measure of how difficult it may be to rectify
the velocity distribution but not necessarily a measure of how
much the precipitator performance would be degraded. At the inlet
of a precipitator, a value of 0.25 or less for the ratio of the
standard deviation of the gas velocity distribution to the average
gas velocity is generally recommended. However, it must be noted
that the gas velocity distribution can change significantly through-
out the length of a precipitator and, depending upon the design of
the precipitator and the manner in which it is interfaced with
other plant equipment, the gas velocity distribution may improve
or degrade along the length of a precipitator.
Gas Sneakage
Gas sneakage occurs when gas bypasses the electrified regions
of an electrostatic precipitator by flowing through the hoppers or
through the high voltage insulation space. Gas sneakage can be
reduced by the use of frequent baffles which force the gas to re-
turn to the main gas passages between the collection plates. if
there were no baffles, the percent gas sneakage would establish
26
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the maximum possible collection efficiency because it would be
the percent volume having zero collection efficiency. With
baffles, the sneakage gas remixes with part of the main gas flow
and then another fraction of the main gas flow re-bypasses in
the next unbaffled region. The upper limit on collection effi-
ciency due to gas sneakage will therefore depend on the amount
of sneakage gas per baffled section, the degree of remixing,
and the number of baffled sections. Gas sneakage becomes in-
creasingly important for precipitators designed for high col-
lection efficiencies where only a small amount of gas sneakage
per section can result in a severe limitation on collection
efficiency.
Particle Reentrainment
Particle reentrainment occurs when collected material re-
enters the main gas stream. This can be caused by several dif-
ferent effects and, in certain cases, can severely reduce the
collection efficiency of a precipitator. Causes of particle re-
entrainment include (1) rapping which propels collected material
into the interelectrode space, (2) the action of the flowing gas
stream on the collected particulate layer, (3) sweepage of material
from hoppers due to poor gas flow conditions, air inleakage into
the hoppers, failure to empty hoppers when required, or the
boiling effect of rapped material falling into the hoppers, and
(4) excessive sparking which dislodges collected material by
electrical impulses and disruptions in the current which is
necessary to provide the electrical force which holds the
material to the collection plates.
Recent studies19'20 have been made to determine the effect
of particle reentrainment on precipitator performance. In studies
where the rappers were not employed, real-time measurements of
outlet emissions at some installations showed that significant
reentrainment of mass was occurring due to factors other than
rapping. These studies also showed that for high-efficiency, full-
scale precipitators approximately 30-85% of the outlet particulate
emissions could be attributed - to rapping reentrainment. The re-
sults of these studies show that particle reentrainment is a
significant factor in limiting precipitator performance.
27
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SECTION 5
USE OF ELECTROSTATIC PRECIPITATORS FOR
THE. COLLECTION OF FLY ASH
REASONS FOR USING ELECTROSTATIC PRECIPITATORS TO COLLECT FLY ASH21
In 1975 utilities burned over 3.63 x 101: kg (400 million tons)
of coal which would produce about 2.72 x 1010 kg (30 million tons)
of fly ash annually, assuming an average ash content of 10% and an
average ash retention of 30% in the furnace. An illustration of
the magnitude of the ash problem can be shown by the output of one
600 MW power plant which typically exhausts 7 x 101* amVmin (2.5
million acfm) of flue gas. With a typical ash loading of 5 grains/
scf at the air preheater outlet, the ash emitted could be about
7.3 x 105 kg (800 tons) per day. To achieve an efficiency of col-
lection of at least 99% and to dispose of almost 7.3 x 105 kg
(800 tons) per day of fly ash is very demanding of a collection
system. The best reasons for using electrostatic precipitators
for the gas cleaning problem described above are:
(1) Electrostatic precipitators can be designed to provide
high collection efficiency for all sizes of particles from
submicroscopic to the largest present in the gas stream.
(2) They are economical in operation because of low internal
power requirements and inherently low draft loss. Gas
pressure drop through a precipitator may be of the order
of 2-3 cm of water or less as compared with pressures
of 8-36 cm of water for '•' filters and. 25-254 cm of water
for scrubbers.22
(3) They can treat very large gas flows.
(4) They are very flexible in gas temperatures used, ranging
in the power field from as low as 93°C (200°F) to as high
as 427°C (800°F).
(5) They have long useful life.
Today a total of more than 1300 fly ash electrostatic precipita-
tor installations having a rated gas flow of over 1.4 x 107 am3/min
(500 million acfm) have been made in the United States. Future ex-
pansion of the power industry due to ever greater energy consumption
by the public and an increased dependence on coal as the major
28
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energy source for power production are factors favoring continued
growth of fly ash precipitation.
DESIGN OF PRECIPITATORS USED TO COLLECT FLY ASH
General Description
The design of an electrostatic precipitator for a particular
installation involves many parameters that can influence both
cost and performance. The most significant variables (besides
fly ash character) involved in the design are:23
Area and type of collection electrodes,
Dimensions of the precipitator shell,
Size, spacing, and type of discharge electrodes,
Size and type of power supply units,
Degree of sectionalization,
Layout of the precipitator in accordance with physical space
limitations,
Design of the gas handling system,
Size and shape of the hoppers,
Type and number of electrode rappers,
Type of ash removal equipment.
Stringent air pollution control standards require low stack
emissions. Also, new regulations have enforcement provisions
which can curtail or even shut down entire production units
in order to comply with emission standards. Optimum precipi-
tator design, therefore, is of paramount importance for economic
reasons as well as aesthetic and health reasons. Some of the
factors involved in designing electrostatic precipitators are
described in detail below to allow an understanding of the impor-
tance of each factor in the total design. Different manufacturers
sometimes have different recommendations as to the type of dis-
charge electrode, power supply, rappers, etc. to use in a fly ash
precipitator, so an attempt has been made to discuss and show
different types of each component.
Precipitator Shell1
/ 2 2
The purpose of the shell is to confine the gas flow for proper
exposure to the electrodes, to avoid excessive heat loss, and to
provide structural support for the electrodes and rapping equip-
ment. The shell is- normally rectangular, where plate electrodes
are used, or cylindrical if tube;-electrodes are used. Cylindrical
shells may also be -iised with plate-type precipitators where rel-
atively high or low gas pressures are encountered. Shell material
is usually steel, but because of some corrosion problems, it may
be lined with or made of tile, brick, concrete, or special cor-
rosion-resistant steels.. Insulation is usually required to main-
tain the shell at a temperature above the dew point if the gases
contain corrosive materials. Access doors and stairways and
29
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safety provisions are provided as auxiliary equipment.
Gas diffuser plates are sometimes provided as part of the
shell in order to improve gas flow. Roof, wall, and hopper baffles
are used to minimize the amount of /-gas which may by-pass the elec-
trodes. Hopper baffles generally extend below the dust level in
the hopper to provide a seal and keep gas from flowing through
the hopper. Design of diffuser plates .and baffles will be covered
in more detail in the section on gas flow.
Cross bracing is generally provided by diagonal members
across the inlet and/or outlet of the shell. Horizonal struc-
tural members are built-up trusses, box beams, or various other
configurations which vary with manufacturer. The structural
members must be capable of supporting the electrodes and main-
taining them in alignment over the range of temperatures and
external load conditions encountered in operation. Some manu-
facturers contend that thermal expansion of the shell constitutes
a major alignment problem unless provision is made to allow for
expansion. Otherwise, buckling of the shell and subsequent dis-
tortion of the electrode system can occur. Since the assembly
occurs at ambient temperature, expansion stresses of the struc-
tural members will obviously occur as the shell is heated to flue
gas temperatures. One method utilized to overcome the expansion
problem is to provide bearings at the base of the support columns
to permit the shell to move without buckling. Figure 10 shows the
details of such a bearing which generally is just two flat plates
without lubrication.24 Many installations have been built without
such bearings, the claim being that expansion takes place uniformly
and that distortion due to thermal expansion is inconsequential.
However, expansion is generally more of a problem for hot-side
units than for cold-side units.
There are other causes of shell distortion, principally inade-
quate foundations. When this occurs, electrode spacings can change
from the designed four to five inches to two inches or less. Such a
shift in spacing limits the operating voltage and seriously impairs
precipitator performance.
Electrical Sections
Electrical Energization—
Historical development25—The purpose of high-voltage equip-
ment in electrostatic precipitation is to provide the intense elec-
tric fields and corona currents needed for particle charging and
collection. In addition, the electrical sets must be highly stable
in operation and have useful operating lives of twenty years or
more. Proper voltage waveform, protection and stability against
precipitator sparkover, proper voltage and current output ratings,
and sturdy electrical and mechanical design are necessary require-
ments of the equipment. Automatic control of rectifier output is
essential for most fly ash precipitators because of'changing load
30
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EXPANSION
JOINT
SLIDING JOINT
3640-318
Figure 10.
Illustration of thermal expansion bearing surface
for precipitator installation.2"
-------
conditions and characteristics of the flue gas and of the fly ash
produced by boilers which are operated at varying loads and fuel
conditions.
Development of high,voltage equipment to energize precipitators
has been an evolutionary process. "Mechanical rectifier sets in the
earliest precipitators were succeeded by more reliable and long
lasting tube rectifier sets. Solid-state rectifiers have made the
mechanical type virtually obsolete. Selenium solid-state rectifiers
provide reliable service and long life but are subject to damage
from high temperatures. Universal adoption of the solid-state rec-
tifier began with the recent development of the silicon type. To
maintain optimum energization levels, modern equipment uses silicon
diode rectifiers, oil or askerel filled high-voltage transformers,
thyristor control elements, and automatic feedback control.
A good summary of the general periods of development of the
various components of high voltage electrical equipment is given
by Hall:26
1906 - 1950 Mechanical rectifiers, generally with simple
rheostat manual control; low power 250 mA dc
sets, either double half-wave (beginning in 1932)
or single full-wave electrical output; generally
small size individual sections (four 10,000 ft2
collecting area per set).
1950 - 1960 Major use of vacuum tube high voltage rectifiers;
increasing use of automatic voltage control based
on an optimum average precipitator sparking rate;
growth of high power rectifier sets to 1000-1500
mA dc sizes and use of very large sections energized
by individual sets. First silicon diode rectifier
set designed in 1955-1956 and applied in 1958.
1960 - 1970 Commercial use of modern, solid-state silicon-
controlled rectifier automatic voltage control
system with linear reactor in 1965; universal
use of silicon diode high voltage rectifiers;
application of linear reactors to the stabiliza-
tion of certain unreliable saturable reactor
control systems (1963) ; use of high pressure
cleaned process gas as dielectric medium for
high voltage transformer design to eliminate
high pressure feed through bushings; development
of more sophisticated automatic voltage control
techniques using fast computer-type logic cir-
cuitry and printed circuit boards capable of
stable rectifier set operation at threshold or
very low sparking rates over a wide range of
loads.
32
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Power supplies22'27—Each power supply consists of four com-
ponents as shown in Figure 11: a step-up transformer, a high
voltage rectifier, a control element, and a sensor for the control
system.27 The step-up transformer increases the voltage from the
line voltage to that required by the precipitator. The high voltage
rectifier converts the high voltage ac power to dc to be com-
patible with precipitator requirements.
One function of the control system is to vary the amplitude
of the dc voltage applied to the electrode system. This control
is usually located on the primary or low voltage side of the trans-
former. The control system can be operated either manually or in
one of several automatic modes, but automatic systems are typically
installed in modern installations. A well-designed automatic con-
trol system serves to maintain the voltage level at the optimum
value, even when the dust characteristics and concentration
fluctuate.
High voltage rectifiers—The rectifiers change the ac to dc,
either full-or half-wave. In general, half-wave power supplies
allow a greater degree of sectionalization. Full-wave may be used
in situations where large dust loading or extremely fine particles
lead to a large space charge which limits the maximum current.
Spark-rate—The spark-rate is the number of times per minute
that electrical breakdown occurs between the corona wire and the
collection electrode. A spark-rate controller establishes the
applied voltage at a point where a fixed number of sparks per
minute occur (typically 50-150 per corona section). As the spark-
rate increases, a greater percentage of the input power is wasted.
One commonly used type of control device utilizes spark-rate as
the primary control. Another type of control circuit utilizes a
thyristor control element.22'28 An explanation of automatic SCR
voltage control is given by Piulle29 and a new precipitator volt-
age control using analog electronic networks is described by
Gelfand.30
Design and operating requirements—Table 1 summarizes the
design and operating requirements'for modern high voltage elec-
trical equipment of the conventional type.26 Figure 12 shows
the schematic circuit diagram of a modern high voltage rectifier
set with SCR (silicon-controlled-rectifier) type automatic control.26
Multiple signal feedback loops are provided to obtain good regu-
lation and fast response to transient spark disturbances. The
linear inductance reactor, although sometimes omitted because of
its added cost, is nevertheless an important factor in obtaining
good current waveform control and ability to;operate the rectifier
set at or near rated .output. A properly designed linear inductor
also eliminates spark bursting and arcing tendencies which con-
.tribute to instability and -can also cause corona wire burning.
Metering should include kilovolt meters, milliammeters, and spark-
rate meters.
33
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.AC VOLTAGE
'INPUT
CONTROL
ELEMENT
STEP-UP
TRANSFORMER
ELECTROSTATIC
PRECIPITATOR
HIGH VOLTAGE
RECTIFIER
MANUAL
AUTOMATIC
CONTROL FEEDBACK
Figure 11. Power supply system for modern precipitators
2 7
34
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TABLE 1, DESIGN AND OPERATING REQUIREMENTS FOR MODERN
HV ELECTRICAL EQUIPMENT IN ELECTROSTATIC
PRECIPITATION26
Item
1. Of first importance
2. Precipitator operating
voltage, kv
3. Precipitator current
density, mA/1000 ft2
4. Precipitator voltage wave-
form
5. Precipitator load
6. Line input
Rectifier circuit,
sets
standard
8. Rated output voltage, R load
9. HV transformer
10. Individual set capacity,
kVa
11. Rated dc output current, itiA
12. Transformer-rectifier
insulation
13. Duty
14. Ambient temperature
15. Voltage control
16. Voltage control range
17. Current limit - no
sparking
18. Peak current limit during
sparking
Specification
High reliability & stability
under transient sparking condi-
tions and occasional short-
circuit load.
30-100+
10-100+
(40-65 kV most common)
Pulsating, negative polarity
full-wave or double half-wave
Capacitive - 0.02 to 0.125
uFD/section
460/480 V, 1 Ph, 60 Hz most
common variation +_ 5% line
voltage
Single phase, FW bridge,
silicon diodes
70 kV peak, 45 kV dc average -
most common, 105 kV peak, 67.5
kV dc average
400 V/53 kV rms or 400 V/78 kV
rms
15 to 100
250 to 1500+ per set (R load)
Oil/askarel convection cooling
Continuous - outdoor or
installation
indoor
50°C max for TR oil-filled tank
55°C max for control cabinet
Automatic control essential
based either on optimum avg
sparking rate (adjustable), or
nominally at spark threshold
Essentially zero to 100% rated
output. Modern systems use SCR
type control with linear reactor
in HV transformer primary-
Automatic limit at rated pri-
mary current. Full rated
current abailability indepen-
dent of voltage
2 to 2.5 times normal peak
current in the best systems
35
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SCR
CONTROL
LINEAR
REACTOR
460 V
1 PH -»•-
60 Hz
-o o
CO
H.V.
SILICON
RECTIFIER
BRIDGE
AUTOMATIC CONTROL MODULE
INCLUDES SLOW START
3S40-OOS
Figure 12.
Schematic diagram - modern HV rectifier set with
SCR type automatic control for electrostatic
precipitators.2 6
-------
Sources of high voltage electrical equipment26 —The sources
of high voltage electrical equipment for precipitators are some-
what limited. The following categories summarize the locations
of these sources:
In-house - all electrical equipment designed and made by the
precipitator supplier. These include Research-Cottrell, Inc. and
CE-Walther (vis Helena Corp.). Buell is also essentially in this
category since only the HV transformer core and coil are purchased.
Hybrid - purchase of HV transformer (usually General Electric
or Westinghouse) to specification with the control unit being made
to one's own design in-house or at a separate local company-
Industrial - HV transformer and controls made by General
Electric or Westinghouse.
Commercial - several suppliers of ordinary high voltage power
supplies offer equipment for electrostatic precipitation.
Specialty Companies - very few companies specialize in selling
high voltage equipment and controls for electrostatic precipitators.
An example of one which does is Environecs in Costa Mesa, California.
Typical oil-filled transformers weigh 1090 kg (2400 Ibs) at
16 KVA to about 1816 kg (4000 Ibs) at 100 KVA. Askarel nonflammable
fluids increase the weight about 454 kg (1000 Ibs). Modern control
cabinets are typically about 454 kg (1000 Ibs) or less, front access.
Discharge Electrode System—
The discharge electrode system is designed in conjunction
with the collection electrode system to maximize the electric
current and field strength. The discharge electrode is also re-
ferred to as the corona electrode, cathode, high voltage electrode,
or corona wire. The shape and size of the discharge electrodes
are governed by the corona current and mechanical requirements
of the system. Where high concentrations of fine dusts are en-
countered, space charge limits the current flow, especially in
the inlet sections. In such cases, special electrodes which
give higher currents may be used to achieve a high power density
within the inlet sections. Variation in the current flow and
electric field within limits is possible by controlling the type
and size of the discharge electrode.
Geometries of discharge electrodes—The shape of the electrodes
may be in the form of cylindrical or square wires, barbed wire, or
stamped from formed strips of metal of various shapes. Some dis-
charge electrode geometries are shown in Figure 13.27 A "square
twisted" wire is usually 0.48 cm (3/16 inch) or 0.64 cm (1/4" inch)
square and is twisted longitudinally to help straighten the rod and to
37
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-------
increase the length of the sharp edge, which increases the corona
current. "Spiral" wires, are formed as a spring and then pulled
for installation. The spring tension helps restrict the lateral
motion. "Barbed" wires are merely commercial grade barbed wire.
A wire considered basic, though not restricted to, the "European"
design explained below has a star-shaped cross section as shown
in Figure 14-a.31 A wire known as Isodyn wire is described by
Engelbrecht3l as being advantageous on a rigid frame system when
a higher current at a given voltage is desired compared to the
star-shaped discharge wire (Figure 14-b). As stated earlier,
mechanical and electrical requirements usually determine the
shape and size of the discharge electrodes.
Types of discharge electrodes—Various types of discharge
electrodes are used in electrostatic precipitators, but one of
the major differences between manufacturers is in the method of
supporting the discharge electrodes. One approach, typical of
European practice, is to provide a frame or tubular support for
the electrodes. The other approach which has been used by most
American manufacturers is to suspend the electrodes from a support
and maintain them in position by weights and guides at the bottom.
A typical weighted-wire electrode is illustrated in Figure
15,32 and a complete weighted-wire electrode system illustrating
the method of fastening the wire at the top and maintaining the
wire in place by bottom weight guides is shown in Figure 16.33
There is considerable variation among manufacturers as to the
method of supporting the discharge wire from the support frame.
Since the discharge wires tend to move under the influence of
both aerodynamic and electrical forces, mechanical fatigue failure
can occur. Various methods of allowing some movement of the sup-
port have been attempted to minimize the fatigue problem. Wires
are also subjected to localized sparking in the regions of high
field strength and shrouds are sometimes used to give a larger
diameter, and hence low field strength, in critical regions near
the ends of the electrodes.
Various types of the "European" discharge wire system or
rigid discharge electrode system are available, and a classifi-
cation may be attempted based on the following criteria:31 (1)
two dimensional frames with rigid discharge wires (Figure 17),
(2) three dimensional frames with discharge wires strung between
horizontal supports (Figure 18), (3) discharge wires supported
off masts (Figure 19), and (4) self-supporting rigid discharge
electrodes (Figure 20).
Rigid discharge electrode systems are now being offered by
manufacturers previously identified only with the weighted-wire
design. The rigid or supported wire electrode system has the
advantage of minimizing .the wire breakage problem since the
electrodes are supported by rigid members and remain in position
and energized even if breakage of the electrode occurs.
39
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a
T
SECTION a a
Figure 14-a. Rigid discharge electrode star wire
3 1
VIEW A
3640-010
Figure 14-b. Rigid discharge electrode isodyn wire.31
40
-------
3540-011
Figure 15 .,• 'Weighted wire corona electrodes.
41
-------
HIGH VOLTAGE
GUIDE FRAME
HIGH VOLTAGE
WIRE HOLDER
HIGH VOLTAGE
WIRE SUPPORT -
WEIGHT RETAINING
COTTER PIN
WIRE
WEIGHT
HIGH VOLTAGE
DISCHARGE WIRE
WEIGHT GUIDE
LOOP
3640-012
Figure 16. Example of weighted wire electrode system.33
42
-------
DISCHARGE
ELECTRODE
DISCHARGE
FRAME
3540-013
Figure 17-
"European" discharge wire system with rigid discharge
wires on a two dimensional frame.31
43
-------
3540-014
Figure 18.
"European" discharge wire system with discharge wires
strung between horizontal supports on a three dimen-
sional frame.31
44
-------
V
•p
3540-015
Figure 19
"European" discharge wire system with discharge wires
supported-off a mast.3: .
45
-------
I
J.
L
L
L
J
ft
I
4W
J'
0
3S40-01E
Figure 20, "European" discharge wire system with self-supporting
rigid discharge electrodes. i
46
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New designs—Research-Cottrell has developed a new rigid dis-
charge electrode, called the Dura-Trode, which is said to offer longer
life and better performance than earlier weighted-wire or rigid-type
electrodes.31* In cross section, the system is similar to a hollow
airfoil. Corona discharge is delivered primarily by thin scalloped
blades at leading and trailing edges. Research Cottrell estimates
that maintenance costs are projected at zero over the unit's 30
year plus lifetime. Units have been tested successfully at five
coal-fired generating stations and four industrial plants since 1975.
Figure 21 shows the Dura-Trode rigid-type electrode.
? 9
Discharge electrode support —The main functions of the
discharge electrode support are to provide the necessary high
voltage electrical insulation and to give mechanical support to
the discharge electrode frame. There are several types of support
systems currently used in precipitator design. One type, shown in
Figure 22, is a support bushing arrangement in which the high
voltage insulators are located on the roof of the precipitator,
and the discharge electrode assembly is suspended from the bus
beam by hanger rods.35 Porcelain pin-type insulators support
the mechanical load of the internal framework and are located in
a relatively low temperature zone with low contamination. These
bushings are not gas tight so a common practice is to provide a
flow of air into the insulator compartment to prevent entrance of
dust-laden air from the precipitator. Another type of discharge
electrode support, shown in Figure 23, is a bushing arrangement
in which the electrode assembly is suspended by hanger rods which
are supported directly by bushings.35 In this case, the bushings
are constructed of alumina or Pyroceram and have higher mechanical
strength and better thermal shock resistance, permitting a much
simpler electrode support design. The low porosity of the in-
sulation materials and better gas seal provided by the gasket
minimize the gas inleaJcage to the insulator compartment. How-
ever, for some applications, the bushings are continuously purged
with air, either induced when the precipitator is under suction
or forced by blowers. The bushings are housed in either individual
roof tunnels or in a common housing on top of the precipitator.
Other types of electrode supports are in use and the type
varies between manufacturers. For some applications, the flue
gases are near the dew point and condensation on cooler parts of
the insulator will cause localized arcing. When arcing occurs, a
low resistance path can be formed which will partially short cir-
cuit the power supply or the heat generated by the arc can fracture
the insulator. When such conditions can occur, special precautions
must be taken to heat the insulators to prevent condensation of
moisture or acid.
Collecting Electrode System—
The collecting electrodes are the individual grounded sur-
faces on which particulate matter is collected. Generally, in
47
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3640-017
Figure 21. Unitized Dura-trade rigid-type electrode.31*
48
-------
H. T. CONDUCTOR
FROM RECTIFIER
INSULATOR
COMPARTMENT
CONVENTIONAL PIN TYPE
PORCELAIN INSULATOR.
HIGH TEMP.-EXTREME
ENVIROMENTAL ZONE
METAL ENCLOSED
H. T. BUS DUCT
PPTR. ROOF
REFRACTORY
TYPE ENTRANCE
BUSHING
H. T. DISCHARGE
ELECTRODE FRAME
3540-018
Figure 22. Example of high-temperature support bushings.
3 5
49
-------
H. T. CONDUCTOR
FROM RECTIFIER
METAL ENCLOSED
H. T. BUS DUCT
PPT.R. ROOF
INSULATOR
COMPARTMENT
METAL
COVER I
PYROCERAM
BUSHING
HANGER
SUPPORT
HIGH TEMP.-EXTREME
ENVIRONMENTAL ZONE
. i H. T. DISCHARGE
ELECTRODE FRAME
S540-019
Figure 23. Example of high-temperature support bushings.
3 5
50
-------
spite of the many elaborate concepts given in the patent litera-
ture, most collection electrodes are simple configurations, the
main considerations being stiffness of the collection plates and
shielding of the collected dust layer to prevent reentrainment.
An additional requirement is that the edge of the collecting
plates be free of sharp edges or protrusions which can provide
localized high field regions, resulting in sparking at low voltage.
If welded structures are utilized, the weld must be smooth to
minimize localized sparking. These considerations are especially
important in the wire-and weight-type discharge electrode since
the wire extends beyond the edge of the collection plate. A
further requirement of the collection electrode is that the rap-
ping impact should be transmitted to all parts of the plate as
uniformly as possible to facilitate uniform dust removal. The
plates should be heavy enough to prevent damage due to rapping,
especially where high impact rapping is used.
Geometries of collecting electrodes—A few types of collecting
electrodes, representative of those most often used by precipitator
manufacturers today, are illustrated in Figure 24.23 This list is
by no means exhaustive since the patent literature contains numerous
other electrode types which have been designed to shield the col-
lected dust and minimize reentrainment. Many of these are un-
acceptable because of excessive weight or cost, or because of high
reentrainment losses.
The shielded flat plate collecting electrode, used chiefly in
horizontal flow, dust-type precipitators, is the most popular in
present day use in the United States. In order to shield the pre-
cipitated dust from the gas passing across the plate, baffles are
mounted along the plate. The baffles are fabricated as formed
shapes and welded to the ends and surfaces of the collecting plate.
Baffle shapes vary from flat strips perpendicular to the collecting
surface to aerodynamic designs to minimize gas turbulence. The
size of the collecting electrodes in.an electrical section ranges
from twenty feet to fifty feet in height, from three feet to twelve
feet in the direction of gas flow, and is usually about 18 gauge
thickness. - , .
Offset plates are made by bending a flat sheet into a square
or angular zig-zag or a corrugated pattern. The dust precipitated
in the troughs is shielded from the main gas stream to minimize
reentrainment. The plates are usually from ten to thirty feet in
height and from three to nine feet in the direction of gas flow.
Two design variations of this arrangement used by Wheelabrator
Lurgi are shown in Figure 25.36
A vee plate is a composite assembly of metal strips bent into
the shape of a vee or chevron. The vees are spaced about 3.18 cm
(1 1/4 inch) apart for the full length of the plate which is about
two inches thick. The points of the vees face upstream and the
spaces between the vee members act as quiescent zones in which
51
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COLLECTING PLATES
WIRES
OFFSET PLATES
V-PLATES
SHIELDED PLATE
-3
3540-020
Figure 24. Various types of collection electrodes.23
52
-------
3540-021
Figure 25.
Exclusive Wheelabrator Lurgi collecting electrodes.
The CSW, with single overlap, and the double overlap
CSH design.3S
53
-------
the dust is precipitated with minimum reentrainment. The col-
lecting plates in use today range from about eighteen to thirty-
five feet in height, and an individual plate is usually three
feet in the direction of gas flow. Two plates are customarily
fastened together in order to make up a six foot section.
Ash Removal Designs
General37—
Once fly ash has been collected on the collecting electrode,
it must be removed to a hopper or storage facility, not only to
remove the material from the precipitator per se, but also to
maintain optimum electrical conditions in the precipitation zones.
The deposits are dislodged by mechanical impulses or vibrations
of the electrodes, a process known as rapping. Many of the pro-
blems associated with poor electrostatic precipitator performance
can be related directly to degradation in rapper system performance.
Because of the complex nature of the dust removal mechanics in an
electrostatic precipitator, a number of factors should be con-
sidered when evaluating rapper system problems. These factors
are related not only to hardward quality and manufacture, but also
to charging process conditions, maintenance procedures, and initial
application of the rapping hardware. Hardware malfunctions have
been a problem in the past. Therefore, the latest technologies
available in solid-state electronics are being incorporated into
system designs to provide continuous on-line monitoring.
Rappers22—
Depending on individual vendor philosophy, rapping impulses
are provided by either single impact or vibratory-type rappers.
These in turn are activated either electrically or pneumatically,
using accelerated or gravitational type impacts. Some commonly
used methods of dry removal of fly ash from collecting and dis-
charge electrodes are discussed below.
Single impact rapper (electromagnetic solenoid) - electro-
magnetic solenoid rappers consist of a plunger which is lifted by
energizing the solenoid. On release of the plunger by deenergizing
the coil, it falls under the influence of gravity against an anvil
which transmits the rap through a rod to the electrodes to be
cleaned (Figure 26). 3e Solenoid-type rappers are used for both
discharge and collecting electrode cleaning and are usually lo-
cated on top of the precipitator. Solenoid rappers can be spring
actuated as well as gravity actuated. Control consists of varying
the electrical energy, which changes the magnitude of the impulse
or the frequency of rapping. The acceleration of the rap can be
as low as 5 g, but raps from 30 g to 50 g are required for most
fly ash precipitators.
54
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CONDUIT BOX
COVER AND GASKET
PLUNGER GUIDE
COIL COVER
COIL ASSEMBLY
PLUNGER
CASING GASKETS
FLANGE BOLTS AND NUTS
LOWER CASING
ADJUSTING NUTS
ADJUSTING BOLT
ADAPTER OR MOUNTING
RAPPER ROD
3540-022
Figure 26. Typical electromagnetic rapper assembly.3
55
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Vibrators (electromagnetic) - electromagnetic vibrators
consist of a balanced spring-loaded armature suspended between
two synchronized electromagnetic coils. When energized, the
armature vibrates at line frequency. This vibrating energy is
transmitted through a rapper rod to the electrodes. When used
for cleaning discharge electrodes, the. rapper rod is provided
with an electrical insulating section in order to isolate the
high voltage electrode charge from ground. Control consists of
varying the electrical energy input, which changes the amplitude
of vibrations, the operation time duration, and the frequency of
vibration. Figure 27 shows a typical electromagnetic vibrator
installation.35'*0
Vibrators (eccentrically unbalanced motors) - this system
consists of mechanical vibrators with an electric motor equipped
with adjustable cam weights mounted on a single shaft or on. both
shafts of a double ended motor. When operated, the eccentrically
positioned cam weights set the entire assembly into vibration.
The motor is mounted directly on the rapper shaft which transmits
the generated vibration to the electrodes to be cleaned. Control
consists of varying the degree of eccentricity by cam weight ad-
justment, the length of time operated, and the frequency of oper-
ation.
Single impact (motor-driven cams) - this mechanism consists
of a motor-driven shaft running horizontally across the precipi-
tator. Cams are located along the shaft which raise small hammers
by their handles. When the rotating cam reaches the end of its
lobe, the hammer swings downward, striking an anvil located on
the end of a single collecting electrode. Rapping control is
limited to adjustment of operating time and shaft speed.
Single impact (motor-driven swing hammers) - this mechanism
consists of a shaft running horizontally across the precipitator
between banks of collecting plates. Hammer heads are connected
to the shaft by spring leaf arms, and the shaft is oscillated by
a motor-driven mechanical linkage. The hammers strike against
anvils attached to the ends of all the collecting plates. Control
is. accomplished by varying operating time and the arc of the hammer
swing.
Single impact mechanical rappers - Figure 28 shows this
system which consists of a drive shaft running across the pre-
cipitator. The shaft rotation carries the swing hammers around
the shaft. When the hammer rods swing over the center cam disc
and raise the hammer rods, the hammers fall due to gravity,
striking an anvil which is attached to the discharge or collec-
ting electrode structure. Rapping control is limited to operating
time and shaft speed.
Vibrators (air) - the major components of this system typi-
cally consist of a reciprocating piston in a sleeve-type cylinder.
56
-------
— ENCLOSURE
OAJICK OPENING
CLAMP
GROUND CONNECTION
ENCLOSURE
VIBRATOR
MOUNTING PLXTE
> L-^STUFFING BOX AND GUlSE
FLEXIBLE CONDUIT
— U"*~-- FITTING
CLAMPS
(RAPPER RODST
CERAMIC SHAFT)
HOUSING
— CERAMIC INSULATING SHAFT
PRECIPITATOR ROOF
VIBRATION
TO
DISCHARGE
WIRE
DUST LADEN
GAS AREA
CLOSURE PLATE
— HIGH VOLTAGE BUSHING
RAPPER ROD ASSEMBLY,
MUST BE PLUMB
HIGH TENSION FRAME
DISCHARGE WIRES 3540-023
Figure 27. Typical vibratory rapper.39'"°
57
-------
3540-024
Figure 28. Mechanical-type rapper."1
58
-------
The assembly is fastened directly to the end of a rapper rod
which transmits the rapping energy to the discharge or collec-
ting electrode to be cleaned. Control consists of varying the
air pressure, the duration of the rapping period, and the time
elapsed between cleaning.
Failure to match rapping requirements to process character-
istics can result in the need for higher rapping intensity than
expected which in turn leads to accelerated degradation in system
hardware. Generally, electric or pneumatic impulse rapped devices
have been more successful in difficult rapping applications.37
New Technology in Rapper Control37—
Many of the problems involved with rapper control are assoc-
ciated with proper rap sequencing or individual rapper energization,
Particularly vulnerable to this type of malfunction are those con-
trols which incorporate mechanical switching and sequencing. Many
solid-state devices are now being substituted for the mechanical-
type devices. New technology has also made available rapper con-
trol systems that permit continual on-line monitoring of rapper
system operation. The use of microprocessor-type control technol-
ogy/ previously uneconomical, has provided a high degree of rapper
control flexibility and has reduced maintenance problems. Where
rapper assembly malfunctions have previously caused control damage
from ground fault currents, new control systems will test each
individual rapper circuit prior to energization. Should that
circuit prove defective, the control will automatically bypass the
grounded rapper or circuit and indicate the defective unit in an
LED display, thus permitting quick and easy location and repair.
New technology has also been developed to incorporate precipitator
power-off rapping techniques which increase rapping effectiveness
for difficult dusts-and reduce system wear.
Hoppers—
Hoppers are used to collect and store dry particulate which
is removed from the electrodes. Insulation and heat tracing of
the hoppers are very important in keeping the fly ash hot and
dry, thereby facilitating removal from the hoppers to storage
areas. If fly ash is allowed to cool, moisture condensation
followed by caking of the ash may occur, making removal very
difficult. Caking may be a potential problem especially when
conditioning agents such as SO3 are utilized to improve precipi-
tator efficiency. Hopper heat tracing systems may be obtained
from the Heat Tracing Division of Cooperheat, Inc., Rahway, New
Jersey.
5.9
-------
If the precipitator system is operated with internal pres-
sures less than ambient atmospheric, air inleakage through the
hopper can cause a reentrainment of the dust from the hoppers.
Baffles are often placed in the hoppers and extend below the
minimum dust level to minimize undesirable gas flows which may
reentrain dusts. Good seals around hopper doors and around the
connections of dust removal systems operating under a vacuum
are a necessity.
Overflow of hoppers with fly ash can be a serious problem
leading to an electrical shorted, electrical system or reentrain-
ment of fly ash, thereby reducing collection efficiency. Because
of the importance of eliminating the overflow problem a number
of hopper level detectors have been developed. These detectors
use several different principles of operation and some of the
more common detection methods and the companies which manufacture
the detectors are given below.1*2 This list is merely a repre-
sentative sampling and should not be considered exhaustive. Also,
the information contained is a condensation of promotional lit-
erature and does not.reflect an opinion of Southern Research or the
Environmental Protection Agency as to which system is superior.
Kay-Ray, Inc.
516 West Campus Drive
Arlington Heights, Illinois 60004
Phone: 312/259-5600
Kay-Ray, Inc. has placed over 1000 level switches on fly
ash precipitators. This system is equivalent to an infinite
number of probe sensors in that it detects ash at any location
along the total width of the collection hopper. The system oper-
ates on a noncontacting radiation principle. A narrow beam of
gamma rays is directed across the hopper (penetrating insulation,
walls, and baffles) to a radiation detector located on the opposite
wall. When ash builds up, the rays are absorbed, causing the de-
tector to activate a relay for alarm or control purposes. The
source of the gamma radiation is Cesium 137 with a half-life of
33 years. The detector consists of two Geiger-Miiller detectors
and associated electronics and produces an output current that
is inversely proportional to the amount of material between source
and detector. The major advantages of this system (Model 4810)
are: (1) the sources and detectors are mounted outside the
hoppers. None of the equipment comes in contact with the hot,
abrasive fly ash; (2) the equipment can be mounted or repaired
without having the fly ash hoppers down; (3) a high alarm is
given whenever fly ash buildup intersects the path of the beam
across the hopper. This assures an alarm condition whenever any
fly ash builds up on either hopper wall or any of the baffles;
(4) equipment operates at fly ash temperatures of 815°C (1500°F).
A typical system is shown in Figure 29. More detailed drawings
and specifications of a typical housing (Model 7063P) and a
typical detector (Model 7316P) are given in Figures 30 and 31,
respectively.
60
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ELECTROSTATIC PRECIPITATOR
SOURCE HOLDER AND DETECTOR
3540-0:5
Figure 29. KAY-RAY fly ash control system.
61
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SPECIFICATIONS
* Welded steel construction
* Rugged, simple mechanical
design
Lead "filled, sealed in steel
* LockaWe shutter mechanism
* Highly collimated radiation
beam to provide inherent safety
Low surface radiation level
Wide range of source sizes
and types
Painted with chemically
resistant epoxy
Weight - 85 pounds (38.6 kg)
65/8"
HOPPER
LAGGING
9/16"
(14.3 mm) Dl A.
(168 mm)
9 1/2"
(241 mm)
INSULATION
3MO-OJ6
Figure 30. Level source housing - Model 7063P.
62
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SPECIFICATIONS
* Reproducibility to ± 1/8"
* Soltd state circuitry
* Two GM sensors
* High sensitivity, operates at
less than 0.5 mr/hr
* Fail safe high or tow
* Fast reponse • 1 second
Output SPOT or DPDT relay contact 10A
Input 115V, 50-60 HZ, 25 VA, 115 or
230VAC, 50-60 HZ
Approx. weight 20 pounds (9.1 kg)
Painted with chemically resistant
epoxy
Factory pre-calibrated
INSULATION
-HOPPER
LAGGING
S12 5/16"
(313 mm)
10 7/16"
3/4-14 NPT
PIPE FITTING
4" O.D.
STEEL TUBING
4 1/2"
(114mm)
3540-027
Figure 31. Fly ash level detector - Model 7316P-
63
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A new system by Kay Ray, the Model 4400 Fly Ash Level Detec-
tion System features a remote electronics annunciator.
Texas Nuclear Division
Ramsey Engineering Company
Post Office Box 9267
Austin, Texas 78766
Phone: 512/836-0801
The Texas Nuclear Fly Ash Level System operates on the prin-
ciple of gamma ray absorption. A radioactive source emits a narrow
beam of gamma radiation from its protective housing. This beam
passes through the hopper walls to the detector. When the fly
ash level rises above, the source, radiation is absorbed. When the
number of gamma rays falls:below a predetermined reference, the
detector logic circuitry concludes that material is present and
an output relay is switched from low to high level indication.
Figure 32 shows a typical two hopper installation*. The Texas
Nuclear System takes advantage of the symmetry which usually ex-
ists in fly ash hopper installations by using a single source
head with dual ports to illuminate opposing hoppers. Thus, most
plants will require only half the number ode sources and source
heads as those using previous level switch system designs. The
electron components are designed for continuous 93°C (200°F)
operation. The system uses a Geiger-Muller radiation detector
tube. One of the major advantages of the system is its 100%
digitial circuitry. Another feature is a remote source actuator
mechanism which provides positive opening, closing, and lock-out
of the source head at locations convenient to the operator. Also,
the mechanical design of the source head and detector eliminates
the necessity of penetrating the insulation and welding mounting
brackets to the hopper walls. Table 2 lists specifications for
the detector and the source and source heads.
Automation Products, Inc.
3030 Max Roy Street
Houston, Texas 77008
Phone: 713/869-0361
Automation Products, Inc. manufactures Dynatrol Detector
Model CL-10DJ which consists of a rod which is installed through
the wall of the collection hopper at the desired level detection.
When the probe is uncovered, the drive coil drives the rod into
self-sustained mechanical oscillations at the natural resonant
frequency of the rod. The pickup coil, located opposite to the
drive coil, is excited by the mechanical oscillations of the rod
and produces an ac signal voltage. The presence of this signal
voltage indicates that the rod is uncovered or that a low level
exists. When the fly ash covers the rod a dampening of the rod
oscillations occurs. The magnitude of the rod oscillations are
greatly reduced and the output from the pickup coil drops to a
64
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BEAM
SHROUD
REMOTE SHUTTER
ACTUATOR & INTERLOCK
BEAM
LIMIT
PNF
DETECTOR
3540-028
Figure 32. Typical hopper installation, Texas Nuclear
Division, Ramsey Engineering Co.
65
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TABLE 2. SPECIFICATIONS FOR TEXAS NUCLEAR
DETECTOR AND SOURCE AND SOURCE HEADS
SPECIFICATIONS
DETECTOR-ELECTRONICS
Level reproducibility: + .64 cm ( + 1/4 Inch). .
Sampling time: 1 to 3 minutes depending on application..
Radiation field required: 0.05 to 0.1 mR/h.
Minimum radiation change for operation: 25%.
Product temperature: Unlimited.
Ambient temperature: Designed for continuous operation at 93°C
(200°F) . Minimum operating temperature, -40°C (-40°F)..
Detector: Single halogen-quenched Geiger-Miiller tube.
Output: DPDT contacts, (10 ampers @ 115 VAC). .
Circuitry: Total digital—all integrated circuits. Premium,
high temperature components.
Controls: None—no adjustments in electronics required.
Power requirements: 115 VAC + 15% @ 10 VA; 50-60 Hz.
Detector housing: Special lightweight aluminum construction.
Dust and waterproof. Integral mounting bracket.
Size: 28.3 cm (II 1/8") long (plus conduit hub) x 15.2 cm (6")
high x 15.2 cm (6") deep including mounting bracket (283mm x 152mm)
Weight: 2 kg (4 1/2 Ib).
SOURCE & SOURCE HEADS
Source material: Cesium-137.
Source sizes: 5 to lOOmCi depending on hopper size.
Head construction: Lead filled, steel encased. Special dual beam
ports. Adaptable to Kirk or Superior key interlocks. Remote
actuator with interlocks available.
Head weight: ^ 16 kg (35 Ibs).
66
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very low value, indicating that the rod is covered or that a high
level exists. A typical installation of the detector is shown
in Figure 33.
United Conveyor Corporation
300 Wilmot Road
Deerfield, Illinois 60015
Phone: 312/948-0400
The United Conveyor Corporation Hopper Level Detector is a
capacitance sensing on-off control instrument used for detecting
or controlling product level in vessels or containers. Control
action is provided by means of relay contact closure and alarm
lamp indication in the display unit. The control is designed
for mounting remotely from the level detector assembly. The
detector assembly senses the change in product or material level
as a function of the capacitance change between the detector and
the vessel wall, and transmits this change to the control instru-
ment. Specifications for this detector assembly are given in
Table 3 and a diagram of a typical installation is shown in
Figure 34.
Bindicator
1915 Dove Street
Port Huron, Michigan 48060
Phone: 1/800/521-6361
Bindicator manufactures several different types of level
controls, but the one which appears most applicable for hopper
level control is the PRTM-CO series 700 radio frequency level
control. This control consists of a vessel, the vessel's com-
ponents, a sensing probe, and an electronic unit. The electronic
unit provides a low power RF signal which is radiated from the
sensing probe and measures any changes in the probe impedence
caused by a change in the material level. Current changes not
caused by change in the material level are eliminated by use
of electronic compensation techniques. On a point control, cur-
rent changes caused by the material cause activation of a relay.
On a continuous control an electrical signal is given which is
proportional to the level of material being measured. Table 4
gives the electrical specifications for both the point control
and continuous control models of PRTMCO.
Removal from Hoppers'*3'22 —
Fly ash materials collected in hoppers will have different
chemical and physical characteristics than those experienced at con-
ditions inside the precipitator. For example, fly ash flows similar
to a liquid well above the dewpoint, but when cooled below 121°C
(250°F) to 149°C (300°F)., its hygroscopic nature causes agglomeration
'and caking. Therefore, as stated earlier, maintaining fly ash
sufficiently above the gas dewpoint temperature will prevent caking
67
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3/4" MPT
HALF COUPLING
DYNATROL
DETECTOR
TYPE CL-10DJ
CONTROL UNIT
TYPE EC-501A
BULK SOLIDS HOPPER
3540-029
Figure 33. Typical installation of detector Type CL-10DJ.
68
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TABLE 3. SPECIFICATIONS FOR UNITED CONVEYOR CORPORATION HOPPER
LEVEL DETECTOR
Operating Temperature Limits;
Control
Detector
Vibration Limits
Enclosure Classification
Operating Humitity Range
Supply Voltage
Supply Power
Output Relay
Zero Adjustment Range
Response Time
Differential (Dead band)
Connecting Cabl-s
-40°C (-40°F) to +71°C (+160°F)
427°C (+800°F)
2 g's 10 to 100 Hz
Weatherproof
0% to 90% RH
117 V AC + 10% 60 Hz
12 VA Maximum
5Af 117 VAC/26.5 VDC, Noninductive;
3A, 230 VAC Noninductive
20 to 225 pf
50 ms
0.1 pf Maximum
TRIAX Cable 61 m (200 ft) max.
69
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VESSEL WALL
0-3403-27 B/M
(1) SENSOR CONNECTION
HEAD ASS 'Y
SK 3403-28 B/M
(1) LEVEL SENSOR ASS'Y
3-2710-14 B/M
(1) WINDOW WITH PADDLE
ASS'Y
FOR MATERIAL UP TO 800°F
REFERENCE PART NUMBERS
1 SENSOR - SK-34164-1
2 - SENSOR SHIELD - SK-45603
3 - MOUNTING PLATE - SK-34164-2
4 PADDLE & ROD SK-34165
5 ADAPTOR - 2-34148-1
6 CLAMPING RING - SK-15328
7 - DETECTOR HANDLE - SK402038
8 - SENSOR FRAME - SK-15327
9 - SENSOR SPRING - SK-34164-5
10 - PACKING GLAND - SK-15359
11 GASKET (2) - SK-408580-1
12 - PACKING (4 pc) - 40638-22
13- GASKET SK-408580-2
14 - SENSOR CONN. HEAD - SK-42093
8640-031
Figure 34. Hopper level detector No. 3-3404-26.
70
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TABLE 4. ELECTRICAL SPECIFICATIONS FOR POINT CONTROL
AND CONTINUOUS CONTROL MODELS OF PRTMCO
ELECTRICAL SPECIFICATIONS:
Point — Model 700
Line Voltage: 115 + 20 VAC, 50/60 Hz
Power: 6 watts
Line Voltage Sensitivity: + 0.05 pf for + 20 VAC
Ambient Temperature for electronic unit: -40UC to +71°C (-40°F
to +160°F)
Temperature Sensitivity: + 0.1 pf for -1°C (30°F)
Output: DPDT, 5A relay at 115 VAC non-inductive
Input Sensitivity: 0.1 pf
Stability: 0.1 pf for 6 months
Output Response Time: 0.02 sec.
Continuous — Model 770
Line Voltage: 115 + 20 VAC, 50/60 Hz
Power: 12 watts
Line Voltage Sensitivity: + 0.5% for + 20 VAC
Ambient Temperature for electronic unit: -40°C to +71°C (-40°F
to +160°F)
Temperature Sensitivity: 0.02% per °F or .08 pf (whichever is
larger)
Span: .25 to 4000 pf
Output and Max. Load Resistance:
1 - 5 ma 6000 ohms
4 - 20 ma 1500 ohms
10 - 50 ma 600 ohms
Load Resistance Sensitivity: 0.1% from zero to full load
Output Line.arity: + 0.5%
Output Response Time: 150 y sec.
Probe Coating Error: max. error for 2000 ohm-cm coating 0.16 cm
(1/16") thick is 3.81 cm (1.5")
71
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and add greatly to ease of ash removal from the hopper. . Vibrators
are sometimes used to prevent bridging.
Several types of systems exist for the removal of dusts
accumulated in hoppers. These systems, include container removal,
dry vacuum, wet vacuum., screw conveyors, and scraper bottom. A
brief description of these ash removal systems is given below.
Dust Removal Systems—
Container removal—This system is used on small installations
collecting dry material in a hopper. The hoppers are usually of
the conical or pyramidal type. The system consists of placing a
transportable container below the hopper. The collected material
stored in the hopper is transferred to the container through a
simple manual valve or slide gate. When filled, the container
is removed for emptying. In some instances the container is
embodied as part of a truck.
Dry vacuum systems—In this system, dry bulk material is
transferred from a precipitator hopper to a transport pipe system
which is under vacuum.. The material is metered from the hopper
to the transport system through automatic rotary feeder valves
or dump valves. The system vacuum is developed by an air pump.
In order to maintain system fluidity, ambient air or hopper gas
is induced as a carrier. The pump discharges the dust into a
silo for storage.
Wet vacuum systems—In this system, dry dust is removed from
a precipitator hopper into a transport pipe system which is main-
tained under vacuum by a water aspirator. The collected dust or
ash is metered from the hopper into the transport system through
automatic feeder valves or dump valves. In order to keep the
dust suspended in the gas carrier, ambient air or additional
hopper gas is induced into the transport line. The dry material
being transported mixes with the water used for aspiration and
forms a slurry. From this point the water-dust mixture is run
to waste.
Screw conveyors—"A screw conveyor system usually starts with
an open screw in the bottom of a trough-type hopper which moves
the dry dust to the outside. At the turns in the system each
screw run passes the dust on to each successive screw by a gravity
drop. The dust is moved on to a system silo or directly to some
mobile conveyance. A screw conveyor system is also applicable
with a conical or pyramidal type hopper. A rotary valve is re-
quired when the system is operating under vacuum.
Scraper bottom—The precipitator hopper is a flat bottom pan.
An endless belt type scraper moves the collected dust to one end
where a screw conveyor is located. The screw moves the dust out
of the hopper. Once outside, the dust is conveyed.to some remote
72
-------
point by any form of system such as container removal, vacuum, or
screw.
Gas Flow Devices
General—
The best operating condition for an electrostatic precipita-
tor will occur when the velocity distribution is uniform. Because
of the logarithmic nature of the Deutsch efficiency formula, an
increased velocity in one plate section will decrease the effi-
ciency of that section more than the decreased velocity in a
parallel section would increase the efficiency of that section.
As a consequence, for a precipitator with nonuniform gas velocity,
the total plate area required to achieve a given efficiency will
be greater than that for a precipitator with uniform gas velocity.
One quantitative criterion describing the quality of gas distri-
bution is that used by the Electrostatic Division of Industrial
Gas Cleaning Institute. It states that acceptable gas distribution
is achieved when 85% of all local gas velocities are within + 25%
of their average, and no single reading differs from the average
by more than 40%. Quality gas distribution is especially important
in the entrance to the gas cleaning device, but acceptable gas
distribution in the transport system typically may be as low as
65% within + 25% depending on the complexity of the system.k<4
Basically, the measurement technique consists of measuring
gas velocities in a prescribed pattern. An imaginary plane is
passed through the duct perpendicular to the gas flow at the lo-
cation to be evaluated and this cross sectional area is broken
down into smaller equal areas. Figure 35 gives an example of a
rectangular system divided into equal areas.1*1*
To achieve uniform flow in a duct according to ASME test pro-
cedures, one should have at least ten diameters of duct before and
after any distrubance such as the elbow, expansion or contraction.
In practice, such conditions cannot always be economically realized
because of space limitations and the high cost of ducts in the
sizes involved. However, given a reasonable space, it is possible
to approach an acceptable quality of flow at the precipitator inlet
by the use of straighteners, splitters, vanes, and diffusion plates.
Straighteners—
Partitions in a straight section of duct for the purpose of
eliminating swirl are called straighteners. They may be "egg
crate" dividers or nested tubes as shown in Figure 36-a.
A straightener will reduce the angle o,f a helical flow path
to some angle less than that defined by arc tan = ng.—
• * spacing
73
-------
warn.
VELOCITY MEASUREMENTS AT EACH LOCATION IN DUCT
SUM OF VELOCITIES = 2,000
AVERAGE VELOCITY = "^p = 100
ACCEPTABLE RANGE = ±25% OF AVG. VEL. = 75 TO 125
17 (WITHIN RANGE)
20 (MEASUREMENTS
85% WITHIN RANGE
3540-031
Figure 35, Computation of gas velocity distribution,
74
-------
: 36a
36b.
36c.
36d.
HARD BEND
EASY BEND
3540-032
Figure 36. Flow devices,
75
-------
The nonuniformity in the velocity in the axial direction will
not be reduced. The scale of turbulence, or eddy diameter, will
be temporarily reduced to the same size as the spacing of the
straighteners, but because the Reynolds number is usually well
above critical, the eddies will not die out, but will grow until
they again reach the order of magnitude of the full duct. It
is theoretically possible to make the spacing of straighteners
small enough to obtain a Reynolds number less than critical and
to obtain laminar flow through the straighteners, and to obtain
nearly absolute uniformity. Unfortunately, such spacing would
only be about the size of soda straws and the stxaightener would
be expected to plug up with dust almost immediately.
A recommended straightener, according to AMCA Bulletin 210,^5
is an egg crate with a spacing of 7 1/2 to 15% of the diameter
of a round duct or the average side of a rectangular duct, and
with a length equal to three times the spacing. This reduces
the swirl angle to arc tan 1/3 = 18 1/2°. An alternate straight-
ener is a simple criss-cross at least one and a half diameters
long. The loss in these straighteners is equal to the loss in
four plain duct diameters. If it is necessary to reduce the swirl
angle to smaller values, the ratio- of length to spacing must be
increased, and the resulting friction will be higher.
Splitters—
A duct section that changes size or direction may be divided
into smaller ducts over the full length of the change by parti-
tions called splitters. Splitters may be used in elbows where
direction is changed, or in transformations where velocity is
changed. Splitters add wall friction, but can reduce total fric.-
tion by optimizing velocity pressure losses.
Losses in elbows depend in part on how sharp the bend is.
A square, or mitered, elbow will have a loss of 1.25 times the
velocity pressure, but an elbow of optimum configuration could
have a loss of only 0,11 to 0.14 velocity pressure. As shown in
Figure 37, the optimum configuration is an elbow with a ratio of
inside radius to outside radius of about 0.66 for a square duct,
or 0,7 for a round duct.23
To design a splitter elbow, therefore, it is only necessary
to divide the given elbow into segments all having a radius ratio
of about 2/3.
Transformation Splitters—
Splitters, shown in Figure 36-b, may also be used in a
diverging duct transformation to divide the flow into nearly
equal parts and then distribute the flow to the larger section.
76
-------
100
0.1
0.2
RATIO
0.3 0.4
INSIDE RADIUS
OUTSIDE RADIUS
0.5
3540-033
Figure 37. Elbow loss as a function of radius ratio.
2 3
77
-------
The gas flow will not be uniform within each segment of the
transformation section, but the volume through every segment can
be made equal to that in every other segment if the splitters are
manufactured to be field adjustable.
**
A sharp angle in the transformation causes the gas to sepa-
rate from the walls of the duct, introducing turbulence and non-
uniform flow. The maximum angle of divergence for no separation
is about 7° included angle. Therefore, splitters in a transfor-
mation should be selected to have 7° to 19° included angle between
successive splitters. For example, a transformation with 60°
included angle could be split into 8 channels with 7 1/2° spread,
or 6 channels with 10° spread as shown in Figure 36-c.
Note that a transformation in one direction is the simpler.
Transforming in two directions would require pyramidal splitters.
Vanes—
Another kind of deflector for redirecting gas flow is the
turning vane. Turning vanes are flat, bent, or curved plates
which are short relative to the duct section in which they are
installed, as opposed to splitters which extend the full length.
A plain flat plate vane used to deflect the air stream is partly
effective, but it tends to increase turbulence as shown in Figure
36-d.
The low pressure area behind the plate also tends to pull
the gas flow back toward its original path. Curved turning vanes
in an elbow can be quite effective if they are spaced to give
about a 6:1 aspect ratio and a 2/3 radius ratio, and are stream-
lined to give constant cross section through the turn.
The streamlined turning vanes shown in Figure 38 will pre-
serve the flow pattern and will have a loss of about 10% of the
velocity pressure.23 A set of single thickness turning vanes
will also preserve the flow pattern, but will have about 35%
velocity pressure loss and may introduce some turbulence because
of the unequal cross sections between them. Single thickness
vanes should have a straight extension downstream with length
aboiAt twice the spacing. In practice, single thickness turning
vanes are generally used because of cost considerations.
For rectangular elbows, one parameter is the aspect ratio,
or the ratio of the depth of the elbow measured parallel to the
axis of the bend to the width of the elbow measured in the plane
of the bend, as shown in Figure 36-e.
It is intuitively obvious from the sketches that a low
aspect ratio elbow is a "hard" bend with high pressure loss which
has very nonuniform flow caused by inertial forces. Any aspect
ratio greater than unity will make a fair elbow, but aspect
ratios from 4 to 6 are recommended.
78
-------
3540-034
Figure 38. Streamlined turning vane elbow.
2 3
79
-------
Turning vanes are also used in transformation elbows; that
is, elbows that change cross section between inlet and outlet.
Although the combination of elbow and transformation is relatively
poor design practice, severe space limitations may force it upon
the designer. If a transformation elbow must be used, then
turning vanes are essential, and they must be closely spaced to
about the same spacing as the- preclprfeator plates. They must
also be followed by additional flow •rectification means such as
diffusion plates.
Diffusion Plates--
Diffusion plates, or screens, are simply perforated plates
or wire screens which improve the uniformity of air flow by a
combination of effects. First, they reduce the scale of tur-
bulence from the order of magnitude of the duct; to the order
of magnitude of the holes. Of course, the kinetic energy that
existed in the large scale eddies will reappear in the small
scale eddies, but the large differences in velocity will be re-
duced. Second, there is a pressure drop across the screen and
a reduction in area. The pressure drop will partly reappear
as a velocity vector perpendicular to the plate. This vector
added to the original velocity vector will give a resultant
velocity always more nearly perpendicular to the plate. Thus,
it might be possible to design a diffuser plate to turn the gas
stream through a precise small angle. However, in practice,
it is usually simpler and less costly to use two or more dif-
fusion screens in series to achieve a fair degree of uniformity.
Perforated plate screens break the gas stream up into a
multiplicity of small jets with high turbulent intensity and
small scale of turbulence. These jets eventually coalesce down-
stream. The turbulent intensity reaches a peak at 2 to 3 mesh
lengths (center to center of holes) downstream and declines
exponentially thereafter. The scale of turbulence is of the
order of the hole size at the screen and increases until it
reaches the size of the duct. There is a critical parameter of
50% open area for diffusion screens. When the percentage of
open area is less than 50%, the jets seem to be too far apart
to coalesce uniformly and the screen introduces nonuniformity.
When the percentage of open area is between 50% and 65%, the
jets appear to coalesce with 5 to 10 mesh lengths (center to
center of holes) with improvement in uniformity.1*6
Screens may be used in series to provide greater uniformity
at the cost of larger pressure drops. Dryden and Schubauer1*7
developed the following relationship for the reduction in tur-
bulent intensity:
r = (1 + k)~*n (5)
80
-------
where
r = reduction factor
k = pressure drop coefficient = —\~n
n = number of screens in series
p = pressure drop
p = density
v = average velocity.
All of the preceding duct work design techniques are avail-
able to the designer. None of the criteria are rigid, so there
is considerable freedom in design. It is the designer's choice
as to whether to use splitters, turning vanes, or screens to
control the air distribution. On the inlet side of a precipitator,
there may be a heavy dust loading of particle sizes large enough
to settle out. Horizontal splitters or vanes form convenient
shelves for the deposition of disastrous quantities of dust.
Therefore, horizontal splitters and vanes are generally used
only when the velocity is higher than the erosion velocity of
deposited dust. Dust will collect by impaction on the diffusion
screens, so some means of cleaning then is required, such as
regular rapping or soot blowing.
TYPES OF PRECIPITATORS USED TO COLLECT FLY ASH
Cold-Side
Most electrostatic precipitators utilized to collect fly ash
are of the cold-side type. That is, they are located downstream
of the air preheater and operate at gas temperatures in the neigh-
borhood of 150°C (300°F). The principal factor responsible for
variations in performance of fly ash precipitators is the resis-
tivity of the ash. Fly ash is composed largely of the oxides
of aluminum, silicon, iron, and'calcium, which at the operating
temperatures of most precipitators, give it a very high elec-
trical resistivity. However, moisture and sulfur trioxide present
in the flue gases will be adsorbed on the fly ash particles and
will reduce, the resistivity. If the coal being burned has a
sufficient sulfur content, the resistivity of the fly ash will
be low enough (^2.0.x 101Q fi-cm) for good precipitator performance.
However, if the sulfur content of the fuel is low, the amount of
sulfur trioxide in the flue gas can be insufficient for proper
conditioning of the ash. Owing to the increasing emphasis on
the use of low-sulfur coals to minimize emission of sulfur oxides
and the simultaneous demands for improvements in fly ash col-
lection, increasing efforts are being made to find methods to
overcome the problem of high resistivity. One method of improving
81
-------
the performance of fly ash precipitators collect-ing high resis-
tivity dust is to reduce the gas temperature so that the resis-
tivity is in a range more favorable."'for;-precipitation:.' However,
most power plants burning coal with sulfur in the range of two
to three percent, operate at gas temperatures from the air pre-
heater in the vicinity of 150°Cf primarily to minimize corrosion
and fouling tendencies. Another method/that _ is used to^improve
precipitator performance is to inject a chemical conditioning
agent in the flue gas. The best known:chemical conditioning
agents are sulfur trioxide and ammonia. Of the two, sulfur tri-
oxide conditioning is the most familiar. Figure 39 is a diagram
of a liquid SO2 system in which liquid sulfur dioxide is vaporized
and passed over a catalytic oxidizer in the presence of air.
Figure 40 is a diagram of a sulfur burning system in which molten
sulfur is burned to produce gaseous sulfur dioxide and catalyti-
cally converted to sulfur trioxide.1+B Other conditioning agents
that are potentially useful include sulfamic acid, ammonium sul-
fate, ammonium bisulfate, and triethylamine. Proprietary chem-
icals have also been used.
Hot-Side
The increasing use of low sulfur coal and the accompanying
high ash resistivity at normal precipitator operating temperatures
has led to the use of hot-side precipitators. Hot precipitators
are located upstream of the air preheater and operate at temper-
atures generally in the range of 316 to 482°C (600 to 900°F).
The resistivity of most fly ash is sufficiently low at these
temperatures that current is not limited by fly ash resistivity.
A schematic of an electrostatic precipitator system when a
hot-side precipitator has been retrofitted to supplement an
existing cold-side precipitator is shown in Figure 41.27 Note
the locations of the two collectors with respect to the air
preheater. Besides the avoidance of. resistivity problems,
secondary advantages of hot precipitators include elimination
of corrosion and hopper plugging problems, easier hopper emptying
and ash transport, and better electrical stability and higher
corona current densities than are possible with low temperature
precipitators treating high resistivity ash. Some of the dis-
advantages of using hot precipitators are: operating voltages
are substantially reduced due to the lower densities of hot
gases, gas viscosity increases with temperature thus reducing
precipitation rate, structural and mechanical problems such as
precipitator shell failures and support structure distortions,
and the necessity for very long interconnecting flues needed
between the precipitator and the boiler, and gas flows are
about 50% higher because of expansion of the gases at the
higher temperatures (Figure 42 illustrates the relationship
between the sizes of a hot-side precipitator and a cold-side
precipitator for the same efficiency, as .the dust resistivity
varies).^9 A number of successful hot precipitator installations
exist, and Table 5 lists some design parameters for the hot-side
units.1*9 Recently, serious electrical problems associated with the
collected ash layer have surfaced in many hot-side precipitators.
This topic will be discussed in some detail later in the text.
82
-------
VAPORIZED SO-
'SULFUR DIOXIDE\ f
STORAGE TANK / f f^-/-^, \
S02 VAPORIZER '
BLOWER AIR HEATERS
.AMBIENT CONDITION
AIR/S02
' 800-825°F 1Mlpr
(427-441°C) ^Qg
| AIR/SO3
/ 820°-1100°F-
\ I (433-593°C)
/ CONVERTER
S02 + /2O2 SO3
ED
AIR IN FLUE GAS TO
PRECIP1TATOR
^
E
>
i
BO
ION
S
\
H
J
LER FLUE C
I
\
Utlii
3AS
AIR
*~ PREHEATER
3540-035
Figure 39. Liquid S02 system.
83
-------
UNLOADING
PUMP
BLOWER
SULFUR STORAGE
TANK
METERING
PUMP
BOILER FLUE GAS
AIR/SO3
820-1100°F
(438-593°C)
SULFUR BURNER
/CONVERTER
AIR HEATERS
urnr
AMBIENT
AIR IN
CONDITIONED
FLUE GAS TO '
PRECIPITATOR
.AIR
PREHEATER
.INJECTION
PROBES
3640-036
Figure 40. Sulfur burning SO2 system.
84
-------
INDICATES GAS FLOW
NOT TO SCALE
HOT SIDE
ELECTROSTATIC
PRECIPITATOR
COAL SAMPLE f
POINT
SUPER HEATER
Wll
STACK
ELECTROSTATIC
AIR PREHEATER V ) PRECIPITATOR
INDUCED DRAFT FAN
3540-037
Figure 41.
Schematic of an ESP system when a hot-side precipitator
has been retrofitted to supplement the existing cold-
side precipitator.27
85
-------
700
- 19,7
1 x 10°
1 x 1010 1 x 1011
FLY ASH RESISTIVITY ohm-cm
1 x TO12
3(40-307
Figure 42.
Illustration of the effects of fly ash resistivity on
precipitator size for 99.5% collection efficiency.
Curves are plotted on the basis of actual cubic feet
per minute of gas flow. For 700°F hot-side and 300°F
cold-side temperature, the ratio of gas flow for the
same size boiler would be about 1.5. Hot-side resis-
tivity is assumed to be not limiting.1*9
-------
TABLE 5. HOT-SIDE PRECIPITATOR INSTALLATIONS'19
Manufacturer
Research Cottrell
Buell
Buell
Buell
Research Cottrell
' :
Research Cottrell
Research Cottrell
Research Cottrell
Research (Jottrell
Western
Research Cottrell
Buell
Research Cottrell
Buell
Research Cottrell
Research Cottrell
Western
Western
Pollution Control Walther
Pollution Control Walther
Pollution Control Walther
Pollution Control Walther
Pollution Control Walther
Pollution Control Walther
Pollution Control Walther
Pollution Control Walther
Pollution Control Walther
—
-
-
Collection
Efficiency,
%
99.2
99.0
99.08
99.0
99.0
99.5
99.5 •
99.0
99.73
99.0-
99.0
99.83
99.15
99.0
99.5
99.57
99.0
99.0
98.5
99.5
99.5
99.0
99.0
99.3
99.3
99.5
99.1
99.5
99.6
99.32
99.5
99.33
Effective
Migration
Velocity,
cm/sec
9.03
9.75
10.0
9.75
10.65
-
8.7
10.8
11.5
10.65
8.5
10.0
11.3
11.1
10.1
9.15
8.91
8.98
8.58
8.78
8.26
7.94
8.94
7.8
7.06
8.21
9.39
Specific
Collecting Temper-
Area, ft2/ ature,
1000 ft3/min °P
270
240
238
240
220
-
310
215
250
220
270
324
215
245
235
235
310
250
260
295
288
325
301
369
359
353
322
366
650
800
690
800
690
810
828
690
650
650
650
640
672
690
550
520
690
809
675
625
800
700
655
721
705
775
660
700
815
820
820
720
700
Volume Outlet Date
Flow Rate, Loading, Opera-
1000 acfm gr/acf tional
1,250
337
640
340
400
2,770
1,322
402
1,160
690
1,000
313
1,118
825
487
4,079
600
250
1,425
670
4,000
470
1,428
1.274
163
440
2,474
1,700
5,142
2,314
5,104
3,000
3,888
72-73
72
74
73
71
0.0163 72
72
0.005 72
0.018 70
73
0.005 67
73
73
72
73
76
76
75
75
76
77
77
78
76
75
73
Generat-
ing Rate,
MW
870
132
486
350
150
250
147
750
412
210
200
1000
52
300
114
750
350
250
125
30
100
550
350
800 ea.
550
818 ea.
500 ea.
660 ea.
-------
COMPILATION OF INSTALLATIONS USING ELECTROSTATIC PRECIPITATORS
TO COLLECT FLY ASH
There are a large number of electrostatic precipitator in-
stallations used for fly ash collection .in the United States.
Table A-l, located in the Appendix, contains a compilation of data
from every precipitator installation used for collection of power
plant fly ash in the U.S. These data were -copied from Federal
Power Commission files and are organized into three subject areas:
(1) coal data, such as the heat content, sulfur, content, and ash
content, (2) boiler data, such as-year placed in service, gen-
erating capacity, coal consumption, air flow, type of firing,
manufacturer, efficiency, and -percent excess air, and (3) pre-
cipitator data, such as manufacturer, year placed in service,
design and tested efficiencies, mass emission rate, and installed
costs.
This information is furnished by each power plant as part of
FPC Form No. 67. Some of the data were not available for every
plant and these cases are indicated by a hyphen. The most fre-
quent omissions are for tested efficiencies of the electrostatic
precipitators. There are other cases in which a range is given
for tested efficiencies instead of exact numbers. These are
instances in which there are more than one precipitator and it
is unclear which efficiency belongs to which precipitator. These
data are based on information furnished by individual electric
utilities. Neither the Environmental Protection Agency nor
Southern Research Institute were responsible for gathering the
data and thus can not attest to its validity.
88
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SECTION 6
ANALYSIS OF FACTORS INFLUENCING ESP PERFORMANCE
PARTICLE SIZE DISTRIBUTION
General Discussion
The particulate matter suspended in industrial gas streams
may be in the form of nearly perfect spheres, regular crystalline
forms other than spheres, irregular or random shapes, or as ag-
glomerates made up from combinations of these. It is possible
to discuss particle size in terms of the volume, surface area,
projected area, projected perimeter, linear dimensions, light
scattering properties, or in terms of drag forces in a liquid
or gas (mobility). Particle sizing work is frequently done on
a.statistical basis where large numbers of particles, rather than
individuals, are sampled. For this reason the particles are
normally assumed to be spherical. This convention also makes
transformation from one basis to another more convenient.
Experimental measurements of particle size normally cannot
be made with a single instrument if the size range of interest
extends over much more than a-^decimal order of magnitude. Pre-
sentations of size distributions covering broad ranges of sizes
then must include data points which may have been obtained using
different physical mechanisms. Normally the data points are con-
verted by calculation to the same basis and put into tabular form
or fitted with a histogram or smooth curve to represent the par-
ticle size distribution. Frequently used bases for particle size
distributions are the relative number, volume, surface area, or
mass of particles within a size range. The size range might be
specified in terms of aerodynamic, Stokes, or equivalent Polysty-
rene Latex (PSL) bead diameter. There is no standard equation for
statistical distributions which can be universally applied to
describe the results given by experimental particle size measure-
ments. However, the log-normal distribution function has been
found to be a fair approximation for some sources of particulate
and has several features which make it convenient to use. For
industrial sources the best procedure is to plot the experimental
points in a convenient format and to examine the distribution in
different size ranges separately, rather than trying to charac-
terize the entire distribution by two or three parameters. The
ready availability of inexpensive programmable calculators which
can be used to convert from one basis to another compensates
greatly for the lack of an analytical expression for the size
distribution.
89
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Characterization Of Particle Size Distributions
Figure 43 shows plots of generalized unimodal particle size
distributions which will be used to graphically illustrate 'the
terms which are commonly used to characterize an aerosol.
Occasionally size distribution plots exhibit more than one peak.
A size distribution with two peaks would be called bimodal. Such
distributions can frequently be shown to be equivalent to the sum
of two or more distributions of the types shown in Figure 43. If
a distribution is symmetric or bell shaped when plotted along a
linear abscissa, it is called a "normal" distribution (Figure 43-c).
A distribution that is symmetric or bell shaped when plotted on
a logarithmic abscissa is called "log-normal" (Figure 43-d).
Interpretation of the frequency or relative frequency shown as
f in Figure 43 is very subtle. One is tempted to interpret this as
the amount of particulate matter of a given size. This interpreta-
tion is erroneous however and would require that an infinite number
of particles be present. The most useful convention is to define
f in such a way that the area bounded by the curve (f) and vertical
lines intersecting the abscissa at any two diameters is equal to the
amount of particulate matter in the size range indicated by the dia-
meters selected. Then f is equal to the relative amount of particulate
matter in a narrow size range about a given diameter.
The median divides the area under the frequency curve in half.
For example, the mass median diameter (MMD) of a particle size
distribution is the size at which 50% of the mass consists of
particles of larger diameter, and 50% of the mass consists of
particles having smaller diameters. Similar definitions apply
for the number median diameter (NMD) and the surface median diam-
eter (SMD).
The term "mean" is used to denote the arithmetic mean of the
distribution. In a particle size distribution the mass mean diam-
eter is the diameter of a particle which has the average mass for
the entire particle distribution. Again, similar definitions hold
for the surface and number mean diameters.
The mode represents the diameter which occurs most commonly
in a particle size distribution. The mode is seldom used as a
descriptive term in aerosol physics.
The geometric mean diameter is the diameter of a particle
which has the logarithmic mean for the size distribution. This
can be expressed mathematically as:
log D + log D, + . . . . log DKT
log Dg = ± ^ N- (6-a)
90
-------
a. Distribution Skewed Left
b. Distribution Skewed Right
LOG
LU
o
cc
LOG o,
63.27%
LOG D
c. Normal Distribution
d. Log Normal Distribution
3540-038
Figure 43. Examples of frequency or particle size distri-
butions. D is the particle diameter.50
91
-------
or as
lfl
<6-b)
The standard deviation (cf) and 'relative standard deviation
(a) are measures of the dispersion (spread, or polydispersity)
of a set of numberSo The relative standard deviation is the
standard deviation of a distribution.-divided'.by the mean,- where
a and the mean are calculated on the same basis; i.e., number,
mass, or surface area. A monodisparse aerosol has a standard
deviation and relative standard deviation of zero. For many pur-
poses the standard deviation is preferred because it has the same
dimensions (units) as the set of interest. In the case of a normal
distribution, 68.27% of the events fall within one standard devi-
ation of the mean, 95.45% within two standard deviations, and
99.73% within three standard deviations.
Table 6 summarizes nomenclature and formulae which are fre-
quently used in practical aerosol research.5l In actual practice
most of the statistical analysis is done graphically.
Field measurements of particle size usually yield a set of
discrete data points which must be manipulated or transformed to
some extent before interpretation. The resultant particle size
distribution may be shown as tables, histograms, or graphs.
Graphical presentations are the conventional and most convenient
format and these can be of several forms.
Cumulative mass size distributions are formed by summing all
the mass containing particles less than a certain diameter and
plotting this mass versus the diameter. The ordinate is speci-
fically equal to M(j) = j M. , where M. is the amount of mass con-
t=l r r
tained in the size interval between D. and D. , . The abscissa
would be equal to D.. Cumulative plots can be made for surface
area and number of particles per unit volume in the same manner.
Examples of cumulative mass and number graphs are shown in Figures
44-b and 44-a, respectively, for the effluent from a coal-fired
power boiler.52 Although cumulative plots obscure some information,
the median diameter and total mass per unit volume can be obtained
readily from the curve. Because both the ordinate and abscissa
extend over several orders of magnitude, logarithmic axes are
normally used for both.
A second form of cumulative plot which is frequently used is
the cumulative percent of mass, number, or surface area contained
in particles having diameter smaller than a given size. In this
case the ordinate would be, on a mass basis:
92
-------
TABLE 6. SUMMARY OF NOMENCLATURE USED TO DESCRIBE PARTICLE
SIZE DISTRIBUTIONS51
Name Symbol Formula
Volume or Mass Mean Diameter D .N
m / v _ n
Surface Mean Diameter D
s
Geometric Mean Diameter D
m \ N
N
OJ
N
Number Mean Diameter D^ v
n L
N
N v1/*
N 3
Surface-Volume Mean Diameter, D „
or Sauter Diameter D _ ._^ j
VS N 2
-------
TABLE 6. (CONT'D.)
Name
Standard Deviation
Relative Standard Deviation
Mass Median Diameter
Surface Median Diameter
Number Median Diameter
Symbol
Formula
a
MMD
SMD
NMD
0 =
a
D
n , s
Medians are most conveniently
determined graphdcallyi For man
slightly skewed distributions
Median = Mean 4- -^(Mode-Mean) .
*j denotes a particular size interval, N is the total number of intervals, £< is the
relative, mass, surface area, or number of particles in the interval, and D-l is the
diameter characteristic of the jtn interval. -*
-------
UJ
ly CO
Q Q
10*2
u.
o o
i!
io11
1010
0.01 0.1 1.0
PARTICLE DtAMHTER,
a. Cumulative No. Graph
10
0.01 0.1 1.0
PARTICLE DIAMETER, um
b. Cumulative Mass Graph
10
1014
10"
wio
109
108
0:01 0.1 1.0
PARTICLE DIAMETER,
c. Differential No, Graph
10
10-2
0.01 0.1 1.0
PARTICLE DIAMETER, ;
d. Differential Mass Graph
3640-039
Figure 44. A single particle size distribution presented in
four ways. The measurements were made in the
effluence from a coal-fired power boiler.52
95
-------
3
Z M
t~ 1
Cumulative percent of mass less than size = — - x 100%. (7)
N M
2 Mt
t=l
The abscissa would be log D . . Special log-probability paper is
used for these graphs, and for log-normal distributions the data
set would lie along a straight line. For such distributions the
median diameter and geometric standard deviation can be easily
obtained graphically. Figures 45-a and 45-b show cumulative per-
cent graphs for the size distribution shown in Figure 44-a and a
log-normal size distribution.53
Differential particle s'iz-e distribution curves are obtained
from cumulative plots by taking the average slope over a small
size range as the ordinate and the geometric mean diameter of the
range as the abscissa. If the cumulative plot were made on log-
arithmic paper, the frequency (slope) would be taking finite
differences:
A (log D) log D.-log D. n
(8)
and the abscissa would be D = -/D.D._, where the size range of
interest is bounded by D. and D._, . M. and M.._. correspond to
the cumulative masses below these sizes. Differential number and
surface area distributions can be obtained from cumulative graphs
in precisely this same way. Differential graphs show visually
the size range where the particles are concentrated with respect
to the parameter of interest. The area under the curve in any
size range is equal to the amount of mass (number, or surface
area) consisting of particles in that range, and the total area
under the curve corresponds to the entire mass (number, or surface
area) of particulate matter in a unit volume. Again, because of
the extent in particle size and the emphasis on the fine particle
fraction, these plots are normally made on logarithmic scales.
Figures 44-c and 44-d are examples of differential graphs of
particle size distributions.
The particulate emissions from many industrial processes
frequently follow the log-normal distribution law rather well.
The particulate emissions from coal-fired boilers can often be
approximated by a log-normal particle size distribution. For log-
normal particle size distributions the geometric mean and median
diameters coincide.
96
-------
re
O
'o
3«
o"
01
u
5
z
V
I
C/5
LU
O
a. Cumulative Percent Graph
99.99
99
90
50
10
1
0.01
.02
b. Cumulative Percent Graph
(Log Normal Distribution)
0.1
1.0
10.0 .02
0.1
PARTICLE DIAMETER,
1.0
10.0
3540-040
Figure 45. Siz.e distributions plotted on log probability paper.
5 3
97
-------
The normal distribution law is, on a mass basis;
dM
dD ~
exp -
(D-D )
m
2o:
(9)
The log-normal distribution law is derived from this equation by
the transformation D -»• log D:
f =
where a
DM
d(log D)
•s/2ir log a.
exp
'log D-log D
gin
log a
(10)
the geometric standard deviation, is obtained by using
the transformation D ->• log D in equation (10) . This distribution"
is symmetric when plotted along a logarithmic abscissa and has the
feature that 68.3% of the distribution lies within one geometric
standard deviation of the geometric mean on such a plot. Mathe-
matically, this implies that log a = log Dg4 ..-log D or log
Dq~l°g D,^ og where Dg. . . is the diameter below which 84.14% of
the distribution is found, etc. This can be simplified to yield:
84
(11)
16
or
(12)
D
16
(13)
When plotted on log-probability paper, the log-normal distri-
bution is a straight^line on any basis and is determined completely
, , .., _ ,. _ , This is illustrated in Figure 45-b.
by the knowledge of D and a
Another important feature is the relatively simple relationships
among log-normal distributions of different bases. If D D
gm gs
and D „ are the geometric mean diameter of the mass, surface
D
gvs' """ "gN
area, volume-surface, and number distribution, then:
log Dgs = log Dgm - 4.6 log2 ag ,
log Dgvs = log Dgm - 1.151 log2 ag.
(14)
(15)
98
-------
log DgN = log D^ - 6.9 log2 ag. (16)
The geometric standard deviation remains the same for all bases.
• Particle size distributions may be expressed in terms of
several different types of particle diameters. It is important
to distinguish which type of particle diameter has been used in
the construction of a particle size distribution since certain
applications require that the particle size distribution be ex-
pressed in terms of a specific type of particle diameter.
If the density of a particle is known, the Stokes diameter
(D ) may be used to describe particle size. This is the diameter
of a sphere having the same density which behaves aerodynamically
as the particle of interest. For spherical particles, the Stokes
number is equal to the actual dimensions of the particle.
The aerodynamic diameter (DA) of a particle is the diameter
of a sphere of unit density which has the same settling velocity in
the gas as the particle of interest. The aerodynamic impaction
diameter (D _) of a particle is an indication of the way that a
particle behaves in an inertial impactor or in a control device
where inertial impaction is the primary mechanism for collection.
If the particle Stokes diameter is known, the D is equal to:
DAI = Ds /pC , (17)
where p(gm/cm3) is the particle density and C is the slip correc-
tion factor.
In optical particle -sizing devices the intensity of light
scattered by a particle at any given angle is dependent upon the
particle size, shape, and index of refraction. It is impractical
to measure each of these -parameters and the theory for irregularly
shaped particles is not well developed. Sizes based on light
scattering by single particles are therefore usually estimated by
comparison of the intensity of scattered light from the particle
with the intensities due to a series of calibration spheres of
very precisely known size. Most commonly these are polystyrene
latex (PSL) spheres. Spinning disc and vibrating orifice aerosol
generators can be used to generate monodisperse calibration aerosol;
of different physical properties. Because most manufacturers of
optical particle sizing instruments use PSL spheres to calibrate
their instruments, it is convenient to define an equivalent PSL
diameter as the diameter of a PSL sphere which gives the same
response with a particular optical instrument as the particle of
interest.
99
-------
Field Methods For Measuring Particle Size Distributions
General Considerations in Making Field Measurements—
An ideal particle size measurement device would be located
in situ and -give real time readout, of particle size distributions
and particle number concentration over the size range from 0.01
ym to 10 ym diameter. At the present time, however, partice size
distribution measurements are made using several instruments which
operate over limited size ranges and do not yield instantaneous
data.
Particle sizing methods used in making field measurements
may involve instruments which are operated in-stack, or out-of~
stack where the samples are taken using probes. For in-stack
sampling, the sample aerosol flow rate is usually adjusted to
maintain near isokinetic sampling conditions in order to avoid
concentration errors which result from under to oversampling
large particles (dia. > 3ym) which liave too high an inertia to
follow the gas flow streams in the vicinity of the sampling
nozzle. Since many particulate sizing devices have size frac-
tionation points that are flow rate dependent, the necessity for
isokinetic sampling in the case of large particles can result in
undesirable compromises in obtaining data — either in the number
of points sampled or in the validity or precision of the data for
large particles.
In general, particulate concentrations within a duct or
flue are stratified to some degree with strong gradients often
found .for larger particles and in some cases for small particles.
Such concentration gradients, which can be due to inertial effects,
gravitational settling, passageway to passageway efficiency vari-
ations in the case of electrostatic precipitators, etc., require
that multipoint (traverse) sampling be used.
Even the careful use of multipoint traverse techniques will
not guarantee that representative data are obtained« The location
of the sampling points during process changes or variations in pre-
cipitator operation can lead to significant scatter in the data.
As an example, rapping losses in dry electrostatic precipitators
tend to be confined to the lower portions of the gas streams, and
radically different results may be obtained, depending on the
magnitude of the rapping losses, and whether single point or
traverse sampling is used. In addition, large variations in re-
sults from successive multipoint traverse tests can occur as a
result of differences in the location of the sampling points when
the precipitator plates are rapped. Similar effects will occur
in other instances as a result of process variations and strati-
fication due to settling, cyclonic flow, etc.
Choices of particulate measurement devices or methods for in-
dividual applications are dependent on the availability of suitable
100
-------
techniques which permit the required temporal and/or spatial
resolution or integration. In certain instances the properties
of the particulate are subject to large changes in not only size
distribution and concentration, but also in chemical composition.
Different methods or sampling devices are generally required to
obtain data for long term process averages as opposed to the
isolation of certain portions of the process in order to determine
the cause of a particular type of emission.
Interferences exist which can affect most sampling methods.
Two commonly occurring problems are the condensation of vapor phase
components from the gas stream and reactions of gas, liquid, or
solid phase materials with various portions of the sampling systems.
An example of the latter is the formation of sulfates due to appre-
ciable (several milligram) quantities on several of the commonly
used glass fiber filter media by reactions involving SOX and trace
constituents of the filter media. Sulfuric acid'condensation in
.cascade impactors and in the probes used for extractive sampling
is an example of the former.
If extractive sampling is used and the sample is conveyed
through lengthy probes and transport lines, as is the case with
several particle sizing methods, special attention must be
given toward recognition, minimization, and compensation for
losses by various mechanisms in the transport lines. The degree
of such losses can be quite large for certain particle sizes.
In the following subsections, established field methods for
measuring particle size distributions are briefly discussed. These
are categorized according to the physical mechanism that is used to
obtain the data: inertial (aerodynamic), optical, diffusional, or
electrical. The purpose of the following subsections is to famil-
iarize the reader with the various methods and instrumentation
which are used to make field measurements of particle size distri-
butions. The capabilities, limitations, advantages, and disad-
vantages of the various methods and instrumentation are presented.
Detailed discussions of sampling procedures and data reduction
techniques are given elsewhere ' and will not be presented here.
Inertial (Aerodynamic) Methods—
Cascade impactors and cyclones are two types of inertial (aero-
dynamic) particle sizing instruments. These instruments employ the
unique relationship between a particle's diameter and mobility in
gas or air to collect and classify the particles by size. In order
to avoid unnecessary complications in presenting data obtained with
these instruments, particles of different shapes may be assigned
aerodynamic diameters. Impactors and cyclones are well suited for
industrial pollution studies because they are rugged and compact
enough for in situ sampling.
Figure 46 is a schematic which illustrates the principle of
particle collection which is common to all cascade impactors.56
101
-------
\ PATH OF
} SMALL
ff PARTICLE
SE40-&41
Figure 46. Schematic diagram, operation of cascade iinpactor.
56
102
-------
The sample aerosol is constrained to pass through a slit or cir-
cular hole to form a jet which is directed toward an impaction
surface. Particles which have lower momentum will follow the air
stream to lower stages where the jet velocities are progressively
higher. For each stage there is a characteristic particle diameter
which theoretically has a 50% probability of striking the collec-
tion surface. This particle diameter, or D50, is called the effective
cut size for that stage. Although single jets are shown in Figure
46 for illustrative purposes, the number of holes or jets on any one
stage ranges from one to several hundred depending on the desired
jet velocity and total volumetric flow rate. The number of jet
stages in an impactor ranges from one to about twenty for various
impactor geometries reported in the literature. Most commercially
available impactors have between five and ten stages.
The particle collection efficiency of a particular impactor
jet-plate combination is determined by the properties of the aerosol;
such as the particle shape and density, the velocity of the air jet,
and the viscosity of the gas; and by the design of the impactor
stage, that is the shape of the let, the diameter of the jet, and
the jet-to-plate spacing.57'58'5§'6°'6r There is also a slight
dependence on the type of collection surface used (glass fiber,
grease, metal, etc..) . 6 2 ' 6 3' 6 "
Most modern impactor designs are based on the semi-empirical
theory of Ranz and Wong.65 Although more sophisticated theories
have been developed,66'67'68 these are more difficult to apply.
Since variations from ideal behavior in actual impactors dictate
that they be calibrated experimentally, the theory of Ranz and
Wong is generally satisfactory for the selection of jet diameters.
Cohen and Montan,57 Marple and Willeke,58 and Newton, et al60
have published papers that summarize the important results from
theoretical and experimental studies to determine the most impor-
tant factors in impactor performance:
(1) The jet Reynolds number should be between 100 and 3000.
(.2) The jet velocity should be 10 times greater than the
settling velocity'of particles having the stage Dso-
(3) The jet velocity should be less than 110 m/sec.
(4) The jet diameter should not be smaller than can be at-
tained by conventional machining technology.
(5) The ratio of the jet-plate spacing and the jet diameter
or width (S/W) should lie between 1 and 3.
(6) The ratio of the jet throat length to the jet diameter
(T/W) should be approximately equal to unity.
(7) The jet entries should be streamlined or countersunk.
103
-------
Smith and McCain51 have observed that the jet velocity for
optimum collection of dry particles may be as low as 10 m/sec,
which places a more stringent criterion on impactor design and
operation.
Figures 47 and 48 are charts that summarize the design cri-
teria for cascade impactors.51'58 It can be seen that it is
almost impossible to achieve Dso's of 0,2^0.3 ym without violating
some of the recommended guidelines.
Table 7 lists six commercially available cascade impactors
that are designed for in-stack use.69 Table 47 in Appendix B_
shows some geometric and operating parameters for the commercial
impactors. Schematics of the commercial impactors are shown
in Figure 49,7 °
The impactors are all constructed of stainless steel for
corrosion' resistance. All of the impactors have round jets, except
the Sierra Model 226, which is a radial slit design, and all have
stages with multiple jets, except the Brink. It is customary to
operate the impactors at a constant flow rate during a test so that
the D50's will remain constant. The impactor flow rate is chosen,
within a fairly narrow allowable range, to give a certain sampling
velocity at the nozzle inlet. Streamlined nozzles of different
diameters are provided to allow the sample to be taken at a veloc-
ity equal to that of the gas stream.
Since the impaction plates weigh a gram or more, and the
typical mass collected on a plate during a test is on the order
of 1-10 rag, it is often necessary to place a luight weight collec-
tion substrate over the impaction plate to reduce the tare. These
substrates are usually glass fiber filter material or greased
aluminum, foil. A second function of the substrates is to reduce
particle bounce.
Gushing, et al have done extensive calibration studies of the
commercial, in-stack, cascade impactors.63 Figure 50 shows results
from calibration of the Andersen Mark III impactor that are typical
of the performance of the other types as well. Similar results
have been reported by Mercer and Stafford,68 Rao and Whitby,62 and
Calvert, et al71 for impactors of different design. Notice that
the calibration curve increases, as particle size increases, up to
a maximum value that is less than 100%. The decrease in collection
efficiency for large particles represents bounce and can introduce
serious errors in the calculated particle size distribution.
There has not been an extensive evaluation of cascade impactors
under field conditions, although some preliminary work was reported
by McCain, et al.72 It is difficult to judge from existing data
exactly how accurate impactors are, or how well the data taken by
different groups or with different impactors will correlate. Pro-
blems that are known to exist in the application of impactors in the
104
-------
10.0
Figure 47.
Approximate relationship among jet diameter, number of
jets per stage, jet velocity, and stage cut point for
circular }et impactors. From Smith and McCain.51
105
-------
W •= Jet Diameter
Re = Reynolds Number
C " Cunningham Slip Correction
« Particle Aerodynamic Dia.
at 50% Cut Point
10°
50 100
NUMBER OF ROUND JETS PER STAGE, n
500 1000
3540-048
Figure 48. Design chart for round impactors. (Pso = aerodynamic
diameter at 50% cut point.) After Marple.58
106
-------
TABLE 7. COMMERCIAL CASCADE IMPACTOR SAMPLING SYSTEMS69
o
-4
Name
Andersen Stack Sampler
(Precollection Cyclone
Avail.)
Univ. of Washington
Mark III Source Test
Cascade Impactor
(Precollection Cyclone
Avail.)
Univ. of Washington
Mark V
Brink Cascade Impactor
(Precollection Cyclone
Avail.)
Sierra Source Cascade
Tmpactor - Model 226
(Precollection Cyclone
Avail.)
MRI Inertial Cascade
Impactor
Nominal Flow rate
(cm3/sec)
236
236
100
14.2
118
236
Substrates
Glass Fiber (Available from
manufacturer)
Stainless Steel Inserts,
Glass Fiber, Grease
Stainless Steel Inserts,
Glass Fiber, Grtase
Glass Fiber, Aluminum,
Grease
Glass Fiber (Available
from manufacturer)
Stainless Steel, Alf-ii-
num, Mylar, Teflon.
Optional: Gold, Silver,
Nickel
Manufacturer
Andersen 2000, Inc.
P.O. Box 20769
Atlanta, GA 30320
Pollution Control
System Corp.
321 Evergreen Bldg.
Henton, WA 98055
Pollution Control
System Corp.
321 Evergreen Bldg.
Renton, WA 98055
Monsanto EviroChem
Systems, Inc.
St. Louis, MO 63166
Sierra Instc urrents, Inc.
P.O. Box 909
Vi 1 Laqe Square
Carmel Valley, CA 939?-!
Mete-- . .ilogy Research,
Inc.
Box &J7
Altadena, CA 91001
-------
PRt COLLECTION
CYCLONE
FILTER
IMPACTOR BASE
JIT STAt,1:
(V TOTAL;
COLLfcCTION
PLATE
r
MRI MODEL 1502
MODIFIED BRINK
COLLECTION
PLATE (7 TOTAL1
COLLECTION PLATE
FILTER HOLDER
UNIVERSITY OF WASHINGTON MARK III 3540-044
Figure 49. Schematics of five commercial cascade impactor's.7 °
108
-------
NOZZLE
INLET CONE
STAGE 0
STAGE <
SIERRA MODEL 226
JET STAGE 19 TOTAU
Figure 49. (Continued)
ANDERSON MARK III
3540-045
109
-------
o
LU
O
H
u.
UJ
O
U
O
U
100
90
I I I I I II
.3 .4 .5 .6.7.8.91.0 2 3 4 5 6 7 8 9 10
PARTICLE DIAMETER, micrometers
3640-046
Figure 50,
Calibration of an Anderson Mark III impactor. Col-
lection efficiency vs. particle size for stages 1
through 8. After Gushing, et al.63
110
-------
field are: substrate instability,68'73 the presence of charge
on the aerosol particles,71* particle bounce, 2'sa and mechanical
problems in the operation of the impactor systems.
It is usually impractical to use the same impactor at the
inlet and outlet of an electrostatic precipitator when making
fractional efficiency measurements because of the large difference
in particulate loading. For example, if a sampling time of thirty
minutes is adequate at the inlet, for the same impactor operating
conditions and the same amount of sample collected, approximately
3000 minutes sampling time would be required at the outlet (a col-
lection efficiency of 99% is assumed). Although impactor flow
rates can be varied, they cannot be adjusted enough to compensate
for this difference in particulate loading without creating other
problems. Extremely high sampling rates result in particle bounce
and in scouring of impacted particles from the lower stages of the
impactor where the jet velocities become excessively high. Short
.sampling times may result in atypical samples being obtained as a
result of momentary fluctuations in the particle concentration or
size distribution within the duct. Normally, a low flow rate
impactor is used at the inlet and a high flow rate impactor at
the outlet. The impactors are then operated at their respective
optimum flow rates, and the sampling times are dictated by the time
required to collect weighable samples on each stage without over-
loading any single stage.
Particle size distribution measurements related to precipitator
evaluation have largely been made using cascade impactors, which
are effective in the size range from 0.3 to 20 um diameter; although,
in some cases, hybrid cyclone-impactor units or cyclones have also
been used. The particle size distributions are normally calculated
from the experimental data by relating the mass collected on the
.various stages to the theoretical or calibrated size cutpoints
associated with the stage geometries. In the past, the reduction
of data from an extensive field test has been excessively tedious
and time consuming. However, computer programs are now available
that significantly decrease the effort required to reduce and ana-
lyze impactor data.75'76
Figure 51 illustrates a typical reverse flow cyclone.77 The
aerosol sample enters the cyclone through a tangential inlet and
forms a vortex flow pattern. Particles move outward toward the
cyclone wall with velocities that are determined by the geometry
and flow rate in the cyclone, and by their size. Large particles
reach the walls and-are collected. Figure 52 compares the cali-
bration curve for a small cyclone with a typical impactor calibration
curve.78 The cyclone can be seen to perform almost as well as the
impactor, and the .problem.of large particle bounce and reentrain-
ment is absent.
Ill
-------
GAS EXIT TUBE
CAP
SAMPLE AIR FLOW
CYLINDER
CONE
-COLLECTION CUP
8640-04?
Figure 51. Hyprothetical flow through typical reverse flow cyclone.
112
-------
CJ
UJ
LU
o
u
LU
O
U
100
90
80
70
60
90
40
30
20
10
0.0
I
.5
1,0 1.5 2.0
PARTICLE DIAMETER / D50
2.5
3.0
3.5
3540-048
Figure 52. Comparison, of cascade impactor stage with cyclone
collection efficiency curve.78
113
-------
An accurate theory for describing the operation of small
cyclones has not yet been developed. Thus, cyclones used for
particle sizing are presently designed and calibrated based on
experience and experiment. As with itnpactors, cyclone perfor-
mance may be conveniently expressed in terms of a characteristic
Dso, which is the diameter of particles that are collected with
50% efficiency. In experiments with small cyclones, Chan and
Lippmann79 have observed that most"cyclone performance data can
be fitted by equations of the form
D5o = KQn , (18)
where:
K = an empirical constant,
Q = the sample flow rate, and
n <= an empirical constant.
Unfortunately, K and n are different for each cyclone geometry,
and apparently are impossible to predict. In their study, Chan and
Lippmann found K to vary from 6.17 to 4591, and n from -0.636 to
-2.13. A similar study by Smith and Wilson80 found K to vary from
44 to 14, and n from -0.63 to -1.11 for five small cyclones.
In addition to the flow rate dependence indicated in equation
(18), cyclone D50's also are affected by temperature through the
viscosity of the gas. Smith and Wilson found this dependence to
be linear, but with a different slope for different cyclone dimen-
sions and flow rates.
It Is mandatory that the gas velocity and temperature through
the cyclones be maintained at a constant setting while sampling,
because the cyclone cut points are dependent upon the gas flow rate
and temperature. This usually means that periods of non-isokinetic
sampling may occur. Depending on the magnitude of the fluctuations
in the velocity of the sampled stream, this may or may not introduce
significant errors in the sizing process.
A series of cyclones with progressively decreasing D50!s can
be used instead of impactors to obtain particle size distributions,
with the advantages that larger samples are acquired and that par-
ticle bounce is not a problem. Also, longer sampling times are
possible with cyclones, which can be an advantage for very dusty
streams, or a disadvantage for relatively clean streams.
Figure 53 shows a schematic of a series cyclone system that
was described by Rusanov81 and is used in the Soviet Union for
obtaining particle size information. This device is operated in-
stack, but because of the rather large dimensions, requires a 20
cm port for entry.
114
-------
INLET NOZZLE
CYCLONE 1
CYCLONE 2
3 5 4 0 -0 4 9
Figure 53. Series cyclone used in the U.S.S.R. for sizing flue
gas aerosol particles. From Rusanov.
a i
115
-------
Southern Research Institute, under EPA sponsorship, has de-
signed and built a prototype three-stage series cyclone system for
in-stack use.62 A sketch of this system is shown in Figure 54.
It is designed to operate at 472 cur/sec d ft3/min). The Dso's
for these cyclones are 3.0, 1.6, and 0.6 micrometer aerodynamic
at 21°C. A 47 mm Gelman filter holder, (Gelman Instrument Co.,.
600 South Wagner Road, Ann Arbor, HI 48106), is used as a back-up
filter after the last cyclone. This series cyclone system was
designed for in-stack use and requires a six inch sampling port.
Figure 55 illustrates a second generation EPA/Southern Re-
search series cyclone system now under development which contains
five cyclones and a back up filter.80 It is a compact system and
will fit through 4 inch diameter ports. The initial prototype
was made of anodized aluminum with stainless steel connecting
hardware, A second prototype, for in-stack evaluation, is made
of titanium,
Figure 56 contains laboratory calibrations data for the five
cyclone prototype system.80 The DSO'S, at the test conditions,
are 0.32, 0.6, 1.3, 2.6, and 7.5 urn. A continuing research pro-
gram includes studies to investigate the dependence of the cyclone
cut points upon the sample flow rate and temperature so that the
behavior of the cyclones at stack conditions can be predicted more
accurately.8 °
The Acurex-Aerotherm Source Assessment Sampling System (SASS)
incorporates three cyclones and a back up filter.83 Shown schemati-
cally in Figure 57, the SASS is designed to be operated at a flow
rate of 3065 cm3/sec (6.5 ft3/min) with nominal cyclone D50's of
10, 3, and 1 micrometer aerodynamic diameter at a gas temperature
of 205°Co The cyclones, which are too large for in situ sampling,
are heated in an oven to keep the air stream from the heated extra-
active probe at stack temperature or above the dew point until the
particulate is collected. Besides providing particle size distri-
bution information, the cyclones collect gram quantities of dust
(due to the high flow rate) for later chemical and biological
analyses. The SASS train is available from Acurex-Aerotherm, Inc.r
485 Clyde Avenue, Mountain View, California 94042.
Small cyclone systems appear to be practical alternatives to
cascade impactors as instruments for measuring particle size dis-
tributions in process streams. Cyclones offer several advantages:
Large, size-segregated samples are obtained.
There are no substrates to interfere with analyses.
They are convenient and reliable to operate.
They allow long sampling times under high mass loading con-
ditions for a better process emission average.
116
-------
TO PUMP
BACKUP FILTER
CYCLONE 2
^=3
a
•CYCLONE 3
• NOZZLE
• CYCLONE 1
3540-0(0
Figure 54.
Schematic of the Southern Research Institute three
series cyclone system.82
117
-------
CYCLONE 1
CYCLONE 4
CYCLONE 5
CYCLONE 2
CYCLONE 3
OUTLET
INLET NOZZLE
S640-OE1
Figure 55. The EPA/Southern Research Institute five series
cyclone system.8 °
118
-------
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90
80
70
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PARTICLE DIAMETER, micrometers
• FIRST STAGE CYCLONE
• SECOND STAGE CYCLONE
£> THIRD STAGE CYCLONE
* FOURTH STAGE CYCLONE
O FIFTH STAGE CYCLONE
20
3540-052
Figure 56.
Laboratory calibration of the EPA/Southern Research
Institute five series cyclone system. (Flow rate of
28.3 2,/min, temperature of 20°C, and particle density
of 1 g/cm3.)30
119
-------
They may be operated at a wide range of flow rates without
particle bounce or reentrainment.
On the other hand, there are some negative aspects of cyclone
systems which require further investigation:
Unduly long sampling times may be required to obtain large
samples at relatively clean sources.
The existing theories do not accurately predict cyclones per-
formance.
Cyclone systems are bulkier than impactors and may require
larger ports for in-stack use.
Optical Methods-
Figure 58 is a schematic illustrating the principles of opera-
tion for optical particle counters.85 A dilute aerosol stream
intersects the focus of a light beam to form an optical "view
volume". The photodetector is located so that no light reaches
its sensitive cathode except that scattered by particles in the
view volume. Each particle that scatters light with enough in-
tensity will generate a current pulse at the photodetector, and
the amplitude of the pulse can be related to the particle diameter.
The rate at which the pulses occur is related to the particle con-
centration. Thus, optical particle counters yield real time in-
formation on particle size and concentration.
The simultaneous presence of more than one particle in the
viewing volume is interpreted by the counter as a large single
particle. To avoid errors arising from this effect, dilution to
about 300 particles/cm3 is generally necessary. Errors in counting
rate also occur as a result of electronics deadtime and from
statistical effects resulting from the presence of high concen-
trations of subcountable (D < 0.3 ym) particles in the sample gas
stream.8 6
In an optical particle counter, the intensity of the scattered
light, and amplitude of the resulting current pulse, depends on the
viewing angle, particle refractive index, particle shape, and par-
ticle diameter. Different viewing angles and optical geometries
are chosen to optimize some aspect of the counter performance.
For example, the use of near forward scattering will minimize the
dependence of the response on the particle refractive index, but
with a severe loss of resolution near 1 ym diameter. The use of
right angle scattering smooths out the response curve, but the
intensity is more dependent on the particle refractive index.
Figure 59 shows calibration data for near forward and right angle
scattering particle counters.87
120
-------
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10 CFM VACUUM PUMP
3640-053
-------
LIGHT TRAP
LAMP
SAMPLE AEROSOL
TO PUMP
PHOTOMULTIPLIER
3540-064
Figure 58. Schematic of an optical single particle counter.
8 5
122
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PARTICLE DIAMETER, n
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b. Neat forward scattering. 3540-066
-------
Figure 60 illustrates some of the optical configurations that
are found in commercial particle counters.88 The pertinent geome-
tric and operating constants of the counters are summarized in
Table 8.89*
The commercial optical counters that are available_now were
designed for laboratory work and have concentration limits of a
few hundred particles per cubic centimeter. The lower size limit
is nominally about 0.3 urn diameter. For use in studies of industrial
aerosols, the gas sample must be extracted, cooled, and diluted; a
procedure which requires great care to avoid introducing serious
errors into calculations of the particle size distribution. The use-
ful upper limit in particle size is limited by losses in the dilution
system to about 2.0 ym diameter.27 In addition, the particle dia-
meter that is measured is not aerodynamicr and some assumptions must
be made in order to compare optical with aerodynamic data. (It is
possible to "calibrate" an optical counter, on a particulate source,
to yield aerodynamic data. This is done by using special calibra-
tion impactors,90 or settling chambers.91) Nevertheless, the
ability to obtain real time information can sometimes be very
important and the special problems in sampling with optical counters
may be justified.
Diffusional and Condensation Nuclei Methods—
The classical technique for measuring the size distribution of
submicron particles employs the relationship between particle
diffusivity and diameter. In a diffusional sizing system, the test
aerosol is drawn, under conditions of laminar flow, through a number
of narrow, rectangular channels, a cluster of small bore tubes, or
a series of small mesh screens (diffusion batteries). For a given
particle diameter and diffusion battery geometry,It is possible to
predict the rate at which particles are lost to the walls by dif-
fusion, the rate being higher for smaller particles. The total
number of particles penetrating the diffusion battery is measured
under several test conditions where the main adjustable parameter
is the aerosol retention time, and the particle size distribution
is calculated by means of suitable mathematical deconvolution tech-
niques. It is only necessary that the particle detector (usually a
condensation nuclei counter) that is used at the inlet and outlet
of the diffusion battery system responds to the total concentration,
by number, of the particles in the size range of interest.
Figure 61-a shows a typical parallel channel diffusion battery,
and Figure 61-b shows the aerosol penetration characteristics of
this geometry at two flow rates.92 The parallel plate geometry is
convenient because of ease of fabrication and the availability of
suitable materials, and also because sedimentation can be ignored
if the slots are vertical, while additional information can be
gained through settling, if the slots are horizontal.
124
-------
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7igure 60. Optical configuration for six commercial particle counters,
125
-------
TABLE 8= CHARACTERISTICS OF COMMERCIAL, OPTICAL, PARTICLE COUNTERS89
Bausch c, Lomb Model 40-1
820 Linden Avel
Rochester, MY 14625
Clinet Models 201, 208
Climet Inst. Co.
1620 W. Colton Ave.
RedlandB, CA 92373
•Model LAS-200
Particle Measuring Systems
1855 S. 57th Ct.
Boulder, CO 80301
Illuminating Cone
HalE Angle, Y
13°
15
Light Trap Half
Angle, a
33"
35
Collecting Aperture
Half Angle, 8
53°
90
Inclination Between Sampling
Illuminating And Viewing Rate
Collecting Cone Axis, i|) Volume
0° 0.5 mm' 170 cm'/min
0.5 7,080
Climet Model 150
Royco Model 218
(-J Royco Inst.
N) 41 Jefferson Dr.
-------
Figure 61-a. Parallel plate diffusion battery-
9 2
20
0.01
PARTICLE DIAMETER,
3540-316
Figure 61-b. Parallel plate diffusion battery penetration curves
for monodisperse aerosols (12 channels, 0.1 x 104
48 cm).92
127
-------
Breslin et al9 3 and Sinclair9* report success with more com-
pact, tube-type and screen-type arrangements in laboratory studies
and a commercial version of Sinclair.1's geometry is available. (TSI
Incorporated, 500 Cardigan Road, St. Paul, MN 55165). Although
the screen-type diffusion battery must be calibrated empirically,
it offers convenience in cleaning and operation, and compact size.
Figure 62 shows Sinclair's geometry.91* This_battery is 21 cm
long, approximately 4 cm in diameter, and weighs 0.9 kg, and
contains 55 stainless steel screens of 635 mesh.
Diffusional measurements are less dependent upon the aerosol"
parameters than the other techniques.-discussed and perhaps are on
a more firm basis from a theoretical •.standpoint:.
Disadvantages of the dif-fusibnal technique are the bulk of
the parallel plate diffusional batteries/ although advanced tech-
nology may alleviate this problem?- the long time required to measure
a size distribution; and problems with sample conditioning when
condensible vapors are present.
A practical limitation on the lower size limit for all methods
used to determine ultrafine particle size distributions (diameters
< 0.5 vim) is the loss of particles by diffusion in the sampling
lines and instrumentation. These losses are excessive for particle
diameters below about 0.01 ym where the samples are extracted from a
duct and diluted to concentrations within the capability of the
sensing devices.
Condensation nuclei (CN) counters function on the principle
that particles act as nuclei for the condensation of water or other
condensable vapors in a supersaturated environment. This process
is used to detect and count particles with diameters in the 0.002 to
0.3 ym range (often referred to as condensation or Aitken nuclei).
In condensation nuclei detectors, a sample is withdrawn from the
gas stream, humidified, and brought to a supersaturated condition
by reducing the pressure. In this supersaturated condition, con-
densation will be initiated on all particles larger than a certain
critical size and will continue as long as the sample is super-
saturated „ This condensation process forms an homogeneous aerosol,
predominantly composed of the condensed vapor containing one drop
for each original particle whose size was greater than the critical
si^e appropriate to the degree of supersaturation obtained; a
greater degree of supersaturation is used to initiate growth on
smaller particles. The number of particles that are formed is
estimated from the light scattering properties of the final aerosol.
Because of the nature of this process, measurements of very
high concentrations can be in error as a result of a lack of cor-
respondence between particle concentration and scattering or at-
tenuation of light. Additional errors'can result from depletion
of the vapor available for condensation. Certain condensation
nuclei measuring techniques can also obtain information on the
128
-------
10
SAMPLING
PORT (TYP)
SECTION CONTAINING
SCrieENS (TYP)
3540-06'!
Figure 62.
Screen-type diffusion battery. The battery is 21 cm
long, 4 cm in diameter, and contains 55, 635 mesh
stainless steel -screens. After Sinclair.91*
129
-------
size distribution of the nuclei; that is, variations in the degree
of supersaturation will provide size discrimination by changing
the critical size for which condensation will occur. However,
the critical size for initiating condensation is also affected
by the volume fraction.of water soluble material contained in the^
original aerosol particle, so the critical siz:e will be uncertain
unless the solubility of the aerosol particles is known.95 At
very high degrees of supersaturation (about 400%), solubility
effects are only minor and essentially all particles in the orig-
inal aerosol with diameters larger^than -0.002 1*& will initiate
the condensation process. Figure'63, after Haberl, illustrates
the condensation nuclei counter operating principle.9 6-
Four models of CN counters are now available commercially.
Two automatic, or motorized, types are the General Electric Model
CNC-2 (General Electric-Ordnance Systems, Electronics Systems
Division, Pittsfield, MA 01201) and the Environment-One Model
Rich 100 (Environment-One Corporation, Schenectady, NY 12301).
Small, manually operated, CN counters are also available from
Gardner Associated, (Gardner Associates, Schenectady, NY 12301),
and Environment-One.
The General Electric CN counter has mechanically actuated
valves and is insensitive to moderate pressure variations at the
inlet. The aerosol concentration is measured by the detection of
scattered light from the test aerosol.
A disadvantage of the flow/valving arrangement in the General
Electric counter is the intermittent (Vsec) flow which introduces
severe pressure pulsations into the sampling system. This problem
has been minimized by the use of antipulsation devices consisting
of a rubber diaphranr7 or two metal cylinders connected by a small
orifice,98 essentially pneumatic R-C networks.
The automatic Environment-One counter has some pneumatic
valves. A pressure of more than 5 cm of water at the inlet can
interrupt the operation. In the E-l, the aerosol concentration
is measured by light extinction. The sampling rate of the E-l
counter can be adjusted from about 0.6 to 4.2 £/min. Soderholm
has reported a modification to the E-l counter that replaces
pneumatic valves with solenoidal ones.99
Fuchs100 has reviewed diffusional sizing work up until 1956,
while Sinclair,101'97'102 Breslin, et al,103 Twomey,™" Sansone
and Weyel, °5 and Ragland, et al,90 have reported more recent
work, both theoretical and experimental.
Figure 64 is a schematic diagram that illustrates an experi-
mental setup for measuring particle size distributions by diffusional
means, and Figure 65 shows penetration curves for four operating
configurations.
130
-------
PHOTO DETECTOR
HUMIDIFIER
J
VALVE
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'COUNTER—* RANGE
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VACUUM VACUUM
REGULATOR PUMP
•J- INNER LIGHT STOP
OUTER LIGHT STOP
, 1 GEAR
~1 1 MOTOR
3540-058
Figure 63.
Diagram of a condensation nuclei counter.
and Fusco,9 6
After Haberl
131
-------
ANTI-PULSATION
DEVICE
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SAMPLE FROM
DILUTER
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CN COUNTER
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Figure 64. Diffusion battery and condensation nuclei counter layout
for fine particle sizing.106
132
-------
0
0.
01
0.02
0.03 0.04 0.05 0.1
PARTICLE DIAMETER,
0.2
0.4 0.5
3540-060
Figure 65. Theoretical parallel plate diffusion battery penetration
curves.105
133
-------
Because of the long retention time required for removal of
particles by diffusion, measurements with diffusion batteries and
CN counters are very time consuming. With the system described
by Ragland, et al, for example, approximately two hours are re-
quired to measure a particle size .distribution with diameters from
0.01 to 0.2 ym.96 Obviously, this method is'best applied to stable
aerosol streams. It is possible that the new, smaller diffusion
batteries will allow much shorter sampling times, but pulsations
in flow may pose a serious problem for the low volume geometries.
Electrical Mobility Method—-
An instrument that was developed for measuring laboratory
and ambient aerosols over the 0.003 to 1 ym range of diameters,
the electrical mobility analyzer, can also be applied to process
streams with a suitable sample dilution and cooling interface.
Figure 66 illustrates the relationship between the diameter
and electrical mobility of small aerosol particles.107 If par-
ticles larger than those of minimum mobility are removed from the
sample, the remaining particles exhibit a monotonically decreasing
mobility with increasing diameter. Several aerosol spectrometers,
or mobility analyzers, have been demonstrated that employ the
diameter-mobility relationship to classify particles according
to their size. 1 o1i' l °9' l! °' l J x Figure 67 illustrates the principle
on which these devices operate.1 Particles are charged under
conditions of homogeneous electric field and ion concentration,
and then passed into the spectrometer. Clean air flows down the
length of the device and a transverse electric field is applied.
From a knowledge of the system geometry and operating conditions,
the mobility is derived for any position of deposition on the
grounded electrode. The particle diameter is then readily cal-
culated from a knowledge of the electric charge and mobility.
Difficulties with mobility analyzers are associated primarily
with charging the particles (with a minimum of loss) to a known
value and obtaining accurate analyses of the quantity of particles
in each size range. The latter may be done gravimetrically,1°8
optically,l°9 or electrically.11°
The concept described above has been used by Whitby,
et al,113'114 at the University of Minnesota, to develope a series
of Electrical Aerosol Analyzers (EAA). A commercial version of
the University of Minnesota devices is now marketed by TSI, In-
corporated as the Model 3030 (Figure 68).ll* The EAA is designed
to measure the size distribution of particles in the range from
0.0032 to 1.0 ym diameter. Since the concentration range fox-
best operation is 1 to 1000 yg/m3, dilution is required for most
industrial gas aerosols.
The EAA is operated in the following manner. As a vacuum
pump draws the aerosol through the analyzer (see Figure 68), a
134
-------
10
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Nt = 3.2 x 1012 sec/M3
SHELLAC AEROSOL K = 3.2
O
C
O
c
_ O
C 0°'
c a
c
a
0.1
PARTICLE DIAMETER,
1.0
3640-061
Figure 66.
Particle mobility as a function of diameter for schellac
aerosol particles charged in a positive ion field
(after Cochet and Trillat3)- K is the dielectric
constant-of the aerosol.107
135
-------
HV
CHARGED PARTICLES
CLEAN AIR
LAMINAR FLOW
LARGER PARTICLES OF I
LOW ELECTRICAL MOBILITY _]_
SMALLER PARTICLES OF
HIGH ELECTRICAL MOBILITY
3640-062
Figure 67. The electric mobility principle.112
136
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ANALY2EH OUTPUT SlGMAL -
DATA READ COMMAND - •
CVCI.E START COMMAND -
CYCLE RESET COMMAND -
• AEROSOL FLOWMETEA READOUT
• • CHAHJER CURRENT READOUT
- CHARGCK VO'.TAGE RLAOOuT
AUTOMATIC HIGH VOLTAGE CONTROL AND READOUT
ELECTROMETER IANALTZER CURRENT I NCACOUT
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corona generated at a high voltage wire within the charging section
gives the sample a positive electrical charge. The charged aerosol
flows from the charger to the analyzer section as an annular cyl-
inder of aerosol surrounding a cone of clean air. A metal rod,
to which a variable, negative voltage can be applied, passes
axially through the center of the analyzer tube. Particles smaller
than a certain size (with highest electrical mobility) are drawn
to the collecting rod when the voltage corresponding to that size
is on the rod. Larger particles pass through the analyzer tube
and are collected by a filter. The electrical charges on these
particles drain off through an electrometer, giving a measure of
current,
A step increase in rod voltage will cause particles of a
larger size to be collected by the rod with a resulting decrease
in electrometer current. This decrease in current is related to
the additional number' of particles being collected. A total of
eleven voltage steps divide the 0.0032 to l.Oimicron size range
of the instrument into ten equal logarithmic size intervals. Dif-
ferent size intervals can be programmed via an optional plug-in
memory card.
