ABMA
American
Boiler Manufacturers
Association
1500 Wilson Boulevard
Arlington VA 22209
DoE
United States
Department
of Energy
Division of Power Systems
Energy Technology Branch
Washington DC 20545
EPA
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
EPA-600/7-81-111a
July 1981
Emissions and Efficiency
Performance of Industrial
Coal Stoker Fired Boilers
Interagency
Energy/Environment
R&D Program Report
-------
EPA-600/7-81-111a
July 1981
Emissions and Efficiency
Performance of Industrial
Coal Stoker Fired Boilers
by
P.L Langsjoen, J.O. Burlingame,
and J.E. Gabrielson
KVB, Inc.
6176 Olson Memorial Highway
Minneapolis, Minnesota 55422
lAG/Contract Nos, IAG-D7-E681 (EPA), EF-77-C-01-2609 (DoE)
Program Element No. EHE624
Project Officers: R. Hall (EPA), W. Harvey, Jr., and W. Siskind (DoE)
Industrial Environmental Research Laboratory
Office of Environmental Engineering and Technology
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
U.S. DEPARTMENT OF ENERGY
Division of Power Systems/Energy Technology Branch
Washington, DC 20545
and
AMERICAN BOILER MANUFACTURERS ASSOCIATION
1500 Wilson Boulevard
Arlington, VA 22209 TT <, „ ,
u-s- Environmental Protection Agency
Region 5, Library (5PL-16)
230 S. Dearborn Street, Room 1670
Chicago, II 60604
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DISCLAIMER
This report has been reviewed by the Industrial Environ-
mental Research Laboratory (RTF), U.S. Environmental
Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the views
and policies of the Agency, nor does mention of trade names
or commercial products constitute endorsement or recommen-
dation for use.
ii
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ABSTRACT
The report gives results of field measurements of 18 coal stoker-fired
boilers including spreader stokers, mass-fired overfeed stokers, and
mass-fired underfeed stokers.
The test variables indued stoker design, heat release rate, excess air,
coal analysis and sizing, overfire air, and flyash reinjection. Measure-
ments included O2, CO2, CO, NO, NO2,SO2, SOs, gaseous hydrocarbons,
uncontrolled and controlled particulate mass loading, particle size dis-
tribution of the flyash, combustible content of ash, sulfur retention in
the ash, and boiler efficiency.
Particulate loading is shown to be largely dependent on stoker type and
degree of flyash reinjection. It increases with heat release rate, but can
be controlled with proper use of overfire air in many cases. Nitric oxide
increases with excess air and grate heat release rate. These relation-
ships are defined in the report. Overfire air, as it exists in current
boiler designs, does not affect NOx. The report also addresses other
relationships between operating variables and measured emissions and
efficiency.
A separate data supplement is available.
iii
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ACKNOWLEDGEMENTS
The authors wish to express their appreciation for the assistance and
direction given the program by project monitors W. T. Harvey and W. Siskind of
the United States Department of Energy (DOE) and R. E. Hall of the United States
Environmental Protection Agency (EPA). Thanks are due to their agencies, DOE
and EPA, for co-funding the program.
We would also like to thank the American Boiler Manufacturers Association,
ABMA Executive Director, W. H. Axtman, ABMA Assistant Executive Director, R. N.
Mosher, ABMA's Project Manager, B. C. Severs, and the members of the ABMA Stoker
Technical Committee Chaired by W. B. McBurney of the McBurney Corporation for
providing support through their time and travel to manage and review the program.
The participating committee members listed alphabetically are as follows:
R. D. Bessette Island Creek Coal Sales Company
D. Clayton Combustion Engineering, Inc.
T. Davis Combustion Engineering, Inc.
N. H. Johnson Detroit Stoker Company
W. E. Krauss Cleaver Brooks Division
K. Luuri Riley Stoker Corporation
K. J. McNamara Riley Stoker Corporation
D. McCoy E. Keeler Company
W. R. Murray Foster Wheeler Limited
E. A. Nelson Zurn Industries, Inc.
E. G. Poitras The McBurney Corporation
P. E. Ralston Babcock & Wilcox Company
D. C. Reschley Detroit Stoker Company
R. A. Santos Zurn Industries, Inc.
J. F. Wood Babcock & Wilcox Company
Finally, our gratitude goes to the host boiler facilities who invited
us to test their boilers. At their request, the facilities identification will
remain anonymous to protect their own interests. Without their cooperation and
assistance, this program would not have been possible.
This document has been reviewed and approved for publication by the
Stoker Technical Committee of the American Boiler Manufacturers Association
(ABMA), by the U. S. Environmental Protection Agency (EPA), and by the U. S.
Department of Energy (DOE).
iv
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TABLE OF CONTENTS
Section Page
ACKNOWLEDGEMENTS IV
TABLE OF CONTENTS V
LIST OF TABLES
LIST OF FIGURES
1.0 EXECUTIVE SUMMARY AND CONCLUSIONS
1.1 Summary of Findings Organized by Measured Parameter 4
1.2 Summary of Findings Organized by Test Variable 14
2.0 INTRODUCTION 23
2.1 The Need 23
2.2 The Objectives 24
2.3 The Project Organization 24
2.4 The Test Reports 25
3.0 SPREADER STOKERS 27
3.1 Description of Units Tested 27
3.2 Performance at Full Load 40
3.2.1 Emission Factors 41
3.3 Response to Heat Release Rate 56
3.3.1 Excess Air vs Heat Release Rate 57
3.3.2 Particulate Loading vs Heat Release Rate 62
3.3.3 Combustibles in the Flyash vs Heat Release Rate ... 66
3.3.4 Combustibles in the Bottom Ash vs Heat Release Rate . 68
3.3.5 Nitric Oxide vs Heat Release Rate 74
3.3.6 Carbon Monoxide vs Heat Release Rate 77
3.3.7 Unburned Hydrocarbons vs Heat Release Rate 79
3.3.8 Boiler Efficiency vs Heat Release Rate 79
3.4 Response to Excess Air 79
3.4.1 Particulate Loading vs Excess Air 82
3.4.2 Combustibles in the Ash vs Excess Air 84
3.4.3 Nitric Oxide vs Excess Air 84
3.4.4 Carbon Monoxide vs Excess Air ..... 88
3.4.5 Unburned Hydrocarbons vs Excess Air 88
3.4.6 Boiler Efficiency vs Excess Air 92
3.5 Response to Coal Analysis and Sizing 97
3.5.1 Particulate Loading vs Coal Properties 97
3.5.2 Combustibles in the Ash vs Coal properties 108
3.5.3 Sulfur Oxides vs Coal Properties Ill
3.5.4 Nitric Oxide vs Coal Properties Ill
3.5.5 Carbon Monoxide vs Coal Properties 118
3.5.6 Unburned Hydrocarbons vs Coal Properties 118
3.5.7 Boiler Efficiency vs Coal Properties 118
3.6 Response to Overfire Air 121
3.6.1 Particulate Loading vs Overfire Air 122
3.6.2 Combustibles in the Ash vs Overfire Air 125
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TABLE OF CONTENTS (Continued)
Section Page
3.6.3 Nitric Oxide vs Overfire Air 125
3.6.4 Carbon Monoxide vs Overfire Air ..... 128
3.6.5 Unburned Hydrocarbons vs Overfire Air 128
3.6.6 Boiler Efficiency vs Overfire Air ..... 131
3.7 Response to Degree of Flyash Reinjection ... 133
3.7.1 Test Description - Site A . . 133
3.7.2 Test Description - Site B ............... 135
3.7.3 Test Description - Site C 135
3.7.4 Particulate Loading vs Flyash Reinjection 136
3.7.5 Combustibles in the Ash vs Flyash Reinjection ..... 138
3.7.6 Particle Size Distribution vs Flyash Reinjection .... 142
3.7.7 Reinjection from an Economizer Hopper - Test Site F . . 151
3.7.8 Stratification and Density of Ash in Collection Hoppers 153
3.8 Particle Size Distribution of Flyash 154
3.8.1 Brink Cascade Impactor Test Results .......... 154
3.8.2 Bahco Classifier Test Results . 158
3.8.3 SASS Cyclone Test Results 161
3.8.4 Coulter Counter and Sieve Analysis Test Results .... 164
3.8.5 Combustibles vs Particle Size Distribution 164
3.8.6 Dust Collector Efficiency vs Particle Size Distribution. 167
4.0 MASS FIRED OVERFEED STOKERS . 171
4.1 Description of Units Tested 171
4.2 Performance at Full Load 185
4.3 Response to Heat Release Rate . 200
4.3.1 Excess Air vs Heat Release Rate • 201
4.3.2 Particulate Loading vs Heat Release Rate ... 201
4.3.3 Combustibles in the Flyash vs Heat Release Rate .... 209
4.3.4 Combustibles in the Bottom Ash vs Heat Release Rate . . 209
4.3.5 Nitric Oxide vs Heat Release Rate 214
4.3.6 Carbon Monoxide vs Heat Release Rate 219
4.3.7 Unburned Hydrocarbons vs Heat Release Rate 219
4.3.8 Boiler Efficiency vs Heat Release Rate ......... 219
4.4 Response to Excess Air 219
4.4.1 Particulate Loading vs Excess Air 223
4.4.2 Combustibles in the Ash vs Excess Air 224
4.4.3 Nitric Oxide vs Excess Air 224
4.4.4 Carbon Monoxide vs Excess Air 225
4.4.5 Unburned Hydrocarbons vs Excess Air ..... 228
4.4.6 Boiler Efficiency vs Excess Air .... ... 228
4.5 Response to Coal Analysis and Sizing 228
4.5.1 Particulate Loading vs Coal Properties 238
4.5.2 Combustibles in the Ash vs Coal Properties ....... 242
4.5.3 Sulfur Oxides vs Coal Properties 242
4.5.4 Nitric Oxide vs Coal Properties ............ 245
4.5.5 Carbon Monoxide vs Coal Properties 249
4.5.6 Unburned Hydrocarbons vs Coal Properties 249
4.5.7 Boiler Efficiency vs Coal Properties 249
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TABLE OF CONTENTS (Continued)
Section
4.6 Response to Overfire Air 251
4.6.1 Particulate Loading vs Overfire Air 252
4.6.2 Combustibles in the Ash vs Overfire Air 252
4.6.3 Nitric Oxide vs Overfire Air 252
4.6.4 Carbon Monoxide vs Overfire Air 253
4.6.5 Unburned Hydrocarbon vs Overfire Air 253
4.6.6 Boiler Efficiency vs Overfire Air 253
4.7 Particle Size Distribution of Flyash 264
4.7.1 Particle Size Distribution of the Uncontrolled Flyash . 264
4.7.2 Particle Size Distribution of the Controlled Flyash . . 270
4.7.3 Combustibles vs Particle Size Distribution 270
4.7.4 Dust Collector Efficiency vs Particle Size Distribution 272
5.0 MASS FIRED UNDERFEED STOKERS 275
5.1 Description of Units Tested 275
5.2 Coal Analysis and Sizing 275
5.3 Test Conditions 285
5.4 Particulate Emission Levels 285
5.5 Combustibles in the Ash 288
5.6 Boiler Efficiency 289
5.7 Particle Size Distribution of the Flyash 290
6.0 TEST EQUIPMENT AND PROCEDURES FOR SITES A THROUGH K 297
6.1 Gaseous Emissions Measurements 297
6.1.1 Analytical Instruments and Related Equipment 297
6.1.2 Wet Chemical Methods and Related Equipment 303
6.2 Particulate Measurement and Procedures 309
6.3 Particle Size Distribution Measurement and Procedure 309
6.4 Coal Sampling and Analysis Procedure 311
6.5 Ash Collection and Analysis for Combustibles 313
6.6 Boiler Efficiency Evaluation 314
6.7 Trace Species Measurement 314
7.0 TEST EQUIPMENT AND PROCEDURES FOR SITES LI THROUGH L7 315
7.1 Mass Emission Measurements and Procedures 315
7,2 Particle Size Distribution Measurement and Procedure 317
7.3 Coal Sampling and Analysis 320
7.4 Ash Collection and Analysis 322
7.5 Boiler Operating Performance and Efficiency 322
REFERENCES 323
APPENDIX A - Conversion Factors 326
APPENDIX B - Conversion Factors 327
APPENDIX C - SI Prefixes 328
APPENDIX D - Emission Units Conversion Factors For Typical Coal Fuel 329
APPENDIX E - Ordering Information for Site Reports 330
vii
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TABLES
Number Page
1-1 Unit Description and Data Base 1
1-2 Range of Data Encountered at High Load 3
3-1 Description of Spreader Stokers Tested ..... 27
3-2 Equipment Data - Test Site A 28
3-3 Equipment Data - Test Site B 30
3-4 Equipment Data - Test Site C 32
3-5 Equipment Data - Test Site E 34
3-6 Equipment Data - Test Site F 36
3-7 Equipment Data - Test Site G 38
3-8 Capacity Range and Data Base for Full Load Tests on Six Spreader
Stokers ......... 40
3-9 Emission Factors for Spreader Stokers Firing Bituminous Coal .... 42
3-10 Emission Factors for Spreader Stokers Firing Sub-Bituminous Coal . . 42
3-11 Design Heat Release Rates 57
3-12 Increase in Uncontrolled Particulate Loading for Each 103Btu/hr~ft2
Grate Area Increase 62
3-13 Uncontrolled Particulate Loading vs Design Heat Release Rates ... 66
3-14 Coefficients from Multiple Regression Analysis on Nitric Oxide Data
from Spreader Stokers ......... 76
3-15 Nitric Oxide vs Design Variables , 77
3-16 Relationship Between Nitric Oxide and Excess Air at Constant Load . 84
3-17 Coal Identification and Classification Spreader Stokers 98
3-18 Proximate Coal Analysis Spreader Stokers . 99
3-19 Ultimate Coal Analysis Spreader Stokers . 100
3-20 Fusion Temperature of the Ash Reducing Atmosphere - Spreader Stokers 101
3-21 Mineral Analysis of the Ash Spreader Stokers ...... 102
3-22 As-Fired Coal Size Consistency Spreader Stokers . . ... 103
3-23 Ash Balance Spreader Stokers 107
3-24 Sulfur Retained in the Ash . ............... 115
3-25 Average Heat Losses at Site C, Percent 121
3-26 Effect of Overfire Air on Uncontrolled Particulate Loading
Spreader Stokers ................ 123
3-27 Effect of Overfire Air on Combustibles in Flyash Spreader Stokers . 126
3-28 Effect of Overfire Air on Nitric Oxide Emissions Spreader Stokers . 127
3-29 Effect of Overfire Air on Carbon Monoxide Emissions Spreader Stokers 129
3-30 Effect of Overfire Air on Heat Losses and Efficiency Spreader
Stokers . ................ 132
3-31 Summary Tables for Flyash Reinjection Test Sets on Sites A, B and C 134
3-32 Particulate Loading Data for Five Reinjection Rate Test Sets .... 137
3-33 Reduction in Particulate Loading Due to Reduced Re injection Rate . . 137
3-34 Uncontrolled Particulate Loading at Full Load ........... 138
3-35 Increase in Combustible Content of Flyash Due to Reduced Reinjection
Rate .......... ............... 141
3-36 Dust Collector Efficiency and Particle Size Distribution vs
Reinjection Rate ................... 142
3-37 Particulate Loading vs Flyash Reinjection Test Site F . . 151
3-38 Boiler Hopper Ash Distribution at Site C • • 153
3-39 Economizer Ash Distribution at Site F ............... 153
3-40 A Comparison of Brink and EPA Method 5 Dust Loading Data 155
3-41 Average Brink Cascade Imp-actor Data for Spreader Stokers ...... 155
viii
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TABLES
(Continued)
Number
3-42 Collection Efficiency of Bahco Samples ......
3-43 Average Bahco Classifier Data for Spreader Stokers
3-44 Average SASS Cyclone Data For Spreader Stokers . .
3-45 Average Sieve Analysis Data for Spreader Stokers .
3-46 Combustibles vs DC Hopper Ash Sizing Site A ...
3-47 Combustibles vs Boiler Outlet Flyash Sizing Site B
4-1 Description of Mass Fired Overfeed Stokers Tested 171
4-2 Equipment Data - Test Site D 172
4-3 Equipment Data - Test Site H • 174
4-4 Equipment Data - Test Site I 176
4-5 Equipment Data - Test Site J 178
4-6 Equipment Data - Test Site K 180
4-7 Equipment Data - Test Site L2 182
4-8 Equipment Data - Test Site L4 183
4-9 Capacity Range and Data Base for Full Load Tests on Seven Mass Fired
Overfeed Stokers 185
4-10 Emission Factors for Mass Fired Overfeed Stokers Firing Bituminous
Coal 186
4-11 Design Heat Release Rates 200
4-12 Increase in Uncontrolled Particulate Loading for Each 10%tu/hr-ft2
Grate Area Increase 206
4-13 Coefficients for an Equation of the Form 214
4-14 Nitric Oxide vs Design Variables 216
4-15 Uncontrolled Particulate Loading vs Excess Air 223
4-16 Combustibles in the Ash vs Excess Air for Mass Fired Overfeed
Stokers 224
4-17 Nitric Oxide vs Excess Air at Constant Load 225
4-18 Coal Identification and Classification Mass Fired Overfeed Stokers . 232
4-19 Proximate Coal Analysis Mass Fired Overfeed Stokers 233
4-20 Ultimate Coal Analysis Mass Fired Overfeed Stokers 234
4-21 Fusion Temperature of the Ash Reducing Atmosphere Mass Fired Over-
feed Stokers 235
4-22 Mineral Analysis of the Ash Mass Fired Overfeed Stokers 236
4-23 As-Fired Coal Size Consistency Mass Fired Overfeed Stokers 237
4-24 Particulate Loading vs Coal Properties Test Site K 239
4-25 Ash Balance Mass Fired Overfeed Stokers 243
4-26 Sulfur Retained in the Ash 245
4-27 Boiler Efficiency vs Coal Properties at Site K, High Load 251
4-28 Effect of Overfire Air on Uncontrolled Particulate Loading Mass
Fired Overfeed Stokers 254
4-29 Effect of Overfire Air on Combustibles in Flyash Mass Fired Over-
feed Stokers 256
4-30 Effect of Overfire Air on Nitric Oxide Emissions Mass Fired Over-
feed Stokers 258
4-31 Effect of Overfire Air on Carbon Monoxide Emissions Mass Fired Over-
feed Stokers 260
4-32 Effect of Overfire Air on Heat Losses and Efficiency Mass Fired
Overfeed Stokers 263
4-33 Average Size Distribution of Uncontrolled Flyash for Overfeed Stoker 264
ix
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Number
TABLES
(Continued)
4-34 Combustibles vs Boiler Hopper Ash - Site D
4-35 Combustibles vs DC Hopper Ash - Site J
4-36 Efficiency with Respect to Particle Size .
5-1 Description of Mass Fired Underfeed Stokers Tested
5-2 Equipment Data - Test Site LI
5-3 Equipment Data - Test Site L3
5-4 Equipment Data - Test Site L5
5-5 Equipment Data - Test Site L6
5-6 Equipment Data - Test Site L7
5-7 Coal Identification and Classification Mass Fired Underfeed Stokers
5-8 Proximate Coal Analysis Mass Fired Underfeed Stokers
5-9 Ash Softening Temperature and Free Swelling Index Mass Fired Under-
feed Stokers . . . .
5-10 As-Fired Coal Size Consistency Mass Fired Underfeed Stokers . . . .
5-11 Boiler Firing Conditions
5-12 Particulate Loading Data for Five Underfeed Stokers
5-13 Particulate Emission Factors Lb/Ton Mass Fired Underfeed Stokers . .
5-14 Combustibles in the Ash Mass Fired Underfeed Stokers
5-15 Heat Losses and Efficiencies Mass Fired Underfeed Stokers
5-16 Average Size Distribution Data for Underfeed Stokers
5-17 Efficiency with Respect to Particle Size
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FIGURES
Number Page
3-1 Test Site A General Arrangement Drawing 29
3-2 Test Site B General Arrangement Drawing 31
3-3 Test Site C General Arrangement Drawing 33
3-4 Test Site E General Arrangement Drawing 35
3-5 Test Site F General Arrangement Drawing ...... 37
3-6 Test Site G General Arrangement Drawing 39
3-7 Grate Heat Release Rates of Six Spreader Stokers Fired at Full Load 43
3-8 Excess Air Operating Levels of Six Spreader Stokers Fired at Full
Load 44
3-9 Excess Oxygen Operating Levels of Six Spreader Stokers Fired at
Full Load . • • 45
3-10 Uncontrolled Particulate Loadings for Three Spreader Stokers Fired
at Full Load with Flyash Reinjection from the Mechanical Collector 46
3-11 Uncontrolled Particulate Loadings of Four Spreader Stokers Fired at
Full Load without Flyash Reinjection from the Mechanical Collector 47
3-12 Percentage of Combustible Material in the Boiler Outlet Flyash of
Six Spreader Stokers Fired at Full Load 48
3-13 Percentage of Combustible Material in the Bottom Ash of Six Spreader
Stokers Fired at Full Load 49
3-14 Nitric Oxide Emissions of Six Spreader Stokers Fired at Full Load . 50
3-15 Carbon Monoxide Emissions of Five Spreader Stokers Fired at Full
Load 51
3-16 Unburned Hydrocarbon Emissions of Two Spreader Stokers Fired at
Full Load . 52
3-17 Heat Loss Due to Combustibles in the Flyash of Six Spreader Stokers
Fired at Full Load 53
3-18 Heat Loss Due to Combustibles in the Bottom Ash of Six Spreader
Stokers Fired at Full Load 54
3-19 Boiler Efficiency of Six Spreader Stokers Fired at Full Load ... 55
3-20 Excess Air vs Grate Heat Release 58
3-21 Excess Air Profiles for Six Spreader Stokers Representing Normal
Operating Conditions 60
3-22 Excess Air Operating Levels of Six Spreader Stokers Showing a Cor-
relation with Size of Grate. The Data Represents a Grate Heat
Release Rate of 500,000 Btu/hr-ft2 ........ 61
3-23 Uncontrolled Particulate Mass Loading Trends with Grate Heat Re-
lease for Six Spreader Stokers 63
3-24 Uncontrolled Particulate vs. Grate Heat Release . 64
3-25 Controlled Particulate vs. Grate Heat Release 65
3-26 Flyash Combustible Profiles for Spreader Stokers as a Function of
Grate Heat Release 67
3-27 Boiler Outlet Flyash Combustibles vs Grate Heat Release 69
3-28 Boiler Outlet Flyash Combustibles vs Grate Heat Release 70
3-29 Bottom Ash Combustibles vs Grate Heat Release 71
3-30 Bottom Ash Combustibles vs Grate Heat Release 72
3-31 Bottom Ash Combustibles vs Grate Heat Release 73
3-32 Nitric Oxide vs Oxygen 75
3-33 Carbon Monoxide Trends with Grate Heat Release for Five Spreader
Stokers 78
3-34 Hydrocarbons vs Grate Heat Release 80
3-35 Boiler Efficiency vs Grate Heat Release 81
3-36 Uncontrolled Particulates vs Excess Air . 83
3-37 Boiler Outlet Flyash Combustibles vs Excess Air .......... 85
xi
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FIGURES
Continued
Number
3-38 Bottom Ash Combustibles vs Excess Air 86
3-39 The Relationship Between Nitric Oxide and Excess Air Under Full Load
Conditions on Six Spreader Stokers 87
3-40 Carbon Monoxide vs Excess Air 89
3-41 Carbon Monoxide vs Excess Air 90
3-42 Hydrocarbons vs Excess Air 91
3-43 Flyash Combustibles Heat Loss vs Excess Air 93
3-44 Bottom Ash Combustibles Loss vs Excess Air 94
3-45 Dry Gas Heat Loss vs Excess Air 95
3-46 Boiler Efficiency vs Excess Air 96
3-47 Uncontrolled Particulates vs Percent Design Capacity 104
3-48 Uncontrolled Particulates vs Percent Design Capacity 105
3-49 Boiler Outlet Flyash Combustibles vs Percent Design Capacity .... 109
3-50 Bottom Ash Combustibles vs Percent Design Capacity 110
3-51 Boiler Outlet Flyash Combustibles vs Percent Design Capacity .... 112
3-52 Bottom Ash Combustibles vs Percent Design Capacity 113
3-53 Sulfur Oxides vs Fuel Sulfur as SO2 114
3-54 Sulfur Trioxide vs Sulfur Oxides 116
3-55 Data from Test Site A Indicates that there is no Discernable ....
Relationship between Nitric Oxide Emissions and Fuel Nitrogen . . . 117
3-56 Carbon Monoxide vs Percent Design Capacity 119
3-57 Boiler Efficiency vs Percent Design Capacity 120
3-58 Uncontrolled Particulates vs Percent Design Capacity 124
3-59 Carbon Monoxide vs Excess Air 130
3-60 Uncontrolled Particulates vs Percent Design Capacity 139
3-61 Effect of Flyash Reinjection on Combustible Content of Flyash .... 140
3-62 Particle Size Distribution of Flyash at Boiler Outlet of Site B for
Case of Full and Reduced Reinjection from the Mechanical Dust Col-
lector 143
3-63 Particle Size Distribution of Flyash at Boiler Outlet of Site C for
Case of Full and Reduced Reinjection While Firing Eastern Coal. . . 144
3-64 Particle Size Distribution of Flyash at Boiler Outlet of Site C for
Case of Full and Reduced Reinjection While Firing Western Coal . . 145
3-65 Mechanical Collector Efficiency vs Percent Design Capacity 146
3-66 Particle Size Concentration for Boiler Outlet Particulates under
Normal and Reduced Flyash Reinjection Conditions - Test Site B. . . 147
3-67 Particle Size Concentrations for Boiler Outlet Particulates under
Full and Reduced Flyash Reinjection Conditions - Eastern Low Fusion
Coal - Test Site C 148
3-68 Particle Size Concentrations for Boiler Outlet Particulates under
Full and Reduced Flyash Reinjection Conditions - Western Coal -
Test Site C 149
3-69 Particulate Concentration Reduction as a Function of Particle Dia-
meter for the Change in Flyash Reinjection Configuration from Full
to No Reinjection - Test Site C 150
3-70 Particle Size Distribution at the Economizer Outlet for Full and
Reduced Reinjection from the Economizer Hopper at Site F 152
3-71 Particle Size Distribution at the Boiler Outlet as Determined by
Cascade Impactor. Data are from Full Load Tests on Spreader
Stokers, Sites E, F and G 156
xii
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FIGURES
Continued
Number
Page
3-72 Particle Size Distribution at the Mechanical Collector Outlet as
Determined by Cascade Impactor 157
3-73 Particle Size Distribution at the Boiler Outlet as Determined by
Banco Classifier 159
3-74 Particle Size Distribution at the Boiler Outlet as Determined by
SASS Cyclones 162
3-75 Particle Size Distribution at the Mechanical Collector Outlet and
the Electrostatic Precipitator Outlet as Determined by SASS
Cyclones 163
3-76 Sieve Analysis of Plyash Collected at the Boiler Outlets of Five
Spreader Stokers 165
3-77 Relationship Between Percentage of Particles Smaller than 20 Micro-
meters, and Dust Collector Efficiency for Spreader Stokers .... 168
3-78 Mechanical Collector Efficiency vs Percent Design Capacity 169
4-1 Test Site D General Arrangement Drawing 173
4-2 Test Site H General Arrangement Drawing 175
4-3 Test Site I General Arrangement Drawing 177
4-4 Test Site J General Arrangement Drawing 179
4-5 Test Site K General Arrangement Drawing 181
4-6 Boiler Schematic for Test Sites L2 and L4 184
4-7 Grate Heat Release Rates of Seven Mass Fired Overfeed Stokers Fired
at or Near Full Load 188
4-8 Excess Air Operating Levels of Seven Mass Fired Overfeed Stokers
Fired at or Near Full Load 189
4-9 Excess Oxygen Operating Levels of Seven Mass Fired Overfeed Stokers
Fired at or Near Full Load 190
4-10 Uncontrolled Particulate Loadings of Seven Mass Fired Overfeed
Stokers Fired at or Near Full Load 191
4-11 Percentage of Combustible Material in the Flyash of Seven Mass Fired
Overfeed Stokers Fired at or Near Full Load 192
4-12 Percentage of Combustible Material in the Bottom Ash of Seven Mass
Fired Overfeed Stokers Fired at or Near Full Load 193
4-13 Nitric Oxide Emissions of Five Mass Fired Overfeed Stokers Fired
at or Near Full Load 194
4-14 Carbon Monoxide Emissions of Five Mass Fired Overfeed Stokers Fired
at or Near Full Load 195
4-15 Unburned Hydrocarbon Emissions of Two Mass Fired Overfeed Stokers
Fired at or Near Full Load 196
4-16 Heat Loss Due to Combustibles in the Flyash of Seven Mass Fired
Overfeed Stokers Fired at or Near Full Load 197
4-17 Heat Loss Due to Combustibles in the Bottom Ash of Seven Mass Fired
Overfeed Stokers Fired at or Near Full Load 198
4-18 Boiler Efficiency of Seven Mass Fired Overfeed Stokers Fired at or
Near Full Load 199
4-19 Excess Air Profiles for Five Mass Fired Overfeed Stokers 202
4-20 Excess Air Operating Levels of Five Mass Fired Overfeed Stokers
Showing a Correlation with Size of the Grate 203
xiii
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FIGURES
Continued
Number Page
4-21 Coal Gate Position as a Function of Load for Four Traveling Grate
and Chain Grate Stokers 204
4-22 Uncontrolled Particulate Loading Profiles for Five Mass Fired Over-
feed Stokers 205
4-23 Uncontrolled Particulates vs Grate Heat Release 207
4-24 Uncontrolled Particulates vs Grate Heat Release 208
4-25 Controlled Particulates vs Grate Heat Release 210
4-26 Boiler Outlet Flyash Combustibles vs Grate Heat Release 211
4-27 Boiler Outlet Flyash Combustibles vs Grate Heat Release . 212
4-28 Bottom Ash Combustibles vs Grate Heat Release 213
4-29 Bottom Ash Combustibles vs Grate Heat Release 215
4-30 Nitric Oxide vs Oxygen 217
4-31 Nitric Oxide vs Oxygen 218
4-32 Carbon Monoxide vs Grate Heat Release 220
4-33 Hydrocarbons vs Grate Heat Release 221
4-34 Boiler Efficiency as a Function of Grate Heat Release for Five Mass
Fired Overfeed Stokers 222
4-35 The Relationship Between Nitric Oxide and Excess Air at Full Load . . 226
4-36 Carbon Monoxide vs Excess Air 227
4-37 Hydrocarbons vs Excess Air 229
4-38 Carbon Monoxide vs Hydrocarbons 230
4-39 Relationship Between Boiler Efficiency and Excess Air ........ 231
4-40 Uncontrolled Particulates vs Percent Design Capacity 240
4-41 Controlled Particulates vs Percent Design Capacity 241
4-42 Bottom Ash Combustibles vs Percent Design Capacity 244
4-43 Sulfur Oxides vs Fuel Sulfur as S02 . 246
4-44 Sulfur In Bottom Ash vs Fuel Sulfur as SO2 247
4-45 Sulfur Trioxide vs Sulfur Oxides 248
4-46 Nitric Oxide vs Fuel Nitrogen at Test Site D 250
4-47 Uncontrolled Particulates vs Percent Design Capacity 255
4-48 Boiler Outlet Flyash Combustibles vs Percent Design Capacity .... 257
4-49 Nitric Oxide vs Overfire Air 259
4-50 Carbon Monoxide vs Percent Design Capacity 261
4-51 Hydrocarbons vs Oxygen 262
4-52 Particle Size Distribution at the Boiler Outlet as Determined by
Cascade Impactor 265
4-53 Particle Size Distribution at the Boiler Outlet as Determined by
Bahco Classifier 266
4-54 Particle Size Distribution at the Boiler Outlet and After the
Mechanical Collector as Determined by SASS Cyclones 267
4-55 Sieve Analysis of Flyash Collected at the Boiler Outlets of Two
Mass Fired Overfeed Stokers 268
4-56 Average Particle Size Distribution at the Boiler Outlet as Determined
by Four Different Methods 269
4-57 Particle Size Distribution After the Mechanical Collector of Three
Mass Fired Overfeed Stokers 271
4-58 Relationship Between Percentage of Particles Smaller than 20 Micro-
meters and Dust Collector Efficiency for Mass Fired Overfeed
Stokers 273
4-59 Mechanical Collector Efficiency vs Percent Design Capacity 274
xiv
-------
FIGURES
Continued
Number
5-1 Boiler Schematics for the Underfeed Stokers 277
5-2 Particle Size Distribution at the Boiler Outlet of Five Underfeed
Stokers as Determined by Cascade Impactor 291
5-3 Particle Size Distribution at the Boiler Outlet of Five Underfeed
Stokers as Determined by Bahco Classifier 292
5-4 Particle Size Distribution Downstream of the Mechanical Collector
on Two Underfeed Stokers as Determined by Cascade Impactor .... 293
5-5 Particle Size Distribution Downstream of the Mechanical Collector on
Two Underfeed Stokers as Determined by Bahco Classifier 294
6-1 Flow Schematic of Mobile Flue Gas Monitoring Laboratory 298
6-2 SOx Sample Probe Construction 305
6-3 Shell-Emeryville Sulfur Oxides Sampling Train ..... 305
6-4 EPA Method 6 Sulfur Oxide Sampling Train 306
6-5 Schematic of Goksoyr-Ross Controlled Condensation System (CCS) . . . 308
6-6 EPA Method 5 Particulate Sampling Train 310
6-7 Brink Cascade Impactor Sampling Train Schematic 312
7-1 RAC Staksampler 316
7-2 Bahco Centrifugal Classifier . 318
7-3 Andersen Mark III In-Stack Impactor 319
7-4 Schematic Diagram of the Sampling Train Used to Collect Particles for
the Centrifugal Classifier and Impactor Analysis 321
-------
1.0 EXECUTIVE SUMMARY AND CONCLUSIONS
This report is the culmination of an extensive testing effort on
eighteen coal-stoker fired boilers.1"24 The effort includes 400 tests on 36 boiler-
coal combinations conducted over a two year period. The boilers, identified by
letter designators, fall into three major stoker classifications: spreader
stokers (Sites A, B, C, E, F, G), mass fired overfeed stokers (Sites D, H, I,
J, K, L2, L4) , and underfeed stokers (Sites LI, L3, L5, L6, L7). Each of these
classifications is presented separately in this report. The units are described
in Table 1-1 along with the number of coals fired and tests conducted.
TABLE 1-1
UNIT DESCRIPTION AND DATA BASE
Stoker
Type
Spreader
Spreader
Spreader
Vibrating Grate
Spreader
Spreader
Spreader
Traveling Grate
Traveling Grate
Chain Grate
Traveling Grate
Multiple Retort
Vibrating Grate
Single Retort
Traveling Grate
Multiple Retort
Multiple Retort
Multiple Retort
Site A
Site B
Site C
Site D
Site E
Site F
Site G
Site H
Site I
Site J
Site K
Site Ll
Site L2
Site L3
Site L4
Site L5
Site L6
Site L7
Design
Capacity^
Ib/hr
300,000
200,000
182,500
90,000
180,000
80,000
75,000
45,000
70,000
70,000
50,000
26,000*
30,000
23,300
27,000
28,460
20,000
50,000
Number
Coals
Tested
3
4
3
3
3
2
3
1
2
2
3
1
1
1
1
1
1
1
Number
Test
Conditions
68
42
76
31
25
38
35
24
23
13
18
1
1
1
1
1
1
1
*The Site L1-L7 report expresses steaming capacity in terms of peak,
or maximum rating. This report expresses the Site L1-L7 steaming
capacity in terms of maximum continuous ratings so as to be consistent
throughout.
KVB4-15900-554
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The major objective of this test program was to update stoker speci-
fication data. This was accomplished by measuring boiler emissions and
efficiency on a variety of boiler-stoker designs and under a variety of oper-
ating conditions. The operating variables included heat release rate, excess
air, overfire air, flyash reinjection and coal properties. The measurements
included both uncontrolled and controlled particulate loading, nitrogen oxides
(NO and NO2) , sulfur oxides (SO2 and 803), oxygen (02), carbon dioxide (CO2),
carbon monoxide (CO), unburned hydrocarbons (HC), combustibles in the flyash
and bottom ash, particle size distribution and boiler efficiency. The tests
were conducted under steady load conditions.
In stoker firing of coal, there are so many variables that even with
the extensive amount of testing conducted during this program it was not possible
to analyze them all. The interactions between these variables are difficult to
assess.
Not all of the parameters were determined on each site nor under the
full range of operating variables. For example, the carbon monoxide analyzer was
out-of-service during testing at Sites G, I and J. The hydrocarbon analyzer was
only operable during testing at four sites, and boiler nameplate rating was not
achieved on three of the units due to retrofit equipment on two units and startup
problems on a third. In addition, the testing at Sites Ll through L7 was con-
ducted under a separate contract and included a more limited number of test
measurements under a single operating condition on each unit.
This summary is organized in two separate formats so as to be a con-
venient reference to the widest possible audience. The first section is organized
by the measured parameter first and the operating variable second. Thus, for
example, all observations on particulate loading are grouped together.
The second format follows the format of the text. It is organized by
operating variable so that, for example, the effects of overfire air on all
emissions are grouped together. As an additional convenience, each subject is
cross referenced to the main body of the text.
The range of data encountered at full load are summarized in Table 1-2.
KVB4-15900-554
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TABLE 1-2
RANGE OF DATA ENCOUNTERED AT HIGH LOAD*
Uncontrolled Particulate, lb/106Btu
Controlled Particulate, lb/106Btu
Mechanical Collector Efficiency, %
Excess Air, %
Nitric Oxide, lb/106Btu as N02
Carbon Monoxide, ppm dry @ 3% O2
Unburned Hydrocarbons, ppm wet @ 3% O2
Combustibles in Flyash, %
Combustibles in Bottom Ash, %
Flyash Combustibles Heat Loss, %
Bottom Ash Combustibles Heat Loss, %
Boiler Efficiency, %
Spreader Stokers
With Reinjection
from D.C.**
12.7 - 36.4
0.60 - 3.5
94.9 - 98.0
18 - 113
.30 - .60
22 - 1600
No Data
7.1 - 65.6
0.0 - 34.4
.54 - 5.5
.00 - 3.0
75.79 - 83.43
Spreader Stokers
W/O Reinjection
from D.C.
2.1
.17
40.6
19
.36
33
0
26.6
0.3
.51
.04
73.00
8.8
3.8
96.0
82
.61
702
41
83.5
27.2
9.2
3.4
83.07
Mass Fired
Overfeed
Stokers
0.57 - 2.2
0.11 - 0.75
10.9 - 92.7
26 - 97
.21 - .50
39 - 2300
5 - 112
21.8 - 56.0
7.1 - 69.1
.16 - 1.1
.42 - 9.4
69.75 - 84.10
Mass Fired
Underfeed
Stokers
0.25 - 0.71
0.46 - 0.58
26.6 - 42.9
33 - 186
No Data
<1000
No Data
20.2 - 20.5
8.1 - 25.0
.07 - .21
1.2 - 3.9
64.13 - 76.81
* Underfeed Stokers were Tested at Loads Ranging from 55-100% of Capacity. Data from the
other Stokers were Obtained within the Upper 10% of the Obtainable Load Range.
** Does not Include Tests in which Reinjection from the Mechanical Collector was Reduced. For example,
a nitric oxide level of .68 lb/10%tu as NO2 measured during one reduced reinjection test is not in-
cluded in this table. A particulate loading of 9.6 lb/106Btu is excluded for the same reason.
KVB4-15900-554
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1.1 SUMMARY OF FINDINGS ORGANIZED BY MEASURED PARAMETER
PARTICULATE LOADING
• Type of Stoker
Spreader stokers with flyash reinjection from their mechanical dust
collectors had by far the highest uncontrolled particulate loadings,
ranging from 13 to 36 Ib/lO^Btu. Spreader stokers without rein-
jection from their dust collectors were next with emissions of
2.1 to 8.8 lb/106Btu, followed by mass fired overfeed stokers with
.57 to 2.2 lb/106Btu and underfeed stokers with .25 to .71 lb/106
Btu. (Sections 3.2, 4.2, 5.4)
• Heat Release Rate
It cannot be said that units with higher design heat release rates
have higher particulate loadings, but for a given unit the uncon-
trolled particulate loading always increased as heat release rate,
or load, increased. The rate of increase varied from site to site,
and at some sites it appeared to accelerate as full load was approached.
On spreader stokers with flyash reinjection from mechanical dust
collectors, the last 10% increase in heat release rate resulted in a
9 to 20% increase in particulate loading. On spreaders without dust
collector reinjection, the increase was 8 to 12%. On mass fired
overfeed stokers, particulate loading increased anywhere from 3 to
20% as heat release rate was increased from 90 to 100% of design.
(Sections 3.3.2, 4.3.2)
• Excess Air
No relationship was established between particulate loading and
excess air. This does not foreclose the existence of such a
relationship, but rather indicates that such a relationship could
not be deciphered from the data due to data scatter and uncontrolled
variables. (Sections 3.4.1, 4.4.1)
• Overfire Air
Uncontrolled particulate loading was reduced by 20 to 50% on four of
six spreader stokers and three of five mass fired overfeed stokers
when overfire air pressures were increased. Two sites showed the
opposite trend and two sites were unaffected by changes in overfire
air pressure. (Sections 3.6.1, 4.6.1)
• Coal Ash
Coal ash could be related to particulate loading at only four of the
ten test sites at which multiple coals were fired. On three of the
spreader stokers it was established that particulate loading in-
creased by .24 to .38 lb/106Btu for each one percent increase in coal
ash. Stated in another way, if the coal ash is doubled at these sites,
KVB4-15900-554
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the particulate loading will increase by 15 to 30%. Thus/ the
relationship between coal ash and particulate loading was not one-
to-one on these three units.
On one of the traveling grate stokers, a 4% ash washed coal and a
10% ash unwashed coal from the same mine were tested. The 250%
increase in coal ash resulted in a 300% increase in particulate
loading. In this case, the dramatic increase in particulate
loading can be attributed to the type of ash, a clay like material
in the surface of the coal, and to a corresponding increase in coal
fines on the unwashed coal. (Sections 3.5.1, 4.5.1)
Coal Fines
Because of the movement of air through the grate and the upward
movement of combustion gases through the furnace, the smallest coal
and ash particles are carried out of the furnace by the gases rather
than staying on the grate. This is called particle entrainment and
is a problem from both a pollution and an efficiency standpoint.
The liklihood of a particle being entrained is a function of its
size and density, and the velocities in the furnace. The test data
from this program showed a mathematical correlation between coal
fines and particulate loading on five stokers. Particulate loading
increased by .10 to .55 lb/10^Btu whenever the percent of coal
passing a 16 mesh screen increased by one percent. No correlation
was found in studies of six other stokers. (Sections 3.5.1, 4.5.1)
Flyash Reinjection
Flyash from the dust collector was reinjected to the furnace of three
of the six spreader stokers. In each case it was demonstrated that
uncontrolled particulate loading was increased as a result of
reentrainment of a portion of the reinjected ash. At one site,
reinjection was completely eliminated for test purposes. As a re-
sult, uncontrolled particulate loading was reduced by 70 to 80% and
controlled particulate loading was reduced by 40 to 50%. Reducing
the degree of flyash reinjection reduced the percentage of larger
particles in the flyash. This in turn reduced the mechanical dust
collector efficiency. (Sections 3.7.4, 3.7.6)
Emission Factors
U.S. Environmental Protection Agency publication AP-42, Compilation
of Air Pollutant Emission Factors, Third Edition, contains factors
used for predicting emissions from stoker-boilers. The data from
this program compares as follows: (Sections 3.2, 4.2, 5.4)
KVB4-15900-554
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Uncontrolled Particulates, Ib/ton
(A = % Ash in Coal)
AP-42 This Program
Spreaders with Reinjection 20A 29A - 50A
Spreaders without Reinjection ISA 14A - 17A
Overfeed Stokers 5A 1.1A - 3.8A
Underfeed Stokers 5A .6A - 1.7A
Particle Size Distribution
Particle size distribution of the flyash was determined by a variety
of methods including cascade impactor, Banco classifier, SASS
cyclones and sieve analysis. The results varied from one method of
measurement to another, but clearly showed that spreader stokers
emit a higher percentage of coarse, more easily collected particles
than mass fired overfeed and underfeed stokers. (Sections 3.8, 4.7,
5.7)
NITRIC OXIDE
Type of Stoker
As a class, spreader stokers emitted higher concentrations of nitric
oxide than did mass fired overfeed stokers. Under full load con-
ditions, spreader stokers emitted between .30 and .61 lb/10^Btu NOx
corrected to NO2 while mass fired overfeed stokers emitted between
.21 and .50 lb/106Btu NOx. However, overfeed stokers operated at
higher excess air levels than did spreader stokers. When compared
at the same excess air levels the difference in NOx levels is even
greater. However, mass fired overfeed stokers generally require
higher excess air than spreader stokers. (Sections 3.2, 4.2)
Heat Release Rate
For spreader stokers, an increase in heat release rate equivalent
to 10% of capacity resulted in an average increase in nitric oxide
emissions of .025 lb/106Btu as N02 at constant excess air. For
mass fired overfeed stokers, the relationship ranged from zero to
.026 lb/106Btu per 10% increase in capacity at constant excess air.
