PARTICULATE POLLUTANT SYSTEM STUDY
VOLUME III-HANDBOOK OF EMISSION PROPERTIES
MRI$
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PARTICULATE POLLUTANT SYSTEM STUDY
Volume III - Handbook of Emission Properties
1 May 1S71
Contract No. CPA 22-69-104
MRI Project No. 3326-C
Prepared for
Air Pollution Control Office
Environmental Protection Agency
411 West Chapel Hill Street
Durham, North Carolina 27701
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BIBLIOGRAPHIC DATA 1- Rep on No. [2.
sheet APTD-0745 ¦ |
3. Recipient's Accession No,
4. Title and Subtitle k
Particulate Pollutant System Study 1
Volume III - Handbook of Emission Properties r
5* Keporr Date
May 1, 1971
6.
7. Author(s) Dr. A. E. Vandegrift, Dr. L. J. Shannon, Dr. E. W.
*Ir' P'G" Gorman» ***• E' E* Sal1®e» and Miss M.
0. Performing Organization Rept.
No.
9. Performing Organization Name aad Address
Midwest Research Institute
Kansas City, Missouri 64141
10. Pfoject/Taslc/Work Unit No.
No. 3326-C
11. Coatract/Craot No.
CPA 22-69-104
12. Sponsoring Organization Name and Address
Air Pollution Control Office
Environmental Protection Agency
411 West Chapel Hill Street
Durham, North Carolina 27701
13. Type of Rep on ft Period
Covered
14.
is. Supplementary Nnrg* disclaimer - mis report was rurmsned to tne uttice ot Air programs
by Midwest Research Institute, Kansas City, Missouri 64141 in fulfillment of Contract
No. CPA 22-69-104
!$. Abstracts
A handbook is presented as part of the documentation for a study of
particulate air pollution from stationary sources. The objective of the
study was to identify, characterize, and quantify the particulate air
pollution problem in the U. S. This document delineates the kind and
number of stationary particulate sources, the chemical and physical
characteristics of Doth the particulates and carrier gas emitted by
specific sources, and the status of current control practices. The first
three chapters of the handbook present general background information \ I
pertaining to source emission factors and emission rates effluent \ *
characteristics, and control technology. Chapter 4 discusses some of t&ey
more Important chemical and physical properties of particulates and
carrier gas emitted by industrial sources. The remaining chapters
present discussions of the major industrial sources of particulate
pollutan ts.
17. Key Words and Document Analysis. 17a. Descriptors
Air pollution
Particles
Emission
Sources
Air pollution control equipment
Particle size
Indus tries
Industrial wastes
17b. Identiiiers/Open-Ended Terms
Particulates
Stationary sources
I
17c. COSAT! Field/Group 13B
18. Availability Statement Unlimi ted 19. Security Class (This 121. No. of Pages
Report)
.. UNCLASSIFIED,
20* Security Class (This
S "Unclassified
FORM HTIS-18 < 10*70) ' ''JSCOMM^OC 4O320-P7I
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PREFACE
This handbook was prepared for APCO under Contract Nc. CPA-22-
69-104, which was monitored by Mr. Timothy Devitt and Mr. Don Felton.
The work was conducted in the Environmental Sciences Section of
the Physical Sciences Division.
The handbook was written by Dr. A. E. Vandegrift, Project Director,
and Dr. L. J. Shannon with the assistance of Dr. E. W. Lawless, Mr. P. G. Gorman,
Mr. E. E. Sallee, and Miss M. Reichel.
Dr. Seymour Calvert and Mr. Paul L. Magill, consutants to MRI, made
many valuable comments and contributions to this document. Dr. Larry Faith,
Er. Louis McCabe, and Dr. Frank Fowler also contributed to the program.
Approved for:
H. M. Hubbard, Director
Physical Sciences Eivision
iii
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TABLE OF CONTENTS
Chapter Page
1 Introduction 1
2 Emission Factors and Rates 3
2.1 Introduction 3
2.2 Emission Hates of Industrial Sources 4
References 12
3 Control Equipment 13
3.1 Introduction 13
3.2 Cyclones 15
3.3 Wet Scrubbers 16
3.4 Electrostatic Precipitators 17
3.5 Fabric Filters 19
3.6 Mist Eliminators 19
3.7 Afterburners 20
References 22
4 Effluent Characteristics 23
4.1 Introduction 23
4.2 Particulate Characteristics 23
4.3 Carrier-Gas Characteristics 39
References 41
5 Presentation of Effluent Data for Specific Industries . . 43
6 Stationary Combustion Processes 47
6.1 Introduction 47
6.2 Electric Utilities 47
6.3 Industrial Power Generation 73
6.4 Commercial, Institutional, and Residential Furnaces 76
References 78
7 Crushed Stone, Sand, and Gravel Industries 81
7.1 Introduction 81
7.2 Crushed Stone 81
7.3 Sand and Gravel 87
References 89
8 Operations Related to Agriculture 91
8.1 Introduction 91
8.2 Agricultural Field Burning 91
8.3 Grain Elevators 94
8.4 Alfalfa Dehydrating Mills 102
8.5 Cotton Gins 104
References m
v
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TABLE OF CONTENTS (Continued)
Chapter Page
9 Iron and Steel Industry 113
9.1 Introduction 113
9.2 Iron and Steel Manufacturing 113
9.3 Emission Rates from Iron and Steel Manufacture . . 113
9.4 Characteristics of Emissions from Iron and Steel
Manufacture 119
9.5 Control Techniques for the Iron and Steel Indus-ry 138
References 167
10 Cement Manufacture 171
10.1 Introduction 171
10.2 Cement Manufacturing Process 171
10.3 Emission Rates from Cement Manufacturing Plants . 173
10.4 Characteristics of Cement Plant Emissions .... 173
10.5 Control Practices and Equipment for Cement Plants 17B
References 187
11 Forest Products Industry ..... 189
11.1 Introduction 189
11.2 Forestry Operations 109
11.3 Sawmill Operations (Lumber Production) 193
11.4 Plywood, Particleboard, and Hardboard Plants . . 202
11.5 Pulp Industry 204
References 236
12 Lime Manufacture 239
12.1 Introduction 239
12.2 Line Manufacturing Process 239
12.3 Emission Sources and Rates 242
12.4 Characteristics of Effluents from Lime
Manufacture 243
12.5 Control Practices and Equipment for Lime
fltenufacture 243
References 255
13 Primary Nonferrous Metallurgy 257
13.1 Introduction 257
13.2 Primary Copper Smelting and Refining 257
13.3 Primary Lead Smelting and Refining 273
13.4 Primary Zinc Smelting 277
13.5 Primary Aluminum Production 281
References 301
vi
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TA3L5 OF C OK TENTS (Continued)
Chapter Page
14 Clay Products 303
14.1 Introduction 303
14.2 Manufacturing Processes 303
14.3 Emission Sources and Rates 306
14.4 Effluent Characteristics 310
14.5 Control Practices and Equipment . 310
References 312
15 Fertilizer Manufacture 313
15.1 Introduction 313
15.2 Phosphate Fertilizers 313
15.3 Ammonium Nitrate Fertilizer 325
15.4 Urea Fertilizer 329
15.5 Ammonium Sulfate 329
15.6 Characteristics of Effluents from Fertilizer
Manufacture 332
15.7 Control Practices and Equipment in Fertilizer
Manufacture 332
References 338
16 Asphalt 339
16.1 Introduction 339
16.2 Airblcwn Asphalt 339
16.3 Hot-Mix Asphalt Faving Plants 342
16.4 Asphalt Roofing Manufacture 352
References 359
17 Ferroalloy Manufacture 361
17.1 Introduction 361
17.2 Ferroalloy Production 361
17.3 Emission Sources and Rates 364
17.4 Effluent Characteristics 368
17.5 Control Practices 368
References 380
18 Iron Foundries 381
18.1 Introduction 381
18.2 Foundry Processes 381
18.3 Emission Rates from Iron Foundries ....... 381
18.4 Characteristics of Effluents from Iron Foundries 384
18.5 Control Practices and Equipment for Iron
Foundries 384
References 400
vii
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TABLE OF CONTENTS (Continued.)
Chapter Page
19 Secondary Nonferrous Metals Industry 401
19.1 Introduction 401
19.2 Secondary Copper Smelting and Refining 401
19.3 Secondary Lead Smelting and Refining 423
19.4 Secondary Zinc Smelting and Refining 428
19.5 Secondary Aluminum Smelting and Refining .... 434
References 441
20 Coal Preparation Plants 443
20.1 Introduction 443
20.2 Coal Cleaning Process 443
20.3 Emission Rates from Coal Preparation Plants . . 455
20.4 Characteristics of Coal-Preparation Plant
Emissions 457
20.5 Control Practices and Equipment for Coal-
Preparation Plants 457
References 462
21 Carbon Black 455
21.1 Introduction 465
21.2 Manufacturing Processes 465
£1.3 Emission Sources and Rates 470
21.4 Characteristics of Effluents from Carbon Black
Manufacture 471
21.5 Control Practices and Equipment 471
References 476
22 Petroleum Refining 477
22.1 Introduction 47 7
22.2 Emission Sources 477
22.3 Catalyst Regenerator Emission Rates 480
22.4 Effluent Characteristics 482
22.5 Control Practices and Equipment for FCC Units . 482
References 493
23 Acid Manufacture 495
23.1 Introduction 495
23.2 Sulfuric Acid Manufacture 496
23.3 Emission Rates 501
23.4 Effluent Characteristics 504
23.5 Control Practices and Equipment for Sulfuric
Acid Plants 504
23.6 Phosphoric Acid Manufacture 508
References 515
viii
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TABLE OF COMTENTS (Continued)
Chapter Page
24 Incineration 517
24.1 Introduction 517
24.2 Municipal Incineration 517
24.3 Commercial Incinerators 539
24.4 Apartment House Incinerators 540
References 545
Appendix A - Economic Considerations in Air Pollution Control . . 547
Appendix E - Minor Sources 603
ix
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TABLE OF CONTENTS (Continued)
List of Tables
Table Title Page
2-1 Major Industrial Sources of Particulate Pollutants .... 6
4-1 Triboelectric Series for Fabrics 35
4-2 Relations of Fabric Requirements to Dust Properties and
Dust in the Categories Listed 36
4-3 Rates of Rise and Total Wetting Times Measured at
Different Dust Samples 38
5-1 Coding Key for Tables of Effluent Characteristics .... 45
6-1 Particulate Emissions, Fuel Combustion in Stationary
Sources 52
6-2 Effluent Characteristics, Stationary Combustion Processes 53
6-3 Polynuclear Hydrocarbon Concentrations 57
6-4 Elemental Analyses of Total Particulates 58
6-5 Dust Collectors for Coal-Fired Heating and Power Plants . 60
6-6 Usual Expected Efficiency Ranges for Commonly Used
Control Equipment 61
6-7 Optimum Expected Performance of Various Types of Gas
Cleaning Systems for Stationary Combustion Sources ... 62
6-3 Air Cleaning Equipment Installed Cost Based on
1,000 m Unit (1968) 63
6-9 Precipitator Costs (1965 - 1969) 67
7-1 Particulate Emissions, Crushed Stone, Sand and Gravel . . 83
8-1 Particulate Emissions from Rye-Grass Burns 92
8-2 Particulate Emissions from Operations Related to
Agriculture 93
8-3 Effluent Characteristics - Operations Related to
Agriculture 97
8-4 Analysis of Airborne Dust Collected in Vicinity of
Railway Cars During Loading 99
8-5 Particulate and Product Analyses (Alfalfa Dehydrating
Mill) 99
8-6 Yields of Various Pollutants from Grasses Burned in
Laboratory Tower 100
8-7 Results of Summer 1967 Field Burns of Various Grasses . . 101
9-1 Potential Particulate Pollutant Emission Sources in Iron
and Steel Manufacturing 115
9-2 Particulate Emissions, Iron and Steel Industry 120
9-3 Effluent Characteristics - Iron and Steel Industry .... 122
9-4 Iron and Sinter Dust Resistivity 134
9-5 Representative Emission-Control Applications in the
Integrated Iron and Steel Industry 139
x
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TA.BLE OF CONTENTS (Continued)
List of Tables (Continued)
Table Title Page
9-6 Design and Operating Data for Sinter-Plant Fabric
Filters on Sinter Strand Discharge 150
9-7 Blast-Furnace Gas-Cleaning Results 152
9-8 Open-Hearth Stack Gas Data 157
9-9 Performance Tests of Electrostatic Precipitator on Open-
Hearth Gases 157
9-10 Scrubber-Pressure Drop vs. Cleaning Efficiency and Out-
let Dust Loading (Nonoxygen Periods) 159
9-11 Scrubber-Pressure Drop vs. Cleaning Efficiency and Out-
let Dust Loading (oxygen Periods) 159
9-12 Basic Oxygen Furnace Installations and Associate
Air-Pollution Control Equipment 161
9-13 Comparison of Equipment Requirements, Energy and Gas
Flow for BOF 162
9-14 Approximate Budge Sizing Chart ..... 165
10-1 Particulate Emissions, Cement Industry 177
10-2 Effluent Characteristics - Cement Manufacture 179
10-3 Ranges of Dust Emissions from Control Systems Serving
Dry- and Wet-Type Cement Kilns 185
11-1 Particulate Emissions, Forest Products Industry .... 192
11-2 Characteristics of Effluents from Forest Products
Industry 194
11-3 Atmospheric Emission Sources in a Kraft Mill 206
11-4 Atmospheric Emissions from Kraft Pulp Mills 207
11-5 Water Usage for Secondary Scrubbing Installations . . . 209
11-6 Average Performance Data for Full-Scale TE Washer . . . 211
11-7 Test Data, Lime Kiln Venturi Scrubber 212
11-8 Ammonia-Base Liquor Burning 233
12-1 Particulate Emissions, Lime Manufacture 244
12-2 Effluent Characteristics - Lime Manufacture 245
12-3 Secondary Collection of Rotary Kiln Lime Dust 249
12-4 Estimate of Rotary Kiln Control Costs 250
12-5 Hydrator 251
12-6 Stone Dryers 252
13-1 Particulate Bnissions, Primary Nonferrous Metals
Industries 262
13-2 Effluent Characteristics, Primary Nonferrous Metals
Industries 263
13-3 Compounds Found in Aluminum Reduction Cell Exhaust
Streams 269
13-4 Atmospheric Pollutants from Secondary Sources in
Aluminum Plants 270
xi
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CABLE OF CONTENTS (Continued)
List of Tables (Continued)
Table Title Page
13-5 Operation Data for Dust Collectors Applied to Primary
Copper Smelting and Refining 272
13-6 Lead Smelter Control Equipment 276
13-7 Typical Zinc Roasting Operations 279
13-8 Cominco Fume and Dust Recovery Plants 283
13-9 Costs for Cleaning Metallurgical Gases (1957 Data) . . . 285
13-10 Collection Efficiencies for the Floating Bed Scrubber
Used on Horizontal Stud Soderberg Cell 294
13-11 Current and Newest Air Pollution Controls for Primary
Aluminum Potline Air Pollution Controls 297
14-1 Particulate Emissions, Clay Products 309
14-2 Effluent Characteristics - Manufacture of Clay Products 311
15-1 Particulate Emissions, Phosphate Rock and Manufacture
of Fertilizer 326
15-2 Effluent Characteristic - Fertilizer Manufacture .... 333
15-3 Summary of Emission Data on Performance of Control
Equipment in Wet-Process Fnosphoric Acid Plants . . . 335
15-4 Summary of Emission Data on Performance of Control
Equipment in Wet-Process Phosphoric Acid Plants . . . 336
16-1 Particulate Emissions - Asphalt 341
16-2 Effluent Characteristics - Asphalt 346
16-3 Dust and Fume Discharge from Asphalt Batch Plants . . . 347
16-4 Findings of Florida Asphalt Plant Testing Program . . . 349
16-5 Comparative Costs of Dust Collectors 351
16-6 Emissions from a Water Scrubber and Low-Voltage Two-
Stage Electrical Precipitator Venting an Asphalt
Saturator 357
16-7 Emissions from a Water Scrubber Venting an Asphalt
Saturator 357
17-1 Particulate Emissions, Production of Ferroalloys .... 369
17-2 Effluent Characteristics - Ferroalloy Manufacture . . . 370
17-3 Ferroalloy Fume Resistivity 372
17-4 Typical Ferroalloy Furnace Fume Characterizations . . . 373
17-5 Approximate Furnace Gas Generation 375
17-6 Comparison of Furnace Gas Volumes 375
17-7 Estimated Cost of Furnace Controls 375
17-8 Examples of Furnace Wet Scrubbers 377
18-1 Particulate Emissions, Iron Foundries 383
18-2 Effluent Characteristics - Iron Foundries 385
18-3 Iron Foundry Dust Collector Efficiency 390
xii
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TABLE OF CONTENTS (Continued)
List of Tables (Continued)
Table Title Page
18-4 Usual Collector Selections for Foundry Operations .... 391
18-5 Efficiency Tests of Dry Multiple Cyclones for Five
Different Installations 392
18-6 Cost Comparison for Various Dust Collectors for Cleaning
Waste Gases of a Hot-Blast Cupola 393
18-7 Approximate Cost of Control Equipment 393
18-8 Collector Characteristics for 15 Tons/Hr Cold-Blast
Cupola Operated on Alternate Days 394
18-9 Comparison of Cupola Dust Control Systems 395
18-10 Cupola Plants with Electro-Precipitators 397
18-11 Cupola Dust Removal Installations with Fabric Filter . . 398
19-1 Particulate Emissions, Secondary Nonferrous Metals . . . 406
19-2 Effluent Characteristics - Secondary Konferrous Metals . 408
19-3 Electrical Resistivity of Collected Bronze Fume 411
19-4 Brass-Melting Furnace and Baghouse Collector Data .... 416
19-5 Baghouse Information Summary - Brass and Bronze Ingot
Institute 417
19-6 Annual Cost of Air Pollution Control Systems 419
19-7 Installed Costs of Gas-Cleaning Equipment Systems, by
Type of Smelter 420
19-8 Installed Costs of Gas-Cleaning Equipment Systems, by
Type of Equipment 421
19-9 Annual Operating Costs of Gas-Cleaning Equipment Systems,
by Type of Smelter 422
19-10 Dust and Fume Emissions from a Secondary Lead-Smelting
Furnace 427
19-11 Dust and Fume Emissions and from an Aluminum- and a
Zinc-Sweating Furnace Controlled by a Baghouse .... 435
19-12 Dust and Fume Emissions from an Aluminum-Sweating Furnace
Controlled by an Afterburner and Baghouse 439
19-13 Scrubber Collection Efficiency for Emissions from
Chlorinating Aluminum 440
20-1 Thermally Dried Coal by Types of Drying Equipment,
1958-1964 454
20-2 Effluent Characteristics - Coal Preparation Plants . . . 458
21-1 Particulate Emissions from the Manufacture of Carbon
Black 472
21-2 Effluent Characteristics - Carbon 31ack 473
xiii
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TABLE OF CONTENTS (Continued)
List of Tables (Concluded)
Table Title Page
22-1 Potential Sources of Specific Emissions from Oil
Refineries 478
22-2 Effluent Characteristics - Petroleum Refining 403
22-3 Typical Plant Operating Conditions 485
22-4 A Summary of Performance Lata of Precipitators in Fluid
Catalytic Cracking Application (1951-1962) 492
23-1 Particulate Emissions, Mineral Acids 503
23-2 Effluent Characteristics - Acid Manufacture 505
23-3 Feasible Systems for Acid Mist Control 506
23-4 Operating Characteristics of Phosphoric Acid Mist
Electrostatic Precipitators 514
24-1 Estimated Municipal Incinerator Emissions 521
24-2 Effluent Characteristics - Incineration 523
24-3 Air Pollution Control System Average Control Efficiency 524
24-4 Distribution and Typical Economics Among Incinerators
and APC Concepts 525
24-5 Maximum Demonstrated Collection Efficiency of Incinera-
tor Control Equipment 526
24-6 Relative In-Plant Space Requirements for Average Air
Pollution Control Systems 535
24-7 Estimated Capital and Operating Costs for Two Control
Systems for an 800 Ton/Day Incinerator 535
24-8 Refractory Furnace 536
24-9 Water-Cooled Furnace 535
24-10 Electrostatic Precipitators Installed on Municipal
Incinerators in North America 538
24-11 Basic Design Elements of European Electrostatic
Precipitators 538
24-12 Peabody Scrubber Performance on Flue-Fed Apartment
Incinerators 543
24-13 Performance and Cost of Devices Installed on Apartment
Incinerator 544
xiv
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TABLE OF CONTENTS (Continued)
List of Figures
Figure Title Page
3-1 Efficiency Curves for Various Types of Dust Collecting
Equipment 14
4-1 Average Size Distributions of Outlet Fume - Kraft Mill
Recovery Furnace 26
4-2 Effect of Humidity on Particle Resistivity 31
4-3 Conditioning of a Weak Acidic Dust by Strong 3ases ... 33
4-4 Laboratory Conditioning Tests, Sulfuric Acid Fume with
Fly Ash 33
6-1 Nomograph for Estimating Particulate Emissions From Coal
Combustion (Without Air Pollution Control Equipment) . 50
6-2 Precipitator Purchase Cost (FOB) as a Function of Gas
Volume Treated (Period 1965 - 1969) 65
6-3 Precipitator Erected Cost as a Function of Gas Volume
Treated (Period 1965 - 1969) 66
6-4 Plant Fly-Ash Disposal Investment 68
6-5 Plant Fly-Ash Disposal Cost for 1967 69
6-6 Effect of Sulfur Content of Coal on Collecting Area
Required in Electrostatic Precipitator 70
6-7 Multiclone Collection Efficiency - Fly Ash 71
7-1 Particulate Size from Rock Processing Operations .... 85
8-1 Alfalfa Dehydrating Process Flow Diagram 103
8-2 Flow Diagram of U. S. Department of Agriculture Cotton
Gin, Stoneville, Mississippi . . . 105
8-3 In-Line Air Filter - Cotton Gin 109
9-1 A Composite Flow Diagram for a Steel Plant 114
9-2 Particle Size Distribution by Weight of Sintering
Machine Dust 127
9-3 Resistivity of Different Dusts in the Same Atmosphere
vs. Temperature 128
9-4 Resistivity in Different Atmospheres vs. Temperature . . 128
9-5 Electrical Resistivity of Sintering Machine Dust .... 129
9-6 Resistivity of Open-Hearth Furnace Fume Under Varying
Conditions of Temperature and Moisture in Gas 130
9-7 Apparent Resistivity of Fume from Open-Keaxth Furnace . . 130
9-8 Apparent Resistivity of Fume from Open-Hearth Furnace . . 131
9-9 Apparent Resistivities of Metallurgical Dusts 131
9-10 Electrical Resistivity of Red Oxide Fume from Various
Oxygen-Blown Steelmaking Processes 132
9-11 Resistivity vs. Gas Temperature for B0F Furnace Dust . ¦ 133
xv
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TABLE OF CONTENTS (Continued)
List of Figures (Continued)
Figure Title P3.ge
9-12 Estimated Installed Cost (1968) of Air-Pollution-Control
Equipment as Related to Different Steel-Making
Processes 140
9-13 Estimated Annual Operating Costs for Air-Pollution-
Control Equipment for Steel-Making Process 141
9-14 Estimated Annual Operating Costs Pius Capital Charges
and Depreciation for Air-Pollution-Control Equipment
for Steel-Making Processes 142
9-15 Estimated Installed Capital Costs of Air-Pollution-
Control Equipment Installed on Electric-Arc Steel-
Making Furnaces 143
9-16 Estimated Installed Capital Costs of Air-Pollution-
Control Equipment Installed on Open-Hearth Furnaces . . 144
9-17 Estimated Installed Capital Costs of Air-Pollution-
Control Equipment Used in Sinter and Pellet Plants . . 145
9-18 Estimated Annual Operating Costs for Air-Pollution
Control Equipment Used in Sir.ter and Pellet Plants
(Depreciation and Capital Charges are Not Included . . 146
9-19 Estimated Capital and Annual Operating Costs for Air-
Pcllution-Control Equipment Used on Scarfing Machines
(Depreciation and Capital Charges are Not Included in
the Operating Costs) 147
9-20 Range of Estimated Operating Costs for Air-Pollution-
Control Equipment/Net Ton of Raw Steel—Open-Hearth
Furnaces, BOFS, and Electric Furnaces (Two-Furnace
Operations) 148
9-21 Effect of Water Rate on Output Dust Loading for a
Venturi Scrubber Handling Blast-Furnace Gas 153
9-22 Effectiveness of Gas Cleaning by a Fixed-Orifice Scrubber
and a Variable-Orifice Scrubber When Gas-Flow Rate is
Varied 154
9-23 Operating Characteristics of a Blast-Furnace Venturi
Scrubber 154
9-24 Relationship of Electrostatic Precipitator Collecting
Surface to Collection Efficiency for Open-Hearth
Emissions (315,000 acfm) 156
9-25 Relationship Between Clean-Gas Dust Loading and Pressure
Drop for a Wet Scrubber on an Open-Hearth Furnace
(Oxygen Lancing Used During the Refining Period) . . . 158
xv i
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TA.BLE OF CONTENTS (Continued)
List of Figures (Continued.)
Title Page
9-26 Typical Side-Draft and Roof-Tap-Hood Systems for
Electric-Arc Furnaces 166
10-1 Sources of Dust Emissions, Cement Plants 172
10-2 Typical Particle Size Range of Cement Kiln Lust 181
10-3 Resistivity of Cement Kiln Dust Under Varying Conditions
of Temperature and Moisture in Gas 192
10-4 Dependence of Specific Electrical Dust Resistance on
Gas Temperature for Various Dusts 182
10-5 Typical Laboratory and Field Resistivities of Cement
Kiln Dusts 183
10-6 Laboratory Resistivities of One Cement Kiln Dust Sample
For Various Gas Moisture Contents 184
11-1 Composite Flow Diagram - Forest Products Industry .... 190
11-2 Electrical Resistivity of Salt Cake 200
11-3 Electrical Resistivity of Sodium Sulfate as a Function
of Moisture in Gas at 300 °F 201
11-4 Particle-Size Efficiency Curve TE Washer-Elack Liquor
Recovery Furnace 210
11-5 Control Method Costs for 99.9$ Efficiency Electrostatic
Precipitator Replacing an Existing Precipitator -
Recovery Boiler 218
11-6 Control Method Costs for 99.5$ Efficiency Electrostatic
Precipitator Replacing an Existing Precipitator -
Recovery Boiler 219
11-7 Control Method Costs for 99.0$ Efficiency Electrostatic
Precipitator Replacing an Existing Precipitator -
Recovery Boiler 220
11-8 Control Method Costs for Packed Tower Added to Smelt-
Dissolving Tank Vent 223
11-9 Control Method Costs for Orifice Scrutber Added to Smelt-
Dissolving Tank Vent 224
11-10 Control Method Costs of Mesh Pad Added to Smelt-
Dissolving Tank Vent 225
11-11 Control Method Costs for Fresh Water Venturi Added to
Lime Kiln - 99.0$ Lime Solids Collection 228
11-12 Control Method Costs for Fresh Water Venturi Added to
Lime Kiln - 99.9$ Lime Solids Collection 229
11-13 Control Method Costs for 99.0$ Efficiency Electrostatic
Precipitator Added to an Existing 90$ Efficiency Dust
Collector Coal-Fired Power Boiler 231
xvii
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TA3L3 OF COX TEN IS (Continued)
List of Figures (Continued)
Figure Title Page
11-14 Control Method Costs for 90,0$ Efficiency Electrostatic
Precipitator Added to an Existing 90$ Efficiency
Dust Collector Coal-Fired Power 3ciier 232
11-15 Sulfite Pulping Process, Ammonia-Base Recovery 234
11-16 Sulfite Pulping Process, Magnesia-3s.se Recovery 235
12-1 Simplified Flowsheet for Liaie and Limestone Products . . 240
12-2 Flow Diagram of a Modern Hydrated Lime Plant from Ground
Quick Lime Feed Silos Through to Bulk Hydrate Storage
Silos and Bagging Department 241
12-3 Dependence of Specific Electrical Dust Resistance on
Gas Temperature for Lime Shaft Kiln Dust 247
13-1 Copper Smelting - Simplified Flow Diagram 258
13-2 Typical Resistivity Graph of Lead Fume. 266
13-3 Apparent Resistivity of Lead Fume from Sintering Plant . 266
13-4 Resistivity of Lead Dross Fume Under Varying Conditions
of Temperature and Moisture in Gas 267
13-5 Apparent Resistivity of Lead Fume from Lead Blast Furnace 267
13-5 Apparent Resistivity of Lead Fume from Slag Treatment
Plant 263
13-7 Typical Flowsheet of Pyrometallurgical Lead Smelting . . 274
13-8 Zinc Smelting Flow Diagram 273
13-9 Dust Composition vs. Roastir.g Temperature in Zinc
Processing 282
13-10 Diagram of the Bayer Process 2S~
13-11 . Aluminum Cell (Prebaked Anode Type) 288
13-12 Prebake 299
13-13 Horizontal Soderberg 289
13-14 Vertical Soderberg 289
13-15 Schematic Drawing of Cross-Sectional View of the New
Sieve-Plate Gas Scrubber 293
13-16 Purification Installation for Cell Gases 293
13-17 The Floating Bed Scrubber Developed for Horizontal Stud
Soderberg Cell Exhausts 295
13-18 Roof Scrubbers 298
14-1 Ceramic Clay Manufacturing Processes 304
14-2 Refractories Manufacture Flow Diagram 307
15-1 Flow Diagram of Phosphate Rock Storage and Grinding
Facilities, Noting Potential Air Pollution Sources . . 314
15-2 Flow Diagram Illustrating Wet-Process Phosphoric Acid
Plant 316
xrviii
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TABLE OF CONTENTS (Continued)
List of Figures (Continued)
Figure Title Page
15-3 Flow Diagram of Normal Superphosphate Plant, Noting
Potential Air Pollution arid Sources 319
15-4 Flow Diagram for Production of Run-of-Pile and Granular
Triple Superphosphate, Noting Potential Air Pollution
Sources 321
15-5 Flow Diagram of Diammonium Phosphate Plant, Noting
Potential Air Pollution Sources 323
15-6 Flow Diagram of the Slurry Granulation Process in the
Manufacture of Fertilizer, Noting Potential Air
Pollution Sources 324
15-7 Flow Diagram of the Process for Manufacture of Ammonium
Nitrate, Noting Potential Air Pollution Souces .... 327
15-8 Sketch of Manufacturing Process for Crystalline Urea
Product 330
15-9 Sketch of Manufacturing Process for Prilled or Shotted
Urea Product 331
16-1 Asphalt Batch Mix Plant 343
16-2 Asphalt Continuous Mix Plant: 343
16-3 Test Data on Air Pollution Control Equipment Serving Two
Hot-Mix Asphalt Paving Plants 348
16-4 Effect of Drum Gas Velocity on Dust Emission 350
16-5 Effect of Scrubber Water-Gas Ratio on Stack Emissions
at Average Aggregate Fired Rate in the Dryer Feed . . . 353
16-6 Schematic Drawing of an Asphalt Roofing Felt Saturator . •355
18-1 Particle Size Ranges for Dusts from Cold- and Hot-Blast
Cupolas 387
18-2 Apparent Resistivity of Dust and Fume in Plant A .... 388
18-3 Apparent Resistivity of Dust and Fume in Plant B . . . . 388
19-1 Apparent Resistivity of Zinc Fume from Slag Fuming Plant 412
19-2 Apparent Resistivity of Zinc Fume from Melting Plant . . 412
19-3 Diagram Showing One Bank of a Belgian Retort Furnace . . 430
19-4 Diagram of a Distillation-Type Retort Furnace 432
19-5 Diagram of a Muffle Furnace and Condenser 433
20-1 Pressure-Type Fluidized-Bed Thermal Coal Dryer, Showing
Component Parts and Flow of Coal and Drying Gases . . . 450
20-2 Exhausting-Type Fluidized-Bed Thermal Coal Dryer, Showing
Component Parts and Flow of Coal and Drying Gases . . . 451
20-3 Schematic Drawing Showing Component Parts of Flash-Drying
Unit 452
20-4 Schematic Sketch of Screen-Type, Thermal Coal-Drying Unit 453
xix
-------
HA.BLE OF CONTENTS (Continued)
List of Figures (Continued)
Figure Title Page
20-5 Typical Particle-Size-Analysis Curves for Material Going
to Cyclones (Coal Thermal Dryers) 459
20-6 Particle Size Distribution of Effluent 461
20-7 Venturi Scrubber Performance on Coal Dryer Effluent . . . 461
21-1 Flow Diagram of Oil-Furnace Process 467
21-2 Flow Diagram of Gas-Furnace Porcess 467
21-3 Flow Diagram of Channel Process 468
21-4 Flow Diagram of Thermal Process 469
22-1 Flow Diagram of Fluid Cracking Unit 481
22-2 Electrical Resistivity of Dust from Catalytic Cracking
Unit 484
22-3 Schematic Flow for Precipitator Installed After Power-
Recovery Turbine 486
22-4 Schematic Flow for Precipitator Installed After CO Boiler 487
22-5 Relationship Between Quantity of Catalyst Carryover and
Particle Size 488
22-6 Calculated Stack Losses as a Function of Particle-Size
Distribution of Cyclone Carryover 489
22-7 Particle-Size Stack Loss Distribution Compared to Cyclone
Carryover Particle Size 490
23-1 Simplified Flow Diagram of Typical Lead-Chamber Process
for Sulfuric Acid Manufacture (Based on Use of Elemental
Sulfur as the Raw Material) 497
23-2 Sulfuric Acid Manufacture by the Contact Process .... 498
23-3 Sulfuric Acid Concentrator, Drum Type 500
23-4 Flow Diagram for Typical Thermal-Process Phosphoric Acid
Plant 509
23-5 Effect of Gas Velocity on Phosphoric Acid Recovery in
Pilot-Plant Packed Tower 513
23-6 Collection Efficiency of Venturi Scrubber as a Function
of Particle Size for Phosphoric Acid Mist 513
24-1 Effect of Underfire Air Rate on Furnace Emission .... 520
24-2 Electrical Resistivity of the < 74 U Fraction of
Particulate Emission from the Furnace at 6% Water Vapor 527
24-3 Air Pollution Control Systems Total Installed Costs . . . 528
24-4 Air pollution Control Systems Annual Operating Costs . . 529
24-5 Air Pollution Control Systems Annual Operating Costs . . 530
24-6 Air Pollution Control Systems Annual Operating Costs . . 531
xx
-------
TABLE OF CONTENTS (Concluded)
List of Figures (Concluded)
Fig-ire Title Page
24-7 Total Annual Operating Cost vs. Particulate Removal
Efficiency, 150 Tons/Day Plant; 1, 2, and 3 Shift
Operation ..... 533
24-8 Total Annual Operating Cost vs. Particulate Removal
Efficiency, 150 and 300 Tons/Day Plant; 2 Shift
Operation 534
24-9 Capital Cost of Incinerators with Varying Degrees of
Air Pollution Control Equipment 541
xxi
-------
CHAPTER 1
INTRODUCTION
This handbook is presented as a part of the documentation for a
NAPCA sponsored study, conducted at Midwest Research Institute, of particu-
late air pollution from stationary sources. The objective of the study
was to identify, characterize, and quantify the particulate air pollution
problem in the United States. This document delineates the kind and number
of stationary particulate sources, the chemical and physical characteris-
tics of both the particulates and carrier gas emitted by specific sources,
and the status of current control practices. Details of the methodology
employed to obtain the data reported in this handbook are presented in the
final report for the project.
The first three chapters present general background information
pertaining to source emission factors and emission rates, effluent char-
acteristics, and control technology. The chapter on emission factors and
rates (Chapter 2) outlines the methods used to calculate the total tonnage
emitted by individual sources, and presents a ranking, on a tonnage emitted
basis, of industrial sources of particulate pollutants. Chapter 3 high-
lights the general aspects of control equipment available for use on a
source of particulate pollution. Distinguishing characteristics and general
areas of application and ranges of performance of control devices are sum-
marized in this chapter. Chapter 4 discusses some of the mere important
chemical and physical properties of particulates and carrier gas emitted by
industrial sources. The discussion is focused primarily on the relation-
ship of the effluent properties to control device selection and/or design.
Chapter 5 presents a coding key for the tables of effluent characteristics
presented in Chapters 6-24.
The remaining chapters (Chapters 6 - 24) present discussions of
the major industrial sources of particulate pollutants. The industrial
categories were selected on the basis of the ranking of tonnage emitted
outlined in Chapter 2. The chapters on industrial sources delineate the
production process, emission sources, emission rates, chemical and physical
properties of the effluents, and control practices and equipment for each
industrial category. Appendix A presents general cost information for con-
trol equipment. Miscellaneous emission data for minor sources are summar-
ized in Appendix B.
1
-------
This handbook constitutes a reference source for available infor-
mation on the distinguishing features of the various particulate pollution
sources and should be of value to air pollution regulatory agencies, con-
trol equipment manufacturers, and industrial concerns.
2
-------
CHAPTER 2
EMISSION FACTORS AND HATES
2.1 INTRODUCTION
To assess the relative contributions of stationary sources of
particulate air pollution, the major types and quantities of particulate
pollutants emitted, must be determined. Methods based on source emission
factors are generally used to calculate quantities of particulates emitted
for individual sources. Material balances and outlet grain loadings can
also be used for these calculations.
The emission factor for stationary sources is a statistical aver-
age of the rate at which pollutants are emitted from the processing or burn-
ing of a giver, quantity cf material. Ideally, emission factors should be
related to aspects of system design, operating practices, and material
processed to permit a definitive statement as to the total emissions char-
acterizing a given source or plant producing a specified product. Unfor-
tunately, the numerous and expensive stack testing studies needed to com-
pletely characterize a source have not generally been performed. Recourse
must be made to existing data, and general comments presented on the prob-
able influence of variables on emission factors. In some cases, especially
industrial sources, "he emission factor may be based upon tests conducted
on only one installation or a few installations.
The source emission factors used ir. this handbook were compiled
from an extensive literature survey and stack sampling data provided by air
pollution control agencies and individual industrial companies. In most
cases, a single number is presented for the emission factor for a specific
source. These source emission factors are, in our judgment, the most accu-
rate currently available. Details of the analysis of all available data for
each specific source are presented in the final report for this project.i/
The industrial categories discussed in Chapters 6-24 were chosen
from a ranking of sources based on the total tonnage of particulates emit-
ted/year. The ranking of sources on the basis of tonnage emitted and its
development are discussed in the following section.
3
-------
2.2 EMISSION KA.3S OF INDUSTRIAL SOURCES
Important particulate pollutant sources based on the total tonnage
emitted/year are presented in this section. The ranking was obtained by
first listing possible sources and then investigating in detail a large
enough segment to account for more than 99$ of the total emissions on a
mass basis.
Several different methods were used to calculate the total tonnage
emitted by individual sources. These methods included the use of emission
factors (both controlled and uncontrolled), material balances, and outlet
grain loadings. The primary method used for establishing the tonnage
emitted by an industry utilized uncontrolled emission factors. Total ton-
nage emitted by a given source was determined from four quantities:
(l) an emission factor for the uncontrolled source; (2) the total tonnage
processed/year by the source; (3) the efficiency of control equipment used:
and (4) the percentage of production capacity equipped with control device;
The mathematical equation for the calculation is:
E = (p)(ef)U-Cc.Ct) (1)
2,000
where E = total particulate emissions for a source, tons/year
P = total production for the industry, tons/year
6f = emission factor for uncontrolled source, pounds/ton
Cc = average efficiency of control equipment used in the industry
for the specific source
= amount of application of control in the industry (on a produc
tion capacity basis) for the specific source
CcCt = net control
Production figures were obtained primarily from government statis-
tics. Efficiency of control equipment was determined from literature
sources and information obtained from discussions with industrial contacts
The extent of application of control equipment in a given industry was
found to be, in most cases, unobtainable from the open literature. There •
some information as to the number of plants that have control equipment, b'
no information as to the production capacity of these plants or to the pla:
4
-------
'hat do noz have control equipment. Industry surveys were used to secure
information on extent of control. Details of these surveys and the emission
calculations are given in Reference 1.
Table 2-1 presents a ranking of important stationary industrial
sources of particulate pollutants. The stationary sources represented in
Table 2-1 were ranked by calculating the emissions from the primary pieces
of processing equipment such as kilns, furnaces, reactors, and dryers. In
several cases, we have included emissions for "secondary sources" which in-
clude crushing operations, materials handling, stockpiles, etc. The cal-
culations involving these secondary sources are in general much less
accurate than those involving the primary processing equipment because data
on secondary sources are meager or nonexistent. The emission quantities
listed for these secondary sources are at best order of magnitude calcula-
tions, and it is possible that secondary sources may emit as much or more
particulate matter than the primary sources. Total emissions for an indus-
try were obtained as a sum of the emissions from primary and secondary
sources.
The leading sources are stationary combustion processes, crushed
stone, agriculture and related operations, iron and steel, and cement.
Emissions from residential and commercial combustion sources, field burning,
ar.d slash burning are not included in the totals shown in Table 2-1 for the
stationary combustion processes, agricultural operations, and forest prod-
ucts categories. However, emissions from these processes are included in
the individual chapters discussing these industries.
The reliability of the emission quantities in Table 2-1 was as-
sessed by evaluating the reliability of each factor in Equation (l). The
quantity of data available, the spread of the data, and the source of the
data were considered in the evaluation. A reliability factor, ranging from
1 to 5 with 1 being the most reliable, was assigned to each factor. A
composite rating, shown in the last column of Table 2-1, was then determined
by averaging the ratings of the individual terms. In those cases where the
emissions were calculated by a method other than Equation (l), a reliability
rating was assigned directly to the final emission quantity.
More detailed discussions of manufacturing processes, particulate
emission sources, particulate emission rates, effluent characteristics, and
control practices and equipment for each industry category are presented in
Chapters 6-24.
5
-------
TABLE 2-1
MAJOR INDUSTRIAL SOURCES OF PARTICULATE POLLUTAOTS
(Based on 1960 production data)
i>ource
1. Fuel Combustion
A. Coal
1. Electric Utility
a. Pulverized
b. Stoker
c. Cyclone
2. Industrial boilers
a. Pulverized
b. Stoker
c. Cyclone
B. Fuel Oil
1. Electric Utility
2. Industrial
a. Residual
b. Diotillate
C. Natural Gas & LFG
1. Electric Utility
2. Industrial
Annual
Tonnage
V
250,400,000 tons of coal
9,900,000 tons ol' coul
20,700,000 tons of coul
20,000,000 tons of ccal
70,000,000 tons of coul
10,000,000 tons ol* coal
7.18 x 109 gal.
7.51 x 109 gal.
2.36 x 109 gal.
3.14 x 10® nil. scf
9.27 x 106 mil. scf
toils :;ioi
Factor
LI'/Tdii
'•f
El l'if iencyk./ Application^/
of Control ol Control
Ct
16A=1'J0!}/ lb/ ton of coal
13A=146 lb/ton of coal
3A-35 lb/ton of coul
1GA=1Y0£/ lb/ton of coul
13A-133 lb/ton of coal
3A^31 lb/ton of coal
0.010 lb/gal
0.023 lb/gal
0.01b lb/gal
15 lb/mil. scf
10 lb/mil. scf
0.92
0.00
0.91
0.97
0.07
0.71
HetS/
Control
C -cf
0.09
0. 70
0.64
Total from Electric Utility Coal
0.05 0.95 0.01
0.05 0. 62 0.52
0.02 0.91 0.75
Total from Industrial Coal
0 0
0 0
Total from Fuel Oil
Bni:,. ion^
Ton::/Yr Reliaoi lity
E Rating!/
0 0 0
0 0 0
Total from Natural Gas & LPG
2,710,000
217,000
182,000
3,109,000
322,000
2,234,000
39,000
2,595,000
36,000
87,000
18,000
141,000
24,000
84,000
100,000
Total from Utility and. Industrial Fuel Combustion
5,953,000
2. Crushed Stone, Sand & Gravel
A. Crushed Stone 601,000,000
B. Sand & Gravel 910,000,000
17
0.1
0.00
0.25
0.20
0
Total from Crushed Stone, Sand & Gravel
4,554,000
46,000
4,600,000
Operations Related, to
Agriculture
A. Grain Elevators
B. Cotton Gins
C. Feed Mills
1. Alfalfa Mills
2. Mills Other Than
Alfalfa
177,000,000 tons tfrain handled
11,000,000 bules
1,600,000 tons dry meal
0,364,000 tons
12 lb/bale
50 lb/ton dry meal
of production
0. 70
0.00
0.05
0.40
0.40
0.50
0.20
0.32
0.05 0.50 0.42
Total from Listed Agricultural Operations
1,700,000*
4b,000
23,000
49,000
1,017,000
-------
Source
Annua]
Tonnage
P
Iron and Steel
A. Ore Crushinc
B. Materials Handling
C. Pellet Plants
D. Sinter Plants
1. Sintering Process
2. Crashing, Screening, Etc.
E. Coke Manufacture
1. Beehive
2. By-Product
3. Pushing & Quenching
F. Blast Furnace
G. Steel Fornaces
1. Open Hearth
2. Basic Oxygen
3. Electric Arc
H' Scarfing
82,000,000 tons of ore
131,000,000 tons of steel
50,000,000 tons of pellets
51,000,000 tons of sinter
1,300,000 tons of coal
90,000,000 tons of coal
91,300,000 tons of coal
80,600,000 tons of iron
65,000,COO tons of steel
40,000,000 tons of steel
16,800,000 tons of steel
131,000,000 tons of steel
Cement
A. Wet Process
1. Kilns
2. Grinders, Dryers, etc.
B. Dry Process
1. Kilns
2. Grinders, Dryers, etc.
43,600,000 tons of cement
31,000,000 tons of cement
Forest Products
A. Wigwam Burners
B. Pulp Mills
1. Kraft Process
a. Recovery Furnace
b. Line Kilns
c. Dissolving Tanks
2. Sulfite Process
a. Recovery Furnace
3. NSSC Process
a. Recovery Furnace
b. Fluid-Bed Reactor
4. Bark Boilers
C. Particleboard, etc.
27,500,000 tons of waste
24,300,000 tons of pulp
2,500,000 tons of pulp
833,000 tons of pulp
3,500,000 tons of pulp
1,167,000 tons of pulp
525,000 tons of pulp
Lime
A. Crushing, Screening
B. Rotary Kilns
C. Vertical Kilns
D. Materials Handling
28,000,000 tons of rock
16,200,000 tons of lime
1,800,000 tons of lime
18,000,000 tons of lime
Factor Efficiency^ Application^/ Net^/ ErJ.3sions
Lb/Ton of Control of Control Control Tona/Yr Reliability
_ /-• /i r> ' r>. /
c»f Cc Ct Cc*Ct S Rating.
? lb/ton of ore
0
0
0
8£,000
4
.10 lb/ton of steel
0.90
0.35
0.32
446,000
4
—
—
—
—
80,000*
4
20 lb/ton of sinter
0.90
1.0
0.90
51,000
2
22 lb/ton of sinter
0.90
1-0
0.90
56,000
c
200 lb/ton of coal
0
0
0
130,000
2
2 lb/ton of coal
0
0
0
90,000
2
0.46 lb/ton of coal
—
--
--
21,00")
3
130 lb/ton of iron
0.99
1.0
0.99
58,000
2
17 lb/ton of steel
0.97
0.41
0.40
337,000
2
40 lb/ton of steel
0.99
1.0
0.99
10,000
2
10 lb/ton of steel
0.99
0.79
0.78
18,000
2
3 lb/ton of steel
0.90
0.75
0.68
63,000
3
Total
from Iron and Steel
1,442,000
167 lb/ton of cement
0.94
0.94
0.88
435,000
1
25 lb/ton of cement
0.94
0.94
0.88
65,000
3
167 lb/ton of cement
0.94
0.94
0.88
310,000
1
67 lb/ton of cement
0.94
0.94
0.88
124,000
3
Total
from Cement
934,000
10 lb/ton of waste
0
0
0
132,000
2
150 lb/ton of pulp
0.92
0.99
0.91
164,000
2
45 lb/ton of pulp
0.95
0.99
0.94
33,000
2
5 lb/ton of pulp
0.90
0.33
0.30
42,000
3
268 lb/ton of pulp
0.92
0.99
0.91
10,000
3
24 lb/ton of pulp
0.92
0.99
0.91
1,000
3
533 lb/ton of pulp
0.70
o
o
0.70
42,000
3
—
—
--
—
82,000*
3
--
—
--
—
74,000*
4
Total
from Forest Products
580,000
24 lb/ton of rock
0.80
0.25
0.20
264,000
3
180 lb/ton of lime
0.93
0.87
0.81
2^4,000
2
7 lb/ton of lime
0.97
0.40
0.3?
4,000
2
5 lb/ton of lime
0.95
0.80
0.76
11,000
3
Total from Lime
573,000
-------
Source
Annual
Tonnage
V
Primary Nonferrous Metals
A. Aluminun
1. Grinding of Bauxite
2. Calcining of Hydroxide
3. Reduction Cells
a. H. S. SoderberR
b. V. S. Soderberg
c. Prebake
4. Materials Handling
B. Coppe r
1. Ore Crushing
2. Roasting
3. Reverb. Furnace
4. Converters
5. Materials Handling
C. Zinc
1. Ore Crushing
2. Roasting
a. Fluid-bed
b. Ropp, multi-hearth
3. Sintering
4. Distillation
5. Materials Handling
D. Lead
1. Ore Crushing
2. Sintering
3. Blast Furnace
4. Dross Reverb. Furnace
5. Materials Handling
13,000,000 tons of bauxite
5,040,000 tons of alumina
000,000 tons of aluminum
700,000 tons of aluminum
1,755,000 tons of aluminum
3,300,000 tons of aluminum
170,000,000 tons of ore
575,000 tons of copper
1,437,000 tons of copper
1,437,000 tons of copper
1,437,000 tons of copper
10,000,000 tons of ore
765,000 tons of zinc
153,000 tons of zinc
612,000 tons of zinc
612,000 tons of zinc
1,020,000 tons of zinc
4,500,000 tons of ore
467,000 tons of lead
467,000 tons of lead
467,000 tons of lead
467,000 tons of lead
TABLE 2-1 (Continued)
Rmicr.ion
Factor Kfficioncy^/ Applieation^/ Net£/ Emissions
Lb/Ton of Control of Control Control Tons/Yr Reliabiliy
Cc Ct Cc-Ct E Rating £/
6
lb/ton
of
bauxite
—
--
0.80
0,000
3
200
lb/ton
of
alum ina
—
—
0.90
50,000
3
144
lb/ton
of
aluminum
0.40
1.0
0.40
35,000
2
04
lb/ton
of
aluninum
0.64
1.0
0.64
10,000
2
63
lb/ton
of
alixninum
0.64
1.0
0.64
20,000
2
10
lb/ tori
of
aluminum
0.90
0.35
0.32
11,000
4
Total
from
Primary Aluminum
142,000
2
lb/ton
of
ere
0
0
0
170,000
3
160
lb/ton
of
Cu
0.05
1.0
0.85
7,000
3
206
lb/ton
of
Cu
0.95
0.05
0.01
28,000
3
235
lb/ton
of
Cu
0.95
0.85
0.01
33,000
3
10
lb/ton
of
Cu
0.90
0.35
0.32
5,000
4
Total
from
Primary Copper
243,000
2
lb/ton
of
ore
0
0
0
18,000
3
2,000
lb/ton
of
Zn
0.90
1.0
0.98
15,000
3
333
lb/ton
of
Zn
0.85
1.0
0.85
4,000
3
100
lb/ton
of
Zn
0.95
1.0
0.95
3,000
3
--
--
--
--
15,000*
4
7
lb/ton
of
Zn
0.90
0.35
0.32
2,000
4
Total from Primary Zinc 57,000
2 lb/ton of ore 0 0 0 4,000 3
520 lb/ton of lead 0.95 0.90 0.06 17,000 3
250 lb/ton of lead 0.05 0.90 0.03 10,000 3
20 lb/ton of lead — — 0.50 2,000 3
5 lb/ton of lead 0.90 0.35 0.32 ltQQQ 4
Total from Primary Lead 34,000
Total from Primary Nonferrous 476,000
-------
Source
Annual
Tonnage
P
9. Clay
A. Ceramic
1. Grinding
2. Drying
B. Refractories
1. Kiln-Fired
a. Calcining
b. Dryir^
c. Grinding
2. Castable
3. Magncsite
4. Jfortars
a. Grinding
b. Drying
5. Mixes
C. Heavy Clay Products
1. Grinding
2. Drying
4,722,000 tons
7,870,000 tons
680,000 tons
1,052,000 tons
3,440,000 tons
550,000 tons
120,000 tons
120,000 tons
120,000 tons
249,000 tons
4,740,000 tons
7,110,000 tons
10. Fertilizer and Phosphate Rock
A. Phosphate Rock 41,300,000 tons of rock
1. Drying
2. Grinding
3. Materials Handling
4. Calcining
8,260,000
tons
Fertilizers
1. AononiiUD Nitrate
2,800,000
tons of granules
2. Urea
1,000,000
tons of granules
3. Phosphates
a. Rock Pulverizing
17,000,000
tons of rock
b. Acid-Rock Reaction
4,370,000
tons of P2O5
c. Granulation and Drying,
etc.
18,100,000
tons of granules
d. Materials Handling
—
e. Bagging
9,000,000
tons of granules
4. AnmoniujQ Sulfate
2,700,000
tons of granules
11. Asphalt
A. Paving Material 251,000,000 tons of material
1. Dryers
2. Secondary Sources
B- Roofing Material 6,264,000 tons of asphalt.
1. Blowing
2. Saturator
fc.Hu:>:>ion
Factor
Lb/Ton
of
Efficiency^/ Application^/
of Control of Control
c, ct
NetSJ
Control
Cc-Ct
Bliss ions
Tons/Yr Rellabil
E Rating^
76 lb/ton
0.80
0.75
0.60
72,000
3
70 lb/ton
0.80
0.75
0.60
110,000
3
200 lb/ton
0.80
0.80
0.64
25,000
3
70 lb/ton
0.80
0.80
0.64
13,000
3
76 lb/ton
0.80
0.80
0.64
47,000
3
?25 lb/ton
0.90
0.85
0.77
14,000
3
?60 lb/ton
0.80
0.70
0.56
7,000
3
76 lb/ton
0.80
0.75
0.60
2,000
3
70 lb/ton
0.80
0.75
0.60
2,000
3
76 lb/ton
0.80
0.75
0.60
4,000
3
76 lb/ton
0.80
0.75
0.60
72,000
3
70 lb/ton
0.80
0.75
0.60
99,000
3
Total
from Clay
467,000
12 lb/ton
0.94
1.0
0.94
14,000
2
2 lb/ton
0.97
1.0
0.97
1,000
2
2 lb/ton
0.90
0.25
0.22
30,000
4
40 lb/ton
0.95
1.0
0.96
8,000
3
28,00O*
4
--
—
--
--
10,000*
4
6 lb/ton of rock
0.80
1.0
0.00
10,000
2
48 lb/ton of P?05
0.95
0.95
0.90
9,000
2
195 lb/ton
0.95
0.95
0.90
169,000
2
--
--
—
—
18,000*
4
--
—
--
—
4,000*
4
—
—
--
«
27,000*
4
Total
from Fertilizers and
Phosphate Bock
326,000
32 lb/ton of material
0.97
0.99
0.96
161,000
2
8 lb/ton of material
0.97
0.99
0.96
40,000
2
4 lb/ton of asphalt
—
0.50
3,000
4
—
—
--
—
14,000*
4
Total
from Asphalt
2.10,000
-------
Source
Amiuul
Tonnage
P
12. Ferroalloys
A. Blast Furnace
B. Electric Furnace
C. Materials Handling
591,000 tons of ferroalloy
2,119,000 tons of ferroalloy
2,710,000 tons of ferroalloy
13. Iron Foundries
A. Furnaces
B. Materials Handling
1. Coke, Limestone, etc.
2. Sand
18,000,000 tons of hot metal
10,500,000 tons of sand
H
O
Secondary Ronferrous Metals
A. Copper
1. Material Preparation
a. Wire Burning
b. Sweating Furnaces
c. Blast Furnaces
2. Smelting fie Refining
300,000 tons insulated wire
64,000 tons scrap
207,000 tons scrap
1,170,000 tons scrap
B. Aluminum
1. Sweating Furnaces
2. Refining Furnaces
3. Chlorine Fluxing
500,000 tons scrap
1,015,000 tons scrap
130,000 tons CI used
C. Lead
1. Pot Furnaces
2. Blast Furnaces
3. Reverb. F«irnaces
53,000 tons scrap
119,000 tons scrap
554,000 tons scrap
D. Zinc
1. Sweating Furnaces
a. Metallic Scrap
b. Residual Scrap
2. Distillation Furnace
52,000 tons of scrap
210,000 tons of scrap
233,000 tons Zn recovered
TABLK 2-1 (Continued)
Finicsion
Factor Efficiency!?/ Application^ Net—' F-Jroiscions
Lb/Ton of Control of Control Control Tons/Yr Reliaoility
ce Ct
-------
Annual
Tonruir.c
P
Bn ion
Far t or
IA./Ton
''r
El't'ic icnry_
ol' Control
C
Applicat lonii/
of Control
C.
Ilet£/
Control
c„-ct
Qnlsiiioric
Ton::/Yr
F
Reliability
Rating**/
li). Coal Cleaning
A. Thermal Dryers
16. Carbon Black
A. Channel Process
B. Furnace Process
1. Gas
2. Oil
73,000,000 tons
-------
REFERENCES
1. "Particulate Pollutant System Study, Vol. I, Mass Emissions," Midwest
Research Institute, NAPCA Contract No. CPA 22-6S-1C4, May 1971.
12
-------
CHAPTER 3
CONTROL EQUIPMENT
3.1 INTRODUCTION
Equipment, available for the control of particulate natter consists
of cyclones, wet scrubbers, electrostatic precipitators, and fabric filters.
Afterburners may also be used for removal of combustible gases and partic-
ulates. The chapters in this handbook discuss the application, advantages,
and disadvantages of these devices in each cf the major industrial cate-
gories of particulate pollution.
The preliminary consideration in selection of the different types
of devices is probably most dependent on the volume of gas to be treated.
Knowing this, rough cost estimates car; be made on the basis of cost figures
and equations presented in Appendix A.i/ Appendix A includes figures il-
lustrating purchase cost, installed cost, and annualized cost of operation
plus equations for annual operating and maintenance costs. It should be
borne in mind that these costs can vary considerably for any specific ap-
plication, as is noted in some of the chapters of this handbook.
Specifications for a particular application require considerably
more information than gas volume. Particle and carrier gas characteristics
are needed including particle size concentration (average and range), par-
ticle size distribution, particle density, particle resistivity, gas flow
rate, gas temperature and moisture content, and other important properties
such as corrosivity or flammability.
The usual objective of installing pollution control equipment is
concerned with the quantity or concentration of particulate natter that will
be emitted. Therefore, the specifications will usually stipulate the maxi-
mum allowable emissions as a quantity in lb/hr or as a concentration in
grains/scf. This will set the efficiency for which the control equipment
must be designed, based on given inlet conditions. An indication of the
relative efficiency of various collection devices, as a function of particle
size, is shown in Figure 3-1.£/ These curves were obtained using one
standard test dust which compares to a typical fly ash.
The opacity of the emission is usually also an important aspect
of the equipment performance. Opacity is related to the outlet concentration
13
-------
*100
£ 80
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/
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25
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Particle liu, microni
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Figure 3-1 - Efficiency Curves for Various Types of Dust Collecting Equipnic
14
-------
of the particulate matter. It should be remembered that the finer par-
ticles, which are the most difficult to collect, affect the light scatter-
ing properties of the stack effluent. This is one of the reasons that the
inlet particle size distribution is so important. If the control equip-
ment must provide a clear stack, the outlet concentration to be specified
may be lower than would otherwise be required. The maximum, permissible
concentration for fly-ash emissions from power plants is of the order of
0.02- 0.03 grain/scf for the discharge to be invisible .£/ Maximum concen-
trations for other industry effluents are presented in some of the industry
chapters of this handbook.
A brief description of each of the general types of control de-
vices is presented below to acquaint the reader with each and to point out
those industries and processes that utilize each type. A more complete
description of each of the devices and treatment of theoretical considera-
tions may be found in References 1, 2 and 3 plus many cf the references given
in the bibliographies following each industry chapter.
3.2 CYCLONES
Cyclonic collectors are round conically shaped vessels in which
the gas stream enters tangentially and fellows a spiral path to the out-
let. The spiral motion produces the centrifugal forces that cause the
particulate matter to move toward the periphery of the vessel and collect
on the walls and fall to the bottom of the vessel.
The centrifugal force is the major force causing separation of the
particulate in a cyclone separator. This force (Fc) is equal to the product
of the particulate mass (Mp) and centrifugal acceleration (Vp^/R), where Vp
is the particle velocity and R is the radius of motion (curvature).
Fc ' (KpXZfi
The centrifugal forces cause the particles to move outward toward
the wall of the cyclone. However, this movement of the particle through
the gas stream is opposed by frictional drag on the particle caused by the
relative motion of the particle and gas. The frictional drag (Ff) is
directly proportional to the product of (Cf), a drag coefficient, the pro-
jected cross-sectional area of the particle (Ap), particle density (p), the
square of the particle velocity relative to the gas stream (Vr^), and an
inverse function of the acceleration due to gravity (g).
Ff = (Cf)(Ap)(p)(Vr2)/2g
15
-------
The centrifugal and frictional forces, plus the force of gravity,
combine to determine the collection efficiency. This collection efficiency
increases with:
(1) dust particle size
(2) particle density
(3) gas velocity
(4) cyclone body length
(5) smoothness of cyclone wall
Although efficiency increases with increasing gas velocity, this
is at a lower rate than that at which the pressure drop increases. For a
given cyclone and dust combination, an optimum velocity exists, beyond whic
turbulence increases more rapidly than separation efficiency, and efficienc
decre ases.i/
The cyclonic collectors are generally of two types: the large
diameter, lower efficiency cyclones, and the scalier diameter, multitube
high-efficiency units. The larger cyclones have lower efficiencies espe-
cially on particles less than about 50 p,. However, they have low initial
cost and usually operate at pressure drops of 1-3 in. of water. The multi-
tube cyclones are capable cf efficiencies exceeding 90$ but the cost is
higher and their pressure drop is usually 3-5 in. of water. They are also
more susceptible to plugging and erosion.
The larger cyclones are often used as a part of the process when
the gas stream is heavily laden with part of the product such as in coal
dryers, alfalfa dehydrators and milling operations. They are widely used
in grain elevators, sawmills, asphalt plants and detergent manufacture.
3.3 WET SCRUEBER3
Wet collectors use water "sprays" to collect and remove particulc
matter. There are many variations of wet collectors but they may generally
be classified as low or high energy scrubbers. Low energy scrubbers of
1-6 in. of pressure drop may consist of simple spray towers, packed towers
or impingement plate towers. Water requirements may run 3-6 gal/l,000 cu
ft. of gas and collection efficiencies can exceed 90-95$. The lower energj
scrubber finds frequent application in incinerators, fertilizer manufactur-
ing, lime kilns, and iron foundries.
The high energy scrubber, or Venturi, imparts high velocity to
the gas stream by means of converging-diverging duct section, and contacts
the stream with injected water. The high velocities provide increased
16
-------
collection efficiency, up to 99.5$, but the pressure drop may range from
10-60 in. of water. This requires a draft fan with high power input. The
Venturi scrubber is often used ir. conjunction with steel furnaces, pulp
mills ar.d foundry cupolas.
The wet scrubbers can provide high collection efficiency but may
involve treatment of liquid wastes with settling ponds. They also saturate
the gas stream and produce a resultant steam plume.
The principal mechanisms involved in wet scrubbing are: (l) in-
creasing the size of the particles by combination with liquid droplets
thereby increasing their size so they may be collected more easily, and/or
(2) trapping then in a liquid film and washing their, away.
Dust collection efficiency is believed by some investigators to
be directly related to contacting power and the properties of the particu-
late matter. Contacting power is that portion of useful energy expended in
producing contact of the particulate matter with the scrubbing liquid, as
well as in producing turbulence and mixing in the scrubber device. The con-
tacting power represents the kinetic energy or pressure head loss across
the scrubber, kinetic energy or pressure head drop of the scrubbing liquid,
and other forms of energy dissipated in the gas stream such as sonic energy
or energy supplied by a mechanical rotor. This means that the higher the
power imput, the higher is the efficiency. However, the efficiency is also
a function of the particulate matter properties and the smaller particles
require higher power input than larger particles.i/
3.4 ELECTROSTATIC PRECIPITATORS
The operating principle of electrostatic precipitation requires
three basic steps:
(1) Electrical charging of the suspended particulate
matter.
(2) Collection of the charged particulate matter on
a grounded surface.
(3) Removal of the particulate matter from the col-
lecting surfaces by mechanical scrubbing or flush-
ing with liquids.
The electrical charging is accomplished by passing the suspended
particles through a high-vcltage, direct-current corona. Peak voltage
17
-------
requirements usually range from 30 to 100 kilowatts. Gas velocities range
from 3 to 15 ft/sec. This low linear velocity promotes deposition and
minimizes re-entrainment. However, this also means that the precipitators
will be large in size, or cross-sectional area, to achieve the low gas vel-
ocities. Uniform flow distribution is also an important factor that must
be considered in design of ductwork.
The collection efficiency of electrostatic precipitators is ex-
pressed by the Deutsch equation as:^/
E = 1-je-wA/Q
where E = weight fraction of dust collected
w = migration velocity of dust particle toward the
collecting electrode, ft/sec
A = area of collecting electrode, ft2
Q = gas flow rate, acf/'sec
This equation shows the exponential relationship of efficiency to
the area of the collecting electrode. Thus, moderate increases in collector
efficiency for en existing unit may require a rather large increase in
collecting surfaces.
The proper operation of an electrostatic precipitator is depen-
dent on the electrical resistivity of the particles. Pre-conditioning
with water sprays may be required to impart beneficial resistivity char-
acter to the particles. Proper control of operating voltages must also be
provided if efficient particulate removal is to be maintained. Ihe pre-
cipitator generally has high initial cost but it is capable of high collect!
efficiency, exceeding 99$, at a pressure drop less than 0.5 in. of water.
Electrostatic precipitators have been used extensively for many
years to reduce particulate emissions from coal-fired power plants. These
units handle very large gas volumes with low pressure drops. They have also
been applied in steel mills to clean the gases from blast furnaces and
basic oxygen furnaces, and in cement plants, pulp mills, and sulfuric acid
plants.
IS
-------
3.5 FABRIC FILTERS
Fabric filter systems, i.e., baghouses, usually consist of tubu-
lar bags made of woven synthetic fabric or fiberglass, in which the dirty
gases pass through the fabric while the particles are collected on the up-
stream side by the filtering action of the fabric. The dust retained on
the bags is periodically shaken off and falls into a collecting hopper
for removal.
Fabric filters usually provide very high collection efficiencies,
exceeding 99.5$, at pressure drops usually ranging from 4-6 in. cf water.
The amount of filter area required is often based on an air-to-cloth ratio
of 1.5-3.0 cu ft/min of gas/sq ft of cloth. The maximum operating tempera-
ture for a baghcuse is 550°F using fiberglass bags. However, there may
also be a minimum temperature limitation so as to maintain the gas tempera-
ture 50°F to 75°F above the dew point. Inlet dust loadings range from 0.1
to 10.0 grains/cu ft of gas. Higher concentrations in some industries are
removed by a precleaning device, such as a low efficiency cyclone.
Baghcuses do provide the high collection efficiency at moderate
pressure drop but initial cost is relatively high especially when precool-
ing systems are required. The baghouses also may be large and take up
considerable space. They frequently entail high maintenance costs for bag
replacement. However, replacement of bags need not impair baghouse oper-
ation if the unit is compartmented so that one section can be taken out of
service for maintenance while the others continue to operate.
The baghouse has found wide application in many industries, in-
cluding mining operations, food processing, grain elevators, soap and de-
tergents, plastics manufacture and numerous others. Some of the industries
that employ large baghouse operations are carbon black, cement, electric
arc furnaces, foundry cupolas and nonferrous smelting operations.
3.6 JUST ELIMINATORS
One cf the most commonly used type of mist eliminators is the
mesh filter which consists of an evenly spaced knitted wire or plastic
mesh, usually mounted in horizontal bed. Rising mist droplets strike the
wire surface, flow down the wire to a wire junction, coalesce, and flow to
the bottom surface of the bed, where the liquid disengages in the form of
large droplets and returns by gravity to the process equipment.!/
19
-------
Operating pressure drop is usually less than 1 in. of water with
gas velocities of 10 to 15 ft/sec. Advantages in the use of -his type of
collector are low initial cost, low maintenance, high removal efficiency
and recovery of valuable products without dilution.!/ However, these units
should not be used in services where the material can cause plugging of
the mesh unless provision is made for flushing out accumulated solids.
Another type of mist eliminator consists of packed beds of fibers.
These may operate at velocities ranging from 5 to 90 ft/sec and, therefore,
have correspondingly higher pressure drops of 5 to 15 in. of water.
Collection efficiencies nay be in excess of 99$ on particles..!/
Other types of mist eliminators are impingement baffle mist
eliminators and packed bed mist eliminators which may not achieve effici-
encies as high as those discussed above but do prevent less or carryover
of larger droplets.
3.7 AFTERBURNERS
Afterburners are gas cleaning devices which use a furnace for
the combustion of gaseous and particulate matter. Combustion is accom-
plished either by direct flame incineration or by catalytic combustion.
The disposal of particulate matter by combustion is limited to
residue-free vapors, mists and particulate matter which is readily combus-
tible, as well as to particle sizes which require short furnace retention
time and small furnace size. Afterburners are usually used to dispose of
furies, vapors, and odors when relatively small vo"
concentrations of particulate matter are involved.
Advantages of the direct flame incineration afterburner include:
(1) high removal efficiency of submicron odor-causing particulate matter;
(2) simultaneous disposal of combustible gaseous and particulate matter;
(3) compatibility with existing combustion equipment; (4) relatively small
space requirements; (5) simple construction; and (6) low maintenance.
Disadvantages include: (l) high operational costs including
fuel and instrumentation; (2) fire hazards; and (3) excessive weight.
Advantages of the catalytic afterburner include: (l) reduced
fuel requirements; and (2) reduced temperature, insulation requirements
and fire hazards.
-LUiycg ox gases arici _low
20
-------
Disadvantages of catalytic afterburners include: (l) high initial
cost; (2) sensitivity to catalytic poisoning; (5) inorganic particles must
be removed and organic droplets must be vaporized before combustion to pre-
vent damage and plugging of the catalyst; and (4) catalysts may require
frequent reactivation.
Afterburner systems have been used successfully in many processes
including asphalt blowing and saturating, paint baking, coffee roasting,
food processing, Kraft paper manufacture, paint and varnish cooking and
wire enameling.
The use of afterburners in conjunction with paint baking opera-
tions may allow recirculation of the combustion gases to the oven or re-
covery by heat exchangers. Fuel savings from, the use of heat of combus-
tion of the paint solvent vapors may be large enough to provide a 50$
return on investment in the case of catalytic combustion.=J
21
-------
REFERENCES
1. U. S. Department of Health, Education and Welfare, Control Techniques
for Particulate Air Pollutants, Washington, D. C., 1969.
2. U. S. Department of Health, Education and Welfare, Air Pollution
Engineering Manual, Cincinnati, Ohio, 1967.
3. Sargent, Gordon D., "Dust Collection Equipment," Chemical Engineering-,
January 1969.
4. White, Harry J., "Characteristics of Particulate Master," Industrial
Water ar.d Wastes Magazine.
22
-------
CHAPTER 4
EFFLUENT CHARACTERISTICS
4.1 INTRODUCTION
The severity of the problems associated with sources of particu-
late air pollution is dependent cn the total amount or rate of emission and
the physical and chemical characteristics of the emissions. Furthermore,
the intelligent selection or design of dust collection equipment must be
based on particle and carrier gas characteristics.
Important effluent characteristics which define the objectionable
aspects of a pollution source include: (l) particle size distribution.;
(2) toxicity; (3) corrcsivity; (4) sailing potential; and (5) optical prop-
erties. Particle and carrier gas properties that are important for control
device selection or design include: (l) particle size distribution and
shape; (2) particle density; (3) electrical resistivity; (4) volumetric
flowrate; (5) gas temperature; and (6) humidity.
Some of the more Important particulate and carrier gas character-
istics are discussed in more detail in the following sections. The discus-
sion will focus primarily on the relationship of the effluent properties to
control device selection and/or design.
4.2 PARTICULATE CHARACTERISTICS
4.2.1 Particle Size
Information on particle size distribution in the gas stream is
important in the proper selection of gas cleaning equipment. Particles
larger than about 10 p, may be removed in inertial and cyclone separators
and simple, low-energy wet scrubbers. Particles smaller than 10 p, require
either high-efficiency (high-energy) wet scrubbers, fabric filters, or
electrostatic precipitators.
Particle size in general cannot be specified uniquely by a single
parameter. For irregular dust particles, the average dimension along three
mutually perpendicular axes may be used, or the diameter of a sphere having
the same volume or the same surface area as the particle may be chosen.
Obviously, the more irregular the shape of the particles, the greater will
be the variations in equivalent diameters. For extremely irregular particles
23
-------
like plates, rods, or stars, some other measure, such as specific surface
or settling rate, will usually be more significant. In many gas cleaning
processes the settling velocity has direct physical meaning, independent
of particle structure, and is preferred to equivalent diameter.
Determination of particle size cannot be unique except for the
special case of spherical particles. For all other cases, the results
will depend on the experimental method used. Methods for determining par-
ticle size and particle size distribution may be classified as follows:
4.2.1.1 Sieve Analysis: Used for relatively coarse particles
above 44 n, corresponding to a 325 mesh screen.
4.2.1.2 Microscopic Analysis: Die maximum resolving power of
optical microscopes permits determination of particles down to about 0.5
jlie much greater resolution of electron microscopes extends this lower limi
to about 0.01 |i.
4.2.1.3 Sedimentation Analysis: This method is based on measure
ment of settling rate of particles in fluids. It gives settling velocities
directly and equivalent diameters indirectly, based on known or assumed
laws of the flow resistance or drag of the particles. Stokes' diameter is
determined by this method, which is useful for particles in the range of
about 0.5 to 50 p,.
4.2.1.4 Elutriation Analysis: This method is based or. separatic
of particles in vertically rising fluids. Fine particles above a certain
size cutoff point are carried upward with the rising fluid, and coarser
particles below the cutoff point fall to the bottom of the elutriation charr.
ber. A series of graded elutriation chambers may be used to separate par-
ticles into a series of size classes.
4.2.1.5 Centrifugal Analysis: Similar in principle to sediments
tion but uses centrifugal forces, which may be as high as one million times
gravity in the best ultracentrifuges. This extends the lower particle size
limit down to giant molecules, or to about 0.01 H.
4.2.1.6 Impaction Methods: Particles are deposited on a plate
surface by impaction from an air.jet. A series of graded impactors, the
so-called cascade iapactor, may be used to separate particles into size
classes.
4.2.1.7 Photometric Methods: Daese methods are based on scatter
ing or absorption of light, both of which depend on particle size. This
method is most useful for fine particles below a few microns in size. Lowe
limit by the best techniques is about 0.03 p, for monodisperse or uniform
particle size dispersions.
24
-------
4.2.1.8 Miscellaneous Methods: Gas absorption methods, air perme-
ability, X-ray diffraction.
No universal method or apparatus for particle size determination
is possible, even in principle. For gas-cleaning applications, the sedi-
mentation and elutriatior. methods have very definite advantages because
they give results ir. terms of settling velocity or Stokes1 diameter. But
these methods usually necessitate redispersion of collected particle samples,
which may be difficult, and any agglomerates present in the original aerosol
cannot be reproduced in the particle size equipment. Another problem con-
nected with sizing of industrial aerosols is the difficulty of procuring
representative samples from the field because of the very large gas flows
and variable conditions that characterize most industrial gas-cleaning sit-
uations .
Die Bahco centrifugal dust classifier is used extensively for
routine measurements by control device manufacturing companies. Uiis in-
strument uses a form of centrifugal elutriation. Dust is fed into an air
stream in the annular space between parallel rotating plates and in each
stage the dust is divided into two fractions, one deposited on the periphery
of the wheel and the other carried forward. By varying the air velocity a
number of fractions can be collected. Instruments of this type require
careful adjustment to ensure a good separation.—
Generally, the purpose of a particle size measurement is to dis-
cover the true frequency distribution of particle size. The observed distri-
bution serves as basic data from which may be derived certain representative
constants, for example, the median size. Modified relative frequency distri-
butions can also be obtained by transformation; for example, percent by
weight from percent by number- Adequate presentation cf data is important
to facilitate utilization.
Tabular and graphical forms can be used. A table can list size
versus one of majiy ways cf expressing distribution; for example, size fre-
quency or size cumulation. It is essential to specify which weighting pro-
cess is employed since distributions are generally radically different
•(e.g. number-size and weight-size distributions) '
Graphical methods for presenting size distributions are: (l)
histograms, (2) size frequency curves and (3) cumulative plots. Cumulative
plots are used extensively and their interpretation and comparison can be
enhanced by using the generally applicable log-normal distribution plot
or one of its modifications.—' Figure 4-1 illustrates a log-normal distri-
bution plot for particulates emitted from a kraft pulp mill recovery furnace.
25
-------
10-
8-
6-
If\ -
Z
° 4
as 4-
u
5
LU
t—
LU
2 2-
<
o
LU
u
0.8-
0.6-
• OUTLET FUME (TEST
a OUTLET FUME (TEST
0.4-
0.2-
10
30 40 50 60 70
20
95
80
90
98
WEIGHT % LESS THAN STATED SIZE
Figure 4-1 - Average Size Distributions of Outlet ?mrie - Kraft
Mill Recovery Furnace
26
-------
Log-normal size distributions are defined "by two parameters:
(l) the intercept of the cumulative curve with the 50$ probability mean di-
ameter, and (2) the polydispersity factor (geometric deviation) defined as;
_ , ,. „ , intercept at 50# probability
Polydispersity factor = , J JLj ^ ¦ . • ..
intercept at 15.87$ probability
A completely monodisperse aerosol has a polydispersity factor of
one.
Figure 4-1 shows that 50$ of the outlet, fume is composed of
particles smaller than 1.4 p. in diameter. The polydispersity factor is 4.2.
Comprehensive discussions of particle size measurement, inter-
pretation, and application are given in References 1, 5 and 6. Readers
interested in more detail are directed to these sources.
4.2.2 Farticle Shape
As noted above, particle size analysis does not account for the
multiplicity of particle shapes. Particle shapes of aerosols are of many
types, from simple spheres to complex stars and chainlike aggregates.
Fogs, mists, and some smokes are composed of spherical liquid or tarry
droplets. Many fly ash particles, produced in the combustion of pulverized
coal, are hollow spheres or cenospheres, frequently with much smaller
satellite particles attached to their surfaces. Dust particles usually
are irregular ir. shape as the result of multiple fractures that occur in
crushing or grinding. Many metallurgical fumes have a starlike or platelike
shapej others are needlelike and tend to form agglomerated chains.
Particle shape and surface condition influence handling char-
acteristics, chemical reactivity, adsorption potential, and flammability
limits among other particulate properties.
4.2.3 Solids Loading
Solids loading is a measure of particulate concentration in the
gas stream. While it is not strictly a particulate property, it is in-
cluded in this category for ease of discussion. Solids loading or grain
loading is usually expressed in grains per cubic foot (l grain = l/7,000 lb).
Grain loading and particle size often dictate the choice of control equip-
ment. Very high grain loadings might require the use of a series control
device configuration to meet air pollution regulations (i.e., cyclone
followed by an electrostatic precipitator or a baghouse).
27
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4.2.4 Electrical Properties
The most important electrical properties of particulates are
their electric charge and conductivity. Practically all natural or in-
dustrial dusts are electrically charged to an appreciable degree. The
fractions of positively and negatively charged dust are generally equal,
so that any given dust suspension is, as a whole, electrically neutral.
4.2.4.1 Particle Resistivity: In the electrical precipitation
method for gas cleaning, the particle deposits on the collection surfaces
of precipitators must possess at least a small degree of electrical con-
ductivity. Theory and experience indicate that the critical or minimum
value of particle conductivity for normal precipitator performance is
about 0.5 x 10 inverse ohm-cm, or as more commonly expressed, a maximu.
resistivity of 2 x 10^0 chn-cm (measured in situ).
In precipitator operation, high particle resistivity is usually
manifested by disturbed electrical conditions in the form of excessive sp
ing with moderately lowered voltages, or-by excessive current with greatl
lowered voltages. These effects in turn cause loss of precipitator effi-
ciency, the loss in performance increasing with resistivity. When resist
ity exceeds about 10 H ohm-cm it becomes very difficult to achieve reason
able efficiencies with precipitators of conventional design. Special typ-
of precipitators must then be used, or, more commonly, measures must be
taken to reduce resistivity.3/
There are a number of factors aj:d combinations of factors which
influence the apparent resistivity of particulates. Among those particle
characteristics which may be important are particle size distributions,
shape, particle temperature, surface energy characteristics, packing con-
figuration, and chemical composition. Carrier gas characteristics includ-
chemical composition and temperature.
Most liquid particles and certain types of solid particles are
intrinsically conducting and, therefore, cannot cause difficulty because
of high resistivity. Most of the dusts and fumes in industrial precipi-
tation applications, however, originate from furnace, smelting, drying,
or calcining operations and are composed of silicates, metallic oxides,
and similar inorganic compounds. Many of these materials in the pure dry
state are among the best insulators known and, therefore, might "be expect-
to cause trouble in precipitators. However, moisture and chemical impuri-
ties present in the gases and adsorbed on the particles provide at least
part of the trace conductivity required. In other cases the gas temperat-
may be sufficiently high to ensure adequate conductivity in the particles
by the temperature conduction effect. Low moisture, absence of certain
28
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specific chemical impurities, and temperatures in the range of 250°F to
450°F are likely to cause high resistivity particles.
4.2.4.1.1 Conduction mechanisms: The electrical conductivity of
a "bulk layer of particles depends on both surface and volume factors. In
surface conduction, electrical charges are carried in the surface moisture
and chemical films adsorbed on the particles. These films usually differ
both physically and chemically from the interiors of the particles owing to
adsorption phenomena. Volume conduction, or the motions of electrical charges
through the interiors of the particles, depends, on the other hand, on the
composition and temperature of the particles. Volume conduction also involves
ancillary factors, such as compression of the particle layer, particle size
and shape, and surface properties.^/
Volume conduction in semi-insulating mineral particles may be
either ionic or electronic. The most common examples of ionic conductors
are metallic halides, such as sodium chloride cr silver bromide, and are
of little importance in electrical precipitation. Electronic conduction
occurs in many materials, such as metallic oxides ana silicates, which are
of primary interest in industrial gases. For the metallic oxides and the
silicates the resistance to volume conduction decreases with rising tempera-
tures in the following maimer:
p = A exp E/kT
where p = resistivity
A = constant
E = electron activation energy
k = Boltzman's constant
T = temperature
Volirne conduction is thought to be the predominant mode at temperatures
above approximately 300-350°F. At lower temperatures, volume conduction
becomes insignificant. It appears that the volume conductivity of dusts
and fumes is caused by temperature excitation of internal electrons. Field
measurements confirm the increase in particle conductivity and the improved
performance of precipitators collecting these materials at higher tempera-
tures .
Surface conduction usually predominates for semi-insulating par-
ticles in the temperature range below about 300°F. As previously noted,
29
-------
conduction at these lower temperatures occurs primarily through adsorbed
moisture and chemical films on the particles. Moisture is present naturally
in most industrial gases controlled "by electrical precipitation in amounts
ranging from e few up to about 50$. Conduction in the surface moisture films
appears to "be electrolytic or ionic in character, with the proton-jump mech-
anism beir.g the predominant mechanism for transfer of charge-—'
Fig-are 4-2 illustrates the effect of temperature and humidity on
particle resistivity. The influence of temperature on volume resistivity of
a typical layer of collected particles is shown by the straight line in
Figure 4-2 labeled "bone do-." In the presence of certain conditioning agents
the total resistivity becomes a function of the conditioning agent and temper-
ature. This combined surface-volume conduction relationship is illustrated by
the lower two curves in Figure 4-2 with water as the conditioning agent.
4.2.4.1.2 Conditioning methods: Control of particle resistivity
by conditioning of the carrier gases plays an important role in electrical
precipitation practice. Although the term conditioning usually implies the
addition of chemicals or moisture to the flue gases, it is used here in a
broader context and includes temperature and composition control.
Conditioning of gases by steam injection, water sprays, or wetting
of raw materials to reduce particle resistivity is widespread, particularly
where the natural moisture content of the gas is low and the temperature rel-
atively high. Moisture also is favorable in raising the dielectric strength
and reducing the viscosity of the gas. Conditioning by humidificatior. is
always more effective at lew temperatures. At room temperature, for example,
most dusts and fumes may be effectively conditioned by or.ly_l$ to 2$ moisture
in the gas, but 10$ to 20$ may be needed at 20C°F to 500°F.—'
Chemical conditioning agents may be effective in minute concentra-
tions. A good example occurs in the fine cleaning of the exhaust gas in the
powdered-catalyst petroleum-cracking process used widely in the production
of high-octane gasoline. In the first full scale operation of this process,
it was found that recovery of the valuable aluminum silicate catalyst dust
in the electrical precipitator was hampered by high resistivity of the par-
ticles . Ammonia was found to be a highly effective chemical conditioner,
and it was added tc the precipitator gas in the proportion of only 1 part
in 60.000 which was sufficient to drop the dust resistivity from 5 x 10-1-1
to 10^-° ohm-cm, and to raise precipitator efficiency from 96$ to 99.8$.^/
Moisture appears to be essential to the effectiveness of chemical
conditioning agents. In general, the action of the conditioner increases
with the amount of moisture in the gas and with decreasing temperature of
the gas. Water vapor is therefore frequently referred to as a primary con-
ditioning agent and chemicals are considered secondary conditioning agents.
The effects of conditioning on particulate resistivity are shown in
30
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IB
10
Bone Dry
.1.4
10'
H HjO
3% HaO
10"
100
Temperature, °F
Figure 4-2 - Effect of Humidity on Particle Resistivity
31
-------
Figures 4-3 and 4-4. The addition of a small amount of ammonia reduces
the resistivity of a powdered catalyst by a factor of about 100, and the
addition of diethylair.ine reduces resistivity by a factor of 103 to 10s
(Figure 4-3). Figure 4-4 illustrates the effects of SO3 conditioning on
fly ash resistivity. Resistivity is plotted in terms of the percent of
sulfuric acid fume added, with gas temperature as a parameter.3/
4.2.4.1.3 Resistivity measurement: Because of conduction modes
and their dependence on operating conditions, particle resistivities measure
directly in plant flues are preferable to those measured in the laboratory.
Gaseous environments usually cannot be duplicated feasibly in the laboratory
In the in-situ measurements, the phenomenon of surface conduction usually
predominates because of the presence of conditioners in the flue-gas stream.
In the laboratory, these conditions are usually not present and conduction
is by the volume mode. When in-situ measurements are compared to laboratory
measurements, the in-situ resistivity is frequently 2 to 3 orders of magni-
tude lower. This discrepancy is most severe with fly ash. Laboratory meas-
urements of fly ash resistivity have very little fundamental meaning, and
the only meaningful measurements are those made in situ. Essentially all
electrical resistivity data currently available in the literature have been
determined under laboratory conditions. A more detailed discussion of par-
ticle resistivity is presented in References 2 and 3.
4.2.4.2 Electrostatic Attraction: Electrostatic attraction is
also important in fabric filtration. Precipitation on the filter will resul
from electrostatic forces drawing particles and filter elements together
when either or both possess a static charge. These forces may be either
direct, when both particle and filter are charged, or induced, when only
one is charged. Such charges are usually not present unless deliberately
introduced during the manufacture of the fiber. Electrostatics assist
filtration by providing an attraction between dust and fabric, and also
affect particle agglomeration, fabric cleanability, and collection efficienc;
The type and quantity of charge acquired by a filter medium is a
function of the filter type and the method of charging. The rate at which
a fabric loses its charge is also an important consideration. This depends
not only on the conductivity of the fibers but also on the humidity of the
gases passing through the filter. Thus fabrics which are poor conductors
retain a charge much longer than good conductors. In humid conditions a
fabric acquires a surface film of moisture which also acts as a conductor.
Charges are induced in fabrics by friction, and the type and exten
of charging that a particular material acquires relative to others can be
measured by charging a series of materials in the same way. The usual tech-
nique consists of placing a strip of the material on an insulated ring and
rubbing it with a strip of the reference fabric which is mounted on an
32
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t
^Moi
stur« only
' 2
1
« pkn NHi
Moil*
i
%
tj
i -
•
k
kylomina
I
0 J 10 13
% Immklity
Figure 4-3 - Conditioning of a Weak Acidic Dust ty Strong Bases.
Catalyst clay dust from a powdered catalyst pe-
troleum-cracking process, 310°F^/
1007
»
.2107
1
% HitO.
Figure 4-4 - Laboratory Conditioning Tests, Sulfuric Acid Fume with Fly Ash
33
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insulating rotating disc. The charge on the test strip is measured after
a standarized number of turns of the charging disc, and again after a set
period (frequently 2 min.) to find the rate of charge leakage. The maxinr
charge, measured immediately after charging, enables the materials to be
placed in relation to one another in a triboelectric series (Table 4-1).—
Dust particles can be arranged into a similar series relative t
one another and to filter fabrics. This arrangement can assist in the sel
tion of filter fabrics with the most favorable charge characteristics for
both particle collection and particle release, if the particles are to be
removed by shaking, vibration or blowing.
Particles can be placed in one of three categories: Those whic'
acquire a charge and do not agglomerate (Class i); those that acquire a
charge and agglomerate (Class II), these being the active classes; .and
those which are not affected by the charge on the filter (Class III),
being inactive. The active groups are divided into fine and coarse parti
cles. Coarse particles do not present a problem in filtration as they arc
easily collected on the surface layers of the fabric, usually form a loos<
cake, and are easily shaken off. Fine particles are much more difficult
to collect because they tend to penetrate the filter medium and often lea;
through. By selecting a highly charged filter medium, fine particles in
Class II will be agglomerated, their collection improved, and they should
form a loosely agglomerated cake on the fiber filter surface. If the fil~
has a high rate of charge loss under these conditions, cake release will
also be assisted.§/
Several dusts in the various categories have been experimentall;
investigated and their properties are listed in Table 4-2..Li§/
4.2.5 Moisture Content
Moisture content influences both selection of control equipment
and particle characteristics. Particle resistivity, flammability, and
handling characteristics are strongly influenced by moisture content.
4.2.6 Toxicity
Toxicity characteristics of particulates and carrier gases def:
important health aspects of particulate emissions. The toxicity aspects
of the particulates might dictate the use of a control device where it woi
not otherwise be required.
34
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XA.BLE 4-1
Positive
TRI30ELECTRIC SERIES FOR FABRICSl/
Electrostatic
Units
+ 25
+ 20
+ 15 -
+ 10
+ 5
- 10
- 15
20
Negative
Wool felt
- Glass filament, heat cleaned and silicone treated
Glass spun, heat cleaned and silicone treated
Wool, woven felt
Nylon 66, spun
Nylon 66, spun, heat set
Nylon 6, spun
Cotton sateen
Orion 81, filament
Orion 42, needled fabrics
Arnel, filament
Dacron, filament
Dacron, filament, silicone treated
Dacron, filament M.31
Dacron, combination, filament and spun
Creslan, spun: Azoton spun
Verel, regular, spun: Orion 81 spun (55,200)
Dynel, spun
Orion 81 spun
Orion 42 spun
Dacron, needled
Dacron, spun: Orion 81 spun (79475)
Dacron, spun and heat set
Polypropylene 01, filament
Orion 33B, spun
Fibraryl, spun
Darvan, needled
Kodel
Polyethylene B filament and spun
Note: Polystyrene, Saran and Vinyon are at the far negative end of the series,
35
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TABLE 4-2
RELATIONS OF FABRIC REQUIREMENTS TO DUST PROPERTIES AND DUST IN THE CATEGORIES LISTED^/
Dust Classification
Relative particle size
Electrostatic properties
Agglomerating tendencies
Criteria for filtration:
Leakage
High flow low Ap
Criteria for cleaning:
Leakage control
Ease of cake removal
Material
IA
IB
IIA
IIB
III
Fine
Active
Little or none
Coarse
Active
Little or none
Fine
Active
Positive
Coarse
Active
Positive
Fine and coarse
Inactive
Const!*/
Const§/
Px to I?
Px to P£
P„
Fabric
Construction
dictates
performance
ConstsJ
Dh
Calcined 1
Calc ium
Silicate
Dh
Flux
Calcined
Diatomaceous
Earth
Commercial
Finished
Cement
Ball \
Clay J
Px to P^
Dh
Processed |
Natural \
DiatomaceousI
Earth J
Wheat \
Starch/
Taconite
Zinc oxidel
Fume /
Nickel furnace fume
Magnesite
Cellulose!
Acetate /
Molybdic oxide
Sugar
Px to P^
Dh
Carbon
SRF
Kaolin
a/ Fabric construction determines property.
b/ Requires low density, rapidly agglomerating dust forming large aggregates.
-------
4.2.7 Wettability a:nd Solubility
These properties can affect dust separation in wet scrubbers,
although they are generally only second-order effects. In general, wetting
is the term applied to the phenomenon of a liquid adhering to a solid. Wet-
tability depends upon the nature of the substance involved, and is related
to boundary surface energies. In principle, wetting occurs when the adhesion
energy batween solid and liquid is greater than, or equal to, the cohesion
energy of the liquid.
The determination of wettability is difficult in the case of
morphologically heterogeneous dusts. Recent studies in Germany have in-
dicated that a wettability trend can be expressed in terms of the velocity
of rise of a liquid in capillaries of powders and the total time required
for a liquid to rise a certain height.*/ Table 4-3 summarizes rates of
rise and total wetting times for several dust samples using water as the
liquid phase. The results indicate that the rates of rise and the wetting
times differ greatly for individual dusts. Highest wettability is shown by
dust from sludge of a wet scrubber operating in the cleaning room of a
foundry. In contrast, the wetting properties of dust samples from the hot-
blast cupola furnaces and the boiler soot are very poor.*/
Subsequent investigations, conducted with a test setup in which
dust particles could be shot at individual droplets of water at different
velocities, indicated that wettability did not markedly affect the efficiency
of wet scrubbing. It was repeatedly shown that, regardless of particle type
and velocity, a dust particle hitting the water droplet was always retained
by the latter, even if the droplet was greatly deformed by the particle.*/
These results indicate, at least for the dust studied, that wetting behavior
of particles in wet scrubbing is of secondary importance.
4.2.6 Flairmbility or Explosive In* "its
These factors influence selection of control equipment and define
handling hazards. Ignition and explosion behavior of dust is affected by
electrostatic charging, chemical composition, the size and state of the solid
surface, moisture content, and dust thermal properties. Carrier-gas temper-
ature, pressure, and chemical composition also affect these limits.
4.2.9 Chemical Composition
Particulate and carrier-gas chemical composition exerts an in-
fluence on choice of control and auxiliary handling equipment. Composition
also influences electrical properties, toxicity, reactivity, wettability,
and most other particle properties.
37
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TABLE 4-3
RATES 0? RISE AKD TOTAL WETTING TIKES
MEASURED AT DIFFERMT DUST SAMPLESj/
(Sample cross section: 0.50 cm2, saniple height:
0.5 en, liquid: distilled water)
Rate of Tctal
Density Rise vetting time
Origin of dust (g/cn^) (cm/sec)*10"3 (sec.)
Eoiler
(largely soot) 2.57 4.46*10 ca. 51,000
Hot-blast cupola
furnace (basic) 2.44 9.48¦10"^ ca. 6,800
Hot-blast cupola
furnace (acid) 2.68 0.226 1,153
Cold-blast cupola
furnace 2.71 5.98 148
Swing grinding shop 3.17 25.72 63.6
Blast furnace 4.68 46.80 21.7
Boiler 2.30 96.32 12.6
Sand preparation
(sludge) 2.51 192.58 6.14
38
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4.2.10 Handling Characteristics
Particle handling and flow properties influence dust separation
equipment and auxiliary devices for dust collectors. Powder flow properties
result from a combination of a number of factors including transmission of
external and body forces through the system, particle size and shape dis-
tribution, ruggedness and resilience of the particles, cohesion, adhesion
of particles to surfaces, and adsorbed films especially of water.
Particle shaking properties are very important for the design of
auxiliary devices for dust collectors and for the further treatment of
separated dust. These properties include:
(1) Shakedown Weight - specific weight of highest packing density
(2) Angle of Repose - angle at which piled dust begins to slide
(3) Slide Angle - angle at which dust begins to slide on a "base.
Shakedown weight exceeds the free bulk weight by a factor of 1.2 to 1.4;
angle of repose lies between 25 degrees to 55 degrees and sliding angle
between 35 degrees to 65 degrees. Both angles are influenced by particle
size, moisture content of dust, particle shape, and cohesion and adhesion
forces.
The abrasive behavior of dust characterizes its mechanical effect
upon a surface with which it cooes into contact. In gas cleaning, the
inner walls of pipe conduits are subject to the highest abrasion. This
dust property cannot be expressed by merely giving its hardness, since hard-
ness expressed as resistance to the penetration of foreign bodies cannot be
determined for dust particles. Furthermore, abrasive behavior is also af-
fected by the shape and size of particles and their specific weight.
The corrosive characteristics of the particulates can influence
the choice of gas-cleaning equipment, and, in many cases, dictate the mate-
rials of construction.
4.3 CARRIER-GAS CHARACTERISTICS
4.3.1 Volume Flowrate, Pressure, Temperature, and Composition
Control equipment choice and size are dictated by these parameters.
The gas temperature also exerts an influence on particle resistivity, moisture
content, and flammability limits. Pressure and composition affect flajama-
bility limits.
39
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4.3.2 Corrosive Properties
Carrier-gas corrosive properties primarily influence selection of
equipment construction materials.
4.3.3 Optical Properties
The optical properties of aerosols are of importance in connectio:
with gas cleaning and air pollution, because the degree of pollution is
commonly judged by visual appearance of stack discharge or of the atmosphere
itself. Visual appearance is subjective and is associated with the observer
character of the sky, and physical character of the stack discharge.
Optical density is closely related to the visual appearance of
the stack exhaust plume. The extinction coefficient is a function of the
number of particles per unit volume, the particle size, shape, and size
distribution.
4.3.4 Odor and Toxicity
Particulate and carrier-gas odor properties are secondary factors.
Concentrations below toxic or harmful levels are primarily a problem from
the standpoint of complaints from nearby residents. Malodorous gases and
vapors include mercaptans, phenolic compounds, naphthenic acids, organic
sulfides, nitrogen bases, aldehydes, and ammonia.
40
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REFERENCES
1. Herdan, G., Small particle Statistics, 2nd Ed. (revised), Butterworths,
London, 1960.
2. "An Electrostatic Precipitator System Study," 2nd Quarterly Progress
Report, Southern Research Institute, NA.PCA Contract CPA 22-69-73,
October 1969.
3. White, H. J., Industrial Electrostatic Precipitation, Addison-Wesley
Publishing Company, Reading, Massachusetts, 1963.
4. Weber, I. 2., "The Influence of Dust Wettability on Wet Scrubbing,"
Staub (English Translation) 28 (ll), 37-42, 1968.
5. Irani, R. R. and C. F. Callis, Paxticle Size: Measurement, Interpreta-
tion, and Applica-jon, John Wiley and Sons, New York, 1963.
6. Cadle, R. D., Particle Size, Reinhold Publishers, New York, 1965.
7. Strauss, W., Industrial Gas Cleaning, Pergaaion Press, London, 19GS.
8. Frederick, E. R., "How Dust Filter Selection Depends on Electrostatics,"
Chemical Engineering, June 1961.
41
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CHAPTER 5
PRESENTATION OF EFFLUENT DATA FOR SPECIFIC INDUSTRIES
Effluent data for specific sources in the major industrial cate-
gories listed in Table 2-1, Chapter 2, are presented in tabular form in
Chapters 6 - 24. Only numerical data are given in these tables. Table 5-1
is provided as a coding key for the tables of effluent characteristics in
Chapters 6-24.
Preceding page blank
-------
TABLE 5-1
CODING KEY FOR TABLES OF EFFLUENT CHARACTERISTICS
I. General Note; All data for uncontrolled sources unless otherwise noted.
II. Specific Notes:
A. Particulates
1. Particle size;
x < y, x > y.
x = veigkt y = particle size (p,).
Measuring technique noted. If no notation is listed,
measuring technique was not reported or is unknown.
2. Solids loading: grains/scf, unless otherwise noted.
3. Chemical composition:
solids - wt. $ (unless otherwise noted).
4. Particle density: g/cm^.
5. Electrical resistivity: ohm-cm, laboratory measurements unless
otherwise noted.
6. Moisture content: wt unless otherwise noted.
7. Toxicity:
a) N.T. - not toxic.
b) numerical value - threshold limit, rag/m^.
8. Solubility:
s. - soluble.
s. si. - slightly soluble.
45 Preceding page blank
-------
TABLE 5-1 (Concluded)
d. - decomposes.
9. Wettability, hygroscopic, flammability, handling; optical;
and odor characteristics: only a descriptive comment general!
given; if numerical value is presented, units will be indicate
B. Carrier Gas
1. Flow rate: flow-rate data presented in two forms:
a) thousands of standard cubic feet per minute, M scfjn,
unless otherwise noted.
b) thousands of standard cubic feet per ton of product
processed, M/sef/ton, unless otherwise noted.
2. Temperature: °F.
3. Moisture content: vol $, unless otherwise noted. Dew point
is in °F if listed under moisture content.
4. Chemical composition: vol unless otherwise indicated.
5. Tbxicity:
a) N.T. - net toxic.
b) numerical value - threshold limit, mg/m^.
6. Corrosivity, odor, flammability, and optical properties: only
a descriptive comment generally given; if numerical value is
presented, units will be indicated.
46
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CHAPTER 6
STATIONARY COMBUSTION PROCESSES
e.1 INTRODUCTION
More than 29 million stationary combustion sources are currently
in operation in the United States: (l) electric-utility power-generating
plants, (2) industrial power plants and process heaters, and (3) space-
heating ur.its. Coal, cil, and gas are turned in a wide variety of equip-
ment.—'
Particulate emissions vary widely from unit to unit tecause
processes, practices, and fuels all affect emission levels. For each
fuel, several different processes are used for stationary combustion.
Coal-fired electric generating plants utilize pulverized, cyclone, and
stoker-fired "boilers. Burners, combustion chambers, draft systems, heat
transfer characteristics, and combustion controls cf industrial units may
vary widely. Steam, hot water,and warm air furnaces are in common use for
domestic heating.
Stationary combustion sources are divided into electric utility,
industrial, and commercial and residential groups for a more detailed dis-
cussion in the following sections.
6.2 ELECTRIC UTILITIES
The production of power by the combustion of coal, fuel oil,
and gas contributes large quantities of particulates, sulfur oxides and
nitrogen oxides to the atmosphere. Coal-fired units are the dominant
source of particulate emissions. Particulate emissions from oil-fired
power boilers are about of emissions from similar coal-fired equipment.
Use of natural gas as a fuel nearly eliminates particulate emissions.
Since emissions depend so strongly on the type of fuel burned, discussion
of emission rates, effluent characteristics, and control practices is
presented for each fuel type in succeeding paragraphs.
6.2.1 Fuel Type
6.2.1.1 Coal-Fired: The modern coal-fired electric generating
plant is comprised of a boiler, generator, condenser, coal handling equip-
ment, dust collection and disposal equipment, water handling and treat-
ment facilities, and heat recovery systems such as economizers and air
47
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heaters. Boilers in present-day usage include eyclcne, pulverized, and
stoker types with pulverized fuel boilers comprising nearly 90$ of the
total.
Pulverized fuel boilers utilize coal ground to a size such that
about 70$ passes 200 mesh. The coal and preheated combustion air are
direct-fired into the boiler as determined by the steam requirements. The
coal-air ratio is automatically regulated to give optimum combustion for
all load conditions. Boilers are classified as horizontal, vertical, cr
tangential, depending upon the firing position of the burners.2/
Pulverized coal-fired boilers are also classified as either wet
bottom or dry bottom, depending on the operating temperature and ash-fusion
temperature. In wet-botton boilers, the temperature is maintained above
the ash-fusion temperature so the slag is molten and can be removed from
the bottom as a liquid. Dry-bottom boilers operate at temperatures below
the ash-fusion point, and the ash is removed in a sclid state.—'
Cyclone boilers operate with much coarser coal, typically 95$
minus 4 mesh. The heater is a water cooler cylinder with combustion air
introduced tangentially. Combustion occurs at temperatures sufficiently
high to melt a high percentage of the ash which is discharged through slag
tap openings.
Less than 5$ of the coal consumed in electric-generating plants
is burned in stoker boilers. A variety of stoker units exist, but spreader-
stcker units have the highest steam output rates.The spreader-stoker
unit combines suspension and fuel-bed firing; the stoker mechanism feeds
from the hopper onto a rotating flipper mechanism, which in turn throws
the fuel into the furnace. Because the fuel is burned partly in suspen-
sion and partly cn the grate, the fuel bed is thin, ar.d response to
fluctuations in load is rapid. The grates are either stationary or con-
tinuous moving from the rear to the. front. Vibrating, oscillating, travel-
ing, and chain grates are used for moving the fuel toward the ash-receiving
pit.zJ Fly-ash reinfection is also practiced in many plants.
6.2.1.2 Oil-Fired: Compared to coal-fired units, oil-fired elec-
tric-generating plants emit a minor amount of particulate matter to the
atmosphere. The rates of emissions from these units are affected by
variable operating conditions and by the nature of the fuel used.
Two different basic designs of furnace are used in oil-fired
plants: tangentially and horizontally fired. The tangentially fired unit
is built so that the flame is propagated in a cylindrical form. The unit
is constructed to produce a spiral upward motion of the flame and combus-
tion products around the walls of the cylindrical firebox. The tangentially
fired unit is a relatively new and infrequently used design.^/
48
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Horizontally fired units are usually fired at right angles to the
walls of the firebox, "but may be fired at various angles. They nay be
fired on one or more sides, or from the bottom of the firebox. The firebox
may be square, rectangular, or cylindrical. Horizontal firing tends tc
concentrate the hot gases in the center of the fire"box.
6.2.1.3 Gas-Fired: Natural gas is also utilized in power plants.
Particulates and oxides cf sulfur emissions are insignificant compared
with those of other fossil fuels. Control equipment has not been required
for natural gas combustion equipment.
6.2.2 Emission Rates
6.2.2.1 Coal-Fired: The emission rate of particulate matter
from a coal-fired furnace is related to many factors, mainly gas velocity,
particle size, particle density, fuel-burning rate, combustion efficiency,
flue gas temperature, furnace configuration, coal composition and size,
and the initial state cf the raw coal.
The following variables are thought to be the most important in
relation to particulate emissions:^/
1. Amount cf ash in the coal;
2. Method of burning the coal;
3. Rate at which the coal is burned.
7cr any specific furnace, coal-ash content is the dominant variable.
Other conditions remaining fixed, the fly-ash emission will be approximately
proportional to the ash content of the coal. The heating value of the coal
is related to its ash content. Figure 6-1 presents a nomograph for esti-
mating particulate emissions from coal combustion.±>/
The method of burning the coal influences particulate emission
rates. When coal is thrown or blown into a furnace, combustion takes place
in suspension. As the pieces of coal burn, they get smaller, and thus
their chance of being exhausted with stack gases is increased. When coal
is pushed cr pulled into a furnace to form a bed, the coal or ash has less
chance of being entrained by the flue gases because of impingement onto
larger particles. When coal is introduced tangentially into a cylinder,
such as in the cyclone furnace, the burner acts as a cyclone separator and
thus reduces emission o.f larger particles.-^/
As the velocity of the gases passing through the furnace increases,
larger particles of coal and ash are carried cut cf the furnace. The velocity
49
-------
PARTICULATE EMISSION,
KEATING YA'.UE,
I.COD Bti/lb
20
I6/10'Btu
REFERENCE
CONTENT,
lb/10 'lb flue it
50* ««cc J> »i r
( Bitwnir.ouJ co
-------
of the gases is directly proportional to the firing rate of a given furnace;
thus, the size of the particle and rate of emission should be a function of
the firing rate. In a similar manner, the excess air, pressure, and tempera-
ture are related to the particulate emissions in that they control the gas
velocity.3/
Emission rates for the various types of coal-burning units Eire
summarized in Table 6-1. As would be expected, over 90$ of the emissions
are from pulverized coal-fired boilers. The influence of firing method is
clearly shown, as the emission factor for cyclone units is 20 to 25$ of that
for pulverized and stoker units.
6.2.2.2 Oil-Fired: The particulate loading of stack gases de-
pends primarily upon the efficiency of combustion and the rate of build-up
of boiler deposits. Poor mixing, low flame temperatures, and short residence
time in the combustion zone cause larger particles, higher combustible con-
tent, and higher particulate loadings.!/ The degree of atomization has an
important effect on particulate emissions. Low-pressure atomization pro-
duces larger fly-ash particles and a higher particulate loading.£/ High-
pressure atomization (400 psig or greater) produces smaller particles, fewer
cenospheres, and lower particulate loadings.*k]
The soot-blowing operation markedly increases the particulate
loading in the stack gases. An increase of 1.7 to 3.3 times the normal
emission level has been reported during soot blowing.i/
Emission rates for oil-fired units are summarized in Table 6-1.
Particulate emissions are estimated at 36,000 ^ons/year.
6.2.2.3 Gas-Fired: Meager data exist on particulate emissions
from gas-fired units. Table 6-1 summarizes available information. Partic-
ulate emissions are estimated to be 24,000 tens/year.
6.2.3 Characteristics of Effluents from Electric Generating Plants
6.2.3.1 Coal-Fired: The chemical and physical characteristics
of effluents from coal-fired electric generating plants are summarized in
Table 6-2. Particulates from pulverized coal furnaces are larger in size
than those from cyclone furnaces. There is also a rather large variation
in particle size for each furnace. Ftirnace design, operating conditions
and coal composition undoubtedly influence the size of emitted particulates.
Outlet grain loadings from pulverized furnaces generally exceed those from
cyclone furnaces.
51
-------
TABLE 6-1
PARTICULATE EMISSIONS
FUEL COMBUSTION IN STATIONARY SOURCES
Source
Amount of Fuel
Burned
Emission
Factor
Efficiency
of Control
(Cc)
Application
of Control
(Ct)
Net
Control
«Vct>
Emissions
(tons/yr)
I. Coal
A. Electric Utility
1. Pulverized
2. Stoker
3. Cyclone
B. Industrial
1. Pulverized
2. Stoker
3. Cyclone
C. Residential and
Commerical
258,400,000 tons
9,900,000
28,700,000
20,000,000
70,000,000
10,000,000
20,000,000
16 A*
13 A
3 A
16 A
13 A
3 A
5 A
0.92
0.80
0.91
0.97
0.87
0.71
0.89
0.70
0.64
Total from electric utilities
0.85 0.95 0.81
0.85 0.62 0.52
0.82 0.91 0.75
Total from industrial units
Total from coal
2,710,000
217,000
182,000
3,109,000
322,000
2,234,000
39,000
2,595,000
300,000
6,004,000
II. Fuel Oil
A. Electric
Utilities
7,180,000,000 gal. 10 lb/l,000 p3al.
36,000
Oi
ro
B. Industrial
1. Residual
2. Distillate
7,510,000,000 pal.
2,360,000,000 pal.
C. Residential and 36,5o0,000,000 p.al.
Ccmmercial
23 lb/1,000 gal.
15 lb/1,000 gal.
8 lb/1,000 L'.al •
Total from fuel oil
87,000
18,000
287,000
III. Natural Gas and
LPG
A. Electric
utilities
B. Industrial
C. Residential and
Commercial
3,143,143,000 mil.
cu. ft.
9,270,000 mil.
cu. ft.
6,250,000 mil.
cu. 1't.
