.Research Triangle Park WC 27711
Technology Tf anffeE
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Manual
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EPA/625/1-85/019
October 1985
FLUE GAS DESULFURIZATION
INSPECTION AND PERFORMANCE EVALUATION
HANUAL
I
by
PEI Associates, Inc.
11499 Chester Rbad, P.O. Box 46100
Cincinnati, Ohio 45246-0100
or
Air and Energy Engineering Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
and
Center for Environmental Research Information
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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FOREWORD
The 1970 Clean Air Act required the U.S. Environmental
Protection Agency (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 sulfur dioxide (SO2) , particulate
matter, and- nitrogen oxides (NOv) from new, modified, and recon-
4&
structed fossil-fuel-fired steam generators used in electric
utility and large industrial facilities. In 1977, amendments
made to the Clean Air Act directed the EPA to tighten emission
standards from new coal-fired utility and large industrial boil-
ers, which resulted in the revised NSPS of June 1979. In addi-
tion to NSPS, air emissions from coal-fired utility boilers are
also governed by State Implementation Plans (SIP's) and the
Prevention of Significant Deterioration (PSD) program.
As of 1985, flue gas desulfurization (FGD) was the most
commercially developed means of ; controlling SO2 emissions from
coal-fired powerplants. Currently, about 16 percent of the
domestic coal-fired generating capacity is controlled by FGD, and
this percentage is expected to double by 1991. Of the 126 FGD
systems (representing 53,189 MM of gross power-generating capaci-
ty in the United States) , only nine are dry systems, and these
represent only 3 percent of the! total controlled capacity. In
contrast, more than 80 percent of the controlled capacity is
equipped with slurry (wet) systems, which use either lime or
limestone as the SO2 scrubbing reagent. (This trend is expected
to continue, as 70 percent of the FGD systems now under construc-
tion or for which contracts have been awarded are of this type.)
XI
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Lime/limestone slurry FGD, however, represents the most dif-
ficult application of scrubbing technology because of the process
design and operation and maintenance (O&M) considerations re-
quired to withstand the inherent problems of erosion, corrosion,
scaling, arid plugging in such systems. Inspectors from Federal
and State environmental regulatory agencies need to be familiar
with the problems that plague Ijime/limestone slurry FGD systems
to aid them in their inspections and performance evaluations of
these, systems with respect to compliance with emission standards.
For this reason, and to aid in the permitting process, this
manual was prepared and has bee
i approved for publication.
111
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ABSTRACT
Flue gas desulfurization (FGD) is the most developed of the
commercial means of controlling sulfur dioxide (S02) emissions
from coal-fired powerplants. Of the 126 FGD systems currently in
service on domestic coal-fired utility boilers, only nine are dry
FGD systems (representing only 3 percent of the total controlled
capacity). Conversely, more than 80 percent of this capacity is
controlled by slurry (wet) systems in which either lime or lime-
stone is used as the SO2 scrubbing agent. This preference is
attributed primarily to favorable costs, demonstrated commercial
operating experience, and simplicity of design and operation.
Because of this widespread usage of lime/limestone slurry FGD,
this manual is devoted exclusively to such systems.
Despite these favorable aspects, however, lime/limestone
slurry FGD represents the-most difficult application of scrubbing
technology for the control of coal-fired boiler flue gas because
of the process design and operation and maintenance considera-
tions required to withstand the inherent problems of erosion,
corrosion, scaling, and plugging of such systems.
The intent of this manual is to provide inspectors from Fed-
eral and state environmental agencies with information regarding
the problems that plague lime/limestone slurry FGD systems that
will aid them in their inspections and performance evaluations of
these systems with respect to compliance with the emission stan-
dards that have evolved since the passage of the 1970 Clean Air
Act.
A unique feature of this manual is its structure as a
"tool," or working document, which will accompany the inspector
on each plant inspection. Thus, the document is presented in
xv
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"user friendly" fashion and tailored to provide practical infor-
mation for its intended use—to assist in the systematic inspec-
tion of an FGD system to determine present and future compliance
status. This approach entails the use of nomographs, checklists,
matrices, simplified diagrams, cross-referencing, and indexing of
textual information, and the presentation of important guidelines
and recommendations in a readily discernible fashion.
With regard to the intended!audience, for purposes of this
manual, the field inspector is defined as the individual who
periodically inspects powerplants to ensure their compliance with
emission standards. The scope o£ 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).
v
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CONTENTS
Foreword
Abstract
Figures
Tables
Metric Conversions
Acknowledgment
1 . Introduction
1.1 Purpose
1.2 Approach
1 . 3 Scope and Content
1.4 Organization of the Manual
2. Lime /Lime stone FGD Technology
2.1 Environmental Regulations
2.1.1 Air Emission Standards
2.1.1.1 1971 NSPS
2.1.1.2 1979 NSPS
2.1.1.3 State Implementation Plans
2.1.1.4 Prevention of Significant
Deterioration
2.1.2 Water and Solid Waste Standards
2.1.2.1 Water Regulations
2.1.2.2 Resource Conservation and
Recovery Act
2.2 Coal Properties and Flue Gas Characteristics
2.3 Basic Principles of Lime /Lime stone Slurry
Processes
2.3.1 Process Description
2.3.2 Operational Factors
2.3.2.1 Stoichiometric Ratio
2.3.2.2 L/G Ratio
ii
iv
xii
XV
xvii
xviii
1
1
1
3
4
8
8
8
8
9
9
11
12
12
12
12
13
15
17
17
18
VI
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CONTENTS I
continued)
2.3.2.3 Slurrjj- pH
2.3.2.4 Relative Saturation
2.3.2.5 Oxidation
2.3.2.6 Chemical Additives
2.4 FGD System Design Configurations
2.4.1 Development of
Technology
2.4.1.1 Historical Perspective
2.4.1.2 Characteristics of Technology
Generation
2.4.2 Existing Desigr
Configurations
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
•
«
•
•
•
•
•
•
•
•
•
*
•
•
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
4.
2.
2.
2.
2.
2.
2.
2.
2.
2.
2.
2.
2.
2.
2.
2.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Fans
Scrubby ers /Absorbers
Mist Eliminators
Reheatiers
Ductv/cjrk and Dampers
Reagent Conveyors and Storage
Ball kills
Slakers
Tanks
Thickeners
Vacuum Filters
Centra
Waste
Waste
Pumps
.fuges
Processing
Disposal
and Valves
2.4.3 Operational Utility Lime and Limestone
Slurry FGD Systems
2 . 5 FGD O&M Considerations;
2.5.1 Failure Modes
2.5.1.1 Coal Characteristics
2.5.1.2 Boiler Characteristics
2.5.1.3 Application Characteristics
2.5.1.4 Desigrji and Operation
Considerations
2.5.2 System Layout,
Design
Accessibility, and
19
19
20
20
21
21
21
25
28
30
32
38
39
42
46
50
52
54
55
55
57
60
61
61
63
63
74
80
80
81
82
83
vxi
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CONTENTS (continued)
2.5
2.5
2.5.2.3
2.1
2.2
Gas Handling and Treatment
Reagent Preparation and Feed
Waste Solids Handling and
Disposal
2.5.3 O&M Practices
2.5.3.1 Standard Operations
2.5.3.2 Initial Operations
2.5.3.3 Startup, Shutdown, Standby,
and Outage
2.5.3.4 System Upsets
2.5.3.5 Operating Staff and Training
2.5.3.6 Preventive Maintenance Programs
2.5.3.7 Unscheduled Maintenance
3. Performance Monitoring
3.1 Key Operating Parameters and Their Measurement
3.1.1 Gas Circuit Parameters
3.1.1.1
3.1.1.2
3.1.1.3
3.1.1.4
3.1.1.5
SO
NO
Opacity
°2
Gas Flo'
3.1.2 Slurry Circuit Parameters
3.1.2.1
3.1.2.2
3.1.2.3
3.2 Instrumentation
pH
Slurry Flow Rates
Solids Content
3.2.1 pH Instrumentation
3.2.2 Slurry Flow Rates
3.2.3 Solids Content
3.3 Testing and Monitoring
3.3.1 Manual Testing
3.3.2 Alternative Methods
3.3.3 Continuous Emissions Monitoring (CEM)
3.3.4 Performance Specification Tests
Page
85
88
89
90
90
93
93
94
95
95
97
99
99
100
100
100
100
100
101
102
102
102
102
103
103
104
107
107
107
110
111
114
Vlll
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CONTENTS (continued)
3.4 Recordkeeping Practices and Procedures
Inspection Methods and Procedures
4.1 Guidelines for Overall Plant Inspection
i
4.2 Inspection Procedures
4.2.1 Gas Handling aikd Treatment
4.2.1.1 Fans
4.2.1.2 Scrubbers /Absorbers
4.2.1.3 Mist Eliminators
4.2.1.4 Reheaters
4.2.1.5 Ductwork and Dampers
4.2.2 Reagent Preparation and Feed
4.2.2.1 Reagent Conveyors and Storage
4.2.2.2 Ball Mills
4.2.2.3 Slakers
4.2.2.4 Tanks
4.2.3 Waste Solids Handling and Disposal
4.2.3.1 Thickeners
4.2.3.2
4.2.3.3
4.2.3.4
4.2.3.5
4.2.3.6
Vacuun
Centri
Waste
Waste
Pumps
Filters
fuges
Processing
Disposal
and Valves
4.3 Summary
Performance Evaluation and Problem Diagnosis/
Correction
5.1 Data Collection Methods
5.1.1 Sources
5.1.2 Forms of Data
5.2 Performance Evaluation
5.2.1 Emissions
IX
Page
115
120
121
123
124
124
124
127
131
131
134
134
138
138
138
138
138
142
142
142
142
148
148
153
154
154
155
156
156
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r
CONTENTS (continued)
5.2.1.1
5.2.1.2
5.2.1.3
5.2.2 Process
5.2.2.1
5.2.2.2
5.2.2.3
5.2.2.4
5.2.2.5
5.2.2.6
5.2.2.7
5.2.2.8
5.2.2.9
S02
Particulate Matter
Opacity
Gas Flow
Gas-side Pressure Drop
Slurry pH
Slurry Flow
Slurry Solids
Reagent Consumption
Solid Waste Production
Makeup Water Source and
Consumption
Energy Consumption
5.2.3 O&M
5.2.4 Observation
5.2.4.1 System Observation
5.2.4.2 Equipment Layout/Access
5.2.4.3 Consumed Equipment
5.2.4.4 General Housekeeping
5.3 Problem Diagnosis and Corrective Measures
5.3.1 Problem Diagnosis
5.3.1.1 Gas Handling and Treatment
5.3.1.2 Reagent Preparation and Feed
5.3.1.3 Waste Solids Handling and
Disposal
5.3.2 Corrective Actions
5.3.2.1
5.3.2.2
5.3.2.3
Gas Handling and Treatment
Reagent Preparation and Feed
Waste Solids Handling and
Disposal
6. Model O&M Plan
6.1 Management and Staff
156
157
158
159
= 160
160
163
163
164
164
166
166
170
174
179
179
182
183
184
185
185
186
196
206
212
213
220
222
225
225
x
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6.1.1
6.1.2
CONTENTS (continued)
Corporate Organization
Plant Organization and Training
6.2 Operating Manuals }
6.3 Maintenance Manuals I
6.4 Troubleshooting Techniques
6.5 Spare Parts
6.6 Work Order Systems
6.7 Computerized Tracking System
7. Safety i
7.1 Inhalation of Toxic Gases
7f2 Skin Irritation and/or IChemical Burns
to the Skin
7.3 Exposure to Fugitive Dust
7.4 Normal Industrial Safety Practices
References
Appendix A - Glossary of Terminology
Appendix B - Equations for Converting Pollutant
Concentrations to tjfSPS Units
Appendix C - FGD System Inspection Checklist
Page
226
226
231
234
236
237
239
244
247
247
249
250
251
R-l
A-l
B-l
C-l
xi
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FIGURES
Number
1.3-1 Lime/Limestone FGD Capacity and Total
FGD-Controlled Capacity Through 1992
2.1-1 S09 Emission Standards for Coal-Fired Units
under 1979 NSPS.
2.3-1 Basic Lime/Limestone FGD Process Flow Diagram
2.4-1 Growth of Operational FGD Capacity for
Utilities
2.4-2 Typical Fan Designs
2.4-3 Venturi Tower Configurations
2.4-4 Spray Tower Types
2.4-5 Tray Tower and Tray Types
2.4-6 Packed Tower and Packing Types
2.4-7 Baffle-type Impingement Mist Eliminators
2.4-8 FGD System Reheat Schematic Diagrams
2.4-9 -Simplified Flow Diagram Showing Damper
Configurations ;
2.4-10 Different Damper Designs
2.4-11 Barge-Based Limestone Handling and Storage
System
2.4-12 Three Types of Conveying Equipment Used to
Transport Lime
2.4-13 Two Types of Ball Mills Used in Limestone
Slurry FGD Systems
2.4-14 Basic Types of Slakers;
Page
10
16
23
31
33
34
36
37
40
41
44
45
48
49
51
53
XII
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FIGURES (continued)
Number
2.4-15
2.4-16
2.4-17
2.4-18
2.5-1
4.2-1
4.2-2
4.2-3
4.2-4
4.2-5
5.2-1
5.2-2
5.2-3
5.2-4
5.2-5
5.2-6
5.2-7
5.2-8
5.2-9
5.3-1
5.3-2
Diagram Showing Components of a Thickener
A Rotary-Drum Vacuum Filter
Components of a Settling Centrifuge
Examples of Pond Types 1 for Waste Disposal
Major Material Flows iih. FGD Systems
Isometric View of a Typical Centrifugal Fan
Typical Tray Tower Absorber
Typical Mist Eliminate]
-
Isometric View of a Tyj
Typical Slurry Recycle
Typical Specific Gravil
Recirculation Slurry :
FGD System
Reagent Requirement Ca.
Sludge (Waste) Product:
Fan Power Requirements
Recirculation Pump Pow«
: Section
>ical Thickener
Centrifugal Pump
:y of Absorber
for Lime /Lime stone
.culation
.on Calculation
>r Requirements
Example Operation Log Sheet
Example Operation Log Sheet
Example of a Handwritten Work Order Form
Example of a Computer-Generated Work Order Form
Gas Handling and Treatment Subsystem
Arrangements |
Reagent Preparation an<
Arrangements
x:
I Feed Subsystem
.ii
Page
56
58
59
62
75
125
128
130
143
150
165
167
168
175
176
177
178
180
181
187
198
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FIGURES (continued)
Number
5.3-3
6.1-1
6.2-1
6.3-1
Waste Solids Handling and Disposal Subsystem
Arrangement
Organizational Diagram for Coordinated FGD
System O&M Program
Outline for FGD Operating Manual
Outline for FGD Maintenance Manual
207
229
233
235
xxv
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Number
2.2-1
2.4-1
2.4-2
2.4-3a
2.4-3b
2.5-1
2.5-2
2.5-3
2.5-4
3.2-1
3.2-2
3.3-1
3.3-2
3.3-3
4.1-1
TABLES
Fuel Properties of Fou:: Representative Coals
Typical Characteristics of First, Second, -and
Third Generation Lime/Limestone Slurry FGD
Systems
FGD Subsystems Requiring Tanks
Design and Operating Data for Operational
Utility Lime/Limeston^ Slurry FGD Systems
in the U.S. (General Data)
Design and Operating Data for Operational
Utility Lime/Limestone Slurry FGD Systems
in the U.S. (Specific
Major Power Plant Cons
Summary Listing of the
Major Equipment Area
Subsystem Outage Times
Hours (MEH)
Summary of Failure Mod
pH Instrumentation on
pH Instrumentation on
FGD Systems
Data)
Lderations
FGD Subsystems by
in Module Equivalent
e Analysis
Lime Slurry FGD Systems
Limestone Slurry
Summary of Manual Emissions Measurement
Methods for an FGD System on a Coal-
Fired Utility Boiler
Principles Used in Gaseous Emission Monitors
GEM System Components
General Plant Data
Page
14
27
54
64
68
73
76
78
84
105
106
109
112
113
122
xv«
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TABLES (continued)
Number
4.2-1 Control Room Checklist
4.2-2 Fan Checklist ,
4.2-3 Scrubber/Absorber Checklist
4.2-4 Mist Eliminator Checklist
4.2-5 Reheater Checklist
4.2-6 Ductwork/Damper Checklist
4.2-7 Reagent Conveyor Checklist
4.2-8 Ball Mill Checklist
4.2-9 Slaker Checklist
4.2-10 Tank Checklist ;
4.2-11 Thickener Checklist
4.2-12 Vacuum Filter Checklist
4.2-13 Centrifuge Checklist
4.2-14 Waste Processing System Checklist
4.2-15 Waste Disposal System Checklist
4.2-16 Pump and Valve Checklist
5.2-1 Design Gas-Side Pressure Drops for Absorbers
in Operational Lime/Limestone FGD Systems
5.2-2 Design Gas-Side Pressure Drops for Mist
Eliminators in Operational Lime/Limestone
FGD Systems
5.2-3 Makeup Water Consumption Rates for
Operational Lime/Limestone FGD Systems
5.2-4 Energy Requirement Calculations
6.6-1 Work Order Priority System
124
126
129
132
133
135
137
139
140
141
144
145
146
147
149
151
161
162
•171
173
242
xvi
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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
' - .,-,,''''! I ..'I'.'.; i . : t, , ••- , .-
States. The following list prcjvides factors for conversion to
metric units.
To convert from
Btu
Btu/lb
cfm
°F
ft
ft/h
ft/s
ft2
ft3
ft3
gal
gal/ft3
gal/min
gr
gr/scf
hp (mechanical)
hp (boiler)
in.
in. H2O
in.2
in.3
Ib
Ib
lb/106 Btu
lb/ft3
Ib/gal
Ib/in.2
Ib-mol
Ib-mol/h
Ib-mol/h per ft2
Ib-mol/min
scfm (at 60°F)
ton
I To
kWh
kJ/kg
m3/h
°C
m
m/h
m/s
m2
liters
m3
liter
liter/[m3
liter/Jmin
g
g/Nm3
kw
kw
cm
kPa
m2
m3
g
kg
g/kj
kg/m3
kg/m3
kPa
g-mol
g-mol /ijnin
g-mol/min per m2
g-mol/s
Nm3/h (at 0°C)
kg
X
7X1
Multiply by
0.0002931
2.326
1.70
(°F - 32)/I. 8
0.305
0.305
0.305
0.0929
28.32
0.02832
3.785
0.134
3.79
0.0648
2.29
0.7457
9.803
2.54
0.2488
0.0006452
0.00001639
453.6
0.4536
429.9
16.02
119.8
6.8.95
453.6
7.56
81.4
7.56
1.61
907.2
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ACKNOWLEDGMENT
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;
Norman Kulujian, Center for Environmental Research Information;
and Kirk Foster arid Sonya Stelmack, Stationary Source Compliance
Division, Technical Support feranch. The PEI Project Director was
Bernard A. Laseke and the PEI Project Manager was E. Radha
Krishnan. The PEI principal investigators were Messrs. Ronald S.
McKibben and Michael T. Melia.
xviii
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SEC
ION 1
Desulfurization Inspection and
s to provide guidance to Federal
INTRODUCTION
1.1 PURPOSE
The purpose of the Flue Ga
Performance Evaluation Manual i
and state environmental regulatory personnel involved in the
inspection and permitting of flue gas desulfurization (FGD)
systems for electric utility cokl-fired steam generators (boil-
ers) in the United States.
The primary intended user of this manual is the field in-
spector 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
ance of potential noncompliance
tal regulatory agency permitter,
the permitter is defined as the
compliance status (i.e., avoid-
episodes).
A secondary intended user of this manual is the environmen-
For the purposes of the manual,
individual who reviews permit
applications for new capacity in accordance with adherence to
environmental regulations and eijiission 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,
SECTION 1-INTRODUCTION
-------
one of the intended user groups is environmental regulatory
personnel. Other similar manuals generally define their intended
users 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 this 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 encpurage use. This is accomplished
through the use of nomographs-, checklists, matrices, simplified
diagrams, cross-referencing and indexing of textual information,
and by presenting important guidelines and recommendations in a
conspicuous fashion.
A final unique feature of the manual is its use for the
interpretation of sulfur dioxide1 (SO2) excess emission reports.
If an FGD-equipped boiler represents a source of frequent SO2
excess emission reporting, the manual will provide guidelines to
determine the cause and to evaluate the remedial actions to be
taken by the plant operator. If'an FGD-equipped boiler repre-
sents a source of infrequent SO» excess emission reporting, the
£* ,
manual will provide guidelines to identify the contributing
factors that are associated with! this situation.
SECTION 1-INTRODUCTION
-------
1.3 SCOPE AND CONTENT
The scope of the manual is Idevoted 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, SO_ in the flus 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 Syst
The scope of FGD technology
limited to tail-end, "wet" lime/
excluding:
0 all tail-end processes
=m Design Configurations).
addressed in this manual is
Limestone slurry processes only,
that do not use calcium-based
(lime/limestone) additives as the SO- reactant (e.g.,
sodium/calcium [dual or double alkalx], sodium/thermal
regeneration [Wellman-JLord] , magnesium oxide [Mag-Ox] ,
and sodium [once-throu
trona, nahcolite]).
all tail-end processes
the flue gas during tr
jh soda ash, sodium hydroxide,
that do not completely saturate
2atment, known as "dry scrubbing"
(spray drying, dry sorpent injection).
0 precombustion and in-sLtu (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 because of
their level of process development and economics. Since the
early application of FGD to control SO2 emissions from boiler
flue gas, there has been pronounced preference for lime/limestone
slurry processes (see Section 2.J4.1.1; 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
SECTION 1-INTRODUCTION
-------
slurry processes is illustrated in Figure 1.3-1. It 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 S02
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 SO2 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 treat-
ment, reagent preparation and feed, and waste -solids handling and
disposal. Moreover, operations and factors that influence the
FGD process envelope are considered, including coal characteris-
tics and consumption, boiler design and operation, and particu-
late 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
SECTION 1-INTRODUCTION
-------
0
72 73 74 75 76 77 78 79' 80 8
Figure 1,3-1. Lime/1imestor
controlled cgpe
aTotals reflect end of year values.
82 83 84 8§ 86 87 88 89 90 91 92
YEAR
e F6D capacity and total F6D-
city through ]992.a
-------
regulatory agency inspector of FGD-equipped, coal-fired, utility
boilers. At the outset, therefore, an overview of lime/limestone
FGD technology is presented (see Section 2). Next, a review of
the environmental regulations which govern utility coal-fired
boilers and, in effect, have driven the commercial application of
FGD technology is provided. A description of lime/limestone
slurry processes including process theory and basic principles,
system and equipment configurations, and operation and mainten-
ance considerations is also discussed.
In succeeding sections, the practical guidelines associated
with inspection and performance evaluation are presented. Sec-
tion 3 deals with FGD performance monitoring, starting with key
I
operating parameters and their measurement. Particular attention
is given to continuous emission monitoring procedures and manual
test methods for determining compliance with SO,, standards. Sec-
tion 4 is the focal point of the manual—inspection methods and
procedures. This information is provided 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 diagno-
sis, 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 lev-
els. 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
SECTION 1-INTRODUCTION
-------
Sections 2 through 7. The append!
of FGD terminology, calculation
dices are devoted to definitions
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.
