United States
Environmental Protection
Agency
Region V
230 South Dearborn Street
Chicago, Illinois 60604
EPA-905/2-79-002
June 1979
Air Programs Branch
Management and
Technical Procedures
for Operation and
Maintenance of Air
Pollution Control
Equipment
Do not WEED. This document
should be retained in the EPA
Region 5 Library Collection.
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MANAGEMENT AND TECHNICAL PROCEDURES
FOR OPERATION AND MAINTENANCE
OF AIR POLLUTION CONTROL EQUIPMENT
by
PEDCo Environmental, Inc.
11499 Chester Roagl
Cincinnati, Ohio 45246
Contract No. 68-02-2535
Task No. 7
Principal Author
David B. Rimberg, PH.D.
North American PEMCO, Inc.
Bardonia, New York 10954
Project Officers
Dr. Indur Goklany and Mr. Henry Onsgard
Air Programs Branch
U.S. ENVIRONMENTAL PROTECTION AGENCY
REGIONAL OFFICE V
CHICAGO, ILLINOIS
June 1979
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DISTRIBUTION AND DISCLAIMER STATEMENT
This report is issued by the United States Environmental
Protection Agency (U.S. EPA) to report technical data of in-
terest to a limited number of readers. Copies are available
free of charge to grantees, selected contractors, and Federal
employees in limited quantities from the Library Services Office
(MD-35), Research Triangle Park, North Carolina 27711 or for a
fee from NTIS 5285 Port Royal Road, Springfield, Virginia
22161.
This report was furnished to the U.S. EPA by PEDCo Environ-
mental, Inc., 11499 Chester Road, Cincinnati, Ohio 45246 and by
subcontractor, North American PEMCO, Inc., P.O. Box 655,
Bardonia, New York 10954 in fulfillment of Contract No.
68-02-2535, Task No. 7. The contents of this report are repro-
duced herein as received from PEDCo Environmental, Inc. The
opinions, findings, and conclusions expressed are those of the
authors and are not necessarily those of the U.S. EPA. Mention
of company or product name is not to be considered as an endorse-
ment by the U.S. EPA.
U,S. Environmental Protection Agency
11
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CONTENTS
Figures v
Tables vi
Acknowledgement vii
1. Introduction 1
1.1 Background 1
1.2 Scope of the report 2
2. Maintenance Management of Air Pollution Control
Equipment 4
2.1 Definitions 4
2.2 The maintenance organization 5
2.3 Maintenance planning, scheduling, and work
measurement 7
2.4 Preventive maintenance 9
2.5 Maintenance performance evaluation 12
2.6 Spare parts and material control 13
2.7 Maintenance budgets 14
2.8 Training and education 14
2.9 Contract maintenance services 16
2.10 Vendor contribution to poor equipment
performance 16
2.11 Conclusions 17
3. Technical Aspects of the Design, Operation, and
Maintenance of Baghouses 18
3.1 Background 18
3.2 Baghouse components and operational
parameters 18
3.3 Baghouse operation and maintenance 24
4. Technical Aspects of the Design, Operation, and
Maintenance of Electrostatic Precipitators 46
4.1 Electrostatic precipitator components and
operational parameters 47
111
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CONTENTS (continued)
4.2 Electrostatic precipitator operation
and maintenance 55
4.3 Wet electrostatic precipitators 75
4.4 Wet electrostatic precipitator operation
and maintenance 75
5. Technical Aspects of the Design, Operation, and
Maintenance of Scrubbers 78
5.1 Scrubber components and operational
parameters 81
5.2 Scrubber operation and maintenance 87
6. Technical Aspects of the Design, Operation, and
Maintenance of Items Common to All Air Pollution
Control Equipment 95
6.1 Introduction 95
6.2 Exhaust ducts 95
6.3 Gas pretreatment 96
6.4 Inlet baffles 96
6.5 Hoppers 96
6.6 Fans 97
6.7 Exhaust stacks 99
6.8 Conclusions 100
7. Inspection, Safety, and Maintenance Equipment 101
8. Summary 105
Bibliography 106
Appendix A 109
IV
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FIGURES
Number Page
1 Typical Organizational Chart for a Small- or
Medium-Sized Plant 6
2 Sample of Routine Daily Inspection Report for
Shaker Baghouse 27
3 Sample of Maintenance Checklist for Shaker
Mechanism 28
4 Sample of Routine Daily Inspection Report for
Pulse-Jet Baghouse 29
5 Sample of Internal Inspection Report for
Shaker Baghouse 31
6 Preoperation and Inspection Checklist for
Electrostatic Precipitator 56
7 Operating Inspection and Maintenance Checklist
for Electrostatic Precipitator 59
8 Preoperation and Inspection Checklist for
Scrubber 88
9 Operating Inspection and Maintenance Checklist
for Scrubber 91
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TABLES
Number Page
1 Baghouse Troubleshooting Guide 36
2 Replacement Parts for Baghouse Filters 44
3 Summary of Problems Associated with Electro-
static Precipitators 63
4 Replacement Parts for Electrostatic Precipi-
tators 69
5 Typical Troubleshooting Chart for an Electro-
static Precipitator 70
6 Guide for Interpreting Abnormal Meter
Readings 74
7 Scrubber Classifications 79
8 Replacement Parts for Scrubbers 92
9 Typical Troubleshooting Chart for Scrubbers 93
10 Basic Inspection and Safoty Equipment 101
11 Basic Testing Equipment 102
12 Maintenance Tools 102
13 Power Tools 103
14 General Equipment 103
VI
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ACKNOWLEDGEMENT
This report was prepared for the U.S. Environmental Pro-
tection Agency by PEDCo Environmental, Inc., Cincinnati, Ohio.
The EPA project officers were Indur Goklany, Ph.D., and Henry
Onsgard. The project director was Mr. Donald J. Henz, P.E., and
the project manager was Mr. Thomas A. Janszen. Principal author
was David B. Rimberg, Ph.D., North American PEMCO, Inc.,
Bardonia, New York.
VI1
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SECTION 1
INTRODUCTION
I.1 BACKGROUND
Regardless of its type and function, processing or manufac-
turing equipment that is electric or mechanical requires service
and maintenance to some degree, and air pollution control equip-
ment is no exception. With the adoption of the Clean Air Act
Amendments in 1970 and 1977, not only have the capital expendi-
tures for this equipment grown exponentially, but the costs to
operate and maintain it have also skyrocketed. To emphasize the
importance of operation and maintenance (O&M), the Ninth Annual
Report (December 1978) of the Council of Environmental Quality
indicated that 1977 expenditure for O&M was 3.1 billion dollars.
This figure includes both public and private sectors, exclusive
of mobile sources. Projected costs for 1985 are 9.4 billion
dollars, with cumulative • costs from 1977 to 1985 estimated at
76.2 billion dollars. The cost of lost production, caused by
defects and deterioration through wear and tear, is calculated
at three to four times the O&M amount. By 'no means are these
conditions inevitable; many can be averted or retarded, along
with their costly consequences. Preventive maintenance is a
means to this end.
Air pollution abatement equipment is purchased, operated,
and maintained under conditions quite dissimilar to processing
and manufacturing equipment. Unless the abatement equipment is
being used for product recovery, it is procured because of
government regulations. Besides requiring large capital expen-
ditures, with the associated O&M costs, it produces no return on
investment (ROI). In the absence of strong regulatory and
managerial enforcement, there is a strong tendency to minimize
O&M even if a quality piece of control equipment was purchased.
In the event that a source is cited for an emissions violation,
subsequent enforcement of the regulations could result in
derating, curtailment, or even shutdown of the process equip-
ment.
Following the initial startup period, the new abatement
equipment is frequently neglected because of the overriding
demands of production. The maintenance department thus finds
itself with a rapidly deteriorating piece of equipment. Because
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government regulations required the procurement of the abatement
equipment, it was probably purchased on a low bid basis, thereby
resulting in an inferior quality product. In due course, the
user blames the vendor for selling him inferior and poorly
designed equipment, and the vendor blames the user for inade-
quate preventive maintenance. Both parties usually have valid
arguments. It is under these conditions that air pollution
control equipment is usually purchased and operated. The ulti-
mate solution for both government and industry is for the abate-
ment equipment to be considered an integral part of the process
and treated with equal respect.
1.2 SCOPE OF THE REPORT
With the aforementioned costs and considerations surround-
ing the procurement, operation, and maintenance of air pollution
abatement equipment, this report will supply agencies and indus-
trial users with management and technical guidelines for effec-
tive operation and maintenance of air pollution control equip-
ment. The report is divided into four major topics:
Section 2
Maintenance management of air pollution control equipment
Sections 3 through 5
Technical aspects of the design, operation, and maintenance
of air pollution control equipment (baghouses, electro-
static precipitators, scrubbers)
Section 6
Technical aspects of the design, operation, and maintenance
of items common to all air pollution control equipment
Section 7
Inspection, safety, and maintenance equipment
Section 2 includes discussions on organizing a maintenance
operation, maintenance job planning and scheduling, maintenance
work measurement, preventive maintenance (PM), maintenance
material control, budgets, and training, emphasizing air pollu-
tion control equipment.
Sections 3 through 5 include discussions of the three major
types of air pollution control equipment: baghouse, electro-
static precipitator (ESP), and scrubber. Emphasis is placed on
simplified startup, operating, and shutdown procedures. Routine
inspection procedures are supplemented with detailed checklists.
A general program is presented for troubleshooting air pollution
control equipment. Case histories for a pulse-jet baghouse, dry
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and wet electrostatic precipitators, venturi scrubber, and
packed tower are included in the appendix to provide the user
with a sample program for improving equipment performance relia-
bility.
Section 6 discusses equipment and components that are
common to all types of air pollution control equipment, such as
hoods, ducts, fans, and stacks.
Section 7 provides the details of the tools and equipment
required to satisfactorily perform inspections and maintenance.
The ultimate purpose of this report is to provide manage-
rial and technical methods and procedures for the user of air
pollution control equipment to maintain his equipment, service
it on a periodic basis, and to keep it within emissions limita-
tion and opacity standards. It will provide details for the
hypothetical user, regardless of the type of equipment used or
the type of maintenance performed.
It would not be possible in a work of this size to cover in
detail every management and technical aspect of air pollution
control equipment maintenance. An attempt has been made, how-
ever, to highlight and develop in appropriate detail the prob-
lems most commonly encountered.
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SECTION 2
MAINTENANCE MANAGEMENT OF
AIR POLLUTION CONTROL EQUIPMENT
2.1 DEFINITIONS
Within the scop of this report, a standard terminology will
be used. In some cases, these definitions may not coincide with
either national or international plant engineering standards, or
with state or Federal guidelines:
Deterioration: Unfavorable and undesirable changes in the
condition of any electrical or mechanical components,
assemblies, or subassemblies.
Defects: The maximum amount of deterioration that could be
tolerated.
Drift defect: Gradual development of defects.
Random defect: Sudden development of defects.
Maintenance: Actions that are performed to restore an item
to an acceptable condition and, therefore, to enable it to
continue to reach its required operating capacity. Note:
The "acceptable condition" can be set by the organization
executing the maintenance, and will probably vary from one
company to another. (Maintenance should not necessarily be
equated wit-h any work undertaken by a maintenance worker).
Emergency maintenance: Maintenance activities that must be
performed immediately, or in the near future, to avoid
serious consequences.
Planned maintenance: Maintenance carried out in accordance
with a well-devised plan.
Corrective maintenance: Maintenance specifically employed
to restore equipment to its acceptable condition.
Preventive maintenance (PM); Maintenance carried out in
accordance with a planned schedule to make sure that the
equipment adheres to an acceptable standard. Unfortun-
ately, the word "preventive" attracts attention to the
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apparent goal of the activity (prevention) instead of the
activity itself (periodic/predetermined interval/planned
schedule).
Breakdown: Any sudden unavoidable failure of air pollution
control equipment or process equipment to operate in a
normal and usual manner.
Excess emissions: An emission rate that exceeds any appli-
cable standard of performance prescribed by Federal, state,
or local rules, or that violates any condition in a permit.
Malfunction: Any failure of air pollution control equip-
ment or process equipment to operate in a normal and usual
manner that is caused entirely, or in part, by poor mainte-
nance, careless operation, or other preventable upset
condition or preventable process equipment failure.
2.2 THE MAINTENANCE ORGANIZATION
The single most important ingredient in effective mainte-
nance management is identification of qualified individuals to
effect and implement the maintenance function. Although plant
management is usually well aware of the need for maintenance
management, few programs are operating as they were intended to
operate. Because nearly all maintenance activities are human
activities, and are, for the most part, controlled by those
individuals doing the work, even the most explicit inspection
checklists and well-written procedures (including this report)
will not achieve the desired goal unless the persons performing
the work have the willingness and integrity to execute the
defined tasks.
In manufacturing operation, performance output can be
measured through careful production control systems. A malfunc-
tion of the system is immediately apparent, and often results in
poor production quality, reduced product output, and failure to
meet a delivery date. There is no reason to assume that mainte-
nance operations for air pollution control equipment cannot
similarly be formalized. The job or task being done, however,
is usually not as obvious, and thus more attention must be paid
to the routine requirements of the maintenance control system.
The O&M of air pollution control equipment must generally
be included within the framework of an existing in-house pro-
gram. Thus management must, as it may appear, intrude upon an
already overworked, understaffed, and underfunded maintenance
department to integrate the new functions into the program. The
equipment is typically viewed with (a) suspicion, (b) caution,
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and (c) annoyance; occasionally it is treated as important and
primary to the overall manufacturing process because its break-
down or malfunction could dictate the level of production for
the plant.
To effect a viable maintenance program, a support organiza-
tion must be available. A typical organizational chart for a
small- or medium-sized plant is shown in Figure 1.
PLANT MANAGER
PLANT ENGINEER
MAINTENANCE
MANAGER
PLANNING AND
SCHEDULING
FOREMAN
CLERICAL
UTILITIES
SUPERVISION
Figure 1. Typical organizational chart for a
small- or medium-sized plant.
The plant manager's primary function is to operate the
plant for maximum profits and minimum costs. The plant engineer
has the responsibility to see that the plant operates effec-
tively and continues to produce goods. He is often also respon-
sible for environmental matters: noise, OSHA regulations,
in-plant fumes, dust and odors, air emissions, water effluents,
permit applications, and codes and standards. To meet this
immense responsibility, which includes the performance of air
pollution control equipment, he must create a supporting organ-
ization around him.
As indicated in Figure 1, the plant engineer usually finds
it necessary to delegate the maintenance function to an indi-
vidual who, for all practical purposes, will be called the
maintenance manager and may, in fact, be an engineer. The
maintenance manager must have a sound knowledge of manufacturing
machines and adapt himself to include air pollution control
equipment. The maintenance manager must also possess management
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abilities, since most of his working hours are spent in getting
the job done through people. His most critical subordinate is
his foreman, whose job it is to see that the workers are proper-
ly instructed and competent to maintain the plant. The foreman
is the vital link between management and job execution. He must
know his workers and their respective capabilities to perform
certain jobs.
Throughout this discussion, the emphasis has been directed
towards people and how they could contribute to equipment per-
formance. Prior to equipment operation, however, in-house
support, such as engineering and purchasing, becomes involved.
It has proven to be extremely beneficial to the performance of
air pollution control equipment to involve from the outset those
individuals who can contribute to its success—engineers, line
workers, and others. Sudden changes in organization and opera-
tions due to equipment acquisition can be interpreted by em-
ployees as actions to tighten management controls, produce more
work, and hence reduce job satisfaction.
The installation and operation of air pollution control
equipment may precipitate the redesign or modification of either
a formal or informal maintenance management information system.
Should this be the case, it is incumbent on the maintenance
manager to:
Clearly define and identify the objectives of the
system
Determine effective methods of work planning and
scheduling
Determine methods of measuring and appraising mainte-
nance performance
Determine the personnel required
Adopt budget and financial control procedures
Although these are some ingredients of a maintenance man-
agement system, it should not be construed as a magic formula
that will provide the best maintenance organization for a par-
ticular plant.
2.3 MAINTENANCE PLANNING, SCHEDULING, AND WORK MEASUREMENT
2.3.1 Planning and Scheduling
The function of maintenance planning and scheduling is as
follows:
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Minimization of idle time. (Only 30 to 40 percent of a
worker's time is spent using his tools; the remainder is
spent traveling to and from the job, acquiring materials
and supplies, waiting for other phases to be completed and
for production equipment to be shut down.)
Maximizing the efficient use of worktime, materials, and
equipment
Operating at a level that is responsive to the needs of
manufacturing production
Before a maintenance work order is scheduled to be exe-
cuted, it must be planned according to its scope, priority,
sequence of performance, methods and materials to be used,
safety requirements, manpower, time estimate, and site availa-
bility. The work order form, which usually emanates from the
production department, is the mechanism that requests work to be
performed. It must include sufficient information for the
planner and scheduler to determine the resources needed for the
project. The replacements of bags, solenoid valves, scrubber
nozzles, and ventilation filters for ESP insulator compartments
are simple requests that can be implemented with little addi-
tional explanation. More complicated situations, such as
troubleshooting baghouse high pressure drops, require greater
effort.
The individual who plans and schedules the work order must
be familiar not only with the productive system, but also with
the major components of the air pollution control equipment
(i.e. pumps, blowers, conveyors). He should perform site visits
to make periodic equipment reviews. Because of the nature of
maintenance, this person must be able to modify plans and
schedules -frequently, and see that adequate materials and spare
parts are available to execute the work order. He should not be
restricted to the way things have always been done: new pro-
cedures, standards, and equipment may be appropriate.
The time for the work to be performed may be scheduled
while the equipment is operating or shut down. It is desirable
to perform the work during regular equipment shutdown, with
priority work being scheduled first. When work schedules must
be changed, substitute work orders may be necessary, thus maxi-
mizing available resources and hence the requirement for backlog
work orders. Although there are scheduling techniques available
to maintenance management, such as the Gantt Charts and Critical
Path Methods (CPM), they will not be discussed in this report.
Safety provisions must be planned should the work order
require it. Special clothing (goggles, masks, boots, gloves),
fire and electrical protection, ventilation, barricades, and
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lights must be specified. As an example, personnel performing
bag changes must use respirators, hard hats, and goggles.
Should it be necessary to enter any type of air pollution con-
trol equipment, the worker must be accompanied by another indi-
vidual .
2.3.2 Work Measurement
Regardless of the type or extent of the work being per-
formed by an individual or team, or the materials used, a method
to estimate costs accurately must be available to the mainte-
nance manager. A method of measurement is needed as a basis for
product pricing and costing, improvement of worker effective-
ness, more efficient manpower utilization, reduced costs of new
and/or improved facilities, efficient scheduling of preventive
maintenance, and identification of worker education require-
ments .
With the ultimate goal of reducing costs and improving
quality, the methods that maintenance management can use to
measure work are experience, historical information, and stan-
dard data. For example, experience has taught that 12 bags
require replacement every month. Therefore, once a month the
manager can estimate the cost, manpower, and materials to be
devoted to a specific task. The primary disadvantage of this
form of work measurement is that periods of inefficiency and
ineptitude are not usually identified since "experience" has
taught maintenance management that "it has always been done
'that way1." With new air pollution control equipment, no
experience is available to estimate the time required for pre-
ventive maintenance and repair.
If a particular job has been performed numerous times,
historical data may be available to estimate the average perfor-
mance time. If the work is being performed in a manner satis-
factory to management, this may be considered standard.
2.4 PREVENTIVE MAINTENANCE
2.4.1 Benefits of Preventive Maintenance
In addition to maintaining compliance with air pollution
emission regulations, an air pollution control equipment preven-
tive maintenance program will enable the user to accomplish the
following:
Assure that production levels are not affected
Minimize maintenance cost
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Maximize scheduled shutdown periods
Significantly reduce equipment breakdowns, downtime, and
malfunction
Extend equipment life
Reduce emergency repairs
Reduce overtime
Reduce overall maintenance and attendant repair costs
Minimize spare parts inventory
The more a plant is oriented toward capital equipment, the
more it can reap the benefits of a preventive maintenance pro-
gram. This is true because this type of plant requires more
maintenance than does a labor-intensive plant.
By definition, preventive maintenance refers to activities
that fight defects in existing equipment without changing the
design of the equipment. In the field of air pollution control,
however, additional onsite and in-house engineering is often
performed on the equipment to reduce user costs of operation and
maintenance. Vendor unfamiliarity with the process, or inade-
quate preventive maintenance, will often necessitate equipment
modifications and redesign to accommodate actual operating
conditions.
2.4.2 Reasons for Minimum Preventive Maintenance
In spite of the tangible and intangible benefits of preven-
tive maintenance, air pollution control equipment nonetheless
remains neglected. Typical reasons given for minimum mainte-
nance are summarized as follows:
Attention and effort are better spent on process equipment.
Pollution equipment and associated components are of poor
quality because they were purchased on a low bid basis.
Plant personnel are not inclined to maintain equipment that
is dirty, dusty, potentially hazardous, and inaccessible
for service.
Equipment is located outside the plant building and there-
fore often goes unnoticed and unattended until problems
exist.
Defects and obsolescence of the electric and mechanical
components are inevitable occurrences.
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Plant personnel are unwilling to stock replacement parts,
supplies, and accessories.
There are not enough maintenance personnel and funds.
Corporate engineering incorrectly specified equipment and
should have consulted the plant.
No one individual is willing to manage and coordinate the
maintenance function.
Insufficient technical knowledge is present to diagnose and
troubleshoot problems.
Management views preventive maintenance as nothing more
than lubrication and cleaning on a scheduled basis. *
The position of management is typically not to spend money
unless the return on investment can be realized in the near
future. The acquisition of additional skilled workers,
materials, spare parts, and power tools is looked upon with
great caution and skepticism, especially since the ROI is not
likely to be felt for as long as 2 years.
A PM program must be appropriately introduced to plant
management if it is to be enlarged and expanded. At this junc-
ture, the attitude of plant management to maintenance could be:
"We bought it, now you take care of it." The task of selling
the preventive maintenance program to management should be well
thought out; especially regarding costs and advantages. Some of
the elements critical to selling the program are described
below:
Identify the individuals in management and operations who
have the authority to make decisions, either directly or
indirectly. (Do not avoid those persons who you think will
not be responsive.)
Discuss program with maintenance workers and supervisors,
because their cooperation and enthusiasm are essential.
Define a means to evaluate the effectiveness of the pro-
gram.
Estimate project cost savings, man-hours, materials, and
similar items.
Goals and objectives should be realistic; therefore, the
scope of the program should be small before a more compre-
hensive one is planned.
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Clearly define the equipment and components that must be
inspected and maintained. (Equipment instruction manuals
must be supplemented by worker information.)
Compile checklists that include not only items to be in-
spected or maintained, but also the sequence of events and
operations.