The electrical aerosol analyzer can be operated either auto-
matically or manually. In the automatic mode, the analyzer steps
through the entire size range. For size and" concentration monitor-
ing over an extended period of time, the analyzer may be inter-
mittently triggered by an external timer. The standard readout
consists of a digital display within the control circuit module,
although a chart recorder output is available. It is almost
always advantageous to use a strip chart recorder to record the
data. This allows the operator to identify a stable reading that
may be superimposed on source variations and also gives a per-
manent record of the raw data.l15
When the EAA is applied to fluctuating sources a peculiar
problem arises. The instrument reading is cumulative, and it is
impossible to tell whether variations in the reading reflect
changes in the distribution or concentration of particles; hencef
recordings that show rapid fluctuations in amplitude must be
interpreted with great care. The lack of sensitivity can also
be a problem at extremely clean sources.
The EAA requires only two minutes to perform a complete size
distribution analysis, which generally makes it advantageous to
use, especially on stable sources.
Other Specialized Particle Sizing Systems For Field Use
Respirable Particle Classifier (RPC) Impactor—
An in-stack sampling system, known as the respirable particle
classifier (RPC) impactor, has been developed by Southern Research
138
-------
Institute to measure the particle emissions from stationary pollution
sources in three size ranges.115 The impactor, shown schematically
in Figure 69, consists of a basic housing, a set of nozzles, a set
of collection plates, and three sets of jet plates (two jet plates
per set). The impactor body is anodized aluminum. The jet stages
and collection stages are stainless steel.
The impactor was tested on two coal-fired power plants. Con-
currently with each test at Plant A a Brink Cascade Impactor was
run to obtain a comparative size distribution. The results of
the testing at Plant A, which occurred at the outlet of a precipi-
tator collecting ash from a low sulfur Southeastern coal are shown
in Figures 70-72. Concurrently with each test at Plant B an
Andersen Stack Sampler was run with the new impactor to obtain
a comparable size distribution. The results of the testing at
Plant B, which occurred at the outlet of a precipitator collecting
ash from a medium-high sulfur Southeastern coal, are shown in
Figure 73.
Large Particle Sizing System (LPSS)—
In order to more clearly define the mechanisms by which rapping
losses occur in dry ESP's, time resolved data are required on the
particulate concentrations and size distribution across typical
portions of ESP exit planes. Conventional sampling methods gener-
ally require rather long integration times which are unsuited for
examining 1 to 5 second transient events such as•rapping puffs.
Of the available measurement methods, only the optical single par-
ticle counters appear to offer the required combination of response
time, dynamic range, and particle size resolution. Modified ambient
air particle counters (Royco Model 225) are used as the measurement
instrumentation in a large particle sizing system (LPSS) developed
by Southern Research Institute,. ! 17 The use of these counters re-
quires", extractive sampling and sample conditioning.
Due to instrumental limitations on the total - concentration
of aerosol particles in the sample gas stream arriving at the
sensor, these particle counters require that the aerosol sample
from the flue be diluted before measurement. Because of the very
steep gradient in the size distribution on a number basis antici-
pated at the exit of a precipitator on a power boiler, the diluter
was made as a size selective device which, under ideal conditions,
dilutes small particles in the sample gas stream by fairly large
factors while passing a. relatively confined and undiluted stream
of the lower concentration large particles directly to the particle
-sensor. Figure 74 illustrate? the operational system for the
particle dilution train.
The geometry of the diluter as shown in Figure 74 is such
that the large particles, having high inertia, tend to pass di-
rectly from, the inlet to, the sample exit of the diluter while
small particles (having relatively low inertia), are mixed to
139
-------
Institute to measure the particle emissions from stationary pollution
sources in three size ranges.116 The impactor, shown schematically
in Figure 69, consists of a basic housing, a set of nozzles, a set
of collection plates, and three sets of jet plates (two jet plates
per set). The impactor body is anodized aluminum. The jet stages
and collection stages are stainless steel.
The impactor was tested on two coal-fired power plants. Con-
currently with each test at Plant A a Brink Cascade Impactor was
run to obtain a comparative size distribution. The results of
the testing at Plant A, which occurred at the outlet of a precipi-
tator collecting ash- from a low stilfur Southeastern coal are shown
in Figures 70-72. Concurrently with each test at Plant B an
Andersen Stack Sampler was run with the new impactor to obtain
a comparable size distribution. The results of the testing at
Plant B, which occurred at the outlet of a precipitator collecting
ash from a medium-high sulfur Southeastern coal, are shown in
Figure 73.
Large Particle Sizing System (LPSS)—
In order to more clearly define the mechanisms by which rapping
losses occur in dry ESP's, time resolved data are required on the
particulate concentrations and size distribution across typical
portions of ESP exit planes. Conventional sampling methods gener-
ally require rather long integration times which are unsuited for
examining 1 to 5 second transient events such as rapping puffs.
Of the available measurement methods, only the optical single par-
ticle counters appear to offer the required combination of response
time, dynamic range, and particle size resolution. Modified ambient
air particle counters (Royco Model 225) are used as the measurement
instrumentation in a large particle sizing system (LPSS) developed
by Southern Research Institute.117 The use of these counters re-
quires extractive sampling and sample conditioning.
Due to instrumental limitations on the total concentration
of aerosol particles in the sample gas stream arriving at the
sensor, these particle counters require that the aerosol sample
from the flue be diluted before measurement. Because of the very
steep gradient in the size distribution on a number basis antici-
pated at the exit of a precipitator on a power boiler, the diluter
was made as a size selective device which, under ideal conditions,
dilutes small particles in the sample gas stream by fairly large
factors while passing a relatively confined and undiluted stream
of the lower concentration large particles directly to the particle
sensor. Figure 74 illustrates the operational system for the
particle dilution train.
The geometry of the diluter as shown in Figure 74 is such
that the large particles, having high inertia, tend to pass di-
rectly from the inlet to the sample exit of the diluter while
small particles (having relatively low inertia), are mixed to
139
-------
(3
a
OT
i
UJ
S
u
1, 11' 11 I I I , 11 11
TWO-STAGE IMPACTOR - PLATE SET I - 94 cm3/sec 5
TEFLON SUBSTRATES
O BRINK CASCADE IMPACTOR - 14 cm3/sec
10'
UPPER SIZE LIMIT ( micrometers )
3540-314
Figure 70. Cumulative mass loading versus particle diameter,
March 11, '1975. i15
141
-------
m
<
NG
LO
CUMULATIVE
UPPER SIZE LIMIT ( micrometcre )
3540-81!
Figure 71. Cumulative mass loading versus particle diameter,
March 12, 1975.116
142
-------
10
UJ
>
3
S
u
10
10
_i — -
il|!!li.!'l
R=
331:
=
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tr^+-
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afe
LA
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~ — T '"• J • 1 — j '
! 1 ' ^ ^=
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i A
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=1
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i
1 •
1 , 1 1
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PH=
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UT^
1 1
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!
i M '
iu
it -
f*^
4-
R
. r
«•
11 1 1 1 1 —
,.
i
,, . . !
TWO-STAGE IMPACTOR - PLATE SET 1 - 94 cm3/sec
GLASS FIBER SUBSTRATES
TWO-STAGE IMPACTOR - PLATE SET III - 19 cm^/sec
GLASS FIBER SUBSTRATES
BRINK CASCADE IMPACTOR - 14cm3/sec
- — r
-±r—
t
— -I
— •(
— -i
1
-
— 1
^
— i
" 1
-— -T.
i
T
-:-
—
-J
-T-
±
-r
X
— *.
-^
T=
•l-'j
Pi
-\
- r
• T
~ T
:i
~ T
10'
10
10 2
3540-312
UPPER SIZE LIMIT ( micrometers )
Figure 72. Cumulative mass loading versus particle diameter,
March 13, 1975.l16
143
-------
100.0
S
u
Cr>
e
en
a
•H
Tl
•H
-P
10.0
1.0
i.o 10.0
Particle Diameter, ym
Figure 73. Cumulative grain loading versus particle size,,116
o Andersen Stack Sampler - July 30, 1975
a Andersen Stack Sampler - July 31, 1975
• Two Stage Impactor - Jet Plate Set I - July 31, 1975
«s Two Stage Impactor — Jet Plate Set JI — July 31, 1975
A Two Stage Impactor — Jet Plate Set III — Juiy 3O r J.97S
100.0
3649-311
-------
SAMPLE
F.LOWRATE
MANOMETER
u
<^}
u
GAS FLOW
PROBE
HEATER
PROCESS EXHAUST
LINE
0.02 urn
FILTER
BLEED
VALVE
VERTICAL
ELECTRICAL
LEADS. ETC.
\ LARGE PARTICLE
COUNTER
MAIN FRAME
3540-064
Figure 74. Large- particle- sizing system.
1 1 7
145
-------
varying degrees, depending on their sizes with the dilution air
thus producing a substantial reduction in concentration of small
particles and condensable vapors in the sample stream while
maintaining the concentration of the less numerous larger particles.
For the purpose of rapping studies, it is desirable to be
able to investigate the concentrations during and between raps and
monitor background fluctuations. For this purpose, five channel
analog ratemeters were constructed as modifications to the particle
counters to provide parallel monitoring of the instantaneous con-
centration of particles in five preselected size intervals. These
analog ratemeters provide approximately a half second response
time, thus permitting monitoring of concentration changes through-
out a rapping puff.
The sampling probes are configured and installed in such a
manner as to permit a vertical traverse to be made along the center
line of one lane at the exit plane of the precipitator. Probe
losses are minimized by installing the particle sampling train
(probe, diluter, particle counter) underneath the outlet duct and
extracting the aerosol sample through a vertical probe with a
single 90° bend between the sampling point and the particle sensor.
The probe and nozzle are constructed from a continuous length of
4 mm I.D. stainless steel tubing. As used in previous tests, the
probe flow was laminar with a Reynolds number of 100. In this con-
figuration the system could conceivably be calibrated to give
absolute concentrations. However, at this time there is not enough
data to warrant its use to detect more than relative concentration
changes.
For those circumstances in which it is not possible to sample
from below the duct, a second sample extraction system is used.
In this case the sample is removed at a high flow rate, 0.0019-
0.0047 ms/sec (4-10 cfm), through a large bore probe (4.06 cm
diameter) and conveyed to a suitable location beside or on the
top of the duct, at which point a secondary sample is extracted
into the diluter and counter as illustrated in Figure 75. This
sampling method provides information on relative concentrations of
particles of various sizes during and between puffs, but does not
provide quantitative concentration data because of the uncertainties
in the probe losses and in the degree to which the secondary sample
represented the average concentration in the high flow rate probe.
Automatic data acquisition can be accomplished as shown in the
block diagram of the electronic package in Figure 76.
Laboratory Methods For Measuring Particle Size Distributions
Measurements of the size distribution of particles that have
been collected in the field and transported to a laboratory must
be interpreted with great caution, if not skepticism. It is
difficult to collect representative samples in the first place,
and it is almost impossible to reconstruct the original size
146
-------
BLOWER
EXHAUST
FLOW
REGULATOR
DILUTER
AND COUNTER
(XL
DUCT TOP
-EXTRACTION PROBE
GAS
FLOW
3540-309
Figure 75. Extractive sampling,system.
1 1 7
147
-------
ROYCO DIGITAL
COUNTER
(5 channels)
PROBE
ROYCO
OPTICAL
HEAD
ROYCO DIGITAL
DATA LOGGER
(5 channels)
ROYCO SIGNAL
CONDITIONER
SRI RATE
METERS
(5 channels)
—
BRUSH
OSCILLOGRAPH
RECORDER
(6 channels)
8640-311
Figure 76. Block diagram of large particle sizing system.
I 1 7
148
-------
distribution^under laboratory conditions. For example, one can
not distinguish from laboratory measurements, whether or not some
of the particles existed in the process gas stream in agglomerates
of smaller particles. Also, unwanted agglomerates can sometimes
be formed in collecting and transporting particulate samples.
In spite of the limitations inherent in laboratory methods,
they must be used in some instances to determine particle size and
to segregate particles for analysis of their composition or other
properties of interest. The following subsections contain dis-
cussions of some of the "standard" laboratory techniques used for
particle size analysis of dust samples.
Sedimentation and Elutriation—
Elutriators and sedimentation devices separate particles that
are dispersed in a fluid according to their settling velocities
due to the acceleration of the earth's gravity.
Large particles in a quiescent aerosol will settle to the
bottom region of the chamber more quickly than smaller particles
that have smaller settling velocities. This principle is used in
gravitational sedimentation and elutriation to obtain particle size
distributions of polydisperse aerosols. In elutriation, the air
is made to flow upward so that particles with settling velocities
equal to or less than the air velocity will have a net velocity
upward and particles which have settling velocities greater than
the air velocity will move downward.
There are a number of commercial devices and methods having
varying requirements of dust amounts and giving different ranges
of size distributions, with a minimum size usually no smaller than
two micrometers.118'119 An important disadvantage is the inability
of most sedimentation and elutriation devices to give good size
resolution. Another disadvantage is the length of time (sometimes
several hours) required to use some of the methods.
Popular methods of sedimentation include the pan balance,
which weighs the amount of sediment falling on it from a suspen-
sion, and the pipette, which collects the particles in a small
pipette at the base of a large chamber. Cahn's electronic micro-
balance, (Cahn Instrument Company, 7500 Jefferson St., Paramount,
CA 90723), has an attachment that permits it to function as a
settling chamber. Perhaps the most popular elutriator is the
Roller particle size analyzer illustrated in Figure 77119 (the
Roller particle size analyzer, is available from the American
Standard Instrument Co., Inc., Silver Springs, MD).
An instrument that measures•the size .distribution of par-
ticles in a liquid suspension is the X-ray Sedigraph, (Micro-
merities Instrument Corporation, 800 Goshen Springs Road, Norcross/
GA 30071). The sample is continually stirred until the sampling
149
-------
SEPARATOR TUBE
AIR SUPPLY
FLEXIBLE JOINT
POWDER
CIRCULATION
3640-066
Figure 11, The Roller elutriator. After Allen.
119
150
-------
period starts. The concentration of the particles is monitored
by means of the extinction of a collimated x-ray beam. Upon
sampling, the x-ray beam is moved upward mechanically to shorten
the sampling time that is required. The particle-size distri-
bution is plotted automatically- The reported range of sensitivity
of the X-ray Sedigraph is from 0.1 to 100 ym.
Centrifuges—
Aerosol centrifuges provide a laboratory method of size-
classifying particles according to their aerodynamic diameters.
The advantage over elutriators is that the settling, or precipi-
tation, process is speeded up by the large centrifugal acceleration.
The sample dust is introduced in the device as an aerosol and
enters a chamber which contains a centrifugal force field.
In one type of aerosol centrifuge, the larger particles over-
come the viscous forces of the fluid and migrate to the wall of
'the chamber, while the smaller particles remain suspended. After
the two size fractions are separated, one of them is reintroduced
into the device and is fractionated further, using a different
spin speed to give a slightly different centrifugal force. This
is repeated as many times as desired to give an adequate size dis-
tribution. One of the more popular lab instruments using this
technique is the Bahco microparticle classifier, which is illus-
trated in Figure 78,I2° and is available commercially from the
Harry W. Dietert Company, Detroit 4, Michigan. The cutoff size
can be varied from about two to fifty micrometers to give size
distribution characterization of a 7 gm dust sample. A similar
instrument is the B.C.U.K.A. (British Coal Utilization Research
Association, Leatherhead, Surrey, U.K.) centrifugal elutriator
which has a range of four to twenty-six micrometers.121
In the second type of centrifuge, the device is run continu-
ously, and the particle size distribution is determined from the
po.sition where the particles are deposited. Examples are a spiral
centrifuge developed by Goetz, et al,lz2'l23'l2" (Figure 79) and
by Stober and Flachsbart,l25 (Figure 80) that can classify poly-
disperse dust samples with particles from a few hundredths of a
micron to approximately two micron in diameter. The conifuge,
first built bv Swayer and Walton126 and modified several times
since then,127'128 is useful in the study of aerodynamic shape
factor, but can also be used for the determination of size dis-
tributions 'especially for particles having aerodynamic diameters
smaller than twenty-five micrometers (see Figure 81).129 In con-
tinously operating centrifuges, the particles are generally
deposited onto a foil strip, where their position yields a mea-
sure of their size, and their number is obtained by microscopy,
radiation, or by weighing segments of the foil.
151
-------
10 11 1.2 13
SCHEMATIC DIAGRAM
1. Electric Motor
2. Threaded Spindle
3. Symmetrical Disc
4. Sifting Chamber
5. Container
6. Housing
7. Top Edge
8. Radial Vanes
9. Feed Point
10. Feed Hole
11. Rotor
12. Rotary Duct
13. Feed Slot
14. Fan Wheel Outlet
15. Grading Member
16. Throttle
3640-066
Figure 78. The Bahco microparticle classifier.12
152
-------
JET
ORIFICE
INLET TUBE
CUP
COLLECTING /
FOII /
3540-067
Figure 79.
A cut-away sketch of the Goetz Aerosol Spectrometer
spiral centrifuge. In assembled form the vertical
axes (1) coincide and the horizontal arrows (2)
coincide. After Gerber.l22'123'l 2 *
153
-------
THERMOCONTROLLED
WATER
AEROSOL
ENTRANCE
SPIRAL
DUCT
CLEAN AIR INPUT
SUCTION PUMP
THERMOCONTROLLED
WATER
8640-068
Figure 80. Cross-sectional sketch of the Stober Centrifuge,
After Stober and Flachsbart.:25
154
-------
.PARTICLE STREAM
CLEAN AIR
LARGER PARTICLES
COLLECTED HERE
OUTER CONE
SMALLER PARTICLES
COLLECTED HERE
AXIS OF ROTATION 3540-069
Figure 81. Cross-sectional sketch of a conifuge.
1 2 9
155
-------
Microscopy —
Microscopic analysis has long been regarded as the established,
fundamental technique of counting and sizing particles that the
human eye cannot comfortably see. Usually, the method involves
one person, a microscope, and a slide prepared with a sample of the
aerosol to be measured. A random selection of the particles would
then be measured and counted, with notable characteristics of color,
shape, transparency, or composition duly recorded. The most diffi-
cult task, especially since the advent of sophisticated computer-
ized equipment has made counting and sizing easier, is the pre-
paration of a slide which contains a representative sample of the
aerosol.
It takes careful technique to obtain a slide sample which
is not biased toward large or small particles, does not contain
agglomerations which were not present in the stack, does not break
up agglomerations which were present in the stack, is not too
dense or too sparse, and has not been contaminated in the process
of preparation. Different methods of slide preparation for optical
and photographic microscopy are discussed by Cadle118 and Allen.119
A particularly good discussion of particle analysis through micro-
scopy is given in Volume I of the McCrone Particle Atlas. One
main disadvantage of microscopic analysis is the type of diameter
measured. Depending on the shape of the particles, several dif-
ferent types of diameter are used to characterize the size of the
particle. Three commonly used types of diameter are shown in
Figure 82 with their definitions. : However, for most control
and standards work, the diameter of interest is the aerodynamic
diameter, which is based on the particles' behavior in air. In
these cases, the data from microscopic analysis is helpful only
insofar as it can be related to the particular need of the exper-
iment .
Particle sizes which can be easily studied on optical micro-
scopes, range from about .2 to 100 micrometers. Electron micro-
scopes have increased the size range of particles capable of being
analyzed by microscopy down to 0.001 micrometers^ Both scanning
and transmission electron microscopes provide much information
on surface features, agglomeration,, size? composition and shape
of particles in size ranges below that of optical microscopes,
Computerized scanning devices have increased the analyzing
ability of present day microscopes and simplified counting and
Several commercial laboratories are equipped to provide
physical and structural characterizations of dust samples quickly
and fairly inexpensively -
Sieves —
Because of its relatively large lower particle size limit
156
-------
F - Feret's diameter, ttie distance between two tangents on opposite
sides of the particle, parallel to a fixed direction.
M Martin's diameter, the length of the line which bisects the image
of the particle, parallel to a fixed direction.
da - Diameter o-f a circle having the same projected area as the particle in the
plane of the surface on which it rests. 3540-070
Figure 82. Thre-e diameters used to estimate particle size in
microscopic analyses.!3'
157
-------
(50-75 micrometers), sieving has a limited use for characterizing
most industrial sources today. However, for particles within its
workable size range, sieving can be a very accurate technique,
yielding adequate amounts of particles in each size range for
thorough chemical analysis.
Sieving, one of the oldest ways of sizing particles geomet-
rically, is the process by which a polydisperse powder is passed
through a series of screens with progressively smaller openings
until it is classified as desired. The lower size limit, is set
by the size of the openings of the smallest available screen,
usually a woven wire cloth. Recently, micro-etched screens have
become available. In the future, the lower size limit may be
lowered by using membrane filters which can be made with smaller
holes than woven, fine, wire cloth,
Sieves are available from several manufacturers in four
standard size series: Tyler, U.S., British, and German. See
Table 9 for a comparison of these series.132 Tyler screens are
manufactured by the W. S. Tyler Co., Cleveland, Ohio.
Other methods of size classification using sieving principles
are currently being studied and improved. Wet sieving is useful
for material originally suspended in a liquid or which forms
aggregates when dry-sieved. Air-jet sieving, where the particles
are "shaken" by a jet of air directed upward through a portion
of the sieve, has been found to be quicker and more reproducible
than hand or machine sieving, although smaller amounts of powder
(5 to 10 g) are generally used. Felvation133 (using sieves in
conjunction with elutriation) and "sonic sifting"13 (oscillation
of the air column in which the particles are suspended in a set
of sieves) are similar techniques that employ this principle.
Coulter Counter—
Figure 83 illustrates the principle by which Coulter counters
(Coulter Electronics, Inc.., 590 West 20th Street, Hialeah, FL 33010)
operate,135 Particles suspended in an electrolyte are forced
through a small aperture in which an electric current has been
established. The particles passing through the aperture displace
the electrolyte, and if the conductivity of the particle is dif-
ferent from the electrolyte, an electrical pulse of amplitude
proportional to the particle-electrolyte interface volume will
be seen. A special pulse height analyzer is provided to convert
the electronic data into a size distribution„ A bibliography of
publications related to the operation of the Coulter counter has
been compiled by the manufacturer and is available on request.
Effect Of Particle Size Distribution On ESP Performance
The distribution of the various particle sizes entering a
given precipitator can have a significant effect on the maximum
158
-------
TABLE 9. COMPARISON TABLE OF COMMON SIEVE SERIES132
British
Tyler
U.S.
Standard
German DIN
Equiv. Openings Mesh Openings Mesh Openings DIN Mesh per Openings
Mesh in mm. No. in mm. No. in mm. No. sq. cm. in mm.
3.5
4
5
6
7
8
9
10
12
14
16
20
24
28
32
35
42
48
60
65
80
100
115
150
170
200
250
270
325
400
5.613
4.699
3.962
3.327
2.794
2.362
1.931
1.651
1.397
1.168
0.991
0.833
0.701
0.589
0.495
0.417
0.351
0.295
0.208
0.208
0.175
0.147
0.124
0.104
0.088
0.074
0.061
0.053
0.043
0.038
3.5
4
5
6
7
8
10
12
14
16
18
20
25
30
35
40
45
50
60
70
80
100
120
140
170
299
230
270
325
400
5.66
4.76
4.00
3.36
2.83
2.38
2.00
1.68
1.41
1.19
1.00
0.84
0.71
0.59
0.50
0.42
0.35
0.297
0.250
0.210
0.177
0.149
0.125
0.105
0.088
0.974
0.062
0.053
0.044
0.037
5
6
7
8
10
12
14
16
18
22
25
30
36
44
52
60
7.2
85
100
120
150
170
200
240
300
3.353
2.812
2.411
2.057
1.676
1.405
1.204
1.003
0.853
0.699
0.599
0.500
0.422
0.353
0.295
0.251
0.211
0.178
0.152
0.124
0.104
0.089
0.076
0.066
0.053
1
2
2.5
3
4
5
6
8
10
11
12
14
16
20
24
30
40
50
60
70
80
100
1
4
6.25
9
15
25
36
64
100
121
144
196
256
400
576
900
1600
2500
3600
4900
6400
10000
6.000
3.000
2.400
2.000
1.500
1.200
1.020
0.750
0.600
0.540
0.490
0.430
0.385
0.300
0.250
0.200
0.150
0.120
0.102
0.088
0.075
0.060
Tyler Standard Screen Scale Series.
U.S. Sieve Series (Fine Series) , National Bureau of Standards LC-584 and
ASTME-11.
British Standard Sieve Series, British Standards Institution, London BS-410:1943.
German Standard Sieve Series, German Standard Specification DIN 1171.
159
-------
THRESHOLD
COUNTER "START - STOP"
8540-071
Figure 83. Operating principle of the Coulter Counter. Courtesy
of Coulter Electronics.135
160
-------
overall mass collection efficiency that can be obtained. This is
due to particles of different diameters having different effective
migration velocities and collection efficiencies in a precipitator.
Figure 84 shows some typical data for effective migration velocity
and collection efficiency as a function of particle diameter.136
The'data were obtained by making measurements with impactors at
the inlet and outlet of a full-scale precipitator collecting fly
ash particles and having a specific collection area of 55.7 m2/
(m3/sec) and an average current density of 20 nA/cm2. In general,
there is a minimum in the collection efficiency versus particle
diameter curve somewhere in the range between 0.3 and 0.9 pm. From
the type of relationship shown in Figure 84, it is evident that
different inlet size distributions will produce different overall
mass collection efficiencies provided other operating variables do
not change significantly.
Figure 85 shows the theoretically calculated effect of inlet
particle size distribution on overall mass collection efficiency.137
Although the particle size distribution will influence to some
extent the voltage-current characteristics of precipitators col-
lecting fly ash particles, the curves were generated by assuming
the voltage-current characteristics remain constant in order to
obtain trends. In the calculations, the specific collection area
and current density were held fixed at 25 m2/(ra3/sec) and 26 nA/cm2,
respectively. It is clear that both the mass median diameter and
geometric standard deviation have a strong effect on overall mass
collection efficiency. The overall mass collection efficiency
increases with increasing MMD and decreasing a .
The above considerations point out the importance of considering
the effect of variations in particle size distribution on overall
mass collection efficiency for a given specific collection area and
set of electrical operating conditions. Any program to evaluate the
performance of a precipitator should include measurements of the
particle size distribution at the inlet and outlet of the precipi-
tator. In designing a new precipitator, particle size distribution
measurements on a gas stream which is sirailax to the one to be
treated should be considered.. A precipitator should be designed
with the capability of meeting emissions standards with a somewhat
less favorable particle size distribution than that currently
existing or that anticipated in order to provide a margin of
safety. This is necessary because changes in the process which
produces the emissions .may result in 'a less favorable particle
size distribution.
As mentioned earlier, the .particle size distribution also
influences the voltage-current characteristics of precipitators
collecting fly ash particles. In addition, the particle size dis-
tribution effects the opacity of the effluent from the precipitator.
These topics will be ..discussed in later sections.
161
-------
99.9
u
1" 99.5
U
LU
LL
LU
O
U
O
O
99.0
95.0
90.0
0.1
i | "I t I I I
O
O
O
O
0
O
O
! I 1 f J I I !
1.0
PARTICLE DIAMETER, jum
12.0
11.0
10.0
9.0
(9
0)
h-
O
O
_J
8.0 e
1
LU
7.0
6.0
5.0
U
LU
10.0
3640-072
Figure 84.
Typical data for effective migration velocity and
collection efficiency as a function of particle
diameter.:36
162
-------
99.99
99.98
GEOMETRIC STANDARD DEVIATION
10.0
20.0
99.95
99.9
o
LU
H 99.8
LU
O
u
LU
O
U
cc
LU
O
99.S
99.0
95.0
90.0
SO.Ot
-b --~i t~r -~'t- -T~: t.L-w-t t-- -TTT" 1-1-:J^:i ~. ^j--; T-J r-j-^-irr U
- - — -r-!-r-~ '_: —---_-. -r— --- j 3=tr^.--n-_=_:e u^l-: ~- i-C,- : : c
-£r. '-Li i !-j-—?~-s r~i i "izL; 7 r ;.'"-t-f?-n -
ap CURVE WITH MMO » 10.0 urn;-,- ;_;
•^^jg^-f MMD CURVE WITH uo ' 2.5 I- -- . LL '-1-
•-UfL-: --_- . . . L -. ." . . ..{ ^. :-_- F --;-^T
98-Qf '": ". t~~JE~-~i
10.0
MASS MEDIAN DIAMETER.
20.0
3540-308
Figure 85.
Effect of. particle size distribution on overall mass
collection efficiency.137
163
-------
Measured Size Distributions From Various Installations
Plant Number One—
Particle size distributions were obtained at the inlet
and outlet to a cold-side electrostatic precipitator collecting
ash from low sulfur Western coals. The precipitator, which is
preceded by a mechanical collector, consists of six fields. The
first and second fields each have 5,351 m2 (57,600 ft2) of col-
lecting, area, while the third through the sixth fields have
6,6S8.8 in2 (72,000 ft2) of collecting arear for a total of 37,457.3
m2 (403,2.0.0 ft2). This gives a specific collection area of 99.2 m2/
(mVsec) (504 ft2/1000 cfm) for the design volume of 377.6 mVsec
(800,000 acfm). The precipitator has twelve-inch plate spacing
and operates at approximately 149°C'(300°F).
The determination of the cumulative inlet partice size dis-
tribution between 0.25 ym and 10.0 ym, shown in Figure 86, was
performed using two modified Brink cascade impactors (seven stages,
precollector cyclone, and back up filter). Outlet particle size
distributions were measured using Andersen stack samplers. Rapping
and nonrapping outlet size distributions on a cumulative basis are
shown in Figures 87 and 88. Figure 89 shows the rap and no-rap
data for the ultra fine system and the rap and no-rap impactor
derived efficiencies. The estimated no-rap efficiencies were
based on the data from the large-particle, real-time system and
are subject to large uncertainties because of poor counting sta-
tistics for the larger particles, coupled with the limited time
span over which the data were taken. However, it is obvious that
very high collection efficiences are achieved in the particle
diameter range from 0.05 to 20.0 ym.
Plant Number Two--
Particle size distributions were obtained at the inlet
and outlet to a cold-side electrostatic precipitator collecting
ash from high sulfur Eastern coals. The precipitator consists of
three fields and is divided into two collectors, A and B. The
test program was performed on Collector Ar the collecting area
of which is 7,374.4 m2 (79,380 ft2). This gives a specific col-
lection area of 34.475 m2/(m3/sec) (175 ft2/1000 cfm) for the
design volume flow of 213.82 m3/sec (453,000 acfm). The precip-
itator has 27.94-cm (11-inch)' spacing and operates at approxi-
mately 149°C (300°F).
Cumulative mass loadings for two groups of inlet runs are
given in Figures 90 and 91. Outlet cumulative mass loadings for
Outlet Group 1 (reduced load, normal precipitator operation),
Outlet Group 2 (normal operation), and Outlet Group 5 (one-half
current_density) are given in Figures 92, 93, and 94. The cor-
responding fractional efficiency curves are presented in Figures
95 through 97- A comparison of Figure 96 with 97 clearly shows the
detrimental effect of reduced current on collection efficiency.
164
-------
GROUP- 8-5-75 THROUGH 8-a-75
\
ID
M
a
a
en
01
Ld
M
= E.H7
10°, r
10
-<->•
:t
I
t
!i
LD
r-1
4-
i
r
i
i
Ui
UJ
L-
4 ^ : ~i- 11 iii
10"1 10° 101 102
PARTICLE DIAMETER CMICRDMETER53
Figure 86.
Plant 1 cumulative inlet distribution between 0.25 urn
and 10.0 iixn particle diameter for a cold-side
electros-tatic precipitator collecting ash from a low
sulfur Western coal.
165
-------
OUTLET GROUP - 1 B-5-75t£Hr75
£.27 M/CC
T±0
U
\
CD
a
en
en
i icrH
u
M
<
U
***»
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U
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CD
i I 1 H-!l!| i ! I hH-HH
0.0"1 10° 101 105
PARTICLE DIAMETER (MICROMETERS)
••«-«
Figure 87. Plant 1 cumulative outlet distribution, rappers on,
for a cold-side electrostatic precipitator collecting
ash from a low sulfur Western coal.
166
-------
8-7-75,8-8-73
-------
PEJSETRATIDN-EFFICIENCY
10I
101:
2-
.
a
M
1-
ry
H
LJ
y 10°,
H-
2
LJ
LJ
LJ
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A Rap
& No rap
i
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• 1
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Estimate from
i jLStJ'iJIji 1 1
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r
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d
_ QQ _ qq
±0'E 10'1 10° 101
PARTICLE DIAMETER (MICROMETERS)
8S40-OT6
Figure 89.
Plant 1, rap/no-rap fractional efficiency including
ultrafine and impactor measurements for a cold-side
electrostatic precipitator collecting ash from a
low sulfur Western coal.
168
-------
INLET GHIF1 1-1B-7S
ac = E.40 aucc
3
cn
cn
u
M
I—
_J
10°, r
"10°
H H
H 1 I ) I I li|
icr1 10° lo1 ios
PARTICLE DIAMETER (MICROMETERS)
u
Q:
ID
i—i
CJ
cn
u
M
t—
i<
D
d
3540-077
Figure 90, Plant 2 inlet cumulative size distribution for a
cold-side electrostatic precipitator collecting ash
from a high sulfur Eastern coal.
169
-------
IHEIGE1F2 1-:
B0 = £.40 OS/EC
TWDUGH 1-3J-75
CD
CD
^ P
M 10*
_J
cn
en
LJ
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10°
10
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PARTICLE DIAMETER CMICRDMET
LL
u
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102
3540-018
Figure 91.
Plant 2 average inlet cumulative size distribution_
for a cold-side electrostatic precipitator collecting
ash from a high sulfur Eastern coal.
170
-------
CUTLET BOP - 1 1-1P-76 (CRML
BC = 2.4) GUI
ID2^
LD
LH
in
ICT1,:
10
-3
-^•1 n-i
U
x
ic
i i i 111H| H—i i 11 ni|—H—i i 11 ni|
10° 101 102
PARTICLE DIAMETER (MICROMETERS)
Figure 92. Plant 2 outlet group 1 size distribution at reduced
load and normal precipitator operation for a cold-side
electrostatic precipitator collecting ash from a high
sulfur Eastern coal.
171
-------
UUILtl WaJUr - c i-13-fOii-or'o nmm. -
*
RK) = 2.40 O/CC I
~
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PARTICLE DIAMETER (MICROMETERS)
3640-080
Figure 93. Plant 2 outlet group 2 size distribution with normal
operation of a cold-side electrostatic precipitator
collecting ash from a high sulfur Eastern coal.
172
-------
OUTLET CROP -5 1-lfr-^.l-lS-TB WBW.
RC = 2.40 QMX
CD
CD
B]
lo-H
!
TlO
CJ
\
HH
Q
a
in
LJ
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H 1 I I I IM| 1 1 I I I III)
icr1 ±cP lo1 lo2
PARTICLE DIAMETER (MICROMETERS)
Figure 94.
Plant 2 outlet group 5 size distribution for a cold-
side pxecipitator operating at one-half current
density collecting ash from a high sulfur Eastern coal,
1.73
-------
PBSETRATIDN-EFFICIENCY
EFFEBCY - Wm. 1-12-71
loH
QL
u
UJ
Q_
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±90 = 0
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IT
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10°
t+H—
101
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PARTICLE DIAMETER (MICROMETERS)
L)
U
H
U
H
U.
I-
u
u
a.
u
G_
99.39
mo-oi:
Figure 95. Plant 2 fractional efficiency, outlet group 1 for
reduced load and normal operation of a cold-side
electrostatic precipitator collecting ash from a
high sulfur Eastern coal.
174
-------
M
i
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CL
U
Ct
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10S
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EFFICIENCY
PERCENT
:99.9
»
-99.99
PARTICLE DIAMETER (MICROMETERS)
3540-083
Figure 96. Plant 2 fractional efficiency, outlet group 2 with
normal operation of a cold-side electrostatic
precipitator collecting ash from a high sulfur
Eastern coal.
175
-------
PEhETRATION-EFFIdENCY
EFFIO9CT - WWL i-tf-7£.i-19-76
lC*r
a
M
LJ
ID1:
ICft:
LJ
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:99.S
10
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1 I I i I I i 11 1 I I i MM
101
102
99.99
PARTICLE DIAMETER (MICROMETERS)
Figure 97.
Plant 2 fractional efficiency, outlet group 5 for
a cold-side electrostatic precipitator operating at
one-half current density collecting ash from a high
sulfur Eastern coal.
176
-------
Plant Number Three—
The size distributions from this plant were obtained at the
inlet and outlet of a cold-side electrostatic precipitator col-
lecting ash from high sulfur Eastern coals. A mechanical collector
precedes the precipitator which consists of four fields in the
direction of gas flow and is divided into collectors A and B.
The test program was conducted on collector B, the total collec-
ting area of which is 5900.64 m2 (63,516 ft2), giving a specific
collection area of 43.48 m2/(m3/sec) (220.9 ft2/1000 cfm) for the
design volume .of 135.70 m3/sec (287,500 acfm). The precipitator
has 25.4 cm (12 inch) plate spacings and operates at approximately
160°G (320°F). Inlet and outlet cumulative size distributions are
given in Figures 98 and 99, and Figure 100 shows the fractional
efficiencies for normal operation. Figure 101 contains the frac-
tional efficiency data for normal operating conditions obtained
from the ultra fine system and the impactors. Reasonable agree-
ment is shown between the ultra fine system and the impactors in
the overlap region.
Plant Number Four—
The size distributions from plant number four were obtained
from the inlet and outlet of a hot-side electrostatic precipitator
collecting ash from a low sulfur Eastern coal. The precipitator
consists of A and B casings each of which has two inlet and two
outlet ducts. Tests were conducted on casing B (consisting of
Chambers Bl and B2). Casing B has four fields in series, each of
which has a collecting area of 3912.95 m2 (42,120 ft2). Although
the precipitator was designed to have an SCA of 53.15 m2/(m3/sec)
(270 ft2/1000 acfm) for a total volume flow of 590 m3/sec (1,250,000
acfm), the gas flow for the two chambers tested was about 430,000
acfm, which resulted, in an SCA of approximately 390 ft2/1000 acfm.
The collecting electrodes have nine inch spacing and the precipi-
tator operates at approximately 343°C (650°F).
Figures 102 and 103 present inlet and outlet size distributions
resulting from impactor measurements made on Duct Bl and B2 (casing
B).
Figure 104 illustrates the fractional efficiencies obtained
with the ultra fine sizing system and impactors for duct Bl with
and without rapping.
Plant Number Five—
The size distributipns from this plant were obtained at the
inlet and outlet of a cold-side.electrostatic, precipitator col-
lecting ash from low..sulfur Western coals.. The electrostatic
precipitator consists of six-divided' chambers, the test program
being conducted on Chamber 5. Each chamber has five electrical
fields each of which has a collection area of 3518.96 m2 (37,879
177
-------
6
CD
a
en
en
<
e-25-7E.M-7£.3-?-7E
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-H-
10°
101
^
10s
PARTICLE DIAMETER (MICROMETERS)
Figure 98.
Plant 3 inlet cumulative size distribution for a
cold-side electrostatic precipitator collecting ash
from a high sulfur Eastern coal.
178
-------
NHtfL
TIC)'1
10^
§ 101.
CD :
CD
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PARTICLE DIAMETER (MICROMETERS)
3540-086
Figure 99, Plant 3 outlet cumulative size distribution for a
cold-side electrostatic precipitator collecting
ash from' a high sulfur Eastern coal.
179
-------
FQSETRATION-EFFICIE3SCY
EFF1O9CY - NBttL 2-5-76.3-2-75
10P::
u
CL
LJ
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CL
10s
99.33
PARTICLE DIAMETER (MICROMETERS)
Figure 100. Plant 3 fractional efficiency for normal operation of
a cold-side electrostatic precipitator collecting
ash from a high sulfur Eastern coal.
180
-------
FEhETTRATIOSH
Plant 3 Efficiency - Normal 2/25/76,3/2/76
la5.
o ultrafine
• impactors
101::
a
M
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10°-:
U
LJ
a.
1C
2
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::90.0
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4-H
10°
U
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M
U.
-99.0
u
u
u
Q.
10
102
99.33
PARTICLE DIAMETER (MICROMETERS)
3640-088
Figure 101.
Plant 3 fractional efficiency data for normal oper-
ating conditions obtained from both the ultrafine
system and impactors for a cold-side electrostatic
precipitator collecting ash from a high sulfur
Eastern coal.
181
-------
DUTQnf-3 ALL BfCrOS 0M (M QUCT Bl AM) B?
MO = 2.H7 O/CC
103,:
en
en
U
H
H
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10
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a
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10-255
U
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h-
10
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icP
I I I Mll| 1—I I I I ||||
101
105
PARTICLE DIAMETER (MICROMETERS)
Figure 102.
3640-089
Plant 4 inlet cumulative size distribution resulting
from impactor measurements made on ducts Bl and B2
of a hot-side precipitator collecting ash from a
low sulfur Eastern coal.
182
-------
CD
a
01
01
<
OUTLET CROP - 3 DUCT K-ft 4-S7-76 MBUL
AC - e.37 our
10
-3
£J
a
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a
a
01
LJ
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1O
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I I I I I I H—: 1 1 I MH)|
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PARTICLE DIAMETER (MICROMETERS) .......
Figure 103. Plant 4 outlet cumulative size distribution resulting
from impactor measurements made on ducts Bl and B2
of a hot-side precipitator collecting ash from a
low sulfur Eastern coal.
183
-------
101-:
10°,:
iO'1::
10
,-e
: 1
x- O.O
OPEN SYMBOLS - NO RAP
CLOSED SYMBOLS • RAP
O«tMPACTOR
i t i !iini i i i ni»i—i i mini t i i MM
10'2 1CT1 10° 101
PARTICLE DIAMETER CMICRDKCT
::9O.O
bJ
M
u
M
33-Otij
fe^M
u
s
LL
10s
99.99
8640-091
Figure 104.
Plant 4 fractional efficiency data obtained with the
ultrafine sizing system and impactors for duct Bl
of a hot-side precipitator collecting ash from a
low sulfur Eastern coal, with and without rapping.
184
-------
ft2)- The precipitator has 25 cm (9.75 in) plate spacing, oper-
ates at 88 to 120°C (190 to 250°F), and is designed to handle
1100 m3/sec (2,330,000 acfm). The actual specific collection
area on the tested chamber was approximately 590 ft2/1000 acfm.
Figures 105 and 106 show the inlet and outlet size distri-
butions, respectively. Figure 107 shows the ultrafine fractional
efficiency data and the impactor derived fractional efficiencies
under normal conditions.
Plant Number Six--
Particle size distributions were obtained at the inlet and
outlet to a hot-side electrostatic precipitator collecting ash
from a low sulfur Western coal. This hot-side precipitator oper-
ates at approximately 360°C (680°F). The precipitator consists
of two separate collectors, each of which has eight isolatable
chambers, the test program being conducted on the number eight
chamber. There are in each chamber six electrical fields in the
direction of^gas flow, and each field has a total collecting area
of 1170.54 m: (12,600 ft2). The complete precipitator installation
was designed to handle 1859.68 m3./sec (3,940,000 acfm) at 350°C
which results in a design specific collection area of 60.43 m2/
(mVsec) (307 ft2/1000 cfm) .
The inlet and outlet size distributions are shown in Figures
108 and 109, respectively- Figure 110 shows the ultrafine and
impactor fractional efficiencies for normal conditions.
Plant Number Seven--
The size distributions from plant number seven were obtained
at the inlet to a cold-side precipitator collecting ash from high
sulfur coals. The in situ particle size distribution measurements
were conducted at the inlets to both the A and B sides of the
precipitator using modified Brink cascade impactors and the re-
sults are shown in Figures 111 and 112.
Plant Number Eight--
The size distributions from plant number eight were obtained
at the inlet and outlet to a cold-side electrostatic precipitator
collecting ash from low sulfur Western coals. Figure 113 shows a
graph of the fractional collection efficiencies for the small par-
ticle fraction using Brink impactor instrumentation.
Plant Number Nine—
Using Brink impactors at the inlet and Andersen impactors at
the outlet, particle size measurements were made at the inlet and
outlet of a cold-side electrostatic precipitator collecting ash
from medium sulfur (1.0-1.5%) Southeastern coals. The precipitator
185
-------
1 - 10/5/75 . lfl/S/76 . 10/7/76
TlO1
y ion
CD
CD
M 102-
Q
in
LD
U
lO1^
u
10
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a
ic
1
^^TT
10°
H 1 I M IIH 1 1 I •! ) 11 H
lo2
PARTICLE DIAMETER (MICROMETERS)
Figure 105. Plant 5 inlet cumulative size distribution resulting
from impactor measurements on a cold-side precipitator
collecting ash from a low sulfur Western coal.
186
-------
OUTLET DWCTORS BOP 1 - 10/S/7E
BC = 2.34 O/tl
10S:
loH
\
a 10°
01
m
i icr1-
LJ
HI
=e«
10
....—•"
r»«»
TIG'1
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110's
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1 "^ i i—i—i i i i i | 1 1 1—i—r~
icr1 10° lo1 10s
PARTICLE DIAMETER (MICROMETERS) ,,
-------
FOSETRATION-
EF -
•r 0.0
10H
M
QL
Lul
U
Q_
LJ
U
(Z
U
CL
10'H
OPEN SYMBOLS O ULTRAFINE
CLOSED " • tMPAGTOR
±30.0
Z I
10-
iiii i
11 lt|
10
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4-4-
II ill
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10°
101
U
U
M
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U_
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Q£
LJ
CL
i33»3
33,
PARTICLE DIAMETER (MICROMETERS)
Figure 107. Plant 5 fractional efficiency data obtained with the
ultrafine sizing system and impactors under normal
conditions on a cold-side precipitator collecting
ash from a low sulfur Western coal.
188
-------
M) = a.-*i G*CC
104-
•
•
^
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3540-095
Figure 108. Plant 6 inlet c^lmulative size distribution resulting
from impactor measurement on a hot-side precipitator
collecting ash from a low sulfur Western coal.
189
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PARTICLE DIAMETER (MICROMETERS) JUM..
Figure 109. Plant 6 outlet cumulative size distribution resulting
from impactor measurements on a hot-side precipitator
collecting ash from a low sulfur Western coal.
190
-------
PSSETRATICN-EFFICIENIY
- MRHL 1/5/77.2/1/77
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PARTICLE DIAMETER (MICROMETERS)
Figure 110.
3540-097
Plant 6 fractional efficiency data obtained with the
ultrafine sizing system and impactors under normal
conditions on a hot-side precipitator collecting
ash from a low sulfur Western coal.
191
-------
CD
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BLETHET-A AVERAGE 3-13.14-77 FULL LOAD
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PARTICLE DIAMETER CMICRDMET
3640-098
Figure 111. Plant 7 inlet cumulative size distribution resulting
from impactor measurements on a cold-side precipitator
collecting ash from a high sulfur coal.
192
-------
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MIT OCT-B AVQWGE 9-15,lfi-77 FULL LOW
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PARTICLE DIAMETER (MICROMETERS)
Figure 112,
3540-099
Plant 7 outlet cumulative size distribution resulting
from impactor measurements on a cold-side precipitator
collecting ash from a high sulfur coal.
193
-------
CO
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Figure 113.
PARTICLE SIZE AERODYNAMIC DIAMETER
Plant 8 fractional collection efficiencies for small
particle fraction obtained with Brink impactors on
a cold-side precipitator collecting ash from a low
sulfur Western coal.
194
-------
consists of collectors A and B each of which has two collectors
in series. Tests were conducted on A side only which has a
collecting area of 28,877 m2 (311,000 ft2). There are twelve
electrical sections in the direction of gas flow. Gas flow at
full load (^700 MW) is about 520 m3/sec at 149°C, giving a
specific collecting area of 55 m2/(m3/sec) or 283 ft2/1000 cfm.
Inlet and outlet size distributions and fractional efficiency
data are shown in Figures 114, 115, and 116.
Plant Number Ten—
The size distributions for plant number ten were obtained
at the inlet and outlet of a hot-side electrostatic precipitator
collecting ash from low-medium (1.0%) sulfur Western coal. The
electrostatic precipitator consists of four individual precipita-
tors of two sections consisting of 13,582 m2 of plate area col-
lecting particulate matter from a gas stream with a flow rate of
about 1.33 x 101* m3/min at a temperature of 371°C at full load
(357 MW). However, tests were conducted at a load with volume
flow rates on the order of 9628 m3/min which corresponds to a
specific collection area of 310 ft2/1000 acfm.
Inertially determined size/mass concentration data were
obtained using modified Brink Cascade impactors for inlet sampling
and Andersen Cascade impactors for outlet sampling. Optically
determined size/concentration data over a size range from about
0.3 to 2.0 um were obtained using Climet and Royco particle
counters. Size/concentration data were obtained by diffusional
methods using diffusion batteries and condensation nuclei counters
simultaneously with the optical data. Figure 117 shows the frac-
tional collection efficiencies of the precipitator and the measure-
ment methods used.
Plant Number Eleven—
Figure 118 shows the fractional collection efficiencies of
a cold-side electrostatic precipitator collecting ash from a
plant burning Midwestern coal and refuse. The measurements were
conducted at three load/percentage coal-refuse combinations.
Plant Number Twelve—
Particle size distributions were obtained at the
inlet and outlet to-a cold-side electrostatic precipitator,
collecting ash from a plant burning high sulfur (^2%) Eastern
coals. Th-e precipitator has a collection electrode area of
19,414 m2 (208,980 ft2),, plate spacing of 25.4 .cm (ten inches),
and a gas volume flow .rate of 28,700 m3/min (1,025,000 cfm) . The
particle size analyses were determined with modified impactor type
devices and the. results are shown in Figures 119 and 120. The
inlet particle size distribution is unusually large for a power
plant. The modified impactor devices were equipped with cyclone
195
-------
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PARTICLE DIAMETER, urn
3 6 4 0 ~l 01
Figure 114. Plant 9 inlet cumulative size distribution resulting
from measurements with a modified Brink impactor on
a cold-side precipitator collecting ash from a
medium sulfur (1.0-1.5%) Southeastern coal (0 and +
represent different sampling conditions).
196
-------
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PRECIPITATOR CHARACTERISTICS:
— TEMPERATURE - 335°C —
SCA - 85 M2/(M3/sec)
CURRENT DENSITY - 35 nA/CM2
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70
80
90
95
3540-106
Figure 119,
Plant 12 inlet cumulative size distribution obtained
with modified impactors on a cold-side precipitator
collecting ash from a plant burning a high sulfur
(^2.0%) Eastern coal.
201
-------
10.0
o
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SMALLER THAN INDICATED SIZE
90
8540-10'
Figure 120. Plant 12 outlet cumulative size distribution obtained
with modified impactors on a cold-side precipitator
collecting ash from a plant burning a high sulfur
Eastern coal.
202
-------
collectors which remove the coarsest size fraction prior to intro-
duction into the impactor.
Plant Number Thirteen—
The performance of a high efficiency cold-side electrostatic
precipitator located in the Midwest was measured with special
emphasis on the efficiency of the precipitator as a function of
particle size over the range from 0.01 ym to 5 urn. The Midwestern
coal burned by the power plant was high in sulfur (^3.6%) content.
Particle size measurements were performed using cascade impactors,
a Climet optical particle counter, and diffusion batteries with
CN counters to obtain particle size distributions. Figure 121
shows the fractional efficiencies calculated from the optical and
diffusional data. Impactor data are not shown because of likely
contamination.
Plant Number Fourteen—
Optical, diffusional, and impactor measurements were performed
on a pilot-scale electrostatic precipitator treating flue gas re-
sulting from the combustion of a low sulfur Western coal. Figure
122 gives the fractional efficiencies for the pilot precipitator.
The temperature of the flue gas was about 160°C (320°F), the sulfur
content of the coal was about 0.47% (dry basis), and the specific
collecting area of the precipitator was 66.9 m2/(m3/sec) (340 ft2/
1000 cfm).
Plant Number Fifteen—
The size distributions shown in Figures 123 - 128 were ob-
tained at the inlet and outlet to a pilot scale electrostatic pre-
cipitator collecting ash resulting from the combustion of a low
sulfur Western coal. Inlet particle sizing was performed using
two six-stage Brink impactors with precollector cyclones and back
up filters. The outlet particle sizing was accomplished with an
eight-stage Andersen impactor with back up filter. In the case
of the Brink impactor> foil substrates were coated with silicone
vacuum grease and baked prior to use if the temperature of the flue
gas was less than 204°C (400°F). Otherwise, ungreased aluminum foil
substrates were used. Glass fiber filter substrates were used in
the Andersen impactor.
The inlet size distribution curves are shown in Figure 123,
and the outlet size distributions are shown in Figures 124 through
128.
Summary Of Inlet Particle Size Distributions
Inlet particle size distributions from most of the plants pre-
viously discussed have been organized into various areas of interest.
Figure 129 shows the inlet size distributions of those plants whose
203
-------
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DIFFUSIONAL DATA , _ OPTICAL DATA ,
1 1 I -- 1
• TEST NO. 3, 10/14/73, 103 MW, HIGH SULFUR, AUTOMATIC, 4th SECT. OFF
O TEST NO. 4, 10/19/73, 103 MW, HIGH SULFUR, AUTOMATIC
• TEST NO. 5. 10/20/73, 103 MW, HIGH SULFUR, 20 juA/ft2
O TEST NO. 6, 10/21/73, 103 MW, HIGH SULFUR, 10 /uA/ft2
A TEST NO. 7, 10/22/73, 103 MW, HIGH SULFUR, 30 ^A/ft2
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T-138°C(280°F)
T=160°C(320°F)
T-160°C(320°F)
T-121°C(250°F)
T=138°C(2800F)
T-138°C(280°F)
SCA-73 m2/(m3/sec),
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SCA»67 m2/(m3/sec),
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SCA=73 m2/(m3/sec),
SCA-69 m2/(m3/sec).
(370 ft2/1000 cfm)
(346 ft2/1000 cfm)
(328 ft2/1000 cfm)
(350 ft2/1000 cfm)
(370 ft2/1000 cfm)
(350 ft2/1000 cfm)
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,_F? A 8-30-73 T=116°C(240°F) SCA»68 m2/(m3/sec), (343 ft2/1000 cfm) ^ _^_
tSnJIES ^ ^4.73 T=149°C(300°F) SCA=68 m2/(m3/sec), (344 ft2/1000 cfm) ^=^
' ' -' - rrr _^ _ .^ — ^ */^«»/««^ >^o**> \ *^^^A__^«^ __ 7// 3./ \ / ^ >• •* £^3 / •! rtrtrt c i 'i1'') < i * - -t—T
T 9-6-73 T=154°C(310°F) SCA=67 m2/(m3/Jec), (342 ft2/1000 cfm) ^±h~
-*rH-—
0.2
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10.0
PARTICLE SIZE, microns
100.0
3540-111
Figure 124.
Plant 15 outlet cumulative particle size distribution
at the conditions indicated obtained by using an
Andersen irapactor with a back-up filter on a pilot
precipitator collecting ash from a low sulfur Western
coal.
207
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4 T=232°C(450°F) SCA=72 m2/(m3/»cc), (364 ft^/IOOQ cfm)
'•'•" I -.
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2.28x11
0.001
2.28x11
0.0001
0.2
PARTICLE SIZE, microns
Figure 125. Plant 15 outlet cumulative particle size distribution
at the conditions indicated obtained by using an
Andersen impactor with a back-up filter on a pilot
precipitator collecting ash from a low sulfur Western
coal.
208
-------
0.01
o
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o
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0.001
0.0001
mtm^.ygp^
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10'3
2.28 x 10"4
PARTICLE SIZE, microns
Figure 126. Plant 15 outlet cumulative particle size distribution
at the conditions indicated obtained by using an
Andersen impactor with a back-up filter on a pilot
precipitator collecting ash from a low sulfur Western
coal.
209
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TiTtT^rT^cTZ^tl- — ~i — -t'rrH' • -^
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i^rrCiii-^iiilsg^agi 2.28 x is
0.0001
10.0
m^lZ2IIaElOII 2.28 x 1
100.0
PARTICLE SIZE, microns
S6O-1H
Figure 127-
Plant 15 outlet cumulative particle size distribution
at the conditions indicated obtained by using an
Andersen impactor,with a back-up filter on a pilot
precipitator collecting ash from a low sulfur Western
coal.
210
-------
o
o
oe
o
Ui
<
Z>
3
O
0.01
2 0.001
• t £i' - • ~Ei;'
::Ti:::rti::;
2.28 x ID'2
::::;:-:rrf:--h; !'.!:.
SH3S
i T<=174°C(345°F) SCA=99 m2/(m3/sec), (504 ft2/1000 cfm) %s
m T=121°C(250°F) SCA=102 m2/(m3/sec), (517 ft2/1000 cfm)p
A T=143°C(290°F) SCA=96 m2/(m3/sec). (486 ft2/1000 cfm) |1
O T=143°C(290°F) SCA=97 m2/(m3/sec), (493 ft2/1000 cfm) ||
0 T=138°C(280°F) SCA=99 m2/(m3/sec), (503 ft2/1000 cfm)
0.0001
1,0 10.0
PARTICLE SIZE, microns
100.0
3540-116
10'3
n
^
O)
10'4
Figure 128.
Plant 15 outlet cumulative particle size distribution
at the conditions indicated obtained by .using an
Andersen impactor with a back-up filter on a pilot
p'recipitator collecting- ash from a low sulfur Western
coal.
211
-------
u
re
I
o~
z
5
o
_i
01
Z)
O
103
102
10°
10-
1 I LI I i i | 1—J:;T I I til | 1 1 I I I It
• PLANT NO. 1 (COLD-SIDE ESP COLLECTING
ASH FROM LOW SULFUR WESTERN COALS)
A. PLANT NO. 3 (COLD-SIDE ESP COLLECTING
ASH FROM HIGH SULFUR EASTERN COALS)
' i i i i I it
J
I I I i M
' ' ' "i
to'
10-1 „.
10-2
O
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CO
n
o
10'3
to-4
10-1
10° 101
PARTICLE DIAMETER, micrometers
3540-116
Figure 129,
Inlet size distributions of cold-side ESPs
preceded by mechanical collectors.
212
-------
electrostatic precipitators were preceded by a mechanical collector.
Figure 130 shows inlet size distributions of ash collected from
hot-side electrostatic precipitator installations. Figure 131
gives the inlet size distributions from cold-side electrostatic
precipitators collecting ash produced from both high and low
sulfur coals.
SPECIFIC COLLECTION AREA
The specific collection area (SCA) which is defined as the
ratio of the total collection area to the total gas volume flow
rate is an important parameter that influences the performance of
a precipitator. The SCA can be changed by changing either the
collection plate area or the gas volume flow rate or both. In
effect, changes in SCA result in changes in the treatment time
experienced by the particles. Thus, increasing the SCA of a pre-
cipitator increases the collection efficiency. In designing a
precipitator, the total gas volume flow rate will be known so
'that the SCA is determined by the choice of total collection
plate area. In existing precipitators, the total collection
plate area is fixed but the SCA can change due to changes in
the gas volume flow rate.
The SCA provides the most flexible variable in designing a
precipitator. Although the SCA has economic and practical limita-
tions, it has no physical limitations and can be increased in-
definitely. Even though a curve of collection efficiency versus
SCA will level off for the larger values of SCA due to the ex-
ponential nature of the collection mechanism, greater efficiency.
can always be obtained from increased SCA.
Figure 132 shows experimental fractional efficiency data
obtained from a laboratory precipitator collecting dioctyl
phthalate (OOP) droplets under essentially idealized conditions
at two different SCAs at two different current densities.133
In these experiments, all variables could be kept essentially
constant except the SCA which was changed by changing the gas
velocity. The fractional efficiency data were obtained by
making particle size distribution measurements with a Brink
impactor at the inlet and outlet of the precipitator. For a
given current density, the experimental data show the increase
in particle collection efficiency with increased SCA.
Figure 133 shows experimental data on the effects of SCA on
overall mass collection efficiency. The data were obtained from
pilot plant studies on the flue gas from a coal fired boiler. Test
velocities through the precipitator were varied, from. 1.13 -to 2.53
m/sec. . The precipitator had two electrical sections in the di-
rection of gas flow. The .inlet section was maintained at approx-
imately 41.7 nA/cm2 while the outlet section was maintained at
approximately 69.5 nA/cm2. Although attempts were made"to hold
flue gas temperatures and boiler operating conditions identical
213
-------
"i—i—I III)
T—I I I I I I
T—I I I I III
104
103
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CD 102
5
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10°
10
rl
10
,-1
PLANT NO. 4 {HOT-SIDE ESP COLLECTING
ASH FROM A LOW SULFUR EASTERN COAL)
PLANT NO. 6 (HOT-SIDE ESP COLLECTING
ASH FROM A LOW SULFUR WESTERN COAL)
PLANT NO. 10 (HOT-SIDE ESP COLLECTING
ASH FROM LOW-MEDIUM (1%) SULFUR
WESTERN COAL
10°
10
1-1
5
co
CO
LLJ
10-2 j=
_j
D
2
D
U
10'3
10-4
10° IO1
PARTICLE DIAMETER, micrometers
102
S540-117
Figure 130.
Inlet size distributions of hot-side ESP
installations.
214
-------
I I
I 11 I
I I I
TIT
I I I 1 IM
104
103
u
2
5
LU
o
102
101
100
• REDUCED LOAD, PLANT NO. 2
HIGH SULFUR EASTERN COAL
A NORMAL LOAD, PLANT NO. 2
HIGH SULFUR EASTERN COAL
D PLANT NO. 5 LOW SULFUR
WESTERN COAL
O PLANT NO. 7 HIGH SULFUR COAL
A PLANT NO. 9 LOW SULFUR
WESTERN COAL
10-1
I t I I I I I
I
I I I I I I I
I I I I II I
10°
10-1
10
,-2
10'0
10
,-4
10' l
Figure 131,
10° to1
PARTICLE DIAMETER, microimters
102
o>
o"
z
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CO
D
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3840-118
Inlet size distributions of cold-side ESPs
collecting ashes from high sulfur and low
sulfur coals.
215
-------
99.8
i .
TT
o
LL
UJ
z
o
o
o
o
99.5
99.0
98.0
95.0
90.0
80.0
70.0
60.0
0.1
Figure 132.
A 24.5 m2/(m3/sec), 344.5 juA/m2
A. 16.1 m2/(m3/sec), 344.5 juA/m2
O 24.5 rn2/(m3/sec), 107.6 /uA/m2
• 16.1 m2/(m3/sec), 107.6 juA/m2
f . » .*
J _
i j:
J 1—''''
1.0
GEOMETRIC MEAN DIAMETER, /im
10.0
2(40-119
Experimental fraction efficiency data obtained
from a laboratory precipitator collecting
dioctylphthalate (DOP) droplets under essentially
idealized conditions at two different SCAs at two
•different current densities.138
216
-------
99.9
a?
o
111
LL
u.
LU
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u
HI
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V)
O)
O
99.8
99.7
99.6
99.5
99.0
98.0
97.0
96.0
•95.0
94.0
93.0
90.0
80.0
10
FIRST SECTION
SECOND SECTION
OVERALL
s
15
20 25
SCA, m2/(m3/sec)
30
3540-120
Figure 133.
Effects of SCA on overall mass collection
efficiency.
217
-------
for each test, inlet gas temperatures ranged from 146 to 174°C
and the inlet mass loading ranged from 0.011 to 0.018 kg/DNCM.
The data represent periods during which both the discharge and
collection electrodes were rapped. Although effects due to
changes in gas temperature, inlet mass loading, and particle
reentrainment, and nonideal conditions influence the data to
some extent, the data show the definite increase in overall
mass collection efficiency with increased SCA.
Data showing the effect of SCA on the overall mass collec-
tion efficiency of a full-scale• precipitator collecting fly ash
particles are given in Figure 134-. The precipitator had a col-
lection electrode area of 7,698 in2,, three electrical sections
in the direction of gas flow, thirty-six gas passages, and a
plate height of 8.9 m. The SCA was varied by changing the
boiler load. The temperature and resistivity of the ash ranged
from 180 to 200°C and 0.4 to 1.0 x 1012 ohm-cm,.respectively.
As with the pilot plant data discussed previously, the effect
of SCA can not be completely isolated since all other variables
can not be held rigidly constant when the SCA is changed. How-
ever, the data again show the definite increase in overall mass
collection efficiency with increased SCA.
VOLTAGE-CURRENT CHARACTERISTICS
Electrical Circuitry For A Precipitator
The electrical equivalent circuit of a precipitator is shown
in Figure 135.139 The voltage normally applied to a precipitator
is either half-wave or full-wave rectified 60 Hertz ac. Neglec-
ting for a moment the effects of C_ and R,.., the capacitor, C ,
charges on the increasing portion of the voltage waveform and
discharges on the decreasing portion. The current from the dis-
charging capacitance flows through the resistance R^ tending to
(j
maintain the peak voltage applied. There is an exponential decay
of this voltage dependent on the time constant of the R C circuit.
This time constant is given by:1"0 ^
T = RQCp , (19)
where T is the time in seconds for the voltage waveform to decrease
to approximately 37% of its peak value after the voltage is re-
moved. The current, I, will flow in the return leg of the circuit
only during the charging of the capacitor. During the remainder
of the cycle, the current supplied to RQ is the discharge current
from C . These relationships are shown in Figure 136. In this
example T is assumed to be greater than 8 milliseconds or 1/2 cycle
of the line voltage.
218
-------
99.9
o
LU
U.
lit
0.02 OUTLET
(0.046 grams/am3)
0.05 OUTLET
(0.114 grams/arn3)
INLET LOADING 19.67 GRAIN/SCF
(45.0 grams/am3)
REQ'D OUTLET 0.02 & 0.05 GRAIN/SCF
(0.046 & 0.114 grams/am3)
REQ'D EFF. 99.00 99.75
99
I
I
I
I
I
200
(39.4)
300
(59.1)
400
(78.8)
500
(98:5)
600
(118)
700
(138)
SCA, ft2/(1000 acfm) (m2/(m3/sec))
800
(158)
3540-121
Figure 134.
Measured efficiency as a function of specific
collection area.
219
-------
-V
Cp
RETURN O-
'.RG
CD
V = VOLTAGE APPLIED ACROSS ELECTRODES IN VOLTS
I = TOTAL CONVENTIONAL CURRENT FLOW IN AMPERES
Cp = EQUIVALENT CAPACITANCE OF THE ELECTRODE SYSTEM IN FARADS
RG = EQUIVALENT RESISTANCE OF THE INTER-ELECTRODE REGION IN OHMS
CD= EFFECTIVE CAPACITANCE OF THE DUST LAYER IN FARADS
RD= EFFECTIVE RESISTANCE OF THE DUST LAYER IN OHMS 3540-122
Figure 135. Electrical equivalent circuit of a precipitator
electrode system with a dust layer. After Oglesby
and Nichols.l 39
220
-------
APPLIED VOLTAGE
CURRENT I
VOLTAGE ACROSS RG
TIME
3940-123
Figure 136. Voltage-current relationship in an ideal capacitor/
resistor parallel combination.
221
-------
Normally the effective impedance presented by the parallel
combination of CD and R_ is negligible compared to the impedance
of FL,. Thus, the time domain response of the precipitator is
G ...... .
determined by the combination of C and R_. However, this is not
p tj
true when the dust layer is in a breakdown condition and possibly
exhibiting back corona. The breakdown may effectively short out
the dust layer and a portion of RG .thereby reducing the time
constant, T, and increasing the current, I. This change in time
constant may be monitored on an oscilloscope presentation of the
voltage waveform and used to support evidence that breakdown of
the dust layer is occurring.
The voltages and currents in a precipitator are most often
measured by the installed power set instrumentation as root-mean-
square (rms) or effective values. The capacitances and resis-
tances vary slowly with time so•that the equivalent circuit of a
precipitator in normal operation can be approximated as a pure
resistance across the terminals of a DC source. The voltage-
current relationship is simply V = RI where R is the effective
value of the resistance in ohms, V is in rms volts, and I is in
rms amperes. An actual precipitator departs from ohmic behavior
in that R is a non-linear function of the current. The graphical
presentation of precipitator voltage versus secondary current is
not the straight line generated with an ohmic resistance, but
generally curved and referred to as a V-I curve.
Measurement Of Voltage-Current Characteristics1 **:
Many precipitator control rooms have panel meters for each
transformer/rectifier (T/R) set which display the primary and
secondary voltages and currents and the sparking rate. The sec-
ondary voltage-current characteristics are needed in order to
analyze the electrical operation of a precipitator. Thus, panel
meters for measuring both secondary voltages and currents should b£
provided. If a precipitator is not equipped with panel meters for
measuring secondary voltages, or if calibrations of existing meter:
are desired, temporary voltage divider networks and accurate volt-
meters can be installed on the precipitator side of the rectifier
networks as shown at point number 1 in Figure 137 to obtain
secondary voltage measurements. In practice, the voltage divid-
ers are inserted in parallel across the high voltage bus sections
of the precipitator. Typically, the resistor R2 has a value of
about 1 x ICr ohms and Ri / has a value of about 12,x 103 ohms.
Because of the voltage drop across R2 , this resistor should be
well insulated electrically.
If it is necessary to measure the secondary current, a volt-
meter can be placed across resistor R3 in the Surge Arrester
network in the return leg of the secondary circuit. The resistor
R3 is typically 50 ohms or less. The entire precipitator sec-
ondary current passes through this resistance. The voltage
developed across R3 is proportional to the current. Some
222
-------
TO VOLTMETER FOR
SECONDARY VOLTAGE
PRECIPITATOR CONTROL
PANEL PRIMARY VOLTAGE
AND CURRENT CONTROL
TO VOLTMETER FOR
SECONDARY CURRENT
TRANSFORMER
S.A. = SURGE ARRESTOR
1. SECONDARY VOLTAGE = V-j I
R *
2. SECONDARY CURRENT
3540-124
Figure 137. Volta-ge divider network for measuring precipitator
secondary voltages and currents.
223
-------
manufacturers utilize a meter calibrated to read current based on
the detection of this voltage. Other manufacturers may place a
current meter with very low internal impedance across R3 and
allow all the precipitator current to pass through the meter.
In this case, the resistor R3 is in the circuit to prevent iso-,..,:
lating the power set if the meter is removed from the circuit.
Point number 2 in Figure 137 shows the .relation of these com-
ponents to the remainder of the system.
In order to calibrate the secondary current meter it must
first be determined whether the meter is a voltage or current
sensing device. If this cannot be determined from the precipita-
tor operation and maintenance manual, a test must be made. If it
is a voltage detecting type current meter, a volt meter placed
across the resistor will read within a few percent of the same
voltage whether the T/R set current meter is attached or not. If
the measured voltage is low with the T/R set meter in the circuit,
the T/R set meter is a current sensing device-. Calibrating a
voltage sensing meter requires accurately measuring the resistance
of the resistor, out of the circuit, and recording the voltages
for various currents. Then, Ohm's law is. applied to obtain the
true currents. Comparison of the true currents with -the meter
readings yields a calibration curve for the meter. If the power
set has a current sensing meter, a calibrated current meter of
appropriate capacity is inserted in series with the meter to be
calibrated. Measurement of various currents with the two meters
and comparison of the readings yield a calibration curve for the
uncalibrated meter.
Figure 138 is a facsimile of a data sheet used to collect
data from which voltage-current relationships may be plotted. In
the general heading, information is recorded which will identify
the test, the power supply (T/R Set), the plate area fed by the
power set, and the determined calibration factors for the voltage
and current. Data is taken as the manual set control is gradually
increased until some current flow is detected. This is recorded
as the corona starting voltage. Subsequent points are taken by
increasing the control for some increment of current and recording
the meter readings at that point. Readings are taken until some
limiting factor is reached. This factor is recorded on the right-
hand side of the data sheet and is usually excessive sparking or
a current or voltage limitation of the power set.
The columns as shown in Figure 138 usually completed for each
point include those labeled PRIMARY VOLTS, PRIMARY AMPS, DCKV T/R
SET METER, DCMA T/R SET METER, SPARK RATE, and DC VOLTS VOLTAGE
DIV. At a later time the DCMA correction factor is applied to the
T/R set meter reading and the DCMA CORR. column is completed.*
*0n a dual half-wave installation where the voltage is'measured on
one independent HV bus but the current is the sum of both sections,
the secondary current must also be multiplied by the ratio of the
plate area of the section under test to the total plate area in
order to approximate the secondary current in that power supply leg-
224
-------
DATE/TIME
POWER SET
VOLTAGE^CURRENT CURVE DATA SHEET
T/RSETNO. COLLECTING AREA
NJ
ro
Ln
PRIMARY
VOLTS
PRIMARY
AMPS
DCKV
T/R SET
METER
DCMA
T/R SET
METER
VC
T/R SET
SPARK
RATE
)LTAGE
DCMA (
DCMA
CORR.
DIV. MUL1
:ORRECTI<
DC VOLTS
VOLTAGE
DIV.
ON
DCKV
CORR,
/jA/
|2
NA/
cm'
TERMINAL POINT
DETERMINED BY:
(CIRCLE ONE)
1. SPARKING
2. SEC. CURRENT LIMIT
3. SEC. VOLTAGE LIMIT
4. OTHER
COMMENTS:
3640-126
Figure 138. Sample V-I curve data sheet.
-------
The DCKV CORK, column is completed by multiplying the DC VOLTS
VOLTAGE DIV. column by the voltage divider multiplier. The last
two columns are completed by dividing the DCMA CORK, by the ap-
propriate collecting area in square feet or square centimeters and
applying a multiplicative factor of 10"3. A plot is then made on
linear graph paper of the DCKV CORK, vs yA/ft^ or nA/cm2 depending
on the experimental requirement.
A typical voltage-current curve is shown in Figure 139.lk2
Voltage is plotted linearly along the horizontal axis and current
density linearly along the vertical axis. Current density at the
collection plate is used rather than total current supplied to
give a basis for comparison. This curve was obtained with 2.67
mm diameter wires in a laboratory scale precipitator.
Effect Of Electrode Geometry
Geometrical factors which affect the electrical character-
istics of a wire-plate precipitator include the plate-to-plate
spacing, wire-to-wire spacing, wire radius, plate area per power
set, and roughness of the wire. Each of these factors contributes
its own distinctive effect on the electrical characteristics.
The plate-to-plate and wire-to-wire spacings affect the
spatial distribution of the current density, electric field, and
space charge density. For the same applied voltage, wire radius,
and wire-to-wire spacing, the effect of increasing the plate-to-
plate spacing is one of distributing the ionic current, origi-
nating from the region near the wire, and the potential difference
over increasing surface areas. This leads to lower and less rapidly
varying values of current density, electric field intensity, and
space charge density in the region outside the corona sheath. For
the same applied voltage, wire radius, and plate-to-plate spacing,
the effect of decreasing the wire-to-wire spacing is to increase
the uniformity of the current density and electric field distri-
butions. It should be noted, however, that there is an optimum
wire-to-wire spacing which will yield a maximum current, and re-
duction of the wire-to-wire spacing below this value will lead
to reduced currents due to an increased interaction of the elec-
tric fields near the wires.
Increasing the radius of the corona wire leads to higher
corona starting voltages and lower electric field intensities at
the surface of the wire at corona onset. For a given applied
voltage, above the corona starting voltage, the Qorona current
will decrease as the wire radius is increased. For the same
average current density at the plate, the space charge density
near the wire decreases as the corona wire radius is increased.
The average current density at the plate is maintained because of
the_higher applied voltages which are necessary to produce ioni-
zation as the corona wire radius is increased. The higher applied
voltages result in higher values of electric field intensity
226
-------
^2
M 6
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LJ
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7 I ' I ' I
PLATE SPACING o 127 m
WIRE SPACING - 0.127 m
MOBILITY -- 2 x 10 4 m2/volt-suc
I
I
1
28 30 32 34
APPLIED VOLTAGE, kV
36
3540-126
Figure 139. Typical voltage-current curve derived experimentally
in a.laboratory wire-duct precipitator. After
McDonald.1"2
227
-------
outside the region of ionization and, consequently, faster migra-
tion of the ions towards the plate.
Figures 140 through 145 show theoretically calculated trends
caused by changes in-wire radius, plate-to-plate spacing, and
wire-to-wire spacing.k The symbols rw, Sx, Sy, and b in the
figures represent the wire radius, one-half the plate-to-plate
spacing, one-half the wire-to*-wire spacing, and the charge carrier
mobility, respectively. The curves in all of these figures were
obtained by taking the values of the relative gas density (6)
and the roughness factor (f) of the corona wires to be unity.
Figures 140, 141, and 142 demonstrate the effects of wire
size, plate-to-plate spacing, and wire-to-wire spacing on voltage-
current characteristics. Figure 140 shows that an increase in
wire size leads to a higher starting voltage and lower currents
for the same applied voltages. An increase in wire size shifts
the voltage-current curve to the right but does not substantially
alter the shape of the curve. Figure 141 demonstrates that in-
creasing the plate-to-plate spacing has only a slight effect on
raising the starting voltage but leads to a large drop in current
for the same applied voltage at voltages above corona start. An
increase in plate-to-plate spacing rotates the voltage-current
curve to the right (produces a decrease in the slope of the curve).
Figure 142 shows that the wire-to-wire spacing has little effect
on voltage-current characteristics over a wide range of values.
Increasing the wire-to-wire spacing generally shifts the voltage-
current curve to the left although the curves for different wire-
to-wire spacings may intersect one another.
Figures 143, 144, and 145 illustrate how the average electric
field at the plate Ep and the average electric field between the
electrodes Ea vary as a function of the average current density
at the plate for different wire sizes, plate-to-plate spacings,
and wire-to-wire spacings. Figure 143 shows that for the same
average current density at the plate the average electric field
at the plate increases slowly with increasing wire size. Figure
144 demonstrates that for the same average current density at the
plate the average electric field at the plate increases rapidly
with increasing plate-to-plate spacing. Figure 145 indicates
that the wire-to-wire spacing has only a small effect on the
average electric field at the plate for any given average current
density at the plate.
In most practical applications, the geometries will differ
to some extent from a true wire-plate design. For example, dis-
charge electrodes may have a design other than round wire, dis-
charge electrodes may be supported in a rigid frame, and the
collection electrodes may contain protrusions such as baffles
and flanges. However, the general trends discussed above for
wire-plate geometries will be evidenced in the geometries uti-
lized commercially-
228
-------
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NE
0.
a
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• a = 1.27;
Ba= 1.27 x 1(T3m
Aa=2.54x 10'3m
wa= 5.08 x 10"3m
I I I
b= 1.8x 10-4 m2/volt-sec
Sx = 0.1143m
5.. = 0.1143m
I
10 20 30 40 50 60
APPLIED VOLTAGE. KV
70
80
3540-127
Figure 14 (K
Theoretical curves showing the effect of wire
size, on .voltage-current characteristics.
229
-------
CM
C
2
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10
Sx = 0.0508 m
Sx = 0.1016 m
Sx = 0.1524 m
Sx = 0.2032 m
Sx = 0-2540 m
Sy
•w
0.1143 m
1.27 x 10'3
m
b * 2.2 x 10'4 m2/volt-$ec
20
30 40 50
APPLIED VOLTAGE, kV
60
70
3640-128
Figure 141.
Theoretical curves showing the effect of plate-
to-plate spacing on voltage-current characteristics.
230
-------
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LU
vs
LU
0
LU
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-------
5 5
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• rw = 1.27 x ID'4 m
• rw = 1.27 x TO'3 m
2.54 X 10^3 m
rw = 5.08 x 10'3 m
A r
w
! 1 1
b = 2.2 x 10'4 m2/volt-sec
Sx = 0.1143 m
SY = 0.1143 m
0 1 2 3 4 5 v 6
AVERAGE CURRENT DENSITY AT PLATE, TO"4 A/m2
3540-180
Figure 143. Theoretical curves showing the effect of wire size
on the electric field and current density.
232
-------
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A Sx =" 0.1524 m
Sx = 0.2032 P-.
0.2540 m
2 3 4 5 6
AVERAGE CURRENT DENSITY AT PLATE, 10'4 A/m2 3540-131
Figure 144.
Theoretical curves showing the ef feet of
plate spacing on the electric field and current
density.
233
-------
in
o
Q
_J
LU
H
O
cc
o
UJ
u
4 —.
1 1
Q SY - 0.0490 m
B SY = 0.1029 m
""" ^ SY - 0.1524 m
V SY = 0.2000 m
• SY = 0.2515 m
- — Ep
— — — E0
1 1 1
Sx = 0.1143 m
rw = 1.27 x TO'3 m
b = 2.2 x TO^/voh-sec "~
_^-*^T
^ — «*^ J
^ '^^^ J
—» -<-** * *"*>*«
12345
AVERAGE CURRENT DENSITY AT PLATE, 10'4 AVm2
8540-122
Figure 145.
Theoretical curves showing the effect of wire-to-
wire spacing on the electric field and current
density.,
234
-------
Figures 146 and 147 show secondary voltage-current charac-
teristics obtained from the inlet and outlet sections of several
cold-side full-scale precipitators having different electrode
geometries. Although the precipitators were treating different
types of fly ash under differing conditions of inlet mass loading
and particle size distribution, temperature, ash resistivity, gas
velocity, etc., the effects of geometry are still evidenced in
the voltage-current curves. Larger plate-to-plate spacings
tend to rotate the voltage-current curve to the right and tend
to lead to higher applied voltages for a given current density.
Larger effective discharge electrode diameters tend to shift the
entire voltage-current curve to the right. In practice, these
effects may be obscured to some extent by the surface properties
of the discharge electrodes and the presence of particles on the
discharge and collection electrodes. These effects will be dis-
cussed later.
The collection plate area per power set is another geometrical
factor of importance in determining the electrical characteristics
of a precipitator because it affects the sparkover voltage. The
optimum spark rate for n wires will be the same as for one wire
since a spark in any of the n wires causes the voltage to collapse
momentarily on all wires. Therefore, the optimum operating voltage
for n wires will be lower than for one wire. If the optimum
operating voltage at the optimum spark rate for one corona wire
is Vi (kV), then the optimum operating voltage Vn (kV) at the,same
optimum spark rate for n identical corona wires is1"*3
Vn = Vi - i loge n , (20)
where b is an empirical constant with a value on the order of one.
Equation (20) can be related to plate area by substituting the
quantity (total plate area)/(plate area per corona wire) for n.
The relationship of the optimum operating voltage to the number of
corona wires is shown in Figure 148 for Vi = 50 kV and various
values of b. In practice, once the plate height and wire-to-wire
spacing are established, the plate area per corona wire becomes
fixed. Thus, the number of wires per power set is determined by
the plate area per power set. For best precipitator performance,
the plate area serviced by a single power set should be made small
enough to avoid a large reduction in the optimum operating voltage.
This normally leads to a precipitator design with a high degree of
electrical sectionalization. A high degree of electrical section-
alization is also beneficial for two other reasons: (1) the outage
of electrical sections produces less degradation in precipitator
performance and (2) particle reentrainment due to sparking and
rapping is less severe.
The roughness (or surface condition) of the corona wires is
another geometrical factor which influences the electrical charac-
teristics of a precipitator. A roughness factor f is used to
235
-------
900
800 —
700
600
< 500
E
H
Z
LU
cc
u
400
300
200
100
• 11 INCH PLATE SPACING SQUARE
TWISTED DISCHARGE ELECTRODES,
PLANT NO. 2
A 12 INCH PLATE SPACING, PLANT NO. 1
MOST DISCHARGE ELECTRODES WITH
.16 IN DIA. SQUARE TWISTED WIRES
JB 10 INCH PLATE SPACING, RIGID
"BARBED" DISCHARGE ELECTRODES,
PLANT NO. 3
T 9-75 INCH PLATE SPACING, SPIRAL
DISCHARGE ELECTRODES, PLANT NO. 4
O 9 INCH PLATE SPACING, ROUND WIRE
DISCHARGE ELECTRODES, PLANT NO. 6
15
20
25
30 35
VOLTAGE, kV
40
45
50
55
3640-183
Figure 146.
Secondary voltage-current curves obtained from the
inlet sections of several cold-side full-scale
precipitators having different electrode geometries.
236
-------
1200 —
1100 —
1000 —
11 INCH PLATE SPACING, SQUARE
TWISTED DISCHARGE ELECTRODES,
PLANT NO. 2
12 INCH PLATE SPACING,
PLANT NO. 1
10 INCH PLATE SPACING, RIGID
"BARBED" DISCHARGE ELECTRODES,
PLANT NO. 3
9.75 INCH PLATE SPACING, SPIRAL
DISCHARGE ELECTRODES, PLANT NO. 4
O 9 INCH PLATE SPACING. ROUND WIRE
DISCHARGE ELECTRODES, PLANT NO. 6
100 —
10
15
20
30 35 40
VOLTAGE, kV
Figure 147.
Secondary voltage-current curves obtained from the
outlet sections of several cold-side full-scale
precipitators having different electrode geometries,
237
-------
10 100
NUMBER OF CORONA WIRES, n
1000
3640-185
Figure 148. Sparking voltage as a function of number of
corona wires.
238
-------
designate the degree of roughness of round corona wires. The
roughness of the wires affects the electrical characteristics
by influencing the corona starting voltage, the electric field
intensity at the surface of the wires at corona onset, and the
space charge densities near the wires. Values of the roughness
factor normally lie in the range 0.5-1.0,l"" and a 0.1 change
in value will result in considerably different electrical charac-
teristics.
For clean, smooth wires used in laboratory experiments in
air, the roughness factor can be taken as unity with good re-
sults. l" **' ' " if the surface of a wire is specked with dirt,
rough, or scratched, the roughness factor will be less than unity
and difficult to determine quantitatively. These types of imper-
fection on the surface of the wire give rise to local regions
which have a smaller radius of curvature than the wire. Higher
electric field intensities will exist where these imperfections
are located arid corona discharge will occur at reduced voltages
at these locations before spreading to the entire surface of the
wire at higher voltages. This results in a nonuniform current
along the length of the wire. The effect of these imperfections
is to decrease the corona starting voltage, electric field in-
tensity at the surface of the wire at corona onset, and, for
any given applied voltage, to increase the space charge density
near the wire and the average current density at the plate. In
the practical observation of the effect of wire roughness, the
voltage-current characteristic will shift to the left with de-
creasing values of roughness factor in a manner which is similar
to decreasing the wire radius.
In industrial applications, the wires can accumulate ash
to the extent that they are completely covered. In these cases,
there is an effect of increasing the wire radius which is dif-
ferent from accounting for the imperfections on the surface of a
wire. Thus, a new radius for the discharge electrode is estab-
lished and imperfections will exist on the surface defined by
this radius.
Since the roughness factor depends on the number, type, ex-
tent, and radii of the imperfections on the surface of a wire,
the possibility of a non-empirical determination of this para-
meter is auite remote. This means that representative values
of the roughness factor must be determined empirically by making
measurements of voltage-current curves and using the roughness
factor as an adjustable parameter in the existing theories in
order to fit the experimental data.
Effect Due To Gas Properties
The voltage-current characteristics of a precipitator are
affected significantly by the temperature, pressure, and compo-
sition of the gaseous conduction medium. The temperature and
239
-------
pressure of the gaseous conduction medium influence the corona
starting voltage, the electric field intensity at the surface of
the discharge electrode at corona onset, the space charge density
near the discharge electrode, and the effective mobility of the
molecular ions. Certain effects due;. to temperature and pressure
can be analyzed through changes in the gas density (6) :
where
60 = gas density at T0 and pe (kg/m3),
TO = standard temperature (273°K) ,
T = actual temperature of the gas (°K),
Po = standard atmospheric pressure (760 mm Hg) , and
p = actual pressure of the gas (mm Hg) .
The parameter 6 decreases with increasing temperature and
decreasing pressure. As 6 decreases, the corona starting voltage,
the electric field intensity at the surface of the discharge
electrode at the corona onset, and the sparkover voltage all de-
crease. These effects can be explained by examining the influence
of 6 on the space charge density near the discharge electrode. As
6 decreases, the effective mobility of the ions increases due to
a reduced number of collisions with neutral molecules. For a
given applied voltage, this leads to a decrease in space charge
density near the discharge electrode and an increase in the aver-
age current density at the collection electrode. The decrease
in space charge density near the discharge electrode results in
the attainment of a given discharge current at a lower value
of electric field intensity at the surface of the discharge elec-
trode. Thus, in order to maintain a given average current density
at the plate as 6 decreases, the applied voltage must be lowered
so that the lower electric field intensities which result will
move the ions away from the region near the discharge electrode
at a slower rate.
Figures 149, 150, and 151 contain experimental data showing
the effects of temperature and pressure on voltage-current charac-
teristics and sparkover voltage.11*6 These data were obtained in
wire-cylinder geometries for negative corona in air. In practice,
if the temperature is increased or the pressure is decreased,
the voltage-current curve will shift to the left and will acquire
steeper slopes. The shift is due to the decrease in corona
starting voltage, and the steeper slopes are due to an increase
in the effective ion mobility. The data in these figures also
demonstrate how the sparkover voltage decreases as 6 decreases.
240
-------
20 40 60 80 100 120
APPLIED VOLTAGE, kV 3540-ue
Figure 149. Effect of air pressure on sparkover voltage.and
voltage-current characteristics . ' **5
241
-------
120
TOO
80
C
Ui
O
C-
co
60
40
20
10 15 20 25
AIR PRESSURE, psia 3640-is:
Figure 150. Effect of air pressure on sparkover voltage.1
242
-------
12
z
Hi
cc
cc
o
<
o
cc
o
o
10
E 8
200°F
(93.
3.3°C)/
SPARK
350° F
(176.700,
20 40 60 80 100
APPLIED VOLTAGE, kV 3540-m
Figure 151..
Effect.of temperature on>sparkover voltage and
voltage-current characteristics.J"6
243
-------
Figures 152 and 153 show voltage-current curves obtained
from outlet electrical fields in several full-scale, cold-Side. .
and hot-side precipitators. These curves approximate those
that would be obtained, for a particle-free gas.,. The.-curves show
the range of voltages that can be-ahticipated.. for .the essentially
clean flue gases at cold and hot-side temperatures. The lower
voltages and smaller voltage range associated with high temper-
ature operation should be noted. . -
The composition,.of the gas can have a significant effect on
the voltage-current characteristics and sparkover voltage which
are obtained in a precipitator. For negative corona discharge,..
the concentrations of the various molecular constituents and the
electron affinities of these constituents are of importance.
Different gas compositions will result in different effective
charge carrier mobilities in a corona discharge. In general, the
current is carried by both molecular ions and free electrons.
The extent of the free electron contribution depends on the elec-
tron-trapping capabilities of the molecular constituents, the
temperature and pressure of the ga's, the spacing of the collec-
tion electrodes, and the applied voltage. In industrial appli-
cation of precipitators to treat gas streams emanating from the
combustion of coal, the contribution of free electrons to the
total current is normally not considered to be significant.
The flue gas resulting from the combustion of coal and
entering a precipitator contains the electron-trapping gases 02,
C02, HoO, S02, SOa, and NOjj in approximate concentrations of
2.0-8.0%, 11.0-16.0%, 5.0-14.0%, 150-3000 ppm, 0.0-30.0 ppm, and•>
200-800 ppm, respectively. The order of importance of the con-
stituent gases with respect to electron-trapping capabilities is
S02, 02, H20, and C02. Minimum amounts of these gases required
to produce a significant effect on the electrical conditions are:
S02, 0.5-1.0%; 02, 2.0-3.0%; and H20, about 5.0%. The effect of
CO2 can normally be ignored due to the presence of the other
electron-trap gases. The experimental data11*7 in Figures 154,
155, and 156 demonstrate the influence of gas composition on the
voltage-current characteristics and sparkover voltages.
The effective mobility of the ionic charge carriers in the
corona discharge is the most important parameter in determining
the electrical conditions which can be established in the gas.
This parameter depends on the composition of the gas, the rela-
tive concentrations of the gaseous components, and the temperature
and pressure of the gas. Since the effective ionvmobility (K) is
a function of temperature and pressure, measured values of this
parameter are usually reported in terms of the reduced effective
ion mobility (K0):
KO = K TlTn * m '-L. 0-70 I (22)
244
-------
1200 -
1100-
I I I
11 INCH (27.9 cm) PLATE SPACING
SQUARE TWISTED DISCHARGE
ELECTRODES, PLANT NO. 2
A 12 INCH (30.5 cm) PLATE SPACING,
m PLANT NO. 1
10 INCH (25,4 cm) PLATE SPACING,
RIGID "BARBED" DISCHARGE
ELECTRODES, PLANT NO. 3
9.75 INCH (24.8 cm) PLATE SPACING
SPIRAL DISCHARGE ELECTRODES.
PLANT NO. 4
9 INCH (22.9 cm) PLATE SPACING,
O ROUND WIRE DISCHARGE
ELECTRODES. PLANT NO. 6
TOO —
It) 15
Figure 152.
30 35
VOLTAGE, kV
Voltage-current curves obtained from outlet
electrical fields in several cold-side electro-
static precipitators.
245
-------
A 22.86 CM (9 IN.) PLATE SPACING,
9-IN."DISCHARGE WIRE SPACING,
0,277 CM (0.109 IN.) IN DIAMETER
• 22.86 (9 IN.) PLATE SPACING
DISCHARGE WIRES 0.268 CM (0.106 IN.)
IN DIAMETER
• 22.86 CM (9 IN.) PLATE SPACING,
DISCHARGE WIRES 0,277 CM (0.109 IN.)
IN DIAMETER
Figure 153.
VOLTAGE, kV
8S 4 0 -1 * 0
Voltage-current curves obtained from outlet
electrical fields in several hot-side electro-
static precipitators.
246
-------
a
2
HI
tr
a:
D
CJ
o
tr
o
o
40 80
APPLIED VOLTAGE, kV
120
3540-141
Figure 154. Influence of gas composition on the voltage-
current characteristics.11*7
247
-------
10
I SPARK AT 37 kV, 16 ma
I
40 60 80
APPLIED VOLTAGE, kV
100
120
3540-142
Figure 155. Influence of gas composition on the voltage-
current characteristics and sparkover voltages.
it?
248
-------
12
10
a
E
H-"
2
LLJ
cc
cc
O
CC
O
u
SPARK
100% AIR
100% H2O
40% H2O
I
10 20 30 40 50
APPLIED VOLTAGE, kV 3540-143
gure 156. Influence of gas composition on the voltage-
current characteristics and sparkover voltages.
'.49
-------
where p (Torr) and T (°C) are the pressure and temperature at
which the measurement was made.
Laboratoryl"8' J **9' 15 ° and in... situ *51 techniques have been
developed for measuring effective .ion mobilities.. The laboratory
techniques involve either the measurement of the time of flight
of the ionsltte or the measurement of the voltages-current charac-
teristics of a corona discharge in, the gas.150. An in situ tech-
nique which has been utilized involves the measurement of the
voltage-current characteristics of a corona discharge in the gas.1S1
Figure 157-a shows a schematic diagram of a mobility tube .,
which has been utilized to make time of flight measurements of ion
mobilities. llt8 Electrons are released from a photocathode by a
pulse of. ultraviolet light. These electrons drift toward the
collector (anode) under the influence of a uniform electric field.
The electrons attach to neutral molecules close 'to the cathode.
The negative ions then drift toward the collector. The grids are
normally transparent so that if a .voltage pul.se::is. applied to the
grids some of the ions or electrons in the vicinity of the grid
are absorbed and the average collector current is decreased. By
varying the delay time of the grid voltage pulse with respect to
the light pulse, a waveform of the ion current as a function of
delay time is obtained. A typical ion-current waveform is shown
in Figure 157-b. An ion-current waveform is obtained for each
grid so that the drift velocity can be obtained from the difference
of ion transit times. Then, the ratio of the drift velocity to
the electric field strength yields the ion mobility.
Figure 158-a shows a schematic diagram of a laboratory
apparatus which has-been utilized to determine effective ion
mobilities from the measurement of the voltage-current charac-
teristics of a corona discharge in the gas. A simulated flue
gas composition flows through a wire-cylinder corona discharge
system and is maintained at the desired temperature. In this
technique, a voltage-current curve is measured for corona dis-
charge in the particular gas. The measured voltage-current curve
is fit to an analytical expression relating voltage and current
for wire-cylinder geometry using the effective ion mobility as an
adjustable parameter. Figure 158-b shows typical voltage-current
data along with the theoretical fits.
Figure 159 shows a schematic diagram of an "ion mobility
probe" which has been utilized to make in situ measurements of
effective ion mobilities.151 The probe, which is- made of stain-
less steel, can be inserted through a standard 10.16 cm (4 in.)
test port into a flue gas environment at temperatures up to 400°C.
The flue gas is filtered and pulled through a wire-cylinder corona
discharge system. A voltage-current curve is measured for corona
discharge in the flue gas. The data obtained are analyzed in
the same manner as the laboratory technique discussed previously.
The in situ technique has the advantage of utilizing the true
250
-------
U V
"
e
ion
o —=
e
CATHODE
<\
°
<
L/0
'' \
GRID 1
I
ANODE
GRID 2
TO PULSE CIRCUITRY 3540-144
Figure 157-a. Schematic diagram of mobility tube. l "
z
LU
IT
CC
O
tr
O
u
o
u
111
u>
u
CC
o
111
Q
10
12
14
16x1 (T12
I
GRID 1
24.6 m
sec
GRID 2
t2 = 50.0 msec
10
20
30
40
50
60
• Figure 157-b.
DELAY TIME. msec sato-us
Ion-current waveform obtained for E/N = 3.1 x 10~18
V-cm2, N = 8.0 x 1018 cm"3, and T = 300°K. The
waveform obtained at the second is smaller in peak
height and broader than that obtained at the first
grid because of diffusion effects. The loss of ions
to the grids under these conditions was negligible.11*
251
-------
PLOW METERS
N2, CO2, O2 S02
STEAM
MIXING CHAMBER
to
Ln
to
GAS SAMPLE
L
i
i
-L
i
_*._
J^
I
i
-* —
i
^ HEAI tM
0-50 kV, NEC
I
'*• — POROUS BAFFLE 1
I* --GUARD RING 1
VOLTMETER (/
— CORONA WIRE 1
DIA. 0.16cm J.
HEATER
x~vPICOAMMET
I
'*- GUARD RING
0.164 M
3640-U6
Figure 158-a.
Cylindrical corona
discharge system for
determining effective
mobility.lSo
UJ
oc
cc
D
O
ui
O
oc
<
X
O
Q 1.0 f—
18 24 30 36 42 48
DISCHARGE VOLTAGE. kV
BI40-H7
Figure 158-b.
Negative corona voltage-
current characteristics for
simulated flue gas with H2O
volume concentration of (1)
0.6%, (2) 8.4%, and (3) 17.8%
Solid line theory, circles
data.150
-------
d
CD
M
Ln
K)
U1
U)
in
a
tr
CD
0)
rt
H-
o
H-
o
Hi
THERMOCOUPLE LEAD H V CABLE
H V LEAD \ CURRENT LEAD
PROBE
PRESSURE
GAUGE
CURRENT WIRE
DISCHARGE COLLECTION THIMBLE
ELECTRODE ELECTRODE HOLDER
WITH
NOZZLE
INSULATING
TUBING (ALUMINA!
PRESSURE
TAP (TO PUMP)
RETAINER
RING
ORING SPRING CONTRA
VACUUM LOADED HELICALLY
SEAL H V WOUND SPRING
CONNECTION
PERFORATED
DISC CORONA
WIRE SUPPORT
CERAMIC GLASS WEBBED
INSULATING DISC CORONA
RINGS W!RE
SUPPORT
H-
O
8
tr
H-
i—
H-
ft
R - COLLECTION ELECTRODE CYLINDER RADIUS = 4.32 cm
L - EFFECTIVE DISCHAGE ELECTRODE LENGTH = 22.86 cm
D - DISCHARGE ELECTRODE DIAMETER = 88.9 mm
A B - TOTAL PROBE LENGTH = 1.22 m
3640-148
10
M
O
cr
(D
-------
flue gas composition in a particular application.
Table 10 gives some measured values of effective ion mobility
for various gas compositions. Several of the values are for gas
compositions which are very similar to those obtained from the
combustion of coal. Figures 160 and 161 contain theoretical pro-
jections showing the effect of effective ion mobility on the
voltage-current and electric field current density relationships
in a wire-plate geometry." Figure 162 shows theoretically pre-
dicted collection efficiency versus reduced effective ion mobility
curves for several particle sizes contained in a typical inlet
particle size distribution found in the combustion of coal and
for a mass loading* of 9.16 x 10~3 kg/m3 (4.0 grains/acf). These
curves indicate that the effective ion mobility can have a signifi-
cant effect on particle collection efficiencies. For example, a
reduced effective ion mobility of 2.2 x 10"1* m2/vs leads to a
collection efficiency of 81.8% for a 0.55 urn particle, whereas
a value of 3.5 x 10~% m2/vs yields 77.8%. 138
Effects Due To Particles
Particles affect the voltage-current characteristics due to
their presence in the gas stream and due to their accumulation on
the discharge and collection electrodes. An analysis of measured
secondary voltage-current characteristics is essential for de-
termining how the operating electrical conditions are affecting
precipitator performance. A correct analysis of measured secondary
voltage-current characteristics depends on an understanding of the
possible effects due to particles. In many cases, the analysis
of voltage-current characteristics is complicated due to competing
effects caused by the particles.
The particles in the gas stream become charged due to col-
lisions with the ions created in the corona discharge. The
charged particles are much less mobile than the ions and move
relatively slowly toward the collection electrode. A particulate
charge distribution (particulate space charge) which has an elec-
tric field associated with it is established in the interelectrode
space. At points near the surface of the discharge electrode, the
electric field due to the charged particles is opposite in direc-
tion to the electric field produced by the surface charge on the
discharge electrode. This effect reduces the electric field
strength which is effective in the ionization process near the
discharge electrode. Thus, for a given applied voltage, the rate
of ion production or current will be reduced due to the particles.
The lowering in current for a given applied voltage due to the
presence of particles in the gas stream is referred to as the
"particulate space charge effect".
In practice, the particulate space charge effect can be
detected by examining the voltage-current curves from successive
electrical sections in the direction of gas flow. In progressing
254
-------
TABLE 10. REDUCED EFFECTIVE NEGATIVE ION MOBILITIES
FOR VARIOUS GAS.COMPOSITIONS
Reduced Effective
Gas Composition r.jTl Mobility
(Volume Percent) (cm2/V-aec}
_ CO; 0_2_ S02 HJ 0
100.0 0.67 ^ 0.1.7a
100.0 2,46 + (;.oeft
100.0 1,08 + 0.0 3b
100.0 0.35C
(Laboratory
(Laboratory
79.
73.
65.
71.
75.
75.
78.
78.
77.
77.
4
5
9
0
7
1
5
3
9
6
14.
13.
12.
11.
11.
11.
10.
19.
10.
10.
7
6
2
2
6
5
9
8
3
7
4
4
3
3
3
3
O
—/
3
3
3
.6
.2
.8
.7
.2
.2
.6
.6
. 6
.7
Air)
Air)
0.
0.
0.
0.
0.
0.
0.
0.
0.
0-
2
•^
2
0
0
1
0
T_
3
7
0.
8 .
17
14
9.
9.
7.
7.
7-
7 .
6
4
,8
.0
4
9
0
0
0
0
5.39^
2.93f
2.35f
3.021
2.74f
3.35f
2.67f
2.70f
2.43f
a. J. J. Lowke and J. A. Rees, Ai-j-Lralian J. Phys. I_6_, 447 (1963),
b. E. W. McDaniel and H. R. Crdno, Pev. Sci. Instru. 2_8_, 684 U959).
c. E. W. McDaniel and M. R. C- McDowell, Phys. Rev. 114, 1028 (1959)
d. B.Y.H. Liu, K. T. Whitby, and H.H.S. Yu, J. Appl. Phys. 38,
1592 (1967).
e. J. Bricard, M. Cabane, G. Modelaine, and D. Vigla, Aerosols
and Atmospheric Chemistry. Edited by G. M. Hidy, New York,
New York, 27 (1972) .
f. H. W. Spencer, III, "Experimental Determination of the Effective
Ion Mobility of Simulated Flue Gas." In Proceedings of 1975
IEEE-LAS Conference, September 28, 1975, Atlanta, Georgia.
255
-------
CM
.E
o
r"
UJ
< 5
_J
6.
h-
>
— £.
tfl
UJ
Q
Z
LU
K ,
C 3
3
111
O
cn •
g 2
—I ' [
f> b = 1.0 x 10"4 m2/volt-sec
« b = 1.4
& b= 1.8
V b = 2.2
« b = 2.5
+> b = 3.0
O b = 3.4
D b = 3.8
rw « 1.27 x ID'3 m
20
SY
0.1143 m
0.1143 m
30
APPLIED VOLTAGE, kV
40
3640-149
Figure 160
Theoretical curves showing the effect of effective
mobility on voltage-current characteristics.1*
256
-------
h = 1.0 x 10"4 m^/volt-sec
• b= 1.4
A b- 1 8
b - 2.2
Sx = 0.1143 m
Sy = 0.1143 m
1 2345
AVERAGE CURRENT DENSITY AT PLATE, 10'4 A/m2
Figure-161.
Theoretical curves...showing the effect of effective
mobility on the electric field and current density. "*
257
-------
99.98
99.95
99.9
99.8
O
LU
O
LT
u.
LU
99.5
O 99.0
H-
U
UJ
O
u
98.0
95.0
90.0
80.0
70.0
^ GRAIN LOADING " 9.16 x 10-3 kg/m3 ~
2 3
REDUCED EFFECTIVE ION MOBILITY m2/volt-$ec x 10-4
3640-161
Figure 162.
Collection efficiency as a function of reduced effective
ion mobility for several particle sizes.
258
-------
from the inlet to the outlet, the voltage-current curves will
shift to the left. This shift to the left is due to a reduction
in the particulate space charge effect as charged particles are
removed from the gas stream along the length of the precipitator.
Figure 163 shows voltage-current curves obtained from three
successive electrical fields in the direction of gas flow in a
full-scale, cold-side precipitator collecting fly ash particles.
This figure demonstrates the expected effect of particles on the
voltage-current curves. The shift of the curve to the left in
moving from the inlet to the outlet and the reduced voltages in
the outlet electrical field are of particular importance in
analyzing the effects of particles and in determining whether
or not the electrical fields are behaving properly. In certain
cases, the voltage-current curve for the second electrical field
may lie to the right of that for the first electrical field and
then the behavior of the following electrical fields is similar
to that shown in Figure 163. This is again due to particulate
space charge and depends on several factors including allowable
electrical conditions, gas velocity, and inlet mass loading and
particle size distribution. Thus, this behavior would not
necessarily indicate abnormal precipitator behavior. Also, for
high efficiency precipitators with six or more electrical fields
in the direction of gas flow, the voltage-current curves for the
electrical fields near the outlet should approach one another.
Since the particulate space charge effect along the length
of a precipitator depends on particle charging and collection,
changes in the gas volume flow through a precipitator will result
in changes in the voltage-current characteristics. In precipi-
tators installed on coal-fired boilers, the gas volume flow can
vary due to changes in the power generation load. Figures 164
through 167 show the effect of gas volume flow on the voltage-
current characteristics as estimated by using a mathematical
model.152 The parameters used in the calculations are typical
of full-scale, cold-side precipitators. There are four, nine
foot long electrical sections in the direction of gas flow. The
electrode geometry consists of plate-to-plate and wire-to-wire
spacings of 22.86 cm and a wire radius of 0.138 cm. The inlet
particle size distribution (HMD = 25 pm, a = 2.8) is representa-
tive of fly ash particles. Although changes in load will also
result in changes in other parameters such as temperature,
resistivity, gas composition, etc. which have their own influ-
ences on the voltage-current characteristics, it has been assumed
that these parameters remain constant. Figures 164, 165, and
166 show the effect of particles in the different electrical
sections for high, medium, and low gas flow rates, respectively-
Figure 167 compares the voltage-current characteristics of the
first and last electrical sections at each gas flow rate.
The collection of particles on the discharge and collection
electrodes may influence the voltage-current characteristics in
259
-------
48.0
44.0
40.0
36.0
CM
O
| 32.0
ra
O
ID
= 28.0
H
i 24.0
O
H
Z
LU
cc 20.0
c:
o
16.0
12.0
8.0
4.0
0.0 C
I 1 1 1 1 l| 1 1
- D INLET ELECTRICAL FIELD O [5
A MIDDLE ELECTRICAL FIELD
O OUTLET ELECTRICAL FIELD
O & D
— —
0 D
0 * a
O
O D
O
^
0 D
^
° D
0 D
o A
O /\L
O A^J ""
^ fl^
^ !*Ql O«l 1 1 I ] \
) 8 16 24 32 4C
VOLTAGE, kV 3640-16
Figure 163.
Secondary voltage-current curves demonstrating the
particulate space charge effect in a full-scale, cold-
side precipitator collecting fly ash.
260
-------
CM
U
<
LU
I-
<
_I
a.
!-
<
>
1-
(/o
2
01
C
K
2
u;
EC
cc
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a
<
(X
111
80L- SCA = *'9'7 rn2/(m3/sec)
j INLET MASS LOADING 9.16x10-3
33
34
35 36 37
APPLIED VOLTAGE, kV
Figure 164.
Theoretical voltage-current curves for a specific
collection area of 19.7 m2/(m3/sec).:52
261
-------
SCA = 59.1 m2/(m3/sec
INLET MASS LOADING
33 34 35 36 37
APPLIED VOLTAGE, kV
38
39
40
3540-154
Figure 165.
Theoretical voltage-current curves for a specific
collection area of 59.1 m2/(m3/sec).152
262
-------
SCA = 98.4 m2/(m3/sec)
INLET MASS LOADING = 9.16 x 10'3 kg/m3
33 34 35 36 37 38 39 40
APPLIED VOLTAGE, kV 3540-155
Figure 166.
Theoretical voltage-current curves for a specific
collection area of 98.4 m2/(m3/sec).l52
263
-------
INLET MASS LOADING = 9.16 x ICT3 kg/m
33 34 35 36 37
APPLIED VOLTAGE, kV
38
39 40
3540-166
Figure 167- Comparison of theoretical voltage-current curves for
different specific collection areas.152
264
-------
several ways. The effect of particulate collection on the dis-
charge electrodes has been discussed earlier in terms of geome-
trical factors. Effects due to particulate collection on the
collection electrodes may result because of dielectric breakdown
of the collected layer, an effective reduction in the discharge-to-
collection electrode spacing, or a nonnegligible voltage drop
across the collected layer.
The most significant factor affecting the operation of a
precipitator collecting fly ash particles is the dielectric break-
down properties of the collected particulate layer. Precipitators
collecting particulate layers with resistivities greater than 10li
ohm-cm are limited to low voltages and currents due to dielectric
breakdown of the particulate layer. As discussed earlier, back
corona can exist well in advance of sparking conditions for col-
lected particulate layers with resistivities greater than 10ll
ohm-cm. A precipitator should be operated at voltages which do not
produce back corona or excessive sparking in order to avoid detri-
mental effects to precipitator performance. A detailed discussion
concerning the resistivity of collected fly ash will be given later.
The thickness of the collected particulate layer is manifested
in the voltage-current characteristics. There is a voltage drop
across the layer that is given by equation (3). This voltage drop
depends on the average current density in the layer and the re-
sistivity and thickness of the layer. This voltage drop is not
effective in producing current in the corona discharge. For low
resistivity (<1010 ohm-cm) fly ash and layers of larger thickness
(>1 cm), the effect of the layer might be to shift the voltage-
current curve to the left. This can result due to the combination
of a negligible voltage drop across the layer for current densi-
ties preceding sparkover and an effective reduction in discharge-
to-collection electrode spacing. However, normally, the combi-
nation of resistivity and thickness of the layer is such that the
effect of the voltage drop across the layer dominates the effect
on the voltage-current characteristic. In this case, the voltage-
current curve is shifted to the right due to the effect of the
layer. When a particulate layer is present, the additional
voltage which is necessary to produce a given clean collection
electrode current density is given approximately by equation (3).
Figure 168 contains experimental data showing the normal effect
that a fly ash layer on the collection electrode has on the
voltage-current characteristics.153 The condition illustrated
is for dc voltage-current curves with and without a one centi-
meter thick dust layer with a resistivity of 1 x 10 !1 ohm-centi-
meter on a typical second electrical field.
In analyzing voltage-current curves, it must be kept in mind
that the effect of the particulate layer on the collection elec-
trode is in addition to the particulate space charge effect in
the gas and the effect of particles collected on the discharge
electrodes. Thus, the various possible effects discussed in this
265
-------
70
60
50
OJ
e
o
CO
LJ
Q
Ul
cc
tr
40
30
20
10
0
10
SECOND
FIELD
CLEAN
ELECTRODE
SECOND FIELD
WITH I CM
LAYER
/* = I x!0"JlCM
20 30 40
APPLIED VOLTAGE,kilovoHs
50
60
S540-1E1
Figure 168.
Voltage vs. current characteristic for second field
clean electrode and 1 cm layer of 1 x 101: ohm-cm dust.
266
-------
section may compensate to some extent for one another and obscure
the individual effects. All possible effects and their different
combinations should be considered Ln order to obtain the best
possible explanation of measured voltage-current characteristics.
Effects Due To Chemical Conditioning Agents
The addition of certain chemical- conditioning agents into
the gas stream prior to treatment by a precipitator may result
in improved electrical operating conditions. It is also possible
that the use of certain chemical conditioning agents will result
in worse electrical operating conditions. Depending on the type
of chemical conditioning agent and the appropriate method of
utilization, the agent may be added to the gas stream in either
the vapor, liquid, or solid phase.
Chemical conditioning agents may affect the voltage-current
characteristics by (1) modifying the resistivity of the collected
particulate layer, (2) changing the composition of ionic charge
carriers in the gas, (3) introducing a space charge effect, or
(4) changing the adhesive and cohesive properties of the collected
material. Chemical conditioning agents have been used primarily
as a means of lowering the resistivity of the collected fly ash.
In principle, the added agents come into intimate contact with
the particles in the gas stream and/or in the collected layer
and produce a larger number of charge carriers or more mobile charge
carriers in the collected layer than in the unconditioned environ-
ment. The availability of a larger number of charge carriers or
more mobile charge carriers to transfer the current through the
layer results in a reduction in the electrical resistivity of the
layer. The possibilities also exist that the addition of certain
chemical conditioning agents will have no effect on the value of
the electrical resistivity or that the value will be increased as
a consequence of binding charge carriers which would have been
free to carry current in the unconditioned environment.
Figures 169 and 170 contain data from two different cold-side
industrial precipitators showing the effect on the voltage-current
characteristics of adding SO 3 in the vapor state to the ga-S stream
at a location prior to the precipitator.15"'155 In both cases,
the electrical conditions are significantly improved due to a
reduction in the resistivity of the collected ash layer resulting
from the injection of the S03. For the data in..-Figure . 169, the
addition of 25 ppm of S03 lowered the value of ash resistivity
from approximately 6 :< 1012 ohm-cm at 118°C (245°F) to 4 x 101 °
ohm-cm at 143°C (290"F). Although the conditioned data were
obtained two months later than the unconditioned data due to dif-
ficulties with the conditioning system, the data definitely show
the pronounced effect of S03 injection.
For the data in Figure 170, the addition of 8 ppm of SOs
'lowered the value of ash resistivity from approximately 6 x 10
267
i i
-------
1.4 r—
1.2
1.0
.6.
<
0.6
0.4
0.2
• V-l CHARACTERISTICS FOR INLET FIELD
(UNCONDITIONED)
4 V-l CHARACTERISTICS FOR OUTLET FIELD
(SO3) CONDITIONED)
AA
A
<
AA •
•
AA •
AA
I
15 20 25 30 35 40 45 50
kV
3640-158
169. Effect on the voltage-cur rent characteristics of adding
SO3 in the vapor state to the gas stream at a location
prior to the precipitator.
268
-------
20.4
17.0
13.6
10.2
6.8
3.4
WITHOUT SO.
WITH S03
10
20
30
VOLTAGE, kV
40
50
60
3540-159
figure 170. Effect on the voltage-current characteristics of adding
SO 3 in the vapor state to the gas stream at a location
prior to the precipitator.
269
-------
ohm-cm to 6 x 1010 ohm-cm at 165°C (330°F). At this installation,
the unconditioned and conditioned data were obtained within the
same week. The reduction in resistivity at this installation is
less dramatic than that at the other installation just discussed
due to the higher temperature of the gas. At the higher temper-
ature, the SO3 was not near the dew point. This results in less
surface adsorption on the particles than would occur at lower gas
temperatures. However, the pronounced effect of SO3 on ash re-
sistivity is still evidenced.
Normally, the SO 3 is injected in concentrations of 25 ppm
by volume or less. When SO3 is injected into the gas stream,
the precipitator will respond with rapid improvement in the
voltage-current characteristics. The voltage-current charac-
teristics will then continue to improve further until an equi-
librium condition is reached where the resistivity.no longer
changes.
Although not as general in application to fly ash as S03,
other chemical conditioning agents have been found to improve the
electrical conditions by reducing the resistivity of certain types
of fly ash.156'157'158 Studies are presently in progress that
may determine which chemical conditioning agents are effective
in reducing the resistivity of fly ashes of various composi-
tions. -159' *6 ° At the present, however, the use of conditioning
agents other than SOs is based on trial and error and past ex-
perience where different agents are tried until one is found that
produces the desired effect. There is evidence161'162'163 that
sodium compounds can be introduced into the gas stream in the
form of solid particles as a means of reducing fly ash resistivity.
Studies are now in progress to determine the feasibility of this
approach in full-scale, cold-side industrial precipitators.!55
The addition of conditioning agents may also have an effect
on the electrical properties of the gas. This could result in an
effect on the voltage-current characteristics that is separate
from the effect of the resistivity of the collected material.