In all cases, nitric oxide emissions were invariant with load at
normal firing conditions because the effects of decreasing excess
air effectively canceled the effects of increasing load. Although
NOx increased with heat release rate on each given unit, it was
not true that units with higher design heat release rates emitted
higher concentrations of NOx. (Sections 3.3.5, 4.3.5)
KVB4-15900-554
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Excess Air
On four spreader stokers without air preheat and one with air pre-
heat, nitric oxide increased by .021 to .036 lb/10^Btu for each
increase of 10% excess air. The sixth spreader stoker used air pre-
heat and its NOx increased by .067 Ib/lO^Btu per increase of 10%
excess air. On five mass fired overfeed stokers, NOx increased by
.016 to .027 lb/105Btu. (Sections 3.4.3, 4.4.3)
Overfire Air
Nitric oxide emissions were not influenced by changes in overfire
air pressure when considered at constant excess air. (Sections
3.6.3, 4.6.3)
Fuel Nitrogen
Variations in fuel nitrogen from .75% to 1.50% by weight had no
measurable effect on nitric oxide emissions. This may simply reflect
difficulties in sorting out the other variables. (Section 3.5.4,
4.5.4)
Flyash Reinjection
Flyash reinjection from the mechanical dust collector had no
measurable effect on nitric oxide emissions. (Section 3.7)
Emission Factors
U.S. Environmental Protection Agency publication AP-42, Compilation
of Air Pollutant Emission Factors, Third Edition, contains factors
used for predicting emissions from stoker boilers. The data from
this program compares as follows: (Sections 3.2, 4.2)
Nitrogen Oxides, Ib/ton
AP-42 This Program
Spreader Stokers 15 9.4-14.2
Overfeed Stokers None 7.1 - 9.4
SULFUR OXIDES
Type of Stoker
The spreader stokers retained an average 4.4 percent of the fuel
sulfur in the ash, while the mass fired overfeed stokers retained
an average 2.1 percent. The remainder was emitted as SO2 and 803,
with SO 3 comprising less than two percent of the total. Operating
parameters such as excess air, overfire air, and load had no effect
on the emissions of sulfur oxides or the retention of sulfur in the
ash' KVB4-15900-554
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Fuel Sulfur
Although good sulfur balances were difficult to obtain, the data
indicates that fuel sulfur conversion efficiencies of 95 to 98%
are reasonable assumptions. (Sections 3.5.3, 4.5.3)
CARBON MONOXIDE
Type of Stoker
Spreader stokers emitted lower concentrations of carbon monoxide
than traveling grate stokers while firing Eastern bituminous coals.
Emissions from three of the spreader stokers were in the range of
50 to 250 ppm at full load. A fourth was in the range of 200 to
600 ppm. By comparison, two traveling grate stokers emitted 50 to
700 ppm CO at full load, and a vibrating grate stoker emitted be-
tween 50 and 2000+ ppm CO. The comparison is limited to these
seven stokers. Carbon monoxide emissions were not measured on three
other stokers due to instrument failure, and a fourth fired only
Western coals. At Test Sites LI through L7, the carbon monoxide con-
centration was measured with an Orsat analyzer having a minimum detection
limit of 0.1% or 1000 ppm. Significantly, the carbon monoxide
emissions were below this detection limit on the Site L stokers.
(Sections 3.2, 4.2)
Heat Release Rate
Carbon monoxide emissions were highest at high heat release rates
under low excess air conditions, and at low heat release rates under
high excess air conditions. At full load, carbon monoxide emissions
could be controlled with proper application of combustion air.
(Sections 3.3.6, 4.3.6)
Excess Air
Carbon monoxide was more prevalent as excess air dropped below about
30-40% on spreader stokers and about 60% on mass fired overfeed
stokers. Carbon monoxide increased gradually as excess air increased
above about 60% on spreader stokers and 100% on mass fired overfeed
stokers. (Sections 3.4.4, 4.4.4)
Overfire Air
Carbon monoxide emissions were reduced by the increased use of
overfire air. (Sections 3.6.4, 4.6.4)
Coal Rank
Carbon monoxide emissions were greatest while firing Western sub-
bituminous coals. On one spreader stoker where both an Eastern
and a Western coal were fired, the full load Western coal emissions
ranged from 163 to 702 ppm and averaged 342 ppm. By comparison,
the full load Eastern coal emissions ranged from 33 to 263 ppm and
averaged 71 ppm. (Sections 3.5.5, 4.5.5)
8 KVB4-15900-554
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Flyash Reinjection
Flyash reinjection from the mechanical dust collector had no
measurable effect upon carbon monoxide emissions. (Section 3.7)
UNBURNED HYDROCARBON
Type of Stoker
Based on limited data, the spreader stokers emitted lower hydro-
carbon emissions than the mass fired overfeed stokers. Full load
emissions from the spreader stokers ranged from 0 to 15 ppm for
Site F and 35 to 41 ppm for Site G. By comparison, the mass fired
overfeed stokers emitted between 5 and 112 ppm for Site H and 80
ppm for a single point on Site J. (Sections 3.2, 4.2)
Heat Release Rate
Unburned hydrocarbons tended to decrease as heat release rate in-
creased on three of four stokers where this emission was measured.
On the fourth stoker, the opposite trend was observed. (Sections
3.3.4, 4.3.7)
Excess Air
Unburned hydrocarbon emissions showed little or no correlation with
excess air on spreader stokers. On mass fired overfeed stokers,
hydrocarbons increased in almost direct proportion to the excess
air. (Sections 3.4.5, 4.4.5)
Overfire Air
Unburned hydrocarbons were reduced 82% by increasing the overfire
air pressure on one traveling grate stoker. No correlation was
found on one spreader stoker. The other two units where hydrocarbon
emissions were measured had insufficient data to make a correlation.
(Sections 3.6.5, 4.6.5)
Coal Properties
The site firing the lower volatile coal had the lowest hydrocarbon
emissions. The 29% volatile coal yielded 19-41 ppm hydrocarbons
while the 41% volatile coal yielded 163 to 702 ppm hydrocarbons.
Volatiles are expressed here on a dry, mineral matter free basis.
(Sections 3.5.6, 4.5.6)
Carbon Monoxide
Unburned hydrocarbons increased with increasing carbon monoxide
emissions on one traveling grate stoker. No correlation was found
on one spreader stoker. (Section 4.4.5)
KVB4-15900-554
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EXCESS AIR
Type of Stoker
At full load, most spreader stokers were capable of operating
at 30% excess air (5% 02). By comparison, the mass fired overfeed
stokers generally required 50% excess air (7% 02)• (Sections
3.2, 4.2)
Size of Stoker
With one exception, the excess air operating level was inversely
proportional to the'size of the stoker. The larger the stoker, the
lower the excess air requirement. (Sections 3.3.1, 4.3.1)
Heat Release Rate
The excess air requirement drops as heat release rate increases on
stoker boilers. The excess air requirement levels off as 30%
excess air is approached. (Sections 3.3.1, 4.3.1)
Coal Properties
Coal properties were not found to alter excess air requirements on
these stoker boilers.
COMBUSTIBLES IN THE BOTTOM ASH
• Type of Stoker
Combustible levels were lower in the bottom ash of spreader stokers
than they were for mass fired overfeed stokers or underfeed stokers.
The average for each of six spreader stokers fired at full load
ranged from 0% to 14%. By comparison, mass fired overfeed stokers
ranged from 16% to 26% with one unit averaging 43%, and underfeed
stokers ranged from 19 to 25% with one unit averaging 8%.
(Sections 3.2, 4.2, 5.5)
• Heat Release Rate
Heat release rate had very little effect on combustibles in the bottom
ash. (Sections 3.3.4, 4.3.4)
9 Excess Air
No correlation was found between excess air and combustibles in the
bottom ash. (Sections 3.4.2, 4.4.2)
• Coal Properties
Small differences in bottom ash combustible levels were observed which
appeared to be related to coal properties at some sites. However,
KVB4-15900-554
10
-------
the particular coal properties causing these differences were not
identified. (Sections 3.5.2, 4.5.2)
Ash Balance
It was found that 65% to 85% of the coal ash remained on the grate
in spreader stokers as compared to 80% to 90% for mass fired over-
feed stokers. For the purposes of computing combustible heat
losses, 75% and 85% are good estimates for spreaders and mass fired
overfeed stokers, respectively. (Sections 3.5.2, 4.5.2)
COMBUSTIBLES IN THE FLYASH
@ Type of Stoker
Combustible levels in the flyash were higher in the spreader stokers
than in either the mass fired overfeed stokers or the underfeed
stokers. With the exception of Test Site C, the spreader stoker
data ranged from 47% to 84% and averaged 60%. On the other hand,
the mass fired overfeed stoker data ranged from 22% to 56% and
averaged 28%. Flyash samples taken from the dust collector hoppers
of two underfeed stokers revealed 20.2% and 20.5% combustibles.
(Sections 3.2, 4.2, 5.5)
® Heat Release Rate
Combustibles in the flyash tended to increase slightly as heat re-
lease rate increased on spreader stokers. On mass fired overfeed
stokers, no significant trend was observed. (Sections 3.3.3, 4.3.3)
® Excess Air
No correlation was found between combustibles in the flyash and
excess air level on either spreader stokers or mass fired overfeed
stokers. (Sections 3.4.2, 4.4.2)
® Overfire Air
Increasing overfire air pressure effectively reduced the combustible
content of the flyash by an average 40% in 74% of the overfire air
tests. This resulted in an average efficiency gain of 1.70% of heat
input for spreader stokers and 0.27% of heat input for the mass
fired overfeed stokers. 26% of the tests gave the opposite result.
(Sections 3.6.2, 4.6.2)
© Coal Properties
At Test Site C, the combustibles in the flyash were 2 to 4 times higher
while firing an Eastern bituminous coal than while firing a Western
sub-bituminous coal. This was the only site where flyash combustibles
could be directly related to coal properties. The particular pro-
perty of the coal responsible for the difference was not identified.
(Sections 3.5.2, 4.5.2)
11 KVB4-15900-554
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Flyash Reinjection
Combustibles In the flyash at the boiler outlet increased by 23%
to 63% when the rate of flyash reinjection was reduced. At the
dust collector outlet, similar increases were observed. (Sections
3.7.5)
Particle Size
The largest flyash particles contain the largest combustible
fractions. Flyash samples from two spreader stokers and two mass
fired overfeed stokers were analyzed. (Sections 3.8.5, 4.7.3)
BOILER EFFICIENCY
Type of Stoker
Boiler efficiencies were determined by the ASME Abbreviated
Efficiency Test (PTC 4.1). At or near full load, the measured
boiler efficiencies ranged from 73.0 to 83.4% for six spreader
stokers, 69.8 to 84.1% for seven mass fired overfeed stokers, and
64.1 to 76.8 for five mass fired underfeed stokers. (Sections
3.2, 4.2, 5.6)
Heat Release Rate
In most cases, boiler efficiencies were relatively constant with
changing heat release rates. At a few sites, efficiency dropped
as heat release rate dropped because increasing dry gas heat losses
predominated. (Sections 3.3.8, 4.3.8)
Excess Air
Boiler efficiency decreased as excess air increased on all of the
extensively tested stokers. Dry gas heat losses dominated this
trend, overshadowing any effects due to combustible heat losses.
For each 10% excess air decrease, boiler efficiency increased by
.33% to 1.0%. (Sections 3.4.6, 4.4.6)
Overfire Air
Boiler efficiency improved by an average one percent when overfire
air was increased on spreader stokers as a result of reduced carbon
carryover. However, on mass fired overfeed stokers, efficiency was
reduced by an average 2.75% when overfire air was increased due to
increased dry gas losses and increased bottom ash combustible
heat losses. (Sections 3.6.6, 4.6.6)
Coal Properties
Coal properties affected boiler efficiencies on two occasions. At
Test Site C, the high moisture western coal produced efficiencies
KVB4-159GQ-554
12
-------
which were 3 to 4% lower than similar tests on low moisture eastern
coals. At Test Site K, the unwashed coal produced lower boiler
efficiencies than either of the others because this coal led to
a greater combustible heat loss. (Sections 3.5.7, 4.5.7)
Flyash Reinjection
Some but not all of the carbon in the reinjected flyash was re-
covered at Sites A, B and C. There was insufficient data to
calculate carbon recovery rates with any accuracy. (Section 3.7.5)
KVB4-15900-554
13
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1.2 SUMMARY OF FINDINGS ORGANIZED BY TEST VARIABLE
DIFFERENCES BETWEEN STOKER TYPES
* Excess Air
At full load, most spreader stokers were capable of operating at 30%
excess air (5% 02). By comparison, the mass fired overfeed stokers
generally required 50% excess air (7% O2). (Sections 3.2, 4.2)
With one exception, the excess air operating level was inversely
proportional to the size of the stoker. The larger the stoker, the
lower the excess air requirement. (Sections 3.3.1, 4.3.1)
® Particulate Loading
Spreader stokers with flyash reinjection from their mechanical dust
collectors had by far the highest uncontrolled particulate loadings,
ranging from 13 to 36 lb/10^Btu. Spreader stokers without reinjection
from their dust collectors were next with emissions of 2.1 to 8.8
lb/10^Btu, followed by mass fired overfeed stokers with .57 to 2.2 lb/
106Btu and underfeed stokers with .25 to .71 lb/106Btu. (Sections 3.2,
4.2, 5.4)
• Combustibles in the Flyash
Combustible levels in the flyash were higher in the spreader stokers
than in either the mass fired overfeed stokers or the underfeed
stokers. With the exception of Test Site C, the spreader stoker
data ranged from 47% to 84% and averaged 60%. On the other hand,
the mass fired overfeed stoker data ranged from 22% to 56% and
averaged 28%. Flyash samples taken from the dust collector hoppers
of two underfeed stokers revealed 20.2% and 20.5% combustibles.
(Sections 3.2, 4.2, 5.5)
® Combustibles in the Bottom Ash
Combustible levels were lower in the bottom ash of spreader stokers
than they were for mass fired overfeed stokers or underfeed stokers.
The average for each of six spreader stokers fired at full load
ranged from 0% to 14%. By comparison, mass fired overfeed stokers
ranged from 16% to 26% with one unit averaging 43%, and underfeed
stokers ranged from 19 to 25% with one unit averaging 8%. (Sections
3.2, 4.2, 5.5)
• Sulfur Oxides
The spreader stokers retained an average 4.4 percent of the fuel
sulfur in the ash, while the mass fired overfeed stokers retained
an average 2.1 percent. The remainder was emitted as SO2 and 803,
with 303 comprising less than two percent of the total. Operating
parameters such as excess air, overfire air, and load had no effect
on the emissions of sulfur oxides or the retention of sulfur in the
ash. (Sections 3.5.3, 4.5.3)
KVB4-15900-554
14
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Nitric Oxide
As a class/ spreader stokers emitted higher concentrations of nitric
oxide than did mass fired overfeed stokers. Under full load conditions,
spreader stokers emitted between .30 and .61 lb/10°Btu NOx corrected
to NOo while mass fired overfeed stokers emitted between .21 and .50
lb/10°Btu NOx. However, overfeed stokers operated at higher excess
air levels than did spreader stokers. When compared at the same
excess air levels the difference in NOx levels is even greater.
(Sections 3.2, 4.2)
Carbon Monoxide
Spreader stokers emitted lower concentrations of carbon monoxide
than traveling grate stokers while firing Eastern bituminous coals.
Emissions from three of the spreader stokers were in the range of
50 to 250 ppm at full load. A fourth was in the range of 200 to
600 ppm. By comparison, two traveling grate stokers emitted 50 to
700 ppm CO at full load, and a vibrating grate stoker emitted be-
tween 50 and 2000+ ppm CO. The comparison is limited to these
seven stokers. Carbon monoxide emissions were not measured on three
other stokers due to instrument failure, and a fourth fired only
Western coals. At Test Sites LI through L7, the carbon monoxide con-
centration was measured with an Orsat analyzer having a minimum de-
tection limit of 0.1% or 1000 ppm. Significantly, the carbon monoxide
emissions were below this detection limit on the Site L stokers.
(Sections 3.2, 4.2)
Unburned Hydrocarbons
Based on limited data, the spreader stokers emitted lower hydro-
carbon emissions than the mass fired overfeed stokers. Full load
emissions from the spreader stoker ranged from 0 to 15 ppm for
Site F and 35 to 41 ppm for Site G. By comparison, the mass fired
overfeed stokers emitted between 5 and 112 ppm for Site H and 80
ppm for a single point on Site J. (Sections 3.2, 4.2)
Boiler Efficiency
Boiler efficiencies were determined by the ASME Abbreviated
Efficiency Test (PTC 4.1). At or near full load, the measured
boiler efficiencies ranged from 73.0 to 83.4% for six spreader
stokers, 69.8 to 84.1% for seven mass fired overfeed stokers, and
64.1 to 76.8 for five mass fired underfeed stokers. (Sections
3.2, 4.2, 5.6)
RESPONSE TO HEAT RELEASE RATE
• Excess Air
The excess air requirement drops as heat release rate increases on
stoker boilers. The excess air requirement levels off as 30%
excess air is approached. (Sections 3.3.1, 4.3.1)
KVB4-15900-554
15
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Particulate Loading
It cannot be said that units with higher design heat release rates
have higher particulate loading, but for a given unit the uncon-
trolled particulate loading always increased as heat release rate,
or load, increased. The rate of increase varied from site to site,
and at some sites it appeared to accelerate as full load was approached.
On spreader stokers with flyash reinjection from mechanical dust
collectors, the last 10% increase in heat release rate resulted in a
9 to 20% increase in particulate loading. On spreaders without dust
collector reinjection, the increase was 8 to 12%. On mass fired
overfeed stokers, particulate loading increased anywhere from 3 to
20% as heat release rate was increased from 90 to 100% of design.
(Sections 3.3.2, 4.3.2)
Combustibles in the Flyash
Combustibles in the flyash tended to increase slightly as heat re-
lease rate increased on spreader stokers. On mass fired overfeed
stokers, no significant trend was observed. (Sections 3.3.3, 4.3.3)
Combustibles in the Bottom Ash
Heat release rate had very little effect on combustibles in the
bottom ash. (Sections 3.3.4, 4.3.4)
Nitric Oxide
For spreader stokers, an increase in heat release rate equivalent
to 10% of capacity resulted in an average increase in nitric oxide
emissions of .025 lb/10°Btu as N©2 at constant excess air. For
mass fired overfeed stokers, the relationship ranged from zero to
.026 lb/10%tu per 10% increase in capacity at constant excess air.
In all cases, nitric oxide emissions were invarient with load at
normal firing conditions because the effects of decreasing excess
air effectively canceled the effects of increasing load. Although
NOx increased with heat release rate on each given unit, it was
not true that units with higher design heat release rates emitted
higher concentrations of NOx. (Sections 3.3.5, 4.3.5)
Carbon Monoxide
Carbon monoxide emissions were highest at high heat release rates
under low excess air conditions, and at low heat release rates under
high excess air conditions. At full load, carbon monoxide emissions
could be controlled with proper application of combustion air.
(Sections 3.3.6, 4.3.6)
Unburned Hydrocarbons
Unburned hydrocarbons tended to decrease as heat release rate in-
creased on three of four stokers where this emission was measured.
On the fourth stoker, the opposite trend was observed. (Sections
3.3.4, 4.3.7)
16 KVB4-15900-554
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Boiler Efficiency
In most cases, boiler efficiencies were relatively constant with
changing heat release rates. At a few sites, efficiency dropped
as heat release rate dropped because increasing dry gas heat losses
predominated. (Sections 3.3.8, 4.3.8)
RESPONSE TO EXCESS AIR
• Particulate Loading
No relationship was established between particulate loading and
excess air. This does not foreclose the existence of such a
relationship, but rather indicates that such a relationship could
not be deciphered from the data due to data scatter and uncontrolled
variables. (Sections 3.4.1, 4.4.1)
• Combustibles in the Flyash
No correlation was found between combustibles in the flyash and
excess air level on either spreader stokers or mass fired overfeed
stokers. (Sections 3.4.2, 4.4.2)
^ Combustibles in the Bottom Ash
No correlation was found between excess air and combustibles in the
bottom ash. (Sections 3.4.2, 4.4.2)
• Nitric Oxide
On four spreader stokers without air preheat and one with air pre-
heat, nitric oxide increased by .021 to .036 lb/106Btu for each
increase of 10% excess air. The sixth spreader stoker used air pre-
heat and its NOx increased by .067 lb/10^Btu per increase of 10%
excess air. On five mass fired overfeed stokers, NOx increased by
.016 to .027 lb/l06Btu. (Sections 3.4.3, 4.4.3)
• Carbon Monoxide
Carbon monoxide was more prevalent as excess air dropped below about
30-40% on spreader stokers and about 60% on mass fired overfeed
stokers. Carbon monoxide increased gradually as excess air increased
above about 60% on spreader stokers and 100% on mass fired overfeed
stokers. (Sections 3.4.4, 4.4.4)
® Unburned Hydrocarbons
Unburned hydrocarbon emissions showed little or no correlation with
excess air on spreader stokers. On mass fired overfeed stokers,
hydrocarbons increased in almost direct proportion to the excess
air. (Sections 3.4.5, 4.4.5)
KVB4-15900-554
17
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Boiler Efficiency
Boiler efficiency decreased as excess air increased on all of the
extensively tested stokers. Dry gas heat losses dominated this
trend, overshadowing any effects due to combustible heat losses.
For each 10% excess air decrease, boiler efficiency increased by
.33% to 1.0%. (Sections 3.4.6, 4.4.6)
RESPONSE TO COAL COMPOSITION AND SIZING
• Excess Air
Coal properties were not found to alter excess air requirements on
these stoker boilers.
9 Particulate Loading
Because of the movement of air through the grate and the upward
movement of combustion gases through the furnace, the smallest coal
and ash particles are carried out of the furnace by the gases rather
than staying on the grate. This is called particle entrainment and
is a problem from both a pollution and an efficiency standpoint. The
likelihood of a particle being entrained is a function of its size
and density, and the velocities in the furnace. The test data from
this program showed a mathematical correlation between coal fines
and particulate loading on five stokers. Particulate loading in-
creased by .10 to .55 lb/10^Btu whenever the percent of coal passing
a 16 mesh screen increased by one percent. No correlation was found
in studies of six other stokers.
Coal ash could be related to particulate loading at only four of the
ten test sites at which multiple coals were fired. On three of the
spreader stokers it was established that particulate loading in-
creased by .24 to .38 lb/10°Btu for each one percent increase in coal
ash. Stated in another way, if the coal ash is doubled at these sites,
the particulate loading will increase by 15 to 30%. Thus, the
relationship between coal ash and particulate loading was not one-
to-one on these three units.
On one of the traveling grate stokers, a 4% ash washed coal and a
10% ash unwashed coal from the same mine were tested. The 250%
increase in coal ash resulted in a 300% increase in particulate
loading. In this case, the dramatic increase in particulate loading
can be attributed to the type of ash, a clay like material in the
surface of the coal, and to a corresponding increase in coal fines
on the unwashed coal. (Sections 3.5.1, 4.5.1)
• Combustibles in the Flyash
At Test Site C, the combustibles in the flyash were 2 to 4 times higher
while firing an Eastern bituminous coal than while firing a Western
sub-bituminous coal. This was the only site where flyash combustibles
KVB4-15900-554
18
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could be directly related to coal properties. The particular pro-
perty of the coal responsible for the difference was not identified.
(Sections 3.5.2, 4.5.2)
Combustibles in the Bottom Ash
It was found that 65% to 85% of the coal ash remained on the grate
in spreader stokers as compared to 80% to 90% for mass fired over-
feed stokers. For the purposes of computing combustible heat
losses, 75% and 85% are good estimates for spreaders and mass fired
overfeed stokers, respectively.
Small differences in bottom ash combustible levels were observed which
appeared to be related to coal properties at some sites. However,
the particular coal properties causing these differences were not
identified. (Sections 3.5.2, 4.5.2)
Sulfur Oxides
Although good sulfur balances were difficult to obtain, the data
indicates that fuel sulfur conversion efficiencies of 95 to 98%
are reasonable assumptions. (Sections 3.5.3, 4.5.3)
Nitric Oxide
Variations in fuel nitrogen from .75% to 1.50% by weight had no
measurable effect on nitric oxide emissions. This may simply reflect
difficulties in sorting out the other variables. (Section 3.5.4,
4.5.4)
Carbon Monoxide
Carbon monoxide emissions were greatest while firing Western sub-
bituminous coals. On one spreader stoker where both an Eastern
and a Western coal were fired, the full load Western coal emissions
ranged from 163 to 702 ppm and averaged 342 ppm. By comparison,
the full load Eastern coal emissions ranged from 33 to 263 ppm and
averaged 71 ppm. (Sections 3.5.5, 4.5.5)
Unburned Hydrocarbons
The site firing the lower volatile coal had the lowest hydrocarbon
emissions. The 29% volatile coal yielded 19-41 ppm hydrocarbons
while the 41% volatile coal yielded 163 to 602 ppm hydrocarbons.
Volatiles are expresssed here on a dry, mineral matter free basis.
(Sections 3.5.6, 4.5.6)
Boiler Efficiency
Coal properties affected boiler efficiencies on two occasions. At
Test Site C, the high moisture western coal produced efficiencies
which were 3 to 4% lower than similar tests on low moisture eastern
coals. At Test Site K, the unwashed coal produced lower boiler
efficiencies than either of the others because this coal led to
a greater combustible heat loss. (Sections 3.5.7, 4.5.7)
19 KVB4-15900-554
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RESPONSE TO OVERFIRE AIR
^ Particulate Loading
Uncontrolled particulate loading was reduced by 20 to 50% on four of
six spreader stokers and three of five mass fired overfeed stokers
when overfire air pressures were increased. Two sites showed the
opposite trend and two sites were unaffected by changes in overfire
air pressure. (Sections 3.6.1, 4.6.1)
^ Combustibles in the Flyash
Increasing overfire air pressure effectively reduced the combustible
content of the flyash by an average 40% in 74% of the overfire air
tests. This resulted in an average efficiency gain of 1.70% of heat
input for spreader stokers and 0.27% of heat input for the mass
fired overfeed stokers. 26% of the tests gave the opposite result.
(Sections 3.6.2, 4.6.2)
• Nitric Oxide
Nitric oxide emissions were not influenced by changes in overfire
air pressure when considered at constant excess air. (Sections
3.6.3, 4.6.3)
• Carbon Monoxide
Carbon monoxide emissions were reduced by the increased use of
overfire air. (Sections 3.6.4, 4.6.4)
• Unburned Hydrocarbons
Unburned hydrocarbons were reduced 82% by increasing the overfire
air pressure on one traveling grate stoker. No correlation was
found on one spreader stoker. The other two units where hydrocarbon
emissions were measured had insufficient data to make a correlation.
(Sections 3.6.5, 4.6.5)
^ Boiler Efficiency
Boiler efficiency improved by an average one percent when overfire
air was increased on spreader stokers as a result of reduced carbon
carryover. However, on mass fired overfeed stokers, efficiency was
reduced by an average 2.75% when overfire air was increased due to
increased dry gas losses and increased bottom ash combustible
heat losses. (Sections 3.6.6, 4.6.6)
KVB4-15900-554
20
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RESPONSE TO FLYASH REINJECTION
* Particulate Loading
Flyash from the dust collector was reinjected to the furnace of three
of the six spreader stokers. In each case it was demonstrated that
uncontrolled particulate loading was increased as a result of
reentrainment of a portion of the reinjected ash. At one site,
reinjection was completely eliminated for test purposes. As a re-
sult, uncontrolled particulate loading was reduced by 70 to 80% and
controlled particulate loading was reduced by 40 to 50%. Reducing
the degree of flyash reinjection reduced the percentage of larger
particles in the flyash. This in turn reduced the mechanical dust
collector efficiency. (Sections 3.7.4, 3.7.6)
• Combustibles in the Flyash
Combustibles in the flyash at the boiler outlet increased by 23%
to 63% when the rate of flyash reinjection was reduced. At the
dust collector outlet, similar increases were observed. (Sections
3.7.5)
* Nitric Oxide
Flyash reinjection from the mechanical dust collector had no
measurable effect on nitric oxide emissions. (Section 3.7)
^ Carbon Monoxide
Flyash reinjection from the mechanical dust collector had no
measurable effect upon carbon monoxide emissions. (Section 3.7)
• Boiler Efficiency
Some but not all of the carbon in the reinjected flyash was re-
covered at Sites A, B and C. There was insufficient data to
calculate carbon recovery rates with any accuracy. (Section 3.7.5)
PARTICLE SIZE DISTRIBUTION
^ Particulate Loading
Particle size distribution of the flyash was determined by a variety
of methods including cascade impactor, Bahco classifier, SASS
cyclones and sieve analysis. The results varied from one method of
measurement to another, but clearly showed that spreader stokers
emit a higher percentage of coarse, more easily collected particles
than mass fired overfeed and underfeed stokers. (Sections 3.8, 4.7,
5.7)
KVB4-15900-554
21
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Combustibles in the Flyash
The largest flyash particles contain the largest combustible
fractions. Flyash samples from two spreader stokers and two mass
fired overfeed stokers were analyzed. (Sections 3.8.5, 4.7.3)
EMISSION FACTORS
Particulate Loading
U.S. Environmental Protection Agency Publication AP-42, Compilation
of Air Pollutant Emission Factors, Third Edition, contains factors
used for predicting emissions from stoker-boilers. The data from
this program compares as follows: (Sections 3.2, 4.2, 5.4)
Uncontrolled Particulates, Ib/ton
(A = % Ash in Coal)
AP-42 This Program
Spreaders with Reinjection 20A 29A - 50A
Spreaders without Reinjection 13A 14A - 17A
Overfeed Stokers 5A 1.1A - 3.8A
Underfeed Stokers 5A .6A - 1.7A
Nitric Oxides
U.S. Environmental Protection Agency publication AP-42, Compilation
of Air Pollutant Emission Factors, Third Edition, contains factors
used for predicting emissions from stoker boilers. The data from
this program compares as follows: (Sections 3.2, 4.2)
Nitrogen Oxides, Ib/ton
AP-42 This Program
Spreader Stokers 15 9.4-14.2
Overfeed stokers None 7.1 - 9.4
KVB4-15900-554
22
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2.0 INTRODUCTION
In late 1977, the American Boiler Manufacturers Association (ABMA)
was awarded a contract to update specifications and design parameters for
coal burning boiler and stoker equipment. The project was jointly funded
by the United States Department of Energy and the United States Environmental
Protection Agency, with the express purpose of increasing coal usage in an
environmentally acceptable manner.
2.1 THE NEED
The need for such a program is clear. In recent years the vast
majority of industrial boiler installations have been packaged or shop assembled
gas and oil fired units. These boilers could be purchased and installed at
substantially lower costs than conventional coal burning boiler-stoker equip-
ment. Because of the declining demand for coal stokers, little or no work has
been done in recent years to improve specification data or product information
made available to consulting engineers and purchasers of coal burning boiler-
stoker equipment.
Furthermore, the market for coal suitable to be fired in industrial
boilers is being held back by critical uncertainties in the environmental and
energy areas, causing potential customers of coal-fired industrial boilers to
shelve plans for capital expansion and conversion. The current implementation
of more rigid air pollution regulations has made it difficult for many coal
burning installations to comply with required stack emission limits.
It is highly desirable to remove these uncertainties and thereby
encourage industrial users to order and install coal stoker fired boilers. This
would lead to significantly increased coal usage and decreased dependence upon
scarce and imported fuels.
KVB4-15900-554
23
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2.2 THE OBJECTIVES
The objectives of this program are:
1. To advance stoker boiler technology through comprehensive
testing of various stoker boiler designs, thereby facilitating
the design and fabrication of stoker boilers which are
economically and environmentally satisfactory alternatives
to gas and oil fired units.
2. To contribute to the design and application of pollution control
equipment by generating a large data base of boiler outlet dust
loading data and particle size distribution data.
3. To provide guidelines for boiler operator's concerning techniques
for clean and efficient stoker boiler operation.
4. To facilitate preparation of intelligent and reasonable national
emission standards for coal fired stoker boilers by the United
States Environmental Protection Agency.
5. To provide assistance in planning for coal supply contracts both
through an increased knowledge of the effects of coal properties
on emissions, and through the development of reasonable emission
regulations.
6. To promote the increased utilization of coal fired stoker boilers
by the United States industry by insuring compatibility of these
units emissions with the applicable environmental requirements.
2.3 THE PROJECT ORGANIZATION
The American Boiler Manufacturers Association formed a Stoker Technical
Committee composed of personnel from member companies to oversee the project.
The committee, in turn, subcontracted the field testing and report work to K.VB,
Inc., a combustion consulting firm located in Minneapolis, Minnesota. The
original scope of work included the testing of six spreader stokers. Testing
on the first unit began August 9, 1977.
As the project progressed successfully, additional funding was obtained
and the scope of work was increased to include five mass fired overfeed stokers.
These units were also tested by KVB, Inc.
A separate subcontract was let to Pennsylvania State University to test
seven small stoker boilers including two overfeed stokers and five underfeed
stokers located in central steam heating plants.
KVB4-159QO554
24
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On November 12, 1979, all testing was completed. A total of 400
tests on 18 stoker boilers and 36 boiler-coal combinations had been conducted.
2.4 THE TEST REPORTS
This report is the final technical report for the stoker test program.
Many reports have preceded it and several are to follow.
A technical report and a data supplement were prepared for each of
1 — *? 9
the eleven extensively tested boilers. These "Site Reports" are identified
by the letter designators A through K to protect the interests of the host
facilities. No mention is made of site location. The seven boilers tested
under separate subcontract were less extensively tested than Sites A through K.
These seven boilers were tested for particulate loading and particle size distri-
bution at a single operating condition. For this reason, these seven sites are
identified as Ll through L7 and their test results are reported under one cover
called the "Site L1-L7 Report."23' 24 Each site report is approximately 100
pages in length and may be obtained through the EPA's Center for Environmental
Research Information (CERI) or through NTIS. Ordering information is included
in the Appendix to this report.
The data supplements accompanying the site reports are only of value
to those who wish to study the data in greater detail than is presented in the
Site report. Each data supplement is a compilation of hand written data sheets,
and is not a required companion to the site report.
The following report consolidates the test results of all eighteen
stoker boilers. It is divided into three major sections according to stoker
classification: spreader stokers, mass fired overfeed stokers, and underfeed
stokers. Within each section the stoker boilers are described and the test
results summarized. Extensive use is made of figures and tables to present
the data.
Because the data base is so large, all of the data from each site can-
not be included in this final report. Instead, a Data Supplement to the final
report has been prepared which contains several hundred data plots and data
tables. The data supplement is not referenced in this report. However, the
data supplement is available to those who wish to study the data in greater
detail.
KVB4-15900-554
25
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This final report does not mention the names of the equipment manu-
facturers. The ABMA Stoker Technical Committee felt that such information
could lead to false association of unit performance with a specific manu-
facturer when, in fact, unit performance can relate to any number of variables
including fuel properties and operating procedures. Any superficial association
between unit performance and manufacturer would be a grievous mistake.
Two additional reports are being prepared under this contract. One
report will be addressed to stoker boiler operators, identifying operating pro-
cedures which lead to increased combustion efficiency and reduced emissions.
The other report will summarize the results of EPA Level 1 chemical analysis
on test sites A through K for polynuclear aromatic hydrocarbons and trace ele-
ments .
KVB4-15900-554
26
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3.0 SPREADER STOKERS
3.1 DESCRIPTION OF UNITS TESTED -
A spreader stoker is an overfeed stoker that discharges the fuel into
the furnace from mechanical feeders located above the grate. These feeders
throw the fuel onto a grate which travels toward the feeder. Spreader
stokers are characterized by a thin fuel bed on the grate and partial suspension
burning. They are studied as a separate group in this report because their
burning characteristics are uniquely different from other types of stokers.
The six spreader stokers tested for this program represent a wide
range of state-of-the-art designs. They were all built between 1973 and 1976.
They span the range of capacities most commonly specified for this type of unit,
ranging in capacity from 75,000 Ib steam/hr to 300,000 Ib steam/hr. Three of the
stokers are equipped with flyash reinjection from their mechanical dust collector.
Two are of the multiple pass or baffled boiler design, and all are equipped with
traveling grates and continuous front ash discharge. Table 3-1 gives a brief
description of each unit tested.
TABLE 3-1
DESCRIPTION OF SPREADER STOKERS TESTED
Site
A
B
C
E
F
G
Year
Built
1976
1974
1975
1973
1976
1974
Steaming
Capacity
lb/hr
300,000
200,000
182,500
180,000
80,000
75,000
Flyash
Reinjection
From DC
Yes
Yes
Yes
No
No
No
Boiler
Passes
Single
Single
Single
Single
Multiple
Multiple
Backend Equipment
by
Order of Occurrence
AH, DC, ESP, ECON,
DC, ECON, ESP
DC, ECON, AH, ESP
ECON, DC
ECON, DC
DC
SCR
The following pages present equipment data and a general arrangement
drawing of each spreader stoker tested. Throughout this report the units will
be referred to by the letter designation assigned in this section.
KVB4-15900-554
27
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TABLE 3-2
EQUIPMENT DATA
TEST SITE: A
BOILER:
Year Built
Configuration
Rated Steaming Capacity —
Design Pressure
Actual Operating Pressure
Feedwater Temperature
Steam Temperature
Operating Air Temperature
1976
Single Pass
300,000 Ib/hr
350 psig
320 psig
240°F
Saturated
315°F
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Spreader with Traveling Grate
19.0 Ft
27.1 Ft
515.4 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
16,712 Ft3
2,982 Ft2
20,186 Ft2
None
13,276 Ft2
Unknown
HEAT RATES AT RATED CAPACITY:
Input to Furnace
Grate Width Heat Release
Grate Heat Release
Furnace Liberation
359,000,000 Btu/hr
13,200,000 Btu/hr-ft
696,000 Btu/hr-ft2
21,500 Btu/hr-ft3
OVERFIRE AIR:
Location
Number of Jets x Pipe Size
Elevation Above Grate
Inclination below Horizontal
Front
Lower
30x3/4"
1.5 Ft
0°
Rear
Lower
27x1"
2.2 Ft
0°
FLYASH REINJECTION:
Flyash Source -
Number of Injectors —
Elevation above Grate
Inclination below Horizontal
Boiler Hopper
6
1.3 Ft
4.5°
AH Hopper
7
1.3 Ft
4.5°
DC Hopper
12
1.3 Ft
4.5°
EMISSION CONTROL EQUIPMENT:
Mechanical Collector
Electrostatic Precipitator
Wet Scrubber
* Front upper and rear upper overfire air jets have openings of 7/8"xl-5/16"
28
KVB4-15900-554
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i
I
on
Cn
6
(D
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TABLE 3-3
EQUIPMENT DATA
TEST SITE: B
BOILER:
Year Built
Configuration
Rated Steaming Capacity
Design Pressure
Actual Operating Pressure
Feedwater Temperature
Steam Temperature
Operating Air Temperature
1974
Single Pass
200,000 Ib/hr
750 psig
185 psig
225°F
500°F
Ambient
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Spreader with Traveling Grate
18.5 Ft
20.0 Ft
370.0 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
12,910 Ft3
2,820 Ft2
15,038 Ft2
1,900 Ft2
4,110 Ft2
None
HEAT RATES AT RATED CAPACITY:
Input to Furnace
Grate Width Heat Release
Grate Heat Release
Furnace Liberation
264,000,000 Btu/hr
13,200,000 Btu/hr-ft
713,000 Btu/hr-ft2
20,400 Btu/hr-ft3
OVERFIRE AIR:
Location
Number of Jets x Pipe Size
Elevation Above Grate
Inclination below Horizontal
Front Upper Rear Upper Rear Lower
7.8 Ft
18°
5.8 Ft
2.5°
2.0 Ft
2.5°
FLYASH REINJECTION:
Flyash Source -
Number of Injectors
Elevation above Grate
Inclination below Horizontal
Boiler Hopper
6
1.5 Ft
7°
DC Hopper
7
1.5 Ft
7°
EMISSION CONTROL EQUIPMENT:
Selective Type Mechanical Collector
Electrostatic Precipitator
KVB4-15900-554
30
-------
BOILER OUTLET
TEST PLANE
SPLIT
MECHANICAL
COLLECTOR
MECHANICAL HOPPER
REINJECTKJN
MECHANICAL COLLECTOR
rOUTLET TEST PLANE
Figure 3-2. Test Site B General Arrangement Drawing
KVB 4-15900-554
31
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TABLE 3-4
EQUIPMENT DATA
TEST SITE: C
BOILER:
Year Built
Configuration
Rated Steaming Capacity
Design Pressure
Actual Operating Pressure
Feedwater Temperature
Steam Temperature
Operating Air Temperature
1975
Single Pass
182,500 Ib/hr
1025 psig
875 psig
370° F
900° F
300° F
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Spreader with Traveling Grate
19.0 Ft
27.1 Ft
515.4 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
12,100 Ft3
2,906 Ft2
21,925 Ft2
10,520 Ft2
8,620 Ft2
22,217 Ft2
HEAT RATES AT RATED CAPACITY:
Input to Furnace
Grate Width Heat Release
Grate Heat Release
Furnace Liberation
249,000,000 Btu/hr
9,190,000 Btu/hr-ft
483,000 Btu/hr-ft2
20,600 Btu/hr-ft3
OVERFIRE AIR:
Location
Number of Jets x Pipe Size
Elevation Above Grate
Inclination below Horizontal
Front
Lower
29x3/4"
1.5 Ft
0°
Rear
Upper
28x1"
6.1 Ft
9°
Rear
Lower
1.5 Ft
0°
FLYASH REINJECTION:
Flyash Source -
Number of Injectors
Elevation above Grate
Inclination below Horizontal
Boiler Hopper
7
1.5 Ft
4°
DC Hopper
16
1.5 Ft
4°
EMISSION CONTROL EQUIPMENT:
Selective Type Mechanical Collector
Electrostatic Precipitator
KVB4-15900-554
32
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BOILER OUTLET
TEST PLANE
Figure 3-3. Test Site C General Arrangement Drawing
KVB 4-15900-554
33
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TABLE 3-5
EQUIPMENT DATA
TEST SITE: E
BOILER:
Year Built
Configuration
Rated Steaming Capacity
Design Pressure
Actual Operating Pressure
Feedwater Temperature
Steam Temperature
Operating Air Temperature
1973
Single Pass
180,000 Ib/hr
250 psig
175 psig
220°F
427°F
Ambient
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Spreader with Traveling Grate
21.5 Ft
16.0 Ft
344.0 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
10,255 Ft3
2,850 Ft2
13,402 Ft2
480 Ft2
6,350 Ft2
None
HEAT RATES AT RATED CAPACITY:
Input to Furnace
Grate Width Heat Release
Grate Heat Release
Furnace Liberation
232,000,000 Btu/hr
14,500,000 Btu/hr-ft
674,000 Btu/hr-ft2
22,600 Btu/hr-ft3
OVERFIRE AIR:
Location
Number of Jets x Pipe Size
Elevation Above Grate
Inclination below Horizontal
Front Upper
8
6.5 Ft
15°
Rear Upper Rear Lower
6.0 Ft
0°
8
2.0 Ft
0°
FLYASH REINJECTION:
Flyash Source -
Number of Injectors
Elevation above Grate
Inclination below Horizontal
Boiler Hopper
Unknown
1.3 Ft
5°
EMISSION CONTROL EQUIPMENT:
Mechanical Collector
KVB4-15900-554
34
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DUST COLLECTOR
OUTLET TEST PLANE
ECONOMIZED
OUTLET —-1
TEST PLANE
- I. D. FA N
Figure 3-4. Test Site E General Arrangement Drawing
KVB 4-15900-554
35
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TABLE 3-6
EQUIPMENT DATA
TEST SITE: F
BOILER:
Year Built
Configuration
Rated Steaming Capacity
Design Pressure
Actual Operating Pressure
Feedwater Temperature
Steam Temperature
Operating Air Temperature
1976
Multiple Pass
80,000 Ib/hr
200 psig
150 psig
228°F
Saturated
Ambient
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Spreader with Traveling Grate
13.0 Ft
10.9 Ft
141.4 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
4,105 Ft3
777 Ft2
8,203 Ft2
None
3,017 Ft2
None
HEAT RATES AT RATED CAPACITY:
Input to Furnace
Grate Width Heat Release
Grate Heat Release
Furnace Liberation
97,300,000 Btu/hr
8,950,000 Btu/hr-ft
688,000 Btu/hr-ft2
23,500 Btu/hr-ft3
OVERFIRE AIR:
Location
Number of Jets x Pipe Size
Elevation Above Grate
Inclination below Horizontal
Front
Lower
11x3/4"
1.5 Ft
0°
Rear
Lower
7x1"
1.0 Ft
0°
FLYASH REINJECTION:
Flyash Source -
Number of Injectors
Elevation above Grate
Inclination below Horizontal
Boiler Hopper
4
1.3 Ft
6.5°
Econ. Hopper
3
1.3 Ft
6.5°
EMISSION CONTROL EQUIPMENT:
Mechanical Collector
KVB4-15900-554
36
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ECONOMIZER
OUTLET
TEST PUfte
FLYASH -—FLY ASH
REINJECTION REINJECTION
DUST COLLECTOR OUTLET
TEST PLANE
Figure 3-5. Test Site F General Arrangement Drawing
KVB 4-15900-554
37
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TABLE 3-7
EQUIPMENT DATA
TEST SITE: G
BOILER:
Year Built
Configuration
Rated Steaming Capacity
Design Pressure
Actual Operating Pressure
Feedwater Temperature
Steam Temperature
Operating Air Temperature
1974
Multiple Pass
75,000 Ib/hr
200 psig
160 psig
212°F
Saturated
Ambient
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Spreader with Traveling Grate
14.2 Ft
9.8 Ft
139.0 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
4,120 Ft3
2,140 Ft2
8,280 Ft2
None
None
None
HEAT RATES AT RATED CAPACITY:
Input to Furnace
Grate Width Heat Release
Grate Heat Release
Furnace Liberation
99,000,000 Btu/hr
10,100,000 Btu/hr-ft
712,000 Btu/hr-ft2
24,000 Btu/hr-ft3
OVERFIRE AIR:
Location
Number of Jets x Pipe Size
Elevation Above Grate
Inclination below Horizontal
Front Lower
12x1"
1.4 Ft
0°
Rear Upper
14x1"
5.6 Ft
Rear Lower
llxl"
1.8 Ft
FLYASH REINJECTION:
Flyash Source •
Number of Injectors
Elevation above Grate
Inclination below Horizontal
EMISSION CONTROL EQUIPMENT:
Boiler Hopper
3
1.8 Ft
5°
Mechanical Collector
KVB4-15900-554
38
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OUST
COLL. OUTLET
TEST PUSSC
BOILER OUTLET
TEST PLANE
Figure 3-6. Test Site G General Arrangement Drawing
KVB 4-15900-554
39
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3.2 PERFORMANCE AT FULL LOAD
This section presents the emissions and efficiency data for six spreader
stokers operated at or near full load. For the purposes of this report, full
load is defined as the upper 10% of the load range obtainable at the time of
testing. For four of the spreader stokers this represents 90 to 100% of name-
plate rating. However, Sites A and E could not be operated at nameplate
rating at the time of these tests. The stoker at Site A was in its first months
of operation after initial startup and had an unresolved problem with its forced
draft system. Thus, Site A was limited to 87% of nameplate rating. The stoker
at Site E had been retrofitted with a new combustion air system which limited
its capacity to 73% of nameplate. The new system was limited by the capacity
of its forced draft fan.
