c/EPA
Fnnrt. D * ,- Industrial Environmental Research EPA-600/7-78-087
tnvironmental Protection Laboratory June 1978
A9encV Research Triangle Park NC 27711
Third Symposium on
Fabric Filters for
Paniculate
Collection
Interagency
Energy/Environment
R&D Program Report
******
*****
*****
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental Protec-
tion Agency, have been grouped into nine series. These nine broad categories were
established to facilitate further development and application of environmental tech-
nology. 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 ENVIRONMENTAL PROTECTION TECHNOLOGY
series. This series describes research performed to develop and demonstrate instrumen-
tation, equipment, and methodology to repair or prevent environmental degradation from
point and non-point sources of pollution. This work provides the new or improved tech-
nology required for the control and treatment of pollution sources to meet environmental
quality standards.
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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EPA-600/7-78-087
June 1978
Third Symposiym on Fabric Filters
for Particulate Collection
Richard Dennis, Compiler
GCA Technology Division
Burlington Road
Bedford, Massachusetts 01730
Contract No. 68-02-2177
Program Element No. EHE624
EPA Project Officer: Dennis C. Drehmel
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
EiwlronmentaJ Prote
U.S. ENVIRONMENTAL PROTECTION AGENCY ^°n v>^orzry
Office of Research and Development *^'' ciou:--1 - !saiborn Street
Washington, DC 20460 Chicago, Illiaoia 60604
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ABSTRACT
The Third Symposium on Fabric Filters for Particle Collection was held on
December 5-6, 1977 in Tucson, Arizona. The Symposium was sponsored by the
U.S. EPA1 s .Industrial Environmental Research Laboratory and was organized by
GCA/Technology Division.
The conference was intended to emphasize current field experience and
engineering-oriented research so that potential users may better select
and/or design their control systems. The technical content of the meeting
focused on fabrics for high temperature filtration, their field behavior with
fly ash and other effluents, design criteria and shakedown experience, and new
filtration concepts that appear amenable to combustion and other process
effluents.
' ' '
This report presents the 17 technical papers presented at the symposium.
. • ' •
111
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ACKNOWLEDGMENT
GCA wishes to express its appreciation for assistance in organizing and
conducting this symposium to Dr. Dennis Drehmel, EPA Project Officer. Members
of the GCA/Technology Division staff who provided assistance were:
Mr. Stephen V. Capone, Dr. Paul F. Fennelly, and Mr. Norman F. Surprenant.
IV
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TABLE OF CONTENTS
Page
Abstract ................. ...
Acknowledgments ............... ........ .
List of Figures . . ............... * . ........ ^±
List of Tables ................ . . . . ......
Paper 1 - Selection Criteria for Emission Control System and
Status Report of Fabric Filter Performance Testing ..... 1
Paper 2 - Modeling Coal Fly Ash Filtration With Glass Fabrics ..... 13
Paper 3 - A Pilot Plant Study of Various Filter Media Applied
to a Refuse Boiler ............... /-,
Paper 4 - Field Tests With a Mobile Fabric Filter ........... 75
Paper 5 - Australian Experience, Filtration of Flyash From Very Low
Sulfur Coals .................. ,Q5
Paper 6 - Demonstration of a High Velocity Fabric Filtration System
Used to Control Flyash Emissions
Paper 7 - Baghouse Performance on a Small Electric Arc Furnace .... 155
Paper 8 - Fume Control at Small Smelters ... .......... 167
Paper 9 - Fabric Filters in the Cement Industry . . ........ . . 177
Paper 10 - New Applications for Fabric Filters
Paper 11 - Effect of Modified Cleaning Pulses on Pulse Jet Filter
Performance .................. 205
Paper 12 - Current and Future EPA Filtration Research ......... 229
Paper 13 - Contributing Role of Single Fiber Properties to Nonwoven
Fabric Performance ................ 235
Paper 14 - Specific Resistance (K2) of Filter Dust Cakes: Comparison
of Theory and Experiments ................ 251
Paper 15 - The Influence of Electrostatically-Induced Cage Voltage
Upon Bag Collection Efficiency During the Pulse-Jet Fabric
Filtration of Room Temperature Flyash ... ...... 289
Paper 16 - Textile Filter Media Durability ............ . 329
Paper 17 - High-Temperature Filtration ...... ........ 331
List of Attendees ............
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LIST OF FIGURES
Figure
PAPER 1
1 Comparison of Costs (%) 6
2 Harrington No. 2 Flue Gas Flow Diagram and
Monitoring Points 11
PAPER 2
1 Schematic, Dust Accumulation on Woven Glass Fabrics 16
2 Massive Pinhole Leaks With all Multifilament Yarns and
Large, ~200 ym, pores 17
3 Typical Drag Versus Loading Curves for Filters With Different
Degrees of Cleaning and a Maximum Allowable Level for
Terminal Drag, S and Terminal Fabric Loading, WT 20
4 Fly Ash Dislodgement From 10 ft x 4 in. Woven Glass Bag
(Inside Illumination) 21
5 Fly Ash Filtration With Completely and Partially Cleaned
Woven Glass Fabric (Menardi Southern) 24
6 Relationship Between Cleaned Area Fraction and Initial
Fabric Loading. GCA Fly Ash and Woven Glass Fabric 26
7 Effect of Inlet Concentration on Predicted Outlet Concen-
trations at a Face Velocity of 0.61 m/min. GCA Fly Ash
and Sunbury Fabric 28
8 Predicted and Observed Outlet Concentrations for Bench
Scale Tests. GCA Fly Ash and Sunbury Fabric 29
9 System Breakdown for I Bags and J Areas Per Bag 32
10 NUCLA Baghouse Simulation, Resistance Versus Time 35
11 Test Run No. 0422 Nucla Baghouse Simulation - Linear
Penetration Versus Time Graph 36
PAPER 3
1 Schematic Diagram of the Enviro-Clean RA-1 Dust Collector
Model 144-RA1-5-104 46
2 Temperature Profile for the Enviro-Systems Baghouse 47
3 Fabric Filter Pilot Plant Installed at Nashville Thermal
Transfer Corp 48
4 Inlet Particle Size Distribution for Two Brinks Impactor
Runs 52
5 Outlet Particle Size Distribution 54
6 Outlet Particle Size Distribution, Globe Albany 55
vi
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LIST OF FIGURES
Figure PAPER 3 (cont)
Page
7 Outlet Particle Size Distribution for Gore-Tex Fabric .... 57
8 Comparison of Three (3) Fabrics for Outlet Concentration
versus Air-to-Cloth Ratio .................. 60
9 Comparison of Installed Costs for Four (4) Filter Media
and Electrostatic Precipitators ............. 62
10 Installed Cost Comparisons for Different Air Pollution
Control Techniques ................... 64
11 Comparison of Annual Operating Costs of Four (4) Filter
Media and ESP Assuming Four Year Bag Life .......... 65
12 Comparison of Annual Operating Costs of Four (4) Filter
Media and ESP Assuming Four Year Bag Life .......... 66
13 Annual Operating Cost Comparison for Three Air Pollution
Control Techniques ....... ........... gg
14 Comparison of Annual Operating Costs of Four (4) Filter
Media and ESP Assuming Two Year Bag Life ........ . . 69
15 Comparison of Annual Operating Costs of Four (4) Filter
Media and ESP Assuming Four Year Bag Life .......... 70
16 Annualized Cost for the Three Air Pollution Control
Techniques ................ -,->
PAPER 4
1 Average Mass Penetration versus Geometric Mean Particle
Diameter ................ , „.,
PAPER 5
1 Typical Coal Analysis ...............
2 ECNSW Fabric Filter Installations .............. 114
3A ECNSW Tallawarra Station - Section A Pilot Unit ...... .115
3B ECNSW Tallawarra Station - Section A and B Full Scale .... 116
4 ECNSW Wangi Station - Units 4, 5, 6 - Pulse Jet Filters . . . 117
5 ECNSW Wangi Station - Unit 5 PC Boiler - Reverse Air
Baghouse Design Conditions ............... 118
VII
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LIST OF FIGURES
Figure Page
PAPER 6
1 SD-10 General Arrangement With Pyramid Hoppers . 123
2 Fabric Filter Module Cell ..... 124
3 Baghouse Pictorial Showing Gas Flow 126
4 Step 2 - The Fabric Filter 127
5 Step 3 - Shock . 128
6 Step 4 - Drag 129
7 Kerr Pilot Plant Photo 131
8 Outlet Concentration versus Air-to-Cloth Ratio for
Various Bag Materials 132
9 Comparison of Operating Pressures for Various Bag
Materials 133
10 Installed Costs versus Air-to-Cloth Ratio 134
11 Operating Costs versus Air-to-Cloth Ratio 135
12 Teflon Felt - Annual Operating Costs versus Air-to-Cloth
Ratio for Different Bag Life Assumptions 136
13 Annualized Cost Comparison 137
14 EPA Demonstration of the Enviro-Systems Fabric Filter Sys-
tem at Kerr Finishing Div. FabricsAmerica, Concord,
North Carolina • • • 139
15 One House on Truck 140
16 House Being Lifted Onto Hopper - Far View 141
17 House Being Lifted Onto Hopper - Near View 142
18 Completed System 143
19 Control Panel • 144
20 Fabric Filter Schematic 145
21 Total Annualized Cost Versus Air-to-Cloth Ratio
Teflon Felt 150
22 Annualized Costs Versus Air-to-Cloth Ratio 152
23 Annualized Costs Versus Air-to-Cloth Ratio 153
Vlll
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LIST OF FIGURES
F1Sure Page
PAPER 7
1 Photograph of Side of Fabric Filter . . . . ......... 157
2 Photograph of End of Fabric Filter ............... 158
3 Concentration Versus Process Cycle for 10 ym Particles. . . . 160
4 Time in Process Cycle at Which Inlet Samples Were
Collected
5 Composited Differential Size Distribution Curves of
Baghouse Inlet Aerosol ................... 153
6 Average Outlet Differential Size Distribution Curves .... 164
7 Fabric Filter Fractional Penetration Curves ......... 165
PAPER 10
1 Flow Sheet
2 Typical Filter Pressure Loss Curve ......... .... 193
3 Coke Oven Exhaust Tar Removal Efficiency .......... 192
4 Coke Oven Pilot Unit .................... 194
5 Coke Oven Pilot Unit ............... ..... 195
6 Galvanizing Line Fabric Filter Operating Conditions ..... 197
7 Galvanizing Line Fabric Filter Design Features ....... 197
8 Sinter Machine Windbox Fabric Filter ............ 199
9 Fabric Filter - Nahcolite System .............. 201
10 s°2 Removal as a Function of Stoichiometric Ratio Under
Optimum Conditions ................. 202
11 Fabric Filter-Nahcolite System Costs ............ 203
PAPER 11
1 Schematic Drawing of Fabric Filter Apparatus Used ...... 210
2 Cumulative Size Distribution by Count for Fly Ash ...... 211
3 Valve Arrangement for Pulse-Air Manifold ........... 212
4 Photograph Tracing of Oscilloscope Display: Pulse Pressure
Versus Time for Normal Pulse . . . ............ 214
ix
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LIST OF FIGURES
Figure PAPER 11 (cont) Page
5 Photograph Tracing of Oscilloscope Display: Pulse Pressure
Versus Time for Modified Pulse . 216
6 Photograph Tracing of Oscilloscope Display: Pulse Pressure
Versus Time for Modified Pulse With Twice Normal Chamber
Volume 217
7 Penetration Versus Filtration Velocity, Pulse Type as
Parameter • 220
8 Penetration Versus Filtration Velocity, Relative Humidity
as Parameter 221
9 Pressure Drop Versus Filtration Velocity, Relative Humidity
as Parameter • 223
PAPER 13
1 Capture Efficiencies of Three Nonwoven PET Fabrics Made of
Various Fibers, as Shown, When Filtering a Flyash Aerosol. . 241
2 Ratios of Outlet Concentrations for Filters Made of Fibers
With 2, 3 and 5 Lobes to Outlet Concentrations for Round
Fiber Filter 242
3 Capture Efficiencies for Nonwoven Rayon Filters Made of Fibers
With Various Levels of Crimp as Shown, When Filtering a
Flyash Aerosol 243
4 Penetration (Equal to 1-Efficiency) for PET and Polypropylene
Filters of Constant Weight and Density but Made of Fibers of
Different Diameters • 244
5 Specific Cake Resistance for the Filters in Figure 4 .... 245
6 Pressure Drops at Beginning and End of Filter Cycle
(APj^ and APf) for Conditioned Bags Made of Round and
Trilobal PET Fibers 246
7 Outlet Concentration Ratios for Bags in Figure 6 247
8 Single Fiber Efficiencies for Each Layer in Layered Filters
Made of Round and Trilobal Fibers 248
9 Calculated Single Fiber Efficiencies for Fibers With Cross
Sections p = 1 + e Cos m (+C) Where m = Number of Lobes
and e Indicates the Lobe Depth 249
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LIST OF FIGURES
Page
PAPER 14
1 Experimental Apparatus . 273
2 Cross Section of Dust Cake on Woven Fabric 275
3 Dust Cake Shadow Cast on Woven Fabric 277
4 Particle Size Distribution 278
5 Specific Resistance Versus Solidity 282
PAPER 15
1 Cage Contact 297
2 Cage Voltage Forms 299
3 Basic Electrical Equivalent Circuit 302
4 Gas Flow Rate Through One Bag of a Four-Row Pulse-Jet
ArraV 304
5 Modified Equivalent Circuit Containing Distributed
Components OQ-:
6 Cage Voltage During Fly Ash Filtration At High Relative
Humidity 314
7 Cage Voltage Under an External Bias of -2000 Volts 316
PAPER 17
1 3-M Company Thermacomb 334
2 Calculated Performance 3.0 ym Alumina Fiber Bed . 339
3 D.O.P. Efficiency fn Airflow Velocity 341
4 D.0.0. Efficiency fn Basis Weight 345
5 Dust Loading of Ceramic Felts 343
6 Dust Loading of Ceramic Paper 349
7 Dust Loading of Woven Ceramic Media . 350
8 Saffil Alumina - Post Test Dust Cake 353
9 Woven Fiberfrax - Post Test Dust Cake .... . 355
10 Fiberfrax Blanket - Post Test Dust Calce 355
xi
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LIST OF TABLES
Table
PAPER 2
1 Required Data Inputs for Specific Model Application ...... 33
2 Predicted and Measured Resistance Characteristics for Nucla
Filter System 34
3 Measured and Predicted Values for Filter System Penetration
and Resistance, Coal Fly Ash Filtration With Woven Glass
Fabrics 38
PAPER 3
1 Nashville Thermal Transfer 49
2 Inlet Emission Profile . . . 50
3 Outlet Concentration and Cumulative % 53
4 Outlet Concentration and Cumulative % 56
5 Outlet Concentration and Cumulative % 58
6 Bag Cost as Percent of Installed Cost 61
PAPER 4
1 Brass and Bronze Foundry Pulse Cleaning Test Results 89
2 Brass and Bronze Foundry Shake Cleaning Test Results 89
3 Hot Mix Asphalt Plant Pulse Cleaning Test Results 90
4 Coal-Fired Power Plant (Cyclone-Fired Boiler) Shake Cleaning
Test Results 90
5 Operating Conditions for Coal-Fired Power Plant (Anthracite
Coal) Tests 91
6 Coal-Fired Power Plant (Anthracite Coal) Mass Efficiency Test
Results 92
7 Operating Conditions for Pulp Mill Lime Recovery Kiln Tests . . 94
8 Pulp Mill Lime Recovery Kiln Mass Efficiency Test Results ... 95
9 Pulp Mill Lime Recovery Kiln Fractional Efficiency Test
Results 96
10 Pressure Drop Results of Pulp Mill Lime Recovery Kiln Tests . . 97
11 Operating Conditions for Coal-Fired Power Plant (Subbituminous
Coal) Tests 98
12 Pressure Drop Results of Coal-Fired Power Plant (Subbituminous
Coal) Shake Cleaning Tests 99
XII
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LIST OF TABLES
Table PAPER 4 (cont) Page
13 Pressure Drop Results of Coal-Fired Power Plant (Subbituminous
Coal) Reverse Cleaning Tests (Teflon/Glass Bags) 100
14 Pressure Drop Results of Coal-Fired Power Plant (Subbituminous
Coal) Reverse Cleaning Tests (Graphite/Glass Bags) 101
15 Coal-Fired Power Plant (Subbituminous Coal) Mass Efficiency
Test Results 102
PAPER 6
1 Alarms and Shut-Down Functions 147
PAPER 7
1 Average Results of Total Mass Measurements 159
PAPER 8
1 Fume Control in Small Smelters 175
PAPER 11
1 Fractional Mass Penetration/Pressure Drop, MM Water Gauge/%
Relative Humidity 219
PAPER 14
1 Minimum Specific Resistance , . 258
2 Comparison of Resistance Factors Predicted by Kozeny-Carman
Equation and "Free Surface" Model 263
3 Comparison of D and D 268
4 Porosities and Particle Diameters for which C =1.1 271
s
PAPER 15
1 Experimental Nomex Test Bags (Scrimless Felts) 311
2 Bag Performance Series 312
3 Control Bag Performance Under Cage Electrical Bias (All Runs
at 50% Relative Humidity) 315
4 Control Bag Performance at Various Cage Electrical Terminations
(All Runs at 50% Relative Humidity) 318
5 Properties of Needled Polyester Felt Fabric 320
6 Filtration Performance of the Test Polyester Felts 322
xiii
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LIST OF TABLES
Table Page
PAPER 17
1 Summary of 3M ThermaComb Performance 336
2 Effect of Changing Cleaning Conditions .... 336
3 Summary Room Ambient Test Data . 342
xiv
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SELECTION CRITERIA
for
EMISSION CONTROL SYSTEM
and
STATUS REPORT OF FABRIC FILTER
PERFORMANCE TESTING
Presented by: Presented at:
Jack D. Jones Third EPA Symposium
Principal Engineer, Mechanical on Fabric Filters for
and Particle Collection
Kenneth L. Ladd, Jr. December 5, 1977
benior Environmentalist
Southwestern Public Service Co
Amarillo, Texas ' Tucson, Arizona
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ABSTRACT
SELECTION CRITERIA FOR
EMISSION CONTROL SYSTEM AND
STATUS REPORT OF FABRIC FILTER PERFORMANCE TESTING
After studying the technological and economic aspects
of emission control devices for its secorid coal-fired
generating unit, Southwestern Public Service Company
selected a fabric filter system for particulate con-
trol. Problems with electrostatic precipitators and
the desire to install an emission control device which
would not require particulate scrubbing prompted South-
western to investigate the feasibility of a fabric filter
installation. The study revealed that a fabric filter
system would be economically justifiable as well as
technically appropriate for the Company's coal-fired
plant which utilizes low sulfur Western coal.
As a result of its choice, Southwestern, under a contract
with the U. S. Environmental Protection Agency, will con-
duct a study to assess the performance of the fabric fil-
ter system as an emission control device. Continuous
monitoring of the flue gas emission stream will be made
at five different sampling points. Special inlet and
outlet sample testing will define the particulate charac-
teristics. The collected data will be processed into a
determination of the economics and industrial acceptability
of operating and maintaining the commercial emission con-
trol system. The resultant report should be a guide on
the selection, design, operation and maintenance of a
fabric filter system for Western coal-fired boilers.
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SELECTION CRITERIA FOR EMISSION CONTROL SYSTEM
PART I
Southwestern Public Service Company is an electric utility
headquartered in Amarillo, Texas, with 2,240 employees serving
approximately 280,000 customers in Texas, Oklahoma, New Mexico
and a small area of Kansas. The Company has a generating capa-
city of 2740 MW produced by five major and three smaller power
stations; seven of these installations are fueled by natural
gas. The number one unit of Southwestern's first coal-fired
station went on line in July, 1976; it has a 356 MW capability.
By July, 1984, the Company will have approximately 2150 MW of
coal-fired steam generating capability on line.
Southwestern Public Service Company designs its own power
plants through the Generation Plant Design Group, which is
part of the System Engineering Department organized in 1945.
When we began design of our first coal-fired unit, the Gener-
ating Plant Design Group had 30 employees, of whom 12 were
engineers. We now have 87 employees in plant design, 36 of
whom are engineers.
The basic problem in designing the Company's second coal-
fired unit was the selection of a coal-fired furnace flue gas
treating and control system which would satisfy EPA's New
Source Standards. These standards require that a coal-fired
facility not emit more than .1 pounds per million Btu particu-
late, and emissions cannot exceed 1.2 pounds per million input
of sulfur dioxide.
Southwestern Public Service Company looked at the alter-
natives for controlling coal-fired boiler emissions and an
effort was made to select a type of emission control device
which would not require scrubbing for particulate removal.
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The 350 MW Harrington Station unit (located near Amarillo,
Texas) uses sub-bituminous low sulfur Western coal, and,
therefore, the EPA standards for S02 could be met by selecting
low sulfur coal as fuel.
The primary systems initially studied for particulate con-
trol were electrostatic precipitators. Since the construction
of Harrington Station Unit #1, electrostatic precipitator guar-
antees, performance and technology had improved to the point
that consideration was given to the purchase of a 99.570 removal-
of-ash electrostatic precipitator. At the time that a decision
was required by Generation Plant Design staff, numerous utili-
ties were having problems with hot-side precipitators; there-
fore, this type of precipitator was not considered.
While obtaining bids and information from suppliers of
electrostatic precipitators some mention was made of the use
of fabric filters for particulate control. The use of this
type of filter system in Southwestern1s service area is very
common (in the carbon black industry) and we were somewhat
familiar with this application. After a study was made of
fabric filters, and how they were applied at the Sunbury and
NUCLA facilities, a decision was made to compare electrostatic
precipitators with baghouse systems.
Baghouse vendors were contacted and the only specifica-
tions given these suppliers for preparing their quotations were
flue gas flow, ash characteristics, and grain loading. Meetings
were held with fabric filter suppliers to determine a common
base for comparison with each other and with electrostatic pre-
cipitator proposals. These comparisons were based on physical
design, physical operation, capital cost and operating cost.
Comparison Charts: This comparison chart (Figure 1) will
show the comparative costs of three fabric filters and three
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99.5% effective precipitators. The comparison is in percentages
with the fabric filter purchased for Harrington Station, Unit #2,
being the base. There are two areas in which the competitors
were lower than the base. The #3 fabric filter was lower in
capital cost due to the cost of bag replacement for fabric fil-
ters being classified as maintenance. Replacement for the fabric
filters was based on a two year life of the bags; however, ex-
perience at Sunbury indicates that bag life is much longer than
two years. From a discounted cash flow analysis it can be seen
that the fabric filters have less effect on the cost to stock-
holders than any of the precipitators. It should be noted, how-
ever, that the parameters used in this analysis may not neces-
sarily apply to other utilities, or to other areas.
Our first fabric filter was selected for Harrington Station,
Unit #2. For the #3 unit at Harrington we wrote a set of speci-
fications and then negotiated a contract for a fabric filter sys-
tem to be supplied by Wheelabrator-Frye, Inc. Essentially it is
the same as the system designed for Unit #2.
The Company's next coal-fired station will be ToIk Station
Units #1 and #2. Unit #1 is scheduled to go on line in June,
1982. Southwestern Public Service will prepare a set of speci-
fications for a fabric filter system based on knowledge gained
from the purchase and use of two fabric filter systems at our
Harrington Station, enhanced by the knowledge gained in studying
the system for Unit #2.
In the second part of this paper, Kenneth Ladd will describe
Southwestern Public Service Company's plans to obtain this
knowledge.
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COMPARISON OF COSTS (%)
FABRIC FILTER
99.5 % PRECIPITATOR
CAPITAL COST
OPERATING COST
MAINTENANCE
COST
COST TO
STOCKHOLPER
BASE
100
too
100
100
2
101
132
101
115
3
86
110
144
105
1
142
228
20
133
2
143
175
20
132
3
166
153
20
148
FIGURE 1
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SELECTION CRITERIA FOR EMISSION CONTROL SYSTEM
PART II
The preceding comments describe Southwestern Public Ser-
vice Company's reasons for selecting a fabric filter system
for emission control. Because such a small amount of informa-
tion is available on the performance testing of fabric filters
at other utility installations, it was necessary for Southwestern
Public Service to make its own evaluation of emission control de-
vices for the specified Harrington Station application.
Southwestern has no previous experience in fabric filter
system operations so when asked the question, "Why a baghouse?"
we encourage each utility to make its own analysis. Factors
to consider are specific requirements, boiler design, fuel,
and other engineering and economic considerations. Southwestern
is not qualified to present general criteria at this time.
To assist in the collection of information to formulate a
more complete data base for fabric filter performance, South-
western and EPA have agreed to make a comprehensive study of a
commercial, operating unit. The study will require two years
to complete the collection and assessment of one full operating
year's worth of data. After this experience and testing, South-
western Public Service can offer more expert opinion concerning
fabric filters. In the last part of this paper, the status of
the testing program will be discussed.
The objective of the study is to implement an overall pro-
gram of testing and evaluation design to (1) fully characterize
the fabric filter system applied to Harrington Station, Unit #2;
(2) study the technical and economic feasibility of the system;
(3) demonstrate long-term reliability of the system; and (4) de-
termine the system's optimum operating conditions.
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A description of the emission source and the fabric fil-
ter system to be tested is as follows:
The emission source is a pulverized coal-fired Combustion
Engineering tangentially-fired boiler. It will use low sulfur
Western coal, supplying steam to a 356 MW rated steam turbine
generator. The fabric filter is a Wheelabrator-Frye, Inc. unit
with 28 compartments, operating at 313° F, cleaning 2,650,000
acfm at full load; the normal net air-to-cloth ratio is 3.4:1.
The fabric filter cleaning method is reverse air and shaking
with the control flexibility of using either or both. The
filter medium is fiberglass coated with silicone and graphite.
The bags are 11.5 inches in diameter and 30.5 feet long.
The test plan will characterize the fabric filter system
by manual sampling and continuous monitoring. The plan also
calls for analyses of all solids and gases in and out of the
system. Additionally, data will be collected and recorded
which describes all significant fuel and operation information.
Major manual sampling and testing of the particulate
entering and leaving the fabric filter system will be used to
determine performance characteristics that cannot be measured
with continuous monitoring equipment. Three detailed manual
samplings will be equally spaced during the year of operating
tests. Five sampling ports will be sampled at the same time
to determine mass particulate flow and particle size distribu-
tion down to .01 ym. The particulate ash will be analyzed for
organic material, elemental constituents, sulfates, sulfites
and nitrates.
Manual sampling and testing will also be used to determine
flue gas characteristics. The parameters to be determined are
hydrogen chloride, hydrogen fluoride, oxides of sulfur, oxide
of nitrogen, organic vapors, and elemental constituents.
All major sampling and testing will be performed according
8
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to EPA and other approved testing procedures. The manual sam-
pling results will be correlated with operating data to define
the performance of the fabric filter at full load on the system.
The same five sampling ports will be used to locate the
continuous monitoring equipment (see Figure 2, Harrington #2
Flue Gas Flow Diagram and Monitoring Points).
The parameters listed below will be continuously monitored
(flue gas stream - at all 5 points):
!• S02 5. 02
2- NOX 6. Temperature
3. Particulate (grain/cu.ft.) 7. Duct pressure
4. Flue gas flow (acfm)
Additional operating parameters that will be measured or
calculated on a continuous basis will be pressure drop across
the system, power consumption, load on the unit, fuel flow,
particulate removal, cleaning mode and frequency and flue gas
flow. There are approximately 30 analog inputs and another 20
contact inputs that will direct operational data into the plant
computer. This data will not be as specialized as the manual
sampling information, but rather will represent every day opera-
tion of the fabric filter system. Daily records will be kept
of the maintenance required by the fabric filter system.
The test program should produce an assessment of the per-
formance of a fabric filter system that determines particulate
collection, pressure drop, temperature, energy consumption,
S02/S03 removal, optimum cleaning procedures, fabric care and
maintenance, corrosion, system reliability and bottom line cost
of operation and maintenance.
An option for a future study exists which would permit the
determination of operation and maintenance parameters for five
years of operation after performance has been defined.
9
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During the present study, the fabric filter system will
operate as designed and required for the generation of electric
power from a commercially operating unit. This limits the
special testing of parameters outside of the normal operation.
Another future option would include special testing of fabrics,
air-to-cloth ratios, or other related research. These objec-
tives would be accomplished by installing a small slipstream
fabric filter test module (about 10,000 acfm).
Southwestern Public Service Company wants to gain experience
in the application of fabric filters as well as provide to other
utilities information which might be useful in their evalua-
tions of their own unique emission control problems. A per-
formance report submitted by a utility would present utility
knowledge and application to the air quality regulatory groups,
and thus better represent the industry's problems and solutions.
As a result of the testing program, Southwestern Public
Service Company will, two years from now, be able to make an
assessment based on sound and well-documented operating experienc
10
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12
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MODELING COAL FLY ASH FILTRATION
WITH GLASS FABRICS
by
Richard Dennis
and
Hans Klemm
GCA CORPORATION
GCA/TECHNOLOGY DIVISION
Bedford, Massachusetts
13
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ABSTRACT
A new mathematical model for predicting the performance of woven glass
filters with coal fly ash aerosols from utility boilers is described in this
paper. The data base includes bench and pilot scale studies in which several
dust/fabric combinations were investigated; field data from prior GCA studies
of coal fly ash filtration with glass fabrics; past GCA studies of fabric fil-
ter cleaning mechanisms and a broad-based literature survey.
Two new concepts were instrumental in model design. The first relates to
the manner in which dust dislodges from a fabric and its subsequent impact
upon resistance and penetration in a multichambered system. The second con-
cept is associated with the relatively large fractions of fly ash that pass
with minimal collection through temporarily or permanently unblocked pores or
pinholes. Additionally, the quantitation of the cleaning action with dust
removal in terms of method, intensity and duration of cleaning was essential
to the overall modeling process. The examination of specific resistance
coefficient, K2, for the dust layer in the light of polydispersed rather than
monodispersed particle components provided improved estimates of K.2- Trial
applications of the modeling technique to field filter systems operating at
Sunbury, Pennsylvania and Nucla, Colorado indicate excellent agreement between
theory and practice for both penetration and resistance characteristics.
14
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SECTION 1
BACKGROUND
The prospect of stricter participate emission regulations for coal-fired
boilers suggests that fabric filtration may be the best control technique for
many applications. Limited field experience with large utility boilers1'2 has
demonstrated that glass fabric filters perform well with respect to moderate
pressure loss, very high collection efficiency and acceptable service life
(at least 2 years). A possible drawback, however, in the eyes of utility
groups has been the inability to predict accurately how a new filter system
will perform without extensive pilot testing and field trials.3.4 Only when
the new plant design replicates an existing (and successful) installation with
respect to power level, boiler design and fuel characteristics can the filter
performance be predicted safely.
In this paper, a filtration model is described which, based upon limited
field validation, provides rational estimates for the performance of woven
glass bags with coal fly ash in real filter systems.4.5 The apparent success
of the model is attributed to the introduction of three new concepts or ap-
proaches to the modeling process.
The first relates to the fact that dust remaining on a fabric surface
after cleaning is characterized by a distinctive, nonuniform distribution in
which the unique resistance and collection properties of cleaned and uncleaned
areas are definable and thus amenable to mathematical analysis. ~ -
The second approach allows us to quantify the relationship between the
amount of dust removed from a filter and the method of cleaning and the filter
dust loading prior to cleaning.5'6
The _third approach centers on the unique dust penetrating properties ob-
served for fly ash/woven glass fabric systems in which the failure to obtain
rapid and/or complete pore bridging allows significant direct leakage (bypassing)
of the upstream aerosol to the clean air side of the system. Such penetration
arises because of a characteristic nonuniformity in both pore dimensions and
in the dispersion of the loose fiber substrate that screens the pore openings.4.5
r K i f°r ^ ab°Ve lmPerfecti°ns, a continuous and highly impene-
trable dust layer would form above the substrate as shown in Figure 1. £n the
tribut?o 'f311 H Y ?°r WeaVe C°Upled With a SparSit? and nonuniform dis-
tribution of substrate fibers can lead to the critical pinhole leak problem
illustrated in Figure 2. The relatively low resistance to gas flow presented
by the larger pores results in the passage of a disproportionately large
15
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YARN
YASN
BULKED FIBERS
DUST
UNUSED
FABRIC
EARLY DUST
BRIDGING OF
FIBER SUBSTRATE
SUB SURFACE
DUST CAKE
DEVELOPMENT
Figure 1. Schematic, dust accumulation on woven glass fabrics.
16
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Figure 2. Massive pinhole leaks with all multifilament yarns and large,
-200 ym, pores.
17
-------
fraction of the uncleaned gas along with most dust particles < 15 ym diameter.
Because the quantity of fly ash penetrating woven glass fabrics via the pore
or pinhole leak route exceeds that which penetrates the unbroken dust cake by
some 100 to 1000 times, the particle size properties of the effluent particles
are essentially the same as those in the entering aerosol.
The above phenonemon explain why the reported fractional efficiencies for
glass fabric systems often indicate the same degree of collection for all
particle sizes. It is also pointed out that periodic rear face slough-off
of agglomerated particles due to mechanical vibration or aerodynamic drag may
contribute significantly to the effluent loading.4'7
Another consideration in the modeling process is the fact that the dust
collection capability for any specified area of a fabric surface depends upon
both the local dust cover and the local filtration velocity.3'4'6'8 Addi-
tionally, the specific resistance coefficient, K2, for a given dust depends
not only upon the physical properties of the particles, gas and bed structure
but also upon the gas velocity at the time of particle deposition.3'5
Introduction of variables and concepts discussed above into the classical
filtration equations constitutes the basis for a comparatively simple model
which can serve two major roles. The first application relates to the design
of a filter system based upon specified dust and fabric properties, air to
cloth ratios, proposed frequency and/or intensity of cleaning and pressure loss
constraints. The second application is that of determining whether the operat-
ing regimen and basic design approach specified by a system designer will allow
the user to meet particle emission requirements while conforming to system gas
flow and resistance requirements. Thus, the second or diagnostic role of the
filtration model should prove particularly valuable to environmental control
groups who must assess the adequacy of proposed control measures.
In the following sections, we have outlined briefly the basic structure
and development of the model and its preliminary trial runs. We have not at-
tempted, however, to describe fine operating details nor the programming rou-
tines per se, both aspects having been dealt with extensively in a recent
study. Although the basic mathematical model has been established, it is em-
phasized that peripheral modifications in the model with respect to what con-
stitutes direct or indirect data inputs are expected based upon specific user
requirements and precise model applications.
18
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SECTION 2
MODEL DEVELOPMENT
BASIC FILTRATION RELATIONSHIPS
leads
.
the characteristic relationship shown by the solid Curve I Figure 3
the CUrvllln "
ve gure
SP whef^ the CUrvlllnrr f°™ °f Curve 1 depicts the true residua! drag"
The linear expression
= SE + K2 W
resultant fllter dr*S> SE the effective residual drag, K2
te coefficient f°r the dust, and W the fabric surface area
When a fabric bag is cleaned by bag collapse and reverse flow or bv
mechanical shaking, the dust sloughs off as flakes or slabs with th^separa-
f \dUSt/fabric int-face where the adhesive 1^ arT
^shows the appearance of a full scale glass bag (10 ft x
represented by Curves 2 through 4, Figure 3.
PARALLEL FLOW CONCEPT
°f *** CU™S' FlgUre 3' have sometimes been incorrectly
19
-------
N5
O
CO
CO
<
oc
a
OL
ui
UI
O
<
a:
LJ
DESCRIPTION
MAXIMUM POSSIBLE CLEANING
HIGHLY EFFICIENT CLEANING
AVERAGE CLEANING RANGE
(MECHANICAL SHAKING)
AVERAGE CLEANING RANGE
COLLAPSE WITH REVERSE
FLOW
Figure 3.
AVERAGE FABRIC LOADING.W
Typical drag versus loading curves for filters with different degrees of cleaning and
a maximum allowable level for terminal drag, ST, and terminal fabric loading, WT.
-------
Figure 4. Fly ash dislodgement from 10 ft x 4 in. woven glass bag
(inside illumination).
21
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pinhole leakage that may divert as much as 20 percent of the approaching gas
flow through as little as < 0.1 percent of the filter face area.4
The path of these curves is governed by several parallel flow paths in
which the approaching gas stream is apportioned according to the local drag
values at any specified time for cleaned and uncleaned surfaces.3'4'9
Aui Au.
\l A
(2)
In Equation (2), S and,A refer to overall drag and filter area, respec-
tively, i designates the i fractional area and its associated properties,
n is the total number of filter areas making up the whole surface, and the
subscripts c and u refer to the cleaned and uncleaned filter areas.
The resulting pressure losses, P, after a time increase, At, for cleaned
and uncleaned filter surfaces are equal and expressable by the following
general relationship:
t ~r At t ~F" At t 4" At
in which Sg is the characteristic effective residual drag, V the instantaneous
face velocity and W the total surface loading at the time t + At. Equations (2)
and (3) form the building blocks for the iteration process from which the local
and overall drag and resistance parameters may be estimated by computer for
any time and/or average filter dust loading during a filtration cycle. Two
critical parameters must be defined, however, before undertaking the modeling
process.
SPECIFIC RESISTANCE COEFFICIENT (K2)
The first parameter is K2, which has been demonstrated in past and current
studies to increase with the velocity of dust deposition, presumably due to
increased dust layer compaction and hence lower cake porosity.3*4 For many
coal fly ash/woven glass fabric systems, K2 values computed as shown below may
be used in Equation (3):
K2 = 1.8 V'5 (Metric units)* (4)
For broader applications, however, Equation (4) is better expressed as
(K2) = (K2) (V2/Vi (5)
2 1
when K2 has been measured at a different velocity. Although several theoretical
approaches have been proposed for the estimation of K2 in terms of particle
V = face velocity, m/min. K2 = specific resistance coefficient, N.min/g.m
22
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and fluid parameters, the direct measurement of K2 is recommended. In the
absence of direct measurements, a modified form of the Carman-Kozeny equation4
provides a rough (± 25 percent) estimate of K2; i.e.,
K2 = 2.5y (S'0)2 (l-e)/Ppe3 (6)
where y is the gas viscosity, e the cake porosity, p the discrete particle
density, and S'o the specific surface parameter for the size distribution as
a whole, i.e.
S' = ^ particle surface area
0 E particle volume
for any unit volume of dust cake. Although cake porosity is a measureable
quantity, it should be noted that a 10 percent error in porosity estimation
will lead to a 50 percent error in the porosity function (l-e)/e3. Particle
density measurements over the size spectrum of polydispersed dusts such as
fly ash are also subject to error. Hence, there is a strong argument for
direct measurement of K2 (and SE) whenever possible.
Use of the parallel flow concept involving Equations (2) and (3) for
several partially cleaned fabrics indicated excellent agreement between ob-
served and predicted drag values.4*5 The modeling process used in Figure 5
is based on the fact that the cleaned area fraction, ac, is always associated
with a characteristic fabric drag, S .
FRACTION OF FILTER SURFACE CLEANED (ac)
The fraction of the filtration surface cleaned by the cleaning process,
ac, must also be determined prior to the modeling effort. In the case of
fabric cleaning by bag collapse and reverse flow, the amount of dust removed
can be related to the fabric dust loading immediately before cleaning (WT), the
characteristic residual dust loading for the cleaned region (W ) and the
average filter dust loading after cleaning, (W '). R
R
, V - WR
*c = X - -w—^ (7)
or l R
ac = 1.51 x l(T8 WT2'52 = 1.51 x 10~8 Wp2-52 (8)
in which the fabric loading prior to cleaning, WT or Wp, is expressed in
grams/m . Equation (7) can only be used to estimate ac when the average filter
dust holding after cleaning, WR', is known. Ordinarily, such data are obtain-
able only when special experimental testing procedures are employed. Hence,
Equation (8) which depends upon the measureable or readily calculable Wp or
WT term, is chosen to compute the cleaned area fraction, ac.^
The term Wp has the special significance of identifying the fabric load-
ing associated with the fabric pressure loss just before initiating the cleaning
23
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77-32.3
1,000
800
1 —r 1 1 1——i 1 i r~
—A WOVEN GLASS FABRIC, COMPLETELY CLEANED
—O WOVEN GLASS FABRIC, PARTIALLY CLEANED
•--x PREDICTED CURVE, PARTIALLY CLEANED
WOVEN GLASS FABRIC
UJ
O
2
f
CO
CO
UJ
a:
a
OL
co
g
600
400
200
TEST PARAMETERS
PARTIALLY CLEANED FABRIC
V=0.6I m/min
C0 = 6.9 g/m3
ac =0.485
QU S0.5I5
Sc = 102.4 N min/m3
Su =1033 N min/m3
K2 =1-81 V^Nmin/g m
200
400 600 800 1,000
AVERAGE FABRIC LOADING, g/m2
1,200
Figure 5. Fly ash filtration with completely and partially cleaned woven glass fabric
(Menardi Southern)
-------
action. In many systems, Wp represents the fabric dust loading corresponding
to the preset pressure loss at which the filter cleaning cycle is to be
activated.
DUST DISLODGEMENT AND ADHESIVE FORCES
Dust separation from any element of the filter surface is assumed to take
place when the local separating force equals or exceeds the local adhesive
force bonding the dust layer to the fabric surface. The dislodging force
for bag collapse-reverse flow systems is that resulting from the tensile or
shear stresses (assumed to be approximately the same) exerted by the local
surface loading in mass per unit area, Ma, in a gravity field, g. If the
system is cleaned by mechanical shaking, the acceleration, a, imparted to the
dust layer by the mechanical shaking action is substituted for the gravitational
acceleration,4»6» 1"
"a = 0.75 4 ir2 f2A (9)
such that the dislodging force is now defined by the relation Ma'a rather than
Ma-g. In Equation (9), f refers to the shaking frequency and A to the ampli-
tude (half-stroke) of the shaker arm motion (assumed to be essentially hori-
zontal) . After cleaning by the above mechanisms, the dust remaining on the
filter is assumed to be held by an adhesive force in excess of the computed
Ma'a or Ma*g values.
The relationship between ac and fabric loading shown in Figure 6 is also
a measure of the distribution of adhesive forces over the fabric surface. The
range of adhesive forces encountered exhibits a pattern similar to that dis-
played for particle to particle adhesive forces3'11'12 while the average
adhesive forces binding the cake to the fabric agree with those described by
Zimon.13 The cleaned area values reflect those to be expected after a fabric
element has undergone successive flexings. Recent measurements have shown
that a single cleaning by bag collapse and reverse flow removes about 67 per-
cent of the dust separable by repeated cleanings at the same initial dust load
level.1*
DUST PENETRATION WITH WOVEN GLASS FABRICS
Extensive laboratory and field measurements coupled with a detailed
analysis of the filtration process with conventional twill-weave glass fab-
rics have shown that coal fly ash emissions are due mainly to gas flow through
the low resistance paths afforded by unblocked pores, pinholes or other lead
regions in a filter.4'5 Furthermore, because relatively few particles are
removed from the gas fraction passing through the pores (nearly 100 percent
penetration for diameters < 15 ym), the particle size distributions are nearly
the same for up- and downstream aerosols provided that size measurements are
made in the immediate vicinity of the dirty and cleaned filter faces.1.4
The above factors suggest, therefore, that mass emissions from glass fab-
rics should depend in part upon (2) the inlet concentration and (b) the total
remaining unblocked pore region at any time. The latter item, (b), is governed
25
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10°
10
INTERFACIAL ADHESIVE FORCE, dynes/cm2
I ,«2
o
, .
O
i-
o
<£
cr.
U.
LU
o:
z !••
UJ
,.J
O
K^j:
r
~
i.
IQ
Figure 6.
l 1 1—i—r~T"T
° ' NUCLA ) HELD
O 2 SUNBURY/ DATA
o
3 BOW
)
oc s|
ief° w
2.52
I I L
_i I,.. ,1 L_. .
JO3
.
j
FABRIC LOADING, W-g/m2
Relationship between cleaned area fraction and initial
fabric loading. GCA fly ash and woven glass fabric
26
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by the amount of dust deposited on the cleaned filter face following resumption
of filtration. Given a glass fabric with no visible signs of weave imperfec-
tions and with a relatively uniform pore structure, the relationship between
outlet concentration, Co, and fabric dust loading, W, appears as shown in
Figure 7 for an average filtration velocity of 0.61 m/min (2 ft/min). After
fabric loadings increase to 60 to 80 grams/m2, however, the direct proportion-
ality between inlet and outlet concentrations disappears because of a second
contributor to outlet loading. The latter is the low level, essentially
steady state, slough-off of agglomerated dust from the downstream region of
the dust deposit as the result of aerodynamic reentrainment augmented by
mechanically generated vibrations.4'7 A conservative estimate of the magnitude
of this source strength place it as less than a 0.5 mg/m3 contributor, CR, to
the overall effluent loading.
Average face velocity has been shown to play a major role in determining
filter effluent concentrations. Following deposition of about 60 to 80 gram/m2,
Figure 8, steady state emissions are seen to increase from ~ 0.5 to 150 mg/m3
over the face velocity range of 0.39 to 3.35 m/min (1.3 to 11 ft/min). This
relationship indicates that seeking to reduce collector size by increasing the
face velocity (air to cloth ratio) may lead to unacceptably high emission
levels.
The solid line curves shown in Figure 8 represent the best mathematical
fits to the indicated data points. The outlet concentration, Co, is defined
by the local penetration level (Pn), the inlet dust concentration (C±), and
the previously cited residual concentration, CR = 0.5 mg/m3.
C0 = Pn C± + CR (10)
The formal equation structures and the precise manner in which they are applied
in the modeling process are presented in Reference 4. For present purposes,
it suffices to point out that the following expression
Pn or C0 * (((,, Clf W, V, CR)
describes penetration or effluent concentration as a function of , a parameter
characterizing the dust/fabric combination under test; constant inlet and
residual concentrations, C± and CR, respectively; and the time and position
dependent variables; i.e., local face velocity, V, and local fabric dust
loading, W.
The total (and average) filter system penetration, Pn, at some time, t,
for a system consisting of I compartments and J areal subdivisions per bag is
determined by successive iterations in accordance with the general summation
I
Pnt = vTT-j A: L> Pnij vij (ID
c i=l i=l Jt Jt
27
-------
o
o
z
o
I-
ff
H-
UJ
o
I
111
3
20
40 60 80 100
FABRIC LOADING {W),g/m2
120
140
Figure 7. Effect of inlet concentration on predicted outlet concen-
trations at a face velocity of 0.61 m/min. GCA fly ash
and Sunbury fabric.
28
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cr.
h-
o
O
o
i-
UJ
h-
O
4.60
3.55
j MCT£5: SOLID LINES ARE CURVES PREDICTED Bf MODEL.
SVMBOS..S REPRESENT ACTUAL DATA POINTS.
10
20 40 60 80 "
FABRIC LOADING (W),
l_._
I4O
Figure 8. Predicted and observed outlet concentrations for bench
scale tests. GCA fly ash and Sunbury fabric.
29
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SECTION 3
MODEL CAPABILITY
In the previous sections, the basic filtration equations and the iterative
approach for treating multicompartment systems have been reviewed. The follow-
ing discussion is intended to demonstrate how closely the predictive model
describes the overall fly ash filtration processes for utility applications.
The only major constraints for the model are that (1) the inlet aerosol should
consist of or possess the general physical properties of a coal fly ash and
(2) the fabric characteristics be similar to the woven glass media of the types
used in the field. Within the above framework, the model is sufficiently
flexible to meet the following criteria:
• The model is adaptable to either constant flow or constant
pressure conditions.