Estimate the frequency of inspection.
These ingredients, plus a presentation of the overall
benefits of the program (as given in 2.4.1), are essential for
selling the PM program. If management wants to streamline the
proposed program, it is generally advisable to adhere to their
requests in order to initiate the program. After a given period
of time/ with the necessary appraisals of performance, the
program will probably need expansion and modification. By its
nature, preventive maintenance is dynamic and constantly in
flux, and close monitoring is needed to see that management and
operations requirements are being fulfilled.
The primary considerations in having the preventive mainte-
nance program approved are financial ones. When the program is
developed, budgets must be estimated with the awareness that
maintenance competes with production for funds. The production
budget is usually based on demand for services, and successful
competition with production requires the use of a method to
calculate ROI.
2.5 MAINTENANCE PERFORMANCE EVALUATION
The resources that are available to maintenance are man-
power, material, and equipment. Of the three, the most diffi-
cult to control is manpower, as reflected in wage rates. Labor
control can easily be effected through careful administration of
how, when, and where the work is to be performed. The simplest
and most direct method to measure manpower production is to
compare the man-hours actually consumed to perform a particular
task with that originally estimated. Significant and frequent
deviations from the estimates require investigation.
The maintenance report is the most important mechanism for
effective maintenance control, i.e., control of labor produc-
tivity. It should contain such ingredients as the skills used
to effect the work, associated labor costs, and comparison of
actual vs. estimated man-hours. It may also contain a compari-
son of the maintenance costs for a particular period or job with
comparable costs derived from some base period. Although they
are indicators, and not maintenance control functions, open work
12
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orders help management monitor the progress of the maintenance
function. A comparison between man-hours spent on planned work
and those on unplanned maintenance, and the ability to forecast
the completion of jobs on schedule, are additional maintenance
control indicators.
As an example of the use of some of these controls and
indicators, a particular baghouse was having frequent bag fail-
ures; the cause was attributed to hot cinders being carried to
the bags. Excessive man-hours and bag replacement were obvious
consequences. Emergency baghouse shutdowns, coupled with
several community complaints, forced management to find a way to
solve the problem. Spark arrestors were subsequently installed
and the ROI realized within 1 year. The motivation to install
equipment was primarily one of cost savings; air pollution
abatement was secondary.
2.6 SPARE PARTS AND MATERIAL CONTROL
The introduction of air pollution control equipment (or any
equipment) to a plant requires the purchase of spare parts and
supplies. The types, quality, and costs incurred are but a few
of the considerations to be reviewed. The spare parts needed
are those typically associated with moving and rotating parts.
At the outset, critical spare parts should be identified.
This information is usually available from the equipment manu-
facturer. With equipment use, plant experience is acquired
thereby further identifying spare parts requirements. In this
regard, a critical part is one that could slow down or abort
production. For instance, a clogged scribber nozzle may affect
emissions somewhat, but substantial mist eliminator buildup
would diminish system flow rate. An available spare set of mist
eliminator media would immediately alleviate the problem, thus
minimizing system shutdown.
Replacement bags, nozzles, gaskets, hose clamps, and other
items that are changed frequently should be in ample supply.
The storeroom personnel must be responsible for this supply and
must maintain an inventory information system to provide lead-
time to procure replacements.
The materials and spare parts inventory for air pollution
control equipment may vary according to season, plant shutdown,
and process modification. For instance, during winter months
the entrained moisture in compressed air lines to pulse-jet
baghouse valves may freeze and cause unit disfunction. Exces-
sive demand for replacement valves and bags may occur, necessi-
tating rebagging and process shutdown.
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Suppliers in remote locations and long leadtime items are
problems of great concern to maintenance. Noncritical items
must be procured with sufficient leadtime to avoid emergency
situations. It is, however, difficult to justify ordering
expensive supplies and equipment when there is only a possi-
bility that they may be needed. An example is a spare high-
horsepower motor for a venturi scrubber fan.
Cost considerations often overlooked are those incurred to
store spare parts and materials. Space, recordkeeping, and
additional taxes and insurance are also significant contribu-
tions to the overall maintenance cost picture. Inventory costs
can be reduced if replacement items can be procured locally.
2.7 MAINTENANCE BUDGETS
A financial plan for the procurement of air pollution
control equipment is usually thoroughly prepared. Annual opera-
tion and maintenance budgets for air pollution control equipment
are estimated at 10 to 12 percent of the capital equipment cost.
This guideline is reasonably accurate, but more of the details
pertinent to maintenance supplies, labor, and equipment should
be analyzed. The most important element of the maintenance
budget is the man-hour estimate. Man-hours may be further
subdivided into such categories as inspection, lubrication,
particular process equipment, and air pollution control equip-
ment. A major advantage of this method of budgeting is expendi-
ture visibility, i.e., cost control and the ability to monitor
the flow of funds.
In addition to manpower and material budgets, the procure-
ment of capital equipment (high-power industrial vacuum clea-
ners, for example) should be included in each annual budget.
Since capital equipment programs can be expressed in terms of
ROI, management is more likely to approve these budget requests
than others.
2.8 TRAINING AND EDUCATION
Regardless of the type of equipment, a well-planned
training and education program is crucial to production improve-
ment and reliable equipment operation. Management usually
resists these programs unless excessive operating problems
arise. In the case of operating and maintaining air pollution
control equipment, even less attention is given to training.
Maintenance management often thinks that the line workers will
acquire the necessary knowledge "on the job."
14
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Besides the maintenance workers, the personnel who should
be familiar with the operation and maintenance of air pollution
control equipment are supervisors, planners, and schedulers. At
startup, the operation and maintenance department should see
that the original equipment manufacturers provide a suitable
training program, supported by the necessary instruction manuals
for service and maintenance. For intensive training, several
equipment manufacturers have prepared video tapes in support of
classroom instruction.
Instruction at the training sessions should also be given
by the manufacturers of the subassembly components and systems.
For example, the supplier of an electrostatic precipitator
should include the manufacturers of the transformer/rectifier
and ash handling systems at the training sessions. If the air
pollution control equipment contains opacity measurement capa-
bility, a representative from the instrumentation manufacturer
should also be present.
The training program should be devised by both user and
equipment manufacturer. The user must identify the personnel
(skilled workers, engineers) who will have some responsibility
for the equipment, and the manufacturers must gear their presen-
tation to this audience.
Although this approach appears to be elaborate, it is the
only reasonable way to guarantee that the equipment will be
operated and maintained satisfactorily. Unless a training
program is defined during original contractual agreement, it
usually does not fall within the framework of the original
equipment capital cost. In this case, plant management may be
reluctant to fund it at a later date.
Air pollution control equipment usually develops problems
before management becomes more conscientious about the need for
training and preventive maintenance. If management does not
endorse an extensive training program, it is incumbent on opera-
tion and maintenance management to measure and evaluate the
long-range outcome of the training program, especially with
respect to ROI.
Another consideration in developing a training program is
the amount and complexity of the abatement equipment. A small
plant may have only one piece of equipment, whereas a large one
could have numerous types and amounts.
15
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2.9 CONTRACT MAINTENANCE SERVICES
In recent years, the concept of contract management has
become more and more acceptable, especially in new plants.
Plants use contract maintenance to buy know-how and reduce
costs, while still retaining flexibility. In-house maintenance
functions, however, cannot be eliminated. The benefits of
contract maintenance, with emphasis on air pollution control
equipment, are given below:
Plant personnel do not have to be thoroughly trained in
equipment maintenance, thus allowing them to devote their
time to process equipment.
Technological troubleshooting and problem diagnosis are not
usually in-house resources.
Plant personnel do not have the knowledge to improve equip-
ment performance.
Plant personnel may lack awareness of alternative supplies
and suppliers.
Expenditures for larger crews, repair facilities, tools,
and measurement instruments are reduced.
Previous experience on similar equipment and applications
can be used.
Interpretations of causes of component failure can be
provided.
Contract maintenance programs are more effectively regu-
lated and administered than are in-house programs.
Dirty and hazardous jobs do not have to be performed by
plant personnel.
Fluctuating workloads due to startup and seasonal varia-
tions can easily be handled.
2.10 VENDOR CONTRIBUTION TO POOR EQUIPMENT PERFORMANCE
Even the most explicit procedures, guidelines, and inspec-
tion checklists will not achieve desired goals unless the person
or organization performing the work has willingness, motivation,
and resources to do the job. Because nearly all operating and
maintenance activities are human activities, they are controlled
by those individuals doing the work. On the other hand, the
16
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reader should not assume that the users of air pollution control
equipment are solely responsible for poor equipment performance.
Vendors also contribute in the following ways:
Misapplication of equipment due to unfamiliarity with
contaminants and process parameters
A highly competitive marketplace, resulting in cost reduc-
tion methods that often have a negative effect on product
reliability and component quality
Inadequate and inept design for ease of maintenance (i.e.,
access doors, blind flanges, internal catwalks, component
accessibility)
Insufficient performance monitoring instrumentation
Improperly located pressure taps, leading to dust buildup
and clogged air lines.
Insufficient stock and inventory of component replacements.
Primary interest in product sales (flange to flange), not
total system design and installation.
New equipment designs that are inadequately tested and
evaluated in the field
2.11 CONCLUSIONS
The installation and operation of air pollution control
equipment covers a wide range of disciplines, from management to
technical aspects, plant managers to skilled workers, emergency
to preventive maintenance, and budgets to training. Much of the
attention in this field has been devoted to the technical
phases, not the managerial and administrative. The reader with
sufficient background should now be familiar with the overall
scope of the management aspect of the operation and maintenance
of air pollution control equipment.
17
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SECTION 3
TECHNICAL ASPECTS OF THE DESIGN,
OPERATION, AND MAINTENANCE OF BAGHOUSES
3.1 BACKGROUND
This section of the report provides the user of baghouses
with sufficient guidelines and procedures to enable him to
operate, service, and maintain this equipment in order to comply
with air pollution emissions regulations. It provides details
on special equipment components; procedures for startup, routine
operation, shutdown, inspection, and maintenance; and recom-
mendations for spare parts and materials. A sample trouble-
shooting case history is presented in Appendix A to give the
user a program for improving equipment performance reliability.
The principles of air pollution control equipment and mechanisms
of contaminant collection will be discussed only in terms of
operation and maintenance.
3.2 BAGHOUSE COMPONENTS AND OPERATIONAL PARAMETERS
Baghouses are categorized according to their cleaning
mechanisms: shaker, pulse jet, and reverse air. The ingre-
dients common to all types of baghouses are: air-to-cloth ratio
(filter rate), pressure drop, cleaning mechanism, frequency of
cleaning, filter cloth characteristics, number of baghouse
modules, materials of construction, and method of handling the
collected contaminant.
The discussion that follows describes the engineering
principles and comments on components that cause problems in
equipment operation and maintenance.
3.2.1 Air-to-Cloth Ratio (Filter Rate)
The quantity of gas (acfm) passing through a given area
(ft2) of filter cloth is defined as the air-to-cloth ratio,
filter rate, or superficial face velocity. Units for this
parameter are cubic feet per minute per square foot, or feet per
minute. Physically, the air-to-cloth ratio represents the
average velocity with which the gas passes through the cloth
18
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without regard to the fact that much of the area is occupied by
fibers. For this reason, the term "superficial face velocity"
is often used.
Depending on the type of fabric and cleaning method, fabric
filters can operate at air-to-cloth ratios of 15:1 and less.
Upon startup with new and clean filter media, the pressure loss
may be less than 0.5 in. H20. After initial operation (season-
ing or conditioning), the pressure loss may approach 2 to 3 in.
H20. At some time, the collected particulates (filter cake) and
cloth must be cleaned, by one or a combination of mechanisms, to
return the cloth to a significantly lower pressure loss.
Typical air-to-cloth ratio for shaker and reverse air baghouses
can range from <1:1 to 4:1 with woven filter media. Pulse-jet
cleaning can use 5:1 to 15:1 air-to-cloth ratios with felted
filter media.
The air-to-cloth ratio is a calculated number used for
design and discussion purposes, and the ratio should not be
assumed to exist throughout the baghouse media. For instance,
the gas flow entering the baghouse may not be uniformly distri-
buted and may be channeled in a preferential direction, resul-
ting in a higher ratio in one section of the baghouse than in
another. This problem may be overcome by providing turning
vanes, flow splitters, and baffle plates.
From an aerodynamic point of view, the baghouse does not
approach, or even come close to, an ideal geometric shape for
gas flow. It should also not be assumed that all particulate
follows the air streamlines in the baghouse. Gravity and other
forces can cause particulates to digress from the streamlines,
resulting in more particulate being filtered in one portion of
the baghouse than another. Particulates measuring 5 pm or less,
however, will follow the air streamlines and behave similarly to
gas molecules.
3.2.2 Pressure Drop
The resistance to airflow (pressure drop) provided by a
clean filter cloth is determined by the configuration and char-
acteristics of the cloth and filtering velocity. One of the
characteristics of clean fabrics frequently specified is the
permeability, which is defined as the air volume (ft3/min) that
will pass through a square foot (ft2) of filter media with a
pressure differential of 0.5 in. H20. According to the type of
fabric (yarn, weave, weight, etc.), the permeability could range
from 15 to 100. This parameter is useful only in comparing one
type of media with another.
19
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In normal filter operation, the pressure loss is primarily
attributed to the dust filter cake and cloth-entrapped
particles, with a small portion of the pressure drop due to the
cloth alone. Other than collection efficiency,- the primary
consideration in maintaining normal operating pressure drop is
the energy cost to drive the air-moving blower: the higher the
pressure drop, the more energy consumed. Continuous operation
at high pressure drops also seriously weakens the filter integ-
rity and structure. In an attempt, to alleviate some of this
high pressure drop, much attention has been given to the cloth
characteristics (fiber diameter, fiber construction, porosity,
cloth finishes, backings, coatings).
Although the resistance to the cloth filter arid dust cake
cannot be separated from the total resistance of the exhaust
system, the operating characteristics of the exhaust blower and
the duct resistance will determine the overall baghouse resis-
tance. If possible, the user of the equipment should obtain
information from the vendor regarding the pressure losses in-
curred because of the system ductwork, without bags being in-
stalled. This information may be valuable when comparing
several equipment designs, because duct pressure drop does not
contribute to filtration, only energy consumption,
Typical operating pressures, according to the application,
can vary from 3 to 10 in. H20. As a rule of thumb, the pressure
drop squares as air-to-cloth ratio (velocity) doubles. Attempts
to increase the blower flow rate to exhaust contaminant more
rapidly will seriously affect system pressure drop. By in-
creasing the intensity or frequency of cleaning, it. is possible
to reduce pressure drops to levels approaching those of the
clean fabrics. If this concept is carried too far,, however, the
collection efficiency may be adversely affected by damaging the
fabric and consuming additional costs in driving the cleaning
mechanism. The selection of an operating pressure loss is a
matter of trade-offs, and may not necessarily conform to origi-
nal design values. It is obvious, therefore, that monitoring
the pressure drop across the baghouse is the single most impor-
tant parameter indicating system performance*
3 •2 •3 General Design
The basic difference between one generic type of baghouse
and another is the cleaning mechanism (shaker, reverse air,
pulse jet). There are, however, common components for each and
the following remarks will thus apply regardless of cleaning
mechanism.
The baghouse casing is usually fabricated of light-gauge
mild steel, and may be insulated to prevent temperature drops
20
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during operation. In applications handling abrasive materials
or corrosive gases, a lining of corrosion-resistant material may
be necessary. The filter bags within the housing are mounted to
a tube sheet with hose, ring, or spring-loaded clamps. The
clamps are mounted at the bottom on shaker and reverse air bag-
houses, at the top on pulse jet baghouses. The replacement of
bags having hose clamps, which is extremely time consuming, is
prevalent in older applications. Quick disconnect clamps and
steel snap rings sewn into shaker bag cuffs are being specified
more often.
The particulate-laden gas is usually introduced into the
upper portion of the hopper. This allows the entering gas
velocity to be reduced suddenly, thereby enabling the coarse
particles to settle directly into the hopper. The finer par-
ticles, along with the gas, pass upward to the fabric filters
(typically cylindrically shaped). According to the generic type
of baghouse, filtration may occur on either the inner or outer
surfaces of the bag. The cleaned gas is subsequently passed to
a plenum before being discharged into a common manifold. As the
amount of collected dust accumulates, the thickness of the
filter cake also increases on the bags, thus producing a corres-
ponding increase in the pressure drop across the collector.
Periodically, either with a programmed timer or by monitoring
the pressure loss with a differential pressure switch, the
collector will go into its cleaning cycle.
The proper installation of bags with accessory hardware is
one of the most important aspects of baghouse performance. The
intention of the manufacturer is to provide efficient bag
arrangement with proper bag clearances. The most common type of
arrangement is bags that form straight rows. Sufficient clear-
ance between bags avoids the possibility of rubbing, and speci-
fications for tensioning should be provided by the manufacturer.
The most prevalent problem in baghouse design, regardless
of type, is ease of access to bags for maintenance. Cost con-
siderations often result in walkways, internal ladders, and
access doors being omitted. Walkways between banks of bags must
be provided; if the bags are long, catwalks are needed at the
top and bottom of the bags. The manufacturer often designs the
housing so that it is impossible to reach bags beyond an arm's
length. A walkway should be provided around the bags to make
them easily accessible. Top access doors are also necessary for
proper inspection and bag maintenance.
3.2.4 Cleaning Mechanism
Shaker—
A baghouse with mechanical shaking consists of a housing
divided into an upper and lower portion by the tube sheet. The
21
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upper portion usually contains woven fabric tubular bags, and
the lower contains pyramidal hoppers, each with its own valve or
with a long, trough-type hopper emptied by a sealed screw con-
veyor. The upper ends of the bags (which are flexibly mounted,
often from a common support structure) are shaken by mechanical
or pneumatic means. During cleaning, the shaking dislodges the
filter cake from the inner surface of the bag and causes the
cake to fall into the hopper. The shaking energy is transmitted
most effectively next to the shaker bars and diminishes grad-
ually to the thimble. Hence, occasions may arise in which the
bags are cleaner at the top than at the bottom.
Upon conclusion of the cleaning cycle (1 or 2 minutes per
hour; 1 to 5 cycles per second; amplitude up to 2 inches; 10 to
100 cycles) the damper opens, thereby returning the compartment
or system to the filtering mode. In large systems, individual
compartments are cleaned one at a time to keep the pressure loss
across the collector at a nominal value.
The mechanical shaker mechanism consists of an electric
motor coupled to a cam or eccentric, which translates the rotary
motion of the motor into an oscillation through a connecting rod
assembly. Bags may be shaken horizontally or vertically. The
shaker motor drives an eccentric crankshaft via pulley belts to
the frame from which the bags are hung. A pillow block bearing
supports the crank shaft on one end of the shaker assembly and a
shaker hanger on the other. Good design practice has the shaker
mechanism mounted outside the baghpuse housing for ease of
maintenance, lubrication, and inspection.
No inflating pressure is permitted within the bags during
shaking, because such a condition would impede fabric movement
and hinder cake release. Butterfly and guillotine dampers,
unless sealed properly, could contribute to air leakage and bag
inflation; poppet valves are therefore recommended. Bag tension
is also critical to proper cleaning. For instance, a 9-ft,
seamed bag will move approximately 3 in. off the center line
during shaking; longer bags will move somewhat more, and seam-
less bags require less movement.
The following situations could directly affect bag cleaning
performance while operating shaker baghouses:
As a result of housing deformity, either from heat stress
warpage, poor fabrication, or installation, bags are
stretched or collapsed.
Housing deformity, with its associated dimensional changes,
produces excessive wear on shaker assembly (crankshaft
becomes misaligned and produces excessive wear on bearings
and shaker hanger).
Dimensions of replacement bags may not coincide with the
actual dimensions.
22
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The bags are fastened to the shaker bars by various means.
An older method consists of attaching the bag to a steel disc or
cap (disposable caps are available) from which a threaded bolt
is coupled to a shaker bar. A newer design consists of a sewn
loop placed over a J-hook. Another fastening method consists of
sewing the end of the bag into a flat strap, which is looped
back and forth over a special hanger.
During cleaning, the pressure across the entire baghouse
may increase somewhat. This increase usually occurs when mod-
ules or sections are isolated to allow for cleaning; overall
performance is not usually affected.
Reverse Air--
This baghouse has a configuration similar to that of the
shaker. The dirty gas can be passed through a single inlet into
the trough-type hopper, or through a common inlet manifold that
serves many pyramidal hoppers. Each tubular bag is clamped to a
thimble at its lower end and to a flexibly mounted cap at the
upper end. Filtration occurs from the inside of the tube to the
outside.
During the cleaning cycle, a valve at the compartment
outlet is closed. Simultaneously, a small air-vent valve is
opened, allowing atmospheric air to rush in and collapse the
bags. The air rushes in because the housing is under negative
pressure. According to the cleaning requirements, a secondary
blower providing the reverse air may be necessary.
Bag collapse breaks the filter cake and allows it to drop
into the hopper. The reverse airflow is maintained by the
suction through the common inlet manifold, which remains open.
Upon conclusion of the cleaning cycle, the valve is opened, and
the air vent and/or secondary blower is closed. Individual
compartments are cleaned one at a time on a predetermined sched-
ule activated by a programmer or by a monitoring of the draft
loss.
Some filter tubes are equipped with rings spaced at given
intervals along their vertical height. When the air is re-
versed, the bags collapse inward, but the rings prevent the
cloth from rubbing against itself and permit the cake to fall
without interference.
Pulse Jet--
Like the shaker, the pulse-jet baghouse is divided into an
upper and lower portion by a tube sheet. The gas is usually
introduced to the lower part of the housing, often through the
hopper. The hopper serves as a settling chamber and allows
large particles to be removed without needing to be filtered.
23
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The gas flow is directed upward and around the cylindrical
filter tubes and then through the filters from the outside
direction. In contrast to the shaker, the filter cake is built
up from the outside, not the inside. The cleaned gas passes
upward through the tube sheet and out the outlet manifold.
The bags are cleaned periodically when sets of compressed
air jets are actuated, blowing air at high pressure through the
individual tubes. This flow is superimposed on the system flow.
The filter bags are fabricated from felted media and supported
by a wire cage or retainer. A venturi-shaped nozzle is often
provided to improve the efficiency of the air pulse. The force
of the pulse jet snaps the bag outward, thereby partially dis-
lodging the accumulated filter cake. The system flow then snaps
the bag onto the retainer and completes the cleaning.
The cleaning pulse usually cleans several bags in a row at
one time. This procedure occurs through sets of manifolds and
is controlled by a timer that activates a solenoid and diaphragm
valve that releases the air pressure provided by a compressor.