The capacity ranges selected to represent full load at each site are
shown in Table 3-8. Also shown are the number of tests which make up the data
base.
TABLE 3-8
CAPACITY RANGE AND DATA BASE FOR FULL LOAD
TESTS ON SIX SPREADER STOKERS
Number of Tests
Site A
Site B
Site C (Eastern Coal)
Site C (Western Coal)
Site E
Site F
Site G
icity Range
80-87
96-100
91-99
95-102
65-73
97-102
97-102
Gaseous
9
9
26
19
10
22
13
Particulate
6
4
9
8
6
7
4
TOTALS 108 44
The Site C performance data are presented in two parts because of the signifi-
cant differences observed when burning an Eastern and a Western coal.
The figures in this section indicate minimums, maximums and averages
of the measured data for each parameter and test site as measured within the
40 KVB4-15900-554
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load ranges specified in Table 3-8. Each figure is accompanied by a brief
discussion of the data.
The data are representative of as-found operating practice. The
range of data shown represents normal variations which might be experienced
in day-to-day operation.
Extremes should be treated with caution when interpreting these data.
There is a certain degree of scatter, or uncertainty, to the data which must
be taken into account, Thus, for example, if a certain unit emitted a very
low particulate loading during one test, it does not follow that this unit can
operate continuously at the low particulate loading by simply duplicating the
stoker settings of the test.
3.2.1 Emission Factors
U.S. Environmental Protection Agency publication AP-42, Compilation of
Air Pollutant Emission Factors, Third Edition, contains factors used for pre-
dicting emissions from spreader stokers. The full load data from this test
program have been converted to the same units used in AP-42 to obtain a set of
measured emission factors. These are presented in Tables 3-9 and 3-10. The
bituminous and sub-bituminous coal data are presented separately since AP-42
addresses only bituminous coal firing. It is observed that the AP-42 emission
factor for uncontrolled particulate loading from spreader stokers is lower than
the measured values, while the AP-42 emission factor for Nitrogen Oxides is
higher than the measured values.
KVB4-15900-554
41
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TABLE 3-9
EMISSION FACTORS FOR SPREADER STOKERS
FIRING BITUMINOUS COAL
Uncontrolled Particulates, Ib/ton
With Without Nitrogen Oxides
Reinjection Reinjection Ib/ton
Site B 29 A* — 9.4
Site C 50 A 14.6 A 11.5
Site E — 13.7 A 14.2
Site F — 15.8 A 11.4
Site G -- 16.8 A 12.5
Average 40 A 15 A 12
AP-42 20 A 13 A 15
TABLE 3-10
EMISSION FACTORS FOR SPREADER STOKERS
FIRING SUB-BITUMINOUS COAL
Uncontrolled Particulates, Ib/ton
With Without Nitrogen Oxides
Reinjection Reinjection Ib/ton
Site A 60 A — 11.4
Site C 58 A 14.5 A 8.6
*The letter A indicates that the weight percentage of
ash in the coal should be multiplied by the given
value.
KVB4-15900-554
42
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-------
120
g
H
C/3
03
W
W
90
60
30
I
h
1 1 I I I I I
KEY
HIGH-*.
AVG — !
LOW—™
B Ce Cw E F
TEST SITE DESIGNATOR
Figure 3-8. Excess Air Operating Levels of Six Spreader stokers Fired
at Full Load.
The ranges of excess air shown here are those at which emissions
tests were conducted at full load. The lower end of the range indicates
the point at which undesirable combustion conditions were encountered. All
but Test Site C were successfully operated at the excess air levels stated
in their design performance statements. At Test Site C, the inability
to operate below 50% excess air without smoking was due at least in part to
a stratified coal bed. Coal fines were much higher at some feeders than
others, and the bed depth was uneven. It is also noted that Site C had a
relatively low design grate heat release and this may have contributed to
its higher excess air operating level. The design excess air levels for
these stokers were: A-25%, B-31%, C-32%, E-30%, F-37% and G-31%.
KVB4-15900-554
44
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12
>T
tf
£
3 9
1
w
ft
13
W
8
§ 6
3
.1
—
1 1
1
|
'1
1 1
1
|
1
|
KEY
HIGH— -
AVG— J
LOW-—'
A B Ce Cw E F G
TEST SITE DESIGNATOR
Figure 3-9. Excess Oxygen Operating Levels of Six Spreader Stokers
Fired at Full Load.
The same comments apply to flue gas oxygen as do to excess air.
For comparative purposes/ it may be noted that thirty percent excess air
is approximately equivalent to five percent oxygen. The data above
are presented on a dry basis. Measurement was made of a multipoint
sample collected at the boiler outlet using a fuel cell type oxygen
analyzer.
KVB4-15900-554
45
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4J
m
a
H
Q
§
EH
U
H
3
§
EH
40
30
20
8 10
—
- 1
a
_ o •
H 0
EH •
U Q
W <#
h) S 0
2O 0
H « H
W Cn
PH
1
1
1
Q
W
U
D
I
1
- •
^ I
< •
o I
w
o
H H
• cn
^^
||
c«> df> c(P dP
O CN O O
\^0 ^* I^> [**•«
i 1 II
KEY
HIGH— —
AVG —?
1
LOW—""
A A B B Ce
TEST SITE DESIGNATOR
Cw
Figure 3-10.
Uncontrolled Particulate Loadings for Three Spreader
Stokers Fired at Full Load with Flyash Reinjection from
the Mechanical Collector.
These particulate loadings represent tests in which a portion of
the mechanical dust collector catch was reinjected to the furnace. At
Site A, three tests were conducted with 100% reinjection from the dust
collector, while the remaining tests were conducted with the reinjection
rate reduced by an unknown amount. Sites B and C had selective type dust
collectors which were designed to reinject 60% and 70%, respectively, of
the collected ash. The actual percentage reinjected was not measured.
During one test at Site B the reinjection rate was reduced to an estimated
42%. The uncontrolled particulate loadings in these tests ranged from 9.6
to 36.4 lb/10^Btu. They were measured using EPA Method 5 equipment and
procedures.
KVB4-15900-554
46
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4J
CQ
0 20
\
O
a
1 15
w
EH
D
U
H
EH
g! 10
@
p-1
i-3
O
n1.
UNCONT]
Ul
"
-
"-
1 1
^H ^B ^1 Hi
< < " • • 1
1 1
• KEY
HIGH— _
AVG -»!
| | 1 1 1 1 1 °WJ
A B Ce Cw E F
TEST SITE DESIGNATOR
Figure 3-11.
Uncontrolled Particulate Loadings of Four Spreader Stokers
Fired at Full Load without Flyash Reinjection from the
Mechanical Collector.
Without flyash reinjection from the mechanical collector the uncon-
trolled particulate data ranged from 2.1 to 8.8 lb/106Btu. Note that Test
Site C was operated both with (Figure 3-10) and without (Figure 3-11) flyash
reinjection from the mechanical collector and had very different particulate
loadings under the two conditions. This illustrates that a portion of the
reinjected flyash is reentrained in the gas stream and is resulting in in-
creased particulate loadings. These boilers had some degree of flyash re-
injection from the boiler hopper, and at Site F from the economizer hopper.
The amount of flyash reinjected depends on duct geometry and whether or not
the boiler is equipped with baffles. In most cases, the actual rate of
reinjection was not known.
KVB4-15900-554
47
-------
-p
•& 80
•H
0)
a
H
EH
en
D
60
40
8 20
I
I
H
o
Ck
a
i i i i i i
B Ce Cw E F
TEST SITE DESIGNATOR
KEY
HIGH-—.
;i
Figure 3-12.
Percentage of Combustible Material in the Boiler Outlet
Flyash of Six Spreader Stokers Fired at Full Load.
Most of the flyash samples collected during the particulate
loading tests were analyzed for total combustible content. The data from
Sites A, B, E, F and G show that combustible content ranged from 47% to
84%. At Site C, combustibles were as low as 24% on the Eastern bituminous
coal (Ce) and 7% on the Western sub-bituminous coal (Cw). Factors con-
tributing to Site C's low combustible levels might be its low grate heat
release rate and high excess air operating levels. However, such a cor-
relation is not supported by data from the other test sites.
KVB4-15900-554
48
-------
I
ffi
s
EH
EH
§
W
33
EH
2
pq
H
EH
CO
D
8
40
30
20
10
EH
2
H
2
I
Q
a
H
: I!
I I I
KEY
HIGH—-
B Ce Cw E F
TEST SITE DESIGNATOR
Figure 3-13.
Percentage of Combustible Material in the Bottom Ash of
Six Spreader Stokers Fired at Full Load.
Bottom ash samples were obtained in several increments at the
dumping end of the grate or from the ash pit. The combustible content
of these samples ranged from 0% to 34%. The averages for Sites B, C,
E, F and G were relatively constant, ranging from 9 to 14%. For Site A,
a single data point was obtained at full load indicating no combustibles.
KVB4-15900-554
49
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.8
-P
PQ
.6
w
P
O
s •«
H
H
a
.2
I
I
i i i i i i
KEY
HIGH-*-.
AVG -*•!
LOW-"-'
B Ce Cw E P
TEST SITE DESIGNATOR
Figure 3-14.
Nitric Oxide Emissions of Six Spreader Stokers Fired at
Full Load.
Nitric oxide (NO) was measured at the boiler outlet using a
chemiluminescent type analyzer. The NO data ranged from .30 to .68 lb/
lO^Btu calculated as NO2 when measured at full load. NO levels were found
to be a function of excess air, heat release rate, and combustion tempera-
ture. Nitrogen dioxide (NO2) did not exceed 4% of the total NOx and was
most often negligible.
KVB4-15900-554
50
-------
800
(M
o
600
S
CM
CM
W
Q
400
o
200
T
i
H
Q
O
i i
KEY
HIGH -~«
AVG—-J
LOW-*-*
;i
A B Ce Cw E F
TEST SITE DESIGNATOR
Figure 3-15.
Carbon Monoxide Emissions of Five Spreader Stokers
Fired at Full Load,
Carbon monoxide (CO) was measured at the boiler outlet of each
unit with a non-dispersive infrared analyzer. This analyzer was out of
service during testing at Site G. Carbon monoxide emissions were highest
while burning low rank coals at Sites A and Cw. When excess air dropped
below 30% at Site A, combustion conditions became unstable. This resulted
in dramatic increases in carbon monoxide levels.
KVB4-15900-554
51
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W 40
O
n
g 30
ft
w
Z
0 20
Q
D
B 10
1
1
_ •
^^
"" <<<;<< 1
EH EH EH EH E-j •
Q Q Q Q Q ^H
§ § § i § 1
1 1 1 1 1 1 1
KEY
HIGH-"—
LOW—*
A B Ce Cw E F G
TEST SITE DESIGNATOR
Figure 3-16.
Unburned Hydrocarbon Emissions of Two Spreader Stokers
Fired at Full Load.
Unburned hydrocarbons (HC) were measured at the boiler outlet of
Sites F and G using a flame ionization type hydrocarbon analyzer. The
gas samples were pulled through a heated teflon sample line. Unburned
hydrocarbon levels ranged from 0 to 41 parts per million by volume (ppm)
on a wet basis.
KVB4-15900-554
52
-------
ft
2
H
CO
w
^
S
EH
CO
D
O
U
Q
10
CO
I
I
•
IB
H
O
I
H
00
I I I I I I
KEY
HIGH—-«
AVG— !
LOW—'
A B Ce Cw E F
TEST SITE DESIGNATOR
Figure 3-17.
Heat Loss Due to Combustibles in the Flyash of Six Spreader
Stokers Fired at Full Load.
The Flyash was not directly Analyzed for its Heating Value.
The heat loss due to combustibles in the flyash was computed by
assuming a heating value of 14,250 Btu/lb in the combustible fraction of
the flyash. Based on this assumption, heat losses ranged from 2% to 9%
at all but Site Cw, where such losses ranged from .5 to 1.1%.
KVB4-15900-554
53
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EH
D
H
1
ffi
§ 4
W
OT
D
8
§
a
CO
w
3
I!
w
EC
H
g
Q
W
J
O
2
H
W
|S
B
•I
I
j i
1
KEY
HIGH -«._
B Ce Cw E F
TEST SITE DESIGNATOR
Figure 3-18.
Heat Loss Due to Combustibles in the Bottom Ash of Six
Spreader Stokers Fired at Full Load.
The Bottom Ash was not Directly Analyzed for its Heating Value,
The heat loss due to combustibles in the bottom ash was computed
by assuming a heating value of 14,250 Btu/lb in the combustible material.
The bottom ash flow rate was computed from a mass balance involving coal
flow, percent coal ash, and particulate loading corrected for its com-
bustible content. Calculated in this manner, heat losses ranged from
negligible to 3.4%. The averages for Sites B, C, E, F and G ranged from
,54% to
KVB4-15900-554
54
-------
90
*
g 80
a
w
1 — 1
o
H
fa
fa
w
cti
£ 70
O
m
60
_
1 = • • !
Hi BB
H H
i .
•
—
EH
a
H
O
EH
"" Q
s
O
a
H
w
1 1 f 1 1 1 1
KEY
HIGH— -
LOW-»"
A B Ce Cw E F
TEST SITE DESIGNATOR
Figure 3-19. Boiler Efficiency of Six Spreader Stokers Fired at Full
Load.
Boiler efficiency was determined by the heat loss method using
the ASME Abbreviated Efficiency Test (PTC 4.1). At full load, the boiler
efficiencies ranged from 73.0% to 83.4%. The lowest efficiency belongs
to Site G, the only site which did not have either an air heater or an
economizer. The design efficiencies of these units were: A-83.68%,
B-84.16%, Cw-81.40%, E~80.41%, F-83.10% arid G-77.04%.
KVB4-15900-554
55
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3.3 RESPONSE TO HEAT RELEASE RATE
This section profiles the emissions and efficiency of six spreader
stokers as a function of heat release rate. Four measures of heat release
rate are considered. They are grate heat release, front foot heat release,
furnace liberation, and percent of steaming capacity. Each of these will
be briefly identified.
Heat release is the quantity of thermal energy above 70°F intro-
duced into the furnace by the fuel each hour. It is the product of the
hourly fuel rate and the fuel's higher heating value. Two of the six spreader
stokers, Sites A and G, were not equipped with coal scales for determining
hourly fuel rate. Therefore, heat release rate on these two units was taken
to be the enthalpy of the steam times the steam flow divided by the fractional
boiler efficiency.
Grate heat release is the most frequently used heat release rate in the
following discussion. It is defined as the heat release per square foot of
effective air admitting grate area, and is presented in units of Btu/hr-ft^.
For a given coal and excess air, grate heat release is proportional to the
upward velocity of gases in the furnace. The American Boiler Manufacturers
Association (ABMA) in its recommendation for stoker applications for bitumin-
ous coal suggests that the maximum grate heat release for spreader stokers with
traveling grates not exceed 750,000 Btu/hr-ft2.
Front foot heat release is the heat release per foot of grate width.
Its maximum value for these stokers ranged from 9,000,000 to 14,500,000 Btu/
hr-ft.
Volumetric heat release, commonly called furnace liberation, is
the heat release per cubic foot of furnace volume. As such, furnace liber-
ation is proportional to the residence time of gases in a furnace for a
given coal and heat release rate. That is to say that two stoker boilers
firing the same coal at the same furnace liberation and excess air would
have similar furnace residence times. The six spreader stokers tested
had maximum volumetric heat release rates ranging from 20,400 to 24,000
Btu/hr-ft3.
KVB4-15900-554
56
-------
Some of the data in this section are presented in terms of load,
or percent of design steaming capacity. Load and heat release rate are
proportional to each other on each unit to the extent that boiler efficiency
is a constant.
Table 3-11 presents the design heat release rates for the six spreader
stokers. Their differences reflect differences in unit design. One aim of
the analysis presented below is to examine what, if any, relationship exists
between these design differences and the unit's emissions and efficiency. The
other aim of this section is to profile the emissions and efficiency as the
heat release rate is changed on a given unit. The results are presented on an
emission-by-emission basis in the following subsections.
TABLE 3-11
Front Foot
Heat Release
Btu/hr-ft
13,200,000
13,200,000
9,200,000
14,500,000
9,000,000
10,100,000
DESIGN HEAT RELEASE RA1
Site A
Site B
Site C
Site E
Site F
Site G
.1 Excess
Furnace
Liberation
Btu/hr-ft3
21,500
20,400
20,600
22,600
23,500
24,000
Air vs Heat
Grate Heat
Release
Btu/hr-ft2
696,000
713,000
483,000
674,000
688,000
712,000
Release Rate
The excess air requirement is greater at lower loads than at full
load in stoker boilers. Although this fact is well known, it is worthwhile
documenting the magnitude of this relationship.
An example of this relationship is shown in Figure 3-20, which pre-
sents Site B data. In this example, a line has been drawn through the data
representing the as-found or normal excess air operating profile for this unit.
KVB4-15900-554
57
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A composite picture of the excess air profiles of six spreader
stokers is shown in Figure 3-21. The slopes of the six curves are similar.
However, there are considerable differences between the excess air require-
ments of the various units. These differences were found to relate to the
physical size of the unit.
The excess air requirements at a grate heat release of 500,000
Btu/hr-ft2 are plotted as a function of grate area in Figure 3-22. The
relationship is clear, with the exception of Site C which will be discussed
separately. The data could be plotted against other size parameters such as
furnace width or furnace volume with similar results.
Two explanations for this relationship are suggested, both relating to
the lower surface to volume ratio of the larger units. First, the larger units
are likely to leak a smaller percentage of air through access doors, casings,
and air seals. Second, the larger units are likely to release a smaller
fraction of their heat to the furnace wall and thus have a more intense flame.
Both explanations are only suggestions. Temperature and gaseous traverses
immediately above the flame zone would be helpful in determining the magnitude
of wall effects in stoker boilers.
As indicated in Figure 3-22, Site C had a higher excess air require-
ment for its size than did the other sites. This was the result of coal
size stratification in the coal hoppers. A disproportionate fraction of the
coal fines were being fed to one side of the stoker. This resulted in one
side of the stoker operating at a lower excess air than the other. Since the
excess air was limited by smoke and clinkering at the low side, the average
excess air was higher than it should be. The lower limit of excess air on
all of the stokers was indicated by excessive carbon monoxide, smoke or
clinkering on the grate.
KVB4-15900-554
59
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150
120
H
90
60
30
SPREADER STOKERS
B
I
I
I
300 400 500 600
GRATE HEAT RELEASE, l03Btu/hr-ft2
700
Figure 3-21.
Excess Air Profiles for Six Spreader Stokers Representing
Normal Operating Conditions.
KVB4-15900-554
60
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100
80
K
H
w
60
40
20
SPREADER STOKERS
B
I
I
1
100
200 300 400
EFFECTIVE GRATE AREA, FT2
500
Figure 3-22.
Excess Air Operating Levels of Six Spreader Stokers Showing
a Correlation with Size of Grate. The Data Represents a
Grate Heat Release Rate of 500,000 Btu/hr-ft2.
KVB4-15900-554
61
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'3.3.2 Particulate Loading vs Heat Release Rate
Uncontrolled particulate loading — particulate loading at the
boiler outlet — was found to increase as heat release rate increased over
its full range. The rate of increase was roughly linear in four of the
units, but accelerated as full load was approached at Sites C and F.
Figure 3-23 presents the particulate loading profiles of the six
spreader stokers as a function of grate heat release. The slope of this
relationship is greatest for Sites A and C. This may be due to the high
degree of flyash reinjection at these two sites, or to properties of the coal
ash. The slope of this relationship was also examined by linear regression
analysis. The results are given in Table 3-12.
TABLE 3-12
INCREASE IN UNCONTROLLED PARTICULATE LOADING
FOR EACH 103BTU/HR-FT2 GRATE AREA INCREASE
Site A - .0328 lb/106Btu
Site B - .0100 lb/106Btu
Site C - .0845 lb/106Btu
Site E - .0079 lb/106Btu
Site F - .0085 lb/106Btu
Site G - .0048 lb/105Btu
Test Site G was unique in that it was tested at loads as low as 16% of
design capacity. The uncontrolled particulate loading data for Site G are
plotted against grate heat release in Figure 3-24. This plot shows only the
data obtained under steady load operation. Three swing load data points were
removed for clarity. Uncontrolled particulate loading clearly increases as
heat release rate increases.
Figure 3-25 shows the controlled particulate loading at Test Site G.
The observed tendency for controlled particulate loading to increase as heat
release rate increases in the upper 50% of its range was common to four of the
spreader stokers. Two spreaders, Sites B and F, showed no change with heat
release rate. Only Site G showed an extremely sharp increase in controlled
KVB4-15900-554
62
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35
30
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SPREADER STOKERS
B
1
I
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300 400 500 600
GRATE HEAT RELEASE, 103BtU/hr-ft2
700
Figure 3-23.
Uncontrolled Particulate Mass Loading Trends with Grate
Heat Release for Six Spreader Stokers.
KVB4-15900-554
63
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SHADED AREA EMPHASIZES THE DATA TREND
0
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GRflTE HEflT RELEflSE 1000 BTU/HR-SQ FT
: WHITE flSH + ! SPURLOCK
• PEVLER
FIG. 3-24
UNCONTROLLED PflRT. VS. GRflTE HEflT RELEflSE
4-15900-554
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SHADED AREA EMPHASIZES THE DATA TREND
T
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GRRTE HERT RELERSE 1000 BTU/HR-SQ FT
O .' WHITE flSH + .' SPURLOCK A .' PEVLER
FIG. 3-25
CONTROLLED PRRT. VS. GRRTE HERT RELERSE
4-15900-554
65
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particulate loading at low heat release rates. This was due to a drop in
mechanical collector efficiency at the unusually low firing rate obtained at
this site.
The effects of design heat release rates on full load uncontrolled
particulate loading were also examined. It might be expected that units with
higher design heat release rates would have higher uncontrolled particulate
loadings. This was not the case.
Table 3-13 presents the data for those sites which were operated at
their design steaming capacity and without flyash reinjection from their
mechanical dust collector. The data show that the unit with the highest heat
release rates, Site G, also had the lowest uncontrolled particulate loadings.
The only conclusion to be drawn from these data is that uncontrolled particu-
late loading cannot be predicted from heat release rates alone. Other factors
are involved.
TABLE 3-13
UNCONTROLLED PARTICULATE LOADING VS
DESIGN HEAT RELEASE RATES
Range of Full Load
Particulate Loading
lb/106Btu
Furnace
Liberation
103Btu/hr-ft3
Grate
Heat Release
103Btu/hr-ft2
Front Foot
Heat Release
106Btu/hr-ft
Site C
Site F
Site G
6.0-8.6
5.2-8.8
2.9-6.8
20.6
23.5
24.0
483
688
712
9.2
9.0
10.1
3.3.3 Combustibles in the Flyash vs Heat Release Rate
In this report, combustibles in the flyash refers to the percentage by
weight of combustible material in the flyash sampled at the boiler outlet.
Combustibles in the flyash tended to increase as heat release rate in-
creased. This trend is shown in Figure 3-26 where the average flyash combustible
level is plotted against grate heat release for each of the six spreader
stokers.
KVB4-15900-554
66
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30
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SPREADER STOKERS
Cw
B
I I
300 400 500 600
GRATE HEAT RELEASE, 103BtU/hr-ft2
700
Figure 3-26.
Flyash Combustible Profiles for Spreader Stokers as a
Function of Grate Heat Release.
KVB4-15900-554
67
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At high heat release rates, the flyash combustible levels appear to
drop at Sites B and G. These apparent drops are not definite. The test
data, shown in Figures 3-27 and 3-28 for Sites B and G, respectively, show
that one or two stray data points could alter this trend.
The magnitude of the combustible vs load trend was highly variable,
ranging from nothing to about 14% combustibles per 100,000 Btu/hr-ft2 increase
in grate heat release. It was difficult to establish trends at some sites due
to data scatter and the many other variables involved.
3.3.4 Combustibles in the Bottom Ash vs Heat Release Rate
The percentage of combustible material in the bottom ash varied very
little with heat release rate. A composite plot indicating the bottom
ash combustible levels vs grate heat release for each site except Site C is
shown in Figure 3-29.
Figure 3-30 presents bottom ash combustible data for a single site,
in this case Site G. Even at the extremely low heat release rate of 150,000
Btu/hr-ft2 grate area, the combustible level was similar to levels found at
high heat release rates.
The data at Site C behaved differently than the others. These data
are shown in Figure 3-31. While firing Eastern bituminous coals at Site C,
the combustible level in the bottom ash showed considerable scatter. That is,
three full load tests produced between 19 and 24% combustibles while eight
others at the same load produced between 1 and 5%. While firing Western sub-
bituminous coal, the combustibles increased as heat release rate decreased,
reaching 50% at 300,000 Btu/hr-ft2 grate area.
One can only speculate on the reasons for this anomalous behavior.
Site C was unique in that it operated at very low grate heat release rates by
design. Site C also had a problem with pancaking, or sheet clinkering on the
surface of the fuel bed. The pancaking could explain the high and variable
combustible levels in the bottom ash.
KVB4-15900-554
68
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BOTTOM RSH COMB. VS.
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4-15900-554
71
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BOTTOM RSH COMB. PERCENT
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3.3.5 Nitric Oxide vs Heat Release Rate
Nitric oxide levels are a function of both excess air and heat release
rate in stoker boilers. Thus, it is necessary to sort out the effects of ex-
cess air before the effects of heat release rate can be determined. Multiple
regression analysis was used to accomplish this.
Before presenting the computer analysis, the data from a single site,
Test Site F, will be presented. Data from this site exhibited the relationships
most clearly and can serve as an example for the behavior of nitric oxide in
spreader stokers.
Figure 3-32 presents the Site F nitric oxide data as a function of ex-
cess air. All tests were run at three distinct heat release rates equivalent
to 100%, 75%, and 50% of the unit's design capacity. This plot shows that the
relationship between nitric oxide and excess air at constant load is roughly
linear over the range of excess air tested. This plot also shows that the
relationship between nitric oxide and heat release rate is approximately linear.
A mathematical model was made for each site assuming a linear relation-
ship between nitric oxide and excess air at constant load, and between nitric
oxide and load at constant excess air. Multiple regression analysis was used
to fit the data to an equation of the form:
NO, lb/106Btu =
a + b (Excess Air, %) + c (Grate Heat Release, Btu/hr-ft2)
The results of this modeling effort are presented in Table 3-14. Along
with the coefficients a, b and c, is the coefficient of determination R2. The
coefficient of determination gives a measure of how well the data fits the
equation. If R2 = 1, it was a perfect fit. The best fit was obtained with the
Site F data, the worst fit was obtained with the Site C Eastern coal data.
Coefficient "c" is of prime interest in this section because it re-
lates nitric oxide emissions to grate heat release at constant excess air. The
average coefficient c (i.e., .00041) indicates that an increase in grate heat
release equivalent to 105 Btu/hr-ft2 grate area will result in an increase in
NO emissions of .041 lb/106Btu as NO2 at constant excess air. Expressed in other
units, an increase in load equivalent to 10% of capacity will result in an in-
-rease in NO emissions of approximately .025 lb/106Btu,
KVB4-15900-554
74
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FIG. 3-32
NITRIC OXIDE VS. OXYGEN
4-15900-554
75
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TABLE 3-14
COEFFICIENTS FROM MULTIPLE REGRESSION ANALYSIS
ON NITRIC OXIDE DATA FROM SPREADER STOKERS
Coefficients for Coefficient of
NO = a+b(Ex Air)+c(Grate Heat Release) Determination
a
.126
.128
.017
.051
.293
-.034
.151
b
.00674
.00243
.00287
.00269
.00214
.00360
.00334
c
.00041
.00022
.00054
.00060
.00032
.00046
.00029
R2
.66
.68
.40
.59
.58
.81
.46
Site A
Site B
Site C (Eastern)
Site C (Western)
Site E
Site F
Site G
This model is a simple one. The true relationship between nitric
oxide and the variables excess air and load are not necessarily linear. In
fact, the model does not explain the 16% load data of Site G. Thus, the model
is only valid between loads of 50% to 100% capacity, and between excess air
limits of about 30% to 150%. Also, the model does not take into account other
possible variables such as combustion air temperature.
Nitric oxide increased with load, or heat release rate, at constant
excess air. However, under normal operation excess air decreases as load in-
creases. The two influences cancel each other out such that nitric oxide con-
centration was relatively invariant with load on the six spreader stoker boilers.
Nitric oxide concentration might also be a function of stoker boiler
design in addition to heat release rate and excess air. This is indicated in
Table 3-15 by the average NOx emissions at full load and 50% excess air for
the six spreader stokers. These averages range from .4 to .7 lb/106Btu NOx.
Some of the variations can be explained. Test Site A's high NOx appears to be
due to its high combustion air temperature. This relationship between high
combustion air temperature and NOx has been noted by other researchers. At
Sites E, F, C, and B, low NOx seems to correlate with low furnace liberation.
Test Site C is unusual in that its NOx was low despite its high combustion air
temperature.
KVB4-15900-554
76
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TABLE 3-15
Site A
Site E
Site G
Site F
Site C
Site B
NITRIC OXIDE VS DESIGN
Nitric Oxide
@ Full Load
& 50% Excess Air
lb/106Btu
.70
.55
.53
.47
.45
.40
3 . 6 Carbon Monoxide
Combustion
Air
Temperature
°F
270
92
75
80
300
60
VARIABLES
Furnace
Liberation
103Btu/hr-ft3
21.5
22.6
24.0
23.5
20.6
20.4
vs Heat Release Rate
Grate
Heat Release
103Btu/hr-ft2
696
674
712
688
483
713
Carbon monoxide increased whenever excess air was too low at high heat
release rates, or too high at low heat release rates. Because of the differing
operating conditions among the six spreader stokers, it was not possible to
typify carbon monoxide emissions for spreader stokers. Each unit behaved dif-
ferently.
At Site A, combustion conditions became unstable at full load when
excess air dropped below 30%. This was indicated by highly variable and ex-
cessive carbon monoxide emissions. Sites C and F showed this same tendency but
to a lesser extent.
At Site B, carbon monoxide emissions were low at full load but increased
sharply at low loads. The tendency for carbon monoxide to increase at low loads
was also evident to a lesser extent at Site F. Test Site E showed neither of
these trends because tests were conducted over too narrow a range of operation.
Figure 3-33 shows the carbon monoxide trends with grate heat release
for five spreader stokers. Carbon monoxide was not measured at Site G because
the CO monitor was out-of-service.
KVB4-15900-554
77
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CARBON MONOXIDE, PPM @ 3% O2 (DRY)
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3.3.7 Unburned Hydrocarbons vs Heat Release Rate
Unburned hydrocarbons were measured only at Sites F and G. At these
two sites, opposite trends were observed. At Site F, hydrocarbons decreased
as full load was approached. At Site G, hydrocarbons increased. The hydro-
carbon data are presented in Figure 3-34.
Unburned hydrocarbons did not correlate well with carbon monoxide
at these two sites. That is to say, hydrocarbon emissions did not necessarily
increase as carbon monoxide emissions increased.
3.3.8 Boiler Efficiency vs Heat Release Rate
The boiler efficiency data for all six spreader stokers are plotted
against grate heat release in Figure 3-35. Boiler efficiency appears to be
relatively constant at all heat release rates in this figure.
Examined separately, Sites B, C, and G had decreasing efficiencies
as the heat release rate dropped. These decreases were related to the rapidly
increasing excess air requirement, and the resultant increase in dry gas heat
loss. It was also observed that boiler efficiencies dropped as full load was
approached at Sites E, F, and G due to increasing combustible losses. There-
fore, peak efficiencies were sometimes obtained in the vicinity of 80% of
design steaming capacity.
It is necessary to sort out the effects of coal properties and ab-
normal operating conditions to obtain these efficiency trends. They are not
immediately evident from the data plots. Nor are they true for all six units
tested. The most unpredictable heat loss was the heat loss due to combustibles
in the ash. Were it not for this, boiler efficiencies could be predicted with
a great deal more accuracy.
3.4 RESPONSE TO EXCESS AIR
This section discusses the influence excess air had on the emissions
and efficiency of spreader stokers. Excess air is primarily a function of load,
decreasing as load increased under normal operating conditions. But, excess air
also varies at constant load and this is the relationship that is of interest
here.
KVB4-15900-554
79
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The normal procedure during testing was to first test the unit at
an as-found, or normal condition. These as-found conditions were, of course,
dependent upon which operator was on duty since each operator set up his
boiler in a slightly different way.
The next step was to test the unit at a higher and at a lower excess
air level while keeping the load constant. Keeping the load constant was
often a problem, as was making significant variations in excess air. The
results are often difficult to interpret because the range of excess air data
at any given load was generally quite limited.
3.4.1 Particulate Loading vs Excess Air
Uncontrolled particulate loading was found to be only weakly related
to excess air, if at all, while other factors predominated.
Figure 3-36 represents a typical plot of particulate loading versus
excess air. The data are from Test Site B, and the three symbols represent
three load ranges: low load being 40-60% of capacity, medium load being
60-80% of capacity, and high load being all tests greater than 80% of capacity.
In this figure, the high load data indicate no trend for particulate
loading versus excess air. The medium load data indicate an increasing trend
based on a single test point at 90% excess air. The low load data indicate
a slightly decreasing trend. Other sites showed a similar lack of orderliness,
and it was usually impossible to determine any trend at all.
An alternate approach to this problem was attempted using multiple
linear regression analysis to correlate the data to the form:
Particulate Loading = a + b (% Load) + c (% Excess Air)
This approach assumes linear relationships between uncontrolled particu-
late loading and the variables load and excess air. The approach did not yield
any trends which could be called statistically significant. It is concluded
that there were too many uncontrolled variables and too narrow an excess air
range to establish a relationship with excess air. The data neither refute
nor support the existence of such a relationship.
KVB4-15900-554
82
-------
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TEST SITE B
0
30.
60. 90. 120,
EXCESS RIR PERCENT
150.
S LOU LOflD + : MED LOFff)
Z HIGH LOflD
FIG. 3-36
UNCONTROLLED PflRT. VS. EXCESS RIR
83
4-15900-554
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3.4.2 Combustibles in the Ash vs Excess Air
As with particulate loading, combustibles in the ash showed little
or no correlation with excess air level. The Test Site B data are presented
as an example. Figure 3-37 shows the percentage of combustibles in the
uncontrolled flyash as a function of excess air for three load ranges.
Figure 3-38 shows the percentage of combustibles in the bottom ash versus
excess air. Again, if a correlation does exist, it is masked by uncontrolled
variables.
3.4.3 Nitric Oxide vs Excess Air
Nitric oxide concentration increased with excess air in a well defined
and consistent manner. The rate of increase averaged .0285 Ib NOx/106Btu per
10% increase in excess air at constant load. This average rate applies to
Sites B, C, D, E, F, and G, but does not apply to Site A which had a rate of
increase equal to .0674 Ib NOx/lO^Btu per 10% increase in excess air.
The nitric oxide-excess air relationships were determined by multiple
regression analysis and by visual means. The visual method considered only the
full load data while the multiple regression analysis took all the data into
account and assumed that the relationship between NOx and excess air was the
same at all loads. The agreement between the two methods was good. Table 3-16
presents the slopes as determined by multiple regression analysis, and
Figure 3-39 presents the same data graphically for the case of full load
operation.
TABLE 3-16
RELATIONSHIP BETWEEN NITRIC OXIDE AND
EXCESS AIR AT CONSTANT LOAD
NOx(lb/106Btu) per 10% Excess Air
Site A .0674
Site B .0243
Site C (Eastern Coal) .0287
Site C (Western Coal) .0269
Site E .0214
Site F .0360
Site G .0334
84 KVB4-15900-554
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T
T
30.
60. 90. 120,
EXCESS RIR PERCENT
150.
: LOW LOflD
: MED LORD
LORD
FIG. 3-37
BLR OUT FLYRSH COMB. VS. EXCESS RIR
4-15900-554
85
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0
30.
60. 90. 120,
EXCESS RIR PERCENT
150.
", LOU LORD + °, MED LORD
° HIGH
FIG. 3-38
BOTTOM RSH COMB.
VS. EXCESS flIR
4-15900-554
86
-------
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CN
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0.6
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ffl
W
Q
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X
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0.5
0.4
0.3
20
40 60
% EXCESS AIR
80
100
Figure 3-39.
The Relationship Between Nitric Oxide and Excess Air Under
Full Load Conditions on Six Spreader Stokers.
KVB4-15900-554
87
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3.4.4 Carbon Monoxide vs Excess Air
Carbon monoxide emissions were very critical to boiler tuning at
Site A when operated at high loads and low excess air levels. Below 30% excess
air, CO ranged from 61 ppm to 2000+ ppm at Site A. This trend was true to
a lesser extent when excess air dropped below 40% excess air at Site F. The
carbon monoxide limit, or point at low excess air where CO becomes difficult
to control, was not established on the other spreader stokers. Generally
speaking, testing was stopped when clinkering, smoking, or other combustion
problems were encountered so as not to disrupt operations, or strain relation-
ships with the host facility.
The carbon monoxide limit is illustrated in Figure 3-40 which is a
composite of all carbon monoxide data from Sites A, B, E, and F. The Site C
data was excluded from this plot because its carbon monoxide levels were
relatively high in the 60% to 90% excess air range, and this tended to cloud
the trends being presented for the other sites. Site G has no data because
the carbon monoxide analyzer was out-of-service during testing at that site.
Another trend noted is that carbon monoxide emissions increased at
lower loads as excess air increased above about 50%. This trend has a more
gradual slope, whereas the low air limit described earlier is quite steep.
This trend may be due to the cooling and quenching effects of high excess air.
Figure 3-41 illustrates the relationships between load and the
carbon monoxide trends at Site F. Not only does medium and low load carbon
monoxide increase as excess air increases, but at 50% excess air the lower
loads have the lower carbon monoxide levels. This may mean that increased carbon
monoxide is being formed at high loads because the residence time in the flame
zone is reduced at higher loads.
3.4.5 Unburned Hydrocarbons vs Excess Air
Unburned hydrocarbons, assumed to be primarily methane, were measured
at Sites F and G. The data are plotted as a function of excess air in Figure
3-42.
The only observed trend with excess air occurred with the 80% load
data at Test Site G. These levels, based on four readings, decreased as ex-
cess air increased. This trend is not illustrated.
KVB4-15900-554
88
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SPREADER STOKERS
m o
a
a
m
m
m
o
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+
30.
60. 90. 120,
EXCESS RIR PERCENT
: SITE R
: SITE B
I SITE E
+ : SITE F
FIG. 3-40
CflRBON MONOXIDE VS. EXCESS flIR
150,
4-15900-554
89
-------
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TEST SITE F
A A
A
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A
30.
T
T
60. 90. 120,
EXCESS RIR PERCENT
150.
O : LOW LORD + : MED LOBD A • HIGH LORD
FIG. 3-41
CRRBON MONOXIDE VS. EXCESS RIR
4-15900-554
90
-------
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It was also determined that hydrocarbon concentration did not
correlate with carbon monoxide concentration at Site F. A similar cor-
relation check could not be made at Site G because Site G lacked carbon
monoxide data.
3.4.6 Boiler Efficiency vs Excess Air
Boiler efficiency decreased as excess air increased on all six
spreader stokers. Dry gas heat losses dominated this trend, overshadowing
any effects due to combustible heat losses.
The combustible and dry gas heat loss data for Test Site G are pre-
sented as an example. Figures 3-43 and 3-44 show the general lack of trend
with excess air for the flyash and bottom ash combustible losses respectively.
Figure 3-45 presents the dry gas heat loss data. Note that the dry gas heat
loss is a function of boiler steaming capacity, or load, in addition to ex-
cess air.
The boiler efficiency data for Site G are presented in Figure 3-46.
Again, it is apparent that steaming capacity was a major variable along with
excess air. At constant excess air, boiler efficiency was higher at reduced
loads.
The other spreader stokers behaved in a manner similar to that of the
stoker at Site G, but exhibited a weaker relationship to excess air. Their
relationships are listed below, with the exception of Site A, for which in-
sufficient efficiency data existed.
EFFICIENCY GAIN PER 10% EXCESS AIR DECREASE
Site B .53%
Site C .55%
Site E .33%
Site F .67%
Site G 1.00%
KVB4-15900-554
92
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TEST SITE G
A
0
30.
60. 90. 120.
EXCESS RIR PERCENT
150.
O : LOU torn -|- : MED LORD A : HIGH LORD
FIG. 3-43
FLYflSH COMB. HT LOSS VS. EXCESS RIR
4-15900-554
93
-------
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BOTTOM RSH COMB. LOSS PERCENT
1.000 2.000 3.000 4.000 5.000
i i i i i
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DRY GRS HERT LOSS PERCENT
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TEST SITE G
T
T
30.
60. 90. 120,
EXCESS flIR PERCENT
150.
O : LOU LORD 4- : MED Lono A : HIGH LOflD
FIG. 3-46
BOILER EFFICIENCY VS. EXCESS flIR
4-15900-554
96
-------
3.5 RESPONSE TO COAL ANALYSIS AND SIZING
Coals from several different mines were fired in each stoker, allowing
for an evaluation of coal properties as a test variable. In most cases the coals
were quite similar to each other, and produced quite similar emissions. In one
case, however, an Eastern bituminous coal and a Western sub-bituminous coal were
fired in the same boiler and did exhibit different emission characteristics.
Where coal properties were similar from one coal to another, it was often
possible to correlate emissions with coal variations observed on a test-by-test
basis. This was made possible by obtaining coal samples close enough to the stoker
that they could be correlated directly with the test being conducted.
The coal properties are summarized in the six accompanying tables. Each
table presents the average analysis for each of eighteen coal-stoker combinations.
