APTD-1102
FIELD OPERATIONS
AND ENFORCEMENT
MANUAL FOR
AIR POLLUTION
CONTROL
VOLUME III:
INSPECTION PROCEDURES FOR
SPECIFIC INDUSTRIES
~
US. ENVIRONMENTAL PROTECTION AGENCY
Office of Air Programs
Stationary Source Pollution Control Programs
Research Triangle Park, North Carolina 27711
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APTD-1102
FIELD OPERATIONS
AND ENFORCEMENT MANUAL
FOR AIR POLLUTION CONTROL
VOLUME III: INSPECTION PROCEDURES
FOR SPECIFIC INDUSTRIES
Prepared by
Melvin I. Weisburd
Pacific Environmental Services, Inc.
2932 Wilshire Boulevard
Santa Monica, California 90403
for
System Development Corporation
2500 Colorado Avenue
Santa Honica, California 90406
Contract No. CPA 70-122
Prepared for
ENVIRONMENTAL PROTECTION AGENCY
Office of Air Programs
Stationary Source Pollution Control Programs
Research Triangle Park, North Carolina 27711
August 1972
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ii
The APTD (Air Pollution Technical Data) series of reports is issued by the
Office of Air Programs, Environmental Protection Agency, to report technical
data of interest to a limited number of readers. Copies of APTD reports are
available free of charge to Federal employees, current contractors and
grantees, and non-profit organizations - as supplies permit - from the Air
Pollution Technical Information Center, Environmental Protection Agency,
Research Triangle Park, North Carolina 27711 or -may be obtained, for a
nominal cost, from the National Technical Information Service, 5285 Port
Royal Road, Springfield, Virginia 22151.
This report was furnished to the Environmental Protection Agency by Pacific
Environmental Services, Inc. of Santa Monica, California (pursuant to a
subcontract with System Development Corporation) in fulfillment of prime
Contract No. CPA 70-122. The contents of this report are reproduced herein
as received from Pacific Environmental Services, Inc. The opinions,
findings, and conclusions expressed are those of the author and not neces-
sarily those of the Environmental Protection Agency.
Office of Air Programs Publication No. APTD-1102
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ill
The Field Operations and Enforcement Manual for Air Pollution Control is
divided into three separate volumes.
Volume I, Organization and Basic Procedures, contains Chapters 1 through 4,
Volume II, Control Technology and General Source Inspection, contains
Chapters 5 and 6.
Volume III, Inspection Procedures for Specific Industries, contains
Chapter 7.
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ABSTRACT
The Field Operations and Enforcement Manual for Air Pollution Control,
Volume III explains in detail the following: inspection procedures for
specific sources, kraft pulp mills, animal rendering, steel mill furnaces,
coking operations, petroleum refineries, chemical plants, non-ferrous
smelting and refining, foundries, cement plants, aluminum reduction plants,
mining, coal preparation, fertilizer industry, paint and varnish manufactur-
ing, galvanizing operations, roofing plants, and asphalt batch operations.
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TABLE OF CONTENTS FOR VOLUME III
LIST OF FIGURES xiii
LIST OF TABLES xvi
CHAPTER 7. INSPECTION PROCEDURES FOR SPECIFIC SOURCES 7.1.1
I. INTRODUCTION 7.1.1
II. KRAFT PULP MILLS 7.2.1
A. Nature of Source Problem 7.2.1
B. Process Description 7.2.1
1. Pulp Cooking 7.2.5
a. Controls 7.2.5
2. Initial Chemical Recovery 7.2.6
a. Controls 7.2.8
3. Final Chemical Recovery 7.2.13
a. Controls 7.2.13
4. Other Mill Sources 7.2.14
C. Inspection Points 7.2.14
1. Environmental Observations 7.2.17
2. Observation of Exterior of Mill 7.2.20
3. Inspection of the Plant Interior 7.2.21
a. The Interview 7.2.21
b. The Physical Inspection 7.2.23
(1) Black Liquor System 7.2.23
(2) TRS Monitors 7.2.24
(3) Recovery Furnace 7.2.26
(4) Lime Kiln System 7.2.27
REFERENCES 7.2.29
III. ANIMAL RENDERING 7.3.1
A. Description of Source 7.3.1
B. Process Description 7.3.1
1. Dry Rendering Processes 7.3.7
2. Wet Processes 7.3.9
3. Feather Cookers 7.3.9
4. Blood Drying 7.3.11
C. Air Pollution Controls 7.3.11
D. Inspection Points 7.3.12
1. Environmental Observations 7.3.13
2. Observation of the Exterior of Plant 7.3.16
3. Inspection of the Interior of the Plant 7.3.17
a. Interview with Plant Management 7.3.17
(1) Inventory of Feedstocks 7.3.17
(2) Plant Sanitation Practices 7.3.18
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vl
b. The Physical Inspection 7.3.18
(1) Dead Stock Skinning Room 7.3.18
(2) Cookers 7.3.18
(3) Vent Lines 7.3.19
(4) Other Sources 7.3.19
(5) Air Pollution Control System 7.3.20
REFERENCES 7.3.22
IV. STEEL MILLS-FURNACES 7.4.1
A. Description of Sources 7.4.1
B. Process Description 7.4.1
1. Blast Furnaces 7.4.3
2. Electric Steel Furnaces 7.4.6
3. Open Hearth Furnaces 7.4.9
4. Basic Oxygen Furnace 7.4.12
C. Emissions and Inspection Points 7.4.15
1. Blast Furnaces 7.4.15
2. Electric Steel Furnaces 7.4.17
3. Open Hearth Furnaces 7.4.17
4. Basic Oxygen Furnaces 7.4.18
REFERENCES 7.4.20
V. COKING OPERATIONS 7.5.1
A. Description of Source 7.5.1
B. Process Description 7.5.1
C. Contaminants Emitted 7.5.6
1. Coke Preparation and Oven Operations 7.5.6
2. By-Product Processing Emissions 7.5.7
D. Inspection Points 7.5.10
1. Dust from Material Transfer 7.5.11
2. Charging Operations 7.5.13
3. Condition and Operation of Oven 7.5.15
4. Coke Transfer and Quench Operations 7.5.18
5. Screening and Sizing 7.5.18
6. Gas and Vapor Losses 7.5.19
REFERENCES 7.5.20
VI. PETROLEUM INDUSTRY 7.6.1
A. Description of Source 7.6.1
B. Process Description 7.6.1
1. Crude Oil Production 7.6.1
2. Oil Refining 7.6.2
a. Separation 7.6.6
b. Treating 7.6.7
c. Conversion 7.6.7
d. Blending 7.6.8
e. Types of Contaminants 7.6.9
3. Marketing 7.6.10
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vii
C. Air Pollution Potential of Petroleum Equipment 7.6.13
1. Refining Equipment 7.6.13
a. Flares and Slowdown Systems 7.6.13
b. Pressure Relief Valves 7.6.13
c. Storage Vessels 7.6.14
d. Bulk-Loading Facilities 7.6.14
e. Catalyst Regenerators 7.6.14
f. Effluent-Waste Disposal 7.6.15
g. Pumps and Compressors 7.6.15
h. Air-Blowing Operations 7.6.16
i. Pipeline Valves and Flanges, Blind Changing,
Process Drains 7.6.16
j. Cooling Towers 7.6.17
k. Vacuum Jets and Barometric Condensers 7.6.17
1. Effective Air Pollution Control Measures 7.6.17
2. Waste-Gas Disposal Systems 7.6.19
3. Storage Vessels 7.6.22
a. Types of Storage Vessels 7.6.22
4. Loading Facilities 7.6.23
5. Catalyst Regeneration 7.6.28
a. Types of Catalysts 7.6.28
b. Regeneration Processes 7.6.31
c. Air Pollution Control Equipment 7.6.33
6. Oil-Water Effluent Systems 7.6.33
a. The Air Pollution Problem 7.6.36
b. Asphalt from Crude Oil 7.6.37
7. Valves 7.6.38
a. Types of Valves 7.6.38
b. The Air Pollution Problem 7.6.39
8. Cooling Towers 7.6.41
9. Miscellaneous Sources 7.6.43
a. Airblowing 7.6.43
b. Blind Changing 7.6.43
c. Equipment Turnarounds 7.6.44
d. Tank Cleaning 7.6.45
e. Use of Vacuum Jets 7.6.45
f. Use of Compressor Engine Exhausts 7.6.46
D. Inspection Points and Process Inventories 7.6.46
1. Initial Inspection Procedures 7.6.46
a. Bulk Plant Data 7.6.51
b. Truck Loading Inspection Data Sheet 7.6.51
c. Oil-Effluent Water Separator Inspection 7.6.57
d. Tank Inspection Report 7.6.57
e. Data Sheet for Natural Gasoline, Gas, and Cycle
Plants 7.6.57
2. Inspection Points and Reinspection Procedures 7.6.60
3. Environmental Observations 7.6.60
4. The Physical Inspection 7.6.62
REFERENCES 7.6.67
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viii
VII. CHEMICAL PLANTS 7.7.1
A. Nature of Source Problem - Unit Processes and Unit
Operations 7.7.1
B. Process Description - Unit Processes and Unit Operations . . . 7.7.2
1. Unit Processes 7.7.3
a. Nitration 7.7.3
b. Sulfonation and Sulfation 7.7.3
c. Halogenation 7.7.6
d. Amination by Airanonolysis 7.7.6
e. Hydrolysis 7.7.6
f. Oxidation 7.7.6
g. Hydrogenation 7.7.6
h. Friedel-Crafts Reactions 7.7.7
2. Unit Operations 7.7.7
3. Control Methods 7.7.7
C. Inspection Points - Unit Processes and Unit Operations . . . . 7.7.9
D. Nature of Source Problem - Sulfuric Acid Manufacturing .... 7.7.10
E. Process Description - Sulfuric Acid Manufacturing 7.7.12
1. Chamber Process 7.7.12
2. Contact Process 7.7.15
F. Control Methods - Sulfuric Acid Manufacturing 7.7.18
1. Sulfur Dioxide Control 7.7.18
2. Sulfuric Acid Mist Control 7.7.21
G. Inspection Points - Sulfuric Acid Manufacturing 7.7.23
1. Environmental Surveillance 7.7.25
2. Inspection of the Premises 7.7.26
a. Interview 7.7.26
b. Physical Inspection 7.7.27
H. Nature of Source Problem - Vinyl Chloride Manufacturing . . . 7.7.30
1. Nature of Air Pollution Problems 7.7.30
I. Process Description - Vinyl Chloride Manufacturing 7.7.31
1. Basic Reactions 7.7.31
2. Current Manufacturing Practice 7.7.32
3. Control Methods 7.7.35
J. Inspection Points - Vinyl Chloride Manufacturing 7.7.37
1. Environmental Surveillance 7.7.37
2. Plant Inspection 7.7.38
a. Interview 7.7.38
b. Physical Inspection 7.7.39
REFERENCES 7.7.40
VIII. PRIMARY AND SECONDARY NON-FERROUS SMELTING AND REFINING 7.8.1
A. Introduction 7.8.1
B. Description of Source—Primary Smelting 7.8.2
1. Process Description 7.8.3
a. Copper 7.8.3
(1) Roasting 7.8.4
(2) Reverberatory Furnaces 7.8.6
(3) Converters 7.8.8
(4) Contaminants Emitted 7.8.10
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ix
b. Lead 7.8.11
(1) Sintering 7.8.11
(2) Blast Furnaces 7.8.15
(3) Lead Refining 7.8.17
(4) Additional Equipment and Operations 7.8.19
(5) Contaminants Emitted 7.8.19
c. Zinc 7.8.20
(1) Roasting 7.8.20
(2) Sintering % 7.8.23
(3) Zinc Extraction 7.8.24
(4) Contaminants Emitted 7.8.24
2. Inspection Points—Primary Smelting and Refining 7.8.25
a. Environmental Observations 7.8.25
b. Observations of the Exterior of Smelters 7.8.26
c. In-Plant Observations 7.8.26
C. Nature of Source-Secondary Smelters 7.8.27
1. Process Description—General 7.8.28
a. Brass and Bronze 7.8.28
(1) Blast Furnaces and Cupolas 7.8.30
(2) Ingot Production—Reverberatory Furnaces .... 7.8.33
b. Lead 7.8.36
(1) Reverberatory Furnaces 7.8.36
(2) Blast and Cupola Furnaces 7.8.38
(3) Pot Furnaces 7.8.40
c. Zinc 7.8.40
d. Aluminum 7.8.44
2. Inspection Points—Secondary Smelting and Refining . . . . 7.8.46
a. Environmental Observations 7.8.46
b. Observation of the Exterior of the Secondary Smelter . 7.8.47
c. The Physical Inspection 7.8.47
REFERENCES 7.8.50
IX. FERROUS AND NON-FERROUS FOUNDRIES 7.9.1
A. Description of Sources 7.9.1
B. Grey Iron Foundries 7.9.1
1. Process Description 7.9.1
2. Inspection Points 7.9.6
C. Non-Ferrous Foundries 7.9.8
1. Process Description—Copper-Base Alloys 7.9.8
2. Inspection Points—Copper-Base Alloys 7.9.16
a. Charging 7.9.16
b. Melting 7.9.17
c. Pouring 7.9.17
3. Process Description—Aluminum Melting 7.9.19
4. Process Description—Zinc Melting 7.9.20
5. Inspection Points—Aluminum and Zinc 7.9.21
6. Process Description—Core Making 7.9.21
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7. Inspection Points—Core Making 7.9.27
8. Process Description—Sand Handling 7.9.27
9. Inspection Points—Sand Handling 7.9.28
10. Environmental Observations . 7.9.30
REFERENCES 7.9.31
X. CEMENT PLANTS 7.10.1
A. Description of Source 7.10.1
B. Process Description 7.10.1
C. Emissions and Controls 7.10.3
D. Inspection Points 7.10.6
REFERENCES 7.10.10
XI. ALUMINUM REDUCTION PLANTS 7.11.1
A. Description of Source 7.11.1
B. Process Description 7.11.2
1. Material Handling 7.11.2
2. Electrode Preparation 7.11.4
a. Cathode Preparation 7.11.4
b. Anode Preparation 7.11.6
3. Potroom Operations 7.11.10
a. Prebake 7.11.10
b. Soderberg 7.11.13
C. Contaminants Emitted 7.11.15
D. Inspection Points 7.11.20
1. Environmental Observations 7.11.24
2. Exterior of Plant 7.11.25
3. Interior of Plant 7.11.26
REFERENCES 7.11.28
XII. MINING 7.12.1
A. Nature of Source Problem 7.12.1
B. Process Description 7.12.1
1. Surface Mining 7.12.2
a. Strip Mining 7.12.3
b. Open-Pit Mining 7.12.5
2. Underground Mining 7.12.8
C. Inspection Points 7.12.10
REFERENCES 7.12.12
XIII. COAL PREPARATION PLANTS 7.13.1
A. Description of Source 7.13.1
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B. Process Description ,
b. Jigs ,
c. Dense-media
d. Classifiers ,
2. Sizing ,
a. Breakers and Crusher
b. Screening
3 . Drying
a. Rotary Dryers
c. Cascade Dryers ,
e. Fluid Bed Dryers
4. Refuse
5. Coal Storage
C. Emissions and Controls
D. Inspection Points
1. Screening, Crushing and Breaking
2. Conveyors and Elevators
3. Pneumatic Classifying and Dedusting
REFERENCES
XIV. FERTILIZER INDUSTRY
A. Nature of Source Problem
2 . Ammonium Nitrate
1. Phosphate Fertilizers
2. Ammonium Nitrate
C. Inspection Points
1. General
3. Plant Inspection
a. Interview
REFERENCES
XV. PAINT AND VARNISH MANUFACTURING
A. Nature of Source Problem
7.13.1
7.13.1
7.13.4
7.13.4
7.13.5
7.13.5
7.13.6
7.13.8
7.13.11
7.13.11
7.13.12
7.13.12
7.13.13
7.13.14
7.13.15
7.13.16
7.13.17
7.13.17
7.13.18
7.13.18
7.13.18
7.13.18
7.13.19
7.13.19
7.13.20
7.14.1
7.14.1
7.14.2
7.14.3
7.14.3
7.14.3
7.14.9
7.14.11
7.14.13
7.14.13
7.14.14
7.14.14
7.14.14
7.14.15
7.14.17
7.15.1
7.15.1
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B. Process Description 7.15.1
1. Alkyd Resin Manufacturing 7.15.2
2. Varnish Cooking 7.15.3
3. Air Pollution Control Techniques 7.15.7
C. Inspection Points 7.15.12
1. Environmental Observations 7.15.13
2. Observations of Plant Exterior 7.15.14
3. Interior Plant Inspection 7.15.15
a. The Interview 7.15.15
b. The Physical Inspection 7.15.16
REFERENCES 7.15.18
XVI. GALVANIZING OPERATIONS 7.16.1
A. Description of Source 7.16.1
B. Process Description 7.16.1
C. Inspection Points 7.16.6
1. Environmental Observation 7.16.10
2. Observations of the Exterior of the Plant 7.16.10
3. Inspection of the Interior of the Plant 7.16.11
REFERENCE 7.16.14
XVII. ROOFING PLANTS—ASPHALT SATURATORS 7.17.1
A. Description of Source 7.17.1
B. Process Description 7.17.1
C. Emissions and Controls 7.17.1
D. Inspection Points 7.17.5
REFERENCE 7.17.7
XVIII. ASPHALTIC CONCRETE BATCHING OPERATIONS
A. Description of Source 7.18.1
B. Process Description 7.18.1
C. Contaminants Emitted 7.18.8
D. Inspection Points 7.18.13
REFERENCES 7.18.15
GLOSSARY ..... G.I
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xiii
Figure 7.2.1.