SECTION 1-INTRODUCTION
-------
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 Perfor-
mance Standards (NSPS) were issued to limit emissions of SO-?
particulate matter; and nitrogen oxides (NO ) from new, modified,
3C
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 for 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)
and the Prevention of Significant Deterioration (PSD) program.
2.1.1.1 1971 NSPS. These standards apply to fossil fuel-fired
steam generating units capable of firing more than 250 million
Btu/h heat input (to the boiler) and upon which construction
commenced after August 17, 1971.
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
8
-------
SO, Standards. Sulfur! dioxide emissions are limited to
1.2 lb/10b Btu heat irlput.
Particulate Standards.
limited to 0.10 lb/106
Particulate emissions are
Btu heat input.
0 NO Standards. Nitrog'en oxide emissions are limited to
0.70 lb/10b Btu heat dlnput.
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
other fuels) and upon which construction commenced after Septem-
ber 18, 1978.
SO, Standards. Sulfur
a maximum of 1.2 lb/10
(alone or in combination with
dioxide emissions are limited to
Btu heat input. In addition, a
percentage reduction in SO2 emissions (based on the
sulfur content and heating value of the fuel) must be
achieved. Figure 2.1-j
P£
depicts the allowable SO.
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 SO2 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 la 30-day rolling average and is
determined with continuous emission monitors.
Particulate Standards.
limited to 0.03 lb/106
Particulate emissions are
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.
° NO Standards. Nitrogbn oxide emissions are limited to
O.BO lb/10b 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-dky rolling average.
2.1.1.3 State Implementation PJLans. State and local standards
for SO2, particulates, and NO , kimed at achieving and maintain-
x1
ing national ambient air quality
gated under the SIP's required under the Clean Air Act. Where
standards (NAAQS), are promul-
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
-------
CO
D
O
CSJ
o
co
co
o -i-
o en
4-
o
(LI
O
o
rs
CO
*
00
O-
en
s-
OJ
•a
cu
s_
o
o
-a
-------
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 S02 emission
limit below 1.2 lb/106 Btu heat input for designated areas within
the state (if not statewide). Differences may also be encoun-
tered in particulate and NO 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
as Class I, II, or III, with each class representing a specific
amount or increment of allowable
below the NAAQS) are classified
deterioration. Class I incre-
ments permit only minor air quality deterioration, Class II
increments permit moderate deterioration consistent with normal
growth, and Class III increments permit considerably more deteri-
oration. 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 -hat each major new or modified
source apply Best Available Control Technology (BACT). Best
Available Control Technology is determined on a case-by-case ba-
sis for each pollutant; it must represent an emission limitation
based on the maximum achievable degree of reduction, taking into
account energy, environmental, a
id economic impacts. At a mini-
mum, BACT must result in emissions not exceeding any applicable
NSPS or National Emission Standards for Hazardous Air Pollutants
(NESHAP). The PSD regulations a
for Class I or "pristine" areas
values", such as visibility.
Lso provide further protection
Ln terms of "air quality related
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
_
11
-------
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 power plant 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. However, it is
temporarily excluded from Subtitle C classification as a hazard-
ous 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 con-
cerns the more general problems of waste disposal. Such a status
is currently 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
The properties of the coal fired in a utility boiler deter-
mine the flue gas characteristics, as well as the degree of SC>2
controls needed for the FGD system. Typical fuel properties of
four widely used types of coal from prominent coal reserves in
the United States are listed in Table 2.2-1.
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
12
-------
The sulfur content and heating value of the coal establish
the amount of SO2 produced during combustion as shown in Figure
2.1-1. The amount of SO2 producid is typically the most impor-
tant factor in determining the type and overall design considera-
tion for the FGD system. Other toal properties which can affect
FGD system design/operation include chlorine and ash content.
The chlorine content of the coal
struction and the ability of an FGD system to operate in a closed
water loop. Chlorine content is
about 0.01 weight percent to mor<
affects the materials of con-
highly variable, ranging from
: than 0.6 percent. Ash content
of coal ranges from less than 3.4 to more than 15 percent. If
large quantities of ash are collected in the FGD system (i.e.,
they are not removed by upstream
ment), erosion and plugging of absorber internals and piping may
occur. In addition, the extra ncnreactive 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 S02 reagent requirements. Ths 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 SO9 absorption.
2.3
particulate .collection equip-
BASIC PRINCIPLES OF LIME/LIMESTONE SLURRY PROCESSES
This section provides a brie:: discussion of the basic prin-
ciples of lime/limestone slurry process chemistry. Principal
chemical reactions are identified
associated with process chemistry
and the operational factors
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
tions) .
(FGD System Design Configura-
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
13
-------
s
r-. co •-; •*
,-t f> ,O O O O
C«:«e«:«t«<:i«-a-a
IZZZZZIZ—IZ
OO
o
o
CSJ t-1 IO
SuJrH^O^
r-,»r r-> «3
i
-------
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 at present considered by
the utility industry to be the 3
among all of the commercially a\
east expensive to own and operate
ailable 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 ScL is removed. The chemical reac-
tion of lime/limestone with SO?
solids, which must be removed cc
These waste solids are concentre
dewatered in a vacuum filter to
from the flue gas produces waste
ntinuously from the slurry loop.
ted in a thickener and then
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 SO? absorption, lime-
stone dissolution, and lime dissolution.
Limestone
CaC03(s) + CaC03(aq)
CaCO,(aq) + Ca++(aq) + C03~(aq)
C03"(aq) + H+(aq) •»• HC03"(aq)
S03=(aq) + H+(aq) -» HS03"(aq)
Ca++(aq) + S03=(aq) + if
Ca++(aq) + S04'(aq) + 2t
CaS04-2HgO(s) HS03"(aq) + J02(aq
* g • gas phase; aq - aqueous phase; and s = solid phase
Absorption *
S02(g) * M2(aq)
S02(aq) + H20 * H2S03(aq)
H2S03(aq) + HSO "(aq) + H^faq
HS03'(aq) - U, (aq) + H+(aq)
S03~(aq) + i02(aq) *_S04-(aq)
Lime
CaO(s) + H20 * Ca(OH)2(aq)
Ca(OH)2(aq) -> Ca+t(aq) + 20H"(aq)
OH'(aq) + H+(aq) -«• H£0
S03=(aq) + H+(aq) + HS03"(aq)
Ca++(aq) + S0,=(aq)
4.-I-. J= _
S04= (aq) + H+(aq) Ca++(aq) + S04"(aq)
CaS04'2H20(s)
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
15
-------
CLEAN
FLUE GAS
FLUE 6AS
LIME/
LIMESTONE
SLURRY
TO DISPOSAL
VACUUM
FILTER
THICKENER
OVERFLOW
TANK
Figure 2.3-1. Basic lime/limestone FGD process flow diagram.
16
-------
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 fact
1
rs one should be acquainted with
when inspecting lime/lime stone silurry. 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
guidelines to be used during an
2.3.2.1 Stoichiometric Ratio.
defined as the ratio of the actu!
addition to providing a set of
inspection.
The Stoichiometric ratio (SR) is
al amount of SO0 reagent, calcium
oxide (CaO), or calcium carbonate (CaCO_) in the lime or lime-
stone feed to the absorber, to the theoretical amount required to
neutralize the SO2 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 because of mass transfer limitations which prevent com-
plete reaction of the absorbent.
If a high SO2 removal efficiency is required, the absorber
may" not be able to achieve such
is provided by feeding excess re
removal unless extra alkalinity
agent. The amount of excess
reagent required depends upon the SO2 concentration in the inlet
gas, gas flow, percent SO., removal required, and absorber design.
^
For lime reagent, the SR employed in commercial FGD systems is
1.05 for newer designs; however,
designs. For limestone reagent,
designs; however, it may be as high as 1.4 in older designs.
it ranges up to 1.2 for older
a SR of 1.1 is used in newer
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
17
-------
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
: *J
upper part of the absorber for lime systems, and calcium sulfite
(CaSOg'Jg H2°^ ' SOItietimes referred1 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 SOy, and form a hard calcium
sulfate (CaSO4«2H20) 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
are typically 30 to 50 gal/1000 ft3 for lime systems2 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 SO2 removal;
this also tends to reduce the potential for scaling since the
spent slurry from the absorber is more dilute with respect to
absorbed SO,,. Increasing the L/G ratio can also increase system
capital and operating costs because of greater capacity require-
ments of the reaction tank and associated hold tanks, dewatering
SECTION 2-L1ME/LIMESTONE FGD TECHNOLOGY
18
-------
equipment, 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.
SO
In both FGD processes, as the SO9 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
1
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
Slurry pH is controlled by adjusting the feed stoichio-
Operation of lime/limestone FGD systems at low pH levels,
value.
metry.
approaching 4.5, will improve reagent utilization but will also
lower SO? removal efficiency and
scale (gypsum) formation because
pH levels (see Section 2.3.2.5).
systems at high pH levels, above
tend to improve SO- removal effi
to maintain sensitive control of
lowered SO2 removal efficiencies
2.3.2.4 Relative Saturation.
the term "relative saturation" (RS) pertains to the degree of
saturation (or approach to the s
also increase the danger of hard
of increased oxidation at lower
Operation of lime/limestone FGD
8.5 and 6.0 respectively, will
ciency but also increases the
danger of soft scale (calcium sulfite) formation. Hence, control
of slurry pH is essential to reliable operation. The inability
the slurry pH can lead to both
and hard/soft scale formation.
In lime/limestone FGD processes,
ilubility 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
product constant. The solution
concentrations) to the solubility
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
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
19
-------
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).
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 (0~), 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 f;rom 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 SO., 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.
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
20
-------
Magnesium oxide additives permit a higher SO, removal rate
per unit volume of slurry. This| is because 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 i
i turn increases the available
I
Dibasic acids enhance SO- removal in a different
alkalinity of the scrubbing liquor, which promotes a higher SO
removal rate.
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 lime-
£
stone systems, because of their added ability to enhance utiliza-
tion by improving dissolution, a
lower stoichiometric ratio can
be used which reduces limestone addition and .the resulting volume
of solid waste. In addition, high liquid phase calcium concentra-
tions permitted by the dibasic acids leads to a reduced potential
for scaling tendencies in the absorber.
2.4 FGD SYSTEM DESIGN CONFIGURATIONS
This section presents a briof 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
2.4.1.1
Development of Technology
i.
Historical Perspective
The rapid expansion in energy
demand that occurred starting aboulb 1950 greatly increased the
amount of all air pollutants resulting from fuel combustion —
particulates, SO», NO , carbon monoxide, organic compounds, and
" ** -|
trace metals. Because of environmental concern over the increas-
ing concentration of pollutants xn the atmosphere in the U.S.,
the Air Quality Act of 1967 becarie law. Its aim was to set
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
21
-------
emission limitations on those pollutants for which adequate
information was believed to be available, i.e., particulates,
SO,
and NO . Eventually new regulations came about in the form
x
of the Federal NSPS and state regulations under the individual
SIP's. As a result, in the early 1970's, important applications
of FGD for SOp control were initiated in the U.S.
The 1950's and 1960's were a time of laboratory and pilot
plant investigations of new processes. During the 1950"s, 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
i
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
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
22
-------
72 73 74 75 76 ll 78 79 80 81 82 83 84
YEAR
Figure 2.4-1. Growt
\ of operational FGD
capacity for utilities.
-------
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
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 S02 and particulates from flue gases generated in
coal-fired boilers. This test program was managed and directed
by EPA's Industrial Environmental Research Laboratoryt/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 SO2 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
"* ~" :
National Air Pollution Control Association until 1970.
Designated^ Control Systems Laboratory until 1975; redesig-
1985 ^ Alr and Energy Engineering Research Laboratory in "
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
24
-------
costs.
This was accomplished through investigations on chemical
additives (see Section 2.3.2.6),
forced oxidation (see Section 2.
A third phase of testing, v
years, from July 1978 to May 19f
removal and improving the reliat
system loop configurations, and
3.2.5).
rhich lasted approximately two
0, was devoted to enhancing SO~
ility and economics of lime/
limestone slurry processes through the use of organic acid
additives (see Section 2.3.2.6).
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
from the level of a research arid
lime/limestone slurry technology
development "tool" to a level of
of the results from the various
commercial acceptability. Many
test programs initiated or re-
fined commercial design strategies, a large number of which are
in commercial practice today:
High utilization/low stoichiometric limestone chemistry
and mist eliminator clteanliness
0 Spray tower absorber djssign
0 Two-loop scrubbing
0 Magnesium additives
0 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:
that remove SO2, and possibly
with gas contactors developed
Designs
for or ipased upon particulate matter
scrubbing concepts. Included are
lime/linestone slurry processes which
use gas
packing-type internals.
contactors with venturi or
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
25
-------
Second generation:
Third generation:
Designs that remove SO2 primarily in gas
contactors developed specifically for
SO2 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.
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 S02 control. In such
systems, particulates and SO2 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.
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
26
-------
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Second generation FGD systems were designed specifically for
SO7 control leaving all or most.particulate control to upstream
ESP's. The SO0 absorbers usually contained gas contacting de-
vices to maximize SO2 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.
Third generation systems are characterized by open spray
towers operating at relatively low stoichiometric ratio chemis-
tries with additives for SO2 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 op-
eration of the system even when individual components are forced
out of service or are undergoing routine maintenance. Third gen-
eration designs provide secondary dewatering- (vacuum filters or
centrifuges), solid waste treatment via chemical fixation or
forced oxidation, and landfill disposal. An integrated plant
- A
water inventory is generally included in these closed loop sys-
tems, 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
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY "
28
-------
each of the equipment items disc-
considerations for the equipment
later in Section 2.5.
issed. Operation and maintenance
described here are presented
The equipment is organized by three major equipment areas:
0 Gas handling and treatment
1. Fans j
2. Scrubbers/absorbers
3. Mist eliminators j
4. Reheaters
5. Ductwork and dampers
Reagent preparation anc
Reagent conveyors
1.
2.
3.
4.
Ball mills
Slakers
Tanks
Waste solids handling and disposal
1. Thickeners
2. Vacuum filters
3. Centrifuges
4. Waste processing
5. Waste disposal
6. Pumps and valves
I
It is noted that there is sone overlap of the equipment
items in all three areas, althoug
one equipment area in the above c
reaction tanks are located in the
feed
and storage
i they may be listed only under
Lassification. For example,
gas handling and treatment
area; pumps and valves are found in all three equipment areas.
Sections 2.4.2.1 through 2.412.5 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
in reagent preparation and feed, including: reagent conveyors
and storage, ball mills, slakers,
2.4.2.9 address equipment used
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, wast^ processing, waste disposal
and pumps and valves, respectively.
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
29
-------
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.1
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
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.
0 Fans used for FGD systems are either centrifugal or
axial (Figure 2.4-2a and b). Most fans used in FGD
systems are of 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.
0 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 (nega-
tive pressure operation). Fans that precede a module
or system (upstream) that push gas through the module
or system are called FD fans (positive pressure opera-
tion) .
0 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.
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
,30
-------
TURNING BEND
WITH GUIDE VANES
Figure 2.4-2. Typical fan designs: (a) centrifugal; (b) axial
31
-------
2.4.2.2 Scrubbers/Absorbers. Strictly speaking, the term
"scrubber" applies to first generation systems which remove both
particulate and SO2. "Absorber" applies to the second and third
generation systems which remove SO2 only, although the term
"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
venturi, the venturi throat opening remains constant (Figure
2.4-3a). However, a number of variable-throat designs are used
to control the opening of the venturi throat 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. H2O 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. H2O)
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.
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
32
-------
FIXED THROAT
OPENING
00.
GAS
SCRUBBING I—1
LIQUOR < >
FEED, V
SUMP
(c)
MOVABLE LIQUID /
DISTRIBUTION DISC'
SCRUBBING ~]
LIQUOR -"-C,
FEED
SIDE-mVABLE
PLATES OR BLADES
Cd)
(f)
GAS
o
(g)
(h)
Figure 2.4-3. Venturi tower configurations: (a) fixed-throat; (b) variable-
throat top-entry plumb bob; (c) variable-throat bottom-entry plumb bob;
(d) variable-throat bottom-entry li
throat side-variable plates or blades;
quid distribution disc; (e) variable-
(f) variable-throat side-movable blocks;
(g) variable-throat vertically-adjusted .rod decks; (h) variable-throat
adjustable-drum.
33
-------
A A A
A A
MIST
ELIMINATOR
SCRUBBING
LIQUOR
FEED
GAS
(a)
SCRUBBING
LIQUOR
FEED
t I \
mr
MIST
ELIMINATOR
Figure 2.4-4.
(b)
Spray tower types: (a) open countercurrent;
(b) open crosscurrent.
34
-------
Slurry is introduced onto the top tray and flows across it and
down across each preceding tray
valve tray tower, the tray level
caps" with each bubble cap surmo
(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/slur:ry contact (Figure 2.4-5). In a
t
consists of a bed of "bubble
nted 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
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
mobile bed of solid spheres whic
bed packing consists of a highly
i 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 2.4J-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
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
35
-------
/•'":
UJ
et «=C
O —1
U_ 0.
OJ
ex
ta
S-
cu
to
co z
h-1 I—I I
*s 1
rd I
OQ C3 Q
OQ.=3 UJ
^3 O-UJ
a: i—i u_
o _J
co
CO
-------
MIST
A A A
SCRUBBING
SLURRY
PACKING
ZONE
A, DIRTY GAS
IV INLET
i a
OVERFLOW
JL A
STATIC BED
(b)
FEED
HEADERS
SCRUBBING
SOLUTION
CONTACT
SPHERES
GAS IN
ENTRAINED BED
(d)
Figure 2.4-6. Packed
"HONEYCOMB"
FIXED BED
(a)
OOoOOOOOOOOO
ooo 0000060
o o ooooo o
"-
SOLID
SPHERES
MOBILE BED
(c)
RODS
(e)
GRIDS
(f)
bower and packing types,
37
-------
areas of the tower, thus permitting separate chemical and physi-
cal conditions to be maintained. Designs which have been devel-
oped 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
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. H2O) , 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
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY ~~ ~~ —
38
-------
flow direction as it passes through the slats. The liquid drop-
lets thus collected coalesce and
scrubbing slurry. Impingement t}
in lime/limestone slurry systems
Baffle-type mist eliminators include the conventional open-vane
(slat) and closed-vane chevron d<
fall by gravity back into the
pe mist eliminators used widely
include baffle configurations.
signs (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 daise 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
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 gas stream downstream of the
The heat exchanger is a set of t
t
the use of- a heat exchanger in
mist eliminator (Figure 2.4-8a).
be 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 psia, respectively. Saturated steam
is preferred because the heat transfer coefficients of condensing
steam are much higher than those
water is used, inlet temperature
of superheated steam. When hot
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 a::e two types of indirect hot air
reheaters: the external heat exchanger and the boiler preheater
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
39
-------
CD
i—i
00
LU
O
00 H-
I
Q.
o
O)
S-
OO
OO
40
-------
TO CH1HHEV
(a)
(b)
Figure 2.4-8.
(c)
FGD system reheat schematic diagrams: (a) in-line-
(b) indirect hot air; (c) bypass. '
-------
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 conse-
quence, the temperature of the combustion air entering the boiler
is lowered, thus somewhat reducing boiler efficiency.
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
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) spe-
cifically 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 sup-
ported by angle frames that are stiffened at uniform intervals.
The following design factors are ^considered for ductwork in
lime/limestone slurry systems: '
0 Pressure and temperature
0 Velocity
0 Configuration (cylindrical or rectangular)
0 Flow distribution
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
42
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Variations in operating conditions
Materials of construction
Material thicknesses
Pressure drop
The ductwork must be designed to
temperatures that occur during n<
that occur during emergency cond:
variety of conditions, depending
withstand the pressures and
irmal operation and also those
tions. Ductwork is subject to a
on location within the system.
The following list identifies thd basic variants:
0 Inlet ductwork
0 Bypass ductwork (all 01 part of the flue gas)
0 Outlet ductwork (with Jeheat and without bypass)
0 Outlet ductwork (with reheat and with bypass for
startup)
0 Outlet ductwork (without reheat and without bypass)
0 Outlet ductwork (withoujt reheat and with bypass
for startup)
Dampers are used to regulate
the flow of gas through the
system by control or isolation functions. The 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.
ally or in combinations. A simplified overview diagram showing
typical damper locations is prese
A variety of damper designs
slurry systems, including louver,
blanking plates. These designs are described below and depicted
in Figure 2.4-10.
Louver or multi-blade d
Dampers may be used individu-
ited in Figure 2.4-9.
are in use in lime/limestone
guillotine, butterfly, and
impers may be of either opposed
or parallel blade desighs (Figures 2.4-10a). Louver
dampers are used to regjilate and isolate flue gas flow.
For isolation, two dampers are used together and sealed
by pressurizing the chaijnber formed by the ductwork
between the dampers with a seal air fan. A single
damper may be used for gas flow regulation.
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
43
-------
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0 A guillotine damper may be of 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. i
0 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.
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. Lime-
stone is transported to feed bins by conveyors and bucket eleva-
tors. 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
from 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
availability of the overall FGD system. There should be enough
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
46
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storage capacity to account for
ping schedule. Figure 2.4-11 shjows an example of a limestone
handling and storage system.
Conveying equipment used td transport lime can be of three
basic types, as shown in Figure
conveying involves simple elevation of the lime from a storage
bin into a smaller feed bin. A
and with less power consumption
Mechanical conveying requires careful arrangement of bins and
equipment. Alignment in a singl
since each change of direction
disruptions in the normal ship-
2.4-12. Most in-plant lime
simple combination of mechanical
devices can move lime from storage at less than the initial cost
than a pneumatic conveyor.
e straight row is preferable
sually 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
rapidly. Unlike the basic components of a mechanical conveyor,
those of a pneumatic system are
elevation. They differ only in
of pnuematic conveying increases
similar regardless of distance or
length of piping and size of the
compressor and motor. Lime is blown up the' inclined pipe by the
force of air from the compressor
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,
system, uses air circulated froir
and back. A minimum amount of fjresh 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
The other basic conveyor type
usually called a closed-loop
the compressor to the conveyor
capacity for 7 days of operation
at maximum rate. Conservative
engineering practice,jgrovides twice this volume, since lime is
often transported on a less-dependable schedule than are other
more expensive bulk chemicals.
used for lime is a steel silo with a cone bottom. Concrete
storage bins have been used in large facilities and are often
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
47
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STORAGE BINS
ROTARY
FEEDER'
OX
; BUCKET
ELEVATOR
SCREW CONVEYOR
SLURRY STABILIZATION
TANK
VENT
DUST COLLECTOR
AND
COLLECTING BIN
ROTARY
FEEDER
CONVEYOR
ADAPTER
SLURRY STABILIZATION
TANK
DUST COLLECTOR AND
COLLECTING BIN
Figure 2.4-12. Three types
transport lime: (a) mechar
conveyor; (c) positive-
of conveying equipment used to
ical conveyor; (fa) closed-loop
pressure pneumatic conveyor.