The tables include: coal identification and ASTM classification, proximate analy-
sis, ultimate analysis, fusion temperature of the ash, mineral analysis of the ash,
and coal size consistency. The data base includes the following number of samples
for each analysis:
Proximate - 141 samples (Table 3-18)
Ultimate - 52 samples (Table 3-19)
Ash Fusion - 33 samples (Table 3-20)
Mineral - 32 samples (Table 3-21)
Size Consist - 136 samples (Table 3-22)
3.5.1 Particulate Loading vs. Coal Properties
Two properties were examined for their relationship to particulate
loading. These are coal ash on a mass percent basis, and coal fines. Each will
be presented separately.
Coal Ash. An examination of Table 3-18, Proximate Analysis, indicates
that coal ash was a significant variable only at Sites A and G. At least, this
is the case when comparing the averages.
The Site A data, shown in Figure 3-47, shows very little difference in
particulate loading between the two coals. The Site G data, on the other hand,
does indicate a considerable difference in loading at full load, yet indicates
no difference at low load. (Figure 3-48)
KVB4-15900-554
97
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TABLE 3-17
Coal
Identification
CD
Site A
Site B
Site C (E)
(W)
(E)
Site E
Site F
Site G
1
2
3
1
2
3
4
1
2
3
1
2
3
1
2
1
2
3
Stansbury
Kemmerer
Consolidation
Kentucky Cumberland
Hatfield
Southeast
Reload
Eastern Low Fusion
Western
Eastern High Fusion
Kentucky
Crushed Kentucky
Eastern Kentucky
Pennsylvania A
Pennsylvania B
White Ash
Spurlock
Pevler
COAL IDENTIFICATION AND CLASSIFICATION*
SPREADER STOKERS
Fixed Carbon
(Dry, Mineral
Matter-Free
ASTM Classification Basis)
Subbituminous A
Subbituminous A
High Volatile C Bituminous
High Volatile A Bituminous
High Volatile A Bituminous
High Volatile A Bituminous
High Volatile A Bituminous
High Volatile A Bituminous
Subbituminous C
High Volatile B Bituminous
High Volatile A Bituminous
High Volatile A Bituminous
High Volatile B Bituminous
Medium Volatile Bituminous
Medium Volatile Bituminous
High Volatile A Bituminous
High Volatile A Bituminous
High Volatile B Bituminous
Volatile Matter
(Dry, Mineral
Matter-Free
Basis)
Calorific Value
(Moist, Mineral
Matter-Free
Basis)
57
56
57
62
62
62
62
59
56
63
60
61
60
70
71
60
58
59
43
44
43
38
38
38
38
41
44
37
40
39
40
30
29
40
42
41
11,300
10,720
11,620
14,450
14,550
14,650
14,450
14,030
9,410
13,190
14,090
14,250
13,980
15,000
15,060
14,120
14,600
13,960
* Coal was Classified by rank using the Parr Formulas
and ASTM D 388.
KVB4-15900-554
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TABLE 3-18
PROXIMATE COAL ANALYSIS
SPREADER STOKERS
Weight Percent as-Fired
Site A
Site B
Site C
Site E
Site F
Site G
Coal Moisture
1 14.38
2 18.80
3 12.82
1 4.27
2 3.93
3 2.90
4 4.38
1 5.31
2 25.63
3 9.09
1 6.12
2 5.69
3 6.30
1 4.06
2 3.85
1 4.56
2 3.01
3 4.59
Ash
6.07
3.47
7.89
7.72
8.79
9.02
6.40
11.17
9.02
9.24
8.52
9.08
8.21
10.55
9.39
8.04
4.42
7.32
Volatile
34.71
34.70
34.15
34.24
33.65
34.19
34.71
35.02
28.94
30.94
35.06
33.50
34.47
26.27
25-. 68
35.19
38.97
36.29
Fixed
Carbon
44.84
43.05
45.14
53.77
53.63
53.89
54.51
48.49
36.35
50.72
50.29
51.73
51.01
59.11
61.09
52.17
53.59
51.79
Btu/lb
10546
10310
10628
13220
13137
13201
13432
12262
8493
11854
12773
12831
12722
13242
13502
12869
13860
12832
%
Sulfur
.93
.63
.40
.90
.93
.78
.77
2.89
.70
.88
.86
.71
.77
1.47
1.00
.78
1.31
.75
KVB 4-15900-554
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TABLE 3-19
ULTIMATE COAL ANALYSIS
SPREADER STOKERS
Weight Percentage as-Fired
Site A
Site B
Site C
Site E
Site F
Site G
1
2
3
1
2
3
4
1
2
3
1
2
3
1
2
1
2
3
Moisture
13.96
18.81
13.06
3.88
3.31
2.95
5.97
3.45
25.04
13.27
6.13
5.69
6.31
3.28
3.69
4.18
3.32
4.63
Carbon
60.47
59.68
62.19
72.74
72.88
73.34
73.45
71.05
50.92
64.30
71.69
71.95
71.31
75.14
70.36
72.26
74.59
72.67
Hydrogen
4.16
4.08
4.11
4.92
4.88
4.92
4.94
4.79
3.28
4.02
4.73
4.72
4.70
4.61
4.69
4.72
5.11
4.88
Nitrogen
0.99
0.85
0.82
1.05
1.43
1.26
1.45
1.18
0.94
1.41
1.30
1.36
1.13
1.23
1.12
0.98
1.12
1.00
Chlorine
0.01
0.01
0.01
0.10
0.10
0.13
0.12
0.07
0.01
0.07
0.13
0.14
0.08
0.15
0.17
0.10
0.18
0.05
Sulfur
0.99
0.66
0.35
0.96
0.93
0.79
0.73
2.76
0.60
0.75
0.86
0.71
0.78
1.42
1.00
0.75
1.31
0.67
Ash
6.85
3.45
7.81
9.22
9.87
10.01
6.72
10.49
8.76
7.93
8.52
9.08
8.21
10.52
8.96
8.92
6.56
7.10
Oxygen
12.59
12.48
11.65
7.13
6.62
6.61
6.65
6.22
10.45
8.25
6.67
6.36
7.50
3.68
4.03
8.09
7.81
9.01
KVB 4-15900-554
100
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TABLE 3-20
FUSION TEMPERATURE OF THE ASH
REDUCING ATMOSPHERE - SPREADER STOKERS
Site A
Site B
Site C
Site E
Site F
Site G
Coal
1
2
3
1
2
3
4
1
2
3
1
2
3
1
2
1
2
3
Initial
Deformation
2000 °F
2200
2170
2490
2550
2607
2700+
2023
2180
2145
2700+
2700+
2700+
2560
2700+
2700+
2420
2700+
Softening
H=W
2190 °F
2300
2265
2643
2700+
2700+
2700+
2155
2250
2235
2700+
2700+
2700+
2650
2700+
2700+
2650
2700+
Softening
H=iW
2240 °F
2393
2355
2673
2700+
2700+
2700+
2288
2317
2330
2700+
2700+
2700+
2675
2700+
2700+
2680
2700+
Fluid
2640 °F
2488
2420
2700+
2700+
2700+
2700+
2410
2375
2420
2700+
2700+
2700+
2700+
2700+
2700+
2700+
2700+
KVB 4-15900-554
101
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TABLE 3-21
MINERAL ANALYSIS OF THE ASH
SPREADER STOKERS
Site B
Site C
Site E
Site F
Site G
§
*>
I
H
On
U>
O
O
I
Ul
Ul
Coal
1
2
3
1
2
3
4
1
2
3
1
2
3
1
2
1
2
3
Silica
SiO?
59.32
51.88
46.02
53.99
54.82
54.14
53.77
43.69
42.61
49.23
52.67
52.03
49.80
45.06
47.85
52.89
43.26
51.00
Alumina
Al?0^
12.90
18.49
18.65
28.44
28.58
29.75
30.36
21.36
17.85
23.21
31.68
33.59
36.27
32.43
33.42
31.29
30.37
37.18
Titania
TiO?
0.55
0.75
0.70
1.21
1.49
1.47
1.38
1.07
0.92
1.14
3.71
1.66
1.63
1.35
1.42
1.40
1.21
1.92
Ferric
Oxide
FeO^j
11.10
5.02
6.96
7.65
7.30
6.92
6.79
23.91
5.67
10.05
6.22
5.34
5.19
13.23
9.95
6.99
13.50
4.14
Lime
CaO
5.90
8.12
14.80
2.24
1.63
1.95
1.94
2.05
13.97
5.50
1.64
1.95
2.07
2.23
1.39
1.61
3.43
1.26
Magnesia
MgO
2.16
2.76
1.62
1.27
1.10
0.84
0.86
2.05
3.83
2.12
0.77
1.08
0.88
0.67
0.66
1.03
1.32
0.81
Potassium
Oxide
K20
1.06
0.90
0.65
2.25
2.18
1.44
1.70
1.75
0.62
1.75
1.88
2.56
2.07
1.90
1.95
2.46
2.05
1.57
Sodium
Oxide
Na2O
0.32
0.32
1.02
0.56
0.60
0.50
0.45
0.56
0.59
0.50
0.26
0.32
0.25
0.29
0.41
0.48
0.61
0.29
Sulfur
Trioxide
SO^
5.71
10.77
8.23
1.39
1.02
1.15
1.43
2.91
12.94
6.24
0.81
0.76
1.15
1.86
1.41
0.79
3.61
0.61
Phosphorus
Pentoxide
p?°5
0.19
0.18
0.78
0.28
0.39
0.45
0.30
0.23
0.19
0.18
0.18
0.49
0.43
0.62
0.38
0.17
0.19
0.16
Undetermined
0.77
0.81
0.57
0.72
0.92
1.39
1.06
0.11
0.82
0.08
0.03
0.06
0.06
0.23
0.96
0.22
0.45
0.27
-------
TABLE 3-22
AS-FIRED COAL SIZE CONSISTENCY
SPREADER STOKERS
Percent Passing Stated Screen Size
Coal
Site A 1
2
3
Site B 1
2
3
4
Site C 1
2
3
Site E 1
2
3
Site F 1
2
Site G 1
2
3
1"
98
97
95
95
96
94
90
93
85
92
93
88
96
97
98
100
97
i"
83
84
56
65
55
48
68
71
63
64
57
62
62
59
73
50
73
i"
58
62
27
34
27
24
46
48
44
37
31
41
27
28
41
22
36
#8
31
36
13
16
13
13
22
27
26
19
15
22
16
17
20
13
16
#16
19
23
9
9
8
8
11
16
16
11
10
14
13
12
12
10
10
KVB 4-15900-554
103
-------
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o
§
si
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O
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O
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GC —i
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g ~
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TEST SITE A
+ LOW ASH COAL (2.9%)
A HIGH ASH COAL (7.9%)
A
4-
. 4-
+
A
T
T
0
20.0 40.0 60.0 80.0 100.0
PERCENT BOILER DESIGN CflPflCITY
: 2.9 flSH
; 7.9 flSH
FIG. 3-47
UNCONTROLLED PflRT. VS. PERCENT DESIGN CflPRCITY
4-15900-554
104
-------
UNCONTROLLED PRRT. LB/MILLION BTU
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The above examination does not take into account the variations in
coal ash experienced between tests on the same coal. This variation was
examined by the use of multiple regression analysis. The data from each site
were fit to a mathematical model of the form:
Particulate, lb/106Btu = a+b(% Load)+c(% Excess Air)+d(% Ash)+e(% Fines)
The results indicated correlations at only three of six sites. Again,
Site A showed no correlation. The three correlations are indicated here along
with their "T-value". The T-value is a measure of the degree to which the
individual variable, in this case coal ash, fit the mathematical model. The
higher the number, the better the fit.
A Particulate, lb/106Btu
per 1% Ash Increase T-Value
Site B .24 1.97
Site F .34 4.13
Site G .38 2.31
This data indicates that a 1% increase in coal ash results in an
average 0.32 lb/10^Btu increase in uncontrolled particulate loading. This trend
covers the range of 4.3 to 16.8% ash and should not be extrapolated beyond these
limits.
The percentage of coal ash carried over with the flyash is shown in
Table 3-23. Sites A, B, and C show unusually high ash carryover numbers. This
is the result of reentrainment of a large portion of the reinjected flyash.
Sites E, F, and G did not reinject flyash from their mechanical dust collectors.
These sites show that 27% of the coal ash is carried over in spreader stokers,
while the remaining 73% remains on the grate. Because this ash contains some
combustible material, the as-found flyash (inorganic ash and combustibles) re-
presents 73% by weight of the coal ash, while 91% by weight remains on the
grate.
KVB4-15900-554
106
-------
TABLE 3-23
ASH BALANCE
SPREADER STOKERS
Site A
Inorganic Ash as %
of Coal Ash
Coal % Carryover
2 201
3 89
% Grate
As-Found Ash as %
of Coal Ash
% Carryover
343
178
% Grate
Site B
1
2
3
4
75
74
73
75
188
160
189
202
Site C
1
2
3
121
211
218
195
228
272
Site E
1
2
3
19
20
33
81
80
67
67
48
83
106
87
77
Site F
Site G
1
2
1
2
3
AVERAGE (Sites E, F, G)
STANDARD DEVIATION
25
17
36
34
32
27
8
75
83
64
66
68
73
8
73
77
85
81
69
73
12
93
106
81
88
86
91
11
*As-Found Ash includes combustible material while Inorganic Ash
does not.
KVB 4-15900-554
107
-------
Coal Fines. Coal fines were related to particulate loading. It is
known that particle entrainment and carryover depends on several variables
including particle size, shape, density, and gas velocity. The standard
measure of coal fines is the percent by weight passing a 1/4 inch screen. When
fitting the data to the mathematical model, it was found that a better correlation
was obtained if the criteria for coal fines was percent passing 16 mesh rather
than percent passing 1/4 inch. Using 16 mesh as the criteria for coal fines,
the following statistical correlations were obtained:
A Particulate, lb/106Btu
Per 1% Fines Increase T-Value
Site B .31 1.75
Site C (Eastern) .55 3.27
Site E .22 1.64
Site F .14 2.62
These data indicate that a 1% increase in coal fines (% passing 16
mesh) results in an average 0.31 lb/106Btu particulate loading increase. As with
coal ash, this relationship is only valid over the range of data included in the
study. Sites A and Cw did not give good correlations, yet these two sites had
the highest percentages of coal fines.
3.5.2 Combustibles in the Ash vs. Coal Properties
Combustible content of the boiler outlet flyash and of the bottom ash
were evaluated on all six spreader stokers. Coal properties were found to be a
factor at two of the test sites. The data from these two sites are presented
below. The particular coal property or properties responsible for the dif-
ferences were not determined.
Test Site C was the stoker which fired both an Eastern bituminous and
a Western sub-bituminous coal. The Site C combustible data for both the boiler
outlet flyash and the bottom ash are presented in Figures 3-49 and 3-50.
Figure 3-49 shows that the Western coal averaged 10% combustibles in
its flyash.as compared to 40% for the Eastern coal's flyash. Figure 3-50 shows
that the Western coal's bottom ash combustible content was unusually high at
reduced loads. This may be due to the Western coals high moisture content.
KVB4-15900-554
108
-------
o
o
z
UJ
LJ
CC o
UJ 00
CD
ZI
o
o
CD
CO
CE
ID
O
CC
_J
CD
O
CM-1
TEST SITE C
A
+
0
20.0 40.0 60.0 80.0 100.0
PERCENT BOILER DESIGN CflPRCITY
O : EBSTERN LO + ! WESTERN A ° EflSTERN HI
FIG. 3-49
BLR OUT FLYRSH COMB. VS. PERCENT DESIGN CflPRCITY
4-15900-554
109
-------
o
v
o -
LO
UJ
o
cc
UJ
Q_
DO
21
O
CJ
CO
CE
o -
O ~
CO
P o
I- CM
O
CD
O
B
O
TEST SITE C
A
0
20.0 40.0 60.0 80.0 100.0
PERCENT BOILER DESIGN CRPflCITY
O S EflSTERN LO + : WESTERN ^ ". ER5TERN HI
FIG. 3-50
BOTTOM flSH COMB. VS. PERCENT DESIGN CRPflCITY
4-15900-554
110
-------
Test Site B also exhibited some combustible data which could be re-
lated to coal properties. However, at this site, the four test coals were
nearly identical. Figure 3-51, the Site B flyash combustible data, shows the
Hatfield coal data to be somewhat lower than the data from the other coals.
Figure 3-52, the Site B bottom ash combustible data, shows the Reload coal
data to be consistently low.
3.5.3 Sulfur Oxides vs. Coal Properties
The sulfur dioxide (SC>2) and sulfur trioxide (803) data are presented
in a series of plots. Figure 3-53 relates the sulfur oxides in the flue gas to
the sulfur in the coal. Both are presented in units of lb/106Btu as SO2 so as
to be directly comparable. The plot shows that a relationship exists, as would
be expected, but that inaccuracies are present in the data. It is not known
if these inaccuracies stem from the coal analysis or the sulfur oxides analysis.
Perhaps a better method of determining the fate of fuel sulfur is to
measure the sulfur retained in the ash directly. These data are summarized in
Table 3-24. The data indicates that between 1% and 6% of the fuel sulfur is
retained in the ash. The high sulfur retention in the Western coal's ash at
Site C is likely related to this coal's high calcium content (see Table 3-21).
Sulfur trioxide (SO3) was found in concentrations of zero to 10 parts
per million. This represents zero to 2% of the total sulfur oxides emitted.
Sulfur trioxide is plotted as a function of total sulfur oxides emitted in
Figure 3-54.
3.5.4 Nitric Oxide vs. Coal Properties
An investigation was made of the relationship between fuel nitrogen
and nitric oxide emissions. No direct relationship was found.
The nitric oxide models previously developed in Section 3.3.5 were
used to sort out the known relationships of heat release rate and excess air.
The differences between the measured NOx and those calculated by the mathemati-
cal model were then plotted as a function of fuel nitrogen. The plot for the
Site A data is shown in Figure 3-55. No relationship is evident. Plots for
the other sites were similar.
A correlation was also attempted by adding a fuel nitrogen factor
to the mathematical model. Again, there was no direct correlation.
Ill KVB4-15900-554
-------
o
o
DC O
LU CO
Q_
O
CO
CE
ID
O
DC
_J
DQ
O
CD
O
CM
TEST SITE B
T
T
T
T
0
20.0 40.0 60.0 80.0 100.0
PERCENT BOILER DESIGN CflPflCITY
: CUMBERLflND + : HflTFIELD
• SOUTHEflST
S RELORD
FIG. 3-51
BLR OUT FLYflSH COMB. VS. PERCENT DESIGN CRPRCITY
4-15900-554
112
-------
o
•
o -
in
z o
LU .
<-> o
cc ^r
LU
Q_
CD
SI
o
CJ
cr
o
o
CD
o
•
o -
CO
o
a
o
C\J
o
•
o
TEST SITE B
+
0
20.0 40.0 60.0 80.0 100.0
PERCENT BOILER DESIGN CRPRCITY
: CUMBERLflND
I HflTFIELO
S SOUTHEAST
FIG. 3-52
BOTTOM flSH COMB. VS. PERCENT DESIGN CRPRCITY
4-15900-554
113
-------
SULFUR OXIDES LB/MILLION BTU
1.000 2.000 3.000 4.000 5.000
co
i
in
ui
cz
rn
CO
ID
CO
CO
o
ro
o x
co
Q (Jl
X CO
i — i
O
rn
co
m m
CT D
m
o
2 8
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co
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a co
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r- o
i— i O
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—I
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oo
-------
TABLE 3-24
SULFUR RETAINED IN THE ASH
Site A
Coal
1
3
'6 Retained
in Flyash
2.5
% Retained
in Bottom Ash
0.5
0.3
Total
2.8
Site B
1
2
3
1.6
0.9
1.6
0.1
0.3
0.1
1.7
1.2
1.7
Site C
1
2
4.6
12.2
1.5
3.4
6.1
15.6
Site E
1
3
1.7
3.0
0.7
0.6
2.4
3.6
Site F
1
2
3.6
3.4
0.5
0.7
4.1
4.1
Site G
1
3
AVERAGE
STANDARD DEVIATION
5.2
3.0
3.6
3.0
0.6
0.6
0.8
0.9
5.8
3.6
4.4
3.9
115
KVB4-15900-554
-------
-------
FUEL NITROGEN
•*- Deviation about Average ->
+ 20%
+20%
-20%
-20%
Figure 3-55,
Data from Test Site A Indicates that there is no
Discernable Relationship between Nitric Oxide Emissions
and Fuel Nitrogen.
KVB4-15900-554
117
-------
3.5.5 Carbon Monoxide vs. Coal Properties
Carbon monoxide emissions were greatest while firing Western sub-
bituminous coals. The clearest evidence of this trend was observed at Site C
which fired both a Western sub-bituminous coal and an Eastern bituminous coal.
These data are presented in Figure 3-56.
At full load, the Western coal produced carbon monoxide emissions
ranging from 163 to 702 ppm, and averaging 342 ppm. By comparison, when
Eastern coal was fired under the same test conditions, the CO emissions ranged
from 33 to 263 ppm, and averaged 71 ppm.
The observations made at Site C are supported by observations made at
Site A. Site A fired a Western sub-bituminous coal and produced higher CO
emissions than Site B which fired an Eastern bituminous coal under similar
conditions.
3.5.6 Unburned Hydrocarbons vs. Coal Properties
Unburned hydrocarbon emissions (HC) were only measured at Sites F and
G of the six spreader stokers. At Site F the HC emissions ranged from zero to
23 parts per million by volume (ppm) on a wet basis, and averaged 9 ppm. At
Site G, they ranged from 19 ppm to 41 ppm and averaged 31 ppm. One explanation
for the difference is that Site F fired a lower volatile coal than Site G
(29% volatile matter at Site F versus 41% at Site G on a dry, mineral-matter-
free basis). The higher volatiles at Site G may have contributed to this
site's higher unburned hydrocarbon emissions.
3.5.7 Boiler Efficiency vs. Coal Properties
Moisture and hydrogen in the coal were instrumental in determining
boiler efficiency at Test Site C. Boiler efficiency was 3-4% lower while
burning a high-moisture Western coal than while burning a low-moisture Eastern
coal. The data for Site C are presented in Table 3-25 and Figure 3-57. Coal
properties did not differ enough to play a significant role at the other
spreader stoker sites.
KVB4-15900-554
118
-------
o
•
CSJ O
0 8
h- *-•
UJ o
CO
h-
01 O
LU
Q
i—i
x o
i o
? 5
CE o
CJ o
Csl
TEST SITE C
0
20.0 40.0 60.0 80.0 100.0
PERCENT BOILER DESIGN CRPflCITY
a. EflSTERN LO
\ WESTERN
° EflSTERN HI
FIG. 3-56
CRRBON MONOXIDE VS. PERCENT DESIGN CRPRCITY
4-15900-554
119
-------
o
o
o
•
o
O)
as
" g
Q_ CO
CJ O
•z. o
LU O
i — i .
LJ O
i— . r--
u_
u_
LU
O
CD
O
CD
O
O
O
•
O
LD
0
TEST SITE C
20.0 40.0 60.0 80,0 100
PERCENT BOILER DESIGN CRPflCITY
; EflSTERN LO + : WESTERN
I EflSTErai HI
FIG. 3~57
BOILER EFFICIENCY VS. PERCENT DESIGN CflPflCITY
4-15900-554
120
-------
TABLE 3-25
Coal
Eastern Low Fusion
Western
Eastern High Fusion
Dry
Gas
8.22
7.95
8.57
AVERAGE
Moisture
in Fuel
0.51
3.51
0.89
HEAT
H20
H2 in
4.
6.
4.
LOSSES
From
Fuel
50
25
56
AT SITE C,
Total
Combustibles
3.25
1.71
1.33
PERCENT
Radiation &
Unmeasured
1.98
1.96
2.08
BOILER
EFFICIENCY
PERCENT
81.56
78.63
82.57
3.6 RESPONSE TO OVERFIRE AIR
Overfire air was studied as an operating variable to determine its impact
on boiler emissions and efficiency. On each unit, the overfire air pressures
were increased and decreased over their range of operation. At Test Site C, over-
fire air was also biased in different ways to determine in which row of jets it
was most effective. Modifications to the overfire air systems were not included
in the scope of this program.
The overfire air configurations of the six spreader stokers studied are
illustrated in Figures 3-1 through 3-6 of Section 3.0, "Description of Units
Tested". Though each was different, the systems had many similarities. All six
had both upper and lower rows of jets on the rear water wall. The rear upper
jets were situated 5.6 to 6.1 feet above the grate and inclined downward between
0° and 11°. The rear lower jets were situated 1.0 to 2.2 feet above the grate
and inclined downward between 0° and 5°.
The arrangement of air jets on the front water wall was peculiar to each
stoker manufacturer. All but Site G had front upper jets situated 6.0 to 7.8
feet above the grate and inclined downward by 15° to 26°. Test Site G did not
have front upper overfire air jets. Most had front lower jets situated under
the feeders and often an integral part of the feeder. These jets were about
18 inches above the grate and were inclined horizontally.
The purpose of overfire air in stoker boilers is to promote complete
combustion. This is accomplished by supplying turbulence to the flame zone to
better mix the air and volatiles/ and by holding the flame away from the cold
KVB4-15900-554
121
-------
water walls thereby preventing premature quenching of the flame. When applied
correctly, overfire air minimizes the products of incomplete combustion, namely
smoke, carbon monoxide, and unburned hydrocarbons. It also allows operation
at reduced excess air levels which boosts boiler efficiency. In general, over-
fire air systems are designed to supply 15 to 20% of the total combustion air.
3.6.1 Particulate Loading vs. Overfire Air
Uncontrolled particulate loading was observed to decrease when overfire
air pressures were increased in the vast majority of tests. This result is
considered significant even though the mechanism accounting for the reduction
was not identified. The data are presented in Table 3-26. The Test Site A
data are plotted in Figure 3-58.
Combustible burnout accounted for all of the particulate reduction in
one test and was a factor in two others. In most tests, however, the inorganic
ash portion of the particulates was also reduced. Reductions in coal fines, an
uncontrolled variable, could account for only three cases of particulate
reductions. Therefore, the turbulence induced by the overfire air apparently
prevented some of the particles from being carried over. Particulate reductions
as high as 53% resulted from increasing the overfire to undergrate air ratio
while holding other known variables constant.
Test Site G was the only site where increasing the overfire air
pressure resulted in increased particulate loading, and this is supported by
only one test set. It is possible that the lower air jets at Site G were
kicking up ash from the grate. The lower rear jets were inclined toward the
grate by 5° and were operated at pressures of up to 23" H20 gauge. It is also
noted that Site G was the only site without front upper air jets. These Site G
observations should not be the basis for any conclusions since the data is
scant, but it was felt that these observations should be recorded. One must
also keep in mind that overfire air systems are not designed for the purpose
of controlling particulate loading.
At Test Site C, the overfire air pressures were biased in different
directions. By this we mean that they were increased in one area and decreased
in another area while keeping the total overfire air flow roughly constant.
These variations at Site C had no significant impact on particulate loading.
For example, when most of the overfire air was put through the upper air jets
KVB4-15900-554
122
-------
TABLE 3-26
EFFECT OF OVERFIRE AIR ON UNCONTROLLED PARTICULATE LOADING
SPREADER STOKERS
UNCONTROLLED PARTICULATE LOADING
% Design
Site Coal Capacity
A 2 85
3 76
3 60
B 1 48
2 73
4 80
C (E) 1 92
C (W) 2 99
E 1 64
Low High Percent
OFA OFA Change Other Overfire
20.48 15.41 -25
20.48 11.89 -42
13.26 6.29 -53
11.75 9.98 -15
12.27 9.25 -25
9.57 7.21 -25
Bias
Upper
21.11 19.02 -10 20.88
31.14 29.22 - 6 33.99
Bias
Front
ND 4.49 ND 4.32
Bias
Lower
22.63
31.59
Bias
Upper
5.23
- LB/l05Btu
Air Conditions
Bias Bias
Front Rear
23.86 25.14
33.09 36.42
High Front*
Medium Rear
2.06
Baseline
F 1 100
G 1 83
3 77
High
Med
8.79 6.14 -30 5.
4.33 4.27 - 1
4.00 4.57 +14
Front
Rear
51
* Test is suspect because particulate loading is
disproportionately low.
ND = No data
KVB4-15900-554
123
-------
GO
O
O
O
LO
CM
o
o
o
•
o
CM
_J O
O
• O
h-
OC LO
CE —i
0_
0 O
UU g
Is
§ o.
LO
TEST SITE A
O LOW OFA (0-4")
+ MED OFA (4-8")
A HIGH OFA (8-12")
A
A +
A
0
20.0 40.0 60.0 80.0 100.0
PERCENT BOILER DESIGN CRPRCITY
: 0-4" H20
: 4-8" H20
! 8-12" H20
FIG. 3-58
UNCONTROLLED PflRT. VS. PERCENT DESIGN CRPRCITY
4-15900-554
124
-------
(Bias Upper) as opposed to putting most of the air through the lower jets
(Bias Lower), particulate loading increased 8% in one set of tests on Western
coal and decreased 8% on one set of tests on Eastern coal. This is inter-
preted as normal data scatter. Similarly, biasing the air to the front jets
as opposed to biasing the rear air jets resulted in increases of 5% and 10%
in the uncontrolled particulate loading. Again, these results may not be
significant due to normal data scatter.
3.6.2 Combustibles in the Ash vs. Overfire Air
The percentage of combustible material in the flyash increased more
often than it decreased when overfire air pressures were increased. This sur-
prising result is not necessarily a trend. As with all tests conducted during
this program there were many uncontrolled variables which could have biased
the results.
Although increased overfire air did not reduce the percentage of com-
bustible material in the flyash, it did reduce the rate at which flyash was
carried over and this in turn led to a reduced carbon carryover and a reduced
combustible heat loss. The effect of overfire air on boiler efficiency is dis-
cussed in Section 3.6.6. The combustible data are presented in Table 3-27.
3.6.3 Nitric Oxide vs. Overfire Air
Overfire air is used in burner-fired combustion devices to produce
staged combustion. This technique is an effective nitric oxide control strategy
on burner-fired combustion devices.
The term "overfire air", when applied to stokers, is something entirely
different, and was designed for a different purpose. Nevertheless, overfire
air on stokers can in theory be used to produce a limited degree staged com-
bustion and this aspect was investigated.
The test results, summarized in Table 3-28, show that increasing the
overfire air to undergrate air ratio at constant excess air has no significant
effect on nitric oxide emissions. It was not possible to set up the degree of
staged combustion necessary for NOx reduction. Limiting factors were clinkering
and overheating of the grate as the undergrate air is reduced, and the limited
capacity of the overfire air jets. The test results show small increases in
KVB4-15900-554
125
-------
TABLE 3-27
EFFECT OF OVERFIRE AIR ON COMBUSTIBLES IN FLYASH
SPREADER STOKERS
PERCENT COMBUSTIBLE MATERIAL IN FLYASH
Site
A
B
Coal
2
3
3
1
2
4
% Design
Capacity
85
76
60
80
73
48
Low
OFA
65.8
70.0
47.2
57.3
53.3
62.6
High
OFA
54.6
66.6
61.3
70.3
55.2
64.0
Percent
Change Other Overfire Air Conditions
-17
- 5
+ 30
+23
+ 4
+ 2
Bias Bias Bias Bias
Upper Lower Front Rear
C (E)
C (W)
1
2
92
99
30.8
ND
47.8
8.7
+55
ND
24.4 46.0 55.9 41.6
12.1 11.7 7.1 ND
Bias Bias High Front
Front Upper Medium Rear
64
ND
70.6
ND
58.6 75.3
62.3
Baseline
High Front
Med Rear
F
G
100
83
77
71.9
52.2
62.9
71.4
58.1
50.6
- 1
+11
-20
70.1
ND = No Data
KVB4-15900-554
126
-------
TABLE 3-28
EFFECT OF OVERFIRE AIR ON NITRIC OXIDE
SPREADER STOKERS
NITRIC
Site
A
B
C (E)
C (W)
E
F
G
Coal
2
3
3
4
2
1
1
2
1
1
1
3
% Design
Capacity
85
76
60
48
73
80
92
99
64
100
83
77
Low
OFA
.718
.541
.559
.374
.371
.478
.330
.533
ND
.401
.483
.488
High
OFA
.715
.500
.539
.400
.469
.465
.391
.562
.552
.358
.394
.573
Percent
Change
0
- 8
- 4
+ 7
+26
- 3
+18
+ 5
ND
-11
-18
+17
EMISSIONS
OXIDE - LB/106Btu*
Other Ovenfire Air Conditions
Bias Bias Bias Bias
Upper Lower Front Rear
.439 .448 .454 .463
.522 .527 .584 .602
Bias Bias High Front
Front Upper Medium Rear
.548 .597 .614
* Both tests in each data set have been corrected to a common
excess oxygen level to eliminate the effects of this variable.
ND = No Data
KVB4-15900-554
127
-------
NOx during five test sets, small decreases in NOx during five test sets,
and no change during one test set. These variations are ascribed to normal
data scatter.
The tests at Site C, in which overfire air was biased in several
directions, shown the lowest NOx when most of the overfire air is passed
through the upper jets, and the highest NOx when the overfire air is passed
through the jets on the rear wall. The implication is that the lower rear
jets, which are most effective in reducing carbon monoxide, also tend to increase
NOx on this unit.
3.6.4 Carbon Monoxide vs. Overfire Air
Carbon monoxide emissions were reduced by the increased use of over-
fire air in these tests. Table 3-29 shows the carbon monoxide test results.
Carbon monoxide was significantly reduced at Test Sites A, C, and F
by increasing overfire air pressure. This is an indication that the turbulence
created by overfire air is helping to complete combustion. Figure 3-59 shows
the effects of low overfire air at Site F.
At Site B, the carbon monoxide emissions were very low under all
overfire air conditions tested. The increase from 36 to 96 ppm at this site
is not considered very significant. More significant are the changes in the
larger emission levels such as the 55% reduction at Site A when CO dropped
from 1076 to 480.
Test Site E had very little CO data and Site G had no CO data due to
problems with the carbon monoxide monitor.
3.6.5 Unburned Hydrocarbons vs. Overfire Air
Test Site F was the only location where unburned hydrocarbons were
evaluated as a function of overfire air conditions. No clear data trends were
observed. The data are presented below.
KVB4-15900-554
128
-------
TABLE 3-29
EFFECT OF OVERFIRE AIR ON CARBON MONOXIDE EMISSIONS
SPREADER STOKERS
CARBON MONOXIDE, PPM (DRY) AT 3% O2
Site
A
B
C (E)
C (W)
E
F
G
Coal
2
3
3
1
2
4
1
2
1
1
1
3
% Design
Capacity
85
76
60
80
73
48
92
99
64
100
83
77
Low
OFA
1076
313
670
44
103
36
* 103
488
378
607
High
OFA
480
300
61
47
34
96
53
311
No Data
163
429
No Data
Percent
Change
-55
- 4
-91
+ 7
-67
+167
-49
-36
-57
-29
Other Overfire Air Conditions
Bias Bias Bias Bias
Upper Lower Front Rear
49 53 37 44
395 287 567 323
Bias Bias
Front Upper
62 147
Baseline
228
382
129
KVB4-15900-554
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CRRBON MONOXIDE PPM flT 3 PERCENT 02
150.0 300.0 450.0 600.0 750.0
J I
CO
o
0 T|
3D >-<
3 " ?
0 o
Z ? ?
1
o co § co -
^ o
o
X ,
1 — 1 1
o
m 1
_^ 1 rn CD -
g s s P
° rn
1 ' 1
CO
rn > co
X
o T 2
rn J5 ;-; CD-
CO • -D o
^ S -o '
rn
3D
H-I 3D
S
5 K.
0
.
i — '
cn -
o
~"~
-j- -j- ,
_i_ 1^, ~r
+ i _j_ O
^-F^" +
, k^
4+++ ++
"t + G
^|r
~l~ —1
m
oo
~n
-.
+
-------
UNBURNED HYDROCARBONS, PPM (WET)
% Design
Capacity
100
99
Excess
Air, %
56
39
Low
OFA
0
16
Baseline
OFA
13
9
High
OFA
13
5
3.6.6 Boiler Efficiency vs. Overfire Air
Boiler efficiency was improved by an average 1% when overfire air
pressures were increased. This efficiency gain is the result of reduced carbon
carryover. As noted earlier, the percentage of combustibles in the ash was not
reduced but the particulate loading was reduced and this in turn reduced the
carbon carryover.
Table 3-30 presents the changes in the individual heat loss categories
which were determined for each overfire air test set. Many of the changes such
as fuel moisture and t^O from H^ are coal related. The radiation losses are
load related, and the dry gas losses are related more to excess air than to
overfire air. The dominating heat loss change appears in the flyash com-
bustible category and this is believed to be a direct result of the increase
in overfire air pressure.
KVB4-15900-554
131
-------
TABLE 3-30
EFFECT OF OVERFIRE AIR ON HEAT LOSSES AND EFFICIENCY
SPREADER STOKERS
CHANGE IN PERCENT HEAT LOSS WHEN OVERFIRE AIR INCREASED
Site
A
B
C (E)
C (W)
E
F
G
Coal
2
3
3
1
2
4
1
2
1
1
1
3
Dry
Gas
.29
-.45
-.06
-.37
1.21
.83
-.26
.11
-.28
-1.41
1.39
1.01
Fuel
Moisture
-.10
-.01
.00
.06
-.10
-.26
-.02
-.05
-.23
-.22
.04
.06
H20
From Hp
.02
-.03
.00
-.04
-.01
-.21
-.22
.13
.01
-.07
.22
.07
Flyash
Combustibles
-1.96
-1.80
- .66
.29
-2.93
- .38
-2.82
.88
-1.37
-2.76
.32
- .30
Bottom Ash
Combustibles
-.02
-.04
-.14
.76
-1.68
- .06
- .33
.11
- .86
- .42
.89
- .04
Radiation
.00
.00
.01
.00
-.02
.02
-.02
.00
.04
.00
-.04
.02
Change In
Boiler
Efficiency
1.77
2.33
.85
-.70
3.53
.06
3.67
-1.18
2.69
4.88
-2.82
-.82
AVERAGE .17 -.07 -.01 -1.12 - .15 .00 1.19
STD. DEV. .82 .11 .12 1.33 .67 .02 2.33
KVB4-15900-554
132
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3.7 RESPONSE TO DEGREE OF FLYASH REINJECTION
Three of the six spreader stokers tested, Sites A, B and C, were
equipped for flyash reinjection from their mechanical dust collectors. The
degree of reinjection was either reduced or stopped completely on each of these
units to determine what effect this had on emissions and efficiency. A similar
test was conducted at Site F which was equipped for reinjection from its
economizer hopper. The following subsections describe the tests and the re-
sults obtained. The test data are summarized in Table 3-31.
It is worth noting that all six spreader stokers reinjected flyash from
their boiler hoppers, and two of them reinjected flyash from an air heater or an
economizer. All used pneumatic reinjection systems, as opposed to the gravity
feed type.
3.7.1 Test Description - Site A
Site A is a 300,000 Ib/hr spreader stoker equipped for flyash rein-
jection from the boiler hoppers, air heater hoppers and mechanical dust col-
lector hoppers. Site A is also equipped with the option of diverting the
mechanical collector flyash to a surge hopper from which it is discarded. This
arrangement made it very convenient to run performance tests on the flyash
reinjection system at Site A.
The procedure for diverting the flyash into the surge hopper was very
simple. Sliding gate valves were located on the downcommers from the dust col-
lector hopper immediately below the high pressure venturies and reinjection
lines. The gate valves were opened and the reinjection air pressure was reduced
as much as possible by closing butterfly valves in the air supply lines. This
allowed much of the flyash to fall into the surge hopper.
Some of the flyash from the mechanical collector hopper may still have
been reinjected when the gate valves were opened. Unfortunately, there was no
way of measuring the rates at which flyash was collected or reinjected in this
configuration without going to considerable expense. Thus, there is no
quantitative data on the percentage reduction in rejected flyash obtained at
Site A.
Two successful test sets were conducted in which a full reinjection
test and a reduced reinjection test were run back-to-back. It was felt that
KVB4-15900-554
133
-------
TABLE 3-31
CO
SITE A
r
Reinfection Configuration
FIRING CONDITIONS
Load, % of Capacity
Excess Air, %
Coal Classification
Coal Sizing, % passing i"
Coal Ash, %
UNCONTROLLED EMISSIONS
Particulate Loading, lb/106Btu
Combustible Loading, lb/106Btu
Inorganic Ash Loading lb/10^Btu
Combustibles in Flyash, %
Combustibles in Bottom Ash, %
02, % (dry)
CO, ppm (dry) @ 3% 02
NO, lb/106Btu
CONTROLLED EMISSIONS
Particulate Loading, lb/10^Btu
Combustible Loading, lb/106Btu
Inorganic Ash Loading lb/10^Btu
Combustibles in Flyash, %
Combustibles in Discarded Ash %
Dust Collector Efficiency, %
COMBUSTIBLE HEAT LOSSES
Emitted Flyash
Discarded Flyash
Bottom Ash
TOTAL Combustible in Refuse
Blr Hpr
Air Htr
82
26
Blr Hpr
Air Htr
100% D.C.
83
23
Sub-Bituminous
45
2.65
12.1
8.7
3.4
72.1
—
4.5
998
0.524
—
—
—
76.7
—
0.57
2.30
—
2.87
70
2.63
16.6
9.7
6.9
58.4
—
4.1
1600
0.492
—
—
—
—
—
0.72
0.00
—
0.72
SUMMARY TABLES FOR FLYASH RE INJECT ION
TEST SETS ON SITES A, B AND C
SITE A SITE B
1
Blr Hpr
Air Htr
59
29
Blr Hpr
Air Htr
100% D.C.
59
26
Sub-Bituminous
67
2.92
8.4
5.1
3.3
60.8
0.5
4.8
150
0.504
—
—
—
—
—
0.36
1.46
0.01
1.83
49
2.86
11.7
5.1
6.6
43.7
0.3
4.4
104
0.525
—
—
—
—
—
—
0.35
0.00
0.01
0.36
*
Blr Hpr
42% D.C.
99
34
1
Blr Hpr
60% D.C.
100
32
1
None
93
72
Bituminous
36
2.60
9.6
5.8
3.8
60.9
14.2
5.5
41
0.343
0.49
0.13
0.36
26.7
79.5
95.0
"it
0.24
8.09*
1.01
9.34
25
10.66
15.8
7.4
8.4
47.0
9.9
5.3
60
0.431
0.60
0.15
0.45
25.0
56.7
96.3
*
0.24
6.76 *
0.64
7.64
43
10.73
6.0
—
—
—
2.3
9.1
55
0.514
0.48
0.11
0.37
23.6
21.6
92.0
0.15
2.32
0.15
2.62
SITE C
Blr Hpr
93
72
*
Blr Hpr
70% D.C.
89
70
Bituminous
50
10.81
7.0
4.0
3.0
57.2
1.6
9.1
53
0.486
0.50
0.14
0.35
28.9
40.9
92.9
0.19
3.86
0.10
4.15
52
12.01
25.0
—
—
—
0.7
8.9
66
0.421
0.82
0.14
0.67
17.4
32.6
96.7
&
0.21
3.43*
0.05
3.69
1
None
98
60
SITE C
Blr Hpr
102
62
it
Blr Hpr
70% D.C.
98
67
Sub-Bituminous
49
8.50
8.6
—
—
—
2.8
8.1
247
0.507
0.52
0.07
0.45
13.7
9.3
93.9
0.11
1.20
0.20
1.51
46
8.56
6.1
26.6
0.3
8.3
280
0.483
0.47
0.06
0.41
12.4
17.6
92.4
0.09
1.45
0.02
1.56
42
8.20
31.1
—
—
--
21.1
8.7
488
0.520
1.03
0.06
0.96
6.2
3.8
96.7
*
0.10
0.50
1.44
2.04
* The percentage of ash reinjected from the dust collectors at Sites B and C was not measured.
Instead, combustible heat loss calculations are based on design data.
KVB4-15900-554
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test variables could be minimized by conducting both tests on the same
day.
A third test set was not entirely successful. The unit tripped
out briefly during the test due to a low drum water level. Although testing
was stopped until the load was restored, the load continued to fluctuate
drastically during the remainder of the test. The results of this question-
able test are not included in Table 3-31.
3.7.2 Test Description - Site B
Site B is a 200,000 Ib/hr spreader stoker equipped for pneumatic
flyash reinjection from its boiler hopper and selective type dust collector.
The selective type dust collector has two hoppers and internal baffles which
are designed to segregate the particles by size so that only the larger
particles are reinjected. By design, 60% of the collected ash is reinjected.
No practical method was found for verifying this percentage. The actual
percentage may vary significantly from the design 60%.
During one test, the mechanical dust collector reinjection rate was
reduced, and emissions were measured. The reduction was accomplished by
extending a pipe from the bottom of each reinjection line into a sealed drum.
Reinjection air pressure was reduced to near zero but the lines were not
capped off. Therefore, some of the ash was reinjected and some was collected
in the drums. In this manner, the reinjection rate was reduced without dis-
mantling the reinjection hardware.
Ash was collected at a rate of 460 Ib/hr over a 2-1/2 hour period.