Figure
Figure
Figure
Figure
Figure
Figure
7.2.2.
7.2.3.
7.2.4.
7.2.5.
7.2.6.
7.3.1.
Figure 7.3.2.
Figure 7.3.3.
Figure 7.4.1.
Figure 7.4.2.
Figure 7.4.3.
Figure 7.4.4.
Figure 7.4.5.
Figure
Figure
Figure
Figure
Figure
7.4.6.
7.4.7.
7.4.8.
7.5.1.
7.5.2.
Figure 7.5.3.
Figure 7.5.4.
Figure 7.5.5.
Figure 7.5.6.
Figure 7.6.1.
Figure 7.6.2.
Figure 7.6.3.
Figure 7.6.4.
Figure 7.6.5.
Figure 7.6.6.
Figure 7.6.6.
Figure 7.6.7.
Figure 7.6.8.
Figure 7.6.9.
Figure 7.6.10.
Figure 7.6.11.
LIST OF FIGURES
Flow Diagram of a Kraft Pulping Process Showing
Principal Emissions at Different Points
A Typical Multiple Effect Evaporator System
Weak Black Liquor Oxidation
Strong Black Liquor Oxidation
Multiple Effect Evaporator System
Continuous Stack Sampler for TRS Compounds
An Integrated Dry Rendering Plant
A Continuous, Vacuum Rendering System Employing
Tallow Recycling (Carver-Greenfield Process)
A Condenser-Afterburner Control System
Production of Carbon Raw Steel in the United States
by Various Processes
A Typical Blast Furnace
A Typical Blast Furnace Stove
Direct Arc-Electric Furnace
Relationship Between Electric-Arc Furnace Capacity
and Transformer Rating
Cross-Section of a Basic Open-Hearth Furnace
Basic Oxygen Furnace
Stora-Kaldo Rotary Oxygen Converter
Process Flow Diagram of Coking Operation
Representative By-Product Plant Flow Sheet
Transverse and Longitudinal Sections Through
Koppers-Becker Underjet-Fired Low-Differential
Combination By-Product Coke Ovens
Schematic Representation of Charging and Leveling
Operations for a By-Product Coke Oven
Approximate Curve Illustrating the Decline in Gas and
Vapor Evolution at the End of the Coking Cycle
Schematic Representation of Pushing Operations for a
By-Product Coke Oven
Representation of Gasoline Distribution System in
Los Angeles County, Showing Flow of Gasoline from
Refinery to Consumer
An Overhead-Controlled Loading Rack
Simplified Flow Diagram of Platforming Process
A Modern Oil-Water Separator
Process Flow Diagram of a Sour Water Oxidizing Unit from
a Field Drawing
Activity Status Report from an Inspection Made of a
Sour Water Oxidizing Unit at an Oil Refinery
Continued
Symbols Used in Petroleum Flow Diagrams
Bulk Plant Data Sheet
Truck Loading Inspection Data Sheet
Oil-Water Separator Inspection Sheet
Natural Gasoline, Gas, and Cycle Plant Survey Summary
7.2.2
7.2.7
7.2.9
7.2.10
7.2.12
7.2.25
7.3.6
7.3.10
7.3.14
7.4.2
7.4.4
7.4.5
7.4.7
7.4.8
7.4.10
7.4.13
7.4.14
7.5.2
7.5.5
7.5.12
7.5.14
7.5.17
7.5.18
7
7
7
7.6
6.24
6.26
6.30
35
7.6.50
,6.52
,6.53
,6.54
.6.55
6.56
6.58
7.6.59
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Figure 7.7.1.
Figure 7.7.2.
Figure 7.7.3.
Figure 7.7.4.
Figure 7.7.5.
Figure 7.7.6.
7.7.7.
7.8.1.
7.8.2.
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure 7.8.8.
Figure 7.8.9.
3.
4.
5.
6.
8.7.
Figure 7.8.10.
Figure 7.9.1.
Figure 7.9.2.
Figure 7.9.3.
Figure 7.9.4.
Figure 7.9.5.
Figure 7.9.6.
Figure 7.9.7.
Figure 7.9.8.
Figure 7.9.9.
Figure 7.10.1.
Figure 7.10.2.
Figure 7.10.3.
Figure 7.10.4.
Figure 7.11.1.
Figure 7.11.2.
Figure 7.11.3.
Figure 7.11.4.
Figure 7.11.5.
Figure 7.11.6.
Figure 7.11.7.
Flow Diagram for Nitration of Methane
Simplified Flow Diagram of Typical Lead-Chamber Process
for Sulfuric Acid Manufacture
Schematic Flow Diagram of Sulfur Burning Plant with
Four-Stage Conversion
Schematic Flow Diagram Wet Gas Plant with 4-Stage
Conversion
Manufacture of Vinyl Chloride from Acetylene and
Hydrogen Chloride
Balanced Process for Vinyl Chloride Using Acetylene
and Ethylene
Oxychlorination Process for Manufacture of Vinyl Chloride
Flow Diagram of a Typical Copper Smelter
Flow Chart for a Lead Smelting Operation
Typical Lead Sintering Plant Major Material Distribution
Usual Treatment of a Sulfide Lead Ore
Typical Zinc Retort Plant Flow Diagram
Diagram Showing One Bank of a Belgian Retort Furnace
Diagram of a Distillation-Type Retort Furnace
Diagram of a Muffle Furnace and Condenser
A 20-Ton Aluminum-Melting Reverbatory Furnace with
Charging Well Hood
Boiling, Pouring, and Melting Points of Metals and
Alloys
The Cupola in Detail
Tilting Crucible Furnace
Rotary-Tilting-Type Reverberatory Furnace Venting to
Canopy Hood and Stack Vent
Rotary-Tilting-Type Brass-Melting Furnace
Shelf Oven
Drawer Oven
Rack Oven
Horizontal, Continuous Oven
Typical Foundry Sand-Handling System
Process Steps—Portland Cement Production
Example of Characteristics of Kiln Dust
Flow Diagram of Cement Plant Operations
Variation of Apparent Resistivity with Temperature and
Moisture for Some Typical Dusts and Fumes
Aluminum Reduction Plant Flow Diagram
Charging Aluminum Reduction Cell with Ground Dispensing
Vehicle
Prebaked Carbon Anode Production Process
Soderberg Anode Paste Production Process
Carbon Anodes Ready for Use in Aluminum Pots
Potline, Showing Anodes Suspended in Pots
Details of Prebaked and Soderberg Aluminum Reduction
Cells
7.7.5
7.7.14
7.7.16
7.7.19
7.7.33
7.7.34
7.7.36
7.8.5
7.8.12
7.8.13
7.8.18
7.8.21
7.8.41
7.8.42
7.8.43
7.8.45
7.8.49
7.9.2
7.9.12
7.9.14
7.9.15
7.9.23
7.9.24
7.9.24
7.9.25
7.9.29
7.10.2
7.10.4
7.10.6
,10.9
,11.3
11.5
11.7
11.8
11.9
11.12
7.11.14
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Figure 7.11.8. Schematic of Electrolytic Cell as Used in Alcoa A-398 7.11.21
Process
Figure 7.11.9. Schematic of Alcoa Gas Cleaning Process 7.11.22
Figure 7.11.10. Cross-Section of Roof Scrubber 7.11.23
Figure 7.13.1. Rejection of Flat Refuse by Slot Shaker 7.13.3
Figure 7.13.2. Diagram of Rheolaveur Coal Launder with Two Rheoboxes 7.13.4
Figure 7.13.3. McNally Norton Standard Washer 7.13.5
Figure 7.13.4. Cross Section McNally Tromp Bath 7.13.6
Figure 7.13.5. Bradford Breaker, for Use at Mine and Plant 7.13.8
Figure 7.13.6. Single-Roll Coal Crusher—Diagrammatic Section 7.13.9
Figure 7.13.7. Double-Roll Coal Crusher—Diagrammatic Section 7.13.9
Figure 7.13.8. Hammer-Mill Coal Crusher—Diagrammatic Section 7.13.10
Figure 7.13.9. Ring Coal Crusher—Diagrammatic Section 7.13.10
Figure 7.13.10. McNally Fine Coal Cascade Dryer 7.13.13
Figure 7.13.11. Suspension-Type Flush Drying System (Thermal Dryer) 7.13.14
Figure 7.13.12. McNally Flowdryer 7.13.15
Figure 7.14.1. Production of Normal Superphosphate 7.14.6
Figure 7.14.2. Phosphoric Acid Acidulation Process 7.14.8
Figure 7.14.3. Flow Diagram for the Manufacture of Ammonium Nitrate 7.14.10
Figure 7.15.1. Uncontrolled Open Kettle for Varnish Cooking 7.15.6
Figure 7.15.2. Typical Direct-Fired Afterburner with Tangential Entries
for Both the Fuel and Contaminated Gases 7.15.9
Figure 7.15.3. Diagram of Combustifume Burner in Vertical Stack 7.15.10
Figure 7.15.4. Schematic Plan for Varnish-Cooking Control System 7.15.11
Figure 7.16.1. Simplified Flow Chart of Galvanizing Process 7.16.2
Figure 7.16.2. Removing Work Through a Clean Zinc Surface 7.16.4
Figure 7.16.3. Open to a Room-Type Hood Over a Galvanizing Kettle 7.16.5
Figure 7.16.4. Slot-Type Hood Serving a Chain Link Fence-Galvanizing
Flux Box 7.16.7
Figure 7.16.5. Photomicrograph of Fumes Discharged from a Galvanizing
Kettle 7.16.8
Figure 7.17.1. Schematic Drawing of an Asphalt Roofing Felt Saturator 7.17.2
Figure 7.17.2. Asphalt Saturator Hood at Felt Feed 7.17.3
Figure 7.18.1. Asphalt Batch Plant with a Cyclone Type Dust Collector 7.18.3
Figure 7.18.2. Flow Diagram of a Typical Hot-Mix Asphalt Paving Batch
Plant 7.18.4
Figure 7.18.3. Composite Asphalt Plant Dust Particle Size Distribution 7.18.10
-------
xvi
LIST OF TABLES
Table 7.2.1. Average Kraft Pulp Mill Potential Emissions
Table 7.2.2. Average Kraft Pulp Mill Air Emissions with Control
Table 7.2.3. Summary of Kraft Mill Emission Standards for
Washington State
Table 7.2.4. Odor Thresholds of Kraft Mill Gaseous Sulfur Compounds
in Air
Table 7.2.5. Characteristics of Kraft Mill Gaseous Sulfur Compounds
Table 7.3.1. Inedible Reduction Process Raw Materials Originating
from Slaughterhouses
Table 7.3.2. Odor Concentrations and Emission Rates from Inedible
Reduction Processes
Table 7.3.3. Odor Threshold Concentrations of Selected Rendering
Compounds
Table 7.3.4. Composition of Typical Inedible Raw Materials Charged
to Reduction Processes
Table 7.3.5. Odor Removal Efficiencies of Condensers or Afterburners,
or Both, Venting a Typical Dry Rendering Cooker
Table 7.5.1. Sequence of Charging Operations
Table 7.6.1. Sources and Control of Air Contaminants from Crude-Oil
Production Facilities
Table 7.6.2. Potential Sources of Emissions from Oil Refining
Table 7.6.3. Hydrocarbon Emission Factors for Refinery Sources
Table 7.6.4. Sources and Control of Hydrocarbon Losses from
Petroleum Marketing
Table 7.6.5. Suggested Control Measures for Reduction of Air
Contaminants from Petroleum Refining
Table 7.6.6. Leakage of Hydrocarbons from Valves of Refineries in
Los Angeles County (1958)
Table 7.7.1. Commonly Used Unit Processes
Table 7.7.2. Examples of Mass Transfer Operations and Air Pollutant
Potential
Table 7.7.3. Expected Performance of Acid Mist Collection Systems
Table 7.8.1. Typical High Quality Concentrate Analysis
Table 7.8.2. Emissions From Copper Roasters, Reverberatory Furnaces,
and Converters
Table 7.8.3. Typical Reverberatory Furnace Operating Conditions
Table 7.8.4. Reverberatory Furnace Off-Gas Composition
Table 7.8.5. Composition of Reverberatory Furnace Molten Products
Table 7.8.6. Emissions from Lead Sintering, Blast Furnaces, and
Reverberatory Furnaces
Table 7.8.7. Typical Zinc Roasting Operations
Table 7.8.8. Typical Zinc Sintering Operations
Table 7.8.9. Nominal Chemical Specifications for BBII Standard Alloys
Table 7.8.10. Types of Copper-Bearing Scrap
Table 7.8.11. Rotary Furnace Particulate Emissions—Test A
Table 7.8.12. Reverberatory Furnace Particulate Emissions—Test C
Table 7.8.13. Cupola Particulate Emissions—Test E
Table 7.8.14. Chemical Requirements for Lead
7.2.3
7.2.4
7.2.16
7.2.18
7.2.19
7.3.2
7.3.4
7.3.5
7.3.8
7.3.15
7.5.16
7.6.3
7.6.4
7.6.11
7.6.12
7.6.18
7.6.40
7.7.4
7.7.8
7.7.24
7.8.3
7.8.6
7.8.7
7.8.7
7.8.8
,8.18
8.22
,8.23
,8.30
8.31
8.34
8.35
8.36
7.8.37
-------
xvii
11.3.