• The model can accommodate to a continuous cleaning regimen;
i.e., the immediate repetition of the cleaning cycle follow-
ing the sequential cleaning of successive individual
compartments, or
• The model can also describe the situation where lengthy
filtration intervals are encountered between the clean-
ing cycles.
• The model can be used with collapse and reverse flow sys-
tems and mechanical shaking systems or combinations of the
above. It is not intended for use with pulse jet or high
velocity reverse jet cleaning systems.
• The model can be used equally well with pressure or time
controlled cleaning cycles.
• The model provides estimates of average and point values
of filter drag or resistance for the selected set of
operating parameters and dust/fabric specifications.
• The model provides estimates of average and point values
for penetration and mass effluent concentration for the
selected set of operating parameters and dust/fabric
specifications.
30
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SECTION 4
MODEL APPLICATIONS
In Figure 9, a schematic flow diagram is shown for a filtration system
in which the approaching aerosol is distributed among I separate compartments
(each containing several bags) and £ separate filtration regions on each bag.
It is assumed for simplification that the performance of each compartment is
represented by the behavior of any single bag within the compartment and that
there are no concentration gradients in the approaching air stream. Con-
sequently, the model must describe the integrated effect of many parallel
flow paths through fabric surface elements bearing different dust loadings.
The local performance of each element, resistance- and penetrationwise, is then
defined by the equations presented in earlier sections of this paper.
An analysis of field measurements performed at the Nucla, Colorado Power
Station2»4 illustrates how the filtration model can be used to predict system
performance characteristics. The data inputs required to model the filtration
process are summarized in Table 1. Items 1 through 3 are based upon system
design or operating data provided by the manufacturer. The 2-minute minimal
time interval, Item 4, was chosen by the model user so that successive stepwise
iterations would always indicate the maximum, minimum and average system
resistance while any one compartment was off-line for cleaning.
Average face and average reverse flow velocities, Items 5 and 6,
respectively, are operating parameters also selected by the filter manufacturer.
Inlet dust concentration and average filtration temperature, Items 7 and 8,
are determined mainly by the combustion process and the type of fuel burned
The estimates of effective residual drag (SE), specific resistance coefficient
(K2), and residual dust loading (WR) (Items 9, 10 and 11, respectively) are
best determined by direct measurement if not already defined in the literature
for the dust/fabric combination of interest.
With respect to the operating parameters set forth in Table 1, it was
required that the system pressure loss just before fabric cleaning'should not
exceed a value of 1160 N/m* (4.7 in. water), (Item 12). Given this constraint,
the model has been used to determine the frequency of cleaning and the operat-
ing ranges for overall system pressure loss and effluent particulate concen-
trations. One key input parameter> i.e., the fraction of cleaned filtration
surface ac, produced when a given compartment (or bag) is cleaned, is presently
evaluated outside of the modeling program. The calculations are performed by
first estimating Wp from the maximum allowable pressure, P , by
ment of Equation (1); i.e., max' y
31
-------
Co
V
w
K)
i ll
w,,
•12
w,
12
CU C2I
W
U
W,
21
C22
W2
12**_iiFij V2il E?
2J
•12
r3I
Figure 9. System breakdown for I bags and J areas per bag.
-------
TABLE 1. REQUIRED DATA INPUTS FOR SPECIFIC MODEL APPLICATION*
Item
1
2
3
Variable
Number of compartments
Complete cleaning cycle
Cleaning time per
Description
6
24 minutes
4 minutes
Comment
System design parameter.
Time to sequentially clean six compartments.
Indicates total compartment off-line time.
5
6
7
8
9
10
11
12
compartment
Minimum time increment for
iterative computations
Average face velocity (v)
Reverse flow velocity (VR)
Inlet dust concentration (C.)
Temperature
Effective (clean)
fabric drag (S,,)
Ct
Specific resistance
coefficient
Residual dust loading (WR)
Cleaned fabric area
fraction (a )
2 minutes
0.824 m/min
0.0415 m/min
Provides data points for maximum, minimum
and average resistance and penetration
during off-line period for on-line
compartments.
Based on total flow and total fabric area.
Weighted average velocity over total (4 min-
utes) cleaning interval.
2.6 g/m3
412° K
434 N min/m3
Average baghouse temperature.
Based on linear extrapolation of drag versus
fabric loading measurements with uniform
dust deposit.
0.76 N min/g.m Value determined at 0.61 m/min and 25°C.
50 g/m2
0.375
Refers to surface loading on freshly cleaned
areas only.
Fraction of cleaned surface exposed when
cleaning is initiated with a fabric
loading corresponding to a resistance
of 1160 N/m2
Modeling of actual field performance of stoker-fired boilers at Nucla, Colorado, Colorado Ute
Electric Association.2'^
-------
Wp = (ISS - SE) /K2 (la)
In Equation (la), Wp is the unique (uniformly distributed) fabric loading
associated with the maximum allowable pressure loss. P
' max
The a value may then be computed as indicated below:
ac = 1.51 x ID"8 Wp2-52 (8)
With the introduction of ac, the program is ready to generate a tabular and/or
graphical printout that can provide interim, individual compartment, and over-
all system performance parameters.
Figure 10 shows the predicted and actual filter resistance characteristics
versus operating time, the latter providing a direct measure of fabric dust
loading when volume flow rate and inlet dust loading are constant. The good
agreement between these curves suggests that the physical concepts used in the
model development are a fair expression of the actual system operation. A
comparison of selected reference points summarized in Table 2 also illustrates
the degree of success attainable with the model.
Figure 11 predicts the changes in overall effluent concentrations that
should be expected during periods of filter cleaning and during those periods
when all compartments are on line. Although there are no field measurements
available to confirm the short term, ~ minutes, predictions for the Nucla
baghouse, the weighted average values derived from these curves, agree will
with the corresponding field measurements.
TABLE 2. PREDICTED AND MEASURED RESISTANCE CHARAC-
TERISTICS FOR NUCLA FILTER SYSTEM
Actual Predicted
N/m2 in. H20 N/m2 in. H20
Maximum resistance during
cleaning
Initial resistance follow-
ing cleaning
Maximum resistance just
before cleaning*
Time between successive
cleaning cycles
1700
850
1160
150
6.8
3.4
4.7
min
1520
720
1160
188
6.1
2.9
4.7
min
*
Fixed value for predicted conditions.
34
-------
ro
i
O
A MEASURED
© PREDICTED
100 200
TIME , minutes
300
400
Figure 10. NUCLA baghouse simulation, resistance versus time,
35
-------
TEST RUN « 0422 NUCLfl^pHGHCUSE S I K'J'.iP.T I CN-L I NEflR
PENETRflTION VS •• - -
TIME GR.-P
ov
280.00 320.00 3BO. 00 400.00 440.00 480.00
40~00 80~00 120.00 160.00 200.00 240.00 2
TIME MINUTES)
Figure 11. Test run No. 0422 Nucla baghouse simulation - linear penetration
versus time graph.
-------
Preliminary model validations were also conducted based upon a combination
of field and laboratory tests relating to the fabric filtration equipment at
the Sunbury Station of the Pennsylvania Power and Light Company1'4 The results
for both Sunbury and Nucla modeling operations are compared with actual test
observations in Table 3. In view of the early development stage of the model,
the overall agreement between actual and predicted values is considered to be
highly satisfactory.
The differences between observed and predicted values are attributed to
a combination of factors including simplifications in the modeling mathematics
and uncertainties in some data inputs. Improvements in model reliability are
expected to result from a sensitivity analysis now in progress and the conduct
of further field and laboratory measurements.
In the preceeding discussions, the reportings on model structure and its
applications represent but a small part of a very extensive study.4 Although
only the linear model is described here, the computer program is also written
to accept the condition where use of the true residual drag, SR, and a
curvilinear drag/fabric loading relationship may afford better estimates of
filter system performance. The detailed studies also indicate several tech-
niques whereby the key data inputs can be adjusted to satisfy a broad range
of operating conditions.
37
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TABLE 3. MEASURED AND PREDICTED VALUES FOR FILTER SYSTEM PENETRATION AND RESISTANCE,
COAL FLY ASH FILTRATION WITH WOVEN GLASS FABRICS
OJ
oo
Data source
Test _ . . . period
Description
case
A Sucla, Colo. 9/21/74
B Sunbury, PA 1/08/75
C Sunbury, PA 3/20/75
to
3/22/75
Penetration
Percent penetration
Bag
service Measured
Average
6 months 0.21
2 years 0.06
1.5 days 0.15
* Predicted
_.Linear model
Average ^Claanin
0.19 1.52
0.20
0.20
.*
Resistance
Test
case
A
B
Measured
Maximum
Average cleaning Maximum
1030 1700 1160§
635 710 710*
Minimum
Average
8505 972
560* 620
Predicted
Linear model
Maximum .
cleaning
1521 1160§
663 663*
Minimum
720§
567*
Based on field measurements. See References 1 and 2.
All values listed as average depict overall system performance (penetration and
.resistance) for combined cleaning and filtering cycles.
All values listed under cleaning describe performance parameter during cleaning
only.
Maximum-minimum with Nucla tests indicate resistance immediately before and
after cleaning.
Maximum-minimum with Sunbury tests indicate values for envelope curve.
-------
SECTION 5
SUMMARY
The mathematical model described here represents a new and very effective
technique for predicting average and instantaneous resistance and emission
characteristics during the filtration of coal fly ash with woven glass fabrics.
Two basic concepts used in the model design, (1) the quantiative descrip-
tion of the filtration properties of partially cleaned fabric surfaces and
(2) the correct description of effluent particle size properties for fabrics
in which direct pore or pinhole penetration constitutes the major source of
emissions, have played important roles in structuring the predictive
equations.
A third factor in the model development was the formulation of explicit
functions to describe quantitatively the cleaning process in terms of the
method, intensity and frequency of cleaning. By cleaning we refer specifically
to the amount of dust removed during the cleaning of any one compartment and
the effect of its removal on filter resistance and penetration characteristics.
The success of the model, based upon limited applications to field data,
suggests strongly that it be further evaluated. Minor changes in existing
compliance type sampling methods and apparatus should provide the key data for
resistance/fabric loading relationships that are fundamental to the applica-
tion of the model. Additionally, such measurements should help to confirm
the present observation that electrical charge and/or humidity factors do not
appear to play an important role in fly ash filtration with glass fabrics.
Application of the concepts presented here and in Reference 4 to other dust/
fabric combinations should provide a rational basis for treating heretofore
unresolved problems in many field filtration applications.
39
-------
1. Cass, R.W., and R.M. Bradway. Fractional Efficiency of a Utility Boiler
Baghouse: Sunbury Steam-Electric Station. GCA/Technology Division,
Bedford, Massachusetts. Control Systems Laboratory, U.S. Environmental
Protection Agency, Research Triangle Park, N.C. Report No. EPA-600/2-76-
077a (NTIS No. PB253-943/AS). March 1976.
2. Bradway, R.M., and R.W. Cass. Fractional Efficiency of a Utility Boiler
Baghouse - Nucla Generating Plant. GCA/Technology Division, Bedford,
Mass. Control Systems Laboratory, U.S. Environmental Protection Agency,
Research Triangle Park, N.C. Report No. EPA-600/12-75-013a (NTIS
No. PB246-641/AS). August 1975.
3. Billings, C.E., and J.E. Wilder. Handbook of Fabric Filter Technology,
Volume I, Fabric Filter Systems Study: GCA/Technology Division. EPA
No. APTD 0690 (NTIS No. PB-200-648). December 1970.
4. Dennis, R., et al. Filtration Model for Coal Fly Ash with Glass Fabrics.
Industrial Environmental Research Laboratory, U.S. Environmental Protec-
tion Agency, Research Triangle Park, N.C. Report No. EPA-600/7-77-084.
August 1977.
5. Dennis, R., R.W. Cass, and R.R. Hall. Dust Dislodgement from Woven
Fabrics Versus Filter Performance. APCA Paper 77-32.3. Presented at
the 70th APCA Annual Meeting, Toronto, Ontario, Canada. June 20-24, 1977.
6. Dennis, R., and J.E. Wilder. Fabric Filter Cleaning Studies. GCA/
Technology Division, Bedford, Mass. Control Systems Laboratory, Research
Traingle Park, N.C. Report No. EPA-650/2-75-009. January 1975.
7. Leith, D., and M.W. First. Particle Collection by Pulse-Jet Fabric Filter.
Presented at 68th Annual APCA Meeting, Boston. 1975.
8. Ensor, D.S., R.G. Hooper, and R.W. Scheck. Determination of the Frac-
tional Efficiency, Opacity Characteristics, and Engineering Aspects of a
Fabric Filter Operating on a Utility Boiler. Final Report. Meteorology
Research Inc., Altadena, California. EPRI-FP-297. November 1976.
9. Robinson, J.W., R.E. Harrington, and P.W. Spaite. A New Method for
Analysis of Multicompartment Fabric Filtration. Atmos Environ.
1:499-508, 1967.
10. Walsh, G.W., and P.W. Spaite. An Analysis of Mechanical Shaking in Air
Filtration. J Air Pollut Control Assoc. 12:57, 1962.
11. LOffler, F. Investigating Adhesive Forces Between Solid Particles and
Fiber Surfaces. Staub (English Translation). 26:10. June 1966.
12. Corn, M. The Adhesion of Solid Particles to Solid Surface. A Review,
J Air Pollut Control Assoc. 11:523, 1961.
13. Zimon, A.D. Adhesion of Dust and Powder. Plenum Press, New York,
1969. p. 112.
40
-------
A PILOT PLANT STUDY OF VARIOUS FILTER MEDIA
APPLIED TO A REFUSE BOILER
By
JOHN C. MYCOCK
Paper Presented At
Fabric Filter Symposium
Tucson, Arizona
December 5, 1977
Sponsored By
Federal Environmental Protection Agency
Industrial Environmental Research Laboratory
41
-------
Acknowledgements
This program was sponsored by the Federal Environmental Protection Agency
with Nashville Thermal Transfer as the prime contractor and Enviro-Systems and
Research, Inc. as the major subcontractor.
The author wishes to acknowledge the vital role played by each of the
participants.
This project has been funded at least in part with Federal funds from the
Environmental Protection Agency under Contract Number R80-4223. Q) The con-
tent of this publication does not necessarily reflect the views or policies
of the U.S. Environmental Protection Agency, nor does mention of trade names,
commercial products or organizations imply endorsement by the U.S. Government.
42
-------
Abstract,
A pilot scale investigation was conducted to determine the techno-economic
feasibility of applying fabric filter dust collectors to solid refuse-fired
boilers. The pilot facility, installed on a slip stream of a 135,000 Ib/hr.
boiler, was sized to handle a 9,000 ACFM at an air-to-cloth ratio of 6 to 1.
Filter media evaluated included PTFE laminate on a woven backing, woven glass
and felted glass.
Overall efficiencies greater than 99.8% were achieved with all three types
of filter media tested when operating at air-to-cloth ratios of 6 to 1 or less
and having an inlet loading of 0.5 gr/DSCF. For the brief exposure period
encountered during the performance testing, all three of the bag materials
tested indicated no wear problems.
The pressure drops obtained for the three filter media were within the
conmercially acceptable range.
The installed, operating and annualized costs for fabric filters were
developed and compared with the economics of wet scrubbing and electrostatic
precipitation. This analysis indicated that the annualized costs of the
electrostatic precipitator and the fabric filter are very close.
43
-------
In June 1976, an EPA sponsored pilot scale investigation was initiated.
The purpose of the study was to determine the techno-economic feasibility of
.applying fabric filter dust collectors to a refuse-fired boiler. Included
in the program was the screening of a variety of filter media. These included
Gore-Tex (a PTFE laminate on a PTFE woven backing), supplied by W.L. Gore and
Associates, Inc.f a woven glass bag (22^ oz. with Q78 finish), supplied by
Globe Albany Filtration and. an experimental needled felt glass bag supplied
by the Huyck Corporation.
The test program was conducted on an existing fabric filter (baghouse)
system that is presently installed on the slip stream of a refuse boiler
owned and operated by the Nashville Thermal Transfer Corporation (NTTC) r a
public authority of the State of Tennessee. By burning approximately 25%,
the city's daily output of refuse, this plant can supply steam and chilled
water to a number of downtown buildings,, including the State Capitol.
An experimental program was conducted by NTTC in 1975 for the purpose of
establishing methods of controlling pollution from refuse-fired boilers.
Enviro-Systems & Research was selected to participate in this program and
provided NTTC with a two (2) module Enviro-Clean RA-1 rectangular dust col-
lector to be used as a vehicle for filter media screening. A second baghouse,
an Ess Tee pulse jet type was also tested. Only a very preliminary screening
of filter media was included in this original program which was terminated
due to monetary considerations, but data obtained indicated that a fabric
filter dust collector was capable of achieving excellent dust collection
efficiencies; therefore the EPA funded program was instituted to confirm and
validate this data.
The Enviro-Systems & Research baghouse is designed to contain a total of
1660 square feet of cloth. The house is subdivided into twelve (12) separate
cells, each cell having twelve (12) bags.
The operation of the baghouse is as follows: the dirty gases enter one
end of the unit, pass through the tapered duct, into the classifier, then
through the bags. The classifier forces the dirty gases to change direction
90°, then 18CP. This quick directional change forces the larger and heavier
44
-------
particles out of the flow so that they will fall directly into the hopper.
Dirty gases enter the classifier through a central duct tapered to feed the
sane quantity of gas into each cell. The gases are forced through the fabric
filter into the center of the bags. The cleaned gases are drawn up and out
through the center of the filtering bag into a center exit plenum via an
open damper in the cell above the tube sheet (to which the bags are locked
on top and bottom via snap rings).
As solid matter collects on the outside of the filter bag, it builds a
cake or crust which begins to restrict the flow of gases. The bags are
cleaned one cell at a time by closing off the cell damper. Clean air enters
through the damper, is forced down the filter bag (opposite the normal flow
direction), and expands the bag with such a shock that the "cake" is cracked
and particulate matter falls off the bag and into the hopper. Damper systems
and control panel arrangements allow for variations in main gas volume,
reverse air volume, duration of cleaning and frequency of cleaning.
The pilot plant was originally installed on one of the NTTC boilers in
September 1975. The slip stream is a 16 inch duct approximately 250 feet
long with numerous turns. This duct is covered with 1^ inch metal-skinned
insulation to decrease heat loss. The outlet and reverse air duct were also
insulated. A temperature profile (Figure 2) shows a maximum temperature of
350° F in the inlet duct while the maximum at the outlet was 18CP F. Figure
3 is a photograph of the plant.
An inlet profile was obtained at the beginning of the ES&R program and
again during the testing of the needled glass fabric. Tables 1 and 2 list
these results. Although chloride and flouride concentrations could result
in increased bag deterioration, we found no evidence of this during the
program.
Rigorous sampling indicated that changes in the inlet loading had no
significant effect on outlet loading. Therefore, an average inlet concen-
tration was calculated from data obtained during concentrated testing efforts
in March of 1977 and used as the basis for all total mass and fractional
efficiencies.
45
-------
ELEVATION
END view
Figure 1
Schematic Diagram of the Enviro-Clean RA-1 Dust Collector Model 144-RA1-5-104
-------
Figure 2
Temperature Profile for the Enviro-Systems Baghouse
-------
Figure 3. Fabric Filter Pilot Plant Installed at
Nashville Thermal Transfer Corp.
48
-------
TABLE 1
NASHVILLE THERMAL TRANSFER
Test Data
Date
Gas Temperature (avg. °F)
Stack Rate (SCFMD)
Flue Gas Composition
H20 (%)
02 (%)
CO (%)
C02 (X)
Particulate Concentration
(Grains/SCFD)
Isokinetic Rate (%)
Cl (ppm)
F (ppm)
[house Inlet Gas Stream Profile
1
7/29/76
F) 411
1583
15.94
7.1
12.9
>n
0.72
109.16
84.1
7.09
Run Number
2
7/30/76
443
1581
16.03
7.1
12.9
1.38
109.3
83.7
0.8
3
7/30/76
410
1520
18.68
7.1
12.9
1.76
94.3
68.04
0.61
49
-------
TABLE 2
INLET EMISSION PROFILE
Date
11/20/76
Stack Temp. (Avg.°F)
Stack Rate (SCFMD)
Stack Rate (ACFM)
Flue Gas Composition
H20 (%)
02 (20
C02 (%)
Metered Gas Volume (SCFD)
Particulate Concentration
(Grains/SCFD)
Emission Rates (Ib/Hr)
Isokinetic Rate (%}
F (ppm)
360°F
2252.2
3826.6
7%
10.88 %
7.25 %
21.90
1.1634
22.46
101.2%
0.2
50
-------
Figure 4 shows the average inlet particle size distribution.
Needled Glass Felt
Outlet particulate concentrations obtained when varying the apparent
velocity or more comonly - the air-to-cloth ratio (A/c ratio) for the glass
felt are provided in Table 3. As is evident in this table, the needled
glass felt proved to be an extremely efficient filter media for this appli-
cation at all A/C ratios studied.
Outlet particle size distribution for air-to-cloth ratios of 3.2, 6.4
and 8.7 to 1 is graphically displayed in Figure 5. In ascending order, the
percentages of fabric penetration of particles less than three (3) microns
are 50%, 41% and 34% respectively.
Woven Glass
The woven glass bags were employed at air-to-cloth ratios of 2.75, 4.2
and 6.7. Figure 6 shows the particle size distribution for the A/C ratios.
The curves also indicate that as the air-to-cloth ratio is increased, the
percentage of sub-micron particles (when compared to total emissions) also
increases.
Average outlet concentrations and relative cumulative percentages are
shown in Table 4. Although not quite as efficient as the other fabrics
tested, woven glass proved more than satisfactory to meet present code
requirements.
; PTFE Laminate
The PTFE laminate was employed at air-to-cloth ratios of 4.2, 5.4 and
6.0 and once again the outlet particulate concentrations and particle size
distributions were determined. Particle size data is shown in Figure 7.
For the lowest air-to-cloth ratio the penetration of sub-micron particles
is 41% of total particulate penetration. Outlet concentration and cumulative
percentages are listed in Table 5. While there seems to be no clear correla-
tion between filtration velocity and outlet dust concentration, it is
51
-------
30.0
2t).0
10.0
IS)
c
o
I 5.0
0)
IM
CO
0)
s_
(O
O-
1.0
0.7
O Run 2
A Run j
JL
_L
JL
J_
J_
JL
_L
_L
JL
J
.512 5 10 20 30 40 50 60 70 80
Percent Less Than Size Indicated
Figure 4
Inlet Particle Size Distribution for Two
Brinks Impactor Runs
(3/33/77)
52
-------
TABLE 3
Ui
OUTLET CONCENTRATION AND
Air-to-Cloth 3.2/1
Avg. (1) Avg. (2)
Part. Outlet
Diam. Cone.
Microns gr/SCFD
9.33
6.23
4.20
2.77
1.33
0.80
0.57
0.30
0.30
TOTAL
.0001834
.0000657
.0000391
.0000459
.0000744
.0000286
.0000434
.0000455
.0000482
.0005742
Cum % (3)
100.00%
68.04
56.6
49.79
41.8
28.85
23.87
16.31
8.39
Huyck Bags
Air-to-Cloth 6.
Avg.. Avg.
Part. Outlet
Diam. Cone.
Microns gr/SCFD
9.33
6.23
4.20
2.77
1.33
0.80
0.57
0.30
0.30
TOTAL
.0001770
.0000502
.0000592
.0000207
.0000154
.0000302
.0000155
.0000156
.0000494
.0004332
CUMULATIVE %
4/1
Cum %
100.00%
59.02
47.43
33.76
28.99
25.54
18.57
15.0
11.40
Air-to-cloth 8.7/1
Avg. Avg.
Part. Outlet
Diam. Cone.
Microns qr/SCFD Cum £
9.33
6.23
4.20
2.77
1.33
0.80
0.57
0.30
0.30
TOTAL
.0005394
.0002472
.0002162
.0001229
.0000849
.0000697
.0000338
.0000485
.0001073
.0014699
100.00%
63.31
46.49
31 . 78
23.42
17.64
12.9
10.6
7.30
(1) Corrected for Stack Temperature
(2 gr/SCFD - Grains Per Standard Cubic Foot Dry (Standard - 7QQF,
(3) Percent of Total Outlet Concentration Less Than Size Indicated
29.92" Hg)
-------
to
•Zi
o
M
i—i
00
a:
-------
10
20 30 40 5.0 60 70
% Less Than Size Indicated
80 90
Figure 6
Outlet Particle Size Distribution, Globe Albany
55
-------
TABLE 4
Outlet Concentration and Cumulative %
Air-to-cloth 2.75/1
Avg. (1) Avg. (2)
Part. Outlet
Diam. Cone.
Microns gr/SCFD Cum%
8.85 ^0003446 100.0~OT
(3)
Ul
6.03
4.10
2.63
1.33
0.84
0.54
0.17
0.17
TOTAL
.0001473
.0000631
.0000625
.0000417
.0000431
.0000515
.0000493
.0008031
57.09
38.75
30.89
23.11
17.92
12.55
6.14
Globe
Albany Bags
Air-to-cloth 4.2/1
Avg.
Part.
Diam.
Microns
78.85
6.03
4.10
2.63
1.33
0.84
0.54
0.17
0.17
TOTAL
Avg.
Outlet
Cone.
gr/SCFD
.0001936
.0000647
.0000536
.0000618
.0000601
.0000558
.0000482
.0001009
.0000843
.0007230
Cum%
1075700%'
73.23
64.28
56.87
48.32
40.01
32.29
25.62
11.66
Air-to-cloth 6.7/1
Avg.- Avg.
Part. Outlet
Diam-. Cone.
Micron gr/SCFD Cum%
78.85 .0001936 10~0.00%
6.03 .0000415 91.63
4.10 .0000411 87.33
2.63 .0000506 83.07
1.33 .0000456 77.83
0.84 .0000828 73.01
0.54 .0001134 64.44
0.17 .0002527 52.69
0.17 .0002563 26.53
TOTAL .0009659
(1) Corrected for Stack Temperature
(2) gr/SCFD - Grains Per Standard Cubic Foot Dry (Standard - 70°F, 29.92"
(3) Percent of Total Outlet Concentration Less Than Size Indicated
Hg)
-------
8.0
7.0
6.0
5.0
4.0
3.0
A
o
KEY
O 4.2/1
A 5.4/1
06/1
I l
10 20 30 40 50 60 70 80 90
% LESS THAN SIZE INDICATED
Figure 7
Outlet Particle Size Distribution for Gore-Tex Fabric
57
-------
Ui
CO
Air-to-cloth 4.2/1
Avg. Avg.
Part. Outlet
Diam. Cone.
Microns gr/SCFD
8.4
5.7
3.9
2.5
1.2
0.77
0.48
0.41
0.41
Cum.%
.0001760 100.00%
.0000235 67.28
.0000512
.0000372
.0000666
.0000637
.0000581
.0000221
.0000402
62.92
53.42
46.52
34.16
22.34
11.56
7.46
TOTAL .0005388
TABLE 5
Outlet Concentration and Cumulative %
Gore-Tex Bags
March
Air-to-cloth
Avg.
Part. Outlet
Diam. Cone.
Micronsgr/scFD
8.4
5.7
3.9
2.5
1.2
0.77
0.48
0.41
0.41
TOTAL
.0001628
.0000961
.0002230
.0000564
.0000423
.0000333
.0000179
.0000179
.0000230
.0006727
1977
5.4/1
Cum.%
100.00%
75.71
61.42
28.27
19.93
13.64
8.74
6.08
3.42
Ai
r-to-cloth
Avg. Avg.
Part. Outlet
Diam. Cone.
Microns gr/SCFD
8.4
5.7
3.9
2.5
1.2
0.77
0.48
0.41
0.41
TOTAL
.0001703
.0000605
.0000688
.0000461
.0000251
.0000346
.0000374
.0000213
.0000482
.0005123
6/1
Cum.%
100.00%
66.75
54.94
41.51
32.51
27.61
20.86
13.56
9.40
1) Corrected for ;Stack Temperature
2) The outlet concentration for the air-to-cloth ratio of 5.4 was not an average of two values
gr/SCFD - Grains Per Standard Cubic Foot Dry (Standard - 70° F, 29.92" Hg)
3) Percent of Total Outlet Concentration Less Than Size Indicated
-------
evident that the PTFE laminate is extremely efficient at the three air-to-
cloth levels studied.
As shown in Figure 8, for air-to-cloth ratios of approximately 3 and 6
to 1 the felted glass snowed the lowest dust concentrations and the woven
glass media the highest. However, as I had stated before, the v.'oven glass
media was considered more than satisfactory to meet present code requirements
for this application.
Economic Considerations
The economics of applying fabric filters to the refuse-fired boilers
were evaluated and comparative costs for an electrostatic precipitator (ESP)
and wet scrubber were developed. Installed costs were calculated for a
fabric filter dust collector sized to handle 140,000 acfm at 46CP F. The
costs were developed for four (4) filter media: woven glass, PTFE laminate,
needled glass felt, and Teflon felt (style 2663). Air-to-cloth ratios con-
sidered were 2.9,5.8, 8.9 and 11.3 Table 6 shows the costs were developed
from actual bag manufacturer quotes obtained during 1976.
The installed costs for an electrostatic precipitator capable of handling
140,000 ACFM at 98.5% efficiency were also developed. This cost was developed
by adding the flange-to-flange cost (supplied by a leading ESP manufacturer)
plus 70% of the purchase price for erection cost (the same figure was used in
the fabric filter case), plus 5% of the purchase price for fans.
A graphical comparison of the installed costs for the four bag materials
versus the installed costs of the electrostatic precipitator is shown in
Figure 9. At air-to-cloth ratios of 5.8/1 or greater, the installed costs
of the fabric filter (for all bags considered) was lower than the electrostatic
precipitator.
Installed costs for a wet scrubber capable of handling 140,000 ACFM with
99% efficiency and a pressure drop of 30" W.G. were derived by doubling the
figure of $316,000 for 70,000 ACFM given in the article "Performance and Cost
Comparison between Fabric Filters and Alternate Particulate Control Techniques"2
and adding 12% for escalation. 59
-------
.0014
.0013
.0012
.0011
in
- .0010
CD
I
C
O
4->
to
o>
(J
c
O)
.0009
.0008
.0007
,§ .0006
.0005
.00041-
O Huyck Experimental
Q Globe Albany
A Gore-Tex
2 3 4 5 67 8
Air-to-Cloth Ratio (ACFM/Ft.2)
10
Figure 8
Comparison of Three (3) Fabrics for Outlet Concentration
vs. Air-to-Cloth Ratio
60
-------
TABLE 6
Bag Cost as Percent of Installed Cost
Globe Albany ($17.25/bag)
2.9
5.8
8.9
11.3
Huyck($32.40/bag)
2.9
5.8
Y1
8.9
11.3
Installed Cost
817,260
421,750
316,734
271,837
928,522
477,381
353,821
301,505
Bag Cost
74,520
37,260
24,840
19,872
139,968
69,984
46,656
37,325
% of Installed
Cost for Bags
9.1
8.8
7.8
7.3
15.1
14.7
13.2
12.4
Gore-Tex/Gore-Tex ($51.50/bag)
2.9 ;
5.8
8.9
11.3
Teflon Felt ($68/bag)
2.9 i
5.8
8.9
11.3
1,068, 792
547,516
400,578
338,912
,189,968
608,104
440,970
371,226
222,480
111,240
74,160
59,328
293,760
146,880
97,920
78,336
20.8
20.3
18.5
17.5
24.7
24.1
22.2
21.1
61
-------
1200
1000 -
800 _
cc.
i—i
-------
A comparison of the three methods of particulate control is seen in
Figure 10. The fabric filter technique for air-to-cloth ratios of 5.8/1 and
greater on all bags considered has the lowest installed cost and the wet
scrubber the highest. However, should an air-to-cloth ratio of 2.9/1 be
required, fabric filters would be the most expensive and the electrostatic
precipitators the least expensive method. Development of the operating and
annualized costs for the three control techniques, employed the formulae
published by Edmisten and Bunyard.3
Operating costs were developed for the fabric filters with two and four
year bag life and compared with those of the electrostatic precipitator.
Fabric filter costs were based on pressure drops of 6", 7", 10.5" and 12.5"
W.G. for air-to-cloth ratios of 2.9, 5.8, 8.9 and 11.3/1 respectively. Pre-
cipitator costs were based on a pressure drop of 2" W.G. (all pressure drop
values included 1.5" W.G. for drop across the inlet duct) and maintenance
costs of 3% of the flange-to-flange price (considered higher than average but
used due to the corrosive elements in the gas stream). Electrical rates for
both cases were actuals obtained from NTTC. These costs presented in Figures
11 and 12 show the electrostatic precipitator to be less expensive to operate
than any of the fabric filter cases considered.
While studying these graphs one must remember that in the formula for
calculating annual operating costs for a specific bag life only two variables
exist:
1. the number of bags (which decrease with increasing A/O.
2. the pressure drop (which increases with increasing A/C) .
It appears that at some point in the increase of the air-to-cloth ratio
for a particular bag life, the effect of the increase in pressure drop out-
weighs the effect of the decrease in number of bags required.
As I had stated previously all bag materials were treated the sane with
regard to pressure drop. Actual pressure drops obtained during the course of
63
-------
Installed Costs x 10 Dollars
zs
to
rt-
Ol
CD
QL
O
O
o
o
O rt- -"•
— '• -s l/l
-h O O
-+1—13
fD to
-S -H
(t> (D -h
300
c-t- rr -s
fD
-+> c:
o
fD
n
fD
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Filtration Precipitation Scrubbing
(A/C 5.8/1)
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A Huyck Glass Felt
Globe Albany Woven Glass
ESP (98.5% Efficiency)
6 8
AIR-TO-CLOTH (ACFM/FT.2)
10
12
Figure 11
Comparison of Annual Operating Costs of Four (4)
Filter Media and ESP Assuming Four Year Bag Life
65
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KEY:
O Teflon Felt
^ Gore-Tex/Gore-Tex
A Huyck Glass Felt
n Globe Albany Woven Glass
-- ESP C98.5% Efficiency)
O
Q
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co
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6 8 10
AIR-TO-CLOTH (ACFM/FT.2)
Figure 12
Comparison of Annual Operating Costs of Four (4)
Filter Media and ESP Assuming Four Year Bag Life
12
66
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the program, although well within the commercially acceptable range, were not
vised for this comparison because of the suspected influence of the sub-dew
point conditions that plagued us throughout the program.
A comparison of the annual operating costs for the three techniques of
control is illustrated in Figure 13. The electrostatic precipitator is seen
to be the most economical while the wet scrubber seems the most expensive
approach.
The annualized costs or total costs of control were developed from the
preceding installed and operating costs. These results shown in Figures 14
and 15 were based on the following assumptions: First, hardware and instal-
lation costs are depreciated over fifteen (15) years. Second, the straight
line method of depreciation (6 2/3% per year) is used. This method has the
simplicity of a constant annual write-off. Third, other costs called capital
charges, which include interest, taxes, insurance and other miscellaneous
costs are assumed equal to the amount of depreciation, or 6 2/3% of the initial
installed costs. Therefore, depreciation plus these other annual charges
amount to 13 1/3% of the installed costs.
As illustrated in Figures 14 and 15, fabric filters, at air-to-cloth
levels of 5.8/1 or greater, and electrostatic precipitators are extremely
competitive on an annualized costs basis.
Figure 16 shows the comparison of the annualized costs of control for
the three techniques studied. Once again the wet scrubber is the most expen-
sive approach, while the costs of the fabric filter and electrostatic precip-
itator are very close. This being the case, the need to replace bag life and
pressure drop assumptions in computations for operating costs with empirical
facts is necessary for final selection of the best alternative.
67
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300
200
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£ 100
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98. 5%
Fabric
F iltration
(A/C 5.8/1)
Electrostatic Wet
Precipitation Scrubbing
Figure 13
Annual Operating Cost Comparison for Three Air
Air Pollution Control Teqhm'ques
68
-------
350
300
250
KEY:
O Teflon Felt
O Gore-Tex/Gore-Tex
A Huyck Glass Felt
Q Globe Albany Woven Glass
— ESP (98.5% Efficiency)
200
GO
D;
O
O
ro
O
oo
O
o
150
~ 100
50
,-
^ 6 8 10
AIR-TO-CLOTH (ACFM/FT.2)
Figure 14
Comparison of Annual Operating Costs of Four (4)
Filter Media and ESP Assuming Two Year Bag Life
69
12
-------
300
250
200
oo
DC
O
Q
150
KEY:
O Teflon Felt
O Gore-Tex/Gore-Tex
A tiuyck Glass Felt
CH Globe Albany Woven Glass
— ESP (98.5% Efficiency)
oo
O
LlJ
t-vl
100
50
JL
6 8 10
AIR-TO-CLOTH (ACFM/fT.2)
12
Figure 15
Comparison of Annual Operating Costs of Four (4)
Filter Media and ESP Assuming Four Year Bag Life
70
-------
CO
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ri
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300
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200
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99. 8%
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0)
98. 5%
Fabric;
Filtration
Electrostatic Wet
Precipitation Scrubbing
Figure 16
Annualized Cost for the Three Air Pollution Control Techniques
71
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CONCLUSIONS
The three filter media tested for dust reiroval capability indicated high
level removal over a range of air-to-cloth ratios (apparent filtration velo-
city) . For air-to-cloth ratios of approximately 3 to 1 and 6 to 1 the felted
glass media showed the lowest outlet dust concentration and the woven glass
media was considered more than satisfactory to meet present code requirements
for this application.
No clear correlation between filtration velocity and outlet dust concen-
tration was demonstrated. There may well be such a correlation, however,
testing circumstances did not allow for determination of it in this program.
The three filter media for dust removal capability did not show signs
of wear or weakening during this test program. It should be noted, however,
that total on-stream time was very limited.
The pressure drops obtained for the three filter media were within the
commercially acceptable range.
Generalizations regarding the costs of particulate removal devices are
inherently dangerous, however, it does appear that of the conventional routes
to particulate control, only fabric filters and electrostatic precipitators
are suitable to refuse-fired boilers. The economic analysis indicates that
the wet scrubber has both higher operating and capital costs (and, therefore,
higher total annualized costs) than either the electrostatic precipitator or
fabric filter.
In view of this and considering its potential for corrosion, the wet
scrubber appears to be an unlikely candidate for this application.
As previously mentioned, the economic analysis indicate that the annual-
ized costs of the electrostatic precipitator and the fabric filter are very
close. Final selection of the best alternative can only be made after bag
life and pressure drop assumptions have been replaced with empirical facts.
72
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References
1) J.D. McKenna, J.C. Mycock, R.L. Miller, K.D. Brandt, "Applying Fabric
Filtration to Refuse Fired Boilers", Report to be published by EPA.
2) J.D. McKenna, J.C. Mycock and W.O. Lipscomb, "Performance and Cost
Comparisons Between Fabric Filters and Alternate Particulate Control
Techniques", JAPCA, V24, N12 December 1974, P1144.
3) N.G. Edmisten and F.L. Bunyard, "A Systematic Procedure for Determining
the Cost of Controlling Particulate Emissions from Industrial Sources",
J. Air Pollution Control Association V20, N7, p.446 (1970).
73
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74
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FIELD TESTS WITH A MOBILE FABRIC FILTER
Dale L. Harmon
Particulate Technology Branch
Industrial Environmental Research Laboratory
Research Triangle Park, N. C. 27711
December 1977
Abstract
In 1973, EPA funded the design and construction of a mobile fabric
filter unit, the first of a series of three mobile research units built
for the assessment of the collectibility of particulate emissions from
industrial sources. The mobile filter unit can be adapted to cleaning
by mechanical shaking, pulse jet or low-pressure reverse flow. Cleaning
parameters can be varied easily over broad ranges. The paper presents
results of tests completed on a brass and bronze foundry, a hot mix as-
phalt plant, a pulp mill lime recovery kiln, a refuse processing plant
the three coalfired boilers. The most recent test was at the Amarillo,
Texas Harrington Station generating plant of the Southwestern Public
Service Company. Low-sulfur subbituminous coal was burned. Woven Teflon
coated fiberglass and woven graphite - and - silicone - coated fiberglass
bags were tested in shake and reverse air cleaning modes. Total mass
efficiency for all tests ranged from 99.56% to 99.99% with an overall
average of 99.87%. Bag blinding problems were encountered with reverse
cleaning.
75
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FIELD TESTS WITH A MOBILE FABRIC FILTER
Dale L. Harmon
Particulate Technology Branch
Industrial Environmental Research Laboratory
Research Triangle Park, N. C. 27711
December 1977
INTRODUCTION
The Environmental Protection Agency and predecessor organizations
have been involved in development of systems for control of emissions
from industrial sources for many years. The EPA R&D program for particulate
control is designed to establish engineering design techniques and
performance models, and to improve the collection capability and economics
of control devices for particulate matter. The objective is the development
and demonstration of control technologies capable of effectively removing
large fractions of the under 3 micron diameter particles from effluents.
In 1973, EPA funded the design and construction of a mobile fabric
filter unit, the first of a series of three mobile research units built
for the assessment of the collectibility of particulate emissions from
industrial sources. These units house the three types of conventional
particulate collectors (fabric filter, wet scrubber and electrostatic
precipitator) that are generally used by industry at the present time.
Actual data on particle collection efficiency of conventional
particulate collectors is sparse. Actual operating data for the optimization
of collection efficiency and cost is not readily available. Design of
control equipment is presently based on projections from historical data
which has been developed by manufacturers for their own devices and is
proprietary. This information is not standardized and cannot be extrapolated
to other devices. On-site testing prior to control device selection is
seldom attempted and the possibility of alternative devices is poorly
defined. The EPA mobile units are highly versatile and will be used to
investigate the applicability of these control methods to the control of
fine particulate emitted from a wide range of sources. The relative
capabilities and limitations of these control devices will be evaluated
76
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and documented. This information, supplemented by data from other EPA
particulate programs, will permit selection by equipment users of collection
systems that are technically and economically optimum for specific
applications. Operation of the mobile units will be coordinated with
other EPA laboratories and regions to provide, when possible, field data
on specific problem sources.
MOBILE UNIT DESIGN
The original mobile fabric filter unit was built by GCA Corporation
for EPA and was mounted on an open 1360 kg (1.5 ton) truck. The equipment
could be operated on the truck or could be removed and operated at
locations not accessible to the truck. The mobile filter unit can be
adapted to cleaning by mechanical shaking, pulse jet or low-pressure
reverse flow. Filtration can be conducted at cloth velocities as high
as 0.1 m/s (20 fpm) with a pressure differential up to 50 cm (20 in.) of
water, and at gas temperatures up to 290°C (550°F). Cleaning parameters
can be varied easily over broad ranges. One to seven filter bags of any
fabric media, 1.2 to 3 m (4 to 10 ft) long and up to 30 cm (12 in.) in
diameter may be used. Gas flows used are from 0.012 to 0.13 m3/s (26
to 280 cfm), as determined by cloth velocity, bag size and bag number.
The mobile fabric filter unit just described operated on effluents
from a brass and bronze foundry, a hot mix asphalt plant, a coal-fired
boiler, a lime kiln and a pulp mill recovery boiler. Operation of the
unit from the open truck was found to be extremely inconvenient and
detrimental to efficient field testing, so the filter system was installed
in a 12 m (40 ft) closed trailer in October 1976. Since then the unit
has been used to determine the performance of a fabric filter on the
effluent from a cyclone collector used on the St. Louis Refuse Processing
Plant and a power plant burning a western subbituminous coal.
The second mobile unit received by EPA was the wet scrubber. This
unit, built by the Naval Surface Weapons Center at Dahlgren, Va., was
delivered in December 1974. The scrubber unit is in a 12 m (40 ft)
trailer and contains a venturi scrubber and a sieve tray scrubber.
77
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Maximum gas flow rate through the scrubbers is 0.28 m3/s (600 cfm).
Maximum L/G ratio is 0.01 m/m (75 gal./acf). The unit can treat gas
at temperatures up to 480°C (900°F).
The mobile electrostatic precipitator was delivered to EPA in
September 1976. This system was also designed and built by the Naval
Surface Weapons Center. The mobile ESP facility consists of two separate
units mounted in 12 m (40 ft) freight vans. The first unit is the
process van which houses a five-section ESP and all auxiliary equipment.
Each section of the ESP has a separate power supply which provides up to
50,000 volts and 7 milliamps DC. The precipitator is designed to operate
at flow rates up to 1.4 m3/s (3000 cfm) at temperatures up to 480°C
(900°F). The second unit is a control/laboratory van containing all
process controls, monitors and recorders plus provisions for an analytical
laboratory and equipment storage.
MOBILE FABRIC FILTER FIELD TESTS
Tests by GCA/Technology Division
After designing and building the mobile fabric filter for the
Environmental Protection Agency, GCA/Technology Division conducted field
tests on the following three sources:
Secondary brass and bronze foundry.
Hot mix asphalt plant.
Coal-fired boiler.
Results of these three tests are discussed briefly below:
Secondary Brass and Bronze Foundry
The mobile fabric filter system was operated in the pulse jet,
mechanical shake, and reverse flow cleaning modes on a secondary brass
and bronze foundry. Three pulse cleaning tests using Nomex felt bags
were conducted. The only parameter varied was the interval between
pulses: two tests were at a 40 second interval and one at a 20 second
interval. Data is summarized in Table 1. During test 3, in
78
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which the filter bags were cleaned twice as often, the average
pressure drop across the filter was only 13 cm (5 inches) as compared to
23 and 25 cm (9 and 10 inches) for the first two tests. However, increasing
the cleaning frequency also doubled the percent penetration.
Four shake cleaning tests using woven Nomex bags were conducted.
Bag tension, shaking frequency and amplitude, and filtration velocity
were varied. Data is summarized in Table 2. Test 4 was designed to
simulate cleaning parameters for a full scale fabric filter which was
operating at the test site. The plant had experienced problems with
excessive pressure drop across the filter. This problem was evident
with the mobile unit during test 4. Very little cleaning was accomplished.
After 2 hours operation the pressure drop had increased to 38 cm (15
inches) and even after shaking was only slightly reduced to 33 cm (13
inches). Tests 5, 6, and 7 indicate that increased shaking frequency
and amplitude (both contributing to higher bag acceleration) reduced the
filter pressure drop and increased filtration capacity but also increased
penetration. This information was helpful in analyzing the plant's
problem.
Only one reverse flow cleaning test was conducted: it was primarily
to state down the mobile fabric filter system in the reverse flow cleaning
»de. Data collected was not sufficient to develop conclusions.
Hot Mix Asphalt Plant
Four pulse cleaning tests on a hot mix asphalt plant using Nomex
felt bags were conducted. Results of these tests are presented in Table
3. The pressure drop performance of the mobile unit was worse than that
o a p ant fabric filter system operating on the source tested. he
Plant f,,ter operated at 5 to 8 cm (2 to 3 inches) pressure drop and had
reported air consumption of 0.5 to 0.8 JMJ (8 to „ H^"
ft ) versus a 28 to 30 cm (1, to 12 inch) pressure drop near the en of
"
79
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which may account for the lower pressure drop, although filter geometry
may have also been an important factor. The continuous rise in filter
pressure drop throughout the field test may have been caused by moisture
problems.
Coal-Fired Power Plant (Cyclone-Fired Boiler)
Three shake cleaning tests on a coal-fired power plant with cyclone-
fired boilers using woven glass bags were conducted. Results of these
tests are presented in Table 4. Pressure drop across the mobile fabric
filter averaged about 13.7 cm (5.4 inches) after 20 hours of testing at
a filtration velocity of 1.4 cm/sec (2.7 fpm). Total mass efficiency
averaged 99.66%.
