EPA-600/2-77-Q06
JANUARY 1977
Environmental Protection Technology Series
                          ELECTROSTATIC PRECIPITATOR
                       MALFUNCTIONS IN THE ELECTRIC
                                         UTILITY INDUSTRY

                                    Industrial Environmental Research Laboratory
                                         Office of Research and Development
                                        U.S. Environmental Protection Agency
                                   Research Triangle Park, North Carolina 27711

-------
               RESEARCH REPORTING SERIES

Research reports of the Office of Research and Development, U.S. Environmental
Protection  Agency,  have been grouped into five series. These  five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:

     1.    Environmental Health Effects Research
     2.    Environmental Protection Technology
     3.    Ecological Research
     4.    Environmental Monitoring
     5.    Socioeconomic Environmental Studies

This report has been  assigned  to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental degradation from point and non-point sources of pollution. This
work provides the new  or improved technology required for the control and
treatment of pollution sources to meet environmental quality standards.
                    EPA REVIEW NOTICE

This report has been reviewed by  the U.S.  Environmental
Protection Agency, and approved for publication.   Approval
does not signify that the contents necessarily reflect the
views and policy of the Agency, nor does mention of trade
names or commercial products constitute endorsement or
recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.

-------
                                   EPA-600/2-77-006

                                   January 1977
  ELECTROSTATIC  PRECIPITATOR

       MALFUNCTIONS IN  THE

   ELECTRIC  UTILITY  INDUSTRY
                     by

        Mike Szabo and Richard Gerstle

     PEDCo. -Environmental Specialists,  Inc.
          Atkinson Square, Suite 13
           Cincinnati, Ohio  45246
           Contract No. 68-02-2105
            ROAPNo. 21BAV-081
         Program Element No.  1AB012
   EPA Project Officer:  Dennis C. Drehmel

 Industrial Environmental Research Laboratory
   Office of Energy, Minerals, and Industry
      Research Triangle Park, NC 27711
                Prepared for

U.S. ENVIRONMENTAL PROTECTION AGENCY
      Office of Research and Development
            Washington, DC 20460

-------
                        ACKNOWLEDGEMENT





      This  report was  prepared  for  the U.S. Environmental



 Protection Agency,  Industrial  Environmental Research Labora-



 tory,  Research Triangle Park,  North Carolina, by PEDCo-



 Environmental  Specialists,  Inc., Cincinnati, Ohio.  The



 project  director was  Mr.  Richard W. Gerstle and the project



 officer  was Mr.  Norman  J. Kulujian.  Principal investigators



 were  Messrs. Norman J.  Kulujian and Lario V. Yerino.  The



 principal  authors of  the  report were Messrs. Michael F.



 Szabo  and  Richard W.  Gerstle.  Editorial review was provided



 by Ms. Anne Cassel.   Graphics  were prepared under the



 direction  of Ms.  Nancy  Wohleber.



     Dr. Dennis  Drehmel was the project officer for the U.S.



 Environmental  Protection  Agency, Industrial Environmental



 Research Laboratory,  Research  Triangle Park, North Carolina.



 The author  appreciates  the assistance and cooperation pro-



 vided by Dr. Drehmel, and the  other utilities and precipita-



 tor manufacturers, who  wish to remain anonymous but contri-



buted information to  this project.
                              11

-------
                          ABSTRACT




     A comparison of the advantages and disadvantages of hot



and cold precipitators is followed by a discussion of design



considerations that apply to hot and cold precipitators.



Common malfunctions found with precipitators operating on



coal-fired boilers in the electric utility industry and



corrective or preventive measures are summarized.  A pre-



cipitator operation and maintenance procedure for minimizing



malfunctions and downtime is presented, procedures followed



by utilities during startups and malfunctions are described,



and costs of precipitator maintenance are discussed.  Pro-



cedures for inspection of a precipitator at a utility



operating a coal-fired boiler are outlined.  Appendices



compare precipitator operation and maintenance guidelines



recommended by precipitator manufacturers versus the utility



which operates the precipitator; an operating history of



precipitators at a major utility is also presented.
                              111

-------
                     TABLE OF CONTENTS

                                                       Page

ACKNOWLEDGMENT                                         ii

ABSTRACT                                               iii

1.0  INTRODUCTION                                      1-1

2.0  TYPES OF ELECTROSTATIC PRECIPITATOR (ESP)         2-1
     SYSTEMS

     2.1  Cold-side and Hot-side ESP's                 2-1

     2.2  Design Considerations for Major ESP          2-4
          Components

3.0  MALFUNCTIONS                                      3-1

     3.1  Types of ESP Malfunctions                    3-1

     3.2  Conditions Specific to Power Plants that     3-16
          Cause Problems in Precipitators

     3.3  Reduced ESP Collection Efficiency as         3-24
          Related to Number of Bus Sections Not
          in Operation

     3.4  Maintainability of ESP Equipment as          3-26
          Related to Frequency of Malfunctions

4.0  MAINTENANCE                                       4-1

     4.1  Maintenance Program for Precipitators        4-1

     4.2  Utility Procedures and Recordkeeping         4-19
          During Startup and Malfunctions

     4.3  Costs of Cold Side ESP Maintenance and       4-23
          Operation
                              v

-------
               TABLE OF CONTENTS  (continued).

                                                       Page

5.0  INSPECTION TECHNIQUES FOR EVALUATING MAINTENANCE  5-1
     PROCEDURES

     5.1  Typical ESP Inspection Procedure             5-1

     5.2  Inspection Checklist for Electrostatic       5-11
          Precipitators in the Electric Utility
          Industry

APPENDIX A  ESP MANUFACTURERS SUGGESTED MAINTENANCE    A-l
            PROCEDURES

APPENDIX B  UTILITY ESP MAINTENANCE PROCEDURES         B-l

APPENDIX C  EXAMPLE OPERATING HISTORY OF COLD-TYPE     C-l
            PRECIPITATORS
                             VI

-------
                      LIST OF FIGURES

No.                                                    Page
2-1   ESP Particle Charging System and Wire Hanging    2-8
      System

2-2   ESP Plate Hanging System                         2-9

2-3   Cutaway View of a Typical ESP and Arrangement    2-16
      of Field and Cells

3-1   Shrouds for Wire-weighted Discharge Electrodes   3-7

3-2   Typical Sparking Levels When Precipitating       3-19
      Dusts with Different Resistivities

3-3   Typical Operating Curve to Meet Emission         3-25
      Regulations with Partial Malfunctions of ESP

5-1   Electrostatic Precipitator Collection            5-8
      Efficiency vs. Delivered Power

5-2   Cold-side ESP.  SCA vs. % S                      5-10
                       LIST OF TABLES

No.                                                    Page

3-1   Summary of Problems Associated with ESP's        3-2

4-1   Maintenance Items for Electrostatic Precipi-     4-2
      tators

4-2   Troubleshooting Chart for ESP's                  4-15

4-3   Summary of Characteristics and Assumption For    4-26
      Model Plants

4-4   Coal Analyses Assumed for ESP Cost Evaluation    4-28

4-5   Capital Costs for Electrostatic Precipitators    4-29

4-6   Annualized Costs for Electrostatic Precipi-      4-31
      tators

5-1   Plume Characteristics and Operating Parameters   5-2
      for Coal-fired Boilers

5-2   Recommended Recordkeeping Requirements           5-5


                              vii

-------
                     1.0  INTRODUCTION






     When an electrostatic precipitator installed on a



utility boiler fails to achieve design efficiency, operators



must determine the causes for poor performance.  Although



the reasons for poor performance are numerous, they can be



grouped in two distinct categories:  degradation of ESP



efficiency is attributable either to hardware malfunctions



or to improper operation.  The purpose of this report is to



examine precipitation malfunctions in the electric utility



industry.  Under EPA sponsorship PEDCo-Environmental Special-



ists has prepared concurrently another document discussing



electrostatic precipitator performance related to operational



and maintenance practices.



     It is assumed that the reader has a working knowledge



of electrostatic precipitators.  The various types of preci-



pitators in the electric utility industry are discussed in



Section 2.0, along with design considerations.  Major types



of malfunctions are summarized in Section 3.0.  For each



type of malfunction, the possible cause, duration, correc-



tive action, and preventive measures are stated.  Section



4.0 presents the maintenance procedures that can minimize



the probability of malfunctions occurring.  Section 5.0
                             1-1

-------
describes inspection techniques for evaluating ESP main-



tenance procedures and describes in detail the items to be



checked during inspection of power plant precipitators.



     Appendix A presents a typical precipitator manufac-



turer's recommended operation and maintenance procedure;



Appendix B is an example of a concientious utility precipi-



tator operation and maintenance schedule.  The precipitator



operating history of a major U.S.  utility is summarized in



Appendix C.
                            1-2

-------
    2.0  TYPES OF ELECTROSTATIC PRECIPITATOR  (ESP) SYSTEMS





     This section discusses the various types of electro-



static precipitators, presenting a detailed discussion of



the major ESP components.  It is assumed that the reader



understands the fundamentals of ESP operation and theory,


                                       123
which are described in many references. '  '



2.1  COLD-SIDE AND HOT-SIDE ESP'S3'4'5



     The two categories of ESP's for use with coal-fired



boilers are based in location relative to  the air preheater



and thus are temperature-dependent.  The cold-side ESP,



currently predominant in the utility industry, is located



downstream of the air preheater, operating in the temperature



range of 200 to 400°F.  It is used mostly  with high-sulfur



coals, since the high resistivity associated with most low-



sulfur coal in the-operating temperature range would require



larger plate areas in cold-side ESP's.



     The hot-side ESP is located upstream  of the air pre-



heater and operates at temperatures above  230°C  (450°F).



The gas flow upstream of the air preheater at 371°C  (700°F)



is about 1.5 times the volume of air downstream of the air



preheater; a relatively -larger ESP is usually required to



handle gases at the higher temperature.  With many low-
                              2-1

-------
 sulfur coals,  however,  because  of  their high resistivity  in


 the 93 to 204°C  (200  to 400°F)  range,  it  is the smaller gas


 volume that requires  the larger ESP.   The greatest advantage


 of the hot-side  ESP over the  cold-side ESP, is its constant


 efficiency under varying fuel conditions.  Changes in  the


 fuel fired in  a  boiler  are  necessitated by such things as


 contract variances, price differentials,  and availability.


 Since the hot-side precipitator is located ahead  of  the air


 preheaters, it operates at  the  temperatures of the boiler


 flue gas exhaust,  and the fly ash  resistivity is  reduced  to


 levels that allow better precipitation.   At this  higher


 temperature resistivity is  not  sensitive  to the fuel's


 sulfur content.


      Since hot-side ESP is  located on  the hot gas side of


 the air preheater, the  fouling  of  heat transfer surfaces  by


 ash should be  eliminated, the plant should operate more


 efficiently, and requirements for  soot blowing from  the air

                            4
 preheater should be reduced.    Use of  high-sulfur coal might


 introduce a detrimental factor,  since  the fly ash often acts


 to remove any  sulfur  trioxide present  in  the gas  stream and,


 if the particulate is removed ahead of the air preheater,


 there  is  a  potential  for corrosive attack in the  preheater.


     The  typical hot-side precipitator operates at relatively


 lower  voltages, but,  if properly designed, it operates at


much higher current densities;  it  is characterized by  rela-
                             2-2

-------
tively high power density, and by stable, current-limited



operation, with sparking usually confined to inlet sections



where dust concentrations are high.



     The cold-side ESP does not undergo the thermal expan-



sion associated with a pronounced temperature increase, as



does the hot-side ESP.  The expansion can result in extreme



misalignment or even duct discontinuities.  Such failures



have been traced to inadequate provision for differential



thermal expansion between the lower shell and support



structure, and between the precipitator shell and roof



housing.  These problems can be minimized with provisions



for differential movement of the precipitator on its support



structure, proper insulation, and adherence to design



stresses, particularly in regions where temperature gradients



cannot be avoided.



     Some ESP manufacturers favor cold-side installations,



whereas others stress hot-side units; there is no clear-cut,


                                                 3 4
all-inclusive criteria for choice of either type. '   The



selection is usually based on operability and economics.  In



general, fcr new construction, if the cold-side unit requires



a specific collection electrode area  (SCA) greater than 500



to 600 square feet per thousand cubic feet of gas flow per



minute, then a hot-side unit would be the proper choice.  If



the SCA can be smaller, a cold-side unit could be used.
                              2-3

-------
      The  situation  is  somewhat more complicated  in  retrofit

 installations.   A hot-side unit requires addition of  duct-

 work  to transport the  gas stream  from the  air preheater

 inlet to  the  ESP and back to  the  air preheater.  The  consi-

 derable expense  that can be involved tends to swing the

 economics  toward a  cold-side  installation  for retrofit.

 systems.

      With  respect to a specific installation the following

 guidelines for selection are  suggested:

      (1)   Determine resistivity as a function of temperature.

      (2)   Evaluate  severity of the potential resistivity
           problem considering consistency  of coal supplies
           and variation in coal characteristics.

      (3)   Conduct comparative cost estimates with emphasis
           on  retrofit  difficulty.

      Neither  type of ESP installation can  provide perfect

 service.   Each requires regular attention  to ensure good

 service and to minimize malfunctions.

 2.2   DESIGN CONSIDERATIONS FOR MAJOR ESP COMPONENTS6

 2.2.1  Rapping Systems;

     Rappers  are incorporated in  the ESP to remove  dust from

the collecting and  discharge  surfaces; effectiveness  and

reliability of the  rappers are essential.  The following

types are generally available:
                              2-4

-------
     0    Electromagnetic impulse, either single or multiple

     0    Electric vibrators

     0    Pneumatic impulse

     0    Various mechanical hammers, usually associated
          with foreign designs, but sometimes furnished by
          others for special applications.

     Each ESP manufacturer develops rapper designs for

compatibility with his suspension system and rapper schedule

 (number of surfaces per rapper), based on experience and

tests.  Generally, pneumatic rappers impart more energy than

either electromagnetic rappers  or electric vibrators and

remove tenacious dusts more readily.  It is important,

however, to be certain that all hardware in the system is

designed to withstand such high energy forces.  Changing

from electrical to pneumatic rappers in an attempt to improve

operation without also strengthening the hardware has led to

structural failure.

     Current designs for horizontal rapping hammers impart

more energy to the plates than  do conventional designs;

these rappers remove fly ash from the plates in a very

efficient manner.

     Mechanical hammers also are often very effective, but

moving parts in a dirty gas stream require frequent mainten-

ance.  Repairs require shutdown of an entire chamber or

system.
                              2-5

-------
     The number and size of rappers required for a par-



 ticular installation vary with precipitator manufacturer and



 nature of  the  dust.  Requirements for collecting surface



 area range from 110 to  550 m2  (1200 to 6000 square feet) per



 rapper.  Discharge electrode rappers serve from 1000 to 7000



 feet of wire per  rapper.  Rapper intensity ranges from about



 35  to  70 J (25 to 50 foot-pounds) per cycle.  Rapping inter-



 vals are adjustable over a range of approximately 30 to 600



 seconds between raps.



     The paramount consideration in rapping is to provide



 ample  acceleration to dislodge the dust without excessive



 reentrainment.  Accelerations of 30 to 50 g per rap, as



 measured on the collection electrode, are required for



 removal of fly ash.  Both cycle and rapping intensity are



 usually adjusted  in the field to optimize rapping operations



 for maximum precipitator performance.



 2.2.2  Wire and Plate Hanging Mechanisms



 2.2.2.1  Wire  Weight System - The wire weight system con-



 sists of individual electrode wires suspended from an upper



 support frame.  The wires are best shrouded in some fashion



 to  prevent arcing to the exposed, sharp ground edges, or



where the  electrical clearance is reduced by passing the




tops and bottoms  of the collecting dust plates.  The wires




are held taut  by  weights suspended from their bottoms.  The




weights in  turn are spaced by a guide frame.  The  frame must
                             2-6

-------
be stabilized against swinging, an action that may be gener-

ated mechanically by the gas stream, by "electrical wind,"

by an improperly functioning automatic voltage-control, or

by some combination of these.

     Commonly, stabilization is accomplished by trusses

extending from the upper support frame to the guide frame.

Rapper energy, transmitted through the trusses, aids in

keeping the lower guide frames clean.  Any design of the

guide frames that permits enough dust buildup to raise the

weights may cause slackening of the wires, arcing, and

eventual wire failure.

     Stabilization of guide frames by ceramic or other

insulators from the casings or hoppers can cause a mainte-

nance problem.  Dust buildup on the insulators during opera-

tion, although resistive in some cases, presents a source of

leakage to ground.  Moisture gathered during shutdown  (or

low-load operation) might lead to complete failure of an

insulator.  Figures 2-1 and 2-2 illustrate the wire and

plate hanging mechanisms of a typical ESP.

     Electrode wire failure can be virtually eliminated by:

     °    Reasonable care, during erection, in alignment of
          the casings and surfaces.

     0    A well-designed support, guide, and stabilizer
          system.

     0    Reliable, properly adjusted automatic voltage-
          controls.
                             2-7

-------
         SUPPORT INSULATOR
              HOUSING
             VIBRATION
             ISOLATORS
HIGH VOLTAGE
BUS DUCT

    BUS CONDUCTOR
                                                       HIGH VOLTAGE
                                                         SWITCH
        TRANSFORMER-
        RECTIFIER
   TENSIONING WEIGHT
                                          DISCHARGE ELECTRODE
                                            SUPPORT FRAME
                                 DISCHARGE ELECTRODE
                                   WEIGHT GUIDE FRAME
(Source:   Rcf.  3)

     Figure  2-1.   ESP particle charging  system  and wire

                         hanging system.


                              2-8

-------
              END PANEL OR
              INTERIOR GIRDER
                                        •COLLECTING SURFACE
                                              SUPPORT
                                  COLLECTING SURFACE
(Source:   Ref. 3)
             Figure  2-2.  ESP  plate hanging system.
                            2-9

-------
      0     Good operating maintenance of the dust-handling
           system.

 2.2.2.2   Rigid Wire Frame - The rigid wire frame design was

 furnished by  U.S.  suppliers prior to 1950 and then was

 abandoned (in favor of  the wire-weight design) because of

 reliability and  operating problems.  Recently U.S. licensees

 of foreign manufacturers have reintroduced frame electrodes

 to this  country;  installations are  now in operation  and on

 order (as wire-weight designs are being installed in European

 plants).

      The rigid frame requires a high degree of quality

 control,  both in fabrication and erection, and is intrin-

 sically  more  costly.  Replacement or repair is expensive and

 time-consuming,  similar to replacement of a dust-collecting

 plate.

      At  lower temperatures, up to 204°C  (400°F), warpage of

 the  frames is uncommon, but for operating temperatures above

 204°C (400°F), or  with  cyclical operation, potential deforma-

 tion  of  the frames becomes serious.

      The  rigid frame entails wider  gas lanes, or ducts, to

 provide electrical clearance between the frame and the dust-

 collecting plate.  This requirement leads to larger  casings

 to house  the  required surface areas.

     It is important that the engineer be fully aware of the

differences and the requirements of each design philosophy
                             2-10

-------
in detail, so that he avoids incorrect evaluations of one



versus another.




