United States
Environmental Protection
Agency
Research and
Development
EPA-600/8-85-024
September 1985
LIME/LIMESTONE FLUE GAS
DESULFURIZATION INSPECTION AND
PERFORMANCE EVALUATION MANUAL
Prepared for
Office of Air Quality Planning and Standards
and
Stationary Source Compliance Division
Prepared by
Air and Energy Engineering Research
Laboratory
Research Triangle Park NC 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and applipation of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. OHKdbeccfflomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the SPECIAL REPORTS series. This series is
reserved for reports which are intended to meet the technical information needs
of specifically targeted user groups. Reports in this series include Problem Orient-
ed Reports, Research Application Reports, and Executive Summary Documents.
Typical of these reports include state-of-the-art analyses, technology assess-
ments, reports on the results of major research and development efforts, design
manuals, and user manuals.
EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental Protection Agency, and
approved lor publication. Approval does not signify that the contents necessarily
reflect the views and policy of the Agency, nor does mention of trade names or
cortiriereial products constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/8-85-024
September 1985
LIME/LIMESTONE FLUE GAS DEStJLFURIZATION
INSPECTION AND PERFORMANCE EVALUATION MANUAL
by
E. R. Kirshnan, R. S. McKibben,
M. T. Melia, and B. A. Laseke
PEI Associates, Inc.
11499 Chester Road, P.O. Box 46100
Cincinnati, Ohio 45246-0100
Contract No. 68-02-3995
Task No. 2
EPA Project Officer: Theodore G. Brna
AIR AND ENERGY ENGINEERING RESEARCH LABORATORY
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
Prepared for:
U. S. Environmental Protection Agency-
Office of Research and Development
Washington, DC 20460
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ABSTRACT
This manual on wet nonregenerable lime/limestone flue gas
desulfurization (FGD) systems is intended to provide guidance to Federal
and State regulatory personnel concerned with the inspection and permitting
of FGD systems for coal-fired steam electric generators in the United
States. The manual is structured as a "working document" for one who
periodically inspects power plants to ensure compliance with emission
standards. Orientation material in the manual on the design, operating,
and performance characteristics of FGD systems may also be useful to the
environmental regulatory agency permitter. With its goal of facilitating
the systematic inspection of an FGD system to determine the system's
present and probable future compliance status, the manual tunita-^process
theory to a necessary minimum and makes ample use of charts, checklists,
and simplified diagrams in providing important guidelines and recommendations.
Following the introductory section defining its purpose, approach,
and scope, the manual contains sections on lime/limestone technology-,
performance monitoring, inspection methods and procedures, performance
evaluation and problem diagnosis/correction, operations and maintenance,
and safety. Appendices provide supplementary reference material,
definitions of FGD terms, calculation sheets, and example checklists, the
latter two items for use by an inspector on a plant inspection.
ii
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CONTENTS
PaSe
Abstract
Figures viii
Tables xi
Metric Conversions xiii
Acknowledgments xiv
1. Introduction 1
1.1 Purpose 1
1.2 Approach 1
1.3 Scope and Content 3
1.4 Organization of the Manual 4
2. Lime/Limestone FGD Technology 8
2.1 Environmental Regulations 8
2.1.1 Air Emission Standards 8
2.1.1.1 1971 NSPS 8
2.1.1.2 1979 NSPS 9
2.1.1.3 State Implementation Plans 9
2.1.1.4 Prevention of Significant
Deterioration 11
2.1.2 Water and Solid Waste Standards 12
2.1.2.1 Water Regulations 12
2.1.2.2 Resource Conservation and
Recovery Act 12
2.2 Coal Properties and Flue Gas Characteristics 12
2.3 Basic Principles of Lime/Limestone Slurry
Processes 13
2.3.1 Process Description 15
2.3.2 Operational Factors 17
2.3.2.1 Stoichiometric Ratio 17
2.3.2.2 L/G Ratio 18
ill
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CONTENTS (continued)
Page
2. Lime/Limestone FGD Technology (continued) 8
2.3.2 Operational Factors (continued) 17
2.3.2.3 Slurry pH 18
2.3.2.4 Relative Saturation 19
2.3.2.5 Oxidation 20
2.3.2.6 Chemical Additives 20
2.4 FGD System Design Configurations 21
2.4.1 Development of Technology 21
2.4.1.1 Historical Perspective 21
2.4.1.2 Characteristics of Technology
Generation 25
2.4.2 Existing Design Configurations 28
2.4.2.1 Fans 29
2.4.2.2 Scrubbers/Absorbers 30
2.4.2.3 Mist Eliminators 36
2.4.2.4 Reheaters 38
2.4.2.5 Ductwork and Dampers 42
2.4.2.6 Reagent Conveyors and Storage 46
2.4.2.7 Ball Mills 49
2.4.2.8 Slakers 50
2.4.2.9 Tanks 53
2.4.2.10 Thickeners 54
2.4.2.11 Vacuum Filters 5 6
2.4.2.12 Centrifuges 56
2.4.2.13 Waste Processing 59
2.4.2.14 Waste Disposal 60
2.4.2.15 Pumps and Valves 60
2.4.3 Operational Utility Lime and Limestone
Slurry FGD Systems 6 2
2.5 FGD O&M Considerations 62
2.5.1 Failure Modes 7 3
2.5.1.1 Coal Characteristics 79
2.5.1.2 Boiler Characteristics 79
2.5.1.3 Application Characteristics 80
2.5.1.4 Design and Operation
Considerations 80
iv
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CONTENTS (continued)
Pa?e
2. Lime/Limestone FGD Technology (continued) 8
2.5.2 System Layout, Accessibility, and
Design 82
2.5.2.1 Gas Handling and Treatment 84
2.5.2.2 Reagent Preparation and Feed 87
2.5.2.3 Waste Solids Handling and
Disposal 88
2.5.3 O&M Practices 88
2.5.3.1 Standard Operations 89
2.5.3.2 Initial Operations 91
2.5.3.3 Startup, Shutdown, Standby,
and Outage 91
2.5.3.4 System Upsets 92
2.5.3.5 Operating Staff and Training 93
2.5.3.6 Preventive Maintenance Programs 93
2.5.3.7 Unscheduled Maintenance 95
3. Performance Monitoring 97
3.1 Key Operating Parameters and Their Measurement 97
3.1.1 Gas Circuit Parameters 98
3.1.1.1 SO- 98
3.1.1.2 NO 98
3.1.1.3 Oplcity 98
3.1.1.4 0, 98
3.1.1.5 G5s Flow Rate 99
3.1.2 Slurry Circuit Parameters 100
3.1.2.1 pH 100
3.1.2.2 Slurry Flow Rates 100
3.1.2.3 Solids Content 100
3.2 Instrumentation 101
3.2.1 pH Instrumentation 101
3.2.2 Slurry Flow Rates 102
3.2.3 Solids Content 102
v
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CONTENTS (continued)
Page
3.3 Testing and Monitoring 105
3.3.1 Manual Testing 105
3.3.2 Alternative Methods 108
3.3.3 Continuous Emissions Monitoring (CEM) 108
3.3.4 Performance Specification Tests 112
3.4 Recordkeeping Practices and Procedures 113
4. Inspection Methods and Procedures 118
4.1 Guidelines for Overall Plant Inspection 119
4.2 Inspection Procedures 121
4.2.1 Gas Handling and Treatment 122
4.2.1.1 Fans 122
4.2.1.2 Scrubbers/Absorbers 122
4.2.1.3 Mist Eliminators 125
4.2.1.4 Reheaters 130
4.2.1.5 Ductwork and Dampers 130
4.2.2 Reagent Preparation and Feed 132
4.2.2.1 Reagent Conveyors and Storage 132
4.2.2.2 Ball Mills 132
4.2.2.3 Slakers 136
4.2.2.4 Tanks 136
4.2.3 Waste Solids Handling and Disposal 136
4.2.3.1 Thickeners 136
4.2.3.2 Vacuum Filters 142-
4.2.3.3 Centrifuges 142
4.2.3.4 Waste Processing 142
4.2.3.5 Waste Disposal 142
4.2.3.6 Pumps and Valves 142
4.3 Summary 149
5. Performance Evaluation and Problem Diagnosis/
Correction 150
5.1 Data Collection Methods 151
5.1.1 Sources 151
5.1.2 Forms of Data 152
vl
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CONTENTS (continued)
Page
5. Performance Evaluation and; Problem Diagnosis/
Correction (continued) 150
5.2 Performance Evaluation 153
5.2.1 Emissions 153
5.2.1.1 SOa 153
5.2.1.2 Particulate Matter 154
5.2.1.3 Opacity 155
5.2.2 Process 156
5.2.2.1 Gas Flow 156
5.2.2.2 Gas-side Pressure Drop 157
5.2.2.3 Slurry pH 157
5.2.2.4 Slurry Flow 160
5.2.2.5 Slurry Solids 161
5.2.2.6 Reagent Consumption 161
5.2.2.7 Solid Waste Production 161
5.2.2.8 Makeup Water Source and
Consumption 164
5.2.2.9 Energy Consumption 166
5.2.3 O&M 172
5.2.4 Observation 176
5.2.4.1 System Observation 176
5.2.4.2 Equipment Layout/Access 179
5.2.4.3 Consumed Equipment 180
5.2.4.4 General Housekeeping 181
5.3 Problem Diagnosis and Corrective Measures 181
5.3.1 Problem Diagnosis 182
5.3.1.1 Gas Handling and Treatment 182
5.3.1.2 Reagent Preparation and Feed 192
5.3.1.3 Waste Solids Handling and
Disposal 202
5.3.2 Corrective Actions 208
5.3.2.1 Gas Handling and Treatment 209
5.3.2.2 Reagent Preparation and Feed 216
5.3.2.3 Waste Solids Handling and
Disposal 217
vii
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CONTENTS (continued)
Page
6. Model O&M Plan 220
6.1 Management and Staff 220
6.1.1 Corporate Organization 221
6.1.2 Plant Organization and Training 221
6.2 Operating Manuals 226
6.3 Maintenance Manuals 22 8
6.4 Troubleshooting Techniques 231
6.5 Spare Parts 232
6.6 Work Order Systems 234
6.7 Computerized Tracking System 239
7. Safety 241
7.1 Inhalation of Toxic Gases 241
7.2 Skin Irritation and/or Chemical Burns
to the Skin 243
7.3 Exposure to Fugitive Dust 244
7.4 Normal Industrial Safety Practices 244
References r-1
Appendix A - Glossary of Terminology A-l
Appendix B - Equations for Converting Pollutant
Concentrations to NSPS Units B-l
Appendix C - FGD System Inspection Checklist C-l
viii
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FIGURES
Number Page
1.3-1 Lime/Limestone FGD Capacity and Total
FGD-Controlled Capacity Through 1992 5
2.1-1 SO,, Emission Standards for Coal-Fired Units
uilder 1979 NSPS. 10
2.3-1 Basic Lime/Limestone FGD Process Flow Diagram 16
2.4-1 Growth of Operational FGD Capacity for
Utilities 23
2.4-2 Typical Fan Designs 31
2.4-3 Venturi Tower Configurations 32
2.4-4 Spray Tower Types 34
2.4-5 Tray Tower and Tray Types 35
2.4-6 Packed Tower and Packing Types 37
2.4-7 Baffle-type Impingement Mist Eliminators 39
2.4-8 FGD System Reheat Schematic Diagrams 41
2.4-9 Simplified Flow Diagram Showing Damper
Configurations 4 4
2.4-10 Different Damper Designs 45
2.4-11 Barge-Based Limestone Handling and Storage
System 47
2.4-12 Three Types of Conveying Equipment Used to
Transport Lime 48
2.4-13 Two Types of Ball Mills Used in Limestone
Slurry FGD Systems 51
2.4-14 Basic Types of Slakers 52
ix
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FIGURES (continued)
Number Page
2.4-15 Diagram Showing- Components of as Thickener 55
2.4-16 A Rotary-Drum Vacuum Filter 57
2.4—17 Components of a Settling Centrifuge 58
2.4-18 Examples of Pond Types for Waste Disposal 61
2.5-1 Major Material Flows in FGD Systems 74
4.2-1 Isometric View of a Typical Centrifugal Fan 123
4.2-2 Typical Tray Tower Absorber 126
4.2-3 Typical Mist Eliminator Section 128
4.2-4 Isometric View of a Typical Thickener 140
4.2-5 Typical Slurry Recycle Centrifugal Pump 147
5.2-1 Typical Specific Gravity of Absorber
Recirculation Slurry for Lime/Limestone
FGD System 162
5.2-2 Reagent Requirement Calculation 163
5.2-3 Sludge (Waste) Production Calculation 165
5.2-4 Fan Power Requirement 171
5.2-5 Recirculation Pump Energy Requirement 173
5.2-6 Example Operation Log Sheet 174
5.2-7 Example Operation Log Sheet 175
5.2-8 Example work Order Form 177
5.2-9 Example Work Order Form 178
5.3-1 Gas Handling and Treatment Subsystem
Arrangements 183
5.3-2 Reagent Preparation and Feed Subsystem
Arrangements 194
X
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FIGURES (continued)
Number Page
5.3-3 Waste Solids Handling and Disposal Subsystem
Arrangement 203
6.1-1 Organizational Diagram for Coordinated FGD
System O&M Program 224
6.2-1 Outline for FGD Operating Manual 227
6.3-1 Outline for FGD Maintenance Manual 230
xi
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TABLES
Number Page
2.2-1 Fuel Properties of Four Representative Coals 14
2.4-1 Typical Characteristics of First, Second, and
Third Generation Lime/Limestone Slurry FGD
Systems 27
2.4-2 FGD Subsystems Requiring Tanks 53
2.4-3a Design and Operating Data for Operational
Utility Lime/Limestone Slurry FGD Systems
in the U.S. (General Data) 63
2.4-3b Design and Operating Data for Operational
Utility Lime/Limestone Slurry FGD Systems
in the U.S. (Specific Data) 67
2.5-1 Major Power Plant Considerations 72
2.5-2 Summary Listing of the FGD Subsystems by
Major Equipment Area 75
2.5-3 Subsystem Outage Times in Module Equivalent
Hours (MEH) 77
2.5-4 Summary of Failure Mode Analysis 83
3.2-1 pH Instrumentation on Lime Slurry FGD Systems 103
3.2-2 pH Instrumentation on Limestone Slurry
FGD Systems 104
3.3-1 Summary of Manual Emissions Measurement
Methods for an FGD System on a Coal-
Fired Utility Boiler 107
3.3-2 Principles Used in Gaseous Emission Monitors 109
3.3-3 CEM System Components 111
4.1-1 General Plant Data 120
xii
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TABLES (continued)
Number
Page
4.2-1
Control Room Checklist
122
4. 2-2
Pan Checklist
124
4.2-3
Scrubber/Absorber Checklist
127
4.2-4
Mist Eliminator Checklist
129
4.2-5
Reheater Checklist
131
4.2-6
Ductwork/Damper Checklist
133
4.2-7
Reagent Conveyor Checklist
135
4.2-8
Ball Mill Checklist
137
4.2-9
Slaker Checklist
138
4.2-10
Tank Checklist
139
4.2-11
Thickener Checklist
141
4.2-12
Vacuum Filter Checklist
143
4.2-13
Centrifuge Checklist
144
4.2-14
Waste Processing System Checklist
145
4.2-15
Waste Disposal System Checklist
146
4.2-16
Pump and Valve Checklist
148
5.2-1
Design Gas-Side Pressure Drops for
in Operational Lime/Limestone FGD
Absorbers
Systems
158-
5.2-2
Design Gas-Side Pressure Drops for Mist
Eliminators in Operational Lime/Limestone
FGD Systems
159
5.2-3
Makeup Water Consumption Rates for
Operational Lime/Limestone FGD Systems
167
5.2-4
Energy Requirement Calculations
170
6.6-1
Work Order Priority System
236
xiii
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METRIC CONVERSIONS
This manual expresses measurements in English units so that
information is clear to the intended audience in the United
States. The following list provides factors for conversion to
metric units.
To convert from
To
Multiply bv
BtU
kWh
0.0002931
Btu/lb
kJ/kg
2.326
cfm
m3 /h
1.70
°F
°C
(°F - 32)/I.
ft
m
0. 305
f t/h
m/h
0.305
ft/s
m/s
0.305
ft2
m2
0.0929
ft3
liters
28.32
ft3
m3
0.02832
gal
liter
3.785
gal/ft3
liter/m3
0.134
gal/min
liter/min
3.79
gr
g
0.0648
gr/scf
g/Nm3
2.29
hp (mechanical)
kW
0.7457
hp (boiler)
kW
9. 803
in.
cm
2.54
in. H,0
kPa
0.2488
in. 2
ma
0.0006452
in. 3
m3
0.00001639
lb
g
453.6
lb
kg
0.4536
lb/10e Btu
g/kJ
429.9
lb/ft3
kg/m3
16.02
lb/gal
kg/m3
119.8
lb/in.a
kPa
6. 895
lb-mol
g-mol
453.6
lb-mol/h
g-mol/min
7.56
lb-mol/h per ft2
g-mol/min per m2
81.4
lb-mol/min
g-mol/s
7.56
scfm (at 60°F)
Nm3/h (at 0°C)
1. 61
ton
kg
907. 2
xiv
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ACKNOWLEDGMENTS
This manual was prepared under the sponsorship of several
divisions of the U.S. Environmental Protection Agency. Those who
provided guidance and coordination were Theodore G. Brna and
Julian W. Jones, Air and Energy Engineering Research Laboratory;
Norm Kulujian, Center for Environmental Research; and Kirk Foster
and Sonya Stelmack, Stationary Source Compliance Division, Tech-
nical Support Branch. The PEI Project Director was Bernard A.
Laseke and the PEI Project Manager was E. Radha Krishnan. The
PEI principal investigators were Ronald S. McKibben and
Michael T. Melia.
XV
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SECTION 1
INTRODUCTION
1.1 PURPOSE
The purpose of the Flue Gas Desulfurization Inspection and
Performance Evaluation Manual is to provide guidance to Federal
and State environmental regulatory personnel involved in the
inspection and permitting of flue gas desulfurization (FGD)
systems for electric utility coal-fired steam generators (boil-
ers) in the United States.
The primary intended audience of the manual is the field
inspector directly involved in the inspection of operational,
FGD-equipped, coal-fired, utility boilers. For the purposes of
the manual, the field inspector is defined as the individual who
periodically inspects power plants to ensure compliance with
emission standards. The scope of the inspector's responsibility
is defined as ranging from confirmation of existing status re-
ports to anticipation of future compliance status (i.e., avoid-
ance of potential noncompliance episodes).
A secondary intended audience of the manual is the environ-
mental regulatory agency permitter. For the purposes of the
manual, the permitter is defined as the individual who reviews
permit applications for new capacity in accordance with adherence
to environmental regulations and emission standards. Although
the permitter is not specifically "targeted" in the manual,
pertinent orientation material is presented on the design,
operating, and performance characteristics of FGD systems.
1.2 APPROACH
The philosophy adopted for the preparation of this manual is
unique in comparison to other FGD technology manuals. As stated
1
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in the Purpose, the intended audience is environmental regulatory
personnel. Other similar manuals generally define their intended
audiences as the owner/operator utility, architect-engineer,
research firm, and/or technology investigator. This manual
represents the first of its kind in addressing solely the needs
of environmental regulatory agency personnel.
Another unique feature of the manual is its intended use.
The manual is structured as a "tool", or working document, which
will accompany the inspector on each plant inspection. This
contrasts to the use of other similar manuals in that they are
often read and then filed away for possible future reference. To
adequately serve as a working document, two major objectives must
be accomplished in the organization of the material. First, the
document must provide practical information tailored to its
intended use; namely, the systematic inspection of an FGD system
to determine present and future compliance status. This requires
that information on process theory be limited to a necessary
minimum. Secondly, the information must be presented in a "user-
friendly" format in order to encourage use. This is accomplished
through the use of nomographs, checklists, matrices, simplified
diagrams, cross-referencing and indexing of textual information,
and presenting important guidelines and recommendations in a
conspicuous fashion.
A final unique feature of the manual is its use for the
interpretation of sulfur dioxide (SC^) excess emission reports.
If an FGD-equipped boiler represents a source of frequent S02
excess emission reporting, the manual will provide guidelines to
determine the cause and to evaluate the remedial actions taken by
the plant operator. If an FGD-equipped boiler represents a
source of infrequent SC^ excess emission reporting, the manual
will provide guidelines to identify the contributing factors that
are associated with this situation.
2
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1.3 SCOPE AND CONTENT
The scope of the manual is devoted exclusively to lime/lime-
stone slurry FGD processes. Flue gas desulfurization systems
are generally the last pieces of equipment used to handle the
boiler flue gas before it reaches the stack. In lime/limestone
slurry processes, SO2 in the flue gas stream is removed with the
aid of dilute limestone or lime slurries. The treated flue gas
is cooled and saturated with moisture in the process. A more
thorough description of the processes is presented in Section 2
(Section 2.3, Basic Principles of Lime/Limestone Slurry
Processes; Section 2.4, FGD System Design Configurations).
The scope of FGD technology addressed in this manual is
limited to tail-end, "wet" lime/limestone slurry processes only,
excluding:
0 all tail-end processes that do not use calcium-based
(lime/limestone) additives as the SO- reactant (e.g.,
sodium/calcium [dual or double alkali]), sodium/
thermal regeneration [Wellman-Lord], magnesium oxide
[Mag-Ox], and sodium [once-through soda ash, sodium
hydroxide, trona, nahcolite]).
0 all tail-end processes that do not completely saturate
the flue gas during treatment, known as "dry scrubbing"
(spray drying, dry sorbent injection).
0 precombustion and in-situ (combustion) SO- control
techniques which may involve the use of calcium alkali
additives (e.g., limestone injection multistage burner
[LIMB], lime furnace injection).
The rationale for emphasizing lime/limestone slurry processes
is based on their widespread use in the power industry due to
their level of process development and economics. Since the
early application of FGD to control S02 emissions from boiler
flue gas, there has been pronounced preference for lime/limestone
slurry processes (see Section 2.4.1.1, Historical Perspective).
Presently, plants equipped with FGD systems using lime or lime-
stone slurry represent over 80 percent of the electric generating
capacity with emissions controlled by FGD. A perspective of the
historical and projected future application of lime/limestone
3
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slurry processes is illustrated in Figure 1.3-1 which shows the
installed capacity controlled by lime/limestone slurry processes
as a function of the capacity controlled by all processes.
Detailed cost studies indicate that both the capital and the
annual costs are generally less than those of other FGD processes.
Additionally, the on-line experience of commercial systems at
utility plants has generated a wealth of operational data which
are being used to enhance system reliability. Advances in waste
disposal technology, such as forced oxidation to produce more
easily dewatered calcium sulfate, have enabled utility operators
to reduce the volume of waste for disposal as well as improving
its handling and disposal properties. Advances in process chem-
istry, such as magnesium salts and organic acid additives, have
enabled operators to improve performance with respect to SO^
removal, process chemistry, service time, and cost effectiveness.
With continuing technological advances and increasingly wider
utilization, lime/limestone slurry processes are considered the
major means of compliance with New Source Performance Standards
promulgated by the U.S. Environmental Protection Agency (EPA) for
control of SC>2 emissions from power plants (see Section 2.1.1,
Air Emission Standards).
The scope of the manual is the complete battery limits of
the entire FGD process. These boundaries are defined from the
inlet gas stream to the final waste disposal site. All opera-
tions in between are examined, including: gas handling and
treatment, reagent preparation and feed, and waste solids hand-
ling and disposal. Moreover, operations and factors that influ-
ence the FGD process envelope are considered, including: coal
characteristics and consumption, boiler design and operation, and
particulate emissions control and operation.
1.4 ORGANIZATION OF THE MANUAL
The manual is structured in accordance with its overall
purpose of providing a constant companion to the environmental
regulatory agency inspector of FGD-equipped, coal-fired, utility
4
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120 i i i i r
110
100
a 70
S 60
-i—i—i—i—i—i—i—r
ACTUAL
PROJECTED
£ J
72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92
YEAR
Figure 1.3-1. Lime/limestone FGD capacity and total FGD-
controlled capacity through 1992.a
aTotals reflect end of year values.
5
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boilers. At the outset, therefore, we present an overview of
lime/limestone FGD technology (Section 2). For this purpose, we
provide a review of the environmental regulations which govern
utility coal-fired boilers and, in effect, have driven the commer-
cial application of FGD technology. We provide a description of
lime/limestone slurry processes including process theory and
basic principles, system and equipment configurations, and opera-
tion and maintenance considerations.
In succeeding sections, we quickly depart from process
theory and design to the practical guidelines associated with
inspection and performance evaluation. Section 3 deals with FGD
performance monitoring, starting with key operating parameters
and their measurement. Particular attention is given to contin-
uous emission monitoring procedures and manual test methods for
determining compliance with SC^ standards. Section 4 is the
focal point of the manual—inspection methods and procedures. We
provide this information in a series of step-by-step detailed
procedures. Section 5 continues with guidelines on how to use
and interpret the data observed and collected by the inspector
with respect to performance evaluation, problem diagnosis, and
correction. Section 6 describes guidelines for general operation
and maintenance (O&M) practices based on acceptable "industry
standards" that are necessary for high performance levels.
Operating practices and maintenance practices are described
separately and in detail by component, equipment, subsystem,
sequence, roles, and activities. The guidelines are used to
develop a model O&M plan summarizing the important aspects of an
adequate O&M program that should be practiced by the owner/oper-
ator utility in order to achieve satisfactory performance.
Section 7 briefly addresses safety procedures and precautionary
measures which should be adhered to during the course of a plant
inspection.
The appendices consist of supplementary reference material,
giving more specific details concerning the topics discussed in
Sections 2 through 7. The appendices are devoted to definitions
6
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of PGD terminology, calculation sheets', and example checklists
which will be used by the inspector during a plant inspection.
The inspector may wish to reproduce and make several copies of
the checklists and keep them separate for the purpose of con-
ducting an inspection. As the inspector becomes more experienced
and relies less on the manual, he or she may be able to tour the
facility without carrying the manual throughout the powerplant.
7
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SECTION 2
LIME/LIMESTONE FGD TECHNOLOGY
This section presents a discussion of lime/limestone slurry
FGD technology. The overview includes a discussion of 1) per-
tinent environmental regulations, 2) coal properties and flue gas
characteristics, 3) basic principles of lime/limestone slurry
processes, 4) design configurations, and 5) operation and main-
tenance considerations. Appendix A presents a glossary of FGD-
related terms used in this manual.
2.1 ENVIRONMENTAL REGULATIONS
2.1.1 Air Emission Standards
The 1970 Clean Air Act required the U.S. EPA to set air
quality goals for a list of priority pollutants. In December
1971, under Section 111 of the Clean Air Act, New Source
Performance Standards (NSPS) were issued to limit emissions of
SO-, particulate matter, and nitrogen oxides (NO ) from new,
2* X
modified, and reconstructed fossil-fuel-fired steam generators
used in electric utility and large industrial facilities. In
1977, amendments were made to the Clean Air Act, directing the
EPA to tighten emission standards from new coal-fired utility and
large industrial boilers, resulting in the revised NSPS of June
1979. In addition to the NSPS, air emissions from coal-fired
utility boilers are also governed by the State Implementation
Plans (SIP's) and the Prevention of Significant Deterioration
(PSD) program. A brief discussion of the different air emission
standards is presented below.
2.1.1.1 1971 NSPS. The standards apply to fossil fuel-fired
steam generating units capable of firing more than 250 million
8
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Btu/h heat input (to the boiler) and upon which construction
commenced after August 17, 1971.
0 SO, Standards. Sulfur dioxide emissions are limited to
1.2 lb/10b Btu of heat input.
0 Particulate Standards. Particulate emissions are
limited to 0.10 lb/105 Btu of heat input.
0 NO Standards. Nitrogen oxide emissions are limited to
0.70 lb/10° Btu of heat input.
2.1.1.2 1979 NSPS. These standards apply to electric utility
steam generating units capable of firing more than 250 million
Btu/h heat input of fossil fuel (alone or in combination with
other fuels) and upon which construction commenced after Septem-
ber 18, 1978.
0 SO, Standards. Sulfur dioxide emissions are limited to
a maximum of 1.2 lb/106 Btu heat input. In addition, a
percentage reduction in SOa emissions (based on the
sulfur content and heating value of the fuel) must be
achieved. Figure 2.1-1 depicts the allowable S02
emissions under the NSPS for different sulfur levels
via a sliding percentage removal scale. The percentage
reduction must be at least 70 percent under all condi-
tions, and the S02 emission rate must not exceed 0.60
lb/106 Btu unless at least a 90 percent reduction is
achieved. Compliance with these requirements is deter-
mined on the basis of a 30-day rolling average, and is
determined with continuous emission monitors.
° Particulate Standards. Particulate emission rates are
limited to 0.03 lb/105 Btu heat input. The opacity
standard limits the opacity of emissions to 20 percent
(6-minute average). Compliance with the particulate
standards is determined through performance tests.
Continuous monitors are required to measure and record
the opacity of emissions.
0 NO Standards. Nitrogen oxide emissions are limited to
O.uO lb/10° Btu heat input for bituminous coals, 0.50
lb/106 Btu for subbituminous coals, and 0.60 lb/106 Btu
for most lignites. Continuous compliance is determined
on the basis of a 30-day rolling average.
2.1.1.3 State Implementation Plans. State and local standards
for S02, particulates and NO , aimed at achieving and maintaining
national ambient air quality standards (NAAQS), are promulgated
9
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>90%
CQ
O
CM
O
«/>
£ 0.8
tu
70%
90%
85%
0.6
tr>
in
Coal
Btu/lb
¦10,000
UJ
LU
o
7,500
5,000
0.5% S*
2.0% S
0.0
SULFUR IN COAL (EXPRESSED AS lb S09/106 Btu)
*Sulfur content of coal expressed in percent as opposed to lb/10^ Btu
given in graph along the x-axis.
Figure 2.1-1. S0£ emission standards for coal-fired units under 1979 NSPS.
-------
under the SIP's required under the Clean Air Act. Where state
and local regulations are more stringent than Federal NSPS, they
govern emission limits from coal-fired steam generating units. A
number of states have set the maximum SO, emission limit below
1.2 lb/106 Btu heat input for designated areas within the state
(if not statewide). Differences may also be encountered in
particulate and N0x standards.
2.1.1.4 Prevention of Significant Deterioration. The 1977
Clean Air Act Amendments incorporate specific sections regarding
PSD of ambient air quality in areas and regions where the air
quality is better than standards. The PSD regulations are
implemented by the individual states through the SIP's on a
case-by-case basis.
Under the PSD program, clean areas of the nation [i.e.,
those where pollutant levels are below the NAAQS] are classified
as Class I, II, or III, with each class representing a specific
amount or increment of allowable deterioration. Class I
increments permit only minor air quality deterioration, Class II
increments permit moderate deterioration consistent with normal
growth, and Class III increments permit considerably more
deterioration; in no case, however, can the deterioration reduce
the area's air quality below that permitted by the NAAQS.
In addition to the increment concept and classification
system, PSD regulations require that each major new or modified
source apply Best Available Control Technology (BACT). Best
Available Control Technology is determined on a case-by-case
basis for each pollutant; it must represent an emission
limitation based on the maximum achievable degree of reduction,
taking into account energy, environmental, and economic impacts.
At a minimum, BACT must result in emissions not exceeding any
applicable NSPS or National Emission Standards for Hazardous Air
Pollutants (NESHAP). The PSD regulations also provide further
protection for Class I or "pristine" areas in terms of "air
quality related values", such as visibility.
11
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2.1.2 Water and Solid Waste Standards
Local, state and federal regulations relating to water
pollution or land use also affect the design of an FGD system.
2.1.2.1 Water Regulations. The Clean Water Act of 1977 reg-
ulates the discharge of powerplant effluents into any natural
water bodies. Under the Federal Clean Water Act and similar
state laws, every discharge of pollutants into surface water must
be sanctioned by a permit, referred to as the National Pollutant
Discharge Elimination System (NPDES) permit.
2.1.2.2 Resource Conservation and Recovery Act. The Resource
Conservation and Recovery Act (RCRA) of 1976 governs the develop-
ment of programs for environmentally safe solid waste disposal
including both hazardous and nonhazardous wastes, including
sludges as well as solids. Flue gas emission control waste
generated from the combustion of coal or other fossil fuels falls
under the Act's definition of a solid waste, but is temporarily
excluded from Subtitle C classification as a hazardous waste
under the 1980 amendment to RCRA, which requires EPA to make a
report to Congress on the environmental hazards, if any, posed by
the disposal of these wastes. Subtitle D of RCRA concerns the
more general problems of waste disposal. Such a status is cur-
rently assigned to FGD waste. Under Subtitle D provisions, the
management of nonhazardous solid waste remains essentially a
state and local function. Subsequent to the submittal of this
report, the EPA administrator may make a determination whether
these wastes will be regulated under Subtitle C or Subtitle D of
RCRA.
2.2 COAL PROPERTIES AND FLUE GAS CHARACTERISTICS
This section continues the overview with a discussion of
coal properties and subsequent flue gas characteristics as they
relate to FGD. The properties of the coal fired in a utility
boiler determine the flue gas characteristics, as well as the
degree of SO^ controls needed for the FGD system. Typical fuel
12
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properties of four widely used types of coal from prominent coal
reserves in the United States are listed in Table 2.2-1.
The sulfur content and heating value of the coal establish
the amount of S02 produced during combustion as shown in Figure
2.1-1. The amount of S02 produced is typically the most impor-
tant factor in determining the type and overall design considera-
tion for the FGD system. Other coal properties which can affect
FGD system design/operation include chlorine and ash content.
The chlorine content of the coal affects the materials of con-
struction and the ability of an FGD system to operate in a closed
water-loop. Chlorine content is highly variable, ranging from
about 0.01 weight percent to more than 0.6 percent. Ash content
of coal ranges from less than 3.5 to more than 15 percent. If
large quantities of ash are collected in the FGD system (i.e.,
they are not removed by upstream particulate collection equip-
ment) , erosion and plugging of absorber internals and piping may
occur. In addition, the extra nonreactive solids may have an
adverse impact on the waste solids disposal subsystem. On the
other hand, the fly ash of western subbituminous and lignite
coals contains sufficient alkalinity to provide some or all of
the SO2 reagent requirements. The principal alkaline species in
coal ash which can be used are calcium, magnesium, sodium, and
potassium oxides. Fly ash alkalinity has been used in numerous
FGD systems for SO2 absorption.
2.3 BASIC PRINCIPLES OF LIME/LIMESTONE SLURRY PROCESSES
This section provides a brief discussion of the basic prin-
ciples of lime/limestone slurry process chemistry. Principal
chemical reactions are identified and the operational factors
associated with process chemistry are defined. The emphasis of
this discussion is on practical considerations of importance to
the agency inspector. A more thorough description of process
design is provided in Section 2.4 (FGD System Design Configura-
tions) .
13
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TABLE 2.2-1. FUEL PROPERTIES OF FOUR REPRESENTATIVE COALS
Wyoniinq subbituminous
Montana
subbituminous
Illinois (raw) bituminous
Gulf Coast lignite
Average
Range
Average
Range
Average
Range
Average
Range
Proximate analysis
Moisture, X
30
28-32
24
23-25
11
10-14
32
30-35
Volatile matter, I
32
30-33
32
30-32
37
32-42
29
NA
fixed carbon, I
32
30-34
40
40-41
42
37-47
27
NA
Ash, 1
6
5-8
4
3.5-6.0
10
10-11
12
10-15
Heating value, Btu/lb
8,000
7,800-8,200
9,200
8,300-10,000
11,000
10,800-11,200
6,800
6,200-7,000
Ultimate analysis (as
received), X
Carbon
48
46-49
55
53-56
60
57-63
41
NA
Hydrogen
3
3-4
4
3-4
4
4-5
3
NA
Nitrogen
0.6
0.5-0.7
0.9
0.8-1.0
1.0
1.1-1.2
0.7
NA
Sulfur
0.5
0.3-0.7
0.5
0.4-0.7
3.9
3.7-4.1
O.B
0.6-0.9
Chlorine
0.03
0.00-0.05
0.0]
0.00-0.02
0.10
0.04-0.60
0.1
0.0-0.2
Oxygen (difference)
11.87
9-12
11.59
11-12
10.0
10-11
10.4
NA
Ash analysis, i
S10.
32
28-36
32
25-40
47
42-51
49
NA
a'A
15
14-17
17
15-20
23
18-24
21
NA
Fe 0,
5
4-5
6
5-9
16
15-21
7
NA
TlO,
1
0.9-1.4
1
1.0-1.1
1
0.8-1.2
1.5
NA
P?05
1
0.2-1.3
1
0.5-1.0
0.1
0.0-0.1
0.3
NA
Cao
23
19-27
15
10-20
6
2-6
9
NA
MgO
5
4-6
5
3-5
0.1
0.1-0.5
2
NA
Na.O
1
1.0-1.6
7
6-9
1.0
0.9-1.3
2
1-3
K-0
0.4
0.3-0.6
0.5
0.4-0.6
1.6
1.5-1.7
0.7
NA
s63
16
14-19
15
10-?0
4
3-5
7
b
Undetermined
0.6
0.5
0.2
0.5
b
HA - Dtt* not available
-------
2.3.1 Process Description
The basic lime/limestone FGD process is shown schematically
in Figure 2.3-1. Although there are systems which produce a
salable byproduct (i.e., gypsum for wallboard construction), the
vast majority use the throwaway process configuration shown in
Figure 2.3-1. This type of system is presently considered by the
utility industry to be the least expensive to own and operate
among all of the commercially available systems.
In the lime/limestone FGD process shown in Figure 2.3-1,
flue gas, from which fly ash has been removed in a particulate
collection device such as an electrostatic precipitator (ESP) or
a fabric filter, is brought into contact with the lime/limestone
slurry in the absorber, where SO^ is removed. The chemical reac-
tion of lime/limestone with SC>2 from the flue gas produces waste
solids, which must be removed continuously from the slurry loop.
These waste solids are concentrated in a thickener and then
dewatered in a vacuum filter to produce a filter "cake" which is
mixed with fly ash. The resulting stabilized mixture is then
transported to a landfill. This lime/limestone FGD system is
called a "throwaway" process because it produces a waste byproduct
for disposal rather than for processing to recover salable gypsum.
The principal chemical reactions for the lime/limestone FGD
process are presented below according to SC>2 absorption, lime-
stone dissolution, and lime dissolution.
S02(g) * S02(i , , .... .
CaC0,(s) + CaC0,(aq)
* * •
Ca(0H)2(aq) ~ Ca++(aq) + 20H"(aq)
CaO(s) + H.O <¦ Ca(0H)-(aq)
Ca++(aq) + S03*(aq) + JH?0 - C&S03-4H20(s)
Ca++Uq) + S04"(aq) + 2H2<3 » CaS04-2H20(s)
C03 (aq) + H+(aq) » HC03"(aq)
$0,*(aq) + H*(aq) - HS0,"(aq)
++, f , ,,, . ,
0H"(aq) + H+(aq) ~ HjO
SOj*(aq) ~ H+(aq) ~ HS03"(aq)
C*++(aq) + S03"(aq) + JHjO - CaS03-iH20(s)
Ca^faq) + S04"(aq) + 2H20 - CaS0,,-2H2O(s)
* g • gas phase; aq * aqueous pnase; and s * solid phase
15
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CLEAN
FLUE GAS
MIST ELIMINATOR
WASH WATER
FLUE GAS
ABSORBER
LIME/
LIMESTONE
SLURRY
MAKEUP
WATER
REACTION
TANK
THICKENER
FLY
ASH
TO DISPOSAL
MIXER
THICKENER
OVERFLOW
VACUUM
FILTER TANK
Figure 2.3-1. Basic 1ime/1imestone FGD process flow diagram.
16
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Although not shown in the process flow diagram, the major
equipment design difference between the two processes is reagent
feed preparation. In the lime process, the reagent is slaked;
limestone is ground in a ball mill.
2.3.2 Operational Factors
The basic operational factors one should be acquainted with
when inspecting lime/limestone slurry FGD systems are discussed
below. Knowing these factors and how they are interrelated with
the process chemistry of each system will provide an understanding
of how each process functions in addition to providing a set of
guidelines to be used during an inspection.
2.3.2.1 Stoichiometric Ratio. The stoichiometric ratio (SR) is
defined as the ratio of the actual amount of SO^ reagent, calcium
oxide (CaO) or calcium carbonate (CaCO^) in the lime or limestone
feed to the absorber, to the theoretical amount required to
neutralize the S0o and other acidic species absorbed from the
flue gas. Theoretically, one mole of CaO or CaCO^ is required
per mole of SO2 removed (SR = 1.0). In practice, however, it is
usually necessary to feed more than the stoichiometric amount of
reagent in order to attain the degree of SO2 removal required.
This is due to mass transfer limitations which prevent complete
reaction of the absorbent.
If a high SO2 removal efficiency is required, the absorber
may not be able to achieve such removal unless extra alkalinity
is provided by feeding excess reagent. The amount of excess
reagent required depends upon the SO2 concentration in the inlet
gas, gas flow, percent SO2 removal required, and absorber design.
For lime reagent, the SR employed in commercial FGD systems is
1.05 for newer designs; however, it ranges up to 1.2 for older
designs. For limestone reagent, a SR of 1.1 is used in newer
designs; however, it may be as high as 1.4 in older designs.^"
If the reagent feed is too much in excess, the results are
wasted reagent and increased sludge volume. Excessive over-
feeding can also result in scaling in the form of CaCO^ in the
17
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upper part of the absorber for lime systems, and calcium sulfite
(CaSO^-H H^O), sometimes referred to as soft scale, in the lower
part of the absorber for limestone systems. Excess reagent can
also be carried up into the mist eliminator by entrainment, where
it can accumulate, react with SC>2, and form a hard calcium
sulfate (CaSO^ • 21^0) scale (by sulfite oxidation). This is
particularly a problem with limestone systems. Calcium sulfate
(or gypsum) scale is especially undesirable because it is very
difficult to remove. Once formed, the scale provides a site for
continued precipitation. Calcium sulfite scale can generally be
easily removed by reducing the operating slurry pH (see Section
2.3.2.3) or rinsing manually with water.
Scale formation is usually more prominent in limestone
systems than lime systems, particularly for high sulfur coal
applications. Lime systems have a greater sensitivity to pH
control because lime is a more reactive reagent. The change in
pH across lime systems is more pronounced than in limestone
systems partly because limestone dissolves more slowly.
2.3.2.2 L/G Ratio. The ratio of slurry flow in the absorber to
the quenched flue gas flow, usually expressed in units of gal/1000
ft"*, is termed the liquid-to-gas (L/G) ratio. Normal L/G values
3 2
are typically 30 to 50 gal/1000 ft for lime systems and 60 to
3 3
100 gal/1000 ft for limestone systems. Lime systems require
lower L/G ratios because of the higher reactivity of lime. A
high L/G ratio is an effective way to achieve high S02 removal;
this also tends to reduce the potential for scaling since the
spent slurry from the absorber is more dilute with respect to
absorbed SC>2 • Increasing the L/G ratio can also increase system
capital and operating costs due to greater capacity requirements
of the reaction tank and associated hold tanks, dewatering equip-
ment, greater pumping requirements, slurry preparation and storage
requirements, and reagent and utility necessities.
2.3.2.3 Slurry pH. Commercial experience has shown that fresh
slurry pH as it enters the absorber should be in the range of 8.0
4 1
to 8.5 for lime systems and 5.5 to 6.0 for limestone systems.
18
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In both FGD processes, as the SC^ is absorbed from the flue gas,
the slurry becomes more acidic and the pH drops. The pH of the
spent slurry as it leaves the absorber is in the range of 6.0 to
6.5 for lime systems and 4.5 to 5.0 for limestone systems.* In
the reaction tank of the absorber, the acidic species react with
the reagent and the pH returns to its original fresh slurry
value. Slurry pH is controlled by adjusting the feed stoichio-
metry. Operation of lime/limestone FGD systems at low pH levels,
approaching 4.5, will improve reagent utilization but will also
lower SC>2 removal efficiency and also increase the danger of hard
scale (gypsum) formation because of increased oxidation at lower
pH levels (see Section 2.3.2.5). Operation of lime/limestone FGD
systems at high pH levels, above 8.5 and 6.0 respectively, will
tend to improve SO2 removal efficiency but also increases the
danger of soft scale (calcium sulfite) formation. Hence, control
of slurry pH is essential to reliable operation. The inability
to maintain sensitive control of the slurry pH can lead to both
lowered S02 removal efficiencies and hard/soft scale formation.
2.3.2.4 Relative Saturation. In lime/limestone FGD processes,
the term "relative saturation" (RS) pertains to the degree of
saturation (or approach to the solubility limit) of calcium
sulfite and sulfate in the slurry; RS is important as an indica-
tor of scaling potential, especially of hard scale, which can
present severe maintenance problems. Relative saturation is
defined as the ratio of the product of calcium and sulfate ion
activities (measured in terms of concentrations) to the solubility
product constant. The solution is subsaturated when RS is less
than 1.0, saturated when RS equals 1.0, and supersaturated when
RS is greater than 1.0. Generally lime/limestone processes will
operate in a scale-free mode when the RS of calcium sulfate is
maintained below a level of 1.4 and the RS of calcium sulfite is
5
maintained below a level of approximately 6.0. Operation below
these levels provides a margin of safety to ensure scale-free
operation. This is achieved through proper design and control of
process variables (e.g., L/G, pH).
19
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2.3.2.5 Oxidation. An important chemical consideration in
lime/limestone processes is the oxidation of sulfite to sulfate.
Uncontrolled oxidation across the absorber leads to sulfate
formation and resultant hard scaling problems on the absorber
internals. Sulfite oxidation can occur either naturally or it
can be artificially promoted (i.e., forced oxidation). Natural
oxidation occurs when sulfite in the slurry reacts with dissolved
oxygen (C>2) , which has been absorbed either from the flue gas or
from the atmosphere (e.g., during agitation in the reaction
tank). With forced oxidation, air is bubbled into the absorber
reaction tank to further promote oxidation. This prevents the
dissolved sulfite in the slurry from returning to the absorber
which minimizes the potential for the oxidation of the sulfite to
sulfate in the absorber and resultant hard scaling problems.
Forced oxidation has additional advantages of reducing the total
volume of waste generated because of improved dewatering char-
acteristics of the sulfate solids and improved characteristics of
the final solid waste product. Oxidation tends to increase with
decreasing slurry pH. For this reason, forced oxidation is
normally employed only with limestone systems.
2.3.2.6 Chemical Additives. In recent years, inorganic and
organic additives have been used to improve SO2 removal effi-
ciency, increase reagent utilization, decrease solid waste vol-
ume, and decrease scaling potential of lime/limestone FGD sys-
tems. Magnesium oxide is the most widely used additive.
Dicarboxylic acids, in the form of adipic acid or dibasic acids,
are also used commercially.
Magnesium oxide additives permit a higher SO2 removal rate
per unit volume of slurry. This is due to the fact that the
salts formed by the reaction of magnesium-based additives with
the acid species in the slurry liquor are more soluble with
respect to those of the calcium-based salts. This in turn in-
creases the available alkalinity of the scrubbing liquor, which
promotes a higher S02 removal rate. Dibasic acids enhance S02
20
-------
removal in a different manner from magnesium additives. Acting
as buffers, they tend to neutralize acid-generated hydrogen ions
(H+) which in turn prevents the decrease of the system pH and SO^
removal. In limestone systems, because of their added ability to
enhance utilization by improving dissolution, a lower stoichiometric
ratio can be used which reduces limestone addition and the result-
ing volume of solid waste. In addition, high liquid phase calcium
concentrations permitted by the dibasic acids leads to a reduced
3
potential for scaling tendencies in the absorber.
2.4 FGD SYSTEM DESIGN CONFIGURATIONS
This section presents a brief discussion of the development
of FGD technology including a historical perspective and a
description of the characteristics of technology generation
followed by a description of equipment used in existing design
configurations. A summary is also included of all operational
utility lime/limestone slurry systems in the U.S. by design
configuration elements.
2.4.1 Development of Technology
2.4.1.1 Historical Perspective. The rapid expansion in energy
demand that occurred starting about 195 0 greatly increased the
amount of all air pollutants resulting from fuel combustion —
particulates, S02, NOx, carbon monoxide, organic compounds, and
trace metals. Because of environmental concern over the increas-
ing concentration of pollutants in the atmosphere in the U.S.,
the Air Quality Act of 1967 became law. Its aim was to set
emission limitations on those pollutants for which adequate
information was believed to be available for standards to be set;
i.e., particulates, SO and NO . Eventually new regulations came
about in the form of the Federal NSPS and state regulations under
the individual SIP's. As a result, in the early 1970s, important
applications of FGD for SO2 control were initiated in the U.S.
21
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The 1950s and 1960s were a time of laboratory and pilot
plant investigations of new processes. During the 1950s, the
Tennessee Valley Authority (TVA) experimented with lime/limestone
slurry and dilute acid processes; in West Germany, the first
major carbon adsorption processes were developed.
Lime/limestone processes were installed in 1964 on an iron
ore sintering plant in the USSR and on a large sulfuric acid
plant in Japan in 1966.
In 1966, Combustion Engineering developed a process consis-
ting of dry limestone injection into the boiler followed by wet
scrubbing. In the U.S., the first commercial system of this type
was installed in 1968; there were five utility installations of
this system by 1972. Because of major problems associated with
dry limestone furnace injection (e.g., boiler tube fouling,
scaling/plugging), these systems proved inadequate. The five
systems were either shutdown or converted to tail-end slurry
processes.
Significant commercial application of utility FGD systems
did not begin in the U.S. until the early 1970's. Figure 2.4-1
shows a yearly status of utility FGD capacity for the past decade
and a half.
There has been a continual evolution in the development of
FGD technology which is reflected in the improved design and
performance levels of these systems, even in an environment of
increasingly more stringent emission limitations. Many design
configurations found in early systems have since been modified or
abandoned. A changing attitude of utilities toward FGD tech-
nology has also improved FGD system performance in older systems
and, in some cases, improved design. Of particular significance
is the attention now directed toward FGD system operating and
maintenance practices.
The most noteworthy site for significant research and devel-
opment work in FGD technology has been the EPA/TVA Shawnee Alkali
22
-------
>-
h—
O
LU
_l
o
cr
(—
z
_i
-------
Scrubbing Test Facility. In June 1968, the U.S. EPA*, through
its Office of Research and Development, initiated a program to
construct and test prototype lime/limestone slurry systems for
removing SC>2 and particulates from flue gases generated in
coal-fired boilers. This test program was managed and directed
by EPA's Industrial Environmental Research Laboratory+/Research
Triangle Park (IERL/RTP). A prototype test complex was inte-
grated into the flue gas ductwork of a coal-fired boiler (Unit
10) at TVA's Shawnee Power Station near Paducah, Kentucky.
At the outset, three major goals were identified for the
test program: (1) characterize as completely as possible the
effect of important process variables on S02 and particulate
removal; (2) develop mathematical models to allow economical
scale-up of attractive operating configurations to full-size
FGD facilities; and (3) perform long-term reliability testing.