Tests by Monsanto Research Corporation
Following completion of the three tests described above, operation
of the mobile filter was transferred to Monsanto Research Corporation
(MRC) under a contract with EPA's Industrial Environmental Research
Laboratory at Research Triangle Park (IERL-RTP) to maintain and operate
various IERL-RTP field and laboratory test facilities. The following
tests were completed by MRC:
Coal-Fired Power Plant (Anthracite Coal)
The mobile fabric filter was operated at the Shamokin Dam, Pennsylvania,
generating station of Pennsylvania Power and Light Company.2 This
station was unusual in two respects: it had a full-scale fabric filter
operating and it burned a mixture of anthracite silt and petroleum coke.
An extensive test was conducted with the mobile filter using three bag
types and three cleaning modes over a range of values of air/cloth
ratio, filtration time, and pulse interval. Operating conditions for
the tests are given in Table 5. Total particulate collection efficiency
and penetration results are given in Table 6. Fractional efficiency
measurements were also made for each run.
80
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Based on collection efficiency of particles 5 m and less in size,
cleaning mode/bag type combinations can be ranked in descending order of
collection efficiency as follows:
1) Reverse clean - Nomex felt bag
2) Reverse clean - glass bag
3) Shake clean - Nomex felt bag
4) Shake clean - Nomex woven bag
5) Pulse clean - Nomex felt bag
This ranking is based on the data at the operating conditions given
in Table 5 and does not necessarily describe optimum performance achievable
for each cleaning mode/bag type combination.
Pulp Mill Lime Recovery Kiln
The mobile fabric filter was operated at the Weyerhauser Corporation's
pulp mill in Plymouth, North Carolina, on a lime recovery kiln.3 Two
cleaning modes and two fabric types were used in this test program.
Operating conditions are given in Table 7. Total particulate collection
efficiency and penetration results are given in Table 8. Fractional
efficiency results are given in Table 9. Overall, integrated mass
collection efficiency was 99.98%. Overall averages of mean fractional
efficiencies by size range were as follows:
size» yfn Efficiency, % Penetration, %
1-3 99.815 0.185
4-6 99.814 0.186
7-10 99.918 0.082
Bag pressure drop (AP) data is summarized as average values in
Table 10. The results show marked differences in bag AP both within and
between cleaning mode/bag groups. The variation within groups is in the
direction expected in response to changing test conditions. A comparison
of results between cleaning modes clearly shows shake mode operating at
a significantly lower AP. in other words, shake appears to provide
81
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considerably more efficient cleaning than reverse flow.
On the basis of collection efficiency, it appears that a high level
of control of lime recovery kiln emissions can be attained by a fabric
filter. However, operating problems during this test program, caused
by the high moisture content in the flue gas which resulted in condensation
and much deposition on occasion, discourages the use of a fabric filter
in this application.
Refuse Processing Plant
The mobile fabric filter was operated at the City of St. Louis
Refuse Processing Plant on the plant's air density separator cyclone
exhaust. The plant receives raw domestic solid waste which is shredded
in a hammermill. The shredded waste is conveyed in an air classifier
which separates heavier particles from lighter ones by gravitational
settling and vertical pneumatic conveyance. The lighter fraction from
the air classifier is separated from its carrier air stream in a cyclone
where the coarse matter settles out and is collected to be burned in a
local power plant. The cyclone separator air is exhausted to the atmosphere.
It is these emissions to which the test was directed.
Only the pulse cleaning mode was used for this test with Dacron
polyester felted bags and one set of cleaning parameters. It was necessary
to run three 6-hour days in order to collect enough material at the
filter outlet to weigh for mass and fractional particulate efficiency
measurements. Total mass penetration was 0.05%. The corresponding mass
efficiency was 99.95%.
Coal-Fired Power Plant (Subbituminous Coal)
The mobile fabric filter was operated at the Amarillo, Texas,
Harrington Station generating plant of the Southwestern Public Service
Company from May to July 1977. Harrington Station is the first coal-
fired electric generating plant in the Southwestern Public Service
Company system. Unit 1, a 350 MW pulverized coal-fired boiler, went on
line in August 1976. It burns low-sulfur subbituminous coal transported
by train from Wyoming. Harrington Station Unit 2, almost identical to
82
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Unit 1, is under construction and is scheduled to go on line in 1978.
Unit 2 will employ a fabric filter designed by Wheelabrator-Frye for
particulate removal. Unit 3 is planned for 1980 and will also have a
fabric filter.
EPA has funded a contract with Southwestern Public Service to
conduct an exhaustive 1 year test program on the Unit 2 fabric filter to
determine the performance of a fabric filter on a large coal-fired
boiler burning low-sulfur coal. The demonstration is expected to show
that fabric filters are cost effective and show superior performance for
collecting particulates from large utility boilers. Options to extend
the demonstration and pilot plant work beyond the 1 year base period are
included in the contract.
The objectives of the mobile fabric filter test program at the
Harrington Station were:
1) To develop filter operating performance data for input to
the design of the full scale filter and development of the
test program.
2) To provide data to compare fabric filter operation and
particulate collection capability for boilers burning
low-sulfur western coal with those for boilers burning high-
sulfur eastern coal.
Two bag materials were tested: woven Teflon-coated fiber glass and
woven graphite-and-silicone-coated fiber glass. The bag materials were
tested in shake and reverse air cleaning modes. Operating conditions
for the tests are given in Table 11. Bags were tested at an air-to-
cloth ratio of 0.0155 m/s (3.05 fpm). This ratio was chosen to approximate
that planned for the Unit 2 and Unit 3 fabric filters at Harrington
Station. Bags were cleaned when the bag pressure drop reached 10.2 cm (4
inches).
83
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Shake cleaning parameters were: frequency - 6.9 cps, amplitude
2.22 cm (0.875 inches), and duration - 10 sec. These parameters gave a
shaker arm acceleration of 4.3 g's and 138 shakes (2 per cycle) per
cleaning. Bag tension was not measured, but was estimated at
0.45 - 0.91 kg (1-2 lb). A delay of 1 min was used between filtration
and shaking and a 2 min delay between shaking and filtration to allow
dislodged dust to settle. Average filtration time with the Teflon/glass
shake bags was 219 min, and with the graphite/glass bags was 181 min.
For the reverse air cleaning tests, the reverse air-to-cloth ratio
was initially set at 0.0102 m/s (2 fpm). During fabric filter operation,
however, bag blinding was observed with this reverse air flow rate. The
reverse air-to-cloth ratio was ultimately increased to 0.0269 m/s
(5.3 fpm), the maximum available from the reverse air fan at the selected
operating conditions. Several time combinations were attempted to help reduce
blinding. The combination settled upon was: first delay - minimum (5
sec), with reverse air fan on; reverse air time - 30 sec; second delay -
1 min, with reverse air fan shut off at about 30 sec. Filtration times
with the Teflon/glass reverse air bags were 20-30 min. The filtration
times with the graphite/glass bags using reverse air cleaning were so
short that these bags were tested using alternating shake and reverse
air cleaning. After shaking, filtration times were 30-60 min; after
reverse air cleaning, filtration times were 10-28 min with an average of
17 min.
In all cases, new bags were conditioned a minimum of 24 hours prior
to sampling. Gas temperature in the slipstream probe was usually between
180 and 200°C (350 and 390°F) during samplng. Heat loss through the inlet
duct caused a temperature drop of 27-32°C (80-90°F) to the inlet sampling
section. The temperature dropped another 27-32°C as the gas passed through
the bag compartment to the outlet sampling section. Gas pressure in the
slipstream probe was between 25 and 43 cm (10 and 17 inches) vacuum.
Pressure drop in the inlet duct to the inlet sampling section was 2.5 to
4 cm (1 to 1.5 inches). Bag compartment pressure drop was usually a
maximum of 10.2 cm (4 inches) except during bag cake resistance tests.
84
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A summary of shake cleaning pressure drop results is shown in.Table
12. Data from the Teflon/glass shake bags on June 9 are questionable due
to low flow rate during the last few hours of operation. Average filtration
time for the other 2 days of particulate sampling was 3 hrs, 39 min.
Average effective residual bag AP for the last 2 days was 38 mm (1.5
inches) and the average terminal bag AP was 107 mm (4.2 inches).
The graphite/glass shake bag average filtration time was 3 hrs, 1
min. Average effective residual bag AP was 44 mm (1.7 inches) and the
average terminal bag AP was 103 mm (4.1 inches).
The filtration times were shorter and residual pressure drops
higher with the graphite/glass bags. These results indicate higher
particulate filtration efficiency and less cake removal during cleaning.
The average boiler load was slightly higher during sampling of the
graphite/glass bags: an average of 336 MW for the 3 days compared to 331
MW for the last 2 days with the Teflon/glass bags. The small difference
in boiler load is not believed responsible for the difference in results.
A summary of the reverse cleaning pressure drop results for the
Teflon glass bags is presented in Table 13. Bag blinding problems were
encountered. In an effort to get better bag cleaning and extend filtration
time the bags were sometimes cleaned 2 or 3 times before filtration was
resumed. Some additional cleaning was accomplished, but not enough to
extend the time between cleans to more than 30 min. Even with multiple
cleanings, the filtration times grew shorter as operation continued.
Extending the delay or reverse air durations did not improve cleaning.
The reverse air flow was 1.7 times the forward rate.
To determine the cause for bag blinding, several factors were
invetigated. First, the bags were observed during cleaning. The bags
collapsed well as the reverse air damper opened at the start of the
first delay and stayed collapsed until the manual reverse air gate valve
was closed during the second delay. The reverse air fan caused no
additional collapse because the negative system pressure pulled in
reverse air without the fan running. As filtration resumed, the bags
85
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inflated. When collapsed, the bags had an hourglass shape between the
spreader rings. The bags did not collapse to the point where the reverse
air flow was choked off due to the bags closing up completely.
Dust cake removal was observed through the bag compartment hopper
window. During the first delay, there was a large quantity of fallout
immediately when the reverse air gate valve opened. Most visible particles
were large flakes. A fairly large portion exited the hopper entrance
into the inlet duct. After the initial puff, flakes settled slowly
toward the dust collection can, with a portion pulled out through the
hopper entrance. When the reverse air fan came on, there was a small
quantity of flaky dust as the fan started—much less than during the
first delay. Flakes again settled slowly. During the second delay, a
few flakes were dislodged at the start. Flakes continued settling for
most of the duration. As filtration was resumed, a puff of dust entered
the hopper. Much of the dust was pulled up into the bags, but did not
appear to be enough to make much difference in the bag cake or pressure
drop. The puff was probably due to the forward air reentraining particles
that settled in the inlet duct during bag cleaning.
The reverse air temperature was at least the same as the bag compartment
outlet temperature at the start of cleaning and rose about 35°C as
reverse flow continued. The reverse air moisture content, measured with
the wet bulb method, was found to be 2 percent by volume less than the
filtration gas moisture content. Condensation on the bags was therefore
a doubtful cause of bag blinding.
The bags never completely relaxed during the delay between cleaning
and the resumption of filtration. This was due to leakage through the
reverse air gate valve. To stop reverse air leakage, the manual gate
valve was also shut about halfway through the second delay, but bag
cleaning was not improved.
On the second day of sampling the Teflon/glass reverse air bags
the bags were cleaned by shaking prior to sampling. The first filtration
time was approximately 2 hours, but decreased to about 25 min when
operation was stopped at the end of the test.
86
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The pressure drop results for the graphite/glass reverse air bags
are shown in Table 14. During bag conditioning, blinding was even more
severe than with the Teflon/glass reverse air bags. After only 10 hours
of operation (having started with new bags), filtration time had decreased
to less than 4 min. and residual bag AP rose to 81 mm (3.2 inches).
For particulate sampling, it was decided to use reverse air cleaning
until the time between cleans decreased to 30 min or less, then shake
the bags and resume reverse air cleaning. The result, as shown in Table
14, was that only every other cleaning was with reverse air. Even after
shake cleaning, filtration times were much shorter than when using shake
cleaning alone.
Table 15 presents the results of sampling for total mass concentrations,
Penetration of both Teflon/glass bag types was higher than that of the
graphite/glass bags. Penetration was about the same for both cleaning
modes with the graphite/glass bags, possibly influenced by the alternating
reverse air and shake cleaning employed with the reverse air bags.
Figure 1 presents mass penetration versus particle size curves for
the four fabric/cleaning mode combinations tested. All four penetration
curves exhibit minima. The minimum penetrations of the shake-type bags
occur at larger particle sizes than those of the reverse-air-type bags.
With both the shake and reverse air bags, the minimum penetrations were
at smaller sizes with the graphite/glass bag material. The maxima for
the two reverse air curves at about 4 Pm may not be real. It is suspected
that characteristics of the impactors produced or magnified these results.
It is possible that the penetrations actually continue to increase above
4 mm. The graphite/glass shaken bags had the lowest penetrations in
the particle size range measured.
Plans are underway to operate the mobile fabric filter at a site
burning eastern high sulfur coal using the same fabric/cleaning mode
combination as used at Harrington Station so a more direct comparison of
fabric filter performance on high sulfur and low sulfur coal can be
presented.
87
-------
SUMMARY
The original objective in building the mobile fabric filter, wet
scrubber and electrostatic precipitator units was to operate all three
units on the same source to compare the relative capabilities and limitations
of the control methods on a given source. In practice the units, more
frequently, have been used individually to answer specific control
problems. The fabric filter unit has been operated on eight field sources
including three utility boilers. A second mobile unit was operated at
only two of these sources. It is anticipated that these mobile units
will find wide application in the future to meet the original objective
as well as to answer specific control problems.
88
-------
Table 1. BRASS AND BRONZE FOUNDRY PULSE CLEANING TEST RESULTS
Parameter
Inlet dust concentration, g/m3 (grains/scf)
Inlet particle size, ym (mass median)
Avg. filter pressure drop, cm water (inches)
Outlet dust concentration, g/m3 (grains/scf)
Interval between pulses, sec
Penetration, %
Efficiency, %
T
3.89 (1.7)
0.5
25 (10)
0.0032(0.0014)
40
0.081
99.919
Fest Number
i *r
3.89 (1.7)
0.5
23 (9)
0.0030(0.0013)
40
0.078
99.922
o
3
3.89 (1.7)
0.5
13 (5)
0.0064(0.0028
20
0.15
99.85
Table 2. BRASS AND BRONZE FOUNDRY SHAKE CLEANING TEST RESULTS
Parameter
Cleaning Parameters
Amplitude, cm (inches)
Frequency, cps
Tension, grams (pounds)
Filtration velocity, cm/sec (fpm)
Maximum pressure drop, cm water (inches)
Average penetration, %
Average outlet dust concentration,
g/m (grains/scf)
••— — — — — — — —
0.95(3/8)
3-6
2270(5)
1.5(3)
38(15)
Ono
. uo
o.oon
(0.0005)
Test Number
5
2.2(7/8)
6
908(2)
1.5(3)
33(13)
.14
0.0027
(o; 00121
6
2.2(7/8)
8
454(1)
1.5(3)
30(12)
0.16
0.020
(0.0087)
7
2.2(7/8)
6
454(1)
1.3(2.5)
18(7)
fi n^
0.00069
(0.0003)
89
-------
Table 3. HOT MIX ASPHALT PLANT PULSE CLEANING TEST RESULTS
Parameter
Filtration velocity, cm/sec (fpm)
Avg. filter pressure drop, cm water (inches)
Inlet particle size, ym (mass median)
Inlet dust concentration, g/m (grains/scf)
Outlet dust concentration, " "
Avg. penetration, %
Avg. efficiency, %
Test Number
1
4.1 (8)
11.7(4.6)
12-15
34.1(14.9)
0.066
(0.029)
0.18
99.82
2
4.1 (8)
14.2(5.6)
12-15
35.5(15.5)
0.034
(0.015)
0.10
99.90
3
3.8(7.5)
18.8(7.4)
12-15
35.0(15.3)
0.039
(0.017)
0.13
99.87
4
3.7(7
26.9(1
12-15
36.9(1
0.08
(0.03
0.23
99.7
Table 4. COAL-FIRED POWER PLANT (CYCLONE-FIRED BOILER) SHAKE CLEANING TEST RESULTS
Parameter
Filtration velocity, cm/sec (fpm)
Avg. filter pressure drop, cm water (inches)
Inlet particle size, pro (mass median)
Inlet dust concentration, g/m (grains/scf)
o
Outlet dust concentration, g/m (grains/scf)
Avg. penetration, %
Avg. efficiency, %
Test Number
1 j
1.4 (2.7)
12.2 (4.8)
5
1.6 (0.7)
0.009(0.004)
0.57
99.43
2
1.4 (2.7)
13.2 (5.2)
5
1.6 (0.7)
0.004(0.0016)
0.23
99.77
3
1.4 (2.7)
13.7 (5.4)
5
1.6 (0.7)
0. 005(0. 002^
0.34
99.66
90
-------
Table '5. OPERATING CONDITIONS FOR COAL-FIRED POWER
PLANT (ANTHRACITE COAL) TESTS
Shake Mode
Filtration period
1st pause
Cleaning period
2nd pause
Shake frequency
Amplitude
Shaker-arm acceleration
Bag tension
A/C
.Pulse Mode
Pulse interval
Pulse duration
Pulse jet pressure
A/C
—— •
Filtration period
1st pause
Cleaning period
2nd pause
Bag tension
A/C
Reverse flow air rate
20 min.
10 sec
10 sec
30 sec
7 cps
2.22 cm
4.4 g's
0.682 kg
0.010, 0.015,
0.020 m/s
I/ 2, 3 min
0.10 sec
4.14 x 105 pa
0.020, 0.031
(max.) m/s
30, 40, 50 min
30 sec
20 sec
30 sec
0.682 kg
0.010, 0.015,
0.020 m/s
0.045 m3/s
91
-------
Table 6. COAL-FIRED POWER PLANT (ANTHRACITE COAL) MASS
EFFICIENCY TEST RESULTS
Run3
S-G-2-20
S-G-3-20
S-G-4-20
Average
S-WN-2-20
S-WN-3-20
S-WN--4--20
Average
S-FN-2-20
S-FN-3-20
S-FN-4-20
Average
P-FN-4-1
P-FN-6.2-1
P-FN-6.2-2
P-FN-6.2-3
Average
R-G-2-30
R-G-3-30
R-G-4-30
R-G--4-40
R-G-4-30
Average
Mass Load
In
2 503
3 108
4 030
3 213
5 828
1 246
1 898
2 991
4 456
4 818
5 299
4 362
3 858
7 855
6 069
7 525
6 325
3 616
3 197
3 075
1 509
1 960
2 672
inq , ma/nH
Ou t
93
I
207
100
14
1
53
23
1
1
1
1
2
35
119
77
58
21
9
8
—
. —
13
Col. Eff. Penetration
% %
96.30
99.97
94.88
97.05
99.76
99.89
97.23
98.96
99.71
99.98
99.98
99.89
99.94
99.56
98.03
98.97
99.13
99.42
99.73
99.74
** ^« H
99.63
3.70
0.03
5.12
2.95
0.24
0.11
2.77
1.C4
0.28
0.02
0.02
0.11
0.06
0.44
1.97
1.03
0.88
0.58
0.27
0.26
— «.
0.37
(more)
92
-------
Table 6. (Cont'd) COAL-FIRED POWER PLANT (ANTHRACITE COAL)
MASS EFFICIENCY TEST RESULTS
Run3
R-FN-2-30
R-FN-3-30
R-FN-4-30
R-FN-3-40
R-FN-3-50
R-FN'-3-30
Average
Mass Loading, raq/m^
3
4
4
3
4
2
3
In
902
122
282
833
889
352
895
Out
1
5
1
—
3
1
2
Col.
I
99
99
99
_
99
99
99
Eff.
»
>
.99
.88
.99
__
.95
.95
. 95
Penetration
0.
0.
0.
^_
0.
0.
0.
01
12
01
^
05
05
05
Average
3 969
31
99 .18
0.82
Run Code
Example: S-G-2-20
First letter = Cleaning Mode: S - Shake
P - Pulse
R - Reverse
Second letter = Bag Type: 6 - Glass
WN - Woven Nomex
FN - Felted Nomex
First Number = A/C Ratio, fpm (x 5.08 x 10~3 = m/sec)
Second Number = Filtration Period, min, for shake and reverse
- Pulse Interval, sec, for pulse
93
-------
Table 7. OPERATING CONDITIONS FOR PULP MILL LIME RECOVERY KILN TESTS
Shake Mode
Filtration period
First pause
Cleaning period
Second pause
Shake frequency
Amplitude
Shaker-arm acceleration
Bag tension
A/C
30, 50 min
30 s
5 s
30 s
7 cps
22.2 mm (0.875 in.)
43.1 m/s2 (4.4 g's)
0.68 kg (1.5 Ib)
0.015, 0.025 m/s (3, 5 fpm)
Reverse Mode
Filtration period
First pause
Cleaning period
Second pause
Bag tension
A/C
R.F. air temperature
R.F. air flow
30, 50 min
30 s
5, 20, 40 s
30 s
0.68 kg (1.5 Ib)
0.015, 0.025 m/s (3, 5 fpm)
113°C (235°F)
4.5 x 10-2 m3/s (95 acfm)
94
-------
Table 8. PULP MILL LIME RECOVERY KILN MASS EFFICIENCY TEST RESULTS
Grain Loading, g/m3 (qr/sdcf)
Run9
S-WN-3-30-5
S-WN-3-50-5
S-WN-5-30-5
Average
S-FN-3-30-5
S-FN-3-50-5
S-FN-5-30-5
Average
R-V7N-3-30-5
R-WN-3-30-20
R-WN-5-30-5
R-WN-3-50-5
Average
R-FN-3-30-20
R-FN-3-50-40
R-FH-3-30-40
Average
Average
a,.
In
8.65(3.78)
8.65(3.78)
7.83(3.42)
'2.79(1.22)
2.33(1.02)
4.39(1.92)
5.77(2.52)
6.86(3.00)
6.86(3.00)
0.597(0.261)
0.309(0.135)
4.3.5(1.90)
8.21(3.59)
4.53(1.98)
11.2(4.91)
8.58(3.75)
6.80(2.97)
5.95(2.60)
24.9(10.9)
5.84(2.55)
5.88(2.57)
5.95(2.60)
9.40(4.11)
8.56(3.74)
4.97(2.17)
6.80(2.97)
9.15(4.00)
13.9(6.08)
7.94(3.47)
8.56(3.74)
7.24 (3.17)
Out
0.00291(0.00127)
0.00318(0.00139)
0.000191(0.0000835)
0.000149(0.0000649)
0.000359(0.000157)
0.00130(0.000569)
0.00135(0.000589)
0.000613(0.000268)
0.000897(0.000392)
0.000831(0.000363) '
0.000570(0.000249)
0.00220(0.000963)
0.00563(0.00246)
0.00179(0.000783)
0.00102(0.000444)
0.00281(0.00123)
0.00110(0.000482)
0.00105(0.000459)
0.00118(0.000516)
0.00113(0.000492)
0.000755(0.000330)
0.00146(0.000638)
0.00131(0.000574)
0.000931(0.000407)
0.00112(0.000490)
0.000490(0.000214)
0.00166(0.000726)
0.00166(0.000726)
0.00180(0.000788)
0.00128(0.000559)
- — '- ii — ._
0.00142 (0.000622)
Collection
Efficiency,
%
99.97
99.96
99.99
99.99
99.98
99.97,
99.98
99.99
99.99
99.86
99.82
99.95
99.93
99.96
99.99
99.97
99.98
99.98
99.99
99.98
99.98
99.97
99.99
99.99
99.98
99.99
99.98
99.99
99.98
99.99
99.98
Penetration,
%
0.0336
0.0368
0.00244
0.00532
0.0154
0.0300
0.0233.
0.00893
0.0130
0.139
0.184
0.0507
0.0685
0.0395
0.00904
0.0328
0.0162
0.0176
0.00471
0.0193
0.0128
0.0245
0.0140
•• -.—.--._
0.0109
0.0226
0.00721
0.0182
0.0119
0.0227
0.0149
0.0222
Run Code - Example: S-WN-3-30-5
First Letter - cleaning mode (Shake - S, Reverse - R)
Second Set of Letters - fabric type (Woven Uomex - WN
First Number - A/C ratio, fpm (x 5.08 :< 10~J - m/sec)
Second Number - filtration period, min ' '
Third Number - cleaning period, sec
95
Felted K7omex - FN)
-------
Table 9. PULP MILL LIME RECOVERY KILN FRACTIONAL EFFICIENCY TEST RESULTS
Mass Median
Biamcter, urn
Run3
S-WN-3-30-5
S-WN-3-50-5
S-WN-5-30-5
S-FN-3-30-5
S-FN-3-50-5
S-FN-5-30-5
R-WN-3-30-5
R-WN-3-30-20
R-WN-3-50-5
R-WN-5-30-5
R-FN-3-30-20
R-FN-3-30-40
R-FN-3-50-40
R-FN-3-50-40
_
In
7.7
7.7
7.5
7.4
7.4
8.3
7.7
7.6
0.4
1.2
8.2
8.2
7.8
7.8
7.6
7.5
7.3
7.2
8.4
8.2
7.8
7.6
7.7
7.6
8.0
8.0
Out
3.6
1.1
0.46
0.45
0.5
0.7
0.5
0.5
2.8
0.6
10.0
5.7
4.5
3.2
3.8
4.7
7.1
5.9
7.0
9.6
4.8
4.9
2.3
3.5
3.2
1.9
Fractional Efficiency^
Min
99.61
99.28
c
~c
c
-Q
99.89
99.51
99.80
99.21
99.84
99.20
99.87
99.03
99.89
99.92
99.97
99.97
99.67
_c
99.97
99.85
99.80
97.15
99.95
97.90
Max.
93
@3
@1
@1
@6
@4
(§6
(§3
<§3
(§4
@4
(§3
@4
@5
(§5
@4
(§4
(§3
(§4
(§7
@4
99.99
99.99
_e
-e
c
c
99.99
99.99
99.86
99.99
99.99
99.95
99.99
99.98
99.99
99.99
99.99
99.98
99.96
_C
99.99
99.99
99.99
99.99
99.99
99.99
eio
@10
010
@ 8
@10
@ 8
@ 3
(§10
610
(§10
(^10
(§10
610
(§10
(§1,10
(9 8
@ 8
(§10
610
0 1
610
Mean Fractional Efficiencv
1 -
99
99
99
99
99
99
99
3 ym
.66
.46
C
C
e
-C
.91
.73
.84
.46
.99
99.38
99
99
99
99
99
99
99
99
99
99
99
99
99
.92
.50
.95
.93
.98
.99
.92
_C
.98
.95
.87
.76
.99
.89
4-6 ym
99.85
99.81
C
_^:
C
c
99.99
_a
99.81
99.52
99.86
99.54
99.96
99.55
99.93
99.96
99.98
99.98
99.71
_c
99.98
99.88
99.93
98.94
9.9.96
99.12
7-
99
10 ym
.97
99,99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
99
C
IC
_q
-£
.99
.98
.84
.98
.90
.90
.99
.96
.99
.99
.99
.98
.90
_C
.99
.99
.99
.98
.96
.99
a
See Table S for code explanation
Number after @ is particle size, ym, at which minimum or reaximum collection
efficiency occurs
c
Test conditions which had apparent fraction efficiencies > 100%
96
-------
Table TO. PRESSURE DROP RESULTS OF PULP MILL LIME RECOVERY KILN TESTS
Run a
S-WN-3-30-5
S-WN-3-50-5
S-WN-5-30-5
S-FN-3-30-5
S-FN-3-50-5
S-FN-5-30-5
R-WN-3-30-5
R-WN-3-30-20
R-WN-3-50-5
R-WN-5-30-5
R-FN-3-30-20
R-FN-3-30-40
R-FN-3-50-40
"" ' ' 'I .—
a
See Table 8
b
= Effective
c
= Residual
d
= Effective
AP b
e
- — • • — „
0.60(2.4)
0.52(2.1)
1.44(5.8)
0.17(0.7)
0.32(1.3)
0.67(2.7)
0.65(2.6)
0.90(3.6)
0.85(3.4)
1.84(7.4)
1.54(6.2)
1.94(7.8)
1.97(7.9)
— • ' - ._.-.-..
AP c
r
1.00(4.0)
0.95(3.8)
1.94(7.8)
0.40(1.6)
0.70(2.8)
1.29(5.2)
1-17(4.7)
1.19(4.8)
1.37(5.5)
2.44(9.8)
2.07(8.3)
2.31(9.3)
2.44(9.8)
i
e
40.2(0.82)
34.8(0.71)
56.8(1.16)
11.3(0.23)
21.1(0.43)
26.9(0.55)
42.1(0.86)
58.8(1.20)
55.4(1.13)
72.5(1.48)
99.4(2.03)
128.4(2.62)
129.3(2.64)
— " -•
S e
JL
"" ' "" •• ' i inn • i ,M-
65.1(1.33)
61.7(1.26)
75.9(1.55)
26.0(0.53)
45.6(0.93)
50.9(1.04)
76.4(1.56)
78.4(1.60)
89.6(1.83)
96.0(1.96)
135.2(2.76)
153.8(3.14)
159.2(3.25)
— "•— —
for code explanation
pressure drop
pressure drop,
drag = AP/U,
, kPa (in. w
kPa (in. w.
kPa/m/s (in.
•c.)
c.)
w.c./fpm)
39,400(33.9)
25,100(21.6)
18,300(15.7)
29,400(25.3)
29,400(25.3)
28,700(24.7)
32,900(28.3)
18,700(16.1)
19,800(17.0)
13,700(11,8)
35,100(30.2)
25,100(21.6)
19,100(16.4)
= Residual drag = AP r/U, kPa/m/s (in. w.c./fpm)
- Cake specific resistance, kPa/m/s • kg • m2 (in. w.c./fpm-lb-ft2)
97
-------
Table 11. OPERATING CONDITIONS FOR COAL-FIRED POWER PLANT
(SUBBITUMINOUS COAL) TESTS
Shake Mode
Graphite/Glass Bags
^_ Avg
Filtration period, min 166-290 219 152-225 181
1st pause, min
Cleaning period, sec
2nd pause, min
Shake frequency, cps
Amplitude, cm
Shaker-arm acceleration, g's
Bag tension, kg 0.
A/C, m/s
Reverse Mode ' '
Teflon/Glass Bags Graphite/Glass Bac
Range Avg Range Avg
Filtration period, min 20-30 23 10-28 17
1st pause, sec 5 5
Cleaning period, sec 30 30
2nd pause, sec 60 60
A/C, m/s 0.0155 0.0155
Reverse air A/C, m/s 0.0102-0.0269 0.0102-0.0269
a
•Alternate shake and reverse air cleaning—data reported is for reverse air only
98
-------
Table 12. PRESSURE DROP RESULTS OF COAL-FIRED POWER PLANT
•/fSUBBITUMINOUS COAL) SHAKE CLEANING TESTS
Date
IT 977)
6-9
6-11
6-13
Avgc
6-22
6-23
6-24
Avg
Fabric Filtration Time
Type (hr:min)
To-firm /rTTTT "~ = — =•= —
i CT ion/b i ass
Teflon/Glass
Teflon/Glass
Teflon Glass
Graphite/Glass
Graphite/Glass
Graphite/Glass
Graphite/Glass
4:ou
2:46
3:31
3:45
3:36
3* A C
• £1 K
* I W
3:39
3:45
2 A ~7
• LL I
• T-y
2. •*> o
:32
2:52 .
2i— *\
* R <
- Do
2:46
3. r\~?
.u/
3:05
2r* />
: 59
3:05
3f\ r"
:25
3:01
Residual Bag
AP (mm H?0)
14 (43) a
18
30(97)
23
25(66)
28
27
30(53)
*> o
33
20
30(119)
i rt
28
33
32
32(112)
on
OU
36
38
31
Effective
Residual AP
(mm H?0)
33
32
41
36
36
38
38
34
42
46
46
48
43
48
43
43
46
43
44
Terminal
Bag AP
(mn HoO)
746
104
109
102
112
107
102
102
102
104
108
102
102
102
103
i \j-\j
102
103
103
: Previous terminal bag AP (nra FLO)
Shut down due to low flow rate
'Data for 6-9-77 not included because of unreliability
99
-------
Table 13. PRESSURE DROP RESULTS OF COAL-FIRED POWER PLANT
(SUBBITUMINOUS COAL) REVERSE CLEANING TESTS
(TEFLON/GLASS BAGS)
Filtration
Date Time, Min
7-15-77 19
15
4
-------
Table 14. PRESSURE DROP RESULTS OF COAL-FIRED POWER PLANT
(SUBBITUMINOUS COAL) REVERSE CLEANING TESTS
(GRAPHITE/GLASS BAGS)
Filtration
Date Min
7-19-77 44
76
17
64
16
31
17
34
16
55
13
17
55
10
109
28
78
Time, Cleaning
Mode
Shake
Shake
Rev. air
Shake
Rev. air
Shake
Rev. air
Shake
Rev. air
Shake
Rev. air
Rev. air
Shake
Rev. air
Shake
Rev. air
Shake
Residual Bag
AP (mm H00)
23
28
58
29
66
38
67
34
66
25
-
74
25
70
18
61
20
Effective Residual
AP (mm H00)
£
61
66
86
74
91
81
88
81
84
71
-
91
71
91
53
88
55
Terminal Bag
AP (mm H00)
102
89
102
102
102
102
102
102
102
102
102
102
102
102
102
99
100
101
-------
Table 15. COAL-FIRED POWER PLANT (SUBBITUMINOUS COAL)
MASS EFFICIENCY TEST RESULTS
Run3
S-T-6-9
S-T-6-11
S-T-6-13
Average
S-G-6-22
S-G-6-23
S-G-6-24
Average
R-T-7-15
R-T-7-16
Average
R-G-7-19
aRun Code
Example
First Letter =
Mass Loading, mg/m
In
368
4830
1450 *
2216
3940
3590
5130
4220
3530
3600
3570
3690
Out
1.63
5.45
4.31
3.80
1.74
2.18
1.15
1.69
4.44
2.38
3.41
1.05
Collection
Efficiency, %
99.56
99.89
99.70
99.83
99.96
99.94
99.98
99.96
99.87
99.93
99.90
99.97
Penetrati on ,
%
0.44
0.11
0.30
0.17
0.04
0.06
0.02
0.04
0.13
0.07
0.10
0.03
: S-T-6-9
Cleaning
Mode: S - Shake
R - Reverse
Second Letter = Bag Type: T - Teflon/glass
G - Graphite/glass
First Number = Month of Test
Second Number = Day of Test
102
-------
O TEFLON/GLASS SHAKE BAGS
OGRAfHJTE/GLASS SHAKE BAGS
A TEFLON/GLASS REVERSE AIR BAGS
OGPAPHSTE/GLASS REVERSE ASR BAGS
PC ~ 2,8 tj/«ni3
L,
I LJ_jJLjJjJjLLL
2 4 6 8 1.0
4 6 8 10
GEOMETRIC MEAN PARTICLE DIAMETER, ftm
Figure 1. Average mass penetration vs geometric mean particle diameter.
103
-------
References
1, Hall, R. H. and Dennis, R., "Mobile Fabric Filter System
Design and Field Test Results," EPA-650/2-75-059, (NTIS No. PB 246-
287/AS), July 1975.
2. Opferkoch, R. E., "Particulate Control Mobile Test Units:
First Year's Operation," EPA-600/2-76-042, (NTIS No. PB 251-722/AS),
February 1976.
3. Zanders, D. L., "Particulate Control Mobile Test Units:
Second Year's Operation," EPA-600/2-77-042, (NTIS No. PB 264-067/AS),
January 1977.
104
-------
AUSTRALIAN EXPERIENCE, FILTRATION OF
FLYASH FROM VERY LOW SULFUR COALS
THIRD SYMPOSIUM ON FABRIC FILTERS
FOR PARTICLE COLLECTION
DOUBLETREE INN TUCSON, ARIZONA
December 5-6, 1977
By
A. C. LEUTBECHER
MARKETING MANAGER, FABRIC FILTERS
WESTERN PRECIPITATION DIVISION
Los Angeles, California
105
-------
BIOGRAPHICAL NOTE
DEL LEUTBECHER is a graduate from Cleveland State
University (1967) with a B.S. desgree in Engineering
Science. He has also attended Graduate School at
Northern Illinois University, majoring in marketing.
Del has eight years sales and marketing experience
in the air pollution control field, specifically in-
volved with scrubbers and bag filters, and presently
is Marketing Manager, Fabric Filters for Western
Precipitation Division of JOY Manufacturing in Los
Angeles, California.
106
-------
AUSTRALIAN EXPERIENCE, FILTRATION OF FLYASH FROM VERY LOW
SULFUR COALS.
Abstract
This paper examines the Australian experience
in applying fabric filters to coal fired boilers
Consequences of burning very low sulfur coal
(0.3%-0.4%) are highlighted. Specific examples
of shaker, reverse air and pulse jet cleaning
mechanisms are discussed and experience with
acrylic filtration media is detailed.
As can be seen by Fig. 1, Australian coal is quite
different from that mined in the United States. U. S. coals
classified as low sulfur generally run .7%-1.0% sulfur content.
Coals with sulfur contents on the order of 0.6% to 0.7% are
considered "high sulfur" varieties in Australia. Low sulfur
coal is defined as containing approximately 0.3% sulfur. Given
this extremely low sulfur content and the mild Australian cli-
mate, air heater gas outlet temperatures on efficient boilers
can run as low as 220°F. At these conditions flyash is highly
resistive and precipitator performance has been unsatisfactory.
As an analogous situation opened the door to baghouse applica-
tion for flyash collection in the United States, so, too, are
the Australians turning to fabric filtration.
107
-------
The single factor making the Australian experience
so unique is low gas inlet temperatures to the baghouse.
Inlet temperatures in the 250 OF to 300 OF range are not un-
common. This phenomenon of low inlet temperatures makes pos-
sible the use of synthetic fibers such as acrylic for filtra-
tion media.
the Electricity Commission of New South Wales has
taken the technical lead in baghouse applications in Australia.
A listing of experience to date is shown in Figure 2. This
paper will discuss some of these installations in detail.
The first significant installation was commissioned
in May of 1972 at the Tallawarra Power Station. This shaker
type filter was installed on a pulverized fuel boiler and
designed to handle 80,000 ACFM of flue gas at 2700p. The intent
upon successful operation of this pilot unit was to retrofit the
entire station with baghouses, amounting to four 30 MW boilers
in Section "A" and two 100 MW boilers in Section "B". Specific
design details of this pilot are shown in Fig. 3A. As can be
seen, pilot experience was very good with pressure drop main-
tained at 3" W. C. and efficiency at 99.9%. This was accompli-
shed at a gross filter ratio of 2.23/1 with a cleaning cycle
initiated every thirty minutes. Based upon successful experience
a 500,000 ACFM full scale baghouse was commissioned at Section "A1
in September of 1974, and four 170,000 ACFM units at Section "B"
108
-------
during the period March 1975 to March 1976. Design details
are shown in Fig. 3B. Operating experience has been consistent
with that of the original pilot unit.
Several comments are worthy of mention with regard to
the fabric material utilized. Polyester bag material was judged
to be unsuitable due to hydrolysis and subsequent acid attack.
Although steps were taken to prevent moisture ingress, the pos-
sibility of accidental wetting such as economizer leaks cannot
be excluded. In addition, high moisture conditions as occur
during soot blowing have caused polyester hydrolysis. Acrylic
fibers have demonstrated resistance to hydrolysis and acid attack.
Acrylic fiber is, however, temperature sensitive and will support
combustion. Necessary steps must be taken to prevent heating
acrylic fiber in excess of 260^F by using air dilution and/or
water sprays. As protection against air heater failure, bypass
is recommended. Finally, care must be taken during operation and
maintenance to avoid a dangerous fire as bags burn fairly readily.
A full water spray or CO2 fire protection system is recommended.
The specific bag recommended by the Commission is
Draylon T, 12 oz/sq yd, 2X2 twill with a permability of 25-33.
As previously mentioned, there are three pulse jet
installations in Australia at Wangi Station Units 4, 5 and 6.
They are essentially identical installations as shown in Fig. 4.
109
-------
Of the units tested, efficiencies have been in excess
of 99.5%, however, problems have been reported. Pressure drop
has averaged 5" W.C. This is primarily due to the high filter
ratio and the Commission is recommending 3.5 - 4.0 ratios to
conserve pressure drop and maximize bag life. The acrylic bags
have experienced an embrittlement problem. It has been theorized
that the cold, compressed cleaning air has caused localized
condensation of flue gas and subsequent acid attack. Bag bleeding
and visible puffing during cleaning have also been reported. The
acrylic bags used were 18 oz/square yard needled felt with a
permeability of 25 CFM/square foot/V W.G.
The final pilot installation to be discussed is the
reverse air cleaned baghouse pilot unit at Wangi Station Unit 5.
Design conditions for this baghouse are shown in Fig. 5. As shown,
this unit has four compartments of six bags each for a total of
twenty-four bags. The bags are 8-inch diameter by 22-foot long
Menardi 601T fiberglass with 10% Teflon B finish. Material is
9.5 oz/sq. yd.,3X1 twill with a permeability of 75.
The baghouse is designed so that one compartment is
always off line in the cleaning mode. When a section is dampered
off for cleaning it automatically goes into a 75 second null
period. The collapse period is adjustable over a wide range,
however, it currently is set very short (5-8 seconds) with the
intention of providing more residual dust cake for acid dew
110
-------
point protection. After collapse, the compartment goes into
a second null period. This second null period can be quite
long as all four compartments are never on line at once.
Overall, the unit has performed extremely well.
Even with the short collapse period, pressure drop is maintained
between 2-3" W.C. Efficiencies are very high. After 400 hours
of service, outlet emissions were less than .006 gr/acf. The
most recent test in October of this year was inconclusive in that
emission levels were so low measurement was impractical. After
some 3500 hours of operation, including 70 starts and stops
(140 dew point excursions) the bags show no signs of wear or
deterioration.
In summary, it is fair to say that since 1972 the tech-
nical experience with baghouses on very low sulfur coal burning
boilers has been good. This paper has focused on two inter-
related variables: cleaning mechanism and type of bag material.
With regard to type of cleaning mechanism, the experience has been
*
most favorable with the reverse air cleaned baghouse in terms of
low pressure drop and projected bag life, with the shaker a close
second. The pulse jet experience has not been good, however,
some design modifications would give more favorable results.
Ill
-------
The question of whether to use acrylic or glass bags
is really the central issue as once this selection is made the
cleaning mechanism follows logically. Acrylic bags have shown
to be suitable at temperatures of 260°F and below. We can
expect that with acrylic bags some type gas cooling will be re-
quired as well as an emergency bypass and a fire protection
system. This auxiliary equipment may substantially change the
economic balance, especially at shaker ratios of 3.0 and lower
in favor of reverse air cleaning with glass bags. Glass bags
with their higher temperature capability of SOO^F are not as
susceptable to temperature variations as may be found in
Australia and do not present the fire hazard.
112
-------
TYPICAL COAL ANALYSIS
U. S. LOW SULFUR WESTERN
MOIST % FIXED CARBON % VOLATILE % ASH % SULFUR %
8-10 40-50
35-40
7-14
.6-.9
AUSTRALIAN LOW SULFUR
MOIST % FIXED CARBON % VOLATILE % ASH % SULFUR %
1-3
60-70
20-30
8-12
0.3-0.5
Fig. 1
113
-------
ECNSW FABRIC FILTER INSTALLATIONS
Mo/Yr
in
Service
May 1972
Sept 1974
March 1975
Aug 1975
Dec 1975
Jan -1976
Mar 1976
April 1976
June 1976
July 1976
Oct 1976
Station/
Boiler
Tallawarra 4
Tallawarra 1-4
Tallawarra 6B
Tallawarra 6A
Wangi 4
Tallawarra 5A
Tallawarra 5B
Wangi 5
Wangi 1A
Wangi IB
Wangi 6
Wangi 2A
Wangi 2B
Wangi 3A
Wangi 3B
Wangi 5
Gas
Flow
ACFM
80,000
500,000
170,000
170,000
320,000
170,000
170,000
320,000
130,000
130,000
320,000
130,000
130,000
130,000
130,000
1,900
Nom. Gas
Tempera-
ture
290
290
270
270
260
270
270
260
300
300
260
300
300
300
300
270
Gross
Ratio
2.23
2.10
2.4
2.4
6.8
2.4
2.4
6.8
3.5
3.5
6.8
3.5
3.5
3.5
3.5
2.29
Fabric
Type
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Glass
Cleanir
Mechan-
ism
Shake
Shake
Shake
Shake
Pulse
Shake
Shake
Pulse
Shake
Shake
Pulse
Shake
Shake
Shake
Shake
R/A
Fig. 2
114
-------
ECNSW TALLAWARRA STATION
SECTION A PILOT UNIT
Gas Volume 80,000 ACFM
Gas Temperature 270°F
Dust Loading 13 gr/cubic foot
Particle Size 4% less than 2.5 microns
Gas Cooling Air dilution/water spray
Gross Filter Ratio 2.23/1
Net Filter Ratio 2.98/1 (one out for cleaning)
Number of Bags 330/compartment (1320 total)
Bag Size 6V dia X 16'-6" long
Bag Material Acrylic, Polyester
Cleaning. Mechanism Shaker
OPERATIONAL RESULTS
Pressure Drop 3" W.C. Flange to Flange
Outlet Emission Less than .004 gr/ft3(99.9%)
Polyester Bag Life 400 hrs rapid deterioration
Acrylic Bag Life Good, no acid attack after
14,000 hrs/340 starts
Fig. 3A
115
-------
ECNSW TALLAWARRA STATION
SECTION A and B FULL SCALE
DESIGN VARIABLE
Gas Volume
Gas Temperature
Gross Filter Ratio
Number of Bags
Bag Size
Bag Material
Cleaning Mechanism
SECTION A
500,000
290
•2.1
7,200
6V X 16'-6"
Acrylic
Shaker
SECTION B
170,000 ea.
270
2.4/1
2,880
6%" X 16 '-6"
Acrylic
Shaker
Fig. 3B
116
-------
ECNSW WANGI STATION
UNITS 4, 5, 6
PULSE JET FILTERS
Gas Volume
Gas Temperature
Dust Loading
Median Particle Size
Gas Cooling
Filter Ratio
Number of Bags
Bag Size
BAg Material
Cleaning Mechanism
160,000 ACFM
260°F
10 gr/cubic foot
12 microns
Air Dilution
6.68/1
2,016
42s" dia X 10'-0" long
Draylon T Acrylic
Pulse Jet
Fig. 4
117
-------
ECNSW WANGI STATION
UNIT 5 PC BOILER
REVERSE AIR BAGHOUSE
DESIGN CONDITIONS
Gas Volume
Gas Temperature
Dust Loading
Avg. Moisture
Median Particle Size
Gas Cooling
Net Filter Ratio
Number of Bags
Bag Size
Bag Material
Cleaning Mechanism
1900 ACFM
260-2700F
5-6 gr/acf
4.67%
2 microns
none
2.29/1 (one out)
24 (4 compartments)
8" Dia by 22'-0" long
(Menardi 601T glass)
(with 10% Teflon B finish)
Reverse Air
OPERATIONAL RESULTS
Pressure Drop
Outlet Emission
Bag Life
.005 gr/acf max.