     The erection sequence usually consists of casings and



hoppers first, followed by collecting surfaces and then



discharge systems.  If the casings are not erected to true



dimensions, plumbed vertically, and square cornered in the



plan view, attempts are often made to compensate during



installation of collecting surfaces, i.e., using guides that



should be free of frictional loads as "jacks," and so



forth.  Then, the discharge system, which should hang



freely, is stabilized in  an offset position to maintain, as



best possible, the wire-to-plate centers.  Such a construc-



tion will probably involve difficulties from the first day



of operation.  There is great need, therefore, to provide



step-by-step quality control and inspection of the installa-



tion, regardless of the pressure of construction schedules.



     Discharge systems are supported from the casing through



standoff electrical insulators.  These must be kept clean



and dry during operation  to prevent accumulation of dust or



moisture coatings, which  provide a path for leakage to



ground.  Wet accumulations are common during shutdown, as



the moisture in the gas condenses.  They can be prevented by



provision of warmed, filtered pressurizing-air supplies.
                             2-11

-------
      The  system must provide distribution to a multiplicity



 of insulators,  none of which may be allowed to "starve"



 because of disproportionate flow.  This design problem is



 similar to that of balancing an air-conditioning  system.



 Some method for checking distribution should be provided to



 the operators.  Maintenance routines for changing filters



 and checking heater elements should be established as soon



 as the  system is  operational.



      Most of the  commonly  used electrical insulators lose



 dielectric strength as temperature increases.  Although the



 maximum temperature varies with the insulating material,



 204°C (400°F) is  a probable limit.  Therefore, the electrical



 insulators must be isolated thermally from hot gases.  The



 purge air system  normally  suffices, but insulators mounted



 on hot  steel casing may be affected by conduction,  at least



 for several inches along the length.  Fortunately,  most



 electric  insulators retain structural strength under higher



 temperatures, and also act somewhat as thermal insulators  so



 that if the electrical path is long enough, the effect of



 the conducted heat is limited to a short distance up the



 insulator.



 2.2.3   Aspect Ratio




     An important variable in precipitator design is the




aspect ratio  (ratio of length to height of gas passage).




Space requirements often determine the overall precipitator
                             2-12

-------
dimensions.  Wherever possible, the engineer  should select



an aspect ratio that will result  in ample opportunity for



reentrained dust from the first sections to be recollected.



The aspect ratio is integrally related to the overall design



of the precipitator, and also depends on such variables as


              3                                          2
gas velocity m /min  (acfm), total plate collection area m


   2                              232
 (ft ), specific collecting area  [m /1000 m /min  (ft /1000


                                  o           2
acfm)], and power density  [watts/m   (watts/ft ) of collec-



ting  plate].  All other factors being equal,  higher ratios



of length to height provide better performances.  Historically



this  value varies between 0.5 and 1.5 with a  present day



average of  0.3.  Plate heights usually range  from 7 to 14 m



 (24 to 45 ft).



      Precipitator collection plates are made  in standardized



size  ranges, typically 7-9-11 m  (24-30-36 ft) height by



0.9-1.2 m  (3-4 ft) length.  Once  the collection area is



selected, the design will incorporate enough  collecting-



plate sections to yield the required surface  area.



      Plate area requirements are  governed primarily by the



properties of the dust and gas and the desired dust collec-



tion  efficiency.  Efficiency is related to the collection



plate area and gas volume by the  relationship



     n = 1 - e~ ( | w)



which is the conventional Deutsch-Anderson equation, where A



is the plate area, V the gas flow, and w the  precipitation
                              2-13

-------
 rate parameter  of migration  velocity.  A  serious  limitation


 in use of the Deutsch-Anderson  equation is  that the  particle


 size distribution and,  subsequently, the  effective migration


 velocity change as precipitation proceeds.  The Deutsch-


 Anderson equation does  not account  for this change.


      A recent empirical modification of the equation by


 Matts and Ohnfeldt  essentially removes the size  dependence

                                              v
 on w.   The equation is:   n = 1  - exp  (~w,  A/Q)  where k is


 said to be equal to about 0.5 in most cases.  This equation


 is an improvement over  the Deutsch-Anderson equation because


 w,  can be treated as a  constant in  any given application.


 2.2.4   Field/Bus Section/TR  Set Breakups


      The electrical system of an ESP is arranged  in  bus


 sections,  each  bus section representing any portion  of the


 ESP that can be energized independently.  This is done by


 subdividing the high-voltage system and arrangement  of the


 support insulators.


     The number of fields, which is the number of bus


 sections arranged  in the  direction  of gas flow, is cal-


 culated as follows:   as a rule  of thumb, manufacturers use


 one  field  for up to  90 percent  collection efficiency, two


 fields  for up to 97  percent,  three  fields for up  to  99


percent, and four  or  more fields for efficiencies above 99


percent.
                             2-14

-------
     The number of cells, or the number of bus sections



arranged in parallel, is established so that if any one



field shorts out the overall ESP efficiency will not fall



below specifications.  Figure 2-3 illustrates the arrange-



ment of fields and cells in a typical ESP.



     Sectionalization is of greatest significance in very



large precipitators for several reasons.  First, if the



precipitator is operating in a sparking mode, increased



Sectionalization will cause less of the precipitator to be



disabled during the interval of the spark.  This results in



higher average voltage, higher electric field, and better



precipitation.  Also, the smaller electrical sets have



higher internal impedances, which give better spark quench-



ing and minimize the tendency of a spark to develop into an



arc.  Third, the effects of localized electrode misalign-



ments are limited to smaller precipitator sections and



thereby permit higher voltages in the remaining sections.



Finally, in very large precipitators, reasonably good



collection efficiencies can still be maintained even if one



section must be deenergized because of wire breakage or



other electrical trouble.



     Increasing the number of electrical sections leads to



increased costs because the cost of the high-voltage power



supply is not linearly related to power handling capability.
                             2-15

-------
K)
 I
M
CTi
                INSULATOR COMPARTMENT
                         ROOF
                         END
 TRANSFORMER
  RECTIFIER

    GAS
DISTRIBUTION
  DEVICE
              GAS FLOW
                    COLLECTING SURFACE
                                           BUS DUCT
RAPPER INSULATOR
 HIGH VOLTAGE SYSTEM
   SUPPORT INSULATOR
        COLLECTING SURFACE
           RAPPER
                ISCHARGE ELECTROD:
                  RAPPER
                                                                                 -SIDE
                                -&KS
                           DISCHARGE ELECTRODE
                                                HOPPER
            (Source:   Ref.  8)

        Figure  2-3.    Cutaway view of  a  typical ESP and  arrangement of field and cells,

-------
The greater portion of the cost is in providing the high-



voltage equipment.  Increased power can then be provided by



using larger components.  Hence it is less expensive to



provide fewer large power supplies than to power the preci-



pitator from a greater number of small sets.  Because of the



lower average voltage, however, the precipitation rate



parameter would be lower, and the necessity for providing



larger collecting surface area would partially offset the


lower cost of the larger set.



     Often, multiple cells are energized from a common high-



voltage electrical set.  However, no more than one field in



any cell should be energized from the same high-voltage



electrical set, because a short would affect more than one



field in the same cell, causing a substantial reduction in



collection efficiency.  In general, one high-voltage elec-



trical set is used for up to 2,320 m2  (25,000 ft2) of col-


                                     2               2
lecting surface.  About 611 mA/1000 m  (55 mA/1000 ft ) of



collecting surface is supplied.



2.2.5  Ash Hoppers


     Whether suspended from the casing or supported directly



on the substructure that is interposed between the casing



and the support steel, hoppers are required for collection



and temporary storage of the collected dust.  The simplest



and most common hopper is pyramidal, converging to a round
                            2-17

-------
or  square discharge.  Frequently, the hoppers are baffled at



the division between two dust-plate sections, to prevent gas



bypassing the treater.



     Hoppers must be kept clean and dry.  Although many



designs do not require vibrators, which are costly and



require maintenance, it may be prudent to install mounting



provision for vibrators initially, to avoid later costly



removal of insulation and lagging if operation shows that



vibrators are needed.



     Moisture-laden dust that hits cold steel hoppers has a



tendency to stick.  Therefore, insulation of hoppers is



vital.  Insulation is sometimes not sufficient, however, and



additional heating of the hoppers may be required for



effective performance.



     When a baffle extends too far down into a hopper, it



may act as a "choke," causing bridging between the baffle



and one or both sides of the hopper.  Stopping the baffle a



liberal distance 0.6 m (2 ft) clear of the sloping hopper



wall should prevent gas bypassing.  A gas sweep under a



baffle of this type, considering the pressure drop of the



turn, is probably a symptom of poor gas distribution to the



precipitator (that is, a downward jet at the entrance).




     Access to hoppers should be by external, key-inter-



locked doors.   Bolt-on doors through baffles should be
                             2-18

-------
avoided because of the dangerous possibility of dust accumu-



lation on the far side of the door.  Liberal "poke-hole"



ports should be provided to allow for clearing a blockage at



the discharge.




     Level alarms are extremely valuable, provided they are



kept in working order.  Too often, because they are located



near the top of the hoppers (even so high as to place them



above the bottom of the structural steel supporting the



precipitator), they are inaccessible for periodic inspection



and maintenance.  Also, the temperature in this confined



area may be so high as to cause the alarm mechanisms to



fail; this point should be considered critically and in



detail before installation of the alarm instrument.



     Hopper capacity should be checked carefully to provide



reasonable time for minor maintenance of the dust-removal



system.  Generally, hoppers are designed to accumulate a 24-



hour load of particulate.



     Alignment of the conveyors is important, depending to a



great extent on the alignment of hopper connections.  Because



of the difficulty of erecting multiple hoppers to close



alignment tolerances, field-adjustable flange connections



are recommended.  Also, the designer should not overlook



provision for expansion between hopper connections and




conveyor troughs.
                              2-19

-------
                       3.0  MALFUNCTIONS




     Many ESP equipment  components are subject to failure or



malfunction, leading  to  an increase  in emissions.  These



malfunctions may  be caused by  faulty design, installation,



or operation of the ESP; they  may entail minor or severe



problems with the ESP system.   This  section identifies



several types of  ESP  malfunctions, giving probable causes



and corrective actions.  A survey of ESP operating experience



of 63  electric utilities is  analyzed.



3.1  TYPES  OF ESP MALFUNCTIONS



     ESP malfunctions can be classified as  electrical, gas



flow,  rapping, or mechanical problems.  Table 3-1 lists



common problems associated with ESP's, their effect on



emissions,  corrective actions,  and preventive measures.



3.1.1  Discharge  Wire Breakage



     Probably the most common  problem associated with



suspended wire electrode type  ESP's  is wire breakage, which



typically causes  an electrical short circuit between the



high-tension discharge wire  system and the grounded collec-



tion plate.  This electrical short trips the circuit break-




er, disabling a section of the ESP,  which will remain dis-
                             3-1

-------
                                         Table   3-1.     SUMMARY  OF  PROBLEMS  ASSOCIATED  WITH  ESP'S
                     &1function
                                                       Cause
                                                                                              Effect on ESP Efficiency*
                                                                                        Corrective
                                                                                         action
                                                                                                                                                          Preventive
                                                                                                                                                           measure*
          X.   Poor electrode aligruaent
          2.   BrcXea electrodes
U)
 I
          3.
               Distorted or skewed
                electrode plates
               Vibrating or
                electrodes
                            •winging
    1)  Poor  design;

    2)  Ash buildup on frame hoppers;
    3}  Poor  gas  flow

    1)  Wire  not  rapped clean, causes an arc
       which embrittles ^..id burns through
       the wire
    2)  Clinktzred wire.  Causes:  a)  poor flow
       area,  distribution through unit is
       uneven; b) excess free carbon due to
       excess air above co.T-bustion require-
       ments or  fan capacity insufficient
       for demand required; c) wires not
       properly  centered; d) ash buildup re-
       sulting in bent frame, same as c) ;
       e) clinker bridges the plates & wire
       shorts out; f) asti buildup, pushes
       bottle weight up causing sag  in the
       wire;  g)  "J" hooks have improper
       clearances to the hanging wire; h) bot-
       tle weight hangs up during cooling
       causing a buckled wire; i) ash build-
       up on bottle weight to the frame
       forms a clinker and burns off the wire

    1)  Ash buildup in hoppers
    2)  Gas flow  irregularities
    3}  High  temperatures

    1)  Uneven gas flow

(    2}  Broken electrodes
                                                                                         Can drastically affect performance,
                                                                                         and lower efficiency
                                                                                         Reduction in efficiency due to reduced
                                                                                         power input, bus section unavailability
                                        Realign electrode*
                                        Correct gas flow
                                         Replace electrode
                                                                                         Reduced efficiency
Decrease in  efficiency due to reduced
power input
                                         Repair or  re-
                                         place plates
                                         Correct gas flow

                                         Repair electrode
Check hoppers  frequently
tor proper operation
Boiler problens:   check  space
between recording  stea.3  *  air
flow pens, pressure gauges;  fouled
screen tubes.

Inspect hoppers
Check electrodes  frequently  for vea
Jnopect rappers frequently
 Check hoppers frequently for
 proper operation; check electrode platafl
 during outages

 Check electrodes frequently
 for wear
          * The effects of precipitation problem can only be discussed  on a qualitative basis.  There are  no known *mi«»ioa
            teats of precipitator* to determine performance degradation  as a function of operational problem*.

-------
                          Table   3-1    (Continued).     SUMMARY  OF  PROBLEMS  ASSOCIATED  WITH  ESP'S
                Malfunction
                                                  Cause
                                                                                       Effect on ESP Efficiency*
                                                                                                                     Corrective
                                                                                                                      action
                                                                                                            Preventive
                                                                                                             measures
U>
 I
u>
        5,   Inadequate level
            ef paver inptit
             {voltage too low)
        6.   Back corona
7.  Broken or cracked insulator
    or flower pot bushing
    leakage
        8.  Air inleakaga throu9h
             hcpp«rs

        9.  Air inleakag* through ESP
             shell

       10,  Gas bypass around ESP:
             - dead passage above
                plates
             - around high tension
                f rane

       11.  Corrosion
1)  High dust resistivity
2)  Excessive ash on electrodes
3)  Unusually fine particle  size
A]  Inadequate power supply
5)  Inadequate sectionalization
6)  Improper rectifier end control operation
7)  Misalignment of electrodes

1)  Ash accumulated on electrodes •» causes
   excessive sparking requiring reduction
   in voltage charge

1)  Ash buildup during operation causes
   leakage to ground

2)  Moisture gathered during shutdown
   Or low load operation

1)  From dust conveyor
                                 1) Flange expansion
                                 1) Poor design - improper isolation
                                   of active portion of ES?
                                         1} Temperature goes below dew point
                                                                           Reduction in efficiency







                                                                           Reduction in efficiency



                                                                           Reduction in efficiency
                                           Lower efficiency - dust reentrained
                                           through ESP

                                           Same as above, also causes  intense
                                           sparking

                                           Only few percent drop in efficiency
                                           unless severe
                                          Negligible until precipitation interior
                                          plugs or plates are eaten away; air leaks
                                          may develop causing significant drops in
                                          performance.
- Clean  electrodes;
  gas conditioning

  in temp, to re-
  duce resistivity?
  Increase section-
  alization

Sane as  above
Clean or replace
insulators £
bushings
                                                                                                                             Seal  leaks
Baffling to direct
gas into active
ES? section
                                                                                                                             Maintain flue gas
                                                                                                                             temperature above
                                                                                                                             dew point.
Check rangd of voltages
frequently to nuke sure they
are correct
In situ resistivity measurements
Cheek frequently
Clean and dry as needed;  check for
adequate pressurixaticn of  top housing
                                                                                                                                             Identify early by  increase in ash concen-
                                                                                                                                             tration at bottom  of exit to ESP
Identify early by measurement of gas
flow in suspected areas
                                                                                                                                             Energite precipitator after boiler systea has been
                                                                                                                                             on line for »apl« period to r*ise flu* gas tam-
                                                                                                                                             erature &bov« acid d»w point.
        * The effects of precipitation problems can only be discussed on a qualitative basis.  There are no known emission
          t*«t» of precipitator* to determine performance degradation as * function of operational problem*.

-------
                    Table  3-1   (Continued).   SUMMARY  OF PROBLEMS  ASSOCIATED  WIH  ESP'S
Malfunction
12. Hopper pluggag.*
13. Inadequate rapping t
vibrators fail
14. Too intense rapping
15. Control failures
16. Sparking
Cause
1) Wires, plates , insulators fouled
because of low temperature
2} Inadequate hopper insulation
4} Boiler leaks causing excess ir.oisture
malfunction ) blower ir.alf unction
} solenoid valves
7} Material dropped into hopper - from
bottle weights
8) Solenoid, timer malfunction
9) Suction blower filter not changed
1) Ash buildup
2) Poor design
3) Sappers roisadjusted
1) Poor design
2) Rappers nisadjusted
3) Improper rapping force
1) power failure in primary system
a. insulation breakdown in trans-
former
b. arcing in transformer between
high voltage switch contacts

d. insulating field contamination
1 ) Inspection door ajar
2) Boiler leaks
3) Plugging of hoppers
4) Dirty insulators
Effect on ESP Efficiency*
Reduction in efficiency
Resulting buildup on « lac t rode & Day
reduce efficiency
Been trains ash, raducas efficiency
Reduced efficiency

Corrective
action
Provide proper
flow of ash
Adjust rappers with
ESP exit Btrean
Same as No. 13
Find source of
failure and
repair or replace
in boiler; unplug
hoppers ; clean
insulators

measures

Frequent checks for adequate operation
of hoppers.
Provide h*at«r thenaal insulation
to avoid &oistur« conder.sition
Frequent checks for adequate operation of
Same as No, 13
Reduce vibrating or impact forco
room instrumentation to spot deviations
normal readings
Regular preventive nuintenance will *\11«

control
froa
viate
U)
I
     • The effect! of precipitation problems can only be discussed on a qualitative basis. There are no known emission
      tests of precipitator. to determine performance .degradation as a function of operational problems.

-------
abled 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 causing
          an arc, which can embrittle the wire and eventu-
          ally break it completely.

     2)   Clinkered or improperly centered wires causing a
          continual spark  from the wire to the bracing.

     3)   Clinker or a wire that bridges the collection
          plates and shorts out the wire.

     4)   Ash buildup under the wire, causing it to sag and
          short out.

     5)   Improper clearance of "J" hooks to the wire, caus-
          ing it to short  out.

     6)   Hangup of a bottle weight during cooling, causing
          a wire to buckle.

     7)   Fly ash buildup  on a bottle weight, which forms a
          clinker or burns off the wire.

     8)   Corrosion around cooler areas of the wire caused
          by condensation.

     9)   Excessive localized sparking causing erosion of
          the wire.

     Electrical erosion, the predominant cause of failures,

occurs when repeated electrical sparkovers or arcs occur in

a localized region.  A sparkover causes localized heating

and vaporization of a minute quantity of metal with each

spark.   If the sparkover occurs at random locations, no

serious degradation of the discharge electrode occurs.  If
                             3-5

-------
 the  sparkover occurs repeatedly at the same location, how-



 ever,  significant quantities of material can be removed,



 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 electric



 field variations caused by "edge" effects where the discharge



 and  collection electrodes are adjacent to each other at the



 top  and the  bottom of  the plates.  Corrective measures for



 eliminating  failure at these points are adding shrouds, such



 as those  shown in Figure 3-1, and providing a rounded sur-



 face at the  edge of the collection electrode to reduce the



 tendency  for sparking.