9
-------
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
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
1
from 70 percent passing through a 200-mesh screen to 95 percent
passing through a 325-mesh 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 va-
riety is a compartmented type (Figure 2.4-13a), and the Hardinge
ball mill is noncompartmented and somewhat conical in shape
(Figure 2.4-13b).
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY ~~ ~~ ~~
50
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a)
Figure 2.4-13. Two types of ball mills used in limestone slurrv
FGD systems: (a) compartmented
mill; (b) Hardinge ball mill
-------
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 combines regulated streams of lime,
water under agitation, and temperature conditions needed to dis-
perse soft hydrated particles. Dispersion must be rapid enough
to prevent localized overheating and rapid crystal growth of the
calcium hydroxide from 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.
0 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
section by means of a mechanical scraper. This 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.
0 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.
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
52
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AGITATOR DRIVE
FEED INLET (LIQUID)
LIME INLET
SLAKING
AGITATOR COMPARTMENT
(a) Detention slaker
TORQUE-CPJITRPU.EO HATER VALVE
OUST SHIELD-,
WATER SPRAYv I /
quiCKiif*
I
1 SLAWS HATER ' \ ^ ~
lfJ/ pr--PADDLES IT**
™^fottitfa
AQ;P/^a.%Cl
DISCHARGE PO IT'
CLASSIFIER
GRIT OISCHftRKE
HATER FOR GRIT HASHING
GRIT ELEVATOR
(b) Pas-;e slaker
I DRY REAGENT
KATER
FRESH REAGENT
SOLUTION
JO PROCESS
(c) Batch slaker
Figure 2.4-14. Basic types of slakers.
53
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0 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 riot 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, 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
Tanks may or may not be covered. Covered tanks are pro-
tected 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 (preventing 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.
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY ~ ~~
54
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2.4.2.10 Thickeners.
a clarifier) is to concentrate s
in order to improve waste solids
The function of a thickener (also known as
ill
'lids in the slurry bleed stream
handling and disposal character-
A typical gravity thickener
large circular holding tank with
istics and recover clarified water. The slurry bleed stream
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.
A thickener is a sedimentation device that concentrates the
slurry by gravity. There are two basic types of thickeners:
gravity and plate. Only the graiity type will be described here
because plate thickeners are rarely used on utility FGD systems.
(Figure 2.4-15) consists of a
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 she.ft; two short arms may be added
area. Plow blades are mounted
•ith a clearance of 1.5 to 3 in.
y can be arranged identically on
so that the bottom is swept
revolution. The bottom of the
8-degree slope from the center„
t on the bottom of the thickener
the central discharge outlet.
ge trench and move the solid
deposits toward the underflow discharge point. The rake arms and
pickets move the settled solids to the central discharge point.
The reclaimed overflow (i.e., clarified water) from the thickener
is usually recycled and reused as i
2.4.2.11 Vacuum Filters. Vacuuir
secondary dewatering devices because they can be operated suc-
cessfully at relatively high turndown ratios over a broad range
of solids concentrations. A vacuum filter also provides more
when necessary to rake the inner
on the arms at an oblique angle
from the bottom of the tank. The
each arm or in an offset pattern
either once or twice during each
tank is usually graded at a 5- tc
The settled sludge forms a blanke
tank and is pushed gently toward
Center scrapers clear the discha:
operating flexibility than other
makeup water.
filters are widely used as
types of dewatering devices
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
55
-------
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56
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as well as producing a drier product. Because a vacuum filter
will not yield an acceptable fii.ter 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 75 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
system designs: drum and horizontal belt. Each has-different
characteristics and applicability. The drum type (Figure 2.4-16)
is the most widely applied. In
slurry is fed to a tank in whict
a rotary-drum vacuum filter, the
. 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 jthe 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 nee
ligible when the air is at room
is removed in the discharge zone
temperature. Finally, the cake
by a scraper.
2.4.2.12 Centrifuges. Centrifdges are used to a lesser extent
than vacuum filters in solids ddwatering operations. The centri-
fuge product is consistent and uniform and can be easily handled.
Centrifuges effectively create high centrifugal forces, about
4000 times 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 filter. The settling centrifuge (Figure 2.4-17),
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
of a settling centrifuge are the
settling. The principal elements
rotating bowl, which is the
settling vessel, and the conveyor, which discharges the settled
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
-------
AIR FILTRATE LINE
CLOTH CAULKING
STRIPS
AUTOMATIC VALVE
DRUM
FILTRATE PIPING
CAKE SCRAPER
SLURRY AGITATOR
VAT
AIR BLOW-BACK LINE
SLURRY FEED
Figure 2.4-16. A rotary-drum vacuum filter.
58
-------
-------
solids. The solid bowl is the only centrifuge design used com-
mercially 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 continuously 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 physically
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: :
o Forced oxidation. Forced oxidation supplements the
natural oxidation of sulfite to sulfate by forcing axr
through the material. The advantages of a calcium
sulfate (gypsum)-bearing material include better set-
tling and filtering properties, less disposal space
required, improved structural properties of the dis-
posed 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.
0 Fixation. Fixation increases the 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
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
60
-------
chemically stable solid. Examples of commercial proc-
esses of this type are those marketed by Conversion
Systems, Inc. (e.g. , Pozj-O-Tec) and Dravo Corporation
(e.g., Calcilox).
Stabilization. Stabili:
ation 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
• •--• ----••' -"".ual leachability potential.
.isposal refers to operations at
'llowing all handling and/or
; basic FGD waste disposal site
stacking. The most common
igure 2.4-18 shows examples of
saturation and has resic
2.4.2.14 Waste Disposal. Waste c
the disposal site for FGD waste f<
treatment stages. There are thre<
types: ponding, landfilling, and
waste disposal type is ponding.
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) landfilled. Stacking
designed to produce gypsum. Presently, only two planned lime-
stone FGD systems are considering
is only used for FGD systems
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
othe_r areas of the FGD system, such as slurry transfer, slurry
bleed, and slurry recirculation.
two generic groups: displacement
Pumps may be classified into
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
slurry FGD systems. Screw pumps Differ from rotary pumps in that
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
61
-------
(a)
(b)
(c)
(d)
Figure 2.4-18. Examples of pond types for waste disposal
(a) diked; (b) incised; (c) side hill; (d) cross valley.
62
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the flow through the pump is axi
like the rotary; they are often
instead of circumferential
ased in utility FGD systems for
transferring reagent feed as they can easily handle a concen-
trated (30 to 40 percent) slurry
The only nondisplacement pu:
FGD systems is the centrifugal p
widely used for water and slurry
water slurry recirculation, fres
fier overflow/underflow, and mis
of lime or limestone.
up used in lime/limestone slurry
ump. Centrifugal pumps are
handling. These include makeup
i slurry feed, thickener/clari-
t eliminator wash water. Of
these, the recirculation pumps are the largest with capacities
ranging from 5,000 to 20,000 gpm.
Valves are used throughout
late the flow of fluids but also
the FGD system not only to regu-
to isolate piping or equipment
for maintenance/repair without interrupting other connected sys-
tems. This helps to provide for
As of the beginning of 1985
limestone slurry FGD systems in
these systems is shown in Tables
indication of the major subsyst
Section 2.4.2.
2.5 FGD O&M CONSIDERATIONS
This section provides a bri
continuous operation and minimal
downtime. The generic classifications of valves are ball, but-
terfly, check, gate, globe, pinch, and plug valves. Among these,
the check and globe values are generally not recommended for
waste and slurry service.
2.4.3 Operational Utility Lime and Limestone Slurry FGD Systems
there were 91 operational lime/
the United States. ,A listing of
2.4-3a and b along with an
and components described in
ems
ef introduction into the O&M
practices associated with lime/limestone slurry:FGD processes as
they relate to system reliability, identification of failure •
modes, system layout and accessibility, and required operating
and maintenance procedures. The purpose of this section is to
introduce and define terminology
that is used extensively in a
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
63
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more thorough treatment of these topics in Section 4, Inspection
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 of design configurations used in lime/limestone
slurry FGD systems now in commercial service. Technically, each
PGD system represents a unique application 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 which sup-
plies the equipment, the architect-engineer (A-E) who designs the
system, and the owner/operator utility which 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
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
72
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•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 equipmer
Power Generation Demand
Base load
Intermediate load
Cycling load
Peak load
Site Conditions
Land availability
Soil permeability
Disposal facility
Climatic and geographic effiects
Quality and availability of
Environmental Regulations
Air
1971 NSPS
1979 NSPS
SIP
PSD
Water
1977 CWA
Solid Waste
RCRA
reagent and makeup water
73
-------
performance (see Section 2. 4.1. 2,; Characteristics of Technology
Generation).
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)r 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
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
-------
H. GAS HANDLING/
TREATMENT
PARTICULATE
REMOVAL
1
GAS
TRANSPORT
|^
COOLING
li
so2
ABSORPTION
||
REHEAT
IJ,
GAS
DISPERSION
•M
B. REAGENT PREPARATION/FEED
BULK
REAGENT
HANDLING
REA
PRE
^
f I
*— TwASHJ
-------
TABLE 2.5-2. SUMMARY LISTING OF THE FQD SUBSYSTEMS BY
MAJOR EQUIPMENT AREA
Gas
handlIng/treatment
Reagent
preparation/feed
Waste solids
handling/disposal
Fans
Scrubber
Absorber
Mist Eliminator
Reheater
Ductwork and Dampers
Stack
Reagent Receiving
Ball Mills and Slakers
Tanks
Thickeners
Vacuum Filters
Centrifuges
Waste Processing
Waste Disposal
Pumps, Pipes., and Valves
76
-------
only at a plant equipped with two
boilers which' share subsystem (s)
lent examples are common reagent :
dewatering and treatment, and due
have no effect on power productio:
may cause a total shutdown of the
of a failure, in addition to bein
the system or subsystem to the re
or more separate FGD-equipped
affected by the outage. Preva-
handling and preparation, solids
twork and stack. A failure may
i, may cause reduced load, or
generating unit(s). The effects
a function of the relation of
st.of the plant, are also a
function of the restrictions unde:r 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 ::ailure. This can be considered
a measure of unreliability. For ~:he purposes of this manual, the
results of a recently completed s-:udy in which PEI Associates,
Inc. (PEI) participated in the analysis of failure modes associ-
ated with lime/limestone slurry FGD systems were used.6 In this
study, unreliability was quantified in terms of outage times as
defined by "module equivalent hours" in order to combine the
impacts of failures into a common
equivalent hours (MEH) is defined
basis for comparison. Module
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 ° Fans
0 Ductwork ° Pipes and valves
0 Absorber ° Thickener
0 Stack ° Dampers
Key failure modes were identi fied for key subsystems for
which major contributions to unreliability occur at the system
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
77
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TABLE 2.5-3. SUBSYSTEM OUTAGE TIMES IN MODULE EQUIVALENT HOURS (MEH)
Subsystem
Mist Eliminator
Ductwork
Absorber
Stack
Fans
Pipes and Valves
Thickener
Dampers
Reagent Preparation
Pumps
Tanks
Expansion Joints
Scrubber
Parti cul ate Matter Control
Reheater
Spray Nozzles
Reagent Receiving
Water System
Instrumentation
Waste Treatment
Disposal Site
Module
downtime/
year.
22,832
739
13,664
0
8,229
3,176
20
640
4,032
7,655
3,096
676
6,764
3,171
192
4,198
0
0
36
10
0
System
component
of
subsystem
MEH,
MEH/year
572
15,392
3,514
12,568
4,288
1,474
4,168
7,929
440
168
4,496
7,024
340
1,308
5,376
60
0
0
0
0
0
Plant
component
of
subsystem
MEH,
MEH/year
0
5,092
0
4,464
1,264
8,466
7,232
640
4,288
0
180
64
0
1,632
0
0
1,728
240
0
0
Total
Subsystem
MEH/year
23,404
21,223
21,178
17,032
13,781
13,116
11,420
9,209
8,760
7,823
7,772
7,764
7,104
6,111
5,568
4,258
1,728
240
oc
OD
10
0
*0ne hour of module downtime is equivalent to one MEH.
'The total subsystem MEH/Year is the sum of the module, system and plant
(station) MEHrs. 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.
78
-------
and plant levels. For a genera
three boilers equipped with PGD
ing station (power plant) having
systems each having two modules,
one hour of module downtime is one MEH. One hour of system or
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 resulting from failures of a
given subsystem. This is calculated by adding the MEH due to
module, system, and plant downtimes.
Ductwork, stacks, pipes and
subsystems with a high percentag
the system and plant levels. Th
valves, and thickeners are key
e of subsystem MEH manifested at
e most troub'lesome failure modes
for the key subsystems are highlighted below:
0 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 (SO0 and
S03) .
x
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
S0_ .
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. |
0 Fiber reinforced plastpLc (FRP) pipe failures appear to
cause more effective dawntime (MEH) than other pipe and
valve failures.
Stack lining acid attack an3 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 system
individual modules are available
The MEH for these low frequency
3) out of service, whether or not
, usually for extended periods. >
failures are, prohibitive. The
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
79
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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
occurrence, reported failure modes were correlated with associated
system design and operating characteristics. The system design
and operating characteristics investigated were as follows:
0 Coal ;
0 Boiler
0 Application
0 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 high sulfur content and unreliability, and between
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
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
80'
-------
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 yeai: increments, are for the most
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 ind:.cation 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
size per absorber module (MW/modu:.e) , were examined. System size
was broken into two groups: less
system size (MW/unit), and the
or greater than 450 MW/unit.
The smaller units exhibited less c.owntime than the larger units.
The size of the unit appears to b^ a much more significant para-
meter in terms of FGD system reliability than the size of the
individual modules (MW/module) in
indicate that smaller units do appear more desirable' in terms of
reliability.
the FGD system. The results
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
81
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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 consid-
eration is provided. ;
0 Reagent type - the gas handling and treatment subsys-
tems of absorber, ductwork, and stack show a strong
correlation between lime systems and unreliability.
This is probably because lime FGD systems are predomi-
nantly used for higher sulfur coal applications. Lime-
stone shows a high correlation with unreliability in
the slurry circuit (limestone slurry is more abrasive
than lime slurry).
0 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".)
0 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.
0 Absorber parameters - results indicated that towers
with internals (packed, tray) have a high correlation
with unreliability. The type of absorber exhibiting
the highest unreliability is the packed tower. Spray
tower absorbers exhibited the highest reliability.
However, mist eliminators showed a high correlation of
unreliability with spray tower absorbers. This is to
be expected when considering the open structure of a
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
82
-------
L
spray tower, the high i/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 "prescrubibers". Prescrubbers include
upstream scrubbers, presaturators, and quench towers.
A number of systems are equipped with one of these
devices to remove particulates, effect initial SO2
absorption and/or condition the gas stream prior to the
absorber. Systems with no prescrubbers appear to be
more reliable than systems with prescrubbers. This is
an expected result becduse systems with prescrubbers
have an additional subsystem that may fail. However,
the presence of a preso.rubber shows a high correlation
with reliability for SO2 absorbers in contrast to their
effect on the total sys|tem. A possible explanation is
that the combination o:
ride, particulate, and
in a prescrubber serves
from failures.
Reheat - the order of
of reheat is no reheat,
and indirect reheat.
flue gas quenching and chlo-
initial S02 removal that occurs
to protect the SO, absorber
decreasing reliability for type
bypass reheat, in-line reheat,
Reagent_preparation - reagent preparation in a ball
mill (limestone) is associated with considerably higher
.downtime for slurry circuit equipment (e.g., pipes,
valves) than is 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 oh reheated gas) from the
FGD system.
A summary of the results of
FGD characteristics discussed in
Table 2.5-4.
the failure mode analysis by the
bhe foregoing is provided in
2.5.2 System Layout, Accessibility, and Design
An essential feature of any
treatment of O&M practices is
consideration of FGD system layoui:, accessibility, and design.
Layout and accessibility are face bs of FGD design and operation
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
-------
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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
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 suppor-ive 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.
dynamic components are fans and
For this equipment area, the
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 as follows:
0 Placement of the fan at grade level, a practice which
is widely accepted because of sheer size and weight of
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
85
-------
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.
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 jleakage 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
necessities are equally demanding because of the cascading effect
their malfunction can have on downstream operations. The in-
ability to properly control and isolate the flue gas stream can
either severely minimize or totally eliminate operating, mainten-
ance, and repair functions, or compromise worker safety necessi-
ties. Layout considerations that enhance accessibility are site
and design specific; however, there are some significant overall
design considerations:
0 The ductwork design should be able to accommodate the
insertion of simple isolation blanking plates to
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY ' ~~
86
-------
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 tojoperate, 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.
0 Damper performance is a direct function of ductwork
location. A straight-run location is preferable to an
elbow or bend because of gas channelling and uneven gas
distribution; the longef 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
associated with the latter. Accordingly, the layout, accessibil-
ity, and design considerations ar<
potentially higher wear rates
correspondingly less crucial,
as noted in the considerations that follow:
0 Cleanout doors should be| provided at various levels in
the scrubber/absorber tower to:
access the base of I the tower,
access the upper level of the tower, generally
in the spray zone,
-' access the mist eliminator, generally below or
inbetween stages, depending on whether it is a
single- or multiple-stage mist eliminator design,
and
access the reheat dhamber.
Visual ports at various
provided to permit visu<
levels in the tower should be
1 inspection during operation,
especially for the absorber (or scrubber) at the inlet
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
87
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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.
0 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 vertical arrangement predomi-
nates because of spatial and cost factors. The hori-
zontal arrangement permits overall easier access
because of equal accessibility at the same elevation to
all portions of the vessel. It also consumes less
power because of lower gas-side pressure drop and lower
slurry pumping height;
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 as follows:
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, mainte-
nance, and repair.
i
0 Provision to accommodate flush-out and flush water
necessities during shutdown and outages through fresh
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
88
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(or clarified) water
drains.
supply and disposal sumps and
The static components are
service environment as the dynam:
duty requirements are less severe
to move within this environment,
those described for the dynamic
considerations include:
subjected to the same slurry
c components. Although their
in that they are not required
the same restrictions apply as
components. Additional design
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.
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 5
the distinction of dynamic and st.atic components, dynamic com-
ponents include thickeners (clarifiers), filters, centrifuges,
conveyors, and pumps. Static components include tanks and stor-
nd Disposal. Continuing with
age bins. Many of the same consi
preparation and feed also apply Y
peculiar to this area include:
derations described for reagent
ere. Additional considerations
Placement of all secondary solids dewatering equipment
(filters and centrifuges and ancillaries) in a central
dewatering house at the grade level.
Minimization of the pipe run between primary dewatering
(thickener) and the dewatering house, as well as the
dewatering house and disposal area.
Sufficient space to stockpile solid waste during
emergency conditions (thickener outage, filter outage,
pump failure, pipe failure).
Access walkways to
operation.
inspect thickeners and filter
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
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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.
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.1, sulfur, ash, and chlorine
characteristics). Some of the current difficulties with lime/
limestone FGD systems relate to poor operating practices, unnec-
essarily complex operating procedures, or both. In some cases,
although the equipment has been correctly installed, it rapidly
deteriorates and breaks down because of improper O&M practices.
The operating characteristics of the FGD system can be estab-
lished 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.
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
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During periods of changing load or variation of any system param-
eter, 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
i -!_.. -,___-, , with each change in load, the
boiler load is reduced.
operator must check the
service modules are ope
system to verify that all in-
rating in a balanced condition.
As the S02 concentratiojn in the inlet flue .gas changes,
the FGD system should bfe able to accommodate and
compensate for such changes. Operator surveillance of
system performance is needed, however, to verify proper
system response (e.g., jslurry recirculation pumps dan
be added and removed from service as the SO2
tion increases or decreases).
concentra-
Verification of Flow Rates. The easiest method of ver-
ifying liquid flow ratefe is for an operator to deter-
mine the discharge pressure in the slurry recirculation
spray header with a hand-held pressure gauge (perma-
nently mounted pressure)gauges frequently plug in slur-
ry service). Flow in slurry piping can be checked by
touching the pipe. If -;he piping is cold to the touch
at the normal operating
the line may be plugged
Routine Surveillance of
temperature of 125° to 130°F,
Operation. Visual inspection
of the absorbers and reaction tanks can identify scal-
ing, 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 sur-
face resulting from inadequate or deteriorated lining
material.
Mist Eliminators. Many
techniques have been employed
to improve mist collect:.on 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.
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
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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 solids in the thick-
ener 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 character-
istics, 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 oper-
ating staff. In addition to normal operations, the
pond site must be monitored periodically for proper
water level, embankment damage, and security for pro-
tection of the public. Landfill disposal involves the
operation of secondary dewatering equipment. Again,
when any of the process equipment is temporarily re-
moved 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
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY I
92
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are often more reliable
and are often needed to
than automatic control systems
prevent failure of the control
— -— — •— %-v £*.A-'vv>vA.Li* a-(-*._i_jL«-4J_c- W -l_ I—lie ^ wil L..LU.L
system. Many problems.ian 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
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. Cojmpliance 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 nonoberating conditions that
necessitate action .by the operating staff are system standby and
extended outage. Each of these situations is of special interest
to the FGD operating staff.
° 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 start-
ing 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) . Wh£n the system is placed in
service, the operating staff must be available to moni-
tor system response as boiler load is increased. As
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
93
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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.
0 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.
o 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. Ex-
cept 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 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 sol-
ids 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 opera-
tions and station output due to waste slurry buildup. Since
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
94
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waste processing systems usually
station output should only be reduced, at worst.
2.5.3.5 Operating Staff and Training. The size, experience
incorporate some spare capacity,
level, responsibilities, and training of the operating staff are.
significant factors in FGD systein 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
to analyze the process chemistry
2.5.3.6 Preventive Maintenance
laboratory technicians are needed
Programs. Preventive mainte-
nance 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 mainte-
nance is to increase availability of the FGD system by eliminat-
ing the need for emergency repair ("reactive maintenance").
The term preventive maintenance is synonymous with periodic
maintenance. Such procedures majy be as simple as lubrication of
a pump or as complex as complete
Absorbers. Of primary
disassembly for inspection and
overhaul. Some of the more impofrtant preventive maintenance pro-
cedures by subsystems are summarized in the following sections:
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.
Mist Eliminators. Scale deposits typically are the
chief maintenance factbr 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 outages.
Reheaters. Both in-lipe and indirect reheaters are
In addition to
subject to scaling and
corrosion.
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
95
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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 equip-
ment 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 exces-
sive 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 re-
placed. Pipelines also must be periodically disassem-
bled 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, especial-
ly 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.
Waste Disposal Equipment. Secondary dewatering devic-
es , 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.
SECTION 2-LIME/L1MESTONE FGD TECHNOLOGY
96
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Process Instruments and, Controls. All electronic
equipment (pH, flow, prjessure, temperature, level,
vibration, noise, and continuous monitors) must be
Numerous installation and
have proved beneficial in
calibrated periodically
maintenance techniques
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. Roujtine comparison of the instru-
ments in a process strejam with similar instruments in
parallel streams can po'int 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 pre-
ventive 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
operating standards. Each subsystem of the FGD system is subject
to malfunctions from a variety of
follows introduces these problems
the system into compliance with
causes. The discussion that
and the probable responses.