This represents 30% of the calculated normal reinjection rate, or a 30%
reduction in the reinjection rate from the mechanical dust collector.
A second test was run under similar conditions to the first except
that flyash reinjection was not reduced. The results of these two tests
are compared in Table 3-31 and in the following discussions.
3.7.3 Test Description - Site C
Site C is a 182,500 Ib/hr spreader stoker equipped for pneumatic
flyash reinjection from its boiler hopper and selective type dust collector.
KVB4-15900-554
135
-------
Based on design specifications, it is assumed that 70% of the dust collector's
ash is reinjected. As with Site B, the actual percentage was not measured.
Unlike Sites A and B, it was possible to completely stop flyash
reinjection at Site C, and to accurately measure the ash flow rates. This
was accomplished by blocking the venturi at the head of the reinjection line
and allowing all of the flyash to drop into tare weighed barrels placed under
each downcommer.
Test sets were run on both an Eastern and a Western coal. Each
test set consisted of full reinjection, boiler hopper reinjection only, and
no reinjection.
3.7.4 Particulate Loading vs Flyash Reinjection
The test results discussed in the following sections will be compared
with the published results of a similar study conducted in 1949 by Battelle
p c
Memorial Institute. The earlier study involved a 100,000 Ib/hr spreader
stoker equipped with a gravity reinjection system, while the boilers tested
under this program had pneumatic reinjection systems.
Reentrainment of the reinjected flyash was found to be very signifi-
cant in our tests. This was evidenced by the significant reductions in particu-
late loading which accompanied each reduction in reinjection rate. The data,
presented in Tables 3-32 and 3-33, show reductions ranging from 27% to 80% at
the boiler outlet, and 19% to 54% after the dust collector. Looked at in
another way, reinjecting flyash from the mechanical dust collector increased
the particulate loading by a factor ranging from 1.4 to 5.1 at the boiler
outlet, and by a factor of 1.2 to 2.2 at the dust collector outlet. The
Battelle data shows similar reductions in particulate loading brought on by
reduced reinjection.
A comparison of the particulate loadings of the spreader stokers with
and without reinjection from the mechanical dust collector is especially re-
vealing. The data are tabulated in Table 3-34.
KVB4-15900-554
136
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TABLE 3-32
PARTICULATE LOADING DATA FOR
FIVE REINJECTION RATE TEST SETS
Uncontrolled
Particulate, lb/106Btu
Reduced Full
Reinjaction Reinjection
Controlled
Particulate, lb/106Btu
Reduced Full
Reinjection Reinjection
Site A
Site A
Site B
Site Ce
Site Cw
12.1 16.6
8.4 11.7
9.6 15.8 0.49 0.60
6.0, 7.0 25.0 0.48, 0.50 0.82
8.6, 6.1 31.1 0.52, 0.47 1.03
TABLE 3-33
REDUCTION IN PARTICULATE LOADING
DUE TO REDUCED REINJECTION RATE
Site A - High Load
Low Load
Site B - High Load
Site C - Eastern Coal
Western Coal
Boiler
Outlet
27%
28%
39%
72%
80%
Collector
Outlet
Battelle - Island Creek Coal 18%
Illinois #6 Coal 45%
19%
39%
54%
43%
21%
KVB4-15900-554
137
-------
TABLE 3-34
UNCONTROLLED PARTICULATE LOADING AT FULL LOAD
Spreaders with Reinj.
Spreaders w/o Reinj.
Test
Site
A
B
Ce
Cw
Ce
Cw
E
F
G
Uncontrolled
P articulate Loading
lb/106Btu
16.6 -
12.7 -
19.0 -
29.2 -
6.0 -
6.2 -
2.1 -
5.2 -
2.9 -
22.5
15.8
28.0
36.4
7.0
8.6
6.5
8.8
6.8
Site C was tested in both configurations, and whereas it had the
highest particulate loading with flyash reinjection, it fell in the same range
as Sites E, F, and G when fired without reinjection. This implies that
the degree of reinjection is by far the major factor contributing to its
excessively high boiler outlet particulate loading. The Test Site C
uncontrolled particulate loading data are presented in Figure 3-60 to
further illustrate the impact which reinjection rate had on this emission.
3.7.5 Combustibles in the Ash vs. Flyash Reinjection
The percentage of combustible material in the flyash increased
when the reinjection rate was decreased. This would indicate that combustibles
in the reentrained flyash are being consumed, and the energy recovered. The
data are presented in Table 3-35 and Figure 3-61.
KVB4-15900-554
138
-------
o
o
o
§8
" §
GO
O
O
O
CC O
CE CO
Q_
§8
°
Is
^ CD
«
o
TEST SITE C
FULL FLYASH REINJECTION
\
REDUCED FLYASH REINJECTION
T
T
T
T
0
20.0 40.0 60.0 80.0 100.0
PERCENT BOILER DESIGN CRPflCITY
: w/o REINJ
"„ WITH REINJ
FIG. 3-60
UNCONTROLLED PRRT. VS. PERCENT DESIGN CRPRCITY
4-15900-554
139
-------
80
ss
2
H 60
w
w
J
ffl
H
H
CO
8 40
frl
20
SPREADER STOKERS
BOILER
OUTLET
SITE A - 80% LOAD
SITE B -100% LOAD
SITE A - 60% LOAD
COLLECTOR
OUTLET
SITE B -100% LOAD
*• SITE C - EASTERN COAL
SITE C - WESTERN COAL
REDUCED
REINJECTION
FULL
REINJECTION
Figure 3-61. Effect of Flyash Reinjection on Combustible Content of
Flyash.
KVB4-15900-554
140
-------
TABLE 3-35
INCREASE IN COMBUSTIBLE CONTENT OF FLYASH
DUE TO REDUCED REINOECTION RATE
Boiler Collector
Outlet Outlet
Site A - High Load 23%
Low Load 39%
Site B - High Load 30% 7%
Site C - Eastern Coal — 66%
Western Coal — 100%
Battelle - Island Creek Coal 38% 43%
Illinois #6 Coal 63% 16%
The recovery rates of the reinjected combustibles were difficult to
assess with accuracy. At Site A, the calculated recovery rates for the two
test sets were 93% and 100%. This is higher than had been expected. By
comparison, the Battelle report concludes that 63% of the reinjected carbon
was recovered in their tests. Both results may be accurate, but it is
recommended that more research be conducted in this area to establish a
broader data base.
There was insufficient data to calculate recovery rates for
reinjected combustibles at Sites B and C. This is because they were equipped
with selective type dust collectors. On such units it is necessary to know
precisely the percentage of collected ash reinjected and the percentage
discarded. It is also necessary to know the combustible contents of each
fraction. It was not within the scope of this program to build the
elaborate setup required to make these measurements.
The difference in flyash combustible heat loss for the two test
sets at Site A were 2.15% for the high load test and 1.47% for the low load
test. These figures represent the increase in boiler efficiency afforded
by the reinjection of flyash from the mechanical dust collector.
KVB4-15900-554
141
-------
3.7.6 Particle Size Distribution vs. Flyash Reinjection
The particle size distribution data for the reinjection test sets
are presented in Figures 3-62, 3-63, and 3-64. This data was derived from
Bahco classifier tests and sieve analysis of flyash samples collected at
the boiler outlet. The data are also presented in Table 3-36 along with
dust collector efficiency data.
TABLE 3-36
DUST COLLECTOR EFFICIENCY AND PARTICLE
SIZE DISTRIBUTION VS REINJECTION RATE
Dust Collector % Particles Below
Efficiency, % 10 Micrometers
Reduced Full Reduced Full
Reinjection Reinjection Reinjection Reinjection
Site B - Eastern Coal
Site C - Eastern Coal
Site C - Western Coal
All three test sets show the same trend. Flyash reinjection reduces
the percentage of fine particles and increases the percentage of coarse
particles. The largest increases occur with the particles larger than 100
micrometers. This shift in particle size distribution towards the larger
particles increases the collection efficiency of the mechanical dust collector
by several percent. This increase in dust collector efficiency due to flyash
reinjection at Site C is graphically presented in Figure 3-65.
Another method of presenting the particle size distribution data is
to combine it with the particulate loading data to create particle size
concentration plots. These plots, presented in Figures 3-66, 3-67, and 3-68,
show that the greatest increase in particulate loading occurs in the range
of 20-300 micrometers. The percentage increase in particulate loading by
particle size resulting from increased reinjection is plotted in Figure 3-69
for two of the three test sets. The trend is consistent.
94.9
92.9
92.4
96.2
96.7
96.7
8.0
7.7
9.5
6.0
5.0
4.8
KVB4-15900-554
142
-------
W
N
H
w
99.9
99
95
80
H 50
w
w 20
w
w
0.1
TEST SITE B
Full Reinjection
^ Reduced
Reinjection
Reduced
Reinjection
Full Reinjection
10 30 100 300
EQUIVALENT PARTICLE DIAMETER, MICROMETERS
1000
3000
Figure 3-62. Particle Size Distribution of Flyash at Boiler Outlet of Site B for Case
of Full and Reduced Reinjection from the Mechanical Dust Collector.
KVB 4-15900-554
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TEST SITE C
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No Reinjection
•Full Reinjection
No Reinjection
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Figure 3-63.
10 30 100 300
EQUIVALENT PARTICLE DIAMETER, MICROMETERS
1000
3000
Particle Size Distribution of Flyash at Boiler Outlet of Site C for Case
of Full and Reduced Reinjection While Firing Eastern Coal.
KVB 4-15900-554
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FIG. 3-65
MECH. COLL. EFF. VS
PERCENT DESIGN CflPflCITY
4-15900-554
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Figure 3-66. Particle Size Concentrations for Boiler Outlet Particulates under Normal and Reduced
Flyash Reinjection Conditions - Test Site B.
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Figure 3-68.
Particle Size Concentrations for Boiler Outlet Particulates under Full and Reduced
Flyash Reinjection Conditions - Western Coal - Test Site C.
KVB4-15900-554
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SITE C - WESTERN COAL
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PARTICLE DIAMETER, MICROMETERS
300
Figure 3-69.
Particulate Concentration Reduction as a Function of Particle Diameter for the
Change in Flyash Reinjection Configuration from Full to No Reinjection -
Test Site C.
KVB4-15900-554
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3.7.7 Reinjection From an Economizer Hopper - Test Site F
Reinjection tests were also conducted at Test Site F. Site F does
not reinject flyash from the mechanical dust collector. However, it does
reinject flyash pneumatically and continuously from the economizer hopper
and from the boiler hopper. During one test, the flyash collecting in the
economizer hopper was diverted to barrels rather than reinjected. This re-
sulted in a 5-27% drop (depending on which test you compare it to) in particu-
late mass loading at the economizer outlet when compared to the full reinjection
test data. The data also indicate that during this test, ten percent of the
flyash entering the economizer was collected in the economizer hopper.
The Site F particulate loading results are presented in Table 3-37
for the case of reduced reinjection and for four comparable full reinjection
tests. As with the tests on Sites B and C, the Site F particle distribution
was shifted towards smaller particles by the reduced reinjection. These
data are presented in Figure 3-70.
TABLE 3-37
PARTICULATE LOADING VS FLYASH REINJECTION
TEST SITE F
Flyash
Reinj .
NO
YES
YES
YES
YES
Test Conditions
% Load % O
100
99
99
99
102
6.3
6.7
7.8
5.5
5.0
OFA
High
Norm
Norm
High
High
Economizer Outlet
Particulate Loading
lbs/106Btu
5.24
5.51
5.93
6.14
7.18
% by Which
Reduced Reinjection
Particulate
Loading is Lower
5%
12%
15%
27%
KVB4-15900-554
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50
N
H
W
20
BC
EH
04
0.1
0.3 1 3
EQUIVALENT PARTICLE DIAMETER, MICROMETERS
Figure 3-70.
Particle Size Distribution at the Economizer Outlet
for Full and Reduced Reinjection From the Economizer
Hopper at Site F.
KVB 4-15900-554
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3.7.8 Stratification and Density of Ash in Collection Hoppers
In the course of performing the reduced reinjection tests at Sites
C and F, the flyash collection rate was measured from each downcomer. These
data are of interest because they show how evenly the ash is distributed
to the various reinjection lines.
At Site C, the ash collected in the boiler hopper of this single
pass boiler was heavier at the sides than in the center of the hopper. These
data are shown in Table 3-38 for two tests. The bulk density of the Eastern
coal ash was determined to be 16.6 Ib/ft-^ at this location.
TABLE 3-38
BOILER HOPPER ASH DISTRIBUTION AT SITE C
Eastern Coal Ash, Ib/hr
Western Coal Ash, Ib/hr
•<- Right
ill!
60 54 59 41
37 43 48 14
Left -»•
I 6 Z
46 69 106
34 71 79
The ash collected from the three economizer hoppers at Site F
showed considerable stratification. Most of the ash was collected in the
center hopper. The results for a two-hour, ten-minute period are shown in
Table 3-39.
TABLE 3-39
ECONOMIZER ASH DISTRIBUTION AT SITE F
Left Hopper Center Hopper Right Hopper
Flyash Collection Rate 12.9 Ib/hr 36.5 Ib/hr 4.4 Ib/hr
153
KVB4-15900-554
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3.8 PARTICLE SIZE DISTRIBUTION OF FLYASH
Particle size distribution of the flyash was determined using several
different methods. These include a Brink cascade impactor, a Banco classifier,
the cyclone train from the Source Assessment Sampling System (SASS), a Coulter
Counter, and sieve analysis. These methods differ in the size range of particles
each classifies, as well as in the method of classification. In addition, the
results obtained from each method differ from one another. Therefore, it is
necessary to present the results of each method separately and to discuss the
peculiarities of each.
3.8.1 Brink Cascade Impactor Test Results
The primary method employed for determining particle size distribution
of the flyash was the Brink cascade impactor. The Brink was selected at the
beginning of this program after consultation with both the Testing Techniques
Group of the U. S. Environmental Protection Agency, and Southern Research Insti-
tute who have considerable experience with cascade impactors. The Brink was
selected over other cascade impactors because its comparatively low sample rate
would allow the largest sampling period under the high mass loading conditions
at the boiler outlets of spreader stokers. A long sampling period was desired
so as to provide a reasonable averaging of transient conditions.
The Brink cascade impactor and the manner in which it was used had its
drawbacks. Because of its low sample rate, it was necessary to use small nozzles
of 2.0 mm diameter in order to maintain isokinetic sampling rates. At the boiler
outlet of spreader stokers, the flyash particles are as large as 2.0 mm, the
same size as the sampling nozzle. As a result, tests in which EPA Method 5
particulate loading were run simultaneously with the Brink revealed that the
Brink was collecting only 26% to 87% of the flyash particles. This had the
effect of biasing the particle size distribution data in favor of more smaller
particles. Table 3-40 compares the Brink and the EPA Method 5 data.
The Brink cascade impactor data has two more drawbacks. First, because
the Brink was used as a single point sampler, stratification of the flyash
particles within the duct could lead to error. Multiple point sampling with a
cascade impactor is only possible by compromising on isokinetics. Secondly,
KVB4-15900-554
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TABLE 3-40
[ OF BRINK AND
Brink Loading
gr/DSCF
.563
1.872
1.463
1.331
2.036
2.205
2.224
EPA METHOD 5 DUS1
EPA Method 5
Loading
gr/DSCF
2.160
3.824
2.748
3.932
3.243
3.102
2.550
Brink as %
Site Test gr/DSCF gr/DSCF of Method 5
E 11 .563 2.160 26%
E 14 1.872 3.824 49%
F 23 1.463 2.748 53%
F 24 1.331 3.932 34%
F 29 2.036 3.243 63%
G 5 2.205 3.102 71%
G 17 2.224 2.550 87%
the size range of particles classified by this 5 stage impactor is 0.3 micro-
meters to 3.0 micrometers. This is too small to be useful for predicting dust
collector efficiencies.
Data reduction was accomplished with the aid of a computer and followed
the procedures outlined in EPA publication 600/2-77-004, Procedures for Cascade
Impactor Calibration and Operation in Process Streams, January, 1977.
Test Data. The Brink data are plotted on the traditional log-probability
scale in Figures 3-71 and 3-72. Examining the data statistically yields the
average size distribution given in Table 3-41.
TABLE 3-41
AVERAGE BRINK CASCADE IMPACTOR DATA FOR SPREADER STOKERS
Mass Percent Less than Stated Size
and Standard Deviation
1.0 ym 3.0 Urn
Boiler Outlet 0.8±1.2 2.211.4 6.613.4
DC Outlet 2.112.0 9.014.4 37.6113.4
KVB4-15900-554
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EQUIVALENT PARTICLE DIAMETER, MICROMETERS
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Figure 3-72.
Particle Size Distribution at the Mechanical Collector Outlet
as Determined by Cascade Impactor. Data are from Full Load
Tests on Spreader Stokers, Sites B and C.
KVB4-15900-554
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3.8.2 Bahco Classifier Test Results
Another method employed for determining particle size distribution
of the flyash was the Bahco classifier. This method has been used in the power
industry for many more years than the relatively new cascade impactors, and
has received wide acceptance. It is described in ASME Power Test Code 28. This
method involves transporting a collected ash sample to a laboratory for analysis.
In this program, the ash samples were collected in the dyclone which
is a part of the EPA Method 5 particulate sampling train. As a result, the
samples collected were spacially representative in that they were isokinetically
collected from a 24-point traverse of the duct. The range of size classification
is 1.5 to 25 micrometers which is more appropriate than the range obtained from
the Brink cascade impactor.
The Bahco classifier method has its drawbacks. As with all cyclone
collected samples, the smallest particles are not collected as efficiently as the
larger particles. The estimated cut point of the cyclone used was 7 micrometers
which is within the size range being classified by the Bahco.
The collection efficiency of the cyclone used in these tests was
accurately determined by dividing the cyclone catch mass by the total catch mass.
The total catch included the cyclone catch, filter catch and acetone rinse. The
results, listed in Table 3-42, show that between 1.4 and 12.2% of the sample was
lost. Average collection efficiency was 94.5%.
Potential drawbacks to the Bahco classifier method include the possibil-
ity that particles may break-up, agglomerate, or absorb moisture during transit,
all of which would affect the outcome of the analysis.
Test Data. The Bahco data are plotted on a log-normal scale in Figure
3-73. Bahco analysis was only run on boiler outlet flyash samples. The average
size distribution of the Bahco data, and its standard deviation, is given in
Table 3-43. As expected, the Bahco data indicates fewer particles below 3 micro-
meters than does the Brink data. The percentages are 1.8% versus 6.6%, respectively.
Because the two methods are believed to be biased in opposite directions, the
true size distribution should lie somewhere in between.
KVB4-15900-554
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w
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2 3456 10
EQUIVALENT PARTICLE DIAMETER, MICROMETERS
20
30
Figure 3-73.
Particle Size Distribution at the Boiler Outlet as Determined
by Bahco Classifier. Data are from Full Load Tests on
Spreader Stokers, Sites A, B, C F and G.
KVB4-15900-554
159
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TABLE 3-42
COLLECTION EFFICIENCY OF BAHCO SAMPLES
Site Test % Collected % Lost
A 30 97.1 2.9
B 4 97.0 3.0
B 23 97.5 2.5
B 24 96.7 3.3
B 25 97.1 2.9
B 26 95.1 4.9
C 9 96.6 3.4
C 10 92.2 7.8
C 24 98.6 1.4
C 36 96.5 3.5
C 42 98.4 1.6
F 5 96.1 3.9
F 21 91.0 9.0
F 23 94.0 6.0
F 24 93.8 6.2
F 29 93.9 6.1
G 4 89.1 10.9
G 5 93.4 6.6
G 8 87.8 12.2
G 17 91.9 8.1
G 18 91.2 8.8
TABLE 3-43
AVERAGE BAHCO CLASSIFIER DATA FOR SPREADER STOKERS
Mass Percent Less than Stated Size
and Standard Deviation
3 ym 10 ym 20 Urn
Boiler Outlet 1.810.5 6.2±2.1 12.1±4.4
KVB4-15900-554
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3.8.3 SASS Cylcone Test Results
A third method employed to measure particle size distributions was the
cyclone train from the Source Assessment Sampling System (SASS). This data is a
byproduct of the SASS sampling for trace elements and organic species. The
method involved drawing a sample isokinetically from a single point in the duct
and passing it through three calibrated cyclones at a controlled temperature and
flow rate.
Like the Brink cascade impactor it has the advantage of sizing the entire
sample without losses. It has an advantage over the Brink in that it is a high
volume sampler using relatively large nozzles of nominally 5/8 inch (1.59 centi-
meters) diameter. Despite the large nozzles, the sampled dust loadings were an
average 23% less than the corresponding EPA Method 5 particulate loadings. A
disadvantage of the SASS data is that it was obtained from a single point and may
be biased in either direction due to stratification within the duct.
Test Data. The SASS cyclone particle size distribution data are shown
in Figures 3-74 and 3-75. It should be noted that the cut points of the calibrated
cyclones used for tests at Sites A, B and C were 1, 3 and 10 micrometers. At Sites
E, F and G, the cut-points were 1.4, 5.9 and 18.5 micrometers. The average and
standard deviation of the boiler outlet data are given in Table 3-44. Since there
were only two tests each at the mechanical collector outlet at Site B, and at the
electrostatic precipitator outlets of Sites A and B, these data are presented with-
out averaging. The Site A data obtained at the ESP outlet reflects the fact that
three of the four precipitator fields were out-of-service during these two tests.
TABLE 3-44
AVERAGE SASS CYCLONE DATA FOR SPREADER STOKERS
Mass Percent Less than Stated Size
and Standard Deviation
1.0 VU
Boiler Outlet
DC Outlet (Site B)
ESP Outlet (Site A)
ESP Outlet (Site B)
KVB4-15900-554
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1.0 10m
1.711.4
3.6-13.2
19.8-20.8
85.2-86.0
3.0 ym
4.9±2.8
17.3-40.8
58.1-62.6
85.2-87.0
10.0 Pm
15.919.0
41.5-78.0
75.5-82.2
88.8-93.8
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2 3456 10
EQUIVALENT PARTICLE DIAMETER, MICROMETERS
Figure 3-74. Particle Size Distribution at the Boiler Outlet as Determined
by SASS Cyclones. Data are from Full Load Tests on Spreader
Stokers, Sites A, B, C, E, F and G.
KVB4-15900-554
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20
Figure 3-75.
Particle Size Distribution at the Mechanical Collector Outlet
and the Electrostatic Precipitator Outlet as Determined by SASS
Cyclones. Data are from Tests on Spreader Stokers, Sites A and
B, at Loads Ranging from 75 to 89% of Design Boiler Capacity.
KVB4-15900-554
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3.8.4 Coulter Counter and Sieve Analysis Test Results
Sieve analysis was performed on 21 flyash samples collected at the
boiler outlets of five spreader stokers. The samples were collected with the
cyclone in the EPA Method 5 train. Seven sieve sizes were used, ranging from
ten mesh (1650 micrometers) to 325 mesh (44 micrometers).
The sieve data are plotted on a log-probability scale in Figure 3-76.
To simplify the presentation, this plot shows only the average of the full load
test data for each of the five spreader stokers. In addition to the seive analysis,
one sample was run through a coulter counter. The results of this test are repre-
sented by the dashed line.
The sieve data show that particles at the boiler outlets of spreader
stokers are as large as 1000 to 2000 micrometers in diameter. The average and
standard deviation of this data is presented in Table 3-45.
TABLE 3-45
AVERAGE SIEVE ANALYSIS DATA FOR SPREADER STOKERS
Mass Percent Less than Stated Size
and Standard Deviation
100 Urn 300 Pm 1000 Urn
Boiler Outlet 13.4±7.1 24.7±12.7 54.1±18.8 97.9±1.5
3.8.5 Combustibles vs Particle Size Distribution
One ash sample from the dust collector hopper at Test Site A was sieved
into three size ranges and baked for combustible determination. The results,
given in Table 3-46, show that the larger particles contain the highest combustible
content. This is in keeping with the results of combustible determinations on the
flyash at the inlet and outlet of the dust collector. At the collector inlet,
the flyash averaged 58.4% combustibles. At the collector outlet after the largest
particles had been removed, the flyash averaged only 30.3% combustibles.
KVB4-15900-554
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w
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H
Q
W
H
30 40 50 60 100 200 300 400
EQUIVALENT PARTICLE DIAMETER, MICROMETERS
1000
Figure 3-76.
Sieve Analysis of Flyash Collected at the Boiler Outlets of Five
Spreader Stokers. Each Line Represents the Average of the Full
Load Data for Each Site. Dashed Line Represents Results of
Coulter Counter Analysis of a Single Ash Sample.
KVB4-15900-554
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TABLE 3-46
Tyler Screen
Mesh
-10+20
-20+100
-100
COMBUSTIBLES VS DC HOPPER ASH SIZING
SITE A
Average Diameter
Micrometers
1,242
490
74
Mass, %
4.3
34.4
61.3
Weighted Average
Combustibles, %
72.6
61.3
5.0
27.3
A similar analysis was run on four flyash samples collected at the
boiler outlet at Test Site B. These samples were sieved into five size ranges.
The analysis of all four samples were nearly identical. Their average analysis
are presented in Table 3-47. Again, the larger particles contained the higher
combustible fractions.
TABLE 3-47
COMBUSTIBLES VS BOILER OUTLET FLYASH SIZING
SITE B
Tyler Screen
Mesh
-8+16
-16+35
-35+80
-80+200
-200
Average Diameter
Micrometers
1,326
713
303
128
38
Mass, %
6
29
19
19
27
Weighted Average
Combustibles, %
91
84
64
34
17
53%
KVB4-15900-554
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3.8.6 Dust Collector Efficiency vs Particle Size Distribution
There are a number of factors which influence dust collector efficiency
besides particle size distribution. These include design, state of repair, in-
let dust loading and pressure drop across the cyclone tubes.
A comparison is made in Figure 3-77 between collector efficiency and
percentage of particles smaller than 20 micrometers. To minimize the other
variables, only full load data are shown, and the test sites are identified.
The data are further restricted to Bahco classifier tests of ash samples which
were accompanied by a simultaneous dust collector efficiency test.
In Figure 3-77, the data from Sites B, C and G behaved very similar.
There is a slight decrease in efficiency as the percentage of particles larger
than 20 micrometers increased. Test Site F had much lower dust collector
efficiencies than the others despite the coarseness of the particles entering
the collector. This could be the result of the collector's design or state of
repair, or it could be measurement error. There is insufficient information
available to resolve this difference.
Finally, it is worth noting that dust collector efficiency did not
drop off significantly as load decreased on spreader stokers except when it
was reduced to 20% of capacity as it was on Test Site G. Figure 3-78 illustrates
the dust collector efficiency data for four spreader stokers. Data from Site E
are not included in this figure. The collector efficiency at Site E deteriorated
during the test program from 84-96% in early tests to 41-68% in later tests as
the result of an undiagnosed problem. Test Site A is also omitted from Figure
3-78 because simultaneous dust loadings were not determined across its collector.
KVB4-15900-554
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80
75
70
GO^££OB
OF
OF
5 10 15 20
MASS PERCENT < 20 MICROMETERS DIAMETER
25
Figure 3-77.
Relationship Between Percentage of Particles Smaller than
20 Micrometers, and Dust Collector Efficiency for Spreader
Stokers. Only Bahco Data from Full Load Tests are Indicated.
Line Represents an Observed Trend.
KVR4-15900-554
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20.0 40.0 60.0 80.0 100.0
PERCENT BOILER DESIGN CRPflCITY
: SITE B
S SITE C
A : SITE F
: SITE G
FIG. 3-78
MECH. COLL. EFF. VS. PERCENT DESIGN CflPRCITY
KVB4-15900-S54
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4.0 MASS FIRED OVERFEED STOKERS
4.1 DESCRIPTION OF UNITS TESTED
Mass fired overfeed stokers differ from spreader stokers in the
manner by which fuel is fed onto the grate. In this type of stoker, a layer
of coal is continuously layed down on one end of the grate. The motion of the
grate conveys this coal continuously through the furnace where it is consumed.
Ash is continuously discharged at the opposite end of the grate. Mass fired
overfeed stokers have burning characteristics which are uniquely different
from spreader stokers and underfeed stokers and are therefore discussed as
a separate group in this report.
The mass fired overfeed stokers tested for this program represent
j
the most common designs specified today. All seven stokers in this group are
balanced draft units having both forced draft and induced draft fans. All are
equipped with overfire air on the front wall, and none have any form of flyash
reinjection. Two of the stokers utilize a water cooled vibrating grate to
transport the coal and ash through the furnace. The other five utilize
continuous traveling or chain grates. Two of the stokers were built in 1977,
while the other five were built between 1959 and 1969. All seven mass fired
stokers represent state-of-the-art designs, since stoker designs have changed
very little over the past twenty years.
TABLE 4-1
DESCRIPTION OF MASS FIRED OVERFEED STOKERS TESTED
Site
D
H
I
J
K
L2
L4
Year
Built
1964
1959
1960
1977
1977
1960
1969
Steaming
Capacity
Ib/hr
90,000
45,000
70,000
70,000
50,000
30,000
27 ,000
Grate
Type
Vibrating
Traveling
Traveling
Chain
Traveling
Vibrating
Chain
Boiler
Passes
Multiple
Multiple
Multiple
Multiple
Multiple
Multiple
Multiple
Backend Equipment by
Order of Occurrence
ECON, DC
None
None
ECON, DC
ECON, DC
DC
DC
The following pages present equipment data and general arrangement
drawings for each of the seven mass fired overfeed stokers tested. Throughout
this report the units will be referred to by the letter designation assigned
in this section.
171 KVB4-15900-554
-------
TABLE 4-2
EQUIPMENT DATA
TEST SITE: D
BOILER:
Year Built
Configuration
Rated Steaming Capacity
Design Pressure
Actual Operating Pressure
Feedwater Temperature
Steam Temperature
Operating Air Temperature
1964
Multiple Pass
90,000 Ib/hr
700 psig
200 psig
250°F
Saturated
Ambient
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Mass Fired Water Cooled Vibrating Grate
16.5 Ft
15.5 Ft
256.3 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
3,520 Ft3
737 Ft2
7,706 Ft2
None
4,275 Ft2
None
HEAT RATES AT RATED CAPACITY:
Input to Furnace
Grate Width Heat Release
Grate Heat Release
Furnace Liberation
103,000,000 Btu/hr
6,630,000 Btu/hr-ft
401,000 Btu/hr-ft2
29,300 Btu/hr-ft3
OVERFIRE AIR:
Location
Number of Jets x Pipe Size
Elevation Above Grate
Inclination below Horizontal
Front Upper
16x1i"
3.4 Ft
30°
Front Lower
16x1J"
1.4 Ft
10°
EMISSION CONTROL EQUIPMENT:
Mechanical Collector
KVB4-15900-554
172
-------
STACK
"TEST
1.0. FAN
Figure 4-1. Test Site D General Arrangement Drawing
KVB 4-15900-554
173
-------
TABLE 4-3
EQUIPMENT DATA
TEST SITE: H
BOILER:
Year Built
Configuration ———
Rated Steaming Capacity
Design Pressure ———•
Actual Operating Pressure
Feedwater Temperature ——
Steam Temperature
Operating Air Temperature
1959
Multiple Pass
45,000 Ib/hr
200 psig
140 psig
220°F
Saturated
Ambient
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Mass Fired Traveling Grate
11.0 Ft
13.0 Ft
140.3 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
1,850 Ft3
820 Ft2
5,780 Ft2
None
None
None
HEAT RATES AT RATED CAPACITY:
Input to Furnace
Grate Width Heat Release
Grate Heat Release
Furnace Liberation
59,600,000 Btu/hr
4,580,000 Btu/hr-ft
425,000 Btu/hr-ft2
32,300 Btu/hr-ft3
OVERFIRE AIR:
Location
Number of Jets x Pipe Size
Elevation Above Grate
Inclination below Horizontal
EMISSION CONTROL EQUIPMENT:
Front Wall
10x2i"
4.2 Ft
45°
None
KVB4-15900-554
174
-------
STACK
TEST PLANE
STACK
Figure 4-2. Test Site H General Arrangement Drawing
KVB 4-15900-554
175
-------
TABLE 4-4
EQUIPMENT DATA
TEST SITE: I
BOILER:
Year Built
Configuration
Rated Steaming Capacity
Design Pressure
Actual Operating Pressure
Feedwater Temperature •
Steam Temperature
Operating Air Temperature
1960
Multiple Pass
70,000 Ib/hr
250 psig
150 psig
220°F
Saturated
Ambient
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Mass Fired Traveling Guide
18.0 Ft
14,0 Ft
252.6 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
3,900 Ft3
9,500 Ft2
None
None
None
HEAT RATES AT RATED CAPACITY: *
Input to Furnace
Grate Width Heat Release
Grate Heat Release •
Furnace Liberation
95,200,000 Btu/hr
6,800,000 Btu/hr-ft
377,000 Btu/hr-ft2
24,400 Btu/hr-ft3
OVERFIRE AIR:
Location
Number of Jets x Pipe Size
Elevation Above Grate
Inclination below Horizontal
Front Upper
Unknown
6.8 Ft
30°
Front Lower
Unknown
4.5 Ft
45°
EMISSION CONTROL EQUIPMENT:
None
*Heat rates are based on measured Fuel Flow data at this site,
manufacturers design data was not available.
KVB4-15900-554
176
-------
STACK
TEST PLANE"
STACK
Figure 4-3. Test Site I General Arrangement Drawing
KVB 4-15900-554
177
-------
TABLE 4-5
EQUIPMENT DATA
TEST SITE: J
BOILER:
Year Built
Configuration
Rated Steaming Capacity
Design Pressure
Actual Operating Pressure
Peedwater Temperature
Steam Temperature
Operating Air Temperature
1977
Multiple Pass
70,000 Ib/hr
250 psig
150 psig
220°F
Saturated
Ambient
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Mass Fired Chain Grate,
15.3 Ft
14.0 Ft
213.0 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
4,005 Ft3
715 Ft2
7,745 Ft2
None
Unknown
None
HEAT RATES AT RATED CAPACITY:
Input to Furnace
Grate Width Heat Release
Grate Heat Release
Furnace Liberation
84,140,000 Btu/hr
6,010,000 Btu/hr-ft
395,000 Btu/hr-ft2
21,000 Btu/hr-ft3
OVERFIRE AIR:
Location
Number of Jets x Pipe Size
Elevation Above Grate
Inclination below Horizontal
Front Wall
15x1-5/8"
3.8 Ft
15°
EMISSION CONTROL EQUIPMENT:
Mechanical Collector
KVB4-15900-554
178
-------
STACK
TETfpTANC"
STACK
BOILER
OUTLET TEST
PUX^IE
I.D. FAN
Figure 4-4. Test Site J General Arrangement Drawing
KVB 4-15900-554
179
-------
TABLE 4-6
EQUIPMENT DATA
TEST SITE: K
BOILER:
Year Built
Configuration
Rated Steaming Capacity
Design Pressure
Actual Operating Pressure
Feedwater Temperature
Steam Temperature
Operating Air Temperature
1977
Multiple Pass
50,000 Ib/hr
200 psig
125 psig
Unknown
Saturated
Ambient
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Mass Fired Traveling Grate
16.0 Ft
10.0 Ft
160.0 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
2,614 Ft3
1,143 Ft2
5,526 Ft2
None
Unknown
None
HEAT RATES AT RATED CAPACITY: *
Input to Furnace
Grate Width Heat Release
Grate Heat Release
Furnace Liberation
65,000,000 Btu/hr
6,500,000 Btu/hr-ft
406,000 Btu/hr-ft2
24,900 Btu/hr-ft3
OVERFIRE AIR:
Location
Number of Jets x Pipe Size
Elevation Above Grate
Inclination below Horizontal
Front Wall
8x1 i"
5.0 Ft
30°
EMISSION CONTROL EQUIPMENT:
Mechanical Collector
* Heat rates are based on measured Fuel Flow data at this site,
manufacturers design data was not available.
KVB4-15900-554
180
-------
Figure 4-5. Test Site K General Arrangement Drawing
KVB 4-15900-554
181
-------
TABLE 4-7
EQUIPMENT DATA
TEST SITE: L2
BOILER:
Year Built
Configuration
Rated Steaming Capacity
Design Pressure —
Actual Operating Pressure
Feedwater Temperature
Steam Temperature — —
Operating Air Temperature
1965
Multiple Pass
30,000 Ib/hr
Unknown
125 psig
212°F
Saturated
Ambient
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Vibrating Grate
Unknown
Unknown
123.1 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
1,665 Ft3
1,641 ft2
4,514 ft2
None
None
None
HEAT RATES AT RATED CAPACITY:
Input to Furnace —
Grate Width Heat Release
Grate Heat Release
'j
Furnace Liberation —
Unknown
Unknown
300,000 Btu/hr-ft2
30,000 Btu/hr-ft3
OVERFIRE AIR:
Location
Number of Jets x Pipe Size —
Elevation Above Grate
Inclination below Horizontal
Unknown
Unknown
Unknown
Unknown
EMISSION CONTROL EQUIPMENT:
Mechanical Collector
KVB4-15900-554
182
-------
TABLE 4-8
EQUIPMENT DATA
TEST SITE: L4
BOILER:
Year Built
Configuration
Rated Steaming Capacity
Design Pressure
Actual Operating Pressure
Feedwater Temperature
Steam Temperature
Operating Air Temperature
1969
Multiple Pass
27,000 Ib/hr
250 psig
150 psig
220°F
Saturated
Ambient
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Chain Grate
11.9 Ft
9.0 Ft
107 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
1,315 Ft3
920 Ft2
2,930 Ft2
None
None
None
HEAT RATES AT RATED CAPACITY:
Input to Furnace
Grate Width Heat Release
Grate Heat Release
Furnace Liberation
Unknown
Unknown
333,000 Btu/hr-ft2
30,300 Btu/hr-ft3
OVERFIRE AIR:
Location
Number of Jets x Pipe Size
Elevation Above Grate
Inclination below Horizontal
Front Wall
9xli"
3.5 Ft
15°
EMISSION CONTROL EQUIPMENT:
Mechanical Collector
KVB4-15900-554
183
-------
BOILER OUTLET
TEST PLANE
D. C. OUTLET
TEST PLANE
BOILER
FURNACE
Figure 4-6. Boiler Schematic for Test Sites L2 and L4.
KVB4-15900-554
184
-------
4.2 PERFORMANCE AT FULL LOAD
This section presents, in graphical format, the emissions and
efficiency of seven mass fired overfeed stokers operated at or near full load.
For the purposes of this report, full load is defined as the upper 10% of the
load range obtainable at the time of testing. For Sites H, I, J and K this
represents 90 to 100% of nameplate rating. At Test Site D, however, the maxi-
mum obtainable load was 89% of nameplate because of draft losses incurred
from a retrofit dust collector. Thus, loads above 80% of design were con-
sidered full load at Site D. At Sites L2 and L4 testing was conducted at a
single operating condition representing 85% and 78-% of steaming capacity,
respectively. Although the data from these two tests are included in this
section, their reduced loading should be kept in mind.
The capacity range of the data presented in this section, and the
number of tests within that range, are given in Table 4-9.
TABLE 4-9 .
CAPACITY RANGE AND DATA BASE FOR FULL LOAD
TESTS ON SEVEN MASS FIRED OVERFEED STOKERS
Percent Number of Tests
Capacity Range Gaseous Particulate
Site D 86-89 9 6
Site H 96-102 10 3
Site I 98-104 15 4
Site J 93-103 8 3
Site K 95-102 9 7
Site L2 85 1 1
Site L4 78 1 1
TOTALS 53 25
The data are represented by bar graphs which indicate the minimums,
maximums and averages of the full load data. These graphs give an indication
of how much the data varied between units and within each individual unit.
The range of data shown is representative of normal variations experienced
in day-to-day operation.
Extremes should be treated with caution when interpreting these data.
There is a certain degree of scatter, or uncertainty, to the data which must
185 KVB4-15900-554
-------
be taken into account. Thus, for example, if a certain unit emitted a very
low particulate loading during one test, it does not follow that this unit
can operate continuously at the low particulate loading by simply duplicating
the stoker settings of the test.
Emission Factors. Environmental Protection Agency publication AP-42,
Compilation of Air Pollutant Emission Factors, Third Edition, contains factors
used for predicting emissions from non-spreader stokers as well as spreader
stokers.
The data from this test program have been converted to the same units
used in AP-42 to obtain a set of measured emission factors for each site.
These factors are presented in Table 4-10.
TABLE 4-10
EMISSION FACTORS FOR MASS FIRED OVERFEED
STOKERS FIRING BITUMINOUS COAL
Uncontrolled Particulates Nitrogen Oxides
_lb/ton Ib/ton
7.2
9.4
7.1
9.3
8.4
NA
NA
AVERAGE, °F 3.6 A 8.3
(D, H, I, J & K)
AP-42 5 A NA
The data clearly show that the emission factor "5A" is too high for
these stokers firing the coals they were firing. The emissions did not
deviate very much from their 3.6 A average.
It is equally evident that coal ash is not the primary variable
affecting particulate loading. At Site K, three forms of coal from the same
mine were fired in the same boiler with widely varying emission levels. The
unwashed coal had an emission factor of 3.7 A as shown in Table 4-10. This
186 KVB4-15900-554
Site
Site
Site
Site
Site
Site
Site
D
H
I
J
K
L2
L4
3.
3.
3.
3.
3.
1.
1.
6 A
3 A
8 A
6 A
7 A
1 A
6 A
-------
same coal when washed, produced lower partlculate yet had a greater emission
factor of 4.9 A. In this case, the coal ash was reduced more than the
particulates were by the process of washing the coal. When the washed coal
was crushed to increase the fines content, the emission factor rose to
7.7 A. This would indicate that coal fines play an equally important role
in determining particulate loading. This subject is discussed further in
Section 4.5, Response to Coal Analysis and Sizing.
KVB4-15900-554
187
-------
500
M-l
4
3
-P
P3
400
W
£
0
200
0
2
H
w
H
2
w
I
H
W
1 1 1 1 1
KEY
HIGH-".
AVG —J
LOW-"'
D H I J K L2
TEST SITE DESIGNATOR
L4
Figure 4-7. Grate Heat Release Rates of Seven Mass Fired Overfeed
Stokers Fired at or Near Full Load.
The ranges of grate heat release rate shown here represent full
load operation as defined in Table 4-9. All seven mass fired overfeed
stokers were designed within the guidelines set by ABMA which specify a
maximum grate heat release of 500,000 Btu/hr-ft2 effective air admitting
grate area for this class of stoker. Note that Test Site D was designed
for 401xl03 Btu/hr-ft2, but achieved only 80% of this rate due to draft
losses from a retrofit dust collector. Test Sites L2 and L4 were tested
once each at a reduced load. The design grate heat release rates for each
stoker in units of 103 Btu/hr-ft2 are: D-401, H-425, 1-377, J-395, K-406,
L2-300, L4-333.
KVB4-15900-554
188
-------
120
w
& 90
w
•H
CO
co
H 60
X
w
30
SINGLE DATA POI
I I 1 I I 1
EH
Z
H
O
04
EH
Q
W
a
H
LO
KEY
HIGH-*.
AVG —I
LOW—'
;i
D H I J K L2
TEST SITE DESIGNATOR
L4
Figure 4-8. Excess Air Operating Levels of Seven Mass Fired Overfeed
Stokers Fired at or near Full Load.
Excess air ranged from 26% to 97% in these tests. The averages
for the five extensively tested sites ranged from 51% to 70%. Excess air
was computed from flue gas analysis obtained at the boiler outlets of
Sites D, J and K, and from the stack at Sites H, I, L2 and L4. As a
reference, 60% excess air is approximately equal to 8% O2-
KVB4-15900-554
189
-------
12
EH
2
W
H
On
a
w
CD
>H
X
O
III
I
S3
H
2
H
CO
H
2
EH
<
Q
W
hH1
CD
2
H
I I I 1 I I I
KEY
HIGH—-
AVG—I
LOW-»"
H I J K L2
TEST SITE DESIGNATOR
L4
Figure 4-9. Excess Oxygen Operating Levels of Seven Mass Fired Overfeed
Stokers Fired at or Near Full Load.
Flue gas oxygen was measured on a dry basis. It ranged from 4.5%
to 10.6% overall. The averages for the five extensively tested sites
ranged from 7.2% to 8.9%.
KVB4-15900-554
190
-------
4-1
ffl
w
§
D
O
H
a
w
8
B
3
8
2.0
1.5
1.0
.5
H
o
ft
e>
z
H
W
H
2;
H
O
ft
I
2:
H
i i i » I i i
D H I J K
TEST SITE DESIGNATOR
L2
L4
KEY
HIGH—-
AVG—!
LOW-*-'
Figure 4-10.
Uncontrolled Particulate Loadings of Seven Mass Fired
Overfeed Stokers Fired at or Near Full Load.
Uncontrolled particulate loadings ranged from .57 lb/10 Btu
to 2.2 lb/10^ on the five extensively tested mass fired overfeed stokers.