The nature and extent of the effect of the conditioning agent on
the gas properties will depend on the type of agent, the concen-
tration, and the physical state of the agent. If the agent is
added to the gas stream in the vapor state, the molecules may
become ionized in the corona discharge. This would change the
composition of the ionic current carriers in the gas. If the
agent is added to the gas stream in the form of liquid or solid
particles, these particles will be charged by the .ions produced
in the corona discharge and will introduce a particulate space
charge effect.
Figure 171 shows voltage-current data obtained from a full-
scale, cold-side precipitator during S03 injection studies.16"
These data show that the injection of SO3 increased voltages and
currents and decreased the spark rate. The segments of the curves
270
-------
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H-
C
w n
H- c
CD ht
CD
T3 3
h{ ft
CD
O &.
H- (D
T3 3
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ft H-
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ft <
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C ft
ft 0>
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P-
ft DJ
tr
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cn c
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(Jj J_l
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3 O
3 Qi
^Q I
CM
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c
3
(j
35
30 -
25
20
15
10
\
WITH
\ INJECTION
\ (14 PPM OF SO3)
\
\
\
INLET
24 28 32
VOLTAGE, kV
36
35
30
25
20
15
10
\
\
WITH INJECTION
(14 PPM OF S03»
OUTLET
20 24 28 32
VOLTAGE, kV
36
36(0-160
-------
with positive slopes portray the data obtained with no sparking
or very light sparking. The segments of the curves with negative
slopes in regions of high current density represent the experi-
mental results with moderate to heavy sparking. The short hori-
zontal lines intersecting each curve indicate the average values
of current density observed with the power supplies under auto-
matic control. An interesting feature. of the data in Figure 171
is the indication that the injection of sulfur trioxide permitted
both higher current densities and higher voltages to be reached
without the occurrence of excessive sparking. Shifts in the
voltage curves to the right along the voltage axis at least sug-
gest the possibility of a space-charge effect resulting from the
introduction of less mobile charge carriers in the gas stream.
One possibility is that the added concentration of sulfur trioxide
assumed most of the ionic space charge and the new ions thus intro-
duced carried current with a lower mobility than the normally
occurring ions produced from oxygen, water vapor, and sulfur
dioxide. An alternative possibility is that part of the added
sulfur trioxide was condensed as a fine mist of sulfuric acid and
then, electrically charged, caused a very pronounced shift in
charge carriers from gaseous ions to relatively immobile acid
particles.
Figures 172 and 173 show voltage-current data obtained from
a full-scale, cold-side precipitator during NHs injection studies
with low and high sulfur coals. 161* Figure 174 shows data from a
different precipitator indicating the almost instantaneous re-
sponse of the electrical conditions to the injection of NHa.161*
Here, much higher voltages could be achieved for the same current
density- This type of response normally does not occur in those
cases when the conditioning agent primarily affects the ash layer.
Figure 175 shows voltage-current data obtained from the precipi-
tator.16" In these studies, the significant shift to the right
of the voltage-current characteristics was attributed to a" parti-
culate space charge effect caused by ammonium sulfate particles
formed due to the chemical reaction of SO-3 and
The addition of conditioning agents can also affect the
adhesive and cohesive properties of the collected fly ash. Ad-
hesive forces refer to those between the ash layer and the col-
lection electrode while cohesive forces refer to those between
the particles in the ash layer. Certain types of conditioning
agents may interact with certain types of fly ash to form a col-
lected layer which is more favorable for precipitator operation
due to modification of the adhesive or cohesive .properties of the
ash. In order to avoid excessive particle reentrainment, it is
desirable that the collected layer adhere favorably to the col-
lection electrode and that the particles in the layer bind to-
gether so that large agglomerates are reentrained during a rap.
The degradation in performance of a precipitator that results
from rapping reentrainment can be reduced if the deposit of fly
272
-------
to
-J
OJ
(0
NJ
H-
rt
tr
(D
HI
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40
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20
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INLET
NO NH3
INJECTED
13 PPM
OF NH3
INJECTED /
100
80
60
40
20
OUTLET
NO NH3
INJECTED
13 PPM
OF NH3
INJECTED
30 35
VOLTAGE, kV
25
30 35
VOLTAGE, kV
40
3640-161
-------
N)
P-
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M
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w O
(D
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vQ I
CM
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P- W >
O rt P- t
O 01 rt
-------
50
40
LU
o
30
20
10
1MH3 ON
(20 PPM)
NH3OFF-
1000
1100
HOUR
1200
3540-163
Figure 174. Rapidity of the effect of ammonia injection on the
voltage supplied to the inlet electrical field of a
full-scale, cold-side precipitator (high-sulfur coal)
275
-------
50 -
40
CM
o
Z
LU
o
K
Z
LU
e
cc
D
CJ
30
20
10
15
INLET
NO NH
OUTLET
NO NH3
OUTLET
20 PPM
OF NH3
I
I
I
20
25
30 35
VOLTAGE, kV
40
45 50
3640-164
Figure 175,
Current density vs. voltage for a full-scale, cold-
side precipitator without and with NH3 conditioning
(high sulfur coal).
276
-------
ash on the electrodes can be made more cohesive. Dalmon and Tidy165
recognized that sulfuric acid vapor may have this effect as the
principal mode of conditioning for an ash that is not high in
resistivity. Other investigators have recognized that added am-
monia may also have this effect in addition to space-charge en-
hancement. 166
Figure 176 is the reproduction orf an obscurometer chart that
shows the effect of ammonia in reducing reentrainment.l66 Before
the gas was added, the optical instrument registered a series of
spikes that were coincidental with rapping puffs. After the gas
was added, a gradual suppression of these spikes occurred. Once
again, after injection of the gas was stopped, the spikes gradually
returned. It is important to observe that the effect of ammonia
on rapping puffs was only gradually observed, as expected from
the requirement of a change in cohesive forces on the ash residing
on the electrodes, whereas the effect of ammonia on space charge—
a gas-phase property—was earlier shown to be rapidly detected.
It should also be pointed out that certain types of conditioning
agents may interact with certain types of fly ash under certain
conditions to form a very sticky or cement-like material on the
discharge and collection electrodes. This situation has occurred
at some installations where conditioning agents were used. If this
occurs, the existing rapping forces may not be sufficient to remove
the collected fly ash from the discharge and collection electrodes.
Eventually, in this type of situation, the buildup of material on
the discharge and collection electrodes would result in very poor
electrical conditions. In addition, hoppers might plug up and
current paths to ground other than through the gas might be
created. The effect of a given conditioning agent on the stick-
iness of the fly ash layer should be examined in the laboratory
or with a pilot unit before injecting the agent into an industrial
precipitator.
Effect Of Voltage-Current Characteristics On Precipitator Performance
The voltage-current characteristics that can be obtained prior
to sparkover or back corona are indicative of how effective a pre-
cipitator will be in removing particles from the gas stream. Ide-
ally, the voltage'-current curves should extend over a wide range
of applied voltage between corona start and the maximum useful
current so that a stable operating point can be chosen and should
extend to high useful values of applied voltage and current. Low
values of operating applied voltage and/or current will result in
reduced performance and will require the use,of a larger precipi-
tator in order to recover the performance loss.
Figure 177 shows voltage-current curves obtained from the
three electrical sections of a laboratory precipitator when par-
ticles are,present .in- the gas ,stream..l B 7 .The carrier .gas was
•ambient''air, T.he particulate source was an'atomizer which pro-
duces-an aerosol of dioctyl phthalate (DOP) containing many
277
-------
1200
1100
1000
0900
0800
100 60
1300 1400
1500
1600
RELATIVE VALUE OF
LIGHT OBSCURATION
1700
1800
1900
60 100
3540-165
Figure 176. Reduction of rapping reentrainment by ammonia.
278
-------
a
K
2
UJ
K
CC
3
<
O
:. O SECTION 1
O SECTION 2
A SECTION 3 + SECTION 4
APPLIED VOLTAGE, kV
3540-166
Figure 177. Experimental voltage-current curves from a wire-plate
laboratory precipitator.
279
1 6 7
-------
different particle diameters. Although the precipitator is divided
into four baffled and independent electrical sections, the last
two sections were connected together. The experimental data were
obtained with a plate-to-plate spacing of 25.4 cm, wire-to-wire
spacing of 12.7 cm, wire radius of 0.1191 cm, and gas velocity
of 0.976 m/sec. These parameters are also characteristic of full-
scale precipitators.
Figure 178 shows the theoretically calculated effect of applied
voltage and current density for the experimental conditions de-
scribed above.167 The curves in Figure 177 were used to determine
various applied voltages and current densities. The overall mass
collection efficiency was calculated for 2, 5, 10, 20, 25.8, 35,
and 45 nA/cm2. The inlet mass loading and particle size distri-
bution and the gas temperature and pressure were also measured
and used in the calculations. In making the calculations, it was
assumed that the normalized standard deviation of the gas velocity
distribution (ag) and the gas bypassage of electrified regions
(S) were negligible (ag = 0, S = 0). Calculations were made with
no rapping reentrainment (the actual case) and with rapping re-
entrainment by simulating what v/ould occur if the collected ma-
terial was fly ash.
The curves in Figure 178 show that if the precipitator is
restricted to operate at low values of current density due to
sparking or back corona, then significantly reduced overall mass
collection efficiencies will result. Thus, in designing a pre-
cipitator, the effect of possible changes in the allowable current
density due to changes in the gas or particulate properties must
be taken into account. If reduced current densities are a possi-
bility, then the possible reduction in collection efficiency must
be compensated for by an excess in specific collection area (or,
more appropriately, collection plate area). The curves in Figure
178 also show that more mass will exit the precipitator due to
rapping reentrainment for the lower values of current density
than the higher values. At 2 nA/cm2, the model predicts that
approximately 3.1% of the mass entering the precipitator will
exit due to rapping reentrainment. This is a consequence of more
mass reaching the outlet sections for the lower current density.
Thus, when considering the effect of reductions in current den-
sity on precipitator performance, one must take into account not
only fundamental reductions in collection efficiency due to lowered
migration velocities but also possible increased reductions due to
increased rapping reentrainment.
As a further consideration, the increase in precipitator
performance that can be achieved by increasing the applied voltage
and current depends on where the change takes place on the voltage-
current curve. In fly ash applications where high current den-
sities can be achieved, the voltage-current curves become very
steep for higher applied voltages with large increases in current
resulting from small increases in applied voltage. For precipi-
tators operating with voltages and currents on the steep portion
280
-------
99.5
99.0
98.0 .TZZZ!=
\
HI
111
o
o
UJ
O
O
«/J
to
5
x.
LU
I
O NO-RAP, og = 0, S = 0
D MO-RAP + RAP, ag = 0, S = 0
10 20 30 40
AVERAGE CURRENT DENSITY AT PLATE, nA/cm2
50
3540-167
Figure 178.
Theoretically calculated effect of current density on
overall mass collection efficiency.157
281
-------
of the voltage-current curve, increasing the current will not have
a very pronounced effect on improving precipitator performance
because only small changes in applied voltage will be realized
and the applied voltage plays the dominant role in limiting par-
ticle charge and controlling the electric field.
The experimental data in Figure 179 show the effect of
applied voltage and current density on the collection efficiency
and migration velocity of different particle diameters.138 The
data were obtained from the laboratory precipitator just dis-
cussed with all parameters being the same except the gas velocity
which is increased to 1.49 m/sec. Since these data are essentially
free of nonideal effects, they clearly demonstrate the significance
of the maximum allowable applied voltage and current density on
precipitator performance.
Figure 180 shows measured overall mass collection efficiencies
obtained from full-scale, cold-side precipitators collecting fly
ash plotted as a function of specific collection area for various
average current densities. Although certain factors which will
affect overall mass collection efficiency such as inlet mass loading
and particle size distribution, geometry, gas composition, applied
voltage, ash resistivity, gas velocity distribution, extent of gas
sneakage, and particle reentrainment characteristics are most
likely different for the various precipitators, the data definitely
show the trend of increased performance with increased current
density.
Measured Secondary Voltage-Current Data From Full-Scale Precipitators
Collecting Fly Ash
Since the secondary voltage-current data from the individual
power supplies in an electrostatic precipitator provide valuable
information for use in (1) troubleshooting and diagnosing precipi-
tator problems, (2) theoretically predicting the performance of a
precipitator, and (3) interpreting the influence of the ash resis-
tivity and particulate space charge suppression of the corona current
on performance, data from several representative precipitators
will be presented and discussed. These data should acquaint one
with the various practical situations that can be encountered during
field measurements on a full-scale precipitator. In examining the
voltage-current curves, one should be systematically looking for
the effects described previously. Chemical analyses of coal, fly
ash, and gas samples are given in Tables 11 - 13 for those plants
where the data were available. These data are needed for proper
interpretation of the voltage-current curves.
Measured Cold-Side Curves--
Plant 1 - Cold-side ESPs collecting ash from low sulfur Western
coal—The electrostatic precipitator installed on Unit 1 of Plant
1 consists of six fields (Figure 181). The first and second fields
282
-------
e~
j_"
U
2
LU
5
u.
LU
2
O
U
O
u
39
98
97
96
95
94
92
90
80
70
60
cn
i i i ' i ' 1 1 I I I i I i 1
CURRENT DENSITY '
O 10 riA/FT2 = 107.64 ^A/m2 —
a 24 A;A/FT2 = 258.33 juA/m2 T
— &32.LA/FT2 = 344.45 fjA/m2 " —
GAS VELOCITY - 4.9 FT/SEC = 149.35 CM/SEC
a ~
*
— —
& —
— 1
^ -n-Mii
— 5 6 -
!L a j.
A I ~_
a ^ § -
T ~"
— A O
1. ^ —
"~ 1 ! 1 1 i 1 1 t 1 1 1 . ! 1. 1 1 I
2C
24
22
20
18
16
14
12
10
8
6
0.1 1.0 10.0
GEOMETRIC MEAN DIAMETER, >jm 3540
0
.y
c
i-
O
0
LJ
>
O
3
5
-168
Figure, 179. Experimental fractional efficiencies and migration
velocities for negative corona with a wire of radius
0.119 cm and gas velocity of 1.49 m/sec.138
283
-------
99.99
99.98 —
99.95
99.9
99.8
o
2
01
O
2
O
H
CJ
111
O
O
5.0 r.A/cm2 or less
10-15 nA/cm2
15-20 nA/cm2
20-25 nA/cm2
30-40 nA/cm2
-f- 25-30 nA/cm2
X
99.5
99.0
98.0
95.0 -
90.0
80.0
60.0
40.0
20.0
A,
100 200 300 400 500
SCA, ft2/1000 acfm
600
700
3540-169
Figure 180.
Measured overall mass collection efficiencies obtained
from full-scale, cold-side precipitators collecting
flyash plotted as a function of specific collection
area for various aArerage current densities.
284
-------
TABLE 11
AS RECEIVED, PROXIMATE CHEMICAL ANALYSES OF COAL SAMPLES FROM COLD-SIDE UNITS
Plant f Moisture Volatile Matte*- Fixed Carbon Ash Sulfur Btu/lb
1
2
3
4
5
6
7
AS RECEIVED,
8
9
10
13
2
3
17
Mi
8
.94
.04
.35
.22
-
dwestern
.80
PROXIMATE
2
8
4
.97
.26
.3
37
39
34
28
coal
.78
.05
.84
.67
-
- chemical
-
CHEMICAL ANALYSES
29
38
.42
.90
-
43.07
47.91
45.27
40.96
-
analyses
-
OF COAL
48.96
43.56
-
5
11
16
13
.21
.00
.54
.15
-
not avai
12
. 30
SAMPLES
18
9
24
.67
.28
.5
0
3
3
0
1
lable
0
FROM
0
0
1
.41
.28
.09
.51
.40
.77
10,
12,
11,
9,
10,
HOT-SIDE
.93
.45
.02
11.
11,
9,
557
421
399
316
-
211
UNITS
613
006
800
-------
TABLE 12
CHEMICAL ANALYSES OF ASH SAMPLES FROM COLD-SIDE AND HOT-SIDE UNITS
Plant #
1*
2*
**
3***
4 **
5
6
7*
Li20 Na20
0.02 0.26
0.02 0.55
0.02 0.54
0.03 0.67
0.02 1.38
0.08 0.42
Midwestern
0.02 0.46
K20
1.72
2.49
2.49
2.12
0.54
2.4
coal -
2.4
MgO
3.61
0.95
0.95
1.00
1.1
1.1
chemica
CaO
8.71
5.64
4.73
4.95
5.8
1.8
COLU-
Fe203
5.49
24,38
22.72
13.13
6.1
9.0
1 analyses
2.6 11.8
6.0
SlUtt UN
A1203
24.64
18.30
18.52
21.76
13.2
28.2
not ava
19.3
j. ID
Si02
50.55
45.08
45.69
50.23
70.8
49.4
liable
55.7
Ti02
1.22
1.31
1.45
1.96
0,87
2U2
0.97
P20S
0.50
0.30
0.30
0.78
0.05
0.59
0.57
SO 3
0.75
1.86
2.77
2.29
0,5
0.35
0.62
LOI
0.61
3.97
5.72
10.92
1.0
5.2
Soluble
SO.,
0.73
1.56
1.10
HOT-SIDE UNITS
8
9*
10
0.04 0.40
0.014 1.78
0.02 1.40
3.1
1.2
1.19
1.3
1.7
0.97
1.2
7.4
4.91
6.7
5.0
3.71
28.8
23.9
26.96
55.2
56.4
57.25
2.4
2.1
1.05
0.24
0.49
0.16
0.59
0.40
0.41
4.0
0.10
0.61
0.29
*Hopper ash sample
**Ash obtained from high volume sampler
***Isokinetically collected ash sample
-------
TABLE 13. GAS ANALYSES FROM COLD-SIDE AND HOT-SIDE .UNITS
COLD-SIDE UNITS
Volume, %
Plant No.
1
2
3
4
5
6
7
Temp,
138
149
152
154
^105
j-155
Not
115
99
°C CO 2
13.5
13.0
15.0
12.5
13.6
-
available
13.3
11.9
02
4.5
7.0
4.0
5.5
6.2
3.1
5.2
7.4
H20
7.1
8.4
^8.0
J-8.0
7.9
10.5
8.2
7.8
SO 2 , ppm
276
223
3081
2521
490
1433
520
-
SO 3 , ppm
<0.5
<0.5
11.9
5.4
<0.5
3.8
9.9
-
8
9
10
HOT-SIDE UNITS
332 15.3 5.0 8.5
350 15.2 3.3 9.1
Not available
788
370
2.3
<0.5
287
-------
00
00
H-
uq
£
h
CD
(H
O
H-
rt
ju
rt
O
OJ
<<
O
c
ft
Hi
O
n
hj
t->
P)
3
rt
H-
rt
GAS
4.42m 4.42m
5.33m
5.33 m
5. 33m
, k
)W W
TR** CIL
TR*C7R
(14. 5 f n
TR**C2L
TR\8R
M4 R f n
TRWC3L
TR**C9R
(17 5 f »)
„,,
TR\IOR
(17 R ft)
TR*C5L
TR^CHR
(17 R n )
,,,
• " "
TR^CIZR
( 17 R fl)
(60
60
(12
0.3
60 GAS PASSAGES AT
5.33 m
DISTANCE BETWEEN EACH FIELD-( 2.5 ft) 0.762 m
COLLECTING PLATES IN I AND 2 FIELDS ARE (12 ft) 3.66 m DEEP
FIELDS 3 THRU 6 ARE (15 ft)4.57 m DEEP
ALL COLLECTION PLATES ARE ( 40 ft) 12 .19 m HIGH
3640-170
-------
each have 5,351 m (57,600 ft2) of collecting area while the third
through the sixth fields have 6,688.8 m2 (72,000 ft2) of collecting
area, for a total of 37,457.3 m2 (403,200 ft2). This gives a
specific collection area of 99.2 m2/(m3/sec)(504 ft2/1000 cfm) for
the design volume of 377.6 m3/sec (800,000 acfm). Each field has
two double half wave transformer rectifiers. The arrangement of
the TR sets is shown in Figure 181. The precipitator has 12"
plate spacing and operates at approximately 149°C (300°F). Flue
gas is supplied and withdrawn through two inlet and two outlet
ducts, and a mechanical collector precedes the precipitator. The
precipitator employs a drop hammer type of rapping system in which
two plates are rapped simultaneously. The first two fields are
rapped six times per hour, the third and fourth fields are rapped
three times per hour and the fifth and sixth once per hour.
Voltage-current density curves from transformer-rectifier
sets for a cold-side precipitator at Plant 1 are shown in Figures
182 and 183, and average operating conditions are given in Table
14. A comparison of the breakdown point in the V-j characteristics
and the operating points under automatic control indicates that
the power supplies were operating at the point at which maximum
voltage was obtained. The V-j characteristics also indicate that
the automatic control of the C1L power set was not operating pro-
perly. The breakdown point in the V-j characteristics of the C12R
power set was abnormally low compared to the other outlet power
sets. This indicates a problem with either the power set or the
precipitator internals.
The low current densities and shapes of the voltage-current
curves for all the electrical fields indicate that the resistivity
of the ash layer was a limiting factor. Since the inlet mass
loading was fairly large and contained a relatively fine particle
size distribution, the particulate space charge effect was greatest
in the third electrical field instead of the first or second. The
low current densities resulted in relatively long residence times
in order to fully charge the fine particles.
Plant 2 --Cold-side ESPs collecting ash-from high sulfur
Eastern" coal—The electrostatic precipitator installed on Unit 4
of Plant 2 consists of three fields in the direction of gas flow
as Figure 184 illustrates. The precipitator is physically divided
into two collectors (A & B). The test program conducted at Plant
2 was performed on the "A" side of the #4 precipitator. The total
collecting area for the "A" side is 7,374.4 m2 (79,380 ft2),
2458.13 m (26,460 ft2) per field. This gives a specific collection
area of 34.475 m2/(m3/sec) (175 ft2/1000 cfm) for the design volume
flow of 213.82 mVsec .(453,000, acfm) per collector. Each collector
has, three double haIf-wave transformer rectifiers, one per field.
The precipitator has 27.94 cm (11 in.) plate.-spacing and operates
at approximately 149°C (300°F). The precipitator employs a drop
hammer 'type of rapping system in which two plates are rapped simul-
taneously with each hammer. The first field is rapped ten times
289
-------
20
18
16
CM
E 14
o
>-
H
CO
- 12
io
or
£T
0
• Operating Points
20
30 40
VOLTAGE , kV
50
3640-171
Figure 182.
Voltage vs. current density for left or north side
of Unit 1 precipitator of Plant 1.
290
-------
Operating Points
30 40
VOLTAGE , kV
50
3540-172
Figure 183. Voltage vs. current density for right or south side
of Unit 1 precipitator of Plant 1.
291
-------
TABLE 14. AVERAGE ELECTRICAL READINGS,
PLANT 1
Transformer Current
Rectifier Set Current Density Voltage
mA nA/cm2 ' kV
C7R 196 7.33 38 2,675
C1L 256 9.57 41 2,675
C7R and C1L 452 8.45 39.5 5,350
C8R 224 8.37 38 2,675
C2L 262 9.79 40 2,675
C8R and C2L 486 9.08 39 5,350
C9R 405 12.10 55 3,344
C3L 476 14.20 54 3,344
C9R and C3L 881 13.15 54.5 '6,688
C10R 500 15.00 38 3,344
C4L 482 14.40 37 3,344
C10R and C4L 982 14.70 37.5 6,688
CUR 524 15.70 43 's 3,344
C5L 486 14.50 36 3,344
C11R and C5L 1,010 15.10 39.5 6,688
C12R 234 7.00 35 3,344
C6L 570 17.00 36 3,344
C12R and C6L 824 12.00 35.5 6,688
292
-------
o
w ',25}
O
^LEARSIEGLER
s^ PORT
-------
per hour, the second field is rapped six times per hour, and the
third field is rapped one time per hour. The emitting electrodes
are square twisted wires with an approximate diameter of .419 cm
(.165 in.) and are 10.0 m (321 9 3/4") long. There are 12 wires
per lane per field for a total of 1512 wires. The discharge
electrodes are held in a rigid frame, and each frame holds 4
wires.
The average daily operating voltages and currents during the
testing period are given in Table 15. Figure 185 contains the
secondary voltage and current relationships obtained on the 3A
TR set with a voltage divided resistor assembly attached. Figures
186 and 187 contain"the V-I relationships for TRs 1A and 2A. These
voltage-current relationships along with resistivity data of around
1.0 x 1010 n-cm indicate that the electrical operating conditions
at this installation are not limited by dust resistivity- The
nature of the voltage-current curve for the inlet set (1A) suggests
that a combination of space charge effects and dust accumulation
on the electrodes cause the sparking at the relatively low values
of current density at which the inlet set operates.
Plant 3 - Cold-side ESPs collecting ash from high sulfur
Eastern coal—A mechanical collector, which was reported to have
been reworked when the precipitator was installed, precedes the
electrostatic collector at Plant 3, Unit 5. The precipitator
consists of four fields in the direction of gas flow (Figure 188)
and is physically divided into two collectors (A and B). The test
program conducted at Plant 3 was conducted on the "B" side of the
#5 precipitator. The total collecting area for the "B" side is
5900.64 m2 (63,516 ft2) with 1475.16 m2 (15,878 ft2) per field.
This gives a specific collection area of 43.48 m2/(m3/sec) (220.9
ft2/1000 cfm) for the design volume of 135.70 m3/sec (287,500 acfm)
per collector. The precipitator has six full-wave transformer
rectifiers; each transformer rectifier has an "A" and "B" bushing,
as seen in Figure 188. The precipitator has 25.4 cm (10 in.) plate
spacings and operates at approximately 160°C (320°F). A tumbling
hammer type of rapping system is employed in which each collecting
plate is rapped with a hammer. The first two fields are rapped
every six minutes, whereas half of the third and fourth fields are
rapped every six minutes. The emitting electrodes are rigid
"barbed" electrodes which are 0.502 m (I17 3/4") apart in the
direction of gas flow.
Table 16 contains the average electrical conditions, and
Figures 189 through 192 illustrate the secondary voltage-current
relationships at Plant 3. These curves indicate excellent elec-
trical operating conditions.
Plant 4 - Cold-side ESPs collecting ash from low sulfur
Western coals—The electrostatic precipitator installed on Unit
1 of Plant 4 consists of six physically divided chambers (Figure
193). The test program was conducted on the #5 chamber of the
Unit 1 precipitator. Each chamber of the precipitator has 44
294
-------
TABLE 15. AVERAGE ELECTRICAL OPERATING CONDITIONS
DURING SAMPLING PERIODS
Da
to
us
ui
TR
1A
2A
3A
1A
2A
3A
1A
2A
3A
1A
2A
3A
1A
2A
3A
1A
2A
3A
1A
2A
3A
Primary
Amps Volts
37.5 360.
82.5 377.5
97. 390.
29.7 31.2.5
78.2 370.8
92.5 385.8
Secondary
32.8
82.
94.
32.8
80.
93.8
37.4
42.6
35
41
326.
401.
401.
331.3
389.2
400.1
238.
338.
350.
243.
4 344.
2 350.
31.5 331.3
76.5 383.3
88.8 398.3
Bushing
Amps
.155
.23
.3
.133
.223
.283
.116
,23
.3
.14
.222
.297
.05
.1
,14
.05
.10
.14
.14
.21
.283
#A
KV
44.8
42.5
42.2
41.1
42.4
42.3
41.9
47.0
44.3
41.8
45.2
44.2
31.7
42.9
41.1
32.9
43.5
42.
42.5
44.5
44.6
Bushing
Amps
.145
.21
.295
.14
.2
.275
.138
.218
.3
.148
.204
.294
.08
.094
.137
.064
.092
.136
.15
.198
.268,
JIB
KV
41.5
42.6
42.4
40.1
41.8
42.6
43.
45.8
44.7
42.4
44.2
45.8
31.1
41.2
41.7
32.3
44.3
41.5
42.
43.7
44.6
Current Density
nA/cm2
12.2
18.
24.3
11.1
17.3
22.8
10.4
18.3
24.5
11.8
17.4
24.1
5.3
7.9
11.3
4.7
7.8
11.3
11.8
16.7
22.5
-------
0.3\-
0.2
LU
cr
e
o
0.1
20
TR
TR *3A
A Bushing
B Bushing
116.3
24.5
CM
P
30 40
VOLTAGE, kV
50
3540-174
Figure 185.
Voltage vs. current relationship for transformer
rectifier #3A, Plant 2.
296
-------
0.2
0.15
0.1
CI
cc
o
u
0.05
i r
TR "1A
25
30
I A Bushing
1 B Bushing
35 40 45
VOLTAGE, kV
50
16.3
8.16
§
3540-175
Figure 186. Voltage vs. current for transformer rectifier
#1A, Plant 2.
297
-------
0.2
0.15
a
E
CO
I 0.1
cc
D
U
0.05
TR*2A
BA Bushing
©B Bushing
B •
16.3
8.16 -il
25
30
35 40
VOLTAGE, kV
50
3640-176
Figure 187.
Voltage vs. current for transformer rectifier
#2A, Plant 2.
298
-------
•n
«il
c
h
(D
CO
00
Plant 3, Unit 5 precipitator layout
299
INLET GAS
DISTRIBUTIOI
SCREEN
/
1
1
GAS
FLOW"
i
1
•//INLET \
f-/ SAMPLING ;
\A PORTS /
».S,«« /
i
1
GAS
FLOW""
1
I
\
x
X
1
OUTLET GAS \
DISTRIBUTION,
' s '
\/
s
^
"A" Bl
/Tl
Uvi
"B" Bl
ISHING
A
"/
JSHING
c
i
"A" Bl
/Tf
VAI
"B" Bl
ISHING
r\
jy
JSIIING
i
"A" Bl
U
"B" Bl
JSHING
R\
ay
JSHING
"A" BUSHING
/TR\
lasy
"B" BUSHING
i-»-~— __
__— «-Q
s
CREEN / /
"A" Bl
0
"B" Bl
JSHING
^
4^
JSHING
GAS FLOW -
"A" BUSHING
A
w
"B" BUSHING
I/
GAS
FLOW
DOWN
RAPPING MOTORS-
3640-177
-------
TABLE 16. AVERAGES OF HOURLY ELECTRICAL READINGS
PLANT 3, "B" SIDE OF PRECIPITATOR 5
Day
1
5
6
TR#
5AB1
BAB 2
5B3
5B4
5AB1
SAB 2
5B3
5B4
5AB1
5AB2
5B3
5B4
KV
53.
53.
51.
47.
51.
52.
47.
48.
44.
51.
48.
48.
0
0
0
5
6
0
9
5
6
7
9
5
MA
339
504
708
679
198
347
466
675
292
402
529
675
nA/cm'
23.1
34.3
48.2
46.2
13.5
23.6
31.7
45.9
19.9
27.3
36.0
45.9
300
-------
0.4
27.2
0.3
o
c
•a
x
m
Z
•H
•3
m
3
m
tn
0.2
0.1
0.0
B" BUSHING
—| 20.4
10
20
30
40
A" BUSHING
13.6
u
I-
y
Zr
Hi
Q
I-
LU
cc
cr
c
6.8
50
60
3540-178
VOLTAGE (kV)
Figure 189. Secondary V-I curve for TR AB1 of Unit 5 of Plant 3.
301
-------
0.4
A" BUSHING
0.3 —
O
a
•O
m
a
m
v>
0.2
0.1
0.0
"B" BUSHING
10
20
50
60
27.2
20.4 rT
5
1
W
u
D
I-
ui
C
13.6 «
6.8
Figure 190,
30 40
VOLTAGE (kV)
Secondary V-I curve for TR AB2 of Unit 5 of Plant 3
302
-------
o
c
JP
3>
m
2
•o
m
3
m
tn
- 54.4
— 40.8
-27.2
O
(A
HI
Q
1-
Z
UJ
cc
IT
U
-13.6
20
50
60
30 40
VOLTAGE (KV) 3540-180
Figure 191. Secondary V-I curve for TR B3 of Unit 5 of Plant 3.
303
-------
0.4
0.3
O
•x
33
m
z
-o
m
•s
m
V)
0.2
0.1
0.0
A" BUSHING
B" BUSHJNG
10
20
30
50
_L
54,4
40.8
27.2
13.6
60
VOLTAGE (kV)
Figure 192. Secondary V-I curve for TR B4 of Unit 5 of Plant 3
304
-------
CHAMBER
NUMBER
GAS
FLOW
INLET SAMPLING
LOCATIONS
GAS
FLOW
IT 1 |l
!| »|
l^11
;®n
i n
V I M
X"
2
s
X
•J
^
s
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Figure 193. Plant 4, Unit 1 precipitator layout.
305
-------
lanes and five electrical fields in the direction of gas flow.
Each electrical field is 3.2 m (10.5 ft) long and has a total
collection area of 3518.96 m2 (37,879 ft2). The precipitator
has 25 cm (9.75 in) plate spacing, and spiral discharge elec-
trodes with a radius of 1.24 mm (0.49 in). Tumbling hammers are
used to rap both the collecting plates and high voltage discharge
frames. The precipitator operates at 88 to 120°C (190 to 250°F)
and was designed to handle 1100 m3/sec (2,330,000 acfm) at 121°C
(250°F), which results in a design specific collection area of
95.97 m2/(m3/sec)(487.6 ft2/1000 acfm). However, the actual SCA
measured on the tested chamber was approximately 590 ft2/1000
acfm. Rapping frequencies in the direction of gas flow are 10,
5, 5, 2, and 1 per hour, respectively.
Table 17 contains average secondary voltage and current
readings, and Figure 194 contains secondary voltage and current
curves obtained at Plant 4 „ The location of the' operating points
for sets B, C, D, and E with respect to the V-I curves suggests
that a significant portion of the secondary current is being
consumed by sparking or back corona.
Plant 5 - Cold-side ESP collecting ash from medium sulfur
Southeastern coal—Figure 195 illustrates the gas flow and pre-
cipitator arrangement. Some of the electrical sets were not oper-
ating on the B side precipitator, apparently due to broken corona
wires; therefore, tests were conducted on the A side only. Each
precipitator consists of two collectors in series, each of which
has 144 gas passages, with 0.229 m plate-to-plate spacing (9 in.),
9.14 m high plates (30 ft), and 5.45 m in length (18 ft). Thus,
each precipitator consists of 144 gas passages 9.14 m high (30 ft),
10.97 m long (36 ft), for a total collecting area of 28877 m2
(311,000 ft ) per precipitator. The precipitators each have
twelve electrical sections arranged in series with the gas flow,
such that the individual sections power 1/12 of the plate area
and 1/12 of the length. Gas flow at full load (^700 MW) for each
precipitator is about 520 m3/sec (1.1 x 10s cfm) at 300°F. The
specific collecting area at these conditions would be 55 m2/(m3/
sec) or 283 ft2/1000 cfm.
Figure 196 shows the voltage-current relationship obtained
for power sets in the front and rear section of Precipitator B.
These data were taken from the "B" side in order that measurements
in progress on the "A" side would not be disrupted. The difference
shown between the two power supplies may be caused, in part, by
space charge suppression of corona current caused by the higher
dust loading experienced by set 10BF, and, in part, by differences
in electrode alignment. Neither set shows any indication of back
corona. Although operating current density is limited to an
average of around 20 nA/cm2 and the power supplies exhibit an
increased sparking tendency as the sulfur content of the coal
drops, the operation of'this unit is not seriously imparied by
high resistivity. A dust of excessively high resistivity often
306
-------
TABLE 17. OPERATING SECONDARY VOLTAGES AND CURRENTS
DAILY AVERAGES UNIT 1, CHAMBER 5
Day
^^_-Av
1
2
3
4
7
TR#
5A
5B
5C
5D
5E
5A
5B
5C
5D
5E
5A
5B
5C
5D
5E
5A
5B
5C
5D
5E
5A
5B
5C
5D
5E
•KV1
38.9
36.5
33.0
37.8
35.1
39.6
36.5
32.9
37.3
35.0
39.6
35.9
33.0
37.0
34.6
39.6
35.9
32.2
37.4
34.6
39.5
34.5
31.6
36.4
34.1
C.D. uA/ft2 pA/m2
,238
624
910
590
,860
,245
.800
,850
,785
,862
,260
,724
,722
.846
.864
.322
,794
.959
.754
.894
,217
.887
.870-
.653
.827
6.28
16.47
24.02
15.58
22.70
6.47
21.12
22.44
20.72
22.76
6.86
19.11
19.06
22.33
22.81
8.50
20.96
25.32
19.91
23.60
5.73
23.42
22.97
17.24
21.83
67.6
177.3
258.6
167.7
244.4
69.6
227.3
241.6
223.
245.
73.8
205.7
205.2
240.4
245.5
91.5
225.6
272.6
214.3
254.
61.7
252.1
247.3
185.6
235.
'Corrected meter readings.
307
-------
30-i
25-
CN
U
< 20
LLJ
Q
5
cr
cc
o
10-
20
O A
O B
D C CLOSED SYMBOLS ARE AVERAGE OPERATING POINTS
& °
~ o o
CD
O
• o
D
D
00
25
30 35
VOLTAGE, kV
40
45
3E40-1E3
Figure 194.
Secondary current-voltage relationship, Plant 4,
Unit 1,' Chamber 5.
308
-------
3540-1S4
Figure 195. Precipitator layout at Plant 5, Unit 10,
309
-------
2
UJ
CC
CC.
0
I I I I I I I
A SET 10 BF (4TH FIELD, 1ST COLLECTOR)
O SET 10 BR (6TH FIELD, 2ND COLLECTOR)
10 12 14 16 18 20 22 24 26 28 30 32 34 36
VOLTAGE, kV
5540-186
Figure 196. Voltage-current relationships obtained on precipitator
"B", Plant 5, Unit 10-
310
-------
results in the occurrence of back corona at a lower voltage than
the sparkover voltage, and would be indicated by drastically re-
duced precipitator performance and by the shape of the voltage-
current relationships for the power supplies.
Plant 6 - Cold-side ESP collecting ash from Midwestern coal—
Secondary voltage-current curves are shown for the inlet and out-
let fields for this Midwestern power plant in Figure 197. The
resistivity of the ash during the test series was between 10ll and
101Z fl-cra.
Plant 7 - Cold-side ESP collecting ash from low sulfur Western
coal—The operating points of the ESP primary and secondary current
meters were monitored routinely during a field test at this Western
plant. The results of these current and voltage measurements are
summarized in Table 18. Figure 198 gives a representative curve
of the voltage-current characteristics.
.Measured Hot-Side Curves—
Plant 8 - Hot-side ESP collecting ash from low sulfur Eastern
coal—The electrostatic precipitator installed on Unit 3 of Plant
8 is a hot electrostatic precipitator which operates at approximately
343°C (650°F). The precipitator consists of two separate casings,
A & B, each of which has two inlet and two outlet ducts. Tests at
Plant 8 were conducted on the "B" side of the #3 precipitator, or
one half of the unit. The "B" side precipitator has four fields
in series; each field has a total collection area of 3912.95 m2
(42,120 ft2) and is powered by one transformer-rectifier. Figure
199 illustrates the hot side precipitator layout. This unit is a
retrofit which was installed in series with an existing cold side
precipitator. The collecting electrodes have 22.9 cm (9 in.)
spacing, are 9.14 m (30 ft) high and are 2.74 m (9 ft) deep per
field. The collecting plates are rapped by solenoid activated
drop hammers. Each drop hammer is activated at least once every
two minutes. The emitting electrodes have 22.9 cm (9 in.) spacing,
both, parallel and perpendicular to the gas flow and are .277 cm
(.109 in.) in diameter. The emitting electrodes are vibrated twice
every hour with electric vibrators. Although the precipitator was
designed to have an SCA of 53.15 m2/ (m3/sec) (.270 ftz/1000 acfm)
for a total volume flow of 590 m3./sec (1,250,000 acfm), the gas
flow for the two chambers tested was about 430,000 acfm, which
resulted in an SCA of approximately 390 ft2/1000 acfm.
Table 19 gives the average electrical condition data for the
hot-side precipitator power supplies tested at Plant 8. Voltage-
current curves for the indicated power supplies are shown in Figure
200. These data indicate good electrical .operating conditions for
a hot-side precipitator, and show the expected decrease in voltage
from inlet to outlet for a given current due to decreasing parti-
culate space charge.
311.
-------
300
200
2
UJ
ce
cc
100
OOUTLETi
Q INLET '
12-6-73
j
10
20
30
VOLTAGE, kV
40
50
3540-186
Figure 197. Secondary voltage vs. current curves from Plant 6.
312
-------
TABLE 18. VOLTAGE CURRENT OPERATING DATA
Day and Primary Primary Secondary Secondary
Time Voltage Current-A Voltage (kV) Current (Ma)
1 10:10 A 150 90 27 400
11:35 A 110 15 25 50
2:00 P 110 15 21 50
5:00 P 110 15 30 50
2 9:30 A 130 40 30 150
11:30 A 142 47 30 150
4:30 P 145 47 29 150
3 9:00 A 140 40 32 150
11:30 A 141 42 31 150
1:45 P 160 43 40 150
11:45 P 170. 43 41 150
4 4.30 P 170. . 44. 40 150
313
-------
0.7
0.6
0.5
V)
c_
S
in
cc
cc
D
o
o
o
LU
CO
0.4
0.3
0.2
0.1
0.0
WITHOUT DUST LAYER
WITH DUST LAYER
V 9-29-72 11:30 AM
O 9-29-72 4:35 AM
I
10
20 30
APPLIED VOLTAGE, kV
40
50
5640-187
Figure 198.
Voltage-current characteristics of Section IB
inlet, Plant 7.
314
-------
H-
iQ
C
N
0)
0*
3
rt
oo
rt
Ul
H
(D
O
H-
13
H-
rt
PI
rt
O
O
O
3
i-h
H-
rt
H-
O
CHAMBER A-2 CHAMBER A-1 CHAMBER B 1 CHAMBER B-2
'/™V
SECTION 4
SECTION 3
SECTION 2
SECTION 1
GAS FLOW
GAS FLOW
GAS FLOW
3640-188
-------
TABLE 19. AVERAGE ELECTRICAL OPERATING
CONDITIONS (PLANT 8)
TR
Set
1
3
5
7
1
3.
5
7
1
3
5
7
1
3
5
7
1
3
5
7
1
3
5
7
Primary
Voltage.
Volts
269.14
265.00
226.29
265.86
269=63
268,13
226.00
232.38
272.00
272.00
226.14
230.71
272.71
272.86
227.43
230.29
274.14
228.14
228.14
230.29
275.00
259.50
230.00
232.71
Primary
Current
Amps
207.43
240.43
233.29
235.57
199.50
241=00
237o88
234.88
200,57
210.71
237.00
232.71
201.86
239.71
236=86
232.57
212.43
234.29
237.14
233.14
196.00
214.70
239.14
236.14
Secondary
Voltage
kV
35.88
33.95
29.13
27.50
35.00
. 34.30
29.00
27.50
36.17
34.83
29.10
27.27
35.14
35.40
29.40
27.27
35.67
35.00
29.43
28.60
35.50
33.65
29.50
27.25
Secondary
Current
Densities
nA/cin2
31.2
42.7
36.3
37.3
30.7
37.6
37.3
37.1
30.7
37.3
37.1
36.8
30.9
37.3
37.1
36.8
31.2
37.1
37.3
37.1
30.2
31.7
37.8
37-6
Spark Rates
Sparks/ruin
27.86
4.71
4.43
4.86
28.75
•2::
.2.
5.
27.43
5.40
2.29
4.86
24.43
10.00
5.14 .
5. • -.
24.57
12.14
4.00
4.43
35.14
26.80
5.14
4.57
Avg. All Tests
1
3
5
7
272.10
260.94
227.36
237.04
202.97
230.14
236.89
234,17
35.56
34.52
29.26
27,57
30.82
37.28
37:15
37.12
28.03
10.18
3.83
4.79
316
-------
o
c
HI
Q
H
OC
40
35
30
25
20
15
10 •
5 -
16
O TR No. 1
O TR No. 3
O TR No. 5
£k TR No. 7
a o o
o o
O O
a o
20
24 28
VOLTAGE, kV
32
36
3640-189
Figure 200. V-I curves for Unit 3, Plant 8.
317
-------
Plant 9 - Hot-side ESP collecting ash from low sulfur Western
coal--The electrostatic precipltator installed on Unit 3 of Plant"
9 is a hot precipitator which operates at approximate 360°C (680°F).
This precipitator consists of two separate collectors, each of
which has 8 isolatable chambers. The test program was conducted
on the #8 chamber of the upper precipitator on Unit 3. Each pre-
cipitator chamber has thirty-five 22.9 cm (9 in.) lanes or gas
passages and six electrical fields in the direction of gas flow.
Each field is 1.83 m (6 ft) deep and has a total collecting area
of 1170.54 m2 (12,600 ft2). The discharge electrodes have a dia-
meter of 0.268 cm (.1055 in.) and are powered in each field by a
full-wave transformer-rectifier which also powers a field in the
adjacent chamber. Figures 201 and 202 illustrate the duct work
and chamber arrangement. The complete precipitator installation
was designed to handle 1859o68 m3/sec (3,940,000 acfm) at 350°C
(662°F), which results in a design specific collection area of
60.43 m-/(ms/sec)(307 ft2/1000 cfm). Both collecting and discharge
electrodes are rappad with solenoid activated magnetic impulse
rappers. The original rapper program installed with the precipi-
tator had a program time of 90 minutes„ During that 90 minutes,
all rappers (both plate and discharge) in the first and second
fields were activated nine times, all rappers in the third and
fourth fields were activated five times, and all rappers in the
fifth and sixth fields were activated four times.
During the test program on this unit, two different rapping
programs, each of which separated the wire and plate rappers, were
examined. The first program tested had rapping frequencies in the
direction of gas flow of 8, 8, 3, 3, 1, 1 per 73 minute period.
Wire rappers were activated eight times in the 73 minute period.
The second program examined had rapping frequencies in the direc-
tion of gas flow of 3, 3, 1, 1, 1, 1 per 22 minute period. Wire
rappers were activated once in the 22 minute period. Although the
different rapping programs probably affected the voltage-current
curves to some extent, the data did not show a significant dif-
ference in the curves.
Figures 203 and 204 show the full load secondary voltage-current
relationships for the inlet (H) and outlet (C) fields for two of the
chambers (7 and 8) of a hot precipitator at Plant 9n Also shown
are the average operating points for Plant 9 and similar secondary
V-I curves and operating points for Plant 8. Note that for full
load conditions the inlet V-I curves for the Plant 8 and Plant 9
units are similar in shape, but Plant 8 achieves higher current
densities prior to sparkover. The outlet V-I curves, however, are
significantly different in shape, with Plant 8 achieving substan-
tially higher operating voltages. The design of the electrodes in
the two precipitators is similar, and the operating temperatures
differ_by only -12°C (10°F) . These observed differences in electrical
operating parameters result in significant differences in theore-
tical prediction of collection efficiency for the two units. Lab-
oratory measurements of resistivity indicate that resistivity and
318
-------
SAMPLING PORTS
i s
GUILLOTINE
DAMPER
SAMPLING PORTS
3540-190
Figure 201. Ductwork arrangement for Plant 9, Unit 3.
319
-------
U)
N;
o
H-
vO
d
u
(D
M
O
O
tr
PJ
(D
l-i
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ro
HI
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H
H-
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UPPER
TR Set Typical, 48 Total
D
G
II
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U U I
35 0 I -> 35 ' 1 + 35 Ql •*• 35 1 -> 35 0 1 -> 35 1 -»• 35
4 J
LLLL
D
E
F
G
H
SOUTH NORTH
16 15 14 13 12 11 10
.
u u u u u u
1 -> 35Vl -*• 35
!..-»- 35 "v 1 -»- 35
LOWER
-------
CD
K>
S 40
H
M
CD
rt"
30
it "1
"CD t
S 8 20
H ^
CD Z
a LU
rt oc
oc
g 3
5 1o
s
Ifl
Hi
a
H
i_j fl
1 1 1 1 1 1 "1
0 PLANT 8 INLETS j
& PLANT9. 800MW
0 PLANT 9, 400MW
- A OPERATING POINTS PLANT 8 A I
1
i
^ A PLANT 9, 800MW
_
^
O 150 250 SPM A
PLANT 9, 400MW _
A O
D &
n
o a
o o
I I I I I I
pi 22 24 26 28 30 32 34 36
VOLTAGE. kV
3540-192
Pi
CD
-------
60
50
O PLANT 8
£ PLANT 9, 800MW
Q PLANT 9, 400MW
A OPERATING POINTS
PLANT 9, 800MW
OUTLETS
40
a.
PLANT 8 A
30
LU
cc
cr.
o
PLANT 9, 400MW
O 150-400 SPM
20
10
D 200-300 SPM
O 25-75 SPM
0
D
1
15 16
18
20 22
VOLTAGE, kV
24
26 28
8J40-1SS
Figure 204. Outlet voltage current curves for Plants 9 and 8.
322
-------
breakdown strength of the dust under laboratory conditions do not
offer an explanation for the low voltages at Plant 9. It is
possible, however, that the effective dielectric strength of the
dust under field conditions may be lower than in the laboratory.
Two other causes which have been hypothesized for the low voltages
are: (1) unexpectedly high values of effective mobility for the
flue gas due to the effect of reduced gas density, and (2) elec-
trode geometry problems. Figure 205 gives V-I curves for all
fields of two of the chambers of the Plant 9 precipitator. The
effects of particulate space charge in progressing from inlet to
outlet are evident.
Figures 203 and 204 indicate the dramatic effect on the power
supply characteristics of reducing the operating temperature (outlet
values) from 329 to 252°C (625 to 485°F) as unit load is dropped to
400 MW. Both inlet and outlet sets became severely spark-rate limited,
and the operating points under automatic control were much lower
.under half load conditions than they were at 800 MW. The collec-
tion efficiency dropped from 99.26 to 92.17% (mass train data),
even though the specific collecting area of the precipitator was
doubled as gas flow decreased. The electrical operating charac-
teristics suggest that dust resistivity increased to the point that
breakdown was occurring in the deposited dust layer, and that the
resulting sparking severely limited the performance of the unit.
Although the V-I curves show that better collection efficiency
could be obtained if the power supplies were adjusted to operate
at lower sparking rates, the available data clearly indicate that
serious degradation in collection efficiency may result in this
unit as load and temperature are reduced unless proper control
is provided for the TR sets.
Table 20 contains the averages of panel meter readings from
the test series. Note that the voltages for all fields were sub-
stantially reduced during the half load condition.
Plant 10 - Hot-side ESP collecting ash from a Western power
plant burning low sulfur coal—The layout of the precipitator and
pertinent information are shown.in Figure 206. The precipitator
power supply secondary voltage and current measurements are given
in Table 21. The current density was consistently lower on the
left side inlet (section A), possibly due in part to some electrode
misalignment for this field. Figure 207 shows typical secondary
voltage-current curves obtained from this unit.
RESISTIVITY OF COLLECTED FLY ASH
Effect Of Ash Resistivity On Precipitator Performance
In many instances, the useful operating current density in a
precipitator is limited by the resistivity of the collected par-
ticulate layer. If the resistivity of the collected particulate
layer is sufficiently high, electrical breakdown of the layer will
323
-------
OU H
50 •
tM
_§ 40 •
c
>
VI
£2 30 •
Q
1-
LU
tr
tc
3 20
10
0
1
0 C • •
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D A
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a a O
OD D A O
CO D A O ^ V
O O DA O ^
00 0£0 ? ^
O O D ^ O
-------
TABLE 20. AVERAGES OF HOURLY METER READINGS CHAMBER 7 AND 8
(kV VALUES ARE FROM VOLTAGE DIVIDER DATA)
Field
DCKV
ACV
ACA
DCMA
Field
H
G
F
r
D
C
Field
H
G
F
E
D
C
Field
H
G
F
E
D
C
31.77
28.38
27.20
24.75
22.75
22.32
DCKV
31.81
29.47
27.69
24.78
22.62
22.28
DCKV
25.52
23.86
23.44
18.99
19.12
16.93
DCKV
31.42
29.57
27.67
25.08
22.93
23.02
215.0
212. 1
220.0
212.9
204. 3
205.0
ACV
215.0
223.9
228.9
214.6
205.0
205.0
ACV
169. 0
139.0
152.0
159.0
150. 0
163.0
ACV
212. 0
217.8
223.9
217.2
205.2
211.0
50-200
50-150
25
--
--
Spark
100-200
65
—
—
—
Spark
50-150
50-200
25-100
50-250
25-200
25-100
Spark
50-100
50-150
60
- —
15
—
95.9
110.0
1 i! 5 . 0
i:r/. 5
2 S 1 . 4
2-2.4
ACA
107.9
136.8
188.0
195.7
250. 5
2M. 9
ACA
.09.0
25.0
44. 0
120. 0
105.0
155.0
ACA
88.3
107. 8
168. 3
201.1
253.1
253.2
390.7
518.9
1017.1
1096.1
1332.1
1387.1
DCMA
413.6
658.6
1023.6
1085.4
1335.0
1383.2
DCMA
234.0
110. 0
135.0
568.0
440. 0
750.0
DCMA
360.0
526.1
921.7
1100.0
1305.6
1376.1
Current Density
nA/cm2 (uA/ft2)
16.7
22.2
43.6
47.0
57.1
59.4
Current
nA/cm2
17.7
28.2
43.8
46.6
57.2
59.3
Current
nA/cm2
10.0
4.8
5.8
24.3
18.9
(15.5)
(20.6)
(40.4)
(43.5)
(52.9)
(55.0)
Density
(yA/ft2)
(16.4)
(26.1)
(40.6)
(43.1)
(53.0)
(54.9)
Density
(uA/ft2)
(9.3)
(4.4)
(5.4)
(22.5)
(17.5)
32.2
(29.8)
Current Density
nA/cm2 (yA/ft2)
15.4
22.6
39.5
47.2
55.9
59.0
(14.3)
(20.9)
(36.6)
(43.7)
(51.8)
(54.6)
325
-------
TABLE 20. (CONT'D)
Day 6
Field
Field
H
G
F
E
D
C
Field
H
G
F
E
D
C
Field
H
G
F
E
D
C
DCKV
ACV
Spark
ACA
DCMA
31.45
29.61
27.72
24.87
22.44
22.85
DCKV
29.75
28.20
26.22
23.70
22.18
22.33
DCKV
30.49
28.53
26.72
24.36
22.50
21.31
DCKV
30.45
28.38
27.00
25.06
22.31
22.20
214.6
221.1
225.0
213.2
204.3
209.7
ACV
194.4
203.9
214.7
210.1
199.9
207.2
ACV
200.7
198.3
213.8
214.5
200.1
199.3
ACV
192.4
182.3
201.8
214.6
196.9
201.6
50-150
25-100
20
—
_-
Spark
50-200
50-150
25-100
10
10
Spark
25-150
25-150
25-100
25
—
Spark
50-200
50-150
25-100
50
—
—
90.4
119.6
189.1
200.7
253.6
248.3
ACA
55.1
100.7
185.9
198.2
243.0
252.9
ACA
67.3
78 . 0
167.7
195.1
248.1
248.1
ACA
43.1
45.8
142.9
194.8
221.4
245.3
374.6
602.7
1007.7
1102.7
1350.9
1351.4
DCMA-
227.7
477.1
998.2
1088.8
1291.5
1387.1
DCMA
284.7
378.7
877.0
1088.0
1322.0
1348.3
DCMA
198.2
206.8
701.4
1040.7
1129.6
1324.6
Current Density
nA/cm2 (uA/ft2)
16.1
25.8
43.2
47.3
57.9
57.9
Current
nA/cm2
9.7
20.4
42.8
46.7
55.3
59.4
Current
nA/cm2
12.2
16.2
37.6
46.7
56.7
57.8
Current
nA/cm2
8.5
8.9
30.0
44.6
48.4
56.8
(14.9)
(23.9)
(40.0)
(43.8)
(53.6)
(53.6)
Density
(uA/ft2)
(9.0)
(18.9)
(39.6)
(43.2)
(51.2)
(55.0)
Density
(yA/ft2)
(11.3)
(15.0)
(34.8)
(43.2)
(52.5)
(53.5)
Density
(yA/ft2)
(7.9)
(8.2)
(27.8)
(41.3)
(44.8)
(52.6)
326
-------
TABLE 20. (CONT'D)
Day 10
Current Density
Field DCKV ACV Spark ACA DCMA nA/cm2 (yA/ft2)
H 30.33 190.0 50-150 46.7 193.3 8.3 (7.7)
G 28.31 180.0 50-150 35.0 165.0 7.0 (6.5)
F 26.48 187.3 50 78.3 340.0 14.6 (13.5)
E 24.40 211.7 25 L96.7 1060.0 45.5 (42.1)
D 22.04 190.0 — 188.0 906.7 38.9 (36.0)
C 21.18 198.3 — 239.0 1275.0 54.6 (50.6)
327
-------
TABLE 21. HOT-SIDE PLANT 10 SECONDARY VOLTAGE-CURRENT READINGS
A B C D
Voltage Current Voltage Current Voltage Current Voltage Current
April 29, 1974
April 30, 1974
May 1, 1974
May 2, 1974
May 3, 1974
u>
to
^> Average 36.8 548.4 31.5 670.0 24.2 690.6 21.2 725.6
Average Current
Density, nA/cm2 32 39.4 40 42.7
Note: Each power set is connected to 1.7 x 107 cm2 (18270 ft2)
(kv)
36.
37.
37.
36.
36.
3
5
4
3
2
(ma)
485
523
634
550
550
(kv)
29.
31.
32.
32.
31.
2
9
2
6
4
(ma)
700
650
684
635
680
(kV)
22
24
25
24
24
. 0
.3
.4
.9
.2
(ma)
675
686
702
688
702
(kv)
20
21
22
20
21
.0
.0
.8
.5
.8
(ma)
755
737
706
708
722
-------
TABLE 21. (CONT'D)
us
U)
o
April 29, 1974
April 30, 1974
May 1, 1974
May 2, 1974
May 3, 1974
Average
Average Current
Density, nA/cm2
E F G H
Voltage Current Voltage Current Voltage Current Voltage Current
(kV)
21.
20 =
21.
23.
22.
5
4
0
0
0
(ma)
900
936
940
915
920
(kV)
19.
17.
19.
20.
19,
0
4
0
0
2
(ma)
925
936
936
940
910
(KV)
16.
16.
17,
17.
16.
3
4
0
7
7
(ma)
995
989
994
948
994
(kV)
15
16
17
15
16
.5
.3
.0
,7
.8
(ma)
922.5
927
932
910
920
21.6 922,2 18.9 929.4 16.8 984.0 16.5 922.3
54.2 54.7 57.9 54.3
Note: Each power set is connected to 1.7 x 107 cm2 (18270 ft2)
-------
70
60
50
<
c
Z
LLI
Q
H
2
UJ
e 30
cc
20
10
OUTLET
INLET
10
Figure 207,
20
30 40
APPLIED VOLTAGE, kV
50 60
3540-196
Typical secondary voltage-current curves obtained from
a hot-side ESP collecting ash from a Western power
plant burning low sulfur coal.
331
-------
occur at a value of current density which in most cases is un-
desirably low. Depending on the value of the applied voltage,
the breakdown of the collected particulate layer will result in
either a condition of sparking or the formation of stable back
corona from points on the particulate layer. Excessive sparking
and back corona are detrimental to precipitator performance and
should be avoided.
Figure 208 shows an experimentally determined relationship
between maximum allowable current density and resistivity-168 it
points out the severe drop in maximum allowable current density
as the resistivity increases over the range 0.5 - 5.0 x 10ll ohm-
cm. Ash resistivities of 2 x 1010 ohm-cm or less generally allow
extremely good electrical conditions to exist in a full-scale pre-
cipitator. Ash resistivities of 1 x 1012 ohm-cm or greater will
cause back corona to ensue at relatively low applied voltages and
will make it difficult to characterize precipitator operation.
Figure 209 shows, the theoretically calculated effect of re-
sistivity on overall mass collection efficiency for a particular
cold-side, full-scale precipitator collecting fly ash particles.
Measurements of inlet mass loading and particle size distribution,
voltage-current characteristics, and gas velocity, volume flow,
temperature, and pressure were used in the calculations. The
operating applied voltage and current density for a given value
of resistivity were determined by using the measured voltage-
current characteristics and the data in Figure 208.
The curve in Figure 209 demonstrates how sensitive precipitator
performance is to the resistivity of the collected ash. For this
particular situation, the calculations project that an increase in
resistivity from 1010 to 5 x 1011 ohm-cm will result in a decrease
in overall mass collection efficiency from 98.1 to 81%. This
example points out why a knowledge of the resistivity of the col-
lected ash layer is crucial in designing a precipitator. The
problem is made even more difficult since the resistivity can
change significantly with changes in the composition, moisture
content, and temperature of the flue gas. In addition, changes
in resistivity due to changes in the coal producing the emissions
must also be considered. Thus, in designing a precipitator, proper
allowance must be made to account for possible values of resis-
tivity that are larger than that anticipated.
Figure 210 shows measured overall mass collection efficiencies
as a function of specific collection area for dif-ferent cold-side,
full-scale precipitators collecting fly ashes with various values
of measured resistivity. Although the data from the different
precipitators cannot be compared on the same basis due to differ-
ences in operating conditions and mechanical features, the data
definitely show that precipitator performance decreases with in-
creasing ash resistivity.
332
-------
100.0
I
IU*
a.
h
IU
a
IU
E
CC
IU
O
cc
u
10.0
BASED ON HALL'S EXPERIMENTAL DATA3 ±=E3
RESISTIVITY, olrm-cm
Figure 208. Experimentally determined effect of resistivity on
allowable current density in a precipitator.:58
333
-------
99.0
ss
>
o
z
ui
« 98.0
u.
i_
UJ
Z
O
o
ai
O
O
VI
CO
LU
O
95.0
90.0
I
80
1010
10"
RESISTIVITY, ohrn-crn
W"
3640-198
Figure 209. Effect of resistivity on overall mass collection
efficiency.
334
-------
19.7
39.4
SCA m2/(m3/sec)
59.1 78.8 98.5
118.2
137.9
99.9
99.8
99.5
99.0
Z
UJ
U
LL
UJ
O
P
O
ui
O
u
98.0
— ;n=rr==i-=s=_---j
' j
_L
__._,,. , |
- - — - • - ' — - - -
—--^.- : ~ '_ : :
-L-'- -:_;. - ---—^
_ . ^_ — :-: ..
-: -]-
I —^—1
|
j ^
r= —
\
,
U-^t -;— --r-
-~ -7-^=^==^==-::= Tf
.... 1
--4 ' "
-+•3
__ . L _
--- - • -' - •
P -.-.-^- -:_.:_-
f : - ,r^-:-.k^^^"r-" !.":.
-^^.-rS = .__4^..:.~,. ;-, ;
E-?—T -_-i..-- >-3jr L- :.^-r.:F33^-f^~~-tr; "r -r ~ "-
•: r : iL > ~r- '-I,.?"
-.-• , •. ^ i ----•:-._
t - ~-.~.i \ ..~^ : •
,..~" :'- >• "} - -
— _ -. - - _f . -. . _r __
:.._;.... | ..-..- 4 - - •
i— : - -i -
- : : ; • • •• •
- t - -
— - ' --+- •-- - ^~
— i -4 .-:-.:•: :
. . 1.
I -
l-^j-Hg^
~.:.: --F.t :--;.r- :
f . r -• :-~ •
I
" ' "h
-f ----- .
j
. - . _ - .i~: .. .
f ^-r-i F :•"•--?
' - j ^ i •.••.•;••-
\
-'.- _ji:i--.-:
r . . ...-[_ . ..
•-rnr-.z.-rr-7- ~ r^." I" — :..--•- f. ; : /.-.-
~^:~ LJ"['I.i -^ |": ^ . i : -r ^
^ -- . — ~rf~_:. ^— f-: - L -. |- - • :- :_[_ • - :
--.--•- •-. u ^-..~^ r:.f -.-. ; -i i^^.:.-:
: - :: ..: ..: 1 i -. : . v . ..•::?•
---=-- f .-••(- . j • i •
r - -- = T - i • ' •
'-.:•--"• -I
-. : ~: -t -.- •:-:"!- i" : I ' • ' t" :" " :
'-- ' --f-.^--— r^ : _ =r-=:..^-:;-
::: . J: j " : -- : $._.- r ---:-..-:_ ." ( I- .- . .- i : -.
-._4 --.-: v^; ^=1=^"^--"; ^ —=4-^—" -4 4 ;•-==-
r= -.:--, -:- -_-:- r" = --* . -?•:- 'V r = .- ; ,; .-f^ -=
- — — r
^
- — t-- -- -
. - .... _
, L_ .^_. . _
f ;r- i" :-.-:i r: ~ :~r - - -
L . , . .
-------
._.:.— |~:-. -
f —
.._ _ , . — -
— _- - - \ ; - — -
:.i>— 7 -:::"4 L_tL-ri.:4::.j «
y.:[r-:^:ir^^r-Jt-^=^A
:-.-'. I-' ^rr : -.- (• ~ ^-T .: > -. -.-
•'• •--'•' rrr^-"r • '
;--:---••- - r -..---f • -Jk- • -: ? t i," :.-r. ;..-
- • •
._:- ^^ -.L— -_- :- •
:—^~r-~ •--:.
•- - : - :;_ jr i • - •
" -----
. . _._,. .
• - - •
. . ~~7" _—
-' •-."• ; | : : . ' :.: | ! : . j
. - i - : t ; ; - .
: •. - - : - )=.-••;
-; .-
• • :- r -
t
. }
^:L.''-:iL;-rLj":-;:.
<1.0 x 1010 n-cm
1.0 x 1010 - 1.0 x 1011 fi-cm
>1.0 x 1011 P.-cm _
- '. r-r-r.-f-i .~ —
" ~ " t. '. '. - " T
-T^r- r - 1- :-r •:-.-:
95.0 h
90.0
30.0
70.0
60.0
50.0
40.0
30.0
-. ._ i _: : I3E:;.-.
-t~
100
Figure 210
200
300
400 500
SCA, ft2/1000 acfm
600 700
3540-199
Measured overall mass collection efficiencies as a
function of specific collection area for cold-side,
full-scale precipitators collecting fly ashes of
various values of measured resistivity.
335
-------
The resistivity of the collected ash layer also influences
the electrostatic force which may hold the entire layer on the
collecting surface or which may tend to pull the ash off from
that surface.169 The..electrostatic force depends on the charge
on the surface of the ash layer. The expression for this force
can be derived by writing expressions for the voltage gradient
in the gas and for that in the ash and using the principle of
virtual work; to find the force. The..resulting equation for the
force is16S ' ""
F = Uo/2)
E2 -
(23)
where
F =.
El
p
E
.force per unit .area (a positive force tends to pull the
ash off the collecting electrode) [nt/m2],
permittivity of free space (coul/V-m),
permittivity of the ash (coul/V-m),
resistivity of the ash (ohm-cm), and
potential gradient in the gas adjacent to the ash surface
"(V/m)
When E = Jpei/eo, the charge on the ash surface changes sign,
and the force reverses its direction of action. Thus, depending
on the values of E, J, p, and £I/ED, the force may act either to
hold the ash to or to pull the ash from the collection electrode.
Figure 211 shows the electrostatic force on the dust layer as
a function of current density for several values of resistivity as
predicted from equation (23). In obtaining the curves, it has been
assumed that a dielectric constant (EI/EO) of 4 and a value of
E = 2.5 kv/cm are typical for full-scale precipitators collecting
fly ash particles. 'For the different values of resistivity, the
curves were determined up to the maximum allowable current densities
given in Figure 208.
As can be seen from Figure 211, ashes with resistivities
between 109 and 1010 ohm-cm may be difficult to collect due to
their tendency to come off the collection electrode. This situ-
ation results in excessive particle reentrainment, especially if
high gas velocities exist in the precipitator. It is also inter-
esting to note that for all values of resistivity there is a lower
range of current densities in which the electrostatic force will
be such as to pull the ash layer off the collection electrode.
Thus, the precipitator must be operated near the maximum allowable
current density for ashes with resistivities greater than 1010
336
-------
CM
£
-------
ohm-cm in order to ensure that the electrostatic force will tend
to hold the ash layer to the collection electrode.
Measured Voltage-Current Curves Demonstrating Back Corona
If the resistivity of the collected ash layer is high (greater
than 10:i ohm-cm), back corona may occur at low applied voltages.
The presence and onset of back corona can usually be detected from
the measured, secondary voltage-current curves. Figure 212 shows
voltage-current curves which demonstrate the behavior resulting
from the occurrence of back corona.15" The data are from a full-
scale, cold-side precipitator collecting fly ash with a measured
resistivity of approximately 6 x 1012 ohm-cm. With this high a
value of resistivity, it would be anticipated that back corona
would occur at low voltages without the presence of excessive
sparking.
At some point on a voltage-current curve demonstrating back
corona, the applied voltage necessary to produce an increased
current will drop below that which was previously needed to pro-
duce a lower current. This results in the slope of the curve
changing from positive to negative. Practically speaking, the
curve starts to bend to the left at some value of applied voltage.
This is referred to as the "knee" of the curve. The inception of
back corona is assumed to occur at an applied voltage which is
just a little greater than that at the "knee". Once back corona
is initiated, the collected ash layer breaks down electrically
and discharges positive ions into the gas stream. This results
in the measurement of a large negative current. The breakdown of
the layer sustains itself at reduced voltages so that reduction
of the applied voltage still results in increased current. Also,
once back corona is initiated, the applied voltage may have to
be completely turned off before the breakdown of the layer will
cease.
In measuring voltage-current curves where back corona may
occur, it is the practice of some investigators to record a curve
by going upward in voltage and to record a second curve by going
downward in voltage. If the two curves are essentially the same,
then back corona does not exist or is not a serious problem.
However, if the downward curve is shifted significantly to the
leftr then extensive back corona exists. This shift to the left
of the downward curve is referred to as a "hysteresis effect".
From the curves and operating points shown i'n Figure 212,
it is obvious that this precipitator was operating in back corona.
This was also evidenced in very low measured mass collection effi-
ciencies which were inconsistent with the relatively high measured
operating current densities. This precipitator probably would
have performed better if it had been operated nearer the "knee"
of the voltage-current Curves for the inlet and outlet electrical
fields. Although the measured currents would be significantly
338
-------
0.6
0.5
0.4
£
0.3
0.2
0.1
• INLET FIELD V-l CHARACTERISTICS
A MIDDLE FIELD V-l CHARACTERISTICS
• OUTLET FIELD v-i CHARACTERISTICS
AVERAGE OFEKATUJG
POINT
•
•
• A
• A
AVERAGE Oi'KHATING
POIWT
A*
15
20
25
30
35
40
kV
45
50
3540-201
Figure 212. voltage-current curves which demonstrate the behavior
resulting from the occurrence of. back corona.
339
-------
reduced, the extreme ill effects of bipolar charging would be
avoided.
It should, be- noted that the particulate space charge effect
is also strongly evidenced in these curves. The particulate space
charge tends to hide the presence of back corona at the lower
voltages in the inlet electrical fields by removing the positive
ions which are discharged from the collected ash layer. However,
as more and more particles are removed from the gas stream, the
evidence of back corona becomes more pronounced as is seen in the
outlet voltage-current curve.
Factors Influencing Ash Resistivity170
Volume and Surface Conduction--
The electrical resistivity of a collected layer of fly ash
varies with temperature in a manner illustrated in Figure 213.
Above about 225°C, resistivity decreases with increasing temper-
ature and is independent of flue gas composition. Below about
140°C, resistivity decreases with decreasing temperature and is
dependent upon moisture and other constituents .of the flue gases.
In analyzing the conduction process, it is convenient to
consider the resistivity as involving two independent conduction
paths, one through the bulk of the material (volume conduction)
and the other along the surface of the individual particles,
associated with an adsorbed surface layer of some gaseous or con-
densed material (surface conduction). Either of these paths may
become the dominant conduction mode under conditions that exist
in operating precipitators, or, as is the general case, both
mechanisms may be important. The volume conduction is dependent
upon the chemical composition of the particulate material, where-
as surface conduction is controlled by the chemical compositions
of both the particulate and the effluent gas stream.
The coal, ash, and flue gas compositions are very important
in determining the mode or modes of conduction in a precipitated
fly ash layer and the resistivity of the layer. Tables ll, 12,
and 13 give data showing several representative coal, ash, and
flue gas chemical analysis for coal-fired boilers followed by
precipitators whose voltage-current characteristics were measured.
In general, the measured voltage-current characteristics and
resistivity can be correlated with the coal, ash, and flue gas
compositions. Table 22 shows coal and flue gas compositions ob-
tained from a large number of utilities in the U.S. From the
tables containing the coal, ash, and flue gas compositions, it
can be seen that a wide range of possible compositions exists.
The wide range of possible coal, ash, and flue gas compositions
is one of several factors which makes the prediction of fly ash
resistivity difficult.
340
-------
1014
1013
o
>"
1012
SJ 1011
109
3.2 3.0 Z8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1 2
—I I I 1 1 1 1 i 1
SURFACE | \
RESISTIVITY
VOLUME RESISTIVITY
COMPOSITE OF
SURFACE AND
VOLUME
RESISTIVITY
70 100 150 100 200 250300 400
(21) (3S) (66) (38) (93) (121) (149) (204)
600 800 1000
(316) (417) (538)
TEMPERATURE, °F (°C)
3540-201
Figure 213. Typical temperature-resistivity relationship for flyash.
341
-------
TABLE 22. COAL AND FLUE ANALYSES OBTAINED FROM UTILITIES INDUSTRY SURVEY
Proximate as Received
Ultimate Dry
Flue Gas
E/W
E
E
E
E
E
E
W
H
W
H
W
W
E
w W
to E
W
E
W
E
E
E
B
g
H
H
W
H
H
E
E
E
B
W
w
Mois-
ture
4.2
3.5
6.4
7.5
6.0
4.9
11.4
20.1
24.2
24.6
24. )
23.3
14.1
23.6
16.3
21.2
4.6
6.3
7.2
7.9
6.9
9.5
7. 7
37.6
36.0
21.1
18.9
12.3
8.5
9.4
6.6
7.4
9.5
29. a
Ash
22.3
13.9
10.9
8.3
8.8
9.5
13.2
NA
NA
8.2
14.1
10.0
11.2
4.3
8.9
6.0
15.2
20.3
15.9
16.3
20.6
19.6
1 c 4
JL J . 1
6.5
6.3
15.2
9.7
8.5
8.5
10.4
13.8
XT. 7
9.O
fi.B
Vola-
tile
HA
28.6
31.1
NA
34.5
32.7
31.4
NA
HA
28.6
30.7
32.4
32.2
33.0
37.0
30.3
26.4
37.2
34.4
30.8
30.3
32.8
01 7
J JL . 1
28.4
26.3
34.8
29.4
37.0
38.0
NA
NA
25. O
36.X
28. a
Fixed
Carbon
NA
53.1
51.6
NA
50.8
52.9
44.1
NA
NA
38.5
30.4
34.3
40.9
39.1
37.8
44.5
58.3
36.3
42.5
45.0
42.1
38.0
AC 7
1J a £
27.5
31.4
28.9
42.0
42.2
45.0
NA
HA
49.9
45.4
34 .6
Sul-
fUL-
2.4
1.0
1.1
1.3
1.0
1.0
0.7
0.2
0.2
0.8
0.6
0.7
2.5
0.4
3.7
0.5
2.6
0.8
3.7
0.8
2.3
4.1
1 ft
-L * O
1.8
1.1
0.6
0.6
0.4
2.8
1.3
2.0
0.7
0.4
O. 3
xio~3
BTU
11.3
12.7
12.4
12.5
12,9
13.1
9.9
8.1
7.8
8.5
7.9
8.7
10.6
9.6
10.6
8.5
12.3
10.1
11.2
11.0
10.6
10.0
6.8
4.5
7.6
9.5
10.8
11.7
11.8
11.9
IX. 5
IX. O
8.2
Car-
bon
64.8
NA
75.1
HA
70,3
73.2
65.8
59.7
61.1
66.7
59.8
56.2
69.4
72.5
67.7
65.9
NA
60.8
64.7
67.7
62.2
60.2
63.5
42.0
57.5
68.5
70.9
72.9
NA
HA
Nft
6S .7
S7 .a
Ilydco-
gen
4.5
NA
4.9
HA
4.6
4.8
4.5
3.8
3.8
NA
4.8
4.5
4.9
5.1
5.5
4.6
NA
4.7
4.5
4.4
4.2
4.3
4.5
6.8
4.3
4.5
5.2
5.1
NA
HA
NA
5.0
4 .a
Nitco-
gen
1.0
NA
1.5
NA
1.4
1.5
1.4
0.8
0.8
0.9
1.2
0.9
1.1
0.9
1.4
1.1
NA
1.4
1.3
1.3
1.3
1.2
1.1
0.6
0.6
1.3
1.1
1.3
NA
NA
NA
X-5
0.9
Chlor-
ine
NA
NA
NA
NA
-
-
0.0
NA
NA
NA
0.0
0.0
NA
HA
NA
NA
NA
0.01
-
-
-
-
MA
NA
0.01
0.02
0.02
NA
NA
NA
NA
NA
HA
Sulfur
2.8
MA
1.2
HA
pyrite 0.38
organ 0.64
sulfate 0.00
pyrite 0.28
organ 0.71
sultate 0.00
0.8
0.2
0.3
1.0
0.8
0.9
2.9
0.5
4.3
0.6
NA
0.8
4.0
0.9
2.5
4.5
2fl
. U
1.1
0.7
0.6
0.7
0.4
4.0
1.4
2.2
NA
0.5
0. 5
Ash
24.2
MA
11.6
NA
9.0
14.9
19.6
18.3
10.8
18.8
13.1
13.0
4.7
9.8
7.5
NA
21.6
17.3
17.7
22.1
21.7
•t f f
io . /
10.4
6.3
18.2
12.0
8.9
9.3
11.5
15.0
NA
9.9
9 . 7
Oxy-
gen
6.5
NA
5.7
NA
7.9
5.2
12.7
15.7
15.7
NA
14.7
14.4
8.8
16.3
11.3
19.0
NA
10.6
8.4
8.0
7.7
8.1
81
. JL.
19.4
43.8
17.9
13.0
13.5
7.4
NA
NA
HA
13. 4
16. 4
Water
7.0
NA
6.0
7.0
10.0
9.5
11.3
10.7
10.5
NA
NA
8.8
8.5
8.1
NA
8.9
8.0
8.0
8.0
8.0
8 A
. U
NA
NA
9.5
9.1
NA
NA
NA
NA
6.5
NA
8 . 0
Oxy-
qen
7.8
3.8
3.6
3.3
NA
4,9
4.8
4.4
5.0
NA
NA
5.2
5.6
5.6
5.5
4.3
5.0
5.0
5.0
5.0
5 , 0
NA
NA
5.6
7.8
NA
NA
3.2
NA
4.X
NA
3.5
3.7
Carbon
Dioxide
11.2
15.2
15.7
14.9
NA
13.5
12.9
11.3
12.5
NA
NA
14.7
13.4
13.4
13.3
13.2
14.0
14.0
14.0
14.0
14.0
NA
NA
13.5
11.6
NA
NA
15.0
NA
X3.6
NA
16 . 3
1 3 »
Sulfur
Dioxide
NA
NA
S90
HA
645
615
575
160
190
650
575
NA
NA
178
2343
283
935
700
2775
600
1725
3075
1350
NA
NA
465
375
NA
NA
NA
NA
556
NA
475
Sulfur
Trioxide
NA
NA
0.3
NA
13.2
11.8
<0.5
0
0
2.0
1.5
NA
NA
2.3
24.0
0.34
9.3
1.0
27.0
6.0
17.0
31.0
Hn
.0
NA
NA
<1.0
3.3
NA
NA
NA
NA
HA
NA
<1- O
Rank
HA
B
NA
B
SB
SB
SB
SB
SB
SB
B
SB
B
B
SB
B
B
B
B
B
I,
X.
SB
SB
SB
B
B
B
B
a
SB
Name
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
-------
Factors Influencing Volume Resistivity—
Volume conduction in fly ash is an ionic process resulting
from the migration of alkali metal ions. Whether the conduction
takes place through the particles or along the particle surface
has not been definitely established. The important distinction
is that volume conduction, or volume resistivity,- is governed
only by the character and composition of the ash and is independent
of gas composition.170
It has been shown161'171 that lithium and sodium are princi-
pal ionic charge carriers in experimental environments excluding
sulfuric acid vapor. Figure 214 shows the relations between the
measured resistivity and the combined atomic concentrations of
lithium and sodium for 33 fly ashes.172 Eastern and Western ashes
are indicated by closed and open symbols, respectively. These
data were obtained from resistivity versus reciprocal absolute
temperature plots for the individual ashes at 1000/T (°K) = 2.4
"(144°C, 291°F). Prevailing test conditions included a simulated
flue gas environment of nitrogen, 5% oxygen, 13% carbon dioxide,
9% water by volume and an electrical stress of 2 kV/cm. The flue
gas environment contained no sulfur dioxide or sulfur trioxide.
In the upper, right corner of Figure 214, the expressions
defining the curve produced by linear regression analysis are
shown. One can either calculate the resistivity for the specific
set of experimental conditions prevailing using these equations
or read the resistivity value from the figure. The slope of
approximately -2 indicates a two order of magnitude decrease in
resistivity for a one order of magnitude increase in the atomic
percentage of lithium plus sodium. A coefficient of correlation
of 0.97 was determined. This coefficient defines the degree of
fit between the data and the linear regression curve, and a value
of 1.00 would define perfect correlation between the two factors.
The high coefficient of correlation suggests that it is
improbable that the relationship can be improved by examining
these data as a function of the concentration of other chemical
species appearing in the ash composition. Of course this state-
ment may not be true if one subjectively selects a specific group
of ashes from the larger universe of ashes shown in Figure 214.
Volume conduction in all dusts encountered in industrial gas
cleaning is temperature dependent. In the case of ionic conduc-
tion, increased temperature imparts greater thermal energy to the
structure of the material, allowing carrier ions to overcome ad-
jacent energy barriers and to migrate under the influence of an
electric field. Thus, for volume conduction, an increase in the
temperature produces an increase in the number of carriers avail-
able to contribute to the conduction of the particulate layer.
343
-------
I 1012
O
O
O
V)
LJ
Q
UJ
c/o
1010
1Q9
0.1
In y " a + b In x
INTERCEPT- a = 25,435
SLOPE - b •= -2.129
COEFFICIENT = R = 0.97
OF
CORRELATION.
• EASTERN ASH
O WESTERN ASH
O
1.0
ATOMIC PERCENT - LITHIUM + SODIUM
10.0
2540-203
Figure 214.
Resistivity as a function of combined lithium and
sodium concentrations for a specific set of test
conditions.l72
344
-------
Figure 215 shows the relationship between volume resistivity
and temperature for two fly ash samples produced by combustion
of coal.173 The change of resistivity with temperature can be
expressed in the form of an Arrhenius equation
P = Po exp (Q/kT) , (24)
where p is the resistivity, p0 is a material constant. For the
fly ash example shown in Figure 215, the material constant p0 is
different for fly ash with different sodium ion contents. Graph-
ically, a shift in po causes a parallel shift in the temperature-
resistivity curve. The experimental activation energy Q is a rate
phenomenon and represents the slope of the temperature-resistivity
curve. The quantities p0 and Q are useful in defining electrical
conduction properties of solid or granular materials as a function
of temperature.
In some types of ashes, conduction may be electronic instead
of ionic. Nevertheless, the Arrhenius equation applies, whether
the conduction is electronic or ionic, the temperature-resis-
tivity relationships are similar, differing only in the values of
the constants in the Arrhenius equation.
Volume resistivity of a dust sample is also related to its
porosity. Intuitively, one would expect a higher resistivity to
be associated with a more porous dust layer due to the smaller
quantity of material in a given volume.
For fly ash samples, a 25% change in specimen porosity causes
a change of one decade in resistivity. A generalized relationship
between specimen porosity and resistivity was found for fly ash to
be
log pc = log
m
S(Pc - Pm)
(25)
where
p = resistivity at porosity PC (ohm-cm) ,
= resistivity at porosity ?m (ohm-cm) , and
S = Alog p/A%P = 0.04.
Factors Influencing Surface Resistivity —
Surface conduction requires the establishment of an adsorbed
layer of some material either to provide an independent conduction
path or to interact with some component of the particulate material
to provide a surface conduction pathway. If the effluent gas stream
contains condensable material (e.g., water or sulfuric acid) and
if the temperature is low enough that an adsorbed layer can form,
then the surface conduction will become significant.
345
-------
10"
E
u
E
>
p
55
UJ
e
1010
108
10?
\
HIGH
LOW SODIUM
100
200 300
TEMPERATURE, °C
400
I
200 300 400 500 600
TEMPERATURE, °F
700
800
3(40-204
Figure 215.
Resistivity vs. temperature for two flyash samples
illustrating influence of sodium content.173
346
-------
For temperatures below about ]50°C (300°F), surface conduc-
tion occurs via the lower resistance path created by the adsorbed
moisture or chemical components which occurs at these lower tem-
peratures. Both moisture and chemically reactive substances such
as sulfur oxides and ammonia are commonly present in many industrial
gases.
Physical adsorption as well as condensation can be involved in
surface conduction. At temperatures below the dew point, the rate
of deposition on the surface of a dust would be high. However, for
most circumstances the adsorbate is deposited on the dust surface
and can provide a surface conduction pathway even at temperatures
considerably above the dew point, as is shown in Figure 216.I72
The data were obtained from laboratory measurements on a particular
fly ash sample under the same simulated conditions discussed earlier
except that the water concentration was varied. The range of water
concentration used was selected based on water concentration mea-
surements made at several different power stations.
Another way of displaying the effect of water concentration
on resistivity is shown in Figure 217. The attenuation of resis-
tivity due to increased water concentration is observable at about
230°C and becomes very significant at the lower temperatures. At
the higher temperatures the effect of water concentration on re-
sistivity is not significant since the adsorption mechanisms
needed for surface conduction are not present.
The data shown in Figure 216 are in a suitable form for use
in the prediction of ash resistivity. In this interpretation, the
resistivity data have been plotted as a function of water concen-
tration for several isotherms. Expressions developed from data
such as these can be used to correct the resistivity value pre-
dicted for a given set of baseline conditions to a value for some
other set of conditions. For example, the average slope of the
resistivity-water concentration curve at a temperature of 1000/T
(°K) = 2.4 was -0.085. This is based on the data accumulated from
16 selected ashes used to evaluate the effect of water concentrations.
A simple algebraic expression can be used to convert the resistivity
value for 9% water shown in Figure 216 to the value for some other
water concentration.172
log pc^w = log pc + (Ww -Wc)Sw (26)
log p : logarithm of resistivity for a specific lithium plus
CfW sodium concentration, c, and water concentration, Ww.
log p : logarithm of resistivity for a specific lithium plus
c sodium concentration, c, and a water concentration of
9 volume percent. Value obtained from Figure 214.
W : volume percent water concentration to which the
w resistivity is to be corrected.
347
-------
1012
o
>
>
w 1Q10
UJ
c:
109
I 1
I I I I I 1
jiooo
T°K
• 2.2
* 2.4
6 2.6
A 2.8
182 359
144 291
112 233
84 183
10
v/o H2O
15
3640-205
Figure 216. Flyash resistivity as a function of environmental
water concentration for various test temperatures.
172
348
-------
1000/T(°K) 2.8
°C 84
°F 183
TEMPERATURE
3540-206
Figure 217.
Typical resistivity-temperature data showing the
influence of environmental water concentration.172
349
-------
W : water concentration used in establishing Figure
c 214, 9 volume percent.
S : A log p/A% H20; -0.085 for 1000/T(°K) = 2.4 and
w water concentrations between 5% and 15%.
In surface conduction, the mechanism of charge transport
appears to be ionic; however, the migration species have not been
identified. They could be ions extracted from or carried on the
dust surface or those deposited from the gas stream.
An example of how surface resistivity of fly ash depends on
the composition of the flue gas is the case of fly ash from coal-
fired boilers burning sulfur containing coals. The burning of
coal containing sulfur produces sulfur dioxide (SOa) in quantities
dependent on the sulfur content. Under normal conditions, about
0.5 to 1% of the SO2 present is oxidized to SO3, which serves to
reduce the resistivity of the fly ash, if -che temperature is low
enough for the SO 3 to be adsorbed on the ash. Thus, high-sulfur
coals tend to produce ash with lower resistivities than coals with
lower sulfur contents. In general, lowering the flue gas temper-
ature increases the SO3 absorption, so that the resistivity of the
fly ash can be controlled to some extent by changes in flue gas
temperature.
The effect on ash resistivity of incorporating sulfur trioxide
in an environment of water and air has been examined using a limited
number of ashes and tests.172 Figure 218 shows the results for six
tests conducted on one ash to demonstrate the combined effect of
sulfur trioxide concentration and temperature on resistivity. The
circles represent data obtained in a linear flow electrode set
while all other data were obtained in a radial flow electrode set.
Data obtained at 147-149°C using 2 kV/cm voltage gradient and
a baseline environment of air containing 9 volume percent water
are shown in Figure 219.172 Eight ashes were used in conjunction
with sulfur trioxide concentrations of nominally 2, 5, and 10 ppm.
Since this data base is so small, it is not possible to quantify
the effect of sulfur trioxide on ash resistivity. However, it is
obvious that the effect can be dramatic in that the presence of
10 ppm of sulfuric acid can reduce the resistivity two or more
orders of magnitude.
The influence of electric field on conduction in insulating
materials has been well documented. In solid materials, increasing
electric field permits a greater number of migrating ions to
participate in the conduction process. In granular materials
additional influences of electric field may become important.
Possible effects are: an increase in temperature at the contact
points between particles caused by joule heating, and an electric
discharge in the dust layer due to the enhanced field near adjacent
particles.
350
-------
10'^
1011
g 1010
5
5
ti
C/l
S io«
10s
: /^\ -
~ I '//' \
I ; \
/ ° ~~
- ' \ -
/ o
/ \
1 °
i \
o
"~ \ -
0
\
0
^^•"*« — •«•.
C TEST STARTING AT 460°C, AIR - 9v/o WATER
- D ISOTHERMAL TEST. AIR - 9
-------
o
5
UJ
IT
CJ
e
E
UJ
S
o
EC
<
o
c
tu
1012
10"
1010
10s
OPEN - EASTERN
CLOSED - WESTERN
I I I I
PPM SULFUR TRIOXIDE
9 10
3540-20S
Figure 219.
Resistivity as a function of environmental sulfur
trioxide concentration for eight flyashes. a 72
352
-------
Figure 220 shows relationships between in situ resistivity
and electric field for fly ash (from coals with low and moderate
sulfur contents) . ** The data were obtained using a point-to-
plane probe ajnd the parallel disc measurement method. The
measurements were made at a temperature of 265°C (330UF) with
a dust layer thickness of 1.0 mm.
Laboratory investigations also show an effect of electric
field on resistivity.175'175 Figure 221 shows the effect of the
electric field applied across the ash layer on the resistivity.172
The upper curve illustrates the almost negligible effect exper-
ienced by a few fly ashes and the lower curve shows the average
effect from the examination of 16 ashes. It should also be pointed
out that the laboratory values of resistivity would increase at a
significantly faster rate as a function of electric field as the
electric field is decreased from 2 kV/cm to smaller values.176
This is also indicated for the field data shown in Figure 220. The
ASMS PTC-28 code suggests that resistivity be determined just prior
•to dielectric breakdown. However, a research program involving
many ashes and a multiplicity of test conditions can not afford to
do this. Therefore, tests were conducted on a few ashes to estab-
lish a relationship between resistivity and electric field, and
other data can be calculated from this relationship using an ex-
pression similar to equation (26). l72
lo? Pc,w,e = 109 Pc,w + (Ee * V Se (27)
log p : logarithm of resistivity for a specific lithium
c'w'e plus sodium concentration, c, a water concentra-
tion W , and an applied voltage gradient EQ.
log p : previously defined.
c, w
E : applied electric field to which log PC w is to
e be corrected. '
E : applied electric field used in establishing
c Figure 221, 2 kV/cm.
S : A log p/AE; -0.030 for 1000/T(°K) = 2.4 and an
e applied voltage gradient range of 2 to 10 kV/cm.
Combined Effects of Volume and Surface Conduction—
The initial evidence suggests that the presence of sulfuric
acid in the environment provides an alternate conduction mechanism.
Therefore, other than the effect of various ashes having differ-
ent affinities for sulfuric acid vapor, there would seem to be no
relationship between the acid and the ash composition with respect
to conduction. It has been suggested that the effect of sulfuric
acid can be combined with the other factors that influence resis-
tivity by considering them as two independent conduction mechanisms
353
-------
10"
V
£
o
>
V)
HI
e
109
io8
riii
LOW SULFUR~1%
HIGH SULFUR-3%
J I
I t
0 2 4 6 8 10 12 14 16 18 20
ELECTRIC FIELD, kV/cm sMo-2oe
Figure 220. Variation in particulate in situ resistivity with
electric field.
354
-------
u
5
X
o
>
V)
V3
1010
109
46
E — kv/cm
10
3540-210
Figure 221.
Typical resistivity values as
ash layer electric field.172
a function of applied
355
-------
and determining a resultant resistivity from the equation for
parallel resistances.172
ps x pc,-w,.e -
pr = p + p (28)
Hs Hc,w,e
p_: resultant resistivity combining the effects of com-
position, water concentration, applied electric field
and sulfuric acid concentration.
p : resistivity resulting from the effect of environ^
mental sulfuric acid concentration taken from1 Figure""
219.
p : previously defined, equation , (27).
c, w, e
Prediction Of Fly Ash Resistivity
Although little practical information exists concerning the
prediction of fly ash resistivity, a recently proposed method of
prediction appears very promising.172 This method and a computer
program used to perform the necessary calculations are described
elsewhere.138 Comparisons of the predictions of this method with
in situ and laboratory measurements of resistivity on a limited
number of fly ash samples have shown good agreement. A key feature
of this method is that fly ash resistivity is predicted based on a
coal sample. This method will be discussed briefly in the following
paragraphs.
The information required to utilize the proposed technique
for predicting resistivity is the as-received, ultimate coal anal-
ysis and the chemical composition of the coal ash. A stoichiometric
calculation of the combustion products is made using 30% excess air
to determine the concentration of sulfur dioxide and water. The
quantity of excess air used in the calculation was established by
comparing stoichiometrically calculated flue gas analyses with
in_ situ analyses for several coals. The coal ash -is prepared by
first igniting the coal at 750°C in air, passing the ash through
a 100-mesh screen, and then igniting the ash a second time at
1050°C + 10°C in air for a period of 16 hours. Good agreement
in chemical analyses has been obtained between coal ashes produced
in this manner and their respective fly ashes.
The usual chemical analysis of the coal ash in weight per-
cent expressed as oxides is performed. The analysis is converted
from weight percent to molecular percent as oxides. The atomic
percentage of the lithium and sodium is taken as 66.6% of the'
molecular percentage of the oxides. The sum of the atomic per-
centages of lithium and .sodium is used to determine the resistivity
value, PC, from data similar to that shown in Figure 214 for var-
ious temperatures.
356
-------
Using the concentration of water determined from the com-
bustion products calculation and equation (26), the predicted re-
sistivity in terms of ash composition and water concentration,
o , is determined.
Mc,w'
For the ash thickness used in the research to develop the
predictive method, -\>S mm, it was found that dielectric breakdown
generally occurred at applied electric fields of 8 to 12 kV/cm.
Therefore, it was arbitrarily decided to use 10 kV/cm as the elec-
tric field at which the resistivity is predicted. Using equation
(27) and Eg = 10 kV/cm, the predicted resistivity is put in terms
of ash composition, water concentration and dielectric breakdown
field, Pc w^e- This value then is the predicted resistivity
exclusive of the effect of sulfuric acid.
Using the information from a variety of field test programs
for which flue gas data were available, it was observed that the
•average sulfur trioxide value was approximately 0.4% of the sulfur
dioxide value at the inlet to cold-side precipitators. This factor
is used to calculate the anticipated level of sulfur trioxide
based on the amount of sulfur dioxide appearing in the stoichio-
metrically calculated flue gas. For example, a typical eastern
coal can produce a flue gas containing 2000 ppm of sulfur dioxide
which it is anticipated would yield 8 ppm of sulfur trioxide.
Referring to Figure 219, a reasonable estimate of the resistivity,
p , resulting from this sulfur trioxide concentration might be
s
2 x 1010 ohm-cm. One then determines the resultant resistivity,
p , from equation (28) and the values for p and p .
IT SO/ W / S
Example of the Calculations Used to Predict Fly Ash Resistivity at
144°C (291°F)~
Step 1: Obtain an as-received, ultimate coal analysis and a
coal ash analysis. Table 23 shows an as-received, ultimate coal
analysis and coal ash analysis obtained for a particular coal. This
information will be utilized in predicting the resistivity of the
fly ash.
Step 2: Make a stoichiometric calculation of the combustion
products using 30% excess air to determine the concentration of
sulfur dioxide and water. Table 24 shows the steps in the calcu-
lation of stoichiometric flue gas from the coal analysis.177
Step 3: Determine atomic percentage of the lithium and the
sodium from the chemical analysis of the coal ash. First, convert
from weight percent to molecular percent as oxides as shown in
Table 25. Second, calculate the atomic percentage of lithium and
sodium as follows:
Atomic % of Li + Na = (.666) (0.096) + (.666) (0.518) = 0.409
357
-------
TABLE 23. AS-RECEIVED, ULTIMATE COAL ANALYSIS AND
COAL ASH ANALYSIS USED IN PREDICTION OF
FLY ASH RESISTIVITY
Coal Constituent
Carbon
Hydrogen
Oxygen
Nitrogen
Sulfur
Water
Ash
As-Received
Ultimate Analysis
lb/100 Ib
57.21
3.74
3.03
1.02
0.79
8.41
25.80
Coal As'h
Constituents
Li20
Na20
K20
MgO
CaO
Fe203
A120S
Si02
Ti02
P205
SO 3
Coal Ash
Composition
(1050°C)
0.04
0.45
3.7
1.4
0.7
6.7
27.6
58.2
1.7
0.1
0.2
358
-------
TABLE 24. CALCULATION OF STOICHIOMETPIC FLUE GAS FROM COAL ANALYSIS177
A. Calculation of combustion products, air, and 02 for 100% combustion.
Coal
con-
stituent
C
H2
02
N2
S
H20
Ash
Sum
As received
ultimate
analysis
lb/100* Ib
57.21
3.74
3.03
1.02
0.79
8.41
25.80
100.00
t
Molecular
weiqht
* 12.01*
* 2.02*
r 32.00*
r 28.01*
* 32.06*
T 18.02*
-
Moles pe
100* Ib
fuel
= 4.764
- 1.852
0.095
- 0.036
- 0.025
0.467
_
7.239
Required, for
combustion
r moles/100* Ib fuel
at 100% total air
Multipliers 62 Dry air
x 1.00* and x 4.76* 4.764 22.677
x 0.50* and x 2.38* 0.926 4.408
x -1.00* and x -4.76* -0.095 -0.452
x 1.00* and x 4.76* 0.025 0.119
5.620 26.752
3. Calculation of air and 02 for 30%* excess air.
Required for
combustion
moles/100* Ib fuel
at 30%* excess a
-------
TABLE 25. CONVERSION OF WEIGHT PERCENT ANALYSES OF
COAL ASH TO MOLECULAR PERCENT AS OXIDES
A. Calculate molecular weights of coal.ash constituents.
Coal ash
constituent
Li20
Na20
K20
MgO
CaO
Fe203
A1203
Si02
Ti02
P205
S03
(2) (6
(2)
(2)
(2)
(2)
(2)
(22.
(39.
24
40
(55.
(26.
28
47
(30.
32
Calculation
.939)
9898)
1020)
,3120
.0800
8470)
9815)
.0860
.9000
9738)
.0640
+ 15.
4 15.
4 15.
4 15.
4 15.
4 (3)
4 (3)
+ (2)
* (2)
4 (5)
4 (3)
9994
9994
9994
9994
9994
(15.
(15.
(15.
(15.
(15.
(15.
9994)
9994)
9994)
9994)
9994)
9994)
K
=
S
=
=
=
ft
=
=
£
=
Molecular
weight
29.
61.
94.
40.
56.
159.
101.
60.
79.
141.
80.
8774
9790
2034
3114
0794
6922
9612
0848
8988
9446
0622
B. Calculate total number of moles per 100 grams of coal ash.
Total f of moles = 5975774 + 6l!9790 * 9472037 + To73~IT4~ + 56*0794 + 159.6922
x _27_JL_ * 58.2 , 1.7 0.1 O.J
101.9612 60.0848 79.8488 141.9446 8T.0622
= 0.000134 4 0.00726 4 0.03928 4 0.03473 4 0.01248 4- 0.04196
4 0.27069 4 0.96863 + 0.02128 4 0.00071 4 0.00250
= 1.40086
C- Calculate molecular percentages of coal ash constituents.
Coal ash Molecular
constituent Calculation - percentage
Li20
f0.00726\
^1.400867 *
K20 ( •.n~, } x 100 = 2.804
MgO (i"nnQC I " 100 = 2.479
CaO
SiOj
yx.4uuee /
/n'3$m}xlo° • !-5i9
I x 100 = 0.051
X^ ' 0.179
360
-------
Step 4: Determine the resistivity value due to ash composition
at 144°C from Figure 214. The value of PC is approximately 1 x 10l2
ohm-cm.
Step 5: Include the effect of the calculated water concentra-
tion of 8.228% by volume by using equation (26).
log p^ = log (1012) + (8.228 - 9.0) (-0.085)
(~ i W
= 12 4- .0656 = 12.0656
p = 1.163 x 1012 ohm-cm
c, w
Step 6: Include the effect of the electric field across the
ash layer by using equation (27). For purposes of illustration,
assume dielectric breakdown occurs at 8 kv/cm.
log P,, „ = log (1.16 x 1012) + (8-2) (-0.03)
c i w/ e
= 12.0656 - 0.18 = 11.8856
p =7.684 x 10ll ohm-cm
c f w, e
Step 7: Include the effect of sulfur trioxide in order to
obtain the final value of resistivity. The sulfur trioxide concen-
tration is obtained by taking 0.4% of the sulfur dioxide concentra-
tion. In this example, the sulfur trioxide concentration is 0.004
x 680 ppm = 2.72 ppm. From Figure 219, a reasonable estimate of
the resistivity resulting from this concentration of sulfur trioxide
might be 1 x 1012 ohm-cm (low sulfur, eastern coal). The resulting
resistivity due to all pertinent parameters is obtained using
equation (28).
(1 x 10 ' 2) (7.684 x 101') 7.684 x 102 3 . .. v .nii ,m ^m
P = —T T « t -i =:—7-n-* -. n i i— = n—-, f n j, -. n i 7= 4.35 x 10 ohm-cm
r 1 x 10J2+ 7.684 x 1011 1.7684 x 1012
The most' conservative estimate of p would have been obtained by
taking p = 1 x 1013 ohm-cm as indicated by one of the data sets
in Figure 219. In this case, p = 7.14 x 101: ohm-cm.
Measurement Of Ash Resistivity
Factors Influencing Measurement of Resistivity—
Resistivity of a dust layer is determined experimentally by
collecting a ""sample-of the .dust from a gas stream and measuring
"the-'current'and- vol-tage characteristics of a -defined geometrical
configuration of the dust. The method of forming the dust layer,
and. the conditions of- measurement all influence the resistivity
measurement.
361
-------
Particle size distribution and porosity—For determination
of the true particle size distribution, the sample should be taken
from the gas stream in a manner (e.g., isokinetically) that insures
that the sample is representative of the particle size distribu-
tion of the fly ash in the gas stream. However/ due to problems
of probe design, most of the resistivity probes either do not
sample isokinetically or do not collect all the particles sampled.
Even if isokinetic sampling were used, the particle s.ize
distribution of the ash layer deposited in each field of a pre-
cipitator differs due to the variation in collection efficiency
as a function of particle size. Consequently, in determining re-
sistivity to correspond to that of each field of a precipitator,
the particle size distribution associated with each field would
have to be simulated. In general, such a procedure would be
impractical, and some means of obtaining a reasonably represen-
tative sample is employed,
It has been shown that the resistivity of a fly ash layer
depends on the particle size distribution in the layer.171'176
Also, the effects of particle size distribution and porosity can
not be considered independently since the particle size distri-
bution will influence the porosity. Thus, depending on the con-
duction mode, effects on resistivity of different particle size
distributions may be attributed to either particle size distribu-
tion or porosity. Laboratory measurements of resistivity as a
function of temperature have been made on two fly ash samples
under identical conditions except that the two samples differed
in particle size distribution and porosity.175 One sample had a
MMD of 40 ym with a porosity of 54% while the other sample had a
MMD of 2.7 ym with a porosity of 75%. These samples were obtained
from a larger size fractionated sample by using the size fractions
< 3 ym and > 25 ym. The resistivity versus temperature curves
for these two samples crossed one another. The lower MMD sample
had lower values of resistivity at the lower temperatures whereas
the higher MMD sample had lower values of resistivity at the higher
temperatures. These results are attributed to the greater specific
surface area available in the lower MMD sample at temperatures
where surface conduction is important and to the lower porosity
of the higher MMD sample at temperatures where volume conduction
is important.
Electric field—Since the resistivity of an ash varies with
electric field,it is important that measurements be made at an
electric field corresponding to that in the precipitator and/or
that the value of the field at which the measurement is made be
specified. In some resistivity measurement techniques the voltage
is increased until the ash layer breaks down, and the resistivity
reported is that corresponding to the condition just prior to
breakdowno Other techniques impose a fixed voltage across a pair
of electrodes to establish an electric field. Generally the
magnitude of the field is very low, of the order of 1 kV/cm for
t
362
-------
this latter type of technique. The reported values of resistivity
would be different depending upon whether the measurement was made
at a low field or near breakdown.
Method of depositing ash layer—In an electrostatic precipi-
tator, the ash layer is deposited electrostatically and the par-
ticles are aligned somewhat as the dust layer is built up. In
soue sampling probes the ash layer is deposited electrostatically,
whereas in other probes the dust is collected by other means and
allowed to fall into the measurement cell. In laboratory measure-
ments the ash layer is mechanically deposited in the measurement
cell.
The significance of the method of deposition has not been
quantitatively determined. However, to the eye, dust layers de-
posited electrostatically appear denser than those established
by free fall of the dust. In probes in which the dust is allowed
•to fall into the measurement cell, some attempt is made to vibrate
the cell or otherwise establish a reproducible density of the de-
posited dust. In other probes, the measurement technique involves
a disc placed on the dust surface. This disc provides some com-
paction of the dust layer.
The method of deposition of the ash layer may influence the
porosity of the layer. Laboratory experiments have shown that the
porosity of the layer will have a significant influence on the
measured value of resistivity.176 Laboratory measurements of
resistivity as a function of temperature have been made on two
fly ash samples under identical conditions except that the two
samples differed in porosity- One sample had a porosity of 70%
while the other sample had a porosity of 50%. The resistivity
versus temperature curve for the higher porosity sample was above
that of the lower porosity sample for all values of temperature.
This difference in; porosity led -to as much 'as a factor of 5 dif-
ference in the measured value of resistivity.
- Thickness of ash layer—Limited laboratory experiments have
been performed to examine the effect of the layer thickness on the
resistivity measurement.175 Laboratory measurements of dielectric
•breakdown strength have been made on three fly ash samples under
identical conditions except that the three samples had three dif-
ferent thicknesses between approximately 3mm and 7mm. For all
three samples, the applied voltage necessary to cause dielectric
breakdown was e-ssentially the same. Thus, the samples experienced
dielectric breakdown at different values of average electric field.
This suggests that the surface charge near one of the boundaries
may be the important factor in determining dielectric breakdown of
a fly ash layer and that the average electric field is not of
significance.
•-. •. Time of current flow—When voltage is applied across an ash
layer, the magnitude of the current will initially be'high and
363
-------
will then fall off, rapidly at first and slowly thereafter. The
initial current surge is due to absorption current, which charges
the capacitance associated with the ash-layer. The subsequent
decrease in current is due to depletion of the charge carriers or
polarization at the ash-electrode interfaces. If the current is
allowed to flow for a considerable time prior to making resistivity
measurements, the value of current will be lower than that ob-
tained immediately following application of a voltage.
Source variability—Another factor influencing resistivity
measurement is source variability. In spite of attempts to obtain
a uniform boiler fuel by blending the coal supply, the chemical
composition of the coal will vary enough to be reflected in obser-
vable changes in the SOz level of the flue gases and in the chemical
composition of the fly ash. Thus, to minimize errors due to source
variability, resistivity measurements should be made on samples
taken over a sufficiently long period of time, and the results
should be averaged to obtain a representative value.
Methods For Measuring Ash Resistivity—
General considerations—The determination of the electrical
resistivity of a fly ash layer is made indirectly. The resistivity
is computed from the resistance of a sample of the fly ash with a
known geometrical configuration. Typically, the geometry of the
sample will be either a rectangular or cyclindrical solid, or
the volume of space between concentric cyclindrical electrodes.
In each instance, the relationship between the resistivity and
resistance of what is considered to be a homogeneous material is ,
given by
p = RA/£, (29)
where
p = resistivity (ohm-cm),
R = resistance (ohm),
A = cross sectional area (cm2),, and
£ = length (cm)„
In each measurement device, the amount of material actually
utilized for the measurement is on the order of one cubic centi-
meter or less. Layer thickness from one-half to "five millimeters
is common. Using this minute sample of material selected from
the^large quantities of fly ash generated during a measurement
period raises serious questions as to just how representative of
the total fly ash material this sample can be. This factor may,
in part, explain the wide range of scatter actually observed in
a resistivity measurement program.
364
-------
Several techniques can be used for measuring the resistivity,
and several types of equipment are available for this purpose,
with no general agreement as to their relative merits. The choice
of technique and equipment can be influenced by the intended use
of the measured resistivity data.
One consideration is whether an absolute resistivity is to
be made for scientific or engineering design purposes or whether
a relative or rank ordering type of measurement is sufficient.
If one is attempting to relate the behavior of an electrostatic
precipitator to theoretically derived relationships, then it is
important to attempt to evaluate the absolute resistivity of the
dust. However, if one has accumulated a considerable quantity of
resistivity data over a period of time with one type of device
and in addition has similarly accumulated experience as to how a
particular type of electrostatic precipitator behaves with the
related particulate resistivity data, then the measured value of
resistivity can be related to precipitator performance.
As discussed earlier, the measured value of resistivity is
dependent upon a number of factors. If the measurements are
contemplated for rank ordering or relative behavior, then wide
latitude is allowed in the selection of a method. For the rela-
tive measurement type of investigation, it becomes important to
merely assure that the measurement conditions are reasonably well
duplicated for each condition, and the selection of method be-
comes of secondary importance. Either in situ or laboratory
methods may be applicable to a study of this nature if the sample
collection conditions, including temperature, are identical. How-
ever, if the purpose of the study is to evaluate how an electro-
static precipitator will behave with a new or significantly dif-
ferent type of dust under a given set of conditions, in situ
measurements will probably be necessary-
For comparative evaluations, in situ and laboratory measure-
ments must be made with the same instrumentation and technique.
Extreme care must be exercised in attempting to compare resis-
tivity data obtained with one device or technique with data
obtained with another device or technique. This will become
evident in the following discussions of the different measurement
techniques.
Laboratory versus in situ measurements—The determination of
whether the particulate resistivity should be measured in the lab-
oratory or in situ is based on an evaluation of the significance
of the surface conduction component. If the surface conduction is
negligible because of high temperature (>200°C) or because of the
absence of any reactive or condensable material (H2O, S03, etc.)
in the effluent gas stream, then laboratory measurements are
appropriate.
365
-------
However, if reactive constituent's are present and if the tem-
perature is in the vicinity of the dew point of the condensable
such that there is a reasonable probability that an adsorbed stfr-
face layer will exist, then it is important that both laboratory
and in situ resistivity measurements be made far comparison.
It is also important to make measurements in the effluent gas
stream in addition to the laboratory even though the chemical
composition of the gas stream can be duplicated in the laboratory.
The reason for this distinction is that as the particulate sample'
is collected, cooled and transported to the laboratory, there is
a reasonable probability for chemical reactions to occur that
would modify the particulate matter prior to measurement.
Laboratory measurements—Standard technique-—The standard
technique for conducting laboratory resistivity measurements is
described in the American Society of Mechanical'Engineers Power
Test Code 28, Determining the Properties of Fine Particulate
Matter.:7 8 This code was adopted by the Society in 1965 as a
standard practice for the determination of all the properties of
fine particulate matter which are involved in the design and eval-
uation of dust-separating apparatus. The tests include such pro-
perties as terminal settling velocity distribution, particle size,
bulk electrical resistivity, water-soluble sulfate content, bulk
density, and specific surface.
The document defines bulk electrical resistivity as the re-
sistance to current flow, expressed in ohm-centimeters, through a
dust sample contained in a cubic volume one centimeter on a side
when exposed to an electrical voltage equivalent to 90% of the
breakdown voltage of the sample, applied uniformly across two
opposite faces of the cube. The code specifies that the property
is to be determined at 150°C (300°F) and at a humidity of 5% by
volume, unless otherwise specified.
Apparatus for standard technique---The basic conductivity
cell is shown in Figure 222. 17SIt consists of a cup which con-
tains the ash sample and which also serves as an electrode, and
an upper electrode with a guard ring. To conform with the code,
the high-voltage conductivity cell must have the same dimensions
as shown, and must use electrodes constructed from 25-micron
porosity sintered stainless steel. The movable disk electrode
is weighted so that the pressure on the dust layer due to gravi-
tational force is 10 grams per square centimeter. The nominal
thickness of the dust layer is 5 millimeters. The actual thickness
is to be determined with the movable electrode resting on the sur-
face of the dust. All electrode surfaces in the region of the dust
layer are to be well rounded to eliminate high electric field
stresses.
The controlled environmental conditions required for the
standard measurement of resistivity in the laboratory can be
366
-------
MECHANICAL
GUIDE
(INSULATED)
1/32 IN.
AIR GAP
GUARD RING
1-1/8 IN. DIA. BY
1/8 IN. THICK .
MOVABLE ELECTRODE
3/4 TO 1 IN. DIA.
BY 1/8 IN. THICK
1
7
DUST CUP
SIN. ID,5mmDEEP
HIGH VOLTAGE SUPPLY
3540-211
Figure 222. Bulk electrical resistivity apparatus., general
arrangement.
1 7 9
367
-------
achieved by an electric oven with thermostatic temperature con-
trol and with good thermal insulation'to maintain uniform inter-
nal temperature, and a means to control humidity. Humidity may
be controlled by any one of several conventional means,.including
circulation of preconditioned gas through the oven, injection of
a controlled amount of steam, use of a temperature-controlled
circulating water bath, or the use of chemical solutions which
control water vapor pressure. It is desirable to circulate the
humidified gas directly through the dust layer; hence the reason
for the porous electrodes. Figure 223 illustrates a suitable set-
up for standard resistivity measurements.180
Experimental procedure for standard technique The first
problem encountered in making any resistivity measurement is ob-
taining an appropriate dust sample. The prescribed procedure for
PTC-28 Code assumes that samples of gas-borne dust are taken from
a duct in accordance with the Test Code for Determining Dust Con-
centration in a Gas Stream (PTC 27-1957) . " The" PTC-27 Code in-1"'"'
volves isokinetic dust sampling at various points in the duct.
It is recommended that samples should not be obtained from a
large bulk of material in a hopper, silo, or similar location.
If it is necessary that samples be obtained from such a location,
procedures which will insure that the sample is representative of
the whole must be used. For any resistivity test to be performed
on a bulk sample, it is necessary that a random sample be obtained.
This can be done by quartering the bulk sample to obtain the test
sample. To break up agglomerates and to remove foreign matter,
e.g., collection plate scale, the specimen can be passed through
an 80-mesh screen.
The procedure for making the resistivity measurement according
to Power Test Code 28 is as follows: (1) The sample is placed in
the cup of the conductivity cell by means of a spatula. Then it
is leveled by drawing a straight edge blade horizonally, across the
top of the cup. (2) The disc electrode is gently lowered onto the
surface. It should rest freely on the sample surface without
binding on any supports. (3) The conductivity cell is mounted
in the environmental chamber and equilibrium temperature and hu-
midity are established. The Code specifies that a temperature of
150°C (300°F) and a humidity of 5% by volume are to be used for
the test, unless otherwise specified. (4) A low voltage is applied
to the cell and then gradually raised in a series of steps up to
the point of electrical breakdown of the sample layer. Current
transients will occur when the voltage is first applied or in-
creased across the cell. A record of the current-voltage charac-
teristic of the dust is obtained. Preferably using another sample,
the above is repeated; when another sample is not available, the
sample layer should be remixed and releveled after each run in
order to break up any spark channels that may have been formed in
the dust layer. A total of three runs should be made. The average
breakdown voltage is then calculated. Before taking the samples to
breakdown, it is necessary to determine whether the temperature
368
-------
1. Pressure regulator
2. Constant temperature bjth
3. Pump
4. Heater
5. Make-up water reservoir
6. Externally heated piping
7. PTC 28 apparatus
3. Environmental sampling port
9. Externally heated exit piping
10. Calibiated C/A thermocouple
11. Power source for oven
12. mV Potentiometer
13. Cold junction 6
14. Oven
15. Fritted disc
16. Environmental chamber
17. Fritted disc air bubbler
18. Bath water in overflow
19. Air flowmeter
20. Air tank 9
10
3540-212
Figure 223. Schematic of apparatus setup, for standard resistivity
measurements.1
369
-------
and moisture content of the sample are in equilibrium with tem-
perature and humidity of the controlled environment. A test for
equilibrium is that the voltage-current measurements are repro-
ducible to within 10% when determined by two successive measure-
ments made 15 minutes apart. (5) The resistivity of the samples
is then calculated in the range of -85 to 95% of the average break-
down voltage, using the corresponding currents from the previously
recorded voltage-current characteristics.
Resistivity can be calculated in the following way. First,
calculate the resistance of the dust layer R at the specified
voltage.
«<«*-> -
Then calculate the resistivity p at the specified voltage.
A(cm2)
p(ohm-cm) = R(ohms)
l(CTl)
The moisture content of the air in the environmental chamber can
be determined by weighing a tube filled with calcium sulfate
(Drierite) before and after passage of a measured volume of air
through it. The volume of dry air passed through the tube is de-
termined from the flow rate and the sampling time.