The dislodged contaminant falls to a hopper and is disposed of
by an airlock, screw conveyor, or by pneumatic means. A vari-
ation in pulse cleaning design is the compartment or plenum
pulse. In this case, an entire compartment is subjected to the
cleaning pulse instead of a row of bags as in the pulse-jet
situation.
Although other baghouse designs are available, the indi-
vidual cleaning mechanisms are similar and may be used in con-
junction with one another for more effective cleaning. Accor-
ding to the application and manufacturer, the filter configur-
ation may range from an envelope shape to a disposable filter
cartridge, the most common type being the cylindrical filter.
3.3 BAGHOUSE OPERATION AND MAINTENANCE
For a baghouse operation and maintenance program to be
highly effective, a logical sequence of events should occur.
Guidelines to be followed before startup and inspection are
given below along with routine startup, operating, and shutdown
procedures. The scope of the inspection procedure varies accor-
ding to whether the unit is operating or shut down. When the
unit is shut, down, the condition of bags and hoppers can be
viewed. The unit is otherwise inaccessible, with only such
parameters as operating pressure and temperature and external
cleaning and dust handling system components open to inspection.
3.3.1 Pre-Startup Inspection
If a new baghouse has been installed, or if one has under-
gone internal service and maintenance, it must be thoroughly
inspected before it is "buttoned up." The inspection should
include the following steps:
24
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Remove such debris as nuts, bolts, tools, welding rods, and
other items that may become airborne and behave as projec-
tiles, puncturing bags or getting caught in operating
mechanisms.
Remove all contaminant and inspect the hoppers for leaks
and debris.
If single bags were replaced, inspect adjacent ones for
damage.
Check bag connection and tension.
If entire unit was rebagged, check again after a few hours
of operation.
Inspect walls for cracked, chipped coatings.
Inspect instrument monitoring locations, especially pres-
sure taps.
Check valve seals on inlet and outlet ducts.
If possible before the unit is buttoned up, operate the
various components to check their operation. It may be feasible
to perform this work while workers are in the unit. If not, the
unit should be closed up, operated without flow, and then shut
down and inspected again.
3.3.2 Routine Startup
One of the most important items to consider in starting up
a baghouse is the condition of the process air. If the air is
moist, it is necessary to preheat the baghouse to avoid conden-
sation, especially on the bags. Ideally, purging the system
with warm, dry air will abort this problem; however, appli-
cations may arise where hot, clean air may not be available
because by virtue of being hot it may already contain contami-
nants. In this case, external means of preheating are recom-
mended, such as strip heaters. Even if the baghouse is insul-
ated and out of service for only several hours, preheat may be
required.
The outline procedure given below for routine startup can
be used for shakers, reverse-air, and pulse-jet units.
1. Secure doors and hatches and notify personnel of
startup.
2. Operate material handling system (airlocks, screw
conveyors, etc.).
25
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3. Open bypass dampers to allow hot, "clean" air to enter
system for preheat.
4. Before starting blower, verify zero settings on moni-
toring instrumentation.
5. Start blower.
6. Engage cleaning circuit.
7. Record data from monitoring instrumentation (fan motor
amperage and voltage, temperature and pressures).
8. Allow contaminant to pass baghouse and note and
changes in monitoring data.
3.3.3 Routine Inspection and Maintenance During Operation
During routine operation, an inspection procedure recording
baghouse operational data should be used. A sample of a routine
daily inspection report for a shaker baghouse is provided in
Figure 2. This document may be used to give the maintenance
department a continuous record of system performance. The two
columns headed "CHECKED" are to be filled in by the inspector to
verify that he observed the condition of the component. The
column "REQ. ATTN." is provided to alert maintenance personnel
that a problem exists. In addition to the inspection, a mainte-
nance checklist for a shaker mechanism is given in Figure 3.
Figure 4 provides an inspection report for a pulse-jet baghouse.
3.3.4 Routine Shutdown
The most important aspect of shutting down a baghouse is
the prevention of condensation. A general procedure includes
the following steps:
When the process is shut down, it is advisable to continue
to operate the baghouse for one complete cycle (including
cleaning). This operation purges it with clean air to
avoid condensation and ensure that bag contaminants are
removed. (In applications where a filter cake is needed
upon startup, cleaning is not recommended.)
Shut down the fan.
If possible, isolate the baghouse by closing dampers.
Continue to operate dust removal system until hoppers are
clear and then shut off the system.
26
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SHAKER BAGHOUSE INSPECTION FEPORT
APPLICATION:
DATE/TIME: CHECKED
FEPORT BY: *ES NO ATTN.
OPERATION OF MATERIAL HANDLING SYSTEM
NOISES a n D
AIR LEAKS CD CD d
LUBRICATION LEAKS CD D CD
GASKETING O CD O
COMMENTS
DUCTS (rNLET/OUTLET)
NOISES a a a
AIR LEAKS O D O
GASKETS d O O
COMMENTS
BAGHOUSE
SHAKER OPERATING CD O C3
SHAKER SEQUENCE CD CD CD
AIR LEAKS O CD a
COMMENTS
OPERATING DESIGN •
COLLECTOR MEASUREMENTS
TEMPERATURE: IN d
TEMPERATURE: OUT D
PRESSURE DROP CD
STATIC PRESSURE: IN D
STATIC PRESSURE: OUT D
FLOW RATE D
COMMENTS
BLOWER
CURRENT D
TOLTAGE C3
BELT TENSION O O CD
BEARING LUBRICATION Da CD
COtHENTS
STACK APPEARANCE
COM-1ENTS
Figure 2. Sample of routine daily inspection report for shaker baghouse.
27
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SHAKER MECHANISM MAINTENANCE CHECKLIST
APPLICATION:
DATE/TIME:
REPORT BY:
CHECKED
YES NO
KEQ.
ATTN.
LUBRICATE
SHAKER NO.
MOTOR
ECCENTRIC BEARINGS
PILLOW BLOCK BEARING
SHAKER FRAME SUPPORT
PULLEY/BELTS
COMMENTS
CD
O
a
a
a
a
a
a
a
a
a
n
a
D
n
a
a
a
o
INLET/OUTLET VALVES AND ACTUATORS
MOTOR
DRIVE FDD
DRIVE SCREW
COMMENTS
a
a
a
O
a
a
n
a
a
n
a
a
SCREW CONVEYORS
MOTOR
SCREW DRIVE
HANCZR BEARING
TAIL SHAFT BEARING
a
a
a
o
a
a
a
n
a
a
CD
a
a
D
D
Figure 3. Sample of maintenance checklist for shaker mechanism.
28
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PULSE- JET BAGHOUSE
APPLICATION:
DATE/TIME:
INSPECTION RE
JORT
( VkY 'KH k
FEPORT BY:
OPERATION OF MATERIAL HANDLING SYSTEM
NOISES
AIR LEAKS
LUBRICATION LEAKS
DRIVE ASSEMBLY
GEAR REDUCER
DRIVE SHAFT
BEARINGS
ACCESS DOORS
GASKETING
COMMENTS
DUCTS (INLET/OUTLET)
NOISES
AIR LEAKS
GASKETS
DAMPERS
COMMENTS
CLEANING MECHANISM
WATER TRAP
AIR REGULATOR
MANIFOLD PIPES
DIAPHRAGM VALVES
SOLENOID VALVES
WIRE CONNECTIONS
HOSE CONNECTIONS
COMMENTS
BLOWER
BELT TENSION
BEARING LUBRICATION
MOTOR
SHEAVES
DAMPER
COMMENTS
COLLECTOR MEASUREMENTS
TEMP. IN
TEMP. OUT
PRESSURE DROP
STATIC PRESSURE IN
STATIC PRESSURE OUT
HEADER AIR PRESSURE
TIMER SETTINGS
STACK OBSERVATIONS
COMMENTS
YES
a
a
o
CD
CD
a
a
a
o
a
a
a
a
D
o
CD
a
n
a
0
a
a
a
a
13
NO
n
a
a
a
a
n
C3
a
a
a
a
a
a
0
o
m
a
a
n
o
a
a
n
o
a
» ••••^••i
•. •••MBVUII
REQ.
ATTN.
a
a
a
O
o
a
a
a
CD
a
n
a
a
o
a
a
a
a
a
a
a
n
a
o
o
Figure 4. Sample of routine daily inspection report for pulse-jet baghouse.
29
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Baghouses are usually shut down for routine or emergency
process shutdown, or for routine or emergency baghouse mainte-
nance.
3.3.5 Maintenance During Shutdown
Maintenance of a baghouse must also occur within the hous-
ing when the baghouse is shut down and entry is possible. All
necessary safety precautions must be followed before entering
the baghouse. At this time, the items requiring greatest atten-
tion are the bags and any moving mechanism on the dirty side of
the baghouse. Figure 5 details an internal inspection of a
shaker baghouse. Other checklists can be prepared for different
baghouses, components, and other types of dust removal systems.
The checklist provided in Figure 5 could be used in conjunction
with that shown in Figure 2 as an excellent mechanism for main-
tenance recordkeeping.
3.3.6 Common Malfunctions
Most baghouse maintenance, regardless of cleaning mecha-
nism, focuses on the bags and moving mechanical parts, espe-
cially those parts on the dirty side of the filters. High-
maintenance items also vary according to the application.
Commonly observed malfunctions are discussed below.
The highest-maintenance item of a baghouse is the bags.
The most common problems are tears or pinholes, blinding (cake
buildup), and bleeding (seepage). These problems can be diag-
nosed and subsequently minimized with frequent: inspection and
preventive maintenance. It should not be construed, however,
that such a program will eliminate bag failure. Variations in
fabric quality, sewing techniques, quality control, and gas flow
distribution within the baghouse also contribute to bag failure.
A small number of bag failures may occur during the first
several months of operation, generally because of manufacturing
or installation defects. Under normal operating conditions, a
sudden increase in frequency of failure indicates that the bags
have reached the end of their operating life.
Visible stack emissions usually indicate bag failure.
Where a stack monitor is used, increased readings are further
indicators. In either case, three methods can be used to iden-
tify leaking bags: 1) inspection of bags for holes, 2) examin-
ation of bags for excessive dust accumulation, 3) use of bag
leak detection device.
Valves that are used to isloate individual bag chambers in
a shaker baghouse often experience sealing problems. An indi-
cation of a poor bag seal is a slight flow and presurization in
the isolated compartment. This condition can be determined by
viewing the shaking process and observing that the bags are
inflated.
30
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SHAKER BAGHOUSE: INTERNAL INSPECTION
APPLICATION:
DATE/TIME: CHECKED
REPORT BY: *ES NO ATTN.
FILTER BAGS
MOUNTING AND CLAMP ACCESSORIES
CORROSION a a a
WARPAGE a a a
BROKEN Odd
CUFFS a a a
COMMENTS
BAGS
VJDRN CUdd
ABRADED CH O O
DAMAGED CD d d
PIN HOLES CUdd
BURNS O C3 O
TENSION d d d
BLINDING CD D d
SEEPING d d d
FLEXURE WEAR ODD
COMMENTS
DUST REMOVAL SYSTEM (TYPE; SCREW CONVEYOR)
WORN BEARINGS d d d
LOOSE MOUNTINGS Odd
DEFORMED PARTS D H] D
WORN OR LOOSE DRIVE MECHANISMS d d d
CONTAMINANT BUILDUP HI D d
DEBRIS d d a
COMMENTS
DUCTS (INLET/OUTLET)
BUTXOOP d d d
ABRASION d d d
CORROSION ddd
LEAKAGE d d d
GASKETING O d d
BOLTS CD O O
WELDS • d C3 O
COMMENTS
Page 1 of 2
Figure 5. Sample of internal inspection report for a shaker baghouse.
31
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VALVES/DAMPERS
BUILDUP
CORROSION
CLEARANCE
COMMENTS
CLEANING MECHANISM (SHAKER)
SHAKER FRAME
SHAKER HANGER
LINKAGE
CONNECTING BCD ASSEMBLY
CRANKSHAFT
DRIVE MOTOR
PILLOW BLOCK BEARING
SHAKER DRIVE SUPPORT
BELTS
COMMENTS
TUBE SHEET
WARPAGE
CORROSION
BUILDUP
COMMENTS
ACCESS DOORS
SEALS
GASKETING
LEAKAGE
COMMENTS
BAGHOUSE HOUSING
WARPAGE
CRACKS
CORROSION
GASKETING
NUTS AND BOLTS
LINING OWCKED
COMMENTS
Page 2 of 2
CHECKED
YES
o
D
D
a
a
a
a
en
a
a
a
a
n
a
n
o
a
a
a
a
a
a
a
a
MO
a
D
a
a
n
a
a
a
n
CD
a
a
a
a
o
a
a
a
a
a
a
a
CD
a
FEQ.
ATTN.
n
a
CD
o
a
a
a
a
a
a
a
o
a
a
a
a
a
a
o
o
a
a
0
C3
Figure 5 (continued)
32
-------
If the push rod from poppet valves is subjected to dust, it
can affect air cylinder operation. The push rod should be
mounted in the vertical position, because horizontal mounting
may cause warpage and malfunction.
3.3.7 Troubleshooting Procedures
Recommendations for troubleshooting a shaker and a pulse-
jet baghouse are provided below.
Recommendations for Troubleshooting a Shaker Baghouse—
1. Check wear pattern before removing old bags. These
patterns may indicate a diffuser problem if abrasion
is causing bag failure. If chemical attack is the
problem, the pattern may indicate where the moisture
originates.
2. Account for shrinkage rate of new bags when adjusting
bag tension.
3. Be sure that the entire clamp (bag and screw) is of a
noncorrosive material (preferably stainless steel).
4. Use stainless steel, hex-head screws on the bands so
that ratchet wrenches or air guns can be used. Air
wrenches with pressure regulators can be calibrated
with a torque wrench to ensure proper band tightening.
5. Keep bag seams straight and do not torsionally twist
the bags.
6. Visually recheck bag tension after the first 8 or 10
hours, sooner if the shaker motor overloads or if the
belts break or squeal.
7. Check availability of other bag materials, especially
if sufficient leadtime is available. This may bring
significant savings and better performance. Current
trend is to purchase polyester or glass material for
most applications. Other materials, such as poly-
propylene or nylon, should be considered because they
may perform better and be less expensive.
8. Place tight-fitting washer on shaker pins if present
holes approach the size of the retaining clip on the
pin (shaker) mechanism.
33
-------
Recommendations for Troubleshooting a Pulse-Jet Baghouse—
1. Stiffen tube sheet if it flexes in order to minimize
bag-to-bag abrasion.
2. Align bags to prevent them from touching each other.
3. Check the coefficient of thermal expansion and the
rate of fabric shrinkage so that the bags do not
deform retainer. If bags are too small for the re-
tainer, they will tear.
4. Align jet in center of bags and make sure it is per-
pendicular to the tube sheet.
5. Use venturi nozzle, if possible. Although it has a
higher initial cost, savings in energy and better
cleaning compensate; it also minimizes the shear
effect on the upper portion of the bags caused by the
cleaning jet pulse. Avoid bag lengths greater than 8
ft., especially if the diameter is not over 4 in.
Long bags cause a problem of overcleaning at the top
and lack of cleaning at the bottom.
6. Change the diaphragm in the right angle valves as part
of routine maintenance. Replace pilot valves if they
have a history of failing or sticking.
7. If undercleaning is a problem, minimize the number of
transitions in the blow tube piping. Ream out the
blow tube orifices to prevent burrs caused by cutting
from restricting the flow.
8. Use headers having at least a 6-in. diameter, with the
last valve being at least one diameter from the end of
the headers.
9. Lubricate or replace all seals and worn bearings as
necessary in all rotating equipment.
10. Install a water trap on the compressed air line up-
stream of the solenoid valve.
11. Check housing for stress cracks caused by pulsing.
12. Weld or braise any loose wires on the retainers.
Replace badly bent retainers.
34
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13. Replace all gaskets or other parts when appropriate.
14. Follow the unit through a full cycle to ensure that
all valves are operating in a proper sequence.
15. Observe that the seal on the hopper discharge is
preventing reentrainment from fan suction or pressure
of air conveying system. Use double airlocks, if
necessary. Leakage in this component has the effect
of creating a higher grain loading, especially with
submicrometer particles. Air leakage could be ob-
served by "whistling" air rushing into the system or
dust patterns forming at infiltration locations.
16. Do not use a woven material in a pulse-jet collector;
use only felted material.
17. If tube sheet leakage is a problem, apply sealer
between the bag retainer and the top of the tube
sheet. When intermittent puffing occurs, it is usual-
ly caused by overcleaning. If all are not puffing,
check the row by sychronizing a stop watch with the
cleaning timer. If possible, check dump rate of the
conveying system.
18. Ensure that hopper operates fast enough to prevent it
from becoming more than two-thirds full.
General Troubleshooting Guide—
An extensive list of procedures for troubleshooting and
correcting baghouse malfunctions is given in Table 1. This
table should be consulted when troubleshooting and diagnosing
operational problems (i.e., when a symptom arises from various
causes during equipment operation). In the absence of symptoms
or malfunction, internal inspection may reveal such problems as
bag tears or pinholes, and the subsequent development or mal-
function is speculative. For instance, bag tears may result in
low pressure drop, high opacity, high air-to-cloth ratio, or
other problems.
3.3.8 Spare Parts
The manufacturer of the equipment usually provides a recom-
mended spare parts list. The most important item to stock is
bags, preferably a full replacement set. Although there is a
bag life expectancy and delivery time, emergencies could arise.
Caution should be exercised when inexpensive bags are quoted by
a bag fabricator. Poor quality control is usually the reason
for cost cutting. A list of replacement parts is provided in
Table 2.
35
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TABLE 1. BAGHOUSE TROUBLESHOOTING GUIDE
The following chart lists the most common problems found in a baghouse
air pollution control system and offers general solutions. In some
instances, the solution is to consult the manufacturer. This may not
be necessary in plants that have sufficient engineering know-how
available.
Where the information applies to a specific type of baghouse,
following code is used:
RP Reverse pulse
PP Plenum pulse
S Shaker
RF Reverse flow
the
Symptom
Cause
Remedy
High baghouse pressure
drop
Baghouse undersized
Bag cleaning mechanism
not adjusted properly
Compressed air pressure
too low (RP, PP)
Repressuring pressure
too low (RF)
Shaking not vigorous
Consult manufacturer
Install double bags
Add more compartments
or modules
Increase cleaning fre-
quency
Clean for longer duration
Clean more vigorously
(must check with manu-
facturer before implemen-
ting)
Increase pressure
Decrease duration and/or
frequency
Check dryer and clean
if necessary
Check for obstruction
in piping
Speed up repressuring fan
Check for leaks
Check damper valve seals
Increase shaker speed
(check with manufacturer)
(continued)
36
-------
Table 1 (continued)
Symptom
Cause
Remedy
Low fan motor amperage/
low air volume
(continued)
Isolation damper
valves not closing
(S, RF, PP)
Isolation damper valves
not opening (S, RF, PP)
Bag tension too loose
(S)
Pulsing valves failed
(RP)
Air volume greater than
design
Cleaning timer failure
Not capable of removing
dust from bags
Excessive reentrain-
ment of dust
Incorrect pressure
reading
High baghouse pressure
Check linkage
Check seals
Check air supply of
pneumatic operators
Check linkage
Check air supply on
pneumatic operators
Tighten bags
Check diaphragm valves
Check solenoid valves
Damper system to design
point
Install fan amperage controls
Check to see if timer is
indexing to all contacts
Check output on all terminals
Condensation on bags (see
below)
Send sample of dust to
manufacturer
Send bag to lab for analysis
for blinding
Dryclean or replace bags
Reduce air flow
Continously empty hopper
Clean rows of bags randomly,
instead of sequentially
(PP, RP)
Clean out pressure taps
Check hoses for leaks
Check for proper fluid in
manometer
Check diaphragm in gauge
See above
37
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Table I (continued)
Symptom
Cause
Remedy
Dust escaping at
source
Dirty discharge at
stack
Fan and motor sheaves
reversed
Ducts plugged with
dust
Fan damper closed
System static pressure
too high
Fan not operating per
design
Belts slipping
Low air volume
Ducts leaking
Improper duct flow
balancing
Improper hood design
Bags leaking
Bag clamps not sealing
Check drawings and reverse
sheaves
Clean out ducts and check
duct velocities
Open damper and lock in
position
Measure static on both sides
and compare with design
pressure
Duct velocity too high
Duct design not proper
Check fan inlet configuration
and be sure even airflow
exists
Check tension and adjust
See above
Patch leaks so air
does not bypass source
Adjust, blast gates in
branch ducts
Close open areas around
dust source
Check for cross drafts that
overcome suction
Check for dust being
thrown away from hood
by belt, etc.
Replace bags
Tie off bags and replace
at a later date
Isolate leaking compart-
ment if allowable without
upsetting system
Check and tighten clamps
Smooth out cloth under
clamp and reel amp
(continued)
38
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Table 1 (continued)
Symptom
Cause
Remedy
Excessive fan wear
Excessive fan
vibration
High compressed air
consumption (RP, PP)
Failure of seals in
joints at clean/dirty
air connection
Insufficient filter
cake
Bags too porous
Fan handling too much
dust
Improper fan
Fan speed too high
Buildup of dust on
blades
Wrong fan wheel for
application
Sheaves not balanced
Bearings worn
Cleaning cycle too
frequent
Pulse too long
Pressure too high
Caulk and tighten clamps
Smooth out cloth under
clamp and reel amp
Allow more dust to build up
on bags by cleaning less
frequently
Use a precoating of dust on
bags (S, RF)
Send bag in for permeability
test and review with
manufacturer
See above
check with fan manufacturer
to see if fan is correct for
application
Check with manufacturer
Clean off and check to see
if fan is handling too much
dust (see above)
Do not allow any water in
fan (check drain, look for
condensation, etc.)