3500 hrs - no visible
deterioration (70 starts)
Fig. 5
118
-------
DEMONSTRATION OF A HIGH VELOCITY FABRIC FILTRATION
SYSTEM USED TO CONTROL FLY ASH EMISSIONS
By
John D. McKenna
and
Kathryn D. Brandt
Presented At
The Third Symposium on Fabric Filters for
Particle Collection
Tucson, Arizona
December 5-6, 1977
119
-------
ABSTRACT
As a follow-up to a pilot plant study, a full scale investigation of
applying high velocity fabric filtration to coal-fired boiler fly ash
control was conducted. Two filter systems were separately applied to two
60,000 Ib./hr. coal fired boilers. Performance evaluations conducted over
the course of a year included total mass removal efficiency and fractional
efficiencies. One filtration system employed Teflon felt as the filter
media while the second system employed Gore-Tex, a PTFE laminate on PTFE
woven backing. During the course of the year a limited number of glass
felt and woven glass bags were introduced into the house containing Gore-
Tex.
Performance results and economic evaluation indicate this method of
fly ash control to be an attractive alternate to electrostatic precipitation.
120
-------
INTRODUCTION
In 1973 Enviro-Systerns & Research, Inc. was awarded an EPA contract.
The purpose of this contract was to determine the technical and economic
feasibility of employing fabric filter dust collectors for fly ash emission
control, particularly as applied to industrial boilers. Initially the
program was jointly funded by the EPA, Kerr Finishing Division of Fabrics-
America and ES&R, Inc.'1) The Kerr Plant located in Concord, North Carolina,
served as the host site for the program and ES&R manufactured and installed
the pilot facility. The pilot plant program provided short term performance
data including dust removal efficiencies and pressure drops for a number of
filter media. ' This data and a preliminary economic analysis indicated
that long term bag life and performance studies were warranted. EPA thus
decided to award a contract for the full scale demonstration of this approach
to fly ash control. The initial demonstration contract awarded to Fabrics-
America with ES&R as the major sub-contractor called for ES&R to design,
fabricate, install and then operate the two fabric filter units for a period
of one year. Contract options called for subsequent additional long term
operation of the units in order to test other filter media and also to eval-
uate the device as an sulfur oxide removal system.
121
-------
KERR - THE HOST SITE
The Kerr Finishing Division of FabricsAmerica is a textile dye and
finishing plant located in the textile belt of central North Carolina.
Kerr's normal production schedule is three shifts per day, five days per
week with 450-500 employees. Plant capabilities include processes to bleach,
mercerize, dye, nap, finish and sanforize both cotton and synthetic fabrics,
as well as cutting and preparing corduroy.
Two Babcock & Wilcox steam boilers are in operation at the Kerr facilities.
Each has a design capacity of sixty thousand pounds of steam per hour and both
are equipped with spreader stokers. Each boiler has a two-hour peaking capac-
ity of seventy thousand pounds per hour. The design efficiency of these units
is 82 percent. Based on the above parameters, the heat input for these units
is 73.2 million BTU/hr. each. Both boilers are equipped with fans for supplying
draft and unit number two, the unit tapped for the pilot plant stream, has
overfire steam injection for better combustion control. In January, 1973,
emission tests had been conducted on these boilers. The particulate emission
rates were found to be approximately 130 pounds/hour versus an allowable of
about 25 pounds/hour. Gas volumes were determined to be about 35,000 ACFM at
a temperature of about 355° F. Thus the grain loading measured was about 0.4
grains per ACFM. Orsat analysis indicated 9.5% C02, 10% 02, 0% CO and 80.5%
N2. Coal analysis indicated the percent sulfur to be about 0.6%.
THE HIGH VELOCITY FILTER
A schematic of the fabric filter dust collector is shown in Figure 1. As
shown, the unit is about 10 feet wide by 27 feet high. It is of modular
construction and the length increases as the number of modules increase. Each
module consists of two thirty-six bag cells as shown in Figure-2. Each addi-
tional module adds 3 feet 4 inches to the length of the house. One baghouse
may contain as many as fifteen modules and thus house 1,080 bags with a total
of 12,400 square feet of filter media.
The bags are 5 inches in diameter and 104 inches long, giving each bag
11.5 square feet of cloth. The bags are set into the tube sheet by the use of
two snap rings incorporated into the bag itself. The snap rings lock in place,
122
-------
General Arrangement SD-IO
Vof For Construction Purposes
Pyramid Hopper
**L" FLANGE. TO
Figure 1
SD-10 General Arrangement With Pyramid Hoppers
-------
fc
-------
one above and one below the tube sheet. A cage is set inside the bag and keeps
the bag from collapsing. The dust ladened gas enters one end of the unit, as
shown in Figure 3, passes through the tapered duct, into the classifier, and
then through the bags. The classifier forces the dirty gases to change direc-
tion 90°, then 180°. This quick directional change forces the larger and
heavier particles out of the flow so that they fall directly into the hopper.
The gas flows through the fabric filter into the center of the bags (Figure 4),
leaving the particulate on the outer surface of the bags where it is removed
periodically during the cleaning cycle. The clean gas then flows up and out
through the center of the filtering bag into a center exit plenum via an open
damper in the cell above the tube sheet. The bags are cleaned one cell (36
bags) at a time by activating the pneumatic cell damper. See Figures 5 and 6.
When the damper is in the up position, the flow is through the bags from the
dirty side to the center plenum or clean side. When the damper is dropped to
the down position, the flow is from the cleaning gas plenum through the bags
to the dirty side or hopper.
The cleaning system employs a unique hybrid method referred to as the
Shock-Drag Cleaning System, designed to prolong bag life by minimizing dis-
tortion of the fibers.
During the cleaning cycle, clean gas enters the cell through the pneu-
matic damper. The clean gas is forced down the filter bag, opposite to the
normal flow direction. The bag expands with a shock (Figure 5) so that the
cake is cracked and the particulate falls off the bag into the hopper. After
the shock has expanded the filter bag and broken off the cake, the clean air
continues to flow providing a drag (Figure 6) which pushes and pulls the dust
particles away from the fabric. The smaller particles are thus forced out of
the fabric and fall into the hopper for removal from the unit. Damper system
and control panel arrangements allow for variations in main gas volume,
reverse-air volume, duration of cleaning and frequency of cleaning.
THE PILOT PLANT
In the summer of 1973 a pilot scale investigation was initiated with the
purpose of determining the techno-economic feasibility of applying a fabric
filter dust collector to coal-fired industrial boilers. The pilot facility,
125
-------
co
ED
O
CD
O
GO
9ZT
> 2
^ a
fD
00
-------
Ftgure 4
127
-------
Figure 5
128
-------
4
Figure 6
129
-------
installed on a slip stream of Kerr's number two boiler, was to handle 11,000
acfm when operating at an air-to-cloth ratio of 6/1. Figure 7 shows the pilot
facility. This prototype facility was actually a two module commercial size
unit containing five inch diameter 104 inch long bags. Thus, future scale up
problems were minimized.
The filter media evaluated were Nomex(R) felt, Teflon
-------
PH
4J
-U
O
PH
r*»
0)
I"
-------
Figure 8
S3
.020
CJ
oo
l/l
C
•r—
CO
CD
ro
4J
C
.015
.0.10
,005
Outlet Concentration
vs.
Air-to-Cloth Ratio for Various Bag Materials
KEY:
O Nomex
O Teflon Felt - Style 2663
Q Gore-Tex/Nomex
A Dralon-T
6 9
Air-to-Cloth Ratio (ACFM/Ft.2)
12
14
-------
Figure 9
Comparison of Operating Pressures for Various
Bag Materials"
LO
Co
to
OJ
o
e
03
CO
in
to
o
u
-------
Figure 10
Installed Costs vs. Air-to-Cloth Ratio
350
in
O
CJ
QJ
300
(/)
% 250
O
O
200
150
TOO
50
O
0
A
O
O
KEY;
Nomex Felt
Gore-Tex/Nomex
Gore-Tex/Gore-Tex
Oral on T
Teflon Felt
6 8
Air-to-Cloth (ACFM/Ft.2)
10
12
134
-------
Figure 11
Operating Costs vs. Air-to-Cloth Ratio
50
40
to
o
Q
CO
o
30
•*->
o
? 20
(O
s_
-------
175
Figure 12
Teflon Felt
Annual Operating Cost vs. Air-to-Cloth Ratio
for Different Bag Life Assumptions
150
125
<0
o
Q
CO
O
X
J/l
o
C_5
CD
01
CL.
O
fO
3
C
c
100
75
50
25
KEY;
Annual Replacement - Avg. Life 1 Yr.
Replacement Over 2 Yrs. - Avg. Life 1.5 Yrs
Replacement Over 3 Yrs. - Avg.
Replacement Over 4 Yrs. - Avg.
Replacement Over 5 Yrs. -
Avg.
Life
Life
Life
2 Yrs.
2.5 Yrs,
3 Yrs.
_L
_L
6 8 10
Air-to-Cloth Ratio (ACFM/Ft.2)
136
12
-------
Figure 13
Annual i zed Cost Comparison
175 —
I / tJ
150
en 125
o
o
CD
« 100
+J
o
O
-------
Gore-Tex had torn in a matter of days when used with a spiral cage. This
problem was overcome by use of a rigid cage.
FULL SCALE OPERATION
In 1976, two full scale fabric filter dust collection systems were designed,
fabricated and installed on each of the two 60,000 Ib/hr Kerr boilers in Concord,
North Carolina. In December of 1976, both dust collectors were brought on
stream under an EPA Demonstration Program (Contract No. 68-02-2148) with
FabricsAmerica being the prime contractor and ES&R the major subcontractor.
Figure 14 is an artist rendition of the full scale baghouse. ES&R was con-
tracted to provide a turn-key system. This contract included system design,
fabrication of ductwork and baghouses, supply and installation of all system
components, start-up and testing of the units for a minimum of one year. The
system was designed to include features accommodating the planned test program.
Long straight duct runs were provided at both the inlet and outlet, platform
and stair access to all major test ports, a sophisticated separate control
house and a penthouse over both fabric filter dust collection systems were
provided. The penthouse covers the outlet test ports, thus allowing testing
in inclement weather at the points where the major share of the testing is to
be done.
Each unit was constructed of a 10 gauge mild steel house and 3/16" mild
steel hoppers. Pyramid hoppers were chosen to eliminate potential problems
with screw conveying of the collected'fly ash. Two inches of Fiberglas insu-
lation with a sheet metal skin overlay was installed on both house and hopper
at the factory. Houses and hoppers were shipped from Roanoke, Virginia to
Concord, North Carolina by truck. Figure 15 shows one house leaving the
factory. Figures 16 and 17 show one of the houses being lifted onto its
hopper. Figure 18 shows the system with all major hardware elements complete.
The common penthouse is shown covering both baghouses and in the foreground
the control house is seen. The dust collection system control panel within the
control house is shown in Figure 19. A system schematic is provided in Figure
20. As is shown in this figure, the dust collection system is brought on line
by closing a boiler stack damper and opening a system inlet damper, the flue
gas then passes into the inlet duct, down by an auxiliary gas fired heater into
a center baghouse inlet plenum, the dust laden gas then enters the hopper turns
138
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Figure 14
EPA DEMONSTRATION OF THE ENVIRO-SYSTEMS FABRIC FILTER SYSTEM
AT KERR FINISHING DIV. FA3RICSAMERICA, CONCORD,NORTH CAROLINA
-------
-------
Figure 16
House Being Lifted Onto Hopper - Far View
141
-------
Figure 17
House Being Lifted Onto Hopper - Near View
142
-------
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Figure 20
Fabric Filter Schematic
-------
and comes up to the filter bags. Once it passes thru the filter media, the now
clean gas passes into the exit plenum thru the exit duct, a vortex damper and
out the main system fan to the dust collection system stack. A portion of the
cleaned flue gas is drawn from the stack by a separate smaller cleaning fan and
returned to the system to be used in backflushing the bags during cleaning.
The auxiliary heater can be employed to preheat the house prior to baghouse
start-up and it can also be employed to purge the house at shut-down. The
vortex damper is employed to maintain a predetermined pressure at the boiler
stack in an attempt to prevent the dust collection system pressure drop fluc-
tucations from influencing the boiler operation. The control system includes
automatic preheat, start-up and purge mode and operation of the vortex is also
automated. The system is arranged so that the entire operation of both bag-
houses is controlled from the console located in the control house. When set
up for automatic operation, either baghouse can be started and stopped from
controls located in the boiler house, however, provision was included on the
control house console for locking-out the boiler house start function. Alarms
and an automatic shut-down have been included for the functions shown on Table 1
A number of temperatures and pressures are permanently recorded. These include
the inlet and outlet temperature of each house and the pressure drop across
each house and main fan. One of the two houses is equipped with an inlet and
outlet transmissometer.
The two houses are identical in terms of the basic hardware. Each house
contains eighteen (18) cells with thirty-six (36) 5" dia. X 8' 8" long bags in
each cell, thus both houses contain a total of 7,440 square feet of cloth.
Initially, House No. 1 contained 648 Teflon felt bags and House No. 2 contained
648 Gore-Tex bags. During the first year of operation one cell (36 bags) of
Gore-Tex was replaced by an experimental felted glass media and subsequently a
second cell of Gore-Tex bags was replaced by a 26 oz. woven glass media.
DEMONSTRATION PROGRAM PURPOSE AND OBJECTIVES
The purpose of the demonstration program is the testing of a full scale
demonstration fabric filter system installed on an industrial size coal fired
stoker boiler. The baghouse system will be operated and tested over the duration
of the program to determine general operating parameters, bag life data and
economic factors necessary for making techno-economic evaluations.
146
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Table 1
Alarms and Shut-Down Functions
Alarm &
Function Alarm Only Shut-Down
Bag Cleaning on Manual X
Boiler House Stop X
Control House Stop X
System Fan Below 1400 RPM X
RA Fan Off X
Hopper Full X
Heater Off X
Pneumatic Air Low X
Stack Pressure Out of Range X
Phase Monitor Tripped X
Inlet or Outlet Temp. High X
Dryer Off X
Alarm Horns Off X
147
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The objectives of the program are to demonstrate the feasibility of apply-
ing fabric filtration to industrial size coal fired stoker boilers and to
accomplish the following:
Obtain operating data that would be generally useful for appli-
cation engineering.
Obtain operating data and bag life data necessary in making
techno-economic evaluations.
Determination of the efficiency of removal for specific
particle size ranges as a function of filter media on-stream
duration.
Determination of filter media property changes as a function
of bag on-stream duration.
An economic evaluation comparing capital, operating and annu-
al i zed costs of baghouses for the filter media tested.
RESULTS: COMPARISON OF FULL SCALE AND PILOT UNITS
The data gathered at this time indicates similarity between full scale and
pilot plant operations. The outlet particle sizing achieved with Andersen
inertia! impactors seem to approximate the results obtained with the pilot
study for Teflon felt; however, demonstration tests at only one air-to-cloth
ratio have been obtained. Outlet grain loading values for Teflon felt acquired
via Andersen impactor confirm pilot plant results although four values from
late August 1977 were higher. Andersen outlet grain loadings calculated for
the Gore-Tex bags showed results higher and lower than the pilot plant value of
0.004 grains/SCF but all values were below 0.01 gr/SCF. The pressure drop
across the house is somewhat higher for the full scale plant than for the pilot
plant; however, the relative position of the pressure drop curves for different
bag materials is very close to the pilot operation. One factor contributing to
the higher pressure drop may be the removal of the cyclones which were present
during the pilot plant studies. Another consideration is the limited on-stream
time of the pilot plant operation.
148
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Hardware problems encountered during the testing program included com-
pressed air in-line freezing during the extreme cold of January and February,
1977, and rapid deterioration of silicone rubber gasketing material employed
around the dampers and hatch covers. All gasketing material was replaced with
asbestos gasketing. Debugging of the system controls was extensive and plug-
gage of the boiler stack pressure tap with moisture and ash required subsequent
installation of a continuous compressed air purge system.
High pressure drop across both houses appeared to be the result of boiler
start-up through the baghouses, plus a number dew point excursions occurring
when the controls were being debugged. In view of the heavy dust pearls on the
surface of the bags it was decided to manually vacuum each bag. After vacuuming
the houses were brought on stream and the pressure drops were reduced to accept-
able levels. In the case of the Teflon felt the pressure drop across the bags
returned to the original clean bag level. Lab permeability analysis confirmed
this. Subsequent to bringing the houses on stream, failure of the Gore-Tex
bags occurred. At the end of the first year of operation about ten percent of
the Gore-Tex bags had failed; no bag failures or obvious signs of deterioration
had occurred with the Teflon felt bags. The failure of the Gore-Tex bags
generally was in the form of either a small round hole, one inch or less in
diameter, or a tear about 1/8 to 1/4 inch wide and one to six inches long.
Occasionally a bag would be found totally shredded. One possibility is that the
impact of the PTFE membrane on the tube sheet during installation and removal
initiates the failure. Another contributing factor may be the stress occurring
as the bags shrink on the rigid cage when going through the temperature eleva-
tion at start-up each week.
CURRENT COSTS
Overall, the economic evaluation executed during the pilot plant program
remains valid. For the 70,000 ACFM case, a baghouse outfitted with Teflon felt
and assuming a two-year bag life continues to be a more economically attractive
alternative than an electrostatic precipitator. During 1977 a major price
reduction for Teflon felt occurred. The installed price was reduced from $75
per bag (5" dia. X 8' 8" long) to $53 per bag. The impact of this price reduc-
tion on annualized cost is shown in Figure 21. This brings the Teflon felt
149
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90
Figure 21
Total Annualized Cost vs. Air-to-Cloth Ratio
Teflon Felt
KEY:
O $75/Bag, Original
^\ $53/Bag, Original
20
Air-to-Cloth Ratio (ACfW/Ft.2)
150
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alternative in line with the cost of Gore-Tex, as can be seen by reviewing the
pilot study annualized cost comparison, shown in Figure 22, with the current
comparison, shown in Figure 23.
FUTURE PLANS
EPA has at this time elected to exercise two of the three proposed options,
thus the two demonstration units will continue to be operated and tested
throughout 1978 and 1979. House No. 1 will continue to be operated with Teflon
felt as the filter media. The program plan calls for replacement of the Gore-
Tex with a series of other filter media, thus obtaining cost, life and perform-
ance data on a variety of candidate media considered potentially suitable for
fly ash control applications. The initial candidate materials include both
woven and felted glass.
151
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Figure 22
AnnualIzed Costs vs. A1r-to-C1oth Ratio
KEY;
O Teflon
A Gore-Tex/Gore-Tex
Q Nomex
Gore-Tex/Nomex
Dralon
20
Air-to-Cloth (ACFM/Ft.2)
152
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Annualized Costs, 103 Dollars
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REFERENCES
J. D. McKenna, "Applying Fabric Filtration to Coal Fired Industrial
?rl!or^"APrel1m1nary P11ot Scale Investigation", July - 1974, EPA
650/2-74-058.
(2)
J. D. McKenna,_J.C. Mycock, and W. 0. Lipscomb, "Applying Fabric Filtra-
154
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BAGHOUSE PERFORMANCE ON A SMALL ELECTRIC ARC FURNACE
by
Robert M. Bradway
GCA/Technology Division
ABSTRACT
This paper presents the results of an evaluation of a fabric filter sys-
tem controlling emissions from either one or two 30-ton electric arc furnaces
producing a high-strength, low-alloy specialty steel. The evaluation involved
measuring the system's total mass collection efficiency and apparent frac-
tional collection efficiency. Testing involved 8 sampling days with one fur-
nace operating, and 2 days with two furnaces. Baghouse influent and effluent
streams were sampled with total mass samplers, inertial impactors, a conden-
sation nuclei counter (CNC), and an optical dust counter. Total mass tests
showed baghouse mean mass efficiency to be 97.9 percent with one furnace op-
erating, and 98.7 percent with two furnaces. Mean outlet mass concentrations
for one- and two-furnace operation were 0.0014 and 0.0019 grains/dscf, re-
spectively. Influent impactor tests showed considerable size distribution
differences as a function of the phase of the process: the greatest concen-
trations for the particles sized occurred during the first melt. Effluent
impactor size distribution tests suggested agglomeration.
155
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INTRODUCTION
The work reported in this paper presents one phase of a program whose
purpose was to characterize the performance of several industrial size fabric
filter systems. The fabric filter tested at the Marathon LeTourneau Company
in Longview, Texas cleaned the emissions of either one or two 30-ton electric
arc furnaces which produce a high strength, low-alloy specialty steel. Each
furnish is fitted with a side draft hood and a canopy hood which is used only
during charging and pouring. The hoods are ducted through a spark arrester
to a 10-compartment American Air Filter baghouse which utilizes Dacron™ bags.
The performance of the fabric filter was characterized by determination
of the particulate removal efficiency as a function of total mass and particle
size. The apparent fractional efficiency, defined as the measured change in
the particulate concentrations as a function of particle size that results
from the filtration process, was determined by upstream and downstream sampling
using mertial cascade impactors. The baghouse influent and effluent streams
were also monitored with a condensation nuclei counter to determine variations
in submicron particle concentrations as a function of the process and the
cleaning cycle.
MARATHON LETOURNEAU STEEL MILL
The steel mill at Marathon LeTourneau produces high strength, low alloy,
specialty steel in two electric arc furnaces of 30 tons each, nominal capacity
The furnaces are 10,000 kVA swing roof top charged units with individual com-
bination side-draft and canopy hooding. The side-draft hoods operate while
the furnace roof is in place and the canopy hoods operate when the roof is re-
moved for charging and tapping. The furnaces use the basic steel making pro-
cess with cold number one oil-free scrap. The furnaces must be back charged
once to reach holding capacity, and the double slag method of refining is
used. Additions of fluorspar are commonly made for slag conditioning and
oxygen lancing is used to lower the carbon content of the melt.
The furnace hoods are ducted to a 10-compartment American Air Filter bag-
house installed in 1973. Photographs of the baghouse are presented in Figures 1
and 2. The baghouse has a cloth area of 52,7782 which results in an air-to-
cloth ratio of 3.22:1 at the design flow of 170,000 acfm at 150°F. The net
air-to-cloth ratio increases to 3.58:1 with one compartment off-line for clean-
ing. The cleaning cycle is actuated by timer such that there is no delay time
between cycles. Each baghouse compart contains 288 Dacron™ filter tubes
which are 5 inches in diameter by 14 feet long.
156
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Figure 1. Photograph of side of fabric filter.
-------
Ijl
O3
Figure 2. Photograph of end of fabric filter.
-------
RESULTS
The primary purpose of the sampling program at Marathon LeTourneau was
to define the total and fractional particulate penetration through a fabric
filter cleaning the emissions from an electric arc furnace. The secondary
reason for testing was to determine the effect of approximately doubling the
particulate loading to the baghouse on the total and fractional penetration.
In addition, the baghouse inlet and outlet submicrometer particle concentra-
tions were measured as a function of the process cycle and the baghouse
cleaning cycle to determine if periods of high penetration are a function of
the process cycle, the cleaning cycle or both. Finally, the inlet particle
size distributions were measured as a function of the process cycle.
Mass Measurements
The baghouse inlet and outlet average particulate mass concentrations
and the resulting efficiency penetration results are presented in Table 1.
Examination of the table shows that the inlet concentrations for the test
days during which there were two furnaces in operation were approximately
twice that of the runs in which there was only one furnace in operation.
TABLE 1. AVERAGE RESULTS OF TOTAL MASS MEASUREMENTS
Tests
Concentration,
gr/dscf Efficiency, Penetration,
— percent percent
Inlet Outlet
All
Two furnaces
One furnace
0.0824
0.1472
0.0662
0.0015
0.0019
0.0014
98.18
98.71
97.94
1.82
1.29
2.06
The mass penetration and the total mass sample outlet concentration sta-
tistics show that the penetration is lower even though the outlet concentra-
tion is higher (40 percent) with the two furnaces in operation indicating the
baghouse particulate removal efficiency varies with inlet grain loading. Thus
the baghouse dampens changes in the outlet concentration or emission rate
caused by variations in the inlet concentration.
The particle size distribution data was not such a straightforward task
as the total mass measurements, however. The duration of the inlet impactor
sampling to collect a weighable sample on each stage without overloading was
quite variable due to differences in the mass concentration as a function of
the process cycle. Figure 3 illustrates in a somewhat simplistic way what
happens to the mass concentration as a function of the process cycle for one
micrometer particle. Other curves were constructed for two, four, six, eight
159
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o
w
0.10
0.05
0.01
9
O
j? 0.005
0.001
I I
FIRST MELT
BACK
CHARGE
I I
0
J L
SECOND MELT
TAP
J 1 1 I I L
60 120
CYCLE TIME.minutts
ISO
Figure 3. Concentration versus process cycle for 10 ym particles.
160
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and ten micrometer particles and all showed the same pattern. The concentra-
tion is highest during the first melt, drops dramatically during back charging,
increases somewhat during the second melt and then decreases again during tap.
Because of the large temporal changes in concentration, it was important
that we sample during phases of the cycle. Figure 4 shows the sequence of
inlet impactor measurements that were taken, showing that nearly every part
of the process cycle was sampled. These results were the time averaged and
composited to construct a single curve for the inlet particle size distribution
with our furnace in operation and another for two furnaces in operation. These
curves are shown in Figure 5. It can be seen from these curves that highest
inlet concentration occurs at about two micrometers and that two furnace op-
eration roughly doubles the concentration over the entire size range covered
by the impactors.
The measurement of the outlet particle size distribution was more straight-
forward. Because of the very low concentrations, however, outlet impactors
were run for 9 to 15 hours each day so that a weighable amount of particulate
could be collected on each stage.
The results of the outlet impactor runs are summarized in Figure 6. As
can be seen, the grain loadings are very low but the particle size of maximum
concentration is 4 micrometers This is compared to a maximum concentration
at 2 ym at the inlet, a phenomenon discussed yesterday by Dick Dennis.
By comparing the inlet and outlet size distribution curves, one can con-
struct a fractional efficiency curve for the baghouse, as shown in Figure 7.
Although we generally do not like to describe baghouse collection performance
in terms of fractional efficiency because many of the outlet particles do not
directly penetrate the filter, it is a conventional method of describing col-
lector performance. These curves show a minimum at about 1 ym, a maximum at
about 6 ym and then a dropoff to 10 ym.
Inlet and outlet measurements were also made in the submicrometer particles
with a condensation nuclei counter. These measurements showed collection ef-
ficiencies of 99.23 to 99.86 percent for particles over the range of 0.0025 ym
to about 0.5 ym. This device, when used on the outlet gas stream, very con-
sistently showed peaks in the small particle concentration immediately after
a compartment was cleaned.
In summary, the baghouse evaluated controlled the emissions to an outlet
concentration of 0.0015 gr/dscf. This is 3k times below the allowable concen-
tration. The baghouse studied also was shown to efficiently collect particles
over a very broad range of particle sizes.
This project has been funded at least in part with Federal funds from the
Environmental Protection Agency under Contract No. 68-02-1438, Task 4. The
contents of this publication does not necessarily reflect the view or policies
of the U.S. Environmental Protection Agency, nor does mention of trade names,
commercial products, or organizations imply endorsement by the U.S. Government.
161
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INLET
RUN NO,
I 1
a-.
8
h-H-
-H
10
POWER ON
. 1 ,
1 f 1 , ,
BACK CHARGE SLAG OFF
-1 Li L 1 ill
REBOIL TAP
v eo iao iso
CYCLE TIME, minutes
Figure 4. Time in process cycle at which inlet samples were collected.
-------
0.2
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0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
>-ONE FURNACE ON
|-TWO FURNACES ON
23456 789
PARTICLE AERODYNAMIC DIAMETER,/im
10
Figure 5. Composited differential size distribution
curves of baghouse inlet aerosol.
163
-------
0.002 r
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O
0.001
0.0009 I-
0.0008 h
0.0007k
0.0006
2 0.0005
0.0004
0.0003
h
0.0002
0.0001
i
>-ONE FURNACE ON
I-TWO FURNACES ON
56789|Q
PARTICLE AERODYNAMIC DIAMETER,
II
Figure 6. Average outlet differential size distribution
curves.
164
-------
0)
Qt
•»
Z
o
cr
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Q.
-ONE FURNACE ON
-TWO FURNACES ON
34567
PARTICLE SIZE./im
Figure 1. Fabric filter fractional penetration curves.
165
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166
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FUME CONTROL AT SMALL SMELTERS
Knowlton J. Caplan
ABSTRACT
In general, fabric filters are successfully applied to fume control in
small smelters. Special considerations need to be provided for hot gases,
possible presence of acid (especially S02), high dew points, and sometimes for
fire prevention. Efficiencies are adequate for present emission standards and
a clear stack is usually obtained. Air-to-cloth ratios are usually quite con-
servative because the permeability of the dust cake is quite low. The dust is
somewhat, but not exceedingly, difficult to handle. A table is provided sum-
marizing the performance of 15 fabric filters in small smelters processing lead,
brass, and copper.
167
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FUME CONTROL AT SMALL SMELTERS
By Knowlton J. Caplan11
Presented at 3rd EPA Symposium on Fabric Filters for Particle Col-
lection, December 6, 1977, Tucson, Arizona
INTRODUCTION
The term "small smelters" covers a very heterogeneous and poorly
described segment of U.S. industry. Almost all small smelters are
secondary smelters, that is, the raw material for the process is
recycled scrap. Obviously, such industries provide a highly use-
ful economic and environmental function. Apparently these
industries are not represented as such by any trade association,
although they may be members of other trade associations related
to the end uses of their product. In a recent study on economic
impact of proposed government regulations on the lead industry,
it proved impossible to closely define or accurately count the
number of secondary lead smelters.
With such a heterogeneous definition of the subject, this paper
will only cover part of it, that part which is represented in our
direct experience. This paper is not a comprehensive literature
survey, but rather a description of general operating characteris-
tics of the industry as related to fume control.
INDUSTRY CHARACTERISTICS
Secondary Lead Smelters
Secondary lead smelters are generally centered around a local
supply of scrapped automobile batteries and those batteries are
the main source of feed material to the plant. Other forms of
lead scrap are handled incidentally. Such secondary smelters may
be associated with a battery manufacturing plant which consumes
the lead produced, or may be independent, producing pig lead.
Although a process does exist for charging the drained batteries,
case and all, into a melting furnace, that process is not widely
used and most plants operate by "breaking" the batteries. A
mechanical saw or guillotine is used to cut the case open, the
lead bearing plates are dumped out of the case, allowed to dry in
piles on the floor, and handled by front end loader for manipulatin<
the stock piles and charging the furnace. Various mechanized schem<
President, Industrial Health Engineering Associates, Inc.,
Minneapolis, Minnesota.
168
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have been proposed and tried without notable success. Obviously
this method of bulk handling is dusty and presents a difficult
occupational health problem, but the dust concentrations are
usually below present emission standards and even if they were
not, the particle size is relatively coarse and collection would
not be difficult.
The major sources of fume in the secondary lead smelter are
either a blast furnace resembling a foundry cupola or a reverb-
eratory furnace, and the associated refining kettles. These will
be described later.
c'
Secondary Copper Smelters
Recycled copper can be recovered by wet chemical methods or by
smelting. The copper scrap going to a smelter is much more hetero-
geneous than is the case with the lead industry. The scrap contains
many other metals besides copper and many alloying elements for
copper, so that the metals separation and refining process is much
more complicated. The same smelter may also receive other non-
ferrous scrap materials involving semi-precious or precious
metals. As far as the copper scrap is concerned, it is even less
homogeneous than the lead battery scrap and is handled by front
end loader in bulk, with the associated hygiene problems. The
first process evolving fume is the charging of the material to
a blast furnace; from there on the melting process resembles in
its process steps a primary copper smelter, with the major ex-
ception that the sulfur content is low and evolution of SC>2 is
not too significant a problem.
Fabric filters are used for fume collection from the blast furnace,
converter and other associated fume sources. Our experience in
this particular problem is limited in that the severe depression
of the copper market has delayed our projects in this area.
Brass Recovery
It is our impression that most brass is recycled by brass foundries
or other brass producers, rather than attempting to smelt the
brass to a marketable grade. Brass melting in brass foundries is
usually conducted in crucible furnaces or in tilting melting fur-
naces using scrap brass of known composition as part of the
charge. The emission from crucible furnaces is quite low, unless
oily scrap is used. The emission from direct fired melting furnaces
169
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is higher, and causes potential problems of baghouse fires either
from carryover of sparks or from finely divided metallics (es-
pecially zinc) that may be generated by the reducing atmosphere
and collected in the baghouse. As far as we know, brass is either
smelted for its copper content in a copper smelter or directly
used in the foundry and there are no "brass smelters" as such.
Secondary Aluminum Smelting
We have no experience with this particular industrial function
other than the typical problems associated with aluminum melting
as practiced in light metal foundries. The major problem associ-
ated with fume in such operations arises from the use of chlorine
as a scavenging gas in the melt, which produces a copious aluminum
chloride fume. Treatment of this source has been extensively
described in literature.
FABRIC FILTER APPLICATION TO SMELTERS
Table I presents a summary of data available to us concerning the
general operating parameters of fabric filters in small smelters.
Much of the data is missing, as is obvious, since the information
was collected incidentally to other work which may have been on
the baghouse itself or only indirectly related. Some information
from AP-40 has been included for the sake of completeness.
Most notable among the missing data is particle size information.
Although scientifically this is regrettable, for practical appli-
cation it is not too important. All the systems are handling a
fine metallurgical fume which would be expected to, and does, have
a mass median aerodynamic diameter of 1 micron or less. Of
greater practical importance is that the fume is "difficult";
that is, the permeability of the accumulated filter cake is low.
The dust is also, in general, somewhat difficult to handle,
somewhat sticky, etc., as distinguished from a free flowing
granular material.
It will be noted that all the filters except one (which is trouble-
some) are operating at quite modest air-to-cloth ratios for the
type of filter involved. Differential pressures across the fabric
are, with the same exception, in the normally expected range even
though accurate data may not be available due to the large varia-
tions in operating conditions for some filters.
170
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Efficiencies are usually in the range of 98 to 99% on a weight
basis, the stack is usually visually clear, and the outlet
grain loading is usually comfortably below the present emission
standard for primary lead smelters. The reason for the efficiency
being somewhat below the 99.9 weight percent that can usually be
expected for a fabric filter is not clear. The duty conditions
are rather severe, involving high temperatures and chemical attack
on the fabric. Furthermore, the baghouses are usually quite
large so that, in view of the high temperatures and noxious con-
ditions, finding and fixing small mechanical leakages through the
fabric is difficult and is not actively pursued as long as the
emissions are satisfactory.
The hot gases from the furnaces may be cooled to suitable bag-
house temperatures by any of the classical methods. If acid is
present, the most favorable design would be to use radiant coolers
to avoid introduction of additional water vapor. When water sprays
are used, they are usually used only for partial cooling, the
remainder being by dilution in order to avoid too high a dew point.
If acid gases are present in significant quantity or if water
spray cooling is used, the hoppers of the fabric filter should be
kept above the dew point. This requires provisions over and above
that required to keep the main housing above the dew point. With
material collected in the hopper, the collected layer of dust
provides an insulating effect so that the metal temperature may
be far below the gas temperature. However, the vapors will still
migrate through the bed of dust, condensing on the cold metal
walls and forming a cake or mud.
Blast furnaces or cupola type furnaces can be operated under
significant draft so that there is no escape of fume from the
furnace itself. There is, of course, fume evolved from the
pouring of the metal or the tapping of slag which should be con-
trolled from a hygiene point of view. The air from such hoods
is usually only 100 - 150°F and is an economical source for
dilution air since it also requires filtration.
Reverb furnaces on the other hand are typically operated at a few
hundredths of an inch water gage draft in order to conserve fuel.
Such furnaces tend to be somewhat leaky and loss of the draft
will result in leakage of fume from the furnace itself or from
various operating ports. In some primary smelters, very elaborate,
fast-acting control systems are installed to regulate the furnace
171
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draft in accordance with operating conditions, the opening of
charge ports, etc. Such elaborate controls are usually not found
in secondary smelters. External hygiene control hoods may be
located over the charge ports, metal and slag taps, and again,
this contaminant-laden air provides a source of dilution air for
cooling the furnace gas on an economic basis. Such hygiene
hoods do not, however, provide for maintenance of adequate furnace
draft to prevent leakage from the furnace itself.
FIRES IN METALLURGICAL BAGHOUSES
Fires are not uncommon in metallurgical baghouses. They usually
but not always occur in the hopper of the baghouse. However, the
circumstances under which they occur are highly variable, and
immediate investigations following a fire usually lack the
application of scientific expertise. As far as we know, no
concerted research has been done on the subject.
Fires occurring in the hopper are almost always caused by the
presence of finely divided unoxidized metallics of a pyrophoric
nature. The presence of metallic zinc is probably the most common
source of such fires, and the presence of metallic lead probably
the second most common source.
Prevention of fires in baghouse hoppers has been most successfully
accomplished by the addition of an inexpensive diluent material.
The most common diluent is agricultural lime, it serving obviously
as a diluent to the combustible materials and also, if a fire does
start, heat will be absorbed in dehydrating of the lime thus
furnishing an additional cooling effect. Some installations have
used various carbonates such as soda ash or ground limestone, the
theory being that the heat of the fire will release carbon di-
oxide which will tend to smother the fire. This latter action
probably would not be effective for a fire in the bags since the
filtering air flow would rather quickly flush the blanket of
carbon dioxide away from the combustion area.
There is an empirical test called a "burning test" which is
applied to controlling fires in metallurgical baghouses. In
general the test consists of taking a shallow pan full of the
collected dust and attempting to light it at one end by ordinary
means such as a match or a burning paper towel. The time of
burning from one end to the other of the pan is then measured, and
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if it is less than some specified value, the diluent is added to
the duct entering the baghouse so as to mix with, dilute, etc.,
the combustible dust. The test is strictly empirical and the
parameters need to be developed for each individual plant or bag-
house situation.
One plant used a pan one-half inch deep, 2 inches wide, and 6
inches long. In this case, the burning was not actually timed;
if the dust burned at all, the diluent was added. The diluent
was hydrated lime (agricultural lime) and was added in amounts
varying from 5% to 20% of the total dust load.
In another plant the test pan was 1 inch deep, 3 inches wide and
9 inches long. If the length of time required to burn from one
end to the other was greater than 2 minutes, it was judged
acceptable; if less than 2 minutes, agricultural lime was added
to the flue.
Fires starting on the bags rather than in the hopper are usually
blamed on the carryover of sparks although there are some indi-
cations that these fires also are sometimes started by metallics.
In one interesting case, the bags of a reverse pulse filter with
bottom inlet caught fire at the top of the bags and there was no
fire in the hopper. Because at times sparks had been observed in
the flue, the fire was blamed on sparks. It is difficult to
understand how such sparks would preferentially migrate to the
top of the bags. Another possible explanation would be that the
reverse pulse air, having more energy and physically agitating
the dust cake more at the top of the bags than further down, may
have started the fire in the metallics present. In any case,
the provision of a spark trap such as a cyclone or a spray cham-
ber would prevent fires from sparks if they cannot otherwise be
prevented. If both sparks and unoxidized zinc or lead are
present, both types of precautions may be required.
DUST HANDLING
The handling of recovered dust in most secondary smelters is a
difficult problem because such plants usually do not have a
multiplicity of processes and options for disposal of such
material. The material may also have a significant monetary
value. Its disposal by means other than to the process would be
an obvious problem in solid waste disposal.
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The dust is usually somewhat difficult to handle. It does not
flow readily from hoppers, etc., unless special provisions are
made. The dust should be capable of conveyance by pneumatic
conveying, but some operators have experienced difficulty with
this operation due, in our opinion, to inadequately designed
systems. Screw conveyors work, but they must be enclosed and
dust control applied. Belt conveyors or other dusting type of
material handling equipment is to be avoided.
The dust is usually significantly different in metallic compos-
ition to the parent material and metallurgical considerations may
govern^the point in the process to which it is returned, or even
if it is to be returned. Leaving aside the metallurgical con-
siderations, dust returned in that form to a blast furnace or
cupola is mostly re-entrained and immediately reappears in the
baghouse, constituting a circulating dust load. The circulating
dust load may be an operating advantage if such recirculation
accumulates unwanted impurities so that a bleed-off or programmed
disposal of the dust can be made. Otherwise, the dust will be
recovered more efficiently by returning it to a different type
of furnace such as a reverberatory furnace. Most secondary
smelters do not indulge in pugging or briquetting of dust to
reduce its loss in the furnace.
SUMMARY
In general, fabric filters are successfully applied to fume con-
trol in small smelters. Special considerations need to be pro-
vided for hot gases, possible presence of acid (especially SO9),
high dew points, and sometimes for fire prevention. Efficiencies
are adequate for present emission standards and a clear stack is
usually obtained. Air-to-cloth ratios are usually quite con-
servative because the permeability of the dust cake is quite low.
The dust is somewhat, but not exceedingly, difficult to handle.
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rTTCgjrraa
FULLER
COMPANY
FABRIC FILTERS IN THE CEMENT INDUSTRY
N. D. PHILLIPS
SENIOR PROJECT ENGINEER
AND
W. C. BRUMAGIN
CHIEF PRODUCT ENGINEER
DUST PRODUCTS DIVISION
FULLER COMPANY
FOR PRESENTATION AT
THIRD SYMPOSIUM ON FABRIC FILTERS
FOR PARTICLE COLLECTION
DECEMBER 5-6, 1977
TUCSON, ARIZONA
177
P.O. BOX aa. CATASAUQUA, PA. 18O32 TELEPHONE: 215-26-4-6O11 TWX: 51O-651-5B1Q TELEX: 03-4-7443 CABLE: CQLFULLER
A GATX COMPANY
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INTRODUCTION
Over the last 20 years, cement producers have been under
considerable pressure to reduce their contributions to the
air pollution problem of the nation. In fact, dust col-
lection equipment has been used for a very long time in
cement plants, much longer than the last twenty (20) years
This has been primarily due to the nature of the materials
used in the process and the materials produced, as well as,
the two initial reasons why any plant will consider in-
stallation of dust collection equipment. The first being
recovery of a product that already has an investment in it
and is usable in the end product of the plant. The second
being the elimination of air-borne dust within the plant
facilities, thereby extending the life of mechanical equip-
ment in the plant and reducing housekeeping expenses in the
facility. For these reasons, 30 or 40 years ago, it was
common to see dust collection equipment within the plant
venting material handling facilities, drying facilities,
pyroprocessing equipment, and milling equipment.
There have been two distinct processes used in the manufacture
of cement that differ primarily in the treatment of the raw
material Before pyroprocessing. The wet process in earlier
^times being the most common, required little in the way of
dust collection equipment, until after the raw feed had been
dried, calcined and clinkered. The dry process plant, has
always required dust collection equipment in greater degree
because of the crushing, drying, milling, and blending of dry,
relatively fine materials. With the advent of the energy
crisis, dry plants in the United States are becoming more
popular, therefore, cement plants will be equipped with dry
filtration dust collection equipment to a greater degree in
uric, T u L u v* G »
In the late 1950's, good neighbor!iness and the move to im-
prove the quality of our environment, caused cement manufactur-
ers to look at replacing their mechanical separation equip-
ment and electrostatic precipitators with more efficient
devices. In the late 1950's, fabric filters began to be ap-
plied to the waste gases from long dry kilns, the initial
small suspension preheater kilns, and somewhat later than
that, to long wet process kilns. This came about largely be-
cause of an increase in production of fiberglass fabrics and
tnrn^i1^r°y^ni-ntS 1n.tre?t1n9 fiberglass fabrics with lubricant;
to prolong their service life. This development gave cement
manufacturers the best available filtration efficiency of the
m.I^nlo a11?wed *hej. *» use a P^ce of equipment that could
?a?e Prin? tem+ly* hl?h effici"ency regardless of production
rate. Prior to this time, plants recovered a substantial amount
of material from the air stream before it ever got to the final
discharge. The installation of higher efficiency filtration
equipment,Required today by EPA, Required in some cases by
local law in earlier days, gave cement manufacturers two ad-
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ditional benefits. The first, a better rapport with local
neighbors, the second being a cleaner plant environment. In
early days, it was not uncommon to see roofs of the plant
facilities with 6 to 8" of dust all over them, causing in
some cases structural damage, in others replacement of roofs
at more frequently than normal intervals.
Today, we break up application of dust collection equipment
into two distinct categories. The first is application of the
equipment to parts of the process that are largely housekeeping
in nature. Examples would be ventilation of material handling
equipment, crushing, storage and withdrawal facilities of both
raw and finished materials, etc. The second category is ap-
plication of equipment to the process train and process gas
itself. Examples here are drying, milling, burning (kiln),
material cooling (clinker coolers), and others.
There are eight (8) basic processes in cement plants which
require dust collection equipment:
1) material handling
2) storage and silos
3) crushing
4 ) d ry i n g
5) milling
6) burning (kiln)
alkali bypass
cooler (clinker)
7)
8)
In some cases, the air streams from several of these can be
combined to form one combination gas stream handled by a
single piece of equipment. We will discuss each of these
separate areas to point out the potential problems for design
and operation of the dust collection equipment.
Duct System Design
An important part of dust ventilation systems is the desiqn
of the ducts .
The design of the duct system used for collecting the vent
air streams and fugitive dust from the material handling equip-
ment or any of the other equipment to be discussed in this paper
can follow either of two general methods of design; each would
be used for different purposes.
The first would be a self-cleaning duct system. This duct
system would be designed with a maximum velocity of about 2000
feet per minute. Because of these low velocities, material may
OnnIen?ULon *5? Plpjs..hence all pipe runs must have a minimum
slope of 450 with no horizontal runs whatsoever. This desiqn
approach should be considered when handling extremely abrasive
material in order to reduce wear on pipe-lines. It should also
be considered where there is large inherent variation in the
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volume within the system, whereby material handling velocities
cannot be guaranteed for a conventional high velocity vent
5 Jr S L ClT) .
syltem 1s expensive to install. This system
to short horizontal distances where the dust col-
*?*1 as. close as Possible to the sources being
^ !J ' "9 s^stems also- present support problems,
n noK^ atJtSe fpex of runs where the ductwork must go
to a 90° bend and back down to filtration equipment.
The advantage of the self-cleaning system is that it provides
the lowest operating static pressure and thus the lowest fan
energy requirement; a consideration that must be kept in mind
today .
The other general method of designing a vent system would be
to use conventional high velocity ventilation techniques The
Jnnn92 Veloc1t1es for this system would be between 3500 and
4000 feet per minute. These velocities must be maintained to
prevent any settling of dust in any long horizontal runs. This
system can be used on any materials, but abrasive materials,
such as clinker dust or sand will present wear problems; and
!5e + £ i?ystem must thel"efore be designed to allow for wear
at the elbows and any intersections or transition points.
inewhirh%h°me Jases.,tn these various material venting systems
in which the material may be hot and moist, and the collected
air and dust could present a caking problem. Insulation of
the ductwork and dust collector or the admission of supple-
mentary warm air might be required.
I. Material Handling
Since a cement plant is required to move large quantities
of- dry materials as either raw feed or finished product,
many belt conveyors and bucket elevators are used. At each
of the transfer points onto or off the belt or from the
thaJem,',«?°!!e <|ry dust emission ts Priced. The air volume
that must be handled is definitely related to the height of
the material fall. The further the material falls, the
bigger the ventilation problem. Also at transfer points,
there is a tendency for the stream of material to drag air
in at the upper end of the transfer. The air migrates to
the lower transfer housing, backing up at the discharge of
the lower transfer housing, and causing dusting primarily
vMnmlSch01?K F°r thts reason> the primary ventilation
volume should be removed from the lower portion of any
transfer housing.