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.
Mist Eliminators. Failure of the mist eliminator is
typically due to scalin
3 and plugging. The scale may
be removed either by thorough washing or by mechanical
methods, in which maintsnance personnel enter the
absorber and manually chip away the scale deposits.
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.
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
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r
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 lime-
stone feeder due to intrusion of moisture. Correction
of these problems will probably necessitate changes in
equipment design.
Pumps, Pipes, and Valves. Excessive wear of the im--_
peller 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 typi-
cally caused by wear-induced misalignment.
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.
SECTION 2-LIME/LIMESTONE FGD TECHNOLOGY
98
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SECTION 3
PERFORMANCE
Performance monitoring is a
MONITORING
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. J Additionally, routine monitoring
can identify potential operating
cantly impact the performance of
problems before they signifi-
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 testirg and continuous emission moni-
toring methods used for emission measurements, and recordkeeping
practices of the operator utility. This information is presentee
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
The key operating parameters
the FGD circuits identified in Se
tions)„ The gas circuit paramete
opacity, O2, gas volume, and pres
parameters of importance are pH,
measurement values associated wit
assessed, give the entire picture
compliance status.
THEIR MEASUREMENT
can be described according to
ction 2.5 (FGD O&M Considera-
rs of importance are SO
NO
,
X
sure. The slurry circuit
solids, and slurry volume. The
these parameters, when
of FGD system performance and
SECTION 3 - PERFORMANCE MONITORING
-------
3.1.1 Gas Circuit Parameters
3.1.1.1 S0?. 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 SO2
continuous emission monitors. They generally take the form of
stack monitors. In many cases, FGD inlet and outlet SO2 monitor;
are provided to continuously measure SO2 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)
continues to provide adequate process control monitoring.
3.1.1.2 NO . A continuous monitor is used in the stack to
.X, !
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
equally spaced data points being used in the average.
22.
An O- monitor is used to convert continuous mon-
3.1.1.4
itoring pollutant (i.e., SO2 and NOx) concentration values to
NSPS units (lb/106 Btu). The 02 basically serves as a diluent
gas. For existing sources, an O2 monitor is required only if
state law requires data for converting to the emissions standard.
The equations used for this conversion are shown in Appendix B.
The O~ monitor must be located at a point where measurements can
be made that are representative of the pollutant gases sampled by
the S09/N0 monitors. The O2 monitor sampling point location
conforms best with this requirement when it is at approximately
the same point in the duct as the SO2/NOx system. The O2 gas
SECTION 3 - PERFORMANCE MONITORING
100
-------
sample may be extracted from a different duct location if the
stack gas is honstratified at both locations and there is no
een the two sampling points. If
at a different location from the
leakage of air into the duct betv
the €)„ monitor sampling point is
SO2/NOx sample point and stratification exists in the duct, a
multipoint extractive probe must be used for sampling. This is
also true for the monitoring system when the O and SO,, /NO
X
monitors are not of the same typ^ (i.e., one is extractive and
A CO2 monitor can also be used in place of
the other in-situ) .
the O monitor.
3.1.1.5 Gas Flow Rate. The FGfi 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. Because 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, alternate
ely, 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,
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
absorber, mist eliminator, and reheater (if present). Each of
these losses is a function of the
and the one used in most FGD
the inlet and outlet ductwork,
gas flow treated by the module.
Modules operating in parallel gensrally have equal pressure drops
because of identical modular designs.
SECTION 3 - PERFORMANCE MONITORING
101
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3.1.2 Slurry Circuit Parameters
3.1.2.1 pH. 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 reac-
tion 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; howev-
er, 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 recir-
culation, 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
the volume of solid waste.
SECTION 3 - PERFORMANCE MONITORING
102
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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 has suffered
This section
reliability problems.
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 includes process control applications
for monitoring pH, slurry flow rates, and solids content. SO»
monitors are addressed in Section
3.2.1 pH Instrumentation
There are two types pf pH ser
8
3.3.
sors; immersion (dip-type) and
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 specie.1 sampling tank, by using
redundant sensors, and by frequent, cleaning and calibration. The
flow-through pH sensor is prone to wear and abrasion. Mainte-
nance to ensure 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
SECTION 3 - PERFORMANCE MONITORING
103
-------
than' limestone. In many existing systems, improper design limits
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. i
3.2.2 Slurry Flow Rates
Instrumentation measuring slurry flow falls 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 of
a stainless steel pipe section lined with an electrically insu-
lated 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 instrii-
ment calibration.
SECTION 3 - PERFORMANCE MONITORING
104
-------
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3.2.3 Solids Content
All lime/lime stone FGD systeirs include instrumentation for
monitoring the solids level of fresh feed slurry, recycle slurry,
Densinometers are used to moni-
and thickener underflow streams.
tor and control the solids in slurry streams and tanks. Slurry
density can be measured directly with special differential pres-
sure instruments, requiring a mininum 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
Nuclear density meters which
from an electrically driven coil.
measure the degree of absorption oE gamma rays from a radioactive
source are the most popular because of ease of application. The
meter can be strapped to a pipe without insertion into the pipe
line. The only problem with these
inaccuracy and inconsistency. At several facilities, density
measurements are often verified by
laboratory analysis of grab samples).
3.3 TESTING AND MONITORING
This section describes manual
sions monitoring (GEM) methods used
data.
3.3.1 Manual Testing
meters has been their periodic
manual measurements (e.g.,
testing and continuous emis-
to collect FGD gas stream
Manual sampling and analysis of the flue gas at the inlet
and outlet of the FGD system are required periodically to evalu-
I
ate 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
SECTION 3 - PERFORMANCE MONITORING
107
-------
representative sample and obtain accurate information regarding
flow rate. Bends and expansion and contraction zones in the flow
path can induce secondary flow's such as vortices, rotation, and
large eddies. Sufficiently long runs of a straight uniform duct
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
9
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 SO2 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 (H2S04) mist and sulfur trioxide (SO3) are respectively
removed using glass wool (borosilicate or quartz) and a solution
of isopropanol; the SO2 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
H2S04 mist and SO3 are discarded, and the collected material
containing the S07 is recovered for laboratory analysis. The
SECTION 3 - PERFORMANCE MONITORING
108
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concentration of SO2 in the sample is determined by a titration
method.
For determination of the total mass emission rate of SC>2,
the moisture content and the volumetric flow rate of the exhaust
gas stream must be measured. The minimum sampling time is 20
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 SO2 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 S00. EPA Method 8 may also be used as an alternative method
Some states specify a sampling method
and SO2. The analysis then gives total
'2'
for stationary sources.
that collects H2SO4/ SO3,
sox.
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 24-
hour timer. This method measures CO2 in addition to SO2. 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-inten-
sive 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 techni-
cians.
SECTION 3 - PERFORMANCE MONITORING
110
-------
3-3.3 Continuous Emissions Monitoring (CEM)
There are many instruments Available for monitoring gaseous
emissions from stationary sourceL Gas monitoring systems may be
either extractive, in-situ, or rimote. The monitors utilize vari-
ous physical or chemical properties to detect and quantify compo-
nents in the flue gas, as shown in Table 3.3-2. The methods used
may be in-situ (the measurements are conducted on the flue gas
inside the stack) or extractive (a sample is withdrawn from the
stack). The basic problem commori 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, therefore1, is to minimize the harsh
effects of the stack environment,
maximize the precision and
accuracy of the effluent pollutant measurements, and accomplish
both at a reasonable cost. To mojnitor SO2, the CEM system must
determine the concentration of the pollutant and also the
concentration of a diluent gas (OJ or CO ) .
Every CEM system can be divijded 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 retro-
reflector is critical. This can te a problem on composite stacks
with fiberglass or stainless steel liners because 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 ithe corrosive stack gas. An air
purging system is provided to keejl the components clean but peri-
odic 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
SECTION 3 - PERFORMANCE MONITORING
-------
TABLE 3.3-2. PRINCIPLES USED IN GASEOUS EMISSION MONITORS'
Extractive systems
Absorption spectroscopy
Nondispersive infrared
Differential absorption
Luminescence methods
Chemiluminescence (NOX)
Fluorescence (S02)
Flame photometry
Electroanalytical methods
Polarography
Electrocatalysis (OJ
Amperometric analysts
Conductivity
Paramagnetism (02)
In-situ systems
Cross-stack
Differential absorption
Gas-filter correlation
In-stack
Second-derivative
spectroscopy
Electrocatalysis (02)
Methods followed by the gas (in parentheses) indicate that the technique is
currently commercially applied only to that gas.
112
-------
CO
o
Q_
O
C_3
CO
>-
CO
ro
CO
CO
UJ
CO
S-
O)
T3
S-
o
o
cu
S-
re
-4-3
re
0
s-
CU
rsi
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SZ
•=E
CU
o
re
c
•r—
CU
^—
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E
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cu
>
•r-
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O
re
s_
-4->
X
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•r-
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•i- re
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+-> re
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CM «
O CM
CO O
^j •*-'
e -i->
re c
r— 3
O M^
<^ r~t
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i-
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4-> (U
CU O
^^ tf—
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4->
cn c
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•r- E
4-* C
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3 -i-
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CU i-
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CU -r-
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re
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S CO Q-
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re s- s-
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4-> 4-> O
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O Cti GO
-------
the FGD process can be a serious problem. Slurry which deposits
on the probe will scrub S02 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.
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, SO0, NO and O9 or C07
I
-------
0 Performance Specification Test 2 - S09/NO Systems
& J\.
0 Performance Specif icatiojn Test 3 - O2 or CO2 Monitors
A detailed description of thepe tests is presented in the
"Continuous Air Pollution Source Monitoring Systems Handbook"
(EPA 625/6-79-005). 7
3.4 RECORDKEEPING PRACTICES AND P
ROCEDURES
The primary reasons for FGD rscordkeeping are cost and envi-
ronmental compliance accountability. The types of records kept
may be in the form of strip charts, numerical data printouts,
manual log books, or work order shket files. The collection fre-
quency depends upon the data. Maintenance records may be updated
daily via log books or whenever wo::k order sheets are filed upon
completion of a given task. Most utilities collect SO0, NO ,
I ^ X
particulate, opacity, and O2 continually, using continuous emis-
sion monitors in the form of strip
charts or computer disk or
tape files.
I
The development of a GEM 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/106 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
Nature and/or cause of ekcess emissions
Corrective and/or preventative action taken to prevent
their recurrence
Zero/span calibration values
SECTION 3 - PERFORMANCE MONITORING
115
-------
0 Normal measurement data
. i
0 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,
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 aforemen-
tioned data requirements. The choice of the data reduction and
reporting system may be the most important factor in the overall
emission monitoring system, because it greatly affects the amount
of manual effort involved in meeting the NSPS requirements".
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 of
analyzers purchased and by the recording method employed. The
SECTION 3 - PERFORMANCE MONITORING
116
-------
measuring requirements are tied in with the recording require-
ments. 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
The regulation, however, speci-
obtained than is actually used.
fies only the minimum number of points that need to be averaged
and recorded. It is often easier.to design systems that inte-
grate the continuous data over the averaging periods.
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.
Because the recorder is a pe
system, the response time, drift,
rt of the continuous monitoring
and accuracy requirements
established in the EPA performance specifications must be con-
sidered when choosing the recorde
chosen that has poor response tin
accuracy, the overall monitoring
many factors that contribute to the relative inaccuracy (relative
to the EPA reference method) of c
ing system does not need to be ore of these factors if a proper
choice of the system is made initially.
The analog chart recorders give a continuous record of the
r itself. If a recorder is
e and limitations in recording
system will suffer. There are
monitoring system. The record-
signal produced by an analyzer.
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
The digital recorder or data
data over intermittent periods.
tenth or hundredth of a second or less; but for such a short
period, the printed data produced
These periods may be short, a
might be unmanageable.
It should be noted that a data logger is not a computer or
microprocessor. A computer can process data, convert it into
SECTION 3 - PERFORMANCE MONITORING
117
-------
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.
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 de-
sired.
The most convenient method of handling continuous monitoring
data is with a data processor. Several firms involved in the
manufacture of stack monitors have seen the need for 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:
0 Analog-to-digital (A/D) large general purpose computer
or data processing system.
0 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 require-
ments. 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
SECTION 3 - PERFORMANCE MONITORING
118
-------
the chart recorders to provide an easily interpreted record of
the trends occurring during the so,urce operation. Cross checks
then can be made between the two systems; if either malfunctions,
',•7
the data may not be lost.
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
of instrument downtime, repair, or
must be documented and explained i
inevitably develop, occasions
significant readjustment also
i the quarterly report to EPA.
Many agencies are now developing inspection programs for these
systems in an effort to ensure thab reliable emissions data can
be obtained. - • . ,
The operator, utility also musb 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.
SECTION 3 - PERFORMANCE MONITORING
119
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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!SO2 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 of 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 (Exist-
ing Design Configurations). Inspection procedures for each
SECTION 4-INSPECTION METHODS AND PROCEDURES "
, 120
-------
equipment item are comprised of
illustration (where applicable)
an inspection checklist, an
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 presented in this sedtion 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 dd
scussed 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
prudent safety procedures to be
Section 7 (Safety) outlines
followed during the inspection..
4.1 GUIDELINES FOR OVERALL PLAN! INSPECTION
Before actually performing kn PGD system inspection, it is
advisable to collect general plakt data such as information on
coal characteristics, boiler datja, and system generation status
(see Sections 2.2, 2.5.1.1 and 2
this type of information include
Steam Electric Plant Factors11.
.5.1.2). Published sources of
the Utility FGD Survey10 and the
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.
SECTION 4-INSPECTION METHODS AND PROCEDURES
121
-------
TABLE 4.1-1 GENERAL PLANT DATA
Boiler Data
o
o
o
o
o
o
o
o
o
o
o
o
peak)
Type of firing (pulverized, cyclone)
Boiler service load (base, intermediate, cycling,
Date of commercial operation (month, year)
S09 emission limitation (lb/10 Btu) g
Particulate emission limitation (lb/10 Btu)
Opacity limitations (%)
Fuel firing rate at maximum continuous rating (tons/hr)
Heat rate (Btu/net kWh)
Average capacity factor (%)
Gross generating capacity (MW)
Outlet flue gas flow (acfm) !
Outlet flue gas temperature (°F)
Fuel Data
Average heat content (Btu/lb)
Average ash content (%)'
Average moisture content (%)
Average sulfur content (%)
Average chlorine content (%)
General FGD System Data
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
FGD process type (lime, limestone)
Generation type (first, second, or third)
Application (new/retrofit)
Initial startup date ;
Commercial startup date
Total system design S0? removal efficiency
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)
Solid waste generation rate (dry) (tons/h)
Total system makeup water consumption (gpm)
Number of operators per shift
Number of maintenance personnel per shift
Maintenance philosophy (dedicated, rotated, pooled)
122
-------
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
the facility (see Section 3.4).
inquire about the current status
recordkeeping procedures used by
Finally, the inspector should
of operation of the FGD system
and recent status preceding the vjisit.
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
area in light of this consideration.
An inspection of the control
are outlined for each equipment
room at the facility should,
however, be undertaken prior to tjhe inspection of the equipment.
The inspector should also note tnat 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 read-
outs to .display general operating! status and/or problems occur-
ring in specific areas of the system. The "live" schematic is
supported by strip charts and meters fed by sampling devices
either throughout the FGD sys'tem
areas. Much of the process-relat
equipment checklists presented later in this section can -usually
or through the more critical
ed information pertaining to thes
I
SECTION 4 -INSPECTION METHODS AND PROCEDURES
123
-------
be obtained in the control room(s). Table 4.2-1 presents a
checklist to be follov.Ted when inspecting the control room.
TABLE 4.2-1. CONTROL ROOM CHECKLIST
0 Ask the operator to point out the monitoring device displays spe-
cific to the FGD system.
0 Note any monitoring device displays that are not in operation.
0 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.
0 Check for high/low readings on S02, particulate, and opacity
monitoring devices (as compared to the design values).
0 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 a
forced system 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 con-
sidered to be very critical to FGD operation and perhaps repre-
sent the most important area of interest to field inspectors.
SECTION 4 - INSPECTION METHODS AND PROCEDURES
124
-------
FAN INLET
DOUBLE-WIDTH
ROTOR
10 ft
MOTOR
FAN DISCHARGE
BACKWARD CURVED
BLADES
Figure 4.2-1. Isometric \
lew of a typical centrifugal .sr:.
125
-------
TABLE 4.2-2. FAN CHECKLIST
OBSERVATION
PROCESS
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 corrosioh and note location. Look for holes at
intake/discharge and analyze duty (ID/FD) contribution.
Note fan function, design application service, and location
(refer to Section 2.4.2.1).!
Unit/booster
Centrifugal/axial
ID/FD !
Wet/dry '
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 inches h^O for gas-side
operation.
126
-------
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
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
towers for similar applications
be larger in height than packed
because spray towers require a
higher residence 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
for a given facility as compared
because lime is a more reactive
ratio and a lower residence time
typical absorber designed to accommodate 100 MW of boiler flue
have slightly smaller absorbers
to those for a limestone process
reagent requiring a lower L/G
of the gas in the tower. A
gas capacity may be between 2 tc
4 stories in height. The
absorber may be rectangular 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 dime
absorber. Because typical abso]
stories high, the inspector may
nsions of a typical tray tower
bers are likely to be several
not be able to collect all the
data for the absorber at one tiire. 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
SECTION 4-INSPECTION METHODS AND PROCEDURES
127
-------
MIST ELIMINATOR
TRAY MIST
PRECOLLECTOR
INTERNAL SPRAY
HEADER AND NOZZLES
INLET GAS FLOW
OUTLET
GAS FLOW
40 ft
EXTERNAL
SPRAY HEADER
SIEVE
TRAYS
SUMP
J
DRAIN TO REACTION TANK
20 ft
Figure 4.2-2. Typical tray tower absorber.
128
-------
TABLE 4.2-3. SCRUBBER/ABSORBER CHECKLIST
OBSERVATION
PROCESS
Observe any tools, debris, of 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.
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 sjlurry leakage due to erosion/corrosion
(e.g., discoloration on the absorber outside walls).
What are the design/actual absorber inlet particulate grain loading
and S02 concentrations? (See Section 5.3.1.1 for significance.)
What are the design/actual absorber outlet particulate and S09
emission levels? (See Section 5.3.1.1 for significance.) '*•
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
What is the pH and slurry so'
tank? (See Sections 5.2.2.3
if these values are high/low
Inquire about the slurry and
operator or other utility contact).
ids content in the absorber reaction
and 5.2.2.5 for significance.) Check
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
Ask if absorbers have,been e:
periencing 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
Are any instrumentation prob
flow, gas flow)?
a flashlight.
If absorbers are idle, ask wh|y (i.e., spare, demand, scheduled
outage, forced outage).
ems evident (pH, AP, % solids, slurry
Inquire about routine maintenance procedures. Check on the
frequency of plant inspection).
129
-------
CHEVRON VANES
WASHER LANCE
BULK ENTRAPMENT SEPARATOR
Figure 4.2-3. Typical mist eliminator section
(baffle-type, continuous vane).
130
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damaged need to be changed rather than the entire mist eliminator
a of approximately 400 sq. ft.
portion which could cover an are,
The mist eliminator is typically
accessed through access doors
usually on the third or fourth level of the absorber.
4.2-4 presents a checklist for mist eliminators.
Table
4.2.1.4 Reheaters .
Indirect h
ibl
ot ai
air reheaters 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
materials failure (e.g., steam tube failure). The impact on the
FGD system may be an increase in
reheat, increased energy consumption, or possibly, a complete unit
shutdown. Reheaters are usually
heat exchange capacity and
AP, a loss of effective flue gas
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
SECTION 4 -INSPECTION METHODS AND PROCEDURES
131
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TABLE 4.2-4. MIST ELIMINATOR CHECKLIST
OBSERVATION
PROCESS
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.)
If absorber is shut down, inspect mist eliminator sections for
signs of plugging/scaling, breakage, deformation, and erosion/cor-
rosion.
If possible, inspect downstream equipment for signs of excessive
mist eliminator carryover in the form of condensation packets and
solids deposits;
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).
Ask if the absorber pH is operated above or below the design range.
(See Section 5.2.2.3 for significance.)
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.
Check on wash water source (see Section 5.2.2.8 for significance.)
Is it fresh makeup, process recycled water, or a blend? Does the
plant water loop type (i.e., open or closed) have any impact on
washing practices?
If problems have occurred, inquire about remedial actions taken or
planned.
Inquire about routine maintenance procedures. How often are the
mist eliminators inspected?
132
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TABLE 4.2-5. REHEATER CHECKLIST
OBSERVATION
PROCESS
If FGD system is shut dovn, inspect indirect reheater mixing
chamber and/or in-line tubes for excessive scaling/plugging. Also
check for signs of corrosion and note location.
If reheater is operational, inspect external ductwork appearance
upstream and downstream o|f reheater for signs of corrosion.
Look for discarded or replacement tubes nearby (primarily for
in-line reheater applications). Ask why the tubes were replaced.
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 acijd 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 occurrec
planned.
, inquire about remedial actions taken or
Ask about reheater cleaning techniques and frequency (e.g., soot
blowers).
Inquire about routine maintenance procedures. How often are the
reheaters inspected? . ^^
133
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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
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.
i
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 po-
tential for reagent preparation and feed equipment failure re-
sulting in downtime of FGD systems is not as great as compared to
equipment comprising the gas-handling circuit. If, for example,
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 may 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.
SECTION 4-INSPECTION METHODS AND PROCEDURES '. ——~~~~~
134
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TABLE 4.2-6. DUCTWORK/DAMPER CHECKLIST
OBSERVATION
PROCESS
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
* .._.*. .1 • i i \
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 sjystems)?
Observe any "new" ductwork.
for their replacement.
sk the plant personnel the reasons
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.
Check to see if the duct runs(are insulated on the outside to
reduce the possibility of condensation/corrosion.
Note ductwork shape (cylindrical versus rectangular) and
configuration (straight runs |ersus 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.)
Ask what process conditions troublesome ducts and dampers are
subject to. What is the gas flow and temperature? Is the gas
saturated?
What materials (if any) are used for duct lining?
Is there a slurry carryover p
^oblem through the mist eliminators?
(continued)
135
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TABLE 4.2-6 (continued)
OPERATION AND MAINTENANCE
Inquire about problems with ductwork.
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?
Inquire about integrity and installation of duct materials. Ask
where problems have occurred and what actions are being taken to
rectify problems.
Are there problems due to fly ash or other solid.s accumulation
which hinder the opening/closing of the damper?
Inquire about routine maintenance procedures.
ductwork/damper's inspected?
How often are the
13:6
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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.
0 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.
0 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 tie site in the reagent) or freeze ups
during the winter months?
If problems have occurred,
planned.
inquire about remedial actions taken or
Inquire about routine maintenance procedures.
137
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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
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
SECTION 4-INSPECTION METHODS AND PROCEDURES ~~
138
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TABLE 4.2-8. BALL
MILL CHECKLIST
OBSERVATION
PROCESS
Look for any discarded balls;. Inquire about the reason for their
replacement. (New ball charges are expected requirements because
the action of milling "consumes" the balls and eventually requires
replacement to maintain desired particle size.)
