FINAL DRAFT
INSPECTION PROCEDURES FOR
EVALUATION OF ELECTROSTATIC
PRECIPITATOR CONTROL SYSTEM
PERFORMANCE
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF ENFORCEMENT
OFFICE OF GENERAL ENFORCEMENT
WASHINGTON, D.C. 20460
-------
INSPECTION MANUAL FOR
EVALUATION OF ELECTROSTATIC
PRECIPITATOR PERFORMANCE
by
Michael F. Szabo, Yatendra M. Shah and S.P. Schliesser
PEDCo Environmental, Inc.
11499 Chester Road
Cincinnati, Ohio 45246
Contract No. 68-01-414*7
Task No. 36
EPA Project Officer: Kirk E. Foster
Division of Stationary Source Enforcement
Research Triangle Park, North Carolina 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Division of Stationary Source Enforcement
Washington, D.C. 20460
January 1981
-------
DISCLAIMER
This report was furnished to the U.S. Environmental Protection
Agency by PEDCo Environmental, Inc., Cincinnati, Ohio, in ful-
fillment of Contract No. 68-01-4147, Task No. 36. The contents
of this report are reproduced herein as received from the con-
tractor. The opinions, findings, and conclusions expressed are
those of the authors and not necessarily those of the Environ-
mental Protection Agency.
ii
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CONTENTS
Page
Figures v
Tables ix
Acknowledgment x
1. Introduction 1-1
2. Overview of Electrostatic Precipitation 2-1
2.1 Introduction 2-1
2.2 Charging mechanisms 2-4
2.3 Resistivity 2-6
2.4 Types of electrostatic precipitators 2-8
2.5 Basic ESP components 2-15
2.6 Methods for sizing of ESP systems 2-21
2.7 Design and sizing parameters 2-31
2.8 Electrical energization 2-36
References for Section 2 2-37
3. Instrumentation and Records 3-1
3.1 ESP instrumentation-location and general
description 3-1
3.2 Recordkeeping 3-14
References for Section 3 3-37
4. Operation, Maintenance, and Common Problems 4-1
4.1 Normal operating procedures 4-1
4.2 Maintenance requirements 4-10
4.3 Precipitator malfunctions 4-13
4.4 Reporting ESP malfunctions 4-23
4.5 Operation, maintenance, and common problems of
wet ESP's 4-24
References for Section 4 4-31
iii
-------
CONTENTS (continued)
Page
5. Inspection Procedures 5-1
5.1 Performing the periodic inspection 5-2
References for Section 5 5-18
6. ESP Performance Evaluation 6-1
6.1 Introduction 6-1
6.2 Technical basis for corona power - emissions
correlation 6-2
6.3 Practical basis for corona power - emissions
correlation 6-8
6.4 Baseline technique using stack test results 6-14
6.5 Corona power data and efficiency estimates 6-17
6.6 Calculator program for ESP performance evaluation 6-19
6.7 Computer model for ESP performance evaluation 6-21
References for Section 6 6-25
7. Case Histories 7-1
7.1 Cold-side electrostatic precipitator on a coal-
fired utility boiler 7-1
7.2 Electrostatic precipitator to control particulate
emissions from cement kilns 7-5
References for Section 7 7-8
Appendix A Startup and shutdown procedures and
maintenance schedule for electrostatic
precipitators (ESP's) A-l
Appendix B Types of electrostatic precipitator
malfunctions B-l
Appendix C Checklists for inspection of ESP's C-l
iv
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FIGURES
Number Page
2-1 Basic processes involved in electrostatic
precipitation 2-2
2-2 Electrostatic precipitator system model 2-3
2-3 Typical temperature-resistivity relationship 2-9
2-4 Typical electrostatic precipitator with top
housing 2-10
2-5 Three types of wet electrostatic precipitators 2-13
2-6 Various designs of collection electrodes 2-17
2-7 Typical forms of discharge or corona electrodes 2-19
2-8 Precipitator charging system and wire hanging
system 2-20
2-9 Supported electrode structures 2-21
2-10 Various combinations of electrical sectionaliza-
tion in an ESP 2-23
2-11 Tumbling hammer assembly for use with rigid
discharge electrode system 2-25
2-12 Action of guide vanes in preventing gas flow
separation at flue turn and at flue expansion 2-26
2-13 Effect of two different methods of gas dis-
tribution on flue characteristics in an ESP 2-28
2-14 Precipitator efficiency versus specific collec-
tion area and precipitation rate wg 2-3 5
2-15 Precipitator efficiency as a function of
specific collection area and modified pre-
cipitation rate parameter w, 2-35
v
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FIGURES (continued)
Number
Page
3-1
Typical ESP control panel
3-3
3-2
Example of ESP control panel console
3-4
3-3
ESP instrumentation diagram
3-5
3-4
Positions of measuring instruments
3-6
3-5
Connestion diagram of the opacity monitoring
system
3-12
3-6
Sample V-l curve data sheet
3-22
3-7
Secondary voltage-current curves demonstrating
the particulate space charge effect in a full-
scale, cold-side precipitator collecting fly
ash
3-23
3-8
Comparison of theoretical voltage-current
curves for different specific collection
areas
3-24
3-9
Current density vs. voltage for a full-scale,
cold-side precipitator without and with NH-
conditioning low sulfur coal
3-27
3-10
Rapidity of the effect of ammonia injection on
the voltage supplied to the inlet electrical
field of a full-scale, cold-side precipitator
3-28
3-11
Secondary V-I curve for inlet field of ESP
controlling high sulfur eastern flyash ¦
3-29
3-12
Secondary V-l curve for second field of ESP
controlling high sulfur eastern flyash
3-29
3-13
Secondary V-I curve for third field of ESP
controlling high sulfur eastern flyash
3-30
3-14
Secondary V-I curve for fourth field ESP con-
trolling high sulfur eastern flyash
3-30
3-15
Current density vs. voltage for a full-scale,
cold-side precipitator without and with
SO^ conditioning
vi
3-31
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FIGURES (continued)
Number Page
3-16 Voltage-current characteristics of inlet field
showing dust layer effect 3-32
3-17 V-I curve for hot-side ESP treating low sulfur
eastern flyash 3-32
3-18 Inlet voltage current curves for two power
plants at different load conditions 3-33
3-19 Outlet voltage current curves for two power
plants at different load conditions 3-33
3-2 0 Typical secondary voltage-current curves
obtained from a hot-side ESP collecting ash
from a Western power plant btirning low
sulfur coal 3-34
3-21 Voltage-current curves obtained from outlet
electrical fields in several cold-side
electrical precipitators 3-36
4-1 ESP current wave form with and without silicon
controlled rectifiers 4-3
4-2 Typical precipitator operating voltage as a
function of gas temperature 4-7
4-3 Vibrator and rapper assembly, and precipitator
high-voltage frame 4-8
4-4 Electrical indications of problems associated
with ESPS 4-19
5-1 A sample opacity chart 5-13
6-1 Relationship between collection efficiency and
specific corona power for fly ash precipitators,
based on field test data 6-7
6-2 Efficiency versus specific corona power extended
to high efficiencies, based on field test data
on recently installed precipitators 6-7
6-3 Real-time particulate emission scenario 6-11
6-4 Real-time corona power scenario 6-11
vii
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FIGURES (continued)
Number Page
6-5 Integrated particulate emission inventory
scenarios 6-13
6-6 Relationship between collection efficiency,
emission levels and specific corona Dower 6-18
viii
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TABLES
Number Page
2-1 ESP characteristics associated with different
levels of resistivity 2-7
2-2 Range of basic design parameters in operating
fly-ash precipitators 2-32
2-3 Design factors for precipitator specification
and evaluation 2-33
3-1 ESP design specifications for which records
should be maintained 3-16
3-2 Baseline test information 3-18
4-1 Maintenance schedule for electrostatic
precipitators 4-11
4-2 Summary of problems associated with ESP's 4-14
4-3 Manufacturer's suggested maintenance schedule
for wet precipitators 4-27
5-1 Plume characteristics and operating parameters
for coal-fired boilers 5-4
5-2 Effects of changes in normal operation on ^SP
control set readings 5-9
5-3 Recommended recordkeeping requirements 5-15
5-4 Important compliance parameters and conditions
for issuance of a citation 5-17
6-1 Corona power - emissions coefficient for several
industrial categories fi-8
6-2 Example data from stack test and inspection
results 6-15
6-3 Input data for ESP computer model 6-19
ix
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acknowledgment
This report was prepared for the U.S. Environmental Protec-
tion Agency under the direction of Mr. Richard W. Gerstle. The
Project Managers were Messrs. Yatendra M. Shah and Michael F.
Szabo; Mr. Steven P. Schliesser also provided assistance in
preparing the report.
Mr. Kirk E. Foster was the Task Manager for the U.S. En-
vironmental Protection Agency. The authors appreciate the as-
sistance and cooperation extended by Mr. Foster and other members
of the U.S. Environmental Protection Agency.
x
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SECTION 1
INTRODUCTION
The Division of Stationary Source Enforcement (DSSE) of the
U.S. Environmental Protection Agency (EPA) the Enforcement Divi-
sions of the EPA Regional Offices, and various state and local
agencies delegated authority to enforce Federal emission stan-
dards have the responsibility for enforcing emission standards
for regulated stationary source and for ensuring continued
compliance with the standards. An important part of the agency's
stationary source compliance monitoring and surveillance program
is the inspection of sources. The EPA field enforcement staff
inspect sources at regular intervals and determine their compli-
ance status by observing major operating parameters of the emis-
sion control systems and process parameters affecting emissions.
At the present time# no guidelines exist for determining
whether a control system is adequately designed or is being
properly operated and maintained. Therefore, DSSE is planning to
prepare technical guidelines for inspection and performance
evaluation of control systems. These guidelines will provide the
inspector with necessary background and information relating to
inspection and performance evaluation of a particular control
system. At present, the emphasis is on sources already in opera-
tion. Another set of guidelines applicable to new sources are
being planned that will provide technical information and proce-
dures specifically for the preconstruction engineering review of
control equipment design and construction and proposed opera-
tional parameters.
This report consists of seven major sections. The first four
sections orient the reader to the basics of ESP operation,
1-1
-------
maintenance, and sizing; the remaining three sections present
guidelines for inspection and performance evaluation.
Section 2 presents the basics of ESP's. A brief history of
electrostatic precipitators is followed by descriptions of ESP
types and components, as well as sizing information. Section 3
deals with ESP instrumentation, the major operational parameters,
and operational records.
Operation and maintenance practices are outlined in Section
4. The discussion includes matching of various operating param-
eters for optimum performance, typical ESP maintenance schedules,
maintenance of peripheral accessories, and common ESP malfunc-
tions and their effects on performance.
Section 5 provides a detailed procedure for inspection of
ESP's, with an inspection checklist that covers all ESP compo-
nents and peripheral systems. Frequency and duration of inspec-
tions and operating conditions during inspection are discussed.
Section 6 presents procedures for evaluating and predicting
ESP performance on the basis of inspection results. A procedure
is provided for relating ESP electrical data (corona power) to
emission level, based on previous stack emission test data.
Brief discussions are made on the use of advanced modeling tech-
niques including a) programmable calculator ESP performance model
and, b) EPA/Southern Research Institute computerized ESP perform-
ance model. Performance case histories of two FSP installations
are included in Section 7 to provide insight into ESP performance
evaluation.
The appendices provide supporting information for the per-
formance evaluation of ESP's. Appendix A outlines a typical
maintenance schedule for ESP's; Appendix B discusses the common
ESP malfunctions; Appendix C presents preinspection and inspec-
tion checklists for evaluation of ESP condition and performance.
1-2
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SECTION 2
OVERVIEW OF ELECTROSTATIC PRECIPITA'tlON
2.1 INTRODUCTION1'2
The three basic processes involved in electrostatic precipi-
tation are: (1) the transfer of an electric charge to suspended
particles in the gas stream, (2) establishment of an electric
field for removing the particles to a suitable collecting elec-
trode, and (3) removal of the particle layers from the precipita-
tor with as little loss to the atmosphere as possible. Figure
2-1 illustrates the basic processes involved in electrostatic
precipitation, and Figure 2-2 shows the processes and their
interrelationship.
In a single-stage precipitator, high-voltage direct current
(d.c.) corona is responsible for producing negative ions, charg-
ing the suspended particles, and creating the electric field.
Two basic hardware components of the precipitation process
are: (1) the precipitation chamber, in which the particles are
electirified and removed from the gas and (2) the high-voltage
transformer and rectifier, which function to create the strong
electrical field in the chamber.
In practice, the precipitation chamber consists of a shell
made of metal, tile or other similar material. Suspended within
the shell are grounded steel plates (collecting electrodes)
connected to the grounded steel framework of the supporting
structure and to an earth-driven ground. Suspended between the
plates are metal rods or wires (discharge electrodes), insulated
from ground and negatively charged at voltages ranging from
30,000 to 100,000 volts (30 to 100 kV). The large voltage
2-1
-------
REGION OF \
CORONA GLOW\
FREE
ELECTRONS
DUST
PARTICLE
WIRE
ELECTRONS
GAS
MOLECULE
ELECTRON
POSITIVE -«—(+
IONS
CORONA GENERATION
CHARGING
BOUNDARY LAYER
® WIRES
TURBULENT
GAS FLOW
RAPPING
x SYSTEM
COLLECTION
COLLECTING
PLATE
:hopper
ASH REMOVAL
SYSTEM
REMOVAL
Figure 2-1. Basic processes involved in electrostatic precipitation.
-------
to
I
u»
RESISTIVITY I
HIRE RAO.
COLLECTOR RAO.
WIRE ROUGHNESS
SEC. EMIS.
AVAL. COEFF.
IONIZING RAO.
ELECTRONEG. GAS
GAS VELOCITY
VELOCITY DIST.
COLLECTION AREA
VOLUME FLOW _
APPLIED WJLTAGE-
GAS DENSITY
ION MOBILITY
SECTIONALI2ATI0N
COLLECTION AREA
WIRE RAO.
COLLECTOR RAO.
PARTICLE SIZE
01 ELECT. CONST.
TIME
TEMPERATURE
OUST LOAD
GAS AND OUST
ION VELOCITY
CORONA
GENERATION
VAN OER HAALS , MOLECULAR,
AND MECHANICAL
NEGATIVE
ION
FORMATION
ELECTRIC
FIELD
PARTICLE
CHARGING
ELECTRIC FIELD
IN DEPOSIT
I GAS VELOCITY I
ELECTRIC WINO
PARTICLE
RETAINING
FORCE
PARTICLE
COLLECTION
PARTICLE
REENTRAINMENT
SPACE CHARGE
DUST LOAD
PLATE DESIGN
HOPPER OESIGN
GAS VELOCITY
GAS DIST.
RAPPING FORCE
RAPPING INTERVAL
DUST R
EMOVAL
GAS AND UNCOLLECTED OUST
COLLECTED DUST
PARTICLE SIZE
DUST PROP.
TEMPERATURE
Figure 2-2.
Electrostatic precipitator system "lodel."^
-------
differential between the wires and the plates sets up a high
electrical field. High electric field levels ionize electronega-
tive gas molecules (e.g., O^, SC^), which impart negative charges
to the suspended particles. Due to the electric field and
particulate charge, a powerful force (about 3000 times gravity)
acts on the particle in the direction of the collection plates.
The solid dust particles are removed by periodic rapping of
the collection plate so that the dust falls in sheets into a
receiving hopper. Solid material can also be removed by irriga-
tion of the collection electrode with water or other fluid in
what is termed a "wet" precipitator. Liquid particles, such as
acid mists or tars, coalesce on the collection plate and drain
into a sump at the bottom of the precipitator.
2.2 CHARGING MECHANISMS1'2
Particle charging and subsequent collection takes place in
the region between the boundary of the corona glow and the col-
lection electrode, where gas particles are subjected to the
generation of negative ions from the corona process. Charging is
accomplished by field and diffusion mechanisms. The predominant
mechanism varies with particle size.
In field charging, ions from the corona are driven onto the
electric field. As the ions continue to impinge on a dust par-
ticle, the charge on it increases until the local field developed
by the charge on the particle causes distortion of the electric
field lines such that they no longer intercept the particle. As
the particle reaches this saturation charge level, no further
charging will take place. This is the predominant mechanism for
particles larger than about 0.5 micrometers (vim).
The time required for a particle to reach its saturation
charge, varies proportionally to the ion density in the region
where charging takes place. Under normal conditions with sus-
tained high-current levels, charging times are only a few milli-
seconds. Limitation of current because of high resistivity or
2-4
-------
other factors can lengthen charging times significantly and cause
the particles to travel several feet through the precipitator
before saturation charge is approached.
The waveform of the secondary voltage can further affect the
charging times. The rectified unfiltered voltage has peaks and
low occurring at regular intervals, which match with the fre-
quency of the primary voltage. Thus, the electric field varies
with time, and the dust particles in the interelectrode region
are subjected to time-varying fields. The particle charging is
interrupted for that portion of the cycle during which the charge
on the particle exceeds that corresponding to the saturation
charge for the electric field existing at the time. This further
lengthens the charging times and, in the case of high-resistivity
dust, degrades precipitator performance.
Diffusion charging is associated with ion attachment result-
ing from random thermal motion, and is the dominant charging
mechanism for particles below about 0.2 ym. As with field charg-
ing, diffusion charging is influenced by the magnitude of the
electric field, since ion movement is governed by electrical as
well as diffusional forces. Neglecting electrical forces, an
explanation of diffusion charging is that the thermal motion of
molecules causes them to diffuse through a gas and contact the
particles. The charging rate decreases as a particle acquires,a
charge and repels additional gas ions, but charging continues to
a certain extent because there is no theoretical saturation or
limiting charge other than the limit imposed by the field emis-
sion of electrons. This is because the distribution of thermal
energy ions will always overcome the repulsion of the dust par-
ticle. 2
The particle size range of about 0.2 to 0.4 ym is a transi-
tional region in which both mechanisms of charging are present
but neither is predominant. Fractional efficiency test data for
precipitators have shown reduced collection efficiency in this
transitional size range, where diffusion and field charging
overlap.
2-5
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2.3 RESISTIVITY
Since dust resistivity can greatly limit preicpitator per-
g
formance when it is outside the preferred range of 10 ohm-cm to
10^ ohm-cm, it is a major factor in preicpitator technology.
Resistivity plays a major role in the electrical conditions of
the collection dust layer, influencing the:
1) electric field stress in the dust layer
2) voltage drop across the dust layer, and
3) electrical force component holding the dust layer to
the collection plate.
Resistivity also affects the electrical operating conditions of
an ESP, due to its impact on particle charging, and 2) the inter-
dependent relationship between dust layer conditions and the
operating voltage and current levels.
Table 2-1 provides a brief description of characteristics
associated with the typical levels of dust resistivity. The
identified characteristics reflect generalized cases and condi-
tions, indicating that an optimum range exists for resistivities
8 10
between 10 and 10 ohm-cm. As resistivity levels deviate from
the preferred range, special design considerations need to be
made to compensate for the respective change in precipitation
characteristics. Accordingly, for ESP's treating streams with
fluctuating resistivity levels, (e.g., different temperature,
moisture, fuel quality), special or different ESP operation may
be necessary to maintain collection performance.
Fly ash resistivity depends primarily on the chemical compo-
sition of the ash, the ambient flue gas temperature, and the
4
amounts of water vapor and SO^ in the flue gas. High resis-
tivity, which is characteristic of certain low-sulfur coals,
causes uncertainly in sizing cold-side ESP's, which generally
operate at temperatures of 120° to 175°C (250°-350°F).
At low temperatures [<80°C (<175°F)], current condxiction
occurs principally along the surface layer of the dust and is
2-6
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TABLE 2-1. ESP CHARACTERISTICS ASSOCIATED WITH
DIFFERENT LEVELS OF RESISTIVITY
Resistivity level
ohitt-cm
ESP characteristics
<108
108 to 1010
1011
>1012
(1) Normal operating voltage and current
levels.
(2) Reduced electrical force component re-
taining collected dust, vulnerable to
high reentrainment losses.
(3) Negligible voltage drop across dust layer.
(4) Reduced collection performance, due to
(2) .
(1) Normal operating voltage and current
levels.
(2) Negligible voltage drop across dust layer.
(3) Sufficient electrical force component re-
taining collected dust.
(4) High collection performance, due to (1),
(2) , and (3) .
(1) Reduced operating voltage and current
levels with high spark rates.
(2) Significant voltage loss across dust layer.
(3) Moderate electrical force component re-
taining collected dust.
(4) Reduced collection performance, due to
(1), (2).
(1) Reduced operating voltage levels; high
operating current levels.
(2) Very significant voltage loss across dust
layer.
(3) High electrical force component retaining
collected dust.
(4) Seriously reduced collection performance,
due to (1), (2), and probable back
corona.
Typical values
Operating voltage :
Operating current density:
Dust layer thickness :
30-70 kV, dependent on design factors
2
5-50 nA/cm
0.5 to 2 cm (1/4-1 in,)
2-7
-------
related to the absorption of water vapor and other conditioning
agents in the flue gas. For fly ash, resistivity is primarily
related in an inverse manner to the amount of SO^ and moisture in
the flue gas. Burning of low-sulfur coal releases smaller
amounts of SC>2/ which is oxidized to SO^. A higher resistivity
fly ash results, except at temperatures below about 80°C (170°F) ,
where significant amounts of SO^ are absorbed onto the fly ash
particles.
At elevated temperatures [<200°C (<400°e)], conduction takes
place primarily through the bulk of the material, and resistivity
depends on the chemical composition of the material. For fly
ash, resistivity above 200°C (400°F) is generally below the
critical value of about 10^ ohm-cm, although it has been shown
to decrease with increasing amounts of sodium, lithium, and
5
iron.
The range of operation of cold-size fly ash precipitators is
120° to 200°C (250° to 400°F), a range in which conduction takes
place by a combination of the surface and bulk mechanisms and
resistivity of the ash is highest. Figure 2-3 illustrates the
relationship between resistivity, temperature, and responsible
conduction mechanisms.
2.4 TYPES OF ELECTROSTATIC PRECIPITATORS
Two types of electrostatic precipitators are used for par-
ticulate control: dry and wet electrode precipitators. Within
each of these categories precipitators can be further classified
by electrode geometry. Most precipitators in use today are the
dry type with plate-type collection electrodes and pyramidal
hoppers. Gas flow is normally horizontal through the ESP.
Figure 2-4 presents an example of this type of precipitator. A
less common electrode arrangement is a wire-pipe (cylindrical)
ESP.
2-8
-------
E
u
i
E
JE
O
>-
»—
•—<
>
i—•
H-
»—i
t/1
LkJ
ec
1000/TEMP., °K
3.2 2.8 2.4 2.0 1.6 1.2
10
14
10
13
10
12
10
11
10
10
103
\
\
\
• VI
SURFACE \ |
¦
'RESISTIVITY \ 1
^ \ 1
VOLUME
RESISTIVITY
/1 COMPOSITeX
/ |0F SURFACE
/ AND VOLUME,
" ' |resistivity|
\ "
1 j 1 -J L 1 1
\ m
1 111
70 150 250 400 600 800 1000
100 200 300
TEMP., °C
Figure 2-3. Typical temperature-resistivity relationship.2
2-9
-------
Transformer-Rectifier
Ground Switch Box
on Transformer
Top End
Frames
High Voltage
Conductor
High Tension
Support Insulators
Perforated
Distribution
Plates
Bottom E nd
Frames
Upper H.T. Hanger Assembly
(Hanger and Hanger Frame
Upper H.T. Wire
Support Frame
J
r
»
r
Bracing
Hopper
Stilts
Horizontal
Bracing Strut
Hopper Baffle
Discharge Electrode
Vibrator
Collecting Electrode
M.I.G.I. Rappers
Top Housing
Hot Roof
Access Door
Hot Roof
Side
Frames
Discharge
Electrode
Access Door
Between
Collecting Plate
Sections
. Precipitator
Base Plate
Slide Plate
Package
Support Structure
Cap Plate
Steadying Bars
Lower H.T.
Steadying Frame
Collecting
Electrodes
Figure 2-4. Typical electrostatic precipitator with
top housing. (Courtesy of Research Cottrell)
2-10
-------
2.4.1 Dry Precipitators
Dry precipitators are installed in industries with widely
varying condition of gas temperature and pressure, such as elec-
tric utility power boilers, cement kilns, and metallurgical
furnaces. In the electric utility industry, precipitators are
classified as cold or hot, depending on the location of the ESP
relative to the air preheater.
The cold-side ESP, located downstream of the air preheater,
operated in the range of 100° to 200°C {200° to 400°P). The
greatest disadvantage of a cold-side ESP is that its efficiency
varies with fuel composition and boiler firing conditions, where-
as the efficiency of a hot-side ESP is less dependent of these
factors.
Hot-side ESP's are located upstream of the boiler air pre-
heater. The operating temperature range is generally between
300° and 450°C (600° to 800°F). At this temperature, the resis-
tivity of fly ash is significantly lessened and, for certain coal
types, collectibility can be greatly increased. Also, because of
the ESP location, the heat transfer surfaces of the air preheater
are less likely to be fouled by fly ash. There are corresponding
reductions in the need for soot blowing of the air preheater and
in hopper plugging. One drawback of locating the ESP upstream of
the air preheaters is that the soot blown from the air preheater
cannot be captured; this may result in occasional increased
emissions.
The typical hot-side precipitator operates at lower voltages
than a cold-side unit. If designed correctly, it operates at
much higher current densities and is characterized by a rela-
tively high-power density and by stable, current-limited opera-
tion.
Thermal expansion has been a problem with hot ESP's. After
construction at ambient temperatures, the internals are main-
tained during operation at approximately 350° to 400°C (650° to
750°P), while the externals remain near ambient temperatures.
2-11
-------
Adequate provision for differential movement of the precipitator
on its support structure, proper insulation, and adherence to
design stress values have largely eliminated this problem.
Some ESP manufacturers favor cold-side installations, others
stress hot-side units; there is no adequate rule of thumb for
choice of either type. The selection is usually based on oper-
ability, economics, and particulate characteristics.
For new construction at a coal-fired power plant, if the
specific collection area (SCA) required for a cold-side ESP is
2.3 2 *
greater than 100 m /m /sec (500 ft /100 acfm), a hot-side unit
would be the proper choice. If the SCA can be smaller, a cold-
side unit could be used.
2.4.2 Wet Precipitators
Wet precipitators are used primarily in the metallurgical
industry, usually operating below 75°C (170°F). Until the late
1960's, their use was restricted mostly to acid mist, coke oven
off-gas, blast furnace, and detarring applications. Their use in
other areas is rapidly increasing as air pollution control codes
for those areas are becoming more stringent. The newer applica-
tions include sources with sticky and corrosive emissions that
must meet these standards. Because of inherent temperature range
limitatons, they are not used for boiler installations.
The fundamental difference between a wet and a dry ESP is
that a thin film of liquid flows over the collection plates of a
wet ESP to wash off the collected particulates. In some cases,
the liquid is also sprayed in the gas flow passages to provide
cooling, conditioning, or sometimes a scrubbing action. When the
liquid spray is used, it is precipitated with the particles,
providing a secondary means of wetting the plates. Three dif-
ferent wet ESP configurations are discussed below and illustrated
in Figure 2-5.
Metric SCA (m^/m^/sec) = 0.197 x British SCA (ft^/1000 acfm).
2-12
-------
MATE* SUm*
SPRAY NOZZLES
PLATES
GAS FLOM
6 TO DRAIN
CORONA HIRES
A. Plate type (horizontal flow)
GAS FION IN
US F10W OUT
HIGH
VOLTAGE
LEADS
MATER PIPES
GAS FLOW
GAS FLOW
HOOD AND STACK
TRANSITION
PRECIPITATOR
SECTION
TYPICAL KETAL
ELECTRODE
DISCHARGE CAGE
CONTINUOUS FILM OF
LIQUOR FLOWS DOWN
POSITIVE COLLECTION
ELECTRODE SURFACES
(CYLINDER WALLS)
VENTURI INLET TO
PRECIPITATOR SECTION
BASE
R. Concentric plate type
C. Conventional pipe type
Figure 2-5. Three types of wet electrostatic precipitators.