Check with manufacturer
Have sheaves dynamically
balanced
Replace bearings
Reduce cleaning cycle if
possible
Reduce duration (after
initial shock all other
compressed air is wasted)
Reduce supply pressure if
possible
(continued)
39
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Table 1 (continued)
Symptom
Cause
Remedy
Reduced compressed
air pressure (RP, PP)
Premature bag failure:
decomposition
Moisure in baghouse
High screw conveyor
wear
(continued)
Damper valves not
sealing (PP)
Diaphragm valve
failure
Compressed air
consumption too high
Restrictions in piping
Dryer plugged
Supply line too small
Compressor worn
Bag material improper
for chemical coposi-
tion of gas or dust
Operating below acid
dew point
System not purged after
shutdown
Wall temperature below
dew point
Cold spots at struc-
ural members
Compressed air intro-
ducing water (RP, PP)
Repressuring air
causing condensation
(RF, PP)
Screw conveyor under-
sized
Check linkage
Check seals
Check diaphragms and springs
Check solenoid valve
See above
Check piping
Replace desiccant or
bypass dryer if allowed
Consult design
Replace rings
Analyze gas and dust and
check with manufacturer
Treat with neutralizer before
baghouse
Increase gas temperature
Bypass and startup
Keep fan running for 5 to
10 minutes after process is
shut down
Raise gas temperature
Insulate unit
Lower dew point by keeping
moisture out of system
Fully insulate structural
members
Check automatic drains
Install aftercooler
Install dryer
Preheat repressuring air
Use process gas as source of
repressuring air
Measure hourly collection of
dust and consult manufacturer
40
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Table 1 (continued)
Symptom
Cause
Remedy
High air lock wear
Material bridging in
hopper
Frequent screw
conveyor/air lock
failure
High pneumatic
conveyor wear
Pneumatic coneyor
pipes plugging
(continued)
Conveyor speed too high
Air lock undersized
Thermal expansion
Speed too high
Moisture in baghouse
Dust being stored in
hopper
Hopper slope insuffi-
cient
Conveyor opening too
small
Equipment undersized
Screw conveyor
misaligned
Overloading components
Pneumatic blower too
fast
Piping undersized
Elbow radius too
short
Overloading pneumatic
conveyor
Slug loading of dust
Slow down speed
Measure hourly collection of
dust and consult manufacturer
Consult manufacturer to see if
design allowed for thermal
expansion
Slow down
See above
Add hopper heaters
Remove dust continuously
Rework or replace hoppers
Use a wide-flared trough
Consult manufacturer
Align conveyor
Check sizing to see that each
component is capable of handling
a 100% delivery from the
previous component
Slow down blower
Review design and slow
blower or increase pipe size
Replace with long radius
elbows
Review design
See above
41
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Table 1 (continued)
Symptom
Cause
Remedy
Fan motor overloading
Air volume too
high
Reduced compressed
air consumption
(RP, PP)
High bag failure:
wearing out
High bag failure:
burning
(continued)
Moisture in dust
Air volume too high
Motor not sized for
cold start
Ducts leaking
Insufficient static
pressure
Pulsing valves not
working
Timer failed
Baffle plate worn out
Too much dust
Cleaning cycle too
frequent
Inlet air not properly
baffled from bags
Shaking too violent (S)
Repressuring pressure
too high (RF)
Pulsing pressure too
high (RP, PP)
Cages have barbs
(RP, PP)
Stratification of hot
and cold gases
See below
See below
Damper fan at startup
Reduce fan speed
Provide heat faster
Replace motor
Patch leaks
Close damper valve
Slow down fan
Check diaphragms
Check springs
Check solenoid valves
Check terminal outputs
Replace baffle plate
Install primary collector
Slow down cleaning
Consult manufacturer
Slow down shaking mechanism
(consult manufacturer)
Reduce pressure
Reduce pressure
Remove and smooth out barbs
Force turbulence in duct with
baffles
42
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Table 1 (continued)
Symptom
Cause
Remedy
Sparks entering bag-
house
Thermocouple failed
Failure of cooling
device
Install spark arrester
Replace and determine cause
of failure
Review design and work with
manufacturer
43
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TABLE 2. REPLACEMENT PARTS FOR BAGHOUSE FILTERS
Bags and accessories: clamps, nuts, bolts, hangers
Bag retainers (pulse jet)
Cleaning mechanism
Shaker: bearings, hangers, crankshaft, connecting
rod, motor belts
Pulse jet: Venturis, solenoid and diaphragm valves,
tubing
Timing mechanism
Screw conveyor: belts, hanger bearings, coupling bolts.
Air locks: bearing and seals
Pneumatic: see manufacturer's recommendations
Damper valves: solenoids, seals, cylinders
Magnahelic gauges
Gasketing, caulking, lubricants, special tools
Electrical switches, relays, fuses
44
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The user of the equipment should supplement the manufac-
turer's recommendations with a spare parts inventory reflecting
the particular application. Spare parts for baghouses are not
costly, but shipping time is often excessive.
45
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SECTION 4
TECHNICAL ASPECTS OF THE DESIGN, OPERATION,
AND MAINTENANCE OF ELECTROSTATIC PRECIPITATORS
Electrostatic precipitators are available in single-stage
and two-stage units. In single-stage units, particle charging
and collection are done simultaneously, and in two-stage units,
particle charging is followed by a separate collection stage.
Because most industrial ESP's are single-stage, this report will
discuss this type only. Two-stage systems are used for low
grain loading and low flow and find application in commercial
and small industrial situations.
Other classifications of ESP's are designated by the method
of removing precipitated dust from the collector surface
(rapper: dry; water spray: wet), shape of collecting surface
(plate or cylindrical), and direction of gas flow within the
unit (horizontal or vertical).
Most industrial ESP's are of the rapper, plate, and hori-
zontal gas flow type. In operation, the ESP allows the dust-
laden gas to flow between negatively charged wire electrodes
(discharge electrodes) and nearby grounded plate electrodes
(collector electrodes). The wire electrodes are charged to a
high electrical potential by an unfiltered d.c. power supply
mounted outside the precipitator housing. The applied voltage
is high enough to produce a visible corona discharge in the gas
immediately surrounding the wire electrodes. Electrons set free
in the discharge collide with gas molecules, producing gas ions
that in turn collide with dust particles and give them a nega-
tive charge. In the strong electric field between the wire and
plate electrodes, the electrically charged dust particles mi-
grate to the plate where they are deposited, giving up their
charge. Eventually, the thick dust layer can be conveniently
removed from the plate by periodic rapping. The dislodged dust
falls into the hoppers in the bottom of the precipitator hous-
ing, from which it is removed for disposal.
As with baghouses, the operation and maintenance of EPS' s
will be discussed according to functioning components, with
emphasis on design deficiencies that may accentuate O&M prob-
lems. The components to be examined are the discharge elec-
46
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trodes, collector electrodes, rappers, dust removal system,
electric power supply, and ancillary equipment. Safety will
also be discussed. General procedures for routine startup,
inspection, shutdown, and troubleshooting are provided. Actual
case histories for a dry and a wet ESP are presented in Appendix
A to give the user a method for troubleshooting performance
problems.
4.1 ELECTROSTATIC PRECIPITATOR COMPONENTS AND OPERATIONAL
PARAMETERS
4.1.1 Discharge Electrode System
The discharge electrode ionizes the gas and establishes the
electric field for particle charging. The electrodes are metal-
lic and are supplied in cylindrical, square, starred, and barbed
wires, in stamped or formed strips. The size and shape of the
electrodes is governed by the corona current required. Regard-
less of the number of fields, the ESP usually contains the same
type of wires per field. This may not be totally satisfactory,
however, since high concentrations of contaminant are present
mostly in the first field. Under these conditions, the high
concentration of particulates limits space charge and current
flow. Electrodes producing higher currents in the first field
should thus be used to achieve higher power density and reduce
the load on the power supply in the first field. This' power
supply could be allowed to operate at less than rated voltage,
thereby subjecting the other fields to higher concentrations of
dust while not affecting overall system performance. Manufac-
turers typically use one field for up to 90 percent collection
efficiency, two fields for up to 97 percent, three fields up to
99 percent, and four fields for greater than 99 percent.
The discharge electrodes commonly used for industrial ESP's
are weighted wire. Rigid wire frame electrodes are becoming
more and more prevalent.
Weighted Wire—
The most common configuration of discharge electrodes is
the weighted wire, which is typical of most U.S. manufacturers.
The material is usually 12-gauge (approximately 0.10-in. diam-
eter) steel spring wire. (The choice of materials is usually
dictated by the requirements of corrosion resistance.) The
wires are suspended from a support frame at the top of the ESP
and held taut by cast iron weights at the bottom. The structure
supporting the wire varies from one manufacturer to another.
The weights are spaced by a guide frame (typically an eye bolt)
and are loosely retained in the guides to allow for wire
47
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expansion. The guide frame has been a source of problems: if
not properly supported, it may resonate and swing in the air-
stream, thus affecting dimensional clearance to collector elec-
trodes and putting mechanical stress on the support structure.
The guide frames are mounted to the hoppers or ESP housing,
usually by a ceramic insulator. Dust buildup and moisture
condensation on the insulator can provide a source of electrical
leakage to ground.
Wires in the first field are often subjected to localized
sparking, especially in regions near the ends of the electrodes.
The excessive sparking in this region may come during plate
rapping from exposure to high concentrations of falling dust. A
shroud surrounding the lower portion (and sometimes the upper)
of the wire is provided to reduce this effect and protect the
wire.
Each of the wire support frames is integrally fastened by a
crossmember, which in turn is connected to a vertical hanger by
supports to two (or more) electrical insulators mounted on the
ESP roof. Maintenance workers have limited accessibility to the
wire supports for wire replacement.
Rigid Frame—
Frame-type electrodes have been commonplace in European
designs and are now becoming more prevalent in the United
States. Unlike the weighted wire system, rigid frame electrodes
require a significantly higher degree of quality control, both
in fabrication and erection, and are more costly. The rigid
wire frames are usually shop-assembled and shipped and installed
in one piece. Poor handling of the frames has often resulted in
deformation and deflection of the assembly, distorting the
dimensional alignment that is critical to proper electrical
performance. Better quality control and shipping precautions
are now being taken by manufacturers.
Several designs of rigid frame discharge electrodes are
available: the rigid discharge frame with integrally mounted
rigid electrodes, mast support discharge wires, and self-suppor-
ting rigid discharge electrodes. The first of these is the most
popular.
The perimeter of the rigid discharge frame and horizontal
frame supports is comprised of pipe or 1-in.-square tubing. The
discharge wires are frequently star shaped in cross-section and
contain extended points or edges. The wire span between adja-
cent, interior horizontal frames ranges from 6 to 8 feet. The
wires are fastened to the frames by several means: inserting a
pair of serrated wedges from opposite sides of the frame to
48
-------
wedge the wire securely, threaded studs with washers, tack
welded bolts, or welded studs only.
4.1.2 Collector Electrode System
The charged particulate matter is removed from the gas
stream by grounded collector electrodes. The particles that
have been charged by the discharge electrode are negative; upon
deposition on the grounded (positive) collector plates, they
become electrically inert and are removed by rapping.
The electrodes are available in many shapes and are de-
signed to maximize the electric field while minimizing dust
reentrainment during rapping. Flat plates have the best elec-
trical characteristics and induce the least turbulence to flow,
but excessive reentrainment tends to occur during rapping. In
practice, all collector electrodes have some sort of baffle
arrangement (aerodynamic shape) to minimize gas velocities near
the dust surface as well as to provide stiffness to the plate.
Opzel, rod curtain, zigzag, V, V-pocket, channel, offset,
shielded, and tulip designs are typically used for baffles.
Plate deformation and distortion are frequently observed.
They occur during fabrication, shipment, and site storage.
Proper quality control methods must be followed during fabri-
cation, and electrodes must be carefully handled during shipment
and storage. The plates should be stored on edge, closely
spaced with appropriate dunnage, to remove direct weight from
the shipping frames. During operation, thermal and chemical
stresses can also result in plate deterioration. Excessive
sparking can similarly produce localized plate distortion.
The plate support structure must be rugged enough, espe-
cially at welded seams, to withstand mechnical impulse, fatigue,
and the vibration provided by the rappers. Facility for align-
ment at erection and realignment after the shakedown operation
must also be provided, especially since thermal stresses contri-
bute to misalignment.
4.1.3 Rappers
Rapping systems for both collector and discharge electrodes
are of the electromagnetic impulse, electric vibratory, or
pneumatic type. Regardless of the type of dust to be removed,
successful removal from the plates depends upon the formation of
a congruent dust layer that, upon rapping, will fall in sheets
or large agglomerates into the hoppers. (Dust layers on the
collection plate can approach 1 inch in thickness before rapping
occurs.) Although dust deposits on the wires are usually small,
accumulated dust may seriously affect the current density,
especially since the electrical forces tend to hold the dust
more tenaciously to the discharge electrode than to the collection
plate.
49
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Each manufacturer prescribes a particular type of rapper,
based on the application and the compatibility with the suspen-
sion system, the requirements of the rapping interval, and the
intensity and length of each cycle. Pneumatic rappers impart
more energy than either electromagnetic rappers or electric
vibrators and are prescribed for removal of tenacious dusts.
Rapper shafts that penetrate the ESP housing must be elec-
trically and thermally insulated to avoid electrical and air
leakage. Thermal expansion shaft couplings must also be pro-
vided, in addition to having positive heated air ventilation for
the rapper insulators.
As with discharge electrodes, rapping systems have dif-
ferent designs in the United States and Europe. The U.S. design
is dominated by pneumatic and electrically operated vibrators or
impactors, and the European design includes mechanical rapping
systems. In the latter case, the rapper drive mechanism is
externally mounted with a shaft that penetrates the ESP shell.
The shaft contains a series of hammers designed to hit anvils at
the lower end of the collector plate electrodes and the center,
or lower end, of the discharge wire frame. The hammers may be
staggered, as in single-frame rapping, or in parallel groups
wherein a section or group of frames is rapped simultaneously.
4.1.4 Dust Removal Systems
Hoppers are used to collect and store particulates removed
from the electrodes. In ESP applications (in contrast to bag-
houses), center dividing baffles are used to prevent gas from
bypassing electrical charging zones. Methods available to
remove dusts accumulated in hoppers include containers, dry
vacuum, wet vacuum, screw, and drag conveyors. Vibrators,
thermal insulation, heating cables, and steam tracing may be
used to make the contaminant fluid for easy removal. For con-
venience in removing buildup and excessive dust accumulation,
poke holes should be provided.
The hopper interiors must be free from all physical projec-
tions, even ladders, that may provide surfaces for buildup.
Access doors to hoppers must be key interlocked. Level alarms
should be installed; if center hopper dividing baffles are used,
a level indicator is needed for each section. If only one
indicator is available, the side that is evacuated would not
alarm even if the adjacent one was full.
Two-thirds of the dust collected by the ESP is deposited in
the inlet hopper. These hoppers also act as settling chambers,
collecting large particulates not exposed to the electrode
system, and must therefore be properly sized. The hopper sec-
tion and conveyor trough of the ESP must also be designed to
accommodate thermal expansion.
50
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4.1.5 Electric Power Supply
Electrostatic precipitators operate on high-voltage d.c.
power which is supplied with negative potential impressed on the
discharge electrodes. The power supply consists of the voltage
control system (which varies the unfiltered voltage wave form as
applied to the discharge electrode); the step-up transformer
(which steps up line voltage to required precipitator poten-
tial); and the rectifier (which converts a.c. to d.c., full or
half wave). The control system can be operated manually or
automatically and should be operated with the largest voltage
possible with minimum arcing. The automatic voltage control
prevents the arcing potential from varying as the type of gas,
composition, humidity, temperature, and dust concentrations
change. If excessive arcing is allowed to occur, the effective
potential to the ESP is lowered, collector electrode dust is
loosened (assists reentrainment), and the discharge electrode
wires tend to fatigue, erode, and melt. When arcing does occur,
the applied voltage must be rapidly reduced to extinguish the
arc. This is the function of the automatic voltage control
system.
The number of times per minute that electrical breakdown
occurs between the discharge wire and collector electrode is
called the spark rate. It depends on the applied voltage for a
given set of precipitator conditions. Increasing the spark rate
results in a greater percentage of input power being wasted.
Typically, a range of 50 to 150 sparks/min is considered normal.
Some precipitators operate at the maximum voltage or current
settings on the power supply with no sparking. In collection of
low-resistant dusts, where the electric fiel'd and ash deposit
are insufficient to initiate sparking, no sparking condition may
arise. A precipitator not sparking does not mean that the unit
is underworked.
The behavior of both clean and dirty electrodes is measured
by the primary and secondary voltage/current relationships from
the transformer/ rectifier (T/R) set. Clean plate data should
be acquired after process shutdown and after completion of
sufficient rapping to remove plate and wire dust accumulations.
This information provides a basis for comparison with subsequent
operational performance and is especially useful for identifying
electrical problems and equipment deterioration.
Dirty plate data should be acquired during process opera-
tion and when rappers are off.
Ideally the control panel should contain display meters to
monitor primary and secondary voltage and secondary current and
spark rate. Although highly recommended, a secondary voltage
51
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meter is often not installed on the transformer. This situation
can be alleviated by the temporary installation of a voltage
divider network. The control cabinet contains all required
devices and instruments needed to monitor (display meters) and
control the operation of the ESP. Positive air ventilation,
provided by a filtered intake air fan, helps to protect the in-
ternal components of the control cabinet.
The T/R set, which is mounted on the ESP roof, is usually
hermetically sealed. These components are submerged in a tank
filled with dielectric fluid used for cooling. The tank is
equipped with high-voltage bushings, liquid level gauge, drain
valve, ground plug, filling plug, lifting lugs, and surge arres-
tors (which discharge any harmful transients appearing across
the d.c. metering circuit to ground).
An electrical conductor in the form of a pipe transmits the
voltage output to the support insulator bushing, which is con-
nected to the high-tension support frame from which the dis-
charge wires are suspended. The insulators are housed in a
casing or compartment that must be kept clean and dry to prevent
ESP dust and moisture from accumulating. Warm, filtered, pres-
sured air is thus supplied to avoid these problems. The pres-
sure of the air delivered to the insulator housings must be
sufficiently positive to override the pressure in the ESP
casing.
4.1.6 Gas Distribution
The overall performance of the ESP, like that of the bag-
house, depends on the uniformity of the gas distribution within
the casing. Adequate distribution of flow is provided by in-
stalling baffle plates or screens in the inlet transition to the
ESP. Laboratory model studies of flow distribution are often
performed to assist in the design of the baffles and the casing.
The ESP provides an inlet transition that slows flow
velocity to values that are difficult to measure by standard
pitot tube methods, thus requiring hot-wire anemometry. Non-
uniform flow can seriously affect performance. If it is sus-
pected, the system may need to be deenergized, so that flow
distribution can be measured. Nonuniform flow may be identified
during a period set aside in the construction schedule to allow
these measurements to be taken before startup.
4.1.7 Safety
The ESP and its associated components require an unusual
set of safety precautions compared with other types of air
pollution control equipment. The high voltage impressed on the
system exposes workers to the danger of electrocution. For this
reason, safety procedures must be developed.
52
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Safety Key Interlock System--
A mechanical safety interlock system must be designed for
all access doors and must be retrofitted on older ESP's. The
system should be an integrally coupled series of keys that
performs the following sequence of controls: when the system is
activated, the power supply is deenergized, the power supply
load for the ESP is grounded by a high-voltage switch; and all
power supplies on a given segment or subdivision of the ESP are
appropriately grounded. Interlock keys are obtained to gain
access to that particular subdivision only. Good design
practice includes the rapping and conveyor components within the
interlock system.
Grounding Hooks—
Every ESP should be equipped with grounding hooks or chains
at usual maintenance access points. The hooks are to be applied
to components within the reach of a worker from the access door.
This precaution ensures that the high-voltage system is' grounded
and that any residual or extraneous electric charge is removed.
Grounding Network--
The grounding conductor should be sized according to the
national electric code and scaled according to the capacity of
the maximum feeder cable feeding the power supply. If the power
supply contains isolable subassemblies, it will have short
circuit capability. The grounding conductor must, therefore, be
continuous, starting at the feeder and forming a network com-
bining all points of the power supply (control cabinets, regu-
lating components, T/R set). The ground should also extend to
the ESP structures (hopper junctions).
During sparking and arcing, high currents flow in the form
of pulses. These currents flow on the surface of conductors
rather than through them, and the ground conductor should thus
be adequately sized for the available surface. Jumpers and
conductors of the appropriate size are necessary to ensure
electrical integrity between key components. For example, a
lack of electrical integrity could arise in the components from
the power supply to the ESP. The typical procedure is to use a
coaxial pipe and a grounded cylindrical duct known as a guard.
The guard is composed of individual sections with bolted
flanges. At the interface of each flange, a jumper must be
provided to allow and maintain continuity of ground.
T/R Sets —
The T/R components are immersed in an oil bath of mineral
oil or askarel fireproof oil. If askarel oil is subjected to
arcing, hydrogen chloride may be generated, and maintenance
personnel should exercise extreme caution when servicing these
components. It should be noted that askarel contains poly-
chlorinated biphenyl (PCB); disposal of this oil thus requires
special consideration.
53
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Mechanical—
The ESP has moving parts that are usually controlled by
timers. A worker could be injured if he enters a component when
the drive is operating, or if the drive is started while he is
inside the system. Coupling these drives (rappers and con-
veyors) to the interlock system is therefore recommended. Dust
buildup on uncleaned collector electrodes could break loose and
liberate large amounts of dust, seriously affecting vision and
breathing.
4.1.8 Conclusions
It is poor economy to shut down a plant to repair or ser-
vice a poorly designed ESP. The following are some of the
features of modern design that contribute directly to opera-
tional reliability.
High-voltage support insulators mounted in individual
roof-mounted, insulator housings provide several operation
advantages:
Insulators are far removed from gas stream.
Insulators can be inspected, cleaned, or replaced from
above without entering casing.
Insulator compartment ventilation system can be ser-
viced easily.
Discharge and collector electrode field must be suspended
from shop-fabricated grids.
Discharge electrode wires must be especially fitted on both
ends to ensure good electrical contact, eliminating arcing
and extending life.
Casing roof, walls, and hoppers must be of clean exterior
design to facilitate application and continuity of thermal
insulation.
Pyramidal hoppers must be equipped with flush access doors,
poke holes, steep valley angles, and large flanged outlets.
Hoppers can be equipped with heating coils, vibrators,
hammers, and dust level indicators.
Safety-key-interlocked, quick-opening doors provide easy
access through roof and sides of casing into suitably sized
access passages above, below, and between every high-
voltage discharge electric field.
54
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4.2 ELECTROSTATIC PRECIPITATOR OPERATION AND MAINTENANCE
The previous sections provided background information on
the various operational components of the ESP, particularly the
design features that will improve performance and reduce main-
tenance. Proper operation and maintenance of an EPS also re-
quires familiarity with procedures for equipment startup, shut-
down, inspection, recognition of common malfunctions, and trouble-
shooting. These procedures are concisely prepared to simplify
the inspection, observations, and interpretations of the various
components. Discussion of the cause and effect relationship and
the impact on performance is also provided.
4.2.1 Pre-Startup Inspection
The inspection performed before startup is critical to the
performance of an ESP. The precipitator may not be operational
for one of three reasons:
New installation requiring shakedown and debugging
Process shutdown resulting in ESP shutdown
ESP shutdown for maintenance
Regardless of the reason for shutdown, an opportunity
exists while the unit is down to perform a thorough inspection.
An example of a checklist for visual and mechanical inspection
is provided in Figure 6.