      Electrical  erosion can also be caused by "swinging"



 electrodes,  which can  occur when the mechanical resonance



 frequency of the discharge wire and weight system is harmon-



 ically related to the  electrical frequency of the power



 supply.   The power supply adds energy to the swinging wire



 and  it continues to approach the collection plate with



 sparking  occurring at  each close approach.  This action



 leads  to  erosion of the electrode and mechanical failure.3




     Poor workmanship  during construction can also cause



electrical failures of the discharge electrode.  If pieces




of the welding electrode remain attached to the collection
                             3-6

-------
(Source:   Rof.  3)
       Figure 3-1.  Shrouds for wire-weighted discharge



                         electrodes.
                           3-7

-------
 plate,  localized  electric  field deformation can  lead to



 sparking  and  ultimate  failure of  the discharge electrode.



      Mechanical fatigue  occurs at points where wires are



 twisted together  and a continued  mechanical motion occurs  at



 one  location.  This situation is  found at the top of a dis-



 charge  electrode  where the wire is  twisted around the sup-



 port collar.   Methods  of reducing mechanical fatigue include



 selection of  discharge electrode  material that is less



 susceptible to cold work annealing  after attachment or



 modification  of the design of the corona wire attachment.



      Chemical attack is  caused by a corrosive material in



 the  flue  gas,  as  is the  case with high-sulfur coal and low



 flue gas  exit temperatures near the acid dew point.  Another



 cause of  corrosion is  use  of ambient air to purge insulator



 compartments,  causing  the  temperature to drop below the acid



 dew  point in  a localized region.  Corrosion can  be minimized



 with higher flue  gas temperatures or by use of hot, dry air



 to purge  insulator compartments.  Use of good insulation on



 the  ESP shell  to  maintain  high temperature also  provides



 adequate  protection within the usual range of temperatures



 and  sulfur  contents.




     The  other causes  of discharge  wire failure, such as




 inadequate  rapping, could  be minimized by routine checking




of vibrators and  rappers.  Inspection may help to prevent
                             3-8

-------
wire failures and tripouts by detecting potential problems



before they become serious.  Because of the large number of



wires contained in an ESP, however, some discharge wire



failures can be expected even with good design and preven-



tive maintenance.



3.1.2  Collection Hoppers and Ash Removal



     Hoppers and ash removal systems often constitute pro-



blems in precipitator operation.  If the hoppers become



full, the collected dust may short-circuit the precipitator.



The power through the dust may  fuse the dust, forming a



large clinker-type structure called a  "hornet's nest."



This structure further  interferes with ash removal and must



be removed.  Most problems associated  with hoppers are



related to providing for proper flow of the dust.  Improper



adjustment of the hopper vibrators or  failure of the conveyor



system are the usual causes of  failure to empty the hoppers.



It may be necessary to  provide  heat and/or thermal insula-



tion for the hoppers to prevent moisture condensation and



resultant cementing of  the collected dust.



     Malfunctions of the evacuation and removal system



include ash water pump  failure, water  jet nozzle failure,



disengagement of vacuum connections, and failure of sequenc-




ing controls.
                              3-9

-------
     The best preventive measure for an ash removal system,



 aside  from proper design, is a good program for operation



 and maintenance.  Since dust buildup can affect so many of



 the ESP components, proper ash removal will eliminate or



 minimize many of the most common ESP malfunctions.



     Gas flow problems affect hoppers as a result of the



 inleakage of air into hoppers from the dust conveyor systems.



 This results in reentrainment of collected dust, which is



 carried back into the ESP.  Air inleakage can also occur



 through the ESP shell or inlet flanges if operation is at



 less than atmospheric pressure.  Often enough air is bled in



 to cause intense sparking.



      'Gas sneakage1 is a term used to describe gas flow that



 bypasses the effective ESP section.   It can occur through



 dead passages of the ESP above the collector plates, around



 the high-tension frame, or through the hoppers.  Gas sneakage



 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 section.




     Reentrainment of dust from hoppers caused by air in-




 leakage or gas sneakage is often indicated by an increase in




dust concentration at the bottom of the exit to the ESP.
                             3-10

-------
Corrective measures for air leakage would include proper
design and fit of components and sealing of areas where the
inleakage occurs.
3.1.3  Rappers or Vibrators
     Rapping is required for both discharge and collection
electrodes.  These systems normally consist of electric or
pneumatic vibrators or electromagnetic or mechanical-impact
rappers.
     In dry removal systems, rapping of the collection
electrode to remove dust is normally done periodically.
Successful rapping depends upon accumulation of material on
the plate thick enough that it falls in large agglomerates
into the hopper.  Although there is always some reentrainment
of dust, effective rapping must minimize the amount of
material reentrained in the gas stream.  Poor performance
can result from rapping forces either too mild or too severe.
Rapping that is too intense and frequent can result in a
clean plate, with the collected dust being reentrained
rather than falling into the hopper.  Excessive gas velocity
or poor gas distribution can lead to turbulence, scouring of
the receiving electrode, and reentrainment of particles.
     Inadequate rapping of the discharge electrodes can
result in heavy dust buildup with localization of the
corona, low corona current, and excessive sparking, as
                             3-11

-------
discussed previously.  Poor gas flow and the condition of


the dust also can cause  formation of deposits on discharge


electrodes.  Often, deposits can reach to 5 cm  (2 in) thick-


ness;  they 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 perfor-


mance, although depending on resistivity, power supply


range, and uniformity of the deposit, efficiency may be


reduced.


     Variations in design of the support structure and of


the electrodes  can also  result in inadequate rapping.


Recent investigations of rapping acceleration in fly ash


ESP's  have shown measured accelerations of 5 g when as much

                         9
as 30  g may  be  required.   The first step in dealing with


problems related to rappers and vibrators would be 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-measur-


ing instrument  in the ESP exit gas stream.


     Discharge  electrodes should be kept as clean as pos-


sible.   Rapping  intensity in this case is limited only by


the possibility of mechanical damage to the electrodes and


support structure.
                             3-12

-------
     Generally, the vibratory types of cleaning mechanisms



require more maintenance than the impulse types.



3.1.4  Insulator/Bushing Failure




     Suspension insulators are used to support and isolate



the high-voltage parts of an ESP.  Inadequate pressurization



of the top housing the insulators can cause ash deposits



and/or moisture condensation on the bushing, which may



result in electrical breakdown at the typical operating



potential of 45 kv-DC.



     Corrective or preventive measures include inspection of



ventilation fans for 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.



3.1.5  Inadequate Electrical Energization



     Since an ESP operates on the basis of electric field



and electric charge, electrical energization must be ade-



quate to provide for particle charging, maintenance of the



electric field, and holding the collected dust to the




collection plates.



     Among several possible causes for inability to achieve



the required level of power input to the ESP, the following




are most common:



     1)   high dust resistivity
                             3-13

-------
     2)   excessive dust accumulation on the electrodes



     3)   unusually fine particle size



     4)   inadequate sectionalization



     5)   improper rectifier and control operation



     6)   misalignment of electrodes



     7)   inadequate power supply range



     If a precipitator is operating at a spark-rate-limited



condition but with low current and voltage, the problem



commonly can be traced to high-resistivity dust, electrode



misalignment, or uneven corona due to buildup on the dis-



charge electrode.



     The effects of high resistivity are discussed in more



detail in Section 3.2 in terms of conditions specific to



utility industry, where resistivity presents the greatest



problem.



     Because of the importance of resistivity in the pre-



cipitation process, in situ resistivity measurements should



be made as one of the first steps in troubleshooting.  If



the resistivity is found to be high  (more than  10   ohm-cm),



most of the difficulty may be due to this cause.  If resis-



tivity is not high, other potential causes of abnormally low



currents should be 'investigated.




     Typical values for normal power supply operation range




from 33 to 103 mA/1000 m (10 to 31 mA/1000 ft)  of collecting
                             3-14

-------
surface.  The spark rate  should be adjusted to give about 10



to 100 sparks/min per  section.  The spark rate should be set



to give maximum average high-tension voltage, usually



resulting in spark rates  in  the range shown above.



     If a precipitator is operating in a spark-limited mode



with abnormally low voltage  on dust with resistivities less



than 10   ohm-cm, the  problems are likely to be associated



with misalignment of electrodes,  uneven deposits on the



discharge wire, or broken corona  wires.



     Occasionally, precipitators  may be found to operate at



the maximum voltage or current settings on the power supply



with no sparking.  This condition is likely to be associated



with the collection of low-resistivity dusts, where the



electric field in the  deposit is  insufficient to initiate



sparking.  These installations are referred to as "power



hogs."  The fact that  the precipitator is not sparking does



not necessarily mean that the unit is underpowered.  These



installations may have sufficient power to provide adequate



charging and collection electric  fields without sparking.



If ESP efficiencies are low  and tests show that sufficient



power is provided, then other disruptive conditions should




be sought.



     Failures in ESP controls can prevent the system from




achieving the level of power required for normal operation.




Following are the most common malfunctions in controls:
                              3-15

-------
     1)   Power failure in the primary system.

     2)   Transformer or rectifier failure in secondary
          system.

          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

 failures is a good maintenance program in which the controls

 are  checked periodically for proper operation.  A daily log

 of instruments that register current, voltage, and spark

 rate can also indicate potential problems.

 3.2  CONDITIONS SPECIFIC TO POWER PLANTS THAT CAUSE PROBLEMS
     IN PRECIPITATORS

     A number of operating conditions specific to power

 plants can cause ESP problems, often requiring special

 equipment designs.  The major operating problems are caused

 by startup, variable fuel quality, boiler malfunctions, fly

 ash  resistivity, temperature fluctuations, and large gas

 volumes.  Each is briefly discussed below.

 3.2.1  Startup

     Normally, during startup of a coal-fired steam genera-

 tor  equipped with an ESP, operation of the ESP must be

delayed until a certain exit gas temperature  (about 110°C

 (230°F))  is attained.  This delay is necessary to protect

the ESP from corrosion and plugging, and to prevent secondary
                             3-16

-------
combustion  (fires) due to  unburned carbon in the flue gas

and ESP sparking.  The latter  is particularly important when

secondary liquid fuels are used during startup.

3.2.2  Fuel Quality Variability

     Variable fuel quality is  a major cause of changes in

operation that lead to fluctuating emissions.  The quality

of fuel from a given  source is continually changing.  As

sulfur and ash content vary, so does the efficiency of the

ESP.  Excess moisture in the coal can lead to wet fly ash,

which could interfere with the dampers and solidify in the

hoppers.  Ash grindability, fineness and other coal charac-

teristics can cause combustion to deviate from the optimum,

requiring changes in  such  operating variables as register

settings and excess air.

     Although the variability  of sulfur and ash contents in

coal cannot be readily controlled, proper drying of the coal

before combustion can minimize the possibility of wet fly

ash and the resultant problems.

3.2.3  Boiler Malfunctions that Indirectly Affect ESP
       Performance

     Firebox flameout, coked or burned burner impellers,

improper combustion due to faulty fans or dampers, irregular

fuel flow to coal mills, pulverizer problems, excess slag

buildup in the firebox, and soot blower usage all can upset

precipitator performance and cause emissions to increase.
                             3-17

-------
 Usually, these upsets are of short duration.  Proper main-


 tenance can minimize these types of boiler malfunctions


 and increase ESP reliability.


 3.2.4  High Resistivity of Fly Ash Resulting 'from Low
        Sulfur Content in Coal


      High resistivity, which is characteristic of low-sulfur


 coal, causes uncertainties in proper sizing of a cold ESP.


 In addition, many operating problems can be traced directly


 or in part to high resistivity.


      High dust resistivity affects ESP efficiency principally


 by limiting the voltage and current at which the ESP operates,


 If the ESP electrodes are clean, the high-tension voltage


 can be increased until a sparking condition is reached.   The


 maximum voltage is determined principally by gas composition


 and ESP dimensions.


      If dust is deposited on the collection electrode,  the


 voltage at which sparking occurs is decreased because of the


 increased  electric field at the dust surface.   If the re-


 sistivity  of the dust layer is increased,  the voltage at


 which  sparking  occurs will be further reduced, as shown in


 Figure  3-2.   Finally,  at very high values  of dust resistivity

    12
 (10   ohm/cm),  the voltage will be reduced enough that


 sparks will not  propagate  across the interelectrode space.


 Under these conditions,  the  gas in the  interstitial regions


of the dust layer will break  down  at very  low values of
                             3-18

-------
       10'
u


5
I
O
 «
>
t-

>
to
IL)
oe
     5x10
        to
        10"
                                              SPARK
                                                                 SPARK
                    10        20        30


                         APPLIED VOLTAGE, K.V.
                                                   40
50
     (Source:   Ref.  10)
      Figure 3-2.   Typical sparking levels when precipitating dusts


                     with different resistivities.
                                  3-19

-------
applied voltage and current density, resulting in a back



corona.  The positive ions resulting from this corona flow



toward the discharge electrode and neutralize the negative



charge previously applied to the dust particles; performance



of the ESP is  thereby limited.



     Back corona results in an increase in current at low



voltage and is manifested visibly as a diffuse glow at the



surface of the dust layer.  Although visual verification is



usually very difficult, back corona can be observed under



very dark conditions.



     If the electrical resistivity of the particulate is in



the intermediate range  (10  -10   ohm-cm), the electrical



behavior is somewhat different in that the electrical break-



down occurs at a somewhat higher applied voltage.  If the



applied voltage is sufficiently high when the electrical



breakdown occurs in the dust layer, then an electrical



sparkover between the collection and corona electrode occurs.



The electrical breakdown in the layer tends to begin in a



localized region.  This localized breakdown behaves as a



small radius of curvature electrode  (a point).   This leads



to electrical  sparkover at reduced voltages in the operating



device, again  forcing the electrostatic precipitator to



operate at reduced voltage and current density.
                             3-20

-------
     The reduction in electrical conditions is much more


severe with back corona than with sparkover at reduced

voltage.


     In addition to electrically limiting the performance of


an ESP, high-resistivity dust can cling much more tena-


ciously to collection electrodes than an intermediate-


resistivity dust.  Therefore, a much greater rapping accel-


eration must be applied to the electrode to remove the dust


layer.  This increased acceleration may be so great as to


cause severe reentrainment of the dust, or damage to the


precipitator if it is not designed to accommodate such high


acceleration.


     Corrective procedures for ESP's that are limited by


high-resistivity ash include collection at low temperatures


[105-110°C  (220-230°F)J, use of very large ESP's, increased


sectionalization, and use of conditioning agents.  "Cond-


itioning agents" have been used for many years to improve


the collection of particulate substances in electrostatic

              I O
precipitators. '   Normally, the use of a conditioning agent


is expected to overcome the problems associated with high


electrical resistivity.  In some instances, however, condi-


tioning agents may alleviate other problems stemming from


adverse particulate properties, one being unacceptably low


resistivity.
                             3-21

-------
      The  best  known conditioning agent is sulfur trioxide or



 the  chemically equivalent compound, sulfuric acid.  In most



 applications,  sulfur trioxide is effective in lowering



 electrical  resistivity by surface deposition along with



 water vapor on gas-borne particles.  In conditioning fly ash



 in power  plants,  it supplements the small quantity of sulfur



 trioxide  that  is  produced naturally when low-sulfur coals


            12  13
 are  burned.   '    On the other hand, in some power plants



 where sulfur content of the coal is not especially low and



 the  fly ash resistivity is not low enough to be detrimental



 to electrostatic  precipitation, the use of sulfur trioxide



 as a conditioning agent may be of value in increasing the



 cohesiveness of fly ash particles and thus minimizing re-



 entrainment losses from the collection electrodes.  Evidence



 of sulfur trioxide conditioning through this mechanism has



 been reported  in  a publication from the Central Electricity


                                       14
 Research  Laboratories in Great Britain;   further evidence



 of this effect has been obtained in recent studies by



 Southern  Research Institute.



      Other  conditioning agents, not as well known as sulfur



 trioxide, include ammonia, ammonium sulfate, ammonium bi-



 sulfate,  and sulfamic acid.  Of these compounds, ammonia has



been most widely  used in the utility industry.  Experience



with ammonium sulfate, ammonium bisulfate, and  sulfamic acid
                             3-22

-------
has thus far been relatively  limited.16  These compounds



occur at normal temperatures  and pressures as solids.  They



are injected into flue  gas  in the  form of either a fine



powder or an aqueous  solution.




     As an alternative  to the above-listed corrective pro-



cedures, use of a hot ESP will  largely eliminate the prob-



lems.




3.2.5  Temperature Fluctuations



     During frequent  startup  and shutdown operations, or



with a boiler that is used  mostly  for peak loads, the flue



gas exhibits a large  temperature gradient.  If the tempera-



ture drops below the  dew point of  sulfuric acid, corrosion



can occur.  In such operations, control of temperature



changes is difficult  but corrosion can be minimized by



covering the interior surfaces of  side frames, end frames,



and roof of the ESP with gunite.



     Another effect of  temperature fluctuations is reentrain-



ment of fly ash, resulting  in excessive fouling of wires,



plates, and insulators.  This fouling leads to ash hopper



plugging, high current, leakage, and excessive power require-



ment for the discharge  electrodes.  The most effective



measure for dealing with unfavorable temperature fluctua-



tions is to evaluate  the range of  expected gas temperatures



when designing the ESP  and  to provide a means of reaching
                             3-23

-------
 the optimum gas temperature for proper ESP operation.  After

 a  unit  is  installed, temperature changes can be dealt with

 by increasing the size of the ESP with add-on equipment.

 3.2.6   Large Gas Volumes

     Utilities treat larger volumes of gas than most other

 industries.  Since  large gas volumes require large precipi-

 tators,  space considerations may become critical.  In

 addition,  as more bus sections are required, the precipitator

 becomes more complex and the chances for problems increase.

 3.3  REDUCED ESP COLLECTION EFFICIENCY AS RELATED TO
     NUMBER OF BUS  SECTIONS NOT IN OPERATION

     Although ESP collection efficiency is reduced by

 malfunctions such as discharge wire breakage and deteriora-

 tion of power supply equipment, rectifiers, insulators, and

 similar equipment,  a unit can often be kept in compliance

 with particulate emission regulations by reducing boiler

 load.   Figure 3-3  (top graph) illustrates collection effi-

 ciency  of  a four-field ESP with 24 bus sections as a func-

 tion of  the gross boiler load, depending on the number of

 bus sections out and whether they are in series or parallel.

 The bottom graph shows the efficiency needed by the ESP to

meet a state regulation of 0.16 g/MJ  (0.38 Ib/MM Btu) as a

 function of the ash content of coal  [(assuming 25.6 MJ/kg

coal (11,000 Btu/lb coal)].
                             3-24

-------
u>
KJ
en
             S9.0
           I 98.0
           o
           *-l
           u.
           u.
           Ul
             97.0
             36.0
              95.0
»«
  98-°
          <*3 97.0
          s*
          I"
          gK 96.0
          u.
          Ul

              95.0
                    140
                     10
                              CURVE A
               160    180
      200    220     240
       GROSS LOAD  - MW.
  260

MOISTURE..
280   300
                                           CURVE B
                                                                             MA A4B AB4A AB4B BAA BAB
                                                                             A3A A3B AB3A AB3B B3A B3B
                                                                             A2A A2B AB2A AB2B B2A B2B
                                                                             A1A A1B ASIA AB1B B1A BIB

                                                                                    COLLECTOR
                                                                 SECTIONS OUT
                                                                 0

                                                                 1 OUT

                                                                 2 OUT IN PARALLEL

                                                                 3 OUT IN PARALLEL

                                                                 4 OUT IN PARALLEL OR
                                                                 2 OUT IN A SERIES
                                                                 5 OUT IN PARALLEL OR
                                                                 2 OUT IN A SERIES & 1 OUT IN PARALLEL
                                                                 6 OUT IN PARALLEL OR
                                                                 2 OUT IN A SERIES & 2 OUT IN PARALLEL
                                          EXAMPLE:  LOAD 290 MW.
                                                  SECTIONS OUT  A1A, A2A, AB2A, BAB
                                              (CURVE A) EFFICIENCY AT 290 MW. WITH
                                              2 OUT IN SERIES & 2 OUT IN PARALLEL • 95.3
                                              COAL - ASH  14%
                                                    MOISTURE  10X
                                              (CURVE E) EFFICIENCY REQ'D. TO MEET
                                              STATE REGULATIONS  - 96.5%

                                              TO MEET STATE REGULATIONS REDUCE
                                              LOAD TO 210 KM.
                12
14     16      18     20
   PERCENT ASH IN COAL
  22
24
              Figure  3-3.    Typical operating  curve  to meet  emission  regulations  with

                                            partial  malfunctions of  ESP.