Variations for the standard technique used in laboratory
studies—-Laboratory investigations using the PTC-28 or a similar
apparatus to study characteristics of ash resistivity usually
involve somewhat different procedures than that specified in the
standard technique. Usually it is not necessary or desirable to
determine the breakdown voltage of the ash layer. Hence, a fixed
potential prior to breakdown is applied across the cell, and then
the parameters under investigation are varied. Other laboratory
techniques may be desirable to determine certain electrical char-
acteristics of the ash, for example, the method being used in
research on the resistivity of fly ash at elevated temperature.
The technique utilizes a self-supporting sintered- disc of fly ash,
rather than loose powder. This technique is commonly used in the
electrical evaluation of ceramic insulators. It was selected for
the study of volume resistivity because it allows certain post-
test analytical work to be done. The details of specimen pre-
paration and measurement technique are given elsewhere.162
Another necessary refinement to the standard laboratory tech-
nique is based on the need to more nearly duplicate the gaseous
environment to which the ash is exposed. This refinement is
needed due to the strong influence on ash resistivity of the
various possible concentration levels of water and sulfur trioxide.
The different laboratories which make resistivity investiga-
tions of fly ash have developed their own measurement procedures
370
-------
and techniques. Table 26 gives a comparison of the test procedures
utilized by several laboratories. As would be expected due to
their independent development, the procedures developed by the
different laboratories differ from one another to some extent.
The differences in the procedures are important because they may
influence the measured value of resistivity and because they make
it difficult to compare resistivity data from the different lab-
oratories.
Other factors which influence the resistivity measurement
that are not addressed in Table 26 are the porosity of the ash
layer and the effect of sulfur trioxide on the measured value of
resistivity and the measurement technique. The value of porosity
at which the resistivity is determined is known to differ by as
much as a factor 1.5 between certain laboratories. In certain
systems which simulate the sulfur dioxide concentration, some of
•the sulfur dioxide may oxidize to sulfur trioxide. The effects of
sulfur dioxide and sulfur trioxide on the measurement technique
will be discussed later.
Laboratory studies simulating flue gases containing S0y181
Experimental apparatus utilizing ASME, PTC-23, test cells -An
experimental arrangement was designed to determine resistivity for
four ash specimens simultaneously using ASME, PTC-28 test cells.
The test cells were contained in a 316 stainless steel chamber
that was housed in a high temperature oven. Simulated flue gas
environments were maintained in the test chamber under a small
positive pressure (2.54 to 5.08 cm of water). The electrical
circuit allowed the cells to be independently energized for re-
sistivity measurements.
Figure 224 illustrates the physical arrangement of the appa-
ratus. !^2 Tank gases including commercially prepared and certified
1% SOz in NZ were metered using precision rotameters to deliver the
desired mixture at a total flow rate of 1.3 liters/minute at stan-
dard conditions. Depending on the temperature, this tlow rate
provided 5 to 10 volume changes per hour for the test chamber. The
standard of baseline simulated environment contained by volume 5%
Oa, 13% COa, 9% H20, 500 ppm S02 and the balance N2.
The gases leaving the rotameters passed through a stainless
steel manifold into a two liter stainless steel mixing vessel held
at 200°C to preheat the gas. At the exit of this vessel an inlet
was provided for the introduction of S03. The proper amount of
SO3to be injected was governed by the temperature of the 20% sul-
-f uric, .acid bath-and the flow rate of the nitrogen used as a carrier.
'"•• -A temperature of 160°C was maintained for the stainless steel
"tubing carrying the gas mixture to the oven. After entering the oven,
the gas was passed through 7.62 m (25 feet) of tubing, maintained at
the test temperature, before it entered the resistivity chamber.
Gas exiting the chamber was passed through a bubbler external to
371
-------
TABLE 26. RESISTIVITY TEST PROCEDURES
COMPARISON OF CERTAIN FEATURES
USED BY VARIOUS LABORATORIES
Laboratory
A
B
to
Resistivity Cell
Design & Geometry
Environmental
Conta inment
Standard
Environment
Standard
H2O Concentrations
Ash Layer Thickness
Usual Test Voltages
"Standard" E (kV/cm)
Time Voltage Applied
Prior to Current
Reading
Load of Electrode
on Ash Layer
Test Temperature
Range
In House
Guarded, Parallel Plate
Environment contained
within test cell
Air - H2O or
N2?O2,CO2,HaO mixture
0,5,10,15 volume percent
0.25 - 0.30 cm
500,1000,1500,2000 volts
20 - 40 seconds
-17g/cm2
120°C ascending to 400°C
in 27°C increments
In House
Guarded, Parallel Plate
Test cell housed in an
environmental chamber
N2,O2,CO2,SO2,H2O mixture
0,3.2,7.8,15,2,22.1 volume
percent
0.5 cm
2,000 volts (can vary as
desired)
3-5 minutes
~12g/cm2
190°C descending to 90°C
in 20°C increments
In House
Unguarded, Parallel Plate
Test cell housed in an
environmental chamber
Air - H2O
A constant value for each
test
0.3 cm
1,000 volts (can vary as
desired)
3.3
30 seconds
~6g/cro:
93°C ascending to 260°C in
27°C increments or 290°C
ascending to 400°C in 27°C
increments > - t
-------
TABLE 26. (CONT'D)
Laboratory
D
E
U)
Resistivity Cell
Design. & Geometry
Environmenta 1
Containment
Standard
Environment
Standard
II 2O Concentrations
Ash Layer Thickness
Usual Test Voltages
"Standard" E (KV/cm)
Time Voltage Applied
Prior to Current
Read j ng
Load of Electrode
on Ash Layer
Test Temperature
Range
ASME, PTC-28
Guarded, Parallel Plate
Test cell housed in an
environmental chamber
Air - H2O or
N2(O2,CO2,H2O mixture
9 volume percent
0.6 - 0.7 cm
1,330 volts (can vary as
desired)
60 seconds
~10g/cm2
460°C descending to 85°C
continuously with readings
taken periodically
In House
Unguarded, Parallel Plate
Test cell housed in an
environmental chamber
Air - IIoO
A constant value for each
test
0.5 cm
500 volts
5 points within tempera-
ture range of interest,
ascending and then descend-
i ng
1 r. House
Guarded, Parallel Plate
Environment contained
within test cell
Air - H2O or
N2/O2,CO2rH2O mixture
0,4.1,8.2,16.5,32.9
volume percent
0.5 - 0.6 cm
1000,1500,2000 volts
5 minutes
-17g/cm2
110°C ascending to 260°C in
50°C increments
-------
.GAS
OUTLET
U)
POSITIVE CENTER ELECTRODE TO COAXIAL
CABLE CENTER, TO ELECTROMETER,
TO GROUND
POSITIVE GUARD ELECTRODE
TO COAXIAL CABLE SHIELD, TO GROUND
ELECTRICAL FEEDTHROUGH
TYPICAL OF EIGHT
RESISTIVITY TEST CELL
ALUMINA
SUPPORT
FINISHED
SURFACE
THERMOCOUPLE
GAS
INLET
TO NEGATIVE
HV POWER
SUPPLY
-------
the oven to provide visual evidence of the maintenance of a small
positive pressure in the chamber.
Experimental procedure Ashes were passed through an 80
mesh screen to remove any foreign material prior to being poured
into the cup of the resistivity cell. While being filled, the
cup was tapped to insure that ash bridging would be minimized.
After the cell surface was leveled, the test cell was attached to
the proper leads in the chamber, see Figure 224. The front piece
of the chamber was sealed with C clamps after the four test cells
were in position. Clamping together two finely machined surfaces
was suitable for maintaining the small internal chamber pressure.
Nitrogen, passed through a drying column and the heated
plumbing leading to the oven, was maintained in the test chamber
overnight as the specimens were thermally equilibrated at 450-470°C.
Prior to converting the environment to a simulated flue gas, the
cell was tested by applying 1000 volts DC (5mm ash layer giving
an E = 2 kV/cm) and determining the current one minute after the
application of voltage.
After the environment was converted to the simulated flue gas,
the current readings were repeated every 10 minutes until the cur-
rent no longer increased with time. This usually took 20 to 40
minutes. At this point the oven was turned off, and current
readings were taken periodically as the chamber temperature de-
creased. The cells cooled from 460°C to 145°C in about four hours
and cooled further to 85°C in an additional two hours.
When, it was of interest to determine resistivity as a function
of ash layer field strength, the decreasing temperature was arrested
at 162°C while the necessary measurements were made. Variation in
water concentration was accomplished by changing the temperature
of the water through which the nitrogen was bubbled prior to enter-
ing the 200°C preheating vessel. The nitrogen was valved so that
it could be introduced dry or through the water bubbler. The water
concentration was determined from an exit gas sample at least once
during each resistivity test. Resistivity was calculated according
to equation (29).
Problems encountered using S0y It was stated above that
the- standard or baseline environment contained ^500 ppm of SOa and
no injection of SC>3 . Preliminary experiments had shown a small
difference between resistivity data acquired using air-wa'ter en-
vironments versus the baseline simulated environment. At the time,
it was believed that the small attenuation of resistivity was
possibly due to the presence of S02-
The scope of research required the investigation of the effect
of simulated environments containing 500, 1000, 2000, and 3000 ppm
of S02. When the larger concentrations of S02 were incorporated,
it was observed that resistivity values were significantly attenuated.
375
-------
Although one could not rule out the possibility that SOa affects
ash resistivity, it seemed likely that large quantities of SOs
were being generated and that the reduction in resistivity was
due to the presence of sulfuric acid. Determination of SOs and
SO2 concentrations in the inlet and outlet gas samples when no
SO3 was being injected verified the presence of SO3.
Several months were spent running ancillary experiments
attempting to understand the problem and develop a way in which
the existing equipment and test procedure could be utilized. When
SO2 was included in the environment, SO3 was produced by catalytic
oxidation of SOo. A few ppm were produced even when oxygen was
excluded. It was concluded that some oxygen was present as a
trace impurity in other gases or that air diffused into the test
chamber at the imperfect seal on the face, Furthermore, the amount
of SO3 catalytically produced was sensitive to the plumbing tem-
perature and the temperature of the test chamber. When S02 was
eliminated and SOs was injected, the difference in SOs concen-
tration in the inlet and exhaust gas samples from the test chamber
was sensitive to the chamber temperature. This indicated the
chamber was capable of adsorbing a significant quantity of avail-
able SOs (H2SOO . Since temperature was one of the test variables
and since it was desired to keep the SOs concentration constant
during a specific test, the above observations indicated that the
procedure and equipment utilized were not satisfactory for the
evaluation of the effect of SOs on resistivity.
Experiments to develop apparatus and procedure to utilize
environments containing SOX A series of modifications took
place in reaction to the observed test results. The first modi-
fication converted all plumbing and hardware from stainless steel
to glass with the exceptions of electrical f eedthroughs, test ''cells,
lead wires, etc. This did not eliminate the formation of SOs from
the S02 and 0$ present in the environment; however, the amount of
SO3 adsorbed by the system was decreased. It was then decided to
convert to an environment of air, water vapor and injected SOs
since no evidence was available to suggest a need for 02? C02
and SO2 to be present.
Under these conditions, the effect of 10 ppm of SOs on re-
sistivity was not observed although a significant amount of SOs
was removed from the environment as indicated by the measured SOs
concentrations for chamber inlet and outlet gas samples. [This is
in contrast to the observed reduction of resistivity reported for
the stainless steel system. It has been rationalized that in the
case of the earlier observations either a very great quantity of
SO3 had been generated and/or condensation of acid had taken place.]
At this point the total environmental flow rate under standard con-
ditions was increased from 1.3 liters/minute to 5.0 liters/minute,
and the number of test cells were reduced from four to one. Under
these conditions and with 25 grams of ash present in the single
test cell, an injection'rate of ^10 ppm SOs could be maintained
in both the inlet and outlet gas samples.
376
-------
However, even overnight exposure to an environment consisting
of air containing 9% water and 10 ppm of S03 did not produce a
significant attenuation of resistivity. The resistivity cell was
the type suggested in ASME PTC-28. The ash is held in a shallow
dish having a porous, stainless steel bottom. The upper ash sur-
face is exposed to the environment except where the measuring
electrode and guard ring rest. Ash specimens were taken at various
elevations between the exposed surface and the porous metal base
at various positions exposed to the environment and beneath the
measuring electrode. The amount of soluble sulfate was determined
for each specimen as a measure of the penetration and adsorption
of sulfuric acid from the environment. The results are shown in
Figure 225 for an ash having a soluble sulfate value of 0.20 -
0.25% before testing.183
These data show that even after 24 hours of exposure at 145°C
to an environment consisting of air, 9% water and 10 ppm of SO3,
•a large concentration gradient of adsorbed acid (soluble sulfate)
exists through the ash layer. The data show that in the area
directly exposed to the environment the acid pickup was signifi-
cant at the surface and a concentration gradient developed from
position 1 to 3. Between the measuring electrodes there was little
adsorption of acid. Therefore, no appreciable attenuation of re-
sistivity was noted. Obviously even a thin ash layer (1-2 mm)
between two parallel, porous electrodes would not be a successful
test geometry under these conditions.
Attempts to utilize vacuum to pull the environment through
the electrodes and ash layer and other schemes to force it through
under pressure failed. Besides the side effects of either com-
pacting or fluidizing the ash layer, the concentration gradient of
acid pickup expressed as soluble sulfate could not be eliminated.
The observations described above suggest that in addition to
the ASME resistivity cell, other designs may be unsatisfactory for
examining the effect of SO3 on resistivity. Nevens, et al13 "* re-
cently -evaluated three general types of laboratory resistivity
test cells. Since these cells require the environment to permeate
a porous stainless steel electrode and about 5 mm of ash, these
designs are probably undesirable for environments involving SOX.
Kanowski and Coughlin were successful in illustrating the
effect of S03 on fly ash resistivity using a cell believed to be
similar to that suggested by ASME PTC-28. a5 Although all appara-
tus and procedural details are not available, it would seem that
the use of very high total environmental flow rates and the use
of high concentrations (^30 ppm) of S03 contributed to this success.
This approach wa.s not attempted in .the subject research, because
the facilities limited the low rates available and interest was
restricted to lo-w S03 concentrations, <10 ppm.
377
-------
ENVIRONMENT
MEASURING
ELECTRODE
fGUARD
RING
POROUS STAINLESS
STEEL ELECTRODE
SCHEMATIC CROSS-SECTION OF ASME, PTC-28 RESISTIVITY CELL
MM
SAMPLE POSITION:
BLANK
1
% SOLUBLE SULFATE; 0.20/0.25 0.80 0.41 0.34 0.25 0.28 0.28
3540-214
Figure 225, Weight, percent soluble sulfate.
\ s 3
378
-------
Development of a radial flow test cell and procedure Equip-
ment The observation that the exposed ash surface adsorbed a
significant amount of sulfuric acid (soluble sulfate), and the
assumption that a thin layer of ash at the surface must become
essentially _ "equilibrated" with the environment in a reasonable
period of time led to the development of a test apparatus and
technique that has provided useful laboratory resistivity data.
Initial experiments showed that surface resistance readily reflec-
ted the effect of sulfuric acid in the environment. The test cell
shown in Figure 226 was constructed to compare simultaneously a
conventional test cell with a radial flow test cell using a 1 mm
thick ash layer.19b With this arrangement, one can alternately
measure resistivity in the conventional parallel plate mode be-
tween electrodes 2 and 3 or in the radial flow mode between elec-
trodes 1 and 2. The cell dimensions selected were based on the
work of Amey and Hamburger regarding optimum geometries for sur-
face and volume resistance measurements. Resistivity can be
calculated for the radial flow cell from the expression:
2 n c V 1.56V ,-._,
p = intrz/n) * I = —I" (30)
where
p = resistivity, ohm-cm,
V = volts, applied between electrodes 1 and 2,
I = amperes, current flowing between electrodes 1 and 2,
c = 0.1 cm, thickness of electrodes 1 and 2,
r2 = 1.90 cm, radius of I.D. of electrode 1,
ri = 1.27 cm, radius of electrode 2.
Figure 227 shows a radial flow cell in the glass environmental
chamber^137 Figure 228 shows the comparative results for the two
electrode geometries expressed as resistivity versus time of_envir-
onmental exposure. For this experiment the apparatus shown in
Figures 226 and 227 was used, and the ash was thermally equilibrated
overnight in dry air at 145°C. Resistivity was determined, about
1.4 x 1013 ohm-cm with either electrode set, and the environment
was changed to include 9% water at time = 0 hours. After 20 minutes,
both electrode sets measured a resistivity of 2 to 3 x 10 ohm-cm.
This response time is typical. At this temperature, flow rate
and chamber size, the time required to dilute a given environmental
composition to 99% of a different composition was about six minutes.
After the minimum resistivity due to water injection is reached,
the resistivity gradually increases with time of exposure. Even
though the injection of 10 ppm of S03 was started at time equal 30
minutes, the linear flow, parallel plate electrode set showed this
379
-------
5 mm
ELECTRODE 1 - 5.1 cm OD x 3.8 cm ID x 0.1 cm THICK, SOLID STAINLESS STEEL
ELECTRODE 2 - 2.54 cm OD x 0.1 cm THICK, SOLID STAINLESS STEEL
ELECTRODE 3 - 7.64 cm OD x 0.1 cm THICK, POROUS STAINLESS STEEL
8640-215
Figure 226„
Combination parallel plate-radial flow resistivity
test cell and electrical circuit.185
380
-------
PYREX
BELL JAR
RADIAL FLOW
RESISTIVITY CELL
PYREX
BASEPLATE 3540-21S
'Figure 221. Glass environmental resistivity chamber.187
381
-------
10
14,—
§1
O n
N O
I M
It,
012
C3-
O RADIAL FLOW ELECTRODE SET
D LINEAR FLOW ELECTRODE.SET
8
16
20
12
TIME, hrs
Figure 228. Resistivity vs. time of environmental exposure
24
382
-------
increase in resistivity; i.e., the parallel plate electrode set
did not respond to the presence of SO3. However, the resistivity
measured with the radial flow electrode set started to show the
effect of SO3 injection about 30 to 60 minutes after injection
was started. After about two hours had elapsed, the attenuation
of resistivity due to S03 injection was quite apparent and con-
tinued at a decreasing rate until a minimum value was attained
about 24 hours after the start of the test. For this ash and set
of conditions, it is assumed that a 24 hour exposure was required
to "equilibrate" the 1 mm thick ash layer between electrodes 1
and 2, Figure 226, with the surrounding environment of air, water
vapor and sulfuric acid vapor.
No effort has been made to formally evaluate the reproduc-
ibility of data using this cell; however, the cursory comparison
of many pairs of tests would indicate the reproducibility is good.
Also, no attempt has been made to evaluate the effect of variations
in the test procedure on the data generated. It has been noted that
the inlet and outlet S03 determinations indicate the environment
is reproducible and that typically the inlet concentration is
slightly greater than the outlet concentration for injections of
<10 ppm SO 3.
Test procedure The following test procedure was used to
determine the resistivity for a number of ashes as a function of
temperature and SO3 concentration. This procedure is started at
11 am each day that a test is to be conducted: load cup of re-
sistivity test cell with ash in the manner previously mentioned,
place cup in chamber, attach lead wires and insert electrodes 1
and 2 by pressing them into the ash layer using a straight edge
until ash slightly flows on to top of electrodes, cover chamber
base plate with bell jar, start flow of dry air and turn .on oven
to desired set point, determine -hot, dry resistivity at 2. pm and
then divert dry air flow through controlled temperature water
bubbler to introduce water vapor, determine resistivity at 2:15
and 2:30 pm and start nitrogen flow to inject desire concentration
of SOa, determine resistivity at 3:30 pm and take inlet and
-------
greater than 19 hours. While the radial flow cell and test pro-
cedure described have not been extensively evaluated and possess
certain disadvantages, both the new cell and test procedure appear
to provide a valid, basis for determining ash resistivity in .a
simulated flue gas environment..
In situ measurements16 9'z 8 e—General considerations—-Several
decisions must be made in setting up and conducting in~situ re-
sistivity measurements. These decisions involve (1) device selec-
tion and operation, (2) site selection, (3) determination of the
number of samples required to characterize the ash, (4) any
auxiliary data required, and (5) necessary safety precautions.
The selection of the device depends on a number of factors, in-
cluding the availability of each device and the past experience
of the intended user. However, selection should be based primarily
on the operating characteristics of the various, available devices.
The first priority in selection of a sampling site is the
location of a point in the operating system where the conditions
of the gas and the gas-borne dust particles are representative of
the environment for which resistivity is being determined. That
is, the gas temperature, gas composition, and particle history '
must be the same as that found, for example, in the precipitator.
Usually the inlet of the precipitator is selected as the point
for making resistivity measurements. However, sampling at several
points across the duct may be required to obtain a representative
measurement where there are variations in temperature across the
duct. Variations in gas flow velocity and dust loading in the duct
must also be taken into account, since these conditions can result
in nonrepresentative dust samples with some types of resistivity
apparatus.
When selecting a site for the measurements, practical consid-
erations must also be remembered. At the site location, sampling
ports must exist or be installed. The normal practice is to use
4-inch pipe for the ports. Electrical power (117-120 VAC, 60 Hz),
must be available at the site location for the operation of the
measuring equipment. In'many locations, adapters will be required
for mating of plant electrical outlets with the standard three-prong
plugs found on most laboratory equipment.
The determination of the number of individual measurements
required to characterize the resistivity of the dust is related to
the range of operating conditions anticipated and the variability
in the particulate matter. It is desirable when designing a new
precipitator installation that the worst operating conditions be
covered in the test schedule.
The variability in plant operating conditions that is of the
greatest concern is the variation in flue gas temperature through-
out the year. The change in the ambient air temperature from
winter to summer can cause the flue gas temperature to vary as
384
-------
much as 30 C (54°F) while the temperature variation across the
duct downstream from a rotating (Ljundstrom) air heater may be
50°C (90°F). This combined temperature spread may cause a signi-
ficant variation in the dust resistivity and care must be exer-
cised to assure that the widest variation is covered.
The day-to-day variations in characteristics of the particu-
late matter may also cause significant variations in the particu-
late resistivity. This variability will show up as a considerable
scatter in the measured value of resistivity over the measurement
period. When this variation occurs, it becomes imperative to make
a sufficient number of measurements at each temperature to obtain
a statistically significant value for the resistivity.
The precipitator acts to smooth out short term variations in
particulate resistivity. Dust layers ranging from perhaps one
centimeter on the inlet plates to some lower value, perhaps only
a millimeter, on the outlet plates build up during several hours
of collection time. The average buildup rate on the precipitator
plates is on the order of one millimeter per hour, exponentially
distributed through the precipitator, such that the dust layer on
the plates may represent an averaging of the instantaneous dust
conditions of many hours of operation. Therefore, there is a
rationale for averaging the measured values of resistivity for each
temperature condition to arrive at the resistivity representative
of the particular installation.
The determination of how many measurement points are required
is therefore based on the variability of the source and the ex-
perience of the technician making the measurements. Typically,
six to ten measurements each at intervals of 10°C (18°F) are
sufficient if plant conditions are reasonably constant.
The auxiliary data required when conducting tests on an
operating precipitator include:- - process samples for proximate
and ultimate analysis, flue gas temperature and composition (in-
cluding concentration of SO3)., precipitator. voltage-current re-
lationships, and particulate samples for laboratory analysis.
Extreme caution must be exercised when conducting measurements
in ducts containing flue gas. Typically, the flue gas at tempera-
tures exceeding 150°C (302°F) will contain a significant quantity
of sulfur oxides and particles. If the access port has been
covered for a period of time, significant amounts of particulate
will accumulate in the port. Some ducts will be under a positive
pressure of a few inches of water; in others, there exists the
probability of "puffing". Therefore, extreme care must be exer-
cised when opening ports and when inserting or extracting probes
•because of this presence of particulate and sulfur oxides in the
gas.
385
-------
Additional care must be exercised when utilizing resistivity
probes with high voltages. Sufficient electrical grounds must be
attached prior to handling any probe connected to an electrical
supply.
A shock hazard also exists when inserting or extracting any
ungrounded probe. An ungrounded probe inserted into a particulate-
laden gas stream may become electrically charged by static elec-
tricity caused by particle impact. Therefore, probes should be
grounded prior to insertion into a flue duct,
A hazard also exists because of the location of the sampling
ports. Often, the ports were installed after the construction of
the plant at locations remote from standard walkways. All scaffolds
and walkways should be tested prior to use and all hazards that can
be reasonably detected should be corrected.
A number of different instruments are available for making
resistivity measurements, These instruments differ fundamentally
in the method of sample collection, degree of compaction of the
dust sample, and the values of the electric field and current
density utilized for the measurement, as well as the method of
maintaining thermal equilibrium and the method of deposition in
the measurement cell. These differences in operation lead to dif-
ferences in the characteristics of the sample and in the values
obtained for the resistivity.
Instruments utilizing electrostatic collection and measurements
on the undisturbed dust layer measure the resistance of a dust layer
that was formed by collecting individual particles aligned by the
electric field under conditions similar to those in a standard pre-
cipitator. This procedure leads to a compact dust layer with good
interparticle contact. Those devices that utilize dust layers col-
lected and redeposited will be operating on a disturbed and re-
compacted layer. This difference in operation may lead to differ-
ences in contact potential between the adjacent particles and to
different porosity in the sample that may influence the value
obtained for the resistivity,,
In the remaining discussion of in situ measurements of resis- ,
tivity, several devices and methods will be described and discussed.
Particular emphasis will be placed on the point-to-plane probe
since it is the most widely used probe in this country- The oper-
ating principles of these devices will be described. Also, the
advantages and disadvantages of utilizing the different devices
will be presented,
In situ resistivity probes——Point-to-plane probe——The point-
to-plane probe for measuring resistivity has been in use since the
early 1940's in this country. Two models of this device are shown
in Figure 229. 189 The probe is inserted directly into the dust-
laden gas stream and allowed to come to thermal equilibrium. The
386
-------
PI CO AMMETER
CONNECTION
HIGH VOLTAGE
CONNECTION
DIAL INDICATOR
PICOAMMETER
CONNECTION
.-MOVABLE
SHAFT
STATIONARY
POINT
GROUNDED
RING
(b)
3540-218
Figure 229. Point-to-plane resistivity probe.
1 8 9
387
-------
particulate sample is deposited electrically onto the measurement
cell through the electrostatic action of the corona point and
plane electrode. A high voltage is impressed across the point-
to-plane electrode system such that a corona is formed in the
vicinity of the point. The dust particles are charged by the ions
and perhaps by free electrons from this .corona in a manner analo-
gous to that occurring in a precipitator.
The dust layer is formed through the interaction of the
charged particulate with the electrostatic field adjacent to the-
collection plate. Thus, this device is intended to approximate.
the behavior of a full-scale electrostatic precipitator and to
provide a value for the resistivity of the dust that would be
comparable to that in a full-scale electrostatic precipitator.
In the point-to-plane technique, two methods of making mea-
surements on the same sample may be used. The first is the "v-I"
method. In this method, a voltage-current curve .is obtained
before the electrostatic deposition of the dust, while the col-
lecting disc is clean. A second voltage-current curve is obtained
after the dust layer has been collected. After the layer has been
collected and the clean and dirty voltage-current curves obtained,
the second method of making a measurement may be used.
In the second method, a disc the same size as the collecting
disc is lowered on the collected sample. Increasing voltages are
then applied to the dust layer and the current obtained is recorded
until the dust layer breaks down electrically and sparkover occurs.
The geometry of the dust sample, together with the applied voltage
and current, provide sufficient information for determination of
the dust resistivity.
In the "V-I" method, the voltage drop across the dust layer
is determined by the shift in the voltage vs current characteristics
along the voltage axis as shown in Figure 23O.190 The situation
shown is for resistivity values ranging from 109 to 1011 ohm-cm.
If the parallel disc (spark) method is used, dust resistance
is determined from the voltage measured just prior to sparkover.
In both methods the resistivity is calculated as the -ratio of the
electric field to the current density.
The practice of measuring the resistivity with increasing
voltage has evolved because the dust layer often behaves as a non-
linear resistor. As the applied voltage is increased, the current
increase is greater than that attributable to the Increase in
voltage. Therefore, as described in the ASME Power Test Code No.
28 procedure, the resistivity reported is the value of resistivity
calculated just prior to sparkover.
There is considerable justification for using the value of
resistivity prior to electrical breakdown as the resistivity, since
388
-------
3.0
2.5
2.0
IU
Q
(-
LU
OC
cc
D
u
1.5
1.0
0.5
SPARK
NO DUST
DEPOSIT ON
PLATE
VOLTAGE DROP ACROSS
DUST LAYER (Vd) FOR
DUST THICKNESS
0.001 METER
20
3540-219
Figure 2.30
Typical voltage-current density relationships for
point-to-plane resistivity probe.190
389
-------
it is precisely at electrical breakdown that the resistivity causes
problems within the precipitator. The electrical breakdown in the
dust layer in the operating precipitator either initiates electrical
sparkover or reverse ionization (back corona) when the resistivity
is the factor limiting precipitator behavior. If neither of these
events occur, the dust layer merely represents an additional voltage
drop to the precipitator power supply.
Even though there are many similarities between the operation
of the point-to-plane device and a full-scale .precipitator,- several :
problems also exist. The first problem encountered is the .deter-
mination of the thickness of the dust layer. Some devices make
use of a thickness measurement system built into the probe. In "
other devices, the instrument is withdrawn from the duct and the
thickness of the layer is estimated visually by inspecting the-,
dust layer. However, the dust layer is almost always disturbed
by the air flow through the sampling port and- extreme care is re-
quired to preserve the layer intact.
The advantages of utilizing the point-to-plane probe for in
situ measurements are: (1) the particulate collection mechanism
is the same as that in an electrostatic precipitator, (2) the
dust-gas and dust-electrode interfaces are the same as those in
an electrostatic precipitator, (3) flue gas conditions are pre-
served, (4) the values obtained for the resistivity are in general
consistent with the electrical behavior observed in the precipitator,
and (5) measurements can often be made by two different methods.
However, the following disadvantages exist: (1) the measure-
ment of the dust layer thickness can be difficult, (2) high voltages
are required for collection, (3) considerable time is required for
each test, (4) a number of measurements are required for gaining
confidence in the measured value, (5) experienced personnel are
required for testing, (6) particle size of the collected dust is
not representative, (7) sample size is small, (8) carbon in the
ash can hamper resistivity measurements, and (9) length of probe.
Description of SoRI point-plane probe186 The SoRI resis-
tivity probe system for making in situ resistivity measurements
includes a probe for insertion in the flue, a high voltage supply/
a voltmeter, an ammeter with overload protection and a temperature
indicator. A schematic diagram of the complete system is shown in
Figure 231.19l
The power supply for the SoRI probe is a modified Spellman
Model UHR30N30 (30 kVDC Neg, 1 mA) with two voltage scales (0-30
kV and 0-3 kV). The ammeter is a Keithley digital multimeter model
150B (sensitivity to currents as low as 10~10 amps). The input to
the multimeter is protected from surge currents during sparkover
by a zener diode protective circuit. This circuit also contains
a 109 Q resistor for testing the probe.
390
-------
HIGH VOLTAGE
SUPPLY
VOLTMETER
f
"1
PUMP
\
I
PROBE I
AMMETER
(MULTIMETER)
X*
T
_ 0.1 *
fjr ~
k—
r
*
1
z
BOP.
ZENER
PROTECTION
CIRCUIT
3540-220
Figure 231. Schematic diagram of SoRI probe system
1 9 1
391
-------
The probe is equipped for collecting the dust, making elec-
trical contact with the dust, and determining the dimensions "of
the collected dust layer, all without removing the probe from a
sampling port. The particulate sample is collected by a point-
plane corona discharge cell mounted in the end of the probe.
The corona point is located 5.72 cm from the 5.2 cm diameter
collecting electrode. The collecting electrode consists of a
guard electrode and a center disc electrode (diameter 2.52 cm',
area 5.0 cm2). The guard electrode is connected directly to
ground. The center disc is isolated from ground by a machinable
glass ceramic insulator and is connected to the external ammeter.
A Chromel-Alumel thermocouple mounted in the back of the guard
electrode is used for measurement of the duct temperature.
Electrical contact with the exposed surface of the collected
dust layer is made by lowering a sliding disc electrode onto the
collected dust. The thickness of the layer is determined by com-
paring the readings of a dial indicator connected to the sliding
electrode. Readings are obtained when the electrode is lowered
before and after the dust layer is collected. The sliding elec-
trode is free to move up and down except for a lock clamp at the
top of the probe and for an acme screw that engages before contact
is made with the collecting electrode. This screw adjustment pro-
tects the dust layer from a sudden impact. The screw adjustment
is also provided with a spring built into the sliding electrode
push rod to limit the compression force applied to the dust layer.
The collection dust layer is removed by removing the probe
from the flue and manually cleaning the electrodes.
General maintenance of SoRI point-plane probe General
maintenance of the probe requires that it be periodically dis-
assembled and cleaned. Instructions for maintenance of the elec-
trical equipment are given in the manuals supplied by the manu-
facturers.
To clean the probe, first remove all externally collected
dust and the shield protecting the point-plane corona discharge
assembly. Remove the high voltage and sliding electrode assembly
from the probe by removing the bolts on the upper flange and the
screws holding the high voltage junction block to the middle bulk-
head (plate from which the corona point protrudes). Now slide
this assembly out of the probe casing and clean.
The high voltage junction block consists of two concentric
cylinders. It can be disassembled by removing the screws in the
top of the junction block. Separating the cylinders exposes the
high voltage connection and the sliding electrode contact. This
area should be cleaned of any accumulated dust. The graphite con-
tacts to the sliding electrode should be checked for electrical
contact and for freedom of motion of the sliding electrode.
392
-------
At the upper end of the high voltage and sliding electrode
assembly is the dial indicator assembly, spring assembly, control
mechanisms for lowering the sliding electrode, Swagelok quick
connect connector, and the high voltage connector. The dial in-
dicator mechanism has a tendency to corrode and should be lightly
oiled. The vertical location of the dial indicator can be adjusted
by loosing the locking screw and sliding the indicator up or down.
When the probe is assembled, the dial indicator should be adjusted
to read 5.00 when the sliding electrode is in contact with the
collecting electrode. The spring assembly should be inspected to
insure that the spring operates freely. If it does not, dust has
probably accumulated in this assembly and it must be disassembled
and cleaned. The electrode lowering control should be easy to turn
and easy to move up and down when the acme screw is not engaged.
The high voltage connector which was fabricated from alumina tubing,
Swagelok connectors, and a banana plug, should be cleaned and the
electrical continuity to the sliding electrode checked.
The collecting electrode electrical connections are accessible
by removal of the flange from the bottom of the probe casing. The
insulator isolating the center disc electrode from ground should
be cleaned and the resistance to ground from the center electrode
should be greater than 1012 ohms.
After reassembly, the probe electrode alignment must be in-
spected. The probe is designed to be self-aligning. In the lowered
disc position, the sliding electrode should be parallel and in
contact with the center disc electrode.
After assembly, the sliding electrode should move freely. When
the sliding electrode is locked in the lower disc position, it should
spring back into position if it is manually pushed into the probe
casing and released.
Operation of the SoRI point-plane probe Pre-field trip pre-
paration Prior to use of the probe in the field, general main-
tenance should be performed to insure that the probe will operate
properly. It is possible to bench test the probe using the 109 n
resistor built into the spark protector box to simulate a collected
dust layer.
Set up the probe system as described later in the operating
instructions. (Lower the sliding electrode so that it makes con-
tact with the collecting electrode and switch the control on the
spark protector to the 109 ft position.) Set the power supply for
an. output of 100 volts (V) and read the current (I) to the multi-
meter. Calculate the resistance (R) of the resistor in the pro-
tective box by Ohm's Law:
393
-------
This value should be 1.00 x 109 Q ± 5%. Electrical connec-
tors and instrument calibration should be checked if the above
value is not obtained.
A pre-field inspection check list is given in Table 27.
(Some of the equipment listed here is not supplied with the probe
arid must be supplied by the user.)
Operating instructions At the site the equipment should
be carefully unpacked and inspected. The electrical instrumentation
package is not sealed to keep out moisture and must be located out
of the weather but within 3 m (10 ft) of the sampling port. Con-
nect the probe to ground. This is necessary to insure proper
operation of the probe, and for operator safety. Before inserting
the probe in the sampling port, lower the sliding electrode until
it makes contact with the collecting electrode. If the metal shield
for the corona discharge cell has been removed, -replace it at this
time. (Between runs it is necessary to remove .this shield to clean
dust from the cell.) Adapters for 6" and 4" pipe nipples are sup-
plied with the probe. For some sampling ports special adapting
flanges must be made, or a temporary arrangement such as rags or
other suitable sealing material, will have to be used. However,
for strongly negative or positive pressure flues an airtight flange
connector should be used.
The large cable (RG - 8/U) supplied with the probe is the
high voltage cable. It connects the high voltage connector on the
back of the power supply to the high voltage connector on the top
of the probe. The 3 m cable (RG - 58/U) connects the BNC connector
on the side of the probe to the input connector on the spark pro-
tector box. The coaxial cable with a double banana plug on one
end connects the spark protector output to the multimeter.
A suitable temperature indicator for a Chromel-Alumel thermo-
couple should be connected to the thermocouple output on the side
of the probe using the supplied connector.
Plug the ac line from the instrumentation package into a 117-
120 VAC line. The black clip lead on the power supply is an extra
ground lead and should be attached to a good ground. Using their
individual power switches, turn on the multimeter and the high
voltage supply-
Assemble the probe completely and make all the necessary elec-
trical connections. Place the spark protector box switch so that
the 109 ohm resistor is in the circuit. Set the power supply for
100 V output. Lower the sliding electrode slowly while watching
the current meter for a reading of approximately 100 nA. If this
does not occur and the power supply current becomes excessive, the
electrodes are misaligned and the probe must be disassembled and
repaired. If all is normal, the initial test may begin.
394
-------
YES NO
TABLE 27. RESISTIVITY PROBE
PRE-FIELD TRIP INSPECTION CHECK LIST
1. Probe - including breakdown inspection and
calibration - wiring - HV cable, etc.
2. Power supply - inspect operation - general
condition,wiring, calibration, etc.
3. Multimeter - inspect operation - general
condition, wiring, calibration, etc.
4. Tool box - insure correct tools are in the box
for in field breakdown repair and inventory
spare parts.
5. Power cords - insure operation of extension cord
and box.
6. Tent - covering for instruments.
7. Field cleaning kit - insure rags, brushes, and
dusters are included for on-site cleaning.
3. Sample containers and data sheets - insure
supply of bottles or plastic bags to collect
-ish samples and supply of data sheets is sufficient,
9. Shipping boxes - insure boxes are serviceable
and in condition to receive rough and abusive
handling. Insure that instruments are sufficiently
padded.
10. Confirmation - insure unusual conditions at test
site are accounted for: flue gas temperature, gas
velocity, flue pressure, sampling port sizes,
hot/cold weather conditions, etc.
Comments:
395
-------
Insert the probe in the flue with the 100 V applied as above
Insure that the holes in the screen are perpendicular to the gas
flow. While the probe is warming up, it may expand sufficiently
to cause a loss or^electrical continuity indicated by reduced
meter current, and 100 V indicated on the power supply, in this
case lower tfte sliding electrode just enough to recontact the
plate. If both the current and voltage drop to zero, the plate
is misaligned and the test might have to be aborted. It is pos-
sible that the'misalignment is due to uneven expansion and mafy
return to normal when the probe reaches an even temperature.
Maintain the electrical contact of the sliding electrode
fand plate throughout the warm-up period. After the temperature
as indicated on the thermocouple readout has equilibrated, a test
may be started.
Check the current meter to insure that the sliding electrode
is down in place. Adjust the dial indicator to have the pointer
set at zero by loosening the lock nut on the dial face and rotating
the scale to the proper location. Leaving the probe cover holes
oriented perpendicular to the gas stream, unlock and unscrew the
sliding electrode control and raise it to'the" up position. Lock
in place. Now run a "clean-plate" V-I curve by placing the multi-
meter on the 100 nA scale and setting the power supply voltmeter
switch to the high position. Check that the slide switch on the
spark protector is in the normal position. Turn the high voltage
on. The use of the high voltage supply is described in the manu-
facturer's manual. Adjust the OUTPUT control through its full
range using the kV meter as a guide and make a current reading
every 1000 volts until a spark level or the maximum output voltage
is reached. Keep the multimeter within its range during these
measurements to prevent excessive overranging. Record these
readings on a data sheet and mark it "clean plate". Adjust the
HV output control for a current of 1 uA and rotate the probe so
the cover plate holes are in the gas stream.
A dust layer is then precipitated on the collecting electrode.
The proper operating current density required for the type of ash
being collected has to be experimentally determined. Thus the
first test may not be useful for obtaining data. The current den-
sity normally used should fall somewhere in the range between 0.2
and 2.0 piA/cm2 for this unit. If a high resistivity dust is en-
countered, reduced current densities may be necessary to obtain a
good layer. Use of the V-I curves will be explained later to
indicate how the proper current for precipitation may be found if
the original selected value proves to be insufficient. A current
of 1 uA, giving a current density of 0.2 uA/cm*, is a good place
to start the initial run. The voltage necessary to obtain this
current is in the vicinity of 15,000 V. Depending on the resis-
tivity of the dust being collected, the mass loading, and the
current density selected, it will take from about thirty minutes
to one hour io precipitate a sufficient sample of a thickness
between 0.5 and 1.5 mm.
* 396
-------
As a layer is being deposited, the current will begin to
drop. This current drop may be used to estimate the collection
time. When current drops significantly or if an hour has passed,
whichever comes first, the test may be stopped. If an insuffi-
cient sample was collected on a short time run, run longer the
next time no matter how the current happens to drop. After a
Sufficient sampling time has elapsed, turn the probe so that the
holes in the cover plate are perpendicular to the gas stream.
Now run a "dirty-plate" V-I curve using the same procedure as
that for the "clean-plate" V-I.
After completing the "dirty-plate" V-I, turn the high voltage
off by turning the control to zero and switching the power supply
off. Place the switch on the spark protector box to the 109 ft
resistor in the circuit and protect the multimeter from an over-
load current when lowering the sliding electrode with the voltage
on. Set the multimeter on the 100 nA range. Turn the voltage
supply on and adjust for a 100 V output.
Unlock and very carefully and slowly lower the sliding elec-
trode until the acme screw is engaged. Then turn the control
lowering the electrode until the multimeter indicates that elec-
trical contact with the dust layer has been made. Turn the control
knob one-quarter turn and lock into position. If the dust resis-
tivity is less than about 109 Q-cm, the multimeter should read
approximately 100 nA. For high resistivity dust smaller currents
will be obtained, the exact current depending on the thickness of
the dust layer and the resistivity- Mow set the multimeter on
the 1000 uA scale and switch the slide switch on the spark pro-
tector back to the normal position. If the power supply does not
indicate an overload (1 mA), "direct contact" can be taken.* in-
crease the voltage across the dust layer in 100 V steps. Read
and record the corresponding currents until a spark occurs across
the dust layer. This will be indicated by the voltmeter jumping
and an erratic reading on the multimeter.
Before starting another run the dust layer must be removed
by mechanically removing the dust. Remove the metal cover from
the discharge cell and clean the cell thoroughly. If saving the
sample for chemical analysis or some other reason is desired, a
sheet of paper placed under the disc will collect the sample when
the operating rod is pulled back to its up and locked position.
At this time the dust layer thickness may be examined to in-
sure the accuracy of the dial indicator. By utilizing an automotive
*0verloads frequently occur with high carbon content samples. The
carbon particles or similar type conductors provide a conducting
path between the disc allowing the full output current of the
power supply to flow. If a short is encountered, it is impossible
to obtain"data for determining the resistivity of the layer be-
tween the parallel discs.
397
-------
type metric feeler gauge the dust layer thickness'may; be" estimated
and compared to the dial indicator reading. The hole in the
sliding electrode leaves an area of uncompressed dust that was
protected from erosion when the probe was withdrawn from 'the flue,
and is an ideal point to gauge the thickness of the uncompacted
layer.
After cleaning, replace the metal cover on the. probe.' -Re-
turn the probe to the sampling port. 'While the"probe is returning
to the flue temperature make the calculations .from"'the rut* just
completed.
Operating outline-- The following outline summarizes the
steps to be taken in operating the point-plane resistivity probe.
1. Prepare sampling port.
2. Clean and align cell.
3. Lower disc and lock.
4. Check current continuity, slide switch in 109 position.
5. Insert into flue, with inlet holes 90 degrees to- flow,
and bolt to flange.
6. Allow cell to reach flue temperature.
7. Zero dial indicator.
8. Raise operating rod.
9. Run "clean-plate" V-I, switch normal position.
10. Turn inlet holes into flow.
11. Apply necessary voltage to supply precipitating current.
12. After desired length of time turn probe so inlet holes
are again 90 degrees to flow. (Leave high voltage applied,
so dust layer will not be shaken off in the turning process.
13. Run "dirty-plate" V-I.
14. Lower disc, in 109 position, voltage 100 V.
15. Record thickness of dust layer.
16. Apply voltage in 100 V steps until sparkover occurs, switch
in normal position.
17. Remove probe to remove collected dust.
18. Observe layer and save if needed.
19. Clean probe and check alignment.
20. Insert back into flue.
21. Make calculations.
Calculations A sample data sheet for a typical run is given
in Figure 232. All the information necessary for making the resis-
tivity calculations is given on this data sheet. The "clean" and
"dirty" plate V-I information should be graphically plotted. The
data on this data sheet is shown plotted in Figure 233.
The formula for calculating the resistivity is:
D = BA
p ~
or
398
-------
SRI POINT PLANE PROBE DATA
Location Power Plant Layer Thickness 1.0 mm
Time-0915 Data - 14 May 1973 Test No. A-6 Temp. 314aF (157°C)
Conditions Normal, full load 56 MW
Unit 1. Port 3
V-l DATA
KV | CLEAN | DIRTY
1
2
3
4
5
6
7
8
9
1.0 NA
0.25 MA
0.65 MA
1.15 MA
1.8 MA
10 2.6 MA
1.0 NA
0.1 MA
0.3 MA
0.5 MA
1.1 MA
1.65 MA
11 3.2 MA 2. 19 MA
12
13
14
15
16
17
18
19 :•
20
4.3 MA
5.1 MA
6.2 MA
7.1 MA
8.2 MA
9.8 MA
11.1 MA
.12.6 MA.
SPARK
2.8 MA
3.7 MA
4.2 MA
4.8 MA
5.6 MA
6.25 MA
SPARK '
SPARK DATA
V | ,
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
850
900
950
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
2300
2400
2500
2600
2700
2800
2900
3000
2.5 NA
5.0 NA
7.5 NA
10.0 IMA
13.5 NA
17.4 NA
23.6 NA
29.0 NA
39.5 NA
55.5 NA
70.5 NA
96.7 NA
0.14 MA
0.17 MA
E
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
6500
7000
0.23 MA 7500
0.36 MA 8000
0.46 MA j 8500
0.61 MA 9000
0.75 MA
1.0 MA
SPARK
9500
10.000
I
Figure 232. Sample data sheet for point-plane resistivity probe
399
-------
<
a.
c:
a
u
O CLEAN PLATE
DIRTY PLATE
J—I—I I I I I I. I.. I. I I I I I I .1 I I I I J.
10 12 14
•*- VOLTAGE, kV
Figure 233. V-I data obtained from point-plane resistivity probe.
400
-------
V x 5.00 cm2
P = I (cm)
where
p = resistivity (ohm-cm),
V
R = resistance =• (ohms) ,
AV = voltage across the dust layer (volts),
I = measured current (amps),
A = area of disc (5.00 cm2),
i = thickness of dust layer (cm).
The quantity A/I is called the cell factor. This factor will re-
main constant for the V-I or spark calculation for each individual
run. For different dust layers it is apparent that the cell factor
will change.
Example: Using the data from Figures 232 and 233, the fol-
lowing procedure shows how the resistivity is calculated. The
following data was obtained from the V-I curve in Figure 233.
V = AV = 850 V
I = 1.0 x 10~6 A
"£ = 1.0 mm =1.0 x 10"*' cm
The value AV is the voltage drop across the dust layer as
interpolated from the V-I curves at a current value of 1.0 x 10~6 A.
Certain considerations must be taken into account when obtaining
this voltage drop. The first is to look at the shape of the V-I
curve. There are. three basic shapes that may be encountered. Dia-
grams-A and B in Figure 234 illustrate two of these shapes.
In Diagram A, the point x shows the voltage at which elec-
trical breakdown .occurs in the dust layer. This would show the
. oas.et.of back corona, a characteristic of a high resistivity dust.
It will be incorrect in this case to use any of the current and
'voltage relationships above the point x for calculating resis-
tivity values.
This V-I curve may be used also to determine the operating
point for the next run. If the point x is located at a lower
current value than .the one selected for collecting the sample,
then there is a good chance that the sample was collected in a
back corona, situation. If this is the case then the current for
401
-------
GLEAN
DIRTY
CLEAN
3540-2:3
Figure 234. Two possible types of "dirty" V-I curves obtainable
with a point-plane probe.
402
-------
the next run should be backed off to the value of current that
corresponds to the point x. A more efficient collection should
be found at this setting.
In Diagram B, the "dirty-plate" curve is on the left side of
the "clean-plate" curve. This is a characteristic of either a
very high or a low-resistivity dust. Since the AV taken from the
curve will have a negative value, it will not be possible to use
the V-I procedure for resistivity calculations in this case.
Figure 233 is the third shape and it shows a standard curve.
The cell factor is the first calculation to be made. For
the sample case, the cell^factor is 50 cm and it comes from the
term A/£, where A is 5 cm2 and £ is 0.1 cm. The next step is
to find the resistance R of the dust layer. For this run, AV
is equal to 850 V, this was taken from the V-I graph at a current
of 1.0 x 10~6 amps. From this relation, R = AV/I, the resistance
is found to be 0.85 x 109 ohm. By multiplying the cell factor
by the resistance, a resistivity of 4.2 x 10 ohm-cm is obtained.
This complete calculation is:
p = A/£ x AV/I
or
5 cm: 0.85 x 103V
r 0.1 cm X 1.0 x 10~6A
p = 4.2 x 101° ohm-cm
After obtaining the resistivity from the V-I data, a check
of this value may be obtained from the spark data information.
The proper values to take^from the spark data information are the
last voltage and current reading before spark. In this case the
layer broke down at 1100 volts and the last reading before break-
down, was at 1000 volts with a current of 1.0 x 10" amps. Using
1;he following formula the resistivity data may be obtained:
p = A/?, x V/I
2 1.0 x 103V
p = 0.1 cm x 1-0 x 10-?A
p = 5.0 x 10'° ohm-cm
The column labeled "E" on the spark data sheet is for the
calculated electric field for the voltage applied and the thick-
ness of the layer. In this example, breakdown of the layer oc-
curred at an electric field of 10,000 volts/cm. When a series of
.measurements are made the resistivities should be calculated not
only at sparkover for each run,- but also af.:-a-fixed value of the
electric field. This will eliminate the electric field dependence
when compar ing run s.
403
-------
Cyclone resistivity probes The cyclone resistivity probe
measures the resistivity of a particulate sample that is extracted
from the effluent gas stream by an inertial cyclone collector.
The dust sample is deposited between two concentric cylindrical
measurement electrodes. The dust-laden gas sample is extracted
through a sampling nozzle by a pump into the cyclone separator
where the collected dust falls into the measurement cell. The
gas flow rate is adjusted to provide an isokinetic sample if de-
sired. The collection characteristics of the cyclone are such
that, even though the sampling system is operating isokinetically,
the dust sample collected is not identical with that in the gas
stream. Notwithstanding this, it is often desirable to use iso-
kinetic conditions.
By applying a voltage across the cell and monitoring the
current flowing through the cell, the filling of the cell can be
observed by the increase in current through the cell. When the
current levels off, the cell is- full and the sampling is stopped.
The current is then monitored until it stabilizes.
The resistivity of the sample is calculated from
P = KR , (31)
where R is the resistance of the dust layer (ohm) and K is a con-
stant for any particular cell (cm). The constant K is defined by
K • in Wr.) ' <32>
where
L = length of cell (cm),
n = radius of inner electrode (cm), and
1-2 = radius of outer electrode (cm) .
The Simon-Carves cyclone resistivity instrument, as described
by Cohen and Dickinson, is one of the more widely used cyclonic
devices.192 The sample collection and measurement cell is located
in a temperature controlled chamber as shown in Figure 235, external
to the duct, with the sample extracted through a sample probe. The
sampling line must be thermally controlled to preserve the flue gas
condition. The dust sample is compacted into the measurement cell
by the action of a vibrator.
A somewhat different design of this device is made to be in-
serted directly in the flue. The dust is collected and measured
while the device is retained in the flue gas environment.
404
-------
THERMOMETER
INLET FROM
SAMPLING PROBE
CYCLONE
HEATER
RESISTIVITY CELL
EXHAUST FROM
CYCLONE.
'CONNECTION TO
MEGOHMMETER
3540-224
Figure 235.
Resistivity apparatus using mechanical cyclone dust
collector (from Cohen and Dickinson).192
405
-------
The probe is operated In the following manner: it* is inserted
into the flue and permitted to come to thermal equilibrium with
the flue gas. A sample is then drawn through the apparatus by a
pump, and the gas flow measured. Isokinetic sampling can be
achieved by adjusting the flow so that the inlet velocity of the
gas to- the probe and the flue gas velocity are the same. A -vi-
brator attached to the probe is used to keep .dust from collecting
on the walls of the probe and to give uniform compaction. Figure
236 shows a schematic of;this instrument.193
The advantages of utilizing the cyclone probe for extractive
or in situ measurements are: (1) low voltage instrumentation may
be usecUf2) dust layer thickness is fixed by cell geometry, and
(3) the electric field is easily duplicated from test to test.
However, the following disadvantages exist: (1) the cylindri-
cal cell yields a nonuniform electric field, (2) the electrical
noise is unusually high, (3) it is.--d.ifficult to>'det ermine when
the sample cell is -full," • (4) compaction of the dust layer is not
reproducible, (5) the thermal control of the external model is
difficult, and (6) the values of resistivity obtained are un-
realistically high for electrostatic precipitator applications,
(7) particle size of dust is not representative, and (8) the dust
layer in the cell is not electrostatically deposited.
Kevatron electrostatic precipitator analyzer The Kevatron
resistivity device is designed to simulate in situ measurements
in an external thermally controlled cell.19" The sampling probe
is inserted directly into the flue gas for extracting an isokinetic
sample. The sampling line leads to a miniature wire-pipe type of
electrostatic precipitator, where the particulate material is col-
lected on the surface of the pipe. The collected dust layer is
removed from the pipe and deposited in a concentric cylindrical
measurement cell by removing the electrical energization and
applying an acceleration to the pipe. A schematic drawing of
the system is shown in Figure 237.
The particulate matter is in the flue gas environment throughout
the entire measurement period. The flue gas flows through the sampliw
lines and wire-pipe precipitator and exhausts to the atmosphere.
Provisions must be made to preserve the thermal conditions in the
flue duct through the sampling line to avoid upsetting the chemical
equilibrium conditions in the flue. Without this precaution, a
temperature drop in the sampling line may lead to an increased
absorption for any naturally occurring conditioning agents such
as sulfur trioxide and moisture in the effluent gas stream.
The instrument is designed to internally compute the resis-
tivity of the dust in the measurement cell, when used with the
graph paper supplied. The system projects a spot of light on the
graph grid, thus eliminating the computation of resistivity that
is required for other instruments. The measurement is conducted
406
-------
d
^
(D
O
-4
U)
cr>
O
'<;
o
i^
o
3
n>
o
tr
fD
en
CD
h(
rt
ro
TO VACUUM
PUMP
ELECTRICAL
CONNECTION
THERMOCOUPLE
PIPE
OUTER
ELECTRODE
CYCLONE / f TEFLON CELLX
COLLECTOR GAS INLET
-VIBRATOR
CENTER
ELECTRODE
S. S. LINER
3540-225
o
-------
TEMPERATURE
CONTROLLER
TEMPERATURE
CONTROLLER
i
PRECIPITATION
CHAMBER
-4-
RESISTIVITY
CHAMBER
ELECTROMAGNETIC
'COMPACTOR
1640-226
Figure 231. Kevatron resistivity probe (from Tassicker, et al)
408 .
-------
with applied voltage of 3, 30, or 300 volts across an electrode
spacing of 0.2 cm for electric fields of 15, 150, or 1500 volts
per centimeter, respectively.
The advantages of utilizing the Kevatron probe for resistivity
measurements are: (1) the resistivity is internally computed,
eliminating field calculation, (2) clean electrode and dust covered
electrode voltage-current curves can be obtained, and (3) some
variation in electric field is allowable in the measurement.
However, the following disadvantages exist: (1) the equip-
ment is very heavy and bulky, difficult for field work, (2) sampling
lines require temperature control, (3) mirror alignment in resis-
tivity computation is critical, (4) particle size of the cast is not
representative, (5) density of dust in the cell is not reproducible,
(6) dust is not deposited in the cell electrostatically, and (7)
resistivity values can be unreasonably high.
Lurgi electrostatic collection resistivity device The Lurgi
Apparatebau-Gesellschaft mbh in Frankfurt, Wes't Germany, developed
an in situ resistivity probe described by Eishold, consisting of
two corona wire electrodes equally spaced from an interlocking
comb arrangement as shown in Figure 238. 195 This device is in-
serted either directly into the flue duct for in situ measurements
or into a thermally and environmentally controlled chamber for
simulated in situ laboratory measurements.
The dust is collected on the interlocking comb structure by
electrostatic forces. The dust layer forms on the surface of the
comb structure and fills the region between the two comb segments.
After the sample is collected, a potential is applied across the
dust layer. The configuration of the cell (the cross-sectional
area and spacing between the electrodes) is such that the resis-
tivity of the sample is ten times the measured resistance. This
factor of ten is based on neglect of any electrical fringing through
the adjacent fly ash. The measurements are made using an ohm-meter
without specifying the electric field at which the measurements are
made.
Comparison of in situ resistivity probes The resistivity
probes previously described differ primarily in the manner of col-
lection of the dust particles from the gas stream, the manner of
dust deposition in the measuring cell, the cell geometry, and the
electrical conditions during measurement.
Because of the nature of the collection devices, the size
distributions of the particles in the samples are not representa-
tive of the size distribution of the dust particles in the duct.
Neither the cyclone nor the electrostatic devices are efficient
collectors of fine particles, so the particle size distribution
in the resistivity sample is biased toward the larger particles.
This condition can cause some variation in the results obtained
with different devices.
409
-------
3540-227
Figure 238. Lurgi in situ resistivity probe.
1 9 5
410
-------
A second difference in the resistivity probes is the manner
of depositing the dust in the, measuring cell. The point-plane
probes and the Lurgi probe deposit the dust electrostatically
onto the surface of the measuring cell. Consequently, some align-
ment of the dust particles occurs and in general the deposited
dust layer is more dense than that in the other types of measure-
ment apparatus. The effect of alignment on dust resistivity has
not been quantitatively determined. However, variations in den-
sity can influence resistivity values by as much as 10-fold, as
reported by Cohen and Dickinson.192
A third difference in the resistivity probes is the value of
the electric field at which resistivity is measured. Standard
procedures for the Kevatron and Simon-Carves probes are to measure
resistivity at relatively low electric fields. By contrast, the
procedure for the point-plane probe is to measure the resistivity
at a field near breakdown. As a consequence, the values of resis-
tivity as measured by the different methods vary by as much as an
•order of magnitude due to electric field differences.
The combined effect of these variables is that the resistivity
values reported by investigators using different techniques vary
widely. Upper values of resistivity measured by a point-plane
probe in the vicinity of 1012 to 10 ohm-cm have been reported,
whereas upper values of 10ll4 to 10 15 ohm-cm have been reported by
other techniques.
There have been no definitive studies to compare results of
resistivity measurements by the various devices. However, limited
studies have been conducted at electric power generating plants
using the instack cyclone, Kevatron, and point-plane probes.195
Resistivity values measured by these probes are compared in Figures
239 and 240. Figure 239 shows the settled-out cyclone data plotted
against the point-plane data, using the point-plane data at 2.5
kv/cm, which" corresponds to the field in the cyclone apparatus.
Figure 240 shows the peak values of resistivity from the
Kevatron and cyclone probes plotted against point-plane'data from
the same (2.5 kV/cm) field. In this case, much better agreement
is obtained between the cyclone and point-plane data. The Kevatron
data are still higher than the average of the cyclone or point-plane
data, although there are statistically insufficient data to draw
firm conclusions regarding the Kevatron values. The logic of com-
paring the peak values of resistivity from the cyclone with the
point-plane data can be rationalized to some extent by the fact that
fresh dust is being deposited on the surface during the precipita-
tion process. In view of the scatter of the data obtained with
any one probe, the discrepancies shown in Figures 239 and 240 are
not unexpected.
LIMITATIONS DUE TO NON-IDEAL EFFECTS
411
-------
T013
u
10"
e
z
o
ec
Q
Z
w io9
O
O
>
108
O O n-'
PERFECT CORRELATION LINE
I
O CYCLONE
ft KEVATRON
I I
109 1010 1011
POINT-PLANT RESISTIVITY, OHM-CM
3640-128
Figure 239.
Comparison of Kevatron and cyclone resistivities with
point-plane resistivities at an electric field of 2.5
kV/cm. Settled values for cyclone peak values for
Kevatron.196
412
-------
1014
103 109 1010 1011 1012
POINT-PLANE RESISTIVITY, OHM-CM
13
10
3 5 4 0 -2 2 9
Figure 240.
Comparison of Kevatron and cyclone resistivities with
point-plane resistivities at an electric field of 2.5
kV/cm. Peak current values used for Cyclone and
Kevatron.
1 9 6
413
-------
Gas Velocity Distribution
General Discussion—
Nonuniform gas velocity distributions result in reduced pre-
cipitator performance due to (1) uneven treatment of particles in
different velocity zones, (2) possible reentrainment of collected
particles from the plate surfaces and hoppers in regions of high
gas velocity, and (3) a possible nonuniforrn' particulate mass loading
distribution entering the precipitator, resulting in excessive dust
accumulation in certain regions of the precipitator. The uniformity
of the gas velocity distribution entering a precipitator is in-
fluenced by (1) the configuration and location of turning vanes,
(2) the location and types of diffuser elements, such as grids and
perforated plates, (3) the ductwork design, and (4) coupling of the
precipitator to the draft fan.
Detailed information on the description, effects, and control
of the gas flow distribution can be found elsewhere in the liter-
ature. :97'l98'!99 Methods and devices for controlling the gas
flow distribution have been discussed earlier in this text. Now,
some major points of interest concerning the gas flov; distribution
will be discussed. These include criteria for determining a good
flow distribution, measurements of gas flow distributions associated
with full-scale precipitators, and the effect of gas flow distri-
bution on precipitator performance.
Criteria for a Good Gas Flow Distribution—
Good uniformity of the gas velocity distribution must be
achieved in order to attain the present requirements of high col-
lection efficiencies (99.5-99.9%) with a minimum in precipitator
size. To be meaningful, the criteria for an acceptable gas velocity
distribution must be stated in terms of measurable quantities. In
1965 a definition of an acceptable deviation from an ideal gas dis-
tribution was introduced by the Industrial Gas Cleaning Institute
(I.G.C.I.), which states:
"Uniform gas distribution shall mean that a velocity
pattern five feet or less ahead of the precipitator
inlet flange shall have a minimum of 85% of the
readings within + 25% of the average velocity in
the area with no reading varying more than + 40%
from the average."200 ~
The above criteria are the most widely used at the present
time. However, some power companies have specified even more
stringent criteria for an acceptable gas distribution at the in-
let of a precipitator; for example:
"A minimum of 8% of the readings within + 10% of the
average velocity and no reading varying more than +
20% from the average."199
414
-------
At the present time, I.G.C.I.'s Committee on Gas Flow Model
Studies is in the process of preparing a new more detailed set
of criteria for an acceptable gas velocity distribution. These
criteria include a restated velocity distribution pattern, an
R.M.S. deviation criteria, and limitations on gas velocity
deviations between individual chambers of large precipitator
installations.
Field Experience with Gas Flow Distribution—
A particular case history which has been reported demonstrates
many of the important aspects associated with gas flow distribu-
tion and precipitator performance.198 In this case, an electro-
static precipitator installed on a 500 MW tangentially-fired
steam generator burning coal was to collect 99.5% of the fly ash
entrained in the flue gas emanating from the combustion process.
The installations reported had the following specifications:
collection efficiency of 99.6%, treated gas volume flow of 723.5
mVsec (1,530,000 acfm) at 126°C (260°F), collecting plate area of
25,154 m2 (270,400 ft2), specific collection area of 35 m2/(m3/sec)
[178 ft2/1000 acfm], and coal with an ash content of 12% dry basis
and with a sulfur content of 3.65% as-fired. The efficiency
achieved during the first three years of operation was measured
several times and ranged from 98.8 to 99.1%. Mechanical remedies,
electrical remedies, and gross gas flow corrections were attempted
without improving the performance. Finally, an in-depth study of
the gas flow distribution revealed serious problems which were
limiting performance.
Figure 241 is a side elevation of the entire precipitator
complex for Unit A. Gas leaves the LjungstromR air preheater and
is divided between the two precipitators of the double deck in-
stallation. During initial operation, gas-flow traverses were
conducted to determine the gross division of gas between the pre-
cipitators. Detailed velocity traverses were also conducted .in
the vertical outlet flue leaving the upper precipitator, and in
the inlets to the i.d. fans. The gas flow passing through the
lower precipitator was determined by subtracting the measured
gas flow leaving the upper precipitator from the measured gas flow
entering the induced draft (i.d.) fan inlets. These initial tests
showed that approximately 54.5% of the gas was going through the
lower precipitator with the remainder going to the upper precipi-
tator. Based on the recommendation of a model study, a perforated
plate was installed in the vertical portion of the flue just before
the turn into the lower precipitator. The turning vanes (Figure
241) shown in the inlet to the upper and lower precipitators and
in the-outlet of the upper precipitator also were installed based
'on recommendations from this same model study.
:; The velocity traverses conducted at the inlets to the i.d.
.fan .also revealed a lateral imbalance of gas flow across the
precipitators. Figure 242 shows the results of these tests. The
415
-------
AIR
HEATER
PERFORATED PLATE
RECOMMENDED AFTER
ORIGINAL START-UP
TO BALANCE GAS FLOW
1 /
"PR /
cn /
LOW -1
7
L
.
r.
_
>f
u\
L\
/
/
LOWER
ELECTRO-
STATIC
PRECIPITATOR
vw
ORIGINAL VANES - TYPICAL
-,INOTTO SCALE)
3540-230
Figure 241. Side elevation of electrostatic precipitator
198
416
-------
FLOW
310,230 ACFM @ 255°F
M46.4 m^'sec @ 124°F)
407,560 ACFM.@ 271°F
(192.4 mS'sec <3> 133°C)
1301,440 ACFM @ 233°F
(142.3 m3/sec @ 112°F)
40T,930 ACFM @ 231°F
(189.7 m^/sec @ 111°C)
3540-231
Figure 242.
Gas-flow imbalance, outlet flues and i.d. fans
(Unit A).198
417
-------
north i.d. fan was receiving 9% more flow than the south but,
more importantly, the inboard legs of each fan received more
flow than the outboard legs. Finally, when dust samples were
taken in the inlet to each i.d. fan :to '.check performance, it was
found that 88% of the total dust collected in each inlet was .col-
lected in sample port $1 as- noted in Figure- 243.
Based on this .history .of.gas-flow related.problems, a de-
cision was made to conduct detailed field evaluations. As shown
in Figure 244, four 20 cm (eight-inch) diameter observation ports
were installed in the roo.f and side wall of the lower precipitator
on the north side of the unit. The system was operated at full
load and high intensity lights were used to illuminate the gas
flow zones of interest through these ports. These observations
pointed out dramatically the effects of poor gas flow distribution
on precipitator performance. Although initial short term obser-
vations showed no apparent problems, extended observations re-
vealed that huge clouds of dust would suddenly appear in the
lower precipitator outlet. Careful observation of this phenom-
enon revealed that these eruptions were occurring only in limited
areas of the precipitator, and usually occurred when one or more
collecting electrodes in these areas were being rapped. At first,
it was thought that plate rappers were occasionally rapping entire
precipitator lanes at once, but this proved not to be the case.
The dust eruptions would occur only when the plates in the im-
mediate vicinity of either of the i.d. fan inlet boxes were rapped.
To further define the problems observed through the observa-
tion ports, the unit was taken out of operation and detailed
internal inspections of both the inlet and outlet flues of each
precipitator was made. A skilled observer, by careful observa-
tion of polishing and deposition on internal pipe struts, vanes,
and dampers, can define areas of flow separation, reverse flow,
and extremely high or low velocity in great detail. The flow
arrows shown in Figure 244 show the result of this type of flow
mapping. The inlet and outlet of the upper precipitator showed
no unusually high or low velocity zones. The situation for the
lower precipitator was quite different. Several feet of fly ash
were found in the bottom of the flue entrance of the lower pre-
cipitator, with the two lowest turning vanes actually buried in
fly ash. The outlet flue of the lower precipitator also exhibited
areas of high velocity (evidenced by dust erosion) and dust drop-
out. In an area approximately four precipitator ducts wide,
adjacent to the outboard leg of the north i.d. fan, the surfaces
of the collecting eleectrodes had been swept clean by the high-
velocity jets created by the pressure gradient of the i.d. fan.
A similar situation existed opposite the inboard leg of the same fan.
Also, hopper sweepage and subsequent drifting of fly ash into the out-
let flue were evidenced. Previous experience had indicated that
velocities of 3.05 to 4.57 m/sec (10 to 15 ft/sec) would be required
to produce the collecting electrode polishing observed. These phenom-
ena were repeated in the south half of the precipitator, but the
418
-------
8 SAMPLE PORTS
EQUAL SPACES
88% OF TOTAL
DUST TO FAN IS
MEASURED HERE
3540-232
Figure 243. Side elevation of i.d. fans (Unit A).
1 9 8
419
-------
3540-233
Figure 244. Gas-flow patterns, plane view of outlet flues
(Unit A) .198
420
-------
problems appeared less severe because of the lower gas flow through
that half of the installation.
Based on the results of the on-line observations and off-line
inspection, it was obvious that the gas flow problems in this unit
were a major contributing factor to its deteriorated performance.
Since the original model study of this installation did not reveal
any of the problems just described, it was decided that a complete
velocity traverse of the inlets to both the upper and lower pre-
cipitators would be conducted. This information could then be
used to check the as-built model results to insure an accurate
representation of the problem. Because of limited unit avail-
ability, the field velocity traverses could not be conducted on
Unit A. They were, however, conducted on Unit B, a duplicate of
installation A, which also had experienced performance problems of
the same nature as Unit A. A quick walk-through of Unit B was
conducted to ensure that the problems observed in Unit A were
evident in Unit B. Unit B was then thoroughly cleaned before
attempting to perform the field velocity traverses so that the
traverses would be indicative of a new system.
A heated thermocouple anemometer was used to obtain velocity
data. The anemometer was traversed down the first two discharge
electrodes of every fourth precipitator duct. Selected traverses
were also obtained in the outlet of each precipitator. Figure
245 shows a sample of the data obtained from one precipitator duct.
The unit was operated on cold air at approximately 60% of
design velocity. This provided a Reynolds Number approximately
equal to that which would be seen under actual full lead operation.
Figure 246 is an example of a typical field velocity profile after
the velocity had been corrected back to a linear scale. Once all
the data curves had been linearized, they were reduced to numerical
form. An overlay grid was prepared of twenty equally spaced lines
representing precipitator elevations. The overlay was placed over
each linearized velocity profile and the value of the velocity
profile at each evaluation was recorded as a point velocity. These
velocity data points were then numerically averaged to establish
an average vertical and horizontal velocity profile for each pre-
cipitator.
Figure 247 illustrates a simplified side elevation view of
the upper and lower precipitators showing the average vertical
inlet velocity profile for each as obtained from the field test.
It is important to note the skewness of the velocity profile in
the lower precipitator and the imbalance of flow between the upper
and lower precipitators. Approximately 58% of the gas was passing
through the upper precipitator with the remainder passing through
the "lower. It should also be noted that this imbalance was not
completely detrimental since previous field tests had indicated
that 80 to 90% of the dust went to the lower precipitator. If
the design velocity had actually been met, the high velocity zones
421
-------
TOP
r
VEL F.P.M.
(m/rnm)
• 200 250 300 350
(61) (76) (91) (107)
aOTTOM
3540-234
Figure 245. Lower precioitator inlet velocity profile duct 68
— *• 1 rt ft
as measured with continuous traverse (Unit B).
196
422
-------
FLUE
OPENING
GAS
FLOW
cr
, SUPPORT
STRUT
TYPICAL
VELOCITY
PROFILE
PERFORATED
PLATE
VAVG
COLLECTING ELECTRODE
3540-235
Figure 246.
Typical measured velocity profile, as installed
lower precipitator inlet (Unit B).198
423
-------
FLOW
UPPER
PflECIPJTATOR
VAVG = 1-48 m/sec
VDESIGN = T-7
' I i ' I I I < I i
0.3 0.5 0.7 0.9j 1.1 1-3 1.5
V
VAVG
VAVG = 2-°
VDESIGN = 1-74 m/sec
LOWER
PRECIPITATOR
I < I i ! i I I.I.I
0.3 0.5 0.7 0.9 1.1 1.3 1.5
3540-236
Figure 247. Average inlet velocity side elevation profiles
as installed (Dnit B).198
424
-------
in the lower precipitator would have further reduced the effici-
ency of the overall system.
Figure 248 demonstrates the dramatic effect that the outlet
flue has on the velocity profile leaving the lower precipitator.
This points out the condition that had to be eliminated if re-
entrainment and hopper sweepage in the lower precipitator were
to be eliminated.
Figures 249 and 250 detail the statistical distribution of
the data points taken in the upper and lower precipitators and
compare these results with those recommended by the IGCI. The
vertical bars of these histograms represent the percentage of
the data points occurring at each velocity. The actual velocity
values have been normalized (divided by the average velocity),
following standard practice. As can easily be seen, neither
precipitator meets the IGCI requirements, with the upper precipi-
tator approximately two times better than the lower precipitator.
A model study in conjunction with the field data resulted in
the correction of several mechanical defects in the existing flow
devices and in the addition of new flow control devices. The
precipitator and flue inlet perforated plates had been installed
in panels 91.5 cm (3 feet) to 122 cm (4 feet) wide by 305 cm
(10 feet) high. These panels had been clipped together for align-
ment to maintain the effect of a large single-piece perforated
plate. Some clips had not been installed while others had broken
loose permitting the adjacent plates to buckle over their 305 cm
(10 ft) height. Where a 2.54 cm (1 inch) gap had been desired,
gaps of 10.16 to 20.32 cm (4 to 8 inches) were found. Gaps of
this type were found in both the inlet flue and precipitator per-
forated plates. This is not uncommon; this particular type of
erection defect has been found in many installations. The gaps
were oriented such that they accounted for the high flows measured
in several of the ducts.
A gap in the flue perforated plate created a jet that moved
northward between the two sets of perforated plates.' This jet
then responded to a combination of a gap in the precipitator inlet
perforated plate and the effects of the north i.d. fan to create
a high velocity in one of the ducts. Similarly, high velocities
measured in three other ducts were created by a 10.16 cm (4 inch)
gap between the end of the flue and precipitator perforated plate
and the north wall of the flue. This gap was the result"of
cumulative inaccuracies in hanging the plate panels.
•"All the perforated plate panels, both flue and precipitator
inlet, were rehung, aligned, and clipped so as to present a flat
plate structure to the gas flow. These corrections improved the
gas flow distribution and brought field and model data into agree-
ment.. ... Based on the'.agreement between field",and-model data, a model
Study could then be performed to determine the design of new flow
425
-------
FLOW
UPPER
PRECIPITATOR
—•*-"
-------
AVG
20
181-
±25%
ACTUAL DATA = 72%
IGCI REQUIREMENT = 85%
±40%
ACTUAL DATA = 52%
I IGCI REQUIREMENT = 100%
RMS DEVIATION
38%
0.2
0.4 0.6 0.8 1.0 1
NON-DIMENSIONAL NORMAL
2 1.4 1.6 1.8
COMPONENTS (V/VAVG)
2.0 2.2_
3540-238
Figure 249
Histogram analysis of upper precipitator inlet
velocity measurements (Unit B).19
427
-------
MVL)
±25%
ACTUAL DATA = 35%
IGCI REQUIREMENT = 95%
ACTUAL DATA = 50%
IGCI REQUIREMENT = 100%
RMS
DEVIATION
45%
0.2
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
NON-DIMENSIONAL NORMAL COMPONENTS (V/VAVG)
S540-JS9
Figure 250. Histogram analysis of lower precipitator inlet
velocity measurements (Unit B).19
428
-------
corrective devices and produce an optimized flow field in the
precipitators.
Because of the very close coupling between the Inlet-flue
expansion turn and the precipitator, it was decided that "ladder
vanes" would be used to replace the inlet radius vanes. Ladder
vanes are a series of flat surfaces that are oriented perpendicular
to the direction of the turn inlet gas flow. The optimum position-
ing of these vanes can only be done under actual flow conditions
or in a model. The model study also indicated that the floor of
the lower precipitator inlet flue would be subject to potential
fly ash dropout. It was, therefore, recommended that a dust
blower be installed in this area to keep the flue clean.
A major problem that still remained was the correction of the
lower precipitator outlet-gas-flow distribution. The upper pre-
cipitator outlet flue did not have to be changed 'once the inlet
flue was corrected. The lower precipitator outlet was still ex-
periencing both vertical and lateral gas-flow problems. It was
again confirmed that this was the result of the close coupling of
the lower precipitator to the i.d. fans.
It was felt that, if a pressure-drop device could be placed
at the lower precipitator outlet, a satisfactory decoupling of the
i.d. fan and the precipitator could be obtained. The installation
of a perforated plate at the lower precipitator outlet was rejected.
It was known that perforated plates installed at the precipitator
outlet tended to plug due to the electrically grounded plate col-
lecting the residual dust leaving the precipitator. Completely new
rapping systems would have to be installed to keep this perforated
plate clean. The solution was to install vertical structural
shaped channels of standard dimensions, which would then form
continuous vertical slots that would not plug. This satisfactorily
decoupled the i.d. fan from the precipitator. The vertical slots
were lined up with the center line of the precipitator ducts.
The net free area required was found to be 15% open. The net
result of the above, "i.e., the removal of the inlet flue flow
biasing perforated plate, the installation of the inlet ladder
vanes, and the installation of the 15% open "picket" fence^at the
lower precipitator outlet, produced a flow distribution slightly
biased to the lower precipitator. The resultant corrected 'flow
patterns are shown for the lower precipitator inlet in Figure 251
and the lower precipitator outlet in Figure 252. The gross improve-
ment is noted when compared to Figures 247 and 248.
Because of the favorable results obtained from the model study
and from mathematical predictions of an improvement in precipitator
efficiency to 99.76%, the full-sized flues were modified' in accor-
dance ,with the model recommendations. The corrections were first
made on Unit B, including the complete rehanging of the inlet
perforated plates. Once this was completed, a fans-running walk-
through inspection was performed. No evidence of high-velocity
429
-------
VERTICAL
GAS FLOW
DISTRIBUTION
o . o '
LOWER PRECIPITATOR INLET
MODEL
CORRECTED
0.8 0.9 1.0 1.1 1.2
8840-240
Figure 251,
Vertical gas flow distribution
inlet — model corrected.198
lower precipitate:
430
-------
MODEL
CORRECTED
VERTICAL
GAS FLOW
DISTRIBUTION
LOWER PRECIPITATOR OUTLET
0.6 0.8 1.0 1.2
3540-241
Figure 252.
Vertical gas flow distribution lower precipitator
outlet -- model corrected.198
431
-------
jets or hopper sweepage could be .found.
Mass efficiency tests were performed on Unit A. The un.it had
been permitted to operate for at Least" one month after the flow
device modifications were made before testing. . Three performance
tests were run. All three tests produced results equal to or'better
than dust collection efficiencies which were required.
The case history just described points out the severe effect
that poor gas flow distribution can have on precipita tor'performance
several possible causes of poor gas flow distribution, devic.es
utilized to control the gas flow distribution, and remedies for
certain specific problems. The studies performed demonstrate that,
if poor gas flow distribution is a contributing factor to poor pre-
cipitator performance, the extent of the problem can readily be
evaluated and appropriate remedial actions taken. The studies also
point out the need for (1) careful design in integrating flues,
flow control devices, precipitators, and i.d. fans, (2) careful
mechanical construction, and (3) model studies of gas flow to
assist in design and troubleshooting.
Figure 253 illustrates the direction of gas flow and precipi-
tator arrangement (chevron) at a second installation where gas
velocity distribution measurements have been made and analyzed.138
Each precipitator consists of two collectors in series, each of
which has 144 gas passages, with 0.229 m plate to plate spacing
(9 in), 9.14 n\ high plates (30 ft), and 5.45 m in length (18 ft).
Thus, each precipitator consists of 144 gas passages 9.14 m high
(30 ft), 10.97 m long (36 ft), for a total collecting area of
28877 m2 (311,000 ft$) per precipitator. The precipitators each
have twelve electrical sections arranged in series with the gas
flow, such that the individual sections power 1/12 of the plate
area and 1/12 of the length. Gas flow at full load (^700 MW) for
each precipitator is about 520 m3/sec (1.1 x 106 cfrn) at 149°C
(300°F). The specific collecting area at these conditions would
be 55 m2/(m3/sec) or 283 ft2/1000 cfm.
Velocity measurements were obtained from Unit A between the
third (C) and fourth (D) sections from an I beam located approx-
imately 2.44 m (8 ft) from the top of the precipitator housing.
Air flow was set at 2.6 x 106 kg/hr (5.7 x 106 Ib/hr), which cor-
responds to full load conditions. Although the unit had been
washed, considerable amounts of suspended and attached dust were
present when the measurements were made. The velocity measure-
ments were made with a thermal anemometer. The anemometer was
calibrated to the "T" position frequently, but the dust concentra-
tion may have been sufficient to influence somewhat the data
obtained with this instrument. The anemometer probe was main-_
tained perpendicular to the gas stream by an aluminum guide which
was held in position by the collecting electrodes. Considerable
short term variation of velocity with time was noted at each point,
and an attempt was made to obtain the time-averaged value at each
432
-------
FLOW
3 i4 0-2 11
Figure 253. Precipitator layout for installation with chevron
arrangement.13 8
433
-------
point. The time of observation at each point was generally less
than 30 seconds. e
Table 28 shows the data obtained from measurements in several
lanes (ducts). Standard statistical calculations on the data
from the rectangular traverse from 0.9-2 m (3 ft), to 9.2 m (30 ft)
from the baffle on lanes 1, 12, 24, 36, and ,47'ar-e shown in Table
29. Note however that the maximum-and minimum'velocities occur
15.24 cm (6 in) and 0 cm (0 in) from the baffle and therefore are
not included in the standard traverse. Thus, the variance is
possibly worse than calculated. Also note that the high velocities
are at the top and bottom, thus inducing greater gas sneakage than
might otherwise occur.
As a cross check, the profiles were plotted with an intention
of using planimeter integrations to determine a better mean velo-
city than the arithmetic mean of a rectangular traverse. In the
raw data, there are some anomalous points that make it difficult
to draw a consistent curve for each lane. However, by averaging
at each elevation across all lanes and omitting the most severely
anomalous points, it was possible to obtain an average profile
for the left, center, and right sections as well as for the entire
unit.
Similarly, the squares of the profiles were constructed and
their mean values determined by the use of the planimeter. Then
the standard deviations were calculated as follows:
0 = - = * *£-= - l"-^ ' ' (33)
where
o = standard deviation,
x = value of variable at a point,
N = total number of measurements,
a = lower limit on region containing the variable, and
b = upper limit on region containing the variable.
The analysis obtained with the planimeter is also shown in Table 29.
By comparison, the arithmetic means lie within 1% of the
planimeter means and the coefficients of variance lie within 50%
of those determined by planimeter. Note that the determination
of the mean square by planimeter is not very accurate because
the averaging over each elevation is poor (the square of the
average is not the average of the squares) and because of the
subjective nature of the fit of the curve to the points. The
standard deviation and coefficient of variance can be expected
434
-------
TABLE 28. VELOCITY DISTRIBUTION FROM UNIT A OF CHEVRON ARRANGEMENT
(Obtained on I Beam between 3rd and 4lh field in direction of flow)
LOCATION FROM TOP
OF BAFFLF., FT. (m) VELOCITY FT./MTN (m/min)
LANE 81L lANE tt12L IANE J.24L LANE 8361, LANE #47L LANE 81R LAND 812R LANE 824R **
0 (0) 18(5.5) 15(4.6) 18(5.5) 18(5.5) 18(5.5) 35(10.7) 20(6.1) 15(4.6)
1/2 (.15) 60(18.3) 210(64.) 260(79.3) 150(45.8) 350(106.8) 450(137.2) 410(125.) 350(106.8)
3 (.92) 250(76.2) 185(56.4) 220(67.1) 240(73.2) 300(91.5) 350(106.8) 330(100.6) 300(91.5)
6 (1.83) 300(91.5) 185(56.4) 265(80.8) 250(76.2) 340(103.7) 370(112.8) 290(LiJ.4) 320(97.6)
9 (2.75) 255(77.8) 160(48.8) 230(70.2) 185(56.4) 250(76.2) 80(24.4) 240(73.2) 280(85.4)
w 12 (3.66) 183(55.8) 150(45.8) 170(51.8) 140(42.7) 270(82.4) 340(103.7) 200(61.) 210(64.)
ui
15 (4.58) 146(44.5) 135(41.2) 135(41.2) 125(38.1) 240(73.2) 320(97.6) 170(51.8) 175(53.4)
18 (5.49).. 135(41.2) 130(39.6) 150(45.8) 155(47.3) 215(65.6) 300(91.5) 180(54.9) 180(54.9)
21 (6.41) 155(47.3) 175(53.4) 175(53.4) 190(58.) 200(61.) 280(85.4) 240(73.2) 190(58.)
24 (7.32) 135(41.2) 148(45.1) 50(15.2) 240(73.2) 200(61.) 280(85.4) 240(73.2) 190(58.)
27 (8.24) 140(42.7) 170(51.8) 170(51.8) 200(61.) 205(62.5) 200*{61.) 250(76.2) 250(76.2)
30 (9.15) 155(47.3) 190(58.) 170(51.8) 240(73.2) 230(70.2) 320M97.6) 300(91.5) 320(97.6!)
* Change to Lane 2R
** Sneakage above the plate hangers 25 ft./min (7.63 m/min) 45° from normal flow, one foot above
wire hanger
-------
*»
U>
LOCATION FROM TOP
OF BAFFLE, FT. (m)
TABLE 23. (CONTINUED)
VELOCITY FT./MIN (m/min)
0 (0)
1/2 (.15)
3 (.92)
6 (1.83)
9 (2.75)
12 (3.66)
15(4.58)
18(5.49)
20(6.10)
21(6.41)
24(7.32)
27(8.24)
29(8.85)
30(9.15)
LANE tt36R
20(6.1)
400(122. )
300(91.5)
280(85.4)
180(54.9)
220(67.1)
200(61. )
180(54.9)
180(54.9)
190(58.)
190(58. )
330(100.6)
LANE #47R
20(6.1)
70(21.4)
310(94.6)
280(.85.4)
270(82.4)
220(67.1)
190(58.)
180(54.9)
230(70.2)
230(70.2)
250(76.2)
230(70.2)
*Sneakage above electrode hanger 35 ft./min
LC30 150 ft./min., LC36 45 ft./min.
HOPPERS-RIGHT
CHAMBER
LANE if LCI*
35(10.7)
300(91.5)
230(70.2)
240(73.2)
220(67.1)
195(59.5)
200(61. )
190(58.)
190(58.)
170(51.8)
180(54.9)
220(67.1)
. , 8 rows
LAME flLC!2
15-20(4.6-6.1)
300(91.5)
250(76.2)
230(70.2)
190(58.)
190(58.)
170(51. 8)
170(51.8)
160(48.8)
150(45.8)
210(64. )
250(76,2)
down 150 ft./min
LANE ILC24
15(4.6)
340(103.7)
270(82.4)
280(85.4)
230(70.2)
200(61.)
140(42.7)
170(51.8)
40(12.2)
230(J0.2)
240(73.2)
300(91.5)
•
LANE #LC36
20(6.1)
450(137.2)
310(94.6)
290(88.4)
200(61. )
190(58.)
190(58. )
180(54.9)
250(76.2)
230(70.2)
280(85.4)
300(91.5)
LANE #LC48
100(30.5)
400(122. )
280(85.4)
270(82.4)
270(82.4)
250(76.2)
260(79.3)
280(85.4)
280(85.4)
300(91.5)
290(88.4)
370(112.8)
Row 12 3 ft. (0.92 m) below plate
Row 24 3 ft, (0.92 m) down
Row 36 3 ft. (0.92 m) down
Row 48 3 ft. (0.92 m) down
40 ft./min. (12.2 m/min)
40 ft./min. (12.2 m/min)
50 ft./min. (15.2 m/min)
40 ft./min. (12.2 m/min)
-------
TABLE 29. STATISTICAL EVALUATION OF VELOCITY
DISTRIBUTION FROM UNIT A OF CHEVRON
ARRANGEMENT
Standard Statistical Calculations
Standard
Coefficient of Variance
Left
Center
Right
Average
Left
Center
Right
Average
Mean
192.6
227.5
246.7
222.3
Mean
191
229
245
221
Deviation (S.D.)
54.7
56.5
61.5
61.5
Planimeter
Standard
Deviation (S.D.)
36.6
88.5
79.4
44.1
S.D. /Mean
.284
.249
.249
.277
Analysis
Coefficient of Variance
S.D. /Mean
.191
.386
.324
.200
437
-------
to be small for the average because averaging reduces the effect
of peaks and valleys. However, the standard deviation of two of
the three groups of data are higher' in the calculation by plani-
metry because the high values at 15.24 cm (6 in.) from the baffle
are included.
Although some improvement could be obtained through corrective
measures, this gas velocity distribution is fairly good. Since the
precipitator could achieve a collection efficiency in excess of
99.5% with an average current density of 20 nA/cm* (21.5 u'A/ft2),
the gas velocity distribution was probably not a serious factor
in limiting precipitator performance. The only bad feature of
the distribution is the location of the peak velocities at the
top ^and bottom baffles. This'might-tend to increase gas sn.eakage
past the electrified regions.
Figure 254 illustrates the direction of gas flow and pre-
cipitator arrangement at a third installation where gas velocity
distribution measurements have been made and analyzed.201 The
electrostatic precipitator consists of three fields in the direc-
tion of gas flow. The precipitator is physically divided into
two collectors (A & B). The test program was performed on the
"A" side of the precipitator. The total collecting area for the
"A" side is 7,374.4 m2 (79,380 ft2), 2458.13 m2 (26,460 ft2) per
field. This gives a specific collection area of 34.475 m2/(m/sec)
(175 ft2/1000 cfm) for the design volume flow of 213.82 m3/sec
(453,000 acfm) per collector. Each collector has three double
half-wave transformer rectifiers, one per field. The precipitator
has 27.94 cm (11 in.) plate spacing and operates at approximately
149°C (300°F). The emitting electrodes are square twisted wires
with an approximate diameter of .419 cm (.165 in.) and are 10.0 m
(32' 9 3/4") long. There are 12 wires per lane per field for a
total of 1512 wires. The discharge electrodes are held in a rigid
frame, and each frame holds 4 wires.
Figure 255 shows the gas velocity distribution obtained under
air load conditions at the face of the first field of the precipi-
tator. These measurements were obtained using a thermal anemometer
after the precipitator was washed during an outage. The average
velocity and the square of the average velocity for all the passages
on which measurements were obtained are plotted as a function of
vertical position. The average velocity and the average of the
velocity squared were obtained by planimetry. The average velocity
obtained was 1.74 m/sec (5.71 ft/sec), and the standard deviation
was 0.955 m/sec (3.13 ft/sec), or 55% of the avera'ge velocity.
This distribution is undesirable because of the large standard
deviation and the location of the highest velocities in the region
near the bottom of the precipitator. However, at the outlet
sampling plane, the flow distribution was changed such that the
highest velocities occurred in the upper portion of the duct. Flow
distribution plates located at the precipitator outlet offered
more flow resistance at the bottom than at the top and thus are
probably responsible for the change in relative flow pattern.
438
-------
I
o
LEAR SIEGLER
PORT
I. D. FANS
© ©
oooooooooo
COLLECTOR B
n.b
— f>
A
oooooooo
COLLECTOR A
•5^
24.28 m
(79'-3"l
1 UPPER INLET
SAMPLING PORTS
3540-243
Figure 254. Precipitator layout for third gas velocity distri-
bution analysis.201
439
-------
3.556
1 2 3
SAMPLE POINT LOCATION
FROM BOTTOM
FROM TOP
860-Hli
Figure 255. Gas velocity distribution.
261
440
-------
Figure 256 illustrates the direction of gas flow and pre-
cipitator arrangement at a fourth installation where gas velocity
distribution measurements have been made and analyzed'.202 A
mechanical collector, which was reported to have been reworked
when the precipitator was installed, precedes the electrostatic
collector at this installation. The precipitator consists of
four fields in the direction of gas flow and is physically divided
into two collectors (A and B). The test program was conducted on
the HB" side of the precipitator. The total collecting area for
the "B" side is 5900.64 m^ (63,516 ft2) with 1475.16 m? (15,373
ft2} per field. This gives a specific collection area of 43.48
m2/(mVsec) (220.9 ftVlOOO cfm) for the design volume of 135.70
mVsec (287,500 acfra) per collector. The precipitator has six
full-wave transformer rectifiers; each transformer rectifier has
an "A" and "B" bushing. The precipitator has 30.5 cm (12 in.)
plate spacings and operates at approximately 160°C (320°F). The
emitting electrodes are rigid "barbed" electrodes which are 0.502 m
(I1 7 3/4") apart in the direction of gas flow.
The gas velocity distribution inside the precipitator was
measured at the leading edge of the second field.. The gas veloc-
ity was measured at 132 points as indicated by the black dots on
the isopleth of the velocity distribution shown in Figure 257.
This isopleth was constructed from air load data obtained with the
F.D. and I.D. fans operating with current settings corresponding
to full load operation. The mean velocity was 1.51 m/sec (4.95
ft/secj with a standard deviation of 0.47 m/sec (1.54 ft/sec) or
34% of the mean velocity. The isopleth shows that the velocity
is higher in the top of the unit than in the lower portion. These
data also show that the upper diagonal support braces in the unit
produced regions of higher than normal gas velocity.
Correlation of Collection Efficiency with Ga-s Velocity Distribution—
At the present time, no exact methods exist for correlating
precipitator collection efficiency with gas velocity distribution.
•However, several approaches have been proposed that demonstrate
the general trends"to be expected due to a nonuniform gas velocity
distribution.198'193'203 All these approaches utilize equation
(2) or one that is similar in form. Thus, a reduced gas flow in
a finite section of the precipitator results in an increased col-
lection efficiency whereas an increase in gas flow will result in
a decrease in collection efficiency.
In order to demonstrate the general considerations to be made
in accounting for the effects of a nonuniform gas velocity distri-
bution on collection efficiency, one203 of the previously referenced
approaches will be developed here. It will be assumed that Equation
(2) as,written applies to each particle size with a known migration
velocity, w, and'that the specific collection area and size of
precipitator are fixed.
441
-------
(0
Ul
CTi
W fP
ft O
n H-
H-tJ
cr P-
a rt
rt fu
H- rt
O O
3 H
I-1
fa
(a
m rt
H-
en H»
• O
(0
Hh
O
tu
CO
INLET GAS
DISTRIBUTION
SCREEN
"A" BUSHING
•B" BUSHING
"A" BUSHING
"B" BUSHING
OUTLET GAS
DISTRIBUTION
SCREEN
"A" BUSHING
"B" BUSHING
GAS FLOW
"A" BUSHING
"B" BUSHING
GAS
fLOW
DOWN
RAPPING MOTORS
3540-146
O
O
H-
-------
TOP OF PLATE
BOTTOM OF PLATE
3.540r246
Figure 257. Gas velocity distribution (ft/min).202
443
-------
Given:
n = 1 - e • Q
It can be seen that
and
-A w
= e AT - ' -<34)
1 a
= ^£ w_ = k_
A u u
1. a a
where
A = plate area (m2),
A.. = inlet cross sectional area (rn2) ,
Q = inlet volume flow rate (in3/sec) ,
w = migration velocity for a given particle size (m/sec) ,
u = average inlet velocity (m/sec),
cL
Aw
k = •£•£— (m/sec) , and
Al
n = ideal collection fraction.
From this form of the Deutsch equation it can be seen that
the logarithm of the inverse of the penetration is proportional
to the inverse of the velocity (and thus the transit time). The
precipitator can now be divided into a number of imaginery channels
corresponding to pitot traverse points. Using the altered form
of equation (2) , the losses for all the channels can be summed
and averaged to obtain the mean loss in the precipitator using
an actual velocity distribution instead of an assumed uniform
distribution. This can be accomplished as follows:
(1) Calculate constant k from the efficiency predicted under
ideal conditions:
k = u In T—-
a 1-T)
(2) Calculate the mean penetration:
444
-------
N
o = -i- V , n >
P Nua ^ UiU-ni) , (36)
or
N k
n » l V ~^T
p Nua ^ Uj_e ' (37)
where
N = number of points for velocity traverse,
u^ » point values of velocity (m/sec), and
ni = point values of collection fraction for the particle size
under consideration.
Note that the average penetration is a weighted average to include
the effect of higlier velocities carrying more particles per unit
time than lower velocities.
For any practical velocity distribution and efficiency, the
mean penetration obtained by summation over the velocity traverse
will be higher than the calculated penetration based on an average
velocity. If an apparent migration velocity for a given particle
size is computed based upon the mean penetration and equation (2),
the result will be a value lower than the value used for calculation
of the single point values of penetration. The ratio of the ori-
ginal migration velocity to the reduced "apparent" migration ve-
locity is a numerical measure of the performance degradation caused
by a non-uniform velocity distribution. An expression for this
ratio may be obtained by setting the penetration based on the
average velocity equal to the corrected penetration obtained from
a summation of the point values of penetration, and solving for
the required correction factor, which will be a divisor for the
migration velocity.
The correction factor "F" may be obtained from:
N
exp (- -
= P
Therefore,
445
-------
F ~ " u (In p) ' (39>
a.
Whether the quantity F correlates reasonably well with statistical
measures of velocity non-uniformity is yet to be established. A
limited number of traverse calculations seem to indicate a cor-
relation between the factor F and the normalized standard deviation
of the velocity traverse. Figure 258 shows F as a function of. the
ideal efficiency for several values of gas velocity standard devi-
ation. These curves were obtained by computer evaluation of
equation (39) , and the data on which the calculations are-based
were obtained from Preszler and Lajos.18 The standard deviations
have been normalized to represent a fraction of the mean. The
overlapping of the curves for standard deviations of 1.01 and 0.98
indicates that the standard deviation alone does not completely
determine the relationship between F and collection efficiency.
The data in Figure 258 were used to obtain the following
empirical relationship between F, the normalized standard deviation
of the gas velocity distribution (aq) , and the ideal collection pre-
dicted for the particle size under consideration:
1 "7 R f, 1
F = 1 + 0.766 na- B0 + 0.0755 a In (Jt-) , (40)
g g 1-n
where
(ua-u.)2
(41)
u
a
This relationship is based on a pilot plant study, and should be
regarded as an estimating technique only- If it is desirable to
simulate the performance of a particular precipitator, the preferred
procedure would be to obtain the relationship between F, n and a
for the conditions to be simulated from a velocity traverse at
the entrance to the unit.
Gas Sneakage--
Gas sneakage around the precipitation zones may occur at the
bottoms of the plates, at the tops of the plates, and on the out-
sides of the plates adjacent to the precipitator shell. Gas sneakage
occurs because of the pressure drop across the precipitator, flow
separation, and in some'cases by aspiration effects. Adequate
measures exist to prevent significant gas sneakage. Gas sneakage
446
-------
99.9
1.01 0.98 1.18
2 3
CORRECTION FACTOR F
4
3540-247
Figure 258.
"F" as a function of ideal efficiency and gas flow
standard deviation.
447
-------
can be reduced by frequent baffles which force the gas -to return
to the main gas passages between the collection plates, subdivision
of collecting zones into several series sections, and maintenance
of good gas flow conditions to and out of the precipitator. The
use of baffles has been discussed earlier in this text.
If there were no baffles, the percent sneakage would establish
the minimum possible penetration because it would be the percent
volume having zero collection efficiency. For example, if 5%
of the gas volume bypasses the precipitation zones, the collection
efficiency can be no better than 95%, even though all other fac-
tors are perfect. Gas sneakage can be an especially serious pro-
blem for precipitators designed for very high collection efficiencies
because only a small percentage of gas bypassage may be sufficient
to prevent the attainment of the desired performance.. With baffles,
the gas sneakage remixes with part of the main gas flow and then
bypassage occurs again in the next unbaffled area. The limiting
penetration due to gas sneakage will therefore depend on the amount
of sneakage gas per baffled section, the degree of remixing, and
the number of baffled sections.
Gas sneakage results in undesirable gas flow and eddy formation
inside and above the hoppers. This can result in considerable
particle reentrainment back into the main gas stream due to hopper
sweepage and hopper boil-up after a section of collection plates is
rapped. Baffles and hoppers must be designed to minimize these re-
entrainment effects due to gas sneakage. Hopper designs have been
discussed earlier in this text. Even with good baffling, some gas
flow will travel through the regions inside and above the hoppers.
Thus, hopper design must be such as to minimize the effects of gas
sneakage. Effective hopper design must consider several aero-
dynamic effects, including Bernoulli's principle, flow separation,
and vortex formation. Actual designs are best determined by model
studies and observations on full-scale precipitators.
If we make the simplifying assumption that perfect mixing
occurs following each baffled section, an expression for estimating
and demonstrating the effect of gas sneakage may be derived as
follows:204
Let S = fractional amount of gas sneakage per section,
n = collection fraction of a given size particle obtained
with no sneakage for total collection area,
r] . = collection fraction per section of a given particle
size = 1 - (1 - n)1/Ns,
N = number of baffled sections, and
5
p. = penetration from section j.
448
-------
Then the penetration from section one is given by;
Pi
and from section 2
Pz =
S + (1 - n_j) (1 - S)
+ (1 - n_.) (i - s)p,
(42;
= Pi [S + (1 - n.) (1 - S) ]
= [S + (1 - n ) (i - s) ]2
(43)
and from section N (the last section),
P = [s + (l - n.) (l - S) ]
J
N
= [s + (l - s) (i - n
1/N N
s s
(44)
Figure 259 shows a plot of the degradation of efficiency from 99.9%
design efficiency versus percent sneakage with number of baffled
sections as a parameter. For high efficiencies, the number of
baffled sections should be at least four and the amount of sneakage
should be held to a low percentage. With a high percentage of
sneakage, even a large number of baffled sections fails to help
significantly. This graph can also be applied to reentrainment due
to hopper sweepage and hopper boil-up as will be described later
when discussing particle reentrainment.
We can define a bypass or sneakage factor, B, analogous to
the gas flow quality factor F, in the form of a divisor for the
migration velocity in the exponential argument of equation (2):
In (1 - n)
B =
N In [S + (1-S)(1-n)
1/N,
(45)
Figure 260 shows a plot of the factor versus sneakage for a
family of ideal efficiency curves for five baffled sections. Similar
curves can easily be constructed for different numbers of sections.
The foregoing estimation of the effects of sneakage is a
simplification in that the sneakage gas passing the baffles will
not necessarily mix perfectly with the main gas flow, and the flow
pattern of the gas in the bypassage zone will not be uniform and
constant. The formula is derived to help in designing and analyzing
precipitators by establishing the order of magnitude of the problem.
Considerable experimental data will be required to confirm the
theory and establish numerical values of actual sneakage rates.
449
-------
99.9
99.5 —
o
z
UJ
O
O
UJ
D
<
c:
o
UJ
0
NUMBER OF
BAFFLED SECTIONS
0.001
1/10%
0.01 0.1
1% 10%
S, % SNEAKAGE PER SECTION
JMO-248
Figure 259. Degradation from 99.9% efficiency with sneakage.
450
-------
0 10 20 30 40
S,%SN£AKAGE PER SECTION FOR A MONODfSPERSE PARTICULATE
3540-249
Figure 260. Correction factor for gas sneakage when N = 5,
451
-------
A rough estimate of the gas sneakage occurring at the second
installation discussed earlier (shown .in Figure 253) has been made
based on velocity measurements made above and below the collection
plates (see Table 28). Calculation's were performed based on
% Sneakage = 100 x
(Peak-Average)
N x Average
(46)
where the peak values recorded in the standard traverse are utilized
and N is the total number of measurements. The calculations yield
the following results:
Right Center
% Top Sneakage 4.2 2.3
% Bottom Sneakage 3.4 6.2
Total 7.6 8.5
Therefore, a rough estimate of the gas sneakage is
Average
3.9
•4.0
7.9
A profile of the hopper sneakage occurring- at the fourth in-
stallation discussed earlier was also measured. This profile is
shown in Figure 261. The sharp increase in air flow observed at
the bottom of the hopper occurred where the center baffle of the
hopper terminated. This flow probably does not occur when the
hopper is partially full. Comparison of Figures 257 and 261 in-
dicates that gas sneakage through the hopper regions is significant
at this installation.
Air Flow Model Studies—
Basis for model studies—Although the first precipitator flow
model studies were performed in the early fifties, a widespread
use of flow modeling techniques was not made until the late sixties.
With the ever increasing size of thermal power stations, uniformity
of gas flow, dust distribution, and the gas temperature profile^
at the inlet of the precipitator become of prime importance. With
prior attention focused primarily on structural and space problems,
negligence of proper ductwork, flow control device, and hopper desigi
resulted in poor performance of the equipment, excessive pressure
losses, large dust accumulations, and corrosion due to uneven gas
temperature distribution. In larger boiler units for modern thermal
power plants, one inch w.g. of pressure drop can be evaluated as
an annual operating cost of $40,000 or more.
The main purposes of a model study are to determine the locatior
and configuration of gas flow control devices, such as vanes, baffles
perforated plates, to satisfy the contractural requirements on gas
velocity distribution in the inlet and outlet of the electrostatic
precipitator, and to minimize the pressure drop through the complete
452
-------
UJ
<
u.
O
O
O
oe
u.
BOTTOM OP PLATES
(0.9)
- (2.7)
12
(3.7)
<
u>
15
- (4.5)
0 ' 50 (15.2) 100 (30.5)
~ GAS VELOCITY. FPM (m/min)
3540-250
Figure 261. Velocity profile in hopper.
2 o 2
453
-------
system. Also, accurate flow model studies offer the potential
of detecting and correcting flow problems in the design stage.
Even if only qualitative results can be obtained in a model study
these can be extremely useful in providing recognition of potential
problem areas. Also, it is the opinion of some that proper at-
tention to details (in both the model and prototype) will produce
a one-to-some correlation between the model and the field. 9e ~-
This was demonstrated quite convincingly in one field and model
study where detailed velocity traverses for both configurations
were in good agreement.196 Since -the investment in a flow model
study is relatively small when compared to the total precipitator
investment and possible financial losses due to poor flow design,
this type of study is probably justified when designing most new
precipitator installations.
Similarity of fluid flows19"1—The gas velocity distribution
in the electrode system of the electrostatic precipitator is.
analyzed using accepted procedures based on similarities of fluid\
flows in the three-dimensional scale model and the full-size system
(prototype) . : . .
The similarity of the fluid flow conditions between the, model
and the prototype are dependent on matching some or all of a
series of dimensionsless parameters, which describe the charac-
teristics of the prototype and model, as well as those of the flows,
as ratios of the fluid forces.
In general, three similarities must be satisfied to obtain
valid results with the fluid flow models. These similarities are:
(1) Geometric Similarity, (2) Kinematic Similarity, and (3) Dynamic
Similarity. Any of two flow systems satisfy geometric similarity,
if all dimensions have the same scale factor,
£.1/2,2 = constant, (47)
where
£ = typical length (indices 1 and 2 distinguish between the
two flow systems) . . •••.
Kinematic similarity requires, in addition, that any two flow
systems have the same relative velocities and accelerations through-
out such that
vj/V2 = constant (48)
bi/b2 = constant (49)
where
v = typical velocity and
b = typical acceleration.
454
-------
It is normally not too difficult to match all of these re-
quirements in a precipitator model.
The third requirement of a dynamic similarity requires, in
addition, the similarity of pressures at corresponding points of
model and prototype such that
Pi/Pz = constant, (50)
where
p = typical dynamic pressure.
To completely satisfy the similarity of dynanic pressures, a
number of ratios of forces in both fluid systems, such as Reynolds.
Froude, Weber, Euler, and Mach Number have to be identical.2"5
Most of the time, this condition can not be met in model study
work.
A different approach would be to maintain equality of Reynolds
and Froude numbers only. Scales for the model can be developed
based on gas viscosities and densities of both systems.
Scales for model and prototype can be developed by using
Reynolds and Froude Numbers of both systems, resulting in a length
scale of:
2/3
\ = It/lz = (Vj/v2) (51)
a time scale of:
I/ 3
T = ti/t2 = (Vi/v2) (52)
and a general force scale of:
=• = Pi/Pz = Pi/Pz (Vi/v2)2 (53)
The general force scale can be extended to cover scales for
inertial,"frictional, and gravitational forces with v representing
gas kinematic viscosity and p gas density-
Scale factors for other units of measurements can be calculated
'•from these basic scales; for example, for gas velocity:
I/ 3
vi/v2 = A/T = (Vi/v2) (54)
.aiid for -gas volume:
5/3
Qi/Q2 = *3/T = (vr/vz) (55)
455
-------
The general use of these ratios in flow model studies of
electrostatic precipitators would require rather large models.
For example, for flue gas with a temperature of 180°C in the pro-
totype and an air temperature of 20°C in the model, the length
scale would be 1 to 1.6; the velocity .s-cale 1 to 1.3; and the
volume scale 1 to 3 . 2 .
A different approach for model studies/ where a significant
decrease In size of the model is intended, would be to -arbitrarily
select a scale factor for a typical length; for example, 1 to 16,
and to match the Reynolds number of the prototype by incre.as.-ing ••
the fluid velocity in the model or changing the '.f;luld~'prqp;erties.
Increasing the system velocity creates significantly larger. •
pressure losses and requires higher head fans. The gas velocity
of the prototype system mentioned earlier may be 1.2 m/sec. To
match the Reynolds Number using air as model fluid in a 1 to 16
scale model would require an air velocity of 9.6 m/sec., an in-
crease by a factor of eight. The system pressure loss would,
thus, increase by a factor of 64; for example, from a design
pressure loss of 250 mm H20 to 16,000 mm H20.
To match the Reynolds Number of the prototype, the model fluid
properties could be adjusted by changing the fluid temperature
or using a fluid other than air, but neither of these approaches
is very practical.
The Reynolds Number is the ratio of inertial to viscous forces.
When the inertial forces predominate, flow separation from the
critical surfaces occurs and is principally a function of the
geometry of the system. If the value of .the Reynolds Number is
well within the turbulent range (Re > 3 x 103, for example), the
behavior of the fluid can be successfully modelled at a Reynolds
Number other than that of the prototype system.
The model flow pattern observed at reduced Reynolds Number
levels will be identical to the full size system, and the model
pressure drop will be only slightly higher due to the influence
of the Reynolds Number on frictional pressure losses.
In industrial flue systems, which are usually designed to
connect major pieces of equipment, many conditions will establish
flow separation and induce turbulence. Therefore, the calculated
value of Re is no indication of the quality of flow or the state
of turbulence. Once the condition of flow separation is established
(inertial forces predominating) the flow pattern tends to remain the
same over a wide range of calculated Re values. That is, kinematic
similarity is established in industrial flues substantially inde-
pendent of variations in average velocity or model factors.
Therefore, the model study does not have to match the full
size Re value. It suffices that:
456
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x 103 (56)
and
'V-Vr>, 3x10' . (57)
However, Reynolds Number must be considered when the conditions
of pressure drop and dust drop-out are studies in the model. It
has been shown that the boundary-layer thickness of gas on any
surface is an inverse function of Re. In the usual industrial
scale model study. Re will be proportionately low due to the scale
factor, and the boundary-layer will be too thick. This condition
tends to give a conservative estimate of pressure drop and dust
drop-out.
Model studies involving two-phase fluid systems or airborne
particulates influenced by gravitational forces, require the ad-
herence to a constant Froude Number, i.e.:
o^4 . (58)
Another approach, which is frequently used, consists of using a
1:16 scale model with the collecting surface plates installed in a
1:8 scale, and, thus, test at a flow condition characterized by a
Reynolds Number in the turbulent range, closer to the Reynolds Number
of the prototype.
The fluid'velocity level in a model should be selected to be
in a range which can be easily and accurately measured (velocity
head above 10 mm H20) but low enough to be incompressible (Mach
Number below 0.2). As a result, the fluid velocity in a duct will
normally range from 10 to 20 m/sec, and in the precipitator model
itself, from 0.5 to 3.0 ra/sec; the latter being measured with a hot
wire anemometer.
If smoke is used to visualize the flow pattern, the fluid
velocity should not exceed 10 m/sec to maintain visibility of the
smoke pattern.
It is recommended to use a fan with a variable speed drive or
to have air dampers between flow model and fan to be able to reduce
the air flow through the model to one-half or one-third of the
design flow volume during the test program.
Flow model construction19 9—Three-dimensional scale models
have become the most widely used means for a fluid velocity dis-
tribution analysis. For purpose of convenience, some or tne models
457
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made in early gas flow studies were constructed on a scale of 1.9 cm
(3/4 in.) in the model being equivalent to ...3048 m .(one foot) in the
prototype; that is, the model was 1/16 of actual .size. This scale
became common and is widely .used in the. industry,, although for more
demanding work, especially for predictions of pressure, drop and chast
fallout, a scale of 1 to 12 or even'1 to 10 could become' increasingly
more necessary.
The model is a precise replica of the entire gas cleaning system
and includes items, such as air preheaters, steam generator econo-
mizers, flues, flow.control devices, precipitators, fans, stacks,
etc. All of the model or parts of it are made of transparent plastic
to make it possible to observe flow indicators, such as cotton tufts
or smoke and dust fallout. Internal parts of the ductwork, such as
flow control devices, may be constructed of light gauge sheet metal.
The precipitator model has sidewalls, hoppers, box girders, and
roof made out of transparent plastic. Collecting surface plates are
made out of flat sheets of plastic or metal and are hung between the
box girders or plate supports. Normally, only the first and last
electrical fields need to be equipped with collecting surface plates.
Walkways, horizontal and vertical baffles are included in the model,
as well as hopper partitions. The discharge system is normally not
included in the model.
Inlet and outlet nozzles are also made out of transparent plastic.
Perforated plates or similar devices used for gas distribution are
selected with equal opening ratios as those to be used in the pro-
totype.
The air preheater is modeled as exact as possible, complete
with transitions between the round axe of the wheel and the rec-
tangular outlet flanges, as well as the wash-out hopper underneath
the air preheater outlet duct.
The model is set up on the suction or pressure side of a fan
with a suitable gas volume, normally following the configuration
used in the prototype.
Larger models need a separate support structure and access plat-
forms next to the test ports.
Instrumentation19 9—Air velocity distributions in the ductwork
of the model can be measured with a calibrated standard pitot tube;
for example, Dwyer 0.32 cm (1/8 inch) diameter, with an inclined
water manometer; for example, Meriain Model M-173-FB with a range of
0-15.2 cm (0-6 inches) and minor graduations of 0.03 cm (0.01 inch).
Static pressures in ductwork can be measured with a calibrated
standard pitot tube connected to an inclined water manometer; for
example, Meriam Model HE 35 WM with a range of 0-35.6 cm (0-14
inches) and minor graduations of 0.03 cm (0.01 inch).
458
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The air_velocity distribution in the model of the precipita-
tor chamber is measured with a hot-wire linear flow flowmeter- for
example, Datametrics (Gould) model 800-LV with a model U-25 probe.
Particle Reentrainment
Rapping Reentrainment—
Background—Rapping reentrainment is defined as the amount of
material that is recaptured by the gas stream after being knocked
from_the collection plates by rapping or vibration. With perfect
rapping, the sheet of collected material would not reentrain, but
would migrate down the collection plate in a stick-slip mode,
sticking by the electrical holding forces and slipping when re-
leased by the rapping forces. However, the rapping forces are
necessarily large to overcome adhesion forces, and a significant
percentage of the material is released into the gas stream as
•sheets, agglomerates, and individual particles. Most of the
material is recharged and recollected at a later stage in the pre-
cipitator.
The purpose of an electrode rapping system is to provide an
acceleration to the electrode which is sufficient to generate
inertial forces in the collected dust layer that will overcome
those forces holding the dust to the electrode. Electrode rapping
systems have been described earlier in this text. A successfully
designed rapping system must provide a proper balance between
electrode cleaning and minimizing emissions resulting from rapping
reentrainment. Presently, two approaches are prevalent with regard
to the removal and transfer of the particulate from the collecting
plates. One approach is to rap often and to provide maximum rapping
acceleration to the plates during each rap in an attempt to minimize
the thickness of the residual ash layer. The other approach is to
vary the intensity an-d frequency of the rapping in an attempt to
minimize the quantity of material reentrained. A determination
of the best rapping technique for a specific application depends
on an understanding of the mechanisms by which ash is actually re-
moved and transferred from the collection plates during a rapping
sequence and of the effects of residual ash layers.
The mechanics of the ash removal process vary with the pro-
perties of the ash, precipitator operating conditions, and rapping
parameters. Ash properties and precipitator operating conditions
affect the adhesion and cohesion of the ash layer. The adhesion
and cohesion of ash layers depend upon particle-to-particle forces.
According to Tassicker,2°8 the component forces are: London-van der
Waals, triboelectric, capillary, surface dipole, and electric-field
corona forces. These component forces are influenced by the fol-
lowing: particle diameter, porosity and compaction of the layer,
complex dielectric constant, humidity in the gas, adsorbed surface
dipolar molecules, work-function interfaces on the material, and
the electric field and current density in the ash layer. The above
459
-------
considerations point out the difficulty and complexity which would
be involved in predicting ash removal properties.
A relationship for the electrostatic force which acts upon the
ash layer as a whole has been presented earlier in equation (23).
In most practical applications, the net electrical force should
be in the direction that forces the dust layer on to the collection
surface. However, in certain cases, the net force can be such as
to pull the ash layer off the collection surface. This can occur...
for low resistivity ashes or for low operating current densities,
as indicated in Figure 211.