11.4.
11.5.
13.1.
Table 7.8.15. Dust and Fume Emissions from a Secondary Lead-Smelting
Furnace 7.8.39
Table 7.9.1. General Recommendations for Operating Whiting Cupolas 7.9.4
Table 7.9.2. Dust and Fume Emissions from Gray Iron Cupolas 7.9.5
Table 7.9.3. Some Collection Efficiencies of Experimental Small-Scale
Control Devices Tested on Gray Iron Cupolas 7.9.7
Table 7.9.4. Dust and Fume Discharge from Brass Furnaces 7.9.9
Table 7.9.5. Relative Volatilities and Melting Temperatures for
Non-Ferrous Metals 7.9.11
Table 7.9.6. Air Contaminant Emissions from Core Ovens 7.9.26
Table 7.11.1. Raw Materials for the Production of One Ton of
Aluminum 7.11.11
Table 7.11.2. Comparison of Requirements for Prebaked and Soderberg
Systems 7.11.11
Emission Sources and Contaminants 7.11.16
Total F Emission - Daily Rate and Control Efficiency 7.11.17
Total SO Emission - Daily Rate and Control Efficiency 7.11.18
Specific Gravities of Coal and Impurities 7.13.3
13.2. Commercial Sizes of Anthracite 7.13.7
14.1. Control of Emissions from Fertilizer Manufacturing 7.14.12
Table 7.16.1. Chemical Analyses of the Fumes Collected by a Baghouse
and by an Electric Precipitator from Zinc-Galvanizing
Kettles 7.16.9
Table 7.17.1. Emissions from a Water Scrubber and Low-Voltage,
Two-Stage Electrical Precipitator Venting an
Asphalt Saturator 7.17.4
Table 7.17.2. Emissions from a Bag Filter and Cyclone Separator
Venting an Asphalt Saturator 7.17.4
Table 7.17.3. Emissions from a Water Scrubber Venting an Asphalt
Saturator 7.17.5
Table 7.18.1. Standard U.S. and Tyler Screen Scales 7.18.5
Table 7.18.2. Mix Compositions 7.18.6
Table 7.18.3. Asphalt Test Specifications 7.18.7
Table 7.18.4. Dust and Fume Discharge from Asphalt Batch Plants 7.18.9
Table 7.18.5. Test Data from Hot-Mix Asphalt Paving Plants Controlled
by Scrubbers 7.18.12
Table
Table
Table
Table
Table
Table
-------
7.1.1
CHAPTER 7
INSPECTION PROCEDURES FOR SPECIFIC SOURCES
I. INTRODUCTION
Specific sources of air pollution, described in this chapter, are comprised
of industrial facilities which may be major targets of air pollution control,
are significant contributors to air pollution as stationary point sources
and are of such complexity that training and familiarization on the part of
the enforcement officer is required before he can assume complete responsi-
bility for the inspection of these plants.
Major metallurgical, chemical processing, mining and other industries which
contribute to the full range of air pollution, including smoke, fumes, dust,
odor, gases and vapors, are described in this chapter. Although not all
industries of possible interest are treated, the operations described are
typical of stationary sources in general and should help to prepare
enforcement officers in entering and inspecting other facilities that may
be unfamiliar to them.
In general, each stationary source section of this chapter is broken down
as follows:
• Nature of Source
• Process Description
• Emissions
• Controls
• Inspection Points
-------
7.2.1
II. KRAFT PULP MILLS
A. NATURE OF SOURCE PROBLEM
Of the major pulping processes—Kraft, sulfite and neutral sulfite semi-
chemical (NSSC)—Kraft is most significant from the standpoint of air
pollution. As of 1968, Kraft mills produced 75% of the domestic pulp
in 116 mills with a total production capacity of 32 million short tons.
They will produce 85% of the total pulp or 60 million short tons by
1985.(1)
Kraft mills present a complex air pollution problem in terms of the
variety and volumes of contaminants emitted. The major problems are
odors and particulates. The malodorous contaminants are inherently
objectionable and persistent at low concentrations (1 to 10 parts per
billion); are non-condensible and hence difficult to control; and are
emitted in large quantities.
B. PROCESS DESCRIPTION
The major sources of pollution in a Kraft mill are concentrated in the
cooking of the pulp and recovery of the process chemicals. An overview
of the cooking and recovery cycle and contaminants emitted from specific
process points is illustrated in Figure 7.2.1. Average uncontrolled
emissions from Kraft mills are shown in Table 7.2.1. Table 7.2.2 lists
typical control equipment and emission rates. Emission rates and pro-
duction capacities, as well as the details of process system design and
operation will vary considerably among Kraft mills.
-------
(18)
CHIPS
RELIEF
HEAT EXCHANGER
CH3SH,CH3SCH3,H2S
MOM CONDENSABLES
CH3SH,CH3SCH3,H2S
NON. CONDENSABLES
I
-
- UJ
• ° ^
o
HAV.
QCCUM.
(3)
STEAM, CONTAMINATED WATER,H2S, 6 CH3SH
PULP
SPENT AIR , CHjSCHj I*—
CH3SSCH3
Particulates
(12)
(15)
Figure 7.2.1. FLOW DIAGRAM OF A KRAFT PULPING PROCESS
SHOWING PRINCIPAL EMISSIONS AT DIFFERENT POINTS
(SOURCE: WASHINGTON STATE AND DOUGLASS,
References 2 and 3)
-------
7.2.3
Table 7.2.1. AVERAGE KRAFT PULP MILL POTENTIAL EMISSIONS
Department '
c
Digester (1, 2, 3)
Batch
Continuous
Washers (4)
Bleach Plant
Evaporators (6, 7)
Recovery Furnace (8)
Dissolving Tank (12)
Lime Kiln (15, 16)
Power Boiler*
(Hog Fuel)
Paper Machine *
(Numbers reference Figure 7.2.1)
(1) SCF - Cubic feet at standard conditions of 1 atmosphere and 68 F
(2) Does not include S02
(3) Six-stage bleach plant
(A) Chlorine as Ib/T
*Not shown on drawing.
**Total reduced sulfur (see definition in text).
***A11 cooking and chemical recovery operations are in terms of amount of emission
per air dried ton of unbleached pulp produced.
'otal Vol.
;CF (I)/T**
300
150
70,000
80,000
300
330,000
30,000
45,000
300,000
430,000
Water Vapor
lb/T**
2,500
1,500
250
220
-
4,300
700
850
3,000
2,700
Total
Particulate
lb/T**
0
0
0
0
0
170
5
45
35
0
255
TRS***
lb/T(2)
2.5
1.5
0.5
2.4
3.5
10.0
0.15
1.0
0.01
0
21.6
(SOURCE: WASHINGTON STATE AND HOUGH AND GROSS,
References 2 and 3.)
-------
Table 7.2.2. AVERAGE KRAFT PULP MILL AIR EMISSIONS WITH CONTROL
Source
(See Figure 7.2.1)
Digesters (1,2,3)
Batch
Continuous
Washers (4)
Bleach Plant
B. L. Oxidation (5)
Evaporators (6,7)
Recovery Furnace (8)
Dissolving Tank (12)
Lime Kiln (15,16)
Power Boiler
(Hog Fuel)
Air Pollution Controls
Thermal oxidation of
non-condensibles in
lime kiln, steam or air
stripping of condensates
Thermal oxidation
N. S.(2)
None
Caustic scrubbing plus
thermal oxidation of
non-condensibles
(3)
Packed tower (4)
Venturi scrubber
Cyclones
(2)
Paper Machine N. S.
(numbers reference Figure 7.2.1)
Total Vol.
SCF/T3
-
-
80,000
35,000
330,000
30,000
45,000
300,000
400,000
Total
Water Vapor Particulate
Ib/T Ib/T
-
-
220
700
4,300 3.5
700 0.5
1,350 1.0
3,000 5.0
1,600
11,870 10.0
Sulfur
lb/T(l
-
-
-
0.3
1.0
0.1
0.2
0.01
-
1.6
(1) Does not include sulfur as S02
(2) Not specified
(3) No direct contact evaporators; electrostatic precipitators employed for particulate removal
(4) Employs weak wash as scrubbing medium
a. Probably wet, judging from figure given for recovery furnace volume, 330,000 scf/ton.
(SOURCE: WASHINGTON STATE AND HOUGH AND GROSS,
tx>
.p-
-------
7.2.5
Pulp Cooking
Wood chips or saw dust together with the cooking chemicals or white liquor
are fed to the digesters ((1) in Figure 7.2.1). The digesters are tall
cylindrical vessels of 10-20 ton capacity. Cooking is typically conducted
at temperatures around 350°F and 110 Ibs. per square inch gauge pressure
for 3 to 4 hours on either a batch or a continuous basis.
The cooking solution consists of approximately 1/3 sodium sulfide and
2/3 caustic soda (sodium hydroxide). The caustic soda serves to
dissolve the intercellular material (lignin) which naturally binds the
wood fibers together. Sodium sulfide reacts with the cellulose to
impart strength to the ultimate product and with the waste wood products
to produce the air pollution problems characteristic of the Kraft
process.
At the completion of the cooking cycle the contents are blown into the
blow tank. The pulp stock is screened to remove knots and undissolved
wood chips and is washed. The stock then enters the bleaching and
paper production sequence.
The digester is a major source of odorous contaminants, particularly
mercaptans and other gases such as methanol, which are released with
steam from digester pop valves, the blow tank, feeder vents, and
accumulator vents ((2) in Figure 7.2.1).
a. Controls
Non-condensible vapors can be vented to the lime kiln, hog fuel
boilers, or to specially constructed gas fired furnaces. In
many operations of this type, condensers (surface or barometric)
must be applied to remove water and other condensible vapors prior
to burning ((3) in Figure 7.2.1). Non-condensible vapors may be
stored in a gas holder or surge tank such as the Vaporsphere to
provide continuous fuel flow to the combustion equipment. Non-
-------
7.2.6
condensible gases from certain operations at some facilities can be vented
to the recovery furnace for firing, as long as these are low volume sources.
For example, gases from brown stock washers can possibly be burned in
the recovery furnace without creating an explosion hazard.
Initial Chemical Recovery
The spent black liquor is separated from the pulp at the stock washer.
The weak black liquor is first concentrated in steam-heated multiple-
effect evaporators (6) which increases the solid content from about 15
percent to 55 to 60 percent in the strong black liquor leaving the
evaporators, as shown in Figure 7.2.2. The solid content is further in-
creased to 60 to 70 percent in the direct contact evaporator where the
liquor is dehydrated by direct contact with the flue gases from the
recovery furnace. Substantial emissions of hydrogen sulfide and other
malodors are released from the condenser following the multiple-effect
evaporators, from hot wells or seal tanks and from the stack of the
recovery furnace, in the case of the direct contact evaporator. Emissions
from the furnace are largely due to stripping of hydrogen sulfide by
carbon dioxide contained in the flue gases. The amount of the emission
depends on how the recovery furnace is operated.
The black liquor is now sufficiently concentrated to support combustion
and is sprayed into the recovery furnace (8) through vertically
oscillating nozzles. The inorganic constituents, sodium sulfide and
sodium carbonate, are reduced in the lower reduction zone of
the furnace and settle out in a molten state or smelt on the
furnace grates. The sulfur organics are oxidized in the upper
zone of the furnace.
The operation of the recovery furnace must be optimized or balanced
to recover the cooking chemicals, to dispose of the sulfur organics
and to satisfy the demand for process steam as well as to control air
pollution. Increased demand for steam, increased or fluctuating firing
-------
non-condensibles
Steam_
45 psi
vaoors
f— -, f~— | f— n f— n
Vapor Hd.
250° F
16 psig
Heating
Element
L k.
1
1
,i
'i
Vapor Hd.
216° F
1 psig
Heating
Element
l
t
1
1
1
1
1
1
L_
1
Vapor Hd.
132° F
10" Hg.vac
Heating
Element
L-
1
1
Vapor Hd
168° F
18" Hg.vac
Heating
r; lament
L_
1
1
1
A :
1 1
r "n
Vapor Hd
145° F
23" Hg.vac
Heating
» Element
i
•steam
condensate
L_
T
1
1
1
i
T
1
water_I_
- -*-
Vaoor Hd.