This checklist is a guideline only. A specific list should
be tailored for each ESP system. The inspection survey during
shutdown should include all ductwork and components from the
upstream emissions source to the stack.
4.2.2 Routine Startup
After the precipitator has been thoroughly inspected, the
unit should be buttoned up (following all safety procedures).
An outline procedure for routine startup is given below. Power
on/off buttons with green and red lights are usually provided
for components.
1. Follow key interlock procedures for closing access
doors.
2. Preheat insulator compartments for several hours
before energizing system.
3. Activate dust handling system (air lock, screw con-
veyors, etc.).
55
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ISP WEOPERATION AND INSPECTION CHECKLIST
APPLICATION '-
DATE/TIME1
REPORT BY:
DISCHARGE ELECTRODES
UPPER SUPPORT FRAME
LOWER SUPPORT FRAME
HANGER SUPPORTS
ANTISWING SUPPORTS
HEIGHTS
WIRES
ALIGNMENT
CORROSION
BUILDUP
COMMENTS
COLLECTOR ELECTRODE
WARPAGE
SUPPORT
SPACERS
GUIDES
ALIGNMENT
CORROSION
BUILDUP
COMMENTS
GAS SNEAKAGE BAFFLES
COMMENTS
RAPPERS (COLLECTOR/DISCHARGE)
MECHANICAL/ELECTRICAL CONNECTIONS
BUILDUP
CORROSION
COMMENTS
HOPPER
DUST LEVEL INDICATORS
OUTLET CONNECTIONS
ACCESS DOORS
POKE HOLES
HEATERS
INSULATORS
OOCMENTS
Page 1 of 2
CHECKED
YES
a
a
a
a
D
a
a
a
a
a
a
a
a
a
a
a
a
a
tn
a
a
a
a
a
a
NO
D
a
a
a
a
a
a
D
a
a
o
a
a
a
a
CD
a
D
a
a
a
a
a
a
a
KBQ.
ATTN.
a
a
0
a
a
n
a
a
a
a
a
a
a
a
a
a
n
a
i=i
a
a
a
a
CD
O
Figure 6. Preoperation and inspection checklist for electrostatic precipitator.
56
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CHECKED
SCREW CONVEYOR
DEBRIS
BUILDUP
CORROSION
MOTOR
SCREW DRIVE
HANGER BEARINGS
TAIL SHAFT BEARING
COMMENTS
T/R SET
SURGE ARRESTOR GAP
TRANSFORMER LIQUID LEVEL
GROUND CONNECTIONS
HIGH TENSION BUS DUCT
CONDUITS
FULL WAVE SWITCH BOX
ALARM CONNECTIONS
GROUND SVJTTCH OPERATION
HIGH VOLTAGE CONNECTIONS
REGISTER BOARD
COMMENTS
INSULATOR COMPARTMENT
FILTER COMPARTMENT
DUCTS/INSULATION
FLOW
TEMPERATURE
MOTOR
PRESSURE
HEATER
COMMENTS
GAS DISTRIBUTION
INLET/OUTLET TRANSITION
JOINTS
BUILDUP
CORROSION
COMMENTS
BAFFLES
VIBRATORS
JOINTS
WARP AGE
BUILDUP
CORROSION
COMMENTS
PUCTS (INLET/DUT/STACK)
LEAKAGE
JOINTS
GASKECTNG
DAMPERS
COMMENTS
Page 2 of 2
YES
a
a
CD
CD
CD
m
CD
a
a
CD
CD
n
a
CD
a
n
a
CD
CD
CD
a
a
CD
a
a
a
a
a
a
CD
CD
a
CD
D
a
a
a
NO
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
D
o
a
a
a
a
a
CD
D
a
o
a
0
n
a
a
n
0
n
CD
a
P
REQ.
MTN.
a
a
a
a
a
CD
0
a
a
CD
CD
a
O
CD
CD
a
a
a
CD
a
a
ID
a
a
n
O
a
a
CD
CD
CD
CD
ED
D
CD
CD
n
Figure 6 (continued)
57
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4. Operate discharge and collector electrode rapping
system.
5. Operate gas distribution baffle plate vibrators.
6. Turn on high voltage (manual mode) for one section
only and bring up input voltage slowly (10 percent
increments) to rated voltage or rated current while
recording panel meter readings. This procedure is
commonly referred to as an airload test. The test
establishes reference readings and checks operation of
electrical equipment, clearances, etc. After these
readings are recorded, turn down high voltage on the
field and similarly perform an airload test on the
next field. If excessive sparking or d.c. readings
are obtained, another internal inspection may be
necessary.
7. If system operates satisfactorily, turn off T/R sets.
8. Open bypass dampers.
9. Start blower
10. If possible, preheat the ESP by pulling hot, clean air
through the system, thus avoiding condensation of
moisture and contaminant gases. Buildup of condensed
material on electrodes is difficult to remove: ener-
gize one field only to minimize the effect.
11. Allow contaminant gases to pass through the unit.
12. Record data from monitoring instrumentation (fan motor
amperage and voltage; temperatures; a.c. voltage/
current; d.c. voltage/current; spark rate).
4.2.3 Routine Inspection and Maintenance During Operation
During routine operation, an inspection procedure that
includes a recording of ESP operation data should be used. A
sample of a routine daily inspection checklist for an ESP is
provided in Figure 7. Only visual inspection of the unit is
possible, and therefore only instrumented operational parameters
can be obtained. The checklist gives direction and guidance to
a maintenance worker for items to observe and check. A tailor-
made checklist should be prepared by the user and vendor that is
based on the specific components and monitors.
58
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ESP OPERATING INSPECTION AND MAINTENANCE CHECKLIST
APPLICATION:
DATE/TIME: CHECKED
REQ.
REPORT BY: YES NO ATTN
T/R SET
LIQUID LEVEL O CD O
TEMPERATURE C3 Q O
NOISES a CD a
LEAKS d D CD
COMMENTS
HIRE RAPPERS
MOTOR/LUBRICATION ODD
SEQUENCING D O a
NOISE D D CD
COMMENTS
COLLECTOR RAPPERS '
MOTOR/LUBRICATION CD O D
SEQUENCING D d CD
NOISE C3 D CD
COMMENTS
INSULATOR COMPARTMENT
MDTOR/BLOWER a D d
FILTER O d O
DUCTS a a a
DAMPER ODD
INSULATION D a a
PRESSURE D d D
TEMPERATURE C3 D CD
OBMENTS
HOPPERS
NOISES an
AIR LEAKS C3 D
GASKETS CD D
HEATERS C3 CD
ACCESS DOORS O D
COMMENTS
Page 1 of 2
Figure 7. Operating inspection and maintenance checklist for an
electrostatic precipitator.
59
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CHECKED
REQ.
YES NO ATTN.
MATERIAL HANDLING SYSTEM
OPERATING D D C3
NOISES D D D
LUBRICATION CD D D
AIR LEAKS OD D
MOTORS O D O
BEARINGS Od O
COMMENTS
DUCTS (INLET/OOTLET)
NOISES o a a
LEAKS EDO O
COMMENTS
TRANSITIONS (INLET/OUTLET)
NOISE D a tn
LEAKS a D a
COMMENTS
STACK APPEARANCE
COMMENTS
OPERATING DESIGM
COLLECTOR MEASUPEMENT
TEMP: IN ; '. D
TEMP: OUT Q
PRESSURE DROP • a
STATIC PRESSURE: IN d
STATIC PRESSURE: OUT a
FLOW RATE £3
PRIMARY VOLTAGE CD
PRIMARY CURRENT Q
SECONDARY VOLTAGE 1-1
SPARK RATE CD
COMMENTS
BLOWER
CURRENT ______ n
VOLTAGE D
RPM . a
STATIC PRESSURE r~l
BELT TENSION D CD O
BEARING. LUBRICATION D D d
DAMPER - D O D
COMMENTS
Page 2 of 2
Figure 7 (continued)
60
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4.2.4 Routine Shutdown
An ESP is shut down primarily because of routine or emer-
gency process shutdown, routine ESP maintenance, or emergency
ESP malfunction. In these situations, the ESP should continue
to be operated until it is purged with clean air. The following
steps are then taken:
1. Stop blower.
2. If possible, isolate ESP by closing inlet/outlet
dampers.
3. Shut down T/R set.
4. Continue to operate rapping and dust removal system
until wires and plates are believed to be clean; then
shut down rappers and dust removal system (make sure
that hoppers are clean).
5. Open access doors following interlock procedure.
Note: Hopper access doors should be opened with
care ' because hot dust may be packed against
them.
6. Use ground hooks to remove extraneous electric charge
buildup.
7. Allow system to cool and dust to settle before enter-
ing.
8. Allow insulator compartment vent system to operate.
4.2.5 Maintenance During Shutdown
When the ESP can be entered, internal inspection can be
commenced. It is advisable to leave the insulator compartment
vent heaters on during shutdown to prevent moisture from con-
densing on the high-voltage insulators. The high-maintenance
items, in decreasing order of prevalence, are:
Discharge electrode breakage
Plugged hoppers
Insufficient rapping
Insulator bushing failure
Electrical component breakdown.
61
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The checklists provided in Figures 6 and 7 can be used to
provide a methodical program of inspection during shutdown.
These checklists will also provide an excellent mechanism for
maintenance recordkeeping.
4.2.6 Common Malfunctions
Other than changes in process conditions, the most common
malfunction associated with ESP performance is from broken
discharge wires and plugged hoppers. A detailed list of the
causes and effects of malfunctions, categorized according to
functioning component, is given in the following pages. In some
cases, solutions to the problems are provided. Table 3 provides
a summary of common ESP malfunctions.
Discharge Electrodes-
In a weighted wire design, a broken wire may swing freely
and cause shorting between discharge and collector electrodes,
usually immobilizing an entire field. Wire breakage results
from electrical, mechanical, or chemical problems.
Electrical:
Electric erosion (arcing) is the principal cause of
failure.
Minimum clearance between electrodes results in re-
peated sparkover, causing local heating and vapori-
zation of metal. The tension from the suspension
weights causes ultimate failure.
Breakage can occur on shroud as well as wire and
usually occurs on the lower portion of wire.
Mechanical:
Excessive rapping breaks wire.
Crimps and bends are sources of fatigue with rapping
and vibration.
Poor electrical alignment causes the wire frame to
oscillate, fatiguing wires and increasing sparking.
Swinging wire frames can often be detected by lis-
tening for the regular snap of the arc-over.
Chemical;
Acid gases corrode wires. Material flakes off during
rapping, thus exposing new surfaces to additional
corrosion attack.
62
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TABLE 3. SUMMARY OF PROBLEMS ASSOCIATED WITH ELECTROSTATIC PRECIPITATORS
Malfunction
Cause
Effect on
ESP efficiency
Corrective action
Preventive measures
Poor electrode alignment
Broken electrodes
U>
Distorted or skewed
electrode plates
Vibrating or swinging
electrodes
Poor design
Ash buildup on frame hoppers
Poor gas flow
Hire not rapped clean, causes an arc
which embrittles and burns through
the wire.
Clinkered wire. Causes: a) poor
flow area, distribution through unit
is uneven; b) excess free carbon due
to excess combustion air or fan
capacity Insufficient for demand
required; c) wires not properly
centered; d) ash buildup resulting
in bent frame, same as c); e) clinker
bridges the plates and wire shorts
out; f) ash buildup, pushes bottle
weight up causing sag In the wire;
g) J hooks have improper clearances
to the hanging wire; h) bottle
weight hangs up during cooling,
causing a buckled wire; 1) ash build-
up on bottle weight to the frame
forms a clinker and burns off the
wire.
Ash buildup In hoppers
Gas flow Irregularities
High temperatures
Uneven gas flow
Broken electrodes
Can drastically affect
performance and lower
efficiency
Reduction 1n efficiency due
to reduced power input,
bus section unavailability
Realign electrodes
Correct gas flow
Replace electrode
Reduced efficiency
Decreases 1n efficiency due
to reduced power Input
Repair or replace plates
Correct qas flow
Repair electrode
Check hoppers frequently
for proper operation
Boiler problems; check
space between recording
steam and air flow pens,
oressure gauges; fouled
screen tubes.
Inspect hoppers
Check electrodes frequently
for wear
Inspect rappers frequently
Check hoppers frequently
for proper operation;
Check electrode plates
during outages
Check electrodes fre-
quently for wear
(continued)
-------
TABLE 3 (continued)
Malfunction
Inadequate level of power
Input (voltage too low)
Back corona
Broken or cracked
Insulator or flower pot
bushing leakage
A1r leaks 1n through
hoppers
Air leaks in through
ESP shell
Gas bypass around ESP:
-dead passage
above plates
-around high tension
frame
Cause
High dust resistivity
Excessive ash on electrodes
Unusually fine particle size
Inadequate power supply
Inadequate sectionalizatlon
Improper rectifier and control
operation
Misalignment of electrodes
Ash accumulated on electrodes
causing excessive sparking.
requiring reduction in voltage
charge
Ash buildup during operation
causes leakage to ground
Moisture gathered during shut-
down or low load operation
From dust conveyor
Flange expansion
Poor design - Improper isolation
of active portion of ESP
Effect on
ESP efficiency
Reduction in efficiency
1
Reduction 1n efficiency
Reduction in efficiency
Lower efficiency; dust
reentrained
through ESP
Same as above, also causes
intense sparking
Only small percentage drop
in efficiency unless
severe
Corrective action
Clean electrodes;
gas conditioning or
alterations in
temperature to reduce
resistivity;
Increase section-
alization
Same as above
Clean or replace
insulators and
bushings
Seal leaks
Baffling to direct
gas into active ESP
section
Preventive measures
Check range of voltages
frequently to make sure
it is correct in situ
resistivity measure-
ments
Same as above
Check frequently
Clean and dry as needed;
Check for adequate
pressurization on top
housing
Identify early by
increase in ash con-
centration at bottom of
exit to ESP
Identify early by measure-
ment of gas flow in sus-
pected areas
(continued)
-------
TABLE 3 (continued)
Malfunction
Cause
Effect on
ESP efficiency
Corrective action
Preventive measures
Corrosion
Hopper pluggage
CTi
Ul
Inadequate rapping,
vibrators fall
Too Intense rapping
Temperature goes below dewpolnt
Wires, plates, Insulators fouled
becaused of low temperature
Inadequate hopper insulation
Improper maintenance
Boiler leaks causing excess
moisture
Ash conveying system malfunction:
gasket leakage, blow malfunction,
or solenoid valves
Misadjustment of hopper vibrators
Material dropped into hopper from
bottle weights
Solenoid, timer malfunction
Suction blower filter not changed
Ash buildup
Poor design
Rappers misadjusted
Poor design
Rappers misadjusted
Improper rapping force
Negligible until pre-
cipitation Interior plugs
or plates are eaten away;
air leaks may develop,
causing significant drops
in performance
Reduction 1n efficiency
Maintain flue gas
temperature above
dewpoint
Provide proper flow
of ash
Resulting buildup on
electrodes may reduce
efficiency
Reentralns ash, reduces
efficiency
Adjust rappers with
optical dust measure-
ing instrument in ESP
exit stream
Same as above
Energize precipltator
after boiler system has
been on line for ample
period to raise flue gas
temperature above acid
dewpoint
Frequent checks for ade-
quate operation of hoppers
Provide heater thermal
Insulation to avoid
moisture condensation
Frequent checks for ade-
quate operation of
rappers
Same as above
Reduce vibrating or impact
force
(continued)
-------
TABLE 3 (continued)
Malfunction
Control failures
Sparking
Cause
Power failure 1n primary system
Transformer or rectifier failure:
a) Insulation breakdown In trans-
former
b) arcing In transformer between
high voltage switch contacts
c) leaks or shorts 1n high voltage
structure
d) Insulating field contamination
Inspection door ajar
Boiler leaks
Plugging of hoppers
Dirty insulators
Effect on
ESP efficiency
Reduced efficiency
Reduced efficiency
Corrective action
Find source of failure
and repair or replace
Close inspection
doors; repair
leaks in boiler;
unplug hoppers; clean
insulators
Preventive measures
Pay close attention to
daily readings of control
room instrumentation to
spot deviations from
normal readings
Regular preventive main-
tenance will alleviate
these problems
-------
Wire buildup is not usually due to insufficient rapping but
to some other factor, such as process change. Uniform buildup
can have the effect of creating a larger diameter wire and
requiring higher voltage to initiate ground current. A sudden
failure or rash of failures can occur from process changes or
extreme malfunction in the ESP.
In a rigid frame design, one broken wire does not result in
the failure of the entire bus section. High "G" forces in
rapping rigid wire frames can lead to premature mechanical
failure near the impact point, at connection to support members,
sharp bends, and welded connections. High resistivity dusts are
very tenacious and need high rapping forces, thus requiring
European design.
Rappers (Vibrators/Impulse)—
Impulse electric or pneumatic rappers are more successful
in difficult rapping applications than are electric vibrators.
Pneumatic rappers are beneficial in warm, high-moisture
ambient environments. If the temperature falls below freezing,
however, pneumatic is not recommended because the entrapped
moisture in the air lines may freeze unless adequate air dryers
are installed.
Rappers (Mechanical Failures)—
Failures occur in the transmission hardware at the inter-
face of a high-strength alloy and mild steel components.
Poor quality of welds from rapper to support frame may
result in cracks; frequently encountered weld types are
butt joint, cup joint, gusset joint. Good welding practice
is to preheat and postheat.
Rapper binds due to misalignment during installation.
Rapper rod seizure occurs from the leakage and improper
seals and dust accumulation.
Collector Electrodes—
Plate corrosion results from gas temperature going below
dew point and allowing condensation to occur on lower portion of
plate. Air leakage into hopper also produces condensation and
corrosion on electrodes.
Mechanical failure at supports can occur from poor con-
struction or assembly and overrapping.
67
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Dust Removal System--
Plugging is the main problem and could result from moisture
condensation, with its associated dust agglomeration and caking
within the hopper. Dust buildup will eventually contact high-
voltage electrode frame and short out high-voltage bus sections,
misalign electrodes, and form clinkers by ash fusion from the
high-voltage current. Hopper and heaters should be operated
continuously to avoid buildup.
Housing and Casing—
Air leaks and infiltration (causing corrosion) can occur at
expansion joints, slip joints, and inlet/outlet ducts. Should
acid/gas temperature go below dew point, condensation can also
result in corrosion.
Coupons of aluminum, corten, and stainless steel are often
placed inside the unit to study the corrosion resistance of
these materials. Coatings such as coal tar epoxy are used to
eliminate corrosion.
Insulators--
Dust and/or moisture accumulation on the insulator surface
could lead to electrical arc-over as evidenced by tracking.
Excessive arc-over could result in insulator cracking or break-
age. Filtered and heated purge air prevents fouling of the
insulators, bus bars, and bus ducts.
4.2.7 Spare Parts
The ESP manufacturer should supply a list of recommended
spare parts. The spare parts required are usually those asso-
ciated with moving and rotating components. A summary list of
replacement parts is provided in Table 4. The user of the
equipment will develop a spare parts inventory according to the
type and frequency of part failure.
4.2.8 Troubleshooting Program
Should a major problem bring the need for a thorough sur-
vey, a multiphase troubleshooting program as outlined is recom-
mended. An actual case history of such a program is provided in
Appendix A.
4.2.9 Troubleshooting Procedures
Guidelines for troubleshooting and correcting ESP malfunc-
tions are provided in Table 5. This chart is used as a diag-
nostic aid to troubleshoot specific symptoms. A supplementary
approach to evaluate operational problems is to interpret abnor-
mal electrical meter readings from the ESP control cabinet.
Table 6 is a general guide prepared for this purpose.
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TABLE 4. REPLACEMENT PARTS FOR ELECTROSTATIC PRECIPITATORS
Discharge electrodes:
Collector electrodes:
T/R set:
Voltage controller:
Dust handling system:
Insulator compartment
ventilation system:
General supplies:
Wires, weights, fastening hardware
Antisway insulator
Insulators, rectifiers
Printed circuit boards, switches, relays,
fuses.
Level indicators, motor bearings, seals,
solenoids.
Filters, motors, heating elements
Gasketing, silicone grease, chamois
cloth, lubricants, special tools
69
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TABLE 5. TYPICAL TROUBLESHOOTING CHART FOR AN
ELECTROSTATIC PRECIPITATOR
Symptom
Cause
Remedy
No primary voltage.
No primary current.
No precipitator
current.
Vent fan on.
Alarm energized.
No primary voltage.
No primary current.
No precipitator
current.
Vent fan off.
Alarm energized.
Control unit trips out
on overcurrent when
sparking occurs at
high currents.
High primary current.
No precipitator
current.
No primary voltage
No primary current.
No precipitator
current.
Vent fan on.
Alarm not energized.
Same as above, even
after replacing com-
ponents or subpanels,
changing wires, or
repair.
Overload condition
Misadjustment of
current limit control
Overdrive of SCR's
Relay panel fuse blown
Circuit breaker tripped
Loss of supply power
Circuit breaker defec-
tive or incorrectly
sized
Overload circuit in-
correctly set
Short circuit condition
in primary
Transformer or recti-
fier short
SCR and/or diode
failure
No firing pulse from
firing circuit and/or
amplifier
SCR's being fired out
of phase
Check overload relay settings.
Check wiring components.
Check adjustment of current
limit control setting.
Check signal from firing
circuit module.
Replace.
Reset circuit breaker.
Check supply to control unit.
Check circuit breaker.
Reset overload circuit.
Check primary power wiring.
Check transformer and
rectifiers.
Replace.
Check signal from firing
circuit and/or amplifier.
Reverse input wires.
(continued)
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Table 5 (continued)
Symptom
Cause
Remedy
Low primary voltage.
High secondary
current.
Abnormally low pre-
cipitator current and
primary voltage with
no sparking.
Spark meter reads
high -- off scale.
Low primary voltage
and current.
No spark rate indi-
cation.
Spark meter reads
high; primary
voltage and current
very unstable.
Neither spark rate,
current, nor voltage
at maximum.
Short circuit in
secondary circuit or
precipitator
Misadjustment of cur-
rent and/or voltage
limit controls
Misadjustment of firing
circuit control
Continuous conduction
of spark counting
circuit
Spark counter counting
60 cycles peak
Failure
Misadjustment of PC-501
Loss of limiting con-
trol
Misadjustment of PC-501
Failure
Failure of signal
circuits.
Check wiring and components
in H.V. circuit and pipe
and guard.
Check precipitator for:
Interior dust buildup
full hoppers
Broken wires
Ground switch left on
Ground jumper left on
Foreign material on H.V.
frame or wires
Broken insulators.
Check settings of current
and voltage limit controls.
Turn to maximum (clockwise)
and check setting of current
and voltage limit controls.
Deenergize, allow inte-
grating capacitor to dis-
charge, and reenergize.
Readjust.