An elementary theory of dust removal which considers only the
tensile strength of the dust layer and the acceleration normal to
the plate has been developed by Tassicker.2°7 The theory predicts
that the dust layer is removed only when
P P
an > Til = (M/A) ' (59)
where
a = acceleration normal to the plate (m/sec2),
P = tensile strength of the dust layer (nt/m2),
6 = bulk density of the dust (kg/m3),
£ = dust layer thickness (m), and
M/A = mass per unit area (kg/m2).
According to this relationship, for removal of a.given dust thick-
ness, the rapping intensity must be of sufficient magnitude to
produce an acceleration greater than the ratio of the tensile
strength of the ash layer to the mass per unit area. For a given
normal acceleration, the dust layer is removed only when
M/A > P/a ; (60)
that is, when the mass per unit area (dust surface density) is
greater than the ratio of dust layer tensile strength to the normal
plate acceleration. Since the mass per unit area depends on the
dust layer thickness, which in turn is related to collection time
between raps, the time interval between the raps is directly re-
lated to the efficiency of dust removal from the plates. As col-
lection time between raps is increased, the mass per unit area is
increased, and the acceleration required for removal is decreased..
Experimental data obtained by Sproull208 and by Penney and Klingler
show that the requirements for removal of a precipitated dust layer
are in basic agreement with Tassicker's elementary theory for dust
removal.
460
-------
«.«** ?£ ii^t. S Conducted a series of experiments which illus-
trate the effect of dust composition, corona forces, accelerations,
and temperature on the removal of dust layers from collection elec-
trodes. Figure 262 presents some of Sproull's data to illustrate
the relative effects of these parameters as a function of the
maximum shear acceleration of the collecting electrodes in multi-
ples of "g"- A comparison of these curves indicates that, under
the conditions of the experiments, the cement dust was more dif-
ficult to_remove than fly ash, even though the particle size
distributions of the two dusts were similar, presumably as a re-
sult of differences in composition. It is also clear that the
electrical holding force was acting to retain the dusts on the
collection electrode surface. Similar data were obtained for
acceleration perpendicular to the electrode plane produced by a
normal rap. Lower values of acceleration were required for re-
moval of difficult-to-remove dust with normal rapping than was
the case for shear rapping.
Figure 263 (also from Sproull) illustrates the effect of
temperature on the removal efficiency of a precipitated layer
of copper ore reverberatory furnace dust. These data indicate
that the net holding force on the dust layer decreases with in-
creasing temperature until softening or partial melting occurs,
excluding the cases in which the dust temperature falls below
the dew point of the surrounding gases.
Particle reentrainment is influenced by factors concerning
the design and operation of the precipitator as well as the
physical and chemical properties of the dust. White209 has sum-
marized the particle properties and precipitator design factors
which affect reentrainment and these are presented in Table 30.
Although hopper design and ash removal system operation do not
influence the manner in which particles are directly- reentrained
as a result of rapping, improper operation of the ash removal
system can increase emissions through hopper boil-up resulting
from raoping or as a result of gas circulation through the hoppers.
Sproull210 has reported that optimum rapping conditions are
-achieved when the collected dust layer is permitted to.accumulate
to a reasonable thickness and then rapped with sufficient intensity
.to progress down the plate in a slip-stick mode. This procedure
has the advantage of resulting in the deposition of only a portion
of the dust on the lower portion of the collecting plate into the
hoppers at any one time. These circumstances would minimize the
disturbance of previously deposited dust since the velocity of
the falling layer would be relatively low.
The foreaoing considerations illustrate that Uis desirable
to vary both rapping intensity and rapping interval in order to
optimize the performance of a dust removal system Since the mass
.rateof dust Collection varies with length through a precipitator,
it follows that rapping frequency variations between the inlet
461
-------
100,
QJ
•o
0) „
5 E
°- «
w re
u£
u- —
Si
0.
c_
80
TOO
120
j
140
MAXIMUM SHEAR ACCELERATION OF COLLECTING
ELECTRODE PLATE PRODUCED BY SHEAR RAP, g
3540-261
Figure 262.
Shear (parallel) rapping efficiency for various
precipitated dust layers having about 0.2 grams
of dust per scjuare inch as a function of maximum
acceleration in multiples of "g". Curve (1) fly
ash, 70° to 300°F, power off. Curve (2) fly ash,
300°F, power on. Curve (3) cement kiln feed, 70°F,
power off. Curve (4) cement kiln feed, 200 or
300°F, power on. Curve (5) fly ash, 70°F, power
on. Curve (6) cement kiln feed, 70°F, power on.208
462
-------
>
DO (204) 500 (260) 600 (316) 700 (371)
TEMPERATURE, °F (°C) 3540-252
Figure 263.
Rapping efficiency for a precipitated layer of
copper ore reverberatory furnace dust,_ rapped
with a ballistic pendulum having an energy of
0.11 foot-pound, at various, temperatures.208
463
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TABLE 30. PARTICLE. PROPERTIES AND PRECIPJTATOR DESIGN
FACTORS. WHICH AFFECT REENTRAINMENT2'99
PARTICLE SIZE
1. Size Distribution
2. Shape
3. Bulk Density
4. Adsorbed Moisture and
Other Vapors
5. Environment-Gas Temperature
6. Resistivity
PRECIPITATOR FACTORS
1. Gas Velocity
,.(>.
2. Gas Flow Quality
3. Collecting Electrode
Configuration and Size
4. Electrical Energization
5. Rappers: Type, Number, and
Amplitude
6. Hopper Design
7. Air In-leakage into Hoppers
or Precipitator Proper
8. Dust Removal System Design
and Operation
9. Single Stage or Two Stage
464
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and _ exit fields would be expected to yield the best rapping con-
ditions. If a precipitator consists of four fields in the dir-
ection of gas flow and exhibits a no-reentrainment efficiency of
99%, the rate of build-up in the first field would be about 30
times that in the outlet field, again neglecting reentrainment
effects. However, the optimum rapping intervals for these fields
would not be expected to correspond to the dust collection rate
ratios.
Recently, work has been performed to develop models for
describing dynamically the vibrational modes and accelerations
produced in a full-scale collection plate with an attached dust
layer by a rapping force of a given intensity.211'212 Although
these studies are still in the elementary stage and are not of
practical value as of yet, they have the potential for answering
several questions pertaining to what is the best method of removing
the dust layer from the collection electrode. For example, are
high frequency, small amplitude vibrations or low frequency, large
amplitude vibrations more effective in removing a dust layer? Also,
what is the relative importance of normal and shear forces in re-
moving a dust layer?
Emissions due to rapping—Emissions due to rapping and their
dependence on rapping parameters have been reported by Sproull,210
Plato,213 Sanayev and Reshidov,2l" Schwartz and Lieberstein,2!5
and Nichols, Spencer, and McCain.215 Some of the results of this
work has been discussed above. In summary, these workers have
observed that (1) reducing the intensities of the raps lead to a
reduction in rapping emissions,210 (2) vertical stratification of
the emissions occurred during rapping, with higher concentrations
in the lower portion of the precipitator,210 and (3) improvements
in the performance of full-scale precipitators occurred when the
time intervals'between raps were increased.2!3'2}"'215'216 Al-
though these studies have added to the understanding of rapping
reentrainment and some of the variables affecting the emissions
due to rapping reentrainment, they do not provide quantitative
data on the amounts of emissions and particle size distributions.
due to rapping reentrainment.
One study on a pilot plant20 and another study on six full-
scale precipitators1^ have yielded quantitative information on the
emissions due to rapping reentrainment. A complete characterization
of rapping reentrainment requires the measurement of a large variety
of variables. A block diagram of an experimental layout for the
pilot study is shown in Figure 264. In addition to the_data that
areobtairved with this arrangement, a complete .characterization
utilizes the precipitator design data.
The field experiments included a similar set of measurements
to those made during the pilot studies. However, sampling view
ports for photographing rapping emissions and for determining the
?ert±cal stratification of the rapping emissions were not available
465
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ELECTRICAL
CHARACTERISTICS
RAPPING
VARIABLES
DUST LOAD
ON PLATES
PLATE
TION
MASS LOADING
TIME INTEGRATED
PARTICLE SIZE
MEASUREMENTS
VELOCITY
DISTRIBUTION
P-RECIP1TATOR
OBiCURATlQfv
METER
TIME INTEGRATED
PARTICLE SIZE
MEASUREMENTS
MASS LOADING
UPPER HALF
TWO SETS AT 3 LOCATIONS. ONE TO MEASURE DURING
RAPE AND ONE TO MEASURE BETWEEN RAPS.
TWO SEPARATE UNITS ONE TO LOOK AT LOWER HALF OF THE
PRECIPITATOR OUTLET ANC ONE TO LOOK AT UPPER HALF OF
THE PRECIPITATOR OUTLET.
CAMERA AND
LIGHT HSIG
MASS LOADING
LOWER HALF
HOPPER
SAMPLES
•• REAL TIME
PARTICLE SIZE
MEASUREMENTS
3640-253
Figure 264.
Block diagram of experimental layout for a
reentrainment study.20
rapping
466
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in the full-scale units nor were load cells for measuring the
quantity of fly ash collected on the collection plates. Hence
these measurements were not included in the field tests.
The quantification of rapping reentrainment requires methods
of measuring the mass and particle size distribution of particulate
exiting the precipitator with and without rapping. During both
the pilot and full-scale precipitator test programs, an optical
real-time system and integrating mass systems were used. For the
full-scale tests, particle size measurements were obtained using a
method based on electrical mobility analysis for particle diameters
between 0.01 um and 0.3 ym.
Mass measurements were obtained with in-stack filters. The
sampling probes used at the inlet and outlet were heated and con-
tained pitot tubes to monitor the velocity at each sampling loca-
tion _ for the full-scale tests. Glass fiber thimbles were used at
the inlet to collect the particulate and Gelman 47 mm filters were
used at the outlet. Different procedures were employed at the
pilot unit compared to the full-scale units.
At the pilot plant facility, two outlet sampling trains were
used: (1) the upper sampling train for the upper 68% of the pre-
cipitator outlet and (2) the lower sampling train for the lower
32% of the precipitator. The outlet sampling locations were about
1 meter from the plane of the outlet baffles, and only one lane
of the precipitator was sampled. Both outlet mass trains were
modified to consist of two systems: one of which was used to
measure emissions between raps and the other was used to measure
emissions during raps. Each outlet sampling probe consisted of a
2.5 cm pipe, to the end of which two 47 mm Gelman filters with
1.25 cm nozzles pointed 110° apart were attached. Separate copper
tubes were run to each filter from a three-way valve. The valve
was used to connect the appropriate filter to the metering box.
Sampling rates at each traverse point were based on velocity
traverses made prior to the sampling.
One of the'two filters on each of the two outlet probes was
designated the between rap sampler and the other the rapping puff
sampler. After stable conditions were obtained, the between rap
sampling systems were started. Before rapping the plates, sampling
was discontinued and the probes were rotated so that both nozzles
on each probe pointed downstream. The dust feed was turned off,
and after a clear flue was obtained, the second filter was rotated
into the gas stream. Sampling was resumed and the plates were
rapped. When dust had settled, sampling with this second set of
filters was discontinued and the nozzles to the filters were again
pointed downstream. The dust feed was then turnea on and the
sampling was resumed again with the between rap system.
Data obtained with the between rap .system were handled in
the usual manner and were used to calculate steady-state mass
467
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emission rates. Data from the second set, or "rap" set of filters
were used to calculate emission rates from the rapping puffs inde-
pendently of the between-rap emissions. These emission rates
were calculated from
E = VSNH
where
E = emission rate from rapping puffs (kg/hr),
M = mass collected by the filter while sampling the flue
gas during rapping (kg),
A = cross-sectional area of precipitator sampled by the
probe (m2),
= cross-sectional area of nozzle (m2),
NR = number of raps per hour (#/hr), and
N = number of raps sampled.
The emission rates between raps and from raps were combined to
obtain the overall hourly emission rate.
For a full-scale precipitator installation one would expect
to be able to measure rapping reentrainment simply by obtaining
data with either a mass train or an impactor sampling system, with
a rapping system energized and subsequently de-energized and then
comparing these measurements. When utilizing these integrating
or time-averaging, inertial systems for the measurement of rapping
reentrainment, a sampling strategy must be developed which will
differentiate between steady-state particulate emissions and those
which result from electrode rapping. At the first full-scale
installation (Plant 1) tested, the strategy employed consisted
of sampling on subsequent days with the rapping system energized
and subsequently de-energized while an attempt was made to main-
tain boiler operating parameters as constant as was practical.
The precipitator was characterized by high collection efficiency
(99.9%), which required extended sampling times to obtain meaningful
mass measurements. However, it was found that the sensitivity of
the electrostatic precipitator to changes in resistivity and other
process variables could mask the differences in total emissions
caused by energizing and de-energizing the rappers. The variation
in precipitator performance caused by the resistivity and other
process variable changes made it impossible to determine rapping
reentrainment losses from a direct comparison of data obtained one
day with rappers in the normal mode and rappers de-energized on
subsequent days.
468
-------
In order to minimize the above
strategy was adopted for the remain!.., *«au«xAJ.«ions. Tfte revisec
strategy consisted of sampling with mass trains and impactorsde-
dicated to designated "rap" and "no-rap" periods. Data with a
rapping system energized and de-energized were obtained by tra-
versing selected ports with dedicated sampling systems in sub-
sequent periods on the'same day. This procedure, while necessarily
distorting the frequency of the rapping program being examined,
minimized the effects of resistivity and other process variable
changes.
The use of the alternating sampling strategy leads to at least
three possible procedures for calculating the frac-ion of losses
attributable to rapping reentrainment. The first procedure con-
sists of the calculation of the ratio of emissions obtained with
rappers_off to^rappers on and subtracting from unity. The emissions
data utilized in this procedure were obtained during the time in
which alternating sampling periods for rap and no-rap sampling
trains were employed. The second procedure consists of subtracting
the mass emissions obtained with the rappers de-energized from those
of the previous day with normal rapping, and dividing by the emis-
sions obtained with the rappers operating normally. The data ob-
tained from the "rap" period will be approximately equal to that
obtained during other test periods in which the rappers are oper-
ating in a normal fashion if: •(!) the distortion of the rapping
frequency does not significantly influence emissions during the
"rap" period and (2) there are no other variations in parameters
affecting the precipitator performance.
A third possible procedure consists of the use of a weighted
time average emission during the rap-no-rap periods as an approxi-
mation to the normal emission rates, subtracting the no-rap emission
from the weighted time average, and dividing the difference by
the weighted time average to obtain the fraction of emissions at-
tributable to rapping. This procedure provides an estimate of
rapping reentrainment with the effective intervals which result
from the alternating sampling periods. All of the above calcu-
lation procedures were used when applicable to analyze emissions
data from the six installations tested.
The three size selective sampling systems which were used in
the measurement programs consisted of a large particle sampling
system (LPSS) containing an optical single particle counter, an
ultrafine' particle sampling system containing an electrical aerosol
analyzer (EAA.)-, and cascade impactor sampling systems. The oper-
ating principles of these sampling systems have been discussed
earlier in.this text. The optical and electrical sampling systems
.provided real.-time . data obtained from an extracted _ gas sample _
while the inertia!•sampling systems provided; time-integrated in
situ data. The large particle sizing system (diameter range 0.6-
27o~Um) was employed only for outlet measurements to provide _
qualitative information on the relative fractions or the emissions
469
-------
that could be attributed to rapping losses in the precipitator.
In addition, this system also provided data on particulate con-
centration changes wi,th time. The ultrafin-e particle sampling
system (0.01 ym to 0.3 ym) was employed at both the inlet and
outlet of the full-scale precipitators for purposes of providing
fractional efficiency data and to give quantitative information
on the contribution of rapping, if any, to emissions in this
particle size range.
The pilot-scale rapping tests were conducted on a' nearly
full-scale pilot precipitator owned and operated by PluiDyn-e"
Engineering. Figures 265 and 266 illustrate the features of the
test facility. This pilot unit effectively represents one elec-
trical section in a full-scale precipitator. The plate height is
6 meters, and the plate length is 2.7 m. The total collecting
area is 167 m2, and wire-to-plate spacing is 11 cm. In the ori-
ginal design, the plates were constructed from expanded metal.
For this rapping reentrainment study, three of these plates were
replaced to provide two lanes with solid plates on each side of
the lane. Outlet sampling was confined to the lanes with solid
plates. The plate rappers are of the single shot pneumatic type.
The rapper weight is supported in a-cylinder by low pressure
compressed air. When a rap is desired, a signal to a solenoid
valve pressurizes the other side of the cylinder and forces a
weight down on top of a rod that transmits the force to a plate
support beam.
Dust feed is supplied from a dust dispersion system which has
an adjustable feed capability. Three oil burners are.. available
to heat the gas stream to the desired temperature level. A water
injection system consisting of three atomization nozzles,each with
a capacity of eleven liters of water per minute, is available to
supply the desired humidity. The water is atomized by compressed
air and is vaporized by the burners that heat the system gas flow
to the design temperature.
Table 31 presents a summary of results obtained from the
experiments on the FluiDyne Pilot Unit. These results indicate
that rapping emissions decreased with increasing time between raps.
Figure 267 shows the effect of rapping interval on efficiency.
The percentage of the collected dust removed from the collecting
electrode also increased with increased time between raps, as
Figure 267 illustrates. These results are consistent with the
theory of dust removal which indicates that the product of the
normal plate acceleration and the dust surface density must be
greater than the tensile strength of the layer.
Figure 268 also illustrates the build-up of a residual dust
layer that was not removed with normal plate accelerations on the
order of 11 Gs. There are several possible causes for the develop-
ment of the residual layer. For one, the dust layer directly in
contact with the collection plates has a much higher tensile
470
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NOMINAL 1.2 M WIDTH
FOR (5) PASSAGES
H2S04
3540-254
Figure 265.
Near full-scale pilot precipitator at FluiDyne
Engineering.
2 o
471
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ft
O
TYPICAL FLOW
9 FT/SEC
300°F
3500 ACFM
SCA 51.4
9 ACCELEFtOMETERS
MOUNTED ON PLATE 4
PLATE ROWS 1, 2, & 6 EXPANDED METAL
PLATE ROWS 3. 4, & 5 SOLID
PLATE ROWS 2-1. 2-3 WERE SMOF1TENED 0.5 M
3540-255
-------
TABLE 31. RESULTS FROM PILOT-SCALE RAPPING EXPERIMENTS
Plate
Penetration due
Type of
test
Rap
Rap
Rap
Rap
No Rap
acceleration Rap
G's intervals,
x,y,z axis min
11 16 15 12
32
52
150
—
Gas
velocity,
m/sec
0.87
Avg. plate
current density,
nA/cm2
23.3
Total
penetration ,
%
11.4
7.6
6.1
6.9
5.2
to rapping
reen trainment ,
%
53
32
18
25
_ _
LO
-------
100
95
o
LJ
o
90
85
WITHOUT RAPPING
I
40 60 100 140 180
TIME INTERVAL BETWEEN RAPS, minutes 3546-256
Figure 267.
Average efficiencies for FluiDyne pilot precipitator
for various rapping intervals.20
474
-------
MASS/AREA GAINED BETWEEN RAPS, kg/m2
0.26 0.78 1.3 1.8 2.3 2.9 3.4
100h-
80L-
u
LU
U.
U.
LU
COLLECTED BETWEEN RAPS
20 40 60 80 100 120 140 160
TIME INTERVAL BETWEEN RAPS, minutei
3540-257
Figure 268. Dust removal efficiency versus the time interval
.. - , 2 0
between raps
475
-------
strength than the remainder of the layer. Estimates for removal
of the layer called for accelerations greater than 103 Gs (9.8 x
105 cm/sec2). Consolidation of the dust that remains on the plate
after a rap also aids in producing residual layers. The vibrations
during a rap can have the effect of compacting the dust layer if
it is not removed making it more difficult to remove. A third
possible cause of the residual layer is the removal.of patches of
dust only from selected locations on the collection plates where,;.',
the removal criteria are met. Dust can be removed from one loca-
tion during one rap and from another location on the 'next rap- d-ue
to changes in distribution of the dust surface density. This-
results in a nonuniform dust layer and the presence of a residual
layer. This is often the result of nonuniform' plate accelerations.
At one location where plate accelerations were on the order of
only 4 to 5 Gs (3.4-4.9 x 103 cm/sec2), residual dust layers as
thick as 2 cm were' observed in the 'vicinity of plate baffles where
the plate accelerations are dampened. Between the baffles, the
residual layers were only 1 to 2 mm thick.
Figure 269 presents particle size distribution of rapping
puffs for the indicated rapping interval. These, data suggest..
that thicker dust layers produce larger reentrairied particles
upon rapping. An inspection of the impactor substrates at the
outlet sampling locations 2 and 3 revealed that the majority of
the large particles in the rapping puffs were agglomerates. Pro-
ducing relatively large agglomerates instead of individual particles
is desirable because the larger agglomerates are recollected faster
than discrete particles or smaller agglomerates. :
In the FluiDyne pilot plant study, it was evident that "boil-
up" from the hoppers comprised a significant portion of the re-
entrainment. The measurement of the vertical distribution of the
rapping loss at the FluiDyne Pilot unit indicated that 82% of the
rapping emission occurred in the lower 32% of the precipitator.
This effect was apparently due to both hopper boil-up and gravita-
tional settling of the reentrained material. Figure 270 illustrates
the vertical stratification as a function of particle size. All of
the particle size bands show a decrease in concentration with in-
creasing distance from the bottom baffle.
Rapping puffs observed in the lower portion of the precipi-
tator occurred in two bursts for both upstream and downstream
raps as shown in Figure 271. The first burst lasted 2-4 seconds.
This burst was interpreted as being the result of particulate re-
entrained directly in the gas stream and being carried out of the
precipitator at the velocity of the gas through the unit. The
longer lasting second burst, which for the larger particles was
a series of puffs, can be interpreted as resulting from hopper
"boil-up". These data indicate that hopper "boil-up" contributes
significantly to rapping reentrainment emissions.
Motion pictures of the dust removal process in the Southern
Research Institute (SoRI) small-scale precipitator and the FluiDyne
476
-------
0.01 0.1 1 10 20 40 60 80
PERCENT LESS THAN INDICATED SIZE, by maw
3S40-J5J
Figure 269. Cumulative percent distribution for rapping puffs,
rapping intervals of 12, 32, and 52 minutes, pilot
test.
477
-------
D
LU
2
2
O
O
Hi
O
M 2
•= O
< v>
2 O
O =-
105
1 I !
* 1.5- 3.0 urn
• 3.0 - 6.0 urn
^6.0 -12.0 urn
• 12,0 - 24.0 um
A > 24 ym
103
2 <
— C/5
2^
D =
O O
K CL
O <
I- CC
B
A
F
L
E
\
20 40 60 80 100 330 350 370
DISTANCE FROM BOTTOM BAFFLE, cm
390 410
3640-259
Figure 270. Spatial distribution of particles in rapping puff.
20
478
-------
o
i
1
o
50
40
30
20
to
24 urn DIAMETER PARTICLES
JII
u
12 - 24 ym DIAMETER PARTICLES
5x103
6- 12 wm DIAMETER PARTICLES
-------
pilot precipitator have produced several observations relating
to the dislodgement of dust after a .rap and to the reentrainment
of dust due to the rap. Motion pictures (32 frames/sec) of the
removal of a dust layer (2-3 nun thick) by rapping in the SoRI
small-scale unit show the. dust layer fracturing along lines of
discontinuity in the dust surface. The resulting fractured sheet
of dust starts to fall as separate sheets which break up as they
encounter other falling sheets and patches of unremoved dust.
The dust appears to fall without being recollected and to become
turbulently mixed as it falls. The motion pictures show the
majority of the dust dropping into the hoppers from which a
portion boils up and becomes reentrained into the gas stream.
Motion pictures taken in the large pilot precipitator at
FluiDyne Engineering showed similar behavior.
In terms of location in the power plant system and type of
fuel burned in the boiler, the six full-scale installations studied
may be classified as follows:
Plants 1 and 5 - Cold-side ESPs" collecting ash from low
sulfur western coals,
Plant 6
Plant 4
Plants 2 and 3
Hot-side ESP collecting ash from low sulfur
western coal,
Hot-side ESP collecting ash from low sulfur
eastern coal,
Cold-side- ESPs collecting ash from high
sulfur eastern coals.
Table 32 summarizes the important design parameters and the
results obtained for the six installations. A mechanical col-
lector preceded the precipitator at Plant 1 and Plant 3. The in-
stallations were characterized by relatively high overall mass
efficiency. Rapping losses as a percentage of total mass emission
ranged from over 80% for one of the hot-side units to 30% for the
cold-side units. The high rapping losses at Plant 4 are probably
due both to reduced dust adhesivity at high temperatures and the
relatively short rapping intervals.
Table 33 lists the rapping intervals for each field at the
various installations.217 Also shown are the effective rapping
intervals resulting from the alternating sampling schedules which
were used to obtain the rap-no rap data. To the extent allowed by
process variations, the range of emissions attributable to rapping
should be established by the calculations using (rap-no rap) and
(normal-no rap) data sets. However, the time weighted average (TWA)
calculation is of interest in, that it indicates the change in rap-
ing emissions caused by the effective increase in time intervals
between raps. With the exception of the normal current density
data set at Plant 2, the time weighted average calculation gives
the lowest percentage emissions due to rapping of the three
480
-------
TABLE 3 2 . SUMMARY OP RESULTS
FROM EPRI TESTS-
Plant 1
Number of Electrical 6
Fields in Direction
of Gas Flow
2
3
3
4
4
4
5
5
6
6
oa
Plate-to-Plate
Spacing, era
Emitting Electrode
Design
Rapper Design
Portion of ESP
Tested
Boiler Load During
Test, MW
Gas Flow During
Test, am3/sec
Temperature During
Test, °C
SCA During Test,
m2/(m3/sec)
30.48
27.94
25.4
22.86
24.76
22.86
Mast with Mast with Rigid Barbed Hanging Round Electrode Frame Hanging Round
Wires
Drop
Total
128
330.2
152.2
113.5
Measured Efficiency, % 99.92
Operating Temp, fJ-cm
% of Mass Emissions 31 f-5-33 30 85
Attributed to
Rapping3
Indicating range of values from two methods of calculation.
Laboratory measurement.
Square
Twisted
Wires
Drop
Hammer
1/2
160
155.2
155
47.6
99.55
1.7xlOl°
Wires
Tumbling
Hammers
1/2
122
117.2
157.2
50.4
99.80
2xl010
Wires
Magnetic Drop
Hammer
1/2
271
203.9
321.1
76.8
99.64
3.2xl010
With Spiral
Wires
Tumbling
Hammers
1/6
508
149.4
106.1
117. -J
99.85
4.6xlOJ '
Wires
Magne
Harame
1/16
800
126.8
358.9
55.4
98.98
1.5xlC
36-29
9b
63-44
-------
TABLE 33. SUMMARY OF REENTRA1NMENT RESULTS
2 17
Plant
Raps/Hr
Rap - No -Rap
One-Half Raps
Normal Normal Raps/Hr Raps/Hr Raps/Hr 773
Field
1
2
03 3
K)
4
5
6
Rapping Losses,
% of 'Emissions
Raps/Hr Current Current
Normal Normal Density Density
6 10 4.29 3.75
6 6 2.57 2.25
3 1 0.43 0.38
3
1
1
Rap- Rap- Rap- Min
Normal No-Rap Normal No-Rap Normal No-Rap Normal
10 1.67 30-60 12.5-25 10 4.17 8
10 1.67 30-60 12.5-25 5 2.08 8
5 0.83 30 12.5 5 2.08 3
5 0.83 30 12.5 2 0.83 3
1 0.42 1
1
Raps/Hr
Rap-
No-Rap
2.74
2.74
1.03
1.03
0.34
0.34
Rap-No Rap/Rap
Normal-No Rap/
Normal
T.W.A.-No Rap/
T.W.A.
31
65
33
45
55
82
38
30
18
85
85
71
29
36
15
44
63
-------
calculation methods, Table 34 provides typical flue gas and fly
ash compositions obtained at the test sites.
„-, u sh°ws the time variations over the test period at
Plant ^1 in boiler load, precipitator power, dust resistivity and
relative particle concentrations in two size bands (0.6 to 1.8 ym
and 1.5 to 3 ym) . August 5 and 6 were "normal" rapper operation
test periods, whereas August 7 and 8 were "no-rap" test periods.
It is readily apparent that, on August 7, changes in variables
other than rapper energization caused exit particulate concentration
changes which masked the effect of rapping system de-energization.
The LPSS system, however, was able to detect rapping puffs, as de-
scribed below.
Figures 273 and 274 show the number of 6-12 and 12-24 ym dia-
meter particles counted in 10 minute intervals through one day of
testing with rapping and one day of testing without rapping, re-
spectively, Cyclic concentration variations with a period of one
•hour were expected when the rappers were on and are fairly apparent
in the data shown in Figure 273. No such cyclic pattern is appar-
ent in the data shown in Figure 274 which were obtained with the
rappers de-energized. Note the obvious effect of losing power to
one of the TR sets. The average counting rate was much reduced in
the 6—12 and 12-24 ym channels with the rappers turned off as can
be seen by comparison of Figures 273 and 274.
As indicated previously, the attempt to determine rapping
losses at Plant 1 by comparison of mass train and impactor data
sets from normal and no-rap periods was not successful due to other
factors influencing outlet emissions. However, an estimate of the
contribution of rapping losses to total mass emissions was made
from data from the LPSS and outlet impactor systems. The estimate
is that 30% of total outlet mass emission during normal rapper
operation can be attributed to rapping reentrainment. Figure 275
shows the rap-no-rap data for the EAA system and the rap and no-
rap impactor derived efficiencies. The estimated no-rap efficiencies
are based on the data from the LPSS system and .these are subject to
large uncertainties because of the poor counting statistics for the
larger particles coupled with the limited time span over which the
data were taken. Fifty percent confidence intervals are shown for
the impactor and EAA data. Even with the existence of the indicated
uncertainties, it is apparent that very high- collection efficiencies
are achieved in the particle diameter range 0.05 to 20.0 ym. The
minimum collection efficiency is approximately 99.2% at 0.20 ym
diameter..
The alternating sampling 'strategy with1 impactors and mass
trains was successfully employed at Plant 2 and subsequent test _
sites to differentiate between reentrainment resulting from rapping.
and steady-state emissions. Figure 276 presents rap and no-rap
-data from Plant 2 from the EAA and the impactor sampling system
The large error bars (50% confidence intervals) on data obtained
483
-------
TABLE 34. TYPICAL FLUE GAS AND ASH COMPOSITIONS
2 1 7
oo
Plant 1 2
Date 8/7/75 1/16/76
Flue Gas
Temp., °C 164 154
SO2, ppm by vol. 282 3200
SO3, ppm by vol. 6.5 12
H2O, vol. % 8,2 7.2
Fly Ash
Lor
10/6/76
106
470
<0.5
8.7
0.61
5.72
10.92
3.5
1.0
6
1/31/77
346
355
<0.5
9.6
Ash Source
Date
Wt. % of1
Li2O
Na2o
K20
MgO
CaO
Fe203
A1203
Si02
Ti02
PzOs
SO3
Hopper 1
8/7/75
0.02
0.9
1.72
3 61
8.71
5.49
24.64
50.55
1 .22
0.50
0.55
High Vol.
Sample
1/15/76
0.02
0.54
2.49
0.95
4.73
22. 72
18.52
45.69
1.45
0.30
2.77
High Vol.
Sample
3/2/76
0.03
0.67
2. 12
1.00
4.95
13.13
21, 76
50.23
1.96
0.78
2.29
High Vol.
Sample
4/27/76
0.04
0.43
3.5
1.3
1.1
7.2
28.4
S3. 8
] .8
0.23
0.50
High Vol.
Sample
10/5 &
10/6/76
0.02
1.38
0.54
1.1
5.8
6.1
13.2
70.8
0.87
0.05
0.50
High Vol
Sample
1/31/77
0.013
1.52
1.4
1.8
6.0
5.0
24.3
57.6
2.1
0.32
0.54
O.ll
1 Chemical analyses obtained from ignited samples
Loss on ignition
-------
GROSS LOAD
MW 120
PWR/TYP.
SECTION, kW
GAS TEMP
°C
RESISTIVITY
1Q11. ohm-cm
COUNT RATE
NO./SEC
(1.5-3 M*n>
PARTICLES
COUNT RATE
NO./SEC
(0.55-1.8 nm)
PARTICLES
155
150
145
140
4
3
2
1
400
300
200
100
0
2000
1000
-/
&
Ck
\
\
-------
7.0
6.0
5.0
LLJ
? 4.0
2
w
LU
_J
o
Q.
3.0
2.0
1.0
! . I
• 6-12 ,um
O 12-24/urn
i ~i
SOOT
BLOWING
T r — i r
9:00 10:00 11:00 12:00 1:00 2:00 3:00 4:00 5:00 6:00
TIME, hours
3640-262
Figure 273. Particles per minute vs. time for large particle
system on August 6, 1975 — rappers on (Plant I).217
486
-------
10:00 11:00 12:00 1:00 2:00 3:00 4:00 5:00 6:00
TIME, hours
3540-263
Figure 274. Particles per minute vs. time for large particle
system on August 7, 1975 — rappers off (Plant I).217
487
-------
PENETRATION-EFFICIENCY
lO'
101
2
O
p
^
e:
h-
LU
uj 100
f—
UJ
O
cc
UJ
Q.
10-1
in-2
IU
1C
« RAP IMPACTOR
_ ESTIMATED NO RAP
- —
-
*
- ^« -
m . — '
^» _
^ /\. A T* ™
. *|™ ™ ^
ITL V-IT
B- **• I
T «— _ T ^
^BB j
J & fr f /"x —
: f *T J1/ \ T- :
: | J W l :
1 ^ I r
ESTIMATE FROM LPSS \ ^
f Illtiii! T ifllllll 1 liftlll 1 litill
r2 io-1 10° 101 K
U.U
90.0
o
z
UJ
5
99.0 t
LU
Z
UJ
O
CC
UJ
c.
99.9
99.99
)2
PARTICLE DIAMETER, micrometers
8E40-264
Figure 275.
Plant 1 rap-no rap fractional efficiency including
ultrafine and impactor measurements.217
488
-------
102
O
P
<
s
LU
2 100
a.
i-
u
O
E
UJ
a.
10-2
PENETRATION-EFFICIENCY
1tT2
OPEN SYMBOLS - NO RAP
CLOSED SYMBOLS - RAP
AA ULTRAFWE
O • IMP ACTOR
a
TJ
90.0
1 1 1 1 II
1 1 1 I 4 11 1 1 1 1 I M
99.0
99.9
10-1 10° lo1
PARTICLE DIAMETER, micrometers
I i i, i i i ii) 99.99
102
3540-265
Figure 276. Rap-no rap ultrafine and impactor fractional
efficiency- Normal current density, Plant 2.215
489
-------
from the ultrafine particle system are a reflection of difficulties
encountered with condensation of sulfuric acid, which created an
interferring aerosol in the ultrafine size range. The data were
screened and those results which were felt to be non-representative
were discarded. It is apparent that rapping losses become signifi-
cant only for particle diameters larger than 1 to 2 ym. The presence
of significant large particle emissions in the absence of rapping
is also indicated by Figure 276, and was confirmed by data .obtained
from the LPSS. These emissions apparently resulted from sparking
or voluntary reentrainment. Plant 2 was operating with a high sul-
fur eastern coal which produced a fly ash with tow electrical re-
sistivity.
Figure 277 illustrates the large particle losses (on a relative
basis) measured at Plant 4, which is a hot-side installation, using
the impactor and ultrafine sampling systems with the rap-no-rap
sampling sequence. -The data obtained' with normal rapper operation
(not shown) show reasonable agreement for sizes greater than 1.0 ym
diameter, indicating the alternating sampling strategy did not
significantly distort the results obtained. As with the previously
discussed data, the results indicate that rapping reentrainment
does not cause a significant change in fine particle emissions.
The rapping emissions obtained from the measurements on the
six precipitators are graphed in Figure 278 as a function of the
amount of dust calculated to have been removed by the last field.
The dust removal in the last field was approximated by applying the
relation
n'/section = 1-exp (-X"/N_), (62)
•tit
where
n'/section = overall mass collection fraction per section,
X' = -in (1-no) , (63)
TI o = overall mass collection fraction determined from mass
train measurements under normal operating conditions, and
N = number of electrical sections in series.
il*
These data suggest a correlation between rapping losses and
particulate collection rate in the last field. Data for the two
hot-side installations (4 and 6) which were tested show higher
rapping losses than for the cold-side units. This would be ex-
pected due to reduced dust adhesivity at higher temperatures.
Data 2a and 2b are for a cold-side unit operating at normal and
approximately one-half normal current density, respectively. The
decrease in current density at installation 2 resulted in a signi-
ficant increase in rapping emissions due to the increased mass
collected in the last field and smaller electrical holding force
for the same rapping intensity.
490
-------
101
z
o
ui
5
a.
I-
2
UJ
u
e
A RAP ) ULTRAFINE
£ NO RAP /
O N^^AP } "VECTOR
4
I
I
' I I I I J I I I I I I I I I I I I I I I 1 I I I I I
90.0
99.0
u
•z
UJ
U
z.
LU
u
cc
ai
99.9
I 1 I I I I I I I nrL nn
10-2 10-1 10° 101 102
PARTICLE DIAMETER, micrometers
3540-266
Figure 277. Ultrafine and impactor rap-no rap fractional
efficiencies, Duct Bl., Plant No. 4, with 50%
confidence intervals.
2 1 7
491
-------
100
o 10
tn
Q
en
O
LLJ
CL
0.1
r i i i i .1 iii i r i i j 11 ii i i T i i, 11 L
Y2 = 0.618X-894
y1 = 0.155X
.905
,l
L I I I I I
10 100
CALCULATED MASS REMOVAL BY LAST FIELD, mg/DSCM 3640-267
Figure 278. Measured rapping emissions versus calculated
particulate removal by last field.19
492
-------
The simple exponential relationships
yi = (0.155)x°'905 (64)
and
'72 = (0.618)X°'894 (65)
can be used for interpolation purposes in determining the rapping
emissions (mg/DSCM) for a given calculated mass removed by the
last field (mg/DSCM) for cold- and hot-side precipitators, respec-
tively. _Figure 278 was constructed using the cal?ulated mass
removed in the last field determined by the measured overall
mass collection efficiency during normal operation of the precipi-
tator. This was done because complete traverses were made by the
mass trains during the normal tests whereas this was not the case
for the measurements made during the no-rap tests. In principle,
.the no-rap efficiencies should be used to calculate the mass removed
in the last field. Obviously, the limited amount of data obtained
thus far is not sufficient to validate in general the approach pre-
sented here. However, this approach gives reasonable agreement
with the existing data and offers a quantitative method for esti-
mating rapping losses.
The apparent size distribution of emissions attributable to
rapping at each installation was obtained by subtracting the cumu-
lative distributions during non-rapping periods from those with
rappers in operation, and dividing by the total emissions (based
on impactor measurements) resulting from rapping in order to obtain
a cumulative percent distribution. Figure 279 contains the results
of these calculations. Although the data indicate considerable
scatter, an average size distribution has been constructed in
Figure 280 for use in modeling rapping puffs.
Summary of the results of rapping studies—Pilot plant studies
indicate that rapping emissions decrease with increasing time be-
tween raps. Also-, the percentage of the collected dust removed
from the collecting electrode increases with increased time between
raps. The buildup of a residual dust layer on the collecting elec-
trodes that could not be removed with the maximum, available normal
plate acceleration has been evidenced. By varying the rapping
frequency, the penetration due to rapping reentrainment could be
varied from 18 to 53% of the total penetration. These results
point out the need for a flexible rapping system in which the
rapping frequencies for the different sections can be varied and
in which the rapping intensities can be varied. With this type
of system, the rapping function can be optimized for specific pre-
cipitator operating conditions and ash properties in order to
minimize-the -penetration of.particulate out of the precipitator
due to rapping reentrainment.
493
-------
£
a.
EC
UJ
LU
g
<
Q
^U
10
9
8
7
5
4
3
2
1
II I i I 1 1 I 1 1 I >
0 PLANT 4 «C
• PLANT 6
A PLANT 2 9 DA
I A PLANT 3
- D PLANT 5 0 »BOA A
- • PLANT 1
—
B O0 A A
-
_
• DO A*
~
D O • A A
Q O • A A
iP * * £ ! Illll | 1
III 1
A a A
' A
-
-
•™
—
_
~
-
| 1 1 1
0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99
% LESS THAN
99.8 99.9
3540-268
Figure 279.
Apparent rapping puff size distribution for six
full-scale precipitators.a9
494
-------
E
3.
tr
UJ
K
UJ
5
Q
10
20 3Q 40 50 60 70
%LESS THAN
80
90 95
3640-289
Figure 280.
Average rapping puff size distribution for six
full-scale precipitators.l9
495
-------
The pilot plant data suggest that thicker dust layers produce
larger reentrained particles upon rapping. The majority of the
particles in the rapping puffs were agglomerates. These data
would indicate that as one proceeds from the inlet section to the
outlet section increased times are -needed between raps in order
to obtain dust layers with sufficient thickness to produce large
reentrained agglomerates, during .rapping. The large agglomerates
can be easily recollected by the precipitator..." Depending on the
rapping frequency, typical mass median diameters "for reentrained
particulate from an inlet section would range from approximately
10 ym to 20 urn with very little of the mass less than 2.0 ym.r
The pilot plant studies also showed significant vertical strat-
ification of particulate matter reentrained as a consequence of
rapping. All particle size bands showed a decrease in concentra-
tion with increasing distance from the bottom baffle. This was
attributed to both gravitational settling and hopper boil-up.
Emissions due to hopper boil-up were observed at some time- after
observation of emissions due to particulate matter reentrained
directly into the gas stream from the collection electrodes. In these
studies, hopper boil-up contributed" significantly to the reentrain-
ment emissions. This points out the need for adequate design of
hoppers and hopper regions to prevent excessive hopper boil-up.
The data obtained from the six full-scale precipitators showed
that rapping losses as a percentage of total mass emissions ranged
from over 80% for one of the hot-side units to 30% for the cold-
side units. The high rapping losses for the hot-side unit were
probably due both to reduced dust adhesivity at high temperature
and relatively short rapping intervals. It was also found that
reduction of the operating current density at Plant 2 resulted in
increased emissions due to rapping. This was due to increased mass
collected in the last field and reduced electrical holding force.
Measurements of fractional efficiency with and without elec-
trode rapping showed that losses in collection efficiency due to
rapping occur primarily for particle diameters greater than 2.0 ym.
The available mass emission data suggest a correlation between
the dust removal rate in the last rapped section of the precipi-
tator and the emissions due to rapping. Apparent rapping puff
particle size distributions measured at the outlets of the full-
scale precipitators had mass median diameters ranging from approxi-
mately 6.0 ym to 8.0 ym. Real-time monitoring of outlet emissions
also revealed sporadic emission of particulate matter due to
factors other than rapping.
Reentrainment from Factors other than Rapping—
Although it is difficult to quantify the complex mechanisms
associated with particle reentrainment due to (1) the action of
the flowing gas stream on the collected particulate layer, (2)'
sweepage of particles from hoppers caused by poor gas flow con-
ditions or air inleakage into the hoppers, (3) bouncing of
496
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particles following impaction on the collection surface (4)
impaction of large particles with small particles previously de-
posited on the collection electrode, and (5) excessive sparking,
the effect of these nonideal conditions on precipitator ptrfo?-
inance can be estimated if some simplifying assumptions are made.
If it is assumed that a fixed fraction of the collected material
of a given particle size is reentrained and that the fraction
does not vary with length through the precipitator, an expression
can be derived which is identical in form to that obtained for
gas sneakage: 8
r
NR = [R + (i-R)(1-ni f {66)
P
where NR is the penetration of a given particle size corrected
for _ reentrainment, R is the fraction of material reentrained, and
NR is the number of stages over which reentrainment is assumed to
occur .
Since equations (44) and (66) are of the same form, the effect
of particle reentrainment without rapping can be expected to be
similar to the effect of gas sneakage, provided that a constant
fraction of the collected material is reentrained in each stage.
It is doubtful that such a condition exists, since the gas flow
pattern changes throughout the precipitator and different holding
forces and spark rates exist in different electrical sections.
However, until detailed studies are made to quantify the losses
in collection efficiency as a function of particle size for these
types of reentrainment, equation (66) provides a means of esti-
mating the effect of particle reentrainment without rapping on
precipitator performance.
Several things should be done in order to minimize the parti-
cle ^eentrainment due to factors other than rapping. The gas
velocity distribution should meet IGCI criteria as a minimum and
should have an average value of -1 . 5 m/sec (5 ft/sec) or less.
Hoppers should be designed with proper baffling to prevent excessive
flow in the ash holding regions and should have no air inleakage.
Excessive sparking should be avoided.
Nonuniform Temperature And Dust -Concentration
Non-uniform temperature and dust concentrations may exist in
a precipitator and may result in adverse effects. A non-unirorra
temperature may result in variations in the resistivity of _ the
collected dust layer, variations in the electrical properties of
the gas, and corrosion in low temperature regions. The first^two
effects may lead to excessive sparking in certain regions of the
precipitator. A nonuniform dust concentration- may result in ex-
.cessive buildups, of dust on corona wires, collection plates, beams,
497
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etc. and excessive sparking due to particulate space "charge effects,
Excessive dust buildups and. possible "doughnut" formations on
corona wires tend to suppress the corona and to cause uneven corona
emission. Excessive dust buildup's on the collection electrodes ' "•'.'
between raps may result in significant .particle reentrainment,
undesirable electrical conditions/ and .reduced cross-section for
gas flow.
The effects of nonuniform -temperature and dust concentration
on precipitator performance have not been analyzed or studied
extensively. Therefore, at the present time,, these effects can
not be quantified. Generally, it is assumed that if a good gas
flow distribution exists, then the temperature and dust distri-
butions will also be good. This may be a poor assumption for
many precipitator arrangements that .are commonly employed.
498
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SECTION 7
EMISSIONS FROM ELECTROSTATIC PRECIPITATORS
PARTICULATE EMISSIONS
The data required for determining the mass efficiency of
control devices collecting fly ash are obtained by sampling the
flue gas upstream and downstream of the pollution control device.
Mass concentrations of particulate matter in flue gas are measured
by drawing a sample of gas through a probe and filter and weighing
the collected material.
Methods For Determination Of Overall Mass Efficiency
Various organizations have proposed specific procedures and
sampling train designs for mass concentration measurements. The
Environmental Protection Agency's Method 5 specifies the use of
an extractive sampler.219 Sampling trains constructed to meet
Method 5 specifications were initially designed to operate at flow
rates up to one cubic foot per minute (23.3 liters/min) . Recently,
a four cubic feet per minute (113 liters/min) extractive sampler
has been developed which is claimed to comply with the requirements
of Method 5. The proposed EPA Test Method 17 specifies the use of
in situ sampling. ° The American Society of Mechanical Engineers
(ASME) Performance Test Code 27 specifies the use of either an
in situ or extractive sampler.221 The ASME will soon be releasing
a new Performance Test Code 38 which will supercede the Performance
Test Code 27. The Industrial Gas Cleaning Institute (IGCI Publi-
cation No. 101) and Western Precipitation Co. (Bulletin WP 50)
have also suggested sampling methods. The American Society of
Mechanical Engineers (ASME) Performance Test Code 27 specifies
the use of either an in situ or extractive sampler.
EPA Test Method 5—-
Official performance testing of stationary sources for parti-
culate emissions from coal-fired power plants must be conducted
with the EPA Test Method 5 "Determination of Particulate Emission
from Stationary Sources".219 Method 5 relies on the removal or
extraction of a dust-laden gaseous sample from the duct or stack
followed by removal of the particles by a filter while monitoring
sample volume. With this method one obtains a measure of_the
average particulate mass concentration for the cross-sectional
499
-------
area of the duct during the time of sampling. There is some dif-
ference of opinion as to how the results should be interpreted,
especially in regard to condensation of vapors in the probe and
filter box which contains the condensers. Originally the Environ-
mental Protection Agency proposed that any material collected in
the condenser portion of the sampling train (shown in Figure 281)222
must be added to that of the dry collector (filter)- portion. After
numerous objections from people in the field, the proposed method
was altered so that compliance now is based only upon material
collected in the filter and in the prob-e preceding the filter.
Hemeon and Black contend, however, that even this modifi cat ion'
is not valid since condensation and chemical reaction occurs .in
the probe prior to the filtering of the sample.223'22" Therefore,
the S02 in the gas forms sulfates which later are collected on the
filter. However.- one might argue that such reactions, if they
occur, would also occur in the atmosphere and should be included
as particulate matter. 'Some investigators conducting performance
tests of control devices on emission sources prefer to use a sampling
train that differs from Method 5 in that the filter for collecting
particulate matter is located in the stack instead of outside the
stack at the end of the sampling probe (ASME Performance Test Code
27) .
With EPA Method 5, one obtains a sample from the duct by
using a prescribed traversing procedure which involves isokinetic
extraction from different points within the duct. This procedure
yields, in effect, an approximate integration of collected mass
and sample volume over the cross-sectional area of the duct.
Before sampling, the number of traverse points must be determined
using EPA Test Method 1, "Sample and Velocity Traverse for Sta-
tionary Sources". The EPA sampling train consists of a thermally
controlled probe, with a variety of sampling nozzles and a pitot
tube assembly, which is connected to a sampling case containing a
heated filter assembly housing, filter, and a number of impingers .
located in an ice bath (Figure 28.1) . The control co-n.sole .-contains
the flow meters, pressure gauges, thermal control"systems, timer,
and vacuum pump required for sampling.
DESCRIPTION OF COMPONENTS
The nozzle removes the sample from the gas stream and should
disturb the gas flow as little as possible. This means a thin
wall and sharp edge. The major requirement of the probe, which
removes the sampled stream from the stack, is that it does not
significantly alter the sample from stack conditions. The sample
temperature should be maintained at 120°C + 14°C (248°F + 25°F)
or at such other temperature as specified by an applicable subpart
of the standards or approved by the Administrator of the EPA for
a particular application. Glass probe liners are desirable over
metal probe liners, but steel probes are allowed for probe lengths
over 2.5 meters. New regulations require a thermocouple to be
attached to the probe end for monitoring the stack gas temperature.
500
-------
IMPINGER TRAIN OPTIONAL:
MAY B£ REPLACED BY AN
EQUIVALENT CONDENSER.
PROBE
I
HEATED
AREA FILTER HOLDER
THERMOMETER
IMPINGERS.
THERMOMETERS
ORIFICE
9
ICE BATH I
BY-PASS
VALVE
{>Or—C*3-
CHECK
VALVE
r~*\ VACUUM
(/)) GAGE
MANOMETER
DRY TEST METER
MAIN
VALVE
AIR-TIGHT PUMP
VACUUM LINE
3540-270
Figure 231. The EPA Method 5 particulate sampling train.
222
501
-------
Pressure drop, generated by the gas velocity in the duct, is mon-
itored by an S-type pitot tube to insure isokinetic sampling ve-
locities. The glass fiber filter should be at least 99.95%
efficient.in collecting 0.3 micron dioctylpthalate smoke particles.
An optional cyclone type of collector precedes the filter and
results, when used, in the removal of larger particles.: The four''
impingers in the train remove water, gases, vapor, and' condensable
particulate matter. The EPA and some states do not require,-'the
measurement of the condensable particulate fraction and hence the
impingers are not specifically required. The impinger 'train may
be substituted by any type condenser such as a piece of coiled
tubing immersed in an ice bath. The condenser should be followed
by a silica gel drying tube to collect the remaining moisture and
protect the vacuum pump and dry gas meter. The sampling box holds
the probe, the filter holder, and the impinger train and its ice
bath. The filter holder is contained in a heated area of the
sampling box and the temperature of this area should be maintained
at 120°C + 14°C. Where the condensable particulate fraction is
not required by state regulation or is of no interest, the sampling
box can be simplified.
The control box contains a vacuum pump capable of maintaining
isokinetic flow during heavy filter loadings, a control valve to
vary the sample stream flow rate, a vacuum gauge for measuring the
sample stream pressure, a dry gas meter equipped for determining
the sample volume, a calibrated orifice meter which is used to
monitor the sample stream flow rate, a pressure gauge to measure
the pitot tube pressure drop, a pressure gauge to measure the
orifice meter pressure drop, a variable voltage power supply to
maintain the probe and filter box at their respective temperature
by means of their individual heaters, and a pyrometer or potentio-
meter calibrated for thermocouple measurements of the duct and
filter box temperature.
Calibration requirements are discussed in the EPA maintenance
procedures.225 Critical laboratory calibrations include the orifice
meter, dry gas meter, and pitot tube. Calibration of the orifice
meter and dry gas meter requires the use of a wet.gas meter. Various
other common laboratory instruments are required for the maintenance
and calibration of the other system components.
Many commercial models for conducting Method 5 tests are avail-
able and a list of some manufacturers is given in Table 35*226
ASTM - Test Method (Figure 282)
227
Both the ASTM and the ASME provide specifications for in situ
samplers. The ASTM Method is similar to the EPA Test Method 5.
The main difference is the use of an instack filter with no re-
strictions on the sampling flow rate used. However, the filter
should be preheated by being allowed to reach temperature equili-
brium in the process stream for at least thirty minutes prior to
502
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TABLE 35. SAMPLING SYSTEMS FOR TESTING
BY EPA METHOD 5226
Company
Aerotherm-Acur ex
Glass Innovations, Inc.
Joy Manufacturing Co.
Lear Siegler, Inc.
Environmental Technology
Division
Misco International
Chemicals, Inc.
Research Appliance Co.
Scientific Glass &
Instruments, Inc.
Lace Engineering Co..
Bendix Corporation
Environmental & Process
Instruments Division
Address and Telephone Number
485 Clyde Avenue
Mountain View, Califir-.ia 94042
(415) 964-3200
Post Office Box B
Addison, New York 14801
Commerce Road
Montgomeryville, Pennsylvania 18936
(215) 368-6100
74 Inverness Drive East
Englewood, Colorado 80110
(303) 770-3300
1021 South Noel Avenue
Wheeling, Illinois 60090
(312) 537-9400
Pioneer and Hardies Road
Gibsonia, Pennsylvania 15044
(412) 443-5935
7246 Wynnewood
Houston, Texas 77001
88.23 North Lamar;::V
Post Office Box 9757
Austin, Texas 78766
(512) 836-5606
1400 Taylor Avenue
Baltimore, Maryland 21204
(301) 825-5200
503
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GLASS FIBER THIMBLE FILTER
HOLDER AND PROBE (HEATED)
SAMPLING
NOZZLE
REVERSE-TYPE
PITOT TUBE
CHECK
VALVE
DRY TEST METER
AIR TIGHT PUMP
3540-271
Figure 282, ASTM-type particulate sampling train
227
504
-------
sampling. _When inserting the filter for preheating, the nozzle
must be pointed in the downstream direction of the qas flow to
prevent accumulation of fly ash in the nozzle. Also, when in-
serting the filter into a duct which is not under ambient pressure,
the sampling lines must be closed to prevent undesirable gas flow
through the filter. *
ASME Performance Test Code 27
The ASME Performance Test Code provides for the use of a
variety of instruments and methods."1 Since testing experience
has not been uniform enough to permit standardized sampler design,
this code merely gives limiting requirements whizr. past experience
has shown gives the least sources of error. The Code is designed
as a source document which provides technically sound options to
be selected and agreed upon by the contractor and the contractee
performaning the sampling. According to ASME Performance Test
Code 27, the sampling device shall consist of a tube or nozzle
for insertion into the gas stream and through which the sample is
drawn, and a filter (thimble, flat dish, or bag type) for removing
the particles. For the purpose of the Power Test Code, 99.0% col-
lecting efficiency by weight is satisfactory, and the filter may
be made of cotton, wool, filter paper, glass wool, nylon, or orlon.
The filter arrangement may be extractive or iri situ.
The main advantage of in_ s i'tu sampling -over extractive sampling
is that substantially all of the particulate matter is deposited
directly on the filter, which means that only a small area other
than the filter contains particulate matter and requires washing.
Also, since the filter is maintained at the stack gas temperature,
auxiliary heating of the filter is not needed. The main disadvan-
tage of the in situ sampler over the extractive sampler is the fact
that the in sTtu sampler is limited to process streams where temper-
atures do~ot exceed the limit of the filter medium and holder. In
fact, thermal expansion of the filter holder may create gas leakage
problems. Of course, the instack filter system cannot yield data
on condensable particulate matter in the plume.
Another difference between the filtration methods is the
sampling flow rate used in each method. Sampling trains constructed
to meet E^>A Method 5 specifications were initially designed to
operate at flow rates up to 28.3 Z/min (1 ftVmin); recently a
113 £/min (4 SCFM) sampler has been developed which complies with
EPA Method 5 specifications. ASTM and ASME Methods do not define
a flow rate range. Some high volume trains can operate at flow
•rates up to 1.98 raVmin (70 ft3/min) .
p.r ed ,o the
505
-------
In a process stream where the mass concentration is highly variable,
a large number of high volume runs would be required to obtain a
value representation of the same average mass concentration obtain-
able from one run of the low volume run. Statistically, it is more
desirable to obtain several samples of a value than just one
sample. For stable streams.-this will give additional, information
revealing, the precision with which the method has been applied.
When using high flow rate extractive samplers the high ratio of
sample gas flow rate to probe wall area minimizes errors due to
loss of particulate matter on the tubing walls between the nozzle
and the filter, minimizes heat losses, and thus helps to prevent
the condensation of vapors in the train. The high ratio .also
can be a disadvantage when cooling of the sample gas stream is
required to protect the equipment since auxiliary cooling equip-
ment may be needed.
STATUS OF RULES AND REGULATIONS GOVERNING PARTICULATE MATTER,
SULFUR OXIDE, NITROGEN OXIDE, AND OPACITY FOR COAL-FIRED POWER
BOILERS IN THE UNITED STATES
Background
228
The Clean Air Act of 1970 gave the Environmental Protection
Agency (EPA) the responsibility and authority to control air pollu-
tion in the United States and its territories. In 1971 EPA issued
National Ambient Air Quality Standards for six pollutants — sulfur
dioxide, nitrogen dioxide, particulate matter,- carbon monoxide,
hydrocarbons, and photochemical oxidants. For each pollutant both
primary and secondary standards were issued. Primary standards
were set at levels necessary to protect the public health and were
to be met no later than three years from the date of promulgation
(subject to limited extensions of up to three years). Secondary
standards were designed to protect the public from adverse effects
to their welfare. Each state was required to adopt and submit to .
the Environmental Protection Agency a plan for attaining, maintaining,'
and enforcing the standards in all regions of the state. The State
Implementation Plans specified all details necessary to insure
attainment and maintenance of the standards. Most of the state
implementation plans were approved by the Environmental Protection
Agency in 1972.
In addition to the state implementation plans, new source
performance standards were issued by the Federal Government. New
sources include newly constructed facilities, new equipment which
is added to existing facilities, and existing equipment which is
modified in such a way that results in an increase of pollutant
emissions. New source standards limit specific pollutant emissions
from categories of sources (such as fossil fuel-fired steam gen-
erators) which are determined to contribute significantly to the
endangerment of public health and welfare.
506
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Current Status Of Emission Regulati
ons
According to the Environmental Protection Agency particu-
late and opacity standards for new coal-fired potboilers If
25 m or more are 0,05 g/105 cal (0.03 Ib/million BtS? anS 20%
(on a six minute average), respectively.230'231 Also final
sulfur standards just released by EPA indicate a "sliding"
standard that requires scrubbing of 70 to 90 percent of the
sulfur from the flue gas, depending upon the sulfur content
of the coal.- For coal with a sulfur content that would cause
an emission, uncontrolled, of less than 3.6 g/106 cal (2 lb/
million Btu), only 70 percent of the sulfur dioxide need be
removed from the flue gas. For uncontrolled emission levels
from 2 lb up to 6 lb the desulfurization must be sufficient to
bring the controlled emission level down to 0.27 kg (0.6 lb) .
For coal-sulfur levels from 2.72 kg (6 lb) to 5.45 kg (12 lb)
the control efficiency must be 90 percent. Above 5.45 kg (12
lb), the degree of desulfurization must be enough to bring the
emission down to no more than 2.16 g/105 cal (1.2 Ib/million
Btu), which was the old limit. The nitrogen oxides standard
is 0.90 g/106 cal (0.50 Ib/million Btu) from subbituminous coal,
shale oil, or any solids, liquids, or gaseous fuel derived from
coal.
Table 48 in the Appendix C gives a compilation of emission
limits for particulate matter, sulfur oxide, and nitrogen oxide
limits for coal-fired power boilers for every state in the United
States. Table 48a gives emission limits for California. Cali-
fornia's counties each have separate rules and regulations. There-
fore emission limits were obtained from most of the counties in
an SoRI survey. Table 49 in Appendix C gives a compilation.of
opacity limits as they apply to those power plants which come
-under the "existing source" category of each state's opacity
regulations. New source limits for opacity were not compiled
since they generally follow the pres-ent Federal limit of 20%.
Performance Evaluation
To evaluate the performance of new stationary sources, the
Environmental Protection Agency has specified reference methods
for the manner in which tests must be conducted at each plant.
The Code of Federal Regulations 40, Part 60-Standards of Perfor-
mance for New Stationary Sources, Appendix A - Reference Methods,
contain the reference methods to be used to check performance
standards. Method 9 is the reference method for visual determin-
ation of the opacity of emissions from stationary sources. This
method is basically a visual determination by a qualified observer.
There are also performance specifications and test procedures for
transmissometer systems which are used to; continuously monitor
opacity of stack emissions. These specifications are found in
Appendix B of the Code of Federal Regulations 40, Part 60 Where
disagreements occur between a qualified visual observer's Determin-
ation (Method 9) and a transmissometer, .Method 9 takes precedence
507
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in the opinion of the Environmental Protection Agency.230 Method
5 is the reference method for.performance testing of stationary
sources for particulate emissions. Method 5 relies on the removal
or extraction of a dust-laden gaseous sample from the duct or
stack followed by removal of the particles on a filter while
measuring sample volume. Methods 6 and 7 in Appendix A describe
the reference methods for determination of sulfur dioxide and
nitrogen oxide emissions from stationary sources, respectively.
In Method 6 .a gas sample is., extracted from the sampling point in
the stack. The acid mist, including sulfur trioxide is separated-
from the gaseous sulfur dioxide. The sulfur dioxide fraction is ••
then measured by the barium-thorin titration method. In Method 7
a grab' sample is collected in an evaporated flask containing, a
dilute sulfuric acid-hydrogen peroxide absorbing solution, and
the nitrogen oxides, except nitrous oxide, are measured colori-
metrically using the phenoldisulfonic acid procedure. Performance
specifications and specification test procedures for monitors of
SOa and NO _ are given' in -.Appendix .B, Performance Specification 2.
X.
A helpful procedure for planning and implementing tests for
control device evaluation can be found in a recent SoRI publi-
cation. 5 **
Discussion And Definition Of Opacity
Suspended particles in an aerosol will scatter and absorb
radiation from a beam passing through it; the remaining portion
is transmitted. The transmittance, T, of a fluid medium con-
taining suspended particles is defined as the ratio of the trans-
mitted radiation intensity to the incident radiation intensity.
T is given by the Bouguer, or the Beer-Lambert, law:
T = exp (-EL) (67)
where L is the path length of the beam through the aerosol medium
and E, the extinction coefficient of the medium, is a complicated
function of the size, shape, total projected area, refractive
index of the particles, and the wavelength of the radiation. Some-
times the measured transmittance is expressed in terms of optical
density defined as
O.D. = Log (1/T) (68)
instead of the transmittance. Consequently, instruments and
methods for aerosol measurement based upon light transmission
principles have been referred to as transmissoineters, smoke den-
sity meters, photo-extinction measurements, or turbidimetric mea-
surements.
While transmittance is defined as the ratio of light trans-
mitted through the aerosol to the incident light, opacity is
defined as the ratio of the light attenuated from the beam by
508
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the aerosol to the incident light (i.e., opacity = 1-T). Aerosols
which transmit all incident light are invisible, have a trans-
raittance of 100%, and an opacity of zero. Emissions which atten-
uate all incident light are totally opaque, having an opacity of
100% and a transmittance of zero.
Many versions of transmissometers, or smoke meters, are avail-
able as stack emission monitors. If the transmissometer is used
to measure instack opacity for purposes of compliance to federal
regulations, it must meet the EPA requirements for opacity measure-
ment systems as specified in the Federal Register of September 11,
1974. The use of visible light as a light source is required
because the response of the instrument is supposed to match
that of the human eye (photopic response) . The angle of view
and the angle of projection is specified, for compliance, as no
greater than 5° (see Figure 283).233
To obtain true transmittance data the collimation angles
(angles of view and projection) for the transmitter and receiver
must be limited to reduce the sensitivity to stray light scatter
(see Figure 283) . A zero degree angle is the ideal collimating
angle, whereas a non-zero angle will introduce a systematically
low reading of opacity. However, a compromise is necessary,
since as a zero degree collimation is approached, instrument
construction costs, operating stability, and optical alignment
problems increase. A transmissometer having a 5° collimating
angle applied to the emissions of a pulverized coal-fired steam
generator gave an opacity measurement that was about 5% low rela-
tive to the 0° value.2 3 *
The error in the transmissometer measurement due to the use
of different light detection angles has been analyzed theoreti-
cally by Ensor and Pilat and shown to be a function of detection
angle and particle size.235 They showed that, in general, the
error associated with a given detector viewing angle increases
with an increase in the particle mean diameter.
All transmissometers require purge air systems to protect
the optical windows or reflectors. Still, regular cleaning is
required with the accumulation rate varying widely from one loca-
tion to another. Most commercial instruments have automatic zero
and span checking capabilities to verify proper functioning and
calibration between cleanings.
Transmissometers can be used to measure the instack opacity
in order to obtain an estimate of the plume opacity for compliance
testing; or they can be used to measure the in situ opacity for
process control or as an estimate of mass concentration.
^ When the required measurement is the opacity of the emissions
at the exit of the stack, a measurement at any other location in
?ne s?a?k haf to have it^ optical path length adjusted to the exit
509
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PROJECTION ANGLE ANGLE OF VIEW
SOURCE
I _J
SAMPLE VOLUME
APERTURE
SCHEMATIC OF A TYPICAL TRAMSMISSOMETER SYSTEM
3640-272
Figure 283. Schematic of a transmissometer showing projection
and view angles which must be no greater than 5°
for EPA compliance.233
51C
-------
diameter. The calculation for this adjustment can be found in the
Federal Register.^6 Figure 284 gives the relationship Tf effluent
transmittance at the stack exit as a function of instack trJnsmit-
°f •*<* -it diameter to transmissometer
As opacity, 1-T, approaches zero the relative error in its
measurement with a transmissometer becomes unavoidably large.
For example, a two per cent error in the transmittance measurement
gives a 100 per cent error in an opacity of two per cent. In such
cases, important during diagnostic studies of control devices, a
nephelometer as used by Ensor,238 may be a more accurate measure of
opacity although it requires a probe and sampling traverses. This
instrument when used as an opacity monitor atter.prs to determine
E, the extinction coefficient, through a measurement of the scat-
tering coefficient alone where E = scattering coefficient + ab-
sorption coefficient. This is performed using a predetermined
relationship between E and the instrument response for a calibra-
tion aerosol. The errors in this type of opacity measurement depend
upon the variation of the ratio, aerosol absorption coefficient
to the scattering coefficient and the errors associated with extra-
active sampling. This ratio varies from zero for non-absorbing
particles to about one for highly absorbing aerosols giving possible
errors in opacity of ~ 100 per cent depending upon the calibration
aerosol. However, if the calibration aerosol is chosen judiciously
(i.e., with optical properties close to those of the sample aerosol)
and the opacity is low, the nephelometer errors are much smaller
than those obtained with the transmissometer at low opacities.
Relationship Between Opacity And Mass Concentration And Particle
Size ~~~~~
Theoretical Relationship —
Because of the interrelation between particle size distribu-
tion in a stack and the opacity, it is possible to meet mass emission
standards and still have an opacity problem. In fact, some changes
in flue gas streams causing a reduction in mass emissions have pro-
duced an increase in opacity. The relevance of this particular
aspect of opacity is described below,
The dependence of opacity upon the total mass concentration,
size distribtuion, and particle composition is given by
0=1- I/Io = 1 - exp (-W-L/p-K) (69)
where
0 = opacity,
I = intensity of transmitted light,
Io = intensity of incident light,
511
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100
90
80
70
_ 60
c
01
o
I 50
o
< 40
i-
30
C
I-
u
20
10
10
20 30 40 50 60
INSTACK TRANSMITTANCE, percent
70
80 90 100
3540-273
Figure 284.
Effluent transmittance vs. in stack transmittance
for varying ratios of stack exit diameter to in
stack path length: A = 1/4, B = 1/2, C = 3/4,
D = 1, E = 4/3, F = 2, G = 4.237
512
-------
W = total participate mass concentration,
L = illumination path length or diameter of plume,
p = particle density, and
K = specific particulate volume/extinction coefficient ratio.
The parameter_K, related to the volume/surface ratio of the
aerosol, is determined by the particle size distribution and re-
fractive index through calculations using the Lorentz-Mie theory
of light scattering for each size class. Illustrative calculations
of K assuming a log-normal size distribution ani ;arious refractive
indices have been carried out by Ensor and Filar.239 The results
for two values of the refractive index are given in Figures 285
and 286. It can be seen that K and thus opacity is very sensitive
to MMD, geometric standard deviation, and refractive index. Since
opacity increases as K decreases the minimum occurring around 0.5
to 0.1 ym in diameter is of particular interest. This light
scattering theory is based on a homogeneous sphere model for the
particl- b.
Sirc'-» control devices generally reduce the MMD while removing
particlej a reduction in the total emitted mass will not effectively
reduce the opacity if the inlet and outlet MMD's are to the right
of the ra:'nima in Figure 285.
For example, if an aerosol originally had an MMD of 10 ym and
a geometric standard deviation of 2 (shown in Figure 286) , and a
control device removed 80% of the mass from the aerosol while reducing
the MMD to 2 ym, then there would still be no change in opacity-
On the other hand, if the inlet MMD is close to the minimum then
a further reduction in total mass and/or MMD will be much more
effective at reducing opacity- Figures 285 and 286 with equation
(69) show that the change in opacity for a given change in total
mass requires knowledge of the aerosol size distribution and re-
fractive index. While the size distribution is of greatest
.importance in determining opacity, the differences in Figures
285 and 286 show that refractive index (determined by the com-
position of the particles) is also important.
Observed Relationship—
Several plants with, which SoRI -has. had experience demonstrate
the importance of particle size distribution to opacity. _A_-
-power plant in Wyoming has a cold-side electrostatic precipitator
with an SCA of about 98.5 mV(nVsec) (500 ftVlOOO cfm) . This
plant is near the particulate emission standard but does not meet
the opacity standard. Three other western plants which have hot
precipitates with SCA's in the 59.1-69 ^mV (mVsec) (300-350 ft /
1000 cfm) range have the same problem. This -can be attributed
in large part to the generally fine particle size distribution of
513
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GEOMETRIC
STANDARD
DEVIATION, og
REFRACTIVE INDEX = 1.50 |
WAVE LENGTH OF LIGHT = 550 nm I
I ! I I I III! I I I I Mill I I I I I Mil I I I I INI
10-2
10-1 10° io1
GEOMETRIC MASS MEAN RADIUS, rgw, microns
Figure 285.
Parameter K as a function of the log-normal size
distribution parameters for a white aerosol after
Ensor and Pilat.2 39
514
-------
cn
u
£ 10°
5
<
cr
<
a.
TO-1
10'2
GEOMETRIC
STANDARD
DEVIATION, ag
REFRACTIVE INDEX - 1.96 - 0.66i
WAVE LENGTH OF LIGHT = 550 nm
I I I II
I I I I I
tO-1 10° 10
GEOMETRtC MASS MEAN RADIUS, rgw, microns
102
3540-275
Figure 286.
Ensor and Pilat.
K as a function of the log-normal size
parameters for a black aerosol after
515
-------
ash obtained from burning western coal. (See discussion of Figure
285.) Another interesting case in point is a northern utility
which was burning an eastern coal at one of its plants equipped
with a normal cold-side electrostatic precipitator. This plant
was meeting the opacity standard but not the emission standard.
After switching to a western coal, the plant was able'to meet the
mass emission standard but could no longer meet the opac'ity require-
ment.
Even more dramatic is the situation at Southwest Public Service,
Harrington Station. This plant burns low sulfur coal and uses an
electrostatic precipitator/scrubber system to meet the particulate
standard. Measured emissions are 19.4 ng/J (0.45 lb/10 Btu) and
the opacity is around 38%. Sparks2393 has analyzed this case
and concluded that the high opacity was primarily due to the fine
aerosol produced by the precipitator/scrubber system.
For a transmissometer to be useful as a monitor of the mass
concentration, the properties of the particles (other than mass)
being monitored must remain fairly constant over the monitoring
period. Experimental data are available showing that good opacity-
mass concentration calibration can be obtained on some sources.
The sources that have been evaluated include coal-fired power
plants; 2" ° ' 2 " : ' 2"2 lignite-fired power plants;2"3 a cement plant ;21t"
a Kraft pulp mill recovery furnace;245 petroleum refinery; asphaltic
concrete plant; and a sewage sludge incinerator. 2 "* °
Nader reported tests that were performed over one 3-mon.th
interval and two 2-month intervals representing different seasons
of power plant operation.2k7 Emissions were increased at various
times by cutting off one or more electrostatic precipitator stages.
Correlation curves were essentially the same for the three dif-
ferent time periods with coefficients of 0.93, 0.98, and 0.99.
The coefficient for the composite correlation curve for the data
for all three time intervals is 0.97 (see Figure 287). Mass con-
centration ranged from 55 to 360 mg/m3. No problem with window
contamination occurred with continuous operation of the trans-
missometer spanning the one year period.
For an emission source with high efficiency particulate control
equipment, the size distribution of the emitted particulate matter
may be relatively constant. Therefore, emission sources with vari-
able emission and low efficiency particulate control equipment (i.e.
cyclone and low energy scrubbers) can be expected to provide
poorer correlation of instack plume opacity to particle mass con-
centration. Transmissometers may be useful indicators of mass
emissions, once calibrated, on sources where the aerosol proper-
ties remain constant.
516
-------
0.1 0.2 0.3 0.4
MASS CONCENTRATION, gm/m2
3540-276
Figure 287.
Correlation data between opacity and mass measure-
ments of particulate matter in emissions for a
coal-burning power plant. After Nader.2"7
517
-------
Example Of Modeling Of Opacity Versus Mass At The Exit Of An
Electrostatic Precipitator
The SoRI-EPA mathematical model of electrostatic precipitation
has been used with certain modifications to simulate the operation
of a power plant precipitator collecting fly ash from the burning
of coal under test conditions. Based on the simulation of test
conditions, the model has been employed to estimate the performance
of the precipitator as a function of current density, specific
collection area, inlet particle size distribution, and inlet mass
loading. Performance of the precipitator has been determined, in
terms of both overall mass collection efficiency and opacity.
The set of parameters used in the simulation of the test con-
ditions yielded an overall mass efficiency of 88.75%, opacities
in the range from 39 to 49%, and an outlet size distribution with
a mass median diameter (MMD) of 2.35 ym and a geometric standard
deviation (o ) of 2,91. The above values compare favorably with
the measured values. The simulation of the test conditions was
based on an inlet size distribution with an MMD of 4.0 urn and o?
of 2.45, a normalized standard deviation of the gas velocity dis-
tribution of 0.25, 5% gas sneakage per stage, a-rapping loss"size
distribution with an MMD of 4.5 ym and a ap of 2.8, and 35% of the
mass collected in the last field being reentrained in the outlet
emissions. The rapping emissions constituted approximately 40%
of the total outlet emissions for the simulation. Although the
parameters characteristic of the rapping losses will vary with
current density, specific collection area, and inlet mass loading
and particle size distribution, they were held fixed in making
projections since these dependences can not be quantified at the
present time.
The results of this particular application of the precipitator
model for design purposes in control of opacity are encouraging.
It appears that inlet and outlet size distribution and opacity
measurements along with precipitator operating parameters will
provide enough information to predict the necessary modification
to the precipitator to achieve a given level of opacity.
Measurement Of Relative Stack Emission Levels And Opacity
A number of optical techniques are used to determine relative
stack emission levels. Usually these techniques involve a deter-
mination of the degree of light transmittance or light scattering.
Some of the representative instrumentation used is discussed below:*
*Southern Research Institute and the Environmental Protection
Agency bear no responsibility for the promotional claims of these
companies.
518
-------
Nephelometers, devices that attempt to measure all of the
seattered_light, have recently been applied to stack monitoring.
One such instrument, call the Plant Process Visiometer (PPV) , has
been developed by Meteorology Research, Inc., 464 West Woodbury Road,
Altadena, California 91001, telephone (213) 791-1901 2kB'2"9'2*°
A diagram of the optical assembly is shown in Figure'288 The
sample, extracted through a probe with no dilution, is passed
through the detector view. The light source is diffused so that
light rays illuminate different portions of the sample in a wide
range of angles from near 0° to near 180U with respect to the
detector view. During operation the detector signal is calibrated
with an opal glass calibrator which has been adjusted to give a
certain scattering coefficient which corresponds to an opacity of
5.4 percent assuming no light absorption. This device gives an
acceptable measure of mass concentration if calibration is per-
formed against a direct mass technique and if the size distribution
and composition of the aerosol remain nearly constant.
An in situ monitor has been developed that is based on the
measurement of backscattered light.251 This instrument, called
PILLS V, was developed by Environmental Systems Corporation, Post
Office Box 2525, Knoxville, Tennessee, 37901, telephone (615) 637-
4741, and uses a laser as the light source. As shown in Figure
289, both the light source and detector are located within the
same enclosure.232 One of the features of the PILLS V is its
ability to determine mass concentration. The instrument optically
defines a sample of 12 cm3 (0.73 in3) at 10 cm from the end of the
probe within the process stream. Detection of the scattered light
at angles greater than 160° relative to the beam produces an elec-
trical signal that is proportional to the mass contained within
the sample volume. Since the sample volume is a constant, the
mass concentration is read directly from an appropriately labeled
scale on the instrument meter. The instrument does not possess
the capability to traverse large stacks in order to obtain multi-
point measurements. Since the particulate mass concentration is
frequently not uniform across the entire cross-sectional area of
the stack, the use of such a small sampling volume and the in-
ability to traverse creates a problem when trying to obtain data
that is representative of the actual total mass concentration
present within the stack.
An improved version of PILLS V, the model P-5A, has been
developed. This instrument has the following specifications: a
measurement range of 0.001 to 10 grams/ACM, response that is
proportional to particle mass concentration and is relatively
independent of the particle size in the range of approximately
0.1 to 8 urn, a process gas pressure limit of +5 inches of water
from ambient (higher limits are optional); a process gas tempera-
ture limit of 260°C (500°F) (negative pressure streams permit use
at higher temperatures), an instrument response that is independent
of gas velocity, an optional automatic zero .and span calibration
at preset intervals without removal from the stack, and a light
519
-------
LIGHT
SOURCE
APERTURES
DETECTOR
OPAL GLASS
SAMPLE VOLUME
LIGHT TRAP
OPAL GLASS
CALIBRATOR
3640-277
Figure 288.
Optical assembly diagram of a nephelometer used in
stack monitoring. The scattering angle 6, for
any light ray from the source,, is the angle
between the ray and the horizontal line a. From
Ensor and Sevan.21*8
520
-------
BACKSCATIERED
BEAM
SAMPLING
VOLUME
LIGHT COLLECTION
LENS
EMITTED
BEAM
LIGHT OMITTING
DIODE
SIGNAL
DETECTOR
3540-278
Figure 289
Optical
Schmitt,
diagram of
et al.252
the PILLS V instrument. From
521
-------
source consisting of a highly collimated beam of monochromatic
laser light whose wavelength is 0.9 ym.
A backscattering instrument, called an LTV monitor, has been
used in making mass measurements, but a commercial model is not
available.253 This device, illustrated in Figure 290, utilizes
a high intensity argon or xenon laser and a television camera with
telephoto lens. The camera optics image the backscatt-ered light
of 175° from the focused view volume, intersecting the laser beam.
Particles that produce illumination above the sensitivity threshold
can be resolved as distinct flashes and the intensity of each can
be measured.
A portable opacity measurement system called RM41P has been
developed by Lear Siegler, Inc., Environmental Technology Division,
74 Inverness Drive, E., Englewood, Colorado 80110, telephone (303)
770-3300. This sytem includes a transmisspmeter to measure light
transmittance through an optical medium such as fly ash. The trans-
ceiver unit contains the light source, the detector, and electronic
circuitry. The retroreflector is housed in the end of a slotted
probe which is attached to the transceiver and is inserted into a
stack or duct through a conventional stack sampling port. The
probe causes negligible flow disturbance, and air flushing keeps
the optical window and retroreflector free of dust and dirt de-
posits. The transceiver output is transmitted to a portable
control unit that simultaneously provides an indication of optical
density and opacity corrected to stack-exit conditions. There is
a switch activated, self-contained, calibration checking of trans-
ceiver zero, instrument (with probe) zero, and instrument span.
Automatic, electronic compensation of instrument zero output is
provided whenever zero calibration is activated. The standard
stainless steel probes will withstand stack temperatures up to
1200°F, though to minimize thermal conduction into the transceiver,
care must be exercised to limit exposures at extreme temperatures.
Some of the other features of the system are as follows: optical
density output for correlation with particulate grain loading,
opacity output corrected to stack-exit conditions to comply with
emission standards, choice of ten measurement ranges and outputs,
chopped light source for total insensitivity to ambient light,
dual-beam measurement technique for maximum accuracy, double-pass
measurement system for high sensitivity and easy calibration, probe
inserts into stack or duct through a conventional 3% inch I.D.
sampling port, continuously variable adjustment on control panel
to correct opacity outputs to stack-exit conditions for any stack
or duct, choice of interchangeable one meter or five foot probe
lengths, provision for permanent installation when so desired,
and manually activated, self-contained transceiver zero, probe
zero, and instrument span calibrations.
Another Lear Siegler, Inc. product is the RM41 Visible
Emission Monitoring System which is being used successvully to
measure opacity and amount of particulate matter in effluent from
522
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STACK GAS
WINDOW
PULSED ARGON OR
XENON LASER
TV CAMERA WITH
TELEPHOTO LENS
PARTICLE SIZE
ANALYZER
3540-279
Figure 290. Schematic of Laser-TV monitor. After Tipton.253
523
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large industrial stacks. The instrument performs automatic cali-
bration and zero correction, and offers a wide choice of built-in
measurement ranges and status indicators on the remote control
unit to maximize system performance and operator effectiveness.
Unattended operation can be expected for three to six months. The
system contains a transmissometer consisting of an optical trans-
ceiver mounted on one side of a stack and a reflector mounted on
the other, a forced-air purge system, and a control room unit.
Containing only the essential optics and electronics required to
implement the dual-beam measurement technique, --the transceiver
incorporates automatic continuous correction for variations in
ambient temperature, line voltage, lamp aging, detector drift, and
associated changes in component characteristic. Output from the
transceiver is interconnected to a remote control unit, which
provides simultaneous readings of opacity, corrected to stack exit
conditions, and optical density, indicating actual two-pass con-
ditions. There is an optical density output for correlation with
particulate grain loading and determination of mass emission flow
rates. In typical applications the standard system can be used
with stack temperatures up to 316°C (600°F).
The RM7A Opacity Monitor by Lear Siegler, Tnc. is a tran's-
missometer consisting of a transceiver mounted on one side of a
stack and a reflector mounted on the other side. The transceiver
unit .contains a light source, dual photocell detectors, and
electronic measuring circuitry. A special corner-cube retro-
reflector is housed in the reflector unit. Both units contain
provisions for optical alignment verification and correction.
Zero and alarm-level adjustments are built into the transceiver.
A manual zero-calibration reflector assembly and storage container
are attached to the transceiver. This system is used on small or
medium sized industrial facilities.
The Model 1100 Double Pass Opacity Monitoring System is
manufactured by Dynatron, Inc., Barnes Industrial Park, Wallingford,
Connecticut 06492, telephone (203) 265-7121. The system works by
measuring variations in "double pass" light transmittance. The
light source and two photo detectors are mounted on one side of
the stack and a retroreflector is mounted on the other side. The
light source projects a collimated beam of light which is split
by a beam splitter into a reference beam and a transmitted beam.
The reference beam is directed to the reference detector. The
transmitted beam is projected to a "double pass" across the stack
to a retroreflector which reflects it back across the stack to
the measurement detector. The measurement detector working on
a ratio basis with the reference detector generates an output
signal directly related to smoke opacity. Some of the features
of the system are: 100% solid state design, a restriction of
ambient light interference, flexible air line which supplies
clean filtered air, and alignment viewing port to allow a visual
check by the operator.
524
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The Model 301 Opacity Monitor by Dynatron is a rugged eco-
nomical monitoring system utilizing a single pass transmissometer
which enables the operator to meet opacity monitoring regulations
and optimize combustion efficiency. Each system includes the
following_design features as standard: an analog panel meter
which indicates single pass opacity at the transmissometer in 2%
increments from 0 to 100% opacity, an optional digital panel
meter is available with an easy to read numeric display, and a
fuel saving early warning system which alerts the operator prior
to a violation.
The following list gives a number of other suppliers of
smoke measuring instruments and supplies:
Bailey Meter Company
Beltram Associates, Inc.
W. N. Best Combustion Equipment Company
Catalytic Products International, Inc.
Cleveland Controls, Inc.
De-Tec-Tronic Corporation
E. I. duPont deNemours & Company, Inc.
Dwyer Instruments, Inc.
Electronics Corporation of America
Environmental Data Corporation
GCA Technology Division
Horiba Instruments, Inc.
Institute for Research, Inc.
International Biophysics Corporation
ITT Barton
Jacoby-Tarbox Corporation
Leeds & Northrup Company
Milton Roy Company
NAPP, Inc.
Photobell Company, Inc.
Photomation, Inc.
Preferred Instruments
Process & Instruments Corporation
Reliance Instrument Manufacturing Corporation
Research Appliance Company
Royco Instruments, Inc.
Von Brand Filtering Recorders
Computer & Instrumentation Div.
525
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- SECTION 8
CHOOSING AN ELECTROSTATIC PRECIPITATOR: COLD-SIDE
VERSUS HOT-SIDE 'VERSUS CONDITIONING AGENTS
ADVANTAGES AND DISADVANTAGES OF THE DIFFERENT PRECIPITATOR OPTIONS
General Discussion
There are presently three accepted methods of utilizing elec-
trostatic precipitators for the collection of fly ash. These
methods include cold-side operation (120-180°C), hot-side opera-
tion (315-480°C) , and chemical flue-gas conditioning (CFGC).
Whether or not one of these methods is preferable to the others
depends primarily on the type of ash to be collected, the space
available for control equipment, and economic considerations.
Depending on the circumstances, each of these methods may have
certain advantages and disadvantages. In this section, the ad-
vantages and disadvantages of the three precipitator options are
discussed. Also, the precipitator requirements and economics
which would be necessary to achieve a given high level of collec-
tion efficiency for high resistivity ashes are estimated for the
three options.
Cold-Side Electrostatic Precipitator
Cold-side electrostatic precipitators provide the most economi-
cal and reliable option for providing high collection efficiency
of fly ash with low-to-moderate resistivity (0.1 - 5 x 1010 ohm-cm).
The low pressure drop across the precipitator, relatively low gas
volume to treat on the cold-side of the air preheater, and good
electrical operating conditions provide significant advantages.
Figure 101 shows measured fractional efficiency data obtained from
a cold-side precipitator collecting fly ash with a measured resis-
tivity of approximately 2.2 x 1010 ohm-cm.251* This unit operated
with an average applied voltage of 51.0 kV and average current
density of 38.0 nA/cm2. A relatively high overall mass collection
efficiency of 99.6+% was measured with a relatively low specific
collection area of 43.5 m2/(m3/sec)(221 ft2/1000 ACFM). This pre-
cipitator was preceded by a mechanical collector and was treating
particulate with an inlet mass median diameter of approximately
10 ym.
The use of a cold-side precipitator becomes questionable when
the resistivity of the fly ash is high (greater than 10:1 ohm-cm).
526
-------
Due to the poor electrical conditions that will be experienced
with a high resistivity fly ash, a cold-side precipiSSr has
to betvery large in size in order to achieve high collection
efficiencies. Although there may be economic and practical draw-
backs, large cold-side precipitators have been utilized success-
fully to collect high resistivity fly ash. Figure 89 shows
measured fractional efficiency data obtained from a cold-side
precipitator collecting fly ash with a measured resistivity of
1.8 x 10 ohm-cm.' This unit operated with an average applied
voltage of 40.9 kV and average current density of 12.1 nA/cm*.
A very high overall mass collection efficiency of 99.9+% was
measured with a relatively high specific collection area of
99.2 m2/(m3/sec)(504 ftz/1000 ACFM).
For sufficiently high values of fly ash resistivity, the
size of a cold-side precipitator that can attain high collection
efficiencies becomes excessively large. The large precipitator
size needed for high efficiency collection of high resistivity
ash results in large precipitator costs, increased space require-
ments, and possible impracticality of enlarging an existing pre-
cipitator which was originally designed to collect a low resistivity
fly ash. Also, for very high values of resistivity (greater than
10 3 ohm-cm), accurate cold-side precipitator design is probably
not possible due to uncertainties regarding the attainable electri-
cal operating conditions and useful operating voltage and current.
In addition to excessive precipitator size, there are other
possible disadvantages of cold-side collection of high resistivity
ash that must be considered. Due to the tendency of high resis-
tivity ash to adhere tenaciously to the collection electrodes,
high intensity impact rappers are required (120-200 g) to remove
the ash from the collection electrodes. To withstand these higher
rapping forces, more costly rigid electrode frames are desirable.
The'high rapping forces increase the possibility of ash reentrain-
ment, structural collection electrode failures, and more difficult
equipment maintenance.
Hot-Side Electrostatic Precipitator
The motivation for locating the precipitator on the hot gas
side of the air preheater where temperatures, are in the neighbor-
hood of 371°C (700°F) rests entirely on data which show that ash
resistivities should be very favorable, As discussed earlier, the
controlling conduction mechanism in the precipitated_ash. layer at
this temperature is intrinsic or volume conduction, instead of the
surface conduction mechanism which predominates on the cold gas
side of the "air preheater. Thus, the fly ash resistivity at high.
temperature, is not sensitive to the SOa or^moisture content of
the flue gas. Most published resistivity data indicate that re-
-sistivities below 2 x 10l ° ohm-cm will occur above 600 F. There-
fare high temperature operation should 'offer an alternative.,approach
.we, nign temperaULU.B * ^fficiencv of fly ash which would have
for. achieving high collection e-triciency ui. ±±3
a high resistivity under cold temperature operation.
527
-------
Another advantage of high temperature operation is that
fouling of the air preheater by fly ash is reduced. However, in
installations burning high sulfur coal- -with a basic fly ash, it
is probable that removal of this ash ahead of the air preheater
would result in increased corrosion rates of air preheater cold
end elements. For installations in which coal and oil firing
are employed, high temperature operation minimizes oil ash' handling
problems.
The decrease in precipitator size that can 'b,evachievedvby--
hot-side collection of a fly ash which would have a .high, r.e.sis-
tivity at cold-side temperatures is moderated by"two factors.
First, a higher gas volume must b-e treated due to the''higher temr
perature. The increase in gas volume dictates that -the precipi-
tator be increased in size by approximately 50% in comparison to
a cold-side precipitator operating at th-e same applied voltage and
current in order to achieve the same collection efficiency. Second,
the decreased gas density results in lower operating voltages and
electric fields prior to sparkover than in the case of-a cold-side
precipitator. Thus, additional precipitator size is needed to
compensate for the reduced operating voltages.
Certain economic disadvantages are associated with a hot-side
precipitator. Special expansion provisions, increased insulation,
increased draft fan requirements, and additional ductwork in an
unconventional configuration add increased costs as compared to a
cold-side precipitator. In addition, the hot-side operation re-
duces boiler efficiency due to heat loss through the precipitator.
Recently, it has been found that hot-side precipitators may
be sensitive to the composition of the ash.256 This sensitivity
is manifested in voltage-current characteristics which are abnormal
and unfavorable for electrostatic precipitation. Figures 203 and
204 show abnormal voltage-current characteristics obtained from a
hot-side precipitator which responded unfavorably to fly ash de-
posits on the collection electrodes. These curves should be com-
pared to those in Figures 200, 203, and 204 for normal hot-side
precipitator operation. The steep voltage-current curves and low
maximum applied voltages shown in Figures 203 and 204 are not
expected at the elevated temperatures and result in decreased
precipitator performance. In addition, the abnormal electrical
conditions could not be attributed to ash resistivity since both
in situ and laboratory measurements indicate a value of less than
10113 ohm-cm. However, these measurements were made over a
relatively short period of time, and there is reason to believe
that the resistivity of the collected dust layer may increase
with time. Due to the above discussion, the most serious dis-
advantage of a hot-side precipitator is the unpredictability of
the electrical conditions. Although adequate electrical conditions
may be obtained with certain fly ashes, inadequate electrical
conditions may result due to other fly ashes. This makes the
design of a hot-side precipitator extremely difficult and makes
hot-side operation less attractive as an option.
528 .
-------
Figure 104 shows measured fractional efficiency data obtained
from a hot-side precipitator collecting fly ash from a low sulfuf
eastern coal.257 This unit had normal hot-side voltage-current
C?a^aSteri! and °Perated with an average applied voltage of
31.7 kV and average current density of 35.6 nVcm2. A relatively
high overall mass collection efficiency of 99.6+% was measured
with a moderate specific collection area of 76.8 mV(m3/sec)
(390 ftVlOOO ACFM). ' ' '
Figure 110 shows measured fractional efficiency data obtained
from a hot-side precipitator collecting fly ash from a low sulfur
western coal. This unit had anomalous hot-side voltage-current
characteristics and operated with an average applied voltage of
25.1 kV and average current density of 32.2 nA/crr.- . An overall
mass collection efficiency of 98.5% was measured for the entire
unit with a specific collection area of 57.1 m2/(m3/sec) (290 ft2/
1000 ACFM). The poor performance of this unit could be attributed
primarily to the low operating voltages, especially in the outlet
electrical fields.
Cold-Side Electrostatic Precipitator With Chemical Flue Gas
Conditioning
Possible Advantages of Chemical Flue Gas Conditioning—
There are several attractive features and possible benefits
of adding chemical conditioning agents to the gas stream on the
cold or hot gas side of the air preheater and upstream from a
cold-side precipitator. First, certain chemical conditioning
agents can be used to lower the resistivity of unconditioned ash
from high values to values which are favorable for electrostatic
precipitation. One manufacturer of conditioning systems will
guarantee that the resistivity of S03 conditioned fly ash will
not exceed 4 x 1010 ohm-cm.25* Second, certain chemical condition-
ing agents can be used to increase the cohesiveness of the pre-
cipitated fly ash.166'250 This capability can be utilized to_
reduce emissions due to particle reentrainment caused by rapping,
high gas velocities, or hopper boil-up. Conditioning can cause
participate, reentrained due to -rapping to consist of large agglo-
merates which can be easily recollected. Third, certain chemical
conditioning agents can be used to introduce a beneficial space
charge effect in the precipitator.164 With a beneficial space
charge effect, higher applied voltages can be obtained at a given
current density than in the unconditioned gas. The increase in
applied voltage can be large enough to make a significant improve-
ment in precipitator performance. The three effects 3ust described
have been substantiated and discussed earlier in this text. Fourth,
certain chemical conditioning agents can be used to increase the
resistivity of unconditioned ash from extremely low values (less
than 10» ohm-cm) to values (approximately 10 oh^cmj which are
more favorable for electrostatic precipitation. The in-
crease in resistivity reduces.particle reentrainment due to
529
-------
scouring and rapping by increasing the electrical forces holding;
the ash layer to the collection electrode. In addition, if -the
low value of resistivity is due to an excess of SOs caused by
burning high sulfur coal, the conditioning ag-ent added in a hot
section of the boiler may remove excess SOs by neutralizing.
reactions on the surfaces of the particles.*6° This is signi-
ficant because high exit gas temperatures are maintained in
order to prevent condensation of excess SO-s from the "flue gas..
which could result in corrosion and .air preheater- pluggage.- ,-This
method of operation not only reduces boiler efficiency, but also
increases the gas volume and velocity through the precipitator,
thus reducing the precipitator performance. Fifth, there have
been claims that certain chemical conditioning agents .can favor-
ably modify the fly ash particle size distribution by causing
agglomeration of particles.261 However, this effect has not
been substantiated. If significant agglomeration of fine
particles can be produced, a larger particle size distribution
which can more easily be collected would be produced. Due to
the wide applicability of chemical conditioning agents, one manu-
facturer of conditioning systems is now offering a performance
guarantee that its system will reduce emissions in excess of
compliance levels by a minimum of 60%, regardless of type of coal,
boiler, or precipitator.262 In order to take advantage of the
multiplicity of mechanisms of fly ash conditioning, the technique
of dual injection can be utilized.260 This technique involves
the application of one additive into a hot section of the boiler,
followed by injection of the same or a different additive into
a relatively low temperature zone, usually after the air heater.
In addition to offering improved precipitator performance,
chemical flue gas conditioning has several favorable economic
aspects. First, the capital costs of a new precipitator installa-
tion can be greatly reduced by using a conditioning system in
conjunction with a relatively small cold-side precipitator.
Second, less space is required when conditioning is used. Third,
the retrofitting of existing precipitators can be accomplished
relatively quickly and with little or no loss in power generating
capacity.
Properties and Utilization of Well-Known Conditioning Agents--
Compounds which have been examined for use as conditioning
agents in cold-side precipitators include sulfur trioxide, ammpnia,
sulfonic acid, sufamic acid, ammonium sulfate, ammonium bisulfate,
sodium carbonate, triethylamine, and several proprietary
agents.156'164'263'2614 Table 36 gives the names, chemical for-
mulas, and physical properties of some of the conditioning agents
which have been studied.263 Some are vapors or liquids that can
be volatilized without much difficulty. Others are solids that
may or may not be liquified or volatilized without decomposition.
All of the compounds listed are highly soluble in water. For those
that are not readily volatilized, aqueous solutions provide a
convenient method for injection into a flue-gas stream.
530
-------
TABLE 36. PHYSICAL PROPERTIES OF CONDITIONING AGENTS
Agent
Sulfur Trioxide
Su If uric Acid
Ammonia
Ammonium Sulfate
Triethylamine
Trie thy 1 ammonium
U)
*-* Sulfamic Acid
Sodium Carbonate
Formul a
SO 3
II 2 SO.,
NH3
(NHt.) 2 SO,,
(C2II5) 3N
Sulfate [ (C2H5) 3NH] 2
H03S-NH2
Na2CO3
State at
21°C(70°F)
Liquid
Liquid
Gas
Solid
Liquid
SO., Solid
Solid
Solid
"C
17
10.6
-78
Dec
-114
-
205
851
Mp,
"P
(62)
(51)
(-108)
b
(-174)
-
(401)
(1564)
Bp,
"C "F
45 (113)
326 (619)
-33 (-28)
-
89 (193)
-
Dec.b
Dec.b
a. All compounds are highly soluble in water and some are used in aqueous solution.
b. Dec. signifies thermal decomposition.
-------
The best known conditioning agent is. sulfur trioxide or the
chemically equivalent compound sulfuric acid. One of the signi-
ficant properties of sulfuric acid in flue gas is its tendency
to undergo condensation from the vapor 'to the liquid state,
the latter consisting of a mixture of sulfuric acid and water.
The dewpoint curve given by Verhoff and Banchero265 for sulfuric
acid in flue gas containing 10% of water vapor is shown in Figure
291. If the gas stream is at a given temperature, it can contain
no more vapor than is indicated by the appropriate point on this
curve. At 138°C (280°F), for example, the maximum vapor concen-
tration that can exist is 10 ppm.
Once condensed, sulfuric acid conducts electricity readily.
Thus, if it condenses on fly-ash nuclei, it provides a conductive
surface film. If absorbed on fly ash particles under conditions
that do not allow condensation, it may again provide a conductive
surface film. Actually, little is known about the chemistry and
physics of adsorbed sulfuric acid, .but there is evidence that
part of the adsorbed material may react chemically with ash con-
stituents to form non-conductive sulfate salts (such as calcium
sulfate) but that part retains its integrity as a conductive
All available data indicate that SOs conditioning will signi-
ficantly lower the resistivity of an unconditioned, high re-
sistivity ash. In this case, SOs conditioning will result in
improved electrical operating conditions and increased collection
efficiency. The effects which can be expected from adding the
other compounds mentioned are not so well defined. The realized
effects, if any, appear to depend strongly on the gaseous envir-
onment and the chemical composition of the ash. In a certain
application, one of these compounds may improve precipitator
performance by one or more of the mechanisms discussed earlier
whereas, in another application, it may have a different or no
effect. A data base which is much larger than that existing is
needed in order to establish the effects on precipitator operation
resulting from adding the various possible conditioning agents to
flue gases of differing gaseous composition and containing par-
ticles of differing chemical composition.
Unlike sulfur trioxide and sulfuric acid, ammonia is not
recognized as an important naturally occurring constituent of flue
gas. The distinguishing feature of ammonia vapor in flue gas is
its behavior as a base. At temperatures that are not too high — say
around 149°C (300°F) — it is capable of combining with sulfuric acid
vapor to form ammonium sulfate, as shown by the following reaction:
2NH3(g) + H2SOi, (g) -»• (NHi») 2SOw (s)
There are other acidic gases in flue gas — sulfur dioxide and
carbon dioxide — but, even though they are present at much higher
concentrations than sulfuric acid, they are unable to react with
ammonia .
532
-------
100.0
TEMPERATURE, °F
. 220 240 260 280
O
10.0
z
LU
O
z
O
u
O
VI
1.0
0.1*
300
T
320
VAPOR + LIQUID
VAPOR
I
110 120 130 140
TEMPERATURE, °C
150
160
3540-280
Figure 291.
Dewpoint curve for sulfuric acid in the presence
of 10% water vapor.
533
-------
The addition"of triethylamine to flue gas can be expected to
lead to similar reactions, for this compound is also a base. It
is stronger as a base than ammonia, however, and thus it may com-
bine with sulfuric acid at higher temperatures or it may even
react with some of the other acidic, gases in flue gas.
Comparatively little is known about the chemical behavior of
addition compounds of sulfur trioxide and ammonia that are used as
conditioning agents. Such compounds as sulfamic acid and ammonium
sulfate are frequently added at temperatures around 1100 or 1200°F.
It is claimed by vendors who sell proprietary blends of these-
agents that injection at high temperatures is needed to decompose..-
the agents to other products that are engaged in the actual con-
ditioning process. Knowledge of what decomposition processes
occur at high temperatures or what reactions of the decomposition
products occur as the gas temperature is lowered is not complete.
However, the following equations give a fairly realistic estimate
of reactions that may be expected at high injection temperatures:261*
H03S-NH2(s) -»• S03(g) + NH3(g)
(NH4)2SCMs) •*• S03(g) + H20(g) + 2NH3(g)
Reversal of these reactions may then occur as the temperature is
lowered.
Sodium compounds may be injected into the boiler along with
coal.266 In such an event, decomposition will occur:
Na2C03(s) -»• Na20(l) + CO2 (g)
The sodium oxide is incorporated in the fly ash and increases the
sodium content of the ash. Sodium compounds may also be injected
into the gas stream near the temperature of the electrostatic
precipitator.267 In this event, no chemical change is to be ex-
pected, and solid particles of the added compound are subject to
co-precipitation with the ash.
Utility Utilization and Capital and Operating Costs of Conditioning
Systems--
Capital and operating costs for cold-side conditioning systems
will depend primarily on the type of conditioning agent and the
system used to inject the agent. One company which makes S03 con-
ditioning systems estimates the capital costs to be between $2.00
to $2.50 per KW with operating costs of $0.02 to $0.03 per ton
of coal burned.262 As of December, 1978, this company had 85
CFGC systems on stream, under construction, or on order, at 13
utilities, serving more than 16,000 MW of generating capacity.
Another company which makes conditioning systems for injecting
proprietary compounds has a system installed with capital costs
of approximately $0.45 per KW and operating costs of less than
534
-------
$0.50 per ton of coal burned.262 As of December TQ7fl ^-i a „„
pany had CFGC systems at 18 utilities wi^^vas^majoritj ol
the units in the range of 200 to 700 MW. "wjoriry or
Recently, it has been reported that chemical conditioning
agents can be utilized to improve the performance of poorly oper-
ating hot-side preclpitators." "*59,2*o Laboratory Studies have
been conducted to evaluate the effectiveness of several different
conditioning agents in improving poor, hot-temperature voltage-
current characteristics which result when certain types of ashes
are deposited on the collection electrodes of a precipitator.lB 3
With respect to effectiveness in improving the voltage-current
characteristics, NaHSO.,, Na2SO.», NaOH, NazHOP,,, :'OH, KKSO^, and
Na2C03 were evaluated as good, NaCl and NaHC03 were evaluated as
moderate to good, NH3 was evaluated as moderate, triethylamine
and ferrous sulfate were evaluated as moderate to poor, and S03,
NH3 + SO3, (NH^);SOu, and Ti02 were evaluated as poor. All these
conditioning agents were in the solid form except NH3, S03, and
NH3 + S03. It has been reported that conditioning with sodium
carbonate and certain proprietary compounds has been successful
in improving the performance of full-scale, hot-side precipita-
tors. 59'2S° This offers another possible option for upgrading
existing hot-side precipitators which are not performing adequately.
A particular sodium based conditioning system has been installed
with capital costs ranging between $1.75 to $2.00 per KW and ,
operating costs between $1.00 to $1.20 per ton of coal.259
Possible Disadvantages of Chemical Flue Gas Conditioning—
Although chemical flue gas conditioning offers several attrac-
tive, potential benefits, there are several possible disadvantages
which must be considered. First, a chemical injection system
must be operated and maintained. Second, certain chemical com-
pounds which are effective in improving precipitator performance
are hazardous. Third, the effects that conditioning with certain
chemical compounds will have on precipitator performance cannot
always be predicted in advance. Fourth, in certain cases, the
injection of chemical conditioning agents has resulted in an ash
which was very sticky. If this situation results, the rapping
forces might not be sufficient to remove the-material collected
on the discharge and collection electrodes. In addition, if the
conditioning agent is injected on the hot gas side of the air
preheater, pluggage and fouling of the air preheater would result.
Fifth, operating costs associated with certain chemical condition-
ing agents can be sianificant. Sixth, possible future regulations
concerning the emissions of chemical conditioning agents may make
535
-------
temperatures will produce a highly visible blue plume due to the
condensation of H2SOit. It has already been emphasized by an EPA
official that any emissions of sulfuric acid, SOs, or ammonia
resulting from chemical treatment should not exceed a combined
total of 10 ppm.262 Also, it should :be pointed .-out that only a
few parts per million of certain conditioning agents contain a
significant amount of mass. For example, 5 ppm of SOa is equi-
valent to 20 yg/m3 (about 0.01 gr/ft3). Thus, the possibility
exists of treating the emissions due to conditioning on a mass
basis and adding this to the mass due to fly ash emissions in
order to obtain the total particulate emissions. This type of
treatment of emissions of chemical conditioning agents would
require that a high percentage of the injected agent be adsorbed
on the surfaces of the fly ash particles.
Precipitator Requirements and Economic Comparisons—
Precipitator requirements and economic comparisons for the
different precipitator options can be estimated by using the
projections obtained from a mathematical model.of.electrostatic
precipitation.137'152 Figure 292 shows projected curves for over-
all mass collection efficiency as a function of specific collection
area for several cases where the different precipitator options
can be compared. The curve for an ash resistivity of 4 x 10lc
ohm-cm at 148°C (300°F) corresponds to an ash with a favorable
resistivity without conditioning or to an ash with an unfavorable
resistivity that can be conditioned to a guaranteed resistivity
of 4 x 10l° ohm-cm. The curves for ash resistivities of 1 x 1011,
5 x 1011, and 1 x 1012 ohm-cm at 148°C (300°F) correspond to
cold-side precipitator operation without conditioning. The curve
for hot-side precipitator operation with normal voltage-current
characteristics was obtained based on electrical operating con-
ditions demonstrated in Figure 200. The curve for hot-side pre-
cipitator operation with anomalous voltage-current characteristics
was obtained based on electrical operating conditions demonstrated
in Figures 203 and 204 and an adjustment to these conditions, as
described elsewhere,255 in order to obtain agreement with measured
data.
All the curves were generated for an electrode geometry con-
sisting of plate-to-plate and wire-to-wire spacings of 22.86 cm
(9 in) and a corona wire diameter of 0.277 cm (0.109 in). The
cold-side precipitator calculations, the maximum allowable current
density for a given value of ash resistivity, was estimated by using
the experimental data shown in Figure 208. Although these values
of current density are probably somewhat conservative for the
higher values of ash resistivity since higher useful currents
might be obtained with the presence of limited back corona, it
is best to be conservative in design due to the lack of predictive
capabilities concerning back corona. Operating current densities
for the resistivities of 4 x 1010, 1 x 1011, 5 x 1011, and 1 x 1C1.2
ohm-cm were chosen to be 22.0, 8.9, 1.7, and 0.9 nA/cm2, respectively.
536
-------
99.99
99.98 -
• 4.0 x 1010 r-cm AT 148°C (300°F)
A 1.0 x 1010 r-cm AT 148°C (300°F)
• 5.0 x TO10 r-cm AT U8°C (300°F)
T 1.0 x 1012 r-cm AT 148°C (300°F)
O NORMAL HOT-SIDE V-l AT 343°C
A ANOMALOUS HOT-SIDE
V-l AT 343°C (650°F)
0 100 200 300 400 500 600 700 800 900 1000 1100 1200
SPECIFIC COLLECTION AREA, ft2/(1000 ft3/min)
3540-281
Figure 292.
Effect of specific collection area on overall mass
collection efficiency (curves based on a fractional
gas sneakage of 0.05 and a normalized standard of
deviation of gas velocity distribution of 0.25).
537
-------
The applied voltage in each electrical section for a specified
current density was estimated by using the experimental voltage-
current curves shown in Figure 196. These data are representative
of a full-scale, cold-side precipitator treating an ash with a
resistivity of approximately 2 x 1010 ohm-cm* The calculations
were based on a precipitator with four electrical sections in the
direction of gas flow. An applied voltage for use in the second
and third electrical sections of the specified precipitator wa-s
obtained by averaging the values from the experimental inlet
and outlet curves.
For all the curves, specific collection area was varied in
the calculations by changing the gas volume flow and holding the
plate area fixed. Although the voltage-current characteristics
will change to some extent with changes in gas volume flow, it
was assumed that they remain constant in making-the calculations.
The number of baffled sections for gas flow redirection was
increased appropriately with increasing specific collection area
in order to account for increased precipitator size.
The measured inlet mass loading and particle size distribution
used in the calculations are typical of fly ash generated by coal-
fired boilers. The inlet mass loading was 5.7 gm/m3 (2.5 gr/acf) .
The log-normal fitted inlet particle size distribution had a mass
median diameter of 25.5 ym with a geometric standard deviation of
5.1. To account for the effect of particle size distribution,
especially in the fine particle range (0.25-3.0 ym), the measured
particle size distribution was divided into size intervals with
midpoints of 0.2, 0.4, 0.7, 1.1, 1.6, 2.5, 3.5, 4.5, 6.0, 8.5,
12.5, 20.0, and 27.5 ym.
The curves were generated based on a fractional gas sneakage
and particle reentrainment without rapping per baffled section
of 0.05 and a normalized standard deviation of the gas velocity
distribution of 0.25. These values are typical of a precipitator
which is in good mechanical condition. All overall mass collection
efficiencies have been corrected for rapping reentrainment using
an empirical procedure based on field test data from full-scale
precipitators as discussed earlier.19'137
The curves in Figure 292 do not address the problems of (1)
opacity, (2) variations in the significant parameters influencing
precipitator performance, and (3) outage of electrical sections.
Therefore, these curves are intended only for use in making
relative comparisons of the different precipitator options for
treating ashes with different resistivities and should not be
used per se for design purposes. Problems (2) and (3) can be
conservatively accounted for by designing the precipitator with
more collection area than that needed to achieve the desired col-
lection efficiency- However, problem (1) requires a somewhat
extensive analysis to determine if the opacity standard will be
met and to determine what safety margins should be included in
538
-------
the precipitator design to account for normal variations in pre-
cipitator parameters that would cause an increase in opacity In
many cases, the mass emissions standard will be attained at
collection efficiencies well below that needed to meet the opacity
standard.
The curves in Figure 292 can be used to make a relative
economic comparison of the different precipitator options in terms
of total fixed (capital) investment for an 800 MW unit. As an
example, the total fixed investment for each of the precipitator
options can be determined based on a required overall mass col-
lection efficiency of 99.5%. The design parameters for the dif-
ferent precipitator options, cold-side ash resistivity values,
and possible hot-side electrical conditions are g^ven in Table 37.
Estimated costs for cold-side, hot-side, and conditioned pre-
cipitators for use on an 800 MW unit have been published recent-
ly.259 These estimates will be used here for comparing the
.relative capital costs of the various precipitator options.
In this particular analysis, cold-side, hot-side, and conditioned
precipitators would cost $14.82, $15.65, and $16.62 per square
foot of collection plate area, respectively-
The quoted costs include the following items:
1. A gas volume flow for the cold-side precipitator systems which
includes 9% leakage at the air heater.
2. Base equipment.
3. Flues which are sized to provide a gas velocity of 18.3 m/sec
(60 ft/sec).
4, Plenums.
5. Necessary expansion joints for thermal motion and dampers for
isolation and gas distribution.
6. Accessories which include safety interlocks, internal walkways,
hopper heaters, hopper level indicators, remote controls, trans-
former-rectifier removal systems, weather enclosures, gas dis-
tribution devices, facilities, and typical instrumentation.
1.'.- Support structures.
8. Erection.
9. Insulation.
"10. S03 gas conditioning system in the case of the cold-side pre-
cipitator with conditioning.
539
-------
TABLE 37. DESIGN PARAMETERS FOR DIFFERENT PPEC1PITATOR OPTIONS AND
OPERATING CONDITIONS OH AN 800 MW UNIT
Gas Volume Flow
m'/min (1,000 ACFM)
Gas Temperature °C (°F)
Collection Efficiency (%)
Collecting Surface Area
1,000 m2 (1,000 ft')
Cold ESP
p=4x!0'°n-cm
(conditioned or
Cold ESP
Cold ESP
Cold ESP
Hot ESP
unconditioned) p=lxlO''ft-cm p=5xl011fi-cm p=lxlO'2ft-cm Normal V-I
78.4 (2,800)
149 (300)
99.5
61.1 (658)
Specific Collection Area
m Mm3/sec) (ft2/!, 000 ACFM} 46.3 (235)
78.4 (2,800) 78.4 (2,800) 78.4 (2,800) 114.5 (4,089)
149 (300) 149 (300) 149 (300) 343 (650)
99.5 99.5 99.5 99.5
98.8 (1,064) 212 (2,282) 289 (3,108) 114. (1,227)
74.9 (380) 160.6 (815) 218.7(1,110) 59.1 (300)
Hot ESP
Anomalous V-I
114.5 (4,089)
343 (650)
99.5
152 (1,636)
78.8 (400)
-------
11. Ash handling system at $5,000 per hopper.
12. Capacity charge at $800/KW.
13. Required land at $10 , 000/acre.
. u °n the above considerations, Table 38 gives a comparison
or the Different precipitator options under different operating
conditions in terms of total fixed investment. The comparisons
in Table 38 and Figure 292 show several points of interest. First,
an unconditioned, cold-side precipitator is the most economically
effective option for ash resistivities of 4 x 10 10 ohm-cm or less
and, in addition, should be considered seriousl^ until the ash
resistivity is greater than 1 x 10 ' l ohm-cm. Second, for ash re-
sistivities greater than 1 x 10 li ohm-cm, flue gas conditioning
and hot-side operation with normal voltage-current characteristics
become attractive options from an economic standpoint when compared
to unconditioned, cold-side operation. However, at best, hot-side
operation will be a factor of 1.76 times as costly as cold-side
operation with conditioning. Third, if a hot-side precipitator
is sized to account for the possibility of anomalous voltage-
current characteristics, then it will cost a factor 1.33 times
that of a hot-side precipitator with normal voltage-current char-
acteristics. This would make the hot-side option extremely
unfavorable when compared to flue gas conditioning and would
make it competitive with unconditioned, cold-side operation
treating ashes with resistivities near 5 x 10 M ohm-cm or less.
Since annual operating and overhead costs will be dominated
by amortization of the debt (including interest, taxes, and in-
surance at approximately 20% of the total fixed investment) , the
relative comparison of these costs between the different pre-
cipitator options should parallel that of the total fixed invest-
ment analysis . The operating --costs include- (1) heat loss for the
hot-side options, <2) an energy charge for all the options that
depend on power input to the transformer/rectifier sets and
pressure drop across the precipitator, (3) cost of the condition-
ing agent for the flue gas conditioning option, and (4) maintenance.
These operating costs are small compared to the amortization and
at most will probablv not exceed 25% of the amortization. The
heat loss penaltv for the hot-side option will probably make the
estimate of its operating costs somewhat higher than the other two
options when all three options are evaluated for the collection
of high resistivity ash. Of course, the cost of the conditioning
agent can varv widely, depending on the type of agent and the
supplier. Finally, the estimation of maintenance costs _ is diffi-
cult -..and would vary significantly from one .type of precipitator
to another.
Due to the uncertainties involved in estimating the operating
costs for the different options, this type _ of analysis will not be
presented here. However, estimated operating costs can be .ound
elsewhere. 2 5 9
541
-------
TABLE 38. TOTAL FIXED INVESTMENT OF PRECIFITATOR OPTIONS UNDER
DIFFERENT OPERATING CONDITIONS FOR AN 800 MW UNIT ($1000)
Cold ESP Cold ESP Cold ESP Cold ESP Cold ESP Hot ESP Hot ESP
p=4x!0'°«-cm p=4xlO'°fi-cm p=lxlO''fi-cm p=5xlO''fi-cm p=lx!0l2n-cm Normal V-I Anomalous V-I
(unconditioned) (conditioned)
01
M Total
Investment
Relative
Investment
Ratio
9,752
1.00
10,936 15,769 33,819
1.12 1.62 3.47
46,061 19,203
4.72 1.97
25,603
2.63
-------
SECTION 9
SAFETY ASPECTS OF WORKING WITH
ELECTROSTATIC PRECIPITATORS
RULES AND REGULATIONS
The only regulations specified by OSHA as being applicable
to safety practices around an electrostatic precipitator are
(1) the National Electrical Code - found in 29 Code of Federal
Regulations 1910 Subpart S, and (2) Occupational Health and En-
vironmental Control - found in 29 Code of Federal Regulations
1910.1000 Air Contaminants. Table 7-3 of the CFR gives exposure
limits to silica and coal dust, and Table 7-1 of the CFR sets an
exposure limit for ozone, which is produced during electrical
discharge, and for sulfur dioxide, which results from coal com-
bustion .