If too high an air velocity of the vent air is used, ex-
^fh1!Ie^USt 1S transP°rted f^orn the point of transfer
rather than removing only the amount of dust and air that
is generated. Generally, the dryer and finer the material
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that is being conveyed, the more fugitive dust that is
generated at the transfer points. Belt conveyors require^
less energy than pneumatic conveying, but have the potential
of greater fugitive dust production.
Either small shaker collectors or high ratio pulse type
collectors are used for these collection points.
11. Storage and Silos
Silos are filled by bucket elevators, belts, or pneumatic
conveying. At the discharge points of bucket elevators,
the material is flung from the buckets. The volume of air
to be removed is dependent upon the cross sectional area
of the housing and its height.
The volume of air to be ventilated from a silo depends upon
any one or combination of:
1. Width and speed of belt conveyor
2. Size of bucket elevator
3. Air volume capacity of pneumatic conveying system
(A surge factor should be included when sizing the
fan and filter).
The first two systems generally require the lowest volume
of air and the least amount of dust to be collected. A
pneumatic conveying system requires the largest volume of
air and generates more dust to be collected.
Silo venting also applies to the homogenizing (blending)
silos for raw feed in dry process plants. The air volume
is determined by the air supply required for blending.
Either intermittent or continuous collectors of the shaker
or pulse type can be used.
Ill. Crushing
The crushers used in a cement plant are generally selected
on the basis of the type of stone being used to supply raw
material for the product, as well as, the size required for
further processing after the crusher. Commonly, hammermills
or impactors are applied to limestone today, and in many
existing plants, the combination of jaw crushers, gyratory
crushers, and cone crushers have been used. The fugitive
dust problem in crushing operations increases as the amount
of energy increases in the crushing operation. The hammer-
mill creates the most serious dusting problem as it is
really analogous to a large fan, thereby creating motion of
an air stream by itself. The hammermill has extremely high
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tip velocities, thus imparting considerable kinetic
energy to the stone being crushed which has to be
"killed" below the crusher and hopefully before the
stone reaches the material handling system below. This
is not true with the other methods of crushing where air
flow is induced primarily due to the flow of stone by
gravity thru the other crusher designs.
In all cases in the crushing operation, it is preferable
to do all of the venting down below the crushers, either
in chutes or in the material handling system below the
chutes. The design of the plant can help to reduce a
fugitive dusting problem if rock boxes are included under-
neath the crushers to kill the motion of the moving materia'
before it reaches the material handling system. A rock box
is a trap, usually formed of concrete that extends the full
width and length of the crusher discharge opening. In the
bottom of this rock box there is a smaller opening, al-
lowing the passage of material to the subsequent operations
downstream. The crushed stone is allowed to fill up and
seek its natural angle of repose and thus any additional
stone falling from the crusher must impact on the en-
trapped stone before it can reach the opening in the rock
box passing the material on to the conveying system.
It should be noted that when a crusher is operating with
a choke of material ahead of it, there is usually no dust-
ing on the top side of the crusher; however, when the choke
is no longer ahead of the hammermill, some minor dusting
can occur at the feed opening to a hammermill.
Most crushers are fed with either front end loaders or dump
trucks. At the time that the crusher is fed with a load
of material, dusting occurs at the initial dump of the
quarried material into the feed hopper for the crusher.
Ventilation of a condition like this has not been usually
attempted as vast quantities of air are required to adequate
prevent fugitive dust from getting into the ambient air awa^
from the crusher. Conventionally., feed points of crushers
should be enclosed and usually have been enclosed with a
small building, open on one side to accept front end loaders
and dump trucks.
Primary crushers usually reduce the quarry-size rock to less
than four inch size, normally, about one inch.
Secondary crushers, generally of the hammermill type, re-
duce the rock to 1/4" x 0. As long as the feed and pro-
duct are dry, there is no particular problem with dust col-
lection on this installation.
Since these facilities usually require large air volumes,
high ratio pulse type collectors are the best selection.
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IV. Drying
Drying of raw feed can be accomplished in a separately
fired rotary dryer, a rotary dryer utilizing some waste
kiln gases, or in a combination dryer-crusher operation.
The main concern for handling the off-gases from a dryer
or crusher/dryer operation is insulation to prevent any
dewpoint occurrence in the collector system. If the off-
gases are at least 100° above the projected water dew-
point of the system, with proper insulation there should
be no particular problem.
Depending upon the gas temperature, the collector could
be either a glass bag reverse air cleaned unit, or a
synthetic bag pulse type collector. Care should be taken
in the choice of fabric on drying operations. Potential
hydrolysis or chemical attack of fabric may occur.
V, Milling
In a cement plant, ball mills are used to grind finished
cement to the size distribution required for the specific
type of cement being produced. The ball mill and the
separator are the two main items of process equipment in
any milling circuit whether it be a finished cement circuit
or a raw feed circuit in a dry process cement plant.
Classification of the mill product is done in an air sepa-
rator where the fines are separated from the coarse ma-
terial using principles of Stokes's Law. The fines are
discharged to the outer cone of the separator and sepa-
rated by centrifugal action, and the coarse product is
returned to the milling circuit from the inner cone of the
separator.
In a finished cement circuit, there is a difference in
the fineness of grinding for different types of cement,
and therefore there is a difference in the size distribution
as well as the amount of material. Masonry cement and Type
III cement are ground to the finest size distribution. It
is often necessary to cool the cement before it is trans-
ported to storage silos. This cooling can be done in the
ball mill by introducing water along with a grinding aid;
it may be done by introducing substantial quantities of
cooling air into the air separator, or independent cement
coolers may be used downstream of the air separator. Cement
coolers usually operate under the principle of cooling the
cement with water either by an indirect heat transfer coil
within the cooler or by allowing a continuous flow of water
on the outer shell of a tank containing aerated finished
cement.
On the raw feed circuit of a dry cement plant, drying of
the raw materials may occur in the mill, or by introducing
preheated air into the air separator to flash dry the material
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Dust collection in a milling circuit for raw feed or cement
can normally be classified as application of process type
dust collectors. Generally, two dust collectors are used,
one to vent the mill along with all the other ancillary
ventilation points that occur at both the feed end and the
discharge of the mill and material handling equipment down-
stream of the mill. In cases where either drying or cool-
ing occurs in the separator, an independent dust collector
is applied on this portion of the mill circuit. There are
two reasons to apply a separate dust collector here, one
being to take advantage of a fan energy saving as drying
and cooling circuits and separators generally operate at
low static pressures; two, if this circuit was applied to
one general ventilation system for the entire mill room,
there can be interaction between the mill and the separator
air volumes that can potentially cause control problems of
the milling process itself.
The air streams coming from the ball mills and from the
separators contain great quantities of material; with the
exception of a roller mill circuit, these two areas are
the highest grain load encountered in a cement plant. Since
most of the material is very fine, the dust collector catch
represents a substantial quantity of the finished product
in the circuit.
Ther-e are several things to be very careful of in applicatioi
of dust collectors in this area. The extreme amount of
material caught from the air stream requires careful choice
of the material handling system within the collection equip-
ment. Introduction of moisture into the mill, must be made
known, as this could affect the choice of the filtering equi|
ment as well as its size. If drying is to occur either in a
mill or in a separator, this must be made apparent as this
also could affect the choice of fabric applied as well as th<
size of the equipment installed.
Both shaker and pulse type collectors have been successfully
applied in this system.
VI- Burning - Kilns
For venting the burning or calcining equipment, kiln, dif-
ferent problems are involved in the three types of processes
wet process, dry process, and preheater process.
Wet Process - In the wet process kiln, since the feed materic
is a slurry or wet cake, the off-gases will contain as much
as 35% by volume moisture producing a high dewpoint temper-
ature, in the order of 165°F but with dry bulb temperatures
of about SOO°F. The prime problem in venting this gas strean
is the necessary insulation required for the system to pre-
vent condensation which produces extreme corrosion on the
housing and potential blinding of the dust cake on the filter
bags.
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Glass bag reverse air units with adequate insulation have
been successfully used for this type of process.
Long Dry Kiln - The off-gases from a long dry kiln are
usually at a temperature of 750 to 1000°F and require
cooling prior to entering the baghouse. Depending on the
alkali content of the waste kiln gases, a cyclone may be
incorporated at the kiln discharge to collect the coarser
fraction for refiring into the kiln with the raw feed or
by the insufflation technique. If the dust is high in
alkali content, then the fines, which contain the larger
percentage of alkali can be wasted. If the alkali content
is low, then the total waste dust stream can be collected
in the fabric filter and returned to the kiln for firing.
Some cooling in the case of the cyclone equipment is
obtained, but, generally, the cooling is accomplished by
water sprays in the discharge end of the kiln.
Water Spray Towers or Air-to-Air Heat Exchangers can be
utilized for cooling of the kiln gases, however, this is
not usually done.
Since the moisture level content of these gases is not of
great concern, generally, uninsulated pressure type bag-
houses are used, however, fully insulated suction type
houses are also employed. Both types use glass bags and
reverse air cleaning.
Preheater Kiln - Since the waste gases from the preheater
kiln are used for warming the incoming raw feed, the off-
gas temperatures are lower than for the long dry kiln and
temperature control is usually accomplished by a bleed-
air damper. The exit gas temperatures are normally 650°F,
when the preheater is operated at rated capacity. Temper-
ing with air brings the gas stream down to 500-550°F allow-
ing application of glass fabric filters.
One variation which can be used with preheater kilns is
an air-swept in-line roller mill used for grinding the
rock, from the secondary crusher size, plus clay, iron
ore or other additives, to the size necessary for raw
feed. The ground material goes directly to the homogeniz-
ing silos.
Generally, the in-line roller mill is used as a raw mill
and drying operation, since sufficient heat is available
in the kiln gases. The dust collection problem associated
with this operation is to insure adequate insulation to
prevent possible water dewpoint conditions in the fabric
collector. Of course, another design consideration must
be for handling the hot gases when the roller mill must be
bypassed for periods of maintenance or emergency outages.
This is generally accomplished with a multi-fan installation
so that normally one fan provides the pressure drop re-
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quirements of the mill while it is in operation and a
separate fan provides drop for the collector alone.
The off-gas from the mill circuit quite often goes thru
a set of cyclones to collect the majority of the milled
material, however, this does not always have to be the
case and the baghouse can handle the total dust load.
All of the dust collected is then supplied as raw feed
to the preheater. If the raw feed contains sufficient
alkali content that some of the dust must be wasted,
this is usually handled in the alkali bypass system.
Fabric collectors for kilns have all been glass bag re-
verse air cleaned units, of either pressure or suction
design. Proper fabric selection depends on the type of
kiln and type of feed material being calcined.
VII. Alkali Bypass. Preheater Kilns
In order to control the alkali content of the finished
clinker, when the alkali content of the raw feed is too
high, a small proportion of the kiln gases are vented at
the kiln exit prior to the preheater and are cooled and
collected in a separate fabric filter. Since the gas
stream leaving the kiln prior to the preheater is in the
1800°F temperature range, the gases must be quickly quenched
by either, or a combination of, air-quenching and water
spray cooling to reduce the gas temperature to 500 to 550°F
for collection in the fabric filter.
Reverse air cleaned glass bag units are used for this
system.
VIII. Clinker Cooler
The clinker cooler's main purpose, of course, is to cool
the clinker quickly enough by air-quenching to set the
chemical properties of the clinker. Another important
function of the clinker cooler is to recover sufficient
heat in the air stream to assist the combustion and burning
of the cement rock. Additional heat is also utilized for
the pulverized coal circuit or additional drying operations
which might be utilized at the plant.
There is always excess waste hot air from the clinker which
must be vented. The main problem in handling this waste
hot air stream to a fabric filter is the temperature control
required during the flushes which occur from the kiln. The
temperature can vary from less than 300°F to 800 or 1000°F.
Cooling of this waste stream can be accomplished in either
of two ways:
1. Water sprays in the cooler onto the clinker bed
plus the addition of large quantities of dilution
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air to the vent stream to reduce the temperature
of the gases sufficient to be handled by the fabric
filter.
2. Air-to-air heat excahngers in which the hot gases
are cooled to the control temperature by passing
them thru a tubular heat exchanger cooled from the
outside by a secondary stream of ambient air moved
by separate low pressure fans. This technique can
produce large volumes of relatively warm air which
might be useful for warming buildings during the
wintertime.
No particular problem is involved in the fabric filters
for the clinker coolers as long as the temperature control
and the surge volumes are adequately provided for. Both Q
Nomex bags, 425° maximum temperature, and glass bags, 550 F
limit, have been successfully utilized. High ratio pulse
type collectors use Nomex felt bags at the 425°F limit,
while glass bags are used in reverse air cleaned collectors.
CONCLUSION
As a reference to define the amount of material to be handled,
cement plants producing 1000 ton per day of finished product
^require a supply of about 1JTDO ton per day of raw feed materials.
Plants are operating at 3000 TPD production and others being
built with capacities up to 7000 TPD. These, usually dry materials
must be handled and conveyed many times through the different
processes. Today plants operate at 99.9998% material efficiency.
This means more saleable product from the raw materials.
Federal E.P.A. emission regulations of 0.3 Ib/ton from kilns and
0.1 Ib/ton from clinker coolers are easily met with fabric filters
when design consideration of the process conditions and proper
selection of filter media are made. Test data shows kiln emissions
to be 0.013 to 0.035 grains/SCFD (.1 to .25 Ib/ton) and cooler
emissions to be 0.0012 to 0.015 grains/SCFD (.011 to .061 Ib/ton)
for a variety of plants.
All of the miscellaneous sources are regulated by opacity, but
with proper fabric no visible emissions occur.
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188
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NEW APPLICATIONS FOR FABRIC FILTERS
R. L. Adams
Wheelabrator-Frye Inc.
Pittsburgh, Pa.
December 1977
189
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NEW APPLICATIONS FOR FABRIC FILTERS
Requirements for improved filtration efficiencies have led to the
use of fabric filtration in many areas that a few years ago were considered
the domain of high-efficiency cyclones and low-energy wet scrubbers. This
paper will review a few of these new applications for fabric filters. It is
recognized that almost any so-called "new" applications will have been tried
somewhere at some time in the past. However, we believe that the applications
discussed herein represent major future potential for fabric filtration and
that developments over the past year or so in these areas have been significant.
It should be noted that three of the five applications to be dis-
cussed employ coated fabric filters. It is this area that provides great
potential for expanding the use of the fabric filtration in the future. The
applications which are discussed in this paper represent only a few of the many
potential uses for coated fabric filters. Expanding research and development
activity in this field will uncover many more in the near future.
We have chosen for discussion five new applications. These are:
1) coke oven emission sources, 2) coke oven combusion stacks, 3) sinter machine
windboxes, 4) galvanizing lines and 5) S02 removal. We would like to give a
brief review of the current state of the art in each of these areas. In some
cases, the work has been done on only a pilot scale in other cases full-scale
production units are in operation.
Coke Oven Emission Controls
A unique application of a fabric filter for coke oven emission control
has recently been disclosed by the Taisei Corporation, Tokyo, Japan. This pro-
cess is covered by United States Patent 4,010,013. The process utilizes a
coated fabric filter called the PRECO Filter to remove particulate and tars
from charging, pushing and other coking side operations. It has not been ap-
plied to coke oven combustion stacks and these will be discussed in another
section of this paper.
Figure 1 shows a typical flow sheet for the process. Coal or coke is
passed through a pulverizer and injected onto the filter bags. Coke oven gas
ventilation sources are then ducted to the filter. The fabric filter utilized
190
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FLOW SHEET
Coal (Coke Dust)
Introduction
Fan
CD
73
Hopper
Baghouse
Filter
Precoat Layer
Adjustment of
Particle Size
Larry Car Hood
Door Leak Hood
Coke Guide
Car Hood
Other Hoods
Coal Yard
Coke Oven
-------
in this application is a standard filter equipped with polyester filter fabric
and bag cleaning is accomplished by mechanical shaking. The protective coating
of coal or coke dust effectively prevents the adhesion of the tar to the fabric.
It also serves as a filter aid in that it contributes considerably to the fil-
tration efficiency of the unit.
Operation of the unit is somewhat different than operation of a stan-
dard fabric filter. Figure 2 shows a typical filter pressure loss curve for
this operation. It can be seen that after an extended period of operation,
breakthrough on the filter aid material is anticipated and substantial increases
in pressure drop may be encountered. The operating goal, therefore, is to begin
cleaning of the filter prior to this time to keep operation on the flat part of
the curve. This has been successfully accomplished in a full-scale factility
operating at Tokyo Gas Company.
Figure 3 shows the extremely high removal efficiencies that have been
obtained in both pilot and full-scale operation. At the filtration temperatures
employed, the tars exist in a condensed state as liquid aerosols and can be effec-
tively removed by the coal or coke precoat layer. The collected material from
the process is returned to the coal yard, mixed with coal, and sent to the coke
oven for reuse.
FIGURE 3
COKE OVEN EXHAUST
TAR REMOVAL EFFICIENCY
P re coating
Material
Coke
Pulverized
Coal
Pulverized
Coal
Temper-
ature
°F
104
104
248
Tar Concentration
Grains/Cu. Ft.
Inlet Outlet
0.083
0.015
0.049
0.169
0.264
0.084
0.223
— : _j
0.00006
0.00001
0.0001
0.0005
0.00009
0.00003
0.000009
Removal
Efficiency
%
99.93
99.93
99.79
99.70
99.97
99.99
99.99
192
-------
12
o
_l
d)
3
% 8-
0>
a_
$-
r-~
u_
4 -
Inches
2^
4
Introduction of Start of
Tar-Containing Increase
Dust Gas Pressure
/*"
r
Fi
01234
Hours
i
i
|
i
i
i
i
!
i
Sudden /
in
Loss
Iter
5
/Gas intro-
/ duction
j s^
Cleaning
6 7
TYPICAL FILTER PRESSURE LOSS CURVE
FIGURE 2
193
-------
We believe that the Taisei PRECO Filter represents a very new and novel
application for fabric filters. The fact that the coating material is the raw
material for the ovens and that the collected material may be returned to the
ovens is significant. We would expect to see application of this type of filter
in the United States in the future.
Coke Oven Combustion Stacks
In many of the older coke ovens, leaks exist between the coking side
and the combustion side of the oven due to deterioration of the bricks. There-
fore, contaminants such as hydrocarbons and tars leak into the combusion side
of the oven where they are partially burned to produce a finely divided form of
carbon black along with condensibles. This leakage is generally intermittent
in nature but as the air pollution codes become more stringent, control of this
source is now being required in some areas.
Early this year, a pilot fabric filter was operated at a major steel
mill. During operation of the pilot unit, the oven was fired with both coke
oven gas and blast furnace gas. During firing of coke oven gas, the filter was
operated both with a precoat of limestone and without a precoat. Performance
with regard to filtration of solid particulate is given in Figure 4. It should
be noted that the average outlet concentration on solid particulate when using
the coated baghouse was 55% less than when using a noncoated baghouse.
FIGURE 4
COKE OVEN PILOT UNIT
Solid Particulate
gr./DSCF
Inlet
(max.)
(min.)
(avg.)
Outlet
(max.)
(min.)
(avg.)
Blast Furnace
Gas (noncoated)
0.1173
0.0101
0.0585
0.0048
0.0007
0.0023
Coke Oven
Gas (precoated)
0.0958
0.0219
0.0657
0.006
0.0014
0.0035
Coke Oven
Gas (noncoated)
0.0841
0.0077
0.0312
0.0096
0.0096
0.0056
194
-------
Performance of the unit with regard to condensibles and sulphuric acid
Is given in Figure 5.
FIGURE 5
COKE OVEN PILOT UNIT
Condensibles
qr./SDCF
Ether Fraction
Inlet
(max. )
( mi n . )
(avg.)
Outlet
(max.)
(min.)
(avg.)
Water Fraction
Inlet
(max. )
( mi n . )
(avg.)
Outlet
(max.)
(min. )
(avg.)
Inlet
(max. )
(mi n . )
(avg.)
Outlet
(max. )
(min.)
(avg.)
Blast Furnace
Gas (noncoatedl
0.0041
0.0014
0.0024
0.0017
0.0003
0.0011
0.1791
0.0225
0.0868
0.0762
0.0077
0.0289
0.1323
0.0166
0.0669
0.0528
0.0047
0.0185
Coke Oven
Gas (precoated)
0.0035
0.0005
0.0015
0.0027
0.0003
0.0013
0.0973
0.0574
0.0685
0.0973
0.0312
0.0422
0.0486
0.0363
0.0432
0.0392
0.0232
0.0282
Coke Oven
Gas (noncoated)
0.0081
0.0000
0.0028
0.0046
0.0000
0.0018
0.2366
0.0503
0.1322
0.1356
0.0122
0.0724
0.1636
0.0244
0.0978
0.0728
0.0260
0.0529
195
-------
An examination of the data shows that the average ether fraction condensibles
were 27% lower when using the coated fabric filter and that the outlet concen-
tration of the water fraction condensibles was 42% less when using the coated
fabric filter. In both cases, either with the use or without the use of the
precoat, stack opacity was less than 5%. The portion of the water fraction of
the condensibles due to sulphuric acid is also given in Figure 5. Since this
fraction would not occur in those ovens firing sulphur-free gases, the sulphuric
acid fraction may be deducted from the water fraction condensibles to give a
true picture of the effectiveness of the fabric filter.
Due to the extremely light grain loading, high air-to-cloth ratios
were utilized. Air-to-cloth ratios ranged from 3.0 to 3.5 to 1 when utilizing
a coated fabric filter and 2.5 to 3.0 to 1 when using the noncoated fabric
filter. The pressure drop using a coated fabric filter was approximately 25%
lower when using the noncoated fabric filter at the same air-to-cloth ratio.
In either case, bag cleaning was carried out only once every 24 hours.
The first commercial unit using a fabric filter in this application
is now being built. We believe that this too represents a major extension of
fabric filters into an area previously considered to be outside of the boundries
of good fabric filter application.
Galvanizing Line Control
There have been infrequent attempts over the years to apply fabric
filters to fume generated from galvanizing lines. Some of these have met with
limited success and, therefore, strictly speaking this is not a new application.
However, to our knowledge, a pulse-jet filter has not been used for this service
in the United States. We would like to review the successful application of
this type filter to a galvanizing line. The unit has been in operation since
June 1977. It was installed after operation of a pilot unit for ten weeks.
Figure 6 gives both the design and the actual measured operating con-
ditions of the unit. It should be noted that while the actual operating air-to-
cloth ratio is approximately 20% greater than design, pressure drop is in the
design range. The design features of this unit are shown in Figure 7. Since
start-up, operation of the unit has been generally satisfactory. However, it
is essential that the unit be kept completely dry. The collected material is
196
-------
FIGURE 6
GALVANIZING LINE
FABRIC FILTER OPERATING CONDITIONS
Design Actual
Gas Volume (ACFM)
Gas Temperature (°F)
Total Cloth Area (sq.
Air-to-cloth Ratio
Pressure Loss (in. w.
Inlet Grain Load (gr.
ft.)
g.)
/ACF)
14,000
250 (max.)
5,040
2.78 to 1
6"
4
16,964
187
5,040
3.37 to 1
6"
2.5
FIGURE 7
GALVANIZING LINE
FABIRC FILTER DESIGN FEATURES
Standard Pulse Jet
Two Modules
16 oz. Dacron Si 1 iconized Finish
Stainless Steel Cages
On-line Pulsing
Completely Insulated
Material Collected —
Zinc Chloride
Aluminum Chloride
Ammonium Chloride
Elemental Zinc
hygroscopic and readily absorbes moisture from the atmosphere. While the material
is light and fluffy in the dry state, the particles tend to agglomerate as they
take on moisture and become very sticky.
Almost all of the operating problems encountered with this unit have
been due to the nature of the collected material. Upon first start-up of the
equipment, insulation of the system was not adequate and the collected material
197
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tended to get wet. Once the defects in the insulation system were corrected,
there have been no more problems in this area. The other areas where difficulties
have been encountered are in the ductwork leading to the collector where the
material tends to fall our or to stick on elbows and other impact surfaces. There
has also been some difficulty in removing the material from the hopper. As long
as the rotary valves are operated continuously, the material flows freely. If,
however, the rotary valves are shut down for any extended period, and plant oper-
ations seem to accomplish this in spite of all instructions to the contrary, the
material tends to build up and bridge in the hoppers. Even though the vanes of
the rotary valves are teflon coated, the material also tends to stick to the vanes
if hopper storage is attempted.
This unit shows that a pulse-jet filter operating at a relatively low
air-to-cloth ratio represents an excellent means for controlling galvanizing
line fume. We would recommend, however, that each galvanizing line be studied as
there are individual differences which may dictate the type of equipment to be
employed. It is necessary to use proper operating precautions with this type of
equipment to preclude moisture in the system and subsequent problems.
Sinter Machine Windbox Ventilation
Fabric filters have been used for many years to ventilate the discharge
end of sinter machines in the steel industry. In addition, we are aware of at
least one installation utilizing a woven fabric filter to ventilate the sinter
machine windbox. However, within the past year, a pulse-jet type filter for
windbox ventilation has been installed and we would like to review briefly the
design and operation of this unit.
The design data is given in Figure 8. These design parameters were
set after extensive pilot testing of a pulse-jet collector. Operation over the
first year has generally been satisfactory but some of the parameters that have
adversely affected operation should be reviewed.
198
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FIGURE 8
SINTER MACHINE WINDBOX
FABRIC FILTER
Gas Volume - 200,000 ACFM
Gas Temperature - 260°F
Inlet Load - 0.5 gr./ACF Solid Particulate
- 0.02 gr./ACF Condensible Hydrocarbons
Filter - 14-module Pulse Jet
Cloth Area - 35,630 sq. ft.
Air-to-cloth - 5.6 to 1
Fabric - 16 oz. Dacron Felt ICR Finish
Pressure Drop - 4.5" to 6" w.g.
Extensive operating experience indicates that the most important
parameter affecting operation of the baghouse is the amount of oil being intro-
duced onto the sinter strands. As you know, this oil is not completely burned
and carries over into the filtration system in the form of oil vapor and, as it
is cooled, in the form condensed liquid aerosols. As long as there is sufficient
dry filter cake on the bags, the effect of the condensed oils is minimal. However,
since the grain loading can be light at times from the operation of the sinter
machine, the dust cake on the bags will be light and in that case a large quantity
of condensed oils can cause increased pressure drop in the fabric filter.
While this unit has not been tested, the discharge stack has remained
optically clear. It is expected that performance tests will be performed in
January. However, there would appear to be little or no problem with condensibles
passing through the baghouse and later condensing at the discharge of the stack.
In spite of the successful operation of this baghouse, we would strongly
recommend that most sinter line windboxes be piloted for an extended period of
time to encounter all expected operating conditions of the sinter machine prior
to installation of the baghouse. In addition to the problem of condensibles noted
above, we have also seen a oilot installation where solids such as zinc amnonium
sulphate pass through the baghouse as a vapor at filtration temperatures and later
desublime into a solid at the discharge stack. Presence of these materials is
almost impossible to predict from observing sinter machine operation and charging
199
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practices; therefore, a pilot unit is recommended to determine the adequacy of
a fabric filter for this application.
SOo Removal
Another novel application for a fabric filter is its use to remove
gaseous contaminents. Proper selection of an additive material allows for
chemical reaction with certain gaseous contaminents as the gases pass, at low
velocity, through the filter cake. One example of this technology is the use
of a fabric filter with the additive Nahcolite, a naturally occuring sodium
bicarbonate, for removal of sulphur dioxide from boiler flue gas.
Figure 9 shows a typical design of this type of system. The flue gases
from the boiler containing both particulate and sulphur dioxide are conveyed to
the fabric filter in a conventional manner. A solids additive system is utilized
to air convey the reactant material into the filter and to utilize this material
to form part of the filter cake and act as a reactant. It is also possible to
feed the reactant into the flue gas stream from the boiler prior to its entry
into the fabric filter.
This "dry scrubbing" system is capable of removing up to 90% of the
S02 contained in the inlet gas stream. Figure 10 shows S02 removal as a function
of the stoichiometric ratio of Nahcolite fed into the fabric filter. The curve
shown is under optimum feeding conditions. It should be noted that at a one-to-
one stoichiometric ratio approximately 73% of the S02 in the inlet gas stream
can be removed. In addition, of course, the fabric filter will remove solid
particulates with efficiencies in excess of 99%. Particulate removal efficiency
in the pilot unit of 99.7% was not considered typical since the pilot unit was
operated in a manner which required that the bags be completely cleaned at the
end of each test cycle in order to check material balances. As a result of
this operating procedure, the filter cake was essentially destroyed each time
the bags were cleaned and this resulted in some inefficiency at the start of
each cycle with regard to particulate removal. This would not occur in an
operating unit since filter cake would be retained during each cleaning cycle.
It may be of interest to examine some estimated costs for the fabric
filter-Nahcolite system. These costs are given in Figure 11. The basis of the
costs is a 500 megawatt unti handling 1.5% sulphur coal with S09 reduction
200
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Cleaned
Flue Gas
From Boiler
Nahcolite
Car Unloading
TI
Nahcolite
Storage
Fabric
F
ilte
r
Flue Gas
IGrinding
[Mill
Air
Main
I.D. Fans
_^ To Waste
Disposal
Injection
Fan
Stack
FABRIC FILTER - NAHCOLITE SYSTEM
-------
S3
o
S3
CD
100
90
80
70
60
50
40
30
20
Limit of Removal for
Full Utilization of
HC03 in Nahcolite
Least Squares Curve
Fit of these runs
SO? REMOVAL AS A FUNCTION
OF STOICHIOMETRIC RATIO
UNDER OPTIMUM CONDITIONS
10
0.2 0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
-------
consistent with present EPA requirements limiting SOp emissions to 1.2 Ibs.
per million Btu's. It can be seen that this system is estimated to be highly
competitive with present day S02-particulate removal systems. It should be
noted that a source of Nahcolite material is not yet available and the future
of this process hinges upon commitments to begin mining operations by those
who hold Nahcolite reserves.
FIGURE 11
FABRIC FILTER-NAHCOLITE SYSTEM
COSTS
Estimated Capital Costs
Annual Operating Costs
Capital Charges @ 14.9%
Raw Material
Disposal
Labor, Maintenance, Utilities & Misc.
$23,100,000
$46.20/kw
$ 3,442,000
3,003,000
1,010,000
1,963,000
$ 9,418,000/year
2.69 mils/kwh
Conclusion
Examination of the above five applications shows in a general way the
directions of expansion for fabric filter technology. These five applications
certainly do not represent the only new applications for fabric filters but were
chosen because we believe that they do show the current general directions of
technology expansion. With the increasing efficiency requirements and with re-
quirements for fine particulate control, which we believe are forthcoming, we
feel that the scope of application of fabric filters will be continually broadened
in the future.
203
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204
-------
Effect of Modified Cleaning Pulses
on Pulse Jet Filter Performance
by
David Leith, Melvin W. First and Dwight D. Gibson
Harvard University
School of Public Health
Department of Environmental Health Sciences
665 Huntington Avenue
Boston, Massachusetts 02115
Abstract
Dust seepage through a pulse-jet filter can be minimized by
gradually reducing air pressure at the end of the cleaning pulse
instead of using the usual square wave pattern. This allows the
pulsed bags to return gently to their rigid supporting cages and
avoids driving dust trapped in the fabric into the cleaned gas
stream. Pulse modification by this method is especially effec-
tive at high filtration velocity but requires 27% more com-
pressed air than normal. Pressure drop is unaffected.
Increased relative humidity was associated with higher pressure
drop but lower dust penetration. Higher humidity should cause
stronger bonds between the dust deposit and its substrate. This
may bring about a thicker dust deposit and thereby cause in-
creased pressure drop as observed. More tightly bound particles
should be less likely to seep through the fabric> thereby reduc-
ing penetration as was also found.
205
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Introduction
An attractive feature of pulse-jet filters is their ability
to operate at higher filtration velocities (air to cloth ratios)
than do filters cleaned by other means. To increase filtration
velocity further is a tempting goal as the resultant decrease
in installed cost can often more than compensate for the in-
creased operating cost caused by higher pressure drop across the
fabric. The filtration velocity associated with least annual-
ized cost increases as the number of operating hours per year
decreases, so that for a process operated one shift per day or
less, relatively high velocities (100 mm/s) at relatively high
pressure drops (^ 250 mm water) may be appropriate.1
However, as filtration velocity increases penetration in-
creases as well for both pulse-jet cleaned filters2'3 and for
ll_7
filters cleaned by other means, ' and in some cases the pene-
tration increase may become unacceptable. Although data are
few, bag life may decrease as well at high filtration veloci-
ties.8
In a conventional cleaning pulse, compressed air enters the
bag rapidly and pushes the bag outward, away from its supporting
cage. Upon approaching full inflation, the bag decelerates
rapidly to a state of metastable rest, during which residual
pulse air flows through the fabric and flushes out dust loosened
by this deceleration.
At the end of a conventional pulse, the backflow of pulse
air stops and normal filtration resumes. The bag accelerates
206
-------
back toward its supporting cage and hits it smartly causing a
rapid deceleration analogous to that observed as the bag snaps
open. This causes additional dust agglomerates and particles
to become loosened. These, together with the agglomerates and
particles that were loosened but not blown free by the cleaning
phase of the pulse, may now be flushed thrugh the bag to the
cleaned air side by the filtration gas. Dust penetration by
3
this mechanism has been called seepage.
Effective cleaning requires interaction between the clean-
ing pulse and the fabric. The bag must be flexible enough to
inflate rapidly as the pulse begins. It should not stretch
radially so that the bag may decelerate rapidly as it reaches
full inflation. However, these same qualities, flexibility and
radial distortion resistance, will also allow the bag to return
to its cage rapidly as filtration resumes and this aggravates
seepage.
Recently it was shown that almost all the dust that pene-
trates through a pulse-jet filter does so by seepage, and that
o
seepage increases with increasing filtration velocity. This
occurs for several reasons. First, higher filtration velocity
increases the fraction of dust feed by a cleaning pulse that
redeposits on the bags, and decreases the fraction of freed
q
dust that falls to the hopper. This causes a thicker dust
deposit to build up, with more dust available to seep through.
Second, higher filtration velocity drives the cleaned fabric
back to its cage faster, causing it to hit with greater impact.
207
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This drives through more dust.
Dennis and Wilder placed a 1.7 liter damping tank after
the outlet of the pulse valve in their single bag, pilot pulse-
jet filter and studied the effect of this tank on both penetra-
tion and pressure drop. They found that for filtration velo-
cities between 30 and 50 mm/s, penetration was reduced by a
factor of about five when damped pulses were used; however,
pressure drop increased about 20%. Some of the air released by
a cleaning pulse was taken up momentarily by the tank, and the
transient reverse pressure gradient across the bag was somewhat
reduced. For this reason, bag cleaning was less effective; the
greater residual dust holding was thought to account for the
higher pressure drop found. Reduced fabric stretching and
reduced transient pressure gradients across the bag were thought
to account for the reduced penetration.
Ideally, a cleaning pulse should: (1) inflate the bag
quickly so that it will decelerate rapidly when it snaps fully
open, (2) provide time after inflation for pulse air to flow
through the bag and flush loosened dust into the housing, and
(3) return the fabric to its cage support gently to prevent
seepage and excessive fabric wear. A conventional cleaning
pulse of sufficient duration produced by a conventional pulse-
jet solenoid valve should satisfy the first two objectives, but
does not satisfy the last. Dennis and Wilder's damped pulses10
should satisfy the last two objectives but not the first.
To satisfy all three objectives simultaneously, conven-
208
-------
tional cleaning pulses were modified in a way that retained
rapid air delivery to each bag at the pulse beginning but that
gently returned the bag to its cage. Modified pulses described
here began normally but at the pulse end, pressure trailed off
gradually allowing each pulsed bag to deflate gradually and
return gently to its cage.
Experiments
To test the effectiveness of modified cleaning pulses, a
three bag pilot filter fitted with polyester felt bags 2.44 m
n
tall and 114 mm in diameter was used. A schematic drawing of
the apparatus is given in Figure 1. The test dust was fly ash
with cumulative size distribution by count given in Figure 2.
Mass concentrations of fly ash upstream and downstream of the
fabric filter were found by sampling isokinetically, onto glass
fiber papers.
Cleaning pulses, either conventional or modified, were
delivered sequentially to each bag once per minute. The valve
arrangement for the pulse-air manifold is shown schematically in
Figure 3. Compressed air entered through a regulator which con-
trolled pressure at 6.8 atmospheres gauge and passed into a
reservoir from which it flowed through a normally open solenoid
valve, A, into a 1.6 L pulse air chamber. This chamber could
be fitted with an extension which doubled its volume. Chamber
pressure was measured on a Bourdon gauge and by a transducer
connected to an oscilliscope.
The volumes of compressed air used for a conventional
209
-------
PULSE VALVE, 8
.PULSE CHAMBER
CHAMBER ISOLATION VALVE, A
COMPRESSED AIR RESERVOIR
HAMPER.
MANOMETER
FOR FILTER
PRESSURE
DROP
—r- BLOWER
DUST FEEDER
MANOMETER FOR VOLUMETRIC
AIR FLOWRATE
FILTHS?
.HOPPER
FIGURE 1. Schematic drawing of fabric filter apparatus used.
210
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0.08
0.01
J_I_JL_J 1
I JL
2 SO 30 SO 70 fO
FRACTION Of PARTICLES BY COUNT SMALLER THAN
STATED DIAMETER
FIGURE 2. Cumulative size distribution by count for fly ash.
211
-------
PRESSURE
6AU3E
DH
OPTIONAL EXTENSION
ISTS GMS.
ULSE CHAMBER, 1575CM3
NORMALLY OPEN
SOLENOID VALVE, A
PRESSURE /PULSE
TRANSDUCER _/ VALVE
Bi
J
PULSE
VALVE
U9f
COMPRESSOR
PRESSURE
REGULATOR
RESERVOIR
.37,OOO CM*
FIGURE 3. Valve arrangement for pulse-air manifold.
-------
pulse, a modified pulse, and a modified pulse with chamber ex-
tension were measured by connecting the outlet from each pulse
to a spirometer. The volume of compressed air per pulse was
found to be 8.6 liters for a conventional pulse, 10.9 liters for
a modified pulse, and 20.7 liters for a modified pulse with
extended chamber volume, all measured at ambient pressure.
For conventional pulse operation the appropriate pulse
valve, EL, B^, or B-, Figure 3, received an electrical signal
to "open" for 75 milliseconds. A photograph of the relationship
between chamber pressure and time for a conventional pulse as
shown on the oscilloscope is given in Figure 4. It shows that
pulse valve B, began to open about 20 ms after receiving an
electrical impulse. Although the electrical on-time was set at
75 ms, the valve continued to pass air for about 220 ms. This
occurred because the pneumatic valve took about 150 ms to build
up enough air pressure behind its diaphram to close, although
once closure bagan it was rapid. Pressure vs. time traces for
valves B, , B?, .and B~, were virtually identical.
To generate a modified cleaning pulse, one of the pulse
valves (B , Bp, or B.J was opened and 240 ms later solenoid
valve A, Figure 3, was closed causing pressure in the chamber
to drop as air bled from it to the pulsed bag. This gradual
reduction in pulse pressure allowed the bag to move back to
its supporting cage gently. After about 560 ms, the pulse
valve closed and pressure within the chamber stabilized. Some
time later, solenoid A was reopened, refilling the chamber with
213
-------
LSE OHAMBE R PRESSURE, PSIG _
P3 * 05 09 O
3 © O © © ©
•- - • • • ..••:• ..-| • ', „•
VALVE "B"
f-OpENS
v^
TTTT
i
i fit
VALVE "B"-
JCLOSES .
^ _J
111!
*p
im
m
M
*•
M
SI |_
m
mm
m
m
m
«•
m
m
mi
a
M
m
P
m
•
w
i«
•*
^
w
IB
TTT
H»
•i
1M
BB
IB
»
IV
N»
•B
•»
BB
bSB
it i
i II I
O 2OO 4OO 6OO
TMIE SINCE VALVE ACTUATED, IfiSLLfSEOONDS
800
FIGURE 4. Photograph tracing of oscilloscope display:
for normal pulse.
pulse pressure vs. time
214
-------
compressed air for the next pulse. A photograph of the oscil-
liscope pressure-time trace for a modified pulse is given in
Figure 5-
The declining portion of the pressure-time relationship for
the modified pulse, and by inference the speed with which the
bag returns to its cage, are determined by the pulse valve flow
characteristics and the volume of the chamber. To determine the.
effect of chamber size on filter performance, its volume was
doubled by adding an extension. The pressure-time trace for
this arrangement is given in the oscilloscope photo shown in
Figure 6.
The effects of pulse modification on dust penetration and
filter resistance were determined for a range of operating con-
ditions. Before taking data the fabric filter was operated at
constant conditions until the bags reached pressure drop equili-
brium. This process took some hours; the length of time neces-
sary depended upon the degree to which experimental conditions
differed from test to test. Tests were run at filtration velo-
cities of 50, 75, 100, 125 and 150 mm/s, using both conventional
and modified pulses, and for normal and extended chamber vol-
umes, so that twenty different operating and cleaning situations
could be studied. All tests were replicated and run in random
order with approximately the same inlet dust mass flux 0.33
^
kg/m /hr, so that the amount of dust fed between pulses would be
the same regardless of filtration velocity.
Increased relative humidity has been shown to reduce both
215
-------
.00
UJ
Ul
DC
OL
Ui
09
S
z
o
Ui
0>
CHAMBER
REFILLED
80O
TIME SINCE VALVE ACTUATED, MILLISECONDS
FIGURE 5. Photograph tracing of oscilloscope display: pulse pressure vs. time
for modified pulse.
216
-------
100
B
•
•
M
m
•
B
"till
MM
K
•»
^
BV
•••
00
1 1 1 1
1 1 I 1
X.
6
1 M 1
III!
BUI
i 1 1 i
VALVE V
CLOSES^
DO
8
00
TIME SINCE VALVE ACTUATED, MILLISECONDS
FIGURE 6. Photograph tracing of oscilloscope display: pulse pressure vs. time
for modified pulse with twice normal chamber volume.
217
-------
pressure drop and penetration in a woven fabric filter cleaned
by shaking the bags. Bench scale tests on Nomex and Dacron
felts also show a decrease in pressure drop with increased humi-
12
dity. Although it was not possible to control the humidity of
the air passing through the present apparatus, relative humidity
was measured for each test. Because replicates were taken, the
data could be sorted into "higher" and "lower" relative humidi-
ties for each replicated experimental condition. The variation
in relative humidity between replicates ranged from less than 1%
to 32%.
Results
Table 1 shows the fractional mass penetration, equilibrium
pressure drop in mm water column, and per cent relative humidity
measured for each test.
Figure 7 is a plot of penetration against filtration velo-
city with pulse type as parameter. An analysis of variance per-
formed on the data after taking logarithms showed that penetra-
tion increased significantly with increased filtration velocity.
However, at all velocities tested penetration was significantly
lower with modified pulses than with conventional pulses. The
penetration reduction due to pulse modification is increasingly
effective as velocity increased. Pulse chamber volume within
the range studied had no significant effect on penetration for
either normal or modified pulses. Penetration is plotted
against filtration velocity with relative humidity as parameter
in Figure 8. The penetration increase with increasing velocity
218
-------
Table 1.
Fractional Mass Penetration/Pressure Drcjp, MM Water Gauge/$ Relative Humidity
Filtration
Velocity
cm/s
7-5
10
12.5
15
Relative
Humidity
H/L
Lower
Higher
Lower
Higher
Lower
Higher
Lower
Higher
Lower
Higher
Normal Pulses
Modified Pulses
Std. Pulse
Volume
0.011/35 mm/38$
0.006/65 mm/W
0.011/82.5 mm/ 38$
0.012/225 mm/60$
0.016/80 mm A 3$
0.027/260 mm/53$
0.029/160 mm/52$
0.005/500 T
0.178/680 wm/h9%
0.006/385 mm/70$
2 x iStd.
Volume
0.008/35 mm/38$
0.005/65 mm/5W
O.OlU/75 mm/33$
0.011/97.5 mm/50^
0.023/115 mm
0.
0.083/^00
0.003/385
0.072/^75
0.027/615 mm/60$
Std. Pulse
Volume
0.007/35 mm/33$
0.007/65 T
0.007/103
0.007/275 mm/ 56$
0.033/150 mm/29$
0.003/230 mm/67$
O.OUl/150 mm/38^
0.005A65
O.OU8/250 mm/55^
0.036/685
2 x Std.
Volume
0.000/75 mm/59$
0.001/70 mm/59^
0.009/70 r
0.007/180
0.032/160 mm/26^
0.007/300 mm/62$
O.OiiO/195
0.009/280 mm/69^'
0.035/625 mm/ 37$
0.033/695
-------
o
FRACTIONAL MASS PENETRATION
NJ
K>
O
B
l-i
BJ
rt
H-
H1
rt
O
O
13
M
0)
CD
m
13
CD
i-i
ro
i-i
-------
0.08
DC
u) 0.06
Ul
a.
0.04
£
0.02
LOWER RELATIVE
HUMIDITY
RELATIVE.
HUMIDITY
50 100
FILTRATION VELOCITY
!30
FIGURE 8. Penetration vs. filtration velocity, relative humidity
as parameter.
221
-------
is significantly more rapid at low relative humidity.
As expected, pressure drop increased rapidly with filtra-
tion velocity as is shown in Figure 9. An analysis of variance
performed on the logarithms of the pressure drop data showed
that this increase was significant. There was not a significant
pressure drop difference between normal and modified cleaning
pulses, or between normal and twice normal pulse volumes.
Relative humidity is the parameter against which pressure
drop and filtration velocity are plotted in Figure 9. For both
relative humidity conditions, pressure drop increased with velo-
city. However, contrary to observations for collection of fly
ash on woven bags cleaned by shaking, pressure drop in the
pulse- jet filter was significantly higher at higher relative
humidity .
Discussion
Pulse form modification is an effective way to reduce dust
seepage through a pulse- jet filter, especially at higher filtra-
tion velocities. At the highest filtration velocity tested,
150 mm/s, pulse modification lowered fractional penetration by
Pulse cleaning effectiveness is associated with fabric
deceleration as the bag snaps fully open, and with pulse dura-
tion sufficient to assure that loosened dust is flushed from the
fabric into the filter housing. Because the initial part of a
modified and a conventional pulse are the same, they should in-
flate and flush bags equally well. Modified pulses backflush
222
-------
800f
HIGHER RELATIVE
HUMIDITY
OV LOWER RELATIVE
^ HUMIDITY
50 100
FILTRATION VELOCITY MM/SEC.
FIGURE 9. Pressure drop vs. filtration velocity, relative humidity
as parameter.
223
-------
bags longer than normal pulses because additional backflow
occurs while pulse pressure falls during the final stage of the
modified pulse. However, if enough backflow occurs to move
loosened dust away from the fabric, additional pulse air brings
diminished returns as has been shown by Dennis and Wilder.10
For these reasons, pressure drops across bags cleaned by con-
ventional and modified pulses were about the same.
There was no difference in penetration between bags cleaned
by modified pulses from the 1.6 L pulse chamber and modified
pulses from the 3.2 L chamber. This implies that chamber size
might be decreased further to save on compressed air, while re-
taining the form and effect of modified pulses.