Replace.
Readjust.
Replace.
Readjust setting.
Replace.
Check signal circuits.
(continued)
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Table 5 (continued)
Symptom
Cause
Remedy
No spark rate
indication;
voltmeter and am-
meter unstable,
indicating sparking.
No response to current
limit adjustment;
however, does respond
to other adjustments.
No response to voltage
limit adjustment;
however, does respond
to current adjustment.
No response to spark
rate adjustment;
however, does respond
to other adjustment.
Failure of spark meter
Failure of integrating
capacitor
Spark counter sensi-
tivity too low
Controlling on spark
rate or voltage limit
Failure
Current signal defec-
tive
Controlling on current
limit or spark rate
Voltage signal defec-
tive
Failure
Controlling on voltage
or current
Failure
Replace spark meter.
Replace capacitor.
Readjust.
None needed if unit is
operating at maximum
spark rate or voltage
adjustment.
Reset voltage or spark
rate if neither is at
maximum.
Replace.
Check signal circuit.
None needed if unit is
operating at maximum
current or spark rate.
Reset current and spark
rate adjustment if
neither is at maximum
Check voltage signal circuit.
Replace.
None needed if unit is
operating at maximum
voltage or current.
Reset voltage and current
adjustment if neither is
at maximum.
Replace.
(continued)
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Table 5 (continued)
Symptom
Cause
Remedy
Precipitator current
low with respect to
primary current.
Low or no voltage
across ground return
resistors.
Surge arresters shorted
H.V. rectifiers failed
H.V. transformer failed
Ground or partial ground
in the ground return
circuit.
Reset or replace surge
arresters.
Replace H.V. rectifiers.
Replace H.V. transformer.
Repair ground return
circuit.
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TABLE 6. GUIDE FOR INTERPRETING ABNORMAL METER READINGS
1. Increasing gas temperature results in a corresponding volt-
age increase and current decrease (arcing can develop).
Conversely, decreasing gas temperature will result in volt-
age diminution and current increase.
2. An increase in moisture content at given process conditions
will result in a relatively small increase in current and
voltage levels,
3. Excessive sparkover may result from additional moisture and
is indicated by a voltage increase.
4. Grain loading increase will somewhat elevate voltages and
reduce current.
5. A particle size decrease will be reflected in a voltage
rise and diminished current.
6. Gas velocity (flow rate) increase will tend to increase
voltages and depress current.
7. Air leakage may cause additional sparkover and reduced
voltage.
8. During normal operation for individual power supplies, the
voltage/current ratio will decrease in the direction of gas
flow.
9. Hopper overflow will result in shorting and drastically
reduced voltage and current increase.
10. Broken, swinging discharge electrode wires result in violent
arcing and extreme and erratic meter behavior.
11. A T/R short results in zero voltage and high current.
12. Buildup on wires is accompanied by a voltage increase to
maintain same current level.
13. Buildup on plates is accompanied by a voltage decrease to
maintain same current level.
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4.3 WET ELECTROSTATIC PRECIPITATORS
The functional design of wet ESP's is similar to that of
the dry ESP's; the main difference is that the collected parti-
culates are dislodged from the collecting surface by continuous
water spray or by a cascading water sheet. The wet electro-
static precipitators (WEP) now in use are of the plate-, concen-
tric-plate-, or pipe-type design. Wet precipitators find appli-
cation in the aluminum, iron, steel, and glass industries.
According to the application, the WEP is an attractive
alternative to the wet scrubber, ESP, and baghouse. For exam-
ple, a condensible, submicron hydrocarbon emission can easily be
removed by WEP rather than by using a high-energy venturi
scrubber. The problem of high or low dust resistivity is elimi-
nated in WEP's because the collector electrode is continuously
flushed. The resistivity of the water film (which is very low)
is the governing factor in the dust discharging process, not the
resistivity of a dust layer formed by collected particulate.
The gas to be treated by a WEP must be saturated with water
vapor before it enters the unit. Consequently, the performance
of the WEP is not very sensitive to gas temperature. Further,
since the internal components are continuously washed, the WEP
will also remove gaseous pollution so long as the gaseous com-
ponent is soluble in the washing liquor.
Many of the components of a WEP are similar to those of a
dry ESP; therefore, many of the remarks made in Sections 4.1.1
through 4.1.7 are also applicable.
4.4 WET ELECTROSTATIC PRECIPITATOR OPERATION AND MAINTENANCE
As one would expect, the WEP has a high potential for
corrosion and scaling and requires a water treatment system. If
the wash liquor is to be recycled through the WEP, which in most
cases is necessary to save on water consumption, the same water
treatment methods used with scrubbers must be applied (see
Section 5). Concentration of suspended and dissolved solids
must be maintained, in addition to pH control. The clarifi-
cation of solids must be sufficient to minimize spray nozzle
plugging and buildup of recycled materials on the internal mem-
bers of the precipitator. If condensible materials are being
collected, means for removing them must be provided (such as
skimming devices or methods for sludge removal).
The dissolved solids concentration must be maintained at a
steady and acceptable level, either by the right amount of
purging, by chemical treatment, or both.
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4.4.1 Pre-Startup Inspection
Before starting up the WEP, a thorough inspection of the
system is required. The procedure and checklist to follow is
provided in 4.2.1, with the exception of items applying to the
water cleaning system.
Water Cleaning System:
Turn on water cleaning system and check all pipe
connections for leaks.
Check for adequate water flow.
Check individual water line pressure
Check angles and direction of nozzle spray. Correct
nozzle positioning is necessary to obtain coverage of
precipitator internals.
Inspect drain system to ensure that wastewater drains
freely. {
Check for adequate clearance between piping and high
voltage system.
A WEP preoperation and inspection checklist can be compiled
from Figures 6 (page 56) and 8 (page 88).
4.4.2 Routine Startup
Follow procedure in 4.2.2, except replace-Items 3, 4, and 5
with activation of spray system as given in 5.2.2, Items 1
through 6.
4.4.3 Routine Inspection and Maintenance During Operation
Only visual inspection of the external components of the
system is possible during operation. Therefore, only instru-
mented operational parameters can be observed, along with in-
spection of electromechanical equipment and structural com-
ponents. A routine daily inspection checklist for a WEP can be
made from Figure 7 (page 59) excluding the entry for Rappers and
Figure 9 (page 91) excluding the entry for Mist Eliminator.
Since actual inspection and maintenance practices are quite
specific to the particular system used, a tailormade checklist
should be prepared by the user and vendor.
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4.4.4 Routine Shutdown
Follow 4.2.4, Items I, 2 and 3; replace 4 with Items 3, 4,
5, and 6 from 5.2.4; then proceed with 5, 6, 7, and 8 from
4.2.4.
4.4.5 Common Malfunctions
Scaling, buildup, and corrosion are commonplace in WEP's.
These conditions are prevalent not only within the liquor recir-
culating system, but also in the electrostatic precipitator
housing. Liquor clarification and chemical treatment are
critical to WEP performance. Thorough familiarity with scrubber
and dry ESP troubleshooting procedures are necessary in order to
properly diagnose WEP malfunction and poor performance.
A case history of a WEP is provided in Appendix A, which
outlines the use of the multiphase troubleshooting program.
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SECTION 5
TECHNICAL ASPECTS OF THE DESIGN,
OPERATION, AND MAINTENANCE OF SCRUBBERS
Wet scrubbers are air pollution control devices that pro-
vide an environment to enable flue gas contaminants to contact
impaction targets, generally water droplets. The wetted contam-
inant impinges on collection surfaces (entrainment separators)
and removes the contaminant-laden droplets from the gas stream.
Although there are devices that use mechanisms such as steam
condensation, electrostatic charging, or sonic agglomeration in
conjunction with conventional scrubber mechanisms, they will not
be discussed here because applications are few and the tech-
nology is still in the early stages of development. The
emphasis in this section is also focused on particulate removal,
not gaseous removal.
The collection efficiency of wet scrubbers varies according
to design and total power expended both in forcing the gases
through the collector and in generating liquid contact surfaces
(droplets). Scrubber manufacturers promote their product ac-
cording to such parameters as particle size collection effi-
ciency and mass collection efficiency.
The scrubbing liquid is introduced into the scrubber in
many ways, the most frequent of which are listed below:
Fine spray nozzles
Coarse spray nozzles
Very coarse spray nozzles (>3/4-in. pipe)
Overflow weir
Impingement of gas onto liquid pool
Introduction of gas under surface of liquid pool
The liquid sprays can be operated at low or high pressure
and introduced into the airstream countercurrent, cocurrent, or
across the direction of gas flow.
The classification of scrubbers is difficult because so
many designs are available. As an example, a list is given in
Table 7.
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TABLE 7. SCRUBBER CLASSIFICATIONS
Basic type
Specific type
Impingement baffle
Packed tower
Submerged orifice
Venturi
(Preformed spray)
(Gas-atomized spray)
Miscellaneous and combination
scrubbers
Tangential inlet wet cyclone
Spiral baffle wet cyclone
Single plate
Multiple plate
Fixed bed
Moving bed
Flooded bed
Multiple bed
Wide slot
Circular slot
Multiple slot
High pressure
Medium spray
Low pressure
Flooded disc
Crossflow packed
Centrifugal fan
Multiple venturi
Combination venturi
Combination fan
79
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Other designs are presently in use or being marketed that
may not have been mentioned in this table. One of the most
popular devices available is the high pressure drop venturi,
because of its ability to control emissions of submicron
particle size distribution.
When the airstream emerges from the scrubber vessel, it
contains billions of contaminant-laden droplets, which must be
removed from the airstream before being emitted to the atmos-
phere. For this purpose, entrainment separators (demisters) are
supplied, which come in numerous designs and configurations.
Frequently encountered types are listed below:
Centrifugal
Vane axial centrifugal
Zigzag baffle
Chevron
Staggered channel
Knitted wire mesh
Geometric woven mesh
The droplets captured in the entrainment separator coalesce
and run off into a liquid reservoir (sump). This liquid is
usually chemically or physically treated for stabilization; a
portion is recycled back to the scrubber, and a portion is
removed (blowdown). Makeup liquid is provided somewhere in the
liquid circuit to compensate for blowdown.
The collected contaminant in the spent liquors must be
concentrated before final disposal is performed. The common
types of waste disposal equipment are listed below:
Settling tank
Settling pond
Clarifier
Thickener
Vacuum filtration
Liquid cyclone
Continuous centrifugal
The contaminant-laden liquors are further concentrated by
such treatments as coagulation, flocculation, chemical precipi-
tation, ion exchange, and desalting. The degree of treatment
depends upon the methods of disposal or recycling and upon state
and Federal regulations. The relative merits of the wastewater
disposal system are beyond the scope of this report, but the
user of scrubbers must be sure that these systems are operated
and maintained in an appropriate fashion.
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5.1 SCRUBBER COMPONENTS AND OPERATIONAL PARAMETERS
The scrubbing system is composed of exhaust hoods and ducts
handling airborne contaminant. Gas pretreatment equipment may
be required for coarse contaminant removal and for cooling
before the contaminant enters the scrubber vessel. The contami-
nant-laden droplets are removed by the entrainment separators.
The clean gas is then passed through an induced-draft fan and up
the stack. Forced-draft fans upstream of the scrubber are also
used. The associated components for liquor handling are the
pumps, piping, valves, motor, and fans. The key parameters
affecting the particulate collection are:
Velocity/gas flow rate
Liquid-to-gas ratio
Particle size distribution
Pressure drop
5.1.1 Velocity/Gas Flow Rate
The collection efficiency of most scrubbers depends on the
velocity of the gas stream through the liquid-contacting section
of the scrubber vessel. The relative velocity between washing
liquids (droplets) and particulates is critical to contaminant
collection. In the case of high-energy venturi scrubbers, a
velocity of 40,000 ft/min can be delivered. Fine droplet size
and high density lead to increased removal efficiency.
When a high-temperature gas stream enters the scrubber, the
volumetric flow rate diminishes accordingly (based on the tem-
perature of the scrubber liquid) because the gas is being cooled
by the scrubber liquors. In poorly designed systems, as the
particulate laden droplets enter from the recycled liquors or
the impaction process and traverse the vessel, the particulates
may become airborne again if sufficient evaporative cooling
takes place. Should this occur, pretreatment with clean liquors
(for quenching) may be required.
When the system flow rate decreases, the resulting relative
velocity may not be sufficient to collect the prescribed amount
of contaminant and emissions wi^l increase. Similarly, a
decrease in liquid flow rate could produce insufficient clean-
ing.
5.1.2 Liquid-to-Gas Ratio
The liquid-tp-gas flow rate (L/G) is a calculated value,
reflecting the liquid recycling rate (gal/min) for every 1000
ft3 of gas cleaned. Typical values range from 2 to 40, and are
a function of inlet gas temperature, inlet solids content, and
81
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method of water introduction. High L/G ratios are used for
high-temperature and high-grain loadings. Should the L/G ratio
fall below design values, collection efficiency will diminish.
5.1.3 Pressure Drop
The pressure drop across a scrubber includes the energy
loss across the liquid gas contacting section and entrainment
separator, with the former accounting for most of the pressure
loss. A low pressure drop scrubber ranges from 2 to 10 in. H20;
a medium from 10 to 30 in. H20; and a high, 30 and above. The
higher the pressure drop, the greater the collection efficiency
for both particle size and concentration.
5.1.4 Particle Size Distribution
Performance of a scrubber depends on the gas stream
particle size distribution. Efficient collection of submicron
contaminant challenges the application of any type of control
equipment. High-energy venturi scrubbers .are designed for
submicron contaminant collection.
5.1.5 Scrubber Vessel
The ultimate goal of the scrubber, regardless of its
design, is to provide the greatest number of droplets to the
contaminant stream in as optimum a fashion as possible. Regard-
less of the method used to introduce the liquid into the vessel,
the wet scrubber requires a uniform and consistent liquid dis-
tribution pattern. One method to accomplish this is with a
spray nozzle. The spray nozzle used in wet scrubbers may be of
the pressure type (hollow and solid cone, impingement, and
impact); rotating (spinning atomizers); or other miscellaneous
configurations. Spray nozzles frequently wear or clog, produc-
ing an uneven liquid pattern and requiring replacement. Carbide
nozzle tips, which are abrasion resistant, can be supplied with
standard stainless steel nozzles. Titanium and ceramic nozzles
are now becoming more prevalent in scrubber vessels. Weir box
distribution, on the other hand, requires little maintenance
after initial leveling.
Other than nozzle abrasion, the presence of dry/wet zones
at the inlet to the vessel or in some other part produces build-
up and eventually causes malfunction. Liquid distribution
components (nozzles, weirs) must be provided at the interface to
avoid this problem.
When the vessel is operated under high negative pressure,
the liquid within the associated components rises an equivalent
height. Therefore, all joints must be sealed to withstand this
pressure; gasketing and hardware must also be corrosion
82
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resistant, especially since the single most prevalent problem in
scrubbers is material failure due to corrosion. Corrosion
occurs because most scrubber applications are associated with
acid gas streams and, upon contact with the scrubbing liquors,
form corrosive liquids. The scrubber vessel is thus usually
fabricated with special alloy steels (stainless 304/316, Hast-
alloy, Inconel) or fiberglass, or it may contain liners of
rubber or plastic. Should high velocities exist within the
vessel, as with the Venturis, the abrasion-resistant qualities
of the materials must also be considered.
Another frequently encountered problem in scrubbers is
scaling. Scaling results from improper chemical balance in the
system and is usually corrected by the proper chemical treatment
of the washing liquors, most often by pH control.
5.1.6 Entrainment Separators
Upon leaving the contaminant washing section, the gas
stream contains contaminant-laden droplets. The droplets are
removed from the gas stream by an "entrainment separator," which
provides the droplets with impingement surface or imparts cen-
trifugal forces that remove the droplets from the gas stream.
The common types available are listed on page 80. The most
important factor in choosing and designing an entrainment
separator is droplet size removal efficiency. Other than for
centrifugal separation, the droplet velocity is not especially
critical because the droplets usually possess sufficient inertia
and thus do not change direction or follow the air streamlines
through the separator; instead they collide on one of the
numerous obstructions (baffles, wires, chevrons) in their path.
The droplets coalesce upon collision in the separator and form
sheets of liquid, which drain off into liquid reservoirs or
sumps.
Because the droplets contain contaminant, particulate
buildup is likely to occur in the mist eliminator. This condi-
tion is often avoided by using an intermittent or continuous
liquid wash for the mesh, channel, chevron, or baffles. The
wash system is usually composed of low-pressure nozzles with
cocurrent and/or countercurrent flow, and the system uses
recycled liquors or fresh water for cleansing. An increasing
pressure drop across the separator is usually caused by buildup.
Mesh separators are most prone to plugging; channel, chevrons,
and baffles are next; and the centrifugal separators are least
likely to plug. Materials of construction of the separator are
usually steel or plastic. A major factor when considering using
plastic is the possibility of meltdown should the scrubber lose
liquid pumping capability, thus exposing the mist media to the
high-temperature gas stream. Although temperature controllers
upstream of the scrubber can shut the blower down, the blower
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slowly diminishes rotating, therefore pulling the unwanted hot
gases through the media. Hence the use of plastic media in
high-temperature applications should be carefully evaluated.
The centrifugal separators allow the droplet-laden gas to
enter tangentially, which imparts a centrifugal force on the
droplets. As the gas spins through the unit, the liquid drop-
lets are forced outward toward the wall. The performance of
this type of separator is extremely dependent on the flow rate
within the unit. A decrease in flow could result in liquid
droplet carryover to the fan and stack.
5.1.7 Liquor Reservoir (Sump)
Liquid runoff from the entrainment separator is captured in
the sump, which is integrally mounted to the scrubber vessel.
It may have a pyramidal shape or some other suitable design.
The contaminant within the sump settles and is pumped away for
additional treatment. Some sump designs incorporate the scrub-
ber pump liquid pickup from the sump itself. In this case, the
piping pickup points should be of sufficient elevation to avoid
entraining the high solids content of the liquors in the sump
bottom. Excessive sludge buildup in the sump often leads to
system shutdown and supplementary cleaning.
5.1.8 Pumps
Scrubber pumps (usually centrifugal) may be operated at low
or high pressure and flow according to the required means of
producing droplets. Pump failure is usually attributed to a
combination of abrasion and corrosion, and may be reduced by
using appropriate materials of construction for impellers and
housing. Some pump protection is provided by inlet strainers;
the lower the suspended solids concentration and the more chem-
ically stable the liquids, the more protection is provided.
High-rpm pumps will fail more frequently. Since pumps
contain moving parts, they are items of high maintenance. The
bearings must be lubricated and inspected regularly, and the
pump seals must also be checked frequently. Most pumps are
directly coupled to the motor shaft. Belt drives may be re-
quired, however, to vary pump rotation (flow).
Insufficient pump suction can cause severe problems. Too
high a negative pressure at the eye of the impeller can cause
"boiling" of the liquid, cavitation, and severe vibration,
leading to erosion of the impeller, noise, and shaking of the
pipework. This is especially true with hot or volatile liquids.
Under the conditions of maximum flow, the system must have a net
positive suction head (NPSH) greater than the NPSH required by
the pump. If insufficient NPSH is available from the system,
cavitation will occur.
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5.1.9 Piping
The piping in scrubber systems handles high solids concen-
trations and chemically corrosive materials. Erosion and wear
tend to occur at sudden changes in pipe cross sections (elbows,
reducers). The required elbows and reducers should have thick
walls and, in the case of elbows, a wide radius. Materials of
construction must provide corrosion and erosion protection.
High-pressure piping must also be specified where high-pressure
pumps are used. Blind flanges allow for ease of pipe cleanout.
Flanged pipe sections and unions also facilitate maintenance.
The gasketing material for the flanges must be compatible with
the liquors.
5.1.10 Valves
Valves are also subjected to corrosion and erosion. Unless
specifically designed for throttling, most valves should be
operated in a fully opened or closed position. Valves that
experience pressure drop should contain abrasion-resistant
linings, especially if the liquors contain a high level of
suspended solids. Should valve throttling be necessary, to
alleviate wear in the valves and compensate for the change in
pressure in the line, orifice plates are installed upstream of
the valve to reduce the pressure rise due to throttling.
5.1.11 Fans
Scrubber fans can be positioned either upstream (forced
draft) or downstream (induced draft) of the vessel. Centrifugal
fans are typically used, and experience corrosion and mechanical
stress. When the fan is used in a forced-draft capacity, it
handles high concentrations of contaminant and can experience
abrasion, caking, and buildup. Most scrubber applications use
the fan in an induced-draft configuration, therefore handling
moisture-saturated air. Some buildup does occur in the fan
wheel; should contaminant flake off, imbalance and vibration
could occur. High negative pressure fans, especially those used
for venturi scrubbers, exhibit extreme mechanical stress because
of the high fan tip speeds. The high mechanical stresses,
coupled with corrosive gases, often result in stress corrosion
and cracking. Abrasion and corrosion resistant fan wheels and
linings must be used in such an environment. Fan drains must be
provided to remove captured liquid.
5.1.12 Instrumentation
The two types of instrumentation necessary for scrubber
systems are safety and performance monitoring:
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Safety:
High temperature interlocks, which actuate pumps for
auxiliary recycling and for additional water
High temperature controls to activate the scrubber
bypass system
Low liquid level alarms and control systems for aux-
iliary pumps
Automatic fan controls to activate the bypass system
if the blower fails
Fan vibration indicator and alarm shutoff system
Fan and bearing high temperature alarm and shutoff
Performance monitoring:
Discharge pressures and flows on all pumps
Recycle blowdown and makeup flow
Pressure drop across scrubber, cleansing section, mist
eliminator, and entire scrubber
Inlet static fan pressure, voltage, and amperage
pH meters/recorder and low level alarm
Inlet and saturated gas temperatures
Suspended solids monitor
The safety interlocks protect equipment and personnel, and
the performance monitoring instrumentation effects reliable
operation and forecast malfunctions.
5.1.13 Conclusions
Because all component surfaces are wetted, in scrubber
applications corrosion can become a substantial problem. There-
fore, corrosion-resistant materials must be used in the piping,
pumps, and blowers; indeed, most of the scrubber system must use
these materials. In the scrubber vessel, where high velocities
are present, erosion may occur, requiring the use of proper
materials of construction. Properly irrigated entrainment
separators are also necessary, and will effectively minimize
contaminant buildup. Adequate monitoring instrumentation is
crucial to equipment operation and performance. If not in
place, it should be procured and installed.
86
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5.2 SCRUBBER OPERATION AND MAINTENANCE
Regardless of the reason for scrubber shutdown, a well-
defined inspection program should be followed before commencing
startup. Preoperation and inspection guidelines are given
below, followed by procedures for routine startup, inspection
and maintenance during operation, and routine shutdown. Guide-
lines for maintenance during shutdown and for detecting common
malfunctions are also described.