HAZARDS
263^259/270/271
Since the operation of an electrostatic precipitator involves
high voltage, extreme caution should be taken when inspecting and
troubleshooting to avoid electrical shock. Also, serious fires
and explosions have occurred, resulting in large losses and long
shut-downs. Other hazards one encounters while inspecting pre-
cipitator internals involve toxic gases, especially ozone and
sulfur oxides, sudden accidental activation of rapping equipment,
possible burns and heat exhaustion from working inside the shell,
eye and lung contamination from foreign particles, especially fly
ash, and the possibility of falling from areas being inspected.
These hazards and preventive measures will b-e discussed In detail
below.
Fire And Explosion Hazards
269,272
Combustion may be defined as the rapid chemical combination
of oxygen with the combustible elements of a fuel. There are just
thre-e combustible -chemical elements of significance - carbon,
hydrogen, and sulfur. Sulfur is of minor significance as a source
of heat. Carbon and hydrogen when burned to completion with oxygen
unite as shown below:
C + O2 = C02 + 14,100 Btu/lb of C
2H2 + 02 ~ 2H20 + 61,100 Btu/lb of H2
543
-------
Excess air, blown into the primary furnace of the steam
generator, is the usual source of oxygen for boiler furnaces.
The objective of good combustion is to release heat while mini-
mizing losses from combustion "imperfections and superfluous air.
Adequate combustion then requires temperatures high enough for
ignition, turbulence or mixing, and sufficient time. These
factors are known as the "three T's" of. combustion. If one of
these requirements is deficient incomplete combustion occurs
with its resultant unburned carbon constituents. Fires can
quickly become a problem with the presence of combustibles,^-
oxygen, and source of ignition (high voltage sparking'),,., •
Some of the areas in which fires have occurred due to poor.:.
combustion are in the electrostatic precipitators.-.themselves,
air heaters, flues, ducts, coal pipes, and precipitator hoppers.
In one case where improper combustion occurred, there was ex-
cessive air in-leakage between the primary furnace and the pre-
cipitator. This air leakage, together with unburned carbon and
arcing in the precipitator, caused a fire. In another case the
formation of clinkers (large carbonaceous ash masses which adhere
to tube surfaces) produced plugged secondary superheaters which
allowed more fuel to carry over to the precipitator.
In summary, poor maintenance and poor operating practices
at the plant facility are the major causes of fires and explosions
in electrostatic precipitators. Poor combustion due mainly to
improper amounts of excess air appears to be the major operating
practice leading to fires.
Electrical Shock Hazards269
Electrical shock to operators of precipitators is due to the
failure, misuse, or faulty condition of electrostatic precipitator
equipment and may cause the following conditions: painful shock
from sudden contact, resultant action from shock contributing to
a secondary hazard (falling, dropping tools, etc.), flesh burns- •
at points of contact, and death if the victim cannot release him-
self from the energized conductor within a reasonable period of
time (this factor depends greatly upon one's physiological con-
dition, amount of current, resistance and path of current flow
through the body, and type of electrical energy in question) .
Pure direct current produces a steady sensation of intense
heating and burning along the current path with only slight muscular
contraction. A direct current flow of ten milliamperes through the
body causes little or no sensation, but secondary hazards, such as
falls, are possible. At about 60 to 80 milliamperes the sensation
becomes unbearably painful, with no tissue damage. However, the
muscular reactions due to breaking contact may 'be sufficient to
throw a person bodily. With higher currents the above effects
are increased and serious burns may be encountered. Fibrillation
appears in the range of 500 to 2000 milliamperes on contacts that
exceed a quarter of a second.
544
-------
Large, high voltage electrostatic precipitators usually have
double interlocking safety controls to prevent electrical shock
accidents. These safety controls prevent entrance into the elec-
trostatic precipitator unless the unit has been deenergized. If
the primary safety control fails and the access door is opened
while the precipitator is in operation, the secondary control
immediately grounds out the transformer and the unit is deenergized,
Sometimes, however, maintenance and operation personnel do not
want to take the time necessary for proper shutdown and bypass the
interlocking safety controls. When safety controls are misused in
this way, accidents often result. Another potential problem with
the safety controls occurs when they are not inspected and main-
tained periodically. An actual case of electrocution occurred
when safety controls, which operated in a corrosive atmosphere,
corroded to the point of not functioning. When a worker entered
the unit, thinking it would be deenergized, electrocution resulted.
Poking the precipitator collection hoppers with long poles
-to facilitate the flow of bridged fly ash is a common practice.
Obviously a non-conductive pole, never a metal pole, should be
used. If a metal pole makes electrical contact between the
energized parts of the unit and the hopper, electrocution could
result.
Toxic Gas Hazard
Purging the inside of the electrostatic precipitator with air
is necessary before allowing personnel to enter because of the
presence of toxic gases. Sulfur oxides and ozone are two gases
which can be present in concentration great enough to cause a
health risk. Sulfur dioxide and sulfur trioxide are common gas-
eous emissions when burning sulfur-containing coal. Sulfur
trioxide (S03) is not likely to be present in large quantities
(a few parts per million) but it readily combines with water
vapor to form sulfuric acid mist and can be dangerous. Sulfur
dioxide (S02) could be present in several hundred or even several
thousand parts per million inside the precipitator depending upon
the sulfur content of the coal. The taste threshold for S02 is
about 0.3 ppm, and S02 is a very unpleasant experience at 1 ppm.
A level of 5 ppm of S02 causes respiratory irritations and even
spasmodic reactions in some sensitive individuals.273 Ozone is
produced by the discharge of high tension electrical current in-
side the precipitator. The body is very sensitive to ozone,
detecting its odor as low as 0.02 ppm. Nasal and throat irrita-
tion occur at 0.3 ppm. At 1 ppm, severe restriction of respiratory
passages occurs and many persons cannot tolerate higher concentra-
tions. Ozone appears to damage lung tissue by accelerating the
aging process, making it more susceptible to infection.
Other More Minor Hazards270
The rapping area contains rotary equipment which is deener-
gized when the weather enclosure door is open. However, if the
545
-------
door is closed the equipment may operate if a padlock is not used
to lock open the disconnect on the panel feeding the rappers.
Heat exhaustion and/or severe burns can result from entering
the precipitator. too soon -after shut-down since the steel takes; a
very long time to cool down.
Eye protection should be worn to protect eyes from fly ash
and other foreign particles.
There are areas within the precipitator from which one could
fall. Ladders should be properly secured and safety belts may be
appropriate.
546
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SECTION 10
MAINTENANCE PROCEDURES
Proper maintenance precautions and procedures can make the
difference between an electrostatic precipitator which operates
satisfactorily and one which is continually beset with operational
difficulties. Most of an installation's problems are mechanical
in nature and, though many of the breakdowns can be traced to poor
structural design or poor installation, poor maintenance is the
cause often enough to merit a detailed discussion. Two general
categories of precipitator maintenance problems exist: those
problems due to lack of proper preventive maintenance and those
problems associated with failure or breakdown of precipitator
components. A careful, step-by-step start-up procedure is an
invaluable preventive maintenance aid, and a typical start-up
procedure and inspection is given in Table 39." After start-up
preventive maintenance schedules should be established to conform
to the requirements for the particular installation. A typical
maintenance schedule for an electrostatic precioitator is given
in Table 40.27U'275' ~76
Several surveys have been conducted in an effort to identify
the major sources of operating malfunctions most commonly encoun-
tered with electrostatic precipitators.277'27a'279'28° A survey
conducted by the Industrial Gas Cleaning Institute in 1969 iden-
tified problems in the order listed in Table 41.279 The number
identified with each problem is a percentage of the respondents
identifying the particular component as a maintenance problem.
Results of a 1974 Air Pollution Control Association (APCA) survey
of electrostatic precipitator maintenance are similar (Table 42).279
Discharge electrode failures are typically caused by electri-
cal arcing, corrosion, and fatigue. When a wire breaks_an elec-
trical short circuit often occurs between the high-tension dis-
charge wire system and the grounded collection plate. The short
trips a-circuit breaker, disabling a section of the precipitator
.until the discharge wire is removed or replaced. Some of the more
common specific causes of discharge wire breakage are:277
(1) Inadequate rapping of the discharge wire which eventually
allows arcing to occur.
(2) Improperly centered wires leading to sparking at those
points too near the bracing.
547
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TABLE 39. INITIAL ELECTROSTATIC PRECIPITATOR
START-UP PROCEDURE AND INSPECTION271*
Ducting
1. Check all ducting for foreign material.
2. Check all welded joints for leakage.
Internals
1. Check collecting plates for straightness ar.a flatness and
give tolerances.
2. Check spacing of collecting plates and give tolerances.
3. Check pendulum movement of collecting plates.
4. Check rappers for freedom of movement >and alignment.
5. Check the spacing between the plates and discharge wires and
give tolerances.
6. Spot check discharge wires for proper tension.
7. Check for foreign material clinging to discharge wires, col-
lecting plates, precipitator chamber bottom, and hopper area.
8. Check all welds on high voltage frames.
9. Check all motors, bearings, reducers, etc. for proper lub-
rication.
10. Check all motors for direction of rotation.
11. Check underside of insulators for cleanliness, foreign
material, and position of high voltage hanger rods.
Insulator Compartment
1. Check insulator compartment for debris.
2. Check insulator for cracks.
3. Check installation of high voltage hanger.
4. Check welds on high tension hangers.
5. Check for dryness.
Access Doors
1. Insure that door is free swinging.
2. Check latches for tightness when door is shut.
3. Check gasket for gas tight seal.
Rapper Drives
1. Check alignment of all rapper shafts.
2. Check for proper installation of insulators through casing
wall for high voltage rapper shafts.
548
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TABLE 39 (CONTINUED)
Hopper Conveyors
1. Check rotation of screw conveyors if used.
2. Check for binding..
Safety Interlock System
1. Check to insure that all keys are in master keyboard.
2. Check all key-locks to insure that safety lock is operating.
Electrical
1. Inspect the control panel and insure that all motor and heater
control circuits, inter-locking arrangements, and remote con-
trols function properly.
2. Arrange that all time relays, end position switches, rotation
guards, etc. be set properly and that the function of all
alarm signals be checked.
3. Check that all electric heaters function and set the thermo-
stats correctly.
4. Inspect the rectifier units with regard to oil level, etc.
(follow rectifier manufacturer's instructions).
5. Inspect all transformer rectifiers.
6. Check all electrical wiring to precipitator.
7. Check wiring between control cabinet and high tension trans-
formers to be certain control cabinet is actually connected
to the proper high voltage transformer and that interlocks
are in the proper sequence. Check ground wiring.
8. Connect cne rectifier unit at a time corresponding to the
emitting system of the precipitator.
9. Start the rectifier.
10. Check current and voltage at different settings and test the
signals circuits.
549
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TABLE 40. TYPICAL MAINTENANCE SCHEDULE
2 7 it , 275*276
1. Check for drift -of meter readings away from baseline .values
established when ESP was installed. Record readings for each
control unit.
2. Keep an accurate log of all aspects of precipitator operation.
In addition to the electrical data, record changes in rapper
and boiler operation and variations in fuel quality.
3. Check insulator heaters for operation mode sni record ammeter
readings of each insulator heater.
4. Check all "Push to Test" lights on panel and replace as
necessary.
5. Check all rapper timers for operation.
6. Test annunciator panel for operation and replace any bad
lights.
7. To warn of hopper ash buildup and ash conveyor stoppage, check
skin temperature of hopper.
8. Check operation of rapper and vibrator controls.
9. Check oil level of all transformer-rectifier units and record
oil temperature.
10. Note and report any leaks on tank of transformer-rectifier.
Weekly
1. Make visual inspection of rapper action and check vibrator
operation by feel.
2. Check control sets internally for deposits of dirt that may
have penetrated the filter. Accumulation of dirt can cause
false control signals and can be destructive, particularly to
large components such as printed circuits.
3. Clean all insulators.
4. Check access doors for tightness.
550
-------
TABLE 40 (CONTINUED)
Monthly
1. Shut down unit, tag switches, apply ground protectors, and
proceed with inspection and maintenance.
2. Using low pressure air, blow out rectifier compartments and
control cabinets.
3. Clean with carbon tetrachloride and check for chips and arc
tracks the following:
a. transformer bushings
b. stand-off insulators
c. potheads
d. rectifier rotor and cross arms
e. rectifier tubes
4. Clean or change ventilating fan air filters.
5. Check rotor and stator shoes for wear and proper adjustment.
6. Inspect on the drag motor the foundation bolts, alignment,
and rotor end play.
7. Inspect on the screw conveyor motor the foundation bolts.
Quarterly
1. Clean inside all panels.
2. Check all electrical components for signs of overheating.
3. Clean and dress electrical distribution contacts, surfaces,
and lubricate pivots.
4. Check vent fan for operation and check clearances between
blades and shroud.
5. Install new filters in control panel.
6. Routine inspection, cleaning., and lubrication of hinges and
test connections.
7. Exterior inspection for corrosion, loose insulation, exterior
damage, and loose joints.
551
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TABLE 40 (CONTINUED)
Annually
1. Remove dust buildup on wires and plates, and adjust intensity
of rappers and vibrators if necessary.
2. Inspect perforated diffuser screen and breeching for dust
buildup.
3. Perform maintenance and lubrication of pressurized fans and
check for leaks in pressurized system-
4. Check for loose bolts in frames, verify that suspension springs
are in good order, and examine wearing parts.
5. Inspect discharge wires for tightness and signs of burning and
measure to see if they hang midway between plates.
6. Check plates for alignment and spacing.
7. Check insulators for cracks.
8. Drain oil, wash out, and refill gear boxes.
9. Check transformer fluid and dielectric strength.
552
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TABLE 41
MOST COMMON MAINTENANCE PROBLEMS279
Component Percent
Discharge Electrode Failure 68
Rapper Malfunctions 40
Insulator Failures 28
General Dust Buildup Causing Shorts 28
Hopper Plugging 24
Transformer Rectifier Failures 20
553
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TABLE 42. POWER PLANT ELECTROSTATIC P-RECIPITATOR
MAINTENANCE. PROBLEMS
279
Component
Discharge
Electrodes
Dust Removal
Systems
Rappers or
Vibrators
Collecting
Plates
Insulators
Major
Maintenance
Problem, %
35.2
31.8
5.7
13.6
1.1
Component Failure Frequency, %
Frequent Infrequent Very Seldom
29.5
36.4
9.1
4.5
8.0
38.6
42.0
38.6
7.9
34.1
28.4
2.0.5
47.7
68.2
48.9
554
-------
(3) Clinker or a wire that bridges the collection plates and
shorts out the wire.
(4) Ash buildup under the wire, causing it to sag and short
out.
(5) Corrosion caused by condensation.
(6) Excessive localized sparking leading to wire erosion.
(7) Fatigue leading to wire breakage, especially at those
points where wires are twisted together.
(8) Fly ash buildup in certain spots which leads to a clinkf. "
and burns off the wire.
Continuous sparking at any one location along a discharge wire will
ultimately lead to wire failure since small quantities of metal are
vaporized with each spark. Localized sparking can be caused by
misalignment of the discharge electrodes during construction or
by electric field variations caused by "edge" effects where the
discharge and collection electrodes are adjacent to each other at
the top and the bottom of the plates. Mechanical fatigue often
occurs when the discharge wire is twisted around the support collar
at the top of the discharge electrode.
Since the existence of temperatures below 121°C (250UF) may
lead to excessive corrosion and fouling of the cold-end elements
of the air heater and corrosion of cold-side precipitator elements,
the topics of corrosion and fouling are of considerable importance
and deserve proper attention. However, since proper design should
.result in temperatures above 121°C (250UF) and since an adequate
coverage of the topics of corrosion and fouling requires extensive
text, a discussion of low temperature corrosion and fouling is
given in Appendix D instead of in the main text. Appendix D in-
cludes discussions of (1) sulfuric acid occurrence in flue gas
based on SOX, H20, and H2SOu equilibria, determination'of the
sulfuric acid dew point, and condensation characteristics, (2)
factors influencing corrosion rates such as acid strength, acid
deposition rate, fly ash alkalinity, and hydrochloric acid, (3)
fouling of low temperature surfaces, (4) laboratory corrosion
studies, and (5) power plant data.
Problems with the dust removal systems are caused primarily
by hopper plugging, followed by screw conveyor and dust valve
deficiencies. Improper adjustment of hopper vibrators or complete
failure of the ash conveyor are common caus-es of hopper overflow.
Heaters and/or thermal insulation for the hoppers to prevent ash
agglomeration may be helpful in some cases.
Rapping is required for both discharge and collection elec-
trodes. A number of different rapping systems are used but those
555
-------
rapping systems using vibrators, either pneumatic or electric,
appear to require more maintenance than impulse-type systems.
Failures of support insulators are caused primarily by arc-overs
from accumulations of dust or moisture on the surface of the
insulator. These failures are often caused by inadequate pres-
surization of the top housing of the insulators.
Other problems which cause difficulty, but to, a lesser extent,
are dust buildup in the upper outside corners .o.f 'hoppers.,.,:corro-
sion in the less accessible parts of the precipitator such as
around the access doors and frames, box girders, and housing,
plugging of gas distribution plates, problems with rapping system
drives, wear of rappers and bushings, and problems of wear and
movement occurring at points of impact.
Another point of inquiry in the APCA survey involved overall
experience with electrostatic precipitators from operational
and maintenance standpoints. The utilities' responses were:
Utilities - Operation of Precipitators
Excellent Good Fair Poor
14.8% 45.5% 29.5% 10.2%
Utilities - Precipitator Maintenance
Excellent Good Fair Poor
13.6% 52.3% 13.6% 20.5%
Some of the data reported represent precipitator installations that
have been in service for many years and often these installations
have not received proper attention.
Proceedings from a recent specialty conference on the operation
and maintenance of precipitators would be extremely useful to
users who experience many of the problems discussed in this sec-
tion.281
556
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SECTION 11
TROUBLE SHOOTING
DIAGNOSIS OF ESP PROBLEMS
Causes for an electrostatic precipitator to fail to achieve
its design efficiency can be due to poor maintenance as dis-
cussed in the previous section, or they can be due to inadequate
design, electrical difficulties, improper gas flow, inadequate
rapping, installation problems, electrode misalignment, or impro-
per operation.
Structural engineering and design considerations are frequently
overlooked by the engineer who specifies and buys electrostatic
precipitators, for he often assumes that the manufacturer's ex-
perience and engineering capability is sufficient. In the com-
petitive atmosphere which exists among precipitator manufacturers,
a manufacturer normally proposes only the equipment and features
absolutely necessary to meet contract requirements.282 Any devia-
tions from a manufacturer's standards would increase costs and
possibly cost him his competitive advantage. An example of one
of the structural problems which has occurred is the lack of
provision for expansion, possibly stemming from a temperature
assumption that allows no' margin, thus causing excessive deflec-
tion of the substructure or the interior precipitator beams and
columns.282 Other structural problems arise from insufficient
attention to fabrication and erection tolerances, which result in
misalignment and operating difficulties.
Indications of electrical difficulties can usually be observed
from the levels of corona power input. Efficiency is generally-
related to power input, and if inadequate power densities are in-
dicated, difficulties can usually be traced to:275
(1) high dust resistivity,
(2) excessive dust accumulations on the electrodes,
(3) unusually fine particle size,
(4) inadequate power supply range,
(5) inadequate sectionalization,
(6) improper rectifier and control operation,
(7) misalignment of the electrodes.
557
-------
Because of the importance of resistivity in the precipitation pro-
cess, in situ resistivity measurements should be one of the initial
trouble shooting steps. If resistivity exceeds 10 10 ohm-cm, the
resistivity may be the blame for most of the difficulty.
Other electrical problems encountered with electrostatic
precipitators are shorting of the high tension frame by dust
accumulation in the hoppers, broken wires, insulator bushing
leakage, and leaking or broken cables.
Quality of gas flow can be determined by measurement of a
gas flow distribution profile at the precipitator inlet. The
IGCI recommends a gas quality such that 85% of the local velo-
cities is within 25% of the mean with no single reading more than
40% from the mean. Poor gas flow often results from dust accumu-
lation on turning vanes and duct work and plugging of distribution
plates. Gas "sneakage", a term describing gas flow which by-passes
the effective precipitator section, can also be a problem. "Sneak-
age" can be identified by measurement of gas flow in the suspected
areas (the dead passages above the collection plates, around the
high tension frame, or through the hoppers) during a precipitator
outage with the blowers on. Also, problems of reentrainment of
dust from the hoppers because of air inleakage or gas "sneakage"
can often be identified by an increase in dust concentration at
the bottom of the exit to the precipitator. Corrective measures
usually involve baffling to redirect gas flow into the electrified
region of the precipitator.
Improper rapping is usually the cause when excessive dust
deposits occur on the discharge and collection electrodes. Ade-
quacy of rapping can be measured by accelerometers mounted on the
electrodes. One should carefully adjust the rapping intensity and ,.
cycle to maintain a practical thickness of dust deposit without
excessive reentrainment.
Most problems associated with hopper and ash removal systems
are usually due to improper adjustment of the hopper vibrators or
failure of the conveyor system. In some instances heat and/or
thermal insulation for the hoppers to avoid moisture condensation
may be necessary.
Severe difficulties with electrostatic precipitators are
usually caused by inadequate electrical energization or excessive
reentrainment. The following is a rather general guide which may
be useful in pinpointing the causes of severe precipitator pro-
blems:275
(1) Measure the high tension voltage, current, and spark
rate.
558
-------
(2) Measure gas flow distribution.
(3) Observe collecting plates for evidence of back corona.
(4) Use an oscilloscope to record the high tension voltage
to determine the duration of the corona current.
(5) Observe the collection plates for evidence of excessive
reentrainment (this requires construction of a glass
plate and wiper for an access port and a means for illum-
ination of the interelectrode space).
(6) Examine alignment and condition of the h-ppers, insulators,
and other components.
(7) Measure rapping accelerations.
Table 43 is a trouble shooting chart for use in determining
the cause of common electrostatic precipitator malfunctions, with
suggestions for remedying these problems.277
AVAILABLE INSTRUMENTATION FOR ELECTROSTATIC PRECIPITATORS
Spark Rate Meters
The term "spark rate" refers to the number of times -per minute
that electrical breakdown occurs between the corona wire and the
collection electrode. A spark-rate controller establishes the
applied voltage at a point where a fixed number of sparks per minute
occur (typically 50 - 150 per corona section). The sparking rate
is a function of the applied voltage for a given set of precipitator
conditions. As the spark rate increases, a greater percentage of
input power is wasted in the spark current, and consequently less
useful power is applied to dust collection. Continued sparking to
one spot will cause errosion of the electrode and sometimes mechan-
ical failure. Therefore, to meet rapid or periodic changes in the
gas and ash composition, the rectifier should be fitted with a
spark rate controller which can automatically adapt the current to
the changing operating conditions. The precipitator is thus sup-
plied with a maximum of current at all times.
The spark rate meter may be supplied as a self-contained unit
or built into the automatic voltage control system. Some of the
companies which supply the spark rate meter and/or total voltage
control system are given below:
• Emrironecs-
16S4 Babeock Street
Gosta Mesa, California 92627
(714) 631-3993
559
-------
TABLE 43
TROUBLESHOOTING CHART
277
Ul
0>
O
Symptom
1. No primary voltage
No primary current
No precipitator (ESP)
current
Vent fan on
Probable Cause
DC overload condition
2. No primary current
No precipitator current
Vent fan off
Alarm energized
3. Control unit trips out an
over current when sparking
occurs at high currents
4. High primary current
No precipitator current
Misadjustment of current limit
control
Overdrive of rectifiers
Fuse blown or circuit breaker
tripped
Loss of supply power
Circuit breaker defective or
incorrectly sized
Overload circuit incorrectly
set
Short circuit condition in
primary system
Too high precipitator voltage
for prevailing operating
conditions
Remedy
Check overload relay setting
Check wiring and components
Check adjustment of current
limit control setting
Check signal from firing
circuit module
Replace fuse or reset circuit
breaker
Check supply to control unit
Check circuit breaker
Reset overload circuit
Check primary power wiring
Lower jbne precipitator voltage
•High voltage circuit shorted by
dust •? foul Idujp.. Jb.e;i-w<=en -«=!fni «-•*• *•-•<-•
Ki:riiove dust buildup
-------
electrode wor-e shooting the
high "V" circuit
remove or- replace broken or
slack wire
Ln
5.
Low primary voltage
High Secondary current
6.
Abnormally low ESP current
and primary voltage with
no sparking
Circuit component failure
Trouble in ESP:
(1) Dust buildup in hopper;
check meters:
- ammeter very high
- KV meter very low (1/2 normal)
- milliamperes very high
(2) Metallic debris left in
unit during shutdown for
maintenance
(3) Unhooked collecting plate
touching emitting frame
(4) Broken support insulator
(5) Excessive dust buildup on
hopper beams or cross member
Short circuit in secondary
circuit or precipitator
Misadjustment of current and/
or voltage limit controls
Misadjustment of firing circuit
control
Check transformer-rectifier
and precipitator: Ground T-R
high "V" Connector to precipi-
tator
Clean off dust buildup
Deenergize ESP and remove
Repair
Repair
Clean
Check wiring and components
in high voltage circuit;
check ESP for:
interior dust buildup
full hoppers
broken wires
ground switch left on
ground jumper left on
broken insulators
fore i_gn material on high
voltage frames or wires
Check settings of current and
voltage limit controls
Turn to maximum and check
setting of current and
voltage limit controls
-------
CTl
to
10.
11,
-
2.5
Spark meter reads high-
off scale
Low primary voltage and
current; No spark rate
indication
Spark meter reads high
primary voltage and
current very unstable
No spark rate indication;
voltmeter and ammeter
unstable indicating
sparking
No response to voltage
limit adjustment
Does respond to current
adjustment
No response to spark rate
adjustment
Does respond to other
adjustment
ntictvy tJUdU-Liiy ua eiiu.uu.my
electrode wires
Stream of cold air entering
ESP from defective door gasket
duct opening, inlet gas system
rupture-condensation
Wet dust clinging to wires
causes extremely low
millampere readings
Severe arcing in the ESP
without tripping out the unit
Continuous conduction of spark
counting circuit
Spark counter counting 60
cycles peak
Misadjustment
Loss of limiting control
Failure of spark meter
Failure of integrating
capacitor
Spark counter sensitivity
too low
Controlling on current limit
or spark rate
Controlling on voltage or
current
L. u-Liiy JLictmt:
and emitting vibration shaf*-
insulator
Repair
Eliminate source of condensation
Eliminate cause of arcing
Deenergize, allowing integrating
capacitor to discharge and
reenergize
Readjust controls;
Readjust ... ...
Replace control
Replace spark meter
Replace capacitor;
Readjust sensitivity
None needed if unit is operating
at m.iximum current or spark rate
Reset current and\spark rate
adjustment if neither is maximum
None needed if unit is operating
at maximum voltage or current
Reset voltage and current
adjustment if neither is at
maximum •" :; .
-------
The Environecs spark rate meter circuit is a standard part
of their total automatic voltage control system (Figure 293*83)
Other standard features of this system (see Figure 294283) other
than the spark rate meter are: (1) Electronic Current Limit,
which prevents drift in the current setting; (2) Soft Start,
which prevents high in-rush current to the high voltage power
supply at start-up; (3,) Recovery Control, which adjusts the rate
at which voltage recovers from the zero level after a spark back
up to the setback point; (4) Setback Control, which determines
the reduction of output voltage after a spark is detected; (5)
Hold Control, which holds the voltage at the adjusted setback
level for a short period of time, allowing the precipitator to
stablize; (6) Rise Rate, which determines the rate at which the
output power increases to the current limit setting or until a
spark is detected; (7) Spark Detection, which senses the spark
on the first half cycle, allowing the control logic circuits to
adjust the precipitator power immediately following the spark;
(8) Automatic/Manual Control with Bumpless Transfer, allows the
operator to select the optimum operating point of the precipitator
in the manual control mode of operation and then switch to the
automatic position and have the thyristor control automatically
start operating at the same output level selected in the manual
mode, (9) Arc Quench circuit, is an added safety feature to insure
against power arcs; (10) Under-Voltage Relay, monitors the AC
voltage across the primary of the high voltage power supply and
can be a useful device for indicating potential problems when
properly adjusted for a plant's particular operation.
• Wahlco, Inc.
3600 West Segerstrom Avenue
Santa Ana, California 92704
(714) 979-7300
The Wahlco Spark Rate Meter is designed for installation in
conjunction with new or existing precipitator controls. The unit
is self-contained requiring 120 VAC input for powering and the
signal input is derived from the ground leg resistor of the trans-
former rectifier set. All detecting and conversion components are
solid state. The only mechanical component is the meter movement.
The solid state system takes the steep wavefront of the spark
.signal, integrates this over a time base, and delivers an analog
signal into the meter movement. The spark sensing input signal
.is fed through a full wave bridge rectifier to eliminate polarity
sensitivity. The unit has multipole filters enabling it to respond
quickly and yet follow a spark signal without the meter bouncing
obj ectionably.
In Figure 295 is a diagram of the Wahlco automatic voltage
control unit.283 The spark detector's circuit memorizes the peak
amplitude attained by the input signal during one half cycle,
compares it to the peak amplitude attained during the next half
cycle, and then memorizes the value of the latter signal. From
563
-------
AUTO VOLTAGE CONTROL UNIT
L1
POWER
INPUT
L2
TRANSFORMER-RECTIFIER SET
[ HV
HIGH
TRANSFORMER VOLTAGE |
DC BRIDGE
I dn ^m I -^ •
RESISTOR | I
I I-
i
® ® SET BACK
PRECIPJTATOR
3640-282
Figure 293. Schematic of Environecs Automatic Voltage Control
Unit.283
564
-------
TYPICAL RESPONSE TO SPARK
TR
CURRENT
SPARK •
CURRENT LIMIT
SETBACK
HOLD
RISE RATE
RECOVERY
QUENCH
TIME
3540-283
Figure 294. Typical response to spark.
283
565
-------
AUTO VOLTAGE CONTROL UNIT
RECTIFIER
Ui
AUTO/MAN
SLOP RECOVERY
3640-184
Figure 295. Diagram of a Wahlco automatic voltage.control unit.283
-------
the controller standpoint a spark has occurred if the signal is
at least 25 instantaneous peak volts and its amplitude is at
least 5 volts greater than the previous half cycle's signal peak
amplitude. Some of the features of the system are: ramp rate
and set-back, current limit, undervoltage relay, and recovery
time control.
• A.V.C. Specialists, Inc.
2612 Croddy Way, Suite 1
Santa Ana, California 92704
(714) 540-2321
Figure 296 is a connection diagram for the external connec-
tions to the A.V.C. self-contained spark rate meter.283 This unit
can be added to any TR set controller providing that the input
power and spark signal are made available. The meter mounts in
the hole pattern for General Electric "Big Look" meters, 3% inch
type 162 (AO/DO91). Depth behind the panel is 4% inches maximum,
.and an additional h inch minimum should be allowed for clearance
at the terminals.
A.V.C. Specialists concentrates on providing voltage controls
for precipitators, both new and existing. Much of their business
is upgrading existing units to achieve better electrical performance,
better collection efficiency, more reliable operation, the elim-
ination of maintenance problems caused by non-responsive "automatic"
controls. Some of the important standard features of the automatic
voltage controllers are: ramp rate control, set back control,
quench control, current limit control, fast acting overload pro-
tection, and manual control mode.
There are two types of voltage controls that A.V.C. Specialists,
Inc. has developed for electrostatic precipitators:
(1) Saturable Core Reactor Type Controller, which is designed
to drive the D.C. control winding of a saturable core reactor.
(See Figure 297283);
(2) Thyristor (SCR) Type Controller, which controls the phase
angle of firing of two SCRs in order to control the output of the
TR set (See Figure 298283).
Secondary Voltage And Current Meters
Most precipitator control rooms have panel meters for each TR
set which show the primary and secondary voltage and current and
the sparking rate. Secondary voltage-current relationships can
be obtained for both clean and dirty plate conditions and inter-
pretations can be made of precipitator behavior based on the V-I
data. The secondary voltage-current meters operate on the same
principle as voltage diviers which were discussed in a previous
.section. Secondary voltage-current meters are supplied by the
i67
-------
T/R SET
FROM VOLTAGE
CONTROLLER >.
SPARK RATE METER
PRECIPJTATOR
MA SHUNT RESISTOR (GROUND LEG RES)
SIZE OF RESISTOR BASED ON
T/R SET RATING S640-286
Figure 296.
Connection diagram for the external connections
to A.V.C. self-contained spark rate meter.283
568
-------
T/R SET
L2-
INPUT
POWER
SATURABLE CORE
REACTOR
115 VAC '
CONTROL I
PRECIPITATOR
AUTOMATIC VOLTAGE CONTROLLER
1540-296
Figure 297. Block-diagram saturable core reactor type system
2 8 3
569
-------
T/ffi SET
L2-
JT
ER
f)
W/"
PT1
INDUCTOR
'
j
<^>^A_J
^S
V ^X
1
K-
FIRING
CIRCUIT
CURRENT
LIMIT
CONTROL
LOGIC
AUTO/MAN
Q ^ ^ Q
/
Re £ rf-
INPUT
SIGNAL
SPARK
DETECTOR
QUENCH
SET BACK
RAMP RATE
AUTOMATIC VOLTAGE CONTROLLER
LL
T
PRECIPITATOR
3640-287
Figure 298. Block diagram Thyristor-type system.283
570
-------
precipitator vendor and are not considered specialty items. Usu-
ally a major manufacturer such as General Electric sells the meters
off-the-shelf, and a meter company such as Meter Master, Simpson,
Triplett, etc. makes and calibrates the meter scale to specifica-
tions .
If meters are not' installed on the transformer secondary, a
quick, temporary voltage divider network can be installed on the
precipitator side of the rectifier network as discussed previously.
Many companies sell voltage dividers and a few of these are given
below:
Beckman Instruments-Helipot Division
2500 Harbor Boulevard
Fullerton, California 92634
(714) 871-4848
CPS Inc.
110 Wolfe Road
Sunnyvale, California 94086
(408) 738-OS30
Del Electronics Corporation
250 East Sandford Boulevard
Mt. Vernon, New York 10550
(914) 699-2000
EECO
1441 East Chesnut Avenue
Santa Ana, California 92701
(714) 835-6000
Electro Scientific Industries
13900 N.W. Science Park Drive
Portland, Oregon 97229
(503) 641-4141
Genrad
300 Baker Avenue
Concord, Massachusetts
(617) 369-8770
Guideline Instruments, Inc.
2 Westchester Plaza
Elmsford, New York 10523
(914) 592-9101
Heath Company
Benton Harbor, Michigan 49022
(616) 982-3200
571
-------
Hipotronics Inc.
Route 22
Brewster, New York 10509
(914) 279-8031
ILC Data Device. Corporation ....
105 Wilbur Place
Prpt. Intl. Plaza
Bohemia, New York 11716
(516) 567-5600
Kepco Inc.
131-38 Sanford Avenue
Flushing, New York 11352
(212) 461-7000
Pearson Electronics Inc.
400? Transport Street
Palo Alto, California 94303
(415) 494-6444
Sensitive Research Instruments
25 Dock Street
Mr. Vernon, New York 10550
(914) 699-9717
A representative example of a voltage divider made by Hipo-
tronics has a guaranteed accuracy of 0.5% DC and 1.0% AC. There
are three stock models available, 50 KV, 100 KV, and 200 KV with
other models with ratings to one megavolt available on request.
Some of the specifications for the standard models are given
below:283
Model KV50A Model KV100A Model KV200A
Accuracy:
DC
AC
Tracking
Movement
Meter:
Scale
Size
Voltage Coefficient:
DC
AC
Frequency response
Connecting cable
Meter ranges (KV)
Volts Division
0.5%
1.0%
0.5%
Taut band
0.5%
1.0%
0.5%
Taut band
0.5%
1.0%
0.5%
Taut band
100 divisions 100 divisions 100 divisions
mirror scale mirror scale mirror scale
5V 5V 5V
0.025%/C
0.025%/C
0.025%/C
DC and 40
to 1000 Hz
25 feet
0-10/25/50
100/250/500
DC and 40
to 1000 Hz
25 feet
0-20/50/100
200/500/1000
DC and 40
to 1000 Hz
25 feet
0-40/100/200
400/1000/2000
572
-------
Model KV5QA Model KV100A Model KV200A
Impedance 190 megohms 380 megohms 760 megonras
ei,o @ 20° Pfd- @ 100 pfd. @ 50 pfd.
5126 8V1 w x 8V W x 9V W x
lOV D x 10%" D x 10V D x
15V H 15V H 40" H
Opacity Meters
Opacity meters can be used effectively in monitoring the per-
formance of emission control equipment continuously- in addition,
optical density output can be correlated with par-iculate grain
loading to allow determination of mass emissions on a continuous
basis. Opacity meters are invaluable in gauging precipitator
performance quickly when small changes are made in coal, precipi-
tator controls, or boiler conditions. Some of the more important
variables which affect performance the most are boiler load, boiler
outlet gas temperature, boiler excess air level, precipitator
operating voltage, precipitator rapping intensity and direction,
and precipitator internal condition.
A number of techniques are used to determine relative stack
emission levels. These techniques and corresponding instrumentation
were discussed in detail in Section 7 of this report.
Hopper Level Meters
Preventing precipitator hoppers from completely filling with
fly ash is extremely important. Overflow can lead to shorted
electrical systems or fly ash reentrainment, either of which
would adversely affect precipitator performance. A number of
hopper level detectors have been developed to help eliminate the
overflow problem. These detectors have been previously discussed
in Section 4. Some of the principles of operation used in de-
tection are:
Non-contacting radiation principle - a narrow beam of gamma
rays is directed across the hopper to a radiation detector located
on the opposite wall. The rays are absorbed when ash builds up
causing a relay to activate an alarm.
Rod oscillation dampening - a rod is installed at the desired
.ash level. A drive coil drives the rod into self-sustained mechan-
ical .oscillations and a signal is produced by a pick-up coil
located opposite the drive coil. When fly ash reaches the level
of the rod, a dampening of the oscillations occurs and the signal
from the pick-up coil is reduced.
Capacitance sensor assembly - the detector assembly senses
a change in ash level as a function of the capacitance change
573
-------
between the detector and the vessel wall. This change is then
transmitted to a control instrument.
Radio frequency - a low power RF signal is radiated from a
sensing probe and changes in the impedance of the probe caused by
a change in ash level are monitored.
After alarms are given indicating dangerous accumulations of
fly ash,, systems for removal of the ash are activated. These
systems are discuss-ed in detail in Section 4.
574
-------
SECTION 12
AN ELECTROSTATIC PRECIPITATOR COMPUTER MODEL
INTRODUCTION
In recent years, increasing emphasis has been placed on
developing theoretical relationships which accurately describe
the individual physical mechanisms involved in the precipitation
process and on incorporating these relationships into a complete
mathematical model for electrostatic precipitation. From 'a
practical standpoint, a reliable theoretical model for electro-
static precipitation would offer several valuable applications:
(1) precipitator design could be easily and completely
performed by calculation from fundamental principles;
(2) a theoretical model could be used in conjunction with
a pilot-plant study in order to design a full-scale
precipitator;
(3) precipitator bids submitted by various manufacturers
could be evaluated by a purchaser with respect to
meeting the design efficiency and the costs necessary
to obtain the design efficiency;
(4) the optimum operating efficiency of an existing pre-
cipitator could be established and the capability to
meet particulate emissions standards could be ascer-
tained; and
(5) an existing precipitator performing below its optimum
efficiency could be analyzed with respect to the different
operating variables in a procedure to troubleshoot and
diagnose problem areas.
In addition to its many applications, a mathematical model
can be a valuable tool for analyzing precipitator performance due
to its cost- and time-savings capability. The approach is cost-
effective because it (1) allows for the analysis and projection
of precipitator operation based on a limited amount of data (ex-
tensive field -testing is not necessary), (2) can predict trends
caused by changing certain precipitator parameters and thus, in
many cases, can prevent costly modifications to a precipitator
which will not significantly improve the performance, (3) can be
575
-------
used as a tool in sizing precipitators and prevent excessive costs
due to undersizing or significant oversizing, and (4) can be used
to obtain large amounts of information without extensive use of
manpower but, instead, with reasonable use of a computer.
The approach is time-effective because (1) large amounts of
information can be generated quickly, (2) it does not necessarily
depend on time-consuming field tests which involve travel, ex-
tensive analysis, and plant and precipitator shut-downs, (3) it
can prevent losses in time due to unnecessary'or insufficient
modifications to a precipitator, and (4) it can prevent losses
in time due to the construction of an undersized precipitator.
In this section, the latest version137'15* of a mathematical
model of electrostatic precipitation developed under the sponsor-
ship of the U.S. Environmental Protection Agency is briefly des-
cribed. Since the model is described in great detail elsewhere,
the capabilities and applications of the model'will be stressed
here, rather than mathematical details. In the latest version,
earlier work153 has been improved and extended. Major improvements
to the fundamental basis of the model include the capability of
generating theoretical voltage-current characteristics for wire-
plate geometries, a new method for describing the effects of
rapping reentrainment, a new procedure for accounting for the
effects of particles on the electrical conditions, and the incor-
poration of experimentally determined correction factors to account
for unmodeled effects. The computer program which performs the
calculations in the model has been made more user-oriented by
making the input data less cumbersome, by making the output data
more complete, by making modifications which save computer time,
and by providing for the construction of log-normal particle size
distributions.
CAPABILITIES OF THE MODEL
The present version of the model has the following capabilities:
(1) it predicts collection efficiency as a function of particle
diameter, electrical operating conditions, and gas properties;
(2) it can calculate clean-plate, clean-air voltage-current
characteristics for wire-plate geometries;
(3) it determines particle charging by unipolar ions as a
function of particle diameter, electrical conditions, and residence
time;
(4) it can estimate the effects of particles on the electrical
conditions under the assumption that effects due to the particulate
layer can be ignored;
(5) it accounts for electrical sectionalization;
576
-------
(6) it predicts particle capture at the collection electrode
based on the assumptions of completely random, turbulent flow,
uniform gas velocity, and particle migration velocities which are
small compared to the gas velocity;
(7) it employs empirical correction factors which adjust the
particle migration velocities obtained without rapping losses in
order to account for unmodeled effects;
(8) it accounts for the nonideal effects of nonuniform gas
velocity distribution, gas bypassage of electrified regions, and
particle reentrainment from causes other than rapping by using
empirical correction factors to scale down the ideally calculated
particle migration velocities; and
(9) it accounts for rapping reentrainment by using empirical
relationships for the quantity and size distribution of the re-
entrained mass.
In its present form, the model has the capability of predicting
trends caused by changes in specific collection area, applied vol-
tage, current density, mass loading, and particle size distribution.
Comparisons of the predictions of the model with laboratory-scale
precipitators138'2 ' 285 and full-scale precipitators collecting
fly ash from coal-fired boilers19'285 indicate that the model can
be used successfully to predict precipitator performance.
BASIC FRAMEWORK OF THE MODEL
The mathematical model is based on an exponential-type re-
lationship given by equation (2). Although the previously discussed
assumptions upon which equation (2) is derived are never completely
satisfied in an industrial precipitator, they can be closely
approached with respect to the treatment of fine particles.
The assumption that the particle migration velocity near the
collection surface is constant for all particles has the most
significant effect on the structure of the model. This assump-
tion implies two things: (1) all particles are of the same diameter
and (2) the electrical conditions are constant.
Because all particles entering a precipitator are not of the
same diameter, the assumption of uniform particle diameters creates
a problem. This problem is dealt with in the model by performing
all calculations for single-diameter particles and then summing
the results to determine the effect of the electrostatic precipi-
tation process on the entire particle size distribution.
Because the electrical conditions change along the length of
a-precipitator, the assumption o.f constant electrical conditions
creates a problem. This problem is dealt with in the model by
dividing the precipitator into small length increments. These
577
-------
length increments can be made small enough that the electrical
conditions remain essentially constant over the increment. The
number of particles of a-given diameter which are collected in
the different length.increments are summed to determine the col-
lection efficiency' of particles o,f. a single diameter over the
entire length of the'precipitator-.
In summary, a precipitator is divided into essentially many
small precipitators in series. Equation (2) is. valid in each of
these small precipitators for fine particles of a given diameter.
The collection fraction, n • +> for the ith particle size in
1 r J
the jth increment of length of the precipitator :s mathematically
represented in the form
n^.. = 1 - exp (~wifj Aj/Q) ,. (70)
where w. . (m/sec) is the migration velocity near the collection
electrode of the ith particle size in the jth increment of length
and A. (m2) is the collection plate-area in the"jth increment -of
J V
length.
The collection fraction (fractional efficiency) n- for a given
particle size over the entire length of the precipitator is deter-
mined from
where KV . is the number of particles of the ith particle size per
cubic meter of gas entering the jth increment.
Effective or length-averaged migration velocities (w?) are
calculated for the different particle diameters from
wi =
where AT (m2) is the total collecting area.
The overall mass collection efficiency n for the entire poly-
disperse aerosol is obtained from
(73)
578
-------
where P. is the percentage by mass of the ith particle size in
the inlet size distribution.
to determine the migration velocities for use in
, the electrical conditions and the particle charging
*.»„« a * Precipitator must be modeled. If the operating vol-
tage and current density are known, then the electric potential
and electric field distributions are determined by using a re-
laxation technique.28-28? In this numerical technique, the
appropriate partial differential equations which describe the
electrodynamic field are solved simultaneously under boundary
conditions existing in a wire-plate geometry. In order to find
the solutions for the electric potential and space charge density
distributions, the known boundary conditions on applied voltage
and current density are held fixed while the space charge density
at the wire is adjusted until all the boundary conditions are
satisfied. For each choice of space charge density at the wire,
.the procedure iterates on a grid of electric potential and space
charge density until convergence is obtained and then checks to
see if the boundary condition on the current density is met. If
the boundary condition on the current density is not met, then
the space charge density at the wire is adjusted and the iteration
procedure is repeated.
Particle charge is calculated by using a unipolar, ionic-
charging theory.8''88 Particle charge is predicted as a function
of particle diameter, exposure time, and electrical conditions.
The charging equation is derived based on concepts from kinetic
theory and determines the charging rate in terms of the probability
of collisions between particles and ions. The theory accounts
simultaneously for the effects of field and thermal charging and
accounts for the effect of the applied electric field on the ther-
mal charging process.
The nonideal effects of major importance in a precipitator
are (1) nonuniform gas velocity distribution, (2) gas bypassage
of electrified regions, and (3) particle reentrainment. These
nonideal effects will reduce the ideal collection efficiency that
may be achieved by a precipitator operating with a given specific
collection area. Since the model is structured around an ex-
ponential-tvpe equation for individual particle diameters, it is
convenient to represent certain nonideal effects in the form of
correction factors which apply to the exponential argument. The
model employs correction factors which are used as divisors for
the ^deally calculated effective migration velocities in order to
account for nonuniform gas velocity distribution, gas bypassage,
and particle reentrainment without rapping.^89"90 The resulting
apparent effective migration velocities are empirical quantities.
LATEST IMPROVEMENTS TO THE MODEL
Calculation Of Voltage-Current Characteristics
579
-------
A new technique" has been developed for theoretically cal-
culating electrical conditions in wire-plate geometries and has
been incorporated into the model. , In this numerical technique,
the appropriate partial differential equations which describe the
electrodynamic field are solved simultaneously, subject to a suit-
able choice of boundary conditions.. ' The procedure yields the
voltage-current curve for a given wire-plate geometry and determine;
the electric potential, electric field, and charge density dis^
tributions for each point on the curve.
The key element in this technique is the theoretical calcu-
lation of the space charge density near the corona wire for a
specified current density at the plate. In order to find the
solutions for the electric potential and space charge density
distributions, the known boundary conditions on space charge-
density near the wire and current density are held fixed while
the electric potential at the wire is adjusted until all boundary
conditions are satisfied. For each choice of electric potential
at the wire, the procedure iterates on a grid of electric po-
tential and space charge density until convergence is obtained
and then checks to see if the boundary condition on the current
density is met. If the boundary condition on the current density
is not met, then the electric potential at the wire is adjusted
and the iteration procedure is repeated. The entire procedure
is repeated for increasing values of current density in order to
generate a voltage-current curve. Comparisons'*'291 of the pre-
dictions of this technique with experimental data show that the
agreement between theory and experiment is within 15%.
Method For Predicting Trends Due To Particulate Space Charge
A new method has been incorporated into the model in order
to provide a more comprehensive representation of the effects of
particulate space charge on the electrical operating conditions
in a precipitator. In this method, the precipitator is divided
into successive length increments which are equal to the wire-to-
wire spacing. Each of these increments is divided into several
subincrements. The first calculation in the procedure involves
the determination of a clean-gas, voltage-current curve which
terminates at some specified value of applied voltage. At the
specified applied voltage, the average electric field and ion
density are calculated in each subincrement. This allows for
the nonuniformity of the electric field and current density dis-
tributions to be taken into account.
As initially uncharged particles enter and proceed through
the precipitator, the mechanisms of particle charging and particle
collection are considered in each subincrement. In each subin-
crement, the average ion density, average particulate density,
weighted particulate mobility, and effective mobility due to both
ions and particles are determined. At the end of each increment,
the effective mobilities for the subincrements are averaged in
580
-------
order to obtain an average effective mobility for the increment.
Then, for the specified value of applied voltage, the average
effective mobility is used to determine the reduced current for
the increment by either calculating a new voltage-current curve
or using an approximation procedure. Although it is not presently
utilized, the method allows for iterations over each length in-
crement so that schemes which ensure self-consistency can be
implemented at a future date.
In its present state of development, this method provides
good estimates of reduced current due to the presence of particles.
The reduced current is a function of mass loading, particle size
distribution, gas volume flow, and position along the length of
the precipitator. However, this method does not have the capability
of predicting the redistribution of the electric field due to the
presence of particles. Work is going on at the present time to
improve the model in this respect.
Method For Estimating Effects Due To Rapping Reentrainment
As part of a program sponsored by the Electric Power Research
Institute, an approach to representing losses in collection effi-
ciency due to rapping reentrainment has been developed based on
studies performed on six different full-scale precipitators
collecting fly ash.19 These studies have been discussed earlier
in this text. In these studies, outlet mass loadings and particle
size distributions were measured both with rapping losses and without
rapping losses. Outlet mass loadings and particle size distri-
butions which can be attributed to rapping were obtained based on
the data acquired in these studies. The results of these studies
have been incorporated into the model.
The rapping emissions obtained from the measurements are
graphed in Figure 273 as a function of the amount of dust calcu-
lated to have been removed by the last electrical section. The
dust removal in the last electrical section was approximated by
using an exponential relationship for the collection process and
the overall mass collection fraction determined from mass train
measurements under normal operating conditions, as described earlier.
These data suggest a correlation between rapping losses and parti-
culate collection rate in the last electrical section. Data for
the two hot-side installations (4 and 6) which were tested show
higher rapping losses than for the cold-side units, and, thus, hot-
and cold-side units are treated differently in the model with re-
. spect to rapping reentrainment.
The apparent particle size distribution of emissions attri-
butable to rapping at each installation was obtained by subtracting
the crumiilative distributions during nonrapping periods from those
with rappers in operation and dividing by the total emissions
(.based on irapactor measurements) resulting-from rapping in order
to obtain a cumulative percent distribution. Although the data
581
-------
indicated considerable scatter,, the average particle size dis-
tribution shown in Figure 280 has been constructed for use in
modeling rapping puffs. In the model, the data are approximated
by a log-normal distribution with a mass median diameter of 6.0
ym and a geometric standard deviation of 2.5 as shown in Figure
299.
In summary, the model determines a rapping puff by -using the
information in Figure 278 to obtain the outlet'mass loading,.due,.,.
to rapping and by using a log-normal approximation -to-'the''"data in
Figure 280 to represent the particle size distribution of the
outlet mass Loading due to rapping. This "rapping puff" is added '
to the "no-rap" outlet emissions to obtain the t?tal outlet emis-
sions as a function of mass loading and partic_e size distribution.
Empirical Corrections To No-Rap Migration Velocities
Comparisons of measured apparent effective migration velocities
for full-scale precipitators under "no-rap" conditions with those
predicted by the model indicate* that the field-measured values
exceed the theoretically projected "values (in the absence of back
corona, excessive sparking, or severe mechanical problems) in the
smaller size range. Based on these comparisons, a size-dependent
correction factor has been constructed and incorporated into the
model.19 This correction factor is shown in Figure 300.
The empirical correction factor accounts for those effects
which enhance particle collection efficiency but are not included
in the present model. These effects might include particle charging
near corona wires, particle charging by free electrons, particle
concentration gradients, the electric wind, and flow field pheno-
mena. In future work which is planned, efforts will be made to
develop appropriate theoretical relationships to describe the above
effects and to incorporate them into a more comprehensive model" for
electrostatic precipitation.
User-Oriented Improvements
The computer program which performs the calculations in the
model has been modified to make the input data less cumbersome and
the output data more complete. The performance of a precipitator •
can be analyzed as a function of particle size distribution, current
density, specific collection area, and nonideal conditions without
repetition of input data which remain fixed. All input data are
now printed out in a format which is easily utilized. A summary
table of precipitator operating conditions and performance is
printed out as the last section of data for a given set of con-
ditions.
Several modifications have been made in order to save computer
time. The particle charging algorithm has been modified, and this
has decreased the computer time required for particle charging
582
-------
20
E
a.
cc
LU
<
Q
10
9
8
7
6
5
• Experimental
I I I I I I I I I I /
/
/
—— Log-normal approximation / ,
for MMO - 6,0 \an.
A
J I
I I
I
I
10 20 30 40 50 60 70 80 90 95
%LESS THAN 35.10-288
Figure 299.
Average rapping puff size distribution and log-
normal approximation for six full-scale precipi-
tators. These data are a result of work sponsored
by the Electric Power Research Institute.1
• 583
-------
_ 3
Z
SI
e
o
o
tu
3 2
O
cr
CO
TT
0.2
0.3
0.4 0.5 0.6
0.8 1.0 1.5
DIAMETER, pm
2.0 2.5 3.0
5.0
3540-289
Figure 300.
Empirical correction factors for the "no-rap"
migration velocities calculated from the mathematical
model. This work was sponsored by the Electric
Power Research Institute.19
584
-------
calculations by approximately 40%. In addition, particle charge
calculations for a given diameter will terminate in a given elec-
trical section whenever the charging rate becomes negligible. This
can reduce the time required to perform particle charging calcu-
lations by up to a factor of two or more in some cases. The
computer program has been modified so that, several sets of nonideal
conditions can be analyzed in conjunction with the results of one
ideal calculation. This allows for the analysis of an extended
range of nonideal conditions with only a small increase in computer
time. As another means of saving computer time, the computer pro-
gram now contains an estimation procedure for use in analyzing
precipitator performance. This procedure results in considerable
savings in computer time since involved numerical techniques are
not employed. The estimation procedure runs approximately 20
times faster than the rigorous calculation. This procedure can
be used to good advantage to determine gross trends or to establish
a limited range of interest in which to apply the more rigorous
calculation. The procedure can also be used to good advantage for
checking the validity of input data before making extensive rigor-
ous calculations.
The computer program now has the capability of constructing
log-normal particle size distributions based on specified values
of the mass median diameter and geometric standard deviation. This.
capability can be used to construct inlet and rapping puff particle
size distributions. Thus, the effects of different log-normal
particle size distributions can be readily obtained. Also, the
program can fit any specified particle size distribution to a log-
normal distribution.
APPLICATIONS AND USEFULNESS OF THE MODEL
The different practical applications of the model have been
discussed elsewhere.3'137'153 These include the examination of
the effects of particle size distribution, electrical conditions,
specific collection area, dust resistivity, and nonideal conditions
on the performance of a precipitator. These applications have now
been incorporated into procedures for troubleshooting and sizing
precipitators.l 37 These procedures, which provide specific guide-
lines for applying the model to troubleshooting and sizing appli-
cations, are discussed next in order to demonstrate the usefulness
of the model.
Use Of The Model For Troubleshooting
The mathematical model of electrostatic precipitation can be
used as a tool in troubleshooting precipitators that are not meeting
the overall mass collection efficiency which is expected or antici-
pated. When using the model for troubleshooting, certain experi-
mental data should be obtained in order to properly utilize the
model. These data include operating voltages and currents in the
different electrical sections, inlet mass loading and particle
585
-------
size distribution, ash resistivity, average gas flow rate and
velocity, and average gas temperature and pressure. By using
these limited experimental data, the geometry of the precipitator,
and the mathematical model, certain steps which are given below
can be taken in an attempt to diagnose the possible reason or
reasons for the level of performance of the precipitator.
Step 1: Determine optimum collection efficiency-
The model is used to simulate the operation of the precipi-
tator under ideal, no-rap conditions (a = 0 and S = 0) with the
g
actual operating parameters, where a is the normalized standard
deviation of the gas velocity distribution and £ is the fraction
of the gas volume bypassing each electrical section. This calcu-
lation establishes the'optimum overall mass collection efficiency
that can be expected under the given operating conditions. It
should be noted that this optimum efficiency may not always repre-
sent the best performance of the precipitator since accumulation
of material on the discharge and collection electrodes, broken
discharge electrodes, electrode misalignment, or operation of the
precipitator at lower than permissible voltages and currents would
result in less than optimum electrical operating conditions. If
possible, measures should be taken to ensure that the electrical
conditions in the precipitator are at their best when obtaining
data for use in the troubleshooting procedure. In any event, the
starting point in the troubleshooting procedure can be taken to be
the calculated optimum efficiency under the actual operating con-
ditions.
Step 2: Check to see if the calculated optimum efficiency is
equal to or less than the measured value.
If the calculated optimum value of efficiency is equal to or
less than the measured value, then the precipitator can be assumed
to be performing as well as possible for the given set of operating
conditions. Changes in the inlet particle size distribution, the
electrical operating conditions,, or the gas volume flow can result
in a reduction of collection efficiency for a given precipitator
even though the precipitator is performing at its best. Thus, in
certain casesf a precipitator may not be able to attain the overall
mass collection efficiency it once achieved or was designed to
achieve solely due to a change in the process variables. As a
consequence, the precipitator may no longer be sized properly for
the operating conditions encountered. The options that are avail-
able for improving the performance of the precipitator are limited
to the possible improvement of the electrical operating conditions
or a reduction in the gas flow rate through the precipitator.
Step 3: Check to see if the calculated optimum efficiency is
only a little larger than the measured value.
586
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If the calculated optimum value of efficiency is only a
little larger than the measured value, then the precipitator is
probably functioning well but nonideal conditions are having some
effect^ on the performance. In this case, calculations should be
made with the model in order to obtain NO-RAP + RAP overall mass
collection efficiencies for various small values of a and S and
^ 9
the rapping reentrainment parameters which are built into the
computer program. If the measured efficiency can be predicted
by the model with values of a £ 0.25 and S <_ 0.1, then it is
questionable whether or not improvements in the gas flow pro-
perties and mechanical design will result in an appreciable im-
provement in precipitator performance. A less ccstly and possibly
more profitable exercise would be to vary the rapping intensities
and frequencies in an attempt to minimize losses in collection
efficiency due to rapping reentrainment. If a > 0.25 or S > 0.1,
then these quantities should be measured. If the measured values
of a and S are consistent with those predicted by the model, then
the gas flow properties and mechanical design should be improved.
Step 4; Check to see if the calculated optimum efficiency
is significantly larger than the measured value.
If the calculated optimum value of efficiency is significantly
larger than the measured value, then the precipitator is functioning
poorly. Poor performance of a precipitator may be due to either
one or a combination of several factors that can be analyzed with
the model. These factors include the electrical operating con-
ditions, nonuniform gas velocity distribution, gas bypassage of
electrified regions, particle reentrainment without rapping, and
rapping reentrainment. In the following steps, procedures are
outlined that can be taken in an attempt to pinpoint the problem
areas.
Step 5: Determine whether or not the operating currents are
completely useful in the precipitation process.
At this point, the electrical operating conditions should be
examined in order to determine whether or not the operating cur-
rents are completely useful in the precipitation process. If
'excessive sparking or back corona is occurring in the precipitator,
then, the measured currents will not be totally useful in the pre-
cipitation process and, in fact, the nature of the currents may
be very detrimental to precipitator performance. Use in the model
of currents measured under these conditions will result in the
.prediction of much higher collection efficiencies than will be
attained, by the precipitator.
Step 5a: Check for exces.sive sparking -
587
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Sparking results in localized currents that are not very
effective in charging particles.. In addition, excessive sparking
can lead to increased particle reentrainment by,, producing dis-
ruptions at the surface of the collected particulate layer and by
producing reduced holding forces over large regions of the col-
lected layer due to reduced currents to -these regions.
If sparking is occurring, then the extent of the sparking
should be determined by using spark rate meters or 'Other appro-
priate instrumentation.. If excessive sparking 'is occurring-, then
the applied voltage .should be low.er-ed. until the spark rate is at
a level which is not detrimental to the performance of the pre-
cipitator. Although the operating voltages and currents will be
reduced, the performance of the precipitator will improve and the
use of these operating electrical conditions -in the model will
give better agreement-between predicted and measured collection
efficiencies.
Step 5b: Check for the existence of back corona.
If excessive sparking is not occurring, then a check should
be made to determine whether or not a condition of back corona
exists in the precipitator. When back corona exists, both positive
and negative ions move in the interelectrode space and this results
in a reduction in the negative charge that can be acquired by a
particle.
Two methods can be used to check for the existence of back
corona. First, the measured value of ash resistivity and Figure
208 can be used to estimate the maximum allowable current density.
If the current density in the precipitator greatly exceeds this
value, then the precipitator is probably operating in back corona.
As a second method of checking for the existence of back corona,
the voltage-current curves for the different electrical sections
can be checked to see if at some point on the curve increased cur-
rent is obtained at a reduced applied voltage. If this is the case
and the precipitator is operating in this region of the voltage-
current curve, then back corona is occurring in the precipitator.
If back corona is occurring, then the applied voltage should
be lowered in order to obtain a current density which will not
lead to the formation of back corona. The reduced voltages and
currents will result in improved performance of the precipitator
and the use of these operating electrical conditions in the model
will give better agreement between predicted and measured col-
lection efficiencies.
Step 5c: Consider electrode misalignment.
As a further consideration concerning the electrical conditions,
the electrode alignment should be taken into account. Consideration
of electrode alignment is especially important when troubleshooting
588
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hot precipitators. In hot precipitators, the collection plates
may buckle if proper precautions have not been taken to allow for
the expansion of the plates at the elevated temperatures. If
buckling of the plates occurs, then higher currents will be mea-
sured but they will be localized. Currents of this type are not
desirable for treating particles. The existence of this type of
misalignment should be, evidenced by steep voltage-current curves
with a narrow voltage range from corona initiation to sparkover.
Use in the model of measured currents obtained from this type of
situation will result in predicted collection efficiencies that
are well above those which are attained.
Step 6; Estimate the effect that various nonideal conditions
could have on the performance of the precipitator.
If the poor performance of the precipitator cannot be traced
to the electrical operating conditions, then the nonideal effects
of nonuniform gas velocity distribution, gas bypassage of elec-
trified regions, and particle reentrainment should be considered
next. The effect of a and S on the NO-RAP + RAP overall mass
collection efficiency of the precipitator should be analyzed in
a systematic fashion with the model.
Step 6a; Estimate the possible effect of nonuniform velocity
distribution on the performance of the precipitator.
In order to determine whether or not a nonuniform gas velocity
distribution could be responsible for the poor performance of the
precipitator, calculations should be made for S = 0 and values of
0 ranging from 0 to at least 2.0. If a certain value of a in
g 9
the chosen range produces the necessary reduction in collection
efficiency and this value is not completely out of line with
available information concerning the gas flow, interfacing of
the precipitator with the duct work, existence of gas diffusion
plates, etc., then the actual value of a should be determined
experimentally by making a velocity traverse in a plane at the
inlet of the precipitator. If the measured value of a is greater
than 0.25, then measures should be taken to improve the gas flow
distribution.
Step 6b: Estimate the possible effect of gas sneakage and/or
particle reentrainment without rapping on the per-
formance of the precipitator.
In order to determine the extent of gas bypassage of the
electrified regions and/or particle reentrainment without rapping
that would be necessary to cause the poor performance of the pre-
cipitator, calculations should be made for a = 0 and values of
S ranging from 0 to 0.9. There will be a value of S in this range
that will result in the necessary reduction in collection efficiency.
589
-------
Depending on the value of S, different interpretations can be
made. If S is not too large (S <_. 0.2), then the poor performance
might be attributed to either excessive gas bypassage of the
electrified regions or.--excessive particle reentrainment without
rapping or very poor gas velocity distribution or a combination
of all three of these effects where neither effect alone is very
detrimental to the performance of the precipitator. In this-
case, measurements should be made under air-load conditions...,to
determine a and the fraction of'the gas volume flow passing
through non-electrified regions in each baffled section. If. the
measured values of these quantities are such that they can. account
for a major part of the reduction in collection efficiency, then
the appropriate corrective measures can be made -o the mechanical
design of the precipitator. If the measured values of these.
quantities are such that they can not account for a major part
of the reduction in collection efficiency, then it is possible
that particle reentrainment without rapping is having an adverse
effect on the performance of the precipitator. This could be due
to factors which include a high average gas velocity, a very non-
uniform gas velocity distribution, a low value of ash resistivity,
excessive sparking, low operating current densities, and hopper
problems. All of these factors can lead to particle reentrainment
from causes other than ;rapping and should be taken into account
in the troubleshooting analysis.
If S is large (S > 0.2), then the poor performance of the
precipitator is probably due primarily to extremely excessive
particle reentrainment. This could be a result of one or more
of the same factors mentioned above. In this case, reentrainment
of particles from the hoppers, caused by poor gas flow qualities
or by hopper malfunctions, should receive more serious attention
as a possible cause of the poor performance. If very large values
of S are needed to predict the reduction in collection efficiency-,
then it is also possible that rapping reentrainment is occurring
to a much greater extent than that predicted by the rapping re-
entrainment calculation and that this is reflected in the value
of S. If the value of S is large, then hopper operation should
be checked, outlet mass loadings should be obtained with and
without rapping, and real-time measurements of the outlet mass
loading should be made. These measures should indicate whether
the problem is due to hopper operation or rapping reentrainment
or reentrainment without rapping or some combination of the three.
The troubleshooting procedure described above can be a valu-
able tool in helping to diagnose the causes of poor performance of
a precipitator. Since the procedure involves only limited experi-
mental data, it is not costly to perform. Use of the procedure
can also result in time and cost savings by giving direction and
helping to focus on those quantities which actually need to be
measured. A further benefit of using the procedure is the possi-
bility that costly modifications to the precipitator that will not
result in significant improvement in the performance can be avoided.
590
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Use Of The Model For Sizing Of Precipitators
The mathematical model of electrostatic precipitation can be
used as a guide in sizing precipitators. Although this method of
sizing precipitators can be very successful, care must be taken to
ensure proper usage of the model and to prevent the use of erroneous
input data. Misuse of the model could result in a large error in
sizing a precipitator.
When using the model for the purpose of sizing a precipitator,
certain data which are used as input to the model should be obtained
from measurements made using the actual gas stream or one which will
be very similar to the actual gas stream. If a cas stream other
than the actual one is used to obtain representative data, then
steps should be taken to assure that the process variables pro-
ducing the effluent gas stream and particles are not too different.
Also, it is very important that the temperature and composition of
the gas stream be close to that which will be experienced in the
precipitator to be sized.
The following is a list and discussion of those quantities
whose values should be determined from measurements under con-
ditions similar to those which will be experienced in the precipi-
tator to be sized:
The temperature, pressure, and composition of the gas stream
should be measured.
The particle size distribution and mass loading in the gas
stream should be measured at a location from the source that would
be representative of where the gas stream would enter the precipi-
tator.
The bulk resistivity of the particles should be measured both
in situ and in the laboratory. In making these measurements, the
gaseous environment must not only be preserved but, in addition,
the electric field strength at which the measurements are made
must be 'close to that which will be experienced in the precipitator
in order to obtain the appropriate measurement. If agreement can
not be obtained between the in situ and laboratory measurement,
then the higher of the two values should be used in order to size
•. 'the. pr ec ip i t a tor.
The effective mobility of the negative ions which would be
produced during negative corona discharge in the gas stream should
be measured.
If any or all of the above quantities are not measured or can not
be mea-sured, then their values can only be estimated by using the
best data available and prior experience for similar sets of con-
ditions. Using values of these quantities that are not obtained
from measurements with the actual or a similar gas stream is risky
and these values should be estimated in a conservative manner.
591
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Once the values of the quantities discussed above are de-
termined, the model can be used in a procedure to predict what
precipitator sizes are needed to attain various.levels of overall.
mass collection efficiency,......The.... steps, which -should be taken in
this procedure are discussed next.'
Step 1: Establish an estimate of the electrical conditions
under which the precipitator should operate'.""
In establishing an estimate of the electrical operating con-
ditions, a determination of the maximum allowable current density
should be made first. The maximum allowable current density can
be estimated by using the determined value of ash resistivity
and the curve given ,in Figure 208. If voltage-c-rrent data are
available for similar conditions, then these should also be used
in helping to determine the maximum allowable current density-.
Once the maximum allowable current density is estimated,
then the applied voltages which will produce this current density
in the different electrical sections must be estimated. These
voltages may be obtained from voltage-current' data which are
available for similar conditions except it is not necessary that
the ash resistivity be duplicated. Alternatively, the model can
be used with the option which calculates voltage-current curves
for a wire-plate geometry in order to determine voltage-current
characteristics with the effect of resistivity being ignored.
Then, the applied voltages necessary to produce the maximum allow-
able current density can be estimated. In utilizing the voltage-
current calculation, a value for the roughness factor of the
discharge electrodes must be specified. The value of this para-
meter normally lies between 0.5 and 1.0 and small changes in"the
value lead to significantly different results. Since the value
of this parameter is difficult to project in advance and the value
changes during the operation of the precipitator, care must be
taken in specifying this value and in analyzing the results ob-
tained. Calculations used to size the precipitator should be
made for several values of the roughness factor between 0.5 and
1.0 and the most conservative prediction of precipitator per-
formance should be used as the basis for sizing the precipitator.
Also, if values of the roughness factor in a particular range
yield results that are obviously out of line with similar appli-
cations, then this range should be eliminated from consideration.
Since the ash resistivity is difficult to determine precisely
and environmental changes can produce significant changes in its
value, the size of a precipitator should be determined based on
a maximum allowable current density which is estimated based on
a somewhat higher value of resistivity than anticipated. A rea-
sonable and conservative approach might be to base the estimated
maximum allowable current density on a value of resistivity that
is one-half an order of magnitude greater than the anticipated
value.
592
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Step 2: Determine the geometrical parameters to be used.
At this point, the geometrical characteristics of the pre-
cipitator should be established since these data are necessary as
input to the model. The values of the plate spacing, discharge
electrode^spacing, and diameter of the discharge electrodes which
are used in the model must be the actual values. In order to
size the precipitator, it is not necessary to know the actual
values of the cross-sectional area, height, area, and number of
the plates, length of the electrical sections, or total elec-
trified length. Although the values of these quantities can be
chosen arbitrarily, they should be as representative as possible.
In the model, different overall mass collection efficiencies
can be determined for different specific collection areas and then,
based on the actual gas volume flow through the precipitator,
the total collection plate area necessary to achieve a given
efficiency can be determined. Knowing the required collection
•plate area, the precipitator can be designed with respect to
cross-sectional area, plate height, and length. In designing the
precipitator so that it will have the required collection plate
area, certain considerations should be made. First, the height
of the collection plates should not be too high since this can
lead to increased reentrainment from rapping and to greater dif-
ficulty in providing sufficient rapping force to the entire area
of the plate. In practice, the height of collection plates ranges
from approximately 3.05 (10) to 12.2 (40) meters (feet). Second,
the precipitator should be long enough so that it can contain
several baffled, independent electrical sections. Increasing
the number of baffled electrical sections leads to better operating
electrical conditions and reduced losses in collection efficiency
due to gas sneakage and hopper boil-up. Third, the gas velocity
through the precipitator should be 1.53 m/sec (5 ft/sec) or less
in order to help prevent reentrainment without rapping and to
allow sufficient residence time to recollect material reentrained
due to rapping.
Step 3: Determine, the nonideal conditions for which the
precipitator will be sized.
Since a certain degree of a gas flow nonuniformity and gas
bypassage of electrified regions and/or particle reentrainment
without rapping can be expected to exist in a precipitator, these
factors must be considered in sizing the precipitator. Experience
in simulating the operation of full-scale, industrial precipitators
indicates that values of a =0.25 and S = 0.1 are appropriate for
modeling precipitators which are in good working condition. Losses
in overall ma.ss collection efficiency due to rapping reentrainment
are built into the model and cannot be varied without changing the
computer program itself. Since the procedure which determines the
effect of rapping reentrainment on precipitator performance is
593
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based on average data acquired from six different full-scale
precipitators, the effects of rapping reentrainment might not
be estimated in a conservative manner.
If a conservative approach is taken in sizing the precipi-
tator, then the values of a and S should be taken to be somewhat
9
higher than 0.25 and 0.1., respectively. Value-s of a = .O.-4'..and
S = 0.2 should be conservative. This value of S should also
allow for above average losses in collection-efficiency due to
rapping reentrainment. If the precipitatbr is sized in a con-
servative manner, then the chances that the precipitator will be
able to meet the particulate emissions standards once it is built
are improved even though undesirable nonideal conditions exist.
As a consequence, the process producing the emissions does not
have to be shut down until the problems with the precipitator
are diagnosed and corrected.. The problems with the .precipitator
can be diagnosed with the troubleshooting procedure while the
precipitator is in operation and appropriate corrective measures
can be made during a scheduled shut down. Thus, in many cases,
the added cost of a conservative. design can .be--partially or- fully.
recovered.
Step 4; Consider the effect of adverse changes in particle
size distribution in sizing the precipitator.
Since any decrease in the mass median diameter or increase in
the dispersiveness of the inlet particle size distribution will
result in a fundamental reduction in precipitator performance,
this factor should be considered in sizing a precipitator. Any '''
changes in the process variables controlling the source of the
emissions can result in significant changes in particle size dis-
tribution. Thus, the possibility of a change from the anticipated
particle size distribution to a less favorable one should be in-
corporated into the sizing procedure. In a conservative approach,
the measured or anticipated inlet particle size distribution can
be fit to a log-normal distribution and the fitted mass median
diameter and geometric standard deviation can be decreased and
increased by 25%, respectively. These new values should then be
used in the model in order to obtain the inlet particle size dis-
tribution for use in sizing the precipitator.
Step 5: Generate a curve of overall mass collection efficiency
versus specific collection area.
At this point, since all appropriate input data have been or
can be determined, the computer program for the mathematical model
can be executed in order to size the precipitator. The precipitator
can be sized by generating a curve of overall mass collection effi-
ciency versus specific collection area.
Based on the curve of overall mass collection efficiency versus
specific collection area and the particulate emissions standard,
594
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the precipitator size needed to attain the required efficiency
can be determined. In sizing the precipitator in a conservative
manner, the precipitator should be sized to attain an efficiency
which is somewhat higher than that which is required. This is
necessary in order to provide a margin of safety in design ir-
respective of any uncertainties in operating parameters and of
any nonidealities which might exist. In order to provide this
margin of safety, the projected collection plate area needed to
attain the required efficiency should be increased by a certain
percentage, possibly 10-15%. This added collection plate area
is also an advantage in that it offers the possibility that the
precipitator will be able to adequately treat gas flows which
are somewhat higher than the design gas flow.
Step 6: Allow for the outage of electrical sections.
In designing the precipitator, a high degree of electrical
sectionalization should be provided. As stated previously, this
leads to improved electrical operating conditions. In addition,
if certain electrical sections are not working, this condition
does not disable a large portion of the precipitator.
In sizing a precipitator, proper allowance should be made
for the possibility that from time to time certain electrical
sections will not be functioning. This can be done by increasing
the collection plate area obtained in Step 5. The additional
collection plate area should be provided in the form of added
electrical sections. If reliable data or past experiences are
not sufficinet for estimating the number of electrical sections
that might be inoperable at any given time, than a reasonable
approach might be to add an extra electrical section for approxi-
mately every four electrical sections that are required in Step 5.
The above guidelines and procedure cover the important con-
siderations which must be made in sizing an electrostatic precipi-
tator. If the guidelines and procedure are followed correctly,
then the mathematical model of electrostatic precipitation can
be a valuable tool for sizing electrostatic precipitators. Since
the procedure includes reasonable conservative measures to account
for several different uncertainties, the cumulative effect should
lead to a precipitator which is sized conservatively but not
excessively oversized.
The procedure for sizing a precipitator can be utilized by
manufacturers to assist in designing a precipitator and by pur-
chasers to assess bids submitted by the various manufacturers.
It can also be used by government regulatory agencies in helping
'to establish particulate emissions standards which are economically
feasible and consistent with the best available control technology.
The troubleshooting and sizing procedures can both be utilized
in conjunction with pilot precipitator studies. The troubleshooting
595
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procedure can be used to characterize the performance of the pilot
precipitator and to establish the values of the parameters charac-
terizing the operation of the precipitator. This will establish
baseline information for which the model predictions and experi-
mental data are in agreement. The sizing"procedure can then be
used to project full-scale precipitator performance under various
operating conditions in order to obtain the size necessary to give
the required collection efficiency.
It should be noted that care should be taken in projecting
full-scale performance based on pilot data. Normally, better
electrical conditions can be obtained in a pilot unit than a full-
scale unit because of the reduced collection electrode area. In
addition, particle reentrainment characteristics, gas velocity
distribution, and gas bypassage of electrified regions in the
pilot unit and the constructed full-scale unit may differ signi-
ficantly.
59.6
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SECTION 13
FEATURES OF A WELL-EQUIPPED ELECTROSTATIC PRECIPITATOR
There are several, important features that a well-equipped
electrostatic precipitator should possess. These features are
necessary in order to achieve high collection efficiency, opera-
tional and mechanical reliability, and ease in locating potential
problems and in troubleshooting existing problems. In this
section, these features are listed and discussed. Most of these
features have been pointed out or discussed earlier in the text.
Thus, the following list serves to bring these features together
in a single location for easy reference.
0 Adjustable gas flow distribution screens (or other devices)
should be located at the inlet of an electrostatic precipi-
tator in order to reduce the turbulence in the gas stream
and to improve the gas velocity distribution. Adjustable
devices are needed because flow model studies or other
methods of prediction may not prove to be reliable. In
some cases two or more devices may be necessary in order
to achieve good gas flow qualities. (It has been demon-
strated that this can be done without incurring excessive
pressure drops). The average gas velocity entering the
electrostatic precipitator should be no higher than 1.22
m/sec (4 ft/sec). The uniformity of the gas velocity
.distribution at the inlet of the electrostatic precipitator
should, as a minimum, meet existing IGCI requirements.
• The electrostatic precipitator should have chambers which
can be isolated for on-line maintenance and repair. It
should have an adequate number of inlet and outlet sampling
ports for each chamber. A minimum of six is necessary at
each location in order to provide proper sampling access.
The sampling ports should be of 6 in. diameter pipe instead
of the commonly used 4 in. diameter pipe. This would
facilitate the design and use of sampling instrumentation.
Thermocouples should be located at the inlet and outlet of
each chamber for proper monitoring of temperature. The use
of induced draft fans will make gas and particulate sam-
pling less difficult and less hazardous. The electrostatic
precipitator should have a totally enclosed roof penthouse.
• The electrostatic precipitator should have hopper baffles
and baffles above the electrodes to minimize gas bypassage
597
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of electrified regions and to prevent significant gas flow
from occurring in the hoppers.
• The electrostatic precipitator should have at least four,
and preferably six, electrical sections in the direction
of gas flow. There should be adequate' electrical section-
alization with no more than between 1,861 - 2,.791 m2
(20,000 - 3-0,.000 ft2) of collection plate area per
.transformer/rectifier (TR) set -with two bushings per TR
set. A rigid discharge electrode system is desirable
because of its stability and reliability. The collection
electrodes should be mounted in guides for proper alignment
and stability. A dried, heated purge air- system should, be
provided for keeping insulator feed-thru s free of particles'
and condensed gases. Secondary current and voltage panel
meters are needed for monitoring actual precipitato-r elec-
trical operating conditions and for troubleshooting. The
power supplies should have -controllers which can operate
in either a spark. rate or--current limit, mode to produce
the maximum useful voltages and currents. Each electri-
cal section should be provided with access from the inlet,
outlet, top, and bottom for ease of inspection, wire re-
placement, alignment, and collection of representative ash
samples, if necessary.
» The electrostatic precipitator should have independent
discharge and collection electrode rappers. The rapping
systems should be programmable with frequency and intensity
adjustment capability so that precipitator performance can
be optimized with respect to the rapping process. The
rapping system for the collection electrodes should be
capable of producing accelerations in all parts of the
plate of over 50 times that of the gravitational accelera-
tion. The discharge electrode system should be cleaned
by impulse rappers rather than vibrators. The hoppers
should be sufficiently heated or insulated to prevent con-
densation and resultant pluggage. Hopper level indicators
should be installed to monitor hopper performance. Ash
collected in the hoppers should be removed with a system
which minimizes air flow into or out of the hoppers and
should be conveyed away with an air transport system.
* The outlet of the precipitator should be instrumented with
an opacity meter for continuous monitoring of precipitator
performance. This will provide continuous information
which will indicate changes in precipitator operation which
could be caused by changes in the process variables or pre-
cipitator malfunctions. The opacity information is also
useful in troubleshooting.
598
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REFERENCES
la. Engelbrecht, H. L. Air Flow Model Studies for Electrostatic
Precipitation, p. 72-73. From: Symposium on the Transfer
and Utilization of Particulate Control Technology: Volume 1.
Electrostatic Precipitators. EPA-600/7-79-:.44a, Environmental
Protection Agency, Research Triangle Park, North Carolina,
February 1979.
b. Szabo, M. and R. Gerstle. Electrostatic Precipitator Mal-
functions in the Electric Utility Industry, section 2, p. 16.
EPA-600/2-77-006, prepared by PEDCo for the Environmental
Protection Agency, Research Triangle Park, North Carolina,
January 1977.
2. Smith, W., K. Gushing, and J. McCain. Procedures Manual for
Electrostatic Precipitator Evaluation, p.18. EPA-600/7-77-059,
prepared by Southern Research Institute for the Environmental
Protection Agency, Research Triangle Park, North Carolina,
June 1977.
3. McDonald, J. and L. Sparks. A Precipitator Performance Model:
Application to the Nonferrous Metals Industry. Proceedings:
Particulate Collection Problems Using ESPs in the Metallurgical
Industry- EPA-600/2-77-208, U.S. Environmental Protection
Agency, Raleigh Durham, North Carolina, 1977. 72 pp.
4. McDonald, J., W. Smith, H. Spencer, and L. Sparks. A Mathe-
matical Model for Calculating Electrical Conditions in Wire-
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York.
328. Kear, R. W. A Constant Temperature Corrosion Probe. J.
Inst. Fuel, 32:267, 1959.
623
-------
329- Alexander, P. A., R. S. Fielder, P. J. Jackson, and E.
Raask. An Air-Cooled Probe for Measuring Acid Deposition
in Boiler Flue Gases. J. Inst. Fuel, 33:31, 1960.
330. CERL (private communication).
624
-------
APPENDIX A
POWER PLANT AND AIR QUALITY DATA FOR
THOSE PLANTS WITH ELECTROSTATIC PRECIPITATORS
625
-------
TABLE 44. POWER PLANT AND AIR QUALITY DATA FOR THOSE
PLANTS WITH ELECTROSTATIC PRECIPITATORS
o\
to
Company Name*
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
Alabama Power
Alabama Power
Alabama Power
Alabama Power
Alabama Power
Alabama Power
Allegheny Power (Monongahela)
Allegheny Power (Monongahela)
Allegheny Power (Monongahela)
Allegheny Power {Monongahela)
Allegheny Power (Monongahela)
Allegheny Power (Monongahela)
Allegheny Power (Monongahela)
Allegheny Power (West Pa.)
Allegheny Power (West Pa.)
Allegheny Power (West Pa.)
Allegheny Power (West Pa.)
Allegheny Power (West Pa.)
Allegheny Power (West Pa.)
Allegheny Power (West Pa.)
Appalachian Power
Appalachian Power
Appalachian Power
Appalachian Power
Appalachian Power
Arizona Public Service
Arizona Public Service
Big Rivers Electric
Big Rivers Electric
Big Rivers Electric
Big Rivers Electric
Cardinal Operating Co.
Cardinal Operating Co.
Carolina Power & Light
Carolina Power & Light
Carolina Power & Light
Carolina Power & Light
Plant Name
Barry
Gorgas
Gorgas
Gorgas
Gadsden
Gadsden
Albright
Fort Martin
Fort Martin
Harrison
Harrison
Harrison
Willow Island
Armstrong
Armstrong
Hatfield
Hatfield
Hatfield
Mitchell
Springdale
Cabin Creek
Cabin Creek
Clinch River
Clinch River
Clinch Rivei
Four Cornell'
Four Corners
Kenneth Coletnan
Kenneth Coleman
Kenneth Coleman
Robert Reid
Cardinal
Cardinal
Asheville
Asheville
Cape Fear
Cape Fear
Boiler
Number
5
8
9
10
1
2
3
1
2
1
2
3
2
1
2
1
2
3
33
88
81,82
91,92
1
2
3
4
5: •.;
1
2
3
1
1
2
1
2
9
10
Average Heat Average
Content of Sulfur
Coal, Btu/lb Content, %
11,995
11,591
11,591
11,591
11,905
11,905
11,757
12,100
12,100
12,24.6
12,246
12,246
11,238
11,327
11,327
12,007
12,007
12,007
12,700
13,266
13,007
13,007
12,012
12,012
12,012
8,924
-' 8,924
10,890
10,890
10,890
10,344
11,338
11,338
11,936
11,936
12,340
12,340
2.34
1.22
1.22
1.22
1.99
1.99
2.09
2.41
2.41
4.05
4.05
4.05
3.82
2.67
2.67
2.46
2.46
2.46
2.17
1,56
1.20
1.20
0.86
0.86
0.86
0.63
0.63
3.76
3,76
3.76
3,72
2.97
2,97
1.38
. 1.38
1.25
1.25
Average
Ash
Content, %
11.67
14.53
14.53
14.53
13.14
13.14
15.84
13.30
13.30
15.31
15.31
15.31
17.36
17.49
17.49
15.39
15.39
15.39
9.85
7.08
8.69
8.69
15.13
15.13
15.13
21.76
21.76
12.54
12.54
12.54
15.40
16.01
16.01
11.03
11.03
11.80
11.80
*The numbers in the first column correspond to the same plant names in Tables 45 and-46 as they do in Table 44,
-------
TABLE 44. (Continued)
Company Maine*
38 Carolina Power & Light
39 Carolina Power & Light
40 Carolina Power & Light
41 Carolina Power & Light
42 Carolina Power & Light
43 Carolina Power & Light
44 Carolina Power & Light
45 Carolina Power & Light
46 Carolina Power & Light
47 Carolina Power & Light
48 Carolina Power & Light
49 Carolina Power & Light
50 Carolina Power & Light
51 Cedar Falls Utilities
52 Central Illinois Light
53 Central Illinois Light
54 Central Illinois Light
55 Central Illinois Light
56 Central Illinois Light
57 Central Illinois Light
58 Central Illinois Light
59 Central Illinois Pub. Service
60 Central Illinois Pub. Service
61 Central Illinois Pub. Service
62 Central Illinois Pub. Service
63 Central Illinois Pub. Service
64 Central Illinois Pub-. Service
65 Central Illinois Pub. Service
66 Central Illinois Pub. Service
67 Central Illinois Pub. Service
68 Central Illinois Pub. Service
69 Central Operating
70 Charleston Bottoms REC
71 Cincinnati Gas & Electric
72 Cincinnati Gas & Electric
73 Cincinnati Gas & Electric
74 Cincinnati Gas & 'Electric
75 Cincinnati Gas & Electric
76 Cincinnati Gas & Electric
77 Cincinnati Gas & Electric
78 City of Colorado Springs DPU
79 City of Colorado Springs DPU
80 City of Colorado Springs DPU
81 City of Peru
Plant Name
H. B. Robinson
H. P. Lee
H. F. Lee
Louis Button
Louis Sutton
Louis Sutton
Roxboro
Roxboro
Roxboro
Roxboro
W. H. Weatherspoon
W. H. Weatherspoon
W. H. Weatherspoon
Streeter
E. D. Edwards
E. D. Edwards
E. D. Edwards
R. S. Wallace
R. S. Wallace
R. S. Wallace
R. S. Wallace
Coffeen
Coffeen
Grand Tower
Grand Tower
Grand Tower
Meredosia
Meredosia
Meredosia
Meredosia
Meredosia
Philip Sporn
H. L. Spurlock
Miami Fort
W. C. Beckjord
W. C. Beckjord
W. C. Beckjord
W. C. Beckjord
W. C. Bf:<-kjord
W. C. Beckjord
Martin Drake
Martin Drake
Martin Drake
Peru
Boiler
Number
1
1
2
1
2
3
1
2
3A
3B
1
2
3
7
1
2
3
7
8
9
10
1
2
7
8
9
1
2
3
4
5
5
1
6-1
1
2
3
4
5
6
5
6
7
2
Average Heat
Content of
Coal, Btu/lb
12,170
12,702
12,702
11,832
11,832
11,832
12,488
12,488
12,488
12,488
12,668
12,668
12,668
12,085
10,376
10,376
10,376
10,338
10,338
10,338
10,338
9,367
9,367
11,252
11,252
11,252
]0,826
10,826
10,826
10,826
10,826
11,453
10,918
10,561
10,561
10,561
10,561
10,561
10,561
11,501
Average
Sulfur
Content, %
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
05
10
10
26
26
26
10
10
10
10
1.13
1.13
1.13
2.73
2.83
2.83
2.83
2.59
2.59
2.59
2.59
4.43
4.43
3.33
3.33
3.33
50
50
50
50
50
Average
Ash
Content, %
10.98
1.26
3.21
2.63
2.63
2.63
2.63
2.63
2.63
2.87
9.90
9.90
14.63
14.63
14.63
9.90
9.90
9.90
9.90
9.15
9.15
9.15
6.49
10.30
10.30
10.30
9.17
9.17
9.17
9.17
20.33
20.33
11.88
11.88
11.88
9.34
9.34
9.34
9.34
9.34
15.10
14.54
18.37
18.37
18.37
18.37
18.37
18.37
9.96
-------
TABLE 44. (Continued)
en
N>
oo
Company Name*
82 City of Springfield Lt. & Pr.
83 City of Springfield Lt. & Pr.
84 City of Springfield Lt. & Pr.
85 City of Springfield Lt. & Pr.
86 City of Springfield Lt. & Pr.
87 City of Springfield Lt. & Pr.
88 City Util. of Springfield, Mo.
89 Cleveland Electric Illumtg.
90 Cleveland Electric Illumtg.
91 Cleveland Electric Illumtg.
92 Cleveland Electric Illumtg.
93 Cleveland Electric Illumtg.
94 Cleveland Electric Illumtg.
95 Cleveland Electric Illumtg.
96 Cleveland Electric Illumtg.
97 Cleveland Electric Illumtg.
98 Cleveland Electric Illumtg.
99 Cleveland Electric Illumtg.
100 Cleveland Electric Illumtg.
101 Cleveland Electric Illumtg.
102 Cleveland Electric Illumtg.
103 Cleveland Electric Illumtg.
104 Columbus & Southern Ohio Elec.
105 Commonwealth Edison
106 Commonwealth Edison
107 Commonwealth Edison
108 Commonwealth Edison
109 Commonwealth Edison
110 Commonwealth Edison
111 Commonwealth Edison
112 Commonwealth Edison
113 Commonwealth Edison
114 Commonwealth Edison
115 Commonwealth Edison
"116 Commonwealth Edison
117 Commonwealth Edison
118 Commonwealth Edison
119 Commonwealth Edison
120 Commonwealth Edison
121 Commonwealth Edison
122 Commonwealth Edison
123 Commonwealth Edison
124 Commonwealth Edison
125 Commonwealth Edison
Plant Name
Lakeside
Lakeside
Lakeside
Lakeside
V. Y. Dallman
V. Y. Dallman
James River
Ashtabula
Ashtabula
Ashtabula
Ashtabula
Ashtabula
Avon Lake
Avon Lake
Avon Lake
Avon Lake
East Lake
Lake Shore
Lake Shore
Lake Shore
Lake Shore
Lake Shore
Conesville
Crawford
Crawford
Dixon
Dixon
Fisk
Fisk
Fisk
Joliet
Joliet
Joliet
Joliet
Joliet
Joliet
Joliet
Kihcaid
Kincaid
Powerton .-
Powerton
Sabrooke
Waukegan
Waukegan
Boiler
Number
5
6
7
8
31
32
5
7
8
9
10
11
9
10
11
12
5
91
92
93
94
18
4
7
8
4 ..
5
18-1
18-2
19
3
4
5
71
72
81
82
1
2
51
52
4
14
15
Average Heat
Content of
Coal, Btu/lb
10,578 .
10,578
10,578.
10,578
10,791
10,791
11,688
11,589
11,589
11,589
11,589
11,589
11,684
11,684,
11,684
11,684
11,845:
12,059
12,059
12,059
12,059
12,059
10,455
9,239
9,239
10,539
10,539
9,261
9,261
9,261
10,033
10,033
10,033
10,033
10,033
10,033
10,033
9,718
9,718
10,699
10,699
10,722
10,045
10,045
Average
Sulfur
Content, %
3.91
3.91
3.91
3.91
3.83
3.83
3.74
3.20
3.20
3.20
3.20
3.20
2.96
2.96
2.96
2.96
3.50
3.32
3.32
3,32
3.32
3.32
4.91
0.42
0.42
2.89
2.89
0.40
0.40
0.40
2.89
2.89
2.89
2.89
2.89
2.89
2.89
3.99
3.99
3.63
3.63
0.92
1.21 ,v
1.21
Average
Ash
Content, %
12.39
12.39
12.39
12.39
11.59
11.59
17.97
14.31
14,31
14.31
14.31
14.31
12.02
12.02
12*02
12.02
11.20
11.82
11,82
ll^R'2
11.82
11.82
18.35
4.98
4.98
10.94
10.94
4: 61
4.61
4.61
13.39
13.39
13.39
13.39
13.39
13.39
13.39
15.16
15.16
8.44
8.44
15.90
9.40 -
9.40
-------
TABLE 44. (Continued)
en
N)
Company Name*
126 Commonwealth Edison
127 Commonwealth Edison
128 Commonwealth Edison
129 Commonwealth Edison
130 Commonwealth Edison
131 Commonwealth Edison
132 Commonwealth Edison
133 Commonwealth Edison
134 Commonwealth Edison/Indiana
135 Commonwealth Edison/Indiana
136 Commonwealth Edison/Indiana
137 Commonwealth Edison/Indiana
138 Commonwealth Edison/Indiana
139 Commonwealth Edison/Indiana
140 Commonwealth Edison/Indiana
141 Commonwealth Edison/Indiana
142 Commonwealth Edison/Indiana
143 Commonwealth Edison/Indiana
144 Commonwealth Edison/Indiana
145 Consolidated Edison/New York
146 Consolidated Edison/New York
147 Consolidated Edison/New York
148 Consolidated Edison/New York
149 Consolidated Edison/New York
150 Consolidated Edison/New York
151 Consumers Power
152 Consumers Power
153 Consumers Power
154 Consumers Power
155 Consumers Power
156 Consumers Power
157 Consumers Power
158 Consumers Power
159 Consumers Power
160 Consumers Power
161 Consumers Power
162 Dairyland Power Cooperative
163 Dairyland Power Cooperative
164 Dairyland Power Cooperative
165 Dairyland Power Cooperative
166 Dairyland Power Cooperative
167 Dairyland Power Cooperative
168 Dairyland Power Cooperative
169 Dairyland Power Cooperative
Plant Name
Waukegan
Waukegan
Waukegan
Waukegan
Will County
Will County
Will County
Will Coqnty
State Line
State Line
State Line
State Line
State Line
State Line
State Line
State Line
State Line
State Line
State Line
Astoria
Astoria
Astoria
Astoria
Astoria
Ravenswood
B. C. Cobb
B. C- Cobb
B. C. Cobb
B. C. Cobb
B. C. Gobi-
D. E. Karn
D. E. Karn
J. C. Weadock
J. C. Weadock
J. H. Campbell
J. H. Campbell
Alma
Alma
Alma
Alma
Alma
Genoa #3
Stoneman
Stoneman
Boiler
Number
16
17
7
8
1
2
3
4
1-1
2-1
3-1
4-1
5-1
6-1
1-2
2-2
3-2
1-3
1-4
10
20
30
40
50
30
1
2
3
4
5
1
2
7
8
1
2
1
2
3
4
5
1
1
2
Average Heat
Content of
Coal, Btu/lb
10,045
10,045
10,045
10,045
9,377
9,377
9,377
9,377
9,730
9,730
9,730
9,730
9,730
9,730
9,730
9,730
9,730
9,730
9,730
11,462
11,462
11,462
11,462
11,462
11,138
11,138
11,240
11,240
11,187
11,187
1],666
11.666
11,666
11,666
11,666
10,600
11.658
11,658
Average
Sulfur
Content, %
1.21
1.21
1.21
1.21
1.58
1.58
1.58
1.58
1.53
1.53
1.53
1.53
1.53
1.53
1.53
1.53
1.53
1.53
1.53
Average
Ash
Content, %
9.40
9.40
9.40
9.40
8.35
8.35
8.35
8.35
11.00
11.00
11.00
11.00
11.00
11.00
11.00
11.00
11.00
11.00
11 .00
3.27
3.27
3.27
3.27
3.27
3.21
3.21
2.73
2.73
3.61
3.61
2.97
2.97
2.97
2.97
2.97
4.10
3.60
3.60
11.34
11.34
11.34
11.34
11.34
14.55
14.55
13.27
13.27
16.12
16.12
17.89
17.89
17.89
17.89
17.89
24.59
18.79
18.79
-------
TABLE 44. (Continued)
Company Name*
170 Dallas Power & Light
171 Dallas Power & Light
172 Dallas Power & Light
173 Dayton Power & Light
174 Dayton Power & Light
175 Dayton Power 6 Light
176 Dayton Power & Light
177 Dayton Power & Light
178 Dayton Power & Light
179 Dayton Power & Light
180 Dayton Power & Light
181 Dayton Power & Light
182 Dayton Power & Light
183 Dayton Power & Light
184 Dayton Power & Light
185 Dayton Power & Light
186 Dayton Power & Light
187 Dayton Power & Light
188 Dayton Power & Light
189 Delmarva Power 6 Light
190 Delmarva Power & Light
191 Delmarva Power & Light
192 Delmarva Power & Light
193 Detroit Edison
194 Detroit Edison
195 Detroit Edison
196 Detroit Edison
197 Detroit Edison
198 Detroit Edison
199 Detroit Edison
200 Detroit Edison
201 Detroit Edison
202 Detroit Edison
203 Detroit Edison
204 Detroit Edison
205 Detroit Edison
206 Detroit Edison
207 Detroit Edison
208 Detroit Edison
209 Detroit Edison
210 Detroit Edison
211 Detroit Edison
212 Detroit Edison
213 Detroit Edison
Plant Name
Big Brown
Big Brown
Monticello
Frank M. Tait
Frank H. Tait
Frank M. Tait
Frank M. Tait
Frank M. Tait
Frank M. Tait
J. M. Stuart
J. M. Stuart
J. M. Stuart
J. M. Stuart
O. M. Hutchings
O. M. Hutchings
O. M. Hutchings
O. M. Hutchings
O. H. Hutehings
O. M. Hutchings
Delaware Gity
Indian River
Indian River
Indian River
Conners Creek
Conners Creek
Conners Creek
Conners Creek
Harbor Beach
Marysvillp
Marysville
Marysville
Marysville
Monroe
Monroe
Monroe
Monroe
Pennsalt
Pennsalt
River Pfuge
St. Clair
St. Clair
St. Clair
St. Clair
St. Clair
Boiler
Number
1
2
1
4
5
7-1
7-2
8-1
8-2
1
2
3
4
1
2
3
4
5
6
4
1
2
3
15
16
17
18
1
9
10
11
12
1
2
3
4
23
24
2
1
2
3
4
6
Average Heat
Content of
Coal, Btu/lb
7,000
7,000
11,465
11,465
11,465
11,465
11,465
11,465
11,053
11,053
11,053
11,053
12,186
12,186
12,186
12,186
12,186
32,186
14,170
12,130
12,130
12,130
11,645
11,645
11,645
11,645
11,500
11,698
li,698
11,698
11,698
12,475
12,475
12,475
12,475
11,635
11,635
11,999
11,790
11,790
J 1,790
11,790
11,790
Average
Sulfur
Content, %
,0.60
0.60
—
0.97
0.97
0.97
0.97
0.97
0.97
.1.68
1.68
1.68
1.68
0.86
0.86
0.86
0.86
0.86
0.86
G.70
1.63
1.63
1.63
1.81
1,81
1.81
1.81
3.03
2.87
2.87
2.87
2.87
2,77
2.77
2.77
2.77
1.44
1.44
3.37
3.01
3.01
3.01
3.01
3.01
Average
Ash
Content, %
10.40
10.40
13.67
13.67
13.67
13.67
13.67
13.67
15.88
15.88
15,88
15.88
10.71
10.71
I0i71
10.71
10.71
10.71
0.30
11,76
11.76
11.76
13.75
13.75
13.75
33.75
13.38
13.46
13.46
13.46
13.46
12.10
12,10
12,10
12,10
13.38
: 13.38
':-. 11.-75
13,48
13.48
13.48
13.48
13.48
-------
TABLE 44. (Continued)
Company Name*
214 Detroit Edison
215 Detroit Edison
216 Detroit Edison
217 Detroit Edison
218 Detroit Edison
219 Duke Power
220 Duke Power
221 Duke Power
222 Duke Power
223 Duke Power
224 Duke Power
225 Duke Power
226 Duke Power
227 Duke Power
228 Duke Power
229 Duke Power
230 Duke Power
231 Duke Power
232 Duke Power
233 Duke Power
234 Duke Power
235 Duke Power
236 Duke Power
237 Duke Power
238 Duke Power
239 Duke Power
240 Duke Power
241 Duke Power
242 Duke Power
243 Duke Power
244 Duke Power
245 Duke Power
246 Duke Power
247 Duke Power
248 Duquesne Light Co.
249 Duquesne Light Co.
250 Duquesne Light Co.
251 Duquesne Light Co.
252 Duquesne Light Co.
253 Duquesne Light Co.
254 Duquesne Light Co.
255 Duquesne Light Co.
256 Duquesne Light Co.
257 Duquesne Light Co.
Plant Name
St. Clair
Wyandotte
Wyandotte
Wyandotte
Wyandotte
Allen
Allen
Allen
Allen
Allen
Belews Creek
Buck
Buck
Buck
Buck
Buck
Cliffside
Cliffside
Cliffside
Cliffside
Dan River
Dan River
Dan River
Lee
:Lee
Lee
Marshall
Marshal 1
Marshall
Marshall
Riverbend
Riverbend
Riverbend
Riverbend
Cheswick
Elrama
Elrama
Elrama
Elrama
Phillips
Phillips
Phillips
Phillips
Phillips
Boiler
Number
7
9
10
11
12
1
2
3
4
5
1
5
6
7
8
9
1
2
3
4
1
2
3
1
2
3
1
2
3
4
7
8
9
10
1
1
2
3
4
1
2
3
4
5
Average Heat
Content of
Coal, Btu/lb
11,790
11,777
11,777
11,777
11 ,777
11,965
11,965
11,965
11,965
11,965
12,125
12,125
12,125
12,125
12,125
12,368
12,368
12,368
12,368
11,963
11,963
11,963
11,545
11,545
11,545
11,737
11,737
11 ,737
11,737
11,834
11 ,834
11,834
11,834
11,038
10,996
10.996
10,996
10,996
11,342
11,342
11.342
11,342
11,342
Average
Sulfur
Content, %
3.01
1.13
1.13
1.13
1.13
0.89
0.89
0.89
0.89
0.89
—
0.88
0.88
0.88
0.88
0.88
1.30
1.30
1.30
1.30
0.92
0.92
0.92
1.17
1.17
1.17
0.96
0.96
0.96
0.96
0.89
0.89
0.89
0.89
2.16
2.13
2.13
2.13
2.13
1.89
1.89
1.89
1.89
1.89
Average
Ash
Content, %
13.48
12.34
12.34
12.34
12.34
12.53
12.53
12.53
12.53
12.53
11.54
11.54
11.54
11.54
11.54
13.57
13.57
13.57
13.57
12.69
12.69
12.69
14.21
14.21
14.21
13.55
13.55
13.55
13.55
13.64
13.64
13.64
13.64
20.33
20.07
20.07
20.07
20.07
16.74
16.74
16.74
16.74
16.74
-------
TABLE 44. (Continued)
U)
K)
Company Name*
258 Duquesne Light Co.
259 East Kentucky Power Coop.
260 East Kentucky Power Coop.
261 East Kentucky Power Coop,
262 East Kentucky Power Coop.
263 Electric Energy, Inc.
264 Electric Energy, Inc.
265 Electric Energy, Inc.
266 Empire District Electric
267 Georgia Power
268 Georgia Power
269 Georgia Power
270 Georgia Power
271 Georgia Power
272 Georgia Power
273 Georgia Power
274 Georgia Power
275 Georgia Power
276 Georgia Power
277 Georgia Power
278 Georgia Power
279 Georgia Power
280 Georgia Power
281 Georgia Power
282 Georgia Power
283 Georgia Power
284 Georgia Power
285 Georgia Power
286 Georgia Power
287 Georgia Power
288 Georgia Power
289 Georgia Power
290 Georgia Power
291 Georgia Power
292 Georgia Power
293 Georgia Power
294 Gulf Power
295 Gulf Power
296 Gulf Power
297 Gulf Power
298 Gulf Power
299 Gulf Power
300 Gulf Power
301 Gulf Power
Plant Name
Phillips
John S. Cooper
John S. Cooper
William Dale
William Dale
Joppa
Joppa
Joppa
Asbury
Arkwright
Arkwright
Arkwright
Arkwright
Hammond
Hammond
Hammond
Hammond
H. L. Bowen
H. L. Bowen
H. L. Bowen
Jack McDonough
Jack McDonough
Plant Harllee
Plant Harllee
Plant Harllee
Plant Harllee
Mitchell
Mitchell
Mitchell
Yates
Yates
Yates
Yates
Yates
Yates
Yates
Lansing Smith
Lansing Smith
Crist
Crist
Crist
Crist
Soholz
Scholz
Boiler
Number
6
1
2
3
4
1-2
3-4
5-6
1
1
2
3
4
1
2
3
4
1
2
3
VI
2
1
2
3
4
1
2
3
1
2
3
4
5
6
7
1
2
4
5
6
7
1
2
Average Heat
Content of
Coal, Btu/lb
11,342
11,435
11,435
11,380
11,380
11,439
11,439
11,439
10,238
11,904
11,904
11,904
11,904
11,329
11,329
11,329
11,329
11,444
11,444
11,444
]'] ,887
11,887
12,156
12,156
12,156
12,156
11,519
11,519
11,519
12,284
12,284
12,284
12,284
12,284
12,284
12,284
11,510
11,510
11,883
11,883
11,883
11,883
T2.455
12,455
Average
Sulfur
Content, %
1.89
2.35
2.35
1.62
1.62
2.38
2.38
2.38
4.43
2.00
2.00
2 1 '.00
2.00
3,25
3,25
3.25
3.25
3,13
3,13
3.13
1.05
1.05
0.94
0.94
0.94
0.94
1.42
1.42
1.42
2.22
2 . 22
2.22
2.22
2.22
2.22
2.22
2.84
2.84
3.11
3.11
3.11
3.11
1.41
1.41
Average
Ash
Content, %
16.74
15.32
15.32
14.00
14.00
10.21
10.21
10.21
24.13
12.77
12.77
12.77
12.77
9.49
9.49
9.49
9.49
10.73
10.73
10.73
12.99
12.99
10.53
10.53
10.53
10.53
15.01
15.01
15.01
9.25
9.25
9.25
9.25
9.25
9.25
9.25
11.18
11.18
10.92
10.92
10.92
10.92
12.55
12.55
-------
TABLE 44. (Continued)
Company Name*
302 Hartford Electric
303 Hartford Electric
304 Henderson Municipal
305 Henderson Municipal
306 Holland Board of Public Works
307 Illinois Power Company
308 Illinois Power Company
309 Illinois Power Company
310 Illinois Power Company
311 Illinois Power Company
312 Illinois Power Company
313 Illinois Power Company
314 Illinois Power Company
315 Indiana-Kentucky Elec. Corp.
316 Indiana-Kentucky Elec. Corp.
317 Indiana-Kentucky Elec. Corp.
318 Indiana-Kentucky Elec. Corp.
319 Indiana-Kentucky Elec. Corp.
320 Indiana-Kentucky Elec. Corp.
321 Indiana & Michigan Elec. Co.
322 Indianapolis Power & Light Co,
323 Indianapolis Power & Light Co.
324 Indianapolis Power & Light Co,
325 Indianapolis Power & Light Co,
326 Indianapolis Power & Light Co.
327 Indianapolis Power & Light Co.
328 Indianapolis Power & Light Co.
329 Indianapolis Power & Light Co.
330 Indianapolis Power & Light Co.
331 Indianapolis Power & Light Co.
332 Indianapolis Power & Light Co.
333 Indianapolis Power & Light Co.
334 Indianapolis Power & Light Co.
335 Indianapolis Power & Light Co.
336 Interstate Power Company
337 Interstate Power Company
338 Iowa Electric Light & Power
339 Iowa Electric Light & Power
340 Iowa Electric Light & Power
341 Iowa Electric Light & Power
342 Iowa Electric Light & Power
343 Iowa-Illinois Gas & Electric
344 Iowa-Illinois Gas & Electric
345 Iowa-Illinois Gas & Electric
Plant Name
Middletown
Middletown
Station 2
Station 2
James Do Young
Baldwin
Baldwin
llertnepin
Ilennepin
Vermilion
Vermi1 ion
Wood River
Wood River
Clifty Creek
Clifty Creek
Clifty Creek
Clifty Creek
Clifty Creek
Clifty Creek
Tanners Creek
C. C. Perry K
C. C. Perry K
C. C. Perry K
C. C. Perry K
C. C. Perry K
C. C. Perry K
E. W, Stout
E. W. Stout
H. T. Prifchard
H. T. Pril.-hard
H. T. Prituhard
II. T. Pritchard
Petersburg
Petersburg
Dubuque
M. I, i. Kapp
Prairie Creek Station 1-2-3
Sixth Creek Station
Sixth Creek Station
Sixth Creek Station
Sixth Creek Station
Riverside
Riverside
Riverside
Boiler
Number
1
2
1
2
5
1
2
1
2
1
2
4
5
1
2
3
4
5
6
4
11
12
13
14
15
16
50
60
3
4
5
6
1
2
1
2
3
3-4
5-6
7-8
9-10
5
6
7
Average Heat
Content of
Coal, Btu/lb
11.746
11,746
10,347
10,347
12,404
10,285
10,285
10,890
10,890
10,858
10,858
10,991
10,991
10,852
10,852
10,852
10,852
10,852
10,852
10,995
11,299
11,299
11,299
11,299
11,299
11,299
11,076
11,076
11,112
11,112
11,112
11,112
10,954
10,954
11,169
11,211
10,941
10,285
10,285
10,285
10,285
10,805
10,805
10,805
Average
Sulfur
Content, %
2.25
2.25
3.80
3.80
3.22
3.27
3.27
3.00
3.00
2.90
2.90
2.97
2.97
3.64
3.64
.64
.64
.64
.64
3.43
2.29
2.29
2.29
2.29
.29
.29
.64
,64
,39
2.39
2.39
2.39
2.98
2.98
2.86
2.92
2.48
2.34
2.34
2.34
2.34
2.48
2.48
2.48
Average
Ash
Content, %
15.00
15.00
15.48
15.48
7.97
12.79
12.79
10.00
10.00
11.33
11.33
10.30
10.30
11.69
11.69
11.69
11.69
11.69
11.69
13.03
9.35
9.35
9.35
9.35
9.35
9.35
9.30
9.30
9.70
9.70
9.70
9.70
9.77
9.77
13.19
10.85
9.10
8.04
8.04
8.04
8.04
8.68
8.68
8.68
-------
TABLE 44. (Continued)
Company Name*
Plant Name
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
£ 364
*•" 365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
3B8
389
Iowa-Illinois Gas & Electric
Iowa-Illinois Gas & Electric
Iowa Power & Light Company
Iowa Power & Light Company
Iowa Power & Light Company
Iowa Power & Light Company
Iowa Public Service Company
Iowa Public Service Company
Iowa Public Service Company
Iowa Southern Utilities
Kansas City Bd. of Pub. Util.
Kansas City Bd. of Pub. Util.
Kansas City Bd. of Pub. Util.
Kansas City Power S Light
Kansas City Power & Light
Kansas City Power & Light
Kansas City Power & Light
Kansas City Power & Light
Kentucky Power Company
Kentucky Power Company
Kentucky Utilities Company
Kentucky Utilities Company
Kentucky Utilities Company
Kentucky Utilities Company
Kentucky Utilities Company
Lansing Bd. of Water & Light
Lansing Bd. of Water & Light
Lansing Bd. of Water & Light
Lansing Bd. of Water 6 Light
Lansing Bd. of Water & Light
Lansing Bd . of Water S Light
Lansing Bd. of Water & Light
Lansing Bd. of Water & Light
Lansing Bd. of Water & Light
Lansing Bd. of Water & Light
Lansing Bd. of Water & Light
Lansing Bd. of Water & Light
Louisville Gas & Elec. Co.
Louisville Gas & Elec. Co.
Louisville Gas 6 Elec. Co.
Louisville Gas 6 Elec. Co.
Louisville Gas & Elec. Co.
Louisville Gas 6 Elec. Co.
Louisville Gas & Elec. Co.
Riverside
Riverside
Council Bluffs
Council Bluffs
Des Moines
Des Moines
Maynard
Neal
Neal
Burlington
Raw
Qaindaro No. 3
Quindaro No. 3
Grand Avenue
Hawthorn
Montrose
Montrose
Montrose
Big Sandy
Big Sandy
E. W. Brown
E . W . Brown
Ghent
Green River
Tyrone
Eckert
Eckert
Eckert
Eckert
Eckert
Eckert
Erickson
Ottawa
Ottawa
Ottawa
Ottawa
Ottawa
Cane Run
Cane Hun
Cane Kun
Cane Run
Cane Run
•Cane Run
Mill Creek
Boiler
Number
8
9
1
2
10
11
14
I
2
1
3
1
2
7
5
1
2
3
1
• 2
- 1
3
1
4
5
1
2
3
4
5
-6
1
1
2
3
.4
"5
1
2
3
4
5
6
1
Average Heat
Content of
Coal, Btu/lb
'10,805
10,805
10,143
10,143
9,549
9,549
10,960
9,981
: 9,981
10,183
11,784
11,492
11,492
12,336
10.566
9,413
9,413
9,413
11,835
11,835
11,804
11,804
10,917
1],364
11,570
12,319
12,319
12,319
12,319
12,319
12,319
12,270
12,437
12,437
12,437
12,437
12,437
11,075
11,075
11,075
11,075
11,075
11,075
11,152
Average
Sulfur
Content, %
2.48
2 . 48
1.09
1.09
2.94
2.94
2.86
0.60
0.60
. 2.58
3.90
1.61
1.61
3.71
1.40
5; 51
5.51
5.51
0.97
0.97
1.72
1.72
2.76
2,58
0.90
2.98
2.98
2.98
2.98
2.98
2.98
2.92
2.74
2.74
2.74
2.74
2.74
3.76
3.76
3.76
3.76
3. -76
V 3.76
3.80,
Average
Ash
Content, %
8.68
8.68
8.96
8.96
13.65
13.65
10.21
11.22
11.22
13.70
13.75
11.14
11.14
11.08
9.53
23.19
23.19
23.19
12.49
12.49
13.25
13.25
10.19
10.15
12.39
10.74
10.74
10.74
10.74
10.74
10.74
11.61
7.96
7.96
7.96
7.96
7.96
14.02
14.02
14.02
14.02
14.02
14.02
13.76
-------
TABLE 44. (Continued)
Company Name*
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
Louisville Gas & Elec.
Louisville Gas & Elec.
Co.
Co.
Co.
Co.
Co.
Co.
Co.
Louisville Gas & Elec
Louisville Gas & Elec
Louisville Gas & Elec
Louisville Gas & Elec
Louisville Gas & Elec
Madison Gas & Elec. Co.
Metropolitan Edison Co.
Metropolitan Edison Co.
Metropolitan Edison Co.
Metropolitan Edison Co.
Metropolitan Edison Co.
Metropolitan Edison Co.
Metropolitan Edison Co.
Michigan State University
Michigan State University
Michigan State University
Mississippi Power Company
Mississippi Power Company
Montana Power Company
Municipal Power & Light
Muscatine Power & Light
N. Y. State Elec. & Gas
N. Y. State Elec. & Gas
N. Y. State Else. & Gas
N. Y. State Elec. & Gas
N. Y. State Elec. & Gas
N. Y. State Elec. & Gas
N. Y. State Elec. & Gas
N. Y. State Elec. & Gas
N. Y. State Elec. & Gas
N. Y. State Elec. & Gas
N. Y. State Elec. & Gas
N. Y. State Elec. & Gas
No. Indiana Pub. Service Co.
No. Indiana Pub. Service Co.
No. Indiana Pub. Service Co.
No. Indiana Pub. Service Co.
No. Indiana Pub. Service Co.
No. Indiana Pub. Service Co.