15 lb/mil cu ft
18 lb/mil cu ft
19 lb/mil cu ft
Total from natural gas
24,000
84,000
59,000
167,000
Total for fuel combustion, stationary sources
6,450,000
-------
Particulate 'Part I)
EFFUrEST CHARACTERISTICS
STATiaimY CQtBUSTIOB PROCESSES^
Electric Generating-
Plants
Particle Size Solide Loadlgg Chesicil Coepoiltlon Partl:le D*BSlty
Electrical Moisture
Resistivity Ccatent
Toxicity
Coal Fired
Type of boiler
a. Pulverized
1. Vertical*
£• Corner*
2. Front wall
horizontal*
4. Korison'.slly
uppoaed
5. Unspecified
25 < 10, 49 < 20,
?»< 44
BA-HCO Analysis
CF £9 )fea-
aureaetts is
fallowing range
€-20 < 3, 12-32
< 5, 28-56 < 1C,
42.73 < SO, 61-93
< 4C
Hott Probable
listrlsutioa
15 < 3, 25 < 5,
42 < 10, 6S <
20, 81 < 40
4.7-4.&*»
2.9-3.7 5 avg.
3.3
2.4-?.5
2.9-4.9; avg.
3.9
1.02-5.6
Hear: 3.3
Typical Ply Aah?
S109
i7-€4 avg. 43,
FejOy 2-36 avg. IS,
AljOj: avg. 24,
CaD; 0.1-2? avg. 4,
HgOt 3.1-5 avg. 1.0,
3a?0; 0.3-4 avg. 0.9
Ignition Lcsi
C.4*36 avg. 6.3
fiaall Aaounta
TIC-, KjD, Fee, P^,
SOj
Pciyauclear hydro-
carbons («e« Table
6-3 for detailed
data)
Bulk Density
30-50 lb/ft"
Particle Density
0.5-5.0, avg. 2.3
Particle shape
varies widely.
May be alnut*
spheres, filivers,
or epoogv, lace -
like entities.
Varies fra
•0®-1015
0.22 (avg.
30 saaples)
W.T., but
aridir
b. Cyclote*
Stoker
1 • Spreader
stcker*
2. Underfeed
stckcr
72 < 10, 97 < 20,
95 < 44
BAKCC Aj&lysis
30-72 < S,avg.
40 < 5; 40-96 <
10, avg. 65 < 10;
70.99 < ?0, *vg.
81 < 20, 81-100
< 40, avg. 92 <43
IK 10, 23 < 20,
42 < 44
7 < .0, 15 < 20,
3D < 44
0.2-3.2
Mean: O.eS
1.5-2.3;
1.5
0.0S-c.2
Jnspecified
boll-r type
Coulter Counter
2-'M< 10, avg.
ia < 10; 4-es <
20, avg. 35 < 20;
20-38 < 44, avg.
59 < 44
Optical and Elec-
trar. Wicrcsccpe
42-66 < 10, avg.
50 < 10; 60-A7 <
20, avg. 79< 2C;
86-33 < 44; avg.
93.5 < 44
Iterative Sedimen-
tation
45-89 < 10, k.vg.
53 < 10; 64-85 <
20, wg. 76 < 20;
t0-91 < 44; avg.
B4 < 44
BICBO Analysis
12-26 <10, avg.
16.6 < 10; 20-36
< TO, avg. 26 <
20; 42-95 < 44,
avg. 63.3 < 44
* See CcdLns Key, Tkble 5-1, C'napter S, p. 45, for units Tor Individual effluent properties.
* Partial */id full lcai tests (partial lead - 75< load); 30-50 excess air.
~•Corrected te 124 COg, dry fcaiia.
53
-------
A. Particulate (Part I, Concluded)
Particle Size
Blectrlc 3eoerfttln£
Plants (Concluded)
TABLE 6-2 (Ccntliw»d)
Electrical Mcifture
Sclldi? Loading Cfcealcal CaBpoeltlon Particle Penalty Realstlvlty Coatept
Toxicity
II. Oil PLred
a. Typical operation 90 < 1
b. Soot Blowing
Industrial Punacei
0.0:3^3.2, avg.
0.05, BOat - rmmin
value - C.C3.
0.035
0.13-0.19
0.01-C.2G5, avg.
0.063
Fly Aab: Set Tabli
6-4 for detailed
data
2.5
Particle shape
varlee, ^ny snail
spheres
fl.T-, bi
acidic
A • Partl^uJa'.g ' ?&rtil)
Source
Electric Genera!
Plants
ScluMllty
1=3
Contains Hj>C scl-ile
cccpcr.er.tfi
Difficult to wat
Hygroaceyic
auraateristlcg
Flascab:".tty or
Explosive Llsltc HaaAllng Characteristics
Difficult to haivile, a£-
generates
Internal Friction Angle
42C-530 u - 25.1'
P95-420 u - 85'
?5c-?ss u - so.y
149-250 u - 18.1-24.2*
105-149 u - 16.3-23.6*
74*105 u - l4.2-?2*
*4- 74 u - S>.3-1(3.7*
0- 44 u - 1.1*
Optical Prcpertlei
Color varies frca
light tan cr grey
to various shades
of black
External miction Angle
(w..th eJ.ufclr.ua;
42C-590
.
16.7*
295-42C
V
-
22'
2SC-295
U
-
19.5'
149-85C
U
-
13.28.4'
1C5-149
U
-
20.5-24'
74-105
-
14.6.27.
44- 74
P
-
12*16.6'
C- 44
U
-
14.4-12.
420-590
U
-is.5 g/m«
295-420
u
- 0.5
25G-29S
w
- 5.4
149-23C
u
- 8.5-20.5
1C6-149
u
- 13.5
74-105
It
- 0.5-5.C
44- 7«
u
• 5.0-14.5
0- 44
- 14.5-21
11. Oil-Pir«d 30-5C^ soluble Difficult to vet
flOlidB
54
-------
•>B:E 6-2 (Continued}
Teap^fi
.M&isture
?ontgn*
CJieej:
CcTsM
7^>iclty
rorror.ivity
Oder
KuBtttUS'.y or
Explosive l:s:-.r
' *1 rirei
?,7* «f -fciier
a. !y'v»r;r-5
.. V?rti-:ai*
Fror.t wall*
horizontal
(a) rS7-53?
ivg. 550
(t> 362-434
avg. 4DO
(a) 294-3G2
avg. 3e\-
(hi 387.4:'
tvg. 4C?
'n.; 2&4-.VS
c.vg. ;-92
» 375-394
avg. 306
(a) 44-6?
ivg. S3
i'.) i3?-;?3
avg. 336
24S-E
avg.
?44-?E7
RVg. -
314-MS
8VS. - 314.5
6.5-6.8
avrf. 6.7
:0n - V-.S-lc.t,
Or, - 6.1-6.5
N2 - bsUrrt
CO - 1?-IT pp»
MOx - i«l-221 y-ri
SOj - i.410-
i.-'CC Pf3t
5.-.^ - 46-66 ppa
:D2 - 14.4-14.9
Cc - 4.2-4.7
Ng - balance
«.•: - 1.-39 rr--
- 393-556 ppa
S3? " 1.12C-
1.150 ppe
2Or, • 9-10 Fjo
CSc, ¦ 13 ."-13.6
02 - 5.3-5.6
Kj - balance
CO - 5-17 PF-
S \< - 4 IS-500 pjrs
SCfc - 1,380-
2,1?0 pps
- 3-11 ppa
u* - •*,
irri t*nt
CO - ICC
CD-.
^2 *
K2 -
CD -
NO,
s% -
^ "
• 1?.8-13.2
S.9-6.C
44-6'j ppn
393-395 ppic
1.56C-
i,?ec ppx
o-iC pps
0;- Fired
u Horizcntil-y
fired
fc. Tir^enti*!
¦>} 444-158
avg. 501
319-64:
svg. iiJ:
(&> 44-54
avg. 43
(i»> 351-363
#va. 367
(a) 47-12,400
(o) 34c-7a0
avg. 44:>
>*S-?7 3
avg - 'PI
0.3-6.C
arg. 6.45
avg. - 411
•7.4-7
*Vfi.
200-688
4vs;. • 315
£.6-9.8
*v«. - S.4
(a) 206-216
(o) 3d4-396
avg. 390
55
:C2 - li.0-12.8
0? - 6.4-5.0
Ng - bsluce
CC - nc data
KGV - 742-1,234 ;
iC* - 1,350-
l 360 nr*=
£0^ - 13-51 pp*
^•V - !?.i
Og - 5.6-6.C-
N- - balance
CO - 13-29 ppn
NO* - 4*0 ppo
SC? - 1.780-
1.3SC- ppn
30; - SS-iS FJO
CCy, - 5.9--.S.4
avg. - H.7
02 - C.7-13.2
avg. - 4.2
Bp - balar.r*
S*> - 110-?,200 pps
avg. . 9^ ppx
SOj - 2-75 ppe
avg. - 19.t ppe
(¦est 'anun value
14-22 ppo)
HC* - 15-9C0 pjrc
avg. . 414 PFn
(oost ccbboq value
460-480 p^*;
CC? - 11.1-18 2
»vg. - 14 .7
02 - 2.2-6.B
avg -4.3
- lf.!"-40C ppa
avg. - ?6C ppx
Hast Cower, vaJ.je,
180-260 ppE
-------
TAK2 6-2 (Concluded)
Carrier Par, (Corclucea;
Moisture CMoical
Source Flow I«arperatur« Content Ccapoiitlco Toxicity
Industrial Pcttj:«
1. Pressure 4*.coiling (a) 0.3-1.2 250-370 1.0-9.8 C&, - 3.9-12.4
(b) U.3-1.1 avg. - 31C avg. - 6.0 avg. - 6.6
avg. 0.6 - 4,5-16.3
avg. - 11.0
CO - 0.002 - C.01
4Vg. - 0.00c
SOj - 93-333 pja
avg. - 214 pptt
SOj - 1.4-3.2 FP®
avg. - 2.3 ppe
NOj - 34-120 ppt
avg. - SO ppe
2. Steaa atnliing la) 1.7-iU 320-710 6.3-12.7 COg - 4-e.?
(b) C-.J.O.G avg. - 546 avg. - S.4 avg. - 6.4
avg. 0.44 02 - 7.8-14.0
avg. - 10.I
CO - 0.0C1-C.003
avg. - 0.CC1
302 " 7"700 ??°
avg. - 366 ppm
SCJ - 1.2-6.7 ypn
avg. - 4.2 pj*
KOj - 15-368 rpa
avg. - c29 ppt
3. Centrifugal (a) 1.2-4.0 240-500 4.4-9.2 COj - 2.7-6.3
atcmiiisg (s) 0.39-0.8 avg. - 3?3 avg. - 6.3 avg. - 4 7
Avfi- *.53 Oj • 3.3-16.2
avg. - 12.7
CC - C.C01-0.02
avg. - C.GOS
Sf- - n-102 ppa
avg. • 4C ppa
SOt - C.5-5.5 ppn
avg. - 2.G j;n
liC* - ?C-7? ppm
avg. - J"' p;n
56
-------
TABLE 6-3
c /
POLYNUCLEAR HYDROCARBON CONCENTRATIONS
(Micrograms/lO^Btu Heat Input)^/
Type of Boiler Firing
Pulverized
Hcri-
Front- zontally Spreader
Compound Vertical Corner Wall Opposed Stoker Cyclone
Fluoranthene 200 300 80 188 50 79
Pyrene 155 140 180 91 105 1,025
Benzo(a)pyrene 19 140 19 81 < 20 223
Eenzo( e)pyrene 86 23 265 30 395
Benzo{ghi)perylene 150 7 645 198
Coronene 7 56 5 6
Perylene 7 1 ]7
a/ After fly-ash collector during full-load operation. Average values
for two tests at eac!:. unit. A blank indicates that the compound
was not detected.
57
-------
TABLE 6-4
ELEMENTAL ANALYSES OF TOTAL PARTICULATES
i/
(Data in Percent)
Test A
Test B
Elements
Carbon
Ether, soluble
Hydrogen
Ash (900°C)
Sulfates as SOj
(incl. H2SO4)
Chlorides as CI
Nitrogen as NO^
Iron as FC2O3
Chromium as CrOg
Nickel as NiO
Vanadium as VgCj
Cobalt as CogOj
Silicon as Si02
Aluminum as AI2O3
Barium as BaO
Magnesium as KgO
Lead as FcO
Calcium as CaO
Sodium as Na2©
Copper as CuO
Titanium as TiOg
Molybdenum as MoOg
Boron as B2O3
Manganese as MnOg
Zinc as ZnO
Phosphorus as P2O5
Strontium as SrO
Titanium as TiO
Total solids from burning
PS£/400 cil (collected in Total solids from burning
a laboratory electrical 4° API oil ( collected in a
precipitator at 230°F) glass filter sock at 500°F)
18.1-/
58.1-/
2.3
17.4
17.5
3.1
0.06
1.8
2.5
0.08
0.6
1.6
0.4
0.2
0.1
0.2
0.9
0.01
0.02
0.01
0.04
0.9
0.04
0.03
4.4
51.2
25.0
0.5
0.3
3.7
0.3
13.2
4.7
0.3
9.7
14.9
0.1
0.7
0.2
0.4
3.0
0.25
0.004
0.03
0.1
0.04
0.06
&/ Pacific Standard,
b/ Value probably includes miner amount of hydrogen.
58
-------
Fly ash (particulate emitted from combustion process) is a hetero-
geneous material and is composed cf a variety cf shapes. Cenospheres,
unburned carbon particles, and mineral matter are the principal components.
Percentages of these constituents vary frcm sample to sample, depending upon
factors such as coal composition and furnace operation.
6.2.3.2 Oil-Jired: Table 6-2 presents data on the effluent charac-
teristics of oil-fired electric-generating plants. Limited data were found
cn particle size distributions for particulate emissions from oil-fired units.
The predominant size (over 90$) is less than 1 p, . Size distribution
will depend upon the degree of atomization of the oil, the efficiency of
mixing, the number of collisions "between fly-ash particles, the flame tempera-
ture, the design of the firebox, and the flue-gas path through the boiler to
the stack. The lighter particles usually contain less carbon and are smaller
in size.
The larger particles are skeletons of burned-out fuel particles,
called cenospheres, which are hollow, black, coke-like spherical particles.—'
The smaller particles formed by the condensation of vapors are of regular
shape and usually have a maximum dimension of about 0.01 p,.1/ Fuel atomization
usually reduces the number of cenospheres.
6.2.2.3 Gas-Fired: No detailed data were found on emissions frcm
gas-fired units. Particulates can "be assumed to be less than 5 p, in size, and
gaseous emissions will contain Og, N2, COg, SOg and NOx.
6.2.4 Control Practices and Equipment for Electric-Generating Plants
6.2.4.1 Co&1-Fired: The dust collectors used for coal-fired power
plants are shewn in Table 6-5 with their usual expected efficiency in Table
6-6.—/ Optimum expected performance of various types of cleaning systems is
shown in Table 6-7=/,
A comparison of the cost cf various types and combinations of
control equipment is given in Table 6-8.-'
The problem of particulate natter is not solved with its collection.
The costly matter of disposal still remains. This ccst ranges from $0.50 to
$2.00/tcn for most utilities. The average is about $0.74/ton. 1/
6.2.4.1.1 Electrical -precipitators; Electrical Precipitators
are used extensively in power plants. A recent survey shows that in recent
years high-efficiency electrostatic precipitators are being installed almost
exclusively.—' Recent trends toward the use of low-sulfur coal may require
increasing the capacity of the electrostatic precipitators. A reduction in
the sulfur content of the coal is apt to increase fly-ash resistivity, thereby
reducing the efficiency of existing electrostatic precipitators.-S/
59
-------
tabu: g-s
DUST COLLECTORS FOR COM,-FIRED KEATING AND POWER PLANTS^
Collector
Type
Cinder trap
Collecting
Action
Gravity
Recommended
Application
Smaller plants with under-
feed, vibrating, chain,
and traveling-grate
stokers
Efficiency Relative
to Particle Size
30 to 40$ for 45 ^
and smaller; 75$
or more for par-
ticles over 45 u
Draft Loss,
Inches of Water Other Considerations
0.1 to 0.5 (nat- Used mainly to eliminat'
ural draft usu- cinder nuisance in im-
ally sufficient) mediate plant area.
Medium draft
loss cyclone
Inertia
Single cyclone Centrifugal force
(large diameter) and inertia
Multicyclone Centrifugal force
(small diameter and inertia
tubes)
Wet scrubber
Electrostatic
precipitator
Siliconized
glass filter
Inertia
Electrical
attraction
Filtering
Smaller plants with
very critical on-
grate firing
On-grate firing at high
rates and some spreader
stokers
Spreader stoker
Spreader stoker and
pulverized-coal-firing
units
Pulverized-coal-firing
unit
Pu 1 ve ri zed-coal-fi ririp,
units
0verall--to 65$,
100$ over 25-^
size
50 to 90$ for
particles over
20 u
75 to 90$ for
particles over
10 u
70 to 90$, de-
pending on
particle size;
75$ over 2 ^
85 to 99$ - < 1
to 10 p,
98 to 99$ for < 1
to 44 n
0.4 to 1.5
0.5 to 2.0
2.0 to 6.0
13 to 20
0.1 to 0.5
1 to 6
Abrasion may occur:
made in variety of
designs to fit job.
Made in variety of
designs. Care required
to fit design to job.
Abrasion may be a
problem.
Caking and corrosion
may be a problem,
also water recovery.
Performance affected by
resistivity of particle
Exit temperature
limited to 600°F.
-------
IkELE 6-6
Type of Firing
or Furnace
Cyclone
Fulverized
Spreader stoker
Other stokers
USUAL EXPECTED EFFICIENCY RANGES FOR
COMMONLY USED CONTROL EQUIPMENT 1/ .
(Percent)
Type of Control Equipment
High- Low-
Electrostatic Efficiency Resistance
Precipitator Cyclone Cyclone
65-99
80-99.9
30-40
65-75
85-90
90-95
20-30
40-60
70-80
75-85
Settling Chamber,
Expanded
Chimney Bases
20-30
25-50
61
-------
TABLE 6-7
OPTIMUM EXPECTED PERFORMANCE OF VARIOUS TYPES OF GAS CLEANING
SYSTEMS FOR STATIONARY COMBUSTION SOURCE^/
Removal of Uncontrolled Particulate Emissions (percent)
Sources
Coal-fired
Spreader, chain grate, and
vibrating stokers
Other stokers
Cyclone furnaces
Other pulverized coal units
Oil-fired
Systems Under
Development
Systems in Operation
8-In.
Settling
Chambers
Large
Diameter
Cyclones
Small
Diameter
Cyclones
Electrostatic
Precipitators
Stack
Sprays
Pressure
Drop
Scrubbers
Fabric
Filters
50
60
85
99.5
60
99 +
99.5
60
65
90
99.5
80
99+
99.5
10 .
15
70
99.5
20
30
80
99.5
99+
99.5
5S/
icfi/
30^/
75.0^/
*/
V
a/ Efficiency estimated—not commonly used,
b/ Insufficient data for estimate.
c/ Designed for 99% efficiency when firing with coal.
-------
TABLE 6-8®/
AIR CLEANING ERULFMMT INgEALLED COST
BASED ON 1,000 MW UNIT.(1968)
Furnish, Deliver, Erect
(Supports and Flues not Included)
Mechanical
(cyclone)
(75*)
Electro-
static
Precip.
(95^)
Electro-
static
Precip.
(99fl)
Comb.
Mech-
Electro.
(95*)
Comb.
Mech-
Electro.
(99^)
Comb.
Electro-
Mech.
(99*)
Bag
Filter
o>
$/mw
at 300°F
$/lb steam/hr
at 300°F
$ 730 $ 3,330 $ 5,200 $ 3,830 $ 4,470 $ 6,160 $ 7,650
0.11
0.48
0.76
0.56
0.69
0.90
1.12
$/ton coal/hr
at 300°F
2,300
10,400 16,200 12,000 14,800 19,300 23,800
$/CIM flue gas
at 300°F
0.25
1.00
1.50
1.15
1.40
1.80
2.25
$/CEM flue gas
at 700°F
0.20
0.85
1.35
1.00
1.15
1.55
-------
For a 500-800 megawatt plant, an electrostatic precipitator with
a design efficiency of 95$, treating 300°F flue gases and handling fly ash
(which is relatively easy to collect) could be installed for a cost between
$800 and $1.200/megawatt generating capacity. An electrostatic precipitator
of 99$ efficiency could be expected to cost between $1,400 and $2,200/mega-
watt of generating capacity.£/
Additional cost data, on the basis of volume flow rate, are given
in Figures 5-2 and 6-3, and Table 6-9.2/ t)ata for fly ash disposal costs
are given in Figures 6-4 and 6-5.
The relationship between the collecting area required in an
electrostatic precipitator and the collection efficiency for coals of dif-
ferent sulfur content is shown in Figure 6-6.^/
6.2.4.1.2 Fabric filters: The principal objections to baghouse
operation, that is, encrustation, blinding and deterioration of the cloth,
can be overcome by injecting dry dolomite dust into the gas stream and
ahead of the collection devices. Sulfur oxides react in the gas stream
and on the surface of the bags to form calcium sulfate, a collectable solid.
Bag filter installations are being tested with hopes of future application.^-
One prototype unit has been tested on an oil-fired boiler in
California. ^This unit handles 820,000 cfta at 258°F, using a gas (ft^/min)
to cloth (ftc) ratio of 6.5:1 along with an alkaline additive. 'This unit
achieves high particulate and sulfur-trioxide collection efficiencies
although a number of design and operating problems have been encountered.il/
The cost of a baghouse installation, including the additive
handling system, has been estimated at $2.25/scfm.i£/
6.2.4.1.3 Cyclones: Multiple small-diameter cyclones are used on
mechanical draft cor.bustion units either as precleaners for electrostatic
precipitators or as final cleaners. Efficiencies of well-designed units
range from 90$ for some stoker-fired units to 60$ for coal-fired cyclone
furnaces.
The efficiency of the cyclone or multicyclone collectors depends
on size, shape, and density of the particles as well as other factors.
It diminishes drastically in the range of 5 to 10 ^ in size. The effect
of particle size on collection efficiency at different pressure drops
(inches of HgO) is shown in Figure 6-7
64
-------
10.00
1.00
< 0.10
c
0.01
0.01
I I I
i—i—r
| | | | | INDICATES DATA SPREAD
EFF C ENCY
99.0* V,
95.0 - 9B. 9 %
90.0 - 95.0%
J I L
J I
0.10 1.00
GAS VOLUME THROUGH PRECIPITATOR - MILLIONS ACFM
10.00
Figure 6-2 - Precipitator Purchase Cost (FOB) as a Function
of Gas Volume Treated (Period 1965 - 1969)£/
65
-------
10.0
o
o 1.0
in
z
o
o
u
Q
UJ
C
0.10
| | | | | INDICATES DATA SPREAD
90.0 - 98.9%-
EFFICIENCY
99.0+ °/=
0.01
J I L
_L
_L
J I L
_L
J L
0.01
0.10 0.2 0.* 0.6 1.00
GAS VOLUME THROUGH PRECIPITATOR - MILLIONS ACFM
10.00
Figure 6-3 - Precipitator Erected Cost as a Function of
Gas Volume Treated (Period 1365 - 1969)£/
66
-------
TABLE 6-9
PRECIPITATOR COSTS (1965 - 1969)g/
Efficiency-
Gas Volume Range
- Millions
ACFM
0-0,
.249
0.250-
-0.499
0.500-0.999
>
1.00
Range ($)
FOB
Erected
FOB
Erected
FOB
Erected
FOB
Erected
90.0-94.9
64.7
59.3
33.8
101.1
25.2
69.2
25.8
No data
(2)
(1)
(1)
(6)
(1)
(2)
(3)
95.0-98.9
75.4
91.6
61.1
88.6
37.1
62.4
31.6
55.3
(15)
(5)
(10)
(12)
(6)
(9)
(21)
(16)
99.0+
98.0
204.5
62.7
103.5
44.3
82.7
34.2
55.5
(4)
(5)
(4)
(5)
O)
(9)
(23)
(17)
Note: (a) Costs are cents/ACFM.
(b) Numbers in parentheses are sample size, i.e., no. of installation contract prices averaged
to obtain indicated costs/ACFM (all precipitator manufacturers represented).
-------
G)
CD
£
Z
UJ
5
3.00
2.00
<
CO
o
X l.oo
1/1
<
I
>
z
5
400 800 1,200 1,600
PLANT INSTALLED GENERATING CAPACITY, 1,000 KW
2,000
Figure 6-4 - Plant Fly-Ash Disposal Investment!/
-------
CD
CD
£
0.30
-o
o
c*.
O
1/1
o
u
<
to
o
Q-
1/1
0.20 -
Q 0.10 _
x
i/i
<
Z
5
400 800 1,200 1,600
PLANT INSTALLED GENERATING CAPACITY, 1,000 KW
2,000
Figure 6-5 - Plant Fly-Ash Disposal Cost for 19671/
-------
99.5
99
U
OL
>
u
z
LU
u
98
97
96
95
Z
o
5 90
o
o
80
70
60
50
t—i—i—I—i—i—i—i—r
» » i I L I I I I
100 200 300 400
COLLECTING AREA PER 1,000 CFM-SQ. FT.
Figure 6-6 - Effect of Sulfur Content of Coal on Collecting Area
Required in Electrostatic Precipitator
70
-------
100
95
£
u 90
Z
LU
u
m 85
z
o
by 80
_J
O
u
75
70
0 20 40 60 80
PERCENT OF MATERIAL
UNDER 10 MICRONS
Figure 6-7 - Multiclone Collection Efficiency - Fly Ash. (As s
function of perticle size et pressure drops of
2 in., 3 in. end 4 in. of HgO.)—¦1
2 IN.
71
-------
6.2.4.1.4 Wet scrubbers: Sprays are used to a limited extent in
the stacks of coal-fired units to control particulate emissions during soot
blowing. The problems that limit the use of wet scrubbing include high
corrosion rates, high or fluctuating pressure drops, adverse effects on
stack gas dispersion, and waste disposal.
A turbulent contact absorber system has undergone testing for
absorption of SOg in alkaline solution and simultaneous removal of fly
ash for a coal burning power plant. With this system, fly ash collection
efficiencies of 98$ and. overall SO2 removal of 91$ can be expected at wet
scrubber pressure drops of about 4.5 in. w.g. For a generating capacity
of 25 megawatt equivalent to 100,000 cftn of flue gases at 300°F, the in-
vestment and operating costs are approximately $10/kw and $1.17/ton of
coal, respectively.14/
Two limestone injection 302 removal systems, designed by Combustio:
Engineering, have been installed on operating boiler units. This design in-
corporates a marble-bed wet scrubber having < 6 in. of pressure drop and
is guaranteed to remove 83$ of the SO2 and 99$ of the particulate matter.iZ/
6.2.4.2 Oil-Fired: The combined ash and unburned particulates
in exhaust gases from gaseous or liquid fuel combustion are net likely to
exceed local air pollution control statutes. For instance, the efficient
burning of a common heavy residual oil of 0.1$ ash results in a stack gas
concentration of only 0.C20 grain/scf at 12$ CO2. Nevertheless, particu-
lates from oil burning are still principally in the submicron range (0.4 ^),
and are in sufficiently large concentration to cause perceptible light
scattering.
The only air pollution control devices that have found ready
acceptance on oil-fired power plant boilers are dust collectors used to
control particulates during soot blowing . This equipment serves princi-
pally to collect particulate matter larger than 10 p.. Small-diameter
multiple cyclones are the most common soot-control devices installed.
The emission from an oil-fired unit without special collection equipment
is comparable to a coal-fired unit of better than 99$ collection efficiency.-
72
-------
The use of an electrostatic precipitator lor particulate removal
on an oil-fired steam generator was tested on a pilot unit and a prototype
unit. Although control was outstanding on the pilot unit, stack, emissions
from the full-scale unit did not comply with opacity regulations
6.2.4.3 Gas-Fired: Control equipment has not been utilized on
natural gas equipment.
6.3. INDUSTRIAL POWER GENERATION
Large industrial plants may generate their own electric power
or process steam by the combustion of coal, fuel oil, and gas. Emissions
from these combustion units parallel those discussed under electric
utilities (Section 6.2) but are lower in total quantity because of a
smaller quantity of fuel burned.
6.3.1 Fuel lype
6.3.1.1 Coal-Fired: The stoker-type boiler is the dominant unit
used in industrial plants. Stoker units accounted for about 70$ of the
coal burned by industrial plants in 1968. Pulverized units (20$) and
cyclone (10$) accounted for the remaining coal consumption. The pulverized
and cyclone units are generally associated with larger industrial com-
plexes, and are similar in design to those discussed under electric
utilities.
Stoker units used include:
1. Spreader stoker,
a. Traveling grate
b. Stationary or dumping grate
c. Vibrating grate
d. Reciprocating grate
2. Chain or traveling grate,
3. Water-cooled vibrating grate,
4. Multiple retort underfeed, and
5. Bituminous Coal Research Automatic "Packaged".
73
-------
Spreader-stoker units were described in Section 6.2.1.1. Travel-
ing grate and chain-grate units have moving grates. These grates move
from the front to the rear and carry coal from the hopper in front through
a grate into the combustion zone. The fuel bed burns progressively to the
rear, where the ash is continuously discharged. Older units with natural
draft are fast disappearing; modern units have zone-controlled forced
draft. Complete combustion-control systems are utilized and overfire
air, especially in the front wall, is an aid to burning the volatiles in
the fuel.^/
The water-cooled vibrating grate unit consists of a water-cooled
grate structure on which the coal moves from the hopper at the front of
the boiler through the burning zone by means of a high-speed vibrating
mechanism automatically operated on a time-cycling control. As in the
traveling grate, the fuel bed progresses to the rear, where the ash is
continuously discharged. Forced air is zone-controlled and regulated,
along with the complete coal and air system, through an automatic com-
bustion-control regulator ..5/
Multiple-retort underfeed boilers usually consist of several
inclined retorts side by side, with rows of tuyeres in between each retort.
Coal is worked from the front hopper to the rear ash-discharge mechanisms
by pushers. The forced-air system is zoned beneath the grates by means
of air dampers, and the combustion control is a fully modulating system.
In the larger furnaces the walls are water-cooled, as are the grate sur-
faces in some units. Multiple-retort underfeed stokers are declining in
use, giving way to spreaders and traveling-grate units.
The 3CR automatic packaged boiler is a complete steam or hot
water generating system, incorporating a water-cooled vibrating grate as
the firing mechanism. Coal is delivered from the storage bin to a hopper
from which it travels on the vibrating grate to the fuel bed. Ash is dis-
charged automatically by means of a screw conveyor. The unit has com-
pletely automatic combustion controls so that coal feed to the hopper from
the bin and ash discharge is coordinated with load conditions. Forced
and induced draft fans are used.^/
6.3.1.2 Oil-Fired: Large industrial complexes will use essentially
the same design of furnace as is used in electric utility plants. These
units are discussed in Section 6.2.1.2. Smeller industrial operations
utilize lower capacity units with attendant lower flame temperatures. In
many cases less attention is given to treatment of fuel and regulation of
combustion air for small units. Neglecting either one often results in
reduced combustion efficiency.l/ Boiler types used in smaller units are:
(l) steam atomizing, (2) pressure atomizing, and (3) centrifugal atomizing.
74
-------
6.2.1.3 Gas-Fired: No detailed information was found on gas-
fired units in industrial applications.
6.3.2 Emission Rates
6.3.2.1 Ccal-Fired: Emissions from coal-fired industrial units
are affected by the same factors discussed in Section 6.2.2.1 for electric
utility plants. Emission rates are summarized in Table 6-1. Emissions
currently total about 2.6 million tons/year with stoker-fired units
accounting for about 85$ (2.2 million tons/year).
6.3.2.2 Qil-Fired: The fly ash loadings for industrial sources
may be slightly higher than those for the larger electric-generating
plants. Emission levels are dependent upon combustion efficiency and
rate of build-up of boiler deposits. Table 6-1 summarizes emission
levels for cil-fired industrial boilers. Current emissions are estimated
at about 100,000 tons/year.
6.3.2.3 Gas-Fired: Meager data exist on emissions from gas-
fired units. Available information on emission rates is tabulated in
Table 6-1. Particulate emissions are estimated to be about 85,000 tons/
year.
6.3.3 Characteristics of Effluents from Industrial Boilers
6.3.3.1 Coal-Fired: The characteristics of effluents from indus-
trial coal-fired units would parallel those from electric-utility sources.
Some differences in composition and particle size of the fly ash will occur
because of the differences in boiler types employed in industrial plants.
6.3.3.2 Qil-Fired: Characteristics of emissions from oil-fired
industrial boilers differ in minor respects from those of electric-utility
boilers. Table 6-2 summarizes available data for these sources.
6.3.3.3 Gas-Fired: No detailed data were found on emissions
from gas-fired boilers.
6.3.4 Control Practices and Equipment for Industrial Boilers
6.3.4.1 Coal-Fired: Control equipment for coal-fired industrial
boilers is very similar to that employed by electric utilities. CycloneSj
multiclones and electrostatic precipitators are used in both groups
although the use of electrostatic precipitators has not been as preva-
lent for industrial boilers.
75
-------
The increased emphasis on reducing air pollution has apparently
prompted many of the industrial coal-fired boiler operators to switch
over to oil or gas. This route to control may be a simpler matter for
the industrial operator than for the electric utility operator who is
consuming larger quantities of fuel.
6.3.4.2 Oil-Fired: The use of control devices on oil-fired
units is usually limited xu periods when soot-blowing operations are in
progress or in areas where restrictive legislation requires low particu-
late loadings and low opacity of stack effluents. Multiple cyclones and
electrostatic precipitators have been used for these purposes.
6.3.4.3 Gas-Fired: Control equipment has not been utilized on
natural-gas equipment.
6.4. COMMERCIAL, INSTITUTIONAL, AND RESIDENTIAL FURNACES
Commercial, institutional and residential furnaces are primarily
used for space heating. The general character of emissions from these
sources would parallel that of electric utility and industrial sources,
with allowance made for differences in furnace types and operating pro-
cedures. In general, combustion efficiency will be lower in these units
and outlet grain loadings higher as a result.
6.4.1 Fuel T\roe
*¦ -
6.4.1.1 Cosl-Flrcd: Small stoker-type boilers are the main units
used in commercial, institutional and residential operations. In some
cases hand-fired equipment may be employed, but such installations are
fast disappearing, and are being replaced with automatic firing.
Stoker units include:
1. Underfeed stokers,
a. Single retort (residential)
b. Multiple retort
2. BCR Auto Packaged, and
3. Small spreader stoker
a. Stationary or dumping grate
b. Water-cooled vibrating grate.
76
-------
In the residential underfeed stoker, the coal is fed from a
hopper or directly from the coal storage "bin to the retort by a continuous,
rotating screw. Coal rises into the firing zone from underneath: thus
the term "underfeed firing''. Air is delivered to the firing zone through
tuyeres (grate openings), also from underneath the actively burning bed.
The coal and primary air control is "all on" or "ail off". Ash is removed
as a clinker from a refractory hearth through the furnace firing door.
The general arrangement of the single retort unit for commercial
and institutional use is similar to the residential unit, with "dead" plates
replacing the refractory hearth. As sizes become larger, screw feeders
are replaced by a mechanical ram, which feeds coal to pusher blocks that
distribute the coal in the fire box. Ash is discharged by side-dump grates.
Modulating combustion controls, i.e., variable control of both fuel and
air rates, are often used. Forced draft is automatically regulated, and
separate over-fire air systems are used, particularly when on-off controls
are used. A bridge wall retains the coal over the stoker grates.
The multiple-retort, BCR automatic packaged boiler, and spreader-
stoker units are described in Section 6.3.1.1.
6.4.1.2 Oil-Flred: Boiler types are similar to the small units
discussed in Section 6.3.1.2.
6.4.1.5 Gas-Fired: No pertinent information is available on gas-
fired units for these installations.
6.4.2 Emission Rates
Data are meager on emissions from all types of units used in these
facilities. In general, lower combustion efficiency than that experienced for
utilities or industrial units is expected to lead to increased outlet grain
loadings.
6.4.3 Characteristics of Effluents
No pertinent data on effluent characteristics were found for this
class of furnaces.
6.4.4 Control Practices and Equipment
Control equipment is not generally used on these small furnaces.
Reference 16 discusses the use of various combustion-improving devices to
reduce emissions of smoke, carbon monoxide, nitrogen oxides, and total gaseous
hydrocarbons from high-pressure atotr.izing-gun burners used in domestic oil-
fired furnaces. The devices (primarily improved nozzles) were designed to
improve combustion in older inefficient furnaces. Laboratory tests indicated
that the devices offer potential for reducing levels of pollutants.
77
-------
REFERENCES
1. "Control Techniques for Particulate Air Pollutants," NAPCA Publication
No. AF-51, Washington, D. C., 1969.
2 "The Application of Electrostatic Precipitators in the Electric Power
Generating Industry," Southern Research Institute, Final Report,
NAPCA Contract CPA 22-69-73, May 1970.
3. Smith, W. S., and G. W. Gruber, "Atmospheric Emissions from Coal
Combustion--An Inventory Guide," FHS Publication No. 999-AP-24,
April 1966.
4. Smith, W. S., "Atmospheric Emissions from Fuel Oil Cocbusticn—An
Inventory Guide," FHS Publication No. 999-AP-2, November 1962.
5. Cuffe, S. T., and R. W. Gerstle, "Emissions from Coal-Fired Power
Plants: A Comprehensive Summary," PHS Publication No. 999-AP-35,
Cincinnati, 1967.
6. "Air Pollution and the Regulated Electric Power and Natural Gas In-
dustries," Fed. Power Comm. Staff Report, Washington. D. C., Sep-
tember 1968.
7. O'Connor, J. R., and J. F. Citarella, "An Air Pollution Control Cost
Study of the Steam-Electric Power-Generating Industry," APCA Annual
Jfeeting in New York, June 1969.
8. Reese, J. T., and J. Grego, "Electrostatic Precipitation--Experier.ee,"
Mschanical Engineering, 34-37, October 1968.
9. Cahill, W. J., Jr., "Control of Particulate Emissions on Electric
Utilities Boilers," APCA Annual Meeting in New York, 1967.
10. "Report on Sulfur Dioxide and Fly Ash Emissions from Electric Utility
Boilers," Public Service Electric and Gas Company (New Jersey),
February 1967.
11. Felgar, D. N., and W. C. Ballard, "Alanitos Bag Filterhouse," Southern
California Edison Company, Los Angeles, California.
12. Gosselin, A. E., Jr., "Pilot-Plant Investigation of the Bag Filter-
house for Control of Visible Stack Emissions from Oil-Fired Steam-
Electric Generating Stations," Vol. XXVI, Proceedings of the Ameri-
can Power Conference, 1964.
78
-------
13. Flodin, C. R., and H. K. Haaland, "Some Factors Affecting Fly-Ash
Collector Performance on Large Pulverized Fuel-Fired Boilers,"
Air Repair £(l), 27-32, May 1955.
14. Pollock, W. A., H. P. Tomany, and G. Frieling, "Flue-Gas Scrubber,"
.Mechanical Engineering, 21-25, August 1957.
15. George, R. E., and R. L. Chass, "Control of Contaminant Emissions
from Fossil Fuel-Fired Boilers," Journal of the Air Pollution
Control Association J^£(6), 392-95, June 1967.
16. Howekamp, D. P., and M. K. Hooper, "Effects of Combustion Improving
Devices on Air Pollutant Emissions from Residential Oil-Fired
Furnaces," presented at 63rd Annual Meeting of the Air Pollution
Control Association, St. Louis, June 14-18, 1970.
17. Miller, D. M., and J. Jonakin, "Kansas Power and Light to Trap Sulfur
with Flue Gas Scrubber," Electrical World. March 4, 1968.
79
-------
CHAPTER 7
CRUSHED STONE, SAND, AND GRAVEL INDUS TRIES
7.1 INTRODUCTION
The conversion of naturally occurring minerals into crushed stone
sand, and gravel involves a series of physical operations. Quarrying, trans-
portation, crashing, size classification, and drying are common to almost
all mineral production procedures. Air pollution problems may te created
"by all of these operations. The dust emitted is usually a heavy dust re-
leased at ambient temperature, and these emissions can be considered to te
a nuisance to the community. Processing methods, particulate emission
sources, emission rates of individual particulate sources, the character-
istics of source emissions, and control practices ar.d equipment are discussed
in the following sections.
7.2 CRUSHED STONE
7.2.1 Production Process
The initial step in the processing of crushed stone occurs at the
quarry site. Rock and stcne products are loosened by drilling and blasting
from their deposit sites. Primary drilling, primary blasting, and secondary
blasting or breakage comprise the principal steps in the quarry operation.
The secondary blasting operation in many quarries is now either eliminated
by better fragmentation during primary blasting, or by the use of "drop ball"
cranes. Tractor-mounted air or hydraulic operated "rock-splitters" have
proven satisfactory for some operations.hJ
The broken rock or stone is transported from the quarry to the
processing plant. Transport is usually by truck or heavy earth moving
equipment. The processing of stone includes such operations as drying,
crushing, pulverizing, screening, and conveying- Primary crushers will
normally reduce stone to 1-3 in. in size. Secondary crushers are used
to reduce stone to sizes below 1 in. Following the processing opera-
tions, the stone or rock is loaded for shipment to the customer or sent to
s torage.
7.2.2 Emission Sources and Rates
Particulate emission sources in the crushed stone industry can be
divided into two categories; first, sources associated with the actual
81 Preceding page blank
-------
quarrying, crushing, screening, and processing operations; and second,
"fugitive" sources involving reentrainment of previously settled dust.
These fugitive sources include vehicle traffic on temporary roads, transfer
operations, and stockpiles.
The use of pneumatic drilling and cutting as well as the blasting
and transferring can cause considerable dust formation at quarry sites. The
transport of stone by vehicle creates dust from unimproved roads. No quan-
titative data is available on emission rates from these sources.
Rock processing operations (i.e., crushing, pulverizing, classify-
ing) are potential dust sources. Dust is discharged from crushers and grinde
inlet and outlet ports. Factors affecting emissions include moisture con-
tent of the rock, type of rock processed, amount of rock processed, and type
cf crusher employed.
Seme minerals require drying prior to processing. Dryers are
usually direct-fired, either parallel or counter flow, rotary units. Par-
ticulate emissions from dryers can be significant, and the amount emitted
varies with type of mineral processed, degree of drying, and dryer type.
A major "fugitive" dust source is stockpiles (i.e., windblown
dust). Losses vary with size cf stored material, density of material, mois-
ture content, and wind speed.
Actual test data on emissions from the above sources are limited.
The limited emission data are presented in Steele 7-1. The factors used in
estimating the particulate emissions from the crushed stone industry were
obtained from Reference 2. Table 7-1 does not include dust blown from stock-
piles. Stockpile losses due to wind erosion have been estimated at 0.5$
cf finished product for crushed stone.—' Hie potential amount of dust
that could arise from stockpiles in crushed stone storage areas is about
3.1 million tons per year. Factors which would reduce this estimate are:
(l) the amount cf product which is loaded for shipment directly from proc-
essing without being sent to stockpiles; (2) the amount stored in bins and
silcs; and (3) amount cf product which has sufficient moisture content at
the time of discharge to stockpiles to inhibit the formation of dust by
wind erosion.
No estimate has been made of dust emissions from quarrying or from
vehicle traffic over unpaved or paved plant roads.
7.2.3 Effluent Characteristics
Meager data exist on the physical and chemical properties of dust
emitted in crushed stone operations. It is usually a heavy dust emitted at
-------
TABLE 7-1
PARTICULATE EMISSIONS
CRUSHED STONE, SAND AND GRAVEL
oo
en
Source
Crushed Stone
A. Primary crusher
Quantity of Material
Emission
Factor
681,000,000 tons (cement, 0.5 lb/ton
lime 8c dolomite not
B. Secondary crushing 8c screening included)
C. Tertiary crushing & screening
D. Fines milling
E. Re-crushing & screening
F. Conveying, general screening,
etc.
G. Dryers
of rock®/
1.5S/
6.0^/
6.0^/
i.oW
15.OS/
Efficiency Application Net
of Control of Control Control
Emissions
1.7 lb/ton
of product
0.80
0.80
0.25
0.25
Cc-Ct (tono/year)
0.20
0.20
4,100,000
454,000
II. Sand & Gravel - crushing and
screening
918,000,000 tons
0.1 lb/ton
of material
46,000
III. Quarrying
A. Drilling
B. Blasting
C. Loading - unloading
IV. In-Plant Vehicle Traffic
Total for Crushed Stone, Sand and Gravel
4,600,000
bJ Ftiunds/ton of rock through the primary crusher.
b/ Listed emission factor is 5 lb/ton of rock re-crushed. Twenty percent of product is assumed to be re-crushed.
-------
ambient temperatures. The majority is fairly coarse and contains some
moisture. Figure 7-1 presents particle size data for the particulates emit-
ted from a jaw crusher and a conveyor system.
7.2.4 Control Practices ar.d Equipment
Control measures consist of vetting and sprinkling to minimize
dusting and proper loading and evacuation to collect dust from crushing and
screening equipment and transfer points. Cyclones and water spray chambers
are the present chief means cf collection of this dust. Bag filters or high-
efficiency water scrubbers are used in locations where stringent emission
standards must be met.
7.2.4.1 Quarry Operations: There are many sources of dust associ-
ated with crushed stone operations and most of these are of the "fugitive"
type. Blasting is one of these sources which occurs intermittently.
In conventional mining of coal, water-filled plastic bags are
used for stemming dust emissions from blast holes. Their use in conjunction
with an air-and-water blast results in a considerable reduction of the dust
from blasting.Ihis technique may be applicable to blasting operations
in stcne quarries.
A method cf suppressing dust from dry percussion drilling in
quarries and open pit mines has been developed. Water with an added wetting
agent is introduced into the air used for flushing the drill cuttings from
the hole. Dilution ratios range from SCO to 3,000 parts of water to one of
surfactant. The proper amount cf solution, about 7 gal/hr for a 3-1/2 in.
dia. hole, causes the drill cutting to be blown from the hole as damp dust-
/
free pellets—'
For primary blowing operations, it has been reported that initi-
ation of detonation with multi-delay devices and the complete combustion of
the explosive compound result in low dust emission
7.2.4.2 Transport Operations: The loading and unloading cf blasted
stone also usually releases dust into the atmosphere. Wetting of the bro-
ken stone can effectively decrease the dust emission but this is not a com-
mon practice. Wetting the surface cf a load in a transport vehicle will
reduce windage loss during transport.
The transport of stone by vehicle creates airborne dust from un-
improved roads. This can be minimized by frequent wetting of the road.
Oiling or wetting with CaClg can reduce the required frequency of wetting.
84
-------
100
00
cn
CO
Z
o
cc
o
50
40
30
20
UJ
IM
10
UJ
_l
o
t-
cc
<
Q.
I
.01
-------
Unpaved plant roads can be a constant source of trouble in dry
weather. Calcium chloride can be applied at a cost cf approximately
$0.15/sq yd treated/year. The principal problem with calcium chloride
treatment of roads is corrosion of vehicle bodies and timing the applica-
tions relative to weather. Treating roads with oils of various types, at
least once a month, will do an excellent Job of controlling unpaved roads
at a cost of approximately $0.10/sq yd treated/year. The use of water
trucks with high velocity side flush can be used to control dust. However,
the opinion has been expressed that the use of a water truck on unpaved
roads in the hot summer is virtually a complete waste of time.^/
7.2.4.3 Crushing, Screening and Transfer Operations: The simplest
and least expensive means of controlling dust in a crushing and screening
operation is through the use of wetting agents and fine water sprays at
critical points.^/
The use of untreated water sprays for suppression of dust from
handling and storing materials requires that approximately 5 to 8$ moisture
by weight be applied. However, when the water has been treated with a
surface active agent the moisture addition required may be reduced to 0.5
to 1^.5/ Once the material has been adequately sprayed and dustproofed
it may be conveyed through several transfer points without requiring further
treatment.
Water sprays are used successfully to control dust at transfer
and unloading points. Experimental use of a high expansion foaming agent
reduced dust counts at belt-conveyor transfer points by 50$
Steam has been used to alleviate dust at transfer points of con-
veyors in coal preparation plants, etc. The effectiveness of dust suppres-
sion by steam is attributed to the reduced surface tension of hot water.2/
7.2.4.4 Stockpiles: Stockpiles of minus 3/lS in. material can be
a dust problem in dry or wind^ weather. An economical solution to this
problem is difficult to find.^/ Various mechanical means can be used to
minimize dust as the product is dropped onto the pile,®/
Another approach to dust control is the use of chemical binders
for application to the surface of stockpiles. The chemical coats the top-
most particles with a thin film causing then to adhere to one another. As
long as the crust remains intact the stockpile is adequately protected
against windage losses. By adding a coloring agent to the binder, treated
areas can be readily identified to detect those that may not have been
86
-------
coated properly. The normal rate of application is 1 gal/100 sq ft of
surface area.5/ Application of water from sprinkler systems has also been
four.d to be a method of reducing stockpile losses.!/
7.3 SAKD AUD GRAVEL
7.3.1 Production Process
The raw materials for sand and gravel plants may be dredged from a
river or quarried ar.d then transferred by vehicle to the crushing and screen-
ing equipment. Jfeterial is frequently washed prior to processing to obtain
a product which meets users' specifications. Preliminary screening, prior
to crushing, is also practiced in some plants. Wet and dry screening may
be used. Following processing and classification., the material is loaded
for shipment or stockpiled in storage areas.
7.3.2 Emission Sources ar.d Rates
Particulate emission sources in sand ar.d gravel processing parallel
those in crushed stone preparation. The crushing, screening, and transfer
operations can all generate significant quantities of dust. Emission rates
are affected by moisture content of processed materials, degree of size re-
duction required, and type of equipment used for processing.
Observations from numerous plants indicate that a major source of
dust, in addition to those associated with the plant equipment, is from
vehicle traffic ever unpaved roads or paved roads covered with dust.®./
Stockpile losses would also contribute to the dust burden. Stoclqpiles of
fir.e sand would be susceptible to wind loss.
No information has been found on emission factors from sand and
gravel plants. One sampling report, furnished by a state agency, listed
overall emissions as 0.06 lb. of dust/"ton of material through the plant.1'
This report listed the discharge of the secondary and reducing crushers
and the elevator boot on the "dry side" as the dust sources. Seventy-five
percent of the dust was estimated to cane from the crushers. Based on
this limited information, an overall emission factor of 0.1 lb. of dust/
ton of product was assumed for sand and gravel plants.
Tfeble 7-1 summarizes the estimates of emission levels from sand
and gravel plants. T&ble 7-1 does not include dust blown from stockpiles.
Stockpile losses due to wind erosion have been estimated at 1$ of finished
product for sand and 0.5$ for gravel.Most stockpiles are merely ground
piles; however, silos and bins are also used. Potential "fugitive" dust
emissions from stockpiles in sand and gravel plants are estimated to be
about 5.5 million tons/year.
87
-------
Ko estimate has been made of dust emissions from quarrying or
from vehicle traffic over unpaved or paved plant roads.
7.3.3 Effluent Characteristics
Limited data were found on the characteristics of effluents from
sand and gravel plants. Stock sampling data for sand and gravel dryers,
obtained from state control agencies.9»10/ indicated that outlet grain
loadings ranged from 5.8 to 38 grains/ft3. Mass median particle size of
the particulates emitted from the dryers varied from 3.5 to 9.4 p,.
7.3.4 Control Practices and Equipment
Specific information on control practices and equipment utilized
in sand and gravel plants is limited. Since many of the operations parallel
those of the crushed stone industry, similar control practices and equip-
ment are -undoubtedly employed.
88
-------
REFERENCES
1. Minnick, J. L., "Control of Particulate Emission from Lime Plants,"
presented at 63rd Annual Meeting of Air Pollution Control Association,
St. Louis, Mo., June 14-18, 1970, Paper No. 70-73.
2. Air Pollutant Emission Factors, U.S.D.H.E.W., Environmental Health
Service, NAPCA, Washington, D. C., April 1970.
3. Anderson, F. G. and R. L. Beatty, "Dust Control in Mining, Tunneling,
and Quarrying in the United States, 1961 through 1967," United States
Department of the Interior.
4. Hankin, M., "Is Dust the Stone Industry's Next Major Problem," Rock
Products, "0, April 1967.
5. Matthews, C. W., "Chemical Binders: One Solution to Dust Suppression,"
Rock Products, January 1966.
6. Anon., "Dust Control on Underground Coal Conveyors," Mining Congress
Journal, 51, December 1965.
7. Trauffer, W. E., "New Hampshire Plant Produces Both Crushed Stone and
Sand and Gravel," Pit and Quarry, February 1968.
8. "Evaluation of Dust and Noise Conditions at Typical Sand and Gravel
Plants," National Sand and Gravel Association, Washington, D. C.
9. Private communication, New Jersey Air Pollution Control, Trenton,
New Jersey.
10. Private ccmmunication, Office of Air Quality, Washington Department of
Health, Seattle, Washington.
89
-------
CHAPTER 8
OPERATIONS RELATED TO AGRICULTURE
8.1 INTRODUCTION
The agriculture industry as considered, here includes such diverse
operations as field "burning, grain elevators, feed mills, and cotton gins.
Obviously, emissions from these operations sure highly variable.
Open burning of agricultural wastes is practiced in many areas
as the most practical means of clearing the land of these wastes. This
practice can contribute a high concentration of pollutants to the atmo-
sphere. Grain handling facilities constitute a major dust problem in some
urban areas. Furthermore, in less densely populated areas a grain facility
may be a nuisance to people in the immediate vicinity. Cotton gins also
present primarily a localized air pollution problem.
Various phases of the agriculture industry, particulate emission
sources, particulate emission rates, effluent characteristics, and control
practices and equipment are discussed in the following sections.
8.2 AGRICULTURAL FIELD BURNING
Disposal of agricultural wastes is imperative because the refuse
piles act as reservoirs of horticultural diseases and agricultural pests.
Open burning is currently the most practical means of accomplishing this
disposal.
Emissions into the atmosphere from the burning straw and stubble
are characteristic of vegetative plant sources generally. Cellulose and
lignin are the primary constituents of plants. Emissions consist of smoke,
made up of carbon particles of varying sizes, ash, and certain gases. Most
of the carbon particles are minute in size and indistinguishable without
visual aid, while others are readily visible. The former are a major factor
in reduced visibility, while the larger particles, which settle out more
readily, are factors in soiling and deposits on property. The principal
gases emitted are the organic hydrocarbons, carbon dioxide, carbon monoxide
and oxides of nitrogen.^/ Open burning emissions are affected by many
91 Preceding page blank
-------
variables including wind, ambient temperatures, moisture content of the
fuel burned, size and shape of fuel, and compactness of fuel bed. Table 8-
gives typical data for particulate emissions from rye-grass burns and
Table B-2 summarizes emission rates. It is estimated that agricultural
field burning emits about 2.4 million tons of particulate/year.
TABLE 8-1
PARTICULATE EMISSIONS FROM RYE-GRASS BlBUsV
Grass
Annual
Annual
Variable
Suspended particulate, mg/m^
Percent organic matter in
smoke
Perennial Suspended particulate, mg/m3
Perennial Percent organic matter in
smoke
Low
11.4
13.3
20.4
19.9
Average
25.6
37.4
39.4
38.8
High
46.8
63.9
56.3
72.8
92
-------
TABLE 8-2
PARTICULATE BCSSKHg FRCM
OPERATIONS RELATED TO AGRICULTURE
Source
Quantity of Material
Emission Factor
Burning of Stubble
280,000,000 tons of stubble 17 lb/ton of stubble burned
Efficiency
of Control
Cc
0.0
Application Net
of Control Control
Ct Cc-Ct
0.0
0.0
Emissions
(tons/yr)
2,400,000
II. Grain Elevators
A. Terminal Elevators
1. Shipping or Receiving
2. Transferring, Conveying, etc.
3. Screening and Cleaning
4. Drying
B. Country Elevators
1. Shipping or Receiving
2. Transferring, Conveying, etc.
5. Screening and Cleaning
4. Drying
177,000,000 tons of grain
Total for Grain Elevators
1 lb/ton of grain handled
2 lb/ton of grain handled
5 lb/ton of grain handled
6 lb/ton of grain handled
5 lb/ton of grain handled
3 lb/ton of grain handled
8 lb/ton of grain handled
7 lb/ton of grain handled
0.70
0.28
1,700,000
CO
HI. Cotton Gine
A. Trailer Unloading
B. Cleaners
C. Stick and Bur Machine plus Huller
front and Mote Discharge Stand
D. Lint Cleaner
E. Condenser
11,000,000 bales
Total for Cotton Gins
5 lb/bale
2 lb/bale
3 lb/bale
1 lb/bale
_1 lb/bale
12
0.00
0.40
0.32
45,000
IV. Peed Mills
A. Alfalfa Detydrators
1. Primary Cooling Cyclone
2. Secondary Cooling Cyclone
3. Air-Heal Separator
a. Cyclone
b. Cyclone + Skinner
4. Pellet-Heal Separator
5. Pellet Re-Grinder
1,600,000 tons of dry meal
Total for Alfalfa Dehydrators
11 lb/ton of dry meal
4 lb/ton of dry meal
47 lb/ton of dry meal
9 lb/ton of dry meal
2 lb/ton of dry meal
2 lb/ton of dry meal
50 (as an average)
0.85
0.50
0.42
23,000
B. Wheat Mill-Feeds
C. Gluten Feed and Mnal
D« Rice Mill-Feeds
E- Brewers' Dried Grains
F. Distillers' Dried Grains
G. Dried Beet Pulp
4,490,000 tons
1,515,000 tons
476,000 tons
336,000 tons
447,000 tons
.1,100,000 tons
Total for Feed Mills Other Than Alfalfa
1^ of end product
l£ of end product
1* of end product
1$ of end product
l£ of end product
1* of end product
0.42
0.42
0.42
0.42
0.42
0.42
26,000
9,000
3,000
2,000
3,000
6,000
49,000
V. Flour Mills
112 lb. per capita
TOTAL FOR LISTED OPERATIONS
4,217,000
-------
8.3 GRAIN ELEVATORS
Grain elevators are primarily transfer and storage units and are
classified into two categories. These are the smaller more numerous
country elevators and larger terminal elevators. In addition many elevator
locations also contain feed manufacturing facilities. Particulate emis-
sions occur because of the dry, light nature of most grains and the way
they are handled via pneumatic and mechanical conveyors. A wide variety
of grain-handling configurations are possible at elevator sites depending
on the number and quantity of grains handled, and the amount of processing
required. At grain elevator locations any or all of the following opera-
tions can occur:
Receiving, transfer and storage
Cleaning
Drying
Milling and grinding.
Receiving arid transfer operations are accomplished by unloading
the grain, usually by dumping into a bin followed by conveyor belt or
pneumatic transfer. Cleaning operations are designed to eliminate im-
purities such as sticks, stones, and other foreign matter. Both screen-
ing and air classifiers are used to separate grain and foreign matter.
8.5.1 Emission Sources and Rates
Emissions from grain operations may be separated into those
occurring at all elevators involving transfer losses, and those occurring
at processing operations such as cleaning, drying, and grinding. Emis-
sions are greatest at the loading and unloading areas, especially when
these operations are carried out in the open. Falling or moving streams
of particles inspirate a column of air moving in the same direction.
When this moving mass of particles strikes an immovable object, the
energy expended causes extreme air turbulence and a violent generation
of dust occurs. This undesirable situation occurs when trucks and rail
cars are dumped into deep hoppers and also when rail cars and the holds
of ships are loaded.
Lesser sources of dust emissions in transfer operations are
conveying equipment and storage bins. Belt conveyors have less rubbing
friction than either screw or drag conveyors and generate less dust.
Dust emissions usually occur at belt transfer points as materials fall
onto or away from a belt. The discharge points of pneumatic conveying
equipment are also potential sources of dust emissions. Storage bins
vent dust-laden air from two sources. One source is air displaced during
94
-------
loading operations. As the incoming material falls freely from a spout
at the top of the bin, dust is mixed with the air in the bin. The other
source is air inspirated by the flow of incoming material.
Factors affecting emissions from grain elevator transfer opera-
tions include the types of grain, the moisture content of the grain
(usually 10-20$), amount of foreign material in the grain (usually 5$
or less), the amount of moisture in the grain at the time of harvest
(hardness), the amount of dirt included with the grain during harvest-
ing, and the degree of enclosure at loading and unloading areas.£•/
The grain processing operations may include wet and dry milling
(cereals), flour milling, oil-seed crushing, and distilling. Wet milling
by its nature is not conducive to major dust formation, although dust may
escape from dryer cyclones. Dry milling, however, is somewhat more dusty
in its operation. Most handling and transfer in these operations is
pneumatic, allowing good dust control. Oil-seed crushing generally is
not conducive to major dust generation, but losses can occur from extract-
ing and drying operations and from cyclone collectors used on these opera-
tions. Grain distilling operations also are not conducive to major dust
formation although particulates can escape during unloading of grains and
"be entrained in the gaseous discharge from cooling operations. The major
problem with these operations is odor emissions .£/
Drying is usually accomplished in rotary, column, or shelf
dryers using heated air as the drying medium. The material emanating
from the dryers is generally not classified as dust but rather chaff or>
in the case of corn, "beeswing." Although the particle size is large,
it is extremely light and filmy. This material will carry for miles on
a windy day if it is released from a source sufficiently high above the
ground.1/
Grinding may be done in a variety of devices in either a wet
or dry state. Common devices used include hammer mills and rollers.
Many of the large terminal elevators also process grain at the same
location.
Factors affecting emissions frcm grain processing operations
include the type of processing (wet or dry), the amount of grain processed,
the amount of cleaning, the degree of drying and heating, the type of
dryer, the amount of grinding, and the type of grain.£/
Emission rates for grain elevators are summarized in Table 0-2.
Current particulate emissions total 1.7 million tons/year.
95
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8.3.2 Effluent Characteristics
Available data on the chemical and physical characteristics of
effluents from grain elevators are summarized ill Table 8-3. Particulates
emitted during railroad car loading of oats and wheat have a geometric
mean size of 3.1 and 2 p,. Grain dust presents a high explosive hazard.
8.3.3 Control Practices and Equipment
Air pollution from feed and grain mills consists entirely of
dusts. These dusts, though varied, may be collected by inertial devices
and fabric filters.
For receiving hoppers used for unloading, the best method of
hooding is to exhaust air from below the dump grating to a fabric filter
or cyclone-filter combination.^/ One of the most difficult to control
emission sources is that occurring when grain is poured into the hold of a
ship.£/
The duct work for a dust-collection system generally is sized
based on the volume of air necessary for each hood inlet, and pickup point,
and a base velocity of 4,000 ft/min in the duct. Velocities of < 3,500
ft/min will permit settling of dust in long horizontal ducts. If dust
settles and accumulates in duct work, it provides a harborage and point
of insect infestation. Careful attention should be given to design of
duct worjs. to avoid projections in the duct which will permit accumulation
of dust and subsequent infestation by insects .11/
One development reported in a recent article^/ is a completely
enclosed belt conveyor. The.basement of the storage elevator, which houses
the conveyor, is kept under slight positive pressure so that no dust can
leak from inside the conveyor.
6.3.3.1 Cyclones:• Cyclones are used with great versatility in
grain elevators and in feed mills. Nearly all cyclones are of the simple,
low or medium efficiency types.
8.3.3.2 Baghauses: Fabric filters can provide high efficiency
dust collection for most services associated with feed and grain operation.
However, they do not find application in grain drying due to the high
moisture content of the effluent gases from the dryer.
96
-------
A (Pir; I)
Agriculture
Industry
TABLE 9-3
EFFT^fSWT CHARACTERISTICS - CPEPJTIOIIE H£:JT!3 T.~. AC.'ZCSLTJPr
Particle Site
Sclldj
Lending
Che&isal cnaysitinn
Partible El«c*.ri:al teiat.re
Eertlty Resistivity Corter.t
TciriMty
1. Field burning
a- Jtye-jrass field
Suapen4»d particulates:
mean pArt-.clc alte:
0.5
11-56* avg.,
52.5
Carbcn, ash
2. Grain elevators
a. Railroad car
loading
Conveyer syatea
(1 plant)
Cleaning
1 Drying
3. Flour nill
Optical: Oar a
Oecaetric Dean
•iae, 3.1
'1 test)
ifhfat; geosetrie
neftn :lt(, 2.1
(1 test)
Screen analysis:
6.4 < 44. 2$ .6
< 74, 45 < 104
See Ta'rle 6*4 fr.r
detaixed coapnM
tirn
Chaff, tran weed
a«fd. poller..
dirt., inseci
Fart a
Chaff
Tiour dust
tlrsLr. dust :ti Cvt.a-d-
erei tox;c . t>.? My
cause respiratory
¦ vnptnpi sV.\r.
rash en prclrr.Red
?Kput>i.re
Tee! Kill
a. Feed barley
ROTeenr-ill
Alfalfa dahydrat.i;4
Bill
a. Prioary eoclirg
cyclor>e
b. Secondary ccelin®
eyclnn*
c. Air seal s^rarBtcr
d. Pellet steal air
separator
e. Pellet regnrd
l*r *-
Average valer.t
Sr.okns' ; i. , 3
O l-C .2
o.:-c .4
0.2-2.3
0.1-^.4
C-.0019-0 .55
(-eper.der.t
jpon aarylir.g
poir.t >
Ir.cir.eratrr
Sec Table 6-5 for
dttsiltiJ sJC-tpt.-
iiL^or.
Trash, d'-i*., l»r.:
ar-d Fest:-"!".e
res:di.f
Fl\ ash, soike .
*rs-ir.:.c
1.25
1.32
1. ?:
*>nr S;.e
A. Par'-l-'uiatc (P*rt II)
hygroseepi.- FlaenaMlity or Ort i-ra .
Sour££__ Solubility Wettability Characteristics Explosive Malts Handling .Th^rgTerisri"* jypfr*'.'d ¦ r
Agriculture Industry
1. Field burning
2. Oraln elevators "rain du?r. presents Gram* ar» g-nn^rsily rmt
a higft eipl-jtive atraclvc. stinky, or
hazard ccrrjsi'.e
3. Gotten ginning
a. Cin
b. Incinerator
Fcatielie residues «ay rv»
~ S«e CodlBg Key, Table 5-1, Chapter 5, page 4Si for units fsr Individual affluent prjpvrtlaa.
* Hllligma ptr cubic a«t«r.
97
-------
TABLE 8-3 (Ccecluied)
Carrier 3a»
TcBperatora
Noitture
Caitcnt
Cbealcal C«pcfil'lOR
FlamaMlity flf
Totlclty Corrcslvlty Cdor Explosive Units
Agriculture
tsdujtry
X. Field buroli*
i. ^«*irui
field
C02, CO, Bj, o2,
hydrocarbons, K0X
(see Table¦ 6-6,
6-7 far acre de-
tailed data)
Qr%ln elevator*
a. AHlroad car
b.
c. Prylai
now alii
reed sin
a. Peed barley
ill
Mllo uid mlted
barley eleanor
(a) 2.6-3.7
(b) 6.8-49
(») S.»
(b) 44 (1 mu)
Alfalfa dehydrat-
lac Bill
a. Prlaary cool-
i&f cyclone
b. Secondary cool-
in$ cyclone
Air aaal
separator
A. P»llet aaal
air eeparator
Pellet regrind
jeparator
(a) 8-15
(b) 460-63)
{») l.i-i.B
(b) 54-74
(a) 2.5-6.4
(b) 144-SM
(»! 3.9-4.9
(t.) 100-180
(») 1.0
(tO 9.5
Dry ^ulb,
340
Wet sulh,
152-175
wry bulb,
125-140
Ve*. bulb,
85-67
Dry bulb,
85-139
Vet bulb,
75-90
Dry 5ult>,
110-127
Vet bu.lb,
94-95
Dry bulb,
120
Vet bulb,
90
3.174-C .48**
d« point
144-172
0.01S-O.C19**
d«v pclct
68-75
0.016-C.02**
dew point
72-78
0.C27-0.C33**
dev pciat
0.C24"
d«v point
82
Cett«B ilrxiaf
a. Gin
b. Inclneretor
C02, cc, :,-2> 32,
ariaclc cattpDur.ds
a&d ether gases
characterlctl:
of ecttoc w»£t«
pjrrolyfiiR
•• Founda/poimd.
98
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TABLE 8-4
ANALYSIS OF AIRBORNE DUST COLLECTED IN
VICINITY OF RAILWAY CARS DURING LOADING
Percent by Weight
Cats Wheat
Organic fraction 82.2 07.2
Inorganic fraction 17.8 12.8
Free silica in total dust 8.0 7.4
Free silica in organic fraction 2.3 1.5
Free silica in inorganic fraction 5.7 5.9
TABLE 8-5
PARTICULATE AND PRODUCT ANALYSES
(ALFALFA DEHYDRATING MILL)
Particulate Source
Company A
Air meal separator
Company B
Air meal separator
Company A
Pellet meal air separator
Company B
Pellet meal air separator
Company C
Pellet regrind air separator
Product
Company A, Pellets
Company B, Pellets
Company C, Meal
Protein
Content
Percentage
21.20
21.60
18.90
19.25
26.60
15.0
14.1
17.3
Carotene
Content
(lU/lb)*
107,600
77,300
88j900
84,900
145,900
100,000
88,000
132,000
* International Unit, IU, for carotene (pro-vitamin A.) is defined as
biological activity of 0.6 |ig of (3 -carotene.
99
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TABLE 8-6
YIELDS OF VARIOUS POLLUTANTS FROM GRASSES 1/
BURNED IN IA BORA TORY TOWER
Pounds/Ton of Grass Burped
C
NOg 8
Percent
Sat.*/
Balance
Temp.
Grass
Moisture
Particulate
C02
CO
C
+
Acet.
Olefins
Ethylene
(*)
(ppn
Dry Series
Blue
5
16.5
2,786
147
18
3.3
3.1
2.4
107
72
Perennial Rye
6
12.0
2,483
104
14
2.1
3.2
1.4
100
49
Bent
2
14.0
2,557
124
14
2.1
2.0
0.9
98
21
Annual Rye
9
10.5
2,666
85
8
0.9
1.2
0.6
103
23
Fescue
9
13.0
2,737
122
12
2.5
2.4
1.2
107
45
Orchard
15
11.5
2,469
89
7
1.2
1.2
0.7
100
27
Dry
-Green
Series
Blue
23
15.0
2,407
95
8
1.0
2.0
1-.2
111
44
Perennial Rye
71
26.0
678
106
19
2.4
5.6
3.4
77
4
Bent
60
24.0
1,277
109
19
2.1
5.0
3.1
94
13
Annual Rye
1
20
9.0
1,855
56
4
0.4 '
1.0
0.6
103
37
2
55
11.0
969
60
6
0.8
2.4
1.8
102
—
Fescue
66
17.0
925
77
9
1.2
2.6
1.8
94
8
Orchard
1
66
18.0
645
86
14
1.4
3.3
2.1
87
12
2
47
17.0
1,558
113
16
1.7
4.0
2.3
90
5
a/ Without methane.
-------
TABLE 8-7
RESULTS OF SUMMER 1967 FIELD BURNS OF VARIOUS GRASSES*/
Ambient
Wind
Burn
Lb. Particulate/
Lb. CO/
Lb. HC/
Temp.
R.H.
Speed
No.
Grass
Ton Fuel
Ton Fuel
Ton Fuel
(°F)
(*)
(mph)
9
2
Blue
81.23
238
14.75
89.8
32
3
Orchard
15.54
130
10.78
71.5
50
6
4
Orchard
8.47
140
11.18
90.2
24
6
5
Perennial Rye
10.23
133
10.68
70.5
61
3
6
Red Fescue
1.31
102
9.14
79.8
64
11
7
Red Fescue
12.65
120
9.90
88.0
34
0
9
Perennial Rye
8.78
118
9.41
80.0
51
2
10
Perennial Rye
8.75
107
9.41
80.0
62
1
11
Red Fescue
5.24
126
10.02
84.0
64
12
12
Annual Rye
3.33
108
10.27
100.0
24
9
-------
8.4 ALFALFA DEHYDRATIKS MILLS
Dehydrated alfalfa is a meal product dried rapidly by artificial
means at temperatures above 212°F. The general method of operation is to
harvest the alfalfa with a self-propelled or tractor-drawn chopping machine.
The chopped alfalfa is then transported as quickly as possible to the
dehydrating plant where It Is dumped onto an automatic feeding device and
fed into a dryer at a uniform rate. Practically all of the dryers are of
the direct-fired, rotary type. The products of combustion leave the com-
bustion chamber of the furnace (most units are gas- or oil-fired) at a .
temperature in the neighborhood of 1800 to 2000°F. The chopped, wet alfalfa
is discharged from the feeder into this hot flue-gas stream which is being
pulled through the dryer by a fan at the outlet end. After passing through
the rotating drum section, the moisture content of the material will be in
the neighborhood of 7 to 9$ and the flue-gas temperature will be 250 to 350®
Customarily, the material is then blown to a primary cooling cyclone in
which the dried material is separated from the new moisture-laden flue-gas
stream. The effluent from this cyclone (Figure 8-1), usually billowing
clouds of condensed steam, is the first of a series of atmospheric emis-
sions from the alfalfa dehydrating plant.
From the primary cooling cyclone, the dehydrated alfalfa is
passed through a secondary cooling cyclone, a grinder, and finally a third
cyclone which collects the meal for bagging, bulk storage or pelletizing.
To minimize storage and shipping space requirements, the meal is
often steam-extruded into pellets which are subsequently air cooled. The
coolant air entrains small pellet chips and unpelletized meal. This par-
ticulate matter is then separated from the coolant air stream and recycled
tc the pelletizer. Separation is accomplished in a fourth cyclone, the
pellet meal air separator, which constitutes a potential source of air
contamination.
For formula feeds the pellets are reground, an operation found
only in the larger dehydrating mills. This process consists of conveying
the pellets from storage to a hammer mill, grinding the pellets into a
meal, and pneumatically conveying the meal to the pellet regrind air
separator, and thence to the blender, bagging equipment, or to bulk ship-
ping facilities. The discharge from the pellet regrind air separator is
a possible source of air pollution.2/
8.4.1 Emission Sources and Rates
Objectionable emissions from alfalfa dehydrating plants include
dust from the various separators, and odors from the volatile matter
driven off the alfalfa with the moisture and combustion products emitted
102
-------
Chopptd Alfilft PtIWiry
Air satl
SipArAtor
Pria*ry
Cool Ing
Cyclone
^Saeondftry
Cool inq
Cyctona
^-jr-Oit Additiv*
IOsPi (Optional
Furnict
Rotary 0rm
Dry#r
» UUr
K«>v jr Tr*«h
Imir Mill
rill it Rigrlnd
Mr S*(«r«ter
Film H*tl Air 8«p«ritor
Cooling Towir r St*
Ftllat
Ho»»»r
^M»Ut Hill
Pill it Hopper
lltAdcr
Miit
Shi pp Ing
Mill
Btgging
U«4l
ihlp»ln«
Moal
Storu*
T«nk
p ! ra
*ot«:
Addition*! Proeooilng to
Product Foroulo Food*
Figure 8-1 - Alfalfa Dehydrating Process Flow Diagraml/
103
-------
tc the atmosphere.U Emission rates from alfalfa dehydrating plants are
summarized in Table 8-2. Particulate emissions currently total about
23,000 tons/year.
8.4.2 Effluent Characteristics
Table 8-3 summarizes available data on the chemical and physical
properties of effluents from alfalfa dehydrating plants. The average
Stokes' diameter of emitted particulates ranges from 1.5 to 10 ll .
8.4.3 Control Practices and Equipment
Alfalfa dehydrating operations are a source of pollution in some
areas. The primary and secondary cooling cyclones, and air meal separators
which are a part of the process, are the major pollution sources. Control
equipment such as multitube collectors and bag filters has been used as
auxiliary dust separators on the air meal separator. However, the oil
additive that is sometimes used in the dehydrating process causes clogging
of bag filters. Other methods suitable for control of effluents dis-
charged to the atmosphere include incineration and electrical precipita-
tion, but in general these are more costly than bag filter units.—!
8.5 COTTON GINS
Modern cotton ginning installations using pneumatic conveying
equipment, air blast equipment, and seed cotton conditioning equipment
have increased the output of normal ginning operations and improved cotton
fiber quality. This gain in output has been accompanied by a major increas
in the volume of air bearing lint and dust discharged to the atmosphere.
Although the discharge of waste material to the atmosphere from an individ-
ual cotton ginning operation generally results in only a local air pollu-
tion problem, the number of such establishments and the gradual urban
encroachment into the areas of ginning operations is sufficient to warrant
consideration of their overall pollution potential.§/
Figure 8-2 illustrates a flow diagram for a cotton gin used by
the Department of Agriculture to study particulate emissions from ginning
operations. This particular operation is considered to be representative
of ginning operations in general.®/ The flow diagram indicates the follow-
ing major sources of particulate emissions: unloading fan, six-cylinder
cleaner, stick and bur machine, gin stand, separator No. 2, seven-cylinder
cleaner, separator No. 3, and the condenser. The unloading fan supplies
the air for the transfer of cotton from the storage bins or from a wagon
to the first separator. These wastes are carried to the dust house by the
104
-------
Figure 8-2 - Flow Diagram of U. S. Department of Agriculture
Cotton Gin, Stoneville, Mississippi®/
-------
moving air stream and consist mostly of sand., dirt, and other fine mate-
rials. Hie dust house is a tall structure open at top and sometimes also
open at bottom and it acts as a settling chamber or elutriator.
The cotton then passes from the first separator onto the feed
control, into the tower dryer, through a boll trap, and then to the six-
cylinder cleaner which opens and cleans the boll cotton. The waste dis-
charge from the six-cylinder cles.ner is carried to the dust house by a
moving air stream and consists of fine particles of leaf trash, dirt, sand,
stems. and small sticks. From the cleaner the cotton is moved to the stick
and bur machine which removes burs, sticks and steins, together with fine
trash not removed by the cylinder cleaner. The discharge duct from the
stick and bur machine joins with the air discharge duct from the gin stand.
Wastes from these sources are carried to the dust house.
From the stick and bur machine the cotton passes to a second
separator, then to a stub tower dryer, and then to a seven-cylinder cleaner.
The discharge from the second separator is emitted directly to the atmo-
sphere outside the building. These wastes, carried through the separator,
consisted mainly of fine particles of leaf trash, dirt, sand and stems.
The waste discharge from the seven-cylinder cleaner is carried
to cyclones. These wastes consist mainly of sand, trash, and dirt.
The seed cotton then passes from the seven-cylinder cleaner on .
a belt distributor to the extractor-feeder and then to the huller front
gin stand. The trash frcm the gin stand (burs, sticks, stems, motes, and
sand)is combined with the waste discharge from the stick and bur machine
and blown to the dust house.
From the gin stand the cotton is transferred first to a separator
which removes fine leaf particles, motes, dust, and sticks, which are dis-
charged directly to the atmosphere outside the building. The cotton next
travels to the lint cleaner, and then to the condenser which discharges
sand and dirt to the dust house. From the condenser the cotton goes to
the baler and out as a finished product.
8.5.1 Emissions
Data on atmospheric emissions from cotton ginning operations are
limited in scope. Reference 8 presents data from a study conducted at the
Cotton Ginning Laboratory, Agricultural Research Service, U.S.D.A., Stone-
ville, Mississippi. This operation was considered to be representative of
ginning operations in general, and the cotton harvested by both machine-
and hand-picked methods and processed during testing was representative of
the cotton from the test area.®/
106
-------
The ginning operation and subsequent incineration of the waste
can release pesticide residues, bacteria, benzene-soluble organic matter,
and arsenic compounds to the atmosphere. Paganini?/ reported data on
particulate matter collected upwind and downwind from cotton gins.
The bacteria and fungi co-ants in samples taken upwind were 88
to 100 and 33 to 70/m^ of air, respectively, when collected on nutrient
agar. The counts in samples taken downwind ranged from 172 to 1,752 and
19 to 129/m^ of air, respectively.
Smoke emitted from incineration of cotton gin waste was found to
contain significant amounts of benzene-soluble organic matter and arsenic,
and to reduce visibility to such an extent at times in some locations that
driving was hazardous on the highway.
Emission rates from cotton ginning are summarized in Table 8-2.
Particulate emissions currently total 45,000 tons/year.
8.5.2 Effluent Characteristics
Available data on the chemical and physical properties of efflu-
ents from cotton ginning operations are summarized in Table 8-3. The
concentrations of arsenic, pesticides, and defoliant in effluents from
various phases of the ginning operation generally exceed many times the
concentration found in natural ambient air.
8.5.3 Control Practices and Equipment
The ginning operations employ small-diameter cyclones for removal
of dust, trash, fibers, etc. The small-diameter cyclone that cane into
widespread use several years ago has proved effective. It creates more
static pressure hut its higher efficiency makes up for this increased cost
of operation.i2/
It is standard practice to place all but one of the cyclones in
a battery beside the gin building. They ail discharge into a screw con-
veyor that has a dust-tight cover. The conveyor in turn discharges trash
through a conventional dropper into an air line that conveys it to a bur
house or incinerator. The air from one of the gin's fans, preferably the
fan handling the lint cleaner's trash, is used for this purpose, because
this fibrous material has a tendency to choke a conveyor. In some areas
the dust coming from the exhaust of the cyclones may be objectionable and
further filtering may be necessary. This can probably best be accomplished
using an in-line filter or other commercial type filter.^2;
107
-------
A guide in selecting the proper cyclone arrangement and dimen-
sions for normal gin plant installations is given in Reference 2. This guide
also describes the sizing of lint fly catchers and in-line air filters. The
in-line air filters have proven to be over 99$ efficient in the collection
of trash and fly (see Figure 8-3).11/
Another source cf emissions is the incinerators at cotton gins
which have been in use for many years for the purpose of burning burs,
sticks, steins, leaf trash, and motes-H/
The concentration of particulates which exit the cyclone collector
on a seven-cylinder cleaner has been found to be as low as 0.005 grains/scf
fcr a 34-in. diameter high-efficiency cyclone.12/
6.5.3.1 Control Equipment: The methods available to the ginr.er
for removal of particulate natter and lint fly from this discharge air are
limited by economic ana practical reasons to the following, listed in order
of increasing capital investment.13/
6.5.3.1.1 Gravity or settling chamber: Air is introduced into a
large enclosure to lose velocity and drop out pajrticles prior to discharge
cf air. The condenser exhaust "dog house" is an example. Condenser exhaust
air introduced into large chambers with screened sides has been observed
to operate satisfactorily where 14 x 18 mesh screen wire was employed. It
is not believed that settling chambers alone are feasible for use on air
exhausts other than from the condensers because of the greater dust loads
from other gin exhausts.13/
In some instances, use of settling to remove larger particles
prior to passage of air through a cyclone collector unit will reduce the
load on the cyclone and increase its collection efficiency.
8.5.3.1.2 Cyclones: The cyclone collector is widely used in
cotton gin emissions. Its first cost compares favorably with other types of
collectors. It is simple, rugged, has a low operating cost, and requires
little attention. The cyclone will operate very well under surprisingly
wide limits. However, careful sizing must be done to avoid excessive pres-
sure drop and at the same time provide for the most efficient collection of
dust and lint.
The smaller the cyclone, the greater the efficiency; therefore,
it is recommended that multiple, parallel units be used rather than one
larger cyclone. Sizing of cyclones is described and illustrated in Ref-
erences 11 and 13.
108
-------
WIPING
BRUSH
FINE MESH FILTERING
^ SCREEN
DUST & IINT
LADEN AIR
CLEAN
AIR
ROTATING
ARM
BRUSH
OUST & LINT
Figure 8-3 - In-Line Air Filter - Cotton Ginii/
-------
8.5.3.1.3 Scrubbers: The use of settling chambers with adequate
water sprays or taiiks has been observed to operate very well in some
instances. However, care must be taken that water disposal does not become
a problem.
13/
8.5.3.1.4 Lint fly catchers and filters: All of the lint fly
units permit a build-up of lint on the screen and this provides additional
filtration. Each of these units must be of sufficient size and properly
installed and maintained to prevent back pressure build-up on the system
they serve.
Cloth filters are efficient collection devices and various commer-
cial units are available. The cost of proper installation of filter units
is high because sufficient particle arrestment capacity must be provided to
allow shutdown of portions of it at intervals for cleaning.
13/
110
-------
REFERENCES
1. Boubel, R. W.. et al., "Emissions from Burring Grass Stubble and Straw,"
APCA Journal .19(7), 497-500, 1969.
2. "Air Pollutant Emission Factors," U.3.D.H.E.W. Report, TRW Systems
Group, Contract No. CPA 22-69-119, April 1970.
3. Anderson, T. H., "Meeting the Challenge of Air Pollution Control in Our
Plant," presented at Grain and Feed Dealers National Association Air
Pollution Symposium, Washington, D. C., January 1967.
4. Kiesner, J., "C-FDNA Air Pollution Symposium Studies Bust Emission,
Control," Feedstuffs, January 21. 1S68.
5. Anderson, T. H., "Some New Approaches to Air Pollution Control,"
Feedstuffs, June 15, 1369.
6. Thimsen, D. J., and ?. W. Aften, "A Proposed Design for Grain Elevator
Dust Collection," Journal of the Air Pollution Control Association,
18, November 1966.
iNA-l
7. "Air Pollution from Alfalfa Dehydrating Mills," iJ.S.D.H.E.W,, Robert W.
Taft Sanitary Engineering Cer.ter, Tecr.rj.cai Report A6C-4. 1960.
8. "Air-Borne Particulate Emissions from Cotton Ginning Operations,"
U.S.D.II.E.W., Robert W. Taft Sanitary Engineering Center, Technical
Report A50-5, 1960.
9. Paganini, 0., "Progress Report - Air Pollution Study of Cotton Gins in
Texas," in Control and Disposal of Cotton-Ginning Wastes, HIS Publi-
cation No. 999-AP-31, Cincinnati, Ohio, 1967.
10. Control and Disposal of Cotton-Ginning Wastes. U.S.D.H.E.W., Cincinnati,
Ohio, 1967.
11. "What We Know About Air Pollution Control," The Texas Cotton Ginners'
Association, Dallas, 1965.
12. Cuffe, S. ?., and J. C. Knudson, "Considerations for Determining
Acceptable Ambient and Source Concentrations for Particulates from
Cotton Gins."
13. "Control of Cotton Gin Waste Emissions," Texas State Department of
Health, 1964.
Ill
-------
CHAPTER 9
IRON MD STEEL INDUSTRY
9.1 INTRODUCTION
The manufacture of iron and steel involves many different pro-
cesses until semifinished products are available for sale or further use.
Some of the processes produce large quantities of particulates and gaseous
emissions, while other processes are relatively free of air pollution prob-
lems. The pyrometallurgical processes inherent in the iron and steel manu-
facturing processes emit a very fir.e-size particulate material.
The major sources of particulate air pollution are: sintering
plants, coke-oven plants, blast-furnace operations, steel-making furnaces
(especially those using large amounts of oxygen for steel making), and
materials-handling operations.
The manufacturing process, particulate emission sources, emission
rates of individual sources, chemical and physical properties of the efflu-
ents, control practices, and control equipment are discussed in the follow-
ing sections.
9.2 IRON AND STEEL MANUFACTURING
A composite flow diagram for an integrated iron and steel plant
is shown in Figure 9-1. The diversity of the operations and the myriad
emission sources are apparent. A compilation of potential emission sources
is presented in Table 9-1. The numbering sequence corresponds to that
shown in Figure 9-1.
A detailed discussion of manufacturing processes has been pre-
sented in a recent NAPCA report and those seeking more information on the
individual processes are referred to it. 1/ Emission rates from individual
sources are discussed in the following sections.
9.3 EMISSION RATES FROM IRON AND STEEL MANUFACTURE
9.3.1 Sinter Machines
Sintering machines generally accept and process a wide variety
of feeds and produce a considerable quantity of emissions of variable
quantity and nature.^ Emissions from sinter plants vary widely in quantity
113
Preceding page blank
-------
on KNh
COKI tREEZE
FLUE OUST MOM
I LAST FURNACE
COKE
IR CAR
• Iff fa
FINIS
MILL SCAU
LUMP Ott
M CAR
IK CAR
© ' © ®' Q
SINTER MACHINE
C«USNER
CONCENTRATION
IENTONI1E
FINES
LIMESTONE
IINS
SINTER PLANT
RR CAR
kALLINC DRUM
GRATE FEEDER
ORYING &
—i HARDENING
PELLETS
PELLETIZING
(AT MINE SITE)
SCRAP
SOAKING fITS
•LAST
FUKNACE
SCARFING
•ASIC
OXYGEN
cL£CTVIC-ARC
FUKNACE
FUtNACi
OPEN KAtTH
FUiNACE
PICK LING
FURTHER
PROCESSING
STEEL FURNACES
GRINOER
•Y-PROOUCT
RECOVERY
RR CAR
COAL
I—I—I—T
COKE OVEN
I I II I
COKE FINES
TO SINTER PLANT
QUENCHING
TOWER
COKING
Figure 9-1 - A Composite Flow Diagram for a Steel Plant
-------
TABLE 9-1
POTENTIAL PARTICULATE POLLUTANT EMISSION SOURCES IN
IRON AND STEEL MANUFACTURING
Source
Particulates
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Ore crushing
Materials handling and stockpiles
Pelletizing dryer
Sinter machine
(a) Windbox
(b) Discharge end
Sinter machine screen
Sinter cooler
Coke ovens
(a) Charging
(b) Coking (no by-product
recovery)
Coke quenching tower
Coke by-product recovery
Blast furnace
(a) Charge
(b) Heat
(c) Tap
Ore, coal and limestone dust
Ore, coal and limestone dust
Ore and coal dust
Iron oxides, calcite,
iron calcium silicates, and
quartz
Coal, smoke, and coke
Hydrocarbon vapors and/or mists
Iron oxides, coke, and limestone
Kish
Steel-Making Furnaces
11.
12.
15.
14.
15.
Open hearth
Basic oxygen
Electric-arc
(a) Charge
(b) Heat
(c) Tap
Scarfing
Pickling
Iron oxides, lime, kish, silica
Particulate emitted
from each furnace
during these stages
Iron oxide
HgSO^, HC1 fumes, Water-oil mist
115
-------
and particle size and depend upon, among other things, raw mix composition,
types of machines, and exhaust-fan characteristics.
Sinter machine emission sources can be divided into two categorie.
(a) windbox emissions, and (b) discharge-end emissions. Windbox emission
dusts are mainly generated early in the sintering process, and again later,
when the flame front has reached the bottom of the bed. Emissions from the
discharge end parallel tho3e of the windbox on a basis of pounds emitted
per ton of sinter. However, grain loadings are higher at the discharge end
9.3.2 Coke Ovens
Metallurgical coke is the major fuel and reducing agent used in
the production of blast furnace hot metal, and will probably be the major
fuel and reductant for many years in the future. Beehive coke is still
made to a limited extent, but 99$ of coke production utilizes the by-produce
coke oven.
Daring the manufacture of coke and during the processing of coke
by-products, emissions are generated in several locations and operations:
(l) coal handling; (2) oven charging; (3) oven operation, pushing and quencl"
ing; (4) coke handling; and (5) by-product processing. Most of the particu-
lates escape during the charging and discharging (i.e., pushing) operations.
At the end of the coking cycle, the incandescent coke is transferred from
the oven into a quenching car by a hydraulic ram. The quantity of smoke
rising from the mass during the period required to transport the coke to
the quenching station is dependent upon the degree of coking. Incompletely
carbonized coke gives rise to considerable quantities of smoke; conversely,
thoroughly carbonized coke gives rise to very little smoke.0/
9.3.3 Blast Furnace
The blast furnace is one of the largest chemical reactors used
by industry. It acts as a counter-current reactor in which solid materials
descend by gravity from the top and react with gases generated near the
bottom.
Iron ore, fluxes, and coke are charged into the top of the furnace
through a succession of two of three seals that serve to limit leakage of
gas at this point. Preheated air (sometimes augmented with oil, gas, oxygen
or steam) is forced through ports (tuyeres) arranged radially near the bottc
of the furnace and just above the hearth. The incoming air and admixed
additives react between themselves and with the hot coke to generate a re-
ducing gas rich in hydrogen and carbon monoxide, at a flame temperature of
up to 3500°F. !Ihe hot reducing gases liberate some of their heat to melt
the iron and slag, then continue upward to carry energy and chemical poten-
tial to the unreduced ore in the upper part of the furnace. Mslten iron
116
-------
and slag drip down into the hearth and are tapped intermittently through
special ports
Iwo emissions come from the top of a blast furnace: top gas and
the dust which it entrains. The top gas is a mixture mainly of steam, ni-
trogen, carbon monoxide, and carbon dioxide. On a dry basis, this gas may
average 25 to 30 vol. $ carbon monoxide. Emissions to the atmosphere occur
from leakage around hoppers and seals. Top gas may leak from openings such
as ports for rods used to determine z:.e height of the charge materials in-
side the furnace. Dust entrained in the top gas is a result of the abrasion
sustained by the burden materials during charging and during the initial
stages of passage down the blast furnace. It is possible to minimize
particulate emissions by choice of raw materials and sound operating prac-
tices, and thereby to reduce the load on the dust-cleaning system.!/
9.3.4 Steel-Makir.g Furnaces
9.3.4.1 Open-Hearth Furnaces: Particulate and gaseous emissions
from the open-hearth process originate from (l) the physical action of
the flame on the charged materials and the resulting pickup of fines,
(2) the chemical reactions in the bath, (3) the agitation of the bath,
and (4) the combustion of fuel.iiixi/ The amount of dust generated during
the open-hearth process varies according to the different stages of the
process and according to operating practices. Oxygen lar.cing produces
mere particulate emissions than open-hearth practice without lancing.
A typical heat is composed of 60$ hot metal and 40$ scrap, and
usually proceeds as follows: the bottom of the furnace is first built up
with dolomite and the burners are fired. The furnace is then charged with
limestone and steel scrap. The time required for this charging and melt-
down of the scrap varies between 2 and 4 hr., depending upon the furnace
size and the ratio of hot metal to scrap. The hot metal is added when the
scrap is partially melted. Decomposition of the limestone begins when the
temperature of the bath increases. The release of carbon dioxide gas from
the limestone increases agitation in the bath. After the lime boil has
been completed and the lime solution is in the slag, the rate of decarbon-
ization increases. When gaseous oxygen is used for decerbonization, the
flow of oxygen is started after the addition of hot metal.?/
Fume generation from the open hearth occurs during the charging,
melting, and refining phase. Emission rates vary considerably during the
process cycle, and quite likely vary from cycle to cycle depending on the
quality of the scrap charged into the furnace. For the furnace utilizing *
oxygen-lancing (i.e., impinging stream of high-velocity oxygen), Reference
5 gives a dust loading of 0.78 grain/scf at 60,000 scfm gas flow at melt-
down, 1.9 grains/scf at 64,000 scflc at hot metal addition, 2.70 grains/scf
117
-------
£t 66,000 scfm at the line boil, up to 5 grains/scf during oxygen lancing
ar.d 0.21 grain/scf at 64,000 scfm during refining.
9.3.4.2 3asic Oxygen Furnaces: Basic oxygen furnaces (BOF) are
becoming the principal method of making steel in the U. S. In basic oxyger
steel-making, the need, for a large-surface bath (such as is required in
open-hearth steel-making) is overcome by forcing a jet of high-purity oxygc
below the surface of the metal. The jet also provides violent agitation,
and therefore increases the area of the slag-metal interface. The BOF pros-
is exothermic to the extent that up to 30% (or more) of steel scrap can be
melted, using as fuel only the carbon and other metalloids dissolved in the
metal. No conventional fuel is added. In terms of emissions, the sulfur
dioxide and unburned hydrocarbons associated with open hearths are non-
existent with BOF furnaces.i/
In the initial stage of basic oxygen steel-making, the charging
of carbon-saturated hot metal upon cold scrap results in a release of kish
as the molten iron is rapidly cooled. Only a part of this kish is con-
tained by the furnace vessel. The initiation of oxygen blowing is marked
briefly by a heavy dark-brown smoke (caused by the direct burning of iron).
This smoke persists until the metalloids begin to oxidize and refining
begins.
As most of the metalloids become oxidized, the oxidation of carbc
increases to consume the rest of the oxygen blown, and the volume of gas
leaving the furnace mouth increases noticeably. An excess of air often is
permitted to mix with the exhaust gases as they pass into the fume-exhaust
system. The use of excess air is a safety precaution to prevent the exist-
ence of a high carbon monoxide content in the flue system, and eliminate a
possible explosion hazard.
During the oxidation of carbon, the fuming appears to be limited
to iron dust either from iron vaporized from the bath or as iron droplets
ejected by the carbon monoxide rising from the molten bath. Factors that
determine the amount of fumes generated during the blowing process include
the type of oxygen lance used, the velocity of the oxygen, the carbon con-
tent of the iron, and the temperature of the iron.1/
9.3.4.3 51ectric-Arc Furnaces: Emissions generated during electri
furnace steel-making originate from the physical nature of scrap used, serf
cleanliness, the nature of the melting operation, and oxygen lancing. Fume
and particulate are emitted from the furnace during the charging and refini
operations. During the charging period, the top of the furnace is opened
to charge cold metal. Exposure of the cold charge to high temperatures wii
the furnace results in the generation of large quantities of fume. Fume
emissions can be affected by the sequence of charge additions to the furnac
116
-------
The method, of refining also has a pronounced effect on fume emis-
sion. An oxygen lance leads to higher fume release rates because of the
breaking of the slag film and because of the high temperatures reached dur-
ing the lancing stage.
The nature of the material charged also has a marked influence on
emission rates. Thin steel scrap will oxidize easily, and result in heavy
fuming and a high metal loss during melting in electric-arc furnaces. Dirty
scrap is a major source of emissions. Electric furnaces melting dirty scrap
can generate as much dust as an electric furnace with oxygen lancing.
9.3.5 Scarfing Operations
Before steel can be rolled, surface defects in the bloom, ingot,
and billets must be removed. The scarfing operation removes these defects.
Jets of oxygen axe directed at the surface of the steel, which is maintained
at high temperature, causing localized melting ana subsequent oxidation of
the steel.
9.3.6 SuTTTiB.ry of Emission Rates From Iron and Steel Manufacture
Table 9-2 summarizes the emission rates from the various operations
that comprise the manufacturing cycle for iron and steel. Particulate emis-
sions currently total about 1.4 x 10^ tons/year. Furnace operations, sinter
machines, coke manufacture, and material handling operations are the dominant
sources of particulate emissions. Emissions from the material handling oper-
ations were calculated using engineering estimates of average efficiency of
control devices and degree of application of control.
9.4 CHARACTERISTICS OF EMISSIONS FROM IRON AND STEEL MANUFACTURE
Table 9-3 presents a summary of the chemical and physical properties
of the effluents from the various processes involved in the manufacture of
iron and steel. The nature of the emissions is highly variable. The pyro-
metallurgical steps present distinct control problems because of the genera-
tion of very fine particulate matter. Emissions from open-hearth, basic-
oxygen, and electric-arc furnaces may consist entirely of submicron metallic
fumes and particulates.
The variation in resistivity of open-hearth furnace fumes shown
in Figures 9-2 to 9-5 gives an indication of the data spread for this type
of data. This variation is to be expected because of the different com-
positions of the heats, especially varying concentrations of limestone.
Therefore, wherever the resistivity exceeds a value of about 2 x 1010 ohm-cm,
in-situ measurements should be made.
Data on particle shapes, which could not be readily presented in
tabular form are detailed in the following paragraphs.
119
-------
TA5IZ 9-2
PARTICULATE EMISSIONS
mou atd $7?xl notrsnrt
Quantity of Material Emission Factcr
I. Ore Crushing
II- Mater.als Handling
A. Loading-Unloading, Freight
Cars, Barges, Ore Boats
Ore and ore fines
Clay (bentonite)
Coal
Scrap metal
3. Conveyors
1- Transfer pcir.ts
c. Discharge to tins
stockplies
C- ^levators
1. Boots
2- Heads
III- Pellet rian*
A. Grate Feeder
B. Dryer
C- Kilr.
IV- Winter Plant
A- Sintering process
3- Crashing, Screening,
uociing
G2,C00,G'CC tons; of
iron ore
131,000, COO tons
of steel
53,000,000 tons
of pellets
^1,ODC,000 tear, of
sinter
Co>e Manufacture
A- Cveas
1. Beehive
a. Charging
b. Coking
c. pushing
By-Profiuct
a. Charging
b. Coking
c. Pushing
Quenching lover
Grinder
Screen
By-Prcduct Recovery plant
lb/tor. of ore
10 lb/ton cf steel
775,OOC tons of
coke - 1,300,000
tons of coal
2C0 2b/ton cf coal
0.00 lb/ten of i-oal^/
0.30 lt/ton of coalS/
/
Effici-
ency of
Control
20 lb/ten sir.ter 0.90
22 lb/ten sinter 0.9G
0.00
0.06 It/ton of ccftl
53 }7C0,D0C tons of P lb/ton of coal 3.00
soke - 9O,O0C,000
tens of cca)
Applica-
tion of
Control
0.i5
1-0
1.0
Net
Control
cc'ct
C.C
C.
-------
TABLE 9-2 (Concluded)
Effici-
ency of
Control
tyor.tity of Material Emission Factor C_
Applica-
tion of
Control
n
Net
Control
C„«C*
Epiissior.s
(tons/year)
VI. B-ast Furnaces
A. Charge
B. Heat
C. Tap
88,800,00 tone ol"
pig iron
130 lb/tcn of pig iron 0.99 1.00 0.99 58,000
VII. Steel Furnaces
A. Op sr. Hearth
1. Ho oxygen laneIng
a. Charge
o. Ks£t
c. Tap
2. Oxygen lancing
a. Charge
fc. Heat
c. Tar
65,600,000 tons of
steel
B. Bas:c Oxygen (BOr)
1. Charge
a. HcaT
3. Tap
C- Electric Arc
1. Charge
2. Heat
3. lap
VIII. Scarfing
Average for open hearth
43,000,000 tons cf
steel
16 ,800,COO tons of
steel
0 lb/ton cf steel
21 lfc/tori of steel
17 lt/ton of szcvl*/
40 lb/ton of steel 0.99
10 lb/ton of steel 0.99
131,000,000 tons cf 3 lb/ton scarfed 0.90
steel
1.00
C. 79
0.75
0.40 337,000
0.99 10,000
0.78
0.68
is,000
63,000
IX- Pickling
a/ Industrial source.
»/ Emission factor is assumed t
Total for Iron and Steel
¦o be an average for the total heat cycle.
1,442,000
121
-------
IA BLi 9 »3
EFFL'JgfT CHARACTERISTICS - I30K AJQ SSSEI ETCUST3Y*
A. Particulate (Part I)
Particle Electrical Moisture
Particle Site Solids Loading Chexlcal Coipcsltion Density Properties Content Toxlclt-
Iron and Steel
a. Sinter Plant
(1) Windbox
15-45 < 40
9-30 < 20
4-19 < 10
1-10 c 5
Also see
Figure 9-?
(2) Discharge end AC < ICO,
10 < 1C
b. Coke Oven
(l) ^iencb tower
(?) Oven charging
{one saaple)
95-97 > 47
C.05-0.1
Fe20T: 45-5C
SiC^T 3-15
CsO: 7-25
K«0: 1-10
Alr»0,: cm&
Ci 0.5-5
S: 0-2.5
Alkali: 0-2
Fluorides
Coke bells, coal
dust, pyrolytic
carbon
Co&l dust
See
Figures
9-3, 3-4 and 9-5
for detailed
date
See
Title 9-4
for date
El ait Furnace
Highly variable
15-90 c 7 4
4-30
7-1C (avg.)
Fe: 36-5C
FeO: 12-47
SlOg: 6-30
Ai^O* • 2-15
MgC:" 0.2-5
C: 3.5-15
CeC: 3.0-23
Kti: C.5-1.0
P: 0.03-0.2
S: 0.2-0.4
d.
Open-Hearth Furnace
(No oJtyger. lance)
Charge to hot
oetal
Hot aetal to
liae uj
Llae up to tap
Tap to charge
Cosposlte for
heat
•d)
«(2)
~(3)
»(4)
«(5)
50 < 5
Electron
microscope
0,01-0.5
Mean count
size: 0.03;
Mass median:
0.65
0.56
0.61
0.1a
0.11
0.1-5.5 (de-
pendent upon
stage of
heat) avg.
for heat,
0.4
Fe?05: 65-90
Small amounts of other
metallic oxides re-
flecting charge coa-
poeltion
SiO£: 0.9-1.6
AlgO^: 0.5-0.7
CaO: C.65-1.0
taO; 0.6
P20^: 0.5-1.2
S; 0.4-1.0
Less oc Ignition: 1.1
Fluorides
Eee
Fig-ores
9-6 - 9-10
for detailed
data
• Data Jrcai one plant only.
** Data from several plants.
~ See Coding Key, Table 5-1, Chapter 5f page 45, for units for individual effluent properties.
122
-------
A. Particulate (Part I) (Continued)
TA.3LE 9-3 (Continued)
Source
particle Size Scllda leading Cbealcal Coapositlon
Particle Electrical Mol3tyre
Jer.slty Properties Content
d. Of* n-Hearth Furnace
(ojygen lance)(Concluded)
~**(1) Qiarge to
hot metal
••*(2) Hot Mtal to
lLxfi up
••*(3) Lime up to
tap
~•~(4) Tap to charge
•~(5) Conqposite for Variable, de-
he at
pendant on
stage of heat
a. Lime boil
45 < 2
75 < a,
92 < 1C
Composite
20 < 2
45 < 5
69 < 10
I+oaeber count:
- ICO <0.1
b.
0.25-0.73
C.45-1.90
0.9-2.7
C.21-0.87
C.2-7.0
(dependent
on stage
of heat)
Avg. for
heat: 1.5
Fe205: 80-90
FeO: 0.3-3.2
Si>)! 0.4-2.0
AI^Oj: 0.2-0.7
CflO: 0.6-1.9
J*0: C.2-1.0
P205: 0.5-1.5
HgO: 0.4-1.1
3: C.4-3.0
Toxic 1 ~.y
5.0-5.2
See
Figures
9-6 - 9-10
for detailed
data
Dp.31c Oxyger. P^rnftce
(1)
Cosiposite for
ha at
Transfer of
hct metal froc
bottle car to
charging ladle
(KI3H)
85-95 <1 2
21ectrcn
micrograph:
count nediar.
disaster C.C12
M&33 median
diameter, 0.03?
Geometric dela-
tion, 2.3
33 > 149
54 > 74
84 > 1C
97 > 1
Typical composition
FejO;: 90
FeC: 1.5
to: C.4-1.5
SiC£: 1.3-2.0
A12C2: 0.2
CaC:" 3-S
MgO: 0.6-1.1
F^Og, C, SIOd
?e2Or, CaO, MgO,
S *"
Sse
Figures
9-9, 9-10
and 9-11
for detailed
data
f. Electric-Arc Furnace
(l) No ox/gen lence
(composite for
heet)
Highly variable,
but generally
60 < 5
BAHC3 analysis
S£ < 5, 64 < 10,
35 < 20, 99 < 40
0.1-2.2
Variable, dependent
on nature cf charge
Fe2C3: 19-44
FeO:~ 4-10
CrgO*: 0-12
31 Og': 2-9
Al^O*: i-13
CboT 5-22
£-15
3-12
0-44
0-1
3.8-3.9
MgO:
MnO:
ZnO:
CuO:
NiO:
J%0i
C: 2-4
Alkalies
S; 0-1
F: 0-1
0-3
0-4
1-11
Apparent re-
sistivity
6 x 10s -
6.6 x 1015
ohm- cm (de-
pendent on
cheaical com-
position )
Also see
Figure 9-9
Data froa tfcree plants.
123
-------
XfcHLB 9-2 (Continued)
A. Particulate (Fart l) (Concluded)
Particle Electrical Moisture
Particle Siae Sclids Leading Chcnlcal Composition Ifrr,3i ty Properties Content Toxic; ty
f. Electric-Arc Furnace (Concluded)
(2) OJtygen iar.ee 1-10
(composite
for heat)
Similar to no Cg
lance composition
g. Miscellaneous
(*.) Scarfing machine
0.4-4.4 Mostly re 303
Comconly used
values 0,4-0,6
See
Figure 9-9
A. Particulate (Part II)
Iror, and Steel
a. Sinter p-ant
b. Blast furr.Gcc
Hygroscopic Fleatabillty cr
So lability tfett ability CharecU;rls tics Sxplosivc Limits Handling Characteristics
CaC - s. HgQ
CaO, SL0-,
FcplH,
A3g03 - s.
10% HCi
CaO - s. R3.O
CaC, SiC>,
Al<5 Cj - S .
10% HCI
Hardness: 3-5 mohs,
Abrasive
Abrasive, fluid cohesive,
will arch and bridge
Optical
Preperti
Open-hearth
FcqOt
difficult '.o
1C-6 HCi wet
Abrasive, high angle of
repose (—90 degrees),
cohesive ar.d vili hriigf:
and arch
d. 3asi:-cxyger.
1 urn see
s. Difficult to
10% HCI wot
Airasiv«, high angle of
repose (—90 degrees),
cohesive ar.d vili bridge
and arch
Eitctric-arc
furna.?e
Difficult to
we t
Abrasive, fluid-cohesive,
high angle of repose,
will bridge and arch
E. Carrier Cis
Flaaccabllity
Mol3ture Cheaical cr Sxpicsive
Scarce Flow Rate Iteaperature Ccntent Cocposition Toxicity Corroslvity Odor Limits
Iron and Steel
fl. Sinter plant
(1) Windbcx (ft) 30-45C 100-400 £-10 Ogt 10-20 SO- - 5
(":>) 143-230 COg; 4-10 lrritar.t
CO: 0-6 CO - IDo
SC5.: 0-0.4
Ng: 64-86
Fluorides
124
-------
B. Carrier 0*3 (Continued.)
a. Sir.ter plant (Concluded)
(2) Discharge end (a) C.03-0.2 10C-300
TAJiLE i-3 (continued)
Flow Rate Iteaperature
Moist-ore
Content
Chenical
Coapcsltioc Ibxiclty Corroalvlty Odor
FlssBBbillty
cr Explosive
L.raits
b. Coke Oven
(l) Qjencb tower
(2) Oven charging
Of the order 140-150
90C M ft5 per
quench
Of the order
2.1 M ft5 per
charge
Stem, air
CCg •
°2 -
N2
CO
h2 -
CH* -
C^K4 -
CfiHs -
C.B
6.1
6.3
46.$
32.1
3.5
0.5
c. Blast furnace
(a) 40-140 390 at
(b) 60-136 throat
3000 in
furnace
9.6 Dew CO: 21-42
point, 95-122 avg. 26
C02: 7-19
avg. 16
Hp: 1.7-5.7
avg. 3.1
CH4: C.2-3
d. Open-Hearth Furnace
(No oxygen lance)
*('-) Charge to (t>) 63.5
not metal
«(2) Hot metal (a) 75.2
line up
•{3) Lime up to (e) 70.7
tap
*(4 ) Tap to { a) 47,6
charge
**(5) Composite (a) 2S-10C 460-18C0
for heat (depe riding
on utiliza-
tion of vaate
heat boiler)
17.2
" fl .5
17.2
13.3
7-1S
CQ£-
V
h'
sp£ :
SO,:
NG.
C9 - 10C
S02 - 5
irritant
Etfplosivsi due
ta CO end Jv,
N2: 50-60
Braces: 3,
%S, set,
e-g
9-9
balance
2-5 ppa
10C-200
ppe
500-800
30g - 5,
irritant
HT - 3
Potentially
corrosive
iue to SCl, ,
'3
SO,
Fpc
Fluorides aqr
by eciitted dua
to fluxing agent
or fluoride con-
tent of ore
(0-30C ppc)
125
-------
3. Carrier Gbs (Concluded)
TABLE 9-3 (concluded)
Flow Rate Teaperstore
Moisture
Cor.tent or
Cor.de ns able
Vapora
Chrmicol
Coapos11 i or
Toxicity Ccrrosivity Odor
F i biiijil
or £xj.
Lir.
d. Cpen-Hearth Furnace
(Concluded)
(Oxygen lance)
**(l) Composite (a) 45-200
for h«at
40C-2000
(depending
on utiliza-
tion of waste
heat boiler)
Varies dur-
ing cycle
15-19
avg. 15
Sinjjlar to
r.o Og lanse
conposition
SO* - 5,
irritant
HF - 3
Potentially
corrosive
due to SOg,
Basic 0)Qrgen Furnace
(l) Composite for (a) 35-250 E6C-3000
heat (depending
on utiliza-
tion of waste
heat boiler)
Before coc-
bu3tion with
aspirated
air:
a. BOF
CCb:
CO*:
b.