The test facility was initially commissioned for service in March
1972. The original test program was conducted from March 1972 to
May 1974. During this first phase of testing, efforts were
concentrated on the characterization of process parameters as
they affected SC^ removal and FGD system reliability.
A second phase of testing, a four-year advanced test pro-
gram, was initiated in June 1974. The major objectives accom-
plished during this phase of testing were achieving reliable
operation of the FGD system, improved performance, and lower
costs. This was accomplished through investigations on chemical
additives (see Section 2.3.2.6), system loop configurations, and
forced oxidation (see Section 2.3.2.5).
A third phase of testing, which lasted approximately two
years, from July 1978 to May 1980 , was devoted to enhancing SC>2
removal and improving the reliability and economics of lime/
limestone slurry processes through the use of organic acid
additives (see Section 2.3.2.6).
*
National Air Pollution Control Association until 1970.
+ Designated as Control Systems Laboratory until 1975; redesig-
nated as Air and Energy Engineering Research Laboratory in 1985,
24
-------
Shawnee provided a needed test site to assist in the develop-
ment and commercialization of conventional and innovative FGD
strategies. Shawnee was instrumental in the development of
lime/limestone slurry technology from the level of a research and
development "tool" to a level of commercial acceptability. Much
of the results from the various test programs initiated or
refined commercial design strategies, a large number of which are
in commercial practice today:
0 High utilization/low stoichiometric limestone chemistry
and mist eliminator cleanliness
° Spray tower absorber design
0 Two-loop scrubbing
0 Magnesium additives
° Organic acid additives
0 Forced oxidation and gypsum production
0 Closed water-loop operation
2.4.1.2 Characteristics of Technology Generation. Although the
designation of "generation" is somewhat subjective, FGD systems
may be distinguished in accordance with the evolution of
technology per the following guidelines:
0 First generation: Designs that remove S0a, and possibly
fly ash, with gas contactors developed
for or based upon particulate matter
scrubbing concepts. Included are
lime/limestone slurry processes which
use gas contactors with a venturi or
packing-type internals.
0 Second generation: Designs that remove S02 primarily in gas
contactors developed specifically for
S0a absorption which utilize features to
improve the chemical process through
chemical or physical means. Included
are lime/limestone slurry processes
using additives or spray towers, combi-
nation towers, or special reactors.
25
-------
° Third generation: Improved second generation designs that
encompass additional process refinements
and are currently under demonstration or
early commercial operation. Included
are open spray tower designs with spare
absorbers, closed water-loop operations,
and gypsum production.
Approximately 53 percent of the operational lime/limestone
slurry FGD systems on utility boilers in the U.S. can be classi-
fied as second generation systems. First generation systems
account for 20 percent, while third generation systems account
for the remaining 27 percent of the total. Often, a given FGD
system will have some characteristics of earlier and/or later
generation systems but will be assigned the generation status
which most closely represents its particular overall design.
Table 2.4-1 summarizes the basic characteristics of the systems
within the three generations.
First generation systems are "early" facilities based on
particulate scrubber designs modified for SO^ control. In such
systems, particulates and SC>2 are collected simultaneously by
venturi, marble bed, or other scrubber/absorber designs in a
once-through scrubbing operation having a characteristically high
stoichiometric ratio. Spent slurry is piped to a pond without
dewatering for final disposal. Typically, little or no water is
brought back from the disposal pond to the process for reuse.
Fresh makeup water is used instead. Few existing FGD systems fit
this description completely. As FGD technology evolved, more
effective measures were adopted and modifications were made to
earlier systems to upgrade performance.
Second generation FGD systems were designed specifically for
SC>2 control leaving all or most particulate control to upstream
ESP's. The SC>2 absorbers usually contained gas contacting de-
vices to maximize SC>2 collection efficiency and operate at a
moderate stoichiometric ratio chemistry. Such systems included
primary solids dewatering, some form of solid waste treatment,
and on-site waste disposal. Second generation systems character-
istically operate in a water loop which more closely approaches
closed loop than first generation systems.
26
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TABLE 2.4-1. TYPICAL CHARACTERISTICS OF FIRST, SECOND, AND THIRD
GENERATION LIME/LIMESTONE SLURRY FGD SYSTEMS
Generation
Characteristics
Fi rst
Second
Third
Duty
S02/fly ash
so2
so2
Absorber Design
Venturi tower
Tower with internals3
Open spray tower
Chemistry
High stoichiometric ratio
Moderate stoichiometric ratio
Low stoichiometric ratio
Water Loop
Open
Closed
Closed with integrated
water inventory
Waste Processing
Ponding (no dewatering)
Primary dewatering and waste
treatment
Primary and secondary
dewatering and solid
waste physical/chemical
treatment
Redundancy
None*5
None'3
Sparing of a number of
system components
aSome spray towers are also included in late second generation systems.
^Most of these systems incorporate minimal redundancy (e.g., pumps); however, spares are usually not
provided for major components (e.g., absorbers).
-------
Third generation systems are characterized by open spray
towers operating at relatively low stoichiometric ratio chemis-
tries with additives for SC^ absorption enhancement and scale
control. These systems also include liberal sparing of key
components and incorporate design features which tend to decrease
interdependency of various subsystems. This allows full load
operation of the system even when individual components are
forced out of service or are undergoing routine maintenance.
Third generation designs provide secondary dewatering (vacuum
filters or centrifuges), solid waste treatment via chemical
fixation or forced oxidation, and landfill disposal. An
integrated plant water inventory is generally included in these
closed loop systems and liquor collected from the various
dewatering devices is recycled and blended with fresh makeup
water. The term "closed loop" takes on a slightly different but
significant meaning when applied to third generation systems
since little water leaves the system via the solid waste. These
systems must be designed to withstand the corrosive effects and
scaling potential of the increasingly high concentrations of
salts that build up in the recycled water. Second generation
systems are less sensitive to this problem because water is not
recycled as extensively.
2.4.2 Existing Design Configurations
This section describes briefly the important equipment items;
one is likely to encounter when inspecting a conventional lime/
limestone FGD system. Descriptions and diagrams are provided for
each of the equipment items discussed. Section 2.5 presents
operation and maintenance considerations for the equipment de-
scribed here.
The equipment is organized by three major equipment areas:
° Gas handling and treatment
1. Fans
2. Scrubbers/absorbers
3. Mist eliminators
28
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4. Reheaters
5. Ductwork and dampers
° Reagent preparation and feed
1. Reagent conveyors and storage
2. Ball mills
3. Slakers
4. Tanks
° Waste solids handling and disposal
1. Thickeners
2. Vacuum filters
3. Centrifuges
4. Waste processing
5. Waste disposal
6. Pumps and valves
It is noted that there is some overlap of the equipment
items in all three areas, although they may be listed only under
one equipment area in the above classification. For example,
reaction tanks are located in the gas handling and treatment
area; pumps and valves are found in all three equipment areas.
Sections 2.4.2.1 through 2.4.2.5 address equipment used in
gas handling and treatment, including; fans, scrubbers/absorbers,
mist eliminators, reheaters, and ductwork and dampers, respec-
tively. Sections 2.4.2.6 through 2.4.2.9 address equipment used
in reagent preparation and feed, including: reagent conveyors
and storage, ball mills, slakers, and tanks, respectively.
Sections 2.4.2.10 through 2.4,2.15 address equipment used in
waste solids handling and disposal, including: thickeners,
vacuum filters, centrifuges, waste processing, waste disposal,
and pumps and valves, respectively.
2.4.2.1 Fans. The fan moves gas by creating a high or low
pressure by mechanical means. Fans are used to draw or push flue
gas from the boiler furnace through the FGD system. Fans used in
FGD systems may be classified in four basic ways: function,
design, application, and service.
0 Function refers to service as either a unit fan or
booster fan. A unit fan is one that is designed to
create draft for the boiler, particulate collection
system, and FGD system. A booster fan accommodates
29
-------
only the FGD system. Retrofit FGD systems usually
include booster fans since existing unit fans are
generally unable to accommodate the pressure drop of
the add-on FGD system. Booster fans are also often
used for FGD systems that have flue gas bypass capabil-
ity., Booster fans may be used for individual modules
on FGD systems to give better control of the gas
passing through them. Unit fans are generally used for
new FGD-equipped boilers, particularly installations
where flue gas bypass does not exist. Using unit fans
allows better balance of the draft throughout the
entire unit.
° Fans used for FGD systems are either the centrifugal or*
axial variety (Figure 2.4-2a and b). Most fans used in
FGD systems are the centrifugal variety. Both fan
designs may be equipped with variable-pitch vanes (or
blades) which provide more efficient fan operation and
better gas flow control.
° Fans are classified as either induced draft (ID) or
forced draft (FD). Fans that are installed immediately
following a module or system ("downstream") that draw
gas through the module or system are called ID fans
(negative pressure operation). Fans that precede a
module or system ("upstream") that push gas through the
module or system are called FD fans (positive pressure
operation).
° Fans may service either a wet or dry gas stream. Fans
that precede absorbers generally operate on hot dry
flue gas and are classified as dry fans. Fans that are
installed downstream of the absorbers and are preceded
by a reheater are also classified as dry fans. Fans
that are installed either between scrubber and absorber
modules or downstream of absorbers but are not preceded
by a reheater are classified as wet fans. Most fans
used in FGD systems are dry fans.
2.4.2.2 Scrubbers/Absorbers. Strictly speaking, the term
"scrubber" applies to first generation systems which remove both
particulate and S02. "Absorber" applies to the second and third
generation systems which remove S02 only, although the tern
"scrubber" is also used by some for this application. The basic
scrubber/absorber types described herein identify the various
gas/slurry contacting devices used in the FGD systems.
Figure 2.4-3 presents different venturi tower configurations
typically used in first generation systems. In a fixed-throat
30
-------
MAINTENANCE
REMOVAL
. SECTION
COOLING
WHEEL
BEARING
SEAL
PEDESTAL-
INLET CONE-
BEARING
ROTOR-
PEDESTAL
DISCHARGE
INLET CONE-
SEAL-
COOLING WHEEL
-HOUSING
(a)
REMOVABLE
HOUSING
FLANGE COVER
-—TURNING BENO
WITH GUIDE VANES
2ND STAGE
1ST STAGE-
INLET BO*
(b)
Figure 2.4-2. Typical fan designs: (a) centrifugal; (b) axial.
31
-------
&A<
US
t^m m )UIUN1I
* LIQUOR
FEED
(a).
6AS
o
SCBUB!
SLJ» =
E!NC—„ N—/-
'G* \ 7 v x /
w
SC*uBP>'-
SlU®c-
ndv'BlT Lioti: /
OlSTRlRUTIOh DISC'
SCRUBBING J
liouoo—c;
f«D
t L
K"1
U'
0;.^—-disc
ACTUATOR
(d)
SCRUBBING
SLURRY
V
(e)
SIDE-UNABLE
HATES OR BLADES
(c)
US
I—
V
SCRUBBING
SLUAK'
side-«ovmu
It OCRS
r V
V
(f)
6A-
!—i
\ /
wo-1
DcruBBBL VENTje:
^»* SECTION
o
us
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SCRUBBING
SLURS'
^ SCRUBS ISC.
qU« SLU»B'
DRUM
ACTUATOR
LIQUID^
outlet^
l 2^7
\ f
-------
venturi, the venturi throat opening remains constant (Figure
2.4-3a). However, a number of variable-throat designs are used
to vary the opening of the venturi-throat opening to accommodate
varying gas flows (Figures 2.4-3b through h). Venturi towers are
considered high energy devices because they typically operate in
a 10 to 30 in. H^O pressure drop range. They are also limited
somewhat as contacting devices for gas absorption because of
limited gas/slurry contacting time in the tower.
In spray towers, slurry is introduced into the gas stream
from atomizing nozzles, resulting in intimate contact for gas
absorption. The pressure imparted to the slurry discharged from
the spray nozzles combined with the velocity of the incoming gas
stream produces liquid droplets from 50 to 4000 microns in dia-
meter. Low gas-side pressure drops (typically 1 to 4 in. H20)
are encountered because of the lack of tower internals. The open
countercurrent spray tower is a simple configuration in which the
gas stream passes vertically upward through the tower with the
liquid droplets falling by gravity countercurrent to the gas flow
(Figure 2.4-4a). Another spray tower design is the open cross-
current spray tower (Figure 2.4—4b). This design requires
somewhat less pumping power because the slurry is pumped to a
lower height. However, it requires more spatial area for the
absorber than vertical designs.
In tray towers, the gas stream enters the base of the tower
and passes upward through one or more trays containing openings.
Slurry is introduced onto the top tray and flows across it and
down across each preceding tray (Figure 2.4-5). In a conven-
tional sieve tray tower, gas velocities are used such that the
gas passing up through the hole bubbles through the liquid on the
tray providing intimate gas/slurry contact (Figure 2.4-5). In a
valve tray tower, the tray level consists of a bed of "bubble
caps" with each bubble cap surmounted by a constraining spider
cage (Figure 2.4-5). The gas flows upward through the caps and
the slurry flowing across the tray is kept in a state of constant
froth by the gas which exits each cap at venturi velocity. This
33
-------
MIST
ELIMINATOR
SCRUBBING
LIQUOR
FEED
7l\"
GAS
(a)
GAS
c>
SCRUBBING
LIQUOR
FEED
t i \
-r
~T~
¦b
/
MIST
ELIMINATOR
o
(b)
Figure 2.4-4. Spray tower types: (a) open countercurrent;
(b) open crosscurrent.
34
-------
ADJUSTABLE
WEIR
to
Ln
MIST
ELIMINATOR
SCRUBBING
LIQUOR
FEED
TRAYS
GAS
SIEVE TRAY
FOAM -
/•oc«) v* r. V*r-i:;;; —
QZ-Z-y plate o;c=z] t=itzzi c=]
*** t
§)
VALVE TRAY
LIQUID
.»•.»—tt. •
• • f
• • f
BUBBLECAPS
v:irn;vrn?
^5^Ez=J^li=Z} PLATE
Figure 2.4-5. Tray tower and tray types.
-------
design, however, is not very common in lime/limestone slurry FGD
systems.
In packed towers, the gas enters the base of the tower and
passes up through the packing countercurrent to the slurry intro—.
duced at the top of the tower (Figure 2.4-6). The packing can be
of a variety of different shapes and configurations. The purpose
of the packing is to provide a large surface area for intimate
gas/slurry contact. Fixed bed consists of a rigid, stationary
packing such as a "honeycombed" material (Figure 2.4-6a). Static
bed consists of a largely immobile bed of packing, such as glass
spheres (Figure 2.4-6b). Mobile bed packing consists of a highly
mobile bed of solid spheres which is fluidized by the gas stream
(Figure 2.4-6c). Entrained bed packing consists of a mobile bed
of solid spheres which are entrained in the gas stream, passed
through the tower, and disengaged for recycling (Figure 2.4-6d) .
Rod decks and grids (Figures 2.4-6e and f) represent internals
which can be used instead of packing and still provide a suffi-
ciently large surface area for intimate gas/liquid contact.
In combination towers, two or more separate tower design
features described in the foregoing are incorporated into one
tower for operation as an integral unit. These combined designs
provide flexibility because extreme operating conditions and/or
selective removal capabilities can be segregated into discrete
areas of the tower, thus permitting separate chemical and phy-
sical conditions to be maintained. Designs which have been
developed for commercial application to date include a spray/
packed tower and a venturi/spray tower.
2.4.2.3 Mist Eliminators. A mist eliminator removes "entrain-
ment" introduced into the gas stream by the scrubbing slurry.
Entrainment can take the form of liquor droplets, slurry solids,
and/or condensed mist.
There are two basic types of mist eliminators used in FGD
systems: the precollector and the primary collector. A pre-
collector precedes the primary collector and is designed to
remove the larger particle entrainment from the gas stream before
36
-------
MIST
ELIMINATOR
^SCRUBBING
A A A f SLURRY
yjp «u>
PACKING
ZONE
a, DIRTY GAS
V INLET
OVERFLOW
STATIC BED
(b)
FEED
HEADERS
GAS OUT
SCRUBBING
SOLUTION
CONTACT
SPHERES
GAS IN
ENTRAINED BED
(d)
•HONEYCOMB'
FIXED BED
(a)
"¦1
'A A A
TV •Jv*
p
OOoOO ooo© ©POO
DOO Q 0 OOOOO o OC
00OOOOO GO o 0 o
SOLID
mmm
•••• »\m
SPHERES
MOBILE BED
(c)
GRIDS
Figure 2.4-6. Packed tower and packtnq types.
37
-------
it passes through the primary collector. A primary collector
typically sees the heaviest duty with respect to entrainment
loading and required removal efficiency.
Precollectors are of the bulk separation or knock-out type.
Bulk separation is effected by baffle slats, perforated trays, or
a gas direction change (90° to 180°). Bulk separation devices
are characterized by a low potential for solids deposition, a low
gas-side pressure drop, and simplicity. Knock-out type precollec-
tors are either the wash tray or trap-out tray design. Knock-out
devices remove large solid and liquid particles; they also pro-
vide a means to recycle the mist eliminator wash water. By
recirculating the relatively clean wash water, the flow rate of
the wash water to the mist eliminator can be significantly
increased which allows greater flexibility in washing operations,
wash water treatment, and the addition of scaling inhibitors.
Despite all these advantages, knock-out type precollectors are
not used at most installations primarily because of plugging,
high pressure drop (_>3 in. H20) , increased complexity, and
operating problems.
Impingement (or inertial impaction) removes mist by. collec-
tion on surfaces placed in the gas streams. Entrained mist is
collected in such devices by forcing the gas to make changes in
flow direction as it passes through the slats. The liquid drop-
lets thus collected coalesce and fall by gravity back into the
scrubbing slurry. Impingement type mist eliminators used widely
in lime/limestone slurry systems include baffle configurations.
Baffle-type mist eliminators include the conventional open-vane
(slat) and closed-vane chevron designs (Figure 2.4-7). The
baffle design mist eliminators are most common and constitute the
simplest method of mist elimination.
2.4.2.4 Reheaters. Reheaters raise the temperature of the
scrubbed gas stream in order to prevent condensation of acidic
moisture and subsequent corrosion in the downstream equipment
(ducts, fans, and stack). FGD systems that do not use reheaters
must be equipped with specially lined stacks and exit ductwork to
38
-------
u>
vo
\\\\\\\\
////////
WWWW
SLATS
GAS
DIRECTION
AV
AV
LOUVERS
i
GAS
DIRECTION
OPEN-VANE DESIGN
CLOSED-VANE DESIGN
Figure 2.4-7. Baffle-type impinaement mist eliminators.
-------
prevent corrosion. Such liners require special attention and FGD
systems using them must be equipped with emergency deluge sprays
in the event of a temperature excursion.
The generic reheat strategies discussed in this section
include: in-line, indirect hot air, and flue gas bypass (Figure
2.4-8). In-line reheat involves the use of a heat exchanger in
the gas stream downstream of the mist eliminator (Figure 2.4-8a),
The heat exchanger is a set of tube bundles through which the
heating medium of steam or hot water is circulated. When steam
is used, the inlet steam temperatures and pressures range from
350° to 720°F and 115 to 200 psig, respectively. Saturated steam
is preferred because the heat transfer coefficients of condensing
steam are much higher than those of superheated steam. When hot
water is used, inlet temperature of the hot water typically
ranges from 250° to 350°F and the temperature drop (water) over
the heat exchanger is 70° to 80°F.
Indirect hot air reheat systems inject hot air into the gas
stream (Figure 2.4-8b). There are two types of indirect hot air
reheaters: the external heat exchanger and the boiler preheater
design. In the external heat exchanger design, reheat is
achieved by heating ambient air with an external heat exchanger
using steam at temperatures of 350° to 450°F. The heating tubes
are usually arranged in two to three banks in the heat exchanger.
Hot air and flue gas may be mixed by use of a device such as a
set of nozzles or a manifold in the reheater mix chamber section.
In the boiler preheater design, reheat is achieved through the
use of the boiler combustion air preheater to provide hot air.
In this case, part of the heat which would have been used to heat
the combustion air is used to reheat the stack gas. As a
consequence, the temperature of the combustion air entering the
boiler is lowered, thus reducing boiler efficiency somewhat.
In the bypass reheat system (Figure 2.4-8c), a portion of
the hot flue gas from the boiler bypasses the absorber(s) and is
mixed with scrubbed flue gas. Two variations of this method are
"hot-side" bypass, in which the flue gas is taken upstream of the
40
-------
fm.
m
TO CMWE
ALTERNATIVE IN-IINC
rehcatcr locations
AISONBE?
S cd
REACTION TANK
(a)
MOT ITMSS MS
REACTION TANK
*£ACTTON TAHi
(b) (c)
Figure 2.4-8. FGD system reheat schematic diagrams: (a) in-line;
(b) indirect hot air; (c) bypass.
41
-------
boiler air preheater and "cold-side" bypass, in which flue gas is
taken downstream of the boiler air preheater. In the former, a
separate particulate removal device (ESP or fabric filter)
specifically for the bypass gas stream is required for fly ash
control when an upstream (i.e., hot-side) particulate collector
is not used.
2.4.2.5 Ductwork and Dampers. Ductwork is used to channel the
flow of gas within the FGD system. Ductwork in an FGD system is
usually made of carbon steel plates 3/16- or 1/4-inch thick
welded in a circular or rectangular cross section, it is
supported by angle frames that are stiffened at uniform intervals.
The following design factors are considered for ductwork in
lime/limestone slurry systems:
° Pressure and temperature
° Velocity
0 Configuration (cylindrical or rectangular)
0 Flow distribution
0 Variations in operating conditions
0 Materials of construction
0 Material thicknesses
0 Pressure drop
The ductwork must be designed to withstand the pressures and
temperatures that occur during normal operation and also those
that occur during emergency conditions. Ductwork is subject to a
variety of conditions, depending on location within the system.
The following list identifies the basic variants:
0 Inlet ductwork
0 Bypass ductwork (all or part of the flue gas)
0 Outlet ductwork (with reheat and without bypass)
° Outlet ductwork (with reheat and with bypass for
startup)
0 Outlet ductwork (without reheat and without bypass)
0 Outlet ductwork (without reheat and with bypass
for startup)
42
-------
Dampers are used to regulate the flow of gas through the
system through control or isolation functions. Entire system or
subsystems may be regulated by the use of dampers. They are
mainly used at the inlet duct to the module, the outlet duct from
the module, and the bypass duct. Dampers may be used individu-
ally or in combinations. A simplified overview diagram showing
typical damper locations is presented in Figure 2.4-9.
A variety of damper designs are in use in lime/limestone
slurry systems, including louver, guillotine, butterfly, and
blanking plates. These designs are described below and depicted
in Figure 2.4-10.
0 Louver or multi-blade dampers may be either opposed
or parallel blade designs (Figures 2.4-10a). Louver
dampers are used to regulate and isolate flue gas flow.
For isolation, two dampers are used together and sealed
by pressurizing the chamber formed by the ductwork
between the dampers with a seal air fan. A single
damper may be used for gas flow regulation.
0 A guillotine damper may be either top-entry or bottom-
entry design and with or without seal air (Figure
2.4-10b). Guillotine dampers for isolation may be
equipped with seal air to pressurize the sealing space.
° Butterfly dampers are often used for secondary duct
runs such as bypass or reheat air ducts (Figure
2.4-10c). Butterfly dampers are mounted by a center
shaft which crosses the duct and about which the damper
plate rotates from a plane parallel to the gas flow
(open) to a plane perpendicular to the gas flow
(closed). Butterfly dampers are more often used for
gas flow regulation than gas flow isolation.
0 The most basic damper is the simple blank-off plate.
Blanking plates are used to isolate absorbers for entry
by operation and maintenance crews. The blanking plate
ensures complete isolation by "breaking" the duct and
inserting the plate. Blanking plates are typically
used with positive ventilation air purge which adds an
additional safety factor. Blanking plates are similar
to guillotine dampers in that they cut across the duct
opening; however, the track for a blanking plate is
designed only to guide the plate as it is put in place
and bolted down.
43
-------
c
o
«3
1.
3
CTl
•t—
<+-
c
o
o
s»
3
a
"O
-------
(a) Louver dampers
(b) Guillotine dampers (c) Butterfly dampers
Figure 2.4-10. Different damper designs.
-------
2.4.2.6 Reagent Conveyors and Storage. Conveying equipment
used to transport limestone from unloading to storage includes
dozing equipment, belt conveyors, and bucket elevators. Limestone
is transported to feed bins by conveyors and bucket elevators.
Limestone can be stored in silos, piles, or a combination of
both. Short-term storage feed bins are used with both systems to
feed limestone to the additive preparation system. Storage piles
require more land to store a given quantity of limestone than
silos. However, silos are more expensive and can experience flow
problems such as plugging and "jamming." Covered piles are
sometimes used for limestone storage. The covers keep precipita-
tion off the limestone pile and prevent freezing or limestone mud
developing. The primary design criterion of a limestone storage
system is capacity. The storage facilities must have sufficient
capacity so that the storage system does not limit the availabil-
ity of the overall FGD system. There should be enough storage
capacity to account for disruptions in the normal shipping
schedule. Figure 2.4-11 shows an example of a limestone handling
and storage system.
Conveying equipment used to transport lime can be of three
basic types, as shown in Figure 2.4-12. Most in-plant lime
conveying involves simple elevation of the lime from a storage
bin into a smaller feed bin. A simple combination of mechanical
devices can move lime from storage at less than the initial cost
and with less power consumption than a pneumatic conveyor.
Mechanical conveying requires careful arrangement of bins and
equipment. Alignment in a single straight row is preferable
since each change of direction usually requires another conveyor.
As conveying distances or elevations increase, or if conveyance
involves several changes of direction or multiple points of
delivery, the economic advantage of pnuematic conveying increases
rapidly. Unlike the basic components of a mechanical conveyor,
those of a pneumatic system are similar regardless of distance or
elevation. They differ only in length of piping and size of the
compressor and motor. Lime is blown up the inclined pipe by the
46
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LIMESTONE
STORAGE
PILE
CLAMSHELL
UNLOADER
BARGE
RECLAIM
HOPPER
RECEIVING
HOPPER
STOCKOUT
CONVEYOR
1 TO FEED
BINS
Figure 2.4-11. Barge-based limestone handling and storage system.
-------
STORAGE BINS
LIME
FEED
BIN
BUCKET
ELEVATOR
SLAKER
SLURRY STABILIZATION
TANK
SCREW CONVEYOR
VENT
AIR COMPRESSOR
rsn
\J\ DUST COLLECTOR
7L and
COLLECTING BIN
AIR-LOCK
STORAGE BIN!
// LIME
/ FEED
' BIN
SLURRY STABILIZATION
TANK
VENT,
OUST COLLECTOR AND
COLLECTING BIN
STORAGE BINS
AIR-LOCK
LIME
feed
BIN
SLAKER
ROTARY
FEEDER
SLURRY STABILIZATION
TANK
FILTER
SILENCER
AIR COMPRESSOR
(c)
Figure 2.4-12. Three types of conveying equipment used to
transport lime: (a) mechanical conveyor; (b) closed-loop
conveyor; (c) positive-pressure pneumatic conveyor.
48
-------
force of air from the compressor. The other basic conveyor type
is the vacuum or negative-pressure system. It draws lime through
the pipe by means of a vacuum exhauster attached to the dust
collector. Another arrangement, usually called a closed-loop
system, uses air circulated from the compressor to the conveyor
and back. A minimum amount of fresh air is drawn in and the
original charge remains dry.
Minimum bulk lime storage capacity is generally considered
to be either 150 percent of a plant's normal shipment size or
capacity for 7 days of operation at maximum rate. Conservative
engineering practice provides twice this volume, since lime is
often transported on a less-dependable schedule than are other
more expensive bulk chemicals. The storage vessel most often
used for lime is a steel silo with a cone bottom. Concrete
storage bins have been used in large facilities and are often
less expensive than steel bins. Lime storage bins must be weather-
proofed and airtight to prevent absorption of water (moisture)
and carbon dioxide from the atmosphere. Storage bins must be
fitted with a cone-shaped or hopper-shaped bottom to allow an
even flow of lime. Steel is most often used for the hopper
section. The number of storage bins and their relative size and
proportion are determined by construction economy. A diameter of
12 ft is often the most economical, with a maximum height of 40
ft. A bin of these dimensions will hold about 100 tons of lime.
A lime storage bin may be connected directly to a lime
feeder that meters the flow of lime into the slaker. Frequently,
however, lime is transferred from a storage bin into a smaller
feed bin at a higher elevation. Lime feed bins are often de-
signed to hold enough lime to permit either 8 or 24 hours of
operation at maximum rate; thus, they can be routinely filled
once per shift or once per day.
2.4.2.7 Ball Mills. Ball mills are used in limestone slurry
systems to grind the limestone to a fine size in order to improve
its reactivity. There is very little basic information that
defines the most economical degree of grinding. However, the
49
-------
trend is toward finer grinding. (A finer grind provides a smaller
particle which exposes more overall particle surface area and
therefore improves limestone reactivity.) Specifications range
from 70 percent passing through a 200-mesh screen to 95 percent
passing through a 325-mesb screen; most are in the range of 60 to
80 percent passing through 325 mesh.
A ball mill consists of a rotating drum loaded with steel
balls that crush the limestone by the action of the tumbling
balls as the cylindrical chamber rotates. Ball mills used in FGD
systems fall into two categories: the long drum or tube mill
variety is a compartmented type (Figure 2.4-13a); the Hardinge
ball mill is noncompartmented and somewhat conical in shape
(Figure 2. 4-13b).
2.4.2.8 Slakers. A slaker is used in lime systems to convert
dry calcium oxide to calcium hydroxide (see Section 2.3.1). The
objective of lime slaking is to produce a smooth, creamy mixture
of water and very small particles of alkali. Depending on the
type of slaker used, the slurry produced contains 20 to 50 per-
cent solids. A lime slaker mixes regulated streams of lime and
water under agitation and temperature conditions needed to dis-
perse soft hydrated particles as they form. Dispersion must be
rapid enouah to prevent localized overheating and rapid crystal
growth of the calcium hydroxide occurring in the exothermic
reaction. However, the mixture must be held in the slaker long
enough to permit complete reaction.
Three basic types of slakers are presently used in lime
slurry systems: detention, paste, and batch. A simplified
diagram of each type is presented in Figure.2.4-14. A brief
description of each is provided below.
° Quicklime and water are fed to the detention slaker in
specific proportions in order to produce a slurry
containing 20 to 30 percent solids. The mixture is
agitated with a high-speed propeller mixer. From the
agitated chamber, slurry flows into a quiet section
where grit settles out. Degritted slurry is then
diluted with additional water and flows to a stabiliza-
tion tank. Grit is continuously removed from the quiet
50
-------
(b)
Figure 2.4-13. Two types of ball mills used in limestone slurrv
FGD systems: (a) compartmented ball mill; (b) Hardinge ball mill.
51
-------
RAKE DRIVE
CLASSIFICATION
COMPARTMENT
RECIPROCATING
rakes
WASHED GhIT
DISCHARGE
\
Kin or UK
arrirr
mutator wire
FEED WtEt (HOMO)
LI* INLET
SIAKIKG
asitator tmmmmi
(a) Detention slaker
qutcutMi-
fBtgue-carrwtii mm mm
OUST SHIHOy
mtm %mmt /
SIm I*6 WATER \ o,,r
-------
section by means of a mechanical scaper. It is rinsed
with a small stream of water and discarded. In a
detention slaker, water is added to each chamber.
Slurry is usually retained in a detention slaker 20 to
30 min at a temperature of about 167°F,
The paste slaker operates on the pug mill principle,
kneading a thick mixture of lime and water. Feed
streams are proportioned to produce a putty-like
mixture containing about 40 -to 50 percent solids. The
mixture is blended in a narrow trough by paddles that
rotate on horizontal shafts. The thick slurry
continuously overflows the end of the trough into a
dilution chamber where more water is added and grit is
separated, rinsed, and discarded. Slurry is retained
in a paste slaker for only 5 to 10 min. The slaking
temperature is usually about 185 to 194°F.
Batch slakers are simple tanks equipped with agitators.
Quicklime and water are fed into the tank and the
mixture is stirred briskly, although simple and
relatively inexpensive, this type of device invariably
produces a poor quality slurry. Even with high-energy
agitation, slaking may not be uniform. Hard,
crystaline lime particles are formed; slaking is
usually incomplete; and part of the lime is lost as a
hard scale that forms in the tank. The slurry is
usually very erosive and reacts slowly in the FGD
system. Batch slakers are seldom used on FGD systems
today.
2,4.2.9 Tanks. Tanks are used extensively in FGD systems to
support the various equipment items in the slurry circuits.
Tanks allow FGD systems to operate in a fluctuating continuous
mode as demanded by the power-plant while various components of
the FGD system itself may operate in a discontinuous "batch"
mode. Tanks may be categorized as reaction, surge, collection,
mix f feed, storage, or combinations of these. Table 2.4-2 shows
a listing of typical subsystems that require tanks.
TABLE 2.4-2. FGD SUBSYSTEMS REQUIRING TANKS
Component/area
Reagent Slurry Product
Presaturator/Quencher
Scrubber/Absorber
Mist Eliminator Wash
Thickener Overflow
Thickener Underflow
Waste:Slurry Bleed
Vacuum Filter filtrate
Centrifuge Centrate
Pond Return
Makeup Water
Solid Waste Additive
53
-------
Tanks may or may not be covered. Covered tanks are protected
from contamination and sometimes may be pressurized as part of
the gas circuit. Tanks may also be covered for safety reasons or
to prevent the possibility of debris falling into the tank (pre-
venting subsequent damage to agitators, pumps, piping, or valves).
Protective liners are often applied to the internal surfaces of
tanks. The types of liners used depend upon the service for
which the particular tank is intended and the tank construction
materials.
2.4.2.10 Thickeners. The function of a thickener (also known as
clarifier) is to concentrate solids in the slurry bleed stream in
order to improve waste solids handling and disposal characteris-
tics and recover clarified water. The slurry bleed steam usually
enters a thickener at a solids level of about 5 to 15 percent and
exits at a concentration of 25 to 40 percent solids. ft thickener
is a sedimentation device that concentrates the slurry by gravity.
There are two basic types of thickeners: gravity and plate.
Only the gravity type will be described here because plate thick-
eners are rarely used on utility FGD systems.
A typical gravity thickener (Figure 2.4-15) consists of a
large circular holding tank with a central vertical shaft that is
supported either by internal structural design, by a center
column, or by a bridge. Two long, radial rake arms extend from
the lower end of the vertical shaft; two short arms may be added
when necessary to rake the inner area. Plow blades are mounted
on the arms at an oblique angle with a clearance of 1.5 to 3 in.
from the bottom of the tank. They can be arranged identically on
each arm or in an offset pattern so that the.bottom is swept
either once or twice during each revolution. The bottom of the
tank is usually graded at a 5® to 8° slope from the center. The
settled sludge forms a blanket on the bottom of the thickener
tank and is pushed gently toward the central discharge outlet.
Center scrapers clear the discharge trench and move the solid
deposits toward the underflow discharge point. The rake arms arid
t i -Ket* move the settled solids to the central discharge point.
54
-------
LAUNDER
CENTER DRIVE
WIT AND
LIFTING DEVICE
DRIVE MOTOR AND
GEAR ASSEHBLT
HIGH PRESSURE
flushing.
DISCHARGE TRENCH
CENTER SCRAPERS
iNDiCJWt!
FEEOWtLL-|
r- *-nUTCH MEII
"k— Feat
SOLUTION LEVEL
CENTER CAGE
ORQUE AKO
RAKE ARMS
¦TMIli TOST
PLOW BLADES
figure 2,4-15, Diagram showing components of a thickener.
-------
The reclaimed overflow (i.e., clarified water) from the thickener
is usually recycled and reused as makeup water.
2.4.2.11 Vacuum Filters, Vacuum filters are widely used as
secondary dewatering devices because they can be operated
succofsfully at relatively high turndown ratios over a broad
range cf solids concentrations. A vacuum filter also provides
more operating flexibility than other types of dewatering devices
as well as producing a drier product. Because a vacuum filter
will not yield an acceptable filter cake if the feed solids
content is too low, it is usually preceded by a thickener. A
vacuum filter produces filter cake of 45 to 7 5 percent solids
from feed slurries containing 25 to 40 percent solids. The
filtrate, typically containing 0.5 to 1.5 percent solids,, is
recycled to the thickener.
Two types of vacuum filters are used in conventional FGD
sybton designs; drum and horizontal belt. Each has different
characteristics and app Licahility. The drum type (Figure 2.4-16)
is the most widely applied. In a rotary-drum vacuum filter, the
slurry is fed to a tank in which the solids are held uniformly in
suspension by an agitator. As the drum rotates, the faces of the
sections pass successively through the slurry. The vacuum in the
sections draws filtrate through the filter medium, depositing the
suspended solids on the filter drum as cake. The cake undergoes
dewatering by the simultaneous flow of air and filtrate in the
cake drying zone. Drying is negligible when the air is at room
temperature. Finally, the cake is removed in the discharge zone
by a scraper.
2.4.2.12 Centrifuges. Centrifuges are usee to a lesser extent
than vacuum filters in solids dewatering operations. The centri-
fuge product is consistent and uniform and can be easily handled.
Centrifuges effectively create high centrifugal forces, about
4 0 0" t.i.es that of gravity. The equipment is relatively small
and can separate bulk solids rapidly with a short residence time.
There are two types of centrifuges: those that settle and
those that The settling centrifuge {Figure 2,4-17),
56
-------
AIR FILTRATE LINE
CLOTH CAULKING
STRIPS
AUTOMATIC VALVE
FILTRATE PIPING
CAKE SCRAPER
SLURRY AGITATOR
AIR BLOW-BACK LINE
SLURRY FEED
Figure 2.4-16. A rotary-drum vacuum filter.
57
-------
DIFFERENTIAL
SPEED GEAR BOX
I
ROTATING
BOWL J
1
1 ROTATING
CONVEYOR
CENTRATE
DISCHARGE
COVER
SOLID PARTICLES
(SETTLED AGAINST BOWL WALL)-
LIQUID SURFACE
(CLEAR LIQUOR)
BOWL WALL-
MAIN DRIVE SHAFT
/
njm.
-FEED PIPE
BEARING
BASE NOT SHOWN
SLUDGE CAKE
DISCHARGE
i
RADIAL CROSS SECTION
ficjyre 2.4-17. Components of a settlinn centrifuoe.
-------
which is the only kind used in commercial lime/limestone slurry
FGD systems, uses centrifugal force to increase the settling rate
over that obtainable by gravity settling which is done by in-
creasing the apparent difference between densities of the phases.
The principal elements of a settling centrifuge are the rotating
bowl, which is the settling vessel, and the conveyor, which
discharges the settled solids. The solid bowl is the only cen-
trifuge design used commercially in FGD systems. Adjustable
overflow weirs at the larger end of the bowl discharge the
clarified effluent, and ports on the opposite end discharge the
dewatered sludge cakes. As the bowl rotates, centrifugal force
causes the slurry to form an annular pool, the depth of which is
determined by adjustment of the effluent weirs. Feed enters
through a stationary supply pipe and passes through the conveyor
hub into the bowl. As the solids settle to the outer edges of
the bowl, they are picked up by the conveyor scroll and contin-
uously overflow the effluent weirs.
2.4.2.13 Waste Processing. Waste may be processed as a treated
or untreated material prior to final disposal in a pond or land-
fill . For untreated waste operation, the waste is "physically11
processed only to the point that it is thickened or dewatered
before disposal or "bleeding" to a pond. The term "processing",
then, refers to the first phase in handling of the waste product
from an FGD system.
Waste from FGD systems may be chemically treated by forced
oxidation, fixation, or stabilization. These terms are defined
as follows:
° Forced oxidation. Forced oxidation supplements the
natural cxidatio'r. of sulfite to sulfate by forcing air
through the material. The advantages of a calcium
sulfate (gypsum)-bearing material include better
settling and filtering properties, less disposal space
required, improved structural properties of the
disposed waste, potential for utilization of the gypsum
(e.g., wallboard production), and minimal chemical
oxygen demand of the disposed material, Forced oxida-
tion , unlike fixation and stabilization, is not typ-
ically a tail-end operation? in many systems, this
operation often occurs in the reaction tank.
59
-------
° Fixation, Fixation Increases tbe stability of the
waste through chemical means. This may be accomplished
by the addition of alkali, alkaline fly ash, or pro-
prietary additives along with inert solids to produce a
chemically stable solid. Examples of commercial proc-
esses of this type are those marketed by Conversion
Systems, Inc. (e.g., Pcz-C-Teo) and Dravo Corporation
(e.g., Calcilox).
0 stabilization. Stabilization is accomplished by the
addition of non-alkaline fly ash, soil, or other dry
additive. The purpose of stabilization is to enable
the placement of the maximum quantity of material in a
given disposal area to improve shear strength and to
reduce permeability. Disadvantages are that the
stabilized material is subject to erosion and rapid
saturation and has residual leacbability potential.
2.4.2.14 Kiu'- Disposal. Waste disposal refers to operations at
the disposal site for PGD waste following all handling and/or
treatment stages. There are three basic FGD waste disposal site
types j ponding,, landfi 11 ing, and stacking. The most common
waste disposal type is ponding. Figure 2,4-18 shows examples of
four pond types. Ponds are either lined or unlined; lined ponds
used for conventional FGD processes are typically clay lined.
Wastes that have been fixated or stabilized are usually (although
not always) landfilied. Stacking is only used for FGD systems
designed to produce gypsum. Presently, only two planned lime-
stone FGD systems are considering producing gypsum.
2.4.2.15 Pumps and Valves. Pumps are used in the solids hand-
ling and disposal area for pond water return, thickener
underflow, waste slurry transfer, etc. Pumps are also used, in
other areas of the FGD system, such as slurry transfer, slurry
bleed, and slurry recirculation. Pumps may.be classified into
two generic groups: displacement and nondisplacement.
Displacement pumps include reciprocating, rotary, and screw
designs. Diaphragm-type reciprocating pumps are sometimes used
in FGD systems for transferring thickener underflow. Rotary
pumps are not designed to handle liquid which contains grit or
other abrasive materials and are rarely used in lime/limestone
60
-------
(a)
(d)
Figure 2,4-18. Examples of pond types for waste disposal:
(a) diked; (b) incised; (c) side nil!; (d) cross valley,
61
-------
slurry FGD systems. Screw pumps differ from rotary pumps in that
the flow through the pump is axial instead of circumferential
like the rotary; they are often used in utility FGD systems for
transferring reagent feed as they can easily handle a concen-
trated (30 to 40 percent) slurry of lime or limestone.
The only nondisplacement pump used in lime/limestone slurry
FGD systems is the centrifugal pump. Centrifugal pumps are
widely used for water and slurry handling. These include makeup
water slurry recirculation, fresh slurry feed, thickener/clari-
fier overflow/underflow, and mist eliminator wash water, of
these, the recirculation pumps are the largest pumps with capa-
cities ranging from 5,000 to 20,000 gpm.
Valves are used throughout the FGD system not only to regu-
late the flow of flures but also to isolate piping or equipment
for maintenance/repair without interrupting other connected
systems. This helps to provide for continuous operation and
minimal downtime. The generic classifications of valves are;
ball, butterfly, check, gate, globe, pinch, and plug valves.
Among these, the check and globe values are generally not re-
commended for waste and slurry service,
2.4.3 Cperat.tonal Utility Lime and Limestone Slurry FGD Systems
As of the beginning of 1985, there were 31 operational lime/
limestone slurry FGD systems in the United States. A listing of
the ;.r ^'-sterns is shown in Table 2.4-3a and b along with an
indication of the major subsystems and components described in
Section 2,4.2,
2,5 FGD O&M CONSIDERATIONS
This section provides a brief introduction into the O&M
practices associated with lime/limestone slurry FGD processes as
they relate to system reliaM lit", identified ion of failure
modes, system layout and accessibility, and required operating
and maintenance procedc • . The purpose of this section is to
introduce and define terminology that is used extensively
62
-------
TABLE 2.4-3a.
DESIGN AND OPERATING DATA FOR OPERATIONAL UTILITY
SLURRY FGD SYSTEMS IN THE U.S. (GENERAL DATA)
LIME/LIMESTONE
6re«
e#f#t itr
Hi
rei
l*p*
m
tfwrstws®
m
im
m/m
M.ooe
!«.?
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I
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IN
a*
.
1
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turn
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f,«6
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tm
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tm*
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iff
m
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M
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»,W
(10
ts.t
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t
9*4
fit
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-------
TABLE 2.4-3a (continued)
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-------
TABLE 2.4-3a (continued)
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-------
TABLE 2.4-3a (continued)
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-------
TABLE 2.4-3b. DESIGN AND OPERATING DATA
SLURRY F6D SYSTEMS IN THE
FOR OPERATIONAL UTILITY LIHE/LIMESTONE
U.S. (SPECIFIC DATA)
Fi£
«¦»«/
! cttttrftfvfKM
| «'1*1
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£Pft»tf8§?§**
ItVTH
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fliHitlse
{continued)
-------
TABLE 2.4-3b (continued)
nli a
ft*
fWVtlM
¦nit/
k«4(*r
lm datl«a
aalal
Fw
awUcbtlan
»/re
fa*
tertrlce
•at/dry
Faa
lacatlaa
Or».
"ST
Oiwttr
type
Nw*er
a'
ab«nrton
Spare
abtarben
TeVto
Natoatcr
type
teayent
prep
efulpaent
tjrp*
Ab«e*tor
aaterlal
ni«i
allalnatM
Material*
Stect
llalni
aaterlal*
bat let
duct .
aaterlal
•eryc1e
P'pr a
aatrrUl*
laalatloM
val*a
type
Central
talvt
ifp*
Sladfa
taatarlR|
eba'paent
fad product
treatment
?J.
na
na
F«n«4 draft
0ry
do
NA
Spray
2
1M
la-Mae
Slater
NA
Poly
mm
NA
M
M
NA
fbtcbanar.
vacaaa fltr
flaatiaa
n.
•mttr
Centrlfwjal
FmH 4raft
*7
u*
M
Packed
ln»r
«
NA
Indirect
lower ail 11
III
NA
NA
M
«
M
NA
Tbktoaar,
•aca«a Fltr
farcad
aaldattaN
79.
•batter
(Mtrlfufil
F«n(4 draft
Dry
H»
M
Packed
tower
4
NA
M*tt.
Indirect
fever alll
M
Mt
M
m
M
M
NA
Tfclcbanar.
vaceaa Fltr
Favcad
aaldatlaa
IP.
Mult
(MtHfvfil
fmt4 inft
•ry
o»
I*.
Spray
tower
)
in
•y*a"
•all «111
Or*
Nly
Ina
M
M
NA
Ttlctoaor,
(KHB fltr
Stabllltatfaa
SI.
Itoitrr
Farce* lufl
•ry
u»
»
Sprajr/frtd
tnwr
4
Ne
Indirect
•all *111
Nab
F»P
«rf
•t
•ICS
Kalfa/
Mep
Knlfa/
•trfly
Ihtcba^ar,
tacwaa fltr
flaation
3*
HUH
Centrifugal
Indacad «nfi
•ry
•aaa
n
J ray
•
Na
Indirect
•all alii
fetal
rap
*r»
Syntb
tnlfe
tlrfly
—
tone
))
Nn11
CentrlFvfal
ftnrt 4nft
•n
up
•on*
Spray
tnwrr
1
Tat
•ypa«
tall ail 11
fetal
FIIP
AR0N
Ina/
Orf
FiP/fA
Knife
fill*
tone
Farced
oaldatlan
34.
Unit
Cwtrlfuftl
Farced draFt
9ry
t»
tone
Spray
t (wr
•
Tat
•ypatt
tall alii
Natal
rap
MtN
In*/
Or»
FPP/CS
Kalfa
Cate
None
Farced
oildetlan
».
Unit
Centrifugal
Forced draft
try
u»
Nana
Spray
tower
4
Vat
trNit
•all bill
Natal
FIP
um
ina/
ftf/CS
inlfe
Gate
Nona
Farced
aildatlan
»
•ootter
Ctctrlfvfil
l*AcN draft
Dry
Pawn
vs
Spray
*
Na
In-line
tall Ntlt
fetal
FRP
lap
total
FRP
In I fa
fiata
Tbicbsiwr
Tarred
odliatlon
V.
•aatter
Centrlfufal
ladacal *r#ft
Dry
Down
«
Spray
trwer
2
Na
In-line
tall pill
Ml
fIF
tno
fetal
r*p
Knife
6a ta
Nana
Farce#
oaldatlan
30.
Iwitir
Centrlfwfat
Forced 0r«ft
Dry
Up
n
Mobile bad
1
Na
Indirect
Slat or
Natal
SS
la*
lob
•tcs/
r»p/«.s
KnlFa
riBf
Nana
Nona
3f.
iNtttr
(inlr((«fil
fdrtrt draft
Irr
Ms
Spray
tower
2
*
Indirect
•all *111
Natal
fnyl
""
Or*
NA
m
NA
Iblctaaar,
«acma fltr
FlaaOan
*0
llMltr
tffitr
-------
TABLE 2.4-3b (continued)
_ . »
F»»
'wxllp
•nit/
kwilfr
ttm «MlfM
coMrlfvoal/
•¦tai
application
IB/Ft
fan
service
vot/dry
fon
local ton
fro-
icobNgr
ll»#
Akiaitfr
tm
Headier
thartwri
Spat*
attorfcert
Tei/No
Metier
IfP*
Reagent
prep
«p1p«e»t
type
(kwrttf,
wterlal
Mlat
Pltwlnatoc
^lerla)
Stack
It.i.1
Mlerlol*
OatlOt
Met
¦aterlal
Perrdo
pipe
¦otftet
Isolation
valro
«rp»
Control
valve
t»pe
Slodfr
dooaterlng
ttnlpavnt
tnd proMoct
tr*at«M(
S3
Mr It
Centrifugal
1 ditUdraft
®T
•0-
«0M*
Vmtvrt/vpra)
lawr
1
Ho
Jn-lloe
Slater
Upryl
Or*
Rtnt
Plnck
Pinch
Hon*
Mt»n«
94
»*ft
Contrlfogol
|o*«od draft
**
Dow
>on«
Vontorl/tpn,
iMcr
I
T«
In-line
Slater
MA
m.
MH
HA
NA
m
HA
MM
Porcod
oat«atlan
«.
Imttr
Ctntrlfvgol
Indocotf draft
Met
0OM
Afcl
Venlurl/ipray
tower
I
M
|-M-e
•all Bill
Netol
Pol f
AM.
MA
HA
MA
MA
Tbtctonor,
mwa fltr
Porcpd
aatdatlaa
M.
Milt
Cmtrlfafll
Induced draft
Dry
0mm
»i
Sp»r
lower
V
m
In-llno
•all arid
r«r
%ta1
Natal
FHP
MA
Plof
1MlcA«n»r
final
N*«tlpl
it.