-------
     These types of graphs are extremely helpful to a utility

operator.  Knowing the ash content of the coal he is firing

and knowing which bus sections of his ESP are inoperative,

he can easily tell from the top graph how much the boiler

load must be reduced to keep emissions in compliance with

regulations.  Charts of this type must be developed for each

boiler-ESP combination.

3.4  MAINTAINABILITY OF ESP EQUIPMENT AS RELATED TO
     FREQUENCY OF MALFUNCTIONS                          '

     To assess the experience of the major industries iri

recent years in operation and maintenance of ESP's, the TC-1

Committee of the APCA embarked upon a survey in 1974.

Four major industries were canvassed:  electric utilities,

cement, paper, and metallurgical.  This section is restricted

to data from the electric utility industry.

     Sixty-three electric utilities reported on eighty-eight

ESP's.  The service life of this equipment was not given,

but the average service for the study ranged from 7 to 10

years.

     The first point of inquiry dealt with the overall

experience with ESP's from an operational and maintenance

viewpoint.  Responses were as follows:

Excellent
Good
Fair
Poor
Operation
14.8%
45.5%
29.5%
10.2%
Maintenance
13.6%
52.3%
13.6%
20.5%
                              3-26

-------
     The second question dealt with specific areas of poten-

tial difficulty.  With respect to failure of discharge

electrodes, results were as  follows:

          Frequency of Discharge Electrode Failures

                     Frequent - 29.5%
                     Infrequent - 38.6%
                     Very Seldom - 28.4%

     Of the three major types of failures normally experi-

enced  (fatigue, corrosion, electrical arcing), 61.7 percent

of all industries indicated  that electrical erosion (arcing)

was the major cause.  Corrosion and fatigue ranked second

and third respectively.  This ranking is probably typical of

the electric utility industry.

     Failure in the rapping  system, which usually includes

electric or pneumatic vibrators or electromagnetic or mechani-

cal impact-type rappers, was evaluated as follows:

          Frequency of Rapper or Vibrator Failures

                      Frequent - 9.1%
                      Infrequent - 38.6%
                      Very Seldom - 47.7%

     As would be expected, the data indicated that the

vibratory type of mechanism  requires more maintenance than

the impulse type.

     Frequency of problems created by collecting surfaces

was listed as follows:
                              3-27

-------
                 Frequent - 4.5%
                 Infrequent - 7.9%
                 Very Seldom - 68.2%

The major cause cited for collecting surface failure was

fatigue at the points of plate suspension.  Corrosion was

ranked as the second major cause.

     Removal of dust, once precipitated, is historically one

of the major causes of precipitator malfunction, contribu-

ting also to other difficulties, such as discharge electrode

failure.  The survey showed the following frequency of dust

removal problems:

                 Frequent - 36.4%
                 Infrequent - 42.0%
                 Very Seldom - 20.5%

By far, the majority of problems cited were with plugging of

the dust hopper.  Difficulties with screw conveyors and dust

valves were ranked second and third.

     Suspension insulators, manufactured of glazed porcelain,

fused silica or alumina oxide, are used to support and

isolate the high-voltage elements of a precipitator.  These

insulators are vulnerable to failure due to electrical arc-

over resulting from accumulations of dust or moisture.

Regarding problems with suspension insulators, the utilities

indicated the following:

                 Frequent - 8.0%
                 Infrequent - 34.1%
                 Very Seldom - 48.9%
                             3-28

-------
It is apparent that this is not a significant source of

operational difficulty.

     The final phase of the survey asked the user's opinion

of which ESP components were the major cause of trouble in

his experience, in terms of both reliability and expense.

The responses, again based on 63 utilities reporting on 88

ESP's, were as follows:

                 Major Maintenance Problems

                 Discharge Electrodes - 35.2%
                 Dust Removal Systems - 5.7%
                 Rappers or Vibrators - 13.6%
                 Collecting Plates - 31.8%
                 Insulators - 1.1%

     Several conclusions may be drawn from the results of

this survey:

     1.   Although precipitator manufacturers obviously can
          improve their products, most of the utilities
          reporting are satisfied with the precipitator as
          a functioning piece of equipment.  Only 10.2
          percent gave a "Poor" rating.

     2.   Discharge electrodes are the principal source of
          malfunction, requiring application of design
          expertise.  Recognizing this, ESP manufacturers
          are concentrating on design improvements.

     3.   Design, operation, and maintenance of the dust
          removal system are extremely important.  The
          utilities reported a high incidence of discharge
          electrode failure along with a high degree of
          hopper pluggage.  Dust buildup into the high-
          voltage system, in addition to inhibiting perfor-
          mance, can accelerate failure of discharge elec-
          trodes.
                             3-29

-------
     The TC-1 Committee of the APCA suggested close coopera-



tion between user and supplier, coupled with exchange of



information between the various user industries.  Such a



program could lead to mutual development of an electrostatic



precipitator that fills the needs of the users.



     The survey was only the initial phase of a comprehensive



study of experience with high-efficiency collectors of



various types.  The survey data are considered preliminary,



in that considerably more detail can be derived statistic-



ally.  The TC-1 Committee is continuing work with this data



base and intends to report additional findings, conclusions,



and recommendations.
                            3-30

-------
                       4.0  MAINTENANCE



      This section presents a program for ESP  surveillance


 and maintenance that could enable a utility to  reduce mal-


 functions and downtime.   It describes typical procedures


 followed  by utilities during startups and malfunctions, and


 discusses costs of ESP maintenance.


 4.1   MAINTENANCE PROGRAM  FOR PRECIPITATORS


      Table 4-1 lists items to consider in establishing


 maintenance procedures for ESP's.   Table 4-2, given at the


 end of  this subsection, is a troubleshooting  chart for use


 in determining the cause  of common  ESP malfunctions, with


 suggestions for remedying these problems.


 4.1.1   Operational Procedure

                      9
 Prestartup Inspection -  Before implementing  startup proce-


 dures,  all precipitator components must be  thoroughly in-


 spected to ensure  that equipment  is ready for operation.


General


1.   Visually  inspect the  mechanical dust collector units,
     induced draft fans,  and dust handling  equipment.


2.   Close  and  secure all  access hatches.


3.   Determine  that all internal areas  are  completely free
     of tools,  scrap  and  foreign material before the fan(s)

     is started.
                             4-1

-------
Table 4-1.  MAINTENANCE ITEMS FOR ELECTROSTATIC PRECIPITATORS
A.   Daily Log

     1.   Boiler operating parameters
     2.   Flue gas analysis
     3.   Coal characteristics
     4.   Particulate collector control readings
     5.   Transmissometer calibration

B.   Daily

     1.   T-R electrical control set readings
     2.   Rapper and vibrator control settings
     3.   Ash removal system
     4.   Check T-R control room ventilation system

C.   Weekly

     1.   Check rappers and vibrators visually for proper
          operation

     2.   Check control sets internally for dirt

     3.   Make sure air filters to control sets and precipi-
          tator top housing are not plugged

D.   Monthly Log

     1.   Check precipitator top housing for pressurization

     2.   Check standby fan operation manually

E.   Quarterly

     1.   Clean and dress HW-FW electrical distribution
          contact surfaces

     2.   Lubricate pivots

F.   Semi-Annually

     1.   Clean and lubricate access door hinges and test
          connections
                            4-2

-------
         Table 4-1  (cont'd).  MAINTENANCE ITEMS FOR

                 ELECTROSTATIC PRECIPITATORS


     2.   Perform exterior inspection for loose insulation,
          corrosion, loose joints, etc.

     3.   Check for gas leakage points in or out

G.   Annually

     1.   Perform thorough internal inspection

          a.   check for possible leaks of oil, gas or air
               at gasketed connections

          b.   check for corrosion of any component

          c.   check for broken or misaligned wires, plates,
               insulators, rappers, etc.

          d.   check high voltage switch gear and interlocks

          e.   clean all insulators and check for hairline
               cracks or tracking

          f.   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
                             4-3

-------
 4.   Verify that primary power is available to thermostati-
     cally controlled heaters if provided.  Circuit breakers
     for  this equipment may have to be energized several
     hours prior to  system operation.

 5.   Check all  interlocks and voltage control modules.

 6.   Check main OFF/TEST Selector Switch and place in OFF
     position.

 7.   Check grounding connections.

 Rapper  System

 1.   Ground the power unit in the control cubicle.

 2.   Check distributor switch rapper connections.

 3.   Check ground  return leads for proper connections to
     sectiorialized control adjustments.

 4.   Check for  proper mechanical adjustment.

 5.   Adjust each manual sectional control for proper rapping
     intensity.

 6.   Check spark rate feedback circuit and  signals for
     proper connections.

 Rectifiers and  Transformers

 1.   Check all  connections, switches, and insulators.

 2.   Check oil  (liquid) levels.

 3.   See  that high-tension duct vent ports  are  installed  and
     free.

 4.   Be sure grounds are completed on transformer-rectifiers,
     bus  duct,  and conduits.

 Routine Startup

     If hot gases  are to be passed through  the  precipitator,

 the system should  be warmed to operating  temperature  before

gas flows are started. (See Section 4.2).   The  following

procedures are  then  performed.
                              4-4

-------
     Close all inspection ports and adjust dampers for
proper air flow.
     Energize high-voltage current.
     Start collector and discharge electrode rappers, if
provided on the system.
     Turn on ash discharge system.
     Bring fan to full rpm with exit damper closed.
     Adjust damper for desired gas flow.
     Record system pressure drop and fan pressure drop.
     If the system is not equipped with external heating
facilities, the procedure should be reversed so that the
inlet gases enter before the precipitator is energized.
When the precipitator reaches operating temperature, turn on
the high voltage power.
     If the precipitator contains air and a potentially
explosive gas mixture is introduced into the unit, the
system must first be purged with an inert gas.
     Any conveying systems that follow the hopper conveyor
must be turned on before the hopper conveyor.
     Routine Operation
     Check pressure drops to prevent unusually high or low
values.
     Maintain precipitator current at normal level.  Correct
any deviations greater than about 5 percent of normal current.
                             4-5

-------
     Maintain sparking rate at optimum density.



     Maintain rapper frequency and intensity to give maximum




 collection efficiency.



     Check to see that thermostatically controlled heaters



 are  properly operating.



     If combustible gases are present in the precipitator,



 check  the gas composition to be sure it is not in the



 explosive range.



     See that all water cooling requirements are properly



 met, including  any water-cooled bearings or pump stuffing



 boxes.  Check all drive belt tensions daily.  Periodically



 test fan inlet  dampers to verify that the dampers are free



 to move to fully closed and fully opened positions.  Inspect



 all  electrode and collector rapper mechanisms daily  for



 defective systems.  Examine insulators daily for potential



 deterioration.  Lubricate hopper conveyors and valves daily.



 Lubricate dampers and louvers to see that they function



 freely.




     Instrumentation to register current, voltage, and



 spark rates to  the precipitator can be red-lined to  indicate



 norms.   Abnormal readings indicate trouble; if these signs



 are ignored, serious equipment failures can result in exces-




 sive emissions  and plant shutdown.  Shutdowns can usually be




prevented if operators heed warning signals.
                             4-6

-------
Routine Shutdown


     Shutdown is performed in reverse fashion from startup.


Deenergize the precipitator, purge if necessary, then shut

off gas flow.  When all collectors and electrodes have been

rapped clean, discontinue use of rappers.  When hoppers are


empty, turn off conveyors and discontinue any liquid washing.
                   Q TO
4.1.2  Maintenance '


     Maintenance of precipitators falls into categories of

preventive maintenance and maintenance to correct failures.


A preventive maintenance schedule should be established for

each installation, detailing the precipitator parts to be

checked and maintained daily, weekly, monthly, quarterly,

semiannually, annually, and on  a situational basis.

     Daily - It is obvious that gross departures from normal

readings on the transformer-rectifier meter and transmis-

someter indicate trouble.  It is not so widely recognized


that small variations, often too slight to be noticed with-


out checking of daily readings, can  indicate impending


trouble.

     Problems that usually have a gradual, rather than


sudden, influence  on precipitator performance include  (1)


air inleakage at air heaters or in ducts  leading to  the


precipitator,  (2)  dust buildup  on precipitator  internals,


and  (3) deterioration of electronic-control components.
                              4-7

-------
 Such problems can be indicated by small, but definite, drift



 of daily meter readings away from baseline values.



     Grossly abnormal readings indicate a serious problem,



 and 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



 to ground through ash accumulating above a plugged hopper or



 from clinker formation on a wire.



     Fluctuating voltage, dipping to low values, suggests a



 broken and swinging discharge electrode.  Fluctuation of



 spark-rate meter readings does not necessarily indicate a



 problem unless there is confirmation by fluctuating voltage



 and/or current readings.



     Operators should never try to correct deviant meter



 readings by adjusting control set points.  An automatic-



 control response range should accommodate normal variations



 in load conditions.  If major changes occur, such as would



 result from switching to a coal substantially different from



 that for which the precipitator was designed, the precipita-



 tor manufacturer should be called in to retune the installa-



 tion.  If no such major changes have occurred, then variant



meter readings indicate problems that must be detected and



corrected.
                             4-8

-------
     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 grow-



ing ash piles can push internal components out of position,



causing misalignment that may drastically affect performance.



Field engineers note that utilities sometimes attempt to



preserve alignment by welding braces to hold collecting-



electrode plates in position.  This practice is inadvisable,



since restraining the plates interferes with the effective-



ness of the rapping action that keeps them clean.



     Although various indicators and alarms can be installed



to warn of hopper-ash buildup and of ash-conveyor stoppage,



the operator car doublecheck by testing skin 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.  Gener-



ally, however, low temperature 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 collected sub-



sequently will pile up at the top.



     If the temperature of all hoppers appears low to the



touch, the operator should check the ash-conveyor system to
                              4-9

-------
 see  if  it has stopped or if dust agglomeration is so great



 that the conveyor can no longer handle all of the fly ash.



      Hopper plugging is sometimes caused by low flue-gas



 temperature, which permits moisture condensation.  This



 results from carrying the boiler exit-gas temperature too



 low  or  from excessive leakage of ambient air into the flue-



 gas  duct.  Hoppers are particularly prone to plugging during



 startup after an outage, when they are cold and normally



 damp.



      Daily checking of the control-room ventilation system



 minimizes the possibility of overheated control components,



 which can cause drift of control set points and accelerated



 deterioration of sensitive solid-state devices.



      Weekly - Solenoid-coil failures, fairly common when



 high voltage was used, are rare with modern low-voltage  i



 equipment.  Still, a weekly check of all units is advisable.



 Rapper  action should be observed visually, and vibrator



 operation confirmed by feel.  In addition, since rapping



 accelerations of 30 g are often required for proper collec-



 tion, an accelerometer mounted on the plates should be



 checked to verify that rapping acceleration is adequate.



 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
                             4-10

-------
dirt can cause false control signals and can damage such



large components as contactors and printed circuits.



     Finally, filters in the air supply lines to control



cabinets and the precipitator top housing should be checked



and cleaned if necessary to prevent plugging.



     Monthly - Most new precipitators incorporate pressurized



top housings that  enclose  the bushings through which high-



voltage connections are made to the discharge electrodes



within the precipitator box.  Pressurization assures that,



if there is gas leakage where the bushings penetrate the



precipitator hot roof, gas flow will be into the precipita-



tor rather than out from it.  Leakage from the precipitator



into the housing could cause ash deposits and/or moisture



condensation on the bushings, with risk of electrical



breakdown at the typical operating potential of 45 kV d.c.



     Inspect bushings visually and by touch for component



vibration.  Check  differential pressure to be sure that the



fan that pressurizes the housing is in good operating condi-



tion.  Also, operate manually the automatic standby fan to



make sure it is service-ready.



     Quarterly - Quarterly maintenance includes inspection



of electrical-distribution contact surfaces, which should be




cleaned and dressed and the pivots lubricated, if this is




not done even more frequently.  These could cause false
                              4-11

-------
 signals.  Further, since transmissometer calibration is



 subject  to drift, calibration should be verified to avoid



 the possibility of false indications of precipitator per-



 formance.



      Semiannually - Routine inspection, cleaning, and lubri-



 cation of hinges and test connections should be done semi-



 annually.  If  this task is neglected, extensive effort



 eventually will be required to free up test connections and



 access doors,  involving expensive downtime.  Performance



 tests may be required at any time, and should not be delayed



 while connections are made usable.  An effective preventive



 measure  is to  recess fittings below the insulation.



      Exterior  inspection for corrosion, loose insulation,



 exterior 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 emis-



 sions.



      Annually  - Scheduled outages must be of sufficient



 duration to allow thorough internal inspection of the preci-



 pitator.  Checks should be made for  (1) possible leakage of



 oil,  gas, or air at gasketed connections,  (2) corrosion



where heat loss is great or gas temperatures are low, and



 (3) possible misalignment of internal components.  Also,



high-voltage switchgear should be inspected for possible
                             4-12

-------
binding, misalignment,  or  defeated  interlocks - defects that
create a safety  hazard  in  addition  to reducing performance.
     All insulator  support bushings, rapper insulators, and
antisway insulators should be cleaned and inspected for
hairline cracks  and evidence of tracking.  Faulty insulators
can cause excessive sparking and voltage loss, and can fail
abruptly, possibly  even explode, if allowed to deteriorate.
     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.
     Situational -  Certain preventive-maintenance and safety
checks are so  important that they should be performed during
any outage of  sufficient length, without waiting for sched-
uled downtime.   Air flow readings should be compared with
baseline values  to  detect  possible  performance deteriora-
tion.  Further,  meter readings taken immediately upon
restoring the  precipitator to service can serve as a check
on any changes that may have resulted from maintenance done
during the outage.
     Critical  internal  alignments should be checked whenever
an outage allows and immediate corrective action taken if
misalignment is  discovered.  Control-cabinet and top-housing
interiors should be checked during  any outage of 24 hours or
                              4-13

-------
more and cleaned if necessary.  Any outage of more than 72



hours provides an opportunity to check grounding devices,



alarms, interlocks, and other safety equipment, and to clean



and inspect  insulators and bushings.



Safety



     It is obvious that high-voltage electricity can be



extremely dangerous.  Therefore, all practical safety



measures must be observed even though the system incorporates



interlocks and other  safety devices.



     The system should never be adjusted with the high-



voltage power on.



     Rectifiers and diodes have heat sinks that could seri-



ously shock  a person  touching them.



     The rapper circuitry, which is independent of the high-



voltage circuitry, is nonetheless also dangerous and must be



treated as such.