5-16
74-91
3-0
Kaldc Process
??.S
CO: 22.?
Hg: l.i
After combus-
tion with
aspirated
air:
BOF
C0Q:
CO:
It:
C.7-
15.5
0-0.3
74.5-
76.9
balance
Highly
mablc :
to oca;
tion wi
aspirat
air
Electric-Arc
Furnace (in-
cludes both
urlar.ced and
lanced furnaces)
(a) 1C-100
Miscellaneous
(l) Scarfing
machine
215-30X
(Dependent
on use cf
cooling
techniques)
C.045 lb/lb
dry g&£
(1 s aaple )
(e) 20-150
Mainly COg, CO,
O5, ar.d Kg
Ccaposition var-
ies with opera-
ting practice.
Fcr Cb lance
composition
varies with time.
iypic«i
variation:
CO: 6-65
CC^: 5-15
5-B5
Flemceh
due tc
conter.t
~* Data fron several plants.
126
-------
99.9
99.0
Sieve
Analysis
95.0
90.0
Size Range by
Bahco Analysis of Dust
to Precipitator Following
Mechanical Collector
sp.gr. 3.35 g/cc
50.0
Size Range of Dust From
Sinter Machine to the
Mechanical Collector
10.0
5.0
0.5
10
1000
100
Particle Diameter (In Microns)
Figure 9-2 - Particle Size Distribtuion by Weight of Sintering Machine Dust3§/
-------
I014
i 1 1 1 r
fO
CD
10
icr
IS
z
o
Z
X
0
1
>-
I01
p 10
w
UJ
K
10 '
10'
to
10
A HOME ORES | DETERMINATIONS
~ FOREIGN 0RES>MA0E IN AIR WITH
O FOREIGN OftEsJ 1.3% HjO
100 200
TEMPERATURE - °F
300
Figure 9-3 - Resistivity of Different Dusts in the
Same Atmosphere vs. Temperature^/
(Sinter Plant)
• MEASURED IN PRECIPITATOR
A MEASURED IN SITE OVEN
~ MEASURED IN LABORATORY
OVEN
10* f-
I
_L
100 200
TEMPERATURE -°F
300
Figure 9-4 - Resistivity in Different Atmospheres
vs. Temperature55/
(Sinter Plant)
-------
6 ^ Moisture
Parameter
CD
Feed Analysis
1. Iron Fines from
Various Sources
2. Fluxing Material
3. Coke Fines
90%
9%
1 %
64%
35%
1 %
Gas Analysis
- 1. Sulfur Oxides
2. Moisture
3. Temperature
300 PPM
15%
250 F
30 PPM
10%
200 F
Dust Analysis
1 . Resistivity
@ 225 F & 6 %
Moisture
2. Particle Size
1.5 x 109
60% - 10/1
5 x 1013
45% - 10p
®
1 I
'
~***Vv"v%«N>6^^Moisture
i i
100 150 200 250 300 350 400
Gas Temperature, °F
are 9-5 - Electrical Resistivity of Sintering Machine Dust^/
129
-------
10^
O*
O
2
u
I
5
x
O
i
>-
i2
UJ
ac.
ac.
<
Q_
Q_
<
10
12
10
11
10
10'
10
108
\i.3«y<
*
in*.
20gfe
f 30ft
200 400
TEMPERATURE °F
600
' Figure shows percent water vapor by volume
Figure 9-6 - Resistivity of Open Hearth Furnace Fume
Under Varying Conditions of Tempera-
ture and Moisture in Gas2J
»/>
UJ
10
13
2 10
u
I
5
x
O
•
>-
12
10
11
1010
ac.
<
Q_
Q_
<
109
10l
vi.:
%*
5%
\
f
lmA
r
20%
200 400
TEMPERATURE °F
600
* Figure shows percent water vapor by volume
Figure 9-7 - Apparent Resistivity of Fume
from Open-Hearth Furnace-i/
-------
1012
5
u
I
5
x
0
1
>-
i/i
i/i
UJ
OL
C£.
<
a.
a.
<
10
11
10
10
10Y
10c
ID'
li.a
%*
\
10%
A
\
\
f
\
\
20%.
\\
355&S
,
200 400
TEMPERATURE °F
600
* Figure shows percent water vapor by volume
Figure 9-8 - Apparent Resistivity of Fume
from Open Hearth Furnace-i/
\\C FURNACE
BOF LIME
SCARFING
JASIC OXYGEN
FURNACE
OPEN HEAR
10 0 100 200 300 400 500 600 700 800
TEMPERATURE, °F
Figure 9-9 - Apparent Resistivities of
Metallurgical Dusts-i/
-------
> 10
(1) ARC FURNACE
(2) LD CONVERTER
(3) OPEN-HEARTH FURNACE
AUSTRALIA
(4) OPEN-HEARTH FURNACE
(5) DESILICONIZATION
LADLE PROCESS
(6) OPEN-HEARTH FURNACE
100 200 300 400 500 600
TEMPERATURE, °C
* Figure shows percent water vapor by volume.
Figure 9-10 - Electrical Resistivity of Red Oxide Fume From Various
Oxygen-Blown Steelmaking Processes i/
132
-------
% Moisture
Gas Temperature, °F
Figure 9-11 - Resistivity vs. Gas Temperature for BOF Furnace Dusl5§/
(Laboratory Measurements)
133
-------
'TABLE 9-4
IRON 5PITER DUST RESISTIVITY*
(ohm-cm)
fofeO 150°? 200°F 250CF
1.4 2 x 1010 3 x 1010 1.6 x 1012
3.0 1 x 1011 6.5 x 10n 1.6 x 1012
9.0 9 x 1010 1.6 x 1012
* Discharge end.
9.4.1 Particle Shape
9.4.1.1 Sinter Plant: Sinter dust may contain particles of iron
oxides, calcite, iron-calcium silicates, and quartz. Iron oxide can be
opaque, black, rounded particles of ira.gr.etite (Fe304) with granular faces,
and/or dense, rounded, elongated, and nearly spherical agglomerates of
hematite (FegOj). Calcite occurs as smooth, rounded particles, and quartz
as a transparent, rounded particle. The iron-calciurr. silicates are trans-
parent, vitreous, colorless to yellow to green. Particles are irregularly
rounded with smooth surfaces.ix§/
9.4.1.2 Coke Ovens: Emissions from coke plants can be identi-
fiedixZ./ as follows:
9.4.1.2.1 Coal dust: Bituminous, or soft coal, is translucent
in thin areas: it is reddish-brown by transmitted light, and brownish-
black with dull to moderately high reflectivity in reflected light. The
surfaces are slightly rough with occasional indications of the original
fibrous structure. These irregular chips have sharp edges, and in places
show conchoidal surface fractures.il/
9.4.1.2.2 Coke balls: Oval in shape with an unusual network-
like internal structure. It has been suggested that coke balls axe pro-
duced during the thermal-drying stages of coal processing. Similar condi-
tions occur during charging or by-product coke ovens, where some coal fines
are carried through the hot zone and out adjacent, open charging holes.iJ
134
-------
9.4.1.2.3 Char: Partially devolatilized coal particles exhibit
optical properties between those of coal and coke. The partial devolatili-
zation of coal particles suggests that they have not been subjected to tem-
peratures high enough or for periods long enough to complete the coking
process ¦1/
9.4.1.2.4 Pyrolytic carbon; A tarry residue comes from the
volatile organic portion of coal. Two forms of pyrolytic carbon have been
identified. The first is an aggregate of minute oval grains; each grain
is relatively uniform in size, extremely smooth in appearance, and exhibits
extreme anisotropy in polarized light. The second normally occurs as a
crenulated band of varying width and length, is smooth in appearance, and
is strongly anisotropic in polarized light. The size of these materials is
extremely variable jJ
9.4.1.2.5 By-product coke: The optical characteristics of par-
ticles of by-product coke are controlled by the rank (reflectance) of the
coal which is carbonized. Because coals of different rank are usually
blended to make an optimum mix, particles of coke produced from these mixes
have coaiplex and highly variable optical properties. Particulates of coke
made from high-volatile and medium-volatile coals may be granular in ap-
pearance, have thick coke walls, and have few internal pores. Particulates
from coke made with low-volatile coals have distinctive ribbon-like tex-
tures, thin coke walls, and comparatively large internal pores JJ
9.4.1.3 Blast Furnace: Particulate emissions generated in the
making of iron in the blast furnace and in its immediate auxiliaries have
the following characteristics:!/
9.4.1.3.1 Iron-ore dust: Particles are rounded to elongated in
shape and can be as small as 2 |ji. Larger particles are opaque and red-
orange in top light. Individual small grains are transparent and blood-
red .6,/
9-4.1-3-2 Coke dust: Particles are opaque, irregularly shaped,
quite porous and rough with some straight, sharp edges. They are gray-
black in reflected light. 6/
9.4.1.3.3 Limestone dust: Calcite. It is colorless, with
light-transmitting characteristics varying from transparent to translucent.
Particles generally occur as rhombohedra because of their perfect rhombo-
hedral cleavage. Fragments may also occur as prisms ..§/
9.4.1.3.4 Flue dust: Blast furnace flue dust typically contains
15% metallic iron, 40$ red iron oxide, 40% magnetic iron oxide, and 5%
limestone,§] but many variations exist:
135
-------
a. Iron--fragments are opaque, black, and sharp, magnetic
with finely granular surfaces ..§/
b. Red iron oxide—particles are traipparent, rounded
grains, usually less than 2 |i in maximum dimension^'
c. Magnetic iron oxide—particles are opaque, black, rough
fragments, partially or completely covered with red iron oxide .£/
d. Limestone dust—particles are transparent, colorless
rhombohedra, and rounded; many may also be covered with red iron oxide «£/
9.4.1.3.5 Kish: Carbon in the form of flaky graphite that is
rejected by the molten iron as it cools during flow from the blast furnace
to ladles. Other types of particles may be entrained with this kish. The
graphite particles are opaque, black, sharply angular flakes with smooth
surfaces. Some are in layered agglomerates, occasionally showing rounded
120-degree angles, and even forming rounded hexagonal tablets. Other
particles accompanying the kish may consist of opaque, black, rather coarse
fragments of magnetic iron oxide, and transparent, deep-red, rounded par-
ticles of hematite. Traces of quartz ana calcite may also be found with
the kish.®' Graphite typically makes up about 90$ of the emission, with
the magnetic oxide at 5$ and hematite at 5$.
9.4.1.4 Open-hearth Furnace: Open-hearth furnaces generate four
major types of particulate emissions.!/
9.4.1.4.1 Open-hearth dust: Charging period. Two components
appear in the dust generated during charging of the furnace. One is a mag-
netic iron oxide of black, opaque spheres, and elongated, rough particles
with sharp jagged edges, all generally coated with red iron oxide. The
second component comprises transparent, rounded particles of red iron oxide,
usually less than 2 ^ in dimension. They occur free or in simple agglome-
rates .^/
9.4.1.4.2 Open-hearth dust: Hot metal to lime-up. Three com-
ponents make up the dust from this period of open-hearth operation, (a)
Loose agglomerates of tiny transparent grains are usually less than 1 p, in
dimension. It is a hydrated iron oxide such as HFeOg- Individual grains
and agglomerates are yellow under top light, (b) Tiny, rounded, trans-
parent, red grains of iron oxide are usually less than 1 p, in dimension,
(c) Opaque, black spheres and rounded particles of magnetic iron oxide.
Some particles are covered with hydrated iron oxide and/or the red iron
oxide .6/
136
-------
9.4.1.4.3 Open-hearth dust: Tap to charge. This is the same as
Item 1 with the addition of black, opaque, frothy, rounded particles of
coke ..§/
9.4.1.4.4 Particulates in combustion product: About 85$ of the
material is transparent, deep red, rounded grains of iron oxide, usually
less than 1 p, in dimension. The remaining 15$ is black, opaque spheres
3 to 5 p, in dimension, of magnetic iron oxide. The smaller grains are
orange in top light and tend to form simple agglomerates or loose lumps.
All lime dust does not occur as a visually apparent particulate;
it is present in open-hearth dust in very small quantities as shown by
chemical analysis. Sulfur in the form of sulphates also occurs in open-
hearth dust, but information in visual characteristics is not available in
the published literature.
9.4.1.5 Basic Oxygen Furnace: The major particulate emissions
from basic oxygen furnaces are:
9.4.1.5.1 Kish: Carbon in the form of graphite is rejected by
the molten iron as it cools during charging into a BOF steel-making vessel.
The graphite particles are opaque, black, sharply angular flakes with
smooth surfaces. Some are in layered agglomerates, occasionally shewing
rounded 120-degree angles, and even forming rounded hexagonal tablets.
Other particles may consist of opaque, black, rather coarse fragments of
magnetic iron oxide and transparent, deep red, rounded particles of hema-
tite. Traces of quartz and calcite may also be found with kish..§/
9.4.1.5.2 Silica fume: Approximately 50 to almost 100$ silica
material often contains small quantities of iron, manganese, magnesium and
carbon. Color of the collected material is grey to off-white.
9.4.1.5.3 Basic oxygen process dust: Tiny (l p. in dimension),
rounded, transparent particles of red iron oxide tend to agglomerate.
Shiny black spheres of magnetite are covered with red iron oxide.
9.4.1.6 Electric-Arc Furnace: Emissions from electric-arc
furnaces include:
9.4.1.6.1 Electric-furnace dust: Opaque, rounded grains are
peach to reddish in color in top light. Small agglomerates are present,
but are not common.^/
-------
The chemical composition of electric-furnace dusts will be in-
fluenced by the composition of the steel being melted. Because of this,
optical characteristics of the dust may also vary because of the different
alloying-element oxides that nay be present. Because electric furnaces
are used for melting a wide range of alloy and stainless steels, the chemi-
cal composition of any particulate dust will reflect the composition of
the alloy melted. 1/
9.4.1.6.2 Dust from scrap preheaters: Information on the physi-
cal and optical characteristics of dust generated during the preheating of
scrap is not available. However, it can be assumed that the composition of
the dust will be influenced mostly by the cleanliness of the scrap, its con-
tent of volatile matter, and presence of surface coatings on some of the
steel. Jl/
9.5 CONTROL TECHNIQUES FOR THE IRON AND STEEL INDUSTRY
9.5.1 Control Practices - General
The operation and types of furnaces associated with the iron and
steel industry vary widely. Therefore, the criteria for the type of con-
trol equipment are determined by the specific operation. A tabulation of
the types of equipment used in the various processes is given in Table 9-5. 1/
The installation of fume control systems in the iron and steel-making pro-
cesses requires considerable instrumentation. This required control instru-
mentation is discussed and graphically depicted in Reference 9.
The cost of the different types of control equipment for these
applications has been reported in a NAPCA document "A Cost Analysis of Air
Pollution Controls in Integrated Iron and Steel Industry." Section V of
that report presents the cost/effectiveness investigation and the cost models
which were developed.®/
The applied control systems are more thoroughly discussed in a
companion document, "A Systems Analysis Study of the Integrated Iron and
Steel Industry."!/ Excerpts of Section VI of that report are included here-
in, and the estimated capital and operating costs are summarized in Figures
9-12 - 9-20.
9.5.2 Control Practices - Specific
9.5.2.1 Sinter Plants: Major sources of dust in sintering plants
are the combustion gases drawn through the bed, discharge end gas, and the
exhaust gases from sinter grinding, screening and cooling operations.12/
Because dust generated in the sintering operation can be returned to the
process, most plants axe at least equipped with cyclones.
138
-------
TABLE 9-5
REPRESENTATIVE EMISSION-CONTROL APPLICATIONS IN THE INTEGRATED IRON AND STEEL INDUSTRY^/
Ircn- or Steel-Making iype of Emission-Control Equipment
Segment
Mechanical
Scrubbers
Precipitators
Fabrics
Sinter plant
17
2
9
3
Blast furnace^/
13k/
51
108
0
Open-hearth furnace
0
6
93
0
Basic oxygen furnace
0
15
23
0
Electric furnace
0
5
1
29
Scarfing
4
4
3
2
a/ Final control equipment.
b/ Dust collectors followed by other equipment are not considered.
-------
6.0
Legend
5.0
4.0
H
LO
8 30
2.0
1.0
0.0
20
Electrostatic Precipitator
High-Energy Wet Scrubber
Fabric Filter
/ / '
Open hearth / /Open hearth
/
BOF / BOF//BOF
/
Electric/' /
Furnace/^' /
/ Open hearth
Electric furnace
J—I I I
J L
j—i i i
30 40 50
100
150 200 300 400 500
1,000
DESIGN CAPACITY, 10J ACFM
Figure 9-12 - Estimated Installed Cost (1968) of Air-
Pollution-Control Equipment as Related to
Different Steel-Making Processes^/
140
-------
u
<
Cxi
UJ
o.
CO
ai
S
_j
o
o
CO
o
u
CD
z
f—
<
LU
Q-
o
—I
<
3
z
z
<
<
5
60*02$ I ' |
Legend
Electric furnace
(HEWS)
Electrostotic Precipitator (ESP), 500 F
High-Energy Wet Scrubber(HEWS), 180 F
Fobric Filter (FF), 275 F
Open hearth •
(HEWS)
200
BOF(HEWS)
Furnace capacity,
net tons
Electric
furnoce (ESPL-60
Open hearth (ESP)
200
Open hearth
(FF)
BOF(ESP)
Electric furnace
(FF)
BOF(FF)
20,000
50,000
100,000 200,000 300,000
DESIGN CAPACITY, ACFM
500,000
1,000,000
Figure 9-13 - Estimated Annual Operating Costs for Air-Pollution-Control Equipment
for Steel-Making Process!./ (Depreciation and Capital Charges
are not Included)
-------
rf>-
ro
z
o
- 6.0
<
u
LLI
CH
O
z
<
o
en
<
x
u
5.0
4.0 —
o.
<
u
-------
LO
Oi
o
o
Ll_
O
CO
z
o
1/1
o
u
a.
<
u
1/1
Z
<
5
2.0
High-enery
wet scrubber, 180 F
/
1.5
1.0
//
/ *//
00' ' » I I I I
Electrostatic
precipitator, 500 F
Number of
furnoces
1 1 ¦ ¦
— 40P00 100,000 200p00 300p00
fc 40,000
Fabric filter,275 F
40,000
100,000 200,000 300,000
DESIGNED CAPACITY, ACFM
100,000 200pOO 400/300
Figure 9-15 -
Estimated Installed Capital Costs of Air-Pollution-Control Equipment
Installed on Electric-Arc Steel-Making Furnaces. Control equip-
ment designed to handle emissions from any one furnace at one time .-i/
-------
5.0
4.0
3.0
2.0
1.0
OX)
High-energy
wet scrubber, 180 F
/
A
/
.//'
//
//
i i
_i_L
30,000 100,000
1
Electrostatic
precipitator, 500 F
- Number of
furnaces—^
3/
//
//I
I
. . . 1 .
500p00 20,000
100,000
Fabric filter 275 F
500,000 40POO 100,000
500pOO I POO,000
DESIGNED CAPACITY, ACFM
Figure 9-16 - Estimated Installed Capital Costs of Air-Pollution-Control Equipment
Installed on Open-Hearth Furnaces. Control equipment designed to
handle emissions from furnaces operating at the same time
-------
00
0£
<
o
Q
cn
z
o
1/1
o
u
a.
<
u
Z
<
5
2.0
i.e
1.6
I A
1.2
1.0
0.8
0.6
0.4
0.2
0.0
20,000
~i 1—i—|—'—j 1—i-1—i—r
' Legend '
-i—|—¦ 1 I i—r—r
¦ Electrostatic Precipitator
— Low-Energy Wet Scrubber
Fabric Filter
— — Cyclone
Sinter-plant
material handling
at 135 F
— — pellet
rsl ci 4
_Sinter-ptant_
"wind box
at 325 F
Pellet plont
I ¦ ¦
i I
50 POO 100,000 200,000 400,000
DESIGNED CAPACITY, ACFM
600,000
Figure 9-17 - Estimated Installed Capital Costs of Air-Pollution-
Control Equipment Used in Sinter and Pellet Plants.1/
145
-------
Li.
Legend
Sinter plont _
material handling
Qt 135 F
Electrostatic Precipitater
Low- Energy Wet Scrubber
Fabric Filter
Cyclone
m
Sinter plant
wind box
ot 325 F
0.5
Pellet plant
lh
m o.ol
20,000
50,000
100,000
200,000
500,000 700,000
DESIGNED CAPACITY, ACFM
Figure 9-18 - Estimated Annual Operating Costs for Air-Pollution-
Control Equipment Used in Sinter ana Pellet Plants
(Depreciation and Capital Charges are Not Included)^
146
-------
450
a
Z H-"
— to
~ o
t— a.
1/1
z
z
<
<
%
£ 0.80
l/i u
o <
UJ
O Q-
Z uo
t- 2r
< 3
Of —I
£ O
O Q
Electrostatic
precipitator,
100 F
High-energy
wet scrubber,
100 F
Operating cost
High-energy
wet scrubber. 100 F
Electrostatic
precipitator, 100 F
0.60
0.40
0.20
50,000 80,000 70,000 80,000 90,000 100,000
DESIGNED CAPACITY, ACFM
Figure 9-19 - Estimated. Capital and Annual Operating Costs for
Air-Pollution-Control Equipment Used on Scarf-
ing Machines (Depreciation and Capital Charges
are Not Included in the Operating Costs)i/
147
-------
00
z
o _
£ o
11
UJ u
Q- yj
to of
0£ LLI
3 Q
I— ^
o o
05
<2
0£ ^
LU a.
Q- <
O u
Q VI
Ml LU
1- Q
< Z>
*u
I.80
1.60
1.40
1.20
1.00
0.80
0.60
0.40
—
fH
-J 1 1 1
¦ 1 1 1
11 j.. 1..
1 1 1 1
1 l 1 _i
1 L--1—.1
0 0.5 1.0 1.5 2.0 2.5 3.0
ANNUAL PRODUCTION OF RAW STEEL, MILLIONS OF NET TONS
Figure 9-20 -
Range of Estimated Operating Costs for Air-Pollution-Control
Equipment/Net Ton of Raw Steel—Open-Hearth Furnaces, BOFS,
and Electric Furnaces (TVo-Furnace Operations)l/
-------
Dry-type cleaners are best suited for this cleaning because the
sulfur content of the gas streams can lead to corrosion problems in wet
systems. Cyclones, electrostatic precipitators, Venturi scrubbers, and
baghouses have been used in various combinations at the various points of
emission. However, there are some problems that limit the application of
these devices.
. Wet scrubbers, which have high maintenance cost because of lime
buildup, add to water-treatment problems. Baghouses suffer from the abra-
siveness of the dust, as do the fans in the sintering machines. With sinter
that contains flux (such as limestone), the efficiency of electrostatic
precipitators decreases as basicity of the sinter increases -V
Dust created at the junction points of conveyors has been sup-
pressed. by water sprays containing a wetting agent .i±/
9.5.2.1.1 Cyclones: Because of the large particle size, cyclones
applied to sintering plants usually operate at over 90$ efficiency by
weight. However, cyclone exit loadings range from 0.2 - C.6 grain/ft^-i2/
S.5 .2.1.2 Electrostatic precipitators and baghouses: High-
efficiency baghouses and electrostatic precipitators offer promise of much
better collection than the cyclones normally used. However, few have been
applied to sintering machines «i2'
Electrostatic precipitators have been installed in series with
cyclones. One such installation is reported to operate at an efficiency of
95$, and the final discharge contains only 0.05 grain/scf Ji' Another in-
stallation handled 457,000 cfm with an inlet loading of 2.5 grains/scf and
yielded an output loading of 0.038 grain/scf, an efficiency of 98.5$. How-
ever, the materials charged to the sintering machine have changed from
straight ore fines to ore, flue dusts, and lime. The characteristics of
the ore used have also changed. These changes in materials have resulted
in an increased output loading of 0.25 grain/scf, a decrease in collection
efficiency to 90$.2;/ The use of self-fluxing sinter has also impaired the
operation of electrostatic precipitators in this service at other plants.
There are only three known applications of baghouses at sinter
plants -i/ Data are given in Table 9-6 •
9.5.2.1.3 Wet scrubbers: Only two known sinter plants have
wet-scrubber installations. Operating problems occur due to erosion and
imbalance of fan blades. Dust carried over to the exhaust fans is moist
and has a tendency to accumulate on the blades.
9.5.2.2 Coke Production and Coke Ovens: Gaseous and particulate
matter relased in the by-product coking operation, except that which es-
capes from ovens to the atmosphere, are conveyed in ducts to a coal chemical
149
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TABLE 9-6
DESIGN AND OPERATING DATA FOR SIUT5R- PLANT*/
FABRIC FILTERS ON SINTER STRAND DISCHARGE
Design or Operating Variable
Volume of Air, cubic feet
per minute:
Suction, inches of water:
Pressure Drop Across Bags,
inches of water
Hoppers in Unit, number
Bags per Hopper, number
Total Bags, number
Bag Size:
Diameter, inches
Length, feet
Bag Type
Bag Life, moirth3
2
Bag Permeability, cfm per ft
of cloth
Air-to-Cloth Ratio (Normal),
cfm per ft2 of cloth
Air-to-Cloth Ratio
(One Compartment Cleaning),
cfm per ft^ of cloth
Air Temperature, F
Theoretical Design Efficiency,
percent
U. S. Steel Corp., Bethlehem Steel Corp.,
Gary, Indiana Bethlehem, Pa.
172,000 at 255 F
12
4
10
88
880
11.5
32.2
Fiberglass
17
12-20
2.17
2.41
175 to 300
99+
240,000 at 350 F
n. a.
n. a.
16
72
1,152
12
28
Fiberglass
36
n. a.
2.29
2.44
200 to 500
99+
n.a. - Not available.
150
-------
processing plant for recovery of chemicals. The coke-oven gas remaining
after these operations has a gross heating value of about 525 Btu/ft- ana
is used as fuel throughout the steel plant.
Emissions occurring from handling operations, primarily charging
and pushing, and leakage from oven doors, etc., present dust containment
problems that are difficult to control. However, a technique to control
emissions during charging is being developed at the Pittsburgh Works of
Jones and Laughlin Steel Corporation, under the sponsorship of the National
Air Pollution Control Administration and the American Iron and Steel Insti-
tute, to eliminate this emission by minimizing the openings through which
smoke can escape and, more importantly, by creating a slight vacuum inside
the oven during charging so that air flows into the openings instead of
smoke coming out. Engineering studies are also under way to develop de-
signs for control of coke-oven emissions during pushing.50/
The quenching of hot coke in quench towers produces a rising
cloud of steam in the chimney which lifts coke dust into the atmosphere.
Most of this dust appears to fall out in the vicinity of the quench tower.
Baffles installed in a quench tower can reduce the emission of particulates
into the atmosphere by 75$ or from 6 lb. down to i-l/2 lb. of dust per load
of coke. This can amount to a capture of 900 lb. of particulates per day
from one tower
S.5.2.3 31ast Furnace: Under normal conditions the untreated gases
from a blast furnace contain from 7 to 30 grains of dust per scf of gas.
Most of the particles are larger than 50 jjt. Blast-furnace gas-cleaning
systems normally reduce particulate loading to less than 0.01 grain/scf
to prevent fouling of the stoves in which the gas is burned. These systems
are composed of settling chambers, cyclones, low-efficiency wet scrubbers,
and high-efficiency wet scrubbers or electrostatic precipitators connected
in series ¦i2/ One of the main reasons for cleaning blast-furnace gas is
to render it sufficiently clear, for use as fuel. Recovered dust is re-
turned to the iron-making process.
Blast-furnace gas is cleaned in three stagesj the first two,.at
least, are used almost universally throughout the industry. The majority
of furnaces have secondary cleaning facilities as well. The three stages
and the equipment used in each, along with average outlet dust loading from
these stages are:
1. Preliminary Cleaning - settling chamber or dry-type cyclone
(3-6 grains/scf)
2. Primary Cleaning - gas washer or wet scrubbers (0.05-0.07
grain/scf)
3. Secondary Cleaning - electrostatic precipitator or high-energy
scrubbers (0.004-0.08 grain/scf).
151
-------
9.5.2.3.1 Electrostatic precipitators: The use of electro-
static precipitators for cleaning blast-furnace gas has come about because
of the requirements for cleaner gas for the hot-blast stoves. The opera-
tion of these units has been relatively trouble free because the blast fur-
nace is an almost continuous producer of gals and because of a high percentage
of the particulate emissions removed by the wet scrubbing systems that have
previously "been used to clean up the gases. The wet scrubbers also serve
to condition the gases, for both temperature and resistivity, prior to their
entry into the electrostatic precipitator.
9.5.2.3.2 Wet scrubbers: High performance of a Venturi scrubber
can be achieved only if the blast furnace is operating at a high enough
top pressure to provide the required pressure drop. Lack of sufficient top
pressure has usually required use of an electrostatic precipitator as the
final gas-cleaning unit.
The effect of water rate at a constant throat velocity on the
outlet dust loading of a Venturi scrubber handling blast-furnace gas is
shown in Figure 9-21 .i/ Other operating characteristics are shown in
Figures 9-22 and 9-23.i/
Great Lakes Steel Corporation (Detroit) has three blast furnaces
equipped with high-energy scrubbers. These units have made it possible
to clean the gas at a low cost, although there have been troublesome problems
in design and operation of equipment. Some of the gas-cleaning results are
given in Table 9-7.12/
TABLE
9-7
BLAST-FURNACE GAS-CLEANING RESULTS^
Dust Loading, Grains
/Ft3
Before
After
After
Date
Orifice
Orifice
Precipitators
March 30, 19S6
6.0881
0.0208
0.0010
May 11, 1966
13.9233
0.0600
0.0104
May 19, 1966
13.0181
0.0160
0.0141
May 25, 1966
7.2084
0.0293
0.0017
June 1, 1966
10.1117
0.0219
0.0048
June 8, 1966
11.6293
0.0258
0.0047
June 22, 1966
12.2045
0.0581
0.0040
June 29, 1966
10.5555
0.0299
0.0206
July 7, 1966
9.7877
0.0214
0.0099
July 13, 1966
11.0075
0.0293
0.0140
152
-------
0.12
Ll_
< 0.10
(~)
z
< 0.08
O
o" 0.06
z
Q
< 0.04
o
-J
£ 0.02
3
o
0
o 2 4 6 8 10 12 14
WATER RATE, GALLONS/1,000 CU FT
Figure 9-21 - Effect of Water Rate on Output Dust Loading for a
Venturi Scrubber Handling Blast-Furnace Ga&l/
J 1 1 I ! L
153
-------
u
\ 0.12
i/i
Z
< 0.10
o
v 0.08
o
z
5 0.06
<
o
-1 0.04
H
00
q 0.02
0
0 20 40 60
REDUCTION IN WIND RATE, PERCENT
Figure 9-22 - Effectiveness of Gas Cleaning by a Fixed-
Orifice Scrubber ana a Variable-Orifice
Scrubber When Gas-Flow Rate is Varied^/
Fixed
orifice
Variable
orifice _
y 7
Increasing blast
furnace blowing
rate
1969
operation
PRESSURE DROP ACROSS VENTURI SECTION, INCHES WATER
Figure 9-23 - Operating Characteristics of a Blast-
Furnace Venturi Scrubber^/
154
-------
9.5.2.4 Open-Hearth Furnace: The small size of the particles
emitted from open-hearth furnaces requires high-efficiency collection equip-
ment such as Venturi scrubbers and electrostatic precipitators. Because
of the cost involved and the growing obsolescence of open-hearth furnaces,
industry has been reluctant to invest money in the required control equip-
ment. Often these furnaces have been replaced by controlled basic oxygen
furnaces and electric furnaces.
However, electrostatic precipitators, Venturi scrubbers and bag-
houses are being used on open-hearth systems.^ 16/ Exit gas loading would
have to be reduced to at least 0.03 grain/scf to be sure of a clear stack.-M/
The use of slag wool filters was investigated about 1958 by the
Harvard School of Public Health. However, efficiencies were only of the
order of 50$ and the project was prior to the advent of oxygen lancing.
9.5.2.4.1 Electrostatic precipitators: Two major problems that
have faced the steel companies and equipment manufacturers in the installa-
tion of electrostatic precipitators for open hearths have been (l) design
of the ducts used to carry the gases from the open hearths to the precipita-
tors, and (2) the design of the gas distribution systems at the entrance to
the precipitators. The use of transparent gas flow-distribution models is
considered to be almost a necessity in the practical design of ducting.
The major problem with respect to actual efficiency of electro-
static precipitators on open hearths is the open-hearth process itself.
The problem stems from the variation in the properties of emissions from the
open-hearth furnace during a heat. During the period of a heat, the moisture
content of the gases may drop from a normal value of 18^> to 2$, with a re-
sultant increase in resistivity and drop in precipitator efficiency. The
situation may be corrected by steam injection.
The relationship between the collection efficiency and size of
a precipitator is shown in Figure 9-24. This figure shows that removing
the dust from 315,000 cftn of open-hearth waste gas required 58,300 ft2
of collecting surface for an efficiency of 95^. An increase in the collect-
ing surface area to 96,500 ft^ resulted in an increase in efficiency to 99.3^6.
References 4 and 18 discuss using electrostatic precipitators to
collect the fume from open-hearth furnaces. Another electrostatic precipita-
tor system was put in service in 1965 by Weirton Steel Division, National
Steel Corporation. This system is used for the control of fumes from 550-ton
and 600-ton capacity oxygen-lanced furnaces. A flow-distribution model was
used to facilitate designing a high efficiency unit.
155
-------
COLLECTING SURFACE, SQ FT
Figure 9-24 - Relationship of Electrostatic Precipitator Collecting
Surface to Collection Efficiency for Open-Hearth
Emissions (315,000 acfCi)l/
156
-------
Table 9-8 gives the gas flow and dust loadings for different phases of a
heat and Table 9-9 shows the results of the performance test conducted
during the part of the heat when the dust loadings were at the maximum.
17/
TABLE 9-0
OPEN-HEARTH STACK GAS DATAiZ/
Scrap Hot
Charge Metal Liaeboil Refine
Dust concentration, grains/scf 0.78 1.9 2.70 0.21
Waste gas flow, scf/min 60,000 64,000 66,000 64,000
Gas temperature, °F 580 600 620 560
TABLE 9-9
PERFORMANCE TESTS OF ELECTROSTATIC PRECIPITATOR ON OPEN-HEARTH GASEsil/
Stack
Sample
Test
Volume
Temp.
Volume,
Discharge Load,
Estimate
No.
Cu. Ft/Min
(°F)
scf
Grains/scf
Efficiency
1
247,000
500
82
0.007
99.8
2
223,000
460
85
0.019
99.4
3
248,000
440
41
0.010
99.7
4
248,000
440
113
0.016
99.4
9.5.2.4.2 Wet scrubbers: Outlet grain loadings of 0.01 to 0.05
grain/scf have been reported for wet-scrubber installations. The relation-
ship between outlet grain loading and pressure drop is illustrated in Figure
9-25, although it is not necessarily representative of present-day practice
using higher oxygen-blowing rates.
A description of the application of Venturi scrubbers to control
open-hearth stack emissions is given in Reference 19. Reference 3 describes
the application of a Venturi scrubber on a 200-ton open hearth. Tables 9-10
and 9-113/ give the dust loadings and pressure drops during the oxygen and
nonoxygen periods. It is pointed out that the investment and operating
costs of a Venturi scrubber system would compete very favorably with those
of a precipitator-waste-heat boiler system for cleaning the gas from open-
hearth shops that have an anticipated operating life of no more than a few
years.
157
-------
0.10
0 Q08
5 Q06
O
o u. 004
-I u
oo
G02
0.0i
Q008
-
-
-
0r<
i and
j workir
ime boi
ig perio
-
>/" an*
d
C
0
horging,
id hot
melt d
metal
own _/
-
-
26 28 30 32 34 36 38 40
PRESSURE DROP, INCHES OF WATER
Figure 9-25 - Relationship Between Clean-Gas Dust Loading
and Pressure Drop for a Wet Scrubber on
an Open-Eearth Furnace (Oxyger. Lancing
Used During the Refining Period)^/
158
-------
TABLE 9-10
SCRUBBER-PRESSURE DROP VS. CLEANING EFFICIENCY MP OUTLET PUS]
LOADING (NONOXYGEN PERIODS)5/*
Pressure
Drop, Inches
Of HpO
26
30
35
40
Dust Loading, Grains/Scfd
Scrubber Scrubber
Inlet
0.35
to
0.45
Outlet
0.06
0.03
0.01
0,008
Cleaning
Efficiency
86
92
96
98
TABLE 9-11
SCRU3BER-PRESSURE DROP VS. CLEARING EFFICIENCY AND OUTLET DUST
Pressure
Drop, Inches
of HpO
26
30
35
40
LOADING (OXYGEN PERIODS)3/*
Past Loading, Grains/Scfd
Scrubber
Inlet
0.82
to
0.67
Scrubber
Outlet
0.10
0.05
0.02
0.01
Cleaning
Efficiency
(*)
89
94
97
99
* C-as flow rate was approximately 40,000 scfin.
159
-------
Republic Steel Corporation of Buffalo, New York, installed a
Venturi scrubber handling 60,000 scfm of waste gases from a 300-tor. oxygen-
lanced open hearth in 1964. This installation is discussed in Reference 20.
The system was designed to reduce the dust content to 0.05 gram/scf of dry
gas provided that the inlet loading did not exceed 5 grains/scf of dry gas.
The waste gases from this open hearth contained sufficient sulfur from the
fuels that the scrubbing slurry had a pH of 3 or less, thus requiring that
all contacted materials be adequately protected against corrosion. The
ma,;or problems experienced were buildup on fan blades, fan noise and failure
of redwood mist eliminator elements ..§27
9.5.2.4.3 Baghouses: One glass-fabric baghouse has been applied
to the collection of fume from an oxygen-lanced open-hearth furnace by
Bethlehem Steel Corporation in Sparrows Point, Maryland. This unit is
described in a 1966 article.
21/
The authors state that the capital cost
estimates favored the baghouses over an electrostatic precipitator and the
subsequent operating experience has shown the maintenance and operating
cost to be approximately half that required on an electrostatic precipita-
tor. This baghouse serves a 380-ton/heat furnace having a waste heat boiler
and economizer which cool the gas to below 500°F~5i/
One baghouse installation was made on an open-hearth system after
several pilot studies. However, the actual system installed experienced
problems of high pressure drop which had not been resolved when this open-
hearth shop was shut down .-i2/
9.5.2.5 Basic Oxygen Furnace: The basic oxygen furnace creates
more emissions than the open-hearth furnace, and the particles are smaller.
All basic oxygen furnaces in the U. S. are equipped with high-efficiency
electrostatic precipitators or Venturi scrubbers. Final effluent from
these control devices will contain 0.03 to 0.12 grain/scf. Inlet loadings
may vary from 2.0 to 5.0 grains/scf. Table 9-12 presents a list of basic
oxygen furnaces and their control equipment.
The major operation causing dust and fume generation is oxygen
blowing. The volume of waste gases produced is proportional to the blowing
rate. Gau arrived at a design volume rating of 25 scfm of waste gases/cfm
of oxygen blowing.£2/ jt is common practice to operate BOFs in pairs so
that one is operating while the other is relined. Therefore, the two fur-
naces are usually ducted to one control device. The hood over the BOFs
gives rise to problems as the substantial variation in temperatures can
cause the structure to warp and crack.
The dust problem in BOFs can be minimized if the entire gas and
dust-handling process is considered as one system. Specially designed
equipment which supplies a controlled amount of excess air to the hood can
reduce the size of requisite waste gas-cooling and dust-collecting equipment.
The effect of "controlled combustion" is shown in Table 9-13.
160
-------
TABLE 9-1?
BASIC OXYGEN FURHACE INSTALLATIONS AMD ASSOCIATED AIR-POLLUTION CONTROL BXjUIFMEffT^
Alan Wood Steel Co.
Allegheny-Ludlum Steel Corp.
Araico Steel Corp.
Bethlehem Steel Corp.
CF & I Steel Corp.
Crucible Steel Corp.
Ford Motor Co.
Granite City Steel Co.
Inland Steel Co.
Interlake Steel Corp.
Jones & Laughlin Steel Corp.
Kaiser Steel Corp.
McLouth Steel Corp.
National Steel Corp.
Great Lakes Steel Div.
Weirton Steel Div.
Republic Steel Corp.
United States Steel Corp.
Wheeling-Pittsburgh Steel Corp.
Wisconsin Steel Div.
International Harvester Co.
Youngstown Sheet & Tube Co.
Conshohocken, Pa.
Natrona, Pa.
Ashland, Ky.
Middletown, Ohio
Bethlehem, Pa.
Burns Harbor, Ind.
Lackawanna, N. Y.
Sparrows Etaint, Md.
Pueblo, Colo.
Midland, Pa.
Dearborn, Mich.
Granite City, 111.
East Chicago, Ind.
Chicago, 111.
Aliquippa, Pa.
Cleveland, Ohio
Fontana, Calif.
Trenton, Mich.
Ecourse, Mich.
Weirton, W. Va.
Buffalo, N. Y.
Cleveland, Ohio
Gadsden, Ala.
Warren, Ohio
Braddock, Pa.
Duquesne, Pa.
Gary, Ind.
Lorain, Ohio
South Chicago, 111.
Monessen, Pa.
Steubenville, Ohio
South Chicago, 111.
East Chicago, 111.
Number
2
2
2
2
2
2
3
2
2
2
2
2
2
2
2
2
3
2
3
2
1
2
2
2
2
2
2
2
2
2
2
3
2
3
2
Net Tons
Per Heat
140
80
160
200
250
250
290
200
120
90
250
225
255
210
75
80
200
225
110
110
110
110
300
200
325
100
240
190
180
220
215
200
220
150
200
250
140
265
Annual Capacity,
(Net Tons)
March 1969 Future Startup Date
1,250,000
500,000
],400,000
2,500,000
4,700,000
2,500,000
1,100,000
1,250,000
2,500,000
2,200,000
3,000,000
730,000
1,000,000
3,000,000
2,250,000
1,440,000
2,800,000
3,500,000
3,400,000
2,400,000
1,500,000
1,600,000
2,400,000
3,700,000
1,500,000
2,000,000
1,200,000
2,000,000
1,800,000
2,000,000
2,000,000
1,000,000
2,250,000
2,250,000
3,000,000
1968
1966
1963
1969
1968
1970
1964-66
1966
1961
1968
1964
1967
1966
1973
1959
1957
1968
1961
1958
1958
1960
1969
1962
1970
1967
1970
1966
1965
1965
1972
1963
1965
1970
1969
1964
1965
1964
1969
Electrostatic
Precipitator
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
High-Energy Wet
X
X
X
X
X
TOTAL
57,320,000 18,700,000
23
15
-------
TABLE 9-13
COMPARISON OF EQUIPMENT R3(JJIR5MENTS, SKERGY AND GAS FLOW FOR BOigg/
System Description
J^iar.tity of gas to be
cleaned.
No. 1
100$ Excess Air,
Injection of Water
and Water-Cooled Flue
920,000 actual cfm
No. g
25$ Excess Air,
Controlled Combustion
and Waste-Heat Boiler
176,000 actual cfm
Note
Size of filter
Energy gain or loss to
the system
High proportion of
leakage air and
vapor in the waste
gas
Controlled combustion..
No vapor in the waste
gas, after cooling
8 electric precipitators 3 electric precipitators
(l for spare) (l for spare)
Approx. 35-kw-hr/ton of Approx. 100-kw-hr/ton
steel of steel
Loss Gain
Energy consumption for
the exhaust fans with
use of scrubbers (45-ir..
H2O pressure drop)
9,500 hp.
1,710 hp.
The gas emanating from the mouth of the furnace is essentially
CO and is burned in the hood with induced air. It is desirable to burn all
of the CO to CO2 in the hood; therefore, the hood should be treated as a
combustion chamber. A Japanese process has been introduced which does not
burn the CO in the mouth of the furnace thereby taking advantage of lower
temperature and less volume of gas. The gases are wet-scrubbed and the
cleaned gas can be burned at the stack or the CO can be used as fuel. The
cost of this system is estimated at $1.0 to $1.5 million for a typical
150-ton B0F.32/
The factors to be considered in the selection of a wet or dry clean-
ing system and the problems associated with each system are clearly presented
in Reference 24.
162
-------
Another source of emissions associated with the BOF is kish that
is emitted during transfer of hot metal from bottle car to charging ladle.
Emissions generated have been reported as 0.16 lb/ton of hot metal with
grain loadings of 0.42 grain/scf. A baghouse handling 100,000 acfm has
been installed for control of these emissions and is reported to operate at
99.9$ efficiency.33/ Experimental studies of fabric filters in this appli-
cation indicated that air-to-cloth ratio of 4.5 to 1 should not be exceeded.
A full canopy hood located just above the ladle, sized for approximately
500 ft/min velocity through all open areas, will usually control the fume.M/
9.5.2.5.1 Electrostatic precipitators: Problems associated with
applications of electrostatic precipitators to basic oxygen furnaces are
basically those of variability in gas flow, in the moisture content, and
in temperature of the entering gases, as well as maintenance. Also, col-
lection is lower during the initial phase of.oxygen lancing before the
temperature and water sprays produce a properly conditioned gas stream
for efficient collection.
The hoods over the BOF are a necessary part of the collection
system, and can result in operating problems. The gap between the BOF and
the hood is usually dictated by the anticipated operating conditions and
the buildup on the mouth of the furnace ("skull"). Excess buildup can
restrict the flow of air required for combustion of the carbon monoxide,
with the result that a significant amount of carbon monoxide may reach
the electrostatic precipitator with possible disastrous results.
The hot gases leaving the BOF are cooled by heat exchange and
water sprays to a preferred temperature of 450° to 500CF. The moisture
content of the gas going to the precipitators is quite important; it
should be kept between 20$ and 30$ to insure adequate conductivity of the
dust layer.
9.5.2.5.2 Wet scrubbers: Problems associated with the use of
wet scrubbers include inadequate water treatment facilities or lack of
sufficient water and the abrasive and corrosive nature of the dust-laden
water. The dirty water from Venturi scrubbers is cleaned by a combination
of liquid cyclones, clarifiers and vacuum filters. The recovered dust may
be sintered if the composition is suitable; otherwise it is hauled to
storage.
References 25 and 26 discuss the use of wet scrubbers on BOF
furnaces. With a wet scrubber system it is not essential to burn all the
CO in the hood since a wet system can tolerate a considerable amount of
CO without danger of explosion.
163
-------
9.5.2.5.3, Fabric filters: No installations of fabric filter
devices exist in the U. S. However, fabric filters have been applied in
Europe. This system uses refractory surfaces in an accumulator to absorb
heat from the gases and depends on the cyclic nature of the 30F for its
operation. The refractory accumulator absorbs the heat from the gases dur-
ing the blowing cycle, cooling the gases to approximately 250°F before the
baghouse. As soon as the blowing cycle is over, the accumulator is cooled
by back-blowing atmospheric air through the accumulator,2jJ
9.5.2.6 Electric Furnace: Electric furnaces are becoming more
popular for many metal melting operations. Particulate emissions from
electric furnaces are difficult to collect because of their small size
and because of a strong tendency to adhere to fabric surfaces, a high
angle of repose, and high resistivity. Nevertheless, except for diffi-
culties inherent in the charging operation, over 95$ effective collection
can be achieved with appropriate hooding and high-efficiency collection
equipment .12/
The characteristically small particle size of electric-arc steel
furnace fume precludes the use of dry centrifugal collectors, settling
chambers, etc. High-efficiency scrubbing systems, electrostatic precipita-
tors and baghouses are used to control fumes from electric-arc steel furnaces.
High-energy scrubbers installed on one oxygen-lanced electric
furnace producing a dust concentration of 3.2 to 6.4 grains/scf reduced the
dust output to the range of 0.256 to 0.0512 grain/scf. Baghouses reduced
it to the range of 0.004 to 0.0064 grain/scf. Electrostatic precipitators,
not performing as well, reduced the dust loadings to a range of only 0.256
to 0.512 grain/scf.1/
The high temperature of the fumes leaving the electric farnace
may require the use of tempering air, evaporative coolers or radiation
chambers prior to the collection equipment.
Effective dust and fume control during melting and tapping can be
achieved. However, a technologically acceptable method has not been found
for capturing the heavily polluted air escaping during the charging period.
Complete shop evacuation can be used for control of all fumes, but large
volumes of air must be handled.
9.5.2.6.1 Electrostatic precipitators: The only known installa-
tion of an electrostatic precipitator on am electric furnace plant is at
Jones and Laughlin Steel Corporation in Cleveland. The precipitators are
considered to be operating satisfactorily. Precipitators installed in 1955
at Bethlehem Steel Corporation in Los Angeles were replaced by baghouses in
1967.
164
-------
9.5.2.6.2 Wet scrubbers: High-energy scrubbers for electric
steel-making furnaces are known to be used in only two plants.
9.5.2.6.3 Baghouses; Fabric filters have been successfully
applied to the control of emissions from electric furnaces ranging up to
100 to 150 net-tons capacity, and for multiple-furnace shops as well as
one-furnace shops. The application and operating problems for a baghouse
installed on a 150-ton electric furnace are discussed in a recent article
by W. W. Bintzer and D. R. Kleinton of Lukens Steel Company.20/
Wherever fluorspar is employed, the fluorides in its off-gas attack
glass-filter media. Hence, fiberglass in any form is not recommended on
furnaces employing fluorspar as a fluxing agent. However, other synthetic
fabrics work well.
The approximate air volumes for various furnace sizes are shown
in Table 9-14. Typical side-draft and roof-tap-load systems are illustrated
in Figure 9-26.29/
TABLE 9-14
APPROXIMATE BUDGET SIZING CHART^S/
(Air Volume at Standard Conditions (scfm) for Electric-Arc Furnaces)
Roof Ring
Diameter
(ft.)
KVA
Capacity
Side Draft
Roof Tap
9
4,500
8 tons
18,000
12,000
11
7,000
15 tons
30,000
22,000
13
10,000
25 tons
65,000
50,000
15
18,000
50 tons
80,000
68,000
17
25,000
70 tons
110,000
85,000
19
40,000
100 tons
155,000
115,000
22
60,000
150 tons
190,000
165,000
165
-------
CLEAN /\
EXHAUST U
BAGHOUSE
SIDE DRAFT
HOOD
AIR
BLEED
DUCT
SPOUT
FAN
(2)
ELECTRIC
ARC FURNACE
SIDE DRAFT HOOD
DIAGRAM OF A TYPICAL SIDE DRAFT HOOD SYSTEM
jnUp
ROOF (OR SHELL) TAP
E-1
any
A-1
U
E-2
i
F - ELECTRIC ARC FURNACE
E - 1 and E-2 ELBOWS
C - CHAMBER FOR COOLING
A-1, A-2A-3 AIR BLEED FOR COOLING
U-U-TUBE COOLER
t
CLEAN A
EXHAUST V
_ru
BAGHOUSE
FAN
DIAGRAM OF A TYPICAL ROOF TAP SYSTEM
Figure 9-26 - Typical Side-Draft and Roof-Tap-Hood Systems for Electric-Arc Furnaces^-?/
-------
REFERENCES
1. Lownie, H. W., and J. Varga, "A SyBtems Analysis Study of the Integrated
Iron and Steel Industry," Battelle Memorial Institute, Contract No.
PH 22-68-65, May 15, 1969.
2. Devitt, T. W., "The Integrated Iron and Steel Industry Air Pollution
Problem," NAPCA, Cincinnati, Ohio, December 1963.
3. 3ishop, C. A., et al., "Successful Cleaning of Open-Hearth Exhaust Gas
with a High-Energy Scrubber," Journal of the Air Pollution Control
Association, 11(2), 83-87, 1961.
4. Schneider, R. L., "Engineering Operation and Maintenance of Electrostatic
Precipitators on Open-Hearth Furnaces," Journal of the Air Pollution
Control Association, 13(8), 348-53, August 1963.
5. Smith, W. M., and D. W. Coy, "Collection of Iron Oxide Fumes with an
Electrostatic Precipitator," Blast Furnace and Steel Plant, September
1966.
6. McCrone, W. C., et al., The Particle Atlas, Ann Arbor Science Publishers,
Inc., Ann Arbor, Michigan, 1967.
7. Herrick, R. A., and L. G. Benedict, "A Microscopic Classification of
Settled Particles Found in the Vicinity of a Coke-Making Operation,"
Air Pollution Control Association Proc., 1968, Paper Ko. 68-137.
8. Barnes, T. M., and K. W. Lownie, "A Cost Analysis of Air-Pollution
Controls in the Integrated Iron and Steel Industry," Battelle Memorial
Institute, Columbus, Ohio, May 1968.
9. Wheeler, D. H., and D. J. Pearse, "Fume Control Instrumentation in
Steel-Making Processes," Annual Meeting APCA, 1965, Paper No. 65-104.
10. Control Techniques for Particulate Air Pollutants, Washington, D. C.,
U. S. Department of Health, Education and Welfare, National Air
Pollution Control Administration, January 1969.
11. Frame, C. P., and R. J. Elson, "The Effects of Mechanical Equipment
on Controlling Air Pollution at No. 3 Sintering Plant, Indiana Harbor
Works, Inland Steel Company," Journal of the Air Pollution Control
Association, December 1963.
167
-------
12. Chapman, E. M., "Experience with Selected Air Pollution Control Installa-
tions in the 3ethlehem Steel Corporation," Journal of the Air Pollu-
tion Control Association, December 1963.
13. Hipp, N. E., and J. R. Westerholm, "Developments in -Gas Cleaning—
Great Lakes Steel Corporation," Iron and Steel Engineer, August 1967.
14. Vajda, S., "Blue Ribbon Steel with Blue Skies," Iron and Steel Engineer,
August 1968.
15. Billings, C, E., L. H. Levenbaum, C. Kurker, E. C. Kickey, and L. Silverman,
"Further Investigations of the Continuous Slag Wool Filter," Journal
of the Air Pollution Control Association, May 1958.
16. Thorn, G. G. W,, and A. A. F. Schuldt, "The Collection of Open-Hearth
Dust and Its Reclamation Using the SL/R2C Process," The Canadian
Mining and Metallurgical Bulletin, October 1966.
17. Smith, W. M., and D. W. Coy, "Fume Collection in a Steel Plant," Chemical
and Engineering Progress, July 1966.
18. Elliott, A. C., and A. J. Lafreniere, "Metallurgical Dust Collection in
the Open Hearth and the Sinter Plant," Transactions of the Canadian
Institute of Mining and Metals, 1962.
19. Broman, C. U., and R. R. Iseli, "Control of Open-Hearth Stack Emissions
with Venturi Type Scrubber," Blast Furnace and Steel Plant, February
1968.
20. Johnson, J. E., "Wet Washing of Open-Hearth Gases," Iron and Steel
Engineer, February 1967.
21. Herrick, R. A., J. W. Olsen, and F. A. Ray, "Oxygen-Lanced Open-Hearth
Farnace Fume Cleaning with a Glass Fabric Baghouse," Journal of the
Air Pollution Control Association, January 1966.
22. Schueneman, J. J., M. D. High, and W. E. Bye, "Air Pollution Aspects
of the Iron and Steel Industry," Public Health Service Publ, 999-AP-l
1963.
23. Gilli, Paul V., and R. Kemmetmueller, "Minimizing Dust Problems in BQF
Shops," Iron and Steel Engineer, September 1966.
24. Henschen, H, C., "Wet vs. Dry Gas Cleaning in the Steel Industry,"
Journal of the Air Pollution Control Association, May 1968.
168
-------
25. Willet, H. P., and D. E. Pike, "The Venturi Scrubber for Cleaning
Oxygen," Iron and Steel Engineer, July 1961.
26. Wilkinson, F. M-, "Wet Washing of BOF Gases—Lackawanna." Iron and
Steel Engineer, September 1967.
27. Finney, J. A., and J. DeCoster, "A Cloth Filter Gas Cleaning System
for Oxygen Converters," Iron and Steel Engineer, March 1965.
28. Blintzer, W. W., and D. R. Kleintop, "Design, Operation and Maintenance
of a 150-Ton Electric Furnace Dust Collection System," Iron and Steel
Engineer, June 1967.
29. Wright, R. J., "Concepts of Electric Arc Furnace Fume Control," 60th
Annual Meeting, Air Pollution Control Association, June 1967.
30. Dancy, T. E., "Control of Coke Oven Emissions," 78th General Meeting
of American Iron and Steel Institute, May 27, 1970.
31. Wheeler, D. I:., "Fume Control in L-D Plants," Journal of the Air Pollution
Control Association, February 1968.
32. "Scrubbing System Removes Dust from Steel Furnace Gas for Pollution
Control," Chemical and Engineering News. August 1963.
33. Personal communication, industrial source.
34. Thaxton, L. A., "Kish and Fume Control and Collection in a Basic Oxygen
Plant," Journal of the Air Pollution Control Association, May 1970.
35. Young, P. A., et al., "Generation and Treatment of Sinter Plant Lusts,"
AIM5 Blast Furnace, Coke Oven, and Raw Materials, 20, 1961.
36. "The Application of Electrostatic Precipitators in the Iron and Steel
Industry," Final Report, NAPCA Contract CPA-22-69-73, Southern Research
Institute, June 1970.
169
-------
CHAPTER 10
CEMENT MANUFACTURE
10.1 INTRODUCTION
Cement, a nonmetallic mineral product, is used as an inter-
mediate product for many materials including concrete, mortar, concrete
block and concrete pipe. Raw materials for cement production include
lime and silica as the principal constituents, with alumina and ferric
oxide as fluxing components. Limestone, cement rock, chalk, marl, shell
residues, and "blast furnace slag are sources of lime. Five types of
cement are produced, the classification determined by limitations on com-
positions of raw materials and production methods.
Cement is a granular material and dust control is a problem in
the industry. Dust emissions result from quarrying and crushing, grind-
ing, kiln, and finish grinding and packaging operations. The manufacturing
process, particulate emission sources, emission rates of individual sources,
chemical and physical properties cf effluents, control practices, and con-
trol equipment are discussed in the following sections.
10.2 CEMENT MANUFACTURING PROCESS
Portland cement is made by either the wet or dry process. Fig-
ure 10-1 presents a schematic of the two processes. There are four major
steps in the production of portland cement: quarrying and crushing, grind-
ing and blending, clinker production, and finish grinding and packaging.
Most deposits of cement rock, limestone, clay, and shale are worked in
open quarries. The rock is transported from the quarry to crushing plants.
The types of primary crushers used depend on the hardness, lamination,
and size of rock produced at the quarry, and include gyratory crushers,
jaw crushers, roll crushers and heavy hammer mills or impact mills. From
the primary crushers the rock is screened and conveyed to the secondary
crusher, where crushing is completed. Typical crushers are hammer mills
that reduce the rock to a maximum of 3/4 in.
In the wet process, the wet, ground material is pumped in the
form of a slurry containing about 40^ water into a series of large mixing
tanks and from these it is pumped into the kiln. In the dry process, the
dry, ground, raw material is carried by a conveyor to the storage bins,
and from the bins it is fed into the kiln.
Preceding page blank
-------
QUARRYING
PRIMARY
CRUSHER
AIR
SEPARATOR
STORAGE
GROUND
STORAGE
FINES
AIR
SECONDARY
CRUSHER
GRINDING
MILL
DRY PROCESS
SLURRY
WATER
OVERSIZE
MIXING &
BLENDING
TANK
STORAGE
•ASIN
GRINDING
MILL
WET PROCESS
AIR
SEPARATOR
CUNKER
GYPSUM
PROOUCT
STORAGE
I RR CAR I A
VP* I IM
GRINDING
MILL
TO
TRUCK,
BOX CAR
RR CAR
PACKAGING
MACHINE
Figure 10-1 - Sources of Dust Emissions Cement Plants
-------
The raw materials, either in the wet or dry form, enter the kiln
at the top end and contact the combustion gases which pass through the
kiln counter-current to the material. As the kiln revolves, the raw
materials fall down toward the clinkering zone, having been first dried
"by the hot gases, and then having the carbon dioxide driven eff from the
calcareous materials. The partially fused product- or cement clinker
passes from the lower end of the kiln to the clinker cooler where some
of its heat preheats air going to the kiln. The clinker, with the addi-
tion of a little gypsun cr water to regulate the setting time, is then
ground in ball and tube mills to the requisite fineness for a finished
product.
10.3 EMISSION RATES FROM CEMENT MANUFACTURING PLANTS
The major source of particulate emissions in cement plants is
the calcining kiln. Dust is generated in kiln operations by the grinding
and tumbling action within the kiln, by the liberation of gases during
calcination which tends to expel particles into the gas stream, and by
the condensation of material that is volatilized during passage through
the kiln. Volatilization and condensation generally produce smaller
particles than the mechanical processes.
The principal secondary sources in the cement industry are
dryers and crushers. Dust emissions from dryers result frcm abrasion of
the material being processed and carry over from the kiln. The magnitude
of the dust problem from crushing operations depends on the type and
moisture content of the raw material, and the characteristics and type
of crusher.
10.3.1 Cement Kilns
Variations in kiln operation and design can contribute to the
nature and quantity of emissions. The types of kilns used in the dry and
wet processes are discussed in the following sections.
10.3.1.1 Dry-Process Kiln Systems: Dry-process kiln systems con-
sist of (l) short rotary kiln with or without a waste-heat boiler, (2)
rotary kiln with suspension preheater, (3) long rotary kiln with or with-
out a built-in preheater, (4) "Lepol" kilns with double gas flow (semi-
dry process), (5) pit kiln, and (6) traveling sintering grate kiln. Rotary
kilns are used in the United States, and almost all new plants utilize
long kilns with chain or other preheating systems.
173
-------
10.3.1.1.1 Rotary kiln: The rotary kiln used in mcst plants is
a steel cylinder with a refractory lining. The kiln feed is introduced
into the upper end of the revolving sloped kiln. During the passage through
the kiln, the raw materials are dried, calcined, and heated to a point of
incipient fusion. The combustion gases pass through the kiln counterflow
to the material, and leave the kiln, along with carbon dioxide driven off
during calcination, at temperatures of 300-lS00oF, depending on kiln length
and the process used.
10.3.1.1.2 Rotary kiln with ascending gas heat exchanger: In
dry-process rotary kilns with suspension-gas heat exchanger the dry raw
material powder is fed into the first and highest of four vertically
arranged stages of a cyclone located ahead of the kiln. While passing
through the four stages of the cyclone, the classifying action of the
cyclone suspends the fines of the raw material in the waste gases and the
dust beyond the heat exchanger is 90$ < 10 U. Collection of this dust is
difficult.
10.3.1.1.3 "Lepol" furnace with double gas flow: In the "Lepol"
kiln with double gas flow, the clinker formed in a drum or on a plate from
raw material powder and water is dried initially on a traveling grate by
the waste gases of the rotary kiln, then heated and partially calcined and
subsequently transformed into clinker in the rotary kiln.£/
The waste gases of the rotary kiln are first drawn upward into
the "hot chamber" through the layer of clinker on the grate, preliminary
dust removal being effected in an intermediate dust removal installation
(cyclone). The waste gases are then transported by means of a blower into
a drying chamber where these gases are again drawn through the moist layer
of clinker. During this process, the residual dust is almost completely
retained in the still moist layer of clinker. The gases are discharged
at a temperature of about 200°F through a stack of a second blower.
High dust-emission levels from these units may have the following
causes:
a. Damaged grate units so that the gases are not filtered in
passing through the grate.
b. Too rapid heating of the granulate. Feed material which has
been heated too quickly, or is too dense, has a tendency to burst. In order
to obtain granulate as resistant to heat as possible, the raw-material pow-
der and water distribution on the granulating plate should be uniform. Tem-
peratures in the drying and in the hot chambers must be continuously con-
trolled, and frequent inspection of the separation well between "hot" and
drying chamber is also required.
174
-------
c. Maladjusted suction fans. Fans must be adjusted so that
vacuum in the hot chanter is always higher than the vacuum in the second
chamber. All gases will then undergo intermediate dust separation in the
moist layer of granulate of the drying chamber.
10.3.1.2 Wet-Process Kiln Systems: Two basic types of wet-
process kilns are in use in the U.S.: (a) short kilns with waste-heat
boilers, and (b) long kilns with internal chain preheaters.
10.3.1.2.1 Rotary kiln with built-in units: In kilns with chain
baffles in the preheating area, the chains serve to distribute the raw
paste over a large surface. 'The effect of the chains increases with their
number. Their position and length in the rotary kilns are arranged so that
the clinker material still contains about 10# moisture upon leaving the
last chain. This percentage is necessary so as not to overheat the chains.
In preheated kilns, chambers ahead of the chain area are arranged
crosswise and rotate with the kiln. Through a suitable arrangement of the
inlet and outlet apertures of the chambers, the paste flowing along the bot-
tom of the kiln enters the chambers and comes in close contact with waste
gases flowing through the chambers.
The dust emission from wet-process rotary kilns is highly dependent
on variations in kiln operation. If the waste-gas temperature becomes too
high, which may be the case when there are variations of the calorific
value of the fuel or through increase of the kiln output, the raw paste may
lose its entire water content in the chain area. Any granulate formed is
reduced to dust by the last cf the chains, and this dust is then carried
out of the kiln by the waste gases.
10.3.1.2.2 Rotary kilns with paste dryers: In wet-process rotary
kilns with paste dryer (concentrator, calcinator), the raw material paste
enters the slowly rotating grate drum through ducts. The drum contains
baffles and is arranged ahead of the kiln. The hot waste gases of the
rotary kiln enter the grate drum from below, heat the baffles and thereby
dry the raw material paste into granulate. Additional drying, as well as
calcination and sintering into clinker, takes place in the rotary kiln.
Heat economizers (e.g., scoops) in the kiln and particularly at
the inlet increase the production of dust. The kiln-inlet chute should
extend very close to the lining of the kiln so that the high-velocity waste
gases will not entrain the fines and return them to the paste dryer, which
will increase the dust content of the gas.2/
175
-------
10.3.2 Effect of Feed Composition on Dust Emission
Different types of feed composition also affect emission rates.
One of the most important causes of dust emissions is the way in which
gases are liberated and expelled from the raw feed during calcination.
Some raw materials remain relatively calm while the liberated gases escape;
others appear to expand and explode, throwing the material into the gas
stream. This may explain why some wet-process plants have a higher dust
loss than some dry-process plants.i/
10.3.3 Secondary Sources in Cement Manufacture
Particulate emissions also originate from dryers, coolers, grind-
ing, and packing operations. Meager data exist on emissions from these
sources.
10.3.4 Summary of Emission Rates
The emission factors for individual sources and total particulate
emissions are summarized in Table 10-1. A statistical analysis of emission-
factor data for wet- and dry-process kilns indicated that the differences
between the average emission factors for each process are not statistically
significant. A single emission factor was therefore used for kilns. The
emission factor, 166 lb/ton, is the geometric mean of 31 items of data.
Smissicn-factor data are meager for the secondary sources (i.e.,
dryers, mills, elevators). Reference 3 indicates that in dry-process plants
emissions from secondary sources are about 40$ of kiln emissions, while in
wet-process plants they axe about 15$ of kiln emissions. On this basis,
emission factors of 67 and 25 lb/ton were selected for secondary sources
in dry- and wet-process plants. Total emissions from these secondary sources
were calculated with the assumption that the average operating efficiency
of control equipment and the percentage of production capacity controlled
were the same as for kilns. Information collected during a survey of the
cement industry indicated that bag filters are used extensively on these
sources. Therefore, the assumption of the same degree of net control as
for kilns is not believed to be unreasonable.
Total particulate emissions, as shown in Table 10-1, currently
total 934,000 tons/year.
176
-------
TABLE 10-1
PARTICULATE EMISSIONS
CEMENT INDUSTRY
Source
Kilns
Production
74,600,000
Emission
Factor
¦ (ef)
167
Efficiency
of Control
(Ce)
0.94
Application
of Control
(C t)
0.94
Net Control
(Cc-Ct)
0.88
Emissions
(tons/year)
745,000
Grinders, Dryers,
elevators, etc.
Wet Process
Dry Process
43,600,000
31,000,000
25
67
0.94
0.94
0.94
0.94
0.88
0.88
65,000
124,000
Total for Cement
934,000
-------
10.4 CHARACTERISTICS OF CEMENT PLANT EMISSIONS
The chemical and. physical properties of cement plant effluents
are summarized in Table 10-2. Mechanical, volatilization, and condensation
processes produce the particulate emissions. Volatilization and condensa-
tion generally produce smaller particles than the mechanical processes.
The mass median size of particulate emissions from kilns is 8.5 M* and the
geometric deviation is 4.1.
10.5 CONTROL PRACTICES AND EQ.UIBIENT FOR CEMENT PLANTS
10.5.1 Control Practices
Dust can be adequately arrested in the cement industry by proper
selection of dust control equipment. Dust emissions as low as 0.03 to 0.05
grain/scf have been obtained in newly designed well-controlled plants.=J
Table 10-3 gives ranges of dust emissions for various combinations of
control devices.i/ An emission level of 0.1 grain/scf is probably the
value needed to preclude nuisance complaints from nearby residents.^./
The hot kiln gases are the main source of emission and they present
a major problem because gas volumes are large; they contain acid gases such
as KgS and S02> varying amounts of H2O, and a temperature range usually
above 500 or 600°?..1/ A kiln producing 20 tons/hr of cement clinker will
produce about 240,000 lb/hr of exit gases, or about 92,000 acfm.^/
10.5.2 Control Equipment
10.5.2.1 Multicyclones: Although a number of types of dust col-
lectors are used in the cement industry, only the high-efficiency collectors
such as the electrostatic precipitator and fabric filter, sometimes used in
series with inertial collectors, effectively collect fine dust. The multi-
cyclones alone are not an acceptable means of reducing dust emission from
the kiln to the atmosphere.
Multicyclones, when preceding other control equipment, can be
expected to scalp off about 70 wt. $ or all of the coarser particles.
10.5.2.2 Electrostatic Precipitators: In a wet-process plant
the performance of an electrostatic precipitator is greatly enhanced by the
extra water vapor present in the exhaust gases from the slurry. Dry-process
kilns do not have this water in the feed and often it is necessary to add
it as an aid to precipitator operation.®/
176
-------
TABIE 1C-2
SFFLVENT CHARACTERISTICS - CBEKT MAHUFACT'JRE*
A. Particulate (Part I)
Solids Particle Electrical .Mcisture
Sour'.e Far tide Size Leading Chemical Combosition Density Resistivity Content Toxicity
Cement plant
a. Kilr. Wagner Turbidiineter Dry Process CaO: 39-53; SiC^: 2.6-3.2 See Figures N.T.
15.5 < 5, 43 < 10 ]-17 (stack 9.0-19; Fe203: 10-3, 10-4,
64 < 20, 89 < 4C conditions) 2-11; AlgO3: 2-0; X2"*2-6; 1Q-5 and 10-6
BAHCO Analysis: Average 6.4 Na^O: O.S-1.1; Mg3: for detailed
25-32 < 5 Wet Process 1.3-2.5 data
Average 3C < 5 1-14 {stack
40-52'< 10 conditions)
Average 47.6 < 10 Average 5.7
55-73 < 20
Average 66.7 < 20
67-63 < 4C
Average 8C .5 < 40
(Also see Figure 10-2)
mass median - 8.5
C e 4.1
b. Dryer
til Standard 40-70 < 10* 11-10*
druc
(2) ^uic/. dryer 50-70 < 10+ 13-100
(3) Unspecified 5-4D (stack
type conditions)
c. Cer.ent Cooler I&EC0 Analysis
(clin/.er dust] 3-6.5 < 5
Average 4.7 < 5
4.8-12 < 10
Average 7.$ < 10 3.6-3.9
10.4-18 »1 < 15
Average 12.4 < 15
A. Particulate (Part II)
Hygroscopic Flanaability or Handling Optical
Source Solubility Wettability Characteristics Explosive I*"'ta Characteristics Properties
Cement Plant
a. Kiln CaO - s. H^O Will absorb mo Angle of repose
CaO, SiGg, Fe^Oj, 59 degrees
A1„0,, TiC-g - s. (Portland Cement)
10? HC1
+ = German data.
* See Coding Key, Table 5-1, Chapter 5, page 45, for units for Individual effluent properties.
179
-------
TA3LZ 10-2 (Concluded)
B.
earner ,ias
Cement Plant
a. Kiln
Moisture
Chemical
Toxic-
Corro-
?lw Rate
Temperature
Content
Composition
ity
sivity
Try Process
Dry Process
Cry Prccess
COg, steam, 0~,
K.T.
Gasps CCB-
&. 54-300
150-845
1-2
small amount3
tain 0-40*1
(stack
Wet Process
Wet Process
SC2, N0X, CO,
steam ar.d
conditions)
£30-650
20-40
and pclysulfides
will cor-
b. 94-€14
Typical Analysis
rode dead
(stacx
CC£: 17-25
spots in
conditions)
02: 1-4
piping
Vet Prccess
CC: 0-2
a. 72-445
N~: 75-80
Flamnability
or Explosive
Limits
(stack
conditions)
166-570
(stack
conditions)
b. Zrycr
(l) Standard &. —
dnas b. ?6-64 + (stack
.5e-302T
conditions;
(2) 3uick a. --
dryer b. 16-48+ (stack 158-3C?+
conditions)
(i) Unspeci- a. 1C-6C (stack
ficd type conditions)
Dew point:
104-156*
5-:2
Gerr:un data.
180
-------
99.9
99.8
99.5
SIEVE ANALYSIS
LU
N
a
LU
<
t—
60
Z
<
x
t—
BAHCO ANALYSIS SP. GR. 2.60-3.20
to
to
LU
0.5
0.2
100
1,000
PARTICLE DIAMETER (MICRONS)
Figure 10-2 - Typical Particle Size Range of Cement Kiln Dusti2/
-------
CD
ro
200 400
TEMPERATURE *F
600
Figure 10-3 - Resistivity of Cement Kiln Dust Under
Varying Conditions of Temperature
and Moisture in Gas H/
* Figure shows percent water vapor by volume.
100 200 300 400
GAS TEMPERATURE-°C
Figure 10-4- Dependence of Specific Electrical
Dust Resistance on Gas Tempera-
ture for Various Dusts12/
Curve 2 originated from a rotary cement kiln
of the older type, operated by a dry process.
Curve 3 pertains to a rotary cement kiln with
heat exchanger.
Curve 4 cement dust rotary kiln with concen-
trator .
Curve 5 cement dust rotary kiln with sludge
injection.
-------
10
12
11
10
2
u
5
° 1010
>
t—
>
>—
l/l
L/1
LU
CL
10y -
3
o
10'
8 _
10'
LAB MEASUREMENTS
(6-7% HjO BY VOL.)
FIELD MEASUREMENTS
(— 30% H20 BY VOL.)
200 300 400
TEMPERATURE - °F
600
Figure 10-5 - Typical Laboratory and Field Resistivities
of Cement Kiln Dustsi2/
183
-------
10
13
10
12 -
5 1011
5
£ 10
<~)
10
10*
1-2% BY VOL.-
5-7% BY VOL.
10% BY VOL.
I0C
20% BY VOL.
A •
10'
_L
100
200 300
TEMPERATURE - °F
400
500
600
Figure 10-6 - Laboratory Resistivities of One Cement Kiln
Dust Sample for Various Gas Moisture
Contents^/
164
-------
TABLE 10-3
RANGES OF DUST EMISSIONS FROM CONTROL SYSTEMS SERVING
DRY- AND WET-TYPE CEMENT KILKSl/
Source
Kiln-dry type
Kiln-wet type
Type of Dust Collector
Multicyclones
Electrical
precipitators
Multicyclone and
electrical pre-
cipitators
Multicyclone and
cloth filter
Electrical pre-
cipitators
Multicyclone and
electrical pre-
cipitators
Cloth filter
Range of Dust Emissions
from Collector
grain/scfS/ lb/ton of Cement
1.55 - 3.06 26.2 - 68.6
0.04 - 0.15
0.03 - 1.3
0.039
1.7 - 5.7
0.6 - 29.4
0.7
0.03 - 0.73 0.52 - 9.9
0.04 - 0.06 4.3 - 24.2
0.015 0.35
a/ Grains/scf - Grains/standard cubic foot of gas corrected to 60°F
and 1 atin. pressure.
185
-------
The operation of electrostatic precipitators has not been entirely
satisfactory in the past because of decreasing efficiency over extended
periods due to the effects of the cement dust on the high voltage compo-
nents.!/ Also, when kilns have been shut down and then restarted, it may be
necessary to by-pass the electrostatic precipitator for periods up to 24 hr.
because of the danger of explosion from the presence of combustible gas or
coal dust.
The total installation cost of an electrostatic precipitator is
shown to be as high as 400$ of the purchase cost in the HEW publication
AF-51.Z/ It is reported that this figure should be somewhat higher based
on costs frequently experienced in the cement industry.8/ Recent cost data
for electrostatic precipitators used in the cement industry indicate that
the installed cost for precipitators having efficiencies of 99.0 - 99.9$
ranges from $1.00 to $3.50/aefm with an average of $1.80/acfsi.l2/
10.5.2.3 Fabric Filters: Fiberglass baghouse filters have had
much success in controlling kiln emissions. Bag life averages 2 years or
more.^/ A big plus in baghouse installations is the fact that duct designs
are simple and uncomplicated, requiring little study for the flow of gases
when compared with the frequently complicated model studies necessary for
good gas-flow patterns in the electrostatic-type dust collector.1/
Moisture condensation in glass-fabric filters can present prob-
lems. However, dew point temperatures are normally avoided by proper appli-
cation of insulation to ducting, etc., and by proper operation to avoid
condensation.
The simplicity of design and operation of the fiberglass filter
system, which lowers the cost, is balanced to some extent by increased fan
power needed to overcome pressure drop across the baghouse. Many baghouses
operate with a pressure drop of 3 to 7 in. of water. Sample data for fiber-
glass baghouses are given in Reference 9.
The total installation cost of fabric filters is shown to be as
much as 400$ of the purchase cost in KEW Publication AP-51.Z/ This figure
is claimed to be in line with cement industry experience.®/
186
-------
REFERENCES
1. Kreichelt, T. E., D. A. Kemnitz and S. T. Cuffe, "Atmospheric Emissions
from the Manufacture of Portland Cement," U. S. Public Health Service
Publication No. 999 AP-17 (1967).
2. "Dust Prevention-Cement Industry, " Vereir. Deutscher Ingenleure; VDI No.
2094, June 1961 (English Translation).
3. Cuffe, S. T., "Report or. the Air Pollution Aspects of the Universal
Atlas Cement Division of United States Steel Corporation at Duluth,
Minnesota," Technical Assistance Branch, Division of Air Pollution,
U. S. Public Health Service, Cincinnati, Ohio, circa 1955.
4. Doherty, R. E., "Current Status and Future Prospects--Cement Mill Air
Pollution Control," Proceedings of the National Conference on Air
Pollution, Washington, D.C. (1956).
5. Burke, E., "Dust Arrestment in the Cement Industry," Chemistry and
Industry, 1312-1319, October 1955.
6. Gale, W. M., "Technical Aspects of a Modern Cement Plant," Clean Air,
7-13, September 1967.
7. "Control Techniques for Particulate Air Pollutants," National Air Pol-
lution Control Administration Publication No. AP-51, Washington, D. C.
(1969).
9. Hailstone, R. E., "Air Pollution Control in the Cement Industry,"
Minerals Processing, 11-15, May 1969.
9. Ballard, W. E., "Glass Bags - From Batch to Baghouse," Rock Products,
October 1962.
10. Brown, R. F., "Major Application Report No. 4, A Report on the Use of
Electrostatic Precipitators in the Rock Product Industries," Research-
Cottrell, Inc., Subcontract No. H-6628, February 2, 1970.
11. Pottinger, J. F., "Collection of Difficult Material by Electrostatic
Precipitation," Australian Chemical Processing and Engineering, pp.
17-23, February 1967.
12. Loquenz, Heinz, Staub-Reinhalt. Luft, 27(5), p. 41 (1967).
167
-------
CHAPTER 11
FOREST PRODUCTS INDUSTRY
11.1 INTRODU CT ION
The forest products industry as considered here encompasses for-
estry, sawmill, plywood, particleboard, hardboard, and pulp mill operations.
Emissions from this industry are highly variable, and range from dust re-
sulting from logging operations to particulates emitted from lime kilns in
pulp mills. Particulate emission sources include wood-waste incinerators,
plywood dryers, sawmill planers, sanders, recovery furnaces, and power
boilers. Figure U-l presents a composite flow diagram for the forest
products industry.
Manufacturing processes, particulate emission sources, particulate
emission rates, effluent characteristics, and control practices and equip-
ment associated with this industry are discussed in the following sections.
11.2 FORESTRY OPERATIONS
Forestry operations center around timber cutting. Trees are har-
vested by logging crews and transported to sawmills, plywood plants, etc.,
for subsequent processing. Logs are transported by truck, floated down a
river, or towed by tugs in the form of "log booms cr rafts."
11.2.1 Emission Sources and Rates
Apart from the dust generation resulting from logging operations,
a major source of air pollution in forestry operations is the burning of
wood residues. Common methods of disposal include open burning and incin-
eration in a "wigwam" burner. The diversity of reasons for burning and the
large land areas involved lead to significant pollution from these prac-
tices.
Determination of the emission potential of slash burning is diffi-
cult because accurate estimates for total acreage or fuel loading for range
burning are not available. Particulate emissions from slash burning have
been estimated by two agencies of the U. S. Department of Agriculture.i/
The Forest Service reported an estimate cf 17 million tons of particulate
matter produced by "Prescribed Fires" in the United States in 1967. Six.
million tons of this total are attributed to slash burning. Slash burning,
primarily practiced in the western United States, is employed to reduce the
flammability of heavy concentrations of slash left after timber cutting.
169
Preceding page blank
-------
CD
O
sawmill
LUMBER
VENEER LOGS
LOGS
VENEER
DRYE
CLIPPER
LATHI
debarring
SLASH
BURNING
DEBARKING
BOILER
CHIPPING
LAY UP AND GLUE
SPREADING
TRIMMING
PRESSING
BLEACH
PLANT
FILTER
BLOW
DIGESTER
SANDING
PLYWOOD
_y
PLYWOOO MANUFACTURE
ELECTROSTATIC
PRECIPITATOR
EVAPORATION
UNLOADING
GRINDING
RECOVERY
FURNACE
SALT CAKE
DISSOLVING
TANK
SIZING
TRIMMING
PRESSING
WIGWAM
BURNER
RR CAR
LIME
STORAGE
SANDING
PARTICLEBOARD
CLARIFIER AND
WASHER
S LAKER
PARTICLEBOARD PLANT
-~§L
-O
PANEL
RESIN
FORMING
BINDER
MULCH, OTHER USE
PULP MILL
Figure 11-1 - Composite Flow Diagram - Forest Products Industry
-------
Prescribed burning in the eastern United States is used primarily to remove
accumulated litter on the forest floor and the 11 million tons emitted are
not included in the slash-burning category. The Forest Service also esti-
mates that the "fuel consumed in the west" is 21 x 10® tons per year.
The Soil and Water Conservation Research Division estimates that
25 million tons of logging debris are burned each year and that 6.5 x 10®
tons of particulates are produced by prescribed burning in the forests.§/
As shown in Table 11-1* emissions from slash burning are taken to be
6 million tons in' accordance with the estimate of the Agriculture Department.
Emissions from vehicle traffic on logging roads were not estimated.
11.2.2 Effluent Characteristics
Data on effluent characteristics from slash burning are meager.
Research is being conducted on the subject at Oregon State University,
Washington State University, and the University of Washington.
Field tests on slash burning conducted by the University of Wash-
ington investigators have resulted in the following observations:l/
1. Ground-level particulate increased to nearly 10 times the back-
ground immediately downwind from a broadcast burn. The particulate in the
smoke plume in the fire vicinity reduced visibility to 0.5 km., but at a
distance of 19 km. from the fire the visibility had increased to the level
found over Seattle.
2. Similarly, high CO and C02 concentrations found at the fire
site decreased rapidly to ambient conditions in horizontal and vertical
directions.
3. Hydrocarbon analyses of the gas samples revealed low concen-
trations of 25 components, the most significant of which appeared to be the
low molecular weight hydrocarbons and alcohols including ethylene, ethane,
propene, propane, methanol, and ethanol. Several unsaturated components
were found, but the quantities were relatively low.
The results of the study of broadcast fires, plus those on pile
and laboratory fires, suggest that broadcast fires can be modeled in the
laboratory with respect to burning characteristics, gaseous and particulate
emissions from different fuel density, packing, quality, and method of igni-
tion. Furthermore, that study indicates that the air pollution aspects of
slash burning can be minimized by establishing a high energy fire with a
strong convection column under conditions favorable for rapid atmospheric
dispersion.
191
-------
tabu; 11-1
PARTICULATE EMISSIONS
FOKEST PRODUCTS INDUSTRY
Source
I. Slash Burning
II. Wigwam Burners
III. Chemical Pulp Mills
A. Kraft Process
1. Recovery furnace
2. Lime kiln
3. Dissolving tanks
B. Sulfite Process
1. Recovery Furnace
C. N.S.S.C. Process
1. Recovery furnace
2. Fluid bed reactor
D. Bark Boilers
to
ro
Quantity of
Material
23,000,000 tons/yr
27,500,000 tons/yr
24,300,000 tons pulp
1/3 of 2,500,000 tons pulp
l/3 of 3,500,000 tons pulp
15$ of 3,500,000 tons pulp
32,000,000 tons pulp
Emission
Factor
10 lb/ton
150 lb/ton
45 lb/ton
5 lb/ton
268 lb/ton
24 lb/ton
533 lb/ton
IV. Plywood, Particleboard
Hardboard 1,500,000,000 sq. ft.
plywood/yr
2.6 lb/ton burned
45 ^ tons
MM sq. ft., plywood
250 lb/MM sq. ft., plywood
A. Boilers
B. Cyclones
C. Veneer Dryers
Efficiency Application Net
of Control of Control Control Emission
Cc Ct Cc'Ct. (tons/yr)
6,000,000
132,000
0.92 0.99 0.91 164,000
0.95 0.99 0.94 33,000
0.90 0.33 0.30 42,000
0.92 0.99 0.31 10,000
0.92 0.99 0.91 1,000
0.70 1.00 0.70 42,000
82,000
Total from Chemical Pulp Mills 374,000
3,000
67,000
Total for Forest Products Industry
6,580,000
-------
Available data on the chemical and physical characteristics of
effluents from forestry operations are summarized in Table 11-2.
11.2.3 Control practices and Equipment
The various forestry operations that emit particulate matter, which
include slash burning and incineration, do not lend themselves to the use
of control equipment. Although some considerations of burning methods and
meteorological conditions would undoubtedly influence these emissions, these
factors do not fall in the category of control equipment.
11.3 SAVMILL OPERATIONS (LUMBER PRODUCTION)
The sawmill or lumber industry includes production of lumber,
shingles and shakes, posts and pilings, and some lumber remanufacture and
planing mills. Operations include debarking, sawing, and planing.
11.3.1 Emission Sources and Rates
The basic lumber production processes create few pollutants.
Sawing and planing equipment generate wood wastes--sawdust, shavings--in
particulate form. Planers usually have effective containment of this waste;
but saws are seldom designed to contain and control fine particles, and wood
dust emissions occur.
Collecting, transferring, and processing wood wastes for by-product
markets or incineration cause significant particulate emissions because of
the huge volume of the material.
Kiln drying of lumber probably does not create hydrocarbon emission,
although this process has not been adequately studied.
Incineration of sawmill wood and bark wastes is the main air con-
taminant source. The "wigwam"-type burner is one common device used for
this purpose. Reference 4 reports on a study of "wigwam" burners in the
Pacific Northwest. Average temperature of the gases leaving the burner was
485gE) which is considerably below the 600-900°F temperature range recommended
for smoke-free operation. Improving the combustion efficiency would reduce
emissions from these burners.
Emissions from "wigwam" burners associated with sawmills are in-
cluded in the 1.32 x 10^ tor.s/year shown for these burners in Table 11-1.
193
-------
TARIJ" 1 I
W Emjrcrrrn krdm
iT)!.ir/:- r:.OL")' t:~ i
A. Particulate (Part i)
Source
Fbrest Products
Industry
1. Forestry
operations
a. Slash burn-
ing
Particle Size
nl i'in ln ftirtlcle Density Electrical Resistivity Mo is tore Content Toxicity
Alkam.-s, alkenes, al-
cohols, ketones,
essentiil oiIs,
fly ash
2. SamlLls
CD
a. Planers
b. Wigvaa burner
5. Plyvood plant
a. Incineration
(see wlgwaa
burner)
b. Veneer dryer
c. Sander
Fine sawdust
Hicroscnpr:
24 < ?
0.004-0.G1 Averse:
0.17 (corrected
to rs% co0)
Drum snnder; Ba]
analyui;;, 5 ,
10 <10, 3!i.b 00,
95.1 <40
OpticnL microscope:
Mean count size,
HydruC'irtxjns
l>awiiu:;t, nander dust
d. Pressing
aachine
Hienolic rc;;;in
4. F*articleboard
plant
a. Incineration
( sec wigvaa
burner)
b. Dryer
c. Pressing
anchinc
d. r>mde.- ( aee
plywood)
Formaldehyde-urea resin
• Mlcroftratno/ruMc meter.
* See Coding Key, Table ft-1, Chapter ft, p. 4ft, Tor units for Individual effluent properties.
-------
A. Particulate (Pnrt l) (Concluded)
Partiili' f»izc
Forest Products Industry
5. PuLp Hills
i. Kraft k Soda
(l) Recovery furnace
Electron microscope
count
16.0 < 0.5
53.2 < 1
30 > L
Cascade iopactor
50 < 0.9S-L.1
(2) Llae kiln 95 < 2f>
(3) Spelt dissolving
tank
(4) Boilers
(a) bark-fired
CD
C/l
(b) oi L-fired
(c) coal-Tired
b. Sulfite.
(l) Recovery furnace
(aagnesiioB bisulfite)
(?) Boilers
(a) bark-fired
(b) oil-fired
(c) coal-fired
N.S.S.C.
(1) Recovery furnace
(2) Saelt dissolving tank
(3) Boilers
(a) bark-fired
( b) oil-fired
(c) coal-fircd
* High HaCl ceo tent due to seavat«r lmmers ion of logs.
Bahco Analysis
19-25 < 5
Average 22 < 5
34-48 < 10
Average 41* < 10
60-66 < ?0
Average G3 < TO
70-79 < 40
Average 74 < 40
TABLr 11-? (Continued)
Particle Electrical Moisture
Solids Loading Chmical Composition Density Resistivity Content
See Figures 0.2-1.2
11-2 and 11-3 Average 0.
for detailed
data
NaCl: 0.6-14*
Average - 2.3
Na?S: 3.3-5.4
Average - 4.4
Carbon, Fly ash
T.-R ( dry)
M«'an lonrlinp,
r-.o
Nagf.04: 14-90
Average - 80
HagCOj: 2.6-73
Average - 11.2
3-20 CaO. CaCOj, NagCOj,
NagSOj, MgCOj,
Fe^Oj) Alo0j,
SiOj
0.17-L.3 HajCOj, HagS, HajSO^
1.3-2.4 (dry)
0.04-0.4 (dry)
S.1-3.L. (dry)
4.94
1.3?
0.04
3.1-3.5
4-6
1.3
2.05-2.4
0.04
3.19 -».£>
-------
A. Particulate (Part II )
Source Solubility Wettability
forest Products Industry
1. forestry operations
a. Slash burning
b. Wigvm burner
2. Satsllls
3. Plyvood plant
4. Particlebosrd plant
5. Pulp sills
NapSO^ - s. HgO, glc.
NapCOj - s. HoO, B.s. al.
NaCl - s. HgO" glyc.
s.3. al.
(2) Line kiln Ha^COj - s. !U>0, s.s.nl.
CflCO; - s. Hj>b
MgCOj - s. HpO
NapS04 - s. KgO, glyc.
I—1 a. Kraft and soda
to
^ (1) Recovery
furnace
(3) Saclt dissolv- NapCO^ - s. HjjO, s.s. al.
ing tank NajS - s. HjO s.s. al.
TABLE 11-2 (Continued)
Hygroscopic Flnonabillty or Handling Optical
Characteristics Explosive Llalts Characteristics Properties Odor
Hygroscopic
Agglomerates,
corrosive
Sodlia salts-
white; char,
fly ash - black
-------
B. Carrier Gas
Source Flow Rate Temperature;
Forest Products
Industry
1. Forestry
operation
». Slash burn-
ing 900-1550
2. SataiLLs
a. Planers
b. WigVM burner Avg. veloc- 166-^66
ity at burner Avp,. 40:>
top, 600 ft/min
3. Plyvood
plants
a. Incineration
(see vlgnaa
burner)
b. Dryer 29G-334
c. Sander a) 40-60*
d. Pressing
machine
4. Farticloboard
plant
a. Incineration
(see vlgvno
burner)
b. Dryer
c. Pressing
¦nchlne
d. Sander (see
plyvood)
* Actual cubic feet/nin.
TftHI.F ll-:' (Coritimi"(j)
Moisture Chemical FLasublllty or
Cunt-iMit Composition Toxicity Corroslvlty Odor Explosive Llaits
COg i CO, Cll|, Cj H0
c?H4, cpHe, c^Hg
N2, 0?
Op, Hp, CO, COg, and
various gaseous
products of wood
pyrolysis
Dew Point Hydrocarbons, air
100-133
Air
Phenolic resin (gis
and vapor) air
Formaldehyde-ur<*H
rosin, air (gas and
vapor)
-------
B. Carrier Gas (Continued)
Source Flow Rate Temperature
Pulp DlllS
a. Kraft & Soda
(1) Recovery (a) 20-568 ?70-650
furnace (b) 278-560 350
CD
a>
(2) Line kiln (a) 7.50
(b) 31-53**
Avg. 44
(3) Saelt dissolving (b) 45**
tank
(4) Boilers
(a) bark-fired (b) 96-125
Avg. 112»«
(b) oil-fired (b) 99-366"
Avg. 218
(c) coal-fired (b) 91.4-340**
Avg. 204
•• Standard ft^/alr-dried ton.
*** Pound/air-drled ton.
X W - Methyl Mercaptan.
DS - Dimethyl Sulfide.
TABLE 11-? (Conl lnu-«l)
Moisture Flamablltt.y or
Content Chualca) (-'opposition Toxicity Corroslvlty Odor Explosive Limits
frt)-40 Typical Orsat analysis
Dew Point COp - IP.5
131)-JHO CO - 0.1
Op - 7.6
N2 - 79.0
Minor components
HpS - 130-935 ppm
J MM - r.O-1,400 ppre
(l-lb ppo new plants)
JDS - 0-125 ppo
SOo - 1-350 ppn
Corrosive due
to sulfur
ennpounds
Mal-
odor-
ous
HpS: upper llait
In air, 45.5*;
lower llait in
air, 4.3* CH3SCH3:
upper llait in
air, 9.19*; lower
llait in air,
2.23* CH^SH:
upper llait in
air, 21.0*; lower
limit in air,
3.9*
400-600***
Avg.b56
C02 - 16.5-22
CO - 0-0.7
0j> - 0.3-5.1
N2 - 77.1-78.4
Minor components
H?S: 0.08-0.23***
S02: 0-2.5***
m, DS: 0-0.6***
S02 -5
irritant
Corrosive due
to sulfur
cca pounds
Mal-
odor-
ous
S02: 0-0.Ob***
HpS: 0.01-0.04***
MM, DS: 0.01-0.09***
Np balance
Corrosive due
to sulfur
conpounds
Mal-
odor-
0us
654-868***
Avg. 774
336-1,240***
Avg. 739
245-908**
Avg. 539
COp, Op1 Np, SOp
COp, Op, N?, SOp
C0?, Og, Mp, SOp
SOp - 5
irritant
-------
B- Carrier Gas (Concluded)
Source Flov Hate Temperature
b. Sulfite
(l) Recovery b)
furnace
(magnesium
bisulfite)
(?) Boiler
(a) bark-fired b) 105-11^.'
Average 113
CD
ID
(b) oil-fired
(c) coal-flred
b) 148-4?0
Average 29b
b) 137-300
Average ?bfl
. N.S.S.C.
(1) Recovery
furnace
b) 107-lfiy 3?5-U00
Average 148
(¦.') auelt dis-
solving tank
(3) Boilers
(a) bark-fired
b) S9-G0
Average 63.b
(b) oil-riri.-d
b) 30G-310
Average 31u
(c) coal-fired
b) P04-317
Average 303
Methyl Mercapt.an.
Dimethyl sulfide.
¦I'ABT.E 11-2 (Concluded)
Moisture Content Chem. Composition Toxicity Corroslyity Odor
Flassaability
or Explosive
Limits
3,000*"*
CGp, » Op, SOp, SOp - 5 Corrosive Mai- See above
HpS, KW, PS irritant due to sul- odor-
fur cam- ous
pounds
700-910
Average 033
CQp» N?, 0?t SOp
bOb-1,430* **
Average 1.000
367-1,040
Average 730
1,100-1,400*** C02, Np, 03, SOp,
Average l,2b0 HpS
1,040-1,000***
Average 1,000
llgS, SOp, W, DS
COp, Np, 0j>, SOp
7b/-oor***
Average 7 70
-------
1 X 10
1 x 10
x 10
! 1 x 10
./i 1 x 1010
z>
Q
(Laboratory Measurement With 1-2% Moisture in Gas)
1 x 108
200 300 400
GAS TEMPERATURE °F
Fig-are 11-2 - Electrical Resistivity of Salt Cak<
,18/
200
-------
East and West
Cascade Outlets
(/V 85 % Na2S04)
Average
Commercial Grade
Na2C03
C.P. Anhydrous Na2SO^
to
to
to
NOTE
RECOVERY FURNACE FLUE GAS
TYPICALLY 20-40% MOISTURE BY VOLUME
30
25
20
15
10
5
0
MOISTURE IN GAS f/o BY VOLUME)
Figure 11-3 - Electrical Resistivity of Sodium Sulfate as a Function of
Moisture in Gas at 300°? (laboratory Measurements)-^/
201
-------
11.3.2 Effluent Characteristics
Limited data vere fcund for the effluent characteristics of
emission sources in sawnills. Available data are summarized in Table 11-2.
11.3.3 Control Practices and Equipment
Comments on control practices for sawmills are included with those
for plywood plants in Section 11.4.3.
11.4 PLYVOCr, PARTICLEBOARD, AID HARDBOARD FLATCTS
Part of the wood wastes from sawmills is utilized in the manu-
facture of plywood, particleboard, and hardfcoard. Fig-are 11-1 presents
typical process flow diagrams for plywood veneer and layout plants and a
particleboard plant.
In the plywood manufacturing cycle, the logs first go through de-
barking, peeling, and clipping to produce a veneer material. Following
drying, the veneer proceeds through layup and glue spreading, pressing,
trimming, and final sanding.
In a particleboard plant, the waste wood is screened, ground, and
dried in the initial processing steps. After the drying step, the material
is mixed with resin tc form panels. The panels are then pressed, trimmed
and sanded to produce the finished product.
11.4.1 Emission Sources and Rates
Particulate pollutants in comparatively small amounts are produced
in these processes. In plywood veneer plants, the disposal of wood waste
creates the major emission problem. In plywood layout and finishing plants
some emission sources also involve wood wastes. Incineration and boiler
plants are the principal means of disposal and "wigwam" burners are used
quite extensively.
Emission sources in a plywood layout and finishing plant, in
addition to incinerators and power boilers, include veneer dryers, panel
pressing operations, and sanders. Green veneer panels (50$ moisture) arc
dried to less than 10$ moisture in long enclosed heated chambers called
ventilated veneer dryers. Two dryers are rarely ever alike. They emit a
visible blue plume which is saturated with water vapor and loaded heavily
with hydrocarbons.
202
-------
Plyvood pressing operations are another source of emissions.
Phenolic resin loss to the atmosphere during pressing of panels may contrib-
ute to local air pollution problems. Overall emissions from this type of
resir. appear to be very minor although detailed data are not available.
Plyvood sanding operations produce a large volume of sanderdust.
Plyvood is either produced as unsanded sheathing or it is sanded on either
one side or tvo sides. Volume of sanderdust generated has been reported to
vary from 33.3 to 99.5 tons/million sq ft of sanded plyvood panels.5/
Emission sources at a particlebcard plant include: (l) transfer
operations, (2) drying operations, (3) pressing operations, (4) sanding
operations, and (5) incineration.
The only waste material at particleboard-hardboard plants is
sanderdust, as other vastes are recycled to the manufacturing process.
Emissions from incineration of this material vould be similar to those de-
scribed for sawmills.
Particleboard plants purchase plyvood trim, planer shavings, and
sawdust, which includes small quantities of sanderdust. as rav materials.
As the loaded tracks dump into receiving hoppers, considerable quantities
of the fine particulate are carried into the atmosphere.
Particleboard and hardboard plants process "green" raw material
through rotary kiln-like dryers. No data were found for emissions from
these dryers.
Emissions of formaldehyde-urea resin during pressing operations
have produced air pollution problems near particleboard and hardboard plants.
The formaldehyde odor of the finished product is the main problem. The bulk
of formaldehyde emission occurs during the high temperature (350°F) press
¦which cures and sets the resin. It has been reported that at a press tempera-
ture of 350°F, and with a 1.8:1 molecular weight ratio of formaldehyde urea
resin, 3$ of the total solids will be leached as free formaldehyde. One
percent would be emitted at a 1.2:1 mole ratio. The resin binder itself
consists of approximately 10$ of the total weight of particleboard and 6$
in hardboard produced by the dry method.
Scissions from sanding operations vculd be similar to those discussed
under plywood manufacture. After being sized in the trim saws, particle-
board is sanded on two sides and the hardboard on one. The quantity of
sanderdust generated depends on sanded depth and density of the board and
has been reported to vary from 42.5 to 156 tons/million sq ft sanded™/
203
-------
Emission rates from these plants are summarized, in Table 11-1.
Limited data are available as these plants have not been thoroughly studied
as air pollution sources.
11.4.2 Effluent Characteristics
Data on effluent characteristics from plywood, particleboard, and
hardboard plants are limited. Table 11-2 summarizes information currently
available. Dust from a arum sander is about 20 wt. # less than 10
11.4.3 Control Practices and Equipment
Emissions from these operations and from sawmills result primarily
from steps producing sawdust or from incineration. Cyclones have wide appli-
cation in the collection of sawdust but very little information is available
on their design or operating efficiency. 3aghouses can probably be used
for the collection of this sawdust in many instances, but the pressure drop
involved would be higher than for cyclones. Afterburners could be used on
sources which emitted combustible vapors or mists.
11.5 PULP rWLUSTRY
Characteristic air-pollution problems of the pulp industry are
associated with the release of malodorous sulfur compounds and particulate
matter. Pulp is made by either the sulfate (kraft), sulfite, semichemical,
soda, or by a mechanical process. Most cf the pulp produced in the United
States is made by the kraft process. The sulfite process accounts for less
than 10$ of the pulp production.
11.5.1 Kraft process
The chemical pulping process known as kraft pulping, employs a
cooking liquor whose main ingredients are sodium sulfide and sodium hy-
droxide in solution. High-pressure digestion of wood chips dissolves the
liquor in wood, and frees its cellulose fiber for use as pulp. A typical
batch digester will reach temperatures of 350°F and pressures of 110 lb/
sa in., and take 3 hr. for a cook. The full cooking pressure is used to
blow the digester contents into the blow pit, ending the cooking cycle.
More recently, new mills have been utilizing continuous digestion
because of improved control over the cooking cycle ana hence a better quality
of pulp. Wood chips, liquor and steam are supplied continuously at one end
of the digestor, while the finished pulp and spent liquor are removed at the
other end. Continuous digesters are also used to produce a low-grade pulp
from sawdust.
204
-------
As shown in Figure 11-1, diluted pulp from the blow pits is sepa-
rated from the spent liquor by filtration and washing. The spent cooking
liquor at this point is black frcm the ligr.in, waste fibers, and dissolved
sulfide salts—and hence called "black liquor." Vitally important to the
economics of the kraft process is the recovery and recycle of inorganic
chemicals in the black liquor. To accomplish chemical recovery, black liquor
is concentrated by evaporation and burned in recovery furnaces. Most of the
organic and inorganic sulfur is reduced in the lower oxygen-poor region of
the furnace to form an ash or smelt of molten chemicals, primarily sodium
sulfide and carbonate. The upper zone of the recovery furnace, ideally an
oxygen-rich zone, serves to oxidize the residual sulfur organics carried
up from the reducing zone below.
Recovery furnaces also produce valuable process steam from the
heat of the burning black liquor. Hot gases frcm the combustion zone relin-
quish most of their heat energy in passing over boiler tubes and heat econ-
omizers. Steam may be used elsewhere in the pulp-making process or sent to
turbines fcr electrical power generation. Additional utilization of the
iXirnace heat is accomplished by the use of a direct contact evaporator. Such
an evaporator utilizes the heat cf the flue gases to farther evaporate black
liquor just prior to its firing in the recovery furnace. Direct contact
evaporation has one serious drawback, however, from an air-pollution stand-
point—the stripping of hydrogen sulfide which occurs when acidic flue gases
contact the black liquor. Following the direct contact evaporator, furnace
gases pass through collectors (such as electrostatic precipitators and scrub-
bers) to remove particulate matter consisting of sodium salts and carbon
particles. Exhaust gases containing the remaining particulates, plus the
malodorous sulfur compounds, then pass to the atmosphere.
The sodium sulfide and sodium carbonate smelt, formed at furnace -
grate level, falls into the smelt tank where it dissolves in water, forming
the "green liquor." The sodium carbonate is converted to sodium hydroxide
by the addition of lime. The reaction performed in the causticizer cr
shaker is shown below, (l) Calcium carbonate precipitates as a lime mud,
and after washing is sent to the lime kiln where it is calcined to calcium
oxide. (2) This fresh lime is then slaked (3) and available for further
causticizing. After conversion of sodium carbonate to the hydroxide, the
"green" liquor becomes "white" liquor and is ready for recycle as cooking
liquor.
(1) Ca( OK2) + Na^COj * 2NaOH + CaCO*
(2) CaCOT » CaO + C0£
(3) CaO + HgO * Ca(OH)2
205
-------
11.5.1.1 Emission Sources and Rates; The kraft pulp mill emits a
wide range cf air pollutants, with the malodorous sulfur gases being the
most objectionable because of their low threshold of detection in the ambient
air. Other categories of kraft mill emissions include particulates, mists,
and less odorous gases which are emitted from numerous process points.
Table 11-3 shows the atmospheric emission sources and the general category
of atmospheric emission which each source contributes.§/ Table 11-4 identi-
fies the emission category by chemical composition.§/
TABLE 11-3
ATMOSPHERIC EMISSION SOURCES IN A KRAFT MILL§/
Source
Digester relief and blow gases
Knotter and brown stock washers,
washer seal tanks
Black liqucr storage
Black liqucr oxidation tower
M. E. evaporators
Recovery furnace
Snelt dissolver tank
Lime kiln
Causticizer
Bleach plant
Power boilers (including oil-fired
and bark-fuel boilers)
Paper incinerators
Materials handling
Emission Categories
Malodorous ga3es and water vapor
Malodorous gases, nists and organic
vapors
Malodorous gases
Malodorous gases and organic vapors
Malodorous gases
Particulates, malodorous gases, other
gases (including sulfur dioxide)
Mists and odorous gases
All categories
Mists
Mists and other gases
Particulates and other gases
Particulates and other gases
Particulates
206
-------
TABLE 11-4
ATMOSfflERIC EMISSIONS FROM KRAFT PULP MILLS®/
General Category
Particulates
Composition
sodium carbonate, sodium sulfate (salt
cake), calcium oxide (lime), sodium
oxide, carbon (char), fly ash
Mists sodium carbonate, sodium sulfate, black
liquor, caustic and hypochlorite + sul-
furous gases
Malodorous 'sulfurous gases)
hydrogen sulfide, methyl mercaptan,
dimethyl sulfide, dimethyl disulfide,
ethyl mercaptan, isopropyl mercaptan,
n-propyl mercaptan, ethyl sulfide,
and others
Other gases (less odors and
including organic vapors)
carbon monoxide, sulfur dioxide, chlorine
and chlorine dioxide, carbon dioxide,
methanol (vocd alcohol), ethanol (rubbing
alcohol), alpna-pinene, acetone
Water vapor
The largest source of potential particulate emission is the re-
covery furnace; other sources of particulate emission include the lime kilns,
smelt tanks, and bark- and/or coal-fired power boilers. The recovery fur-
nace can also account for half of the total potential sulfur emissions, al-
though other sources such as the digesters and multi-effect evaporators
should not be ignored as malodorous emission sources.
In the recovery furnace, heat is obtained from the combustion of
the organic constituents of the black liquor, and the inorganic constituents
are recovered as a molten smelt. The concentrated black liquor at 60 to 65$
solids content is sprayed into the furnace where the water content is flashed
off.
When the black liquor is burned in the furnace, an appreciable
quantity cf particulate is liberated. Chemical content of the solids en-
trained in the recovery furnace flue gases is a function of furnace oper-
ating conditions and feed liquor composition. Usually N&2S04, N^COj, and
2C7
-------
K.iCl constitute 75 to 90$ of the particulate weight. The remainder is com-
posed of NaHCOj, unburncd organic material, and water-soluble fly ash. The
relative mass fractions of Ka^SO^, W&2CO3, and NaCl in the fume can vary
greatly from mill to mill. For example, NaCl is present in measurable Quan-
tities when logs have been stored in salt water before chipping; inland
mills have less NaCl passing through the recovery system.
The smelt recovered from combustion of black liquor in the re-
covery furnace is dissolved in water and weak wash in the dissolving tank.
As a result of violent reaction and flashing, a considerable quantity of
moisture containing dissolved sodium compounds is discharged from the dis-
solving tank to the atmosphere.
Boilers which are wholly or partially fired with bark are another
source of particulate emissions. Fly ash is the dominant particulate emitted
from this source.
Emission levels for the kraft pulping process are summarized in
Table 11-1. Particulate emissions from kraft mills currently total about
239,00C tons/year.
11.5.1.2 Effluent Characteristics: The chemical and physical prop-
erties of effluents from kraft pulping processes are detailed in "able 11-2.
Particulates emitted from the recovery furnace range from 50 to 85 wt. $
less than 2 jj.. Lime kiln particulates are 95 wt. % less than 25 y,, while
those from the smelt tanks are 90 wt. $ less than 5 Li-
11.5.1.3 Control Practices and Equipment: Electrostatic precipita-
tors are normally used to recover particles emitted from the recovery fur-
naces. Electrostatic precipitators may remove 85 to 97$ of the particulate
matter while Venturi scrubbers may remove 60 to 95$.Z/
The recovery of particulate matter from the flue gases leaving
the recovery furnace, lime kilns, and dissolving tanks is described in
Reference 8. Uncontrolled emissions from the snelt tank may be as high as
20 lb/ton of pulp. Use of a simple water spray may reduce this tc 5 lb/ton,
while a mesh demister may further reduce this to 1 or 2 1h/ton J >9/ The
control equipment used to decrease smelt tank emissions are mesh pads, packed
towers, orifice scrubbers, or cyclonic scrubbers. The pressure drop for an
orifice scrubber is approximately 8 in. of water. The pressure drop across
a mesh pad is usually less than 1 in. of watei) but sprays located above the
pads may be required periodically t.o remove collected chemicals.ii/ The
recovery of particulate matter from the flue gases leaving the recovery fur-
nace (and from the lime kilns and dissolving tanks) is described in Refer-
ence 8.
206
-------
To reduce fallout in the mill vicinity and/or comply vith stack
emission standards, some mills practice secondary wet scrubbing as an adjunct
to the use of primary recovery devices on the recovery furnace flue gases.
Six types of secondary scrubbers for particulate matter removal in flue
gases are in use in the U. S. industry at the present time.i^/ These are
usually low-pressure-drop devices of less than 2 in. of water. They may be
constructed of fiberglass or lined with acid resistant brick or concrete.