•nit
Ccntrlfogol
Infer* ir*tt
9atm
n
t«»r
1?
r«t
In-line
•all sill
Or*
f»
ftetaf
Natal
rap
Mil
Plot
IMIclonor
Ported
o*t da tie*
»
¦nil
C**trlf»«o1
Forced draft
Mat
icrmtrf
atiMtcr
n
Ve«tvr1
t«er
•
•a
Nino
Siaker
n»
M
•a
•ICS
Plot
PlncM
IHtMwr
Fliatlaa
Unit
C*ntr1f*9«l
FartN Mraft
Hat
Scn*Wr/
abAOeWr
n
ftntorl
toner
«
Mo
None
Vdef
~l
FMP
~t
0r|
Hirs
Plat
PtncM
|Mlcl««*t
fliadan
tkilt
Ccntrffofo)
fam^ Irift
U»
JN
Sprs, tawr
(kortimtil)
4
fai
•_
S*«»+r
«r»
«rr»
%ui
H
ACS
PW
Cnlft
Mtt
IMIflonar
Pfaottoo
•1.
NA
HA
M
HA
M
•A
JWf
tawer
HA
m
MA
•all
HA
MA
M
MA
HA
MA
MA
MM
StaMIlliatlon
Iwtttf
C#ntr1f«fol
flWl dr»*t
•t
»»P
AM
$r*r »«•'
(HorlranUl)
«
HA
Indirect
•an «tn.
)1et*r
Ino
poly
HA
In*
NH
an
MA
IHHHmii t
IKMB rtftp
Ft.atloa
11.
••Otter
Centrtfogol
ftmtf Mr»»l
•nr
up
AM
Sp**ar twar
(fcarllMlol)
?
Ho
•all arid
Naryl
FMP
MICS
Pinch
•lapNrttH
IHIctaMPP
Nona
*4.
Imtir
Centrifugal
r«KM Irift
•ry
«~
«f
Iprpp taHof
(korltontal}
t
Ha
•pt*«s
•all «m
0r|
Horyl
m
•l
•ICS
Plnrb
•lapMrttpi
Ikldawr
Hone
6S.
Unit
Aa (el
Up
T rl|
Or)
HA
AHfiN
HA
NA
NA
NA
Ihutewr,
varuun fltr
Stibl 1 Wat Ion
to.
HA
CtnUtfufal
Forced draft
*7
lip
00
Spray
lower
5
Te*
NA
Nil aril!
Hub
HA
MlftH
Org
NA
NA
NA
HA
forced
nmdatlon
(¦;.
ha
Ailit
forced draft
Or,
lip
MA
Vrnlyrt
3
Tea
HA
flail anil
Or?
HA
Or)
NA
NA
NA
NA
None
Hone
6H.
HA
MA
Hk
MA
HA
00
<.pray
ttwer
MA
Tot
Indirect
Rail miW
HA
NA
(h-»
HA
NA
HA
NA
HA
Stabilization
Hfotter
Centrifuge)
forteti drift
&r,
Up
0
Ira,
J
Ho
B,p*l3
Rail nlll
Rub
f«P
FPP
Ino 0r9
Hetal
rn.es/
SS
Knife
Knife
Hone
Hone
'0.
8»oittr
CtRlrlfujil
forced draft
Dry
l'p
0
Tray
tower
?
ftl
1ndlrect
tall aiill
Dub
HIP
FHP
Or)
RLSC/
SS
Knife
Knife
Thickener
None
NA
Centrifugal
forced draf1
Dry
00
Spray
tower
HA
No
Indirect
•all «ll»
ha
HA
NA
NA
KA
NA
MA
Iftlcfcener
hone
>?.
Unit
Centrifugal
farced draft
D r,
Up
None
Aod deck
tower
1
Ho
•ypm
•all «U1
Org
Noryl
AHBM
Hast G
•ICS/
fRP
Plug
Plug
TMcfcm»er,
iirvua fltr
FlaatInn
7*.
Unit
Centrlfuoal
forced draft
Drr
Up
None
Rod deck
tower
1
Ho
tyiuif
Ball >111
Org
Horjfl
Men
Hast 6
•tcs/
FHP
rt«t
Plug
Thickener,
vacuum fltr
Fixation
74.
Bister
Centrifugal
forced draft
Or,
up
Q
Tr*y
tnwer
?
Ho
None
•all olll
MP
ANBH
Org
NA
NA
NA
Thickener,
centrifuge
Stabilisation
75.
llnlt
Cfntrifvqii
Forced draft
up
00
'r*jr
tow*r
2
to
None
•all -HI
Rwb
fHP
ARBH/
Org
(h-9
HICS
Plog
Plug
Thickener.
vacuu* fltr
Stefellijallon
76.
Rooster
Centrifugal
Forced draft
Or,
Up
Abs
Paifed
tower
2
Ho
•jrpass
Ball "ill
Netat
foly
APW
Org
Org
tics
Plug
PlncH/
Btrfly
Hydrocycl.
vacvwa fltr
Forced
oa itfatton
n.
Booster
Centrifugal
Induced draft
Dry
Down
VS
Venturi/spray
tnwer
«
*ei
In-line
Ball «I1I
Hetal
NA
AAPM
NA
HA
NA
MA
Thickener,
«1{«M fltr
Forced
of idatlon
18.
Booster
CentrffuqaT
Induced draft
Or,
(torn
*s
VeAturi/%pray
tnwfr
6
res
In-line
Ball «HI
NrUl
MA
um
MA
NA
M
MA
Thickener,
iacuw> fltr
forced
oaldation
19.
Booster
Centrifugal
Induced draft
Dry
Dnwn
*5
Venturi/spray
t(*er
HA
Mo
Indirect
BUI Ml 11
fti*
FHP
ABfltl
NA
HA
MA
NA
None
forced
o>tdation
80.
iintt
Cental fugal
Forced draft
•rr
Up
Hone
Cri4
tower
4
Mo
Indirect
Ball *111
Hub
SS
APBH
Metal
ftl. CS
NA
Knire
None
Forced
oaldatlon
(continued)
-------
TABLE 2.4-3b (continued)
NJriber*
Fan
function
unit/
boulter
Fan design
centr 1 f*n|a V
anal
Fin
application
10/F 0
Fan
service
wel/rtry
Fan
location
Pre-
scrubber
ijr*
Absoi her
»>i*
Hvnber
of
absorbers
ihiiMhrrs
tesyho
ftehcjier
lyl*
Br men I
4,1 pi.
equiiwrnt
typf
A: >rtiir<
uli i ialC
risi
el iNKialoc
autrrtal
V«.
1 ininq
animal'
Outlet
iluct f
Material
A»j« y le
pipe
antral*
Isolatio*
waive
type
Control
vaUe
type
Sli'f'ir
itewat'T inq
equipment
(nd proiuct
treatnrnt
•1.
ft/.
Altai
forced draft
Dry
Up
Hone
S|i«'ay
tower
3
In.1ine
8oH kin
HiUl
SS
APfiH
ftetal
NA
NA
KA
Thirlrner,
vacuo* fltr
Flialion
0?.
M
NA
Forced draft
Dry
Up
None
Sl»ray
tower
4
res
Repays
Ball atll
Metal
NA
NA
NA
NA
M
NA
Hone
None
H.
unit
Centrifugal
Forced draft
Cry
Up
M>S
Faded
tower
B
No
Bypass
Ball alii
Org
Poly
ANBH
Or,
5S
Plug
Ball/
Btrfly
Thickener,
centri fuge
SUhlH/ation
M.
Unit
Centrifugal
Forced draft
Ory
Up
Ab*
Packed
tnwer
i
Mo
Bypass
Ball alii
Org
Paly
ARBM
Org
SS
Plug
Ball/
Btrfly
Thickener,
centrifuge
SUbil liation
#S.
Unit
lentrifugal
Forced draft
Ory
up
Abs
Packed
Ltwr
1
No
Bypass
UU -Ml
Org
Poly
AR6N
Org
SS
PI *9
1*11/
Btrfly
Thickener,
Centrifuge
SUbilltatlon
«6.
Ufltl
Centri fuoal
Forced draft
Ory
wp
None
Spray
towrr
3
No
Indirect
Ball attl
Org
Poly
AKBH
I no
RIC5
Itrfty
Pinch
None
None
17.
Booster
Centrifugal
Forced drift
Ory
Up
¦one
Spray
toMr
4
*ei
Hyp*!*.
Ir>d trect
Slaker
Orq
Paly
A MM
Jno /
Org
SS
Blrfly
Pinch
Ihiclfrer,
vaci/u* fltr
SUbllliatton
M.
0ooiter
(Vntrlfu9a1
forced draft
Dry
Up
Mrvne
Spray
tfiMer
4
Tes
Bypass,
Indirect
Slaker
Org
Poly
AR6H
Irs/
Org
SS
Btrfly
Pinch
TMiiener,
watuua fltr
SUblMtallw
•9.
Booster
Centrifugal
forced draft
Ory
Iff
ffo«te
Spiay
tower
4
*«s
Indirect
Slaker
Org
Poly
AflfW
Ino/
O^B
SS
Btrfly
ffnth
Thickener,
vacuum fltr
Stabllliatio*
90.
Booster
Centrifugal
Forced draft
Ory
up
None
Spray
tower
4
res
Bypass.
Indirect
Slaker
Org
Poly
AftBM
Ino
PI CS/
FRP
Plug
Btrfly
Pinch/
Gat*
Thickener,
vacuus fltr
Stabilisation
91.
Booster
Centrifugal
forced draft
Dry
up
Nona
Spray
towrr
3
NA
MA
Slaker
Org
Poly
NA
KA
M
NA
Thickener*
vactfua fltr
fUattM
'The nutters shown h»re correspond to those listed for etch unit 4n Tabic
bAbs • fn Absorber . none • no prescrubber, QO ¦ separate quench duct, 0 * separate quencher, VS * venlwrl scrubber (alio used f«r
pirtlrulitt mttrr control)
c0rg • Organic, Inn - Inorqanlc, Pub ¦ Jlubber
"VvC • Polyvinyl c+>lnr|ife, SS • stainless siffl, Poly • polypropylene. Hast 6 - Hastel loy G, Vnyl - Vinyl ester, Moryl • polypHenytenc.
(tyton « special pclyner, FtP - fiber-reinforced plastic
*0rg • Organic. [no • Inorganic. ARBM * Acid-Peslstant Brick and Mortar, MP ¦ Fther-Belnfnrced Plastic.
*0rg * Organic, I no ¦ Inorganic, Hast G ¦ Hastelloy G
^Rl CS • Bwbber lined carbon steel, SS • Stainless steel, CS • Carbon steel, fHP ¦ Fiber-Reinforced Plastic.
NCTf: NA - Jnformtlon not available.
-------
in a more thorough treatment of these topics in Section 4 (Inspec-
tion Methods and Procedures), Section 5 (Performance Evaluation
and Problem Diagnosis/Correction), and Section 6 (Model O&M
Plan).
The preceding section (2.4) provides a description of the
various types and varieties of design configurations used in
lime/limestone slurry FGD systems presently in commercial
service. Technically, each FGD system represents a unique appli-
cation which varies according to plant, process, and historical
considerations.
Plant considerations are conditions which relate to the
power plant and its operation. They involve the power-generating
unit's coal supply, boiler design, power demand, geographical
site, and applicable environmental regulations. Table 2.5-1
lists the major power plant considerations.
Process considerations relate to the FGD vendor who supplies
the equipment, the architect-engineer (A-E) who designs the
system, and the owner/operator utility who operates the system.
Each FGD supplier provides a process design with proprietary or
unique characteristics. These characteristics can vary in
significance from items as minor as spray nozzle design to items
as major as absorber tower design. The A-E is generally
subordinate to the system supplier in exerting influence on
process design; however, no two FGD systems are engineered alike.
The owner/operator utility will also exert an independent
influence on the process design generally in accordance with
their level of previous FGD operating experience.
Historical considerations relate to system purchase and
service dates. These considerations lock the process design
characteristics into a particular generation of technology (first,
second, or third). A particular generation of technology will
define certain levels of performance and operating expectations
as well as flexibility in instituting modifications to upgrade
performance (see Section 2.4.1.2, Characteristics of Technology
Generation).
71
-------
TABLE 2.5-1. MAJOR POWER PLANT CONSIDERATIONS
Coal Properties and Supplies
Sulfur content
Ash content
Fly ash composition
Chlorine content
Moisture content
Heating value
Availability of coals
Transportation considerations
Flexibility for firing alternative coals
Steam Generator Design
Type of steam generator
Size of steam generator
Flue gas
weight flow rate
volume flow rate
temperature
dewpoint
fly ash loading
Additional control equipment
Power Generation Demand
Base load
Intermediate load
Cycling load
Peak load
Site Conditions
Land availability
Soil permeability
Disposal facility
Climatic and geographic effects
Quality and availability of reagent and makeup water
Environmental Regulations
Air
1971 NSPS
1979 NSPS
SIP
PSD
Water
1977 CWA
Solid Waste
RCRA
72
-------
Even under the supposition that every lime/limestone slurry
FGD system is a unique application, there are also sufficient
similarities among the systems to permit a comparative evaluation
in terms of O&M considerations. In Section 2.4.2 (Existing
Design Configurations), lime/limestone slurry FGD processes were
described in terms of three major equipment areas: gas handling
and treatment, reagent preparation and feed, and waste solids
handling and disposal. These equipment areas can be further
subdivided into subareas, and the subareas further subdivided
into unique subsystems. Figure 2.5-1 shows the organization and
relationship of the equipment areas in a typical FGD system.
Table 2.5-2 provides a summary listing of the FGD physical sub-
systems by major equipment area.
The physical subsystems represent the basis by which all
lime/limestone slurry systems can be evaluated on a common basis.
This evaluation will be conducted in the balance of this section
in terms of the pertinent O&M considerations of lime/limestone
slurry FGD processes. Section 2.5.1 identifies the failure modes
which plague FGD systems through an analysis of the subsystems
which are directly affected in terms of their impact on system
stream time and reliability. The analysis is then extended into
facility considerations (Section 2.5.2, System Layout, Accessi-
bility, and Design). And finally, the various O&M practices
associated with lime/limestone slurry FGD processes are defined
(Section 2.5.3, O&M Practices).
2.5.1 Failure Modes
Failure modes are defined as operating problems that may
lead to downtime (outage) of a subsystem or-system. Failures may
lead to an outage isolated to the subsystem affected, or to a
multiple subsystem outage, or to a total system outage, or to a
multiple system outage. A multiple system outage is possible
only at a plant equipped with two or more separate FGD-equipped
boilers which share subsystem(s) affected by the outage. Preva-
lent examples are common reagent handling and preparation, solids
73
-------
B. REAGENT PREPARATION/FEED
A. GAS HANDLING/
TREATMENT
BULK
REAGENT
HANDLING
PARTICULATE
REMOVAL
MAKEUP
WATER
REAGENT
PREPARATION
GAS
TRANSPORT
WASH,
SEALS
COOLING
REAGENT
CIRCULATION
ABSORPTION
WASTE
SOLIDS
SEPARATION
WASTE
TREATMENT
REHEAT
C. WASTE SOLIDS
HANDLING/DISPOSA
GAS
DISPERSION
WASTE
DISPOSAL
GAS ¦¦ SOLID * LIQUID/SLURRY
Figure 2.5-1. Major material flows in FGD systems.
-------
TABLE 2.5-2. SUMMARY LISTING OF THE FGD SUBSYSTEMS BY
MAJOR EQUIPMENT AREA
GetS
hand! i rig/treatment
Reagent
preparation/feed
Waste solids
handling/disposal
Fans
Reagent Receiving
Thickeners
Scrubber
Ball Mills and Slakers
Vacuum Filters
Absorber
Tanks
Centrifuges
Mist Eliminator
Waste Processing
Reheater
Waste Disposal
Ductwork and Dampers
Pumps, Pipes, and Valves
Stack
75
-------
dewatering and treatment, and ductwork and stack. A failure may
have no effect on power production, may cause reduced load, or
may cause a total shutdown of the generating unit(s). The effects
of a failure, in addition to being a function of the relation of
the system or subsystem to the rest of the plant, are also a
function of the restrictions under which the plant is operating
(see Section 2.1, Environmental Regulations) and the redundancy
which is built into the FGD system.
Failure modes can be described in terms of the downtime or
outage time that result from the failure. This can be considered
a measure of unreliability. For the purposes of this manual, we
used the results of a recently completed study in which PEI
Associates, Inc. (PEI) participated in the analysis of failure
modes associated with lime/limestone slurry FGD systems. In
this study, we quantified unreliability in terms of outage times
as defined by "module equivalent hours" in order to combine the
impacts of failures into a common basis for comparison. Module
equivalent hours (MEH) is defined as the product of the number of
scrubber/absorber modules affected by a given type of failure,
the average duration of that type of failure in hours, and the
number of times the failure occurs in a given performance period
(year). The overall results of the subsystem MEH analysis are
presented in Table 2.5-3. The key subsystems in order of highest
MEH are (from top to bottom and left to right):
0 Mist eliminators 0 Fans
° Ductwork 0 Pipes and valves
° Absorber 0 Thickener
0 Stack 0 Dampers
Key failure modes were identified for key subsystems for
which major contributions to unreliability occur at the system
and plant levels. For a generating station (power plant) having
three boilers equipped with FGD systems each having two modules,
one hour cf module downtime is one MEH. One hour of system or
76
-------
TABLE 2.5-3. SUBSYSTEM OUTAGE TIMES IN MODULE EQUIVALENT HOURS (MEH)
Subsystem
Module
downtime/
year
System
component
of
subsystem
MEH,
MEH/year
Plant
component
of
subsystem
MEH,
MEH/year
Total
Subsystem
MEH/year
Mist Eliminator
22,832
572
0
23,404
Ductwork
739
15,392
5,092
21,223
Absorber
13,664
3,514
0
21,178
Stack
0
12,568
4,464
17,032
Fans
8,229
4,288
1,264
13,781
Pipes and Valves
3,176
1,474
8,466
13,116
Thickener
20
4,168
7,232
11,420
Dampers
640
7,929
640
9,209
Reagent Preparation
4,032
440
4,288
8,760
Pumps
7,655
158
0
7,823
Tanks
3,096
4,496
180
7,772
Expansion Joints
676
7,024
64
7,764
Scrubber
6,764
340
0
7,104
Particulate Matter Control
3,171
1,308
1,632
6,111
Reheater
192
5,376
0
5,568
Spray Nozzles
4,198
60
0
4,258
Reagent Receiving
0
0
1,728
1,728
Water System
0
0
240
240
Instrumentation
36
0
0
36
Waste Treatment
10
0
0
10
Disposal Site
0
0
0
0
aOne hour of module downtime is equivalent to one MEH.
bThe total subsystem MEH/Year is the sum of the module, system and plant
(station) MEH's. The three categories are mutually exclusive in that
extensive MEH downtime for modular problems such as a complete mist
eliminator failure due to a boiler temperature excursion forcing an entire
FGD system out of service would appear under system component rather than
module downtime. In this way the relative impact of problems logged for a
particular subsystem can be gauged on a modular, total system, and plant
(station) level as well as on an overall basis.
77
-------
unit downtime is equivalent to two MEH (1 hour of system downtime
x 2 modules/system). One hour of plant downtime is equivalent to
six MEH (1 hour of plant downtime x 6 modules/plant). The total
subsystem MEH is the sum of the MEH due to failures of a given
subsystem. This is calculated by adding the MEH due to module,
system, and plant downtimes.
Ductwork, stacks, pipes and valves, and thickeners are key
subsystems with a high percentage of subsystem MEH manifested at
the system and plant levels. The most troublesome failure modes
for the key subsystems are highlighted below:
° Most duct failures occur in the outlet duct. The key
ductwork failure mode is corrosion of the outlet duct
due to moisture carryover and residual SO (SO- and
S03). x 2
° Stack failures are almost exclusively related to the
lining. The key failure mode is acid attack of the
stack lining due to moisture carryover and residual
° Thickener failures are primarily design related.
Approximately 30 percent of the design-related failures
were to supporting equipment rather than the thickeners
themselves. Joints, lining, and shaft failures are key
failure modes for thickeners.
° Fiber reinforced plastic (FRP) pipe failures appear to
cause more effective downtime (MEH) than other pipe and
valve failures.
Stack lining acid attack and outlet duct corrosion were key
FGD system failure modes identified in this analysis. Stack
lining and outlet duct failures are low frequency failures with
high penalties (effects) associated with them because they force
the entire FGD system (or systems) out of service, whether or not
individual modules are available, usually for extended periods.
The MEH for these low frequency failures are prohibitive. The
downtime they cause may be catastrophic in terms of lost power
production. There are seldom spares provided for stacks and
outlet ductwork.
In order to better understand lime/limestone slurry FGD
system failure modes and the factors associated with their
78
-------
occurrence, reported failure modes were correlated with associated
system design and operating characteristics. The system design
and operating characteristics investigated were:
0 Coal
0 Boiler
0 Application
8 Design and operation
A brief description of this analysis is presented below. A more
thorough treatment of this topic is provided in Section 5 (Per-
formance Evaluation and Problem Diagnosis/Correction).
2.5.1.1 Coal Characteristics. The coal characteristics of
importance to FGD systems are sulfur and chlorine contents (see
Section 2.2). These characteristics can be classified as low
(less than 1 percent), medium (1 to 3 percent), and high (greater
than 3 percent) for sulfur; and low and high (less/greater than
0.1 percent) for chlorine. The gas handling and treatment sub-
systems of absorbers, ductwork, and stack show a strong correla-
tion between: 1) high sulfur content and unreliability, and 2)
high chlorine content and unreliability. The predominant problem
is corrosion attack in the "wet" service areas.
2.5.1.2 Boiler Characteristics. The boiler characteristics of
importance to FGD systems are load profile and age. Load profile
represents the production output and schedule of the generating
unit (boiler). Four basic categories are defined: base load
(high production level), intermediate load (moderate production
level), cycling load (low production level), and peak load
(intermittent production level). Boiler load profile shows a
correlation between unreliability and base load units, with
downtime decreasing for cyclic load units and decreasing still
further for peak load units. The overriding reason for this
trend appears to be the amount of scheduled downtime available
for the unit and the greater opportunity to perform FGD main-
tenance. The results of unreliability as a function of age,
where age is divided into one year increments, are for the most
79
-------
part, indeterminant and lack any correlation. This may result
from confounding the effects of depreciation and improved human
skills. If corrosion and wear were causative factors in equip-
ment failure, the expected results would be increasing unreli-
ability with age. If a learning process was involved in improved
equipment operation, a correlation between age and reliability
should exist.
2.5.1.3 Application Characteristics. The application charac-
teristics of importance are new versus retrofit, first versus
second system, and size. For new versus retrofit, fans and
absorbers show a strong correlation between retrofit and
unreliability. For first versus second system, a number of
utilities were examined which have more than one FGD system
either within their power-generating system or at the same power
plant. A comparison of the first versus the second FGD system at
the same plant should give an indication of the effect of opera-
ting experience on system reliability. Comparisons for the most
part do indicate slightly improved reliability for the second
system. For system size, overall system size (MW/unit), and the
size per absorber module (MW/module), were examined. System size
was broken into two groups: less or greater than 450 MW/unit.
The smaller units exhibited less downtime than the larger units.
The size of the unit appears to be a much more significant para-
meter in terms of FGD system reliability than the size of the
individual modules (MW/module) in the FGD system. The results
indicate that smaller units do appear more desirable in terms of
reliability.
2.5.1.4 Design and Operation Considerations. Section 2.4.3
provides design data for operational FGD systems. The design and
operation considerations of importance are reagent type, water
loop, solids dewatering, absorber parameters, reheat, reagent
preparation and fan location. A brief summary for each
consideration is provided below.
80
-------
Reagent type - the gas handling and treatment subsystems
of absorber, ductwork, and stack show a strong correla-
tion between lime systems and unreliability. This is
probably because lime FGD systems are predominantly
used for higher sulfur coal applications. Limestone
shows a high correlation with unreliability in the
slurry circuit (limestone slurry is more abrasive than
lime slurry).
Water loop - the reliability of open and closed water
loop FGD systems is another test for chloride (and
other dissolved salts) as a failure mechanism. Expec-
tations are that closed water loops, high in chloride,
will be associated with high unreliability. Contrary
to expectations, results indicated that unreliability
was associated with open water loop systems. One
explanation for this observation is that virtually all
of the early generation commercial lime/limestone FGD
systems were originally designed for closed water loop
(no discharge) operation. However, due to a variety of
problems (e.g., buildup of dissolved salts), the water
loop was eventually opened up as one of the first
measures to relieve these problems. (In other words,
the water loop variable is an "effect" rather than a
"cause".)
Solids dewatering - results confirmed the expectation
that FGD systems without dewatering were expected to be
more reliable than systems with dewatering because they
have less equipment to cause downtime and lower concen-
trations of dissolved salts that build up in the liquor
loop.
Absorber - results indicated that towers with internals
(packed, tray) have a high correlation with unrelia-
bility. The type of absorber exhibiting the highest
unreliability is the packed tower. Spray tower ab-
sorbers exhibited the highest reliability. However,
mist eliminators showed a high correlation of unrelia-
bility with spray tower absorbers. This is to be
expected when considering the open structure of a spray
tower, the high L/G ratio, and the upward flow of the
gas without impediment or a change in direction.
Absorbers with internals have been associated with a
high degree of unreliability and are generally excluded
from new designs. Another consideration in absorbers
is the use of "prescrubbers". Prescrubbers include
upstream scrubbers, presaturators, and quench towers.
A number of systems are equipped with one of these
devices to remove particulates, effect initial SO
absorption and/or condition the gas stream prior to the
absorber. Systems with no prescrubbers appear to
81
-------
be more reliable than systems with prescrubbers. This
is an expected result since systems with prescrubbers
have an additional subsystem that may fail. However,
the presence of a prescrubber shows a high correlation
with reliability for S02 absorbers in contrast to their
effect on the total system. A possible explanation is
that the combination of flue gas quenching and
chloride, particulate, and initial S0_ removal that
occurs in a prescrubber serves to protect the S0_
absorber from failures.
0 Reheat - the order of decreasing reliability for type
of reheat is no reheat, bypass reheat, in-line reheat,
and indirect reheat.
° Reagent preparation - reagent preparation in a ball
mill (limestone) exhibits considerably higher downtime
for slurry circuit equipment (e.g., pipes, valves) than
does reagent preparation in a slaker (lime).
° Fan location - fan unreliability was affected by fan
location between the scrubber and the absorber. This
location means that the fan operates completely wet and
the downtime results are as expected. There was little
difference between downtime for fans located either
upstream (operating on hot, particulate-cleaned gas) or
downstream (operating on reheated gas) from the FGD
system.
A summary of the results of the failure mode analysis by the
FGD characteristics discussed in the foregoing is provided in
Table 2.5-4.
2.5.2 System Layout, Accessibility, and Design
An essential feature of any treatment of O&M practices is
consideration of FGD system layout, accessibility, and design.
Layout and accessibility are facets of FGD design and operation
that go hand-in-hand. System layout refers to the physical
arrangement of the equipment comprised by the FGD system. System
accessibility refers to the approach and entry of the equipment
comprised by the FGD system. System accessibility is a direct
function of system layout. A physical arrangement of equipment
that is more open and less restrictive will improve approach and
entry to the equipment. Conversely, a physical arrangement that
is close and constrictive will diminish approach and entry to the
82
-------
TABLE 2.5-4. SUMMARY OF FAILURE MODE ANALYSIS
System Characteristic
Results
Conclusions (cause and effect)
Reagent Type
Lime correlates with system
unreliabi1ity
Lime systems are used primarily
for high sulfur applications
Sulfur Content of Coal
Positive correlation with
unreliabi1ity
Sulfur content affects
reliability
Chlorine Content of Coal
Positive correlation with
unreliability
Chlorine content affects
reliability
Open Versus Closed Water Loop
Open loop correlates with
unreliability
Opening water loop is an effect
caused by system unreliability
Load Profile
Positive correlation between base
load and unreliability
Reliability is affected by use
Age of System
No correlation
Depreciation and skills may
counterbalance
Solids Dewatering
No dewatering correlates with
reliabi1ity
Additional subsystems cause more
unreliability
-------
equipment. Obviously, the FGD system does not have a limitless
amount of space available to permit a physical arrangement of the
equipment in a completely open fashion to maximize accessibility
to all equipment. Moreover, spatial necessities are assigned in
priority to the power-generating unit operations and peripherals.
Pollution control operations are generally assigned lowest
spatial priority at the plant. Hence, within the given framework
of a low spatial priority, an FGD system layout must be defined
which minimizes spatial requirements while maximizing accessibil-
ity .
This section will be devoted to layout, accessibility, and
design features that are supportive of adequate O&M practices.
These features will be addressed in terms of the various physical
subsystems previously defined in Section 2.4.2. (Existing Design
Configurations).
2.5.2.1 Gas Handling and Treatment. Typically, O&M necessities
are more rigorous for the "dynamic" (moving) components than for
"static" (immobile) components. For this equipment area, the
dynamic components are fans and dampers; the static components
are scrubbers, absorbers, mist eliminators, and reheaters. With
respect to the dynamic components, fans represent a greater O&M
concern because of their constant high rate of motion. System
layout, accessibility, and design considerations that enhance fan
O&M are:
0 Placement of the fan at grade level, a practice which
is widely accepted because of sheer size and weight of
the equipment. Some of the earlier (and smaller)
systems used elevated fan placements. Accordingly,
maintenance and repair activities were severely
limited.
0 Placement of the fan before (upstream) the absorbers, a
practice which is widely accepted and implies the
existence of an upstream particulate collection device
(typically ESP). These fans are generally larger than
those that follow (downstream) the absorber because of
higher volumetric flow rate (operation at 300°F vs.
175°F). However, downstream fans require larger motors
because of the additional mass added to the gas stream
in the form of moisture.
84
-------
0 Upstream fans produce a positive pressure operating
environment. Therefore, any leaks in the downstream
equipment will allow emission of flue gas into the
local environment. Any leakage problem is further
aggravated where the FGD system is located in an
enclosure. Special attention to leak-proof designs is
a necessity.
0 Fan capacity to overcome FGD system gas-side pressure
drop can be provided by a separate booster fan or
incorporated into the unit ID fan. The latter practice
is widely accepted because it is easier to operate one
fan instead of operating and balancing two fans.
However, a separate booster fan is easier to maintain
and repair because of size.
The function and duty of the various types of dampers pre-
sent in lime/limestone slurry FGD systems is described in Section
2.4.2.5. Dampers are less dynamic than fans in that their opera-
tion is much slower and intermittent. However, their O&M necessi
ties are equally demanding because of the cascading effect their
malfunction can have on downstream operations. The inability to
properly control and isolate the flue gas stream can either
severely minimize or totally eliminate operating, maintenance,
and repair functions, or compromise worker safety necessities.
Layout considerations that enhance accessibility are site and
design specific; however, some overall design considerations are:
0 The ductwork design should be able to accommodate the
insertion of simple isolation blanking plates to
isolate ducts for the protection of the maintenance
crew during inspection and repair. The plates and
insertion point should be arranged such that the duct
can be easily "broken" and the plate quickly rolled
into position.
0 Guillotine dampers are the most widely used design
because of superior seal-off capability. However, they
are more troublesome to operate, maintain, and repair
than other designs. Guillotine dampers are generally
top-entry design. This tends to limit observation and
inspection opportunities. Emergency operation is
difficult in that manual operation (in the event of an
operator or drive malfunction) is timely and labor
intensive. Dampers should be arranged to provide
prompt access via conventional catwalk and handrails.
85
-------
° Damper performance is a direct function of ductwork
location. A straight-run location is preferable to an
elbow or bend because of gas chanelling and uneven gas
distribution; the longer the straight run, the better
the performance.
The O&M necessities for static components in the gas handling
and treatment equipment area are typically less demanding than
dynamic components because of the potentially higher wear rates
associated with the latter. Accordingly, the layout, accessibil-
ity, and design considerations are correspondingly less crucial,
as noted in the considerations that follow:
° Cleanout doors should be provided at various levels in
the scrubber/absorber tower to:
access the base of the tower
access the upper level of the tower, generally
in the spray zone
access the mist eliminator, generally below or
in-between stages depending on one or multiple-
stage mist eliminator design
access the reheat chamber
° Visual ports at various levels in tower should be
provided to permit visual inspection during operation,
especially for the absorber (or scrubber) at the inlet
gas/slurry, hot/dry interface area; gas/slurry contact
zone; and mist eliminator.
0 Manways should be provided at other levels in the tower
which do not require rapid access and entry.
* A drainage system should be provided that allows for
complete drainage of the towers for inspection and
maintenance.
0 Vertical tower versus horizontal tower arrangement is a
major consideration. The former tower arrangement
predominates because of spatial and cost factors. The
latter tower arrangement permits overall easier access
because of equal accessibility at the same elevation to
all portions of the vessel. The latter tower consumes
less power because of lower gas-side pressure drop and
lower slurry pumping height.
36
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0 Horizontal (vertical gas flow) versus vertical (hori-
zontal gas flow) mist eliminator and reheater (in-line
tube bundles) designs involve the same O&M advantages
and disadvantages as vertical and horizontal towers.
2.5.2.2 Reagent Preparation and Feed. Similar to gas handling
and treatment, reagent preparation and feed equipment can be
distinguished according to dynamic and static service. Dynamic
components include conveyors, ball mills, slakers, and pumps;
static components include tanks, piping and valves, and storage
bins. Again, the dynamic components are of more concern than the
static components. The dynamic components operate in a slurry
service environment. Slurry suspensions of 5 to 75 percent
solids are continuously or intermittently transferred or recycled
at low to high flow rates in the slurry circuit. Access and
design considerations that enhance O&M are:
0 Placement of the slurry pumps in a central "pump house"
at grade level. Segregation of pumps with similar or
identical service requirements or location of pumps in
a "sump area" (below grade or beneath the equipment in
slurry service) limits operating versatility,
maintenance, and repair.
0 Provision to accommodate flush out and flush water
necessities during shutdown and outages through fresh
(or clarified) water supply and disposal sumps and
drains.
The static components are subjected to the same slurry
service environment as the dynamic components. Although their
duty requirements are less severe in that they are not required
to "move" within this environment, the same restrictions apply as
those described for the dynamic components. Additional design
considerations include:
0 Provision of sufficient space to minimize elbows,
bends, restrictions, reducers, and expansions in the
slurry piping.
° Provision of ample drainage to quickly accommodate
planned and unscheduled outages.
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° Provision of sufficient surge capacity within the
tankage network to accommodate extended peak load
operation or to withstand the loss of a tank for a
limited period of time.
2.5.2.3 Waste Solids Handling and Disposal. Continuing with
the distinction of dynamic and static components, dynamic com-
ponents include thickeners (clarifiers), filters, centrifuges,
conveyors, and pumps. Static components include tanks and stor-
age bins. Many of the same considerations described for reagent
preparation and feed also apply here. Additional considerations
peculiar to this area include:
0 Placement of all secondary solids dewatering equipment
(filters and centrifuges and ancillaries) in a central
"dewatering house" at the grade level.
0 Minimization of the pipe run between primary dewatering
(thickener) and the dewatering house, as well as the
dewatering house and disposal area.
0 Sufficient space to stockpile solid waste during
emergency conditions (thickener outage, filter outage,
pump failure, pipe failure).
0 Access walkways to inspect thickeners and filter
operation.
0 Protective covers for tanks, thickeners, and other open
vessels.
2.5.3 O&M Practices
This section introduces the various types of operation and
maintenance (O&M) practices for lime/limestone slurry FGD
processes, the conditions under which the practices are imple-
mented, and specific activities involved in each. A more
thorough treatment of the subject can be found in Section 6
(Model O&M Plan). This section introduces the O&M requirements
for these processes: standard operating practices, routine
startup and shutdown, and operating modes for system upset condi-
tions. The size, duties, and training needs of an operating crew
are reviewed. Maintenance practices are described separately;
the requirements for maintenance personnel, in terms of numbers,
duties, experience level, and training are also reviewed.
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2.5.3.1 Standard Operations. With increasingly more stringent
requirements on plant emissions, the owner/operator utility must
make a strong commitment to FGD operation, including adequate
staffing. Operators should be assigned specifically and solely
to the FGD system during each shift. FGD system operation must
be coordinated with the unit's power generation schedule and even
into the purchasing of coal (i.e., sulfur, ash, chlorine charac-
teristics) . Some of the current difficulties with lime/limestone
FGD systems relate to poor operating practices, unnecessarily
complex operating procedures, or both. In some cases, although
the equipment has been correctly installed, it rapidly deterio-
rates and breaks down due to improper O&M practices. The
operating characteristics of the FGD system can be established
during the initial startup period, which is also a time for
finalizing operating procedures and staff training. Once steady-
state operating conditions are reached, the system must be closely
monitored and controlled to ensure proper performance. During
periods of changing load or variation of any system parameter,
additional monitoring is required. Some standard O&M procedures
are described below.
° Varying Inlet SO., and Boiler Load. As boiler load is
increased, additional modules are placed in service
and, conversely, modules are removed from service when
boiler load is reduced. With each change in load, the
operator must check the system to verify that all
in-service modules are operating in a balanced condi-
tion. As the S02 concentration in the inlet flue gas
changes, the FGD system should be able to accommodate
and compensate for such changes. Operator surveillance
of system performance is needed, however, to verify
proper system response (e.g., slurry recirculation
pumps can be added and removed from service as the S02
concentration increases or decreases).
0 Verification of Flow Rates. The easiest method of
verifying liquid flow rates is for an operator to
determine the discharge pressure in the slurry
recirculation spray header with a hand-held pressure
gauge (permanently mounted pressure gauges frequently
plug in slurry service). Flow in slurry piping can be
checked by touching the pipe. If the piping is cold to
the touch at the normal operating temperature of 125°
to 130°F, the line may be plugged.
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Routine Surveillance of Operation. Visual inspection
of the absorbers and reaction tanks can identify
scaling, corrosion, or erosion before they seriously
impact the operation of the system. Visual observation
can identify leaks, accumulation of liquid or scale
around process piping, or discoloration on the ductwork
surface resulting from inadequate or deteriorated
lining material.
Mist Eliminators. Many techniques have been employed
to improve mist collection and minimize operational
problems. The mist eliminator can be washed with a
spray of process makeup water or a mixture of makeup
water and thickener overflow water. Successful,
long-term operation without mist eliminator plugging
generally requires continuous operator surveillance,
both to check the differential pressure across the mist
eliminator section and to visually inspect the appear-
ance of blade surface during shut down periods.
Reheaters. In-line reheaters are frequently subject to
corrosion by chlorides and sulfates. Plugging and
deposition can also occur, but are more rare. Usually,
proper use of soot blowers prevents these problems.
Reagent Preparation. Operational procedures associated
with handling and storage of reagent are similar to
those of coal handling. Operation of pumps, valves,
and piping in the slurry preparation equipment is
similar to that in other slurry service.
Pumps, Pipes, and Valves. Operating experience has
shown that pumps, pipes, and valves can be significant
sources of trouble in the abrasive and corrosive
environments of a lime/limestone FGD system. The flow
streams of greatest concern are the reagent feed
slurry, the slurry recirculation loop, and the slurry
bleed streams. When equipment is temporarily removed
from slurry service, it must be thoroughly flushed.
Thickeners. Considerable operator surveillance is re-
quired to minimize the suspended golids in the
thickener overflow so that this liquid can be recycled
to the system as supplementary pump seal water, mist
eliminator wash water, or slurry preparation water.
For optimum performance, the operator must maintain
surveillance of such parameters as underflow slurry
density, flocculant feed rate, inlet slurry
characteristics, and turbidity of the overflow.
Waste Disposal. For untreated waste slurry disposal,
operation of both the discharge to the pond and the
return water equipment requires attention of the
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operating staff. In addition to normal operations, the
pond site must be monitored periodically for proper
water level, embankment damage, and security for
protection of the public. Landfill disposal involves
the operation of secondary dewatering equipment.
Again, when any of the process equipment is temporarily
removed from service, it must be flushed and cleaned to
prevent deposition of waste solids. For waste treat-
ment (stabilization or fixation), personnel are re-
quired to operate the equipment and to maintain proper
process chemistry.
° Process Instrumentation and Controls. Operation of the
FGD system requires more of the operating staff than
surveillance of automated control loops and attention
to indicator readouts on a control panel. Manual
control and operator response to manual data indication
are often more reliable than automatic control systems
and are often needed to prevent failure of the control
system. Many problems can be prevented when an opera-
tor can effectively integrate manual with automated
control techniques.
2.5.3.2 Initial Operations. Very seldom does a system perform
properly when it is first placed in service. Even though string-
ent quality control may be exercised during the construction
phase, it is usually necessary to optimize the control functions
and to correct minor problems. Although the individual components
may be completely checked out during construction tests, the
integrated system performance can be evaluated only when the
system is placed in operation. Compliance testing is normally
accomplished immediately after initial startup. Tests conducted
under the proposed normal operating procedures can verify the
procedures and familiarize the station staff with the system.
After the initial startup tests have established a norm for
system operation, additional testing is conducted for two pur-
poses: to verify performance guarantees and to demonstrate
continuing compliance with regulations.
2.5.3.3 Startup, Shutdown, Standby, and Outage. Startup and
shutdown are two nonsteady-state operating modes that occur
frequently. Furthermore, two nonoperating conditions that
necessitate action by the operating staff are system standby and
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extended outage. Each of these situations is of special interest
to the FGD operating staff.
0 Startup and Shutdown. Before flue gas is introduced
into the system, slurry is added as a "lean" stream
(low slurry solids content). A prerequisite to
starting slurry flow is the initiation of the limestone
grinding or lime slaking to ensure the availability of
slurry feed. After integrated operation begins and
reaction product solids are permitted to build up to a
specified control level/ the staff must be ready to
process the slurry bleed stream (i.e., slurry purged
for waste disposal). When the system is placed in
service, the operating staff must be available to
monitor system response as boiler load is increased.
As the flue gas flow rate through the modules
approaches the maximum design value, additional modules
are systematically brought into service. As boiler
load is reduced in preparation for unit shutdown, the
startup sequence is executed in reverse.
° System Standby. A module that is ready to process flue
gas is said to be on standby. The module may have been
removed from service because of a reduction in station
load and is now prepared for service because of an
anticipated increase in load. When a module is removed
from service because of a load reduction, the slurry
bleed stream must be terminated and the bleed line
flushed. When a module is brought into service, the
operator must prepare the bleed stream line to accept
flow.
0 Extended Outage. Additional attention is necessary
when a module is removed from service for an extended
period. The slurry recycle pumps and the recycle line
should be drained and flushed. During the outage, the
operating staff should conduct inspections of equipment
that is normally inaccessible.
2.5.3.4 System Upsets. Upsets are associated with the boiler,
particulate control system, the FGD system, or the waste disposal
system. A boiler "trip" (actuated shut-off of equipment item)
will terminate the flow of flue gas through the FGD system.
Except for the possible discharge of unreacted slurry to the
waste processing equipment, there should be no adverse impact on
the FGD system. Transient conditions causing an increase in flue
gas flow may produce scaling of the mist eliminator or excess
liquid carryover. A trip of the upstream particulate control
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device can result in a system shutdown because the FGD system
will generally not be able to withstand the impact of fly ash
{increase in solids loading) for an extended period of time.
Inability of the FGD system to process flue gas can lead to a
boiler upset and removal of the unit from service. Failure of a
single module can lead to a reduction of unit/station output.
The inability to process slurry bleed for waste disposal could
impair FGD operations and station output due to waste slurry
buildup. Since waste processing systems usually incorporate some
spare capacity, station output should only be reduced, at worst.
2.5.3.5 Operating Staff and Training. The size, experience
level, responsibilities, and training of the operating staff are
significant factors in FGD system performance. In staffing, the
absorber and waste disposal operations must be considered sep-
arately. In addition to the normal complement of equipment
operators and supervisory personnel on the operating crew of each
shift, certain specialists should always be available to assist
them. Chemical engineers are essential for evaluating system
operating conditions. Chemical laboratory technicians are needed
to analyze the process chemistry.
2.5.3.6 Preventive Maintenance Programs. Preventive maintenance
is the practice of maintaining system components in such a way as
to prevent malfunctions during periods of operation and to extend
the life of the equipment. The goal of preventive maintenance is
to increase availability of the FGD system by eliminating the
need for emergency repair ("reactive maintenance").
The term preventive maintenance is synonymous with periodic
maintenance. Such procedures may be as simple as lubrication of
a pump or as complex as complete disassembly for inspection and
overhaul. Some of the more important preventive maintenance
procedures by subsystems are summarized in the following sections;
0 Absorbers. Of primary concern in the absorber module
is the integrity of the structural materials. Main-
tenance personnel should enter and inspect the absorber
module at least semi-annually.
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Mist Eliminators. Scale deposits typically are the
chief maintenance factor with mist eliminators. The
mist eliminator may be subject to nonuniform flow or a
faulty wash system. Wash spray pressure should be
monitored. Mist eliminators should be inspected
during forced or scheduled storages.
Reheaters. Both in-line and indirect reheaters are
subject to scaling and corrosion. In addition to
visual inspection, pressure testing and measurement of
heat transfer efficiency are useful in quantifying the
magnitude of a reheater problem. In an indirect reheat
system, the mixing chamber and the air heating
equipment must be checked routinely.
Dampers, Fans, Ductwork, and Chimneys. All points in
the system must be checked for integrity of lining
materials and for damage resulting from collection of
condensation products in stagnant air spaces (e.g.,
duct elbows and corners). Components located in the
wet portion of the system are subject to scaling and
corrosion. Upstream fans and ductwork may be subjected
to erosion.
Reagent Preparation. Reagent preparation subjects the
ball mill or slaker to abrasive wear. Because the
equipment sees intermittent service, it should be
inspected visually each time it is placed in service.
Annual disassembly is also needed to check for
excessive wear.
Reagent Feed. Maintenance of the reagent slurry feed
system is critical because failure of this equipment
strongly impacts the FGD system operation. The slurry
storage tank should be checked daily for leakage and
associated equipment inspected for proper operation.
Pumps, Pipes, and Valves. Slurry pumps are normally
disassembled at least annually. The purpose of the
inspection is to verify lining integrity and to detect
wear and corrosion or other signs of potential failure.
Bearings and seals are checked but not necessarily
replaced. Pipelines also must be periodically dis-
assembled or tested in other ways (e.g., hand held
nuclear and ultrasonic devices) both for solids
deposition and for wear. Valves must be serviced
routinely, especially control valves.
Thickeners. Thickener coatings should be inspected
periodically to prevent corrosion. Drag rakes, torque
arms, and support cables must also be inspected for
wear.
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0 Waste Disposal Equipment. Secondary dewatering
devices, mixing components, and transport equipment
must also have periodic maintenance to check for
abrasive wear and solids deposition. Vacuum filters,
both drum and belt type, require periodic replacement
of the filter media. In a centrifuge, both the scroll
coating and the bowl surfaces are subject to wear.
° Process Instruments and Controls. All electronic
equipment (pH, flow, pressure, temperature, level,
vibration, noise, and continuous monitors) must be
calibrated periodically. Numerous installation and
maintenance techniques have proved beneficial in
ensuring the reliability of sensors. Ease of access to
the sensors is very important. The sensors should be
cleaned and calibrated routinely. Experience with
process instrumention and controls in FGD systems has
shown that a good preventive maintenance program begins
with daily operating procedures. Proper use of instru-
ments will include daily flushing of most instrument
lines in slurry service just before monitoring of
process variables. Routine comparison of the instru-
ments in a process stream with similar instruments in
parallel streams can point out incipient failures.
Operating data, especially from the startup test
program, can also indicate potential problem areas.
2.5.3.7 Unscheduled Maintenance. Even the most rigorous
preventive maintenance program will not prevent random failures
to which the maintenance staff must respond. Most malfunctions
are correctable by unscheduled (reactive) maintenance. In some
situations, usually during initial system startup, design modifi-
cations may be required to bring the system into compliance with
operating standards. Each subsystem of the FGD system is subject
to malfunctions from a variety of causes. The discussion that
follows introduces these problems and the probable responses.
0 Absorbers. Structural failure of absorber internals
and recycle pump suction screens have occurred as a
result of excessive vibration, uncorrected corrosion
damage, or high pressure differentials. These malfunc-
tions must be repaired immediately before operation is
resumed.
0 Mist Eliminators. Failure of the mist eliminator is
typically due to scaling and plugging. The scale may
be removed either by thorough washing or by mechanical
methods, in which maintenance personnel enter the
absorber and manually chip away the scale deposits.
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Reheaters. Reheater malfunctions include tube failures
in in-line reheaters, damper problems in bypass reheat,
or nonuniform flows in indirect reheaters. Correction
of these problems will probably necessitate changes in
equipment design.
Fans. Fans can develop vibrations resulting from
deposition of scale in wet service or from erosion of
blades in dry service. The cause of the vibration must
be eliminated and the fan repaired and rebalanced.
Ductwork. Most problems associated with ducts develop
over a long period. Sudden or gross failures, such as
a major leak, call for immediate repair. Temporary
repair or patching may suffice until the next scheduled
outage. Acid condensation in a chimney can cause
lining deterioration and subsequent damage to the base
metal. These problems are usually identified during
preventive maintenance inspections and require
long-term solutions.
Reagent Feed. Malfunctioning components such as ball
mills or slakers must be repaired in accordance with
the manufacturer's instructions. Some facilities have
experienced trouble with plugging of the lime or
limestone feeder due to intrusion of moisture. Correc-
tion of these problems will probably necessitate
changes in equipment design.
Pumps, Pipes, and Valves. Excessive wear of the
impeller or separation of the lining from the pump
casing is a common problem. Operation of slurry
pipeline with insufficient flow velocity can cause
clogging. High flow velocity or extended service can
cause erosion. Malfunction and binding of a valve
actuator are typically caused by wear-induced mis-
alignment .
Thickeners. The thickener underflow can become plugged
because of excessive solids in the slurry or failure of
the underflow pump. A plugged underflow or rapidly
settling waste solids will produce a "heavy" blanket in
the bottom of the thickener. The rake must then be
raised so that the torque remains within acceptable
limits. If the torque cannot be kept within limits,
the thickener must be drained and the sludge blanket
removed manually.
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SECTION 3
PERFORMANCE MONITORING
Performance monitoring is a major element in the O&M activ-
ities of every lime/limestone slurry FGD system. Monitoring the
FGD system is required to demonstrate compliance with applicable
standards as well as to demonstrate that the system meets the
vendor performance guarantees. Additionally, routine monitoring
can identify potential operating problems before they signifi-
cantly impact the performance of the system and/or the generating
unit. This section is devoted to lime/limestone slurry FGD
system performance indicators and their measurement. Addressed
in this section are the instrumentation systems that measure
process parameters, manual testing and continuous emission moni-
toring methods used for emission measurements, and recordkeeping
practices of the operator utility. This information is presented
from the perspective of the agency inspector. Namely, what
monitoring techniques will yield what kinds of data, how are
these data recorded and logged, and how to interpret these data
in terms of SO2 compliance status.