The averages for these same five stokers ranged from .78 to 1.4 lb/10^
Btu. Site L2 and L4 had lower particulate loadings of .56 and .50 lb/106
Btu, respectively, but these were obtained at lower loads of 85% and 78%
of design capacity, respectively. The site L2 and L4 particulate data is
not out of line when compared with data obtained at the same grate heat
release from the other stokers.
KVB4-15900-554
191
-------
K 80
O
H
S
>i
ffl
cW
K 60
CO
X
I-H*
p4
H
EH
4BUSTIBLES IN
*>
o
5 20
u
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I.I.
^_
1 1 1 1
H
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ft
-------
EH
S3
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H
>H
CQ
33
CO
W
33
EH
*Z,
H
CO
3
m
H
EH
CO
D
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U
80
60
40
to
0
<
§
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a
H
CO
,"
I I I I I
H I J K L2
TEST SITE DESIGNATOR
H
O
ft
Q
W
S
X
H
CO
L4
KEY
HIGH—
Figure 4-12.
Percentage of Combustible Material in the Bottom Ash of
Seven Mass Fired Overfeed Stokers Fired at or Near Full Load.
The percentage of combustible material in the bottom ash ranged
from 7% to 69%. The averages for Sites D, H, I, and J ranged from 21%
to 31%. For some reason, Site K's bottom ash combustibles were higher
than the others, averaging 43%.
KVB4-15900-554
193
-------
.8
PQ
O
-6
NITRIC OXIDE
O
3
EH
Q
O
I I 1 I I i I
HIGH—.
AVG —J
LOW—"
D H I J K L2
TEST SITE DESIGNATOR
L4
Figure 4-13.
Nitric Oxide Emissions of Five Mass Fired Overfeed Stokers
Fired at or Near Full Load.
Nitric oxide emissions ranged from .21 to .50 Ib/lO^Btu computed as
NO2- Site averages ranged from .27 to .41 lb/10^Btu. Some of the variations
between sites are the result of different excess air operating levels. For
example, Site H was operated at an average excess air of 70% compared to
51% for Site I. As a result, Site H's NOx emissions were higher.
KVB4-15900-554
194
-------
CN
O
M
g
ft
w
Q
s
a
o
0
800
600
200
IS
<
0
0
o
o
o
W
w
w
I I I
D
I J K L2
TEST SITE DESIGNATOR
S
ft
ft
o
o
o
CO
w
i-q
KEY
HIGH—.
AVG —j
LOW-»'
L4
Figure 4-14.
Carbon Monoxide Emissions of Five Mass Fired Overfeed
Stokers Fired at or Near Full Load.
Carbon monoxide concentrations were highly sensitive to combustion
conditions. They were highest near full load under low excess air conditions,
or when overfire air was reduced too much. At Site D, carbon monoxide con-
centration exceeded 2000 ppm during one low overfire air test. In all other
tests, they remained below 900 ppm. At Sites L2 and L4, CO was measured
with an Orsat gas analyzer and found to be less than 1000 ppm (0.1%) which
is the minimum detection limit of this instrument. The CO monitor was out of
service at Sites I and J.
KVB4-15900-554
195
-------
£120
O
*
ro
W 90
S
ft
0)
la
O
U 60
Q
Q
K
Q
g
« 30
5
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• ft
I £
< 1 « s
B H EH W EH H EH
^ • < H^ < < <
Q • Q 0 Q Q Q KEY
g 1 § s § § § HIGH1
^^1 AVG ""*"•
1 T 1 1 1 1 1 owJ
D H I J K L2
TEST SITE DESIGNATOR
L4
Figure 4-15.
Unburned Hydrocarbon Emissions of Two Mass Fired Over-
feed Stokers Fired at or Near Full Load.
Unburned hydrocarbons (HC) were successfully measured at only two
of the five extensively tested mass fired overfeed stokers. A troublesome
flame ionization hydrocarbon monitor and problems with a heated sample line
prevented these measurements from being made on the other three stokers.
The data ranged from 5 ppm to 112 ppm (wet) corrected to 3% C>2-
KVB4-15900-554
196
-------
EH
D
CM
a
Is
H 1.2
MH
CO
pa
H
EH
3
8
SG
a
a
CM
O
EH
W
P
Q
LO
CO
^m
EH
23
H
O
8
W
H
CO
D H I J K L2
TEST SITE DESIGNATOR
H
O
I
Q
W
H
CO
I I I I I 1
KEY
HIGH—.
L4
Figure 4-16.
Heat Loss Due to Combustibles in the Flyash of Seven Mass
Fired Overfeed Stokers Fired at or Near Full Load.
Heat loss due to combustibles in the flyash ranged from .16% to
1.1%. The averages for the five extensively tested stokers ranged from
.35% to .52%. These heat loss calculations are based on an assumed heating
value of the combustible material of 14,250 Btu/lb. The Flyash was not
directly analyzed for its heating value.
KVB4-15900-554
197
-------
PH
O
CO
PQ
H
3 6
8
S 4
EH
EH
§
w
D
Q
CO
CO
s
EH
I!
i
H
g
I
2
H
H I J K L2
TEST SITE DESIGNATOR
la
H
o
I
Q
W
H
CO
i i i i i
KEY
HIGH—-
AVG ->!
LOW-»"
L4
Figure 4-17.
Heat Loss Due to Combustibles in the Bottom Ash of Seven
Mass Fired Overfeed Stokers Fired at or Near Full Load.
Heat loss due to combustibles in the bottom ash ranged from 0.4%
to 9.4%. The averages of Sites D, H, I and J ranged from 1.4% to 2.8%.
Test Site K averaged 4.0% due to its higher bottom ash combustible content.
These heat loss calculations are based on an assumed heating value of the
combustible material of 14,250 Btu/lb. The bottom ash was not directly
analyzed for its heating value.
KVB4-15900-554
198
-------
90
<*>
>7 80
u
2
W
H
O
H
fn
Cn
W
1 7°
H
O
CQ
60
EH
•» 2
H
O
CM
<
• (£
. Q
- Ill
1 |
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••
^ .
1 1 1 1 1 1
EH
2
hH
o
CM
^
EH
Q
O
2
H
W
KEY
HIGH— —
AVG -»!
I LOW-»"
D
I J K L2
TEST SITE DESIGNATOR
L4
Figure 4-18.
Boiler Efficiency of Seven Mass Fired Overfeed stokers
Fired at or Near Full Load.
Measured boiler efficiencies for these units ranged from 69.8%
to 84.1%. Sites D, J and K, which were equipped with economizers, had the
highest average efficiencies at 83.8%, 81.8% and 78.4%, respectively.
Sites H and I, which did not have economizers, averaged 75.4% and 73.9%
boiler efficiencies, respectively. Boiler efficiencies were determined by
the ASME heat loss method (PTC 4.1).
KVB4-15900-554
199
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4.3 RESPONSE TO HEAT RELEASE RATE
This section profiles the emissions and efficiency of five mass fired
overfeed stokers as a function of heat release rate. Four measures of heat
release rate are considered. They are grate heat release, front foot heat re-
lease, furnace liberation, and percent of steaming capacity.
Heat release rate is the quantity of thermal energy introduced into
the furnace by the fuel each hour. It is the product of the hourly fuel rate
and the fuel's higher heating value. Three of the five mass fired overfeed
stokers, Sites H, I and J, were equipped with coal weigh lorrys which did not
provide accurate fuel flow rates for the relatively short three-hour test
periods. Therefore, heat release rate on these three units was taken to be
the enthalpy of the steam times the steam flow divided by the fractional boiler
efficiency.
Table 4-11 presents the design heat release rates for the five mass
fired overfeed stokers. Their differences reflect differences in unit design.
One of the aims of this section is to determine if a relationship exists be-
tween these design differences and the unit's emissions and efficiency. The
other aim is to profile emissions and efficiency as heat release rate is varied
on a given unit. The results of this study are presented in the following sub-
sections.
TABLE 4-11
Site D
Site H
Site I
Site J
Site K
DESIGN HEAT RELEASE RATES
Furnace
Liberation
Btu/hr-ft3
29,300
32,300
24,400
21,000
24,900
Grate Heat
Release
Btu/hr-ft2
401,000
425,000
377,000
395,000
406,000
Front Foot
Heat Release
Btu/hr-ft
6,630,000
4,580,000
6,800,000
6,010,000
6,500,000
KVB4-15900-554
200
-------
4.3.1 Excess Air vs Heat Release Rate
The excess air requirement in stoker boilers is a function of heat re-
lease rate. At reduced heat release rates, more excess air is required to
maintain good combustion.
Excess air profiles for the five mass fired overfeed stokers are shown
in Figure 4-19. With the exception of Test Site K, they have similar slopes.
As full load is approached, an increase of 100,000 Btu/hr-ft2 is accompanied by
an average 20% drop in excess air.
The larger stokers are able to operate at reduced excess air levels.
This observation is illustrated in Figure 4-20 where the average as-found ex-
cess air operating levels, at 350,000 Btu/hr-ft2, are compared with the grate
areas. This same relationship was observed for the spreader stokers.
One possible explanation for this relationship was suggested in Section
3.3.1 when discussing the same observation on spreader stokers. That is, the
larger units are likely to leak a smaller percentage of air through access
doors and around the grate due to their smaller surface-to-volume ratio.
One more observation worth mentioning is the coal gate position, i.e.,
bed depth, as a function of load. Figure 4-21 shows this relationship for the
four traveling grate and chain grate stokers. The fact that Site K was operated
with a lower, static fuel bed than the others may relate to some of the dif-
ferences in emissions observed for this unit. The coal gate position was not
recorded during tests at Site D.
4.3.2 Particulate Loading vs Heat Release Rate
Uncontrolled particulate loading increased as heat release rate in-
creased. The trends, as visually determined from data plots, are shown in
Figure 4-22. Sites D, H and J showed a distinct increase in slope at high heat
release rates. Sites I and K (washed coal only) had approximately linear re-
lationships with grate heat release.
The relationship between uncontrolled particulate loading and heat
release rate was also examined statistically. A line was fit to the data from
each site using linear regression analysis. The slopes of these lines are pre-
sented in Table 4-12 along with the coefficient of correlation (r2). The
KVB4-15900-554
201
-------
150
120
90
0
60
30
MASS FIRED OVERFEED STOKERS
100
200
300
400
500
GRATE HEAT RELEASE, 103Btu/hr-ft2
Figure 4-19.
Excess Air Profiles for Five Mass Fired Overfeed Stokers.
The Lines Represent Average As-Found Operating Conditions.
KVB4-15900-554
202
-------
100
80
MASS FIRED OVERFEED STOKERS
60
pa
u
x
w
40
20
5C
100 150 200
EFFECTIVE GRATE AREA, FT2
250
Figure 4-20.
Excess Air Operating Levels of Five Mass Fired Overfeed
Stokers Showing a Correlation with Size of the Grate,
The Data Represents a Common Grate Heat Release of
350,000 Btu/hr-ft2.
KVB4-15900-554
203
-------
10
w
M
O
S
H
13
O
H
&
H
W
2
I
"H
8
TRAVELING AND CHAIN GRATE STOKERS
K
60 70 80 90 100
STEAM LOADING, % OF DESIGN CAPACITY
Figure 4-21.
Coal Gate Position as a Function of Load for Four Traveling
Grate and Chain Grate Stokers.
KVB4-15900-554
204
-------
2.5
•tJ
m
2.0
9
3
w
D
U
H
tit
Q
W
8
^-t
8
1.5
0.5
MASS FIRED OVERFEED STOKERS
I I I I I
100 200 300 400
GRATE HEAT RELEASE, 103Btu/hr-ft2
500
Figure 4-22. Uncontrolled Particulate Loading Profiles for Five Mass
Fired Overfeed Stokers.
KVB4-15900-554
205
-------
correlation coefficient indicates how well the data fit the equation, with
1.0 being a perfect fit.
TABLE 4-12
INCREASE IN UNCONTROLLED PARTICULATE LOADING
FOR EACH 103 BTU/HR-FT2 GRATE AREA INCREASE
Site D .0025 lb/106Btu .52
Site H .0020 lb/106Btu .55
Site I .0028 lb/106Btu .28
Site J .0027 lb/105Btu .46
Site K .0007 lb/105Btu .11
The slope of uncontrolled particulate loading versus grate heat release
was similar for Site D, H, I and J. This is evident both in Figure 4-22, and
in Table 4-12 where it ranged from .20 to .28 lb/105Btu for each grate heat
release increase of 100,000 Btu/hr-ft2. Test Site K1s uncontrolled particulate
loading, on the other hand, was less sensitive to grate heat release. At
Site K, the corresponding slope was .07 lb/106Btu per 100,000 Btu/hr-ft2.
The uncontrolled particulate profile at Site K was also a function of
coal properties. The data, shown in Figure 4-23, show that when the primary
coal was crushed to increase its fines or not washed to increase its ash content
the sensitivity to grate heat release increased.
Another variable affecting the particulate profiles was overfire air
pressure. Sites H and I have dis-similar particulate profiles in Figure 4-22,
which is based on normal operation. However, when the data from both sites are
plotted together and segregated by overfire air pressure as in Figure 4-24, they
begin to look quite similar. In other words, the differences in particulate
loading between these two sites are related more to stoker-boiler operation than
to design.
Boiler design, in terms of design heat release rates, did not correlate
with particulate loading. Looking back at Table 4-11 we see that Test Site H
stands out as having the highest design furnace liberation and grate heat release,
206 KVB4-15900-554
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and the lowest front foot heat release. Yet, Site H emitted particulates in
the same range as the other stokers. In fact, most of the differences in
particulate loading between these five stokers appear to be related to oper-
ating conditions and coal properties rather than stoker-boiler design.
Particulate loading was also measured after the dust collector at
Sites D, J and K. The other two extensively tested sites, H and I, were not
equipped with mechanical dust collectors.
The controlled particulate loading data for sites D, J and K are
shown in Figure 4-25. At sites J and K the controlled particulate loading
changed very little with grate heat release. Collector efficiencies ranged
from 64 to 93%. At Site D, however, the data tend to increase with grate
heat release and have considerably more scatter. It is suspected that cyclone
tubes were plugging at this site since collector efficiency varied considerably
from 16% to 63%.
4.3.3 Combustibles in the Flyash vs Heat Release Rate
The combustible content of the uncontrolled flyash did not show a
consistent trend with heat release rate. The combusbible content at Sites D, I
and K tended to increase as heat release rate increased. Combustibles at
Sites H and J tended to decrease with increasing heat release rate. In most
cases, data scatter tended to obscure the trend.
Figure 4-26 presents a composite picture of the flyash combustible data
for Sites D, H, I, J and K. The data for Site D alone are presented in Figure
4-27 to illustrate the degree of data scatter and the difficulty in determining
a trend.
4.3.4 Combustibles in the Bottom Ash vs Heat Release Rate
The combustible content of the bottom ash was even more difficult to
relate to heat release rate than the combustible content of the flyash. Figure
4-28 shows a composite picture of the data for Sites D, H, I and J. Except for
Site I which had a decreasing trend, the bottom ash combustible data was
relatively invariant with load.
KVB4-15900-554
209
-------
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FIG. 4-26
BLR OUT FLYflSH COMB.
VS. GRRTE HERT RELERSE
4-15900-554
211
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BOTTOM RSH COMB. VS. GRRTE HEflT RELERSE
4-15900-554
213
-------
Figure 4-29 shows the Site K data which exhibits an unusually high
degree of scatter. The four highest data points are so unreasonable as to be
suspect. Perhaps some of the bottom ash samples at Site K were not repre-
sentative .
4.3.5 Nitric Oxide vs Heat Release Rate
Nitric oxide is a function of both excess air and heat release rate
in stoker boilers. It is, therefore, necessary to sort out the effects of ex-
cess air before the effects of heat release rate can be determined. Multiple
regression analysis was used to accomplish this.
Two assumptions were required. First, that the relationship between
nitric oxide and excess air is linear, and second that the relationship between
nitric oxide and heat release rate, or load, is linear. These assumptions are
applied over the load range 50 to 100% of design capacity, and the excess air
range of 30 to 180%. It would not be wise to extrapolate beyond these limits.
These assumptions allow the data to be fit to an equation of the form:
Nitric Oxide, lb/106Btu = a + b (% excess air) + c (grate heat release)
The coefficients of this equation were determined for each site separately and
are presented in Table 4-13. The Site K data did not fit well to the model
and its coefficients are not shown. The coefficient of determination (r2) is a
measure of how well the data fit the equation with 1.0 being a perfect fit.
TABLE 4-13
COEFFICIENTS FOR AN EQUATION OF THE FORM
NOx = a + b (excess air) + c (grate heat release)*
a b c r2
Site D
Site H
Site I
Site J
.0615
.0430
.1425
.0770
.00239
.00158
.00161
.00257
.00024
.00061
.00000
.00031
.74
.52
.94
.40
* Grate heat release expressed as 103Btu/hr-ft2 grate
area
KVB4-15900-554
214
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100. 200. 300. 400. 500,
GRflTE HEflT RELERSE 1000 BTU/HR-SQ FT
; MRSHED
-f- S UNWflSHED
S CRUSHED
FIG. 4-29
BOTTOM flSH COMB.
VS. GRflTE HEflT RELEflSE
4-15900-554
215
-------
This model indicates that the relationship between nitric oxide and
grate heat release ranges from nill to .061 Ib NOx/106Btu for each 100,000
Btu/hr-ft2 increase in grate heat release. A visual examination of the data
confirms this. For example, the Site I data for Kentucky coal are plotted
against excess air in Figure 4-30. The data for three different heat release
rates all fall on the same line indicating that NOx was not a function of
heat release rate at this site. At the opposite extreme is Site H. The NOx
data for Site H are shown in Figure 4-31. These data show a very clear distinc-
tion between heat release rates with the greatest spread occurring at high
oxygen levels.
Another investigation involved the relationship between NOx emissions
and stoker-boiler design parameters. While no unequivocal relationships were
found, the NOx test results show (Table 4-14) that the highest NOx emissions,
at full load and 50% excess air, were from the stoker having the highest grate
heat release rate and highest furnace liberation. The lowest NOx emissions,
on the other hand, were from the stoker having the lowest grate heat release
rate and second lowest furnace liberation. As Table 4-14 shows, however, this
relationship is not clearly borne out by the stokers with intermediate heat
release rates.
TABLE 4-14
NITRIC OXIDE VS DESIGN VARIABLES
Site
Site
Site
Site
Site
H
J
K
D
I
Nitric Oxide @
Full Load &
50% Excess Air
lb/106Btu
.38
.33
.31
.27
.22
Steaming
Capacity
Ib/hr
45,000
70,000
50,000
90,000
70,000
Furnace
Liberation
103Btu/hr-ft3
32.3
21.0
24.9
29.3
24.4
Grate
Heat Release
103Btu/hr-ft2
425
395
406
401
377
216
KVB4-15900-554
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OXYGEN PERCENT (DRY)
O ! 150-250GHR + ! 250-350GHR A ! 350-450GHR
FIG. 4-31
NITRIC OXIDE VS. OXYGEN
12.0
218
4-15900-554
-------
4.3.6 Carbon Monoxide vs Heat Release Rate
Carbon monoxide emissions were measured at Test Sites D, H and K.
The carbon monoxide analyzer was out of service during testing at Sites I
and J.
At the three former sites the carbon monoxide concentration could be
maintained below 400 ppm over the entire load range. When carbon monoxide ex-
ceeded 400 ppm, it generally occurred at the higher loads and was attributed
to low excess air or insufficient overfire air.
A composite plot of all the carbon monoxide data for Sites D, H and
K is shown in Figure 4-32.
4.3.7 Unburned Hydrocarbons vs Heat Release Rate
Unburned hydrocarbons were measured at Sites H and J. In both cases,
hydrocarbons tended to decrease as heat release rate increased. A composite
plot of the data from both sites is shown in Figure 4-33.
4.3.8 Boiler Efficiency vs Heat Release Rate
The boiler efficiency trends with heat release rate are shown in
Figure 4-34. Site K has the most unusual trend. At Site K the boiler efficiency
dropped off rapidly at reduced loads due to increased dry gas heat losses. The
excess air profiles illustrated earlier in Figure 4-19 help explain this drop.
In this figure, Site K is seen to have the highest excess air of all the
stokers at low loads.
Sites H and I, which have the lowest boiler efficiencies at high loads,
were not equipped with economizers, while Sites D, J and K were.
4.4 RESPONSE TO EXCESS AIR
This section discusses the influence of excess air on the emissions and
efficiency of five mass fired overfeed stokers. As with spreader stokers, excess
air operating level was directly related to boiler load. The variation of excess
air at constant load was often very small, making it difficult to determine the
influence of this variable on stoker emissions and efficiency. The following are
the results of this study.
219 KVB4-15900-554
-------
CRRBON MONOXIDE PPM RT 3 PERCENT 02
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MASS FIRED OVERFEED STOKERS
I
1
100 200 300 400
GRATE HEAT RELEASE, 103Btu/hr-ft2
500
Figure 4-34. Boiler Efficiency as a Function of Grate Heat Release for
Five Mass Fired Overfeed Stokers.
KVB4-15900-554
222
-------
4.4.1 Particulate Loading vs Excess Air
No correlation was found between uncontrolled particulate loading and
excess air in mass fired overfeed stokers. However, the data base is small
and any correlation which may exist could be disguised by one or more uncon-
trolled variable.
At each site there were at least two tests run at different excess air
levels in which the controlled variables of load, overfire air, and coal source
were constants. These are listed in Table 4-15.
TABLE 4-15
UNCONTROLLED PARTICULATE LOADING VS EXCESS AIR
Site D
Site H
Site I
Site J
Site K
% Excess
Air
57
64
76
97
43
62
56
68
40
51
59
67
% Overfire Air % Coal
Load "H20 Ash
86
87
99
97
100
103
103
97
102
96
100
97
10.0
10.0
11.7
11.2
10.8
10.5
7.8
7.7
2.5
2.6
2.5
2.5
8.47
9.14
8.73
12.34
10.37
9.15
10.22
8.23
3.51
3.44
3.32
5.55
% Fines
-------
uncontrolled particulate loading, percent load and excess air. The results
were just as irregular as those for spreader stokers. However, because the
data base is small, the results of this method may not be valid and are,
therefore, not included.
4.4.2 Combustibles in the Ash vs Excess Air
The percentage of combustible material in the flyash and in the bottom
ash did not correlate with excess air. The same examples cited for particulate
loading in Table 4-15 are presented for combustible content in Table 4-16.
TABLE 4-16
COMBUSTIBLES IN THE ASH VS EXCESS AIR
FOR MASS FIRED OVERFEED STOKERS
% Combustibles % Combustibles
Excess Air in Flyash in Bottom Ash
Site D 57 28.8 15.1
64 22.1 18.7
Site H 76 23.0 20.7
97 25.2 14.6
Site I 43 25.6 ND*
62 22.0 35.9
Site J 56 23.7 ND*
68 ND* 30.9
Site K 40 30.9 46.8
51 40.8 69.1
59 36.7 47.6
67 32.2 27.6
*ND = No Data
4.4.3 Nitric Oxide vs Excess Air
Nitric oxide increased with excess air in a well defined and consistent
manner. The rate of increase averaged .0216 Ib NOx/106Btu per 10% increase in
excess air at constant load. The relationships, presented in Table 4-17, were
KVB4-15900-554
224
-------
determined by multiple regression analysis for Sites D, H, I and J, and by
linear regression on the full load data for Site K. The Site K data did not
fit the model when all loads were considered, but the full load data cor-
related with excess air, which was consistent with that of the other sites in
this class.
TABLE 4-17
NITRIC OXIDE VS EXCESS AIR
AT CONSTANT LOAD
Ib NOx/106Btu per 10% Excess Air
Site D .0239
Site H .0158
Site I .0161
Site J .0257
Site K .0265
These data are presented graphically in Figure 4-35. This figure gives
the magnitude as well as the slope of the data for the case of full load on the
boiler.
4.4.4 Carbon Monoxide vs Excess Air
Carbon monoxide emissions rose sharply as excess air dropped below
about 60% at Sites D and H, and rose more gradually as excess air increased above
120% at Site H.
The Site K data show more scatter, probably because overfire air was
a major factor at this site. When only the high overfire air tests at Site K
are considered, the data fall in line with that measured at Sites D and H.
The data for Sites D, H and K are presented in Figure 4-36, and the
general trend is outlined. Carbon monoxide was not measured at Sites I and J
because the CO analyzer was out of service at these two sites.
KVB4-15900-554
225
-------
.5
CM
o
3
to
rt
-P
pq
w
Q
H
X
o
u
H
OH
EH
H
.1
MASS FIRED OVERFEED STOKERS
H
20
40 60
% EXCESS AIR
80
100
Figure 4-35. The Relationship Between Nitric Oxide and Excess Air at
Full Load.
KVB4-15900-554
226
-------
CflRBON MONOXIDE PPM flT 3 PERCENT 02
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4.4.5 Unburned Hydrocarbons vs Excess Air
Unburned hydrocarbons were measured at Sites H and J. Unlike the
spreader stoker data, the hydrocarbon data for these two stokers tended to
increase as excess air increased. This trend is illustrated in Figure 4-37.
The unburned hydrocarbons at Test Site H also showed a correlation
with carbon monoxide. As shown in Figure 4-38, carbon monoxide appears to
increase exponentially as hydrocarbons increase.
4.4.6 Boiler Efficiency vs Excess Air
The relationship between boiler efficiency and the variable excess air
was determined visually for each site. Boiler efficiency trends are plotted
in Figure 4-39 and show efficiency to decrease by about 0.5% for each 10% in-
crease in excess air. This is not based on constant load but rather takes into
account all tests conducted. At Sites H and I, the boilers were not equipped
with economizers and boiler efficiency at a constant excess air is about 4 to
6% less than the other three mass fired overfeed stokers.
Excess air influences boiler efficiency primarily because the dry gas
losses increase with increasing excess air. The additional air absorbs heat
which would otherwise have been absorbed by the boiler and carries that heat
out the stack.
4.5 RESPONSE TO COAL ANALYSIS AND SIZING
Coal samples were obtained and analyzed during each test which included
a particulate loading determination. As a result, it was possible to compare
test results with coal analysis on a test-by-test basis. At Sites D, I, J and
K, more than one coal was fired in the same unit, thus allowing a comparison
of emissions from different coals. This section examines the effect which
varying coal properties had on stoker emissions.
The coal properties are summarized in Tables 4-18 through 4-23. Table
4-18 identifies the coals and gives the ASTM classification based on the average
of samples obtained during these tests. The following five tables include
proximate analysis, ultimate analysis, ash fusion temperature, mineral analysis
KVB4-15900-554
228
-------
MASS FIRED OVERFEED STOKERS
120,
EXCESS flIR PERCENT
: SITE H u
. 4-37
HYDROCflRBONS
: SITE J
VS. EXCESS flIR
150,
4-15900-554
229
-------
o
LD
IxJ
O O
CC .
LU O
0- O
-------
90
80
u
s
w
H
0
H
fe
H 70
w
^
H
O
PQ
60
50
MASS FIRED OVERFEED STOKERS
D
L J I 1 I
30
60 90 120
% EXCESS AIR
150
Figure 4-39. Relationship Between Boiler Efficiency and
Excess Air.
KVB 4-15900-554
231
-------
TABLE 4-18
KJ
U)
K)
Coal Identification**
Site D 1 Century
2 Perfect 8
3 Victoria
Site H 1 Sands Hill
Site I 1 Ohio (C&W)
2 Kentucky (Spurlock)
Site J 1 Ohio (C&W)
2 Kentucky (Spurlock)
Site K 1 Washed (Brilliant)
2 Unwashed
(Brilliant)
3 Washed & Crushed
(Brilliant)
Site L2 1
Site L4 1
C&C
Consolidation
COAL IDENTIFICATION AND CLASSIFICATION*
MASS FIRED OVERFEED STOKERS
ASTM Classification
High Volatile A Bituminous
High Volatile A Bituminous
High Volatile A Bituminous
High Volatile C Bituminous
High Volatile A Bituminous
High Volatile A Bituminous
High Volatile A Bituminous
High Volatile A Bituminous
High Volatile B Bituminous
High Volatile B Bituminous
High Volatile B Bituminous
High Volatile A Bituminous
High Volatile A Bituminous
Fixed Carbon
(Dry, Mineral-
Matter-Free Basis)
56
59
59
57
57
58
58
58
59
60
59
64
60
Volatile Matter
(Dry, Mineral-
Matter-Free Basis)
44
41
41
43
43
42
42
42
41
40
41
36
40
Calorific Value
(Moist, Mineral-
Matter-Free Basis)
14,440
14,590
14,490
12,630
14,430
14,840
14,390
14,700
13,890
13,840
13,720
15,300
14,920
* Classification of coals is by rank (ASTM D388) using the Parr Formulas.
** Coals are identified by the names used in the published Site reports.
Alternate names are given in parenthesis.
KVB4-15900-554
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TABLE 4-19
Site D
Site H
Site I
Site J
Site K
Site L2
Site L4
PROXIMATE COAL ANALYSIS
MASS FIRED OVERFEED STOKERS
Weight Percent as-Fired
Coal
1
2
3
1
1
2
1
2
1
2
3
Moisture
3.23
2.68
3.11
11.56
3.28
2.26
3.59
2.24
6.49
6.19
7.35
Ash
8.71
5.86
6.72
8.62
9.57
6.04
7.85
6.57
4.14
10.24
4.68
Volatile
39.17
38.44
37.25
35.16
38.02
38.79
37.83
39.09
37.46
33.69
36.72
Fixed
Carbon
48.89
53.02
52.94
44.66
49.05
52.92
50.73
52.10
51.91
49.88
51.25
Btu/lb
13003
13629
13405
11417
12858
13823
13117
13607
13237
12280
12994
%
Sulfur
2.60
1.23
1.11
1.88
2.77
1.49
1.70
1.58
1.11
1.01
1.31
1.60
1.60
13.00
8.50
32.70
37.50
53.60
53.00
13100
13500
1.40
1.60
KVB 4-15900-554
233
-------
TABLE 4-20^
ULTIMATE COAL ANALYSIS
MASS FIRED OVERFEED STOKERS
Weight Percentage as-Fired
Site D
Site H
Site I
Site J
Site K
1
2
3
1
2
1
2
1
2
3
Moisture
3.23
2.68
3.11
11.76
3.02
2.24
3.05
1.96
6.80
4.76
5.84
Carbon
72.07
76.08
74.96
63.73
71.46
76.83
74.74
76.77
73.85
72.21
74.25
Hydrogen
5.01
5.15
5.00
4.36
4.93
5.24
5.13
5.09
5.00
4.68
4.97
Nitrogen
1.23
1.33
1.30
1.08
1.51
1.47
1.66
1.23
1.55
1.44
1.42
Chlorine
0.12
0.13
0.07
0.07
0.28
0.13
0.19
0.13
0.07
0.05
0.06
Sulfur
2.60
1.23
1.11
1.72
2.42
1.40
1.75
1.43
1.39
1.10
0.94
Ash
8.71
5.86
6.72
8.93
9.22
5.71
7.05
7.25
3.91
7.98
4.15
Oxygen
7.03
7.54
7.76
8.87
7.17
6.97
6.43
6.14
7.43
7.78
8.37
234
KVB 4-15900-554
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TABLE 4-21
FUSION TEMPERATURE OF THE ASH
REDUCING ATMOSPHERE
MASS FIRED OVERFEED STOKERS
Site D
Coal
1
2
3
Initial
Deformation
2050 °F
2680
2590
Softening
H=W
2320 °F
2700+
2700+
Softening
2380 °F
2700+
2700+
Fluid
2520 °F
2700+
2700+
Site
Site
Site
Site
Site
Site
H
I
J
K
L2
L4
1
1
2
1
2
1
2
3
1
1
2205
2060
2070
2100
2205
2100
2110
2190
2363
2195
2230
2250
2335
2280
2470
2330
2650
2500
2403
2335
2390
2400
2465
2310
2510
2360
2598
2465
2555
2535
2580
2600
2700+
2610
KVB 4-15900-554
235
-------
TABLE 4-22
MINERAL ANALYSIS OF THE ASH
MASS FIRED OVERFEED STOKERS
Site D
Coal
1
2
3
Potassium Sodium Sulfur Phosphorus
Oxide Oxide Trioxide Pentoxide
K2O Na2O 503 P2O5 Undetermined
0.13
0.32
0.53
0.25
0.92
0.92
OJ
en
Site H
Site I
Site J
Site K
1
1
2
1
2
1
2
3
43.83
38.94
43.28
42.48
44.08
38.35
52.64
43.86
25.34
23.04
24.44
26.60
26.46
26.25
24.64
26.25
1.09
1.22
1.51
1.29
1.51
1.14
0.88
1.10
22.21
27.22
18.33
22.09
17.80
21.19
12.41
15.86
1.75
2.39
3.22
2.11
2.28
5.59
2.62
4.73
0.67
0.81
0.77
0.83
0.78
1.57
1.32
1.47
1.89
1.93
1.62
1.91
1.78
1.75
2.75
2.15
0.26
0.33
0.85
0.35
0.80
0.25
0.27
0.27
0.35
1.55
3.36
1.43
1.85
1.99
1.63
3.59
0.72
0.34
0.27
0.40
0.31
0.10
0.05
0.05
1.80
2.23
2.38
0.38
1.89
1.82
0.79
0.67
KVB 4-15900-554
-------
Site D
TABLE 4-23
AS-FIRED COAL SIZE CONSISTENCY
MASS FIRED OVERFEED STOKERS
Percent Passing Stated Screen Size
Coal
1
2
3
1"
99
96
89
i"
49
50
40
i"
9
15
16
#8
4
6
8
#16
3
4
5
Site H
Site I
Site J
Site K
1
1
2
1
2
1
2
3
93
85
95
84
94
75
62
95
57
55
51
41
36
37
38
70
26
30
24
18
10
20
25
44
12
14
13
10
5
9
15
22
8
9
9
7
4
5
11
13
KVB 4-15900-554
237
-------
of the ash and coal size consistency. The data base and table number for
each analysis are as follows:
Analysis Data Base Table No.
Proximate
Ultimate
Ash Fusion
Mineral
72 samples
32 samples
14 samples
14 samples
Table 4-19
Table 4-20
Table 4-21
Table 4-22
Size Consist 72 samples Table 4-23
4.5.1 Particulate Loading vs Coal Properties
Two coal properties were examined for their relationship to particulate
loading. These were coal ash on a mass percent basis, and coal fines as mass
percent passing a 1/4 inch screen. Test Site K was the only site where there
was enough variation in these variables to cause a change in the particulate
loading. Therefore, this discussion will center around the Site K test results.
The Test Site K particulate data are summarized in Table 4-24. The particulate
data are plotted as a function of boiler load in Figures 4-40 and 4-41.
At Site K, three forms of the same coal were tested. The primary coal
was a l-l/4"xO washed coal. In one series of tests, unwashed coal from the
same mine was tested. The unwashed coal contained clay and other impurities
which increased its ash content from 4% to 10%. Apparently, the impurities
were of a size to be easily carried over, but at the same time, easily collected
by the dust collector. Particulate loading of the unwashed coal was three times
greater than that of the washed coal at the boiler outlet. The particulate
loading after the dust collector was only slightly greater for the unwashed
coal.
In another series of tests, the washed coal was put through a crusher
which reduced its top size from 1-1/4" down to 3/4" and at the same time increased
its fines (
-------
TABLE 4-24
PARTICULATE LOADING VS COAL PROPERTIES
TEST SITE K
Coal Ash, %
Coal Fines, % < J"
Excess Air, %
50% Capacity
75% Capacity
100% Capacity
Washed
5.18
25
162
Unwashed
8.40
23
148
Crushed
5.28
42
98
Washed
4.24
17
93
Unwashed
8.35
32
113
Crushed
4.57
54
84
Washed
4.16
20
53
Unwashed
13.96
22
62
Crushed
4.19
39
37
to
Ul
Uncontrolled Particulate,
lb/106Btu .61 1.25 .70 .75 2.06
Controlled Particulate,
lb/106Btu .17 .24 .14 .17 .20
Dust Collector Efficiency, % 72.0 80.9 79.4 77.5 90.4
1.13
.15
87.0
.78
.14
81.2
2.20
.16
92.7
1.23
.14
88.6
KVB 4-15900-554
-------
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UNCONTROLLED PRRT. LB/MILLION BTU
.5000 1.0000 1.5000 2.0000 2.5000
_L
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Mechanical dust collectors are seen as great normalizers to particu-
late loading. More often than not during this program, changes to the particu-
late loading at the boiler outlet were diminished or lost after the dust
collector.
Coal ash makes up a major portion of the particulate material emitted
from mass fired overfeed stokers. However, combustible material also makes up
a portion of the particulate. Table 4-25 summarizes the coal ash disposition
for Sites D, H, I, J and K. These data show that an average 13% of the coal's
ash is carried over in the flyash while the remaining 87% stays on the grate.
The as-found ash carryover (includes combustible material) equalled 19% of the
coal ash, while bottom ash mass was equivalent to 128% of the coal ash.
4.5.2 Combustibles in the Ash vs Coal Properties
Combustible content of the boiler outlet flyash and of the bottom ash
were evaluated for their relationship to coal properties at four sites where
more than one coal was fired. There is no clear evidence from these data that
coal played a part in combustible levels.
For example, at Sites I and J, the same two coals were tested. At
Site I, the Kentucky coal (coal 2) gave the lowest combustible levels in the
bottom ash while at Site J no difference was found. The same was true for com-
bustibles in the flyash. Site J showed Kentucky coal producing higher com-
bustible levels while Site I showed no change. It is concluded from these re-
sults that the apparent differences in combustibles at Sites I and J are not
due to the coal. Perhaps they are the result of data scatter, or an unknown
variable.
At Test Site D, Victoria coal appears to produce the highest bottom
ash combustible levels. These data, shown in Figure 4-42, could also be mis-
leading. Nothing could be found in the coal properties to account for this
apparent difference. The difference is based on only two data points.
4.5.3 Sulfur Oxides vs Coal Properties
Sulfur balances were not successful on the mass fired overfeed stokers.
The problem could lie with the representativeness of the coal sample, or with
KVB4-15900-554
242
-------
TABLE 4-25
ASH BALANCE
MASS FIRED OVERFEED STOKERS
Inorganic Ash as %
of Coal Ash
As-Found Ash as %
of Coal Ash
Site D
Site H
Site I
Site J
Site K
Coal '•
1
2
3
1
1
2
1
2
1
2
3
AVERAGE
STD. DEV.
fc Carryover
9
17
11
11
10
18
10
10
15
15
19
13
4
% Grate
91
83
89
89
90
82
90
90
85
85
81
87
4
% Carryover
12
24
15
15
14
32
12
15
23
23
29
19
7
% Grate
98
100
139
112
139
116
121
113
158
126
183
128
26
* As-Found Ash includes combustible material while Inorganic Ash
does not.
KVB 4-15900-554
243
-------
BOTTOM RSH COMB. PERCENT
10.0
20.0
30.0
40.0
50.0
t
»-*
tn
i
t/i
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the analysis of the coal sample or flue gas sample. For whatever reason, the
sulfur oxide data shown in Figure 4-43 do not correspond with the fuel sulfur
as closely as they should.
An alternate measure of fuel sulfur conversion is obtained by measuring
the sulfur retained in the ash and assuming the difference was converted to
sulfur oxides. This method yields conversion efficiencies of 97 to 99%. The
sulfur retention data are shown in Table 4-26.
TABLE 4-26
SULFUR RETAINED IN THE ASH
Coal
Site D 1
3
Site H 1 .4 2.9 3.3
Site J 1 .1 1.2 1.3
2 .3 2.6 2.9
Site K 1 .2 .9 1.1
% Retained
in Flyash
.7
.6
% Retained
in Bottom Ash
1.3
1.4
Total
2.0
2.0
AVERAGE .4 1.7 2.1
STD. DEV. .2 .8 .9
The amount of sulfur retained in the bottom ash was found to be re-
lated to the sulfur content of the coal. The data substantiating this relation-
ship is shown in Figure 4-44.
Sulfur trioxide was found to make up 1.4% or less of the total sulfur
oxides in the flue gas. Sulfur trioxide was also found to increase as total
sulfur oxides increased. These data are shown in Figure 4-45.
4.5.4 Nitric Oxide vs Coal Properties ;,
Nitric oxide (NO) was found to be unrelated to fuel nitrogen. To make
this correlation, the mathematical models previously developed in Section 4.4.3
were employed. Nitric oxide concentration was calculated with the model for
KVB4-15900-554
245
-------
ID
I—
O
o
o
o
LO
o
•*v o
GO O
_J O
CO CO
LJJ
CD
O
O
o
MASS FIRED OVERFEED STOKERS
100% CONVERSION LINE
0
1.000 2.000 3.000 4.000 5.000
FUEL SULFUR RS 302 LB/MILLION BTU
Q] : SITE D
X : SITE K
: SITE H
: SITE i
-j- ; SITE j
FIG. 4~43
SULFUR OXIDES VS. FUEL SULFUR flS 302
4-15900-554
246
-------
o
o
LO _|
ID
I—
CD
CD
CO
CM
LO _
CD CD
O
2: o
cc
ID
u_
=i g
MASS FIRED OVERFEED STOKERS
0
.600 1.200 1.800 2.400 3.000
FUEL SULFUR RS S02 LB/MILLION BTU
: SITE D
: SITE H
" SITE j
+ : SITE K
FIG. 4-44
SULFUR IN BOTTOM flSH VS. FUEL SULFUR flS S02
4-15900-554
247
-------
o
UJ
o
DC
LU o
DL_ (\J
CO
Q_
Q_
LU
Q
i—i
X
O
I—1
DC
DC
ID
cn
L0 _
o _
ID -
0
MASS FIRED OVERFEED STOKERS
-O-
T
400. 800. 1200. 1600. 2000,
SULFUR OXIDES PPM RT 3 PERCENT 02
Q]: SITE D o "SITE l A •SITE J + '•SITE K
FIG. 4-45
SULFUR TRIOXIDE VS. SULFUR OXIDES
4-15900-554
248
-------
each test which included an ultimate coal analysis. The fuel nitrogen from the
ultimate analysis was then plotted against the difference between the calculated
nitric oxide and the measured nitric oxide.
Figure 4-46 illustrates the results for Test Site D. Although the
highest fuel nitrogen test point correlated with the greatest positive devia-
tion from the model, there is no indication of a trend.
Nitrogen dioxide (NC>2) was found in only very small concentrations.
It was generally measured as zero but occasionally reached measurable concentra-
tions of up to 13 parts per million. The highest measured concentration was
less than 5% of the total nitric oxides in the flue gas.
4.5.5 Carbon Monoxide vs Coal Properties
Carbon monoxide was measured only at Sites D, H and K because the
carbon monoxide monitor was out of service during testing at Sites I and J. No
correlations were found between carbon monoxide levels and coal properties
during these tests.
4.5.6 Unburned Hydrocarbons vs Coal Properties
Unburned hydrocarbons were measured at Sites H and J. There are in-
sufficient data to correlate this emission with coal properties. At Site H
only one coal was test fired, and at Site J only two hydrocarbon data points
were obtained.
4.5.7 Boiler Efficiency vs Coal Properties
Test Site K was the only site at which coal properties varied sig-
nificantly. At this site a washed coal, unwashed coal, and a washed and crushed
coal all from the same mine were fired in the boiler. The washed coal and the
washed and crushed coal had similar boiler efficiencies under similar operating
conditions. The unwashed coal produced a lower boiler efficiency than either
of the others because of its greater combustible heat loss. This increased
combustible heat loss resulted not from an increase in the percentage of com-
bustible material in the ash, but rather from the increased ash throughput. The
unwashed coal's ash was 10% as compared to 4% for the washed coal. The data
are given in Table 4-27.
KVB4-15900-554
249
-------
NJ
Ui
o
Ul
VD
O
O
Ul
On
ua
c
H
CD
Oi
2
H-
rt
H
Hi
O
CD
Cfl
\->
a
rt
h
0
fl)
rt
0)
w
rt
H-
rt
fD
D
MEASURED NITRIC OXIDE
Deviation from Model -
O
<#>
K)
^T
o
*>
?
H-
EU
rt ^
0 M
^g
0 H
C »
rt O
H
JD
-------
TABLE 4-27
BOILER EFFICIENCY VS COAL PROPERTIES
AT SITE K, HIGH LOAD
Boiler Heat Losses
-
Coal
Washed *
Unwashed
Washed & Crushed
* Washed coal data is average of four similar tests while the other
two coals are represented by single tests.