The wide variation in water usage rate for these secondary scrubbing instal-
lations is shown in Table 11-5.12/ It has been reported that the initial
installation cost of various secondary scrubbing systems ranges from $35,000
to $55,000/100 tons pulping capacity.±2/
TABLE 11-5
WAT5R USAGE FOR SECONDARY SCRUBBING INSTALLATIONS]-/
gpn/1,000 cfm
Water Use
Shower
Type
Rate
Rate
Vertical impingement screen
0.4-2.3
1.0-2.3
Multiple Venturi impingement
4.6-11.3
10.8-22.6
Chevron baffle plate
0.3
r-*-
co
Pease-Anthony cyclonic
0.5-4.1
1.2-7.6
Vertical baffle plate
0.6
1.2
The installation of scrubber units downstream of an electrostatic
precipitator is discussed in Reference 14. Table 11-6 shows average per-
formance data for this type cf unit and Figure 11-4 gives the particle size
efficiency curve. Tests showed conclusively that dust collection efficiency
decreased when the flue gas entered the washer saturated with water vapor
(at the dew point temperature). It is surmised that when flue gas enters
the washer at a temperature considerably above the dew point, large quan-
tities of steam or fog are produced at the first bank of spray nozzles,
where the gas is cooled to the dew point. Solid particles carried in the
gas act as condensation nuclei for the saturated steam, thereby resulting
in the high collection efficiency for the 5 to 30 u range particles as
shown in Figure 11-4.
209
-------
w
o
W 100
>- BO
5 60
Ui
40
<3 20
0
8
16
24
32
PARTICLE SIZE-MICRONS
Figure 11-4 - Particle-Size Efficiency Curve TE Vas.her-
Blac> Liquor Recovery Furnace*!^./
* Pressure drop less than 1 in. w.g.
210
-------
TABLE 11-6
AVERAGE PERFORMANCE DATA FOR KJLL-SCALE TE WASHER*il/
Gas flow, ft^/rain 57,000
Dust loading, grains/std ft~
Inlet 0.21
Outlet 0.027
Efficiency, $ 88
Soda ash recovered, lb/min 1.7
Liquid effluent from scrubber, gpm 25.3
Concentration, g/liter as NaHCOj 7.73
Gas temperature, 0 F
Inlet:
dry-bulb 272
vet-bulb 159
Outlet:
dry-bulb 166
wet-bulb 1S2
* Pressure drop less than 1 in. w.g.
Venturi scrubbers are used on stack gases from recovery furnaces
to serve as direct-contact evaporators by using black liquor as the scrub-
bing medium. The particulate collection efficiency of one such unit is re-
ported to be 74.2$.5/ The pressure across this unit was not given. It was
stated that steam-atomizing nozzles were installed in an effort to improve
collection efficiency.
Wet scrubbers are also used on lime kiln stack gases. Test data
for one unit are given in Table 11-7.
16/
Pilot plant studies have been conducted making use of electro-
static pre-agglomeration of black liquor boiler fume followed by a flooded
disk or Venturi scrubber.17/
Large diameter cyclones of 48 in. tc 60 in. are commonly used for
collection of the emissions from bark boilers. Recovery efficiencies are
in the range of 98$ with a pressure drop cf 3 to 4 in. w.g.
10/
211
-------
TABLE 11-7
TEST DATA,
LIME KIE
VETTURI S
CRUBBERri/
Inlet gas temperatures
, °F
309-244
Exit gas temperatures,
°F - sat
'd
156-168
Scrubbing slurry temperatures,
°F
155-166
Inlet gas volume, cfm
at STP -
32°F, 29.9
in. Hg
17,400-24,700
Inlet gas volume cftn
at duct c
enditions
27.800-40,000
Outlet gas volume, cfm
at STP -
32°F, 29.
9 in. Hg
20,400-25,800
Outlet gas volume, cfm
at duct
conditions
26.200-32,900
Run Ho
1
4
5
6 7
8
Pressure drop across venturi
and cyclone, in w.g.
11.25
6.75
10.75
6.75 5.5
5.5
Scrubbing liquid used
Filtrate Filtrate
Slurry
Slurry Slurry Slurry
Scrubbing liquid gpm
510
290
410
160 200 100
Scrubbing liquid, $ solids
3.3
--
46.7
16
~
Inlet dust load, tons/day
Acid insoluble
0.C6
0.16
0.06
__
—
CaCOj
4.14
14.70
19.62
--
—
Na2S04
0.30
0.03
0.06
—
—
NaoC03
2.34
2.41
1.64
--
—
Total
6 .86
17 .3 0
21.38
Outlet dust load, tens/day
Acid insoluble
0.01
0.05
C.02
0.01 0.09
0.03
CaC03
0.03
0.10
0.15
0.15 0.08
0.37
Na2S04
0.04
0.01
0.02
0.02 0.02
0.01
Na^CO^
0.86
0.48
0.45
0.75 0.30
0.31
Total
0.94
0.64
0.64
0.93 0.49
0.72
Dust loading, grains/ft3*
Inlet
2.94
6.66
11.94
—
Outlet
0.45
0.24
0.30
0.40 0.18
0.27
Dust removal efficiency $
For CaCOj
99.3
99.4
99.5
—
—
For Ua2S04
86.5
63.3
59.6
—
--
For NagCOj
63.0
80.0
72.5
--
--
Overall
86
96
97
--
* Wet gas at STP 32CF, 29.9 in. Hg.
212
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It has been reported that the large cyclones are preferred to
the smaller diameter multicyclone systems. Part of the reason for this is
the low density of the bark char which is easily re-entrained and does not
flow well out of the collection hoppers.
10/
11.5.1.3.1 Control costs in kraft pulp mills: The cost of con-
trol equipment for the wood pulping industry is a major part of a NAPCA study
conducted by Environmental Engineering, Inc., and the J. E. Sirrine Company,ll/
Detailed cost studies for many different control systems and combinations
were developed for this study. A portion of this cost information has been
extracted from the above report and is included in the following section.
The reader is directed to the original report for more detailed information
and for a complete set of ccst studies.
11.5.1.3.2 Descriptions of capital cost items:
Purchased equipment; Cost of the emission control device
and all accessories and auxiliaries required for its full operation.
Equipment erection: The erection of purchased equipment
only. The erection cost of building and foundations, piping and wiring is
included elsewhere.
Equipment foundations and building: The installed cost of
all equipment foundations, building and building foundations, floors, roof,
stairs, and walkways, that are required for support, access, ar.d enclosure
of the control device.
Process and instrument piping: Cost of all pipe and pipe
supports, erected, and including insulation and protective coating where
required.
Power wiring and lighting: The installed cost of all power
wiring and lighting is included. Wherever required, any substation, trans-
formers, or switchgear costs are included under "Purchased Equipment."
Indirect capital cost: The summation of the above capital
cost composes the total direct capital cost to which is added indirect
cost as a percentage of direct cost. The following is a breakdown of
this indirect cost:
213
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15% Contingency--Unforeseen conditions and items
not practical to estimate
7$ Engineering--Preparation of specifications and
working drawings, selection, and evaluation
of equipment
156 General Construction Overhead—Includes tempo-
rary facilities, contractual supervision,
timekeeping, etc.
3# Start-up Cost—Loss of production not included
2$ Spare Parts
2% Sales Tax
3C56 TOTAL
11.5.1.3.3 Description of annual cost items:
General: Any estimated annual cost may vary considerably
from mill to mill. The following values may be considered typical and
should provide reasonable comparisons of emission-control-device annual
cost:
Direct operating cost: Direct operating cost consists of
charges for:
(1) Operating labor, including overhead. A national average
hourly rate of $4.25 has been assumed. To this rate, an additional 29$ is
added for vacations, sick pay, holidays, payroll taxes, insurance, and
fringe benefits. (Total $5.50/hr)
(2) Power, electric, and/or steam. An electric cost of
$0.01 per KWH, and a steam cost of $0.65/1,000 lb of steam has been used.
(3) Water. A water cost of $0.13/1,000 gal has been used.
(4) Maintenance, including maintenance labor, replacement
parts, and maintenance materials.
214
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Taxes and insurance: Local property taxes vary widely over
the country. Generally, this is applied as a millage on the assessed valua-
tion. Assuming the property is assessed az 50$ and 30 mills tax is applied,
then the property tax would be l-l/2$ of the construction cost.
1.5$ of Capital Cost
An average insurance cost has been
used for the entire pulp and paper mill.
0.5$ of Capital Cost
Total Taxes and Insurance 2.0$ of Capital Cost
Administrative costs: This is an average cost applied to
the overall plant and includes all salaried personnel (officers and super-
visors), fringe benefits for salaried personnel, legal and other profes-
sional services, public relations, contributions, and office supplies and
expenses. This does not include any marketing costs.
5.0$ of Capital Cost
Depreciation and interest (capital recovery): Depreciation
plus interest charges were calculated from the following formula which is
one of several commonly used for this purpose. An interest rate of 10$
was assumed.
Equal annual payment = 1(1"*"^) x 130$
(1 + i)» - 1
i = interest rate
n = life in years
SUMMARY OF CAPITAL CHARGE ITEMS
(As $ of Capital Cost)
Estimated Life of Equipaent in Years
Item
10
16
Taxes and Insurance
Administration
Depreciation and Interest
(Capital Recovery)
TOTAL
2$
5$
ie.7$
25.7$
2$
5$
16.3$
23.3$
2$
5$
12.8$
19.8$
215
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Net annual ccsts have teen computed on basis of equipment
life as follows:
Electrostatic Precipitators - 10 years
Venturi Scrubbers - 8 years
Packed Towers - 10 years
Cyclones - 16 years
UTILITY COST
I ten
Steam $/l,00C lb.
Based on 1,000 BTU/lb
Electricity $/KWH
V&ter $/l,000 gal.
Kraft Waste Treatment
$/l,000 gal.
(primary ar.d secondary
treatment)
Fixed
Charges
$0,116
C.0023
0.104
Operating Costs
Fuel, Labor, Mair.t
Etc.
$0,535
C.0G77
C.046
0.13
!.03
Total
(Rounded to
Nearest Cent)
$0.65
0.01
0.15
.16
These are values that may be considered typical in a general sense. All of
these values vary considerably from mill to mill--any proper evaluation of
control cost should be specifically calculated for the individual mill.
However, the above costs should provide reasonable comparisons of emission-
control method for this study.
Salt Cake
Lime (CaO)
Sulfur
Soda Ash
Caustic Soda
Magr.es ium Hydroxide
Chlorine (Papermakers)
chemical cogrs
Per Ton Except as Noted
$34.00 East
24.50 West
15.00
39.00 to
42.00/long ton
31.00 to
32.00
57.00/tor. of NaOH
in a 50# solution
37.68/ton 100# solids-
tank car lots, FOB, Michigan
3.35/100 lb.
Average: $30.00
Average: 15.00
Average:
Average:
40.00
31.00
216
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Case descriptions: The following cases have been considered,
for application of control methods to recovery systems. (See Reference 11
for complete study.)
Case 1. Replacement of an existing 90$ AOE* precipitator
with a higher efficiency precipitator.
Case 2. Installation of additional control equipment in
series with an existing 90$ AOE precipitator.
Case 5. Installation of a cyclonic scrubber in series
with an existing 95$ precipitator located on the roof.
Case 4. Application of additional control methods to an
existing recovery system with an 80$ AOE black liquor Venturi.
Case 5. Installation of a black-liqucr oxidation system
to an existing recovery system.
Case 6. Capital costs of new recovery systems.
11.5.1.3.4 Recovery furnace system:
Application; This case is based on the replacement of an
existing 90$ AOE precipitator with a higher efficiency precipitator. Most
of the existing older recovery precipitator installations are arranged
with the precipitator on the ground. Usually there is no additional space
on the ground in the vicinity of the recovery unit; therefore, an additional
precipitator would have tc be installed above the existing precipitator.
Further, the existing precipitator could not be removed and replaced with
a new one since this would require a lengthy mill shutdown resulting in a
high dollar cost due to the loss of production.
Costs: The capital costs are based on a double chamber,
conmon wall, tile construction precipitator. Auxiliaries included are:
agitators, dampers, circulation pumps, instruments and controls for proper
operation of the above, and revised ductwork to connect the addition of re-
placement precipitator in the system. The cost also reflects the structure
required to support this addition, and the demolition cost for removal of
the existing precipitator. Capital costs and net annual costs are presented
in Figures 11-5 through 11-7.
Effectiveness: Particulate removal. Methods are considered
for replacing a 90$ AOE precipitator on an existing recovery boiler. These
methods and their particulate efficiencies axe as follows:
* Average operating efficiency.
217
-------
o 210
o
o
x 180
v»
£
o
u
150
_j
<
t-
120
CL.
<
U
-j
<
b
t-
o"
X
20 -
i
<
13
z
z
<
10 -
z
10
20
30
40
GAS VOLUME (CFM X 10,000)
J I I I 1 I I I I
3456789 10 11
ADT/DAY X 100
BASED ON 350 CFM/ADT/DAY
Figure 11-5 - Control Method Costs for 99.9$ Efficiency
Electrostatic Precipitator Replacing an
Existing Precipitator - Recovery Boiler
(99.5$ A.C.E.)
218
-------
o
X
ts>
O
u
<
D
Z
z
<
10 20 30 40
GAS VOLUME (CFM X 10,000)
J 1 I I I I i I I
3456789 10 11
ADT/DAY X 100
BASED ON 350 CFM/ADT/DAY
Figure 11-6 - Control Method Costs for 99.5# Efficiency-
Electrostatic Precipitator Replacing an
Existing Precipitator - Recovery Boiler
(99.0$ A.O.E.)
219
-------
z 0
10 20 30 40
GAS VOLUME (CFM X 10,000)
J I I I I I I I L
34 56 7 8 910 11
ADT/DAY X 100
BASED ON 350 CFM/ADT/DAY
Figure 11-7 - Control Method Costs for 99.0$ Efficiency
Electrostatic Precipitator Replacing an
Existing Precipitator - Recovery Boiler
(98.5$ A.O.E.)
220
-------
Annual Operating
Control Method Guaranteed Efficiency Efficiency
Precipitator 99.9 99.5
Precipitator 99.5 99.0
Precipitator 99.0 98.5
11.5.1.3.5 Smelt-dissolving tanks:
Application: The molten inorganic chemicals leave the fur-
nace through smelt spouts to an agitated dissolving tank which contains
weak vash liquor obtained from washing lime sludge in the succeeding causti-
cizing operation. After being cooled and dissolved in the weak wash, the
smelt solution is referred to as green liquor. Shatter nozzles are used to
inject steam and/or recirculated green liquor into the solid smelt stream
from the furnace to disperse the molten chemicals and ensure its safe
dissolution.
Large quantities of water vapor are released by the green
liquor which cools the molten smelt and by the steam from the shatter jets.
Particles of smelt and droplets of green liquor "become entrained in these
vapors and are exhausted through the smelt-dissolving-tank vent.
The gas vented from the -smelt-dissolving tank has a tempera-
ture of approximately 200°F and contains traces of organic sulfur compounds
and particulate matter with a concentration of 1 to 1.5 grains/sCFD. The
particulate matter is mostly sodium sulfide and sodium carbonate.
The majority of mills provide control equipment to minimize
the emission of these chemicals and droplets to the atmosphere. Control
equipment which is currently in use is as follows:
(1) Mesh pads. Mesh pads are used extensively to collect
chemicals in dissolving-tank vents. Sprays located above the mesh pads
operate periodically to remove the collected chemicals which are returned
to the smelt-dissolving tank. A fan is not normally required due to the
low pressure drop.
(2) Packed towers. Packed towers have been reported at two
mills where they operate successfully. One concern with packed towers is
the possibility of plugging; however, periodic use of condensate as scrub-
bing liquid is reported to remove any solids buildup.
221
-------
(3) Orifice scrubber. This scrubber has been installed at
several mills and Is reported to be successful where the scrubber is ade-
quately sized. Due to the pressure drop (approximately 8 in. H2O) of this
scrubber, inadequate sizing or improper operation may have a significant
effect on emissions (for example, higher than design flows may require by-
passing the scrubber).
Costs:
Cyclonic scrubber. This control method is based on the in-
stallation of a single cyclonic scrubber on an elevated floor within the
confines of an existing recovery boiler building and adjacent to the existing
vent stack. Since the capital cost and operating cost of the cyclonic scrub-
ber is very similar to a packed tower, costs have not been calculated for
the cyclonic scrubber. The reader is referred to the costs on the packed
tower.
Packed tower. This control method is based on the installa-
tion of a single packed tower on an elevated floor within the confines of
an existing recovery boiler building and adjacent to the existing vent stack.
In addition, the following auxiliaries are included: an axial flow fan and
motor located in the outlet of the tower, a circulation pump and motor,
instruments and controls for proper operation of the above, piping for
make-up circulation and tower effluent to dissolving tank, and revised duct-
work including a by-pass to connect the tower to the existing vent stack
{Figure 11-6).
Orifice scrubber. This control method is based on the in-
stallation of a single low-energy scrubber on an elevated floor within the
confines of an existing recovery boiler building and adjacent to the exist-
ing vent stack. In addition, the following auxiliaries are included: an
axial flow fan and motor located in the outlet of the tower, a circulation
pump and motor, instruments and controls for proper operation of the above,
piping for make-up circulation and scrubber effluent to dissolving tank,
and revised ductwork including a by-pass to connect the scrubber to the
existing vent stack (Figure 11-9).
Mesh pad. This control method is based on the installation
of a mesh pad assembly in an existing recovery boiler vent stack.
Allowances have been included for the following: alterations
to existing vent stack, normal piping for spray wash, and instruments and
controls for proper operation. Cost curves are presented in Figure 11-10.
222
-------
10 20 30 40
GAS VOLUME AY X 100
BASED ON 35 CFM/ADT/DAY
Figure 11-9 - Control Method Costs for Packed Tower
Added to Smelt-Dissolving Tank Vent
223
-------
o
o
o
l/>
o
u
o.
<
U
_i
<
H-
o
o
x
in
o
u
_i
<
z
z
<
10 20 30 40
GAS VOLUME (CFM X 10,000)
J I 1 I I I I I I
3456789 10 11
ADT/DAY X 100
BASED ON 35 CFM/ADT/DAY
Figure 11-9 - Control Method Costs for Orifice Scrubber
Added to Smelt-Dissclving Tank Vent
224
-------
8
o
o
x
i/i
O
u
a.
<
U
_j
<
5
20
18
16
14
12
10
o
x
in
o
u
_i
<
3
z
z
<
10 20 30 40
GAS VOLUME (CFM X 10,000)
J I l_l I I I I L
34 56 789 10 11
ADT/DAY X 100
BASED ON 35 CFM/ADT/DAY
Figure 11-10 - Control Method Costs of Mesh Pad Added
to Smelt-Dissolving Tank Vent
225
-------
Effectiveness:
Particulaoe removal. Efficiencies for the methods considered
are as follows:
Annual Operating
Control Method Efficiency
Cyclonic Scrubber 80
Packed Tower 9C
Orifice Scrubber 97
Mesh Pad 75
Reduced sulfur and sulfur dioxide removal. Depending on the
scrubbing liquid used, both the packed tower and orifice scrubber would
have potential for removing sulfur compounds.
Operation. Of the methods considered, the orifice scrubber
should be the least subject to plugging.
Siiwinn.ry. The orifice scrubber and the packed tower are the
most effective control methods for either particulate or gaseous pollutant
removal. The orifice scrubber is less susceptible to pluggage and has the
highest particulate collection efficiency.
11.3.1.3.6 Lime kiln:
Application; This control method is based upon the addition
of a high-energy Venturi scrubber tc replace existing 80$ AOE cyclonic-type
dust collectors. The system is to be arranged such that change over to a
new system may be made with a minimum of lost production.
As a matter of convenience and water conservation, most
kraft mills use contaminated condensate as a scrubbing liquid in the kiln
scrubber. The condensate system is backed up with a fresh water supply.
During time of chemical unbalance or lack of supply of condensate, fresh
water is substituted as a scrubbing medium.
Any mercaptans which are emitted from the kiln stack come
from the contaminated condensate used as a scrubbing liquid and make-up
wash water in this system. Substitution of fresh water in these systems
would eliminate emission of mercaptans from the kiln stack.
This substitution of fresh water as a scrubbing medium
appears simple and relatively inexpensive. However, it must be emphasized
that the lime kiln and causticizing areas are the prime users of contaminated
226
-------
condensate generated in ether areas of the mill. If fresh water is used
in place of contaminated condensate, the load to the waste-treatment system
will be increased by the amount cf water substituted.
The emissions from incineration of noncondensible sulfur-
bearing compounds in the lime kiln are net being considered in this particu-
lar control method.
Costs; The capital costs are based upon purchase cf equip-
ment and installation of the new scrubbing system while the existing system
is in operation. Items included are as follows:
(1) New induced draft fan with drive
(2) New scrubber, mist eliminator and stack
(i) New pumps with drives
(4) Modification to existing hot gas ductwork
Also included in the costs are new foundations and structures
required to support the equipment and demolition cost for removal of the
existing scrubbing system, once the new system is placed in operation. Cost
curves are presented in Figures 11-11 and 11-12.
Effectiveness: This study considers a single method of re-
placing a lev? efficiency cyclonic-type dust collector with a high-energy
Venturi scrubber. The new method is to have a 99.0 or 99.9$ lime solids
collection efficiency. AOS and design efficiencies are considered to be
the same.
(1) The new system will replace an existing and operating
inefficient system.
(2) The efficiency cf solids collection of high-energy scrubb
is a direct factor of the pressure drop taken across the throat of the scrub-
ber. Eecause of this item the capital cost between a 99.0$ and 99.9$ effi-
ciency would be very similar. Equipment sizing would be essentially duplicat
in either case and the only variable would be a higher horsepower motor for
driving the induced draft fan. Variables in operating cost are shown on
the cost curves.
(3) High-efficiency scrubbers are Important to the pulping
industry for recovery of soda. Volatile soda compounds in the kiln exhaust
gases are more difficult to recover than solids but are also more valuable.
Equipment manufacturers presently estimate that a scrubber with 99.9$ lime
227
-------
o
X
i/i
O
u
<
ID
z
Z
<
6 9
ADT/DAY X 100
Figure 11-11 - Control Method Costs for Fresh Water Venturi Added to Line
Kill: - 99.0$ Line Solids Collection
228
-------
o
X
LO
o
u
i
<
z
z
<
6 9
ADT/DAV X 100
Figure 11-12 - Control Method Costs for Fresh Water Verituri Added to Lime
Kiln - 99.9$ Lime Solids Collection
229
-------
solids collection efficiency will recover 90 to 95+$ cf tne soda fume in
the kiln exhaust gases. Ninety-nine percent lime solids collection should
be equivalent tc approximately 70$ collection of scda fume.
11.5.1.3. Power boilers:
Application; This case is based on the addition of an elec-
trostatic precipitator following an existing dust collector for a coal-
fired power boiler. Two precipitator sizes are considered.
Costs: Curves for capital costs and net annual operating
costs are presented in Figures 11-13 and 11-14.
The equipment costs are based on a double chamber, steel
shell precipitator. All labor and material for a complete installation
are included in the capital cost and the r.et annual operating cost. The
precipitator size is based on firing coal containing 2$ sulfur.
Effectiveness:
Particulate removal. Guaranteed particulate efficiencies
for the two precipitators considered are 99.0$ and 90.0$. The resulting
total annual operating efficiencies are:
Precipitator
Precipitator
Dust Collector
Total
Guaranteed Efficiency
A0E
A0E
AOS
99. 0$
98.0$
80.0$
39.0$
90.0$
B9. 0$
80.0 $
CD
CD
O
Reduced sulfur ajid sulfur dioxide removal. Precipitators
are ineffective for removing sulfur compounds.
Operation. The operating characteristics of the precipi-
tators should be identical.
11.5.2 Sulfite Process
Little attention has been paid to the air pollution aspects of
sulfite pulping. The pollution problem is not nearly as severe as in the
kraft process. Some terpene-lihe odors, SO2 leaks, and particulates from
recovery furnace and steam power plants are the principal effluents.
230
-------
o
GAS VOLUME (CFM X 10,000)
Figure 11-13 - Control Method Costs for 99.0$ Efficiency Electrostatic
Precipitator Added to an Existing 90$ Efficiency Dust
Collector Coal-Fired Power Boiler (99.0$ AOE)
231
-------
o
X
O
u
OL
<
U
_i
<
<5
i i
Figure 11-14
o
8
o
x
CO
o
U
i
<
D
Z
Z
<
16 24 32
GAS VOLUME (CFM X 10,000)
Control Method Costs for 90.0$ Efficiency Electrostatic
Precipitator Added to an Existing 90$ Efficiency Dust
Collector Coal-Fired Power Boiler (99.0$ AOE)
232
-------
Little consideration is currently being given to calcium or sodium
as a future case in U. S. sulfite mills. Burning of calcium spent sulfite
liquor yields combustion products in a form precluding reuse of the base
chemical or sulfur value. Incineration of sodium liquor produces a mixture
of sodium compounds requiring processing in satellite operations to recon-
stitute the base chemical for pulping. Ammonia and magnesium liquor can be
burned in a relatively simple system yielding the sulfur combustion product
in the form of sulfur dioxide for recovery. Only the magnesia-base affords
direct recovery of the base chemical.
Figure 11-15 illustrates a flow diagram for an ammonia-base pulping
and recovery plant while Figure 11-16 presents the essential aspects of the
magnesia-base liquor recovery process.
Meager data on emissions from sulfite mills exist in the litera-
ture. Table 11-8 summarizes some data from a pilot ur.it for ammonia-base
liquor burning. Other emission data for sulfite mills are presented in
Tables 11-1 and 11-2.
TABLE 11-6
AMMONIA-BAS3 LIQUOR BURKING
(Filot Unit)
Dust loading: 1-2 lb/l,000 lb. of gas
Particle density: 1.5 - 2.0 g/cm^
Particle size (average): IOC jjl
Furnace exit gas temperature: 1,750 - 2,240°F
3O2 at stack volume: 10 - 350 ppm
11.5.3 Semi-Chemical Pulping
Emissions from seni-chemical pulping plants are less intense than
those from conventional pulping processes because of milder conditions.
Emissions vary depending on process employed; e.g., neutral sulfite, or
kraft. In the latter case, the air pollution problems will parallel those
described under kraft pulping, but will be of a lower order of magnitude.
Very little data on emissions from semi-chemical pulping have
been reported. Available information is summarized in Tables 11-1 ar.d 11-2.
233
-------
STEAM FOR PROCESS
AND POWER
CHIPS
STACK
DIGESTER
MECH. DUST
COLLECTOR
ASH
MAKE-UP
SULFUR
BLOW
TANK
WATER
SCREENS
WASHERS
ACID
FILTER
HEAVY
LIQUOR
FILTRATE
LIQUOR
CONDENSATE
FURNACE
HEAT
EXCHANGER
FORTIFICATION
UNBLEACHED
STORAGE
COOKING
ACID
STORAGE
BLEACH PLANT
WEAK
LIQUOR
STORAGE
MULTIPLE-EFFECT
EVAPORATORS
SULFUR BURNER AND
GAS COOLER
BLEACHED
PULP
STORAGE
SO2
ABSORPTION
COOLING
TOWER
DIRECT-
CONTACT
EVAPORATOR
Figure 11-15 - Sulfite Pulping Process, Ammonia-Base Recovery
-------
Mg(HS03)2+H2S03 COOKING LIQUOR
TO ATMOS.
TO
STACK
COOLED GASES
(1% SO,)
CHIPS
MgO SLURRY
BLOW GAS
DIGESTER
BLOW
TANK
BLOW
FAN
GASES
(1% so2)
TO ATMOS.
VENT
SULPHUR
MAKE-UP
CYCLONE
GASES
(RED)
CONC'D
MgO + SO.
SPENT LIQUOR
RED LIQUOR
PULP
MAGNESIA
MAKE-UP
WATER
MgO SLURRY
SCRUBBER
SCRUB-
BER
PULP
FILTER
SLURRY
TANK
ABS.
TOWER
ABS.
TOWER
ABS.
TOWER
MULT.
EFF.
EVAPO-
RATORS
SCRUBBER
RECOVERY
FURNACE
Figure 11-16 - Sulfite Pulping Process, Magnesia-Base Recovery
-------
REFERENCES
1. Private communications, Mr. Charles Buck, Forest Service, United
States Department of Agriculture, March 1970.
2. Wadleigh, C. H., "Wastes in Relation to Agriculture and Forestry,"
Soil and Water Conservation Research Division, United States Depart-
ment cf Agriculture, Miscellaneous Publication Nc. 1065, March 1968.
3. Bovee, Harley, et al., "The Study of Forest Fire Atmospheric Pollution,''
Interim Report 68 - 1, University of Washington, January 1969 (Refer-
ence U3FS 4040 (4000)).
4. Boubel, R. W., ''Particulate Emissions from Savmill Waste Burners,"
Engineering Experiment Station, Bulletin No. 42, Oregon State
University, Ccrvallis, Oregon, August 1968.
5. Mick, Alier, and Dean McCargar, "Air Pollution Problems in Plywood,
Particlebcard, and Hardboard Mills in the Mid-Willamette Valley,"
Report by the Mid-Willamette Air Pollution Authority, Salem, Oregon,
March 24, 1969,
6. Hildebrant, P., et al., "Air Pollution from the Kraft Pulping Industry,"
A report to Washington Air Pollution Control Bc.ard, prepared by Office
of Air Quality Control, Washington State Department of Health,
Seattle, Washington, Kay 1969.
7. United States Department of Health, Education ar.d Welfare, "Air Pol-
lution and the Kraft Pulping Industry,1' November 1963.
8. Shah, I. S., "Pulp Plant Pollution Control," Chemical Engineering
Progress, 64(9), 66-77, September 1968.
9. Bernhardt, A. A., and J. S. Buchanan, "Recovery of Dissclver Vent
Stack Soda Losses," TAPPI, 43(6), 191A-193A, June 1960.
10. Crabtree, V. F., "Abatement Procedures Presently in Use or Feasible."
11. "Control of Atmospheric Emissions in the Wood Pulping Industry," for
the National Air Pollution Control Administration, Report by Environ-
mental Engineering, Inc., and J. E. Sirrine Company,'March 15, 1970.
12. Blosser, Russell 0., and Hal B. H. Cooper, "Trends in Reduction of
Suspended Solids in Kraft Mill Stack," Paper Trade Journal, March 1967.
236
-------
13. Landry, Joseph E., and Daniel H. Longvell, "Advances in Air Pollu-
tion Control in the Pulp and Paper Industry," TAPPI, June 1965.
14. First, M. W., H. E. Friedrich, and R. P. Warren, "Reduction of Emissions
from a Recovery Eoiler," TAPPI, June 1960.
15. United States Department of Health, Education and Welfare, Lewiston,
Idaho—Clarkston, Washington Air Pollution Abatement Activity,
February 1967.
16. Collins, T. T., "The Ver.turi-Scrubber on Lime Kiln Stack Gases,"
TAPPI. January 1959.
17. Walker, A. B., "Enhanced Scrubbing of Black Liquor Boiler Fume by
Electrostatic Pre-Agglomeration: A Pilot Plant Study," Journal
of the Air Pollution Control Association, December 1963.
18. "The Application of Electrostatic Precipitators in the Pulp and Paper
Industry," Final Report, Southern Research Institute, National Air
Pollution Control Administration Contract No. CPA 22-69-73, May 1970.
237
-------
CHAPTER 12
LIKE MANUFACTURE
12.1 INTRODUCTION
Line is one cf the most widely used chemicals. It is used for
medicinal purposes, insecticides, plant and animal food, gas absorption,
precipitation, dehydration, and causticizing. It is al30 employed as a
reagent in the sulfite process for papermaking, manufacturing of high-grade
steel and cement, manufacturing of soap, rubber, varnish, refractories, and
sand-lime brick.i/
The major air contaminant from lime manufacture is dust: limestone
dust from handling, crushing, and screening operations; quicklime dust from
kiln discharge, handling, shipping, and milling operations; hydrate lime
dust from hydrater operations, milling, and packing.£/
The manufacturing process, particulate emission sources, particu-
late emission rates, effluent characteristics, ar.d control practices and
equipment are discussed in the following sections.
12.2 LIME MANUFACTURING PROCESS
A simplified flowsheet for lime manufacture is presented in
Figure 12-1. Following crushing and screening, the limestone is fed to kilns
for calcination or burning. Lime burning is conducted in vertical, rotary,
grate, fluosolid, and calcimatic kilns. Rotary kilns are used by a majority
of plants.
Although the major tonnage of lime is sold as quicklime, there is
still a substantial production of hydrated lime. (This hydrated lime dees
net include production by the many consumers of quicklime -who slake their
own lime into a putty, slurry, or nilk-of-lime preparatory to their use.)
This product is made by the lime manufacturer in the form of a fluffy,
micron-sized, dry, white powder, and its use obviates the necessity of slaking
by the consumer. A flow diagram of a commercial dry hydration plant is
shown in Figure 12-2.
This process consists of adding water slowly to a crusjaed or ground
quicklime in a premising chamber or a vessel known as a hydrator which mixes
and agitates the lime and water. The amount of water to be added is critical.
If too much water is added, it will be impossible (or require costly drying)
to produce the desired dry form; if too little is added, incomplete hydra-
tion will cause degraded quality, namely, chemical instability and structural
unsoundness.
239 Preceding page blank
-------
,6-8 in. limestone
for vertical kilns
k-2>i in.
limestont for
rotary kilns
Fuel
Screening and clarification
Fines
High-calcium
— and dolomitic
quicklime
Dolomitic
quicklime —
only
Water
*-|nd/Of
steam
Inspection
Cooling
Screening
Hydrator
By-product
lime
Secondary crushing
Primary crusher
Pebble and lump
quicklime
Screening and classification
Dotom'itic pressure
hydrated lime
Ground and pulverized
quicklime
Calcination
(rotary and vertical kilns)
Limestone and Dolomite
High-calcium and dolomitic
normal hydrated lime
Figure 12-1 - Simplified Flowsheet for Lime and Limestone Products£/
240
-------
300-ton
limedust
bins
800-ton
product
To truck
or nil
To track
or nil
To buck or rail
Cilibratinf I Ctlibntinf
dbchirii I dscharss
1 'AVtV*%V>ViV VtVtVtVtViVtVtViVtVi
MiN feed
5Z255EBE
VMt
Biuini
machines
material
Hydntar
mM
Figure 12-2 - Flew Diagram of a Modern Hydrated Lime Plant from Ground Quick Lime
Feed Silos Through to Bulk Hydrate Storage Silos and Bagging
Department.
-------
12.3 EMISSION SOURCES AND RATES
The major potential source of particulates in lime manufacture
is the calcining kiln. Emissions vary with kiln type and the composition
of limestone burned.
Vertical kilns do not produce as much dust as dc rotary kilns
because of the larger size of the limestone charged., the low gas velocities,
and the smaller amount of attrition. Nevertheless vertical kilns are apt
to be considered dusty by modern air pollution standards.
Rotary kilns constitute the largest single source of particulate
matter in the lime industry. Abrasion of limestone in the kiln produces
dust. The stone becomes more friable as it approaches the decomposition
temperature, and dusting increases. Simultaneously with dusting from attri-
tion, the high-velocity gases from direct-fire-fuel combustion blow the dust
from the kiln. This is a vexing dust to control and collect. It is hot,
dry, difficult to wet, and prone to be electrostatically charged. It is of
mixed composition, varying all the way from raw limestone to final calcined
product. It will also be mixed with fly ash, tars, and unburned caxbon if
pulverized coal is used as the fuel.
«
Dust blown from a kiln varies greatly with gas velocity. The
literature reports doubling of the dust blown out when a kiln production
rate was increased from 100 to 135$ of design capacity, while dropping pro-
duction rate to 75$ of capacity decreased the dust loading only by 8$.1/
Da^a on dust emissions from new kiln processes are largely lacking.
Grate-type kilns are stated to produce less dust than rotary kilns.si Fluo-
solid kilns emit copious quantities of dust in the exhaust gases and require
very efficient dust control equipment. Plants using the Calcimatic Process
appear to be remarkably free of dust since the stone is stationary during
calcination on a revolving hearth. The major sources of dust in this process
are the exhaust from the stone preheater. the lime cooler, and the discharge
lime conveyor.
The hydration of line presents a potential dust problem. Steam
and moisture laden air sweep fine dust from the hydrating operation into
the exhaust stack. High calcium hydratcrs operate at ambient press-ore with
''lazy" exhaust gas velocity. Pressure dolomitic hydrators discharge steam,
air, and product through small orifices to maintain the pressure created by
the reaction, and thus impart a high velocity to the exit gases.
Secondary sources of particulate emissions include crushers, coolers,
dryers, transfer points, and hydrate bagging operations.
242
-------
12.3.1 Summary of Emission Rates
Table 12-1 presents a summary of particulate emissions from lijne
manufacture. Total emissions are about 573,000 tons/year. The emission
factors for the lime kilns include emissions from coolers. Emission factors
and net control for primary crushing operations are assumed tc be the same
as those quantities used for these operations in the crushed stone industry
(Chapter 7). Emissions from fugitive sources such as stockpiles, traffic
and wind action on read dust, leaky bins, and truck spillage have not been
determined.
12.4 CHARACTERISTICS OF EFFLUENTS FRCM LIME MANUFACTURE
The chemical and physical properties of effluents frcm lime plants
are summarized in Table 12-2. About 30$ of the dust from rotary kilns is
less than 10 p.. The mean size is 30 u and the geometric deviation is 7.5.
Rotary kiln dust is difficult to wet and prone tc be electrostatically
charged. Particle shape data are summarized below:
(1) Limestone Dust - Mineral name: calcite. Colorless, with light-
transmitting characteristics varying from transparent to trans-
lucent. Particles generally occur as rhombohedra because of their
perfect rhombohedral cleavage. Fragments may also occur as prisms.
(2) Dolomite Dust - Mineral name: dolomite. In the pure state,
dolomites are colorless and the fine particles are generally
transparent to translucent.
(3) Lime Dust - Lime is usually white in color of varying shades
but some may have a light cream, buff, or gray cast depending
on the nature of the impurities in the lime.
12.5 CONTROL PRACTICES AND EQUIBtENT FOR LIME MANUFACTURE
Many plants in isolated areas carry out materials preparation
operations with no control equipment or only the crudest kind of collection
system.Other plants collect the dust from exhaust systems with simple
cyclones, water spray chambers, or baghouses.
The gases leaving a rotary kiln are usually first passed through
a settling chamber to settle out the coarse particles. In some cases,
dry cyclones may also be used for this primary collection. From 65-85# of
the particulate matter may be collected here.5/ The major dust control
problem is the dust passing the primary collector.
243
-------
TABUS 12-1
PARTICULATE EMISSIONS
LIME MANUFACTURE
Source
Kilns and Coolers
A. Botary Kilns and Coolers
B. Vertical Kilns
C. Fluid-Bed Kilns
Quantity of Material
18,000,000 tons line (excl.
16,200,000 tons
1,800,000 tons
Qnission Factor
pulp & paper)
180 lb/ton lime
7 lb/ton lime
II. Minor Sources
A. Stone Crushing and Screening
1. Primary Crusher
2. Secondary Crusher
3. Pulverizing, Quicklime
4. Milling, Hydrated Lime
B. Hydrator
C. Materials Handling
to
¦I*
•I*
28,000,000 tons of rock
crushed for lime
1, Conveyors
a. Transfer Paints
b. Discharge to Bins,
Stockpiles
2, Elevators
a. Boots
b. Heads
3, Shipnent of Product
a. Bagging Machines
b. Bulk Loading
(1) trucks
(2) freight cars
22 lb/ton of
rock crushed
2.0 lb/ton of
rock crushed
24 lb/ton of
rock crushed
Assumed for hydrator plus
materials handling
5 lb/ton of
lime produced
Efficiency of Application of
Control (Cc) Control (Ct)
Not
Control
(C<:'Ct)
Emissions
( t< r,:;/year
0.93 0.87 0.81 294,000
0.97 0.40 0.39 4,000
0.80 0.25 0.20 264,000
0.95 0.80 0.76
0.95 0.80 0.76
0.9:> 0.80 0.76 11,000
Total for Lime Manufacture £.7,4.000
-------
TABLE 12.?.
Erru-prr iHAanrrsaigrics . _rw h*h rArr =r*
; tarti.-ulat* l»*rt ! 1
Moisture
lisLJL PwticU Slae S.-liJs L**i:r.e C^pc»;tiar. Pn-tlcl- >nsity K1 ¦••••¦r-.c»l F.-sist i-m f rentcnt ?r.Kl:ity
(i. te?* J
Pt^vr^l i;H &AHCO ar.alvsis.
vent (1 test) 61- tr.4i.viis:
; i tfaU *• <5, 60 <10
?4 .,
91-9* <10. ?5-99
< \1. Avg. : »2
5: .i:C uwlysSi: Se? rotary kiln 2.<-2.7
n«^er 9-2*: .ila
r.:tarv K.ln sAh^C 2-C5, Avj.: 1£ raCO,: 5J-fl; C»C: = .•£-?.0. ..*< y.fe. . _•• j;.7., lire \£ ;r-
t::.'.: <-, Av<£ . ¦ Ss-CC,: -.4; f;.r ,-wsii'" '-*: ritftti--;
2: <5; 15-55 <1C, HrfXj; l"4-lB.7, d. » f_-..'.: .r "f res^ira;.rv
/Vi.: 26 <1C; CI- Fe^ .Al^C*: 2.9
• ' '
rsr-e • 4 i -"*;;
i--is :?0 aL".*ly*-is:
»ur. S2 <5, 83 <10,
:i &£.: <2D. P9.5
<4^
-in BAHCC tntlysl*;
v«nt fl tetll 71
-------
TA^LE 12-2 (Concluded)
; >'••-•. H'
Hygrsnopie r.«m*tlil*.y or Kinilirv
Sgfjtli'.ty Ch>T»et*rl«lea Splnm™ UnlH Shtr»ct«r:stie.i Promts 2«_r
difficult te i
K-f»ry kiln C»nc, • «.h£0,
td'ii c»: • a.
rijO; 1^0 - l.
il. H»0, a.
ssii: Ct$0, - a.
s!. M.£Op a. tf.6
. vucr.cr "» < 16-2
• - :«£*.'
:• ay-.T.:
•'t,ne •• ••,'*" *.• U
(i Jrvtr"
Mir pro-
T«rpertfir< Car.tc-.t tt-.cr.ic>: ?aefcslti™ ?£xU^v C*rr:g-r1ty ^ -;xt.;r.jv» ---.f- ;--r»rV.P
. r~-26:c.isCD; tr?- c^, n2. h?o,
< f'-^r.ctiar. 32' ictl exha-jct i J,
: -i*. *.*•¦•.?. Vt-t '•
} ft.
XiL". is 125i*}
"oS' ft. of
Jyrie'-^
'<-» 0S» *2' W;Cl,
246
-------
u
Z
<
K/1
l/l
UJ
0£
1/1
D
O
u
UJ
a.
i/i
Lime Shaft Kiln Dust
0 100 200 300
GAS TEMPERATURE °C
figure 12-3 - Dependence of Specific Electrical Dust Resistance
on Gas Temperature for Lime Shaft Kiln Dust Jj
247
-------
Plants in sone areas have installed high-efficiency cyclonic
secondary collectors on their kiln operations. Table 12-3 lists data on
a number of installations with secondary collectors. However, to meet emis-
sion requirements plants are increasingly turning to wet scrubbers and glass
bag collectors. Electrostatic precipitators have also been found satisfac-
tory. However, economics in the lime industry are such that precipitators
are generally not installed as long as scrubbers and bag collectors give
acceptable performance. Table 12-4 presents the estimated cost of three
basic types of control equipment for a rotary kiln. 6/ The control equipment
costs are listed for two different efficiencies. These costs compare
closely with general cost data given in Appendix A, except that the fabric-
filter operating cost of $14,000 is about double the typical value computed
from Appendix A.
When making cost estimates of a collector system, the precooling
or preconditioning section that may be required must be included. This can
be very significant for baghouses and electrostatic precipitators.
Lime-hydrating processes can also be an important source of dust
emissions. The loss of hydrated-lirae dust represents loss of valuable prod-
uct since the dust is high purity. It is easily wetted and can be scrubbed
from the stack gases with a water scrubber. The recovered water slurry can
be fed back to the hydrator as make-up water. Venturi-type scrubbers or
other commercial wet scrubbers are used for this service. Effluent loadings
of 0.01-0.07 grain/cu ft are reported.Table 12-5 presents data and
costs reported for control equipment associated with various hydrate opera-
tions . §/" Dryers also present a difficult dust control operation in a lime
or limestone plant. Table 12-6 contains data and costs for control equip-
ment associated with this operation.®/
12.5.1 Cyclone Collectors
High-efficiency cyclones are suitable as primary collectors and
precleaners for removal of the +10 ^ size dust. One installation reports
handling 80,000 acfta of kiln gas at 450-500°F and 30-35$ moisture content
in 72 9-in. size cast iron cyclones with a pressure drop of 2-1/4 in. of
water and l&fo collection efficiency.5/
12.5.2 Bag Filters
A number of installations are reported making use of glass fiber
bag collectors handling gas flows as high as 150,000 acfm at temperatures
in the range of 350-550°F, with average particle sizes of 25 ^ after pre-
cleaning with dust settlers. For the larger gas volumes the baghouse is
compartmented so that only one section at a time is cleaned. A 12-compart-
ment baghouse for a 500 ton/day kiln has been reported. The cleaning cycle
(shaking is not employed with glass bags) depends on dust loading but is
248
-------
TABLE 12-3
SECONDARY COLLECTION OF ROTAKY K1UI LIME DUST^/
ro
rf*
CD
Installation No.:
Primary Collection
Type of Secondary
Collector
Inlet loading
grains/8cfm
Outlet loading
grains/scfm
Collection efficiency
Pressure drop in
secondary collector-
inches of water
1 2
Dust Chambers Dust Chambers
Glass Bag 4-Stage Cyclonic
Collectors Dynamic Scrubber
10.0
2.0-2.9
0.001 0.071-0.000
99.99$ 97.5$
4-5 8
Duct Chambers
4-Stuge Cyclonic
Dynamic Scrubber
9.5
0.02
99.7$
9-In. Tube Cyclones**/
Single Otage Electro-
static Precipitator
4.3
0.22
95$
1-2
Dust Chambers
Venturi Scrubber
arid Cyclonic
Scrubber
4-7
0.12
97-96.3^
15
Dust Chambers
Spray and
Impingement
PLate Scrubber
16
0.3-0.4
97.5*
5-6
a/ Primary collector consists of 9-in. tube cyclones. Inlet loading to cyclones, 14.5 grains/cu ft; outlet loading, 4.3 grains/cu ft; efficiency, 7of,.
-------
TABLE 12-4
ESTIMATE OF ROTARY KILN CONTROL COSTS B/
Capacity - 350 tons/day
Exhaust Gas Volume - 100.COO cfm
Exhaust Gas Temperature - 550°F
Power Cost - $0.Cl/kvft
Type of
Collector
Baghouse
Installed
Cost of Unit
Operating
Cost/Year
For 99# Efficiency
$150,COO
$14,000
Electrostatic
Precipitator
Scrubber
200,000
60.000
2,300
65,000
For 97$ Efficiency
Baghouse $150,000 $14,000
Electrostatic
Precipitator 100,000 2,3C0
Scrubber 50,000 32,0C0
Maintenance
Cost/Year
$o,GOO
2,000
6,000
$8,000
2,000
6,000
250
-------
TABLE 12- 5§/
HYDRATOR
Type of
System
Bag Filter
Bag Filter
Air Flow
(cfln)
13,000
11,000
(5 in. w.g.)
Filter
Area
(sq. ft.)
1,750
9,660
Air-
Cloth
Ratio
No.
of
Bags
128
112
No. of
Compartments
Scrubber
Cyclone
Pre-cleaner
Capital
and
Installed
Cost
$19,000
30,000
Bag
Filter
-
1,668
3.55:1
-
-
9,500
Bag
Filter
5,000
1,050
-
-
-
-
Bag
Filter
10,000
-
-
-
3
30,000
Bag
Filter
14,850
-
-
-
-
-
Bag
Filter
4,250
-
-
43
-
-
Bag
Bag
Filter
Filter
6,000
5,000
576
1,050
—
10,000
Bag
Filter
2,500
(150°F)
344
.
16,000
9,500
10,000
Type of Application
Bagging
Fines from cyclone
Fines from pre-cleaner
Bagging
Bagging
Bagging
Quicklime grinding
Raymond Mill
Note: Bags used are cotton, dacron, and glass; dacron most common.
-------
TABLE 12-6®/
STONE DRYERS
Cloth- No.
Area of No. of
Plant Collecting System ( sq. ft.) Bags Compartments
Cyclone and Baghouse 2,550 360
Baghouse 6,250 112
3 Primary, Secondary
10 Cyclone and
Baghouse 3,120 312
4 Cyclone (only)
5 2-Stage Cyclone and (400 gpn
Hi-Energy Scrubber HgO)
Air Flow
(cfm) Efficiency
15,000 at
220° F
4,500-7,500
at 12 in.
Capital and
Installed Cost
$10,000 Cyclone
36,000 Baghouse
20,000
18,100 at
230°F
8,800
99+$ 50,000
(508 lb/hr) 12,000
50,000 at
30 in.
99.9$ 215,000
-------
usually a 10-15 min. cycle. Design air-to-cloth ratio with one compartment
out for cleaning is in the range of 1.95:1 to 2.2:1. Since kiln gases are
frequently discharged hotter than can be handled directly by the tags, it
is usual practice to ccol the gases by water spray, air dilution, or a com-
bination. Insulation of the baghouse is not usually required unless the
moisture content of the gases is quite high, as might be the case with wet
feed. Bag life up to 2 years is reported. Collection efficiency is almost
100$ between bag cleanings because a thin layer of dust on the bag forms an
additional filtering media. Particles 5 p, and less in size are apt to be
lost through the bag immediately after cleaning. Capital cost is reported
to be $1.80/cfm handled, with annual operating plus maintenance costs running
$0.20/cfm.ry
The capital cost of $1.80/cfin agrees reasonably well with the
higher cost curves of installed cost for fabric filters given in Appendix A.
Annual operating and maintenance cost of $0.20/cfm corresponds to the "high"
values given in Appendix A but this cost is largely a function of power cost.
12.5.3 Electrostatic Precipitators
While the use of electrostatic precipitators tends to be costly
for the lime industry, one installation has been reported using a single
stage precipitator as a secondary collector at a capital cost of $1.25/cfm.
It handles 160,000 cffci at 450-500°F inlet conditions in which 90-95$ of the
inlet dust is -10 ti. It is designed with a gas velocity of 3.3 ft/sec and
a resident time cf 5.2 sec. and has an on-stream efficiency of 95$.5/
12.5.4 Wet Scrubbers
One of the advantages of a wet scrubber is that it can include a
pre-humidification section and eliminate the need for pre-cooling the gases.
A typical installation for a 180-200 ton/day kiln with 40-50,000 acfa at
900-1400cF and a 5-10 grains/cu ft dust loading, would require a 9-10 ft.
diameter scrubber 32 ft. tall. Scrubbing water requirement is 4 gal/1,000 cu.
ft. of gas processed. Pressure drop is 8 in. of water. For the 200 ton/day
kiln installation, fan brake horsepower would be 150. Collection efficiency
is stated to be 99.7$. Scrubber cost is reported to be $0.50/cfm of cooled
saturated exhaust gas for 304 stainless steel construction and $0.25/cfm
for carbon steel.The cost for carbon steel construction compares closely
with purchase cost in Appendix A.
A dust removal efficiency of 96-97$ has been reported for a 335
ton/day kiln using a combination Venturi scrubber and cyclonic separator.
A pressure drop of 7-11 in. water was used. Inlet gas volume was 60-62,000
cfm at 350°F. Water supplied to the Venturi throat was 1,500 gpm at 50 psig
pressure. Cleaned exhaust gases were discharged at 160-165eF nearly satu-
rated with water vapor.5/
253
-------
While vet scrubbing may frequently be cheaper, problems can occur
which axe not present with dry collection. Examples are discharge of a hot
humid gas, scale buildup, and corrosion. The presence of sulfur oxides may
dictate the use of corrosion resistant alloys for wetted parts including
the exhaust fan. Some producers report operating costs for £ wet scrubber
three times as great as for a bag filter even though initial cost is con-
siderably less. The scrubber slurry is also a potential water pollutant if
not properly confined or consumed.5/
254
-------
REFERENCES
1. Shreve, R. N., The Chemical Process Industries, 2nd Ed., McGraw-Hill,
195S.
2. Kirk-Othmer, Encyclopedia of Chetalcal Technology, 2nd Ed., Interscience
Publishers, 1967.
3. Lewis, C. J., and B. B. Crocker, "The Lime Industry's Problem of Air-
borne Dust," Journal of the Air Pollution Control Association, 19,
p. 31 (1969).
4. Stern, Arthur C., Ed., Air Pollution, Vol. Ill, New York, Academic Press,
1968.
5. Control Techniques for Particulate Air Pollutants, U.S.D.H.E.W. Pat.
AP-51, Washington, D. C., 1969.
6. Minnick, J. L., "Control of Particulate Emissions from Lime Plants,"
presented at 63rd Annual Meeting, Air Pollution Control Association,
St. Louis, June 1970.
7. Loquenz, Heinz, Staub-P.einhalt Luft, 27(5), p. 41, 1967.
255
-------
CHAPTER 13
PRIMARY NONFERROUS METALLURGY
13.1 INTRODUCTION
Primary nonferrous metallurgy, as used here, will include smelt-
ing and refining of copper, lead, zinc, and aluminum. The air pollution
problems of the nonferrous metallurgical industry are extremely varied.
However, one typical characteristic exists—in almost all the processes
in the production of nonferrous metals, the particulates emitted are
metallic fumes generally submicron in size. Table 13-1 summarizes particu-
late emissions from the primary nonferrous metals industry.
The production processes, particulate emission sources, particu-
late emission rates, effluent characteristics, and control practices and
equipment for copper, lead, zinc and aluminum smelting ar.d refining are
discussed in the following sections.
13.2 PRItftRY COPPER SMELTING AND REFINING
Copper is obtained from copper ores by smelting. The tern "smelt-
ing" can be used, in a wide sense, to cover the successive operations of
roasting, reverberatory smelting, coverting, and fire refining. Although
there are considerable variations in practice from smelter to smelter, the
basic principles are essentially the same. A simplified flow diagram of
a typical smelter operation is shown in Figure 13-1.
The ores are smelted down either as they come from the mine or are
subjected (in particularly the sulfur-containing copper ores) to a prepara-
tory process of grinding and flotation. This transforms the low-percentage
ores into a high-percentage copper/sulfur concentrate. The latter is sub-
sequently smelted down either directly or after partial roasting. Roast-
ing removes part of the sulfur giving a favorable balance of copper, iron,
and sulfur for the reverberatory feed. In the reverberatory furnace the
iron present as oxide combines with siliceous flux to form a slag, leaving
a material known as matte, which contains copper, iron, and some sulfur,
preferably combined with the copper. The matte is reduced to copper in
the converter in two stages of blowing with air. The first stage eliminates
sulfur, and forms the iron oxide which is slagged off by the addition of
siliceous flux. The copper sulfide remaining in the converter is reduced
to metal and the sulfur is eliminated as SO2 in the "finish" blowing stage.
The copper at this stage is called blister copper. This crude copper under-
goes further refinement by fire refining to reduce the sulfur and oxygen,
and then is cast into anodes for electrolytic refining.
257
Preceding page blank
-------
CONCENTRATE
1
FLUX
ATMOSPHERE
t
STACK
CONCENTRATE
STORAGE BINS
HEARTH
ROASTER
£
FLUX
STORAGE BINS
CALCINE
FLUX
WASTE
HEAT BOILER
GAS
1
1
ELECTROSTATIC
PRECIPITATOR
GAS
REVERBERATORY
MATTE
FURNACE
™ SLAG
1
SLAG DUMP
I
PLATE TREATER
HOOD
DUST
CONVERTER
ANODE
FURNACE
SCRUBBER
ELECTROSTATIC
PRECIPITATOR
GAS
~
ACID PLANT
ANODE
CASTING WHEEL
QUENCHING
TANK
RR CAR
Figure 13-1 - Copper Smelting - Simplified Flow Diagram
1
ANODES
~
REFINERY
-------
13.2.1 Emission Sources and Rates
Dust is emitted from all pyrometallurgical operations. The vari-
ous phases of the process and their particulate emission potential are
discussed briefly in the following sections.
13.2.1.1 Roasting: Copper- roasting at smelters in the U. 3. is
slowly being phased out. The older multiple-hearth roasters have been
abandoned in some plants in favor of more modern equipment.
Recent installations are generally fluid-bed roasters. These
have been ir. use in copper smelters for about 10 years. The feed material
may be sprayed into the top of the roaster as a water slurry or charged
as a solid.
Multiple-hearth roasters usually operate at a temperature of
about 1200°F. Sulfur dioxide concentration ir. the wet off gas is usually
only 5 to 10$ because of lew efficiencies in the furnace and dilution by
air. The dust load in the off gas is around 3 to 6<]k of the weight of the
feed, and a large portion of the dust is recovered in the flues.
Fluid-bed roasters operate in the same temperature range as
multiple-hearth roasters. However, about 85$ of the feed is carried
in the gas stream, and most of it is immediately recovered ir. cyclone
collectors. The wet off gas runs 12 to 14 vol. $ sulfur dioxide.
After preliminary solids collection, the gas from either type of
roaster is cooled to 600°F bv air dilution, water sprays, or heat exchangers
before the final cleaning.
The dust content of the waste gases depends or. the characteristics
of the copper concentrates as well as on the volume of air aspirated by
the roasting furnace. Another factor of importance in hearth furnaces is
the extent to which the concentrates remain continuously in suspension when
descending from the upper to the lower hearths. The size and number of
the apertures in the hearths has an influence on the creation of dust ir.
the furnace, and consequently also on the dust content of the waste gases,
13.2.1.2 Reverberatory Furnaces: The reverberatory furnace melts
the metal-bearing charge and forms the matte and slag. The charge is
introduced through openings in the side wall or in the roof.i/
259
-------
Collection and recovery of dust from the furnace gas is a substan-
tial problem. The heavier particles settle below the waste heat boilers,
and into the hoppers of the balloon flues or settling chambers. Practically
all copper smelters have a main collector system that includes drag or screw
conveyors that remove the dust from the various places where it accumulates.
The dust is then moved to locations where it can be worked back into the
system. The amount of dust will depend upon variables such as the fineness
of the charge, the degree of agitation ir. charging and working, and specific
gravity.
13.2.1.3 Copper - Matte Converter: Molten natts produced in the
reverberatory furnace is transferred in ladles to the converters by over-
head cranes. The function of the converters is to oxidize and separate
the iron and sulfur from the matte. Air is blown into the liquid matte
through openings called "tuyeres." The oxidation reactions supply enough
heat to maintain the converter at a temperature cf about 2250°F and no
fuel is required. The sulfur dioxide is carried out with the other flue
gases. Silica flux is added to combine with the iron oxide to form a
fluid iron silicate slag. The slag is skimmed from the converter and
returned to the reverberatory furnace. Additional matte is added to the
converter and the process repeated until a suitable charge of copper sulfide
has been accumulated. Blowing is then continued without further matte
additions until the remaining sulfur has teen eliminated. The resulting
blister copper is usually more than 99$ pure. It is removed from the con-
verter to be cast or further refined.
Dust leads in converter gases may amount to 10 to 20 tons/day/
unit. About 75 to 65$ of these solids settle in the flue system. The
remaining 15 to 25$, composed of the smaller particles, is largely removed
in dust collectors.%]
The dust content of the gases depends to a large extent on the
chemical composition of the copper matte. An increase in the operating tem-
perature of the converter causes higher volatilization of the metals and
consequently higher dust content in the raw gas.
13.2.1.4 Fire Refining: Blister copper, the ena product of the
converter, contains about 0.04$ sulfur and requires further refining in
order to meet most purity specifications for fabricated copper products.
Of the 16 copper smelters in the U.S., five produce blister copper only.
The others fire-refine part or all of the blister copper for anodes or
other shapes.i/
260
-------
Furnaces commonly used, are either of the reverberatory or tilting
cylindrical type. The type of furnace used depends on the operational
continuity at the particular plant.
13.2.1.5 Summary of Emission Rates: Table 13-1 summarizes the
emission rates from the various processes involved in the production of
primary copper. Limited data on control efficiency and degree of appli-
cation of control were found. The emission totals in Table 13-1 are con-
sidered as conservative estimates.
13.2.2 Characteristics, of Effluents from Primary Copper Production
The chemical and physical properties of effluents from primary
copper smelters are summarized in Table 13-2. Particulate emissions from
the furnaces are predominantly metallic fumes of submicron size. The
fiur.es are difficult to wet and readily agglomerate. In addition, they
are cohesive and will bridge and arch in hoppers and other collection
bins.
13.2.3 Control Practices and Equipment for Copper Smelting Refining
Copper sulfide concentrates received at the smelter are normally
roasted in multiple-hearth roasters to remove moisture, to burn off part
of the contained sulfur, and to preheat the material before smelting.
One copper smelter is using a fluidized roaster, and the gases
are cleaned in a Peabody scrubber prior to entering the sulfuric acid
manufacturing process.:!/ In recent years the roasting step has been
eliminated at many smelters.hi
The value of volatilized elements, as well as air pollution
considerations, dictates efficient collection of fumes and dusts from
process off gases. Balloon flues may serve as gravity collectors, and
cyclones may be used also. For collection of the finer particulates,
electrostatic precipitators are most often used. Collection efficiencies
up to 99.7^ for copper dust and fume are attained by careful conditioning
of flue gases.hi
Or.e installation which used an electrostatic precipitator to
clean the gases from a copper smelter has been described. This system
was revised to separately clean the roaster, reverberatory and converter
gas streams in the electrostatic precipitator system. A baghouse was
added for further cleaning of the combined reverberatory and converter
gas streams at the exit of the precipitator.
261
-------
T/VBIJ-: l.'.-l
particumti-: wiksion:;
rnrMAHY uurii'iimou:: mktali; nn>u:;THtk:;
^uuii.ity of Material
Emisu ion Fnctor
Effici-
ency of
Control
(Cc)
App1 ica-
tion of
Control
(Ct )
Not
Control
Ccc-ct)
Em ir>t> ions
(tonj/yr)
I. Aluminum
ro
a>
ro
Preparation of Alumina
1. Grinding of Bauxite
2. Calcining of Hydroxide
Aluminum Mills
1. Soderberg Cells
a. Horizontal stud
b. Vertical stud
2. Pre-Bake Colls
Materials Handling
II. Copper
A. Ore Crushing
B. Roasting
C. Reverberatory Furnace
D. Converter
E. Fire RefiJiing
F. Slag Furnaces
G. Materials Handling: Ore, Limestone
Slag, etc.
Zinc
A. Ore Crushing
Roust ing
1. Flu idized-Bed, Suspension
2. Ropp, Multiple-Hearth
Sintering and Sinter Crushing
Distillation
Materials Handling
13,000,000 tons of bauxite
B.
IV. Lead
A.
Ore Crushing
B.
Sintering
C.
Blast Furnace
D.
Drossing Kettle
E.
Softening Furnace
F.
De-Silvering Kettles
G.
Cupeling Furmces
H-
Refining Kettles
I.
Dross Reverberatory Furnace
J.
Materials Handling
5,040,000
tons
of
a Luminu
200 lb/ton of alumina
-
-
0.90
58,000
000,000
tons
of
aluminum
144 lb/ton
of aluminum
0.40
1.0
0.40
35,000
700,000
tons
of
aLuminum
04 lb/ton
of aluminum
0.64
1.0
0.64
10,000
1,755,000
tons
of
aluminum
63 lb/ton
of aluminum
0.64
1.0
0.64
JO ,000
3,300,000
tons
of
aluminum
10 lb/ton
of aLuminum
0.90
0.35
0.3?
11,000
Total from
primary aluminum industry
142,000
170,000,000
ton^
of
ore
? lb/ton
of ore
0.0
0.0
0.0
170,000
0
o
1,437,000
tons
of
copper
168 lb/ton
copper
0.85
1.0
0.85
7,000
1,437,000
tons
of
copper
206 lb/ton
copper
0.95
0.85
0.81
26,000
1,437.000
tons
of
copper
P35 lb/ton
copper
0.95
0.05
0.81
33,000
L,437,000
tons
of
copper
10 lb/ton
copper
0.90
0.35
0.32
5,000
Total from
primary copper industry
243,000
10,000,000
tons
of
ore
2 lb/ton
of ore
0.0
0.0
0.0
18,000
75 $
of
1,020,000
tons
of
zinc
2,000 lb/ton
zinc-
0.90
1.0
0.98
15,000
]5*
of
1,020.000
tons
of
zinc
333 lb/ton
zinc
0.85
1.0
0.85 •
4,000
60*
of
1 ,0^0,000
tons
of
sine
100 lb/ton
zinc
0.95
1.0
0.95
3,000
60%
of
1,020.000
tons
of
7. inc
0.0
0.0
0.0
lL-,000
L,020,000
tons
of
z inc
7 lb/ton
z inc
0.90
0.35
0.32
2,000
Total from
primary zinc
industry
57,000
4,500,000
tons
of
ore
2 lb/ton
ore
0.0
0.0
0.0
4,000
467,000
tons
of
lead
520 lb/ton
1 cad
0.95
0.90
0.86
17,000
467,000
tons
of
lead
250 lb/ton
lead
0.85
0.98
0.83
10,000
467,000
tons
of
lead
eO lb/ton
lead
0.50
, ooo
467,000
ton
of
lead
5 lb/ton
lead
0. 'JO
0.35
0.32
1.000
Total Iron
primary load
industry
34,000
Total from
nonferroun m<
;tuj:; jndu:;tr i t
4/0,000
-------
TttIJ 13-2
-lQrl
Particle ;>:te Sclidi loaalag Chw&cal Ccapoiltion Particle Z>
£¦• ctrlgH Beilaslvlty HoUture
r. 1
r..6*
Cv"nv*rter
^Pt^i re: In-
: v.>*i ici'.
s'j rfJ j
Cu: ?, S: 10, ?9: ?6*
Cu: t.4, Zn; 11.5, S:
Cu: €.2, Za: L3.0, S:
13.t*
Trace* of •
tier of are: CatidM cf
unnic, fccciwony, »lur*.-
nua silicon r-ir»t««.
Cu: 1.?, Z.n: 18.0, f.: JC*
(ci>v IM civtrb«rit$r> f-rnic«)
C'j: S. !.£•
t. blaci.
o. Jtev»rt«ratjr/
f Lir^ni**
4. a.ar: r»vjlv.
ir^ rever-
5er*t.:ry
1.3-s.e*
ft: 40-65, ZD. 10-?C,
3: 8-15»
TTKC8 oT eleants cor-
tion of i
of trsenie, ?a£*liB,
s«Isr.lji, fcivl teUuri-.in.
Ma geld and silver,
alfates, o*ide», Iffcl
sulfide, cok* dust,
ft?, ZaC, C40. ft504.
1*0 for d«tailed
detailed data
?: irrrr :j-ci
(i" Sopf rsMttrS'^M'T. B#: -o
• "...it-ple- Aoaiyil*:
liBii/th 14 r
a, .'^rticii
muSflt
r,8-70*. J%: *-s
Zn: Pb: 8, S: l.h
neltir^ pl*rt
• $99 Csilr.g Key, Table S-i, CUaptar 5, p.
-------
TABIX 15-2 (Contirv-«0
0.?C-C.50
fi«;.niri£ a.nd
:-.s- ng
I'U.-Tift.tS
Range 'n site
down >o au--
sl-r<-.n level a
?-?0 (High
value JarinM
ehlorine flu.-
ln«)
AJ^-Ot, AlCL^.
Aissee
Taoie 12-4
S3UTJ6
l. -3p:«r
SolutlU'.y
Wet'.a;lli
Hymrissop}.-
Cfcarscveristics
riere*Bi:ilV.y or
Lxsloslve Lieits
'.cult ta v*t
Handling Characteristics
AfglsMrates, cohesive,
will bri"ls* and ar?h
Optical
ProprUas
4. kl< - **. ?.tr'.r..r-z A..";, - s H«c
Corrosive, Crutvj
n'iru errroa
Me*.a2t
1. <::pj»r
a. toast.
. Blast
furr.acc
. Pev»rS*r»-
furnace
d. Capper r>atte
c w.'arwor
«. wopper refin-
ing f<*rna-«
('.oil doit
f.r«4:
%) ro.ii:
b) 47.3*
a) 21.2
b) 76.S*
a) C-4SO
b) '!•
Sci stars riamaMllty vpticvL
TT.peratar* Cr-r-^nt Chesisul c*»;-cs'.tlor Toxicity Corroslrlty Cdor Limits ?r3pertle-:
603-G9C
248*
15j-/St 4-10
30
-------
'-•r-
TABIi: 13-2 (Concluded)
Chvil-i L Cob
''--on Corrmlvl-.v
Pr°j*r--.«
c :r.*.cr
r.» r.-.r.e
a) :*o~
b] -.30~
a) '
c)
S »v«*rwr»lcry *) i-3
furr.i-' d} 3.5-17.5*
On-:'. rev-iving O ,s< . 5.j,fiG-
rveryertiiry
1400-18W
(Furnace cuc>t)
SOj, Op, »5, r.s, HjO,
poaalbie tr*cei cf
HT ud S L74
«a*lysla:
C02: 4.?, 0?: 15.0.
CO: 1.3. SSy: C.H
t . ) a) 2i.-30
ronttcr
(21 ''ii.• ir.'i»-B
nnrth
li' ;j: y«.*nsle»s 1C > 1 -
rrar1:?:-
>' r uU-trf-r. r.-.c:
r-'tr -.tr
RI liCr*
i) *.30-5.100
7JO-SOO
MC'..SiX5
S3-,: 0.7-1.C, Oj. s2
:o.. uo H^c
SO.,: 4.5-G.h,
02, «J.
10.17., C2, Bj,
I H^C
r.-y Cj,. Hj,
-cs
S'-V cs- "z-
:c, «>< v-r.
%
i v:zf-
Drw Point* SO*: 4.6-7*
;y?-uo
-.urn- *w-
ni 42-r.-r.4n*
0S--5O*
2.1-lA
¦:V :>
a' no-::: so.*!-.
•+: :S-:3£ Z-50-72C 4-5-M CO., ??, N.,, Hj"
;r *ri-r >- !l?. CC', S:;>. SOji 5, r.ridu.
ro>j-5w)
^f^2' '
riucriJes, hyd/-- irr:'.a='v
co: ::c
* iv
-------
ro
en
cr>
0 200 400 600
TEMPERATURE °F
* Figure shows percent water vapor by volume.
Figure 13-2 - Typical Resistivity Graph of
Lead Fumei®/
1.3%*
200 400 600
TEMPERATURE °F
* Figure shows percent water vapor by volume.
Figure 13-3 - Apparent Resistivity of Lead Fume
from Sintering PlantiZ/
-------
ro
a>
-j
10
13
5
O
i
5
x
O
i
>-
V)
1/1
ae.
<
10
12
H>
11
10
10
10v
10
8
/
\
1.3%
ft
/
10%
\
/
A
i!(H
L
3f1P>
\
I
1 III
V
\
\
600
200 400
TEMPERATURE °F
• Figure shows percent water vapor by volume.
Figure 13-4 - Resitivity of Lead Dross Fume Under
Varying Conditions of TemDerature
and Moisture in Gas i§/
) 400
TEMPERATURE °F
• Figure shows percent water vapor by volume.
Figure 13-5 - Apparent Resistivity of Lead Fume
from Lead Blast Furnace M/
-------
10
13
sio12
u
I
5
x
O
> 10n
|io«»
« 10'
I0e
\l.
10%
20%,
\
\
\
\
200 400
TEMPERATURE °F
600
Figure shows percent water vapor by volume.
Figure 13-6 - Apparent Resistivity of Lead Fume
from Slag Treatment PlantM/'
268
-------
TABLE 13-3
COMPOUNDS FOUND IN ALUMINUM REDUCTION CELL EXHAUST STREAMSi£/
Chemical
Category Chemical Compound Formula
1. Fluorides Sodium fluoride NaF
Particulate form Aluminum fluoride AlFi
Calcium fluoride CaFg
Fluoroaluminate (Cryolite) Na3AlFg
Gaseous form Carbon tetrafluoriae CF
Hydrogen fluoride HF
Silicon tetrafluoride SiF4
Hexafluorcethane c2^6
2. Other particulates Carbon C
(Nonfluoride) Aluminum oxide A^O^
3. Other gases Carbon monoxide CO*/
Hydrogen sulfide HpS
Hydrocarbons £/
bJ Especially during periods of anode effects.
bj Too numerous to mention; type and quantity will depend upon cell employed.
269
-------
TABLE 13-4
ATMOSPHERIC POLLUTANTS FROM SECONDARY SOURCESg/lN ALUMINUM PLANT £>j^/
Atmospheric Pollutants
Source
Raw materials handling
Alumina unloading and transfer
Cryolite unloading and transfer, grinding
Pot lining operation
Anthracite coal grinding and transfer
Coal and pitch mixing
Anode preparation (prebake plants, only)
Coke unloading, transfer and grinding
Pitch unloading and transfer
Mixing of coke and pitch
Anode baking furnaces
Cleaning of baked anodes
Cleaning of copper rods and steel stubs
Electric arc cast iron furnace
Pas te making (Soderberg plants, only)
Aluminum refining
Ingot casting furnaces
Chlorine fluxing
Gaseous
hydroc arbons
hydrocarbons
SOg, CO, hydrocarbons, AF
hydrocarbons
Clg, HC1
Particulate
NagAlFg. A1F„
Coal dust
Coke dust
Pitch dust
Carbon dust, particulate
Coke dust
Copper and iron
Iron oxide
Carbon dust
AICI3, AI2O3
a/i.e., excluding the pot line and monitor emissions.
-------
The application of control methods for copper smelter operations
has been described in a translation of a 1960 German studySignificant
parts of this study are included in the following paragraphs. However,
it should be noted that German practice does not necessarily correspond
to present-day practice in U.S. smelters. Table 13-5 summarizes operating
data for dust control equipment reported in Reference 2.
12.2.3.1 Cloth Filters: Cloth filters are utilized for secondary
dust collection from converter gases. Depending on the purpose of utiliza-
tion, the following types of fabrics are employed:
Cloth woven from natural fibers (wood, cotton);
Cloth woven from synthetic fibers (Redon, Pan, etc.)
The dust content of the exhausted air is strongly influenced by
the air-to-cloth ratio (ft of raw gas per ft of filter surface) as well
as by the structure and density of the filter weave. In order to maintain
the full nominal rating of the filter in continuous operation, cleaning of
the filter cloth is of the greatest importance.
The disadvantage of all cloth filters is the high wear and expen-
sive replacement, the high cost of maintenance and the high consumption
of energy due to the pressure drop of 2-5 in. w.g. However, with filters
properly maintained, efficiencies up to 99.9$ can be attained.
13.2.3.2 Centrifugal Separators: Centrifugal separators installed
on furnaces generally have maximum efficiencies of 80^85$ and are therefore
usually employed for primary removal of coarse dust.—'
13.2.3.3 Electrostatic Precipitators: Electrostatic precipitators,
usually preceded by mechanical collectors, are near-universally applied to
the control of particulates from copper smelting. The equipment is normally
more massive and rugged than counterparts in the power or other industries,
and dust-handling techniques are far more positive. In the 50,000 to
2,000,000 cfm flow ranges under consideration, installed costs for combined
mechanical collector-electrostatic precipitators would be $6.00 to $3.00,
respectively. Mechanical collectors are typically of the large-diameter
(24 in. or more) multicyclone type.
Mild-steel construction is accommodated by maintaining sufficient
gas temperatures to preclude corrosion, with temperatures ranging from 300
to 650"F on converters and from 600 to 900°F on roasters. Actual collection
efficiency usually is reported in the 98.5 to 99.5$ range.§2/
271
-------
TABLE 13-5
OPERATION DATA FOR DUST COLLECTORS APPLIED TO
PRIMARY COPPER SMELTING AJID RSFININGg/
Type of
Separator
1. Dust
chambers
Maximum
Efficiency*
(*>
30-60
Draft
Required
in. vater
< 0.2
3-6
Utilization
Beyond sintering machine
and shaft furnace
2. Cyclones
<. 16 in.
in diameter
85-95
3-4 For secondary purification
beyond reverberatory
furnaces
3. Electrostatic
precipitators
96-99
0.2-0.6 For higher demands and fine
dust beyond roasting,
sintering and shaft fur-
naces
4. Cloth filters
99$+
2-6 For dry air beyond coolers
for converter gas. Effi-
ciency depends on weave
a/ Largely dependent on type of dust, content of dust, particle-size dis-
tribution, gas and operating factors.
272
-------
13.3 PRIMARY LEAD SMELTING AND REFINING
All primary lead smelters in this country use essentially the
same processing steps, although there are differences in the equipment
used and the details of operation. The principal pz-ocess steps are sinter-
ing, reduction in a blast furnace, and refining. Refining includes opera-
tion of the dress reverberatory furnace. Smelter operations usually include
cadmium recovery and slag fuming for zinc recovery.
Lead sulfides are converted to oxides of lead and sulfur in the
sintering step at a relatively low temperature. The oxidized solid mate-
rial is then reduced with ccke in the blast furnace at a high temperature
to form impure metal and slag. A preliminary refining operation is per-
formed on the impure lead from the blast furnace. Lead bullion, 95 to 99$
pure, is the principal product of lead smelting operations.
There are a number of secondary products. Some, such as zinc
oxide products and cadmium dusts, may be ready for marketing as they
leave the plant, and some, such as slag, matte, or dusts, may be shipped zo
other plants for extraction of values, primarily zinc, cadmium, silver, and
copper. These other products vary from plant to plant, as one plant may
put out several finished products, while another may ship only lead and
unrefined materials.
Figure 13-7 shows the overall process cf the operation.
13.3.1 Emission Sources and Rates from Primary Lead Smelting and
Refining
13.3.1.1 Sintering Machines; Sintering is a universal practice
in the lead-smelting industry. Its purpose is to remove sulfur by roast-
ing and at the same time sinter to produce a calcine that is consolidated
in a strong and porous mass suitable for reduction in a blast furnace.
The main chemical reactions taking place on the sintering machine are the
oxidation of lead and other metal sulfides with oxygen.
Sintering machines are continuous conveyors made of grate-bar
pallets joined together. They are known as Dwight-Lloyd machines. Most
of the older and smaller machines are of the downdraft type. A sectionalized
windbox installed beneath the pallet line is used to regulate the burning
rates in the machine. Kewer installations usually have a single large
updraft machine with the windbox located above the pallets. Emission points
include the windbox and discharge points.
Sulfur dioxide concentration in the sinter machine off gas may
be 0.6 to 1.8$ by volume. Gas volumes run 100 to 220 sefm/sq. ft of bed
273
-------
Lead Siliceous
¦ncentrjfe I ore*
Crude
ore'
4
IZinc plant
^rt|icoi ^ Limerock* i Sl°g'i By-produets'g
P-essce leaching
AUTOCLAVE
•CuSO^, ZnSO^ solution 1
to zinc plant or sclvent I
•¦troction ond e lectrolytici
Cu recovery I
j^bSO^ residue
-H
j
" TheM products o1^ oil crashed ond
ground In o rod mill to -1/B in. size
CHARGE PREPARATION
Return
j inter
E
[palletizing
E
CoVe
L
-jp t. L sintering)-^ fcj COnRELi~|—
Si nter Refinery droit**
f
Slog she1!
Low-grade Zr
±
f
Leaded
jinc oxide
to ino'ket
F'JMING HANT
T
PfcO
Zinc axide
D? LEADING KILNl
Deleaded 21'nc
O*.id* to market
Dezinced ^roiulated .
slag to itofoge
-I BLAST FURNACE)-
T!
—Slog
" Fun^e
\
BwHion
Concentrator for codrnium-..
ewfroction electric furnace
Copper dross
| DROSS KETTLES
T
1
Bullion
i BY-PRODUCT FURNACE I-
Buiiii
Siag to
blest fjrnace
Speiss
Stag "o blal? fjrngce
|softening furnace}-
P..1 Zinc
-Parke* gald crust*
Porkes silver cui'«
j RE TOR"
RETORTS
f i f"
DESILVERIZING
GCLD KETTLE
f
DE5ILVERI7ING
Zinc
SILVER KETTLE
|
VACUUM DEZINCING
Zinc
KETTLE
McH« and speiss
to market
Antimory skin
Coke
~
Baghouse
r
^ Fun
[ electric"furnace| [
STORAGE
NoOH
CJPEi.
LJ
T I
UP EL j
' 'Fsiag to
REFINING KETTLE
1 ^
b last furnaee
Gold dore Fine silver
to Tcrfcet to racket
Casting
Refined leod
to merited
NoNO-j
1 F
Slag to Bull
blalt ^umace
PbO s
J—i
I REFINING Keniil
—_—
Casting
I
Hard lead
to marker
n
1
fr-EACH Tank]
Cadmium sponge to
electrolytic refining
FILTER
~^r
Residue
ta blast
furnaee
PRECIPITATION
TANK
ZnS04
to market
figure 13-7 - Typical Flowsheet of Pyrometallurgical Lead Smelting 19/
274
-------
area. When the off gas is to be fed to a sulfuric acid unit, the machine
is operated to produce a smaller volume of gas with 4 to 6$ or more of
sulfur dioxide. The dust and fume load carried by the gas is usually from
5 to 20$ of the feed to the machine.i/
13.3.1.2 Blast Furnace: The purpose of the blast furnace is to
reduce the lead oxide in the sinter to metallic lead. The reducing agent
is carbon monoxide derived from coke fed into the furnace. Dilution of
the flue gas at the top of the furnace is necessary, since without it the
gas would have a temperature near 1100° to 1300°F and contain 25 to 50$
carbon monoxide. The dilution air barns the carbon monoxide to carbon
dioxide, but the volume is large enough to also cool the gas.—/
13.3.1.3 Lead Refining: The lead-refinir.g process in a primary
smelter consists of the dross reverberatory furnace and lead refining
kettles. The product is lead bullion. The dross reverberatory produces
also matte and speiss, which are shipped to a copper smelter for recovery
of the large percentage of copper they contain.
The dross furnace usually operates only 50 to 70$ of the time the
refinery operates. A very small amount of sulfur oxide is emitted. Matte
and speiss both contain sulfur, but most of this remains in the material that
is shipped from the lead plant. A layer of dross on the hot material in the
furnace permits oxidation of only a small portion of the sulfur. Particulates
emitted from these operations would be principally metallic fumes.!/
13.3.1.4 Other Smelter Operations: Some lead smelters operate such
other equipment as cadmium roasters, slag fuming furnaces, and deleading
kilns. The slag furnace recovers zinc oxide from blast furnace slag.
13.3.1.5 Summary of Emission Rates: Table 13-1 summarizes the
emission rates from the various processes involved in the production of
primary lead. Limited emission data were found for various processes in
primary lead production, and the totals in Table 13-1 are considered as
conservative estimates.
13.3.2 Characteristics of Effluents from Primary Lead Production
The chemical and physical properties of effluents from primary
lead smelters are summarized in Table 13-2. Particulate emissions from
primary lead production are similar in character to those from copper
processing. The metallic fumes are submicron size, difficult to wet,
readily agglomerate, cohesive, and will bridge and arch in hoppers.
A typical sample of lead blast furnace dust contains many differ-
ent kinds of particles, including a range of lead oxides, quartz, limestone,
275
-------
iron pyrites, iron-lime-silicate slag, arsenic compounds and a host of
other compounds containing metals associated with lead ores. The major
constituents are (l) light red-orange to red fragments of litharge; (2)
yellow, rounded particles of massicot; (3) red birefringent, fragments of
Pb304. Also present are a variety of vitreous iron-lime-silicate slag
particles; these can have almost any color (yellcw, green to brown).
13.3.3 Control Practices and Equipment for Lead Smelting and Refining
The sulfur content of lead concentrates is reduced by sintering
them on Dwight-Lloyd sintering machines. Dust and fume are recovered from
the sinter machine gas stream by settling in lerge flues and electrostatic
precipitators or baghouses.§/ Collection efficiencies are up to 96$ for
precipitators and 99.5$ for baghouses.5/
Blast furnace gases, after cooling, may be cleaned in baghouses
using wool or fiberglass bags. The collected dust from the blast-furnace
operation contains up to 65$ lead and usually appreciable quantities of
cadmium and arsenic. Therefore, it is recycled back tc the sintering
machine. Lead refineries also have baghouses for recovery of fume from
softening furnaces and cupeling furnaces..5/
The processes and control methods for lead smelter operations have
been described in a translation of a 1961 German study.Table 13-6
summarizes some of the more pertinent data from this study. However, German
practice may not correspond to current practice in U.S. smelters.
TABLE 13-6
LEAD SMELTER CONTROL EQUIPMENT^
Control Device
Efficiency
Process
Sinter Machine
Primary
Centrifugal
Blast Furnace Centrifugal
Reverberatory
Furnace
Waste heat
boilers,
tubular
coolers
Secondary
Electrostatic pre-
cipitator, bag
filter
Electrostatic
precipitator
Electrostatic
precipitator,
bag filter
Primary
80-90
80-90
70-80
Secondary
95-99
95-99
95-99
276
-------
13.4 PRIMARY ZINC SMELTING
Since practically all zinc ores as mined are too low in zinc
content for direct reduction processes, they must first be concentrated.
After concentration, the first step in the extractive metallurgy of zinc
is virtually always roasting the concentrate. If the roasted concentrate,
or calcine, is to he subjected to high-temperature reduction with carbon,
it is usually first sintered in order to minimize dusting loss, volatilize
impurities, and permit better circulation of reducing gases around the
sintered particles. If the calcine is to be reduced electrolytically,
it is dissolved directly in the spent electrolyte, consisting primarily
of dilute sulfuric acid, just returned from the electrolytic cells.
Figure 13-8 illustrates a simplified flow diagram for a zinc
smelter.
13• -•1 Emission Sources and Rates from Primary Zinc Smelting
13.4.1.1 Zinc Ore Roasting: Zinc sulfide concentrates are usu-
ally converted to zinc oxide calcines by a roasting process. There are 12
plants in the United States roasting sulfide concentrates.1/ Two of
these use the old Ropp roasters, which produce a roaster gas too low in
sulfur dioxide for recovery by an acid plant. One plant uses multiple-
hearth roasters that produce a much-diluted waste gas with < 1$ sulfur
dioxide, also too lew for recovery by an acid plant. Nine plants recover
a large part of the sulfur with acid plants. One of these uses multiple-
hearth furnaces only for the first stage of a two-stage roasting process.
Roasting capacity in the remaining plants is about equally divided between
fluid bed and suspension roasters.
Operating conditions for zinc-sulfide concentrates vary from
plant to plant according to the composition of the raw material and the
specific use of the roaster calcine. Higher roasting temperatures (1800°F
and over) eliminate more cadmium, and increase the formation of ferrites.
Excess oxidizing air results in lower temperatures and good sulfur elim-
ination, but also lowers the sulfur dioxide concentration in the roaster
gas .i/
Depending on the type of furnace, the gases escaping from the
furnace contain greater or lesser amounts of dust of different composition
and grain size. Table 13-7 lists several types of roasters and some
operating conditions.
277
-------
CLAY-
5IZE m BLEND
SHAPE
DRY
PREFIRE
CONCENTRATE Si
ro
CD
DISCARD
BLEND
SINTER
ROASTING
FURNACE
STACK
SINTER
FLUXES
COAL
DUST COLLECTION
ROASTING
PURIFICATION
BRIQUET
CAST
¦MAGNETIC
RESIDUE
•ZINC: PLATES
r
"•ZINC: SPECIAL SHAPES
ZINC: DUST
REFINER
Cd OXIDE
•ZINC, SHG: PLATES
BALLS
JUMBOS
•DIE CAST ALLOYS
PbS04 RESIDUE
• CADMIUM: BALLS
STICKS
ANODES
INGOTS
Figure 13-8 - Zinc Smelting Flow Diagram
-------
TABLE 13-7
TYPICAL ZINC ROASTING OPERATIONS^'
/V
Type of Roaster
Multihearth
Mult ihear tbS/
RoppSJ
Fluid-bed£/
Dorr-Oliver
Fluid-bed£/
Dorr-Oliver
Fluid-bed
Lurgi
Suspension
Fluid-column
Operating
TemP- (°F)
1,200-1,350
1,600-1,650
1,200
1,640
1,650
1,700
1,800
1,900
Feed
Capacity
(tons/day)
50-120
250
40-50
140-225
240-350
240
120-350
Dust in Off Gas
Percent of Feed
5-15
5-15
5
70-80
75-85
50
50
17-18
aJ Dead roast except where noted otherwise.
_bj First stage is a partial roast in multihearth, second stage.
is a dry-feeu dead roast in Dorr-Oliver fluid bed.
cj Partial roast,
d/ Slurry feed.
13.4.1.2 Sintering: Sintering in the zinc industry is used mainly
to agglomerate the roaster calcine for subsequent processing. The process
is sometimes used with only raw sulfide concentrates or a mixture of cal-
cine and raw concentrates as feed.
Sintering machines have continuous conveyors made of grate-bar
pallets, upon which the feed material is placed and processed. Dcwndraft
machines are universally used in the zinc industry. The dcwndraft is
produced by sectionalized wind boxes installed beneath the line of travel
of the pallets. This construction permits draft regulation in separate
areas of the grate. The gases may be recirculated from one end of the
machine to the other.i/
With air at three to five times the theoretical amount to burn
the coke and residual sulfur, the temperature of the combined exit gas
ranges from 500°to 700°F. Sinter exit gas is further cooled by air dilu-
tion and water sprays to condition it for cleaning in dust collectors.
279
-------
13.4.1.3 Calcining: Calcining is a heat-treatir.g process that is
used, for oxidized, materials, e.g., oxide ore concentrates; material from
roasting of sulfide ore concentrates. It may "be called nodulizing, since
hard nodules of random sizes are produced when the calcining is done in
a rotary kiln. The nodulized kiln product is subsequently treated for
zinc extraction. Sulfur oxides are evolved only when roaster calcine
that contains small amounts of sulfur is "being processed, and in such
cases the waste gas from the kiln may have from 0.1 to 0.2$ sulfur dioxide.
The waste gas also contains seme fume, which is removed in bag filters
and treated for recovery of lead ana cadmium.i/
13.4.1.4 Metal Extraction: Roasting, sintering, and calcining
are preliminary steps to one of the extraction methods: pyroreduction
or leaching and electrolysis. Pyroreduction distillation or retorting
of the sinter or calcine is performed in horizontal or vertical retorts,
electrothermal open or submerged arc furnaces, or "blast furnaces. Hori-
zontal retorts are small ceramic cylinders that are mounted horizontally
in racks that hold several rows of retorts mounted one over the other.
They are fed with coal and sinter and produce liquid zinc metal, as do
the larger and more modern vertical retorts. Vertical retorts make a
by-product carbon monoxide gas that is used as fuel in other parts of
the plant. Particulate emitted is zinc-oxide fume.
Zinc fuming can be either an extraction or a pre-extraction
operation. In this step, zinc is reduced to metal by carbon or carbon
monoxide, vaporized, and reoxidized to form a zinc-oxide fume which is
collected in bag filters. The zinc oxide collected may be fairly pure,
in which case it is a final product. If it contains appreciable quanti-
ties of lead and cadmium it is usually treated further.~U
13.4.1.5 Summary of Emission Rates: Table 13-1 summarizes the
emission rates from the various processes involved in the production of
primary zinc. The roasting operations produce about 40$ of the particu-
late emissions, while ore crushing and materials handling account for
nearly 45$ of the total.
13.4.2 Characteristics of Effluents from Primary Zinc Production
The chemical and physical properties of effluents from primary
zinc smelters are summarized in Table 13-2. Particulate emissions com-
prise metallic fumes frcm furnace and coarse dust from mechanical proc-
esses. The metallic fumes are difficult to wet, readily agglomerate, and
will bridge and arch in collector bins.
280
-------
13.4c.3 Control Practices and Equipment for Zinc Smelting and Refining
For efficient recovery of zinc, the sulfur content of the con-
centrate is reduced to 2^> by roasting. Multiple-hearth or Ropp roasting
my be followed "by sintering, or double-pass sintering may be used alone.
Sintering in zinc smelters produces SOg which is converted into sulfuric
acid by the contact process. The sinter plant gases can be precleaned
by electrostatic precipitator, baghouses, or wet scrubbers.!/ The collection
of sintering fume involves a large volume of gases in the range of 1,300,000
scf/ton of zinc product. Zinc smelter sintering fume is difficult to collect
efficiently by electrical means because of its inherently high electrical
resistivity. This requires close control of gas temperature and moisture
content to maintain efficient collection.8/ Horizontal-flow, plate-type
precipitators have been installed on most of the newer zinc sintering machines.
Moisture and/or steam is normally added to improve dust resistivity for op-
timum precipitation. Mild-steel construction is common, and installed costs
fcr base collectors of 50,000 cfm would be $3.50/cfm.22/
Fluid-bed roasters have been used to process agglomerated feed.
Exhaust gases were cleaned in a waste-heat boiler, cyclones, and an electro-
static precipitator in series. The metallic composition of the dust is a
function cf roasting temperature, Figure 13-9.9/"
The fume-recovery facilities at a Canadian smelter operation have
been described.
10J
Data for the facilities are shown in Tables 13-8 and
13-9. These facilities used electrostatic precipitators for controlling
zhe emissions from zinc-roasting and lead-sintering operations. The zinc
roaster gases entered the precipitator at 420°F without pretreatment. The
lead sintering gases required conditioning in a spray tower.il/ The pre-
cipitators were very versatile, but the paramount problem was corrosion
caused by condensed vapors. The Doyle scrubber (Table 13-8) operates on
the principle of high velocity impingement of the dirty gas into water.
Recovery efficiencies were in the range of 98 to 99+$. The installed costs
(Table 13-9), are 1957 year costs, but are two to three times higher than
general cost figures given in Appendix A. However, the costs in Table 13-9
include gas pretreatment, inlet and outlet flues, and all accessories such
as rectifiers, dust conveyors, pumps, liquid cyclones, and instrumentation.
13.5 PRIMARY ALUMINUM PRODUCTION
Aluminum is produced by the electrolysis of alumina (AI2C3) in
fused cryolite (AIF3 - 3 NaF). Essentially all the alumna used is
extracted from bauxite. Alumina recovery from bauxite consists of sep-
arating the alumina from the various impurities of bauxite, a process
281
-------
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60
TO
60
50
40
30
20
10
1 1
ROASTER OVERFLOW
cyclone a flue ousts
PRECIPITATOR OUST
y
ZINC O
IRON A
Pa,Co a ao ~
/
/
/
/
/
/
- J.
* 0
-*•— /
\ X
~
/
s
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/ \
/
/
/
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*-
/ ' "
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t
/
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/
/
v.
«N.
»». •
V
p —. — — -CH
.IK
• —• — --—
930
1000 1050
MOO 1150
BED TEMPERATURE C.
Figure 13-9 - Dust Conposition vs. Roasting Temperature in Zinc Processing^/
282
-------
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TABLE (Concluded)
Treataer.t Plant
Tctai
Bo«
Bag
Total
Clcaaiaf
;
Xo. of (
:cBccr.cni
is/ 3tfs/
Mc. of
Dl&apt*
r Longth
Sq. ?t.
Cycle
TVpr- l? "qu'.pirr.t
•jnizs
Unit-
Caapmep.
t Ea us
(la.)
(ft.)
C.irth
fiatioi/
(dir..)
Fabric
?i-^hcjsr r.
L/>id rlist Furr.ic^i
50
1
396
7,320
5
ioi
.07,700
2.4
15
Or lor.
Slag Fusiing
".6
:c
le
2,eoo
5
iO
54,COO
3.5
S
Or lor;
Silver Rcfinrry Sc. 1
2
4
25
2C0
5
iC
2,750
2.3
2
Wcel
Siivur ref-ncry .Nu, 2
£
e
25
4C0
5
"0
7,5C0
1 .6
2
Or lor
Ar.t_swr.itk: L«*d Plant
4
i
25
ICO
3
10
1,075
4.1
15
Op ion
Cj*1 Crushing
3
l
:44
422
5
10s
5 ,920
2.3
35
Cotter,
Cdi.'ine Elevator
Rcas'.ers!-
¦;
:
120
260
5
10}
4,860
1.6
15
Cotter
r'i.w-
i
i2C
260
5
4,220
1.6
15
Criers
Leas SiJiterir.fi Nn. J*/ 5
i:s- P^sf-rc *
No cf if-cr.rts/
0A3
Velonty
4.S
*irts Fiat* s
Iran Aitcaimar
Trrvi Ircn
Material cf
Vcxtfcge Cinsjlr-j.-ticc
6C,000 u ia. ZsrirK wa_i, onck-
lin?d dust hcp7«rs,
voMen d**Kinfl-
60,000 3ricr rcnstru^tioa with
-«a.ld 5<®-s
nc. -f of
[Hi r.s Ccr.structi.cn
7ca'. Tryir.g 2
r.in; Piaster: .5
Pilot Plir.t Xiir. 1
Mild stcci
Mill ctcci
Mil i ctissl
Ecjle w.-t 3-rAbers
5:nt«r I'.ar.t Tryers
Sljvr?r rlinz
Total
ifo'.er J.K vf
of cn<«' Material ef F.ev iffiueat
Cccitructlcs STH Ccair^rf:.
1/3
**tic
36,COO with
31ess due
2,500
;_ S;«el «o;d
2C ,C-J0 l«au
4,00 Miic steei,
r»cp
Svwt:«
Velocity
it'/**:)
150
£ia: Suiphid
i'av.ucas
5,000 Wood v:th
CrxT. ".ry?"?
Pi.:ct rlint Klin
IS,COO Mild seee: 12 £ C-.1S 152
C-,C00 3:6 Stainless 3 3 C.24 150
steel
a O** then tc -DsoriAiun plant* fcr further vleaning tod SC'2 reeevery.
b/ At effitienry.
zj Iriet vo:ue« it t«creriture civided py a^iare feet of clcih.
i/ :ni«t vc.uce at teep«r\ture.
284
-------
TABLE 13-9
COSTS FOR CLEANING METALLURGICAL GASES (1957 DATAjg/)
Cost Items Included
Installed Maintenance
Inlet
Plant
Blast furnace
baghouse
Slag fuming
baghouse
Sintering electro-
static precipitator
Zinc roaster electro-
static precipitator
Four tadanac
dryer cyclones
Sinter dryer
scrubbers
Sinter ventila-
tion scrubber
CFM
Operating and
Installed Maintenance Tons of
Cost ^/l,000 No. of Dust/
$/ACFM Cu. Ft. Fans Pretreatment Building Day
262,000 225 4.35
193,000 250 4.80
160,000 150 5.10
147,000 420 4.65
38,800 300 1.93
106,000 275 1.90
3,000 100 2.23
0.19
0.26
0.22
0.13
Cooling
Cooling
Nil
Nil
Nil
Nil
Yes 70
Yes 250
Humidifying Yes 15
Yes 50
No
No
No
All sinter
scrubbers
292,000
0.07
20
Nil
No
20
-------
accomplished by chemical means. For this purpose, advanta.ge is taken of
the amphoteric properties of the aluminum ion, which permit the metal to
be solubilized in the form cf an alkaline aluninate, particularly the form
of sodium aluminate.
The Bayer process, shewn in Figure 13-10, is used in most cases to
recover the alumina. As shown in Figure 13-10,'following separation and wash-
ing hydrated alumina is fed to large rotary furnaces, similar to cement
kilns, wherein the alumina is calcined at about 1200"C. This operation is
necessary not only for the purpose of eliminating the 45# of water (including
the 30# combined water present in the hydrated material), but also for
giving some of the alumina the crystalline q- (or corundum) form, which is
most advantageous for electrolysis. These furnaces or kilns are significant
sources of particulate emissions. The calcined alumina for aluminum pro-
duction obtained from these kilns is in the form of a white powder consist-
ing of aggregates which range in size up tc about 100 p,, and which are made
up of monocrystals of anhydrous alumina at various stages of crystallization.
The alumina is next sent to a primary aluminum processing plant
where the alumina is converted to the metal by electrolysis. The heart of
the operation is the electrolytic cell where direct current dissociates
alumina into oxygen and molten aluminum metal. These cells are called
"pots" and are arranged to form potlines having several hundred cells per
potline. Each cell requires 40,000 to 100,000 amp. of current under normal
operating conditions. As shown in Figure 13-11 (prebaked anode cell), the
molten aluminum collects at the bottom of the bath above a carbon lining
which acts as the cathode. Oxygen migrates tc the carbon anode, forming
carbon dioxide or carbon monoxide at high cell temperatures which usually
reach 940°C.
Periodically aluminum metal is withdrawn, and fresh alumina feed
and bath chemicals added by piercing the frozen crust of the bath. Crust-
breaJcing agitates the bath and is a time of increased particulate and gaseous
emissions. Thermal buoyancy of heated air plays a large part in sweeping
finely divided alumina and bath fumes out of the cell. Ducts over the cells
capture some of the escaping fumes, but some elude capture and are emitted
into the building atmosphere and find their way to the atmosphere through
roof ventilators or "monitors," also shown in Figure 13-11.
While all aluminum production employs the basic Hall-Heroult
process, several variations in cell construction have evolved, based upon
the method of ancde manufacture. It is important to understand the dif-
ferences in cell construction because the type of cell employed will affect
the types and quantities of pollution generated. The types of cells are:
(l) the prebake cell; (2) the horizontal stud Soaerberg cell; (3) the
vertical stud Soderberg cell. Figures 14-12, 13 and 14 illustrate the
various cells.
286
-------
NaOH or NajCC^
Lime (if used)
Steam
recovered
steam
AL (OH3)
Priming
Wash water
Gas or fuel oi
Wash water
Calcined commercia
Alumina
Grinding
Mixing
Evaporation
Expansion
Final
filtering
Reheating
Calcination
Dilution
Temperature
exchange
Separation of
red muds
Precipitation
of AI (OH)3
Washing of
AI (OH)-,
Red muds
to waste
Separation of
Al (OH^
Washing of
red muds
Solution of
alumina
under
pressure
Figure 13-10 - Diagram of the Bayer Processi^/
-------
ROOF MONITORS
FUMES NOT
CAPTURED BY
POT LINE HOODING
EXHAUST TO
POTLINE SCRUBBERS
ANODE BUS BAR
ALUMINA
HOPPER
GAS COLLECTION
HOOD^>y
GAS AND FUME \
EVOLUTION
CARBON
ANODE
CRUST
MOLTEN ELECTROLYTE
ALUMINA
. MOLTEN ALUMINUM
CATHODE (-)
COLLECTOR
BARS
CARBON LINING
NSULATION
Figure .13-11 - Aluminum Cell (Prebaked Anode Type)i±/
288
-------
aluminum reduction cells
GAS COLLECTION HOODS
FROZEN CRUST OF
ELECTROLYTE AND
ALUMINA
STEEL SHELL
INSULATION
CARBON LINING
-VL
ELECTROLYTE
MOLTEN ALUMINUM
ANODE BUS BAR
ALUMINA HOPPER
.CARBON ANODES
GAS AND FUME EVOLVING
CATHODE COLLECTOR BAR
ro
CD
to
PREBAKE
Figure 13-12 - Prebake
ALUMINA HOPPERS
REMOVABLE CHANNELS
FROZEN CRUST OF
ELECTROLYTE AND
ALUMINA
STEEL SHELL
INSULATION
CARBON LINING
, VAMOl'tN .aiOminumi
FLUID PASTE
PARTIALLY BAKED ANODE PASTE
PASTE COMPARTMENT GASING
—POT ENCLOSURE DOOR
ANODE STUDS
FULLY BAKED CARBON
GAS AND FUME EVOLVING
CATHODE COLLECTOR BAR
ANODE CASING-
FROZEN CRUST OF
ELECTROLYTE AND —
ALUMINA
STEEL SHELL
CARBON LINING -
THERMAL INSULATION-
3
HORIZONTAL SODERBERG
Figure 13-13 - Horizontal Soderberg
U:
-BUS BAR
-RISERS
'—STUDS TO GAS'
! TREATMENT PLANT
ELECTROLYTE
MOLTEN ALUMINUM,^
LIQUID CARBON PASTE
BURNER
GAS AND TAR BURNING
BAKED CARBON PASTE
GAS EVOLVING
CATHODE COLLECTOR BAR
VERTICAL SODERBERG
Figure 13-14 - Vertical Soderberg
-------
In a prebake anode plant, pitch end coke are mixed, pressed and
baked before use In the cell. The carbon anodes are rectangular In cross
section and supported by copper or aluminum har.gers to the electrical bus-
bars overhead.
The other types of cells bake anodes at the cell itself by Intro-
ducing a carbon paste directly and using the heat of the melt to form the
carbon anode. Prebaking of the anode is therefore avoided, and continuous
operation of the cell is possible. Known as the Soderberg cell, one type,
the vertical stud Soderberg cell, is shewn in Figure 13-14. Paste is added
to the top of the cell and slowly carbonized as it moves toward the bath.
Metal studs carry electric current to the carbonized portion through the
top, and are positioned vertically with respect to the anode: hence, its
name. Cell construction allows gases liberated by the cell to be easily
collected and burned. Both vertical stud and horizontal stud Soderberg
exhausts are rich in hydrocarbons from the baking operation.
Hooding requirements for the horizontal stud Soderberg, shown
in Figure 13-13, are much more difficult because of the stud positions
along the side of the electrode rather than at the tcp. Continuous con-
sumption of the anode forces repositioning of the studs and necessitates
easy access to the anode. Requirements for easy anode access complicate
fume collection and do not allow burning of gas and tar at the cell
itself, as is practiced with the vertical stud Soderberg cell.
13.5.1 Emission Sources and Rates from Primary Aluminum Production
Little information is available about ejnounts of particulate
emissions from aluminum production plants. The major source of particu-
late emissions is the reduction cells, as discussed below. Secondary
sources are summarized in Table 13-4,Secondary sources include raw
materials handling, pot lining operations, anode preparation (prebake
plants), cleaning operations, and aluminum refining.
13.5.1.1 Reduction Cells: Reduction cell emissions can be divided
into roof monitor emi66ions and the potline control system emissions.ii/
The roof monitor emissions are emitted at the building height along the
entire length of the building and may be considered a line source. Pot-
line control system emissions are emitted from stacks.1^/
Actual emissions vary widely from plant to plant, depending upon
age, cell type, operating procedure, and efficiency of the hoods over the
ceils.
290
-------
13.5.1.2 Anode Furnace: The anode furnace is a source of fluoride,
sulfur dioxide, and particulates in prebake plants. Sulfur dioxide emis-
sions will depend upon the sulfur content in the pitch and the coke of the
anode.
13.5.1.3 Casting Furnace: Aluminum casting furnaces also emit
particulate pollutants. In the casting furnace aluminum from the primary
cells is refined by heating and by chlorination. Products of the reaction
are aluminum chloride, aluminum oxide and heavy metal chlorides liberated
from impurities. Free chlorine and hydrochloric acid are likely to be
present in the off gas.
13.5.1.4 Summary of Emission Rates; Table 13-1 summarizes the
emission rates from the various stages in the production of primary alumi-
num. Emissions from the reduction cells currently total about 65,000 tons/
year.
13.E.2 Characteristics of Effluents from Primary Aluminum Production
The chemical and physical properties of effluents from primary
aluminum production are summarized in Table 13-2. Particulates emitted from
the refining and casting furnaces range in size down to submicron levels.
The particulates are abrasive and corrosive. Fluorides, both gaseous ar.d
particulate, are a component of emissions from the reduction cells.
13.5.3 Control Practices and Equipment for Primary Aluminum Production
The control of emissions from the on-site operations of bauxite
drying and alumina calcining involve high dust concentrations which fre-
quently dictate the use of multicyclones for preliminary particulate col-
lection, usually followed by electrostatic precipitators. Fabric filtra-
tion can be used if close temperature control is practiced. Collection
efficiencies of 99.7+$ have been reported for such systems.^2/
Reported process flows of from 25,000 to 250,000 acftn result in
small-to-moderate sized installations. Installed costs for combined multi-
cyclone/electrostatic precipitators would range from $4.60/cfm for the lower
volumes, through $2.30/cfm for the higher, at 99+# overall collection effic-
iencies. These costs exclude auxiliaries.^2/
Control of fluoride and particulates frcm aluminum cell rooms can
be classed as;.
(1) Capture of cell effluents by potline hooding,
(2) Subsequent collection of captured pollutants in scrubbers, etc.
(3) Scrubbing of roof "monitor" emissions.
291
-------
Because the choice of electrolytic cell determines the design of hooding
and collectors, controls will "be discussed separately for the prebake and
Soderberg cells. Most of the following discussion and information is . *
from the report "Air Pollution from the Primary Aluminum Industry" by
the Washington State Department of Health.
13.5.3.1 Vertical Stud Soderberg Cell: The vertical stud
Soderberg cell captures cell effluents most effectively because placement
of the anode studs in a vertical position allows a metal skirt to be fixed
to the lower end of the steel anode jacket. The skirt reaches down to the
encrusted bath and effectively encloses the fuming bath. Gases are, there-
fore, drawn off with little dilution by air and are concentrated enough
to allow combustion of the tarry hydrocarbons. During burning, hydro-
carbons are reportedly reduced from 3 to 0.1$ by volume, and most fluori-
dated carbon compounds converted to hydrofluoric acid. The effective
oxidation of tar is a great aid to subsequent collection because tar con-
tamination and plugging of ducts are avoided. After burning, exhaust
fumes from each pot are sent tc a central header fan and control equip-
ment. One piece of control equipment will commonly treat exhaust fumes
from 15 pots.
Control devices used for vertical stud Soderberg cells have
included multiclor.es and spray-type scrubbers. The scrubbers use high
pressure sprays to contact countercurrently the gases and particulate.
Such a system can remove 95$ of the fluorides entering the control sys-
tem, but no figures for total particulate collection efficiencies are
reported. Exhausts may be treated by bag filters coated with lime cr
alumina, or by electrostatic precipitators, but the residual tar creates
a fouling problem in the collection system.
A recent addition to the family of collectors is the sieve plate
scrubber shown in Figure 13-15. The device has been put into operation
in Norway. A three-plate tower has removed 97$ of the hydrogen fluoride,
80$ of the solid fluoride particles and 70$ of the total particulate in
incoming gas streams. Higher absorption efficiencies are possible with
the addition of a fourth plate. The design allows self-cleaning of the
plates by the use of sprays directed at the underside of each plate where
heavy tar and particle deposition occur. High-velocity droplets, impelled
by the air flowing through the restriction, are blown against the plate
and are forced to the top by the air stream, thereby preventing plugging
of the sieves. Particulate collection is by impingement on the plates and
the water droplets . The tower produces hydrofluoric acid used as recircu-
lation liquor for the first plate.
Another collection system is shown in Figure 13-16. The system
incorporates dry cyclones, an electrostatic precipitator and two scrubbers.
292
-------
GAS OUTLET
DROP CATCHER
SIEVE PLATE
FUNNEL
OVERFLOW DEVICE
WATER INLET
GAS INLET
ACID PRODUCT
CIRCULATION PUMP
Fier-ire 13-15 - Schematic Drawing of Cross-Sectional View of the
New Sieve-Plate Gas Scrubber!®/
ELECTROSTATIC
PRECIPITATOR
WET SCRUBBERS
STACK
MAIN DUCT
BURNER
« -I
SPRAY
SEPARATOR
COOLING Vg
WATER r-Hf
FAN
CYCLONE
Figure 13-16 - Purification Installation for Cell Gasesi^/
293
-------
The system achieves 99.9$ gaseous fluoride collection, but particulate ef-
ficiencies were not given. When a scrubber is used for both gaseous and
particulate fluorides, the particulates are frequently more difficult to
collect, and dictate the power requirements of the scrubber.
13.5.3.2 Horizontal Stud Soderberg Cell: Effective capture of
all effluents for a horizontal stud Soderberg cell is much more of a prob-
lem, because open channels are required for replacement and readjustment of
the studs. As a result, hooding is less complete; therefore, larger volianes
of air are entrained. Large volumes of exhaust air create a dilute mixture
of hydrocarbons. Because burning is not possible, a tar-fouling problem
occurs in ducts and control equipment. Cyclones or multiclones and bag
houses have fouled too easily to be an effective answer to control with
horizontal stud Soderberg cells. Where electrostatic precipitators are
attempted, the plates require water flushing to prevent fouling by tars.
Existing controls have consisted of scrubbers, either grid packings in a
vertical scrubber or the high-velocity spray type. The lack of primary
collectors makes these scrubbers especially susceptible to plugging by
particulate matter.
To solve this problem, the Alcan Company developed the floating
bed scrubbers whose principle is shown in Figure 13-17. A bed of light
polyethylene spheres is shown at rest with no air-liquor flow. The bed
becomes fluidized upon operation and the spheres are free to rotate and
agitate. Liquor flows down through the interstices, contacting the gases
in the air stream, while at the same time washing the spheres. Most
importantly, the constant motion of the spheres prevents accumulation of
tars on the spheres. Collection efficiencies for the floating bed scrubber
are detailed in Table 13-10 for a single bed installation having pressure
drops 4 to 6 in.