3.1 KEY OPERATING PARAMETERS AND THEIR MEASUREMENT
The key operating parameters can be described according to
the FGD circuits identified in Section 2.5 (FGD O&M Considera-
tions). The gas circuit parameters of importance are S0n, NO ,
X
opacity, 0^, gas volume, and pressure. The slurry circuit
parameters of importance are pH, solids, and slurry volume. The
measurement values associated with these parameters, when
assessed, give the entire picture of FGD system performance and
compliance status.
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3.1.1 Gas Circuit Parameters
3.1.1.1 S02• Coal-fired boilers governed by the revised NSPS
of June 1979 are required to continuously monitor S02 emissions
to demonstrate compliance with standards. In general, all FGD-
equipped, coal-fired, utility boilers are equipped with S02
continuous emission monitors. They generally take the form of
stack monitors. In many cases, FGD inlet and outlet S02 monitors
are provided to continuously measure S02 removal efficiency
across the system (and/or the individual absorber modules).
Theoretically, these monitors can be instrumented into the proc-
ess control network through feedforward or feedback reagent feed
control loops. To date, these control strategies have been
researched and developed and used intermittently in commercial
operations. However, simple slurry pH control (Section 3.1.2.1)
2
continues to provide adequate process control monitoring.
3.1.1.2 NO . A continuous monitor is used in the stack to
comply with NSPS monitoring requirements.
3.1.1.3 Opacity. To satisfy the NSPS continuous monitoring
regulations, the opacity at the outlet of the FGD system, (stack
monitor) must be measured every 10 seconds. The data must be
averaged and recorded every 6 minutes, with a minimum of 24
7
equally spaced data points being used in the average.
3.1.1.4 O2• An °2 monitor is used to convert continuous mon-
itoring pollutant (SO,, NO ) concentration values to NSPS units
(lb/10 Btu). The 02 basically serves as a diluent gas. For
existing sources, an 02 monitor is required only if the State
requires data for converting to the emissions standard. The
equations used for this conversion are shown in Appendix B. The
02 monitor must be located at a point where measurements can be
made that are representative of the pollutant gases sampled by
the S0_/NO monitors. The 0_ monitor sampling point location
fa X »
conforms best with this requirement when it is at approximately
the same point in the duct as the SO /NO system. The 0_ gas
^ X fa
sample may be extracted from a different duct location if the
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stack gas is nonstratified at both locations and there is no
leakage of air into the duct between the two sampling points. If
the 02 monitor sampling point is at a different location from the
SO,/NO sample point and stratification exists in the duct, a
to X
multipoint extractive probe must be used for sampling. This is
also true for the monitoring system when the 02 and S02/N0x
monitors are not of the same type (i.e., one is extractive and
the other in-situ).^ A C02 monitor can also be used in place of
the 02 monitor.
3.1.1.5 Gas Flow Rate. The FGD system must continuously re-
spond to variations in gas flow rate. If multiple absorbers are
used, a dependable system to balance flow rates between parallel
modules must be provided. Since the boiler and FGD system are
often designed as separate units and frequently have separate
control rooms, controller coordination is essential."*
The flue gas flow rate is a major operating variable and is
controlled in proportion to the generating unit load by adjusting
control dampers on the unit or FGD booster fans (see Section
2.4.2.1). The volumetric flow rate can be estimated from the
stack gas velocity or, alternatively, from the fan performance
curves provided by the manufacturer. The latter procedure should
be used only as a check to validate the data from the first
method.
Gas pressure sensors are extremely important as a means of
gas flow rate indication, load-following control, and problem
indication. The simplest method, and the one used in most FGD
systems to equalize gas flow through the multiple modules, is the
use of pressure drop. The total pressure drop through a module
is the sum of the losses through the inlet and outlet ductwork,
absorber, mist eliminator, and reheater (if present). Each of
these losses is a function of the gas flow treated by the module.
Modules operating in parallel generally have equal pressure drops
because of identical modular designs.
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3.1.2 Slurry Circuit Parameters
3.1.2.1 gH. Slurry pH is the most important control parameter
in lime/limestone slurry processes. Measurement of pH in slurry
service is more difficult than pH measurements in many other
process applications. The pH electrodes are fragile devices,
easily damaged by extreme weather conditions, floating debris,
and the slurry environment. Slurry can also form a deposit on
the electrodes, acting as an electrical insulator and giving a
false value of the electrode potential. For this reason, it is
essential that pH electrodes be kept clean. However, despite
these limitations, slurry pH is universally accepted because of
its simplicity and widespread use. The pH measurement location
is an important consideration. There are three main choices:
(1) the spent slurry upstream of the reaction tank, (2) the fresh
slurry feed to the absorber, and (3) in the slurry reaction tank
itself. The favored choice of the utility industry is the
reaction tank.
3.1.2.2 Slurry Flow Rates. Measurement of slurry flow rates is
vital to the optimization of the process. The flow rate of fresh
slurry is perhaps the most important control application; however,
the flow rates of slurry recirculation and slurry bleed streams
are also vital control operations. The slurry flow rates are
used to control the absorber L/G (see Section 2.3.2.2) which is a
vital operational and performance factor.
3.1.2.3 Solids Content. There are three areas where the solids
content of the slurry is controlled: slurry feed, slurry recircu-
lation, and thickener underflow. Once the stoichiometric ratio
is properly maintained, the solids level can vary without being
critical to the operation of the absorber. A consistent slurry
solids level, along with proper stoichiometry, can reduce plugg-
ing and deposits in the absorber, minimize erosion, and reduce
3
the volume of solid waste.
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3 . 2 INSTRUMENTATION
To date, the extent of instrumentation used on lime/lime-
stone FGD processes has been relatively limited. Moreover, much
of the instrumentation used in existing systems have suffered
reliability problems. This section describes the different types
of instrumentation used for the measurement of some of the impor-
tant performance monitoring parameters addressed in Section 3.1.2.
Instrumentation described include process control applications
for monitoring pH, slurry flow rates, and solids content. S02
monitors are addressed in Section 3.3.
3.2.1 pH Instrumentation
There are two types of pH sensors: immersion (dip-type) and
o
flow-through. The immersion sensor is merely inserted into a
tank and can be removed for maintenance and calibration. A
flow-through sensor depends upon a continuous flow in the sample
line. Both have advantages and disadvantages. The immersion
sensor is easier to operate and maintain. Performance can also
be improved by locating the sensor in a special sampling tank, by
using redundant sensors, and by frequent cleaning and calibration.
The flow-through type pH sensor is prone to wear and abrasion.
Maintenance to insure good performance of flow-through sensors is
much easier when (1) the sample lines are short and relatively
large in diameter, (2) the sample taps are located at the top or
side of the slurry line, (3) back-flushing capability is provided,
and (4) a deflector bar is installed upstream from the sensor to
reduce erosion. Redundant sensors are also desirable for the
flow-through type but are not as easy to provide.
Practice has differed in regard to both the method and
frequency of cleaning the pH sensors to remove scale. Ultrasonic
self-cleaning devices have been used, but in numerous cases have
caused cell breakage. The best method seems to be manual removal
and washing with acid on a regular schedule. Lime systems are
less susceptible to scale formation problems on sensor elements
than limestone. In many existing systems, improper design limits
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the access to the pH sensors, resulting in inadequate service.
Some utilities have reported the buildup of a film on the probes
of immersion sensors. A properly designed electrode station
should have easy access for pH sensor maintenance. If possible,
each pH sensor should have a maintenance station equipped with a
workbench, a cabinet to hold spare parts, small tools, and stand-
ardizing solutions. Tables 3.2-1 and 3.2-2 summarize the pH
instrumentation used in a number of representative lime and
limestone slurry FGD systems.
3.2.2 Slurry Flow Rates
Instrumentation measuring slurry flow fall into three broad
categories: mechanical measurement of pressure differential,
electronic measurement, and measurement in open channels. Each
category has its specific applications.
Mechanical flowmeters are not suitable for abrasive slurry
environments. The more acceptable meters for this service are
electronic devices. Electronic measurement of flow rate are
accomplished with Doppler-effeet ultrasonic meters and electro-
magnetic flowmeters. The Doppler-effeet ultrasonic meter is a
fairly new development for slurry applications. The principal
advantage of this device is that the electrodes are attached to
the outside of the pipe through which the slurry is flowing;
there is no penetration of the pipe. The electromagnetic flow-
meter, or "magnetic meter," is the best proven instrument avail-
able for the measurement of pressurized slurries. It consists cf
a stainless steel pipe section lined with an electrically insula-
ting material. The magnetic meter does not require installation
in straight piping. It has no operating parts in contact with
the fluid, produces very little pressure drop, and is fairly
accurate. The only disadvantage of the magnetic meter is its
high capital cost and the closer attention required for instru-
ment calibration.
3.2.3 Solids Content
All lime/limestone FGD systems include instrumentation for
monitoring the solids level of fresh feed slurry, recycle slurry,
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TABLE 3.2-1. pH INSTRUMENTATION ON LIME SLURRY FGD SYSTEMS2
pH Electrode Assembly
Plant name
Manufacturer
Type
Location
Single/
multiple
Cleaning type
Pleasants 1 and 2
Uniloc
Flow-through
Absorber inlet,
outlet
Multiple
Ultrasonic
Four Corners 1, 2, and 3
Uniloc
Immersion
Slurry bleed
Multiple
Manual
R. D. Green 1 and 2
Leeds &
Northrup
Immersion
Reaction tank
Multiple
Ultrasonic
Conesville 5 and 6
Foxboro
Immersion
Slurry bleed,
reaction tank
Multiple
Manual
Coal Creek 1 and Z
Uniloc
Immersion
Reaction tank
Multiple
Ultrasonic
Elrama
Uniloc
Flow-through
Slurry bleed
Single
Ultrasonic
Phillips
Uniloc
Flow-through
Slurry bleed
Single
Ultrasonic
Green River
Uniloc
Immersion
Reaction tank
Multiple
Manual
Cane Run 4
Uniloc
Immersion
Reaction tank
Multiple
Manual
Mill Creek 3
Uniloc
Immersion
Reaction tank
Multiple
Air
Paddy's Run 6
Uniloc
Immersion
Reaction tank
Multiple
Manual
Clay Boswell 4
Uniloc
Immersion
Reaction tank
Multiple
Ultrasonic
Milton R. Young 2
Uniloc
Immersion
Slurry bleed
Single
Manual
Bruce Mansfield 1 and 2
Uniloc
Flow-through
Slurry bleed
Single
Manual
Bruce Mansfield 3
Uniloc
Immersion
Reaction tank
Multiple
Manual
Hunter 1 and 2
Uniloc
Flow-through
Slurry bleed
Single
Ultrasonic
Huntington 1
Uniloc
Flow-through
Slurry bleed
Single
Ultrasonic
-------
TABLE 3.2-2. pH INSTRUMENTATION ON LIMESTONE SLURRY FGD SYSTEMS3
Plant name
Manufacturer
Type
Location
Single/
multiple
Cleaning type
Tombigbee 2 and 3
T. B. I.
Flow-through
Reaction tank
Single
None
Apache 2 and 3
Great Lakes
Instrument Co.
Immersion
Quencher sump
Single
Manual
Laramie 1 and 2
Great Lakes
Instrument Co.
Flow-through
Recirculation
slurry
Single
Ultrasonic
Craig 1 and 2
Uniloc
Immersion
Reci rculation
slurry
Single
Ultrasonic
Powerton 51
Uniloc
Immersion
Reci rculation
slurry
Single
Ultrasonic
Petersburg 3
Leeds & Northrup
Flow-through
Recirculation
slurry
Multiple
Ultrasonic
LaCygne 1
Uniloc 320-K-l
Flow-through
Reci rculation
slurry
Multiple
Water flush
Jeffrey 1 and 2
Uniloc
Immersion
Reaction tank
Single
Ultrasonic
Lawrence 4 and 5
Uniloc
Immersion
Reaction tank
Multiple
Ultrasonic
Sherburne 1 and 2
Uniloc
Flow-through
Reci rculation
slurry
Single
Manual
Coronado 1 and 2
Uniloc
Flow-through
Reci rculation
slurry
Multiple
Ultrasonic
San Miguel 1
Leeds & Northrup
Flow-through
Recirculation
slurry
Single
Ultrasonic
Sikeston 1
Leeds & Northrup
Flow-through
Reci rculation
slurry
Single
Ultrasonic
Winyah 3
Leeds & Northrup
Flow-through
Recirculation
slurry
Multiple
Ultrasonic
Winyah 4
Leeds & Northrup
Flow-through
Reaction tank
Multiple
Ultrasonic
R. D. Morrow 1
and 2
Leeds & Northrup
Immersion
Reaction tank
Single
U1trasonic
Marion 4
Uniloc
Flow-through
Recirculation
slurry
Single
Manual
Southwest 1
Beckman/Foxboro
Immersion
Reaction tank
Multiple
Manual
Dallman 3
Beckman
Flow-through
Recirculation
slurry
Multiple
Water flush
Sandow 4
Uniloc
Immersion
Reaction tank
Single
Ultrasonic
-------
and thickener underflow streams. Densinometers are used to
monitor and control the solids in slurry streams and tanks.
Slurry density can be measured directly with special differential
pressure instruments, requiring a minimum liquid depth of 6 ft to
measure a span of 0.1 specific gravity units. Ultrasonic devices
directly measure the suspended solids. Vibrating reed instru-
ments measure the dampening effect of the slurry on vibrations
from an electrically driven coil. Nuclear density meters which
measure the degree of absorption of gamma rays from a radioactive
source are the most popular due to ease of application. The
meter can be strapped to a pipe without insertion into the pipe
line. The only problem with these meters has been their periodic
inaccuracy and inconsistency. At several facilities, density
measurements are often verified by manual measurements (e.g.,
laboratory analysis of grab samples).
3.3 TESTING AND MONITORING
This section describes manual testing and continuous emis-
sions monitoring (CEM) methods used to collect FGD gas stream
data.
3.3.1 Manual Testing
Manual sampling and analysis of the flue gas at the inlet
ana outlet of the FGD system are required periodically to eval-
uate its performance. Sampling ports must be incorporated during
the design and construction of the FGD system to facilitate
several sampling procedures which require a variety of probes and
collection equipment. Sampling operations for FGD systems are
aimed primarily at characterizing the gas flow, particulate mass
loading and size distribution, and gas composition. The gas flow
at the sampling points must be stable to ensure collection of a
representative sample and obtain accurate information regarding
flow rate. Bends and expansion and contraction zones in the flow
path can induce secondary flows such as vortices, rotation, and
large eddies. Sufficiently long runs of a straight uniform duct
105
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are recommended at the sampling location before and after the
sampling point. Another factor is the ease in the operation of
the sampling equipment. Proper orientation of the sampling port
and availability of a clear platform area near the port are other
necessary'criteria for testing.
Most interfaces for sampling from ducts are designed to be
compatible with 3-inch Schedule 40 pipe nipples used as sampling
ports. Occasionally, an experimental system has required a 4- or
6-inch opening. The size of the port necessary to insert a probe
also depends on the length of the port opening. Other considera-
tions include availability of diametrically opposite ports so
Q
that opacity monitors may be installed, if necessary.
Table 3.3-1 presents a list of gas stream characteristics
and measurement methods for lime/limestone FGD systems. Of
particular interest to FGD technology is the SO2 manual sampling
method. EPA Method 6 is the reference method for determining
emissions of SC2 from all stationary sources except sulfuric acid
plants. In sampling for SO2, a gas sample is taken at a single
sampling point located at the center of the stack or no closer to
the wall than 3.28 feet. The sample must be extracted at a
constant volumetric rate. This requires adjustments of the
extraction rate to compensate for any changes in stack gas veloc-
ity. As the gas goes through the sampling apparatus, the sulfuric
acid (f^SO^) mist and sulfur trioxide (SO^) are respectively
removed using glass wool (borosilicate or quartz) and a solution
of isopropanol? the S02 is then removed by a chemical reaction
with a hydrogen peroxide solution. The sample gas volume is
measured by a dry gas meter. Upon completion of the run, the
H.SO, mist and SO, are discarded, and the collected material
2 4 3
containing the SO, is recovered for laboratory analysis. The
concentration of SO^ in the sample is determined by a titration
method.
For determination of the total mass emission rate of S02,
the moisture content and the volumetric flow rate of the exhaust
gas stream must be measured. The minimum sampling time is 20
106
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TABLE 3.3-1. SUMMARY OF MANUAL EMISSIONS MEASUREMENT METHODS FOR AN FGD SYSTEM ON A
COAL-FIRED UTILITY BOILER
Measurement
Sampling method
Apparatus
Reference
Traversing points
Method 1
40 CFR 60, Appendix A,
July 1, 1985
Velocity and volumetric
flow rate
Method 2
Type "S" pi tot tube
40 CFR 60, Appendix A,
July 1, 1985
Particulate mass
loading
Method 5
Sampling train cyclone/
filter holders (>225°F)
40 CFR 60, Appendix A,
July 1, 1985
so2
Method 6
Pyrex probe, impingers
40 CFR 60, Appendix A,
July 1, 1985
NO
X
Method 7
Pyrex probe, collection
flask
40 CFR 60, Appendix A,
July 1, 1985
SO^, SO^, and H^SO^
Method 8
Pyrex probe, impingers
40 CFR 60, Appendix A,
July 1, 1985
Opacity
Method 9
Visual, qualified observer
40 CFR 60, Appendix A,
July 1, 1985
-------
minutes per sample and two separate samples constitute a run.
Three runs are required, resulting in six separate samples. An
interval of 30 minutes is required between each sample. Longer
sampling times may be required if a larger sample is needed.
SO^ concentrations of 50'to 10,000 parts per million (ppm)
can be determined with this method. Collaborative tests have
shown that an experienced test team using quality controls can
conduct a source test for SC^ within an accuracy range of ±4
percent.
Other sampling methods are available which utilize different
chemical solutions, such as a sodium hydroxide solution, to trap
the SO^. EPA Method 8 may also be used as an alternative method
for stationary sources. Some states specify a sampling method
that collects H,,S04, SC>3, and S0n. The analysis then gives total
SO .
x
3.3.2 Alternative Methods
There is an alternative manual method to EPA Method 6. This
is the proposed Method 6B. In this method, intermittent samples
are drawn through a modified Method 6 sample train using a twentv-
four hour timer. This method measures CO2 in addition to S02.
The samples collected in the train are recovered and analyzed on
a daily basis. Collaborative testing to demonstrate this method
is now underway. The high capital intensity of a conventional
CEM program could be replaced with a low cost but equally
O&M-intensive Method 6B testing program. Method 6B could also be
used as a back up to generate data during CEM outages, thus
eliminating the need for expensive parts inventory and highly
trained technicians.
3.3.3 Continuous Emissions Monitoring (CEM)
There are many instruments available for monitoring gaseous
emissions from stationary sources. Gas monitoring systems may be
either extractive, in-situ, or remote. The monitors utilize
various physical or chemical properties to detect and quantify
components in the flue gas, as shown in Table 3.3-2. These
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TABLE 3.3-2. PRINCIPLES USED IN GASEOUS EMISSION MONITORS3
Extractive systems
In-situ systems
Absorption spectroscopy
Nondispersive infrared
Differential absorption
Cross-stack
Differential absorption
Gas-filter correlation
Luminescence methods
Chemiluminescence (NO »
* /
Fluorescence (S02)
Flame photometry
In-stack
Second-derivative
spectroscopy
Electrocatalysis (02)
Electroanalytical methods
Polarography
Electracatalysis (02)
Amperometric analysis
Conductivity
Paramagnetism (02)
aMethods followed by the gas (in parentheses) indicate that the technique is
currently commercially applied only to that gas.
109
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methods may be used in-situ whereby the measurements are con-
ducted on the flue gas inside the stack, or extractive wherein a
sample is withdrawn from the stack. The basic problem common to
all CEM systems is that any sophisticated analytical technique
will suffer when exposed to a hostile flue gas environment (e.g.,
heat, humidity, corrosive gases, and fly ash). The challenge in
designing, installing, and operating a CEM system, therefore, is
to minimize the harsh effects of the stack environment, maximize
the precision and accuracy of the effluent pollutant measure-
ments, and accomplish both at a reasonable cost. To monitor SO^,
the CEM system must determine the concentration of the pollutant
and also the concentration of a diluent gas (02 or CC^).
Every CEM system can be divided into three components, as
shown in Table 3.3-3. The immediate drawback to the in-situ
system is the very fact that the analyzer is mounted on the
stack. The optical alignment of the light source and the
retroreflector is critical. This can be a problem on composite
stacks with fiberglass or stainless steel liners since these
liners have the ability to flex. A slotted pipe can be added
across the stack to insure the absolute alignment of the optical
components. Further, in in-situ systems, the optical components
on either side of the stack are exposed to the corrosive stack
gas. An air purging system is provided to keep the components
clean but periodic maintenance will still be required.
Extractive CEM systems depend on the reliable operation of
the sample interface. Many potential problems exist in an
extractive sample interface. The probe is constantly subjected
to a corrosive and erosive atmosphere. Carryover of slurry from
the FGD process can be a serious problem. Slurry which deposits
on the probe will scrub SC>2 out of the sampled gas. The buildup
of particulate and slurry solids will plug the probe. Shielding
the coarse filter with a baffle will reduce the problem. A
periodic blowback to purge the probe (air or steam) is also
common.
The sample pump is another point in the system that has
potential problems because it is subjected to constant wear.
110
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TABLE 3.3-3. CEM SYSTEM COMPONENTS
Sample interface
Analyzer
Data recorder
Insitu
Extractive
Mounting brackets
Probe
Strip chart recorder
Alignment devices
Filters
Pollutant (S02, N0x)
Data logger
Optical components
Moisture removal
Diluent (CO,,, 0^)
Remote (shared) computer
Retroreflectors
Sample line
Microcomputer
Blowers
Pump
-------
Preventive maintenance programs are necessary to keep the pumps
operable. The sample line and probe must be heated to prevent
condensation prior to the moisture removal system. The large
number of fittings needed to connect all of these components
contribute to leaks in the extractive interface. As a result,
this type of system will require constant attention although this
maintenance does not require special training.
A comparison of in-situ and extractive systems reveals that
neither system is superior overall. However, most stack moni-
toring systems are extractive rather than in-situ. A single
extractive analyzer can monitor one component in the gas stream
at more than one source, whereas a single in-situ analyzer can
monitor more than one component but only at a single source.
High levels (90 percent or greater) of reliability have been
reported for at least one of every type of CEM system in use.
The extent of trouble-free operation generally appears to be
directly proportional to the level of management commitment to
the ongoing maintenance of the CEM system.
3.3.4 Performance Specification Tests
Continuous monitoring instruments must pass the Performance
Specification Test requirements given in Part 60, Appendix B of
the Code of Federal Regulations (CFR). These tests evaluate the
performance characteristics of opacity, SO_, NO and 0„ or CO,,
monitors. There are three types of tests:
0 Performance Specification Test 1 - Transmissometer
Systems
° Performance Specification Test 2 - SO-/NO Systems
£ X
0 Performance Specification Test 3 - 0^ or CO2 Monitors
A detailed description of these tests is presented in the
"Continuous Air Pollution Source Monitoring Systems Handbook"
(EPA 625/6-79-005)J
112
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3.4 RECORDKEEPING PRACTICES AND PROCEDURES
The primary reasons for FGD recordkeeping are cost and
environmental compliance accountability. The types of records
kept may be in the form of strip charts, numerical data print-
outs, manual log books, and/or work order sheet files. The
collection frequency depends upon the data. Maintenance records
may be updated daily via log books or whenever work order sheets
are filed upon completion of a given task. Most utilities
collect S02, N0x, particulate, opacity and 02 continually using
continuous emission monitors in the form of strip charts or
computer disk or tape files.
The development of a CEM system extends beyond the choice of
a set of analyzers. The analyzers must measure emissions within
specified time periods. The measurements, however, must then be
recorded in some manner. After the data are recorded, they must
be converted into units of the emissions standard, (lbs/10^ Btu).
Calculated emission values that are in excess of the standard
must then be reported on a quarterly basis to the EPA Adminis-
trator. In addition, the guidelines stipulated in the Federal
Register (40 CFR, Part 60.7, Appendix B) require the reporting of
the following:
0 Time and magnitude of excess emissions
0 Nature and/or cause of excess emissions
0 Corrective and/or preventative action taken to prevent
their recurrence
0 Zero/span calibration values
0 Normal measurement data
° Log of inoperative periods
0 Repair and maintenance logs
0 Performance, test, calibration data
For sources subject to the June 1979 NSPS, calculated emis-
sions reports are required as 24-hour averages whether in excess
of the standard or not. A complete emissions monitoring system,
113
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therefore, requires some means of recording the analyzer data.
Strip-chart recorders have been used most often, but data loggers
and computer systems are beginning to become popular. Data
processors have been developed specifically to reduce the time
necessary to evaluate and report excess emissions.
A data reporting system may encompass anything from the
manual reduction of raw strip chart data and compilation of
associated data to the near fully automatic preparation of com-
plete excess emission reports, including most of the afore-
mentioned data requirements. The choice of the data reduction
and reporting system may be the most important factor in the
overall emission monitoring system, since it greatly affects the
amount of manual effort involved in meeting the NSPS require-
ments .
The data generated by the monitoring instruments give much
more information than is actually required. The actual data that
can be used to satisfy measuring requirements may be of three
types:
0 Instantaneous values taken at the end of each time
period
0 Values obtained by integrating data over each time
period
0 Values obtained by averaging a number of data points
over each time period
The method used will often be determined by the type ana-
lyzers purchased and by the recording method. The measuring
requirements are tied in with the recording requirements. A
consideration of both will dictate the choice of the complete
monitoring system.
A monitor may produce a continuous trace on a strip chart
for a 6-minute or 1-hour period; a larger amount of data may be
obtained than is actually used. The regulation, however,
specifies only the minimum number of points that need to be
averaged and recorded. It is often easier to design systems that
integrate the continuous data over the averaging periods.
114
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There are a variety of methods used to record data from
analytical devices. The strip-chart recorder is encountered most
frequently in continuous source monitoring applications. A
continuous analog record is obtained by using some type of chart
recorder.
Since the recorder is a part of the continuous monitoring
system, the response time, drift, and accuracy requirements
established in the EPA performance specifications must be con-
sidered when choosing the recorder itself. If a recorder is
chosen that has poor response time and limitations in recording
accuracy, the overall monitoring system will suffer. There are
many factors that contribute to the relative inaccuracy (relative
to the EPA reference method) of a monitoring system. The record-
ing system does not need to be one of these factors if a proper
choice of the system is made initially.
The analog chart recorders give a continuous record of the
signal produced by an analyzer. The digital recorder or data
logger, however, selects some value (either an instantaneous or
integrated value) after a given time period and records it. For
this reason, a digital system may be characterized as recording
data over intermittent periods. These periods may be short, a
tenth or hundredth of a second or less; but for such a short
period, the printed data produced might be unmanageable.
It should be noted that a data logger is not a computer or a
microprocessor. A computer can process data, convert it into
emission rates, and record it in specified formats. Data loggers
merely record data at specified intervals. There are two options
available on digital recorders that extend their utility. These
are an alarm-monitoring capability and the ability to print out
by exception. A data logger, therefore, could be set to send off
an alarm or print out data once a specified value is reached. It
could not, however, compute the emission rate by any specific
method and print it. A microprocessor or computing system would
be necessary in this case.
115
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The difficulty of detecting trends has been overcome in some
systems by recording the digital data on floppy disk or cassette
tape. The disk or tape can be read on a computer and the data
then can be graphed automatically with a plotter. This method
provides a convenient means of storing the continuous monitoring
record. Diskettes and cassette tapes are easily handled and
cataloged and detailed graphs need only be reproduced when
desired.
The most convenient method of handling continuous monitoring
data i.s with a data processor. Several firms involved in the
manufacture of stack monitors have seen the need for the instrumen-
tation that will rapidly average and compute data in terms of the
emission standard. There are two data processing methods that
generally are used in continuous monitoring systems. These are:
0 Analyzer - Analog-to-digital (A/D) large general
purpose computer or data processing system.
0 Analyzer - Dedicated continuous monitor data acquisition
system.
The dedicated systems may save time and money in the long
run. Many source operators will first purchase the gas analyzers
and rely on strip-chart output for the data-recording requirements.
If the monitoring system is working properly and the data are
reliable, consideration is given to a data processor in order to
reduce the amount of time spent analyzing what can amount to
volumes of data. Many operators have found it convenient to keep
the chart recorders to provide an easily interpreted record of
the trends occurring during the source operation. Cross checks
then can be made between the two systems; if either malfunctions,
the data may not be Icst."^
The problem of monitoring equipment malfunctions is a matter
of serious concern to the continuous monitoring program. Obvious-
ly, an improperly operating continuous monitor serves neither the
source operator nor the control agency. In order to keep aware
of the instrumental problems that inevitably develop, occasions
of instrument downtime, repair, or significant readjustment also
must be documented and explained in the quarterly report to EPA.
1.16
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Many agencies are now developing inspection programs for these
systems in an effort to insure that reliable emissions data can
be obtained.
The operator utility also must maintain a file of all of the
continuous monitoring data, including records of the Performance
Specification Test, adjustments, repairs, and calibration checks.
The file must be retained for at least 2 years and is required to
be maintained in such a condition that it can be easily inspected
by an agency field inspector.
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SECTION 4
INSPECTION METHODS AND PROCEDURES
This section presents detailed procedures and guidelines for
the inspection of lime/limestone slurry FGD systems. The objec-
tive of this section is to assist the agency inspector in his/her
duties of examining the FGD system, looking first for telltale
signs that might suggest misrepresentations of emissions such as
faulty monitors or leakage in or out of ducts, and looking sec-
ondly for factors in addition to S02 removal efficiency that
suggest poor reliability of the FGD system. If excess emissions
are reported, this section guides the inspector in collecting
information for the determination of causes for the problem and
the assessment of remedial action (s) taken by the utility. When
no excess emissions are reported, procedures suggested herein
allow the inspector to assess the preventive actions taken by the
utility. It is important that the inspector make specific obser-
vations and record pertinent data in order to make intelligent
decisions for resolving compliance problems or processing var-
iance requests.
The information in this section is presented in a practical
fashion that facilitates comprehension by regional/state agency
personnel; theoretical principles underlying the inspection
procedures are not discussed. The inspection procedures are
presented in a user-friendly format.
The section begins with a brief discussion on inspection
procedures for the overall plant and is followed with detailed
inspection procedures addressed by equipment area and equipment
items in the order presented previously in Section 2.4.2
(Existing Design Configurations). Inspection procedures for each
equipment item comprise an inspection checklist, an illustration
118
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(where applicable) showing the relative sizes of the associated
components, and brief supporting text. Performance parameters
addressed in the equipment inspection checklists are classified
under three categories (observation, process, and operation and
maintenance) to facilitate the interpretation and evaluation of
data obtained during inspections. The various checklists pre-
sented in this section are compiled together in Appendix C to
assist the inspector during an inspection.
The interpretation of the performance data observed and
collected by the inspector is discussed in the following section
(Section 5, Performance Evaluation and Problem Diagnosis/Correc-
tion) . The checklists in this section include references to
appropriate locations in Section 5 which address the significance
of the recommended inspection procedures. Section 6 (Model O&M
Plan) elaborates on the O&M practices surveyed by the inspector
during the inspection procedures. Section 7 (Safety) outlines
prudent safety procedures to be followed during the inspection.
4.1 GUIDELINES FOR OVERALL PLANT INSPECTION
Before actually performing an FGD system inspection, it is
advisable to collect general plant data such as information on
coal characteristics, boiler data, and system generation status
(see Sections 2.2, 2.5.1.1 and 2.5.1.2). Published sources of
this type of information include the Utility FGD Survey^ and the
Steam Electric Plant Factors^. Nonpublished but available
sources include the Energy Information Administration (EIA)
General Utility Reference File (GURF) data base and the utility
filed EIA Form 767 (formerly the Federal Power Commission [FPC]
Form 67). Table 4.1-1 shows a checklist containing types of
information that should be obtained prior to the FGD system
inspection.
In addition to general plant data, the plant layout and
accessibility should also be reviewed as this governs the ap-
proach and entry to the equipment (see Section 2.5.2). The
inspector should also review the recordkeeping procedures used by
119
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TABLE 4.1-1 GENERAL PLANT DATA
Boiler Data
0 Type of firing (pulverized, cyclone)
0 Boiler service load (base, intermediate, cycling, peak)
0 Date of commercial operation (nonth, year)
0 SCL emission limitation (lb/10 Btu) g
° Particulate emission limitation (lb/10 Btu)
° Opacity limitations (%)
0 Fuel firing rate at maximum continuous rating (tons/hr)
0 Heat rate (Btu/net kWh)
0 Average capacity factor (%)
° Gross generating capacity (MW)
° Outlet flue gas flow (acfm)
0 Outlet flue gas temperature (°F)
Fuel Data
° Average heat content (Btu/lb)
0 Average ash content (%)
° Average moisture content {%)
0 Average sulfur content (%)
° Average chlorine content {%)
General FGD System Data
° FGD process type (lime, limestone)
° Generation (first, second, or third)
0 Application (new/retrofit)
° Initial startup date
0 Commercial startup date
0 Total system design SOp removal efficiency (%)
0 Percent flue gas bypassing FGD system (%)
° Total system energy consumption (kWh)
° Annual reagent consumption (tons/year)
° Water loop type (open, closed)
° Waste disposal type (landfill, pond)
0 Solid waste generation rate (tons/hr - dry)
0 Total system makeup water consumption (gpm)
° Number of operators per shift
° Number of maintenance personnel per shift
° Maintenance philosophy (dedicated, rotated, pooled)
120
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the facility (see Section 3.4). Finally, the inspector should
inquire about the current status of operation of the FGD system
and recent status preceding the visit.
4.2 INSPECTION PROCEDURES
This section presents detailed inspection procedures for the
different equipment areas. The inspection procedures are ordered
sequentially by the FGD system equipment subsystems in order of
their appearance in Section 2.4.2. In the field, the actual
inspection will most probably be undertaken more according to
convenience rather than process logic. The office location of
the inspector's primary utility contact and the layout of the FGD
system usually dictate the most convenient starting point for the
inspection. Separate checklists are outlined for each equipment
area in light of this consideration.
An inspection of the control room at the facility should,
however, be undertaken prior to the inspection of the equipment.
The inspector should also note that not all plant control rooms
are centralized; some plants have decentralized control rooms
associated with specific operations (boiler, FGD, waste disposal,
etc.). The inspector should inquire about this. A control room
usually includes a process schematic above the main control panel
with warning or other indicator lights as well as parameter
readouts to display general operating status and/or problems
occurring in specific areas of the system. The "live" schematic
is supported by strip charts and meters fed by sampling devices
throughout the FGD system or at least the more critical areas.
Much of the process-related information pertaining to the equip-
ment checklists presented later in this section can usually be
obtained in the control room(s). Table 4.2-1 presents a check-
list to be followed when inspecting the control room.
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TABLE 4.2-1. CONTROL ROOM CHECKLIST
Ask the operator to point out the monitoring device displays spe-
cific to the FGD system.
Note any monitoring device displays that are not fn operation.
Ask the operator or other utility contact the reason the display
device is out of service and what action has been taken for correc-
tion.
Check for high/low readings on S02, particulate and opacity
monitoring devices (as compared to the design values).
If the facility has an integrated computerized control (ICC) system
equipped with CRT displays, ask to see sample readings for some
subsystems. Feel free to ask for explanations interpreting the
figures and numbers displayed.
4.2.1 Gas Handling and Treatment
4.2.1.1 Fans. Fans used in FGD systems vary in size depending
on the number of fans used and their service classifications,
e.g., unit or booster (see Section 2.4.2.1). Fans are generally
high-maintenance equipment items. Figure 4.2-1 shows an iso-
metric view of a typical centrifugal fan. Table 4.2-2 presents a
checklist for the actual fan inspection.
4.2.1.2 Scrubbers/Absorbers. The discussion in this section
focuses on absorbers because these are the most popular in second
and third generation systems. The SO^ absorber ranks third on
the list of equipment areas most likely to be the focus of an fcd
system forced outage (see Section 2.5.1). Many of the third
generation FGD systems include spare absorber modules to minimize
the impact of a single module forced outage". Absorbers are
considered to be very critical to FGD operation and perhaps
represent the most important area of interest to field inspec-
tors .
The dimensions of absorbers vary widely depending on the
type of absorber, the boiler gas flow, the number of absorbers
included in the system design, the process type (e.g., lime or
122
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FAN INLET
DOUBLE-WIDTH
ROTOR
MOTOR
FAN DISCHARGE
BACKWARD CURVED
BLADES
Figure 4.2-1. Isometric view of a typical centrifuaal fan.
123
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TABLE 4.2-2. FAN CHECKLIST
OBSERVATION
° Listen for excessive vibration. If the fan is not operating or if
it is not obvious whether the vibration is excessive or not,
consult with the utility contact. Ask if vibration/noise is moni-
tored. If so, what are the correct readings? Is there an alarm
cutoff?
Look for signs of unusually high levels of maintenance (e.g., worn
rotors on site, debris on and around housing, unusually worn access
doors).
° Check for signs of corrosion and note location. Look for holes at
intake/discharge and analyze duty (ID/FD) contribution.
PROCESS
° Note fan function, design application service, and location
(refer to Section 2.4.2.1).
Unit/booster
Centrifugal/axial
ID/FD
Wet/dry
0 What is the design/actual APa provided by each fan? (See Section
5.2.2.2 for significance.)
° What is the design/actual gas flow rate and temperature through
each fan? (See Section 5.2.2.1 for significance.)
° What is the design/actual energy consumption rate of each fan?
(See Section 5.2.2.9 for significance.)
OPERATION AND MAINTENANCE
° Inquire about the incidence of bearing failure, fan blade erosion/
corrosion, and rotor cracking. What were the contributing causes
of these problems? What remedial actions were taken or planned?
° Inquire about routine maintenance procedures (balancing, cleaning,
rotor/fan repair). What is the frequency of inspection?
aAP refers to pressure drop, typically measured in in. H^O for gas-side
operation.
124
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limestone) and the coal characteristics. A utility may choose to
install three 50 percent capacity absorbers (including one spare),
five 25 percent capacity absorbers (including one spare) or as
many as 12 absorbers (including one spare) for a given facility.
Spray towers need to be larger in height than packed towers for
similar applications because spray towers require a higher resi-
dence time for a given volume of flue gas to make up for the lack
of liquid/gas contacting area provided by packing materials.
Lime systems should have slightly smaller absorbers for a given
facility as compared to those for a limestone process because
lime is a more reactive reagent requiring a lower L/G ratio and a
lower residence time of the gas in the tower. A typical absorber
designed to accommodate 100 MW of boiler flue gas capacity may be
between 2 to 4 stories in height. The absorber may be rectang-
ular or cylindrical in shape. A horizontal configuration (see
Figure 2.4-4b) may be adopted instead of the more common vertical
configuration (see Figure 2.4-4a).
Figure 4.2-2 shows the dimensions of a typical tray tower
absorber. Because typical absorbers are likely to be several
stories high, the inspector may not be able to collect all the
data for the absorber in entirety at one time. It is often
easier to inspect all components found at each level of the tower
before moving to the next level. Table 4.2-3 provides an
inspection checklist for absorbers.
4.2.1.3 Mist Eliminators. Mist eliminators are the most trou-
blesome of all FGD system components (see Section 2.5.1, Table
2.5-3). They are prone to scaling, plugging, breakage, and
deformation from high temperature excursions. Figure 4.2-3 is an
illustration of a typical mist eliminator section. The sections
are replaceable so that only those sections that are permanently
damaged need to be changed rather than the entire mist eliminator
portion which could cover an area of approximately 400 sq. ft.
The mist eliminator is typically accessed through access doors
usually on the third or fourth level of the absorber. Table
4.2-4 presents a checklist for mist eliminators.
125
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MIST ELIMINATOR
TRAY MIST
PRECOLLECTOR
INTERNAL SPRAY
HEADER AND NOZZELS
INLET GAS FLOW
20 ft
20 ft
OUTLET
GAS FLOW
40 ft
EXTERNAL
SPRAY HEADER
SIEVE
TRAYS
SUMP
DRAIN TO REACTION TANK
Figure 4.2-2. Typical tray tower absorber.
126
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TABLE 4.2-3. SCRUBBER/ABSORBER CHECKLIST
OBSERVATION
° Observe any tools, debris, or other materials that may suggest
excessive maintenance problems: scaling, plugging in spray nozzles
and headers — look around for broken or eroded spray nozzles.
(See Section 5.2.4.3 for significance).
° Look for signs of materials failure (e.g., corrosion, liner
bubbling or peeling). Note the location of the failure.
0 Observe any signs of leaky piping due to erosion (e.g., corrosion,
accumulation of liquid or scale around process piping).
° Look for signs of absorber slurry leakage due to erosion/corrosion
(e.g., discoloration on the absorber outside walls).
PROCESS
° What are the design/actual absorber inlet particulate grain loading
and SO2 concentration? (See Section 5.3.1.1 for significance.)
0 What are the design/actual absorber outlet particulate and S0?
emission levels? (See Section 5.3.1.1 for significance.)
0 What is the AP across the absorber? (See Section 5.2.2.2 for
significance.) Note if AP is low or high (if not sure of the
acceptable AP range, ask the operator or other utility contact).
0 What is the pH and slurry solids content in the absorber reaction
tank? (See Sections 5.2.2.3 and 5.2.2.5 for significance.) Check
if these values are high/low.
0 Inquire about the slurry and gas flow rates to determine the L/G
ratio. (See Sections 2.3.2.2 and 5.2.2.4 for significance.)
OPERATION AND MAINTENANCE
0 Ask if absorbers have been experiencing chronic problems of any
kind. If so, what remedial actions were taken or planned? Inspect
internals of any absorbers which may be shut down by looking
through the access door with a flashlight.
0 If absorbers are idle, ask why (i.e., spare, demand, scheduled
outage, forced outage).
0 Are any instrumentation problems evident (pH, aP, % solids, slurry
flow, gas flow)?
c Inquire about routine maintenance procedures. Check on the
frequency of plant inspection.
127
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CHEVRON VANES
'WASHER LANCE
BULK ENTRAPMENT SEPARATOR
Figure 4,2-3, Typical mist eliminator section
(baffle-type, continuous vane).
128
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TABLE 4.2-4. MIST ELIMINATOR CHECKLIST
OBSERVATION
° Observe any discarded mist eliminator sections that may be nearby.
Inspect for excessive plugging/scaling on vanes, breakage due to
structural stress or deformation due to high temperature
excursions. (See Section 5.2.4.3 for significance.)
0 If absorber is shut down, inspect mist eliminator sections for
signs of plugging/scaling, breakage, deformation, as well as
erosion/corrosion.
0 If possible, inspect downstream equipment for signs of excessive
mist eliminator carryover in the form of condensation packets and
solids deposits.
PROCESS
0 What is the design/actual AP? (See Section 5.2.2.2 for signifi-
cance.) Note if it is low or high (if not sure of the acceptable
AP range, ask operator or refer to Table 5.2-3).
0 Ask if the absorber pH is operated above or below the design range.
(See Section 5.2.2.3 for significance.)
0 Inquire about the flue gas velocity. (See Section 5.2.2.1 for
significance.) How does this compare with the design rate?
OPERATION AND MAINTENANCE
° Ask about mist eliminator automatic and manual washing techniques
and practices.
0 Check on wash water source (see Section 5.2.2.8 for significance.)
Is it fresh make-up, process recycled water or a blend? Does the
plant water loop type (open, closed) have any impact on washing
practices?
0 If problems have occurred, inquire about remedial actions taken or
planned.
° Inquire about routine maintenance procedures. How often are the
mist eliminators inspected?
129
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4.2.1.4 Reheaters. Indirect bet air rebeaters which operate on
ambient air are seldom responsible for system shutdowns. In-line
reheaters, however, are troublesome equipment items. Although
they require less energy to elevate the flue gas temperature
above dew point (typically 125°F), they are subject to the haz-
ards associated with the scrubbed gas environment. In-line
reheaters are subject to corrosion from acid attack and solids
accumulation resulting from carryover from inefficient mist
eliminators and/or process chemistry problems. The impact this
has on the reheater is a loss of heat exchange capacity and
materials failure {e.g., steam tube failure). The impact on the
FGD system may be an increase in AP, a loss of effective flue gas
reheat, increased energy consumption, or possibly a complete unit
shutdown. Reheaters are usually located above the mist eliminator
section at the top of the absorber or in the exit duct just
downstream of the absorber. In-line reheat systems are located
in the ductwork at or near the top of the absorber (see Figure
2.4-8a), whereas indirect hot air reheat systems are located
anywhere along the exit duct downstream of the absorber (see
Figure 2.4-8b). Table 4.2-5 presents an inspection checklist for
reheaters.
4.2.1.5 Ductwork and Dampers. Ductwork and dampers also account
for a large proportion of FGD system outage hours (see Section
2.5.1, Table 2.5-3). The duct areas of greatest concern are at
the scrubber/absorber inlet where the hot dry flue gas first
encounters the slurry sprays. This area, called the wet/dry
interface, is typically found near the bottom of the absorber
just above the reaction tank. During the inspection, it would
probably appear on the second story of the FGD system. The other
duct areas of importance are the absorber outlet ductwork leading
to the stack, particularly where the reheat gas encounters the
wet scrubbed flue gas. Any wet gas ductwork requires special
attention. All dampers need to be inspected, particularly the
isolation dampers before and after the absorber sections. Again,
only dampers seeing wet gas require special attention. As shown
130
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TABLE 4.2-5. REHEATER CHECKLIST
OBSERVATION
° If FGD system is shut down, inspect reheater mixing chamber (in
direct) and tubes (in-line) for excessive scaling/plugging. Also
check for signs of corrosion and note location.
0 If reheater is operational, inspect external ductwork appearance
upstream and downstream of reheater for signs of corrosion.
0 Look for discarded or replacement tubes nearby (primarily for
in-line reheater applications). Ask why the tubes were replaced.
PROCESS
0 For in-line steam tube designs, note gas-side AP. A high AP could
indicate plugged reheater tubes.
° What is the energy consumption of the reheater? (See Section
5.2.2.9 for significance.)
° What is the design/actual AT across the reheater? Is the outlet
temperature above the acid dewpoint temperature to avoid corrosive
attack?
OPERATION AND MAINTENANCE
° For in-line reheaters, inquire about incidence of tube failure.
What types of tubes are used (plate, shell-and-tube, finned tubes)?
What are they made of? Are they made of the same material as the
baffles to avoid galvanic corrosion?
° For in-line steam tube reheaters, ask about plugging problems.
° If problems have occurred, inquire about remedial actions taken or
planned.
° Ask about reheater cleaning techniques and frequency (e.g., soot
blowers).
0 Inquire about routine maintenance procedures. How often are the
reheaters inspected?
131
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previously in Figure 2.4-9 of Section 2.4.2.5, dampers may appear
in many places throughout the gas circuit. Expansion joints will
also be found throughout the gas circuit ductwork. Expansion
joint failures can result in leakage into or out of the FGD
system (depending on whether the system is an induced or forced
draft design). This, however, does not usually result in forced
unit shutdowns. Table 4.2-6 provides an inspection checklist for
ductwork/dampers.
4.2.2 Reagent Preparation and Feed
The inspection of the reagent preparation and feed equipment
can be considered secondary to the gas handling circuit. The
potential for reagent preparation and feed equipment failure
resulting in downtime of FGD systems is not as great as compared
to equipment comprising the gas-handling circuit. If for exam-
ple, a slaker or ball mill should fail, the FGD system could
still operate for several hours drawing fresh slurry from the
reagent preparation tank fed by the faulty component. There mav
be enough time to repair and put the faulty component back on
line before the last batch supply is exhausted.
4.2.2.1 Reagent Conveyors and Storage. Reagent conveyors and
storage facilities may be associated with chronic minor problems
but they are seldom responsible for FGD system shutdowns. The
operation of this equipment, however, has an impact on the FGD
system as a whole and the attention it receives by the operating
and maintenance staff will be somewhat representative of the
utility's attitude toward the FGD system in general. Table 4.2-7
is an inspection checklist for reagent conveyors.
4.2.2.2 Ball Mills. Ball mills (see Figure 2.4-13) are gener-
ally located at ground level along the perimeter of the FGD
system building adjacent to the limestone conveying equipment.
Their size depends upon 1) the size of the FGD system, 2) the
number of ball mills, 3) the design limestone quality and 4) the
coal sulfur content. Ball mills are problem areas for utilities;
however, the potential for failure resulting in downtime in the
132
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TABLE 4.2-6. DUCTWORK/DAMPER CHECKLIST
OBSERVATION
0 Check for signs of corrosion. Note severity (e.g., discoloration,
pitting, penetration) and size of area affected. Note the gas flow
location of the ductwork/damper with respect to other equipment
areas {e.g., mist eliminator, reheater, absorber).
° Observe duct expansion joints. (See Section 5.2.4.1 for
significance.) Are there obvious ruptures where flue gas is
leaking out (forced draft systems) or is ambient air being drawn
into the duct (induced draft systems)?
0 Observe any "new" ductwork. Ask the plant personnel the reasons
for their replacement.
° Check for bypass ducting and verify if it is part of the original
design (refer to Table 2.4-3a), If there is a contradiction, ask
plant personnel the reasons for the change.
0 Check to see if the duct runs are insulated on the outside to
reduce the possibility of condensation/corrosion.
0 Note ductwork shape (cylindrical versus rectangular) and
configuration (straight runs versus elbows). (Stagnant/dead air
spaces and sharp bends are vulnerable to erosion and the collection
of condensation products. Rectangular ducts are more prone to
non-uniform gas flow distribution, channeling and associated
problems.)
PROCESS
° Ask what process conditions troublesome ducts and dampers are
subject to. What is the gas flow and temperature? Is the gas
saturated?
c What materials (if any) are used for duct lining?
° Is there a slurry carryover problem through the mist eliminators?
(continued)
133
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TABLE 4.2-6 (continued)
OPERATION AND MAINTENANCE
° Inquire about problems with ductwork.
0 Inquire about problems with dampers. Do the dampers function
properly - do isolation dampers effectively isolate a module so
that workers can enter the module while other modules are in
service? Are there problems due to fly ash or other solids
accumulation which hinder the opening/closing of the damper? Are
dampers equipped with seal air to aid isolation/operation?
0 Inquire about integrity and installation of duct materials. Ask
where problems have occurred and what actions are being taken to
rectify problems.
0 Are there problems due to fly ash or other solids accumulation
which hinder the opening/closing of the damper?
c Inquire about routine maintenance procedures. How often are the
ductwork/dampers inspected?
134
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TABLE 4.2-7. REAGENT CONVEYOR CHECKLIST
OBSERVATION
0 Check for belt misalignment, tears or frayed edges (if belt con-
veyor is used).
0 If pneumatic, check for leaks near elbows or bends due to erosion
caused by the reagent.
° If bucket elevator is used, look for discarded chain sections
and/or buckets, welding equipment and signs of "jury rigging."
Look for areas where track/chain jamming may have occurred.