5.2.1 Pre-Startup Inspection
Whether the scrubber has recently been installed or has
undergone internal service and maintenance, before it is
"buttoned up" it must be thoroughly inspected. A checklist for
preoperation and inspection is provided in Figure 8. This
checklist is to be used as a guideline only, and should be
tailored for each specific system. The inspection survey during
shutdown should include internal and external observations from
the ducts up through the stack. If possible, as part of the
pre-startup inspection before the unit is put into service, it
is advisable to operate pumps and other components to observe
their performance.
5.2.2 Routine Startup
After the scrubber has been thoroughly inspected, the
following general startup procedure should be followed:
1. Close all drain valves.
2. Fill vessels to normal level.
3. Activate circuit breakers for all controls and com-
ponents .
4. Open pump suction valves.
5. Start pumps.
6. Open discharge valves slowly.
7. Open isolation dampers.
8. Start fan (if fan has an inlet control damper, it
should normally be closed until fan reaches speed).
9. Record data from monitoring instrumentation.
10. Note changes in monitoring data as gases pass through
system.
87
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SCRUBBER PHEOPERATION AND INSPECTION CHECKLIST
APPLICATION:
DATE/TIME:
REPORT BY: YES NO ATTN.
DUCTS
WARPAGE O D D
CORROSION a D a
ABRASION D C3 CJ
GASKETING D D O
SLIP JOINT DP C3
BUILDUP an D
COMMENTS
GAS PRETREATMEOT? EQUIPMENT
NOZZLES a a a
BUILDUP a D a
GASKETTNG d O D
CORROSION CD Q D
VALVE OPERATION CD D D
SUMP SLUDGE tD D D
COMMENTS
SCRUBBER
NOZZLES an cu
- CLOGGING an a
- WEARING D d d
- ABRASION a a D
ABRASION a a a
BUILDUP an a
CORROSION a a a
PIPING an a
- SCALING C3 C3 O
- RUSTING an a
- FITTINGS an a
- LEAKAGE a D C3
SUMP SLUDGE a O CD
COMMENTS
Page I of 2
Figure 8. Preoperation and inspection checklist for scrubbers.
88
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CHECKED
MIST ELIMINATOR
NOZZLES
- CLOGGING
- WEARING
- ABRASION
PIPING
- RUSTING
- PITTING '
- LEAKAGE
VALVE OPERATION
CORROSION
CCfWENTS
MIST ELIMINATOR MEDIA
BUILDUP
CLEANED
REPLACED
COMMENTS
LIQUOR TREATMENT
pH CONTROL
- CALIBRATION CHECK
- PROBE BUILDUP
CAUSTIC HOLD TANK
SLUDGE BUILDUP
VALVE OPERATION
PIPING LEAKAGE
CCfMENTS
YES
0
a
a
a
a
a
D
a
D
ID
n
a
a
n
n
a
a
a
a
a
Page 2 of 2
NO
n
a
n
a
Q
n
a
a
CD
a
tn
a
tu
D
n
n
n
a
D
a
REQ.
A3TN
D
a
a
a
a
a
a
a
n
a
a
a
a
n
a
o
n
a
n
a
Figure 8 (continued)
89
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5.2.3 Routine Inspection and Maintenance During Operation
During normal operation, the preoperation checklist (Figure
8) can be used with the instrumentation measurements noted in
5.1.12. A checklist for inspecting an operational scrubber is
given in Figure 9. A tailormade operational checklist should be
prepared for each specific type of equipment.
5.2.4 Routine Shutdown
A general procedure for scheduled shutdown is outlined
below:
1. Stop blower.
2. Isolate scrubber vessel by closing dampers.
3. Shut down makeup water.
4. Allow system to cool.
5. Continue to blow down at normal rate until liquid
levels reach pump inlet, and then shut pumps off.
6. Stop all other pumps.
7. Deactivate all circuit breakers.
8. Open access door and use necessary safety procedures
for inspection.
5.2.5 Common Malfunctions
Areas on which to focus attention are:
Buildup in wet/dry zones
Clogged nozzles
Abrasion in areas of high velocity, throats, orifices,
elbows, etc.
Corrosion in ducts, piping, scrubber vessel
Entrainment separator buildup
Fan vibration
Pump wear
90
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SCRUBBER OPERATING INSPECTION AND MAINTENANCE CHECKLISTS
APPLICATION:
DATE/TIME:
CHECKED RBQ_
BEPORT BY: YES NO ATTN.
PKt-TKEATMENT EQUIPMENT
PIPING LEAKAGE CD CD CD
VALVE OPERATION CD CD CD
LEVEL CONTROL CD CD CD
PUMP/LUB. CD CD CD
COMMENTS
SCRUBBER
PIPING LEAKAGE CD CD CD
VALVE OPERATION CD CD CD
LEVEL CONTROL CD CD r~l
PUMP/LUB. CD CD CD
COMMENTS
MIST ELIMINATOR
PIPING LEAKAGE CD CD CD
VALVE OPERATION d CD CD
PUMP/LUB. CD CD CD
COMMENTS
LIQUOR TREATMENT
PIPING LEAKAGE CD CD 'CD
VALVE OPERATION CD D CD
LEVEL CONTROL tD CD CD
PUMP/LUB. a a a
COMMENTS
OPERATING DESIGN
COLLECTOR MEASUREMENTS
TEMP. IN d
TEMP. OUT CD
FLOWRATE ED
STATIC PRESSURE IN CD
STATIC PRESSURE OUT CD
PRETREATMENT PUMP PRESSURE CD
SCRUBBER PUMP PRESSURE [D
MIST ELIMINATOR PUMP PRESSURE O
pH PUMP PRESSURE C3
BLOWER CURRENT Q
BLOWER VOLTAGE CD
STACK APPEARANCE pj
COMMENTS
Figure 9. Operating inspection and maintenance checklist for scrubbers.
91
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Most scrubber malfunctions do not in fact occur in the
scrubber vessel, but in the interconnecting ductwork, dampers,
fans, centrifugal pumps, valves, and piping. Alarms are often
used to signal malfunction of scrubber pressure drop, pump and
blower failure, and liquid levels. Changes in process condi-
tions usually affect scrubber performance.
5.2.6 Spare Parts
Scrubber manufacturers supply a list of recommended spare
parts. Spare parts for auxiliary equipment, such as pumps,
fans, piping, dampers, valves, and instrumentation, are also
required. Table 8 shows the spare parts inventory that is
recommended.
TABLE 8. REPLACEMENT PARTS FOR SCRUBBERS
Motor (fan, pump, seals, bearings, impeller)
Mist eliminator media (full set)
Gauges (temperature, pressure)
pH probe and required reagent
Piping
5.2.7 Troubleshooting Program and Procedures
The multiphase program to diagnose and troubleshoot opera-
tion problems is provided in Appendix A. The troubleshooting
chart present in Table 9 gives guidelines for cause and remedies
of problems in scrubbers. Although there is some discussion of
pumps in this chart, it is by no means exhaustive. Fans are not
mentioned because of the extensive scope of troubleshooting
guides from manufacturers. The probable cause of fan noise, low
or high flow rates, and static pressure are too numerous to
itemize.
92
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TABLE 9. TYPICAL TROUBLESHOOTING CHART FOR SCRUBBERS
Symptom
Cause
Remedy
Low pressure drop
(scrubber section)
High pressure drop
(scrubber section)
Low pressure drop
(mist eliminator)
High pressure drop
(mist eliminator)
High temperature
in stack
Pump leaks
Pump pressure
increase
Pump flow rate/
pressure
diminished
Pump noise/heat
Corrosion
Erosion
(continued)
Low airflow rate
Low liquid flow rate
Eroded cleaning section
Meters plugged
High airflow rate
Plugging in ducts
or scrubber
Low airflow rate
Low liquid flow rate
Media dislocated
High airflow rate
High liquid flow rate
Clogging
Flooding
Insufficient wash
liquor
Liquid temperature too
hot
Packing or seals
Nozzle plugging
Valves closed
Impeller wear
Nozzle abraded
Speed too low
Defective packing
Obstruction in piping
Misalignment
Bearing damage
Cavitation
Inadequate
neutralization
Incompatible materials
High recycled solids
content
Check blower
Check pump/nozzles
Inspect
Clean lines
Check blower
Inspect
Check blower
Check pump/nozzles
Inspect
Check blower
Check pump/nozzles
Inspect/clean
Inspect/drain
Check pump/nozzle
Check sump tempera-
ture
Replace
Reduce nozzles
Open valves
Replace
Replace
Check motor
Replace
Check pipes, strainer,
and impeller
Check
Replace
Check
Check pH control
Replace materials
Wastewater system
93
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TABLE 9 (continued)
Symptom
Cause
Remedy
Scaling
Pipe plugging
Improper chemical
treatment
High solids content
Abrupt expansion/con-
traction/bends
Change treatment
Cleaning
Change pipe fittings
94
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SECTION 6
TECHNICAL ASPECTS OF THE DESIGN, OPERATIONS, AND MAINTENANCE OF
ITEMS COMMON TO ALL AIR POLLUTION CONTROL EQUIPMENT
6.1 INTRODUCTION
Regardless of the nature of the process that generates the
airborne contaminant and the method used to clean and filter the
gas stream before it is emitted to the atmosphere, the contam-
inant must be captured and transported efficiently to the
control equipment. The hoods, enclosures, and interconnecting
ducts used to exhaust contaminant are common to all types of air
pollution control equipment. Therefore, exhaust system design
is critical to effective control equipment performance.
6.2 EXHAUST DUCTS
Problems often encountered with exhaust systems are insuf-
ficient contaminant capture velocity, abrupt duct transitions,
long horizontal runs, and incompatible materials of construc-
tion. Access doors for cleanout and inspection are often not
provided. Door fastening hardware and gasketing should be
corrosion resistant and compatible with other materials of
construction. Thermal insulation is also necessary if condensa-
tion is expected to occur, otherwise corrosion may result.
The presence of duct elbows or shape transitions could lead
to abrasion. Duct redesign coupled with baffle plates to
achieve a more uniform flow distribution could alleviate the
problem along with the installation of appropriate abrasive
resistant linings. Flanged ducts are also recommended to facil-
itate duct cleaning and replacement.
Dampers are sometimes necessary upstream of the control
equipment. In this condition, the damper is exposed to the
contaminant stream. Buildup in the damper mechanism is likely,
and would adversely affect its operation. Abrasion and corro-
sion are frequently observed. Turbulent flow with its skewed
velocity profile created by the damper can seriously affect the
performance of downstream blowers and control equipment. If
dampers are necessary, flow straighteners may be required prior
to allowing the gas stream to enter any sort of operating equip-
ment.
95
-------
Control equipment ductwork is usually operated under nega-
tive pressure. As a consequence, any extraneous air infiltra-
tion through cracks, seams, joints, or welds can produce buildup
and corrosion due to acid/gas condensation. Proper location of
pressure taps and temperature probes with a suitable method for
avoiding buildup and clogging is critical for these measure-
ments. The preferred arrangement of these two probes is the use
of strip chart recorders. Regular maintenance of the taps and
probes is necessary.
6.3 GAS PRETREATMENT
Cyclones may be provided to remove the large particulates,
thus reducing contaminant loading to the respective control
equipment. The cyclone produces a pressure drop in the system,
which (according to the designed collection efficiency) may be
substantial. Materials of construction must be compatible with
the gas stream.
Temperature reductions of the contaminant stream entering
the control equipment can be accomplished by evaporative cool-
ing. Among the configurations available are tangential inlet
nozzle sprays, in-line high pressure countercurrent sprays, and
sonic nozzle water atomization. Regardless of the configura-
tion, extreme caution must be exercised in maintaining the
designated liquid flow (and gas temperature) to avoid the aq,id/
gas dewpoint. The existence of dry/wet zones within treatment
equipment can produce buildup and flow choking.
6.4 INLET BAFFLES
Baffles are often installed at the inlet to the control
equipment to achieve a more uniform flow distribution. On
occasion, the baffles behave as impaction surfaces and accumu-
late material or exhibit abrasion. If the baffle is not adjust-
able and these problems occur, the baffle may have to be
removed.
6.5 HOPPERS
In either a baghouse or ESP, the collected contaminant is
dislodged from the bags or collector plates and falls into the
hopper. The hoppers are emptied according to the amount collec-
ted. Some type of automatic or semiautomatic method is advis-
able. The design of the hopper slope and contaminant handling
system is based on the physical and chemical properties of the
dust. Dust bridging, agglomeration, and mudding can occur in
the hopper. Methods for alleviating these problems are hopper
96
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vibrators, heaters, fluidizing air, rappers, poke holes, housing
insulation, and access doors. Materials of construction are a
prime consideration, not only to avoid corrosion but also to
ensure structural integrity. Workers frequently rap the hoppers
with hammers and pipes to assist the flow of collected dust.
Hoppers are usually operated under negative pressure and
need appropriate valving at the bottom apex to allow hopper dust
to be removed without admitting air to reentrain dust. A rotary
airlock valve suits this purpose; it consists of a paddle wheel
that rotates at a given rpm and can discharge materials to a
screw conveyor or storage container. New installations should
have air locks with wiper blades for each vane to ensure air-
tight sealing and cleaning. Packing glands and bearings should
be set away from the housing to avoid contact with high tempera-
tures .
For low solids flow and nonautomatic installations, slide
gates may be used. These gates are used only when the compart-
ment is offline. Air leakage into the hoppers and the asso-
ciated problems of condensation are prevalent with this method,
which is thus not recommended for new installations.
Although costly, the new, larger capacity hoppers are
specified with air conveying materials handling systems. These
are used when the contaminant is easily handled and has a high
solids content. One of the major problems experienced with
these systems is moisture condensation and icing in the air
lines. Heat tracing, insulation, and moisture separation can
alleviate these problems.
When inspecting the hopper, the presence of excessive
buildup or bridging may be attributed to a malfunctioning level
indicator, nonexistent or inoperative hopper heaters, and
vibrators.
6.6 FANS
The fan, along with the ducts, hoods, and air pollution
control equipment, make up the pollution control system. The
fan generates the suction in the system that draws the air
contaminants from the process and passes them to the air pollu-
tion control equipment.
The ducts before and after the fan can almost be considered
part of the fan itself. These ducts establish smooth airflow
into and out of the fan so the fan can do the maximum work
moving air. Poor design of these ducts can lead to turbulence
and uneven flow pattern at the fan inlets and outlet, and the
fan capacity will be lower than expected.
97
-------
Air density is critical to flow performance. The primary
factors affecting density are air temperature and plant altitude
above sea level. In either case, the volume capacity of the fan
varies with the air density. If the air temperature or altitude
increases, the air becomes less dense. For example, a fan
moving 20,000 ft3/min of less dense air is moving less mass than
a fan moving the same quantity of "standard air." Consequently,
the fan does not have to develop as much static pressure when it
is moving less dense air. The horsepower requirements are also
lower, because less air mass is being moved.
Fan ratings are developed under ideal laboratory condi-
tions, and typically do not perform as well as the manufacturer
predicts. Therefore, fan curves should be heavily relied upon;
pitot or S-type velocity probes should be used. Fan blades are
designed to be most efficient when air enters in a straight
line. Elbows and fan inlet boxes that impart a spin to air
entering the fan in the direction of fan rotation decrease the
amount of air moved, because the fan blades have to "catch up"
to the air before acting on it. If the air spin is opposite to
the fan rotation, the output will also be reduced.
Ideally, the fan outlet should be a straight duct length of
5 to 10 duct diameters with no elbows or other interferences.
Air discharged from a fan outlet does not normally have a uni-
form velocity distribution because the mass of air discharged
experiences a centrifugal force from the spinning fan wheel,
resulting in higher velocities at the outer edge of the outlet
than at the inner edge. Several duct diameters downstream from
the fan outlet ensure the air velocity returning to near uniform
distribution across the duct.
The centrifugal fan (of the radial blade type) is used in
systems handling contaminants that are likely to clog and result
in fan buildup. The flat radial blades tend to be self cleaning
and are built with thick blades to withstand erosion and impact
damage from airborne solids. When the material being handled is
explosive or flammable, the fan should be manufactured of a
nonsparking component and material.
The motors that drive the fans can be direct drive (motor
shaft directly coupled to fan shaft) or belt driven. Direct
drive fans are more compact and assure constant fan speed
because they eliminate belt slippage. Slippage may occur when
belt-driven fan drives are not maintained. Fan speeds are thus
limited to available motor speeds when the direct drive config-
uration is used. Belt-drive fans are more flexible when in-
creases (or decreases) in fan speed are required.
The fan may be the only moving part in the air pollution
control system; therefore, it requires a great deal of scrutiny
98
-------
during operation and maintenance. If a problem is suspected,
duct pressure and velocity readings should be obtained and
compared to design specifications. Visual inspection of the
ducts may reveal closed dampers or open inspection parts.
Problems such as loose fan belts, dirty fan blades, plugged
ducts, and overheating fan shaft bearings are frequently en-
countered in air pollution control equipment systems.
According to the application, space requirements, and
costs, the fan may be located either upstream (forced draft) or
downstream (induced draft) of the control equipment. Forced-
draft fans push air through the system; induced-draft fans draw
air through the control equipment. Forced-draft fans experience
corrosion and abrasion because they are exposed to heavy dust
concentrations. When the contaminant accumulates on the fan
blades and a portion then breaks off, vibration and imbalance
occur. These fans are usually present in older systems (10
years and greater) where the air pollution control equipment was
added to the system and the fan remained the same or was up-
graded. This configuration is noticeably present in utility
boiler ESP applications. Induced-draft fans are operated on the
clean side of the pollution control equipment where they are
subject to less contaminant. This configuration is usually
present in scrubbers and baghouses.
6.7 EXHAUST STACKS
An exhaust stack on a pollution control system serves two
purposes: it helps to disperse the gas stream by discharging
the exhausted air above roof level, and it improves fan perform-
ance because the uneven velocity distribution at the fan outlet
causes a high velocity pressure at the outlet.
All systems should have at least a short, straight stack on
the fan. A high stack discharge velocity (3000 ft/min or
higher) helps to disperse contaminants, because the air jet
action can increase the effective stack height except under
severe wind conditions.
If rain entering the stack is a problem, a vertical dis-
charge sleeve that induces ambient airflow and does not block
the stack opening is effective in keeping rain out of the stack.
The old-style weather cap deflects exhausted air downward and is
no longer recommended. Fan discharges should not be directed
horizontally to keep rain out because contaminant dispersion is
hindered. When the fan is operating, rain entering the stack is
not a problem.
99
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6.8 CONCLUSIONS
The simplest way to diagnose a system problem is to inspect
and to take pressure and velocity measurements at strategic
locations. The visual inspection will reveal closed dampers,
open inspection ports, damaged hood and ducts, and malfunction-
ing components related to the control equipment. Loose fan
belts, dirty filters, plugged ducts, or dirty fan blades may be
present. Static pressure measurements at hoods, elbows, and on
both sides of the control equipment will show the contribution
of each to the overall pressure drop in the system and should be
compared with previous data. The primary problems usually
encountered in systems is insufficient airflow and excessively
high contaminant levels.
100
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SECTION 7
INSPECTION, SAFETY, AND MAINTENANCE EQUIPMENT
Various tools and equipment are required for the efficient
performance of inspection and maintenance. Table 10 lists the
items that are basic to an inspection.
TABLE 10. BASIC INSPECTION AND SAFETY EQUIPMENT
Hard hat Safety shoes
Safety glasses or goggles Dust and gas respirators
(nonfogging, no vents) (disposable)
Suitable gloves Tape measure (50 ft)
Flashlight Paper pad, pen (inspection checklist)
Ear protection Camera
Body protection (disposable garments, chemical/fire-resistant clothing)
Table 11 lists the testing equipment that should be readily
available, and Table 12 lists the hand tools that are needed.
For more extensive maintenance, air-operated power tools
are recommended, especially when maintenance is to be performed
within the pollution control equipment housing or vessel.
Air-operated tools are lighter in weight and more convenient to
use. Electrical tools can spark and possibly cause fires or
explosions when working inside dusty environments. Table 13
lists the power tools that are recommended, and Table 14 lists
items that are required to support the maintenance efforts.
A relatively new way to identify leaking or poorly in-
stalled bags is to inject a quantity of fluorescent or highly
reflective powder into the baghouse, and then inspect with
either black light or a high-intensity lamp. This technique can
reveal very small leaks although the need to span large areas is
time consuming. Use of the powder is also effective in spotting
broken welds or other leaks at joints and seams.
101
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TABLE 11. BASIC TESTING EQUIPMENT
Dial thermometer (50° to 1000°F, 12-in. stem)
LJ-tube manometer (flexible)
Stopwatch
pH (litmis) paper
Pi tot tube (S-type for contaminant streams, 600 ft/min
and greater)
Velometer (25 ft/min and greater)
Plastic sample bottles (wide mouth)
Grab sampling detector tubes (Draeger type)
Photo tachometer
Amprobe (a.c. clamp on volt-ohm-ammeter)
Multimeter.
TABLE 12. MAINTENANCE TOOLS
Open-end wrenches
Socket wrenches
Adjustable wrenches
Pipe wrenches
Locking pliers
Pliers (side cutters, slip joint)
Screwdrivers
Hex keys
Hammers
Hacksaw
Knife and shears
Scissors
Calipers
Carpenter's rule
Scraper
Wire brushes
Toolbag and canvas bucket.
102
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TABLE 13. POWER TOOLS
Air screwdriver
Power scissor shears
Impact wrench
Air nut wrench
Air-driven hacksaw
Hydraulic cutters
Pneumatic chisel
Heavy-duty drain cleaner
Blowgun
Air-operated vacuum cleaner (hand held and 55-gal drum type)
Portable air compressor with in-line pressure regulator; filter and
moisture trap.
TABLE 14. GENERAL EQUIPMENT
Ladders (wood or fiberglass)
Electric extension cords
Safety (fluorescent) drop lights
Tool pouches
Penetrating lubricant
Fire extinguisher
First aid kit
Protective hand creams
Wood platform truck
103
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In scrubber applications, high-pressure, hot-water cleaning
equipment may be used periodically to rejuvenate vessel walls
and housing. Rapping equipment may also be required to elim-
inate pipe scale and buildup.
Stack monitoring instrumentation often utilized for con-
tinuous and reliable pollution equipment operation are opacity
meters and/or broken bag detectors. This type of instrumenta-
tion is usually found in large, high-capacity systems.
104
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SECTION 8
SUMMARY
When management is prevailed upon to purchase, install,
operate, and maintain air pollution control equipment, resist-
ance often arises. Regardless of the aesthetic values derived,
management considers the equipment to be a large capital expend-
iture and, after installation, to be a significant contributor
to plant overhead. These factors are often coupled with in-
ferior quality hardware that leads ultimately to poor equipment
performance, resulting in conflicts between government, indus-
try, and equipment manufacturers.