No. Indiana Pub. Service Co.
No. Indiana Pub. Service Co.
No. Indiana Pub. Service Co.
Plant Name
Mill Creek
Paddy's Run
Paddy's Run
Paddy's Run
Paddy's Run
Paddy's Run
Paddy's Run
Dlount3 Street
Crawford
Crawford
Portland
Portland
Titus
Titus
Titus
Power Plant '65
Power Plant '65
Power Plant '65
Jack Watson
Jack Watson
J. E. Corette
Station One
Muscatine Municipal
Goudey
Goudey
Goudey
Greenidge
Greenidge
Greenidge
Hickling
Hickling
Hickling
Hickling
Mil liken
Milliken
Uailly
Bailly
Dean II. Mitchell
Dean II. Mitchell
Dean H. Mitchell
Dean H. Mitchell
Michigan City
Michigan City
Michigan City
Boiler
Number
2
1
2
3
4
5
6
9
7
8
1
2
1
2
3
1
2
3
4
5
1
6
8
11
12
13
4
5
6
1
2
3
4
1
2
7
8
4
5
6
11
4
5
6
Average Heat
Content of
Coal, Btu/lb
11 ,152
11 ,368
11,368
11,368
11,368
11,368
11,368
11,535
12,660
12,660
12,473
12,473
12,224
12,224
12,224
12,639
12,639
12,639
11,885
11,885
8,582
10,712
11,341
11,341
11,341
11,638
11,638
11,638
10,917
10,917
10,917
10,917
11,317
11,317
11,109
11,109
11,146
11,146
11,146
11,146
10,558
10.558
10,558
Average
Sulfur
Content, %
3.80
3.42
3.42
3.42
3.42
.42
3.
3.42
3.
1.
1.
1.
.06
,21
.21
.53
1.53
0.96
0.96
0.96
0.98
0.98
0.98
2.70
2.70
0.67
3.09
2.20
2.20
2.20
1.98
.98
.98
.98
.98
.98
.98
.08
.08
.62
.62
,18
.18
3.18
3.18
36
.36
3.
3.
3.36
Average
Ash
Content, %
13.76
12.57
12.57
12.57
12.57
12.57
12.57
8.79
10.70
10.70
11.35
11.35
11.97
11.97
11.97
9.70
9.70
9.70
10.88
10.88
8.22
10.22
18.45
18.45
18.45
15.20
15.20
15.20
15.20
15.20
15.20
15.20
16.37
16.37
10.00
10.00
9.32
9.32
9.32
9.32
11.14
11.14
11.14
-------
TABLE 44. (Continued)
Company Name*
Plant Name
o>
Ixi
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
45B
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
No. -Indiana Pub. Service Co.
No. Indiana Pub. Service Co.
No. Indiana Pub. Service Co.
No. Indiana Pub. Service Co.
Northern States Power Co.
Northern States Power Co.
Northern States Power Co.
Northern States Power Co.
Northern States Power Co.
Northern States Power Co.
Northern States Power Co.
Northern States Power Co.
Northern States Power Co.
Northern States Power Co.
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Edison Company
Ohio Electric Company
Ohio Power Company
Ohio Power Company
Ohio Power Company
Ohio Power Company
Ohio Power Company
Ohio Power Company
Ohio Power Company
Ohio Valley Elec. Corp.
Michigan City
ADVANCE
ADVANCE
ADVANCE
A. S. King
Black Dog
Black Dog
Black Dog
Black Dog
High Bridge
High Bridge
High Bridge
High Bridge
Minnesota Valley
Edgewater
Edgewater
Edgewater
Gorge
Gorge
Nor walk
R. E. Burger
R. E. Burger
R. E. Burger
R, E. Burger
R. E. Burger
R. E. Burger
R. E. Burger
R. E. BUJ *ier
W. H. Sammis
W. H. Sammis
W. II. Sammis
W. H. Sammis
W. H. Sammis
W. H. Sammis
W. H. Sammis
Gavin
Mitchell
Mitchell
MuskitKium River
Muskinyum River
Muskingum River
Muskingum River
Muskingum River
kyger Creek
Boiler
Number
12
1
2
3
1
1
2
3
4
9
10
11
12
4
11
12
13
25
26
5
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
1
1
2
1
2
3
4
Average Heat
Content of
Coal, Btu/lb
10,558
12,341
'12,341
12,341
10,567
10,108
10,108
10,108
10,108
9,666
9,666
: 9,666
9,666
10,044
12,267
12,267
12,267
10,792
10,792
11,322
:il,457
11,457
11,457
11,457
11,457
11,457
11,457
11,457
11,367
11,367
11,367
11,367
11,367
11,367
11,367
11,601
11,601
10,448
10,448
10,448
10,448
10,448
ll.SBfi
Average
Sulfur
Content, %
3.36
2.38
2.38
2.38
3.32
2.27
2.27
2; 27
2.27
1.82
'• 1.82
1.82
1.82
1.28
2.68
2.68
2.68
3.22
3.22
3.55
3.25
3.25
3.25
3.25
3,25
3,25
3,25
3.25
2.99
2.99
2.99
2,99
2.99
2.99
2.99
3,35
3.35
4.64
4J64
4.64
4.64
4.64
3.89
Average
Ash
Content, %
11.14
8.95
8.95
8.95
15.17
11.73
11.73
11.73
11.73
9.71
9.71
9.71
9.71
.9.20
10.13
10.13
10.13
15.25
15.25
13.10
13.93
13.93
13.93
13.93
13.93
13.93
13.93
13.93
15.79
15.79
15.79
15.79
15.79
15.79
15.79
15.20
15.20
19.35
19.35
19.35
19. 35
19.35
14.52
-------
TABLE 44. (Continued)
en
U)
Company Name*
478 Ohio.Valley Elec. Corp.
479 Ohio Valley Elec. Corp.
480 Ohio Valley Elec. Corp.
481 Ohio Valley Elec. Corp.
482 Omaha Public Power Dist.
483 Omaha Public Power Dist.
484 Omaha Public Power Dist.
485 Omaha Public Power Dist.
486 Omaha Public Power Dist.
487 Otter Tail Power Company
488 Otter Tail Power Company
489 Owensboro Munic. Utilities
490 Owensboro Munic. Utilities
491 Owensboro Munic. Utilities
492 Owensboro Munic. Utilities
493 Owensboro Munic. Utilities
494 Owensboro Munic. Utilities
495 Pacific Power & Light Co.
496 Pacific Power & Light Co.
497 Pacific Power & Light Co.
498 Pella Munic. Power & Light
499 Pella Munic. Power & Light
500 Pennsylvania Electric Co.
501 Pennsylvania Electric Co.
502 Pennsylvania Electric Co.
503 Pennsylvania Electric Co.
504 Pennsylvania Electric Co.
505 Pennsylvania Electric Co.
506 Pennsylvania Electric Co.
507 Pennsylvania Electric Co.
508 Pennsylvania Electric Co.
509 Pennsylvania Electric Co.
510 Pennsylvania Electric Co.
511 Pennsylvania Electric Co.
512 Pennsylvania Electric Co.
513 Pennsylvania Electric Co.
514 Pennsylvania Electric Co.
515 Pennsylvania Electric Co.
516 Pennsylvania Electric Co.
517 Pennsylvania Electric Co.
518 Pennsylvania Electric Co.
519 Pennsylvania Electric Co.
520 Pennsylvania Electric Co.
521 Pennsylvania Power Company
Plant Name
Kyger Creek
Kyger Creek
Kyger Creek
Kyger Creek
North Omaha
North Omaha
North Omaha
North Omaha
North Omaha
Hoot Lake
Hoot Lake
Elmer Smith
Elmer Smith
Owensboro Plant 1
Owensboro Plant 1
Owensboro Plant 1
Owensboro Plant 1
Centralia
Centralia
Jim Bridger
Pella
Pella
Homer City
Homer City
Conemaugh
Conemaugh
Front Street
Front Stroet
Front Street
Front Street
Keystone
Keystone
Seward
Seward
Seward
Shawville
Shawville
Shawville
Shawvi11e
Warren
Warren
Warren
Warren
New Castle
Boiler
Number
2
3
4
5
1
2
3
4
5
2
3
1
2
1
2
3
4
1
2
1
6
7
1
2
1
2
7
8
9
10
1
2
12
14
15
1
2
3
4
1
2
3
4
1
Average Heat
Content of
Coal, Btu/lb
11,586
11,586
11,586
11,586
10,953
10,953
10,953
10,953
10,953
7,093
7,093
10,993
10,993
11,027
11,027
11,027
11,027
7,552
7,552
9,410
9,410
11,766
11,766
11,437
11,437
12.101
12,101
12,101
12,101
11,640
11,640
12,076
12,076
12,076
12,461
12,461
12,461
12.461
12,196
12,196
12,196
12,196
12,462
Average
Sulfur
Content, %
89
89
89
89
48
48
1.48
1.48
1.48
0.72
0.72
3.11
3.11
3.12
3.12
3.12
3.12
0.49
0.49
6.43
6.43
2.40
2.40
2.29
2.29
2.12
2.12
2.12
2.12
2.24
2.24
2.97
2.97
2.97
2.06
2.06
2.06
2.06
2.12
2.12
2.12
2.12
3.24
Average
Ash
Content, %
14.52
14.52
14.52
14.52
9.12
9.12
9.12
9.12
9.12
6.16
6.16
10.48
10.48
10.35
10.35
10.35
10.35
14.88
14.88
17.24
17.24
19.30
19.30
18.68
18.68
13.17
13.17
13.17
13.17
20.36
20.36
18.16
18.16
18.16
12.53
12.53
12.53
12.53
11.92
11.92
11.92
11.92
10.70
-------
TABLE 44. (Continued)
Company Name*
en
w
00
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
Penn.
Penn.
Penn.
Penn.
Penn.
Penn.
Penn.
Penn.
Penn.
Penn.
Penn. Power
Penn.
Penn.
Pennsylvania Power Company
Pennsylvania Power Company
Pennsylvania Power Company
Pennsylvania Power Company
Penn. Power & Light Co.
Power & Light Co.
Power & Light Co.
Power & Light Co.
Power & Light Co.
Power & Light Co.
Power & Light Co.
Power S Light Co.
Power & Light Co.
Power & Light Co.
Power 6 Light Co.
6 Light Co.
Power 6 Light Co.
Power & Light Co.
Philadelphia Electric Co.
Philadelphia Electric Co.
Potomac Electric
Potomac Electric
Potomac Electric
Potomac Electric
Potomac Electric
Potomac Electric
Potomac Electric
Potomac Electric
Potomac Electric
Potomac Electric
Potomac Electric
Potomac Electric
Potomac Electric
Public Serv. Co. of Colorado
Co. of Colorado
Co. of Colorado
Co. of Colorado
Co. of Colorado
Co. of Colorado
Co. of Colorado
Co. of Colorado
Co. of Colorado
Co. of Colorado
Public Serv.
Public Serv.
Public Serv.
Public Serv.
Public Serv.
Public Serv.
Public Serv.
Public Serv.
Public Serv.
Public Serv. Co. Of Colorado
Plant Hame
New Castle
New Castle
New Castle
New Castle
Brunner Island
Brunner Island
Brunner Island
Holtwood
Martins Creek
Martins Creek
Montour
Montour
Sunbury
Sunbury
Sunbury
Sunbury
Sunbury
Sunbury
Eddystone
Eddystone
Benning
Benning
Chalk Point
Chalk Point
Dickerson
Dickerson
Dickerson
Mprgantown
Morgantown
Potomac River
Potomac River
Potomac River
Potomac River
Arapahoe
Arapahoe
Arapahoe
Cameo
Cherokee
Gherqkoe
.Cherokee
Cherokee
Gomariche
Valmont
; Zuni
Boiler
Number
Average Heat
Content of
Coal, Btu/lb
2
3
4
5
1
2
3
17
1
2
1
2
1A
IB
2A
2B
3
4
1
2
25
26
1
2
1
2
3
1
2
1
2
3
4
2
3
4
2
1
2
3
4
1
5
3
12,462
12,462
12,462
12,462
12,460
12,460
12,460
10,205
12,639
12,639
12,565
12,565
11.407
11,407
11,407
11,407
11,407
11,407
13,026
13,026
13,106
13,106
12,341
12,341
12,209
12,209
12,209
12,693
12,693
12,683
12,683
12,683
12,683
10,234
10,234
10,234
11,008
10,768
•10,768
10,768
10,768
8,620
10,400
- — .-
Average
Sulfur
Content, %
3.24
3.24
3.24
3.24
1.99
1.99
1.99
0.70
2.07
2.07
1.79
1.79
1.99
1.99
1.99
1.99
1.99
1.99
2.37
2 . 37
0.90
0.90
1.70.
1.70
1.64
1.64
1.64
1 . 7.8
1 » 78
0.84
0.84
0.84
0.84
0.73
0 . 73
0.73
0.52
0,51
0.51
0.51
6.51
:0.30
0.82
Average
Ash
Content, %
10.70
10.70
10.70
10.70
13.74
13.74
13.74
19.20
11.46
11.46
13.17
13.17
15.52
15.52
15.52
15.52
15.52
15.52
8.62
8.62
9.01
9.01
12.16
12.16
12.86
12.86
12. 86
13.34
13.34
10.69
10.69
10.69
10,69
7.48
7.48
7.48
10.08
8.47
8.47
8.47
8.47
5.10
7.53
-------
TABLE 44. (Continued)
Company Name*
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
Public Serv. Co. of Indiana
Public Serv. Co. of Indiana
Public Serv. Co. of Indiana
Public Serv. Co. of Indiana
Public Serv. Co. of Indiana
Public Serv. Co. of Indiana
Public Serv. Co. of Indiana
Public Serv. Co. of Indiana
Public Serv. Co. of Indiana
Public Serv. Co. of Indiana
Public Serv. Co. of Indiana
Public Serv. Co. of Indiana
Public Serv. Co. of Indiana
Public Serv. Co. of Indiana
Public Serv. Co. of Indiana
Public Serv. Co. of Indiana
Public Serv. Co. of Indiana
Public Serv. Co. of Indiana
Pub. Serv. Co. of N. Hamp.
Pub. Serv. Co. of N. Hamp.
Pub. Serv. Co. of N. Mexico
Richmond Power & Light
Riclunond Power & Light
Rochester Dept. of Pub. Utl
Rochester Gas & Elec. Corp.
Rochester Gas & Elec. Corp.
Rochester Gas & Elec. Corp.
Rochester Gas & Elec. Corp.
Rochester Gas & Elec. Corp.
Salt River Project
Salt River Project
S. Carolina Elec. & Gas
S. Carolina Elec. & Gas
S. Carolina Elec. & Gas
S. Carolina Elec. & Gas
S. Carolina Elec. & Gas
S. Carolina Elec. & Gas
S. Carolina Elec. & Gas
S. Carolina Elec. & Gas
S. Carolina Elec. & Gas
S. Carolina Elec. & Gas
S. Carolina Elec. & Gas
S. Carolina Elec. & Gas
S. Carolina Elec. & Gas
Plant Name
Cayuga
Cayuga
Edwardsport
Edwardsport
Edwardsport
Gallagher
Gallagher
Gallagher
Gallagher
Noblesville
Noblesvj1le
Noblesvilie
Wabash Rj ver
Wabash River
Wabash River
Wabash River
Wabash River
Wabash River
Merrimack
Merrimack
San Juan
Whitewater Valley
Whitewater Valley
Silver Lake
Rochester 3
Rochester 7
Rochester 7
Rochestei 7
Rochestei 7
Navajo
Navajo
Canadys
Canadys
Canadys
McMeekin
McMeekin
Urquhart
Urquhart
Urquh.trt
Waterce
Wateree
Winyah
Grainger
Grainger
Boiler
Number
1
2
7-1
7-2
8-1
1
2
3
4
1
2
3
5
6
1
2
3
4
1
2
2
1
2
4
12
1
2
3
4
1
2
1
2
3
1
2
1
2
3
1
2
1
1
2
Average Heat
Content of
Coal, Btu/lb
10,363
10,363
10,231
10,231
10,231
1] ,149
11,149
11,149
11,149
10,742
10,742
10,742
10,907
10,907
10,907
10,907
10,907
10,907
13,443
13,443
8,838
11,506
11.506
12,400
12,680
12,706
12,706
12,706
12,706
12,407
12,407
12,407
12,304
12,304
12,378
12,378
12,378
12,179
12,179
11,655
11,655
Average
Sulfur
Content, %
2.17
2.17
2.79
2.79
2.79
3.40
3.40
3.40
3.40
2.74
2.74
2.74
2.54
2.54
2.54
2.54
2.54
2.54
2.08
2.08
0.80
3.00
3.00
1.95
1.98
2.06
2.06
2.06
2.06
--
--
1.20
1.20
1.20
1.55
1.55
1.69
1.69
1.69
1.48
1.48
—
1.33
1.33
Average
Ash
Content, %
13.38
13.38
12.56
12.56
12.56
10.73
10.73
10.73
10.73
9.87
9.87
9.87
11.58
11.58
11.58
11.58
11.58
11.58
7.09
7.09
21.20
10.00
10.00
7.20
9.75
9.78
9.78
9.78
9.78
12.68
12.68
12.68
12.44
12.44
12.79
12.79
12.79
12.29
12.29
13.51
13.51
-------
TABLE 44. (Continued)
Company Name*
610 S. Carolina Pub. Serv. Auth.
611 S. Carolina Pub. Serv. Auth.
612 S. Indiana Gas 6 Elec. Co.
613 S. Indiana Gas S Elec. Co.
614 S. Indiana Gas & Elec. Co.
615 Southern California Edison
616 Southern California Edison
617 Southern Elec. Gen. Co.
618 Southern Elec. Gen. Co.
619 Southern Elec. Gen. Co.
620 Southern Elec. Gen. Co.
621 Southern 111. Power Coop.
622 Southern 111. Power Coop.
623 Southern 111. Power Coop.
624 Tampa Electric Company
625 Tampa Electric Company
626 Tampa Electric Company
627 Tampa Electric Company
628 Tampa Electric Company
629 Tampa Electric Company
630 Tampa Electric Company
631 Tampa Electric Company
632 Tennessee Valley Authority
633 Tennessee Valley Authority
634 Tennessee Valley Authority
635 Tennessee Valley Authority
636 Tennessee Valley Authority
637 Tennessee Valley Authority
638 Tennessee Valley Authority
639 Tennessee Valley Authority
640 Tennessee Valley Authority
641 Tennessee Valley Authority
642 Tennessee Valley Authority
643 Tennessee Valley Authority
644 Tennessee Valley Authority
645 Tennessee Valley Authority
646 Tennessee Valley Authority
647 Tennessee Valley Authority
648 Tennessee Valley Authority
649 Tennessee Valley Authority
650 Tennessee Valley Authority
651 Tennessee Valley Authority
652 Tennessee Valley Authority
653 Tennessee Valley Authority
Plant Name
Jefferies
Jefferies
F. B. Cullay
F. B. Culley
F. B. Culley
Mohave
Mohave
Gaston
Gaston
Gaston
Gaston
Marion
Marion
Marion
Big Bend
Big Bend
F. J. Gannon
F. J. Gannon
F. J. Gannon
F. J. Gannon
F. J. Gannon
F. J. Gannon
Allen
Allen
Allen
Bull Run
Colbert A
Colbert A
Colbert A
Colbert A
Colbert B
Cumberland
Cumberland
Gallatin
Gallatin
Gallatin
Gallatin
John Sevier
John Sc'/ier
John Snvier
John Sevier
Johnsonville
Johnsonville
Johnsonville
Boiler
Number
3
4
1
2
3
1
2
1
2
3
4
1
2
3
1
2
1
2
3
4
5
6
1
2
3
1
1
2
3
4
5
1
2
1
2
3
4
1
2
3
4
7
8
9
Average Heat
Content of
Coal, Btu/lb
11,771
11,771
10,756
10,756
10,756
]2,288
12,288
11,744
]1,744
11,744
11,744
10,770
10,770
10,770
11,131
11,131
11.235
11,235
11,235
11,235
11,235
11,235
11.058
11,058
11,058
11,171
11,116
11,116
11,116
11,116
11,254
10,536
10,536
10,749
10.749
10,749
10,749
11,517
11,517
11,517
11,517
10,970
10,970
10,970
Average
Sulfur
Content,
0.96
0.96
3.72
3.72
3.72
0.40
0.40
1.17
1.17
1.17
1.17
4.17
4.17
4.17
3.46
3.46
3.12
3.12
3.12
3.12
3.12
3.12
3.12
3.12
3.12
0.85
3.98
3.98
3.98
3.98
65
65
35
35
3.35
3.35
1,88
• 1.88
. 3 . 63
3.63
3.63
Average
Ash
Content, %
13.39
13.39
11.46
11.46
11.46
9.86
9.86
14.40
14.40
14.40
14.40
14.81
14.81
14.81
11.41
11.41
11.22
11.22
11.22
11.22
11.22
11.22
11.48
11.48
11.48
15.31
15.03
15,03
15.03
15.03
15.02
16.27
16.27
16.25
16.25
]6.25
16.25
15.10
15.10
15.10
15.10
14.28
14.28
14.28
-------
TABLE 44. (Continued)
Company Name*
654 Tennessee Valley Authority
655 Tennessee Valley Authority
656 Tennessee Valley Authority
657 Tennessee Valley Authority
658 Tennessee Valley Authority
659 Tennessee Valley Authority
660 Tennessee Valley Authority
661 Tennessee Valley Authority
662 Tennessee Valley Authority
663 Tennessee Valley Authority
664 Tennessee Valley Authority
665 Tennessee Valley Authority
666 Tennessee Valley Authority
667 Tennessee Valley Authority
668 Tennessee Valley Authority
669 Tennessee Valley Authority
670 Tennessee Valley Authority
671 Tennessee Valley Authority
672 Tennessee Valley Authority
673 Tennessee Valley Authority
674 Tennessee Valley Authority
675 Tennessee Valley Authority
676 Tennessee Valley Authority
677 Tennessee Valley Authority
678 Tennessee Valley Authority
679 .Tennessee Valley Authority
680 /Tennessee Valley Authority
681 -Tennessee Valley Authority
682 Tennessee Valley Authority
683 Toledo Edison
684 Toledo Edison
685 Toledo Edison
686 Toledo Edison
687 Toledo Edison
688 Toledo Edison
689 Toledo Edison
690 Toledo Edison
691 Toledo Edison
692 Toledo Edison
693 UGI Corp. Luzerne Electric
694 UGI Corp. Luzerne Electric
695 Union Electric
696 Union Electric
697 Union Electric
Plant Name
Johnsonville
Kingston
Kingston
Kingston
Kingston
Kingston
Kingston
Kingston
Kingston
Kingston
Paradise
Paradise
Paradise
Shawnee
Shawnee
Shawnee
Shawnee
Shawnee
Shawnee
Shawnee
Shawnee
Shawnee
Shawnee
Watts Bar
Watts Bar
Watts Bar
Watts Bar
Widows Creek "B"
Widows Crfiek "B"
Acme
Acme
Acme
Acme
Acme
Acme
Bay Shore
Bay Shore
Bay Shore
Bay StiOre
Hunloc k Creek
Hunlock Creek
Labadie
Labadie
Labadie
Boiler
Number
10
1
2
3
4
5
6
7
8
9
1
2
3
1
2
3
4
5
6
7
8
9
10
A
B
C
D
7
8
13
14
15
16
91
92
1
2
3
4
2
6
1
2
3
Average Heat
Content of
Coal, Btu/lb
10,970
10,688
10,688
10,688
10,688
10,688
10,688
10,688
10,688
10,688
10,268
10,268
10,268
10,500
10,500
10,500
10,500
10,500
10,500
10,500
10,500
10,500
10,500
11,142
11,142
11,142
11,142
11,234
11,234
11,410
11,410
11,410
11,410
11,410
11, 4 10
12,143
12,143
12,143
12,143
8,732
8,732
11,134
11,134
11,134
Average
Sulfur
Content, %
3.63
2.21
2.21
2.21
2.21
2.21
2.21
2.21
2.21
2.21
4.18
4.18
4.18
2.87
2.87
2.87
2.87
2.87
2.87
2.87
2.87
2.87
2.87
3.75
3.75
3.75
3.75
3.90
3.90
2.68
2.68
2.68
2.68
2.68
2.68
1.93
1.93
1.93
1.93
0.70
0.70
3.07
3.07
3.07
Average
Ash
Content, %
14.28
20.35
20.35
20.35
20.35
20.35
20.35
20.35
20.35
20.35
18.66
18.66
18.66
15.51
15.51
15.51
15.51
15.51
15.51
15.51
15.51
15.51
15.51
15.62
15.62
15.62
15.62
15.01
15.01
15.19
15.19
15.19
15.19
15.19
15.19
10.78
10.78
10.78
10.78
23.55
23.55
9.80
9.80
9.80
-------
TABLE 44. (Continued)
a\
ib
to
Company Name*
698 Union Electric
699 Union Electric
700 Union Electric
701 Union Electric
702 Union Electric
703 Union Electric
704 Union Electric
705 Union Electric
706 Union Electric
707 Upper Peninsula Generating
708 Upper Peninsula Generating
709 Upper Peninsula Generating
710 Upper Peninsula Generating
711 Upper Peninsula Generating
712 Utah Power & Light
713 Utah Power S, Light
714 Utah Power & Light
715 Utah Power & Light
716 Utah Power & Light
717 Utah Power & Light
718 Virginia Electric & Power
719 Virginia Electric & Power
720 Virginia Electric & Power
721 Virginia Electric & Power
722 Virginia Electric & Power
723 Western Massachusetts
724 Western Massachusetts
725 Western Massachusetts
,726 Wisconsin Electric Power
727 Wisconsin Electric Power
728 Wisconsin Electric Power
729 Wisconsin Electric Power
730 Wisconsin Electric Power
731 Wisconsin Electric Power
732 Wisconsin Electric Power
733 Wisconsin Electric Power
734 Wisconsin Electric Power
735 Wisconsin Electric Power
736 Wisconsin Electric Power
737 Wisconsin Electric Power
738 Wisconsin Electric Power
739 Wisconsin Power & Light
740 Wisconsin Power & Light
741 Wisconsin Power & Light
Plant Name
Labadie
Meramec
Meramec
Meramec
Meramec
Sioux
Sioux
Venice
Venice
Presque Isle
Presque Isle
Presque Isle
Presque Isle
Presque Isle
Gadsby
Gadsby
Hale
Huntington No. 2
Naughton
Naughton
Bremo
Brerao
Mt. Storm
Mt. Storm
Mt. Storm
West Springfield
West Springfield
West Springfield
North Oak Greek
North Oak Creek
North Oak Creek
North Oak Creek
Port Washington
Port Washington
Port Washington
Port Washington
Port Washington
Valley
Valley
Valley
Valley
Edgewater
Edgewater
Edgewafeer
Boiler
Number
4
1
2
3
4
1
2
7
8
1
2
3
4
5
2
3
2
2
1
3
3
4
1
2
3
1
2
3
1
2
3
4
1
2
3
4
5
1
'•2
3
4
1
2
3
Average Heat
Content of
Coal, Btu/lb
11,134
11,810
11,810
11,810
11,810
10,939
10,939
11,912
11,912
12,415
12,415
12,415
12,415
12,415
12,072
12,072
12,013
9,509
9,509
12,391
12,391
11,276
11,276
11,276
11,457
11,457
11,457
11,457
12,118
12,118
12,118
12,118
12,118
11,848
11,848
11,848
11,848
10,930
10.930
10,930
Average
Sulfur
Content, %
3.07
1.53
1.53
1.53
1.53
2.99
2.99
1.31
1.31
1.30
1.30
1.30
1.30
1.30
0.50
0.50
0.53
0,50
0.50
0.89
0.89
1.95
1.95
1.95
2.09
2.09
2.09
2.09
3.43
3.43
3.43
3.43
3.43
3.22
3.22
3.22
3.22
2.53
2.53
2.53
Average
Ash
Content, %
9.80
9.39
9.39
9.39
9.39
15.27
15.27
7.90
7.90
8.20
8.20
8.20
8.20
8.20
8.51
8.51
9.80
4.50
4.50
10.99
10.99
18.77
18.77
18.77
10.71
10.71
10.71
10.71
10.56
10.56
10.56
10.56
10.56
10.39
10.39
10.39 :
10.39
8.94
8.94
8.94
-------
TABLE 44,
(Continued)
Company Name*
742
743
744
745
746
747
748
749
750
751
752
753
754
Wisconsin
Wisconsin
Wisconsin
Wisconsin
Wisconsin
Wisconsin
Wisconsin
Wisconsin
Wisconsin
Wisconsin
Wisconsin
Wisconsin
Wisconsin
Power & Light
Power & Light
Power & Light
Power & Light
Power & Light
Public Service
Public Service
Public Service
Public Service
Public Service
Public Service
Public Service
Public Service
Plant Name
Edgewater
Nelson Dewey
Nelson Dewey
Rock River
Rock River
J. ±. Pulliam
J. P. Pulliam
J. P. Pulliam
J. P. Pulliam
J, P. Pulliam
J. P. Pu11i am
Weston
Weston
Boiler
Number
4
1
2
1
2
3
4
5
6
7
8
1
2
Average Heat
Content of
Coal, Btu/lb
10,930
10,837
10,837
11,107
11,107
11,863
11,863
11,863
11,863
11,863
11,863
11,786
11,786
Average
Sulfur
Content, %
2.53
3.62
3.62
2.82
2.82
2.80
2.80
2.80
2.80
2.80
2.80
2.93
2.93
Average
Ash
Content, %
8.94
10.37
10.37
10.06
10.06
10.89
10.89
10.89
10.89
10.89
10.89
9.43
9.43
-------
TABLE 45.
POWER PLANT AND AIR QUALITY DATA FOR THOSE
PLANTS WITH ELECTROSTATIC PRECIPITATORS
*Co.
Name
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
Year Boiler
Placed in
Service
1971
1956
1958
1972
1949
1949
1954
1967
1968
1972
1973
1974
1960
1958
1959
1969
1970
1971
1963
1954
1942
1943
1958
1958
1961
1969
1970
1969
1970
1972
1965
1967
1967
1964
1971
1956
1958
Generating
Capacity, MW
788.8
187.5
190.4
788.8
69.
69.
145.
552.
550.
650.
650.
650.
186.
183.
178.
576.
576.
576.
294.
142.
—
—
223.
223.
223.
818.1
818.1
170.
170.
173.
80.
590.
590.
206.635
207.00
140.625
187.85
Design Coal
Consumption,
tons/hour
250.
66.7
73.0
250.0
28.5
28.5
80.
186.
179.
250.
250.
250.
95.
80.
80.
200.
200.
200.
100.
46.
19.5 ea.
19.5 ea.
83.
83.
83.
421.
421
7J .5
71.5
70.0
35.9
247.5
247.5
70.
72.
48.2
59.2
Air Flow at
100% Load,
scf/min
1,275,000
274,000
285,000
1,275,000
140,000
140,000
440,000
1,250,000
1,250(000
1,500,000
1,500,000
1,500,000
590,000
450,000
450,000
1,169,000
1,169,000
1,169,000
630,000
265,000
93,750
93,750
317,292
317,292
317,292
1,893,000
1,893,000
319,222
319,222
365,333
169,666
800,000
800,000
600,000
576,000
222,000
280,000
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Type of
Firing
coal /Tangential
coal/Tangential
coal /Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal/Opposed
coa I/Opposed
coal/Opposed
coal/Opposed
Cyclone
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul .
Pul .
Pul.
Pul.
Pul .
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul .
Pul.
Pul.
coal/Opposed
coal/Opposed
coal/Opposed
coal /Opposed
coal/Opposed
coal/Tangential
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Opposed
coal/Opposed
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal /Tangential
coal /Tangential
Boiler
Manufacturer
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
B S W -:
Foster Wheeler
Foster Wheeler
Foster Wheeler
B & W
Foster Wheeler
Foster Wheeler
B & W
B & W
fi & W
Combustion Eng.
fl & W
Foster Wheeler
B S W
B & W
B & W
B & W
B & W
B 1. W
Foster Wheeler
Foster Wheeler
Riley Stoker
Riley Stoker
B & W
B S W
Riley Stoker
B & W
Combustion Enr- .
Combustion Enc; .
Boiler
Efficiency
at 100% Load
89.1
88.52
88.52
89.10
86.5 •
86,5
87.0
88.6
90.7
88.99
88.99
88.99
88.8
88.
88.
91.0
91.0
91.0
89.8
89.9
87.7
87.7
89.8
89.8
89.8
88.68
88 ^8~
8B.02
88.0.2
87.92
86. 9 :
-£- ' ;
' -'- ; -
90,00
PtJ.60:
B <> ; 9
' 90.0
% Excess
Air Used
18.
15.
15.
18-
20-
20.
20.
20-
20-
25-
25-
25.
20-
20-
20-
30-
30-
30.
2f> -
20.
20.
•'. 20.
' 20.
.20.
20.
16.
16.
18.
18.
18.
22.
20.
20.
20-
18.
20.
20 ,
*The numbers in the first column correspond to the same plant names in Tables 45 and 46 as they do in Table 44.
-------
TABLE 43. (Continued)
*Co.
Name
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
Year Boiler
Placed in
Service
1960
1952
1951
1954
195S
1972
1966.
1968
1973
1973
1949
1950
1952
1973
1960
1968
1972
1949
1949
1952
1958
1965
1972
1950
1950
1958
1948
1948
3949
1949
1960
1960
' — "'
I960
1952
1953
1954
1958
1962
1969
1962
1968
1974
1959
Generating
Capacity, HW
206.635
75.
75.
112.5
112.5
446.616
410.85
657.00
745.20
46.
46.
73.5
37.8
125.
250.
322.
35.
35.
84.
100.
388.9
616.
38.
38.
110.
34.
34.
34.
34.
239.4
450.
300.
168.
100.
100.
125.
163.
240.
434.
50.0
80.0
132.
22.
Design Coal
Consumption,
tons/hpur
68.42
26.3
31.6
48. :
40.'
197.4
130.7
223.0
151.8
151.8
19.5
19.5
26.3.
18.0.
60.9
130.9
153.5
17.
17.
39.
50. •.
200.
277.7
18.75 '
18.75
47.1
32.5
1^.5
12.5
12.5
91.
149.
131. '
62.
38.2
37.5
47.6
62.0
86.8
173.0
31 .0
39.6
61.5
12.
Air Flow at
100% toad.
scf/min
286,000
121 ,000
127,000
231,000
210,000
868,000
700,000
1,130,000
733,049
733,049
95,500
95,500
121,000
92,000
316,100
572,700
827,894
100,000
100,000
222,000
270,000
875,760
1,310,082
86,890
86,890
201,333
67,555
67,555
67,555
67,555
397,777
608,958
621,664
240,500
161,000
158,300
196,900
240,500
351,900
669,200
93,985
143,163
228,109
Pul.
Pul .
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul .
Pul,
Pul.
Pul .
Pul.
Pul.
Type of
Firing
coal/Tangential
coal/Tangential
coal /Front
coal/Tangential
coal/Front
coal/Front
coal/Opposed
coal/Tangential
coal/Front
coal/Front
coal/Tangential
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
Cyclone
Cyclone
Pul.
Pul.
Pul.
Pul.
Pul .
Pul .
Pul.
Pul .
Pul .
Pul .
Pul.
Pul.
Pill.
Pul.
Pul.
Pul .
Pul.
Pul.
Pul.
Pul.
Pul.
coal/Front
coa] /Front
coal/Front
coal/Tangential
coal/Tangential
coal /Tangential
coal /Tangential
coal/Tangential
coal/Opposed
coal/Opposed
coal /Front
coal /Tangential
coal/Tangential
coal/Front
coal/Tangent ia 1
coa 1 /Ta ngen t i a 1
coa] /Tangential
coal/Front
coal/Front
coal/Front
coal/Front
Boiler
Boiler
Efficiency
Manufacturer at 100% Load
Combu a t i on Eng .
Combustion Eng.
B & W
Combustion Eng.
B & W
Riley Stoker
Riley Stoker
Combustion Eng.
Riley Stoker
Riley Stoker
B & W
B & W
Combustion Eng.
B & W
Riley Stoker
Riley Stoker
Foster Wheeler
Riley Stoker
Riley Stoker
Riley Stoker
Riley Stoker
B & W
B & W
B & W
B & W
B & W
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
B & W
B & W
Combustion Eng.
Combustion Eng.
Combustion Eng.
B i W
Combustion Eng.
Combustion Eng.
Combustion Eng.
Riley Stoker
B & W
B & W
90.00
89.48
87.8
89.95
89.1
88.58
90.0
90.0
88.71
88.71
88.
88.
90.
88.1
87.2
87.4
88.1
85.
85.
85.
89.
87.93
87.58
86.6
86.6
89.05
85.2
85.2
85.2
85.2
87.24
89.7
88.88
90.05
89.4
89.4
89.33
90.05
89.99
89.01
82.7
88.1
87.7
87.0
% Excess
Air Used
20.
20.
25.
4.0
4.0
5.0
20.
20.
20.
20.
20.
20.
20.
20.
20.
20.
18.
20.
20.
20.
20.
16.
16.
25.
25.
25.
25.
25.
25.
25.
25.
20.
20.
20.
24.
24.
25.
20.
20.
20.
20.
18.
20.
25.
-------
TABLE 45. (Continued)
f.
*Co.
Name
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
Year Boiler
Placed in
Service
1947
1951
1961
1965
1968
1972
1970
1958
1948
1948
1948
1948
1949
1949
1959
1970
1972
1941
1941
1951
1951
1962
1973
1958
1961
1945
1953
1949
1949
1959
1950
1950
1959
1965
1965
1966
1966
1967
1968
1972
1972
1961
1931
1931
Generating
Capacity, MW
20.
20.
37.5
37.5
80.
80.
105.
256.
46.
46.
46.
46.
86.
86.
233.
680.
680.
60.
60.
69.
69.
256.
787.
239.
358.
50.
69.
173.
—
374.
107.
—
360.
660.
—
660.
—
660.
660.
892.8
—
54.
115.
—
Design Coal
Consumption,
tons/hour
IS. 6
16.6
18.2
18.2
37.4
37.4
40.2
92.
21.5
21.5
21.5
21.5
46.
46.
85.
230.
230.
25.2
25.2
33.3
33.3
88.4
332.5
100.
145.
30.
37.
44. r.
44. '•
139.
37.
37.
144.
145.
145.
145.
145.
282.5
282.5
176.5
176.5
26.
20.
28.
Air Flow at
100% Load,
scf/min
64,700
64,700
73,000
73,000
155,800
155,800
316,000
482,000
228,000
228,000
228,000
228,000
242,620
242,620
471,520
1,106,700
1,106,700
167,120
167,120
195,150
195,150
487,340
2,257,232
433,000
545,000
110,000
120,000
152,000
152,000
464,000
128,000
128,000
470,000
578,000
578,000
578,000
578,000
1,100,000
1,100,000
1,217,000
1,217,000
86,800
92,000
116,000
Type of
Firing
Pul. coal/Front
Pul. coal/Front
Cyclone
Cyclone
Cyclone
Cyclone
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Opposed
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Cyclone
Cyclone
Pul. coal/Tangential
Cyclone
Cyclone
Cyclone
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Cyclone
Cyclone
Cyclone
Cyclone
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Boiler
Manufacturer
•__:"
'
B S W
B K W
B & W
B & W
Riley Stoker
Combustion Eng,
B & W
n s w
B & W
B & W
Cxambustion Eng .
Combustion Eng.
Combustion Eng.
B S, W
B S W
B & W
B & W
B S, W
B S W
Combustion Eng.
Combustion Eng,
Combustion Eng.
Combustion Eng.
B s W
B & W
B & W
B S W
Combustion Eng.
B S W
B & w
B & W
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
B & W
B & W
B & W
B S W
foster Wheeler
a & w ;
B & W
Boiler
Efficiency
at 100% Load
83.1
83.3
88.1
87.3
87.47
88.67
87.7 ':.
90.2
'
:
— •— :
87.9
87.9
90.3
89.9
89.9
88.7
88.7
88.5 '
88.5
89, 7
88. Oi
89.4
89.4
86.4
87.0
86.6
86. 6:
89. '4
87.0
87.0
89.4
89.3
89.3
89.3
89.3-
88.2
88.2
89.03
89.03
84. 5 v
83.3 •
83.8
% Excess
Air Used
15.
15.
15.
15.
15.
15.
22.
24.
22.
22.
22.
22.
22.
22.
22.
18.
18.
20.
20.
23.
23.
22.
25.
15.
14.6
20.
25.
22.
22.
18.
20.
20.
16.
14.
14.
14.
14.
16.
16.
15.
15.
22.
-—
-------
TABLE 45. (Continued)
*Co.
Name
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
Year Boiler
placed in
Service
1931
1952
1958
1962
1955
1955
1957
1963
1929
1929
1929
1929
1929
1929
1938
1938
1938
1955
3962
1953
1954
1958
1961
1961
1965
1948
1948
1950
1956
1957
1959
1961
1955
1958
1962
1967
1947
1947
1950
1957
1959
3969
1951
1952
Generating
Capacity, MW
__
121.
326.
355.
188.
184.
299.
598.
208.
—
—
—
—
—
150.
—
—
225.
389.
200.
200.
376.
387.
387,
1028.
66.
66.
66.
156.25
156.25
265.
265.
156.25
156.25
265.
385.
38.7
18.7
18.7
54.4
81 .6
345.6
19.
33.
Design Coal
Consumption,
tofla/hour
28.
56.
138.
150.
80.8
80.8
125.
224.
24.
24.
24.
24.
24.
24.
25.
25.
25.
84.
124.
64.
64.
130.4
134.2
134 .2
321.0
31.
31.
31.
btl.
CH.
92.
89.
88.
88.
100.
150.
10.0
]0.0
12.0
25.0
37.9
137.
13.95
13.95
Air Flow at
100% Load,
scf/min
116,000
191,000
463,000
685,000
276,000
276,000
467,000
798,000
100,000
100,000
100,000
100,000
100,000
100,000
122,200
111,000
111,100
310,300
470,000
360,500
360,500
734,500
755,900
755,900
1,808,100
190,000
190,000
190,000
340,000
340,000
645,576
625,071
340,000
340,000
630,000
907,400
65,830
69,700
86,590
124, 570
230,630
611,000
75,600
63,290
Type Of
Firing
Pul . coal/Front
Cyclone
Pul . coal/Tangential
Pul. coal/Tangential
Cyclone
Cyclone
Pul. coal/Tangential
Pul. coal /Tangential
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Tangential
Cyclone
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Opposed
Pul. coal/Front
Pul. coal /Front
I'ul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Boiler
Boiler Efficiency
Manufacturer at 100% Load
B & W
B & W
Combustion Eng.
Combustion Eng.
B & W
B & W
Combustion Eng.
Combustion Eng.
B & W
B & W
B & W
B & W
B & W
B & W
B & W
B & W
B & W
Combustion Eng.
B & W
B & W
B & W
B S W
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
B & W
Combustion Eng.
Combustion Eng.
Combustion Eng.
B & W
B S, W
B S W
Riley Stoker
Kiley Stoker
Riley Stoker
Combustion Eng.
Riley Stoker
Riley Stoker
83.8
88.6
89.4
89.4
89.1
89.1
89.5
89.0
75.6
75.6
75.6
75.6
75.6
75.6
82.8
82.8
82.8
89.3
89.4
90.3
90.3
90.3
90.6
90.6
90.8
88.05
88.05
88.05
89.33
89. 33
88.9
88.9
88.
88.
90.26
90.47
85.6
85.6
86.0
8fi.5
86.1
88.35
86. 0
Sfi.O
% Excess
Air Used
20.
18.
24.
10.
10.
15.
20.
25.
25.
25.
25.
25.
25.
20.
20.
20.
18.
16.
25.
25.
25.
25.
25.
25.
15.
15.
15.
18.
18.
17.
17.
--
--
18.
18.
37.3
36.8
17.7
20.0
23.9
20.0
17.7
17.7
-------
TABLE 45. (Continued)
*»
CO
*Co.
Name
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
Year Boiler
Placed in
Service
1971
1972
1974
1958
1959
1937
1937
1940
1940
1971
1970
1972
1974
1948
1949
1950
1951
1952
1953
1961
1957
1959
1970
1951
1951
1951
1951
1968
1942
1943
1947
1943
1971
1973
1973
1974
1948
1949
1957
1953
1953
1954
1954
1961
Generating
Capacity, MW
593.
593.
593.
147.
147.
37.
37.
37.
37.
610.
610.
610.
610.
69.
69.
69.
69.
69.
69.
75.
81.
81.
176.
67.
67.
67.
67.
121.
50.
50.
50.
50.
817.
822.
822.
817.
9.
9.
292.
169.
156.
156.
169.
353.
4
4
4
1
5
5
5
5
2
2
2
2
6
6
8
5
5
5
5
2
6
6
2
25
25
Design Coal
Consumption,
tons/hour
375.
375.
418.
54.
54.
21.
21.
21.
21.
250.
250.
250.
250.
24.0
24.0
23.4
23.4
23.4
23.4
23.5
32.
32.
65.
31.5
31.5
31.5
31.5
4r>.
21.
21.
21.
21.
281.
281.
281.
281.
11.55
11.55
99.
61.
61.
61.
61.
120.
Air Flow at
100% Load,
scf/min
1,189,000
1,189,000
2,600,000
240,000
240,000
94,500
94,500
94,500
94,500
1,311,656
1,311,656
1,311,656
1,311,656
105,777
105,777
103,333
103,333
103,333
103,333
160,000
228,000
228,000
360,000
130,000
130,000
130,000
130,000
214,000
97,000
97,000
97,000
97rOOO
1,530,000
1,530,000
1,530,000
1,530,000
59,000
59,000
426,250
258,000
258,000
258,000
258,000
542,000
Pul.
Pul.
PuJ .
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pu] .
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Type of
Firing
coal /Tangential
coal/Tangential
coal /Tangential
coal /Tangential
coal /Tangential
coal/Front
coal/Front
coal/Front
coal/Front
coal/Opposed •
coal /Opposed
coal/Opposed
coal/Opposed
coal/Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal /Tangential
coal /Opposed '
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal /Front
coal/Front
coal/Front
coal/Tangential
coal /Tangential
coal/Tangential
coal /Tangential
coal /Opposed
coa I/Opposed
coal/Opposed
coal /Opposed
coal/Front
coal/Front
coal/Tangential
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
Roller
Boiler
Efficiency
Manufacturer at 100% Load
Combustion
Combustion
Combustion
Combustion
Combustion
B & W
B & W
B S, W
B & W
B R W
B & W
B & W
B S W
Combustion
Combustion
Combustion
Combustion
Combustion
Combustion
Eng.
Eng.
Eng .
Eng.
Eng.
Eng.
Eng.
Eng.
Eng.
Eng.
Eng.
Foster Wheeler
B & W
B & W
B & W
B, S W
B S W
B & W
B & W
Riley Stoker
Combustion
Combustion
Combustion
Combustion
B S W
B & W
B S W
B S, W
Combustion
Combustion
Combustion
B & W
B & W
B S W
B & W
Combustion
Eng.
Eng.
Eng.
Eng .
Eng.
Eng.
Eng.
Eng.
82.58
82.58
81.5
88.6
88.6
85.2
85.2
85.2
85.2
89.9
89.9
89.9
89.9
87.9
87.9
87.7
87.7
87.7
87.7
87.
90.
90.
90.
87.3
87.3
87.3
87.3
88.4
87.7
87.7
87.7
87.7
90.92
90.92
90.92
90.92
87.6
87.6
89.17
88.4
88.4
88.4
88.4
90.16
% Excess
Air Used
20.
20.
20.
20.
20.
25.
25.
25.
25.
18.
18.
18.
18.
20,
20.
20.
20.
20.
20.
20.
20.
20.
20.
24.5
24.5
24.5
24.5
20.
22.
22.
22.
22.
18.
18.
18.
] 8 .
22.
22.
18.
23.
23.
23.
23.
18.
-------
TABLE 45. (Continued)
*Co.
Name
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
« 231
*• 232
10 233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
Year Boiler
Placed in
Service
1969
1948
1948
1968
1968
1957
1957
1959
1960
1961
1974
1941
1941
1942
1953
1953
1940
1940
1948
1948
1949
1950
1955
1951
1951
1958
1965
1966
1969
1970
1952
1952
1954
1954
1970
1952
1953
1954
1960
1942
1942
1949
1950
1950
Generating
Capacity, MW
544.
11.4
11.4
11.4
11.4
165.
165.
275.
275.
275.
1080.
40.
40.
40.
125.
125.
40.
40.
65.
65.
70.
70.
150.
90.
90.
165.
350.
350.
650.
650.
100.
100.
133.
133.
525.
80.
80.
100.
165.
— !
—
—
—
—
Design Coal
Consumption,
tons/hour
198.
15.4
15.4
15.3
15.3
56.
56.
91.
91 .
91.
360.
17.4
17.4
17.4
48.
48.
17.4
17.4
27.9
27.9
30.
30.
55.
40.
40.
58.9
117.
31 / .
200.
208.
40.6
40.6
52.
52.
224.5
41.5
41.5
47.8
75.0
23.8
23.8
37.6
37.6
37.6
Air Flow at
100% Load,
scf/min
862,000
74,000
74, BOO
69,000
69,000
292,520
292,520
487,640
487,640
487,640
1,874,400
85,077
85,077
85,077
233,587
233,587
82,077
82,077
123,265
123,265
144,867
144,867
276,447
185,800
185,800
292,520
561,037
561,037
973,350
973,350
]98,442
198,442
253,946
253,946
841,323
385,000
385,000
430,000
636,000
240,000
240,000
342,000
342,000
342,000
Pul.
Pul.
Pul.
Pul.
Pu] .
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul .
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul .
Pul.
Pul.
Pul.
Pul.
Pul .
Pul.
Pul.
Pul.
Pul.
Pul.
Type of
Firing
coal /Tangential
coal/Front
coal/Front
coal/Front
coal/Front
coal/Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal/Opposed
coal/Tangential
coal/Tangential
coal/Tangential
coal /Tangential
coal/Tangential
coal/Tangential
coal /Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal /Tangential
coal/Tangenti al
coal /Tangential
coal /Tangential
coal/Tangential
coal /Tangential
coal/Tangential
coal/Tangential
coal/TangenLial
coal /Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
Boiler
Manufacturer
Combustion Eng.
B & W
B & W
Foster Wheeler
Foster Wheeler
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
B & W
Combu s t ion Eng .
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
B & H
B & W
D S W
B & W
Foster Wheeler
Foster Wheeleu
Foster Wheeler
Foster Wheeler
Foster Wheeler
Boiler
Efficiency
at 100% Load
90.62
87.4
87.4
87.78
87.78
88.99
88.99
89.59
89.59
89.59
90.23
86.3
86.3
86.3
88.82
88.82
86.8
86.8
87.5
87.5
88.2
88.2
88.75
88.66
88.66
88.95
89.74
89.74
90.12
90.32
88.8
88.8
89.2
89.2
89.4
88.6
88.6
88.9
88.4
85.5
85.5
85.5
85.5
85.5
% Excess
Air Used
18.
26.
26.
18.
18.
20.
20.
20.
20.
20.
20.
19.
19.
19.
23.
23.
23.
23.
23.
23.
22.
22.
19.
22.
22.
22.
18.
18.
18.
18.
23.
23.
20.
20.
18.
25.
25.
23.
18.
2G.
26.
26.
26.
26.
-------
TABLE 45. (Continued)
*Co.
Name
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
SI 276
o 277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
Year Boiler
Placed in
Service
1956
1964
1969
1957
1960
1953
1954
1955
1970
1941
1942
1943
1948
1954
1954
1955
1970
1971
1972
1974
1963
1964
1965
1967
1968
1969
1948
1948
1964
1950
1950
1953
1957
1958
1974
1974
1965
1967
1959
1961
1970
1973
1953
1953
Generating
Capacity, MW
125.
100.
220.85
74.
74.
180.876
180.876
180.876
200.
46.
46.
40.
40.
125.
125.
125.
578.
806.
789.
952.
245.
245.
250.0
319.0
480.7
490.0
22.
22.
125.
100.
100.
100.
125.
125.
350.
350.
149.6
190.4
93.75
93.75
370.
578.
49.
49.
Design Coal
Consumption,
tons/hour
64
42
92
40
39
75
75
75
100
25
25
27
27
41
41
41
195
269
269
375
94
94
97
122
185
185
12
.1°
8*
50
50
50
55
55
139
139
56
71
32
32
125
197
19
19
.0
.5
.5
f
,
.85
.85
.85
.
.
.
.
.
.
.
m
.
.
.
.
.25
.25
.1
.9
.7
.7
.0
.0
0
.0
.0
.0
.0
.0
.0
.0
.4
.3
.1
.15
„
.1
.6
.6
Air Flow at
100% Load,
scf/min
400,
280,
492,
368,
353,
368,
368,
368,
404,
225,
225,
225,
225,
187,
187,
187,
1,006,
1,382,
1,382,
1,775,
1.050,
1,050,
401,
563,
714,
714,
80,
80,
500,
195,
195,
195,
259,
269,
587,
587,
277,
334,
152,
152,
597,
934,
91,
91,
000
000
000
000
000
501
501
501
440
000
000
000
000
159
159
159
Oil
440
440
706
000
000
600
500
200
200
000
000
000
041
041
041
426
436
087
087
300
200
705
705
294
100
405
405
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Type of
Firing
coal/Front
coal/Front
coal /Front
coal/Front
coal/Front
coal/Tangential
coal/Tangential
coal/Tangential
Cyclone
Pul.
Pul.
Pul.
Pul.
Pul .
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
coal/Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal/Front
coal/Front
coal/Front
coal/Opposed
coal/Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal /Tangential
coal/Opposed
coal/Opposed •
coal/Opposed
coal/Opposed
coal/Front
coal/Frpnt , .
coal/Tangential
coal/Tangent iai
coal/Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal/Tahgential
coal/Tangential
coal /Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal/Front
coal/Opposed
coal/Front
coal/Front
Boiler
Manufacturer
Foster Wheeler
B & W
B S W
Riley Stoker
B & W
Combustion Eng .
Combustion Eng.
Combustion Eng.
B S W
Combustion Eng.
Combustion Eng.
B S W
B & W
B & W
B & W
B & W
Foster Wheeler
Combustion Eng.
Combustion Eng.
Combustion Eng.
' Combustion Eng.
Combustion Eng.
B & W
Riley Stoker
B & W
B & W
B & W
B & W
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Etig .
Combustion Eng.
Combustion Eng.
Combu s t i on Eng .
Combustion Eng.
Foster Wheeler
-Foster Wheeler
B & W '
B & W
Boiler
Efficiency
at 100% Load
88.0
89.07
87.14
87.27
89.21
88.22
88.22
88.22
87.15
85.0
85.0
86.0
87.0
88.6
88,6
88.6
89.01
89.10
89.10
88.70
89.3
89.3
89.08
89. 10
89.09
89.09
80.0
80; 6
89.0
88.5
88.5
88,5
88.3
88.3
89.1
89. 1
89.2
89.1
89.4
89.4
88.8
89.01
87.2
B7.2
% Excess
Air Used
26.
20.0
20.0
20.0
20.0
18.0
18.0
18.0
. 13.0
22.0
22.0
22.0
22.0
23.0
23.0
23.0
18.0
18.0
18.0
18.0
18.0
18.0
18.0
20.0
38.0
18.0
20.0
20.0
18.0
20.0
20.0
20.0
20.0
20.0
18.0
18.0
18.0
18,0
17.0
17.0
18.0
18.0
25.0
25.0
-------
TABLE 45. (Continued)
*Co,
Name
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
3-11
342
343
344
345
Year Bpiler
Placed in
Service
1954
1958
1973
1974
1969
1970
1973
1953
1955
1955
1956
1954
1964
1955
1955
1955
1955
1955
1956
1964
1938
1938
1946
1947
1953
1953
1958
.1961
1951
1953
1953
1956
1967
1969
1959
1967
1958
1941
1944
1945
1950
1937
1944
1949
Generating
Capacity, Mw
69.
113.636
175.
175.
28.7
623.
634.5
75.
231.25
73.5
108.8
103.
387.
217.26
217.26
217.26
217.26
217.26
217.26
113.64
,113.64
50.
69.
690.
113.64
253.44
471.00
37.5
218.45
50.0
: '•
12.15
12.15 :
24.15
Design Coal
Consumption,
tons/hour
26.9
40.3
70.
70.
14.5
267.
267.
34.
93.
30.8
44.0
42.7
151.
89.
89.
89.
89.
89.
89.
232.
18.
18.
18.3
18.3
42.
42.
18..,
37. y
37.9
46.5
96.
199.
25.15
92.
25.5
15.0
15.0
15.0
19.5
13.1
14.75
14.35
Air Flow at
100% Load,
scf/min
151,120
224,221
365,333
365,333
75,000
1,730,000
1,730,000
140,900
389,900
141,100
201,900
202,800
647,600
400,000
400,000
400,000
400,000
400,000
400,000
800,000
180,000
180,000
170,000
170,000
150,000
150,000
387,000
387,000
482,000
963,000
114,000
410,000
104,200
59,200
59,900
59,900
79,800
47,000
52,000
51,000
Type of
Firing
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Cyclone
Cyclone
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul . coal/Front
Cyclone
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Spreader Stoker
Spreader Stoker
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul . coal/Tangential
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Pul. coal /Front
Pul . coal/Front
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Boiler
Manufacturer
B & W
Riley Stoker
Riley Stoker
Riley Stoker
General Electric
B & W
B & W
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
B & W
B & W
B & W
B & W
B & W
B & W
B & W
Foster Wheeler
Foster Wheeler
B & W
B & W
B & W
B & W
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Riley Stoker
Combustion Eng.
Riley Stoker
B & W
Combustion Eng.
Riley Stoker
Riley Stoker
Boiler
Efficiency
at 100% Load
88.9
90.0
87.92
87.92
90.
89.1
89.1
87.0
87.3
87.2
87.2
87.0
88.8
88.8
88.8
88.8
88.8
88.8
88.8
90.1
85.5
85.5
86.2
86.2
79.
79.
87.1
87.1
85.44
85.82
85.82
87.15
89.06
89.06
85.5
87.0
85.0
80.56
81.0-1
82.89
85.52
84.2
83.8
85.0
% Excess
Air Used
15.
18.
18.
18.
1.5
16.
16.
25.
31.
24.
24.
25.
20.
17. -18.
17. -18.
17. -18.
17. -18.
17. -18.
17. -18.
20.
kO.
20.
13.
13.
33.
33.
—
--
—
—
—
-_
—
—
25.
18.
22.
20.
20.
20.
25.
5.
5.
5.
-------
TABLE 45. (Continued)
*CO.
Name
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
3 364
*° 365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
Year Boiler
Placed in
Service
1949
1961
1954
1958
1954
1964
1958
1964
1972
1968
1962
1966
1971
1950
1969
1958
1960
1964
1963
1969
1957
1971
1973
1954
1953
1954
1958
1961
1964
1968
1970
1973
1939
1939
1949
1951
1951
1954
1956
1958
1962
1966
1969
1972
Generating
Capacity, MW
24.15
125.
49.
81.6
70.
110.
50.0
138.7
349.2
212.
65.28
81.6
157.5
514.8
187.5
187.5
188.1
265.
737.6
100.
438.
511.
75.
75.
50.
46.
50.
75.
80.
80.
165.
81.5
___
_ —
___
112.5
112.5
147.1
163.2
209.44
272.0
355.5
Design Coal
Consumption,
tons/hour
14.35
61.5
24.8
40.9
42.
50.
27.0
55.
145.
89.22
24.5
33.
51.1
21.
204.8
34.4
84.4
83.0
100.
291.5
38.7
167.0
219.5
36.85
33,8
17.9
20.15
20.15
31.35
31.35
31.35
78.4
10.25
10.25
12.60
12.60
12.60
55.0
56.0
65.0
78.8
91.0
105.75
136.5
Air Flow at
100% Load,
scf/min
50,600
221,000
151,209
246,957
79,500
109,000
135,321
421,670
500,000
504,148
114,000
178,000
287,000
1,196,073
581,600
581,600
573,000
395,833
1,100,000
203,111
810,810
1,640,000
282,000
274,000
77,700
91,200
91,200
144,700
144,700
144,700
383,597
47,600
47,600
50,800
50,800
50,800
221,221
230,384
265,727
295,616
378,083
467,749
609,000
Type of
Firing
Pul. coal/Front
Pul . coal/Tangential
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Cyclone
Pul. coal/Front
Pul. coal/Tangential
Cyclone
Cyclone
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Pul . coal/Front
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Front
Pul . coal/Front
Pul. coal/Front
Pul . coal/Tangential
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Pul. coal/Froht
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul . coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Tangential
Boiler
Manufacturer
Pi ley Stoker
Combustion Eng.
B .& W
Combustion Eng.
I) & W
B & W
niley Stoker
B & W
Foster Wheeler
Combustion Eng.
B S W
B & W
Riley Stoker
Combustion Eng.
Combustion Eng •.
Combustion Eng.
Combustion Eng.
Combustion Eng.
B & W
.Foster Wheeler
B {, W
Combustion Eng.
Combustion Eng.
B & W
B & W
B S W
Combustion Enq.
Combustion Eng.
B S W
.B & W
B S W
,6 & W
:B .& w
B f. W
B S W
B fi W
B & W
Foster Wheeler
Foster Wheeler
Foster Wheeler
Foster Wheeler
Riley Stoker '
Combustion Enq.
Combustion Enq.
Boiler
Efficiency
at 100* Load
85.0
87.4
88.5
89.22
86.5
88.4
87.5
89.0
87.99
86.39
88.7
87.61
88.5
85.7
89.1
88.68
88.6
88.68
89.4
89.3
• 88.8
89.1
88,67
88.2
90.
88.1
88.0
88.0
88.4
88. 4
88.4
89.61
88.2
88.2
88.0
88.0
88.0
86.3
86,2
86.1
86.8
87. '2
88.2
88. -28
% Excess
Air Used
5.
5.
23.
22.
23.
19.
25.
10.4
20.
20.
16.
16.
20.
12.5
20.
20.
20.
20.
20.
20.
25.
20.
20.
25.
25.
18.
18.
18.
18.
18.
18.
25.0
18.
18.
18.
18.
18.
25.
21.
21.
25.
21.
21.
21.
-------
TABLE 45. (Continued)
*Co.
Name
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
Year Boiler
Placed in
Service
1974
1942
1942
1947
1949
1950
1952
1961
1947
1947
1958
1962
1951
1951
1953
1965
1966
1974
1968
1973
1968
1968
1969
1943
1943
1951
1950
1950
1953
1948
1948
1952
1952
1955
1958
1962
1968
1956
1959
1959
1970
1950
1950
1951
Generating
Capacity, MW
355.5
25.
25.
69.
69.
74.75
74.75
44.
26.
26.
171.7
255.
75.
75.
75.
12.5
12.5
15.0
299.2
578.
172.8
26.
66.
21.875
21.875
60.
29.4
29.4
100.
15.
15.
20.
20.
135.
135.
194.
421.6
138.1
138.1
138.1
115.1
140.03
Design Coal
Consumption,
tons/hour
136.5
18.6
18.6
39.7
39.7
39.7
39.7
20.7
12.
12.
55.
79.
26.8
26.8
26.8
12.
12.
19.6
97.
197.1
91.
18.1
45.
9.03
9.0-3
29.4
T5.7
1 '» .7
33.1
10.45
10.45
12.75
12.75
43.9
43.9
90.
182.
55.8
55.8
55.8
49.
20.
20.
20.
Air Flow at
100% Load,
scf/min
609,000
72,050
72,050
158,000
158,000
158,000
158,000
82,400
76,527
76,527
330,000
382,000
114,500
114,500
114,500
73,000
73,000
83,400
474,000
951,556
318,000
164,300
150,192
55,000
55,000
200,000
103,500
103,500
250,000
131 ,000
131,000
155,000
155,000
312,800
312,800
317,778
646,667
2-12,200
242,200
242,200
220,000
398,000
398,000
398,000
Type of
Firing
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Opposed
Pul. coal/Opposed
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Opposed
Pul. coal/Opposed
Pul. coal/Tangential
Spreader Stoker
Cyclone
Pul. coal/Opposed
Pul. coal/Opposed
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Pul. coal/Tangential
Stoker
Stoker
Stoker
Stoker
Pul. coal/Tangential
Pul. coal/Tangential
Cyclone
Cyclone
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Front
Cyclone
Cyclone
Cyclone
Boiler
Manufacturer
Combustion Eng.
Combustion Eng.
Combustion Eng.
Foster Wheeler
Foster Wheeler
Foster Wheeler
Foster Wheeler
B & W
Foster Wheeler
Foster Wheeler
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Erie City Iron
Riley Stoker
Foster Wheeler
Combustion Eng.
Erie City Iron
B & W
Foster Wheeler
Foster Wheeler
Combustion Eng.
B £, W
B & W
Combustion Eng.
Combustion Eng.
Combustion Eng.
B & W
B & W
Combustion Kng .
Combustion Eng.
B & W
B & W
Combustion Eng.
Combustion Eng.
Combustion Eng.
B £, W
B & W
B & W
B & W
Boiler
Efficiency
at 100% Load
88.28
85.2
85.2
86.0
86.0
86.0
86.0
87.4
87.
87.
89.47
90.57
89.0
89.0
89.0
86.0
86.0
86.9
88.9
89.0
86.46
82.88
88.
86.67
86.67
89.10
87.5
87.5
89.6
83.9
83.9
84.6
84.6
89.34
89.34
88.6
88.4
87.74
87.74
87.74
88.3
87. 3
87.3
87.3
% Excess
Air Used
21.
25.
25.
25.
25.
25.
25.
25.
26.
26.
22.
22.
23.
23.
23.
19. -22.
19. -22.
15. -31.
20.
18.
21.
40.
12.
31.
31.
—
25.
25.
22.
25.
25.
28.
28.
24.
24.
17.
]6.
18.
18.
18.
19.
20.
20.
20.
-------
TABLE 45. (Continued)
*co.
Name
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
SJ 452
*> 453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
Year Boiler
Placed in
Service
1974
1953
1953
1967
1968
1952
1954
1955
1960
1942
1944
1956
1959
1953
1949
1949
1957
1943
1948
1969
1944
1944
1947
1947
1956
1950
1955
1955
1959
1960
1961
1962
1967
1969
1971
1974
1971
1971
1953
1954
1957
1958
1966
1955
Generating
Capacity, MW
520
7
7
22
598
81
112
113
179
57
62
113
163
46
87
87
105
43
43
18
31
31
31
31
50
50
159
159
185
185
185
185
317
623
623
1300
816
816
213
213
225
225
590
217
.968
.5
.5
.
.4
.0
.5
.635
.52
.5
.5
.635
.2
_
.87
.87
.
.75
.75
.328
.25
.25
.25
.25
.0
.0
.5
.5
f
^
.
m
.5
f
f
t
.3
.3
.
f
f
f
.8
.26
Design Coal
Consumption ,
tons/hour
226.
4.6
4.6
10.3
246.
51.
56.
58.
94.
40.
40.
67.
93.
30.
17.8
17.8
42.5
26.5
26.4
8.93
17.85
17.85
17.85
17.85
26.1
26.1
62.5
62.5
72.5
72.5
72.5
72.5
117.95
234.5
234.5
480.
291.6
291.6
77.
77.
81.4
81.4
247.5
89.
Air Flow at
100% Load,
scf/min
1,214
21
21
45
910
124
169
183
304
102
102
195
277
83
84
64
161
94
97
40
74
74
74
74
107
107
257
257
350
350
350
350
548
1,092
1,092
2,500
975
975
278
278
317
317
.800
400
,000
,700
,700
,960
,000
,480
,750
,330
,530
,000
,000
,470
,160
,000
,204
,204
,010
,604
,650
,100
,064
,064
,064
,064
,920
,920
,833
,033
,087
,087
,087
,087
,520
,254
,254
,000
,000
,000
,125
,125
,292
,292
,000
,000
Type of
Firing
Cyclone
Pul. coal/Front
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
coal/Front
coal/Front
coal/Tangential
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
Coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coal/Front
coa I/Opposed
coal/Opposed
coal/Opposed
coa I/Opposed
coal/Opposed
coal/Opposed ,
coal/Front
coal/Front
Cyclone
Cyclone
Pul.
P;Ul.
coal/Front
coal/Front
Boiler
Boiler Efficiency
Manufacturer at 100% Load
B & W
B S W
B S W
Combustion Eng .
Foster Wheeler
.B & W
B & W
B S W
B & W
B & W
,B & W
i Riley Stoker
B S, W
B S W
:B & W
B 8 W
B & W
B & W
/ B & W
B S W
B & W
. fc & W
',B Sr W
B S W
B & W
'B & W
Foster Wheeler
Foster Wheeler
Foster Wheeler
Foster Wheeler
B & W
B s W
B S W
•B & W
Foster Wheeler
Foster Wheeler
"B & W
B & W
B s W
.B & W
B & W
B S W
88.3
86.98
86.98
88.5
88.
85.
87.
87.
87.
86.
86.
87.
84.
86.
86.98
86.98
89.1
85.9
86.2
87.0
85,05
85.05
85.05
85,05
87.48
87.48
89.1
89.1
88.88
88.88
88.88
88.88
89.13
88.99
88.99
88.45
88.8
88.8
88.8
88.8
89.3
89.3
87.4
88.8
% Excess
Air Used
15.
20.
20.
19.
16.
23.
25.
23.
23.
25.
25.
20.
20.
20.
25.
25.
27.
25.
30.
18.
,-' 25.
25.
25.
25.
25.
25.
25.
25.
20.
20.
20.
20.
18.
18.
18.
20.
18.
18.
15.
15.
17.
17.
20.
17. -18.
-------
TABLE 45. (Continued)
*Co.
Name
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
* 495
ui 496
01 497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
Year Boiler
Placed in
Service
1955
1955
1955
1955
1954
1957
1959
1963
1968
1959
1964
1964
1974
1939
1939
1948
1954
1971
1972
1974
1964
1972
1969
1969
1970
1971
1944
1944
1952
1952
1967
1968
1942
1950
1957
1954
1954
1959
1960
1948
1948
1949
1949
1967
•-,.
' Generating
Capacity, MW
217.26
217.26
217.26
217.26
77.4
104.5
104.5
134.0
225.6
54.4
75.
151.
265.
7.5
7.5
7.5
30.
665.
665.
508.6
38.
38.
660.
660.
936.
936.
12.5
12.5
46.9
46.9
936.
936.
35.
50.
156.2
133.
133.
187.
187.
21.2
21 .1
21.2
21.1
42.5
Design Coal
Consumption,
tons/hour
89'.
89.
89.
89'.
34.5
44.85
44.85
57.
84.75
41.1
60.5
70.
116.
7.75
7.75
6.92
20.5
400.
400.
255.
9,25
11,75
255.
255',
325.
325.
8.85
R.85
21 1
21.1
316.
316.
15.4
15.4
56,
47.
41.
62.8
62.8
8.7
8.7
8.7
8.7
20.5
Air Flow at
100% Load,
scf/min
400,000
400,000
400,000
400,000
150,000
199,000
199,000
246,000
440,000
167,000
275,000
279,200
2,325,500
26,100
26,100
26,000
78,200
1,524,000
1,524,000
2,313,30rf
38,000
46,000
1,114,012
1,114,012
1,412,472
1,412,472
46,363
46,364
94,685
94,685
1,412,472
1,412,472
57,680
57,680
230,737
215,665
215,665
328,951
328,951
45,300
45,300
45,300
45,300
107,550
Type of
Firing
Pul. coal/Front
Pul . coal/Front
Pul. coal/Front
Pul . coal/Front
Pul . coal/Tangential
Pul. coal/Tangential
Pul . coal/Tangential
Pul. coal/Tangential
Pul. coal/Front
Pul . coal/Tangential
Pul. coal/Front
Cyclone
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Spreader Stoker
Spreader Stoker
Pul. coal/Opposed
Pul. coal/Opposed
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Front
Pul. coal /Front
Pul. coal/Tangential
Pul . coal/Front
Pul. coal/Front
Pul. coal/Tangential
Pul . coal/Tangential
Pul . coal/Front
Pul. coal/Front
Pul . coal/Front
Pul . coal/Front
Pul. coal/Front
Boiler
Manufacturer
B & W
B & W
B & W
B & W
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Foster Wheeler
Combustion Eng.
B & W
B & W
Combus t ion Eng .
B & W
B & W
B & W
Riley Stoker
Combustion Eng.
Combustion Eng.
Combustion Eng.
Erie City Iron
Erie City Iron
Foster Wheeler
Foster Wheeler
Combustion Eng.
Combustion Eng.
Erie City Iron
Erie City Iron
Erie City Iron
Erie City Iron
Combustion Eng.
Combustion Eng.
B S W
B & W
Combustion Eng.
D & W
B & W
Combustion Enq.
Combustion Eng.
Erie City Iron
Erie City Iron
Erie City Iron
Erie City Iron
Foster Wheeler
Boiler
Efficiency
at 100% Load
88.8
88.8
88.8
88.8
88.66
88.18
88.18
88.20
88.79
82.69
83.28
90.2
87.4
77.6
77.6
84.1
86.7
85.5
85.5
88.39
79.
78.
89.69
89.69
90.41
90.41
83.41
83.41
88.0
88.0
90.41
90.41
87.3
87. 3
88.59
89.88
89.88
89.73
89.73
85.9
85.9
85.9
85.9
88.6
% Excess
Air Used
17. -18.
17. -18.
17. -18.
17. -18.
25.
22.
22.
22.
20.
23.
17.
16.
20.
20.
20.
20.
22.
20.
20.
20.
->U .
35.
20.
20.
20.
20.
15.5
15.5
15.0
15.0
20.
20.
25.
25.
22.
15.
15.
15.
15.
15.
15.
15.
15.
20.
-------
TABLE 45. (Continued)
*CO.
Name
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
Year Boiler
Placed in
Service
1967
1966
1958
1964
1961
1965
1969
1954
1954
1956
1971
1973
1949
1949
1949
1949
1951
1953
1959
1960
1947
1952
1964
1965
1959
1960
1962
1970
1971
1949
1950
1954
1956
1951
1951
1955
1960
1957
1959
1962
1968
1973
1964
1954
Generating
Capacity, MW
42.5
303.0
105.0
132.8
363.
405.
790.
75.
156.25
156.25
734.
800.
40.
40.
40.
40.
107.
156.
353.6
353.6
55.
82.
364.
364.
190.
190.
190.
573.
575.
95.
95.
108.
108.
44.
44.
100.
44.
100.
110.
150.
350.
382.5
166.
66.
Design Coal
Consumption,
tons/hour
26
42
42
58
135
150
281
44
57
57
279
279
20
20
20
20
38
48
100
104
23
31
116
116
55
55
55
186
186
55
55
55
55
30
30
60
20
61
61
62
151
214
94
45
.4
.5
.5
.4
.
.
.
.
.5
.5
.
.
.7
.7
.7
.7
.7
.6
.8
.5
.
.
.
.
f
.
f
t
.
.
.
.
.
.85
.85
.25
.9
.35
.35
.4
.1
.
.25
.9
Air Flow at
100% Load,
scf/min
139,
223,
223,
325,
625,
711,
1,463,
248,
417,
414,
1,540,
1,510,
125,
125,
125,
125,
243,
376,
480,
500,
126,
144,
466,
466,
318,
318,
318,
1,000,
1,000,
220,
220,
222,
222,
160,
155,
312,
132,
288,
292,
330,
810,
791,
240,
151,
050
610
610
060
000
000
000
000
780
670
000
000
000
000
000
000
000
000
000
000
447
076
000
000
400
400
400
000
000
000
000
000
000
000
500
000
000
000
000
000
000
000
000
000
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
Pul.
(-
Type of
Firing
coal/Front
coal/Front
coal/Front
coal/Front
coal/Tangential
coal/Tangential
coal/Tangential
coal/Front
coal/Front
coal/Front
coal/Tangential
coal/Tangential
coal/Opposed
coal/Opposed
coal/Opposed
coal/Opposed
coal/Front
coal/Front
coal /Tangential
coal/Tangential
coal/Front
coal/Tangential
coal/Opposed
coal /Opposed
coal/Tangential
coal/Tangential
coal/Tangential
coal/Tangential
coal /Tangential
coal /Tangential
cpa I/Tangential
coal/tangential
coal/tangential
coal/Front
coal/Front
coal/Tangential
coa 1 /Tangent ia 1
coal/Tangential
Boiler
Boiler
Efficiency
Manufacturer at 100% Load
B S W
B & W
B S W
B S W
Combustion Eng.
Combustion Eng.
Combustion Eng.
Foster Wheeler
Foster Wheeler
Foster Wheeler
Combustion Eng.
Combustion Eng.
Foster Wheeler
Foster Wheeler
Foster Wheeler
Foster Wheeler
Foster Wheeler
Foster Wheeler
Combustion Eng.
Combustion Eng.
B & W
Combustion Eng.
B & W
B & W
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng .
Combustion Eng.
B s W
B S W
fl S W
B & W
B 6 W
B & W
B S W .
Combustion Eng.
Combustion Eng.
Combustion Eng.
B; & W
86.5
89.1
89.1
89.1
88.9
89.
90.
84.2
88.
88.
90.
90.
83.4
83.4
83.4
83.4
88.0
88.0
89.77
89.91
88.6
89.0
91.2
91.2
92.1
92.1
92.1
91.8
91.8
88.9
88.9
91.18
91.18
84.0
84.0
85.97
87.78
86,33
86.39
87.69
88.29
84,65
86.66
84.4
% Excess
Air Used
20.
20.
20.
20.
20.
20.
20.
40.
20.
20.
20.
20.
40.
40.
40.
40.
20.
20.
15.
15.
20.
23.
18.
18.
20.
20,
20;
IB.
18.
18.
1 8 .•
18.
18.
28.5
28.5
26.3
23.
27.5
26.5
18.
27.
27.
27-
28,5
-------
TABLE 45. (Continued)
*Co.
Name
566
567
568
569
570
571
572,
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
Year Boiler
Placed in
Service
1970
1972
1949
1949
1951
1959
1959
1960
1961
1950
1950
1950
1956
1968
1953
1953
1954
1954
1960
1968
1973
1955
1973
1969
1959
1949
1951
1953
1957
1974
1974
1962
1964
1967
1958
1958
1953
1954
1955
1970
1971
1974
1966
1966
Generating
Capacity, MW
531.
531.
43.3
43.3
43.3
150.
150.
150.
150.
33.3
33.3
33.3
125.
387.
99.
99.
99.
99.
113.636
345.6
330.0
33.
60.
54.4
81.6
46.0
62.5
62.5
81.6
750.
750.
139.
139.
220.
125.
125.
75.
75.
100.
355.8
355.8
315.
81.6
81.6
Design Coal
Consumption,
tons/hour
237.
257.
25.82
25.82
25.83
64.
64.
64.
64.
17.9
17.9
17.9
49.6
160.0
42.5
42.5
42.5
42.5
43.5
112.5
200.
17.5
28.0
23.9
29.3
18.7
23.0
?T.O
2H .0
32b.
326.
43.
43.
70.5
43.1
43.1
26.8
26.8
36.75
120.
120.
120.5
31.15
31.15
Air Flow at
100% Load,
scf/min
1,292,000
1,292,000
100,000
100,000
100,000
266,000
266,000
266,000
266,000
130,000
130,000
130,000
226,000
610,000
191,000
191,000
191,000
191,000
221,000
573,000
824,827
102,500
196,000
103,652
222,000
137,000
155,000
155,000
222,000
1,317,000
1,317,000
336,000
336,000
550,000
336,000
336,000
164,500
164,500
229,000
738,933
738,933
524,000
182,900
182,900
Type of
Firing
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Pul, coal/Front
Pul. coal/Front
Pul. coal/Frortt
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Cyclone
Cyclone
Pul. coal/Front
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Opposed
Pul . coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Opposed
Pul. coal/Opposed
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Boiler
Manufacturer
Combustion Eng.
Combustion Eng.
Riley Stoker
Riley Stoker
Riley Stoker
Riley Stoker
Riley Stoker
Riley Stoker
Riley Stoker
Riley Stoker
Riley Stoker
Riley Stoker
Riley Stoker
Combustion Eng.
Foster Wheeler
Foster Wheeler
Foster Wheeler
Foster Wheeler
B & W
B & W
Foster Wheeler
Riley Stoker
Combustion Eng.
B & W
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Foster Wheeler
Combustion Enq.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Riley Stoker
Riley Stoker
Riley Stoker
Riley Stoker
Riley Stoker
Boiler
Efficiency
at 100% Load
88.85
88.85
87.1
87.1
87.1
88.9
88.9
88.9
88.9
87.4
87.4
87.4
88.
89.
88.11
88.11
88.11
88.11
90.45
89.66
88.05
87.
87.5
91.7
89.0
87.7
88.0
88.0
89.0
88.77
88.77
89.6
89.6
89.2
89.55
89.55
88.99
88.99
89.25
89.8
89.8
89.1
88.5
88.5
% Excess
Air Used
20.
20.
20.
20.
20.
20.
20.
20.
20.
25.
25.
25.
24.
20.
24.
24.
24.
24.
16.
16.
18.
17.
30.
18.
25.
25.
25.
25.
25.
18.
18.
22.5
22.5
22.5
22.5
22.5
22.5
22.5
22.5
20.
20.
20.
23.
23.
-------
TABLE 45. (Continued)
*Co.
Name
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
S 628
00 629
630
631
632
633
634
635
636
637
636
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
Year Boiler
Placed in
Service
1969
1970
1955
1966
1973
1970
1971
1960
1960
1961
1962
1963
1963
1963
1970
1973
1957
1958
1960
1963
1965
1967
1958
1959
1959
1966
1954
1955
1955
1955
1962
1972
1973
1956
1957
1959
1959
1955
1955
1956
1957
1958
1959
1959
Generating
Capacity, MW
172.8
172.8
46.
103.7
265.23
718.1
718.1
272.
272.
272.
244.8
33.0
33.0
33.0
335.
325.
125.
125.
179.52
187.5
239.36
414.0
330.
330.
330.
950.
200.
200.
223.25
223.25
550.
1300.
1300.
300.
300.
327.6
327.6
223.25
223.25
200.
200.
172.8
172.8
172.8
Design Coal
Consumption ,
tons/hour
55.4
55.4
23.85
47.5
110.
392.5
392.5
100.
100.
100.
100.
19.0
19.0
19.0
182.3
182.1
49.7
49.7
64.9
71.3
93.4
151.4
98.
98.
98.
316.5
76.1
7K.1
7(. I
76.1
213.5
509.
509.
99.5
99.5
111.5
111.5
69.85
69.85
69.85
69.85
61.75
61.75
61.75
Air Flow at
100% Load,
scf/min
312,000
312,000
183,816
403,774
1,020,633
1,492,583
1,492,583
550,000
550,000
550,000
550,000
121,560
121,560
121,560
680,000
680,000
222,000
222,000
296,500
325,000
423,500
696,500
1,512,770
305,610
305,610
305,610
305,610
780,800
2,234,600
2,234,600
392,927
392,927
468,238
468,238
308,230
308,230
308,230
308,230
264,575
264,575
264,571
Type of
Firing
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Opposed
Pul. coal/Opposed
Pul. coal/Opposed
Pul. coal/Opposed
Cyclone
Cyclone
Cyclone
Pul . coal/Opposed
Pul. coal/Opposed
Cyclone
Cyclone
Cyclone
Cyclone
Pul. coal /Opposed
Pul. coal/Opposed
Cyclone
Cyclone
Cyclone
Pul. coal/Tangential
Pul. coal/Opposed
Pul. coal/Opposed
Pul . coal/Tangential •,'
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal /Tangential
Pul. coal/Tangential
,
Boiler
Manufacturer
Riley Stoker
Hiley Stoker
B S W
B & W
B & W
Combustion Eng.
Combustion Eng.
B S W
B & W
B S W
B & W
B S W
B S W
B & W
Riley Stoker
Riley Stoker
B S W
B & W
B fi W
B S W
Riley Stoker
Riley Stoker
B S W
B & W
B S W
Combustion Eng.
B S H
B S W
B S W
B S W
B S W.
B & W
B & ft
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng .
Combustion Eng.
. Poster Wheeler
Foster Wheeler
Foster Wheeler
Boiler
Efficiency
at 100% Load
88.4
88.4
86.4
86.96
88.04
87.46
87.46
89.66
89.66
89.66
89.66
88.6
88.6
88.6
88.3
88.3
88.7
88.7
89.6
89.2
88.7
88.7
--
T-
-'-
90.08
•88.5
88.5
88.5
38.5
89.59
88.87
88.87
88.5
88.5
89.8
89.8
88.85
88.85
88.85
88.85
89.66
89.66
89.66
% Excess
Air Used
23.
23.
24.
26.
20.
18.
18.
23.
23.
23.
23.
10.
10.
10.
15.
15.
13.
13.
16.
16.
15.
15.
13.
13.
13.
20.
20.
:2o.
20.
20.
20.
20.
20.
20.
20.
20.
20.
20.
20.
20.
. 20.
120.
"20.
20..
-------
TABLE 45. (Continued)
*Co.
Name
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
Year Boiler
Placed in
Service
1959
1954
1954
1954
1954
1954
1955
1955
1955
1955
1963
1963
1969
1953
1953
1953
1954
1954
1954
1954
1955
1955
1956
1942
1942
1943
1945
I960
1964
1938
1941
1941
1951
1949
1949
1955
1959
1963
1968
1947
1959
1970
1971
1972
Generating
Capacity, MW
172.8
175.
175.
175.
175.
200.
200.
200.
200.
200.
704.
704.
1150.2
175.
175.
175.
175.
175.
175.
175.
175.
175.
175.
60.
60.
60.
60.
575.01
550.
71.
71.
71.
72.
112.5
112.5
140.
140.
140.
218.
15.
50.
555.
555.
555.
Design Coal
Consumption,
tons/hour
61.75
57.9
57.9
57.9
57.9
76.5
76.5
76.5
76.5
76.5
306.
306.
434.5
58.15
58.15
58.15
58.15
58.15
58.15
58.15
58.15
58.15
58.15
26.2
26.2
26.2
26.2
200.
22b.25
11.
15.
15.
31.
23.
23.
49.
49.
50.
75.
12.
31.
238.
238.
238.
Air Flow at
100* Load,
scf/min
264,571
220,476
220,476
220,476
220,476
308,230
308,230
308,230
308,230
308,230
1,166,120
1,166,120
1,829,000
238,158
238,158
238,158
238,158
238,158
238,158
238,158
238,158
238,158
238,158
117,442
117,442
117,442
117,442
877,538
846,977
89,000
126,000
126,000
262,000
192,000
192,000
249,400
249,400
250,000
380,500
78,000
160,000
1,023,530
1,023,530
1 ,023,530
Type of
Firing
___
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/tfangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Cyclone
Cyclone
Cyclone
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Boiler
Manufacturer
Foster Wheeler
Combustion Bng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
B fc W
B & W
B & W
B & W
B & W
B & W
B & W
B & W
B & W
B & W
B & W
B & W
B & W
B & W
B & W
B & W
B & W
Combustion Eng.
Combustion Eng.
B & W
B & W
B & W
B & W
B & W
B & W
B & W
B & W
B & W
B & W
Foster Wheeler
Foster Wheeler
Combustion Eng.
Combustion Eng.
Combustion Eng.
Boiler
Efficiency
at 100% Load
89.66
88.64
88.64
88.64
88.64
88.64
88.64
88.64
88.64
88.64
89.66
89.66
89.22
88.33
88.33
88.33
88.33
88.33
88.33
88.33
88.33
88.33
88.33
88.03
08.03
88.03
88.03
89.62
89.83
86.1
84.2
84.2
87.6
87.3
87.3
89.51
89.51
90. 38
90.43
73
79.
P8.44
88.44
88.44
'% Excess
Air Used
20.
16.
16.
16.
16.
20.
20.
20.
20.
20.
16.
16.
20.
20.
20.
20.
20.
20.
20.
20.
20.
20.
20.
20.
20.
20.
20.
20.
20.
25.
25.
25.
25.
25.
25.
23.
23.
18.
17.
40.
4T, .
23.
23.
23.
-------
TABLE 45. (Continued)
*Co.
Name
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
S 716
o 717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
Year Boiler
Placed in
Service
1973
1953
1954
1959
1961
1967
1968
1950
1950
1955
1962
1964
1966
1974
1952
1955
1950
1974
1958
1971
1950
1958
1965
1966
1973
1949
1952
1957
1953
1954
1955
1957
1935
1943
1948
1949
1950
1968
1968
1969
1969
1931
1941
1951
Generating
Capacity, MW
555.
137.5
137.5
289.
359.
549.8
549.8
25.0
37.5
57.8
57.8
90.
69.
113.636
44.
411.
152.6
306.
69.
185.277
570.24
570.24
522.0
46.
50.
113.636
120.
120.
130.
130.
80.
80.
80.
80.
80.
70.
70.
70.
70.
30.
30.
60.
Design Coal
Consumption,
tons/hour
238.
54.
54.
109.7
133.5
193.5
193.5
50.4
50.4
12.7
19.6
23.0
23.0
37.0
29.8
38.9
21.3
175.
62.
175.
30.
55.8
215.
215.
214.
18.75
18.75
4 .'. . 4
44 5
44.5
45.25
45.25
39.3
39.6
37.9
38.3
36.3
32.89
32.89
32.89
32.89
21.6
21.6
48.
Air Flow at
100% Load,
scf/min
1,023,530
230,000
230,000
471,000
574,000
830,000
830,000
217,000
217,000
59,800
91,900
97,500
97,500
162,000
149,500
191,000
112,800
258,000
690,000
134,114
265,826
953.872
953,872
1,278,000
94,806
94,806
225,000
222,500
222,500
228,100
228,100
209,600
' 214,500
205,200
207,500
207,500
164,500
164,500
164,500
164,500
150,000
150,000
240,000
Type of
Firing
rul. coal/Tangential
Pul. coal/Tangential
Tul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Cyclone
Cyclone
Pul. coal/Front
Pul. coal/Tangential
•Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Pul. coal/Tangential
Pu]. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Tangential
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Cyclone
Boiler
Manufacturer
Combustion Eng.
Combustion Eng.
Combustion Eng.
Foster Wheeler
Foster Wheeler
B & W
B s W
B S W
B S W
Riley Stoker
Combustion Eng.
Combustion Eng.
Combustion Eng.
Riley Stoker
Riley Stoker
Combustion Eng.
Riley Stoker
Combustion Eng.
Combu s t i on Eng .
Combustion Eng.
B S W
B S W
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion fing .
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combustion Eng.
Combu s t i on Eng .
Combustion Eng.
Combustion Eng.
Combustion Enq .
Combustion Eng.
Combustion Eng.
Riley Stoker
Riley Stoker
Riley Stoker
Riley Stoker
n s w
B & W
B jt W
Boiler
Efficiency
at 100% Load
88.44
88.1
88.1
88.82
86.77
89.32
89.12
86.05
86.05
85.6
86.7
88.7
88.7
87.3
87.5
88.6
81.4
89.18
87.9
86.63
87.6
89.3
90.04
90.04
89.72
88.
88.
88.2
88.76
98.76
88.68
88.68
88.08
B7.71
87.49
88.78
90.23
87.85
87.85
87.85
87.85
m
84.
89.7
% Excess
Air Used
23.
23.
23.
23.
23.
23.
23.
23.
23.
23.
21.
18.
18.
20.
18.
18.
20.
--
21.0
21.')
25.
18.
23.
23.
23.
20.
20.
20.
20.
20.
20.
20.
28.
30.
30.
30.
30.
20.
20.
20.
20.
12.
12.
12.
-------
TABLE 45. (Continued)
Year Boiler
. Generating
Capacity, MW
330.
113.6
113.6
,79.6
79.6
30.
30.
50.
60.
75.
125.
60.
75.
*Co.
Name
742
743
74-4
745
746
747
748
749
750
751
752
753
754
Placed in
Service
1969
1960
1962
1954
1955
1943
1947
1949
1951
1958
1964
1954
1960
Design Coal
Consumption,
tons/hour
133.
45.
45.
49.
49.
18.5
20.5
34.5
42.0
45-6
68.0
38.7
36.0
Air Flow at
100% Load,
scf/min
650,000
220,000
220,000
250,000
250,000
130,000
142,000
227,000
227,000
223,000
371,000
258.000
252,000
Type of
Firing
Cyclone
Cyclone
Cyclone
Cyclone
Cyclone
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Pul. coal/Front
Boiler
Boiler Efficiency
Manufacturer at 100% Load
B W
B W
B W
B W
B W
B W
B W
B W
B W
B & W
B & W
B & W
Combustion E
88.
90.
90.
89.
89.
86.
86.
86.
85.
88.
87.
86.
ng. 87.
8
0
0
8
8
3
2
2
8
05
6
2
7
% Excess
Air Used
12.
15.
15.
15.
15.
24.
22,
25.
25.
18.
22.
23.
23.
-------
TABLE 46.
POWER PLANT AND AIR QUALITY DATA FOR THOSE
PLANTS WITH ELECTROSTATIC PRECIPITATORS
*Co. Type Fly Ash
Name
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
— ^.-.i — -
ESP
Collector** Manufacturer
E
E
E
E
E
E
C
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
C
E
E
E
E
E
E
«_ — m —
Buell
Western
Western
Buell
American
UOP
UOP
American
American
American
Koppers
Koppers
Buell
Research
Research
Research
Standard/UOP
Standard
Standard
Standard
Cottrell
Cottrell
Cottrell
Buell/American Standard
Koppers
Koppers
Koppers
Research
Research
Research
Research
Research
Western
Western
Research
Research
Buell
Buell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Year ESP
Placed in
ESP Design
Service Efficiency, %
1971
1972
1972
1972
—
—
1954/1957
1967
1968
1972
1973
1974
1960
1958
1959
1969
1970
1971
1963/1973
1954/1968
1970
1970
1975
1974
1974
1969
1970
1969
1970
1972
1972
1967
1967
1973
1971
1973
1974
98.
99.
99.
99.
97.
97.
97.
99.
99.
99.
99.
99.
90.
95.
95.
99.
99.
99.
99.
98.
97.
97.
99.
99.
99.
97.
97.
99.
99.
99.
99.
95.
95.
99.
99.
99.
99.
5
0
0
5
0
0
5
5
5
5
00
5
5
5
7
7
7
9
21
0
43
48
ESP Tested
Efficiency, %
93.00
99.4
99.4
73.00
96.3-96.4
96.3-96.4
•
99.5
83.00
97. -98. 4
97. -98. 4
^ -.'
•f--.
-.: — ' .
-• —
97.6-99.9
97.6-99.9
97.6-99.9
98.40
' --.-
_•.:_
-_:_
-.--
~Z — T£ — T7T3 — TT£ — ^i_
Mass Emission
Rate, Ibs/hr
634.
r
i---
_
440.
440.
313.
313.
31J.
350.
900.
900.
450.
450.
450.
53.
650.
950. each
'971. each
73.6
73.6
73.6
4080.
4080.
183.
183.
168.
51.7
2424.'
2401.
180. ;
381.
91.9
104.
Installed
$1
2
2
2
3
1
2
2
2
2
-
1
1
1
2
4
4
1
1
2
1
2
,000'
,550.
,30i.
,301.
,728.
~ —
___
673.
,668.
,453.
,025.
,700.
,700.
407.
632.
706.
,958.
,401.
,417.
,167.
934.
CSC.
650.
• •- —
L^_
---
,172.
,172.
579.
597.
480.
396'i
,351*
,351.
,389.
525.
,832.
,178.
Cost,
s***
7
9
0
7
**Some plants have a combination mechanical collector - electrostatic precipitator.• Those with an ESP only are designated
as "E" under this heading, and those with a combination collector are designated as "C".
***Costs are reported as the original costs recorded on the utility's books of accounts and unitized as prescribed in th'e
FPC List of Units of Property effective January 1, 1961. Certain items called for in this report are'.not specifically
unitized in the referenced list of property units. In this case the most accurate figure available is desired. In the
case of stacks without foundation, the stack cost plus those added costs essential to the stack operation and support
are included.
-------
TABLE 46, (Continued)
*CO.
Name
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
Type Ply Ash
Collector**
E
E
C
E
C
C
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
C
E
E
E
C
E
E
C
C
E
E
ESP
Manufacturer
Buell
Research Cottrell
Buell
Research Cottrell
Boell
UOP
Buell
Buell
UOP
UOP
Buell
Buell
Research Cottrell
Research Cottrell
Koppers
Koppers
Koppers
Koppers
Western
Buell
Western
Western
Research Cottrell
Western,
Western.
Western
Western
Koppers
Research Cottrell
UOP
Research Cottrell
Research Cottrell
Research Cottrel1
Research Cottre]1
Research Cottrell
Buell
Buell
American Standard
UOP
American Standard
Year ESP.
Placed in
Service
1974
1974
1974
1973
1975
1973
1974
1974
1973
1973
1975
1975
1974
1973
ESP Design
Efficiency, %
99.43
99.33
99.24
99.44
99.46
99.00
99.59
99.53
99.
99.
99.27
99.27
99.25
99.5
ESP Tested
Efficiency, %
—~_
99.5
Mass Emission
Rate, Ibs/hr
920.
49.6
65.
75.
87.
208.
380.
39.
39.
51.
12.0
Installed Cost,
$l,000's***
884.
3,050.
_-,_
2,580.
5,100.8
7,788.4
1.448.4
575.
1949
1949
1952
1958
1973
1972
1969
1969
1970
1972
1972
1972
1972
1961
1960
1976
1960
1974
1974
1973
1958
1962
1969
1971
1968
1974
95.
95.
96.
97.
99.0
99.0
97.1
97.1
97.1
98.0
98.0
98.0
98. 0
97.0
95.
99. 5
96.00
99.5
99.5
99.5
96.
96.
98.
96.0
99.5
99.35
97.7-98.7
97.7-98.7
97.7-98.7
99.6
83.2
107.
107.
244.
125.
444.
569.
77.5
77.5
239.6
36.0
30.2
40.3
41.1
749.5
2423.
290.
400.
437.7
670.1
246.1
76.5
256.0
133.7
66,250.
66,250.
110,700.
163,500.
7,991.
5,031.
640.5
640.5
992.
569.
569.
569.
569.
1,396.
2,987.
535.
3,129.
3,257.
3,647.
627.
454 .
1.006.
500.
224.1
1,942.
-------
TABLE 46. (Continued)
*Co.
Name
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
Type Fly Ash
Collector**
E
E
E
E
C
E
E
E
C
C
C
C
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
C
C
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
ESP
Manufacturer
American
American
American
American
American
American
Research
Buell
Research
Research
Research
Research
Research
Buell
Research
Research
Research
Research
Research
Research
Hoppers
Research
Research
Research
Research
Research
Western
Western
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Western
Western
Western
Standard
Standard
Standard
Standard
Standard
Standard
Cottrell
Cottrell/Koppers
Cottrell/Koppers
Cottrell/Koppers
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell/Koppers
Cottrell/Koppers
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrpl1
Cottrell
Cottrell
Year ESP
Placed in
Service
1971
1971
1971
1971
1968
—
1970
1958
1958
1958
1958
1958
1949
1949
1959
1970
1972
1941
1941
1951
1951
1962
1973
1958
1961
1945
1953
1949
1949
1959
1971
1971
. 1966
1965
1965
1966
1966
1967
1968
1972
1972
1961
, 1955
1955
ESP Design
Efficiency, %
97.5
97.5
97.5
97.5
97.5
97.5
98.0
95.
96.
96.
96.
96.
95.
95.
97.
99.5
99.5
90.
90.
95.
95.
99.4
99.3
99.0
98.0
92.
95. •
98.
98.
98.5
98.0
98.0
98.0
99.
99.
99.
99.
98.
98.
99.5
99.5
98.
95.
95.
ESP Tested
Efficiency, %
93.00
93.00
93.00
93.00
93.2
93.2
93.2
93.2
97.1
99.5
98.00
99.3
97.5
95.8
93.4
95.8
90.9
_^_
94.3
94.3
93.9
Mass Emission
Rate, Ibs/hr
84.
84.
84.
84.
13.8
27.55
81.
576.
200.3
200.3
200.3
200.3
355.
355.
608.
224.
224.
292.
292.
238.
238.
110.
408.6
374.5
500.4
221.1
171.6
32.0
32.0
558.3
33.3
33.3
147.5
309.2
309.4
283.5
283.6
235
235.
74.
74.
3.41 .1
120.3
120.3
Installed Cost,
Sl,000's***
259.1
259.1
259.1
259.1
128.9
94.6
200.
424.
480.
468.
543.
888.
1,311.4
151.
149.
403.
402.
705.
2,752.
1 ,041.
1,359.
122.
306.
715.
715.
1,588.
365.
365.
2,327.
2,135.
1,992.
2.253.
2.089.
— _
f _
379.
977.
949.
-------
TADLE 46. (Continued)
*Co.
Name
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
Type Fly Ash
Collector**
E
E
E
E
E
E
E
E
E"
E
E
E
E
E
E
E
E
E
E
-
-
-
-
-
• -
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
ESP
Manufacturer
Western
Research
Koppers
Koppers
Western
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Western
Western
Research
Research
Research
Research
Western
Western
Western
Western
Western
Koppers
Koppers
Western
Western
Koppers
Buell
OOP
OOP
OOP
UOP
OOP
Research
UOP
UOP
Cpttrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Year ESP
Placed in
Service
1955
1971
1958
1962
1955
1973
1973
1963
1929
1929
1929
1929
1929
1929
1938
1938
1938
1955
1962
1953
1953
1955
1957
1957
1965
1969
1969
1969
1968
1969
1959
1961
1971
1971
1967
1967
1974
1974
1974
1974
1974
1969
1974
1974
ESP Design
Efficiency, %
95.
98.
98.
98.
90.
99.0
98.5
98.
96.
96.
96.
97.
97.
97.
96.6
96.6
96.6
98.
98.
97.
97.
99.
99.
99.
99.
99.
99.
99.
99.
99.
95.
95.
99.
99.
95.
98.
99.5
99.5
99.5
99.5
99.5
99.0
99.5
99.5
ESP Tested
Efficiency, %
___
95.2-98.6
95.2-98.6
95.2-98.6
95.2-98.6
95.2-98.6
59. -88.
59. -88.
96.9-97.6
96.9-97.6
89.9
95.5
-.--
Mass Emission
Rate, Ibs/hr
120.3
39.2
405.
401.7
380.5
35.79
316.25
840.8
100.5
100.5
100.5
72.9
72.9
72.9
74.5
74.5
74.5
297.6
124.1
286.6
286.6
184.6
192.0
192.0
4944.
63.87
63.87
63.87
127.75
127.75
1328.26
1307.32
168.
168.
670.8
981 .3
3.27
11 .95
] .39
c.63
8.08
224.
3.763
5.825
Installed Cost,
Sl.OQO's***
___
1,800.
1,205.
1,438.
394.
3,500.
7,000
1,560.
_ —
-:__
519.
1,807.
962.
962.
2,187.
2,022.
2,079.
10,300.
470.
470.
470.
1,115.
1,115.
486.5
527.5
1,311.
1,331.
374.9
595.7
987.5
983.5
983.5
] ,610.
2,212.8
811.
929.0
929.0
-------
TABLE 46. (Continued)
*Co.
Name
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
Type Fly Ash
Collector**
E
E
E
C
C
C
C
C
C
E
E
E
E
E
E
E
E
E
E
E
C
C
C
C
C
C
C
E
E
E
E
E
E
E
E
E
C
C
C
e
C
0
c
C
ESP
Manufacturer
Research Cottrell
Research Cottrell
Research Cottrell
Buell
Buell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Buell
Buell
Buell
Buell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
OOP
Western
Western
Western
Western
American Standard
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Western
Western
Western
Western
Western
Western
Western
Research Cottrell
Year ESP
Placed in
Service
1971
1972
1974
1958
1958
1937
1954
1940
1954
1971
1970
1972
1974
1973
1973
1973
1972
1972
1972
1969
1957
1959
1970
1951
1951
1951
1951
1968
1942
1943
1947
1948
1971
1973
1973
1974
19C7
1967
1957
1953
1953
1954
1954
1961
ESP Design
Efficiency, %
97.3
97.3
98.6
97.5
97.5
95.0
95.0
97.0
97.0
98.
98.
99.5
99.5
99.5
99.5
99.5
99.5
99.5
99.5
97.5
98.
98.
99.5
98.
98.
98.
98,
99.6
99.6
99.6
99.6
99.6
97.66
97.66
97.6
98.1
98.1
98.1
98.1
98.3
ESP Tested
Efficiency, %
97.5-97.9
97.5-97.9
67.9-93.2
67.9-93.2
67.9-93.2
67.9-93.2
67.9-93.2
67.9-93.2
99.8-99.9
99.8-99.9
99.8-99.9
99.8-99.9
99.8-99.9
99.8-99.9
—,.— '
98.6
98.6-98.9
98.6-98.9
98.6-98.9
98.6-98.9
99.4
— -
98. -99.
98. -99.
98. -99.
96.5-98.5
96.5-98.5
— -.-
_^_ .
•>•-,-
Mass Emission
Rate, Ibs/hr
1707.
1707.
1570.
393.
393.
873.
873.
873.
873.
1286.
1286.
321.
321.
321.
321.
321.
5.
129.2
129.2
65.0
88.
88.
88.
88.
33.
237.
237.
237.
237.
224.
-~_
---
_-_
41.
41.
390.
200 :•..
200.
200.
200.
330.
Installed Cost,
51,000's***
1,726.
1,725.
1,887.
412.
384.
135.
135.
134.
134.
1,251.
1,486.
4,259.
2,720.
B03.
838.
857.
862.
827.
996.
•-•''-
260.
275.
461.
566.
566.
565.
565.
455.
204.
203.
258.
235.
4,564.
4,431.
4,826.
4,377.
-548.
548.
1,746.
789.
789.
789.
789.
1,943.
-------
TABLE 46. (Continued)
*CO.
Name
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
Type Fly Ash
Collector**
E
C
C
E
E
C
C
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
C
C
E
E
E
E
E
E
E
C
C
C
C
C
C
C
C
C
ESP
Manufacturer
American Standard
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research CottrelI/Western
Research CottrelI/Western
Research Cottrel1/Western
Research Cottrell
Buell
Buell
Buell
Buell
Buell
Buell
Buell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Buell
Research Cottrell
Research Cottrell
Buell
UOP/Buell
UOP/Buell
Research Cottrell
Research Cottrell
Buell
Buell
Buell
Buell
Research Cottrell
Research Cottrell
Research Cottrell'
Research Cottrell
Research
Research
Research
Research
Research
Cottreil
Cottrell
Cottrell
Cottrell
Cottrell
Year ESP
Placed in
Service
1969
1968
1968
1967
1967
1971
1971
1973/1959
1972/1960
1973/1961
1974
1972
1972
1972
1973
1973
1972
1972
1973
1973
1971
1971
1972
1970
1970
1973
1972
1971
1972
1972
1973
1972
1972
1973
1970
1952
1953
1954
1960
1942
1942
1949
1950
1950
ESP Design
Efficiency, »
99.6
99.6
99.6
99.0
99.0
99.0
99.0
99.5
99.5
99.5
99.7
99.0
99.0
99.0
99.0
99.0
99.0
99.0
99.0
99.0
99.
99.
99.2
99. ,
99.
99.
99.0
99.0
99.7
99.7
99.03
99.03
99.06
99.06
99.5
98.1
97.9
97.9
98.3
95.0
95.0
97.5
97.5
97.5
ESP Tested
Efficiency, %
98.7
98.5-98.9
98.5-98.9
98.5-98.9
98.5-98.9
— -
98.73
98.73
99.55
99.4
Mass Emission
Rate, Ibs/hr
140.
12.
12.
30.
30.
91.
91.
107.
107.
107.
280.2
43.3
43.3
43.3
110.
110.
43.3
43.3
65.0
65.0
69.
69.
91.7
93.
93.
141.
187.
187.
124.5
124.5
82.7
82.7
92.5
92.5
285.7
215.7
238.3
282.
351.
235.
235.
300.
300.
300.
Installed Cost,
$l,000's***
3,910.
497.
497.
585.
585.
681.
582.
4,359./458.
4.359./4S8.
4,359./458.
___
2,369.
2,369.
2,369.
2,175.
2,175.
2,517.
2,517.
1,382.
1,382.
1,008.
1,008.
2,322.
1,191.
1,191.
3,508.
222. /2, 114.
222. /2. 114.
4,298.
4,298.
2,619.
2,619.
2,619.
2,619.
1,473.
378.6
370.6
501.7
552.6
185.4
175.1
442.9
477.6
493.3
-------
TABLE 46. (Continued)
*CO.
Name
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
:292
293
294
295
296
297
298
299
300
301
Type Fly Ash
Collector**
C
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
B
E
E
E
E
E
E
E
E
E
E
E
E
E
E
.- E
E
E
ESP
Manufacturer
Research
American
American
American
American
Research
Research
Research
UOP
Research
Research
Western
Research
Buell
Western
Western
Buell
Research
Research
Buell
Buell
Buell
American
Research
Research
Buell
Research
Research
American
Buell
Buell
Buell
Buell
Buell
Buell
Buell
American
American
Buell
Buell
Buell
Buell
Buell
Buell
Cottrell
Standard
Standard
Standard
Standard
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Standard
Cottrell
Cottrell
Cottrell
Cottrell
Standard
Standard
Standard
Year ESP
Placed in
Service
1956
1973
1973
1974
1974
1971/1972
1972/1972
1972/1972
1970
1945
1945
1973
1948
1971
1969
1969
1970
1971
1972
1974
1972
1972
1965
1967
1968
1969
1948
1948
1964
1971
1968
1969
1970
1968
1974
1974
1965
1967
1968
1969
1970
1973
1974
1974
ESP Design
Efficiency, %
98.2
98.0
98.0
96.0
96.0
98.6
98.6
98.6
98.2
90.0
90.0
99.4
90.0
98.7
98.0
98.0
98.4
98.0
98.0
99.0
99.0
99.0
98.0
98.0
98.5
98.3
98.0
98.0
98.0
98.3
98.3
98.3
98.3
98.3
99.0
99.0
98.0
98.0
98.2
98.2
98.0
98.2
99.5
99.5
ESP Tested
Efficiency, %
98.7-98.9
98.7-98.9
98.7-98.9
98.0
- —
98.12
98.12
99.3-99.5
99.3-99.5
78.0-94.0
78.0-94.0
78.0-94.0
___
:
94.5
94.5
93.06
94.5
.
Mass Emission
Rate, Ibs/hr
450.
50.1
94.5
146. /157.
151. /151.
151. /151.
3240.
220.
220.
26.
220.
72.
72.
" .
260.
260.
300.
360.
540.
540.
143.
144.
266.
340.
340.
340.
374.
374.
622.
622.
153.
170.
106.9
106.9
430.
544.
14.0
14,0
Installed Cost,
$l,000's***
711.3
820.
1,396.
1,100.
1,100.
;
561.962
59.
59.
1,063.
51i
1,032.
510.
535;
1,535.;
1,270;
1,167.
4,103.
3,496;
3,496.
331.
510.
650.
658.
80.
80.
212.
1*006.
665.
902.
824.
816,
2,247,
2,241.
283.
•306.
522.
462;
690.
2,191.
1,472,7
1,327.6
-------
TABLE 46. (Continued)
*Co. Type Fly Ash
Name Collector**
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
C
E
E
E
C
E
E
E
E
E
E
C
E
C
C
C
C
C
C
E
E
E
E
E
C
C
C
C
E
C
C
E
E
E
E
E
C
E
E
E
E
E
E
E
ESP
Manufacturer
Western
Research Cottrell
Research Cottrell
Research Cottrell
UOP
Western
Western
Buell
Due 11
Buell
Hue 11
Research Cottrell
Buell
Western
Western
Western
Western
Western
Western
Western
Research Cottrell
Research Cottrell
Research Cottrell/UOP
Research Cottrell/UOP
American Standard/Research Cottrell
American Standard/Research Cottrell
Western/Research Cottrell
Western/Buell
Buell.
Western/Research Cottrell
Western/Research Cottrell
Buell
Research Cottrell/UOP
Western
American Standard
American Standard •
Western
UOP
UOP
UOP
UOP
Buell
Buell
Buell
Year ESP
Placed in
Service
1954
1958
1973
1974
1969
1970
1973
1974
1972
1973
1974
1972
1970
1955
1955
1955
1955
1955
1956
1964
1969
1968
1974
1974
11 1973
U 1973
1969
1971
1974
1973
1972
1971
1968/1974
1969
1973
1967
1972
1969
1970
1970
1974
1973
1973
1973
ESP Design
Efficiency, 4
97.
98.5
99.
99.
97.
99.
99.
99.5
99.
99.5
99.5
99.67
99.
96.1
96.1
96.1
96.1
96.1
96.1
90.
97.
97.
90./98.93
90./98.93
99.78
99.78
98,9
99.5
99.25
99.0
99.0
99.0
98.4
97.00
99.
98.
99.
98.
98.
98.
99.3
99.1
99.1
99.2
ESP Tested
Efficiency, %
__—
97.
96.63
96.63
99.16
99.50
99.30
99.10
65.30
99.2
99.4
99. -99. 5
99. -99. 5
99. -99. 5
99. -99. 5
97.00
92.00
99.70
99.10
-T-
99.4
99.4
99.8
Mass Emission
Rate, Ibs/hr
100.
53.
112.
112.
304.
69.
19.
175.
15.5
22.38
285.
642.8
642.8
642.8
642.8
642.8
642. B
3564.
72.2
72.2
109./21.86
108./21.86
51.43
51.43
51.7
168.
36.3
57.6
57.6
167.5
801.0
26.7
326.
32.17
96.
107.
60.
41.
20.67
22.29
23.17
Installed Cost,
$l,OOQ's***
— —
1,500.
1,500.
150.
2.900.
1.752.7
1,697.
2,690.
1,418.
1,528.
980.
2,200.
565.
565.
565.
565.
565.
565.
10,004.
308.8
214.2
139.2/2,522.6
2.228.7
415.5
840.89
1,168.5
706.6
606.
633.
718.1/1,559.
836.0
1,314.7
365.
602.
323.
386.
381.
1.126.
850.
850.
970.
-------
TABLE 46. (Continued)
*Co.
Name
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
3 364
0 365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
Type Fly Ash
Collector**
E
E
E
E
E
E
E
E
E
E
E
E
E
C
B
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
R
E
E
ESP
Manufacturer
Buell
Buell
UOP
UOP
UOP
UOP
Western
Research Cottrell
Research Cottrell
UOP
American Standard
Research Cottrell
UOP
Koppers
Buell
Research Cottrell
Research Cottrell
Research Cottrell
Koppers
Research Cottrell
Buell
Research Cottrell
Western
Buell
Research Cottrell
UOP
UOP
Western
American Standard
American Standard
UOP
UOP
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Buell
Western
Year ESP
Placed in
Service
1973
1972
1973
1973
1974
1974
1973
1972
1972
1968
1968
1966
1971
1969
1969
1964
1972
1972
1970
1969
1973
1971
1973
1973
1974
1954
1958
1961
1964
1968
1970
1973
1939
1939
1949
1951
1951
1954
1956
1958
1962
1966
1969
1972
ESP Design
Efficiency, %
99.2
99.2
99.3
99.3
99.3
99.3
99.0
99.
99.
98.
97.
97.
99.35
97.
99.
95.
99.5
99.5
98.5
98.5
98.5
98.0
98.5
98.5
99.5
97.5
97.5
97.5
97.5
97.5
97.5
99.5
97.5
97.5
97.5
97.5
97.5
97.5
97.5
97.5
98.5
98.5
99.40
99.4
ESP Tested
Efficiency, %
99.8
99.8
99.51
- —
98.82
99.5
99.5
97.40
97.70
97.70
97.40
98.5
96.9-98.0
96.9-98.0
96.9-98.0
96.9-98,0
96.9-98.0
96.9-98.0
99.5
T-
99.5
99.5
99.5
97.5
97.5
97.5
97.5-99.7
97.5-99.7
99.70
99.5
Mass Emission
Rate, Ibs/hr
23.17
87.5
27.
43.
30.9/73.5
48.3/115.5
38.2
47.4
183.0
257.
50.2
150.8
63.8
77.
290.
1527.
219.
219.
477.
1306.
166.
1636.
345.
43,12
49.4
57.5
60.5
60.5
P4.5
94.5
94.5
75.0
20.1
20.1
26.8
26,8
26. B
2.82.
286.
-333.
248.
303.
J03.
192.
Installed Cost,
$l,000's***
970,
1,960,
1,324.4
] ,603.8
1,596,8
2,036.1
1,375.
2,454.
1V597.
367.
247.
245.
350.
852.
1,294;
440.
r-
-. 4-
1,453.
1,641,
1,675.1
759/9
:756v
1,687:36
1,460.5
105.0
144/1
116.3
10B.O
J32;b
162.0
326.21
66.3
,66:3
64 v 2
82.5
82<,5
340 1
339.
433-
489.
503,
899.
1,486.
-------
TABLE 46, (Continued)
*Co.
Name
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
Type Fly Ash
Collector**
E
E
E
E
E
E
E
C
E
E
C
C
E
E
E'
C
C
E
E
E
E
C
E
E
E
g
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
ESP
Manufacturer
Western
Research
Research
Research
Research
Research
Research
American
Research
Research
Buell
Buell
Buell
Buell
Buell
American
American
American
Western
Western
Research
Western
Research
Western
Western
Western
Buell
Buell
Research
Koppers
Koppers
Koppers
Koppers
Research
Research
Western
Western
American
American
American
American
Western
Western
Western
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Standard
Cottrell
Cottrell
Standard
Standard
Standard
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Standard
Standai rl
Standard
Standard
Year ESP
Placed in
Service
1974
1942
1942
1947
1949
1950
1952
1961
1947
1947
1958
1962
1974
1965
1974
1965
1966
1975
1968
1973
1968
1968
1969
1973
1973
1973
1971
1971
1953
1974
1974
1974
1974
1955
1958
1962
1968
1968
1969
1969
1970
1969
1970
1970
ESP Design
Efficiency, t
99.4
96.0
96.0
97.5
97.5
97.5
97.5
99.5
94.00
94.00
99.00
99.00
98.5
99.0
98.7
97.
97.
99.8
98.
99.0
97.
98.5
94.5
99.8
99.8
99.8
98.
98.
98.
99.5
99.5
99.5
99.5
98.
98.
99.0
99.0
98.0
98.0
98.0
98.0
98.0
98.0
98.0
ESP Tested
Efficiency, %
99.5
98.1
98.1
99.5
99.3
99.5
99.5
85.90
93.50
97.3-98.2
97.3-98.2
93.0
97.3
95.2
95.14
- -----
---
Mass Emission
Rate, Ibs/hr
192.