° Inquire about the duty of the conveyors (i.e., separate for reagent
and coal, or shared). If shared, has this ever caused any contam-
ination problems?
OPERATION AND MAINTENANCE
0 Inquire about problems experienced with the conveying device.
0 Are there problems reported with respect to lime/limestone quality
(e.g., debris shipped to the site in the reagent) or freeze ups
during the winter months?
0 If problems have occurred, inquire about remedial actions taken or
planned.
0 Inquire about routine maintenance procedures.
135
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FGD system is not as great as compared to other equipment areas.
Ball mills require a good deal of operator and maintenance crew
attention and repairs can be expensive. Table 4.2-8 shows an
inspection checklist for ball mills.
4.2.2.3 Slakers. Slakers (see Figure 2.4-14), like ball mills,
are found at ground level along the perimeter of the FGD system
main building or in a separate building nearby. The size of a
given slaker depends upon 1) the size of the FGD system, 2) the
number of slakers, 3) the lime quality, and 4) the coal sulfur
content. Slakers are areas of concern for utilities but they are
usually not critical to the continuous operation of the FGD
systems. Table 4.2-9 shows a slaker inspection checklist.
4.2.2.4 Tanks. Tanks are seldom responsible for unit outages.
They are, however, significant sources of module downtime.
Problems encountered with tanks depend upon the tank service.
Tanks handling slurry are prone to abrasion, corrosion, plugging,
agitator failure, and liner failures. Table 4.2-10 is a tank
inspection checklist.
4.2.3 Waste Solids Handling and Disposal
The waste solids handling and disposal area is somewhat less
critical to the operation of the FGD system than the reagent
preparation and feed circuit. When problems occur they can often
be rectified without the need for a forced outage, or at least
temporarily "bandaged" until the next scheduled plant outage.
4.2.3.1 Thickeners. With respect to operation, thickeners can
be regarded as mechanically-aided settling tanks. When properly
operated and maintained, thickeners generally perform well.
However, if thickener problems occur, complete unit shutdowns may
occur because there is no way to bypass the thickener. Thickener
failures are primarily design-related (e.g., shaft failures,
lining failures). Figure 4.2-4 shows an isometric view of a
typical thickener. Table 4.2-11 is an inspection checklist for
the thickeners.
136
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TABLE 4.2-8. BALL MILL CHECKLIST
OBSERVATION
0 Look for any discarded balls. Inquire about the reason for their
replacement. (New ball charges are expected requirements since the
action of milling "consumes" the balls and eventually requires
replacement to maintain desired particle size.)
PROCESS
° Inquire about problems that have resulted due to the quality of the
delivered reagent (refer to "Reagent Preparation" in Section
5.3.1.2 for significance). Poor grade reagent (e.g., impurities,
hardness, chemical composition) can reduce the design output of a
ball mill. Was the ball mill properly sized for the facility?
0 Inquire about the source/qua!ity of water used in the ball mill.
(Water having high levels of dissolved chemicals may inhibit
dissolution.)
OPERATION AND MAINTENANCE
0 Inquire about problems that have occurred (e.g., liner failure,
rapid ball loss, poor quality product, motor failure, bearing
failure).
° If any problems have occurred, inquire about remedial actions taken
or planned.
0 Ask about routine maintenance procedures on mills.
137
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TABLE 4.2-9. SLAKER CHECKLIST
OBSERVATION
° Observe whether the slaker is operational. If not, inquire why.
° Is the slaking equipment properly sized for the facility? What is
the dry reagent feed rate? How does this compare with the design
level and the current demands of the FGD system?
° Inquire about problems that have resulted due to poor quality of
the delivered reagent. (Poor grade reagent [e.g., impurities,
chemical composition] can reduce the design output of the slaker.)
0 Inquire about the source/quality of water used in the slaker.
(Water having high levels of dissolved chemicals may inhibit
reagent dissolution.)
OPERATION AND MAINTENANCE
° Ask about problems associated with slaking equipment.
° If any problems have occurred, inquire about remedial actions taken
or planned.
° Ask about routine maintenance procedures on the slakers.
138
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TABLE 4.2-10. TANK CHECKLIST
OBSERVATION
0 Are there signs of tank repairs (e.g., patches welded on outside)?
Inquire why the repairs were made.
0 Note tank configuration (cylindrical versus rectangular). Rectangu-
lar tanks are more prone to corrosion due to stagnant areas.
(Rectangular tanks are more prone to insufficient mixing and "short
circuiting".) Check placement of internal baffles to aid in
nixing.
0 Inquire or note if tanks are open or closed. If open, has it ever
resulted in any problem?
0 Look for signs of slurry leakage due to erosion/corrosion.
° Check for floating debris in open tanks (e.g., absorber packing,
liners). Inquire about the origin of the foreign material. Are
the tanks equipped with strainers and have they ever become plugged?
OPERATION AND MAINTENANCE
0 Ask about liner and baffle failures. Have any tanks had to be
taken out of service and drained in order to make repairs? What
caused the failure?
Inquire about problems associated with support equipment (e.g.,
agitators, pumps, instrumentation).
0 If problems have occurred, inquire about the remedial actions taken
or planned.
0 Inquire about routine maintenance procedures.
139
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DIAMETER: 100 ft
HEIGHT: 12 ft
WALKWAY
FEED
EFFLUENT
LAUNDER
FEEDWELL
TORQUE AND
\RAKE ARMS
UNDERFLOW
HIGH-PRESSURE
BACK-FLUSHING
WATER LINE
Figure 4.2-4. Isometric view of a typical thickener.
140
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TABLE 4.2-11. THICKENER CHECKLIST
OBSERVATION
0 Are there signs of repairs to the tank portion of the thickener
(e.g., patches welded on the outside)? Inquire why the repairs
were made.
0 Look for signs of slurry leakage due to erosion/corrosion.
0 Does the thickener have a protective covering (e.g., screen)? If
not, look for floating debris.
PROCESS
0 How is water recycled back to the system (gpm) and how is it used?
(See Section 5.2.2.8 for significance.)
0 What is the actual/design percent solids the thickener produces at
the underflow? Overflow? (See Section 5.2.2.5 for significance.)
0 What is the thickener actual/design solid waste production rate?
(See Section 5.2.2.7 for significance.)
0 What is the approximate ratio of calcium sulfite to sulfate of the
inlet waste to the thickener? (See Sections 2.3.2.5 and 5.2.2.7
for significance.)
OPERATION AND MAINTENANCE
0 For equipment protection purposes, is the thickener rake drive
shaft and motor equipped with a torque control/alarm system? If
not, how is it monitored?
0 Have there been problems reported with rake binding or rake drive
shaft/motor failure?
0 Have there been sump pump failures?
0 Have there been liner failures?
0 If problems have occurred, inquire about remedial actions taken or
planned.
0 Inquire about routine maintenance procedures. How often inspected?
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4.2.3.2 Vacuum Filters. Vacuum filters (see Figure 2.4-16) are
generally located at ground level in the main FGD system building
adjacent to the holding area for the filtercake material. Vacuum
filters are not generally responsible for unit shutdown because
spares are usually provided. Table 4.2-12 provides an inspection
checklist.
4.2.3.3 Centrifuges. Centrifuges (see Figure 2.4-17) seldom
cause unit outage because of their batch-type operation and
because spares are generally provided. An FGD system usually has
enough tank surge capacity to provide several hours during which
time repairs could be made. If more time was required (and no
spares were available), the boiler load could be cut back to slow
the rate of waste slurry accumulation in the holding tank. Table
4.2-13 provides a centrifuge inspection checklist.
4.2.3.4 Waste Processing. Except for the forced oxidation
waste processing alternative, this equipment area has little
impact on the FGD system itself. The waste processing system
can, however, have an impact on the FGD system when failures
cause back-ups beyond the storage capacity of the waste slurry
holding tanks. Table 4.2-14 provides a waste processing system
checklist.
4.2.3.5 Waste Disposal. The inspector should be aware of the
area of waste disposal; however, it has little effect on the FGD
system itself. Examples of typical pond types used for handling
waste from a lime/limestone slurry FGD system were shown
previously in Figure 2.4-18. Table 4.2-15 provides a waste
disposal system checklist.
4.2.3.6 Pumps and Valves. Figure 4.2-5 shows a typical slurry
recycle centrifugal pump used in an FGD system. Pumps of great-
est concern with respect to operation and maintenance are slurry
recycle pumps. Valves are generally not major failure related
items. Table 4.2-16 provides a pump and valve checklist for the
inspection. Pumps are major areas of concern because of their
very high maintenance requirements. Most utilities accept
142
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TABLE 4.2-12. VACUUM FILTER CHECKLIST
OBSERVATION
° Inspect -filter cloth for tears.
0 Observe surroundings for spare or discarded filter cloths.
0 Observe filter cake consistency. Does the material fall from the
filter cloth upon hitting the blade in dry cake-like chunks or does
it stick and fall to the conveyor in a damp gum-like mass?
PROCESS
° What is the actual/design percent solids in the filter cake pro-
duced by the vacuum filter? (See Section 5.2.2.5 for signifi-
cance.) Is the inlet solids content high enough to allow adequate
filter cake formation?
r What are the design/actual solid waste and wastewater effluent
production rates of each vacuum filter? (See Section 5.2.2.7 for
significance.)
0 How much vacuum filter filtrate is recycled back to the system
(gpm) and how is it used? (See Section 5.2.2.8 for significance.)
0 What is the approximate ratio of calcium sulfite to sulfate of the
filter cake? (See Sections 2.3.2.5 and 5.2.2.7 for significance.)
OPERATION AND MAINTENANCE
0 Have there been any filtrate or vacuum pump failures?
0 Have there been problems with filter cloth replacement?
° Have there been any problems due to filter cake conveyors?
0 If any problems have occurred, inquire about remedial actions taken
or planned.
° Inquire about routine maintenance procedures.
143
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TABLE 4.2-13. CENTRIFUGE CHECKLIST
OBSERVATION
° Are any centrifuges operational? If not, is it the result of a
forced outage or normal maintenance?
° Observe the filter cake consistency. Does the material empty from
the centrifuge in dry cake like chunks or does it stick to the
conveyor in a damp gum-like mass?
PROCESS
° What is the actual/design percent solids in the filter cake pro-
duced by the centrifuge? (See Section 5.2.2.5 for significance.)
Does it yield a quality product consistently? Is the inlet solids
content high enough to allow adequate filter cake formation?
What are the design/actual solid waste and wastewater effluent
production rates of each centrifuge? (See Section 5.2.2.7 for
significance.)
0 How much centrifuge filtrate is recycled back to the system (gpm)
and how is it used? (See Section 5.2.2.8 for significance.)
0 What is the approximate ratio of calcium sulfite to sulfate in the
end product? (See Sections 2.3.2.5 and 5.2.2.7 for significance.)
OPERATION AND MAINTENANCE
° Ask the utility contact about problems associated with the centri-
fuge and related equipment.
° If any problems have occurred, inquire about remedial actions taken
or planned.
0 Inquire about routine maintenance procedures.
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TABLE 4.2-14. WASTE PROCESSING SYSTEM CHECKLIST
PROCESS
° What type of waste processing technique is used at this facility?
(See Section 2.4.2.13.)
Forced oxidation
Fixation
Stabilization
Untreated
0 What is the energy consumption of the waste processing system?
OPERATION AND MAINTENANCE
° Ask utility contact about problems associated with this equipment
area.
0 If any problems have occurred, inquire about remedial actions taken
or planned.
0 Inquire about routine maintenance procedures.
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TABLE 4.2-15. WASTE DISPOSAL SYSTEM CHECKLIST
PROCESS
° Is the FGD system water loop open or closed? (See Section 5.2.2.8
for significance.)
° What type of waste disposal system is used at this facility? (See
Section 2.4.2.14.)
Ponding
Landfilling
Stacking
° If a pond is used, is wastewater circulated back to the process?
How much? What are the waste characteristics (solids content, pH,
chlorine content, other salts content)? (See Section 5.2.2.8 for
significance.)
OPERATION AND MAINTENANCE
° What problems have been reported with respect to this area? If any
problems have occurred, inquire about remedial actions taken or
pianned.
0 Inquire about routine maintenance procedures.
146
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DISCHARGE
SHAFT
SUCTION
(a)
FRONT VIEW
SUCTION
DISCHARGE
5 ft
SIDE VIEW
4 ft
(b)
Fiqure 4.2-5. Typical slurry recycle centrifuqal pump:
(a) isometric view; (b) side and front view with
approximate dimensions.
147
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TABLE 4.2-16. PUMP AND VALVE CHECKLIST
OBSERVATION
° Observe any discarded pump impellers or pump liners in the area
around each pump. (See Section 5.2.4.3 for significance.) Inspect
for excessive erosion/corrosion.
0 Are there any leaks around the pump seals, pump bearings or other
areas?
° Check for excessive pump vibration (if it is questionable as to
whether the vibration is normal or not, ask the operator or primary
utility contact).
° Look for abrupt expansion, contraction and bends in piping located
at the inlet/outlet of valves that could lead to solids accumula-
tion and valve malfunction.
PROCESS
° Inquire about process conditions that failure-prone pumps/valves
are subject to? How does this compare to the design duty in each
case?
0 How does the actual energy consumption of the absorber recycle
pumps compare with the design value? (See Section 5.2.2.9 for
significance.)
c Ask about pump redundancy provided.
OPERATION AND MAINTENANCE
° Ask the operator if there have been problems with plugging, cavita-
tion, shaft, impeller or liner failure. If problems have occurred,
inquire about remedial actions taken or planned. Identify specific
pumps in question and record details.
0 Inquire about the types of valves and location where failures have
occurred. What remedial action has the utility prescribed?
° Inquire about routine pump/valve maintenance procedures.
148
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impeller and liner failures as normal to operations. Utilities
track the expected life of each major pump, and schedule complete
overhauls around the time failures are projected. In addition,
particularly in newer systems, a good deal of pump redundancy is
included in the overall FGD system design to minimize the impact
of failures. It is important for the inspector to be aware of
signs of excessive pump failure. Excessive failures in this area
could give clues to problems in other parts of the FGD system.
An example of this might be corroded pump impellers due to
lowered slurry pH.
4.3 SUMMARY
To simplify the inspector's data collection process, the
individual checklists presented earlier have been abbreviated and
assembled into a single inspection worksheet titled "FGD System
Inspection Checklist", and presented in Appendix C. Copies of
the inspection worksheet should be made prior to each plant
inspection.
As mentioned in the beginning of this section, the actual
layout of the FGD system may differ greatly from one plant to the
next. In addition, an inspector is likely to encounter items
pertaining to one area while inspecting another, e.g., pallets of
new mist eliminator sections could be stacked outside the FGD
system main building, near the reagent handling area, or adjacent
to the waste processing area. Also, a typical FGD system may be
several stories high. It may be more convenient for the inspec-
tor to inspect equipment items level by level rather than by
equipment area. In such a case, the inspector would look at the
equipment observable at each level.
As stated earlier in Section 4.1, the general plant data
portion of the FGD system inspection checklist should be com-
pleted prior to the inspection because it can provide valuable
input for 1) evaluating the FGD system performance, 2) diagnosing
problems, and 3) recommending corrective measures.
149
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SECTION 5
PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
This section describes guidelines that can be used by the
field inspector to interpret FGD system performance data with
respect to present and future compliance status. The guidelines
presented are "independent" in that they are designed to assist
the field inspector irrespective of performance interpretation or
"biasing" by the plant operator. The guidelines presented are
designed to be used in both immediate and long-term performance
evaluations. The latter consideration is important in that an
FGD system may yield performance data indicating compliance at
the time of the inspection; however, process data may indicate
the existence of problems which will jeopardize future compliance
status.
This section represents a continuation of Section 3, wherein
we describe lime/limestone slurry FGD performance indicators and
their measurement, and Section 4, wherein we describe lime/lime-
stone slurry FGD inspection methods and procedures. We describe
in this section both the sources of data available to the field
inspector as well as the "form" these sources of data take. We
describe techniques that are available to aid the field inspector
in performance evaluation. We identify cause-and-effeet problem
relationships and corrective measures through simplified sequence
diagrams. We present followup procedures to verify the success
of the corrective measures taken.
The information presented in this section is organized in
accordance with the equipment areas and subsystems identified in
Section 2.4.2 (FGD System Design Configurations).
150
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5.1 DATA COLLECTION METHODS
The following two sections give a brief description of
sources of performance data and modes by which these data are
available to the field inspector.
5.1.1 Sources
Sources of information available to the field inspector
during the plant inspection include performance data, process
data, operation and maintenance data, and observational data.
FGD system performance data includes any information con-
cerning SO2 removal, particulate removal, and opacity levels. As
mentioned in Section 3.4, most operator utilities collect S02,
particulate, and opacity data continually using CEM's in the form
of strip charts, computer disk, and/or tape files. Other sources
of performance data include stack test results for compliance
testing, acceptance testing, certification of the CEM's, and/or
smoke stack readings by a trained observer for opacity
compliance.
Process data includes any information concerning the various
physical operating parameters of the FGD system. These param-
eters include gas flow, gas-side pressure drop, slurry pH, slurry
flow, slurry solids, reagent consumption, solid waste production,
wastewater discharge, makeup water consumption, and energy
consumption (see Section 5.2.2). Most operator utilities record
this type of data hourly on operation log sheets. If not, the
field inspector, with the aid of the operator, can obtain most of
these measurements directly from the control panel. Certain
other parameters, such as slurry pH and slurry solids, are also
measured manually with grab samples to check automatic
instrumentation readings. On request, the field inspector should
also have easy access to these recorded data. However, other
parameters such as makeup water consumption and equipment energy
consumption might not be measured directly; they can be obtained
directly from the operating staff.
151
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Operation and maintenance data include any information which
is manually recorded in the form of operation log books, mainten-
ance log books, work orders, maintenance requests, and equipment
purchase orders. A detailed description of these types of data
is presented in Section 5.2.3.
The last and most important source of data is observational
data and information obtained firsthand by the field inspector.
The field inspector should try to ask questions concerning system
O&M as well as take notes (and/or photographs) on equipment
layout, visual appearance of equipment, general housekeeping, and
any consumed equipment or parts observed during the inspection
(see Section 5.2.4). In some cases, recorded data will not be
available and the field inspector will have to take readings
directly from the control panel (s) or orally from the operating
staff. All of these data and information will be of use when the
field inspection is completed and the inspector has returned to
the office for data assimilation and analysis.
5.1.2 Forms of Data
The forms of data and information available to the field
inspector are mentioned in Section 5.1.1. These include computer
output, control room panels, O&M records, other written documents,
and observational data and information. Most CEM's have a means
for viewing or printing on-line results of SO,,, particulate, and
opacity emission {as well as NO ) results in a variety of units
6
(ppm, lb/10 Btu). Regarding control panels, the field inspector
should be aware that FGD control panels may be decentralized
(i.e., at more than one location in the plant) versus a central
location such as the boiler control room. fteagent preparation
and feed, gas handling and treatment, and waste solids handling
and disposal instruments might be located on separate panels at
different locations in the plant. Written records available to
the field inspector include O&M log books, work orders, stack
test reports, purchase orders, lab reports, and any other written
152
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documentation concerning the operation' and performance of the FGD
system. The final and most important means for gathering data
and information is the recording by the field inspector during
the plant inspection.
5.2 PERFORMANCE EVALUATION
This section provides the field inspector with independent
guidelines on how to collect and interpret performance data
during a plant inspection. These guidelines are organized accord-
ing to emissions (Section 5.2.1), process (Section 5.2.2), O&M
(Section 5.2.3), and observation (Section 5.2.4). These sections
emphasize collection techniques and performance interpretation.
To the extent possible, the interpretation guidelines exclude any
discussion of problem diagnosis and corrective actions; these are
taken up in Sections 5.3.1 and 5.3.2, respectively.
5.2.1 Emissions
The following discussion on emissions addresses S02, partic-
ulate matter, and opacity. The discussion on particulate matter
and opacity is presented in terms of FGD performance. Section
3.1.1 introduces the gas stream measurement parameters and the
associated monitoring technigues used by the operator utility to
collect these data.
5.2.1.1 S02* Inlet SO2 concentration is largely dependent on
the sulfur content of the coal fired in the boiler (see Section
2.2, Coal Properties and Flue Gas Characteristics). To estimate
S02 emissions (in units of lb SO2/10^ Btu), the field inspector
should refer to Figure 2.1-1 or use the following equation:
S02 emission rate = (coal wt. % sulfur) x (2 x 104) x (fractional
conversion of sulfur in coal to S02)/(heating
value of coal in Btu/lb).
EXAMPLE:
S02 emission rate = (3.5% S) x (2 x 104) x (0.92 conversion)/
(11,OOOBtu/lb) - 5.85 lb SO2/106 Btu.
153
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(If the conversion of sulfur to SC>2 is unknown, use EPA AP-42
emission factors that assign SO^ conversion factors as follows:
0.97 for bituminous coal, 0.88 for subbituminous coal, and 0.75
12
for lignite. )
Sulfur is present in the coal in three forms: organic,
pyritic (primarily FeS2), and inorganic sulfates. The organic
sulfur is liberated when the coal is burned; however, not all the
inorganic sulfates and pyritic sulfur is liberated during combus-
tion. Some of it is converted to bottom ash or fly ash. The
coal should be tested to determine what fraction of the organic
and inorganic sulfur is converted to S02> Typically, 95 percent
of the sulfur in coal is converted to S02; about 0.5 to 1.0
percent may be converted to sulfur trioxide (SO^); and the re-
mainder is trapped in the bottom ash or fly ash. The SO^ is
converted to sulfuric acid mist during the absorption process.
Due to the fineness of its particle size, very little is removed
by the FGD system.
An increase in inlet SC>2 concentration due to a change in
coal sulfur content may lead to several operating consequences
including: increased reagent consumption, increased solid waste
production, and lowered slurry pH (i.e., S02 loading exceeds
design) with increased potential for gypsum scale formation and
corrosion in the absorber (see Section 5.3.1.1, Absorber).
5.2.1.2 Particulate Matter. Particulate matter consists pri-
marily of finely divided solid particles entrained in the flue
gas stream. The particles can be either fly ash, uncombusted
coal fines, or S02 reactants/products.
Increases in coal fines and fly ash in-the flue gas can
contribute to plugging in the absorber. Added levels of fly ash
and coal fines can also increase solid waste production. If not
accounted for in the design of the FGD system, the alkalinity of
the collected fly ash from its available calcium oxide (CaO) and
magnesium oxide (MgO) constituents can result in high pH levels
and unreacted reagent. This in turn may increase the potential
154
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for scale formation, plugging, and unnecessarily high solid waste
production. If the fly ash has a low alkalinity value (or,
conversely, high acidity value), it can have the opposite effect.
The fly ash (and coal fines) can dilute the slurry solids level
of the chemical reactants thereby lowering the SC^ removal effi-
ciency and pH of the system. This in turn can promote gypsum
scale formation. Increased amounts of fly ash and coal fines, in
addition to absorber-generated particulate matter, can also lead
to opacity problems.
Decreases in particulate removal efficiencies can be attrib-
uted to a number of factors including mechanical problems, poor
maintenance, and changes in coal characteristics. For example, a
change in coal sulfur content from 2.5 to 1.0 percent can reduce
the ESP particulate removal efficiency from 98 to 90 percent due
to changes in particle resistivity. If the particulate matter
removal device is not working properly, the carryover of the
solids to the FGD system might lead to the adverse consequences
indicated in the foregoing paragraphs.
Increased particulate matter loading due to higher ash
content in the coal can overload particulate matter removal
devices and subsequently increase opacity levels. Ash content of
coal ranges from less than 3.5 to more than 15 percent. A por-
tion of the ash leaves the boiler with the flue gas as fly ash,
and the remainder leaves the boiler as bottom ash. The split of
fly ash to bottom ash depends on coal grade and characteristics
and boiler firing configuration. For any application, an accu-
rate determination can only be made empirically. However, for
field inspections, a number of quick-estimating techniques are
available. For pulverized coal boilers, the split of fly ash to
bottom ash is 80:20. For cyclone-fired boilers, the split is
30:70 (almost a complete reversal of pulverized coal).
5.2.1.3 Opacity. Opacity is the degree to which particulate
emissions in the plume leaving the FGD stack reduce the transmis-
sion of light and obscure the vision of objects in the background.
155
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Increases in opacity levels are usually the result of decreased
particulate matter removal, an increase in particulate matter
loading (i.e., higher ash content in coal), and/or the generation
of FGD particulate matter.
A decrease in particulate matter control efficiency can
easily contribute to higher opacity levels. In some cases,
FGD-generated particulate matter contributes to the opacity
level. There are several mechanisms which account for this. For
example, prior to contacting the slurry, quenching or presatura-
tion may be used to reduce the flue gas temperature. The water
used in this spray may contain significant quantities of sus-
pended solids or dissolved salts which can form a solid aerosol
on evaporation. If the aerosol is small enough, it could then
penetrate the absorber and become part of the overall emissions
from the FGD system. Another example is the slurry from the
absorber. The mechanical equipment required to pump and spray
the slurry also generates liquid and solid aerosols. These
aerosols could be entrained by the gas stream and pass through
the mist eliminator to the stack. Additionally, certain species
such as sulfuric acid or volatile elements may be present as
vapors in the flue gas. As the gas temperature is reduced during
passage through the absorber, these species may condense. The
small particle aerosols may pass through the absorber to the
stack.
5.2.2 Process
The following discussion on process addresses the operating
parameters of gas flow and pressure drop; slurry pH, flow and
solids; reagent, solid waste, and makeup water consumption; and
wastewater effluent and energy consumption. Section 3.1 (Key
Operating Parameters and their Measurement) provides background
information on these measurement parameters and monitoring tech-
niques .
5.2.2.1 Gas Flow. The gas flow rate to the FGD system is
primarily a function of boiler load. Variance from design caused
by sudden changes in boiler load, leaks in ducts and expansion
156
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joints, or the malfunction of the control dampers can lead to
several operating consequences. Gas flow rates above the design
value can result in several consequences including the reduction
of S02 removal. Another result of high gas flow rate is the
carryover of entrainment from the mist eliminator to the down-
stream subsystem. Higher than normal gas flow rates can result
in increased particulate loadings from upstream particulate
collection devices (e.g., ESP's, scrubbers). The added partic-
ulate matter can also increase solid waste disposal. Reduced gas
flow may decrease S02 removal efficiency, depending on the design
and operating characteristics of the absorber.
5.2.2.2 Gas-side pressure drop. Gas-side pressure drop consists
of losses in the bends, contractions, and expansions in the inlet
and outlet ductwork, pre-scrubber (if present), absorber, mist
eliminator, reheater (if present), and stack. Emphasis is placed
here on the absorber and mist eliminator because they constitute
the major portion of the total pressure drop. The pressure drop
across the absorber and mist eliminator is a function of flue gas
velocity and design. For reference, reported design pressure
drops for specific types of absorbers and mist eliminators used
in commercial lime/limestone slurry FGD systems are summarized in
Tables 5.2-1 and 5.2-2, respectively.
An increase in pressure drop across the absorber and mist
eliminator can cause an increase in system energy consumption due
to increased energy demand by the unit or booster fans. An
increase in pressure drop across the absorber/mist eliminator is
commonly attributed to either plugging or scaling. Other contrib-
uting factors include high gas flow rates and high slurry flow
rates (which compresses the gas flow).
A decrease in pressure drop although not as common, can
cause improper slurry atomization and distribution in the absorber.
A decrease in pressure drop can be attributed to dislocated
packing, low slurry flow rates, or low gas flow rates.
5.2.2.3 Slurry pH. Control of slurry pH is essential to reli-
able FGD system performance. Removal of SC^ from the flue gas
157
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TABLE 5.2-1. DESIGN GAS-SIDE PRESSURE DROPS FOR ABSORBERS IN
OPERATIONAL LIME/LIMESTONE FGD SYSTEMS
Absorber type
Number
of
plants
Gas-side
drop,
pressure
in. ^0
Range
Average
Venturi
Fixed-throat
2
6
6
Variable/throat/side movable blades
1
8
8
Variable-throat/top-entry plumb bob
1
8
8
Packed
Entrained
3
3-6
5
Grid
1
2
2
Mobile bed
5
2-9
6
Rod deck
3
8-12
9
Static bed
1
11
11
Tray
Sieve
7
2-14
6
Combination
Spray/packed
8
1-6
3
Spray
Open/countercurrent spray
24
1-8
3
Open/crosscurrent spray
4
2
2
158
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TABLE 5.2-2. DESIGN GAS-SIDE PRESSURE DROPS FOR MIST ELIMINATORS IN
OPERATIONAL LIME/LIMESTONE FGD SYSTEMS
Mist eliminator type
Number
of
plants
Gas-side pressure
drop, in. HgO
Range
Average
Primary collectors
Impingement
Baffle/closed vane
56
0.1-4.0
1.0
Baffle/open vane
2
0.2-0.8
0.5
Centrifugal separation
Radial vane
1
2.3
2.3
Precollectors
Bulk separation
Perforated trays
2
0.5
0.5
159
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takes place in the absorber and neutralization and precipitation
reactions occur in the slurry recirculation and holdup tanks.
The pH of the recirculation slurry entering the absorber should
be in the range of 8.0 to 8.5 for lime slurry and 5.5 to 6.0 for
limestone slurry. The pH of the spent slurry leaving the absorb-
er should be in the range of 6.0 to 6.5 and 4.5 to 5.0 for lime
and limestone slurry, respectively. Slurry pH is controlled by
adjusting reagent feed rate. However, slurry pH can also be
affected indirectly by slurry feed rate and the quantity and
characteristics of flue gas being treated. Operation at high pH
levels, which tends to increase SO^ removal efficiency, can lead
to soft scale formation, lowered reagent utilization, and in-
creased solid waste volume. Operation at low pH levels, which
tends to improve reagent utilization and lower the amount of
solid waste production, will also lower SOremoval efficiency
and promote gypsum formation.
5.2.2.4 Slurry Flow. The field inspector should obtain read-
ings from all instruments used to measure the flow of the differ-
ent process streams (see Section 3.2.2). Pump discharge pressure
is commonly used to determine slurry flow characteristics. Flow
in noninsulated slurry piping can be checked by touching the pipe
(warm and/or vibrating, the pipe is operational; cool and/or
quiescent, the pipe is inoperative). Deviations from anticipated
values can indicate potential problems, either in the absorber or
with the instrumentation.
The rate of slurry flow (feed) to the absorber is determined
primarily by the design L/G ratio. An increase in slurry flow
rate above the design L/G may improve S02 removal? however, high
slurry flow rates mean high pumping costs, increased reagent
usage, lower reagent utilization, and greater solid waste produc-
tion. High flow rates also promote the erosion of piping, pumps
impellers, absorber linings, spray headers and nozzle orifices,
and valves. High slurry flow rates can also lead to slurry
carryover from the mist eliminators. A decrease in slurry flow
below the design L/G is usually an indication of plugging which
160
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is detectable by either an increase in recycle pump discharge
pressure or absorber slurry recycle piping that is cold to the
touch (normal operating temperatures are 125° to 130°F). By
decreasing the recirculation slurry flow rate, S02 removal effi-
ciency will be lowered. As slurry flow is drastically reduced
or stopped, pump cavitation may occur. Moreover, pump liners can
be sucked into the path of impellers and shreaded which may
become additional material to reduce flow rate by plugging down-
stream slurry handling equipment.
5.2.2.5 Slurry Solids. Operation at a consistent solids con-
tent in the various slurry process streams can improve the relia-
bility of the absorber and slurry handling equipment and improve
process control. Specific gravity is a commonly used measure for
determining slurry solids content (see Section 3.2.3). The
design specific gravity of the recirculating slurry for lime/
limestone FGD systems is usually between 1.05 and 1.14 (approxi-
mately 7 to 20% solids). A graphic representation of specific
gravity as a function of the solids content of the slurry in
lime/limestone FGD systems is presented in Figure 5.2-1.
5.2.2.6 Reagent Consumption. Reagent consumption is set by
stoichiometry of the process. As noted in Section 2.3.2.1, it is
necessary to feed more than the stoichiometric amount of reagent
in order to attain the degree of S02 removal required (stoichio-
metric ratio). However, excessive reagent can lead to several
operating problems including wasted reagent, scale formation, and
erosion of slurry-handling equipment. Figure 5.2-2 is a graphic
representation of reagent consumption as a function of the S02
emission limitation and boiler size (i.e., equivalent FGD
capacity in MW). This figure can be used by the field inspector
to estimate reagent feed rates.
5.2.2.7 Solid Waste Production. Solid waste (sludge) produc-
tion will vary as a function of the inlet flue gas character-
istics and FGD system design and operating characteristics. The
constituents usually include solid phase SO^ reaction products,
unreacted reagent, fly ash, and adherent liquor.
161
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1.3
1.1
Q_
to
a\
ro
>~
OtL
a:
1.0
0 5 10 15 20 25 30 35
SOLIDS, WEIGHT %
Figure 5.2-1. Typical specific qravity of absorber recirculation slurry for
lime/limestone FGD system.
-------
>>
•o
z
o
LIME
o
o
MAG/LIME
H-
z
Ui
C9 0.5
<
UJ
cc
1.8
2.5
1.2
0.6
lb S02/million Btu
Figure 5.2-2. Reaqent requirement calculation.
-------
Increases in solid waste increases the burden on solids
handling and disposal. This can mean higher energy consumption,
possible deviation from closed water loop operation due to exces-
sive amounts of wastewater effluent, and reduced land area avail-
able for disposal. Variations in the quality of the slurry bleed
stream to the thickener with respect to high ("rich") or low
("lean") solids content can either overload or under-utilize the
primary dewatering subsystem, respectively. The ratio of sulfite
to sulfate contained in the spent slurry stream is also important
because of the size differences between gypsum (1 to 100 microns
in length) and calcium sulfite crystals (0.5 to 2.0 microns in
length). These differences can have a significant impact upon
the dewaterability of the solid waste material. Generally, as
the ratio of sulfite to sulfate increases, the liquor content of
the dewatered solid waste also increases. Figure 5.2-3 provides
a nomograph to convert between dry and wet sludge production.
5.2.2.8 Makeup Water Source and Consumption. Water is lost
from the FGD process in the form of water vapor and small amounts
of entrained liquid in the saturated flue gas. Water is also
lost in the disposal of solid waste material or byproduct.
Makeup water is added in order to off-set these losses. Major
addition points and/or uses of makeup water include reagent
preparation and dilution, mist eliminator wash, pump seal water,
and recirculation tank level control. Sources of makeup water
include fresh water, recycled water, and plant inventory water.
Fresh water may come from a river, lake, a municipal water sys-
tem, or an untreated well; recycled water is recovered from the
solid waste disposal system either in a settling pond or in a
settling or filtration step; and plant inventory water is cooling
tower blowdown. The amount and type or quality of makeup water
used is important when considering its effect on closed water
loop operation, reagent preparation, and operability and clean-
liness.
For closed water loop operation, makeup water addition
should not exceed losses in the flue gas and solid waste material.
164
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1600'
1500'
250
1400'
500
1300'
750
1200
0000
1101
¦a 1000'
0 500
i/i
•o
900'
•1750
800'
2000
•C
S 700'
o
2250
2500
2750
400'
3000
300'
3250
200
3500
100
3750
4000
Figure 5.2-3. Sludge (waste) Droduction calculation.
165
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High makeup water consumption could le&d to discharges (or in-
creased rates of existing discharge streams) to existing water-
ways. Contributing factors to high makeup water consumption
include inefficient pump seals, excessive mist eliminator wash
rates, and* inefficient water recovery in the FGD process.
For reagent preparation and dilution, the importance of the
quality of makeup water used for limestone slurry is typically
not of critical concern and recycled (recovered process) water is
used. The quality of makeup water required for slaking lime is
very critical. The use fresh water (of or near potable quality)
is required.
Concerning equipment performance, mist eliminator wash water
can be fresh, recycled, plant inventory, or a blend of the above.
Ideally, fresh water should be used; however, to attain closed
water loop operation, a blend is frequently used. A number of
problems may be encountered due to the excess usage of recycled
or plant inventory water. The high levels of dissolved salts in
recycled water can promote scale formation on mist eliminator
surfaces as well as mist eliminator wash lances. With the use of
plant inventory water, the dissolved solids, suspended solids,
and residual chlorine contaminants can subsequently lead to the
scaling and/or erosion/corrosion of the mist eliminator wash
lances, absorber, piping, pumps and other slurry handling equip-
ment. Another major use of makeup water is addition to the
recirculation tank for level control. Water quality is not a
concern here except that residual alkalinity is desirable. Typi-
cal makeup water consumption rates and addition points are summar-
ized in Table 5.2-3 for several operational lime/limestone slurry
FGD systems.
5.2.2.9 Energy Consumption. FGD energy consumption is attribu-
ted primarily to reheat, flue gas flow, slurry preparation, and
slurry recirculation. Other energy consuming operations include
slurry transfer (pumping), tank agitation, solids dewatering
(thickeners, vacuum filters, centrifuges), steam tracing,
electrical instrumentation, and air supply. An increase in
166
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TABLE 5.2-3. MAKEUP WATER CONSUMPTION RATES FOR OPERATIONAL LIME/LIMESTONE F6D SYSTEMS
III i 111 y
lln) I
No.
FGO
capaiity,
MM
Pi ncess
type
1 oop
Makeup
water,
'Jl«n
Makeup water addition points - gpm
Big Rivei Llei ti ic
Green
i
242
L line
Closed
366
Slakers - 290 ypu; pump seals - 76 9pm
Dig Rivers Electric
Green
2
24?
1 iine
Closed
366
Slakers - 290 9pm; pump seals - 76 gpm
Cincinnati Gas t Electric
East Bend
2
650
L ime
Closed
464
Slaker - 1060 gpm
Columbus i Southern Ohio Electric
Conesv i lie
5
350
1 inie
Closed
500
Columbus & Southern Ohio Electric
Conesvi 1 le
6
350
I ime
C1osed
500
Duquesne 1ight
Phil 1 ijis
1-6
408
time
Open
350
Slaker, pump seals, fans, and nist
eliminators
Kentucky Utilities
Green River
1-3
65
Lime
Closed
75
Louisville Gas t Electric
Cane Nun
4
188
Lime
Closed
100
Louisville Gas & Electric
Hill Creek
1
358
L ime
Closed
1984
Reaction tank - 1412 gpni; other -
572 gpm
Louisville Gas & Electric
Hill Creek
2
350
Lime
Closed
1984
Reaction tank - 141? gpm; other -
572 gpm
Louisville Gas i Electric
Mill Creek
3
427
Lime
Closed
150
Louisville Gas & Electric
Paddy's Run
6
12
Lime
Closed
50
Utah Power & Light
Hunt i rig ton
1
366
Lime
Closed
300
Alabama Electric
Tomb I'jh* r
?
179
L imestone
Closed
157
Seal water - 18 gpm; mist eliminator
139 gpm
Alabama Electric
Tombigbee
3
179
Limestone
Closed
157
Seal water - 18 gpm; mist eliminator
139 gpm
Arizona 1 lectric Power
Apa< lie
p
90
Limestone
Open
1840
Mist eliminator wash and slurry
preparation
Arizona 1 lectric Power
Apache
3
98
t imestone
Open
1840
Mist eliminator wash and slurry
preparation
Arizona Public Service
Choi la
1
119
t imestone
Open
120
Arizona Public Service
Choi la
?
?H5
Limestone
Open
1?0
Associated Electric
Ihomas Hill
3
670
Limestone
Closed
772
Has in f If- trie: Pnwer
1 arainie River
1
570
1 iiirstnne
Closed
269
Mist eliminatur wash, pump seals and
tower makeup
(continued)
-------
TABLE 5.2-3 (continued)
utility
(Jul L
No.
fUi
< apdi l ty,
MM
Process
type
1 oop
Makeup
watci ,
gpm
Mjleup water addition points - grmi
Has in Llet trie Power
Laramie River
1
5/0
I iniestone
Closed
?69
Mist eliminator wash, pump seals and
tower makeup
Centra) Illinois Light
Duck Creek
1
416
t lines tone
Closed
600
Mist eliminator, ball mill, pump seals
Colorado lite Electric
Craig
1
455
L iinestone
C1 osed
3? 1
Wash tanks - 204 gpm; pump seals -
117 gpm
Colorado lite Electric
Craig
?
455
1 lines tone
Closed
3? 1
Wash tanks - 204 gpm; pump seals -
117 gpm
Indianapolis Power & Light
Petersburg
3
632
1imestone
Closed
882
Mist eliminator wash tank
Kansas City Power & light
La Cygne
1
874
1imestone
Open
114B
Fresh water - ball mill; settling
pond return water - recycle tank
Kansas Power & Light
Jeffrey
1
540
L iniestone
Closed
577
Kansas Power & Light
Jeffrey
2
540
Limestone
Closed
577
Lakeland Utilities
McIntosh
3
364
Limestone
Closed
228
Michigan So. Central Power Agency
Project
1
S5
1imestone
Closed
85
Public Service Indiana
Gibson
5
670
Limestone
Closed
609
Salt River Project
Coronado
1
320
L imestone
Open
270
Mist eliminator wash tanks and
thickener
Salt Rivei Project
Coronado
320
1 iniestone
Open
270
Mist eliminator wash tanks and
thickener
San Miguel Electric
Sari Miguel
1
400
1 iniestone
Closed
600
Silestown brd of Municipal Utilities
Sikes ton
1
235
Limestone
Open
1B6
Snulli Carolina Public Service
Uinyati
140
1imestone
Open
100
Springfield Water, light & Power
Da 11 ma n
3
205
I imestone
Closed
239
Mist eliminators and pump seals
lex.r. Municipal Power Agency
Gibbons Creek
1
400
1 iniestone
Closed
580
Texas lit 11 i t ies
Hart in lake
1
595
L i Hies tone
C1osed
550
Tunas Ut i 1 ities
Mai t in Lake
',95
1 imestone
Closed
550
Itur Utilities
Ma rt iii 1 a!.e
1
¦>05
1 iniesLiiiie
Closed
550
Ii" 1 III 1 1 1 t ICS
Ht'ii 1 i ¦ i-11 ii
1
;UI0
1 uiies t our
Ilosed
'.46
-------
energy consumption in any of these areas usually indicates a
problem.
Reheating the saturated flue gas consumes more energy than
any other part of the FGD system (assuming reheat is used).
Reheat provides buoyancy to the flue gas and thus reduces the
nearby ground-level concentrations of pollutants. Reheat also
prevents condensation of acidic, saturated gas from the absorber
in the I.D. fan, outlet ductwork, or stack. Further, reheat
minimizes the settling of mist droplets (as localized fallout)
and the formation of a heavy steam plume with resultant high
opacity. An increase in reheater energy consumption is generally
indicative of plugged or scaled in-line reheater tube bundles.
Energy consumption is increased because the heat transfer effi-
ciency of the reheater tubes is lowered. Table 5.2-4 provides a
quick approximation method to determine reheat energy consump-
tion.
Driving flue gas through the FGD system consumes energy.
Forced or induced draft fans use energy to overcome the gas-side
pressure drop of the FGD system. An increase in fan energy
consumption usually indicates either a mechanical problem with
the fan and/or an increase in pressure drop somewhere in the FGD
system. Table 5.2-4 provides a quick approximation method to
determine FGD fan energy consumption. Figure 5.2-4 provides a
quick determination method if only plant size and gas-side press-
ure drop are known.
The grinding of limestone and the slaking of lime consume
relatively small amounts of energy as compared to other energy
consuming equipment. Any increases are usually due to either
poor quality makeup water (see Section 5.2.2.8) or mechanical
problems with the slaker or ball mill.
Energy is consumed to recirculate the slurry to the absorb-
er, to transfer water and slurry streams to various parts of the
FGD system, and to treat and dispose the solid waste material.
Similar to fans, an increase in pumping energy consumption usu-
ally indicates either a mechanical problem and/or an increase in
169
-------
TABLE 5.2-4. ENERGY REQUIREMENT CALCULATIONS
CP ¦
Specific heat, Btu/(lb)(°F)
P =
Power required, kilowatts
E =
Heat energy, Btu
Hs =
Head, ft
L/G =
Ratio of slurry flow to flue gas rate, gal/1000 acf at the
outlet
0
m =
Air flow rate at the inlet of reheat section, lb/min
&p =
Pressure drop through FGD system, in. H^O
Q =
Gas flow rate at the outlet of absorber, acfm
AT =
Degree of reheat, °F
1. Slurry recirculation pumps (70% pump efficiency assumed)
P = 0.000269 x H x (L/G) x -9-
s 1000
= Hs (L/G) Q x (2.69 x 10"7)
2. Flue gas fans
P = 0.0002617 x 4P x Q (assuming 80% efficiency)
3. Reheat of absorber flue gas
E = 0.01757 ° Cp AT
170
-------
20,000
PLANT CAPACITY = /1000 MW
500 MW
15,000
10,000
5,000
100 MW
60
0
40
50
20
30
10
AP, in. ^0
Figure 5.2-4. Fan power requirements.
171
-------
slurry side pressure drop in the system. Table 5.2-4 provides a
quick approximation method to determine pumping energy consump-
tion. Figure 5.2-5 provides a quick determination for slurry
recirculation pumping requirements if plant size and L/G are
known.
5.2.3 O&M
Operation and maintenance data include recorded data in
operation log books, maintenance requests, maintenance log books,
work orders, and equipment purchase orders.
Operation log books and the types of information recorded
varies from plant to plant. Example log sheets are shown in
Figures 5.2-6 and 5.2-7. In Figure 5.2-6, the operation log
sheet simply records the status of equipment and the time of
operational changes. In Figure 5.2-7, the operation log sheet
records only information on certain process parameters (slurry
pH, slurry level, slurry density, etc.).
With the increasing complexity of present generation FGD
technology, most utility operators have gone to computerized
maintenance planning systems. Work orders are first written by
operators during shift inspections. In some cases, work orders
are preceded by "tagging" in which the plant or shift supervisor
routinely inspects the system and tags equipment in need of
apparent maintenance and repair. These work orders specify the
equipment needing repair, the estimated number of man-hours,
possible causes of the problem, and the urgency of completion
(i.e., date needed by). The work order is then sent to the
maintenance department for action. The maintenance crew com-
pletes the maintenance portion of the work order form by noting
the actual cause of the problem, the work conducted, and the
man-hours needed to complete the job. All of this information is
then computerized for later reference. As this database expands,
it becomes a source for forecasting equipment repairs which can
be implemented during scheduled FGD outages, unit outages, and/or
periods of low demand. For certain recurring repairs, work
172
-------
4000
PLANT CAPACITY «/1000 MW
3000
500 MW
in
2
O
2000
1000
100 MW
10
20
0
30
40
50 - 60
L/G, gal/1000 acf
Figure 5.2-5. Recirculation pump energy requirement.
173
-------
ARSORBER OPERATION LOG
(Indicate Status of Equipment and Time of Operational Changes)
DATE
ABSORBER
MODULES IN
ABSORBER
MODULES OUT
BYPASS
OPEN-PARTIAL-CLOSED
REASONS FOR ABSORBER
BEING OFF OR BYPASSED
Figure 5.2-6. Example operation log sheet.
174
-------
0*TE
HAY
2A
ABSORBER (AB)
UNIT 2
RECIRCULATION
TANK (RT)
DAILY READINGS
2B
ABSORBER (AB)
AB
LEVEL
AB
DENSITY
AB
pH
HIST
EL IN.
GAL.
SEAL
AIR PRES.
RT
DENSITY
RT
PH
AB
LEVEL
AB
DENSITY
AB
pH
MIST
ELIM.
GAL.
STAL
AIR PRES.
RT
DENSITY
LIMESTONE
MILL
REAGENT GAL.
UNIT 2
FT
GRAMS
IN
OUT
GRAMS
FT
GRAMS
IN
OUT
GRAMS
DENSITY
GRAMS
AMPS
PRES.
PREV.
TOTAL
MM
REAGENT GAL.
UNIT 3
0600
mot
1000
1200
PRES.
MM
PREV.
1666
TOTAL
iflM
LIMESTONE TONS
2000
2?M
J4M
PRES.
3A
ABSORBER (AB)
UNIT 3
RECIRCULATION
TANK (RT)
3B
ABSORBER (AB)
PREV.
TOTAL
MILL HOURS
PRES.
PREV.
TOTAL
AB
LEVEL
AB
DENSITY
«
AB
PH
MIST
ELIM.
GAL.
SEAL
AIR PRES.
RT
DENSITY
RT
P«
AB
LEVEL
AB
DENSITY
AB
PH
MIST
ELIM.
GAL.
SEAL
AIR PRES.
REAGENT
TANK
LEVEL
FT
GRAMS
IN
OUT
GRAMS
FT
GRAMS
IN
OUT
FT
REMARKS
0200
fiTTTil
liM'lil
KWl
IMiTil
INOI
ILI'I'l
ILlul
i
OPERATOR
MMl
mm
1 ' *
GRAVEYARD
wwi
I
DAYS
|?40O| |
1 EVENINGS
Figure 5.2-7. Example operation log sheet.
-------
orders can be generated automatically by the computer versus
being hand written by an operator. Figures 5.2-8 and 5.2-9 are
examples of handwritten and computer generated work orders/main-
tenance forms, respectively.
The accounting department of the operator utility should
have records on equipment purchase orders. This type of data can
be used to spot recurring purchases which may indicate chronic
problem areas.
5.2.4 Observation
Sources of observational data include the operation of the
FGD system, layout of and access to the equipment contained in
the FGD system, equipment "consumed" by the FGD system, and
general housekeeping of the FGD system area.
5.2.4.1 System Observation. During an inspection, the field
inspector should look for signs which indicate possible problem
areas. Several examples of these include gas leakage; slurry
leakage; tower, vessel, and ductwork appearance; and the behavior
of moving components.
Gas leakage usually occurs through expansion joints, dampers,
or ductwork. With positive pressure (forced draft) systems, flue
gas can escape to the surrounding plant environment (which may be
further complicated by an enclosed operation). Such a problem
will not be readily observable in negative pressure (induced
draft) systems in which air is drawn into the FGD system. This
air can promote corrosion, promote scaling due to uncontrolled
oxidation, and increase the amount of gas to be handled by the
gas handling and treatment subsystems.
Broken slurry lines and leaky pumps and valves can provide
information concerning equipment maintenance, materials of con-
struction, and/or characteristics of the slurry. Absorber tower
appearance, inside and outside, also provides information con-
cerning equipment maintenance, materials of construction, and/or
characteristics of the slurry. Vibrating fans and pumps and pump
cavitation all provide clues regarding maintenance, materials of
176
-------
WORK ORDER
Priority / Laval
Station
Component
Roquaatad By Qroup
Attach Litt: Work O
Wort Description:
WORK ORDER NO. 90 046041 9
Unit Data Printed
Equipment No
.Unit Statu*
Raquoatad Completion Data
Ina paction Q Salting* O
Spacial Instruction*:
RESPONSIBLE
QROUP
SUPERVISOR
SCHEDULED
COMPLETION
WORK
TYPE
PURCHASE
OROER NO
DATE ISSUED
CHG'CWO'RWO
NUMBER
PLANNER
EST. MANHOURS ACT.
i
FERC «
PLANNED WORK
A
B
C
D
WELD.