Dry Gas
10.25
12.69
12.00
Moisture
Related
4.64
4.98
4.87
Combustible
3.91
9.03
3.15
Other
2.14
2.11
2.35
% BOILER
EFFICIENCY
79.06
71.19
77.63
4.6 RESPONSE TO OVERFIRE AIR
The purpose of overfire air in stoker-boilers is to control smoke and
carbon monoxide emissions by providing turbulence for better mixing in the flame
zone, and by holding the flame away from the cold water walls where it would be
quenched. In these tests, overfire air was studied as an operating variable to
determine its relationship to boiler efficiency and emissions. Boiler modifica-
tions were not included in the scope of this test program. Therefore, overfire
air tests were limited to increasing and decreasing the overfire air flow rates
through the existing jets. Tests were also run to determine overfire air flow
rate as a function of static pressure in the overfire air headers. These tests
indicate that at full load, overfire air supplies about 12% of the combustion
air for the mass fired overfeed stokers studied.
Three of the boilers tested (Sites H, J and K) had only one row of
overfire air jets. These overfire air jets were situated between 3.8 and 5.0
feet above the grate on the front wall, angled downward between 15° and 45°.
The remaining two boilers tested (Sites D and I) had two rows of
overfire air jets on the front wall. The upper overfire air jets were 3.4 and
6.8 feet above the grate, respectively, and were angled downward by 30°. The
lower overfire air jets were 1.4 and 4.5 feet above the grate, respectively,
and angled downward by 10° and 45°, respectively.
KVB4-15900-554
251
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4.6.1 Particulate Loading vs Overfire Air
Uncontrolled particulate emissions were observed to decrease for three
of the five mass fired overfeed stokers tested when overfire air pressures were
increased. Of the remaining two stokers, Site D showed conflicting trends,
while Site Jshowed the opposite trend. Table 4-28 gives a summary of particu-
late emissions for varying overfire air settings.
Particulate emissions at Sites H, I and K were reduced by as much as
54% at the boiler outlet when overfire air pressure was increased from the
minimum to the maximum settings. Part of this reduction can be attributed to
more complete carbon burnout at Sites I and K. There was insufficient combustible
data at Site H to correlate with overfire air. Figure 4-47 graphically illustrates
the particulate reduction achieved at Site I by increasing the overfire air.
No definite trend occurred at Site D where mixed results were obtained.
On Century coal, particulate emissions decreased with increasing overfire air
pressure, and on Perfect 8 coal particulate emissions increased with increasing
overfire air pressure.
Site J was the only site where particulate emissions increased with
increasing overfire air under all test conditions. However, the percentage of
fines in the coal was also higher during the high overfire air tests raising
the possibility that fines were responsible for the increase in particulate
emissions.
4.6.2 Combustibles in the Ash vs Overfire Air
The percentage of combustible material in the flyash decreased when
overfire air pressure was increased. The percentage reduction in combustible
material ranged from 12% to 40% in nine test sets, and averaged 27%. During
one test set the combustible material increased by 13% when overfire air
pressure was increased. The data are presented in Table 4-29. Figure 4-48
illustrates the data for Test Site I.
4.6.3 Nitric Oxide vs Overfire Air
Nitric oxide emissions were not influenced by overfire air pressure.
No significant trend was seen for the five sites tested. Table 4-30 gives a
KVB4-15900-554
252
-------
summary of the nitric oxide emissions for the overfire air tests. Figure
4-49 presents the results of overfire air tests at Site D.
Attempts to set up staged combustion by use of the overfire air jets
on the mass fired overfeed stokers were unsuccessful. Staged combustion is
used successfully as a nitric oxide control strategy on burner fired combustion
devices. However, on present design coal fired stokers it is not practical to
produce fuel rich flame conditions at the grate because of clinker formation
increase in opacity and grate overheating as undergrate air is reduced.
4.6.4 Carbon Monoxide vs Overfire Air
The effect of overfire air pressure on carbon monoxide emission levels
is shown in Table 4-31. At Sites D, H and K, carbon monoxide emissions were
reduced by 44% to 97% when overfire air pressures were increased. This re-
duction is the result of the overfire air induced turbulence in the flame zone.
No carbon monoxide data were obtained at Sites I and J because the carbon
monoxide monitor was out of service at these two sites.
Figure 4-50 presents the carbon monoxide data from Site K as a function
of load and overfire air. The four high overfire air data points are the lowest
emission levels.
4.6.5 Unburned Hydrocarbon vs Overfire Air
Unburned hydrocarbon emissions were examined as a function of over-
fire air pressure at Test Site H. At a low overfire air pressure of 3" H20,
the unburned hydrocarbons were measured at 112 ppm @ 3% 02 (wet). When the
overfire air pressure was increased to 11-12" t^O, the unburned hydrocarbon
concentration dropped to 5-35 ppm. This represents an average 82% reduction
in concentration due to the increased overfire air. The data are presented
in Figure 4-51.
4.6.6 Boiler Efficiency vs Overfire Air
Boiler efficiency decreased by an average 2.75% when overfire air
pressure was increased. Part of the decrease was due to increased dry gas loss
due to an increase in the excess air. Another part of the decreased efficiency
KVB4-15900-554
253
-------
was due to an increase in the bottom ash combustible heat loss which may or
may not be due to the increased overfire air.
The data, shown in Table 4-32, show the changes in the various heat
loss categories for each test set in which overfire air was increased. The
changes were not always consistent, but they resulted in decreased boiler
efficiency in all but one case. The change in flyash combustible heat loss
which was instrumental in the spreader stoker efficiencies, was too small to
be instrumental in the efficiencies of these mass fired overfired stokers.
Site
K
TABLE 4-28
EFFECT OF OVERFIRE AIR ON UNCONTROLLED PARTICULATE LOADING
MASS FIRED OVERFEED STOKERS
UNCONTROLLED PARTICULATE EMISSIONS
Coal
1
2
2
1
1
1
2
2, 1
2, 1
1, 2
1
1
1
% Design
Capacity
85
88
64
99
101
100
101
100
74
49
97
99
46
Mean*
Excess
Air, %
60
55
77
77
63
41
55
61
83
107
62
49
162
Low
OFA
1.418
0.837
0.694
2.195
1.763
1.430
0.699
0.574
0.369
1.240
0.758
0.755
0.737
lb/10bBtu
High
OFA
1.033
1.010
1.097
0.793
1.130
0.897
0.999
0.904
0.984
1.442
0.779
0.617
0.655
0.639
0.850
0.477
Percent
Change
- 28
+ 31
+ 14
- 54
- 44
+ 74
+ 36
+ 67
- 34
- 2
- 35
* Excess air increased with increasing overfire air pressures at sites
D, H, I and J, but remained stable at Site K. Numbers shown are
averages
KVB4-15900-554
254
-------
UNCONTROLLED PRRT. LB/MILLION BTU
to
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TABLE 4-29
EFFECT OF OVERFIRE AIR
Site Coal
D 1
2
2
H 1
I 1
1
2
J 2,1
2, 1
1, 2
K 1
1
1
MASS
% Design
Capacity
85
88
64
99
101
100
101
100
74
49
97
99
46
ON COMBUSTIBLES
IN FLYASH
FIRED OVERFEED STOKERS
Mean
Excess
Air, %
60
55
77
77
63
41
55
61
83
107
62
49
162
COMBUSTIBLE
MATERIAL
% by Weight
Low
OFA
40.1
28.2
21.9
ND*
36.7
ND
ND
26.8
36.0
26.7
32.2
36.7
40.8
36.0
High
OFA
28.1
23.6
22.1
16.0
23.0
25.2
22.0
25.6
ND
ND
23.7
24.9
30.1
29.4
27.0
29.4
24.0
Percent
Change
- 36
- 22
- 27
ND
- 40
ND
ND
- 12
- 31
+ 13
- 15
- 31
- 33
* ND = No Data
KVB4-15900-554
256
-------
0=
Lul
Q_
CD
O
O
CO
CC
o
•
o
LT)
O
CD-
CO
O
5 0
O CM
CC
_l
CD
O
•
O
TEST SITE I
LOW OFA
(3.0-4.0" H20)
HIGH
(10.5-10.8" H20)
0
20.0 40.0 60.0 80.0 100.0
PERCENT BOILER DESIGN CRPRCITY
O : 0-4" H20 -}- ; 4-8" H20 A 5 8-12"H20
FIG. 4-48
BLR OUT FLYRSH COMB. VS. PERCENT DESIGN CRPRCITY
4-15900-554
257
-------
TABLE 4-30
EFFECT
Site Coal
D 1
2
2
H 1
I 1
1
2
J 2, 1
K 1
1
1
OF OVERFIRE AIR ON
MASS
% Design
Capacity
85
88
64
99
101
100
101
103
97
99
46
NITRIC OXIDE
EMISSIONS
FIRED OVERFEED STOKERS
Mean
Excess
Air, %
60
55
77
77
63
41
55
56
62
49
162
NITRIC OXIDE*
lb/106Btu
Low
OFA
.368
.334
.262
.371
__
.279
.242
.282
.303
.300
.302
.311
High
OFA
.324
.343
.228
.297
.382
.305
.396
.326
.258
.393
.311
.320
.353
.303
Percent
Change
- 9
- 32
+ 13
- 7
+ 17
+ 7
+ 39
+ 3
+ 11
- 3
* Calculated as N02
KVB4-15900-554
258
-------
o
o
LO J
o
o
X. O
CD O
_j i_n
CO
o
o
X
o
0
TEST SITE D
0
ff \
5.00
I I I I
7.50 10.00 12.50 15.00
OVERFIRE RIR
IN. H20
: LOW LORD
FIG. 4-49
NITRIC OXIDE
: HED LORD
: HIGH LOflD
VS. OVERFIRE flIR
Each line represents a series of tests run in sequence in which
overfire air pressure was the only variable.
KVB4-15900-554
259
-------
TABLE 4-31
EFFECT OF OVERFIRE AIR ON CARBON MONOXIDE EMISSIONS
MASS FIRED OVERFEED STOKERS
CARBON MONOXIDE
Mean PPM (DRY) @ 3% 02
% Design Excess
Site Coal Capacity Air, %
D 1 85 60
2 88 55
2 64 77
H 1 99 77
K 1 97 62
1 99 49
1 46 162
Low
OFA
618
1.225
87
513
537
275
208
339
High
OFA
34
39
321
29
41
69
70
126
105
187
Percent
Change
- 94
- 97
- 66
- 89
- 83
- 44
- 45
KVB4-15900-554
260
-------
o
O
UJ
UJ O
Q_ o
^ o
UJ
O
i—i
x o
§ o
o
DO o
CC
cc o
CJ LD
TEST SITE K
LOW OFAv
(1.9-3.8" H20] X...
HIGH OFA -
(4.9-7.5" H20)
0
20.0 40.0 60.0 80.0 100.0
PERCENT BOILER DESIGN CflPRCITY
: 0-4" H20
: 4-8" H20
° 8-12"H20
FIG. 4-50
CflRBON MONOXIDE VS. PERCENT DESIGN CRPflCITY
4-15900-554
261
-------
•y
,^V v°
-------
TABLE 4-32
EFFECT OF OVERFIRE AIR ON HEAT LOSSES AND EFFICIENCY
MASS FIRED OVERFEED STOKERS
CHANGE IN PERCENT HEAT LOSS WHEN OVERFIRE AIR INCREASED
Site
D
Coal
1
2
2
Dry
Gas
.10
.85
.60
Fuel
Moisture
-.06
.02
.02
H20
From H?
.01
.01
.02
Flyash
Combustibles
-.37
-.18
.00
Bottom Ash
Combustibles
-.01
-.63
.30
Radiation
.02
.01
.02
CHANGE IN
BOILER
EFFICIENCY
.31
-.08
-.96
H
I
J 2
2
1
K
1
1
1
2
, 1
, 1
, 2
1
1
1
1
2
2
3
-4
AVERAGE
STD.
DEV.
1
.08
.83
.09
.65
.18
.79
.22
.62
.57
.30
.71
.86
.31
-.05
.10
-.05
.18
.12
.02
.06
.16
-.09
.06
.11
.23
.02
.24
.06
.24
.31
.28
.15
.12
-.10
.12
.13
ND
-.61
-.06
.04
.15
-.01
.12
-.21
-.16
-.23
-.13
.22
1
2
2
-
-
3
-4
14
1
4
.13
.33
.77
.11
.08
.95
.58
.25
.47
.56
.38
.39
.03
-.03
-.01
-.01
-.01
.00
-.03
.01
-.03
.28
.02
.08
-2
-3
-2
-2
-3
—
_ o
-3
-10
-2
2
ND
.49
.13
.80
.82
.26
.01
.88
.81
.12
.75
.77
KVB4-15900-554
263
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4.7 PARTICLE SIZE DISTRIBUTION OF FLYASH
Particle size distribution of the flyash was determined on the overfeed
stokers by a variety of means. These include the Bri k cascade impactor for
Sites D, H, J, and K, the Anderson cascade impactor for Sites L2 and L4, the
Bahco classifier for Sites D, H L2, and L4, SASS cyclones for Sites D, H, I,
J, and K, and sieve analysis for Sites D and H. The drawbacks of each method
were covered in detail in Section 3.8, Particle Size Distribution of Flyash, and
will not be discussed again in this section.
The intent of these particle size distribution tests was to document
the size distribution of the flyash under high load and normal operating
conditions. No attempt was made to look at other variables such as overfire
air, excess air, or coal properties.
4.7.1 Particle Size Distribution of the Uncontrolled Flyash
The particle size distribution test results are presented on log normal
plots in Figures 4-52, 4-53, 4-54, and 4-55. Each plot represents a different
particle sizing method and a different size distribution range. Figure 4-56
combines the mathematical average of each method on a single plot to give an
overall view of the uncontrolled flyash size distribution for mass fired over-
feed stokers and spreader stokers. It is clear that differences do exist be-
tween the various particle sizing methodologies. However, the data clearly
show that mass fired overfeed stokers have a finer flyash than do spreader
stokers.
The average and standard deviation of the data are presented in Table
4-33 for selected particle sizes. The sieve data, listed separately for lack of
space in the table, averaged 29.6±14.4 below 44 micrometers, 50.5116.5 below
100 micrometers, 85.7112.0 below 300 micrometers, and 97.912.3 below 1,000 micro-
meters .
TABLE 4-33
AVERAGE SIZE DISTRIBUTION OF UNCONTROLLED FLYASH FOR OVERFEED STOKERS
.3ym lym 3ym IQyim 20ym 44yim
Impactor Data 3.5+3.7 9.014.6 19.2110.2 30.1+6.9 45.3+4.8 68.71 1.3
Bahco Data — — 3.01 1.9 14.516.5 27.018.4 62.6+17.8
SASS Data — — 9.41 5.0 14.7+5.9 21.015.2
KVB4-15900-554
264
-------
w
N
H
Q
1
a
CO
I
di
98
95
80
60
40
20
.1
.01
.2
.4 .5 .6 1 23
EQUIVALENT PARTICLE DIAMETER, MICROMETERS
5 6
Figure 4-52.
Particle Size Distribution at the Boiler Outlet as Determined
by Cascade Impactor. Data are from Full Load Tests on Mass
Fired Overfeed Stokers.
KVB4-15900-554
265
-------
Hi
CD
PERCENT SMALLER THAN STATED SIZE
Ui
W
O
h-1
to
O
CO
o
on
00
K3
cn
CD
J^
I
O
O
I
O W TJ
-------
w
H
01
Q
H
CO
a
rt
W
W
w
CM
98
95
80
60
40
20
.1
.01
I
I
2 3456 10 20
EQUIVALENT PARTICLE DIAMETER, MICROMETERS
30
Figure 4-54.
Particle Size Distribution at the Boiler Outlet and After the
Mechanical Collector as Determined by SASS Cyclones. Data
are from Full Load Tests on Mass Fired Overfeed Stokers.
KVB4-15900-554
267
-------
w
tsi
H
a
1
CO
ill ill
30 40 50 60 100 200 300 400
EQUIVALENT PARTICLE DIAMETER, MICROMETERS
1000
Figure 4-55. Sieve Analysis of Flyash Collected at the Boiler Outlets of Two
Mass Fired Overfeed Stokers.
KVB4-15900-554
268
-------
(Ti
Q
W
w
W
99.9
99
95
80
50
on
20
.1
.01
100
1000
PARTICLE DIAMETER, MICROMETERS
Figure 4-56.
Average Particle Size Distribution at the Boiler Outlet as Determined by Four Different
Methods. The Spreader Stoker Data are Included with the Mass Fired Overfeed Stoker Data
for Comparison.
KVB4-15900-554
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4.7.2 Particle Size Distribution of the Controlled Flyash
Size distribution data was obtained after the dust collector at Sites
J, L2, and L4. This data, representing several different methodologies, is pre-
sented in Figure 4-57. Sites L2 and L4 appear to have a coarser particulate
matter after the dust collector than Site J. This corresponds with their lower
dust collector efficiencies.
4.7.3 Combustibles vs. Particle Size Distribution
The variation of combustible content with particle size was investigated
at Test Sites D and J. At Test Site D, four boiler hopper ash samples were ob-
tained and sieved into five size fractions. Each fraction was analyzed for com-
bustible content. The results for all four samples were nearly identical. The
average results are presented in Table 4-34. The larger sized particles clearly
contained the highest combustible fractions.
TABLE 4-34
COMBUSTIBLES VS. BOILER HOPPER ASH - SITE D
Tyler Screen Average Diameter
Mesh Micrometers Mass % Combustibles %
-8+16 1,325 3 74
-16 + 35 713 17 29
-35 + 80 303 44 8
-80 + 200 128 24 8
- 200 38 12 8
Weighted Average: 14%
Nine ash samples collected from the dust collector hopper at Test Site J
were also analyzed. This time, however, the samples were only divided into two
size ranges. The results, given in Table 4-35, again show that the larger
particles contain the higher combustible fraction.
TABLE 4-35
COMBUSTIBLES VS. DC HOPPER ASH - SITE J
Tyler Screen Average Diameter
Mesh Micrometers Mass % Combustibles %
- 20 + 100 490 18 43
- 100 74 82 21
KVB4-15900-554
270
-------
99.9
W
N
I
co
co
EH
a
W
FM
20
100
300
PARTICLE DIAMETER, MICROMETERS
Figure 4-57.
Particle Size Distribution After the Mechanical Collector of Three Mass Fired
Overfeed Stokers. Data Represents Several Measurement Methodologies.
KVB4-15900-554
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4.7.4 Dust Collector Efficiency vs. Particle Size Distribution
Dust collector efficiency with respect to particle size was calculated
from size distribution data obtained at the inlet and outlet of the dust collector
at Sites L2 and L4. These results are summarized in Table 4-36.
TABLE 4-36
EFFICIENCY WITH RESPECT TO PARTICLE SIZE
Collector Efficiency
Site L2
Impaction Results
13.2
5.6
0.0
9.8
8.9
Site L2
Banco Results
21.2
22.3
0.0
0.0
7.2
Site L4
Impaction Results
3.2
0.0
2.3
4.7
2.8
Particle Size Ranges
Micrometers
125 - 30
30 - 20
20 - 10
10-1
Overall Efficiency
The dust collector efficiencies of these two units are very low. The
three other units with dust collectors, Sites D, J, and K, had higher collection
efficiencies. When collector efficiency is plotted as a function of mass percent
of particulate material smaller than 20 micrometers, a loose correlation is found.
This is shown in Figure 4-58.
Figure 4-59 shows how dust collector efficiency behaved as a function of
load on three mass fired overfeed stokers. In each case, there was a tendency
for efficiency to drop off as load decreased.
There are many other variables which play a part in dust collector
efficiency. These include the collector's design, state of repair, inlet dust loading,
and pressure drop through the cyclone tubes. These variables are not included in
this analysis.
KVB4-15900-554
272
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PERCENT
80.0
100.0
B
B
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B
-------
5.0 MASS FIRED UNDERFEED STOKERS
This section of the report is organized differently than Sections 3.0
Spreader Stokers and 4.0 Mass Fired Overfeed Stokers because each of the five
underfeed stokers discussed in this section was tested under a single operating
condition, and for a more limited number of parameters.
5.1 DESCRIPTION OF UNITS TESTED
Mass fired underfeed stokers differ from mass fired overfeed stokers
in that coal is introduced to the grate through retorts at a level below the
location of air admission to the fuel bed, instead of from above. Ash can be
discharged continuously at the rear of the stoker into the ash pit or it can
be discharged by intermittent dumping from either the side or the rear of the
stoker.
The five underfeed stokers studied in this program were tested under
normal operating conditions with boiler loads ranging from 55 to 100 percent
of design steaming capacity. The types of mass fired underfeed stokers tested
include one single retort and four multiple retort stokers. The five units
represent typical state-of-the-art designs firing bituminous coals, and were
installed between 1950 and 1968.
Two of the units tested are equipped with cyclone dust collectors.
However, the three units not equipped with dust collectors discharge into
expansion breechings and tall stacks that provide a degree of emission control.
Table 5-1 provides a brief description of the five units tested. Tables 5-2
through 5-6 and Figure 5-1 describe the combustion equipment in more detail.
5.2 COAL ANALYSIS AND SIZING
Coal delivery to each site was by truck. It was received into an out-
door truck hopper and transported to an overhead bunker which fed into a suspended
weigh lorry. Coal sampling during each test was from the weigh lorry. Samples
were tested by the Pennsylvania Bureau of Standards for proximate analysis,
KVB4-159QQ-554
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TABLE 5-1
DESCRIPTION OF MASS FIRED UNDERFEED STOKERS TESTED
Rated *Peak
Steaming Steaming
Year Capacity Capacity Dust
Site Built Ib/hr Ib/hr Stoker Type Collector
LI 1966 26,000 34,500 Multiple Retort Yes
L3 1956 23,300 31,000 Single Retort No
L5 1950 28,460 38,000 Multiple Retort No
L6 1957 20,000 27,000 Multiple Retort No
L7 1968 50,000 55,000 Multiple Retort Yes
*Peak Steaming Capacity was used throughout in the Site L Report
heating value, sulfur, ash softening temperature, and free swelling index.
These data are presented in Tables 5-7, 5-8, and 5-9. Coal samples for three
of the sites were also sized at the Mineral Preparation Laboratory of the
Pennsylvania State University. These data are presented in Table 5-10.
The coals fired at all five sites were very similar with a few excep-
tions. As shown in Table 5-7, four of the five coals are classified as high
volatile A bituminous coals. One of the coals is classified as a low volatile
bituminous coal.
The proximate analysis given in Table 5-8 shows that the inherent
moisture, ash, and heating value are nearly identical for all five coals. Fuel
sulfur was highest at Site Ll where it was 3%, but was quite similar among the
other four sites.
KVB4-15900-554
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"1"
-------
Sites
L3
L5
L6
ROI 1 PR
D wl L_ t rt
fe. ^
BLR. OUT. BREECHING
TEST PLANE TEST PLANE
i
Sites
LI
L7
r^\
( )
vy
BOILER
BLR. C
TEST 1
)UT.
DLANE
D. C.
k x
\x
STACK
TEST PLANE ""
^^
/ \
( ' D )
v y
n
Figure 5-1. Boiler Schematics for the Underfeed Stokers
KVB4-1590Q-554
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TABLE 5-2
EQUIPMENT DATA
TEST SITE: LI
BOILER:
Year Built
Configuration
Rated Steaming Capacity
Design Pressure
Actual Operating Pressure
Peedwater Temperature
Steam Temperature
Operating Air Temperature
1966
Multiple Pass
26,000 Ib/hr (34,500 peak)
Unknown
125 psig
212°F
Saturated
Ambient
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Multiple Retort Underfeed
Unknown
Unknown
97.3 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
1,225 Ft3
717 Ft2
4,283 Ft2
None
None
None
HEAT RATES AT RATED CAPACITY:
Input to Furnace
Grate Width Heat Release
Grate Heat Release
Furnace Liberation
45,300,000 Btu/hr
Unknown
466,000 Btu/hr-ft2
37,000 Btu/hr-ft3
EMISSION CONTROL EQUIPMENT:
Mechanical Collector
KVB4-15900-554
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TABLE 5-3
EQUIPMENT DATA
TEST SITE: L3
BOILER:
Year Built
Configuration
Rated Steaming Capacity
Design Pressure
Actual Operating Pressure
Feedwater Temperature
Steam Temperature
Operating Air Temperature
1951
Multiple Pass
23,300 Ib/hr (31,000 Ib/hr peak)
Unknown
120 psig
212°F
Saturated
Ambient
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Single Retort Underfeed
Unknown
Unknown
73.0 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
Unknown
Unknown
4,490 Ft2
None
None
None
HEAT RATES AT RATED CAPACITY:
Input to Furnace
Grate Width Heat Release
Grate Heat Release
Furnace Liberation ———
EMISSION CONTROL EQUIPMENT:
40,700,000 Btu/hr
Unknown
558,000 Btu/hr-ft2
Unknown
None
KVB4-15900-554
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TABLE 5-4
EQUIPMENT DATA
TEST SITE: L5
BOILER:
Year Built
Configuration
Rated Steaming Capacity
Design Pressure
Actual Operating Pressure
Feedwater Temperature
Steam Temperature
Operating Air Temperature
1950
Multiple Pass
28,460 Ib/hr (37,950 Ib/hr peak)
Unknown
150 psig
212°F
Saturated
Ambient
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Multiple Retort Underfeed
Unknown
Unknown
80.6 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
1,250 Ft3
1,050 Ft2
4,440 Ft2
None
None
None
HEAT RATES AT RATED CAPACITY:
Input to Furnace
Grate Width Heat Release
Grate Heat Release
Furnace Liberation
50,000,000 Btu/hr
Unknown
620,000 Btu/hr-ft2
40,000 Btu/hr-ft3
EMISSION CONTROL EQUIPMENT:
None
KVB4-15900-554
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TABLE 5-5
EQUIPMENT DATA
TEST SITE: L6
BOILER:
Year Built
Configuration
Rated Steaming Capacity
Design Pressure
Actual Operating Pressure
Feedwater Temperature
Steam Temperature
Operating Air Temperature
1957
Multiple Pass
20,000 Ib/hr (27,000 Ib/hr peak)
Unknown
110 psig
212°F
Saturated
Ambient
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Multiple Retort Underfeed
Unknown
Unknown
83.3 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
1,130 Ft3
720 Ft2
3,280 Ft2
None
None
None
HEAT RATES AT RATED CAPACITY:
Input to Furnace
Grate Width Heat Release
Grate Heat Release
Furnace Liberation
EMISSION CONTROL EQUIPMENT:
33,900,000 Btu/hr
Unknown
407,000 Btu/hr-ft2
30,000 Btu/hr-ft3
None
KVB4-15900-554
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TABLE 5-6
EQUIPMENT DATA
TEST SITE: L7
BOILER:
Year Built
Configuration
Rated Steaming Capacity
Design Pressure
Actual Operating Pressure
Feedwater Temperature
Steam Temperature
Operating Air Temperature
1968
Multiple Pass
50,000 Ib/hr (55,000 Ib/hr peak)
Unknown
150 psig
218°F
Saturated
Ambient
STOKER:
Classification —
Effective Length
Width
Effective Grate Area
Multiple Retort Underfeed
Unknown
Unknown
161.1 Ft2
HEATING SURFACES:
Furnace Volume
Water Wall
Boiler
Superheater
Economizer -
Air Heater -
2,300 Ft3
1,503 Ft2
6,057 Ft2
None
None
None
HEAT RATES AT RATED CAPACITY:
Input to Furnace
Grate Width Heat Release
Grate Heat Release
Furnace Liberation
76,360,000 Btu/hr
Unknown
474,000 Btu/hr-ft2
33,200 Btu/hr-ft3
EMISSION CONTROL EQUIPMENT:
Mechanical Collector
KVB4-15900-554
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Site Identification
TABLE 5-7
COAL IDENTIFICATION AND CLASSIFICATION"
MASS FIRED UNDERFEED STOKERS
Fixed Carbon
Dry Mineral
Matter-Free
Basis
Volatile Calorific
Matter Value
Dry Mineral Moist Minera]
Matter-Free Matter-Free
ASTM Classification
Basis
Basis
LI C and C High Volatile A Bituminous
L3 Mclntire High Volatile A Bituminous
L5 Glessner Low Volatile Bituminous
L6 Mclntire High Volatile A Bituminous
L7 Mclntire High Volatile A Bituminous
Classification of coals is by rank (ASTM D388) using the Parr Formulas
64
54
80
64
64
36
46
20
36
36
15,360
15,260
15,600
15,360
15,090
TABLE 5-8
PROXIMATE COAL ANALYSIS
MASS FIRED UNDERFEED STOKERS
WEIGHT PERCENT AS-FIRED
Site
Site
Site
Site
Site
LI
L3
L5
L6
L7
Inherent
Moisture
.8
.6
.4
.6
.7
Ash
13.
11.
12.
12.
12.
0
0
0
7
5
Volatile
32
41
18
32
32
.0
.4
.9
.0
.2
Fixed
Carbon
54
47
68
54
54
.2
.0
.7
,7
.6
Btu/lb
13
13
13
13
13
,100
,400
,500
,200
,000
Percent
Sulfur
3.0
1.3
2.1
1.6
1.7
KVB4-15900-554
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TABLE 5-9
ASH SOFTENING TEMPERATURE AND FREE SWELLING INDEX
MASS FIRED UNDERFEED STOKERS
Ash Softening Free Swelling
Temperature Index
Site LI 2550°F 6.0
Site L3 2650 6.0
Site L5 2450 8.0
Site L6 2550 7.5
Site L7 2550 7.5
TABLE 5-10
AS-FIRED COAL SIZE CONSISTENCY
MASS FIRED UNDERFEED STOKERS
Percent Passing Stated Screen Size
Site L5
Site L6
Site L7
1-1/2"
97
89
95
3/4"
59
24
34
1/2"
36
15
18
1/4"
20
9
11
#16
11
5
2
KVB4-15900-554
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5.3 TEST CONDITIONS
Each of the five underfeed stokers was tested under a single
operating condition. Test dates were selected to obtain loads in the range
of 55% to 100% of design capacity. This corresponds to a maximum steaming
capacity range of 50% to 75%. Each boiler was tested under normal operating
conditions at the available load. The boiler firing conditions are summarized
in Table 5-11.
TABLE 5-11
BOILER FIRING CONDITIONS
Site LI
Site L3
Site L5
Site L6
Site L7
% Design
Capacity
100
80
73
88
55
% Maximum
Capacity
75
60
55
65
50
% Excess
Air
71
186
33
61
116
Grate
Furnace
Heat Release Heat Release
103Btu/hr-ft2 103Btu/hr-ft3
412
272
348
315
264
32.7
Not Available
22.4
23.3
18.5
5.4 PARTICULATE EMISSION LEVELS
The particulate emission levels of the five underfeed stokers are pre-
sented in Table 5-12. On the three units without dust collectors, uncontrolled
particulate loadings ranged from .25 to .71 lb/106Btu. On the two units with
mechanical collectors, the controlled particulate loadings were .46 and .58
lb/106Btu.
KVB4-15900-554
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TABLE 5-12
PARTICULATE LOADING DATA FOR FIVE UNDERFEED STOKERS
PARTICIPATE LOADING
Site
Site
Site
Site
Site
LI
L3
L5
L6
L7
lb/10b
Uncontrolled
No Data
.709
.249
.403
No Data
Btu
Controlled
No
No
No
.456
Collector
Collector
Collector
.577
% Excess
Air
71
186
33
61
116
Stack Velocity
ft/sec
51.0
11.6
3.8
5.0
49.5
% Fines
<*"
No Data
No Data
20
9
11
The most surprising result is that emissions from those units equipped
with dust collectors were no lower than from those without. In fact, if we
overlook site L3 because it is the only single retort stoker, we see that the
stokers with dust collectors had higher stack emissions than those without.
Two factors which may have contributed to this result are particle size
distribution and stack gas velocity. The particles at the boiler outlet were
very fine; 45% smaller than 10 micrometers and 57% smaller than 20 micrometers at
Site L7 based on cascade impactor data. Particles of this size are not efficiently
collected by mechanical dust collectors. It is also noted that the three units
without dust collectors had tall, large diameter stacks which resulted in low
stack velocities. These low velocities could allow much of the particulate matter
to settle out before leaving the stack, thus providing some degree of particulate
control.
The variation in particulate loadings among the three underfeed stokers
not equipped with dust collectors could be explained by a number of factors. It
is noted in Table 5-12 that the particulate loadings at Sites L3, L5 and L6 are
proportional to both excess air level and stack gas velocity. It is also noted
that the highest particulate loading occurred while firing the coal with the
lowest volatiles and the highest free swelling index, and it occurred in the only
single retort stoker tested.
KVB4-15900-554
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Several other variables also correlate with particulate loading.
However, it is clear that there are more variables here than there are test
sites. Therefore, it is impossible to identify which variables had the
strongest effect on emissions. The underfeed stoker study was not designed
or intended to accomplish this task.
Table 5-12 gave the measured particulate loading data for the five
underfeed stokers. Uncontrolled particulate emissions were not measured at
Sites LI and L5, the two sites equipped with mechanical collectors. To pro-
vide a means of comparing uncontrolled emission rates at all sites, uncontrol-
led particulate emissions from Sites Ll and L7 were calculated by applying
collector efficiency data derived from particle size distribution test results.
This method, discussed in more detail in Section 5.6 Particle Size Distribution
and Dust Collector Efficiency, yields uncontrolled particulate loadings of
.684 lb/106Btu for Site Ll and 1.464 lb/106Btu for Site L7.
Emission factors were determined for the five underfeed stokers. The
particulate emission factor for coal combustion without control devices for all
stoker types except spreaders, as reported in the U.S. Environmental Protective
Agency Publication AP-42, Compilation of Air Pollution Factors, Third Edition,
is 5A (potential emission rate in pounds of particulate per ton of coal fired
is equal to five times the weight percentage of ash in the coal). The uncon-
trolled emission rates were converted to equivalent particulate emission factors
provided by this publication. A summary of the calculated factors are listed
in Table 5-13. These data indicate that emissions were considerably lower than
those predicted by AP-42.
KVB4-15900-554
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Site
Site
Site
Site
Site
LI
L3
L5
L6
L7
—
1.7A
0.6A
0.8A
TABLE 5-13
PARTICULATE EMISSION FACTORS LB/TON
MASS FIRED UNDERFEED STOKERS
By Calculated
By Test Emission Rates
Emission Rates Average High Low
1. 4A 1. 4A 1. 3A
3.0A 3.6A 2.1A
AP 42 5A
5.5 COMBUSTIBLES IN THE ASH
The combustible fraction of the bottom ash was determined for each
site. The data, shown in Table 5-14, indicate that four of the sites had
nearly identical combustible fractions ranging from 22.4% to 25.0%. One site
had only 8.1% combustibles in its bottom ash. No explanation was found for
this low value, but it is noted that variations of this magnitude were not un-
common at some of the other test sites in this program. See for example Figures
3-13 and 4-12 in Sections 3.2 and 4.2 of this report.
TABLE 5-14
COMBUSTIBLES IN THE ASH
MASS FIRED UNDERFEED STOKERS
% Combustibles % Combustibles
In Bottom Ash In Flyash
Site LI 22.4 20.5
Site L3 25.0 No Data
Site L5 22.5 No Data
Site L6 8.1 No Data
Site L7 22.4 20.2
KVB4-15900-554
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The combustible fraction of the flyash was determined from samples
collected at the base of the mechanical collector at the two sites which had
mechanical collectors. The combustible fractions were very similar at 20.5%
and 20.2% for Sites LI and L7, respectively.
5.6 BOILER EFFICIENCY
Boiler efficiencies were not an objective of the test program on the
underfeed stokers. However, sufficient data were generated to calculate boiler
efficiency by the heat loss method (ASME PTC 4.1). The heat loss and boiler
efficiency data are listed in Table 5-15. Heat losses are bracketed where
major assumptions were required.
TABLE 5-15
Site
LI
L3
L5
L6
L7
Dry
Gas
15.11
25.34
15.03
15.19
21.09
Moisture
In Fuel
.08
.06
.04
.06
.07
HEAT
MASS
Hydrogen
In Fuel
(4.36)
(4.14)
(4.13)
(4.19)
(4.45)
LOSSES AND EFFICIENCIES
FIRED UNDERFEED STOKERS
Flyash
Combustibles
.13
(.21)
(.07)
(.11)
.17
Bottom Ash
Combustibles
3.93
3.64
3.59
1.17
3.76
Radiation
.75
.98
.97
.97
.97
Other
1.50
1.50
1.50
1.50
1.50
BOILER
EFFICIENCY
74.14
64.13
74.67
76.81
68.01
Among the assumptions were the following. Combustibles in the flyash
of Sites L3, L5 and L6 were assumed to be 21%. Combustible material was
assumed to have a heating value of 14,500 Btu/lb. Combustion air temperature
was assumed to be 80°F. Because only proximate fuel analysis were obtained,
fuel hydrogen was assumed to be 5% and fuel carbon was calculated as percent
fixed carbon + .6 (percent volatiles). This empirical formula is based on eleven
proximate and ultimate fuel analysis from Sites D, H, I, J and K which yielded
a factor of .606±.032 as the fraction of carbon in the volatile material.
KVB4-15900-554
289
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Finally, it should be noted that the heat loss due to moisture in the fuel is
based on inherent moisture only. Surface moisture would be expected to add
about .10% to this heat loss.
Despite the many assumptions, the boiler efficiencies are thought to
be accurate within ±1%. The lowest boiler efficiency, Site L3, resulted from
excessively high excess air. The second lowest, Site L7, resulted from a com-
bination of high excess air and high stack gas temperature.
5.7 PARTICLE SIZE DISTRIBUTION OF THE FLYASH
Particle size information was obtained from the mass fired underfeed
stokers with an Anderson in-stack cascade impactor, and with a Bahco centrifugal
classifier.
The boiler outlet sizing data are displayed on log probability plots
in Figures 5-2 and 5-3. The stack data are similarly displayed in Figures 5-4
and 5-5. The log probability plot is useful in that one can determine the per-
centage of particles smaller than any given size.
Table 5-16 gives the average and standard deviation of the size distri-
bution data at selected points. This allows for a convenient comparison with the
size distribution data obtained on the overfeed stokers and the spreader stokers.
Because of the relatively wide variations in magnitude and the few data points
included, these averages should be seen for what they are and used accordingly.
TABLE 5-16
AVERAGE SIZE DISTRIBUTION DATA FOR UNDERFEED STOKERS
Mass Percent Smaller Than Stated Size & Standard Deviation
. 3ym lym 3ym IQum 20pm 44ym
Boiler Outlet
Impactor Data 11.7± 6.6 23.5±18.0 29.5120.0 44.3121.4 59.4+20.1 71.8+12.2
Boiler Outlet
Bahco Data — — 9.31 3.5 22.71 8.9 32.7+12.1 46.4116.6
Collector Outlet
Impactor Data* 11.0-20.0 18.8-34.2 29.0-51.3 50.0-82.5 78.2-95.6 85.3-95.6
Collector Outlet
Bahco Data* — — 14.2-35.7 48.0-50.0 51.2-71.5 54.7-87.3
*Since only two of the units had collectors, the actual collector outlet
data are shown for each test rather than the average and standard deviation.
KVB4-15900-554
290
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98
95
80
60
w
IS]
H
Q
w 40
£ 20
.01
.3
.5 .6 1 2 3456
EQUIVALENT PARTICLE DIAMETER, MICROMETERS
10
Figure 5-2. Particle Size Distribution at the Boiler Outlet of Five
Underfeed Stokers as Determined by Cascade Impactor.
KVB4-15900-554
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98
95
80
W 60
H
CO
EH
CO
40
20
w
CM
.1
.01
456 10 20 30 40 50 60
EQUIVALENT PARTICLE DIAMETER, MICROMETERS
Figure 5-3. Particle Size Distribution at the Boiler Outlet of Five Under-
feed Stokers as Determined by Bahco Classifier.
KVB4-15900-554
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98
95
H
C/2
Q
H
EH
en
EH
W
to
W
W
Oi
80
60
40
20
.01
.3
i i i
_L
_L
J_
i i i
.5 .6 1 2 345
EQUIVALENT PARTICLE DIAMETER, MICROMETERS
10
Figure 5-4. Particle Size Distribution Downstream of the Mechanical Collector
on Two Underfeed Stokers as Determined by Cascade Impactor.
KVB4-15900-554
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w
N
H
W
Q
W
I
M
EH
W
CM
456 10 20 30 40 50 60
EQUIVALENT PARTICLE DIAMETER, MICROMETERS
Figure 5-5. Particle Size Distribution Downstream of the Mechanical
Collector on Two Underfeed Stokers as Determined by Banco
Classifier.
KVB4-15900-554
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Dust collector efficiency with respect to particle size was calculated from
impactor size distribution data obtained at the inlet and outlet of the dust
collectors at Site LI and L7. The results are summarized in Table 5-17. It is
noted that the collector at Site Ll was operating at 80% of its design flowrate,
while the collector at Site L7 was operating at 95% of its design flowrate.
TABLE 5-17
EFFICIENCY WITH RESPECT TO PARTICLE SIZE
Collector Efficiency
Particle Size Ranges
Micrometers Site Ll Site L7
125 - 30 72 93
30 - 20 74 74
20 - 10 14 69
10-1 0.4 57
Overall Efficiency 37 66
KVB4-15900-554
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6.0 TEST EQUIPMENT AND PROCEDURES FOR SITES A THROUGH K
This section describes the test equipment used and the sampling pro-
cedures followed to obtain accurate and representative data at Test Site A
through K. The test equipment and procedures used for Test Site LI through L7
are described in Section 7.0.
6.1 GASEOUS EMISSIONS MEASUREMENTS
Gaseous emission measurements were made with analytical instrumentation
and by wet chemical methods to determine emission concentrations of oxides of
nitrogen (NO, NOx), carbon monoxide (CO), carbon dioxide (CO2), oxygen (02),
gaseous hydrocarbons (HC), and oxides of sulfur (SO2, 803).
6.1.1 Analytical Instruments and Related Equipment
A description is given below of the analytical instrumentation, re-
lated equipment, and the gas sampling and conditioning system, all of which are
located in a mobile testing van owned and operated by KVB. The
systems have been developed as a result of testing since 1970, and are operational
and fully checked out.
The analytical system consists of six instruments and associated equip-
ment for simultaneously measuring the constituents of flue gas. The analyzers,
recorders, valves, controls, and manifolds are mounted on a panel in the vehicle.
The analyzers are shock mounted to prevent vibration damage. The flue gas con-
stituents which are measured are oxides of nitrogen (NO, NOx), carbon monoxide
(CO), carbon dioxide (CO2), oxygen (02) , gaseous hydrocarbons (HC), and sulfur
dioxide (SO2).
The gas'sampling and conditioning system consists of probes, sample
lines, valves, pumps, filters and other components necessary to deliver a repre-
sentative, conditioned sample gas to the analytical instrumentation. The entire
gas sampling and conditioning system shown schematically in Figure 6-1 is con-
tained in the emission test vehicle. A slightly different test vehicle was used
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to
t£>
CD
~£U ^SL JOJ
'> A A A
I
Vst'^
Figure 6-1. Flow Schematic of Mobile Flue Gas Monitoring Laboratory
KVB4-15900-554
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at Test Sites F and H. All the analytical instruments contained in this test
vehicle were the same, with the addition of an SC>2 analyzer.
Boiler access points for gaseous sampling were selected in the same
sample plane as were particulate sample points. Each probe consisted of one-
half inch 316 stainless steel heavy wall tubing. A 100 micrometer Mott Metal-
lurgical Corporation sintered stainless steel filter was attached to each probe
for removal of particulate material.
Gas samples to be analyzed for O2, CC>2/ CO and NO were conveyed to the
KVB mobile laboratory through 3/8 inch nylon sample lines. After passing through
bubblers for flow control, the samples passed through a diaphragm pump and a
refrigerated dryer to reduce the sample dew point temperature to 35°F. After
the dryer, the sample gas was split between the various continuous gas monitors
for analysis. Flow through each continuous monitor is accurately controlled
with rotometers. Excess flow is vented to the outside. Gas samples may be drawn
both individually and/or compositely from all probes during each test.
A detailed discussion of each analytical instrument follows:
Oxides of Nitrogen. The instrument used to monitor oxides of nitrogen
was a Thermo Electron Model 10 chemiluminescent nitric oxide analyzer. The instru-
ment operates by measuring the chemiluminescent reaction of NO and O^ to form
NO2- Light is emitted when electronically excited N02 molecules revert to their
ground state. The resulting chemiluminescence is monitored through an optical
filter by a high sensitivity photomultiplier, the output of which is linearly
proportional to the NO concentration.
Air for the ozonator is drawn from ambient air through a dryer and a
ten-micrometer filter element. Flow control for the instrument is accomplished by
means of a small bellows pump mounted on the vent of the instrument downstream of
a separator that prevents water from collecting in the pump.
The basic analyzer is sensitive only to NO molecules. To measure NOx
(i.e., NO+NO2), the NO2 is first converted to NO. This is accomplished by a con-
verter which is included with the analyzer. The conversion occurs as the gas
passes through a thermally insulated, resistance heated, stainless steel coil.
With the application of heat, N02 molecules in the sample gas are reduced to NO
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molecules, and the analyzer now reads NOx. NO2 is obtained by the difference
in readings obtained with and without the converter in operation.