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., problems with
purity, hardness, or chemical composition) can reduce the design
output of a ball mill. Was I the ball mill properly sized for the
facility?
Inquire about the source/quality of water used in the ball mill.
(Water having high levels of dissolved chemicals may inhibit
dissolution.)
OPERATION AND MAINTENANCE
Inquire about problems that
rapid ball loss, poor quali
failure).
Ask about routine maintena
have occurred (e.g., liner failure,
ty product, motor failure, bearing
0 If any problems have occurred, inquire about remedial actions taken
or planned.
ce procedures on mills.
139
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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., problems with
purity or 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
0 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.
140
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TABLE 4.2-10.
TANK CHECKLIST
OBSERVATION
Are there signs of tank repairs (e.g., patches welded on outside)?
Inquire why the repairs were made.
Note tank configuration (cylir
tangular tanks are more prone
drical versus rectangular). Rec-
to corrosion due to stagnant areas.
Rectangular tanks are also more prone to insufficient mixing and
short circuiting; check placement of internal baffles to aid in
mixing.
Inquire or note if tanks are qpen or closed. If open, has it ever
resulted fn any problem?
Look for signs of slurry leakc
ge due to erosion/corrosion.
Check for floating debris in cpen tanks (e.g., absorber packing,
liners). Inquire about the origin of the foreign material. Are
the tanks equipped with strairers and have they ever become plugged?
OPERATION AND MAINTENANCE
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 associe
agitators, pumps, instrumentation).
If problems have occurred, inquire about the remedial actions taken
or planned.
Inquire about routine maintenance procedures.
ted with support equipment (e.g.,
-------
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. ;
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 filter cake 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 continue to operate for 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
i
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
SECTION 4 - INSPECTION METHODS AND PROCEDURES ~~
142
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DIAMETER: 100 ft
HEIGHT: 12 ft
EFFLUENT
LAUNDER
WALKWAY
TORQUE AND->
RAKE ARMS V
FEED
HIGH-PRESSURE
BACK-FLUSHING
WATER LINE
UNDERFLOW
Figure 4.2-4, Isometric 4iew of a typical thickener.
143
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TABLE 4.2-11. THICKENER CHECKLIST
OBSERVATION
PROCESS
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.
Look for signs of slurry leakage due to erosion/corrosion.
Does the thickener have a protective covering (e.g., screen)? If
not, look for floating debris.
How is water recycled back to the system (gpm) and how is it used?
(See Section 5.2.2.8 for significance.)
What is the actual/design percent solids the thickener produces at
the underflow? Overflow? (See Section 5.2.2.5 for significance.)
What is the thickener actual/design solid waste production rate?
(See Section 5.2.2.7 for significance.)
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
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?
Have there been problems reported with rake binding or rake drive
shaft/motor failure?
Have there been sump pump failures?
Have there been liner failures?
If problems have occurred, inquire about remedial actions taken or
planned.
Inquire about routine maintenance procedures. How often inspected?
144
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TABLE 4.2-12. VACUUM FILTER CHECKLIST
OBSERVATION
0 Inspect filter cloth for te
ars.
Observe surroundings for spare or discarded filter cloths.
Observe filter cake consistency. Does the material fall from the
filter cloth upon hitting the blade in dry cake-like chunks or do
it stick and fall to the conveyor in a damp gum-like mass?
does
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
filter cake formation?
What are
production
significance.)
content high enough to allow adequate
s the design/actual solid waste and wastewater effluent
ion rates of each vacuum filter? (See Section 5.2.2.7
for
How much vacuum filter filtrate is recycled back to the system
(gpm) and how is it used?
What is the approximate rat
filter cake? (See Sections
See Section 5.2.2.8 for significance.)
o of calcium sulfite to sulfate of the
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 wr:h filter cloth replacement?
0 Have there been any problems due to filter cake conveyors?
0 If any problems have occurred, inquire about remedial actions taken
or planned.
0 Inquire about routine maintenance procedures.
145
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TABLE 4.2-13. CENTRIFUGE CHECKLIST
OBSERVATION
PROCESS
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?
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.)
How much centrifuge filtrate is recycled back to the system (gpm)
and how is it used? (See Section 5.2.2.8 for significance.)
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.
Inquire about routine maintenance procedures.
146
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TABLE 4.2-14. WASTE
PROCESSING SYSTEM CHECKLIST
PROCESS
What type of waste processi
(See Section 2.4.2.13.)
ng technique is used at this facility?
OPERATION AND MAINTENANCE
Ask utility contact about
area.
If any problems have
or planned.
Forced oxidation
Fixation
Stabilization
Untreated
What is the energy consumption of the waste processing system?
problems associated with this equipment
occurred, inquire about remedial actions taken
Inquire about routine maintenance procedures.
L47
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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
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
SECTION 4-INSPECTION METHODS AND PROCEDURES
148
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TABLE 4.2-15. WASTE
DISPOSAL SYSTEM CHECKLIST
PROCESS
Is the FGD system water loop
for significance.)
What type of waste disposal
Section 2.4.2.14.)
Ponding
Landfill ing
open or closed? (See Section 5.2.2.8
system is used at this facility? (See
Stacking
If a pond is used, is
How much? What are the
chlorine content, other
significance.)
wasteWater circulated back to the process?
waste characteristics (solids content, pH,
salts content)? (See Section 5.2.2.8 for
OPERATION AND MAINTENANCE
0 What problems have been reported with respect to this area? If any
problems have occurred, inquire about remedial actions taken or
planned.
Inquire about routine maintenance procedures.
149
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DISCHARGE
SUCTION
SHAFT
-7.5 ft-
FRONT VIEW
/-SUCTION | /-DISCHARGE
SIDE VIEW
5 ft
Cb)
Figure 4.2-5. Typical slurry.recycle centrifugal pump:
(a) isometric view; (b) side and front viev\Twith
approximate dimensions.
150
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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.
Are there any leaks around the pump seals, pump bearings, or other
areas?
Check for excessive pump vihration (if it is questionable as to
whether the vibration is norjmal or not, ask the operator or primary
utility contact).
Look for abrupt expansion,
at the inlet/outlet of valvejs
tion and valve malfunction.
contraction, and bends in piping located
that could lead to solids accumula-
PROCESS
Inquire about process
are subject to. How does
case?
tM
conditions that failure-prone pumps/valves
s compare to the design duty in each
How does the actual energy consumption of the absorber recycle
pumps compare with the design value? (See Section 5.2.2.9 for
significance.)
Ask about pump redundancy p*
OPERATION AND MAINTENANCE
Ask the operator if there he
tion, or shaft, impeller or
curred, inquire about remed-
specific pumps in question
Inquire about the types of
occurred. What remedial ac
•ovided.
ve been problems with plugging, cavita-
liner failure. If problems have oc-
al actions taken or planned. Identify
nd record details.
•alves and location where failures have
;ion has the utility prescribed?
Inquire about routine pump/valve maintenance procedures.
151
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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 complet-
ed prior to the inspection because it can provide valuable input
for evaluating the FGD system performance, diagnosing problems,
and recommending corrective measures.
SECTION 4-INSPECTION METHODS AND PROCEDURES
152
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SECTION 5
PERFORMANCE EVALUATION AND
PROBLEM DIAGNOSIS/CORRECTION
This section describes guide]
ines 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 considerction is important in that an
FGD system may yield performance c
the time of the inspection; howeve
the existence of problems which wi
status.
This section represents a coritinuation of Section 3, wherein
we describe lime/limestone slurry
their measurement, and Section 4,
stone slurry FGD inspection methoc
ata indicating compliance at
r, process data may indicate
11 jeopardize future compliance
FGD performance indicators and
wherein we describe lime/lime-
s 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 prqcedures to verify the success
of the corrective measures taken.
The information presented in
this section is organized in
accordance with the equipment aree.s and subsystems identified in
Section 2.4.2 (FGD System Design Configurations).
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
153
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5.1 DATA COLLECTION METHODS i
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.
PGD 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 SO2,
particulate, and opacity data continually using CEM's in the form
of strip charts, computer disk, arid/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.
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION ~~™ ~~ ~~
154
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Operation and maintenance data
is manually recorded in the form of
include any information which
operation log books, mainte-
nance 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 obi
erved 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 anjd 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 GEM's have a means
for viewing or printing on-line results of SO_, particulate,
opacity emission, and NO measurements in a variety of units
6
(ppm, lb/10 Btu). Regarding control panels, the field inspector
should be aware that FGD control pajnels may be decentralized
(i.e., at more than one location in, the plant) versus a central
location such as the boiler control
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.
the field inspector include O&M log
test reports, purchase orders, lab
room. Reagent preparation
Written records available to
books, work orders, stack
reports, and any other written
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
5
-------
documentation concerning the operation and performance of the EGD
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 SO_, 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 techniques used by the operator utility to
collect these data. 1
5.2.1.1 SO,,. Inlet SO,, 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
SO_ emissions (in units of Ib SO»/10 Btu), the field inspector
should refer to Figure 2.1-1 or use the following equation:
4
SO- emission rate = (% sulfur in coal by weight) x (2 x 10 )
x (fractional conversion of sulfur in coal
to SO2)/(heating value of coal in Btu/lb).
EXAMPLE:
4
S02 emission rate = (3.5% S) x (2 x 10 ) x (0.92 conversion)/
(ll,OOOBtu/lb) = 5.85 Ib SO2/106 Btu.
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION "
156
-------
(If the conversion of sulfur to Sol is unknown, use EPA AP-42
£*
emission factors that assign SO2 cqinversion factors as follows:
0.97 for bituminous coal, 0.88 for
12
for lignite. )
Sulfur is present in the coal
pyritic (primarily FeS2), and inorcanic sulfates. The organic
sulfur is liberated when the coal a
subbituminous coal, and 0.75
in three forms: organic,
s burned; however, not all the
inorganic sulfates and pyritic sulfur is liberated during combus-
tion. Some of it is converted to tottom ash or fly ash. The
coal should be tested to determine what fraction of the organic
and inorganic sulfur is converted to SO9. Typically, 95 percent
of the sulfur in coal is converted
percent may be converted to sulfur
2'
to SO2; about 0.5 to 1.0
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 particld size, very little is removed
by the FGD system.
An increase in inlet SO2 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 (li.e. , SO2 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 SO2 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
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
is;
-------
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 SO- 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.
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION ~~
158
-------
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), 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 flt.e 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
penetrate the absorber and become
small enough, it could then
part of the overall emissions
from the FGD system. Another exarrple is the slurry from the
absorber. The mechanical equipmert required to pump and spray
the slurry also generates liquid and solid aerosols. These
aerosols could be entrained by the
the mist eliminator to the stack.
such as sulfuric acid or volatile
vapors in the flue gas. As the gas temperature is reduced during
passage through the absorber, thes
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
wastewater effluent and energy con
gas stream and pass through
Additionally, certain species
elements may be present as
e species may condense. The
makeup water consumption; and
sumption. Section 3.1 (Key
Operating Parameters and their Measurement) provides background
information on these measurement parameters and monitoring tech-
niques.
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
159
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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
joints, or the malfunction of the control dampers can lead to
several operating consequences. Gas flow rates above the design
value can have several consequences, including the reduction of
SO0 removal. Another result of high gas flow rate is the carry-
£+
over of entrainment from the mist eliminator to the downstream
subsystem. Higher-than-normal gas flow rates can result in in-
creased particulate loadings from upstream particulate collection
devices (e.g., ESP's, scrubbers). ! The added particulate matter
can also increase solid waste disposal. Reduced gas flow may
decrease S0~ removal efficiency, depending on the design and
operating characteristics of the absorber.
5.2.2.2 Gas-side Pressure Drop. Gas-side pressure drop con-
sists 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 con-
stitute the major portion of the total pressure drop. The pres-
sure 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 elimina-
tors 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 con-
tributing factors include high gas flow rates and high slurry
flow rates (which compresses the gas flow).
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
160
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TABLE 5.2-1. DESIGN GAS-SIDE PRESSURE DROPS FOR ABSORBERS IN
OPERATIONAL LIME/LIMESTONE FGD SYSTEMS
Absorber type
Venturi
Fixed-throat
Variable-throat/side movable blades
Variable-throat/top-entry plumb bob
Packed
Entrained
Grid
Mobile bed
Rod deck
Static bed
Tray
Sieve
Combination
Spray/packed
Spray
Open/countercurrerit spray
Open/crosscurrent spray
Number
of
plants
2
1
1
3
1
5
3
1
7
8
24
4
Gas-side pressure
drop, in. H20
Range
6
8
8
3-6
2
2-9
8-12
11
2-14
1-6
1-8
2
Average
6
8
8
5
2
6
9
11
6
3
3
2
161
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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
Primary collectors
Impingement '
!
Baffle/closed vane
Baffle/open vane ;
Centrifugal separation
Radial vane
Precollectors
Bulk separation
Perforated trays
Number
of
plants
56
2
1
2
Gas-side pressure
drop, in. HpO
Range
0.1-4.0
0.2-0.8
2.3
0.5
Average
1.0
0.5
2.3
0.5
162
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A decrease in pressure drop
cause improper slurry atomizatio
er. A decrease in pressure drop
packing, low slurry flow rates, or low gas flow rates.
5.2.2.3 Slurry pH. Control of
, although not as common, can
i and distribution in the absorb-
can be attributed to dislocated
slurry pH is essential to reli-
able FGD system performance. Removal of SO2 from the flue gas
takes place in the absorber, and)neutralization and precipitation
reactions occur in the slurry recirculation and holdup tanks.
The pH of the recirculation slur::y 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
er should be in the range of 6.0
spent slurry leaving the absorb-
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
t
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 SO9 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 SO2 removal 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 I 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
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
163
-------
rate above the design L/G may improve SO2 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
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, SO2 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 SO2 removal required (stoichio-
metric ratio). However, excessive reagent can lead to several
operating problems including wasted reagent, scale formation, and
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
164
-------
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165
-------
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 capaci-
ty 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 SO2 reaction products,
unreacted reagent, fly ash, and adherent liquor.
Increases in solid waste increase 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 can either overload (high or "rich" sol-
ids content) or under-utilize (low or "lean" solids content) the
primary dewatering subsystem. 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 dewater-
ability 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 offset these losses. Major
addition points and/or uses of makeup water include reagent
preparation and dilution, mist eliminator wash, pump seal water,
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
166
-------
IT)
CM
OO
C.
o
CM
O
00
c
o
fO
(O
O
§
(1)
-------
Figure 5.2-3. Sludqe (waste) production calculation.
168
-------
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 materi-
al. High makeup water consumption could lead to discharges (or
increased 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 of fresh water (of or near potable quali-
ty) 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 or erosion/corrosion of the mist eliminator wash lances,
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
169
-------
absorber, piping, pumps, and other slurry handling equipment.
Another major use of makeup water is addition to the recircula-
tion tank for level control. Water quality is not a concern here
except that residual alkalinity is desirable. Typical makeup
water consumption rates and addition points are summarized in
Table 5.2-3 for several operational lime/limestone slurry FGD
systems.
5.2.2.9 Energy Consumption. FGD energy consumption is attrib-
uted 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
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 ID fan, outlet ductwork, or stack. Further, reheat mini-
mizes 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 indica-
tive of plugged or scaled in-line reheater tube bundles. Energy
consumption is increased because the heat transfer efficiency of
the reheater tubes is lowered. Table 5.2-4 provides a quick
approximation method to determine reheat energy consumption.
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
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
170
-------
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TABLE 5.2-4. ENERGY REQ
UIREMENT CALCULATIONS
P
E
Hs
L/G
o
m
AP
Q
AT
Specific heat, Btu/(lb)(°F)
Power required, kilowatts
Heat energy, Btu
Head, ft
Ratio of slurry flow to
outlet
flue gas rate, gal/1000 acf at the
Air flow rate at the inlet of reheat section, Ib/min
Pressure drop through FGD system, in. HJ3
Gas flow rate at the outlet of absorber, acfm
Degree of reheat, °F
Slurry recirculation pumps (70% pump efficiency assumed)
P = 0.000269 x H x (L/G)
= Hs (L/G) Q x (2.69 x
2. Flue gas fans
P = 0.0002617 x AP x Q (assuming 80% efficiency)
3. Reheat of absorber flue gas
E = 0.01757 ° C AT
1000
173
-------
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 power requirements. Figure 5.2-4 provides a
quick determination method if only plant size and gas-side pres-
sure 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 of the solid waste material.
Similar to fans, an increase in pumping energy consumption usu-
ally indicates either a mechanical problem or an increase in
slurry side pressure drop in the system. Table 5.2-4 provides a
quick approximation method to determine recirculation pumping
requirements. Figure 5.2-5 also 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 current FGD technology,
most utility operators employ computerized maintenance planning
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
174
-------
20,000
15,000
O
10,000
5,000
—1 T
PLANT CAPACITY =f/1000 MW
500 MW
60
AP, in
, H00
Figure 5.2-4. Fan power requirements.
175
-------
4000 -
3000 -
to
4->
ra
2000 -
1000 _
I I I I
PLANT CAPACITY =/1000 MW
20 30 40 50 60
L/G, gal/1000 acf
Figure 5.2-5. Recirculation pump power requirements,
176
-------
ABSORBER
(Indicate Status of Equipment
OPERATION LOG
and Time of Operational Changes)
DATE
ABSORBER
MODULES IN
ABSORBER
MODULES OUT
OPE
BYPASS
^I-PARTIAL-CLOSED
REASONS FOR ABSORBER
BEING OFF OR BYPASSED
Figure 5.2-6. Example operation log sheet.
177
-------
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§
178
-------
systems. Work orders are first written by operators during shift
inspections. In some cases, work
ging" in which the plant or shift
orders are preceded by "tag-
supervisor routinely inspects
the system and tags equipment apparently in need of maintenance
or 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 completes 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 becqmes a source for forecasting
equipment repairs which can be implemented during scheduled FGD
outages, unit outacres. or ceriods of low demand. For certain
unit outages, or periods, of low demand.
recurring repairs, work orders can be generated automatically by
the computer versus being handwritten by an operator. Figures
5.2-8 and 5.2-9 are examples of,
respectively, handwritten and
computer-generated work order/maintenance forms.
The accounting department ofl 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 dat
FGD system, layout of and access
a include the operation of the
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 thes4 include gas leakage; slurry
leakage; tower, vessel, and ductv
of moving components.
•ork appearance; and the behavior
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
:.79
-------
r
WORK ORDER
Priority/Laval
Station
Component
Requested By Group
Attach List: Work D
Work Description:
WORK ORDER NO.
Unit
Equipment No.
1 Unit Status
Raquantad Completion
Inspection LJ
90046041 9
Data Printed
Date
Settings LH
Special Instructions:
QRQUP
WORK
TYPE
CHQ/CWO/RWO
NUMBER
FERCK
OUTAGE INDICATOR
SUPERVISOR
PURCHASE ;
ORDER NO.
PLANNER
PLANNED WORK
EST.
CREW SIZE
Ciuca of Problem:
WORKFORCE MGT. CODE
9-Labor (Productive)
1 -Travel Time
2-lnclem Weather
3-Delay Time
4-Down Time
'Use code as last digit of
work order number on pay
SCHEDULED
COMPLETION
DATE ISSUED
EST. MANHOURS-ACT.
A
B
C
D
WELD.
MACH.
OPER.
CONTR.
OTHER
TOTAL
MH
CO
— 25
-rSO
— 75
— 100
%
MPLETE
Work Performed:.
D«1e t Tim* Tagged:
WORK
PERFORMED BY
ACTUAL
CREW SIZE
WORK PERFORMED
TYPE CODE
COMPLETED BY
DATE
COMPLETED
Figure 5.2-8. Example of a handwritten work order form.
180
-------
PM03
POUER MAIHTENWICE HtFORHATIOW SOURCE RUN DATE: 2/12/«5
JOB ORDER-BOILER A
FREQUENCY: 0006!
1JOB NO: 02585 BEPT: 3892 SCHIJD UEEK: 10/1965
IJOB TITLE: INSPECT, REPAIR, ADJUST S LUBRICATE
iUNIT: 1 SYSTEM: SCR EQUIP: 56/BAMPjER/OlOO/ A/C EQ.NO: AC-2892-2
[DESCRIPTION: MODULE "E" OUTLET ISOLATION DAMPER
iDESC CONT.: .
[MANUFACTURER: AIRCLEAN MODEL NO^ N/A
(LOCATION: BL6. SCR NORTH-SOUTH E.O
!CAPABILITY REDUCTION: 0000 PRIORITY: 05 CLEARANCE REQUIRED: YES
[ESTIMATED MANHOURS: 3: 0000.00 2: 0002.5 1: 0002.5 6t 0000.00 T: 5.00
EAST-UEST 11.5 EL. 182.6
INSTRUCTION BOOK:
DRAWINGS:
LAST COMPLETED: 09/07/84
HAD TO CLIMB BEAMS TO PERFORM - COMPLETED - BERNIE AND RADHA
JOB STEPS:
DAMPER CHAIN P.M. - ISOLATION DAHfERS
01 UORK SAFELY - CHECK ALL CLEARANCES.
02 CLEAN OIL AND DUCT ACCUMULATION FROM CHAIN UITH SOLVENT.
03 RELUBRICATE UITH SPECIFIED LUBRICANT.
04 CHECK CHAIN TENSION. ADJUST AS NEEDED.
05 CLEAN UORK AREA.
PAGE 1 OF 1
AREA: 004 ACCT: 512.15 UORK ORD
ASSIGNED TO
COMPLETED BY
REMARKS
APPROVAL
:R:
DATE
DATE
FAILURE CODE
HOUR
HOUR
Figure 5.2-9. Example of a computer-generated work order form.
181
-------
Gas leakage usually occurs through expansion joints, damp-
ers, 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 (in-
duced draft) systems in which air!is drawn into the FGD system.
This air can promote corrosion, promote scaling due to uncon-
trolled 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 characteristics of the slurry. Absorber tower
appearance, inside and outside, also provides such information.
Vibrating fans and pumps and pump;cavitation all provide clues
regarding maintenance, materials of'construction, and system
operation. Dampers which are inoperative 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 types 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 for 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
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION ~~~~~
182
-------
reaction tank. Tons of deposits may have to be removed each
maintenance period; doors should thus be large enough for easy
removal of such quantities of material/- To simplify repairs,
mist eliminator access should allbw for easy cleaning or replace-
ment 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 maintenance per-
sonnel to save man-hours. Slurry recirculation pumps are often
located in a limited space with difficult access, especially in
retrofit applications. Because tiese pumps must be dismantled
periodically, sufficient access should be made available 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 pump
of the FGD facility. A constant
area is the most unsightly part
stream of seal water, slurry, an
d
the FGD facility.
oil leaks from the pumps are
found even in well-maintained systems. Therefore, the pump area
should be designed for easy cleaning, with such features as
sloping floors, wide floor trenches, and a good supply of water.
Other equipment items such as fans, agitators, and instrumenta-
tion (pH meters, density meters,
etc.) should also have adequate
spacing for maintenance. Equipment located in confined or inac-
cessible spaces tend to see less
maintenance and prolonged main-
tenance repair times.