MACH.
OPER.
CONTR.
OTHER
OUTAGE INDICATOR
EST
CREW SI2
E
j-»
r»
Causa ol Problam:
WORKFORCE MGT. CODE
•-Labor (Productive)
1-Traval Tlma
2-lnclam. Waathar
3-Dolay Tima
4-Down Tlma
*Usa coda «a iaat digit of
work ordar numbar on pay
rocorda.
_rs
— 100
%
TOTAL
MH
'complete
Wort Performed:
Data A Tlma Taggad:_ Data « Tlmo Datagged:
WORK
WORK PERFORMED
PERFORMED BY
TYPE CODE
ACTUAL
DATE
CREW SIZE
COMPLETED BY
COMPLETED
Figure 5.2-8. Example work order form.
177
-------
PH03
POWER MAINTENANCE INFORHATION SOURCE KUN DATE: 2/12/85
JOB ORDER-BOILER A
I JOB NO: 02585 KEPT! 3892 SCHED UEEK: 1 0/1 985 FREQUENCY: 0006
!JOB TITLE: INSPECT, REPAIR, ADJUST S LUBRICATE
: L:NIT : 1 SYSTEM: SCR EQUIP: 56/DAHPER/01 00/ A/C EQ.NO: AC-2892-2
I DESCRIPTION: NODULE "E" OUTLET ISOLATION DAMPER
:DE5C CONT.:
I MANUFACTURER: AIRCLEAN MODEL NO: N/A
:iOCATIO*: B L G. SCR NORTH-SOUTH E.O EAST-UEST 11.5 EL. 182.(4
:CAPABILITY REDUCTION: 0000 PRIORITY: 05 CLEARANCE REQUIRED: YES
!ESTIMATED MANHOURS: 3: 0000.00 2: 0002.5 1; 0002.5 G: 0000.00 T: 5.00
INSTRUCTION BOOK:
DRAUINGS:
LAST COMPLETED: 09/07/84
HAD TO CLIMB BEAMS TO PERFORM - COMPLETED - BERNIE AND RADHA
JOB STEPS:
DAMPER CHAIN P.M. - ISOLATION DAMPERS
UORK SAFELY - CHECK ALL CLEARANCES.
CLEAN' OIL AND DUCT ACCUMULATION FROM CHAIN UITH SOLVENT.
RELUBRICATE UITH SPECIFIED LUBRICANT.
04 CHECK CHAIN TENSION. AEJl'ST AS NEEDED.
OZ CLEAN wORK AREA.
01
o:
03
PAGE 1 OF 1
AREA: 004 ACCT; 512.15 UORK ORDER:
ASSIGNED TO
COMPLETED BV
REMARKS
DATE
DATE
HOUR
hour"
APPROVAL
FAILURE CODE
Figure 5.2-9. Example work order form.
178
-------
construction, and system operation. Dampers which are inopera-
tive due to mechanical failure or absorber recirculation lines
which are cold to the touch because of plugging are examples of
equipment items which also provide information concerning system
operation.
5.2.4.2 Equipment Layout/Access. Equipment layout and access
can influence performance (see Section 2.5.2, System Layout and
Accessibility). For example, layout of ductwork and piping is
very important when considering system operation. Excessive
bending in ductwork can result in added pressure drop, increased
erosion, poor gas distribution, and convenient host sites for
collecting solids and moisture. Excessive bending of piping can
result in high slurry pressure drop, pump cavitation, and host
sites for erosion and solids buildup. These type of problems are
more prevalent in retrofit FGD systems (versus new systems) due
to spatial constraints.
Access to equipment, also a function of plant layout, is
important due to maintenance purposes. Major and minor cleanout
is required periodically. Manholes should be present at each
stage of the absorber. Similarly, side doors should be located
in the reaction tank. Tons of deposits may have to be removed
per maintenance period, hence doors should be large enough for
easy removal of such quantities of material. To simplify re-
pairs, mist eliminator access should allow for easy cleaning or
replacement of the components. A walkway should be available for
worker safety and the prevention of damage to mist eliminator
assemblies and blades. Mist eliminator sections should be light
in weight and come in small sections for easy removal by main-
tenance personnel to save man-hours. Slurry recirculation pumps
are often located in a limited space with difficult access,
especially in retrofit applications. Since these pumps must be
dismantled periodically, sufficient access should be made avail-
able to facilitate maintenance. A winch-and-trolley system for
moving heavy parts, ample space for dismantled components, and
good lighting will simplify repairs. Often the recirculation
179
-------
pump area is the most unsightly part of the FGD facility. A
constant stream of seal water, slurry, and oil leaks from the
pumps are found even in well-maintained systems. Therefore, the
pump area should be designed for easy cleaning, with such fea-
tures as sloping floors, wide floor trenches, and a good supply
of water. Other equipment items such as fans, agitators, and
instrumentation (pH meters, density meters, etc.) should also
have adequate spacing for maintenance. Equipment located in
confined or inaccessible spaces tend to see less maintenance and
prolonged maintenance repair times.
5.2.4.3 Consumed Equipment. Used equipment can provide insights
to possible operating problems. Commonly observed items include
pump impellers and liners, spray nozzles, mist eliminator blades,
and absorber internals.
Erosion, plugging, and thermal stress are common reasons for
spray nozzle replacement. Eroded and plugged spray nozzles may
indicate a process chemistry problem or a mechanical problem due
to slurry distribution or flue gas distribution in the absorber.
Mist eliminator packing is usually replaced because the
packing is either damaged or plugged. Mist eliminators construc-
ted of certain plastics can easily be damaged (thermal stress) at
high temperatures. Melted or brittle mist eliminators usually
indicate a gas temperature control problem (i.e., high tempera-
ture excursion). Mist eliminator replacement because of plugging
is usually the result of gypsum scale formation.
Displaced, plugged, or damaged absorber internals (packing,
supports, spray headers, nozzles) are also indicative of system
reliability and performance. Packing material can be commonly
observed in the recirculation tank or thickener due to the high
flue gas flow and/or high slurry flow. Plugged packing is an
indicator of gas slurry distribution and/or process chemistry
problems.
Pump impellers are usually replaced due to plugging, corro-
sion and/or loss of lining material. Plugged impellers may
indicate excessive solids in the slurry. Corroded impellers
180
-------
indicate either problems with material of construction or process
chemistry. Erosion or loss of pump liners may indicate improper
lining materials, poor installation, high slurry solid levels, or
pump cavitation due to low slurry flow.
The above items and their possible reasons for replacement
are just common examples of what the field inspector will come
across during a plant inspection.
5.2.4.4 General Housekeeping. The overall cleanliness of the
FGD facility provides insight to the following: quality of
maintenance procedures, size and type of maintenance staff, and
the priority the operator utility gives to the FGD system in
comparison to other plant unit operations. A clean and well-
maintained facility will most likely be the result of a well-
organized and managed staff who are probably using some sort of
computer-based maintenance planning system. Good housekeeping is
also an indication that the maintenance staff is well-manned and
is more likely dedicated versus borrowed from other service areas
(boiler staff, on-site contractors, etc.). When compared to the
boiler facility, how well the FGD system is maintained gives a
good indication of how the FGD system is looked upon by the
operator utility.
5.3 PROBLEM DIAGNOSIS AND CORRECTIVE MEASURES
This section describes guidelines to aid the field inspector
in diagnosing problems affecting lime/limestone slurry FGD sys-
tems and in recommending potential corrective measures to remedy
these problems. This section represents a continuation of Sec-
tion 5.2 in which guidelines were described"to interpret perform-
ance data with respect to compliance status. We extend this
discussion by identifying the cause-and-effeet relationships of
the various problems which affect FGD systems (Section 5.3.1).
These relationships are analyzed by the "triggering" event which
initiates the problem sequence and the "terminating" symptom by
which the problem is manifested (see Section 2.5.1, Failure
131
-------
Modes). This discussion is then extended to the corrective
measures instituted to rectify these problems (Section 5.3.2).
This division of material is provided because the corrective
measure sequence is typically a more involved procedure than a
simple reversal of the problem sequence.
5.3.1 Problem Diagnosis
Diagnosing problems affecting lime/limestone slurry FGD
systems involves the identification of problem sequences (failure
modes). Problem sequences are cause-and-effeet relationships
consisting of a triggering event which initiates the problem and
a terminating event which manifests the problem. These problem
sequences are distinguished as either the simple variety (where
the sequence of events are closely connected) or cascading variety
(where the sequence of events are connected through a series of
intermediate events). These sequences can be described in terms
of simplified block diagrams representing the equipment areas and
subsystems identified in Section 2.4.2 (FGD System Design Config-
urations) .
5.3.1.1 Gas Handling and Treatment. The gas handling and
treatment equipment area is comprised of the subsystems of fans,
scrubbers, absorbers, mist eliminators, reheaters, ductwork,
dampers, and stack (Section 2.4.2). These subsystems can be
arranged in a variety of configurations according to process,
application, and duty considerations. The various configurations
presently used in commercial lime/limestone slurry FGD systems
are presented in Figure 5.3-1
As indicated in Figure 5.3-1, there are ten configurations
presently in commercial use in lime/limestone slurry processes.
These configurations are divided according to scrubber-absorber
combinations (listed in the top portion of Figure 5.3-1) and
absorber (only) configurations (listed in the lower portion of
Figure 5.3-1). Of the configurations listed, more pertain to
scrubber-absorber combinations than to absorber combinations
182
-------
00
u>
•CRUBBEk
ABSORBER
CONFIGURATIONS
ABSORBER
CONFIGURATIONS
Inlet
ductwork'
i' I" {
-------
simply because of the additional variation of fan placement
between the scrubber-absorber train (Gas Configurations III and
IV) .
Each configuration listed includes a set of "fixed" sub-
systems that are common to all the configurations listed;
namely—inlet ductwork, absorber, mist eliminator, outlet duct-
work, and stack. All the other subsystems (fan, scrubber, and
reheater) can vary according to presence (scrubber and reheater)
and position (fan and reheater) in the configuration. Of the gas
configurations listed (designated as Gas Configurations I through
X), some are used far more extensively than others. The more
prevalent configurations are consistent with the characteristics
of technology generation described in Section 2.4.1.2 (Gas Con-
figuration IX and X). These characteristics include placement of
the fan upstream (forced draft) of the absorber, elimination of
the scrubber in favor of segregated particulate control (upstream
ESP), use of the absorber for segregated S02 control, and the use
of a reheater to maintain gas temperatures above dew point in the
discharge ductwork and stack.
The cause-and-effeet problem sequences which occur in the
gas handling and treatment area are described below in terms of
the triggering event causing the problem and the terminating
symptom manifesting the problem.
0 Fan. Forced draft fans (upstream of the scrubber/
absorber), as depicted in Gas Configurations I, II, ix,
and X of Figure 5.3-1, depend on the operation of the
upstream particulate matter collection device (typi-
cally ESP). Variations or degradation of performance
in the particulate matter collector can lead to solids
deposition or erosion of the rotor, inlet box, housing,
and discharge duct (see Section 2.4.2.1, Fans). The
following simple and cascading problem sequences can
result:
Accelerated wear and holes in fan housing
Erosion ("sandblasting") of rotor causing loss of
draft across system (inability to overcome gas-
side pressure drop) which can lead to loss of
absorber S02 removal efficiency, loss of duct
184
-------
velocity and settling out of gas-entrained solids
in the duct, or premature motor failure (motor
compensates for mechanical failures).
Inleakage of air into fan (through inlet ductwork
or fan intake), causing gas temperature drop and
dew point corrosion attack in fan and inlet duct;
greater volume of gas into system, causing
increase in pressure drop, loss of absorber S02
removal efficiency, premature motor failure;
greater amount of of oxygen in system, causing
uncontrolled oxidation and process chemistry
problems of gypsum scaling in absorber tower.
Induced draft fans (downstream of the scrubber/absorb-
er) , as depicted in Gas Configurations V through VIII,
have a less cascading influence on FGD operation due to
the minimization of downstream equipment. Any impacts
on downstream equipment will be similar to those de-
scribed above for F.D. fans. However, I.D. fans are
more influenced by the operation of upstream subsystems
than F.D. fans. Accordingly, they can be involved in a
greater number of cascading problem sequences associated
with the scrubber, absorber, mist eliminator, or reheater.
These sequences are described below as these particular
subsystems are discussed.
Scrubber. Scrubbers, as depicted in Gas Configurations
I through VI of Figure 5.3-1, provide supplemental or
primary particulate removal and supplemental S03 removal.
The scrubber subsystem also includes presaturator and
quench towers that condition the gas stream prior to
S02 absorption (see Section 2.4.2.2, Scrubbers/Absorb-
ers) . A scrubber that is part of an S0? scrubber-ab-
sorber train is generally of the venturi (particulate
scrubber) or spray tower (presaturator or quench)
design. These represent "open" (i.e., lacking inter-
nals) designs that are generally not subject to plug-
ging or scaling. Variations or degradation in scrubber
performance can result in a number of simple and cascad-
ing problem sequences.
If the scrubber is preceded by an ESP, degradation
in the performance of the ESP can lead to increased
particulate loading to the scrubber and a sub-
sequent degradation in scrubber performance. This
can be evidenced either by increased scrubber
pressure drop to maintain performance levels, and
therefore greater system power consumption (by the
fans), or erosion of scrubber internals due to the
increased loading.
185
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If the fans are forced draft with respect to the
scrubber, degradation in their performance can
cause variations in gas volume and draft, result-
ing in degradation of particulate capture and S02
removal across the scrubber.
Venturi scrubbers typically operate at a turndown
ratio of 2 to 2.5:1. At high and low gas volumes,
the scrubber has a difficult time maintaining
performance level (i.e., load-following is compli-
cated by limitations in mechanical ability of
scrubber to control pressure drop across throat).
Subsequent degradation in particulate matter
capture and S02 removal are experienced at these
conditions.
Degradation in scrubber performance can affect
absorber performance by increased particulate
matter loading or S02 loading. If the former,
erosion of internals can result. This can cascade
to the mist eliminator, resulting in plugging,
which can carryover to the in-line reheater,
resulting in decline of heat transfer efficiency,
which in turn can result in dew point corrosion to
downstream subsystems of I.D. fans, outlet duct-
work, and stack. If the latter (i.e., S02 load-
ing) , degradation of S02 removal efficiency can
result because of greater than design S02 loading
entering the absorber tower.
If the scrubber also provides physical condition-
ing of the gas (quenching or saturation to reduce
temperature and volume), degradation in perform-
ance can result in thermal stress damage to ab-
sorber internals.
Solids buildup at the wet/dry interface area where
scrubber slurry contacts the gas can result in gas
stream channeling or buildup in pressure drop,
which can lead to degradation of scrubber tower
performance and subsequent cascading results as
noted above.
Absorber. Absorbers are depicted in every configura-
tion shown in Figure 5.3-1 (fixed subsystem). The
absorber can be part of a scrubber-absorber train (Gas
Configurations I through VI) or as the absorber only
(Gas Configurations VII through X). The absorber
represents the heart of FGD system in that the primary
role of the FGD system is fulfilled there—the removal
of S02 from the flue gas. As the focal point of the
FGD system, the absorber is also the focal point of
186
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problem sequences—either as the initiating or termin-
ating event in both simple and cascading relationships.
A number of absorber impacts from the upstream subsys-
tems of fans and scrubbers are described in the pre-
ceding sections. Other significant problem sequences
are described below.
Degradation in the performance of the absorber can
lead to loss of S02 removal efficiency and result
in non-compliance.
Degradation of absorber performance can occur due
to a variety of contributing factors in the up-
stream gas circuit. They include variations in
gas flow, resulting in tower overloading or "flood-
ing" (high gas flow) or tower "weeping" (low gas
flow)*; variation in gas (S02) composition, result-
ing in reduced S02 removal (high S02) or chemistry
(high pH, soft scale formation) upsets (low S02);
degradation in upstream particulate collection
(ESP and/or scrubber) devices (described above);
degradation in upstream fan performance (described
above); and degradation in upstream scrubber per-
formance (described above).
Degradation in absorber performance can occur due
to a number of contributing factors in the slurry
feed circuit (see Section 5.3.1.2, Reagent Prep-
aration and Feed). Insufficient slurry feed, low
slurry pH, and high slurry pH can result in low
S0? removal, solids accumulation and pressure drop
buildup across the tower, solids entrainment in
absorber discharge gas stream, and corrosion/ero-
sion of internals.
Degradation in absorber performance (due to gas-
side or slurry-side factors) can affect downstream
subsystems through a series of simple or cascading
sequences. Solids deposition on the mist elimi-
nator can occur through scaling or plugging. Mist
eliminator pressure drop buildup can take the
absorber out of service. Inefficient mist elimi-
nator performance can contribute to carryover of
~Flooding is a condition which occurs in a packed tower where gas
flow is increased at a given slurry flow rate and slurry is
suspended at the top of the packing and entrained in the dis-
charge gas stream. Weeping is a condition which occurs in a
tray tower where gas flow is insufficient to maintain a slurry
suspension on the trays and the slurry flows unimpeded downward
through the tower.
187
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entrainment to the downstream damper(s), rebeater
(if present), I.D. fans, duct, or stack. Subse-
quent solids buildup and corrosion/erosion can
take these subsystems out of service. If an
in-line reheater exists, solids can buildup on the
tubes, cutting down heat transfer efficiency.
Reduced reheater efficiency can result in dew
point corrosion to downstream I.D. fans, ductwork,
dampers, and stack.
Mist Eliminator. Mist eliminators are shown as a
separate subsystem in every gas configuration in Figure
5.3-1 (fixed subsystem). Before proceeding, however, a
clarification of the mist eliminator subsystem is in
order (see Mist Eliminator, Section 2.4.2.3). First,
although the mist eliminator is shown as a separate
subsystem downstream of the absorber, it is typically
contained within the absorber tower in the proximity
(downstream) of the slurry spray zone. Therefore, it
is not a separate physical entity. Secondly, both
scrubbers and absorbers are typically equipped with
mist eliminators. In FGD systems, however, the absor-
ber mist eliminator is of overriding importance. Since
the mist eliminator is, in effect, a specialized opera-
tion within the absorber, many of the same considera-
tions that apply to the absorber apply to the mist
eliminator as well. In effect, the mist eliminator is
extremely sensitive to the mechanical and chemical
operating aspects of the absorber. Any upset in the
absorber will most of the time also manifest itself in
the mist eliminator. Any mist eliminator outage will
also require the absorber to be taken out of service.
Other problem sequences peculiar to the mist eliminator
are described below.
Mist eliminator self-cleaning occurs through an
automatic water wash system which systematically
cleans the mist eliminator assembly. The wash
water is delivered through high pressure spray
nozzles and piping. Mechanical failure in this
system can result in localized or generalized
solids buildup, resulting in.gas channeling and
carryover of entrainment and/or pressure drop
buildup across the mist eliminator.
The mist eliminator wash water may typically
consist of some portion of clarified liquor re-
covered from primary solids dewatering, secondary
solids dewatering, or the disposal site (see
Section 5.3.1.3, Waste Solids Handling and Dis-
posal) . This liquor can contain high levels of
dissolved salts which represent S02 reactants or
188
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products (calcium sulfite, sulfate, carbonate,
chlorides, etc.). Depending on concentration
levels, these salts can precipitate and accumulate
on the mist eliminator through physical or chem-
ical (i.e., the alkaline salts react with the
residual S0a in the gas stream from the absorber,
forming sulfite/sulfate reaction products) means.
With few exceptions, the mist eliminators are
constructed of plastic (with or without fiberglass
reinforcement). These materials are subject to
thermal stress. (N.B. Many mist eliminators are
now constructed of materials designed to withstand
high temperatures [400°F]. However, these mater-
ials are designed ["guaranteed"] to withstand
limited exposures to high temperatures. As ex-
posure time accumulates, the effects of thermal
stress begin to take place.) In the event of a
sudden loss of slurry or liquor feed to the ab-
sorber or preceding scrubber (including quencher
or presaturator), the hot gas (300°F) may melt or
disfigure the mist eliminator vanes.
Reheater. Reheaters represent an optional subsystem
that always follow the absorber and mist eliminator and
precede the I.D. fan and/or discharge ductwork and
stack. (Gas Configurations I, III, V, VIII, and X of
Figure 5.3-1.) As described in Section 2.4.2.4, three
generic reheat strategies are used: in-line, indirect
hot air, and flue gas bypass. Of these, in-line reheat
is the most sensitive to problems because of its pres-
ence in the gas stream making it vulnerable to upsets
in upstream operations. Upstream operations of impor-
tance are the scrubber/absorber and mist eliminator. A
number of problem sequences involving these subsystems
affecting the reheater were described earlier. Problem
sequences that are peculiar to the reheater alone are
described below.
Reheater self-cleaning occurs through an automatic
soot blowing system which systematically cleans
the tube bundles with either, steam or air. The
steam or air is delivered through retractable high
pressure lances which rotate axially through 360°
for maximum coverage. Mechanical failure in this
system can result in localized or generalized
solids buildup, which can result in reduced heat
transfer, downstream dew point corrosion, and
ultimately, tube bundle failures.
189
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Reheater tube failures typically occur at the weld
in the tube bend facing the discharge gas stream
from the mist eliminator (absorber). A tube
failure obviously causes a decline in the heat
transfer to the gas, resulting in insufficient
temperature boost and the danger of downstream dew
point corrosion (especially in the upper portions
of the stack since a partial failure will show up
at the point of maximum radiative heat loss). A
tube failure, if not attended to immediately, will
trigger other tube failures in the immediate
vicinity due to the corrosive/erosive action of
the heating medium and flue gas environment.
Flue gas bypass reheat is extremely dependent on
proper design and operation of control dampers
regulating the flow of gas into the absorber and
bypass duct. Improper operation in the form of a
partial to a complete (inability to go to a fully
opened or closed position) failure can allow
either too much or too little gas flow into the
bypass duct (meaning low or high gas flows into
the absorber, respectively). This can cause low
SO- removal in the absorber (noncompliance);
thermal stress in the outlet ductwork and stack;
dew point corrosion attack in the outlet ductwork
and stack; and carryover of entrainment to the
outlet ductwork and stack (scrubber-generated
particulate matter, opacity violation, stack
rainout).
Indirect hot air reheat is extremely dependent on
the proper flow and distribution of hot air in-
jected into the scrubbed gas stream to achieve the
desired level of reheat. This is more of a design
consideration than an operating consideration.
Insufficient residence time and/or mixing can
cause an uneven (stratified) gas temperature
profile, resulting in localized dew point corro-
sion attack and/or localized thermal stress damage
in the downstream I.D. fan (optional), ductwork,
and/or stack.
Ductwork. Inlet and outlet ductwork are fixed subsys-
tems of every configuration depicted in Figure 5.3-1.
Many of the simple and cascading problem sequences
associated with the ductwork have been described in the
preceding discussion. A number of additional problem
sequences associated with the ductwork subsystem are
discussed below. These sequences are associated more
with design considerations than operating considera-
tions. A problem specifically inherent to ductwork is
190
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the inability of obtaining a representative gas sample
or gas flow measurement. This could bias any manual or
continuous monitoring performance or guarantee measure-
ments .
Insufficient or excessive cross-sectional area of
t*he ductwork's inner diameter will result in
excessive or insufficient gas velocities, respec-
tively, causing carryover of entrainment, settling
out in the ducts, and ultimately, erosion or
corrosion attack.
Rectangular ductwork (typically observed in gas
distribution manifolds and breeching for some
systems) is subject more to nonuniform gas
distribution than circular ductwork, causing
associated variations in performance and attendant
problems as described in the preceding sections.
The use of turning vanes (gas flow distribution
baffles) in rectangular ductwork is beneficial,
though not always a complete solution.
Bends, expansions, and contractions in duct runs
also contribute to nonuniform gas flow and atten-
dant variations in performance and subsequent
problems.
Stack. Similar to the ductwork, the stack is also a
fixed subsystem of every configuration depicted in
Figure 5.3-1. Moreover, since the stack occupies the
tail-end of the gas handling and treatment equipment
area, it is always the subsystem affected by a simple
or cascading problem sequence rather than the trigger-
ing or initiating event. Much of the foregoing dis-
cussion on outlet ductwork also applies to the stack.
A consideration unique to the stack is due to its
dimensions and position in the gas circuit. Typically,
stacks rise very high above grade. Heights vary from
200 ft to 1200 ft. Present day stack height has been
somewhat standardized by the "Good Engineering Prac-
tice" of the June 1979 NSPS (see Section 2.1.1.2)
specifying credit for 2.5 times the source or tallest
adjacent structure (i.e., roughly equivalent to 500 to
600 ft above grade). Added to this consideration is
the stack's tail-end position in the gas circuit.
Unique problems associated with these considerations
are radiative heat loss in the discharge ductwork and
stack base which can cause downstream dew point corro-
sion to the top portion of the stack, even if the
required degree of reheat is being achieved. Concur-
rent considerations associated with this concern are
plume visibility, plume rise, and pollutant dispersion.
191
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Dew point corrosion to the top portion of the stack is
compounded by the inability to inspect it during rou-
tine operation, maintenance, or scheduled maintenance.
0 Damper. As indicated in Figure 5.3-1, dampers are not
shown as a separate subsystem. Instead, they are
associated with the operation of the subsystems of
ductwork, fans, scrubbers/absorbers, and reheaters.
Dampers are used to regulate the flow of flue gas
through these subsystems through control and isolation
functions. These functions are critical to the proper
operation and performance of these subsystems. Damper
malfunctions can be either a triggering or terminating
event in a simple or cascading problem sequence.
Dampers in the inlet or outlet ductwork are sensitive
to the performance of upstream particulate controls or
S02 absorbers. Degradation in performance can result
in accumulation of solids (fly ash, S02 reactants and
products) on damper drives and seals, causing damper
regulation problems with associated gas control and
(in)leakage problems. Gas control problems include
regulation of the fan, scrubber/absorber, and bypass
and hot air injection reheaters. Leakage problems
include gas bypass for scrubbers/absorbers during low
load or maintenance situations. Gas flow regulation
problems can cascade into performance degradation for
the subsystems being served through low and high gas
flows, as described in the preceding sections on the
various subsystems in the gas handling and treatment
equipment area. Isolation problems can prevent timely
inspection and preventative maintenance, which, if
avoided, can ultimately manifest itself in major un-
scheduled maintenance. Dampers in the absorber dis-
charge are subject to the harshest operating environ-
ment. Corrosion attack commonly occurs through entrain-
ment carryover of solids and the collection of corro-
sive condensate (the solids carryover deposit, forming
convenient host sites for the collection and buildup of
corrosive condensate, leading to pitting corrosion of
the surface material). Entrainment carryover generally
occurs as a result of poor mist eliminator performance,
which can be caused by poor absorber performance, which
in turn can be caused by poor scrubber performance.
5.3.1.2 Reagent Preparation and Feed
The reagent preparation and feed equipment area is described
in Section 2.4.2 (Existing Design Configurations). As is the
case for the gas handling and treatment equipment area discussed
in the preceding section, the subsystems contained in the reagent
192
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preparation and feed area can be arranged in a variety of config-
urations. However, unlike the gas handling and treatment equip-
ment area, the number of permutations are limited. This is a
result of process considerations, which represent the primary
determinants in the selection of a s*ubsystem configuration. In
effect, there are two basic configurations presently in use—one
for lime slurry processes and one for limestone slurry processes.
These configurations differ because in the former, a more reac-
tive and pre-prepared (calcined) chemical additive—lime—is
used, requiring special handling and preparation considerations.
In the latter, a less reactive chemical additive—limestone—is
used, requiring less sophisticated handling and preparation
techniques. A simplified block diagram of these configurations
is presented in Figure 5.3-2.
Figure 5.3-2 defines two basic configurations comprised of
the subsystems of receiving, conveying, bulk storage, slurry
preparation (milling and slaking), and slurry distribution (prod-
uct slurry storage, product slurry feed, and slurry recircula-
tion). Of these subsystems, only conveying, bulk storage, and
slurry preparation show a variance.
The cause-and-effeet problem sequences which occur in the
reagent preparation and feed equipment area are described below
by subsystem in terms of the triggering event and the terminating
event for both simple and cascading varieties.
0 Receiving. Receiving and off-loading of reagent sup-
plies to the plant can occur through any one or combin-
ation of river barge, rail car, or road truck. Most
modern day plants incorporate the flexibility of re-
ceiving supplies through more than one mode of trans-
portation (in many cases, all thrfee). Factors which
govern this selection include geographical location,
existing infrastructure, source of supply, and mode of
coal transportation. Although receiving and off-load-
ing are not considered sophisticated or specialized
functions of the FGD process, a number of simple pro-
blem sequences can occur.
193
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LIMESTONE
SLURRY
PROCESS
vo
LIME
SLURRY
PROCESS
Feed
Bins
Gall mill
Slakers
Slakers
Ball
Truck
Receiving
Rai 1
Receiving
Bulk
Storage
Piles
Bulk
Storage
Bins
Pneumatic
Conveying
Barge
Receiving
Mechanical
Conveying
Slurry
Distribution
~Slurry distribution includes product slurry storage, product slurry feed, and slurry recirculation.
Figure 5.3-2. Reagent preparation and feed subsystem arrangements.
-------
Weather conditions can interrupt the supply of
reagent to the plant, especially river barge
deliveries during severe winter weather (freezing
conditions). Extended interruptions can even-
tually affect FGD service time, especially if
plant supplies are low. This is more of a concern
for lime than limestone because on-site bulk
storage is limited to storage silos and bins
whereas limestone bulk storage can be accommodated
through large, unprotected storage piles (typical
limestone storage pile is 30 days of operation).
Weather conditions also can hamper or interrupt
unloading operations because of frozen shipments,
especially rail cars.
Conveying. Conveying equipment includes covered belt
conveyors, screw conveyors, and pneumatic conveyors.
The former two are of the "simple" mechanical variety;
the latter uses compressed air. Limestone is normally
conveyed to storage by mechanical means; lime by pneu-
matic means. Interruption of conveying from receiving
to bulk storage or from bulk storage to slurry prepara-
tion can obviously affect (interrupt) FGD operation.
However, a more subtle problem occurs where conveying
equipment is shared (in order to save on capital costs) .
This situation exists at a number of coal-fired plants
which use limestone slurry FGD. The coal and limestone
supplies share a considerable portion of the belt
conveying equipment. Contamination of supplies invar-
ibly occurs. Contamination of the limestone supply by
coal fines may plug or erode feed equipment in the
slurry circuit. As a consequence, there is added
potential for absorber plugging or scaling.
Bulk Storage. Open storage piles are used for bulk
limestone storage and storage silos and bins are used
for the bulk lime storage. Open storage piles are
subject to problems beset by ambient environmental
conditions in the form of freezing and precipitation
(subsequent dissolution of reagent by water). Silos
and bins are a more expensive means of storage. They
can periodically experience flow problems such as
jamming or plugging. Lime storage bins must be weather-
proofed and airtight to prevent absorption of water and
carbon dioxide from the atmosphere. Lime storage is
much more limited in supply capacity than limestone
(typically 100 tons per storage bin ). Lime storage
also is generally served by more complex conveying
equipment than limestone. These two factors make lime
storage a more difficult proposition than limestone.
Supply interruptions or conveyor failures can impact
195
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FGD operation relatively quickly, possibly causing a
curtailment or interruption of operation. Conveyor
failures can occur through the loss of a compressor,
screw conveyor, or bucket elevator.
Feed Bins. Feed bins receive the reagent from storage
(piles or silos) and transfer the material to slurry
preparation. Feed bins are similar to storage bins and
therefore are subject to the same type of problems. A
feed bin is a somewhat more complex operation, however,
due to the presence of dust collecting equipment, air
locks, and feeder. The feeder feeds and meters the
flow of reagent into the ball mill or slaker. Failure
of the bin or ancillary equipment can cause slurry
interruption and curtailment of FGD operation. Improp-
er operation can impact the operation of reagent prep-
aration equipment, causing variations in slurry product
quality and subsequent degradation in S02 removal and
absorber reliability (plugging, scaling of internals).
Reagent Preparation. Limestone slurry is typically
prepared by a ball mill (Section 2.4.2.7) and lime
slurry is typically prepared by a slaker (Section
2.4.7.8). A limited number of lime slurry FGD systems
use ball mill slakers to improve slurry product quality
(slurry particle size). Where the absorber is con-
sidered the central operation of the gas handling and
treatment equipment area, so the ball mill or slaker is
considered the central operation of the reagent pre-
paration and feed equipment area. The ball mill pro-
duces a product quality of typically 90 percent minus
200 mesh (design specifications can range from as low
as 70 percent minus 200 mesh to as high as 95 percent
minus 325 mesh). The slaker produces a product quality
of all hydrated particles of one micron or less in
size. A number of problem sequences associated with
these subsystems are noted below.
Variations in specified chemical and physical
properties of the bulk reagent delivered to the
plant can cause degradation in ball mill or slaker
performance. Physical characteristics of lime-
stone grindability and lime porosity may limit
desired particle size, available particle surface
area, and reactivity of final slurry product which
in turn can affect absorber SO^ removal and reli-
ability (plugging, scaling). Chemical character-
istics of active alkali components (CaCOa, CaO,
MgC03, MgO) and impurities (silica) will affect
S02 removal and mechanical reliability. With
respect to the former, insufficient active alkali
can limit the amount of alkalinity available in
196
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the slurry liquor to absorb SO,. With respect to
the latter, impurities in the form of silica,
chirt, and flint can result in an extremely abra-
sive slurry product which can erode absorber
internals, slurry spray nozzles, and slurry stor-
age and feed equipment. Degradation in reagent
quality will also increase the quantity of bulk
material consumed, resulting in a more costly and
more solid waste-producing operation.
Ball mill performance is a direct function of the
quality of the milling surface. The initial
charge of balls in the mill is eroded away over
time with use. Degradation in slurry product
quality will result. Periodic recharging is an
inherent must. Degradation in bulk limestone
quality (impurities) may also accelerate mill
surface wear and subsequent product slurry qual-
ity.
Slaker performance is a direct function of resi-
dence time and temperature of the slaking opera-
tion. The mechanism by which hydration reactions
are carried to completion require the heat of
reaction to convert water into steam at the sur-
face of the lime pebble. Steam expansion plus
slurry agitation causes reaction products to be
carried away from the surface of the pebbles as
they form, thereby exposing fresh surfaces for
further reaction, thus improving reagent utiliza-
tion. Depending on slaker type (Section 2.4.2.8),
retention time and temperatures range from 5 to 30
minutes and 167 to 194°F, respectively. Insuffic-
ient residence time and temperatures cause ineffi-
cient particle dispersion, rapid crystal growth,
"blinding", localized overheating, and lime loss
through hard scale formation in the tank. These
effects in turn result in a poor quality slurry
product, resulting in possible degradation of S02
removal across the absorber, increased lime con-
sumption, and scaling and plugging within the
absorber tower.
The quality of the lime slurry product is highly
dependent on the quality of the slaking water
used. High concentrations of S02 products_and
reactants and anions such as carbonate (CO~), and
bicarbonate (HC03) will precipitate in the pres-
ence of calcium and cause scaling. Similarly,
high concentrations of metal cations that will
precipitate as hydroxide salts are objectionable.
High chloride concentrations do not appear to be
197
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detrimental to the slaking process; however, high
concentrations of chlorides may increase the
degree of chloride corrosion. The result of using
a poor quality slaking water is a reduction in the
slaking rate and the production of large, dense
particles of partially hydrated lime. The slurry
is more abrasive, thereby accelerating erosion
attack.
The quality of lime slurry dilution water is not
as critical as slaking water, provided that com-
plete slaking of the lime slurry is accomplished
using high quality fresh water. Dilution with
recycled water should be satisfactory and only
minimal use of fresh water as a blend should be
required. If recycled water is used for slaking,
recycled water for dilution will react with dis-
solved anionic species and the resulting compounds
will precipitate on the suspended lime particles,
preventing dissolution and reaction ("blinding").
This in turn will result in a degradation of
performance as noted above. This problem arises
because the pH of slaked lime slurry is very high
(in the range of 11 to 12).
The quality of the limestone slurry product is
largely independent of the quality of milling and
dilution water used. Limestone differs from"lime
in this regard in that it is much less reactive
(i.e., much lower pH) and, therefore, dissolves
less readily in water. Thus, in order to get
sufficient alkalinity into the slurry liquor, a
ball mill is needed to pulverize the limestone to
finely ground particles and expose sufficient
surface area to generate reactivity. The pulver-
ization operation supercedes any effect the quality
of water may have on dissolution. Recycled water,
cooling tower blowdown, and waste water from other
operations can substitute for fresh water without
significant impact on limestone slurry product
quality, absorber performance, and the performance
of other subsystems.
Slurry Distribution. The slurry distribution subsystem
includes slurry product storage, slurry feed to the
absorber, and slurry recirculation within the absorber
loop. The slurry distribution network is where reagent
preparation and feed equipment area interfaces with the
gas handling and treatment equipment area. As such,
any problem sequences which originate or cascade in the
slurry distribution subsystem are eventually manifested
in the performance of the gas handling and treatment
198
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equipment area. A number of these problem sequences
have been described in the preceding sections for the
upstream subsystems in the reagent preparation and feed
equipment area. A number of additional sequences
peculiar to the slurry distribution subsystem are
identified below.
Lime slurry product storage not only provides
surge volume between the slaker and absorber, but
also allows time for the slurry to "stabilize".
Addition of dilution water to a concentrated
slurry causes a series of chemical reactions
between the lime and dissolved minerals in the
water such as the alkaline earth salts (Group IIA
metal oxides), chlorides, sulfates, and phosphates.
These reactions, which are typically completed in
less than 15 minutes, cause the formation of hard,
insoluble, crystalline solids. The primary func-
tion of slurry storage is to hold freshly diluted
slurry until these scale-forming reactions are
completed. Once completed, the trapped suspended
solids are allowed to settle out of the slurry
before being introduced along with the slurry to
the FGD system. In a well-designed system, a
large storage tank is used so that most of the
scale compounds are present as a suspension. As
additional scale compounds are formed, they adhere
to the suspended crystals, which increase in size
and eventually settle to the bottom of the tank.
The slurry is then said to be stabilized. If no
more water is added and the slurry does not absorb
significant quantities of C02 from the air, no
further scale reactions occur. If insufficient
residence time is provided in the lime slurry
product tank, or the addition of dilution water is
uncontrolled, or too much residence time in the
lime slurry product tank is provided (increasing
C0_ uptake from the air), or if the suspended
solids are not allowed to settle, the "unstabi-
lized" slurry contributes to the erosion of down-
stream transfer pumps and piping, decreased S02
removal in the absorber, plugging and scale for-
mation in the absorber, and possible downstream
effects to the mist eliminator, reheater, I.D.
fans, ductwork, and stack.
Limestone slurry product storage provides surge
capacity within the slurry distribution subsystem
in order to permit disruptions in the operation of
the grinding system without affecting the opera-
tion of the absorber. Limestone slurry product
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storage also provides residence time for disso-
lution and generation of sufficient slurry liquor
alkalinity. Unlike lime, limestone exhibits a
much less reactive and more buffered process
chemistry. Accounting for process surge capacity
and limestone dissolution, limestone slurry stor-
age tanks provide a residence time of a minimum of
8 hours to a maximum of 40 hours. If residence
time is below the minimum, or if the fresh lime-
stone slurry "short circuits"* the product slurry
storage tank, the limestone slurry feed to the
absorber may be insufficient in slurry liquor
alkalinity, causing degradation of S02 removal
across the absorber, increased limestone consump-
tion, plugging and scaling in the absorber, and
cascading downstream effects in the mist elimin-
ator, reheater, I.D. fan, ductwork, and stack.
All slurry distribution tanks must be sufficiently
agitated to keep the solids in suspension. In the
event of insufficient agitation or agitator fail-
ure, solids will settle out and plug up discharge
lines, pump intakes, and valves.
Slurry recirculation tanks receive product slurry
from the reagent preparation subsystem, spent
slurry from the absorber ("downcomer"), and, in
some cases, makeup water (process recycle or
fresh). The slurry recirculation tank fulfills a
number of mechanical and chemical functions in the
process. In the way of mechanical functions,the
recirculation tank provides surge capacity within
the system to balance the operation of the reagent
preparation and feed, gas handling and treatment,
and waste solids handling and disposal equipment
areas. As the nexus of these equipment areas, the
recirculation tank represents the logical point to
monitor and control process chemistry. The pro-
cess chemistry parameters monitored include slurry
pH and percent solids. The process chemistry
variables of importance include solid phase resi-
dence time, liquor phase residence time, lime/
limestone dissolution, crystal precipitation,
particle size, relative saturation, percent oxida-
tion, individual cation and anionic concentra-
tions, and liquid phase alkalinity. Thus, the
*Short circuiting is the inability of the slurry to use the
entire residence time provided by the tank due to the positioning
of the inlet and outlet feed streams or insufficient backmixing.
200
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complexity of the functions of the recirculation
tanks make it both extremely important and ex-
tremely sensitive to problem sequences within the
entire process. A number of considerations pecu-
liar to the recirculation tank are enumerated
below.
(1) Slurry residence times of 8 to 15 minutes are
typical for lime/limestone systems. All
other factors being equal, the lower range
suffices for lime slurry and the higher range
suffices for limestone (due to chemical
reactivity considerations). An undersized
recirculation tank can impair the mechanical
and chemical aspects of process operation.
Namely, the inability to "surge", insuffi-
cient volume to avoid pump cavitation, in-
sufficient slurry alkalinity to remove S02 in
the absorber, tower scaling and plugging,
high reagent consumption, and increased solid
waste volumes.
(2) Improper mixing in the recirculation tank can
short circuit the available residence time
and affect the process chemistry which in
turn can cause reduced S02 removal across the
absorber, scaling and plugging in the
absorber, increased reagent consumption, and
increased solid waste production. Improper
mixing can occur through insufficient
residence time, tank geometry, arrangement of
feed and discharge streams, insufficient
agitation, and position of agitators (top
entry preferred to side entry).
(3) Open external tanks are subject to debris
falling into the tank, which can clog up pump
intakes, feed lines, and spray nozzles,
causing inefficiency of operation and/or
component malfunctions. Open tanks also emit
slight corrosive vapors which can eventually
rust/corrode the undersides of equipment
directly above, most notably absorbers.
(4) Internal tanks provide limited access for
inspection, operation, and maintenance. This
can result in the lack of proper attention or
early detection of minor operating problems
which can compound into major problems (noted
above). Noteable examples are agitator
operation (motor, shaft, and blade assembly
201
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integrity and lubrication), proper liquid
level, corrosion of internals and undersides
of equipment directly above.
(5) Cylindrical tanks contain superior mixing
characteristics to rectangular tanks which
have a higher potential for short circuiting
and localized poor mixing. The impacts of
this condition on process performance are
noted above.
5.3.1.3 Waste Solids Handling and Disposal. The waste solids
handling and disposal equipment area is described in Section
2.4.2 (Existing Design Configurations). Similar to the
discussion for the previous two equipment areas, the subsystems
contained in the solids handling and disposal equipment area can
be arranged in a variety of configurations. For this particular
equipment area, a large number of permutations are possible.
Figure 5.3-3 presents a summary of the various configurations
used in commercial lime/ limestone slurry FGD systems. Figure
5.3-3 is organized according to the solid waste treatment method
used. As indicated, three major types of treatment methods are
possible—untreated, physical treatment, and chemical treatment.
Untreated is self-explanatory. The recirculation slurry bleed is
handled and disposed without the benefit of an external treatment
step. Physical treatment involves the use of forced oxidation to
"physically" treat the waste product. Physical treatment is
somewhat of a misnomer in this context because forced oxidation
involves the conversion of the "unoxidized" sulfite to sulfate,
generating a gypsum-bearing waste product. Chemical treatment
involves the use of chemical additives to treat the waste product.
One form of chemical treatment is stabilization which involves
the addition of chemically non-reactive materials and the other
is fixation which involves the addition chemically reactive
materials. All the subsystem configurations described in Figure
5.3-3 are applicable irrespective of process, application, and
duty considerations.
The cause-and-effeet problem sequences which occur in the
waste solids handling and disposal equipment area are described
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Slurry
Bleed
Physical
Treatment
Primary
Secondary
Dewatering
chemical
Treatment
Final
D1sposal
ewaterinq
SIurry
leed/
c 1 u rry
ank
Interim
Pond
Thickener
hickener
vacuum
Filter
Thickener
vacuum
Filter
LandTiT1
Thickener
Centrifuge
Thickener
Centrifuge
Landfi1i
Slurry
='eea/
Si urry
ank
Forced
Oxidation
Thickener
acuum
Filter
Landfim
Stack
Centrifuge
Landfii1
SIurry
Bleed/
SIurry
ank
Thickener
Fixation
Thickener
vacuur.
Fi Iter
S tab11izaticn
Centri fuae
Stabilization
Centri fuae
Stad^jaticr
Fixation
La^dfi;
/acuum
F i1ter
Landfii1
Centrifuge
Fixation
Landf-n
Figure 5.3-3. Waste solids handling and disposal subsystem arrangement.
203
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below by subsystem in terms of the triggering and terminating
events for both simple and cascading varieties.
° Slurry bleed. Purging spent slurry from the absorber
slurry recirculation loop can be accomplished by bleed-
ing 'directly from the slurry recirculation line or the
slurry recirculation tank. In the former, the bleed
line extends directly off the recirculation line on the
discharge side of the recirculation pump(s) feeding the
absorber. This operation is actuated by a control
valve. In the latter, spent slurry is taken directly
out of the bottom of the slurry recirculation tank
through the use of a separate pump and discharge line.
Both operations are controlled by monitoring physical
and chemical parameters in the recirculation tank,
namely—slurry liquid level, slurry pH, and slurry
percent solids. The bleed stream method is more preva-
lent due to favorable costs; however, bleeding from the
tank offers superior process control and reliability.
A number of simple and cascading problems sequences are
identified below:
Bleeding spent slurry is controlled primarily by
monitoring the solids content of the slurry in the
recirculation tank to a specified level. The
solids control level is typically 10 percent,
although levels as low as 5 percent and as high as
15 percent are practiced. In an unsteady-state
situation, if the solids level is allowed-to fail
below the set point (i.e., the solids level of the
recirculation slurry is maintained below design),
absorber process chemistry may be upset and down-
stream solids dewatering operations may be over-
loaded. Absorber process chemistry upsets can
occur through depletion of slurry alkalinity and
depletion of slurry seed crystals. In the former,
S02 removal declines; in the latter, the precipi-
tation of S02 reaction products declines and
uncontrolled scaling occurs in the absorber.
Downstream dewatering operations are sized accord-
ing to the mass inlet loading of solids. Continua-
tion of unsteady-state operations above this
design value can result in insufficient clarifica-
tion of recovered water or subsequent overloading
of downstream secondary dewatering equipment. On
the other hand, if the solids level is allowed to
rise above the set point (i.e., the solids level
of the recirculation slurry is maintained above
design), absorber operation can be affected
through erosion of slurry pumps, valves, and
piping, and plugging and scaling of tower intern-
als. Downstream operations are also affected
204
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in that insufficient solids loading may create too
much water in the solid waste product for proper
processing or dewatering.
Bleeding spent slurry off the recirculation line
limits the amount of redundancy available to
overcome component failure. (Generally, the
absorber is served by one main slurry recircula-
tion line which manifolds into several recircula-
tion pumps.) A failure in the control valve can
affect absorber performance (as noted above) and
upset downstream operations (as noted above).
Bleeding spent slurry directly out of the recircu-
lation tank offers more flexibility in the event
of a component failure. Redundancy can be provided
through spare pumps and valves, which can be
placed quickly into operation without affecting
absorber and downstream dewatering equipment
performance. In addition, a failure here (i.e.,
recirculation tank bleed line) would have little
or no short-term effect to absorber recirculation
feed because of greater surge capability of tank
versus bleed line.
Forced Oxidation. Forced oxidation involves the conver-
sion of sulfite to sulfate to produce a gypsum-bearing
waste product. Typically, forced oxidation is grouped
with the chemical methods of fixation and stabilization.
However, forced oxidation is treated separately here
because of its position in the process flow sheet.
(Forced oxidation is accomplished in the slurry recir-
culation tank before dewatering, whereas stabilization
and fixation are accomplished after dewatering.)
Forced oxidation is used in selective applications —
exclusively limestone slurry processes and primarily
low sulfur coal applications (due to the high degree of
natural oxidation which occurs in these systems).
Forced oxidation is accomplished by an air compressor
and sparger pipe or ring situated in the base of the
slurry recirculation tank. A number of problem se-
quences are noted below:
Process chemistry upsets can reduce the efficiency
of converting sulfite to sulfate and therefore the
amount of gypsum produced. One key variable is
slurry pH. Oxidation efficiency increases as
slurry pH is reduced (i.e., becomes more acidic).
In'the limestone slurry process, this means any pH
approaching 5 or below. At "high" pH levels, any
pH approaching 6 or above, more dissolved sulfite
precipitates out as a solid phase salt and sulfite
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oxidation efficiency drops correspondingly (i.e.,
sulfite oxidation occurs in the aqueous phase
only; oxidation of the solid sulfite is extremely
limited). This can have a number of ramifications
on process operation. Solids dewatering becomes
increasingly more difficult (calcium sulfite
crystals are more difficult to dewater because of
crystalline properties). Solid waste disposal
increases in volume and solid waste quality de-
clines. Desupersaturating the process liquor of
S02 reaction products declines, increasing the
likelihood of scaling in the absorber.
Another key process chemistry variable is slurry
solids. If an insufficient amount of seed crys-
tals is not maintained in the slurry recirculation
loop, gypsum desupersaturation becomes impaired,
contributing to the likelihood of scaling in the
absorber.
A compressor failure or insufficient agitation in
the slurry recirculation tank can impair sulfite
oxidation conversion efficiency, with consequences
noted above.
Solids buildup on the forced oxidation sparger
holes at wet/dry interface can impair oxidation
efficiency, with consequences noted above.
Primary Dewatering. Primary dewatering is accomplished
by a thickener or interim pond. Current use emphasizes
the former. Interim ponds, which were used extensively
in early FGD systems, have been largely abandoned due
to inefficiency of clarification of process liquor
coupled with a greater emphasis on closed water loop
operation (most of these applications were solar evap-
oration ponds [located in arid regions of the south-
west] used in once-through, open water loop systems).
The thickener is an extremely problem-sensitive opera-
tion because of its central role in balancing the
chemistry and flow of the FGD process. A number of
notable problem sequences are identified below:
Process chemistry upsets can alter the flow and
composition of the spent slurry stream, affecting
solids dewatering (solids content of underflow)
and clarification (residual solids content in
overflow). Subsequent impacts include mist elimi-
nator cleanliness, increased makfeup water consump-
tion (pump seals, mist eliminator wash, slurry
precipitation, slurry dilution), increased solid
waste production, ineffectual secondary solids
206
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dewatering, inefficient chemical treatment, and
final disposal difficulties.
Inefficient thickening due to insufficient resi-
dence time for settling out S0a reaction products
can contribute to the consequences noted above.