For a dust particle or agglomerate to be separated from the
fabric, interparticle adhesive forces must be overcome by the
deceleration force acting on dust as the bag snaps open at the
beginning of a cleaning pulse, or snaps back onto its cage at
the end of the pulse. In the former case, the dust flies into
the housing from which it can fall to the hopper; in the latter
case, the dust separated from the fabric penetrates the filter
by seepage. It has been demonstrated that increased relative
humidity leads to stronger particle-to-particle and particle-to-
12 13
fiber bonds, ' which should make separation of the dust depo-
sit from the fabric more difficult. Flay ash may have adsorbed
sulfuric acid, which absorbs water at high relative humidities,
there strengthening interparticle bonds.
Because the dust deposit is more firmly anchored to the
224
-------
fabric at higher relative humidity, seepage penetration should
decrease. The data confirm this trend. At the same time,
stronger interparticle bonds caused by increased relative humi-
dity should make the dust deposit more difficult to clean from
the fabric. A dust deposit with higher areal density would
account for the higher pressure drops at high relative humidity
found in these experiments.
Data for woven fabrics cleaned by shaking and for bench
~i O
scale new felts show that pressure drop decreases with in-
creasing relative humidity, opposite to the trend found here.
Higher interparticle forces could cause a more porous dust depo-
sit structure,12 one more resistant to compaction with continu-
ous dust addition. Theory15 confirms that for the same amount
of deposited dust, a thicker, more porous structure should have
less pressure drop than a thinner, more dense one. However, in
the pulse-jet filter cleaning is not wholly effective at remov-
ing deposited dust. The effect of increasing the amount of dust
retained on the bag at high humidity may be more important than
the effect of the more porous structure which that dust forms.
Summary
Pulse-jet filter show higher seepage penetration at higher
filtration velocities. This seepage occurs when the bags return
to and strike their rigid support cages at the end of a cleaning
pulse, as loosened dust is driven from the bags into the cleaned
gas stream. Seepage can be reduced by cleaning the bags with
pulses which are identical with conventional pulses at the be-
225
-------
ginning, but which gradually decrease in pressure at the pulse
end, allowing the bags to return gently to their cages. Modi-
fied pulses are increasingly effective at reducing dust penetra-
tion as filtration velocity increases. At the highest velocity
tested, 150 mm/s, modified pulses reduced penetration by 46$ but
had no effect on pressure drop.
Increased relative humidity caused significantly lower
penetration but increased pressure drop. Because increased
humidity causes an increase in interparticle bond strength, dust
collected at high humidity may be bound more tightly in place
and be less likely to seep through the fabric, causing reduced
penetration. However, when dust is tightly bound it becomes
more difficult to separate from the fabric. At high humidities,
an equilibrium dust deposit with higher areal density may build
up on the bags causing higher pressure drop.
Acknowledgement
This work was supported by EPA Grant R 804700-01, Dr. James
H. Turner, Project Officer.
References
1. Leith, D. and M. W. First, "Pressure Drop in a Pulse-Jet
Fabric Filter", Filtration and Separation, l4(5):473
(1977). —
2. Leith, D., S. N. Rudnick and M. W. First, High Velocity,
High Efficiency Aerosol Filtration, EPA Report EPA 600/
2-76-020, Office of Research and Development, Washington,
D.C., 1976.
3. Leith, D. and M. W. First, "Performance of a Pulse-Jet Fil-
ter at High Filtration Velocity, III. Penetration by
Fault Processes", J. Air Poll. Control Assoc . , _2_7(8) : 754
4. Spaite, P. ¥. and G. Walsh, "Effect of Fabric Structure on
Filter Performance", Am. Ind. Hyg. Assoc. J., 2^:357 (1963)
226
-------
5. Ensor, D. S., R. G. Hooper and R. W. Scheck, Determination
of the Fractional Efficiency, Opacity Characteristics
Engineering and Economic Aspects of a Fabric Filter
Operating on a Utility Boiler. EPRI Report FP-297,
Palo Alto, CA, 1976.
6. McKenna, J. D., J. C. Mycock and W. 0. Lipscomb, "Perfor-
mance and Cost Comparisons Between Fabric Filters and
Alternate Control Techniques", J. Air Poll. Control
Assoc., 2J£:ll44 (1974).
7. Turner, J. H., "Extending Fabric Filter Capabilities", J.
Air Poll. Control Assoc., 24:1132 (1974).
8. Hobson, M. J., "Review of Baghouse Systems for Boiler
Plants", in Proceedings, the User and Fabric Filtration
Equipment II, Air Pollution Control Association, 4400
Fifth Ave., Pittsburgh, PA (1975).
9. Leith, D. and M. W. First, "Performance of a Pulse-Jet Fil-
ter at High Filtration Velocity, II. Filter Cake Redepo-
sition", J. Air Poll. Control Assoc., 27.(7):636 (1977).
10. Dennis, R. and J. Wilder, Fabric Filter Cleaning Studies,
EPA Report EPA-650/2-75-009, Office of Research and
Development, Environmental Protection Agency, Washington,
D.C. (1975).
11. Durham J. F. and R. E. Harrington, "Influence of Relative
Humidity on Filtration Resistance and Efficiency", Paper
4e presented at 63rd Annual Meeting of American Institute
of Chemical Engineers, Chicago, IL, 1970.
12. Ariman, T. and D. J. Helfritch, "How Relative Humidity Cuts
Pressure Drop in Fabric Filters", Filtration and Separa-
tion, 14:127 (1977).
13. Corn, M. and F. Stein, "Re-entrainment of Particles from a
Plane Surface", Am. Ind. Hyg. Assoc. J'., 26:325 (1965).
14. Lflffler, F., "Investigating Adhesive Forces Between Solid
Particles and Fiber Surfaces", Staub (English Transla-
tion), 2^6:19 (1966) .
15. Stephan, D. G., G. W. Walsh and R. A. Herrick, "Concepts in
Fabric Air Filtration", Am. Ind. Hyg. Assoc. J., 21:1
(I960).
227
-------
228
-------
CURRENT AND FUTURE EPA FILTRATION RESEARCH
James H. Turner
Environmental Protection Agency
Industrial Environmental Research Laboratory
Research Triangle Park, N. C. 27711
3rd EPA Fabric Filter Symposium
Tucson, Arizona
December 5-6, 1977
229
-------
CURRENT AND FUTURE EPA FILTRATION RESEARCH
Introduction
The Third EPA Fabric Filter Symposium is itself largely a review of
current and future EPA filtration research:
Kenneth Ladd and Jack Smith: reasons for using a baghouse on a
large utility boiler burning low sulfur western coal.
Richard Dennis: formulation of a mathematical model of fabric
filtration for combustion sources using glass bags. This model is based
on extensive field and laboratory testing.
John Mycock: performance of a pilot baghouse on a trash-to-energy
incinerator.
Dale Harmon: use of a mobile pilot baghouse to perform field
tests and relate field and laboratory results.
John McKenna: demonstration of a high velocity fabric filter
system on two industrial boilers.
Robert Bradway: performance of a fabric filter system on a small
electric arc furnace.
Melvin First, David Leith and Steven Rudnick: high velocity filtration
in a pulse-jet baghouse and fundamentals of fabric filtration and cake
formation.
George Lamb: effects of fiber properties (rather than fabric
properties) on filtration performance.
Robert Donovan: electrostatic effects in a pulse-jet baghouse.
Dennis Drehmel and Mike Shackleton: filtration under conditions of
high temperature and high pressure.
230
-------
Purpose
These various programs all fall into just a few categories:
Assessment of full scale projects.
Field and laboratory testing and measurements.
Fundamental studies.
Most of the work is done in external programs; i.e., contracts,
grants or interagency agreements. The purpose of EPA's fabric filtration
research is to aid in the improvement of particulate control technology
by supporting appropriate projects. These projects may originate either
within or outside EPA.
Other Projects
In addition to the projects identified above, two others are being
supported by IERL-RTP. These are fabric comparisons and math modeling
being done in Poland, and work on electrostatic effects being done at
Carnegie-Mellon University.
The Polish work is being performed at the Institute of Cement
Building Materials (IPWMB) in Opole, Poland, and the Principal Investigator
is Jan Koscianowski. At the laboratory and pilot level he is directing
an effort to compare the performance of both U.S. and Polish fabrics
in Polish equipment. There are several differences between U. S. and
Polish practice: the Poles use fabrics with plied yarns and high counts;
they clean (at least in this case) with a short stroke, vertical shake.
There is also some work with reverse air cleaning. Comparisons are
being made with cotton, polyester, glass and Nomex fabrics. As well as
comparing fabrics, the Poles are endeavoring to describe the filtration
process mathematically. The final reports for the work should be available
by mid- to late 1978.
231
-------
Probably the most challenging work being done, other than convincing
the new purchaser that baghouses are the perfect answer, is in the area
of trying to understand the role and importance of electrostatics in
fabric filtration. Gaylord Penney and Edward Frederick (Carnegie-
Mellon) have been jointly exploring this area: one from the viewpoint
of determining basic electrical effects, and the other of empirically
classifying various dust/fabric systems according to electrostatic
properties and applying these observations to select the optimum fabric
to collect a specific dust. As with the earlier Frederick paper (1),
the final report from Carnegie-Mellon (due about April) is bound to be
read and re-read.
Future Work
The work at Southwestern Public Service will continue for at least
the next 2 years, and there are options for extended testing and for a
slaved pilot baghouse to test various operating modes or fabrics.
The Dennis model for fabric filtration will be tested against a
variety of operating conditions and also will be put in simplified form
for use by a greater number of people. Computer tapes of the model will
be available through the National Technical Information Service.
The mobile baghouse will be used next to compare the filterability
of eastern and western low sulfur coal flyashes from pulverized coal
boilers. A report, based on tests at Southwestern Public Service Company's
Harrington Station and at Michigan State University's boiler house will
be prepared during the summer of 1978.
The high velocity Enviro-Systems baghouse at Kerr Industries will
be operated for a second year, and other fabrics (besides the current
Teflon and GoreTex) will be tested. There is also an option for SO
removal using an injected sorbent ahead of the baghouse.
Fundamental work on high velocity filtration, mechanisms and fiber
property influence will continue under the grants held by Harvard and
232
-------
the Textile Research Institute. The in-house work at EPA will continue
on electrostatic effects, new fabric evaluation, and investigation of
fine particle penetration. Additional work will be done in the area of
high-temperature filtration and high- temperature/high- pressure filtration
both in-house and under contract.
One new contract that is expected will be for pilot scale assessment
of dry sorbent collection of SOV in a baghouse. This work will be a
A
three party endeavor involving the City of Colorado Springs, Buell/Envirotech
and EPA. Given the water problems, high resistivity coal and close
source of a good sorbent (nahcolite) in the west and southwest, the dry
sorbent/baghouse approach should be attractive. The pilot assessment
will consider disposal methods for spent sorbent/flyash as well as the
process techniques and economics. The contract for this work should be
signed in mid-1978.
Summary
EPA's programs in fabric filtration are meant to encourage development
and dissemination of technology primarily in areas mandated by the Clean
Air Act and its amendments. With a few exceptions, the individual
projects are described in detail in other papers presented at the Third
EPA Fabric Filter Symposium. Emphasis has been on control of combustion
sources.
Now that baghouses are beginning to be used on utility and industrial
boilers, perhaps the greatest need, and one voiced by many people at the
Symposium, is for reliable field measurements to be taken and distributed
to designers and potential users.
References
1. Frederick, E. R., "How Dust Filter Selection Depends on Electrostatics,"
Chemical Engineering, pp. 107-114, June 26, 1961.
233
-------
234
-------
CONTRIBUTING ROLE OF SINGLE FIBER PROPERTIES TO
NONWOVEN FABRIC PERFORMANCE
G. E. R. Lamb, P. A. Costanza, and D. O'Meara
Textile Research Institute
Princeton, New Jersey
An early study [1] established that geometric properties of
the constituent fibers in a nonwoven fabric could affect its
filtration performance. Table I shows results of a 2* factorial
experiment which examined the effect of cross-sectional shape,
surface roughness, crimp, and fiber diameter. A second phase [2]
of this work therefore examined these effects over a wider range
of variables. Figure 1 shows that the effects of surface roughness
and of cross-sectional shape on capture efficiency are evident in
the capture of particles smaller than 1 ym. Figure 2 shows that
in comparison with a filter made of round fibers, one made of
bilobal fibers is less efficient but one made of tri or pentalobal
fibers is more efficient. The poor performance of bilobal fibers
appears to be due to the strong dependence of single fiber
efficiency on fiber orientation. Figure 3 and Table II show that,
while the presence of crimp gives an advantage over a filter made
of uncrimped fibers, the crimp frequency does not affect performance,
Figures 4 and 5 show the effect on penetration and on specific
cake resistance of varying the fiber diameter for two weights of
polyester fabric, at constant fabric density. Measurements with
fibers having a range of surface roughness were not made because
such fibers are not available.
235
-------
A one-bag baghouse was made and two bags were tested, one
made of round, the other of trilobal polyester fibers. Figures 6
and 7 show that the trilobal bag gave lower pressure drop and
higher efficiency, the penetration for the trilobal bag being
approximately one half that for the round bag. This is the only
baghouse-scale confirmation of an effect of fiber geometry. It
indicates that this approach can be expected to give better
performance in commercial application. The cost of the modifi-
cation would be almost zero.
Current efforts are aimed at finding explanations for the
effects described above. To date, only the effects of cross-
sectional shape have been studied in greater detail. The effi-
ciency E of a filter is given by In(l-E) = -2ax/(l-a) irR where
unpacking density, x = filter thickness, and R = fiber radius.
Figure 7 shows that the ratio of penetration (round to trilobal)
between two 15-oz. fabrics is about 2. This would be consistent
with a difference in single fiber efficiency of about 20%, which
is roughly the increase in effective diameter due to the change
in shape. However, measurements on layered filters indicate that
the different performance is only associated with the presence of
dust deposits. Figure 8 shows calculated single fiber efficiencies
for the various layers in a 4-layer filter, and the trilobal
efficiency is higher for the trilobal only in the upstream layer,
where the dust cake is located. An interesting consequence of
this finding is shown in Table III, which compares performance
236
-------
of layered fabrics in which the upstream layer was different
from the rest of the filter. The table shows that the performance
of the filters is dominated by the thin upstream layer. These
facts prompted a study of dust cake structure, aimed at the
determination of any features of the structure built on different
substrates that would explain the lower pressure drop given in
some cases by trilobal fabrics as well as the higher efficiencies
and the patterns described above. Microscopical examination has
so far proved unsuccessful in describing any such features.
In a separate approach, single fiber efficiencies have been
calculated for capture in the presence of an electric field.
Figure 9 shows collection efficiency for fibers having different
numbers of lobes, and shows that it increases both with increasing
number of lobes and with increasing lobe height. It is possible
that the effects we have seen may originate from interactions of
charged particles with electric fields due to previous deposition
of charged particles. Experimental verification of this hypothesis
is the object of future work.
237
-------
REFERENCES
1. B. Miller, G. E. R. Lamb, and P. Costanza, "Influence of
Fiber Characteristics on Participate Filtration," EPA-650/2-72-
January 1975.
2. B. Miller, G. Lamb, P. Costanza, and J. Craig, "Nonwoven Fabri<
Filters for Particulate Removal in the Respirable Dust Range,"
EPA-600/7-77-115, October 1977.
238
-------
FIGURE CAPTIONS
Fig. 1 Capture efficiencies of three nonwoven PET
fabrics made of various fibers, as shown, when
filtering a flyash aerosol.
Fig. 2 Ratios of outlet concentrations for filters
made of fibers with 2, 3 and 5 lobes to outlet
concentrations for round fiber filter.
Fig. 3 Capture efficiencies for nonwoven rayon filters
made of fibers with various levels of crimp as shown,
when filtering a flyash aerosol.
Fig. 4 Penetration (equal to 1-efficiency) for PET
and polypropylene filters of constant weight and
density but made of fibers of different diameters.
Fig. 5 Specific cake resistance for the filters in
Figure 4.
Fig. 6 Pressure drops at beginning and end of filter
cycle (AP. and AP,.) for conditioned bags made of
round and1trilobal PET fibers.
Fig. 7 Outlet concentration ratios for bags in Figure 6,
Fig. 8 Single fiber efficiencies for each layer in
layered filters made of round and trilobal fibers.
239
-------
Fig. 9 Calculated single fiber efficiencies for fibers
with cross sections p = 1 + e Cos m (+c) where m =
number of lobes and e indicates the lobe depth.
240
-------
CAPTURE EFFICIENCY (Tenth cycle)
P P
bo c£
o
o
INJ
•*»
o
O x
-------
N)
.0
NJ
Co (Normalized
for round)
5,0
4.0
3,0
2.0
0
oh-
G Bllobal
A Trilobal
Pentalobal
©
.024 .042 .075 .133 .24 42 i.O 1.6 2.7 4.0
PARTICLE DIAMETER Cftm)
-------
O
CAPTURE EFFICIENCY (%)
oo
O
O .
r rr,
m
g
>
m
CM
'91
en
GO
c~>
3E
f)
"O
oo
n
3:
12
-o
oo
-------
th
(I-E)( 15" cycle)
,o2
10
4
0 PET
0 PP
3 oz/yd
0
20
FIBER DIAMETER
14 oz/yd
Z
30
244
-------
K( 15th cycle)
(l04N-s/kq.m)
14 -
12
10
8
4
O PET
A
3oz
1
10 20
FIBER DIAMETER (
14 oz/yd'
30
245
-------
AP
(mmH20)
Round
Round
Trilobal
15 30 45
FACE VELOCITY ( mm/s)
60
75
246
-------
ISJ
Cft(trilobol)
Co(round)
1.2 r
1.0
OB
0.6
0.4
O.2
.01
30mm/s
I5mm/s
.024 .04 .06.08.10 .2
.4 .6 .8 1.0
PARTICLE DIAMETER (ftm)
-------
SINGLE FIBER
EFFICIENCY
10
OB
0.6
0.4
.02
x TRSLOBAL
©ROUND
.04 .06 .08 JO-
DEPTH INTO FILTER (cm)
.12 ' .14
248
-------
1.8 r
0.0 0.05 0.1 0.15 0.2 0.25 0.3
249
-------
250
-------
inocHMc h'Ci'.Uitanco (K2) of Kilter Dust Cakou:
Comparison of Theory and Experiments
by
Stephen N. Rudnick* and Melvin W. First
Harvard University
School of Public Health
Department of Environmental Health Sciences
665 Huntington Avenue
Boston, Massachusetts 02115
.Abstract
The specific resistance (K2) of filter cakes formed from elutri-
ated AC-Fine test dust was measured at air to cloth ratios be-
tween 7.1 and 56 mm/s (1.4 and 11 fpm) in an apparatus in which
other operating conditions including aerosol size distribution
remained invariant. Cake porosity and particle size distribu-
tion, shape, and density, which affect the specific resistance of
dust cakes, were also measured. It was found that the Kozeny-
Carman equation, which treats a dust cake as a collection of
capillaries, seriously underestimated specific resistance. It
is believed that this discrepancy occurs because the high poro-
sity of air-deposited filter cakes makes them more closely re-
semble an assembly of individual particles than a collection of
capillary passages. A simple model based on Stokes' law indi-
cates that the Kozeny-Carman equation predicts K2 values for
air-deposited filter cakes which are less than the minimum theo-
retical specific resistance. Predictions of K2 made from the
Happel "free surface" model, which treats the dust cake as an
assemblage of particles rather than capillaries, compared favor-
ably with experimental values after accounting for nonuniform par-
ticle size, nonspherical shape, and gas slip. No empirically
fitted constants derived from the measured values of K2 were re-
quired .
*To whom inquiries should be addressed
251
-------
Nomenclature
Roman
a cloth area with dust deposit, m2
A constant which characterizes interaction between gas and
solid surface, dimensionless
B permeability coefficient in Darcy's equation, m3i-s/kg
Cs slip correction factor, dimensionless
D particle diameter, ym
Dg diameter of sphere with same volume as particle, ym
Dp projected area diameter, ym
D sedimentation diameter, ym
Dvl volume-length mean (sedimentation) diameter in Equation (15),
ym
DVS volume-surface mean diameter in Equation (10), ym
k Kozeny constant, dimensionless
K2 specific resistance of dust cake, sec"1
Kn modified Knudsen number, dimensionless
L dust cake thickness, m
m mass of dust cake, kg
n number fraction, dimensionless
N number of particles in dust cake
R resistance factor, dimensionless
S specific surface area of particles, m"1
V superficial velocity, m/s
w weight fraction, dimensionless
W areal density, kg/m2
252
-------
Greek
a solidity, dimensionless
A? pressure drop, Pa
e porosity, dimensionless
A mean free path of gas, m
y viscosity, Pa-s
p particle density, kg/m3
T particle relaxation time, s
T particle relaxation time based on DVI, s
shape factor relating D^ to D in Equation (19), dimension-
vl less P S
shape factor relating D to DVS in Equation (11), dimension-
X dynamic shape factor, dimensionless
Subscript
i particle size category
253
-------
Introduction
Determination of the permeability of porous media to fluids
has produced a voluminous literature1'2 concerned to a large
extent with the prediction of permeability from the properties
of the porous structure and gaseous medium and confirmation of
these relationships by experiment. Various theories and empiri-
cal formulations have been proposed, but the general consensus,
until recently, has been that the Kozeny-Carman equation^ is the
most reliable, and considerable experimental data have been pub-
lished to support this contention.
The Kozeny-Carman equation was first applied to the filtra-
tion of dusts on fabrics by Williams, Hatch, and Greenburg^ and,
despite a lack of experimental verification, has found wide
acceptance ' ' . Generally, only the permeability of the dust
cake has been measured as it is considerably more difficult to
determine the parameters required for insertion in the Kozeny-
Carman equation. In particular, measurement of filter cake
porosity is especially difficult because the dust cake is nor-
mally a very thin, fragile structure supported on a fabric which
is not flat and whose fibers mingle to varying degrees with the
particles in the cake. For these reasons, the porosities of
dust deposits on operating fabric filters have not previously
o
been measured experimentally .
Darcy's Law
The fundamental relationship governing noncompressible,
creeping flow through porous media, Darcy's law, states that the
254
-------
rate of flow is directly proportional to the pressure gradient
causing the flow , i.e.:
V = B^ (1)
LJ
where V is superficial velocity, B is Darcy's permeability coef-
ficient, AP is pressure drop, and L is thickness of the porous
medium. Because the thickness of a dust cake is difficult to
measure, Williams, Hatch, and Greenburg4 substituted the areal
density, W, (i.e., weight of dust on the filter per unit of
cloth area) from the following expression:
T - ,w (2)
-^n^y
where p is the density of the particles in the dust cake and
e is the dust cake porosity (void fraction). After substituting
Equation (2) into (1), Darcy's law becomes:
K - AP (3)
K2 ~ VW
where K2 = [Bp (1-e)]"1. The quantity "K2", the specific resis-
tance of the dust cake, has been employed extensively in fabric
filtration studies4'5'7. It was first called "K2" by Billings
and Wilder9 and this designation has become synonomous with spe-
cific resistance. The reciprocal of K2, the permeability, of the
dust cake, has also been used for characterizing dust cakes .
Equation (3) is a definition of specific resistance and Darcy's
law simply states that it is constant for a given porous and
255
-------
flow medium.
Stokes ' Law
Because a dust cake is composed of small particles, Stokes'
law can be used as a model to predict specific resistance if it
is assumed that there is no hydrodynamic interaction between
particles. For spheres of uniform size, the sum of the drag
forces on each particle in a unit mass of dust cake is equal to
pressure drop per unit of areal density, or:
M = Z Drag Force _ (3TryVD/Cs)N
W I, Mass 7T~1 : (**)
(^D3pp)N
where N is number of particles in the dust cake, y is gas visco-
sity, D is particle diameter, and C is slip correction factor.
O
Combining Equation (4) with the definition of K2 (Equation 3)
yields:
(K2) = =
2 minimum p D^C rC -(5;
PS s
where T = ppD2/l8y. Inasmuch as the velocity on the surfaces of
the particles is zero (ignoring slip), as the particle get closer
together the absolute value of the velocity gradient between par-
ticles increases resulting in larger shear stress in the fluid and
greater drag on the particles10. Therefore, Equation (5) is an ex-
pression for the minimum specific resistance because the particles
are assumed to be far apart (i.e., e + 1). It is also important
to note that the minimum specific resistance is equal to the
reciprocal of the slip-corrected particle relaxation time, T,
256
-------
which plays a prominent role in the mechanics of aerosols. Al-
though K2 depends on .the density of the particles, as does the
terminal settling velocity of a particle, pressure drop is inde-
pendent of density. For a dust cake composed of unit specific
gravity spheres, the minimum specific resistance for ambient air
flow based on Equation (5) is shown in Table I.
It may be deduced from Equation (5) that smaller values of
the minimum specific resistance will be obtained whenever small
particles accumulate in clusters which mimic larger particles.
As observed by Carman and Malherbe11, this situation can exist
with uncompacted fine powders because of the presence of a rela-
tively large surface force compared to the gravitational force
on the particles. A different situation exists in a dust cake
because the flow, itself, creates the porous medium. Therefore,
when flow resistance in one portion of the dust cake is less
than in another, the flow rate is greater in that portion with
lower resistance, and hence a larger number of particles will
deposit in this region causing an increase in flow resistance.
Consequently, the distribution of particles in the dust cake
tends toward uniformity. An exception to this tendency occurs when
the aerosol being filtered is composed predominantly of complex
aggregates because particle deposition in the internal recesses
of an aggregate may not be possible.
Inasmuch as Stokes' law places a minimum constraint on any
model proposed for predicting pressure drop across a dust cake,
257
-------
TABLE I. Minimum Specific Resistance
Specific Resistance
Particle Diameter, ym (ms) 1 in. water/(fpm-lb/ft2)
50 0.13 0.013
10 3.2 0.32
5 13 1.3
1 280 28
0.5 980 98
258
-------
a new quantity, the resistance factor, R, may be defined by the
following equation:
K2=J (6)
R is a number greater than one which, when multiplied by the
minimum specific resistance, defined in Equation (5)3 gives
the specific resistance of the dust cake (for C equal to
S
unity). R generally is only a function of dust cake porosity,
although the porosity is influenced by the conditions prevailing
when the dust cake is formed (e.g., velocity, humdity) and the
properties of the dust. The value of T is affected solely by
the properties of the dust. The slip correction factor, C , is
S
a function of both particle size distribution and porosity and
will be discussed in detail later.
Kozeny-Carman Equation
The Kozeny-Carman equation is a semi-empirical relationship
which assumes that a dust cake can be represented by a collection
of parallel capillaries whose total surface area is equal to the
surface area of the particles and whose total volume is equal to
the void volume of the dust cake. It can be written as follows:
.
where k is the Kozeny constant which Carman determined to be
equal to 4.8 for spheres and 5.0 for various irregularly shaped
particles over a wide range of experimental conditions. Substi
tuting the former value into Equation (7), it is found that the
259
-------
oretlcally the Kozeny-Carman equation is invalid at porosities
greater than 0.92 because higher porosities would correspond to
a value of R less than unity.
The porosity above which the Kozeny-Carman equation is no
longer useful is somwhat nebulous. Billings and Wilder12 stated
that the Kozeny-Carman equation does not apply to high porosity
dust cakes because the theory is based on discrete passageways.
Specifically, they suggest caution for porosities in excess of
13
0.7. Carman contended that his theory does not break down until
porosity exceeds 0.8.
Although in situ porosities of dust cakes on cloth filters
have never been reported in the literature, there are some clues
to the range of porosities which can be expected. Billings and
1*1
Wilder indicated that the porosities of granular powders vary
from about 0.40 to 0.99. Orr15 listed porosities from 0.51 to
0.94 for dust filter cakes composed of particles with diameters
from 0.24 to 33 ym. Although these dusts were collected on fab-
rics, the porosities were apparently those that resulted when
the same dusts were placed in glass containers and tapped16.
"IV "1 fit
Kimura and linoya '* used the Kozeny-Carman equation to back-
calculate the porosities of dust cakes from experimentally de-
termined values of specific resistance. Their calculated poro-
sities ranged from 0.55 to 0.99. Because a porosity greater
than 0.92 calculated from the Kozeny-Carman equation is theore-
tically impossible, their data is suspect.
In conclusion, it is evident that the Kozeny-Carman equa-
260
-------
tion Is probably of limited utility for the prediction of dust
cake specific resistance. In particular, at high porosities, ...
which are not uncommon for dust filter cakes, the Kozeny-Carman
equation will seriously underestimate pressure drop.
"Free Surface" Model
An alternate approach to a capillary model is to recognize
that a dust cake consists of an assemblage of individual parti-
cles subjected to aerodynamic drag which can be represented by
a collection of uniformly distributed cells, each composed of a
spherical particle and a concentric, fluid-filled envelope of
such proportion that the porosity of the cell and of the entire
granular medium is identical. If appropriate boundary conditions
are formulated, the Navier-Stokes equation (neglecting Inertial
effects) can be solved rigorously.
19
Happel postulated a "free surface" cell ; mo die!' in' which the
salient boundary condition is the disappearance of tangential
stress on the surface of the spherical envelope. If the size of
the spherical envelope is infinite, the result becomes identical
with Stokes' law. For prediction of pressure drop through a
dust cake, the "free surface" model of Happel can be written in
terms of the resistance factor as follows:
3 + 2(l-e)^3
R =
3 - 4.5(1-£)V3 + 4.5(l-e)5/3 - 3(l-e)2
Theoretically, this relationship should be valid for all values
of porosity and it yields the proper limits, i.e., for c = 0,
R Is infinite and for e = 1, R = 1. It shows good agreement
261
-------
with published experimental data for hindered settling in the
high porosity range (0.95 to l.O)19; and, for packed beds in the
low porosity range (0.30 to 0.60), it gives results essentially
identical to those derived from the Kozeny-Carman equation, as
shown in Table II. The close agreement between the semi-empiri-
cal Kozeny-Carman equation and the theoretical relationship of
Happel in the low porosity range (<.6o) is striking considering
that the "free surface" model contains no empirical constants.
In the intermediate porosity range (0.60 to 0.95), the experi-
mental results are contradictory, indicating that porosity does
not uniquely characterize permeability. Inasmuch as most of the
data in this porosity range come from fluidized and sedimenting
particle systems, circulation and agglomeration effects would be
expected to play an important role and result in increased per-
meability. This would explain qualitatively discrepancies be-
tween the "free surface" model and experimental results. The
"free surface" model, however, is in satisfactory agreement with
the rather limited experimental data in which circulation and
agglomeration effects were eliminated or minimized19'20. It
seems likely that there are no agglomeration effects present
when a dust cake is formed primarily from a nonaggregated aero-
sol. As discussed previously, a dust cake forms dynamically and
it is reasonable to assume that particle deposition tends toward
uniformity.
Inasmuch as the "free surface" model is theoretically valid
at all porosities, it is tempting to adopt it for dust filter
262
-------
TABLE II. Comparison of Resistance Factors Predicted by Kozeny-Carman
Equation and "Free Surface" Model
Resistance Factor (R)
Kozeny-Carman Equation
Porosity (Eq. 7, k =.4.8)
.30
.40
.50
.60
.70
.80
.90
1.00
250
90
38
18
8.4
3.7
1.3
0.0
Happel Model Ratio
(Eq. 8) Happel/Kozeny-Carman
230
85
38
19
10
5.6
3.1
1.0
0.92
0.94
1.0
1.1
1.2
1.5
2.4
oo
-------
cakes but certain Important considerations remain unresolved. In
particular, the "free surface" model assumes uniform spheres, and
does not indicate how nonuniform particle sizes and nonspherical
shapes should be handled. In addition, the "free surface" model
assumes that particles are sufficiently large that the fluid can
be considered as a continuum. This may not be correct for a dust
cake composed of very small particles.
Effect of Particle Size Distribution and Particle Shape
When the Kozeny-Carman equation is employed, the correct
mean particle diameter as given by the hydraulic radius theory
is a function of the specific surface area of the granules, S,
(i.e., the surface area exposed to the fluid per unit volume of
solid material), or
°vs = 6/S (9)
where Dys is the mean diameter to be used in the Kozeny-Carman
21
equation . This approach automatically corrects for particle
shape. For spherical particles,
_ En.D.3
where n± is the number fraction and w± the weight fraction of
particles with diameter D±. Dys is often referred to as volume-
surface mean diameter or the Sauter mean diameter. For irregu-
larly shaped particles
vs ~ *vs Zn.(Dz). (11)
264
-------
where $ is a shape factor which is assumed here to be indepen-
vs
dent of particle size and D is the projected area diameter ob-
tained from microscopy.
Some experimental studies using mixtures of various particle
sizes have shown agreement with the Kozeny-Carman equation when
using D as the mean diameter22. Carman also showed that the
VS
use of D gave good results for mixtures of spheres in which
VS
the diameter ratio was 2:1 whereas when the diameter ratio was
5:1, the calculated value for DVS was not able to compensate
23
entirely for changes in permeability. Krumbein and Monk used
sands having equal mass median diameters but different size dis-
tributions and obtained a significant effect of particle size
dispersity on specific resistance. Correcting their data to a
constant volume-surface mean diameter does not substantially
Oil
change their results. Carman stated that whereas the permea-
bility method for measurement of particle size does not require
particles of uniform size, an excessively wide distribution of
sizes should be avoided, and this warning is frequently echoed
pc
in texts .
19
In his original "free surface" model derivation, Happel
did not treat nonuniformity in size or nonsphericity, but
later2 , he supported the use of a volume-surface mean diameter.
Rather then follow this empirical approach, it can be shown that
a mean diameter follows logically from either the Stokes' law or
Happel model. For illustrative purposes, if Equation (4), based
on Stokes' law is rewritten to apply to a distribution of irregu-
265
-------
larly shaped particles of various sizes, and if slip is neglected,
Equation (4) assumes the following form:
AP = Z Drag Force _
W T, Mass ~ i ~~r" -- (12)
where x is a dynamic shape factor defined by Puchs27 as the ratio
of the resistance of a given particle to that of a spherical par-
ticle having the same volume, and DS is the diameter of a sphere
having the same volume as the particle. Prom the definition of
the sedimentation (Stokes) diameter, D , it can be shown27
s
that:
D2
X = D^ (13)
s
Hence, if it is assumed that x is independent of particle size,
substituting Equation (13) into Equation (12) yields:
(Ko) = AZ. = !8y -^ » j- , . .
minimum WV p In. (D3). (••L^)
p i s i
Comparing Equations (14) and (5), it will be seen that the re-
quired mean diameter is the volume-length mean diameter based on
the distribution of sedimentation diameters: ': '
1/2
D
vl
(15)
Alternatively, pp, can be set equal to unit specific"gravTEy~Ir
Equation (ilj) and an aerodynamic diameter substituted for the
sedimentation diameter in Equation (15). The same result is
obtained for the "free surface" model with slip included pro-
vided the dynamic shape factor is not influenced by porosity.
Equation (6) can then be rewritten as follows:
266
-------
K2 -
where
2
vl s
T = pvl (17)
vl
When D T is to be determined by microscopic methods,
• ~^ (-p, 3 •>! —| 1/2
D = A __^^ (18)
Dvl
where , is a shape factor which is assumed to be independent of
vl
particle size and porosity and which relates the sedimentation
diameter to the projected area diameter, i.e.,
Although the volume-length mean diameter, D¥IJ given by
Equation (15) differs from the volume-surface mean diameter, DVS,
given by Equation (10), the difference is small for spherical
particles unless the particle size distribution is fairly broad.
For example, if the particle sizes are log normally distributed,
these two diameters can be related using the Hatch-Choate equa-
po
tion as shown in Table.III. For most of the studies done on
granular media, usage of DTrc, or D , would give nearly the same
V S v _L
results, but for most industrial dust cakes, the difference can
be expected to be large because industrial dusts tend to have a
geometric standard deviation greater than 2.5.
Slip Flow
When particle diameters in a dust cake become small, the gas
267
-------
TABLE III. Comparison of D and D
vs vl
Geometric
Standard _ _
Deviation Dvs/Dvl
LO 1.0
1'5 1.09
2.0 1<27
2-5 1.52
3-0 !
268
-------
can no longer be regarded as a continuum and the specific resis-
tance will be less than predicted by theory because the gas velo-
city will not be zero at the particle surface. Inasmuch as the
derivation given by Happel does not account for this slip, the
"free surface" model was rederived using the classical slip flow
29
procedure in which the Navier-Stokes equation is solved using
boundary conditions which account for noncontinuum effects. This
method is valid only for small (<0.25) Knudsen numbers (gas mean
free path/particle radius). The result of this derivation is
given below in terms of the slip correction factor for use in
Equation (16):
(En.D1)-( ) (20)
C =
I
5/3
+
2 _ 3a 5/3 + Sa5/3 - 2a* + 6Kn. (l-a1/3-a5/3+a:
i
where a is dust cake solidity (1-e) and Kn. is a modified Knudsen
number for a particle of size D., i.e., Kn. = ±m.3 where A is a
i 1 DJ
number close to unity vwhich "characterizes the interaction of the
gas molecules with the particle surface and A is the mean free
path of the gas.
From Equation (20), when the Knudsen number approaches zero
(i.e., no slip), the slip correction factor approaches unity.
When porosity is equal to unity and the particles are single-
sized:
c _ l+3Kn . ,
s " l+2Kn (21)
269
-------
Equation (21) is identical to the result given by Fuchs30 for
the slip correction factor for a single particle in an infinite
medium, which is valid only for small Knudsen numbers and is
approximately equal to the Cunningham slip correction factor.
Prom theory, Equation (20) should be valid at all porosities
(for Knudsen numbers <0.25). It gives excellent agreement with
published experimental results for compacted fine powders having
porosities from Q.H to 0.6* and, as stated above, is in fair
agreement with the Cunningham slip correction factor for porosi-
ties approaching unity. If a slip correction factor = 1.1 is
ignored, a 10* error in the specific resistance will be obtained.
From Equation (20), this error corresponds to the particle sizes
and porosities shown in Table IV. When either porosity or particle
diameter becomes smaller than the value shown in Table IV,
neglect of the slip correction factor will yield a value for
specific resistance from Equation (16) that will exceed the cor-
rect value by more than 10*.
Experimental Apparatus
Experimental apparatus was designed to fulfill two key ob-
jectives: (1) determination of filter cake specific resistance,
and (2) preparation of filter cakes for porosity measurement.
Figure 1 shows the bench scale equipment in which dust cakes were
formed on various cloth and paper supports at a constant air-to-
cloth ratio over a wide range of air-to-cloth ratios such that
other parameters (e.g., aerosol particle size distribution and
relative humidity) could be held ' essentially constant during a
"pSbl^pi??^ ^ !tatement can be f°urid in Harvard School of
progress d^toral dissertation by S. Rudnick currently in
270
-------
TABLE IV. Porosities and Particle Diameters for which C =1.1
o
Particle
Diameter,
Porosity ym
0.3 32
0.4 22
0.5 16
0.6 11
0.7 8.2
0.8 5.7
0.9 3.6
1.0 1.1
271
-------
a run and from run-to-run.
As shown In Figure 1, filtered compressed air was fed to a
Wright31 dust feeder which dispersed the test dust. The resul-
tant aerosol passed through an elutrlator In which all particles
with an aerodynamic diameter greater than 8.4 ym were removed
before reaching the experimental filter. Aerosol in excess of
the amount needed for filtration was vented at the inlet to the
elutrlator. To avoid flow disturbances, a circular frustum with
a 7° half angle was used upstream of the filter. The filter
holder was composed of two cylindrical pieces with large flanges
between which a supporting substrate such as cloth could be
clamped with the cloth acting as its own leak tight gasket. Plow
measuring and controlling devices, located downstream from the
filter, included a manually adusted control valve to giwe con-
stant flow over the duration of a run plus a sensitive and accu-
rate pressure gauge placed upstream of a calibrated critical ori-
fice to make it possible to measure mass flow rate. The critical
orifice also served to isolate the system from downstream dis-
turbances caused by the vacuum pump. The control valve acted as
a high flow resistance in series with the filter so that changes
In pressure drop across the filter cake had little effect on mass
flow rate. At face velocities below 50 mm/s (10 fpm) flow rate
remained constant throughout a run without need to readjust the
control valve. Pressure drop across the filter was recorded con-
tinuously on a chart recorder. Filter approach velocity was
adjusted by varying filter area, i.e., changing the diameter of
272
-------
PRESSURE
TRANSDUCER
(TO CHART RBOROER)
NJ
•vl
U)
VERTICAL
ELUTRIATOR
COMPRESSED
AIR»» —
PRESSURE
REGULATOR
PRE- FILTER
TEST
FILTER
POST- FILTI
INFLOW CONTROL VAU/E
CRITICAL
ORIFICE
XACCUUM
PUMP
WALLACE 8 TIERNAN GAUGE
•VENT
WRIGHT
DUST
FEEDER DUST HOPPER
FIGURE 1. Experimental Apparatus
-------
filter holder and connecting pieces. Inasmuch as the filter area
was always less than the elutriator cross sectional area, the
aerosol size distribution was not affected by changes in filter
face velocity.
Porosity Determinations
The porosity (e) of dynamically formed dust cakes was cal-
culated from the following working relationship in terms of the
measurable parameters:
e = 1 - m
appL (22)
where Pp Is the density of individual particles, m is the mass
of filter cake exclusive of dust retained in the interstices of
the fabric, a is area of the dust deposit, and L ds average thick-
ness of the dust cake. Density of particles removed from filter
cakes was evaluated by pycnometry using a nonadsorbing gas, filter
cake mass was determined by weighing to the nearest tenth of a
milligram, area of the dust deposit was equal to the open area of
the filter holder, and cake thickness was measured by the follow-
ing procedure: A fracture could be induced in most dust cakes by
bending the cloth and then the cake could be removed cleanly from
one side of the fracture by tapping. This would expose a cross
section of the cake such as that shown in Figure 2 on which
thickness measurements could be made. During the cleaning cycle
of a bag filter, a similar process of fabric bending and cake
separation takes place2*. Alterations of the portion of the dust
cake remaining on the fabric that might be caused by the bending
274
-------
Figure 2. Cross Section of Dust Cake on Woven Fabric
275
-------
procedure could be detected easily with a stereoscopic microscope.
Dust cake thickness was measured by three techniques:
A. Measuring cake thickness with a calibrated graticule in
an 84x stereoscopic microscope. The circular dust cake was al-
ways flat in the vicinity of its center but it tended to decrease
in thickness, near the edge. /Therefore, dust cake thickness was
measured as a function of diameter and converted to a single
value of average cake thickness by graphical integration. As
this is a lenghthy procedure, it was done once at each filter
velocity and, thereafter, an experimentally determined correction
factor, calculated for each filter velocity, was applied to con-
vert from thickness at the cake center to average dust cake
thickness. ••'•-•-
B. Measuring the shadow formed in a scanning electron micro-
scope using backscatter electrons, because the edge of the sha-
dow is cast on a cleaned portion of fabric, this method automat-
ically compensates for the unevenness of the fabric. This pro-
cedure is not applicable to the flight microscope because of in-
sufficient depth of field. A micrograph of a shadow cast on a
woven fabric is shown in Figure 3.
C. Measuring the amount of rotation of a calibrated fine
focusing adjustment of a light microscope with a 22x objective
by focusing first on the cake surface and then on the fabric
surface.
All of these methods worked reasonably well for flat cake sup-
ports (paper) but for fabrics, method C gave very inconsistent
276
-------
4
i
3
f 2
4.
s
w
5 s
O 4
-
a 3
PARTICLE SIZE OF AC-FINE TEST OUST
PENETRATING A 0229* (9 INCH) DIAMETER
VERTICAL ELUTRIATOR AT A GAS FLOW RATE
OF 2.7 L/«i«
.05
0.01
J_
I I
J.
0.1 I 10
CUMULATIVE PERCENT
90 90
UNOER8IZE BY COUNT
96 99 99.8 99.99
FIGURE 4. Particle Size Distribution
277
-------
100)jm
Figure 3. Dust Cake Shadow Cast on Woven Fabric
278
-------
results. Methods A and B gave reasonably good agreement. Method
A is the most accurate and most time consuming.
Characterization of the Aerosol
Employing the apparatus shown in Figure 1, representative
samples of the aerosol generated from AC-fine test dust (GM
Phoenix Laboratory, Flint, Michigan), were collected on two 0.2
ym diameter Nuclepore filters in series separated by an open
fibrous mat (Nuclepore D24? FOR). All parameters remained the
same as during dust cake formation except that the concentration
of the aerosol was reduced to produce a deposit suitable for
sizing. The filter samples were photographed in a scanning
electron microscope at magnifications appropriate for stratified
counting. Particles were sorted into geometrically spaced size
categories with a transparent overlay patterned after the May-
Porton graticule^. it was intended that the second Nuclepore
filter would be used to measure the fractional efficiency of
these filters, but no particles were detected on the second fil-
ter.
The projected area diameter distribution of the aerosol used
in this study is shown on log probability paper in Figure 4. The
volume-length shape factor, , (Equation 18), used to convert
projected area diameter to sedimentation diameter, was estimated
based on (1) the? projected area diameter of the largest particles
passing through the elutriator determined for photomicrographs,
and (2) the sedimentation diameter of the largest spherical par-
ticle capable of penetrating the elutriator based on the elutria-
279
-------
tor center-line velocity assuming Poiseuille flow. This approach
is likely to give somewhat large values of $ , because the big-
gest particles penetrating the elutriator may go undetected by
microscopy due to their scarcity. The volume-surface shape fac-
tor, vs (Equation 11), used to convert projected area diameter
to volume-surface mean diameter, was determined from (1) pro-
jected area diameter distribution, and (2) specific surface area
measurements on polished cross sections of particles embedded in
plastic resin employing the methods of Chalkley, Cornfield, and
34
Park . It was found for the aerosol used in this study that
4>vl = 0.66 and $vs = 0.62. Both are within the range of values
cited in the literature for similarly shaped particles35,36^
Results
Elutriated AC-Fine test dust was collected at various face
velocities from 7.1 mm/s (1.4 fpm) to 56 mm/s (11 fpm) on paper
and woven fabric supports that included Teflon, polypropylene,
Dacron (all 3x1 twill, monofilament yarns), cotton sateen, What-
man 41, and 8.0 ym Millipore filter. Specific resistance, K2,
was determined from the following equation:
K, - x (AP)2-(AP)!
*2 ~ V W>¥^ (23)
where subscript "1" refers to the point at which AP became
essentially linear with areal density and subscript "2" refers
to dust flow termination.
Measured values of solidity (1-e) have been plotted against
experimentally derived values of the specific resistance, K2,
280
-------
in Figure 5. Also included in Figure 5 is a curve showing the
functional relationship between specific resistance and solidity
that we recommend based on Equations (8), (15), (16), (17) and
(20) or their composite given as follows:
n, (D ) {3 + 2a5/3 + 6Kn.( 1-a5/3)}
_1_ O J_ -L
'3 _ 4.5C11/3 + 4.5a5/3 - 3a2 + 9Kn. (l-a^-a^+a2)
i
K, = ""
PpZ[n.(D3).]
The experimental results are in considerably better agreement
with Equation (24) than with the Kozeny-Carman equation also
shown in Figure 5 which greatly underestimated the specific re-
sistance of the experimentally filtered dust cakes. This was
expected because the porosity of these dust cakes lies outside
the range of validity for the Kozeny-Carman equation. A large
portion of the Kozeny-Carman curve lies below the minimum possi-
ble specific resistance predicted from the Stokes' law model
shown as a single point in Figure 5.