Management's best approach to reconciling this apparent
dilemma is to analyze critically the possibility of a return on
the investment in the equipment. Although the ROI is not
obvious at the outset, management should explore direct or
indirect ways within its operation to effect savings. A return
on investment is also calculable for operation and maintenance,
by preventing equipment breakdown and loss of production with a
well-planned and controlled preventive maintenance program. In
this regard, nearly all maintenance activities are human activ-
ities, and for the most part, controlled by those individuals
executing the work. Even the most explicit inspection check-
lists, charts, guidelines, methods, and training will not
achieve the desired goal unless plant management, engineering,
and labor have the commitment and willingness to include an
effective operation and maintenance program.
With the understanding that air pollution control equipment
is an integral part of the process equipment, discussion of
operation and maintenance procedures becomes more palatable to
those responsible for its performance.
105
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Chemical Engineering, May 26, 1975.
Scrubbers
Calvert, S., et al. Scrubber Handbook. APT Inc. PB-213016,
NTIS, Springfield, Virginia, 1972.
General
Cross, F. L., and H. E. Hesketh, eds. Handbook for the Opera-
tion and Maintenance of Air Pollution Control Equipment.
Technomic, Westport, Connecticut, 1975.
PEDCo Environmental, Inc. Industrial Guide for Air Pollution
Control Handbook. EPA 625/6-73-004, Technology Transfer,
June 1978.
Richards, J. R. Plant Inspection and Evaluation Workshop Ref-
erence Material. Appendix 1-1, 1-2, 1-3. PEDCo Environ-
mental, Inc. USEPA, Div. of Stationary Source Enforcement,
Washington, D.C., November 1978.
107
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Richards, J. R. Reference Material for Technical Workshop on
Plant Inspection and Evaluation. Vols. 1-2. PEDCo Envir-
onmental, Inc. USEPA, Div. of Stationary Source Enforce-
ment, Washington, D.C., November 1978.
Szabo, M. F., and R. W. Gerstle. Operation and Maintenance of
Particulate Control Devices on Coal-Fired Utility Boilers.
EPA 600/2-77-120, July 1977.
Szabo, M. F., and R. W. Gerstle. Operation and Maintenance of
Particulate Control Devices on Selected Steel and Ferro-
alloy Processes. EPA 600/2-78-037, March 1978.
U.S. Environmental Protection Agency. Seminar on Operation and
Maintenance of Air Pollution Equipment for Particulate
Control. Sponsored by USEPA, Cincinnati, and Pollution
Engineering Magazine, Harrington, Illinois, 1979.
108
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APPENDIX A
TROUBLESHOOTING PROGRAM
INTRODUCTION
Frequent equipment malfunction, breakdown, and excessive
emissions indicate improper equipment performance. A multiphase
program must be implemented to diagnose system problems (hoods,
ducts, control equipment, and fan). As a guideline, the follow-
ing program should be followed:
Phase 1. Problem Identification
This phase should incorporate a detailed inspection of the
system during operation and shutdown and culminate with a report
listing all observations (positive and negative), providing
interpretations of these observations (why things were the way
they were); and recommending methods and items to improve per-
formance. Pressure and velocity measurements may also be
needed.
Phase 2. Implementation
The recommendations provided in Phase 1 should be imple-
mented after thorough cost and technical analysis and discus-
sion. These recommendations may be in the form of engineering
design and modification, component and accessory part replace-
ment, or fabrication of new equipment. Following this aspect of
the program, repair and replacement of the procured and fabri-
cated components must be executed. Finally, the entire system
must be started up and debugged.
Phase 3. Sampling and Testing
A test must now be performed to evaluate the work. This
may be stack sampling or, more often, a pressure and velocity
measurement program coupled with close observation of the opera-
tion of the system.
Case histories using the multiphase program for a pulse-jet
baghouse, dry and wet precipitator, venturi scrubber, and packed
tower are presented in this appendix. It should be emphasized
109
-------
that the most effective approach to troubleshooting and diag-
nosing problems is familiarity with the process and detailed
knowledge of the contents of the various troubleshooting guides
provided herein and by the equipment manufacturer.
110
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CASE HISTORY
PULSE-JET BAGHOUSE
INTRODUCTION
Excessive emissions from two pulse-jet baghouses on fly ash
storage silos were frequently observed. Internal observations
of the units indicated bridging of the dust between bags. The
conclusion drawn by the user was that the filter medium was
incorrectly specified and that the majority of the particle size
distribution was submicrometer. Rebagging with different types
of media was tried several times, to no avail. The baghouses
under consideration were an internal part of an experimental
sludge fixation process (see Figure A-l), and their malfunction
thus had serious economic implications for the utility. The
operators of the fixation process contracted an independent
pollution control equipment services and maintenance company to
troubleshoot the problem.
Phase 1. Problem Identification
General Comments--
Design, construction, and installation of the two units
appeared to be more than satisfactory.
A conscientious housekeeping and maintenance program on the
units was obvious.
Observations--
The following observations were made both while the units
were operating and while they were shut down.
Airflow, static pressure, temperature, and dimensional data
were recorded (Tables A-l, A-2, and A-3).
The baghouses were cleaning air that is discharged from a
pneumatic conveying system, which is delivering fly ash
from electrostatic precipitator hoppers.
Both systems operate identically and exhibit identical
symptoms.
The baghouses operate for up to 50 days with new bags
before plugging.
ill
-------
GASES TO
ATMOSPHERE
ESP
STEAM
COAL
AIR HEATER
ECONOMIZER
SUPERHEATER
FIREBOX
WATER
AIR
BAGHOUSE
SILO
BAGHOUSE
SLUDGE FIXATION
SILO
SLUDGE
FIXATION
SLUDGE
FIXATION
Figure A-l. Application of pulse-jet baghouse.
112
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TABLE A-l. SYSTEM PARAMETERS: EAST UNIT (FAN NOT OPERATING)'
Ambient air temperature
Ambient air humidity
Barometer
Inlet air temperature: dry
Inlet air temperature: wet
Outlet air temperature: dry
Inlet air pressure
Outlet air pressure
Bag AP
Outlet air velocity
Outlet dia./area
Outlet air flow
42°F
Approximately 95% (raining)
29.91 in. Hg
62°F
48° F
62°F
3.4 in. H20 (silo pressure)
1.1 in. H20
2.3 in. H20
3200 ft/min
16 in./I.4 ft2
4480 ftVmin
Pressure relief vent on this silo is leaking.
113
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TABLE A-2. SYSTEM PARAMETERS: WEST UNIT (FAN NOT OPERATING)
Ambient air temperature
Ambient air humidity
Barometer
Inlet air temperature: dry
Inlet air temperature: wet
Outlet air temperature: dry
Inlet air pressure
Outlet air pressure
Bag AP
Outlet air velocity
Outlet dia./area
Outlet airflow
42°F
Approximately 95% (raining)
29.91 in. Hg
62°F
49°F
62°F
5.2 in. H20 (silo pressure)
3.7 in. H20
1.5 in. H20
2700 ft/min
18 in./I.77 ft2
4780 ftVmin
114
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TABLE A-3. DIMENSIONAL DATA
Header pressure static
Header pressure firing
Header diameter
Header length
Silo diameter
Free space in silo
Particle size distribution
Contaminant
Diaphragm valve
Solenoid valve
Blow tube diameter
Port diameter
Bags (glazed polyester)
100 lb/in2
90 to 95 (adjusted timer to obtain)
3-in. pipe
8 to 10 ft.
26 ft
8 to 10 ft minimum
Not applicable
Fly ash from ESP hopper
2009 - 3
30
3/4 in.
5/16 in. (no measured)
4Jrin. diameter, 99 in. long
115
-------
One discharge fan has been removed, and the other was not
operated. The operator had found that the conveyor blowers
alone provide adequate airflow to transport the fly ash to
the baghouse, thus enabling the discharge blowers to be
shut down.
The bag dimensions and media were correct for this applica-
tion. The bags fitted properly. The inside surfaces of
the bags are very clean, indicating excellent filtering
operation and performance.
The bags were well sealed into the tube sheet; no evidence
of leaking was observed.
Airflow was adequate and within specifications.
No moisture/dewpoint problems were evident on the bag
surface although the operator indicated previous moisture
problems on the housing walls.
Air supply to the pulse-jet cleaning system is adequate.
The timer design and operation are excellent.
Bag wear is not a problem at this time; previous bag leaks
were attributed to punctures made while knocking caked
contaminant off the bags during manual cleaning.
Review of a particle size data report suggested that col-
lection and sizing methods used were not proper for air-
borne fly ash and probably indicate a size distribution
much larger than actually present.
The pulse-jet bag cleaning system is not generating an
adequate shock wave in the bag when it fires.
The bags were not releasing contaminant during the cleaning
pulse. The contaminant agglomerated in large lumps on the
dirty side of the bag media (approximately 3/16 inch thick
at time of visit).
The buildup on the bags was dry and exhibited no caking
characteristics. It released well when the bag was tapped
with a finger, leaving a 2-inch-diameter area of clean
media.
A spare diaphragm valve and a spare solenoid valve were
disassembled and inspected. The size and porting of these
valves appeared to be inadequate to obtain a proper shock
pulse in the cleaning air jets.
116
-------
The timer was adjusted to provide a shorter "on" time than
previously operated, thus resulting in a plenum pressure
drop of 5 to 10 lb/in.2
Interpretations—
The following conclusions were made:
The baghouses were properly sized for this application.
The bag media were appropriate.
The air supply to the cleaning valve system was adequate.
The bags were not releasing contaminant because a suffi-
cient shock wave was not being generated by the cleaning
pulse.
A shock wave was not being generated because the valve
system was not opening fast enough. The peak-induced
pressure was sufficient; however, a quick rise time was
needed to generate the necessary shock wave.
The valve system was slow operating because the internal
porting in the valve system configuration created too much
restriction and thus prevented the right angle valves from
"dumping" fast enough.
To create the required shock wave during the cleaning
pulse, a rise time of approximately 5 milliseconds was
required from valve opening to maximum pressure measured in
the blowtube.
Recommendations—
The following corrective actions were recommended.
Replace 3-inch-diameter header with 6-inch.
Replace the diaphragm valves with properly sized, faster
acting units.
Replace the solenoid (pilot) valves with units providing a
large release port.
Mount the solenoid valves directly on the diaphragm valve
release ports.
Rework porting on new valves if necessary to obtain a
pressure rise time of approximately 5 milliseconds.
117
-------
Insulate housings to minimize condensation on inside walls
during cold weather operation. (During the inspection, no
moisture problem was observed. If the process air drops
below 44°F—the present dewpoint—condensation will occur,
and thus heaters are required.)
Phase 2. Implementation
The following recommendations were implemented:
A 6-inch header was installed.
Diaphragm and solenoid valves were replaced.
Insulation and strip heaters were installed.
Phase 3. Sampling and Testing
Visual observation of the units indicated no opacity.
No velocity measurements were made on the system.
Followup discussions with the operator indicated continuous
and reliable performance.
118
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CASE HISTORY
DRY ELECTROSTATIC PRECIPITATOR
INTRODUCTION
A fertilizer company owned a weighted wire electrostatic
precipitator (see Figure A-2) that frequently exhibited exces-
sive sparking and reduced operating voltage. When operating,
the system was in compliance for mass particle emission but not
for opacity; intermittent "puffing" from the stack was noticed.
Several vendors recommended replacement of the existing unit for
an approximate installed cost of $500,000. Before the fertil-
izer manufacturer appropriated this large capital expenditure,
the previously described multiphase program was instituted.
Phase 1. Problem Identification
Observations/Interpretations—
The pretreatment simple cyclone was not significantly
reducing particulate loading to fan and precipitator.
Indication of this was apparent from previously obtained
particle size sampling data, which revealed particles
approximately 50 percent by weight larger than 10 micro-
meters .
The product elevator duct bleeds ambient air to the exhaust
fan. Aside from the duct handling particulate emissions
from the conveyor system, the ambient air with entrained
moisture may promote sporadic condensation with subsequent
contaminant buildup in the fan and precipitator.
Previous information and onsite observations indicated
correlation of stream moisture and opacity. A major por-
tion of the moisture entered the stream through cooling
water injection nozzles. The excess moisture was believed
to affect particle resistivity.
Frequent temperature changes in process were thought to be
reaching dewpoint in the precipitator.
Nine of the 17 rappers (vibrators) were inoperative,
malfunctioning, or missing. The complete rapper system
contained many inoperable components.
119
-------
FEED
CYCLONE
CYCLONE
CALCINER
WATER
INJECTION *
1
ESP
TO ASH
STORAGE
CYCLONE
AFTERCOOLER
-»- PRODUCT
Figure A-2. Application of dry electrostatic precipitator.
120
-------
Rappers were not sequenced or timed properly.
One high-voltage insulator was cracked.
The wire frame stabilizer insulator was loose.
Gasketing on three bus duct hatches was missing, as were
some of the bolts.
Insulator compartment ventilation system contained air
leaks and dirty filters; the blower was incapable of over-
coming positive pressure in the precipitator housing.
No temperature monitor was present at the inlet of the
precipitator.
Recommendations—
A sampling and testing program was devised to characterize
the cyclones and precipitator inlet and outlet streams. Param-
eters measured included grain loading, particle size, moisture,
temperature, opacity, and pertinent process variables.
Observe stack opacity while manually controlling water
injection.
Renovate, repair, and replace old rappers.
Replace broken insulator.
Secure stabilizer insulators.
Install new gaskets and insulator compartment blower and
filter.
Install thermocouple probe upstream of precipitator.
Phase 2. Implementation
Replacement parts and components were requisitioned.
Onsite supervision of repairs was arranged.
Components were repaired or replaced.
Individual precipitator components were operated and
tested.
Phase 3. Sampling and Testing
A definite correlation between moisture and opacity was
observed. An automatically controlled water cooling system
121
-------
coupled to the inlet precipitator temperature monitor was sub-
sequently installed.
Air load testing was performed to obtain a reference data
base.
Inlet and outlet of the precipitator were sampled to deter-
mine if the equipment could adequately control process
emissions.
Results of testing indicated a reduction in average grain
loading from 0.152 gr/dscf to 0.010 gr/dscf. The cost of the
overall program was $20,000, thereby saving the company $480,000
in the purchase of new equipment. A preventive maintenance
program was subsequently executed as the final phase.
122
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CASE HISTORY
WET ELECTROSTATIC PRECIPITATOR
INTRODUCTION
A wet electrostatic precipitator was installed to remove
suspended participate from the vent gases of a phosphate rock
dryer (see Figure A-3). The electrostatically collected mater-
ial was washed from the plates by water from spray nozzles. A
collecting hopper received the effluent, which was carried to a
liquor treatment system through a drain system.
The operator of the system experienced frequent opacity
violations and attributed the problem to insufficient system
voltage. Dry/wet zones produced contaminant buildup, which
would occasionally dislodge and either clog drains or short out
wires and collector electrodes. The operator of the system
asked that an independent survey be made.
Phase 1. Problem Identification
Observations--
Duct buildup in dry/wet zone
Inlet ducts not sloped enough with evidence of pretreatment
tangential spray liquid backing upstream into system
Buildup on dry/wet zones in upper WEP support structure
adjacent to nozzles
Dry/wet areas on collector electrodes
Spray nozzle clogging
Pipe and housing scale
Sump drains partially clogged with dislodged contaminant
Large amounts of buildup in outlet duct transition
123
-------
FEED
AMMONIA
t
DCArTflR
WASH
LIQUORS -
FLUORIDES
AMMONIA ~*t 1
AMMONIA
\
•^ AMMAN T ATf
— »••
)R
t
WEP
—
SCRUBBER
/•
SPENT
h n •• LIQUORS
t
M. 5CRUBRER
\
DRYER
f
FUEL
Figure A-3. Application of wet electrostatic precipitator.
-------
Recommendations—
Wide angle, high-capacity cocurrent nozzles should be
installed to prevent buildup, cleanse ducts properly, and
avoid liquid runoff upstream.
Spray nozzle pattern did not coincide with manufacturer's
specifications; new, wide-angle, solid cone nozzles were
specified.
Pump strainers containing openings slightly smaller than
the nozzle orifice should be installed.
pH probe should be relocated to provide a more representa-
tive sample of the liquor.
Outlet duct transition cleaning is required.
Phase 2. Implementation
All nozzles and strainers were procured and installed.
pH probe was relocated adjacent to recirculating pump
suction side.
Outlet duct transition was cleaned.
Phase 3. Sampling and Testing
Opacity was substantially improved.
Pump pressures and flows remained constant for 3 months.
125 ,
-------
CASE HISTORY
VENTURI SCRUBBER
INTRODUCTION
A fiberglass manufacturer owned a venturi scrubber that was
installed to control the emissions from the forming line (see
Figure A-4). Submicrometer emissions produced an opacity of 40
percent and greater. The system was in compliance for grain-
loading. Recommendations to improve system performance varied
from ionizing the water droplets to replacing the system with
wet electrostatic precipitators. Before a major capital invest-
ment program was embarked upon, the multiphase program was
executed.
Phase 1. Problem Identification
Observations—
Upstream cooling water nozzles, which were mounted
tangentially in the ducts, produced a dry/wet zone with
large amounts of contaminant buildup.
Venturi spray nozzles were abraded.
Venturi pump impellers were abrading.
High solids content present in recirculating liquors.
Velocity through mesh mist eliminator media was too high.
Recommendations—
Redesign nozzle arrangement to minimize buildup.
Install carbide tip nozzles for venturi spray.
Electroplate abrasive resistant lining on pump impeller.
Perform more frequent sump blowdown and fresh water makeup;
install efficient pump strainers.
126
-------
GASES TO
ATMOSPHERE
BAGHOUSE
I
SCRUBBER
INCINERATOR
FEED
FURNACE
FUEL
_J
FORMING
CURING
PRODUCT
FUEL
BINDER
Figure A-4. Application of venturi scrubber.
127
-------
Closed sections of mist eliminator should be opened to
decrease air velocity, and freshwater wash used instead of
contaminant-laden water wash.
Phase 2. Implementation
Install countercurrent nozzles.
Replace stainless steel nozzle tips with carbide tips.
Install impellers with abrasion-resistant plating.
Provide freshwater makeup for sump and mist eliminator
spray nozzles.
Open appropriate mist eliminator- sections.
Phase 3. Sampling and Testing
Opacity observations indicated 20 percent or less.
More conscientious preventive maintenance alleviated dust
buildup and abrasion within operating components.
128
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CASE HISTORY
PACKED TOWER SCRUBBER
INTRODUCTION
Odor complaints from local residents and in-plant employees
were being received by a company that was refining precious
metals (see Figure A-5). A countercurrent packed tower was
being utilized to absorb the acid vapors emitted within numerous
laboratory hoods. Occasionally, a plume was noticed that was
attributed to the contaminant gas being condensed. The main-
tenance department checked the functioning components, and all
seemed operational. It was then decided to recruit outside
assistance to troubleshoot the program.
Phase 1. Problem Identification
Observations—
Plant under high negative pressure.
Hood velocity below Occupational Safety and Health Admini-
stration standard of 100 ft/min.
No evacuation slot at hood benchtop.
Hood exhaust ducts were not located properly to effect
proper ventilation.
Packed tower nozzle orifices were partially clogged with
plastic chips from the packing.
Pump impeller shaft broken.
Blower belt slippage.
Recommendations—
Increase makeup air to plant.
Extend hood baffle plate to benchtop and provide slot.
129
-------
GASES TO
ATMOSPHERE
i
WASH
LIQUOR
PACKED
TOWER
SPENT
"*"" LIQUOR
HOOD
GASES
GASES
Figure A-5. Application of packed tower scrubber.
130
-------
Provide in-line strainers upstream of pump.
Replace impeller shaft.
Tighten pulley belts.
Phase 2. Implementation
Canvas makeup duct installed in two plant locations.
Fiberglass baffle plate extended to benchtop.
Strainer with holes slightly smaller than nozzle orifice
installed.
Impeller shaft replaced.
New blower pulley belts installed.
Phase 3. Sampling and Testing
Hood face velocity measured at 100 ft/min.
Exhaust duct flowrate increased 30 percent.
No apparent odor at stack.
131
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before i ompleliUKl
1 REPORT NO 2
EPA-905/2-79-002
4 TITLE AND SUBTITLE
Management and Technical Procedures for
Operation and Maintenance of Air Pollution
Control Equipment
7. AUTHOR(S)
Dr. David B. Rimberg
North America PEMCO, Inc.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
PEDCo Environmental, Inc.
11499 Chester Road
Cincinnati, Ohio 45246
12 SPONSORING AGENCY NAME AND ADDRESS
U.S. EPA Region V
Air Programs Branch
230 S. Dearborn
Chicago, Illinois 60604
3 RECIPIENT'S ACCESSION NO
5 REPORT DATE
June 1979
6 PERFORMING ORGANIZATION CODE
8 PERFORMING ORGANIZATION REPORT NO
PN 3280-G
10 PROGRAM ELEMENT NO. 1
11 CONTRACT/GRANT NO
68-02-2535, Task No. 7
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
Project Officers: Dr. Indur Goklany and Mr. Henry Onsgard
16 ABSTRACT
This manual supplies agencies and industrial users with management and technical
Guidelines for effective operation and maintenance of air pollution control
equipment. The manual covers four major topics. Section 1 discusses organization
of maintenance operation, maintenance job planning and scheduling, maintenance
work measurement, preventive maintenance, maintenance material control, budgets,
and training. Sections 2 through 4 discuss the three major types of air pollution
control equipment: baghouses, electrostatic precipitators, and scrubbers.
Emphasis is placed on simplified startup, operating, and shutdown procedures.
Routine inspection procedures are supplemented with detailed checklists. A
general program is presented for troubleshooting air pollution control equipment.
Case histories for a pulse-jet baghouse, dry and wet electrostatic precipitators,
venturi scrubber, and packed tower are included in the appendix to provide the
user with a sample program for improving equipment performance reliability.
Section 5 discusses equipment and components common to all types of air pollution
control equipment, such as hoods, ducts, fans, and stacks. Section 6 provides
the details of the tools and equipment required to perform inspection and
maintenance satisfactorily.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
Air Pollution
Dust
Filters
Scrubbers
Electrostatic Precipitators
Air Pollution Control
Stationary Sources
Particulate
13B
11G
13K
07A
131
18. DISTRIBUTION STATEMENT
Unlimited
16. SECURITY CLASS (This Report)
None
21. NO. OF PAGES
140
20. SECURITY CLASS (This page)
None
22. PRICE
EPA Form 2220-1 (»-73)
132
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