Key design factors are liquid surface area (thick-
ener diameter) and liquid level (thickener height).
Inefficient secondary dewatering resulting in high
residual solids in filtrate or centrate recycled
back to the thickener can overload thickener
operation.
Inefficient thickening due to an insufficiently
sloped bottom cone can impair sludge blanket
formation and solids content of underflow.
Rake drive speed variations (or failure) on the
low or high side can cause clogging of solids
underflow stream or high turbulence in thickener
with insufficient clarification of overflow stream.
Secondary Dewatering. Secondary dewatering is accomp-
lished by vacuum filter or centrifuge. Current use
emphasizes the former. The problem sequences identi-
fied in the foregoing for the thickener also apply to
secondary dewatering. A number of special considera-
tions which differentiate secondary and primary dewater-
ing are worth noting. First, the vacuum filter (or
centrifuge) is mechanically a more complex operation.
Therefore, there is a greater risk of failure or im-
proper operation. Second, however, size and cost
factors permit the use of spare vacuum filters which
compensate for the higher degree of risk.
Physical/Chemical Treatment. Physical/chemical treat-
ment involves the use of additives to stabilize or
"fixate" the solid wastes prior to final disposal.
Stabilization process involves no significant chemical
reactions between the wastes and the additive; the
additives provide physical stability primarily by
increasing the solids content of the wastes. Fixation
involves pozzolanic (cementitious) chemical reactions
between the wastes and the additives (e.g., lime, fly
ash). Some western coal ashes are so alkaline that
addition of lime is not necessary for fixation. Fix-
ated material is more often subsequently used for
off-site landfill where product quality and secondary
environmental impacts are of primary concern. The
problem sequences in the upstream subsystems that can
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cascade to the physical/chemical treatment subsystem
are noted above. Other notable problem sequences
include:
Insufficient curing time prior to disposal will
inhibit the material's ability to set up properly
in the disposal site, resulting in variations in
landfill quality and increased tendency for second-
ary environmental affects associated with permea-
tion or runoff of dissolved chemical components.
Excessive curing time prior to disposal inhibits
the handling and transportation of the material to
the final disposal site. The material can set up
in the curing pile or the pipe line delivering the
material to the disposal site.
Variations in monitoring of additive chemicals or
quality control (such as often exhibited in the
transition from startup to sustained operation)
can result in stratified variations of final dis-
posal material. This can limit the end use of the
disposal site, especially in a structural fill.
° Final Disposal. Three major types of final disposal
are available: pond, landfill, and stacking. Stacking
(i.e., systematic piling of waste material above ground
level) is applicable only for forced oxidation, secondary
dewatering, gypsum waste-producing systems. To date,
no such systems are in commercial operation. Of the
pond and landfill methods available, a variety of types
are used in accordance with the considerations of
off-site/on-site, surface/subterranean, and minefill/-
structural fill. A number of problem sequences associ-
ated with the final disposal operation are identified
above. A problem commonly encountered with lime/lime-
stone slurry systems is insufficient capacity of the
final disposal site. Conditions which contribute to
this (in descending order of importance) include open
water loop (purging) operation (affecting pond capacity),
inefficient dewatering, high reagent consumption, high
S02 loadings (versus design), and-underdesign of disposal
capacity requirements.
5.3.2 Corrective Actions
Following problem identification and problem diagnosis,
corrective measures are then taken to rectify the problem and
restore the FGD process to steady-state operating conditions. As
noted previously in this section, the corrective action sequence
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is, in many cases, a more involved procedure than a simple rever-
sal of the problem sequence. The corrective action sequence
generally begins by correcting the initiating or triggering
event. The subsystems affected in the simple or cascading se-
quence are restored to previous operating status. The subsystem
manifesting the symptom or terminating event is then monitored to
verify resumption of steady-state operation.
Corrective sequences are described in the following sections
for the problem sequences described in Section 5.3.1 (Problem
Diagnosis). The approach adopted for the presentation of this
material is to describe remedial actions for those subsystems
that are vital and unique to the operation of lime/limestone FGD
systems. This information is organized according to the equip-
ment areas and subsystems described in Section 5.3.1 and defined
in Section 2.4.2 (Existing Design Configurations).
5.3.2.1 Gas Handling and Treatment. All of the subsystems
contained in the gas handling and treatment area are considered
both vital and unique to the operation of lime/limestone FGD
systems. Accordingly, corrective actions are described below for
each.
0 Fan. Forced draft fans tend to have a more pronounced
cascading influence on FGD operation than I.D. fans due
to position in the process flow sheet. The triggering
event in fan-related problems is loss of upstream
particulate collection efficiency. Accordingly, the
following corrective sequence is instituted:
(1) Take fan out of service (which usually involves
taking the absorber module out of service also).
(2) Remove deposits from internals and rotor.
(3) Repair (welding, patching) or replace failed
components.
(4) Rebalance fan rotor, inspect and lubricate bear-
ings and motor.
(5) Determine particulate collection efficiency of
upstream device via inlet/outlet measurements (EPA
Method 5) to determine particle loading, particle
size distribution, and particle resistivity.
209
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(6) Correct particulate collection device through
mechanical modifications, flue gas conditioning,
or possibly modifying characteristics of coal
fired in boiler (last resort).
(7) Startup fan and monitor performance via differen-
tial pressure readings across the fan in accord-
ance with fan performance curves provided by the
manufacturer.
Scrubber. Scrubbers include Venturis for particulate/S02
control and presaturators and quenchers for physical
conditioning of the gas stream prior to absorption.
Venturi scrubbers may achieve insufficient particulate
and S02 removal. The following corrective measures may
be instituted:
(1) Increase gas-side pressure drop across the
scrubber through the variable-throat adjustment
(obviously/ this first step is not possible for
fixed-throat designs).
(2) Increase scrubber L/G ratio by increasing slurry
flow rate through increased pumping (increase
output of variable-drive pumps or bring installed
spare pumps into service).
(3) Measure particulate and/or S02 removal across
scrubber before and after throat and/or L/G adjust-
ments (EPA Method 5).
(4) If adjustments are insufficient, take scrubber out
of service.
(5) Remove deposits from wet/dry interface areas.
(6) Remove deposits from slurry spray nozzles.
(7) Check/replace slurry spray nozzles.
(8) Modify slurry spray pattern through nozzle and
piping modifications (optional, if problem per-
sists) .
(9) Return scrubber to service and monitor performance
by S02, particulate, temperature, pressure, flow
differentials across tower.
Absorber. Absorbers may encounter solids deposition in
the form of plugging or scaling of internals. Although
plugging and scaling represent different chemical
210
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phenomena, they cannot be readily distinguished by
conventional performance monitoring. Even visual
inspection cannot distinguish one from the other.
Chemical analyses of the deposits (and slurry liquor)
are generally needed. Solids deposition is also a
problem for open spray tower designs (although somewhat
less debilitative), as solids can buildup at wet/dry
interface areas, slurry spray headers, slurry spray
nozzles, and various internal supports. Solids depo-
sition is generally remedied through the following
corrective sequence:
(1) Reduce (acidify) slurry pH by small incremental
amounts (0.1 pH units).
(2) Monitor gas-side pressure drop and S02 removal
while reducing slurry pH. (The time frame over
which this action is taken will vary according to
the system and the situation. However, we
recommend that several days of continuous
steady-state operation be given to this activity.)
(3) A reduction in pressure drop denotes solids
deposition due to soft scale caused by calcium
sulfite/calcium carbonate. Lowering the pH causes
the solids to dissolve into the slurry liquor.
(4) If pressure drop is not alleviated and S02 removal
drops significantly during pH reduction, solids
deposits may form consisting most likely of gypsum
and possibly fly ash.
(5) Take absorber out of service.
(6) Remove solids from absorber internals (including
wet/dry interface, spray headers, spray nozzles,
supports)
(7) Check/replace slurry spray nozzles.
(8) Check/replace slurry spray headers.
(9) Modify slurry spray pattern through nozzle and
piping modifications (optional, if problem per-
sists ) .
(10) Return absorber to service and monitor performance
by measuring SOa removal and pressure drop across
the tower.
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Mist Eliminator. Mist eliminators are prone to solids
deposition on the blades and vanes. Solid deposits can
occur due to plugging or scaling ("fouling"). As noted
previously/ the mist eliminator is a specialized opera-
tion within the absorber. Therefore, the mist elimin-
ator is extremely sensitive to the mechanical and
chemical operating aspects of the absorber. Mist
eliminator fouling is generally remedied by the follow-
ing corrective sequence.
(1) Measure dissolved salts in mist eliminator wash
water. If high in S0a products/reactants, in-
crease amount of fresh makeup in wash.
(2) Increase mist eliminator wash by increasing wash
duration (preferred), wash frequency (secondary
preference), and wash rate (final preference).
Changes in the mist eliminator wash rate should be
carefully balanced against makeup water consump-
tion and closed water loop operating requirements.
(3) If mist eliminator pressure drop is not reduced,
reduce absorber recirculation slurry pH
incrementally, monitoring, pressure drop and S02
removal (see preceding discussion on absorber).
(4) If mist eliminator pressure drop is not reduced,
take absorber out of service.
(5) Remove deposits and conduct chemical analyses.
(6) Inspect wash system nozzles, piping, and pump(s).
Repair and replace where necessary.
(7) Measure relative saturation (RS) of slurry. If RS
is in critical range, adjust process chemistry.
(8) Inspect mist eliminator blades for thermal stress
and melting.
(9) If accessible, inspect downstream components for
solids carryover, condensate collection, and dew
point and pitting corrosion.'
(10) Return absorber to service. Monitor gas-side
pressure drop, gas flow rate, and wash water flow
rate.
Reheaters. Inline reheaters represent the lowest cost,
most efficient, but most problem prone form of gas
reheat. For this reason, only corrective actions for
this type of reheater are discussed here. Problem
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tendencies are due to its presence in the gas stream
and its interdependency on the performance of upstream
subsystems. Major problems are solids deposition on
the tube surfaces with subsequent corrosion/erosion
attack to tube bundles. Reheater fouling is remedied
by the following corrective actions.
(1) Monitor temperature differential of gas stream
across reheater. If temperature differential is
less than design or declining, check flow and
temperature of heating medium. If below design,
correct, and monitor gas stream temperature
differential.
(2) If temperature differential problem persists,
investigate performance of soot blowers. Verify
supply of soot blowing medium (steam or air) and
delivery (lances). If failures are observed,
correct, and monitor temperature differential.
(3) If no soot blower problems are observed, monitor
gas stream pressure drop across reheater. If
pressure drop is greater than design, increase
soot blowing frequency.
(4) If problem persists, remove reheater (including
absorber) from service.
(5) Inspect reheater tubes for deposits. Remove
manually.
(6) Inspect reheater tubes for failures (steam leaks),
especially at welds and tube bends. Repair
through spot welding. Replace tube bundles if
leaks are extensive.
(7) Inspect tube bundles in immediate vicinity of
failure to determine if other failures were trig-
gered by initial failure. Spot weld or replace,
if necessary.
(8) Inspect downstream subsystem^ for dew point cor-
rosion attack. Repair and replace where neces-
sary.
(9) Return reheater to service. Monitor gas-side
temperature differential and pressure drop and
heating medium flow and temperature.
Ductwork. The outlet ductwork (on the discharge side
of the absorber) is most problem prone portion of
ductwork in the FGD system. This is due to service in
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saturated conditions or interdependency on the perform-
ance of upstream subsystems. The most prevalent prob-
lem is corrosion. Corrective measures can be instituted
in the following fashion.
(1) Inspect the ductwork shell for pits and cracks.
(2) Inspect internal liner or shell for corrosion
attack (general or pitting) during outage oppor-
tunities .
(3) Monitor emissions (stack) for SOa, opacity, and
acid rainout. If S02 measurements vary signifi-
cantly below expectations or S03 measurements
obtained upstream, air inleakage and subsequent
dilution may be occurring. If opacity increases
or exceeds expectations, or stack rainout is
observed (low pH condensate in the vicinity of the
stack), entrainment carryover may be occurring due
to high flow rates and correspondingly high duct
velocities.
(4) If these problems persist, remove duct from service,
(5) Inspect ductwork for pockets of condensate and any
significant solids deposition. If observed,
sample and analyze.
(6) Inspect duct liner and shell. Patch repair where
possible, replace sections where necessary.
(7) Inspect upstream reheater (in-line tube bundles or
mixing chamber) for failures and cleanliness of
heat exchanger surfaces. Maintain and repair,
where necessary.
(8) If solids deposition or carryover to reheater are
observed, inspect upstream mist eliminator for
cleanliness and operability. Maintain and repair,
where necessary.
(9) If mist eliminator performance is suspect, eval-
uate operability (mist eliminator blade assembly,
wash system) and inspect absorber for operability
and performance.
(10) Return ductwork (and any upstream subsystems) to
service. Monitor stack emissions and measure gas
velocities at various load levels and operating
conditions.
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Stack. The stack is very similar to outlet ductwork in
terms of major problems and corrective actions. As
noted previously, the stack requires special considera-
tion because of its dimensions and location in the gas
circuit. If a problem is suspected, a major unit
outage is required to inspect the stack and stack flue,
identify damage, and institute corrective measures.
Moreover, if the stack flue liner is damaged, special
application techniques and skills are needed for re-
pairs. This is a very time consuming operation. In
the event of a stack flue liner failure due to dew
point corrosion attack, the following corrective action
sequence is instituted:
(1) If dew point corrosion attack in the outlet duct-
work is observed, similar damage to the flue liner
is likely.
(2) Inspect flue liner during next scheduled unit
outage.
(3) If flue liner is failing or failed, schedule
repairs during extended unit outage. If failure
is severe, an immediate unit forced outage may be
necessary.
(4) During outage, inspect upstream subsystems for
proper operation and performance (see preceding
discussion on absorber, mist eliminator, and
reheater).
(5) During outage, conduct engineering analysis of
liner failure determining (at a minimum): gas
velocities and temperature profiles, radiative
heat losses, necessity and amount of reheat,
corrosivity and acid dew point.
(6) Incorporate any design and operating changes in
accordance with inspection and engineering analy-
sis .
(7) Return unit to service.
Damper. The inability of isolation dampers to effec-
tively seal off the absorber tower during flue gas
bypass represents the major damper operating problem.
Solids accumulation and corrosion are typically en-
countered. On the inlet side of the absorber, fly ash
is generally the cause. On the discharge side of the
absorber, entrainment carryover is generally the cause.
As described in the preceding sections, upstream sub-
system operation must be improved. Maintenance and
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repair to the damper itself involves cleaning and
readjustment during a unit outage.
5.3.2.2 Reagent Preparation and Feed
The reagent preparation and feed equipment area contains two
subsystems that are of vital concern to overall FGD system opera-
tion and performance. They are the reagent preparation and
slurry distribution subsystems. These subsystems involve the
operations of the ball mill for limestone and the slaker for lime
as well as product slurry storage, product slurry feed, and
slurry recirculation in the absorber. Although mechanical pro-
blems associated with the preparation and transfer of the product
slurry to the absorber loop are frequently encountered, the
problem of overriding concern is the reactivity of the product
slurry. Insufficient reactivity will affect the operation of all
downstream subsystems as well as carrying over into the gas
handling and treatment equipment area and waste solids handling
and disposal equipment area. These effects will include insuffi-
cient SC'2 removal in the absorber; scaling and plugging in the
absorber; erosion of pumps, piping, valves, and tanks in the
slurry distribution network; increased reagent consumption; and
increased solid waste production. Using the quality of the
product slurry as a gauge, corrective measures can be instituted
to ensure adequate performance. These measures can be imple-
mented for both the reagent preparation and slurry distribution
subsystems per the following:
(1) Sample and measure the slurry at each stage in the
preparation and distribution process. The slurry will
be analyzed for reactivity per the following measure-
ments: liquor pH, slurry solids,'particle size, alka-
linity, reaction products, dissolved salts, and inerts.
(2) If slurry reactivity is inadequate, determine quality
of bulk reagent with respect to specified chemical and
physical characteristics. If the quality of the current
supply is determined to be inadequate, change supply.
(3) If bulk reagent supply is determined to be adequate,
determine quality of preparation and dilution water per
the following measurements: pH, carbonate, bicarbonate,
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sulfite, sulfate, chloride, and metal cations. If
current supply is determined to be inadequate, change
water supply by adding more fresh makeup or a filtering
step.
(4) If water supply characteristics are determined to be
adequate, inspect the ball mill or slaker. Typically,
ball mills and slakers operate on a batch basis (e.g.,
8 hours for every 24-hour operating day). Hence, there
is sufficient opportunity to empty and inspect these
subsystems without taking either them or the entire FGD
system out of service.
(5) If ball mill milling surfaces are worn, take ball mill
out of service and recharge balls.
(6) If slaker "surfaces" (paddles, agitators, rakes) are
worn, take slaker out of services and replace.
(7) Return ball mill or slaker to service and monitor
product quality (chemical reactivity).
(8) If slurry reactivity is still inadequate, determine
residence times in each holdup tank.
(9) If residence times are inadequate, vary liquid levels
(height), pumping rates, and/or operating schedules to
increase residence times.
(10) If reactivity is still inadequate, determine suffi-
ciency of backmixing and the possibility of short
circuiting in the tanks. Determine adequacy of agi-
tation and identify flow patterns in each tank. If
insufficient, modify or change agitators and modify
inlet/outlet feed stream configurations. (Product
slurry and feed tanks may not require forced outage to
complete modifications; however, slurry recirculation
tank will because of its continuous mode of operation.)
If required, "baffle" the tanks to improve agitation
and backmixing. Baffles, which break up the circular
motion of the slurry, should not be attached directly
to the sides and bottom of the tank because solid
deposits will form behind them, decreasing the effec-
tive volume of the tank and hampering slurry agitation.
(11) Return tanks to service and monitor product quality
(chemical reactivity).
5.3.2.3 Waste Solids Handling and Disposal
The waste solids handling and disposal equipment area con-
tains one subsystem that is vital to overall FGD system operation
and performance—primary dewatering. As noted in Section 5.3.1.3,
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primary solids dewatering typically is accomplished by a thick-
ener. The thickener is an extremely problem-sensitive operation
because of its central role in balancing the chemistry and flow
of the FGD process. An index of the overall performance level of
the thickener is the quality of the clarified water (overflow)
recovered by the thickener and returned to the process. An
overflow high in suspended solids or dissolved salts can have
detrimental impacts on mist eliminator cleanliness, product
slurry quality, and absorber SC>2 removal and reliability. Con-
currently, an overflow of poor quality also indicates a poor
quality underflow stream, which can cascade and affect the down-
stream subsystems of secondary dewatering, physical/chemical
treatment, and final disposal. Accordingly, the following cor-
rective actions can be taken to resolve problems or improve
performance.
(1) Monitor the quality of the thickener overflow stream
with respect to suspended solids (typically 50 to 100
ppm) dissolved salts (total weight), pH, and ionic
concentrations of calcium, magnesium, sulfite, sulfate,
carbonate, hydroxide, and chloride.
(2) If thickener overflow quality exceeds specifications,
monitor inlet (feed) and underflow characteristics with
respect to flow rate and solids content.
(3) If inlet feed stream exceeds design flow rate or solids
content, the thickener may be "overloaded" (mass load-
ing of solids exceeds design) and insufficient clarifi-
cations results. Consequently, increase thickener
underflow pumping rate to increase solids discharge
rate and restore steady-state operation.
(4) If increasing thickener underflow pumping rate does not
resolve problem or is not possible, add a flocculant to
improve settling characteristics (or increase rate of
addition if a flocculant is already added). Flocculant
addition should not exceed recommended concentration
levels (typically 5 to 7 ppm).
(5) If thickener overflow quality is still determined to be
inadequate, analyze chemistry of suspended solids and
dissolved species. Determine level of excess (unreac-
ted) reagent, sulfite/sulfate ratio, and fly ash. If
reagent exceeds design excess, reduce stoichiometric
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ratio in absorber recirculation slurry. If sulfite/
sulfate ratio exceeds design, investigate forced oxida-
tion system (if present) and absorber slurry recircu-
lation loop (slurry pH, recirculation tank residence
time). If fly ash presence exceeds expectations,
investigate the performance of the particulate collec-
tion device.
(6) If thickener underflow stream exceeds design flow rate
or solids content (thickener overload), monitor perform-
ance of downstream secondary dewatering subsystem (if
present). Secondary dewatering may in turn be over-
loaded, resulting in a poor quality filtrate or cen-
trate returned to the thickener. This may in turn
aggravate thickener problems. Increase secondary
solids dewatering by activating installed spare (if
present) as a temporary measure.
(7) If the solids content of the thickener underflow is
below design, recycle underflow stream back to thick-
ener to buildup solids inventory to proper level. If
this measure proves inadequate, monitor chemistry of
thickener feed stream to determine excess reagent
level, sulfite/sulfate ratio, and fly ash. If neces-
sary, adjust as described above.
(8) If thickener performance is still inadequate, take
thickener out of service. Due to large liquid inven-
tory, this will be a time-consuming process. Forced
outage of FGD system may be avoided by temporarily
bypassing thickener and going to an emergency pond or
directly to disposal (if an on-site pond). Inspect and
repair and replace any components (where needed).
Attend closely to rake drive assembly, underflow line,
and motor drive and gear assembly.
(9) During episodes of poor thickener performance, closely
monitor gas-side pressure drop across the mist
eliminator (solids deposition), product slurry
reactivity, pump seals, secondary solids dewatering,
chemical treatment, and final disposal.
(10) The physical/chemical treatment subsystem must be able
to control additive feed rates in accordance with solid
waste feed stream characteristics. This operation
should be closely monitored during thickener upsets.
This monitoring should be extended to the final disposal
material to ensure proper curing and characteristics
(permeability, compressive strength). This can be
accomplished through periodic core sampling and anal-
ysis.
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SECTION 6
MODEL O&M PLAN
This section highlights a model O&M plan for lime/limestone
slurry FGD systems. The purpose of this section is to introduce
the field inspector to the elements of an "idealized" O&M plan
which the field inspector can use as a benchmark from which to
evaluate (compare) actual FGD systems. "Idealized", in this
context, refers to practices that are determined to be "prefer-
able" based upon their successful application in specific systems
throughout the industry. To our knowledge, no one plan is
currently in use that contains all of the elements discussed in
this plan.
This section is a continuation of the material introduced in
Section 2.5.3 (FGD O&M Practices) and Section 5.2.3 (O&M). This
section addresses the operator utility's management and staff
(Section 6.1) at both the corporate and plant levels. Operating
and maintenance manuals are described (Section 6.2 and 6.3,
respectively) complete with suggested outlines. Troubleshooting
techniques (Section 6.4) are described in terms of an organized
multiphase program. Necessary spare parts necessities are de-
scribed for inventories of shelf spares (Section 6.5). The work
order system is described in terms of its importance for monitor-
ing O&M response (Section 6.6). Computerized tracking is dis-
cussed as a necessary function to store, retrieve, and analyze
the current and projected status of FGD performance (Section
6.7) .
6.1 MANAGEMENT AND STAFF
The field inspector should be acquainted with two levels of
management structure and staff organization that are prominent
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elements of an operator utility's O&M plan for an FGD-equipped
coal-fired unit. They are corporate level and plant level.
Corporate level represents the upper management attention pro-
vided by the operator utility. Plant level represents the O&M
attention provided by the operator utility. These levels are
described below for the idealized O&M plan.
6.1.1 Corporate Organization
The environmental manager at the corporate level is gener-
ally responsible for all pollution control activities and issues
for the plants within the operator utility's generating system.
Typically, the environmental manager can occupy one of the three
positions at the corporate level: vice-president of environ-
mental affairs, manager of environmental affairs, and principal
engineer of environmental affairs. Generally, the higher the
ranking of the environmental manager, the higher the operator
utility prioritizes its commitment to FGD O&M. Moreover, assign-
ing this responsibility at the vice-presidential level can free
up positions at the manager and principal engineer levels to
concentrate on more specific pollution control-related matters,
with FGD representing one specialty function.
6.1.2 Plant Organization and Training
The management structure and staff organization at the plant
level is organized in a fashion parallel to the corporate manage-
ment and structure level. The highest position at the plant
level is the plant superintendent. Organization in descending
order are designated as assistant superintendent, operations
manager, shift supervisor, shift engineer, foreman, technician,
and support personnel. Similar to the corporate structure and
organization, the higher the ranking of the air quality control
system (AQCS) manager, the higher the operator utility prioritizes
its commitment to FGD O&M. Moreover, assigning this level of
responsibility at the superintendent level can free up positions
at lower levels to concentrate an FGD O&M. One approach being
adopted by many operator utilities is to establish a completely
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separate AQCS staff that is organized and managed parallel to the
"power-side" staff. This approach involves maintaining a separate
AQCS O&M staff with its own separate job titles, functions,
incentives, and promotional structure. FGD O&M can be assigned a
separate function within this structure or embody the entire FGD
responsibility in itself. Some of the functional concerns associ-
ated with these strategies are described below.
Personnel operating and servicing the FGD system must be
familiar with the components of the FGD system, process theory,
equipment limitations, and proper procedures for maintenance and
repair.
For optimum performance, one person (the AQCS manager)
should be responsible for the entire FGD system O&M program. All
requests for major repair and/or investigation of abnormal opera-
tion should go through this individual for coordination of efforts.
When repairs are completed, final reports also should be trans-
mitted to the originating staff through the AQCS manager. Thus,
the AQCS manager will be aware of all maintenance that has been
performed, chronic or acute operating problems, and any work that
is in progress. The manager, in consultation with the operation
supervisors, also can arrange for and schedule all required
maintenance. He/she can assign priority to repairs and order the
necessary repair components, which sometimes can be received and
checked out prior to installation. Such coordination does not
eliminate the need for certain functions but it does avoid dupli-
cation of effort and helps to ensure an efficient operation.
The size, experience level, responsibilities, and training
of the O&M staff are significant factors in FGD system perform-
ance. The number of support staff required for proper O&M of a
FGD system is a function of unit size, design, and operating
history. Staff requirements must be assessed periodically to
ensure that the right personnel are available for normal levels
of maintenance. Additional staff will generally be needed for
such activities as a major refurbishing of the FGD system. This
additional staff may include plant personnel, outside (contract)
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hourly laborers, or contracted personnel from service companies
or FGD equipment suppliers. In all cases, outside personnel
should be supervised by experienced plant personnel. The services
of purchasing personnel and computer analysts may also be needed.
The coordinator should be responsible for final acceptance and
approval of all repairs. Figure 6.1-1 presents the general
concept and staff organizational diagram for a coordinated FGD
system O&M program.
The supervisors and staffing of the absorber (including
reagent preparation and storage) and waste solids disposal opera-
tions should be considered separately. The permanent assignment
of key personnel to specific work areas will allow them to become
completely familiar with the process equipment and its chemistry.
As the operating personnel gain understanding of the system, they
will be able to anticipate problems before FGD system operations
become impaired. In addition to the normal complement of shift
supervisors and equipment operators on the operating crew of each
shift, certain specialists should be available to assist them.
For example, a chemical engineer is a valuable resource during
atypical operating conditions. A chemical laboratory technician
should also be available to analyze the process chemistry in the
event of suspected trouble. During normal operations, this
technician can monitor routine system performance through
sampling and testing and need not be dedicated full time to the
FGD system.
The maintenance supervisors and staff for the FGD system
must include personnel from a number of disciplines. Mechanics
are needed for component repairs. Electricians are also needed,
as well as instrument technicians familiar with the system.
These specialists can be supported by laborers from the operating
staff. Assignment of maintenance personnel to shift coverage
will vary with individual facilities. Where maintenance on the
back shift is performed by "on-call" personnel, the standard
day-shift maintenance requirements such as instrument flushing,
can be reduced. The potential number of unscheduled maintenance
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SUPPORT
SUPPORT
SUPPORT
COMPUTER
ANALYSTS
CORPORATE
MANAGEMENT
CHEMICAL
ENGINEERS
PURCHASING
PERSONNEL
MECHANICAL
FOREMAN
MECHANICS
ELECTRICAL
FOREMAN
LABORATORY
TECHNICIANS
ELECTRICIANS
MAINTENANCE
SUPERVISORS
PLANT
SUPERINTENDENT
AQCS FGD MANAGER
SHIFT (ENGINEERS)/
EQUIPMENT OPERATORS
ABSORBER/WASTE
SOLIDS DISPOSAL
OPERATIONS SUPERVISORS
Figure 6.1-1. Organizational diagram for coordinated FGD
system O&M program.
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activities (i.e., related to equipment malfunctions) must also be
considered in sizing the maintenance staff.
Many plants have a relatively high rate of personnel turnover
and, therefore, new employees are assigned to work on the FGD
system who may have had no previous contact with air pollution
control equipment. To provide the necessary technical expertise,
the operator utility must establish a formal training program for
each new employee assigned to FGD system O&M. The training
program should include the supervisors, shift managers, foremen,
and support staff. The time period following initial startup and
operation of the FGD system presents an excellent opportunity for
training the O&M staff. When the FGD system is first placed in
operation, system supplier personnel are usually available on
site to ensure that the equipment is operating properly. During
this period, all equipment should be operated and maintained by
the operator utility staff personnel under guidance of the system
supplier. VJhenever possible, written procedures should be followed
so that any error can be identified and corrected.
Safety is an important aspect of any training program (see
Section 7.0). Each person associated with the system should have
complete instructions regarding confined-area entry, first aid,
and lock-out/tag-out procedures.
The O&M training program should also emphasize optimum and
continuous performance of the FGD system. The staff should never
get the impression that less-than-optimum FGD performance is
acceptable. Redundancy is established in the system solely to
provide a margin of safety for achieving compliance during emer-
gency situations. Once a pattern is established that allows a
nonoptimal condition to exist (i.e., reliance on built-in redun-
dancy) , this condition then becomes the norm and the margin of
safety begins to erode.
To reinforce the training program, follow-up written mate-
rial should be prepared. Each plant should prepare and contin-
ually update an operating manual (see Section 6.2) and a main-
tenance manual (see Section 6.3) for each FGD system. A generic
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manual usually is insufficient because each system supplier's
design philosophy varies. The use of actual photographs, slides,
and drawings aids in the overall understanding of the system and
reduces lost time during repair work.
Training material and courses available from the system
supplier should be reviewed and presented as appropriate. Further,
responsible staff should attend workshops, seminars, and training
courses presented by the Electric Power Research Institute (EPRI),
EPA, and other organizations to increase their scope of knowledge
and keep current with the evolving technology. A typical FGD
training program should include safety, theory of operation,
physical descriptions of equipment, review of subsystems, normal
operation (indicators), abnormal operations (common failure
mechanisms), troubleshooting procedures, preventive and reactive
maintenance, and recordkeeping.
6.2 OPERATING MANUALS
Operating manuals for FGD systems should contain the follow-
ing types of information: the operating norm or baseline of the
FGD equipment, the particular operating variables which affect
their operation, abnormal operating characteristics, and (as in
the maintenance manual) safety precautions along with step-by-
step startup/shutdown instructions. The operating manual should
also parallel the maintenance manual (see Section 6.3) in terms
of introductory material so that the operators and maintenance
staff have the same basic understanding of all the FGD equipment
and their function and of the overall operating theory. Figure
6.2-1 presents a suggested outline for a typical operating
manual. The introductory material of the manual would begin with
a basic description of the FGD system and outline the major
equipment areas and their associated components. The manual
should continue with separate sections on each of the equipment
items presented in the introduction. In these sections, the
material outlined above would then be addressed.
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I. Introduction
A. F6D System Description
B. Major Equipment Areas
II. Gas Handling and Treatment Components
A. Fans
1. Operating norm or baseline®
2. Major operating variables
3. Abnormal operating characteristics
4. Startup/shutdown procedures
5. Safety precautions
B. Scrubbers/Absorbers
C. Mist Eliminators
D. Reheaters
E. Ductwork and Dampers
III. Reagent Preparation
A. Reagent Conveyors and Storage
B. Ball Mills
C. Slakers
D. Tanks
IV. Waste Solids Handling and Disposal
A. Thickeners
B. Vacuum Filters
C. Centrifuges
D. Waste Processing
E. Waste Disposal
F. Pumps and Valves
V. Emissions Monitoring and Process Control
A. Gas
1. Pressure (differential)
2. Temperature (differential)
3. Flow
4. Continuous Emissions Monitoring
a. S02
b. Particulate matter
c. N0X
B. Slurry
1. pH
2. Density (solids)
3. Flow
C. Solids
1. Density (solids)
2. pH
3. Flow
aThese considerations apply to all items in Section II, III, IV, and V.
Figure 6.2-1. Outline for FGD Operating Manual.
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The operating norm or baseline information for FGD equipment
basically describes the mechanical parameter(s) used for gauging
whether the equipment is functioning properly. An example of
this would be electrical usage (i.e., amperage readings) for
motor driven equipment (e.g., pumps, fans, ball mills). The
material should also discuss the particular operating variables
which affect the equipment operation. Each parameter should be
defined, its set point or range given and information provided on
how that parameter is controlled. This type of information is
helpful in determining present or future equipment malfunctions
or failures. The manual should also list the normal operating
characteristics for each piece of FGD equipment. These internal/-
external visual aids are extremely critical for determining
proper equipment performance. With the use of these aids, opera-
tors can possibly alleviate the problem in its earlier stages
before it actually manifests itself into a more serious problem
(i.e., equipment malfunction or failure). The sections on equip-
ment should also provide step-by-step shutdown procedures and
safety precautions for each piece of FGD equipment to insure
sequential outage of FGD equipment and/or boiler to aid mainten-
ance activities to eliminate startup problems, and to insure
worker safety. Unless these proper startup/shutdown procedures
are followed, operation and/or maintenance actions could result
in either further damage to the equipment, increased emissions,
repeated failure, or worse, a worker accident.
The remainder of the operating manual should discuss the
operation of the continuous emissions monitoring and process
control systems. This section would address the same factors
described above for the components comprising the two systems.
6.3 MAINTENANCE MANUALS
Specific maintenance manuals should be developed for each
FGD system of the operator utility. The basic elements of design
and overall operation should be specific to each FGD system and
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incorporate the manufacturer's documentation and in-house expe-
rience for that particular system design. Equipment descriptions
(vendor documentation) should be brief and to the point; long
narratives without direct application should be avoided.
Figure 6.3-1 presents a suggested outline for a typical
manual. The manual should begin with a basic description of the
FGD system and outline the major equipment areas and their asso-
ciated components. The manuals should continue with separate
sections on each of the equipment items presented in the intro-
duction. In these sections, the following material would be
presented:
0 detailed description of the equipment item and its
components
0 equipment layout and schematics
0 internal/external inspection and maintenance procedures
(i.e., inspection and maintenance checklists)
0 startup/shutdown procedures
0 safety precautions particular to that equipment iter.
The equipment descriptions should show the component parts
of the equipment item. In addition, detailed drawings and an
explanation of the function of each component and its normal
conditions should be presented.
The material should discuss the internal/external inspection
and maintenance procedures of the equipment and components, both
of which are extremely critical in maintaining equipment perform-
ance. Periodic external checks of all equipment are required in
order to spot symptoms or clues which may indicate probable
equipment/process deterioration and/or failure (e.g., failed
expansion joint, leaky pump). More importantly, however, most
FGD equipment (e.g., absorbers, pumps, fans) have internal parts
which must be inspected and overhauled periodically in order to
assure that these items continue to function properly.
The remainder of the section on the equipment should focus
on startup/shutdown procedures and safety precautions particular
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I. Introduction
A. FGD System Description
B. Major Equipment Areas
II. Gas Handling and Treatment Components
A. Fans
1. Component descriptions3
2. Layout and schematics
3. Internal/external inspection and reactive and preventative
maintenance procedures
4. Startup/shutdown procedures9
5. Safety precautions3
B. Scrubbers/Absorbers
C. Mist Eliminators
D. Reheaters
E. Ductwork and Dampers
III. Reagent Preparation
A. Reagent Conveyors and Storage
E. Ball Mills
C. Slakers
D. Tanks
IV. Waste Solids Handling and Disposal
A. Thickeners
B. Vacuum Filters
C. Centrifuges
D. Waste Processing
E. Waste Disposal
F. Pumps and Valves
V. Emissions Monitoring and Process Control
A. Gas
1. Pressure (differential)
2. Temperature (differential)
3. Flow
4. Continuous Emissions Monitoring
a. S02
b. Particulate matter
C. N0X
B. Slurry
1. pH
2. Density (solids)
3. Flow
C. Solids
1. Density (solids)
2. pH
3. Flow
a
These considerations apply to all items in Sections II, 111» IV, and V.
Figure 6.3-1. Outline for FGD Maintenance Manual.
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to the equipment in order that it can be inspected, repaired, and
brought back on-line without harm to either the maintenance crew
or the equipment itself.
The remainder of the maintenance manual should discuss the
maintenance and inspection of the continuous emissions monitoring
and process control systems. An additional section describing
the correct procedures for completing and processing work orders
(see Section 6.6) is also recommended.
6.4 TROUBLESHOOTING TECHNIQUES
Troubleshooting a lime/limestone FGD system requires a
multiphase program that should be organized along the following
lines.
Phase 1: Problem Identification. This phase begins with a
detailed inspection of the system utilizing the procedures
described in Section 4. All observations (positive and negative)
are listed, interpretations are developed (why things were the
way they were), and finally, methods and items that will improve
performance are recommended. Recommendations may call for design
modifications, replacement of components or accessories, or the
fabrication of new equipment.
Phase 2; Implementation: After thorough analysis, the
Phase 1 recommendations should be implemented by repair, and by
replacement with procured and fabricated components. The system
is then started up and debugged.
Phase 3: Testing and Sampling. A performance test must be
conducted to evaluate the effects of the work on system operation
(see Section 3.3). Testing may be done by stack sampling and/or
measurements with the system in continuous operation.
Phase 4: Operational Troubleshooting. Certain symptoms are
attributable to more than one cause. Section 5.3 (Problem Diag-
nosis and Corrective Measures) gives typical symptoms, probable
causes, and suggested remedies. The information presented in
this section should not be regarded as exhaustive of all possibil-
ities; no report, maintenance protocol, or operator instruction
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manual can take the place of a well-trained maintenance staff
familiar with the equipment and its operating history.
6.5 SPARE PARTS
Two separate categories of spare parts can be identified,
designated as installed spares and shelf spares. Installed
spares are redundant components that are built into the system.
These components can be activated and placed into service
expeditiously in the event of a forced outage or scheduled outage
or "furloughing". Shelf spares are components that are stored
for replacement of in-service components. Shelf spares are
considered true spare components in that they are required to
replace components that fail in service. Accordingly, the
balance of this section will be devoted to a discussion of shelf
spares.
An inventory of spare parts should be maintained on-site to
support the required maintenance activities. Because all compon-
ents or subassemblies cannot be stocked, a rational system must
be developed that establishes a reasonable inventory of spare
parts. Decisions regarding which components to include in the
spare parts inventory should be based on the following considera-
tions :
1. Probability of failure
2. Cost
3. Impact on system/unit operation
4. Availability (specialty or custom-fabrication item vs.
stock item)
5. Replacement time (installation)
6. Whether the part can be stored as a component or sub-
assembly (i.e., conveyor belt assembly vs. individual
components)
7. Repair center (i.e., in-house technical repair
capabilities)
8. Spatial constraints
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The probability of failure can be developed from outside
studies (e.g., Reference 6), supplier recommendations, and past
histories of the system components. It is reasonable to assume
that components subject to environments of erosion, scaling/-
plugging, corrosion, weather, extreme and sudden temperature
differentials, or wear are the most likely to fail. Components
of this type are no different from those in the entire FGD pro-
cess, and reasonable judgement must be used in deciding what to
stock. Maintenance staff members should be consulted for recom-
mendations concerning some items that should be stocked and the
number required. Adjustments to the initial spare parts inven-
tory can be made as operating experience is gained and decisions
are made regarding the degree of redundancy (installed spares) in
the system.
Another factor in defining a spare parts inventory is the
cost of individual components. Although stocking slaker agita-
tors, rakes, and other slaker components may not be costly,
stocking a spare compressor for the reagent conveying system
could be quite costly. Maintaining an extensive inventory of
high-cost items that have low probability of failure is not
justified.
The impact that a failed component has on system/unit opera-
tion should strongly influence whether an item should be spared.
These components represent items which are essential to main-
taining FGD system/unit operation. Non-replacement of these
components would impact FGD operation relatively quickly, possibly
causing a curtailment or total system/unit interruption of opera-
tion. Example components that fall into this category include
spare parts of major items comprising the reagent preparation and
feed equipment area.
The availability of the component (i.e., specialty items
versus stock items ) and the time required to replace the compon-
ent are additional factors which must be considered. If the lead
time to order a part from the supplier is a matter of weeks or
months because it must be specially fabricated instead of taken
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directly from stock, and/or if the repair is a time-consuming
procedure, stocking such items is advantageous.
Many operator utilities have implemented electrical and
mechanical shops (i.e., repair centers) where trained staff can
coordinate the repair or rebuilding of components to meet origi-
nal design specifications. The establishment of such a service
facility can greatly reduce the need to maintain component parts
or subassemblies. In these cases, one replacement part can be
stocked for installation during the period when repairs are being
made.
If the plant has very limited space, as is the case for most
retrofit applications, spatial constraints may come into play.
The number, type, and size of spare parts may have to be reduced
to fit the available space allotted for plant inventory.
6.6 WORK ORDER SYSTEMS
A work order system is a valuable tool that allows the AQCS
manager to track FGD system performance over a period of time.
Work order and computer tracking systems (see Section 6.7) are
generally designed to ensure that the work has been completed and
that charges for labor and parts are correctly assigned for
accounting and planning purposes. With minor changes in the work
order form and in the computer programs, the work order also can
permit continuous updating of failure-frequency records and can
indicate whether the maintenance performed has been effective in
preventing repeated failures. In general, the work order serves
three basic functions:
1. It authorizes and defines the work to be performed.
2. It verifies that maintenance has been performed.
3. It permits the direct impact of cost and components
data to be entered into a computerized data handling
system.
To perform these functions effectively, the work order form must
be specific, and the data fields must be large enough to handle
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detailed requests and to provide specific responses. In many
computerized systems, the data entry cannot accommodate a narra-
tive request and specific details are lost.
Most systems can accommodate simple repair jobs because they
do not involve multiple repairs, staff requirements, or parts
delays. Major repairs, however, become lost in the system as
major events because they are subdivided into smaller jobs that
the system can handle. Because of this constraint, a large
repair project with many components that may have a common cause
appears to be a number of unrelated events in the tracking
system.
For diagnostic purposes, a subroutine in the work order
system is necessary that links repairs, parts, and location of
failure in an event-time profile. Further, the exact location of
component failures must be clearly defined. In effect, it is
more important to know the pattern of failure than the cost of
the failure.
The goal of the work order system can be summarized in the
following items:
0 To provide systematic screening and authorization of
requested work.
0 To provide the necessary information for planning and
coordination of future work.
0 To provide cost information for future planning.
0 To instruct management and craftsmen in the performance
of repair work.
0 To estimate manpower, time, and materials for
completing the repair.
0 To define the equipment that may need replacement,
repair, or redesign (work order request for analysis of
performance of components, special study, or consulta-
tion , etc.).
Repairs to the FGD system may be superficial or cosmetic in
nature or they may be of an urgent nature and require emergency
response to prevent damage or failure. For a typical utility FGD
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system, numerous work order requests may be submitted as a result
of daily inspections or operator analysis. Completing the jobs
in a reasonable time requires scheduling the maintenance staff
and ordering and receiving parts in an organized manner.
For effective implementation of the work order system, the
request must be assigned a level of priority as to completion
time. These priority assignments must take into consideration
plant and personnel safety, the potential effect on emissions,
potential damage to the equipment, maintenance personnel avail-
ability, parts availability, and boiler or process availability.
Obviously, all jobs cannot be assigned the highest priority.
Careful assignment of priority is the most critical part of
the work order system, and the assignment must be made as quickly
as possible after requests are received. An example of a five-
level priority system is shown below in Table 6.6-1.
TABLE 6.6-1. WORK ORDER PRIORITY SYSTEM
Priority
Action
1
Emergency Repair
2
Urgent repair to be completed during the day
3,4
Work which may be delayed and completed in the future
(during periods of low demand)
5
Work which may be delayed until a scheduled outage
If a work order request is too detailed, it will require
extensive time to complete. Also, a very complex form leads to
superficial entries and erroneous data. The form should concen-
trate on the key elements required to document the need for
repair, the response to the need (e.g., repairs completed), parts
used, and manpower expended (see Figure 5.2-8). Although a
multipage form is not recommended, such a form may be used for
certain purposes. For example, the first page can be a narrative
describing the nature of the problem or repair required and the
response to the need. It is very important that the maintenance
staff indicate the cause of the failure and possible changes that
would prevent recurrence. It is not adequate simply to make a
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repair and respond that "the repairs have been made." Unless a
detailed analysis is made of the reason for the failure, the
event may be repeated several times. Treating the symptom (making
the repair; replacing spray nozzles, pump impellers, etc.) is not
sufficient; the cause of the failure must be treated.
In summary, the following is a list of how the key areas of
13
a work order request are addressed:
1. Date - The date is the day the problem was identified
or the job was assigned if it originated in the planning,
environmental, or engineering sections.
2. Approved by - This indicates who authorized the work to
be completed, that the request has been entered into
the system, and that it has been assigned a priority
and schedule for response. The maintenance supervisor
or AQCS manager may approve the request, depending on
the staff and the size of the system. When emergency
repairs are required, the work order may be completed
after the fact, and approval is not required.
3. Priority - Priority is assigned according to job urgency
on a scale of 1 to 5.
4. Work order number - The work order request number is
the tracking control number necessary to retrieve the
information from the computer data system.
5. Continuing or related work order numbers - If the job
request is a continuation of previous requests or
represents a continuing problem area, the related
number should be entered.
6. Equipment number - All major FGD equipment should be
assigned an identifying number that associates the
repair with the equipment. The numbering system can
include major equipment area, subsystem, module, and
component. This numeric identification (ID) can be
established by using a field of grouped numbers. The
purpose of the ID system is to enable analysis of the
number of events and cost of repair in preselected
areas of the FGD system. The fineness or detail of the
equipment identification system will specify the detail
available in later analyses.
7. Description of work - The request for repair is usually
a narrative describing the nature of the failure, the
part to be replaced, or the work to be completed. The
description must be detailed but brief because the
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number of characters that can be entered into the
computerized data system is limited. Additional pages
of lengthy instruction regarding procedures may be
attached to the request (not for computer storage).
8. Estimated labor - Assignment of personnel and scheduling
of outages of certain equipment require the inclusion
of an estimate of manhours, the number of in-house
staff needed, and whether outside (contract) labor is
needed. The more complex jobs may be broken down into
steps, with different personnel and crafts assigned
specific responsibilities. Manpower and procedures in
the request should be consistent with procedures and
policies established in the O&M manual.
9. Material requirements - In many jobs, maintenance crews
will remove components before a detailed analysis of
the needed materials can be completed; this can extend
an outage while components or parts are ordered and
received from suppliers or retrieved from the spare
parts inventory. Generally, the cause of the failure
should be identified at the time the work order request
is filled, and specific materials needs should be
identified before any removal effort begins. If the
maintenance supervisor knows in advance what materials
are to be replaced, expended, or removed, efficiency is
increased and outage time reduced. Also, if parts are
not available, orders may be placed and the parts
received prior to the outage. Material requirements
are not limited to parts; they also include tools,
safety equipment, etc.
10. Action taken - This section of the request is the most
important part of the computerized tracking system. A
narrative description of the repair conducted should be
provided in response to the work order request. The
data must be accurate and clearly respond to the work
order request.
11. Materials replaced - An itemized list of components
replaced should be provided for tracking purposes. If
the component has a preselected IP number (spare parts
inventory number), this number should be included.
Actual man-hours expended in the repair can be indicated by
work order number on separate time cards and/or job control cards
by craft and personnel number.
Copies of work orders for the FGD system should be retained
for future reference. The AQCS manager should review these work
orders routinely and make design changes or equipment changes as
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required to reduce failure or downtime. An equipment log also
should be maintained and the work should be summarized and dated
to provide a history of maintenance on the system.
6.7 COMPUTERIZED TRACKING SYSTEM
Again, it should be emphasized that the purpose of the
computerized tracking system is not to satisfy the needs of the
accountants or to state that the plant has such a system. Rather,
the purpose of a computerized tracking system is to provide the
necessary information to analyze FGD O&M practices and to reduce
equipment failures, system/unit outages, and emission excursions.
The O&M staff and AQCS manager must clearly define the kinds of
data to be collected, the level of detail, and the type of analysis
required prior to the purchase/lease of any computer equipment
and the preparation of the data-handling and report-writing
software.
The operator utility has many options regarding the physical
location of its computerized tracking system. The system could
range anywhere from an in-house personal computer (PC) to a time-
share system by which data are inputed and accessed interactively
via remote terminals on either a mainframe or minicomputer. The
operator utility may even choose to purchase and operate their
own computer and timeshare versus leasing computer space. The
operator utility must weigh many factors before chosing any of
the above alternatives. The key factors are the complexity of
the tracking system, number of FGD systems, computer staff,
available software, number of users, input/output features,
available storage space, and computer costs..
The data base for the computerized tracking system should
contain the following type of information: work orders, prevent-
ative maintenance manhours, operating parameters, and service
hours.
If the work completed and parts used are documented on the
work orders (see Section 5.2.3 and 6.6) and entered into the
computerized tracking system with sufficient detail, maintenance
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and management personnel can easily evaluate the effectiveness of
FGD system maintenance.
Preventive maintenance (see Section 2.5.3.6} man-hours
versus reactive maintenance man-hours can be compared to evaluate
the effectiveness of the current preventive maintenance (PM)
program. The level of detail may allow tracking of the impact of
PM on particular components as changes are made in PM procedures.
The effectiveness of the PM program may be further evaluated by
the required number of emergency repairs versus scheduled repairs
over a period of time (i.e., priority 2 versus priority 5, etc.).
In addition to tracking work orders and PM man-hours, the
computer can be used to develop correlations between unit/FGD
operating parameters and observed equipment malfunctions/fail-
ures. Depending on the parameter type and cycles expected in
unit operation, the data may be continuously entered into the
tracking system or it may be entered from operating logs or daily
inspection reports once or twice per week. The key parameters
for tracking FGD equipment performance should include boiler
load, coal properties (see Section 2.2), gas flow (see Sections
3.1.1.5 and 5.2.2.1), slurry flow rates (see sections 3.1.2.2 and
5.2.2.4), reagent consumption (see Sections 2.3.2.1 and 5.2.2.6),
waste solids production (see Section 5.2.2.7), and makeup water
consumption (see Section 5.2.2.8).
Finally, equipment service time is another data item that
should be tracked in order that it can be analyzed/correlated
along with the other data items. This type of data can also be
utilized to evaluate overall FGD system operation through the
development of dependability factors such as FGD system avail-
ability and reliability.