2-13
-------
Plate-type (Horizontal Flow)—
The effluent gas stream is usually preconditioned to reduce
temperature and achieve saturation. As the gas enters the inlet
nozzle, its velocity decreases because of the diverging cross
section. At this point, additional sprays may be used to create
good mixing of water, dust, and gas as well as to ensure complete
saturation before the gas enters the electrostatic field.
Baffles are often used to achieve good velocity distribution
across the inlet of the precipitator.
Within the charging section, water is sprayed near the top
of the plates in the form of finely divided drops, which become
electrically charged and are attracted to the plates, coating
them evenly. Simultaneously, solid particles are charged; they
"migrate" and become attached to the plates. Since the water
film is moving downward by gravity on both the collecting and
discharge electrodes, the particles are captured in the water
film, which is disposed of from the bottom of the precipitator in
the form of slurry.
Concentric-plate ESP—
The concentric-plate ESP consists of an integral tangential
prescrubbing inlet chamber followed by a vertical wetted-wall
concentric-ring ESP chamber. Concentric cylindrical collection
electrodes are wetted by fluids dispensed at the top surface of
the collection electrode system. The discharge electrode system
is made of expanded metal with uniformly distributed corona
points on the mesh background. This system is intended to com-
bine the high, nearly uniform, electric field associated with a
parallel plate system and the nearly uniform distribution of
corona current density associated with closely spaced corona
points. Higher gas flows can be handled by adding concentric
electrode systems and by increasing the length of each electrode.
Conventional Pipe-type ESP—
This system consists of vertical collecting pipes, each
containing a discharge electrode (wire type), which is attached
2-14
-------
to the upper framework and held taut by a cast-iron weight at the
bottom. A lower steadying frame keeps the weights and thus the
wires in position.
The upper frame is suspended from the high-voltage insula-
tors housed in the insulator compartments, which are located on
top of the precipitator shell (casing). Heating and ventilating
systems help to prevent accumulation of moisture and dust in the
insulator compartments.
The washing system usually consists of internal nozzles
located at the top of the plates. At specified intervals, the
tubes are washed thoroughly. During the washing, the louver
damper to the exhaust fan is closed to prevent carryover of
droplets.
2.5 BASIC ESP COMPONENTS
This section briefly describes major ESP components and
presents current nomenclature for a typical ESP configuration.
2.5.1 Precipitator Casing
The precipitator casing is of gas-tight, weatherproof con-
struction. Major casing parts are the inlet and outlet connec-
tions, the shell and hoppers, inspection doors, and insulator
housing. The casing is fabricated of steel of a type suitable
for the application (type of process, heat range, etc.). The
shell is reinforced to handle maximum positive or negative
pressure, support the weight of the internals, and sustain en-
vironmental stresses such as those imposed by wind, snow, and
earthquake. The shell and insulator housing form a grounded
steel chamber, completely enclosing all the voltage equipment to
ensure the safety of personnel.
2.5.2 Dust Removal System
Dust hoppers are required for temporary storage of the
collected dust. They should be large enough to hold the dust
2-15
-------
collected in a 24-hour period. The most common hopper design is
pyramidal, converging to a square or round discharge area.
To prevent plugging, hoppers should be kept clean, dry, and
if the dust is moisture-laden, warm. Many hoppers do not require
vibrators, but it is economical to install mounting devices for
future installation of vibrators should operation show that they
are necessary. If insulation does not keep the hopper warm
enough, additional heating of the hoppers may be required for
effective performance.
Frequently, hoppers are baffled at the divisions between two
dust-plate sections to prevent gas from bypassing the precipita-
tor.
Access to hoppers should be by external, key-interlocked
doors to prevent dangerous dust accumulations on the interior
side of the door. Enough "poke hole" ports should be provided to
allow for cleaning a blockage at the discharge.
Systems for removal of dusts accumulated in hoppers include
containers, dry vacuum, wet vacuum, screw conveyors, and scrape
bottom systems.
2.5.3 Collection Electrodes
Collection electrodes are the grounded metal plates upon
which the dust collects. Many shapes of flat collecting elec-
trodes are used in ESP's, as shown in Figure 2-6, and some ESP's
are designed with cylindrical collection surfaces. All plate
configurations are designed to maximize the electric field and to
minimize dust reentrainment. All collection plates have a baffle
arrangement to minimize gas velocities near the dust surfaces as
well as to provide stiffness. Collection plates are commer-
cially available in lengths ranging from 1 to 3 meters (3 to 9
feet) and heights from 3 to 15 meters (9 to 50 feet). Generally,
these panels are grouped within the precipitator to form inde-
pendently rapped collection modules. The total effective length
of these plates divided by their effective height is referred to
2-16
-------
GAS
FLOW
WIRE DISCHARGE
ELECTRODES
0PZEL PLATEj7
GAS_
FLOW
ROD
CURTAIN
oooooooo
»-•••••
oooooooo
ZIG-ZAG
PLATE
DISCHARGE GAS
ELECTRODES*" wvw FLOW
GAS
FLOW
V-POCKETS
4<4<4<4<4<
• • • •
4<4<4<4<4<
GAS.
FLOF
CHANNEL
•••••••
OFFSET
PLATES
GAS.
FLOW
GAS
FLOW
SHIELDED
PLATES
—K hr—
GAS
FLdvr
V-PLATES
< ((<«
• ••44
<<<<<<
A GAS
JFLOW
" •' ii
TULIP PLATE
if • Y ELECTRODES
~ ~
DUST
Figure 2-6. Various designs of collection electrodes.2
2-17
-------
as the aspect ratio. Aspect ratios larger than 1.0 provide
longer residence time for the gas and increase collection effi-
ciency, all other factors being equal.
2.5.4 Discharge Electrodes
The discharge electrodes are maintained at high electrical
voltage during ESP operation. The high-voltage electrodes ionize
the gas and establishes the electric field, which imparts a
charge to the particle and causes precipitation.
Discharge electrodes are also referred to as corona elec-
trodes, corona wires, cathodes, and high-voltage electrodes.
Discharge electrodes are metal, the type determined by the
composition of the gas stream. The form of the electrodes may be
cylindrical or square wire, barbed wire, or stamped or formed
strips of metal of various configurations (see Figure 2-7).
Discharge electrodes are mounted in a variety of ways. They
may be suspended from an insulating superstructure with weights
at the bottom holding them tightly in place, or they may be
rigidly mounted on mats or frames. Regardless of how they are
mounted, they must be stabilized against swinging in the gas
stream. Examples of the wire weight and rigid wire systems are
shown in Figures 2-8 and 2-9.
2.5.5 Electric Power Supplies
The electrical energizing sets consist of high-voltage
silicon diode power packs developed specifically for the high
loads required for supplying high-voltage direct current to
electrostatic precipitators.
The power supply system consists of four components: a
step-up transformer, a high-voltage rectifier, a control element,
and a control system sensor. The system is designed to provide
voltage at the highest level without causing arc-over (sparking)
between the electrode and the collection surface. The automatic
control system maintains optimum voltage value, adjusting to
2-18
-------
Figure 2-7. Typical forms of discharge or corona electrodes.
2-19
-------
SUPPORT INSULATOR
HOUSING
HIGH VOLTAGE
BUS DUCT
VIBRATION
ISOLATORS
BUS CONDUCTOR
~C HIGH VOLTAGE
SWITCH
TRANSFORMER-
RECTIFIER
ACCESS
DOOR
Av^\\
PROTECTOR
TUBE
DISCHARGE ELECTRODE
SUPPORT FRAME
DISCHARGE ELECTRODE
TENSIONING WEIGHT
WEIGHT GUIDE FRAME
Figure 2-8.
Precipitator charging system and wire
hanging system.
2-20
-------
SUPPORT FRAME
frame-type
RAPPER ANVIL
CORONA ELECTRODES
MAIN MAST SUPPORT
SUPPORT PIPES
MAST-TYPE
WIRES
Figure 2—9. Supported electrode structures,^
2-21
-------
fluctuations in characteristics and concentrations of the dust.
A more detailed description of the operation of an automatic
control system is given in Section 3.1.
The electrical system of an ESP is arranged in bus sections,
each section representing any portion of the ESP that can be
energized independently. This is accomplished by subdividing the
high-voltage system and arranging the support insulators. Some
power system arrangements are shown in Figure 2-10.
The sectionalization of precipitators is very important.
First, if the precipitator is sparking, less of the precipitator
is disabled during the spark interval if the system is highly
sectionalized. Higher average voltage and higher electric field
levels are maintained, and precipitator efficiency is not re-
duced. Also, the smaller electrical sets have higher internal
impedances, which facilitate spark quenching and minimize the
tendency of a spark to arc. Smaller precipitator sections
localize the effects of electrode misalignment and permit higher
voltages in the remaining sections. Finally, with adequate
sectionalization in very large precipitators, reasonably good
collection efficiencies can be maintained if a section must be
deenergized because of wire breakage or other electrical trouble.
All new ESP's are designed so that if one field shorts out, the
overall ESP efficiency will not fall below specifications.
2.5.6 Rappers
Rapping systems are incorporated in an ESP to dislodge dust
from the collecting and discharge surfaces; their effectiveness
and reliability are essential. Generally available types of
rappers are pneumatic or electromagnetic impulse units, electric
vibrators, and mechanical hammers.
Rapper systems are designed to be compatible with the in-
ternal suspension system and the number of surfaces affected by
the rapping shock. Pneumatic rappers supply the most shock and
dislodge tenacious dusts most readily. It is important in any
2-22
-------
GAS FLOW
I-®
PA 11-11
GAS FLOW
M~~i
i i
PA 21-11
GAS FLOW
I
i—i ^ i—ii—i _ n
! KS>{ !i KSH !
I-J i--li—-l I !
PA 41-21
j"®
PA 12-12
1 '
KI5H 1
__iw 1 1
PA 22-12
PA 42-22
]^5)
> w
PA 13-13
Ktr>-< 1
_ j 1 1
1
PA 23-13
1 KjifH 11 }tfR)i 1
1—
PA 43-23
1 j ^
[ J-®
PA 14-14
PA 24-14
1—1
i i 1
-1 1 n_jw i 1
I K™>1 ir r^R)-i 1
1 iwi 11 !w 1
1 1
n®c]n®c]
PA 44-24
KEY: PA
TRANSFORMER RECTIFIERS IN DEPTH
TRANSFORMER RECTIFIERS IN WIDTH
FIELDS IN DEPTH
CELLS IN WIDTH
Figure 2-10. Various combinations of electrical
sectionalization in an ESP.12
2-23
-------
rapper system that all hardware is designed to withstand high
energy forces.
Pneumatically or electromagnetically operated rappers may be
of the impact of vibratory type. The impact type rapper func-
tions by lifting a weight to a controlled height and then allow-
ing it to fall against an anvil, which transmits the shock to the
discharge and collection surfaces. Vibratory rappers impart
vibrations to the discharge and collecting surfaces by means of
rods extending through the precipitator shell.
Rapping hammers, which are used with rigid discharge elec-
trode ESP's, remove dust very efficiently, but when installed in
a moving gas stream may require frequent maintenance. One type
of tumbling hammer design is illustrated in Figure 2-11.
The number and size of rappers and rapping frequencies vary
with the manufacturer and the nature of the dust. Generally one
2 2
rapper unit is required for 110 to 150 m (1200 to 1600 ft ) of
collecting area. Discharge electrode rappers serve from 350 to
2000 m (1000 to 7000 ft) of wire per rapper. Intensity of
rapping intervals are adjustable over a range of approximately 30
to 600 seconds.
The paramount consideration in rapping is to provide accel-
eration to dislodge the dust without causing excessive reentrain-
ment. Operation of rappers is discussed further in Section 3.1.
2.5.7 Gas Flow Distribution
Proper gas flow distribution is critical for optimum pre-
cipitator performance. The plant flue system and its connections
to the ESP are more important than the precipitator itself in
determining the quality of gas flow through the precipitator. A
set of guide vanes, which is the most common device used to
direct gas flow, allows a streamlined flow of gas. Figure 2-12
illustrates how guide vanes prevent flow separation.
Diffusion screens and baffles are also used to reduce tur-
bulence and maintain uniform gas flow. A diffuser consists of a
woven screen or a thin plate with a regular pattern of small
2-24
-------
ro
l
N)
Ul
ELECTRODE
CARRIER
ANGLES
TUMBLING
HAMMER
ASSEMBLY
RAPPING
ANVILS
Figure 2-11. Tumbling hammer assembly for use with
rigid discharge electrode system.15
-------
— -.0 0
00 0(?* o 3
FLOW SEPARATION
FLOW SEPARATION-
FLOW CONFIGURATION WITHOUT GUIDE VANES
"In
-¥•
Figure 2-12.
Action of guide vanes in preventing
of
separation at flue "turn ancTat f lue^x^sion^ fl°W
2-26
-------
openings. The effect of a diffuser is to break large-scale
turbulence into a large number of small-scale turbulent zones,
which in turn decay rapidly and in a short distance coalesce into
g
a relatively low-intensity turbulent flow field. Two or three
diffusers may be used in series to provide better flow than could
6
be achieved with only one diffusion plate {see Figure 2-13).
2.6 METHODS FOR SIZING OF ESP SYSTEMS
Methods in current use for sizing electrostatic precipita-
tors include design by analogy to similar installations and by
theoretical application of fundamental preciptitation principles.
Design by analogy is most reliable for industrial process ESP
installations where few process variabilities influence the
collection conditions. This method cannot be applied to sizing
of ESP's for the collection of fly ash emitted from coal-fired
sources, primarily because of the wide range of coals, boilers,
and operational methods.
The first equation for predicting particle collection prob-
ability was developed by Anderson in 1919. It was derived again
by Deutsch, who used a different method, in 1922. In various
forms, this equation, n = 1-e f has become the basis for
estimating precipitator efficiency on the basis of gas flow,
precipitator size, and precipitation rate parameter. In this
equation, n is the precipitator collection efficiency, A is the
total collecting electrode surface area, V is the gas flow rate,
and w is the migration velocity of the particles. When deter-
mined empirically, the precipitation rate parameter, w, includes
effects of rapping losses, gas flow distribution; and particle
size distribution.
The Deutsch-Anderson model assumes that particulate concen-
tration is uniform in any cross section perpendicular to the gas
flow of an ESP. This assumption is made because of the turbu-
lence of the gas, which takes the particles near the collection
surface and allows them to become electrically charged. A
2-27
-------
GAS
FLOW
(3) PERFORATED
DISTRIBUTOR PLATES
RIGHT
(1) PERFORATED
DISTRIBUTOR PLATE
HIGH FLOW
LOW FLOW
GAS FLOW
WRONG
Figure 2-13. Effect of two different methods of eras
distribution on flue characteristics in an ESPI7
2-28
-------
serious limitation in use of the Deutsch-Anderson equation is
that it does not account for changes in the particle size dis-
tribution and subsequently the effective migration velocity as
precipitation proceeds. This limitation affects the accuracy of
sizing estimates for units operating at very high efficiencies
(approximately 98% and above because of the change in w with
particle size.
In practice, factors such as particle reentrainment and gas
leakage cannot be accounted for theoretically. In addition, some
of the most important physical and chemical properties of the
particles and gases often are not known. Therefore, most de-
signers use an effective precipitation rate parameter, wg, that
is based mainly on field experience rather than theory.** Data
from operating installations form a general basis for selection
of w , and these data are modified to fit the particular situa-
tion being evaluated. Thus, wg becomes a semiempirical parameter
that can be used in the Deutsch-Anderson equation or its deriva-
tives to estimate the collection area required for a given effi-
ciency and gas flow. The most important parameters that deter- .
mine w^ in practice are resistivity, particle size distribution,
gas velocity distribution through the ESP, particle loss due to
reentrainment, rapping and gas sneakage, ESP electrical condi-
g
tions, and required efficiency.
A semiempirical modification of the Deutsch-Anderson equa-
tion that essentially removes the size dependency from w was
developed by Matts and Ohnfeldt. This equation is n = l-e~Wk
In most cases, k equals approximately 0.5. The modified migra-
tion velocity, w^, can be treated as being independent of charg-
ing voltage and current levels and of particle size distribution
within an ESP, as precipitation proceeds in the direction of gas
flow. Other changes, however, such as in properties of the gas
entering the ESP, resistivity, and size distribution, produce a
change in just as they change the conventional w.
2-29
-------
Another design technique applied to existing installations
or new processes to aid in a full-scale design is the pilot-scale
precipitator. The use of analog methods for the investigation of
gas flow and precipitation rate may be advisable in view of the
complexity of the phenomena and the asymmetry of many gas-flow
systems. Theoretical calculations have various limitations. The
general principles of fluid mechanics and similitude may be
applied to yield useful results by using laboratory size models.
Flow patterns can be readily determined by the use of micro-pitot
tubes and various types of electrical anemometers. Pilot models
enable the use of smoke and several other techniques for flow
9
pattern determination. The main problem with use of a pilot-
scale ESP is that the pilot unit almost always performs better
3 8
than a full-scale unit. ' This can be attributed to better gas
3
flow distribution, sectionalization, and electrode alignment.
The result is operation at higher current densities and voltages
than in a full-scale unit. Application of a scale-up factor, as
in spark-limited operation of a pilot-scale ESP, can cause un-
certainties in sizing the full-scale ESP. Therefore, pilot
precipitator data should be supplemented as fully as possible by
basic data on particle and gas properties, especially resis-
tivity.4
Combustors are also used in conjunction with pilot scale
ESP's for design purposes. Use of combustors can allow develop-
ment of design data without transporting tons of coal to a power
plant for use in pilot-scale precipitators. Information gained
from operation of combustor-precipitator combinations is usually
qualitative, and much additional information is needed for ap-
Q
plication of the data to full-scale precipitator design.
Precipitator designers also make use of laboratory-scale
gas-flow models, which are very important to proper operation of
a full-scale ESP. Modeling techniques are well documented, and
close correlation of gas flow performance in laboratory models
Q
and field installations is often achieved.
2-30
-------
The Industrial Environmental Research Laboratory (IERL) of
U.S. EPA has done significant work in the area of pilot particu-
late collection systems. Pilot-scale versions of conventional
control devices such as electrostatic precipitators, fabric
filters, and wet scrubbers are mounted in mobile vans and carried
to various test sites.
The mobile ESP facility is designed for the purpose of
experimentally determining the effects of dust properties,
rapping, dust resistivity, and conditioning agents on electro-
static precipitation performance. Precipitation studies can be
conducted as gas flows up to 300 acfm and at gas temperatures up
to 540°C (1000°F). Experimental pilot results are able to be
reduced and compared to full scale performance results. Further
analysis is available through use of the IERL-developed ESP
performance computer model.
Pilot ESP performance results have been reported on several
utility boiler studies, including: 1) hot-side precipitation, 2)
sodium carbonate conditioning, 3) waste-as-fuel co-firing, 4)
comparison between conventional and pre-charger ESP performance,
and 5) atmospheric-ESP control of pressurized fluidized-bed-
combustion emissions. Actual experience from operating, main-
taining, troubleshooting, and upgrading the mobile ESP has been
obtained from these test programs and incorporated into several
sections of this report. The number and variety of applications,
"trial and error" experiences, along with technical guidance from
IERL staff, sponsored contractors, and several conferences
Comprise the practical and technical basis for some of the in-
formation shared in this report.
2.7 DESIGN AND SIZING PARAMETERS
Table 2-2 summarizes ranges of values for important basic
design parameters that are discussed in this section. Additional
factors that should be considered in precipitator design specifi-
cations and evaluations are summarized in Table 2-3. The three
2-31
-------
TABLE 2-2. RANGE OF BASIC DESIGN PARAMETERS IN
OPERATING FLY-ASH PRECIPITATORS8
Parameter
Range of values
Plate spacing
Precipitation rate parameter for
Deutsch-Anderson equation (w )
e
Collection surface
Gas velocity
issia °j gssi
Corona power
Corona current density
Plate area per electrical set
No. of high-tension sections in
the direction of gas flow
Degree of sectionalization
20 - 30.5 cm
0.015 - 0.18 m/sec
18 - 145 m^/m^/sec
1.2 - 2.4 m/sec
0.5 - 1.5
30 - 300 watts/1000 iri^/sec
2
5-75 nanoamps/m
450 - 7400 m2
2-8
0 25 - 2 5 high-tension bus sections
100,000 mVsec
2-32
-------
TABLE 2-3. DESIGN FACTORS FOR PRECIPITATOR
SPECIFICATION AND EVALUATION8
1. Corona electrodes: type and method of supporting.
2. Collecting electrodes: type, size, mounting, mechani-
cal, and aerodynamic properties.
3. Rectifier sets: ratings, automatic control system,
number, instrumentation, and monitoring provisions.
4. Rappers for corona and collecting electrodes: type,
size, range of frequency and intensity settings,
number, and arrangement.
5. Hoppers: geometry, size, storage capacity for col-
lected dust, number, and location.
6. Hopper dust removal system: type, capacity, protection
against air inleakage, and dust blow-back.
7. Heat insulation of shell and hoppers, and precipitator
roof protection against weather.
8. Access doors to precipitator for ease of internal
inspection and repair.
9. Provisions for obtaining uniform, low-turbulence gas
flow through precipitator. This will usually require
a high-quality gas flow model study made by experienced
people in accord with generally accepted techniques,
with full report to precipitator purchaser before field
construction.
10. Quality of field construction of precipitator, includ-
ing adherence to electrode spacing and rigidity re-
quirements .
11. Warranties: performance guarantees, payment schedules,
adequate time allowance for performance tests, penalties
for nonperformance.
12. Support insulators for high-tension frames: type,
number, reliability. Air venting, if required.
13. Inlet and outlet gas duct arrangements.
14. structure and foundation requirements.
2-33
-------
most important parameters that affect the size of an ESP are
collection area, gas velocity, and aspect ratio.
2.7.1 Collection Area
Some variation of the Deutsch-Anderson equation is generally
used to estimate the required collection plate area. Figures
2-14 and 2-15 present the relationships of specific collecting
areas (SCA's) developed with the Deutsch-Anderson w and Matts
w
• •
Ohnfeldt w^., respectively.
2.7.2 Gas Velocity
Designers calculate an average (superficial) value for gas
velocity from gas flow and cross sectional area of the precipi-
tator, independent of the localized variances within the pre-
cipitator. The primary importance of the superficial gas veloc-
ity is to indicate the average velocity level and to subsequently
calculate the average residence time. Above some critical veloc-
ity (v2 m/sec) rapping and reentrainment losses tend to increase
rapidly because of the aerodynamic forces on the particles. This
critical velocity is a function of gas flow, plate configuration,
precipitator size, and other factors such as resistivity. Values
for gas velocity in fly ash precipitators range from 0.9 to 1.2
m/s (3.0 to 4.0 ft/s) in high-resistivity, cold-side ESP applica-
tions, and in all low-resistivity applications (hot or cold
side). For most other applications, the values range from 0.9 to
1.7 m/s (3.0 to 5.5 ft/s).
2.7.3 Aspect Ratio
Aspect ratio is defined as the ratio of the length to the
height of gas passage. Although space limitations ofter deter-
mine precipitator dimensions, the aspect ratio should be high
enough so that the reentrained dust carried forward from inlet
and middle sections can be collected. In practice, aspect ratios
range from 0.6 to 1.5. For efficiencies of 99 percent or higher,
the aspect ratio should be at least 1.0 to 1.5 to minimize
carry-over of collected dust.
2-34
-------
o
o
TOO 200 300 400 500 600
SPECIFIC COLLECTION AREA, FT2/1000 ACFM
METRIC CONVERSION: FT2/1000 ACFM x .055- m2/1000 m3/sec
Figure 2-14. Precipitator efficiency versus specific
collection area and precipitation rate
u
cc
©
M
H
100 200 300 400 500 600
SPECIFIC COLLECTION AREA, FT2/!000 ACFM
METRIC CONVERSION: FT2/1000 ACFM x.055 ¦ m /1000 m / sec
Figure 2-15. Precipitator efficiency as a function of specific
collection area and modified precipitation rate parameter w,. 8
K
2-35
-------
2.8 ELECTRICAL ENERGIZATION
The way in which a precipitator is energized has a strong
effect on its performance. Electrical energization involves the
number and size of the transformer-rectifier (T-R) sets, number
of electrical sections in half wave/full wave (HW-FW) operation,
and changes in the voltage current characteristics as precipita-
tion proceeds in the direction of gas flow.
Corona power is another important design factor, along with
being a quantitative indicator of collection performance on an
operating ESP (see Section 6 for use in ESP performance evalua-
tions) . Corona power is a measure of the presence and intensity
of the electrical energy (driving force) used in the precipita-
tion process. The extent of corona power used in precipitation
is measured by the primary or secondary voltage and current
meters. A technological basis is substantiated in Section 6
which correlates ESP corona power with particulate emission
level.^ Although factors other than corona power are responsible
for determining the performance level (e.g., electrode alignment,
rapper operation and sequence, etc.), the influence of these
degradation factors is reflected by corona power levels. When
problems with electrode alignment or rapper operation arise, they
evidence themselves by reducing the operating voltage and current
levels of the fields affected. Conversely high corona power
levels can compensate for some design short comings. Since
corona power is the product of voltage and current, reduced
operating voltage and current levels produce reduced corona power
levels proportional to their products.
2-36
-------
REFERENCES FOR SECTION 2
1. White, H.J. Electrostatic Precipitation of Fly Ash, Part I,
Journal of the Air Pollution Control Association. January
1977.
2. Oglesby, Sabert, Jr. and Grady B. Nichols. Electrostatic
Precipitation In: Air Pollution, 3rd Edition, Vol. IV.
Engineering Control of Air Pollution. Academic Press. New
York, San Francisco, London. 1977. pp 189-256.
3. Smith, Wallace B. et al. Procedures Manual for Electro-
static Precipitator Evaluation. Southern Research Insti-
tute. Birmingham, Alabama. EPA 600/7-77-059. June 1977.
4. White, H.J. Electrostatic Precipitation of Fly Ash, Part
II, Journal of the Air Pollution Control Association.
February 1977.
5. Bickelhaupt, R.E. Journal of the Air Pollution Control
Association. 1974.
6. White, H.J. Electrostatic Precipitation of Fly Ash, Part
IV. Journal of the Air Pollution Association. April 1977.
7. Bump, R.L. Electrostatic Precipitators in Industry. Chem-
ical Engineering. January 7, 1977.
8. White, H.J. Electrostatic Precipitation of Fly Ash, Part
III. 'journal of the Air Pollution Control Association.
March 1977.
9. White, H.J. Industrial Electrostatic Precipitation.
Addison-Wesley Publishing Company, Inc. Reading, Mass.
1963. 376 p.
10. Oglesby, Sobertr Jr. Electrostatic Precipitation. South-
ern Research Institute Bulletin-Winter, 1976.
11 Oqlesby S. and G.B. Nichols. A Manual of Electrostatic
Precipitator Technology, Part 1, Fundamentals, PB 196 380.
12. Ross, R.D. Editor. Air Pollution and Industry, Van Nostrand
Reinhold Companyf New York, 1972.
2-37
-------
Mcllvaine Precipitator Manual, Chapter VI, Section
August 1976, p. 5613.
2-38
-------
SECTION 3
INSTRUMENTATION AND RECORDS
The continued optimum performance of an ESP depends upon
effective control of operating parameters, which can vary because
of the physical characteristics of an ESP or changes in charac-
teristics of the flue gas being treated. Recent ESP installa-
tions are generally equipped with instrumentation for monitoring
and recording the major operating parameters. ESP instrumenta-
tion and records of electrical operating levels are the major
indicators of ESP performance; the inspector should thoroughly
understand the function of each instrument and record to evaluate
ESP performance.
3.1 ESP INSTRUMENTATION-LOCATION AND GENERAL DESCRIPTION
ESP instrumentation consists mainly of monitors for power
input, gas flow, rapper intensity, and hopper dust levels. The
power input parameters are precipitator current, voltage, and
spark rate. Gas flow parameters are the input gas flow rate and
input gas temperature.