TABLE 13-10
COLLECTION EFFICIENCIES FOR THE FLOATING BSE SCRUBBER
USED ON HORIZONTAL STUD SODERBERG CELL
Substance Collection Efficiency (j)
Total fluorides 90+
Hydrogen fluorides 98+
Particulates 80-90^/
a/ Anticipated efficiency at higher pot ventilation rates of 3,600 scfm
and when doors are closed.
294
-------
CLEAN GAS
MIST ELIMINATOR
FROM
RECIRCULATION
PUMP
SCRUBBING LIQUOR
RETAINING GRID
FLOATING BED OF
LOW-DENSITY SPHERES
RETAINING GRID
FEED GAS
MAKEUP LIQUOR
TO
RECIRCULATION
PUMP
'"////////////////////////////////////A
r /"//////////////////////////////"//'}
\S///////////s///////////////S/JS/£jjS
TO DRAIN
OR RECOVERY
Figure 13-17 - The Floating Bed Scrubber Developed for Horizontal
Stud Soderberg Cell Exhaustaii/
295
-------
A second floating bed can be added, increasing the collection ef-
ficiencies and the pressure drop another 4 in. of water. However, an addi-
tional bed will require use of a larger horsepower fan to overcome increased
press-ore drops.
In summary, control problems of the horizontal stud Soderberg cell
have lessened its economic advantage over the prebake cells. Additional
research to overcome the hydrocarbon fouling problem will be needed.
13.5.3.3 Prebake Cells: The prebake potline operation requires
an on-site carbon-anode baking plant. Particulate emissions from these
ovens include tars and inorganic ash. Detarring by electrostatic precipi-
tation has been reported at over 99.9$ abroad. Close temperature control
is required both to fractionally condense the volatile tars, as well as to
maintain free-flowing properties of the precipitate. Detarring gas temper-
atures of from 115°F to 160°F have been reported.£2/
Hooding for prebake cells is similar to the vertical stud
Soderberg, but ventilation rates are much greater. One exception to this
generalization is the Pechiney process which employs no local exhaust ven-
tilation over cells at all, but instead relies upon roof-monitor emissions
control to collect pollutants.
Particulate emissions from prebake pots contain none of the tar
found in the horizontal stud Soderberg; instead, "dusting" of the carbon
anode produces carbon particles in addition to alumina, etc. Current con-
trols have consisted of dry-type cyclones or electrostatic precipitators fol-
lowed by wet scrubbers. Scrubbers are 12 to 15 ft. in diameter and 40 to
60 ft. high with internally mounted spray headers.
The newest controls being developed have relied upon a dry ab-
sorption of fluoride gases (and perhaps particulates) upon finely divided
alumina powders. The alumina dust and any other particulate are then col-
lected in a baghouse, and the catch is sent to the cell as the feed. A
solid particle coating of alumina on the inside bags also aids in fluoride
collection. Dry collection avoids all the plugging and high water costs of
scrubbing towers, while allowing the dust to be returned directly to cells
in a dry form. Performance data are extremely scarce on this unit as it is
still in the development stages, but total particulate collection of 99$ and
gaseous fluoride efficiencies of 95$ have been estimated.
13.5.3.4 Efficiency of Current Potline Controls: Efficiency data
for current and prototype control devices are summarized in Table 13.11.
Existing particulate control efficiencies vary from 40 to 60$, except where
an electrostatic precipitator is used in conjunction with other devices.
296
-------
TABLE 13-11
CURRENT AND NEWEST AIR POLLUTION CONTROLS FOR PRIMARY ALUMINUM POTLINE AIR POLLUTION CONTROLSii/
Type of
Cell
H.S.
Existing
Collectors
Soderberg
Spray scrubbers
Est. Removal Efficiencies, $
Fluor idesjj/Particulates
80-90
40-50
Latest
Collectors
1. Floating bed
scrubber-2/
2. Wetted plate
electrostatic
(with condi-
tioning of
flue gases)
Est. Removal Efficiencies,
Fluorides^/ Particulates
90
90
80-90
99
Prebake
V.S.
1/
Multiclones
Dry electrostatic
precipitators
Spray scrubbers
Soderberg multi-
clones
Spray scrubbers
80-90
0
80-90
< 60
90
40-50^/
< 10^/
< 60
40-50
Fluidized 99
alumina con-
tacts cell
exhausts, fol-
lowed by collec-
tion in alumina
coated baghouse
Counterflow 90
packed scrubber
Sieve plate 95
scrubber
96-98
95
70
a/ Gaseous and particulate fluorides,
b/ H.S. = horizontal stud,
cJ One section of bed employed.
d/ When used after multiclones,
ej When used after e.s.p.
f/ V.S. = vertical stud.
-------
13.5.3.5 Roof Monitor Controls: Pot fumes that escape collec-
tion by the hooding are emitted through roof vents, called monitors. The
sources of building ventilation air are usually adjustable louvers located
in the building wall along the side to cool the building and sweep contam-
inants away from worker's breathing zones. Air may also enter through grat-
ings in the floor. The volume of monitor discharges will depend upon the
louver adjustment as well as wind speed and temperature difference. Air
turnover in the building approaches 30 to 40 changes per hour.
Most aluminum plants presently have no monitor controls. Where
controls have been applied, filament mats or screens are placed in the path
of monitor fumes and wetted by sprays. Figure 13-18 shows a roof monitor
scrubber—r.o fans are employed. Efficiency of gaseous fluoride collection
is reported at 60-70$. No efficiencies for particulate collection have
been reported. However, it .is doubtful that much, if any, total partic-
ulate collection occurs, given the low pressure drop of the scrubber.
i—EXHAUST FAN
oo
SPRAY NOZZLES
SPRAY SEPARATOR
ELECTROSTATIC
FILTERS
SPRAY NOZZLES
WATER COLLECTING TROUGH
Figure 13-18 - Roof Scrubbers*^/
298
-------
A more advanced version of the spray chamber scrubber has been
reported in the German literature. The spray mats are preceded by electro-
static filters to remove particulate and spray scrubbers dispensing water
over wire mesh. Nozzles are positioned so as to clean the mesh of particu-
late matter and prevent clogging. Ninety percent removal of gaseous fluor-
ide is reported, but no figures are given for particulate natter. Exhaust
fans are mounted at the outlet of the spray chamber.
For the plant practicing no hooding ventilation (Pechiney process)
and instead emitting all fumes from the monitor, washers appear to be sim-
ilar to the C-eman roof monitors. However, nc electrostatic prefilter is
present, and the sprays are horizontal rather than vertical. Nc collec-
tion efficiencies have been supplied for the pechiney process controls.
13.5.3.6 Other Sources: In addition to roof monitors and pot-
lines, aluminum plants also emit particulates and gases from auxiliary op-
erations. Data on emissions and possible control systems for other sources
are even scarcer than for the reduction cell exhaust. In prebake plants, the
anode furnace is a source of fluoride, sulfur dioxide, ar.d particulate emis-
sions. In the prebake furnace, carbon anodes are baked for periods of two
or three veeks prior to their use in the reduction cell. Natural gas is
usually employed to take the anodes. Existing controls consist of the spray
scrubber, which is efficient in removing fluorides and fairly efficient for
control of sulfur dioxide, but the controls are, unfortunately, very poor
for particulate emissions control. In fact, one plant in Washington State
using Pease Anthony scrubbers on the bake ovens emitted an effluent plume
¦with a No. 3 and Nc. 4 Ringelmann rating because the relatively inefficient
scrubbers cannot touch the fine smoke fume. Incineration, followed by
medium pressure drop scrubbing, has been suggested, but natural-gas costs
for incineration are regarded by aluminum companies as being prohibitively
high. Particulate emissions for an uncontrolled anode furnace are reported
at under 5 lb/ton of aluminum produced. Sulfur dioxide emissions will de-
pend upon the sulfur content in the pitch and the coke cf the anode.
Aluminum casting furnaces also emit particulate and gas. In the
casting furnace aluminum from the primary cells is refined by heating and
by chlorination. Products of the reaction are aluminum chloride, aluminum
oxide and heavy metal chlorides which are given off as fume. Free chlorine
and hydrochloric-acid may also be present in the gases from the casting
furnaces. Control of emissions from the casting furnaces present many of
the same problems that are present with reduction cell exhausts. One
potential control device is a multistage floating bed scrubber.±£/ In
this system, caustic is used as the scrubbing medium, not only to effect
particulate matter removal, but also to react with the acid gases.
Reportedly, the particulate can be lowered to 0.04 grain/scf.i^/
299
-------
One piece of data on uncontrolled units estimates emissions at
4 l"b/ton of aluminum, expressed as chloride. Uncontrolled units would emit
a characteristic white plume.
Other miscellaneous sources in aluminum reduction plants are raw
materials unloading in transfer operations which have been controlled by
baghouse collectors. One Washington plant has also calculated that coke
dust emissions from a coke calciner have been controlled to a O.S lb/ton
when cyclones are used.
13.5.3.7 Control Costs: Literature data on the cost of control
devices for the aluminum industry are sparse. One plant manager in Washington
State produced information that a recent installation of a new potline re-
sulted in an expenditure of 14$ of the capital cost for control devices.
However, these devices do not meet regulations currently being imposed or
contemplated by regulatory agencies in Washington State.
300
-------
REFERENCES
1. "Systems Study for Control of Emissions—Primary Nonferrous Smelting
Industry," Final Report, Contract FH 86-65-85, National Air Pollution
Control Administration, Arthur G. McKee & Company, June 1969.
2. "Restricting Dust Emissions from Copper-Ore Smelters," Verein Deutscher
Ingenieure, VD 1, p. 2101, January 1960.
3. Personal communication, industrial source.
4. Stern, A. C., Air Pollution, Vol. Ill, New York, Academic Press, 1968,
pp. 174-179.
5. Ibid., pp. 179-182.
6. "Restricting Dust and Sulfur Dioxide Emission from Lead Smelters,"
Verein Deutscher Ingenieure, VD 1, p. 2285, September 1961.
7. Wallis, E., "Atmospheric Pollution and the Zinc Industry," Chemistry
and Industry, October 1955.
8. Johnson, G. A., "Air Pollution Prevention at a Modern Zinc Smelter,"
Air Repair, February 1954.
9. Roggero, C. E., "High Temperature Fluid Bed Roasting of Zinc Concen-
trates," Transactions of the Metallurgical Society of AIME, February
1963.
10. Hargrave, J. H. D., "Recovery of Fume and Dust from Metallurgical Gases
at Trail, B. C.," The Canadian Mining and Metallurgical Bulletin,
June 1959.
11. Bainbridge, R., "New Developments in Smoke Control at Cominco," Journal
of Metals, November 1956.
12. "Air Pollution from the Primary Aluminum Industry," A Report to Washington
Air Pollution Control Board, Office of Air Quality Control, Washington
State Department of Health, Seattle, Washington, October 1969.
13. Tomany, J. P., "A System for Control of Aluminum Chloride Fumes,"
Journal of the Air Pollution Control Association, Vol. 19(6), 420-423,
June 1969.
301
-------
14. Robertson, D. J., "Filtration of Copper Smelter Gases at Hudson Bay
Mining and Smelting Company, Ltd.," The Canadian Mining and Metal-
lurgical Bulletin, May 1960.
15. 'J. S. Department of Health, Education and Welfare, Control Techniques
for Particulate Air Pollutants, January 1969.
16. Sproull, W. T., "Collecting High Resistivity Dusts and Fumes," Industrial
and Engineering Chemistry, Vol. 47(5), 940-943, 1955.
17. Sproull, W. T., "Operation of Cottrell Precipitator," Industrial and
Engineering Chemistry, Vol. 43(6), 1350-1358, 1951.
18. Pottinger, J. F., ''Collection of Difficult Materials by Electrostatic
Precipitation," Australian Chemical Proc. and Eng., Vol. 20(2), 17-23,
1967.
19. Kirk and Othmer, Encyclopedia of Chemical Technology, 2nd edition,
Interscience Publishers, New York, 1968.
20. Koncnka, A. P., "Particulate Control Technology in Primary Nonferrous
Smelting," Presented at Third Joint Meeting of AIChE, Denver, Colorado,
September 1970.
302
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CHAPTER 14
CLAY PRODUCTS
14.1 INTRODUCTION
The clay product, or ceramic, industries have as their finished
materials a variety of articles that are essentially silicates. These
products may be classified as: (1) whitewares; (2) heavy clay products;
(3) refractories; (4) enamels and enameled metal; and (5) glass. The
three main raw materials used in caking common. ceramic products are:
(l) clay, (2) feldspar, and (3) sand. In addition, a wide variety of other
minerals, salts, and oxides (borax, soda ash, cryolite, alumina, chromite,
and magnesite) are used as fluxing agents and special refractory ingredients.
Clay or ceramic products are manufactured "by a series cf processes
involving grinding, screening, calcining, blending of the raw materials,
forming, drying or curing, firing, and final cutting and shaping. Particu-
late emissions occur during handling of raw materials, grinding, calcining,
screening and blending, and during cutting and shaping operations. Meager
data were found for emission rates from these sources. The particulate air
pollution potential of this industry group is not well defined.
Manufacturing processes, particulate emission sources, particulate
emission rates, effluent characteristics, and control practices and equip-
ment for the major portions of the clay products industry are discussed in
the following sections.
14.2 MANUFACTURH'G PROCESSES
14.2.1 Ceramic Clay
The manufacture of ceramic clay involves the conditioning of the
basic ores by several methods. These include the separation and concentra-
tion of the minerals by screening, floating, wet and dry grinding and blend-
ing of the desired ore varieties (Figure 14-1). The basic raw materials
in ceramic clay manufacture are kaolinite (Al203*2Si02'2H20) and montmoril-
lonite (Mg, Ca) 0"Al203"5Si02*nH20) clays. These clays are refined by
separation and bleaching, blended, kiln dried, and formed into such items
as whiteware, heavy clay products (brick, etc.) and various stoneware and
other products, e.g., diatomaceous earth used as a filter aid.£/
303
-------
Beneficiation
Raw
Material
Trommel
P- Particulates
NO* - NO, N02
F" - Fluoride
Thickener
Waste
lU
+++
Filter
T
Waste
Selective
J Settling
Dryer
By product
waste
P, NO., F"
P
t
Bagging
-*-Clay storage
Shipment
1 1
t
Clay
P, NO„F'
Bleaching
Air, Reaction Gos
Bleached
Product
P, NO,, F"
Reacted gas*
* Reaction Gas may include
chlorine and carbon tetrachloride
or other bleaching agents.
Figure 14-1 - Ceramic Clay Manufacturing Processes^/
304
-------
Halide bleaching for preparation of kaolinite utilizes the re-
activity of the halide to remove the chemically active and unwanted con-
stituents of the clay ore leaving behind a purified white product suitable
for ceramics manufacture. Figure 14-1 includes a schematic diagram of this
process.2/
The manufacture of filter and activated clays includes grinding
and wet or acid treating, followed by drying and regrinding. The drying is
accomplished in rotary kilns, which reduce moisture content from 15-20$
to 10$.
Ceramic clay is manufactured from a mixture of wet talc, whiting,
silica clay, and other ceramic materials. This mixture is dried in a
spray dryer.
14.2.2 Heavy Clay Products
The manufacture of brick and related products such as clay pipe,
pottery, ana some types of refractory brick involves the grinding, screen-
ing, blending of raw materials, forming, drying or curing, firing, and final
cutting or shaping«/ Bricks are manufactured by one of three processes:
the soft-mud, the stiff-mud, or the dry process. The soft-mud process con-
sists in molding the clay mixture containing 20-30$ water in molds coated with
a thin layer of either sand or water to prevent sticking. The molded brick
is then burned. This soft-mud process is used for firebrick.i/
In the stiff-mud process, the clay is just wet enough (12-15$) to
stick together when worked. The clay is forced out through a die in a
screw or auger machine.i/ The extruded clay bar passes along a short belt
conveyor onto a cutting table, on which a frame with a number of wires
automatically cuts the bar into appropriate lengths. The bricks are then
burned. 1/ ' "
The stiff-mud process is employed for the manufacture of prac-
tically every clay product, including all types of brick, sewer pipe, drain
tile, hollow tile, fireproofing, and terra cotta. The greater percentage of
clay ware is made by the stiff-mud process.i/
In the dry-press process the water content is from 4-7$, which
makes the clay relatively nonplastic. The brick unit is molded at pressures
around 5 tons/sq in. and then dried.
The drying and firing of bricks, both common and refractory, is
accomplished in many types of ovens. The most popular type is the long
tunnel oven in which the bricks, loaded on steel carts, pass counter-
currently against the heat flow. Total heating time varies, but is usually
305
-------
50-100 hr. for 9 in. refractory bricks. Normally gas or oil fuel is used
for heating, but coal may be used. Temperatures up to about 2C00°F are
used in firing common brick.
14.2.3 Refractories
Refractories are those materials which are used to withstand the
thermal, chemical, and physical effects that occur in furnaces. Refrac-
tories are sold in the form of firebrick, silica brick, magnesite brick,
chromite brick, magnesite-chromite brick, zirconia refractories, and others.
In making a refractory, the main material is selected on the basis of the
thermal, chemical, and mechanical conditions to be encountered in service
applications.1/
The usual operations in manufacturing refractories include grind-
ing ar.d screening, calcining, mixing, pressing or molding and repressing,
drying, and burning. Usually the most important single property required
is high-bulk density, which affects many of the other important properties.
The multiplicity of refractory products results in a highly
variable process flowsheet. Depending upon the desired product, raw ma-
terials may be calcined or dried prior to mixing and blending. Figure 14-2
illustrates an overall flowsheet for a typical plant producing a kiln-fired
refractory. li The decision to calcine or dry the raw material depends upon
its end use. The type of clay, refractory brick, and ultimate density are
among the factors that influence the decision.3/
Castable or fused-cast refractories are manufactured by carefully
blending such components as alumina, zirconia, silica, chrome, and magnesia,
melting the mixture in an electric-arc furnace at temperatures of 3200-4500°F,
pouring into molds, and slowly cooling to the solid state. Fused refrac-
tories are less porous, and more dense than kiln-fired refractories. 2/
Castable refractories are employed in glass furnaces, as linings
of hot zones of rotary kilns, in boiler furnaces exposed to severe duty,
and in metallurgical equipment such as forging furnaces.i/
14.3 EMISSION SOURCES AND RATES
14.3.1 Ceramic Clay
Particulate emissions occur from raw materials handling, grinding,
drying, and firing kilns. Fluorides and acid gases may also be emitted in
the drying process. Factors affecting emissions include type and quantity
of material processed, the type of grinding (wet and dry), the temperature
306
-------
CALCINER
DRYER
MIXING
STOCKPILE
BURNING
RAW CLAY
PRIMARY
CRUSHING
BLENDING
(USUALLY WET)
QUARRY
BLASTING, MINING
SECONDARY
GRINDING OR
MILLING
PRODUCT
Fig-ore 14-2 - Refractories Manufacture Flew Diagram
207
-------
of the drying kilns, gas velocities in the drying kilns, the flow direction
in drying kilns, and the amount of fluorine in the ores.£/ Insufficient data
exist to determine if there is a correlation between dryer types and emissions.
14.3.2 Heavy Clay Products
Particulate emissions occur during handling of raw materials,
grinding,screening, and "blending, and during cutting and shaping operations.
Fluorides, largely in a gaseous form, are also emitted from brick manufac-
turing operations.£/
The extent of raw material handling and processing greatly affects
the dust emissions from this phase of the manufacturing process. Emissions
when firing and/or curing the formed bricks are affected by the temperature
in the ovens and the type ana quantity of trace components in the brick.
Thus, sulfur and/or fluoride compounds may be emitted when the bricks are
subjected to high temperatures. The type of fuel used to heat the ovens
also has a direct bearing on the combustion emissions.
14.3.3 Refractories
Particulate emissions in kiln-fired refractory plants occur from
raw materials handling, crushing, calcining, drying, mixing, and burning
operations. Emissions from the calcining and drying operations depend upon
the type and quantity of material charged, kiln and dryer types, and final
moisture content.
Particulate emissions from the manufacture of castable refrac-
tories are created by the drying, crushing, handling, and blending phases
of this process, the actual melting process, and in the molding phase.
Fluoride emissions, largely In the gaseous form, may also occur during the
melting operations. Particulate emissions are affected by the amount of
material handling and pre-treatment required before melting, and by the
components in the melt. Generally, increasing concentrations of silicon will
cause increased particulate emissions.
14.3.4 Summary of Emission Rates
Table 14-1 presents a summary of emission rates from the manu-
facture of clay products. Current emissions are estimated at 467,000 tons.
Data available on emission rates, processing variations, and control equip-
ment practices and utilization are meager, and emission figures in Table
14-1 are considered to be engineering estimates.
308
-------
TABLE 14-1
PARTICULATE EMISSIONS
CLAY PRODUCTS
Efficiency Application Net
of Control of Control Control
Source Quantity Bnission Factor Cc Ct Cc*Ct
Ceramic Clay
7,870,000
tons
A. Grinding
60$ of ceramics
76
lb/ton
prod.
0.60
B. Drying
100$ of ceramics
70
lb/ton
prod.
0.60
Refractories
3,440,000
tons
A. Kiln-Fired
1. Calcining
20$ of kiln-fired
200
lb/ton
prod.
0.64
2. Drying
30$ of kiln-fired
70
lb/ton
prod.
0-64
3. Grinding
100$ of kiln-fired
76
lb/ton
prod.
0.6-1
B. Castable Refracts.
550,000
tons
225
lb/ton
prod.
0-77
C. Dead-Burned Magnesite
125,000
tons
250
lb/ton
prod.
0.56
D- Mortars
120,000
tons
1. Grinding
76
lb/ton
prod.
0.60
2. Drying
70
lb/ton
prod.
0.60
E. Gunning Mixes
250,000
tons
76
lb/ton
prod.
0.60
III. Heavy Clay Products 23,700,000 tons
A. Grinding 20$ of heavy clay 7G lb/ton prod. -- -- 0.60
B. Drying 30$ of heavy clay 70 lb/ton prod. — — 0.60
Total for Clay Products
Emissions
tons/yr
72,000
110,000
25,000
13,000
47,000
14,000
7,000
2,000
2,000
4,000
72,000
99,000
467,000
Note: Values reported for net control are assumed numbers
-------
14.4 EFFLUENT CHARACTERISTICS
Limited data were found on the chemical and physical properties
of effluents from clay products manufacture. Available data are presented
in Table 14-2.
Emissions from the electric-arc furnace are condensed fume and
consist of very fine particles, largely 2 (j, or smaller' Kaolin and bauxite
particulates emitted from rotary calcining kilns rar.ge from 25-40 wt. $
less than 10 (j,, while particulates from a magnesite kiln may be 50 wt. $
< 10 |A.
14.5 CONTROL PRACTICES AND EQUIPMENT
Common control techniques for the ceramic clay manufacturing
processes include settling chambers, cyclones, wet scrubbers, electrostatic
precipitators and bag filters. Cyclones for the coarser material followed
by wet scrubbers, bag filters or electrostatic precipitators for dry dust
are the most effective control techniques.
A variety of control systems may be used to reduce both particulate
and gaseous emissions from heavy clay products manufacturing. Almost any
type of particulate control system will reduce emissions from the materials
handling process. However, good design and hooding are required to capture
the emissions. Fluoride emission can be reduced to very low levels by using
a water scrubber. 2/
The general types of particulate controls may be used on the ma-
terials handling aspect of refractory manufacturing. However, emissions
from the electric-arc furnace are largely condensed fume and consist of very
fine particles, largely 2 |j, or smaller. Baghouses may be used to control
particulate emissions from the furnace.i/
Ntilticyclones, beghouses, and electrostatic precipitators have
been used on rotary and vertical kilns in kiln-fired refractory plants..5/
310
-------
TABLE 14-2
A. Particulate
EFFLUENT CHARACTERISTICS - MANUFACTURE OF CLAY PRODUCTS*
Source
Refractories
a. Bauxite calcine
kiln
b. Magnesite cal-
cine kiln
c. ELectric arc
furnace
Particle Electrical Moisture
Particle Size Solids Loading Chemical Composition Density Resistivity Content Toxicity
25-40 < 10
50 < 10
100 < 2
B. Carrier Gas
Source
Ceramic Clay
a. Rotary dryer
b. Kiln and
cooler
c. Spray dryer
Flovrate
Tempera-
ture
a) 23.8 (one
dryer)
a) 23.9-27.3
(tvo units)
a) 10.5 (one
unit)
66
159-160
244
Moisture Chemical
Content Composition Toxicity
Flanmability
Corro- or Explosive Optical
sivlty Odor Limits Properties
* See Coding Key, Table 5-1, Chapter 5, page 45, for units for individual effluent properties.
-------
REFERENCES
1. Shreve, R. N., Chemical Process Industries, 2nd Ed., McGraw-Hill, 1956.
2. Air Pollution Tftnission Factors, NAPCA Report, Contract No. CPA 22-69-119,
April 1970.
3. Private Communication, R. Besalke, A. P. Greene Company, Merch 1970.
312
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CHAPTER 15
FERTILIZER MANUFACTURE
15.1 INTRODUCTION
Fertilizer consumption has increased so rapidly in the past
quarter century that manufactured fertilizer has become the major product
of the chemical industry throughout the world. The primary manufactured
fertilizers are phosphates, nitrates, ureas, and sulfates.
The pollution potential of a fertilizer plant can "be divided
intc separate types: coarse dust, wet solids, odorous or corrosive gases,
and vapors. Emissions result from roasting, acidulation processes, dry-
ing, granulation, and blending operations.
Manufacturing processes, particulate emission sources, particulate
emission rates, effluent characteristics, and control practices and equip-
ment for each major fertilizer category are discussed in the following
sections.
15.2 PHOSPHATE FERTILIZERS
15.2.1 Phosphate Rock Preparation
Phosphate rock preparation involves beneficiation to remove
impurities, drying to remove moisture, and grinding to improve reactivity.
Phosphate rock deposits have widely varying compositions and properties.
The presence of a high content of organic matter is undesirable. Organic
matter tends to stabilize a foam blanket on the surface of the acid reactors,
and it produces a slimy gypsum filter cake which is slow filtering and
difficult to wash. Organics are removed by roasting the rock between
1200 and 1600"F. The roasting is done in a variety of furnaces.
Usually, direct-fired rotary kilns, 25-100 ft. long, 8-10 ft.
in diameter, are used to dry phosphate rock (Figure 15-1), These dryers
use natural gas or fuel oil as fuel and are fired countercurrently. From
the dryers, the material may be ground before storage and is finally con-
veyed to large storage silos. Emissions from these processes consist
primarily of fine rock dust, but some sulfur dioxide may be present in
the dryer exhaust from the combustion of sulfur in the fuel.
313
-------
EXIT
(PARTICULATE)
EXIT
(PARTICULATE S02)
EXIT
(PARTICULATE)
WET
PHOSPHATE
ROCK
IFULE: NATURAL GAS OR FUEL OIL
DRYER
STORAGE SILO
GRINDING MILL
STORAGE BINS
PHOSPHATE ROCK
DUST SILO
Figure 15-1 - Flow Diagram of Phosphate Rock Storage and Grinding Facilities,
Noting Potential Air Pollution Sources
-------
Other points of emission in a phosphate rock grinding and prep-
aration plant are transfer points on conveying systems and discharge points
at storage hoppers and silos.
15.2.2 Wet Process Phosphoric Acid
Wet-process acid is produced by treating fluorapatite
[Ca10(P04)gF2] or phosphate rock, with sulfuric acid. Phosphoric acid is
formed, calcium sulfate is precipitated and filtered off, and the acid is
concentrated from about 32$ to about 54$ P20s- Virtually all the wet-
process acid produced in this country is used in the manufacture of various
phosphate fertilizers.§/
Most current process variations for producing wet-process phos-
phoric acid depend on decomposition of phosphate rock by sulfuric acid
under conditions where gypsum (CaSC>4 • 2H2O) is precipitated. Several
variants of this process are offered by various contractors. The Dorr-
Oliver, St. Gobain, Prayon, and Chemico processes are among the better
known.6/ In spite of the number of contractors in the field, new plants
do not seem to differ fundamentally among themselves. In addition, several
general trends are evident, such as the use of single-tank instead of mul-
tiple-tank reactors, one or two large horizontal tilting-pan filters, large
plants of 1,000 ton/day capacity and more, and closed systems where
atmospheric emissions are minimized. Figure 15-2 is a flow diagram of a
modern, wst-process phosphoric acid plant.6/
Finely ground phosphate rock is metered accurately and continu-
ously into the reactor, and sulfuric acid is added. The single-tank reac-
tor illustrated in Figure 15-2 is a circular, two-compartnent system wherein
reactants are added to the annular volume and the central volume is used
for growing gypsum crystals. Some years ago, plants were built with several
separate reaction tanks connected by launders, which are channels for slurry
flow. The tendency now is to use a single tank with several compartments.
In some of these designs, the slurry flows over and under a series of baffles.
Proper crystal growth depends on maintaining sulfate ion concen-
tration within narrow limits at all points in the reaction slurry. The
proper sulfate ion concentration appears to be slightly more than 1.5$.
Lower levels give poor crystals that are difficult to filter; higher con-
centrations interfere with the reaction by causing deposition of calcium
sulfate on unreacted rock. Good reactor design will prevent sudden changes
of sulfate ion concentration, will maintain this concentration and tempera-
ture near optimum, and will provide sufficiently long holdup time to allow
growth of large, easily filterable crystals without the formation of ex-
cessive crystal nuclei.
215
-------
WATER
FAN
GYPSUM
PONO WATER
5UC* | J WASH I J WASH
LIQUOR
REMOVI
TILTING PAN FILTER
.VACUUM*
TO VACUUM •
AND HOT WCLL
VACUUM
FLASH
STEAM
STEAM
PHOSPHATE'
VACUUM
ist-stacc
EVAPORATOR
WEIGH FEEDER
SINGLE-TANK
REACTOR
STRONG
SURGE
CVPSUM SLURRY
TO POND
J-a
TO SCRUBBER
HVDROFLUOSILICIC ACID
Figure 15-2 - Flow Diagram Illustrating Wet-Process Phosphoric Acid Plant£/
-------
Concentrated sulfuric acid is usually fed to the reactor. If
dilute acid is used, its water content must be evaporated later. The only
other water entering the reactor comes from the filter-wash water. To
minimize evaporation costs, it is important to use as little wash water as
is consistent with practical H3PO4 recoveries.
Considerable heat of reaction is generated in the reactor and
must be removed. This is done by blowing air over the hot slurry surface
or by vacuum flash cooling part of the slurry and sending it back into the
reactor. Modern plants use vacuum flash cooling. Figure 15-2 illustrates
this method of cooling.
The reaction slurry is held in the reactor for periods up to
8 hours, depending on the rock and on reactor design, and is then sent to
be filtered. The circular, horizontal, tilting-pan vacuum filter is illus-
trated in Figure 15-2. Older and smaller plants may use other types of
filters.
In washing the resultant gypsum cake on the tilting-pan filter,
wash water flow is countercurrent to the rotation of the cake, and heated
fresh water is used to wash the "cleanest" cake. These filters can be
built in very large sizes, and designs are now approaching 1,000 ton/
day P2®5 capacity.
The 32$ acid from the filter generally needs concentrating for
further use. Current practice is to concentrate it to 54$ by evaporation
in two or three vacuum evaporators.
15.2.2.1 Emissions from Wer-Process Phosphoric Acid Manufacture:
Emissions from wet-process phosphoric acid manufacture consist of rock
dust, fluoride gases, particulate fluoride, and phosphoric acid mist, depend-
ing on the design and condition of the plant. Fluorine exists as various
compounds in the collection equipment; as fluorides, silico-flucrides, sili-
con tetrafluoride, and mixtures of the latter and hydrogen fluoride, the
mole ratio of which changes in the vapor with the concentration of fluorosili-
cate in the liquid and with temperature. Because of the complex chemistry,
the composition of emissions is variable.
The reactor, where phosphate rock is decomposed by sulfuric acid,
is the main source of atmospheric contaminants. Acid concentration by
evaporation provides another source of fluoride emissions. The filter is
a third source of fluoride emissions. For circular filters, and for filters
of the Georgini pan-filter type, most of the emissions are at feed and wash
points. Emissions from filters are not large and can be controlled by the
use of hoods, vents, and scrubbers.
317
-------
In addition tc- these three main sources of emissions, there are
many miscellaneous minor sources. These include vents from such sources
as acid splitter boxes, sumps, and phosphoric acid tanks. Collectively,
these sources of fluoride emissions are significant, and they are often
enclosed and vented to a suitable scrubber.
15.2.3 Normal Superphosphate Production
"Normal superphosphate" is the term applied to the fertilizer
produced by reacting sulfuric acid with phosphate rock. Normal super-
phosphate contains from 16 to 21# phosphoric anhydride (P2O5).
While there have been developments and refinements, the three
basic steps in the production of normal superphosphate have remained the
same over the years (Figure 15-3). Sulfuric acid and rock are intimately
mixed, dropped into a den, held for sufficient time to allow the slurry
mixture to set into a solid porous form, and stored to permit the acidula-
tion to go to completion. Plants are described as batch or continuous,
depending upon the type of den used. Over 75$ of U.S. plants use the
batch process.
Following the curing period, three alternates are available:
(l) the product can be ground and bagged for sale; (2) the cured super-
phosphate can be sold directly as run-of-pile product: or (3) the mate-
rial can be granulated for sale as granulated superphosphate or used as
a component of granular mixed fertilizer.
For the latter alternative, normal superphosphate is blended
with some or all of the following ingredients—ammonia, sulfuric acid,
phosphoric acid, triple superphosphate, potash. Steam or water is added,
if needed, to aid in granulation. The mixture is then passed through a
rotary dryer, which removes sufficient moisture to eliminate the chance
of the pellets binding together. From the dryer the material passes
through a rotary cooler and is conveyed to storage bins for sale as a
bagged or bulk product.
The gases released from the acidulation of phosphate rock con-
tain silicon tetrafluoride, carbon dioxide, steam, and sulfur oxides.
From 20 to 28$ of the total fluoride in the phosphate rock is evolved in
the acidulation and curing operation. Curing building emissions are not
usually controlled in normal superphosphate plants.
Vent gases from a granulator-ammoniatcr may contain ammonia,
silicon tetrafluoride, hydrofluoric acid, ammonium chloride, and fertilizer
dust. Emissions from the dryer will include gaseous and particulate
fluorides, ammonia, and fertilizer dust. Some emissions will also con-
tain sulfur oxide, especially if high-sulfur oil is used as fuel to the
dryer. Emissions from the cooler will contain primarily fertilizer dust,
and may also include traces of the aforementioned pollutants.
318
-------
EXIT (GASEOUS FLUORIDE,PARTICULATE AND SULFUR DIOXIDE)
EXIT (GASEOUS FLUORIDE)
PHOSPHATE ROCK
EXIT (PARTICULATE)
EXIT (AMMONIA, PARTICULATE)
EXIT (AMMONIA, PARTICULATE
GASEOUS FLUORIDE)
NH
CD
RUN OF PILE PRODUCT
BAGGING PRODUCT
GRANULATED
PRODUCT
DEN
COOLER
CURING
DRYER
MIXER
GRINDER
SCREEN
BAGGING
AMMONIATOR
GRANULATOR
Figure 15-3 - Flow Diagram of Normal Superphosphate Plant, Noting Potential
Air Pollution and Sources. Control devices are not shewn.
-------
15.2,4 Triple Superphosphate Production
"Triple superphosphate'' is the popular name for the product
resulting from the reaction between phosphate rock and phosphoric acid.
Unlike normal superphosphate, the production of triple superphosphate
is usually a continuous operation in large plants located near phosphate
rock deposits. The phosphate rock is ground to a fineness ranging from
80$ through a 100-mesh screen to 95# through a 200-mesh Tyler screen.
Although either furnace or wet process phosphoric acid may be used as
the acidulant, at the present time wet-process acid is used almost exclu-
sively. Concentrated acid with a P2O5 content of 50-55$ is used. Fluoride
content of wet-process acid may be as high as 1-2$.
Two major processes are used in the production of triple super-
phosphate (Figure 15-4). The first uses a mixing cone to achieve intimate
contact between the acid and rock. The resulting mix falls tc a conveyor
belt which moves the material to the curing building. On its way to the
curing building the mix is passed through several mixers or blungers (pug
mills) to aid in the contact of the rock and acid as well as to release
fluorine vapors. Fluoride-containing fume is collected along the entire
length of the belt by a tight hood over the belt, the blungers, and the
mixer. After curing for 3C-60 days, the product can be sold as run-of-
pi2e (ROP). or it can be granulated in separate equipment.
With the increased demand for granulated products, a second
process has been introduced to produce granulated fertilizer directly.
In one commercial process, the acid and phosphate rock are placed in mix-
ing tanks, fed through a blunger for intimate mixing and release of some
of the effluent gases, and then dried in a rotary dryer using oil or gas
as fuel. The product is a directly granulated material which is rather
hard and dense and normally not amenable to ammoniating.
Most triple superphosphate is of the nongranular type. The exit
gases from a plant producing the nongranular product will contain con-
siderable quantities of silicon tetrafluoride, some hydrogen fluoride,
and a small amount of particulates. In cases where ROP triple super-
phosphate is granulated or mixed as a granulated-mixed fertilizer, one
of the greatest problems is the emission of dust and fumes from the dryer
and cooler. Screening stations and bagging stations are a source of
fertilizer dust emissions in this type of process.
320
-------
EXIT EXIT
(AMMONIA, FLUORIDE AND PARTICULATE)
(FLUORIDE)
EXIT
(PARTICULATE AND
EXIT
(FLUORIDE)
PHOSPHORIC ACID
FLUORIDE)
NH-
GRANULATED
PRODUCT
PHOSPHATE ROCK
RUN OF PILE PRODUCT
MIXER
DRYER
BELT DEN
COOLER
GRANULATOR
CURING BLDG
EXIT
(FLUORIDE) EXIT
(PARTICULATE, FLUORIDE AND SULFUR OXIDE)
PHOSPHORIC ACID
EXIT (PARTICULATE)
GRANULATED
PRODUCT
DRYER
MIXER
BLUNGER
SCREEN
PHOSPHATE ROCK
Figure 15-4 - Flow Diagram for Production of Run-of-Pile and Granular Triple Superphosphate,
Noting Potential Air Pollution Sources
-------
15.2.5 D1ammonium Pnosnhate Production
In the manufacture of diamznoniun phosphate the initial reaction
between ammonia and phosphoric acid takes place in a reactor tank lined
with acid brick (Figure 15-5). Both acid from the gas scrubbers and fresh
acid are used as feedstock. In many plants some 93% sulfuric acid is used
to control the composition of the final product. The relative amounts of
phosphoric and sulfuric acid usually depend on the purity of the incoming
phosphoric acid. The product of the reactor is pumped as a slurry to a
rotary anmor.iator. In the ammoniator additional ammonia is sparged under-
neath the mixing bed to achieve a final mole ratio of 1.8 to 2.0. While
the equipment is rotating, agglomeration takes place and the ammoniation
is completed. Diaamcnium phosphate granules are discharged from the
ammoniator tc a rotary dryer, thence through a screening station and a
rotary cooler to storage. Fines and oversize particles from the screening
station are recycled back to the ammoniator for product control.
The major pollutants from diammonium phosphate production are
fluoride, particulates, and ammonia. Dust-producing areas are the cage
mills, where oversized product from the screens is ground before being
recycled to the ammoniator. Dust from these points is usually vented
through cyclone collectors, and then to either an impingement or a venturi
scrubber. Vent gases from the reactor and ammoniator tanks, which contain
high quantities of ammonia, are usually scrubbed with acid to recover the
residual ammonia.
15.2.6 Granulation
Granulation is a method of processing that has been widely
adopted as a means of improving the storage and handling properties of
fertilizer materials and mixtures by increasing their normal particle
size to material that will largely be retained on a 16-mesh sieve, and
which includes particles in the range of 1 to 4 mm in diameter.
In the granulation of ammonium phosphate fertilizer, a gypsun-
acid slurry is obtained by by-passing the filter in a phosphoric acid
plant (Figure 15-6). Ammonia is introduced into this slurry and into
acidulated phosphate from the acidulation tank. The mixture then flows
to the dryer.
After the dryer, the product is screened. Large lumps are
crushed and recycled to the granulator along with the fines passing the
screens.
322
-------
Ol
ro
OJ
EXIT
(FLUORIDES, AMMONIA, PARTICULATE)
EXIT
(FLUORIDES, AMMONIA, PARTICULATE)
EXIT
FLUORIDES, AMMONIA
AMMONIA AMMONIA
1
PHOSPHORIC ACID
REACTOR
AMMONIA
SULFURIC ACID
AMMO NI AT OR
V
-
DRYER
-
SCREEN
-
COOLER
Ifuel
FUEL DIAMMONIUM PHOSPHATE
GRANULES
J
Figure 15-5 - Flow Diagram of Diamraonium Phosphate Plant, Noting
Potential Air Pollution Sources
-------
EXIT
(nh4 salts, nh3)
WATER
CO
CO
CO
WATER BACK TO PROCESS
ACIDULATED SLURRY
(pH6$phAtE>
AMMONIA
AMMONIATED PHOSPHATE PRODUCT
SCRUBBER
DRYER
GRANULATOR
REACTION TANK
Figure 15-6 - Flow Diagram of the Slurry Granulation Process in the Manufacture
of Fertilizer, Noting Potential Air Pollution Sources
-------
Water scrubbers of various types are used for recovery of
ammonia and axmonium salts, which are then recycled to the process. The
greater portion of the ammonia is recovered. However, ammonium salts
are not easily recovered because of their very fine size.
In nonslurry granulation, part or all of the neutralization
reaction is carried out in the granulation vessel. The number of sources
of air pollution is reduced by elimination of the reaction tanks. This
method of granulation is widely used for mixed fertilizers based on super-
phosphates .
Dust from granulation is mainly from dryers and coolers. Dust
frail screens, hammermills, and materials handling also is important since
the granulation process involves recirculation of material to build up
the size of granules. The manufacture of salt grades (fertilizers con-
taining potash) produces a fume of KH^Cl which is composed of particles
< 5 Li and is difficult to collect. The amount of chloride fune produced
depends cn the raw materials used; ammoniating solutions and sulfuric
acid tend to increase the amount of fume.
15.2.7 Emission Rates from Phosphate Fertilizer Manufacture
Particulate emission rates from the various processes comprising
phosphate fertilizer manufacture are summarized in Table 15-1. Both
fluoride particulate and fertilizer dust are included in the emissions.
Dust losses from materials handling operations are estimated at 2 lb/ton
of granulated material.
15.3 AMMONIUM KITRATE FERTILIZER
Commercial processes for the manufacture of ammonium nitrate
depend almost entirely on the neutralization of nitric acid with ammonia
in liquid or gaseous form (Figure 15-7). Synthetic ammonia, as the
anhydrous liquid, and nitric acid produced from the oxidation of ammonia
are used.
Essentially three steps are involved in producing ammonium
nitrate: neutralization, evaporation of the neutralized solution, and
control of the particle size and characteristics of the dry product.
325
-------
TABLE 15-1
pAmcvutt pgasicas
PHSSPHAtt HQS AX> WHlgACIWg OF fPTTUZIF
As»cr.rj» tfitraw
A. Evaporator
£. Prilling '.over
C. Dryer and cceler
D. Jfeterials handling
1. Elevators
a. beets
b. heads
2. Conveyers
a. transfer points
b. discharge t? bins, sll^s
I. Shiptvn? cf prriAuft
a. baggie^
b. bulk lw&dlug
2,800,000 tons of NK^SDj granules
1 lb/tor. of end product
12 It/its of end product
III. Uraa--saj
si AoDualua Nitrate
1 Ib/tcc (controlled)
Total for AeD^nlus .Nitrate As suae lit of tnd produc
1,000,030 twos granules Afsos 1% jf product
Phnsphate Fertilizers
A. Rock pulverizing
B- Flo^rlde particulate frto
acid«r9?fc reaction
1. Wet-proems reaetnr
2. Fil-cr
3. Mixers superphosphate nr/ofac
C Pre-neutralizer
D. SramAiitl-ig e^uipaMit
1. B lunger
2. Gra.'.ulat'jr
£ • Dryer
F. Cooler
3. Screen*
H. Kills
I Materials Handling
1. Unloading of rtv-sat.erial
shipments
a. phosphate rock
b pnrash
2. Conveyors
a. transfer points
b. discharge tc bias, sllus
5. Elevators
a. boots
b. heads
*. Shipaent of product
a. bagging oachines
fc. bulk loading
Br.iua Sulfate
Cry&talllur
Drying
Shipping
1. Baggie EHChlQCE
2. Bulk loading
17,000,000 tons cf phosphate rock
4,370,000 tone cf FgO- froa phosphate
10,000,003 tnns of granular naterial
6 Ib/tcr. cf rock
18 Lbc part lc . /tan <
0.5 lb/tun
105
90 lh/*or.
195
0.30
0.95
SO0 or IB,000,000 tans
2,700,000 tcna
c lb/ton of granular aatarlal
1 ll/too (controlled)
14 of product*
1.0 0.00
C.35 0.9C
Applica-
Efficiency
tion of
Net
of Control
Control
Control
Eclssicr.s
StfUTCC
Quantity of
Jfcterial
Ealoeion Faetcr
cc
ct
Ct-Ct
( tcr.s/vr)
Fhosphate Rick
41,300,000 toss per
3HM
A. Dryer
12 lb/tot oP tod product
0.94
1.0
0.94
14,00C
B. Grinder
2 lto/ten of end prcdurt
0.97
1.0
C .97
1,0CC
C. ffcterials handling
2 lb/ton of end product
0.90*
3.25*
C.22
50,000
E. Calcining
40 lb/ten of sod product
0.9£
1.0
C.95
0.000
20,000
10,000
10,000
9.0X1
lfl.OOC
Total for Fbasphate Rock and Pertlllxer
3W,00C
326
-------
EXIT
(NHV NITROGEN OXIDES)
(PARTICULATES)
(NITROGEN OXIDES, NH^NO^,H20, NH3)
WATER
HNO
AMMONIA
AMMONIUM NITRATE TO
SCRUBBER
NEUTRALIZER
EVAPORATOR DRYER
GRANULATOR
STORAGE AND PACKAGING
Figure 15-7 - Flow Diagram of the Process for Manufacture of Ammonium
Nitrate, Noting Potential Air Pollution Sources
-------
Is.3.1 Neutralization
Direct neutralization is practiced when pure reactants are used,
in an aqueous medium. The reaction of ammonia with nitric acid is strongly
exothermic; both reactants are volatile at the resulting elevated tempera-
tures. This condition oust "be controlled to prevent loss of materials.
Usually a slight excess of nitric acid, the less volatile of the two
reactants, is maintained during neutralization.
15.3.2 Evaporation
Procedures vary depending on the water content of the reactants
and the control of temperatures. In methods formerly in wide use, the
neutral ammonium nitrate solution was evaporated to a high degree of con-
centration, with subsequent cooling and granulation of the product. Other
processes carry the evaporation to a lesser degree of concentration and
complete the separation of the solid ammonium nitrate by crystallization
or, more frequently, by continuous evaporation in specially designed
apparatus.
15.3.3 Centre! of Particle Size ar.d Properties
Various procedures, such as graining, flaking, and spraying,
have been practiced ever the years to obtain nitrate particles or grains
for the final product. The method that has been adopted by the great
majority of plants is prilling. Prilling is spray drying cf a concen-
trated solution.
The prilling step is followed by rotary or fluidized-bed drying
and cooling. The product prills may then be coated with a clay material,
to prevent caking, in a rotary coating drum. These drying and cooling
operations use large quantities of heated air which entrains the dust
and fines. However, the emissions from these operations are usually
controlled with low pressure drop wet scrubbers using dilute salt solu-
tions to collect the material and recycle it back to the process.
The prilling operation may be as large an emission source as
the drying and cooling operations. In the prilling process losses are
dependent upon the velocity of the air in the prilling tower. Total
fines lost from the process can be kept to < 1$ of the product.
328
-------
15.3.4 Emission Rates from Ammonium Kitrate Fertilizer Manufacture
Particulate emission rates from the manufacture of ammonium
nitrate fertilizer axe summarized in Table 15-1. Limited data were found
for particulate emissions fran nitrate fertilizer manufacture, and the
emission totals in Table 15-1 are considered as conservative estimates.
•15.4 UREA FERTILIZER
The commercial production of urea is based on the exothermic
synthesis of ammonium carbamate with its subsequent dehydration to urea.
Ammonia and carbon dioxide are reacted together in a high-pressure reactor
to form a melt containing urea, ammonium carbamate, and water, along with
same unreacted ammonia. Depending upon the particulate process used, the
temperature of the melt in the reactor is maintained between 175°C and
210°C and the pressure between 170 atm. and 400 atm.
Eight processes are currently used in the manufacture of urea.
The method of treating the off gas (ammonia and carbon dioxide) from the
carbamate-urea reactor represents the major differences among the variety
of competing processes for the manufacture of urea. Figures 15-8 and 15-9
illustrate two methods of final preparation.
The aqueous solution of urea from any of the processes must be
concentrated to remove the excess synthesis water as well as traces of
dissolved synthesis gases and then filtered to remove any solid impurities.
15.4.1 Emission Rates from Urea Fertilizer Manufacture
Emission rates for urea fertilizer manufacture are summarized
in Tteble 15-1. No detailed data were found on emission rates, and an
emission factor of 1$ of the end product was used to estimate the particu-
late emissions.
15.5 AMMONIUM SULFATE
Most ammonium sulfate produced is a by-product of coke-oven
operations. Sulfuric acid is used to scrub the ammonia out of the coke-
oven gas and the scrubbing produces an ammonium sulfate solution. The
solution is further concentrated, and crystals of ammonium sulfate are
extracted in a centrifuge. The crystals are then dried. Since all other
operations are carried out in the wet state the only potential source cf
particulate emission is the dryer. The dryer is usually controlled by
cyclones or wet scrubbers.
329
-------
UREA SOLUTION
FROM CARBAMATE
STRIPPER
MOTHER LIQUOR
FINISHED PRODUCT
DRYER
CLAY
COATER
CONCENTRATOR
- FILTER
CENTRIFUGE
- CRYSTAL
SEPARATOR
Figure 15-8 - Sketch of Manufacturing Process for Crystalline Urea Product
-------
FINAL SOLUTION
CONCENTRATOR
AIR BLOWER
UREA SOLUTION FROM
CARBAMATE STRIPPER
PRILLING
OR
SHOTTING
TOWER
COOLER
SCREENS
CONCENTRATOR
- FILTER
FINISHED
PRODUCT
Figure 15-9 - Sketch of Manufacturing Process for Prilled or Shotted Urea Product
-------
15.6 CHARACTERISTICS OF EFFLUENTS FROM FERTILIZES MANUFACTURE
The chemical and physical characteristics of effluents frcm fer-
tilizer manufacture are summarized in Table 15-2. Particulates emitted
from phosphate fertilizer production equipment are hot, moist, partially
water-soluble, corrosive, hydroscopic, disagreeable to the sense of smell,
and have a tendency to stick to and build up on almost any surface. Dusts
emitted from superphosphate dryers are about 12 wt. $ < 10
15.7 CONTROL PRACTICES AND EQUIPMENT IN FERTILIZER MANUFACTURE
Control equipment which has been used in various phases of fer-
tilizer manufacture include cloth filters, electrostatic precipitators,
and mechanical systems for dust; wet collectors for dust, gases, and
flucrifie mists. 17 Wet scrubbers are probably the most common piece of
dust arid fume collection equipment being utilized in fertilizer plants.—/
15 .7.1 Control Equipment
15.7.1.1 Wet-Process Phosphoric Acid: Because the principal
atncspheric contaminants generated in the process are gaseous fluorides,
vapcr scrubbing is universally employed to control emissions. Specific
devices used for control include Yenturi scrubbers, impingement scrubbers,
and various kinds of spray towers. Fluoride removal efficiency of these
devices varies widely, and staging may be required for satisfactory con-
trol. Plugging, or difficulty in removing precipitates and dust, may also
be experienced .A/
Table 15-3 summarizes the results of Public Health Service tests
conducted on 10 wet-process phosphoric acid plants in various parts of the
country ..§/ For nine of these plants, the range of gaseous fluoride emis-
sions frcm various types of collectors was 0.006 to 0.17 lb. of fluoride
per ton of P2O5 produced. The concentration range of gaseous fluorides in
the gases frcm collectors was 3 to 40 ppm, and 0.0011 to 0.0147 grain/scf
for eight of the 10 plants. Public Health Service stack-test data agree
reasonably well with results from plant questionnaires and information
from miscellaneous sources, both of which are tabulated in Table 15-4
Scrubber efficiency is affected substantially by the loading of
the gas stream. Heavy loading enhances scrubber efficiency, and light
loading reduces scrubber efficiency. Therefore, scrubber-exit-gas concen-
tration is a better indicator of overall plant emission control than is
scrubber efficiency. The best criterion of plant performance is the weight
of emission per ton of ^2^5 produced ..§/
332
-------
1AHLE 15-2
OTlUEyr CHARACTERISTIC - FERTILIZES HAKUFArnFRg"
Particle Electrical Mol«tur*
Particle Size Solids loading Chealcal Cogpoittlon Penalty Pre;>ertlea Content
V , .-7 "vat*
i>"'iliser
i. ?•-. ¦ p-.MR
-cCk
: 1) ck
dryer
(.:) S::k
grinder
(?) Router vr
calc iner
;*) Fl.iid >*rt (Lust frco cyrlcr.e
roaster collector) 26 «r I,
•o'.-rfcess
' 1 ) Proctor cr
digester
•: 5) Til*.e:
[11 ari-i re*~tcr
(der)
' ^: orar.ulator-
Arrrr iarir
. 2) Dryer
?rir>
61 < 5, 96 < 10,
ICO < 25
0.4:-3."»
0.01"
tA.WCC a?.«lysis: 0
1-12.2 < 5, avg.
6.3 < £i 2-20 < 10,
avp. 12 < 10; 3-46
< ?0 avg. 27 05, 32.5;
SiOg, 11.0; AljOs, 2.C;
M^C, C.!; C«C, 45.5;
Fe^Or, 0.6.
Buck dust, see rock
dryer
Flonnde, a?ld alst
Fluoride, acid aist
jy-Tj, S10.
.VjiiCl. fertilizer djst
Fljorides, fertiliser,
C%, Mfc, P, Fe, uC A1
coipcunds
Fertilizer dust
Fluorides are re*l
Fluorides are tr.xl
Irritating tr. eyrr.
nose, ar»d throat
Flu«rii* - tf.xtc
FlucrIde
Fluoride, fertiliser dust
Fluoride, fertiliser dust
Fluoride, fertilizer dust
pr'd ::ticr.
I 1) Eryer
<£) C».c-1 fer
AT?-rr.iJT. rltrn.te
fcr;ilt:cr
£•* fV.;J•.~if\ Key, TaM» 5-1, Chapter 5, page 45, for units for indlvldjai effluent properties.
333
-------
TABLE 15-2 (Cane Lode*)
A. (?a:t II*
Hyprosrapie Tlasaability cr Optlcel
Sc.r.-» Solubility ¦l-Jllillv OiiraetcrUtlci BrolM'.va tlalu gusClrj CUft;t«rU-.Ut Promr-Ul fiiSI
lliier
.trtUi
aclutl®
rcds.ctic:.
S. =aff,«r :i;
Moisture Fl0 CL, Ng, HgC, SOj
T;.*ir
TfKiC
SlT
-------
Plant timber
SUMMARY OF EMISSION DA'LA ON PERFORMANCE OF COHTROI"
KQumnCHT in wkt-phockss pikcphortc actd pi a wis*/
y
10
CH
Oi
cn
Collector type Rectangular
spray
chamber
Gaseous fluo- 1.265-2.16
ride entering
collector per
ton of P2O5
produced,
pound
Gaseous fluo- 0.52-0.63
ride emitted
from collec-
tor per ton
^2^5 produced,
pound
Square hori-
zontal spray
duct
Not deter-
mined
Venturl scrub- Veriturl scrub- Spray cross- Twu impinge- Spray cross-
be r, water-
actuat.ed
ber, water-
actuated
flow packed
scrubber
0.078-0.007
ment scrub- flow packed
bers in scrubber
series
0.013-0.016 1.20-1.40
Spray cross-
flow packed
scrubber
0.05-0.06
Cyclone spray
tower
Spray cross-
flow packed
scrubber
Not deter-
mined
0.072-0,101 0.027-0.047 0.020-0.03B 0.006-0.010 0.006-0.011 0.10-0.17
0.0170-0.022 0.047-0.082 0.135-0.157
57-72 64.2-07.0 92-96 80-92.4 15-62 06-93 56.7-68.4 90.4-95.3
0.075-0.090 0.0026-0.0035 0.0104-0.0147 0.018-0.023 0.0011-0.0032 0.0020-0.0037 0.0054-0.0088 0.0022-0.0029 0.0016-0.0029
Collection ef-
ficiency, ^
Concentration
of gaseous
fluoride
emitted from
collector,
grain/scf
Parts per
million
Articulate
emitted
from col-
lector per
ton P2O5
produced,
pound
Total par-
ticulates
Efficiency, i>
Insolube par- 0.0006-0.000 0-0.0013
ticulate
fluorides
0.0120-0.014
0.20-0.50
Efficiency, i>
Soluble par- 0,050-0.094
ticulate
fluorides
Efficiency, ^
0.0075-0.036
0-0.029
98.5-100
None found
100
0.0023-0.0029
0.006-0.09
a/ Plants 1-10 were tested by National Air Pollution Control Administration.
-------
TABLE 15-4
SUMMARY OF EMISSION DATA ON PERFORMANCE OF CONTROL EQUIPMENT-/
IN WET-PROCESS PHOSPHORIC ACID PIANTSS/
Plant Number 11 12 13 14 15 16
Collector type
Venturi scrubber,
water-actuated
Gaseous and water-soluble
particulate fluoride
entering collector per
ton of P2O5 produced, pound
Cyclonic Spray cross-flow Spray cross-flow Impingement Packed tower, two-
spray packed scrubber packed scrubber stage cyclonic
scrubber, in paral-
lel
2.0
7.6
0.53
77
0.037
0.0073
Gaseous and water-soluble
particulate fluoride
emitted from collector
per ton of P2O5 produced,
pound
0.26
1.23
0.044
0.038
0.0087
0.00035
Efficiency, £ 87 84 92 99.9 24 1
Concentration of gaseous
and water-soluble par-
ticulate fluoride
emitted from collector
Grain/scf 0.058 0.031 0.0032 0.0019
Parts per million 167 87 9 5
a/ Information on plants 11 through 13 acquired through private communication; information on plants 15 and 16
acquired through questionnaire.
-------
15.7.1.2 Acidulation Prccess - Superphosphate: Acidulation cf
ground phosphate rock with H2SO4 to produce superphosphate results in emis-
sions consisting of silicon tetrafluoride, dilute fluosilicic acid, COg,
steam, and SO2.—' An injector-type gas scrubber was reported to be only
80$ efficient for controlling these emissions, allowing IfoSiFg ar.d traces
of SO2 and SO3 as a mist to te discharged into the air..!/ This unit sub-
sequently was replaced by a low-velocity cell type, wet scrubber which was
reported to achieve 100$ rencval of silica fluoride.^/
Current practice is to scrub gases with either copious quanti-
ties of water or with dilute fluosilicic acid. Spray towers, grid-packed
towers, and high-velocity jet scrubbers have been used.3/
15.7.1.3 Triple Superp'nosphate: Water scrubbers are the primary
method for controlling emissions of gaseous fluorides from triple super-
phosphate production. lacked towers, venturi scrubbers, wet-pad and im-
pingement scrubbers and cyclonic scrubbers have been investigated.^/ A
cyclonic scrubber system was reported tc eliminate 97$ of the total fluorides
liberated by all sources in one plant producing triple superphosphate.2./
15.1.1.4 Granulation: Control of emissions from fertilizer
granulation involves collection of dry dust from rotary dryers, rotary
coolers, and gas and dust from liquid-solid reactor units. Various high-
duty cyclones have been used for removal of dust in exist gases. Effi-
ciencies of 94-96$ have been reported in British plants.3/ It is also
customary to supplement cyclones by a wet scrubber to further reduce dust
content and to remove acid constituents.-^/ A multiple-tube collector,
operating with 5 in. .w.g. pressure drop, has been reported to remove 100$
of all dust > 14 y,.—'
337
-------
Fto'-KKENCES
1. "Industry Answers the Challenge," Farm Chemicals, pp. 21-26, June 1967.
2. "Fume and Dust Control," Farm Chemicals. pp. 24-33, 40, January 1962.
3. Shervin, K. A., "Effluents from the Manufacture of Superphosphate and
Compound Fertilizers," Chemistry and Industry, pp. 1274-1281,
October 1955.
4. Richter, F., "Pollution Control Equipment Pays Off in Two Years,"
Air Engineering, pp. 27-29, 53, July 1960.
5. Timberlake, R. C., "Fluorine Scrubber," Southern Engineering. 85(6),
62-64, June 1967.
6. "Atmospheric Emissions from Wet-Process Phosphoric Acid Manufacture,"
National Air Pollution Control Administration Publication No. AP-57,
Raleigh, North Carolina, April 1970.
338
-------
CHAPTER 16
ASPHALT
16.1 INTRODUCTION
Asphalt is a raw material for several industries. Two of the
more important with regard to air pollution are hot-mix asphalt paving
plants and asphalt-roofing manufacturing facilities.
The preparation of hot-nix asphalt paving involves proportional
feeding of cold aggregates, heating and drying of aggregates to predeter-
mined levels of moisture content and temperature, and uniform mixing and
coating with hot asphalt tc produce a specific paving mix. After mixing,
the hot paving mixture is discharged into trucks which transport it to
the paving site. Dust sources are the rotary dryer, hot-aggregate elevator,
vibrating screens, hot-aggregate storage bins, weigh hopper, mixer, and
transfer points. The major dust source is the rotary dryer.kJ
The manufacture of asphalt roofing felts and shingles involves
saturating a fiber media with asphalt by means of dipping and/or spraying.
Whiie not always done at the same site, an integral part of the operation
is the preparation of the asphalt saturant. This preparation consists of
oxidizing the asphalt and is accomplished by bubbling air through liquid
asphalt for 8-16 hr. This operation is known as "blowing." The principal
particulate emission sources are the saturator and blowing "bperations.
Manufacturing processes, particulate emission sources, particu-
late emission rates, effluent characteristics, and control practices and
equipment for the hot-mix asphalt paving and the asphalt roofing industries
are discussed in the following sections.
16.2 AIRBLOWN ASHiALT
Asphalt is a dark brown to black, solid or semi-solid material
found in naturally occurring deposits or as a colloidal suspension in crude
oil. Analytical methods have been used to separate asphalt into three com-
ponent groups—asphaltenes, resins, and oils. A particular grade of asphalt
may be characterized by the amounts of each group it contains. The asphal-
tene particle provides a nucleus about which the resin forms a protective
coating. The particles are suspended in an oil that is usually paraffinic
but can be naphthenic or naphtheno-aromatic.
339
-------
Over 90$ of all asphalt used in the United States is recovered
from crude oil (Kirk and Othmer). The method of recovery depends upon the
type of crude oil being processed. Practically all types of crudes are first
distilled at atmospheric pressure to remove the lower boiling materials such
as gasoline, kerosene, diesel oil, and others. Recovery of nondistillable
asphalt from selected topped crudes may then be accomplished by vacuum dis-
tillation, solvent extraction, or a combination of both.i/ Economical removal
of the gas-oil fraction from topped crude, leaving an asphaltic product, is
occasionally feasible only by airblowing the crude residue at elevated tem-
peratures. Excellent paving-grade asphalts are produced by this method.
Another important application of airblowing is in the production of high-
quality specialty asphalts for roofing, pipe coating, and similar uses.
These asphalts require certain plastic properties imparted by reacting with
air.i/
Airblowing is mainly a dehydrogenation process. Oxygen in the air
combines with hydrogen in the oil molecules to form water vapor. The pro-
gressive loss of hydrogen results in polymerization or condensation of the
asphalt to the desired consistency. Blowing is usually carried out batch-
vise in horizontal or vertical stills equipped to blanket the charge with
steam, but it may also be done continuously. Vertical stills are more effi-
cient because of longer air-asphalt contact time. The asphalt is heated
by an internal fire-tube heater or by circulating the charge material through
a separate tubestill. A temperature of 300° to 400°F is reached before the
airblowing cycle begins. Air quantities used range from 5 to 20 cu ft/nin/ton
of charge. Little additional heat is then needed since the reaction becomes
exothermic. Figure 499 in Reference 1 depicts the flow through a typical
batch-type unit.
16.2.1 Effluents and Control Methods
Effluents from the asphalt airblowing stills include oxygen, nitro-
gen and its compounds, water vapor, sulfur compounds, and hydrocarbons as
gases, odors, and aerosols. An estimate of particulate emissions for asphalt
blowing associated with asphalt roofing manufacture is given in Table 16-1.
Control of effluent vapors from asphalt airblowing stills has
been accomplished by scrubbing and incineration, singly or in combination.
Most installations use the combination. Essential to effective incineration
is direct-flame contact with the vapors, a minimum retention time of 0,3 sec.
in the combustion zone, and maintenance of a minimum combustion-chamber
temperature of 1200°F. Other desirable features include turbulent mixing
of vapors in the combustion chamber, tangential flame entry, and adequate
instrumentation. Primary condensation of any steam or water vapor allows
use of smaller incinerators and results in fuel savings. Some of the heat
released by incineration of the waste gases may be recovered and used for
340
-------
TABLE 16-1
PARTICULATE EMISSIONS
- ASPHALT
Source
I. Asphalt Roofing
A.Blowing
B.Saturator
II. Hot-Mix Paving
Plants
A. Dryer
B. Bins, weigh
hopper, etc.
Quantity of
Material
6,264,000 tons/year
(asphalt used in
roofing manufacturer)
251,000,000 tons/year
(hot-mix asphalt)
Emission
Factor
4 lb/ton
4 (controlled)
32*
_8
40
Efficiency
of Control
(Cc)
Application
of Control
(Ct)
Net
Control Emission
(Cc'^t) (tons/yr)
0.50
3,000
14,000
0.97
0.99
0.96
201,000
Total for Primary Users of Asphalt
218,000
* Prior to any control equipment.
-------
generation of steam. Catalytic fume burners are not recommended, for the
disposal of vapors from the airblowing of asphalt because the matter entrained
in the vapors would quickly clog the catalyst bed.i/
16.3 HOT-MIX ASPHALT PAVING PLANTS
Generally, a hot-mix asphalt plant consists of a rotary dryer,
screening and classifying equipment, an aggregate weighing system, a mixer,
storage bins and conveying equipment. Hot-mix plants can be classified
according to permanence of location or according to the method of measuring
and mixing the hot aggregate and asphalt. Portable plants are designed to
be readily dismantled and transported on trailers from one job site to
another, whereas permanent (or stationary) plants are set up for efficient
operation in a relatively permanent location, usually in a metropolitan
area.£/
With regard to the final mixing process, plants are either of
the batch or continuous-mix type. Both types of plants have the same
pattern of material flow up to the point of measuring the aggregate from
the hot bins into the mixer. In the batch-type plant, the operator weighs
out the correct quantity of aggregate from each hot bin in succession into
the mixer. The total batch of aggregate is then dry mixed in the pug-
mill for a prescribed time, during which time the operator proceeds to
accumulate another batch in the weigh hopper. When the dry-mix cycle is
complete, hot asphalt is added to the mixer by either metering or weigh-
ing the correct amount. The hot asphalt may be sprayed or dumped into
the pugmill, and upon completion of the proper mixing cycle, the hot-mix
asphalt is delivered through a hopper into trucks hauling to the job site.
Figure 16-1 shows a typical batch plant and identifies potential sources
of air pollutants.^/
The continuous-mix plant transfers a preblended mixture of the
dried and graded aggregate from the gradation unit by means of a bucket
elevator to the mixer. Dry mixing in the mixer is not required, as it is
in the batch plant. The hot asphalt is sprayed on the aggregate as it
falls from the top of the elevator into the mixer. The length of the
mixing cycle in a continuous-mix plant is governed by an adjustable dam
at the discharge end of the pugmill; the hot-nix asphalt flows over the
dam into the discharge hoppers. Mixing time can be varied without changing
the hourly tonnage output by varying the height of the adjustable dam.
In Figure 16-2 a typical continuous plant is shown with potential sources
of pollutants identified.3/
342
-------
Indicoto* fugitive dutl Ioiim
if not wall incloiid
Hot *cr«on»
To tocondory
colloetor
Weigh hoppor
Miitr
.Primory
du«t
cot lie tor.
7- /
Figure 16-1 - Asphalt Batch Mix Plant*-/
\ Indlcotti dull Isttti
I If not I MClsitd
Prlmorj
dutl
ColUclor
Hoi >CIMIII
Hoi M*l
Figure 16-2 - Asphalt Continuous Mix Plant^/
343
-------
16.3.1 Emission Sources and Rates
Pollutants released to the atmosphere during the operation of a
hot-mix asphalt paving plant are both particulate and gaseous in nature.
The major source of dust is the rotary dryer. However, while dust from
the rotary dryer is the greatest source, dust collected from the vibrating
screens, the bucket elevator, storage, bins, and weigh hopper is also
significant. In some plants, the dryer dust problem is handled separately
from the other sources. However, the trend is to combine both the dryer
and ventline or fugitive sources together with a single collector fan
system.
Dust loadings and particle-size distribution vary widely from
plant to plant. The dryer design and operation, pai-ticle-size distribu-
tion of feed materials, and the specific grade of asphalt mix will have
a very marked effect on emissions.
Studies in the Los Angeles area indicated that stack emissions
increase linearly with an increase in the amount of -200 mesh material
processed and that emissions were higher when the dryer was oil-fired
rather than gas-fired.£/
A study conducted in Germany provided extensive test data on
the influence of feed composition, plant size, and control techniques on
emissions.i2/ The quantity and particle size of dust in the waste gases
from the drum dryer was found to extend through a wide range and to depend
largely on whether the starting material was washed, unwashed, or proc-
essed in mixed components. Completely washed raw material caused the
lowest dust load. Values ranged between 9.7-17.2 grains/scf. Mean value
was 13.2 grains/scf.
In processing partly washed and partly unwashed raw material,
dust contents measured during production of fine concrete were about 30.8
grains/scf.
Processing unwashed raw material resulted in maximum dust levels
in waste gases. Dust content rose sharply with increasing proportion of
fine particles in the materials for base, binder, and fine concrete manu-
facture. Measured values ranged from 19-72 grains/scf. .12/
Table 16-1 summarizes emission levels from hot-mix asphalt
paving plants. Currently paving plants emit about 200,000 tons/year of
particulate matter.
344
-------
16.5.2 Characteristics of Hot-Mix Asphalt Plant Effluents
The chemical and physical properties of hot-mix asphalt plant
effluents are summarized in Table 16-2. Particulate pollutants involved
in asphalt plant operations include stone dust, fly ash, soot, and un-
burned droplets of fuel oil. Stone dust is caused by the release of
dust from the surface of the larger aggregate particles due to the heat
and vibration of the dryer and other components cf the plant and to some
extent to the fracture of aggregate during the drying and screening
processes.
Particulates emitted from the dryer have a highly variable
particle size ar.d may range frcm 10-90 vrt. $ < 10 ^ .
16.3.3 Control Practice and Equipment for Hot-Mix Asphalt Plants
Total ventilation requirements for the rotary dryer and the sec-
ondary dust sources vary according to the size of plant. For a 6,000 lb/
batch plant, 22,COO scfm is typical, of which ~ 3,000 scftn is required for
the secondary sources. Table 16-3 and Figure 16-3 illustrate test data on
air pollution equipment serving two hot-mix asphalt paving plants.1/
A typical asphalt plant dryer effluent will contain 20-30 grains/
cu ft.i/ However, the loading can vary widely as shown in the table cf
effluent characteristics. Test data for some Florida asphalt plants are
given in Table IS-4.£/
The dust carried cut of the dryer into the dust collection system
increases rapidly with a rise in drum gas velocity. Figure 16-4 shows the
effect of increasing dram gas velocity on the dust carry-out for a typical
aggregate.5/
16.3.3.1 Cyclones: The collection of asphalt plant dusts is
usually by means of cyclones for the primary dust collection followed by a
higher efficiency type of secondary collector. One recently installed con-
trol system consisting of cyclones followed by low-pressure drop wet scrub-
bers is reported to attain 99.89$ overall collection efficiency.!/ Measure-
ments of eyelone-scrubber systems on 14 asphalt plant dryers showed >98.0$
efficiency.®/ Comparative cost data are presented in Table 16-5.5/ The
ranges shown for installed cost and power consumption are in good agreement
with general cost curves and equations presented in Appendix A. Therefore,
these curves could be used for a more accurate estimate of costs if the
total gas flow is known.
16.3.3.2 Electrostatic Precipitators: Electrostatic precipita-
tion units do not find much application to asphalt plants since they have a
rather high first ccst.~/
345
-------
TABLE 1G-2
EFFLUEOT CHARACTERISTIC!; - ASPIALT*
A. Particulate
Source
Particle Size
Solids Loading Chemical Composition
Particle Electricul
Density Resistivity Moisture Content Toxicity
1. Hot-Mix Asphalt Batch
Plants
1. Rotary Dryer
Highly variable, extreme
range: 13-91 < 10, 32-
99 < 20, 55-100 < 44
Bahco Analysis: (2 samples)
19-24 < 5; avg. 22 < 5
30-44 < 10; avg. 36 < 10
45-60 < 20; avg. 53 < 20
64-75 < 40; avg. 69 < 40
Extreme range: Stone dust, fly ash,
11-200
Typical range:
20-70
Avg.: 30
soot, and unbumed
droplets of oil
2.6 (avg.
value)
N.T.
2. Vent Line (Fugitive
Sources)
39-46 < 10, 61-07 < 20,
86-99 < 44
23-02; avg.: 53
11. Asphalt Roofing Manu-
facture
1. Saturator
Hydrocarbon or oil
mist
B. Carrier Gas
Flow Rate
Temperature
Moisture
Content
Chemical Composition Toxicity
Flainraability or Optical
Corrosivity Odor Explosive Limits Properties
I. Hot-Mix Asphalt
Batch Plants
1. Rotary Dryer (a) 7.7-46
Avg.: 20
(b) 3.9-24.6
Avg.: 9
05-525
Avg.: 240
Dew point
140-160
C0?, N0X, N2> Or,, CO
CO - 100
2. Vent Line (a) 2.0-3.7
200-215
II. Asphalt Roofing
Manufacture
1. Saturator (a) 10-20
135-217
2.7-6.4
50t opacity
over saturat.-T
tank
+ See Coding Key, Table 5-1, Chapter 5, page 45, for units for individual effluent properties.
-------
Test No.
Batch Plant Data
TABLE 16-3
DUST AND FUME DISCHARGE FROM
asphalt batch plants if
C-426
C-52
Mixer capacity, l"b.
Process weight, lb/hr**
Dryer Fuel
Type of mix
Aggregate feed to drier
+ 10 mesh, wt. fo
- 10 to + 100 mesh
- 100 to + 200 mesh
- 200 mesh
6,000
354,000
Oil, PS 300
City street, surface
70.8
24.7
1.7
2.8
6,000
346,000
Oil, PS 300
Highway, surface
68.1
28.9
1.4
1.6
Dust and Fume Data
Vent Line*
Gas volume, scfm 2,800
Gas temperature, CF 215
Dust loading, lb/hr 2,000
Dust loading, grain/scf 81.8
Sieve analysis of dust
+ 100 mesh, wt. $ 4.3
- 100 to + 200 mesh 6.5
- 200 mesh. 89.2
P&rticie size of - 200 mesh
C - 5 microns, wt. 56 19.3
5-10 microns, wt. $ 2C.4
10 - 20 microns, wt. $ 21.0
2C - 50 microns, wt. ^ 25.1
> 50 microns, wt. $ 14.2
21,000
180
6,700
37.2
17.0
25.2
57.8
10.1
11.0
11.0
21.4
46.5
Vent Line*
3,715
200
742
23.3
0.5
4.6
94.9
18.8
27.6
40.4
12.1
1.1
Dryer
22,050
430
4,721
24.98
18.9
32.2
48.9
9.2
12.3
22.7
49.3
6.5
* Vent line serves hot elevator, screens, bin, weigh hopper and mixer.
*+ "Frocess weight"—a process weight definition is given in Rule 2 j,
of the Rules and Regulations of the Los Angeles County Air Pollution
Control District.
347
-------
¦€?—|
lit (I AND KUO
iltTUWI TO HOT UIWOI
I, at 16/bf
1,515 Ib/hr
BIT BUST
VENT UMf
J4J it/kr
HI Ib/hr
t.m it/hi
HOI MYC*
' i • i
4,720 16/fcf " 1 I
fin
-£?
wncihct
> its
V
•
MM* TO HOT flfy«T0*
t, 10T Ib^r
l,»44 ll/kl
WILT I Pit
CTUONC
[friCKNCT
¦ II.»
MTIFK
tUTRiruui
JCIUI8CR
tffltltKCI
• II.Jl
TO tTHOSPHCIjt
| «.l It/df *
li
j'ATtl ANO NUO
M.I Ib/nr *"
NT OUST
Figure 16-3 - Test Data on Air Pollution Control Equipment Serving
!Two Hot-Mix Asphalt Paving Plants (Vent Line Serves
Screens, Hot Bins, Weigh Hopper, and Mixer)}J
546
-------
TABLE 16-4
FINDINGS OF
FLORIDA ASPHALT
PLANT TESTING PROGRAM
6/
Before Cyclone
After
Cyclone
Scrubber
Outlet
Name of Asphalt Plant
Production
(tph)
(gr/cu
ft) (lb/hrj
(gr/cu
ft)
(lb/hr)
(gr/cu
ft)
(lb/hr)
1.
Houdaille Duval
Asphalt Plant
96
0.51
240
_
2.
Basic Asphalt
90
-
-
-
2.30
509
3.
(a) Jaxon Const. Co
(b) Jaxon Const. Co
120
21.2 6,830
5.42
1,883
0.765
0.433
205
116
4.
Florida Four Const.
Co.
33.7 12,000
15.2
14.3
3,120
2,930
-
-
5.
Dunn Const. Co.
99
0.370
0.301
0.283
54.0
43.9
41.4
6.
Mac Asphalt
200
- -
-
-
0.229
0.349
26.8
40.6
7.
Florida Hot Mix
120
~ -
9.47
5.73
1,020
620
0.135
0.227
25.7
43.2
8.
Rubin Const.
140
0.279
0.297
0.311
8.34
8.15
8.55
-------
Drum Gas Velocity (% Increase)
0 20 40 60 80 100
S 200
u
c
o
3
a
600 800 1000 1200
Drum Gas Velocity (Ft/Min)
Figure 16-4 - Effect of Drum Gas Velocity on
Dust Emission^/
350
-------
TABLE 16-5
COMPARATIVE COSTS OF DUST COLLECTORS
Type
Primary
Settling chamber
Cyclone, large dia.
Cyclone, medium dia.
Installed Cost
0.1
C.l - 0.2
C.2 - 0.3
Power
Consumption
(kw/l,C00 cfm)
0.1
C.l - 0.5
C.3 - 0.8
Pressure
Drop
(in. water)
0.1 - 0.5
0.5 - 3.0
1.0 - 4.0
Secondary
Cyclone, multiple 0.3 - 0.6
Filter, cloth tubular 0,3 - 2.0
Precipitator, electric 0.6 - 3.0
Scrubber, spray tower 0.1 - 0.2
Scrubber, wet cyclone 0.3 - 1.0
Scrubber, packed tower 0.3 - 0.6
0.5 - 2.C
0.5 - 1.5
0.2 - 0.6
0.1 - 0.2
0.6 - 2.0
0.6 - 2.0
2.0 - 10.C
2.0 - 6.C
0.1 - 0.5
0.1 - 0.5
2.0 - 8.C
0.5 - 10.0
351
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16.3.3.3 Fabric Filters: Fabric filters provide excellent collec-
tion of fine particles with little or no visible emissions. Although fabric
filters frequently are more expensive than wet scrubbers, they collect dry
"fines'" which may be usable in high-grade asphaltic concrete mixes. In ad-
dition, they obviate the need for holding ponds and preclude water problems.£/
Filters are subject to operating difficulties when installed in
an intermittent process such as asphalt dryers.5/ Precautions must be
taken to prevent overheating and to prevent condensation during shutdowns.
The air-to-cloth ratios for fabric filters will vary from 3.5:1 to
6.25:1. Reverse air supply is normapLy heated, and the collector housing
insulated, to prevent condensation.^/
16.3.3.4 Wet Collectors: Wet collectors are in wide use in the
asphalt paving industry and generally give good results without serious
maintenance problems. The scrubbing liquid from these collectors requires
a settling pond of adequate size. This pond should be at least; 6 ft.
deep and hold at least 2 hr. discharge of the scrubber. The sludge col-
lected in the pond must be pumped or dredged out and removed to an appro-
priate disposal area avoiding any chances for stream pollution.5/
The effect of scrubber water/gas ratio on stack emissions is a
very important factor as shown in Figure 16-5.1/ The best utilization of
water is achieved up to a ratio of 6 gal/1,000 scf of gas. Above this
ratio, efficiency still increases but at a lesser rate as illustrated in
Figure 16-5.
16.4 ASPHALT ROOFIXG MANUFACTURE
Asphalt-saturated felt is manufactured in high-speed, continuously
operating machines, referred to as asphalt saturators. An integral part
of the operation is the preparation of the asphalt saturant. This prep-
aration consists of oxidizing the asphalt and is accomplished by bubbling
air through liquid (450-500°F) asphalt for 8 to 16 hr. The industry refers
to this operation as "blowing." The time required for blowing depends on
the desired properties of the saturant. It had been the practice to blow
the_asphalt in horizontal stills where the material loss ranges from 3 to
5$.=i/ Most of this material is recovered by venting the exhaust gases
through oil knock-out tanks which are an integral part of the process.
The recaptured mist is not reintroduced into the saturant but is used for
other products such as cut-back asphalt. Thus, in horizontal stills, it
requires— 1.05 tons of asphalt to produce 1.00 ton of saturant. However,
most roofing manufacturing firms are currently using vertical stills from
which the material loss is 1 to 2$ over a 1-1/2 to 5 hr. cycle. il/
352
-------
50
45
40
35
30
25
20
15
10
Multiple Centrifugal Scrubber - Oil Fired Dryer
Baffled Tower Scrubber - Oil Fired Dryer
Baffled Tower Scrubber - Gas Fired Dryer
Multiple Centrifugal Scrubber - Gas Fired Dryer
1
I
J L
1
1
2 4 6 8 10 12 14 16
Scrubber Water-Gas Ratio - Gal/Scf x 10~^
18 20
Figure 16-5 - Effect of Scrubber Water-Oas Ratio on Stack Emissions
at Average Aggregate Fired Rate in the Dryer Feed
i/
353
-------
After blowing, the saturant is transported to the saturation
tank or spray area. Figure 16-6 is a schematic drawing of an asphalt
roofing saturator. The asphalt saturator consists of a dry looper, an
asphalt spray section, a saturating tank, and a wet looper. The felt is
continuously fed from rolls into the dry looper where it is arranged over
rollers into a series of vertical loops used as live storage in the process
to permit maintenance of feed at a uniform rate to the saturating process
during roll changes. The liquid asphalt at 400°F to 450°F may then be
sprayed on one side of the felt. This spray of hot asphalt drives moisture
in the felt out the unsprayed side and prevents the moisture from forming
blisters when the felt is saturated. After being sprayed, the felt passes
through a tank of molten asphalt that saturates the felt. The saturated
felt then enters the wet looper where the material is arranged over another
set of rollers into long, vertical loops to permit cooling of the asphalt.
The web of saturated felt is then rolled up from the discharge end of the
wet looper fcr use as roofing felt or building paper, or a snail quantity
of bituminous material and mica schist or rock granules is applied to the
surface to make composition roofing paper and shingles.1/
16.4.1 Emission Sources and Rates
The main sources of particulate emissions are the saturator and
"blowing" stills. The relatively high application temperature results in
the vaporization of the lower boiling components of the asphalt. Vapor-
ization of moisture in the felt also occurs. These vaporization processes
produce a highly opaque mist. Additional vapors and mists are emitted
from the saturated felt in the wet looper. The mass emission rate is a
function of felt feed rate, felt moisture content, number of sprays used,
and asphalt temperature.i/ Table 16-1 presents the emission rates for
asphalt roofing manufacture. Limited test data are available on emission
rates, and emission totals for roofing manufacture in Table 16-1 are con-
servative estimates.
16.4.2 Characteristics of Asphalt Roofing Manufacture Emissions
The chemical and physical properties of asphalt roofing manu-
facture effluents Eire presented in Table 16-2. Limited data were found
on the properties of effluents from asphalt roofing manufacture. Although
no quantitative data were found on particle size for particulates emitted
from the saturators, the particles are formed by condensation processes,
and, therefore, are likely to be of the order of 1 u .
354
-------
SPRAY
SECTION
WET
LOOPER
w
cn
cn
LOOPER
ASPHALT
TANK
TO ASPHALT
ASPHALT
SATURANT
TO ROLL PRODUCT
OR SHIN6LE
PRODUCT OPERATIONS
HEATER
Figure 16-6 - Schematic Drawing of an Asphalt Roofing Felt
-------
16.4.3 Control Practices and Equipment for Asphalt Roofing Manufacture
Common methods of air pollution control at asphalt saturating
plants include complete enclosure of the spray area and saturator followed
by good ventilation through one or more collection devices including com-
binations of wet scrubbers, and two-stage low-voltage electrical precipi-
tators, or cyclones and fabric filters.
Hoods for collecting the emissions should be installed so that
there is a single continuous enclosure around the points of emission,
extending down to the floor. Since operating personnel must have access
to the saturator for operating adjustments, doorways or other provisions
for entrance in the hood must usually be supplied. These should be kept
as small as possible. In addition, openings in the hoods must, be provided
for the entrance of felt and exit of the saturated material. These open-
ings should be as close to the floor as possible. Experience indicates
that a minimum indraft velocity of 200 fpm is required at all hood open-
ings. Air volumes handled by the exhaust system vary with hood design
ar.d saturator size but are about 10,000 to 20,000 scfm. The large volume
of air required in controlling the saturator equipment generally makes
incineration impractical.
16.4.3.1 Electrostatic Precipitators: The low-voltage, or two-
stags, electrical precipitator preceded by a spray scrubber as a pre-
cleaner gives relatively high collection efficiency as well as substantial
reduction in the opacity of the saturator effluent. Table 16-6 shows the
test results on a scrubber precleaner followed by a two-stage precipitator.
16.4.3.2 Fabric Filters: Eaghouse filters are occasionally used
as air pollution control devices for asphalt saturators, but their use is
limited as a result of maintenance problems associated with filter bag
upkeep and their high power requirement. Oil collected by the filter fabric
is oxidized and polymerized by the air strean, causing plugging of the
fabric and increasing the pressure drop across the filter unit. The air
volume handled by the exhaust system then decreases because of increased
pressure drop and results in loss of mist capture at the saturator's
hood openings.
16.4.3.3 Scrubbers: Spray-type scrubbers have net with limited
success as air pollution control devices for saturators. Some spray
scrubbers may have an efficiency, based on weight removed, as high as
90$, but the scrubber's effluent may be from 50 to 100$ opaque. This
opaque discharge is due to the extremely low collection efficiency of
spray scrubbers for particles< 1 p, in diameter. These small-diameter
particles, when emitted from the scrubber discharge, cause maximum light
scattering and, therefore, high opacities. Table 16-7 shows the results
of tests made on a scrubbing system venting an asphalt saturator.2/
356
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TABLE 16-6i/
EMISSIONS FROM A WATER SCRUBBER AM) LOW-VOLTAGE
TWO-STAGE SIECTRICAL PRECIPITATOR
VENTING AN ASPHALT SATURATORj^
Volume, scfta
Temperature, °F
Emission rate,
grains/scf
lb/hr
Water vapor,
percent
Collection
efficiency
Scrubber Inlet Precipitator Inlet Precipitator Outlet
=0,000
139
0.416
71.4
3.7
20,234
85
0.115
20
4.9
20,116
82
0.058
10
4.8
Scrubber, 11$ Precipitator, 50% Overall, 86%
TABLE 16-71/
EMISSIONS FROM A WATER SCRUBBER VENTING
AN ASPHALT SATURATO!
Volume, scfta
Temperature, °F
Emission rate,
grains/scf
lb/hr
Water, percent
Collection efficiency, percent
Scrubber Inlet
12,000
138
0.535
55
2.7
Scrubber Discharge
12,196
82
0.0737
7.7
4.2SJ
86
a/ At 3.7 volume % of water, vapor is saturated air. Other qualitative
tests run simultaneously showed no particulate water.
357
-------
Theoretical evidence indicates that Venturi-type scrubbers re-
move contaminants with particle sizes of < 1 p, in diameter, but the initial
equipment cost and high energy requirements of the Venturi scrubber make
its use economically unattractive compared with other forms of air pollu-
tion control equipment.!/ However, such devices may be necessary if high
efficiency collection is required to comply with air pollution regulations.
358
-------
REFERENCES
1. "Air Pollution Engineering Manual," PHS Publication No. 999-40,
Cincinnati, Ohio, 1967.
2. "Control Techniques for Particulate Air Pollutants," IlAPCA Publication
No. AP-51, Washington, D.C., 1969.
3. "Guide for Air Pollution Control of Hot Mix Asphalt Plants,"
National Asphalt Pavement Association, Riverdale, Maryland.
4. Danielson, J. A., N. R. Shaffer, and R. M. Ingels, "Control of Asphaltic
Concrete Plants in Los Angeles County," Journal of the Air Pollution
Control Association, 10(1), 29-33, February I860.
5. Gallaer, C. A., "Fine Aggregate Recovery and Dust Collection," Roads
and Streets, pp. 112-117, October 195S.
6. Cross, F. L., Jr., "How One State Set Air Pollution Standards for Asphalt
Plants," Roads and Streets, pp. 132-140, June 1965.
7. Schell, T. W., "Cyclone/Scrubber System Quickly Eliminates Dust Prob-
lems," Rock Products, pp. 66-69, July 1968.
6. Friedrick, H. E., "Air Pollution Control Practices and Criteria for
Hot-Mix Asphalt Paving Batch Plants," Air Pollution Control Associa-
tion, Paper No. 69-160, June 1969.
9. Personal communication.
10. Weimer, I. P., "Dust Removal from the Waste Gases of Preparation
Plants for Bituminous Road-Building Materials," Staub (England Trans.),
_27(1), 9-22 (1967).
11. Air Pollution Emission Factors, NAPCA Report, Contract CPA 22-69-119,
April 1970.
359
-------
CHAPTER 17
FERROALLOY MANUFACTURE
17.1 INTRODUCTION
Ferroalloys are used for deoxidation, alloying, and graphitization
of steel. In the nonferrous metal industry, silicon is used primarily as
an alloying agent for copper, aluminum, magnesium, and nickel. Ferrosilicon,
in the form of 75$ ferrosilicon, is used as a reducing agent in the produc-
tion of magnesium by the Fidgeon process.£/ Manganese is the most widely
used element in ferroalloys, followed by silicon, chromium, and phosphorus.
Others include molybdenum, tungsten, titanium, zirconium, vanadium, boron,
and columbium.
The production of ferroalloys has many dust or fume producing
steps. Materials-handling operations and crushing and grinding generate
coarse dust, while the pyrometallurgical steps release metallic fumes.
The manufacturing process, particulate emission sources, emission rates of
individual sources, chemical and physical properties of effluents, control
practices, and control equipment are discussed in the following sections.
17.2 FERROALLOY PRODUCTION
There are four major methods used to produce ferroalloy and high-
purity metallic additives for steelmaking. These are (l) blast furnace,
(£) electric smelting furnace, (3) alumino silico-thermic process and
(4) electrolytic deposition. The choice of process is dependent upon the
alloy produced and the availability of furnaces. Ferromanganese is the
principal metallurgical form of manganese. This product contains 80$ or
mere of manganese, the balance being mainly iron. It is produced in the
blast furnace or electric-arc furnace and is available in several grades.
A few steel companies produce ferromanganese for their own use since they
have their own ore sources and suitable blast furnaces available.
The coke-burning blast furnace, even with high blast temperature
(1800 to 2000CF), is not a completely efficient smelter for ferroalloys of
manganese, chrome and silicon since the waste slags are relatively high in
unreduced Mn and Cr oxides, and not much more than 20$ silicon can be
reduced economically. This is due to the limitation of temperature genera-
tion at the tuyere plane.
Preceding page blank
-------
The submerged, arc, or the roofed-in open bath electric smelter
with intense heat zones (4000 to 5000eF) near the arc can more effectively
complete the reduction of the oxides; hence, higher overall yields of the
various metallic components and with more general flexibility and control
over the operation than is possible in the coke blast furnace. For these
reasons the electric furnace is more often used for the production of ferro-
alloys .
Metallic silicon and aluminum are intense deoxidizers and are
often used as reducing agents in the so-called metallothermic reduction
processes for ferromolybdenum, ferrcvanadium, ferrotitanium, a combination
of carbon and aluminum as reductant for ferrozirconium, and the alumino-
thermic reduction of ferrocolumbium.
Since the reduction cf oxides by silicon, and particularly alumi-
num metal, is exothermic, quite often enough heat is given off by the reac-
tion, so that the ferroalloys can sometimes be smelted outside the furnace.
The pure metals of manganese, nickel, copper and chromium, etc.,
are most often produced by electrofinning via the electrolytic bath. In
the case of manganese, for example, the ores are calcined and leached,
usually to form MnSO^ mixed with ammonium salts and delivered in solution
to bath. The pure manganese collects as a film about l/Q in. thick on the
cathode, is removed, melted and cast to ingots of 99.7-99.9$ Mn.
The blast furnace and electric smelting furnace production method
are the major sources of air pollution, and these methods are discussed in
more detail in the following paragraphs.
17.2.1 Ferromanganese Blast Furnaces
Ferroalloys are produced in the blast furnace by carbon reduction
of manganese ore and iron ore in the presence of coke and limestone. Ferro-
manganese blast furnaces are usually smaller than pig-iron furnaces and the
hot-blast temperatures are lower, approximately 1100-1200°F. The ferro-
manganese furnaces are blown at a much slower rate and therefore operate
without hanging or slipping. Because of the freedom from these mechanical
troubles, the shape of ferromanganese furnaces has not been given the same
consideration as that of a pig-iron furnace. Oxygen enrichment of the
blast has been tried on a commercial scale with a marked increase in furnace
capacity.i/
There are no rigid specifications for ores used for producing
ferromanganese. The use of a particular ore depends on its cost and grade
in comparison with other ores available at a specific point. A mixture of
a number of different ores is generally charged to the blast furnace, and
362
-------
they are so proportioned as to meet definite specifications for the final
alloy composition. Blending a number of ores improves the physical char-
acter of the charge. Low-silica ores are preferred since the volume of
slag increases with increased silica in the charge, causing losses in man-
ganese, increased fuel consumption, and loss of tonnage.
The physical structure of the ore is important to economical blast
furnace operation. Dust losses are curtailed by mixing hard, coarse ores
with fine ores. Although some of the dust is recovered from the flue gases
and recharged into the furnace as briquets, there is always a loss of man-
ganese due to the deposition of dust in stoves and boilers.
The physical character of the ore is important with relation to
resistance to gas flow. Although large amounts of coarse coke tend to form
porous columns offering little resistance to gas flew, fine ore particles
do not, which makes it difficult to get a uniform distribution of gas
throughout the charge. Nonuniform gas distribution interferes with furnace
efficiency as it affects the heat exchange between solid and gas. In pig-
iron furnaces, the limit of capacity is reached when the air pressure is so
high that it interferes with the settling of the charge, but in ferromanga-
nese furnaces, the loss of manganese by volatilization is what limits the
capacity.
Low blast pressure characterizes the operation of a ferromanganese
blast furnace. The silicon is easily controlled and no problem is presented
by sulfur. Low fuel consumption and the maximum manganese recovery in the
metal are the chief operating goals. High manganese recovery is favored
by (1) small slag volume, (2) a basic slag, (3) high blast temperatures, and
(4) coarse ores.
Although a large amount of fuel is used, the temperatures of ferro-
manganese furnaces are lower than those of pig-iron furnaces. Several fac-
tors are influential in causing this lower temperature. The reducing reac-
tion between MnO and solid carbon or CO is highly endothermic, and since the
slag is formed at a comparatively low temperature and is fluid just above
its melting point, it carries a relatively snail amount of heat down into
the furnace crucible. A chilling effect is caused by the large thermal head
between the relatively cold slag and the tuyeres in this zone. The result
is that the slag reaches the combustion zone at a low temperature. Since
the region below the tuyeres depends chiefly on the slag and metal for its
supply of heat, this means comparatively low temperatures in the crucible.
The low free-running temperature of the ferromanganese slag is not conducive
tc the high-temperature needs for the reduction of manganese oxide, and a
longer time is required. The requisite time interval is accomplished by
bringing fresh slag into the crucible at a lower rate; the low blast
pressure effects this.
363
-------
17.2.2 Electric-Arc Furnaces
The majority of ferroalloy furnaces are termed submerged arc,
although the mode of energy release in many cases is resistive heating.'zJ
Raw ore, coke, and limestone or dolomite mixed in proper proportions con-
stitute the charge for the electric-arc furnace process. A large supply
cf electric power is necessary for economical operation. Important operat-
ing considerations include power and electrode requirements, size and type
of furnace, amount and size of coke, and the nature of slag losses.
Submerged-arc furnaces generally operate with continuous power
except for periods of power interruption or mechanical breakdown of com-
ponents. 'Operating times average 90 to 98$. The electrodes operate 3 to
6 ft. above the hearth, and are submerged 3 to 5 ft. below the mix level
so that some heat exchange and mass transfer can occur between the reaction
gas and the mix. The products produced in this type furnace are chiefly:^/
1. Silicon Alloys - Ferrosilicon (50 to 98# Si) and CaSi
2. Chromium Alloys - High carbon FeCr in various grades and FeCrSi
3. Manganese Alloys - Standard FeMn and SiMn
There are a smaller number of furnaces which do not operate with
deep submergence of the electrodes and produce a batch melt which is usually
removed by tilting the furnace. Mix additions and power input would usually
be cyclic. Examples of products produced in this type of furnace are:
1. Manganese Ore - Lime melt for subsequent ladle reaction with
silicomanganese to produce medium carbon and low carbon ferromangenese
2. Chrome Ore - Lime melt for subsequent ladle reaction with
ferrochrom-silicon to produce low carbon ferrochrome
3. Special Alloys, such as Aluminum - Vanadium, Ferrocolumbium
17.3 EMISSION SOURCES AND RATES
The production of ferroalloys has many dust or fume producing
steps. Particulates are emitted from raw material handling, mix delivery,
crushing, grinding, and sizing, and furnace operations. The dust resulting
from the solids-handling steps does not present a difficult control problem.
Emissions from furnaces vary widely in type and quantity, depending upon
the particular ferroalloy being produced, type of furnace used, and the
amount of carbon in the alloy.
364
-------
In the operation of a blast furnace, a large quantity of dense
fume may be emitted to the atmosphere. The amount and types of particles
which make up this fune are different from those commonly found in the gases
from blast furnaces producing basic pig iron.5/ One type, comprising
about 20$ cf the dust present, consists of particles above 20 y, in size,
which appear to originate in the disintegration of coke and ore in the fur-
nace burden, me other type, which accounts for 80$ of the solids present
in the gas, is a typical fume varying in size from 0,1 to 1.0 jj,. This mate-
rial is formed by a process of vaporization and condensation. Particulate
emissions can be reduced by raw materials choice and sound operating prac-
tices.
The conventional submerged-arc furnace utilizes carbon reduction
of metallic oxides and continuously produces large quantities of carbon
monoxide.!/ Other sources of gas are moisture in the charge materials,
reducing agent volatile matter, thermal decomposition products of the raw
ore, and intermediate products of reaction. The carbon monoxide normally
accounts for about 70 vol. $ of the gases. The gases rising cut the top
of the furnace carry fume or fume precursors and also entrain the finer size
constituents of the mix or charge. Submerged-arc furnaces operate in steady-
state and gas generation is continuous.—'
In an open furnace, all the CO burns with induced air at the top
cf the charge, resulting in a large volume of gas. In a closed furnace
most or all of the CO is withdrawn from the furnace without combustion with
air.
Fume emission also occurs at furnace tap holes. Because most
furnaces are tapped intermittently, tap hole fumes occur only about 10 to
20$ of the furnace operating time. Another source of fune occurs in handling
the metal after the tapping step. Conveying the ladle, pouring, and casting
give rise to fumes on an intermittent basis.£/
Some processes conduct additional reactions in the ladle, such as
chlorination, oxidation, and slag-metal reactions. In these cases, there
may be actual gas generation in addition to the treatment gas, and possibly
gross ejection of a portion of the ladle contents. These are batch processes
with intermittent fume generation.
Melting operations may be conducted in an open arc furnace in some
plants. While no major quantities of gas sire generated in this operation,
thermally induced air flow may result in fume emission.£/
A minor source of particulate pollution on furnaces with self-
baking electrodes is the fume resulting from the electrode paste during
heating and baking. This fume is usually directly vented.
365
-------
Emissions and emission, rates will vary with (1) type of alloy pro-
duced, (2) process (i.e., continuous or batch), (3) choice of raw materials,
(4) operating techniques, and (5) maintenance practices.
With silicon alloys, as the percentage of silicon in the alloy
increases, the loss of SiC2 increases, so that a silicon metal furnace pro-
duces substantially more fume than a 50$ FeSi furnace at the same load.2/
In addition, the higher ferrcsilicon operations (75$ Si and above) are known
as "hot" operations; i.e., the gas exiting from the mix is at a high tempera-
ture and the furnace is subject to blows (frequently jets of gas issue at
high velocity directly from the high temperature reaction zone). Higher
silicon operations are also subject to hearth build-ups of silicon carbide.
Under these conditions, electrodes operate in a higher position and more
fume can result.£/
Because manganese ores contain a significant amount of water, as
well as higher manganese oxides which release oxygen upon heating at tempera-
tures below 1000°C, a manganese furnace can be subject to "rough" operation.
Sudden release of gas can result in substantial mix ejection from the fur-
nace. In furnaces with self-baking electrodes, the relatively oxidizing
atmosphere can result in "fluting" of the electrodes, furnishing a direct
gas passage from the high temperature zone of the furnace, with increased
fume emission.Silicomar.ganese furnaces are subject to "slag boils,"
where slag rises up to cover the top surface of the charge, impeding mix
delivery and uniform gas ascent.
Emissions from batch-operated furnaces are periodic. As a result
of sudden addition of mix containing volatile constituents (coal volatiles,
moisture, aluminum) to a hot furnace container, substantial violent gas
eruptions can occur. This is best exemplified by the manganese ore-lime
melt furnace where momentary gas flow following mix addition can be five
times the average flow (as contrasted with variation of 20$ or less in a
well-running submerged-arc furnace). Temperature and dust loading peaks
also correspond to the gas flow peak.
In contrast, chromium ore-lime melt furnaces, to which little or
no gas releasing constituents are fed, are not subject to this violent
behavior. In seme circumstances, solids or molten material ejected from
the furnace continue to burn in the air, giving rise to collection problems.
Some of the special alloys are also produced by aluminothermic
reactions without the addition of electrical energy. These reactions, if
unconfined, give rise to momentary peaks of gas flow.£/
366
-------
Volatile materials in the furnace charge give rise to rough opera-
tion. Another significant contributor to rough operation is the presence
of fines or dense material in the feed. These materials promote bridging
and nonuniform descent of the charge, resulting in gas channeling and by-
passing. Sudden collapse of a bridge then gives rise to a momentary gas
burst. A porous charge will give good gas distributions and use of good
quality scrap will also reduce emissions. On some products, economics dic-
tate the use of raw materials with more fines, or with more volatile matter.
Each of these has an adverse effect on the smooth operation of the furnace,
and consequently pollution may increase.
Differences in operating techniques can have a significant effect
an fume generation. The average rate of furnace gas production is roughly
proportional to electrical input, so that a higher load on a given furnace
generally results in at least a proportional increase in fume emission.
In some circumstances, fume emission increases at a rate greater than the
load increase, as a result of rougher operation and inadequate gas with-
drawal capacity.
At a fixed load, even though the gas generation is almost constant,
fume concentration and, hence, the weight per hour emitted can vary by a
factor of 5 to 1. Operation with insufficient electrode submergence pro-
motes increased fume emission. There is also some evidence that higher
voltage operation, in addition to promoting a higher electrode position,
alters the mode of energy release beneath the electrodes, increasing locally
the energy supplied per unit volume, promoting higher local temperatures,
and increasing the fume concentration.^/
On some operations, silicon metal production in particular, where
stoking of the charge is necessary to break up crusts and partially agglomerated
material and to cover up areas of blows, fume emission can be a function of
how well and how often the furnace is stoked.
On other operations, where a mix seal and cover are used to allow
collection of most or all of the furnace gas, direct venting and increased
fume emission can occur if lack of mix prevents making a seal either be-
cause of poor mix placement or insufficient mix delivery. Direct venting
can also take place during startup, shutdown, and "burndown" to remove
undercover accumulations.£/
Loads on existing furnaces have been progressively increased as
operating techniques improved and as more knowledge of transformer capacity
became available. This tendency has taxed the furnace gas collection sys-
tems and, in the case of open furnaces, has certainly presented a more con-
centrated source of fume.£/
367
-------
Maintenance practices significantly affect fume emission on covered
furnaces, where accumulation of material under the cover and in gas off-
takes and ducts reduces gas withdrawal capacity. -Plugging of gas or water
passages in cleaning apparatus results in reduced efficiency of gas cleaning.
Water leaks from electrode suspension equipment and other compo-
nents above the furnace can result in some increase in gas flow (as steam or
hydrogen).
17.3.1 Summary of Emission Rates
Table 17-1 presents a summary of emission rates from ferroalloy
production. Particulate emissions currently total 160,300 tons/year. Electric-
arc furnaces account for over 90$ of this total (150,000 tons), and electric-
arc furnaces producing ferrosilicon emit over 40$ of the particulates
(71,000 tons).
17.4 EFFLUENT CHARACTERISTICS
The chemical and physical properties of effluents from ferroalloy
production processes are presented in Table 17-2. Properties of the emitted
particulates depend upon the alloy being produced and furnace type. Par-
ticle size of the metallic fume emitted from "uhe furnace ranges from 0.1-
1.0 ii with a geometric mean of 0.3 p,. Grain loadings and flowrates are
dependent upon furnace type. Open electric furnaces have high flowrates
and moderate grain loadings while closed furnaces have moderate flowrates
and generally high grain loadings.
With silicon alloys the fume produced is gray and contains a high
percentage of SiOg. Some tars and carbon are also present arising from the
coal, coke, or wood chips used in the charge. Chromium furnaces produce a
Si02 fume similar to a ferrosilicon operation with some additional chromium
oxides. Manganese operations produce a brown fume. Analyses indicate the
fume to be largely a mixture of SiOg and manganese oxides.
17.5 CONTROL PRACTICES
Limited sources of information have been found which describe con-
trol practices for ferroalloys. However, one very complete writeup by R. A.
Personi/ has been reviewed and excerpts used in the following description
of control techniques and practices.
368
-------
u>
CO
UD
II. Materials Handling
TABLE 17-1
PARTICULATE EMISSIONS
PRODUCTION OF FERROALLOYS
Source
I• Furnaces
A. Blast Furnaces
B. Electric-Arc Furnaces
Efficiency
Application
Net
of Control
of Control
Control
Emissions
Quantity of Material
Emission Factor
cc
Ct
Cc"Ct
(tons/yr)
591,000 tons, ferromanganese
410
lb/ton product*
0.99
1.0
0.99
1,200
317,000 tons, ferromanganese
44
lb/ton
0.80
0.50
0.40
4,200
285,000 tons, siliccmanganese
195
lb/ton
0.80
0.50
0.40
16,500
665,000 tons, ferrosillcon
357
lb/ton
0.80
0.50
0.40
71,200
96,000 tons, silicon metal
583
lb/ton
0.80
0.50
0.40
16,800
166,000 tons, silvery iron
120
lb/ton
0.80
0.50
0.40
6,000
590,000 tons, ferrochrome,
ferrophosphorus
200
lb/ton
0.80
0.50
0.40
35,400
,710,000 tons of metal pro-
duced
10
lb/ton of metal
produced
0.90
0.35
0.32
9.000
Total from Ferroalloys
160,300
* All emission factors are "per ton of product.
-------
TABLE 17-2
EFFLUENT CHARACTERISTICS - FERROALLOY MANUFACTURE
A. Particulate
Source
Particle Size
Chemical Particle Moisture
Solids Loading Composition Density Electrical Resistivity Content
Toxicity
I. Blast (a) Dust (20$ of emitted
Furnace particulate)
100 > 20
(b) Fume (80$ of emitted
particulate)
Range: 0.1-1
Avg. 0.3
4.5-17
Mn: 15-25
Fe: 0.3-0.5
Na20 + K^O:
Si02: 9-19
Al2°3: 5-11
CaO: 8-15
MgO: 4-G
S: 5-7
C: 1-2
8-15
See Table 17-3 for
detailed data
Manganese compounds
are poisonous
II. Electric
Furnace
OJ
-J
o
(a) Ferrosili- Optical Count Range during
con (50$) Range: 0.01-4 cycle 0.2-
(open fur- Geometric mean: 0.3 2.7
nace) Standard deviation: Mean: 1.5
2-4
Hydrated silica:
92.8
X-Ray diffraction
showed presence
of: Si, Fe, Al,
Ca, Mg, Mn, Cu
and Ti
See Table 17-3 for
detailed data
(b) Miscellane- See Table 17-4 for
ous alloys detailed data
0.4-30
See Table 17-4 for
detailed data
See Table ]7-3 for
detailed data
A. Particulates (Concluded)
Source
Solubility
Wettability
Hygroscopic Flammability or
Characteristics Explosive Limits
Handling Characteristics
Optical
Properties
Odor
I. Blast Furnace
Fume is pyro-
phoric
Light, floury (fume com-
ponent) ferromanganese
fume forms a hard,
cement-like deposit
when wetted
Gray (ferro-
manganese)
II. Electric Fur-
nace
(a) Ferrosilicon 1.5-4$ in.H^O
(50$)
* See Coding Key, Table 5-1, Chapter 5, page 45, for units for individual effluent properties.
-------
TAHlJi 1/-;.' (Cuncluded)
B. Carrier Gas
Source
Flowrate
1. Blast Furnace (a) 135 (one
furnace)
(b) 270* (one
furnace)
Temperature
350-750
Moisture
Content
Variable over
cycle:
2-30
Chemical.
Composition
CO, N:,
5 oU^
Toxicity Corrosivity 'xior
' lirr.-ilil i w
or Lxploci/e
Limits
Explosive be-
cause of C .
content
'.pU f..-al
Properties
II. Electric
Furnace
(a) Ferrosilicon
(50$, open
furnace)
95-176
(b) Ferroman- (a) G*v.'
ganese
(closed fur-(b) 25.6-30.4
nace)
(c) FeCr Alloy (a) 662
(closed
furnace) (b) 20.8-33.6
c;: 72
C0o:LI
\{,y. 6
|C,: 10
CIi4: 1
CO: 7?
CO?: 11
Ho: 6
(d) FeSi(75$ Si, (a)
closed fur-
nace) (b) 54.4-57.6
1032
CM.: 1
4
(e) Miscellane-
ous alloys
(1) Open
furnace
(a) 100-630*
(b)
(a) 100«
(2) Semi-
closed
furnace (b)
(3) Closed (a) 11-56
furnace
250-550
400-1200
« Actual conditions.