5.2.4.3 Consumed Equipment. Used equipment can provide insights
to possible operating problems.
pump impellers and liners, spray
and absorber internals.
Erosion, plugging, and thermal stress are common reasons for
spray nozzle replacement. Eroded
Commonly observed items include
nozzles, mist eliminator blades,
and plugged spray nozzles may
indicate a process chemistry problem or a mechanical problem due
to slurry distribution or flue ga.s distribution in the. absorber.
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
183
-------
Mist eliminator packing is usually replaced because the
packing is either damaged or plugged. Mist eliminators con-
structed of certain plastics can easily be damaged (through ther-
mal stress) at high temperatures. Melted or brittle mist elimi-
nators usually indicate a gas temperature control problem (i.e.,
high temperature 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 in-
dicator of gas slurry distribution or process chemistry problems.
Pump impellers are usually replaced due to plugging, corro-
sion, or loss of lining material. Plugged impellers may indicate
excessive solids in the slurry. Corroded impellers indicate
either problems with material of construction or process chemis-
try. 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 main-
tenance procedures, size and type of maintenance staff, and the
priority the operator utility gives to the FGD system in compari-
son 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 in-
dication that the maintenance staff is well-manned and is more
likely dedicated versus borrowed ifrom other service areas (boiler
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
184
-------
staff, on-site contractors, etc.)
facility, how well the FGD system
indication of how the FGD system
utility.
5.3 PROBLEM DIAGNOSIS AND CORRECTIVE MEASURES
.idili
When compared to the boiler
is maintained gives a good
is looked upon by the operator
This section describes guid<
in diagnosing problems affecting
terns and in recommending potenti.
lines to aid the field inspector
lime/limestone slurry FGD sys-
.1 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
Modes). This discussion is then
measures instituted to rectify these problems (Section 5.3.2).
This division of material is pro
extended to the corrective
rided 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 vari-
ety (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
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
185
-------
areas and subsystems identified in Section 2.4.2 (FGD System
Design Configurations).
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-rl, there are ten configurations
now in commercial use in lime/limestone slurry processes. These
configurations are divided according to scrubber-absorber combi-
nations (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 simply be-
cause 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" subsys-
tems that are common to all the configurations listed; namely—
inlet ductwork, absorber, mist eliminator, outlet ductwork, and
stack. All the other subsystems (fan, scrubber, and reheater)
can vary.according to presence (scrubber and reheater) and posi-
tion (fan and reheater) in the configuration. Of the gas config-
urations listed (designated as Gas Configurations I through X),
some are used far more extensively than others. The more preva-
lent configurations are consistent with the characteristics of
technology generation described,in Section 2.4.1.2 (Gas Configu-
ration IX and X). These characteristics include placement of the
fan upstream (forced draft) of the absorber, elimination of the
scrubber in favor of segregated jparticulate control (upstream
ESP), use of the absorber for segregated SO~ control, and the use
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
186
-------
c -o
01 C
•r- tO
t-ja
O fO
CO
>>
CO
O>
(O
0)
-
L 0)
O.
ce a; i-«
LU UJ f—
ea OQ
-------
of a reheater to maintain gas temperatures above dew point in the
discharge ductwork and stack.
The cause-and-effect 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/ab-
sorber) , as depicted iti Gas Configurations I, II, IX,
and X of Figure 5.3-1, depend on the operation of the
upstream particulate matter collection device (typical-
ly 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 SO2 removal efficiency, loss of duct
velocity and settling out of gas-entrained solids
in the duct, or premature motor failure (motor
compensates for mechanical failures).
Leakage 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 in-
crease in pressure drop, loss of absorber S02
removal efficiency, premature motor failure;
greater amount of:oxygen in system, causing uncon-
trolled 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 FD fans. However, ID fans are more
influenced by the operation of upstream subsystems than
FD fans. Accordingly, they can be involved in a great-
er number of cascading problem sequences associated
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
188
-------
with the scrubber, absorber, mist eliminator,
heater.
or re-
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 SO2 remov-
al. The scrubber subsystem also includes presaturator
and quench towers that condition the gas stream prior
to SO2 absorption (see Sefation 2.4.2.2, Scrubbers/Ab-
sorbers) . A scrubber that is part of an SO2 scrubber-
absorber train is generally of the venturi (particulate
scrubber) or spray tower (presaturator or quench) de-
sign. These represent "open" (i.e., lacking internals)
designs that are generally not subject to plugging or
scaling. Variations or degradation in scrubber per-
formance can result in a number of simple and cascading
problem sequences.
If the scrubber is preceded by an ESP, degradation
in the performance oJE the ESP can lead to in-
creased particulate {Loading to the scrubber and a
subsequent degradation in scrubber performance.
This can be evidenced either by increased scrubber
pressure drop to maintain performance levels (and
therefore greater syjstem power consumption by the
fans) or erosion of jscrubber internals due to the
increased loading.
If the fans are forced draft with respect to the
scrubber, degradation in their performance can
cause variations in bas volume and draft, result-
ing in degradation oif particulate capture and SO2
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
cated by limitations
scrubber to control
.e., load-following is compli-
in mechanical ability of
pressure drop across throat).
Subsequent degradation in particulate matter
capture and SO2 removal are experienced at these
conditions.
Degradation in scrubber performance can affect ab-
sorber performance by increased particulate matter
loading or SO2 loadibg. Particulate loading can
result in erosion ofj internals. This can cascade
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
18S
-------
to the mist eliminator (resulting in plugging) and
on to the in-line reheater (resulting in decline
of heat transfer efficiency); this in turn can re-
sult in dew point corrosion to downstream subsys-
tems of ID fans, outlet ductwork, and stack. SO2
loading can result in degradation of SO2 removal
efficiency because of greater-than-design SO2
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 rep-
resents the heart of the 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
problem sequences—either as the initiating or termi-
nating event in both simple.and cascading relation-
ships. A number of absorber impacts from the upstream
subsystems of fans and scrubbers are described in the
preceding sections. Other significant problem sequenc-
es are described below.
- Degradation in the performance of the absorber can
lead to loss of SO2 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
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
190
-------
flow)*; variation!in gas (SO2) composition, re-
sulting in reduce^ SO2 removal (high S02) or
chemistry upsets such as high pH or soft scale
formation (low SoL); degradation in upstream par-
ticulate collection devices (ESP and/or scrubber)
described above; degradation in upstream fan
performance described above; and degradation in
upstream scrubber
performance described above.
Degradation in ab sorber performance can occur due
to a number of cohtributing factors in the slurry
feed circuit (see Section 5.3.1.2, Reagent Prep-
aration and Feed) j. Insufficient slurry feed, low
slurry pH, and hijjh slurry pH can result in low
S02 removal, solids accumulation and pressure drop
buildup across thjs tower, solids entrainment in
absorber discharge gas stream, and corrosion/ero-
sion of internalsL
Degradation in absorber performance (due to gas-
side or slurry-sijle 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
entrainment to thfe downstream damper(s), reheater
(if present), ID fans, duct, or stack. Subsequent
solids buildup and corrosion/erosion can take
these subsystems put 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 corro-
sion to downstream ID fans, ductwork, dampers, and
stack.
Mist Eliminator. Mist
separate subsystem in
5.3-1 (fixed subsystem)
eliminators are shown as a
svery gas configuration in Figure
Before proceeding, however, a
*Flooding is a condition which occurs in a packed tower where gas
flow is increased at a giveri slurry flow rate and slurry is
suspended at the top of the. packing and entrained in the dis-
charge gas stream. Weeping is ja condition which occurs in a
tray tower wherfe gas flow is insufficient to maintain a slurry
suspension on the trays and the slurry flows unimpeded downward
through the tower.
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191
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clarification of the mist eliminator subsystem is in
order (see Section 2.4..2.3, Mist Eliminator). 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 absorb-
er 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 con-
sist of some portion of clarified liquor recovered
from primary solids dewatering, secondary solids
dewatering, or the 'disposal site (see Section
5.3.1.3, Waste Solids Handling and Disposal).
This liquor can contain high levels of dissolved
salts which represent S02 reactants or products
(calcium sulfite, sulfate, carbonate, chlorides,
etc.). Depending on concentration levels, these
salts can precipitate and accumulate on the mist
eliminator through physical or chemical means
(i.e., the alkaline salts react with the residual
SO 2 in the gas stream from the absorber, forming
sulfite/sulfate reaction products).
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
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
192
-------
now constructed of
high temperatures
als are designed [
materials designed to withstand
[400°F]. However, these materi-
1 guaranteed"] to withstand lim-
ited exposures to high temperatures. As exposure
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 absorber or
preceding scrubber (including quencher or presatu-
rator), the hot gas (300°F) may melt or disfigure
the mist eliminator vanes.
Reheater. Reheaters represent an optional subsystem
that always follows the absorber and mist eliminator
and precede the ID 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,
in upstream operations.
making it vulnerable to upsets
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 whjich rotate axially through 360
degrees for maximum coverage. Mechanical failure
in this system can' result in localized or general-
ized solids buildup, which can result in reduced
heat transfer, downstream dew point corrosion, and
ultimately, tube bundle failures.
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 (ejspecially in the upper portions
of the stack because a partial failure will show
up at the point of maximum radiative heat loss).
A tube failure, id not attended to immediately,
will trigger othed tube failures in the immediate
vicinity due to thje corrosive/erosive action of
the heating medium) and flue gas environment.
.iuirj
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
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- 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 or a complete failure (inability to go to
a fully opened or closed position) 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
SO2 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 ID fan (optional), ductwork, 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
an inability to obtain 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
the 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.
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
194
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Rectangular ductwojrk (typically observed in gas
distribution manifplds and breeching for some
systems) is subject more to nonuniform gas distri-
bution than circular ductwork, causing associated
variations in perfprmance and attendant problems
as described in this preceding sections. The use
of turning vanes (jgas flow distribution baffles)
in rectangular ductwork is beneficial, though not
always a complete solution.
Bends, expansions,
also contribute to
dant variations in
problems.
and contractions in duct runs
nonuniform gas flow and atten-
performance and subsequent
Stack. Similar to the ductwork, the stack is also a
fixed subsystem of every configuration depicted in
Figure 5.3-1. Moreover', because 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-
Much of the foregoing discus-
ing or initiating event
sion on outlet ductwork
consideration unique to
also applies to the stack. A
the stack is due to its dimen-
sions and position in the gas circuiti 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
specifying credit for 2
adjacent structure (i.e
ISTSPS (see Section 2.1.1.2)
.5 times the source or tallest
roughly equivalent to 500 to
600 ft above grade). Added to this consideration is
the stack's tail-end pojsition in the gas circuit.
Unique problems associated with these considerations
are radiative heat loss in the discharge ductwork and
stack base which can caase downstream dew point corro-
sion to the top portion
quired degree of reheat
of the stack, even if the re-
is being achieved. Concurrent
considerations associated with this concern are plume
visibility, plume rise, and pollutant dispersion. Dew
point corrosion to the pop portion of the stack is com-
pounded by the inability to inspect it during routine
operation, maintenance, or scheduled maintenance.
Damper. As indicated i.i Figure 5.3-1, dampers are not
shown as a separate subsystem. Instead, they ar"e
associated with the operation of the subsystems of
ductwork, fans, scrubbejrs/absorbers, and reheaters.
Dampers are used to regiulate the flow of flue gas
through these subsystemjs through control and isolation
functions. These functions are critical to the proper
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
195
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operation and performance of these subsystems. Damper
malfunctions can be either a triggering or terminating
event in a simple or cascading problem sequence. Damp-
ers 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, SO2 reactants and
products) on damper drives and seals, causing damper
regulation problems with associated gas control and
leakage problems. Gas control problems include regula-
tion of the fan, scrubber/absorber, and bypass and hot
air injection reheaters. Leakage problems include gas
bypass for scrubbers/absorbers during low load or main-
tenance situations. Gas flow regulation problems can
cascade into performance'degradation for the subsystems
being served through low and high gas flows, as de-
scribed in the preceding;sections on the various sub-
systems in the gas handling and treatment equipment
area. Isolation problems can prevent timely inspection
and preventative maintenance, which can ultimately
manifest itself in major,unscheduled maintenance.
Dampers in the absorber discharge are subject to the
harshest operating environment. Corrosion attack
commonly occurs through entrainment carryover of solids
and the collection of corrosive 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
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;subsystem configuration. In
effect, there are two basic configurations now in use—one for
lime slurry processes and one for limestone slurry processes.
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
196
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These configurations differ becajuse 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 slaking1) , 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 car occur by river barge, rail car,
and/or road truck. Mojst modern-day plants incorporates
the flexibility of receiving supplies through more than
one mode of transportation (in many cases, all three) .,
Factors which govern this selection include geographi-
cal location, existing infrastructure, source of sup-
ply, and mode of coal (transportation. Although receiv-
ing and off-loading arje not considered sophisticated or
specialized functions of the FGD process, a number of
simple problem sequences can occur.
Weather conditions can interrupt the supply of
reagent to the plant, especially river barge
deliveries during severe winter weather (freezing
conditions). Expended interruptions can eventu-
ally affect FGD s|ervice time, especially if plant
supplies are low.! This is more of a concern for
lime than limesto'ne because on-site bulk storage
is limited to sto'rage silos and bins whereas
limestone bulk storage can be accommodated through
large, unprotected storage piles (typical lime-
stone storage pile supplies 30 days of operation).
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
1.97
-------
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198
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Weather conditions also can hamper or interrupt
unloading operations because of frozen shipments,
especially on ra
Conveying.
conveyors,
Conveying
screw conv
1 cars.
equipment includes covered belt
yors, and pneumatic conveyors.
the "simple" mechanical variety;
The former two are of
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 interrupt FGD operation. However, a
more subtle problem occurs where conveying equipment is
shared (in order to save on capital costs). This situ-
ation exists at a number of coal-fired plants which use
limestone slurry FGD.I The coal and limestone supplies
share a considerable portion of the belt conveying
equipment. Contamination of supplies invariably oc-
curs. 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.
j
Bulk Storage. Open storage piles are used for bulk
limestone storage and}storage silos and bins are used
for bulk lime storage] Open storage piles are subject
to problems of ambient environmental conditions in the
form of freezing and precipitation (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 stor-
age bins must be weatlixerproofed and airtight to prevent
absorption of water and carbon dioxide from the atmo-
sphere. 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 FGD operation relatively quickly,
possibly causing a curtailment or interruption of oper-
ation. 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 I to the same types of problems. A
feed bin is a somewhai more complex operation, however,
due to the presence of dust collecting equipment, air
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
199
-------
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 SO2 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 prepa-
ration and feed equipment area. The ball mill produces
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 SO2 removal and
reliability (plugging, scaling). Chemical charac-
teristics of active alkali components (CaCO3, CaO,
MgCO3, MgO) and impurities (silica) will affect
SO2 removal and mechanical reliability. With
respect to the former, insufficient active alkali
can limit the amount of alkalinity available in
the slurry liquor to absorb SO2. With respect to
the latter, impurities in the form of silica,
dirt, 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.
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
200
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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
required. Degradation in bulk limestone quality
(impurities) may klso accelerate mill surface wear
and subsequent prbduct slurry quality.
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 fromi the surface of the pebbles as
they form, thereby exposing fresh surfaces for
further reaction and 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. Insuffi-
cient residence time and temperatures cause inef-
ficient 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 th(J2 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 (HCO~j will precipitate in the pres-
ence of calcium aijid cause scaling. Similarly,
high concentrations of metal cations that will
precipitate as hydroxide salts are objectionable.
High chloride concentrations do not appear to be
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,
attack.
thereby accelerating erosion
SECTION 5 - PERFORMANCE EVALUATION AND PRJOBLEM DIAGNOSIS/CORRECTION
501
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- 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 quali-
ty 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 the
reagent preparation arid 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 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 se-
quences peculiar to the slurry distribution subsystem
are identified below.
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
202
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Lime slurry product! storage not only provides
surge volume between the slaker and absorber, but
also allows time fojr the slurry to "stabilize".
Addition of dilution water to a concentrated slur-
ry causes a series
of chemical reactions between
the lime and dissolved minerals in the water such
as the alkaline eau+th salts (Group IIA metal ox-
ides) , chlorides, sjulfates, and phosphates. These
reactions, which are typically completed in less
than 15 minutes, cg.use the formation of hard,
insoluble, crystalline solids. The primary func-
tion of slurry storage is to hold freshly diluted
slurry until these1 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. Iii a well-designed system, a
large storage tank is used so that most of the
scale compounds ar4 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 thenjsaid to be stabilized. If no
more water is adde4 and the slurry does not absorb
significant quantities of CO2 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 .
CO9 uptake from the air), or if the suspended sol-
ids are not allowed to settle, the "unstabilized"
slurry contributesjto the erosion of downstream
transfer pumps andjpiping, decreased SO2 removal
in the absorber, plugging and scale formation in
the absorber, and possible downstream effects to
the mist eliminator, reheater, ID fans, ductwork,
and stack.
Limestone slurry product storage provides surge
capacity within th& slurry distribution subsystem
in order to permit!disruptions in the operation of
the grinding systeijn without affecting the opera-
tion of the absorber. Limestone slurry product
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 stpr^-
age tanks provide a residence time of a minimum of
SECTION 5 - PERFORMANCE EVALUATION AND PFJOBLEM DIAGNOSIS/CORRECTION
i
203
-------
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 SO2 removal
across the absorber, increased limestone consump-
tion, plugging and scaling in the absorber, and
cascading downstream effects in the mist elimina-
tor, reheater, ID 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
process chemistry parameters monitored include
slurry pH and percent solids. The process chemis-
try variables of importance include solid phase
residence 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
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.
*Short circuiting is the inability of the slurry to use the
entire residence time provided by the tank due to the position-
ing of the inlet and outlet feed streams or insufficient back-
mixing. :
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION ~
204
-------
(1)
(2)
(3)
(4)
(5)
Slurry residence times of 8 to 15 minutes are
typical for lijme/limestone systems. All
other factors being equal, the lower range
suffices for llime slurry and the higher range
suffices for Ijimestone (due to chemical
reactivity considerations). An undersized
recirculation tank can impair the mechanical
and chemical ajspects of process operation.
Namely, the inability to "surge", insuffi-
cient slurry alkalinity to remove SO2 in the
absorber, towqr scaling and plugging, high
reagent consumption and increased solid waste
volumes.
Improper mixinjg in the recirculation tank can
short circuit {the available residence time
and affect the process chemistry which in
turn can cause; reduced SO2 removal across the
absorber, scaling and plugging in the absorb-
er, increased jreagent consumption, and in-
creased solid jwaste production. Improper
mixing can occur through insufficient resi-
dence time, tank geometry, arrangement of .
reed and discharge streams, insufficient
agitation, and^ position of afitators (top
entry preferred to side entry).
Open externaljtanks are subject to debris
falling into the tank, which can clog up pump
intakes, feed {lines, and spray nozzles, and
cause inefficiency of operation and/or com-
ponent malfunctions. Open tanks also emit
slight corrosive vapors which can eventually
rust or corrode the undersides of equipment
directly above, most notably absorbers.
Internal tanks provide limited access for
inspection, operation, and. maintenance. This
can result injthe lack of proper attention or
early detection of minor operating problems
which can compound into major problems (noted
above). Noteable examples are agitator
operation (moior, shaft, and blade assembly
integrity and{lubrication), proper liquid
level, and corrosion of internals and under-
sides of equipment directly above.
Cylindrical tanks contain superior mixing
characteristics to rectangular tanks which
have a higher
and localized
potential for short.circuiting
poor mixing. The impacts of
SECTION 5 - PERFORMANCE EVALUATION AND
EM DIAGNOSIS/CORRECTION
205
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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 discus-
sion for the previous two equipment areas, the subsystems con-
tained 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 of without the benefit of an external treat-
ment step. Physical treatment involves the use of forced oxida-
tion to 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 addi-
tion of chemically non-reactive materials; the other is fixation,
which involves the addition of chemically reactive materials.
All the subsystem configurations described in Figure 5.3-3 are
applicable irrespective of process, application, and duty con-
siderations .
.The cause-and-effeet problem sequences which occur in the
waste solids handling and disposal equipment area are described
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
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION ———
206
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CHEMICAL
TREATMENT
Landfill
Landfill
Landfill
Figure 5.3-3. Waste solids handling and disposal subsystem arrangement.
207
-------
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 per-
cent solids. The bleed stream method is more prevalent
due to favorable costs? however, bleeding from the tank
offers superior process control and reliability. A
number of simple and cascading problem 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 fall
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 or
depletion of slurry seed crystals. In the former,
SO2 removal declines? in the latter, the precipi-
tation of SO2 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 pip-
ing and plugging and scaling of tower internals.
Downstream operations are also affected in that
insufficient solids loading may create too much
water in the solid waste product for proper
processing or dewatering.
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
208
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Bleeding spent slurry off the recirculation line
limits the amounij. of redundancy available to
overcome component failure. (Generally, the
absorber is servejd by one main slurry recircula-
tion line which njtanifolds 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 provid-
ed through spare pumps and valves, which can be
placed quickly into operation without affecting
absorber and downstream dewatering equipment
performance. In
or no short-term
tion feed because
tank versus bleec
addition, a failure here (i.e.,
recirculation tank bleed line) would have little
effect to an absorber recircula-
of greater surge capability of
line.
Forced Oxidation. Forced oxidation involves the con-
version 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 recirculation 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 redirculation tank. A number of
problem sequences are
noted below:
Process chemistry upsets can reduce the efficiency
of converting suljfite to sulfate and therefore the
amount of gypsum 'produced. One key variable is
slurry pH. Oxidajtion efficiency increases as
slurry pH is rediiced (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 labove), more dissolved sulfite
precipitates out jas a solid phase salt and sulfite
oxidation efficiency drops correspondingly (i.e.,
sulfite oxidation occurs in the aqueous phase
only; oxidation o|f the solid sulfite is extremely
SECTION 5 - PERFORMANCE EVALUATION AND PftOBLEM DIAGNOSIS/CORRECTION
209
-------
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
SO2 reaction products declines, increasing the
likelihood of scalihg 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 makeup water consump-
tion (pump seals, mist eliminator wash, slurry
precipitation, slurry dilution), increased solid
waste production, ineffectual secondary solids
dewatering, inefficient chemical treatment, and
final disposal difficulties.
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
210
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Inefficient thickening due to insufficient resi-
dence time for settling out SO2 reaction products
can contribute to j:he consequences noted above.
Key design factors
ener diameter) and
are liquid surface area (thick-
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 accom-
plished 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. {& number of special considera-
tions which differentiate secondary and primary de-
watering are worth notilng. First, the vacuum filter
(or centrifuge) is mechanically a more complex opera-
tion. Therefore, there! is a greater risk of failure or
improper 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 olf additives to stabilize or
"fixate" the solid wastes prior to final disposal.
Stabilization involves jno 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 (cejmentitious) chemical reactions
between the wastes and I the additives (e.g., lime, fly
ash) . Some western coa1! ashes are so alkaline that
addition of lime is noii necessary for fixation. Fix-
ated material is more often subsequently used for
off-site landfill where product quality and secondary
environmental, impacts sire of primary concern. The
problem sequences in the upstream subsystems that can
cascade to the physical/chemical treatment subsystem
are noted above. Other notable problem sequences
include:
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
211
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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.