The ESP instruments are generally located in close vicinity
of the ESP unit; when a plant has more than one ESP, a centrally
located control room houses the instrumentation for all the ESP
units. The location of the ESP control room depends upon the
availability of space at the plant; however, it is generally
located close to ESP units. Two common control room locations
are: on top of the ESP units and directly under the ESP unit for
an elevated unit. The ESP control room is generally located
3-1
-------
close to the ESP's and separately from the plant control room to
avoid long cable runs from the ESP to the plant control room.
The instruments for each ESP unit are assembled and housed
in a simple sheet metal cabinet. A typical ESP control room may
consist of a number of control cabinets arranged in a line and
each cabinet labeled to identify the ESP unit it serves. A
typical ESP control panel and control panel console are shown in
Figures 3-1 and 3-2, respectively.
An ESP instrumentation block diagram is shown in Figure
3-3. Figure 3-4 shows the positions of various measuring instru-
ments in an ESP circuit. The ESP in Figure 3-3 has four T-R
sets, and each T-R set has two bus sections. Primary voltage and
primary current are measured for each T-R set; secondary voltage,
secondary current, and spark rate and measured for each bus
section. Gas flow rate and temperature are measured at the ESP
inlet. An opacity measurement at the ESP outlet roughly indicates
emission levels. The ESP shown in Figure 3-3 has four primary
voltmeters and four primary ammeters; the secondary side instru-
mentation consists of eight secondary voltmeters, eight secondary
ammeters, and eight spark rate meters. The instrumentation
schemes for different ESP installations may vary slightly from
the basic scheme shown in Figure 3-3.
The relative location of each instrument in the circuit is
decided by its function. The primary ammeter, for example, is
always located ahead of the transformer primary in order to
indicate the current available for transformation. The inspector
should understand the relative positions of various ESP instru-
ments. The function of each ESP instrument is discussed in the
following paragraphs.
3.2.1 Primary Instrumentation
Primary Voltmeter—
Energization power for an ESP is supplied at the primary
side of the T-R set. The a.c. electrical power is normally
3-2
-------
: v SI* .. f V^ . • VL ' H« ' . :-
- *>•'• -5 ~,..V.
^ •ui»Ai0tuei»ie
Figure 3-1. Typical ESP control panel.
(Courtesy of Babcock and Wilcox Co.)
3-3
-------
Figure 3-2. Example of ESP control panel console.
(Courtsey of Babcock & Wilcox Company)
3-4
i
-------
SV SI SR PV PI
SI SR
SV SI SR PV PI SV SI SR
u>
U1
SI S* PV PI SV SI SR SV SI SR PV PI SV SI S*
SV SI SR PV PI SV SI SR
OUTLET DUCT N.
TO STACK
ESP UNIT
I*ET DUCT
HOPPERS
\l 'I ASH LEVEL INDICATOR
PACITY
INDICATOR
Lf 1GAS FLOW METE*
P flNLET GAS TEMPERATURE INDICATOR
SV: SECONDARY VOLTAGE
SI: SECONDARY CURRENT
SR: SPARK RATE
PV: PRIMARY VOLTAGE
PI: PRIMARY CURRENT
Figure 3-3. ESP Instrumentation diagram.
-------
sen
CONTROL
H.V.
SILICON
RECTIFIER
BRIDGE
~60 V
SPARK
RATE
NET Eft
FEEDBACK
NETWORK
PPTR.
w
60 HZ
CONTROL
TRANS. rrrr^
H.V.
TRANSF.
OFF
K.V.
HETER
CURRENT
SENSOR
I HETER
SPARK
RATE
WffTftft
AUTOMATIC CONTROL MODULE
INCLUDES SLOW START
VOLTASE
LIMIT
TRANSIENT
LIWT
Figure 3-4. Positions of measuring instruments.
-------
supplied at 220 or 460 volts. Each T-R set for an ESP is normally
provided with a voltmeter and an ammeter to indicate input voltage
and input current.
The range of a voltmeter dial for primary voltage is 0 to
480 volts. Normal operating voltage is around 220 to 460 volts,
depending on the selection of supply voltage. A temporary mar-
ginal deviation of about 5 percent from the rated supply voltage
is common and should not be considered a major operating problem.
Generally, a label on the primary voltmeter indicates the maximum
permissible voltage reading.
The voltmeter on the primary side is located ahead of the
T-R set but after the power control circuit, linear reactor, and
feedback network. This positioning of the voltmeter ensures
measurement of regulated voltage available at the T-R set for
transformation.
An indication of no voltage on the primary side may be due
to an open primary circuit. The circuit breaker may be open or
tripped, or the reactor secondary may be open. The open circuit
breaker can be closed with power on, but replacement of the
reactor secondary requires power switchoff and ESP shutdown.
An indication of high voltage on the primary could result
from an open transformer primary or improper connection of an
ESP. A faulty, open, or disconnected precipitator, an open bus,
or a faulty rectifier will cause indication of high primary volt-
age. An ESP shutdown is mandatory for correcting these faults.
An indication of low voltage on the primary side could
result from several conditions such as a leak in the high-voltage
insulation, high dust level in hoppers, excessive dust on elec-
trodes, or swinging electrodes. Correction of the fault may
require shutdown.
Primary Ammeter—
The ammeter on the primary side indicates the current drawn
by the ESP. The current and voltage readings on the primary
indicate the power input to a particular section of an ESP.
3-7
-------
An ammeter for primary current measurement is located be-
tween the T-R set and the power control circuit, linear reactor,
and feedback network. Figure 3-4 indicates the location of an
ammeter for primary current. Positioning the ammeter between the
T-R set and the control circuit ensures measurement of the
current available for transformation.
The ammeter is generally labeled to indicate the normal
range of primary current. Any deviation from this range indi-
cates abnormal operation of the following ESP section. A reading
that shows no primary current associated with no primary voltage
indicates an open primary circuit, which may be due to open
circuit breakers or an open reactor secondary. Minimal primary
current associated with high primary voltage is generally caused
by an open transformer primary or open secondary circuit. Pre-
cipitator shutdown is mandatory to correct these faults. Indica-
tion of low primary current with low primary voltage results from
an open d.c. reactor. Again, precipitator shutdown in mandatory.
Irregular primary current coupled with low primary voltage
indicates a high resistance short in the circuit. Possible
causes are an electrode short with dust in the hopper, excessive
dust on collecting surfaces, exccesive dust on electrodes, sup-
port insulator arcing, and the presence of foreign materials. A
broken swinging electrode causes an intermittent short, which is
indicated by low primary voltage and cycling primary current.
3.1.2 Secondary Instrumentation
Instrumentation ont he secondary side of the T-R set indi-
cates the power input parameters to an individual ESP bus section-
This instrumentation is of primary importance to the inspector.
The secondary instrumentation generally consists of a voltmeter,
an ammeter, and a spark rate meter for each bus section. The
combination of these meter readings indicates the overall opera-
ting conditions on the secondary side of the T-R set.
3-8
-------
Secondary Voltmeter—
The secondary voltmeter is calibrated in kilovolts to
measure the high voltage of the power input to the discharge
electrodes. The secondary voltmeter is labeled to indicate the
upper limit and normal range of the operative voltage.
The second voltmeter is located between the rectifier output
side and discharge electrodes to indicate the d.c. voltage across
the discharge electrodes.
An indication of no voltage on the secondary may be due to
an open primary circuit. The circuit breaker may be open or
tripped, or a reactor secondary may be open. As indicated
earlier, the circuit breaker can be closed with power on, but
replacement of a reactor secondary will require power switchoff
and ESP shutdown. A faulty, open, or disconnected precipitator,
an open bus, or a faulty rectifier will indicate high voltage on
the primary side and no voltage on the secondary side. Shutdown
of the ESP is mandatory for correcting these faults.
Low voltage on the secondary side coupled with the low
voltage on the primary side could result in several operating
problems such as those mentioned earlier, a leak in the high-
voltage insulation, excessive dust in the hoppers or on elec-
trodes, or swinging electrodes. Correction of the fault may
require shutdown.
Secondary Ammeter--
The ammeter on the secondary side indicates the current
being supplied to the discharge electrodes. The combination of
current and voltage readings on the secondary side indicates the
power input to the discharge electrodes. The location of the
secondary ammeter is shown in Figure 3-4.
The secondary current is stepped down in the transformer and
is measured in milliamperes. The secondary ammeter is therefore
calibrated in milliamperes and is labeled to indicate the maximum
value and normal range of secondary current. Deviation from the
3-9
-------
normal operating range indicates improper operating conditions in
the precipitator.
A combination of no secondary current with no secondary
voltage indicates an open primary circuit. Minimal secondary
current associated with high voltage is generally due to an open
transformer primary or open secondary circuit. Precipitator
shutdown is mandatory to correct these faults. An open d.c.
reactor will cause a low current flow and low voltage in the
circuit.
As with primary circuitry, irregular secondary current
coupled with low secondary voltage indicates a high-resistance
short in the circuit; possible causes are the same, usually
related to excessive dust, foreign materials, or arcing. Again,
a broken swinging electrode causes an intermittent short, indi-
cated by low voltage and cycling current.
Spark Rate Meter—
The spark rate meter on an ESP is a major indicator of its
performance. The spark rate meter is generally connected in the
secondary circuit; it indicates the number of sparks in the pre-
cipitator section and is calibrated in number of electrical
sparks per minute.
The number of sparks together with secondary voltage and
secondary current give a fair presentation of the ESP operating
condition. Theoretically, the power input to a section is
maximum when no sparks occur and voltage and currents are at
their rated maximum; in actual practice, however, the optimum
power input occurs at a preset spark rate. For ESP's on coal-
fired utility boilers, the optimum spark rate is around 100
sparks per minute. Optimum spark rate depends on the physical
and design characteristics of the ESP.
Because excessive sparking indicates power loss, less power
is available for particle charging. A sparking rate below the
optimum level indicates a power supply rate below optimum.
3-10
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3.1.3 External Instrumentation
Certain instruments external to the ESP indicate parameters
that relate strongly to ESP operation. These include instruments
that measure inlet gas-flow rate, inlet gas temperature, opacity
of flue gas at the ESP outlet, hopper ash discharge, and rapping
systems.
Inlet Gas Flow and Temperature—
The gas-flow rate and temperature are indicators of ESP
loading. Any variations from the normal design ranges will
affect ESP performance and should be investigated. At most
installations, the gas flow and temperature measurements are
taken at the exit of the process unit or boiler. The instruments
for recording the flow and temperature are generally located in
the main control room. Some installations maintain continuous
records of gas flow and temperature.
Opacity at the ESP Outlet—
Federal and state regulations generally regulate the opacity
of the flue gases in addition to limiting particulate emissions.
The more recent ESP installations are equipped with continuous
opacity recorders.
A general configuration of the opacity monitoring system is
shown in Figure 3-5. The system includes an opacity detector
unit that senses the opacity of the gases passing through the
ductwork. This unit includes a light source and a detector, tho
difference between the amount of light transmitted by the light
source and that received by the detector indicates the particulate
concentration of the gases. The difference is calibrated as
percent by the opacity meter. An opacity reading of zero percent
indicates a minimal particulate concentration; an opacity reading
of 100 percent indicates a maximum particulate concentration.
The variation in opacity gases cannot be solely attributed to the
particulate matter; however, it gives a fair indication of
particulate concentration.
3-11
-------
LIGHT SOURCE
TRANSITION
DUCT
ESP UNIT
DUCT TO STACK
FJdetector
CONTROL UNIT
STRIP CHART RECORDER
Figure Connection diagram of the opacity monitoring system.
3-12
-------
Ash Discharge--
Efficient removal of ash from the hoppers is important for
proper ESP performance. Ash removal systems at ESP installations
are generally equipped with instrumentation that indicates empty-
ing of the hoppers and continuously records the vacuum in the
system.
Hopper level alarms are another common and useful type of
instrument. Level detectors can utilize gamma radiation, sound
capacitance, pressure differential, or temperature. The alarms
should be located so that filling of hoppers does not occur but
frequent alarms are avoided. A low-temperature probe and alarm
can be used in conjunction with the level detector. Control
panel lights are used to indicate the operation of hopper heaters
and vibrators. Automatic phase-back of T-R sets in conjunction
with full hopper level alarms are also incorporated into the
instrumentation of some ESP designs.
In general, although various vendors provide different ash
discharge systems, the instrumentation and records are similar.
Zero motion switches are used on rotary air lock valves to detect
malfunction, as well as on screw conveyors. Pressure switches
and alarms are normally used with pneumatic dust handling systems
to detect operating problems.
Rappers/Vibrators—
Microprocessor type technology is available for a high
degree of rapper control flexibility and ease of maintenance.
For example, in order to prevent control damage from ground
faults, new controls will test each circuit before energizing it.
If a ground fault occurs, the control will automatically bypass
the grounded circuit and indicate the problem on an LED display,
thus permitting fast location and solution of the problem.
/
Instrumentation should be used in conjunction with a trans-
missometer to help in troubleshooting ESP problems. Separate
rapping instrumentation should be provided for each field.
3-13
-------
Readings of frequency, intensity, and cycle time can be used with
T-R set controls to properly set rapper frequency and intensity,
in the case of the weighted-wire electrodes.
For rigid frame mechanical rappers, cycle time and rap
frequency of both internal and external types are easy to measure.
Individual operation of internal rappers is not easily instru-
mented, nor is intensity control possible without a shutdown of
the ESP.
3.2 RECORDKEEPING
Recordkeeping of pertinent ESP operating data can be used
for:
1. Assurance of proper operating status
2. Diagnostic mean for troubleshooting operational prob-
lems
3. An indicator for performance excursion from peak or
previously documented performance levels (see Section
6)
Technical engineers for ESP manufacturing and consulting
companies customarily use pertinent ESP operating data and spe-
cific reference information as feedback on the performance of a
precipitator system. Operating data and specific reference
information can be interpreted to gain insight into the behavior
characteristics of a given ESP unit. ESP behavior is considered
to be the electrical operating conditions and associated collec-
tion performance levels over the normal range of treatment condi-
tions. In order to interpret the available information, one
needs: (1) a general understanding of precipitator technology,
(2) familiarity with ESP hardware components, and (3) experience
with the normal set of difficulties encountered with conventional
precipitators.
The proceeding discussions will identify the tools needed to
assess the operational conditions of an ESP. Explanations and
3-14
-------
examples will be provided to show how these tools (information)
can be used (interpreted) to evaluate an ESP system. On-site
operators and agency inspectors can readily learn and regularly
use this evaluation technique. This technique will provide
concerned personnel a reasonable account of the prevailing condi-
tions internal to an ESP. A principal advantage of this tech-
nique is that valuable information can be acquired and used
without an internal inspection.
3.2.1 ESP Design Specifications
Specifications of the ESP design parameters is the fundamen-
tal reference point of any inspection technique. A comprehensive
set of ESP design specifications should be provided by the vendor,
and if lost, should be requisitioned, copied, filed, and made
available to the concerned operating and regulating personnel. A
copy of such specifications should be readily available for the
ESP operators, inspectors, and/or analysts.
Table 3-1 presents a comprehensive listing of ESP design
specifications, organized in three categories: hardware, elec-
trical, and application. The hardware category identifies
several mechanical and dimensional characteristics of the ESP
system. Corresponding diagrams depicting the layout of the
influent and effluent gas manifolding, and the internal chamber-
ing should be included with the specifications. These diagrams
will provide a useful perspective for the operating staff in
understanding the general layout and associated nomenclature of
the system. The tabulated specifications will facilitate subse-
quent troubleshooting and performance analysis over the years of
service. The listed electrical specifications include general
and specific indicators of voltage and current at both primary
and secondary (if available) levels. These design values should
be frequently referenced to actual operating electrical data
throughout the service life of the equipment. If the electrical
3-15
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TABLE 3-1. ESP DESIGN SPECIFICATIONS FOR WHICH
RECORDS SHOULD BE MAINTAINED
A. Hardware Specifications
Manufacturer
Model
Year installed
Collection plate area (total)
Number of chambers
Number of fields
Plate spacing
Plate height
Plate width
Number of lanes/section
Cross-sectional area/section
Linear feet of discharge wire
Rapper type, plate
Rapper type, wires
Rapper acceleration, plate
Rapper acceleration, wires
B. Electrical Specifications
Corona power total
Corona power per unit volume of gas
Number of T-R sets
Rating(s) of T-R set
Average primary voltage
Average primary current
Average secondary voltage
Average secondary current
Average current density per plate area*
Average current density per electrode length*
C. Application Specification
Gas flowrate, total
Gas temperature, inlet
Gas temperature, outlet
Gas composition (N2, 02, SOx» etc.)
Gas velocity, superficial*
Gas velocity, distribution, Standard Deviation
Specific collection area*
Collection efficiency
Particulate concentration, inlet
Particulate concentration, outlet
Particle size distribution, inlet
Particle size distribution/ outlet
Precipitation rate parameter* (particle migration velocity)
Resistivity value (or range)
* Parameters that can be calculated from other given values.
3-16
-------
equipment is replaced, or internal changes or upgrades are made,
then corresponding adjustments in the electrical specification
package should be entered. The specifications defining the
application of this mechanical and electrical hardware includes
the important gas and particulate characteristics. The design or
expected application parameters should be likewise referenced to
measured data.
The hardware and electrical specification packages should
and probably will be well-defined. These two design areas repre-
sent the technical areas that manufacturing companies are most
familiar with, and mainly responsible for. The application
details represent an interface area in which both the manufactur-
ing and operating companies participate. This area is probably
the most vulnerable area of the three categories, due to possible
problems from (1) the extent of technical qualities of each the
buyer and seller, (2) the extent of technical cooperation between
the buyer/seller, and (3) the extent of technical stability
between the initial gas/particulate specification provided and
the actual experienced gas/particulate stream. This technique is
not offered to replace regularly scheduled internal inspections.
Instead, it is offered to discover important symptoms when an ESP
is on-line. Furthermore, proper recordkeeping and use of this
technique will streamline and prevent unnecessary internal
inspections.
3.2.2 ESP Operating Data Recordkeeping
Table 3-2 presents a listing of process and ESP conditions
that will provide useful and meaningful information. Compilation
of this information on a regular basis will supply an account and
history of the operational and performance levels.
The significant descriptors of the process generating the
gas particulate stream to the ESP should be identified and logged.
It is fundamentally understood that the process characteristics
3-17
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TABLE 3-2. BASELINE TEST INFORMATION
Process Conditions
Gas flowrate
Gas temperature - point A, B, C, etc
Static pressure
Process level (load, % capacity)
Process feed rate(s)
Process feed descriptor(s)
Process product level(s)
Process product descriptor(s)
B. ESP Operating Conditions
Gas temperature, ESP inlet(s)
Gas temperature, ESP outlet(s)
Primary voltage
Primary current
Secondary voltage
Secondary current
Spark rate
Rapper frequency, plate"]
Rapper frequency, wire ( for eaoh T_R set
Rapper duration, plate ( *
Rapper duration, wire J
per T-R set for each field
3-18
-------
impact the design, operating, and performance levels of the ESP.
In order to establish a relationship between process and ESP
conditions, corresponding records of the significant descriptors
must be acquired, tabulated, and organized.
All the significant input and output ratings of the process
should be recorded. Qualification of feed materials and/or fuels
should be noted, including feed rates, temperatures, pressure,
moisture content, and analytical results. Any irregularities
concerning these qualifiers should be noted. Additionally,
similar treatment should be afforded to noting and qualifying the
different outputs or products for the process. An abbreviated
record can be created, or a copy of the comprehensive operator's
log sheet can be duplicated, to regularly account for the process.
Most processes ential some form of treatment on the gas/par-
ticulate stream between the primary process and the ESP systems.
This intermediate treatment step varies for the different indus-
trial streams controlled by an ESP, but typically is dedicated to
recover viable energy, products, or by-products. Certain process
designs include a Subsystem dedicated to prepare or condition the
process stream for the purpose of improving ESP collection per-
formance. Appropriate qualifications of any changes on the
gas/particulate stream should be likewise monitored and recorded.
Pertinent changes include physical or chamical adjustments to the
stream, regarding energy/material additions or deletions. Rec-
ords accounting for the intermediate treatment system should be
maintained to describe the prevailing conditions and materials
input/output.
Primary meters indicate voltage and current levels fed to
the T-R sets. The purpose of secondary meters is to measure the
voltage and current levels leaving the T-R set, enroute to the
internal fields of the ESP. Primary metering is only an
indirect measure of the high-voltage power necessary to energize
to energize an ESP. Secondary metering is the direct method of
measuring the delivered high voltage power.
3-19
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3.2.3 ESP Operating Conditions
The significant descriptors of the ESP system need to be
measured and recorded in order to account for its operationally
and associated performance. Since it is an electrostatic device
designed to effectively use high voltage levels to charge and
precipitate entrained particles, it is necessary that the voltage
and current levels be measured and recorded. It is important for
inspectors to realize that the primary and/or secondary elec-
trical data are the vital parameters of an ESP. Without excep-
tion, all technical engineers of ESP manufacturing and consulting
companies realize the cruciality of delivering high voltage power
to the internal electrodes. Failure to deliver high voltage
power to the electrodes transforms a would-be electrostatic
precipitator into a chemical collector. Primary electrical
meters are useful instruments to meter the electrical circuitry
of an ESP. However, secondary electrical meters are more useful,
since they directly indicate the voltage and current levels
experienced by the precipitating components.
Unfortunately, there is not a linear relationship (or con-
stant coefficient) between primary and secondary electrical
levels.
Obtaining voltage-current data over the electrical operating
range of each T-R set is a very useful method for evaluating
and/or troubleshooting an ESP. The relationship of the voltages
applied...and the resultant currents may be analyzed and, coupled
with knowledge of other relevent parameters, gives insight into
9
the operation and expected performance of the precipitator.
Data are taken as the manual set control is gradually increased
until some current flow is detected. This is recorded as the
corona starting voltage. Subsequent points are taken by in-
creasing the control for some increment of current and recording
the meter readings at that point. Readings are taken until some
limiting factor is reached. This factor is recorded on the
right-hand side of the data sheet and is usually excessive
3-20
-------
sparking, or a current or voltage limitation of the power set.
Figure 3-6 is an example of a data sheet used to collect data
from which voltage—current relationships may be plotted. The
term "V-I.curve" will be used subsequently to signify the volt-
age-current relationship discussed above.
3.2.4 Ideal V-I Patterns
For a multi-field ESP, the assembly of on-line V-I curves
should look like the pattern shown in Figure 3-7. Note the inlet
field V-I curve is on the far right, and the middle and outlet
field curves are progressively shifted to the left, respectively.
As the caption in Figure 3-7 states, this gradual shifting is due
to space charge effects. The space charge effect diminishes as
the particulate concentration diminishes and the gas stream
passes through the series of energized fields.
The relative slope of the on-line V-I curve is dependent on
several factors, one of which is particulate flux. Particulate
flux is the combined product of particulate loading and gas
flowrate; an increase in either component will proportionally
increase the particulate flux level. Figure 3-8 illustrates the
principle of various levels of particulate flux from a theoret-
ical approach. The uppermost left curve represents the expected
V-l curve with no particulate flux. The remainder of the V-I
curves represent various levels of particulate flux for different
gas flow levels (numbers represent SCA levels with, SCA values
inversely proportional to gas flow levels) and for inlet and
outlet fields, respectively. As particulate flux levels in-
crease, the V-I curves progressively shift to the right. For the
same gas composition and voltage, increasing levels of particu-
late loading (especially in the fine particle size range) will
reduce or suppress current levels. Charged particles migrate
orders of magnitude slower than the rest of the charge carriers
(i.e., free electrons and ionized gas molecules). As more charge
or current is carried by the relatively slow migrating particles,
the slower the overall current-carrying process proceeds, and
3-21
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POWER SET
VOLTAGE-CURRENT CURVE DATA SHEET
DATE/TIME T/R SET NO. COLLECTING AREA
VOLTAGE DIV. MULT.
T/R SET DCMA CORRECTION
PRIMARY
VOLTS
PRIMARY
AMPS
DCKV
T/R SET
METER
DCMA
T/R SET
METER
SPARK
RATE
DCMA
CORR.
VOLTAGE
DIV.
DCKV
CORR.
v%
NA/
cm
TERMINAL POINT
DETERMINED BY:
(CIRCLE ONE)
L.
SPARKING
2.
SEC. CURRENT
LIMIT
3.
SEC. VOLTAGE
LIMIT
4.
OTHER
COMMENTS
g
Figure 3-6. Sample V-I curve data sheet.
-------
60
50 —
40
C\i
E
u
'—
e£
c
>-
w> 30
LlJ
o
cc
en
20
10 —
-INLET ELECTRICAL FIELD
¦MIDDLE ELECTRICAL FIELD
OUTLET ELECTRICAL FIELD
10
40
VOLTAGE, kV
Figure 3-7. Secondary voltage-current curves demonstrating the particulate
space charge effect in a full-scale, cold-side precipitator collectinq
fly ash.6
3-23
-------
98 59
NO MASS
LOADING
OUTLET FIELD;
NUMBERS REPRE-
SENT SCA LEVELS
£ 30
UJ
O
o
40
20
30
0
50
10
VOLTAGE, kV
NO MASS
LOADING
INLET FIELD;
NUMBERS REPRE-
SENT SCA LEVELS
^ 30
VOLTAGE, kV
Figure 3-8. Comparison of theoretical voltage-current
curves for different specific collection areas.®
3-24
-------
thus the reduced current levels for the same applied voltage.
Technically, the concentration of fine particulate is the con-
trolling factor for space charge or current suppression effects.
2
In other words, a 1 gr/ft stream composed of fine particulate
will cause higher space charge effects (lower current levels)
3
than a 2 gr/ft stream of large particles.
The general message concerning this section on on-line
recordkeeping is that primary and/or secondary electrical data
and profiles (V-I curves) are the telltale indicators of ESP
performance. The general rule is that the ideal V-I patterns
need to be approached in real systems, and the extent of devia-
tions from the appropriate pattern is a significant measure for
performance degradation. Examination of these electrical pro-
files and other records are very effective for troubleshooting.
Normally-experienced V-I curves and patterns will reflect
the prevailing conditions and associated problem areas in an ESP.
Some case studies will possess V-I conditions that are a result
of several causes. In general, most of these causes will evi-
dence themselves in the form of substantially reduced voltage
levels, and corresponding reduced current levels. Only two
problems (current leakage and severe back-corona) will be evi-
denced by higher than design current values. (A complete second-
ary V-I curve will distinguish between these two exceptional
cases, and consequently account for the dependent voltage level).
The more general case of reduced corona or operating points
(i.e., reduced endpoint of actual V-I curve) may possess such a
limited curve that identification or interpretation of signifi-
cant problem(s) becomes only remotely possible.
The technical principles behind the V-I evidence are stead-
fast. The following figures and short descriptions will symptom-
ize problems or conditions related to on-line treatment of
industrial streams. Cases of cause - singularity are presented
from actual field V-I data to illustrate and reinforce the
characterizable relationship of V-I patterns and prevailing
conditions.
3-25
-------
A common factor effecting the slope and relative position of
the V-I curve is resistivity. Figure 3-9 compares the V-I
curves with and without ammonia conditioning. Figure 3-10 offers
convincing evidence that ammonia injection is responsible for
this V-I shift-
Figures 3-11 through 3-14 show V-I curves for an ESP indica-
tive of excellent electrical characteristics treating flyash from
high sulfur eastern coal. Bushings A and B in these figures
represent two ESP's side-by-side.
Sparking is another factor that shows up in V-I traces.
Figure 3-15 shows V-I curves with and without SO^ conditioning.
The portions of the curves with positive slopes portray data
collected with no sparking or very light sparking. The segments
of the V-I curves with negative slopes represent moderate-to-
heavy sparking conditions.
Dust layer thickness will influence V-I character. Figure
3-16 compares V-I curves at start-up (no dust layer) with condi-
tions 5 hours later (with dust layer). Note the shift and the
reduced operating point associated with a dusty F.SP treating fly-
ash from a low sulfur western coal.