Discussion
A filter dust cake can be modeled as a collection of capil-
laries or as an assemblage of particles. Although the latter is
clearly a more realistic representation, the Kozeny-Carman
equation utilizes the former, and consequently suffers certain
limitations. In particular, as the porosity of a dust cake
approaches unity, the Kozeny-Carman equation predicts that the
specific resistance (K2) will approach zero, whereas in this
case, the cumulative frictional and form drag of the isolated
particles will define the value of K2. As a limiting case,
281
-------
SPECIF.C RESISTANCE ( K, ),
OR
IO"
058
o § § 3 S 8 8
N)
00
NJ
O
13
(D
n
H-
Hi
H-
O
K °
•"4
laS
1^
m
* V
6>
35
-------
applying Stokes' law to flow through a dust cake, leads to Equa-
tion (5) which, solely from hydrodynamic considerations, gives
the minimum value of K2 for a given dust. It is clear from Table
I that the minimum specific resistance for small particles will
be large. For example, a 0.5 um particle diameter yields a mini-
mum K2 equal to 980/ms (98 in. water/fpm»lb/ft2). This example
incorporates an important concept: the specific resistance for
small particles will always be large, regardless of the magni-
tude of porosity. A common misunderstanding of fabric filter
vendors and users is that fine fumes produce nonporous filter
cakes with high flow resistance. Although fine fumes do cause
high flow resistance, the dust cakes are, nonetheless, likely
to exhibit high porosity. The high flow resistance is due pri-
marily to the small particle size.
An understanding of minimum specific resistance can be help-
ful in determining whether or not data from lab or field studies
are of the correct order of magnitude. When K2 values less than
the calculated minimum specific resistance are obtained, the data
must be suspect.
Although the Kozeny-Carman equation (with a suitable cor-
rection for slip flow) is presumably valid for dust cakes with
porosities less than 0.65, the "free surface" model, modified
to treat nonuniform particle sizes, nonspherical shapes, and slip
flow, is preferable because it gives good agreement with experi-
mental measurements for the entire range of dust cake porosities.
Either model yields essentially the same specific resistance for
283
-------
porosities less than 0.65. This is fortunate in light of the
extensive experimental support of the Kozeny-Carman equation at
these porosities. But at porosities above 0.65, which are com-
mon in fabric filter dust cakes, the Kozeny-Carman equation under-
estimates specific resistance whereas the modified "free surface"
model gives adequate agreement with experimental results. This
is shown in Figure 5.
Both the Stokes' law model and the "free surface" model con-
sider a dust cake to be an assemblage of particles but the "free
surface" model differs because the drag force on a particle given
by Stokes' law is multiplied by a factor that is greater than
unity and increases as dust cake porosity decreases. When poro-
sity approaches one, the two models become identical. The mean
diameter appropriate for these models is given by Equation (15)
and is calculated directly from the sedimentation diameter distri-
bution or aerodynamic diameter distribution when particle specific
gravity is taken in unity in Equation (17). The diameter distri-
bution may be expressed on a number or weight basis, and can
often be measured with the aid of an inertial sampling device such
as an impactor provided particle size is not too small. In addi-
tion to correcting for particle shape based on the aerodynamic
properties of particles, this measurement method may also compen-
sate for particle orientation inasmuch as a particle is likely to
remain in an aerodynamically stable position after incorporation
into the dust cake.
284
-------
Inasmuch as the "free surface" model also predicts the flow
field surrounding a particle in a dust cake, it may be possible
to predict S02 collection efficiency in fabric filters which re-
move S02 in a reacting chemical precoat or upstream injection.
•37
Pfeffer derived a solution for heat and mass transfer in par-
ticulate systems based on the "free surface" model which is valid
for high Peclet number. Although S02 removal in a fabric filter
dust cake usually occurs at low Peclet number, development of an
approach similar to Pfeffer's which can be applied to S02 removal
in a fabric filter, may be possible. This type of modeling capa-
bility may become very useful if all new coal-fired utility plants
are required to use scrubbers or fabric filters with nahcolite
injection, as appears likely .
Acknowledgement
This work was supported in part by Stone & Webster Engineer-
ing Corporation, Boston, Mass. It was performed in partial ful-
fillment of the requirements for the Sc.D. degree at the Harvard
School of Public Health.
References
1. Carman, P. C., "Flow of Gases Through Porous Media",
Academic Press, New York, NY, 1956.
2. Scheidegger, A. E., "The Physics of Plow Through Porous
Media", University of Toronto Press, Toronto, Canada,
1974.
3. Carman, P. C., "Fluid Flow Through Granular Beds", Trans-
actions - Institution of Chemical Engineers, 15:150-166,
1937.
4. Williams, C. E., Hatch, T. and Greenburg, L., "Determina-
tion of Cloth Area for Industrial Air Filters", Heating
Piping and Air Conditioning, 12:259-263, 19*10.
285
-------
Silverman, L., "Filtration Through Porous Media", American
Industrial Hygiene Association Quarterly, 11:11-20, 1950.
Stephan, D. G., Walsh, G. ¥. and Herrick, R. A., "Concepts
in Fabric Air Filtration", American Industrial Hygiene
Association Journal, 21:1-14, I960.
Billings, C. E. and Wilder, J., "Handbook of Fabric Filter
Technology, Vol. I, Fabric Filter Systems Study", National
Technical Information Service, PB-200 648, Springfield,
8. Ibid., p. 2-131.
9, Ibid. , p. 2-160.
10. Fuchs, N. A., "The Mechanics of Aerosols", Pergamon Press
Oxford, England, 1964, p. 49.
11. Carman, P. C. and Malherbe P. le R., "Routine Measurement of
Surface of Paint Pigments and Other Fine Powders", Journal
of the Society of Chemical Industries, London (Trans-
actions), England, 69:134-143, 1950.
12. Billings, C. E. and Wilder, J., Op. Cit., p. 2-117.
13. Carman, P. C., 1956, Op. Cit., p. 15.
14. Billings, C. E. and Wilder, J., Op. Cit., p. 2-134.
15. Orr, C. >Jr., "Particulate Technology", MacMillan, New York,
16. linoya, K. and Yamamura, M. ,_ "Fundamental Experiments With
Dust-Collectors", Kagaku Kogaku, Japan, 20:163-171 1956
(in Japanese) . '
17. Kimura, N. and linoya, K., "Pressure Drop Characteristics
oo ^t??,,C1°t5 f°? Dust Collecti°n", Kagaku K5gaku, Japan,
29:166-174, 1965, (in Japanese) .
18. Kimura, N. and linoya, K., "Pressure Drop Characteristics
of Filter Cloth for Dust Collection".; Kagaku KSgaku, Japan,
3:193-196, 1965, (abridged edition in English).
19. Happel, J "Viscous Flow in Multiparticle Systems: Slow
f^ion of Fluids Relative to Beds of Spherical Particles",
A.I.Ch.E. Journal, 4:197-201, 1958.
20. Happel, J., "Fluid Flow in Multiparticle Systems", Trans-
actions of the New York Academy of Sciences, 20:404-410,
286
-------
21. Carman, P. C., 1956, Op_. Cit., p. 11.
22. Ibid, p. 18.
23. Krumbein, W. C. and Monk, G. D., "Permeability as a Function
of the Size Parameters of Unconsolidated Sand", Trans-
actions of the American Institute of Mechanical Engineers,
151:153-163, 1943.
24. Carman, P. C., 1956, Op. Cit. , p. 83.
25. Allen, T., "Particle Size Measurement", Chapman and Hall,
London, England, 1968.
26. Happel, J. and Brenner, H., "Low Reynolds Number Hydrodyna-
mics With Special Applications to Particulate Media ,
2nd Ed., Noordhoff International Publishing, Leyden,
Netherlands, 1973, pp. 395, 4l8.
27. Fuchs, N. A., Op_. Cit., pp. 39-40.
28. Silverman, L., Billings, C. E. and First, M. ¥., "Particle
Size Analysis in Industrial Hygiene", Academic Press, New
York, NY, .1971, p. 242.
29. Hidy, G. M. and Brock, J. R., "The Dynamics of Aerocolloidal
Systems", Pergamon Press, Oxford, England, 1970, p. 147.
30. Fuchs, N. A., Op_. Cit., p. 25.
31. Wright, B. M., "A New Dust-Feed Mechanism", Journal of
Scientific Instruments, 27:12-15, 1950.
32. Dennis, R., Cass, R. W. and Hall, R. R. , "Observed Dust
Dislodgement from Woven Fabrics and Its Measured and
Predicted Effect on Filter Performance", Presented at
the 70th Annual Meeting of the Air Pollution Control
Association, Toronto, Canada, June 20-24, 1977-
33. May, K. R., "A New Graticule for Particle Counting and
Sizing", Journal of Scientific Instruments, 42:500-501
1965.
34. Chalkley, H. W., Cornfield, J. and Park, H., "A Method for
Estimating Volume-Surface Ratios", Science, 110:295-297,
1949.'
35. Mercer, T. T. , "Aerosol Technology in Hazard Evaluation",
Academic Press, New York, NY, 1973, p. 83.
36. Herdan, G., "Small Particle Statistics", Academic Press, New
York, NY, I960, p. 175-
287
-------
37. Pfeffer, R., "Heat and Mass Transport In Multiparticle Systems",
Industrial and Engineering Chemistry Fundamentals, 3:380-
383, 1964. '
38. Mcllvaine, R. W., ed., "Fabric Filter Newsletter", No. 23,
Mcllvaine Company, Northbrook, IL, September 10, 1977,
p. 8.
288
-------
THE INFLUENCE OF ELECTROSTATICALLY-INDUCED CAGE VOLTAGE
UPON BAG COLLECTION EFFICIENCY DURING THE PULSE-JET
FABRIC FILTRATION OF ROOM TEMPERATURE FLYASH
R. P. Donovan*
R. L. Ogan+
J. H. Turner+
*Research Triangle Institute
Process Engineering Department
P. 0. Box 12194
Research Triangle Park, N. C. 27709
+Environmental Protection Agency
Industrial Environmental Research Laboratory
Research Triangle Park, N. C. 27711
289
-------
Abstract
In a previous paper an experimental arrangement was described
for measuring the effect of electrostatic charge buildup on fabric
filters during the room temperature, pulse-jet filtration of re-
dispersed flyash—flyash which was originally collected by an electro-
static precipitator scrubbing the effluent of a pulverized coal boiler.
A prime justification and advantage of that experimental arrangement
was that it required only the attachment of one electrical lead to the
cage supporting the bag filter. This simple modification was assumed
not to change or influence the dust/fabric interaction being studied
in any way.
From the qualitative concepts previously presented, a simple
analog equivalent circuit is proposed for relating the charge buildup on
or in the fabric to the cage voltage detected by the measuring technique.
Since the simple equivalent circuit to be presented explains at least
some of the cage voltage features observed so far, it is concluded to
be a useful starting point for modeling the interaction.
A second general goal of the experimental program is to relate
the electrostatic properties of a given dust/fabric system to its per-
formance as a fabric filter. The initial observation of this portion
of the program concludes the paper.
290
-------
HISTORICAL BACKGROUND
At least as long ago as 1913 [Reference 1] experiments were being
performed which showed that raising clouds of dust produced large amounts
of electricity, that the sign of the resultant charge depended on the
dust composition and that particle size affected charge quantity. The
work included passing particles through metal mesh and light cotton
fabrics, and measuring voltages and signs of charge at the mesh or
fabric surface and beyond. Passing dust through long tubes (20 feet)*
also generated strong charges.
By 1926 Deodhar [Reference 2] (and Shaw [Reference 2] in discussion
following Deodhar's paper) showed that temperature and humidity also
affected charge. The beginnings of a triboelectric series for dusts
were discussed. In 1950, Kunkel [Reference 3] refined previous work
and presented quantitative information about dust clouds. With highly
reproducible measurements, he concluded that (1) the particles in a dust
cloud are charged, probably as a result of particle to particle separation
after contact, (2) the clouds have about equal numbers of positively
and negatively charged particles and are therefore neutral (unless a
significant portion of the particles strike a dissimilar material),
(3) the effect holds for at least over the size range from 0.5 to 30 ym,
(4) for the case of metals and insulators being the dissimilar materials,
*Use of metric units exclusively would seriously inconvenience the
majority of the intended reading audience. For those readers more familiar
with the metric system a conversion table for changing the British units
used in the report to their metric equivalent appears in the appendix.
291
-------
the insulator will invariabley have a predominantly negative charge, and
(5) because, at least for the quartz powder studies, a one or two
molecule thick layer of water remained on the particles even to several
hundred degrees centigrade (water vapor moisture plays only a minor
role in the electrification process).
About this time interest was generated in the deposition of particles
on fibers (and other surfaces) and the effects of electrostatic pheno-
mena on the process. Kraemer and Johnstone [Reference 4] presented
equations of motion for a particle influenced by an electrostatic force
in a resisting fluid, and equations for the electrostatic force on a
particle approaching a collector at constant voltage and for a collector
at constant charge. Experimentally they studied charged collector with
corona-charged OOP, charged collector with only naturally charged
aerosol, and grounded collector with corona-charged aerosol. Their
results agreed reasonably well with the various collection parameters
they had presented, and led to the suggestion of an electrified mat
filter assumed to yield several orders of magnitude increase in col-
lection efficiency over its non-electrified analog. No mention was made,
however, of collection by cake established on a fiber or fabric support.
Rossano and Silverman [Reference 5] did experimental work with charged
aerosols and/or charged fiber filters (not fabric}. They used low concen-
trations of methylene blue particles (0.1 to 1.7 mg/m3, 2 Pm mass median
diameter [MMD]) and Saran fiber beds 1 in. thick (35 to 70 ym curled fibers
packed to 2.6 lb/ft3). Filtration velocity was 33 to 66 fpm. Their
292
-------
conclusions were that filtration efficiency increased with increasing
fiber charge and decreasing fiber diameter for a negatively charged
filter and relatively uncharged aerosol. In the range studied, velocity
was not a significant variable (contrary to Kraemer and Johnstone's
prediction). For a negatively charged bed and positively charged
particles, collection efficiency increased with increasing charge and
increasing filter packing density. It should be pointed out that the
fiber beds were charged by hand carding just prior to each experiment.
An experimental loss in collection efficiency of the bed over a 3 day
period (to 45% from 75%) was presumed to be caused by electrical dis-
charge of the bed. Further experimentation of particular (and disturbing)
interest to the present work showed that passage of dust through an
uncharged bed produced no measurable charge on the bed. Methylene blue
at 1.0 mg/m3 at velocities of 33 and 70 fpm, and atmospheric dust at 33
to 364 fpm were used.
Although of closer interest to the present work and to baghouse
users than much of the preceding work, the Rossano and Silverman experi-
ments still have important differences when compared to fabric filtration.
They used thick, open fiber beds which were not cleaned and had no
appreciable cake. The fibers were relatively large in diameter and the
aerosol loading was low. Velocity was an order of magnitude higher than
those used with fabric filters and efficiency much lower (which may be
an unfair criticism in view of the low inlet loading).
293
-------
Rao et al. [Reference 6], in a paper with "Fabric Filtration" in
the title, develop a strictly theoretical description and equations for
a particle being collected by an array of three parallel cylinders.
There may be some confusion in the minds of the authors between fiber
and fabric filters. Cleaning and existence of a cake are not mentioned.
Makino et al. [Reference 7], with a reverse twist, studied removal
of dust from a filter paper backed up by electrodes. They filtered dusts
(Lycopodium, ABS and sinter dust) through the filter with no current
through the electrodes, then stopped the dust (but not air) flow, and
turned on the electrodes in order to remove dust from the filter (pre-
sumably the filter surface was vertical). They used alternating current
in three different electrode/filter configurations and concluded that
removal efficiency was a function of electrode distance from the filter,
electrode diameter, and distance between electrode wires. They also
found that removal efficiency increased as the initial electric charge
of the dust increased and that filtering velocity was not significant
even up to about 50 cm/sec. Optimum removal depended on frequency, with
lower frequency being better. Finally, the authors found that continuously
moving the filter in relation to the electrodes improved cleaning effi-
ciency (presumably the motion wasn't vigorous enough to approximate
shake cleaning).
Numerous authors have studied particle deposition on fibers with
the influence of charges or electric fields. When fabrics or filter mats
were used the conclusion reached is invariably that charging aids filtration
294
-------
The experimental method includes measurement of efficiency for clean
fabric without, and then with, charging. The efficiency usually goes
from some low value to something in the 90's. What is not brought out
is the difference between non-cleaned fresh fabrics or mats which
filter without significant cake formation, and cleanable fabric filters
which depend on the dust itself for very high collection efficiency.
One refreshing change has been the work done by Frederick
[Reference 8], and Penney and Frederick [Reference 9] in exploring
the role of fabric electrical properties and dust electrical properties
in the fabric filtration process.
The present work is predicated on trying to gain still further under-
standing of electrical effects in an operating fabric filter by taking
measurements in a commercial pulse-jet baghouse operated in a laboratory
atmosphere.
295
-------
REVIEW OF EPA ELECTROSTATIC EXPERIMENT
The experimental apparatus used throughout this work consists of a
commercially available, nine-bag MikroPul pulse-jet baghouse. This unit
is one of the smallest commercially available baghouses. Asisuch
it retains all the features of fuller sized units and lends itself well
to laboratory simulation of field experience.
For the electrostatic measurements to be reported here (and as
reported previously [Reference 10]), the bag mounting technique was
altered from the conventional mounting as shown in Figure 1. The at-
tachment of a banana jack to the cage is the only change from the stan-
dard bag mounting procedures. The purpose of this banana jack is to
allow monitoring of the electrostatic properties of the dust/fabric
system by using the cage as an electrode or electrical contact to the
system. As evident in Figure 1, the cage is electrically isolated from
the baghouse housing by a single thickness of fabric. Since most of the
synthetic fabrics investigated here have high electrical resistivity, the
electrical isolation of the cage is generally high. By connecting a high
impedance electrometer to the cage, the cage voltage can be monitored
without disturbing or altering the filtration conditions.
296
-------
VENTURI
PLENUM FLOOR
\VENTURI SHOULDER
HOSE CLAMP
BANANA JACK
FIGURE 1. CAGE CONTACT
297
-------
The primary experimental measurement made in this work has
been the monitoring of cage voltage as a function of various
independent parameters of filtration. As previously described
[Reference 10], the voltage on the cage typically displays behavior
similar to that illustrated in Figures 2a and 2b. Figure 2a,
showing the cage voltage of a polyester felt bag (Dacron*) filtering
flyash, typifies the characteristic of a low resistivity fabric.
Figure 2b, showing the cage voltage of a heat treated experimental
Nomex* felt bag, presents the characteristics of a higher resistivity
fabric. In both voltage traces, the pulse-jet cleaning of the bags
produces a sharp voltage spike, especially when the row of bags
pulsed is that to which the electrometer is attached (Row 1,
Figure 2a). When neighboring rows are pulse-cleaned, the voltage
spike is of opposite polarity and reduced magnitude. The time
constants associated with cage voltage recovery depend strongly on
fabric resistivity, as is evident in the plots of Figure 2.
Among the conclusions drawn in Reference 1 were the following:
1. The electrostatic charge originates primarily because of
triboelectric interactions between the fabric and the
dust. Charges on the dust alone do not dominate the
observed cage voltage, as is made evident by the
*Tradename of E. I. duPont de Nemours and Company.
298
-------
I20r
90
uj 60
o
h 30
-30
-60
-90 L-
DACRON FELT (EST. R - 109 OHMS)
DUST FEED RATE: 9 g/m3 (4 grains/ft3)
AIR/CLOTH: 3 em/see (6 fpm)
PULSE PRESSURE: 0.62 N/mm2 (90 psi)
RELATIVE HUMIDITY: 50%
2 3 I 2
ROW BEING PULSED
a) BAG OF LOW ELECTRICAL RESISTANCE (POLYESTER FELT)
sooor
UJ
UJ
-5000
EXPERIMENTAL NOMEX FELT
(MEASURED R = 5 X 1011 OHMS)
DUST FEED RATE: 9 g/m3
AIR/CLOTH: 3 cm/sec
PULSE PRESSURE: 0.62 N/mm2
RELATIVE HUMIDITY: 50%
b) BAG OF HIGH ELECTRICAL RESISTANCE (EXPERIMENTAL NOMEX FELT)
FIGURE 2. CAGE VOLTAGE FORMS
299
-------
dependence of cage voltage upon fabric type. Switching
fabrics, while maintaining comparable electrical iso-
lation and filtration conditions, causes significant
differences in the observed cage voltage.
2. The pulse-cleaning action creates a voltage spike of
sign and magnitude dependent on the bag charge. In
this sense the pulse-jet cleaning enhances the signal-
to-noise ratio for the detection of electrostatic effects.
3. Pulse-jet cleaning removes charge as well as dust from
the bags during cleaning. When a neighboring row of
bags is pulse-cleaned, the shift in bag charge is
opposite to what it is when the monitored bag's row
itself is pulse-cleaned.
4. Air flow alone produces only small cage vsltages. With the
addition of flyash to the air flow (4 gra.ins/acfm), the cage
voltage increases significantly in magnitude and changes
sign.
Further exploration of the relationship between electrostatic
charge buildup and the resultant cage voltage is one of the two
major purposes of this paper and is discussed next. Following that,
the final section of the paper relates these cage voltages to fabric
filtration performance, the second major purpose of the paper.
300
-------
ELECTRICAL EQUIVALENT CIRCUIT
The measurement of static charges on insulators is most often
performed by an inductive technique such as the Faraday "pail"
method [Reference 11]. In such methods the insulator charges are
not required to move but merely to terminate their lines of force
on charges induced in an adjacent conducting surface. Since that
surface is a conductor, these induced charges can be measured by
direct coupling to a conventional electrometer and a measure of the
insulator charge is obtained even though no direct contact to it
is established.
In the baghouse apparatus employed here, the electrically
conductive cage serves as the "adjacent surface" used to detect the
charges on or in the fabric. The cage, however, is more than
adjacent; it actually makes direct contact with the fabric as well
so that the possibility also exists for direct charge flow from the
fabric to the cage.
A similar relationship couples the cage charge to the baghouse
housing which is electrically grounded. Consequently, at a minimum,
the electrical equivalent circuit should consist of two capacitors
and resistors in series as sketched in Figure 3.
301
-------
HOUSING
CAGE
COLLAR
FABRIC
SURFACE
O VELECTROSTATIC
CAGE
FIGURE 3. BASIC ELECTRICAL EQUIVALENT CIRCUIT
302
-------
The forcing function, V^, . . .. , represents the voltage
created by two separate actions:
1. the electrostatic charge generated on the fabric by the
dust flow, and
2. the fabric motion during the pulse-cleaning of each
row of bags.
If electrostatic charge generation is proportional to gas
flow through the bag, this contribution to the forcing function
could take on a form such as illustrated in Figure 4. This plot,
reproduced from Reference 12, is the calculated gas flow through
one bag of a specific pulse-jet baghouse. This calculation is
for a 4 x 4 matrix of bags but shows the variation of gas flow to
be expected in a pulse-jet baghouse in general. The rapid rise
in flow coinciding with the cleaning pulse comes about because of
the low flow resistance of a freshly cleaned bag--a bag with
little or no filter cake in place. As the cake rebuilds on the
cleaned bag,.the air flow through it decreases rapidly until the
adjacent row is cleaned. The rapid increase in gas flow through
this neighboring bag causes a corresponding rapid decrease in
flow through the monitored bag which subsequently recovers as the
flow through the just cleaned row decreases. And so on for the
remaining rows in the baghouse until the monitored bag is pulse-
cleaned again.
303
-------
cc
CM
I
a
o
DC
X
1,000
o
t 500
u.
o
K
UJ
O
4 8
TIME, MINUTES
FIGURE 4. GAS FLOW RATE THROUGH ONE BAG OF A FOUR-ROW PULSE-JET ARRAY (REF. 12)
-------
Even without a charge generation function of the form illus-
trated in Figure 4, the pulse-cleaning action should induce a
voltage spike on the cage—simply because of the bag motion during
the cleaning. Charge in or on the fabric undergoes a change in
position and hence in capacitive coupling to the cage when the bag
is pulse-cleaned. This action alone causes a cage voltage spike.
In addition the cleaning action can cause a change in the bag
charge; the net bag charge may be changed because of the dust
removed by the cleaning action.
The cage voltage, therefore, depends upon a number of variables
which are not well defined or easy to measure. While the initial
simulation of the cage voltage is being carried out with the simple
circuit of Figure 3, additional elements, as illustrated by the
distributed resistances and capacitances sketched in Figure 5, seem
more realistic and will be added as necessary.
Once having settled upon an adequate equivalent circuit, the
problem becomes one of accurately describing the forcing function.
Many variables could influence the form of the forcing function so
that selecting a realistic representation may be neither trivial
nor obvious. Further experimentation will be carried out in order
to further define its dependencies.
Various combinations of equivalent circuits and forcing func-
tions are now being studied on an Electronics Associates 380 analog
computer as preliminary work in the development of a quantitative
model.
305
-------
FIGURE 5. MODIFIED EQUIVALENT CIRCUIT CONTAINING DISTRIBUTED COMPONENTS
306
-------
RELATIONSHIP BETWEEN FABRIC ELECTROSTATIC
PROPERTIES AND COLLECTION EFFICIENCY
Ultimately, interest in the electrostatic properties of a
dust/fabric system depends upon the relationship between these
electrostatic properties and the performance of the fabric as a
filter for the dust. If electrostatics exert little or no influence
upon filtration performance, interest in the electrostatic
properties of fabric filters will diminish rapidly and rightly
so. If, however, electrostatics are important or are important
under certain conditions, this information should be better known
and increased study of the interaction is warranted.
Evidence is slowly accumulating to suggest that electrostatic
interactions can be important second or even first order effects
in fabric filtration performance [Reference 9]. Some additional
data to further support the significance of electrostatic properties
are presented in this section. Both the data reported here as
well as those in Reference 9 are based on fabric filtration
systems in which the major filtration action comes from conventional,
high performance fabric filters—those which conventionally
filter with collection efficiencies on the order of 99+%. Variation
in the electrostatic properties of the dust/fabric system has
307
-------
been shown in Reference 9 to alter the operating costs of filtra-
tion (by varying the time required between fabric cleaning cycles;
i.e., by influencing the drags and specific cake resistance
during filtration). In this work we show what we interpret to be
an electrostatic influence upon dust cake formation with its
attendant effect upon dust collection efficiency.
Collection Efficiency Experiment
The relationship between electrostatic properties and collection
efficiency suggested itself from independent routine laboratory
evaluation of various fabric filters [Reference 13]. In comparing
the collection efficiency of an experimental Nomex felt with that
of a standard Nomex fabric not having gone through the special
heat treatment associated with the preparation of the experimental
Nomex, a correlation between the observed electrostatic properties
and the collection efficiency was noted. The experimental Nomex
bags exhibited very high cage voltages during filtration--the
highest values seen in our measurements.
At the same time, they filtered redispersed flyash with
uncharacteristically low collection efficiency (~97%). Conventional
Nomex felt bags routinely filter this dust source with efficiencies
in excess of 99%. The fabric manufacturer (DuPont) expressed
surprise at this result and cited his own measurements of collection
efficiency in which similarly prepared experimental Nomex bags
and comparable-weight standard Nomex bags performed similarly
when filtering cement dust. Both filtered cement dust with
collection efficiency in excess of 99%.
308
-------
The thought occurred to us then that the significantly
different cage voltage noted on the experimental Nomex was perhaps
related to the fabric performance as a filter. The reason for the
high cage voltage was hypothesized to be the result of the heat
treatment associated with the preparation of these experimental
fabrics.* During the preparation of these fabrics, the fibers are
exposed briefly (2-3 min) to a temperature of about 315°C (600°F).
This heat treatment probably volatilizes the anti-static coatings
normally found on Nomex, rendering the fabric electrical resistance
much higher than before the treatment. As can be seen from the
equivalent circuits proposed in the previous sections, increasing
the resistance between the cage and ground (R-j in Figure 3) increases
the magnitude of vCaqe» assuming all other parameters, including
the charge generation function, VE, remain constant.
In order to verify the role of the anti-static coating, two
new sets of fabric filters were prepared:
1. The first was the control group, prepared as before,
including the heat treating step.
2. The second group was identical to the first except
that all bags were sprayed with an anti-static coating
after the heat treatment.
*This hypothesis was originated by Dr. H. Forsten, E. I. duPont de
Nemours and Company, Wilmington, Delaware.
309
-------
Table 1 lists the manufacturer's description of the two test
fabrics. The fabrics are nominally identical except for the anti-static
coating of the second fabric.
Results
Electrostatically the two test fabrics, not surprisingly, are not
identical. The control bags exhibited cage voltage spikes in excess of
1000 volts, while the maximum cage voltage of the coated bags was about
50 volts. While not the actual voltage traces recorded on these test
bags, the traces contrasted in Figure 2 correspond roughly to those
recorded on the test bags, Figure 2a representing the coated bag and
Figure 2b, the control.
Table 2 summarizes the measurements of collection efficiency and
outlet concentration. The important conclusion from the data of Table 2
is that the addition of the anti-static coating (Run No. 1) improved bag
collection efficiency over that of the uncoated control bag (Runs No. 2
and 4). The run numbers correspond to the chronological order in which
the measurements were made. When the measurements are made on the same
fabric, the run number tells the order in which the run was made. (In
Table 2, Run 4 followed Run 3 which followed Run 2--all on the same set
of bags.)
Increasing the relative humidity from 50% to 70% improved col-
lection efficiency even more (Run No. 3). At 70%, relative humidity,
the cage voltage changes its character significantly from that
at 50% relative humidity (Figure 2b). The voltage spikes associated
with the cleaning pulse are reduced in magnitude to the order of
310
-------
TABLE 1
EXPERIMENTAL NOMEX TEST BAGS*
(SCRIMLESS FELTS)
BAG SET 2
BAG SET 1 (CONTROL + ANTI-STATIC
(CONTROL) COATING)*
BASIS WEIGHT 17.0 17.4
(oz./yd.2)
THICKNESS 93 89
(mils)
AIR PERMEABILITY 12 17
(cfm/ft2 at 0.5 in. H20)
v»*
•Courtesy of H. Forsten, E. I. du Pont
**Sprayed with 1% "Avitex" DN
311
-------
TABLE 2
BAG PERFORMANCE SERIES
p—'
K)
RUN
NO
1
4
FABRIC
CONTROL WITH ANTI-STATIC COATING
(50% RELATIVE HUMIDITY)
CONTROL ALONE
(50% RELATIVE HUMIDITY)
CONTROL ALONE
(70% RELATIVE HUMIDITY)
CONTROL ALONE
(50% RELATIVE HUMIDITY)
COLLECT.
EFF. (%)
98.7*
97.1
99.3
96.8
OUTLET CONC.
(GRAINS/103 ft3)
44.6*
118
28.2
128
BAG PRESSURE
CHANGE DURING
ONE FILTRATION
CYCLE (in. H20)
"*! ' APf)
0.50
(3.15 - 3.65)
0.20
(2.80 - 3.00)
0.20
(2.80 - 3.00)
0.15
(3.55 - 3.70)
* Average of two runs, 2 days apart
-------
50-70 volts (Figure 6). What also differentiates this cage voltage
trace from that of Figure 2a is the relatively high steady state
voltage evident in Figure 6. The cage signal in Figure 6 is still
better isolated electrically from ground than that in Figure 2a.
Whatever else the high relative humidity does, it seems not to
degrade R-, in the elementary equivalent circuit of Figure 3.
These data immediately suggest that a negative cage bias is a
desirable operating condition. Such a bias could be externally
applied to the cage via the same leads previously used to monitor
the cage voltage. The effectiveness of such a bias depends upon
the values of C? and R? (Figure 3) of any given fabric/dust system,
since the voltage appearing at the physically poorly-defined
Electrostatic tern"na^ of Figure 3 1S most likely what the dust
being filtered will sense.
Any improved collection efficiency anticipated for operation
with a negative bias on the cage did not materialize (Table 3). A
g
bias of -2000 volts applied to all nine cages through a 10 series
resistor produced a cage voltage trace as shown in Figure 7. The
Row 3 cleaning pulse appears to be less effective than those of
Rows 1 and 2, as indicated by the smaller voltage spike associated
with its firing. This condition was also evident in some of the
data presented in Reference 10, and was attributed to blow pipe
misalignment, pressure leaks, or some other condition not involving
electrostatics.
313
-------
200
100
0
-100
-200
EXPERIMENTAL NOMEX FELT
I min
UJ
2 3
ROW BEING PULSED
DUST FEED RATE: 9 g/m3 (4 grains/ft3)
AIR/CLOTH: 3 cm/sec (6 fpm)
PULSE PRESSURE: 0.62 N/mm2 (90 psi)
RELATIVE HUMIDITY: 70%
FIGURE 6. CAGE VOLTAGE DURING FLY ASH FILTRATION AT HIGH RELATIVE HUMIDITY
314
-------
OJ
f—'
Ui
TABLES
CONTROL BAG PERFORMANCE UNDER CAGE ELECTRICAL BIAS
(ALL RUNS AT 50% RELATIVE HUMIDITY)
BAG PRESSURE
COLLECT.ON OUTLET CONC CHANGE «*L HjO)
RUN MQ. CAGE BIAS EFF. (%) (GRAINS/1Q3 tf) 7 (AP, A"''
6 FLOATING 96.6 136 ^8
GROUNDED 98.1
75'9
8 -2000 VOLTS 97.6 97.0 (4.14-4.31)
-------
BAGS
u>
Id
0
-1000
-2000
-3000
9
9
-2000 V ~O9fl V
1 1 "VW '
1 1 1
1 1 1
N *_ _A
23 1
9
9
9
^
2
9
9
9
3
3
2
1
— 1 min »
i i
i 1
. L
1
PULSING ORDER
FIGURE 7. CAGE VOLTAGE UNDER AN EXTERNAL BIAS OF -2000 VOLTS
-------
Table 3 shows that the presence of this electrical bias
doesn't significantly alter the collection efficiency of the
bags--at least not nearly as significantly as the higher humidity
operation did (Run 3, Table 2). The opposite polarity (+2000
volts on the cage) also produced no significant change in collection
efficiency.
In spite of this low sensitivity to bias levels, cage electrical
termination is important as the data of Table 4 show. Low resistance
terminations to the cages are superior to the high resistance,
floating termination; that is, filtration performance with various
cage electrical terminations (Table 4) shows that controlling the
electrical termination of the cage does influence filtration per-
formance. These data show that the coupling between the fabric
charges (the VE terminal, Figures 3 and 5) and the cage is strong
enough to allow different cage terminations to influence enough
of the active filtering surface as to be detectable by the measurement
of collection efficiency. Having the bags tied together electrically
(Run 6, Table 4) does not produce a significant change in performance
from operation with each bag electrically floating alone (Run 4,
Table 4).
The conclusion from the termination and bias data of Tables
3 and 4 is that having a low leakage path for the electrostatically
generated cage charges is more important than any arbitrary cage
voltage level. Operating with the cage at high electrical isolation
from ground degrades collection efficiency. Reducing the cage
electrical isolation (whether by humidity, conductive fabrics or
317
-------
TABLE 4
CONTROL BAG PERFORMANCE AT VARIOUS CAGE ELECTRICAL TERMINATIONS
(ALL RUNS AT 50% RELATIVE HUMIDITY)
RUN NO.
00
CAGE ELECTRICAL
TERMINATION
FLOATING
GROUNDED*
FLOATING*
GROUNDED*
COLLECTION
EFF. (%)
96.8
97.9
96.6
98.1
OUTLET CONC.
(GRAINS/103 ft3)
128
83.8
136
75.9
BAG PRESSURE
CHANGE DURING
ONE FILTRATION
CYCLE (in. H2O)
(APj - APf)
0.15
(3.55 - 3.70)
0.15
(3.55 - 3.70)
0.28
(4.52 - 4.80)
0.18
(4.23-4.41)
*AII nine bags tied together electrically.
-------
direct contact to ground) produces superior performance with
respect to dust collection efficiency.
Charge generation is also part of the overall effect and the
influence of each of these "corrective" actions upon charge generation
is not so clear as their effects upon cage electrical isolation.
The total problem, therefore, has only been partially considered; the
influence of these variables upon VE is yet to be determined.
Polyester Felt Experiment
To better establish the tentative relationship illustrated by
the measurements made on the experimental Nomex fabrics described
in the preceding sections, the experiment was repeated on two sets
of felted polyester bags. Both of these sets of needled Dacron
felt bags have nominal properties as listed in Table 5.
What has been previously shown is that a bag of high electrical
resistance and relatively low collection efficiency can be converted
into a bag of lower electrical resistance and higher collection
efficiency by spraying the bag with an anti-static coating prior to
the filtration tests.
With the two sets of polyester bags (Table 5) the bag electrical
properties were changed in the opposite direction to that of the Nomex
experiment. Initially both sets of bags have been manufactured with
anti-static coatings, the standard procedure. With one set of bags this
anti-static coating was removed, at least partially, by repeated soaking
(no agitation) in perch!oroethylene. Bag resistance increased as a result
of this soaking, presumably because of coating removal.
319
-------
TABLE 5
PROPERTIES OF NEEDLED POLYESTER FELT FABRIC*
WEIGHT (oz/yd2) 16.0
THICKNESS (mils) 58.0
AIR PERMEABILITY 25.9
(pfm/ft2 at 0.5 in. H2O)
•Measurements by FRL, an Albany International Co., Dedham, MA
320
-------
Table 6 shows that the bags from which the anti-static
coating has been removed filter less efficiently than those standard
bags on which it remains.
This result corroborates the results of the experimental
Nomex bag, linking the bag electrical resistance to its filtration
performance. The cage voltage of the soaked polyester felt bags
was, perhaps, an order of magnitude greater than what has been seen
on standard polyester felt bags (Figure 2a). The lone voltage
trace made with the soaked polyester bags was noisier than typical
but the magnitude of the primary voltage spikes was about 500
volts, as compared with 50-70 volts usually seen on the standard
polyester felt bag.
321
-------
TABLE 6
FILTRATION PERFORMANCE OF THE TEST POLYESTER FELTS
FABRIC TESTED
jj» STANDARD POLYESTER
FELT
STANDARD POLYESTER FELT
AFTER MULTIPLE SOAKS
IN PERCHLOROETHYLENE
ELECTRICAL
RESISTANCE
OF MOUNTED
BAGS (ohms)
108 _109
> 1010
COLLECT.
EFF. (%)
99.8
97.2
OUTLET CONC.
(GRAINS/103 ft3)
6.9
111
BAG PRESSURE
CHANGE DURING
ONE FILTRATION
CYCLE (in. H2O)
(APj - APf)
0.10
(1.50- 1.60)
0.10
(2.60 - 2.70)
-------
CONCLUSIONS
1. Bag collection efficiency is highest when:
a) Relative humidity is high (70% is better than 50%).
8 10
b) Fabric resistance is low (10 ohms is better than 10
or 10 ohms).
c) The cage is electrically grounded (grounded cage is
better than floating).
2. These conclusions are valid only for the redispersed flyash
used in these experiments and over the specified range of
the variables considered, but they show that electrostatic
properties can be important in fabric filtration.
323
-------
ACKNOWLEDGMENT
Dr. Herman H. Forsten, Textile Research Laboratory, E. I.
duPont de Nemours and Company, Wilmington, Delaware, provided advice
and assistance in our attempts to relate the cage voltage measure-
ments to the collection efficiency of flyash. He arranged for the
fabrication of the Nomex test bags which were donated by DuPont.
He also advised us on methods for removing the anti-static coating
from the Dacron felts.
324
-------
REFERENCES
1 Rudge, W. A. D., "On the Electrification Produced during the Raising
of a Cloud of Dust," Proceedings of the Royal Society. Vol. XC-A,
pp. 255-272, 1914.
2 Deodhar, G. B., "Electricity of Dust Clouds - Part I," Institute
of Physics and the Physical Society. Proceedings of the Physical
Society. Vol. 39, pp. 243-249, 1927.
3. Kunkel, W. B., "The Static Electrification of Dust Particles on
Dispersion into a Cloud." Journal of Applied Physics, Vol. 21,
pp. 820-832, 1950.
4. Kraemer, H. F. and H. F. Johnstone, "Collection of Aerosol Particles
in Presence of Electrostatic Fields." Industrial and Engineering
Chemistry, Vol. 47. No. 12, pp. 2426-2434, 1955.
5 Rossano, A. T., Jr. and L. Silverman, "Electrostatic Mechanisms in
Fiber Filtration of Aerosols," Report No. NYO-1954, Harvard School
of Public Health, 1955.
6. Rao, K., S. T. Ariman, K. T. Yang and R. L. Hosbein, "Collection of
Dust by Fabric Filtration in an Electrostatic Field." 2nd Annual
Environmental Engineering and Science Conference, Louisville,
April 1972.
7. Makino, E., K. linoya, M. Shibamoto, S. Toyama, and F. Ikazaki,
"Experiments on Electrical.Dislodging of.Dust Layers," Trans. Japan
Chemical Engineers Society. Vol 2. No. 1, pp. 31-37, 1976.'
8. Frederick, E. R., "How Dust Filter Selection Depends on Electrostatics,"
Chemical Engineering, pp. 107-114, June 26, 1961.
9. Penney, G. W. and E. R. Frederick, "Electrostatic Effects in Fabric
Filtration, final report for EPA Research Grant No. R803020, in
preparation.
10. Donovan, R. P., R. L. Ogan, and J. H. Turner, "Electrostatic Effects
in Pulse-Jet Fabric Filtration of Room Temperature Flyash," pres-
entation to the Engineering Foundation Conference, "Theory, Practice
and Process Principles for Physical Separations," Asilomar Conference
Grounds, Pacific Grove, California, October 30 - November 4, 1977.
11. Hersh, S. P., "Resistivity and Static Behavior of Textile Surfaces,"
Chapter 6 in Surface Characteristics of Fibers and Textiles. Part 1,
edited by M. J. Schick, Marcel Dekker, inc., z/u Madison Avenue,
New York, N. Y. 10016 (1975).
325
-------
REFERENCES (Continued)
12. Theodore, L., J. Reynolds, A. Corvini, and A. Buonicore,
"Particulate Control by Pulsed-Air Baghouse Filtration: De-
scribing Equations and Solution," pp. 90-103 in The User and
Fabric Filtration Equipment II. APCA Specialty Conference Proceed-
ings, Buffalo, New York, October 1975, Air Pollution Control Assn.,
4400 Fifth Avenue, Pittsburgh, PA 15213 (1975).
13. Turner, J. H., "EPA Research in Fabric Filtration: Annual Report
on IER1,-RTP In-house Program," EPA-600/7-77-042 (NTIS No. PB
267441/AS), May 1977.
326
-------
To Convert From:
foot
yard
Ib (force)
foot
inch
mil
yard
grain
Ib (mass)
inch of-water (60°F)
Winch? (psi)
foot/mi n (fpm)
foot?
inch.,
yard
oz/yd2
grains/ft
grains/1000 ft
APPENDIX
CONVERSION FACTORS
To:
meter,
meter'
meter'
newton
Multiply By:
,-2
9.29 x 10
6.45 x 10
8.36 x 10
4.45
-4
-1
meter
meter
meter
meter
kilogram
kilogram
2
newton/meter^
newton/mete^
newton/meter
meter/sec
3
meter.
meter..
meter
0
kg/nr
kq/m3
g/nr
3.05 x
2.54 x
2.54 x
9.14 x
6.48 x
4.54 x
2.49 x
6.89 x
4.79 x
5.08 x
2.83 x
1.64 x
7.65 x
3.39 x
2.29 x
2.29 x
10_2
10 i
10 1
10"1
"I?
10 '
10t?
10Ii
10 '
io-2
_9
10-5
10-1
10 '
_2
10 d
ID'3
_ J
10 J
'K = -4 (°F +459.67)
327
-------
328
-------
TEXTILE FILTER MEDIA DURABILITY
Winston F. Budrow
In reviewing the requirements for a textile filter media, three basic pri-
mary functions are generated. The first primary function of the filter media
is to separate and collect suspended particulate matter from a gaseous stream
and allow the cleaned gaseous stream to pass through.
As the filter media collects particulate matter, the fabric achieves a
diminishing return in which the filter media will no longer pass air through
it at an acceptable level. At this point, it becomes necessary to remove the
collected particulate matter and regenerate the filtering qualities of the
filter system. For this reason, cleanability becomes a primary function also.
The filtering and cleaning qualities are referred to as a cycle. The cycles
of filtering and cleaning must be performed in a repetitive fashion, as dic-
tated by economic factors. Therefore, the third primary function is determined,
that of durability. These three primary and equally important functions,
namely: filterability, cleanability and durability, depict the filter media's
ability to perform.
This paper concerns itself with the primary function of durability. Dura-
bility can best be defined as the resistance to the chemical and physical break-
down associated with fabric filtration.
The physical breakdown results generally from the filtering and cleaning
functions, whereas the chemical breakdown results generally from the chemistry
and thermo characteristics of the environment to which the filter media is
being exposed.
Chemical breakdown of the filter media is the most common cause of premature
fabric failure in filtration, primarily due to the fact that it is the least un-
derstood. Synthetic organic fibers are generated through chemical reactions to
form the polymer phase from the monomer phase. In chemistry, chemical reactions
yield the resultant, which indicates the reactions are reversible. There lies
the weak link in fabric technology. Any substance or condition which tends to
reverse or break down the polymer structure of the fiber will cause premature
deterioration of the filter fabric.
In most filtration systems, the one critical ingredient which activates the
chemistry of the dust and the gases is moisture. Normally, dust materials, when
in a dry phase or void of moisture, are relatively inactive; whereas, in the wet
phase or presence of moisture, the dust material or gases are liquified and
329
-------
become chemically very active and attack the fiber structure, either through a
direct reaction or a catalytic reaction. Moisture in itself can cause damage
to certain filter media through hydrolysis or oxidation. These reactions can
be catalyzed or accelerated due to the presence of an acid condition, alkaline
condition and/or temperature elevation.
To combat deterioration situations, a proper fiber selection most resistant
to the environmental conditions is the first primary step. Secondly, by under-
standing the potential chemical activity of the gases and the dust, one can
establish the necessary controls and precautions to be taken for prolonging the
durability of the filter media.
Physical breakdown of the filter media presents a different type of fiber
fatigue or distruction. All fiber filter media will, of course, fail at some
point due to use; however, it is the extension of the physical breakdown which
is of concern to us.
Normal physical filter media breakdown is the result of work performed.
The work performed can be defined as the filtering actions, cleaning actions,
and the stress strain associated with those functions.
The filtering phase is probably the most vulnerable to excess physical
attack,^due to the unpredictable aerodynamics of the air volume. The air volume
in combination with the particulate matter enters the cylindrical filter bag at
high velocities. If the entry is not perpendicular, dust impingement occurs
and gives a sand blasting effect, resulting in premature failure. Even when
the dust entry is perpendicular to the bag, however, attack will occur if the
bag is not properly installed. An improperly installed bag will result in
fabric deformation which allows folds or pleats to be contacted by the high
velocity dust, resulting in the same premature failure.
Naturally, many forms of excessive physical attack can occur due to the
variety of baghouse designs, filter media types and applications. The important
message concerning fabric premature deterioration is to detect the condition and
correct the situation.
^In summary, durability is a primary function of filter media performance
and is the most important subject for proper economical baghouse performance.
Filter media life or durability can be substantially extended in most systems
by a complete investigation and evaluation of filter media which could yield
substantial savings in both the cost of the filter media and the operating costs
involved with baghouses.