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SECTION 7
SAFETY
The safety of agency personnel during field inspections is
of primary importance. The field inspector should take adequate
precautions to guard against: 1) inhalation of toxic gases, 2)
skin irritation and/or chemical burns, and 3) exposure to
fugitive dust. In addition, normal industrial safety practices
should be followed such as attention to electrical power lines
and connections, attention to steam lines and connections,
attention to rotating equipment, and protection against falling
objects. During an FGD inspection, many of these concerns are
simultaneous and can result in potentially serious injuries to
the inspection personnel. Familiarization with safety procedures
and use of necessary safety equipment can result in inspections
being performed safely without risk of injury.
This section discusses many of the potential hazards and
addresses proper safety procedures. Further information con-
cerning safety precautions/considerations can be found in spe-
cific vendor equipment O&M manuals for the FGD systems and
subsystems, Occupational Safety and Health Administration (OSHA)
publications, and National Institute for Occupational Safety and
Health (NIOSH) publications.
7.1 INHALATION OF TOXIC GASES
There are two major classes of toxic gases which can be
present in and around areas of the FGD systems: irritants and
asphyxiants.
Irritants are gases, which at very low concentrations, are
mildly irritating to the eyes, throat, upper respiratory system,
and nervous system. At higher levels, they can even cause death.
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Sulfur dioxide and hydrogen sulfide (H2S) are both irritants
which are present in boiler flue gas. Sulfur dioxide is present
in much greater concentration than H^S and is the subject of this
particular manual.
Inhalation of SO^ at concentrations of 8 to 12 ppm causes
throat irritation, coughing, constriction of the chest, and
tearing of the eyes. A concentration of 150 ppm is extremely
irritating and can be endured only for a few minutes. A con-
centration of 500 ppm is acutely irritating to the upper res-
piratory tract and causes a sense of suffocation, even with the
first breath. While SC^ is extremely irritating to the eyes and
mucous membranes of the upper respiratory tract, it has excep-
tionally good warning powers. The normal person can detect 3 to
5 ppm in the air. The Threshold Limit Value (TLV) established by
the American Conference of Governmental Industrial Hygienists
(ACGIH) establishes the airborne concentration of substances to
which persons may be exposed without adverse health effects. The
TLV for SC>2 is 5.0 ppm (0.0005 percent by volume).
Hydrogen sulfide is another toxic irritant which could be
present in very low concentrations in the flue gas. Concentra-
tions of H2S as little as 100 ppm (0.01 percent by volume) may
cause death if exposure occurs for more than a few hours. In
lower concentrations, it is classified as an irritant because it
inflames the mucous membranes and results in the lungs filling
with fluid. This colorless gas has a characteristic rotten egg
odor. Since the gas renders the olfactory nerve ineffective, an
inspector may be lulled into a false sense of security not real-
izing that a toxic concentration of the gas may be present. The
TLV for H^S is 10 ppm (0.001 percent by volume).
Substances which render the body incapable of utilizing an
adequate oxygen supply are referred to as chemical asphyxiants.
Carbon monoxide (CO) is a chemical asphyxiant which is present in
boiler flue gas. It is formed by incomplete combustion of the
coal. Exposure to high levels of CO can, over prolonged periods,
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lead to death. The TLV for CO is 50 ppm (0.005 percent by
volume).
The aforementioned toxic gases can be present in potentially
dangerous concentrations in confined nonventilated areas such as
the interiors of scrubber/absorber towers and ductwork. Although
these equipment areas may be out of service for maintenance and
appear safe for entrance, precautions should be taken prior to
internal inspection. Isolation dampers may not be properly
closed or pressurized with adequate amounts of seal air to elimi-
nate the possibility of boiler flue gases from leaking into these
equipment areas. Entrance should only be made upon clearance
from plant personnel who have first taken the precaution of
ventilating and monitoring the gaseous concentrations within the
equipment area.
7.2 SKIN IRRITATION AND/OR CHEMICAL BURNS TO THE SKIN
Irritation and chemical burns to the skin can result from
inadvertent contact with either alkaline slurry or acid condensa-
tion. Areas where possible contact with slurries can easily
occur include: slurry preparation equipment, slurry pipe lines
and valves, scrubber/absorber towers, and equipment used for
solid waste handling and treatment. The inspector should be
especially aware of airborne slurry from sources located over-
head. Acid condensation from the flue gas usually occurs in
certain internal wet areas of the scrubber, absorber, ductwork,
and stack. Skin contact with acidic condensation in these areas
could cause severe burns. To prevent possible irritation or
burns to the body areas, gloves and protective clothing should be
worn at all times when entering or inspecting the equipment areas
noted above. If exposure does occur, the affected areas should
be washed with water thoroughly.
Skin irritation or burns may also result from contact with
dust particles depending on their acidic, alkaline, hygroscopic,
or abrasive nature. Section 7.3 discusses potential locations of
these dust sources in the PGD system. Inspection personnel can
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limit skin contact area and thus prevent potential irritation by
wearing long-sleeved shirts and gloves during internal inspec-
tions of equipment.
7.3 EXPOSURE TO FUGITIVE DUST
Sources of fugitive dust include ground surfaces, surfaces
of access scaffolds, ladders and handrails, equipment surfaces,
and stagnant areas found within equipment. This material can
easily be dislodged and suspended by wind, drafts, moving equip-
ment, and/or by plant and agency personnel. Fugitive dust around
the FGD system may consist of any or all of the following mate-
rials: coal dust, reagent (lime/limestone) particles, fly ash,
gypsum particles, dirt, and solid waste material. Fugitive dust
is an irritant because of its abrasive nature (i.e., sharp-edged
or crystalline form). However, fugitive dust can also subject
the eyes and lungs to chemical damage depending on the chemical
composition of the dust. Of special concern are sulfuric acid
and alkaline slurry agents. The heaviest concentrations of coal
dust and reagent particles exist in and around coal and reagent
stockpiles, conveyors, storage silos, coal pulverizers, and
reagent preparation equipment such as ball mills and slakers.
Fly ash is normally only encountered within equipment items
(e.g., particulate scrubbers, dampers, ductwork, fans). However,
fly ash may also be encountered in and around the solid waste
disposal system (e.g., fly ash silo, pug mill) if utilized to
fixate or stabilize the solid waste material. Dust consisting of
dirt, gypsum, and dried solid waste material may be encountered
in high concentrations in and around the waste disposal handling
conveyors and disposal area (e.g., stockpiles, landfill area).
To prevent irritation, goggles and dust masks should be worn,
especially on windy days or when inspecting equipment internals.
7.4 NORMAL INDUSTRIAL SAFETY PRACTICES
This section discusses normal industrial safety practices
which should be followed during plant inspections. The field
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inspector should take to the plant or obtain from plant personnel
the necessary personal protective equipment needed for conducting
the plant inspection. This consists of safety glasses with side
shields, a hard hat, gloves, protective clothing, steel-toe shoes
with nonslip soles, and a dust mask. As discussed previously,
some of the protective equipment will be required only in certain
areas of the plant. It is also advisable to remove prior to the
inspection any jewelry, neck ties, and other loose objects in
order to safeguard against moving machinery or other catch/snare
points (i.e., jagged edges on ladders, handrails, access doors).
While conducting the inspection, the inspector should obey plant
safety rules, not smoke, walk slowly, observe any interlock
procedures, avoid opening equipment access doors, avoid touching
or entering operating equipment, avoid manipulating valves or
controls, ensure that foreign objects (e.g., hard hats) do not
fall into open tanks or thickeners, and should not try in any way
to physically change the operating characteristics of the plant
equipment. In addition, the field inspector should use handrails
when using scaffolds and steps and have both hands free for
climbing ladders. Inspectors should avoid ladders which-are
either not equipped with safety cages or are too strenuous to
climb. Use of a flashlight is recommended when inspecting
interiors of different equipment. The field inspector should try
to avoid poor footing areas; these include slippery surfaces
(e.g., wet slurry, ice, snow), tripping hazards (e.g., unguarded
openings, hoses, tools, equipment items), and damaged or worn
surfaces. Finally, the field inspector should be wary of
overhead hazards such as falling objects (e.g., tools, slurry),
and low head clearance areas (e.g., piping, steel supports).
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REFERENCES
1. Jones, D. G., et al. Lime/Limestone Scrubber Operation and
Control Study. Research Project 630-2. Prepared for
Electric Power Research Institute, Palo Alto, California.
1978.
2. Smith, E. O., et al. Lime FGD Systems Data Book - Second
Edition. CS-2781. Research Project 982-23. Prepared for
Electric Power Research Institute, Palo Alto, California.
January 1983.
3. Smith, E. 0., et al. Limestone FGD Systems Data Book.
CS-2949. Research Project 1857-1. Prepared for Electric
Power Research Institute, Palo Alto, California. March
1983.
4. Lime FGD Systems Data Book. FP-1030. Research Project
982-1. Prepared for Electric Power Research Institute, Palo
Alto, California. May 1979.
5. Henzel, D. S., et al. Limestone FGD Scrubbers Users Hand-
book. Prepared for U.S. Environmental Protection Agency,
Industrial Environmental Research Laboratory, Research
Triangle Park, North Carolina. April 1981.
6. Kenney, S. M., et al. Failure Mode Analysis for Lime/
Limestone FGD Systems. Volume I - Description of Study and
Analysis of Results. Prepared for U.S. Department of Energy,
Morgantown Energy Technology Center, Morgantown, West
Virginia. DOE/METC/84-26 (DE84011958). August 1984.
7. Jahnke, J. A., and G. J. Aldina. Continuous Air Pollution
Source Monitoring Systems. EPA 625/6-79-005. June 1979.
8. Delleney, R. D., and P. K. Beekley. Process Instrumentation
and Control in SO- Scrubbers. CS-3565. Research Project
2249-1. Prepared for Electric Power Research Institute,
Palo Alto, California. June 1984.
9. Kashdan, E. R., and M. B. Ranade. Design Guidelines for an
Optimum Scrubber System. EPA-600/7-79-018. January 1979.
R-l
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REFERENCES (continued)
10. Melia, M. T., et al. Utility FGD Survey, July 1982 - March
1983. Volume 2: Design and Performance Data for Operational
FGD Systems. CS-3369. Research Project 982-32. Prepared
for Electric Power Research Institute, Palo Alto, California
and U.S. Environmental Protection Agency, Industrial
Environmental Research Laboratory, Research Triangle Park,
North Carolina. April 1984.
11. Steam Electric Plant Factors. National Coal Association,
Washington, D.C. 1983.
12. U.S. Environmental Protection Agency. Compilation of the
Air Pollutant Emission Factors. 3rd ed. (including Supple-
ments 1-13). AP-42. Research Triangle Park, North
Carolina. 1977.
13. Vuchetich, M. A., and R. J. Savoi. Electrostatic Precipita-
tor Training Program and Operation and Maintenance Manual
Development at Consumers Power Company. In: Proceedings
Conference on Electrostatic Precipitator Technology for
Coal-Fired Power Plants. EPRI CS-2908. April 1983.
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APPENDIX A
GLOSSARY OF TERMINOLOGY
A-l
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GLOSSARY OF TERMINOLOGY
acfm - (actual cubic feet per minute) a gas flow rate expressed with respect
to operating conditions (temperature and pressure).
Absolute humidity - The weight (or mass) of water vapor in a gas water-
vapor mixture per unit volume of space occupied.
Absorber - General term for those gas/liquid contacting devices designed
primarily for the removal of S0x pollutants.
Absorption - The process by which gas molecules are transferred to a liquid
phase during scrubbing.
Additive reagent - That particular chemical compound or element which is
added to the FGD process as an additional reagent to promote improved process
operation (see process additives).
Agitator/mixer - A slowly rotating rake, or set of blades or paddles fastened
to a shaft and motor used in tanks and thickeners to promote completion of
chemical reaction, maintain underflow solids in a fluid state, maintain a
homogenous slurry, or to rake underflow solids to a center discharge sump.
Alkaline fly ash scrubbing - An FGD process that uses the alkaline constit-
ueFtTirrTfj^lWTFTTected froo the burning of western coals as the primary
absorbent.
Alkalinity - Represents the amount of carbonates, bicarbonates, hydroxides,
or phosphates contained in the water, scrubber liquor, or wastes.
Ambient - Pertaining to the pressure, air quality, temperature, etc. condi-
tions of the surrounding environment of a plant or scrubbing system.
Annual outage - A scheduled period of time (generally four to six weeks) set
aside by the utility once per year to shut down the-boiler and/or FGD system
for inspection and maintenance.
Atonizer - A device used to disperse a liquid (water/slurry) into a gas
stream by reducing the liquid into a fine spray.
Axial flow fan - A mechanical air mover that consists of propeller-like
blades rotating in a plane perpendicular to the gas stream about a shaft
resting in a plane parallel to the gas stream.
A-Z
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Ball mill - A rotating drum loaded with steel balls that is used to crush and
slurry materials such as limestone to a particle size suitable for efficient
chemical reactivity.
Base load - A generating station which is normally operated to take all or
part of the base load of a system and which, consequently, operates at a
constant output.
Blanketing plate - The simplest of dampers consisting of a steel plate which
is bolted into place to close off and isolate ducts and/or scrubbers.
Blinding {reagent) - A phenomena where chemical reaction of a reagent
particle in a scrubbing slurry is primarily limited to the surface of that
particle so that less than 100 percent of the reagent molecules within the
particle are exposed to the gas molecules that are to be collected.
Bottom ash - Heavy solid particles of noncombustible ash that fall to the
bottom of the boiler.
British thermal unit (Btu) - The amount of heat required to raise the
temperature of one pound of water one degree Fahrenheit, averaged from 32 to
212°F.
Butterfly damper - A damper consisting of a simple plate that opens or closes
by turning the plate parallel or perpendicular to the gas flow.
Bypass reheat - A system which boosts the temperature of the saturated flue
gas leaving an FGD system above dew point by ducting a slip stream of particle-
cleaned flue gas from the ESP exit duct past the FGD system to the absorber
outlet duct or directly to the stack preventing stack damage from acid rain-
out.
Byproduct (recoverable byproduct) - Saleable materials produced by various
regenerable type FGD systems are considered recoverable byproducts.
Byproduct nature - The nature (e.g., gypsum) and disposition (e.g., stockpile
on site, marketed) of the end product by FGD systems that generate a saleable
product.
Capacity factor - The ratio of the average load on a boiler for the period of
time considered to the capacity rating of the boiler (actual kWh produced/
theoretical kWh produced x 100).
Carryover - Entrained solids, slurry droplets, and/or mist that leaves with
the flue gas stream exiting a particular stage of a scrubber or absorber.
Centrifugal fan - An air mover that consists of a drum of blades or slat type
vanes aligned parallel to the entering gas stream that rotates rapidly about
an axis also parallel to the entering gas stream casting the gas outward into
the housing and through an exiting duct connected tangentially to the hous-
ing.
A-3
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Centrifuge - A drum and worm gear type machine that separates solids from the
entering slurry stream by centrifugal force as the drum and gear rotate at
slightly different speeds.
Chloride - A compound of chlorine with another element or radical.
Closed water loop - The water loop of an FGD system is closed when fresh
makeup water added exactly equals the evaporative water loss leaving via the
stack and the water chemically or physically bonded to the sludge product.
Cocurrent flow - The process in which absorbent liquor or slurry enters the
absorber from the same direction as the gas stream so that SO, collection
occurs as the gas and liquid pass simultaneously through the lower absorber.
Cold-side ESP - An ESP located downstream of the boiler air preheater.
Combination tower - An absorber type that consists of a combination of two or
more absorber types within the same tower such as a level of sprays followed
by a level of absorber packing material (spray/packed type combination tower).
Configuration (horizontal/vertical mist eliminator) - A horizontal configura-
tion Is one in which the mist eliminator lays across the vertical duct or
absorber tower with the wet gas rising up through the mist eliminator. A
vertical configuration is one in which the mist eliminator is fastened ver-
tically in a horizontal duct run downstream of the absorber tower.
Continuous analyzer - Gas or liquid monitoring devices which automatically
take readings or measurements on a continual basis (e.g., SO , NO , 0^, etc.
continuous stack monitors).
Cooling tower blowdown - The wastewater characterized by high concentrations
of soluble salts periodically purged from the boiler cooling tower and some-
times used as makeup for the FGD system.
Corrosion - The deterioration of a metallic material by electrochemical
attack.
Countercurrent flow - The process in which absorbent liquor or slurry enters
the absorber tower from the opposite direction of the gas stream so that S05
collection occurs as the gas and liquid collide in the tower. *
Crosscurrent flow - The process in which absorbent liquor or slurry enters
the absorber perpendicular to the gas stream flow so that S0~ collection
occurs as the absorber and liquid paths intersect.
Cycling load - A generating station which is operated continuously but fluc-
tuates its load throughout a given day based on electrical demand.
Cyclone - A piece of air pollution hardware used for particle removal that
uses centrifugal separation tc effect particle collection.
A-4
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Damper - A plate or set of plates or louvers in a duct used to stop or regu-
late gas flow.
Density meter - Electronic device used to measure fixed density (mass per
unit volume).
Dewpoint - The temperature at which vapor contained in saturated flue gas
begins to condense.
Direct combustion reheat - A flue gas reheat system that boosts the tempera-
ture of the saturated gas from absorber above dewpoint by injection into the
gas stream of the hot combustion products generated by oil or gas reheater
burners.
Disposal - (Also referred to as waste disposal.) Removal of and discarding
of non-saleable waste from an F6D system in the form of ponding, landfilling,
mine filling, etc.
Dolomite (dolomitic lime or limestone) - A crystallized mineral consisting of
calcium magnesium carbonate (CaMgtCO^).
Efficiency - Ratio of the amount of a pollutant removed to the total amount
introduced to the normal operation.
End product:
Salable—The SO-, removed from the flue gas is recovered in a usable or
marketable form^e.g., gypsum).
Throwaway--The SCL removed from the flue gas is not recovered in a
usable or marketable form and the resulting sulfur-bearing waste prod-
ucts must be disposed of in an environmentally acceptable fashion.
Entrainment - The suspension of solids, liquid droplets or mist in a gas
stream.
Equivalent scrubbed capacity (ESC) - The effective scrubbed flue gas in
equivalent MW based on the percent of flue gas scrubbed by the F6D system.
Erosion - The action or process of wearing away of a material by physical
means (friction).
ESP (Electrostatic precipitator) - An air pollution device used to remove
particles from an exhaust stream by initially charging them with electrodes
and then collecting them on oppositely charged plates.
Excess air (percent) - The percentage of air supplied for combustion in
excess of that theoretically required for complete oxidation.
A-5
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Expansion joint - A small section of ductwork or piping that is designed to
passively expand or contract as required by the flexing of more rigid duct
runs, piping or pieces of equipment as such components are exposed to varying
external and internal temperatures.
Fan - A piece of equipment designed to move air by creating a high or low
pressure through mechanical means.
FD (forced draft) - A fan or blower used to produce motion in an enclosed
stream of gases by creating a positive pressure in the stream, effectively
pushing it through the system.
Feedback control - An automatic control system in which information about the
controlled variable (SCL, temperature, pH, etc.) is 'fed back1 after scrub-
bing has taken place as the basis for control of the process variable (re-
agent feed, steam, etc.).
Feedforward control - An automatic control system which measures an 'up-
stream' process variable (gas flow rate, temperature, slurry flow rate,
and/or pH, etc.) and compensates immediately without waiting for a change in
the controlled variable (SCL, temperature, pH, etc.) 'downstream' to indicate
a change has occurred.
FGD - (flue gas desulfurization) The process by which sulfur is removed from
the combustion exhaust gas.
FGD battery 1imits - An imaginary boundary that encompasses all equipment,
ponds, special liners, etc. that would not otherwise be installed if an FGD
system was not required.
Fixation - Increasing the chemical stability of FGD waste through chemical
means such as addition of alkali, alkaline fly ash, etc. usually in conjunc-
tion with dewatering and blending of inert solids; or through the use of
commercial processes (e.g., POZ-O-TEC, Calcilox, etc.) to produce a chemi-
cally stable solid.
Fly ash - Fine solid particles of noncombustible ash carried out of the
boiler by the exiting flue gas.
Forced outage - The FGD system is taken out or forced out of service to make
necessary repairs or modifications regardless of boiler availability such
that the system is unavailable for service.
Forced oxidation - A process in which sulfite-containing compounds are fur-
ther oxidized to sulfate compounds by aeration with air or pure oxygen to
promote dewatering, ease of handling, and/or stability in the waste product.
Gas contacting device - Grids, balls, marbles, trays, rods, or other obsta-
cles in the gas path within a scrubber/absorber intended to effect intimate
mixing and promote the gas-liquid transfer of SO2 to the scrubbing liquor or
slurry.
A-6
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Gas/1iguid distribution (in absorber scrubber) - The presence of random
mixing of flue gas with scrubber liquor throughout a wet scrubbing device
without the occurrence of static pockets or streams of uncontacted gas and
1iquor.
Guillotine damper - A damper whose operation is characterized by a vertical
or horizontal sliding gate or plate resembling a guillotine as it is moved
into and out of the gas path.
Heat exchanger - Device used to transfer sensible and/or latent heat from one
stream of material to another to raise or lower the temperature of one of the
materials.
Heat rate - A measure of generating station thermal efficiency, generally
expressed in Btu per net kilowatt-hour. It is computed by dividing the total
Btu content of fuel burned for electric generation by the resulting net
kilowatt-hour generation.
Hot-side ESP - An ESP located immediately upstream of the boiler air pre-
heater.
ID (induced draft) - A fan used to move an enclosed stream of gases by creat-
ing a negative relative pressure in the stream to effectively draw the gas
through the sysem.
Indirect hot air - A flue gas reheat system in which reheat is achieved by
Treating ambient air with an external heat exchanger using steam at tempera-
tures of 350° to 450°F.
In-line reheater - A heat exchanger installed in the wet flue gas duct down-
stream of the mist eliminator usually consisting of hot water or steam coils
used to boost the wet flue gas temperature above dewpoint.
Knock-out tray - A wash tray type pre-mist eliminator using valve or bubble
cap type mechanisms to capture the bulk of the entrained solids, droplets,
and mist carrying over from the scrubber/absorber of an FGD system.
Landfill - A method of waste disposal in which the dried FGD byproduct wastes
are dumped and packed, or buried between layers of earth near ground level or
below ground level.
L/G ratio (liquid-to-gas ratio) - The ratio of the total liquid exposed to
the gas stream in an FGD system (in gallons) to the inlet gas flow rate (in
increments of 1000 acf).
Liner - A metal, or organic or inorganic type material applied to a shell of
an FGD system component which is intended to protect the shell from abrasion,
heat, and/or corrosion.
Load factor - The ratio of the average load in kilowatts supplied during a
"cjesignated period to the peak or maximum load in kilowatts occurring in that
period.
A-7
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Louver damper - A damper consisting of several blades each pivoted about its
center and 1 inked together for simultaneous operation.
Makeup water - Water added to an FGD system to maintain a certain slurry
solids level by making up for water losses to evaporation and exiting waste
streams.
Mechanical dewaterinq equipment - Devices used to decrease the moisture level
of FGD waste to a degree that the material can be handled more easily and
disposed of as a stable solid suitable for landfill (e.g., vacuum filter,
centrifuge, hydrocyclone, etc.).
Mist - Dispersion of relatively large liquid particles in a gas stream:
carryover from a gas-liquid contact operation.
Mist eliminator - A piece or section of pollution hardware used to remove a
dispersion of liquid particles from a gas stream.
Primary collector—A mist eliminator that removes entrained solids,
water droplets, and mist not collected by the precollector.
Precollector--A mist eliminator that directly follows the scrubber/
absorber and is intended to remove the bulk of the entrained solids,
water droplets, and mist from the flue gas stream.
Mist eliminator passes/stage - The number of direction changes the gas stream
must make before it exits the mist eliminator stage.
Mist elimirator stages - The number of separate individual mist eliminators
(e.g., 2-stage mist eliminator - bulk separator followed by an impingement
collector).
Mist eliminator vane angle - The angle measured between the intersection or
vertex of any two interconnecting vanes.
MW - (megawatt) unit used to describe gross or net power generation of a
particular facility. One watt equals one joule per second. One megawatt
equals 10 watts.
New (as opposed to retrofit for FGD systems) - FGD unit and boiler were
designed at the same time or space for addition of an FGD unit was reserved
when the boiler was constructed.
N0X - A symbol meaning oxides of nitrogen (e.g., NO and NO^)-
NSPS (New Source Performance Standards) - Environmental regulations that
apply to a new installation referring primarily to the Federal NSPS that
applies to installations beginning construction on or after August 17, 1971.
Opacity - The degree to which emissions reduce the transmission of light and
obscure the view of an object in the background.
A-8
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Open water loop - The water loop of an FGD system is open when the fresh
makeup water added exceeds the evaporative water loss leaving via the stack
and the water chemically or physically bonded to the sludge product.
Outage - That period of time when the boiler and/or FGD system is shut down
for inspection and maintenance. Outages may be either forced or scheduled.
Overflow - (Also referred to as supernatant.) The clear liquor that is drawn
from the top of settling tanks (e.g., thickener) or settling ponds.
Oxidation - A chemical reaction in which oxygen unites or combines with other
elements or compounds in an FGD system (primarily with respect to the sulfite-
sulfate reaction).
Packed-bed absorber - A piece of pollution equipment using small plastic or
ceramic pieces, with high surface area-to-volume ratios, for intimate contact
between liquid and gas for mass transfer of a pollutant.
Particulate matter - Finely divided solid particles entrained in the gas
stream (fly ash, coal fines, dried reaction byproducts, etc.)
Peak load - A boiler that is normally operated to provide power during maxi-
mum load periods.
Perforated tray absorber - pollution control equipment that passes the un-
treated gas through holes in a series of plates on which liquid flows, caus-
ing an intimate contact between phases by breaking the gas flow up into
bubbles.
pH - The hydrogen ion concentration of a water or slurry to denote acidity or
aTkalinity.
H meter - Electronic instruments which measure the potential difference
etween a reference half-cell electrode and an indicator electrode sensitive
to hydrogen ions.
Plume (stack plume) - The visible emission from a flue (stack).
ppm (parts per million) - units of concentration; in wastewater applications
equal to milligrams per liter; in air pollution applications equal to moles
of pollutant to million moles diluent.
Preheater - Heat transfer apparatus through which ambient air is passed and
heated by higher temperature boiler flue exhaust gases for boiler combustion.
Presaturator - An external vessel or section of incoming flue gas ductwork
prior to the main scrubbing vessel where hot flue gas is presaturated.
Pressure drop - The difference in force per unit area between two points in a
fluid stream, due to resistive losses in the stream.
A-9
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Process additives - A chemical compound or element which is added to the
process or normally found with the main process reagent in small quantities
(e.g., Mg, adipic acid) to promote improved process operation (e.g., scale
reduction, increased SO2 removal efficiency).
Process type - The generic name for the F6D process based on the absorbent
used except for a few specialized processes which are referred to by patented
titles (e.g., lime, limestone).
Pug mill - A mechanical device used for blending ash and/or other dry solid
materials with FGD waste to enhance its handling characteristics for disposal
purposes.
Quencher - The inlet portion of the main scrubbing vessel where hot flue gas
is cooled and saturated.
Reagent - The substance which contains or produces the desired reactant
reagent material utilized by an FGD process for pollutant removal (e.g.,
lime, limestone).
Reagent preparation equipment - Equipment and/or mechanical devices involved
in the handling and preparation of the scrubber reagent (slakers, wet ball
mi 11s, pug mills, etc.).
Reagent utilization - (Also referred to as utilization.) That fraction of
reagent material (e.g., lime, limestone) fed to the FGD system which is
consumed (utilized) and chemically converted into product material (e.g.,
CaSO^, CaSO^, etc.).
Reheater - Device used to raise the temperature of the scrubbed gas stream to
prevent condensation and corrosion of downstream equipment, avoid visible
plume, and/or enhance plume rise and dispersion.
Relative humidity - (Also referred to as relative saturation.) The ratio of
the weight (or mass) of water vapor present in a unit volume of gas to the
maximum possible weight (or mass) of water vapor in unit volume of the same
gas at the same temperature and pressure.
Relative saturation - (Also referred to as relative humidity.) The term
"saturation" refers to any gas-vapor combination, while "humidity" refers
specifically to an air-water system.
Removal efficiency:
Particulate matter--The actual percentage of particulate matter removed
by the emission control system (mechanical collectors, ESP, or fabric
filter and FGD) from the untreated flue gas.
SCL—The actual percentage of SO2 removed from the flue gas by the FGD
system.
A-10
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Total unit design removal efficiency—The designed percentage of mass of
S02 or particulate matter entering the stack to the mass of the material
in the flue gas exiting the boiler regardless of the removal efficiency
of an individual component or the percentage of the exiting flue gas
actually being scrubbed.
Residence time - The amount of time a unit volume of gas or liquid spends in
a pollution control device.
Retrofit - The FGD unit will be/was added to an existing boiler not speci-
fically designed to accommodate an FGD system.
Rod deck absorber - Gas/liquid contacting device used for pollutant removal.
Untreated flue gas is contacted countercurrently with slurry with mixing
being aided by decks of cylindrical rods positioned perpendicular to the gas
and 1iquor flows.
scfm (standard cubic feet per minute) - Units of gas flow rate at 60°F and 1
atmospheric pressure.
Saleable end product - Any material produced from the byproducts or inlet
materials of an FGD process, with the original purpose being pollutant remov-
al, which is resaleable (e.g., gypsum).
Saturated - The situation when a gas or liquid is filled to capacity with a
certain substance. No additional amount of the same substance can be added
under the given set conditions.
Saturation temperature - The temperature to which flue gas drops when it is
saturated by scrubbing in a wet FGD system.
Scale - Deposits of slurry solids (may be calcium sulfite and/or calcium
sulfate) that adhere to the surfaces of FGD equipment, particularly absorber/
scrubber internals and mist eliminator surfaces.
Scheduled outage - A planned or "scheduled" period of time set aside period-
ically for inspection and maintenance of the boiler and/or FGD system.
Scrubber - A device that promotes the removal of pollutant particles and/or
gases from exhaust streams of combustion or industrial processes by the
injection of an aqueous solution or slurry into the gas stream.
Settling pond - Waste dewatering ponds which generally are not preceded by
dewatenng equipment. Absorber bleed is normally introduced at one end of
the pond and supernatant drawn off at the other end and recycled back for
absorber reuse. Settling ponds may or may not be final disposal areas.
Slaker - Mechanical devices which slake dry lime (calcium oxide) or magnesium
oxide into calcium or magnesium hydroxide alkali.
A-ll
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SIudge - The material containing high concentrations of precipitated reaction
byproducts and solid matter collected and/or formed by the FGD process (com-
posed primarily of calcium-based reaction byproducts, excess scrubbing reagent,
flyash, and scrubber liquor).
Sludge disposal - (Also referred to as waste disposal.) Removal of and
discarding of non-saleable waste from an FGD system in the form of ponding,
landfilling, mine filling, etc.
Sludge pond - Sludge dewatering ponds which generally are preceded by either
dewatering equipment and/or settling ponds. The sludge pond is usually the
final disposal area.
Slurry - A watery mixture of insoluble matter (usually lime or limestone).
S£x - A symbol meaning oxides of sulfur (e.g., SOg and SO^).
Spray tower - Gas/liquid contacting device used for pollutant removal.
Untreated gas is contacted countercurrently, crosscurrently, or cccurrently
with scrubber liquor via spray nozzles in a horizontal or vertical chamber.
Stabilization - Physical stabilization is accomplished by reducing the mois-
ture content of the sludge by addition of non-alkaline flyash and/or using a
vacuum filter or centrifuge to the point that structural properties are
optimized when the material is disposed of in a landfill.
Stabilization pond - Sludge ponds containing stabilized sludge.
Stack flue - The inner duct or channel in a stack through which the flue gas
is conveyed.
Stack gas velocity - The exiting velocity of the flue gas out the top of the
stack.
Standard conditions - A set of physical constants for the comparison of
different gas volume flow rates (60°F, 1 atmosphere pressure).
Stoichiometric ratic - A molar ratio of reactants in a chemical process;
indicates to what extent lime (or other reagent) is added to the reaction in
excess of the theoretical amount required.
Superficial gas velocity - The average flue gas velocity through a mist
eliminator or other component of an FGD system.
Supernatant - (Also referred to as overflow.) The clear liquor that is drawn
from the top of settling tanks (e.g., thickener) or settling ponds.
System supplier - A firm that fabricates and supplies flue gas desulfuriza-
tion systems.
Temperature, dry-bulb - The temperature of a gas or mixture of gases indi-
cated by an accurate thermometer after correction for radiation.
A-12
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Temperature, wet-bulb - Wet bulb temperature is a measure of the moisture
content of air (gas). It is the temperature indicated by a wet bulb psy-
chometer.
Theoretical kWh production - Period hours x gross unit operating capacity in
kilowatts.
Thickener - A continuous settling basin used to increase solids concentration
from influent to underflow.
Throwaway end product - Those byproduct materials formed by FGD systems which
have no resale value with or without additional processing.
Total controlled capacity (TCC) - The gross rating (MW) of a unit brought
into compliance witn FGD, regardless of the percent of flue gas treated at
the facility.
Tray tower - Gas/liquid contacting device used for pollutant removal. Un-
treated gas enters the base of the tower and passes upward through trays
containing openings countercurrent to downward cascading scrubber liquor
introduced from above each tray.
Treatment - The specific type of dewatering preparation used on FGD waste
material (sludge) to prepare it for final disposal (e.g., fixation, stabili-
zation, vacuum filters, thickeners, etc.).
Turnaround - Common term referring to an annual scheduled outage period.
Turndown ratio - The ratio of maximum gas flow capacity of a absorber to the
minimum it can handle without reducing SOp removal or causing unstable opera-
tion.
Underflow - Concentrated solids flow from the bottom of an absorber or thick-
ener.
Unit rating:
Gross - maximum continuous generating capacity in MW.
Net - Gross unit rating less the energy required to operate ancillary
station equipment, inclusive of emission control systems.
Utilization - (Also referred to as reagent utilization.) That fraction of
reagent material (e.g., lime, limestone, etc.) fed to the FGD system which is
consumed (utilized) and chemically converted into product material (e.g.,
CaS03, CaS04).
Vacuum filter - A drum and belt-type machine that separates solids from
slurry by use of vacuum pressure.
Wash water type - The nature of wash water spray utilized for mist elimin-
ators (e.g. /continuous, periodic).
A-13
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Water loop - All aqueous mass flows from inlet (e.g., seal water, quench
water, scrubber liquor) to outlet of an FGD system (e.g., evaporation via
stack, pond evaporation, waste disposal).
Mater losses - Water leaving the FGD system via the stack (evaporation),
pond, and/or thickener and also water that is chemically or physically bonded
to the waste disposal product.
Wet stack - Stacks equipped with special liners for handling the continual
condensation of moisture contained in the exiting scrubbed flue gas.
Zero discharge - A pollution regulation requiring that no effluent waste
stream be discharged back into the environment, with the exception of evapo-
ration via ponds and stacks (e.g., pond runoff or direct piping of spent
slurry or waste into nearby waterways or contributories would be prohibited).
A-14
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APPENDIX B
EQUATIONS FOR CONVERTING
POLLUTANT CONCENTRATIONS TO
NSPS UNITS
B-l
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EQUATIONS FOR CONVERTING POLLUTANT CONCENTRATIONS
(lb/ft3) TO NSPS UNITS (lb/105 Btu)*
F = 1Q& [5.S6(^H)+1.53(%C)+0.57(%S)+q.l4(%N)-0.46(%0,)+0.21(%H,0)1
c - r c 20.9
E " Cwshw 20.9 (I - Bwa) - * 02w
Where:
F = Coal analysis factor on a wet basis, std. ft3/10e Btu
w J
GCV (Gross Caloric Value) = high heating value of coal, Btu/lb
E = Pollutant emission rate, lb/106 Btu
C = Pollutant concentration given as a wet basis, lb/ft3
ws 3
B = Ambient air moisture fraction
wa
O2w = Percent oxygen in flue gas on a wet basis
Note: Standard F factors for coal:
w
Bituminous - 10680
Subbituminous - 11500
Lignite - 1200C
*Refer to Section 3.1.1.4.
B-2
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APPENDIX C
FGD SYSTEM INSPECTION CHECKLIST
C-l
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FGD SYSTEM INSPECTION CHECKLIST
GENERAL INFORMATION
Utility/Plant name Date
Plant Address
Plant Representative Phone No.
Plant Manager _____ Phone No.
Inspector Agency Name
Inspector Name Phone No.
PLANT DATA (Table 4.1-1)
Boiler Data
0 Type of firing
° Boiler service load
n Date of commercial operation
0 S0o emission limitation, 1b/10® Btu
6
0 Particulate emission limitation, lb/10 Btu
° Opacity Limitations, %
° Fuel firing rate at max. rating, tons/hr
° Heat rate, Btu/net kWh
0 Average capacity factor, %
0 Gross generating capacity, MW
0 Outlet flue gas flow, acfm
^ Outlet flue gas temperature, °F
Fuel Data Design Actual
° Average heat content, Btu/1b
0 Average ash content, %
C-2
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Fuel Data (continued) Design Actual
0 Average moisture content, %
0 Average sulfur content, %
0 Average chlorine content, %
General F6D System Data
0 FGD process type
0 Generation type
0 Application (new/retrofit)
0 Initial startup date
0 Commercial startup date
0 Total system design S0£ removal efficiency, %
0 Percent flue gas bypassing FGD system, %
0 Total system energy consumption, kWh __
0 Annual reagent consumption, tons/yr
0 Water loop type (open, closed)
0 Total system makeup water consumption, gpm
0 Waste disposal type
0 Solid waste generation rate (dry), tons/hr
0 Number of operators per shift ¦
0 Number of maintenance personnel per shift
0 Maintenance philosophy
CONTROL ROOM (Table 4.2-1)
Observation
0 Operator indicated location of FGD monitors? Yes No
All monitors operational? Yes No
O
nperation and Maintenance
0 Reason/corrective action regarding non-operational FGD monitors.
-------
Operation and Maintenance (continued)
0 Emission Readings Design Actual
° S02, ppm
° Particulate, gr/scf
° Opacity, %
° Facility has computerized control
with CRT displays Yes No
° CRT Readings
GAS HANDLING AND TREATMENT
FAN (Table 4.2-2)
Observation
c Excessive fan vibrations [ 1 Yes [ ] No. If yes, note readings
and inquire why.
Signs of debris/maintenance.
Signs of corrosion/location.
C-4
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Process
0 Fan function, design application service, and location.
Unit/boOster Centrifugal/axial
ID/FD Wet/dry
Design Actual
0 Fan AP, in.
0 Fan gas flow rate, acfm
0 Fan gas temperature, °F
0 Fan energy consumption
rate, kW
Operation and Maintenance
0 Fan failure incidences/causes/remedial actions.
Routine maintenance procedures/inspection schedules.
SCRUBBER/ABSORBER (Table 4.2-3)
Observation
0 Signs of debris/maintenance.
-------
Observation (continued)
0 Signs of materials
failure/location.
Signs of leaky piping.
Signs of leaks on absorber vessel walls.
Process Design Actual
0 Inlet particulate grain
loading, gr/scf .
0 Outlet particulate grain
loading, gr/scf
0 Inlet S02 concentration, ppm
0 Outlet S02 concentration, ppm
0 Absorber L/G, gal/1000 acfm
c Absorber AP, in. H^O
0 Slurry solids content in
absorber reaction tank, %
0 Slurry pH in absorber reaction
tank
Operation and Maintenance
0 Absorber failure incidences/causes/remedial actions.
C-6
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Operation and Maintenance (continued)
° If idle, inquire why and inspect internals (if possible).
Absorber instrumentation problems/causes/remedial actions.
Routine maintenance procedures/inspection schedules.
MIST ELIMINATOR (Table 4.2-4)
Observation
° Discarded sections/causes of failure.
If idle, inspect installed mist eliminator-section for:
Yes No
Plugging/scaling
Breakage
Deformation
Signs of mist eliminator carryover in downstream equipment.
C-7
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Process Design Actual
° Mist eliminator AP, in
0 Absorber pH
0 Mist eliminator flue aas velocity,
ft/s "
Operation and Maintenance
0 Washing techniques utilized [ ] Automatic [ ] Manual.
Wash water source/water loop type/problems.
Mist eliminator failure incidences/causes/remedial actions.
Routine maintenance procedures/inspection schedules.
REHEATER (Table 4.2-5)
Observation
0 If idle, check for excessive scaling/plugging (if possible).
C-8
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Observation (continued)
0 Discarded reheater tubes/causes of failure.
If operational, check nearby ductwork for corrosion caused by
reheater malfunctions.
process Design Actual
0 In-line reheater AP, in. HgO
0 Reheater energy consumption
rate, kW
° Reheater inlet temperature, °F
° Reheater outlet temperature, °F
° Is reheater outlet temperature above acid dew point? [ ] Yes [ ] No.
Operation and Maintenance
0 In-line tube failure incidences/causes/remedial actions.
Tube type/baffle and materials of construction.
Plugging problems encountered with In-line reheaters.
-------
Operation and Maintenance (continued)
° Reheater failure incidences/causes/remedial actions.
Cleaning techniques utilized [ ] Automatic [ ] Manual.
Routine maintenance procedures/inspection schedules.
DUCTWORK/DAMPER {Table 4.2-6)
Observation
r Signs of ductwork/damper corrosion/severity and location.
Check for ruptured expansion joints/location.
Newly installed ductwork/reasons for replacement.
C-10
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Observation (continued)
0 Does actual bypass ducting agree with original system design?
[ ] Yes [ ] No. If no, inquire why.
Is ductwork insulated? [ ] Yes [ ] No.
Note ductwork shape and configuration/associated problems.
process
° Process conditions (e.g., gas flow, gas temperature) to which
troublesome ductwork/dampers are subject to.
Is ductwork lined? [ ] Yes [ ] No. If yes, what materials of
construction are used.
—" " 1 "" ¦ ¦ 1 1 11 | i ..i ..I in.i ¦¦¦¦
Ductwork/damper problems due to mist eliminator carryover/causes/
remedial actions.
C-ll
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Operation and Maintenance
0 Ductwork failure incidences/causes/remedial actions.
Damper failure incidences/causes/remedial actions.
Ductwork/damper problems due to improper installation and/or
materials of construction/remedial actions.
Are dampers equipped with seal air? [ ] Yes [ ] No. If no, note
any isolation problems.
Damper problems due to fly ash or solids accumulation.
Routine maintenance procedures/inspection schedules.
C-12
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REAGENT HANDLING AND FEED
REAGENT CONVEYOR (Table 4.2-7)
Observation
0 Signs of belt misalignment, tears, or frayed edges.
Signs of leaks on pneumatic conveyor lines.
Signs of bucket elevator debris/jamming/maintenance.
Conveyor duties/problems.
Operation and Maintenance
0 Conveyor failure incidences/causes/remedial actions.
C-13
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Operation and Maintenance (continued)
0 Conveyor failures caused by reagent quality/weather.
Routine maintenance procedures/inspection schedules,
BALL MILL (Table 4.2-8)
Observation
° Signs of discarded balls/maintenance.
Process
p Failures caused by poor reagent qua!ity/undersizing.
Water source/problems.
C-14
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Operation and Maintenance
° Ball mill failure incidences/causes/remedial actions.
Routine maintenance procedures/inspection schedules.
SLAKER (Table 4.2-9)
Observation
° Is slaker operational? [ ] Yes [ ] No. If no, inquire why.
Process
° Dry reagent feed rate of slaker, tons/hr. [ ] Actual [ ] Design.
0 Slaker capacity problems/causes.
Failure caused by poor reagent quality.
C-15
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Process (continued)
0 Water source/problems.
Operation and Maintenance
0 Problems associated with slaker support equipment.
Slaker failure incidences/causes/remedial actions.
Routine maintenance procedures/inspection schedules.
TANKS (Table 4.2-10)
Observation
0 Signs of tank repairs/maintenance.
C-16
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Observation (continued)
° Note tank configuration/associated failures.
Note if tanks are covered or open.
If open, check for floating debris/associated failures.
Signs of slurry leakage.
Operation and Maintenance
0 Tank(s) drained to repair liners/bafflers.
Problems associated with tank support equipment.
C-17
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Operation and Maintenance (continued)
0 Tank failure incidences/causes/remedial actions.
Routine maintenance procedures/inspection schedules.
WASTE SOLIDS HANDLING AND DISPOSAL
THICKENER (Table 4.2-11)
Observation
Signs of thickener repairs/reason for repairs,
Signs of slurry leakage.
Are thickeners covered? [ ] Yes [ ] No..
If not covered, check for debris/associated failures.
C-18
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Process Design Actual
0 Overflow rate, gpm
° Underflow rate, gpm
0 Solids content in underflow, %
° Sulfite/sulfate ratio of inlet
slurry
0 How is thickener overflow used?/rate (gpm).
Operation and Maintenance
° Is thickener rake drive shaft and motor equipped with a torque
control alarm system? [ ] Yes [ ] No.
0 Problems with rake binding or rake drive shaft/motor failure.
Problems with sump failures.
Problems with liner failures.
Thickener failure incidences/causes/remedial actions.
C-19
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Operation and Maintenance (continued)
0 Routine maintenance procedures/inspection schedules.
VACUUM FILTER (Table 4.2-12)
Observation
0 Inspect filter cloth for tears.
Check for spare or discarded filter cloths.
Check filter cake consistency/product quality.
Process Design Actual
° Filter cake production rate,
tons/hr
0 Solids content of filter cake, %
0 Inlet slurry solids content, %
° Wastewater effluent production
rate, gpm
0 Sulfite/sulfate ratio in
filter cake
C-20
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Process (continued)
0 Inlet slurry solids content adequate? [ ] Yes [ ] No.
0 How is the vacuum filter filtrate used?/rate (gpm)
Operation and Maintenance
0 Problems/failures associated with vacuum filtrate pump.
Problems regarding filter cloth replacement.
Filter cake conveyor failures.
Vacuum filter failure incidences/causes/remedial actions.
Routine maintenance procedures/inspection schedules.
C-21
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CENTRIFUGE (Table 4.2-13)
Observation
° Centrifuge(s) operational? [ ] Yes [ ] No. If no, inquire why.
Check centrifuge cake consistency/product quality.
Process Design Actual
° Filter cake production rate,
tons/hr
0 Solids content of filter cake, % .
° Inlet slurry solids content, %
0 Wastewater effluent production
rate, gpm
° Sulfite/sulfate ratio in
filter cake
° Inlet slurry solids content adequate? [ ] Yes [ ] No.
° How is the centrifuge filtrate used?/rate (gpm)
Operation and Maintenance
0 Problems due to support equipment factors.
C-22
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Operation and Maintenance (continued)
° Centrifuge failure incidences/causes/remedial actions.
Routine maintenance procedures/inspection schedules.
WASTE PROCESSING SYSTEM (Table 4.2-14)
Process
° Type of waste processing system:
[ ] forced oxidation [ ] fixation [ ] stabilization [ ] None.
0 What is the energy consumption rate? Is this typical or excessive?
Operation and Maintenance
° Problems associated with the equipment area.
Waste processing failure incidences/causes/remedial actions.
C-23
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Operation and Maintenance (continued)
0 Routine maintenance procedures/inspection schedules.
WASTE DISPOSAL SYSTEM (Table 4.2-15)
Process
0 Type of water loop [ ] open [ ] closed.
0 Type of waste disposal system [ ] ponding [ ] landfilling
[ ] stacking (gypsum)
0 If ponding is used, how much waste water is returned back to system
(gpm)?/quality of water.
Operation and Maintenance
0 Waste disposal failure incidences/causes/remedial actions.
Routine maintenance procedures/inspection-schedules.
C-24
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PUMP AND VALVE (Table 4.2-16)
Observation
° Check for discarded pump impellers and liners/note appearance.
Signs of leaky pump seals, bearings, etc.
Excessive pump vibrations [ ] Yes [ ] No. If yes, inquire why.
Locate and inspect abrupt expansion, contraction, and bends in
piping around valves/note any problems.
Process
0 Process conditions associated with failure-prone pumps/valves.
C-25
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Process (continued).
0 Energy consumption rate of absorber recycle pumps, kW.
Design Actual
° Inquire about pump redundancy for different operations.
Operation and Maintenance
° Pump failure incidences/causes/remedial actions.
Valve failure incidences/causes/remedial actions.
Routine maintenance procedures/inspection schedules.
C-26
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO. 2.
EPA- 600 / 8-85-024
3. RECIPIENT'S ACCESSION NO.
4. TITLE ANO SUBTITLE
Lime/Limestone Flue Gas Desulfurization Inspection
and Performance Evaluation Manual
8. REPORT DATE
September 1985
6. PERFORMING OROANIZATION CODE
7. AUTHOR(S)
E. R. Kirshnan, R. S. McKibben, M. T. Melia, and
B.A. Laseke
8. PERFORMING ORGANIZATION REPORT NO.
PN 3650-2
9. PERFORMING OROANIZATION NAME ANO ADDRESS
PEI Associates, Inc.
P. O. Box 46100
Cincinnati, Ohio 45246-0100
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-02-3995, Task 2
12. SPONSORING AGENCY NAME ANO ADDRESS
EPA, Office of Research and Development
Air and Energy Engineering Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT ANO PERIOD COVERED
User manual; 10/84 - 3/85
14. SPONSORING AGENCY CODE
EPA/600/13
is. supplementary notes^EERL project officer is Theodore G. Brna, Mail Drop 61, 919/
541-2683.
16. abstract The manuai—on wet nonregenerable lime/limestone flue gas desulfuriza-
tion (FGD) systems—is intended to guide Federal and State regulatory personnel con-
cerned with the inspection and permitting of FGD systems for coal-fired steam elec-
tric generators in the U. S. It is a working document for someone who periodically
inspects power plants to ensure their compliance with emission standards. Orien-
tation material on the design, operating, and performance characteristics of FGD
systems may also be helpful to the environmental regulatory agency permitter. With
its goal of facilitating the systematic inspection of an FGD system to determine the
system's present and probable future compliance status, the manual limits pro-
cess theory to a necessary minimum and makes ample use of charts, checklists,
and simplified diagrams in providing important guidelines and recommendations.
Following the introductory section defining its purpose, approach, and scope, the
manual contains sections on lime/limestone technology, performance monitoring*
inspection methods and procedures, performance evaluation and problem diagnosis/
correction, operation and maintenance, and safety. Appendices provide supplemen-
tary reference material, definitions of FGD terms, calculation sheets, and example
checklists, the latter two for use by someone inspecting a plant.
17. KEY WOROS ANO DOCUMENT ANALYSIS
g. DESCRIPTORS
b. IDENTIFIERS/OPEN ENOSO TERMS
c. COSATl Field/Group
Pollution Calcium Carbonates
Inspection Coal
Performance Evaluation
Flue Gases Electric Generators
Desulfurization
Calcium Oxides
Pollution Control
Stationary Sources
13B
14G 2 ID
05A
2 IB 10B
07A.07D
07B
If. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
31. NO. OF ^a6eS
305
20. SICURITV CLASS (Thit pap)
Unclassified
aa. price
tPA form 2220-1 (••73) C"27
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