115
° F
27" Hg.vac
Heating
» Element
i
1
1
! i
1
i
.
. _±. J"
feed
condtnsates
. CONDENSATE
VAPORS
Figure 7.2.2. A TYPICAL MULTIPLE EFFECT EVAPORATOR SYSTEM
(SOURCE: DOUGLASS, Reference 4).
-------
7.2.!
rates, or inadequate supply of primary and secondary air can cause
large-scale releases of products of partial combustion. Odorants
include hydrogen sulfide, mercaptans (especially methyl mercaptan),
dimethyl sulfide and other organic sulfides and dimethyl disulfide
and other disulfides. Particulates include sodium sulfate, sodium
carbonate and carbon and may be emitted at about 170 pounds
per ton of air dried pulp produced by the mill. These are
particles one micron in diameter or less.
a. Controls
Black Liquor Oxidation processes (5) are applied to prevent H S
and other malodorous emissions from the evaporators. In this
process, sodium sulfide is oxidized to thiosulfates, which are
relatively unreactive to the carbon dioxide produced in the recovery
furnace.
The Weak Black Liquor Oxidation Process (14 to 18 percent solids)
reduces malodorous emission in the direct contact evaporator
and in the multiple evaporators (Figure 7.2.3), and produces cleaner
condensates. A bubble tray or packed tower provides counter-current
contact between the black liquor and air. Entrained droplets are
subsequently collected by cyclone. The oxidized liquor is collected
in a foam tank (retention time 5 minutes), where foam is dissipated at
the surface by mechanical agitators or foam breakers. The liquor is then
pumped to the multiple-effect evaporators for further concentration.
Strong Black Liquor Oxidation, a more recent development, is
applied after the multiple-effect evaporators. The system, shown
in Figure 7.2.4, introduces compressed air by means of a sparger or
airheader. To reduce foaming, strong black liquor is sprayed into
the top of the tank. Cyclones are used to collect entrained
-------
t
A I R
LOWER
OXIDIZE DHL I Q U O R
COURTESY A. n. IUNDBERC.IKC.
Figure 7.2.3. WEAK BLACK LIQUOR OXIDATION
(SOURCE: KNUDSON, Reference 6.)
-------
STRONG
LIQUOR
Y C L 0 N E
FOAM
BREAKER
t
I
I
AIR SPARGER
OXIDATION TANK
A I R
COMPRESSOR
COURTESY: CHEMI CO
Figure 7.2.4. STRONG BLACK LIQUOR OXIDATION
(SOURCE: KNUDSON, Reference 6.)
-------
7.2.11
droplets. A retention time of over 2 hours is required. Effective-
ness depends, in part, on proper recovery furnace operation to avoid
excess hydrogen sulfide formation.
Polishing oxidation, instituted recently at a number of Northwest
mills, is a final oxidation stage immediately before the liquor is
fired. It usually is conducted in comparatively small units, like
eductors or a small tank, for counteracting reversion of previously
oxidized liquor.
New recovery furnaces designed to minimize emission of malodors
evaporate the black liquor prior to burning in the recovery furnace
by use of combustion air rather than flue gas. The hot flue
gases are used in a special heat exchanger to heat the combustion
air to 600°F. The heated air is then used in a direct contact
evaporator to concentrate the black liquor prior to firing. The
combustion air then carries any malodorous gases that are released
into the furnace when they are burned.
Another design modification is the direct-firing furnace. The
direct-contact evaporator is replaced by a multiple-effect evaporator
system augmented with a forced circulation concentration evaporator
(Figure 7.2.5). This system is capable of concentrating the black
liquor to about 64 percent solids.
Chemical oxidation, although not used on recovery furnaces but on
other sources indirectly helps to reduce recovery furnace emissions.
A sodium carbonate-bicarbonate scrubbing medium is used to
selectively remove hydrogen sulfide from flue gas and to recover
the sulfur. Reduced furnace firing rates to prevent overloading
of the recovery furnace and utilization of black liquor oxidation
to reduce emissions from the direct-contact evaporator are also
desirable. A corresponding loss of pulping production capacity
may result.
-------
ADDITIONAL
EVAPORATION
CONVENTIONAL
EVAPORATOR
SYSTEM
Steam 50 PSIG
Product
Tank
To Strong
Forced
Circulation
Concentrator
ng
or
^
ag
6
e
4%
, 5C
_G
A;
,
n
\—
F
C
1
rr u
Thv^pp
Pass
' 'Section
39%
/-N C9C/
G
Two
Pass
35%
_o-
Soap
Skimming
Tank
_G-
J
,, Weak
Black
Liquor
13%
Solids
Figure 7.2.5. MULTIPLE EFFECT EVAPORATOR SYSTEM
(SOURCE: HENDRICKSON AND KOOGLER, Reference 1.)
-------
7.2.13
Electrostatic precipitators are applied to recovery furnaces.
Precipitators operate at 97+ to 99+ percent control efficiency and
emit in the range of a tenth of a grain per cubic foot. Scrubbers
are often additionally required to prevent precipitator snowing
(discharge of agglomerated fumes not collected by the precipitator).
The particle sizes emitted are easily collected by low efficiency
scrubbers.
3. Final Chemical Recovery
The smelt flows in bulk from the recovery furnace to the smelt
dissolving tank where it is dissolved in water and weak liquor to form
green liquor, resulting in a violent release of large volumes of steam
and particulates in mist or dust form (12 in Figure 7.2.1).. These
emissions contain highly caustic materials, particularly sodium
hydroxide and sodium hydrosulfide. Uncontrolled emissions may run about
20 pounds/ton of pulp.
The green liquor is pumped to a causticizer (13 in Figure 7.2.1) where it is
treated with slaked lime (calcium hydroxide), clarified and returned to the
digester. Calcium carbonate precipitates from the causticizer solution
as mud which is then filtered, washed and recycled to the lime
kiln where it is calcined to produce lime (calcium oxide). The
uncontrolled lime kiln is a major source of particulates, and can emit
more than 10 tons/day from some plants. Hydrogen sulfide odors also
may form from stripping of residual quantities of sodium sulfide carried
over from the smelt by the carbon dioxide from the lime mud and kiln fuel.
a. Controls
Fine mesh pads and fans are used to improve performance of
demisters and water showers. Venturi, packed tower, and impingement
type scrubbers are also used to control smelt tank emissions.
-------
7.2.14
Lime kiln emissions can be controlled by means of Venturi
Scrubbers. Entrained dust particles are collected in cyclone
collectors following the Venturi. Impingement scrubbers may
also be used, but plugging of nozzles and orifices is frequently
encountered. New fluidized bed lime kilns utilizing Venturi
scrubbers for control of particulates are planned.
4. Other Mill Sources
Steam and electricity required to operate the mill are supplied
from power boilers, combination boilers, and hog burners.
Power plant boilers may be fired by coal, oil or gas and the operation
and pollution problems are similar to other power plant operations,
described in Chapter 6, Section II of this manual. Fly ash and
sulfur dioxide emissions are the primary contaminants of interest.
A combination boiler is usually used to burn bark and at least
one other fuel. The bark boiler or hog fuel burner is used to burn
waste wood materials, including saw dust. These are usually of the
Dutch Oven type equipped with low set spreader stokers. The charge is
fed through chutes. Secondary air is used to control combustion, and
multiclones are used to collect dust and fly ash (see Chapter 6, Section II)
C. INSPECTION POINTS
The control of Kraft emissions may be currently characterized as a
best technology effort, i.e., the air pollution problem is inherent in
the Kraft process, is industry-wide, and control technology continues
to undergo research, development and testing. In some states, emission
standards are set and compliance plans are negotiated specifically
geared to the control of Kraft Mills. Emission standards are set in terms
-------
7.2.15
of pounds of pollutants allowed, for each specific equipment or process
unit, per ton of air dried unbleached pulp (Ib/ADT) processed by
the plant. Malodorous gases are termed Total Reduced Sulfur or TRS,
and are distinguished from sulfur oxides. Examples of emission standards
in effect for the State of Washington are shown in Table 7.2.3.
Specific inspection procedures, especially the citation of(violations,
will depend on the control program and policies of the air pollution
control agency involved. In general, the inspector performs the following
functions:
• Reporting or verifying progress made by the mill in meeting
compliance plan schedules.
• Assuring that day-to-day operation and maintenance practices
serve to minimize pollution wherever possible.
• Reporting breakdown, shutdown or by-passing of process equipment
and changes in pulp production schedules or cooking and chemical
recovery procedures.
• Citing violations that are clearly flagrant in nature.
• Correlating public complaints with air quality measurements,
emission rates and control practices.
The ability to distinguish between odors by character and process (e.g.,
direct contact evaporator, stock washer, terpentine recovery, etc.) is
particularly important in view of the variability in the emission constituents.
The inspector should be trained in the conduct of an odor survey (see
Chapter 6, Section V).
-------
Table 7.2.3. SUMMARY OF KRAFT MILL EMISSION STANDARDS
FOR WASHINGTON STATE
SOURCE
Recovery furnace (s)
Recovery furnace (s)
Digesters and
multi-effect
evaporators
Lime kiln(s)
Smelt tank(s)
POLLUTANT
Total reduced sulfur
(TRS)
Particulates
Total reduced sulfur
Particulates
Particulates
EMISSION STANDARD
ppm, dry Ib/ton
70 and 2C
17.5 and 0.5°
A
Equivalent to reduction
achieved by thermal oxi-
dation in a lime kiln
1
1/2
COMPLIANCE DATE
d
July, 1975
July, 1975
July, 1972
July, 1975
July, 1972
a. As defined in WAC 18-36: for mills less than 200 ton/day, daily emissions equalling
a 200 ton/day are allowed
b. Includes hydrogen sulfide, mercaptans, and disulfides
c. Whichever is the most restrictive
d. Compliance date adjusted by the Board to meet individual mill requirements
(SOURCE: WASHINGTON STATE, Reference 2)
-------
7.2.17
1. Environmental Observations
The environment in the vicinity of Kraft mills should be periodically
surveyed for odors and damage to vegetation and materials, and these
findings correlated with public reactions in neighboring communities
and with specific mill operations wherever possible. Damage to
residences, other structures, automobile surfaces, and other materials
habitually located near the mill should also be investigated.
The principal odors from a Kraft mill are characteristic in terms
of their quality and pervasiveness. Tables 7.2.4 and 7.2.5 illustrate odor
thresholds and qualities by sulfur compound. Other odors, such as
terpenes and methanol, sufficiently differ from hydrogen sulfide and
mercaptans, and are easily recognized. These have the odor of terpentine
or are "medicinal" in character, and tend to be localized around
process equipment particularly stock washers and oxidation towers.
The sulfides and mercaptans, in contrast, can be detected many miles
from the plant.
The inspector should note wherever possible wind direction, wind
speed, humidity and atmospheric stability in his observations and
he should develop a systematic procedure for patrolling and noting
the location, quality and intensity of the odor. Odors may be noted
on an intensity scale or a scentometer may be used. The inspector may
organize a community odor panel consisting of carefully selected citizens
who may help to establish the significance of day-to-day ground level
variations within the normal odor intensity range. An expert odor panel
working under controlled, closed room conditions may also help to isolate
the effect of posi
Chapter 6, Odors.
the effect of possible changes in mill operations. See Section V,
Sulfur compounds (particularly tLS) can discolor and damage
lead based paints and paints containing mercury-based fungi-
cides and may accelerate tarnishing of silver and copper. Dis-
-------
7.2.18
Table 7.2.4. ODOR THRESHOLDS OF KRAFT MILL
GASEOUS SULFUR COMPOUNDS IN AIR
ppm (by volume)
Sulfur Dioxide 1.0-5.0 (a)
Hydrogen Sulfide 0.0085 (b_) , 0.0047 (a). 0.0009 (d.)
Methyl Mercaptan 0.0021 (a.), 0.040 (c) , 0.0006 (d)
Dimethyl Sulfide 0.0001 (a.), 0.0036 (c_) , 0.0003 (d.)
(a) Leonardis, G., Kendall, D., Barnard, N., "Odor Threshold Determinators
of 53 Odorant Chemicals," J.A.P.C.A. (2), 91-5, 1969.
(b) Lederlof, R., Edfor, M. L., Friberg, L., Lindvall, T. , Nordisk Hygenish
Tidskrfit 46, 51, 1965.
(c) Young, F. A., Adams, D. R., Sullivan, Dobbs, "The Relationship between
Environmental-Demographic Variables and Olfactory Detection and Objection-
ability Thresholds" to be published in Perception and Psychophysics.
(d) "Handbook of Air Pollution," U.S.DHEW, PHS, Bureau of State Services,
Division of Air Pollution, Cincinnati, Ohio.
(SOURCE: HENDRICKSON AND KOOGLER, Reference 1.)
-------
7.2.19
Table 7.2.5. CHARACTERISTICS OF KRAFT MILL
GASEOUS SULFUR COMPOUNDS
Compound
Sulfur Dioxide
Hydrogen Sulfide
Methyl Mercaptan
Dimethyl Sulfide
Characteristic
Odor
strong,
suffocating
rotten eggs
rotten cabbage
vegetable
sulfide
(SOURCE: HENDRICKSON AND KOOGLER, Reference 1.)
-------
7.2.20
coloration usually takes the form of browning or blackening of materials
and is enhanced if the surfaces have been moistened or weathered,
depending on the lead content. Fungi will also darken unprotected paints,
so the inspector should, in doubtful cases, have the cause of damage
verified by experts. Vegetation damage also may result from sulfur
dioxide emitted from boiler equipment, as well as from hydrogen sulfide.
Deposits of particulates may result from the fallout of saltcake particles,
fly ash, soot, burned particles and lime, which are usually confined to
within 1/4 to 2 miles from the plant. Some of the fallout is of a
comparatively caustic nature and can damage vegetation, materials and
painted surfaces particularly on vehicles located near the plant. Particles
may be sampled and taken to the laboratory for analysis to help identify
the process sources responsible. Particles high in calcium are generally
emitted from the lime kiln; particles high in sodium may originate from
the recovery furnace and smelt tank; charred or insoluble material
originates from hog burning equipment. Sodium salts, which tend to be more
volatile than other particulates, may be the principal offender. Particulates
which fall out as snow may be due to flocculation of particles in the
electrostatic precipitator. These consist of fluffy aggregates up to 1
millimeter in diameter. The larger aggregates are largely responsibl
for damage to paint and vegetation.