Treatment temperature also impacts V-I shapes. Figure 3-17
shows V-I curves from a hot-side ESP treating low sulfur eastern
flyash. Note the gently increasing slopes for each of the
fields, typical of good electrical characteristics. Figures
3-18 and 3-19 show the dramatic effect on V-I character for full
load conditions at 625°F and half-load conditions at 485°F.
Figure 3-20 shows typical V-I curves from a hot-side ESP treating
low sulfur western flyash. Compare these curves back to Figure
3-17 for low sulfur eastern flyash. Differences in resistivity
between the eastern and western low sulfur flyashes account for
distinctions in V-I curves.
Since there are a variety of corona electrodes, plates (see
Figures 2-6 and 2-7) and vendor designs, each specific ESP
application will have slightly different V-I characteristics.
3-26
-------
C\J
E
o
c
c
>-
t—
•—"
«/¦>
z
DJ
o
a:
60
50
40
30
20
10
INLET FIELD
NO NH,
INJECTED
0
13 PPM OF
nh3 INJECTED,
60
50
CNJ
E
u
c
m
UJ
o
40
30
oc
cc
ZD
o
20
10
10 20 30 40
VOLTAGE, kV
OUTLET FIELD
NO NH, _
INJECTED
/ 13 PPM
. —OF NH,
' INJECTED_
10 20 30
VOLTAGE, kV
40
50
Figure 3-9. Current density vs. voltage for a full-scale,
cold-side precipitator without and with NH3 conditioning
low sulfur coal
3-27
-------
1000
1100
HOUR
1200
re 3-10. Rapidity of the effect of ammonia injection on the voltage
supplied to the inlet electrical field of a full-scale, cold-side
precipitator (high-sulfur coal).®
3-28
-------
o
< 40
£ 30
B" BUSHING-
A" BUSHING;
20
30
40
0
10
50
VOLTAGE, kV
Figure 3-11. Secondary V-I curve for inlet field.of ESP
controlling high sulfur eastern flyash.
CM
A" BUSHING'
B" BUSHING-
o
en
cc
VOLTAGE, kV
Figure 3-12. Secondary V-I curve for second field
of ESP controlling high sulfur eastern flyash.6
3-29
-------
60
50
U
< 40
/_
A" BUSHING'
B" BUSHING
o
t—
20
cc
DC
10
0
40
50
30
0
20
10
VOLTAGE, kV
Figure 3-13. Secondary V-l curve for third field of
ESP controlling high sulfur eastern flyash.®
60
50
cv
A" BUSHING-
B" BUSHING'
UJ
O
20
o
10
0
0
10
20
30
40
50
VOLTAGE, kV
Figure 3-14. Secondary V-I curve for fourth field
ESP controlling high sulfur eastern flyash.6
3-30
-------
60
50
rj
E
u
40
- 30
-------
60
50
CNJ
E
u
< AO
>~
g 30
LU
O
t-
z
o£
cc
=5
O
20
10
i—r
"A" BUSHING-
•B" BUSHING-
0 10
VOLTAGE, kV
Figure 3-13. Secondary V-I curve for third field of
ESP controlling high sulfur eastern flyash.®
60
50
CNJ
e
a
< 40
c
£ 30
cc
cc
=3
20
10
0
"A" BUSHING-
"B" BUSH1NG-
10
VOLTAGE, kV
Figure 3-14. Secondary V-I curve for fourth field
ESP controlling high sulfur eastern flyash.°
3-30
-------
(VJ
WITH INJECTION
(14 PPM OF SO,)
< 40
o
WITHOUT
INJECTION
t-
t_>
^OUTLET FIELD
VOLTAGE, kV
< 40
WITH INJECTION
\ (14 PPM OF S02)
o
cc
cc
WITHOUT \
INJECTION
/ INLET FIELD
VOLTAGE, kV
Figure 3-15. Current density vs. voltage for a full-scale,
cold-side precipitator without and with SOg conditioning.®
3-31
-------
60
50
CvJ
E
o
< 40
c
£ 30
LU
O
WITHOUT DUST LAYER
WITH DUST LAYER
a:
a:
ZD
C_J
20
10
INLET FIELD
La
10
20
30
40
50
Figure 3-16
VOLTAGE, kV
. Voltage-current characteristics of inlet
field showing dust layer effect.®
FIELD NO. S
40
li
30
/
10 20 30 40 50
VOLTAGE, kV
Figure 3-17. V-I curve for hot-side ESP treating
low sulfur eastern flyash.6
3-32
-------
60
50
c\j
40
PLANT B
PLANT A
400 MW
o
20
PLANT A
// 800
o
10
0
20
0
30
40
10
50
VOLTAGE, kV
Figure 3-18. Inlet voltage current curves for two power
plants at different load conditions.6
PLANT B
PLANT A !
800 MW |
{X.
cc
PLANT A
400 MW
o
VOLTAGE, kV
Figure 3-19. Outlet voltage current curves for two power
plants at different load conditions.6
3-33
-------
INLET
OUTLET
^ 30
VOLTAGE, kV
Figure 3-20. Typical secondary voltage-current curves
obtained from a hot-side ESP collecting ash from a
Western power plant burning low sulfur coal.6
3-34
-------
Figure 3-21 illustrates several V-I curves from outlet fields on
cold-side ESP's treating flyash. These V-I curves reflect the
different operating characteristics associated with various wire
and spacing designs under similar application.
3-35
-------
1200
1100
1000
900
800
700
600
500
400
300
200
T
_ 11 Inch (27.9 cm) PLATE SPACING
9 SQUARE TWISTED DISCHARGE
ELECTRODES, PLANT NO. 2
A 12 Inch (30.5 cm) PLATE SPACING
PLANT NO. 1
¦ 10 inch (25.4 cm) PLATE SPACING,
RIGID "BARBED" DISCHARGE
ELECTRODES, PLANT NO. 3
W 9.75 Inch (24.8 cm) PLATE SPACING,
SPIRAL DISCHARGE ELECTRODES.
PLANT NO. 4
O 9 inch (23.9 cm) PLATE SPACING,
ROUND WIRE DISCHARGE
ELECTRODES, PLANT NO. 6
1
1
10
15
20 25 30 35
VOLTAGE, kV
40
45
50
5!
Figure 3-21. Voltage-current curves obtained from outlet
electrical fields in several cold-side
electrical precipitators.6
3-36
-------
REFERENCES FOR SECTION 3
1. McDonald, J.P., and A.H. Dean. A Manual for the Use of
Electrostatic Precipitators to Collect Fly Ash Particles,
EPA-600/8-80-025. May 1980.
2. White, H.J. Electrostatic Precipitation of Fly Ash, APCA
Reprint Series. July 1977.
3. Oglesby, S., and G.B. Nichols. A Manual of Electrostatic
Precipitator Technology, Parts I and II, PB 196 380 and
PB 196 381. August 1970.
4. Banks, S.M., J.R. McDonald, and L.E. Sparks. Voltage-
Current Data From Electrostatic Precipitators Under Normal
and Abnormal Conditions, In: Proceedings: Particulate
Collection Problems Using ESP's In the Metallurgical In-
dustry, EPA-600/2-77-208. October 1977.
3-37
-------
SECTION 4
OPERATION, MAINTENANCE, AND COMMON PROBLEMS
The following sections provide the inspector with operating
procedures, maintenance requirements, and common malfunctions of
modern ESP's. This information is presented to orient the in-
spector with the operation and maintenance requirements that are
necessary to obtain the highest possible collection efficiency.
This will aid the inspector in determining whether the company
has an adequate maintenance program. The ESP can then be main-
tained at its highest performance level with minimum loss of time
because of malfunctions. Much of the discussion is based on the
wire-weight type of ESP as applied in removal of fly ash. How-
ever, the inspector can apply many of these procedures to ESP's
on other processes. Further, the discussion chiefly concerns dry
ESP's since these units are more widely used than wet ESP's and
many of the operating problems for different applications are
similar. Section 4.5 deals with some procedures specific to
operation of wet ESP's.
4.1 NORMAL OPERATING PROCEDURES1
Because the basic functions of an ESP are charging and
collection of particles, the components and control associated
with the power supply, rappers, and vibrators, are the most
important operating systems.
4.1.1 Power Supply
During normal operation, the power to the precipitator is
optimized by automatic power controls, which vary the power
Parameters in response to a signal generated by the spark rate.
4-1
-------
The automatic controls also make the circuit sensitive to over-
<1
load and provide safety controls in the event that spark level
cannot be reached.
The automatic control circuit controls spark rate, current,
and voltage. Although earlier ESP's used saturable reactors for
power control, modern ESP's use silicon controlled rectifiers
(SCR's); this report discusses only SCR's. The components of an
automatic control system were previously shown in Figure 3-2.
The silicon controlled rectifiers provide a wide range of precip-
itator current, and the current-limiting reactor limits the
swinging of current during precipitator sparking.
Silicon Controlled Rectifiers (SCR's)—
The SCR's act as a variable impedance in controlling the
flow of power in the circuit. An SCR is a three-junction semi-
conductor that is normally an open circuit until an appropriate
signal is applied to the gate terminal, at which time it rapidly
switches to the conducting state. Its operation is equivalent to
that of a thyroton. The flow of current is controlled by the
forward blocking ability of the SCR's, which in turn is con-
trolled by the firing pulse to the gate of the SCR. The current-
limiting reactor reshapes the wave form of the current and the
peak that occurs during sparking. Current wave form with and
without SCR's is illustrated in Figure 4-1.
Sparking Control--
Conventional spark control is based on storing electrical
pulses in a capacitor for each spark that occurs in the precipi-
tator. If the voltage of the capacitor exceeds a preset refer-
ence value, an error signal will phase the mainline SCR's back to
a point where the sparking will stop. Usually this snap-action
type of control tends to overcorrect and thus leads to longer
downtime than is desirable. At low sparking rates, about 50
sparks per minute, the overcorrection is more pronounced and
voltage is reduced for a longer period, with subsequent loss of
dust and low ESP efficiency.
4-2
-------
VOLTAGE-NEGATIVE CORONA
ePEAK
AVERAGE
v71 / 2tt TIME
V ,L
V./
AC VOLTAGE WAVE
CURRENT WITHOUT SCR
,A. A
0 it/2 tt 2tt
2tt TIME
APPROX.
CURRENT WITH SCR
AAV
2t» TIME
APPROX.
Figure 4-1. ESP current wave form with and without silicon
controlled rectifiers.
4-3
-------
Proportional control, another method of spark control, is
also based on storing electrical pulses for each spark that
occurs in the precipitator. In this system, however, phaseback
of the mainline SCR's is proportional to the number of sparks in
the precipitator. The main advantage of proportional control
over conventional spark control is that the precipitator deter-
mines its own optimum spark rate, based on four factors: temper-
ature of the gas, dust resistivity, dust concentration, and
internal condition of the precipitator. With proportional spark
rate control, therefore, the precipitator determines the optimum
operating parameters, whereas with conventional spark control,
the operator selects the parameters, which may not be optimum.
Some precipitators operate at the maximum voltage or current
settings on the power supply with no sparking. In collection of
low-resistivity dusts, where the electric field and the dust
deposit are insufficient to initiate sparking, a no-spark condi-
tion may arise. This condition does not necessarily indicate
that the unit is underpowered, since it may have sufficient power
to provide charging and electric fields without sparking.
Voltage Limit Control—
The voltage-limit unit of the automatic control module
limits the primary voltage of the high-voltage transformer to its
rated value. A potential transformer across the primary circuit
supplies a voltage signal that is compared with a preset voltage
value. The voltage control is set at the primary voltage rating
of the high-voltage transformer. Primary voltage above this
value generates a signal that retards the firing pulse of the
firing module and brings the primary voltage back to the control
setting.
Current-limit Control—
For current-limit control, a current transformer in the
primary circuit of the high-voltage transformer monitors the
primary current. The voltage from this current transformer is
4-4
-------
compared with the setting of the current control, which corres-
ponds to the rating of the T-R unit. Any primary current that
exceeds the unit's rating generates a signal that regards the
firing pulse of the firing circuit (as with spark control) and
reduces the current to the current-limit setting.
With all three control functions properly adjusted, the
control unit energizes the precipitator at its optimum or maximum
level at all times. This level is determined by conditions
within the precipitator and results in one of the three automatic
control functions operating at its maximum, i.e., primary volt-
age, primary current, or spark rate. When one of the three
maximums is reached, the automatic control prevents any increase
in power to reach a second maximum. If charges within the pre-
cipitator so require, the automatic control will switch from the
maximum limit of one function to that of another.
The system also includes secondary overload circuits and an
undervoltage trip device that operates when voltage on the pri-
mary of the high-voltage transformer falls below a predetermined
level and remains below that level for a period of time. Another
device provides a delay period in the annunciator circuit while
the network of contacts is changing position to stabilize the
circuit in response to undervoltage. The corona voltage-current
characteristics of ESP's are controlled basically by gas and dus,t.
loading, electrode geometry and alignment, and size of the indi-
vidual section energized.
The electrical equipment ratings must be properly matched
2
with load requirements. Over a wide range of gas temperatures
and pressures in different applications, practical operating
voltages range from 15 to 80 kV&v at average corona current
densities of about 100 to 3200 mA/1000 m^ (10 to 300 mA/1000 ft^)
of collecting area.
4-5
-------
The following are some of the problems that can occur when
2
power supply and load are mismatched:
° The ESP is underpowered because of too few electrical
.sets, sets of wrong capacity, or too much collecting
area energized from a single set.
° Reduction of operating voltage with gas temperature, as
shown in Figure 4-2, can result from failure to fully
evaluate effects of gas density and temperature on
required operating levels. While voltage goes down,
the current demands go up. At high pressures the
reverse can occur.
° A rectifier set larger than is required for the appli-
cation, as when 1500 mA saturable reactor sets are
operating on high resistivity ash at perhaps 100 mA,
can lead to loss of control, excessive sparking, and
poor efficiency.
4.1.2 Rappers
The rapper system is electrically operated to remove dust
from the precipitator's collecting plates. The most common
system consists of magnetic-impulse, gravity-impact rappers that
are energized periodically to rap the collecting plates to remove
dust deposits. The main components of the system are the rappers
and the electrical controls.
The magnetic-impulse, gravity-impact rapper, shown in Figure
4-3, is a solenoid electromagnet consisting of a steel plunger
surrounded by a coil, both enclosed in a watertight steel case.
The control unit contains all the components (except the rapper)
needed to distribute and control the power to the rappers for
optimum precipitation. The electrical controls provide separate
adjustments so that the rappers can be assembled into different
groups, each of which can be independently adjusted from zero to
maximum rapping intensity. The controls are adjusted manually to
regulate the release of dust from the collecting plates and
prevent undesirable "puffing" from the stack.
During normal operation, a short-duration d.c. pulse through
the coil of the rapper supplies the energy to move the steel
4-6
-------
10
23 cm (9 inch) DUCT SPACING
0.277 cm (0.109 inch) DIAMETER WIRES
NEGATIVE POLARITY
1 atm
'0 38 98 149 204 260 315 371 426
(100) (200) (300) (400) (500) (600) (700) (800)
GAS TEMPERATURE, °C (°F)
Figure 4-2. Typical precipitator operating voltage as a
function of gas temperature.
4-7
-------
DISCHARGE
ELECTRODE
VIBRATOR
DISCHARGE
ELECTRODE
VIBRATOR
DISCHARGE ELECTRODE VIBRATOR
AND INSULATOR ASSEMBLY
COLLECTING
ELECTRODE
RAPPER
RAPPER
COUPLING
COLLECTING ELECTRODE RAPPER
AND INSULATOR ASSEMBLY
Figure 4-3. Vibrator and rapper assembly, and
precipitator high-voltage frame.1
4-8
-------
plunger. The plunger is raised by the magnetic field of the coil
and then is allowed to fall back and strike a rapper bar, which
is connected to a bank of collecting electrodes within the
Precipitator. The shock transmitted to the collecting electrodes
dislodges the accumulated dust.
In some applications, the magnetic-impulse, gravity-impact
rapper is used to clean the precipitator discharge wires. For
this purpose, the rapper strikes the electrode supporting frame
in the same manner, except that an insulator isolates it from the
high voltage of the frame.
Some installations have mechanical rappers, in which a
single hammer assembly mounted on a shaft raps each frame (see
Figure 2-11). A low-speed gear motor is linked to the hammer
shaft by a drive insulator, fork, and linkage assembly. Inten-
sity of rapping is governed by the hammer weight, and frequency
is governed by the speed of rotation of the shaft.
4.1.3 Vibrators
A vibrating system creates vibrations in either the collect-
ing plates or the discharge wires to dislodge accumulations of
particles. Vibrators are not normally used to clean the collect-
ing electrodes of precipitators that collect fly ash.
The vibrator is an electromagnetic device, the coil of which
is energized by alternating current. Each time the coil is
energized, the resulting vibration is transmitted through a rod
to the high-tension wire supporting frame or collecting plates
(see Figure 4-3). The number of vibrators depends on the number
of high-tension frames or collecting plates in the system.
The control unit contains all devices for operation of the
vibrators, including means of adjusting the intiensity and period
of vibration. Alternating current is supplied to the discharge
wire vibrators through a multiple cam-type timer to provide
sequencing and duration for energization of the vibrators.
4-9
-------
For each installation, a certain intensity and period of
vibration will produce the best collecting efficiency. Low
intensity will result in heavy buildup of dust on the discharge
wires. Dust buildup reduces the sparkover distance between the
electrodes, thereby limiting the power input to the precipitator.
It also tends to suppress the formation of negative corona and
the production of unipolar ions required for precipitation.
Further, dust buildup alters the normal distribution of electro-
static forces in the treatment zone and can lead to oscillation
of the discharge wires and the high-tension frame.
Recent studies have investigated reentrainment caused by
rapping in terms of the percentage of material reentrained and
3 4
its particle size distribution. ' One report describes the
testing of six full-scale electrostatic precipitator installa-
tions. Losses from rapping ranged from over 80 percent of the
total mass emissions from one hot-side unit to 30 percent of
emissions from cold-side units. The losses consist mostly of
relatively large particles, primarily those larger than 2.0 pm in
diameter.
Tests of a pilot-scale precipitator showed that rapping
4
emissions decreased as time between raps was increased.
Because reentrainment from rapping can be a significant
portion of the total emissions, it is important that the rapping
system is adjusted to minimize reentrainment.
4.2 MAINTENANCE REQUIREMENTS 5' 6 ' 7 '8
At each precipitator installation, the inspector should
require that a preventive maintenance schedule be kept, listing
the precipitator parts to be checked and maintained daily,
weekly, monthly, quarterly, and in specified situations. Table
4-1 summarizes the maintenance procedures discussed in this
section and can be used by an inspector as an example to be
compared with procedures used by the company.
4-10
-------
TABLE 4-1. MAINTENANCE SCHEDULE FOR ELECTROSTATIC PRECIPITATORS8
Enter on daily log
1. Boiler operating parameters
2. Flue gas analysis
3. Coal characteristics
4. ESP electrical data
5. Transmissometer calibration
Check daily
1. T-R control set readings
2. Rapper and vibrator control settings
3. Ash removal system
4. T-R control room ventilation system
Check weekly
1. Operation of rappers and vibrators
2. control sets (for internal dirt)
3. Air filters to control sets and precipitator top
housing
Enter on weekly log
1. ESP voltage-current data
2. Graph ESP voltage-current data
Check monthly
1. Pressurization of precipitator top housing
2. Standby fan operation (manually)
Perform quarterly
1. Clean and dress contact surfaces of HW-FW electrical
distribution
2. Lubricate pivots
Perform semiannually
1. Clean and lubricate access door hinges and test
connections
2. Inspect exterior for loose insulation, corrosion, loose
joints, other defects
(continued)
4-11
-------
TABLE 4-1. (continued).
3. Check for points of gas leakage (in or out)
Perform annually
1. Thorough internal inspection:
Check for possible leaks of oil, gas, or air at gas-
keted connections
Check for corrosion of any component
Check for broken or misaligned wires, plates, insulators
rappers, etc. '
Check high-voltage switchgear and interlocks
Clean all insulators and check for hairline cracks or
tracking
Check expansion joints on hot precipitators
2. Check for signs of hopper leakage, reentrainment of
particulate, and poor gas distribution
3. Check for dust buildup in inlet and outlet flues
4. Check for dust buildup in hoppers
4-12
-------
Startup and shutdown procedures and a maintenance schedule
for ESP's are presented in Appendix A. These procedures can be
applied to wire-weight and rigid-frame precipitators, with the
noted differences regarding rappers. This information is in-
tended to give the inspector an idea of what the company should
be doing to properly operate and maintain their ESP.
4.3 PRECIPITATOR MALFUNCTIONS
Many ESP equipment components are subject to failure or
malfunction that can cause an increase in emissions. Malfunc-
tions may be caused by faulty design, installation, or operation
of the ESP. They may involve electrical, gas flow, rapping, or
g
mechanical problems, which can be minor or severe. The inspec-
tor should orient himself with the comjion ESP malfunctions, their
effects on emissions, corrective actions, and preventive mea-
sures. Table 4-2 lists common problems associated with fly-ash
ESP's. Appendix B identifies and describes the major types of
ESP malfunctions, giving probable causes and corrective actions.
Two surveys of ESP operating experience are summarized.
To further illustrate the effectiveness of troubleshooting
with voltage-current data and curves, a supplementary figure to
Table 4-2 is provided. Figure 4-4 presents the same list of
malfunctions as Table 4-2 with graphic illustrations of voltage-
current (V-I) curves indicative of the respective malfunctions.
Two columns of V-I curve comparison, and a multi-field V-I curve
comparison. A single field comparison is made by showing a
reference V-I curve, representative of proper operating condi-
tions, along with a V-I curve indicative of the respective mal-
function. A multi-field comparison is made by showing the V-I
curve for the malfunctioning field along with V-I curves repre-
sentative of normal conditions for the remaining operating ESP
fields. The single field and multi-field comparisons are made on
the premise of cause-singularity and field-singularity. For the
case of back corona, all fields are shown to experience the
4-13
-------
7
TABLE 4-2. SUMMARY OF PROBLEMS ASSOCIATED WITH ESP'S
Malfunction
Cause
Effect on
ESP efficiency*
Corrective action
Preventive measures
Poor electrode
alignment
Poor design
Ash buildup on frame and hoppers
Poor gas flow
Can drastically affect
performance and lower
efficiency
Realign electrodes.
Correct gas flow.
Check hoppers fre-
quently for proper
operation..
Broken electrodes
Wire not rapped clean, causes
an arc that embrittles and burns
through the wire
Reduction in effi-
ciency due to reduced
power input, bus sec-
tion unavailability
Replace electrode.
Boiler problems: check
for Insufficient ex-
cess air, insufficient
pressure reading on
gauges, fouled screen
tubes, and fouled air
preheater.
Cllnkered wire. Causes:
poor flow area, distribution
through unit is uneven; excess
free carbon due to excess air
above combustion requirements or
fan capacity Insufficient for
demand required; wires not
properly centered; ash buildup
resulting in bent frame, same
as above; clinker bridges the
plates and wire shorts out; ash
buildup, pushes bottle weight up
causing sag in the wire; "J"
hooks have improper clearances to
the hanging wire; bottle weight
hangs up during cooling causing
a buckled wire ; and ash buildup
on bottle weight to the frame
forms a clinker and burns off
the wire.
Inspect hoppers; check
electrodes frequently
for wear; Inspect
rappers frequently.
*The effects of precipitation probleas can only be discussed on a qualitative basis. There are no known emission tests of
precipitators to determine performance degradation as a function of operational problems.
(continues)
-------
TABLE 4-2 (continued)
Malfunctions
Cause
Effect on
ESP efficiency®
Corrective action
Preventive measures
Distorted or
skewed elec-
trode plate9
Ash buildup In hoppers
Gas flow Irregularities
High temperatures
Reduced efficiency
Repair or replace
plates.
Correct gas flow.
Check hoppers fre-
quently for proper
operation; check
electrode plates
during outages.
Vibrating or
•winging elec-
trodes
Uneven gas flow
Broken electrodes
Decrease in effi-
ciency due to re-
duced power input
Repair electrode.
Check electrodes fre-
quently for wear.
Inadequate level
of power Input
(voltage too
low)
High dust resistivity
Excessive ash on electrodes
Unusually fine particle size
Inadequate power supply
Inadequate sectlonallsation
Improper rectifier and control
operation
Misalignment of electrodes
Reduction In efficiency
Clean electrodes; gas
conditioning or al-
terations In tempera-
ture to reduce resis-
tivity; Increase sec-
tionallzation.
Check range of vol-
tages frequently to
make sure they are
correct.
In-situ resistivity
measurements
Back corona
Ash accumulated on electrodes
causes excessive sparking.
Requiring reduction in volt-
age charge.
Reduction in efficiency
Same as above
Same as above
Broken or cracked
Insulator or flow-
er pot bushing
leakage
Asti buildup during operation
causes leakage to ground.
Moisture gathered during
shutdown or low-load operation
Reduction in efficiency
Clean or replace in-
sulators and bushings.
Check frequently;
clean and dry as
needed; check for
adequate pressurl-
zation of top housing.
*The effects of precipitation problems can only be discussed on a qualitative basis. There are no known emission tests of
precipitators to determine performance degradation as a function of operational problems.
(continued)
-------
TABLE 4-2 (continued)
Halfunctions
Cause
Effect on
ESP efficiency8
Corrective action
Preventive measures
Air inleakage
through hoppers
From dust conveyor
Lower efficiency -
dust reentrained
through ESP
Seal leaks.
Identify early by
increase in ash con-
centration at bottom
of exit to ESP.
Air Inleakage
through ESP
shell
Flange expansion, improper
sealing of inspection hatches
Same as above, also
causes Intense spark-
ing
Seal leaks.
Check frequently for
corrosion around In-
spection doors and
for flange expan-
sion.
Gas bypass
around ESP:
dead passage
above plates and
tension f rame
Poor design - improper Isolation
of active portion of ESP
Only a small percent
drop in efficiency
unless severe
Baffling to direct
gas Into active ESP
section
Identify early by
measurement of gas
flow in suspected
area, around high
Corrosion
Temperature goes below dew
point.
Negligible until pre-
cipitation interior
plugs or plates are
eaten away; air leaks
may develop causing
significant drops
In performance.
Maintain flue gas
temperature above
dew point.
Energize precipitator
after boiler system
has been on line for
ample period to raise
flue gas temperature
above acid dew point.
*The effects of precipitation problems can only be discussed on a qualitative basis. There are no known emission tests of
precipitators to determine performance degradation as a function of operational problems.
(continued)
-------
TABLE 4-2 (continued)
Malfunctions
Cause
Effect on
ESP Efficiency3
Corrective action
Preventive measures
Hopper pluggage
Wires, plates, and insulators
Reduction in efficiency
Provide proper flow
Frequent checks for
fouled because of low temperature
of ash.
adequate operation
Inadequate hopper lnsulaton
of hoppers; Provide
Improper Maintenance
heaters and/or
Boiler leaks causing excess
thermal insulation
moisture
to avoid moisture
Ash-conveying system malfunc-
condensation.
tion - gas leakage
- blower Malfunctions
- solenoid valves
Misadjustment of hopper vibra-
tors
Material dropped into hopper
1
from bottle weights
t—*
Solenoid and timer malfunction
Suction blower filter not
changed
Inadequate
Ash buildup
Resulting buildup on
Adjust rappers with
Frequent checks for
rapping, vi-
Poor design
electrodes may reduce
optical dust- measure-
adequate operation
brators fall
Rappers misadjusted
efficiency.
ing instrument in
of rappers
ESP exit stream.
Too intense
Poor design
Reentrains ash and
Same as above
Same as above; reduce
rapping
Rappers misadjusted
reduces efficiency
vibrating or impact
Improper rapping force
force.
"the effects of precipitation problems can only be discussed on a qualitative basis. There are no known emission tests of
precipitators to determine performance degradation as a function of operational problems.