     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 main-



tenance or adjustment is attempted.




     Explosive gas mixtures could be created if air is



introduced into systems.  If necessary, the system should be



purged with an inert  gas before introducing air.  In all




cases,  a system should be purged with fresh air before it is



entered.
                             4-14

-------
                   Table  4-2.   TROUBLESHOOTING CHART  FOR  ESP'S
     Symptom
     Probable cause
          Remedy
1.   No primary voltage
     No primary current
     No ESP current

     Vent fan on
     No primary current
     No ESPcurrent
     Vent  fan off
     Alarm energized

     Control unit trips
     out an overcurrent
     when  sparking
     occurs at high
     currents

     High  primary current
     No ESP current
DC overload condition
Misadjustment of current
limit control

Overdrive of rectifiers

Fuse blown or circuit breaker
tripped

Loss of supply power

Circuit breaker defective
or incorrectly sized

Overload circuit incorrectly
set

Short circuit condition in
primary system

Too high ESP voltage for
prevailing operating
conditions

High-voltage circuit
shorted by dust buildup
between emitting &
collecting electrodes
Check overload relay setting

Check wiring and components

Check adjustment of current
Limit control setting

Check signal from firing circuit module

Replace fuse or reset circuit  breaker


Check supply to control  unit

Check circuit breaker


Reset overload circuit


Check primary power wiring


Lower the ESP voltage



Remove dust buildup

-------
                            Table  4-2  (continued).   TROUBLESHOOTING CHART  FOR  ESP'S
                     Symptom
I
M
CTi
                5.    Low primary voltage
                     High  secondary cur-
                     rent
     Probable cause
                                             Slack or broken  emitting
                                             electrode wire shooting
                                             the high "V"  circuit

                                             Circuit comnonent  failure
Trouble in ESP

1) Dust buildup  in hopper;
   check meters:

       - ammeter very high
       - kv meter very low
         (1/2 normal)
       - milliamperes very high

2) Metallic debris left in
   unit during shutdown for
   maintenance

3) Unhooked collecting plate
   touching emitting frame

4) Broken support insulator

5) Excessive dust buildup
   on hopper beams or cross
   member

Short circuit in secondary
circuit or pptr.
                                                                                        Remedy
                                  Deenergized ESP &  remove or replace broken
                                  or  slack wire
                                  Check transformer-rectifier & ESP:   ground T-R high "V"
                                  connector to ESP
                                                                               Clean off dust buildup
                                                                               Deenergize ESP and remove



                                                                               Repair


                                                                               Repair

                                                                               Clean
Check wiring and components in  high voltage
circuit;   Check ESP for:

-------
            Table  4-2   (continued).    TROUBLESHOOTING CHART FOR ESP'S
     Symptom
I
M
-J
6.
7.
     Abnormally  low ESP
     current and p
     voltage with no
     sparking
                   Spark  meter reads
                   high-off  scale
                                  Probable  cause
                                           Misadjustment  of current and/or
                                           voltage limit  controls
Misadjustment of firing circuit
control

Heavy coating on emitting
electrode wires

Stream of cold air entering
ESP from defective door gasket
duct opening, inlet gas
system rupture - condensation

Wet dust clinging to wires
causes extremely low milli—
ammeter readings

Severe arcing in the ESP
without tripping out the unit

Continuous conduction of
spark counting circuit
                                                                                      Remedy
                                    Interior dust buildup
                                    Full hoppers
                                    Broken wires
                                    Ground switch left on
                                    Ground jumper left on
                                    Foreign material on high  voltage frame or wires
                                    Broken insulators

                                  Check settings of current and voltage limit controls
                                                               Turn  to maximum and check  setting of current
                                                               and voltage limit controls

                                                               Check emitting frame vibration and emitting
                                                               vibration shaft insulator

                                                               Repair
                                                               Eliminate source of condensation
                                                               Eliminate cause of arcing
Deenergize, allow integrating capacitor to discharge
and re-energize

-------
                           Table  4-2  (continued).   TROUBLESHOOTING  CHART  FOR ESP'S
                    Symptom
>£>
 I
M
00
               10.
               11.
Low primary voltage
and current
No spark rate indi-
cation

Spark meter reads
high
Primary voltage and
currant very un-
stable

No spark rate indi-
cation voltmeter and
ammeter unstable
indicating sparking
No response to vol-
tage limit adjust-
ment
Does respond to
current adjustment

No response to spark
rate adjustment
Does respond to
other adjustment
                                                 Probable cause
Spark counter  counting
60 cycles peak

Misadjustment

Loss of limiting control



Failure of spark meter

Failure of integrating
capacitor
Spark counter  sensi-
tivity too low

Controlling on current
limit or spark rate
Controlling  on voltage
or current
                                                                                       Remedy
Readjust controls


Readjust

Replace control



Replace spark meter

Replace capacitor

Readjust sensitivity
None needed  if unit is operating at maximum current
or spark rate

Reset current and spark rate  adjustment if neither
is at max

None needed  if unit is operating at maximum voltage
or current
Reset voltage and current adjustment if neither
is at max

-------
Records

     Accurate daily logs should be kept of all aspects of

precipitator operation, including electrical data, changes

in rapper and boiler operation, and variations in fuel

quality.  Such logs aid the preventive-maintenance effort by

providing clues to probable causes for changes in perform-

ance.

     Following the prescribed maintenance procedures and

maintaining accurate logs will provide benefits that justify

the effort.

4.2  UTILITY PROCEDURES AND RECORDKEEPING DURING STARTUP
     AND MALFUNCTIONS

4.2.1  Utility Startup Procedures

     Upon restarting of a coal-fired boiler that has been

out of service for a period of time, it is fired with oil or

gas for 4 to 5 hours.  During this time the pulverizers are

turned on for about 5 minutes at a time until operation is

sustained and stable; more than one mill is always run.

About 8 hours is required to bring a unit on line, i.e. when

the steam pressure reaches 2.8 MPa  (400 psi); the turbines

are then turned over.  The ESP is not energized until the

temperature reaches the design range, which is about  107-

135°C (225-275°F) for cold-side ESP's.  The precipitator is

turned on manually, usually 1 hour after the unit is  firing

coal.
                             4-19

-------
     Times required to bring the boiler to proper operating



temperature vary, but the described procedure is representa-



tive of that for a coal-fired boiler.



4.2.2  Utility Procedure and Recordkeeping During

       Malfunctions



     Part 60 of Title 40, Code of Federal Regulations,



Section 60.7, as amended, December 16, 1975, requires that



a utility report excess emissions caused by malfunctions or



other reasons by submitting a written report to the Admini-


                                  19
strator for each calendar quarter.    The report is to



include the magnitude of excess emissions as measured by the



required monitoring equipment, reduced to the units of the



applicable standards; it is to give the date and time of



commencement and completion of each period of excess emis-



sions.  Periods of excess emissions due to startup, shut-



down, and malfunction are be be specifically identified.



The nature and cause of any malfunction if known, the cor-



rective action taken, or preventive measures adopted are to



be reported.  Each quarterly report is to be submitted by



the 30th day following the end of the calendar quarter.



     This section compares the methods of reporting ESP



malfunctions practiced by two U.S. utilities.  The reporting



procedures of most other U.S. utilities probably encompass



similar features.
                             4-20

-------
     In the case of  the  first utility, a reportable malfunc-

tion is considered to  be any sudden or unforeseen malfunc-

tion of particulate  control equipment that causes or could

cause any of  the utility's units  to exceed specified limits

for a period  of 4 or more hours.  When this occurs the

following procedure  is followed:

     1.   The malfunction is reported by phone or telegram
          to  the EPA regional office and to state or local
          officials.   The air quality branch of the utility
          is  also contacted.

     2.   The plant  superintendent submits a report to the
          EPA regional office,  with copies to various
          branches of  the utility.  The report includes the
          following:

          a.   Time  and date excess emissions began and
               ended.

          b.   Time  and date the  breakdown causing the
               excess  emissions began and ended.

          c.   Type  of emission,  estimated rate, and copies
               of the  opacity monitor records.

          d.   Cause of the malfunction.

          e.   Operation and maintenance procedures, prior
               to and  during the  malfunction, designed to
               prevent such an  occurrence.

          f.   Additional steps taken to minimize the extent
               or duration of the malfunction.

          g.   Future  plans to  minimize the possibility of
               similar malfunction.

     Monthly  records are kept,  by plant and unit, of all

malfunctions, total  hours transformer-rectifier  (T-R) sets

are operated, number of  hours T-R sets are not operating
                              4-21

-------
 (broken down into 24 hours and >24 hour intervals), maximum



number of sets out at one time, and the monthly/yearly



availability of the ESP unit in percent.  In addition, daily



logs are kept on each ESP unit, with remarks on outages of



various sections of the ESP.  Costs for operation and



maintenance on all ESP's are also tabulated.



     With the second utility, an ESP is considered to be



malfunctioning if opacity is 20 percent or greater.  There-



fore, an ESP could be operating at less than its design



efficiency and still remain in operation.  If 20 percent



opacity is reached, EPA is subsequently notified, but the



boiler and ESP are not taken out of service until the



following weekend; the necessary maintenance is then per-



formed.  Corrective actions and preventive measures are



reported to EPA in a brief letter, which may not be sent



until a month or two after the malfunction has occurred.



4.2.3  Outages - Forced and Scheduled



     Forced outages result from unpredicted malfunctions



requiring immediate shutdown.  Planned outages are scheduled



for maintenance and inspection.




     Forced outage malfunctions, by definition, involve



shutdown and startup.  Some malfunctions, however, can be



resolved online and do not require a shutdown.  In these



instances boiler operation may be reduced to as low as 10




percent of design load without appreciably increasing emis-



sions.




                             4-22

-------
     Planned outages require complete shutdown of the unit

to enable maintenance personnel to perform such tasks as

slag cleanout, ESP repair, and boiler tube repair.

4.3  COSTS OF COLD SIDE ESP MAINTENANCE AND OPERATION20

     The annualized costs of maintenance and operation of 18

model cold-side ESP's have been estimated.  These annualized

costs are comprised of the following items:

     Utilities, including water for ash slurries and clean-
     ing; electricity for fans, valves, lighting, controls,
     hoppers, rappers, and charge of plates.

     Operating labor, including supervisory and skilled and
     unskilled labor required to operate, monitor, and
     control the ESP.

     Maintenance and repairs, consisting of manpower and
     materials to keep the unit operating efficiently.  The
     function of maintenance is preventive and corrective.

     Overhead, a business expense that is not charged
     directly to a particular part of a process but is
     allocated to it.  Overhead costs include administra-
     tive, safety, engineering, legal, and medical services;
     payroll; employee benefits; and public relations.

     Fixed Charges, which continue for the estimated life of
     the system and include costs of the following:

     0    Depreciation - the charge for losses in physical
          assests due to deterioration  (wear and tear,
          erosion and corrosion) and other factors, such as
          technical changes making the physical assets
          obsolete.

     0    Interim replacement - costs expended during the
          year for temporary or provisional replacement of
          equipment that has failed or malfunctioned.
                             4-23

-------
      0    Insurance - costs of protection from loss by a
          specified contingency, peril, or unforeseen event.
          Required coverage could include losses due to
          fire, personal injury or death, property damage,
          embezzlement, explosion, lightning, or other
          natural phenomena.

      0    Taxes - including franchise, excise, and property
          taxes leveed by a city, county, state, or Federal
          government.

      0    Capital costs due to interest on borrowed funds.

 4.3.1 Basis of ESP Annualized Cost Estimates for 18 Model
       Plants

      The capital and annualized costs of electrostatic

 precipitators can vary significantly with design philosophy

 and  site-specific factors.  Factors having a major cost

 impact are plant size  (capacity), remaining life, and capa-

 city factor; sulfur and ash content and heating values of

 the  coal; maximum allowable particulate emission rate;

 control system status  (new plant or retrofit); and replace-

 ment power requirements.

      As a means of illustrating the impact of site and

 process factors on total installed and annualized costs of

 ESP's, 18 model plants have been defined and cost estimates

 prepared for each.  The coverage here is restricted mainly

 to annualized operation and maintenance costs.  These esti-

mates, presented in the following sections, are in January

 1976 dollars and do not include escalation through project

completion or replacement power.
                             4-24

-------
     The 18 model plants  analyzed  for ESP costs were selected


to incorporate  three  factors  that  affect costs:  plant size


 (capacity), installation  status, and degree of participate


control required.   Boiler capacities of 150 MW, 300 MW, and


450 MW were considered.   Both new  and existing ESP applica-


tions are  considered  for  each boiler size.  Each plant size


is also analyzed in terms of  three particulate control


requirements:   94 percent control  on Eastern high-sulfur


coal and corresponding  to a specific collecting area (SCA)


of 640  (200); 99 percent  control on Eastern low-sulfur coal,


corresponding to an SCA of 1920  (600); and 99.9 percent (10%


opacity) control on Western low-sulfur coal, corresponding


to an SCA  of 4570  (900).   Specific collecting area  (SCA) is


the ratio  of the area of  the  collecting plates in the ESP to

                                      033        23
the flue gas flow rate  in thousands  [m /10 m /min  (ft /10


acfm)].


     Other variables  such as  remaining plant life and plant


capacity factor are selected  to be representative of each


model plant.  Operating costs for  such items as utilities,


which vary with geographical  location, are considered repre-


sentative  of a  midwest  location.   Table 4-3 identifies the


characteristics and major assumptions for the model plants.


Table 4-4  presents  the  analyses of the coals used in the


study.   Table 4-5 gives capital costs for all 18 model



plants.
                              4-25

-------
            Table 4-3.   SUMMARY OF CHARACTERISTICS AND ASSUMPTION FOR MODEL PLANTS
                 Model plant  parameters
I
to
            Plant capacities,  megawatts

            Plant status

            Particulate control  require-
             ment
            Boiler data

              Capacity factor

              Heat rates,  flue gas flow
              rates, and remaining life
            Operating cost factors

            Electricity cost

            Taxes
          Characteristics and assumptions
150,  300,  and  450  (single boilers)

Existing (retrofit.) and new

Assumed levels of  99.0 percent control required
on Eastern high sulfur coal  99.0 percent control
required on Eastern low sulfur coal; and 99.9  percent
control (10% opacity) required on Eastern low  sulfur coal.
Assumed 0.6 for all  plants
Capacity
   MW

  150 existing
  150 new

  300 existing
  300 new

  450 existing
  450 new
            Flue gas   Remaining
Heat rate^,  flow rate,    boiler
 Btu/kWh    acfm/MW    life, yrs.

  10,000       3,400        10
   9,300       3,200        35

   9,500       3,275        15
   9,200       3,175        35

   9,300       3,140        20
   9,200       3,080        35
Based on averages for midwest  region

20 mills/kWh

4%
            a MJ/kWh - Btu/kWh x 1055.87 J/Btu *  10°  J/MJ

            b m3/min/MW = acfm/MW x ( '  £•£—-)

-------
I
to
-J
               Table 4-3  (Continued)
SUMMARY OF CHARACTERISTICS AND ASSUMPTIONS


 FOR MODEL PLANTS
               Capital cost

               Retrofit characteristics


               Capacity derating


               Energy penalty

               Replacement capacity cost
   9%

   Longer duct runs,  tight space'constraints,  increased
   construction labor costs

   ESP - 0.5 percent
   Eastern coal 0 percent

   ESP - 0.5 percent

   S400/KW

-------
I
CO
00
                 Table 4-4.  COAL ANALYSES ASSUMED FOR ESP COST EVALUATION
Coal type
Eastern high sulfur
Eastern low sulfur
Sulfur content,
percent
3.0
1.0
Ash content,
percent
15
15
a
Heating value ,
Btu/lb
11,000
11,000
MJ/Kg - Btu/lb x
                             105'|;*7
                                   Ib
0.4535924 Kg
1000 J
  MJ

-------
                    Table  4-5.   CAPITAL COSTS FOR ELECTROSTATIC PRECIPITATORS
Cost
element
Existing Plants
0 Electrostatic
precipitator
@ 200 SCA
0 Electrostatic
precipitator
@ 600 SCA
0 Electrostatic
precipitator
@ 900 SCA
New Plants
e Electrostatic
precipitator
@ 200 SCA
0 Electrostatic
precipitator
@ 600 SCA
0 Electrostatic
precipitator
@ 900 SCA
Plant size/capital cost
150 MW
$, MM

3.74

8.35

12.14


3.34

6.69

9.93

$AW

24. -9

55.7

80.9


22.3

44.6

66.2

$ per ft*
plate area

35.73

27.32

26.46


33.95

23.25

23.00

300 MW
$, MM

7.75

13.94

20.21


6.13

11.63

17.15

$/kW

25.8

46.5

67.4


20.4

38.8

57.2

$ per ft*
plate area

38.17

23.67

22.87


31.15

20.36

20.02

450 MW
$, MM

12.06

20.13

29.15


9.90

17.14

25.18

$/kW

26.8

44.7

64.7


22.0

38.1

56.0

$ per ft*
plate area

41.16

23.76

22.93


34.44

20.63

20.20

I
NJ
VO
      Metric conversion:   SCA -  1  ft /10   acfm x 3.2 = 1 m2/103 m /min.

-------
4.3.2  Annualized Costs



     Annualized costs for the 18 model plants are presented



in Table 4-6.  The annual costs in mills per kilowatt hour



decrease as the size of the units increases for most cases.



Costs for retrofit cases are higher because of the effects



of the higher capital cost for retrofitting.
                            4-30

-------
              Table 4-6.  ANNUALIZED COSTS FOR ELECTROSTATIC PRECIPITATORS
I

U>
Cost
element
Existing Plants
Electrostatic
pfecipitator
@ 200 SCA
Electrostatic
precipitator
@ 600 SCA
Electrostatic
precipitator
@ 900 SCA
New Plants
Electrostatic
precipitator
@ 200 SCA
Electrostatic
precipitator
§600 SCA
Electrostatic
precipitator
@ 900 SPA
Plant size/annual cost
150 MW
$, MM

1.11

2.43

3.50


0.77
'
1.50

2.19

mills/kWh

1.41

3.08

4.44


0.97

1.89

2.77

300 MW
$, MM

1.98

3.57

5.15


1.35

2.57

3.76

mills/kWh

1.25

2.26

3.26


0.85

1.62

2.38

450 MW
$, MM

2.83

4.79

6.91


2.14

3.75

5.49

mills/kWh

1.19

2.02

2.92


0.90

1.58

2.32

                                        23                 233
          Metric conversion:  SCA - 1 ft /10  acfm x 3.2 = 1 m /10 m /min.