2. Observation of Exterior of Mill
Points of emissions in a Kraft mill include stacks and vents at roof
level, the recesses between plant structures, inside the structures
and ground level. The obvious emissions are the steam plumes and
mists, particularly from the recovery furnace. These can be voluminous
and may travel over great distances and altitudes. The steam and
vapor emissions make it difficult to isolate and read the dry portions
of the plumes. Long plumes, however, are always suspect in view of
the relatively rapid dissipation of steam. Reading visible emissions,
while taking into account the dry and liquid contaminants'is tenable,
-------
7.2.21
but the practice will depend on the policy of the air pollution
control agency involved.
The inspector should become familiar with the quality and intensities
of odors and the visual character of mill emissions as they vary
through the day and with weather conditions. Where abnormal conditions
occur, source testing should be requested. Where an unusual number of
public complaints are reported, the possibility of odors bfeing released
with intermittent emissions from starting up and shutting down of
equipment, opening of digesters, condenser or heat recovery system
failures, overloading of recovery furnace, faulty oxidation tower
operations, etc., should be investigated. Vents on bleaching and other
mill operations, also, should not be ignored, as highly toxic chlorine
gas can be accidentially released.
3. Inspection of the Plant Interior
a. The Interview
In Kraft Mills, the interview is usually conducted with staff that
has been permanently assigned to the air pollution problems of the
plant. The interview should be primarily directed at ascertaining
factors which affect process emissions, control progress and
changes in operating procedures which cannot be noted during the
physical inspection. Recording charts, logs and charts relating to
process performance and emissions can be examined in the office
with the air pollution staff of the mill. The inspector should
clearly establish normal operating procedures in order to be
able to identify abnormal or changing conditions. A procedure
should be adopted and practiced by which the mill reports upsets and
outages to the enforcement agency. Scheduled maintenance,
especially if it involves taking control equipment out of operation,
should be announced in advance.
-------
7.2.22
Information obtained by interview should include:
• Type of Wood Used: resinous content, softwood, hardwood
extent of use of saw dust, etc. The methyl group contained
in certain sulfur based emissions derive from the methoxyl
content of woods. Hardwoods contain more methoxyls than
softwoods, and have greater process odor material.
Resinous woods can cause foaming in oxidation systems.
• Sulfidity. Malodor from the major sources of pollution in the
recovery operation is generally in direct proportion to the
sulfide content of the white liquor, other conditions being
equal. The sulfidity may vary from 12 to 35 percent.
• Cooking Variables. Malodorous emissions can be increased when
cooks are shortened and pressure and temperatures are increased.
• Pulping capacity of the mill should be determined in terms of
tons of unbleached air dried pulp. The inspector should become
familiar with variations in pulping capacity. Substantial
increases in pulping output may cause the capacities of existing
process equipment to be exceeded, including overloading of the
recovery furnace, and excessive emissions from power plant and
other supporting equipment.
• Plant program for monitoring emissions. The inspector should
be familiar with the mill schedule for conducting source
testing and maintenance of continuous monitors, such as the
titrator, discussed later. It is extremely important that the
equipment be kept in good working order. The inspector should
clearly establish any modifications made by the plant to the
instrumentation, and should assure that a formal procedure for
maintaining the accuracy of continuous monitors be adopted.
-------
7.2.23
• Emission inventories, negotiated compliance plans and permits.
The inspector should have available with him information
concerning the equipment and emission inventories of the plant
to determine if significant changes have been made in any of
the major sources that will affect emissions and odors. It is
desirable to compare inventories, process flow diagrams, and
plot plans on file with existing conditions. This can be
accomplished either before or after the tour through the plant.
The black liquor flow, the exact points of emission and firing
rates to the recovery furnace, the lime kiln and the power
boilers and hog burners, in particular, should be noted.
b. The Physical Inspection
The inspection should be organized around two closed systems: (1)
the black liquor system, including the digesters, relief valves,
accumulators, oxidation towers, direct contact evaporator, recovery
furnace, and smelt tank, and (2) the lime kiln and the lime recycling
system. The bleaching plant should also be inspected, particularly
the brown stock washer where water vapor and malodorous contaminants
may be collected by hood and discharged to the atmosphere.
(1) Black Liquor System
In the black liquor system, the inspector should become
familiar with the vents, valves and condensers, the types of
condensers, and associated odors and emissions. The design,
condition and operation of the oxidation towers should be
noted, as these bear on the release of odors from the furnace
and the evaporators. If the foam produced in the towers is
excessive, the foam breakers may become overloaded, causing
them to kickout and allow foam to spill out of the tower.
Systems in which air and black liquor flow concurrently
generally cause less foaming than countercurrent systems.
-------
7.2.24
Spills, indications of poor maintenance and low level odors
should be noted at this point. The foaming action in
oxidation towers can cause operational and maintenance
problems especially from the use of certain softwoods such
as pine and from silt. Problems include corrosion of the
aluminum alloy tank construction due to the alkaline
atmosphere. Also an increase in overall plant pulping
capacity can cause a decrease in the oxidation rate and
hence reformation of sulfides.
(2) TRS Monitors
The operation of the instrument used to monitor total reduced
sulfur should be inspected. A recommended procedure for TRS
measurement is the use of an electrolytic titrator monitor.
This instrument is based on coulometric principles. ' ' '
Readout is based on cell voltage which varies with the
consumption of bromine in the electrolyte as it reacts with
the reduced sulfur compounds (see Figure 7.2.6).
Sources to which the titrator are applied typically include
recovery furnaces and the lime kiln or a gas-fired furnace
if used for disposal of noncondensibles. Particulates are
typically measured at the recovery furnace and lime kiln and
smelt tank, by means of filtration followed by adsorption in
a water bubbler on a batch basis, or by use of other approved
continuous methods.
The recorder is usually located in the instrument room
adjacent to the furnace. The location of the probe in the
duct work should be checked; it is usually located after
the direct contact evaporator. Titrators are temperamental
-------
Recorder
Instrument
Flue
Gas
Pump
Micro _L
Metering V
Valve V
N>
Ui
PRE
SCRUBBER
Titration Dessicant Flow
Cell Meter
Figure 7.2.6. CONTINUOUS STACK SAMPLER FOR TRS COMPOUNDS
(SOURCE: KNUDSON, Reference 10).
-------
7.2.26
instruments, and are usually modified at the plant to
improve sturdiness and reliability. Empirical readings on
these recorders measure up to about 1200 ppm, with a
10 percent loss of accuracy around the 1000 ppm point. Peaks
on strip charts may be due to soot blowing, which may occur
on a two-hour cycle, or to upsets in air ratios. The
inspector should check for tight sampling points to assure
absence of sample dilution.
(3) Recovery Furnace
The inspector should become familiar with the specific design
and operation of the recovery furnace in the plants to which
he is assigned. Many factors enter into achieving optimum
combustion in the furnace from an air pollution standpoint
including the firing rate, secondary air, percent excess
oxygen in the flue gas, black liquor spray droplet size and
time and turbulence. Factors which may be noted on inspection
are excess air and secondary air, and liquor firing rates. In
the recovery furnace control room the following items should
be checked on the operator's log sheet or by instrument
readings:
• Sulfidity of white liquor.
• Percent solids of black liquor.
• Sodium sulfide content of black liquor in and out of
black liquor oxidation unit.
• Voltage and amperage readings of the electrostatic
precipitator.
The following lime kiln operational data should be obtained
from the log sheet:
-------
7.2.27
• Sodium content of washed cake, taken once per day or
shift.
• Scrubber water flow rate and source, by flow meter
reading, once an hour.
• Scrubber pressure drop, by manometer.
The direct reading oxygen recording instrument should also be
checked. Readings below 3 percent may indicate furnace over-
loading. Oxygen recording instruments will usually be located
near the titrator recorder.
A furnace operating log may also be noted in the recovery
furnace area which records the black liquor firing rates as
well as steam output, usually every hour. This information
should be correlated with recovery furnace emissions so that
overloads can clearly be recognized from this performance data.
The inspector should check to see whether the air ports in
the recovery furnace are regularly routed to prevent plugging
and that excess oxygen and proper operating temperature
(usually around 1100°F) are maintained in the upper oxidation
zone of the furnace. The shutting down of secondary air for
any reason can cause an increase in emissions. The inspector
should recognize, however, that steps may have to be taken
on occasion to prevent dangerous situations, such as furnace
or digester explosions.
(4) Lime Kiln System
The lime kiln system should be checked for both particulates
and odors. The make-up rate for saltcake (Ibs./saltcake
added per ton pulp produced) indicates how much of the
-------
7.2.28
sodium and saltcake is being lost to the atmosphere and to
waste water reuse and/or treatment. A loss of 100 Ibs.
saltcake/ton pulp may be reasonable, but the proper figure
must be established with each plant. This information will
be found on the recovery furnace log sheet. Hydrogen sulfide
can form> particularly in long kilns, due to reactions.of carbon
dioxide with sodium sulfide in the carbonate sludge, and to
the introduction of carbonate at the cooler end of the kiln.
In some plants noncondensibles from the hot water accumulators
are carried to the lime kiln for incineration.
-------
7.2.29
REFERENCES
1. Hendrickson, E. R., J. E. Roberson, and J. B. Koogler. Control of
Atmospheric Emissions in the Wood Pulping Industry, Vol. 1-3, Final Report,
Contract No. CPA 22-69-18. March 15, 1970.
2. A Report to the Washington Air Pollution Control Board Prepared in
Conjunction with Rules and Regulations for Kraft Pulp Mills in Washington
Office of Air Quality Control. Washington State Department of Health,
Seattle, Washington. May, 1969. [Figure 7.2.1 based on Figure 1 of
reference 4, p. 42.]
3. Hough, G. W., and L. V. Gross. Air Emission Control in a Modern Pulp and
Paper Mill. Portland, Oregon, Fall Pacific Coast Division Meeting.
Paper Industry Management Association. December 5-7, 1968.
4. Douglass, I. B. The Chemistry of Pollutant Formation in Kraft Pulping.
In: Proceedings of the International Conference on Atmospheric Emissions
from Sulfate Pulping, E. R. Hendrickson (ed.). PHS, National Council
for Stream Improvement. University of Florida, April 28, 1966.
5. Kenline, P. A., and J. M. Hales. Air Pollution and the Kraft Pulping
Industry, an Annotated Bibliography. Environmental Health Series.
DREW, PHS, November 1963.
6. Knudson, J. C. Air Pollution Controls to Meet Washington State Kraft Mill
Standards. Department of Ecology, Redmond, State of Washington. Spokane,
Washington, International Section, Air Pollution Control Association,
November 16-18, 1970.
7. Major, W. D. Variations in Pulping Practices which may Affect Emissions.
In: Proceedings of the International Conference on Atmospheric Emissions
from Sulfate Pulping, E. R. Hendrickson (ed.). PHS, National Council for
Stream Improvement. University of Florida. April 28, 1966.
8. Pulp and Paper Titrator, Model 400, Installation and Operation Manual.
Barton ITT, Process Instruments and Controls. Monterey Park, California.
9. Barton Xitrators, Training Manual, Model 400, Installation and Operation
Manual. Barton ITT, Process Instrument and Controls. Monterey Park,
California.
10. Knudson, J. C. Air Pollution Controls to Meet Washington State Kraft Mill
Standards. Department of Ecology, Redmond, State of Washington. Spokane,
Washington, International Section, Air Pollution Control Association,
November 16-18, 1970.
-------
7.2.30
11. Ayer, C. A Report on the Kraft Pulping Industry's Progress in Complying
with the Emission Regulations of April, 1969. Oregon Department of
Environmental Quality (unpublished).
-------
7.3.1
III. ANIMAL RENDERING
A. DESCRIPTION OF SOURCE
The rendering of animal matter falls into two categories: the salvaging
of edible products and the reclamation of inedible products. Similar
types of processing equipment and air pollution problems are involved
in both activities. This section is primarily concerned with inedible
product recovery.
As unpleasant as rendering operations are, they serve a necessary as well
as a beneficial community function. They provide a method for disposing
of dead animals, meat cutting scraps and poultry dressing scraps which
would otherwise present a health hazard.
Carcasses, meat bone scraps and offal are delivered to the rendering plant.
Preparation of this matter usually consists of skinning and dissecting the
dead animal into segments small enough to be fed to a hogger. Blood and
feathers can also be fed to the process.
Depending on the feedstock, the processing will yield tallow from meat
scraps and offal, and high protein meal for poultry feed from blood and
feathers. Table 7.3.1 describes typical yields of feedstock from
slaughterhouse operations. The table demonstrates the potential quantities
of materials that must be treated in communities where these operations
are located.
B. PROCESS DESCRIPTION
Odors present the principal air pollution problem from rendering, drying
and refining of animal matter. Dust from blood drying, meal grinding and
-------
7.3.2
Table 7.3.1. INEDIBLE REDUCTION PROCESS RAW MATERIALS
ORIGINATING FROM SLAUGHTERHOUSES
Source, Ib live wt
Steers, 1,000
Cows
Calves , 200
Sheep , 80
Hogs, 200
Inedible offal and bone,
Ib/head
90 to 100
110 to 125
15 to 20
8 to 10
10 to 15
Blood,
Ib/head
55
55
5
4
7
(SOURCE: AIR POLLUTION ENGINEERING MANUAL, Reference 1.)
-------
7.3.3
handling are secondary problems. Malodors emanate from most animal matter
operations, especially from rendering cookers. Table 7.3.2 describes
emission rates from the various equipment units and systems found in
rendering operations. Table 7.3.3 quantifies odor threshold values for the
substances associated with the breakdown of animal fat., Some odor threshold
concentrations are in the range of 10 parts per billion.
The reduction of animal matter is carried out in captive plants as an
integral part of the meat packing industry or in separate scavenger plants.
A typical operation is shown in Figure 7.3.1 where skinned carcasses, bone and
meat scraps are loaded into a dump pit, ground in a hogger and screw
conveyed to a steam-heated cooker. Digestion takes place over a 2 to 4
hour cooking cycle on a batch or a continuous basis. The water vapor is
released to the vent system and the residual hot solids are dumped into a
percolator which allows the free tallow to drain to the settling tank. The
cracklings, which still contain a significant quantity of tallow, are
conveyed to a steam-heated press where the remaining tallow is expelled and
drained to a settling tank. The remaining solids are conveyed to a surge
bin or holding vessel and then ground into meal. Final tallow extraction
processes can be aided by the use of soda ash or sulfuric acid to enhance
phase separation. Solvent extraction techniques using hexane in a vapor
tight system, with venting of the solvent vapors to condensers, can be
used for extremely high quality control. Air blowing of the tallow
provides for additional removal of remaining water.