(continued)
-------
TABLE 4-2 (continued)
Malfunctions
Cause
Effect on
ESP efficiency3
Corrective action
Preventive measures
Control
failures
Power failure in primary system
Transformer or rectifier fail-
ure:
insulation breakdown In
transformer
arcing In transformer between
high-voltage switch contacts
leaks or shorts in high-
voltage structure
insulating field contamination
Reduced Efficiency
Find 9ource of fail-
ure and repair or
replace.
Pay close attention
to daily readings of
control room instru-
mentation to spot
deviations f rom
normal readings.
Sparking
IB i' SSSSSSSiST.JST ~ —
Inspection door ajar
Boiler leaks
Plugging of hoppers
Dirty Insulators
Reduced efficiency
Close inspection
doors; repair leaks
in boiler; unplug
hoppers; clean Insu-
lators.
Regular preventive
maintenance will
alleviate these
problems.
*The effects of precipitation problems can only be discussed on a qualitative basis. There are no known emission tests of
precipitators to determine performance degradation as a function of operational problems.
-------
malfunction
SINGLE V-I
CURVE
INDICATOR
MULTI-FIELD
V-I CURVE SET
POOR ELECTRODE
ALIGNMENT
°REDUCED VOLTAGE AND
CURRENT LEVELS
BROKEN ELECTRODE
A) FREQUENT CIRCUIT
BREAKING
B) HIGHLY ERRATIC
ELECTRICAL LEVELS
C) REDUCED VOLTAGE
AND CURRENT
LEVELS
DISTORTED OR SKEWED
COLLECTION PLATES
A
'REDUCED VOLTAGE AND
CURRENT LEVELS
VIBRATING OR SWINGING
ELECTRODE
A) FREQUENT CIRCUIT
OVERLOAD
B) HIGH CURRENTS
INADEQUATE LEVEL I
OF POWER INPUT
LOOK FOR OTHER OPERATIONAL
PROBLEMS; OR COULD BE
DESIGN RELATED
V
Figure 4-4. Electrical indications of problems associated with ESPS.
4-19
-------
Figure 4-4 (continued)
MALFUNCTION
SINGLE V-I
CURVE
INDICATOR
MULTI-FIELD
V-I CURVE SET
BACK CORONA
A) HIGH CURRENT LEVELS
WITH LOW VOLTAGE
B) INCREMENTAL CURRENT
INCREASES WITH
STEADY OR DECREAS-
ING VOLTAGE LEVEL
BROKEN OR CRACKED
INSULATOR OR FLOWER
POT BRUSHING LEAKAGE
'HIGH CURRENT AT LOW
VOLTAGE
AIR INLEAKAGE
THROUGH HOPPERS
A
°HIGHER SPARKING
CONDITIONS
AIR INLEAKAGE
THROUGH ESP SHELL
A
"HIGHER SPARKING
CONDITIONS
°REDUCED VOLTAGE AND
CURRENT LEVELS
£.
GAS BYPASS
NONE
4-20
-------
Figure 4-4 (continued)
SINGLE V-I MULTI-FIELD
MALFUNCTION CURVE INDICATOR V-I CURVE SET
CORROSION N0NE
HOPPER PLUG6AGE WITH
ASH PILING UP INTO
THE ENERGIZED FIELD
°HIGH CURRENT AT LOW
VOLTAGE
INADEQUATE PLATE
RAPPING
Z
°REDUCED VOLTAGE AND
CURRENT WITH SPARKING
TOO INTENSE
PLATE RAPPING
"NORMAL VOLTAGE AND
CURRENT LEVELS WITH
NOTICEABLE OPACITY
SPIKES CYCLES
COINCIDENT WITH
CAPPING CYCLES
CONTROL FAILURES
°SLIGHTLY REDUCED
VOLTAGE AND CURRENT
LEVELS
4-21
-------
Figure 4-4 (continued)
MALFUNCTION
SPARKING
SINGLE V-I-
CURVE
INDICATOR
MULTI-FIELD
V-I CURVE SET
NOTE: SPARKING IS A RESULT OF
A MALFUNCTION NOT A
CAUSE
SHARP EDGES
zJ
°REDUCED VOLTAGE AND
CURRENT LEVELS
t
INADEQUATE WIRE
RAPPING
h
°INCREASED VOLTAGE
LEVEL WITH REDUCED
CURRENT LEVEL
TOO INTENSE WIRE
RAPPING
NONE
NO MALFUNCTION
-------
problem, as this is the normal case. Both curve sets are offered
without graduated voltage and current axes to extend the appli-
cability for both primary and secondary electrical data. A no-
malfunction case is provided to reference the graphical nature of
these V-I curves for an ESP with properly operating fields.
4.4 REPORTING ESP MALFUNCTIONS
Generally, plant officials are required to submit a report
of excess emissions causes by ESP malfunctions; the inspector
should review these reports to keep informed of the ESP operating
practices at the plant. Part 60 of Title 40, Code of Federal
Regulations, Section 6 0.7, as amended, December 16, 1975, re-
quires that a source report excess emissions caused by malfunc-
tions or other reasons in a quarterly report to the EPA Adminis-
trator.^ The reportris to include the magnitude of excess
emissions above the applicable standards; it is to give the date
and time of beginning and end of each period of excess emissions.
Periods of excess emissions resulting from startup, shutdown, and
malfunction are to be specifically identified. The nature and
cause of any malfunction, if known, and the corrective action
taken, or preventive measures adopted, are to be reported. Each
quarterly report is to be submitted within 30 days following the
end of the calendar quarter.
A reportable malfunction is considered to be any sudden or
unforeseen malfunction that causes or could cause any of the
plant's sources to exceed specified particulate emission limits
for a period of 4 or more hours. When this occurs, a procedure
such as the one listed below should be followed:
0 The malfunction should be reported by phone or telegram
to the EPA regional office and to state or local offi-
cials. The air quality branch of the company should
also be notified.
° The plant superintendent should submit a report to the
EPA regional office, with copies to various branches of
the utility. The report should include the following:
4-23
-------
Time and date excess emissions began and ended
Time and date the breakdown causing the excess
emissions began and ended
Type of emission, estimated rate, and copies of
the opacity monitor records
Cause of the malfunction
Operation and maintenance procedures, prior to and
during the malfunction, designed to prevent such
an occurrence
Additional steps taken to minimize the extent or
duration of the malfunction
Plans to minimize the possibility of a similar
malfunction in the future
Monthly records should be kept by plant and unit of all
malfunctions, total hours that T-R sets are operated, number of
hours T-R sets are not operating (in intervals of 24 hours and
>24 hours), maximum number of sets out at one time, and monthly/
yearly availability of the ESP unit (in percent). Daily logs
should be kept on each ESP unit, with remarks on outages of
various sections of the ESP.
4.5 OPERATION, MAINTENANCE, AND COMMON PROBLEMS OF WET ESP'S11
The several available types of wet precipitators can be
categorized with regard to structure as the plate type or the
pipe type and also with regard to the method in which water is
introduced. Plate units have either a combination presaturation
continuous spray or a spray with intermittent wash and gas flow
in the horizontal or vertical directions. The pipe type usually
has a weir-over-flow arrangement or a continuous spray, with gas
flow vertically downward. Brief descriptions of the operation of
these three types of wet ESP's were presented in Section 2.4.2.
This section describes the operation and maintenance related
facets of typical wet ESP installations. Wet precipitators are
4-24
-------
made in different configurations; they are less widely applied
than the more conventional devices, and there is little published
information on operating and maintenance practices. When the
components of a wet precipitator are similar to those of a dry
precipitator, the operation and maintenance procedures outlined
in Section 4.2 and Appendix A are considered applicable.
4.5.1 Operation and Maintenance During Normal Operation
Heaters and blowers are usually energized first during
normal operation. The spray system is always activated just
before the high-voltage system is energized. Gas flow is moni-
tored by damper. Operators must monitor the pH of the water at
the waste discharge.
Because inspection and maintenance of wet ESP's are highly
specific to the system, operators should follow closely the
instructions provided by the manufacturer. Since precipitators
operate with very high voltage, precautions must be exercised to
ground the precipitator internals properly. The gas flow must be
stopped and the unit cooled to a safe temperature before any
person enters the precipitator. Protective apparatus such as a
respirator may be needed.
The inspector should familiarize himself with the general
inspection and maintenance practices that the company should be
following; these are briefly outlined below.
Mechanical Maintenance—
All internal components should be checked for alignment,
dust buildup, tightness of bolts, structural soundness of welds,
and structural integrity of cross bracing and other support
members. Since the support insulators perform such a vital
function in electrostatic precipitation, the structural support
end of the high-voltage insulator in the high-voltage housing
must be thoroughly inspected for cracks, chips, or other defects.
4-25
-------
Water System—
All pumps, internal spray nozzles, and related valving and
piping should be checked. Nozzles are subject to plugging and
therefore -should be routinely disassembled, cleaned, and/or
replaced as necessary. Other required checks include the main
supply pumps for water pressure, all pipe joints for leaks, and
all couplings for tightness. Nozzle orientation should be
checked and adjusted as necessary to maintain the intended spray
pattern.
Electrical System—
Inspection should include the high-voltage control panel,
heater and blower control panel, high-voltage insulators, heater
system thermostats, T-R sets, and all related electrical connec-
tions. When components of wet precipitator systems are similar
to those of dry units, many of the inspection and maintenance
practices outlined earlier will apply.
Schedule—
Table 4-3 summarizes a typical maintenance schedule, as
recommended by the manufacturer and given to the plant at the
time of wet ESP installation.
4.5.2 Wet ESP Operating Problems
Data on operating problems of wet ESP's are minimal. How-
ever, the following information obtained on a recent sinter plant
wet ESP installation is considered typical of the problems an
inspector might encounter.
Pilot tests of a wet ESP on a sinter plant in New York State
showed that use of acidic recirculated water involves great
potential for corrosion of reasonably priced alloys such as 316L
12
stainless steel. Operation of pH greater than 7.0, however,
caused buildup of calcium and magnesium carbonate scale on spray
nozzles and other critical components of the ESP, rendering it
inoperable. In pilot tests of a second brand of wet ESP, the
water distributor became plugged and recirculation of liquor
containing acidic solids caused deposition of solids.
4-26
-------
TABLE 4-3. MANUFACTURER'S SUGGESTED MAINTENANCE SCHEDULE FOR WET PRECIPITATORS
Component
Interval
Maintenance procedure
Key interlocks
Yearly
Yearly
Yearly
Check for corrosion and clean.
Check that key fits and turns easily; lubricate
as required.
Check proper positioning of dust caps.
Ducts and dampers
Quarterly
Quarterly
Open and close dampers; operation must be smooth
and positive.
Check ducts for an accumulation of dust; clean
as necessary.
Precipitator
Quarterly
Quarterly
Check condition of paint; retouch as necessary.
Clean corroded areas inside casing thoroughly.
Access doors
Quarterly
Quarterly
Check seal for tightness.
Inspect gaskets and replace if damaged.
Collecting plates and
discharge electrodes
Quarterly
Quarterly
Clean thoroughly.
Check hanging fixtures for damage.
Baffles
Quarterly
Clean thoroughly.
Hopper
Quarterly
Quarterly
Clean thoroughly.
Check drain lines for clogging.
High-voltage system:
T-R set
Quarterly
Yearly
Yearly
Yearly
Yearly
Yearly
Yearly
Check oil level; add oil if required.
Check and tighten electrical connections.
Replace damaged wiring.
Clean output bushing.
Check output bushing for cracks or damage.
Check continuity of ground wire.
Check grounding switch for positive action.
(continued)
-------
TABLE 4-3. (continued).
Component
Interval
Maintenance procedure
High-voltage system:
(continued)
Insulators
Quarterly
Quarterly
Quarterly
Clean thoroughly and dry.
Check for cracks or other damage.
Tighten electrical connections.
Control panel
Quarterly
Yearly
Yearly
Yearly
Yearly
Check panel switches for positive action.
Check and tighten electrical connections.
Check condition of internal components.
Clean inside and outside of panel.
Check condition of fuses.
Heater and blower system:
Heaters
Yearly
Yearly
Yearly
Check continuity of each shipment.
Check and tighten electrical connections.
Check clearance around insulator.
Blower
Weekly
Yearly
Replace air filters.
Check condition of blower and blower motors.
Control panel
Yearly
Yearly
Yearly
Yearly
Yearly
Check panel switch for positive action.
Check and tighten electrical connections.
Check condition of internal components.
Clean inside and outside of panel.
Check condition of fuses.
(continued)
-------
TABLE 4-3. (continued).
Component
Interval
Maintenance procedure
Spray system
Weekly
Weekly
Check pressure at nozzle head.
Check spray pattern.
Operating checks
Daily
Daily
Daily
Check pH of water system.
Visually check indicators for burned-out lamps.
Check input and output meters for correct readings.
Dampers
Monthly
Lubricate operators.
i
KJ
VD
-------
In full-scale testing at the same sinter plant, however, the
first wet ESP performed very well with regular weekly maintenance
and inspection. Considerable attention to the recirculating
water system was required to maintain the water quality that is
12
needed for successful wet ESP operation.
4-30
-------
REFERENCES - SECTION 4
1. Szabo, M.F., and R.W. Gerstle. Operation and Maintenance of
Particulate Control Devices on Coal-Fired Utility Boilers.
PEDCo Environmental, Inc., Cincinnati, Ohio. EPA-600/
2-77-129. July 1977.
2. Hall, H.J. Design and Application of High Voltage Power
Supplies in Electrostatic Preicpitation, H.J. Hall Asso-
ciates, Inc. Presented at Symposium on Electrostatic Pre-
cipitators for the Control of Fine Particles. Pensacola
Beach, Florida. EPA-650/2-75-016.
3. Spencer, Herbert W. III. Rapping Reentrainment in a Nearly
Full Scale Pilot Precipitator. EPA-600/2-76-140. May 1976.
4. Sparks, Leslie E. et al. Studies of Particle Reentrainment
From Electrode Rapping, presented at the 2nd US/USSR Sympo-
sium on Particulate Control. Research Triangle Park, North
Carolina. September 26-29, 1977.
5. Bibbo, P.P., and M.M. Peacos. Defining Preventive Mainte-
nance Tasks for Electrostatic Precipitators, Research
Cottrell, Inc. Power. August 1975, pp 56-58.
6. Engelbrecht, H.L. Plant Engineer's Guide to Electrostatic
Precipitator Inspection and Maintenance, Air Pollution Div.
of Wheelabrator Frye, Inc., Plant Engineering. April 1976.
pp. 193-196.
7. Szabo, M.F., and R.W. Gerstle. Electrostatic Preicpitator
Malfunctions in the Electric Utility Industry. PEDCo En-
vironmental, Inc., Cincinnati, Ohio. EPA-600/2-77-006.
January 1977.
8. Hesketh, H.E., and F.L. Cross, Jr. (ed.) Handbook for the
Operation and Maintenance of Air Pollution Control Equipment
Technomic Publishing. Westport, Connecticut. 1975.
9. Oglesby, Sabert, Jr. A Manual of Electrostatic Precipitator
Technology. Southern Research Institute. August 1970.
10. Federal Register, Part 60 of Title 40, Section 60.7 as
amended December 16, 1975.
4-31
-------
11. Szabo, M.F., and R.W. Gerstle. Operation and Maintenance of
Particulate Control Devices on Selected Steel and Ferroalloy
Processes. PEDCo Environmental, Inc. Cincinnati, Ohio.
EPA-600/2-78-037. March 1978.
12. Jaasund, S.A., and M.R. Mazer. The Application of Wet
Electrostatic Precipitators for the Control of Emissions
From Three Metallurgical Processes. Presented at symposium
on Particulate Collection Problems Using Electrostatic
Precipitators in the Metallurgical Industry. June 1-3,
1977.
4-32
-------
SECTION 5
INSPECTION PROCEDURES
The most important task of an environmental control agency
in terms of ESP performance is to establish and execute a program
to ensure that ESP's at each plant continue to operate in compli-
ance with particulate emission regulations. This program should
include (1) a system by which the plant reports key information
to the control agency, and (2) random unannounced inspections as
well as periodic announced inspections.^ The frequency of
inspection will vary with the policy of each control agency and
with the size and quality of the enforcement staff. Quarterly
inspections are recommended for most plants, but many control
2
agencies can manage only an annual inspection.
Comparison of operating parameters observed during inspec-
tion with those recorded in the performance test should indicate
whether emissions are within allowable limits. Major emphasis is
placed on checking plant records, ESP instrumentation, and emis-
3
sion monitors.
The following sections present step-by-step inspection
procedures and a checklist of key process and control equipment
components. These guidelines are designed to aid enforcement
personnel in conducting on-site assessment and evaluation of ESP
performance and operating conditions. In general, a coal-fired
power plant serves as an example of a facility regulated by a
State Implementation Plan (SIP).
5-1
-------
5.1 PERFORMING THE PERIODIC INSPECTION
5.1.1 File Review
Unless it is a first-time inspection, the control agency
should have a file containing operating data on the power plant
and existing ESP's. Based on a review of these data, the inspec-
tor should know whether or not the plant can achieve compliance
under normal circumstances. Particular attention should be given
to pending compliance schedules and any construction and/or
operating permits pertaining to processes or ESP's within the
plant. The inspector should also review the number of emissions
violations, malfunctions of the ESP, and complaints since the
last inspection.
If not already present, the inspector should prepare a
concise file summarizing the basic plant and ESP information,
process descriptions, flow sheets, and ranges of acceptable
operating parameters. An example of these type data is presented
4 5
in Appendix C-l. ' Section 3.2 provides a more detailed discus-
sion of recordkeeping for ESP and process related parameters.
5.1.2 Arranging for the Inspection
If the inspection is to be announced in advance, lead peri-
ods of one day to one week are usually adequate to insure that
the necessary personnel will be available. The inspector should
obtain a schedule of plant operations during the inspection
period, and should request that plant records are current and
available for inspection.
Basic equipment the inspector should have to perform his job
both properly and safely, are listed below. Optional equipment
is marked with an asterisk.
Plume evaluation equipment
Polaroid camera
Compass
Wind-speed indicator
Flashlight
5-2
-------
Thermometer (50°-800°F)
Stop watch
Tape measure
6-foot rule
Hard hat
Safety glasses
Safety shoes
Asbestos gloves
~Manometer or pressure/vacuum gage (0-30 in. Hg and 0-10 in.
H2)
*Gas detection equipment
~Full sample containers
~Thermocouple
~Portable millivolt meter (temperature compensated)
5.1.3 External Plant Inspection
Before entering the plant, the inspector should observe the
plume and determine its opacity using revised Method 9, as con-
tained in the Federal Register. Opacity of the plume is the most
indicative guide to the performance of the ESP. Water vapor
condensation should not be mistaken for particulate emissions.
If visible emissions are exceeding applicable standards, the
inspector should use the standard form and follow established
procedures for recording the violation. Table 5-1 lists possible
operating factors that may be causing visible emissions.
The inspector should also note any visible emissions, odors,
or dust fall in the surrounding area. He should document all
significant observations, noting the date, time of day, and
weather conditions.
5.1.4 Plant Entry
Upon arrival to the plant offices, the inspector should
contact a responsible plant official to gain access to the plant.
Visitor release forms should not be signed because this restricts
insurance coverage for the inspector and may disqualify him from
inspecting certain portions of the plant. The inspector has the
legal right to fully inspect the air pollution sources within the
plant without signing a release form. If entry to the plant is
refused, the inspector should obtain a search warrant.
5-3
-------
TABLE 5-1. PLUME CHARACTERISTICS AND OPERATING
PARAMETERS FOR COAL-FIRED BOILERS*
Stack
plume
Associated
pollutant
Occurrence
Possible operating
factors to investigate
White
Particulate
common
Excessive combustion air
Gray
Particulate
common
Inadequate air supply or
distribution
Black
Particulate
common
Lack of oxygen; clogged
or dirty burners or in-
sufficient atomizing
pressure; improper coal
size or type
Reddish-
brown
Nitrogen
dioxide
rare
Excessive furnace tempera-
ture, burner configuration,
too much excess air
Bluish-
white
Sulfur
trioxide
rare
High-sulfur content in
fuel
Yellow
or
brown
Organics
rare
Insufficient excess air
a Based on data from Reference 3.
5-4
-------
5.1.5 Preinspection Interview
The purpose of the inspection should be discussed with the
appropriate plant official. Any changes in plant management
should be "noted, and data sheets on the process and ESP should be
updated to confirm that operational parameters on file still
pertain. This includes items such as the results from perform-
ance tests of changes in operation since the last inspection.
Examples of operational changes in the process or ESP that
an inspector might check are summarized below:
Process Operational Changes
1. Has the rate of production increased or decreased?
(Tons per hour, megawatts generated increased or de-
creased, or any other measure of production changed.)
2. Has there been a change in the product mix? For a
boiler this would include a new fuel source, a change
in the chemical analysis of the coal or oil. For a
cement plant it would include a change in the moisture
content of the slurry, or a different coal or oil as a
heat source.
3. Has there been a conversion from gas or oil to coal?
4. Operating temperatures could have been changed by the
addition of energy conservation retrofits. Examples
are the addition of economizers to a boiler, or the
addition of air or raw material preheaters in a molten
metal process, or in a cement process it should include
the addition of more chains in the kiln.
5. Have there been any changes in startup or shut-down
procedures? Is there any new day/night schedule
changes such as "Bottling Up" the boiler overnight; or,
has the unit been shifted from "Baseload" to "Standby"
status?
6. Have there been any changes such as the addition of new
forced-draft fans or new induced-draft fans? Any
addition or removal of afterburners?
7. Has there been any change made in the use of the col-
lected dust in the process, such as, reinjection or
return of the dust to the raw material mix?
5-5
-------
8. Has the amount of excess air been changed? Has the
soot blowing schedule been revised? Where applicable,
has the angle of burner tilt been changed?
9. Has there been any change in the size of the fuel, or
-has there been any change in the fuel preparation and
distribution to the burners?
Changes in ESP Operation
1. Has the effective size of the dust collector been
altered? (ESP fields out of service, or new fields
added.)
2. Have power input levels to the dust collector been
increased/decreased? (Additional power supplies, new
ESP power controls, additional reactors, power factor
or rectification revisions.)
3. Have new sources of emissions been added to the dust
collector such as vents from tanks in a paper mill?
4. Have any retrofits been added or removed in the ESP
system? Examples are gas conditioning, sectionaliza-
tion of power, additional or more powerful rappers,
power off rapping, new rapping sequence controls, new
power controller systems, etc.
5. Have there been changes in the dust removal system,
power off rapping, new dust conveying equipment or
arrangement of dust conveyors, vacuum/pressure system
changes, evacuation sequence changes, combination or
isolation of dust removal systems from several units?
Maintenance of Production Equipment and Dust
1. Are there established quality control and periodic
maintenance schedules set up for the operations that
are pertinent to the dust collector performance.
Examples are fuel pulverization, fuel distribution to
the burners, air louver maintenance, temperature,
pressure drop, oxygen content meter calibration, and
air heater cleaning.
5.1.6 Inspection Inside the Plant - Safety Considerations
On the first visit to the plant, the inspector should review
all safety rules with plant personnel. He should never tour the
plant without an escort, and should not open furnace doors,
manipulate valves or controls, or in any way try to change the
5-6
-------
operating characteristics of the plant equipment. Obviously, the
high-voltage electricity used in the ESP is extremely dangerous,
and all practical safety measures must be observed even though
the system incorporates interlocks and other safety devices.
5.1.7 Procedures for External Inspection of ESP's Control Sets
The first item that the inspector should check is the con-
trol sets for the ESP, which are usually located in a room on top
of, or remote from, the ESP. Plant personnel should provide a
diagram showing which fields are served by which TR sets, as a
guide to determining out-of-service fields when reading the TR
sets. Control panels can include primary and secondary current
and voltage meters, and a spark rate meter. If the ESP has four
sections, the voltage, amperage, and spark rate should be re-
corded for each section. The control set readings should be
compared with calibrated or design values for each section. The
inspector should check the daily log of control readings to
determine whether the readings have been drifting from normal.
Drift is indicative of such problems as air inleakage at air
heaters or in ducts leading to the ESP, dust buildup on ESP
interhals, and/or deterioration of electronic control components.
He should also make note of inoperative meters, the number of
power supplies on "manual" control, and TR sets on "auto" that
are held to operating levels below design specifications (such as
might be done to reduce wire breakage).
The inspector can utilize the meters to aid in diagnosing
other problems with an ESP. General examples of the effect of
changing conditions in the gas stream and within the ESP on
control set meters are presented below:6
1. When the gas temperature increases, the voltage will
increase, and the current will decrease. Arcing can
develop. When the gas temperature decreases, the
voltage will decrease, and the current will increase.
2. When the moisture content of the gases increases for
any given condition, the current and voltage will also
tend to increase in value.
5-7
-------
3. If reduced voltage exists because of a sparkover, a
rise in moisture may allow for an increase in the
precipitator voltage level.
4. An increase in the concentration of the particulate
¦will tend to elevate voltages and reduce current flow.
5. A decrease in the particle size will tend to raise
voltage while suppressing current flow.
6. A higher gas velocity through the precipitator will
tend to raise voltages and depress currents.
7. Air inleakage may cause sparkover in localized areas
resulting in reduced voltages.
8. A number of precipitator fields in series will show
varying readings with voltage-current ratio decreasing
in the direction of gas flow.
9. If a hopper fills with dust causing a short, the volt-
age will be drastically reduced, and the current will
increase.
10. If a discharge electrode breaks, violent arcing can be
observed with the meters swinging between zero and
normal.
11. If a transformer-rectifier unit shorts, voltage will be
zero at a high current reading.
12. If a discharge system rapper fails, the discharge wires
build up with dust; the voltage increases to maintain
the same current level.
13. If a plate rapper fails, the voltage decreases to
maintain a current level under sparking conditions.
Table 5-2 presents specific examples of the effect of chang-
ing conditions on ESP control set readings. These examples are
typical of what the inspector could expect to find. He should
become familiar with these meter reading techniques, so that he
is aware of problems during his inspection. Sections 3.2 and 4.3
present more detailed analyses of V-I curves and their use in
troubleshooting. Corona power readings can also be used to
estimate operating efficiency of the ESP, as will be discussed in
Section 6.
5-8
-------
TABLE 5-2. EFFECTS OF CHANGES IN NORMAL OPERATION ON ESP
CONTROL SET READINGS6
Condition
Effect
Primary
voltage
V, a.c.
Primary
current
A, a.c.
Secondary'
current
mA, d.c.
1. Normal full load
-
300
50
200
2. System load fall by 1/2
Gas volume and dust concen-
tration decrease, resistance
decreases
260
55
230
3. System load constant,
but increase in dust load
Resistance increases
350
40
175
4. Gas temperature
increases
Resistance rises, sparking
increases because of
increased resistivity
300-350
50-60
20-250
5. Gas temperature decreases
Resistance decreases
280
52
210
6. ESP hopper fills with dust
Resistance decreases
180
85
300
7. Discharge electrode
breaks
Resistance may fall to 0 (may
vary between 0 and normal if
top part of electrode is left
swinging inside the ESP).
Violent instrument fluctu-
ations, Arcing can be heard
outside the ESP
0-300
0-50
0-200
8. Transformer-rectifier
shorts
No current passes from T-R
set to the ESP
0
100+
0
9. Discharge system rapper
fails
Dust builds up on discharge
electrodes. Resistance in-
creases because corona dis-
charge decreases. Additional
voltage required to keep
current constant
330
50
200
10. Collection plate rapper
fails
Sparking increases. Voltage
must be reduced to keep
current constant
265
50
200
-------
5-1.8 Control Room Ventilation
Next the inspector should check control room temperature to
see that ventilation is adequate, as well as general housekeep-
ing. He should check the control sets internally for dirt, which
can cause false signals and cause components to deteriorate.
5.1.9 T-R Sets, Rapper/Vibrators, and Insulators
Many times the T-R sets and rappers and/or vibrators are
located in the same room as the control sets, on top of the ESP.
In any event, the T-R sets, insulators, and rapper/vibrators,
should be inspected next.