330
-------
HIGH-TEMPERATURE FILTRATION
Dr. Dennis C. Drehmel
U.S. Environmental Protection Agency
Research Triangle Park, N.C. 27711
Michael A. Shackleton
Acurex Corporation
Mountain View, Calif. 94042
Abstract
Research on high temperature particle control using ceramic
fiber barrier filtration has shown this technique offers
promise of successful development. Results of testing of rigid
ceramic membrane structures and of ceramic fiber beds including
woven, paper and felt ceramic filters are presented.
331
-------
HIGH-TEMPERATURE FILTRATION
Introduction
Removal of particles from high temperature gas streams
has been studied for many years. Some of the motivation for
this research was the desire to operate coal fired gas tur-
bines.1 Recently there is renewed interest in the utilization
of coal. The processes most actively being studied are pres-
surized fluid bed combustion (PFBC) and gasification combined
cycle (GCC) plants. Both processes are called combined cycle
since they generate power by means of gas turbines as well as
steam turbines.
in the PFBC, coal is burned in a fluid bed of limestone
(which removes the S02) and heat is transferred to.tubes in the
fluid bed. Up to 80% of the recoverable heat value of the coal
is removed in the fluid bed, and the gas exits at 1500°F and
10 atm pressure. The gas must now be expanded through a gas
turbine to recover the remaining energy. However, previous
investigations showed that large particles erode turbine blades
and small particles cause deposits that choke the turbine. To
protect the turbine, some high-temperature particulate control
is required. Moreover, since it would not be economical to
duplicate particulate control for environmental regulations at
another point of the process, high-temperature control must
also meet new source performance environmental standards for
coal-fired utilities. Currently, this allows emissions to be
no greater than 0.1 ft/million Btu.
To meet both the environmental and turbine requirements,
a system consisting of two cyclones and a filter is being
studied. The two cyclones lower the overall particle concen-
tration but fail to remove small particles. Concentrations
leaving the second cyclone can be as high as 1.0 grains/scf
and have a mass median diameter of 5.0 pm. The filter can be
a ceramic bag filter, a ceramic membrane, or a granular bed.
332
-------
Research to date has concentrated on the granular bed since it
has been considered available technology. However, results of
tests at the Exxon PFBG Miniplant have been disappointing.2
The granular beds tested could barely meet the environmental
standard at the beginning of a run and lost efficiency contin-
uously from 95% to as low as 50% within 24 hours. Although
granular bed filters may still prove to be a solution to high-
temperature particle control, it is now apparent that they will
require more developmental work.
Alternative high-temperature filters, using either a
ceramic bag or ceramic membrane, are being developed. The
remainder of this paper will be devoted to describing ongoing
work by the Environmental Protection Agency to assess these
high-temperature filters as part of environmental control for
the PFBC, although it is expected that results can be extrapo-
lated to the GCC or to high-temperature metallurgical operations
Ceramic Membrane Filters
Several ceramic materials in many configurations were
screened as possible high-temperature filters. One of the
most promising materials tested was a ceramic cross flow
monolith produced by 3M Company under the trade name of Therma-
Comb. This material is composed of alternate layers of corru-
gations separated by thin filtering barriers. This type of
configuration affords a large amount of filter surface in a
very small volume. Figure 1 shows a piece of this material
illustrating the construction.
Bench side experiments were conducted in the high-
temperature ceramic test facility at 970°K. Provisions were
made to blow back from the clean side and also down the chan-
nels on the dirty side so that various cleaning schemes could
be investigated. A sequencer was designed to automatically
start and operate the cleaning cycle. A 17 cm diameter by
38 cm deep tubular furnace was used to heat the filter. An
additional furnace was added to preheat the dust-laden air.
333
-------
Figure 1. 3-M Company Thermacomb.
334
-------
Cascade impactors were used to determine the size dis-
tribution of the test dust (limestone). The typical mass median
diameter was 1.4 ym and the geometric deviation was 3.0 urn. There
was some difficulty in maintaining constant feed rate, but dust
3 3
loadings were maintained at levels from 2 gm/m to 7 gm/m .
Typical results for filtering the limestone test dust
with the 3M ThermaComb are summarized in Table 1. Table 2
shows the effect of varying the initial pressure of a 0.6-
second pulse. Table 2 also shows the result of a similar set
of runs except that the pulse time was increased from 0.6
seconds to 5 seconds. These data show that the length of the
pulse does not have much effect on the cleaning results. In
both runs the collection efficiency was very high (99.6 to
100%) at a linear velocity of 0.41 m/min (1.33 ft/min). Using
the 103.4 kPa pressure pulse for cleaning, it was possible to
return to a stable pressure drop across the filter in spite
of the relatively high dust loadings which in these two runs
were 2.6 and 3.75 gm/m .
Tests using the 3M ThermaComb as a filtering media
showed filtering efficiency to be close to 100% even though
the test dust had a mass median diameter of 1.4 ym and a sig-
nificant fraction of sub micron material. Cleanability of the
media was verified in experiments evaluating the effect of
cleaning pulse intensity and duration. It was determined
that the ceramic filter behaved similarly to fabric filters
in that the pressure drop could be attributed to a residual
pressure drop and that across an incompressible cake.
Ceramic Fiber Barrier Filters
Ceramic fibers are produced by several manufacturers.
In general, these materials are sold for refractory insulation
applications. Many of these ceramic fiber materials are pro-
duced in smaller fiber diameters (3 ym) than are generally
335
-------
Table 1. Summary of 3M ThermaComb Performance
Flow rate
3, .
m /nun
Filter area
2
m
Inlet/Concentration
gm/m
Temperature
°K
Efficiency
Percent
Average Range Tested
0.095 0.04 - 0.16
0.0227
3.6
990
96.6
2.2 - 5.4
953 - 1088
85 - 99.6
Table 2. Effect of Changing Cleaning Conditions
Pulse
Test Pressure
Number KPa
1 34.5
1 69.0
1 103.4
2 103.4
2 103.4
Pulse
Duration
seconds
0.6
0.6
0.6
0.6
5
Cycle
Time*
minutes
2-4
8
12 - 20
12
12
Residual Pressure
KPa
3.5 increasing to
3.0 increasing to
2.8
2.8
2.8
Drop
limit
limit
*as required to lower pressure drop away from the upper limit
available for filtration applications at room temperature (20 urn)
This smaller fiber diameter, coupled with high temperature and
corrosion resistance characteristics, makes these fibers
intriguing candidates for high-temperature filtration
applications.
336
-------
Available ceramic fiber configurations can be classified
into the following three groups of materials:
* Woven structures - cloth woven from long-filament
yarns of ceramic fibers
• Papers — Ceramic structures produced from short
lengths of fibers, generally held together with
binders.
• Felts — Structures produced to form mats of relatively
long fibers. These materials are known as blankets in
the insulation industry. They tend to be less tightly
packed than conventional felt materials.
Theory
Filtration theory supports the contention that ceramic
fiber filters should perform adequately at high temperatures
and pressures.
There are three particle collection mechanisms generally
considered to account for the performance of a bed of fibers in
removing particles from gas streams. These mechanisms are:
direct interception, diffusion, and inertial impaction. Exam-
ining these mechanisms under high temperature and high pressure
(800°C and 10 atm) indicates that direct interception and dif-
fusion will be roughly the same as their performance at room
temperatures and ambient pressures, while the inertial impac-
tion mechanism will be slightly less effective at high temper-
atures and pressures. This statement is true when comparing
the performance of a clean filter bed (no dust cake) at low
temperature/pressure and at high temperature/pressure. This
relatively minor performance reduction can be compensated for
in the design of the filter media. For example, using smaller
diameter fibers in the filter bed can increase collection
efficiency far more than the viscosity effect of high temper-
ature reduces it. A fiber bed consisting of 3 ym diameter
337
-------
fibers, as compared with 20 ym fibers, can be expected to pro-
vide equal collection efficiency with a 3 ym fiber bed weighing
only one tenth as much on a weight per unit area basis. Figure
2 presents a calculated prediction of collection efficiency
for a 3.0 ym fiber bed, consisting of alumina fibers, collect-
ing a 0.5 ym fly ash particle from an air stream at 815°C and
10 atm pressure. The four curves show that for a decrease in
solidity* (a) a reduction in efficiency, for a given basis
weight, should be expected. Similarly, an increase in airflow
velocity causes a small reduction in collection efficiency for
a given filter bed (constant basis weight). Note also that by
adding fibers (increasing basis weight), all of these effects
can be nullified.
The magnitude of predicted efficiency is also interest-
ing. This analysis shows that for a ceramic fiber bed consist-
ing of 3.0 ym alumina fibers a basis weight of 500-600 g/m2
should provide 80 to 90 percent collection of a 0.5 ym particle
even at the reduced performance levels encountered at high
temperatures and pressures.
For comparison, a standard filter media consisting of
20 ym fibers and having a basis weight of 540 g/m2 (16 oz/yd2)
can be expected to collect only about 20 percent of 0.5 ym
particles at room ambient conditions. Thus, to provide collec-
tion efficiency performance equal to a conventional filter
requires only about one-tenth the weight of fibers for a 3.0
ym fiber bed. Or, put another way, a ceramic fiber bed of
equal media weight to a conventional filter, but made from 3.0
ym fibers, will be much more efficient even at high tempera-
tures and pressures than is normally sufficient in the filtra-
tion industry.
'Solidity (a) is the fraction of the fiber bed which is solid
°f °'°2 ±ndicates that 2* °f the bed ifoccupLd
338
-------
COLLECTION EFFICIENCY — %
g g 2 S
"•*)
H-
fD
NJ
o
0)
M
o
ft
ft)
(0
3
0)
E
(D
U)
•c
3
0)
H
d
3
H-
hh
H-
tr
tr
(D
bo o
H
(O t
I ~-. 3
Is
>
TJ
O
m
A-I87O4
-------
Room Ambient Filter Media Tests
A large number of ceramic fiber filter media candidates
have been subjected to a series of filtration tests at room
ambient conditions. These tests included some examples of con-
ventional filter media for comparison. Included among the
tests were:
• Dioctylphtalate smoke (D.O.P) penetration as a
function of air flow velocity
• Determination of maximum pore size (in micrometers)
• Measurement of permeability
• Flat-sheet dust loading tests using A.C. Fine test
dust. Over-all collection efficiency and dust
loading required to develop 3.7 KPa (15 in H?0)
pressure drop are determined from this test which
is operated at 10 cm/sec (20 ft/min) Air-to-cloth
ratio.
Data collected from these tests are summarized on Table 3.
Penetration tests using D.O.P. smoke measure the ability
of the clean fiber bed to stop fine particles. The D.O.P.
smoke generator is adjusted to provide a nominal particle size
of 0.3 um diameter which is a "most penetrating" particle size
because of the minimal effect of diffusion and inertial impac-
tion at this particle size. The D.O.P. test results should
correlate well to the results predicted by analysis since
particle collection is provided only by the fibers and not
by the dust cake. Figure 3 provides a plot of the OOP effi-
ciency as a function of air flow velocity for all the media
tested. Ceramic media data are plotted in solid lines and con-
ventional media in dotted lines. Numbers on the curves refer
to those on Table 3. Several interesting observations can be
made concerning this data:
• Several of the ceramic materials, especially the
ceramic papers and felts, are capable of higher
340
-------
100
90
80
70
0)
•g 60
V)
a.
O
O
| 50
CO
o
:p 40
20
10
0
25
34
15
Figure 3,
5 10
Airflow Velocity cm/sec
D.O.P. Efficiency fn airflow velocity.
341
-------
Table 3
SUMMARY ROOM AMBIENT TEST DATA
N>
(W) Woven
(P) Paper
(F) Felt
1. Carborundum Fiberfrax cloth
(W) with nichrome wire insert
2. Zircar Zirconia felt ZFY-100
(F)
3. ICI Saffil alumina paper
(P) with binder
4. ICI Saffil mat
(F)
5. Babcock & Wilcox Kaowool
(F)
6. Carborundum Fiberfrax
(F) durablanket
7. John Mansville Fiberchrome
(F)
8. Stevens Astroquartz
(W) style 581
9. Hitc-0 Refrasil C-100-96
(W) heat cleaned
10. Hitco Refrasil C-100-48
(W) not heat cleaned
11. Stevens Astroquartz cloth
(W) style 570
12. 3M AB-312 basket weave
(W) cloth
Basis
Weight
1366
615
165
355
746
1363
1297
283
1284
667
677
311
Percent
Efficiency
on ACF @
10 cm/sec
(20 ft. min)
96.55
95.64
99.805
98.74
98.464
99.507
99.654
60.77
81.97
83.37
56.83
51.38
Dust Loading
g/m2 to 3.735 KPa
(g/ft2 to 15" H2O)
239.9
(22.2912)
Media Fractured
159.4
(14.81)
Media Fractured
118.2
(10.980)
146.9
(13.6523)
253.9
(23.59)
Test Stopped —
Low Eff.
5.9
(.5482)
11.56
(1.074)
Test Stopped
Low Eff.
Test- Stopped
Low Eff.
Permeability
cm3/sec/cm2 for 0.1245 KPa
(ft3 /miry ft2 for 0.5" #2° AP)
8.687
(17.1)
10.861
(21.38)
9.307
(18.32)
12.395
(24.4)
8.067
(15.88)
5.583
(10.99)
11.897
. (23.42)
37.236
(73.3)
1.240
(2.44)
3.099
(6.1)
22.758
(44.8)
13.553
(26.68)
Maximum
pore size
Micrometers
248.6
59
43
61.1
66.9
68.2
112.3
248.6
112.3
133.8
267.7
870
Percent Efficiency on
0.3 Mm OOP at cm/sec
2.68 5.35 14.22
45 47 50
75 70 72
82 65 62
79 80 73
96.5 93.5 86
97.1 94.6 90.5
78 73 74
0 9 12
0 19 34
0 11 10
0 13 32
0 5 8
-------
Table 3 (Continued)
OJ
13.
(W)
14.
(W)
15.
(W)
16.
(W)
17.
(W)
18.
(W)
19.
(W)
20.
(W)
21.
(W)
22.
(F)
23.
(W)
24.
(W)
(W) Woven
(P) Paper
(F) Felt
3M AB-312 twill weave
cloth
HITCO Refrasil cloth
UC-100-48
Zircar Zirconia cloth
ZFY-30A
FMI-Stevens Astroquartz
cloth crowfoot satin
3M AB-312 twill weave
cloth coated with 3M
coating
3M AB-312 basket weave
cloth coated with 3M
coating
3M AB-312 twill weave
cloth Menarde coating
HITCO Kefrasil cloth
UC-100-96 not heat
cleaned
Carborundum Fiberfrax
no insert wire L-126TT
HITCO Refrasil batt B100-1
HITCO Pefrasil standard
not heat cleaned
very thin UC-100-28
HITCO Irish Refrasil
chromized C-1554-48
Basis
Weight
g/m2
231
643
60S
352
227
281
254
1249
1544
807
335
683
Percent
Efficiency
on ACF @
10 cm/ sec
(20 ft. min)
48.55
69.26
99.014
76.19
47.64
45.65
55.078
68.46
99.21
99,229
84.41
81.476
Dust Loading
g/tn2 to 3.735 KPa
(g/ft2 to 15" H20)
Test Stopped
Low Eff. (same)
21.3
(1.98024)
88.1
(8.1853)
91.6
(8.5057)
Test Stopped
Low Eff.
Test Stopped
Low Eff.
Test Stopped
Low Eff.
13.68
(1.2708)
173.5
(16.1213)
169.1
(15.706)
22.88
(2.1257)
11.97
(1.1116)
Permeability Maximum Percent Efficiency on
cm3/sec/cra2 for 0.1245 KPa pore size 0.3 urn DOP at cm/sec
(ft3/"un/ft2 for 0-5" H20 AP> Micrometers 2.68 5.35 14.22
28.448 435 032
(56)
8.687 193.3 043
(17.1)
5.791 248.6 29 37 34
(11.40)
16.556 267.7 056
(32.59)
65.181 870 0 3 10
(128.31)
47.595 __ 580 ' 070
(93.69)
51.211 580 0 6 10
(100.81)
3.414 316 0 11 16
(6.72)
7.447 91.6 55 55 57
(14.66)
8.900 64.4 84 79 72
(17.52)
11.897 139.2 010
(23.42)
5.121 124.3 2 8 10
(10.08)
-------
Table 3 (Concluded)
Percent
Efficiency
25.
(P)
26.
(P)
27.
(P)
28.
(W)
29.
(W)
30.
(W)
31.
(W)
32.
(W)
33.
(F)
34.
(W)
(W) Woven Basis
(P) Paper Weight
(F) Felt g/m2
Carborundum Piberfrax 604
paper (with binder) 970J
ICI Saffil Zirconia paper 212
(with binder)
Carborundum Fiberfrax 152
paper (no binder) 970-AH
3M AB-312 double thick 1035
plain weave
FMI crowfoot satin cloth 905
astroquartz
3M AB-312 12 harness satin 675
weave
630 Tuflex fiberglass* 564
15-011-020 woven filment* 175
polyester
25-200-070 polyester felt* 524
HITCO Refrasil cloth (std) 637
not heat cleaned, med.
thickness
on ACF @ Dust Loading
10 cm/sec g/m2 to 3.735 KPa
(20 ft. min) (g/ft2 to 15" H2O)
99.99 73.7
(6.8442)
93.20 82.2
*Probable hole (7.6374)
99.91 84.4
(7.8369)
43.86 Test Stopped
Low Eff.
40.08 Test Stopped
Low Eff.
53.73 Test Stopped
Low Eff. ,
93.982 47.6
(4.4187)
96.078 28.0
(2.60163)
99.193 135.3
(12.5688)
48.40 34.5
(3.2063)
Permeability Maximum Percent Efficiency on
cm3/sec/cm2 for 0.1245 KPa pore size 0.3 ym OOP at cm/sec
(ft3/min/ft2 for 0.5" H2O AP) Micrometers 2.68 5.35 14.22
26.899 47.7 99.5 99.0 97.6
(52.95)
8.692 37.4 83 78 74
(17.11)
12.416 43.5 88 - 73
(24.44)
84.836 too large to 0 10 41
(167) measure with
our equipment
62.078 497 0 10 32
(122.20)
75.529 696 0 8 24
(148.68)
16.038 174 10 9 19
(31.57)
6.828 74 604
(13.44)
11.897 128.9 34 24 29
(23.42)
6.934 -
(13.65)
#These materials are conventional (not ceramic) media.
-------
efficiency collection of fine particles than are
media normally used successively in commercial
filter units.
* Many of the woven ceramic materials had zero D.O.P.
efficiency at low velocity and higher D.O.P. effi-
ciency at higher velocity.
This is contrary to what theory suggests and to the
behavior normally seen in tests of conventional
filter materials. A likely explanation for this
performance is that it is caused by the presence of
many large pores in the media. Examination of the
pore size data in Table 3 shows that the woven
ceramic materials as a group are characterized by
larger pore size than are conventional filter materi-
als. Thus, at low airflow velocity, most of the flow
passes through the large pores and little filtration
takes place. As velocity is increased, flow through
the large pores becomes restricted and some of the
flow is caused to pass through smaller pores where
more filtration can take place.
• The D.O.P. data also supports the theoretical analy-
sis. Efficiency as a function of basis weight for
selected ceramic materials is plotted in Figure 4.
The materials selected are ceramic papers and felts.
These materials provide a fiber bed similar to that
for which the analysis summarized in Figure 2 was
based. Figure 4 shows that the nominally 3 ym fibers
do indeed provide higher collection efficiency on a
weight-per-unit area basis than conventional media
produced with larger diameter fibers.
Maximum pore size data shows that many of the woven
ceramic materials had pores larger than those characteristic
345
-------
200 400 600 800
Basis Weight — gm/cm2
1000 1200
1400
Figure 4. D.O. P. efficiency fn basis weight,
346
-------
of filter materials. Also, many of the felt and paper materials
had pore sizes similar to those of conventional filter materials.
Permeability is measured as the flow per unit area at a
constant pressure drop. Thus, a material with low permeability
offers a high restriction to gas flow and one with high perme-
ability allows more gas to penetrate for a given pressure drop.
Table 3 shows that some ceramic materials are available which
have low permeability, while others have high permeability.
Some of the woven materials have low permeability and large
pore size, while others have high permeability and large pore
size. Most of the paper and felt materials have permeability
similar to that of commonly used filter materials.
Flat sheet dust loading tests were performed as follows:
A 7.62 cm (3 inch) diameter disc of media is suspended across
an air stream which is maintained at 10.16 cm/sec (20 ft/min)
velocity through the filter media. In this test the media
supports itself against the pressure drop (no screen is used).
Standard A.C. Fine test dust (0-80 pm silica) was fed to the
3 3
media at a nominal rate of 0.883 g/m (0.025 g/ft ) until a
pressure drop of 3.735 KPa (15 in H20) is reached. Pressure
drop as a function of time is monitored during the test. This
data is presented in Figures 5, 6, and 7 for selected materials.
2
From the data collected, dust loading (g/m ) necessary to cause
a given pressure drop 3.735 KPa (15 in H?0) is determined.
Examination of this data in Table 3 shows that some of the woven
materials reached high pressure drops while collecting only a
small weight per unit area of dust. This is true also of the
commercial woven materials (items 31 and 32). Other woven
ceramics were penetrated so severely that they would not develop
a pressure drop of 3.735 KPa (15 in H?0).
Two of the non-woven samples (which were unsupported)
fractured as a result of the pressure drop across them. Several
of the ceramic paper and felt materials exhibited dust loading,
similar to that which is expected from conventional filter
papers and felts.
-------
Pressure Drop ~- KPa
CD
-------
A.C. Fine Test Dust
0.883 g/M3
A/C 10.16 cm/sec
10 20
Time ~ Minutes
30
40
Figure 6. Dust loading of ceramic paper.
349
-------
CO
Ol
o
AC Fine Test Dust
0.883 g/m 3
A/C 10.16 cm/sec
#31, 32 Conventional Woven Filters
10
20
30
40 50
Time ~ Minutes
60
70
80
Figure 7. Dust loading of woven ceramic media.
-------
The flat sheet loading tests also provided overall col-
lection efficiency (mass basis) data for the tested materials.
Dust penetrating the media was collected in an absolute filter
downstream of the test media. Table 3 reveals that most of
the woven ceramic materials did not achieve high collection
efficiency in this test. On the other hand, woven commercial
materials were only moderately efficient. Several of the
ceramic paper and felt materials, however, did provide collec-
tion efficiency of 99 percent or better. The two materials
which fractured would have provided higher efficiency perform-
ance had they not fractured. The test was stopped as soon as
the fracture was detected.
General Conclusions from Room Ambient Tests
• Several of the ceramic paper and felt materials are
capable of removing fine particles at high efficiency
without excessive filter weights.
• The ceramic paper and felt materials have filtration
characteristics and performed similar to paper and
felt commercial filter media in a series of filter
media tests.
• The ceramic woven materials in general were charac-
terized by large pores and poor collection effi-
ciency in the dust loading tests. The range of
parameters exhibited by the various materials, how-
ever, indicate that an acceptable woven ceramic
filter media can probably be fabricated, but such
a filter media would have the same limitations as
currently available woven filters. That is, accept-
able performance is only probable at low air-to-
cloth ratios.
351
-------
* "Blanket" ceramic fiber materials (felts) consisting
of small diameter fibers (3.0 ym) appear to be the
most promising materials for high temperature and
pressure tests because of their combination of good
filtration performance and relatively high strength.
High Temperature/Pressure Tests
Two major questions concerning the suitability of ceramic
fibers for filtration need to be answered. These are:
1. How durable are ceramic fiber structures when sub-
jected to environmental conditions associated with
filtration applications.
2. How well do ceramic fibers perform as filters in the
HTHP environment.
Some preliminary answers are available concerning the first of
these questions.
Three ceramic filter media configurations have survived
a test during which the filter elements were subjected to 50,000
cleaning pulses. The objective of these tests was to simulate
approximately one year of operation of mechanical loads on the
media at high temperature and pressure. Test conditions were
as follows:
Temperature — 815°C
Pressure - 930 KPa
Air-to-cloth-ratio - 5 to one (2.54 cm/sec)
Cleaning pulse pressure — 1100 KPa
Cleaning pulse interval — ~10 seconds
Cleaning pulse duration — 100 m second
Dust — recirculated fly ash
The three filter media configurations tested were:
• Saffil alumina mat contained between an inside and
an outside layer of 304 stainless steel knit wire
screen. Figure 8 shows how easily the residual
352
-------
Figure 8. Saffil Alumina—Post Test Dust Cake (Clean strip using Vacuum Cleaner)
353
-------
dust cake was removed from this media after the
test.
• Woven Fiberfrax cloth with nichrome wire scrim
insert. Figure 9 shows the dust cake following
the 50,000 Pulse test.
• Fiberfrax blanket contained between an inside and
an outside cylinder of 304 stainless steel square
mesh screen similar to common window screen. The
ceramic fiber blanket was held in position between
the screens with 302ss wire sewn between the screens.
This resulted in about 100 penetrations of the ce-
ramic fiber bed. Figure 10 shows the dust cake fol-
lowing the test.
Pressure drop during the tests was controlled by the rapid clean-
ing pulses and in general remained less than about 5 KPa (20 in
H20).
Dust penetrating the ceramic test media was collected
on a high efficiency filter located downstream (after cooling)
of the test chamber. This data is not reported for the Saffil
Alumina or for the Woven Fiberfrax Cloth because of a leak
discovered in a gasket in the test rig. This problem was cor-
rected before the fiberfrax blanket test was performed. Average
outlet loading during this test was 0.0055 g/ m3 (0.0024 gr/ ft3).
Figure 10 shows that the dust was concentrated near the places
where wire penetrated the filter element. This concentration
of dust near the wire penetration points could be seen on the
inside of the element also. Thus, most of the dust which pene-
trated apparently did so through the holes made by the wires.
It is reasonable to expect that a filter element without holes
will experience less penetration. Also a less frequent clean-
ing pulse interval will reduce penetration. Therefore even
better performance than that achieved in this test should result
from future tests.
354
-------
Figure 9. Woven Fiberfrax - Post Test Dust Cake
355
-------
Figure 10. Fiberfrax Blanket - Post Test Dust Cake
356
-------
Conclusions
Research on bench scale indicates that fine particle
control at high temperature and pressure can be achieved using
barrier filtration by ceramic filter beds. Evidence in support
of this contention includes the following:
• A theoretical basis exists for it.
• Room temperature tests show that particles including
fine particles are collected at high efficiency.
• Tests at high temperatures and pressures show that
several ceramic filter structures are capable of
surviving in excess of 50,000 cleaning pulses while
maintaining pressure drop at acceptable levels and
providing efficiency close to the lowest reported
turbine requirements.
REFERENCES
Hazard, H. R., "Coal Firing for the Open-Cycle Gas Turbine."
Proceedings of the Joint Conference on Combustion, 1955, ATME
and IME.
Hoke, R., "Ducon Gravel Bed Filter Testing," EPA/ERDA Sym-
posium on High Temperature/Pressure Particle Control,
Washington, D.C., Sept. 1977.
357
-------
358
-------
SYMPOSIUM ATTENDEES
K. P. ANANTH
Midwest Research Institute
425 Volker Blvd.
Kansas City, MO 64110
GRANT D. APPLEWHITE
American Air Filter Co., Inc.
215 Central Avenue
Louisville, KY 40277
MARYLIN ARDELL
Mcllvaine Company
2970 Maria Ave.
Glenview, IL 60025
B. ARNOLD
SF Products Canada Ltd.
4480 Cote de Liesse Road
Montreal, Quebec
Canada H4N 2R1
PAUL ATLAS
J. P. Stevens & Company
141 Lanza Ave.
Garfield, NJ 07026
JAMES BALL
Midland-Ross Corp.
Capitol Castings Div.
P.O. 750
Phoenix, AZ 85001
JOHN BARANSKI
General Battery Corporation
Box 1262
Reading, PA 19603
DUANE BECKNELL
Lear Siegler, Inc.
74 Inverness Drive East
Englewood, CO 80110
WALLACE P. BEHNKE
E. I. du Pont de Nemours & Co., Inc.
701 Bldg. Chestnut Run Location
Wilmington, DE 19898
STEVE BELLMORE
Fabric Filters
525 South Hayden Rd.
Tempe, AZ 85281
LARRY BENNETT
Fabric Filters
525 South Hayden Rd.
Tempe, AZ 85281
ROBERT P. BENNETT
Apollo Chemical Corp.
35 South Jefferson Road
Whippany, NJ 07981
LUTZ BERGMANN
Milliken & Company
1304 Washington Street
LaGrange, GA 30240
CARL H. BILLINGS
Arizona Bureau of Air Quality Control
1740 West Adams St.
Phoenix, AZ 85007
GERRIT W. BLYDORP
Mobay Chemical Corp.
Baytex Fibers Div.
425 Park Avenue
New York, NY 10022
JOHN BRANCACCIO
Western Electric Company
222 Broadway
New York, NY 10038
ROGER I. BRANDSTETTER
Industrial Filtration Inc.
1500 Daisy Ave.
Long Beach, CA 90813
FREDERICK E. BRANDT
Johns-Manville Sales Corp.
Ken-Caryl Ranch
Denver, CO 80217
359
-------
WILLIAM J. BRINKMAN
Magna Copper Co.
P.O. Box M
San Manuel, AZ 85631
PETER R. CAMPBELL
Globe Albany Filtration
2405 West University
Tempe, AZ 85281
J. MICHAEL CANTY
Viking Sales Co.
Box 50025
Tucson, AZ 85703
STEPHEN V. CAPONE
GCA Corporation
GCA/Technology Division
Burlington Road
Bedford, MA 01730
BENGT CARLSSON
Bahco Systems, Inc.
3402 Oakcliff Rd., Suite B-l
(P.O. Box 48116-Atl 30362)
Atlanta, GA 30340
HUNG BEN CHU
Los Angeles Department of
Water & Power
111 N. Hope St.
Los Angeles, CA 90051
W. A. CHENEY
United Air Specialists
6665 Creek Rd.
Cincinnati, OH 45242
PETER CHMARA
Mines Accident Prevention
Association of Ontario
290 Second Ave. West
North Bay, Ontario
Canada P1B 3K9
JACK CLEMENTS
Standard Havens, Inc.
8800 E. 63rd
Kansas City, MO 64133
JOHN F. COBIANCHI
J. P. Stevens & Co., Inc.
1185 Avenue of the Americas
New York, NY 10036
WILLIAM COLUMBUS
Arizona State BAQC
5055 E. Broadway C-209
Tucson, AZ 85204
ROBERT C. COMER
W. W. Criswell Co.
800 Industrial Highway
Riverton, NJ 08077
EDWARD B. COOPER
W. L. Gore & Associates, Inc.
104 Bent Lane,
Newark, DE 19711
FLOYD B. CORONER
State of Utah Department of Health
150 West North Temple
P.O. Box 500
Salt Lake City, UT 84110
RICHARD T. COX
Huyck Felt-Division of Huyck Corp.
Washington Street
Rensselaer, NY 12144
FRED CROWSON
Naval Surface Weapons Center
Code CG-31
Dahlgren, VA 22448
VICTOR M. DAY
Lear Siegler Inc.
74 Inverness Dr. E.
Englewood, CO 80110
EDWARD DE GARBOLEWSKI
W. L. Gore & Associates, Inc.
P. 0. Box 1220, Rt. 213 North
Elkton, MD 21921
RONALD L. DEPOE
J. P. Stevens & Co., Inc.
1185 Avenue of the Americas
New York, NY 10036
360
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GORDON A. DICK
Wheelabrator - Canada
235 Speers Rd.
Oakville, Ontario
Canada L6H-2K9
THOMAS DONNELLY
Donaldson Company, Inc.
P.O. Box 1299
Minneapolis, MO 55440
DAN DOYLE
Flakt, Inc.
1500 East Putnam Ave.
Old Greenwich, CT 06870
DELMAR J. DOYLE
American Air Filter Co., Inc.
215 Central Avenue
Louisville, KY 40277
T. REGINALD DRISCOLL
Globe Albany - Canada
Morrow
Barrie, Ontario
Canada
STEPHEN B. DUERK
J. P. Stevens & Co., Inc.
1185 Avenue of the Americas
New York, NY 10036
JOHN M. EBREY
Lodge-Cottrell
601 Jefferson
Houston, TX 77005
HEINZ ENGELBRECHT
Wheelabrator-Frye
600 Grant St.
Pittsburgh, PA 15219
DONALD R. ENNS
Endur Limited
5379 Fairview St.
Burlington, Ontario
Canada L7L 5K4
DAVID S. ENSOR
Meteorology Research, Inc.
464 W. Woodbury Rd.
Altadena, CA 91001
P. S. ESHELMAN
General Motors Corporation
Industrial Hygiene Dept.
GM Technical Center
Warren, MI 48090
REGINALD G. EVANS
Canadian Johns-Manville Co.
P.O. Box 1500
Asbestos, Quebec
Canada J1T3N2
J. P. PAGAN
E. I. du Pont de Nemours
85 Mill Plain Rd.
Fairfield, CT 06430
L. W. FERGUSON
Owens-Corning Fiberglas Corporation
P. 0. Box 415
Granville, OH 43023
PETER FINNIS
Wheelabrator - Canada
235 Speers Rd.
Oakville, Ontario
Canada L6H-2K9
E. R. FREDERICK
Air Pollution Control Association
P.O. Box 2861
Pittsburgh, PA 15230
GENE FREDERICK
Clark-Schweble Fiber Glass Corp.
14530 South Anson Ave.
Santa Fe Springs, CA 90670
ROBERT E. FREY
Torit Div. Donaldson
P.O. Box 43217
St. Paul, MN 55164
DALE A. FURLONG
Buell Division of Envirotech Corporation
200 N. Seventh Street
Lebanon, PA 17042
JOHN H. FURSE
Rexnord APC Div.
3300 Fern Valley Rd.
Louisville, KY 40213
361
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R. G. GARCIA
Duval Sierrita
Box 125
Sahuarita, AZ 85629
ROGER L. GIBBS
Naval Surface Weapons Center
Code CG-31
Dahlgren, VA 22448
RONALD GITTELSON
Southern Silk Mills
Spring City, TN 37381
HARRY J. GIULIANI
Wheelabrator-Frye Inc.
600 Grant Street
Piitsburgh, PA 15219
A. GOMEZ
Duval Corp.
4715 E. Ft. Lowell Rd.
Tucson, AZ 85712
MANUEL GONZALES
Los Alamos Scientific Laboratory
P.O. Box 1663
Los Alamos, NM 87545
EUGENE E. GRASSEL
Donaldson Co. Inc.
P.O. Box 1299
Minneapolis, MN 55440
PAUL GRIM
Stearn Rogers
700 S. Ash St.
P.O. Box 5888
Denver, CO 80217
THERON GRUBB
Burlington Glass Fabrics Co.
110 Andrew St.
Greenboro, NC 27406
ARNOLD G. GRUSHKIN
Research-Cottrell, Inc.
P.O. Box 750
Bound Brook, NJ 08805
THOMAS L. HARSELL, JR.
Harsell Engineering Corp.
10,000 Santa Monica Blvd., Suite 307
Los Angeles, CA 90067
BARRY J. HASWELL
Blast-Tech Ltd.
1100 Invicta Drive, Unit 12
Oakville, Ontario
Canada L6H-2K9
TOM HAYES
3M Company
3M Center, Bldg. 230-BE
St. Paul, MN 55101
J. M. HENRICKS
Tucson Gas & Electric
P.O. Box 711
Tucson, AZ 85702
RICHARD B. HOGUE, JR
Viking Sales Co.
Box 50025
Tucson, AZ 85703
MARK HOLCOMBE
Chromalloy, Textile Service Division
900 N. Alvarado
Los Angeles, CA 90026
ROBERT P. HOSEMANN
Pacific Gas & Electric
77 Beale Street
San Francisco, CA 94106
RICHARD G. HOSPER
MRI
464 W. Woodburg Rd.
Altadena, CA 91001
CHARLES B. HOTCHKISS
Menardi-Southern
1201 Francisco St.
Torrance, CA 90502
TOM HOYNE
Buell - Envirotech
7462 N. Figueroa St.
Los Angeles, CA 90041
362
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JACK D. JONES
Southwestern Public Service Company
Box 1261
Amarillo, TX 79170
INGEMAR KARVEGARD
Bahco Systems, Inc.
3402 Oakcliff Rd., Suite B-l
(P.O. Box 48116 - Atl. 30362)
Atlanta, GA 30340
MICHAEL T. KEARNS
Air Pollution Sysrems Inc.
1114 Andover Park West
Tukwilla, WA 98188
THOMAS P. KELLY
Clark-Schwebel Fiber Glass Corp.
5 Corporate Park Drive
White Plains, NY 10604
WILLIAM KELLY
Environmental Elements
7249 National Drive
Hanover, MD 21076
STANLEY K. KEMPNER
Western Electric
222 Broadway
New York, NY 10038
THOMAS J. KILEY
Griffin Environmental Company, Inc.
P.O. Box 86
Baldwinsville, NY 13027
JERRY KRAIM
Stansteel Corporation
5001 S. Boyle Avenue
Los Angeles, CA 90058
PAUL LANGSTON
DuPont Co.
114 Mulberry Rd.
Newark, DE 19711
G. D. LANOIS
Wheelabrator-Frye Inc.
600 Grant St.
Pittsburgh, PA 15219
RICHARD C. LARSON
Torit Division
Donaldson Co. Inc.
1133 Rankin St.
St. Paul, MN 55165
JOE LEDBETTER
University of Texas at Austin
Cockrell Hall
Austin, TX 78712
WAYNE H. LEIPOLD
Phelps Dodge
P. 0. Drawer E
Douglas, AZ 85607
BENJAMIN LINSKY
West Virginia University
Fattersall House
Morgantown, WV 26506
W. 0. LIPSCOMB
Acurex/Aerotherm
c/o EPA Research Triangle Park
Durham, NC 27711
JOE LOFLIN
Texas A & M University
Zachery Bid. Ind. Eng.
College Station, TX 77840
ROBERT L. LUCAS
E. I. DuPont
Louviers Bldg.
Newark, DE 19711
CARL E. LUNDBERG
Contamination Control, Inc.
1310 Genoa
So. Houston, TX 88587
TSHIEN MA
Buell Div. of Envirotech
200 North Seventh St.
Lebanon, PA 17042
TERRY MACRAE
Industrial Clean Air
2929 Fifth St.
Berkeley, CA 94710
363
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BRIAN MEAD
DuPont Company
PP&R D 13126
Wilmington, DE 19898
MANAN MEHTA
Mikropul Corp.
10 Chatham Rd.
Summit, NJ 07901
ROBERT C. MEYER
Envirotech Corporation
P.O. Box 1211
Salt Lake City, UT 84117
JAMES A. MITCHELL
Lodge-Cottrell-Dresser
601 Jefferson, 27th Floor
Houston, TX 77005
FRED MORENO
Acurex Corporation
485 Clyde Ave.
Mountain View, CA 94042
ANDY MURPHY
Acurex Corporation
3301 Womens Club Drive, Suite 147
Raleigh, NC 27611
WALLACE G. MURRAY
Cities Service Co.
P. 0. Drawer 1149
Franklin, LA 70538
RAYMOND Z. NAAR
Huyck Research Center
Washington Street
Rensselaer, NY 12144
WILLIAM G. NELSON
U.S. Borax
Borax Road
Boron, CA 93516
JOE NOLL
Flakt, Inc.
1500 East Putnam Avenue
Old Greenwich, CT 06870
PETE PETREY
American Air Filter Co. Inc.
215 Central Ave.
Louisville, KY 40277
WALTER PIULLE
EPRI
3412 Hillview Avenue
Palo Alto, CA 94303
CHARLES J. 0'BOYLE
EPA Region VIII
1860 Lincoln St.
Denver, CO 80295
PALMER PARSONS
Filtered Air Corp.
Perry, OH 44081
MUKESH N. PATEL
Illinois Institute of Technology
I. I. T. Centre
Chicago, IL 60616
MICHAEL A. PETRILLI
Monsanto Enviro-Chem Systems
Corporate Square Office Park
Box 14547
St. Louis, MO 63178
THOMAS PLUNKETT
Standard Havens
8800 E. 63rd
Kansas City, MO 64133
ED POLLOCK
SF Products Canada Ltd.
4480 Cote de Liesse Road
Montreal, Quebec
Canada H4N 2R1
W. WALTER RENBERG
Envirotech Corporation
Two Airport Office Park
400 Rouser Rd.
Pittsburgh, PA 15108
RONALD J. RENKO
C-E Air Preheater
P.O. Box 372
Wellsville, NY 14895
364
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LAMSON RHEINFRANK
Standard Havens, Inc.
8800 E. 63rd
Kansas City, MO 64113
DON RICHMOND
C-E Air Preheater
Andover Rd.
Wellsville, NY 14895
ENRIQUE RODRIGUEZ T.
Accion Social Regiomontana A.C.
Box 2034
Monterrey, N.L.
Mexico
RICHARD ROLFE
Joy Manufacturing Co.
4565 Colorado
Los Angeles, CA 90039
DONALD H. RULLMAN
American Air Filter Co., Inc.
215 Central Ave.
Louisville, KY 40291
DOUGLAS RYDER
Globe Albany Corp.
2405 W. University
Tempe, AZ 85281
ALBERTO SABADELL
Mitre Corp.
McLean, VA 22101
CHARLES A. SALOTTI
University of Wisconsin - M
P.O. Box
Milwaukee, WI 53201
HARRY N. SANDSTEDT
DuPont
Centre Rd. Bldg.
Wilmington, DE 19898
ROBERT W. SCHECK
Stearns Roger, Inc.
Box 5888
Denver, CO 80217
S. P. SCHLIESSER
Acuretex/Aerotherm
c/o EPA Research Triangle Park
Durham, NC 27711
TOM SCHNEIDER
Bay Area Industrial Filtration
6355 Coliseum Way
Oakland, CA 94621
M.P. SCHREYER
Wheelabrator-Frye Inc.
14920 So. Main
Gardena, CA 90248
FREDERICK D. SCHULER
Donaldson Company
P.O. Box 1299
Minneapolis, MN 55440
JOHN H. SCOTT
Donaldson Company, Inc.
P.O. Box 1299
Minneapolis, MN 55440
WILLIAM E. SEBESTA
300 Florence
Bay Village, OH 44140
MIKE SHACKLETON
Acurex Corp. Aerotherm Div.
485 Clyde Ave.
Mountain View, CA 94042
JERRY SHANG
Mitre Corp.
McLean, VA 22101
J. R. SHEPPARD
Milliken & Company
1304 Washington Street
LaGrance, GA 30240
365
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JOE SIBRAVA
Flakt, Inc.
1500 East Putnam Ave.
Old Greenwich, CT 06870
GLENN A. SMITH, JR.
BHA Company Div. of Std. Havens
8800 E. 63rd Street
Kansas City, MO 64133
GORDON L. SMITH
American Air Filter
215 Dentral
Louisville, KY 40201
JOHN D. SQUIBBS
Ford Motor Company
Michigan Casting Center
22000 Gibraltar Road
Flat Rock, MI 48134
J. STEPHENSON
Ontario Hydro, Central Health
Physics Services
757 Mackay Rd.
Pickering, Ontario
Canada L1V 2R5
SHARON STORY
Fabric Filters
525 South Hayden Rd.
Tempe, AZ 85281
EMIL STUDINKA
Texas A & M University
Zachery Bldg. Ind. Eng.
College Station, TX 77840
HERB SUERTH
CEA Carter Day Co.
500 73rd Avenue, NE
Minneapolis, MIN 55432
NORM Surprenant
GCA Corporation
GCA/Technology Division
Burlington Rd.
Bedford, MA 01730
ROBERT D. Button
Public Service Co. of Colorado
5900 E. 39th Avenue
Denver, CO 80207
DONALD P. TEIXEIRA
EPRI
3412 Hillview Avenue
Palo Alto, CA 94303
LARRY A. THAXTON
Buell Emission Control Division
Envirotech Corporation
200 N. 7th Street
Lebanon, PA 17067
FERNANDO ORTIZ THOMAS
Cristales Mexicanos, S.A.
Galeana y Ruiz Cortines
Monterrey, N.L.
Mexico
TIM THURMAN
Great Lakes Filter
18475 Sherwood
Detroit, MI 48234
ROBERT TISCONE
Environmental Elements
7249 National Drive
Hanover, MD 21076
DAVID W. TOWNSEND
W. W. Criswell Co.
3901 W. Beech Ave.
P.O. Box 130
McAllen, TX 78501
JOHN W. VAKLYES, JR.
C-E Air Preheater
Andover Rd.
Wellsville, NY 14895
MIGUEL ANGEL VARGAS
Cristales Mexicanos, S.A.
Galeana y Ruiz Cortines
Monterrey, N.L.
Mexico
366
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THOMAS C. WAGNER
PPG Industries - Fiber Glass Division
One Gateway Center
Piitsburgh, PA 15222
KEN A. WALKER
Environmental Elements Corp.
Box 1318
Baltimore, MD 21203
JACK A. WAUGH
Kaiser Aluminum & Chemical Corporation
P. 0. Box 98
Ravenswood, W. VA 26164
FRANK T. WEEMS
Envirotech Corporation
3000 Sand Hill Road
Menlo Park, CA 94025
WAYNE .WELLAN
Combustion Equipment Association
502 73rd Avenue, NE
Minneapolis, MN 55432
VINCENT J. WEMLINGER, II
E. I. DuPont F & F Dept.
1007 Market St.
Wilmington, DE 19898
ANDERS WIKTORSSON
AB Svenska Flaktfabrikon
S-35187
Vaxjb, Sweden
CHARLES WRIGHT
Fabric Filter
525 Hayden Road
Tempe, AZ 85281
PAUL YOSICK
American Air Filter
215 Central Ave.
Louisiana, KY 40222
DAVID YOUNG
Bekaert Steel Wire Corporation
800 Third Avenue
New York, NY 10022
JAMES ZARFOSS
Environmental Elements
7249 National Drive
Hanover, MD 21076
JOHN ZUTTERMEISTER
Bechtel Power Corp.
50 Beale Street
San Francisco, CA 94598
367
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368
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-78-087
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Third Symposium on Fabric Filters for Parti culate
Collection
5. REPORT DATE
June 1978
6. PERFORMING ORGANIZATION CODE
GCA-TR-78-33-G
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO,
N. Suprenant, Compiler
9. PERFORMING ORGANIZATION NAME AND ADDRESS
GCA Technology Division
Burlington Road
Bedford, Massachusetts 01730
10. PROGRAM ELEMENT NO.
EHE624
11. CONTRACT/GRANT NO.
68-02-2177
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD CO
Proceedings; 6/77-3/78
VERED
14. SPONSORING AGENCY CODE
EPA/600/13
15.SUPPLEMENTARY NOTES TERL_RTP project officer is Dennis C. Drehmel, Mail Drop 61,
919/541-2925.
16. ABSTRACT
The report presents the 17 technical papers given at an EPA-sponsored
symposium, held in December 1977 in Tuscon, Arizona, on fabric filters for particle
collection. Emphasis was on current field experience and engineering-oriented
research so that potential users could better select and/or design particulate control
systems. Technical content focused on fabrics for high temperature filtration, their
field behavior with fly ash and other effluents, design criteria and shakedown exper-
ience , and new filtration concepts that appear amenable to combustion and other
process effluents.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution
Dust
Dust Filters
Filtration
Fabrics
Fly Ash
Pollution Control
Stationary Sources
Particulate
Fabric Filters
13B
11G
13K
07D
HE
21B
3. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
383
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
369
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