Equipment configurations differ considerably among plants. Modern plants
consist of continuous flow systems. The design of these systems will be
largely based on capacities, types and specifications of products, and the
cooking and drying processes employed. Typical processes include the following:
-------
Table 7.3.2. ODOR CONCENTRATIONS AND EMISSION RATES
FROM INEDIBLE REDUCTION PROCESSES
Source
Rendering cooker,
dry-batch type
Blood cooker,
dry-batch type
Feather drier,
steamtubec
Blood spray
drierc'd
Grease-drying tank,
air blowing
156T
170°F
225°F
Odor concentration,
odor unite/scf
Range
5, 000 to
500, 000
10, 000 to
1 million
600 to
35, 000
600 to
1, 000
Typical average
50, 000
100, 000
2,000
800
4,500
15,000
60, 000
Typical moisture
content of
feeding stocks, %
50
90
50
60
< 5
Exhaust products,
scf/ton of feeda
20, 000
38, 000
77, 000
100, 000
100 scfm
per tank
Odor emission
rate, odor unit/
ton of feed
1, 000 x 106
3, 800 x 106
153 x 106
80 x 106
aAssuming 5 percent moisture in solid products of system.
''Noncondensable gases are neglected in determining emission rates.
cExhaust gases are assumed to contain 25 percent moisture.
dBlood handled in spray drier before any appreciable decomposition occurs.
Definition see Odor Detection and Evaluation, Chapter 6, Section 7.
(SOURCE: AIR POLLUTION ENGINEERING MANUAL, Reference 1.)
-------
7.3.5
Table 7.3.3. ODOR THRESHOLD CONCENTRATIONS OF SELECTED RENDERING COMPOUNDS
Substance
Acrolcln
Ally! amine
Ally) mercaptan3
Ammonia
Dibutyl sulf.de
Ethyl mercapldna
Hydrogen sulfide
Oxidized oiU
Skatole
Sulfur dioxide
Foi mula
CH2:CI-1 CHO
CH2:CIi- CH2- NH2
CI12:CH- CH2-SH
(C4H,,)2S
C2II5 SH
II2S
C.H.NH
so2
Threshold concentration,
me/liter
0.038
0. 067
0. 00005
0. 037
0. 0011
0. 00019
0. 0011
0. 0011
0.0012
0. 009
ppm by volume
16
28
0.016
52
0. 180
0. 072
0.770
0.220
3. 3
obtained with material of varying purity.
(SOURCE: AIR POLLUTION ENGINEERING MANUAL Reference 1.)
-------
7.3.6
EXHAUST VAPORS TO CONTROL EQUIPMENT
HOGGER
A
COOKER
NO. 1
*
PERCOLATOR
HO. 1
1
COOKER
NO. 2
t
PERCOLATOR
NO. 2
1
COOKER
NO. 3
t
PERCOLATOR
NO. 3
FINISH
TALLOW
SETTLING
TANK
MEAL
GRINDER
SURGE
SIN
TALLOW
CRACKLINGS TROUGH KITH SCRE* CONVEYOR
EXPELLER
PRESS
DRAINED CRACKLINGS
Figure 7.3.1. AN INTEGRATED DRY RENDERING PLANT EQUIPPED WITH
BATCH COOKERS, PERCOLATORS, A CRACKLINGS PRESS,
AND A TALLOW-SETTLING TANK. (SOURCE: AIR POLLUTION
ENGINEERING MANUAL, Reference 1.)
-------
7.3.7
1. Dry Rendering Processes
In dry process rendering, animal matter is fed into steam
jacketed cookers to separate the tallow and solids by removing the
moisture from the pulpy mass formed during cooking. Cookers are
operated at, above, or below atmospheric pressure. Cooking under
pressure is conducted at 50 psig and 300°F for 3/4 to 4 hours,
depending on the type of material to be digested. Refractory stocks
such as bones, hooves, hide and hair require relatively greater
temperatures and pressures than organs and tissues.
After pressures are reduced the batch is further cooked at atmospheric
pressure or dried to remove additional moisture and to complete
separation of tallow from solids. Emission rates of odorous contaminants
are a function of the rate of moisture evaporation. The maximum
emissions from atmospheric cookers occur in the initial portion of the
cook, while in pressure cookers the moisture evaporation rate and
emissions proceeds as the temperature builds up.
When cooking is performed under vacuum, moisture is removed at
comparatively lower temperatures to reduce product degradation. A
precondenser, steam ejector and aftercondenser are used to produce
high quality tallow, but incomplete cooking of bones, hair and other
refractory materials may occur. Moisture evaporation and emission
rates are a function of the rate at which the steam generated can be
removed.
The composition of the material usually charged and the tallow (or
grease), solid-, and moisture content are shown in Table 7.3,4. The
moisture content which carries the malodorous contaminants must be
taken into account in the design of air pollution control equipment
which should include surge tanks, condensers and hot wells.
-------
7.3.8
Table 7.3.4. COMPOSITION OF TYPICAL INEDIBLE RAW MATERIALS
CHARGED TO REDUCTION PROCESSES
Source
Packing house offal and bone
Steers
Cows
Calves
Sheep
Hogs
Dead stock (whole animals)
Cattle
Cows
Sheep
Hogs
Blood
Feathers (from poultry houses)
Butcher shop scrap
Tallow or grease,
wt %
15 to 20
10 to 20
8 to 12
25 to 35
15 to 20
12
8 to 10
22
30
37
Solids ,
wt %
30 to 35
20 to 30
20 to 25
20 to 25
18 to 25
25
23
25
25 to 30
12 to 13
20 to 30
25
Moisture,
wt %
45 to 55
50 to 70
60 to 70
45 to 55
55 to 67
63
67 to 69
53
40 to 45
87 to 88
70 to 80
38
(SOURCE: AIR POLLUTION ENGINEERING MANUAL. Reference 1.)
-------
7.3.9
An example of a completely mechanized system using steam jacketed screw
conveyors to facilitate handling in an almost completely enclosed system
is shown in Figure 7.3.2. This is a continuous cooking system in which
the tallow and steam are continuously tapped from the charge at various
points. The charge is slurried with recycled hot tallow prior to
cooking.
2. Wet Processes
In the wet process, the oldest of the animal reduction methods, live
steam is introduced into a closed vessel at pressures of about 60 psig
and 300°F. After separation of the materials to water, tallow and
solids, the pressure is released causing some flashing of steam. Cooking
continues at atmospheric pressure until the phase separation is completed.
Since the resulting water contains a relatively high percentage of
solids, 6 to 7 percent, further evaporation to recover these solids may
be desirable. This process finds application in the rendering of whole
animals but its use is being superceded by dry processing wherever
possible. Vapor emission rates are lower than from dry cookers, as the
bulk of the moisture is removed in the form of water.
3. Feather Cookers
Blood and feather dryers are the same type of equipment as meat and
bone cookers. The charging procedures are different, however. Feathers
must be charged wet and loose. The charging opening should be maintained
under a slight vacuum and vented to the afterburner by-passing the condenser.
Feathers contain mostly protein and virtually no fat and are
processed to produce meal only. This is accomplished by pressure
in a dry cooker. Moisture is removed at ambient pressure in the cooker or
-------
7.3.10
S7EAB SUPPU -
IAIER SUPPLY
BAROMETRIC CONDENSER .
DISINTEGRATOR
STEAM SUPPLY
-AIR AND NON CONDEHSIBIE EIECTOR
SLUDGE HOPPER
IRAdP «Et»l OISCHASGE
»AIE» OISCHAUCE
Figure 7.3.2. A CONTINUOUS, VACUUM RENDERING SYSTEM EMPLOYING
TALLOW RECYCLING (CARVER-GREENFIELD PROCESS)
(SOURCE: AIR POLLUTION ENGINEERING MANUAL,
Reference 1.)
-------
7.3.11
drier. If an air drier is used, the material is transferred to it in
a wet condition. Odor concentrations are generally less and more
variable than from rendering cookers and will depend on freshness of
the feedstock and completeness of previous cooking.
4. Blood Drying
Blood also contains essentially no fat and is used primarily to produce
meal and glue. Packing houses, where blood drying is mostly performed,
usually utilize a continuous process starting at the killing room which
is constructed to drain the blood to holding tanks and to the cookers.
Most processing is accomplished in dry rendering cookers. Dust
emissions can occur during the final portions of the drying cycle.
Tubular evaporators are sometimes used to reduce initial water content
to about 65% prior to transfer of material to the dry rendering cooker.
Spray drying is sometimes used to produce plywood glue. In this air
drying process high quantities of dust-entrained exhaust gases are
produced. Blood can be concentrated in evaporators prior to spray
drying. Blood drying can be very odorous if the blood has insufficiently
aged before processing.
C. AIR POLLUTION CONTROLS
Controls for the reduction or elimination of odors from inedible animal
matter processing are usually condensation, high temperature incinera-
tion, scrubbing, carbon adsorption, or a combination of these methods.
The principal odor-causing constitutents in the steam exhausted from
reduction operations are noncondensible.
-------
7.3.12
The residuals from condensing the large volumes of steam should
either be incinerated, preferably in a waste heat recovery device at
1200°F for no less than 0.3 seconds or adsorbed in an activated carbon
filter. The use of carbon filters presents a problem of regeneration.
The adsorbed material must be stripped from the carbon. This process
cannot be vented directly to the atmosphere since it woul,d have the same
effect as venting the cooking steam to the atmosphere. Therefore, high
temperature incineration is necessary to burn the material stripped
from the carbon. This can be as costly as incineration directly after
condensation.
An operating hazard for vapor collection systems occurs when the vapor
exhaust line becomes plugged with solid material which can be carried
over from the cooking operation (Figure 7.3.3). The system pressure
will build until the material causing the blockage is set free. Unless
there is a surge tank or interceptor in the system, the solid matter
could carry over into the condenser or even the incinerator causing
malfunctions of the odor control equipment. Therefore, a good design
calls for the inclusion of an interceptor vessel in the system.
Table 7.3.5 describes efficiencies of various odor removal systems.
Because of these difficulties, afterburners and condensers should be used
instead of boiler fireboxes to dispose of vapors.
D. INSPECTION POINTS
Due to the severity of the odor problem, rendering plants usually are
covered by public nuisance and permit system regulations. The degree
of control and types of control systems used will depend on whether the
objective is to materially alleviate the odor problem, or to
virtually eliminate it altogether. If the objective is to alleviate
the odor problem, then the use of scrubbers as the ultimate control
device may be acceptable in some regions. If the objective is to
-------
7.3.13
eliminate the odor, then the use of an afterburner, or combination after-
burner and scrubber will be mandatory.
The inspector's primary function with respect to controlled plants will be
to assure that (1) hooding and ventilation systems and control systems are
operated and maintained to meet intended control objectives, (2) feedstocks
are rapidly processed, and (3) effective plant sanitation is practiced.
Control objectives may be stated in terms of design performance
standards, or odor concentration units. The latter may be defined as any
odor or mixture of odors that, when dispersed in one cubic foot of odor-free-
air, produces a median threshold odor detection response as measured by
ASTM D 1391-57 (see Section V, Chapter 6). Table 7.3.2 shows odor
concentrations and emission rates from typical process sources.
1. Environmental Observations
Objectionable odors from rendering plants travel long distances and
are readily reported by citizens. For any rendering source a complaint
pattern defined by prevailing weather conditions and air flow will
emerge. This pattern will serve as a baseline for "monitoring" the
emissions of the plant which can be correlated with attempts to control
the odors, and with operational and maintenance problems and practices
at the plant. If the number of complaints increase above normal, if new
complaints are identified, or odors are reported at new or more distant
locations, then breakdown, negligence or other unusual conditions
should be suspected. The inspector's objective will be to
reduce or eliminate the incidence of complaints by the corresponding
degree of odor reduction at the plant.
-------
7.3.14
Figure 7.3.3. A CONDENSER-AFTERBURNER CONTROL SYSTEM WITH
AN INTERCEPTOR LOCATED BETWEEN THE RENDERING
COOKER AND CONDENSER (95% CONDENSIBLE)
(SOURCE: AIR POLLUTION ENGINEERING MANUAL,
Reference 1.)
-------
Table 7.3,5. ODOR REMOVAL EFFICIENCIES OF CONDENSERS OR AFTERBURNERS,
OR BOTH, VENTING A TYPICAL DRY RENDERING COOKER3
Odors Irom cookers
Concentration,
odor units/scf
50, 000
Emission rate,
odor units /min
25, 000, 000
Condenser
type
None
Surface
Surface
Contact
Contact
Condensate
•F
__
80
140
80
140
Afterburner
•F
1.200
None
1, 200
None
1,200
Concentration,
odors
units /scf
100 to 150
(Mode 120)
100, 000 to
1 0 million
(Mode 500, 000)
50 to 100
(Mode 75)
2, 000 to
20,000
(Mode 10. 000)
20 to 50
(Mode 25)
Modal emission
rate, odor
units/mm
90,000
12, 500, 000
6,000
250, 000
2,000
Odor removal
efficiency,
%
99.40
50
99.93
99
99. 99
.
U)
M
Ln
Based on a hypothetical cooker that emits 500 scfm of vapor containing 5 percent noncondens able gases.
(SOURCE: AIR POLLUTION ENGINEERING MANUAL, Reference 2.)
-------
7.3.16
Knowledge of the citizen response pattern and the specific operations
of rendering plants is very important in tracking down the specific
plant sources responsible, particularly where many rendering plants
are concentrated in a given area. Procedures for tracking odors and
sampling malodorous gases are described in Chapter 6, Section V.
2. Observation of the Exterior of Plant
The structure and layout of individual facilities will differ. Older
plants may tend to be less efficient and more improvisational, with
many of the transfer and storage operations conducted outdoors
or in partially open buildings. The ground surfaces may be unpaved
or cracked and hence difficult to clean and to maintain. Newer plants
should include enclosable structures, washable surfaces, the use of
stainless steel materials, and plant and work layout features which
minimize open storage, treatment and transfer of feedstocks. All
grounds should be paved with Portland cement concrete (not asphalt)
for easier and more complete cleaning. Pit areas should be kept clean
and covered.