The inspector should examine insulators for moisture and
tracking from arc-over. Cracks can be spotted with a bright
g
light during inspection. Corrosion of the insulator compartment
(if applicable) is another indication of moisture buildup. The
inspector should check to see that the pressurization fan for the
top housing or insulator compartment is operating properly, and
that air filters for control sets and top housing are not plug-
ged. He should also note the condition of access hatch covers.
The inspector should check rapper and vibrator action visu-
ally and/or by feel. A uniform rhythmic tapping of metal to
metal should be noted for rappers, and a loud buzzing sound from
vibrators. Any irregular sounds are an indication of improper
operation of rappers or vibrators. The plant should provide a
diagram of the rapping system sequence so that the inspector can
verify that all of the rappers or vibrators are operating prop-
erly. Rapping intensity should be checked against design as
stack opacity can be improved by reducing rapping intensity.
Therefore, indications that rapping intensity has been reduced,
should be questioned.
5.1.10 Exterior Condition of ESP
The inspector should next examine the exterior of the ESP
for corrosion, loose insulation, exterior damage, and loose
5-10
-------
joints. The ducts entering the ESP should be checked; if they
show corrosion, the interior of the ESP may also be corroded.
The inspector should check for fugitive emissions at loose joint,
and as a result of other exterior damage.
5.1.11 Ash Handling
The inspector should next check to see that the exacuation
rate for the ash hoppers is often enough to prevent buildup of
ash over the tops of the hoppers. Inlet field hoppers, for
Example, normally collected from 6 0 to 80 percent of the total
catch, and must be evacuated much more often than the downfield
hoppers. If level alarms are used, he should determine that they
are operating properly. The inspector can check the temperature
at the hopper throat with the back of his hand, and if one is
comparatively low in temperature, this could indicate that a
Malfunction of the ash removal system could cause bridging or
Plugging of the hoppers and subsequent ash buildup.
Problems the inspector should look for in the ash evacuation
and removal system include water pump failure, disengagement of
Vacuum connections, malfunction of rotary air lock valves, and
failure of sequencing controls.
If ash is removed from a collection silo by truck, the
inspector should insure that the discharge pipe extends far
enough into the truck to minimize fugitive emissions.
5.1.12 Process Instrumentation
After finishing with the ash handling system, the inspector
should then proceed to check a number of process parameters that
can affect the ESP performance. For example, readings of gas
flow, gas velocity, excess air, gas temperature, pressure drop
across the ESP, moisture content, flue gas analysis (0CO^>
etc.) soot blowing intervals, and opacity should be taken if
Possible. Many of these instruments are located in the boiler
control room and have continuous readouts. An example trace from
5-11
-------
a continuous opacity monitor is shown in Figure 5-1. Variations
in readings from process instruments from the normal design
ranges should be investigated as to their possible effect on ESP
performance, in conjunction with ESP control set readings, and
visual observations made during the inspection.
5.1.13 Internal Inspection of an ESP During Scheduled or
Emergency Outages
If an ESP is down for scheduled maintenance or because of a
malfunction, and an inspection is being done, the inpsector
should take time to perform some checks in addition to those
already mentioned. These inspection techniques are similar to
those the company should be doing during an annual inspection,
but are not as detailed. These techniques were covered in
Section 4 and are discussed further in Appendix A.
As mentioned previously in this section, no inspection
should be undertaken until it is certain that the ESP is deener-
gized and grounded, and necessary precautions are taken to ensure
that the equipment cannot be energized during the inspection.
5.1.14 Collection Plates/Discharge Wires
The inspector should observe the dust accumulation on both
plates and wires. The discharge wires should only have a slight
coating of dust with no corona tufts (doughnut-shaped ash accu-
mulations) . Thickness of dust buildup on plates is normally
between 0.3 and 0.6 cm (1/8 to 1/4 in,). If the plates have more
than 0.6 cm (1/4 in.) of dust, the rappers are not cleaning
properly. If the collecting plates are almost metal clean, this
i
may be an indication of high gas velocity, extremely coarse fly
ash, too high a rapping intensity, or too low an operating volt-
age for good precipitation. The inspector may notice this if a
section has been shorted out prior to his inspection.
The inspector should note whether or not the discharge
electrodes are centered between the collecting plates from top to
bottom to ensure optimum performance. He should note any broken
5-12
-------
1300 1400
100 80 60 40 20 0 0 20 40 60 80 100
^ RELATIVE VALUE OF _
LIGHT OBSCURATION
Figure 5-7..
7
A sample opacity chart.
-------
or missing discharge electrodes. Records of wire breakage should
be kept by the company to help determine the cause of continued
wire breakage in the same area, possibly caused by alignment
problems. -Random wire breakage is probably caused by dust build-
up on wires or plates.
The inpsector can check for air inleakage from door openings
by noting the amount of corrosion on collecting plates adjacent
to inspection hatches, and from hoppers by checking on the lower
portion of the collecting plates. Air inleakage also causes
nonuniform gas flow, and can reduce efficiency.
5.1.15 Hoppers
The inspector should have plant personnel open the hopper
access door and check for corrosion, which indicates air inleak-
age as mentioned previously. He should check for dust buildup in
the upper corners of the hopper, and debris such as fallen wires
and weights in the hopper bottom and valves. If discharge elec-
trode weights have dropped 3 inches or more, this indicates a
broken wire. Chronic buildup of ash is an indication of low
operating temperatures, insufficient heat insulation, or inade-
quate hopper emptying.
5.1.16 Review of Operating Records
The inspector should review operating records from the
process and ESP, both for completeness and for changes in opera-
tion that may have affected ESP performance. Table 5-3 lists a
number of items for which records should be kept. Malfunctions
from both the process and the ESP should be discussed with plant
officials, and the inspector should determine what plant offi-
cials are doing to remedy any recurrent problems.
5.1.17 Inspection Form
Data obtained during an inspection should be summarized on a
form such as that presented in Appendix C-2. The form also
serves as a record of the inspection.
5-14
-------
TABLE 5-3. RECOMMENDED RECORDKEEPING REQUIREMENTS3
Frequency
Comments
ESP
Controls
Instrument calibration
Primary current, A
Primary voltage, V
Operating current, mA
Operating voltage, kV
Spark rate, sparks/min
Initial measurement
Daily
Daily
Daily
Daily
Daily
Compare daily measurements
with redlined readings.
Check for gross misreadings
or slow drift from redline.
Pressure drop through system, in.
Daily
Compare with initial pressure
Rapper operation
Daily
Check frequency and intensity
Insulator condition
Daily
Check for deterioration
Hoppers
Daily
Level alarms, evacuation system
BOILER
Fuel quality
Sulfur, %
Ash, »
HHV, Btu/lb
Monthly
State range of values and
average
Recording instrumentation
Fuel flow-air flow control
Steam flow-air flow control
Daily
Daily
Maintain circular charts for
3 months
Maintain circular charts for
3 months
Changes in boiler operation
As occurring
Flue gas analysis, % by vol.
(Circle COj or 02>
Spot checks
Soot blowing intervals
Daily
State hours or blows per day
Malfunctions (boiler or ESP)
As occurring
Use standard form to describe
malfunctions
-------
5.1.18 Compliance Action
If conditions observed during the inspection indicate that a
citation is warranted, the inspector must clearly state to plant
officials the grounds for such a citation. An onsite citation is
justified only by clear-cut violations such as excessive opacity,
reduced corona power, or failure of the plant to report malfunc-
tions or to maintain or provide required records for review.
Table 5-4 lists important compliance parameters and conditions
3
for issuance of citations.
After a review of the inspection report by the inspector's
supervisor, a copy of the inspection checklist should be sent to
the utility with a letter confirming that the inspection was
made, stating any deficiencies, requesting that they be corrected
within a reasonable time. Recommendations can be given for
further improvements in operation and maintenance of the ESP,
although emphasis should be towards indications of trouble and
not the solution.
The utility should know what is expected and the time frame
it will have to accomplish the required action. Some type of
implementation plan may be requested.
5-16
-------
TABLE 5-4. IMPORTANT COMPLIANCE PARAMETERS AND CONDITIONS FOR
ISSUANCE OF A CITATION3
Compliance parameter
Visual emissions
Opacity monitors
ESP instrumentation
Records
ui
I
Conditions for issuance of a citation
Federal Register, Section 60.11 and Appendix A - Method 9 -
promulgated.
a) Not in operation: issue citation
b) Not properly calibrated or zeroed: advise plant personnel
to implement a calibration program, which might include
services of outside consultants.
a) Not in operation: request in followup letter a schedule for
repair of instruments.
b) Values indicating unit out of compliance: determine reasons;
request that plant take appropriate corrective action.
a) Not Kept: issue citation
b) Values indicating plant is out of compliance:
Monitors - If opacity standard is ever exceeded for
more than 2 continuous hours, issue citation.
Fuel records - If ash/sulfur content is frequently over values
recorded during performance test, determine reason.
Generating capacity - Disregard short-term peak loads.
If electrical output/fuel usage is consistently
higher than emission test values, request
another performance test.
c) Daily instrument zero/calibration: issue citation if ESP
instruments are not zeroed and calibrated within 3 or more
consecutive days.
d) Fuel analysis: units without S02 control equipment must record
fuel analysis daily.
e) Malfunction records: if complete information (time, levels,
malfunction description, problem correction methods) is not
recorded for all malfunctions, issue citation.
Based on data from Reference 3.
-------
REFERENCES FOR SECTION 5
1. Test Manual for Fossil Fuel-Fired Steam Generators. Pre-
pared by PEDCo Environmental, Inc., Cincinnati, Ohio, for
Environmental Protection Agency. January 1977.
2. Industrial Air Pollution Guide. Chapter 7.0. Prepared by
PEDCo Environmental, Inc., Cincinnati, Ohio, for Environ-
mental Protection Agency. 1978.
3. Devitt, T.W., and Norman J. Kulujian. Inspection Manual for
the Enforcement of New Source Performance Standards: Fos-
sil-Fuel-Fired Steam Generators. PEDCo Environmental, Inc.
January 1975.
4. Szabo, Michael F., and Richard W. Gerstle. Electrostatic
Precipitator Malfunctions in the Electric Utility Industry.
PEDCo Environmental, Inc., Cincinnati, Ohio, EPA-600/2-77-
006. January 1977.
5. Devitt, T.W. , and R.W. Gerstle, and N.J. Kulujian. Field
Surveillance and Enforcement Guide: Combustion and Incin-
eration Sources. PEDCo Environmental, Inc., Cincinnati,
Ohio. June 197 3.
6. Englebrecht, H.L. Electrostatic Precipitator Inspection and
Maintenance. Plant Engineering. April 29, 1976. p. 193-
196.
7. Dismukes, Edward B. Techniques for Conditioning Fly Ash.
In: Symposium on Particulate Control in Energy Processes.
EPA-600/7-76-010.
8. Szabo, Michael F., and Richard W. Gerstle. Operation and
Maintenance of Particulate Control Devices on Coal Fired
Utility Boilers. PEDCo Environmental, Inc., Cincinnati,
Ohio. EPA-600/2-77-129. July 1977.
5-18
/
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SECTION 6
ESP PERFORMANCE EVALUATION
This section presents procedures for evaluating and predict-
ing ESP performance on the basis of previous stack test inspec-
tion results. A procedure is provided for relating ESP elec-
trical data (corona power) to emission level, based on previous
stack emission test data. Brief discussions are made on the use
of advanced modeling techniques including: a) programmable
calculator ESP performance model, and b) computerized ESP per-
formance model.
6.1 INTRODUCTION
An approach can be developed which will enable regulating
agencies to account and check for continuous compliance for
conventional electrostatic precipitators (ESP). Analysis of
recordkeeping logs of process and ESP operating conditions can be
used along with baseline test results to determine a correspond-
ing emission level for a defined set of ESP operating conditions.
A technological basis can be substantiated to correlate ESP
corona power input with partiuclate emission levels. This gen-
eral relationship between corona power and emission level is
consistent with theoretical and practical design methodologies.
The same empirical (engineering) adjustments that ESP vendors
customarily incorporate into their design considerations and
criteria can be likewise incorporated and engineered into emis-
sion regulations.
A comprehensive set of baseline test results will establish
the specific relationship between corona power and emission level
6-1
-------
for a specific process/ESP combination. Known ranges of the
correlation factor are available for several major industries
typically using conventional ESP's (see Section 6.2). Once this
relationship (and coefficient) is established, both the operating
and regulating parties will have a known corona power level to
use as a technical measure of ESP performance for a corresponding
emission level. Refer to Table 3-2 for an outline of the base-
line test information needed for this regulation measure.
The established relationship between corona power and per-
formance level can be verified again during compliance testing.
If the ESP is upgraded, or if significant changes in process,
feed materials, or fuel quality occur, then an updated baseline
test is required to redefine the corona power - emission level
relationship.
More comprehensive baselining with sophisticated measurement
and analytical techniques can be incorporated into this approach
as future air quality needs and resources deem practical. Alter-
nate methods of ESP performance analysis can be performed through
use of a calculator program (Section 6.6) or a computerized model
(Section 6.7). However, EPA has not endorsed any method other
than stack testing for emission level determination. Consequent-
ly, these analytical methods can only be used to indicate, but
not to define, emission levels. Subsequent stack testing under
similar ESP conditions (i.e., with reduced corona power levels)
would need to be performed to determine the actual emission
level.
6.2 TECHNICAL BASIS FOR CORONA POWER - EMISSIONS CORRELATION2
The following demonstration of technical material provides
convincing but only fundamental evidence of the relationship
between corona power and emission levels. Limited resource
dedication restricts the level of treatment for substantiation of
this relationship in this text. Additional resource allocation
6-2
-------
is necessary to expand the basis and technical materials for
suitable substantiation for this evolutionary step to occur in a
new regulation process.
The preceding sections of this report emphasized the basis
and use of secondary electrical data for O&M purposes. This
section will likewise use and base electrical data measured and
recorded by secondary metering, but will use the term (adjective)
corona instead of secondary. The term corona is preferred for
use in this treatment for reasons of: 1) consistency with the
reference material applied, and 2) technological aptness. The
presence, intensity, and distribution of the corona phenomena
determine the effectiveness of collecting particulate in electro-
static precipitation. Corona power is a measure of the presence
and intensity of the electrical energy (driving force) effec-
tively utilized in the precipitation process. The extent of
corona power effectively used in precipitation is measured by the
secondary voltage and current meters. The primary electrical
meters measure the power components fed to the T-R sets, and
represent indirect measurement of the intended power usage level.
Furthermore, complications (e.g., O&M difficulties) and energy
transmission losses through the T-R set discourage the use of
primary electrical levels for definitive purposes. Since second,-
ary metering is direct, available, and cost-effective, its use is
emphatically encouraged.
The precipitation rate of particles increases with the
electric field strength in the precipitator, evidenced by the two
following equations:^
w = HI 1 + ° I Equation 1
and
Z e E E a
w = o c p Equation 2
e
6-3
-------
where w = precipitation rate parameter
(or migration velocity)
q = particle charge
Ep = the precipitating field
0 = gas velocity
a = particle radius
A = mean free path
a = dimensionless parameter » 0.86
E = charging field strength
c
ec = permittivity of free space
The electric field strengths are dependent on the corona (second-
ary) voltage and current levels experienced in the precipitator.
Corona power may be calculated by the formula:
Po =
-------
Pc
w = K, Equation 4
e X A
where = dimensionless parameter
A = collection surface area
Numerical values of can be calculated from performance test
data taken during the baseline test, and are usually in the range
of 0.1 to 0.7 for conventional ESP's over the spectrum of indus-
2
trial source categories.
Corona power may also be related to collection efficiency by
itut
equation)
substituting the value of wg given by Equation (Deutch-Andersen
- (A/V) w
n = 1 - e Equation 5
where n = collection efficiency
V = volume of gas treated
w = particle migration velocity
to give:
-Kn(Pc/V)
n = 1 - e 1 Equation 6
where Pc/V = corona power density, watts/unit of gas volume.
If corona power density is expressed in watts per 1000 acfm, then
Equation 6 can be rewritten in the form
. -0.06K..(Pc/V)
n = 1 - e 1 Equation 7
Approximate values of can be theoretically determined;
accurate values of can be empirically determined from per-
formance tests, especially over the limited range of normal
process and precipitator operating conditions.
The use of penetration facilitates calculation of emission
levels, as penetration levels are directly proportional to emis-
sion levels. Equation 7 can be rearranged and simplified in the
form of penetration as:
6-5
-------
-0.06 K., (Pc/V)
p = e X
Equation 8
where p = penetration = 1 - efficiency
Actual performance results on precipitator efficiency versus
specific corona power (Pc/V) from many fly ash studies are shown
in Figure 6-1. The solid line in Figure 6-1 represents the
theoretical relationship between efficiency and specific corona
power for = 0.55 using the following equation (Equation 9) to
account for variations in gas throughput:
Reasonable correlation exists between the theoretical curve and
experimental results, considering that the experimental results
represent a large number of preciptiator installations on sources
of fly ash.
During recent years it has become common practice to install
high performance ESP's exhibiting higher collection efficiencies
(99+%) than earlier installations. Another common practice of
recent ESP installations is that large-sized units are becoming
popular due to their cost-effective control of larger sized
industrial processing facilities. These modern day trends do not
change the theoretical basis of electrostatic precipitation, but
do impact ESP performance characteristics and engineering design
details. Extension of ESP performance results to include high
performance cases of 99+% efficiency are shown in Figure 6-2.
The above-mentioned change in performance characteristics is
reflected by the inflection point of the best-fit curve at or
near the 99.0% efficiency level. The significant change in the
slope of the curve relating efficiency to specific corona power
reflects the substantial increase in corona power to attain
higher performance. The linear relationship plotted on the semi-
log graph for the below 99% cases does not depict the actual
relationship for the above 99% cases.
Equation 9
where P - penetration = 1 - efficiency
6-6
-------
*—
99
z
1 1 1
UJ
o
98
ec
¦ 11
a.
97
>-
cj
95
UJ
•—t
o
(—t
90
LL.
u.
LlJ
z
80
o
»—«
70
I—
t \
w
Ui
_i
1
50
O
o
30
0
t 1 1 r -"T
TEST DATA •
THEORETICAL CURVE
FOR k * 0.55
25 50 75 100 125 150
CORONA POWER, WATTS/1000 acfm
METRIC CONVERSION: (watts/1000 acfm) (2500) watts/1000 m3/sec
Figure 6-1. Relationship between collection efficiency and
specific corona power for flv ash precipitators, baso5
on field tost data.l
<_>
ec
<_>
z
o
o
o
0 100 200 300 400 500 600
CORONA POWER, WATTS/1000 acfm
METRIC CONVERSION: (watts/1000 acfm) (2500) - watts/1000 m3/sec
Figure 6-2. Efficiency versus specific corona power extended
to high collection efficiencies, based on field test data on
recently installed precipitators.2
6-7
-------
Further inventory and inspection of performance results need
to be conducted in order to qualify the general relationship of
corona power and emission level in this high performance range
(^99%) . Until further resources are dedicated to examine and
better define the characteristics in the high efficiency range, a
concession will be made for the remainder of this text, and
exclusion of the characteristically different regime will be
made.
Table 6-1 presents values or range of values for the co-
efficient (K^) relating corona power and collection efficiency
for several industrial source categories. These coefficient
values were calculated using Equation 7 and Reference 1. More
source categories and corresponding coefficients are achievable
with further inventorying.
TABLE 6-1. CORONA POWER - EMISSlbNS COEFFICIENT FOR
SEVERAL INDUSTRIAL CATEGORIES1
Industrial category
coefficient
Electric utility fly ash
0.55
Pulp and paper
0.129
Recovery boiler
0.106
Cement plants (range with wet
and dry process)
0.785 (wet)
0.226 (dry)
Municipal incinerators (range)
0.57 - 1.88
Steel - open hearth furnace
0.19
6.3 PRACTICAL BASIS FOR CORONA POWER - EMISSIONS CORRELATION
Fundamental in this treatment of ESP performance is the
axiom (and later the demonstration) that conventional ESP per-
formance will degrade with time. This axiom simply means that
normal "wear and tear" occurrences with ESP's cause deterioration
6-8
-------
in collection performance. Almost without exception# the per-
formance of any system will degrade over a period of time, and
servicing of components is needed to restore performance.
Conventional precipitator performance becomes less effective as a
direct result of usage. The intentional collection of particu-
late material on the plates and wires reduces collection perform-
ance relative to clean internal conditions. Other factors con-
tribute to degradation, such as reentrainment. ESP reentrainment
losses are at a minimum level with clean internal conditions due
to the reduced availability of particulate material to become
reentrained.
Factors that affect the rate and extent of performance
degradation are:
1. Competency of engineering design,
2. Competency of O&M practices, and
3. Characteristics of process operations.
It is not pertinent in this text to delineate or prioritize these
factors and their relationship with performance degradation. It
is, however, pertinent to establish the reality, typical rates,
and extent of performance degradation to be expected, and the
means of identifying performance degradation. Identification is
the first step for resolving performance degradation. This
degradation is real and can be proven by a number of facts such
as:
1. The common sense realization that all control systems
have wear and tear factors which lower performance.
2. ESP performance will diminish due to the presence and
accumulation of particulate material.
3. ESP operators "strategically" schedule compliance
testing during peak performance periods.
4. ESP vendors acknowledge performance degradation due to
a) particulate accumulation and b) a need for regularly
scheduled ESP outages for servicing and cleaning for
performance maintenance.
6-9
-------
5. Regulating and inspecting ESP personnel have evidence
of degradation from stack emission and visual emission
data.
The rate and extent of degradation cannot be quantified at
this time by referenceable material. Variation in degradation
characteristics is expected to be extensive across the spectra of
industrial source categories, ESP types and vintages, and O&M
practices. Non-referenceable sources (i.e., private communica-
tion with ESP operators, vendors, and'researchers) indicate that
ESP degradation is analogous to other natural decay phenomena.
Figures 6-3 and 6-4 illustrate the expected degradation profile
of typical ESP performance and corona power levels. The perform-
ance and corona power trends in Figures 6-3 and 6-4 are:
1. Presumed for full-scale systems, projected from EPA's
mobile pilot ESP performance trends taken from several
short-term performance test programs;
2. Time-extrapolated to asymptotically approach a minimum
performance level;
3. Independent of severe, sudden changes in ESP-internal
conditions or significant process variations; and
4. Offered to be qualitative and not quantitative.
A continuing performance tracking over a continuing time
period is the object of a continuing compliance pursuit. Failure
to account for continuing emissions tracking will preclude and
negate continuing compliance pursuits. The particulate emissions
curve in Figure 6-3 portrays real-time emission tracking for a
hypothetical ESP-controlled emission source. The curve in
Figure 6-3 includes the scenario of "strategic" compliance
testing shortly after washdown/servicing and the "acceptable"
stack emission results. As time continues from washdown/servic-
ing, performance degradation occurs, resulting in a gradually
increasing emission level. Eventually, the actual emission level
6-10
-------
>)
IB
"O
in
c
o
4
ir>
z
o
tn
in
ZD
O
cc
Cl
p 1
I
i
-j
c
UJ
D£
200 —
E 100
REAL TIME CORONA POWER TRACK-
ING (RECORDKEEPING)
2 4 6 8 10
TIME» months
Figure 6-4. Real-time corona power scenario.
6-11
12
-------
rises above the prevailing emission standard level, and approaches
steady-state performance and emission level conditions.
The curve in Figure 6-4 illustrates the corresponding corona
power levels over this presented scenario. As demonstrated
previously, a relationship exists between collection performance
and specific corona power. Recordkeeping of corona power levels
with secondary electrical metering would provide real-time evi-
dence for correlation with emission levels, once this relation-
ship is established.
Time integration of the projected and actual emission in-
ventories is illustrated in Figure 6-5. The difference between
the projected (assumed) and actual emission inventory levels is
significant, and, without adequate instrumentation and record-
keeping, "strategic" compliance testing scheduling is effective
in circumventing compliance standards. Actual emission levels
become several-fold higher than projected levels, and ambient
concentrations of particulate material fall short of modeled
(projected) levels. Excessive ambient concentration levels then
become construed to indicate a need for lower emission levels,
and/or inappropriate dispersion modeling methodology. Erroneous
conclusions then promote ineffective appropriations to study the
economic impact of lower emission levels, and/or improved ambient
modeling methodology. Since the fundamental problem has yet to
be realized, the solution to restoring cleaner air quality levels
is not achieved even though money is appropriated and spent to
further study the symptoms.
Certain qualifications in determining effective corona power
levels will need to be provided if/as corona power relationships
with emission levels are to be implemented. There are two cir-
cumstances which serve as exceptions to the corona power correla-
tion. However, both exceptional cases can be qualified in ex-
actly the same manner. Both problem-related cases involve
secondary-current levels which are excessive to design current
6-12
/
-------
1000
zr
©
800
z:
UJ
UJ
f—
600
ACTUAL EMISSION INVENTORY
400
o
ct
cc
o
UJ
t—
z
200
UJ
s:
t—
PROJECTED EMISSION INVENTORY
2
0
4
6
8
10
12
TIME, months
Figure 6-5. Integrated particulate emission inventory scenarios.
6-13
-------
levels, and the excessive current levels are not effectively used
in the precipitation process. These two problem-related excep-
tional cases are: 1) primary or secondary current leakage (leak-
age meaning current levels that are generated, but not delivered
to the corona wires), and 2) back—corona conditions due to ex-
cessive resistivity. Since corona power is the product of sec-
ondary voltage and current levels, either of these exceptions
will increase corona power levels without a corresponding in-
crease in collection performance.
An appropriate qualification or criterion can be made to
assure that the effective corona power determined is indeed
"effective" in the precipitation process by the use of Ohm's law:
resistance = voltage/current. Stipulation of a minimum secondary
resistance denotes that this determination is made from secondary
voltage and secondary current levels. The minimum secondary
resistance level criterion can be stipulated on a general or
specific basis. A general basis will be offered in this text,
but a more specific resistance criterion could (and perhaps
should) be stipulated for nontypical ESP design cases. Based on
typical secondary voltage and current density levels experienced
in conventional ESP's, a minimum secondary resistance level near
9 2
or at 1 x 10 ohm/ft is usable as the necessary criterion. This
criterion includes consideration of collection plate area in the
units (ohm/ft2) for resistance to allow for flexibility and
variation in ESP size across the spectrum of industrial applica-
tion.
6.4 BASELINE TECHNIQUE USING STACK TEST RESULTS
When recent stack test results are available and complete
(use Table 3-2 for a guide to evaluate completeness), the corona
power-emissions relationship can be used to estimate the emission
level using the corona power levels obtained during the inspec-
tion. The following example case will demonstrate this technique
for a power plant, using data from Table 6-2, and Equation 8.
6-14
-------
TABLE 6-2. EXAMPLE DATA FROM STACK TEST
AND INSPECTION RESULTS
Stack
test results
Data from
inspection
Production rate, MW net
640
640
Gas temperature, °F
300
300
Total corona power, W
156,250
125,000
Gas flow rate, acfro
1,250,000
1,250,000
Specific corona power,
watts/kacfm
125
100
Particulate emission level,
lb/106 Btu
0.32
?
6-15
-------
Table 6-2 presents abbreviated results from a recent stack
test and inspection. For the sake of simplicity, abbreviated
results are provided in this hypothetical, but representative
example. Most other operating data and conditions listed in
Table 3-2 are virtually the same for the stack test and inspec-
tion time periods. Notice, however, that the total corona power
and specific corona power levels are at reduced levels during the
inspection as compared to the power levels during the stack test.
The following calculations will demonstrate a method of esti-
mating the emission level during the inspection.