-------
          5.0  INSPECTION TECHNIQUES FOR EVALUATING
                   MAINTENANCE PROCEDURES

     This section describes procedures for inspection of an
ESP at a utility operating a coal-fired boiler.  The circled
numbers correspond to those on the example inspection check-
list in Section 5.2.
5.1  TYPICAL ESP INSPECTION PROCEDURE
                                                     21
     (A)   Observe the plume before entering the plant''
Opacity of the plume is the most indicative guide to  the
performance of an ESP.  If plume opacity is greater than it
was  under similar boiler load conditions at an earlier time,
either the collection efficiency of the ESP has decreased or
the  fuel quality has decreased.
     Determine the plume's equivalent opacity.   (Do not
mistake water vapor condensation for particulate emission.)
Table 5-1 illustrates possible operating factors that may be
causing a visible emission.  If visible emissions exceed
applicable standards, use the standard form and follow
established procedures for recording the violation.
     (1)   Obtain basic boiler data or update boiler data
from the previous inspection.  Check for changes in fuel
quality that might affect ESP operation and emissions.
                             5-1

-------
      Table 5-1.  PLUME CHARACTERISTICS AND OPERATING

             PARAMETERS FOR COAL-FIRED BOILERS
 Stack
 plume
 Associated
 pollutant
Occurrence
   Coal
     Possible operating
   factors to investigate
White

Gray


Black
Reddish-
 brown
Bluish-
 white

Yellow
  or
brown
Particulate

Particulate


Particulate
Nitrogen
dioxide
Sulfur
trioxide

Organics
  common

  common


  common
   rare
   rare
   rare
Excessive combustion air

Inadequate air supply or
distribution

Lack of oxygen; clogged
or dirty burners or
insufficient atomizing
pressure; improper coal
size or type
Excessive furnace tempera-
ture, burner configuration,
too much excess air

High sulfur content in
fuel

Insufficient excess air
(Source:  Ref. 21)
                            5-2

-------
    (3)   Obtain or update general ESP data, noting any

efficiency tests since the last inspection or changes in the

operating parameters.  Find out what operating problems the

ESP has had.  The plant should provide a diagram showing

what fields are served by what transformers as a guide to

determining what fields are out when reading ESP controls.

    (T)   Check control set readings and compare with cali-

brated values for these controls.  Many times problems that

develop gradually can be recognized by small variations from

normal.  Check daily log to determine whether readings have

been drifting from normal.  Drift is indicative of such

problems as:

     a.   Air inleakage at air heaters or in ducts leading
          to the ESP.

     b.   Dust buildup on ESP internals.

     c.   Deterioration of electronic control components.

     If grossly abnormal readings are noted, they indicate a

serious problem and can aid in diagnosing the probable

cause.  Following are some examples:

     a.   One section grounded out - A voltage drop will be
          observed in the precipitator  (kV, d.c.), and
          primary transformer (V, a.c.).  There will be an
          increase in the primary transformer amps (I, a.c.),
          in the average precipitator amps, (I, d.c.), and
          in the precipitator spark rate.

     b.   Ash buildup on wires and plates will reflect high
          amps.
                             5-3

-------
      c.   A broken wire, not grounded, that is bouncing  from
          one collecting plate to another would show a
          decrease in precipitator voltage  (kV, d.c.), the
          transformer primary voltage  (V, a.c.), would
          increase.  Also, the needles will bounce as the
          wire  travels from one collecting plate to another.

      d.   A broken wire to the insulator  (shorted out) will
          be most noticeable if the T-R set is on full wave.
          The primary transformer amps (I, a.c.) will decrease,
          precipitator average amps  (I, d.c.) will decrease,
          transformer primary voltage  (V, a.c.), will
          increase, and precipitator voltage  (kV, d.c.)
          will  increase.

      Typical ranges of ESP control readings for proper

 operation are given below:

                            minimum   maximum   typical

 1.  Primary voltage, volts                     460/480 + 5%
 2.  Primary current, amps      50       200       125
 3.  ESP voltage kilovolts      30       100+    40-65
 4.  ESP current milli amps    250      1500+      750
 5.  Spark rate/min             10       100+       75


      It may be  difficult to determine whether a section  is

 out by reading  the ESP controls.  You may need the help  of

 the utility's malfunction records to determine which sec-

 tions are experiencing problems.

    (5)   Check pressure drops through the system and com-

 pare with the normal pressure drops.

    (j)   Check ash hoppers for proper operation.  Determine

 the interval between hopper cleanouts.  Check hopper skin

 temperature with the back of your hand.  Comparatively low

 temperature of  one or more hoppers could indicate a malfunc-

 tion of the ash removal system, causing bridging or plugging

of the hoppers  and subsequent ash buildup.


                             5-4

-------
    (l)   If possible, check the precipitator control room



and make sure that ventilation is adequate; check control



sets internally  for dirt, which can cause false signals and



cause components to deteriorate.



    (¥)   If possible, check insulators for signs of deteri-



oration such as  moisture and tracking from arc-over.  Make



sure air filters to control sets and top housing are not



plugged.



    Qf)   If possible, check rapper action visually and



confirm vibrator operation by feel.  You will not be able to



tell whether all of the rappers are operating properly



unless you  know  the sequence of rapping action.



    ^B)    Check  exterior of ESP for corrosion, loose insula-



tion, exterior damage, and loose joints.  Give special



attention to points where gas can leak, causing fugitive




emissions.



    dQ)    Review operating records for all aspects of preci-



pitator operation including electrical data, changes in



rapper and  boiler operation, and variations in fuel quality.



     Table  5-2 lists recommended recordkeeping requirements.



These records can provide clues to probable causes of changes



in performance.   Malfunctions since the last inspection



should be evaluated.  The inspector should spot-check these



records to  ensure that the plant is adhering to proper



operating procedures between inspections.
                              5-5

-------
                      Table 5-2.   RECOMMENDED RECORDKEEPING  REQUIREMENTS
                   Item
                                           Frequency
                                                                Comments
en
I
(Ti
ESP Controls

 Instrument calibration
 Primary current, A
 Primary voltage, V
 Operating current, mA
 Operating voltage, kV
 Spark rate, sparks/min

Pressure drop through system,
 in.

Rapper operation

Insulator condition

Fuel quality

 Sulfur, %
 Ash, %
 HHV, Btu/lb

Changes in boiler operation

Flue gas analysis,
 % by vol.
 (Circle CO2 or O2)

Soot blowing intervals

Malfunctions
                                       Initial measurement
                                            Daily
                                            Daily
                                            Daily
                                            Daily
                                            Daily

                                            Daily
Daily

Daily

Monthly
                                          As occurring

                                           Spot  checks



                                             Daily

                                          As occurring
                       Compare daily measurements
                       with red-lined readings.
                       Check for gross misreadings
                       or slow drift from redline.
Compare with initial
pressure drop measurement

Check frequency and intensity

Check for deterioration

State range of values  and
average
                        State hours or blows per day

                        Use standard  form for
                        describing malfunctions

-------
    Qj)    Estimation of ESP control efficiency

     Use design or, preferably, test efficiency after ascer-

taining that present operating conditions are consistent

with design or test conditions  (e.g., boiler load, ash and

sulfur contents of coal, precipitator operating temperature).

If such data are not available, perform the following calcu-

lation:

     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 precipi-
     tator field as follows:

       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.
                                        33        33
     Calculate corona power input per 10  m /sec  (10  ft /min)
     of flue gas  (i.e. watts per 103 m3/sec  (103 ft3/min).

     Obtain precipitator collection efficiency value from
     Figure 5-1.

     If power data are not available from meters on the

precipitator power supply panel, perform the following

calculation:
                             5-7

-------
            LU
            I—i
            o
            I—I
            U_
            u_
            LU

            IB
            z
            I—I
            I—
            o
            o
            o
                      25    50    75    100    125

                       CORONA POWER, WATTS/1000 CFM
150
      Figure 5-1.   Electrostatic precipitator collection


                efficiency vs. delivered power.



Metric conversion:   w/10 m /min = w/103 ft3/min f 0.028
                               5-8

-------
   .  Determine total square feet of precipitator collecting
     area  (plate area) from manufacturer's specifications.

     Obtain sulfur content of coal being burned from opera-
     tor.

     Use these values to determine expected collection
     efficiency from Figure 5-2.

     Actual emissions.  Actual emissions are computed

according to the following formula.

     AE =  (UE) (100-E)

where:

     AE = actual emissions  [(kg/hr)  (lb/hr)]
     UE = uncontrolled emissions  [ (kg/hr)  (lb/hr)]
      E = control device efficiency, percent

    ^J)    Comments

     Use this  section for describing items too long to be

entered on the form, such as deficiencies found during the

inspection and malfunctions occurring since the last inspec-

tion.

     The results of the inspection could also be summarized

here.  A copy of the entire checklist could be sent to the

utility with a letter that confirms that the inspection was

made, states any deficiencies, asks that they be corrected,

and makes recommendations for further improvement in opera-

tion and maintenance of the ESP.
                             5-9

-------
           700 -
        o
        «c
        o
        o
        o
                                                Bituminous
                                                Pulverized coal
Coal:
Boiler:
                                   Note:   each curve represents
                                   a band of values which could
                                   be expected to deviate above
                                   or below the curve.
                       1.0         2.0

                             % SULFUR IN COAL
     3.0
4.0
                       Figure 5-2.  Cold-side ESP.

                                 SCA vs.  % S

Metric conversion:  SCA - 1  ft2/103 acfm x  3.2 =  1  m2/103 m3/min
                                   5-10

-------
5.2  INSPECTION CHECKLIST FOR ELECTROSTATIC PRECIPITATORS IN
     THE ELECTRIC UTILITY INDUSTRY

FACILITY IDENTIFICATION

Facility Name: 	
Facility Address:

Inspection Date:
Person to Contact:

Source Code Number:
PREINSPECTION DATA SHEET

     Adequate information

     Inadequate information  (Obtain needed data during first
          inspection)
    (1)   PREENTRY DATA

Stack Plume  - Equivalent Opacity
                 (Circle one):
                         0  20  40  60  80  100
     Opacity regulation

         In compliance

     Smoke

   White             Grey

   Reddish Brown     Bluish White

BOILER DATA

a)   Service:  Baseload, standby,
       floating, peak:

b)   Total hours operation  (19	):

c)   Average capacity factor  (19	):

d)   Year boiler placed in  service:
                                      Not in compliance
                                               Black or Brown

                                               Yellowish Brown
                              5-11

-------
           e)    Generating capacity (MW):

           f)    Served by stack No.:

           g)    Fuel  consumption:
                Coal  Mg/yr (ton/yr)
                Oil m3/yr (bbl/hr)
                Gas mcm/yr (mcf/hr)

 Primary fuel  composition:  Circle  one   Coal
                                         Oil
                                         Gas
Range
Ash % to
%
Average
%
Sulfur % to %
J/Kg (Btu/lb)
J/l (Btu/gal)
J/m3 (Btu/ft3)
T) ELECTROSTATIC
to
to
to
PRECIPITATOR -



GENERAL DATA
 ESP  No.:

 Manufacturer:

 Type:

 Efficiency  (Design/Actual):

 Mass emission rate:

     g/acm  (gr/acf)
     Kg/hr  (#/hr)
     Kg/MJ  (#/MM Btu)

No. of cells or individual bus  sections:

No. of fields:

No. of cells:

Total plate area:
                            5-12

-------
Flue gas temperature @ inlet to
 ESP @ 100% load °C (°F):

Stack diameter:

Stack height:

Stack gas exit temperature:

    (?)   CONTROL PANEL READINGS

 Present    Calibrated    Present    Calibrated
operating    operating   operating    operating
 voltage
              voltage
current
voltage
                            Sparks/min.
     Spark rate: 	

    (D   AIR FLOW READING

     Pressure before ESP 	

     Pressure after ESP 	

    (?)   HOPPERS

Interval between hopper cleanouts
                                                 Field 1

                                                 Field 2

                                                 Field 3

                                                 Field 4

                                                 Field 5

                                                 Field 6
                                       Pascals (in)

                                       Pascals (in)



                                        hours.
     Cleanout and transport
       procedure

     General housekeeping
                                Satisfactory  Unsatisfactory

                                    D            D
                             5-13

-------
      CONTROL ROOM
                            Satisfactory  Unsatisfactory
 Ventilation

 Control sets condition          ||             j  I

(D    CONDITION OF INSULATORS

(?)    RAPPER OPERATION

id)    ESP EXTERIOR CONDITION

l])    MAINTENANCE AND OPERATIONS
      Records Kept:                 Yes    No

 Instrumentation calibration

 Collector control readings         |   |    ["""]

 Fuel analysis, changes in quality  |   I    [""]

 Pressure drop through system       j   |    j  |

 Rapper operation, changes          |   |    |  ]

 Boiler operation, changes          |   |    Q]

 Flue gas analysis                  |   [    P"]

 Soot blowing intervals             |   |    r~j

 Malfunctions                       |   j    r~j

 )    ESTIMATION OF ESP EFFICIENCY

                          Kg/hr    g/scm   Kg/MJ
                         (Ib/hr)  (gr/scf)  (Ib/MM Btu)

 Uncontrolled emissions

 Actual emissions

 Control device efficiency _ %

 )     COMMENTS
                          5-14

-------
                          REFERENCES


 1.  Oglesby,  Sabert, Jr.  A Manual of Electrostatic Pre-
     cipitator Technology.  Southern Research Institute,
     Birmingham, Alabama.  August  25, 1970.

 2.  White, Harry J.  Industrial Electrostatic Precipitation.
     Addison-Wesley.  1963.

 3.  The Electrostatic Precipitator Manual.  The Mcllvaine
     Co.  Copyright 1976.

 4.  Walker, A. B.  Characteristics and Electrostatic
     Collection of Particulate Emissions from Combustion of
     Low-Sulfur Western Coals.  Research-Cottrell, Inc.
     (Paper 74-11, presented at Air Pollution Control
     Association 67th Annual Meeting.  Denver, June 9-13,
     1974).

 5.  Walker, A. B.  Experience with Hot Electrostatic
     Precipitators for Fly Ash Collection in Electric
     Utilities.  Research-Cottrell, Inc.   (Presented at
     American  Power Conference.  Chicago, April 29-May 1,
     1974) .

 6.  Schneider, Gilbert G., et al.  "Selecting and Specify-
     ing Electrostatic Precipitators."  Chemical Engineering.
     May 26, 1975.

 7.  Matts, S. and P-0 ohnfeldt, "Efficient Gas Cleaning
     with SF Electrostatic Precipitators."

 8.  Industrial Gas Cleaning Institute, Inc., "Terminology
     for Electrostatic Precipitators."

 9.  Hesketh,  Howard E.,  and Frank L. Cross, Jr.  Handbook
     of Air Pollution Control Equipment.

10.  Aimone, R. J. et al.  "Experience with Precipitators
     when Collecting Ash  from Low-Sulfur Coals," presented
     at the 36th annual meeting of the American Power
     Conference, Chicago, Illinois.  April, 1974.
                            5-15

-------
 11.  Dismukes, E. B.   "Conditioning of Fly Ash with Ammonia,"
     Southern Research Institute, presented at the Symposium
     on Electrostatic Precipitators for the Control of Fine
     Particles, in Pensacola Beach, Florida.  September  30-
     October 2, 1974.

 12.  Busby, H. G. T., and K. Darby.  Efficiency of Electro-
     static Precipitators as Affected by the Properties  and
     Combustion of Coal.  J. Inst. Fuel  (London) .  36^184-197,
     May, 1963.

 13.  Dismukes, E. B.  A Study of Resistivity and Condition-
     ing of Fly Ash.  Southern Research Institute, Contract
     CPA 70-149, Environmental Protection Agency.  Publica-
     tion Number EPA R2-72-087.  February, 1972.  NTIS PB
     212607.  138 p.

 14.  Dalmon, J. and D. Tidy.  The Cohesive Properties of Fly
     Ash in Electrostatic Precipitation, Atmos. Environ.
      (Oxford, England), 6:81-92, February, 1972.

 15.  Dismukes, E. B.  Conditioning of Fly Ash with Sulfur
     Trioxide and Ammonia.  Southern Research Institute  for
     Environmental Protection Agency and Tennessee Valley
     Authority.  1975.

 16.  Dismukes, E. B.  Conditioning of Fly Ash with Sulfuric
     Acid, Ammonium Sulfate, and Ammonium Bisulfate.
     Southern Research Institute, Contract No. 68-02-1303,
     Environmental Protection Agency.  October, 1974.

 17.  Bump, Robert L.  "Electrostatic Precipitator Mainten-
     ance Survey," TC-1 Committee of Air Pollution Control
     Association.

 18.  Bibbo, P. P., and M. M. Peaces.  "Defining Preventative-
     Maintenance Tasks for Electrostatic Precipitators,
     Research Cottrell, Inc., Power, August, 1975.  pp.  56-
     58.

19.  Federal Register, part 60 of Title 40, Section 60.7 as
     amended December 16, 1975.

20.  PEDCo-Environmental Specialists, Inc., "Electrostatic
     Precipitator Cost Study," prepared for Division of
     Stationary Source Enforcement, U.S. Environmental
     Protection Agency, Research Triangle Park, North
     Carolina.   August, 1976.
                           5-16

-------
21.  Devitt, Timothy W., Richard W. Gerstle, and Norman J.
     Kulujian.  "Field Surveillance and Enforcement Guide:
     Combustion and Incineration Sources."  PEDCo-Environ-
     mental Specialists, Inc.  June, 1973.
                            5-17

-------
           APPENDIX A






ESP MANUFACTURERS SUGGESTED MAINTENANCE




           PROCEDURES

-------
                         APPENDIX A

    ESP MANUFACTURERS  SUGGESTED MAINTENANCE PROCEDURES


     Guidelines  for  ESP maintenance from five manufacturers

have been  evaluated  in compilation of a list of typical

recommended maintenance procedures for all types of ESP's.

These procedures,  typical of  those the manufacturer presents

to  the purchaser of  a  new ESP, include the following cate-

gories:

     A.I   Description  of major ESP components and general
           maintenance

     A.2   Preliminary  or preoperational checkout and testing

     A.3   Startup

     A.4   Routine  of preventive maintenance on a daily,
           weekly,  monthly, quarterly, and annual basis.

A.I  DESCRIPTION OF  ESP COMPONENTS AND GENERAL MAINTENANCE

A.1.1  Gas Distribution System

     A gas distribution system, composed of one or more rows

of distribution  plates, is located in the inlet duct immedi-

ately before the ESP.  This distribution system ensures that

an even flow of  dust-laden gas enters the precipitator, thus

providing  optimum  operating efficiency.

A.1.2  Precipitator  Shell

     Combustion of coal usually produces a small amount of

S02 and SO- as well  as C02, 02, and moisture.  The traces of
                            A-l

-------
SO- can cause fairly rapid corrosion of the interior of gas



ducts, fans, and dust-collecting equipment if these interior



surfaces become cool for any reason.  It is therefore recom-



mended that thorough internal inspection be made during the



first year of operation.  If interior corrosion is noted,



some means of correction should be applied as soon as



possible.  Applying heat insulation to exteriors of the



corroded components will normally correct this condition.



In installations where the boiler periodically operates at



low loads, covering the interior surfaces of side frames,



end frames, and roof with gunite will prevent any corrosive



damage to the steel.



A.1.3  Collecting Plates



     The gas flows horizontally in the precipitator through



individual gas ducts formed by the collecting plates.  The



discharge electrodes are located midway between the plates



for the purpose of ionizing the gases and imparting an



electrical charge to the dust particles.  It is important



that the plate and electrode spacing be held to close



tolerances.  If not, close clearances can cause high local-



ized sparking, which reduces the maximum precipitator vol-



tage and thus the collection efficiencies.




     Whenever the precipitator is out of service and internal



inspections are possible, the collecting plates should be
                            A-2

-------
checked for proper alignment and spacing.  Hangers should be



checked, and spacers at the bottom of the plates should not



bind plates to prevent proper rapping.  The lower portions



of all plates and the portion of plate adjacent to any door



opening should be checked for signs of corrosion.  Corrosion



usually is indicative of air inleakage through hoppers or



around doors.  Causes of such inleakage should be repaired



at once.