Observation of the exterior of the plant will provide much information
on the operation of the possible emissions from scrubbers, afterburners,
and roof vents should be checked. Steam emissions may be noted, as well
as misting of scrubbers. Dry visible emissions are uncommon, except for
possible dusts emitted from grinding and other dry material handling procedures
which do not as a rule extend beyond the plant boundaries. The plant
should be observed periodically, with observations made during evenings,
as well as days, to establish whether abnormal practices are occurring.
The practice of using 55 gallon drums for storage of waste materials
outdoors which have not been properly cleaned should be discouraged.
-------
7.3.17
3. Inspection of the Interior of the Plant
As in all processes which emit odors, gases, and vapors it is important
that a complete source inventory be made and that the inspector become
familiar with the processes and operations that produce the most odors,
so that a baseline of pollution control performance can be established.
The inspector should attempt to distinguish between housekeeping and
process odors and odors which may result from improperly controlled
rendering equipment. The latter are generally dryer and mustier in
quality than the former.
a. Interview with Plant Management
The inspector should attempt to obtain information on the following:
(1) Inventory of feedstocks. Records should be examined or
estimates made of the quantity and. type of feedstocks re-
ceived especially with respect to bone, meat scraps,
carcasses, blood, feathers, stomachs and intestines.
Some feedstocks such as intestines and blood are more odorous
than others. Bone and meat scraps from slaughterhouses and
butcher shops tend to be less odorous. Captive rendering
operations, because they are close to fresh supplies of
animal wastes, usually present less of an odor problem than
do independent Tenderers.
It is important to establish periods when feedstocks are
backlogged. This can be determined from the plant operating
schedule. Odors will substantially increase when backlogs
remain over weekends and holiday shutdown periods,
particularly in warm weather. Plants should be observed on
Monday mornings.
-------
7.3.18
(2) Plant Sanitation Practices. The inspector should determine
if clean-up procedures are regularly practiced as part of
the work schedule. It is important that work tables, drums,
bins, ground surfaces, and sidings be hosed, scrubbed or
otherwise cleaned and that contaminated water not be allowed
to stagnate.
b. The Physical Inspection
The inspector should inspect all facilities and equipment and
should observe the complete operating cycles, including material
handling procedures and storage areas. Special attention should
be given to sources which have high odor potentials, and the
effectiveness of the operation of the control equipment. The
inspector should note the following:
(1) Dead Stock Skinning Room: Relative quantities of carcasses
skinned, in process of skinning, and backlogged; ventilation
rates of the work area; and chemical counteractants used to
relieve employee discomfort.
(2) Cookers! Type and capacities of cookers, temperatures and
pressures on recording equipment, steam and vapor emissions
from equipment doors during loading and unloading, length of
cooking cycle, rotational speed of agitator, and addition
of chemicals such as soda ash to control acidity.
The type and condition of packings and mechanical seals on
doors, hatches and valves should be checked.
The rate of noncondensible emissions is related to the
ventilation and moisture evaporation from the cookers.
Emission rates from dry cookers are generally greater than
from wet cookers. Emissions from continuous operations will
-------
7.3.19
tend to be lower than from batch systems. Emissions from
blood and feather cookers will be comparatively lower. In
the vacuum cooking procedure, the cooking cycle is adjusted
to the rate of steam removal by condensation. Emission
rates tend to increase with pressure cookers. Steam and
vapors must be relieved through by-pass lines.
(3) Vent Lines; Design and condition; leaks in ductwork; type
of condensers (contact, air-cooled, water cooled, surface);
condensate temperatures; quantity of cooling water used5
condition of cooling equipment; handling of condensates; use
of interceptors to prevent fouling of condensers and control
devices'; and type of corrosion resistant materials, such as
stainless steel, used in the construction of the vent lines
and condensers. Where interceptors are not used the
incidence of "wild blows" should be noted, particularly in
dry rendering operations. Wild blows are releases of large
amounts of animal matter at high velocity due to increasing
line pressure. They occur whenever cooker vents become
blocked.
(4) Other Sources.' The inspector should note dumping of cooker
contents into percolators, and collection of offgases by
hoods; the type and operation of the air driers (which are
usually continuous) including moisture content, temperatures
and capacities; and odors from the expeller presses. Emissions
from the percolator pans should be vented to the control
system. The occurrence of visible emissions from the expellers
should be noted.
-------
7.3.20
The grinders, conveyers and handling of pressed solids
should also be noted for possible dust emissions. Particles
are coarse and dust emissions problems are not likely to be
significant.
(5) Air Pollution Control System; The control system may consist
of afterburners, condenser-afterburner combinations, scrubbers
and scrubber afterburner combinations, depending on the
degree of control required. In most cases any
control device which is as effective as incineration at
1200°F is acceptable for use. Minimum required retention
time is 0.3 seconds. A temperature and pressure recording instru-
ment can be furnished to the inspector. Measurement of time
interval should be taken from the inlet to the point where tem-
perature is measured. Removal of exhaust moisture by use of
condensers or scrubbers is required. Hot wells should be
covered and vented to the afterburner. The hot well dis-
charge should not exceed 140°F. Cyclone collectors are
required on the control system if dust emissions are involved.
The inspector should determine the amount of gas available in
relation to the amount required to provide the minimum re-
quired temperature. The combustion zone of the fire box and
calibration of the pyrometers should be checked to assure that
they have not been altered. The inspector may verify the
temperature by using a pyrometer furnished to him by his agency.
Scrubber designs based on packed towers, mobile
beds, meshes, woven clothes, etc. may result in clogging
with resultant releases of odorous emissions. Scrubbers
based on high velocity eliminators (both air and circulating
-------
7.3.21
water) with countercurrent spraying to achieve high saturation
(2)
efficiency may be effective in reducing odor complaints.
Addition of soda ash solution to the scrubber water may also
help to reduce odors, although this must be determined
empirically in each installation. Strong oxidizing solutions
such as chlorine dioxide also may be used. The inspector
t
should note these operational details as well as the capacity
of the water storage tank, the number of water changes, and
the amount of makeup water added to the scrubber. Misting of
the scrubber should also be noted.
Carbon adsorbers may also be as effective as afterburners,
but are largely limited to drier exhaust, or to systems
which cool and dry the gases prior to treatment by control
equipment. Where adsorbers are used, the inspector should
check temperature and moisture contents of exhausts before
and after, carbon life and capacity, frequency of replacement,
and the quality and quantity of carbon used. The desorbed
gases must be contained or destroyed by incineration during
regeneration of the carbon elements.
-------
7.3.22
REFERENCES
1. Walsh, R. T., and P. G. Talens. Reduction of Inedible Animal Matter.
In: Air Pollution Engineering Manual, J. A. Danielson (ed.).
Cincinnati, DHEW, PHS, National Center for Air Pollution Control and the
Los Angeles County Air Pollution Control District. PHS No. 999-AP-40.
1967.
2. Anderson, L. W. Odor Control in Rendering by Wet Scrubbing - A Case History.
Greensboro, North Carolina.
-------
7.4.1
IV. STEEL MILLS-FURNACES
A. DESCRIPTION OF SOURCES
The production of ferrous metals may generally be divided into (1) pig
iron and steel production and (2) secondary metals or product production.
Pig iron production consists of the reduction of iron ore in blast
furnaces. Steel production consists of the reduction of carbon in the
iron and the addition of alloys to specifications usually performed in
electric steel furnaces, open hearth furnaces, and Basic Oxygen Furnaces
(EOF). Secondary ferrous metal production is based on the charging of
either scrap metal, pig iron (ingot) or both, and is treated in Section IX,
Ferrous and Non-Ferrous Foundries.
Emissions from steel mills occur primarilly from charging, oxygen blowing
and tapping operations and take the form of smoke, fumes, dust, and carbon
monoxide. Particulates include, principally, iron oxide, silicon, and
manganese and phosphorous oxides.
Figure 7.4.1 shows the trends in carbon steel production in the United
States by furnace type indicating virtually no production from Bessemer
converters after 1966 and a decline in the use of open hearth furnaces.
Small gains in electric steel operations and a sharp increase in the use
of basic oxygen furnaces (EOF) may be noted. Production of iron and
steel once concentrated in the east and midwest has expanded to the south,
far west and northwestern regions of the United States.
B. PROCESS DESCRIPTION
Steel production begins with the mining of iron ore, coal and limestone.
Iron ore is sintered or pellitized; limestone is crushed and graded, and
coal is processed into coke. These materials are then fed to a blast
furnace and are transferred in the molten state to an open hearth or basic
-------
7.4.2
Process
Open hearth furnace
Basic Oxygen furnace (EOF)
Electric furnace
Total
Production of Raw Steel in 1968
Percent
of Total
Millions of Net Tons
66. 1
48. 6
16.4
133. 1
50.4
37. 1
12.5
100
130
120
I 10
||00
~ 90
o
£ 80
£ 70
I 60
.1 50
~ 40
30
eo
10
o'
- Open Hearth
"Carbon - Steel Ingots
1955 I960 1965 1970 1975
Year
Figure 7.4.1. PRODUCTION OF CARBON RAW STEEL IN TH:
UNITED STATES BY VARIOUS PROCESSES
(SOURCE: BATTELLE, Reference 1)
-------
7.4.3
oxygen furnaces for processing into steel, or in the form of solid pigs
to electric steel furnaces. Some scrap steel is used in all of the steel
making processes. After alloying and reducing carbon, the steel is poured
into ingots for transport to the rolling mill. The furnaces described
below are utilized in steel production.
1. Blast Furnaces
Pig iron or molten iron for steel producing furnaces is produced from
the reduction of iron ore FE 0, (hematite) or Fe 0, (magnetite) to
iron in the blast furnace. Production ranges from 400 to 2400 tons/
(2)
day per furnace. Physically the furnace appears cylindrical but
the diameter increases near the base where a Bustle Pipe or hot blast
air manifold circumscribes the furnace and introduces blast air to
the tuyeres as shown in Figure 7.4.2.
Blast furnace operations are continuous and are only interrupted for
repairs or production cutbacks. The furnace charge or burden consists
of alternate layers of iron ore, coke and limestone. At furnace
startup, wood or other readily ignitable material is used to initiate
combustion of the coke. Blast air, used to support combustion and force
the gases through the burden, is preheated in stoves which are 28' x 100'
cylinders lined with refractory brick. The refractory houses checkerwork
which serves to store heat to increase the temperature of the incoming
air (Figure 7.4.3).
Two or three stoves are used per blast furnace depending on the air
requirements. Since air is the largest single ingredient in the
production of pig iron—4 to 4 1/2 tons of air per ton of iron
produced—the air handling and preheating equipment becomes very
important.
-------
7.4.4
Figure 7.4.2. A TYPICAL BLAST FURNACE
(SOURCE; BATTELLE, Reference 1)
-------
7.4.5
Figure 7.4.3. A TYPICAL BLAST FURNACE STOVE
(SOURCE; BATTELLE, Reference 1)
-------
7.4.6
The typical solid constituents of the burden, 1.7 tons of iron ore, 0.9
ton of coke, 0.4 ton of limestone and 0.2 ton of sinter, scale and
scrap are charged through the top of the furnace by a mechanical
loader. As the melt progresses (the iron ore is reduced by the CO
and hydrogen rising through the burden) a pool of molten iron covered
by slag forms at the bottom of the furnace. Removal of metal and
slag occurs every 4 to 5 hours with the slag usually removed more.
frequently. The molten iron runs into either a ladle or a ladle car
for transport to the steel furnace while still in the molten state,
completing the reduction process.
Electric Steel Furnaces v
Electric steel furnaces are used for the refining and alloying of steel,
especially stainless and specialty steels. The charge consists of
steel scrap and pig iron. It is not common practice to use molten
iron as a part of the charge in electric steel furnaces as it is in
open hearth and EOF operations. Figure 7.4.4 shows a cutaway view
of an electric furnace. Furnace capacities range from 2 to 250 tons
with a melting time of 4 to 5 hours. Most electric steel furnaces
used in production mills in the United States have a basic refractory
lining. The few furnaces that are acid lined are Used for special
steels in foundries.
Physical dimensions of the furnace will, of course, vary with
its capacity but the shape is usually similar to the circular
cross-section and three carbon electrodes projecting from the top of
the furnace, as shown in Figure 7.4.4. The production rate of the
furnace is dependent upon the electrical energy supplied to the
electrodes. Figure 7.4.5 shows the relationship between furnace
capacity and energy input (KVA rating of transformers).
-------
7.4.7
Carbon electrodes
Port fur tlnrd electrode
Figure 7.4.4. DIRECT ARC-ELECTRIC FURNACE
(SOURCE: BATTELLE, Reference 1)
-------
7.4.8
in
e;
E
o
in
c
e
OVJ
70
60
50
40
30
20
10
O
1 1 I 1
0
- —
©
-
* t •
-
e« ® .. *
e e
CC»
w
- f*^-^®o —
€^''*- ^ w
s*^
-
-------
7.4.9
Use of thin sheet iron scrap is generally avoided in electric
furnaces since it tends to burn rather than melt. Care is also
taken not to charge large quantities of dirty scrap which will cause
excessive emissions by its nature. Operating procedures may include
oxygen lancing to shorten the refining cycle, which causes dense
emissions from the boiling of the molten metal.
3. Open Hearth Furnaces
Open hearth furnaces are the major steel producers in the United States.
During the last 5 years production from the basic oxygen process has
more than doubled and there is speculation that by 1990 open hearth
furnaces will be completely replaced by EOF. Open hearths, however,
will remain a factor in air pollution control for many years.
This method of producing steel uses either molten or solid pig iron,
scrap iron and steel, iron ore and limestone and the furnace can be
either acid or basic lined. The open hearth furance (Figure 7.4.6)
is regenerative, i.e., uses the heat removed from the exhaust gases
to preheat the combustion air in two regenerator or checkerwork
sections. Each section serves alternately as the exhaust passage for
the hot products of combustion and the inlet passage for combustion
air and fuel (coke oven gas, natural gas, etc.). Every 15 to 20
minutes dampers are mechanically actuated to change the direction of
flow of the gases, thus the term regenerative furnace.
-------
7.4.10
Furnace Hearth
Figure 7.4.6.