0 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, second-
ary dewatering, and 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 capaci-
ty) , inefficient dewatering, high reagent consumption,
high SO2 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
is, in many cases, a more involved procedure than a simple rever-
sal of the problem sequence. The corrective action sequence
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
212
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j
generally begins by correcting the initiating or triggering
event. The subsystems affected Jin 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).
i
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 ID fans due
to their position in iihe process flow. The triggering
event in fan-related p!roblems is loss of upstream
particulate collection efficiency. Accordingly, the
following corrective sequence is instituted:
(1)
(2)
(3)
(4)
(5)
Take fan out of service (which usually involves
taking the absorb'er module out of service also) .
Remove deposits from internals and rotor.
Repair (weld or
ponents.
atch) or replace failed corn-
Rebalance fan rotor, inspect and lubricate bear-
ings and motor.
Determine particulate collection efficiency of
upstream device via inlet/outlet measurements (EPA
Method 5) to determine particle loading, particle
size distribution, and particle resistivity.
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
213
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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 particu-
late/SO2 control and pregaturators and quenchers for
physical conditioning of the gas stream prior to ab-
sorption. Venturi scrubbers may achieve insufficient
particulate and SO2 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 SO2 removal across
scrubber before and after throat and/or L/G ad-
justments (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 SO2, particulate> temperature, pressure, and
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
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
214
-------
phenomena, they cannot be readily distinguished by
conventional performance monitoring. Even visual
inspection cannot distinguish one from the other.
Chemical analyses of tile deposits (and slurry liquor)
are generally needed. Solids deposition is also a
problem for open spray
less debilitating), as
tower designs (although somewhat
solids can build up 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 slurry pH
acidify) by small incremental
amounts (0.1 pH units).
(2) Monitor gas-side pressure drop and SO2 removal
while reducing slurry pH. (The time frame over
which this action I is taken will vary according to
the system and the situation. However, we recom-
mend that severalj days of continuous steady-state
operation be giverji to this activity. 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. If pressure drop
is not alleviated|and SO2 removal drops signifi-
cantly during pH reduction, solids deposits may
form consisting most likely of gypsum and possibly
fly ash.
(3) Take absorber out
of service (if pressure drop or
SO2 removal problems persist).
(4) Remove solids from absorber internals (including
wet/dry interface} spray headers, spray nozzles,
supports) I
(5) Check/replace slurry spray nozzles.
(6) Check/replace slurry spray headers.
(7) Modify slurry spray pattern through nozzle and
piping modifications (optional, if problem per-
sists) .
(8) Return absorber to service and monitor performance
by measuring SO2 Removal and pressure drop across
the tower ^
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
215
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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 elimi-
nator 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 S02 products/reactants, in-
crease amount of fresh makeup in wash.
(2) Increase mist eliminator wash by increasing wash
duration (preferred method), wash frequency (sec-
ondary preference), and wash rate (final prefer-
ence) . Changes in the mist eliminator wash rate
should be carefully balanced against makeup water
consumption and closed water loop operating re~
quirements.
(3) If mist eliminator pressure drop, is not reduced,
reduce absorber recirculation slurry pH incremen-
tally, 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, qondensate 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
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
2i6
-------
reheat. For this reason, only corrective actions for
this type of reheater are discussed here. Frequency of
problems is due to the reheater's presence in the gas
stream and its dependency on the performance of up-
stream subsystems. Major problems are solids deposi-
tion on the tube surfaces with subsequent corrosion/
erosion attack to tube)bundles. Reheater fouling is
remedied by the following corrective actions.
(1)
(2)
(3)
(4)
Monitor temperature differential of gas stream
across reheater. I If temperature differential is
less than design pr declining, check .flow and
temperature of hekting medium. If below design,
correct and monitor gas stream temperature
differential.
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.
If no soot blower problems are observed, monitor
gas stream pressure drop across reheater. If
pressure drop is breater than design, increase
soot blowing frequency.
If problem persists, remove reheater (including
absorber) from service.
(5) Inspect reheater
manually.
tubes for deposits. Remove
(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 subsystems 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.
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
217
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Ductwork. The outlet ductwork (on the discharge side
of the absorber) is the most problem-prone portion of
ductwork in the FGD system. This is due to service in
saturated conditions and dependency on the performance
of upstream subsystems. The most prevalent problem 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 SO2, opacity, and
acid rainout. If SO2 measurements vary signifi-
cantly below expectations or SO2 measurements ob-
tained upstream, air leakage into the ductwork 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 ser-
vice .
(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.
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
218
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(10) Return ductwork (and any upstream subsystems) to
service. Monitor jstack emissions and measure gas
velocities at various load levels and operating
conditions.
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 fflue 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
outage.
during next scheduled unit
(3) If flue liner is failing or has failed, schedule
repairs during extended unit .outage. If failure
is severe, an immediate forced unit 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 dejsign and operating changes in
accordance with inspection and engineering analy-
sis.
(7) Return unit to service.
Damper. The inability
>f isolation dampers to effec-
tively seal off the absorber tower during flue gas
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
219
-------
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
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 prob-
lems 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 han-
dling and treatment equipment area and waste solids handling and
disposal equipment area. These effects will include insufficient
S02 removal in the absorber; scaling and plugging in the absorb-
er; erosion of pumps, piping, valves, and tanks in the slurry
distribution network; increased reagent consumption; and in-
creased 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 implemented
for both the reagent preparation and slurry distribution subsys-
tems 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.
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION ~~
220
-------
(2)
(3)
(4)
. (5)
(6)
(7)
(8)
(9)
(10)
If slurry reactivity is [inadequate, determine quality
of -bulk reagent with reSpect to specified chemical and
physical characteristics. If the quality of the cur-
rent supply is determined to be inadequate, change
supply.
If bulk reagent supply is determined to be adequate,
determine quality of preparation and dilution water per
the .following measurements: pH, carbonate, bicarbo-
nate, sulfite, sulfate, jchloride, and metal cations.
If current supply is determined to be inadequate,
change water supply by adding more fresh makeup or a
filtering step.
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 takir
system out of service.
g either them or the entire FGD
If ball mill milling surfaces are worn, take ball mill
1
out of service and recharge balls
If slaker "surfaces" (paddles, agitators, rakes) are
worn, take slaker out of service and replace.
Return ball mill or slaker to service and monitor
product quality (chemical reactivity).
If slurry reactivity is still inadequate, determine
residence times in each holdup tank.
If residence times are inadequate, vary liquid levels
(height), pumping- rates ,| and/or operating schedules to
increase residence times.
If reactivity is still inadequate, determine sufficien-
cy of backmixing and the possibility of short circuit-
ing in the tanks. Determine adequacy of agitation 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 modifica-
tions; however, slurry recirculation tank will because
of its continuous mode 4f 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
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
221
-------
and bottom of the tank because solid deposits will form
behind them, decreasing the effective 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 dewaterihg. As noted in Section
5.3.1.3, primary solids dewatering typically is accomplished by a
thickener. The thickener is an extremely problem-sensitive oper-
ation 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 pro-
cess. An overflow high in suspended solids or dissolved salts
can have detrimental impacts on mist eliminator cleanliness,
product slurry quality, and absorber SO2 removal and reliability.
Concurrently, 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), resulting in insuffi-
cient clarification. Consequently, increase thickener
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
222
-------
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 flocculknt is already added). Flocculant
addition should not exceed recommended concentration
levels (typically 5 to 7 ppm).
(5) If thickener overflow
(6)
quality is still determined to be
inadequate, analyze chemistry of suspended solids and
dissolved species. Determine level of excess (unreact-
ed) reagent, sulfite/sulfate ratio, and fly ash. If
reagent exceeds design excess, reduce stoichiometric
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.
If thickener underflow stream exceeds design flow rate
or solids content (thickener overload), monitor per-
formance of downstream secondary dewatering subsystem
(if present). Secondary dewatering may in turn be
overloaded, resulting in a poor quality filtrate or
centrate 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
below design, recycle
of the thickener underflow is
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, arid 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 ^ime-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.
SECTION 5 - PERFORMANCE EVALUATION AND
PROBLEM DIAGNOSIS/CORRECTION
223
-------
(9) During episodes of poor thickener performance, closely
monitor gas-side pressure drop across the mist elimi-
nator (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 dis-
posal material to ensure1 proper curing and characteris-
tics (permeability, compressive strength). This can be
accomplished through periodic core sampling and analy-
sis.
SECTION 5 - PERFORMANCE EVALUATION AND PROBLEM DIAGNOSIS/CORRECTION
224
-------
SECTION 6
MODEL O&M PLAN
• i
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 us
evaluate actual FGD systems.
e as a benchmark from which to
idealized, in this context, refers
to practices that are determined
their successful application in
to be "preferable" based upon
specific systems throughout the
one plan is currently in use that
industry. To our knowledge, no
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 Practiced) 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 desdribed (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. Spare parts requirements are described for
inventories of shelf spares (Section 6.5). The work order system
is described in terms of its importance for monitoring O&M re-
sponse (Section 6.6). Computerized tracking is discussed 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
management structure and staff
be acquainted with two levels of
organization that are prominent
SECTION 6 - MODEL O&M PLAN
225
-------
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 three po-
sitions at the corporate level: vice-president of environmental
affairs, manager of environmental affairs, or principal engineer
of environmental affairs. Generally, the higher the ranking of
the environmental manager, the greater the operator utility's
commitment to FGD O&M. Moreover, assigning 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. Other positions in descending
order are designated as assistant superintendent, operations man-
ager, shift supervisor, shift engineer, foreman, technician, and
support personnel. Similar to the corporate structure and organ-
ization, the higher the ranking of the air quality control system
(AQCS) manager, the higher priority the operator utility assigns
to FGD O&M. Moreover, assigning this level of responsibility at
the superintendent level can free;up positions at lower levels to
SECTION 6 - MODEL O&M PLAN
226
-------
concentrate on FGD O&M. One approach being adopted by many oper-
ator utilities is to establish aj completely 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 promo-
tional structure. FGD O&M can be assigned a separate function
within this structure or embody
itself. Some of the functional
the entire FGD responsibility in
concerns associated 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, ons 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 ef-
forts. When repairs are completad, final reports also should be
transmitted to the originating sjtaff 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 oper-
ation 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 f
cation of effort and helps to en
The size, experience level,
of the O&M staff are significant
inctions but it does avoid dupli-
3ure an efficient operation.
responsibilities, and training
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
history. Staff requirements mus-; be assessed periodically to
size, design, and operating
SECTION 6 - MODEL O&M PLAN
227
-------
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)
hourly laborers, or contracted personnel from service companies
or PGD equipment suppliers. In all cases, outside personnel
should be supervised by experienced plant personnel. The servic-
es of purchasing personnel and computer analysts may also be
needed. The coordinator should be responsible for final accept-
ance and approval of all repairs. Figure 6.1-1 presents the
general concept and staff organizational diagram fc-r a coordi-
nated 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 tech-
nician can monitor routine system performance through sampling
and testing and need not be dedicated full time to the FGD sys-
tem.
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.
SECTION 6 - MODEL O&M PLAN
228
-------
PURCHASING
PERSONNEL
AQCS FGD MANAGER
PLANT
SUPERINTENDENT
1
1
ABSORBER/WASTE
SOLIDS DISPOSAL
OPERATIONS SUPERVISORS
\f
SHIFT (ENGINEERS)/
EQUIPMENT OPERATORS
t
LABORATORY
TECHNICIANS
T
)
'
CHEMICAL
ENGINEERS
i
f
SUPPORT
4
J
MAINTENANCE
SUPERVISORS
^
ELECTRICAL
FOREMAN
\
ELECTRICIANS
\t
SUPPORT
*
MECHANICAL
FOREMAN
V
MECHANICS
\<
SUPP
ORT
Figure 6.1-1. Organizational diagram for coordinated FGD
system O&M program.
229
-------
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
activities (i.e., related to equipment malfunctions) must also be
considered in determining the size of the maintenance staff.
Many plants have a relatively high rate of personnel turn-
over and, therefore, new employees are assigned to work on the
FGD system who may have had no previous contact with air pollu-
tion 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. Whenever 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
be given 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
SECTION 6 - MODEL O&M PLAN
230
-------
emergency situations. Once a patiern is established that allows
a nonoptimal condition to exist (i.e., reliance on built-in
redundancy), this condition then becomes the norm and the margin
of safety begins to erode.
To reinforce the training program, follow-up written materi-
al should be prepared. Each plan^; should prepare and continually
update an operating manual (see Section 6.2) -and a maintenance
manual (see Section 6.3) for each
FGD system. A generic 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 sup-
plier 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 subsys^-
tems, normal operation (indicators), abnormal operations (common
failure mechanisms), troubleshooting procedures, preventive and
reactive maintenance, and recordk^eping.
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, safety
precautions, and 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 opera-
tors and maintenance staff have the same basic understanding of
SECTION 6 - MODEL O&M PLAN
31
-------
all the FGD equipment and their function and of the overall oper-
ating 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 compo-
nents. 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.
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 identifying present or predicting 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 deter-
mining proper equipment performance. With the use of these aids,
operators can possibly alleviate the problem in its earlier stag-
es before it actually manifests itself as 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 ensure
sequential outage of FGD equipment arid/or boilers, to aid mainte-
nance activities, to eliminate startup problems, and to ensure
worker safety. Unless these proper startup/shutdown procedures
are followed, operation or maintenance actions could result in
either further damage to the equipment, increased emissions,
repeated failure, or in the worst case, a worker accident.
SECTION 6 - MODEL O&M PLAN
232
-------
I.
II.
III.
IV.
V.
Introduction
A. FGD System Description
B. Major Equipment Areas
Gas Handling and Treatment Components
A. Fans
Operating norm or baseline9
Major operating variables
Abnormal operating characteristics'
Startup/shutdown procedures
Safety precautions
1.
2.
3.
4.
5.
B. Scrubbers/Absorbers
C. Mist Eliminators
D. Reheaters
E. Ductwork and Dampers
Reagent Preparation
A. Reagent Conveyors and Storage
B. Ball Mills
C. Slakers
D. Tanks
Waste Solids Handling and Disposal
A. Thickeners
B. Vacuum Filters
C. Centrifuges
D. Waste Processing
E. Waste Disposal
F. Pumps and Valves
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. NOX
J. Slurry
1. pH
2. Density (solids)
3. Flow
Solids
1. Density (solids)
2. pH
3. Flow
C.
These considerations apply to all items in Section II, III, IV, and V.
Figure 6.2-1. Outline fior FGD Operating Manual,
-------
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
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 man-
ual. The manual should begin with a basic description of the FGD
system and outline the major equipment areas and their associated
components. The manuals should continue with separate sections
on each of the equipment items presented in the introduction. 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 item
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
SECTION 6 - MODEL O&M PLAN
234
-------
I. Introduction
A. FGD System Description
B. Major Equipment Areas
II. Gas Handling and Treatment Components
III.
IV.
V.
B.
C.
D.
E.
Fans
1.
2.
3.
4.
5.
Scrubbers/Absorbers
Mist Eliminators
Reheaters
Ductwork and Dampers
Component descriptions0
Layout and schematics
Internal/external inspection and reactive and preventative
maintenance procedures j
Startup/shutdown procedures
Safety precautions
Reagent Preparation
A. Reagent Conveyors and Storage
B. Ball Mills
C. Slakers
D. Tanks
Waste Solids Handling and Disposal
A. Thickeners
B. Vacuum Filters
C. Centrifuges
D. Waste Processing
E. Waste Disposal
F. Pumps and Valves
Emissions Monitoring and Process, Control
A. Gas
C.
1. Pressure (differential)
2. Temperature (differentia
3. Flow
4. Continuous Emissions Mor
a. S02
b. Particulate matter
c. NOX
Slurry
1. pH
2. Density (solids)
3. Flow
Solids
1. Density (solids)
2. pH
3. Flow
D
i tori ng
JThese considerations apply to all it
-------
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 or failure (e.g., failed expan-
sion 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
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 de-
scribed 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
SECTION 6 - MODEL O&M PLAN
236
-------
replacement with procured and fabricated components. The system
is then started up and debugged.
Phase 3; Testing and Sampling. A performance test must be
of the work on system operation
conducted to evaluate the effects
(see Section 3.3). Testing may b = 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 possi-
bilities; no report, maintenance protocol, or operator instruc-
tion manual can take the place of
staff familiar with the equipment
6.5- SPARE PARTS
a well-trained maintenance
and its operating history.
Two separate categories of spare parts can be identified—
installed spares and shelf spares. Installed spares are redun-
dant components that are built in-:o the system. These components
can be activated and placed into service expeditiously in the
event of a forced or scheduled outage. .Shelf spares are compo-
nents 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. Accord-
ingly, the balance of this section will be devoted to a discus-
sion of shelf spares.
An inventory of spare parts should be maintained on-site to
support the required maintenance activities. Because all compo-
nents or subassemblies cannot be stocked, a rational system must
be developed that establishes a reasonable inventory of spare
parts. Decisions regarding which
spare parts inventory should be based on the following considera-
tions:
components to include in the
SECTION 6 - MODEL O&M PLAN
237
-------
1. Probability of failure
2. Cost :
3,
4,
5,
6,
Impact on system/unit operation
Availability (specialty or custom-fabrication item vs.
stock item)
Replacement time (installation)
Whether the part can be stored as a component or sub-
assembly (i.e., conveyor belt assembly vs. individual
components)
8,
Repair center (i.e.,
capabilities)
Spatial constraints
in-house technical repair
The probability of failure can be developed from outside
studies, 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 process, and reasonable
judgment must be used in deciding what to stock. Maintenance
staff members should be consulted for recommendations concerning
some items that should be stocked and the number required.
Adjustments to the initial spare parts inventory 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.
SECTION 6 - MODEL O&M PLAN
238
-------
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-gain-
FGD system/unit operation.
nents would impact FGD operation relatively quickly, possibly
causing a curtailment or total
that fall into this category in
Non-replacement of these compo™
system/unit outage. Components
elude 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 compo-
nent 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 directly from stock, or ijf 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
made.
retrofit applications, spatial
The number, type, and size of ;
the period when repairs are being
If the plant has very limited space, as is the case for most
constraints may come into play.
'pare parts .may have to be reduced
to fit the available space allcjtted 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
SECTION 6 - MODEL O&M PLAN
239
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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 igeneral, 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
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 de-
lays. 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.
SECTION 6 - MODEL O&M PLAN
240
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The goal of the work order
following items:
0 To provide systematic
requested work.
system can be summarized in the
screening and authorization of
To provide the necessary information for planning and
coordination of future work.
To provide cost information for future planning.
To instruct management
of repair work.
To estimate manpower,
ing the repair.
and craftsmen in the performance
time, and materials for complet-
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 PGD system nay 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 PGD
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 damage to the equipment, maintenance personnel avail-
ability, parts availability, anc
Obviously, all jobs cannot be as
potential effect on emissions,
boiler or process availability.
signed 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. Ah example of a five-
level priority system is shown below in Table 6.6-1.
SECTION 6 - MODEL O&M PLAN
241
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TABLE 6.6-1. WORK ORDER ..PRIORITY SYSTEM
Priority
Action
1
2
3,4
Emergency Repair
Urgent repair to be completed during the day
Work which may be delayed and completed in the future
(during periods of low demand)
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
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 (mak-
ing 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
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 plan-
ning, 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
SECTION 6 - MODEL O&M PLAN
242
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3.
4.
5.
the staff and the size' q'f' the system. When emergency
repairs are required, tlhe work order may be completed
after the fact, and approval is not required.
Priority - Priority is
assigned according to job urgen-
cy on a scale of 1 to 5.
Work order number - The work order request number is
the tracking control number necessary to retrieve the
information from the computer data system.
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 aifield 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.
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 dejtailed but brief because the
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).
Estimated labor - Assignment of personnel and sched-
uling of outages of cejrtain equipment require the
inclusion of an estimate of man-hours, 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.
Material requirements - In many jobs, maintenance crews
will remove components before a detailed analysis of
the needed materials can be completed; this can-extend
SECTION 6 - MODEL O&M PLAN
243
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an outage while components or parts are ordered and re-
ceived 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 identi-
fied before any removal effort begins. If the mainte-
nance supervisor knows in advance what materials are to
be replaced, expended, or removed, efficiency is in-
creas'ed 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 ID 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
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 com-
puterized tracking system is not to satisfy the needs of the ac-
countants 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
SECTION 6 - MODEL O&M PLAN
244
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equipment failures, system/unit outages, and emission excursions.
The O&M staff and AQCS manager iriust clearly define the kinds of
data to be collected, the level of detail, and the type of anal-
ysis required prior to the purchase/lease of any computer equip-
ment and the preparation of the
software.
data-handling and report-writing
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 input and accessed interactively
via remote terminals on either a mainframe or minicomputer. The
operator utility may even choose^ to purchase and operate its own
computer and time-share versus leasing computer space. The
operator utility must weigh many factors before choosing any of
the above alternatives. The ke4- 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 man-hours, operating parameters, and service
hours.
If the work completed and parts used are documented on the
work orders (see Section 5.2.3 -md 6.6) and entered into the
computerized tracking system wi;h sufficient detail, maintenance
and management personnel can easily evaluate the effectiveness of
FGD system maintenance.
Preventive maintenance (ses Section 2.5.3.6) man-hours
versus reactive maintenance manphours can be compared to evaluate
the effectiveness of the current preventive maintenance (PM)
program. The level of detail mLy 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
SECTION 6 - MODEL O&M PLAN
245
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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 so that it can be analyzed/correlated along
with the other data items. This type of data can also be uti-
lized to evaluate overall FGD system operation through the devel-
opment of dependability factors such as FGD system availability
and reliability.
SECTION 6 - MODEL O&M PLAN
246
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SAFETY
The safety of agency personnel during field inspections is
of primary importance. The fiel
3. inspector should take adequate
precautions to guard against inhalation of toxic gases, skin
irritation or chemical burns, and 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 againsb falling objects. During an FGD
inspection, many of these conceris are simultaneous and can re-
sult 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
dresses proper safety procedures
of the potential hazards and ad-
Further information concerning
safety precautions/considerations can be found in specific vendor
equipment O&M manuals for the FGD systems and subsystems, Occupa-
tional 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
present in and around areas.of t
asphyxiants.
Irritants are gases, which
mildly irritating to the eyes, t
of toxic gases which can be
lie FGD systems: irritants and
at very low concentrations are
tiroat, upper respiratory system,
SECTION 7 - SAFETY
2j47
-------
and nervous system. At higher levels, they can even cause death.
Sulfur dioxide and hydrogen sulfide (E^S) are both irritants
which are present in boiler flue gas. Sulfur dioxide is present
in much greater concentration than H-S.
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 SO? 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 SO2 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. Because the gas renders the olfactory nerve ineffective,
an inspector may be lulled into a false sense of security not
realizing 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
SECTION 7 - SAFETY
248
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coal. Exposure to high levels-df CO can, over prolonged periods,
lead to death. The TLV for CO is 50 ppm (0.005 percent by vol-
ume) .
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
closed or pressurized with adegv
dampers may not be properly
ate 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 caseous concentrations within the
equipment area.