     At each inspection, the dust deposits on the collecting



plates should be observed before any cleaning of the preci-



pitator is started.  The normal thickness of the collected



fly ash should be about 3.2 mm  (0.125 in), with occasional



buildups to 6.4 mm  (0.25 in).  If the buildup exceeds this



amount, the intensity of the plate rappers should be in-



creased.  If the collecting plates are almost metal clean,



however, the lack of dust buildups may indicate high gas



velocity, extremely coarse fly ash, or an operation voltage



too low for good precipitation.  This condition may be noted



if a section has been shorted out prior to the inspection.



A.1.4  Discharge Electrodes



     The discharge electrodes are small-diameter wires



suspended from a structural steel wire supporting frame,



held taut by individual cast iron weights at the lower end



and stabilized by a steadying frame at the top of the cast
                           A-3

-------
 iron weights.  Whenever possible, the condition of the



 discharge electrodes should be checked with regard to dust



 buildup.  The amount of buildup will indicate whether the



 high-tension vibrators, when furnished, are operating at the



 proper intensity.



     The discharge electrodes should be perfectly centered



 between the plates from top to bottom for optimum precipi-



 tator operation.  Any broken discharge electrodes should be



 removed and, if time permits, replaced with new wires.



 A.1.5  Rapping Equipment



     The purpose of the rapping or vibrating equipment is to



 dislodge the collected material from plates and/or wires



 before the accumulation becomes so heavy that it interferes



 with electrical operation.  The "Operation and Maintenance



 Manual" supplied by the seller for each installatiDn provides



 complete descriptions and instructions for operation and



 maintenance of the rapping equipment and their controls.



 A.1.6  Hopper Emptying



     It is extremely important that a regular schedule of



 hopper emptying be established at the start of operation and



 followed as closely as possible, preferably once each



 shift.   If the hoppers are allowed to fill over a 24-hour



period or longer, electrical components may short out and



precipitation will cease.  Also, if a fly ash hopper is
                             A-4

-------
allowed to stand for more than  24 hours, the dust tends to



pack, cool, and absorb  some moisture  from the gases.  The



dust is then extremely  hard to  remove, and the moisture can



start corrosion of the  hopper steel.  Dust often tends to



build up in the upper corners of the  hoppers, especially if



they have been filled completely at any time.  Any abnormal



buildups should be removed.  If this  condition becomes



chronic, it is an indication of low operating temperatures,



insufficient heat insulation, or inadequate hopper emptying.



Heat tracing of the hopper will usually correct this condi-



tion.  In any event, scheduled  hopper emptying is critical



to efficient ESP operation.



A.1.7  Insulator Compartments or Housing



     The insulator enclosures are vented with air to prevent



flue gases from entering this space,  which houses the



supporting insulators.  If the  precipitator is under nega-



tive pressure, the air  is admitted through open vents in the



housing sides.  If it is under  positive pressure, the venti-



lating air is introduced by means of  a ventilating fan,



sized to maintain a pressure within the housing slightly



higher than the precipitator pressure.  This air flows



downward around the inside of the bushings, which separate



the treating zone from  the insulator  enclosures; the flow of



air prevents the gases  from entering  these cooler enclosures



and condensing on the interior  surfaces and also helps keep
                            A-5

-------
 the  insulators  clean.  The interior condition of the en-

 closures  should be carefully noted.  All insulators should

 be cleaned  and  the exterior and interior of the bushings

 cleaned if  necessary.  The interior of the bushings can be

 cleaned easily  with an air lance.  The interior surfaces of

 '-he  enclosures  should be carefully inspected for signs of

 corrosion.   Signs of corrosion or an abnormal buildup of

 dust in the enclosure can indicate insufficient ventilation.

 All  high-tension connections to the bus beams should be

 checked to  see  that all connections are secure.  If heaters

 are  provided, they should be serviced as described in the

 maintenance manual for insulator compartment heaters.

 -.1-8  Transformer-Rectifier Power Supply

      a.   The transformer-rectifier power supply is con-
          tained in an oil-filled tank and consists of the
          following equipment:

          1.  High-voltage supply transformer.
          2.  Silicon rectifier assembly.
          3.  Inductor in series with the high-voltage
                    output bushing.
          4.  Low-voltage bushing for primary supply.
          5.  Metering and d.c. ground connection.

     The  transformer rectifier tanks are maintained by

checking  for leaks and for proper oil level; if Askarel  is

used as the dielectric, any spills must be cleaned up care-

fully because Askarel is flammable.

A.2  PRELIMINARY CHECKOUT AND TESTING

     1.   Check the line voltage for proper phase and mag-
          nitude.
                           A-6

-------
 2.   Inspect the transformer-rectifier tanks for any
      signs of oil leakage or physical damage.  Check
      the oil tank gauge and refill if necessary.
      Follow manufacturer's instructions for pertinent
      information.  DO NOT OVERFILL THE OIL TANK.

 3.   Inspect the dust-conveying equipment and the
      hopper discharge valves.

 4.   Inspect main exhauster  (if applicable).

 5.   Follow the procedure outlined under "Key Interlock
      System" to gain access to the precipitator.

 6.   Inspect the rapper motors prior to and during the
      initial equipment startup for proper rotation and
      alignment.

 7.   Inspect any gear motor that has been mechanically
      serviced for proper rotation and alignment.

 8.   Check the position of each collecting surface
      rapper hammer.  These hammers must be in a posi-
      tion that conforms to the normal function of the
      hammer shaft.  A hammer that has been manually
      tripped in advance of its normal function may
      cause damage upon gear motor startup.

 9.   Inspect the precipitator control cabinets and the
      transformer-rectifier for evidence of loose con-
      nections.

10.   Inspect the precipitator chamber for foreign
      material, such as tools, rags, cleaning material,
      etc.

11.   Disconnect the high-voltage conductor at the
      support insulator and check the discharge wires to
      ground prior to initial startup.  Resistance to
      ground should be 100 megohms or greater.

12.   Check the condition of all explosion relief doors
      (if applicable).

13.   Check all access doors for operation and alignment
      and then lock them.  Return the door keys to their
      proper location in the key interlock transfer
      block.
                        A-7

-------
     14.    Operate  the  insulator heaters a minimum of  2 hours
           before energizing the precipitator.  The  ammeters
           on the heater control panel  should be balanced  and
           should read  the  equivalent of approximately 4kW/
           line  voltage.

           a.    For a precipitator operating with positive
                pressure, the pressurizing fan(s) must be
                started prior to starting the main exhauster.

           b.    The high-voltage heaters should not  be turned
                off until after the precipitator has reached
                operating temperature.

           c.    Energize precipitator.

A.3   STARTUP

      1.    Switch on the dust-handling  system.

      2.    Switch on the discharge electrode and plate
           rapping  systems.

      3.    Switch on the precipitator control circuit  breaker.

           a.    Allow precipitator high-voltage insulator
                heaters to  warm up before switching  on high
                voltage.

                Possible explosions are avoided by not
                switching on the high-voltage power  while  a
                combustible mixture is  in the precipitator.

      4.    Place the precipitator power supply on automatic
           and press "ON" button.

A.4   ROUTINE PREVENTIVE MAINTENANCE

     A program  for  maintaining the precipitator and its

auxiliary  equipment is recommended to  ensure proper opera-

tion of the unit and to prevent outages caused by lack of

maintenance.
                            A-8

-------
     Inspection of the unit on a daily, weekly, monthly,

quarterly, and annual schedule is recommended.  Data sheets

and instructions supplied to the customer are of a recom-

mended format, which may be altered by the customer to suit

specific conditions.  Following is a typical list of main-

tenance procedures that an ESP manufacturer might provide.

A.4.1  Daily

     Control House

     1.   Check all precipitator control panels for vent fan
          operation.

     2.   Note conditions of filters on control panels.

     3.   Take precipitator control panel readings.

     4.   Maintain a daily log for reference.

     Auxiliary Control Panels

     1.   Check insulator heaters for operation mode.

     2.   Record ammeter readings of each insulator heater.

     3.   Check all "Push to Test" lights on panel, replace
          as necessary.

     4.   Check all selector switches for proper operation
          in manual and automatic mode.

     5.   Check all rapper timers for operation.  Rapper
          "on" time and "off" time is set by the service
          engineer and should not be changed except by
          authorized plant personnel.  If times are re-
          adjusted, this should be noted on maintenance
          records.  Record initial settings and final set-
          tings.

     6.   Test annunciator panel for operation.  Replace any
          bad lights as necessary.
                           A-9

-------
Precipitator

     Dust Removal Level

     1.   Check hopper/dust-removal equipment for
          operation or signs  of leakage.   Record any
          faulty areas.

     Side Access Level

     1.   Collecting Surface  Rapper Drives

          a.   Check all collecting surface  rapper
               drive motors and reducers;  note any
               leakage of reducer lubricant.

          b.   Check all couplings for  adequate lubri-
               cation.

          c.   Check for operation temperature of
               reducer and motor.   If rapper drive is
               operating, listen for rapping sound of
               hammers.

          d.   Check any auxiliary equipment on this
               level.

     Gas Inlet Level

     1.   Gas Distribution System Rapper  Drives if
          equipped - same procedure as  side  access
          level.

     Roof Level

     1.   Transformer-Rectifier

          a.   Check all units  for proper oil level.
               See instruction  book for type, amount,
               and method of  adding oil,  if  necessary.

          b.   Record transformer-rectifier  oil tem-
               perature.

          c.    Note and report  any leaks  on  tank of
               transformer-rectifier.   If dielectric is
               Askarel (G.E.  -  Pyranol  -  Westinghouse -
               Inerteen),  the manufacturer should be
               contacted immediately and  extreme cau-

-------
                    tion should be taken in cleanup of
                    spill.  See instruction book concerning
                    handling of Askarel dielectric material.

     Discharge Surface Rapper Drives

     1.   Check all discharge surface rapper drive motors
          and reducers.  Note any leakage of reducer lubri-
          cant.

     2.   Check for operational temperature of reducer and
          motor.

     3.   Check all couplings for adequate lubrication.

     4.   Inspect each discharge surface cam drop mechanism
          for wear and operation.  Check all rollers on cam
          drops for binding or restriction of movement when
          they drop off cam.  If roller slides down face of
          cam, roller must be adjusted or disassembled and
          cleaned to eliminate this condition.

A.4.2  Weekly

     1.   Clean all insulators.

     2.   Check access doors for tightness.

A.4.3  Monthly

     1.   Check grounding switches on rapping cubicle doors
          and lubricate gate switches.

     2.   Check that safety interlocks operate freely.

     3.   Check rapping chains for slackness and grease.

     4.   Check rapping gear boxes and lubricate cam tips.

     5.   Check electrical contacts and connectors in the
          high-voltage control panel.

     6.   Check sealing bellows on connector drop rod
          rappers.
                            A-ll

-------
A.4.4  Quarterly

     Control House

     A.   Precipitator Controls and Auxiliary Control Panels

          1.   Clean inside all panels.

          2.   Check all electrical components for signs of
               overheating.

          3.   Check for loose electrical connections.

          4.   Lubricate all door latches and adjust as
               necessary.

          5.   Check relays for freedom of movement.

          6.   Check vent fan for operation and check
               clearances between blades and shroud.

          7.   Install new air filters in control panel.

     Side Access Level

     A.   Collecting Surface Rapper Drives

          1.   Check reducer for leaks.

          2.   Check coupling for signs of excess wear.

A.4.5  Annual

     1.   Remove dust buildup on wires and plants, if any.

     2.   Adjust vibrator and/or rapper intensity and cycle
          to prevent serious material buildup.

     3.   Inspect perforated diffuser screen and breeching
          for dust buildup.

     4.   Perform maintenance and lubrication of pressurized
          fans;  check for leaks in the pressurized system.

     5.   Check  for loose bolts in frames, verify that
          suspension springs are in good order, and examine
          wearing parts,  hammers, anvils, etc.
                           A-12

-------
     6.   Inspect discharge wires for tightness and signs of
          burning, and discharge system for correct align-
          ment, broken parts, and welds.

     7.   Clean lead through insulators on underside.

     8.   Check all insulators for cracks.

     9.   Check complete collector grounding bonding wires
          and connections.

    10.   Drain oil, wash out, and refill gear boxes.

    11.   Check transformer fluid and dielectric strength.

    12.   Check relays, contactors, and starter contacts.

A.4.6  Recommended Spare Parts

     Following is a typical list of spare parts recommended

by manufacturers.

     - support insulator/gaskets
     - shaft insulator
     - emitting electrodes
     - H.V. bushings
     - emitting electrode weights
     - cap and pin insulators
     - H.V. resistor assembly
     - Lamp bulbs
     - contractor operating cord and contact set
     - shunts
     - diodes
     - filter circuit
     - transformers
     - relays
     - capacitor
     - silicon diode
     - potentiometer
     - resistors
     - fuses
     - printed circuit card
                           A-13

-------
            APPENDIX B




UTILITY ESP MAINTENANCE PROCEDURES

-------
                         APPENDIX B

             UTILITY ESP MAINTENANCE PROCEDURES


     This section presents an example of a conscientious ESP

maintenance procedure for utilities.  Although this level of

ESP maintenance is not practiced by all utilities, neglect

of proper maintenance can lead to degradation of performance

and ultimately to higher maintenance costs.  These procedures

are considered reasonable and representative of sound ESP

maintenance practices for utility applications.

B.I  ASH REMOVAL SYSTEM

     The document, "Operating and Maintenance Instructions,"

prepared by the Allen-Sherman-Hoff Co., Inc., provides

detailed instructions for operation and maintenance of the

ash-handling system.  Operators of this equipment should be

thoroughly familiar with information given in their manual

and with the following supplementary items, required to

ensure successful operation and maintenance of the ash

removal equipment.

     1.   Obtain from the manual the recommended values of
          settings for timers, water pressure and flow, air
          pressure, and vacuum high and low settings.

     2.   Determine that compressed air supplied to this
          system is clean and moisture free.
                            B-l

-------
      3.   Values assigned to settings for timers and vacuum
          high  and low settings are theoretical and are
          listed as a starting point.  Therefore, some field
          adjustment may be required for optimum operation.

      4.   Observe the air separator tanks overflow at least
          once  weekly, since this may signal restricted ash
          slurry flow.

      5.   Give  particular attention to vacuum highs and lows
          observed, since these readings will help in detec-
          ting  worn hydrovactors and excessive air leakage.

      6.   At  least once each day, determine whether each ash
          hopper is emptying and whether all control panel
          indicator lights are working.  This can be accomp-
          lished by observing the panel lights, locating
          each  hopper on the vacuum recorder sheet and
          looking for abnormal deviations in operation, and
          by  touch to determine whether a hopper is full,
          empty, or evacuating ash at the appropriate time.

      7.   During outages, refer to the maintenance section
          of  the manual and perform the preventive main-
          tenance recommended.

 B.2   ELECTROSTATIC PRECIPITATOR INSPECTION AND MAINTENANCE

 B.2.1 General

      To keep  abreast of current operating problems and

 internal faults, review precipitator operating logs daily.

 This  will ensure cognizance of unusual conditions and will

 expedite inspection and repair procedures, especially during

 emergency outages.

      To maintain optimum collection efficiencies, it is

essential that  internal faults be corrected at the first

unit outage following their discovery.  External faults can

be corrected as they occur.
                            B-2

-------
     If the plant staff cannot determine the reason for a



fault, request immediate assistance from the central office.



Any unusual condition or equipment problems should also be



brought to the attention of the central office staff.



     Make a thorough inspection of each precipitator during



each scheduled outage and summarize the findings and cor-



rective actions in the outage report.  To facilitate the



detailed inspection it is usually necessary to wash down the



precipitator internals.  If this is not done, it is almost



impossible to inspect all components because of the fly



ash buildup on the internals.



B.2.2  Clearance Procedures



     Follow established clearance procedures in tagging out



and placing grounds on the precipitator before any inspec-



tion or maintenance work is performed.



     When a unit is shut down, keep the precipitator plate



and wire rappers and ash-removal system in service for 24



hours to ensure that all loose dust is removed.  During



short outages it may not be possible to adhere to this



procedure because of maintenance work inside the precipita-



tor.



B.2.3  Insulator Heaters



     Do not turn off the insulator heaters until the insula-



tors have been wiped clean of fly ash accumulation.  Other-
                            B-3

-------
 wise,  the  accumulated ash will become  sticky  from absorbed



 moisture and will  form  a conductive path to ground.  Also,



 once the ash has absorbed moisture it  is very difficult  to



 remove.  If the heaters have been turned off  following



 cleaning of the insulators during an extended outage, they



 should be  energized at  least 24 hours  prior to firing the



 unit to ensure that they are dry and above the acid dewpoint.



 A  conductive path  across an insulator  assembly could result



 in a catastrophic  failure of the insulator from a high-



 voltage flashover.



 B.2.4  Removal of  Foreign Materials



     Remove all scaffold boards and other foreign material



 from the precipitator before it is released for service.



 B.2.5  Prestart Tests



     Conduct air load tests following  maintenance work on



 the precipitator to ensure that all sections  are clear of



 grounds and alignment is satisfactory.  During the air load



 test,  increase the voltage slowly on manual control to



 preclude severe arc-over, which could  damage  an insulator.



 Compare data with  initial and previous air load data.



     During unit startups place the ash-removal system in



 service before a coal fire is established.  Energize the



precipitator as soon as possible after the pulverizers are



placed in service.  Each plant should  determine optimum  time
                            B-4

-------
for energizing the precipitators  and prepare  appropriate



operation instructions.



B.2.6  Inspections and Maintenance During ESP Operation



     Inspection and maintenance of components such as those



in the penthouse of the precipitators may be  done with the



unit in  service/  Work in  any  section of the  caged area will



require  deenergizing and grounding of the transformer-



rectifier set serving that section.  Since each transformer-



rectifier serves at least  two  bus sections, at least two bus



sections must be out.  If  the  remaining sections of the



precipitator are in service and at their normal operating



level of 40 kV or above, particulate emission limits can be



met provided unit loads do not exceed the recommended limit.



The high-voltage section must  be  grounded when inspecting



the second or third fields because, even though these are



deenergized, they can pick up  a significant static charge



from the upstream fields.



B.2.7  Critical Components - Caged Area



     Inspect and maintain  the  critical components in the



caged area on a routine basis.  These include the upper



portion  of the insulators,  insulator heaters  and thermostats,



high-voltage support insulators,  high-voltage bus standoff



insulators, voltage dividers,  and the plate and wire rapper



machanism.  It is very important  that the insulator heaters
                            B-5

-------
and thermostats be kept in good working order since their

failure could result in tracking and insulator failure

during operation at low gas temperature.  Attention shall

always be given the following:

     a.   Wipe insulators clean and inspect for cracks and
          air infiltration through the asbestos sealing
          rings.

     b.   Wipe high-voltage support and standoff insulators
          clean and inspect for cracks or evidence of track-
          ing.

     c.   Check plate and wire rapper drive shaft bearings,
          drive motors, speed reducers, and chains and
          sprockets to ensure that they are properly lubri-
          cated.

     d.   Examine rapper cams and lift plates for wear and
          inspect the wire rapper shaft insulator for
          cracks; wipe clean.

     e.   Check resilient bellows seals on the wire and
          plate rappers for cracks and evidence of air
          infiltration; replace as needed.

     f.   Clean voltage dividers and examine for oil leakage.