-------
TABLE 17-3
FERROALLOY FUME RESISTIVITY^/
(ohm-cm, 200-300°F Temperature Range)
With Conditioning
Without of Gas to 20^
Product
Conditioning
Moisture
SMZ *
8.7
X
1013
8.5
x 1011
50$ FeSi
1.2
X
1013
9.3
x 1011
FeMn
4.7
X
1011
3.2
x 108
FeCr
9.4
X
1010
2.1
x 1010
SiMn
1.3
X
1010
2.4
K
H
O
GO
3i -
60-65/&
Mr, -
5-7$
Zr -
5-1%
372
-------
TABLE 17-4
TYPICAL FERROALLOY FURNACE FUME CHARACTERIZATIONS
Furnace Product:
Furnace Type
Fume Shape
50$ FeSi
Open
Spherical,
sometimes
in chains
SMZ»
Open
sometimes
in chains
SiMn»»
SiMn**
Covered
FeMn
Open
H.C.FeCr
Covered
Chrome Ore- Mn Ore**-
Lime Melt Lime Melt
Open
ular
Open
Spherical, Spherical Spherical Spherical Spherical Spherical Spherical
and irreg- and irreg-
ular
Fume Size Char-
acteristics (n)
Maximum
Most Particles
0.75
0.05-0.3
0.8
0.05-0.3
0.75
0.2-0.4
0.75
0.2-0.4
0.75
0.05-0.4
1.0
0.1-0.4
0.50
0.05-0.2
2.0
0.2-0.5
X-Ray Diffraction
Primary
Trace Con-
stituents
FeSi
FeSig
Fe3°4
Fe203
Quartz
SiC
All fumes were primarily amorphous
Mn,04
MnO
Quartz
Quartz
SiMn
Spinel
Mn-* 0,
'3U4
Spinel
MnO Quartz
Quartz
Spinel
CaO
Chemical Analysis -
*
Si Os
63-88
61.12
15.68
24.60
25.48
20.96
10.86
• 3.28
FeO
14.08
6.75
4.60
5.96
10.92
7.48
1.22
MgO
1.08
1.12
3.78
1.03
15.41
7.43
0.96
CaO
1.01
--
1.58
2.24
—
15.06
34.24
MnO
6.12
31.35
31.92
33.60
2.84
--
12.34
AI2O3
2.10
5.55
4.48
8.38
7.12
4.88
1.36
LOI
—
23.25
12.04
--
—
13.86
11.92
TCr as Cr^Oj
SiC
1.82
—
—
—
29.27
14.69
—
ZrOg
R)0
1.26
0.47
_ _
::
—
—
0.98
NagO
BaO
—
—
2.12
—
—
1.70
2.05
1.13
KgO
* Si - 60-65$; Mn - 5-7$; Zr - 5-7$.
** Manganese fume analyses in particular are subject to wide variations, depending on the ores used.
13.08
-------
The controls used are affected, by the two types of electric fur-
naces. In the open furnace, all the CO produced burns with induced air at
the top of the charge, resulting in a large volume of high temperature gas.
In a closed furnace most or all of the CO is withdrawn from the furnace
without combustion with air. When the furnace gas bums with air, as with
an open furnace, a significant volume increase occurs. Depending on the
amount of induced air, the volume to be treated for dust collection may
increase by a factor of 50. Table 17-5 shows furnace gas generated without
combustion while Table 17-6 gives a comparison of gas flows for open and
closed furnaces.i^
Semicovered furnaces have also been used. The gas is usually
cleaned in a multistage centrifugal fan with water spray nozzles. However,
existing units are restricted to a capacity of about 2,000 acftn and are
higher power and water consumers than a Venturi scrubber.
17.5.1 Control Equipment
17.5.1.1 Open Furnaces: Modern open furnaces require a hood to
protect the superstructure and the electrode column components. A hood at
least the diameter of the furnace shell, with the minimum opening between
the hood and operating or charging floor, and an air inlet velocity of at
least 3 ft/sec have been the criteria for recent installations. Sufficient
hood depth must also be provided to assure that combustion is substantially
complete within the hood.
Installed cost of fume collectors depends on the particular instal-
lation and the degree to which utility services are available. Estimated
costs for units recently installed or planned on open furnaces, excluding
furnace hood and interior ductwork and liquid waste disposal systems, are
shown in Table 17-7.1/' These installed costs are 200-300$ higher than would
be estimated on the basis of general cost curves given in Appendix A.
17.5.1.1.1 Wet scrubbers: The only currently feasible type of
wet collector for cleaning the large gas volumes from open furnaces is the
Venturi type scrubber. With required pressure drops on the order of 60 in.
w.g. the power consumption approaches 10$ of the furnace rating (for a low
hood design).i/ Most Venturi designs allow recirculation of scrubbing
liquor so that water consumption is reduced to that evaporated into the gas
plus that exiting with the concentrated solids stream. The Venturi has the
advantage of being able to absorb gas temperature peaks by evaporating more
water. For a ferrosilicon or ferrochrome-silicon operation substantially
all of the sulfur in the reducing agent appears in the gas phase, and a
corrosion problem occurs in any liquid recycle system unless neutralizing
agents or special materials of construction are used.
374
-------
TA3LE 17-5
APPROXIMATE FURNACE GAS GENERATION!/
(Without Combustion)
Product (SCIM/MW)
Silicon Metal 140-150
50$ Ferrosilicon 130-140
Standard. Ferromanganese 160-170
Silicomanganese 120-130
Ferrochrome-Silicon 110-120
H.C. Ferrochroae 80- 90
Calcium Carbide 70- 80
(Based on gas saturated at 100°F, scf at 30 in. Hg, 60°F)
TABLE 17-6
:0MPARIS0N OF FURNACE GAS VOLUMESl/
Closed Furnace
Cpen Furnace
(Low Hoed)
FeCrSi, 25 W
ACFK at Temp,
scfn
501b FeSi, 50 MW
ACFK at Temp,
scfm
8700 at 1100°F
2900
20,000 at 1100°F
6,600
230,000 at 430 F
135,000
410,000 at 760°F
175,000
TABLE 17-7
ESTIMATED COST OF FURUACE CONTROLSi/
Venturi Scrubber
Bag Filter
Electrostatic Precipitator (with conditioning)
Estimated Installed Cost
(1959) $/ACM at Furnace Hood
2.40 - 3.60
2.90 - 3.60
3.80 - 4.20
375
-------
Recent wet scrubber installations are summarized in Table
17.e.i/
17.5.1.1.2 Baghouses: Cloth-type filters do an effective Job
of cleaning the combustion gases fron open furnaces sc long as the filter
media remain intact. Baghouse installations often utilize the pressure-type
baghouse, with the fan on the dirty-gas side, to simplify the collector
housing construction and to allow access into the collector during operation.
To prevent carryover of burning mix particles, a mechanical collector ahead
of the baghouse is desirable .i/
Because of temperature limitations on the cloth (500°F for
treated fiberglass), the gas must often be cooled by passing through heat
transfer surfaces or by dilution. Cooling by water spray injection is pos-
sible, but can lead to control complications and possible blinding of the
tags.
The amount of gas a cloth filter can handle when operating on
silica fume without bag blinding is a maximum of about 2 acfn/sq ft of
filter area. This limit results in a large number of bags, up into the
thousands, in order to treat the combustion gas from an open furnace.
A significant problem associated with the use of fiberglass
bags on silica fume collection is the buildup of electrostatic charge, which
in turn leads to a high residual pressure drop across the bags.
17.5.1.1.3 Electrostatic precipitators: Electrostatic precipi-
tators have been installed on open furnaces producing silicon, ferrosilicon,
ferrochrome-silicon, and silicomanganese.
Unfortunately, most ferroalloy fumes at temperatures below
500°F have too high an electrical resistivity, i.e., greater than 1 x 10^
ohm-cm. The resistivity is in an acceptable range only if the gas tempera-
ture is maintained above 500-600°F. Water conditioning would lower the re-
sistivity, but a large spray tower is required for proper humidification.
Stainless steel construction would be a necessity for ferrosilicon or fer-
rochrome-silicon operations. The alternate use of steam is feasible only
if low-cost steam is available.
The resistivity problem could be overcome by using a wet precipi-
tator, but water usage appears to be greater than that for a wet scrubber
without recycle.i/ Wet electrostatic precipitators have been used at one
installation in Europe. However, all parts of the precipitators exposed
to the dirty water and to the wet gas were reconstructed of stainless
steel. £/ An electrostatic precipitator is being installed on a ferroalloy
furnace by AIRC0 at Charleston, South Carolina.
376
-------
TABLE 17-8
EXAMPLES OF FURNACE WET SCRUBBERS^/
Open Furnace - Low Hood
Collector
Original Completion Date
Furnace Rating for Collector Design
Furnace Product
Measured Collection Efficiency, Avg.
Inlet Loading, grains/scf
Outlet Loading, grains/scf
Design Volume at Furnace Hood
Design Temperature
Actual Duct or Offtake Temperature
Design Volume Handled by Fans or
Blowers
Operating Pressure Drop across
Collector, inches water
Installed H.P. - Fans
- Auxiliaries
Tons/Day Collected Dust
Tons/Day Uncollected Emission
Water Circulation
Water Usage
II
Problems:
1967
25 MW
FeCrSi
92.6$
1.43
0.106
230,000 ACFM
430°F
500 to 570°F
55
2,600
50
11 to 13
0.75 to 1
1,800 gpm
310 gpm
1968
30 MW
SiMn
98.6$
1.31
0.017
255,000 ACFM
620° F
490 to 550°F
(1) System falls 25$
short of design
flow.
(2) High fan outage.
(3) Necessity to add
lime to neutra-
lize scrubbing
liquid.
57
2,800
50
14 to 17
0.20
1,800 gpm
350 gpm
(1) High fan
outage.
Ill
1968
30 MW
H.C. FeCr
98.2$
I.07
0.019
210,000 ACFM
590°F
480° F
194,000 ACFM 196,000 ACFM 196,000 ACFM
57
2,800
50
11 to 17
0.26
1,800 gpm
350 gpm
(1) High fan
outage.
Semi-Closed Furnace
IV
1965
45 MW
50$ FeSi
98.4$ (particulates)
79$ (organics)
4.93
0.08
1100 to 1200°F
6,500 scfm
72 to 80
600
5 to 8
None
75-100 gpm
75-100 gpm
(l) Continuous kerosene
injection necessary
for blowers.
-------
17.5.1.2 Covered Furnaces: Seinicovered furnaces, while collecting
a majority of the fume, may not in many cases be satisfactory for current
or pending regulation.
The sealed furnace, which has a cover including sliding seals
around the electrodes and mix spouts, is primarily a European development.
It has thus far been applied only to calcium carbide, pig iron, standard
ferromanganese and silicomanganese. Sealed covers are difficult to adapt
tc an existing furnace because of the extensive revisions that are usually-
required .
A modified cover, incorporating electrode seals, but covering
only the "reaction zones" around the electrodes and leaving the outer rim
of the furnace open, has been developed. This approach, called gas collec-
tion sleeves or smoke rings, has the advantages of collecting the gas in the
observed region of maximum generation, of allowing partial stoking of the
mix, and of being cheaper than a complete cover. Initial installations
were made on ferromanganese furnaces and subsequently on calcium carbide
and silicomanganese furnaces.i/
17.5.1.2.1 Wet scrubbers: The disintegrator type of scrubber
does a good cleaning job when properly maintained and has the additional
advantage of producing a slight pressure head (about 2 in. w.g.). However,
the capacity limitation and high water and power consumption make it uneco-
nomical for most new furnace installations.
The Venturi type scrubber has been installed or. CO gas cleaning
installations but the required pressure drops are high. The characteristics
of a typical installation are included in Table 17-8.i/
17.5.1.2.2 Electrostatic precipitator; The electrostatic pre-
cipitator is a possible CO gas cleaning device, but has found limited
ferroalloy application.
17.5.1.2.3 Baghouses: It would be possible to use a bag col-
lector to clean CO gas, but no applications on ferroalloy furnaces are
known.
17.5.1.5 Blast Furnaces: Blast furnaces are also used for ferro-
alloy production including ferromanganese. Wet scrubbers are used in clean-
ing the emitted gases. High maintenance costs may attend such an operation
because of the cementing properties of the fume. It also requires a large-
scale water-treating plant to avoid stream pollution.
For these reasons, one producer conducted pilot testing of an
electrostatic precipitator preceded by a spray cooler. The collected dust
378
-------
from the precipitator, being pyrophcric, was burned in a rotary kiln and
the product was then hrinupf.t.pii.3>7,8/
One Venturi scrubber installation in England reportedly cleaned
the gases from a ferromanganese blast furnace to less than 0.02 grain/cf.
This unit required a pressure drop of 24 in. w.g. and a water flow of 5 gal/
1,000 cf of gas.
10/ *
Sonic agglomeration of fume from a ferromanganese blast furnace
was investigated in 1950 tut was not economically attractive.^/
379
-------
REFERENCES
1. Person, R. A., "Control of Emissions from Ferroalloy Furnace Processing,1'
Union Carbide Corporation, Niagara Falls, New York, 1969.
2. Kirk and Othmer, Encyclopedia of Charm'cal Technology, 2nd Edition,
Interscience Publishers, 1968.
3. Bishop, C. A., "Some Experience with Air Pollution Abatement in the Steel
Industry." United States Steel Company, Pittsburgh, Pennsylvania,
June 1952.
4. Rozenburg, V. L., et al., "Influence of Electrical Conditions and
geometry of Closed Ferroalloy Furnaces on Amount of Gas and Dust
Evolved," Stal (English Translation), pp. 894-895, November 1966.
5. 'J. S. Department of Health, Education and Welfare, Control Techniques
for Particulate Air Pollutants, Washington, D. C., Public Health
Service, 1959.
6. Ferrari, Renzo, "Experiences in Developing an Effective Pollution
Control System for a Submerged Arc Ferroalloy Furnace Operation,"
Journal of Metals, April 1968.
7. Specht, 3. E., and R. W. Sickles, "New Uses of Electrical Precipita-
tion for Control of Atmospheric Pollution," Air Repair, 4, November
1954.
8. Good, C. H., "The Ferro-Manganese Gas Cleaning Installation at Duquesne
Works," Air Repair, February 1955.
9. Brisse, A. H., "Sonic Agglomeration of Fume in Ferromanganese Blast
Furnace Gas," Industrial Heating, November 1950.
10. Thring, M. W., and R. J. Sarjant, "Dust Problems of the Iron and Steel
Industry," Iron and Coal Trades Review, March 29, 1957.
380
-------
CHAPTER 18
IRON FOUNDRIES
18.1 INTRODUCTION
Gray iron foundries range from primitive, unmechanized hand oper-
ations to highly mechanized plants in which operators are assisted by elec-
trical, mechanical, and hydraulic equipment. Cupola, electric-arc, electric-
induction, and reverberatory air furnaces are used to obtain molten metal
for production of castings.
The iron melting process in foundries is the principal source of
emissions. Secondary sources include materials handling, casting shakeout
systems, buffing and grinding operations, and core ovens. The production
process, particulate emission sources, particulate emission rates, effluent
characteristics, and control practices and equipment are discussed in the
following sections.
18.2 FOUNDRY PROCESSES
The gray iron cupola in its simplest form is a vertical, hollow
shaft having a steel shell either lined with refractory or backed by a
water curtain for temperature control. A charging door located above the
bottom of the cupola admits the charge which consists of alternate layers
of coke, iron materials, and flux. Tuyeres, located near the bottom of
the cupola, admit air for combustion. Provision is made for removing slag
and molten iron from openings below the tuyeres, the iron being tapped from
the bottom level and slag tapped or skimmed from above the iron.
Electric-arc and induction furnaces are mostly used to produce
specially alloyed irons. Fuels are not used in the heating process in these
furnaces.
18.3 EMISSION RATES FROM IRON FOUNDRIES
Hiysical processes, chemical reactions, and the quality of scrap
affect the emissions of dust and fumes from cupolas. Physical processes in-
clude entrainment of coke, lime and oil or grease particles. Non-uniform
combustion results in variations in emissions. An oily charge can evolve
huge volumes of black smoke and fine chips can significantly increase metal
fuming rates. Because of the wide divergence of ratios of charge materials
381
-------
utilized, and the varying quality of the scrap, no simple accurate estimate
can be made of the nature and quantity of pollutants emitted from foundry
cupolas.
Quality and composition of emissions vary between cupolas and
even at intervals in the same cupola. This variation is caused by changes
in iron-to-coke ratios, air volume/ton melted, and quality of scrap. A
charge containing limestone with a low degree of hardness and a large portion
of fines will produce a relatively high dust content in the waste gases.
The abrasion resistance and ash content of the coke also has an effect on
the dust emission level. Qnissions from hot-blast cupolas are generally
higher than from cold-blast cupolas. This is probably due to larger quan-
tities of small steel scrap being charged into the hot-blast cupolas, and
is not a direct function of the combustion air temperature, blast volume,
or other operating parameters.
Emissions of sulfur compounds axe usually low because sulfur con-
tent of coke is generally 0.6$ or less. 3O2 concentrations have been ob-
served to vary between 25 and 250 ppm.^/ These concentrations, when combined
with moisture, can form enough sulfuric acid to corrode surrounding equip-
ment. Fluorine and/or HF from fluorspar may be emitted, probably in small
cuantitites.]J
Electric-arc furnace emissions are less of a problem than cupola
emissions. Since these furnaces are mostly used to produce special alloy
irons, the quality of material charged is better and freer from dirt and
oils. Emissions are primarily metallic fumes; the quantity emitted varies
from 5 to 1C lb/ton of metal charged.2/
Emissions from electric-induction furnaces are even less of a
problem than those from the electric-arc furnaces. Use of clean scrap,
minimum exposure of the metal to air while in the furnace, and uniform
operation of the furnace usually result in negligible quantities of emis-
sions. The auantitv of emissions, primarily metal oxides, is about 2 lb/ton
of netal charged.£/
Apart from the cupola, other sources of iron foundry emissions
are casting shakeout systems, buffing and grinding, and core ovens. The
magnitude of these emissions is low compared to cupolas.
Table 18-1 summarizes emissions from operations associated with
gray iron foundries. Cupola emissions are dominant, and currently total about
105,000 tons/yr. No estimate of emissions from casting shakecut systems,
buffing and grinding operations, and core ovens was made due to lack of
emission data from these secondary sources.
382
-------
Oi
CO
Oi
Source
I. Furnaces
A. Cupola
1. Hot blast
a. externally fired
b. recuperative
2. Cold blast
B. Electric
1. Arc
2. Induction
C. Reverberatory
II. Materials Handling
A. Freight Unloading --Coke
and Limestone
B. Conveyors
1. Transfer points
2. Discharge to storage
a. bins, silos
b. stockpiles
C. Elevators
1. Boots
2. Beads
D. Sand Handling
III. Core Ovens
IV. Shell Core Machines
V. Casting 9iake-out System
VI. Grinding and Buffing
TAPIS 10-1
PARTICULATE EMISSIONS
IRON FOUNDRIES
Quantity of Material
18,000,000 tons of hot metal
10,500,000 tons of sand
0.3 lb/ton of sand
0.3 lb/gal of core oil
0.35 lb/ton of cores
Emission Factor
1.0 lb/ton of hot metal 0.80
15 lb/ton of hot metal
23 lb/ton of hot metal
5-10 lb/ton
*5 lb/ton of hot metal *0.80
Efficiency Application Net
of Control of Control Control
Cc Ct
-------
16.4 CHARACTERISTICS 0? EFJUJENTS FROM IRON FOUNDRIES
The chemical and physical properties of effluents from iron
foundries are summarized in Table 18-2. Cupola dust is a very heterogeneous
mixture. Particulates contain coke and flux particles, various metals,
their oxides, and some sulfates. Silica content is high, particularly in
the 0-10 n fraction. Of the metals portion, 60$ are oxides of Si and Fe.
Significant zinc and lead oxides are also found. Other elements found in
the particulates include manganese, chromium, tin, titanium, molybdenum,
zirconium, nickel, copper, cobalt, and silver.About 25-30 wt. $ of
the particulates are less than 10 The particle size distribution ranges
"between vide limits, depending on melt rate, coke usage, scrap formulation,
and furnace operating variables. Under some conditions, over 50$ of the
dust may be less than 1 |i in diameter, whereas in other cases less than 5$
by weight of the total particulate may be under 2 g, in diameter. Older data
indicate no more than 10$ of the particles by weight are in the size range
below 10 p,. However, later studies indicate that particle sizes under 1 (i
may constitute 40$ and more of the total weight. Some of the scatter be-
tween the various investigations may be a result of differences in sampling
equipment and techniques and of sampling at different locations in the
ductwork.
18.5 CONTROL PRACTICES AND EQUITMENT FOR IRON FOUNDRIES
IS.5.1 Electric Melting Furnaces
The extremely fine particle size and large surface area of electric-
furnace fume result in discharge to the atmosphere of a plume that may not
meet the visibility restrictions in some air pollution codes, even when
weight requirements are met. The concentration of particulate in the ef-
fluent air from an electric-furnace fume control system may have to be less
than 0,05 grain/cu ft of air if an emission is to satisfy an equivalent
opacity restriction.§/
There have been several electrostatic precipitator installations
to control particulates from larger furnaces and there are about 50 instal-
lations employing fabric filter collectors. Fabric filter collectors gen-
erally result in an effluent nearly free from visible particulates.5/
The collection of fumes from the electric furnace has been done
by using canopy hoods to gather the expanding, rising gas column, by local
exhaust around electrodes and charging doors, and by direct evacuation of
the furnace itself.£/
384
-------
TA1U-;
THO'
Pnriii-uLaLe
Source
Part L'.'lc Size
Sol I.d:; Load Lnc
Chemical Compocilion
Parl.i'- lo Density
El':''.
He.. iz
Consent
Tox in l\y
Iron Foundry
Cray Iron Cupola:
1. Light-off
period
0.001-0.30
Melting
period
0.0-1. r.
Ui
CO
cn
Complete
heat
2-30 < 5, 2-35 < 10,
10-40 < 20, 20-60 < 50
Average distribution:
10 <5, 22 < 10, 25
< 20, 35 < 50
Bahco analysis: (two tests)
20-54 < 5, 37-63 < 10,
52-72 < 20, 66-77 < 40
Also see Figure 10-1
Extreme raryc:
0.3-i:>
Usual ranfle:
1-3
Averuge: 1.2
Mean range:
SiO^: 20-40
CaO: 3-6
Al2C^: 2-4
IfeO: 1-3
FeO(Fc203,Fe): 12-1G
MnO: 1-2
Ignition losu
(C,S): 20-50
Other components may be
present depending on
charge composition
Mean value:
3.1
See Figures
18-2 and
10-3 for
detailed data
Source
Foundry
Solubility
Wettability
Hygroscopic
Characteristics
Flaamability or
Explosive Limits
Handling Characteristics
Optical Properties
Cray Iron
Cupola
CaO- s. H20
CaO, SiOp,
Al90» - s.
n lo*
10*
3
HC1
Difficult to wet
Abrasive, cohesive, cor-
rosive
Variable, depen-
dent on charge
composition
+ See Coding Key, Table 5-1, Chapter 5, page 45, for units for individual effluent properties.
-------
Carr i er Has
Mo Lst.ure
Source Flow Hate Temperature Content
Iron Foundry
Cray Iron
Cupola
1. Light-orf (a) 3-16
period
2. Melting (a) 5-21.5
point
O*
CD
^ Avg. 92
Complete (a) 3-30.5 210-1410 Top gas
heat Avg. 10.8 dew point,
(b) 60-135 60
T/' I tJ-7' ( (.'uj| -1 ¦ idcrcl)
Otiemi ca I
Comiton i t i on To/ ; <• i ty Ccri-r;tj
C02: 0.3-10.3
02t 10.1-20.5
N2: balance
CO2: 2-13.4
02: 6.5-19.2
SO2: 0.002-0.013
C02: 2.0-12.3 SO2 - 5, Potentially
02: 11.8-12.7 irritant corrosive
CO: 0-0.1 CO-100 due to SO2
S02: 0.002-0.013
Fluorides may
also be emitted
depending on flux
material
-------
Particle Size, Microns
Figure 18-1. Particle Size Ranges for Dusts from Cold-
and Hot-Blast Cupolas
307
-------
O)
CD
CD
10
13
2
u
I
5
x
O
i
>~
10
12
10
11
oo
^ 10 0
<
o.
o.
<
109
10c
^1%*
r
\
10$
\
\\
f
/
\
1
\
f
\
\
200 400
TEMPERATURE °F
600
Figure shows percent water vapor by volume.
Figure 18-2 - Apparent Resistivity
of Dust and Fume in Plant A.
200 400
TEMPERATURE °F
600
* Figure shows percent water vapor by volume.
Figure 18-3 - Apparent Resistivity
of Dust and Fume in Plant B.
-------
18.5.2 Cupola Furnace
Only electrostatic precipitators, high-energy scrubbers, and
fabric filters are capable of removing the fine particles from cupola gases.
Regardless of whether electrostatic precipitators or baghouses are used as
the means of gas cleaning, it is necessary to maintain efficient secondary
combustion in the cupola stacks (recuperative preheater). Otherwise, the
operation of the gas-cleaning equipment is adversely affected. Maintaining
a reducing atmosphere in the cupola stack will allow unburned oil vapor
and tarry matter, as well as coke fines and other combustibles, to be car-
ried over into the gas-cleaning equipment. The secondary combustion process
does, however, cause an increase in the volume of the gases to be treated. 5/
General collector selections and efficiency for the various
foundry operations are shown in Tables 18-3, -4, and -5 taken from "Foundry
Pollution Control Manual."2/
Relative cost comparisons of the various types of dust collectors
applied to hot-blast cupola waste gases are presented in Table 18-6. This
table gives costs with respect to a Venturi type collector which has been
assigned an index value of 1.00 and does not show absolute dollar costs.
Another cost comparison for different types of collectors for a 12 ton/hr
cupola is given in Table 18-7.4/ Collector characteristics for a 15 ton/hr
cola-blast cupola are shewn in Table 18-8.5/ The approximate cost of cupola
collector systems is shown in Table 18-9.6/
389
-------
Application
Shakeout
Particle
Size
Fine to
mediim
Typical
In I et
Load Lng
(gr/:;cf)
1/2-1
TABLE 10-3
IRON FOUNDRY DUST COLLECTOR EFFICIENCY!/
Typical Outlet loading (cr/:'c^)
Wet.
Cap
6 in. AP
Scrubbers
0.01
30-70 in. AP*
Scrubbers
low Bff.
Cyclone
Fabr i c
Arrester
Connents
Wet scrubbers are used because
of moisture.
Sand cooler
Medium
0.01-0.05
Wet scrubbers are used because
of moisture.
Airless abrasive
cleaning
Fine to
coarse 1/2-5
0.01-0.05
0.01
Fabric filters and wet scrubbers
most common.
Grinders
Coarse to
medium
1/2-2
0.01
Cyclones used when fines are
not present.
Dry sand
reclaimer
Coarse to
fine
10-40
0.1
0.02-0.05
Disposal problems generally
influence choice of equipment.
Screens and
transfer points Medium
1/2-3
0.005-0.01
0.01
Electric-arc
furnace
1/2-2
0.02
0.01
Fabric filters more frequently
used than others.
Gray Iron
Cupola
Coarse to
fine 1/2-10 0.4 0.3
0.05
0.4
0.01
All types in use.
Notes: Coarse +20 Medium 2.20 Fine -2 i*.
* Or equivalent energy input.
X Not applicable or rarely used on this application.
-------
TABLE IQ-i
USUAL COLLSETOB SELBITrTOrS TCP. FOUNDRY OPERATIC^'
1/
Dust Qti
Concentration*
ssion
Particle Size**
Ccqnos
Cyclone
High Eff.
Cvclcne
Vet
Fabric
Electrostatic
Catalytic
Ccabus¦
<81
ti
IXI
3hfiKe.-":t
^Mechanical)
"nc Ho.-* d
Moderate
Fine to medius
Rare
Occasional
Usual
Occasional
Kc
No
1
SlfJe hcod
Light
Fine
Kc
Rare
Usual
Occasional
No
Ko
1
Sar.d Har.dlir.fj
Molding seed from
ihakerut
Moderate
Fine to tedium
Rare
Occasional
Usual
Rare
Flo
Ho
2
New eand
Moderate
Fine to medliB
Rare
Occasional
Usual
Occasional
Be
No
3
C-Te ;snd
light
MedUa
Rare
Occasional
Usual
Occasional
Ho
No
4
Casting Clearing
Air'ess abrasive
Heavy
Fine tn coarse
No
Rare
Occasional
Usual
Kare
No
5
Blast 30OO9
Moderate
Fine to medium
No
Rare
Usual
Usual
Bo
No
5
Tustb". ing mil Is
Heavy
Fine to coarse
Ho
Rare
Usual
Usual
No
No
6
Sprte mills
Moderate
Fine to ccarse
Bo
Occasional
Usual
Usual
No
No
6
Grinding
Moderate
Medium to coarse
Frequent
Frequent
Frequent
Frequent
Ho
No
Swinp fraae
Light
Fine
Rare
Frequent
Frequent
Frequent
Ho
We
Prrtable
Light
Fine to aedixa
Rare
Frequent
Usual
Usual
Ho
No
Crre
Heavy
Medium to coarse
Rare
Occasional
Usual
Usual
Ho
No
7
Meltinf
Cupola 'ferrous]
federate
Fine to coerce
Rare
Occasional
Frequent
Occasional
Occasional
Ho
6
> « Light
Fine
Ho
No
Occasional
Frequent
Rare
He
9
Brass Belting
Light
Fine
No
Bo
Occasional
Frequent
Hare
No
10
Patten; Shop
Woodworking
Moderate
Medium to ccarse
Usual
Rare
R*re
Occasional
No
No
12
Boiler F'.y Ash
Chain grate
light
Kedivra
So
Occasional
No
so
No
No
12
Spreader stoker
Media
Mediio to coarse
*3
Usual
No
Sc
No
No
12
Pulverizer
Heavy
Medium
Ho
Usual
No
Ko
Frequent
Jic
12
Cnre ovens
?oGb. fuees
Comb, funes
.No
No
Rare
No
Ko
Frequent
Pair.t ovens
Cocb. f«e s
Ccnb. fuies
.Ho
N-j
No
No
Frequent
furnaces
wottb. fines
Comb. f\ses
No
Nj
Rare
So
No
Frequent
» Concentration:
Light - up to 1 gr/cu
ft, {tolerate - 1
to 2 gr/cu ft
' Heavy - over
; gr/ca ft
11 ?»rticle Size: Fiae - under 2 Ked.ua - 2 to W Coarse - oj«t 2C |
(1) Loadings increase with metal to aacd ratio or.4 with ljver moisture content of aaad at tine of shakeout. Saoke from burring seacoal tnd core bi.idere
often involved ab veil as steam.
(2) Concentration of duet is a function of moisture remaining in sand following the shakeout operation. Traps or dry centrifugal collectors sometimes
uced to return coarser particles to sand systeL. Water frcz wet collectors aaietimes used at sixer to persit salvage of seacoal and bccd as veil
as retard slurry formations in recirculated water.
(3) Cj1!'ecti-'D equipment for aoldiag sand handling systen car. often be used for dust collection duriog the shorter pericd of niv sand handling.
(4! Dust prob'«i very siallax to tnose for molding bu
-------
TABLE 18- 5i/
EFFICIENCY TESTS OF DRY MULTIPLE CYCLONES
FOR FIVE DIFFERENT INSTALLATIONS
Dust Loading
Melting Collector Collector
Rate Inlet Outlet
(ton/hr) (lb/l,000 lb)* (lb/l,000 lb)*
14.4 1.053 0.335
21.6 1.324 0.515
15.5 1.040 0.300
22.5 0.855 0.288
14.7 1.061 0.262
* Pounds of particulate matter per 1,000 lb. of flue gas.
Overall
Efficiency
69
61
71
66
75
392
-------
TA3LE 18-53/
COST COMPARISON FOR VARIOUS DUST COLLECTORS FOR CLEANUP
WASTE GAS-5 OF A HOI-BLAST CUPOLA
(index value 1 for Venturi tube duet separation)
Waste gas quantity to be cleaned: 7,350 scfta Depreciation: 20^ per annum
Plant
Wet Dust
Venturi Tube Collector, Dry Electro-Precipitator Wet Zlectro- Fabric Dust Collectcr
Dust Collector Simple Design Offer 1 Offer 2 precipitator Offer 1 Offer 2
guaranteed clean
dust content: lb.'hr i.TC 7.70 3.85 5.70 3.So 5.2S 3.30
gr/scf 0.122 0.122 0.0S1 0.09 0.061 0.064 0.0S2
Initial investment costs
(indax value) i.03» 1.04» 3.24 1.50 1.59* 1.45 2.3t;
Depreciation and interest
(index value; L.CO* 1.04* 3.24 1.66 1.59» 1.45 2.36
fewer consumption
(index value) L.00 0.62 0.23 0.36 0.24 0.S5 0.43
Maintenance, servicing,
water consumption, neu-
tralization (index value) L.00 1.0S 0.62 0.536 0.83 0.5S U.t4
Costs per operation hour
(index value! 1.00* a.BS* 1.67 1.01 0.36* 1.14 1.50
* Uithoiit facilities for water supp'y anc settling tanjt.
Table does not include erection costs.
1£3LE 18-7i/
APPROXIMATE COST OF COKTROL EQUIPMENT
(12 ton/hr cupola)
Weather Cap $ 30,000
Dry Centrifugal 60,000
Medium Pressure Wet 90,000
High-Tenperature Fabric 150,000
High-Energy Wet 170,000
393
-------
TAULI- lB-Oii/
COLLECTO» CI iAKACT ERISTICS FOR 15 TONS/HR CQLD-BIAST CUPOLA
OPERATED ON ALTERNATE LAYS
Ui
CO
Assume Blast Volume
= 8,000 efm
at
70°F
Assume
Emissions
.15
hr. ton melt
Charging Door 40 sq.
ft. at 300
fpm = 12,000 eftQ
at
70°F
Consisting of Cinders 8 ~
hr. ton melt
Total Gas Volume
= 20,000 cftn
at
70 ®F
Dust 4 -
hr. ton melt
= 62,500 cfm
at
1,200°F
Fumes 3 =
hr. ton m'jlt
HpO Vapor
Probable
Approx.
Discharge
at Exit Tomp.
Lower
Col lector
H.P.
Probable
Eraiss ion
Instal.
Gas
Added for
Effec.ti vc
Pressure
Note 1
Water
Note 2
Cost on
Collector
Temperature
Cool, ing
Total Vol.
Collect ion
Drop W.G.
Exit
Required
(grains/
Grains/cfm
Existing
Type
(*F)
(cfm)
at Exit Temp.
Range (n)
(in - )
Temp.
70
(fipm)
scf)
at 500
Cupolas
Wet cap
400-700
9,050
47,850 cfm
44
0.25
200
0.45
0.25
$ 35,000
at 550°F
Low pressure drop
centrifugal with
cooling tower
350-500
10,200
43,600 cfm
30
1.5
24
40
34.3
0.36
0.20
50,000
at 425°F
With heat exchanger
600-700
None
41,000 cfm
30
1.5
34
71
0
0.45
0.25
150,000
at 650°F
High eff. dry
centrifugal
350-500
10,200
43,600 cfm
7
3.0
34.3
57
34.3
0.27
0.15
55,000
at 425°F
Wet collectors
125-190
9,750
33,750 cfm
1
5.0
52.5
63
48-100
0.11
0.062
75,000
at 175*F
Electric precipitator
250-300
10,200
38,000 cfm
0.1
0.5
18
25
41.2
0.039
0.021
100,000
at 275°F
Fabric arresters
Synthetic faoric
250-275
9,600
36,800 cfta
0.1
4.0
42.5
57.5
41.8
0.0096
0.0053
75,000
at 260®F
Glass fabric
400-500
10,200
44,200 cfm
0.1
4.0
40.5
69.5
33.2
0.0206
0.0114
75,000
at 450° F
Note 1: Horsepower calculations assume pressure loss through ducts and cooling tower of 2 in. added to stated collector loss except for wot cap (5 in. with
heat exchanger).
Note 2: Lower than the usual boiler stack acceptable emission regulations of 0.257 grain/cu ft at 500WF (0.465 grnin/scf).
-------
TABLE 18-9
COMPARISON OF CUPOLA DUST CONTROL SYSTEMS^/
(Two No. 8 Cupolas—7,800 cfm blast air alternate usage—1 grain/scf dust load)
Equipment
Wet cap
Multitube cyclone
6 in. AP scrubber
70 in. AP scrubber
Fabric filter
Initial Cost
Installed
In $1,000's^'
50
150
150
225
250
M & 0 Cost/Year
In $1,000's^/
3
10
10
25
Wide variations
Outlet
Emission,
Grain/scf^/
0.5
0.3
0.2
0.05
< 0.02
Connected
Horsepower^/
20
100
100
325
100
a/ With water clarification system and ductwork, electrical, etc.
b/ Maintenance and operating cost per year, including power costs for 16 hr/day operation, but not
depreciation.
£/ Outlet emission also dependent on particle size distribution, which in turn is dependent on scrap
quality, etc.
d/ Connected horsepower, including pump for wet units.
-------
18.5.3 Electrostatic Precipitators
Electrostatic precipitators have failed to attain consistently
high collection efficiencies due to wide variation of gas stream conditions.
To satisfactorily apply electrostatic precipitation to foundry-cupola-fume
collection, it is essential to determine the temperature at which the peak
resistivity of the fume occurs, and to design the gas conditioning system
to provide a gas temperature well away from that at which the resistivity
reaches its maximum. Electrostatic precipitators have been employed in
Europe to a greater degree for cupola operations and utilize both wet and
dry electrode cleaning techniques. Data on some of these units are given
in Table 18-10.3/
18.5.4 Fabric Filters
"here are several installations employing completely automatic,
tubular dust collectors using synthetic filter bags in conjunction with
cooling of the hot gases prior to filtration. The primary difficulty in
their use arises from poor control of inlet gas temperature. When it is
too high, the "bags burn out; when it is too low, the fabric blinds from
condensation of water vapor.5/ The fabric collector temperature is gen-
erally limited to the capability of the fabric media and, at present, glass
is operable Tip to 550°F.
Fabric filters are being used increasingly for cleaning cupola
gases whenever high collection efficiencies are desired. Operating charac-
teristics for three installations are given in Table 18-11.3/
The temperature of the gas stream from the top of a cupola may
be as high as 2200°F. Therefore, the gases must be cooled, prior to enter-
ing the baghouse. Cooling can be effected by evaporative water or other
means of heat exchange or by dilution with ambient air.
It should be remembered that if fluorspar is used as a fluxing
agent in the cupola, this can be damaging to glass-fiber bags.
General cost data for fabric filters given in Appendix A indicate
that an installed cost of $3.50/acfm would apply to a unit handling about
10,000 acfm. This decreases to less than $2.00/acfm for 50,000 - 100,000
acfm.Z/
Installed cost of baghouses ranges from $0.93 to $3.50/acfm.
Installation expense ranges from 12-43$ of the FOB price with the average
being 25$. Annual operating and maintenance expense ranges from 5-16$
of the installed cost with an average of 11.6$.i/
396
-------
ffc
1
2
¦*
4
5
6
7
8
*
»•
TABLE 18-10
CUPOLA FLAWS WITH Br.Rr.TRfl-PRBCIPITATORsS/
(European Installations)
Furnace
Type
Hot
B1 ast
Hot
Blast
Hot
Blast
Hot
Blast
Hot
Blast
2 Hot
Blast
Units
Hot
Blast
Exter-
nally
heated
Hot
Blast
6.6
6.6
0.0
19.0
13.4
Gas Temperature
Clean
Gas
Dust Content
Melting
Rate
(T/hr)
13.2
16.5
Raw
Gas
Clean
Gas
Dust
Emission Pressure
Collection in the Loss of
Type Before Before After Volume
Filter of Cooler Filter Filter scftn Grain/scf Grain/scf Efficiency Atmosphere the Unit
Dry
Type Gas (°F) {*¥) (*F)
Dry Top
Dry Top
Dry Waste
Wet
Up to App.
750 570
930- 570
1,110
~ 149
Top
Plus
Waste
140
Wet Waste 390
20.0 Wet Waste 750-040 *
Wet Top
Top 500
Plus
Waste
104
Dry
6,500 7-9.2
6,800 Up to 4.3
0,200 »
Dry
J£L
4,000
19,000
7,200
9,200
i.2;>
0.70
29,000 2.2
3.09
4.65
0.05-0.07 9Q.5-
99.7
0.065
0.021
0.033
0.037
0.062
98.5
97.6
90.3
95.0
0.043 90.0
90.85
97.0
(Lb/Hr)
3.26
3.79
0.045
2.26
6.17
(In. W.G.)
1
5.30 6.3*
11.00
6.5
3.5
No data available.
Pressure loss inclusive connecting pipelines.
-------
TABLE 18-11 .
CUPOLA DUST REMOVAL INSTALLATIONS WITH FABRIC FILTER^/
Dust Content
No.
Furnace
- Tvpe
Cold
Blast
Melting
Rate
(T/hr)
5.0
Dust
Removal
Plant
Waste gas
cleaning
closed glass
fabric filter
Gas Temperature
Pressure
Drop
In. W.G.
Cupola
Exit
(°r>
1,380
Kilter
Inlet
446
Filter
Exit
C F)
Gas Quantity
Before Filter
After
Cupola
scftn Grain/scf
Dry Dry
230 8,400 4,500
Before
Fabric
Filter
Grain/scf
Dry
1.19
After
Fabric
Filter
Grain/scf
BSC
0.0015
Collection
Effic iency
m
99.83
Dust
Discharge
in Atmosphert
(lb/hr)
0.073**
O)
CD
CD
Hot
Blast
Hot
Blast
33.0
17.6
Top gas
cleaning
{part of
g8s quanti-
ty) closed
glass fabric
filter
Waste gas
cleaning,
open glass
fabric filter
About 14
in. W.G.
filter
plus
pipeline
930
3-6
1,830
248
Approx.
13,000
7,300
3.52
C5,000 38,000
2.84
0.35
0.041
99.0
0.530
* No data available.
** Before cleaned gas measuring point after fabric cleaner, approximately 1,200 scftn false air was drawn in.
-------
18.5.5 Wet Scrubbers
Various types of wet scrubbers are widely used for control of
cupola emissions.®/ The SO2 content of the cupola waste gases must be con-
sidered in designing a wet scrubber system. It is often overlooked that it
is not sufficient to neutralize the scrubbing water to a pB value of 7 so
that it enters the scrubber in a neutral state. An acidic reaction occurs
after it contacts the cupola waste gases and a serious corrosion danger
exists. The wash water thus should be adjusted to a pi of 9 so that in
the gas washer itself the acidic range is not reached.
Although the wet-scrubber systems absorb some of the SO2 from the
waste gases, the odor of SO2 nay be more perceptible than with other collec-
tion systems because wet scrubbing lowers the temperature of the gases
which causes a decrease in plume rise.£/ The carbon content of the dust makes
wetting more difficult and thus puts higher requirements on wet scrubbers.
Wet scrubbers pose the problem of sludge removal and potential
water pollution which must be taken into account in computing the cost of
this type of collector.
Wet caps have been in common use on cupola gases but these only
remove the coarser particles and are usually not adequate for compliance
with local codes.
18.5.6 Dry Cyclones
Centrifugal dust collectors are used in many ways in the foundry
industry. They can function satisfactorily up to temperatures over 800°F.
They are used for cupola waste gases provided the fine grain proportion in
the cupola dust is not too high. The collection efficiency may run 80-90$.
However, the raw gas dust content and its particle size distribution should
be determined by measurement to ascertain the efficiency that can be ex-
pected for any specific application.^/ The results of five tests on differ-
ent installations using dry multiple cyclones are given in Table 18-5.i/
399
-------
REFERENCES
1. American Foundrymen's Society, Foundry Air Pollution Control Manual,
Des Plaines, Illinois, 1967.
2. National Emission Standard. Study, "Appendix D, Report to Congress,"
National Air Pollution Control Administration, November 1969.
3. Cowen, P. 3., editor, Cupola Emission Control, Cleveland, Ohio, Gray
and Ductile Iron Founders' Society, 1969.
4. Kane, John M., "Foundry Air Pollution...A Status Report," Foundry,
November 1968.
5. Kane, John M., "Equipment for Cupola-Emission Control."
6. Mcllvaine, Robert W., "Air Pollution Equipment for Foundry Cupolas,"
Journal of the Air Pollution Control Association, 17, August 1967.
7. Control Techniques for Particulate Air Pollutants, U5DHEW, Washington,
D. C., January 1969.
8. O'Mara, R. F., and C. R. Flodin, "Electrostatic Precipitation as Applied
to the Cleaning of Gray Iron Cupola Gases," Air Report, 3(2), pp. 105-
108, 1953.
9. Shaw, F. M., "Emissions from Cupolas," Foundry Trade Journal, pp. 217-227,
August 30, 1956.
400
-------
CHAPTER 19
SECONDARY NONFERROUS METALS INDUSTRY
19.1 INTRODUCTION
The secondary nonferrous smelting and refining industry comprises
establishments primarily engaged in recovering nonferrous metals and alloys
from scrap and dross. The secondary nonferrous industry, as used here, will
include copper, lead, zinc, and aluminum recovery. Copper, including brass
and bronze alloys, and lead production from secondary smelters account for
about 50$ of the yearly total production of these metals in the United
States.5/
The nature of furnace operations in this industry is such that
emissions vary widely during the cycle from charging the scrap to pouring the
melt. Peak emission surges occur in nearly all the furnace operations. The
principal emission from the secondary copper, lead, zinc, and aluminum indus-
tries is particulates—smoke, dust, and metallic fumes. Sinall amounts of
sulfur oxide may also be evolved. Table 19-1 summarizes particulate emis-
sions from the secondary nonferrous metals industry.
The production processes, particulate emission sources, particu-
late emission rates, effluent characteristics, and control practices and
equipment for the secondary copper, lead, zinc, and aluminum industries are
discussed in the following sections.
19.2 SECONDARY COPPER SMELTING Arm REFINING
Obsolete domestic and industrial copper-bearing scrap are the baeic
raw materials for the secondary copper industry. The overall industry is com-
posed of cany groups, including dealers, collectors, foundries, ingot makers,
and smelters. Scrap as received is frequently not clean and may contain any
number of metallic and nonnetallic impurities. These impurities can be re-
moved by mechanical methods, heat methods, or gravity -separation.i/
A number of types of furnaces are used for the melting, smelting,
refining, and alloying of the processed scrap metal. Reverberatory, rotary,
or crucible furnaces are used, depending on the size of the melt and the
desired alloy. Processing is essentially the same in any furnace except
for the differences in the types of alloy being handled. Crucible furnaces
are usually much smaller, whether electric or nonelectric, and are used
principally for small quantities of special-purpose alloys.i/
401
-------
19.2.1 Emission Sources and. Hates
Emissions that may contribute to atmospheric pollution are re-
leased from various operations in secondary copper smelting and. refining.
Included, are the handling and concentrating of raw materials (i.e., scoop
processing); the burning of oil, grease and insulating materials; the re-
fining and concentrating of low-grade scrap and metallurgical wastes in a
blast furnace; plus the firing up, charging, alloying, and pouring opera-
tions connected with the furnace. The types and ranges of emissions depend
on factors such as fuel, composition, ana melting temperature of the alloys,
types of' furnaces, and operating factors such as methods of charging, melt-
ing, refining, removing slag, adding alloy metals, and pouring.
Individual emission sources in the various operations mentioned
in the preceding paragraph are discussed in more detail in the following
sections.
19.2.1.1 Scrap Processing: The mechanical methods of processing
scrap cause few or no pollutant problems, while pyrometallurgical processes
all create air pollutants to some degree.
Sweating is carried out at medium temperatures to remove low-
melting-point metals such as lead, solder, and babbit metal from radiators
and other scrap. Metal fume losses are very low, but fume and combustion
products of antifreeze residues, soldering salts, and hose connections may
be released.£/
Burning also removes insulation that was not mechanically
stripped from wire or cable. Source tests indicate that uncontrolled emis-
sions can be a dense black smoke containing particulate matter in concen-
trations as large as 29 grains/'scf at 12# CC^.x/
A heated rotary kiln is often used to vaporize excess cutting
fluids from machine shop chips or borings. This drying operation creates
considerable amounts of hydrocarbons. The nature of the combustion process
that eliminates these hydrocarbons will determine whether fumes and soot
escape or whether emissions are clean and fully oxidized. The vaporized
fumes must be burned in afterburners to oxidize the hydrocarbons and pre-
vent air pollution.
The blast furnace (or cupola) produces a concentrated product
called "black copper" or "cupola melt" from low-grade materials such as slag
and skimmings. The product actually has variable proportions of copper,
tin, lead, zinc, nickel, and other metals. The charge is introduced.at
the top of a vertical furnace, along with coke for fuel and a reducing agent,
plus limestone or other materials for fluxing. Slag and concentrated alloy
402
-------
are tapped near the bottom of the furnace. Slag is often tapped continu-
ously while metal is obtained at intervals. A large volume of air is in-
troduced through tuyeres spaced around the periphery of the furnace. Tem-
peratures in the smelting zone are sufficient to reduce oxides to molten
metal. These temperatures drop rapidly while the gas rises through the
charge material to the top of the furnace. The particulate matter and
gases emitted from the blast furnace are likely to be rather variable be-
cause of the large variety of scrap, slag, skimmings, and spills that are
processed.i/
19.2.1.2 Smelting and Refining: Direct-fired (or open-flane) fur-
naces such as reverberatory and rotary types will produce larger concentra-
tions of zinc oxide fume than will indirect-fired furnaces such as crucibles
and electric-induction furnaces.
Since the hot, high-velocity combustion gases come into direct
contact with the metals in the charge, metal losses are high when there
is an appreciable proportion of zinc in the alloy. The direct-fired type
of furnace is often more difficult to hood effectively. Except for the
physical arrangements, however, the actual smelting and refining that
produce high-quality ingots are similar in both direct-fired and indirect-
fired farnaces.
A number of factors in furnace operation can affect the type and
quantity of emissions. .Among these ere the type of fuel used, control of
air-fuel ratios, control of temperatures, the order of adding metals to
the furnace, provision of proper slag cover, and good housekeeping in the
furnace area. 1/
19.2.1.2.1 Heating: Fuel used in the various furnaces can have
important effects on the types of emissions from the plants. Electric
furnaces do not add any objectionable emissions and, what is more important,
they do not have the effects of hot gases sweeping across the surface of the
melt. Indirectly heated furnaces also avoid this sweeping effect.
The choice of oil or gas as a fuel is usually made on the basis
of lowest cost for a given heat content, but gas is often more trouble-free,
both in minimizing pollution and in maintaining proper combustion conditions.
When oil is used, very careful control of the air-fuel ratio is necessary
to reduce pollutants such as soot, smoke, and unburned fuel particles to a
minimum.
19.2.1.2.2 Charging: The type and condition of the scrap raw
material are factors that may affect the amount and character of each emis-
sion. Scrap that is oily, greasy, or dirty may have these contaminants re-
moved by preliminary treatment, or the operations may be done directly in
403
-------
the main furnaces. In either case considerable smoke emissions are apt to
occur. With combustion there will be emissions of the normal products of
combustion plus unburned hydrocarbons, fly ash, and dust in the stack gases.
When the scrap material being used has relatively large proportions of low-
volatility constituents such as zinc, metallic oxide fume will be in the
stack gases of the furnaces.
During the charging cycle, emissions are also dependent upon factors
such as location of the charging doors, the percentage of volatile alloy con-
stituents (principally zinc), and upon whether the entire charge is made at
the beginning of the heat or at intervals during the melting stage. Over-
head charging doors in reverberatory furnaces will permit large losses of
hot gases, fly ash, and fume into the plant when charges are loaded at
intervals during the heat. Effective hooding of overhead charge doors
poses difficult problems because of the necessity of providing access for
loading equipment into the space between the charge door and the hood. End
and side doors are not as vulnerable to the loss of furnace gases, especially
end doors that load the charge in the direction of the induced flow of the
furnace gases.
Some of the greatest air pollution problems occur during charging.
It is physically difficult to place the entire charge into the furnace at
one time. Later charges are, therefore, added to molten metal, and the
combustible materials (and plain dirt) are emitted in tremendous bursts
that are almost impossible to burn completely or even to contain within the
capacity of the collection system.i/
19.2.1.2.3 Melting: After material is charged, all doors and
openings of the furnace are closed. Burners are set to maximum efficiency
for fastest melt-down and superheating of the molten metal. Supplemental
oxygen may be used at this time. Excessive fuming may occur whenever zinc
is present or combustible contaminants are present in the charge. The lat-
ter may include items such as grease, oils, and rubber. Much of the combust-
ible emissions may be controlled by proper draft regulation and burner set-
ting. The lack of uniformity in scrap, however, makes this control diffi-
cult .
19.2.1.2.4 Refining: Refining, a chemical process of purifica-
tion, is that cycle of the heat in which impurities and other constituents
of the charge, present in excess of specifications, are reduced or removed.
Many different processes are employed to bring the composition of the melted
scrap within permissible limits. Refining methods vary with the type of
furnace, the type of alloy being produced, the condition or availability of
different types of scrap in the charge, and the experience and opinions of
the personnel involved.
404
-------
The chemicals used in refining, commonly termed, fluxes, may be
gaseous, liquid, or solid. By far the most extensively used gas for refin-
ing is compressed air (oxygen). Blowing air into the molten bath of metal
causes a selective oxidation of metals in accordance with their position
in the electromotive series. Iron, manganese, silicon, and aluminum are
high in the series and are, therefore, oxidized in preference to copper,
tin, and other metals. Part of the zinc is oxidized, but this is an unavoid-
able loss. Below certain concentrations, the undesirable metals are oxidized
simultaneously. Solid fluxes as a whole do not contribute to air pollution,
except in releasing impurities that must be removed from the alloy in one
way or another. Flux covers, which are eventually skimmed off, have a gen-
erally beneficial effect on the quality of stack emissions by preventing
excessive volatilization losses. Some of the more common fluxes are broken
glass, charcoal, borax, sand, limestone, iron scale, soda ash, and caustic
soda.i/
19.2.1.2.5 Alloying: Modification of the alloy during the heat
by addition of virgin metal or specialized scrap may lead, to an increase in
fume emission. Excessive formation of fume becomes greater as the percent-
age of volatile constituents increases. Owing to its very low boiling point,
zinc is the most serious problem.
19.2.1.2.6 Pouring: Physical methods of pouring the molten alloy
into molds vary. The furnaces may be tapped directly to a moving, automat-
ically controlled mold line, the alloy sometimes filling one or more molds
at once and then being shut off while a new set of molds moves into position
on the endless conveyor. In other variations, the metal is tapped from the
furnace into a ladle, which should have a slag cover, especially for high-
zinc alloys. The molten alloy is then moved to a mold line, which may be
movable or stationary.
Metal-oxide fumes are produced as the hot molten metal is poured
through the air, even over these short distances. Other dusts may be pro-
duced, depending upon the type of linings or coverings associated with the
mold as it is filled with hot molten metal.
19.2.1.3 Summary of Emission Rates: Table 19-1 summarizes emission
rate data for the various sources in the secondary copper-production cycle.
Materials-preparation processes account for about 70# of the particulate
emissions. The wire-burning step of the materials preparation emits about
41,000 tons/year. Emissions from smelting and refining furnaces total
about 17,000 tons/year.
405
-------
TAB'-E 19-1
PARTICULATE EMISSIONS
SECONDARY NONTERKO'JS M5TALS
Efficiency Application Met
entity of Emission of Ccr.trcl of Control Control Esis
Material Factor ~c ^t
•,r.i hr
Materials Preparation
1. Wire burning
2. Swentinft furnncc3
3. 3iast furnaces
Sneltir# and Refining
1. In :;eccr.dory
shelters, etc.
(a) charge
(b) refine
( c ) j;OuT
Alu:
A.
awjetirx Pjrnoces
flnir.P Pjrr.ncs
Heverberatcry
?o* (crucible)
Induction
.uxing
Dross Processing
1. Hot prcces3
0. Milling process
300,000 tons insulated wire
64,000 tons, autc radiators
2^5 lb/ton
15
0.55
o.?c
0.75
?S?,000 ton::, scrop end residue 50 lb/ton scrap 0.50
1,170,03c tons scrap
30 lt/tor charge
39
0.6
70 0.05 0.5C
Total from Secondary Copper
500,000 tons of scrap
,015,000 tens screp
115,000 tons CI used
32 lb/ton scrap
¦4 lt/ton sera?
P lb/ton 3crnp
1,000 lb/ton Cl used
0.£--
O.oC
41,dc:
0.13 40C
0 .69 2, 5*- 0
3.5? 17,00
£0,700
0.1S 6,XC
0,57 9C
r. .25 51 ,ooc
Total i'rosi Secondary AijE.in\un
?, 500
cia nirr.acL'i
A. Fct
3. Slast Furnace
C. Reverteratory
D. P.ctary aeverheratnry
Average, revcrteratory
53,000 tons scrap
119,00C tons scrap
554,00C tons scrap
0.8 lb/ton screp 0.95
190 " ' 0.35
130
70
10C lb/ton screp 0.95
Total from Secondary Lead
0.95
0.95
0.95
0.SC
J. 9C
0.9C
;,OOC
4,000
A, Sweating
1. Metallic scrap
2. Residual scrap
B. Distillation Furnace
1. Distillation retort
2. M:ffle
Average, dlst illation
52,000 tons scrap
210,000 tons scrap
233,OX tons Zr recovered
furnaces
12 lb/ton charge 0.95
20 C..35
4 7 lb/ton Zn
40 lb/ton Zn
*5 lb/ton £n 0.35
Total from Secondary
Total frc® Secondary
0.20 0.19 300
0,20 ¦ 0.19 2,6X
C.60 0.57 2.200
Zinc 5,ICO
Nonferroue Me'.alj 127,.'X
406
-------
19.2.2 Characteristics of Effluents
The chemical and physical properties of effluents from secondary-
copper production are summarized in Table 19-2. The metallic fumes emitted
from the smelting and refining furnace are submicron in size. The fumes
also readily agglomerate, and the exhaust plume is usually opaque.
19.2.3 Control Practices and Equipment
19.2.3.1 General Control Practice: Air pollution control practices
for the secondary nonferrous metals industry were investigated in a 1969
study done by the U. S. Department of Commerce.®/ While the study did not
pertain solely to secondary copper, the results will be summarized in this
section for convenience.
19.2.3.1.1 Baghouses: Most smelters observed had completely dry
collection systems. Water quenching was not used; instead, outside air was
mixed with the hot flue gases.®/ This latter procedure has the drawback of
requiring a design to accommodate not only the furnace flue gas, but also
the volume of outside air injected into the system. In addition, there is
considerable fire hazard. The hot flue gases axe often deficient in free
oxygen, and if the furnace charges contain oily scrap or other combustible
materials, admission of oxygen-rich outside air can cause low-order explo-
sions and fire.§/
Of the 23 plants considered in the Commerce Department study,
eight had efficiently functioning dry baghcuse systems. Cne had an equiva-
lent system but used some water as a gas cooling spray before the baghcuse.
Most of these plants were brass or bronze ingot producers and lead smelters.
In addition to baghouse systems, and at other plants, small modular bag-
houses of simple design are used to filter gases and in-plant air from ducted
hoods over kettles, furnace charging doors, open hearths, and slag melt draw
points.6/
19.2.3.1.2 Electrostatic precipitators; Electrostatic precipi-
tators are used to clean furnace flue gases. This system of gas cleaning
is efficient when properly designed and engineered for the individual plant.
Collection efficiency drops when residence time is insufficient. Surges in
furnace flue gas volume can easily cause too short a residence time unless
equipment is designed for capacity to accommodate peak volumes and peak
loading of flue gases. Efficiency is also temperature sensitive owing to
the relation of temperature to resistivity.®/
407
-------
TA5LB 19-?
ErrrrrsT raptes'sticc - secssimhy scntepj:ijs metais*
Electrical
Parti;Le Slic Solids Leading Chealral Cccpcsitlor. Particle [tensity Realitlvity Koiature Content Tonicity
..»n-
irr- .i y.'f.i-
Met nil ir f'jr.e
C.07-0.5 (-una
Ty?l:al cnnstltuer.ts:
Zr.O, ftO, C, fly asn,
and & variety cf sec-
ondary constituent
representing charge
ccitpoaition. Fcr spe-
cific alloyr the fcllov-
ir.« aie representative.
Zr.O ar.d ftO distribu-
tions :
C-PP«r-8r>8s All^y
Znf:
Avg. - 59
»0: 5-29
Avfl. - ly.b
Ocppor.Sl.-kf!' A—icy.i
Zr.C: 54-87
Av^jt. - 57
Cr-'r-er-Lieftd
AUojrs
ZnCs 5-fl
Avg. - 5-5
PjC; 51-62
Avg. - 5.'
Secondary Conitituentc:
Tin, ciriai'-C8, copper,
silica, ar.o carbon
&»e Table 19-3
for fuller
atateaent of
int«rreiat#d
variables
Mc-: till c fline
C.07-0.5 (unaa-
1-20
{r.iir. v»lues vr".tr.
compressed Air is
jnjected :nte
tath)
Tj-p-i-ril coapos'stlnn
range uf ra^nouse catch:
Zn: 45-77; ft»; 1-12;
Sn: t.*-?; Ju: C.Cb-l.J;
S: C.1-0.7.
Very r-.r.e; typlca.
range: C«07-0.4
MedJi size; 0.3
{una£gl*w»mted)
2-12 .llasx furnace
1-b ;rev»r-
loratory furnace)
PbO, SnC, ZnO, tar, fly
aah, ccXc dust, su.-
fii'jii, si^lfidco
See Figures
19-1 ar.d 1S-2
for derail*
v.fie 5.03-C.S
furnace f ujinflg lemur-
at.-'d)
Zr., CI:, Zr.O
N?sCl" Alp 0^
Oxides or
Mg, 5n, th, iii,
::c, Na
(dependent on
charge composi-
tion and quantity
of flax)
. S*vfrbT- Ko detailed 0.6-1
*'.ory datai probably
f-rnace al>cut I *
stmir. ICC < f (cryolite C.1-2.0
fluxing, electron
p r.o t oai cTogr aph}
i00 < 1 (.-hlorir.stlr^g
process }
iisdlar to
Histt'e furnace
Highly variable, a^r con-
tain AlpC,, AlCij, KaCl,
fluorides, oxides of
alkali netals
Taxic due -.e
fluorides a'
chlorides
l:ee
Table 5-1, Chapter 5, p*#* *5. f3r unite for individual effluent, properties.
408
-------
TABLE 19-2 Cjr.tlQuad)
.r'.:,-ulato (rirt II)
?lamAblllty cr
s.vir.^ Solubility Wettability Hygroscopic Characteristic! Expljelve Lialts Handling Ctaracttrlitica Optical Proggrties Od^r
Sewniary Njn-
ferra-w Metric
I. .'.Tpper - s. al. tlk. Absorbs water, terida to Agglomerates, cohesive
iunp and/or iua
i. Lsa.2 " Difficult tn wet
S. 2i"; " "
K. Ai-:niriua Abraalve, corrosive
Moistur*! FlMn«b^ lity Cpti-hl
r.nv Rat* Tcsperatare Content Chr_B:-jn:»r; tbn-
ferry 13 M-ta-ls
foundries
Ail-y Type
hr ass
a. Occil- (a) 3.1*
latir.j (b) 0.4VC*
barrel
furnace
t. Sotatir.g 'e) 7.6*
barrel Jb) 2.390*
furnace
Tilting- '») ifl.*-22.2»
Kettle (b) 0.996-1.344*
furnare
Cruci-
ble
(>) 5-3.:•
(b) 0.54-C
.4*
Typical rarpositien
(siailor for all
furnace types'
Pomace Cvtlot
C jg- 10.6-14
Og-: 1.1-4.9
c:«. 0-3.3
balance
trk.:e
K-:
SCS:
Stack
CC~
C.4-?. 4
16.3-13.fi
c
balar.ee
trace
(¦) £-!.«•
(t) c.5-o.e»
i-.ee-
tric
arc
(a) C.72S-
«€
fur-
nace
(a) 2.1-2 .5*
(b) 0.30-C.S*
:
-------
TA3LE 19-2 (Ccncludad).
~»rr.er G ;a • Jonclu.Jft.1)
c. notary (k) ll.4*5£.
fumarc
?. C'jpoln (: ) 13..
{e ; 2.I (ene
bias
furiM-«)
2.1 (on«
Tenperature
i«5-~00 it bog-
hcucc Inlet
5c: :iix«t:
950 'rever-
b^rvory;
furnace j
,1-c.S (tvo
'^maces >
A. S-ea:
P:rr«;<
F; ii*
Ktas;?
Moisture
Content Chtalcai Cocgcsltija
1.7-2.3 Stack
ZOg: Q.14-1.11
Avg.' C.51
03: u.ie.s
Avg.: 10.2
H2 ; balance
CO: 6.9-lC.e PI*
Avg.: 8.4
SO,: 10 FIE
HytLTOcarbcne:
D.lfc-0.37 ppir.
Kalagena: < 1 pjfc
!0 s < 1 PJB
H?S: < i pjc
Flunabiltty Optical
toxicity Carrotivlty Odor Explosive Haiti Proprtles
Stack
CO...: 0.5-1.4
Avg.: 0.6
Og: 18.9-19.4
Avg.: 19.2
N~: balance
CO: U0C-1S75 PTtt
Avg. r 121.-0 ppm
EOj! 1 ppr.
N C'x: < 1 ppx
Ho3: < 1 psc
Halogens: < - FFR
CC^, CO, C^, Hg,
so.,, ?,o
- 5,
irritant
- 100
furnace (b)
Appraxlaate
0c:21
'd. Rrv*rt*r- ( r>)
alory (two furn/i-:?r.)
furnace fb) -4CC-S00
IVpical
CCh) :2 .4
KgC:4 .5
^ t"»fi .£
&-> ;1S .a
IV. Aluniaum
. to'
r- (-) 1-'
or/ 'b) 2.
Typical Orsat
CC^:6.a
C0:C.C£
rfc:?-',3
JfeO:7.3
Trace SC.
SCj - 5
Lrri'.Wi-
CO - .00
410
-------
TABLE 19-3
ELECTRICAL RESISTIVITY OF COLLECTED B30NZ5 FJNE^/
(Laboratory Measurements)
Water Content Temperature Resistivity
iH (°F) (ohm-cm)
6 280 4 x 1013
6 330 1.8 x 1013
5 380 5 x 1012
6 430 1.8 x 1012
6 480 5 x 10
411
-------
10"
H
ro
5
u
I
5
X
0
1
>
10
12
10
11
S ,010
I,,
10°
1
\
,1.3%
w
\
1
\
200 400 600
TEMPERATURE °F
* Figure shows percent water vapor by volume.
Figure 19-1 - Apparent Resistivity of Zinc Fumeii/
from Slag Fuming Plant
As function of temperature at 1.3$ moisture
content by volume
1
\
\
1.3%
1
0 200 400 600
TEMPERATURE °F
* Figure shows percent water vapor by volume.
Figure 19-2 - Apparent Resistivity of Zinc Fume ii/
from Nfelting Plant
As function of temperature at 1.3$ moisture
content by volume
-------
19.2.3.1.3 Wet scrubbers: Five of the 23 plants considered in
the Commerce Department study had a wet scrubber as the major component of
their flue gas cleaning system. Three were aluminum alloy ingot producers,
one a zinc renelt alloy shop, and one a producer cf brass and bronze ingots.
The vet scrubbers are best applicable to cleaning furnace gases with low
particulate grain loading but high loading of soluble gases and mists such
as hydrochloric and sulfuric acids..§/
The packed tower is a popular wet-scrubber design in use in the
secondary nonferrous metals industry, particularly in aluminum plants where
chlorine is used to purge magnesium from the furnace melt. The scrubber
towers may be constructed by using a steel shell suitably lined with rubber
or acid-resistant brick to isolate the shell from the highly corrosive gases.
19.2.3.1.4 Incinerators and afterburners: Most grades cf scrap
metal require incineration of attached foreign nonmetallic constituents
before smelting and refining. Insulation on wire is a major contaminant
which is usually removed by incineration. Generally, the incinerator oper-
ating temperature must be maintained high enough to either bum or volatil-
ize the contaminant and low enough to prevent excessive oxidation of the
metal. J^/
Copper wire scrap, with its various kinds of insulation, sometimes
presents incineration problems. Mechanical stripping of fine gauge wire is
being done at some plants, thereby obviating the need for incineration.
Burning of copper wire to free the copper from insulation sheaths
of plastic, rubber or paper is most efficiently dene in a two-stage incin-
erator. In the primary chamber the temperature is maintained hot enough to
support combustion of the insulation but low enough to prevent excessive
oxidation of copper. The only partly burned hydrocarbons escape in a sooty
gas stream into a secondary chamber equipped with an afterburner. Very
hot temperatures ana an excess of oxygen convert the hydrocarbons to CO2
and KpC.
Polyvinyl chloride-coated wire presents an incineration problem.
The FVC is fire resistant and it resists normal incineration methods.
Furthermore, combustion of ?VC liberates chlorine which combines either
with water vapor to font hydrochloric acid or with metallic elements in the
scrap to form harmful metal chlorides. Fhthalic anhydride is also generated
by burning polyvinyl chloride. To prevent the escape of noxious components
through the flue, combustion gases must be passed from the afterburner cham-
ber through an additional packed wet scrubber. The resulting effluent is
neutralized with sodium hydroxide or other chemical base. Obviously, dispo-
sition of the scrubber effluent could cause water pollution problems.£/
413
-------
Seme other coatings on scrap metal have compositions that require
special caution during incineration. Teflon contains fluorine, and unreg-
ulated burning of Teflon-coated scrap releases toxic gaseous fluorides. A
source of white smoke is silicon rubber, -which burns with release of SiOg.—'
One of the deficiencies of air pollution control equipment in
secondary nenferrous metals plants is in the afterburner units on inciner-
ators. Many do not have the precise temperature control needed for complete
combustion, and it seems doubtful that the design features insure adequate
mixing of the hot gases -with proper quantities of oxygen from the air.
Another possible fault in many afterburner designs is the failure to pro-
vide sufficient retention time of the hot gases for combustion in the area
of appropriate temperature and oxygen availability .•§/
Experimental testing of a Feabody scrubber operating at a total
gas pressure drop of 43 in. v.g. shewed dust collection efficiency of 34.5%
for an incinerator burning insulated copper wire (equipped with an after-
burner).—'
19.2.3.2 Specific Control Practices for Secondary Copper: The
principal source of atmospheric emissions in the brass- and bronze-ingot
industry is the refining furnace. The exit gas from the furnace may con-
y tain the normal combustion products such as fly ash, etc. Because zinc is
a major low-boiling-point constituent, appreciable amounts of zinc oxide
are normally present in the exit gases also.
Fumes and dust from the blast furnace or cupola are similar tc
those from ingot furnaces. A common practice is to direct these fumes to
the same collection device used for ingot furnace emissions. A dry ir.ertial
collector frequently precedes a baghouse in order to remove the large abra-
sive particles, but high-efficicncy particulate collection equipment is
necessary to remove the fine particulate.=J
Hooding a rotary-tilting-type reverberatory furnace for complete
capture of fumes is difficult, and complete collection is seldom achieved.
Tr.ese furnaces are undoubtedly the most difficult type of brass furnace to
control.
Capturing the (Just-laden gases generated during charging and pour-
ing operations is particularly difficult. One reverberatory furnace in-
stallation, using top charging, is covered by a 12 ft. x 24 ft. hood, with
an air intake capacity of nearly 40,000 cfm. This size is still sometimes
insufficient to capture all the emissions.i/
414
-------
The only air pollution control equipment to receive general accep-
tance in the brass- and bronze-ingot industry is the baghouse collector.
Recent NAFCA data indicate that the concentration of particulate matter
escaping baghouses ranges from 0.006 to 0.036 grain/scf, and operating
efficiencies were generally between 95 and 99.6$. Filter ratios of 2.0 to
2.7 cftn/sa ft and pressure drops of 2 to 6 in. of water are usually encoun-
tered.!/
The cooling of gases prior to filtration is a major engineering
design consideration to prevent burning of the bags and to maintain the
gas above the condensation temperature.^/ The gases leaving a reverbera-
tory furnace msy be 100" to 200°F hotter than the molten metal and must
be cooled before reaching the filter cloth. Direct cooling, by spraying
water into the hot combustion gases, is not generally practiced because
(l) corrosion of ductwork, and equipment increases] (2) vaporized water in-
creases exhaust gas volumes; and (3) temperature of the gases in the bag-
house must be kept above the dewpoint. Water-j acke ted coolers and radia-
tion convection coolers are used to cool the gases without water-injected
sprays.§/
The baghouse designs must take into account the variations in
temperature, gas volume and emissions during the entire refining cycle so
that plant operations may be continued at full capacity under any conditions.
The baghouse should have a sufficient number of compartments so that one
compartment can be bypassed while the others continue to operate and thus
permit replacement of broken bags or allow for unusual cleaning require-
ments. The use of four compartments normally satisfies this requirement.^/
Maintaining duct velocities of 2,500 - 3,000 ft/min is desirable to minimize
buildup of dusts in the duct.
Table 19-4 shows the results of tests performed on baghouses vent-
ing brass furnaces. Larger baghouses are necessary for crucible gas-fired
furnaces because of the heat end volume of the products of combustion from
the gas burners.§/ A summary of information on baghouses for brass and
bronze furnaces is given in Table 19-5.l/
While baghouses have been found to be the most successful device
for collecting large quantities of zinc oxide, there has been no universal
acceptance of a particular filter fabric. These fabrics must be able to-
withstand fairly high temperatures in spite of the dilution and precooling
of gases. They must also withstand considerable physical abuse and vibra-
tion. The use of glass fabric in baghouses allows higher temperature opera-
tion (550°F continuous) than the use of synthetic organic fabrics. However,
the inherently low mechanical strength of glass fabric requires cleaning
methods of a lower intensity than the mechanical shaking methods used with
the synthe t i c s.i/
415
-------
TABLE 19-4
BRASS-MELTING FURNACE AND BAGHOUSE COLLECTOR DATA§/
Case
Furnace data
Type of furnace
Fuel used
Metal melted
Composition of metal melted, %
Copper
Zinc
Tin
Lead
Other
Melting rate, lb/hr
Pouring temperature, °F
Slag cover thickness, in.
Slag cover material
Baghouse collector data
Volume of gases,cfm
Type of baghouse
Filter material
Filter area, sq. ft.
Filter velocity, ft/min
Inlet fume emission rate, lb/hr
Outlet fume emission rate, lb/hr
Collection efficiency, $
Crucible
Gas
Yellow brass
Crucible Low-frequency induction
Gas Electric
Red brass Red brass
70.6
24 .8
0.5
3.3
0.8
388
2,160
1/2
Glass
85.9
3.8
4.6
4 .4
1.3
343
2,350
1/2
Glass
82.9
3.5
4.6
8.4
0.6
1,600
2,300
3/4
Charcoal
9,500
Sectional
tubular
Orion
3,836
2.47
2.55
0.16
93.7
9,700
Sectional
tubular
Orion
3,836
2.53
1.08
0.04
96.2
1,140
Sectional
tubular
Orion
400
2.85
2.2V
0.086
96.0
a/ Includes pouring and charging operations.
-------
TABLE 19-!,
BAGHOUSE IMTOHMATION JUMMAlIt - ItHAT.J Attll BHONZK IHnOT INolIUlTE^
No. of Bags -
Size of Beghouse, cl'a Diameter, In.
10,000 '.-fm (design)
27,500 (dcsicn)
18,000 (actual)
30,000 (design
?9,000 (actual)
2 units - 24,000 each (design) 1,914 - C
18,000 (actual)
3 units - 13,000 each (design) 2,2G0 - G
100 - 15
'P4 - n
5.°o - n
Dfic
Material
Or 1 on and
daeron
Orion and
d-jc ron
Or Ion and
•i.'icron
Type and oi/.c ol
Furnaces Vented
to the Doghouse
? Rev-GO tons/ht each
V Rot-2 tons/ht each
4 Kleo-l at 4 tons/ht
3 nt 1/2 ton/ht
T HfV-fiO tons/ht each
P Hot-4 tons/ht each
1 Cupola
1 Rndiutor Sweater
4 Nov-GO tons/ht each
3 Rot-4 tons/ht each
Material Collected in Baghouses
Ll>/'lon l-b/'ion
Produced
Charged
r>8
67
eoi*/
t ZnO
03
rj&/
PbO
8
n nJ
Frequency
of Bw.
Replacement
18 months
10 to 15
months
-J
Squexe-filter type
20,000 (design)
Multiple-bag type
(\is torn-do s i gned
1^,500 efm/chftmber
(No. of chambers not
reported)
30,000 (design and actual)
50,000 (design and actual)
1,500 - r.
No Mow diiir.rrun pro-
vided; equipment
layout not
ascertainable
?> !U'V-'0-75 tons/ht 55
each
1 Rot-lo tons/ht
Cupola NR
2 Hev-flO tons/ht each
5 Rot-7-l/?-3S
tons/ht each
Ho flow diagram pro-
vided; layout of
i-quipncn1. not
ascertainable
3 Kev-2-7!> tons/ht each NR
3 Kot-P./ tons/ht each
3 Orucible-0.P5
tons/ht each
1 Eire-3 ton:;/ht
1 Cupola-no tonnage
repor ted
3 Rev-?-3U tons/ht each
1 - L? toru/ht each
1 Slug-15-PS tons/ht NH
each
NR S8 3 12 months
NR 65 i. to 6 6 months
NR 51 months
NR NR NR 12 months
a/ Not st jjHil.-ilM il' these fjf^ur-T, are toLfipire:; lor the three unit.;.
-------
Electrostatic precipitators and wet scrubbers have not proved
entirely satisfactory on lead and zinc furies from brass and bronze furnaces.
Load oxide in particular is difficult to collect by electrostatic precipi-
tators because of its relatively high resistivity. In addition, high-voltage
precipitators have not been available in small units suitable for small non-
ferrous foundry use and the first cost may, moreover, be prohibitive. 8/
A number of dynamic and static scrubbers have been tested on brass
furnaces and all have been found unsatisfactory. The scrubbers failed to
reduce the particulate matters sufficiently and opacity was excessive.
These scrubbers were replaced by baghouses.®/
The Commerce Department study also reported cost data for air
pollution control in the secondary nenferrous metals industry. Ihe average
operating cost, for three dissimilar systems, was about $0.60/year per cfm
of capacity ar.d ranged from $0.36 to $I.07/year per cftn. Since some larger
plants have air-cleaning equipment with a capacity to treat 150,000 cfm,
their associated costs of servicing and maintaining this equipment could
be as much as $120,000/year..§/
The cost of air pollution control as computed in the Commerce
Department study of baghouse systems, shown in Table 19-6, averaged about
3/4$ of the value of annual shipments. The study indicated that these in-
stallations and operating costs may have the effect of reducing net after-
tax profits by 8 to 10$. A breakdown of cost findings is shown in Tables
19-7, 1S-S ana 19-9.6/
The costs reported in the Commerce Department study^/ are much
higher than the general cost figures presented in Appendix A. For example,
the installed cost for a baghouse ranges from $2.66 to $8.33/acfm as given
in Table 19-8. However, Appendix A indicates that the average installed
cost of a baghouse should be about $2.00/acfm and the highest expected
cost should not exceed $3.00/acfm. Also, the operating (and maintenance)
costs shown in Table 19-9 range from $0.36 to $1.07/acfm which is three
to ten times higher than would be expected on the basis of cost equations
in Appendix A.
Other data available on air pollution costs at brass and bronze
smelters indicate a broad range for installed costs. It is reported that
a cost of $5.00 per cfm might be "typical" for an installed system, the
baghouse itself representing about 40% of the total cost.!/ ihis installed
cost agrees with cost data shown in Table 19-8 but, as previously discussed,
this is considerably higher than the general cost figures in Appendix A.
418
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TABLE 19-6
ANNUAL CCSI OF AIR POLLUTION CONTROL SYSTEMS§/
(Secondary Konferrous Metals Industry)
5~Year 7-Year
Depreciation Depreciation
Basis Basis
Annual cost as percentage of annual value
of shipments $ $
Me en
Installed equipment 0.46 0.33
Operating and maintenance 0.44 0.44
TOTAL 0.S0 0.77
Median
Installed equipment 0.52 0.37
Operating and maintenance 0.45 0.43
TOTAL 0.95 0.80
Annual per cubic-fcot-per-minute (cfm)
of gas-cleaning capacity (dollars)
Mean
Installed equipment
Operating and maintenance
TOTAL
0.86
0.76
1.62
0.61
0.76
1.37
>fedian
Installed equipment
Operating and maintenance
TOTAL
0.80
0.88
1.68
0.60
C .88
1.48
Source: 1968 BDSA survey interview of six plants with installed dry
baghouse systems.
419
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TABLE 19-7
INSTALLED COSTS OF GAS-CLEANING EQUIPMENT SYSTEMS, BY TYPE OF SMELTER^/
All nonferrous smelters:
11 plants
9 plants
8 plants^/
Brass and bronze ingot makers:
5 plants
4 plants
Copper producers:
2 plants
Aluminum ingot producer
1 plant
Lead smelters:
2 plants
Zinc alloy producer:
1 plant
Dollars/Cubic-Foot-Per-
Minute of Capacity to
Treat Smelter Flue Gases
High Low Average High Low Average High Low Average
Cents/Pound of Annual
Metal Production
2.03 0.30
1.53 0.50
0.72 0.30
0.97
0.95
1.35
0.51
Cents/Dollar of Annual
Metal Shipments
6.60 0.58
3.16 1.25
3.06 1.25
2.00 1.64
2.67
2.14
2.07
2.83
1.82
8.33 2.50
8.33 4.09
4.00 3.04
4.66
6.23
3.52
2.50
Not available, not compiled separately, or not applicable,
a/ Excludes 2 highest and 1 lowest of 11 plants.
-------
TABLE 19-8
INSTALLED COSTS OF GAS-CLEANING EQjJIfMENT SYSTEMS, BY TYPE OF ECyJIPMENT^/
Cents/Pound of Annual
Metal Production
High Low Average
Cents/Dollar of Annual
Metal Shipments
High Low Average
Dollars/Cubic-Foot-Per-
Minute of Capacity to
Treat Smelter Flue Gases
High
Low
Average
Baghouses:
8 plants
7 plants
6 plants
2.03 0.50 1.07
5.08 1.25 2.68
8.33 2.66
5.09
Wet scrubbers:
2 plants
1 plant
1.35 0.67 1.01
2.50
Combined baghouse and wet
packed scrubber:
1 plant
4 .84
Electrostatic precipitators:
2 plants
1 plant
0.75 0.33 0.54
1.29
4.09
Not available, not compiled separately, or not applicable.
-------
TABLE 19-9
ANNUAL OPERATING COSTS OF GAS-CLEANING EqJIFMENT SYSTEMS, BY TYPE OF SMELTER^/
Cents/Pound, of
Mstal Production
High Low Average
Dollars/Cubic-Foot-Per-
Minute Cleaning Capacity-
High Low Average
All nonferrous smelters:
4 plants
3 plants
0.28 0.05
0.12
1.07 0.36
0.82
Brass and bronze ingot maker:
1 plant
0.06
1.07
Lead smelter:
1 plant
0.08
Multi-product smelters:
2 plants
0.28 0.05 0.16
1.03 0.36
0.69
Not available, not compiled separately, or not applicable.
-------
Die costs of maintenance and operation of an air pollution con-
trol system have been reported by four smelters at $2.00, $0.90, $1.50,
$1.73/ton of ingots produced. These costs include credits for value of
byproduct material but the amortization of the capital cost of the system
is not included.!/ These operating and maintenance costs are consistent
with data in Table 19-8.§J Again, this is much higher than would be ex-
pected based on general cost equations in Appendix A.
19.3 SECONDARY LEAD SMELTING AND REFINING
Reverberatory, blast, and pot furnaces are the three furnace types
most commonly used in secondary lead smelting and refining. In addition to
refining lead, most of the secondary refineries also produce lead oxide by
the Barton process.
Various grades of lead metal along with the oxides are produced
by the lead industry. The grade of product desired determines the type
of equipment selected for its manufacture. The most common grades of lead
produced are soft, semisoft, and hard. By starting with one of these grades
and using accepted refining and alloying techniques, any special grade of
le ad or le ad alloy c an be made.
Soft lead may be designated as corroding, chemical, acid copper,
or common desilverized lead. These four types are high-purity leads and
are the products of the pot furnace after a considerable amount of refining
has been done.
Semisoft lead is the product of the reverberatory-type furnace
and usually contains from 0.3 to 0.4$ antimony and up to 0.05$ copper.
Hard lead is made in the blast furnace. A typical composition
for hard lead is 5 to 12$ antimony, 0.2 to 0.6$ arsenic, 0.5 to 1.2$ tin,
0.05 to 0.15$ copper, and 0.001 to 0.01$ nickel.^/
19.3.1 Mission Sources and Rates
The emission sources in secondary lead processing are similar to
those discussed for secondary copper in Section 19.2.1. The main emission
sources are the furnaces. The types and ranges of emissions from the
furnaces will depend upon factors such as fuel, composition and melting
temperature of the alloys, furnace type and operating factors. Individual
emission sources in the various operations comprising the production cycle
for secondary lead are discussed in more detail in the following sections.
423
V
-------
19.3.1.1 Scrap Processing: The sweating of lead from scrap and
dross is widely practiced. Junk automobile storage "batteries supply most
of the lead. In addition, lead-sheathed cable and wire, aircraft tooling
dies, type-metal dresses, and lead dross and skims are also sweated. The
rotary furnace, or sweating tube, is usually used when the material processed
has a low percent of metal to be recovered. The reverberatory box-type
furnace is usually used when the percent of metal recovered is high.
The discharge from a lead-sweating furnace may contain dust,
fumes, smoke, sulfur compounds, and fly ash. This is particularly true
when junk batteries are sweated. The battery groups and plates removed
from the cases contain bits of asphaltic case, oil and grease around the
terminals, sulfuric acid, lead sulfate, lead oxide, and wooden or glass-
fiber plate separators. The organic contaminants burn poorly and the sul-
fur compounds release SCb and SO3. Hie sulfur trioxide is particularly
troublesome; when hydrolized to sulfuric acid, the acid mist is difficult
to collect and is extremely corrosive.
Uncontrolled rotary lead-sweat furnaces emit excessively high
quantities of air contaminants. Although the other types of scrap lead
and drosses sweated in a reverberatory furnace ere normally much less
contaminated with organic matter and acid, high emission rates occur
periodically.
Blast furnaces are used quite extensively in secondary smelting
of lead storage batteries. The lead blast furnace cr cupola is constructed
similarly zo those used in the ferrous industry. The materials forming
the usual charge for the blast furnace, and a typical percentage composi-
tion, are 4.5$ rerun.slag, 4.5$ scrap cast iron, 3$ limestone, 5.5$ coke,
and 82.5$ drosses, oxides, and reverberatory slags. Hard lead is charged
into the cupola at the start of the operation to provide molten metal to
fill the crucible. Normal charges are then added as the material melts
down. The limestone and iron flux that floats on top of the molten lead
retard its oxidation.3/
19.3.1.2 Remelting, Alloying, and Refining Processes: Pot-type
furnaces are used for remelting, alloying and refining processes. Remelt-
ing is usually done in small pot furnaces, and the materials charged are
usually alloys in the ingot form, which do not require any further process-
ing. Ihe quantity of air contaminants discharged from pot furnaces as a
result of remelting, alloying, and refining is much less than that from
reverberatory or blast furnaces.
%
A rather specialized phase of the industry is the production of
lead oxide. Battery lead oxide, containing about 20$ finely divided free
lead, is usually produced by the Barton process. Molten lead is run by
424
-------
gravity from a melting pot into a kettle equipped with paddles. The pad-
dles axe rotated at about 150 rpm, rapidly agitating the molten lead, which
is at a temperature of 700° to 90C°F. Air is drawn through the kettles by
fans located on the air outlet side of a baghouse. The lead, oxide thus
formed is conveyed pneumatically to the baghouse where it is collected and
delivered by screw conveyor to storage.
Other lead oxides requiring additional processing but coinnonly
made are red lead oxide (minimum, Pb^O.^), used in the paint industry, and .
yellow lead oxide (litharage or massicot, R)0), used in the paint and ink
industries.
Since the process requires the use of a "baghouse to collect the
product, and no other contaminants are discharged, no air pollution control
system as such is needed.^/
19.3.1.3 Summary of Emission Rates: Table 19-1 summarizes
emission rate data for the various sources in the secondary lead production
cycle. Reverberatory furnaces account for nearly 75$ (3,000 tons/year) of
the particulate emissions in secondary lead production.
19.3.2 Effluent Characteristics
The chemical and physical properties of effluents from secondary
load production are summarized in Table 19-2. Metallic fumes emitted from
the furnaces are submicron in size. iMean diameter is about 0.3 p, for un-
agglomerated material.
19.3.3 Control Practices and Equipment
In general, plants which are engaged in secondary lead smelting
with either a blast furnace or a reverberatory furnace require an extensive
system for air pollution control. The baghouse has long been considered
as the most acceptable device for collecting lead fumes. The gas stream
from the smelting furnaces is first passed through a series of water- or
air-cooled tubes and then sent to a baghouse. The temperature of the bag-
house must be kept fairly high to prevent the tar volatiles from condensing
and blinding the bags. Lime is also added as the gas stream enters the bag-
house to help prevent this blinding action. On leaving the baghouse the gas
stream is discharged to the stack or in some instances further treated in
an electrostatic precipitator in order to meet local ordinance requirements.§/
Reverberatory furnaces are used in lead-smelting operation. All
the smoke and fume produced by this type of furnace must be collected and,
425
-------
since they are combined with the products of combustion, the entire volume
emitted from the furnace must pass through the collector. Baghouses have
"been found to operate satisfactorily in this service. Provisions should be
made to prevent sparks from contacting the filter cloth and temperature
must be controlled by preceding the baghouse with radiant cooling ducts,
water-jacketed cooling ducts or other suitable devices. Dacron bags are
being used successfully in this service. Test results of secondary lead-
smelting furnaces venting to a baghouse are shown in Table 19-10.®/
One of the largest secondary lead smelters in the U. S. uses
fiberglass bags for fume collection, at higher than 400°F, of combined
effluent from a reverberatory furnace and a lead blast furnace. Die 400°F
filtering temperature was desired to eliminate deposition of organic tars
on the bags.£/
!Zbe control system for a lead blast furnace is similar to that
employed for gray-iron cupola furnaces. Electrostatic precipitators are
not used for economic reasons. Moreover, difficulties can be encountered in
conditioning the particles to give them resistivity char&cteristics in the
range that will allow efficient collection.§/
In the refining and alloying of secondary lead the air pollution
problems are not as complex as those arising from the smelting of lead
scrap. The fumes produced can be effectively treated by collecting them
from the kettle hoods with a flow of around 200 cfm and passing them
through a baghouse.i2/
Available data on control equipment costs are presented along
with the data for secondary copper in Section 12.2.3.2.
42S
-------
lAfiLa 19-LO
DUS: ANT FUML EMISSIONS FROM P SECONDARY L3AD-SMSLTI?JC FUHKACrf/
lest dumber
KirnaC'j dflto
iypc of furnace
tv.o1 used
M- •\2 r i al ch ar ce d
Process weight, lb/hr
Reverberetory
Natural gas
Battery groups
2,500
Blast
Coke
Battery groups, dross, slag
2,670
Control equipment dots
"ype of ?ontro.: equipment
rilter meterial
Filter arop, sq. ft.
Filter velocity, ft/mir. at 327"F
Sectioned tubular beghousc®-
Eacron
IS,000
/
Sectioned tubular baghouSfr^
Decron
16,000
0.93
st and fume lata
C&3 flow rale, scfm
Furnace outlet
Baghcuse cutlet
Jas temperature, °F
f\;rnece cutlet
Beghouse outlet
Co.ncsntration, grelns/scf
Furnace outlet
Beghouse outlet
Lust and fume emission, lh/hr
Furnace outlet
Baghouse out2ct
E&ghouse efficiency, %
Baghouse catch, wt. %
Particle size 0 to 1 y,
1 to 2
2 to 3
? to 4
1 to It
Sulfur compounds as SCt>j vol. %
Eaghcuse outlet
3,060
10,400k/
951
327
4 .38
0 .013
130.5
1.2
99.1
13.3
45.2
19.1
14.0
O.'l
0.104
2,170
12,00CW
50C
175
12.5
0.035
SP9
3.9
33.3
13.3
45.2
15.1
14 .0
8.4
C .03
bj The sane baghouse alternately ser.'es the reverberator!' furnace ar.d the blast furnace.
b/ Dilution air aamlt-cid to cool gas stream.
427
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19.4 SECONDARY ZINC SMELTING AND REFINING
Zinc is incited in crucible, pot, kettle, reverberatory, or elec-
tric-induction furnaces for use in alloying, casting, and galvanizing and
is reclaimed from higher melting point metals in sweat furnaces. Secondary
refining of zinc is conducted in retort furnaces, which can also be used
to manufacture zinc oxide by vaporizing and burning zinc in air.
19.4.1 Emission Sources and Rates
The emission sources in zinc recovery parallel those in the pre-
vious secondary processes, and the emissions are influenced by the fuel,
composition and melting temperature of the alloys, furnace type, and opera-
ting factors. Individual emission sources in the various operations com-
prising the production cycle for secondary zinc are discussed in more detail
in the following sections.
19.4.1.1 Scrap Processing: Zinc can be recovered by sweating in
a rotary, reverberatory, or muffle furnace. Zinc-bearing materials fed to
a sweating furnace usually consist of scrap die-cast products such as auto-
mobile grilles, license plate frames, and zinc skims and drosses.
Air contaminants released from a zinc-sweating furnace consist
mainly of smoke and fumes. The smoke is generated by the incomplete com-
bustion of the grease, rubber, plastics, and so forth contained in the
material. Zinc fumes ere negligible at low furnace temperatures, because
zinc has a low vapor pressure even at 900oF. With elevated furnace tempera-
tures, however, heavy fuming can result .'zJ
19.4.1.2 Zinc Melting: The melting operation is essentially the
same in all the different types of furnaces. Zinc to be melted may be in
the form of ingots, castings, flashing, or scrap. Ingots, rejects, and
heavy scrap are generally melted first to provide a molten bath to which
light scrap and flashing are added. After sufficient metal has been melted,
the bath is heated to the desired pouring temperature, which may vary from
800° to 1100°F. Before pouring, a flux is added and the batch agitated to
separate the dross accumulated during the melting operation.
The discharge of air contaminants from melting furnaces is gen-
erally caused by excessive temperatures and by the melting of metal con-
taminated with organic material. Fluxing can also create excessive emis-
sions, but fluxes that clean the metal without fuming are available.!/ .
The first visible discharge noted from a furnace is from organic
material. Before the melt is hot enough to vaporize any zinc, accompanying
organic material is either partially oxidized or vaporized, causing smoke
423
-------
or oily mists to be discharged. Ihis portion of the emissions can be con-
trolled either by removing the organic material before the charging to the
furnace or by completely burning the effluent in a suitable incinerator or
afterburner.
Normally, zinc is sufficiently fluid for pouring at temperatures
below 1100°F. At that temperature, its vapor pressure is 15.2 mm. of mer-
cury, low enough that the amount of fumes formed cannot be seen. If the
metal is heated above 11G0°F, excessive vaporization can occur. Zinc can
vaporize and condense as metallic zinc if existing temperatures and etmo-
spheric conditions do net promote oxidation. Finely divided zinc so formed
is a definite fire hazard, and fires have occurred in baghouses collecting
this material.-^/
19.4.1.3 Zinc Vaporization: Retort furnaces are used for operations
involving the vaporization of zinc including (1J reclaiming zinc from alloys,
(2) refining by distillation, (3) recovering zinc from its oxide, (4) manu-
facturing zinc oxide, and (5) manufacturing powdered zinc.
Belgian retorts, distillation retorts, and muffle furnaces are
used as retort furnaces.3/ Belgian retorts are used to reduce zinc oxide
to metallic zinc. Distillation retorts, used for batch distillations, re-
claim zinc from alloys, refine zinc, make powdered zinc, and zinc oxide.
Muffle furnaces, used for continuous distillation, reclaim zinc from alloys,
refine zific, and make zinc oxide.
The Belgian retort furnace is one of several horizontal retort
furnaces that for many years have been the most common device for the re-
duction of zinc. Die horizontal retort process is now being replaced by
other methods capable of handling larger volumes of metal per retort and
by the electrolytic process for the reduction of zinc ore.3/
Figure 19-3 illustrates a typical Belgian retort. One end is closed
and a conical-shaped clay condenser from 18 to 24 in. long is attached to the
open end. Hie retorts are arranged in banks with rows four to seven high and
as many retorts in a row as are needed to obtain the desired production. Die
retorts are generally gas-fired. Hie air contaminants emitted vary in com-
position and concentration during the operating cycle. During charging oper-
ation very low concentrations are emitted. Hie feed is moist, and, therefore,
not dusty. As the retorts are heated, steam is emitted. After zinc begins
to form, both carbon monoxide and zinc vapors are discharged. These emissions
burn to form gaseous carbon dioxide and solid zinc oxide. During the heating
cycle, zinc is poured from the condensers about three times at 6- to 7-hr.
intervals. Hie amount of zinc vapors discharged increases during the tapping
operation. Before the spent charge is removed from the retorts, the tempera-
ture of the retorts is lowered, but zinc fumes and dust from the spent charge
are discharged to the atmosphere.5/ In addition, the retorts sometimes break
and the zinc charge is emitted to the atmosphere in the combustion gases.
429
-------
FRONT Mil
Of FURNACE
CONDENSED METAL
VAPORS
CERAMIC RETORT
FLAME FROM
COMBUSTIBLE GASES
METALLIC OXIOE CHARGE
1ITH REDUCING MATERIALS
BURNER PORT
Figure 19-3 - Diagram Showing One Bank of a Belgian Retort Furnace^/
430
-------
The distillation retort furnace (shown in Figure 19-4) consists
of e pear-shaped, graphite retort, which mey be 5 ft. long by 2 ft. in
diameter at the open end and 3 ft. in diameter at its widest cross-section.
Normally, the retort is encased in a brick furnace with only the open end
protruding and it is heated externally with gas- or oil-fired burners. The
retorts are charged with molten, impure zinc through the open end, and a
condenser is attached to the opening to receive and condense the zinc vapors.
After the distillation has been completed, the condenser is moved away, the
residue is removed from the retort, and a new batch is started.
During the 24-hr. cycle of the distillation retorts, zinc vapors
escape from the retort (l) when the residue from the preceding batch is
removed from the retort and a new batch is charged and (2) when the second
charge is added to the retort. As the zinc vapors mix with air, they oxi-
dize and form a dense cloud of zinc -oxide fumes. Air contaminants are dis-
charged for about 1 hr. each time the charging hole is open. When the
zinc is actually being distilled, no fumes escape from the retort; however,
a small amount of zinc oxide escapes from the speise hole in the condenser.
Although the emission rate is low, air contaminants are discharged for
about 20 hr. per day.
Muffle furnaces (similar to that shown in Figure 19-5) are con-
tinuously fed retort furnaces. They generally have a much greater vaporizing
capacity than either Belgian retorts or bottle retorts, and they are opera-
ted continuously for several days at a time. Heat for vaporization is sup-
plied by gas- or oil-fired burners by conduction and radiation through a
silicon carbide arch that separates the zinc vapors and the products of
combustion. Molten zinc from either a melting pot or sweat furnace is
charged through a feed well that also acts as an air lock. The zinc vapors
are conducted to a condenser where purified liquid zinc is collected, or
the condenser is bypassed and the vapors are discharged through an orifice
into a stream of air where zinc oxide is formed.
Any discharge of zinc vapor from the condenser forms zinc oxide
of product purity; therefore, the condenser vents into the intake hood of
a product-collecting exhaust system. Since some zinc oxide is always pro-
duced, even when the condenser is set to produce a maximum of liquid zinc,
the product-collecting exhaust system is always in operation to prevent
air contaminants from escaping from the condenser to the atmosphere.5/
19.4.1.4 Summary of Emission Rates: Table 19-1 summarizes emission-
rate data for the various sources in secondary zinc processing. Zinc sweat-
ing furnaces account for about 60$ of the total quantity of particulates
emitted in secondary zinc production.
431
-------
SPtlSl HOLt
¦tmm
CONDthSIR
ccramic
IE TORT
imms
432
-------
tUKNlt POM
OUC1 (OR OI1DE
COLLCC1tOK
ROLliN KEUL
num condimscr
UNI I
MUFFLE
' , '
^ .f< i....
Figure 19-5 - Diagram of a Muffle Furnace and Condenser
433
-------
19.4.2 Effluent Characteristics
Hie chemical and physical properties of effluents from secondary-
zinc production axe summarized in Table 19-2. Mstallic fumes emitted from
the furnaces are submicron in size, and range from 0.03 to 1 u (unagglomer-
ated material).
19.4.3 Control Practices and Equipment
An afterburner should be provided to incinerate the combustible
matter discharged from a low-temperature sweating furnace. A baghouse
should be used with the afterburner to capture the dust and fumes. Table
19-11 shows test results for a zinc die-cast sweating operation controlled
by a baghouse.^/
Air pollution control for retort furnaces is achieved with a
baghouse. Glass bags have been found adequate when gas temperatures ex-
ceed the limits of cotton or orlon. Filtering velocities of 3 ft/min are
generally employed.^/
Available data on control equipment costs are presented along
with the data for secondary copper in Section 19.2.3.2.
19.5 SECONDARY ALUMINUM SMELTING AMD REFINING
Secondary aluminum smelting is essentially the process of remelt-
ing aluminum, but encompasses the following additional practices: (l) flux-
ing, (2) alloying, (3) degassing, and (4) demagging.
Aluminum for secondary smelting comes from three main sources:
1. Aluminum pigs. These may be primary metal but may also be
secondary aluminum produced by a large secondary smelter to meet standard
alloy specifications.
2. Foundry returns. These include gates, risers, runners, sprues,
and rejected castings. In foundries producing sand-mold casting, foundry
returns may amount to 40 to 60$ of the metal poured.
3. Scrap. This category includes aluminum contaminated with oil,
grease, paint, rubber, plastics, and other metals such as iron, magnesium,
zinc, and brass.
The melting of clean aluminum pigs and foundry returns without the
use of fluxes does not result in the discharge of significant quantities of
air contaminants. The melting of aluminum scrap, however, frequently re-
quires air pollution control equipment to prevent the discharge of excessive
air contaminants.
434
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TABLE 19-11
DUST AND FUME EMISSIONS FROM AN ALUMINUM-
AND A ZINC-SWEATING FURNACE CONTROLLED BY A BAGHOUSE^/
Ttest Number
Furnace data
"type of furnace
Size of furnace
Process weight, lb/hr
Material sweated
Reverberatory
5 ft. 9 in. wide x 6 ft.
4 in. long x 4 ft. high
760
Aluminum skims
Reverberatory
5 ft. 9 in. wide x 6 ft.
4 in. long x 4 ft. high
2,000
Zinc castings
Baghouse data
Type of baghouse
Filter material
Filter area, sq. ft.
Filter velocity, ft/min
Precleaner
Sectioned tubular
Orion
5,184
1.9
None
Sectioned tubular
Orion
5,184
1.05
None
Dust and fume data
Gas flow rate, scfta
Baghouse inle t
Baghouse outlet
Average gas temperature, °F
Baghouse inlet
Baghouse outlet
Concentration, grains/scf
Baghouse inlet
Baghouse outlet
Dust and fume emission, lb/hr
Baghouse inlet
Baghouse outlet
Control efficiency, %
8,620
9,500
137
104
0.124
0.0138
9.16
1.133/
87.7 V
7,600
7,420
190
173
0.205
0.0078
13.5
0.5
96.3
a/ Visible emissions released from the baghouse indicated that a bag had broken during the latter
part of the test.
-------
Crucible and reverberatory furnaces are commonly used for melt-
ing aluminum. Both gas- and oil-fired units are common. Electric-induc-
tion furnaces axe becoming common. Most electric furnaces are relatively
small.1/
13.5.1 Emission Sources and Rates from Secondary Aluminum Smelting
All the pyrometallurgical processes associated with aluminum
smelting create air pollutants to some degree. Individual emission sources
in the various operations comprising the production cycle for secondary
aluminum are discussed in more detail in the following sections.
19.5.1.1 Scrap Processing: Open-flame, reverberatory-type fur-
naces are used by secondary smelters to produce aluminum pigs for remelting.
These furnaces are constructed with the hearths sloping downward toward
the rear of the furnace. All types of scrap aluminum are charged into one
of these furnaces, which operate at temperatures of 1250° to 1400°F. In
this temperature range, the aluminum melts, trickles down the hearth, and
flows from the furnace into a mold. The higher melting materials such as
iron, brass, and dross oxidation products formed during melting remain
within the furnace. This residual material is periodically raked from the
furnace hearth. Some large secondary aluminum smelters separate the alumi-
num suspended in the dross by processing the hot dross immediately after
its removal from the metal in the refining furnace. The aluminum globules
suspended in the dross can also be separated and reclaimed by a cold, dry-
milling process. This process is used primarily to process drosses having
a low aluminum content.
In theory, an aluminum-sweating furnace can be operated with minor
emissions of air contaminants if clean, carefully hand-picked metal free of
organic material is processed. In practice, this selective operation does
not occur and excessive emissions periodically result from uncontrolled
furnaces. Stray magnesium pieces scattered throughout the aluminum scrap
are not readily identified, and charging a small amount of magnesium into
a sweating furnace causes large quantities of fumes to be emitted. Emis-
sions also result from the other materials charged, such as skims, drosses,
scrap aluminum sheet, pots and pans, aircraft engines, and wrecked airplanes.
Smoke is caused by the incomplete combustion of the organic con-
stituents of rubber, oil and grease, plastics, paint, cardboard, and paper.
The sweating of dross and skims is responsible for the high rates of emis-
sion of dust and fumes. Residual aluminum chloride flux in the dross is
especially troublesome because it sublimes at 352°F and is very hygroscopic•
In addition, it hydrolyzes and forms very corrosive hydrogen chloride.
436
-------
In the dry-milling process, dust is generated at the crusher,
in the mill, at the shaker screens, and at points of transfer. These loca-
tions must be hooded to prevent the escape of fine dust to the atmosphere.
When aluminum is reclaimed by the hot dross process, some fumes
are emitted from the flux action; however, the main air pollution problem
is the collection of the mechanically generated dust created by the rotation
of the dross barrel.
19.5.1.2 Aluminum Melting: For melting small quantities of alumi-
num, up to 1,0C0 lb., crucible or pot-type furnaces are used extensively.
Almost all crucibles are made of silicon carbide or similar refractory
material. Small crucibles are lifted out of the furnace and used as ladles
to pour into molds. The larger cruqibles are usually used with tilting-
type furnaces. For die-casting, molten metal is ladled out with a small
hand ladle, or it can be fed automatically to the die-casting machine.
The reverberatory furnace is commonly used for medium- and large-
capacity heats. Small reverberatory furnaces of up to approximately 3,COO lb.
capacity may be of the tilting type. Sometimes a double-hearth construction
is employed in furnaces of 1,000 to 3,000 lb. holding.
Small crucible furnaces are usually charged by hand with pigs
and foundry returns. Many reverberatory furnaces are also charged with
the same type of materials, but mechanical means are used because of the
larger quantity of materials involved.
Frequently, a large part of the material charged to a reverbera-
tory furnace is low-grade scrap and chips. Faint, dirt, oil, grease, and
other contaminants from this scrap cause large quantities of smoke and fumes
to be discharged. Even if the scrap is clear-, large surf ace- to- volume ratios
require the use of more fluxes, which can cause serious air pollution problems.
The extent of visible emissions discharged from degassing aluminum
with chlorine gas depends on metal temperature, chlorine flow rate, and mag-
nesium content of the alloy. Other factors affecting the emissions to a
lesser degree ere the depth at which the chlorine is released and the thick-
ness and composition of the dross on the metal surface
When chlorine is used for demagging, it is added so rapidly that
large quantities of both aluminum chloride and magnesium chloride are formed,
the molten bath is vigorously agitated, and not all of the chlorine reacts
with the metals. As a result, a large quantity of aluminum chloride is
discharged along with the chlorine gas and some entrained magnesium chloride.
The aluminum chloride is extremely hygroscopic and absorbs moisture from the
air, with which it reacts to form hydrogen chloride. These air contaminants
are toxic, corrosive, and irritating.
437
-------
19.5.1.3 Summary of Emission Rates: Table 19-1 summarizes
emission-rate data for the various sources in secondary aluminum processing.
Chlorine fluxing operations for degassing and demagging steps account for
51,000 tons/year out of a total of approximately 58,000 tons/year of emitted
particulates.
19.5.2 Characteristics of Effluents
The chemical and physical properties of effluents from secondary
aluminum production are summarized in Table 19-2. Emitted particulates
are less than 2 ^ in size. The particulates may be toxic because of the
fluorides and chlorides that are emitted.
19.5.3 Control Practices and Equipment
In aluminum-swe ating operations, raking the residual metal and
dross from the furnace is e critical operation from an air pollution stand-
point, and hoods should be installed to capture emissions at these locations.
An afterburner followed by a baghouse is recommended as control
equipment for an aluminum-sweating furnace. Baghouse filtering velocities
should not exceed 3 ft/min. The afterburner must be so designed that the
carbonaceous material is intimately mixed with the exhaust air and held
at 12C0° to 1400CF for a retention time of about 0.3 sec. Secondary air
msy have to be admitted to the afterburner to ensure complete combustion.
The hot gases must be cooled before entering a baghouse, and
radiant cooling or dilution with cold air is recommended in preference to
evaporative cooling with water. If hot furnace gases are cooled with water,
the aluminum chloride hydrolyzes, producing hydrochloric acid that attacks
the ductwork and bags. Even the condensation from night air during shut-
down provides sufficient moisture to corrode the equipment in the presence
of these chemicals. Tables 19-11 and 19-12 show test results on control
systems for aluminum-sweating furnaces.^/
The wet scrubber is particularly suitable for the aluminum smelter.
Spray quenching of the hot furnace gases creates steam which reacts with
aluminum chloride gas to form soluble hydrated aluminum oxide and hydro-
chloric acid; both of these are relatively easy to remove in an appropriately
designed and operated scrubber. In order to obtain adequate collection ef-
ficiency, the use of high-efficiency wet scrubbers, with a caustic solution
as the scrubbing medium, has been found necessary. Table 19-13 shows typi-
cal test data on collection efficiency for various wet scrubbers.§/
To adequately control emissions from chlorinating aluminum, the
wet scrubber may be followed by a baghouse or electrical precipitator. At
present the trend in control equipment for aluminum-fluxing emissions appears
to be away from electrical precipitators and toward the scrubber-baghouse
combination.
438
-------
TABLE 19-12
DUST AND FUME EMISSIONS FROM AK AIUIJHUM-SWEATIMC
FuTCIACS CONTROLLED BY All AFTEEEUKSR ALT' BAGHOUSE^/
Furnace data
Type of furn9ce
FUrnace hearth area
Process weight, lb/hr
Material sweated.
Reverberator!' with integral afterburner
4 ft. 7 in. wide x 8 ft. 1C in. long
2,870
Scrao aluminum
Baghouse data
Type of bags
Filter material
Filter area, sq. l't.
Filter velocity, ft/min
Precieaner
Djst and fuir.e data
Gas flow rate, scfc
Average gas temperature, °F
Concentration, grains/scf
Dust and fume emission, lb/hr
Particulate control efficiency,
Tubular
Dacron
Settling chamber
Settling
Ch aabe r Inle *
1,360
350
0.505
5.89
4,800
2.16
Furnace Charge Baghouse
Door Hood Outlet
5,580
204
c.cai
3.03
S,35oV
:77
0.58
94.1
Orsat analysis at settling
chamber inlet, volume %
C02 6.8
0-, 8.6
CO 0.02
n2
KoO
77.33
7 or,
Particle size analysis at baghouse
outlet, wt. %
+6C mesh 85.9
-6C mesh 14.1
Parti
Lcle size
analysis
cesh
portion,
wt. %
0
to 2 |i
6 .9
2
to 5 n
32.4
5
to 10 a
30.9
10
to 20 u
17 .7
2C
to 40 a
7.7
<
40 n
4.4
Conbustible carbon in particulate
discharge, dry wt. %
Settling chamber
inlet 83.7
Furnace chamber
door hood exit 67.3
a/ Volume is greater at the baghouse exit than at the inlet because cf leakage.