Use Equation 8 and stack test results to determine penetra-
tion:
p = e-0.06 (.55)(Pc/V)
= e 0*°6 (-55)125 where Pc/V = 125 watts/kcfm
= 0.0161
Since penetration is proportional to emission level, the coeffi-
cient of proportionality can be calculated by:
P(C) = E.L.
where c = coefficient
E.L. = emission level
Rearranging to determine the coefficient value, and using stack
test results for E.L. = 0.32 lb/10^ Btu
c = E.L./P
= 0,32/0.0161
= 19.8
Using Equation 8 and the inspection data to determine penetra-
tion :
D _ -0.06 (.55) 100
r — 6
= 0.0369
6-16
-------
Using the coefficient value from the stack test, and the cal-
culated penetration value for the inspection period, calculate
the estimated emission level by using:
E.L. = P(c)
= 0.0369(19.8)
=0.73 lb/106 Btu
A graph can be constructed to show the relationship between
emission levels and specific corona power. Figure 6-6 illus-
trates such a relationship, using the data supplied in Table
6-3.
6.5 CORONA POWER DATA AND EFFICIENCY ESTIMATES
6.5.1 Control Set Data
Read secondary currents and voltages for each field of the
precipitator. Calculate delivered corona power for each section
according to the following formula:
Delivered power = (secondary voltage) x (secondary current)
If there are no meters for secondary voltage and current,
calculate delivered power for each precipitator field as follow^:
Delivered power = (input power) x (power supply efficiency)
Input power = (primary current) x (primary voltage)
Typical power supply efficiency is 90 percent.
Determine total corona power input by summing the delivered
power for each section. Calculate corona power input as watts
3 3'
per 1000 m /s (1000 ft /min) of flue gas. Obtain precipitator
collection efficiency value from Figures 6-1 or 6-2.
If one or more bus sections are not operating, this will be
reflected in the reduced total corona power available, resulting
in lower collection efficiency.
6-17
-------
99
95
90
50
1 1 1
i
THEORETICAL V
CURVE FOR /
k = 0.55 /
—
/
/
/'iii
1
0.198
0.32
0.73
0.988
1.98
25 50 75 100 125 150
SPECIFIC CORONA POWER, watts/1000 acfm
9.88
19.8
Figure 6-6. Relationship between collection efficiency,
emission levels and specific corona power
(for the example case specified by Table 6-?).
6-18
-------
TABLE 6-3. INPUT DATA FOR ESP COMPUTER MODEL
ESP specifications
Gas/particulate specifications
Estimated efficiency
Gas flow rate
Precipitator length
Gas pressure
Superficial gas velocity
Gas temperature
Fraction of sneakage/reentrain-
ment
Normalized standard deviation
of gas velocity distribution
Gas viscosity
Particulate concentration
Particulate resistivity
Number of stages for sneakage/
reentrainment
Number of electrical sections in
direction of gas flow
Particulate density
Particle size distribution
Dielectric constant
For each electrical section:
Ion mobility
Length
Ion speed
Area
Applied voltage
Current
Corona wire radius
Corona wire length
Wire-to-wire spacing (1/2)
Wire to plate spacing
Number of wires per linear
section
6-19
-------
6.5.2 Design Data
From ESP design data, obtain gas flow, temperature at ESP
inlet, total ESP plate area, plate area for each bus section, and
precipitation rate parameter (may need to be recalculated when
coal sulfur content has changed significantly). Make sure that
the design values for gas flow and temperature at ESP inlet are
still accurate for the current operating conditions.
Using the Deutsch equation or one of its derivatives (see
Section 2), calculate the ESP collection efficiency, accounting
for loss in plate area because of bus section outage. Consider
the following example (English units):
° precipitation rate parameter (w) = 0.35 ft/sec (21
ft/min).
° gas flow (V) = 300,000 acfm @ 300°P
0 total plate area (A) = 84,000 ft2 (21,000 ft2/bus
section, four bus sections total). One bus section is
out of service, reducing effective plate area to 63,000
ft2.
From the Deutsch equation:
n = 1 - exp - y w
n _ , 63,000^ / n\
- 1 - exp - (300,000^ (2 *
= 1 - 0.0122 = 98.78%
Note that the outlined procedures are based on generalized
or design data and are not precise enough to reflect quantita-
tively the changes caused by readily measurable variations in
operating parameters. Thus emission estimating procedures are
normally used as a part of the initial permit evaluation process
to judge the adequacy of the system for complying with emission
3
regulations.
6.6 CALCULATOR PROGRAM FOR ESP PERFORMANCE EVALUATION5
A report describes the latest version of calculator programs
to simulate and predict ESP performance, and to use the predicted
6-20
-------
particle size data penetrating the ESP to predict venturi scrub-
ber performance and, similarily, project in-stack opacity from
the scrubber effluent particle size distribution. The programs
are written specifically for a Texas Instruments, Inc. TI-59
programmable calculator with a PC-100A printer. The advantates
of using a programmable calculator for these purposes are con-
venience, economy, and simplicity. The program results are
considered to be as accurate as the input data, meaning the
errors in the input data are likely to be more than errors intro-
duced by the program. Complete listing of the calculator pro-
grams are included in the report, along with step-by-step in-
structions and examples.
The ESP calculator programs are based on the EPA/Southern
Research Institute (EPA/SoRi) ESP Computer Model Revision I. A
more complete discussion of the theory and programming details is
contained in References 7 and 8. The programs are equipped with
computations to determine particle charging and particle collec-
tion levels. Corrections for non-ideal factors are provided to
account for non-uniform gas flow, gas sneakage, and particle
reentrainment.
Two ESP programs are provided to use either log-normal or
histogram formats of particle size distribution data as input.
Other input data required to exercise the model include the
following:
ESP specifications Gas/particulate specifications
Wire to plate spacing Temperature
Specific collection area Pressure
Length of precipitator Gas velocity
Superficial gas velocity Dielectric constant
Applied voltage Ion mobility
Secondary current density Ion speed
Number of sections for sneakage Particle size distribution
Normalized standard deviation of
gas velocity
Sneakage fraction
6-21
-------
The calculator programs run 30 minutes for the log-normal
particle size input and 60 minutes for the histogram particle
size input. The program will calculate the overall penetration,
the ideal and corrected outlet size distribution, ideal migration
velocity as a function of particle size, and the ideal and cor-
rected penetrations as a function of particle size. A copy of
the results will be displayed by the printer. These results can
be used with other input data in the opacity programs to cal-
culate the associated in-stack opacity level.
The calculator program can be used to evaluate precipitator
performance and to indicate emission levels based on ESP operat-
ing conditions and previous stack test results. An approach,
similar to the one described in the previous section, can be used
to correlate secondary voltage and current levels (corona power)
with emission levels. Comprehensive stack test results can be
incorporated into the program to establish a relationship between
ESP conditions and emission level. Iterative exercise of the
program will probably be needed to adjust estimated values for
sneakage and gas distribution in order to obtain reasonable
agreement between predicted and measured emission levels. Once
these empirical factors are obtained and agreement between pre-
dicted and measured emissions is reached from use of stack test
results, then reasonable prediction of emission levels can be
made for other cases of ESP conditions.
6.7 COMPUTER MODEL FOR ESP PERFORMANCE EVALUATION
An ESP mathematical model has been developed under EPA
sponsorship by Southern Research Institute (SoRI) which relates
collection efficiency to ESP size and operating parameters. [The
model is applicable for dry, wire-plate ESP's.] The computerized
mathematical model has been revised in order to reduce computer
time and extend its use for different levels of analysis. Com-
plete discussions on the programming, use, and revisions of the
6-22
-------
REFERENCES FOR SECTION 6
1. Oglesby, Sabert Jr. A Manual of Electrostatic Precipitator
Technology. Southern Research Institute, Birmingham,
Alabama. August 1970.
2. White, H.J. Electrostatic Precipitation of Fly Ash.
JAPCA. March 1977.
3. Devitt, T.W., R.W. Gerstle, and N.H. Kulunian.¦ Field
Surveillance and Enforcement Guide: Combustion and Incin-
eration Soruces. APTD-1449. June 1973.
4. Sparks, L.E. SR-52 Programmable Calculator Programs for
Venturi Scrubbers and Electrostatic Preicpitators. EPA-600/
7-78-026. March 1978.
5. Cowen, S.J., D.S. Ensor, and L.E. Sparks. TI-59 Program-
mable Calculator Programs for In-stack Opacity, Venturi
Scrubbers, and Electrostatic Precipitators. EPA-600/8-80-024.
May 1980.
6. Gooch, J.P., J.R. McDonald, and S. Oglesby, Jr. A Mathe-
matical Model of Electrostatic Precipitation. EPA-650/
2-75-037. April 1975.
7. McDonald, J.R. A Mathematical Model of Electrostatic
Precipitation (Revision 1): Volume 1. Modeling and Pro-
gramming. EPA-600/7-78-llla. June 1978.
8. McDonald, J.R. A Mathematical Model of Electrostatic
Precipitation (Revision 1): Volume II. User Manual.
EPA-600/7-78-11lb. June 1978.
9. Mosley, R.B., M.H. Anderson, and J.R. McDonald. A Mathe-
matical Model of Electrostatic Precipitation (Revision 2).
EPA-600/7-80-034. February 1980.
6-25
-------
SECTION 7
CASE HISTORIES
The purpose of presenting these case histories is to famil-
iarize the inspector with some actual operating problems of ESP's
in the field, and the attempts made to correct these problems.
Although it is not the responsibility of the inspector to tell
the company how to resolve problems with a precipitator, he may
be able to provide some suggestions as to what a problem might
be, and methods that could be used to rectify it.
7.1 COLD-SIDE ELECTROSTATIC PRECIPITATOR ON A COAL-FIRED UTILITY
BOILER
This section presents the operating history of a cold-side
ESP installation at a coal-fired power plant located in the
Southern United States. The information presented here was
obtained during a site visit and from discussions with engineer-
ing personnel.
7.1.1 System Description and Operating. History
The precipitator was originally installed in 1960 and was
. . 2 3
guaranteed for 90 percent efficiency with an SCA of 18 m /m /s
2
(91 ft /1000 acfm). Actual precipitator efficiency was 55 per-
cent or less at the normal gas temperature of 132°C (270°F) and
about 90 percent at 155°C (310°F). This is a common effect
observed in marginally designed precipitators operating at aver-
age gas velocities of approximately 2.4 m/s (8 ft/s) with medium-
to high-sulfur coals. Studies with ammonia injection showed a
significant improvement in performance at 132°C (270°F), with
7-1
-------
3
efficiencies ranging from 85 percent at 0.0009 m /s (2 scfm)
3
ammonia per ESP to 95 to 97 percent with 0.005 to 0.01 m /s (10
to 20 scfm) ammonia.
In 1970-72, the ESP was modified to improve performance.
2 3 2 3 2
The SCA was increased from 18 m /m /s to 27 m /m /s (91 ft /1000
acfm to 136 ft2/1000 acfm), and the number of T-R sets per col-
lector was increased from 2 to 5. The present arrangement con-
sists of four separate collectors, each with four fields in the
direction of gas flow. Collection efficiencies about 98 percent
were obtained with ammonia injection in 1972, when the utility
began using ammonia on a full-time basis.
Recently, however, performance has decreased to 90 percent
or less, and outlet emissions are several times greater than the
state regulation of 47.26 ng/J (0.11 lb/10^ Btu). Some of the
major causes for poor performance at this unit are summarized
below.
1. initial design was marginal, calling for a small ESP to
operate at excessively high gas velocities for the
sulfur and temperature conditions. The expected level
of performance for the system at the time of the modi-
fications was only 95 percent.
2. Poor equipment availability and component malfunctions.
3. Unstable T-R electrical sets, "limited power cutput
capability, poor match to load conditions, and uncon-
trolled sparking, causing excessive dust reentrainment.
4. The ammonia injection rate is now limited to 8 to 10
ppm because sticky ash buildup on ID fans has caused
severe imbalances and buildup in hoppers has caused
difficulty in ash removal. Higher levels of ammonia
injection are needed to prevent excess air reentrain-
ment, which is caused by low ash resistivity with the
high-sulfur coal used by the utility at gas tempera-
tures of 116° to 138°C (240° to 280°F) . The untreated
ash can be readily collected but is easily reentrained
before being rapped off of plates into the hopper.
5. Cyclic boiler load operation aggravates the problems of
condensation and sticky ash, especially in ash hoppers,
which are marginally sized and have no heaters. In
addition, boiler tubes leak frequently.
7-2
-------
6. Possibly serious gas sneakage under the plates through
the top of the hopper has resulted in untreated gas and
or reentrainment of ash that has build up in the hop-
per. The plant reports that although ash buildup
occurs often, there is little problem with T-R sets
being shorted out by the ash. This suggests the pos-
sibility that gas sneakage carries dust across the top
of the hoppers and out of the precipitator, thus pre-
venting ash buildup beyond a certain level.
7. Possible electrode misalignment, loose wires, or other
factors prevent operation at optimum electrical condi-
tions. During the plant visit about five T-R sets (25%
of total) were operating far below normal capability.
8. A recent preliminary test with ammonia indicated a
performance that was typical of the expectations with-
out an additive. It is possible that many nozzles are
plugged with ash encrustations and the ammonia distri-
bution is poor enough to negate its usefulness in
retention of collected ash.
Some pertinent recommendations to improve performance,
suggested by a well-known ESP consultant, are as follows:
1. A major reduction in the amount of dust reentrained is
needed. This involves many aspects:
a. Proper hopper baffling and baffles between fields
to eliminate gas flow under collecting plates and
dust sweepage out of hoppers. Proper gas distri-
bution should be assured. Gas must enter the ESP
horizontally with no significant upward or down-
ward vectors, particularly the latter, which can
reentrain hopper dust. Regions of excessively
high gas velocity in the ESP should be eliminated.
b. Continued use of a properly functioning ammonia
injection system with good distribution and design
to minimize ash deposition and pluggage. A high
injection velocity should be maintained through
the nozzles into the gas stream [minimum 60 m/s
(200 ft/s)]. The minimum amount of ammonia to
effect desirable agglomeration and ash retention
should be used. At- low boiler loads, less ammonia
may be needed, but caution should be taken to
ensure that plugging does not occur. If the
ammonia system is shut off, suitable air flow
through nozzles should be maintained.
7-3
-------
c. Increasing gas temperature to a minimum of 140°C
(280°F), preferably to 155° to 160°C (310° to
320°F), can be a corrective measure in lieu of
ammonia injection. The able level to aid reten-
tion. The correct level is one that will not
seriously degrade electrical conditions. High
power input aids collection and retention of dust,
but less power is required for a somewhat higher
ash resistivity than is prevalent with high-sulfur
coal and low gas temperature.
d. Boiler additives to chemically absorb excess
SO3/H2SO4 in flue gas are also a possible alterna-
tive to injection or increased gas temperature.
The advantage of such additives is some control of
ash resistivity at low gas temperature where
boiler efficiency is good. Possibilities could be
investigated.
e. The location of the ID fan suggests the possibil-
ity of downward pull of gases through the precipi-
tator if outlet vaning is not adequate. A verti-
cal profile of dust concentration in outlet or
precipitator is useful. Perhaps a 0.9 to 1.2 m (3
to 4 ft) high baffle at the outlet of the ESP
would be helpful.
2. The voltage ratings of the T-R sets and saturable
reactor type control should be improved to provide a
better match to the requirements of the precipitator
load. The electrical control circuits can be modified
to improve stability and response and to provide addi-
tional corona power capability. It is recommended that
linear reactors be added in the primary circuit in
series with the present saturable reactors.
For conditions at this plant, electrical sets should be
operated with very little or no sparking. It is par-
ticularly important in the outlet sections to operate
at just under the sparking threshold.
3. Rapping effectiveness and optimum conditions (duration,
frequency, and force) should be investigated. A pro-
gram to accomplish this is now underway. Determining
the extent of dust being reentrained is the first step.
With regard to rapping frequency and force, fairly
frequent, light blows are probably best. With vibra-
tors installed at this plant, the operating duration
must be reduced to the minimum possible. Outlet sec-
tion rapping can also be very critical; usually only
the minimum amount of rapping needed to maintain elec-
trical conditions used.
7-4
-------
4. The best possible effort should be made to control
condensation and sticky ash.
7-2 ELECTROSTATIC PRECIPITATOR TO CONTROL PARTICULATE EMISSIONS
FROM CEMENT KILNS
This case history covers the use of an ESP on a cement kiln
in a plant located in the Eastern United States. The information
was obtained during a site visit and from discussions with engi-
neering personnel.
"7.2.1 System Description
The plant has two cement kilns, which consume over 500
metric tons of coal per day. The ESP, which controls particulate
emissions from both kilns, was manufactured by Western Precipita-
tion and installed in 1962. It is designed to handle 172 m^/s
(430,000 cfm) at approximately 260°C (500°F) and, according to
plant personnel, operated within + 15 percent of design rate.
Gas flow is split into an upper and a lower precipitator.
Both have four active fields and an empty one. The first three
upper and lower fields are each energized by one T-R set, whereas
the outlet fields on the upper and lower precipitators are each
energized by a separate T-R set. Thus, the entire system con-
tains a total of five T-R sets.
Approximately 70 percent of the collected dust is recycled
to the kilns, and the remainder is sluiced to a spray pond.
Sluice water is recycled.
^*2*2 Operating History
Many modifications have been made to the precipitator since
1972 to meet state particulate emission regulations. The modifi-
cations have eliminated most maintenance problems, and the col-
lection efficiency is reported to be as high as 99.5 percent with
outlet loadings as low as 16 kg/h (36 lb/h). Following is a
brief discussion of the total maintenance problems that have
Plagued this installation and the efforts that have been made to
alleviate these problems:
7-5
-------
A 19 72 inspection revealed that the discharge and
collection electrode alignment were not correct at the
bottom of the frame because of expansion and contrac-
tion of the frame and hoppers, and weak guide supports;
warpage and buckling of some plates were also noted.
Correction of the frame misalignment has markedly
improved collection efficiency.
Air inleakage into screw conveyors continued to cause
reentrainment of dust and corrosion of metal on the
screw conveyors. Holes are patched as they occur, and
a new design of screw conveyor with better slide gate
seals is gradually being substituted. Because ex-
pansion joints at the inlet and outlet of the precipi-
tator initially were not insulaed, the metal rotted out
and caused air in-leakage. Proper insulation solved
this problem.
Because insulator compartments on top of the ESP are
not insulated, pressurized, or heated, moisture con-
densation has caused severe corrosion in a number of
the compartments and occasional failure of an insula-
tor. The company has designed a new insulator compart-
ment, which is insulated and may be pressurized with
heated air. Present insulator compartments are gradu-
ally being replaced.
Shafts of vibrators on discharge wires have failed
repeatedly. Two men are engaged full time in welding
crecked vibrator shafts. A new Syntrom vibrator used
on some sections of the ESP has been successful, re-
quiring almost no maintenance.
Difficulties caused by control panel overheating were
compounded by numerous failures of fans used to cool
the control compartments. This was solved by moving
the saturable reactors to a better ventilated room
behind the control compartment.
Excessive sparking in the inlet fields of the ESP has
caused failure of a large number of wires because of
arcing. The company is considering replacing the
saturable reactors on these sections with silicon
controlled rectifier/linear reactor combinations in an
attempt to improve current limit control and current
wave form to reduce sparking.
Gas distribution has always been a problem with this
ESP because the gas flow is split into an upper and
lower ESP. The addition of a damper in the common
«*
7-6
-------
ductwork on top of the ID fan has improved the balance
of flow; turning vanes would probably improve gas
distribution even further, but the company believes
they are too expensive.
8. The rapping system was improved by installing stronger
supports for the discharge electrode vibrators on the
top level and on bent collecting electrode supports.
The rapping duration and intensity were then readjusted
until satisfactory results were obtained.
7.2.3 Maintenance Procedures
A regular maintenance schedule is followed, and malfunctions
are recorded. The state environmental control agency is notified
when serious problems arise.
7.2.4 Conclusion
Plant personnel have shown great initiative in making the
modifications needed to improve the performance of the precipita-
tor and bring the kiln emissions into compliance with state
particulate emission regulations. By following a regular mainte-
nance schedule and continuing to improve the quality of the
precipitator components/ plant personnel are confident that the
present high level of performance can be maintained indefinitely.
7-7
-------
REFERENCES FOR SECTION 7
1. Oglesby, Sabert Jr. A Manual of Electrostatic Precipitator
Technology. Southern Research Institute, Birmingham,
Alabama. August 1970.
2. White, H.J. Electrostatic Precipitation of Fly Ash. JAPCA.
March 1977.
3. Devitt, T.W., R.W. Gerstle, and N.J. Kulujian. Field Sur-
veillance and Enforcement Guide: Combustion and Incinera-
tion Sources. APTD-1449. June 1973.
7-8
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APPENDIX A
STARTUP AND SHUTDOWN PROCEDURES AND
MAINTENANCE SCHEDULE FOR
ELECTROSTATIC PRECIPITATORS (ESP's)
A-l
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PRECIPITATOR STARTUP AND SHUTDOWN PROCEDURES
Operation of an electrostatic precipitator (ESP) involves
dangerously high voltage. Although all practical safety measures
are incorporated into the equipment, extreme caution should be
exercised at all times. An ESP is, in effect, a large capacitor
that when deenergized can retain dangerous electrical charges.
Grounding mechanisms provided at each access point should there-
fore be used before entering the precipitator.
Preoperational Checklist - Before placing the equipment in oper-
ation, plant personnel should perform a thorough check and visu-
ally inspect the system components in accordance with the manu-
facturer's recommendations. Some of the major items that should
be checked are summarized below:
Control Unit
Proper connections to control
Silicon Rectifier Unit
Rectifier-transformer insulating liquid level
Rectifier ground switch operation
Rectifier high-voltage connections made
High-voltage bus transfer switch operation
High-Tension Connections
High-tension bus duct
Proper installation
Vent ports properly installed
Equipment Grounding
Precipitator grounded
Transformer grounded
Rectifier controls grounded
High-tension guard grounded
Conduits grounded
Rapper and vibrator ground jumpers in place
Air Load Tests - After the precipitator is inspected (i.e.,
preoperational check adjustment of the rectifier control and
check of safety features), the air load test is performed. Air
A-2
-------
load is defined as energization of the precipitator with minimum
flow of air (stack draft) through the precipitator. Before
introduction of an air load or gas load (i.e., entrance of dust-
laden gas into the precipitator), the following components should
be energized:
Collecting plate rappers
Perforated distribution plate rappers
High-tension discharge electrode vibrators
Bushing heaters - housing/compartments
Hopper heaters - vibrators - level indicators
Transformer rectifier
Rectifier control units
Ventilation and forced-draft fans
Ash conveying system
The purpose of the air load test is to establish reference
readings for future operations, to check operation of electrical
equipment, and to detect any improper wire clearances or grounds
not detected during preparation inspection. Air load data are
taken with the internal metal surfaces clean. The data consist
of current-voltage characteristics at intervals of roughly 10
percent of the T-R milliamp rating, gas flow rate, gas tempera-
ture, and relative humidity.
For an air load test, the precipitator is energized on
manual control. The electrical characteristics of a precipitator
are such that no sparking should occur. If sparking does occur,
an internal inspection must be made to determine the cause.
Usually, the cause is (1) close electrical clearances and/or (2)
the presence of foreign matter, such as baling wire, that has
been left inside the precipitator.
After the precipitator has been in operation for some time,
it may be necessary to shut it down to perform internal inspec-
tions. At such times, it would be of interest to take air load
data for comparison with the original readings.
Gas Load Tests - The operation of a precipitator on gas load
differs considerably from operation on air load with respect to
voltage and current relationships. The condition of high current
and low voltage characteristizes the air load, whereas low cur-
A-3
-------
rent and high voltage characterize the gas load. This effect
governs the operation of the precipitator and the final setting
of the electrical equipment.
MAINTENANCE SCHEDULE FOR ESP's
Daily
An accurate log should be kept on all aspects of precipi-
tator operation including electrical data, changes in rapper and
vibrator operation, fuel quality, and process operations.' Such a
log can provide clues to the probably cause of any change in
performance.
For example, it is obvious that gross departures from
normal readings on the T-R meter and transmissometer indicate
trouble. It is not so widely recognized that small variations,
often too slight to be noticed without checking daily readings,
can indicate impending trouble."''
Problems that usually affect precipitator performance
gradually, rather than suddenly, include (1) air inleakage at
heaters or in ducts leading to the precipitator, (2) dust buildup
on precipitator internals, and (3) deterioration of electronic
control components. Such problems are often indicated by slight
but definite drift of daily meter readings away from baseline
values. "*¦
Grossly abnormal readings, usually indicating a serious
problem, also may aid in diagnosing the probable cause. For
example, sudden tripout of an apparently normal electrical set
probably indicates a short or ground in the secondary circuitry.
A low but steady Voltage reading indicates a high-resistance
ground, such as that from discharge wires, which may be caused to
ground by accumulation of ash above a plugged hopper or formation
of clinker on a wire."*"
Fluctuating voltage that dips to low values suggests a
broken and swinging discharge electrode. Fluctuation of spark-
A-4
-------
rate meter readings does not necessarily indicate a problem
unless voltage or current readings fluctuate also.1
An operator should never try to correct deviant meter
readings by adjusting control set points. An automatic-control
response range should accommodate normal variations in load.
When major changes occur, such as would result from firing a coal
substantially different from that for which the precipitator was
designed, the precipitator manufacturer should be called in to
retune the installation.1 If no such major changes have occurred,
then variant meter readings indicate problems that must be
detected and corrected. Figure A-l exemplifies a log of electri-
cal readings that are checked several times each day at a coal-
fired utility. These readings are used in troubleshooting
problems with ESP operation.
Probably 50 percent of all electrical set tripouts are
caused by ash buildup. Short of set tripout, buildup above the
top of hoppers can cause excessive sparking that erodes discharge
electrodes.^ Further, the forces created by growing ash piles
can push internal components out of position, causing misalign-
ment that may drastically affect performance. Sometimes utility
operators attempt to preserve alignment by welding braces to hold
collecting-electrode plates in position. This practice is inad-
visable because restraining the plates reduces the effectiveness
of the rapping action that keeps them clean.1
Although various indicators and alarms can be installed to
warn of hopper-ash buildup and of ash-conveyor stoppage, the
operator can doublecheck by testing temperature at the throat of
the hopper with the back of the hand. If the temperature of one
or more hoppers seems comparatively low, the hopper heaters may
not be functioning properly.1 Generally, however, low tempera-
ture indicates that hot ash is not flowing through the hopper and
that bridging, plugging, or failure of an automatic dump valve
has held ash in the hopper long enough for it to cool. The ash
subsequently will pile up at the top.1
A-5
-------
PRECIPITATOR LOG SHEET
UNITS 1 • 2
NO
1 PRCClPlTATOR
12 MfO
3AM
(AM
9AM
12 NOON
3PM
6PM
9PM
PPTn CABlC 1 K V
AVG SPAR'- RATf
*
PCtR CABl E 2 "V
u>
l/l
TRANS PWi VOLTS V
PPTB AVG CURRENT MA
TRAnS PRi CURRENT
PPTR C*8wC 1 *V
AVC SPARK fMT£
PPTB CABcE 2 KV
w
TRANS PRt VOLTS V
pptr avc current mil
trans PRi CURRENT
PPTR CAB^C 1 KV
AVG SPARK RATI.
rg
PPTR CABLE 2 KV
a
TRANS PRi VOLTS V
PPTR AVC CURRENT MA
tran* PR* current
PPTR CABvE 1 KV
AVG &PARK RATE
PPTR CABL.E 2 KV
u
4/1
TRANS PR" VOLTS V
PPTR AVG CURRCNT MA
trans PR' CURRENT
NO
2 precipitator
PPTB CABuC 1 KV
AVG SPAR' RATE
PPTR CABwE 2 KV
&
TRANS PRi VOLTS V
PPTR AVG CURRENT MA
trans PR' Current
pptr CAB.E \ KV
AvG SPARk Rate
PPTB CABwE 2"V
S
TRANS PR* VOLT S V
PPTR AVG CURRENT ma
trans pr> current
PPTR CA§lE 1 KV
AVG 5PAR' RATE
WD
RRTR CABlC 2 *v
w
TRAN5 P*1 VOL7 S V
PPTB AVG CURRENT MA
TRANS PR' CURRENT
PPTR CABvE \ *V
AvG SPARK RATE
PPTR CABLE 2 KV
TRav, PR' V^L T b V
PPTR AVG CuRBCN7 MA
TRANS PR' CURRCn'
R£MARr «,
ORCRATORS i?-a >.l *-t?