B.2.8  Critical Components - Outside Caged Area

     Critical components outside the caged area include the

transformer-rectifier sets and their control cabinets and

the rapper and insulator heater control cabinets.  To

ensure optimum performance of the precipitator controls, a

plant electrician who is familiar with the precipitator

controls should inspect them daily and make any required

adjustments.  This requirement is necessary to detect pro-

blems such as excessive sparking that are not evident from

the daily operating logs.
                            B-6

-------
B.2.9  Inspections and Maintenance During Shutdowns



B.2.9.1  Short Emergency Outages - Internal ground faults in



a section that indicates high amperes and zero or very low



voltage on the control panels are usually due to broken



discharge electrodes, ash hopper buildup, or bridging of ash



between the high-voltage frames and the collection plates.



Such faults can also occur from cracked high-voltage insula-



tors or from debris such as welding rods or pieces of wire



that are left inside the precipitator during maintenance.



These faults should be corrected during short emergency



outages.



     Cut broken wires at the unbroken end and remove them.



Replacement of a cracked or failed insulator will required



placing that section on temporary suspension.  Check the



alignment of this section following replacement of the



insulator and removal of the section from temporary suspen-



sion.  Minimum and maximum distances between the high-



voltage frames and the collection plates are shown in the



manufacturer's handbook.



     Install the asbestos sealing rings in the insulators



with care to ensure a good seal and prevent the inleakage of



air, which will result in internal corrosion.  The insulator



assembly is shown in the manufacturer's handbook.
                            B-7

-------
      Clean  all  insulators  if time permits.  If there is



 sufficient  time after completion of the work mentioned,



 inspect other sections of  the precipitator.  Look for indi-



 cations of  electrical tracking; air infiltration; unusual



 accumulations of dust on the plates and wires, which may



 indicate ineffective rapping; misalignment; loose bolts,



 particularly on the center mast brace assemblies and rapper



 anvils; and any indications of corrosion or distress on the



 precipitator internals.  Document the results of each in-



 spection to aid in future  inspections and planning for



 maintenance work.



 B.2.10  Long Scheduled Outages



 B.2.10.1  Prewash Inspection - Inspect the precipitator



 internals as soon as possible after the unit comes off the



 line before it  is washed.  Note any unusual dust accumula-



 tions; polished areas, which indicate gas bypassing; swept



 areas, which may be the result of air infiltration; and



 other items that may require significant repair work.



Arcing between  the wire mast and the high-voltage support



 frame resulting from loose bolts is shown by dark spots in



the fly ash adhering to these areas; such spots can readily



be seen before  the precipitator is washed.  Wipe insulators



clean before washing.  After cleaning the insulators, shut



off the heaters to preclude grounding during washing or
                            B-8

-------
possibly breakage of heater insulators from cold raw water



impingement.  This work can usually be done while prepara-



tions are being made to wash the precipitator.



B.2.10.2  Washing - Thoroughly wash down the precipitator



internals with raw water.  Washdown pads are provided for



this purpose.  Washing should be done with a fog nozzle, and



personnel must be instructed not to direct the spray into



the insulators.  The asbestos sealing rings will become



soaked with water and lose their resiliency upon drying.



Also, they might not dry completely before the unit is



returned to service.



     Following the washing, begin repairs on the known



faults.  While this work is in progress, perform a detailed



inspection of the other sections.  Some items to be inspected



in each area of the precipitator are as follows.



B.2.10.3  Upper Area



     Insulators - Check for cracks or any signs of arc-over



on both the lower and outer insulators.  Replace broken or



severely cracked insulators.  Reseal insulators that show



indications of significant air infiltration.  If the sealing



rings have deteriorated, these must be replaced.  There



should be some clearance between the inner and outer insula-



tors.
                            B-9

-------
      Wire Masts  -  Check  for  loose bolts where the masts are



 connected to  the upper high-voltage support  frame.  Tighten



 loose bolts.   Exercise caution  in tightening these because



 this  can distort the mast, causing misalignment between the



 mast  and the  collecting  plates.  Cut out and remove any



 broken discharge wires accessible from this  area.  Keep



 records of wires that are removed.  Loose or bowed wires can



 be  tightened  by  crimping in  the direction of gasflow.  This



 must  be done  carefully so as not to distort  or bend the mast



 arms.



      High-Voltage  Support Frame - Check for  loose bolts and



 nuts  and broken  or failed springs; repair as needed.



      Collection  Plates - Check  for loose nuts on plates and



 plate hanger  eyebolts, broken or failed springs, and  loose



 nuts  on the plate  rapper anvils.  Check anvil striker plate



 for wear.  Visually check plates for bowed or wavy areas and



 plate-to-wire misalignment.



      General  - Note any  beams or frames that have slipped or



 tilted; broken welds; and the general condition of the



 internals, shell,  access doors, and gaskets.



 B.2.10.4  Lower Walkway  Area



     Alignment - Check alignment between the masts and the



collection plates.  Gross misalignment can usually be



detected by visual observation.  Questionable areas should
                           B-10

-------
be checked with a rule or gauge.  Note any out-of-tolerance
spacing.  Also check the horizontal distance between the
center mast bracing frame and the edge of the plates.  Note
any burned areas resulting from arcing.
     Correct the alignment to the tolerances noted in manu-
facturer's handbook.
     Plates - Note any warped, buckled, or wavy areas.
Check lower plate foot and guide to ensure that plates are
hanging free.  Note any missing bolts or rivets in the plate
assembly.
     Wire Masts - Inspect wire masts for broken, loose, or
bowed wires.  Cut and remove broken wires and tighten bowed
or loose wires by crimping.  Check for loose or missing
bolts on the lower mast spacer frame.  These bolts must not
be tight but should be snug.  Close checks of these and any
repairs will require a scaffold board in the ash hoppers for
access.
     General - Note any broken welds; evidence of air infil-
tration leakage; baffle distortion; ash hopper condition;
and the general condition of the internals, shell, access
doors, and gaskets.
     Ducts - Inspect inlet ducts; inlet distribution baffle
half rounds; and outlet ducts for distortion, corrosion,
leakage, and ash buildups.
                            B-ll

-------
B.2.11  Records



     Maintain detailed records of all inspections and



maintenance performed on fly ash collectors.  Copies of



reports or other applicable records should be available at



the plant for review by state air pollution control represen-



tatives or others and should also be maintained in the



central office files.



B.2.12  Conclusions



     This example of a utility precipitator maintenance



requirements sets forth concise and detailed instructions,



emphasizing the components that need the greatest attention



in order for an ESP to operate properly.  If used properly,



those recommended maintenance procedures can serve as an



excellent supplement to the manufacturer's procedures,



providing further guidelines for an ESP operator in solving



operating difficulties.
                            B-12

-------
       APPENDIX C




EXAMPLE OPERATING HISTORY




           OF




 COLD-TYPE PRECIPITATORS

-------
                         APPENDIX C



   EXAMPLE OPERATING HISTORY OF COLD-TYPE PRECIPITATORS






     This section is a review of maintenance and operational



problems a major U.S. utility has encountered with cold-type



precipitators over a number of years.  Their plants are well



maintained, and extensive records are kept.  The operation



and maintenance problems they report are a typical example



of what could be expected at other power plants utilizing



precipitators and operating under similar conditions.



     In assessment of equipment operability, the best infor-



mation concerning operation and maintenance of precipitators



most likely will come from utilities with well-maintained



plants, such as the one discussed in this section.  Utilities



with moderately or poorly maintained plants probably do not



keep comprehensive records, and many problems may not be



recognized or reported.



C.I  INTRODUCTION



     This utility began the change from mechanical collectors



to ESP's on new plant construction in the late 1950's.



Further retrofitting of ESP's on existing units was made in




1967 and subsequent years.
                           C-l

-------
      Sixteen different types of ESP's serve 51 generating



 units,  ranging in capacity from 60 to 1300 MW.  These ESP's



 are  supplied by  five manufacturers, four domestic and one a



 domestic  subsidiary of a foreign manufacturer.  Coal comes



 from eastern and midwestern sources.  Sulfur contents of the



 eastern coal range from 0.5 to 3.0 percent; sulfur content



 of the  midwestern coal ranges from 3.0 to 5.0 percent.  Each



 type of coal imposes special problems for ESP performance



 and  reliability.



 C.2   RELIABILITY AND MAINTENANCE EXPERIENCE



      Very few of this utility's precipitator installations



 have demonstrated the expected reliability or maintenance



 cost.   Major problem areas affecting reliability and main-



 tenance involve  (1) physical features of the collector



 design,  (2) ash removal problems,  (3) operating conditions



 such as gas temperature and coal sulfur, and  (4) operating



 and  maintenance practices.



     All  plants equipped with precipitators maintain operat-



 ing  and maintenance logs, which provide information relating



 to electrical operating conditions, ash removal operations,



maintenance activities, faulty conditions, and sectional



outage  times.   From these records, periodic summaries of




precipitator operation are prepared for management review.



These summaries contain various indices of precipitator
                            C-2

-------
reliability, including a precipitator availability factor
defined as the ratio of the average bus section hours of
operation to the hours of unit operation.
     Figure C-l shows the average availability record for
all precipitators  for a recent year of operation.  The
overall weighted average availability for this period was
92.6 percent.  Only 6 of the 37 units in service during this
period had 100 percent precipitator service availability.
Four of these 6 units were 60-MW standby units, which oper-
ated only for short periods of time.  The other two units
with 100 percent availability were in the 150-MW class.
     The principal cause of unavailability of precipitator
bus sections was grounding of the high-voltage electrode
systems resulting  from malfunctions of the ash removal
system and excessive ash accumulations on the electrodes.
These problems accounted for 50 percent of the total bus
section unavailability.  The second most serious cause of
bus section unavailability was discharge wire failures,
which accounted for 36.5 percent of the unavailability.  All
other fault conditions such as failures of controls, switch-
gear, transformer rectifiers, and support insulators accounted
for the balance, or 13-5 percent of the unavailability.
C.2.1  Ash Removal Problems
     Failure to maintain adequate evacuation of the collector
ash hoppers can lead not only to collector malfunction but
                           C-3

-------
O
 I
                   S2 4
                   o
                   of.
                                                            AVERAGE
                                                              92.6
                          65-      70-     75-      80-      85-     90-     95-     97-     98-     99-
                         69.9      74.9   79.9     84.9     89.9    94.9     96.9    97.9    98.9     99.9
                                                       BUS SECTION AVILABILITX X
100

 37 UNITS TOTAL
                                    Figure  C-l.    Precipitator availability.

-------
also to possible wire burning, formation of ash clinker,



distortion of the high-voltage frames, and misalignment of



collecting plates.  Most ash removal problems result from



insufficient capacity and flexibility of the ash removal and



disposal systems.  Other contributing factors are operation



of low gas temperatures in combination with high-sulfur



coal, inadequate hopper insulation, substantially higher



quantities of ash in recent coal receipts, and less-than-



desirable operating and maintenance practice.



     Most of this utility's precipitators are equipped with



sequentially operated dry ash removal systems.  These systems



have proved acceptably reliable when they are designed,



operated, and maintained properly.  For satisfactory opera-



tion, the precipitator hopper ash  removal and disposal



systems should be completely divorced from other refuse



handling systems and should be of  adequate capacity and



arrangement to permit evacuation of each ash hopper often



enough to prevent any appreciable  accumulation  in the hop-



pers.  Unsatisfactory operation and maintenance of ash water



pumps, water jet nozzles, vacuum connections, and sequencing



controls can lead to loss of ash removal efficiency and  to



possible precipitator malfunction.

-------
 C.2.2   Discharge Wire Failure



     The  impact of wire  failures on precipitator avail-



 ability is  a  function not only of the frequency of  failures,



 but  also  of the degree of sectionalization and the  diffi-



 culty  of  removing failed wires from the precipitator during



 unit operation.  Most precipitators do not have suitable



 isolation dampers to permit safe internal access while the



 boiler is in  operation;  therefore, only broken wires that



 can  be reached from access hatches can be removed during



 unit operation.  The attachment designs for some types of



 discharge wires require  unit shutdown to make replacements;



 some attachments, however, are simple loops or hooks, which



 permit removal of broken wires during operation of  some



 units.



     The  incidence of wire breakage varies from essentially



 zero on some  collectors  to several failures a day on other



 collectors.   The most severe case of wire failures  occurred



 on collectors serving cyclone furnace boilers burning coal



 with about  4  percent sulfur and operating with about 150°C



 (300°F) exit-gas temperature.  The wire failures, which



 occur  immediately below  the top hanger hook and corona



 shield, are characterized by a progressive thinning of the



wire until  failure occurs.  This condition became pronounced



 after about the first year of operation and led to  the



ultimate failure or replacement of nearly all wires.
                             C-6

-------
Figure C-2 shows the frequency rate of wire failures on this
installation for two operating periods during the second
year of collector operation.  These collectors have also
undergone widespread failure of collecting plate support
members, which were fabricated of carbon steel rather than
the low-alloy, corrosion-resistant steel that was specified.
The collector manufacturer attributes all of these problems
to low gas temperature and high-sulfur coal, although operat-
ing conditions are very close to the specified design condi-
tions.  The total maintenance cost on these collectors for
the first 3 years of operation was 25 percent of the purchase
cost of the collectors.  This is substantially higher than
the acceptable annual cost of 1.5 percent suggested by one
manufacturer.
     Wire failures on other classes of precipitators occur
at a frequency of about 0.3 percent a year; nevertheless,
even this rate of failure can seriously impair collector
availability on units that do not permit removal of broken
wires during unit operation and on collectors of low sec-
tionalization.
C.2.4  Tran s f o rimer - Re cti f i e r Fai1ure s
     Power set failures occur at an annual average frequency
rate of about 0.6 percent of the total number of sets
installed and contribute a small fraction of total collector
                            C-7

-------
O
 I
oo
                    100
                     80
                  8  60
40
                     20
             -J	,	



               ELECTROSTATIC PRECIPITATOR

                WIRE FAILURE EXPERIENCE
                                                          _l_
                                                                                  _L
          15           20      .     25


NUMBER OF SUCCESSIVE BUS SECTION FAILURES
                                                                                              30
                                                                                     35
                            Figure  C-2.   Number of successive  bus  section failures,

-------
unavailability.  Most failures involved insulation break-
down, arcing between internal high-voltage switch contacts,
and contamination of the insulating fluid.
     One spare 700-mA power set is maintained as an emer-
gency replacement for about 300 sets ranging in size from
400 to 1400 mA.  Some large collector installations present
problems in the removal of power supplies, but recent
installations incorporate original design provisions for
handling power sets.
C.2.5  Support Insulator Failures
     High-voltage electode system support insulators of the
cylindrical-tub type show a high rate of failure (about 5
percent a year) on  installations operating with low gas
temperature and high-sulfur coal.  This type of insulator is
subject to excessive fouling and to arc-over.  Most insulator
failures involve fine hairline surface cracking and not
complete physical collapse.  Insulator fouling and cracking
reduce effective voltage levels and collector performance
but rarely completely decommission a bus section.
C. 2. 6  Rapper and Vibrator Problems
     Inadequacies of design, installation, operation, and
maintenance of rappers and vibrators can lead to excessive
dust accumulations  on the electrodes, impaired performance,
and possible grounding of the high-voltage system.  A fre-

-------
 quent  trouble  source is binding of the collecting plate



 rapper or vibrator rods at the points of roof penetration.



 This trouble is commonly neglected and may lead to ineffect-



 ual rapping.   Pneumatic impact rappers installed on two of



 the collectors have the highest maintenance cost and the



 poorest reliability of all types.  Severe misalignment has



 occurred on one type of collector in which the collecting



 plate  assemblies are supported by the rapper rods.



 C.2.7   Miscellaneous Items



     Other common problems adversely affecting performance



 and reliability are overheating and failure of automatic



 control components and breakers, mechanical instability of



 high-voltage electrode systems, oscillation of wires, mis-



 alignment of wires and plates, infiltration of air, bypass



 of dust through inactive zones, and reentrainment of dust



 from hoppers.  Precipitators that follow mechanical collec-



 tors are sometimes erroneously charged with poor performance



 as a result of air leakage and impaired efficiency of the



mechanical collectors.



C.3.8  Conclusions



     The unsatisfactory performance of some of this utility's



early collectors resulted from inadequate definition of the



requirements with respect to the range of operating condi-



tions  and also from the marginal sizing of collectors for



the specified operating conditions.  Recent specifications
                            C-10

-------
more realistically define the expected operating conditions



and contain minimum acceptable  sizing parameters and other



inducements for contractors to  provide conservatively



designed precipitators.



     Unfavorable reliability experience of some precipitator



installations has resulted mainly from shortcomings of ash



removal systems and excessive failures of discharge wires.



Adverse operating conditions of coal sulfur content and gas



temperature also contribute to  poor reliability.



     The emphasis of this utility on performance and reliabi-



lity problems is not meant to suggest that electrostatic



precipitators are not satisfactory for control of fly ash



emissions.  The utility officials state that successful



installations are economically  attainable by realistic



definition of the requirements, proper design, and adequate



operation and maintenance.
                           Oil

-------
                          /«     TECHNICAL REPORT DATA
                          (fiease read Instructions on the reverse before completing)
 . REPORT NO.
 EPA-600/2-77-006
2.
                            3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Electrostatic Precipitator Malfunctions in the
  Electric Utility Industry
                            5. REPORT DATE
                             January 1977
                            6. PERFORMING ORGANIZATION CODE
 1. AUTHOR(S)

 Mike Szabo and Richard Gerstle
                            8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
 PEDCo. -Environmental Specialists, Inc.
 Atkinson Square, Suite 13
 Cincinnati, Ohio 45246
                            10. PROGRAM ELEMENT NO.
                            1AB012; ROAP 21BAV-018
                            11. CONTRACT/GRANT NO.
                            68-02-2105
 12. SPONSORING AGENCY NAME AND ADDRESS
 EPA, Office of Research and Development
 Industrial Environmental Research Laboratory
 Research Triangle Park, NC 27711
                            13. TYPE OF REPORT AND PERIOD COVERED
                            Final;  9/75-8/76     	
                            14. SPONSORING AGENCY CODE
                             EPA-ORD
 15. SUPPLEMENTARY NOTES JERL-RTP project officer for this report is D. C. Drehmel,
 919/549-8411 Ext 2925, Mail Drop 61.
  . ABSTRACT
               report discusses precipitation malfunctions in the electric utility indus-
 try.  When a utility electrostatic precipitator (ESP) fails to achieve its design effi-
 ciency, there must be a reason.  Although the reasons are numerous, they can be
 placed in two distinct categories:  ESP degradation is attributable either to hardware
 malfunctions or operation under improper conditions. The report discusses the vari-
 ous types of ESPs in the electric utility industry , along with design considerations .
 It summarizes the different types of malfunctions.  For each type of malfunction, it
 gives  the cause, duration,  corrective  action, and preventive measures.   The report
 also gives the maintenance required to minimize the probability of malfunction. It
 describes inspection techniques  for evaluating maintenance procedures ,  including
 what an inspector should look for during power plant ESP inspections.
17.
                              KEY WORDS AND DOCUMENT ANALYSIS
                 DESCRIPTORS
                                            b.lDENTIFIERS/OPEN ENDED TERMS
                                                                     c. COSATI Field/Group
Air Pollution              Maintenance
Electrostatic Precipitators
Failure                   Inspection
Electric Utilities
Flue Gases
Dust
                Air Pollution Control
                Stationary Sources
                Particulate
13B

14D

21B
11G
15E
 13. DISTRIBUTION STATEMENT

 Unlimited
                19. SECURITY CLASS (ThisReport)
                Unclassified
                                                                      1. NO. OF PAGE
                20. SECURITY CLASS (This page)
                Unclassified
                                          22. PRICE
EPA Form 2220-1 (9-73)

-------