7.2 SKIN IRRITATION AND/OR CHEMICAL BURNS TO THE SKIN
i
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 oc-
cur 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 overhead. 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 se-
vere 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,
SECTION 7 - SAFETY
249
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or abrasive nature. Section 7.3 discusses potential locations of
these dust sources in the FGD system. Inspection personnel can
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, or by plant and agency personnel. Fugitive dust around the
FGD system may consist of any or all of the following materials:
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.
SECTKDN 7 - SAFETY
250
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7.4 NORMAL INDUSTRIAL SAFETY PRACTICES
This section discusses normal industrial safety practices
which should be followed during plant inspections. The field
inspector should take to the plant or obtain from plant personnel
the necessary personal protectiv4 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 any jewelry,
neck ties, and other loose objects prior to the inspection 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,1 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 (pages or are too strenuous to
climb. Use of a flashlight is recommended when inspecting inte-
riors 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 open-
ings, hoses, tools, equipment items), and damaged or worn surfac-
es. Finally, the field inspector should be wary of overhead
hazards such as falling objects
head clearance areas (e.g., piping, steel supports).
(e.g., tools, slurry) and low
SECTION 7 - SAFETY
251
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7.
8.
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. I
I
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. O., 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. Rosenberg, H., et al. Lime FGD Systems Data Book. FP-1030.
Research Project 982-1. Prepared for Electric Power Re-
search Institute, Palo Altol 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.
!
ilu
Kenney, S. M., et al. Failure Mode Analysis for Lime/
Limestone FGD Systems. Voliitne 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.
Jahnke, J. A., and G. J. Aldina. Continuous Air Pollution
Source Monitoring Systems. Prepared for U.S. Environmental
Protection Agency, Environmental Research Information
Center, Research Triangle Park, North Carolina. EPA-625/6-
79-005. June 1979.
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.
REFERENCES
R-l
-------
REFERENCES (continued)
10.
11,
12,
13,
Kashdan, E. R., and M. B. Ranade. Design Guidelines for an
Optimum Scrubber System. Prepared for U.S. Environmental
Protection Agency, Environmental Research Information
Center, Research Triangle Park, North Carolina. EPA-600/7-
79-018. January 1979.
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.
Steam Electric Plant Factors.
Washington, D.C. 1983.
National Coal Association,
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.
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.
REFERENCES
R-2
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APPENDIX A
GLOSSARY OF TERMINOLOGY
APPENDIX A - GLOSSARY OF TERMINOLOGY
A-l
-------
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 SO pollutants.
X
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 rake underflow solids to a center discharge sump.
Alkaline fly ash scrubbing - An FGD process that uses the alkaline constit-
uents of fly ash collected from 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 conditions (pressure, air quality, temperature,
etc.) 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.
Atomizer - 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-2
-------
Ball mill - A rotating drum loaded wi
slurry materials, such as limestone,
cient chemical reactivity.
th steel balls that is used to crush and
to. a particle size suitable for effi-
Base load - A generating station whicjh is normally operated to take all or
part of the normal load of a system and which, consequently, operates at a
constant output.
Blanketing plate -.The simplest of dahipers consisting of a steel plate which
is bolted into place to close off and! isolate ducts and/or scrubbers.
Blinding (reagent) - A phenomenon where chemical reaction of a reagent par-
ticle in a scrubbing slurry is primarjily 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 moleclules that are to be collected.
Bottom ash - Heavy solid particles of
bottom of the boiler.
noncombustible ash that fall to the
British thermal unit (Btu) - The amoupt of heat required to raise the tem-
perature 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 F6D system above dew pbint by ducting a slip stream of parti-
cle-cleaned flue gas from the ESP exit duct past the F6D system to the ab-
sorber outlet duct or directly to the
acid rainout.
Byproduct (recoverable byproduct) -
regenerable-type FGD systems.
stack, preventing stack damage from
Saleable materials produced by various
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). I
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 consisting 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
housing.
A-3
-------
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 F6D system is closed when the 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.
Cpcurrent flow - The process in which absorbent liquor or slurry enters the
absorber from the same direction as the gas stream so that S02 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 that consists of a combination of two or more
types of absorbers 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 measuremen'
continuous stack monitors).
take readings or measurements on a continual basis (e.g., SO , NO , 02, etc.
. • _». i • .•_ \ /\/\
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 abs-orbent liquor or slurry enters
the absorber tower from the opposite direction of the gas stream so that S02
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 S02 collection
occurs as the gas 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 to effect particle collection.
A-4
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Damper - A plate or set of plates or |1 Olivers in a duct used to stop or regu-
late gas flow. i
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 the absorber above dewpoint; this is
accomplished by injection of the hot
non-saleable waste from an FGD system
mine filling, etc.
combustion products generated by oil or
gas reheater burners into the gas stream.
Disposal (also referred to as waste disposal) - Removal of and discarding of
in the form of ponding, landfill ing,
Dolomite (dolomitic lime or limestone) - A crystallized mineral consisting of
calcium magnesium carbonate (CaMg(C03i)2).
Efficiency - Ratio of the amount of a
pollutant removed to the total amount
introduced to the normal operation.
End product:
Salable - The S0§ removed from tjhe flue gas is recovered in a usable or
Salable - The SO, removed from td
marketable form (e.g., gypsum).
Throwaway - The S02 removed from' the flue gas is not recovered in a
usable or marketable form, and tjhe 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) -
equivalent MW based on the percent of
The effective scrubbed flue gas in
Erosion - The action or process of wearing away of a material by physical
means (friction).
ESP (electrostatic precipitator) - An
particles from an exhaust stream by i
and then collecting them on opposite!,
Excess air (percent) - The percentage
excess of that theoretically required
air pollution device used to remove
m'tially charging them with electrodes
y charged plates.
of air supplied for combustion in
for complete oxidation.
flue gas scrubbed by the FGD system.
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 vary-
ing 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 (S02, temperature, pH, etc.) is fed back after scrubbing
has taken place and is used as the basis for control of the process variable
(reagent feed, steam, etc.).
Feedforward control - An automatic control system which measures an upstream
process variable (gas flow rate, temperature, slurry flow rate, and/or pH,
etc.) and compensates immediately without waiting for a change in the con-
trolled variable (S02, 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 limits - 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-0-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 S02 to the scrubbing liquor or
slurry.
A-6
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Gas/liquid 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
liquor. |
Guillotine damper - A damper whose bperation 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 immedi
heater.
ately upstream of the boiler air pre-
ID (induced draft),- A fan used to move an enclosed stream of gases by creat-
ing a negative relative pressure in the stream to pffprtiviaiv Hraw tho nac
ing a negative relative pressure in
through the system.
the stream to effectively draw the gas
Indirect hot air - A flue gas reheat system in which reheat is achieved by
heating 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-
_ ____ ~ —-.„. . w . . ^ v . • • • w WM • i X-w ill IfllV* TV V_ I* I IUG MUW UU\*> l« VlwWIl
stream of the mist eliminator, usually consisting of hot water or steam coils
used to boost the wet flue gas tempejrature above dewpoint.
Knock-out tray - A wash-tray type prje-mist eliminator using valve or bubble-
cap type mechanisms to capture the b'ulk of the entrained solids, droplets,
and mist carrying over from the scrubber/absorber of an FGD system.
Landfi11 - A method of waste disposal in which the dried FGD byproduct wastes
are dumped and packed, or buried betjween layers of earth near ground level or
below ground level. i
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, 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 averaje load in kilowatts supplied during a
designated 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 linked 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 resulting from evaporation and
exiting waste streams.
Mechanical dewatering equipment - Devices used to decrease the moisture level
of FGD waste to the point where 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.
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.
Primary collector - A mist eliminator that removes entrained solids,
water droplets, and mist not collected by the precollector.
Mist eliminator passes/stage - The number of direction changes the gas stream
must make before it exits the mist eliminator stage.
Hist eliminator stages - The number of 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 106 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.
NO - A symbol meaning oxides of nitrogen (e.g., NO and N02).
^™"™""V\ ^
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 physicall^ bonded to the sludge product.
\
Outage - That period of time when thejboiler and/or FGD system is shut down
for inspection and maintenance. Outages may be either forced or scheduled.
!
Overflow (also supernatant) - The cle^r 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 are4-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
mum load periods.
operated to provide power during maxi-
Perforated tray absorber - Pollution dontrol 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.
pti - The hydrogen ion concentration of a water or slurry to denote acidity or
alkalinity.
pH meter - Electronic instruments which measure the potential difference
between a reference half-cell electrode and an indicator electrode sensitive
to hydrogen ions.
Plume (stack plume) - The visible emission from a flue (stack).
T
ppm (parts per million) - Units of concentration that in wastewater applica-
tions is equal to milligrams per liter and in air pollution applications is
equal to moles of pollutant to million moles dilutent.
Preheater - Heat transfer apparatus through which ambient air is passed and
heated by higher temperature boiler f
ue 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.
-9
-------
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 S02 removal efficiency).
Process type - The generic name for the FGD process based on the absorbent
used (e.g., lime, limestone) except for a few specialized processes which are
referred to by patented titles.
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
mills, pug mills, etc.).
Reagent utilization (also 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., CaS03, 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 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. 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.
SO, - The actual percentage of SO,
system.
removed from the flue gas by the FGD
A-10
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Total unit design - The designed percentage of mass of S02 or particu-
late matter entering the stack to. the mass of the material in the flue
gas exiting the boiler regardless of the removal efficiency of an indi-
vidual component or the percentage of the exiting flue gas actually
being scrubbed.
Residence time - The amount of time
a pollution control device.
unit volume of gas or liquid spends in
Retrofit - The FGD unit will be/was added to an existing boiler not specif-
ically designed to accommodate an FGD system.
Rod deck absorber - Gas/liquid contacting device used for pollutant removal.
Untreated flue gas is contacted counllercurrently with slurry with mixing
being aided by decks of cylindrical rods positioned perpendicular to the gas
and liquor 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, the original purpose of which is pollutant
removal, which can be resold (e.g., gypsum).
Saturated - The situation when a gas
No additional amount
certain substance.
under the given conditions.
or liquid is filled to capacity with a
of the same substance can be added
Saturation tempera t u re - The temperature to which flue gas drops when it is
saturated by scrubbing in a wet FGD system.
Scale - Deposits of slurry solids (calcium sulfite or calcium sulfate) that
adhere to the surfaces of FGD equipment^particularly absorber/scrubber
internals and mist eliminator surfaces!
Scheduled outage - A planned period of time set aside periodically for in-
spection 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
dewatering equipment. Absorber bleed
the pond and supernatant drawn off at
absorber reuse. Settling ponds may o
Slaker - Mechanical devices which sla
oxide into calcium or magnesium hydroxide alkali.
is normally introduced at one end of
the other end and recycled back for
may not be final disposal areas.
-------
Sludge - The material containing high concentrations of precipitated reaction
byproducts and -solid matter collected and/or formed by the F6D process (com-
posed primarily of calcium-based reaction byproducts, excess scrubbing reagent,
flyash, and scrubber liquor).
Sludge disposal (also waste disposal) - Removal of and discarding of non-
saleable waste from an F6D system in the form of ponding, landfill ing, 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).
SOV - A symbol meaning oxides of sulfur (e.g., S02 and S03).
""""'X
Spray tower - Gas/liquid contacting device used for pollutant removal.
Untreated gas is contacted countercurrehtly, crosscurrently, or cocurrently
with scrubber liquor via spray nozzles in a horizontal or vertical chamber.
Stabilization - Physical stabilization is accomplished by reducing the
moisture 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
d i fferent gas violume flow rates (60°F, 1 atmosphere pressure).
Stoichiometric ratio - 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 F6D system.
Supernatant (also 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 - A measure of tpe moisture content of air (gas) indi-
cated by a wet bulb psychometer.
Theoretical kWh production - Period ho
capacity in kilowatts.
Thickener - A continuous settling basi
from influent to underflow.
jrs multiplied by gross unit operating
i used to increase solids concentration
Throwaway end product - Those byproduct materials formed by F6D systems which
have no resale value with or without additional processing.
Total controlled capacity (TCC) - The gross rating (MW) of a unit brought
into complian
the facility.
capa<
into compliance with FGD, regardless of the percent of flue gas treated at
Tray tower - Gas/liquid contacting dev
ce 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 dewatsring 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! S02 removal or causing unstable opera-
tion.
Underflow - Concentrated solids flow f
ener.
Unit rating:
rom the bottom of an absorber or thick-
Gross - Maximum continuous generating capacity in MW.
Net - Gross unit rating less the (energy required to operate ancillary
station equipment, inclusive of enission control systems.
Utilization (also reagent utilization) - That fraction of reagent material
(e.g., lime, limestone, etc.) fed to the FGD system which is consumed (uti-
lized) and chemically converted into p
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).
oduct material (e.g., CaS03, CaSOiJ.
-.1.3
-------
Water loop - All aqueous mass flows from inlet (e.g., seal water, quench
water, scrubber liquor) to outlet of an F6D system (e.g., evaporation via
stack, pond evaporation, waste disposal).
Water losses - Water leaving the F6D system via the stack (evaporation),
pond, and thickener or that is chemically or physically bonded to the waste
disposal product.
Het 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 tributaries would be prohibited).
A-14
-------
APPENDIX B
EQUATIONS FOR CONVERTING
POLLUTANT CONCENTRATIONS TO
NSPS
UNITS
APPENDIX B - EQUATIONS FOR CONVERTING POLLUTANT CONCENTRATIONS TO NSPS UNITS
B-l
-------
EQUATIONS FOR CONVERTING POLLUTANT CONCENTRATIONS
(lb/ft3) TO NSPS UNITS (lb/106 Btu)*
106 C5.56(XH)+1.53(XC)+0.57(aSS)+0.14(%N)-0.46(XOi,)+0.21(%HgO)]
• in- i in— i *" *" ' • "
w
GCT
20.9
" wsw 20.9 (1 - Bwa) - % 02w
Where:
F = Coal analysis factor on a wet basis, std. ft3/106 Btu
W
6CV (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
B = Ambient air moisture fraction
wa
02 = Percent oxygen in flue gas on a wet basis
Note: Standard FW factors for coal:
Bituminous - 10,680-
Subbituminous - 11*500
Lignite - 12,000
Refer to Section 3.1.1.4.
B-2
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APPENDIX C
I .... ....
FGD SYSTEM INSPECTION CHECKLIST
APPENDIX C - FGD SYSTEM INSPECTION CHECKLIST
C-l
-------
FGD SYSTEM INSPECTION CHECKLIST
GENERAL INFORMATION
Utility/Plant Name
Plant Address
Plant Representative
Plant Manager
Inspector Agency Name
Inspector Name
Date
Phone No.
Phone No.
Phone No.
PLANT DATA (Table 4.1-1)
Boiler Data
Type of firing (pulverized, cyclone)
Boiler service load (base, intermediate,
cyclic, peak)
Date of commercial operation (month, year)
S00 emission limitation, lb/10 Btu
' 6
Participate emission limitation, lb/10 Btu
Opacity limitations, %
Fuel firing rate at maximum continuous rating,
tons/hr
Heat rate, Btu/net kWh
Average capacity factor, %
Gross generating capacity, MW
Outlet flue gas flow, acfm
Outlet flue gas temperature, °F
Fuel Data
Design
Average heat content, Btu/lb
Average ash content, %
Actual
C-2
-------
Fuel Data (continued)
Design
Actual
0 Average moisture content, %
° Average sulfur content, %
0 Average chlorine content, %
General FGD System Data
0 FGD process type (lime, limestone)
0 Generation type (first, secpnd, or third)
0 Application (new/retrofit)
0 Initial startup date
0 Commercial startup date
0 Total system design S02 removal efficiency,
Percent flue gas bypassing
rGD system, %
Total system energy consumption, kWh
Annual reagent consumption,
tons/year
Water loop type (open, closed)
Waste disposal type (landfi
Solid waste generation rate
11, pond)
(dry), tons/hr
Total system makeup water consumption, gpm
Number of operators per shirt
Number of maintenance personnel per shift
Maintenance philosophy (dedicated, rotated,
pooled)
CONTROL ROOM
Observation
(Table 4.2-1)
Operator indicated location; of FGD monitors?
All monitors operational?
Operation and Maintenance
0 Reason/corrective action regarding non-operational FGD monitors.
Yes
Yes
No
No
C-3
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Operation and Maintenance (continued)
0 Emission Readings
S02, ppm
0 Particulate, gr/scf
0 Opacity, %
Design
Actual
Facility has computerized control
with CRT displays,
CRT Readings
Yes
No
GAS HANDLING AND TREATMENT
FAN (Table 4.2-2)
Observation
Excessive fan vibrations [ ] Yes [ ] No. If yes, note readings
and inquire why.
Signs of debris/maintenance.
Signs of corrosion/location.
C-4
-------
Process
Fan function, design application service, and location
Unit/booster
ID/FD
Centrifugal/axial
Wet/dry
Design
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.
Actual
Routine maintenance procedures/inspection schedules.
Us/
Observation
>n
Signs
SCRUBBER/ ABSOR
of debris/maintenance
5ER (Table 4.2-3)
C-5
-------
Observation (continued)
0 Signs of materials failure/location.
Process
Signs of leaky piping.
Signs of leaks on absorber vessel walls.
Design
Actual
Inlet particulate grain
loading, gr/scf
Outlet particulate grain
loading, gr/scf
Inlet S02 concentration, ppm
Outlet S02 concentration, ppm
Absorber L/6, gal/1000 acfm
Absorber AP, in. H20
Slurry solids content in
absorber reaction tank, %
Slurry pH in absorber reaction
tank
Operation and Maintenance
° Absorber failure incidences/causes/remedial actions.
C-6
-------
Operation and Maintenance (continued)j
0 If idle, inquire why and inspect internals (if possible).
0 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
Erosion/corrosion
Signs of mist eliminator carryover in downstream equipment.
0-7
-------
Process
Design
Actual
0 Mist eliminator AP, in. H20
0 Absorber pH
0 Mist eliminator flue gas 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
-------
Observation (continued)
0 Discarded reheater tubes/causes of failure.
If operational, check nearby ductwork for corrosion caused by
reheater malfunctions.
Process ,
0 In-line reheater AP, in. H9()
Design
Actual
Reheater energy consumption
rate, kW
Reheater inlet temperature,
Reheater outlet temperature
Is reheater outlet temperat
, °F
Operation and Maintenance
In-line tube failure incide
jre above acid dew point? [ ] Yes [ ] No.
ices/causes/remedial actions.
Tube type/baffle and materi
ils of construction.
Plugging problems encountered with in-line reheaters.
C-9
-------
Operation and Maintenance (continued)
0 Reheater failure incidences/causes/remedial actions.
Cleaning techniques utilized [ ] Automatic [ ] Manual
0 Routine maintenance procedures/inspection schedules.
DUCTWORK/DAMPER (Table 4.2-6)
Observation
Signs of ductwork/damper corrosion/severity and location.
Check for ruptured expansion joints/location.
Newly installed ductwork/reasons for replacement.
C-10
-------
Observation (continued)
0 Does actual bypass ducting
[ ] Yes [ ] No. If no, i
agree with original system design?
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/dampens are subject to.
0 Is ductwork lined? [ ] Yes
construction are used?
[ ] No. If yes, what materials of
Ductwork/damper problems due to mist eliminator carryover/causes/
remedial actions.
Q-ll
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Operation and Maintenance (continued)
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 CONVEY*
Observation
0 Signs of belt misalignment,
0 Signs of leaks on pneumatic
0 Signs of bucket elevator de
0 Conveyor duties/problems.
Operation and Maintenance
0 Conveyor failure incidences,
)R (Table 4.2-7)
tears, or frayed edges.
conveyor lines.
>r is/ jamming/maintenance.
- . ,
'causes/remedial actions.
;-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
0 Failures caused by poor reagent quality/undersizing.
Water source/problems.
C-14
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Operation and Maintenance i
0 Ball mill failure incidences'/causes/remedial actions.
Routine maintenance procedures/inspection schedules.
res/ii
SLAKER (Table 4.2-9)
Observation
Is slaker operational? [ ]
Yes [ ] No. If no, inquire why.
Process
Dry reagent feed rate of si a
Slaker capacity problems/cat
ker, tons/hr. [ ] Actual [ ] Design.
ses.
Failure caused by poor reagent quality.
G-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
Signs of tank repairs/maintenance.
C-16
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Observation (continued)
0 Note tank configuration/associated failures.
0 Note if tanks are covered or open.
If open, check for floating
debris/associated failures.
Signs of slurry leakage.
Operation and Maintenance
Tank(s) drained to repair 1
iners/bafflers.
0 Problems associated with taik 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 debr,is/ass.ociated failures.
C-18
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Process
Design
Actual
Overflow rate, gpm
Underflow rate, gpm
Solids content in underflow, %
Sulfite/sulfate ratio of inlet
slurry
How is thickener overflow used?/rate (gpm).
and Maintenance
Is thickener rake drive sli
control alarm system? [ ]
Problems with rake binding
lift and motor equipped with a torque
Yes [ ] No.
or rake drive shaft/motor failure.
Problems with sump failures.
0 Problems with liner failun
0 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
Inspect filter cloth for tears.
Check for spare or discarded filter cloths.
Check filter cake consistency/product quality.
Process
o
o
o
Filter cake production rate,
tons/hr
Solids content of filter cake,
Inlet slurry solids content, %
Wastewater effluent production
rate, gpm
S.ulfite/sulfate ratio in
filter cake
Design
Actual
C-20
-------
Process (continued) j
0 Inlet slurry solids content Adequate? [ ] Yes [ ] No.
0 How is the vacuum filter filirate used?/rate (gpm)
Operation and Maintenance
0 Problems/failures associated
with vacuum filtrate pump.
Problems regarding filter cloth replacement
Filter cake conveyor failures.
0 Vacuum filter failure incidejices/causes/remedial actions
0 Routine maintenance procedures/inspection schedules.
es/ii
C-21
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CENTRIFUGE (Table 4.2-13)
Observation
Process
Q
O
O
Centrifuge(s) operational? [ ] Yes [ ] No. If no, inquire why.
0 Check centrifuge cake consistency/product quality.
Design
Actual
Filter cake production rate,
tons/hr
Solids content of filter cake,
Inlet slurry solids content, %
'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)
0 Centrifuge failure incidences/causes/remedial actions.
Process
Routine maintenance procedur
WASTE PROCESSING SY
js/inspection schedules.
STEM (Table 4.2-14)
Type of waste processing system:
[ ] forced oxidation [ ] ffixation [ ] stabilization [ ] none
What is the energy consumption rate? Is this typical or excessive?
Operation and Maintenance
0 Problems associated with the
equipment area.
Waste processing failure indidences/causes/remedial actions.
]-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.
0 Locate and inspect abrupt expansion, contraction, and bends in
piping around valves/note any problems.
Process
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
0 Inquire about pump redundancy for different operations.
Operation and Maintenance
0 Pump failure incidences/causes/remedial actions.
Valve failure incidences/causes/remedial actions.
Routine maintenance procedures/inspection schedules.
C-26
ft U.S.GOVERNMENTPRINTSNQ OFFICE: 1985 - 559-111/20706
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