91.
91.
169.
169.
169.
169.
17.7
1350.
1350.
185.
299.6
60.
121.
60.
89.
89.
12.
202.
257.2
426.14
75.98
149.
28.0
28.0
17.0
93.3
93.3
78.5
8.
9.
166.
99.5
60.8
128.5
191.
200.
193.
166.
44.9
44.9
44.9
Installed Cost,
$1,000*8***
1,709.
56.
56.
188.
213.
230.
247.
810.
60.
60.
637.
794.
1280.
280.
1280.
75.
75.
555.
393.5
1728.2
1030.
75.
136.
1500.
1500.
3000.
218.2
218.2
218.2
357.5
419.8
650.
860.
650.
712.
665.
401.
620.
583.
584.
-------
TABLE 46. (Continued)
*Co.
Name
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
Type Fly Ash
Collector**
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
C
C
E
E
E
E
E
E
E
E
E
E
E
E
E
E
•E
C
ESP
Manufacturer
Koppers
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
UOP
Western
Western
Western
Western
Western
UOP
Western
Western
Western
Western
Western
Western
Buell
Buell
Buell
Buell
American Standard
Western
Western
Koppers
Research Cottrell
Research Cottrell
Western
Western
Western
Western
Western
Western
Year ESP
Placed in
Service
1974
1971
1971
1972
1968
1952
1954
1955
1960
1972
1972
1972
1972
1972
1970
1970
1957
1969
1969
1969
1971
1972
1971
1971
1971
1971
1955
1955
1959
1960
1961
1962
1967
1969
1971
1974
1971
1971
1972
1972
1972
1971
1968
1955
ESP Design
Efficiency, %
99.75
94.
94.
94.
99.
97.
97.
97.8
97.
99.
99.
99.
99.
99.
99.
99.
99.
98.
98.
98.
99.
99.
99.
99.
99.
99.
97.
97.
97.
97.
97.
97.
99.
99.
99.
99.75
98.5
98.5
99.5
99.5
98.5
98.5
96.5
96.1
ESP Tested
Efficiency^ %.
98.00
89.1
89.1
95.2
89.1
99.00
—^
94.4-97.5
94.4-97.5
;.99.8
99.8
99.8
99.8
99.8
99.8
67.8
67.8
61.3
B1.3
.81.3
fll.3
: 87.6
87.6
B7.6
-T-
---
94.7-97.7
94.7-97.7
94.7-97.7
94.7-97.7
94.7-97.7
(lass Emission
.Rate, Ibs/hr
52.3
42.
42.
56.
599.
265.
580.
713.
991.
30.
28.
45.
88.
66.
43.
43.
193.
130.
129.
30.
48.3
48.3
48.3
48.3
70.6
70.6
506.8
506.8
617.
617.
617.
617.
333.
666.
666.
370.
1511.
1497.
95.
95.
293.
295,
2969.
;' 642.8
Installed Cost,
$l,000's***
1,630.
185.
185.
37?.
1,370.
233.
385.
342.
346.
1,444.
1,444.
1,789.
2,257.
772.
473,
473.
335.
512.
463.
- -. — -
1,198.
1,198.
1.198;
1,198.
1,869.
1,869.
362.
362.
396:
390.
414.
435.
671.
1,239.
1,238.
6,000.
3,426.
3,426.
4,213.
4,213.
4,213.
4,213.
1,885.
:535.
-------
TABLE 46. (Continued)
*Co.
Name
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
type Fly Ash
Collector**
C
C
C
C
C
C
C
E
E
E
E
.E
E
E
E
E
E
E/B
E/E
E
E
E
E
E
E
E
E
E
E
E
E
E
C
C
C
C
C
C
C
E
E
E
E
E
ESP
Manufacturer
Western
Western
Western
Western
Buell
Buell
Buell
Buell
Buell
Research Cottrell
Research Cottrell
UOP
American Standard
Buell
Buell
Buell
Buell
Koppers/
Koppers/
American
American
Buell
Buell
Buell
Buell
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Standard
Standard
Cottrell
Cottrel.1
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrel1
Cottrel1
Cottrell
Cottrell
Cottrell
Cot troll
Cottrell
Cottrell
Cottrell
Cottrell
Year ESP
Placed in
Service
1955
1955
1955
1955
1954
1957
1959
1963
1968
1972
1972
1964
1974
1955
1955
1955
1955
1971/1974
1972/1974
1974
1972
1972
1969
1969
1970
1971
1944
1944
1952
1952
1967
1968
1950
1950
1957
1954
1954
1959
1959
1948
1948
1949
1949
1967
ESP Design
Efficiency, %
96.1
96.1
96.1
96.1
96.
96.
96.
96.
98.
99.
99.
97.0
98.0
90.
90.
90.
90.
99.4/95.
99.4/95.
99.33
95.
95.
99.5
99.5
99.5
99.5
83.
83.
98.
98.
99.5
99.5
98.
98.
98.
95.
95.
95.
95.
94.
94.
94.
94.
98.
ESP Tested
Efficiency, %
»— -•
_ —
95.6
95.6
95.6
95.6
96.10
99.4-99.7
99.4-99.7
97.4
- —
99.5
99.5
99.6
99.6
89. -99. 1
89. -99.1
89. -99.1
89. -99.1
93.3
93.3
97.6-98.4
97.6-98.4
97.6-98.4
89.6-96.4
89.6-96.4
89.6-96.4
89.6-96.4
80.9-94.
80.9-94.
80.9-94.
80.9-94.
Mass Emission
Rate, Ibs/hr
642.8
642.8
642.8
642.8
156.8
204.6
204.6
259.1
204.8
41.7
26.5
214.
1196.6
866. /577.
866. /577.
400.
23.77
23.96
509.6
509.6
430.
430.
434.
434.
150.
150.
430.
430.
112.8
112.8
358.
805.
805.
1170.
1170
131.2
131.2
1/31.2
131.2
143.8
Installed Cost,
$l,000's***
535.
535.
535.
535.
226.
218.
332.
259.
388.
890.
1,060.
610.
363.
43.0
43.0
43.0
43.0
16,720.
115.
115.
2,579.8
2,579.8
3,406.8
3,417.4
68.3
68.3
331.3
331.3
2,754.1
2.738.6
379. 3
379.3
565.1
895.4
895.4
627. 2
627.2
61.6
61 .6
61.6
61.6
322.
-------
TABLE 46. (Continued)
*CO.
Name
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
3 540
*• 541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
Type Fly Ash
Collector**
E
E
E
E
E
E
E
C
E
E
E
E
C
C
C
C
E
E
C
C
E
C
E
E
E
E
E
E
E
C
C
C
C
C
C
C
E
E
E
E
E
E
E
E
ESP
Manufacturer
Research
Buell
Buell
Buell
Research
Research
Western
Research
Buell
Buell
Western
Western
Western
Western
Western
Western
Research
Research
American
American
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
UOP
UOP
OOP
UOP
Western
Research
Western
Koppers
Research
Research
Buell
Cottrell
Cottrell/Buell
Cottrell
Cottrell
Cottrell
Cottrell
Standard/Western
S tandard/Wes tern
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
CottreJ 1.
Cottrell
Cottrell
Year ESP
Placed in
Service
1967
1966
1958
1954
1961/1966
1965
1969
1954
1970
1970
1971
1973
1949
1949
1949
1949
1951
1953
1959
1960
1947
1952
1964
1965
1959
1960
1962
1970
1971
1949
1950
1954
1956
1969
1966
1965
1965
1965
1968
1964
1968
1973
1964
1962
ESP Design
Efficiency, %
98.
98.
95.
98.
99.
98.
99.5
94.3
99.5
99.5
99.5
99.5
70.
70.
70.
70.
96.
96.
95.
95.
96.0
98.4
97.5
97.5
97.5
97.5
97.5
99.5
99.5
99.3
99.3
99.7
99.7
97.5
90.0
87.0
87.0
90.0
94.2
87.0
87.0
87.0
37.0
ESP Tested
Efficiency, %
^ —
- —
99. -99. 4
99. -99. 4
95.6
96.1
94.9-96.6
94.9-96.6
90.9-95.9
90.9-95.9
90.9-95.9
98.84
98.84
87.6
87,6
98.1
98.1
93.2-97.5
93.2-97.5
93.2-97.5
61.85
Mass Emission
Rate, Ibs/hr
185.9
298.8
747.4
385.
387.
2438.
811.
277.
118.
67.
2129.
388.
T-
--"-
_
442.
777.
173.
179.
166.3
56.0
847,
847.
1759.
1759.
1759.
: :
---
1096.
1096.
1096.
1096.
270.
778.
1200.
315.
1260.
1135.
900.
1615.
3457.
567.0
842.
Installed Cost,
$l,000's***
293.
434.
162.
300.
1,426.
1,052.
1,100.
1,035.
• — ^
2,388.
2,337.
439.6
439.6
439.6
439.6
910.
910.
990.
990.
116.
177.
456.
451.
465.
466.
378.
695.
695.
21 5 .
215.
250.
243.
416.5
244.6
425.6
237.12
349.73
720.01
340; 53
744.01
7,000.
518.98
198.5 •
-------
TABLE 46. (Continued)
-4
U1
*Co.
name
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
Type Fly Ash
Collector**
E
E
E
E
E
E
E
E
E
E
E.
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
ESP
Manufacturer
Western
Western
Buell
Buell
Buell
Western
Western
Western
Western
Western
Western
Western
Research
Research
Research
Research
Research
Research
UQP
OOP
Western
Research
Research
Research
Research
Research
Research
Western
Western
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
American
American
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottruil
Cottrell
Cottrell
Standard/PCW
Standard/PCW
Year ESP
Placed in ESP Design ESP Tested
Service Efficiency, % Efficiency, %
1970
1972
1973
1973
1973
1969
1969
1968
1968
1972
1972
1972
1969
1968
1971
1970
1971
1969
1960
1968
1973
1974
1973
1969
1959
1949
1951
1953
1957
1974
1974
1972
1972
1970
1971
1970
1968
1968
1969
1970
1971
1974
1966/1975
1966/1975
99.
99.
98.6
98.6
98.6
99.
99. :
99.
99.
98.
98.
98.
98.5
98.
98.5
98.5
98.5
98.5
90.0
92.4
99.5
99.8
99.8
99.
97.5
97.5
97.5
97.5
97.5
99.5
99.5
99.6
99.6
99.6
99.9
99.9
99.6
99.6
99.6
99.
99.
99.
98.
98.
91.15-93.78
91.15-93.78
98.8
98.8
98.8
99.
99.
99.
99.
98. -98. 6
98. -98. 6
98. -98. 6
98.5
98.0
98.5
98.5
98.5
98.5
88.9
97.5
95.0
90.4-95.3
90.4-95.3
90.4-95.3
90.4-95.3
99.0-99.12
99.0-99.12
99.0-99.12
39.-50./—
39.-50./
Mass Emission
Rate, Ibs/hr
7031.8
7229.8
64.94
64.94
64.94
172.
172.
172.
172.
42.82
42.82
42.82
147.
407.
121.
121.
121.
121.
537.
194.
47.0
___
27.5
405.
39.4
42.3
42.3
102.2
420.
420.
2055.
3263.
11801.
8.2
8.9
31.5
48.1
66.5
234.39
234.39
330.
170.
170.
Installed Cost,
51,000's***
1,035,
1,000.
874.
874.
874.
1,493.
1,493.
1,493.
1,493.
1,354.
819.
1,133.
1,181.
1,133.
1,130.
259.
1,172.
4,185.
200.
300.
192.
358.8
142.5
169.7
182.4
217.9
13,000.
13,000.
494.8
476.8
360.15
388.69
447.91
736.60
620.62
1,298.
211.5/600.
211.5/600.
-------
TABLE 46. (Continued)
*CO.
Name
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
Type Fly Ash
Collector**
E
E
C
E
E
E
E
E
E
E
E
C
C
C
E
E
E
E
E
E
E
E 1
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
ESP
Manufacturer
Buell
Buell
Western
Western
Research Cottrell
Research Cottrell
Western
Western
Research Cottrell
Research Cottrell
American Standard
American Standard
American Standard
Western
Western
Research Cottrell
Research Cottrell
Research Cottrell
American Standard
Research Cottrell
American Standard/Research Cottrell
American Standard
Koppers
American
American
Research
Research
Research
Research
Standard
Standard
Cottrell
Cottrell
Cottrell
Cottrell
Year ESP
Placed in
Service
1969
1970
1973
1974
1973
1970
1971
1960
1960
1974
1973
1974
1974
1974
1970
1973
1957
1958
1960
1963
1965
1 1967/1974
1972
1971
1972
1966
1971
1972
1972
1972
1962
1972
1973
1969
1970
1970
1969
1973
1973
1974
1974
1974
1974
1974
ESP Design
Efficiency, %
95.
95.
97.6
99.28
99.0
98.6
98.6
95.
95.
99.
99.
96.
96.
96.
99.0
99.78
90.
90.
93.
95.5
98.5
98.5/99.78
99.0
99.0
99.0
99.0
97.0
97.0
97.0
97.0
90.0
99.0
99.0
95.
95.
95.
95.
98.5
98.5
98.5
98.5
98.5
98.5
98.5
ESP Tested
Efficiency, %
92.1-94.5
92.1-94.5
99.0
99. -99. 8
99. -99. 8
99.6
99,6
98.4
T
'•. *•
97.2 '•:
•,
97.. 5 ;
97.5
97.5 .
81,00
— :- '
---
•- 1- •
80.00
99.06-99.1
99.06-99.1
--—
99.2-99.3
99.2^99.3
',
-1 — '
'Mass Emission
Rate, Ibs/hr
662.
662.
50.1
101.6
300.1
600.
600.
800.
800.
714.
714.
9.5
13.0
10.6
504.
219.
354.
354.
220.2
174.7
291.
484. /183.
216.9
216.9
216.9
616.
155.3
155.3
155.3
155.3
4804.
805.4
805.4
150.
150.
295.
295.
157.7
157.7
157.7
157.7
180.
180-
180.
Installed Cost,
$l,000's***
177.
177.
733.
1,611.
1,535.
2,317.
2,317.
r —
720.34
720.34
720.34
540.
. . . "
, 250.
216.
325.
249.
394.
567. /7, 113.
3,261.
3,261,
3,261.
1,606.
1,982.5
1,982.5
1,982.5
1,982.5
625.
3,887.5
3,887,5
1,323.8
1,323.8
1,323.8
1,323.8
3,269.4
3,269.4
3,269.4
3,269.4
1,327.3
1,327.3
1,327.3
-------
TABLE 46. (Continued)
*Co.
Name
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
Type Fly Ash
Collector**
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
. E
E
E
E
E
E
E
E
C
C
C
C
C
E
E
C
C
E
E
E
ESP
Manufacturer•
Research
Research
Research
Research
Research
Research
Research
Research
Research
American
American
American.
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Research
Western
Hoppers
Western
Western
Western
Research
Research
Research
UOP
OOP
Western
Western
Research
Research
Research
Research
Research
Cottrell
Cpttrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Standard
Standard
Standard
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrel1
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottrell
Cottreli
Cottrell
Cottrell
Cottrell
Cottrell
Year ESP
Placed in
Service
1974
1960
1960
1960
1960
1959
1960
i960
1960
1960
1967
1967
1969
1970
1969
1969
1969
1970
1969
1970
1970
1969
1969
1969
1969
1969
1969
1960
1964
1$70
1971
1970
1951
1950
1950
1955
1959
1963
1968
1969
1959
1970
1971
1972
ESP Design
Efficiency, %
98.5
95.
95.
95.
95.
95.
95.
95.
95.
95.
98.
98.
98.
90.
90.
90.
90.
90.
90.
90.
90.
90.
90.
95.00
95.00
95.00
95.00
95.00
90.0
99.5
99.5
99.5
98.7
97.4
97.4
98.5
98.8
98.5
99.5
93.8 .
95.0
99.5
99.5
99.5
ESP Tested
Efficiency, »
___
95.00
95.00
95.00
95.00
50.00
99.00
97.4-98.7
97.4-98.7
97.4-98.7
97.4-98.7
97.4-98.7
97.4-98.7
95.1
91.0
96.
96.
96.
Mass Emission
Rate, Ibs/hr
180.
84.6
84.6
84.6
84.6
112.
112.
112.
112.
112.
672.
672.
829.
170.
170.
170.
170.
170.
170.
170.
170.
170.
170.
117.
117.
117.
117.
4017.
5119.
12.
18.
18.
151.
248.
248.
156.
161.
101 .
101.
1250.
1700.
161.6
161.6
161.6
Installed Cost,
$l,000's***
1,327.3
155.2
155.2
155.2
155.2
217.6
217.6
217.6
217.6
217.6
1,441.8
1,428.2
2,901.3
710.6
710.6
710.6
710.6
710.6
710.6
710.6
710.6
710.6
710.6
460.
460.
460.
460.
1,809.
648.
457.
641.
421.
310.
245.
245.
578.
642.
439.
688.
1,325.
353.
2,169.
2,669.
2,900.
-------
TABLE 46. (Continued)
*Co.
Name
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
Type Fly Ash
Collector**
E
E
E
E
E
E
E
E
E
E
E
E
E
E
C
C
C
E
E
E
E
E
E
E
E
E
B
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
E
ESP
Manufacturer
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Buell
Buell
Buell
Buell
Buell
Western
Western
Western
Buell
Lodge Cottrell
Buell
Western
Western
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrel1
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Year ESP
Placed in
Service
1973
1953
1954
1959
1961
1973
1973
1950
1950
1972
1972
1972
1972
1974
1952
1955
1950
1974
1974
1971
1973
1973
1973
1973
1973
1949
1952
1957
1970
1970
1967
1967
1967
1968
1967
1965
1966
1968
1968
1969
1969
1951
1951
1973
ESP Design
Efficiency, %
99.5
97.5
97.5
98.0
97.5
99.6
99.6
95.
95.
95.
95.
95.
95.
99.6
97.0
97.0
97.0
99.5
97.0
96.0
99.38
99.38
99.83
99.83
99.2
95.0
95.0
97.5
99.5
99.5
99.0
99.0
99.2
99.2
99.2
99.2
99.2
99.0
99.0
99.0
99.0
90.0
90.0
99.5
ESP Tested
Efficiency, %
96.
97.4
88.5-90.5
88.5-90.5
— -
___
97.0
99.7-99.75
99.7-99.75
85.00
— _
- —
_ —
98.73
98.73
98.4
98.4
___
— i-
98.43-99.36
98.43-99.36
98.43-99.36
98.43-99.36
T
Mass Emission
Rate, Ibs/hr
161.6
200.
200.
233.
465.
52.
52.
502.
502.
27.
46.
47.
47.
72.
— -—
446,
226.9
74.2
158.
47,6
79.0
110.5
110.5
660.0
9.88
9.88
19.76
72.
7?,
72.
72.
42.
42.
42.
42.
42.
47.
47.
47.
47.
150.
150.
9.3
Installed Cost,
$l,000's***
4,538.
425.
470.
981.
1,097.
2,973.
2,912.
263.
263.
666.
1,038.
1,026.
1,017.
1,045.
298.6
382.2
148.399
5,000.
7,000.
814.
1,595.
2,193.
9,748.
9,374.
4 , 608 .
184.
140.
310.
^u.i.
1,575,
583,-
600.
534.
486,
513.
474.
BIO.
• _.i_
643.
-— '-
586.
126.
126.
2,000.
-------
TABLE 46. (Continued)
*Co.
Name
742
743
744
745
746
747
748
749
750
751
752
753
754
Type Fly Ash
Collector**
E
E
E
E
E
E
B
E
E
E
E
E
E
ESP
Manufacturer
Buell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Research Cottrell
Western
Western
Western
Western
Year ESP
Placed in
Service
1969
1974
1974
1971
1972
1973
1974
1974
1951
1958
1974
1972
1972
ESP Design
Efficiency, %
99.0
99.5
99.5
99.5
99.5
98.0
98.0
97.0
90.0
92.0
97.0
99.0
99.0
ESP Tested
Efficiency, %
___
T-
88.3
99.7-99.8
99.7-99.8
Mass Emission
Rate, Ibs/hr
118.
114.0
114.0
8.6
8.6
76.1
37.9
205.7
258.6
98.5
220.1
10.8
9.9
Installed Cost,
$l,000's***
854.
2,400.
2,400.
1,350.
1,350.
713.
760.
970,
237.
296.
1,632.2
1,857.
1.220.
0\
-J
VO
-------
APPENDIX B
CASCADE IMPACTOR STAGE PARAMETERS —
ANDERSEN MARK III STACK SAMPLER, MODIFIED
BRINK MODEL B, MRI MODEL 1502, SIERRA
MODEL 226, AND UNIVERSITY OF WASHINGTON
MARK III '
680
-------
TABLE 47.
CASCADE IMPACTOR STAGE PARAMETERS
ANDERSEN MARK III STACK SAMPLER
Stage
0% NQ-
oo
1
2
3
4
5
6
7
8
No. of
Jets
264
264
264
264
264
264
264
156
D.-Jet
Diameter
(cm)
.1636-
.1253
.0948
.0759
.0567
.0359
.0261
.0251
S-Jet
to Plate
Distance
(cm)
.254
.254
.254
.254
.254
.254
.254
.254
S
°3
1.55
2.03
2.68
3.35
4.48
7.08
9.73
10.12
Reynolds
Number
45
59
78
98
131
206
284
500
Jet
Velocity
(m/sec)
0.4
0.8
1.3
2.0
3.6
9.0
17.1
31.5
Cumulative Frac-
tion of Impac-
tor Pressure Drop
at each stage
0.0
0.0
0.0
0.0
0.0
0.2
0.3
1.0
-------
TABLE 47. (Continued)
CASCADE IMPACTOR STAGE PARAMETERS
MODIFIED BRINK MODEL B CASCADE IMPACTOR
en
00
N)
Stage
No.
0
1
2
3
4
5
6
No. of
Jets
1
1
1
1
1
1
1
D.-Jet
Diameter
(cm)
.3598
.2439
.1755
.1375
.0930
.0726
.0573
S-Jet
to Plate
Distance
(cm)
1
0
0
0
0
0
0
.016
.749
,544
.424
.277
.213
.191
S
V
2.82
3.07
3.10
3.08
2.98
2.93
3.33
Reynolds
Number
326
481
669
853
1263
1617
2049
Jet
Velocity
(m/sec)
1
3
6
9
21
35
58
.4
• 0
.0
.7
.2
.3
.8
Cumulative Frac-
tion of Impae-
tor Pressure Drop
at each stage
0
0
0
0
0
0
1
.0
.0
.0
.0
.065
.255
.000
-------
CD
u>
TABLE 47. (Continued)
CASCADE IMPACTOR STAGE PARAMETERS
MRI MODEL 1502 INERTIAL CASCADE IMPACTORS
Stage
No.
1
2
3
4
5
6
7
No. of
Jets
8
12
24
24
24
24
12
D -Jet
Diameter
(cm)
0.870
0.476
0.205
0.118
0.084
0.052
0.052
S-Jet
to Plate
Distance
(cm)
0.767
0.419
0.191
0.191
0.191
0.191
0.191
S
D.
.88
.88
.96
1.61
2.27
3.60
3.60
Reynolds
Number
281
341
411
684
973
1530
3059
Cumulative Frac-
Jet tion of Impac-
Velocity tor Pressure Drop
(m/sec) at each stage
0.5
1.1
3.2
8.9
18.2
45.9
102.3
0.0
0.0
0.0
0.0
0.045
0.216
1.000
-------
00
TABLE 47. (Continued)
CASCADE IMPACTOR STAGE PARAMETERS
SIERRA MODEL 226 SOURCE SAMPLER
Stage
No.
1
2
3
4
5
6
W-Jet
Slit
Width
(cm)
0.3590
0.1988
0.1147
0.0627
0,0358
0.0288
Jet
Slit
Length
(cm)
5.156
5.152
3.882
3.844
3.869
2.301
S-Jet
to Plate
Distance
(cm)
0.635
0.318
0.239
0.239
0.239
0.239
S
W I
1.77
1.60
2.08
3.81
6.68
8.30
Reynolds
Number
(@14.16 1pm)
602
602
800
808
802
1348
Jet
Velocity
(m/sec)
(014.16 ipm)
1.3
2 . 3
5.4
10.0
17.4
36.9
Cumulative Frac-
tion of Impae^"
tor Pressure Drop
at each Stage
0.0
0.0
o-C
0,154
0,308
1 .000
-------
TABLE 47. (Continued)
CASCADE IMPACTOR STAGE PARAMETERS
UNIVERSITY OF WASHINGTON MARK III SOURCE TEST CASCADE IMPACTOR
Stage
cri NO.
00
in
1
2
3
4
5
6
7
No, of
Jets
1
6
12
90
110
110
90
D.-Jet
Diameter
(cm)
1.842
0.577
0.250
0.0808
0.0524
0.0333
0.0245
S-Jet
to Plate
Distance
(cm)
1.422
0.648
0.318
0.318
0.318
0.318
0.318
S
°D
.78
1.12
1.27
3.94
6.07
9.55
12.98
Reynolds
Number
1073
565
653
269
340
535
929
Cumulative Frac-
Jet tion of Impac-
Velocity tor Pressure Drop
(m/sec) at each Stage
0.9
1.5
4.1
5.2
10.2
25.4
60.0
0.0
0.0
0.0
0.019
0.057
0.189
1.000
-------
APPENDIX C
PARTICULATE MATTER, SULFUR OXIDE, AND
NITROGEN OXIDE EMISSION LIMITS FOR COAL-
FIRED POWER BOILERS IN THE UNITED STATES.
REGULATIONS APPLICABLE TO VISIBLE EMISSION
ALLOWED FOR FUEL-FIRED BOILERS.
686
-------
TABLE 48. PARTICULATE MATTER, SULFUR OXIDE, AND NITROGEN OXIDE EMISSION
LIMITS FOR COAL-FIRED POWER BOILERS IN THfc UNITED STATES1'2
State
Alabama
Alaska
Arisona
Arkansas
California
Colorado
Connecticut
Participate Matter
0.12 lb/10* Dtu for existing sources
with input > 250 x 10* Btu/hr
0.10 lb/10* Btu for new sources
with input > 250 x 10s Btu/hr
0.05 grains/scf except 0.10 grains/
scf prior to 7/1/72
Sulfur Oxides
Emission Rate = 17.OQ0'"'2
input > 4200x10' Btu/hr
Emission Rate = 1.02Q0-7'9
input < 4200xl06 Btu/hr
for
for
Emission Rate = 17.31P0'" for input
> 60,000 Ibs/hr after July, 1973
where P = process weight, tons/hr
Category I Counties/1.8 Ib SO,/10s
Btu heat input-existing, 1.2 Ib-new
Category II Counties/4.0 Ib SOS/106
Btu heat input-existing, 1.2 Ib-new
500 ppm as SO2
0.80 Ib SO2/106 Btu heat input -
new
1.0 Ib S02/10£ Btu heat input -
existing
0.2 ppm S02 for any 30 min. avg.
beyond source premises
Nitrogen Oxidea
0.7 Ib NOx/10* Btu
for new > 250 x 10' Btu/hr
No standards
0.7 Ib NOx/10s Btu heat input
for new sources (maximum 2 hour
average)
No standards
Each county has own regulations. See Table 4a for summary from counties responding to SoRI survey.
0.10 lb/106 Btu for units with input
>_ 500 x 10' Btu/hr
0.10 lb/10' Btu heat input - new
0.20 lb/106 Btu heat input - existing
500 ppm
Fuels restricted to maximum S
Content of 0.5% by weight
0.7 Ib NOx/10' Btu heat input
0.7 Ib NOx/10' Btu - new
above 250 x 106 Btu/hr input
0.9 Ib NOx/106 Btu - existing
above 250 x 106 Btu/hr input
'The Electrostatic Precipitator Manual by the Mcllvaine Co., Chapter XIII, Section 4.1, pp. 53.1-54.0, August, 1977.
2Survey of all state air pollution agencies by Southern Research Institute in 1978.
-------
TABLE 48. (Continued)
State
Delaware
Florida
Georgia
Hawaii
to Idaho
oo
Illinois
Indiana
Iowa
Participate Hatter
Sulfur Oxides
0.10 lb/10s Btu heat input for new
sources > 250 x 10* Btu/hr
0.1 lb/10s Btu for new sources >
250 x 106 Btu/hr (maximum 2 hour
average)
0.1 lb/10* Btu for new sources >
250 x 10* Btu/hr ':
Mo standards
0.10 lb/10* Btu for new sources >
250 x 10s Btu/hr
0.12 lb/106 Btu for existing (before
12/5/74) sources > 10,000 x 10* Btu/hr
0.10 lb/106 Btu for new and existing
sources >
one hour
250 x 10* Btu/hr in any
0.10 lb/10s Btu for new souices >
250 x 10s Btu/hr
0.6 lb/10* Btu for new sources <_
250 x 10s Btu/hr
0.6 lb/10* Btu for new sources
0.8 lb/10* Btu for existing outside
SMS A*
0.6 lb/10* Btu for existing inside
SMSA*
Fuel restricted to 1% S by weight
.8 Ib SOj/10* Btu for sources >
250 x 106 Btu/hr
1.2 lb/106 Btu for new sources > •
250 x 106 Btu/hr (maximum 2 hour
average)
1.5 lb/106 Btu for existing > 250
x 10s Btu/hr
1.2 lb/10* Btu for new sources >
250 x 10* Btu/hr (maximum 2 hour
average)
No standards for coal
Coal limited to 1% sulfur by
weight - existing
1.2 lb/106 Btu for new sources >
250 X 10s Btu/hr
1.8 Ib SO2/10* Btu in any one hour
for major metro areas - existing
1.2 Ib SOz/10* Btu new sources >
250 x 10* Btu/hr
1.2 Ib S02/10* Btu for new sources
> 250 x 10* Btu/hr
1.2 Ib SOz/lO* Btu for new sources
> 250 x 10s Btu/hr
Nitrogen Oxides
0.7 Ib NOx/106 Btu for new sources
> 250 x 106 Btu/hr
0.7 Ib NOx/106 Btu heat input
(maximum 2 hour average)
0.7 Ib NOx/10* Btu heat input for
sources > 250 x 10* Btu/hr
No standards
0.7 lb/10* Btu for new sources >_
250 x 10* Btu/hr
0.7 lb/10* Btu new sources > 250
x 10* Btu/hr (maximum 1 hour period)
0.7 lb/10* Btu new sources >. 250
X 10* Btu/hr
No standards
•Standard metropolitan statistical area.
-------
State
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Particulate Matter
TABLE 48. (Continued)
Sulfur Oxides
0.12 lb/hr/10* Btu for input ?• 10,000
x 10' Btu/hr
0.10 lb/10' Btu for input >_ 250 x 10'
Btu/hr
0,6 lb/10' Btu heat input for new
and existing not subject to Federal
Regulations
0.1 lb/10' Btu for input > 250 x 10'
Btu/hr
0.03 grains/scf for input > 250 x 106
Btu/hr (new and existing sources)
0.05 lb/10' Btu for new sources >
250 x 106 Btu/hr
0.15 lb/106 Btu for existing
For pulverized coal equipment rated
larger than 10s Ib steam/hr or other
modes of firing coal rated larger
than 3 x 10s Ib steam/hr, one must
apply to commission for specific limits
0.1 lb/106 Btu for new sources > 250
x 106 Btu/hr for most of the state
0.19 lb/10' Btu for input > 10,000 x
106 Btu/hr
0.18 lb/10' Btu for sources > 10,000
x 10' Btu/hr
Nitrogen Oxides
1.5 lb/10' Btu/hr for input >_ 250
x 10' Btu/hr
1.2 lb/106 Btu/hr for input of
250 x 10' Btu/hr
2000 ppm by volume
O.B lb/106 Btu for input > 250 x
106 Btu/hr
Fuel limited to 1% sulfur in Areas
I, III, IV
3.5 lb/106 Btu for input of 100 x
106 Btu/hr for Areas II, V, VI
0.28 Ib SOx/106 Btu in some areas,
0.55 Ib sulfur/106 Btu in others
1* sulfur coal as of 7/1/78
1.2 Ib SOx/106 Btu for new sources
> 250 x 106 Btu/hr for most of
state
4.8 Ib SOx/106 Btu heat input for
sources > 250 x 106 Btu/hr
1000 Ib S02/hr
0.90 lb/10' Btu/hr for input ^ 250
x 10' Btu/hr
0.7 lb/10' Btu/hr for input >_ 250
x 106 Btu/hr
No standards
No standards
0.5 lb/106 Btu (maximum 2 hour
average) for new sources > 250 x
10' Btu/hr
0.3 Ib NOx/106 Btu for new sources
> 250 x 10' Btu/hr
No standards
0.7 Ib NOx/10' Btu for new sources
> 250 x 106 Btu/hr
No standards
No standards
-------
TABLE 48. (Continued)
State
Montana
Nebraska
Nevada
Particulate Hatter
Sulfur Oxides
0.1 lb/106 Btu for new sources
(maximum 2 hour average)
0.1 lb/106 Btu for new sources
(maximum 2 hour average)
0.1 lb/106 Btu for new sources >
250 x 10s Btu/hr
New Hampshire 0.10 lb/106 Btu for new sources >
250 x 10s Btu/hr and 0.19 for
existing sources > 10,000 x 10s
Btu/hr
o, New Jersey
vo
o
New Mexico
New York
1000 Ib/hr for source of 10,000 x
10s Btu/hr
0.05 lb/106 Btu for new sources >
250 x 106 Btu/hr
Fine particulate emissions (<2
microns) cannot exceed 0.02 lb/
10* Btu
0.1 lb/106 Btu for new sources
(maximum 2 hour average)
North Carolina 0.10 lb/10s Btu for sources >
10,000 x 10s Btu/hr
North Dakota 0.8 lb/10s Btu for existing
~6.1. lb/10* Btu for new sources >
250 x 10* Btu/hr
Ohio 0.1 lb/10s Btu for new and existing
> 1,000 x 10s Btu/hr in Priority 1
regions, .15 lb/106 Btu in Priority
2 and 3 regions
1.2 lb SO2/106 Btu
(maximum 2 hour average)
1.2 lb S02/106 Btu
(maximum 2 hour average)
0.6 lb sulfur/106 Btu for new
sources > 250 x 10s Btu/hr
1.5 lb sulfur/106 Btu for new
2.8 lb sulfur/106 Btu for existing
0.2% by weight of sulfur in coal
with several exceptions
0.34 lb SO2/106 Btu for new and
1.0 lb SOz/106 Btu for existing
> 250 x 10s Btu/hr input
0.60 lb sulfur/10* Btu for new
sources > 250 x 10s Btu/hr for
most areas
1.6 lb SOj/106 Btu for new sources
2.3 lb SO,/10S Btu for existing
1.2 lb SOj/lO6 Btu for new sources
> 250 x 10s Btu/hr
1.0 lb SOi/106 Btu, new and
existing
Nitrogen Oxides
0.7 lb NOx/106 Btu
0.7 lb NOx/106 Btu
0.7 lb NOx/106 Btu for new sources
> 250 x 10s Btu/hr
Ho standards
Mo standards
0.45 lb NO2/10S Btu for new sources
> 250 x 106 Btu/hr and 0.7 lb Nbz/
10s Btu for existing
0.7 lb NOx/108 Btu for new sources
> 250 x 10* Btu/hr
1.3 lb NO2/106 Btu for sources'
^ 250 X 10s' Btu/hr
.No standards
0.9 lb NOx/lo* Btu for new sources.
>_ 250 x 10s Btu/hr
-------
State
Oklahoma
Oregon
Pennsylvania
Rhode Island
Particulate Matter
TABLE 48. (Continued)
Sulfur Oxides
0.1 lb/10* Btu for new and existing
> 1,000 x 10s Btu/hr
0.1 lb/10' Btu for new sources
0,2 lb/10* Btu for existing
0.1 lb/10* Btu for new sources
> 600 x 10' Btu/hr
0,10 lb/106 Btu for sources >
250 x 106 Btu/hr
South Carolina For sources — 1,300 x lp' Btu/hr •
E = 57.84P-"•637. where E = emission
rate, P = 106 Btu heat input/hr
South Dakota 0.1 lb/106 Btu,for new sources >
250 x 10* Btu/hr
Tennessee 0.1 lb/106 Btu for existing sources
>. 10,000 x 10" Btu/hr
0.1 lb/106 Btu for new sources >.
250 x.106 Btu/hr
Texas 0.1 lb/106 Btu for new sources >
250 x 10s Btu/hr
0.3 lb/10& Btu.for existing sources
Utah 0.1 lb/10' Btu for new sources >.
250 x 10s Btu/hr
85% control and 40% opacity for
existing
1.2 Ib SOx/106 Btu, new
It by weight sulfur limit
in fuel
1.8 Ib SOj/106 Btu for sources
2. 2,000 x 10* Btu/hr (for most
areas)
0.55 Ib sulfur/10' Btu in fuel
or emissions of 1.1 Ib SOx/lO*
Btu
Most counties are 3.5 Ib SO2/
106 Btu
1.2 Ib SO2/106 Btu for sources
? 250 x 106 Btu/hr
1.2 Ib SOz/106 Btu for new
sources > 250 x 106
3.0 lb/106 Btu for existing
1.2 Ib SO2/106 Btu for new
1.2 Ib SO2/106 Btu for new
1% sulfur coal by weight
Nitrogen Oxides
0.7 Ib NOx/106 Btu for new sources
>_ 50 x 10" Btu/hr
No standards
0.7 Ib NOx/10" Btu
No standards
No standards
0.7 Ib NOx/106 Btu
0.7 Ib NOx/10' Btu for new sources
> 250 x 106 Btu/hr
0.7 Ib NOx/106 Btu for opposed-
fired units, 0.5 for front-fired,
0.25 for tangentially-fired
0.7 Ib NOx/106 Btu for new sources
> 250 x 106 Btu/hr
-------
State
Vermont
Virginia
Washington
Particulate Matter
0.1 lb/106 Btu for new and existing
sources :> 250 x 105 Btu/hr
0.1 lb/106 Btu for new sources >
250 x 10s Btu/hr
0.1 lb/106 Btu for existing sources
> 10,000 x 10 G Btu/hr
0.1 grains/scf for new and existing
sources
'TABLE 48. (Continued)
Sulfur Oxides
West Virginia .05 lb/106 Btu
Wisconsin
Wyoming
0.10 lb/106 Btu for new sources
> 250 x 106 Btu/hr
0.10 lb/106 Btu for all sizes of
new units
1.2 Ib SOj/106 Btu for new sources
> 250 x 106 Btu/hr
1.2 Ib SO2/106 Btu for new sources
> 250 x 106 Btu/hr
1000 ppm SOz for new and existing
sources
Nitrogen Oxides
0.3 Ib NOx/106 Btu for new sources
> 250 x 10s Btu/hr
Ho standards
No standards
2.0 Ib SOz/106 Btu/hr as of 6/30/78 No standards
1.2 Ib SOz/106 Btu for new sources
> 250 x 10s Btu/hr
0.2 Ib SOj/lO6 Btu for new sources
> 250 x 106 Btu/hr
0.7 Ib NOx/106 Btu for new sources
> 250 x ID6 Btu/hr
0.7 Ib NOx/LD6 Btu for new sources
> 250 x 106 Btu/hr
-------
TABLE 48a. COUNTIES OF CALIFORNIA - EMISSION
REGULATIONS FOR POWER PLANTS*
Partieulate Matter
Santa Barbara
Merced
Tehama
en
>£>
Placer
0.2 grains/ft' for 1,000
cfm source
0.0635 grains/ft1 for
20,000 cfiR source
0.0122 grains/ft' for
1,500,000 cfm source
0.1 grains/Bcf
0.3 grains/ft3
0.3 grains/scf for existing
0.1 grains/scf for new and
10 Ibs/hr of combustion
contaminants
North Coast Air Basin -
Del Norte \
Humboldt I
Trinity >
Mendocino I
Sonoma /
.23 grains/SCM
(.10 grains/scf)
Opacity
Sulfur Oxides
20%
20%
40% (no more than 3
minutes in any hour)
20% (no more than 3
minutes in any hour)
for new sources
40% for existing
40% opacity (no more
than 3 minutes in any
one hour except 20% in
Mendocino County
Nitrogen Oxides
0.2% by volume SO:
0.2% by volume and 200
Ibs/hr of sulfur com-
pounds
225 ppm for source input
> 1,775 x 10' Btu/hr
140 Ibs/hr of nitrogen
oxides
Plumas
40% for existing, 20%
for new sources
*Regulations were obtained from most of the Air Pollution Control District in California and summarized in this table as an
indication of the emission limits experienced across the state. Each district has its own regulations. This survey was
conducted in 1978.
-------
County
Fresno
Kings
Monterey
Hadera
Ventura
South Coast -
San Bernadino
Zone
Glenn
Shasta
Particulate Matter
0.10 grains/scf (0.23
grains/SCM)
10 Ibs/hr of combustion
contaminants
0.1 grains/scf
0,10 lb/10fi Btu for new
Sources 5 250 x 106 Btu/
hr
0.1 grains/scf and 10
Ibs/hr of combustion
contaminants
0.1 grains/scf
combustion contaminants
which exceed both 11 Ibs/
hr (5 kg/hr) and 0.01
grains/scf
(23 mg/m3) for new sources
> 50 x 10s Btu/hr
0.3 grains/scf
0.10 grains/scf for new
sources (.05 gr/scf for
particulate matter < 10
microns)
TABLE 48a. (Continued)
Opacity Sulfur Oxides
nitrogen Oxides
20%
20%
20% except 40% allowed
for 2 minutes in any
one hour
20% except 40% for no
more than 2 minutes in
any one hour
20%
20%
40%
0.2% by volume SOs
and 200 Ibs/hr of sulfur
compounds
1.2 lb/10s Btu
1.2 lb/106 Btu
0.5% sulfur by weight
0.2% by volume (2,000 ppm)
1,000 ppm for new sources
140 Ibs/hr of nitrogen
oxides
0.70 lb/106 Btu
0.70 lb/106 Btu
225 ppm HOx
Tulare
0.1 grains/scf
20%
-------
TABLE 48a.
El Dorado
BuLte
Sacramento
Imperial
o>
10
01 Siskiyou
San Diego
Lake
Yolo-Sol£»no
Kern
Parfciculate Hatter
0.3 grains/see and 10 Ibs/
hr of combustion contaminants
0.10 grains/act and 10 Ibs/
hr of combustion contaminants
Q.30 grains/scf
0.30 grains/scf (expected to
be changed to 0.10 grains/
scf for new sources)
0,3 grains/scf existing
0.2 grains/scf new (after
July 1, 1972)
0.3 grains/scf
0.1 lbs/106 Btu for sources
'> 250 x 106 Btu/hr (after
August 17, 1971)
Opacity
(Continued)
Sulfur Oxides
40*
40%
40% (expected to be
changed to 20% for new
sources)
40* existing
20% new (after July 1,
1972)
40%
20% except 40% for no
more than 2 minutes in
any hour
No fuel-fired power boilers or associated regulations.
40% - existing
0.3 grains/scf and 40 Ibs/
hr of combustion parti-
culates - existing
existing - 0.1 grains/scf.
Valley Basin
existing - 0.2 grains/scf.
Desert Basin
new - 0.1 grains/scf (3/19/74)
20% for more than 3
minutes in any one
hour
0.2% sulfur compounds and
200 Ibs/hr sulfur compounds
Nitrogen Oxides
140 Ibs/hr nitrogen oxides
200 Ibs/hr sulfur compounds 140 Ibs/hr nitrogen oxides
0.2% by volume (expected to
be changed to 0.5% sulfur
in fuels)
1.2 lb/106 Btu
0.2% SOz and 200 Ibs/hr
of sulfur compounds -
existing
0.2% SO2 by volume
0.70 lb/106 BtU
140 Ibs/hr of nitrogen
oxides - existing
140 Ibs/hr NOx, Valley
Basin
0.7 lb/106 Btu, Desert
Basin (after 8/17/71)
-------
Particulate Matter
San Joaquin
Bay Area -
Alameda
Contra Costa
Harin
Ma pa
San Francisco
San Mateo
Santa Clara
Solano
Sonoma
Araador
0.1 grains/scf - existing
0.10 lb/10s Btu - new
generally, 0.15 grains/
scf - existing
0.10 lbs/10s Btu for
new sources > 250 x
10s Btu/hr
0.10 grains/scf and 10 Ibs
of combustion contaminants
TABLE 48a. (Continued)
Opacity Sulfur Oxides
20% except 40% for 2
minutes in any one
hour
20% except 40% for
not more than 2
minutes in any one
hour
20% for more than 3
minutes in any one
hour
0.2% SO2 by volume -
existing
1.2 lbs/106 Btu - new
1.2 lbs/105 Btu for
new sources
200 Ibs of sulfur com-
pounds (calculated as
SOz)
Nitrogen Oxides
225 ppm - existing
0.7 lb/10G Btu - new
0.70 lb/10* Btu for
new sources
140 Ibs of niti~gfn
oxides (calculated as
NOZ)
-------
CTv
U>
-J
TABLE 49.
REGULATIONS APPLICABLE TO VISIBLE EMISSION ALLOWED FOR FUEL-FIRED BOILERS
Existing Sources - Limits
1. Alabama
2. Alaska
3. Arkansas
4. Arizona
5. California
6. Colorado
7. Connecticut
8. Delaware
9. Florida
10. Georgia
20% opacity or No. 1 on the Ringelmann chart except 60% or
No. 3 on the Ringelmann chart for not more than 3 minutes in
any 60 minutes.
may not exceed 20% opacity for a period or periods aggregating
more than 3 minutes in any hour.
may not be equal to or exceed 40% except for not more than five
minutes in a 60 minute period (3 times in 24 hour maximum).
may not exceed No. 2 Ringelmann (equivalent to 40% opacity).
each county has its own regulations.
may not exceed 20% except 40% for no more than 3 minutes in any
one hour.
may not exceed 20% except 40% for a period aggregating not more
than 5 minutes in any 60 minutes.
may not exceed either No. 1 on the Ringelinunn chart or 20%
opacity for more than 3 minutes in any one hour or more than
15 minutes in any 24 hour period.
may not exceed No. 1 of the Ringelmann chart (20% opacity) except
No. 2 of the Ringelmann chart (40%) shall be permissible for not
more than 2 minutes in any hour.
may not have emissions equal to or greater than Ringelmann chart
(20% opacity) except for emissions up to Ringelmann No. 2 for
-------
Existing Sources - Limits (continued)
vo
oo
(Georgia,
cont'd.)
11. Hawaii
12. Idaho
13. Illinois
14. Indiana
15. Iowa
16. Kansas
17. Kentucky
18. Louisiana
19. Maine
20. Maryland
two minutes in any one hour. This is for fuel burning equipment
constructed after January 1, 1972. Opacity requirements for
equipment constructed prior to January 1, 1972, is 40%.
may not exceed 40%.
may not exceed No. 2 on the Ringelmann chart (40% opacity).
The new source standard for Idaho does not allow the emission's
aggregating more than 3 minutes in any one hour which is greater
than 20% opacity.
may not exceed 30% opacity except may have opacity greater than
30% but not greater than 60% for a period or periods aggregating
8 minutes in any 60 minute period (limit to 3 times in any
24 hours).
may not exceed 40% opacity for more than a cumulative total of
15 minutes in a 24 hour period.
may not exceed 40% opacity except for a period or periods aggregat-
ing not more than 6 minutes in any 60 minute period.
may not be equal to or greater than 40% opacity.
may not be equal to or greater than 40% opacity except for 60%
for 6 minutes in any 60 minute period.
may not exceed 20% opacity.
may not exceed 40% opacity except for periods of not exceeding
5 minutes in any one hour or 15 minutes in any continuous 3
hour period.
may not exceed 20% opacity except for 40% for a period or periods
aggregating no more than 4 minutes in any sixty minutes.
21. Massachusetts emissions may not be equal to or greater than 20% except 40% for
a period or aggregate period of/time in excess of 6 minutes
during any one hour.
-------
Existing Sources - Limits (continued)
22. Michigan
23. Minnesota
24. Mississippi
25. Missouri
26. Montana
27. Nebraska
28. Nevada
may not exceed 20% except 40% for not more than 3 minutes in any
60 minute period for no more than 3 occasions during any 24
hour period.
may not exceed 20% except 60% for 4 minutes in any 60 minute
period and 40% for 4 additional minutes in any 60 minute period.
may not exceed 40% except 60% for no more than 10 minutes per
billion Dtu gross heating value of fuel in any one hour per
24 hours.
may not be equal to or greater than 40% except 60% for a period
or periods aggregating not more than 6 minutes in any 60 minutes.
Kansas City's opacity limit is 20% except 60% for 6 minutes in
any 60 minutes,
for equipment built before 1969, may not exceed 40%; after 1969,
may not exceed 20%. Exception - 60% for 4 minutes in any 60
minutes.
may not be equal to or exceed 20%.
may not be equal to or exceed 20% for a period or periods aggregat-
ing more than 3 minutes in any one hour.
29. New Hampshire may not exceed 40%.
30. New Jersey
31. New Mexico
32. New York
may not exceed 20% except for smoke which is visible for a period
of not longer than 3 minutes in any consecutive 30 minute period.
may not exceed 20%.
may not exceed 20% except for 3 minutes during any continuous
60 minute period.
33. North Carolina may not exceed 40% for an aggregate of more than 5 minutes in
any one hour or more than 20 minutes in any 24 hour period.
-------
Existing Sources - Limits (continued)
34. North Dakota maximum allowable is 40%.
35. Ohio may not exceed 20% except 60% for no more than 3 minutes in
any 60 minutes.
36. Oklahoma may not exceed 20% except 60% for no more than 5 minutes in any
60 minutes or more than 20 minutes in any 24 hour period.
37. Oregon may not be equal to or greater than 40% for a period aggregating
more than 3 minutes in any one hour except more stringent for
special control areas.
38. Pennsylvania may not be equal to or greater than 20% for more than 3 minutes
in any one hour or equal to or greater than 60% at any time.
39. Puerto Rico may not be equal to or greater than 20% except 60% for not more
than 4 minutes in any 30 minutes
40. Rhode Island may not be equal to or exceed 20%-
41. South Carolina may not be equal to or exceed 40% except 60% for 5 minutes in
one hour or 20 minutes in a 24 hour period.
42. South Dakota may not exceed 20% except 40% is permissible for not more than
2 minutes in any hour.
43. Tennessee may not exceed 40% for more than 5 minutes aggregate in any one
hour or more than 20 minutes in any 24 hour period
44. Texas may not exceed an opacity of 30% averaged over a 5 minute
period.
45. Utah may not exceed 40%.
46, Vermont may not exceed 40% for more than 6 minutes in any hour. Opacity
may never exceed 60%.
-------
Existing Sources - Limits (continued)
47. Virgin Islands may not be equal to or greater than 40%.
48. Virginia may not exceed 20% except for brief periods when starting a
new fire, blowing tubes, or cleaning a fire box.
49, Washington may not exceed 40% except for 15 minutes in any consecutive
8 hours.
50. Washington, D.C. no visible emissions except less than 20% for 2 minutes in
any 60 minute period and for an aggregate of 12 minutes in any
24 hour period.
51. West Virginia may not be equal to or exceed 20% except 10% after June 30, 1975.
52. Wisconsin may not be equal to or exceed 40% except 20% in Milwaukee and
Lake Micigan AQCR's. Also 80% for 5 minutes in any one hour
for cleaning or starting new fire in combustion equipment
(3 times a day maximum) .
53. Wyoming may not exceed 40%.
-------
APPENDIX D
702
-------
LOW TEMPERATURE CORROSION AND FOULING292
INTRODUCTION
Flue gas temperatures which are in the range of 104-121°C
(220-250°F) may result in corrosion and fouling of air heater
elements and corrosion of precipitator elements. Operation at
such low temperatures has caused corrosion and fouling of air
heater elements in some installations, while others have exper-
ienced no difficulty with air heater exit temperatures as low as
104°C (220°F) . An understanding of the factors which cause cor-
rosion and fouling problems is important when operating with flue
gases at low temperatures. The purpose of this appendix is to
relate corrosion and fouling to fly ash and flue gas composition,
fly ash resistivity, and temperature.
SULFURIC ACID OCCURRENCE IN FLUE GAS
SOx, H20, and HaSOi* Equilibria
A knowledge of the SO 3 concentration in the air heater and
precipitator region of power plant exhaust systems is important
from a standpoint of both corrosion and fly ash resistivity. The
principal cause of corrosion in air heaters, and the most im-
portant factor in determining fly ash resistivity, is sulfuric
acid, which results from the reaction of SO3 with water vapor.
Most of the sulfur in power plant flue gases appears as S02,
with typical S03 levels ranging from 1 to 2.5% of the SOa- However,
as Figure 301 shows, the equilibrium constant for the reaction
so2 (g) + ho* (g) = so3 (g)
strongly favors the formation of S03 at temperatures below 537°C
(1000°F) with 3% oxygen. This graph was calculated from data cited by
Hedley.293 The kinetics of the reaction are, of course, unfavorable
in the absence of a catalyst, but it is thermodynamically feasible
for SO 3 concentrations to exist at levels much greater than those
normally encountered. Ratios of S03 to S02 as high as 0.1 have
been reported. 29 * Thus, since the formation of S03 is controlled
•by catalytic effects as well as the amount of excess air present,
the concentration of S03 resulting from the combustion of a
particular fuel can only be .estimated in the absence of direct
measurement s... ....
703
-------
600
(315.0)
700
(370.6)
800
(481.7)
900
(481.7)
1000
(537.3)
1100
(592.8)
TEMPERATURE, °C (°F)
1200
(648.4)
3640-290
Figure 301. Equilibrium conversion of SOz to 80s
704
-------
The reaction between water vapor and S03 is given by
H20(g) + S03(g) = H2SC\(g).
Figure 302 shows the equilibrium conversion of S03 to H2SCU as a
function of temperature for a typical flue gas water concentration
of 8%. At temperatures below 204°C (400°F), essentially all of
the SO3 present is converted to H2SO<4 at equilibrium. in contrast
to the formation of S03, the formation of H2SCU occurs rapidly in
the thermodynamically feasible temperature range.295 Thus, all
S03 below the air heater in a power plant will exist as H2SOn,
either in the vapor or liquid state. Since corrc-ion problems
are associated with the presence of liquid phase sulfuric acid, the
determination of the condensation characteristics of sulfuric acid
from flue gas containing sulfuric acid and water vapor is a neces-
sary step in evaluating the corrosion potential of a particular
stack gas.
Determination Of The Sulfuric Acid Dew Point
Fly ash particles can influence the apparent dew point, or
saturation temperature of H2SOu in flue gas, but experience has
shown that one commits practically no error by neglecting the
presence of other gases and considering only the system sulfuric
acid - water.295 A thermodynamic analysis of the sulfuric acid -
water - flue gas system, ignoring for the present the effect of
fly ash, provides a theoretical basis for predicting acid dew
points and condensate composition from vapor-liquid equilibria
data.
For the case of ideal or quasi-ideal binary solutions, dew
points of vapor mixtures composed of the binary solution vapor
and noncondensable gases can easily be calculated from a knowledge
of the pure component vapor pressures as a function of temperature.
The H2SO^-H20 system presents special problems because:
the K2SO* and water undergo chemical reaction to form
the various hydrates of sulfuric acid, and therefore
the equilibrium relationships are strongly composition-
dependent , and
H.2SOM. has a very low pure component vapor pressure, thus
making direct measurements extremely difficult.
The total vapor pressure of H2SCK at low temperature is essentially
the partial pressure of water above the acid solution, and this is
available from the existing literature. In order to determine the
dew point, however, the HzSO» partial pressure at low temperature
must be known, and the literature lacks such data.2
705
-------
100
90
80
CO
O
V)
u.
O
O
VI
70
60
50
O
O
s
2
E
30
§
LJJ
20
10
200
(93.3)
,_J
300
(148.91
I
400
(205)
I
500
(260)
I
600
(315.0)
TEMPERATURE, °F (°C)
700
(371)
8640-291
Figure 302.. Equilibrium conversion of S03 to H2 SOt, at 8-0
volume % H20 in flue gas.
706
-------
As a result of the experimental difficulties encountered in
low temperature vapor pressure measurements, efforts have been
made to calculate the partial pressure from liquid phase thermo-
dynamic data. Abel297 was the first to derive a relationship en-
abling the calculation of H2SOu, H20, and S03 partial pressures
from standard state values of enthalpy,- entropy, and heat capacity;
and partial molal values of enthalpy, entropy, free energy, and
heat capacity. Muller,295 using Abel's calculated data, computed
dew points of gases with low H2SOi» concentrations. Gmitro and
Vermuelen 8 utilized thermodynamic data, which are claimed to be
more recent and more complete, to calculate H2SOi», S03, and H20
partial pressures from -50 to 400°C with solutions ranging from
10 to 100 weight percent H2SC\. Snowden and Ryar.°q5 have used
Gmitro and Vermulen's partial pressure data to construct a chart
which gives the dew point temperature of a gas as a function of
EzSOtt and H20 partial pressures. The composition of the acid
condensate occurring at a given dew point is also provided.
The dew points predicted from Abel's data are about 30°F
higher than those arrived at with Gmitro and Vermuelen's data.
The difference in these two works lies mainly in the data avail-
able for the calculation of the partial pressures. Gmitro and
Vermuelen had access to much more accurate data and should have
obtained the more accurate results. However, their results do
not agree with direct dew point measurements by the condensation
technique, whereas Abel's partial pressures have been verified
in part by use of this method.
A suspect assumption common to predictions of acid dew
points based on both the Abel and Gmitro calculations is that
the vapor state is an ideal gas, and that the vapor solution is
also ideal- A gas mixture may behave nearly ideally volumetri-
cally, but a component present in small amounts may exhibit
significant departure from ideality if that component is assoc-
iated in the vapor state.
Among the limitations of some presentations in the literature
of the Muller correlation with 10% water vapor is that they do
not indicate the effect of variations in the water vapor concen-
tration on sulfuric acid dew points. The concentration of the
condensate is also not provided. Figures 303 and 304 were pre-
pared to present this information.
Figure 303 is a sulfuric acid - water dew point chart pre-
pared from Abel's H2SO<* partial pressures and Greenewalt' s"
water partial pressures above sulfuric acid solutions, the.
partial pressure data were calculated by computer from' the fol-
lowing equations:
+ E • T) 1 (74)
707
-------
100
6 8 TO
WATER VAPOR. VOL %
Figure 303. Dew point and condensate composition for vapor
mixtures of H2 0 and ffc SOi, at 76'0 mm Hg total
pressure (Abel and Greenewalt),299
708
-------
100
80
60
40
S 20
a.
a.
cc
O
a.
«T 10
O
v>
J> 8
220
(103.9)
240
(115.0)
$L
260
(126.1)
280
(137.3)
300
(148.4)
DEW POINT, °F (°C)
320
(159.5)
3640-293
Figure 304
H2SCK dew points for typical flue gas moisture
concentrations.
709
-------
and
[2.303CA1 - |^)] ., . (75.)
where T is in degrees Kelvin and..-partial pressures are in mm Hg.
The constants in these equations are 'given by' Abel and Greenewalt
for various sulfuric acid concentrations. It should be noted that
the range of uncertainty indicated by Abel for the constant B in
equation 301 results in a dew point uncertainty of 4.45°C (24°F)
at 10% water vapor.
The information contained in Figure 303, if it were accurate,
would be of value in assessing the corrosion poz^ntial of a flue
gas. The dew point temperature can be predicted from an analysis
of H2SCX and water vapor content, and if the gas is cooled to sore
temperature below the dew point, the equilibrium-concentration of"
condensate and the amount condensed can be obtained. It should
be pointed out, however, that the amount o.f condensate predicted
from the use of a dew point chart such as Figure 303 is actually
a prediction of the amount available for condensation. The amount
of condensate depositing on a metal surface may differ from the
chart prediction because of mass transfer considerations.
As an example of the use of the chart, consider a flue gas
containing 10 ppm J^SCu and 10% HsO. Condensation would occur
at about 275°F, and the condensate composition at that point
would be about 79% HaSOi, by weight. If the gas were cooled to
250°F, 85% of the H2SOit should be removed from the gas phase, and
an insignificant amount of the water vapor would also be condensed.
The condensation, therefore, follows the 10% water .line, result-
ing in a condensate which would be the equilibrium composition of
the condensate at 121°C (250°F), assuming the vapor phase is in
equilibrium with the total liquid condensed. The composition
change of the liauid is small over the temperature interval given
as an example, ranging from 79% at. 135°C (275°F) to 75% at 121°C
(250°F).
It is apparent from Figure 303 that a knowledge of water
vapor concentration is of fundamental importance. Appreciable
changes in this variable can have a rather significant effect on
the predicted sulfuric acid dew point, and if a gas is saturated
with H2S04, the condensate composition is determined by the water
vapor content and temperature. Thus, if a surface is maintained
at a known temperature lower than the sulfuric acid dew point,
but higher than the water dew point, the concentration of acid
condensate which occurs can be predicted from Figure 303 if the
water vapor content of the gas is known.
In addition to the procedure based on calculated partial
pressures, a number of efforts have been made to determine sul-
furic acid dew points using instrumental and chemical procedures.
710
-------
Two methods will be discussed briefly: the condensation method
and an electrical conductivity method.
The problem of measuring S03 concentration and acid dew
point has been studied since Johnstone300 examined the pro-
blem in 1929. Many papers301'312 have been presented which employ
the electrical conductivity method which Johnstone originated.
The_British Coal Utilization Research Association (BCURA) designed
an instrument which has found widespread usage employing Johnstone's
concept. This instrument, known as BCURA dew point meter, has
been described in detail by Flint.301 It is a portable instru-
ment which measures the conductivity of a condensing film. The
detector element is glass and contains two electrides mounted
flush with the surface. A tube inside the glass probe transports
compressed air which is used to maintain the glass surface of the
probe at the desired temperature. A thermocouple provides a read-
out of the glass surface temperature.
If an electrically conductive film forms on the detector
element, a current will flow that is proportional to the magnitude
of the externally impressed voltage and the conductivity of the
condensing film. The current flow is measured with a microammeter.
A dew point is determined by inserting the detector element into
a gas stream with the instrument temperature held at some value
above the dew point. The element temperature is then alternately
increased and decreased slowly to establish the exact temperature
'at which the increase in conductivity, and thus the dew point,
occurs.
The condensation method is widely used for determinations of
S03 in stack gases. The basic procedure employed consists of
pumping the flue gas through a condenser coil maintained below
the dew point of sulfuric acid, but above the normal water dew
point. A heated sampling probe is used to obtain the flue gas
samples, and a filter is inserted at the probe entrance to exclude
particulate matter. A fritted glass filter follows the condenser
to serve as a spray trap. When the sampling period is concluded,
the E2SOk is washed from the condenser, and the washings are col-
lected and titrated.313
The condensation of a binary vapor mixture from a noncon-
densable gas is normally path-dependent, and the composition of
the- vapor leaving a condenser is not fixed merely by stating that
the gas is saturated at a particular temperature. This is true
because the degree of fractionation occurring during condensation
depends on conditions which exist in the condenser. For the case
of H2SOu-H20 vapor mixtures in flue gas, however, the water vapor
is in large excess, and no appreciable change in its concentration
occurs until the water dew point is reached. The composition of
the gas is, therefore, not path-dependent, and the state of the
system is fixed if the gas is saturated with HjSCX at a certain
temperature and water vapor content. As a result, the condensation
711
-------
method can be used to obtain dew points of HsSO^-flue gas mixtures.
Since the gas leaving the condenser is saturated with EzSQu at
the condenser exit temperature, the.concentration of the exit
vapor represents the dew point,-"of'''saturation-"'temperature, of
the gas.
Figure 305 presents the results obtained for flue gas dew
points as a function of H2SCMg) content by various investigators.
To make an exact comparison, all of the curves should' be for a.
gas of the same volume percent water vapor. However, reference
to Figure 303 will indicate that a variation in water vapor concen-
trations from 7 to 10% can cause only about a 2.78 to 4.45°C (37- to
40°F) change in the dew point. Taylor's results -'ere obtained with
the BCURA dew point meter in a mixture of air, water vapor, and
sulfuric acid. Lisle's data were obtained using the condensa-
tion method, again with a mixture • of'air,,.water-vapor-, .-and-sulfuric .
acid.313 The dew point curves of Gmitro, Miill.er,,, and .from .Figure
303, are based on the previously discussed calculated rpartial
pressures.
It is obvious from Figure 305 that, except for Lisle and
Sensenbaugh's checks of the data based on Abel's sulfuric acid
partial pressures (Miiller's data and Figures 303 and 304), there
is little agreement between the results of the various investi-
gators. The data obtained from calculated partial pressures agree
in form, which is to be expected since the equations used to calcu-
late the partial pressures are also of the same form. The nature
of the disagreement between the calculated dew point and those
obtained with the dew point meter suggest there is a sensitivity
problem with the instrument at low sulfuric acid partial pressures.
In view of the difficulties with calculations based on liquid
phase thermodynamic properties and the probable inaccuracy of dew
point meters at low acid partial pressure, it can be concluded
that the only reliable method of correlating sulfuric acid dew
points with water and HaSO^ vapor concentration is a carefully
planned experimental program based on the condensation method
employed by Lisle and Sensenbaugh. In the absence of such data,
the dew points based on Abel's partial pressure data can be used,
since they have been verified in part by experiment and by the
operational experience of several power plants.
Condensation Characteristics
As stated previously, the amount of acid condensate predicted
from the use of a chart such as Figure 303 as a result of cooling
to a temperature below the sulfuric acid dew point is a prediction
of the amount available for condensation. Figure 306 shows that
the predicted percentage of HzSCu condensed increases and asymp-
totically approaches 100% as the temperature is lowered below the
dew point. However, peak values of acid deposition rates at temper-
atures between the water and acid dew points have been observed by
numerous investigators.
712
-------
ou
50
40
30
20
O.
a
g 1°
a.
> 8
V
O R
tft 0
CM
X
4
3
2
1
S\
^
^
D P. MULER CALCULATED
DATA POINTS 10% H2O
A.
8.
r
S
A. -
5% h
^
S
FAY
2°
'
LOR
^
-
J. . GMITRO ,
10% H2O J
>
X
f
/
/
/
J
1
I
J.
f
4.
l/i
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ri
f
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/
y
/
/
1
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I
/ A
1
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BEL AND
RENWALT -
0% H2O
S. LJ
- 9.
SLE
4% H
20
)
(
160 180 200 220 240 260 280 300
(70.6) (81.7) (92.8) (103.9) (115.0) (126.1) (137.3) (148.4)
DEW POINT, °F (°C)
3540-294
Figure 305.
HZ 304 dew.points obtained by various investiga-
tors.
713
-------
TEMPERATURE, °F (°C)
3540-295
Figure 306.
Percent H2 SO^ available for condensation 'for flue
gas of 100 ppm B2SO* and 10% H20 vapor (calculated
from Figure 303).
714
-------
The occurrence of such a peak in the condensation rate may
be caused by a change in the diffusivity of the E2SOk in the
region close to the condensing surface. The rate of condensation
is dependent on the diffusion rate of H2SCu and water vapor to the
surface. Small droplets of H2SCU will form in the cooled gas ad-
jacent to the surface, and the size of these droplets is likely to
increase with decreasing temperature. The growth of the droplets
would slow their diffusion to the surface and increase the prob-
ability that they would be carried forward in the gas stream. Thus,
a temperature can be reached at which the slowed diffusion becomes
dominant over the increased amount of condensate available for
collision with the surface. This explanation is similar to one
offered by Flint and Kear.305 A typical condensu-2 rate curve,
obtained in a spiral condenser with a vapor mixture consisting of
7.5 vol % H20, 69 ppm H2SOi», and the balance air, is shown in Fiquie
307.314
FACTORS INFLUENCING CORROSION RATES
Acid 'Strength " "•
If a flue gas is known to be saturated with H2SOi+ vapor at
a temperature below the acid dew point, it is possible to predict
the initial condensate composition as a function of the water
vapor partial pressure and temperature. Since data are available
in the literature concerning the corrosion rates of various ma-
terials as a function of acid concentrations, it is of interest
to determine whether there is any relationship between corrosion
rates measured in flue gas and the acid condensate strength pre-
dicted from a gas analysis.
A study of flue gas corrosion of low alloy steels by Piper
and Van Yliet315 provides data which illustrate the difficulty
encountered in predicting corrosion rates of metals from acid
condensate strength alone. The compositions of the low alloy
steel specimens used in this study are given in Table 50. The
corrosion tests were conducted by inserting specimens maintained
at known temperatures into stack gas produced from a pulverized-
fuel-fired steam generator. The average H2SOi» content of the
stack gas was about 30 ppm. Figure 308 gives the predicted sul-
fur ic. acid condensate compositions for the range of stack gas
water vapor concentrations experienced during the study.
Figure 309 shows the average corrosion rate of selected
steel specimens as a function of predicted H2SOu condensate
strength. The condensate strengths shown in Figures 308 and
309 were obtained from the computer printout of partial pressure
for the H2SOi*-H20 system, using Greenewalt's equation (equation
75) for the partial pressure of water over sulfuric acid solu-
tions. The widths of the surface in Figure 309 indicate the
possible acid concentrations at each temperature over the range
of water vapor partial pressures encountered in the stack gas.
715
-------
48
o
o
o
O
IN
32
16
50
75
100 125
TEMPERATURE, °C
150
175
S 5 4 0 -2 9 «
Figure 307.
Variation in condensation rate with surface
temperature (From H. D. Taylor).31lt
716
-------
TABLE 50. COMPOSITION, PERCENT BY WEIGHT, SPECTROGRAPHIC
ANALYSIS OF SPECIMENS TESTED (from Piper and
Van Vliet)3l5
Name
Cor- ten
NAX-A
NAX-B
NAX-C
Mn
0.40
0. 85
0. 82
0.53
Si
0.38
0.90
0.79
0.54
Cu
0.23
0.07
0.29
0.07
Ni
0.29
<0 . 1
<0. 1
<0 . 1
Cr
0.61
0.59
0.60
<0.1
Zr
—
Present
Present
Present
717
-------
154
o
o
D
<
cc
(310)
143
(290)
132
(270)
171
(250)
110
(230)
99
(210)
88
(190)
77
(170)
66
(150)
54
(130)
43
(110)
20
.
3
•
0
^*
4
7.5
^
*•*
0
VOL %
^
^^
5
H20
X^
X"
0
X
X
6
/
s >
5.1 V
0
/
'/
OL % I-
7
/ j
'A
I20
0
//
/
8
/
//
7
0
/
r
91
WEIGHT % H2S04 CONDENSATE
3540-297
Figure 308. Equilibrium sulfuric acid condensate composition.
718
-------
Ul
i 3
O
U)
O
e
cc
O
O
<
cc
5.1 VOL % H2O
(NAX - A, - B, • C,
(AND COR-TEN
7.5 VOL % H2O
1
25
30
35 40 45 50 55 60 65
CONDENSATE STRENGTH, weight percent H2SO4 3540-298
Figure 309.
Corrosion of steel in flue gas as a function of
calculated H2SOu condensate strength (corrosion
data from Piper and Van Vliet; HzSOt* data from
Greenewalt) .1l5 2"
719
-------
Figure 310 is a plot of corrosion rates of steel given by
M. G. Fontana316 at 2.3.4°C (75°F) as a function of acid concen-
tration. The corrosion rates for steel specimens immersed in
acid are orders of magnitude higher than those observed by Piper.
Since corrosion increases with temperature, the differences be-
tween the Fontana and Piper data are even greater than indicated
because the latter's data were obtained at high temperatures.
The low alloy steels used in the Piper study would not be
expected to exhibit greatly different corrosion rates in sulfuric
acid solution than the ordinary carbon steel on which Fontana's
data are based. Therefore, the orders of magnitude differences
in corrosion rates indicated are largely a reflection of the
differences in environment between the two situations. Another
contributing factor is the parabolic nature of the corrosion-time
relationship usually found in corrosion work. Thus, because of
the effects of fly ash and condensate deposition rates, it is not
practical to predict or correlate corrosion rates of materials in
flue gas solely on the basis of equilibrium condensate compositions.
Acid Deposition Rate
The corrosion rate of metal surfaces in flue gas at tempera-
tures well above the water dew point is more strongly related to
the amount of condensate deposited than to the concentration of
the condensate. Consider, for example, a steel surface at 126.1°C
(260°F) exposed to a flue gas with a bulk gas phase concentration
of 10 ppm sulfuric acid vapor and 10% water vapor. A condensate
strength of 77% HzSOi, would be expected, and if fly ash neutral-
izing ability is ignored, some nonzero rate of corrosion would be
expected. If the same steel surface were exposed to a similar
flue gas with 80 ppm sulfuric acid vapor, the predicted conden-
sate strength would remain at 77% H2SOi,r but the corrosion rate
would be greater because of the increased quantity of acid conden-
sate depositing on the metal. In both cases, decreasing the metal
surface temperatures.to a value approaching the water dew point
[37.3 to 42.8°C (100 to 110°P)] of the flue gas would result in
increased corrosion rates because of the highly corrosive dilute
acid formed at these temperatures.
The temperature at which the maximum condensation rate of
acid occurs has been correlated with the temperature of maximum
corrosion in flue gases. Figure 311 was taken from a study by
G. G. Thurlow, in which an air-cooled corrosion probe was exposed
to flue gas produced from burning a 0.8% sulfur coal.317 The
rate of sulfate deposition shows a peak at the same surface tem-
perature as the corrosion rate. This peak rate effect is often
not observed with coal firing, but Black310 and Clark311 have
found this phenomenon quite useful in correlating corrosion of
air preheaters in oil fired units. The sulfur content of the
fuel used in these studies ranged from 1.4 to 4.0%.
720
-------
10*
103
10'
o
-------
20
10
o
cc
t 20
£
LU*
H
LL
CO
10
0
160
(71)
200
(93)
I
240
(116)
280
(138)
320
(160)
SURFACE TEMPERATURE, °F (°C)
360
(182)
S 54 0-3 00
Figure 311.
Variation of condensation and corrosion with
surface temperature (data from Thurlow).3l7
722
-------
Black and Clark's work was done with the BCURA dew point
meter, and the peak rate of acid deposition was indicated by a
peak rate of increase in current, measured as microamps per
minute. The maximum corrosion rate is expected to occur in a
regenerative air preheater at the point where the average metal
temperature corresponds to the peak rate temperature indicated by
the BCURA meter. By superimposing a plot of the dew point meter
readings in the region of the peak over lines of average metal
temperature, it was possible to match the peak rate temperatures
with actual corrosion experience.
The above authors also found that the BCURA indication of
the acid dew point was a poor indicator of flue g-s corrosion
potential, particularly when oil and gas mixtures are fired. This
observation is not surprising since, as Figure 303 indicates, the
dew point alone does not specify how much acid is available for
condensation. The accuracy of the dew point meter may also be an
important factor, because instructions for use of the meter state318
that changes in dew point readings of less than 11°C (52°F) are not
to be regarded as significant. Referring again to Figure 303, a
change of dew point at 10% water vapor from 132 to 143°C (270 to
290°F) indicates a 370% increase in the H2S04 vapor content of
the flue gas.
Studies conducted by Lee, Freidrich and Mitchell,308 in
which the BCURA meter was employed with flue gas produced from
burning low sulfur lignite, showed that the meter was unable to
detect acid dew points with low sulfur coals. In one experiment,
no acid dew point was detected by the meter in the presence of
sulfuric acid vapor levels as high as 27 ppm. The author's ex-
plantation for this is that the condensed acid was completely
neutralized by. basic constituents in the fly ash.
Thus, since high fly ash resistivity is associated with low
sulfuric acid vapor concentrations, the BCURA meter is not likely
to be of value in assessing the low corrosion potential associated
with a flue gas containing high resistivity fly ash.
Fly Ash Alkalinity
Although fly ash can cause severe plugging problems in air
heaters, it is well established that alkaline ashes can neutralize
a portion of the SOs and HaSOi, occurring in stack gases, thereby
acting to reduce corrosion. Lee provides data which illustrate
the interaction of acid condensate with fly ash. Figure 312 illus-
trates the effect of surface temperature on acid condensation rate
when burning a 7% sulfur coal with 3% excess oxygen. The RBU
plotted on the y axis in the upper graph is a measure of the rate
of acid condensation when the BCURA dew point meter is maintained
at the indicated temperatures. Data for the lower graph were
obtained by isokinetically sampling the flue, gas and collecting
the fly ash and acid condensate in a Teflon vial maintained at
723
-------
600
a
a
I-
Z
Z
o
o
O
CO
to
LU
O
X
ui
Figure 312.
SURFACE TEMPERATURE, °F (°C)
3640-301
Variation in rate of acid buildup (RBU) and excess
cation content of fly ash as a function of surface
temperature. Coal contains 7% sulfur with 3%
excess O2 (data from Lee).307
724
-------
82, 100, 118, and 135°C (180, 212, 245, and 275°F). The contents
of the vial were then extracted, and the extract was analyzed for
acid or base content. If the extract pH was less than 7, the
solution was titrated with sodium hydroxide, and the results were
reported as a negative cation content. If the extract was basic,
the solution was titrated with HC1, and the results were reported
as an excess cation content, indicating that the condensed sul-
furic acid had been completely neutralized.
The acid neutralizing ability of fly ash with various base
contents is illustrated in Figure 313 for a flue gas with a typical
dust loading of 11.4 gm/scm (5 gr/scf). The parallel lines each
represent a base content of fly ash, expressed as milliequivalents
reactive base per gram fly ash. Data obtained on Contract CPA 70-
149 (A Study of Resistivity and Conditioning of Fly Ash) indicate
that fly ash produced from burning a high sulfur coal has as much
as 0.6 milliequivalents soluble base (1.7% CaO) per gram fly ash.319
This quantity of base is capable of neutralizing 80 ppm H2SOi» in
'the gas phase, assuming that the flue gas has an ash concentration
of 11.4 gm/scm (5 gr/scf). This is not to say that complete neu-
tralization will occur, since the degree of neutralization obtained
in the flue gas is a function of the rate of transfer of H2SOi»
to the fly ash particles and the rate of reaction occurring on
the particle surface.
Hydrochloric Acid
Sulfur, chlorine, and alkali metal compounds are associated
with high temperature corrosion in coal-fired boilers, but low
temperature corrosion is usually thought of only in terms of sul-
fur ic acid. However, metals with surface temperature below the
moisture dew point would be subjected to HCl attack if the chlorine
content of the coal is converted to HCl. Although not all of
the chlorine in coal appears as NaCl, it is of interest to examine
the chemical reactions undergone by NaCl in the combustion process.
The following discussion is taken from a study by Halstead3"0 in
which chloride and sulfate deposit .formations were examined with
probe tests and by thermodynamic calculations.
In pulverized coal firing, the NaCl can be expected to evapo-
rate and undergo some degree of vapor phase hydrolysis.
NaCl(g) + H20(g) = NaOH(g) + HCl(g)
The reactions of the chloride and NaOH with S02 to form Na2SOu are,
however, of greater importance. They are
2NaCl(g) + H20(g) + S02(g) + h02 (g) = Na2SOu(g) + 2HCl(g)
2NaOH(g) + S02(g) + hO2 (g) = Na2SC%(g) + H20(g)
725
-------
100
o" 10
111
V)
O
CJ
LU
in
<
ca
CO
<
1.0
0.1
i i r
,1
I ! I
0.1
10
ppm
100
3640-30J
Figure 313,
Consumption of the available base on fly ash as a
function of the concentration of neutralizing acid
in flue gas with 5 gr/scf fly ash.
726
-------
Halstead calculated the equilibrium partial pressures of
Na2SCK and NaCl in flue gases produced from burning the coals
listed_in Table 51 at 5% 02 excess, stoichiometric 02, and 2%
02 deficient. These calculations, together with deposition
studies conducted with a cooled probe, indicate that almost
total conversion of NaCl to Na2SOlt takes place with 3 to 5% ex-
cess oxygen in large bpilers with good mixing of fuel and air.
With lower oxygen levels, and when poor mixing and short resi-
dence times are encountered, the conversion of NaCl to Na2S0lt
may be incomplete.
Thus, it can be seen that significant concentrations of HCl
are likely to result from the combustion of chlorine-containing
coal. The subject of HCl corrosion in flue gases has received
comparatively little attention in the literature because it is
not likely to occur unless temperatures near the water dew point
are encountered. Air preheater elements, however, can drop below
the moisture dew point if excessive water vapor, such as would
occur from a steam leak, is present.
'-"• Figure 314, taken from a stady by R. W. Kear,321 illustrates
the effect of HCl in a flue gas on corrosion of a test probe.
This experiment was conducted using an apparatus which produced
a synthetic flue gas by addition of S02 and C12 to the fuel supply
of a small laboratory burner. Analysis of the flue gas indicated
that all chlorine was converted to HCl, resulting in 400 ppm HCl
by volume. It should be noted, however, that corrosion could be
caused by the presence of chlorine gas. The assumption that
Figure 3l4 is an illustration of the effect of HCl gas is there-
fore dependent upon Kear's conclusion that all chlorine is con-
verted to HCl in the burner flame. The SOa , or H2SOit, content of
this gas was reported as 36 ppm. The temperature at which the
corrosion rate- accelerates corresponds to the water dew point of
the synthetic flue gas, which is about 7% by volume water vapor.
When the metal surface temperature is above the water dew point,
the presence of HCl has no effect on .corrosion, but it can be
seen from Figure 314 that drastic increases in corrosion occur
due to HCl as the metal surface falls below the water dew'point.
The corrosion probe was exposed for a 30-minute period in each
experiment.
Data obtained.by Piper and Van Vliet315 confirm Rear's re-
sults. Piper's data were obtained by exposing metal condensers,
which could be cooled to selected temperatures, to flue gas pro-
duced from burning a 0.066% chloride coal. Analysis of the flue
gas showed that HCl concentrations ranged from 16 to 82 ppm, and
•the sulfuric acid vapor concentration averaged 30 ppm. The re-
lative rates of corrosion of low alloy steel specimens maintained
at 71, 60, 46, and V30°C (161, 141, 115, and 87*F) for 2-month
exposures were 1., 1,; 3., and 66, respectively- The water dew
point -of the flue gas during the exposure period ranged from
32 to 40°C (91 to 104°F) . It is thus apparent-that the rate of
727
-------
TABLE 51. SULFUR AND CHLORINE CONCENTRATIONS
IN FLUE GAS (from Halstead)320
3 3
Sulfur in Chlorine in Sulfur compounds Chlorine compounds
coal coal in flue gas ir. flue gas
vol ppm vol ppm
0. 8
1.2
1. 8
0.
0.
0.
8
4
07
750
1100
1700
680
340
60
a. Calculated by assuming complete volatilization of all sulfur
and chlorine in coal and one atom of sulfur or chlorine present
in each gas molecule.
728
-------
0.1% OF S02 + 0.02% OF C\2 IN
FLUE GAS
0.1% OF SO2 IN FLUE GAS
30 40
60 70 80 90 100 110 120 130 140 150
SURFACE TEMPERATURE, °C 35*0-303
Figure 314.
The effect of chlorine addition or corrosion
of mild steel in a synthetic flue gas (from
R. W. Kear).32'
-------
attack greatly accelerated below the water dew point. This cor-
rosion is a result of both H2SCK and HCl, but the importance of
the effect of HCl is indicated by the fact that at the water
dew point, the chemical equivalents of chloride exceeded those
of sulphate. Another important observation of the Piper study
was that a vitreous enamel coating on Cor-Ten,. which was used
in a pilot-plant air preheater, was considerably attacked at
temperatures below the water dew point.
Since high resistivity fly ash usually occurs in the absence
of sulfuric acid vapor, it is of interest to consider such a
situation in which appreciable concentrations of HCl- exist. Piper
analyzed the vapor-liquid equilibria data for the system HCl-HaO,
and concluded that, with an HCl vapor concentra-ion1 of 82 ppm,
the hydrochloric acid dew point would be 3.9°C (39°F) above the
water dew point. A similar analysis of the water-S02 system in-
dicated that the sulfurous acid dew point, for a stack gas with
about 1900 ppm SOz and typical water vapor concentrations, would
be the same as the water dew point.
FOULING OF LOW TEMPERATURE SURFACES
Deposit formation, or fouling, in air heater elements is a
combination of chemical and physical processes. At 600 to 700°F,
which is the range of temperature normally encountered at the hot
end of regenerative air heaters, the saturation partial pressure
of the mineral components of fly ash is extremely low. Thus
deposit formation in this region is not a result of condensation
from the vapor phase, but is instead a mechanical process in which
slag and refractory material are carried by the flue gas into the
air heater elements. These particles can lodge within the passages
of hot end elements and thereby accumulate additional deposits of
finer dust particles.322 Procedures are reported in the literature
for removing such deposits.
If the flue gas contain^ appreciable amounts of H2S04, corrosion
and deposit buildup will occur simultaneously in the cooler regions
of the air heater. The following reaction will occur on steel
surfaces which are below the H2SOi, dew point.
Fe + H2SOi, -* FeSOu + H2
The ferrous sulfate can then oxidize to form ferric sulfate.
+ 02 -* 2Fe2(SOi»)3 + 2H20
An extensive study of regenerative air heater deposits by the
Bureau of Mines324 found that deposits built up in thickness at
the cold end of the air heater, and that this area was the prin-
cipal region of corrosion and destruction of the element. All
deposits found in this area exhibited the following characteristics:
partial solubility in water, presence of sulfates, and acidity.
730
-------
The solubilities in water of these deposits varied over a wide
range—13 to 98%. Deposits with highest solubilities were found
on preheater test plates which were most severely attacked by
acid. Some of the variations in deposit solubility were attri-
buted to variations in the ability of the deposits to trap fly
ash.
Reaction of the ferrous and ferric salts formed during cor-
rosion with alkaline compounds sometimes used in washing air heaters
can produce compounds that will result in additional fouling.
Ferric sulfate, for example, can undergo the following reactions.323
Fe2(SOi,)3 + 3Ca(OH)2 (lime) •»• 2Fe(OH)3 -r SCaSO.,
Fe2(SOi,)3 + 6NaOH •*• 2Fe(OH)3 + 3Na2SOu
Fe2(SCU)3 + 3Na2C03(soda ash) + 3H2O -> 2Fe(OH)3 + 3Na2SCK
+ 3C02
The Fe(OH)3 (ferric hydroxide) is undesirable because it is a
sticky, gelatinous precipitate which can cause severe fouling.
The above reactions indicate that, in washing air heater elements
or tubes, removing the soluble sulfates with a neutral water wash
is desirable prior to a caustic wash.
It is important to note that deposit formation can occur in
air heater elements in the absence of significant amounts of H2SOif.
Chemical analysis of deposits from air heaters installed in some
lignite-burning power stations has revealed no chemical evidence
of deposition. In one instance, moisture from steam cleaning
action was found to be responsible for trapping ash deposits. De-
posits formed in this manner are similar to cement and very difficult
to remove.
In.the absence of moisture and acid condensate problems, the
nature of the fouling mechanisms discussed herein suggests that
lowered cold end temperature would not result in increased deposit
formation.
LABORATORY CORROSION STUDIES319
Samples of fly ash were obtained for corrosion studies from
the precipitator hoppers of two plants with high dust resistivity
problems. These ash samples have widely different soluble base
contents, as can be seen from Table 52. Sulfur contents of the
coal burned in the two plants range from 0.6 to 1.0%. Laboratory
experiments were conducted to determine whether deposited layers
of these ashes exhibit differing capabilities for neutralizing
acid and inhibiting corrosion.
731
-------
TABLE 52. FLY ASH PROPERTIES
-j
to
Neutral (from Plant 1)
As received
Following experiment
(Experiment 4, Table 6.4)
Basic (from Plant 6)
As received
Following experiment
(Experiment 3, Table 6.4)
pH of
suspension
6.70
1.69
12.25
8.72
Soluble
sulfate
wt %
0. 31
23.4
1.2
23.1
Soluble base
as CaO
meg/g wt %
0 0
0 0
2.7 7.6
Not deter-
mined
Mass median
particle
diameter, y
38
18
-------
A schematic diagram of the apparatus used for the experiments
is given in Figure 315, and the data obtained are presented in Tables
52 and 53. The corrosion specimen was a 2.54 cm (1 in.) diameter
mild steel disc, and the amount of corrosion occurring as a result
of exposure to HZSCU was determined by measuring the weight loss.
The_experiments in Table 53 can be divided into two groups.
In Experiments 1 through 4, the acid condensation rate on the disc
was relatively low, but high condensation rates were achieved in
Experiments 5 through 10 by increasing the strength of oleum used
as an SOs vapor source and by lowering the temperature of the
water bath. Water vapor concentrations of 2 - 2.5% by volume were
provided by the water spargers. Since the air streams bearing
H20 and S03 vapor mix in the heated glass "T", a saturated mixture
of air and H2SOu is formed, and the condensation rate will depend
on the temperature of the condensing surface and the concentration
of HaSOi, in the gas phase. For both sets of experimental con-
ditions, an examination of the corrosion rates (meq basis) and
acid deposition rates in Table 53 shows that an excess of acid
was present with respect to the amount of iron corroded in all
experiments.
For the experiments with fly ash, the ash was deposited in
the sample container in such a manner that the disc was covered
to a thickness of approximately 0.2 mm. Acid did not sufficiently
penetrate the ash to reach the underside of the disc in Experiments
3 and 4, and the penetration rates were calculated on the basis of
one side only. Corrosion was observed on both sides in all other
experiments; therefore, the total area of both disc surfaces was
used as a basis of calculation.
A comparison of data from Experiment 3 with those from Ex-
periment 4 indicates that the basic fly ash was more effective in
reducing corrosion than the neutral ash. The equilibrium pH values
of the ash samples prior to and following these experiments are
given in Table 52. As would be expected, the neutral ash slurry
is much more acidic than that of the basic ash after both have
experienced an equivalent sulfate gain due to HzSOu condensation.
The fact that the basic ash produced a pH greater than 7 following
the experiment shows that it was capable of neutralizing all of
the condensed acid. Complete neutralization did not occur, until
the acid-ash mixture was slurried in water, however, as evidenced
by the measurable degree of corrosion which occurred in Experiment
3.
For the experiments with low acid condensation rates, both
the neutral and basic ash deposits reduced the weight loss rate of
the disc, but the penetration rate calculated for Experiment 4
(neutral ash) is not significantly different from those of Ex-
periments 1 and 2 (no ash). These results are to be expected,
since the neutral character of the material from Plant 1 indicates
that any corrosion inhibiting, value which it-exhibits is likely
to be the result of physical rather than chemical factors.
733
-------
ROTOMETER
ROTOMETER.
ROOM AIR-
SPARGERS
HEATING
TAPE,
THERMOSTATED
H,O BATH '
3 x 3/4 IN. DIA x 6 IN. DRYING
TUBES WITH 8-MESH DRIERITE
MAGNETIC STIRRERS AT LOW SPEED
1=120 rpm)
THERMOCOUPLE
LEAD
MIST ELIMINATOR
o_ ^THERMOCOUPLE
STEEL DISC
THERMOMETER
ROOM AIR
CHARCOAL TEST
METER
VACUUM PUMP
3640-304
Figure 315. Schematic diagram of apparatus used in corrosion
experiments.
734
-------
TABLE 53. CQKKOSION RATE EXPERIMENTS
Experiment
No.
1
2
3
4
5
6
7
8
9
10
II2SOi,
Vapor Condensate
Generator, Duration Composition
% Acid Used Ilr wt % HjSO,, C
104
104
104
104
107
107
107
107
107
107
2
1
2
2
1
1
1
1
1
1
.0
.9
.1
.0
.0
.0
.0
.0
.0
.0
56 195
52 193
198
212
36 176
40 190
198
200
199
198
II2SO..
Temperature, °C (°F) Condensate
lag
(383)
(379)
(388)
(412)
(349)
(374)
(388)
(392)
(390)
(388)
Water
Bath
25
29
26
26
2.8
3.9
2.8
2.8
2.2
3.9
(78)
(84)
(79)
(79)
(37)
(39)
(37)
(37)
(36)
(39)
Disc
Surface
—
--
--
—
32
25
35
30
30
27
—
--
--
--
(90)
(77)
(95)
(86)
(86)
(81)
Rate
ineg/hr
--
1.
1.
1.
5.
6.
10.
8.
12.
12.
3
5
6
0
0
1
6
4
4
H2SO.,
Reacting
Apparent Corrosion Rate Ash With Disc
mg/hr
1.05
0.90
0.20
0.40
32
32
18
17
53
41
me
0
0
0
0
1
1
0
0
2
2
g/hrD
.056
.048
.011
.022
.7
.7
.97
.91
.8
.2
mils/yr Layer
46
39
17a
34a
1400
1400
790
740
2300
1800
None
None
Basic
Neutral
None
None
Basic
Basic
Neutral
Neutral
Wt %
--
3.7
0.7
1.4
34
28
10
11
23
18
a. Based ori exposure of one side of disc to acid rather than both sides as in all other runs.
b. Assuming formation of Fe2(SOi,)3.
-------
High corrosion rates were obtained in Experiments 5 through
10 due to increased acid condensation rates and decreased conden-
sate composition. The high percentage of H2SOu reacting with the
disc in these experiments is an indication of the greater corrosive-
ness of acid in the 36 - 40 wt % range. Some difficulty was en-
countered in maintaining constant experimental conditions, as
indicated by variations in the disc surface temperatures and the
acid condensation rate's. Once again, the data suggest that the
neutral ash has little corrosion inhibiting value, but signifi-
cantly lower corrosion rates were obtained with the basic ash.
In contrast to the conditions of Experiment 3, an excess of acid
was present with respect to the base content of the ash layer for
Experiments 7 and 8. If it is assumed that the same amount of
base reacts per unit weight of basic ash in both sets of experi-
ments, it can be shown that less than 30% of the condensing acid
could have been neutralized in Experiments 7 and 8. The princip.a.
mechanism by which corrosion rates were reduced in Experiments 7
and 8 appeared to be the formation of a cement-like "deposit which
reduced the amount of acid reaching the metal surface. Such de-
posits would be likely to cause plugging of air -heater elements
in plant operation.
Generalizations concerning the direct effect of basic and
neutral fly ashes on corrosion rates from these experiments are
hazardous because of the complex nature of the corrosion process.
However, it is possible to draw some conclusions regarding the
interaction of the fly ash with condensing acid.
The reduced corrosion rate obtained in Experiment 3 indicates
that the basic fly ash from Plant 6 neutralized a major portion
of the acid a_s it. condensed. This is an important observation
because the data obtained has revealed the presence of unreacted
acid on the surface of fly ash containing amounts of water soluble
base substantially in excess of the apparent surface acidity. Thus,
basic ash deposited on metal surfaces could conceivably present an
acidic, and hence corrosive, environment to a metal surface and
exhibit little or no neutralizing capability. A layer of CaSOi*,
formed by reaction between HaSOi* and CaO, apparently can prevent
the underlying soluble base from being utilized. The ash from
Plant 6 contained appreciable sulfate when received from the pre-
cipitator hoppers (1.2%), but the experimental data presented here
indicate that the sulfate did not present an impermeable barrier
to the liquid condensate.
The neutral ash from Plant 1 would not be expected to pro-
vide a significant degree of protection from condensing acid, and
the experimental data tend to confirm this. However, even a
neutral ash can reduce the amount of acid available for corrosion
in a flue gas by adsorbing SO3. The small amount of sulfate (0.31%)
present on the ash from Plant 1 when received indicates that some
adsorption of SO3 at high temperatures occurred. The operating
temperature of the precipitator at Plant 1 is about 160°C (320 F),
which is well above the H2SOi» dew point.
736
-------
In conclusion, then, the data from these experiments indicate
that a basic ash such as that from Plant 6 can be of significant
value in neutralizing condensed acid and reducing air heater cor-
rosion rates. However, in the presence of an excess of condensing
acid, serious deposit formation problems could be expected. The
neutral ash was of little or no apparent value in reducing corrosion
rates, but it exhibited a lesser tendency to form cement-like
deposits than did the basic material. The most important benefit
to^be expected from the presence of a basic fly ash from the stand-
point of corrosion is the consumption of SOs by the basic material
in the high temperature region prior to the air heater. Unfortunately,
this also creates a high resistivity problem for precipitators op-
erating in the 148°C (300°F) range.
SUMMARY OF FIELD EXPERIENCE AND PLANT DATA292
Table 54 is a compilation of available data from a number of
power plants concerning fly ash, flue gas and coal composition, and
fly ash resistivity. The data reported in this table were either
obtained by SoRI personnel under Contracts CPA 70-149 and CPA 70-166
sponsored by the U.S. Environmental Protection Agency or made avail-
able to SoRI by the utility companies.
Of all the plants listed in Table 54, only Plants 10 and 9
have experienced significant air heater corrosion problems. As the
following discussion will indicate, the factors that result in
high resistivity fly ash usually indicate that no corrosion pro-
blems are to be expected.
The ash samples for which analyses are given in Table 54 were
either collected from the precipitator hoppers or obtained with a
resistivity apparatus at the precipitator inlet. The values of
pH and free acid obtained in a 95% ethanol slurry, which are given
for selected samples, are an indiation of acid present on the sur-
face of the ash. Samples which show an acidic pH in 95% ethanol
generally exhibit a minimum pH in water, followed by a rise to a
basic equilibrium value as the water soluble base is dissolved.
The presence of significant amounts of unreacted acid on the ash
surface is thought to be an indication that the fly ash has been
"conditioned" by sulfuric acid.
Data for S02 - SO3 were obtained by SoRI personnel using
procedures described elsewhere.319 Resistivity data were also
obtained by SoRI using either a point-plane or cyclone resistivity
apparatus, with the exceptions of Plants 6 and 11. For these two
plants, the data were given to SoRI by the operating utilities.
Plant 6 has successfully overcome a high dust resistivity
problem by lowering the precipitator operating temperature to
about 104°C (220°F) at full load. An inspection of the low temper-
ature zone of this installation was conducted while the unit was
off the line for routine maintenance. This plant had nine months
of operation with low gas temperatures.
737
-------
TABLE 54.
Fly Ash Analysis
PROPERTIES OF FLUE GAS AND FLY ASH
FOR VARIOUS COAL-FIRED BOILERS
Flue Gas Analysis
Coal Analysis
(Dry Basis)
Plant Sulfur
Designation %
6 0.
1.
1 0.
2a 0.
11 0.
o 8-3a 0.
5 0.
1.
7a 2.
4 3.
9a,b _3
I0a'b 3.
7-
0
6
5
5
5
95-
90
1
6
5
2
Ash
8.5
12
5.9
15-25
8.6
15.8-
16.0
21.9
16.4
-14
11.2
Water Slurry Etlianol Slurry
pll
12.2
8.2
11.1
11.2
9.4
9.4
5.1
11.0
9.8
6.4
Sol base
as CaO
7.6
Negligible
2.10
1.50
0.35
0.19
0
1.65
0.35
0
Free acid
Sol SO,, as H2SOi,
% pll %
1.2 >9.1 0
0.23 4.6 0.008
1.50 8.1 0
0.17
0.77
0.41-
0.47
0.36
0.77 3.8 0.037
1.15 3.9 0.088
0.40 4.4 0.02
Precipitator Inlet
S02 I
vol ppm
--
375
387
--
365
610-
1030
1650
2680
--
—
(Wet Basis)
l2SOu vapor !12O T
vol ppm vol %
10.7 1
1
<1 7.7 1
<1 8.9 3
4
<1 7.7 1
0.8- 7.0 3
4.4 1
8.7 5.7 1
2
15 •. 8.0 1
— 1
— i —
ypical Fly Ash Resistivity
Si -cm
.9
.0
.9
.8
.5
.0
X
.5
.0
.0
.0
.0
X
X
X
X
X
X
10
X
X
X
X
X
10"
10".
10)2
1012
10"
10'2
1 1_
1012
1012
10"
10"
10'
temp
150
104
160
135
110
154
124-
160
160
149
142
143
— —
C ("F)
(302)
(220)
(320)
(275)
(230)
(309)
(256-)
(319)
(319)
(300)
(287)
(290)
a. Precipitator preceded by mechanical collector.
b. Corrosion of air heater has occurred.
-------
^ areas examined for evidence of corrosion were the cold
and intermediate zones of the air heater elements, the plates and
wires in the precipitator, and the sides of the duct encompassing
the precipitator assembly. No evidence of corrosion was found in
the air heater elements. Thin deposits were noted in some areas
of the cold-end elements, but these were insufficient to cause
measurable draft losses. Minor corrosion was observed on the
perforated plate distributors at the precipitator inlet. The
rusted areas corresponded to regions of low gas velocity caused
by duct geometry. The only significant corrosion in the entire
assembly was found on the under side of the top plate of the
precipitator housing. The top side of this plate is exposed to
streams of low temperature bleed air from the plant exterior,
and it is probable that temperatures below the wa-.er dew point
were reached. The purpose of the bleed air is to maintain a
positive pressure for prevention of dust buildup on the rapper
bushings.
There as no direct measurement of S03 at Plant 6, but mea-
surements from Plant 2, which uses a similar fuel, show that SO3
levels above and below the air heater are less than 1 ppm. The
soluble sulfate content of fly ash taken from the precipitator
hoppers of Plant 6, if a dust concentration of 3.4 gm/m^ (1.5
gr/ft3) is assumed, is equivalent to an SOa concentration of 10
ppm. It is possible, however, that a "portion of the sulfate
originated from oxidation of S02 on the ash surface rather than
from S03 in the bulk gas phase. Figure 303 shows that the dew
point of a flue gas with 10 ppm SOa and 10.7% water vapor is
estimated as 135°C (275°F). The minimum cold end average
temperature of the air heater at Plant 6 is 60°C (140°F). It
is therefore probable that some acid condensation, and possibly
corrosion, would have occurred if the basic ash had not been
present to combine with the SO3 in the high temperature zone
prior to the air heater, thus preventing the formation of HaSOi*
vapor in the air heater region. Furthermore, the data in Tables
52 and 53 and the lack of surface acidity indicated in Table 54
show that any H2SOi» which may form in the air heater region is
likely to be neutralized.
In view of the known dependence of fly ash resistivity on
temperature and the presence of H2SOn on the fly ash surface,
the hypothesis of negligible H2S04 in the low temperature zone
at Plant 6 may seem inconsistent with the decrease in resistivity
with temperature which occurs at this installation. This apparent
inconsistency can be qualitatively resolved by attributing the
resistivity behavior to increasing adsorption of water vapor on
the fly ash surface with decreasing temperature. It is also
possible that oxidation of S02 to SO3 occurs on the ash surface,
and provides surface HaSOu. for conditioning for a brief time
period, after which the acid is.-neutralized. The following re-
action sequence may be used to represent this hypothesis.
739
-------
so2 (g) + ho2 (g) •* S03 (g)
S03(g) + H20(g) •> H2SCMg) •*-»• H2SOi, (1)
H2SCMg or 1) + CaO(s) -> CaSOu(s) + H2O(g)
Thus, by adsorption of, water and/or surface formation of 80s, it
is possible to explain the lowering of resistivity with decreasing
temperature in the absence of appreciable SO3 concentrations in
the bulk gas phase.
Plant 11 and Plant 10 are the other plants listed in Table
54 with lowered cold-end temperatures. Plant 11 operates" with
a low sulfur coal which produced a highly basic fly ash with a
high resistivity. No corrosion problems have been experienced at
this installation, as would be expected. Precipitator inlet
temperatures range from 110-122°C (230-253°F).
Plant 10 has operated with precipitator inlet temperatures
from 108-118°C (228-246°F). Excessive deterioration of air heater
cold end elements occurred when gas temperatures were lowered to
108°C (228°F), and as a result, operating temperature has now been
raised to 117-118°C (243-246°F). "The reason for lowering the exit
temperature was said to be a desire to increase boiler efficiency
rather than a need to lower fly ash resistivity. Fly ash and coal
samples supplied to SoRI were analyzed and are reported in Table
54o However, the sulfur content of the coal normally used was
reported by the utility to be 1.2-1.35%. Analysis of the fly ash
indicates a neutral ash similar to that from Plant 1, and little
or no acid neutralizing ability would be expected. The low sulfate
content indicates that, in spite of the high sulfur content of the
coal and the relatively low temperature at which the ash was col-
lected, a comparatively small amount of H2SOi» is collected by the
ash. From the ash content of the coal, the mass loading at Plant
10 is estimated, prior to the mechanical collector, as 6.9 gm/scm
(3 gr/scf),326 and the sulfate content of the fly ash is equivalent
to only 6.4 ppm H2SOu. It is therefore probable that most of the
H2SOi, formed from the combustion of this relatively high sulfur
coal remained in the gas phase and was available for condensation.
Although there are no resistivity measurements from Plant 10,
it is possible to infer from the coal and fly ash analysis that
a low resistivity fly ash (significantly less than 2 x 1010 fi-cm)
is probable at this installation at the precipitator operating
temperatures. It has been shown from studies of H2SOi, conditioning
under EPA Contract CPA 70-149 at Plant 1 that a sulfate gain of only
0.1-0.2% due to adsorption or condensation of H2SCU is sufficient
to lower resistivity by two orders of magnitude for a neutral fly
ash.326a
Plants 9 and 4 normally operate with a high sulfur coal, and
typical air heater exit temperatures for both units range from
740
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135-140 C (275-285 F). These plants have low fly ash resistivities
at normal operating temperatures, and at times the resistivity value
at Plant 4 has been too low for proper precipitator operation with
high gas velocity. The cold-end portion of the air heaters at
both of these installations operates below the acid dew point, but
the corrosion experience has been somewhat different. Plant 4 has
an average cold-end temperature of about 93°C (200°F), and Figure
303 shows that most of the H2SOi4 vapor is available for condensation
at this temperature. Furthermore, measurements of S03 before and
after the air heater have indicated, on at least one occasion, a
significant drop in S03 concentration across the heater. It is
therefore probable that significant amounts of H2SCH are condensed,
either on the ash in the cool boundary layer adjarent to the metal
surface, or on the metal surface itself. In spite of this fact,
the cold-end baskets (made of low-alloy steel) have been in service
for at least ten years at Plant 4 without requiring replacement.
Table 54 shows that the fly ash at this unit is highly basic, and
would be expected to have significant acid neutralizing ability.
"However, the presence of surface acidity, as indicated by data
obtained in a 95% ethanol slurry, suggests that a sulfate layer
on the ash is preventing a portion of the water soluble base from
being utilized.
Plant 9 has required some replacement of cold-end air heater
elements, but not at an excessive rate. The data in Table 54
indicate that the fly ash from Plant 9 is less basic than that
from Plant 4, but the presence of a mechanical collector at Plant
9 makes a direct comparison of the two fly ash analyses difficult
because of the difference in particle size distribution. It is,
however, reasonable to conclude that without the presence of the
basic fly ashes at both installations, corrosion would have been
more severe.
Plant 7 operates at high air heater exit temperatures with
an intermediate sulfur coal. The resistivity values indicated
in Table 54 for this plant would be classified as high, but the
near-neutral character of the ash, together with the presence of
appreciable concentrations of HaSOu vapor in the gas phase and
the slope of the resistivity temperature curve, suggest that
acceptable resistivity values would occur at about 137°C (280°F) .
With an 26°C (80°F) inlet air side temperature, this would give
a cold-end average of 82°C (180°F) for the air heater. The Air
Preheater Company's cold-end temperature and material selection
guide gives a suggested minimum average cold-end temperature of
about 71°C (160°F) for a coal of 2.1% sulfur content and corrosion-
resistant, low-alloy steel cold end elements.327 Some degree of
corrosion may occur because the cold-end metal temperatures fall
appreciably below the acid dew point, and because the neutral ash
at Plant 7 could be expected to have no significant acid neutralizing
ability. However, the experience of the Air Preheater Company as
represented by their materials and temperature guide, and the lack
of excessive HaSOi* vapor concentrations found at 148-160°C (300-320°F)
741
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are indications that a severe corrosion problem should not occur
at Plant 7 with the presently used fuel if air heater exit tem-
peratures as low as 137°C (280°F) were employed.
The corrosion experience of Plant 5 (Unit 1)- is of interest
because the average air heater exit temperature is .'about- 126 °C -'•• "
(260°F) . Sulfur content of the coal normally bur.ned at this unit
is approximately 1%, and a typical dust load would be 8.5 gm/scm
(3.7 gr/scf). Coal composition varied during the time period in
which resistivity data were taken, and possibly as a result, the
resistivity data show considerable scatter and no strong variation
with temperature. Nonetheless, the relatively high resistivity
values are to be expected on the basis of the COB! sulfur content
and the moderately basic character of the fly ash. No corrosion.
problems have occurred at this unit, and none would be expected
with the relatively low H2SOi4 vapor concentrations which were
measured.
Plants 8-3 and 2 are typical o.f'Installations burning very
low sulfur coal; that is, no appreciable EzSO^ vapor concentrations
are found in the bulk gas phase, the fly ash produces a basic water
slurry, and the resistivity is unfavorably high in the normal oper-
ating temperature range of 135-148°C (275-3Q06F).
If the design of these plants were such that operation in the
104-115°C (220-240°F) range were possible, no corrosion problems
would be expected because of the absence of H2SOi» vapor. Unfor-
tunately, there is not a sufficient quantitative knowledge of the
relationship between resistivity and temperature to predict with
confidence that low temperature operation at these installations
would produce resistivity below the critical value of 2 x 1010 fi-cm.
The fact that the flue gas water concentrations at Plants 2 and 8-3
are about 30% 'lower than that at Plant 6 is an unfavorable condition
for achieving lowered resistivity. However, the fly ashes from
Plants 2 and 8-3, and in particular, that from Plant 8-3, are less
basic than the ash produced at Plant 6. Data obtained under Con-
tract CPA 70-149 indicate that a highly basic ash requires a
greater gain of HjSOu, either by condensation or adsorption, to
lower resistivity than does a neutral ash. Thus, if lowering of
resistivity is due to the combined effects of water adsorption and
the formation of SOs on a fly ash surface discussed earlier, it
could be argued that the resistivity of the extremely basic ash
of Plant 6 would show less sensitivity to decreasing temperature
than the fly ash at Plants 2 and 8-3. Since the variables of ash
composition and flue gas water concentrations indicate opposing
effects when comparing Plant 6 with Plants 2 and 8-3, it would
be hazardous to equate the resistivity-temperature experience of
Plant 6 with the other two installations.
METHODS OF ASSESSING CORROSION TENDENCIES OF FLUE GASES
Introduction
742
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A comprehensive discussion of methods developed in England
for assessing the corrosion and fouling potential of flue gases
is given in a bulletin entitled, "Testing Techniques for Deter-
mining the Corrosive and Fouling Tendencies of Boiler Flue Gases"
published by the Boiler Availability Committee.318 The following
discussion is a brief summary of the purpose and method of oper-
ation of those procedures which relate to low temperature corrosion
and fouling,
Corrosion Probes
The purpose of corrosion probes is to measure the amount of
corrosion produced by acid condensed on metal surfaces in a flue
gas environment. These probes provide a means of supporting a
prepared metal test specimen in flue gas streams at a selected
temperature. The BCURA probe is an air-cooled device in which
the surface temperature of the test specimen is monitored with a
thermocouple brazed to the body of the probe. Exposure periods
of 15-30 minutes are recommended, and the amount of corrosion is
determined by measuring weight loss of the specimen.
Probes designed for short term experiments are of value for
comparing relative effects of variations in operating parameters,
such as temperature and fuel composition. However, for prediction
of actual corrosion rates over extended periods, long term tests
of 100 hours or more are desirable. A liquid-cooled probe has
been designed by the Sheel Petroleum Company, Ltd., for such ex-
tended experiments.3 2 8
Acid Deposition Probes
An indirect measurement of the rate of acid deposition on a
cooled surface is given by the BCURA dew point meter, which has
been described previously. Since the conductivity readings of
the dew point meter can be influenced by substances other than
sulfuric acid, it is of interest to consider a direct means of
measuring acid.deposition rates.
Alexander329 has described an air-cooled deposition probe
which accomplishes this purpose. The probe consists of an air-
cooled, one-inch diameter stainless steel tube in which the cooling
air passes through the tube and discharges into the flue gas. The
amount of acid depositing on test areas of the probe, the surface
temperature of which is known, is determined by analysis of de-
posits obtained from the test surfaces.
Gas And Ash Analysis
An analysis of flue gas for S03, S02, H20, and dust loading,
along with analysis of the fly ash for soluble components, is_
necessary for a qualitative assessment of the flue gas corrosion
potential. Procedures used by SoRI for these analyses are described
in the final report from Contract CPA 70-149.319
743
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SUMMARY AND CONCLUSIONS
It has been established that.-the principal cause of corrosion
in the low temperature zone of power plant exhaust systems is
condensation of sulfuric acid, either directly onto metal sur-
faces or onto fly ash particles which subsequently come in contact
with the metal. Other, acids, in particular hydrochloric acid, can
be responsible for corrosion at temperatures approaching the water
dew point of flue gas, but such temperatures are not normally en-
countered.
Fouling in the low temperature zone of air heaters - is primarily
caused by reaction of sulfuric acid with fly ash and the metal
surfaces of the heat exchanger. A basic fly ash can neutralize
appreciable quantities of SO3 upstream from the air heater region
but laboratory experiments suggest that reaction.-pf highly basic
fly ashes with high concentrations of "-H'zSOir- in" the 'low'- temperature
zone can result in problems with deposit formation. This conclusion
is supported by the experience, of the Central-'Electricity Generating
Board of England, in which medium sulfur coals with alkaline ashes
have produced fouling,330 but little air heater wastage accompanied
the deposit formation. It is also possible to have deposit for-
mation in the low temperature zone in the absence of sulfuric acid
if excessive moisture from steam leaks or soot blowing is present.
Severe corrosion and fouling problems in regenerative air
heaters are associated with the temperature at which peak rates
in acid deposition occur. These peak rates often are not observed
with coal firing due to the presence of fly ash, but in any case,
the existence of such a peak is a manifestation of relatively
high concentrations of free H2SOi, vapor. Thus, the resistivity
of fly ash, due to the presence of excessive H2SOi,, would be ex-
pected to be lower than desirable for proper precipitator operation
with high gas velocity under these conditions. Resistivity data
taken at plants burning high sulfur coals with alkaline fly ashes
have demonstrated that resistivity values below the critical 2 x
1010 fi-cm are obtained at temperatures above 137°C (280°F). There-
fore, lowering precipitator operating temperatures is neither
necessary nor desirable for the case of high sulfur coals, which
produce relatively high concentrations of H2SOn vapor.
An analysis of the factors which cause corrosion, and the
operating experience of at least two power plants, have demonstrated
that low temperature operation of precipitators [104-121°C (220-
250°F)] will not cause low temperature corrosion and fouling pro-
blems with a flue gas containing a basic fly ash and no appreciable
concentrations of sulfuric acid vapor. The occurrence of corrosion
and high fly ash resistivity thus tend to be mutually exclusive
phenomena. A possible exception to the rule would be a stack gas
with high (over 100 ppm) HC1 concentration.
For the case of a plant burning a low to medium sulfur coal
which produces a near-neutral, high resistivity ash at approximately
744
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148°C (300°F) and low concentrations of HjSOi, vapor, the occurrence
of some degree of corrosion as a result of lowered cold-end tem-
peratures cannot be rigorously excluded. However, data obtained
have shown that amounts of sulfuric acid sufficient to "condition"
a neutral ash can be adsorbed at temperatures well above the
sulfuric acid dew point.319 It is therefore probable that an
acceptable fly ash resistivity could be obtained at a temperature
sufficiently high to avoid appreciable condensation of sulfuric
acid on the cold-end elements of an air preheater. A quantitative
evaluation of resistivity and corrosion under such circumstances
would require fly ash resistivity data and relative corrosion rates
(obtained with a corrosion probe such as described earlier) as a
function of temperature in the flue gas.
'45
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TECHNICAL REPORT DATA
fPicsse read Inunctions on the r?\erse bfjore comnicr.ng'.
REPOP~ iv I
12.
J3. RECIPIENT'S ACCESSION NO.
EFA-600/8-80-025
-;. TITLE AND SUBTITLE
A Manual for the Use of Electrostatic Precipitators
to Collect Fly Ash Particles
15. REPORT DATE
Mav 1980
|6. PERFORMING ORGANIZATION CODE
7 AUTMORISi
Jack R. McDonald and Alan H. Dean
E. PERFORMING ORGANIZATION REPORT NO.
SORI-EAS-80-066 (3540-7)
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Southern Research Institute
2000 Ninth Avenue, South
Birmingham, Alabama 35205
10. PROGRAM ELEMENT NO.
EHE624
11. CONTRACT/GRANT NO.
I68-Q2-2|14, Task 7
12. SPONSORING AC-ENCN NAME AND ADDRESS
EPA. Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC. 27711
113. TYPE OP REPORT AND PERIOD COVERED
Task Final; 12/78-2/80
14. SPONSORING AGENCY CODE
EPA/60.0/13
.15. SUPPLEMENTARY NOTES IERL-RTP project officer is Leslie E. Sparks, Mail Drop 61,
919/541-2925.
16. ABSTRACT m, , , . ,.
ihe report incorporates the results of many studies into a manual oriented
toward the collection of fly ash particles (produced by the combustion of pulverized
coal) by electrostatic precipitation (ESP). It presents concepts, measurement tech-
niques, factors influencing ESP performance, data, and data analysis from a prac-
tical standpoint. Extensive use of data from full-size ESPs should* familiarize the
user with what to expect in actual field operation. The manual covers fundamentals
of ESP, mechanical and electrical components of ESPs, factors influencing ESP per-
formance, measurement of important parameters, advantages and disadvantages of
cold-side, hot-side, and flue-gas-conditioned ESPs. safety aspects, maintenance,
troubleshooting, the use of a computer model for ESP, and features of a well-
equipped ESP. Studies considered in this report include those, by various individ-
uals and organizations, on comprehensive performance evaluations of full-scale
ESPs, in situ and laboratory measurement of fly ash resistivity, rapping reentrain-
ment, evaluations of the effects of flue gas conditioning agents on ESP performance,
fundamental operation of hot-side ESPs, basic laboratory experiments, and develop-
ment of a mathematical model of ESP. Information from these studies can be used
by power plant personnel to select, size, maintain, and troubleshoot ESPs.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
COS AT i l-'icld/Group
Pollution
Electrostatic Precipitation
Fly Ash
Measurement
Maintenance
Mathematical Models
Electrical Resistivity
Pollution Control
Stationary Sources
Operation
Troubles hooting
13B
13H
2 IB
14B
15E
12A
20C
12 DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (Thu Report/
Unclassified
J21. NO. OF PAGES
I 782
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-72)
746
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