OAT£ p*Y
Figure A-l. Precipitator log sheet.
A-6
-------
If the temperatures of all hoppers seem low to the touch,
the ash-conveyor system should be checked; the system may have
stopped or dust agglomeration may be so great that the conveyor
can no longer handle all of the fly ash.
Hopper plugging is sometimes caused by low flue gas temper-
ature, which permits moisture condensation.-^ Temperature of gas
at the boiler exit may be too low, or ambient air may be leaking
into the flue gas duct. Hoppers are particularly prone to plug-
ging during startup after an outage, when they are cold and
usually damp.
Daily checking of the control room ventilation system
minimizes the possibility of overheated control components, which
can cause the control set points to drift and can accelerate
deterioration of sensitive solid-state devices.
Weekly
Solenoid-coil failures, fairly common when high voltage was
used, are rare with modern low-voltage equipment.1 Still, a
weekly check of all units is advisable. Rapper action should be
observed visually, and vibrator operation confirmed by touch. If
inadequate rapping force is suspected, an accelerometer mounted
on the plates should be used to verify that rapping acceleration
is adequate (often, up to 30 g is required). This is best done
on a pretest check.
Control sets must be checked internally for deposits of dirt
that may have penetrated the filter. Accumulation of dirt can
cause false control signals and can damage such large components
as contactors and printed circuits.
Finally, filters in the lines supplying air to control
cabinets and to the precipitator top housing should be checked
and cleaned if necessary to prevent plugging.1
Monthly
Most new precipitators incorporate pressurized top housings
that enclose the bushings through which high-voltage connections
A-7
-------
are made to the discharge electrodes within the precipitator box.
Pressurization ensures that if gas leakage occurs where the
bushings penetrate the precipitator hot roof, gas will flow into
the precipitator rather than out from it. Leakage from the
precipitator into the housing could cause ash deposits or mois-
ture condensation on the bushings, with risk of electrical break-
down at the typical operating potential of 45 kv d.c.1
Monthly maintenance also should include inspection of
bushings visually and by touch for component vibration, checks of
differential pressure to ensure good operation of the fan that
pressurizes the housing, and manual operation of the automatic
standby fan to make sure it is service-ready.
Quarterly
Quarterly maintenance includes inspection of electrical-
distribution contact surfaces. These should be cleaned and
dressed and the pivots should be lubricated quarterly if not more
frequently,1 since faulty contacts could cause false signals.
Further, because transmissometer calibration is subject to drift,
calibration should be verified to prevent false indications of
precipitator performance.
Semiannually
Inspection, cleaning, and lubrication of hinges and test
connections should be done semiannually. If this task is ne-
glected, extensive effort eventually will be required to free
test connections and access doors, often involving expensive
downtime. Performance tests may be required at any time; they
should not be delayed while connections are made usable. An
effective preventive measure is to recess fittings below the
insulation.
Inspection of the exterior for corrosion, loose insulation,
surface damage, and loose joints can identify problems while
repair is still possible. Special attention should be given to
points at which gas can leak out as fugitive emissions.1
A-8
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Annually
Scheduled outages must be long enough to allow thorough
internal inspection of the precipitator. Following is a summary
of items to be checked during an annual inspection, abstracted
primarily from Reference 2.
1. Dust Accumulation - The upper outside corners of a
hopper usually show the greatest accumulation. A spotlight can
be used to check for dust buildup, eliminating the need to enter
the hopper.
2. Corrosion - Inaccessible parts of the ESP are often
attacked by corrosion. Access doors and frames, which are diffi-
cult to insulate, are usually attacked first. Condensation can
occur in penthouses that contain support insulators; the pent-
houses are at lower temperature than the gas, and moisture is
added also by purge air from the outside.
Corrosion can occur at several places in the ESP housing:
the underside of roof plates, the outside wall, the space between
outside collecting surface plates and sidewall, the back of
external stiffening members that act as heat sinks, and any area
not continuously subject to gas flow, such as corners and the
upper portion of the hopper connection to inlet and outlet ducts.
All gas connections should be checked for inleakage of oil, gas,
or air.
Corrosion in these areas can be minimized by keeping interi-
or surfaces hot and by effective thermal insulation of outside
surfaces, use of heaters during routine shut downs or operation
at low loads also may help prevent corrosion.
3. Rappers - Maintenance of the magnetic-impulse, gravity-
impact rapper has been discussed. Many rigid-wire ESP's, how-
ever, have mechanical rappers. The drives for collecting and
discharge electrode rappers should be checked for high motor
temperature, unusual noise, and level and condition of the
lubricant.
A-9
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Mechanical rappers should be checked for excessive wear,
shifting of point of impact, free movement of wire-frame rapper
release, free movement of hammers, and wear on hammer shaft
bushings.
4. Hoppers - On both wire-weight and rigid-wire precipi-
tators, the hopper discharge should be checked for such objects
as broken pieces of rappers, wires, shotcrete, and scale. Pres-
ence of foreign objects indicates a problem that should be
investigated further.
5. Gas Distribution Plates - Although perforated plates
usually do not become plugged, uneven distribution of uneven low
gas load can sometimes cause plugging of a portion of the plates.
If a rapping system is not used, manual cleaning is required.
6. Discharge Electrodes - Frames in rigid-frame, dis-
charge-electrode-type precipitators should be centered between
two rows of collecting surface plates with a maximum deviation of
+ 0.6 cm (+ 0.15 in.). Discharge wires must be straight and
securely connected to the discharge frame.
Wire-weight precipitators should be checked for missing or
dropped weights. Common causes of wire failure and remedial
action are discussed in the following section on malfunctions.
Removal of a broken wire that is not replaced should be recorded
on a permanent log sheet.3 Discharge wires should be cleaned
manually as required.
7. Collecting Electrodes - Collection plates should be
inspected for warping due to excessive heat. Corrosion of lower
portions of the plates and portions of plates adjacent to door
¦a
openings indicates air inleakage through hoppers or around doors.
Plates should be cleaned manually as required.
8. Suspension Insulators - When insulators become heavily
coated with moisture and dust, they may become conductive and
crack under high-voltage stress. Cracks can be spotted with a
bright light during inspection. Faulty insulators can cause
excessive sparking and voltage loss and can fail abruptly or even
explode if allowed to deteriorate.
A-10
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Housing - Thick dust deposits on interiors of housings
indicate high gas velocities resulting from excessive gas vol-
umes, a condition that should be corrected.
If the precipitator is located between the air heater and
the boiler, expansion joints must be checked and slide plates
lubricated. Finally, if necessary, all collection plates and
electrode wires should be cleaned manually.1
Situational Maintenance
Certain preventive maintenance and safety checks are so
important that they should be performed during any outage of
sufficient length, without waiting for scheduled downtime. Air
load readings should be compared with baseline values to detect
possible deterioration in performance. Readings taken immedi-
ately upon restoring the precipitator to service can serve as a
check on any changes resulting from maintenance done during the
outage.
Critical internal alignments should be checked whenever dn
outage allows; any misalignment warrants immediate corrective
action. Interiors of control cabinets and top housing should be
checked during any outage of 24 hours or more and cleaned if
necessary. Any outage of more than 72 hours provides an oppor-
tunity to check grounding devices, alarms, interlocks, and other
safety equipment and to clean and inspect insulators and bushing
Safety
Because high-voltage electricity can be extremely dangerous
all practical safety measures must be observed even though the
system incorporates interlocks and other safety devices.4
The system should never be adjusted with the high-voltage
power on.
Rectifiers and diodes have heat sinks that could seriously
shock a person touching them.
The rapper circuitry, which is independent of the high-
voltage circuitry, is nonetheless also dangerous and must be so
treated.
A-ll
-------
Spark-rate feedback signals are often taken from the primary
of the high voltage supply and can be 400 V a.c. or more. Fuses
on these lines should be removed before maintenance or adjustment
is attempted.
Explosive gas mixtures could be created if air is introduced
into the systems. If necessary, a system should be purged with
an inert gas before air is introduced. A system should always be
purged with fresh air before it is entered.
A-12
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REFERENCES - APPENDIX A
1. Bibbo, P.P., and M.M. Peacos. Defining Preventive Mainten-
ance Tasks for Electrostatic Precipitators, Research
Cottrell, Inc. Power. August 1975, pp. 56-58.
2. Engelbrecht, H.L. Plant Engineer's Guide to Elec-
trostatic Precipitator Inspection and Maintenance, Air
Pollution Division of Wheelabrator Frye, Inc., Plant
Engineering. April 1976, pp. 193-196.
3. Szabo, M.F., and R.W. Gerstle. Operation and Maintenance of
Particulate Control Devices on Coal-Fired Utility Boilers.
PEDCo Environmental, Inc., Cincinnati, Ohio. EPA-600/2-77-129.
July 1977.
4. Hesketh, H.E., and F.L. Cross, Jr. (ed.) Handbook for the
Operation and Maintenance of Air Pollution Control Equip-
ment. Technomic Publishing. Westport, Connecticut. 1975.
A-13
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APPENDIX B
TYPES OF ELECTROSTATIC
PRECIPITATOR MALFUNCTIONS
B-l
-------
TYPES OF ELECTROSTATIC PRECIPITATOR MALFUNCTIONS
Discharge Wire Breakage
Probably the most common problem associated with suspended
wire electrode ESPs is wire breakage, which typically causes an
electrical short circuit between the high-tension discharge wire
system and the grounded collection plate. The electrical short
trips the circuit breaker and disables a section of the ESP,
which remains disabled until the broken discharge wire is removed
from the unit.
Following are the principal causes of discharge wire breakage:
1) Inadequate rapping of the discharge wire causes an arc,
which can embrittle the wire and eventually break it
completely.
2) Clinkered or improperly centered wires cause a contin-
ual spark from the wire to the bracing.
3) A clinker or wire bridges the collection plates and
shorts out the wire.
4) Ash buildup under the wire causes it to sag and short
out.
5) Improper clearance of "J" hooks to the wire causes it
to short out.
6) Hangup of a bottle weight during cooling causes a wire
to buckle.
7) Fly ash buildup on a bottle weight forms a clinker or
burns off the wire.
8) Corrosion caused by condensation around cooler areas of
the wire.
9) Excessive localized sparking causes erosion of the
wire.
Electrical erosion, the predominant cause of failures,
occurs when repeated electrical sparkovers or arcs occur in a
localized region. Heating and vaporization of a minute quantity
of metal occur with each spark. Sparkover at random locations
will cause no serious degradation of the discharge electrode.
B-2
-------
Repeated sparkover at the same location, however, can remove
significant quantities of material, with subsequent reduction of
cross-sectional area and ultimate failure at that point.
Localized sparking can be caused by misalignment of the
discharge electrodes during construction or by variations in the
electric field resulting from "edge" effects of adjacent dis-
charge and collection electrodes at the top and the bottom of the
plates. Measures that will eliminate failure at these points are
adding shrouds, such as those shown in Figure B-l, and providing
a rounded surface at the edge of the collection electrode to
reduce the tendency for sparking.1
Electrical erosion can also be caused by "swinging" of
electrodes, which can occur when the mechanical resonance fre-
quency of the discharge wire and weight system is harmonically
related to the electrical frequency of the power supply. The
power supply adds energy to the swinging wire, and sparking
occurs with each close approach to the collection plate. This
action leads to erosion of the electrode and mechanical failure.1
Poor workmanship during construction can also cause electri-
cal failure of the discharge electrode. If pieces of the welding
electrode remain attached to the collection plate, localized
deformation of the electric field can lead to sparking and fail-
ure of the discharge electrode.
Mechanical fatigue occurs at points where wires are twisted
together and mechanical motion occurs continually at one loca-
tion. This occurs at the top of a discharge electrode where the
wire is twisted around the support collar. Methods of reducing
mechanical fatigue include selection of discharge electrode
material that is resistant to cold work annealing after attach-
ment.
Chemical attack is caused by "a corrosive material in the
flue gas, which can occur when high-sulfur coal is burned and
flue gas exit temperatures are low and near the acid dew point.
Use of ambient air to purge insulator compartments also can cause
B-3
-------
Figure B-l. Shrouds for wire-weighted discharge electrodes.'
B-4
-------
the temperature to drop below the acid dew point in a localized
region. Corrosion can be minimized by operation at higher flue
gas temperatures or by use of hot, dry air to purge insulator
compartments. Use of good insulation on the ESP shell to main-
tain high temperature also provides adequate protection within
the usual range of operating temperatures and fuel sulfur con-
tents .
The other causes of discharge wire failure, such as in-
adequate rapping, could be minimized by routine checking of
vibrators and rappers. Inspection helps to prevent wire failures
and tripouts when potential problems are detected before they
become serious. Because an ESP contains many wires, however,
some discharge wire failures are to be expected, even with good
design and preventive maintenance.
Collection Hoppers and Ash Removal
Hoppers and ash removal systems often constitute problems in
precipitator operation. If the hoppers become full, the col-
lected dust may short-circuit the precipitator. Electrical power
may fuse the dust, causing formation of a large, clinkerlike
structure called a "hornet's nest," which must be removed. Most
problems associated with hoppers are related to flow of the dust.
Flow may be inhibited by improper adjustment of the hopper vi-
brators or failure to empty the hoppers. Heat and/or thermal
insulation of the hoppers may be required to prevent condensation
of moisture and resultant cementing of the collected dust.
Malfunctions of the ash evacuation and removal system
include water pump failure, water-jet nozzle failure, disengage-
ment of vacuum connections, and failure of sequencing controls.
The best measure for preventing malfunction of an ash
removal system, aside from proper design, is a good program of
operation and maintenance. Since dust buildup can affect so many
of the ESP components, proper ash removal will minimize or
eliminate many of the most common ESP malfunctions.
B-5
-------
Gas flow problems occur as a result of the inleakage of air
into hoppers from the dust conveyor systems. This results in
reentrainment of collected dust into the ESP, as discussed ear-
lier. Air inleakage can also occur through the ESP shell or
inlet flanges if operation is at pressures lower than atmospheric.
Often enough air is bled in to cause intense sparking.
The term "gas sneakage" describes gas flow that bypasses the
effective ESP section. Sneakage can occur through dead passages
of the ESP above the collector plates, around the high-tension
dust concentration at the bottom of the outlet section of the
frame, or through the hoppers. It will reduce ESP efficiency by
only a few percent unless it is unusually severe. Gas sneakage
can be identified by measuring gas flows in suspected areas in a
nonoperating or cold test. Corrective measures usually involve
baffling to direct gas into the active ESP action.
Reentrainment of dust from hoppers caused by air inleakage
or gas sneakage is often indicated by an increase in dust concen-
tration at the bottom of the outlet section of the ESP. Correc-
tive measures for air leakage would include proper design and fit
of components and sealing of areas where inleakage occurs.
Rappers or Vibrators
In dry removal systems, rapping of the collection electrode
to remove dust is normally done periodically. Effective rapping
can occur only when the accumulation of material on the plate is
thick enough that it falls in large agglomerates into the hopper.
Although there is always some reentrainment of dust, effective
rapping must minimize it. As discussed earlier, rapping forces
that are either too mild or too severe can cause poor perform-
ance.
Poor gas flow and the condition of the dust can also cause
formation of deposits on discharge electrodes, often as much as 5
cm (2 in.) thick. Their deposits are generally composed of the
finer dust particles and often cling tenaciously to the discharge
wire. Deposits on the discharge wire do not necessarily lead to
-------
poor performance, but efficiency may be reduced, depending on
resistivity, power supply range, and uniformity of the deposit.
Design of the support structure and of the electrodes can
also cause inadequate rapping. Recent investigations of rapping
acceleration in fly-ash ESP's have shown measured accelerations
2
of 5 g when as much as 30 g may be required. The first step in
dealing with problems related to rappers and vibrators is to
determine the adequacy of the rapping acceleration with an
accelerometer mounted on the plates. A common method of adjusting
rappers is with the use of an optical dust-measuring instrument
in the exit gas stream of the ESP.
Discharge electrodes should be kept as clean as possible.
Rapping intensity is limited only by the possibility of mechani-
cal damage to the electrodes and support structure.
The vibratory types of cleaning mechanisms usually require
more maintenance than the impulse types.
Insulator/Bushing Failure
Suspension insulators support and isolate the high-voltage
parts of an ESP. As mentioned earlier, inadequate pressurization
of the top housing of the insulators can cause ash deposits or
moisture condensation on the bushings, which may cause electrical
breakdown at the typical operating potential of 45 kv d.c.
Corrective or preventive measures include inspection of fans
that ventilate the top housing and availability of a spare fan
for emergencies. Frequent cleaning and checking for damage of
the fans by vibration is also necessary to ensure trouble-free
operation.
Inadequate Electrical Energization
Since an ESP operates on the basis of electric field and
electric charge, electrical energization must be adequate to
charge the particles, maintain the electric field, and hold the
collected dust to the collection plates.
B-7
-------
Among several possible causes of failure to achieve the
required level of power input to the ESP, the following are most
1
common:
° High dust resistivity
° Excessive dust accumulation on the electrodes
° Unusually fine particle size
0 Inadequate sectionalization
° Improper rectifier and control operation
° Misalignment of electrodes
0 Inadequate power supply range
If a precipitator is operating at a spark-rate-limited
condition but current and voltage are low, the problem can
commonly be traced to high-resistivity dust, electrode misalign
ment, or uneven corona resulting from buildup on the discharge
electrode.
The effects of high resistivity were discussed in more
detail in Section 2, in terms of conditions specific to utility
industry, where resistivity presents the greatest problem.
Because of the importance of resistivity in the precipita-
tion process, a first step in troubleshooting should be in situ
resistivity measurements. High resistivity (more than 1010 ohm-
cm) may be causing the abnormally low currents. If resistivity
is not high, other potential causes should be investigated.
Failures in ESP controls can prevent the system from achiev-
ing the level of power required for normal operation. Following
are the most common malfunctions in controls:
1) Power failure in the primary system
2) Transformer or rectifier failure in secondary system
caused by:
a. insulation breakdown in transformer
b. arcing in transformer between high-voltage switch
contacts
c. leaks or shorts in high-voltage structure
d. contamination of the insulating field
The most effective measure for correction of control fail-
ures is a good maintenance program in which the controls are
checked periodically for proper operation. A daily log of
B-8
/
-------
instruments that register current, voltage, and spark rate can
also indicate potential problems.
SURVEYS OF PRECIPITATOR MALFUNCTIONS
Two surveys are cited to support the preceding information
on precipitators, one by the Industrial Gas Cleaning Institute
(IGCI)^ and the other by the TC-1 Committee of the Air Pollution
Control Association (APCA).4 Both surveys give similar results.
The IGCI survey lists the following problems, in order of
frequency and severity:
0 Discharge electrode failure
0 Rapper malfunction
0 Insulator failure
0 Dust buildup (causing electrical shorts)
0 Hopper plugging
° Transformer rectifier malfunctions
The APCA survey covers four major industries: electrical
utilities, cement, paper, and metallurgical. The equipment
reported on had been in service ranging from 3 months to 50
years, with an average service life of 7 to 10 years.
Responses from 174 users indicate the following problem
areas in order of importance and cost:
Discharge electrodes 30.5%
Dust removal systems 25.1
Rappers or vibrators 21.4
Collecting plates 14.8
Insulators 5.8
The TC-1 Committee notes that manufacturers are making
design improvements in discharge electrodes, the largest source
of problems. They also cite the importance of the design, opera-
tion, and maintenance of dust removal systems, noting the indus-
try that reported the highest incidence degree of hopper plugging.
The committee concludes that although problems do occur with
precipitator equipment, most users are satisfied with the ESP as
a functioning unit. They suggest close cooperation between user
and supplier, coupled with exchange of information among the user
industries to facilitate development of an ESP that meets the
needs of all users.
B-9
-------
REFERENCES - APPENDIX B
1. Electrostatic Precipitator Manual. The Mcllvaine Co. 1976.
2. Hesketh, H.E., and F.L. Cross, Jr. (ed.) Handbook for the
Operation and Maintenance of Air Pollution Control Equip-
ment. Technomic Publishing Co. Westport, Connecticut.
1975.
3. Engelbrecht, H.L. Plant Engineer's Guide to Electrostatic
Precipitator Inspection and Maintenance. Plant Engineering.
April 1976, pp. 193-196.
4. Bump, Robert L. Electrostatic Precipitator Maintenance
Survey. TC-1 Committee of the Air Pollution Control
Association. 1974.
B-10
i
-------
APPENDIX C
CHECKLISTS FOR INSPECTION OF ESP'S
C-l
-------
TABLE C-l. PREIKSPECTION. CHECKLIST FOR
FLY ASH ELECTROSTATIC PRECIPITATORS
A. FACILITY IDENTIFICATION
Facility Name:
Facility Address:
Person to Contact:
Date Information Gathered:
Source Code No. : ___
B. DATE INFORMATION GATHERED:
C. SITE DATA
1. UTM Coordinates:
2. Elevation Above Mean Sea Level, ft:
3. Soil Data - Bearing Value:
Piling Necessary:
4. Attach Drawings:
a) Plot Plan
b) Equipment Layout and Elevation
c) Aerial Photographs of site Including Power Plant,
Coal Storage and Ash Disposal Area
(continued)
-------
TABLE C-l. (continued) .
D. BOILER DATA
X- Service: Base Load
Standby, Floating, Peak
2. Total Hours Operation (19 )
3. Average Capacity Factor (19 )
4. Served by Stack No.
5. Boiler Manufacturer
6. Year Boiler Placed in Service
7. Estimated Remaining Life of Unit
8. Rated Generating Capacity, MW
Coal
Oil
Gas
9. Design Fuel Consumption:
Coal, 106 tons/yr
Oil, 106 gal/yr
Gas, 10^ ft"Vyr
Notes:
(continued)
-------
TABLE C-l. (continued).
10. Actual Fuel Consumption
n
i
E.
Boiler number
Coal, 10 tons/yr
Oil, 10^ gal/yr
Gas, 106 ft3/yr
11. Wet or Dry Bottom
12. Excess Air, %
13. Fly Ash Reinjection (Yes or No)
14. Stack Ht Above Grade, ft
15. I.D. of Stack at Top, in.
COAL DATA
1. Coal Seam, Mine, Location
a .
b.
c.
d.
Notes:
(continued)
-------
TABLE C-l. (continued).
2. Quantity Used by Seam and or Mine
a. _
b .
c -
d.
3. Analysis
GHV, Btu/lb
S, %
Ash, %
Moisture, %
F. FUEL OIL DATA
1• Type
2. S Content, %
3. Ash Content, %
4. Specific Gravity
5. GHV, Btu/gal
Notes:
(continued)
-------
TABLE C-l. (continued).
G. FLUE GAS CLEANING EQUIPMENT
1. Mechanical Collectors
Manufacturer
Type
Efficiency: Design Actual,
Mass Emission Rate:
gr/acf
? lb/h
-------
TABLE C-l. (continued).
2. Electrostatic Precipitator
(continued)
Mass Emission Rate
gr/acf
lb/h
lb/106 Btu
No. of Fields
No. of T-R Sets
i No. of Independent Bus Section
Total Plate Area, ft^
Flue Gas Temperature
@ Inlet ESP @ 100% Load, °F
H. I.D. FAN DATA
1. Maximum Static Head, in
2. Working Static Head, in H20
3. Design Flue Gas Rate, acfm
@ 100% Load
@ 75% Load
§ 50% Load
Notes:
(continued)
-------
TABLE C-l. (continued).
4. Design Stack Gas Exit
Temperaturef °F
@ 100% Load
@ 75% Load
@ 50% Load
5. Exit Gas Stack Velocity, ft/s
@ 100% Load
@ 75% Load
@ 50% Load
6. Exhaust Duct Dimensions @
Stack, ft
7. Elevation of Tie-in Point to
Stack, ft
I ASH DISPOSAL
1. Fly Ash: Total Collected,
tons/yr
Disposal Method
Disposal Cost, $/ton
Notes:
(continued)
Boiler number
-------
TABLE C-l. (continued) .
2. Bottom Ash: Total Collected,
tons/yr
Disposal Method
Disposal Cost, $/ton
J. SCHEDULED MAINTENANCE SHUTDOWN-MAJOR
(ATTACH PROJECTED SCHEDULE)
Notes:
-------
PREINSPECTION DATA SHEET - ATTACHMENT 1
BLOCK DIAGRAM OF FACILITY
-------
PREINSPECTION DATA SHEET - ATTACHMENT 2
BLOCK DIAGRAM AND POWER SUPPLY DATA FOR EXISTING ESP' S
Example:
(Include design primary amps, primary volts, secondary
milliamps, and secondary kilo-volt-amp ratings for each T-R set.)
GAS FLOW
t
0
1
4.5
ft
4.5
ft
9
ft
9
ft
<>
<>
-C>
Ol 400 MA
5 1400 MA
4 1400 MA
3 1000 MA
O
2 400 MA
"A"
42 DUCTS
10 in.
24 ft HIGH PLATES
T-R set ratings
T-R set no.
Primary
amps
Primary
volts
D.C.
kilovolts
D.C.
mil 1iamDS
A 1
75
420
55
400
A 2
75
420
55
400
A 3
238
420
50
1000
A 4
238
420
50
1400
A 5
261
420
55
1400
TOTAL 4 PPTRS AS ABOVE A, B, C, D - MANUFACTURER - W.P.
-------
TABLE C-2. INSPECTION CHECKLIST FOR ELECTROSTATIC PRECIPITATORS
A.
FACILITY IDENTIFICATION
Facility Name:
Facility Address:
Person to Contact:
Inspection Date:_
Source Code No-:
Boiler number
B. PRE-ENTRY DATA
1. Stack Plume Equivalent
Opacity, %
2. Opacity Regulation, %
3. Smoke Color (white, grey, black,
brown, reddish brown, bluish
white, yellowish brown)
(continued)
-------
TABLE C-2. (continued).
C. ELECTRICAL ENERGIZATION ARRANGEMENT AND CONTROL SET READINGS FOR ESP NO.
Location
T-R set
no.
Primary
voltage, V
Primary
current, A
ESI
voltac
>
je, V
ESP
current, A
Spark rate,
sparks/min
Present
Design
Present
Design
Present
Design
Present
Design
Present
Desigr
'
(continued)
-------
TABLE C-2. (continued).
D. ESP CONTROL ROOM*
1. Ventilation
2. Control Sets Condition
E. ESP TOP HOUSING*
1. Condition of Insulators
2. Rapper/Vibrator Operation
3. T-R Sets Condition
F. ESP EXTERIOR
1. Corrosion Problems?
2. Condition of Transition Ducts
3. Fugitive Emissions?
G. ASH HANDLING
1. Interval Between Hopper
Evacuations, h
2. Level Alarm Operation*
3. Evacuation and Removal
Procedure*
4. General Housekeeping*
* Indicate as satisfactory or unsatisfactory.
(.continued}
-------
TABLE C-2. (continued).
H. BOILER ROOM CONTROL READINGS
1. Gas Flow - Inlet to ESP, acfm
2. Flue Gas Temperature, °F
3. Pressure Readings
a. Before ESP, in. H^O
b. After ESP, in. H20
4. Excess Air, %
5. Moisture Content, %
6. Flue Gas Analysis '
co2, %
°2' %
7. Steam Flow, psi
8. Steam Temp., °F
9. Soot Blowing Schedule
10. Pressure Drop Through Air
Preheaters, in. F^O
(continued)
Boiler number
-------
TABLE C-2. (continued).
11. FD Fan Current, Amperes
Rated
Present
12. ID Fan Current, Amperes
Rated
Present
I. PLANT RECORDKEEPING*
0 1. Calibration of Instruments
1
i—*
2. ESP Control Readings
3. Boiler Control Room
4. Auxiliary Equipment Maintenance
5. Preventive Maintenance and
Inspection of ESP's
6. ESP and Process Malfunctions
* Indicate as satisfactory or unsatisfactory
(continued)
-------
TABLE C-2. (continued) .
J. COMMENTS ON THE INSPECTION
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