Specifications:
Accuracy 1% of full scale
Span stability ±1% of full scale in 24 hours
Zero stability ±1 ppm in 24 hours
Power requirements 115±10V, 60 Hz, 1000 watts
Response 90% of full scale in 1 sec. (NOx mode),
0.7 sec. NO mode
Output 4-20 ma
Sensitivity 0.5 ppm
Linearity ±1% of full scale
Vacuum detector operation
Ranges: 2.5, 10, 25, 100, 250, 1000, 2500 and 10,000 ppm
full scale
Carbon Monoxide. Carbon monoxide concentration was measured by a Beck-
man 315B non-dispersive infrared analyzer at Sites A through F and H. A Series
Five Model AB non-dispersive infrared analyzer made by Sensor, Inc. was used at
Site K. These instruments measure the differential in infrared energy absorbed
from energy beams passed through a reference cell (containing a gas selected
to have minimal absorption of infrared energy in the wavelength absorbed by the
gas component of interest) and a sample cell through which the sample gas flows
continuously. For the Beckman instrument the differential absorption appears as
a reading on a scale from 0 to 100 and is then related to the concentration of
the species of interest by calibration curves supplied with the instrument. Carbon
monoxide concentrations from the Sensors instrument are read directly in parts per
million.
Beckman
Specifications:
Sensor
Specifications:
Span stability ±1% of full scale in 24 hours
Zero stability ±1% of full scale in 24 hours
Ambient temperature range 32°F to 120°F
Line voltage 115±15V rms
Response 90% of full scale in 0.5 or 2.5 sec.
Precision ±1% of full scale
Output 4-20 ma
Ranges: 0-500 ppm and 0-2000 ppm
Linearity,2.6% full scale
Span stability ±1% of full scale in 24 hours
Zero stability ±1% of full scale in 24 hours
Ambient temperature range 32°F to 120°F
Line voltage 115115V rms
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Response: 90% of full scale in 0.5 or 2.5 sec
Precision: ±1% of full scale
Output: 0-1 volt
Ranges: 0-500 ppm and 0-1000 ppm
Carbon Dioxide. Carbon dioxide concentration was measured by a Beckman
Model 864 short path-length, non-dispersive infrared analyzer. This instrument
measures the differential in infrared energy absorbed from energy beams passed
through a reference cell (containing a gas selected to have minimal absorption
of infrared energy in the wavelength absorbed by the gas component of interest)
and a sample cell through which the sample gas flows continuously. The dif-
ferential absorption appears as a reading on a scale from 0 to 100 and is then
related to the concentration of the specie of interest by calibration curves
supplied with the instrument.
Specifications: Span stability ±1% of full scale in 24 hours
Zero stability ±1% of full scale in 24 hours
Ambient temperature range 32°F to 120°F
Line voltage 115±15V rms
Response 90% of full scale in 0.5 or 2.5 sec.
Precision ±1% of full scale
Output 4-20 ma
Ranges: 0-5% and 0-20%
Oxygen. The oxygen content of the flue gas sample was automatically and
continuously determined with a Teledyne Model 326A Oxygen analyzer. With this
instrument, oxygen in the flue gas diffuses through a Teflon membrane and is re-
duced on the surface of the cathode. A corresponding oxidation occurs at the anode
internally and an electric current is produced that is proportional to the con-
centration of oxygen. This current is measured and conditioned by the instrument's
electronic circuitry to give a final output in percent C>2 by volume.
Specifications: Precision ±1% of full scale
Response 90% in less than 40 sec.
Sensitivity 1% of low range
Linearity ±1% of full scale
Ambient temperature range 32-125°F
Fuel cell life expectancy 40,000%-hours
Power requirement 115 VAC, 50-60 Hz, 100 watts
Output 4-20 ma l
Ranges: 0-5%, 0-10%, and 0-25%
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Hydrocarbons. Hydrocarbons were measured using a Beckman Model 402
hydrocarbon analyzer which utilizes the flame ionization method of detection.
The sample for this instrument was drawn to the analyzer through a heated line
to prevent the loss of higher molecular weight hydrocarbons. It was then
filtered and supplied to the burner by means of a pump flow control system. The
sensor, which is the burner, has its flame sustained by regulated flows of fuel
(40% hydrogen plus 60% helium) and air. In the flame, the hydrocarbon components
of the sample undergo a complete ionization that produces electrons and positive
ions. Polarized electrodes collect these ions, causing a small current to flow
through a circuit. This ionization current is proportional to the concentration
of hydrocarbon atoms which enter the burner.
Specifications: Full scale sensitivity, adjustable from 5 ppm CH4 to
10% CH4
Ranges: Range multiplier switch has 8 positions: XI,
X5, X10, X50, X100, X500, XlOOO, and X5000. In
addition, span control provides continuously variable
adjustment within a dynamic range of 10:1
Response time 90% full scale in 0.5 sec.
Precision ±1% of full scale
Electronic stability ±1% of full scale for successive
identical samples
Reproducibility ±1% of full scale for successive
identical samples
Analysis temperature: ambient
Ambient temperature 32°F to 110°F
Output 4-20 ma
Air requirements 350 to 400 cc/min of clean, hydrocarbon-
free air, supplied at 30 to 200 psig
Fuel gas requirements 75 to 80 cc/min of pre-mixed fuel
consisting of 40% hydrogen and 60% nitrogen or helium,
supplied at 30 to 200 psig
Electrical power requirements 120V, 60 Hz
Automatic flame-out indication and fuel shut-off valve
Sulfur Dioxide. Sulfur dioxide was measured at Sites F and H by a
Dupont Model 400 photometric analyzer. This analyzer measures the difference
in absorption of two distinct wavelengths (ultraviolet) by the sample. The
radiation from a selected light source passes through the sample and then into
the photometer unit where the radiation is split by a semi-transparent mirror
into two beams. One beam is directed to a phototube through a filter which re-
moves all wavelengths except the "measuring" wavelength which is strongly absorbed
by the constituent in the sample. A second beam falls on a reference phototube,
KVB4-15900-554
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after passing through an optical filter which transmits only the "reference"
wavelength. The latter is absorbed only weakly, or not at all, by the con-
stituent in the sample cell. The phototubes translate these intensities to
proportional electric currents in the amplifier. In the amplifier, full cor-
rection is made for the logarithmic relationships between the ratio of the inten-
sities and concentration or thickness (in accordance with Beer's Law). The out-
put is, therefore, linearly proportional, at all times, to the concentration
and thickness of the sample.
Specifications: Noise less than 1/4%
Drift less than 1% full scale in 24 hours
Accuracy (±1% of analyzer reading)+(±1/4% of full scale
range)
Sample cell 304 stainless steel, quartz windows
Flow rate 6 CFH
Light source is mercury vapor, tungsten, or "Osram"
discharge type lamps
Power rating 500 watts maximum, 115V, 60 Hz
Reproducibility 1/4% of scale
Electronic response 90% in 1 sec.
Sample temperature 378 K (220°F)
Output 4-20 ma d.c.
Lower detection limit of 2 ppm
Ranges: 0-200 ppm and 0-2000 ppm
Recording Instruments. The output of the O2, CO, CO2 and NOx analyzers
was displayed on front panel meters and was simultaneously recorded on a Texas
Instrument Model FLO4W6D four-pen strip chart recorder. The recorder specifi-
cations are as follows:
Chart size 9-3/4 inch
Accuracy ±0.25%
Linearity <0.1%
Line voltage 120V±10% at 60 Hz
Span step response: one second
6.1.2 Wet Chemical Methods and Related Equipment
A description of the three wet chemical methods used to determine SO2
and SO 3 emissions are given below. The Shell-Emeryville method was performed at
all test sites except F and H during this test program. EPA Method 6 was used
at Test Sites E, G, I, J and K in addition to and as a check with the Shell-Emery-
ville method. At Test Sites F and H the Dupont Model 400 photometric analyzer
was used to determine SO2 for all tests run. The Goksoyr-Ross controlled con-
KVB4-15900-554
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densate method was then used for SO^ emission determinations to supplement the
data at these two sites.
Shell-Emeryville Method. The gas sample is drawn from the stack through
a glass probe (Figure 6-2), containing a quartz wool filter to remove particulate
matter, into a system of three sintered glass plate absorbers (Figure 6-3). The
first two absorbers contain aqueous isopropyl alcohol and remove the sulfur tri-
oxide; the third contains aqueous hydrogen peroxide solution which absorbs the
sulfur dioxide. Some of the sulfur trioxide is removed by the first absorber,
while the remainder, which passes through as sulfuric acid mist, is completely
removed by the secondary absorber mounted above the first. After the gas sample
has passed through the absorbers, the gas train is purged with nitrogen to trans-
fer sulfur dioxide, which has dissolved in the first two absorbers, to the third
absorber to complete the separation of the two components. The isopropyl alcohol
is used to inhibit the oxidation of sulfur dioxide to sulfur trioxide before it
gets to the third absorber.
The isopropyl alcohol absorber solutions are combined and the sulfate
resulting from the sulfur trioxide absorption is titrated with standard lead
perchlorate solution using Sulfonazo III indicator. In a similar manner, the
hydrogen peroxide solution is titrated for the sulfurate resulting from the sulfur
dioxide absorption.
The gas sample is drawn from the flue by a single probe made of quartz
glass inserted into the duct approximately one-third to one-half way. The inlet
end of the probe holds a quartz wool filter to remove particulate matter. It is
important that the entire probe temperature be kept above the dew point of sul-
furic acid during sampling (minimum temperature of 260°C). This is accomplished
by wrapping the probe with a heating tape.
EPA Method 6. This alternative method for determining SO2 (Figure 6-4),
employs an impinger train consisting of a bubbler and three midget impingers. The
bubbler contains isopropanol. The first and second impingers contain aqueous
hydrogen peroxide. The third impinger is left dry. The quartz probe and filter
used in the Shell-Emeryville method is also used in Method 6.
Method 6 differs from Shell-Emeryville in that Method 6 requires that
the sample rate be proportional to stack gas velocity. Method 6 also differs
from Shell-Emeryville in that the sample train in Method 6 is purged with am-
KVB4-15900-554
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Flue Wall
Asbestos Plug
Ball Joint
Pryometer
and
Thermocouple
Figure 6-2. SOx Sample Probe Construction
Spray Trap
Dial Thermometer
Pressure Gauge
Volume Indica-;
Vapor Trap Diaphragm
Pump
Dry Test Meter
Figure 6-3. Shell-Emeryville Sulfur Oxides
Sampling Train
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00
o
CTi
PROBE (END PACKED'
WITH QUARTZ OR
PYREX WOOL)
STACK WALL
MIDGET IMPINGERS
THERMOMETER
MIDGET BUBBLER
GLASS WOOL
ICE BATH
THERMOMETER
SILICA GEL
DRYING TUBE
DRY
GAS METER
jl RATE METER NEEDLE
SURGE TANK
Figure 6-4. EPA Method 6 Sulfur Oxide Sampling Train
PUMP
KVB4-15900-554
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bient air, instead of nitrogen. Sample recovery involves combining the solutions
from the first and second impingers. A 10 ml aliquot of this solution is then
titrated with standardized barium perchlorate.
Two repetitions of Shell-Emeryville and two repetitions of EPA Method 6
were made during each test.
The Goksoyr-Ross Controlled Condensate (G/R) Method. This is a desirable
method because of its simplicity and clean separation of particulate matter, SO2
and H2SO4 (SO3). This procedure is based on the separation of H2SO4(S03) from
SO2 by cooling the gas stream below the dew point of H2S04 but above the H2O dew
point. Figure 6-5 illustrates schematically the G/R test system.
Particulate matter is first removed from exhaust gas stream by means of
a quartz glass filter placed in the heated glass filter holder. Tissue-quartz
filters are recommended because of their proven inertness to H2SC>4. The filter
system is heated by a heating tape so that the gas out temperature of 260°C (500°F)
is maintained. This temperature is imperative to ensure that none of the H2SC>4
will condense in the filter holder or on the filter.
The condensation coil where the H2SC>4 is collected is cooled by water
which is maintained at 60°C (140°F) by a heater/recirculator. This temperature is
adequate to reduce the exhaust gas to below the dew point of H2SC>4.
Three impingers are shown in Figure 6-5. The first impinger is filled
with 3% H2O2 to absorb S02. The second impinger is to remove carryover moisture
and the third contains a thermometer to measure the exhaust gas temperature to
the dry gas meter and pump. The sampling rate is 2.3 1pm (0.08 CFM) .
For both SO2 and H2SO4 determination, the analytical procedure is identi-
cal. The H2SC>4 sample is washed from the back part of the filter holder and the
coil using distilled water. The sample from the first impinger which is assumed
to be absorbed and reacted SO2 in the form of H2SC>4 is recovered with distilled
water washing. The amount of H2SC>4 is the condensate from the coil and from the
H2O2 impinger is measured by H+ titration. Bromphenol Blue is used with NaOH as
the titrant.
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Adapter for Connecting Hose
TC Wei
Asbestos Cloth
Insulation
Glass-Cloth Heating
Mantle ~~~ {
Stack
Gas Flow
Rubber
Vacuum
Vacjun
Ga jce
Reclrculator
•Tnemiometer
Styrofoam Ice Chest
3-way
Valve
Dn er ite
Figure 6-5. Schematic of Goksoyr-Ross Controlled
Condensation System (CCS).
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6.2 PARTICULATE MEASUREMENT AND PROCEDURE
Particulate samples were taken at the same sample ports as the gaseous
emission samples using a Joy Manufacturing Company portable effluent sampler
(Figure 6-6) . This system, which meets the EPA design specifications for Test
Method 5, Determination of Particulate Emissions from Stationary Sources (Federal
Register, Volume 36, No. 27, page 24888, December 23, 1971), was used to perform
both the initial velocity traverse and the particulate sample collection. Dry
particulates are collected in a heated case using first a cyclone to separate
particles larger than approximately five micrometers, and a 100 mm glass fiber
filter for retention of particles down to 0.3 micrometers. • Condensible particulates
are collected in a train of four Greenburg-Smith impingers in an ice water bath.
The control unit includes a total gas meter and thermocouple indicator. A pitot
tube system is provided for setting sample flows to obtain isokinetic sampling
conditions.
All peripheral equipment is carried in the instrument van. This includes
a scale (accurate to ±0.1 mg), hot plate, drying oven (212°F), high temperature
oven, desiccator, and related glassware. A particulate analysis laboratory is
set up in the vicinity of the boiler in a vibration-free area. Here filters are
prepared, tare weighed and weighed again after particulate collection. Also,
probe washes are evaporated and weighed in the lab.
6.3 PARTICLE SIZE DISTRIBUTION MEASUREMENT AND PROCEDURE
Particle size distribution of the flyash was measured using several
methods. These include the Brink Cascade Impactor, SASS cyclones, and the Banco
Classifier.
Brink. The Brink cascade impactor is an in-situ particle sizing device
which separates the particles into six size classifications.
The sampling procedure is straight forward. First, the gas velocity at
the sample point is determined using a calibrated S-type pitot tube. For this
purpose a hand held particulate probe, inclined manometer, thermocouple and in-
dicator are used. Second, a nozzle size is selected which will maintain iso-
kinetic flow rates within the recommended .02-.07 ft-Vmin rate at stack conditions.
KVB4-15900-554
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TEMPERATURE SENSOR
IMPINGER TRAIN OPTIONAL,MAY BE REPLACED
BY AN EQUIVALENT CONDENSER
CHECK
VALVE
VACUUM
LINE
REVERSE-TYPE
PITOTTUBE
THERMOMETER
FILTER HOLDER
IMPINGERS ICE BATH
BY-PASS VALVE
PITOT MANOMETER
ORIFICE
THERMOMETERS
DRY GAS METER
AIR TIGHT
PUMP
Figure 6-6. EPA Method 5 Particulate Sampling Train
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Having selected a nozzle and determined the required flow rate for isokinetics,
the operating pressure drop across the impactor is determined from a calibration
curve. This pressure drop is corrected for temperature, pressure and molecular
weight of the gas to be sampled.
A sample is drawn at the predetermined Ap for a time period which is
dictated by mass loading and size distribution. To minimize weighing errors, it
is desirable to collect several milligrams on each stage. However, to minimize
reentrainment, a rule of thumb is that no stage should be loaded above 10 mg.
A schematic of the Brink sampling train is shown in Figure 6-7.
Bahco. The Bahco classifier is described in ASME Power Test Code 28. It
is an accepted particle sizing method in the power industry and is often used in
specifying mechanical dust collector guarantees. Most Bahco samples are collected
by cyclone separation; thus, particles below the cut point of the cyclone are lost.
The Bahco samples in these tests were obtained from the cyclone in the EPA Method 5
particulate train. These samples are spatially representative because they are
taken from a 24-point sample matrix. However, that portion of the sample below
about seven micrometers is lost to the filter. The percentage of the sample lost
to the filter is noted in this report. Bahco test data are presented in combina-
tion with sieve analysis of the same sample.
SASS. The Source Assessment Sampling System (SASS) was not designed
principally as a particle sizing device, but it does include three calibrated
cyclones which were used as such. The SASS train was used as a single point, iso-
kinetic sampler like the Brink cascade impactor. However, the SASS train is a
high volume sampler allowing the use of .25 to 1.0 inch nozzles as opposed to the
typical .08 inch nozzle used on the Brink. The cut points of the three cyclones
were 10, 3 and 1 micrometers at Test Sites A, B and C. At the remaining sites,
the cut points were 18.5, 5.9 and 1.4 micrometers.
6.4 COAL SAMPLING AND ANALYSIS PROCEDURE
Coal samples were taken during each particulate and SASS test. The
samples were processed and analyzed for both size consistency and chemical com-
position. The samples were taken as close to the furnace as possible in order
to obtain samples representative of the coal fired during testing. Samples were
KVB4-15900-554
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PRESSURE TAP
FOR 0-20"
MAGNAHELIX
EXHAUST
ELECTRICALLY HEATED PROBE
DRY GAS
METER
FLOW CONTROL
VALVE
DRYING
COLUMN
Figure 6-7. Brink Cascade Impactor Sampling Train Schematic
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taken from the coal scales or weigh lorries at sites with coal weighing devices,
while at sites without them, samples were taken from ports installed directly
above the feeders.
The sampling procedure was as follows. At the start of testing one
increment of sample was collected. This was repeated twice an hour during the
test (three to five hours duration) so that a 6 to 10 increment sample is ob-
tained. The total sample is then riffled using a Gilson Model SP-2 Porta Splitter
until two representative twenty pound samples are obtained.
The sample to be used for sieve analysis was air dried overnight.
Drying of the coal is necessary for good separation of fines. If the coal is
wet, fines cling to the larger pieces of coal and to each other. Once dry, the
coal was sized using a six tray Gilson Model PS-3 Porta Screen. Screen sizes
used were 1", 1/2", 1/4", #8 and #16 mesh. Screen area per tray is 14"xl4". The
coal in each tray was weighed on a triple beam balance to the nearest 0.1 gram.
The coal sample to be used for chemical analysis was reduced to 2-3
pounds by further riffling and sealed in a plastic bag. All coal samples were
sent to Commercial Testing and Engineering Company, South Holland, Illinois.
Each sample associated with a particulate loading or particle sizing test was
given a proximate analysis. In addition, composite samples consisting of one
increment of coal for each test for each coal type receive ultimate analysis, ash
fusion temperature, mineral analysis, Hardgrove grindability and free swelling
index measurements.
6.5 ASH COLLECTION AND ANALYSIS FOR COMBUSTIBLES
The combustible content of flyash was determined in the field by KVB
in accordance with ASTM D3173, "Moisture in the Analysis Sample of Coal and Coke"
and ASTM D3174, "Ash in the Analysis Sample of Coal and Coke." The flyash sample
was collected by the EPA Method 5 particulate sample train while sampling for
particulates.
The cyclone catch is placed in a desiccated and tare-weighed ceramic
crucible. The crucible with sample is heated in an oven at 230°F to remove its
moisture. It is then desiccated to room temperature and weighed. The crucible
with sample is then placed in an electric muffle furnace maintained at a
KVB4-15900-554
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temperature of 1400°F until ignition is complete and the sample has reached a
constant weight. It is cooled in a desiccator over desiccant and weighed. Com-
bustible content is calculated as the percent weight loss of the sample based
on its post 230°F weight.
Bottom ash samples were collected in several increments from the grate
during testing or from the ash pit after testing was completed. These samples
were mixed, quartered, and sent to Commercial Testing and Engineering Company
for combustible determination.
Multiclone ash samples were taken from ports near the base of the
multiclone hopper. This sample, approximately two quarts in size, was sent to
Commercial Testing and Engineering Company for combustible determination.
6.6 BOILER EFFICIENCY EVALUATION
Boiler efficiency was calculated using the ASME Test Form for Abbreviated
Efficiency Test, Revised, September, 1965. The general approach to efficiency
evaluation is based on the assessment of combustion losses. These losses can be
grouped into three major categories: stack gas losses, combustible losses, and
radiation losses. The first two groups of losses are measured directly. The
third is estimated from the ABMA Standard Radiation Loss Chart.
Unlike the ASME test in which combustible losses are lumped into one
category, combustible losses were calculated and reported separately for com-
bustibles in the bottom ash and combustibles in the flyash leaving the boiler.
6.7 TRACE SPECIES MEASUREMENT
The EPA (IERL-RTP) has developed the Source Assessment Sampling System
(SASS) train for the collection of particulate and volatile matter in addition
to gaseous samples. The "catch" from the SASS train is analyzed for polynuclear
aromatic hydrocarbons (PAH) and inorganic trace elements.
More information can be found on the SASS equipment, test procedures,
and the test results in a separate final report that deals with 'the SASS testing
portion of this program only.
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7.0 TEST EQUIPMENT AND PROCEDURES
FOR SITES LI THROUGH L7
This section presents details of the test equipment and sampling pro-
cedures that were used to obtain accurate and reliable data at Test Sites Ll
through L7.
7.1 MASS EMISSION MEASUREMENTS AND PROCEDURES
Particulate mass samples were taken at the sampling ports using a RAC
STAKSAMPLER (Figure 7-1). This system meets the EPA design specifications for
Test Method 5, Determination of Particulate Emissions from Stationary Sources
(Federal Register, Volume 36, No. 27, page 24888, December 23, 1971). Both the
initial velocity and temperature traverse and the particulate sample collection
were obtained using this device. Method 5 was followed in setting up and con-
ducting all particulate emission tests.
This method calls for the probe to be attached to a cyclone collector
and a filter holder; four impingers, connected in series, follow the filter holder.
The first, third and fourth are the modified Greenburg-Smith type while the
second is a standard Greenburg-Smith. The control unit is equipped with a pump,
a dry gas meter, orifice meter, and two manometers. Temperatures were measured
using both dial thermometers and chromel-alumel thermocouples. The pitot tube,
the dry gas meter, and the orifice meter were calibrated prior to each series of
tests in accordance with the procedures outlined in EPA bulleting No. APTD-0576
(Maintenance, Calibration, and Operation of Isokinetic Sampling Equipment by J.
J. Rom).
Particle matter is collected by the cyclone and filter in a case heated
to 120°C; the water vapor in the gas stream and the condensible particles condense
out in the impinger train which is in an ice bath. The percent moisture in the
stack gas is calculated from the increased water volume. Millipore filters are
used to separate the insoluble condensibles from the impinger water and the
soluble fraction is measured by driving off the water and weighing the residue.
The molecular weight of the stack gas was determined by withdrawing a
sample from the gas stream and storing it in a teflon bag. The analysis was per-
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PITOT LINES
SAMPL
RLE BOX
METER BOX
ELECTRICAL CONS
POWER CORD
CHECK VALVE
Figure 7-1. RAC Staksampler
KVB4-15900-554
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formed on site using a standard orsat and checked in the laboratory using infra-
red analysis for CO and CO2 and by the use of a micro-fuel cell (Teledyne Instru-
ment) for O^.
An on-site sampling van was used for sample train clean-up; all particle
matter, filters, and liquid samples were stored in sealed containers for labora-
tory analysis. The clean-up and laboratory procedures were those specified in
the Federal methods and were performed in the particle laboratory at the Pennsyl-
vania State University. Calculations were performed using the Method 5 equations.
7.2 PARTICLE SIZE DISTRIBUTION'MEASUREMENT AND PROCEDURE .
The Bahco centrifugal classifier and the Anderson in-stack impactor are
devices used to obtain particle size information. Figures 7-2 and 7-3 are
schematic diagrams of the two units. The method for using the Bahco is described
in Power Test Code 28 distributed by the American Society of Mechanical Engineers;
the "Procedures for Cascade Impactor Calibration and Operation in Process
Streams" (EPA-600/2-77-004) is the manual that details the use of impactors.
The centrifugal classifier requires that large samples (1 to 50 grams)
be removed from the gas stream by some sampling technique prior to sizing. In
the laboratory, the dust sample is introduced into a hopper in the center of the
device. Particles are fed into an air flow pattern whose spiral current imparts
velocities that carry the larger, heavier particles by centrifugal force to the
periphery of the instrument while the smaller particles are swept toward the
center of the wheel where they are deposited in a chamber. By varying the air
flow, the particle matter can be separated into the size fractions. A complete
description of the instrument, the method, and the operating principles can be
found in the test code.
The cascade impactor operates directly in the gas stream. The Mark III
Anderson device used in this work is shown disassembled in Figure 7-3. It is
designed for use in gas streams with temperatures up to 815°C (1500°F). The pre-
separator at the intake end removes large particles (>10 ym). Stack gas is drawn
in through a nozzle (not shown), passes through the preseparator and impactor
cone to the plate section. There are eight plates (or stages), each with holes
slightly smaller than those in the preceding plate. The holes in each plate
KVB4-15900-554
317
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I. ROTOR CASTING
2. FAN
3 VIBRATOR
4. ADJUSTABLE SLIDE
5. FEED HOPPER
6. REVOLVING BRUSH
7. FEED TUBE
8. FEED SLOT
9. FAN WHEEL OUTLET
O. COVER
II. ROTARY DUCT
12. FEED HOLE
13. BRAKE
M, THROTTLE SPACER
& MOTOR-3520 RPM
«. GRADING MEMBER
f7. THREADED SPINDLE
A SYMMETRJCAL DISC
19. SIFTING CHAMBER
20. CATCH BASIN
21. HOUSING
22. RADIAL, \*NES
Figure 7-2. Bahco Centrifugal Classifier
KVB4-15900-554
318
-------
00
I.PRESEPARATOR
2 IMPACTOR CONE
3 IMPACTOR PLATES
4. IMPACTOR PLATE HOLDER
5. HOUSING
Figure 7-3. Andersen Mark III In-Stack Impactor
KVB 4-15900-554
-------
are offset from the plate above and the plate below so that the air passing
through a set of holes must impact on the surface of the lower plate and turn
sharply in order to pass through the holes in that plate. Since the hole size
decreases from plate to plate, the velocity increases and successively smaller
particles are collected at each level. The eight stages are followed by an
absolute back-up filter that captures the final particle fraction.
A glass fiber collecting media was used on each stage; the media was
perforated to keep the holes clear and the collection surface covered. Before
and after exposure the media and the final filter were dried over Drierite for
24 hours and weighed. The difference in the weights was the mass in that size
fraction. Calibration of the impactor, based on the assumption of spherical
particles of 1.0 g/cc density, was accomplished in the laboratory prior to field
tests.
The sampling train employed for both the centrifugal and impactor
methods is shown in Figure 7-4. A preseparator was used on both trains to
collect the large particles; this allowed these particles to be sized by sieving.
Power Test Code 28 specifies that the particulate matter be removed directly
from the gas stream by a sampling technique. A glass fiber filter was utilized
in this case, and multiple samples were taken until about 2 grams of material
were collected for particle size analysis in the centrifugal classifier. To
strengthen confidence in the particle size distribution obtained by impaction,
multiple samples were taken at different points within the duct or stack. A
standardized laboratory procedure was instituted for the cleaning and handling
of the collected particle matter.
7.3 COAL SAMPLING AND ANALYSIS
^
The coal storage and handling systems at Test Sites Ll through L7 are
very similar. Each receive coal by truck delivery to a receiving hopper, from
which it is transported to an in-plant overhead storage bunker. Coal is
weighed and transported to individual boiler stoker coal hoppers by a suspended
weigh lorry. To obtain coal samples representative of the coal fired during the
testing, incremental samples were obtained, using a standard coal shovel, from
the weigh lorry discharge at the stoker hopper. The frequency of sampling from
the weigh lorry load was varied to obtain a minimum 100 pound sample per test.
KVB4-15900-554
320
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47 mm FILTER HOLDER
OJ
NJ
HJfr-
t
PRESEPARATOR
t
(HIM
EPA SAMPLING TRAIN
Figure 7-4. Schematic Diagram of the Sampling Train Used to Collect
Particles for the Centrifugal Classifier and Impactor Analysis
KVB4-15900-554
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As each incremental sample was collected it was placed in a clean metal con-
tainer with tight fitting cover.
The gross coal sample at each test site was prepared in a sample crushing
machine provided with riffle buckets. The final riffling of the gross col-
lection weighed approximately 12 pounds. This was placed in four standard
metal sample cans having a capacity of three pounds each. The cans were sealed
and delivered to an approved testing laboratory for analysis of moisture,
heating value, ash, sulfur, volatile matter, fixed carbon, ash softening tempera-
ture, and free swelling index.
At Test Sites L5, L6, and L7 a portion of the uncrushed sample was sub-
jected to a sizing test conducted on a Gilson Porta Screen Model PS-3, with
Tyler square screens.
7.4 ASH COLLECTION AND ANALYSIS
Bottom ash samples were collected from the stoker ash pit at completion
of testing. The samples were manually crushed, mixed, quartered, and placed in
a standard three-pound metal sample container.
Flyash samples were collected from a port near the base of the mechanical
collectors on those sites equipped with mechanical dust collectors. The samples
were placed in a standard three-pound metal sample container. All samples were
delivered to an approved test laboratory for analysis of combustible content.
7.5 BOILER OPERATING PERFORMANCE AND EFFICIENCY
Boiler efficiency testing was not included in the scope of Test Sites Ll
through L7. However, operating data recorded every one-half hour provides infor-
mation necessary to evaluate steaming rates, heat release rates, excess air
(oxygen), and combustion efficiency. Coal scales, instruments, and controls
at the seven sites are checked and calibrated by the manufacturer's service
engineer at regular intervals. Special test equipment, other than an orsat for
boiler outlet gas analysis, was not provided.
KVB4-15900-554
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REFERENCES
1. Gabrielson, J. E , P. L. Langsjoen, and T. C. Kosvic. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site A. EPA-600/7-78-136a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, July, 1978. 106 pp.
2. Gabrielson, J. E., P. L. Langsjoen, and T. C. Kosvic. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site A (Data Supplement). EPA-600/7-78-136b, U.S. Environmental
Protection Agency, Research Triangle Park, NC, December, 1978. 278 pp.
3. Gabrielson, J. E., P. L. Langsjoen, and T. C. Kosvic. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site B. EPA-600/7-79-041a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, February, 1979. 113 pp.
4. Gabrielson, J. E., P. L. Langsjoen, and T. C. Kosvic. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site B (Data Supplement). EPA-600/7-79-041b, U.S. Environ-
mental Protection Agency, Research Triangle Park, NC, February, 1979.
361 pp.
5. Gabrielson, J. E., P. L. Langsjoen, and T. C. Kosvic. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site C. EPA-600/7-79-130a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, May, 1979. 138 pp.
6. Burlingame, J. O., R. A. Parker, J. Cook, W. M. Jackson, and J. D. Demont.
Field Tests of Industrial Stoker Coal-Fired Boilers for Emissions Control
and Efficiency Improvement - Site C (Data Supplement). EPA-600/7-79-130b,
U.S. Environmental Protection Agency, Research Triangle Park, NC, July,
1979. 441 pp.
7. Gabrielson, J. E. , P. L. Langsjoen, and T. C. Kosvic. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site D. EPA-600/7-79-237a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, November, 1979. 115 pp.
8. Burlingame, J. O., R. A. Parker, W. M. Jackson, and J. D. Demont. Field
Tests of Industrial Stoker Coal-Fired Boilers for Emissions Control and
Efficiency Improvement - Site D (Data Supplement). EPA-600/7-79-237b,
U.S. Environmental Protection Agency, Research Triangle Park, NC, December,
1979. 232 pp.
9. Langsjoen, P. L., J. O. Burlingame, and J. E. Gabrielson. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site E. EPA-600/7-80-064a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, March, 1980. 102 pp.
KVB4-15900-554
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10. Burlingame, J. O. R. A. Parker, W. M. Jackson, and J. D. Demont. Field
Tests of Industrial Stoker Coal-Fired Boilers for Emissions Control and
Efficiency Improvement - Site E (Data Supplement). EPA-600/7-80-064b,
U.S. Environmental Protection Agency, Research Triangle Park, NC, April,
1980. 252 pp.
11. Langsjoen, P. L., R. J. Tidona, and J. E. Gabrielson. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site F. EPA-600/7-80-065a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, March, 1980. 113 pp.
12. Tidona, R. J.,H. L. Stix, J. E. Cook, and M. G. Gabriel. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site F (Data Supplement). EPA-600/7-80-065b, U.S. Environ-
mental Protection Agency, Research Triangle Park, NC, April, 1980. 219 pp.
13. Langsjoen, P. L., J. 0. Burlingame, and J. E. Gabrielson. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site G. EPA-600/7-80-082a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, April, 1980. 114 pp.
14. Burlingame, J. O., R. A. Parker, B. Crockett, W. M. Jackson, and J. D.
Demont. Field Tests of Industrial Stoker Coal-Fired Boilers for Emissions
Control and Efficiency Improvement - Site G (Data Supplement). EPA-600/7-
80-082b, U.S. Environmental Protection Agency, Research Triangle Park, NC,
April, 1980. 266 pp.
15. Langsjoen, P. L. , R. J. Tidona, and J. E. Gabrielson. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site H. EPA-600/7-80-ll2a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, May, 1980. 90 pp.
16. Tidona, R. J., J. E. Cook, W. M. Jackson, and M. G. Gabriel. Field Tests
of Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site H (Data Supplement). EPA-600/7-80-112b, U.S. Environ-
mental Protection Agency, Research Triangle Park, NC, May, 1980. 101 pp.
17. Langsjoen, P. L., J. O. Burlingame, and J. E. Gabrielson. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site I. EPA-600/7-80-136a. U.S. Environmental Protection
Agency, Research Triangle Park, NC, May, 1980. 77 pp.
18. Burlingame, J. O., R. A. Parker, J. E. Cook, W. M. Jackson, and J. D. Demont.
Field Tests of Industrial Stoker Coal-Fired Boilers for Emissions Control
and Efficiency Improvement - Site I (Data Supplement). EPA-600/7-80-136b,
U.S. Environmental Protection Agency, Research Triangle Park, NC, May,
1980. 119 pp.
19. Langsjoen, P. L., J. O. Burlingame, and J. E. Gabrielson. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site J. EPA-600/7-80-137a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, May, 1980. 83 pp.
KVB4-15900-554
324
-------
20. Burlingame, J. 0., R. A. Parker, W. M. Jackson, and J. D. Demont. Field
Tests of Industrial Stoker Coal-Fired Boilers for Emissions Control and
Efficiency Improvement - Site J (Data Supplement). EPA-600/7-80-137b,
U.S. Environmental Protection Agency, Research Triangle Park, NC, May,
1980. 143 pp.
21. Langsjoen, P. L., J. O. Burlingame, and J. E. Gabrielson. Field Tests of
Industrial Stoker Coal-Fired Boilers for Emissions Control and Efficiency
Improvement - Site K. EPA-600/7-80-138a, U.S. Environmental Protection
Agency, Research Triangle Park, NC, May, 1980. 96 pp.
22. Burlingame, J. O., R. A. Parker, W. M. Jackson, and J. D. Demont. Field
Tests of Industrial Stoker Coal-Fired Boilers for Emissions Control and
Efficiency Improvement - Site K (Data Supplement). EPA-6QO/7-80-138b,
U.S. Environmental Protection Agency, Research Triangle Park, NC, May,
1980. 237 pp.
23. Davis, J. W., and H. K. Owens. Field Tests of Industrial Stoker Coal-Fired
Boilers for Emissions Control and Efficiency Improvement - Sites Ll - L7.
EPA-600/7-81-020a, U.S. Environmental Protection Agency, Research Triangle
Park, NC, February, 1981. 65 pp.
24. Davis, J. W., and H. K. Owens. Field Tests of Industrial Stoker Coal-Fired
Boilers for Emissions Control and Efficiency Improvement - Sites Ll - L7
(Data Supplement). EPA-600/7-81-020b, U.S. Environmental Protection Agency,
Research Triangle Park, NC, February, 1981. 80 pp.
25. Morrow, C. H., W. C. Hoiton, and H. L. Wagner. Investigation of Gravity
Reinjection of Flyash on a Spreader Stoker Fired Boiler Unit. Transactions
of the ASME, October, 1953. pp. 1363-1372.
KVB4-15900-554
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APPENDIX A
CONVERSION FACTORS
ENGLISH AND METRIC UNITS TO SI UNITS
To Convert From
To
Multiply By
ppm
ppm
Ppm
ppm
g/Kc
in
in2
ft
ft2
ft3
Ib
Ib/hr
lb/106Btu
g/Mcal
Btu
Btu/lb
Btu/hr
J/sec
J/hr
Btu/ft/hr
Btu/ft/hr
Btu/ft2/hr
Btu/ft2/hr
Btu/ft3/hr
Btu/ft3/hr
psia
"H20
Rankine
Fahrenheit
Celsius
Rankine
APPROXIMATE CONVERSION
@ 3% O2 (SOx as S02)
@ 3% O2 (NOx as NO2)
@ 3% O2 (CO)
@ 3% O2 (CH4)
j of Fuel
cm
cm2
m
m2
m3
Kg
Mg/s
ng/J
ng/J
J
J/kg
W
w
w
W/m
J/hr/m
W/m2
J/hr/m2
W/m3
J/hr/m3
Pa
Pa
Celsius
Celsius
Kelvin
Kelvin
FACTORS FOR A TYPICAL COAL
ng/J (lb/106Btu)
ng/J (Ib/lO^Btu)
ng/J (lb/106Btu)
ng/J (lb/106Btu)
ng/J (lb/106Btu)
2.540
6.452
0.3048
0.09290
0.02832
0.4536
0.1260
430
239
1054
2324
0.2929
1.000
3600
0.9609
3459
3.152
11349
10.34
37234
6895
249.1
C = 5/9R-273
C = 5/9(F-32)
K = C+273
K = 5/9R
FUEL
0.851 (1.98xlO~3)
0.611 (1.42xlO~3)
0.372 (8.65xlO~4)
0.213 (4.95xlO~4)
4300 (10)
326
KVB4-15900-554
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APPENDIX B
CONVERSION FACTORS
SI UNITS TO ENGLISH AND METRIC UNITS
To Convert From
To
cm
cm2
m
m2
m3
Kg
Mg/s
ng/J
ng/J
J
J/kg
J/hr/m
J/hr/m2
J/hr/m3
W
W
W/m
W/m2
W/m3
Pa
Pa
Kelvin
Celsius
Fahrenheit
Kelvin
APPROXIMATE CONVERSION
ng/J
ng/J
ng/J
ng/J
ng/J
in
in2
ft
ft2
ft3
Ib
Ib/hr
lb/106Btu
g/Mcal
Btu
Btu/lb
Btu/ft/hr
Btu/ft2/hr
Btu/ft3/hr
Btu/hr
J/hr
Btu/ft/hr
Btu/ft2/hr
Btu/ft3/hr
psia
"H2°
Fahrenheit
Fahrenheit
Rankine
Rankine
FACTORS FOR A TYPICAL COAL FUEL
ppm @ 3% O2 (SOx as SO
ppm @ 3% O2 (NOx as NO
ppm @ 3% O2 (CO)
ppm @ 3% O2 (CH4)
g/kg of fuel
2}
2'
Multiply By
0.3937
0.1550
3.281
10.764
35.315
2.205
7.937
0.00233
0.00418
0.000948
0.000430
0.000289
0.0000881
0.0000269
3.414
0.000278
1.041
0.317
0.0967
0.000145
0.004014
F = 1.8K-460
F = 1.8C+32
R = F+460
R = 1.8K
1.18
1.64
2.69
4.69
0.000233
KVB4-15900-554
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APPENDIX C
SI PREFIXES
Mialtiplication
___ Factor _ Prefix SI Symbol
10 18 exa E
1015 peta P
1012 tera T
109 giga G
10 mega M
103 kilo k
10 hecto* h
10^ deka* da
10 deci* d
10~2 centi* c
10~3 mi Hi m
10~6 micro y
10~"9 nano n
10~12 pico p
lO^15 femto f
10~18 atto a
*Not recommended but occasionally used
KVB4-15900-554
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APPENDIX D
EMISSION UNITS CONVERSION FACTORS
FOR TYPICAL COAL FUEL (HV = 13,320 BTU/LB)
Multiply
To ~"~\ By
Obtain
% Weight
In Fuel
lbs/106Btu
SO-,
NO,
so2
grairs/106Cal
NO,
SOX
PPM
(Dry @ 3% 02)
NOx
SO,
Grains/SCF
(Dry @ 12% C0~2)
NO,
HOPE: 1. Valu
oxid
2. Stan
Weight in Fuel
S N
1.50
2.70
758
.676
2.47
4.44
1736
1.11
lbs/106Btu
S02 NO2
(1.8)
505
(-448)
(1.8)
grams/106Cal
SO2 N02
0.370
0.225-
(.556)
(.556)
704
(.448)
281
(.249)
391
PBM
(Dry @ 3% O2)
SOx NOx
13.2xlO~4
19.8x10
-4
35.6x10
-4
5.76xlO~4
14.2x10'
,-4
25.6x10
Grains/SCF,
(Dry @ 12% C02)
S02 N02
1.48
(2.23)
(4.01) '
(.249)
8.87x10
-4
6 . 39x10
1127
.903
(2.23)
(4.01)
1566
les in parenthesis can be i;--,ed for all flue gas constituents such as oxides of carbon,
es of nitrogen, oxides of sulfur, hydrocarbons, particulates, etc.
dard reference temper"ture of 530°R was used.
KVB4-15900-554
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APPENDIX E
ORDERING INFORMATION FOR SITE REPORTS
The individual test site reports referenced in this report may be obtained
at no charge, if available, from EPA's Center for Environmental Research Information
(CERI). It is only necessary to include the EPA report number given in the follow-
ing table. When CERI's supply of reports is exhausted, paper or microfiche copies
may be obtained through the National Technical Information Service (NTIS). When
ordering through NTIS, use the NTIS report number found in the following table. Re-
quest a copy of the latest price code schedule to translate the NTIS price codes.
CERI: ORD Publications
U.S. EPA
26 West St. Clair
Cincinnati, OH 45268
Telephone: (513)684-7562
Test Site EPA Report No.
A
A sup*
B
B sup
C
C sup
D
D sup
E
E sup
F
F sup
G
G sup
H
H sup
I
I sup
J
J sup
K
K sup
L1-L7
L1-L7 sup
EPA-600/7-78-136a
EPA-600/7-78-136b
EPA-600/7-79-041a
EPA-600/7-79-041b
EPA-600/7-79-130a
EPA-600/7-79-130b
EPA-600/7-79-237a
EPA-600/7-79-237b
EPA-600/7-80-064a
EPA-600/7-80-064b
EPA-600/7-80-065a
EPA-600/7-80-065b
EPA-600/7-80-082a
EPA-600/7-80-082b
EPA-600/7-80-112a
EPA-600/7-80-112b
EPA-600/7-80-136a
EPA-600/7-80-136b
EPA-600/7-80-137a
EPA-600/7-80-137b
EPA-600/7-80-138a
EPA-600/7-80-138b
EPA-600/7-81-020a
EPA-600/7-81-020b
NTIS: 5285 Port Royal Road
Springfield, VA 22161
Telephone: (800)336-4700
or (703)487-4700
NTIS Price Code
Paper Copy Microfiche
NTIS No.
PB285172
PB293731
PB295535
PB295544
PB80-119324
PB80-119340
PB80-144991
PB81-175465
PB80-181266
PB80-212921
PB80-183023
NA**
PB80-187271
PB80-187289
PB80-212947
PB80-212954
PB80-212822
PB80-212962
PB80-219744
PB80-212970
PB80-220817
PB80-212988
PB81-196628
NA
A06
A13
A06
A16
A07
A19
A06
All
A06
A12
A06
NA
A06
A12
A05
A06
A05
A06
A05
A07
A05
All
A04
NA
A01
A01
A01
A01
A01
A01
A01
A01
A01
A01
A01
NA
A01
A01
A01
A01
A01
AOl
A01
AOl
AOl
AOl
AOl
NA
* sup - Data supplement to the report. This is a compilation of raw data
sheets and is useful only to the researcher who needs to examine
the data in greater detail than that provided in the main report.
** NA - No't available at the time of publication but expected to be
available soon.
KVB4-15900-554
330
ttUSGPO: 1982 — 559-092/0413
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