439
-------
TABLE 19-13
Contaminants
HCL
CLg
Particulates
SCRUBBER COLLECTION EFFICIENCY FOR EMISSIONS
" FROM CHLORINATING ALUMHW^/
(Scrubber Collection Efficiencies,
Slot Scrubber
Water
. 90 to 95
30 to 50
30 to 50
lOjt Caustic
Solution
95 to 99
50 to 60
50 to 6C
Packed-Column Scrubber
10# Caustic
Water Solution
95 to 98 99 to 100
75 to 85 90 to 95
70 to 80 80 to 90
a/ Collection efficiency depends mainly upon scrubbing ratio (gal/l,000 ca.
velocity of gas in scrubber, and contact time and, to a lesser extent
on other aspects of the design. These values are typical efficiencie
obtained by actual tests but do not reflect the entire range of resul
More precise controls need to be developed and methods need to
be found to adapt the wet scrubber to the peak chlorine "burn-off" cycle
wher. the temperature of the aluminum furnace is raised to Volatilize all
residual chlorine from the system.®/
Available data on control equipment costs are presented aicng
with the data for secondary copper in Section 19.2.3.2.
440
-------
REFERENCES
1. "Air Pollution Aspects of Brass and Bronze Smelting and Refining
Industry," National Air Pollution Control Administration Publication
No. AP-58.
2. Schwartz, H. E., et al., "Controlling Atmospheric Contaminants in the
Smelting and Refining of Ccpper-Base Alloys," Journal of the Air
Pollution Control Association, .5(1), May 1955.
3. Air Pollution Engineering Manual, Air Pollution Control District,
County of Los Angeles, HIS Publ. No. 999-AP-40.
4. U. S. Department of Health, Education and Welfare, Control Techniques
for Particulate Air Pollutants, Washington, D. C., 1969.
5. National Association of Secondary Material Industries, Inc., The
Secondary Material Industries and Environmental Problems, New York:
HASMI, 1966, R-127.
6. U. S. Department of Commerce, Economic Impact of Air Pollution Controls
on the Secondary Nonferrous Metals Industry, Washington, D. C., 1969,
3-132.
7. Kaiser, E. R., and J. Tolciss, "Control of Air Pollution from the Burning
of Insulated Copper Wire," Journal of the Air Pollution Control
Association, 13, January 1953.
~ 1 " ¦
8. U. S. Department of Health, Education and Welfare, Air Pollution Engi-
neering Manual, Cincinnati, Ohio, Public Health Service, 1967.
9. Spaite, P. W., P. G. Stephan, and A. H. Rose, Jr., "High Temperature
Fabric Filtration of Industrial Gases," Journal of the Air Pollution
Control Association, 11, May 1961.
——— ¦ — ¦ ¦ - — ¦ —¦ ¦ ' w
10. Elythe, D. J., Ed., "Lead and Arsenic Reports," Journal of the Air
Pollution Control Association, _10, August 1960.
11. Sproull, W. T., "Collecting High Resistivity Dusts and Fumes,"
Industrial and Engineering Chemistry, 47(5), 940-944, 1955.
12. Private Communication, Research-Cottrell, March 1970.
441
-------
CHAPTER 20
COAL PREPARATION PLANTS
20.1 INTRODUCTION
An expanding market demand for high-quality fine-mesh coal has
necessitated improvement and enlargement of fine-coal preparation facili-
ties. The primary purpose of a preparation plant is to crush the coal,
remove impurities, and classify the product into standard sizes. The
equipment and processes involved in coal preparation are similar to those
used in the beneficiation of most mineral ores. These are generally wet
processes which dc not, in themselves, cause air pollution problems. How-
ever, when the wet product must be dried to prevent freezing due to cold
weather or tc satisfy customer specifications, significant air pollution
problems car. occur.
The major air pollution problems associated with coal-preparaticn
procedures are gaseous emissions from ignited coal-refuse disposal areas,
dust from refuse and coal-storage piles, and particulate matter from coal
dryers and de-dusting operations.—/ The coal-cleaning process, particulate
emission sources, particulate emission rates, effluent characteristics,
and control practices and equipment are reviewed in the following paragraphs.
20.2 COAL-CLEANING PROCESS
The great increase in mechanization and full seam mining has re-
sulted in substantial increases in the impurity content of the raw coal as
well as in a finer size content. As a result, the percentage of coal
cleaned by mechanical methods has increased from only 24$ of the total pro-
duction of bituminous and lignite coal in 1942 to 65$ in 1965. The amount
of refuse discarded during preparation for the same period increased from
13 to 21$. Changes in the equipment used in the cleaning process were as
follows:
443 Preceding page blank
-------
MECHANICAL
CLEANING BY PROCESS,
PERCENT—/
Process
1942*/
195;
Jig
47
46
Dense-medium
9
29
Table
2
13
Pneumatic
14
B
Classifier
7
2
Launder
13
1
Flotation
< 1
2
a/ Unclassified nearly 8%. Data on the amount cleaned by flotation was
not collected until 1960 when 1.8 million net tons was so treated.
In 1965 this figure increased to 6.9 million tens.
The principal mechanical cleaning processes are discussed in
more detail in the following paragraphs.
20.2.1 Hydraulic Separation and Concentration
20.2.1.1 Hydraulic Separation - Jigging: Jigging is a process
of particle stratification in which the particle rearrangement results from
an alternate expansion and compaction of a ted of particles "by a pulsating
fluid flow. The particle rearrangement results in layers of particles
which are arranged by increasing density from top to bottom of the bed.
This response, developed from the many and continuously varying forces acting
upon the particles, is a solid-fluid separation more related to particle
density and less to particle size than any other "hydraulic type" process.
The stratification is usually carried out in a rectangular, open-top con-
tainer, called a jig, in which the mass of particles (termed a "bed") is sup-
ported on a perforated base through which the water flows in alternating
directions. Following the particle stratification, the particle bed is
physically "cut" at any desired particle density plane thus creating the
desired quality products. The jig includes means for continuously introducing
the raw ccal, for moving the water through the coal bed in a controllable
manner as well as for separating and removing the stratified particles from
the system as two or more product streams. In coal preparation, this highly
versatile unit operation is more preferably applied to a wide size-range .of
particles with top sizes up to B in. than tc a closely sized fraction.—2/
Single jig washers have capacities from 5 tc > 700 tons/hr of
feed coal. The separation results attainable by jigging have favored this
unit operation as optimum for creating a clean coal product as required by
steam coal specifications. Although the jig is used in preparing coals which
444
-------
are difficult to separate, its limitations to achieve both quality products
and high recovery are being recognized in comparison with heavy media-based
processes which make sharper separations from feeds having high "near-
gravity" contents. Thus the accuracy of the densimetric stratification in
the upper portions of the jig bed is less precise. In jigging, es in most
mineral-preparation unit operations, high recovery and product quality are
interdependent and inverse process characteristics.
20.2.1.2 Hydraulic Concentration: Hydraulic concentrating de-
vices depend on the physical characteristics, size, shape, and density of
particles suspended in a liquid medium to effect a concentration of desired
quality.
The principal fine-coal washers utilized in the United States
today are wet concentrating tables, cyclones, launders, feldspar Jigs and
hydrotators. Of these the concentrating table is the most popular, espe-
cially in the cleaning of bituminous coal. Cyclone types are becoming in-
creasingly important in washing both anthracite and bituminous coal. The
launders and feldspar jigs are utilized cn a limited scale for cleaning
bituminous coal and the hydrotator is used extensively for cleaning anthra-
cite .
Fine-coal hydraulic concentrating devices generally include those
devices which clean 3/8 in. tcp-size coal. This is an arbitrary size which
seems most consistent with actual practice, although certainly these de-
vices can effectively clean coarser or finer coal.15/
20.2.2 Dense Medium Separation
Dense medium separations include those coal-preparation processes
which clean raw coal by immersing it in a fluid having a density inter-
mediate between clean coal and reject. As there is a general correlation
between ash content and specific gravity, it is possible to achieve the re-
quired degree of removal of ash-forming imparities from a raw coal by
regulating the specific gravity cf the separating fluid.
Dense medium processes offer the following advantages over other
coal cleaning processes:
1. Ability to make sharp separations at any specific gravity
within the range normally required even in the presence of high percentages
of the feed in the range of + 0.1 specific gravity units.
2. Ability to maintain a separating gravity that can be con-
trolled with i 0.005 specific gravity units.
445
-------
3. Ability to handle a wide range cf sizes (up to 14 in.).
4. Relatively low capital and operating costs when considered in
terms cf high capacity and small space requirements.
5. Ability to change specific gravity cf separation to meet,
varying market requirements.
6. Ability to handle fluctuations in feed both in terms of
quantity and quality.^/
Commercial application of the dense medium process is a practical
extension of the familiar laboratory float-and-sink test, which is used as
a standard (100# efficiency) gravimetric separation. Commercial plants .in
net exactly duplicate laboratory float-and-sink separations for the fcli<-":.:*x
reasons: suspensions, rather than true liquids, usually are used as sepa-
rating media; the introduction of feed and removal of the float and sir.!-;
introduce disturbances in the separating medium; agitation, cr upv/ard cur-
rents in the vessel, normally are required tc keep the separating medium in
suspension; and the practical need for high throughput does not allow suf-
ficient retention time for perfectly separating near-gravity material.
Theoretically, any size particle can be treated by dense jnedi a:
processes; practically, the sizes treated range from about 0.5 mm. (32
mesh) to about 6 in., although sizes ranging up to 14 in. occasionally are
washed. Sizes coarser than about l/4 in. normally are treated in static
dense medium separators, while the size range 0.5 mm. tc about 1/4 ir..
normally is washed in separators employing centrifugal force: for exar/rle,
the dense medium cyclone washer.15/
20.2.3 Froth Flotation
Flotation is a chemical process that depends on the selective
adhesion to air of some solids and the simultaneous adhesion to water of
ether solids. A separation of coal from coal waste then occurs as finely
disseminated air bubbles are passed through a feed coal slurry. Air-adhering
particles (usually the ccal) are separated from nonadhering particles,
floated tc the surface of the slurry and then removed as a concentrate.
This process involves the use of suitable reagents to establish a hydrcphotic
or air-adhering surface on the solids to be floated, and to render the other
solids hydrophilic. As shown in Section 20.2, the flotation process ac-
counted for about 2# cf the coal cleaned by mechanical methods in 1965,i§/
20.2.4 Dry Cleaning ar.d Concentration
The particular field of application of machines utilizing air
currents as the primary separating medium is in the cleaning of the fine
446
-------
sizes of bituminous coal. Approximately 25,400,000 tor.s of bituminous
ccal were cleaned "by air machines during 1965. No application has been
found for cleaning anthracite.
Seven successful pneumatic coal-cleanir.g machines have been de-
veloped and introduced to the American coal-mining industry:
1. Feale Davis: "Pneumo-Gravity" machine
2. Arms "Concentrator," oscillating table
3. Heyl ar.d Patterson oscillating table
4. ''Stump Air-Flow," pulsating air jig
5. "Super Airflow," pulsating air jig
6. Ridge air jig
7. Phillip air jig
While not all coals can be beneficiated by air washing, the air
washing of coals that are easy to clean can be readily proved advantageous.
Of all the preparation methods, pneumatic cleaning is the most acceptable
from the standpoint of delivered Btu cost. This is based on the premise
that a percent of moisture is just as detrimental as a percent of ash.
Historically most air-cleaning devices used a vertical upward
current of air through the bed of material. They differed by the method
of imparting mobility to the bed and the method of removing the refuse.
In general terms, the air nachines were divided into three types:
1. Pneumatic jigs where the air current was pulsated.
2. Pneumatic tables where the refuse was diverted from the
direction of flow of the clean coal by a system of riffles fixed to the
deck.
3. Pneumatic launders where the products flowed in the same
direction, and the clean coal was skimmed off the top of the bed and/or
the refuse was extracted from the bottom in successive stages.
In recent years, however, the latter two types of units have
declined in popularity. In fact, a survey of the industry revealed that
all of the air-cleaning machines in use in 1966 depended on pulsating air
as the medium of concentration.
447
-------
Dry concentration of coal has cone a long way in recent years.
Today, there are numerous examples of successful plants treating 3/8 in.
by 0 and 1/& in. by 0 coal and coal as large as 2-1/2 in. in capacities
up tc 350 tons/hr. Although the rate of installations has tapered off,
there were over 200 full-size units of airflow equipment in operation in
1965 processing over 20 million tons of coal annually
These are indications that the downward trend in new air-cleaning
installations may be reversed in the not toe distant future. Governmental
regulations are placing greater and greater emphasis on control cf bcth
stream and air pollution originating from preparation plants. Pneumatic
cleaning has the inherent advantage in this regard in that it does net con-
tribute to stream pollution at all, as may water cleaning techniques.
Similarly, although air cleaning plants admittedly can be dusty, the major-
ity of the dust is confined within the plant and particulate emission to
the atmosphere away from the plant is minor if cloth filters are used. Also,
dry concentration obviously will net cause themal or chemical pollution
of the air. These considerations may therefore weigh heavily in favor cf
air cleaning as regulations inevitably become more stringent through in-
creased governmental action.
A second factor which may contribute heavily to increased use of
dry cleaning techniques is the fact that recent evidence indicates that
less extensive cleaning of some coals may tend to minimize corrosion of
fire-side boiler tubes in power plants. With some coals, extensive clean-
ing to minimize the ash content in the washed coal contributes to boiler
tube corrosion by removing ash constituents such as alkaline earth mate-
rials (e.g., CaO and MgC) which are corrosion inhibitors while removing
lesser amounts of corrosion-promoting constituents such as alkalies (e.g.,
and KgO). Thus, by cleaning at lower specific gravities to reduce
ash, the ratio of corrosion promoters to corrosion inhibitors in the ash
increases when preparing some coals for market. Extensive cleaning and
the resultant lower yield may therefore, in some instances, contribute to
corrosion rather than reducing it as is desired. In fact, it has been
shown that, some run-of-mine coals are more desirable from both a corro-
sion and a yield standpoint than they are after cleaning.
In addition to these factors, several other major advantages
are inherent to dry concentration techniques. The largest advantage is
the simple fact that dry concentration requires the lowest initial capital
investment and has the lowest maintenance costs of all currently used
methods of upgrading fine coal. There is also continuing realization on
the part of operators and consumers of the necessity for providing a dry
coal for freeze-free shipments. Air-washed coal is also more amenable to
oil treatment for dust control and it flows freely and does not arch in
bins and hoppers. In transit, dry-cleaned coal will shed rain and arrive
448
-------
with only the surface of the car wetted whereas wet-washed, thermally dried
coal may act as a sponge and soak up water. The rigid enforcement of stream
pollution laws gives a permament advantage to dry concentration as discussed
above. Admittedly, wet fine coal cannot be cleaned with air and Federal
regulations cause more and more coal to be wetted at the face. However, it
is more economical to pre-dry the coal for dry concentration than to dry
the washed coal after it is recovered from the water. A further factor
influencing the choice of pneumatic equipment is the lack of sufficient
water in arid regions, localities of high altitude or cold climates.
15/
20.2.5 Thermal Drying
The continuing increase in the percentage of minus l/4 in. coal
produced as a result of the increased use of mechanical mining methods
has, over the years, tended to shift considerable portions of the work of
producing salable coal to the fine-coal cleaning section of the prepara-
tion plant. Because a given weight of fine coal will contain substantially
greater surface area than an equivalent weight of coarse coal, it follows
that, when subjected to wet-cleaning processes, the fines will absorb and
retain considerable more moisture than coarser fractions. Increased mois-
ture pickup in the finer size complicates fir.e coal cleaning since beneficia-
ticn may not be limited to the removal of ash and sulfur but often must be
expanded to include the additional step of thermal drying to remove exces-
sive moisture. Thus, water which provides the medium for cleaning fine
coal is in itself detrimental and, like ash and sulfur, reduces ccal quality.
Removal of surface moisture by drying is done for one or more of
the following reasons: (l) to avoid freezing difficulties and to facilitate
handling during shipnent, storage and transfer to the points of use; (2) to
maintain high pulverizer capacity; (3) to reduce heat loss due to evapora-
tion of surface moisture from the coal in the burning process, thus increas-
ing heating efficiency; (4) to improve the quality cf coal used for special
purposes, such as in the production of coke, briquettes, and chemicals;
(5) to decrease transportation costs; and (6) to facilitate dry coal clean-
ing processes. w
Ccal dryers can be grouped into six basic types. The six basic
dryer types are: (l) fluidized bed; (2) suspension or flash; (3) multi-
louvre; (4) vertical tray and cascade; (5) continuous carrier; and (6) drum
or rotary type..15/ Figures 20-1 to 20-4 illustrate various types cf thermal
dryers.
Recent coal industry trends in the application cf the preceding
types of drying facilities are indicated in Table 20-1. The expanding
general application of coal drying (from 31.5 to 58.7 million tons between
1956 and 1964) and the expanding specific application of fluidized-bed coal
drying (from 10.6 to 38.3$ of all coal dryers between 1958 and 1964) are
noteworthy.
449
-------
Explosion vents
Bypass
stack
Damper
l
' Dust
collector
Dust
collector
Wet
coalbin
Scrubber
Bed-
plate
KEY
Gasflow
—— Coalflow
Feeder
Discharge
gate
Rotary discharge
o o
Furnace
Fluidizing fan
Pulverizer
Control
panel
Figure 20-1 -
Pressure-Type Fluidized-Bed Thermal Coal Dryer,
Showing Component Parts and Flow of Coal
and Drying Gases5/
-------
KEY
Exhaust fan
Gasflow
• Coalflow
Explosion vent
Bypass
stack
Scrubber
Wet coalbin
Dust
collector
Discharge
\ gate
Damper
Feeder
'Rotary
discharge
Bedplate
Tempering
louvers
Control
panel
Furnace
Figure 20-2 - Exhausting-Type Fluidized-Bed Thermal Coal Dryer,
Showing Component Parts and Flow of Coal
and Drying Gases^/
-------
t
Exhaust fan
Cyclone
Drying duct
Airlock
discharge
valve
Bypass stack
Hot gas
damper
Coal feeder
Damper
Drying Chamber
o o
Control
instrument
board
Air-tempering louvers
Furnace
Figure 20-3 - Schematic Drawing Showing Component Parts
of Flash-Drying Unit!/
452
-------
Bypass stack
Thermocouple
, Coal ~
X^/~
2d floor
it*
U1
t*
Air tempering
dampers
Furnace
Blower
Fan
Coal discharge
conveyor
Ground floor
Figure 20-4 - Schematic Sketch of Screen-Type, Thermal Coal-Drying Uniti/
-------
TABLE 20-1
THERMALLY DRIED COAL BY TYPES OF DRYING EQUIPMENT, 1958-1964—^
Year
Rotary
Continuous
Carrier
Vertical
Tray and
Cascade
Multi-Louvre
Suspension
or Flash
Fluidized
Bed
Total
Number of Plants
1958
1959
1960
1961
1962
1963
1964
6
9
11
11
11
11
9
64
66
63
66
60
57
56
58
57
58
64
59
54
50
50
55
57
56
49
44
42
44
48
47
40
58
49
49
6
12
16
23
29
38
49
228
247
252
260
266
253
255
Net Tons Dried
2
1958
1959
1960
1961
1962
1963
1964
405,057
717,948
771,014
1,007,814
1,998,254
2,549,294
1,959,496
7,774,090
8,381,332
8,099,827
8,989,457
8,931,633
9,499,674
9,658,965
5,775,347
5,682,861
5,023,497
5,574,594
5,856,812
6,048,360
5,507,522
9,416,368
9,734,894
11,469,532
10,611,069
9,631,349
9,469,847
9,943,032
4,834,324
6,625,409
6,479,501
5,681,477
8,105,551
8,131,081
9,154,519
3,336,929
4,622,292
6,025,026
7,768,609
12,432,991
14,857,074
22,478,004
31,542,125
35,764,736
37,868,397
39,633,040
46,956,590
50,555,330
58,701,538
Percent of Total
1958
1959
1960
1961
1962
1963
1964
1.3
2.0
2.0
2.5
4.2
5.0
3.3
24.7
23.5
21.4
22.7
19.0
18.8
16.5
18.3
15.9
13.3
14.1
12.5
12.0
9.4
29.8
27.2
30.3
26.8
20.5
18.7
16.9
15.3
18.5
17.1
14.3
17.3
16.1
15.6
10.6
12.9
15.9
19.6
26.5
29.4
38.3
100.0
100.0
100.0
100.0
100.0
100.0
100.0
-------
20.3 EMISSION RATES FROM COAL PREPARATION PLAKTS
Because coal is relatively friable, the mining and subsequent
handling operations break part of the coal into dust that can be readily
carried by currents of air. In a coal preparation plant mechanical handling
operations such as unloading, transferring from one belt to another, screen-
ing, cleaning, and crushing in a dry state result in the generation and
release of varying amounts of additional dust. The dust problem, of course,
is much less serious in plants employing entirely wet processing. In addi-
tion to dust from handling operations, thermal drying of the fine coal
product frequently presents another dust collection problem.
All industrial coal dryers new in use are the continuous direct
contact type which employ convection as the major principle cf heat trans-
fer. Thus, hot gases and wet coal are brought into intimate contact with
each other on a continuous gas flow-coal feed basis. To achieve drying,
hot gases are generated in a combustion chamber and brought into contact
with wet coal by a fan or blower. The size consistency of the coal being
dried and the velocity of the gases through the bed are major factors in
determining the air pollution potential of the plant. Emissions include
products of combustion and entrained coal fines.
The calculation of emissions from thermal dryers based or. the use
of an emission factor is not accurate since the emissions from each type of
dryer vary over a wide range depending on operating methods. The flash
dryer carries all of the product into a product separation cyclone, while
the fluid-bed type may carry over from 5$ to 50$ of the product into the
cyclone collection system. For these reasons, the emissions are test
calculated on the basis of average cutlet grain loadings from control equip-
ment, as was done in a recent internal JIAPCA study.—/
The NAPCA study included a survey of thermal dryers operated at
eight of the largest coal companies. The survey covered about 60$ of the
total coal dried yearly in the U. S. It determined a total air flow from
these dryers of 1.16 x 10^2 scf/year
This survey also indicated that 50$ of the dryers were equipped
with cyclones, while the remaining 50$ were equipped with cyclones plus
some type of wet scrubber. Total emissions were then calculated to be in
the order of 300,000 tons/year assuming an outlet grain loading of 4.0 grains/
scf from cyclones, 0.15 grain/scf fron low-energy scrubbers, and 0.04 grain/
scf from high-energy scrubbers.
The assumed grain loadings have been found to correspond with
data in the literature and data from the West Virginia Air Pollution Control
Commission. However, the fact that 50$ of the dryers are equipped with only
455
-------
cyclones seemed low in view of a 1957 West Virginia Air Pollution Control
Commission survey which indicated that less than 15$ of the dryers in that
state had cyclones only. 6/
Further analysis of the KAPCA survey showed that 50$ of the
dryers did have cyclones only, tut these represented only 13.8$ of the
total air flow. On this basis, the emissions are calculated in the fol-
lowing manner:
(1.16 x 10^ scf/year)( 13. 8$) ( 4 Rraips^ ^ 1 ton j _ 45^730 tons/year
scf 14 x 10^ grains
(1.16 x 1012 scf/year)( 86.2$) ( grains^ ^ 1 ton ) = 10,700 tons/year
sc^ 14 x 106 grains
Tctal 56,400 tons/year
If this represents about 60$ of the ccal dried, the total annual particulate
emissions from thermal dryers are 94,000 tens/year.
A second method of calculating emissions, for comparison purposes,
can be done on the basis of emission factors for the dryers. Data in
Reference 17 show that the emission factor for the outlet of the dryer
cyclone is 12 lb/ton for flash dryers and 13 lb/ton for fluid bed dryers.
The emission factor for the other types of dryers is probably somewhat
lower since their mode of operation should not carry out as much dust to
the cyclone. This includes the rotary, continuous carrier, cascade, and
multi-louvre dryers.15/ However, it might be assumed that the average
overall emission factor is 12 lb/ton, although this may be somewhat high.
The calculation of the emissions also involves the question of what per-
cent of the coal is dried in units that are equipped with wet scrubbers.
The two calculations given below show the quantities emitted on the basis
of two different assumptions. The efficiency of the wet scrubbers has
been estimated at 95$ for both cases.
a. It is assumed that 50$ of the coal is dried in units
equipped with wet scrubbers. This is similar to the KAPCA study which
assumed that 50$ of the total air flow for all dryers is cleaned in wet
scrubbers. The NAPCA survey actually showed that 50$ of the number of
dryers were equipped with wet scrubbers and it was presumed that this also
represents 50$ of the total air flow. The emissions for this assumption
are calculated as:
456
-------
( 73,000,000 tons/year) (2i000 ,ltl.Zj:P,2)( 1 - (0,50)(0.95)) = 230,000 tons/year
12 lb/ton
b. II is assumed that 85$ cf the coal is dried in units
equipped with wet scrubbers. This assumption is based on our analysis of
the data in the KAPCA survey and is supported by information from the West
Virginia Air Pollution Control Commission. The emissions for this assump-
tion are calculated as:
(73,000,000 tons/year)( 12 lb/ton )(l - (0.85)(0.95)) = 83,000 tons/year
2,000 lb/ton
These results support the previously discussed emission calcula-
tions but do not resolve the question of the extent to which thermal dryers
are equipped with wet scrubbers. Based on the present information and cal-
culations described in this section it is felt that the emission quantity
of 94,000 tons/year is the mere accurate figure.
Insufficient data were available to calculate particulate emis-
sion rates from "he secondary sources. Also, data could not be found on
particulate emissions from burning coal refuse banks. Reference 7 reports
an emission level cf 400,000 tons/year of particulate from coal refuse.
This figure was calculated assuming that the emission factor fcr refuse
piles corresponds to that fcr open burning. This is a questionable assump-
tion, and the number of 400,000 tons/year is considered a gross estimate.
20.4 CHARACTERISTICS OF COAL-PREPARATION-PLANT SMIS3I0IS
The chemical and physical properties of coal-preparation-plant
emissions are summarized in Table 20-2. Particulates geiierated during
thermal drying present fire and explosion hazards both within drying cham-
bers and cyclones, fans, and duct work beyond the drying chamber.
20.5 CONTROL PRACTICES AND EQUIPMENT FOR COAL-PREPARATION PLANTS
20.5.1 Thermal Drying Plant
In most thermal drying plants a system of control units is
utilized with dry collectors serving as primary dust separators and wet
collectors serving as secondary dust separators.9/
457
-------
TABLE 20-2
SFFl-UENT CHARACTERISTICS - CQftL PREPARATION PLANTS*
A. ¦ rut-i.-'-ilate
iaiticle Electrical Moisture
¦Vurjc Particle "c* .frlirts {ending Chetr.ic&l Composition ^fer.s:ty Resl3tlvity Cor.tcnt Tex." 1 ty
. ;Vrrjvi Dryer
i'1 Multi-louvre Cyclone Outlet 2-2QC* Coal Dust, i'ly Ash
*>T? ICC <
-------
m
FROM
3" O
96 99.8 99.99
0.01 0.2 2
20 50 80
% LESS THAN STATED SIZE (WT. %)
Figure 20-5 - Typical Particle-Size-Analysis Curves for Material
Going to Cyclones (Coal Thermal Dryers)—/
A recent NAPCA survey^/ indicated that all thermal coal dryers
are equipped at least with dry cyclones, and about 50# also have low-energy
wet scrubbers while about 4$ have high-energy scrubbers.
The cyclones used as primary collectors can produce an exit
solids loading of 3 to 3.5 grains/cu ft.S/ However, this loading can exceed
12 grains/cu ft in some cases.19./ The cutlet grain loading from a low-
energy wet scrubber (preceded by a cyclone) is usually about 0.15 grain/scf,
although it may vary from 0.05 to 0.42 grain/scf.§J
One coal company described the use of impingement-screen liquid
scrubbing units but they have never operated satisfactorily because the
impingement screens were easily blocked. These units had to be bypassed
because of uncontrollable fires in them and the danger of explosion. They
were later replaced with a different type of wet scrubber with a water
usage rate of 3 gal/l,000 cu ft giving an exit grain loading of 0.035 to
0.048 grain/cu ft.
The installation of Venturi-type scrubbers at another coal com-
pany for cleaning the exhaust from a fluid-bed dryer is described in Ref-
erence 2. Installation was preceded by investigation of a 1,000 cfm test
459
-------
unit. Grain loading cf the gasas leaving the dry collectors was 3 grains/
scf (see Figure 20-6). The outlet grain concentration loading from a
Venturi scrubber as a function of pressure drop is shown in Figure 20-7.
As a result of the tests, a commercial-size unit was installed for the
175 ton/hr dryer handling 95,000 cfm with a specified outlet loading of 0.05
grain/scf. This loading required 1,200 hp. for the combined pressure drop
of 42 tc 44 in. of H2O of which about 20 in. is required fcr the Venturi.
The installed cost was about $1.00/cfm of gases, although much existing
equipment was utilized. If existing equipment had not been available, it
was estimated that the cost would probably have been $1.50/cu ft.2/ These
costs compare closely with general cost figures given in Appendix A.
Another recent Venturi scrubber installation is reported to have
been installed at a cost of $0.90/acfm. This 35-in. w.g. Venturi scrubter
was installed downstream of the cyclones, which served a 400 ton/day fluid-
bed dryer, and handled approximately 200,000 acfm of gas. This installed
cost of $0.90/acfm also compares very closely with the cost figures in
Appendix A. However, this actual cost figure includes stainless steel con-
struction for all surfaces in contact with water.2i/
Careful consideration should always be given toward elimination
or reduction of dust at its source. In connection with thermal dryer in-
stallations, it has often been found necessary tc evaporate all water to
attain successful operation cf the dryer itself. This requirement leads
to very high dust loadings to the collectors. It may be found possible tc
redesign or modify the thermal dryer to permit successful operation at a
level cf evaporation whereby 0.5 to 1.0$ surface moisture remains on each
coal particle. The dust loading to secondary collection equipment can some-
times be substantially reduced, providing increased collector efficiency
and more satisfactory final emission to the atmosphere as well as reduced
recirculation cf ultra-fine coal ir. a plant water circuit.^/
20.5.2 Coal Refuse
Coal refuse, which is discarded as a part of the ccal preparation,
forms large piles which often catch on fire. A survey in 1962 identified
488 burning mine waste piles. 11/ These are a source of particulate and
gaseous pollution but no information has been located that would allow an
assessment of the quantity of particulate emitted.
One of the methods used to control these coal refuse bank fires
involves the use cf high-pressure water nozzles followed by compaction.
Overall cost has "been estimated at $0.65/cu yard of material.12/
460
-------
99.9 i—i—i i i iii| 1—i—i i i i 11 j i—i i i ii i i i rr
99.5 -
98 -
v
$
x 90 -
t>
N
^ 70 -
J 50 -
5 30 •
O
6 io - -
c Whitby Centrifuge Analysis of Coal Dust
y 2 - Bird Coal Company
(£ Average Particle Diameter by Curve -11,8 Microns
v ( J
0.1 1—i—iii'i 11 i i i i i 1111 i.. i i-i 11 i 1111
0.1 1.0 10.0 100.0
Stokes' Equivalent Particle Diameter - Microns
Figure 20-6 - Particle Size Distribution of Effluent^/ (Fluid-Bed Dryer,
Grain Loading, 3 Grains/scf)
t—i—i i i iii| 1 1—i i i i 11 j i—i i i 11 i i i rr
Whitby Centrifuge Analysis of Coal Dust
Bird Coal Company
Average Particle Diameter by Curve -11,8 Microns
—i—i—i i i 1111 i i t i i 1111 ii i-i 11 i i 111
0.10
o
ft 0.08
v
t—i—i—i—i—i—i—i—i—i—i—i—i—i—r
o
c
o
c
w
u
c
o
U
3
a
0.06
0.04
0.02
0.00
J L
j I i I I I I l_
0 2
10 14 18
Venturi
22
J I L
26 30
Figure 20-7 - Venturi Scrubber Performance on Coal DryerEffluent
(Inlet Leading, 3 Grains/scf)
461
-------
REFERENCES
1. Stern, A. C., Air Pollution (2nd Ed.), New York: Academic Press. 1968.
2. Northcott, Elliott, "Dust Abatement at Bird Coal," Mining Congress
Journal, 55, November 1967,
3. Schrecengost, H. A., and Maurice S. Childers, "Fire ar.d Explosion
Hazards in Fluidized-Bed Thermal Coal Dryers," Bureau of Mines
Report, 1965.
4. Brown, H. R, et al., ''Fire and Explosion Hazards in Thermal Coal-
Drying Plants," Bureau of Mines Report of Investigations 5198.
5. Unpublished National Air Pollution Control Administration report on
coal dryers, 27 February 1970.
6. Private communication with Dr. David Ellis, West Virginia Air Pol-
lution Control Commission.
7. National Emission Standard Study, Senate Document No. 91-63, March
1970.
8. King, D. T., "Dust Collection in Ccal Preparation Plants," Mining
Engineering. August 1967.
9. Jones, Donald W,, "Dust Collection at Moss No. 3," Mining Congress
Journal, July 1969.
10. Data from Pennsylvania Department of Health.
11. MacKenzie, Vernon G., "Air Pollution and the Coal Industry," Annual
Meeting of the National Coal Association, Chicago, Illinois,
June 15, 1965.
12. Hall, Ernst P., "Air Pollution from Coal Refuse Piles," Mining
Congress Journal, December 1962.
13. U. S. Department of Health, Education and Welfare, Control Techniques
for Particulate Air Pollutants. Washington, D. C., 1969.
14. Private communication.
15. Leonard, J., and D. Mitchell, Coal Preparation. 3rd Ed., Seeley W.
Mudd Series, American Institute of Mining, New York, 1968.
462
-------
16, Vailing, J. C., "Air Pollution Control System for Thermal Dryers,"
Coal Age, pp. 74-79, September 1969.
17. Research Triangle Institute, Fin'al Report, "Comprehensive Economic
Costs Study of Air Pollution Control Costs for Selected Industries
and Selected Regions," National Air Pollution Control Administration
Contract Nc. CPA 22-69-79, February 1970, p. 5-4.
463
-------
CHAPTER 21
CARBON BLACK
21.1 INTRODUCTION
Carbon black is ultrafine soot manufactured by the burning of
hydrocarbons in a limited supply of air. This finely divided material
(10 to 400 u, in diameter) is of industrial importance as a reinforcing
agent for rubber and as a colorant for printing ir.k, paint, paper, and
plastics.
Three basic processes currently exist in the United States for
producing this compound. They are: the furnace process, accounting for
about 83$ of production; the older channel process, which accounts for about
6$ of production; and the thermal process (1970 figures). Atmospheric pol-
lutants from the thermal process are negligible since the exit gases which
are rich in hydrogen are used as fuel in the process. In contrast, the pol-
lutants emitted from the channel process are excessive and characterized by
copious amounts of highly visible black smoke. Emissions from the furnace
process consist of carbon dioxide, nitrogen, carbon monoxide, hydrogen,
hydrocarbons, particulate matter, and some sulfur compounds. For the fur-
nace process, collection equipment is an integral part of the process for
collection of the product.
The manufacturing processes, particulate emission sources, par-
ticulate emission rates, effluent characteristics, and control practices
and equipment are discussed in the following sections.
21.2 MANUFACTURING PROCESSES
The fundamental steps in carbon black (frequently referred to as
black) manufacturing, regardless of the process used are:
1. Production of black from feed stock,
2. Separation of black from the gas stream, and
3. Final conversion of the black to a marketable product.
In the channel and furnace process, the black is produced by
burning the feed stock. In the thermal process, the feed.stock is thermally
decomposed into black and hydrogen; there is no burning.—
465
Preceding page blank
-------
21.2.1 Furnace Process
The furnace process is subdivided ir.to either the gas or oil pro-
cess depending on the primary fuel used to procuce the carbon black. In
both cases, gas (gas process) or gas and oil (oil process) is injected into
a reactor with a limited supply of combustion air.
21.2.1.1 Gas-Furnace Process: Figure 21-2 shows a schematic flow
diagram of the gas-furnace process. The furnace or reactor is refractory
lined and is designed with special inlets or ports for natural gas and for
air. An annular nixing orifice formed of refractory material is located
within the converter. The flue gases, largely carbon monoxide, hydrogen,
nitrogen, and water vapor, carry the hot carbon from the furnace through a
long horizontal brick-lined flue, to a cooling tower where water sprays
reduce temperatures from 1800 to 500°F. Agglomeration of the fine black
particles occurs either in an electrostatic field provided by an electrical
precipitator or by centrifugal force in cyclone collectors. When the elec-
trical precipitator is used, about 30$, depending on the grade of black
produced, is shaken off the electrodes intc the collecting hopper attached
to the bottom of the precipitator. The remainder of the flocculated black
is caught, to a very large extent, in the cyclone collectors and bag filters
which generally follow the precipitator. The gases including the carbon
monoxide and condensable vapors (steam) are discharged through the stack of
the final collector directly to the atmosphere. The black is carried to the
finishing area by screw or pneumatic conveyors."~J
21.2.1.2 Oil-Furnace Process: The oil-furnace process is similar
to the gas-furnace process except that the raw material used is oil instead
of natural gas and the furnace design is also different. Each producer has
developed and patented furnace designs. The design of the furnaces and
burners constitutes an important part of carbon black technology. A flow
diagram of the oil furnace process used at a large modernized plant is
shown in Figure 21-1.
21.2.2 Channel Process
A schematic flow diagram of the channel process is shown in
Figure 21-3. A typical channel plant may cover many acres and may be com-
posed of several hundred steel buildings (called "burner houses" or "hot
houses") housing some 2,000 to 4,000 flames and the appropriate number of
channel irons, upon which the flames impinge and deposit carbon black.
466
-------
ft TY
rNEUMATfC SYSTEM
SECONDARY
secondary
BAG FILTER
CYCLONES
D&YER
STORAGE
ELEVATOR BIN
SURGE t\H PELLETlZEA
Figure 21-1 - Flow Diagram of Oil-Furnace ProcesaJ
s
K
O
u
\\
uu
ui UI
Ui O.
o
a
u
>•
u
AIR
GAS 1
FURNACE
It"
FY YY LW
PNEUMATIC SYSTEM
SECONDARY
CYCLONES
SURGE BIN PELLETIZER
DRYER
STORAGE
ELEVATOR BIN
Figure 21-2 - Flow Diagram of Gas-Fumace
Process^/
467
-------
channel
P? FLAME
TIP
BURNER PIPE
BURNER HOUSES
Fig-ore 21-3 - Flow Diagram of Channel Process
Air is supplied through openings at the base of each building.
The spent gases and products of combustion pass out of the hot house through
openings and stacks in the roof. Gas rates are on the order of 45 to 80 cu
f't/24-hr day/burner tip, and may range from 150,000 to as high as 260,000
cu ft/24-hr day/hot house. Combustion is controlled by natural draft open-
ings in the top and bottom of each house. Draft control is visual and de-
pendent upon the skill of the operators. A large excess of air holds the
temperature of the house below 1000°?. However, this large excess of air
does not completely burn the natural gas because the combustion time from
the gas tip to the channel is very short, and complete mixing of air and
gas in this interval does not occur.
Screw conveyors pick the black up from the various houses and
convey it to the processing area where an air separator removes particles
of grit (hard calcined carbon). The fluffy black is then further processed
through a high-speed hammer mill (micropulverizer) to break up lumps that
form in the conveyors, and also to render any remaining grit particles
extremely fine. It also pulverizes oversize product pellets that recycle
from downstream screening. The black then passes to the pelletizing step
and subsequent packaging.
21.2.3 Thermal Process
Thermal blacks are produced by the thermal decomposition of natural
gas in the absence of air or flame, (l) The thermal process, Figure 21-4,
comprises: (l) the cracking units (termed generators) consisting of
checkerwork furnaces; (2) coolers; (3) carbon collectors; and (4) packing.
The furnaces are 12 to 14 ft. in diameter and 25 to 35 ft. high, and consist
of a riveted steel shell, insulated and lined with refractory brick and
filled with checker brick similar to that of a blast-furnace stove. Id/
468
-------
(Ti
CD
Cicess H,
to tire "v
baler \ Hydroftn
Bucket elevator
Dust and reject
separator
H. scrubber
H, holder
^Bag-filter exhaust (H,)
Bucket elevator
Vibrating screen
Magnetic separator
Pulverizer
Recycle conveyor belt
Belt conveyor
Furnaces
N. 111 collector
\r Hr
Bag
packing
tank
Storage
tank
Pelleting drum
1
Screw conveyor
Agitator tank
Fluffy bag packer
Semiautomatic
peflet bag packet
Screw conveyors
Figure 21-4 - Flow Diagram of Thermal Process^'
-------
Thermal black differs from other carbon black operations in that
it is cyclic rather than continuous-^/ The process is intermittent, the
eheckerwork being first heated to 2400 to 2800°F by the complete comoustion
of a blast of natural gas and air introduced at the bottom. When the bricks
are brought up to the required temperature, the stack (vent to the atmos-
phere) is closed and natural gas is admitted from the top of the furnace
for the decomposing part of the cycle. Thermal black is produced w.ien tne
heat from the brickwork decomposes the gas into a smoke of thermal carbon
plus quantities of hydrogen.^7 When the bricks become cool, the natural
gas flow is shut off and the remaining carbon smoke is flushed out into the
cyclone separators. The complete cycle for a single generator requires ap-
proximately 10 mi:;. Of this time, about half is required for heatup and
half for the cracking process.^/
The effluent gas from the generator, which is on the production
cycle, consisting of about S0$ hydrogen, 6$ methane, and a remaining com-
plex mixture of higher hydrocarbons, carries the suspended black.U The
smoke from the furnace is passed by countercurrent flow through a water-
sprayed coolir.g tower to cool the smoke to about 125°C. This temperature
allows it to be safely filtered through the cloth bags in the collectors
and yet not wet either the bags or the carbon. Recovery is about 40 to 50$
of the carton in the fuels.
The collected black is transported by screw conveyors to the
processing area where it is passed through a magnetic separator, screen,
ana hammer mill. It may then be packed through an auger packer as fluffy
black in 25 or 50 lb. paper tags, or passed through pelletizing equipment,
which transforms the fluffy black ir.to a free-flowing product.
21.3 EMISSION S0UECES AUD RATES
The most important factor affecting emissions is the basic manu-
facturing process and its inherent efficiency. Thus, emissions from the
channel black process are excessive, while those from the thermal process
are negligible. Particulate emissions from the furnace process are affected
by the type of collection equipment used. Gaseous emissions are largely
determined by the overall yield, type of fuel (that is, liquid or gas),
the reaction time and temperature, the ratio of gas to oil in the feed, and
the amount of combustion air.Q/
Additional emissions may result from the conveying, grinding,
screening, drying, and packaging operations at a carbon-tlack plant. Poorly
designed or maintained equipment can result in leaks and spills. Spillages
of the fluffy black before pelleting are the source of pollution.
470
-------
After pellets have ceased to form in the dry pelleting process
the drum is emptied, and reloaded with fresh loose black, and reseeded,
¦and then pelleting resumes. The emptying of the drum will naturally result
in black spillage.
Maintenance operations will often result in carbon-black spillage.
The cleaning of clogged screens, located either at the top cf the storage
tank into which the finished black is screened or at the pelleting section
where oversized pellets are screened out, causes black to be discharged into
the atmosphere. Whenever a production line is plugged, the remedial mea-
sures are either to pound the line or use a vibrator. If this proves in-
effective, high-pressure air is used to dislodge the black. Carbon black
is generally emitted to the atmosphere in this operation.
Carbon black is so finely divided that whenever a leak develops
in plant equipment, such as in the conveyor system, or in the bins, or at
the tagging equipment, black will seep out into the atmosphere.
Table 21-1 summarizes emission rates for carbon black manufacture.
Emission factors for the channel black process are questionable because of
a complete absence of emission data.9/ Emissions due to conveying, grind-
ing, etc., were not estimated because of the variability of these emissions.®/
Particulate emissions currently total about 93,000 tons. The channel process,
which accounts for only about 6$ of the total production, emits nearly SO$
(32,225 tons) of the particulates.
21.4 CHARACTER 1STICS OF EFFLUENTS FROM CARBON-BLACK MANUFACTURE
Limited data were found on the chemical and physical properties
of effluents from carbon-black plants. Available data sire summarized in
Table 21-2. The particle size of the emitted carbon black is extremely
fine (i.e., of the order 0.1-0.5 p,). The carbon monoxide content of the
offgas may be as high as 20$ by volume.
21.5 CONTROL PRACTICES AND EQUIPMENT
The channel process emits large quantities of carbon because no
way has yet been developed to separate the escaping black and avoid up-
setting the burning conditions, which in turn •vrould drastically affect yield
and quality. 1/ Production by the channel process has declined over the
years, and at present only 3 plants are known to be in operation.®/
These three plants produce a total of approximately 71,500 tons/yr repre-
senting about 6.0$ of the total carbon black produced in the U. S.
471
-------
TABLE 21-1
PARTICULATE EMISSIONS FROM THE
MANUFACTURE OF CARBON BLACK
Source
I. Channel process
Quantity of
Material
71,500 tons,
carbon black
Emission
Factor
2,300 lb/ton
product
Application
of Control
Cc
0.0
Efficiency
of Control
Ct
0.0
Net
Control
Cc'Ct
0.0
Emissions
(tons/yr)
82,000
rf>-
-j
ro
II. Furnace process
A. Gas
B. Oil
156,000 tons,
carbon black
1,180,000 tons,
carbon black
60 lb/ton
product*
10 lb/ton
product*
5,000
6,000
Total
93,000
* Controlled emission factor. Cyclone followed by scrubber; 97$ efficiency.
** Controlled emission factor. Fabric filter; 99.5$ efficiency.
-------
TABLE 21-2
A. Particulate
EFFLUENT CHARACTERISTICS - CARHON BLACK
Source
I. Ttiem&l
Process
Particle
Size
0.1-0.5
Solids
Loading
Chemical
Composition
Carbon
Particle
Densi ty
1-5 lb/ft3
(Bulk Density)
Electrical
Resistivity
Moistvire
Content
Toxicity
II. Furnace
Process
(oil)
0.02-0.4
10-50
(Reactor
Outlet)
Carbon
B. Carrier Gas
Source
Flcwrate
Temperature
Moi sture
Content
Chemical
Composi tion
Toxicity
Corroslvity Odor
Flamnability or
Explosive Limits
Optical
Properties
I. Furnace
Process
&. Oil
a) 3-5
b) 120-150
b. Gas a) 3
b) 360
Typical Composition
C02: 3.0
02: 0.3
Co: 6.0
H.
2-
ch4,
etc.:
0.0
0.5
C2Hg
0.2
41
40
+ See Coding Key, Table 5-1, Chapter 5, page 45, for units for individual effluent properties.
-------
For the f xr.ace process, collection equipment is an integral part
o.' the process for collection of the product. The types of equipment com-
monly used for effectively separating and collecting finely divided black
'rorr. a gas stream are agglomerators, electrostatic precipitators, cyclone
separators, scrubbers, and baghouses.i/
In old plants, the black-laden gases arc first cooled to about 450
to 550°F, and then passed through a dry electrostatic precipitator which ag-
glomerates the black. The increased diameter and density of the agglomer-
ated black permits it to be removed effectively from the gas stream by using
several cyclone separators. Together these have a recovery efficiency of
85 to ?0#, leaving about 10# of the initial carbon in the off-gases. Col-
lection or removal of' nearly all the remaining 10# is accomplished when
the off-gases are passed through either a bag filter to give 99# recovery
or a wet-scrubber system with 37 to 95# collection overall. The scrubber
system may comprise water scrubbing ar.d wet electrostatic precipitation or
wasr.ing in a slot scrubber followed by a wet cyclone scrubber. In order
to recover the black, the slurry is circulated back to the reactors where
it is used for quench. The black is thus re-entrained in the sncke and re-
covered.
The electrostatic precipitator is rapidly disappearing from use
in the carbcr.-tlac's industry. ¦ Even at some older plants they are no longer
in operation, since they have been shut off to save operating and maintenance
expenses. They are not energized, and nc carbon black is removed from them.
The current trend is to do without electrostatic precipitators in new fur-
nace-black plants. The trend is to a mechanical agglomeration device (i.e.,
cyclones) placed ahead of bag filters. When the older plants were built,
suitable filters had not yet been developed, and the use of cyclones by
themselves was inadequate.
In recent years, the carbon-black industry turned to agglomera-
tion apparatus of lower first cost and of equivalent or superior performance
compared with the electrostatic precipitator. Accordingly, in most plants,
the black-laden gases, cooled to about 550°F, enter a series of large diam-
eter cyclones (usually four) which separate about 70# of the carbon. The
gases with the remaining black may be cooled further to about 350aF. They
are then passed to a bag filter which separates the remaining black from
combustion gases for an overall recovery of 99+#.
In some plants, cyclones (as well as electrical precipitators)
have been eliminated and the design for carbon-black separation calls for
a system with an agglomerating device and a single bag filter connected in
series.i/
474
-------
21.5.1 Control Equipment
21.5.1.1 Wet Scrubbers: Wet scrubbers, despite their high re-
covery efficiency, have very limited use in the United States for separat-
ing carbon black from a gas stream. Nor are wet electrostatic precipitators
currently in use by the carbon black industry in this country.
21.5.1.2 Cyclone Separators: Two main types of cyclone separat-
ors are utilized in carbon-black collection: (l) medium-efficiency or
high-capacity cyclones, generally of fairly large diameter and used singly;
(2) modern high-efficiency, high-velocity cyclones, usually nested in
groups of two, four, eight, or more. Primary cyclones are of various
sizes. A typical cyclone used (old design) is 11 ft. in diameter and
35 ft. high. The cyclone based on the new design (high efficiency) is
6 ft. in diameter and 15 ft. high. Secondary cyclones are only 54 in. in
diameter and 10 to 12 ft. high. Cyclones have an agglomerating effect or.
the black because of the centrifugal motion created within the equipment.
21.5.1.3 Baghouses: In bag filters, the black-laden gas stream
enters the open bags at the bottom and passes through the cloth, depositing
solids on the cloth, and the clean gas discharges to atmosphere. The bags
are cleaned by reversing the flow of the gas and repressuring. The tempera-
tures involved rule out the use of cheap reliable filter media, such as
cotton, wool, and "orlon." The maximum working temperature of these mate-
rials is about 275°F. These filters faced a considerable corrosion problem
until bags of woven glass fabric made from staple yarn were introduced.
Filtration can thus be carried out at temperatures up to 550°?. However,
the brittle fibers cannot stand up to the shaking required to free the black
collected on the cloth, and the cloth wears out quickly. To solve this prob-
lem, cloth manufacturers coat the fibers with resins and silicone oils to
help fibers slip over each other more easily.
In carbon-black manufacture, bag filters are eliminating the need
of electrostatic precipitators, scrubber units, and even cyclone separators.
Filter-bag life varies greatly depending on several factors, such
as gas-to-cloth ratio (or how heavily the cloth is loaded), the grade of
black being produced, and the type of cloth used. Typical bag life is about
12 months.
475
-------
REFERENCES
Drogin, I., "Carton Black," Journal 0? the Air Pollution Control
Association, 18(4), 216-228, 1968.
Strasser, M. Dale, "From Hydrocarbons to Carton Black," Petroleum
Refiner, 33, 177-180, December 1954.
Moore, Robert L., "Thermatomie Process for Cracking of Gaseous Hydro
carbons," Industrial and Engineering Chemistry, 24, 21-33, 1932.
Jones, F. E., and Louthan, C. P., "Cabot Thermal Blacks," Technical
Report RG-118.
Paulsen, D. C. , "Cyclic, Yet Continuous," Ins tr'jmentation, 6(3),
35-37, 1953.
Pyzel, F. M., "Process for the Thermal Decomposition of Hydrocarbons
U. S. Patent 1,983,992, December 11, 1934.
Smith, W. R., "Carbon Black," Encyclopedia cf Chemical Technology,
Interscience, New York, 2nd Edition, Vol. 4, pp. 243-247, 280-281,
1964.
Air Pollution Emission Factors, NAPCA Report, Contract CPA 22-69-119
Washington, D. C., April 1970.
Personal communications, June 1970.
476
-------
CHAPTER 22
PETROLEUM REFINING
22.1 INTRODUCTION
The petroleum industry can logically "be divided into three major
divisions: production, refining, and marketing. Production includes the
operations involved in locating and drilling oil fields, removing oil from
the ground, pretreatment at the well site, and transporting the crude to
the refinery. Refining is limited to operations necessary to convert the
crude into salable products. Marketing involves the distribution and sale
of finished petroleum products. Only the refining operations will be con-
sidered in this discussion.
The emission of particulate matter from refineries may originate
from catalyst regeneration, decoking operations, airblown asphalt stills,
sludge "burner, boilers, process heaters and incinerators.—^ Flare systems
may also produce particulate emissions because of formation of carbon par-
ticles but this is a result of the combustion process at the flare.
Production processes, particulate emission sources, particulate
emission rates, effluent characteristics, end control practices and equip-
ment for petroleum refining are discussed in the following sections.
22.2 EMISSION SOURCES
Refineries vary greatly in both the quantity and type of emissions.
The most important factors affecting refinery emissions are crude oil ca-
pacity, air pollution control measures in effect, general level of mainte-
nance and good housekeeping in the refinery, and the processing scheme
employed. The emissions which may contribute to air pollution are sulfur
oxides, nitrogen oxides, hydrocarbons, carbon monoxide, and malodorous
materials. Other emissions of lesser importance include particulates, al-
dehydes, ammonia, and organic acids. Table 22-1 indicates potential sources
of the various contaminants from refineries and emphasizes the variety of
equipment and operations which must be considered in a complete survey of
refinery emissions.^/
Many processes and operations in oil refineries necessitate the
use of high-pressure steam, or require feedstock at an elevated temperature.
A wide variety of boilers and process heaters are used to fill these needs.
Heaters may be of unique design, although most units are the box, or cy-
lindrical, vertical type. Boilers are generally of conventional design.
477
-------
TABLE 22-1
POTENTIAL SOURCES OF SPECIFIC EMISSIONS FROM OIL REFINERIES^/
Emission
Potential Sources
Oxides of sulfur
hydrocarbons
Oxides of nitrogen
Particulate matter
Aldehydes
Ammonia
Odors
Carbon monoxide
Boilers, process heater, catalytic cracking
unit regenerators, treating units, HgS
flares, decoking operations
Loading facilities, turnarounds, sampling,
storage tanks, waste-water separators,
blow-down systems, catalyst regenerators,
pumps, valves, 'blind changing, cooling
towers, vacuum jets, barometric condensers,
air-blowing, high-pressure equipment
handling volatile hydrocarbons, process
heaters, boilers, compressor engines
Process heaters, "boilers, compressor engines,
catalyst regenerators, flares
Catalyst regenerators, boilers, process
heaters, decoking operations, incinerators
Catalyst regenerators
Catalyst regenerators
Treating units (air-blowing, steeon-blowing),
drains, tank vents, barometric condenser
sumps, waste-water separators
Catalyst regeneration, decoking, compressor
engines, incinerators
476
-------
The fuel may be refinery gas, natural gas, heavy fuel oil, coke, cr combi-
nations, depending on economics and operating conditions. Particulate
emissions from boilers and process heaters are included in the stationary
combustion sources discussed in Chapter 6.
Daring catalytic cracking, reforming, and hydrogenation, coke
formed on the surface of the catalyst is burned off in regenerating vessels
by controlled combustion. The flue gases from the catalyst regenerator
may contain fine catalyst dust, and the products of combustion of the coke
may include some of the impurities contained in the charging stock. Crack-
ing unit regenerators are usually large, operate continuously, and are
potential sources of dust, carbon monoxide, hydrocarbon (nearly all methane),
and sulfur-oxide emissions. Reforming and hydrogen treating units usually
regenerate catalysts intermittently and are a less important source of
emissions.
15/
The catalyst regenerator is a major particulate emission source,
and it is discussed in more detail in the following sections.
22.2.1 Catalyst Regenerator
Catalytic cracking is the backbone of the modern refinery. The
capacity of these units amounts to about 4 million barrels per day, equiv-
alent to about 40% of total refinery crude capacity. Cracking over a cat-
alyst, usually an alumina-silicate, is accomplished at slightly greater than
atmospheric pressures and about 900°F. It gives a higher gasoline yield
and better quality gasoline than thermal cracking. The charge stock is
usually gas oil, a distillate intermediate between kerosene and fuel oil.
Catalytic cracking yields a "synthetic crude" which is separated into
gaseous hydrocarbons, gasoline, gas oil, and fuel oil.
During the cracking process, which is usually continuous, coke
deposits on the catalyst and is burned off in separate regenerating vessels.
Catalytic cracking units nay be classified according to the
method used for catalyst transfer. There are four main methods: (l) fixed-
bed, utilizing a number of reaction-regeneration chambers in a batch-type
operation, (2) moving-bed, (3) fluidized-bed, and (4) a once-through
catalyst system which does not attempt catalyst regeneration. Fixed-bed
and once-through systems are no longer used to any great extent. The
mcving-bed system, typified by the Thermofor Catalytic Cracking Units (TCC)
and the Houdriflow Units, and the fluidized-bed or Fluid Catalytic Crack-
ing Units (FCC), are now almost universally used in refinery operations.
479
-------
A typical flow diagram of a fluid cracking unit is shown in
K:r.;re 22-1. In the production of high-octane gasoline, oil and powdered
catalyst are nixed in a reactor. Spent catalyst, containing residual carbon
(or coke) from the catalytic cracking process taking place in a reactor,
is mixed with combustion air and fed to the regenerator in order to reac-
tivate the catalyst by burning off the coke or residual carbon formed on the
catalyst during the cracking process. After regeneration, the hot incinerated
catalyst is mixed with crude oil and is transported back to the reactor
where the oil is distilled off ("cracked") and the cycle repeated.
Ihe gaseous products of combustion from the top of the regen-
erator are exhausted through a series of mechanical collectors which return
their catch directly to the fluid bed. The finer fractions of the catalyst
escape along with the discharged gas. The exhaust gases may be further
cleaned with additional cyclones or an electrostatic precipitator.
In order to protect the collectors and other down-stream equip-
ment against high-temperature damage, temperature control water sprays are
used in the combustion zone over the fluid bed. The regenerator is followed
by waste-heat steam boilers in order to recover some of the heat energy and
reduce the gas temperature. Further gas cleaning is then accomplished by
electrostatic precipitators in many plants.
Large amounts of carbon monoxide gases are discharged with the
regeneration flue gases of an FCC unit. The carbon monoxide waste-heat
boiler is a means of using the heat of combustion of carbon monoxide and
ether combustibles, and the sensible heat of the regeneration gases. Re-
generation gases from an FCC unit are normally delivered to the inlet of
the CO boiler at about 1100°F and 2 psig.£/
22.3 CATALYST REGENERATOR EMISSION RATES
Due to the high extent of control, emission rates from catalytic
cracking units could not be calculated using the methods of emission factors.
Available data indicate that one 6,000 BPSD (barrel/stream day) FCC unit
emits 0.135 ton of dust per day based on 0.016$ dust in the air stream out
of the final separator.—/ Ihe total capacity of FCC units is 3,609 , 000
BPSD. By direct ratio:
Emission from FCC = 3,609,000 (0.135 ten/day)
6,000
m 81 tons/day = 24,000 tons/year
460
-------
CYCLONES
FLUE GAS WASTE
HEAT BOILER
REGENERATOR
COTTRELL
PRECIPITATOR
REGENERATOR
STANDPIPE ^
FCC PRODUCT TO
FR ACTION AT OR
REACTOR
AIR
BLOWER
OIL FEED
figure 22-1 - Flow Diagram of Fluid Cracking Unit-
10/
4B1
-------
The emissions may be calculated by another method. Information
from Reference 14 indicates catalyst "losses" range from 0.05-0.1 lb/bbl
fresh feed. Using the average of 0.075 lb/bbl, the emissions would be:
(0.075 lb" )(3.609 x in6 bbl- Vw, dayy Ton ) = 44
,700 tons/'year
bbl. day yr 2,000 lb.
The latter figure of 44,700 tons/year is probably mere repre-
sentative because the former figure is based on data from only one plant.
22.4. EFFLUENT CHARACTERISTICS
Available data on the chemical and physical properties of
effluents from catalytic cracking units ere summarized in Table 22-2. par-
ticle size of particulates at the inlet of secondary collectors ranges from
10-45 wt. $ less than 2 y,.
22.5. CONTROL PRACTICES AND EQJIPNENT FOR FCC UNITS
22.5.1 Cyclones
The use of cyclones, in one, wo or three stages is common prac-
tice for control of dust from FCC units. In typical installations, multi-
stage cyclones are located in the regenerator vessel for catalyst recovery
and re-utilization. In some esses external cyclones are installed to re-
duce the particulate content of the flue gases. Catalyst dust losses from
the regenerator equipped with internal cyclones and, in some cases, supple-
mented by external cyclone equipment can range in the order of 100 to 350
lb/hr.
The maximum efficiency which can be obtained with external
cyclones would depend on the efficiency of the preceding cyclones, but it
may range as high as 90$ recovery of the solids leaving the preceding vessel.
The installed cost for a set of external cyclones designed for maximum
efficiency will run between $1.25 and $1.75/acfm of gas leaving the vessel
(before the pressure regulating valve) for units discharging between 40,000-
60,000 acfn of gas. The cost of a system designed to recover approximately
60% of the solids leaving the vessel would be about half as much as the
system designed for maximum efficiencyJJ These costs are two to three
times higher than the general cost figures in Appendix A but installation
in a refinery FCC unit is a special application involving different materials
of construction, higher pressures and more difficult installation problems.
482
-------
T'»; t.i-
A. Particulate
Source
Petroleum
Refining
Particle Size
EFFLUIJIT CHAUACTIMKTIC:; - PfffROLEUM KEKINJiK; '
Solidr. Loading
Chemical
Compos j Hon
Particle
Dens i ty
Electrical
Resistivity
M'-isV-r*:
Cor.ter •.
t.x :-
Catalytic
cracking
unit.
Cyclone Inlet;
21-45 < 2
avg. 27 < 2
33-72 < 5
avg. 49 < 5
47-89 < 10
avg. 64 < 10
Dependent on catalyst
type. Varies from
natural earth clays
to the synthetic
varieties which arc
mostly oxides of
silica and alumina.
2.2-3.1
See Figure
S
Precipitator
Inlet (Bahco)
10 < 2, 20 < 4
35 <8, 40 < 10
62 < 25
B. Carrier Gas
Source
Catalytic
cracking
unit
Flowratc
(a) 70.5
(1 plant)
Temperature
Outlet Temp.
1050-1150
Moisture
Content
10-30
Chemical
Composition
Dry:
CO?:
CO:
02:
No:
GO?:
Flue Gar,
6-9
6-7
1-3
81-87
t met:
Hydrocarbons:
trace
Toxicity
Contains CO
Corrosjvi ty
Flammablli ty
Limits
Opti cnl
Proper"i
'3ee Codinr Key, Table 5-1 , Chapter 5, pare 45, for units lor individual effluent properties
-------
(23% MOISTURE CONTENT BY VOLUME)
J I I I
0 100 200 300 400 500 600
GAS TEMPERATURE-°F
igure 22-2 - Electrical Resistivity of Dust from Catalytic Cracking
Un-it.lQ/ (Dust at Precipitator Inlet)
484
-------
The application of a specie! third-stage, high-efficiency multipi
tube, swirl-vane typ^ g^ntrifugal separator to FCC units is described in
two recent articles' This third-stsge separator allows the main body of
the gas stream to be utilized in a turboexpander without serious problems.
22.5.2 Electrostatic Precipitators
A third mechanical cyclone external to the regenerator improves
dust removal but generally it is not sufficient to comply with stringent
emissions standards. Electrostatic precipitators have been used for this
service with good success and some refiners have reported catalyst dust
losses as low as 40-60 lb/hr, although typical current installations have
higher emission rates.—' The precipitator may be preceded by a power re-
covery turbine or a CO boiler. Schematic flow diagrams are shown in
Figures 22-3 and 22-4.1/
The fluid-bed catalytic cracking units may emit 0.0035$ of the
catalyst circulated when equipped with electrical precipitators, or 0.005$
when not so equipped. This may be contrasted with moving-bed catalytic
crackers that emit 0.002$ of the catalyst circulated when equipped with
centrifugal separators.£/
Reference 12 reports cn a study of stack losses from a FCC unit
equipped with cyclones and an electrostatic precipitator. The catalyst
carryover and the weight percentage of 0-20 p, material in the carryover are
shown in Figures 22-5 to 22-7 for the operating conditions given in Table
22-3. Figure 22-5 shows that catalyst carryover from the cyclone increases
rapidly as the quantity of fines in the air stream increases. It was there-
fore concluded that carryover of material to the precipitator, and hence
stack loss, may be controlled by regulation of the amount of fines in the
unit. Figure 22-6 is a calculated curve of stack loss as a function of
particle size distribution of catalyst carried over from the cyclones for
three different precipitator collection efficiencies (computed from Figure
22-5 and a fractional efficiency curve). Figure 22-7 is a calculated curve
of size distribution of the stack loss, derived in the same manner as Figure
22-6
TABLE 22-3
TYPICAL PLANT OPERATING CONDITIONS
Fresh feed rate to reactor, bbl/day
Air rate, lb/hr
Coke burning ratio, lb/hr
Fresh catalyst-addition rate,
tons/day
Fresh catalyst type
465
25,000
235,000
20,000
6.1
MSA-2
-------
PRODUCTS TO
RECOVERY
CYCLONE
70,500 - SCFM
750 - F
0.01 - GRAIN/SCF
70,500 - SCFM
1200 - F
25 - PSIG
0.28 - GRAIN/SCF
REACTOR
CATALYST STRIPPER
STRIPPING
STEAM
CYCLONE-80 %
EFFICIENCY
BIN TO CATCH
CATALYST
EFFICIENCY
POWER
RECOVERY TURBINE
— REGENERATOR
0 - PSIG I 1
750 - F
0.06 - GRAIN/SCF
62,900 SCFM
AIR
RECYCLE FROM
RECOVERY
RAW OIL
CHARGE"
Figure 22-3 - Schematic Flow for Precipitator Installed After
Power-Recovery Turbine^/
-------
PRODUCTS TO
RECOVERY
CYCLONE
82,800 SCFM
O.Of GRAIN/SCF
70,500 - SCFM
1200 - F
25 - PSIG
0.28 - GRAIN/SCF
REACTOR
CATALYST STRIPPER
STRIPPING
STEAM
82,800 SCFM
650 - F
0 - PSIG
0.05 - GRAI N/SCF
PRECIPITATOR
98.2% EFFICIENCY
COBOILER
oooco egg
ooo
— REGENERATOR
15,300 SCFM
62,900 SCFM
AIR
82,800 SCFM
650 - F
0 - PSIG
0.28 - GRAI N/SCF
RECYCLE FROM
RECOVERY
RAW OIL
CHARGE"
Figure 22-4 - Schematic Flow for Precipitator Installed
After CO Boiler®/
-------
on
o
X
6,400
5,600
r i i i
•
Q.
uo
o
z
3
n
4,800
•
•
TOTAL CARRYOVER/*
• /
•
a.
4,000
-
-
z
0
u
3,200
o
o
o o
U
2
0
LL.
QZ
2,400
1,600
• • ° o ~o
° o
+ 20 MICRON CARRYOVER
>
O
>
a:
800
-
-
<
U
n
i i i i
0 10 20 30 40 50
0-20 MICRON MATERIAL IN CARRYOVER,
PERCENT BY WEIGHT
Figure 22-5 - Relationship Between Quantity of Catalyst
Carryover and Particle Sizei=/
-------
h-
LU
Q.
on
| 25 -99.0'
Z)
O
Q_ - _
l/l
£ 15
o
99.3"»
99.5
0-20 MICRON MATERIAL
IN CYCLONE CARRYOVER,
PERCENT BY WEIGHT
NOTE: THE FIGURES AT THE
LOWER END OF EACH CURVE ARE
AVERAGE COLLECTION EFFICIENCY
AT 30% 0-20 MICRON MATERIAL
IN CYCLONE CARRYOVER
Figure 22-5 - Calculated Stack Losses as a Function of Farticle-Size
Distribution of Cyclone Carryoveri^/
489
-------
10 20 30 40
0-20 MICRON MATERIAL
IN CYCLONE CARRYOVER,
PERCENT BY WEIGHT
Figure 22-7 - Particle-Size Stack Loss Distribution Ccmtiared
to Cyclone Carryover Particle Sizai^/*
490
-------
Typical costs for e precipitator following an expansion turbine
at 900°F are $2/scfm, while the cost at 700°F following a CO boiler is only
about $1.50/scfm. Water infection into the effluent stream to further re-
duce the 'emperature to about 550°F will reduce the cost still more.^/
These costs compare well with the general figure for purchase costs of
electrostatic precipitators given in Appendix A.
Electrostatic precipitators can continuously achieve 99$ ef-
ficiencies, but in order to obtain these high efficiencies in precipitators
following regenerators, it is sometimes necessary tc add a small amount of
ammonia to the gases entering the precipitator to lower the resistivity of
the material handled by the precipitator. In designing these units, the
following items are taken into consideration2J
1. With periods of continuous operation for FCC units and
fluid coking units extending to three years or more, one should select a
precipitator with more than one chamber so that part of the unit can be
isolated from the gas stream for maintenance while ail of the gases pass
through the rest of the units.
2. The precipitator should have a large number of bus sections
which are individually energized to achieve the highest power input; and to
minimize any decrease in efficiency if any one section is shorting out.
The dust concentration entering the precipitator depends on the
type of catalyst used, the particular process and the kind of mechanical
collectors used. Ihe normal dust concentration varies between 5 and 25
grains/scf dry. It has been reported that no new catalyst recovery pre-
cipitators have been sold in recent years in this country.ii/
Changes in fuel demands have reduced the number of catalytic
cracking units and consequently the number of new electrostatic precipitators
needed for this service has declined. However, electrostatic precipitators
are still being used on some existing catalytic crackers and at least three
units were sold for this purpose during the 1966-1967 period.—/ A summary
of performance data for precipitators in fluid catalytic cracking applica-
tions during the period 1951-1962 is shown in Table 22-4.iZ/
491
-------
TABLE 22-4
A SUMMARY OF PERFORMANCE DATA* OF PR3CIFITAT05S IN FLUID
CAIALYT-,IC GRACKIKG APPLICATION (1951-1952
Parameter
Maximum
Minimum
Average
Gas Vol'ime, ICOO's acfm/'Pptr.
254
6
152.6
Gas Temperature, °F.
850
45C
610
Inlet Loading, lb/hr
2,800
77
1,444
Coil. Efficiency, %
99 .7
80
S5
* These data based on seven installations.
492
-------
REFERENCES
Stern, Arthur C., Ed., Air Pollution,Vol. Ill, New York, Academic Press
1968, pp. 97-109.
Ibid., p ¦ 116-
Control Techniques for Particulate Air Pollutants, Washington, D. C.,
U. S. Deaprtment cf Health, Education and Welfare, 1969.
Dsnielson, John A., Ed., Air Pollution Engineering Manual, Cincinnati,
National Center for Air Pollution Control, 1967.
McCsllum, I., "Air Pollution Problems and Control,'1 Proceedings Fourth
World Petroleum Congress—Section IIl/l.
Hardison, L. C., "Air Pollution Control Equipment," Petro/Cher, Engineer,
1968.
Tenr.ey, Edwin D., "Remove Solids from Refinery Gases," Hydrocarbon
Processing 45, 3;cember 1967.
Wilson, J. C-., "The Removal cf Particulate Matter from Fluid Bed Catalyti
Cracking Unit Stack. Clases," Journal of the Air Pollution Control Asso-
ciation 17, October 1967.
Franzel, H. L., "Cleaner Stack: Gases Are a Bonus," The Oil and Gas
Journal, March 1969.
Sui, C. T., "A Report on the Use of Electrostatic Precipitators in the
Petroleum Refining Industry," Bound Brook, N. J., Research-Cottrell,
Inc ., 19 7 0.
Ibid., p. 67.
Seibert, C. A., "Withdrawal of Catalyst Fines to Reduce FCC Stack Losses,
Tr.e Petroleum Engineer, August 1954.
Private communication, industrial scarce, March 1970.
Hydrocarbon Processing, 1968 Refining Process Handbook, Gulf Publishing
Company, Houston, Texas, September 1966, p. 147.
"Atmospheric Emissions from Petroleum Refineries," PHS Publication
No. 763, 1960.
493
-------
REFERENCES (Concluded)
Manufacturers'Report of Air Pollution Equipment Sales," Industrial
Gas Cleaning Institute.
Hie Application of Electrostatic Precipitators in the Petroleum
Industry," Southern Research Institute, for the National Air Pollution
Control Administration, Contract CPA-22-69-73, 1970.
494
-------
CHAPTER 23
ACID MANUFACTURE
23.1 INTRODUCTION
Acid manufacturing processes include those for sulfuric, phosphoric,
nitric, and hydrochloric. Only sulfuric and phosphoric acid manufacture dis-
charges significant particulate emissions.
More sulfuric acid is produced in the United States than any other
chemical. The chamber process for the production of sulfuric acid has been
largely displaced by the contact process. About 97$ of current output is
from contact plants. Elemental sulfur accounts for about 75$ of all raw
materials consumed in sulfuric acid production. Most of the remaining new-
acid comes from pyrites or other iron sulfides, smelter gas, hydrogen sulfide,
crude sulfur, and copper, zinc, and lead ores. Increasing amounts of used
sulfuric acid are recovered for reuse. Primary sources are petroleum refining,
alcohol manufacture, nitric acid and chlorine drying, and detergent and other
sulfonations.
The principal emissions from sulfuric acid plants are acid mists
and sulfur dioxide.
Phosphoric acid is produced in two distinct processes. The wet-
process acid is produced and consumed primarily in the fertilizer industry.
The wet process for producing phosphoric acid is discussed in Chapter 12.
The other commercial process for manufacturing phosphoric acid is the thermal
process, also referred to as the furnace or phosphorus burning process. The
thermal process acid is used in plasticizers, detergents, pharmaceuticals,
and food grade acid.
The principal emission from the thermal process is acid mist.
Manufacturing processes, particulate emission sources, particulate
emission rates, effluent characteristics, and control practices and equip-
ment for sulfuric and phosphoric acid production are discussed in the
following sections.
495
-------
23.2 SULFURIC ACID MANUFACTURE
23.2.1 New Acid
All sulfuric acid is made by either the chamber or the contact
process. Elemental sulfur, or any sulfur-bearing material, is a potential
raw material for both these processes. The 215 contact-process establish-
ments account for about 97$ of the U. S. production. The 35 chamber-
process establishments account for the balance of U. S. production.
23.2.1.1 Chamber Process: Originally the chamber process employed
sulfur dioxide gas produced from sulfur, but roaster gas or smelter gas was
substituted later. The process employs the following principal units in ad-
dition to the combustion chamber or SCb source (see Figure 23-1):
1. The Glover tower which receives the hot burner gas. It is fed
at the top with the nitrous vitriol from the Gay-Lussac tower, and with 52°
Be (65$) acid from the chambers. The functions of the Glover Tower are tc
denitrify the Gay-Lussac acid, thus reducing niter requirements to a small
makeup for process loss; to evaporate water from the chamber acid, thus con-
centrating it to about 60° Be (78$); cooling the gas to the point at which
it can be safely introduced into the lead chambers; and supplying water
vapor, equivalent to about one-third of the water requirement of the set
(when producing acid of 52° Be).
2. A series of large lead chambers, usually comprising from three
to as many as ten, in which the reactions between sulfur dioxide, oxygen
from the air, oxides of nitrogen, and water are carried cut with resultant
production of chamber acid.
3. Usually two Gay-Lussac towers in series, in which the oxides
of nitrogen leaving the final chamber are absorbed in sulfuric acid of about
60° Be, and form nitrous vitriol.
4. An ejector or fan to provide the necessary flow of air through
the system. The ejector may be located in the exit stack from the Gay-
Lussac tower; a fan is usually placed between the final chamber and Gay-
Lussac tower. Occasionally the fan is placed between the Glover tower and
first chamber, although this location is not preferred because of its high
temperature.
23.2.1.2 Contact Process: The contact process was first dis-
covered in 1631 by Phillips, an Englishman, whose patent included the
essential features of the modern contact process, namely, the passing of a
mixture of sulfur dioxide over a catalyst followed by absorption of the sulfur
tricxide in water.
Figure 23-2 illustrates a typical flow diagram for this process.
The flow diagram can be divided into the following sequences:£•/
496
-------
NITROUS VITRIOL
EXIT GAS: AIR, S02,
ACID MIST,
NO, AND NOj
TO
STACK
78% TO ACID STORAGE-
CHAMBER ACID
AMMONIA
AIR
AMMONIA
OXIDATION
UNIT
OXIDES OF
NITROGEN
SECONDARY AIR —|
¦ SULFUR
-PRIMARY AIR
SULFUR
BURNER
GLOVER
TOWER
COMBUSTION
CHAMBER
SUPPLY
TANK
WATER ATOMIZERSH
GAS
FAN
r
—*-
78% ACID
(60»BE)
I COOLING WATER
LEAD CHAMBER
(One lo 20 of 5,000 to
500,000 cu. ft. copocity
•och in plants of various
capacities)
ACID COLLECTING PAN
LEAD CHAMBER
ACID COLLECTING PAN
GAY
UJSSAC
TOWER
(USUALLY
TWO)
PUMP
60-70%
CHAMBER
ACID
SUPPLY
TANK
¦Q"
PUMP
7H nitrous
vmioL
J-Q
SUTPLY
TANK
PUMP
Figure 23-1 - Simplified Flow Diagram of Typical Lead-Chamber Process for Sulfuric Acid
Manufacture (Based on Use of Elemental Sulfur as the Raw Material)!/
-------
(RAW GAS - BRIMSTONE PUNT, VANADIUM CATALYST)
TO ATMOSPHERE
CO
CD
STEAM
PROCESS MATERIALS
SULFUR
AIR
COOliR
OLEUM
ABSORBER
98*
ABSORBER
STEAM
WASTE
COOLER
BOIlf R
MELTING'
TANK
r
AIR-DRYING TOWER
USING 96% ACID
FILTER
NO. 2
CONVERTER
66 B*
OLiUM
CONVERTER
SULFUR
WATER
ELECTRICITY
DIRECT LABOR
STEAM*
688 IB.
4,000 GAL.
5 KW.HR.
0.64 MAN-HR
POO LB.
PER ION 100% ACID IN A
PLANT Of 50 TONS PER DAY CAPACITY
ACID COOLERS
' WASTE HEAT BOIlfR WILL FURNISH UP TO 2,000 LB. STEAM
Figure 23-2 - Sulfuric Acid Manufacture by the Contact Process
2/
-------
1. Transportation of sulfur or sulfides to plant
2. Melting of sulfur
3. Pumping ar.d atomizing of melted sulfur
4. Burning of sulfur
5. Drying of combustion air
6. Recovery of heat from or cooling of hot SOg gas
7. Purification of 302 gas
8. Oxidation of SO2 to SO3 in converters
9. Temperature control to secure good yields of GOj
10. Absorption of SO3 in strong acid
11. Cooling of acid from absorbers
12. Pumping acid over absorption towers
23*2.2 Regenerated Acid
Substantial quantities of "fresh clean acid" are made by regenera-
tion or decomposition of spent acid from petroleum refineries or other chem-
ical processes. Sulfuric acid may be concentrated to around 66° Be by heat.
Any further fortification is usually done by the addition of oleum or sulfur
trioxide. Two types of equipment for concentrating dilute acid operate
under a vacuum while the third operates at atmospheric pressure using
air-blown combustion gases.
A typical air-blown concentrator is shown in Figure 23-3. The
burner supplies the hot gases at about 1100°F by the combustion of oil or
fuel gas. These hot combustion gases are blown countercurrent to the sul-
furic acid in two compartments in the concentrating drum and remove water
as they bubble up through the acid. The off-gases at 440 to 475°F from the
first compartment of the drum pass to the second compartment along with a
portion of the hot gases from the combustion furnace. They leave at 340
to 360°F to enter a gas-cooling drum where they are cooled to 230 to 260°F
in raising the dilute acid to its boiling point. Since some sulfuric acid
is entrained as a mist, the hot gases then pass through a Cottrell-type
precipitator for the acid mist before discharge to the atmosphere. A
Venturi scrubber with cyclone separator is also giving competitive results
499
-------
Conitonf-
•v«ltonk
Rolorr*t-*r
BurntrK
Platform
Sub-stoTton
Acid J-
Blower Furnoce
Concert! rotor
cooler
Precipforor
Acta ro
AC/a trtltr
To sewer
Weok-octd
storage
Strong-ocid
tonk
Sludge-receiving
~onk
Figure 23-3 - Sulfuric Acid Concentrator, Drum Type
£/
500
-------
in removing acid mist by washing with feed acid. This procedure will give
an acid with a final concentration of 93$ or slightly higher. The hot gases
also burn out any impurities that may be in a spent acid being concentrated-:
There are five types of vacuum concentrators which will permit
concentration of practically any acid, though clean acid is preferred to
avoid fouling of interfaces. The necessary heat is supplied by high-pres-
sure steam or Dow-therm. The Type E concentrator is the largest and desir-
able for high concentrations. For the latter reason, this type of concen-
trator is employed on relatively clear, acids such as some nitration acids.
It is a vertical steel shell lined first with lead followed by acid-proof
brick. The metallic tubular heaters inserted through the vertical wall of
the vessel are constructed of Duriron or Hastelloy C. Usually there are
two or more units in series. The Type D concentrator is a small batch ur.it
with vertical tubes in a vertical cylindrical tank., suitable for acid con-
centrations up to 93$. The Type C unit consists of many snail compartments
with individual heaters in series through which the acid to be concentrated
flows continuously. The Type B concentrator, a batch unit, is a vertical
tank with lead heating coils used mainly for acid concentration up to 80$.
The Type A unit can be operated continuously or batchwise. This special
corrosion-resistant, high-circulation evaporator is used quite often for
the removal of sodium sulfate from the waste acid liquor being discharged
from the viscose spinning bath, as well as reconcentrating the remaining
acid values. Types C and E have a practical concentration limit of 95$
acid.2/
23.2 EMISSION RATES
23.3.1 New Acid
23.2.1.1 Chamber Plants : The primary source of emissions in the
chamber process is the final Gay-Lussac tower. Emissions include nitrogen
oxides, sulfur dioxide, and sulfuric-acid mist and spray.
Concentrations of total nitrogen oxides in these exit gases
range from about 0.1 to C.2 vol. $. Sulfur dioxide concentrations occur
in the same range. About 50 to 60$ of the total nitrogen oxides is nitrogen
dioxide, which characterizes the exit gas by a reddish-brown color.
Combined sulfuric acid mist and spray in the exit gas varies from
5 to 50 mg/scf. The sulfuric acid mist contains about 10$ dissolved
nitrogen oxides.
-------
23.3.1.2 Contact Plants: The major source of emissions from con-
tact sulfuric acid plants is the exit gas from the absorber. This gas con-
tains unreacted sulfur dioxide, sulfuric acid spray and mist, and unabsorbed
sulfur trioxide. Trace amounts of nitrogen oxides may also be present under
some conditions, e.g., use of a raw material feed containing nitrogen com-
pounds. Acid mist err.issions prior to any control equipment average between
5-10 mg/scf for sulfur-burning plants producing no oleum and about 15-30
mg/scf for those plants producing oleum.
Unconverted sulfur dioxide gas, which is colorless, passes through
the absorption system and is discharged tc the atmosphere. The quantity of
this gas emitted is a direct function of the degree of conversion of sulfur
dioxide to sulfur trioxide and may vary from 0.1 to 0.5$ by volume of the
stack gases. During startup or during some emergency shutdowns, higher con-
centrations will occur.
Unabsorbed sulfur trioxide usually constitutes a small part of
the absorber exit gas. When discharged to the atmosphere it is hydrated
and forms a visible white plume of acid mist. Although the concentration
of unabsorbed sulfur trioxide can vary appreciably, from 0.5 to 48 mg/scf
of gas, it is usually closer to the lower figure and is a small part of the
total acid mist emission.!/ Other emission sources for this type of sulfuric
acid plant include:
1. acid concentrators
2. tank car and drum-loading,
3. storage tar.k ver.ts
4. storage piles
Table 23-1 summarizes particulate emission rates for chamber and
contact plants. Chamber plants currently emit about 2,000 tons/yr, while
contact plants emit about 4,000 tor.s/year.
23.3.2 Regenerated Acid
The concentration of sulfuric acid in vacuum-type concentrators
does not produce atmospheric pollution problems.
The effluent gases from air-blown concentrators contain sulfuric
acid mist and sulfur dioxide resulting from the decomposition of sulfuric
acid by carbonaceous materials in spent acid,22/ Spent gases go to a
scrubbing tower, or more generally to an electrostatic precipitator, for the
removal c-f sulfuric acid mist. Limited data in the cper literature indi-
cate that fume emission rates are a function of plant operating and main-
tenance practices.il/
Emission rates for acid regenerators are summarized in Table 23-1.
Emissions are estimated at 8,000 tons/year.
502
-------
TAbI.£ i-"-l
PARTICULATE EMISSIONS
MINERAL ACIDS
Oi
O
W
Source
I. Sulfuric Acid
A. Processing Units
1. Gay-Lussac tower
(chamber process)
2. Absorber (contact
process)
B. Spent-Acid Concentrators
1. Air-blown
2. Vacuum
II. Phosphoric Acid - Thermal
Process
Quantity of Material
28,000,000 tons of H2S04
1,000,000 tons of H2S04
27,000,000 tons of HgS04
11,200,000 tons of spent
acid
1,020,000 tons of P2O5
Emission Factor
Efficiency Application
of Control of Control Net Control Emissions
Cc Ct C.,-Ct ton/yr
5 ]b/ton HgSO^
2 lb/ton H2S04
30 lb/ton of spent 0.95
acid
134 lb. particulate/
ton of P2O5 pro-
duced
0.0 0.0 0.0
0.95 0.90 0.85
0.85 0.80
0.97 1.0 0.97
Total from Acids
2,000
4,000
8,000
Neg.
2,000
16,000
-------
23.4 EFFLUENT CHARACTERISTICS
The chemical and physical properties of sulfuric acid plant efflu-
ents are summarized in Table 23-2. Acid mists emitted from chamber plants
contain particles which are 10 wt. $ less than 3 u. Contact plants emit
particulates which range from 7-95 wt. $ less than 3 p, with an arithmetic
mean of 64 wt. $ less than 3 p,. A large percentage of smaller particles
is emitted when producing cleum. Approximately 85-95 wt. $ of the par-
ticles are less than 2 y, when producing oleum as compared to 30$ less than
2 jx when producing 98$ acid.
23.5 CONTROL PRACTICES AID E&UIMEM: FOR SULFURIC ACID PLANTS
Recovery equipment is rarely employed in chamber plants.i/ Elec-
trostatic precipitators, packed-bed separators, mesh-type mist eliminators,
ceramic filters and sonic agglomerators have been used to reduce the emis-
sion of acid spray and mist from contact acid plants.Most modern plants
are equipped with high-efficiency electrostatic precipitators or mesh-type
eliminators in which 99$ of the mist is recovered.3/
The electrostatic precipitator and mesh-type eliminator can pro-
vide removal efficiency of up to 99.9$. However, when oleum is produced,
the portion of acid mist particles smaller than 3 (j in diameter is higher.
This size seriously affects the lew-pressure drop nesh-type eliminators;
efficiency decreases sharply, and may be less than 40$.i/
Also, small amounts of nitrogen oxides in the inlet gas to the
absorber interfere with the absorption of sulfur trioxide, and hence cause
- / '
visible acid mist in the absorber exit gases—'
The visibility of acid mist depends more on particle size than
on mist loading. Thus, a high percentage of particles 3 ^ or less in the
acid mist usually causes a heavy plume from the absorber stack. High-
efficiency control devices do not necessarily result in an invisible plume
unless there are few particles less than 3 p, and inlet mist-loading is not
excessive.
1/
Acid mist composed of particles of less than 10 y, in size is
visible in the absorber tail gas if present in amounts greater than 1 mg/
ft^. Larger particles deposit readily on dust and stack walls and con-
tribute little to the opacity of the plume.£/ Internal spray catchers
are installed in the top section of many absorbers to aid in the removal
of large acid particles entrained in the exit gasFrom a plume visi-
bility standpoint, plants producing a maximum of 99$ acid (i.e., no oleum)
often have clean stacks if bright, or uncontaminated, sulfur is used and
the absorber is operating properly. However, plants producing oleum
504
-------
TABLE 23-2
A. Particular.* '^rt l)
ZFTTJL'gr? CaWACTB^ICTICG - ACID MA.'n^A^TJRR*
Sulfurir acts
a. cSantfr plant
b. contact plant
r. rrgcnerfttcr
(air-tlowTy
P'rv.3p:if rlr acid;
ther»l process
Particle 312$
90-9S > 3
7.5-95 < 3; arlth.
csean S3.5 < 3 (sire
dependent on plant
->T<0
0.4-2.6; m*a ttedian
riiar.eter - 1.6
Solldt; Loading
0.017-0.76; arlth.
aean - 0.2
0.9-1.6
1,55-93 without
collector
0.001-0.26 with
collector
Cfccalcal
Cogposltlon
Vt
Hj30t
Particle
p»mitY
1.7
i.*> - i.e
Electrical
Resistivity
Moisture
Content
Toxicity
1.5' . 1.66
1.0,
1.0,
1.0,
irritant
Irritant
Irritant
Irritant
A. rsrtlc :late (Part IT)
Hygrsicopic Flansmtllity or
Sol-utility Wettability Characteristics Explosive Lir.lU Handling Charactcristi
$
Kg " balance
S02
5;
Irritant
SO?
SOg - 0.15-0.54
arlth. stan - 0.26; 5;
air - balance Irritant
Optical
Properties
C5»eity -
we^iuo
QpaeUy -
ncre to
der.se
c, regenerator
( air-blown)
a) SB.5
1 one plant)
PicsprvrrJ'.- aeifl;
themal process
a) 3.4-33.2
d) 35-160 136-201
10-60 HgO, KO,, Air-balanc«
See Coding Key, Table 5-1, Chapter 5, pa^a 45, lor units for Individual affluent properties.
0-100%
opacity
505
-------
generally need either high-efficiency electrostatic precipitators or high-
efficiency mist collectors. Table 23-3 presents a summary cf "feasible
systems" for acid mist control.16/
The concentrating of sulfuric acid in air-blovm concentrators
can also result in emissions of sulfuric acid mist and spray. These
emissions can be controlled by the use of electrostatic precipitators,
Venturi scrubbers or fiber-mesh eliminators.!/
TABLE 25-3
FEASIBLE SYSTEMS FOR ACID MIST CONTROL±§/
1. Dual Mist Pads
2. Tubular-Typ e
Mist Eliminator
Efficiency
> 3 y
(*)
99+
100
Efficiency
< 3 (J,
(*)
15-30
95-99+
Emission
Level
99$ Acid
Plantsf/
(ma/scf)
2
0.1
Emission
Level
Oleum
Plants^/
(mg/scf)
0.1
3. Panel-Type Mist 100
Eliminator
90-98
0.5
0.5
Electrostatic 99
Precipitator
Venturi Scrubber 98
Near 100
Low
0.1
0.5
Ineffective
with 3 y,
mist
a/ Based upon manufacturers' generally expected results.
506
-------
One company studied the removal of sulfuric acid mist, on piict
plant scale, by low-pressure water sprays, high-pressure water sprays, and
hag filters, ana "by decomposition with heat. This study led to installa-
tion of a high-pressure water spray system on a facility concentrating
700 tons/day of acid from 70$ to 95$ in air-blown concentrators. The unit
was designed to spray 500 gpm of water at 540 psi spray nozzle pressure.
Fuel gas turners were installed in the base of the acid fume stack to raise
the temperature of the effluent gases from 140°F to 212°F.^/
23.5.1 Control gauipnent
23.5.1.1 Vfire-Mesh Mist Eliminators: This control device has
the lowest first cost for effective removal of particles larger than about
3 n in diameter. However, corrosion possibilities may require frequent
replacement of this type of control device; therefore costs will rise and
these increased costs must be considered.^/
The wire mesh eliminator is commonly constructed with two beds
in series and operates with pressure drops of 1-3 in. of water.2/ Typical
gas velocities for these units range from 11 to 16 ft/sec,—/
23.5.1.2 Glass-Fiber Mist Eliminators: The high-efficiency
glass-fiber mist eliminator is capable of operating, with collection effi-
ciencies of over 99$. Pressure drop is usually 5-10 in. w.g. The glass-
fiber mist eliminator is also capable of maintaining high efficiency at
varying tail-gas flow rates.i/
A recent development in this area involves the use of a teflon
fiber mist pad. This device is reported to be 98$ efficient even when
inlet loading is as low as 10 mg/ft^ ..§/
23.5.1.3 Electrostatic Precipitators: Electrostatic precipitators
are highly efficient regardless of size of the acid-nist particles. They
operate with pressure drops less than 1 in. w.g.
Electrostatic precipitators may be either wet or dry type. The
dry type, which is suitable only for concentrated acid, is much less expen-
sive but more susceptible to corrosion. Wet-type precipitators are suit-
able for use only with dilute acid, and this necessitates prior humidifi-
cation of stack gases. This alsc permits removal of SO3 by converting it
to acid mist. However, the humidification step appreciably increases the
cost of a wet-type installation ..i/
507
-------
The lead constructed electrostatic precipitator, for low-strength
acid mist emissions, is used throughout the industry as the primary means
of emission control. The use of mild steel electrostatic precipitators
for oleum stack cleanup has been reported as successful with considerable
savings in cost jJ
23.5.1.4 Ceramic Filters: This German device is_ reported to operate
with high efficiency at constant tail-gas flew rates. It has not been
accepted in the U, S. because of high maintenance costs and inflexibility in
handling varying gas volumes.2/
23.5.1.5 Venturi Scrubbers: Venturi scrubbers are capable of high
efficiency but at the expense of high pressure drop. They have not been
used en contact acid plants, but have been used cn sulfuric-acid concen-
trators to give outlet (i.e., grain loading) mist loadings cf 0.5-3.0 mg/ft^.i/
23.5.1.6 Packed Bed Separators: These low-efficiency devices were
used in the past, but none are known to be operating today.2/
23.6 PHOSPHORIC ACID MANUFACTURE
Phosphoric acid is manufactured by two processes: l) the thermal
process and (2)the wet process. The thermal process proceeds by burning
elemental phosphorous to the pentoxide, followed by a hydration step. The
wet-acid process involves treatment cf phosphate rock with sulfuric acid.
About 75$ of the phosphoric acid produced comes from the wet acid process,
and about 92$ cf the vet-process phosphoric acid goes into fertilizer pro-
duction. About 19$ of the thermal process phosphoric acid goes into fer-
tilizer production, with the rest of the acid from both processes going into
the production of other industrial chemicals.
23.6.1 Thermal Process
In the manufacture of phosphoric acid from elemental phosphorus,
three steps are involved: (l) burning of the phosphorus, (2) hydration of
the resulting phosphorus pentoxide, and (3) collection of the mists formed.
A schematic diagram of the thermal process is shown in Figure 23-4. In
most plants the elemental phosphorus is burned as a liquid. The problem of
building a burner for liquid phosphorus is complicated by the fact that red
phosphorus tends to form at elevated temperatures and can plug the burner
completely or give rise to color in the resulting acid. The build-up of
red phosphorus is usually avoided by a design in which rapid atomization of
the phosphorus takes place.
508
-------
STACK ACID treating plant
EFFLUENT STACK EFFLUENT
(AIR + H3PO4 MIST) (AIR+H2S)
BLOWER
BLOWER
HYDROGEN SULFIDE,
SODIUM HYDROSULFIDE
OR SODIUM SULFIDE
WATER
PRODUCT
AIR
ACID TO
STORAGE
ABATEMENT
EQUIPMENT
BLOWER
cn
O
CO
FILTER
PHOSPHORUS
PUMP
STRONG
H-jPO,.
COOLER
COOLING WATER
PHOSPHORUS
COMBUSTION
CHAMBER
HYDRATOR-
ABSORBER
AIR TO
SPARGER
RAW ACID TO STORAGE
BURNING AND HYDRATION SECTION
ACID TREATING SECTION
(USED IN THE MANUFACTURE OF ACID
FOR FOOD AND SPECIAL USES)
Figure 23-4 - Flew Diagram for Typical Thermal-Process Phosphoric Acid Plant^/
-------
Phosphorus is transferred from the liquid-phosphorus feed tank to
the burner tower by a pump or by liquid displacement at feed rates that
range from 1 to 5 gal/nin. At the burner the phosphorus is mixed with air
and is oxidized at temperatures of 3000° to 5000°F in the combustion chamber.^/
The resulting mixture of phosphorus pentoxide vapor and excess air passes
from the combustion tower and into the hydrator.
Although many plants have refractory or graphite-lined combustion
towers, a few new burning towers are constructed of water-jacketed stairless
steel. In stainless steel towers weak phosphoric acid introduced into the
combustion tower flows down the walls to remove excess heat. The phosphorus
pentoxide vapors from the combustion tower are contacted with weak and pro-
duct acid to hydrate the oxide to phosphoric acid and to absorb acid mist.
These steps may be accomplished in one unit, but many plants use separate
absorbing towers. In some new designs the acid sprayed into the hydxator
is cooled prior to recycle. This spraying permits use of a smaller quantity
of acid and allows the production of higher strength acid.
Some product acid is drained from the bot-ori cf the hydratcr-
absorber. Gases containing acid mist leave t'r.e hydratcr-absorber and enter
air pollution abatement equipment.
The yields from thermal production cf phosphoric acid are excep-
tionally high. In efficient plants about 99.9$ of the phosphorus burned is
recovered as acid. The loss of acid through leaks and discharges to sewers
is usually negligible. Losses of phosphoric acid to the atmosphere repre-
sent direct product loss; therefore, efficient collection devices are nor-
mally installed in the gas stream before the gas is discharged from the
plant.
23.6.2 The Wet Process
The oldest and still the most economical method for making crude
phosphoric acid is to treat phosphate rock with sulfuric acid, thereby
precipitating calcium sulfate and releasing phosphoric acid. However, to
make phosphoric acid for any application other than fertilizers, it is
necessary to purify the crude material obtained by the wet process. This
purification may range from the removal cf coloring materials such as iron
and vanadium to the preparation of a food-grade acid. The wet-acid process
for the manufacture of phosphoric acid is described in the chapter on
Fertilizer Manufacturing.
23.6.3 Mission Rates
The principal atmospheric emission from the manufacture of phos-
phoric acid by the thermal process is acid mist in the absorber discharge
gas. In the normal operation of the plants the hydration of phosphorus
510
-------
per.toxide (P4O10) creates phosphoric acid mist. Acid mist loadings within
the process car. be quite high. Loadings as high as 6,000 mg/dry scf of
stack gas have been reported. It is not uncommon for as much as half of
the total phosphorus pentoxide to be present as liquid phosphoric acid par-
ticles suspended in the gas stream. Economical operation of the process
depends on agglomeration of the acid mist particles and subsequent separa-
tion from the gas stream. For this reason all plants are equipped with
some type of emission control equipment.
Thermal-process acid manufacture employs high-temperature com-
bustion that is normally conducive to the formation of nitrogen oxides.
Kany factors such as flame temperature, residence time, and quantity of
excess air affect the amount of nitrogen oxides formed.
No serious problems are encountered in the startup or shutdown of
a thermal phosphoric acid manufacturing unit that affect losses from the
fir.al collector. Maintenance of proper liquid flows and pressure differ-
entials on the absorbers and collectors allows little or no increase in
acid mist discharged to the atmosphere during either startup or shutdown.
Maintenance is not usually considered to be a major problem.
Sprays, fans, mist eliminators, and other equipment obviously must be main-
tained in good operating condition. If a continuous-emission monitor is
used on the collector exhaust, problems with the abatement equipment will
be apparent to the operator quickly. Operators are normally concerned with
keeping losses at a minimum because any loss is a direct loss of product.
Table 23-1 summarizes particulate emission rates for phosphoric
manufacture by the thermal process. Emissions currently total about 2,000
tons/year.
23.6.4 Effluent Characteristics
The chemical and physical properties of thermal phosphoric acid
plant effluents are summarized in Table 23-2. The mass median diameter
of the emitted particulates is 1.6 p,.
Data on the wet process are presented in the chapter on Fertilizer
Manufacturing.
23.6.5 Control Practices and Equipment
Venturi scrubbers, packed scrubbers, glass-fiber mist eliminators,
wire-mesh mist eliminators, and electrostatic precipitators are used as
abatement equipment at phosphoric acid plants.
511
-------
Operating practices have little effect cn emissions of acid mist.
The acid mists escaping collection are extremely hygroscopic so that visible
emissions are pronounced unless high collection efficiencies are achieved.^
The stack gases leaving phosphoric acid plants cam be made completely in-
visible when the mist loading is reduced to 0.02 mg. of P205/scf of stack
gas, the concentration of the mist in the collector is at least 75% phos-
phoric acid, and the stack gas temperature is above 176° J.%1
23.6.5.1 Scrubbers: Packed and open tower scrubbers have been used
widely to collect phosphoric acid mist. An important factor in efficient
collection is gas velocity. The effect of gas velocity on efficiency in a
pilot plant packed tower is given in Figure 23-5.-2/
Scrubbing is inexpensive ar.d simple, but high collection effi-
ciency is not usually obtained. Some plants have improved efficiency by
installing wire-mesh mist eliminators after the scrubber.
23.6.5.2 Venturi Scrubbers: Venturi scrubbers are capable of oper-
ating at high collection efficiencies cn phosphoric acid mist.®/ The ex-
tremely small size of the mist particles usually requires pressure differ-
entials in excess of 40 in. of water. Figure 23-&i^/ illustrates the effect
of particle size on collection efficiency. It is reported that Venturi
scrubbers can reduce emissions to 0.10 mg/scf.i2/
Venturi scrubbers are not used solely for abatement as they can
actually hydrate part of the phosphorus pentoxide vapor, agglomerate the
mist particles and cocl the stack gases; they may ther. be followed by
cyclcnic separators. This combination can recover up to 99.9% of the acid
mist at pressure drops of 35-50 in. w.g.
23.6.5.3 Cyclonic Separators: Cyclonic-type collectors are used in
seme plants but because cf the snail particle size of the emitted acid mist,
other devices usually supplement these collectors. Supplemental collectors
are typically wire-mesh mist eliminator pads cf low pressure differential.
23.6.5.4 Glass-Fiber Mist Eliminators: Glass-fiber mist elimina-
tors are capable of high collection efficiency in removing phosphoric acid
mist from absorber effluent gas streams. When the mist eliminators are
operating at a superficial vapor velocity of less than 1 fps and at pressure
differentials of about 20 in. of water, collection efficiencies of 99.9$
are attainable.ii/ It is reported that these units can reduce emissions
to as low as 0.10 mg/scf.
10/
23.6.5.5 High-Energy Wire-Mesh Contactors: This is a recently de-
veloped device which is reported to give collection efficiencies that exceed
99.9$ at pressure differentials ranging frcin 35 to 41 in. of water.12/
512
-------
100
80
60
40
20
1 1 1 1 1
/
- /
- /
- /
-
/ APPROXIMATE ~
-
~ r FLOODING
VELOCITY
I I I I 1
0
12
4 8
Tower Packing: 1£ Ft. of 1-In. Carbon Rascfcig Rings
Acid Concentrations: 81-37$ E-^PO^
Inlet Gas Temperature:
?P0z Content of Gas: 2.
44.0 - 550°?
0-2.5 Lb/1,000 Ft2
Figure 23-5 - Effect of Gas Velocity on Phosphoric Acyi
Recovery in Pilot-Plant packed Tower®/
100
0 1.0 2.0
Dp, MICRONS
Figure 23-S - Collection Efficiency of Venturi Scrubber
as a Function of Particle Size for
Riosphoric Acid Mistil/
513
-------
The unit lias the advantage of operating at relatively high super-
ficial vapor velocities of 20 to 30 fps which results in low capital cost.2/
Installed cost is reported to "be approximately $1.50 per acfin of stack gas.12/
23.6.5.6 Electrostatic Precipitators: Phosphorus pentoxide losses
froir. electrostatic precipitators are affected only slightly "by rate of gas
flow or by temperature, as long as design conditions are not exceeded.
Acid mist losses are affected by cleanliness of the equipment and the elec-
trical conditions employed. Precipitators operate at a pressure drop of
about 0.5 in. of water. Table 23-4 shows electrostatic precipitator data
for six installations.^/
TAELE 23-4
OPSRATING CHARACTERISTICS OF PHOSPHORIC ACID MIST
gLECTH0SIATIC PRECIPITATORS^/
Gas
Inlet
Inlet
Outlet
Flow
Temper-
Mist
Mist
Collector
Rated
Instal-
RateS/
ature
Cone.
Cone.
Efficiency
Capacity
lation
fscfm)
(°?)
As Noted
As Noted
(*)
K)
1
3,160
227
7.45^/
o.oa^/
93.9
147
2
14,100
292
14.21^/
0.415^/
97 .1
119
3
3,540
173
3458^/
o.ios/
99.9+
75
4
3,900
192
36502/
0.161/
99.9 +
114
5
3,570
195
406C£/
0.24£/
99.9+
104
6
7,300
234
278!*/
10.43^/
96.3
101
a/ 29.92 in. Hg and 32°F.
b/ Grains/scf dry gas as P2O5.
c/ Milligrams 80$ ^PO^cf dry gas at temperature.
&/ Milligrams mist/scf dry gas at 60°F as
514
-------
2
3
4
c
6
7
9.
9.
10.
11.
12.
13.
14.
REFERENCES
"Atmospheric Emissions from Sulfuric Acid Manufacturing Processes,"
Public Health Service Publication No. 999-AP-13, Cincinnati, Ohio,
1965.
Shreve, R. N., The Chemical Process Industries, McGraw-Hill, 2nd Edi-
tion, 1956.
"Control Techniques for Particulate Air Ebllutants," National Air
Pollution Control Administration Publication No. AP-51, Washington,
D. C., 1969.
Air Pollution Engineering Manual, PES Publication No. 999-AP-40,
Cincinnati, Ohio, 1967.
Clauss, N. W., "The Reduction of Atmospheric Pollution from Sulfuric
Acid Recovery Processes," Air Repair, 5(5), 151-35, February 1954.
"Teflon Monofilament Cleans Up Acid Stack Gases," Chemical Engineering,
112, October 25, 1965.
Stastny, E. P., "Electrostatic Precipitation," Chemical Engineering Progress,
62(4); 47-50, April 1966.
Slack, A. V., Ed., Phosphoric Acid, Marcell Dekker, Inc., New York,
Vol. 1, Fart II, p. 967, I960.
"Atmospheric I&iissions from Thermal-Process Phosphoric Acid Manufacture,"
liAPCA Publication No. AP-48, Durham, North Caroline, 1958.
Strauss, W., Industrial Gas Cleaning, Pergamon Press, New York, 326,
1966.
Brink, J. A., "Air Pollution Control with Fiber Mist Eliminators,"
The Canadian Journal of Chemical Engineering, 41, 135-39, June 1965.
Anon., "Collector 99.9$ Efficient: Pressure Drop Moderate," Chemical
Processing, pp. 46-50, Mid-November 1966.
Clauss, N. W., "Reduction of Atmospheric Pollution from Sulfuric Acid
Recovery Processes," Air Repair, 3(3), 131-136, 1954.
Berger, J. H.. and A. J. Gloster, "'Chenico' Drum-Type Sulfuric Acid
Concentrator," Chemical Engineering Progress, 43(5), 225-236, 1947.
515
-------
15. Chemical Construction Corporation, "Engineering Analysis of Emissions
Control Technology for Sulfuric Acid Manufacturing Process/' for
the National Air Pollution Control Administration, Contract CPA 22-
69-81, March 1970, p. II-l.
15. Ibid, p. IV-51.
17. Brink, J. A., ar.d C. E. Constant,."Experiments on an Industrial Venturi
Scrubber," Industrial and Engineering Chemistry, 50; pp. 1157-50,
August 1958.
516
-------
CHAPTER 24
INCINERATION
24.1 INTRODUCTION
Incineration is not strictly an industrial process. However,
incineration is used in many industries for waste disposal, and this com-
bustion process is a significant source of particulate pollution on a
nationwide basis. This chapter on incineration is included for the sake
of completeness.
Incineration is a combustion process, and like all combustion
processes incineration will cause air pollution unless carefully controlled.
In comparison with the potential air pollution emissions from electric
generating plants and chemical/manufacturing industries, incineration ap-
pears as a relatively unimportant source. This perspective is deceiving,
however, since incinerators are often located in residential areas and are
often equipped with inadequate or no control equipment
The air pollutants arising from incineration of solid wastes
fall into three categories: (l) mineral particulate; (2) combustible
solids and gases; and (3) noncombustible gases. Emissions are dependent
upon incinerator design and operating factors, refuse composition, refuse-
charging rate, and combustion efficiency.
To facilitate discussion, incinerators will be grouped into three
types: (l) municipal; (2) commercial; and (3) apartment house. Emission
sources, emission rates, chemical and physical properties of effluents,
control practices, and control equipment are discussed for each incinerator
group in the following sections.
24.2 MUNICIPAL INCINERATION
Municipal incineration is a useful, effective method of solid
waste disposal. However, poor design, management, or operator judgment,
may culminate in ineffective, costly operations that in turn result in
air pollution, odor, and other problems.
517
-------
The basic elements of a municipal incinerator are the storage
pit, where refuse is deposited from collection trucks; the furnace, where
the refuse is ignited and most of the combustion takes place; the secondary
combustion chamber where additional combustion of volatile gases and par-
ticulate matter occurs; a settling chamber; and the stack or chimney. In
addition, a plant will usually have scales to weigh incoming vehicles, a
means of transferring refuse from the storage pit to the furnace and a
residue removal system.^/
The general types of incinerators for municipal use can be
divided into two classes: (l) batch, or intermitt&nt feed incinerators,
where refuse is admitted into the furnace at intervals; and (2) continuous-
feed furnaces, wherein refuse is fed into the furnace in a steady flow.
The former furnaces generally burn down each charge on the grates before
admitting another charge. To some extent batch feed furnaces may operate
in an approximately continuous fashion by admitting increments of refuse
at close intervals. Continuous-feed furnaces utilize one or more forms
of mechanical grates. Residue is usually dumped and removed continuously.
Some types of grates ccnvcy a tumbling action to the refuse to provide
more rapid and complete burning and to promote ash removal3J Design
details of various units are presented in References 2-4.
24.2.1 Emission Sources and Rates
Particulates from refuse incineration originate from dust raised
in the refuse dumping and handling processes, smoke discharged through
semiporous furnace walls and stoking doors, and entrained dust in the
gases discharged from the furnaces. The first two are minor sources and
are extraneous to the burning process.
The mass emission rate for particulates from the combustion process
is a function of many variables: (l) uxidergrate air velocity; (2) refuse
ash content; (3) burning rate or combustion quality; (4) grate agitation in
a continuous feed incinerator; (5) size, method, and frequency of feeding
for batch ur.its; and (6) combustion chamber design. Items 1 and 2 are the
major factors.
A systematic study by the Public Health Service of the effects of
underfire air, secondary air, excess air, charging rate, stoking interval,
and fuel moisture content on particulate emission rates from an experimental
incinerator led to the conclusion that the velocity of the underfire air
was the dominant factor influencing the emission rate.ii^/ Subsequent
field evaluation of emission rates from municipal units indicated that the
effect of underfire air rate was less pronounced than that observed in the
experimental unit. For the two municipal incinerators tested, the effect
518
-------
was small for undergrate velocities below 35 to 40 scfm/sq ft of grate
area; but significant above that rate.iz^/ Test results reported by other
investigators parallel the effects noted in the experimental unit.-/
Figure 24-1 illustrates a comparison of the data cn the experimental in-
cinerator and the field tests. The spread in the data is not surprising
in view of probable differences in refuse composition, furnace size, and
other factors.^/
The influence of refuse ash content on emission rates was also
studied in an experimental incinerator.^/ In one series of laboratory
tests the level of underfire combustion air was varied from 3 to 60 scfln/
sq ft of grate area, and the resulting particulate emissions ranged from
1.6 to 8.6 lb/ton of combustible material burned. The fuel was a mixture
of newspaper, cardboard, and wood chips. When a high ash content paper
was substituted for the newspaper portion, a similar series of tests pro-
duced even higher particulate emissions, ranging from 3.2 to 35 lb/ton
of combustible material for the same range of underfire air flow rates.
In a second laboratory study which was made to evaluate emissions
produced by burning a high volatile material composed of asphalt felt roof-
ing and newspaper, tests were made under conditions in which the level of
underfire air was varied while all other variables were held constant. The
resulting particulate emissions increased from 5.3 to 19.8 lb/ton of fuel
burned. In this case, the level of underfire air ranged from 6 to 34 scfm/
sq ft of grate area on tests made at 100$ excess combustion air. With 200$
excess air, particulate emissions increased from 11.2 to 47.2 lb/ton of
material burned when underfire air was varied from 8.5 to 50 scfm/sq ft
of grate area.
The dependence of particulate emission rate on ash content of
the refuse has also been noted by German investigators .i/ These findings
show that the ash content of the refuse is a major factor in determining
emission rates.
Reference 1 contains a discussion of the influence of secondary
variables on emission rates.
24.2.1.1 Summary of Emission Rates: Particulate emissions from
municipal incineration have been estimated at 100,000 tons/year.A/ Table
24-1 gives the distribution of the various types of emissions from municipal
incinerators.
519
-------
PHS Field Teit—'
(250-Ton 2 Sect. Trav. Grate)
40.0
20.0
Walker and Schmitr Data—'
o 250-TPD 2 Sect Trav. Grate
D 250-TPD Reciprocating Grate
• 120-TPD Rocking Grate
10.0
PHS Field Teit"
(50-tpd Unit)
3 4.0
¦o 2.0
PHS Experimental Incinerator
(25% and 50% Moisture Fuel)
&.
1.0
0.8
0.6
0.4
0.2
0.1
40 60 80 1 (X) 200 400
SCFM Underfire Air Per Sq. Ft. Grate Area
Figure 24-1 - Effect of Underfire Air Rate on Furnace Emission^/
520
-------
TABLE 24-1
ESTIMATED MUNICIPAL INCINERATOR EMISSIONS!/
(thousands of tons/year)
1968 Eitissions Estimate
Pollutant Furnace Stack
Mineral particulate 90 56
Combustible particulate 38 32
Carbon monoxide 280 280
Hydrocarbons 22 22
Sulfur dioxide 32 32
Nitrogen oxides 26 22
Hydrogen chloride 8 6
Volatile metals (lead) 0.3 0.3
Polynuclear hydrocarbons 0.01 0.005
Total 496. 450.
521
-------
24.2.2 Effluent Characteristics
The physical and chemical characteristics of effluents from
municipal incinerators are presented in Table 24-2. The particle size,
particulate grain loading, and particulate chemical composition axe highly
variable and depend upon combustion efficiency, underfire airflow, incin-
erator design, and character of refuse. Furnaces operated in excess of
design capacity generally emit a low percentage of particles smaller than
10 in size, while furnaces operated at less than capacity and low under-
fire air rates emit larger percentages of particles smaller than 10 (j, in
size. Electron micrographs (30-80,000 magnification) of particulate mate-
rial from stacks show a very heterogeneous material. No characteristic
shapes predominate. Occasional shapes could be identified such as the
round spheres indicative of carbon particles, or cubes indicating magnesium
oxide or the needle shape forms of zinc oxide. 1/
The toxic and corrosive properties of the effluents from munici-
pal incinerators are dependent upon the composition of the refuse burned
in the unit. In addition to the fly ash and normal gaseous products of
combustion (i.e., CO2, CO, etc.)> pclynuclear hydrocarbons, organic acids,
and aldehydes are liberated during incineration. The combustion of halo-
genated. hydrocarbons can result in the formation of decomposition products
which are corrosive and toxic, e.g., fluorides and chlorides can be emitted
when aerosol cans cr PVC containing materials are included in the refuse.
The thermal decomposition of pclyurethane-type plastics could constitute
a toxic hazard because of the liberation of phosgene and/or toluene diiso-
cyanate. The quantity and nature of these emissions are also dependent
upon operating factors and incinerator design.
24.2.3 Control Practices and Equipment
A NAPCA report on municipal incineration presents average effi-
ciency data for air pollution control systems used on municipal incinerators.
Table 24-3 summarizes the efficiency data.l/ The actual application of
these devices, together with investment and operating cost, is shown in
Table 24-4..i/ Table 24-5 indicates the maximum efficiency of incinerator
control equipment.9/
Lata for installed cost and operating cost are shown in Figures
24-2 to 24-6. It should be noted that Figures 24-4 through 24-6 show
annual operating costs based on operating periods of one, two and three
shifts per day, respectively. An explanation of the basis for these costs
is given in Section VII of Reference 1. The installed costs shown in Figure
24-3 are higher, by as much as 200^ in some cases, than the general cost
data given in Appendix A.
522
-------
RPLE 24-2
, u ^ 1
S*u: -j
In--1 kTu'.or
5'-'
C.-ul'-.'f '3 _ .
as.2 - tt, 30 < 09. vr. j^cttLcg jt
Sv.lds fading
ighly i
PTLlTHT aumCTP.TSTIJS - ZKl&rATlM
ral
l-i0"
4 « «r A\ \ < U\
s< S
&\HCC
.V)»5J < 50, r-g.
40 < so
27«4i < 20, avg.
< J5 c X
2J-M < Id. avg.
?; < >p
1I.5-J3.5 c 2,
J.',.;. IJ.e^
veiur-'*.
Riir^r: C. 1-O.D
at l?t CD., avg.
0.4 '
1 Resistivity Moisture Swotent
Fly Ash
Sic.: 14-51'
Al2£3: 0-20
FegCi: 4-19
CaC:~9-22
JfcO; 2.8*3.4
SfcgO - K/-0:
9-10
Ti0at
Also, organic
•eld* and priy-
nu clear hydro-
Sr* ricare 24-? fc.r
detailed Jaia
NOT REPRODUCIBLE
e ospft.'.lT.ir.r, sf
refuse t±rr.cd
.'rsa-rci'i.i
la 'nerav.'r
0.06-0.5 at. Iv*
CO .. ava. 0.?
.K-y f P*.rr. ; i)
Inclr-fV.ar
t vfr;-u.? to
v< •.
Flune.bl.12ty :>r I Lsg
miu SHi£Hii£li£=
rp-!.-*:
Properties
j;.. ir.?:«tcr
ui'iTafn." watc;
iciull'f c»-
p«n»n:s
Dlfflc\i-t to
Ai/.ii'tcf.w
Ir.-
•ir.-r i'vr
Ccnnin- wo*- r
-ra.-
y.n-.T.T.'
D^rr.cjit
wr t
1 :) ;4-:50, *vfi.
.0
i;
srs-vj;
t?. c:. v;.
H2L
CC,: 3.?
Tv«laJ'.j
i:r
;;
¦ i':!
rsTusp burLrd r«fuJe birn-jJ
cc: o.:
K-: 64.C
K-0: ifi
Also * "
Ir."ir.T::cr
'») O.O:-.
(iidtad
CCp, CO, Xf,
crr» H'.C
(,) '
'Lisitcu
¦iata)
, VC„, Co
of U:a
pl«td
f,'*e Kry, 7»M« --1, C>j»?ter pag<* 45, tf>r unite for individual effljrnt properties.
523
-------
TABLE 24-3
AIR POLLUTION CONTOOL SYSIfM AVERAGE CON TOOL EFFICIENCY-^
APC System Removal Efficiency (vt. )
lype
Mineral
Particulate
Combustible .
Particulate^'
Carbon
Monoxide
Nitrogen
Oxides
Hydro-
carbons
Sulfur
Oxides
Hydrogen
Chloride
Polynuclear .
Hydrocarbons—'
Volatil<
Metals^-
None (Flue Settling Only)
20
2
0
0
0
0
0
10
2
Dry Expansion Chamber
20
2
0
0
0
0
0
10
0
Wet Bottcm Expansion Chamber
33
4
0
7
0
0
10
22
4
Spray Chamber
40
5
0
25
0
0.1
40
40
5
Vetted Wall Chamber
35
7
0
25
0
0.1
40
40
7
Vetted, Close-Spaced Baffles
50
10
0
30
0
0.5
50
85
10
Mechanical Cyclone (Dry)
70
30
0
0
0
0
0
35
0
Medium Energy Wet Scrubber
90
80
0
65
0
1.5
95
95
80
Electrostatic Precipitator
99
90
0
0
0
0
0
60
90
U)
ro
a/ Assumed primarily < 5 |i,
b/ Assumed two-thirds condensed on particulate, one-third as vapor.
c/ Assumed primarily a fume < 5 n,
-------
TAT
24-4
Incineration Systems
DISTRIBUTION AIC TYPICAL ECONOMICS AMON:
INCINERATORS A NT' APC CONCEPTS.!/
Average
1966
Inventory TFD
/I V CI Cfc&C
CapacityS/ Investment
$/T
c.d/
Operating Costs
_ $/?on^
Tvre
10.
11.
12.
13.
14.
15.
Continuous, Refractory, Rocking Grate
Continuous, Refractory, Reciprocating
Grate
Continuous, Refractory, Traveling Grate
Continuous, Refractory, Grate & Kiln
Batch, Refractory, Circular
?atc;i, Refractory, Rectangular Cell
Batch, Refractory, Hearth
Continuous, Water Wall, Rocking Grate
Continuous, Water Wall, Reciprocating
Grate
Continuous, V.'ater Wall, Traveling Grate
Cont.naous, Water Wall, Suspension
Burning
Continuous,
Continuous,
Continuous,
Continuous,
_a /
Slagging Type 1^/ ,
Slagging Type 11^''
Fluid Bed
Pyrolyals
Total
7.30$
4.20
20.87
7.05
24.30
23.13
13.15
0.00
0.00
0.00
0.00
0.00
0.00
0.00
C.OO
100.00$
225
225
225
300
130
150
75
350
350
350
30C
175
225
60
100
$ 6,400
6,400
S,400
3,900
5,350
5,100
5,100
6,750
C-,750
6,750
2,350
11,600
6,400
16,400
7 ,250
$ 6.16
6.16
6. 16
5.75
6.59
7.16
6.56
5. 4fc
5.46
5.4fc
6. OG
6.63
G. 16
21.25
11.54
APC Systems
1. None (Flue settling only) 17.40$ 110 0.C5
2. Dry Expansion Chancer 21.65 140 0.05
3. '..'et Sot torn Expansion Cnaniber 2.09 170 0.14
4. Spray Chamber 12.15 175 0.30
5. Wetted Wall Chamber 16.87 175 0.30
6. "Wetted, Close-Spaced Baffles 15.64 215 0.32
7. Mechanical Cyclone (dry) 9.22 340 0.77
[ediun Energy, Wet Scrubber 4.78 760 0.32
3. Electrostatic precipitator 0.00 900 O.SS
0. Fabric Filter 0.00 900 1.10
Total 100.00$
Slagging Type I comprises systems where a major port of the syster. is maintained at
temperatures > 2800°F.
£/' Slagging Type IX comprises systems where residue fusion taker place almost or entirely
as a separate operation.
2,/ Capacity expressed in units of tons per 24-hr. day (TPS).
d/ 19c2 dollars, 2 shift/day operation.
525
-------
TABLE 24-5
MAXIMUM DEMONSTRATED COLLECTION TZFFTCTmCY
OF INCINERATOR CONTROL EQUIB£EM=/
Collection Device
Settling Chamber
Wetted Baffles
Cyclones
Impaction Scrubbers (with
pressure drop less than
ten inches of water)
Collection Efficiency (%)
35
53
75 to 30
94 to 96
Electrostatic Precipitators
99 +
526
-------
10"
10"
tlJ
10*
-110*
O INSTALL ATtON NO. I
D INSTALLATION NO.2
A INSTALLATION NO. 3
10*
0 100 200 300 400 500 600 700
TEMPERATURE-'F
Figure 24-2 - Electrical Resistivity cf the < 74= g, Fracti
of Particulate Emission from the Furnace
at 6$ Water Vapor
527
-------
6.00
4.00
3.00
£2.00
0 1.00
* .90
5 .80
^ .70
1 .60
£ .50
.40
Settling Chamber
10
20
40
60 80 100
200
400
600
Capacity (lO^acfm)
Figure 24-3 - Air Pollution Control Systems Total Installed Costsi/
528
-------
300
200
15" AP Scrubber
Fabric Filter
6" AP Scrubber.
99% Precipitator
> 60
£ 50
95% Precipitator
5" AP Cyclone
3 V AP Cyclone
Settling Chamber.
For: t Shift Per Day
-4— (2000 Hours Per Year!
10
100
30 40 50
200 300
20
Capacity (10^ acfm)
Figure 24-4 - Air Pollution Control Systems Ar.nual Operating Costs±.
(l 3hif*u/Day - 2,000 Hr/Year)
529
-------
300
200
15"AP Scrubber
100
90
5" AP Scrubber
Fabric Filters
99% Precipitator
95% Precipitator
5" AP Cyclone
> 60
£ 50
£ 40
3'/," AP Cyclone
Settling Chamber
4~
For: 2 Shifts Per Day
(4000 Hours Per Year)
100
Capacity (103 acfm)
200 300
Figure 24-5 - Air Pollution Control Systems Annual Operating Costs!/
(2 Shifts/Day - 4,000 Hr/Year)
530
-------
300
15" AP Scrubber
200
5"AP Scrubber
Fabric Filter
100
99% Precipitator
95% Precipitator
5" AP Cyclone -
s
2
o
«
§
8
Settling Chamber
9*
m
For: 3 Shifts Per Day
(6000 Houn Per Year)
100
20
30 40 50
200 300
10
Capacity (10^ acfm)
Figure 24-6 - Air Pollution Control Systems Annual Operating Cos
(3 Shifts/Day - 6,000 Hr/Year)
531
-------
Figures 24-7 and 24-6 indicate the relationship "between collec-
tion efficiency and total annual cost (including capital charges). Table
24-6 summarizes the relative in-plant space needs for the air pollution
control systems (disregarding auxiliary facilities such as settling ponds,
clarifiers, etc.).2/
Reference 10 describes a study of a proposed 800 ton/day incin-
erator plant for the District of Columbia. Estimated capital and operating
costs for an electrostatic precipitator preceded by a cyclone and for a
wet-scrubber system are shown in Table 24-7. 12/ The costs shown are as
much as 200-300$ higher than costs computed from data in Table 24-4. The
advantages and disadvantages of both systems were discussed in Reference
10. It is pointed out that the wet scrubber requires a rather extensive
water conditioning system and also produces a large vapor plume which may
be objectionable. The electrostatic precipitator system had not previously
been used in the U. S. and may have potential operating problems such as
corrosion, fouling, and inefficient collection of large, flaky particulate
matter. Mention was made of the installation of a pilot baghouse on the
municipal incinerator of the city of Pasadena, California. However, it was
concluded that a baghouse filter should not be considered due to lack of
sufficient satisfactory experience.12./
The cost of applying various types of control equipment to two
municipal incinerator designs has also been calculated as shown in Tables
24-8 and 24-9.ill
12/
These data are for a 2d0 ton/day furnace and control
equipment efficiencies are typical for that generally attributed to these
devices, except that electrostatic precipitators and high-energy wet scrub-
bers can exceed 99# efficiency but, of course, their cost is higher. Con-
struction costs include cost of cooling chamber, ash separating cyclones,
strainers, pumps, baffles, collector, and induced-draft fans as applicable
to each alternate. Breechings and stacks are not included. Cooling water
and power costs are computed on a 5-1/2 day week, 24 hr/day, 52 weeks/year,
at $0.30/1,000 gal and $0.02/kw-hr.il/ These cost data indicate higher
control costs (by as much as 200$) than Table 24-4. However, the operating
costs are in closer agreement.
Although not a control device, it should be pointed out that the
present excess air and the quantity of underfire air can have a very sig-
nificant effect on the particulates discharged from an incinerator. This
will be reflected in the emission and the operation of any associated con-
trol devices .J^/
532
-------
— —
'
7
As
7
u
01
A
Ji
^ • ^1 6
4
/
Ay
V
> x;
6
/
jC
r' /
2)/{\
//
' Oa
/ ,
'/
<
•
Y)
/
//
V
i
i/\
/
LE
GEN
D
e nrs/ Ci
t n.
i
f
1 seining ^namoer o 3370 tn. rietipiwiui
2 3V4" AP Cyclone 6 Bag Filter
3 5" AP Cyclone 7 5" AP Scrubber
4 99% Eff. Precipitator 8 15" AP Scrubber
O 3 Shifts Per Day
A 2 Shifts Per Day
O 1 Shift Per Day
150 TPD Plant
i i i l III
a
i
10 20 30 40 50 60 70 80 90 95
Percent Efficiency
98 99
99.99
Figure 24-7 - Total Annual Operating Cost vs. Particulate Removal
Efficiency, 150 Tons/Day Plant; 1, 2, and 3 Shift
Operations/
533
-------
too
80
40
300 Ton/Day Plant
150 Ton/Day Plant
& 20
07
LEGEND
1 Settling Chamber
2 3>4"AP Cyclone
3 5"AP Cyclone
4 99% Eff. Precipitator
5 95% Eff. Precipitator _
6 Bag Filter
7 5"AP Scrubber
8 15"AP Scrubber
A 300 TPD- 141,000 cfm
O 150 TPD-70,500 cfm
2 Shifts/Day
10
20 30 40 50 60 70 80
90 95
98 99
99.8 99.9 99.95 99.99
Percent Efficiency
Figure 24-8 - Total Annual Operating Cost vs. Particulate Removal
Efficiency, 150 and 300 Tons^Day Plant; 2-Shift
Operation^/
534
-------
TABLE 24-6
RELATIVE IN-PLANT SPACE REQUIREMENTS FOR
~AV3RAGE AIR POLLUTION CONTROL SYSTEMS!/
Relative Space Require-
Equippent Type ment (j>)
Eaghouse filter 100
Electrostatic precipitator 90
Scrubber - spray type 50
flooded plate 30
Venturi 25
Mechanical cyclone -
multiclone 25
60 in. diameter tangential inlet 30
wetted wall 25
Settling chamber with sprays 60
TABLE 24-7
ESTIMATED CAPITAL AKD OPERATING COSTS FOR TWO CONTROL SYSTEMS
FOR AN 800 TOST/DAY IHCIKERATCRIQ/
Capital Annual Operating
Cost Cost
(»> (*)
Electrostatic precipitator
with mechanical collector 2,409,200 512,500
High energy scrubber 1,838,600 401,000
525
-------
TABLE 24-8
REFRACTORY FURNACE (250 TONS/DAY)
(1966 Costs) 11.12/
Annual
Annual
Annual
Annual
Water
Power
Maint.
Arao rt. •
Cost/K)]
Efficiency
Stack
Construction
Cost
Cost
Cost
Cost
Burned
Equipment
(#)
Outlets/
Cost ($)
(*)
($)
(*>
(t)
Baffled Spray Chamber
50
1.75
188,200
32,700
6,450
23,700
13,900
0.77
Spray Chamber/Cyclone
78
0.77
237,650
32,700
51,600
10,300
17,550
1.12
Wet Scrubber
96
0.14
400,900
58,400
105,300
16,800
29,400
2.10
Spray Chamber/Precipitator
95
0.175
434,910 = 1,700
32,700
35,300
10,300
32,100
1.10
Spray Chamber/Fabric
Collector
99 +
< 0.035
622,310
36,600
47,200
33,100
46,100
1.63
a/ Pounds of particulate/1,000 lb gas at 50$ excess air.
a
cr>
TABLE 24-9
WATER COOLED FURNACE (250 TONS/DAY)
( 1966 Costs) 11.12/
Annual
Annual
Annual
Annual
Water
Power
Maint.
Amort.
Cost/Tc
Efficiency
Stack
Construction
Cost
Cost
Cost
Cost
Burned
Equipment
(*)
0utlet§/
Cost ($)
(*)
(*)
(*>
(*)
(*)
Cyclone
78
0.77
91,300
29,600
2,000
6,800
0.38
Precipitator
96
0.175
210,300
14,600
9,000
15,600
0.39
Fabric Collector
99+
< 0.085
243,000
34,400
12,100
18,000
0.65
a/ Pounds of particulate/1,000 lb gas at 50$ excess air.
-------
24.2.3.1 Spray Chambers and Wetted Baffles: The most effective
spray chambers are those utilizing continuously vetted baffles. The mere
effective of these involve tortuous gas passages and attendant larger pres-
sure drops, Sprayed-baffle systems with flue-gas pressure drops lower
than 0.5 in. are necessary if the use of ar. induced draft fan is to be
avoided. The chamber in which the baffles are installed is normally de-
signed for a baffle slot velocity not exceeding 3,000 ft/min. The water con-
sumption for sprayed baffle systems is normally about 0.5 gpm/ton of re-
fuse burned per day. Natural draft sprayed-baffle systems are capable of
meeting a criterion of 0.83 lb. of particulate/1,000 lb of flue gas (at 50$
excess air) but may not be suitable for more stringent criteria.il/ The
efficiency of wetted baffle collectors on two municipal incinerators has
been reported as 53$ and 10$.^-ii5/
Conversion of a wetted-baffle municipal incinerator to employ
neutralization of the water with soda ash to permit recirculation has shown
that the savings in water usage will amortize the cost of the additional
facilities in less than two years.—/
24.2.3.2 Wet Scrubbers: Wet scrubbers have been used in a few
municipal incinerator applications. Water circulation rates required in
scrubbers are high, and this may introduce a disposal problem or require
treatment equipment tc permit recirculation. The power requirements for
the pumps that provide the spray water and for the induced-draft fan sys-
tem are significant and should be considered in any evaluation.ii/ The
scrubbers are capable of removing gaseous air pollutants but, in so doing,
the acidic solutions that result will require special selection of mate-
rials of construction.—/
It is reported that a Chemico Venturi scrubber is operating on
the East 73rd Street incinerator in New York City and is controlling emis-
sions to less than 0.05 grain/scf,—/
24,2.3.3 Electrostatic Precipitators: Several electrostatic
precipitators have been installed and successfully operated in Europe.
Some have also been installed in the U. S., as shown in Table 24-10.Ei/
Several devices with collection efficiencies of over 95$ are scheduled
for new and existing units.—' The 1,200 tons/day Des Carrieres Plant in
Montreal was to be built with an electrostatic precipitator. M/
The electrostatic precipitator is capable of high collection
efficiencies at low pressure drop. Gas cooling is required for protection
cf the precipitator from excessive temperatures. Although precipitators
do not require the use of an induced-draft fan, such use is normal, pri-
marily to produce a steadier rate of combustion and consequent rate of gas
flow, thus making performance more reliable and more predictable. li/
537
-------
TABLE 24-10
ELECTROSTATIC PRECIPITATORS INSTALLED OK MUNICIPAL
INCINERATORS IK NORTH AMERICA^/
Location
Collector
Manufacturer
Refractory Units
City of Stamford, Connecticut
NYC South Shore Brooklyn
NYC Southwest Brooklyn
Dade Cour.ty, Florida
Water-Wall Units
City of Montreal, Quebec (Von Roll)
City of Braintree, Massachusetts
(Detroit Stoker)
City of Hamilton, Ontario
( C&E Bciler)
City of Chicago, Illinois
Univ. Oil. Prod. (Aerctech)
Research-Cottrell
VJheelabrator/Lurgi
Kheelabrator/Lurgi
Research - Cottrell
Wheelabrator/Lurgi
Wheelabratcr/Lurgi
Vade/?.cthenuhle
Major characteristics of European electrostatic precipitator
units are shown in Table 24-11. !§/ The success of their ur.its is attributed
to differences in the design of furnaces, grates and auxiliary equipment.
TABLE 24-11
BASIC DESIGN ELEMENTS OF EUROPEAN ELECTROSTATIC PRECIPITATORS.^/
27 Incinerator Plants
52 Precipitator Units
Size of Furnaces (tens/day)
Raw Gas Volume ¦ cfs)
Dust Lead in Raw Gas
(lb/l,000 lb gas)
Gas Entry Temperature ( °F)
Overall Particulate Cleansing
Efficiency (percent)
Range
Median
to 1,060
270
to 7,200
1,450
to 12.3
5.'
to 520
490
tc 99.5
95. (
538
-------
A Swedish article describes the use of multicyclone after collec-
tors following an electrostatic precipitator to reduce emission of paper
flakes which are difficult to collect in the precipitator due to their
large area, low specific gravity and lew resistivity.HU
24.3 COMMERCIAL INCINERATORS
Commercial and industrial incinerators fcr burning general refuse
may be either single- or multiple-chamber types. The multiple-chamber units
are usually associated with large institutional or industrial facilities,
while the smaller single-chamber furnaces are used by markets and restaurants.
24.3.1 Emission Sources and Rates
While there are many factors involved in controlling the gaseous
and other combustible emissions from commercial types of incinerators,
the most important single factor is to maintain a sufficiently high tem-
perature for good combustion. Temperatures above 1000'F can be maintained
when burning refuse of low moisture content ( after the initial warmup) by
maintaining a relatively uniform release of heat from the refuse. This
procedure requires frequent charging and stoking by a well-trained operator.
In the majority of cases, it is not economically feasible to provide a
full-time operator; most incinerators are operated by a janitor or custodian
who has many other duties. Therefore, auxiliary fuel has been found to be
necessary in airiest all cases to maintain temperatures above 1000°F. High
temperatures (plus excess air, turbulence,and residence time) effectively
oxidize unburned gases and combustible particles and droplets.
Small-sized commercial incinerators with relatively poor com-
bustion produce larger emission rates for polynuclear hydrocarbons than
the intermediate and large-sized municipal units. The higher temperatures
and longer residence times characteristic of the municipal incinerators
account for the lower rates cf polynuclear hydrocarbon emission in these
units ..!§/
Pathological waste incinerators differ from the standard multiple-
chamber unit in several respects. Major differences are the use of large
burners in the primary chamber, side loading rather than front loading,
a solid hearth rather than a grate, and a somewhat different arrangement
of the chambers.
No data were found on tonnage of material burned in these units,
and estimates of the current level of particulate emissions from commercial
and industrial incinerators were not attempted.
539
-------
24.3.2 Effluent Characteristics
The physical and chemical properties of effluents from industrial
and commercial incinerators are outlined in Table 24-2. Limited data are
available for these units. Particulate matter emitted is probably larger
in size than that discharged from municipal incinerators because of lower
quality combustion.
Grain loadings given in Table 24-2 are for units in which good
combustion was attained. If these conditions are not met and poor com-
bustion results, clouds of dense smoke are emitted and particulate load-
ings will be much higher than those shown in Table 24-2.
24.3.3 Control Practices and Equipment
Single-chamber units have generally proven inadequate to meet
most emission regulations. Multiple-chamber units produce minimum emis-
sions but may require a good gas washer to meet more stringent regulations.
NAPCA has tentatively found that scrubbers having at least l/2 in. H2O
pressure drop and a water rate of 4 gal/l,000 cfm are required on incin-
erators tc meet emission standards for Federal facilities.9/
Design factors for multiple-chamber incinerators are presented
and discussed in Reference 3. Initial incinerator cost depends mainly on
the capacity of the unit and the degree of air pollution control desired.
In a 1966 article, concerning industrial and household incinerators, E. M.
Voelker of the Incinerator Institute of America presented the cost of
incinerators with varying degrees of control, as shown in Figure 24-9„i§./
24.4 APAR3ME1
-------
500 1,000 1,500
CAPACITY OF INCINERATORS (LB/HR)
2,000
Figure 24-9 - Capital Cost of Incinerators with Varying Degrees of
Air Pollution Control Equipmentii/
541
-------
24,4.2 Effluent Characteristics
The chemical and physical characteristics of effluents from
apartment house incinerators are summarized in Table 24-2. Limited data
are available for these units. Poor quality combustion is probable for
these units and particulate matter emitted is larger in size than that
discharged from municipa] units.
24.4.3 Control Practices and Equipment
Preventing the discharge cf air pollutants from this type of in-
cinerator involves the use of afterburners or conversion to multiple-chambe
¦zl
incineration.—/ Test data, including costs, for various secondary combus-
tion devices and a Peabody gas scrubber are shown in Tables 24-12 and 24-13
Scrubbers which increase the velocity cf the gases and contact
them with low-velocity water appear to be preferable to spray nozzle units
because plugged nozzles reduce collection efficiency. Evaluation cf im-
pingement-type scrubbers operating at pressure drops in the range of 4 to
8 in. w.g. on flue-fed incinerators indicates efficiencies in the range cf
73 to 94$.22/
A preliminary test cf a dry cyclone or. a flue-fed apartment in-
cinerator showed deposition of fats on the cyclone surface indicating
eventual clogging in servic e.2l/
542
-------
TABLE 24-12
PEABODY SCRUBBER PERFORMANCE OH FLUE-FED
APARTMENT INCirCSRAIORSjg/
Refuse charge, lb/test 275
Scrubber operating time, min. 96
Scrubber exhaust, avg. cfm
(corrected tc 70°F, 29.22 in. Hg) 2,S70
Gas temperature, °F
Scrubber inlet, range 153-250
Average 196
Scrubber outlet, range 94-108
Average 102
Scrubber trays, number in use 2
Pressure across fan, in. w.g. 7.6
Electric consumption, fan kw. 5.35
punp kw. 0.4
Scrubber water
Input, gal/hr 60
Evaporated, gal/hr 24
To drain, gal/hr 36
Emissions
Particulate matter, lb. for test
Collected by scrubber water, avg. 1.88
Ir. exhaust, avg. 0.12
Scrubber collection efficiency, $ 94
Noxious gases, lb. for test, avg.
In flue gas before scrubber 8.33
In scrubber exhaust 6.92
Removed by scrubber, difference 1.91
Removal efficiency for noxious gases, $ 21.6
543
-------
TABLE 24-13
PERFORMANCE AND COST OF DEVICES INSTALLED ON APARTMENT INCINERATOR^/
Basic
Incinerator
Werner
Device
One Pipe
Overfire
Jets
Hartmann
Device
Gas
Burner
and
Overfire
Jets
Peabody
Scrubber
Peabody
Scrubber
and
Overfire
Jets
en
it*
it*
Daily Operation, minutes
Burning only (no. of burns)
Residue removal
Total min., hoppers locked
Furnace Capacity, lb
Emissions, lb/lOO lb of charge
Particulates
Noxious gases
183(2)
15
198
275
1.31
2.48
38(2)
15
53
240
1.29
3.01
141(2)
15
156
275
0.79
1.61
24(fi/(3) 125^/(2) 183(2)
15 15 15
255 140 198
200
0.72
1.75
275
0.51
0.73
275
O.IS^/
1.94£./
141(2)
15
156
275
0.09^/
1.26£/
Cost
Investment
Annual, total
Annual, per room
$1,200
166
$0.30
$2,700
426
$0.83
$1,600
250
$0.49
$3,150
1,292
$2.52
$2,200
1,117
$2.18
$5,200
1,072
$2.09
$5,600
1,151
$2.25
a/ Adjusted for equal burn-out of residue,
b/ Based on 90$ collection of particulate matter.
c_j Based on 22$ removal of noxious gases.
-------
REFERENCES
1. Xiessen, W., et al., "Systems Study of Air Pollution from Municipal
Incineration," prepared by A. D. Little, Inc., for the National Air
Pollution Control Administration, Contract No. CPA 22-69-23, 1970.
2. Bogue, M. E. V., "Municipal Incineration," presented at New York State
Health Department In-Service Training Course, Albany, New York,
December 1, 1965.
3. Danielson, J. A., Ed., Air Pollution Engineering Manual, PKS No. 999-
AP-40, Cincinnati, Ohio, Public Health Service, 1967.
4. I. I. A. Incinerator Standards, Incinerator Institute of America, New
York, New York, May 1966.
5. Stenburg, R. L., et al., "Effects of Design and Fuel Moisture on Inciner-
ator Effluents," Journal of the Air Pollution Control Association 11,
1966.
6. Stenburg, R. L-, et al., "Field Evaluation of Combustion Air Effects on
Atmospheric Emission from Municipal Incinerators," Journal of the Air
Pollution Control Association 12, 1962.
7. Walker, A. 3., and F. W. Schmitz, "Characteristics of Furnace Emissions
from Large, Mechanically Stoked Municipal Incinerators," Proceedings
of 1966 National Incinerator Conference, pp. 64-73, American Society
of Mechanical Engineers, New York, 1966.
8. Stenburg, R. L., R. P. Hangebrauck, D. J. Lehmden, and A. H. Rose, Jr.,
"Effects of High Volatile Fuel on Incinerator Effluents," presented
at the Annual Meeting of the Air Pollution Control Association, June
1960, Paper No. 60-67.
9. U. S. Department of Health, Education and Welfare, Control Techniques
for Particulate Air Pollutants, Washington, D. C., January 1969.
10. Day and Zimmermann, Engineers and Architects, Special Studies for
Incinerators for the Government of the District of Columbia Department
of Sanitary Engineering, Cincinnati, Ohio, Public Health Service,
1968.
11. Fife, J. A., and R. H. Boyer, "What Price Incineration Air Pollution
Control," Proceedings of 1966 National Incinerator Conference,
American Society of Mechanical Engineers, New York.
545
-------
12. Bump, R. L., "The use of Electrostatic Precipitators on Municipal
Incinerators," Journal of the Air Pollution Control Association 18,
December 1968.
13. Rose, A. H., "Air Pollution Effects of Incinerator Firing Practices
and Combustion Air Distribution," Journal of the Air Pollution Control
Association 8, February 1959.
14. Fife, J. A., "Control of Air Pollution from Municipal Incinerators,"
Panel "D," Solid Waste Disposal, December 1965.
15. Jens, W., and F. R. Rehm, "Municipal Incineration and Air Pollution
Control," Proceedings of 1956 National Incinerator Conference, American
Society of Mechanical Engineers, Sew York.
16. Rogus, C. A., ''Control of Air Pollution and Waste Keat Recovery from
Incineration," Public Works 97, June 1966.
17. Cederholm, C., "Collection of Dust from Refuse Incinerators in Electro-
static Precipitators Provided with Multicyelone After-Collectors,"
Proceedings of the International Clean Air Congress, 1966.
18. Hangebrauck, R. P., et al., "Emissions of Polynuclear Hydrocarbons
and Other Pollutants from Heat-Generation and Incineration Processes,"
Journal of the Air Pollution Control Association 14, July 1964.
19. Voelker, E. M., "Control of Air Pollution from Industrial and Household
Incinerators," Panel "D," Solid Waste Disposal, December 1966.
20. Kaiser, E. R., et al., "Performance of a Flue-Fed Incinerator," Journal
of the Air Pollution Control Association 9, August 1959.
21. Kaiser, E. R., "Modifications to Reduce Emissions from a Flue-?ed
Incinerator," Journal of the Air Pollution Control Association 10,
June 1960.
22. Walker, A. 3., "Air Pollution Control Equipment for Incinerators,"
Proceedings of MECAR symposium.
23. Private communication with T. W. Devitt, National Air Pollution Control
Administration, Cincinnati, Ohio.
24. "Electrostatic Precipitator System Study" by Southern Research Institute
for the National Air Pollution Control Administration, Contract CPA
22-69-73.
546
-------
APPENDIX A
ECONOMIC CONSIDERATIONS IN AIR POLLUTION CONTROL
This appendix, illustrating cost relationships for the various
types of collectors, has been taken from Chapter 6 of "Control Techniques
for Particulate Air Etellutants," U. S. D. H. E. W., Washington, D. C., 1969.
It contains three curves for each type of collector showing purchase cost,
installed cost, =nd annualized cost of operation, as a function of gas
volume handled i.r; acfm. It a].so contains cost data and equations for the
determination of operating and maintenance cost for each type of collector.
This cost information contains an explanation of all assumptions
and cost bases used. It is included as a basis for cost comparisons with
data presented in the industry chapters and as a source of data for the
reader's own use in estimating the cost of collection equipment.
A.l SELECTION OF CONTROL SYSTEM
Most air pollution emission control problems can be solved in
several ways. In order to select the best method of reducing pollutant
emissions, each solution should be thoroughly evaluated prior to imple-
mentation. Steps such as substitution of fuels and raw materials and modi-
fication or replacement of processes should not be overlooked as possible
solutions. Such emission reduction procedures often can improve more than
one pollution problem. For example, particulate matter and sulfur oxides
emissions both may be reduced by switching from high-sulfur coal to natural
gas or low-sulfur oil. Such steps also may have the benefit of reducing
or eliminating solid waste disposal and water pollution problems. Often
it is cheaper to attack two air problems together than to approach each
problem individually. If steps such as process alterations and substitution
of fuels are not feasible, it may be necessary to use gas-cleaning equipment.
Figure A-l shows the factors to be considered in selection of
gas-cleaning system. The first consideration is the degree of reduction of
emissions which may be required to meet emission standards. The degree of
emission reduction or the collection efficiency required is dependent upon
the relationship between emissions and emission standards as shown at the
top of the figure. This is an important factor in making the choice among
control equipment alternatives. Although a control system may include two
or more pieces of control equipment, collection efficiency, as used in this
chapter, applies to individual pieces of control equipment. The usual ranges
of collection efficiency for various equipment alternatives are shown in
547
-------
EMISSIONS AND EMISSIONS
STANDARDS
DETERMINES COLLECTION EFFICIENCY
FABRIC
FILTER
CONTROL EQUIPMENT ALTERNATIVES
MECHANICAL
COLLECTOR
ELECTROSTATIC
PRECIPITATOR
WET
COLLECTOR
AFTER
BURNER
y VOLUME
35 TEMPERATURE
2= MOISTURE CONTENT
«ui CORROSIVENE5S
vi y ODOR
2< EXPLOSIVENESS
0< VISCOSITY
X
u
PROCESS
v>
IGNITION POINT c
SIZE DISTRIBUTION iu»
ABRASIVENESS -J 5
HYGROSCOPIC NATURE
ELECTRICAL PROPERTIES £5
GRAIN LOADING <<
DENSITY AND SHAPE 5
PHYSICAL PROPERTIES ?
EXPLOSIVENESS 0
I
WASTE TREATMENT
SPACE RESTRICTION
PRODUCT RECOVERY
PLANT
FACILITY
WATER AVAILABILITY
FORM OF HEAT RECOVERY
(GAS OR LIQUID)
'
POWER
ENGINEERING STUDIES
WASTE DISPOSAL
HARDWARE
WATER
AUXILIARY EQUIPMENT
COST OF
CONTROL
MATERIALS
LAND
GAS CONDITIONING
STRUCTURES
LABOR
INSTALLATION
TAXES
START-UP
INSURANCE
RETURN ON INVESTMENT
« .. i ¦
SELECTED
GAS-CLEANING SYSTEM
J
DESIRED EMISSION RATE
Figure A-l - Criteria for Selection of Gas-Cleaning Equipment
548
-------
Table A-l. The important factors to "be considered next are the gas stream
and particle characteristics of the process itself, as shown in the center
of Figure A-l. High gas temperatures without cooling, for example, preclude
the use of fabric filters; explosive gas streams prohibit the use of electro-
static precipitators; and submicron particles cannot generally be efficiently
collected with mechanical collectors. A number of factors that relate to
the plant facility should also be considered, some of which are listed in
Figure A-l. Each alternative will have a specific cost associated with it,
and the components of this cost should be carefully examined. Those alter-
natives which meet the requirements of both the process and the plant facility
can then be evaluated in terms of cost; on this basis, the gas-cleaning
system may "be selected.
TABLE A-l
AIR POLLUTION CONTROL EQUIMENT
COLLECTION EFFICIENCIES!^/
Equipment Type
¦MMMdfeMMMMdlkMMMMMMMMMMMMMBdiMdfefaMMMI
Electrostatic precipitator®/
Fabric filters*!'
Mechanical collector
Wet collector
After burner:
Catalytic^
Direct flame
Efficiency Range
(on a total weight basis)
m
80 to 99.5+
95 to 99.9
50 to 95
75 to 99+
50 to 80
95 to 99
a/ Most electrostatic precipitators sold today are designed for 98 to 99.5$
collection efficiency,
b/ Fabric filter collection efficiency is normally above 99.5$.
c/ Not normally applied in particulate control; has limited use because
most particulates poison or desensitize the catalyst.
A.2 COST-EFFECTIVENESS RELATIONSHIPS
Meaningful quantitative relationships between control costs and
pollutant reductions are useful in assessing the impact of control on product
prices, profits, investments, and value added to the product.* With such
* Value added is generally considered to be the economic worth added to a
product by a particular process, operation, or function.^'
549
-------
relationships at hand the alternates for solution of an air pollution problem
can be evaluated for more effective program implementation by the user of
the control equipment and by the enforcement agency. These cost-effectiveness
relationships sometimes are applied collectively to a meteorological or air
quality control region, where they describe the total cost impact on pol-
lsters as a result of controlling sources; the discussion here, however,
centers around cost-effectiveness as applied to an individual source. Cost-
effectiveness is a measure of all costs to the firm associated with a given
reduction in pollutant emissions. For computing the costs for a given system,
one should consider (l) raw materials and fuels used in the process, (2)
alterations in process equipment, (3) control hardware and auxiliary equip-
ment, and (4) disposal of collected emissions.
Figure A-2 shows an example of a theoretical cost-effectiveness
relationship.2/ The actual total costs of control may depart from this
curve because some cost elements, such as research and development expendi-
tures and fixed charges (taxes, insurance, depreciation) are not directly
related to the operation of the equipment and to the level of emissions in
a given year. The cost of control is represented on the vertical axis and
the quantity of pollutants emitted on the horizontal axis. Riint P indicates
the uncontrolled state, in which there are no control costs. As control
efficiency improves, the quantity of emissions is reduced and the cost of
control increases. In most cases, the marginal cost of control is smaller
at the lower levels of efficiency, near Point P of the curve. The curve
also illustrates that as the cost of control increases, greater increments
of cost usually are required for corresponding increments of emission re-
duction. Process changes sometimes may result in emission reduction with-
out increased costs. Research and development expenditures resulting in
new or improved equipment design, improved process operations, or more
efficient equipment operations will improve the economics of control. All
these factors may substantially reduce control costs at most emission levels
and shift the cost of the control curve (CC) as illustrated by CC]_ in Figure
A-3. Note that as control technology develops, the cost of attaining a
desired emission level will be reduced from
to C>
QUANTITY OF POLLUTANTS
Figure A-2 - Cost of Control
QUANTITY OF POLLUTANTS
Figure A-3 - Expected New Cost of Control
550
-------
Cost-effectiveness information is useful in emission control
decision-making. Several feasible systems usually are available for con-
trolling each source of emissions. In most cases, the least-cost solution
for each source can be calculated at various levels of control. After
evaluating each alternative and after considering future process expansions
and more rigid control restrictions, sufficient information should be avail-
able on which to base an intelligent control decision.
Cost-effectiveness relationships vary from industry to industry
and from plant to plant within an industry. The cost for a given control
system is significantly dependent on the complexity of the installation and
the characteristics of the gas stream and pollutant. Geographical location
is another significant factor that influences the total annual cost; for
example, the components of annual cost, such as utilities, labor, and the
availability of desired sites for waste material, vary from place to place.
A.3 COST DATA
It is the purpose of this Appendix to develop basic information
and techniques for estimating the costs of installing and operating control
equipment. Such information can be useful in developing cost-effectiveness
relationships for application of various control systems.
A.4 UNCERTAINTIES IN DEVELOPING COST RELATIONSHIPS
Cost information for control devices is given in Section A.7
where, for various types of equipment, operating capacity is plotted against
cost. The upper and lower curves indicate the expected range of costs, with
the expected average cost falling approximately in the middle. Although
quantitative values for collection efficiency and gas volume capacity are
not listed, higher collection efficiency, which involves more intricate
engineering design, results in higher costs. Control equipment is designed
for a nominal gas volume capacity, but under actual operating conditions the
volume may vary. Similarly, the efficiency of control equipment will vary
from application to application as particle characteristics, such as wetta-
bility, density, shape, and size distribution, differ. For example, a con-
trol device designed to operate on 50,000 acfm of gas with a nominal collection
of 95$ may have an effective operating range of from 45,000 to 55,000 acfm,
and its collection efficiency may range from 90 to 97$.
The effect of these independent variations is to make single point
estimates of cost versus size and efficiency difficult to determine. Based
on the data available, all estimates must be constructed over an interval of
uncertainty for each of the three variables. To make the cost estimation
551
-------
problem manageable in this report, nominal high, medium, and low collection
efficiencies have been selected for each type of control equipment, except
fabric filters. For fabric filters, the nominal high, medium, and low curves
reflect construction variations. The purchase, installation, ana total annu-
alized costs of operation are plotted for each of the three efficiency levels
over the gas volume range indicated. Purchase, installation, and total annum-
alized costs for fabric filters are plotted for variations in filter construc-
tion and cleaning methods.
Generalized categories of control equipment are discussed rather
than specific designs feecause of uncertainties in size, efficiency, and
cost. If required, more detailed information on the cost of various engi-
neering innovations (e.g., packed tcwers of specific design to accommodate
a corrosive gas stream) should be requested from the manufacturers of the
specific equipment. Cost variations associated with wet collectors are
reported in Table A-2^
Other difficulties exist in developing cost information for
existing control devices, especially cost estimates on the maintenance and
operation of control equipment. Individual firms may remember what a con-
trol device cost originally, but they may forget what it costs to install
and operate. In addition, internal bookkeeping and auditing systems often
bury these expenditures in total plant operating costs. For example, water
and electricity used by a control operation are not always separately metered
and accountable as a specific air pollution control cost item. Some of these
costs can be identified and assessed on the basis of industrial experience
or engineering estimates.
552
-------
TABLE A-2
APPROXIMATE COST OF WET COLLECTORS IN 1965^/
Cost, dollars/cfln
Capacity, cfta
Type of Collector- 1,000 5,000 20,000 40,000
Cyclonic: ]Li£/
Small diameter multiples 0.50 0.30 0.20 0.20
Single chamber, constant
water level 1.40 0.45 0.35 0.25
Single chamber, multiple
stage, overhead line
pressure water feed 0.95 0.40 0.25 0.20
Single chamber, internal
nozzle spray 3.00 1.50 1.00 0.75
Self-induced spray^!^/ 0.80 0.40 0.25 0.25
Wet impingement^^/ 1.00 0.50 0.25 0.25
Venturi^/ 3.00 1.50 1.20 0.50
Variable pressure drop
ir.ertia l£i1.00
MechanicalS-2^/ 1.75 0.75 0.35
0.30
a/ Basic designs, mild steel construction.
b/ Add 30 to 40$ to base price for fan, drive, and motor (standard con-
struction materials).
of Special materials construction costs for 1,000- to 40,000-cftn range
units are approximately as follows:
Rubber lining - base increase of 65 to 115$.
Type 304 stainless steel - base increase of 30 to 60$.
Type 316 stainless steel - base increase of 45 to 100$.
d/ Add from 10 to 40$ to base price per additional stage as in some cyclonic
and wet impingement designs
553
-------
A. 5 DESCRIPTION OF CONTROL COST ELEMENTS
A.5.1 General
The actual cost of installing and operating air pollution control
equipment is a function of many direct and indirect cost factors. An analysis
of the control costs for a specific source should include an evaluation of
all relevant factors, as outlined in Figure A-4. The control system must
be designed and operated as an integral part of the process; this will
minimize the cost of control for a given emission level. The definable con-
trol costs are those that are directly associated with the installation and
operation of control systems. These expenditure items from the view-
point of the control equipment user have a breakdown for accounting pur-
poses as follows:
Capital Investment
Engineering studies
Land
Control hardware*
Auxiliary equipment*
Operating supply inventory
Installation*
Startup
Structure modification
Maintenance and Operation
Utilities*
Labor*
Supplies and materials*
Treatment and disposal of collected material
Capital Charges
Taxes*
Insurance*
Interest*
* Denotes cost items considered in this report.
Of the expenditure items shown above, only those denoted by an
asterisk were considered in developing the cost estimates used in this
Appendix- Other factors, such as engineering studies, land acquisition,
operating supply inventory, and structural modification, vary in cost from
place to place and therefore were not included. Costs for the treatment
and disposal of collected material, while also not included, are discussed
in some detail in Section A.8.
554
-------
OPERATIONAL
VARIABLES INFLUENCING
CONTROL COSTS
GAS-CLEANING SYSTEM
FACTORS INFLUENCING
CONTROL COSTS
Ol
Ol
Ol
ENGINEERING
STUDIES
COST AREAS DETERMINING
THE NET COST OF CONTROL
LAND
WASTE
DISPOSAL
SITE
PREPARATION
TYPE
CONTROL
HARDWARE
VOLUME
( SOURCE I
$
CONSTRUCTION
MATERIAL
AUXILIARY
EQUIPMENT
GAS-CLEANING
SYSTEM
POLLUTANT
EFFICIENCY
INSTALLATION
TYPE
COST
MATERIALS AND
SUPPLIES
PRESSURE DROP
WASTE
MATERIAL
UTILIZATION
MAINTENANCE
AND OPERATION
POWER AND FUEL
BENEFIT
COSTS
CAPITAL
CHARGES
Figure A-4 -
Diagram of Cost Evaluation for a Gas-Cleaning System
-------
A.5.2 Capital Investment
Trie "installed cost" quoted by a manufacturer of air pollution
equipment usually is based on his engineering study of the actual emission
source. This cost includes three of the eight capital investment items--
control hardware ccsts, auxiliary equipment costs, and costs for field instal-
lation.
The purchase cost curves that are shown in Section A. 7 illustrate
the control .hardware costs for various types of control equipment. These
purchase costs are the amounts charged by manufacturer for equipment of
standard construction materials. Basic control hardware includes built-in
instrumentation and pumps. Purchase cost usually varies with the size and
collection efficiency o? the control device. The purchase costs plotted on
the curves are typical for the efficiencies indicated, but these costs may
vary - 20$ from the values shown. Of course, equipment fabricated with special
materials (e.g., stainless steel or ceramic coatings) for extremely high
temperatures or corrosive gas streams may cost much more.
The remaining capital investment items, auxiliary equipment and
installation costs, are aggregated together and referred to as ''total
installation costs." These costs are shown in Table AS, expressed as
percentages of the purchase costs. These costs include a reasonable incre-
ment for the following items: (l) erection, (2) insulation material,
(3) transportation of equipment, (4) site preparation, (5) clarifiers and
liquid treatment systems (for wet collectors), and (6) auxiliary equipment
such as fans, ductwork, motors, and control instrumentation. The low values
listed in the table sire for minimal transportation and simple layout and
installation of control devices. High values are for higher transportation
cost and for difficult layout and installation problems. The extreme high
values are for unusually complex installations on existing process equip-
ment. Table A-4- lists the major cost categories and related conditions
that establish the installation cost range from low to high. The "installed
cost" estimates reported in Section A-7 are the sum of the purchase costs
and the total installation costs.
A.5.3 Maintenance and Operation
The following sections describe the working equations for the
operation and maintenance costs of various control devices. Numerical values
for the variables expressed in these equations are found in Tables A-5 and
A-6.
556
-------
TABLE A-3
TOTAL INSTALLATION COST FOR VARIOUS TYPES OF CONTROL DEVICES
EXPRESSED AS A PERCENTAGE OF PURCHASE COSTS
Cost, Percent
Equipment Type Low Typical High Extreme High
Gravitational 33 67 100
Dry centrifugal 35 50 100 400
Wet collector:
Low, medium energy 50 100 200 400
High energy.^ 100 200 400 500
Electrostatic
precipitators 40 70 100 400
Fabric filters 50 75 100 400
Afterburners 10 25 100 400
a/ High-energy wet collectors usually require more expensive fans and motors.
557
-------
TABLE A-4
CONDITIONS AFFECTING INSTALLED COST CF CONTROL DEVICES
Cost Category
Equipment transportation
Plant t£t
Available apace
Corrosiveness of gas
Complexity of startup
Instrumentation
Guarantee on performance
Degree of assembly
Degree of engineering
design
Utilities
Collected waste material
handling
Labor
Lev Cost
Minima distance; aiaple
loading and unloading
procedures
Hardware designed as an
integral part of new
plant
Vacant area for location
of control system
Noncorrosive gas
Simple startup, no exten-
sive adjustment required
Little required
None needed
Control hardware shipped
completely assonbled
Autonomous "package" con-
trol system
Electricity, water, waste
disposal facilities
readily available
No special trea"taent
facilities or handling
required
Low wages in geographical
area
High Cost
Long distance; complex procedure for loading
and unloading
Hardware installed into confines of Old pleat
requiring structural or process modification
or alteration
Little vacant space requires extensive steel
support construction and site preparation
Acidic eailsslons requiring high alloy accessory
equl;sien.t using special handling and con-
struction techniques
Requires extensive adjustments; testing; con-
siderable down tiAe
Complex instrumentation required to assure
reliability of control or constant monitoring
of gas stream
Required to assure designed control efficiency
Control hardware to be assembled and erected
In the field
Control systen requiring extensive integration
into process, insulation to correct ton-
perature problem, noise abatement
Electrical and waBte trea-^aer.t facilities
Bust be expanded, water supply must be
developed or expanded
Special treatanent facilities and/or handling
required
Overtime and/or high wages In geographical
area
558
-------
TABLE A-5
ANNUAL MAINTENANCE COSTS FOR ALL GENERIC TYPES OF CONTROL' DEVICES
Dollars Per ACIW
ui
CJI
CD
Generic Type
Gravitational and dry
centrifugal collectors
Wet collectors
Electrostatic precipitators:
High voltage
Low voltage
Fabric filters
Afterburners:
Direct flame
Catalytic
Low
0.005
0.02
0.01
0.005
0.02
0.03^
0.07
Typical
0.015
0.04
0.02
0.014
0.05
0.06^/
0.20
High
0.025
0.06
0.03
0.02
0.08
o.ic£/
0.35
a/ Metal liner with outside insulation,
b/ Refractory lined.
-------
1A3LE A-6
MISCELLANEOUS COST AND ESIGIKEE3IUG FACTORS
Fan Efficiency •
60*
Pump Efficiency = 5016
Brrfer Cost
, Dollars/Kllovatt-Hr^'
Low
Typical
High
All devices
0.005
0.C11
0.020
Hou
rs of Operation
0,760 hr/yr - 24 hr/day x
365 days/yr - 8,763
R>wer requirements vs. efficiency for high-voltage
electrostatic precipitators,
10_
3 tcw/acfm
Low
Medium
High
0.19
0.25
0.40
Ibwer requirements vs. efficiency for low-voltage electrostatic precipitators 1C
-
3
to.7 acfc
Low
High
0. CIS
0.040
Liquor cost in 10"^ dollars/gal
(for
wet system)
Low
Typical
High
Wet scrubber
0.15
0.50
1.00
Makeup liquor requirements,
0.0005 gal/hr-acfm
ftrw
"?r Requirements
Low Efficiency
Medium Efficiency
High Efficiency
' Scrubbing' (contact) power, h::rnep~ver/9cfir
0.0013
0.0035
0.015
Scrubber Liquor Data
Low
typical
High
Liquor circulation rate, gal/acfm
0.301
0.006
0.020
b/
MinimuE head requirements, feet water
1-
30
60
Pressure drop through equipment,
.nches of water
Generic Type
Lcw
Typical
High
Dry centrifugal collector
-
2-3
4
Fabric filter
2-3
4-5
6-6
Afterburners
0.5
1.0
2
Electrcstatic precipitators and gravitational
col lectors
0.1
0.5
1
a/ Based on national average of large consumers.
b/ 1 psig « 2.3 ft. water.
560
-------
A.5.3.1 General: The costs of operation and maintenance will
vary widely because of different policies of control equipment users. This
variance will depend on such factors as the quality and suitability of the
control equipment, the user's understanding of its operation, and his vigilance
in maintaining it. Maintenance and operation usually are very difficult to
define and assess, but often may be a significant portion of the overall
cost of controlling air pollutant emissions. Although the combined operating
and maintenance costs may be as low as 10$ of the annualized total cost for
a gravitational settling chamber, for example, they may be as high as 90$
of the total annualized cost for a high-efficiency wet collector.
Maintenance cost is the expenditure required to sustain the operation
of a control device at its designed efficiency with a scheduled maintenance
program and necessary replacement of any defective parts. On an annual
basis, maintenance cost in the following equations is assumed proportional
to the capacity of the device in acfir.. Table A-5 shows annual maintenance
cost factors for all types of particulate control devices. Simple, low-
efficiency control devices have low maintenance costs; complex, high-efficiency
devices have high maintenance costs.
Annual operating cost is the expense of operating a control device
at its designed collection efficiency. This cost depends on the following
factors: (l) the gas volume cleaned, (2) the pressure drop across the
system, (3) the operating time, (4) the consumption and cost of electricity,
(5) the mechanical efficiency of the fan, and (6) the scrubbing-liquor con-
sumption and costs (where applicable).
A.5.3.2 Gravitational and Centrifugal Mechanical Collectors: In
general, the only significant cost for operating mechanical collectors is
the electric power cost, which varies with the unit size and the pressure
drop. Since pressure drop in gravitational collectors is low, operational
costs associated with these units are considered to be insignificant.
Maintenance cost includes the costs of servicing the fan motor, replacing
any lining worn by abrasion, and, for multicyclone collectors, flushing ths
clogged small diameter tubes.
Cost equation - The theoretical annual cost (g) of operation and
maintenance for centrifugal collectors can be expressed as follows:
= S
0.7457 HOC
63563
+ M
(1)
561
-------
where:
S = design capacity of the collector, acfrr.
? = pressure drop, inches of water (see Table A-5)
E = fan efficiency, assumed to be 60$ (expressed as 0.6)
0.7457 = a constant (l horsepower = 0.7457 kilowatt)
H = annual operating time (assumed 8,760 hr.)
K = power cost, dollars/kilowatt-hr (see Table A-6)
M = maintenance cost, dcllars/acfm (see Table A-5)
For computational purposes the cost formula can be simplified as follows:
A.5.3.3. Wet Collectors: The operating costs for a wet collector
include power and scrubbing-liquor costs. Power costs vary with equipment
size, liquor circulation rate, and pressure drop. Liquor consumption varies
with equipment size and stack gas temperature. Maintenance includes servicing
the fan or compressor motor, servicing the pump, replacing worn linings,
cleaning piping, and any necessary chemical treatment of the liquor in the
circulation system.
Cost equation - The theoretical annual cost (G) of operation and
maintenance for wet collectors can be expressed as follows:
G = S 195.5 x 10"6 FHK + M
(2)
1722F 3960F
(3)
where:
S a design capacity of the wet collector, acfm
0.7457 * a constant (l horsepower = 0.7457 kilowatts)
H = annual operating tine (assumed 8,760 hr.)
562
-------
K = power costs, doll ars/kilowatt-hr
P = pressure drop across fan, inches of water (see Table A-6)
Q = liquor circulation, gal/acfta (see Table A-6)
g = liquor pressure at the collector, psig (see Table A-6)
h = physical height liquor is pumped in circulation system,
feet (see Table A-6)
W = make-up liquor consumption, gal/hr/acfm (see Table A-6)
L = liquor cost, dollars/gal (see Table A-6)
M = maintenance cost, dcllars/acfir. (see Table A-5)
E = fan efficiency, assumed to be 60$ (expressed as 0.60)
F = pump efficiency, assumed to be 50$ (expressed as 0.50)
The above equation can be simplified according to Semrau's total
"contacting power" concept..§/ Semrau shows that efficiency is proportional
to the total energy input to meet fan and nozzle power requirements. The
scrubbing (contact) power factors in Table A-6 were calculated from typical
performance data listed in manufacturers' brochures. These factors are in
general agreement with data reported by Senrau. Using Semrau's concept the
equation for operating cost can be simplified as follows:
G = S
(Z+—)+
\ 1990/.
0.7457 HK l Z + -^-}+ WHL + M
where Z = contact power (i.e., total power input required for collection
efficiency), horsepower/acfm' (see Table A-6). It is a combina-
tion of:
1. Fan horsepower/acfm (= F ) , and
V 6356E/
2. Pump horsepower/acfm (~ the P°wer to atomize water \
V 1722F through a nozzle J
The pump horsepower, Qh/1980, required to provide pressure head
is not included in the contact power requirements.
5G3
-------
A 5.3.4 Electrostatic Precipitators: The only operating cost
considered in the operation of electrostatic precipitators is the power
cost for ionizing the gas and operating the fan. As the pressure drop
across the equipment is usually less than l/2 in. of water, the cost of
operating the fan is assumed to be negligible. The power cost varies with
the efficiency and the size of the equipment.
Maintenance usually requires the services of an engineer or highly
trained operator, in addition to regular maintenance personnel. Maintenance
includes servicing fans and replacing damaged wires and rectifiers.
Cost equation - The theoretical annual cost (G) for operation and
maintenance of electrostatic precipitators is as follows:
G = S [JHK + M] (4)
where
S = design capacity of the electrostatic precipitator, acfm
J = power requirements, kilowatts/acfn. (See Table A-6)
H = annual operating time (assumed 9,760 hr.)
K = power cost, dollars/kilowatt-hr (see Table A-6)
M = maintenance cost, dollars/acfm (see Table A-5)
A.5.3.5 Fabric Filters: Operating costs for fabric filters
include power costs for operating the fan and the bag cleaning device.
These costs vary directly with size of equipment and the pressure drop.
Maintenance costs include costs for servicing the fan and shaking mechanism,
emptying the hoppers, and replacing the worn bags.
Cost equation - The theoretical annual cost (G) for operation ajid
maintenance of fabric filters is as follows:
G = S 0<7457 PHK + M
6356E
(5)
564
-------
where:
S - design capacity of the fabric filter, acfm
P = pressure drop, inches of water (see Table A-6)
E x fan efficiency, which is assumed to be 60$ (expressed
as 0.60)
0.7457 = a constant (l horsepower = 0.7457 kilowatt)
H - annual operating time (assumed 8,760 hr.)
K = power cost, dollars per kilowatt-hr. (see Table A-6)
M = maintenance cost, dollars/acfm (see Table A-5)
For computational purposes, the cost formula can be simplified as follows:
G - S [195.5 x 10"6 PHK + Ml (6)
A.5.3.6 Afterburners: The major operating cost item for after-
burners is fuel. Fuel requirements are a direct function of the gas volume,
the enthalpy of the gas, and the difference between inlet and outlet gas
temperatures. For most applications, the inlet gas temperature at the source
ranges from 300° to 400°F. Outlet temperatures may vary from 1200° to 1500°F
for direct flame afterburners and from 730° to 1200°F for catalytic after-
burners.—' The use of heat exchangers may bring about a 50# reduction in
the temperature difference.li®/ Table A-7 lists hourly fuel costs based on
a natural-gas cost of $0.60/million Btu. No credit was given for heat of
combustion of particulate or other matter. These costs were developed from
enthalpies (heat content) of the process gas at given temperatures.*!/ Main-
tenance includes servicing the fan, repairing the refractory lining, washing
and rinsing the catalyst, and rejuvenating the catalyst.12/
565
-------
TABLE A-7
HOURLY FUEL COSTS
Device
Temperatun
Inlet
CP)
Outlet
A
Temperature,
(°F)
Fuel Cost,^/
Dollars/acfm-Hr
Direct flame (DF)
380
1400 *
1020
0.00057
DF with heat exchanger
1000
1400
400
0.00023
Catalytic afterburner (CAB)
380
900
520
0.00028
CAB with heat exchanger
650
900
250
0.00014
a/ These figures include the cost of heating an additional 50$ excess air.
It is assumed there is no heat content in the material or pollutant
being consumed.
The equation for calculating the operation and maintenance costs
(G) is as follows:
0.7457 FHK + ^ + M
6356 E
(7)
where:
S = design capacity of the afterburner, acfm
P = pressure drop, inches of water (see Table A-6)
E = fan efficiency, assumed to be 60$ (expressed as 0.60)
0.7457 = a constant (l horsepower = 0.7457 kilowatt)
H = annual operating time (assumed 8,760 hr.)
K = power cost, dollars per kilowatt-hour (see Table A-6)
F ® fuel cost, dollars per acf:n/hr (see Table A-7)
M = maintenance cost, dollaars/acfm (see Table A-5)
566
-------
7or computational purposes, the cost formula is simplified as fellows:
G = S
195.5 x 1CT6 PHK + HF + M
(8)
A.5,4 Capital Charges
Capital charge includes overhead expenses such as taxes, insurance,
and interest incurred in the operation of a control device. Such costs
frequently lose specific identity because of internal accounting practices.
It is possible, however, by reasonable assumptions, to include capital
charges in the annualized cost of control.
A.5.5 Annualization of Costs
Annualized capital costs are estimated by depreciating the capital
investment (total installed cost) over the expected life of the control
equipment and adding the capital charges (taxes, interest, and insurance).
Adding the recurring maintenance and operation costs to this figure gives a
total annualized cost of control. Total annualized cost estimates are
shown in Section A.7.
A.5.6 Assumptions in Annualized Control Cost Elements
Annualized control costs will differ from installation to installation
and from region to region, and certain simplifying assumptions have been
necessary to develop the cost figures of this section. If more information
for a given location is available, it is desirable to substitute this for
the assumptions used here.
A.5.6.1 Annualized Capital Cost Assumptions: The simplifying
assumptions for computing the total annualized capital cost are as follows:
1. Purchase and installation costs are depreciated over 15 years,
a period assumed to be a feasible economic life for control devices.
2. The straight-line method of depreciation (6-2/3$/year) is used
because it is the most common method used in accounting practices. This
method has the simplicity of a constant annual writeoff.
3. Other costs called capital charges--which include interest,
taxes, insurance, and other miscellaneous costs--are assumed to be equal
to the amount of depreciation, or 6-2/3$ of the initial capital cost of the
control equipment installed. Therefore, depreciation plus these other
annual charges amounts to 13-1/2/6 of the initial capital cost of the equipment.
567
-------
A.5.6.2 Operating Cost Assumptions: The following assumptions
were taken into account for computing operation and maintenance costs.
1. Power costs included in annual operating expense reflect
electricity used by all systems directly associated with the control equip-
ment. Electrical power requirements are computed on a constant usage basis
at a specified gas volume.
2. For wet collectors, it is assumed that the liquor is recircu-
lated in a closed system. Liquor consumption consists of the makeup liquor
which must be added from time to time. Stack gas temperature influences
the rate of liquor loss; this influence is partially accounted for by assum-
ing a constant loss per cubic foot of stack gas volume. This assumption
is necessary because of the extremely wide range of stack gas temperatures.
3. The costs for electricity and water are computed on the marginal
rate classes for each size user, which assumes that any additional consump-
tion will be priced at the lowest rate-highest volume class available. Except
where specifically indicated, the typical values for the pressure drop and
cost of electricity (see Table A-7) were assumed in all control cost cal-
culations and illustrations.
4. The disposal cost and/or recovered value of collected effluents
are not included in the operating cost calculations because of cost differ-
ences from process to process. Disposal cost figures for several major
industrial categories are reported in Section A.8.
A.5.6.3 Maintenance Cost Assumption; It is assumed that a user
of control equipment establishes a preventive (scheduled) maintenance program
and carries it out to maintain equipment at its designed collection efficiency.
Further, it is assumed that unscheduled maintenance, such as replacement of
defective parts, is undertaken as required. The cost incurred for equip-
ment modification or repair due to an operational accident is not included.
A.6 METHOD FOR ESTIMATING ANNUAL COST OF CONTROL FOR A SPECIFIC SOURCE
A.S.I General
As previously indicated, it is beyond the scope of this Appendix to
identify and assess the cost of control for a specific source. Such assess-
ments can, however, be calculated by applying the steps outlined below.
A.S.2 Procedure
The following procedure can be used to determine the expected cost
of control for any source.
569
-------
Step i. Describe the source (including characteristics of the
process), the characteristics and consumption of fuel for combustion, and
the total number of hours in operation annually. Emissions can he determined
by making stack gas tests or can be estimated by making calculations using
the emission factors.
Step 2. Select the applicable types of control equipment.
Figure A-l illustrates what must be considered in selecting the optimum
type of control equipment.
Step 3. Specify pressure drops, efficiencies, construction material,
energy and fuel requirements, and size limitations for the selected control
equipment, taking into account any existing equipment.
Step 4. Determine the gas flow in acfm at the point of collector
location. For wet collectors, this would be the water saturated gas volume.
This should be done by taking measurements at maximum operating conditions.
Step 5. Determine the estimated total purchase cost for the
specific selected device (curves found in Section A. 7) at the required gas
volume and control efficiency. For fabric filters, select the proper filter
medium for the process.
Step 6. Multiply the cost found in Step 5 by the low, typical,
and high installation cost factors (Table A-3), and add the result to the
estimated total purchase cost to obtain the corresponding low, typical,
and high total installed costs. Conditions affecting the cost of installation
are listed in Table A-4.
Step 7. Calculate the total annual capital cost as follows:
Annualized capital cost = depreciation + capital charges
= 0.133 x total investment cost*
Step 8. Compute the cost of electricity, maintenance, and liquor
consumption.
Step 9. Compute low, medium, and high operating and maintenance
costs from the appropriate formulas:
Dry centrifugal collectors
G x S [195.5 x 10~6 PHK + m]
* Based on the assumptions in Section A.5.6.1,
569
-------
Wet scrubbers
0.7457 HK ( Z + )+ WHL + M
L ^ 1980J J
Electrostatic precipitator
G = S [JHK + M]
Fabric filters
G - S [195.5 x 10-6 PHK + M]
Afterburners
G = S [195.5 x 10"6 PHK + M + H?]
where:
G = theoretical value for operating and maintenance costs
S = the design, capacity of the collection device, acini
F = pressure drop cf the gas, inches of water
H = annual operating time
K = power costs, dollars per kilowatt-hour
Q ¦= liquor circulation, gal/acfm
h = physical height that liquor is pimped in circulation system,
feet
Z = total power input required for scrubbing efficiency, horsepower/
acfm
M = maintenance cost, dollars/acfm
W = liquor consumption, gal/hr/acfm
L x cost of liquor, dollars/gal
J s power requirement, kilowatts/acfm based on efficiency
F = fuel cost, dollars/hr/acfm
570
-------
Step 10. Add the typical annualized capital cost to the typical
operating and maintenance cost to yield the estimated total annualized cost
of control.
Step 11. Because the above calculation is a point estimate, the
range of costs should be investigated. For this, a variance is calculated
and applied to the total estimated annual cost. The low cost variance (V-^)
and high cost variance (V^) of an equipment combination can be computed by
using the square root of the sum of the squares. The formulas for these
variances are as follows:
h = ^(Cm - CX)2 + (Gta - GX)2
Vh - y (ch " °m)2 +
where:
Cl5 Cjj, and Ch are the low, typical, and high annual capital cost estimates,
respectively, and G]_, and are the low, typical, and high operation
and maintenance cost estimates. These formulas are taken from the usual
definition of the standard error of a linear combination of statistically
independent variables. They permit computation of the most probable, rather
than the extreme, range of costs.
Step 12. The high cost variance (V^) is added to the total esti-
mated annual cost to yield the high cost limit.
Step 13. The low cost variance (V]_) is subtracted from this
total estimated annual cost to yield the low cost limit.
A.6.3 Sample Calculations
The following calculations illustrate the method used to determine
the total estimated annual cost of control. The following example shows
the estimation of annualized cost for a 60,000 cfto, 90$ (medium efficiency)
wet collector.
Step 1. Annual operating time = 8,760 tar. (H)
Step 2. Wet collector (given)
Step 3. 90$ efficiency (given)
Scrubbing power required - 0.0035 horsepower/acfm (z)
571
-------
Step 4. Actual gas flow = 60,000 acfm (given)
Step 5. Purchase cost = $17,000 (from Section A.7.4 for wet
collectors)
200$
Step 6. Installation factors from Table A-3 are 50$, 100$, and
Installation factor 50$ 100$ 200$
Installation cost 8,500 17,000 34,000
Purchase cost 17,000 17,000 17,000
Total capital cost $25,500 $34,000 $51,000
Step 7. 0.133 x [Total capital cost] * annual capital cost (C)
CL = 0.133 x $25,500 = $3,400
Cm = 0.133 x $34,000 = $4,530
Ch = 0.133 X $51,000 = $6,800
Step 8. Power cost, dollars/kilowatt-hr (K)
Low Typical High
0.005 0.011 0.020
Maintenance cost, dollars/acfm (M)
Low Typical High
0.02 0.04 0.06
Liquor cost, 10"^ dollars/gal (L)
Low Typical High
0.35 0.50 1.00
Heat required for circulation in system, feet (h)
Low Typical High
1 30 60
Liquor circulation, gallons/acfm (tj)
572
-------
CO
st (G)
Low Ifypical High
0.001 0.008 0.020
Makeup liquor rate, 10"^ gal/hr/acfm, (W) = 0.5
Step 9. Using the following formula to determine annual operating
G = S
[z + Q*1 )(0.7457 HK) + WHL + M
\ 1980/
The low, typical, and high operating and maintenance costs
are as follows:
= $8,200 G^ = $18,100 Gh = $35,900
Step 10. From the steps 7 and 9,
Cm = $4,530 Gm - $18,100
Then, the total estimated annual cost is as follows:
+ Gm = $22,600
Step 11. Using the square root of the sum of the squares of the
differences, the high and low cost variances are as follows:
vi = >1K - ci)2 + (Gm - Glr
vx = ^(4,530 - 3,400)2 + (18,100 - 8,200)2
= $10,000
Vt> * " °i/
Vh - I\j (6,BOO - 4,530)2 + (35,900 - 18,100)^
Vh = $17,900
573
-------
Step 12. From Step 10, the total estimated, annual cost = $22,500
From Step 11, V-^ ¦ $10,000
Low cost limit = $22,600 - $10,000 = $12,600
Step 13. Total estimated annual cost = $22,600
From Step 11, Vh > $17,900
High cost limit = $22,600 + $17,900 = $40,500
Step 14. The amount of particulate matter emitted may be cal-
culated if the inlet conditions are known.
A.6.4 Annualized Cost Variation
The previous section illustrated the probable high and low cost
limits for a single installation, taking into account the variation in costs
for installation, maintenance, and operation. To compute the annualized
cost for a given emission reduction system, one must take into account four
variables: (l) collection efficiency of the system, (2) cost of installing
the system, (3) cost of operation, and (4) maintenance cost. A more com-
plete summary of the range of total annualized costs is shown in Table A-8
for a 60,000 acfm wet collector. This table illustrates cost fig-Lires for
81 possible combinations of each of the four variables, with each variable
taking on three independent values--low, typical, and high. It is constructed
by the procedure outlined in Steps 1 through 10 in the previous section.
The constants for computing these values are taken from Tables A-5 and A-6.
Table A-8 shows that a low-efficiency 60,000 acfn wet collector with low
installation, maintenance, and operation costs will cost approximately $6,100/
year to operate (extreme upper left-hand corner). The most efficient (99$
efficiency) wet collector, according to the table, will cost as high as
$137,400/yr to operate. The most likely costs for efficiencies of 75$,
90$, and 99$ are $11,300., $22,700, and $74,500, respectively. The type of
data shown in Table A-8 is useful in developing cost-effectiveness relation-
ships. Note that this table does not show the variances, and V^; these
should be used only when the probable cost limits are desired.
574
-------
TABLE A-8
ILLUSTRATIVE PRESENTATION OF ANNUAL COSTS OF CONTROL
FOR 60,000 ACFM WET SCRUBBER (DOLLARS)
Ex = 75$^/
= 90$
Ejj = 99$
e/
If
Is.
h
fl
Zs
h
£l
h
h
Mi
6,100
6,800
8,100
11,800
13,000
15,200
35,500
37,800
42,300
°i
%
7,300
8,000
9,300
13,000
14,200
16,400
36,700
39,000
43,500
"h
8,500
9,200
10,500
14,200
15,400
17,600
37,900
40,200
44,700
Ml
9,500
10,100
11,500
20,300
21,500
23,700
71,100
73,300
77,900
°m
%
10,700
11,300
12,700
21,500
22,700
24,900
72,300
74,500
79,100
Mh
11,900
12,500
13,900
22,700
23,900
26,100
73,500
75,700
80,300
Ml
18,300
18,900
20,300
36,900
38,100
40,300
128,200
130,500
135,000
°h
"m
19,500
20,100
21,500
38,100
39,300
41,500
129,400
131,700
136,200
Mh
20,700
21,300
22,700
39,300
40,500
42,700
130,600
132,900
137,400
a/ E = efficiency factor.
b/ Subscripts 1, n, and h indicate low, medium, and high ranges, respectively,
c/ I = installation factor,
d/ M = maintenance factor.
e/ 0 = operating factor.
Note: A similar table can be generated to show the various control costs for any type of control equipment by specifying
operating conditions and calculating each entry. This procedure provides complete information to aid in the
assessment of existing controls or other control alternatives.
-------
A. 7 COST CURVES BY EQUIPMENT TYPE
A. 7.1 General
The following sections contain a series of control cost curves
(see Figures A-5 through A-24). For each type of control equipment, a
series of curves is presented: (l) purchase cost curves, (2) installed
cost carves, and (3) annualized cost curves.
The estimated purchase cost curves show the dollar amounts
charged by manufacturers for "basic control equipment, exclusive of trans-
portation charges to the installation site. This basic control equipment
includes built-in auxiliary parts of the control unit, such as instrumen-
tation and solution pumps. The installed cost curves include the purchase
costs, additional auxiliary equipment costs, and installation costs, as
described in Section A.5.2. The annualized cost curves include elements
discussed in Sections A.5.2 through A.5.6. The assumptions, sources of
data, and the limitations used to develop this information are discussed
in Sections A.3 and A.4.
A.7.2 Gravitational Collectors
In computing the cost of gravity collectors, three collection
efficiencies were considered. These efficiencies were based on the assump-
tion of essentially complete removal of 67-y,, 50-^, and 25-|j, particles, and
are designated as low, medium, and high efficiencies, respectively. The low
and medium efficiency collectors are simple expansion chambers, and the high
efficiency collector is a multiple-tray settling chamber, commonly called a
Howard separator.
In actual operation, the collection efficiency for a gravitational
collector depends on the particle size distribution. In cleaning the flue
gas from a stoker-fired coal furnace, for example, low-, medium-, and high-
efficiency collectors would have particle removal efficiencies of approxi-
mately 64$, 75$, and SS%, respectively. In cleaning the flue gas from a
pulverized-coal furnace, these same collectors,. because of the smaller sized
particles emitted by the combustion unit, would have approximate efficiencies
of 21$, 34$, and 56$, respectively.
The purchase costs of gravitational collectors are shown for three
different efficiencies in Figure A-5. These are approximate costs for
typical installations. If it were necessary to include insulation or a
corrosion-resistant lining, the costs would be higher. The total installed
cost was also calculated for each efficiency and is shown in Figure A-6.
The total installed cost is the sum of the purchase and installation costs.
576
-------
a?
—4
100
50 -
1—I I I I I 1M
io -
- 5.0 -
O
LU
«/)
<
X
a l.o
Z>
a.
0.5 -
0.1
Costs may vary by - 20 p«rc«nt(
l l l 111 ii i i i i 11 ii
1 5 10 50 100
GAS VOLUME THROUGH COLLECTOR, 103 ocfm
Figure A-5 - Purchase Cost of Gravita-
tional Collectors
too
«•
O
o
TJ
r>
©
K
i/)
O
U
a
Ui
<
»-
(/>
z
0.5
10
50
5
100
GAS VOLUME THROUGH COLLECTOR, 103 ocfm
Figure A-6 - Installed Cost of Gravita-
tional Collectors
-------
CoiTt may v©ry hy i 20 pcreaH,
,1 l I 11 I l ill l t I l 111 il
10 50 100 SOB >000
GAS VOLUME THROUGH COLLECTOR, 103 acfm
Figure A-7 - Purchase Cost of Dry
Centrifugal Collectors
100
O
©
-9
o
m
iy
-I
_j
<
h
Z
500 800
10 SO 300 S00 1000
GAS VOLUME THROUGH COLLECTOR, lO^cfm
Figure A-8 - Installed Cost of Dry
Centrifugal Collectors
570
-------
100
so
o
U 10
o
111
M
3 5
<
D
Z
Z
<
r I II IIIUI li
1
_ HICH EFFICIENCY ^
J&zr -
— MEDIUM EFFICIENCY ^
— LOW EFFICIENCY -j/Kp?
—
_ 100
Z .V jcjBL
£ J&z?
1
Hi
- A£f^ -
- AWf 50
-M :
— jM&fr
- -
i M i ii
300 500
7 III mill I
1111 n
10 SO 100 500 1000
GAS VOLUME THROUGH COLLECTOR, 103 aefm
Figure A-9 - Annualized Cost of Operation of
Dry Centrifugal Collectors
1000
500
100
50 100
500 1000
Ceata moy vary by - 20 P«fCint,
I I lllllll I I Hi III
J 10 50 100 500 1000
GAS VOLUME THROUGH COLLECTOR, !03 oclm
Figure A-10 - Purchase Cost of Wet Collectors
579
-------
1000
500
*o 100
HIGH
EFFICIENCY
50
r MEDIUM
EFFICIENCY
10
5
LOW
EFFICIENCY
I I ' mill
11 nm I I 111 III
I 5 10 SO 100 500 1000
GAS VOLUME THROUGH COLLECTOR, 103oefm
Figure A-ll - Installed Cost of Wet Collectors
1000
500
•»
2 10C
in
u
a
UJ
N
< 10
3
Z
Z 5
<
'I 5 10 50 100 500 1000
GAS VOLUME THROUGH COLLECTOR, 10J ocfm
Figure A-12 - Annualized Cost of Operation
of Wet Collectors
111111111 1 1 1 11111
580
-------
1000
o
r>
o
H
\A
O 100
u
z
u
oc
3
a.
Coiti moy v«ry by - 20 p«re«nl.
10
50
100
1000
500
GAS VOLUME THROUGH COLLECTOR, 103 ocfm
Figure A-13 - Purchase Cost of High-Voltage
Electrostatic Precipitators
1000
o
a
UJ
u
u
<
300 500
[ 11 fin
10 SO 100 S00 1000
GAS VOLUME THROUGH COLLECTOR, 103 oefm
Figure A-14 - Installed Cost of High-Voltage
Electrostatic Precipitators
581
-------
300 500
1 I J I 1 ¦ 11 1
10 50 100 500 1000
CAS VOLUME THROUGH COLLECTOR, 103 aelm
Figure A-15 - Annualized Cost of Operation of
High-Voltage Electrostatic
Precipitators
100
r so
_o
"e
O
<
I
Figure A-16 - Purchase Cost of Low-Voltage
Electrostatic Precipitators
582
-------
1000
u loo
5 10 50 100
CAS VOLUME THROUGH COLLECTOR, 103 aclm
Figure A-17 - Installed Cost of Low-Voltage
Electrostatic Precipitators
I Mill'-
U 10
Mill
1 S 10 SO 100
GAS VOLUME THROUGH COLLECTOR, lO3 aclm
Figure A-18 - Annualized Cost of Operation of
Low-Voltage Electrostatic
Precipitators
583
-------
o
D
n
o
«/)
O
O
UJ
«/)
<
o:
D
0.
cn
CD
A - high-temperature synthetics, WOVEN ano
FELT. CONTINUOUS AUTOMATIC CLONING.
B • MEDIUM-TEMPERATURE SYNTHETICS. WOVEN AND
FELT. CONTINUOUS AUTOMATIC CLEANING.
C-WOVEN NATURAL FIBERS. INTERMITTENTLY
CLEANEO - SINGLE COMPARTMENT.
50
10
= i i i 111 m
;l Mil'-
_ K/ /
/ soo
- / >
_ y' b//
yc/
/ 100
c 5/
— 50
i
1 Mil-
— 100
soo —
Cot**
moy vary by
t 20 p«fc«nt.
1 1 1 1 1 III
i
1 1 IIII
1
10 50 1 00 500 1000
CAS VOLUME THROUGH COLLECTOR, 103 ocfm
Figure A-19 - Purchase Cost of Fabric Filters
100
••
o
o
T>
n
©
«/)
O
u
Q
1000
UJ
-J
<
H
500
«/»
z
10
50
100
500
1000
GAS VOLUME THROUGH COLLECTOR, 103 ocfm
A - HIGH-TEMPERATURE SYNTHETICS, WOVEN AND
FELT. CONTINUOUS AUTOMATIC CLEANING.
B • MEDIUM-TEMPERATURE SYNTHETICS, WOVEN AND
FELT. CONTINUOUS AUTOMATIC CLEANING.
C-WOVEN NATURAL FIBERS. INTERMITTENTLY
CLEANED-SINGLE COMPARTMENT.
Figure A-20 - Installed Cost of Fabric Filters
-------
100
50
o
~
Uj
N
_l
<
3
Z
Z
<
10
- 1 ! 1 i II II 1
1 1!_L
B —
— j&y joo
: a a
EfiE
1 LI III
2oo 500
1 1 1 I 1 1 III 1
1 1 1 1 1 II
10 SO too SOO 1000
GAS VOLUME THROUGH COLLECTOR, 103 ocfm
•HIGH-TEMPERATURE SYNTHETICS, WOVEN AND
FELT. CONTINUOUS AUTOMATIC CLEANING.
MEDIUM-TEMPERATURE SYNTHETICS, WOVEN AND
FELT. CONTINUOUS AUTOMATIC CLEANING.
• WOVEN NATURAL FIBERS. INTERMITTENTLY
CLEANED - SINGLE COMPARTMENT.
Figure A-21 - Annualized Cost of Operation
of Fabric Filters
mrTj
I I 11 Mill
I 5 10 100
GAS VOLUME THROUGH COLLECTOR, 10^ ocfm
Figure A-22 - Purchase Cost of Afterburners
585
-------
<
cn
CD
o>
in
llllll
1 5 10 SO 100
GAS VOLUME THROUGH COLLECTOR, 103 ocfm
CABHE
DFHE
CAB
DF
catalytic afterburner with heat
EXCHANGER
DIRECT FLAME AFTERBURNER WITH HEAT
EXCHANGER
CATALYTIC AFTERBURNER
DIRECT FLAME AFTERBURNER
Figure A-23
- Installed Cost of Afterburners
1 5 10 50 100
GAS VOLUME THROUGH COLLECTOR, 1(>3 ocfm
CABHE
DFHE
CAB
DF
•CATALYTIC AFTERBURNER WITH HEAT
EXCHANGER
DIRECT FLAME AFTERBURNER WITH HEAT
EXCHANGER
¦CATALYTIC AFTERBURNER
DIRECT FLAME AFTERBURNER
Figure A-24 - Annualized Cost of Operation
of Afterburners
-------
The installation costs were assumed to range from 33$ to 100$ of the purchase
cost (see Table A-3), and this range results in a cost band for each efficiency,
as shown in the figure. No annualized cost curves are presented for these
collectors because operation and maintenance costs, other than for removal
and disposal of collected material, usually are negligible, except where
corrosion may be a problem. Section A.8 provides specific information on
the disposal of collected material.
A.7.3 Dry Centrifugal Collectors
The costs of purchasing, installing, and operating mechanical
centrifugal collectors are given in Figures A-7, A-Q, and A-9, respectively.
The curves in these figures show costs for collectors that operate at nominal
efficiencies of 50$, 70$, and 95$ (see Section A.4). Costs are plotted for
equipment sizes ranging from 10,000 to 1,000,000 acfm. The assumptions used
in calculating annual operation and maintenance costs for dry centrifugal
collectors are as follows:
1. Annual operating time = 8,760 hr.
2. Collector pressure drop = 3 in. of water
3. Power cost = $0.011/kilowatt-hr
4. Maintenance co3t = $0.0L5/acfm
A.7.4 Wet Collectors
The costs of purchasing, installing, and operating wet collectors
are given in Figures A-10, A-11, and A-12, respectively, as a function of
equipment size. The curves in these figures show costs for collectors that
operate at nominal efficiencies of 75$, 90$, and 99$ (see Section A.4).
The basic hardware costs for medium and high collection-efficiency equipment
are reported by manufacturers to lie in the same cost range and both appear
on the same curve in Figure A-10. The higher installed cost of a high
collection-efficiency system in Figure A-ll results from the need for larger,
more expensive auxiliary equipment (based on Table A-3). The assumptions
used in calculating annual operating and maintenance costs for wet collectors
are as follows:
1. Annual operating time = 8,760 hr.
2. Contact power requirements:
0.0013 horsepower/acfn for 75$ efficiency
0.0035 horsepower/acfm for 90$ efficiency
0.015 horsepower/acfm for 99$ efficiency
587
-------
3.
Power cost * $0.Oll/kilowatt-hr
4. Maintenance cost =» $0.04/acfm
5. Head required for liquor circulation in collection system = 30 ft.
6. Liquor circulation = 0.008 gal/acfm
7. Liquor consumption = 0.0005 gal/hr-acfn
8. Liquor cost > $0.0005/gal
A.7.5 High-Voltage Electrostatic Precipitators
The costs of purchasing, installing, and operating high-voltage
electrostatic precipitators are given in Figures A-13, A-14, and A-15,
respectively. The curves in these figures show costs for collectors that
operate at nominal efficiencies of 90$, 95$, and 99.5$. These costs are
plotted for equipment sizes ranging from 20,000 to 1,000,000 acfm. The
assumptions used in calculating annual operation and maintenance costs for
high-voltage electrostatic precipitators are as follows:
1. Annual operating time = 8,760 hr.
2. Electrical power requirements:
0.00019 kilowatt/acfm for low efficiency
0.00025 kilowatt/acfm for medium efficiency
0.00034 kilowatt/acfm for high efficiency
3. Ibwer cost « $0.Oll/kilowatt-hr
4. Maintenance cost = $0.02/acfm
A.7.6 Low-Voltage Electrostatic Precipitators
The curves in Figures A-16, A-17, and A-18 indicate purchase
cost, installed cost, and operation cost of low-voltage electrostatic pre-
cipitators for low and high collection efficiencies based on design gas
velocities of 150 and 125 ft/min, respectively. Packaged modular low-voltage
precipitators with flow rates of less than 1,500 acfm are used to collect
oil mist from machining operations. Purchase cost of such a unit usually
is less than $1,200. The assumptions used in calculating annual operation
and maintenance costs for low-voltage electrostatic precipitators are as
follows:
586
-------
1. Annual operating time = 8,760 hr.
2. Electrical power requirements:
0.000015 kilowatt/acfm for low efficiency
0.000040 kilowatt/acfm for high efficiency
3. Power cost = $0.Oll/kilowatt-hr
4. Maintenance cost = $0.02/acfm
k.1.1 Fabric Filters
Figures A-19, A-20, and A-21 show purchase cost, installed cost,
and annualized cost of control for three different types of filters. Each
of the three filters is designed with about the same efficiency—99.9$. Costs
are plotted for equipment sizes ranging from 10,000 to 1,000,000 acfm.
The control costs curves represent the following different types
of filter installations:
1. Curve A represents a fabric filter installation with high-
temperature synthetic woven fibers (including fiberglass) and felted fibers
cleaned continuously and automatically.
2. Curve B represents an installation using medium-tenderature
synthetic woven and felted fibers, such as Orion or Dacron, cleaned contin-
uously and automatically.
3. Curve C is the least expensive installation. Woven natural
fibers Eire used in a single compartment. Filters are intermittently cleaned.
This equipment is rarely designed for processes handling over 150,000 acfm.
These control cost curves do not include data for furnace hoods, ventilation
ductwork and precoolers that may appear only in certain installations. The
assumptions for calculating operating and maintenance costs are as follows:
1. Annual operating time = 8,760 hr.
2. Pressure drop of the gas through the three types of fabric
filters = 4 in. of water
3. Power cost = $0.05/acfm
4. Maintenance cost ¦ $0.05/acfm
589
-------
A. 7.8 Afterburners
Afterburners are separated into four categories: (l) direct flame,
(2) catalytic, (3) direct flame with heat recovery, and (4) catalytic with
heat recovery. Equipment and installation costs were obtained from both the
literature and manufacturers of afterburners. Sufficient data were received
on catalytic afterburners to define the narrow purchase cost range shown in
Figure A-22. The figure shows that purchase costs of direct flame after-
burners have a wider range than those of catalytic afterburners.
Figure A-23 shows the installation costs for afterburners. Heat
exchangers are considered accessory equipment and appear as part of the
installation cost. Installation costs may range from 10# to 100# of the
purchase costs, although in some situations they may be as high as 400#.
Differences in installation costs are due to the differences in burner
locations relative to the emission source, and differences in structural
supports, ductwork, and foundations. Installation costs for the addition
of equipment to existing plant facilities will be higher than similar costs
for new plants. Other factors accounting for different installation fees
are the degree of instrumentation required, engineering fees in manufacturers'
bids, startup tests and adjustments, heat exchangers, auxiliary fans, and
utilities. The assumptions for calculating operation and maintenance costs
are as follows:
1. Annual operating time ¦ 8,760 hr.
2. Fuel cost:
$0.57/1,000 acfm-hr for direct flame afterburner with no
heat recovery
$0.23/1,000 acfm-hr for direct flame afterburner with heat
recovery
$0.28/1,000 acfm-hr for catalytic afterburner with no heat
recovery
$0.14/1,000 acfm-hr for catalytic afterburner with heat
recovery
3. Maintenance cost:
$0.06/acfm for direct flame afterburner
$0.20/acfm for catalytic afterburner
590
-------
4. Press-ore drop through all afterburner types = 1 in. of water
5. Power cost = $0.01l/kilowatt-hr
Cost comparisons presented in Figure A-24 show that the direct
flame afterburner without a heat exchanger is the most expensive. The
lower curve in Figure A-24 shows that the annualized cost of a direct flame
afterburner with heat recovery is lower than the cost of a catalytic after-
burner without heat recovery.
A. 8 DISPOSAL OF COLLECTED PARTICULATE EMISSION'S
A.8.1 General
The installation of any pollution control system designed to
collect particulate matter demands a decision regarding the disposal of
the collected particulate material. This section discusses the relevant
factors and illustrates the economic consequences of disposal of the collected
material.
In the past, pollution control equipment often was installed either
to reduce a severe nuisance or to recover valuable material. Such equipment
not only prevented valuable material from escaping to the atmosphere, but also
reduced costly cleaning of the plant grounds and facilities.
As industrial plants become more crowded together and as the public
desires a higher quality of air, more emphasis will be placed on intensive
control activities. This emphasis will increase the demand for more effective
air pollution control. Generally, most air pollution control systems collect
material that has little economic worth.
Basically, the alternatives for handling collected particulate
material are as follows:
1. Return the material to the process.
2. Sell the material directly as collected.
3. Convert the material to a salable product.
4. Discard the material in the most economical manner.
The process of selecting an alternative should take into account the following
questions:
591
-------
1. Can the material be used within the company?
2. Is there a profitable market for the material?
3. What is the most economical method of disposal?
4. Is there land available for a landfill?
5. Is there a source of water available for:
a. A wet pipeline system
b. Disposal at sea
c. Transportation by barge
6. Is there space available for a settling basin or filtering
system?
7. Is there process-related equipment presently available for
:rar.sporting or treating the collected material?
8. Is there access to a municipal waste treatment system?
9. Can technology and/or markets be developed for utilization
of the waste material?
A.8.2 Elements of Disposal Systems
After examining feasible solutions to the disposal problem, the
least costly alternative that is most compatible with other operating factors
in the plant should be chosen. The decision should result from consideration
of each of the four functional elements of the disposal system described
below and their relationships to the manufacturing process.
1. Temporary storage, which allows gathering sufficient quantities
of the collected material to make final disposal more economical. The unit
cost of disposal usually is lower for greater quantities. Temporary storage
may be convenient at many points in the overall disposal scheme, such as in
the hopper or settling chamber of a pollution control device, or in a silo
some distance-'from the plant.
2. Transportation that moves the collected material from the
particulate control device to some location where disposal is relatively
economical. In most cases, transportation displaces the material to a
location where accumulation minimizes any potential interference with plant
activities. Any single disposal system may require more than one method of
-------
transporting the material. For example, a conveyor system may be used at
the control device, a truck nay be used to transport the material to a
landfill area, and a bulldozer may be used to push it to its final disposal
location.
3. Treatment that changes physical and/or chemical characteristics
for easier disposal. Such treatment may simplify operations and reduce costs
for handling and disposal of wastes. Frequently, for easier transport,
particulate matter is made into a slurry by adding water to it. This permits
the use of a pipeline, which is often the most economical method for trans-
porting wastes over long distances. Slurries from wet-scrubbing pollution
control systems frequently are treated in an opposite manner: the water is
removed and the particulate matter is concentrated by filtration or sedimen-
tation. This permits the ultimate disposal of a solid waste, rather than a
sludge or a slurry. The method of treatment should be selected with a view
to minimizing contamination of the environment. Examples of such treatment
methods are the wetting of fine dust to prevent air pollution, the neu-
tralization and filtration of slurries to prevent contamination of receiving
waters, and the proper burial of solid material in a sanitary landfill.
4. Final disposition, which pertains to discarding the unusable
material. Material which cannot be sold, converted, or reused ultimately
can be discarded in landfills; or sometimes it can be disposed of in lagoons
or the sea.
The following list shows some examples of the four functional
elements for both wet and dry disposal systems.
A. Storage
(l) Slurry of suspended particulate matter in water
(a) Settling basin
(b) Lagoon
(c) Tank
(2) Dry collected particulates
(a) Mound
(b) Rail car
(c) Bin
(d) Silo
593
-------
Transportation
(1) Slurry of suspended particulates in water
(a) Barge
(b) Pipeline
(c) Truck
(d) Rail
(2) Dry collected particulates
(a) Truck
(b) Rail
(c) Front-end loader
(d) Conveying system
(e) Barge
Treatment
(l) Slurry of suspended particulate in waterii/
(a)
Sedimentation
00
Filtration
(c)
Flotation
(d)
Thickening; wet combustion
(e)
Lagoons and drying beds
(f)
Vacuum filtration
(g)
Centrifugation; incineration
(h)
Neutralization
594
-------
(2) Dry collected material
(a) Compressing
(b) Wetting
D. Final Disposition
(1) Landfill
(a) Public or private disposal sites
(b) Quarry
(c) Evacuated coal mine
(2) Lagoon
(3) Dump at sea
The arrangement of these elements in an overall disposal scheme
is shown in Figure A-25. This flow diagram 3hows the movement of the collected
material through various stages toward final disposal.
Environmental factors s-ch as space, utilities, disposal facilities,
and the desired form of collected waste material usually have an important
bearing on the selection of a disposal system compatible with a specific
type of particulate pollution control equipment. Therefore, a specific type
of particulate pollution control equipment may not always call for the sane
waste disposal system.
A.8.3 Disposal Cost for Discarded Material
Table A-9 describes various disposal systems and the related costs
within specific industries. Each system listed is specifically designed to
cope with the disposal problem and available facilities of the individual
plant shown. Therefore, drawing general conclusions about the relative costs
of systems listed in the table would be erroneous. The disposal costs shown
include capital charges and costs for labor and material. The disposal
cost/ton will be higher the smaller the quantity of material, because capital
charges for investment in facilities will remain the same regardless of
quantity.
Fly ash, a residue from the combustion of coal and residual oil,
probably is the most common, material collected in emission control systems.
595
-------
PRODUCT
HjO
STORAGE
STORAGE
COLLECTION
EQUIPMENT
STORAGE
PROCESS
TREATMENT
OPERATION
TRANSPORT
METHOD
CONVERSION
TO
SALEABLE
PRODUCT
DISPOSITION OF UNUSABLE MATERIAL
Figure A-25 - Flow Diagram for Disposal of Collected Particulate Material
from Air Pollution Control Equipment
596
-------
TABLE A - 9
COSTS OF SPECIFIC DISPOSAL SYS T-MS
lud ;stry
i.*wer veneration
iv>wer feneration
Power generation
Power generation
Collectec Materi
Fly ash
Fly ash
Fly ash
Fly ash
Treatment
Form pellets
Transport
Sedimentation Pipeline
rage
Settlnf*
pond
Truck Mound
Truck Mcund
Vacuuc aya- Transfer
stem, truck, bins,
barge
storage
silo
Final
Disposal
".anrif i 1"
(sediment)
Landfill
City diaaj,
L'r.if; 11
cr dianp
-.ate.
Power generation Fly Ash
Power generation Fly aih
Fora slurry Fipeline
Wetted
ftieisnatic
pipeline
truck
Settling
pond
Storage
silc
Landf11;
(c;edir.er.t)
Landfill
. oc
,co
rwer generation
for cr.err.ical
j"! ant
Fly ash
Sedimentation Pineline
* ^'cr feneration
for ?heaical
r* ar.t
Ihenical
rt'eak acid ea
Daren fct.
•vv:er ^snerat: >
f -ir ps.lr ar.vl
paper
ira,* :r-n
re' rcl® jh
refining
retro] c.-j-
refining
Petroleum
refining
f-etrole-.®
refining
Petrel eum
refining
?. rt^and
ceraer.t.
."•^aps and
detergents
Fly ash
Cupola d^st
^Jondevatered
sludge
Devatered
sludge
Sludge, filter coke,
oily solids
Oily solids
Catalyst fines
Waste dust
Suspended
soli-is
Sedimentation Pir.elinr
L'-pocn
Water
clarification
Sedinent
"by truck
Ccntract
hauling
Contract
hauling
Truck
Barge
i>empst er
dump
Contract
hauling
Slight wetting Conveyor, Bins
truck
Pipeline
Landfill
Landfill
In-plant
landfill
Dump at
sea
Landfill
Landfill
Munic '.pal
treatment
V1 ar.t
1.40
10.00
:. os
597
-------
An estimated 20 million tons of fly ash was produced in the United States
in 1965. Only 3$ of this total was sold as a marketable product.i£/ If the
cost for discarding the remaining 97$ of the fly ash as unusable waste were
$i.00/ton or more, this would represent a total cost of $20 million or more.
Based on the data in Table A-9, a cost of $1.00/ton is a typical unit cost.
In certain situations, the disposal cost of fly ash can be a major
portion of the total annualized cost for a complete pollution control system
(including disposal facilities). For example, the disposal costs cam be
as high as 80$ of the total annualized cost for an emission control system
with older electrostatic precipitators which are no longer depreciated. The
disposal cost still can be as high as 50$ for similar systems with newly
installed electrostatic precipitators, which usually have high depreciation
charges.
Table A-10 shows a summary of fly ash disposal costs for material
collected from electrostatic precipitators and mechanical collectors installed
in electric utilities and is taken from a recent survey.—' This survey
analyzed the costs of disposal, the sales, and the uses of fly ash collected
by 54 electric utilities and reported an average disposal cost of $0.74/ton.
Analysis of the data for individual utilities revealed that disposal cost
is partly a function of geographical location. The average disposal cost/ton
in the heavily-populated East is higher than that reported elsewhere.
TABLE A-10
COST OF ASH DISPOSAL BY 3LECTHIC UTILITIES
Disposal
Costs, Dollars/
'Ton
Type and Collection Method
Low
Medium
High
Fly ash (mechanical collector)
SO. 15
$0.5S
$1.67
Fly ash (electrostatic precipitator)
0.12
0.77
1.74
Bottom ash
0.15
1.04
4.76
A.8.4 Return of Collected Material to the Process
In some process operations, collected material is sufficiently
valuable to warrant its return to the process. In these situations, the value
of the recovered material can partially or wholly pay for the collection
equipment. In many applications, however, the cost for the high efficiency
control systems necessary to achieve desired ambient air quality will be
598
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greater than the revenue returned for recovery of the material collected.
This is illustrated by the hypothetical example in Figure A-2G.
The figure shows a linear relationship between collection efficiency
and value of material recovered. It also shows a curvilinear relationship
between collection efficiency and related equipment costs. Up to the break-
even point D (which corresponds to an efficiency of about 97$), the recovery
value of material collected is greater than the cost to achieve the recovery.
Equipment designed for efficiencies greater than 97$, according to the curve,
would have a higher cost than the potential recovery value.
If profit were the only control incentive, 85$ collection efficiency
would achieve the maximum profit, as illustrated by the profit line AB. If,
however, emission standards made 97$ collection efficiency necessary, no
profit would be achieved at the break-even point D. For collection efficiency
greater than 97$, equipment costs would exceed recovery costs. At 99$ effi-
ciency, for example, control equipment would cost the amount shown by FH,
and the value recovered would be the amount GH. The difference PG would
represent an expense and can be considered as the net control cost.
A survey conducted in 1956 shows that, out of 383 kilns, a total
of 349 return collected dust to the process.il/ Not only does recovered
dust, in such situations, have value as a raw material, but its recovery
also reduces disposal costs and decreases other related costs for the prepa-
ration of raw materials used in the process.
A.8.5 Recovery of Material for Sale
Although material collected by air pollution control equipment
may be unsuitable for return to a process within the plant, it may be suit-
able for another manufacturing activity. Hence, it may be treated and sold
to another firm that can use the material. Untreated pulverized fly ash,
for example, which cannot be reused in a furnace, can be sold as a raw material
to a cement manufacturer. It also can be used as a soil conditioner, or as
an asphalt filler, or as landfill material. For such uses, pulverized fly
ash requires no treatment and can be sold for as much as $1.00/ton. Pul-
verized fly ash which is treated can yield an even more valuable product.
A limited number of utilities, for example, sinter pulverized fly ash to
produce a lightweight aggregate which can be used to manufacture bricks
and lightweight building blocks.
At the present time, however, the sale of raw or treated collected
process material usually does not offer an opportunity to offset control
costs to a significant extent.
599
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ASSUME: CFM. GRAIN loading constant
BREAK EVEN
POINT-\
PROFIT MAXIMUM
VALUE OF MATERIAL
RECOVERED^
"PROFIT''
COST OF EQUIPMENT
100
EFFICIENCY. %
Figure A-26 - Theoretical Effect of Dust Value on Control Cost
6C0
-------
REFERENCES
1. Wilson, E. L., "Statement Presented at Hearings before the Subcommittee
on Air and Water Pollution of the Committee on Public Works, U. S.
Senate, SOth Congress, First Session on S. 780, Part 4," U. S.
Government Printing Office, Washington, D. C., 1967, p. 2632.
2. Danielson, J. A., Ed. "Air Pollution Engineering Manual," U. S.
Department of Health, Education, and Welfare, National Center for
Air Pollution Control, Cincinnati, Ohio, FHS-Pub-999-AP-40, 1S67.
3. "Air Pollution Manual - Part II - Control Equipment," American Indus-
trial Hygiene Association, Detroit, Michigan, 1968.
4. "Census of Manufacture 1963," Volumes 1, 2, and 3, U. S. Bureau of
Census.
5. Ridker, R. G., Economic Costs of Air Pollution. Frederick A. Praeger
Publishers, New York, 1967.
6. Semrau, K. T., "Dust Scrubber Design - A Critique on the State of the
Art," Journal of the Air Pollution Control Association, 13, 567-594,
December 1963.
7. Sandomirsky, A. G., D. M. Benforado, L. D. Grames, and C. E. Pauletta,
"Fiune Control in Rubber Processing by Direct-Flame Incineration,"
Journal of the Air Pollution Control Association, 16, 673-676,
December 1966.
8. Hein, G. M., "Odor Control by Catalytic and High-Temperature Oxidation,"
Annals, New York Academy of Science, 116(2):656-662, July 1964.
9. "North American Combustion Handbook," 1st Edition, North American
Manufacturing Co., Cleveland, Ohio.
10. Decker, L. D., "Odor Control by Incineration," (Presented by the Meeting
of the Middle States Air Pollution Control Association Section,
November 1965).
11. Eckenfelder, W. W., Industrial Water Pollution Control, McGraw-Hill,
New York, 1966, p. 4.
12. Gambs, G. C., "Report on Fly Ash in England, Europe, and Soviet Union,"
Research Div. Library, Consolidated Coal Co., July 1, 1966, p. 1.
601
-------
13. "53 Utilities Give Data on Fly Ash Sales and Uses," Electrical World,
I_68, 61-33, August 21, 1967.
14. Kannewurt, A. S., and Clausen, C. F., "1956 Survey, Fbrtland Cement
Association," Report MP-54, Chicago, May 1958, p. 37.
15. Gale, W. M., "Technical Aspects of a Modern Cement Plant," Clean Air,
l(2):7-13 (1967).
602
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APPENDIX B
MINOR SOURCES
In addition to the data compiled or. major industrial particulate
pollutant sources discussed in Chapters 5-23, information of various types
has been accumulated on several minor sources. Table B-l presents emission
factors and other assorted facts for these sources.
TABLE B-l
EMISSION FACTORS FOR MINOR SOURCES
Source of Particulate
CHEMICAL PROCESS INDUSTRY
Hienolic resin handlingi/
Pigment process!/
Grinder
Blender
FVC Manufacturing^/
Polypropylene
manuf acturing§/
Rubber process^/
Mixer
Grinder
Production
(tor.s/yr)
1.1 x 10e
3.2 x 105
2.7 x 1C6
Control
Device
Emission
Factor
Range
(lb/ton)
water
spray
j and oilj
[filters]
FF
baghouse
cyclones
Average
Emission
Factor
(lb/ton)
48
0.33*
1.9*
0.35*
3.0
0.13*
~ 20
1.4*
FOOD INDUSTRY
Coffee roasting
Roaster^/
Direct fired
Indirect fired
1.5 x 106
cyclone
cyclone
7.6
2.2*
4.2
1.2*
603
-------
TABLE B-l (Continued)
Source of Particulate
Coffee roasting (concluded)
Stoner and cooler
Instant Coffee
Spray dryer
Roasteri/
Coffee/tea processing—'
Roaster
Citrus plants 1/
Peel dryer
Orange pulp dryer
Production
(tons/yr)
104 f
Control
Device
cyclone
cyclone +
wet scrubber
cyclone
cyclone
Emission
Factor
Range
(lb/ton)
1.8 - 9.6
Average
Emission
Factor
(lb/ton)
1.4
0.4*
1.4*
1.9*
3.1*
5.0*
75.3
MINERAL PRODUCTS INDUSTRY
Abrasive grit
manufac turingi/
Blast grit and roofingi/
Granule manufacturing
Dryer
Screens
Calcium carbide
manufac turing^/
Coke dryer
Electric furnace hood
Furnace room vents
Main stack
Concrete batchingi/
Fiberglas manufacturing^/
Melting furnace
Regenerative
Recuperative
Forming line
Curing oven
Frit manufacturing
Rotary melteri/ .
Reverberatory furnace^/
baffle sedimentation
chamber
cyclone
cyclone
9.2 x 105
cyclone +
spray dryer
impingement
scrubber
0.11*
0.42*
4.1*
0.2*
1.7
2.6
2.0*
5.2
1-4
3
0.5 - 1
1
23.5 - 100
62
3.4 - 14
6.9
17
5.9 - 45.5
16.5
604
-------
TABLE B-l (Continued)
Source of Particulate
MINERAL PRODUCTS INDUSTRY
(Concluded)
Glass manufacturing
Furnace3/
Reverberatory furnac&i/
Furnacei/
Furnaces—'
Ground brick planti/
Gypsum board manufacturing
Grinderi/
Trim sawl/
Gypsum manufacturing2/
Dryer
Grinder
Calcir.er
Conveyor
yU
Magnesite plant-
Perlite manufacturing*^
Furnace
Plaster of Paris
mairaf actur ingi/
Qiartz plant!/
Rock wool manufacturing^/
Cupola
Reverberatory furnace
Blow chamber
Curing oven
Cooler
Cupolsi/
Production
(tons/yr)
4.1 x 10"-
Control
Device
Emission
Factor
Range
(lb/ton)
ESP
FF
cyclone +
ESP 4-40 (2)
FF
FF
FF
ESP
(3)
7.8 - 9.5
Average
Emission
Factor
(lb/ton)
1.5 - 7.9
0.02 - 1.]
0.14 - 0.24
lb/350 ft2
2
3
3
0.31
120
0.19*
22
0*, 0.
1
neg.*
90
C.l*
0.7
neg.*
430
21
0.9*
6.6*
16 - 28
21.6
4.8
4-56
21.6
1.5 - 5.9
3.6
0.4 - 5.5
2.4
32.4
605
-------
TAELS B-i (Concluded)
Source of Particulate
MISCELLANEOUS
Electric arc weldin
Soldering^
Plywood manufacturing^/
Dryer
Mercury snelting-5/
Production
(tons/yr)
Control
Device
Emission
Factor
Range
(lb/ton)
Average
Emission
Factor
(lb/ton)
0.01 - 0.02
lb/lb
electrode
0.005
lb/lb
solder
0.51
40.0
* Controlled emission factor based on indicated control device.
£ Tea production only.
606
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REFERENCES
1. Private communication, Air Pollution Control Agency.
2. Private communication, Resources Research.
3. Duprey, R. L., "Compilation of Air Pollutant Emission Factors,1' U. S.
Department of Health, Education and Welfare, 1968.
4. Private communication, GCA.
5. Shigehara, R. T., and R. W. Boubel, ''Particulate ar.d Total Gaseous
Hydrocarbon Einissicns from a Gas-Heated Veneer Dryer," 62nd Annual
Meeting, Air Pollution Control Association, June 196G.
6. Stahl, Q. R., "Air Pollution Aspects of Mercury and Its Compounds,"
Litton Systems, Incorporated, 1S69.
607
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