CROSS-SECTION OF A BASIC OPEN-HEARTH FURNACE
(SOURCE: BATTELLE, Reference 1)
-------
7.4.11
PERCENT OF TIME IN
PHASE OF OPERATION INDICATED PHASE
Tap to start (completion of one heat to 6
start of another)
Charging 12
Meltdown 12
Hot-metal addition 3
Ore and lime boil 38
Working-refining 19
Tapping 2
Delay 8
Open hearth furnaces usually produce 100 to 200 tons of steel per
heat which require 12 hours of furnace time without the use of
oxygen, 8 hours with "light" oxygen lancing and 4 hours with "heavy"
oxygen lancing. The process starts after the tap of the previous
heat. This "tap to start" time is used for repairs to the hearth or
other refractory material.
The next step or ore and lime boil, involves the generation of
carbon monoxide from the oxidation of carbon. Gentle bubbling occurs
initially followed by violent bubbling from the release of carbon
dioxide from the calcining of limestone.
-------
7.4.12
During the working or refining phase, the phosphorus and sulfur
are reduced to specification limits, the carbon content is lowered,
proper slag formation is attained and the oxygen is introduced by a
lance immersed in the bath. This final step will consume 900 to
1667 standard cubic feet per minute of oxygen during the injection
period totaling 600 to 1000 cubic feet per ton of metal. The heat is
tapped to a ladle at approximately 3000°F and then either poured into
an ingot mold or conveyed to the foundry to be poured into castings.
4. Basic Oxygen Furnace
This process for making steel is coming into increasing use in the
United States due to the large reduction in the time required to
produce
hearth.
(1 2)
produce a heat, 33 minutes vs. 8 to 12 hours ' for the open
Two principal furnace designs are the upright and the rotary
(Figures 7.4.7 and 7.4.8, respectively). The process in both designs
uses a hot metal charge of scrap steel and flux. The upright furnace
uses a ratio of 70% hot metal to 30% scrap. Rotary furnaces can use
more scrap but require longer heat time. External application of
heat is not required. The hot metal and the exothermic reaction (heat
release) from the oxygen and the carbon and silicon provide the
necessary heat.
In the EOF process a water cooled lance blows oxygen at high velocity
below the surface of the bath causing a violent reaction. The lance
serves to agitate the metal, add heat to the process and to reduce,
by oxidation, the carbon and other elements that are required to
meet the specification of the steel being produced. Furnaces range
from 75 to 325 tons per heat. There are 60 existing upright furnaces
-------
7.4.13
TYPICAL B4SIC OXYGEN FCE
(B.OFJ
Figure 7.4.7. BASIC OXYGEN FURNACE
(SOURCE: BATTELLE, Reference 1)
-------
7.4.14
Figure 7.4.8. STORA-KALDO ROTARY OXYGEN CONVERTER
(SOURCE: BATTELLE, Reference 1)
-------
7.4.15
in the United States and 2 rotary furnaces (1969) which have
a total capacity of approximately 57 million tons/year. The follow-
ing represents a typical 150-ton EOF operation:
Charge Scrap 1 minute
Charge Hot Metal 2 minutes
Oxygen Blow 20 minutes
Chemical Tests 5 minutes
Tapping Time 5 minutes
TOTAL TIME 33 minutes
C. EMISSIONS AND INSPECTION POINTS
Inspection points relative to emissions from iron and steel processes
have certain fundamental characteristics which are the same for all of
the furnace types used. These include furnace charging operations,
melting, working and pouring. In addition, the maintenance of the
furnaces, ductwork and dust/fume collectors must be continually
inspected to determine the effectiveness of the air pollution control
equipment.
1. Blast Furnaces
Most blast furnaces are charged by skip loader from the stock house
for lime and ore and from the coke pile for coke. This operation will
emit dust (iron ore, limestone, coke) when the skips are loaded and
when the load is dumped into the top of the furnace. Since this is
a continuous process some of the dust from the burden will be
entrained in the exhaust gases, which have a high CO content, and will
enter the dust/fume collector. On almost all blast furnaces leaks
around seals and the top of the furnaces are prevalent.
-------
7.4.16
The condition of the material charged to make up the burden can have
a significant effect on the dust emissions. For example, the greater
the ratio of sinter to ore the lower the dust loading in the effluent
gas stream (top gas). As in most systems where there are high
temperature or high pressure gases a by-pass or relief valve (bleeder)
is required for short periods of time to relieve excess pressure
caused by a buildup in the furnace.
Slips, sudden movements or shifts in the burden, create high
pressures in the furnace causing the bleeders to open. Depending on
the make-up of the burden, i.e., ratio of sinter and pellets to
screened ore, large quantities of dust can be emitted at this time.
Because slips cause the bleeder to open, the inspector should record
the frequency and duration of this occurrence and the opacity of the
resultant emissions.
Since the top gas is rich in CO, it is valuable as a fuel for other
steel mill operations which include heating coke ovens, stoves and
for waste heat boilers. This is the major economic factor in the
use of dust/fume removal equipment for blast furnace top gas since
the entrained dust would clog checkerwork in the coke ovens and
stoves. It is anticipated that technology advances in blast furnace
operations involving higher temperatures will require the top gas
to be "cleaned" to 0.001 grams/SCF. The gas cleaning train usually
consists of a cyclone for large particle removal, a wet scrubber
(which also serves as a gas conditioner) and an electrical precipitator,
or venturi scrubber.
To complete the inspection of the furnace cycle the inspector should
also observe the slag and iron tapping operations and record the
opacity and duration of emissions.
-------
7.4.17
2. Electric Steel Furnaces
Air contaminants emitted include smoke from dirty scrap and dust and
fumes from melting. The operation of these furnaces requires the
furnace roof to be removed during charging which poses a control
problem in loading the furnaces. The Bethlehem Steel Corporation in
its Los Angeles plant has abandoned conventional hooding in favor of
using the entire building as a hood and collecting the emissions
(3)
through the roof monitors. Most electric furnaces are controlle
with baghouses, although scrubbers and precipitators are also used.
During the melting period fumes are generated but pose no particular
collection problem. The oxygen blow produces large quantities of
brownish smoke and fumes and is probably the major source of air
pollution in terms of opacity and duration of emissions and the most
difficult to control with conventional hooding. The inspection report
should include the quantity of oxygen used during lancing. This data
is available from the operator's log.
Other observations which must be recorded include the adequacy of the
dust and fume pick up system during pouring; the condition of the
material charged and the charging time; a check of the air pollution
control equipment to determine its operating condition and state of
maintenance (see Chapter 2 for details); the condition of the entire
exhaust system including the state of repair of hoods and ductwork,
exhaust fan and drive belt condition; and opacity of emissions from
the air pollution control equipment exhaust duct.
3. Open Hearth Furnaces
Most open hearth furnaces use hot metal directly from the blast furnace.
The hot metal comprises about 60 percent of the metal charge. The
remainder is scrap steel. Limestone and iron ore are added to provide
a source of oxygen and to form slag. The sources of contaminants from
this process include charging; products of combustion of fuel which
-------
7.4.18
may have a high sulfur content; iron oxide fume from oxygen blowing;
and fumes from tapping and pouring operations. Oxygen lance blowing
also causes large volumes of smoke and fumes. The furnace gases take
a long path through the inside of the furnace, the checkerwork, and
the slag pocket and frequently are passed through a waste heat boiler
which serves to eliminate the larger size particles from the gas stream.
The conventional control equipment applied to this process is an
electrical precipitator; however, venturi scrubbers and baghouses have
also been used.
The inspector should observe emissions from the scrap charged, oxygen
blow, and pour that may escape the dust/fume collection train. The
collection train usually includes an electrostatic precipitator.
Excessive emissions from a stack usually mean either (1) poor condition
of the control equipment because of inadequate maintenance, or (2) a
change in the furnace process, such as use of oxygen lancing where not
previously used, or a considerable increase over the previous lancing
rate.
4. Basic Oxygen Furnaces
Emissions from this process center around the oxygen blowing phase of
the process. The emissions range from iron oxide from the initial
burning of iron when the oxygen blow starts, to silicon, manganese
and phosphorous oxides, and carbon monoxide. In this process, the
hood design for collection of the effluent is critical to (1) capture
of the large volumes of emission from the oxygen blow and (2) to dilute
the concentration of the carbon monoxide to prevent an explosion
hazard. CO combustion to C0_ may also be considered.
Air pollution control equipment predominantly consist of water scrubbers
and electrical precipitators.
-------
7.4.19
The inspector can, by visual observation, determine the effectiveness
of the ventilation system for the collection of emissions from this
furnace. His observations during the oxygen blow and the pour can
help to determine the efficiency of the hood design since most
emissions from this operation are in the visible range. The inspector
should also record the oxygen flow rate and total amount used.
Many of the older EOF's have undersized ventilating and collection
systems because oxygen lancing rates have been increased considerably
beyond what was practiced when these furnaces and control systems
were designed and built. The efficiency of the control equipment,
however, may call for stack testing,
-------
7.4.20
REFERENCES
1. Varga, Jr., J., and H. W. Lownie, Jr. A Systems Analysis Study of the
Integrated Iron and Steel Industry. Columbus, Ohio, Battelle Memorial
Institute. May 15, 1969.
2. Schueneman, J. J., H. D. High, and W. E. Bye. Air Pollution Aspects of
the Iron and Steel Industry. DREW, PHS, DAP. Cincinnati, Ohio. June 1963.
3. Venturini, J. L. Operation Experiences with a Large Baghouse in an
Electric Air Furnace Steelmaking Shop. J. Air Pollution Control Association,
Vol. 20, No. 12.
-------
7.5.1
V. COKING OPERATIONS
A. DESCRIPTION OF SOURCE
The primary use for coke in the United States is in blast furnace pro-
duction of iron and steel. Two types of coking processes are employed:
by-product ovens, which recover volatiles, and beehive ovens which emit
volatiles directly to the atmosphere.
Since 98.5% of the total U.S. coke output, as of 1967, came from by-
product ovens, beehive ovens are not treated in this discussion. The
use of beehive ovens is economically feasible only during periods of high
steel production. Increasingly stringent air pollution regulations should
all but eliminate their use.
The location of coke plants is dictated by the largest user of its product,
the iron and steel producing industry (See Section IV). Many steel mills
conduct their own coking operations, while many coke plants are in-
/
dependent operations. The national distribution of coke plants by
location follows very closely the distribution of major steel producing
facilities although some plants are located near major coal producing
areas. Approximately 60 coke manufacturing plants with an annual capacity
of 60,000,000 tons per year are operated in the United States.
B. PROCESS DESCRIPTION
In coke manufacturing high rank bituminous coals with low ash and sulfur
content are blended, reduced in size, and mechanically conveyed to coke
ovens for carbonizing. Five basic steps are involved (see Figure 7.5.1):
-------
Products of Combustion
From Heating
Storage
Coal
Preparation
and
Blending
Ovens
85 to 90% 1/8"
2— By-products to
control equipment &
chemical recovery
plant.
Hot coke to
quench cars
Quench
Tower
Screening
and Sizing
Storage
Ol
ro
Fuel to heat ovens;
blast furnace gas,
coke gas or a mixture
of both.
Figure 7.5.1. PROCESS FLOW DIAGRAM OF COKING OPERATION
-------
7.5.3
1. Coal blending and preparation to provide the coal properties re-
quired for the physical and chemical characteristics of the coke
desired.
2. Carbonizing in retort ovens to drive off the volatiles from the coal.
3. A pushing sequence in which coke is removed from the ovens and pushed
into gondola quench cars in an incandescent state.
4. Quenching of the coke in quench towers by applying large quantities
of water.
5. Size reduction of the coke to a prescribed specification.
A sixth step, while not a processing operation, is the storage of the coke
in huge piles usually at an area adjacent to the oven. This storage
results in large quantities of dust being blown several miles distant
from the storage piles.
The by-product coke oven is a retort which is externally heated by either
blast furnace gas or coke oven gas to an inner wall temperature of from
2000°F to 2200°F. Coal is formed into coke in the retort oven in the
absence of air. The oven is rectangularly shaped, 39 to 42 feet long,
between 10 and 20 feet high and 14 to 20 inches wide with a 1-1/2 to
4-inch taper from push to discharge end. The oven is charged from a larry
car (hopper car) into three or four ports on its top side. The ovens are
arranged in banks with the larry car riding on rails on the top of the
ovens.
Coal charging rates vary from 16 to 20 tons per oven per charge with a
carbonizing period of 17 to 18 hours. A battery of ovens can consist of
up to 100 slots (individual retort type rectangular cross-section ovens)
operating as a continuous process with alternate charges and "pushes" of
the distillation residue (fused coke) at about 2000 F.
-------
7.5.4
The by-products generated from the coking operation are ducted to ascension
pipes at either or both ends of the retort ovens and are transported under
negative pressure by means of exhaust fans in collector mains to a
conventional chemical treatment plant. The by-products include mixtures of
organic (usually aromatic) compounds, combustible gases (carbon monoxide,
hydrogen, methane, hydrogen sulfide, ammonia, and nitrogen). The organics
include tarry compounds (e.g., anthracene), benzene, toluene, xylene, naththa-
lene, phenols, and pitch. The processing system, shown in Figure 7.5.2,
serves to condense, separate, absorb, distill, clarify, segment and recover
the valuable substances contained in the raw gas.
The coal tar is either sold to refiners or used as fuel in the open hearth
furnaces. The ammonia and pyridine materials can be removed by absorption
in sulfuric acid. The ammonium sulfate which forms in the sulfuric acid
solution is removed and sold to the fertilizer industry while the pyridines
are sold in a crude state to chemical plants where they are further
refined. The coal and gas from the coke ovens yields crude naphthalene >
and various light oils such as benzol, toluol, xylol, etc., which can be
removed by absorption. These are stripped and refined. A prime
product is the recoverable coke oven gas with a gross heating value of
between 500 and 550 Btu per cubic foot. This gas is generated at about
11,000 cubic feet per ton of coal charged to the process. The gas can
be used in various operations, to fire boilers or to provide a source of
energy for other heating needs of the coke plant or its adjacent steel
plants/2^
Serious consideration has been given to technological changes in the
production and manufacture of coke, such as pipeline charging. Any maior
change in operation or control is about two years away, though new pushing and
quenching changes are available now. Since blast furnaces are the
largest consumer of coke, the rate of growth of coke production will
stabilize due to improved technology in blast furnace operations which
-------
7.5.5
i t
Raw Gas and | Coke |
Condensate
|
' n
Gas and Flushing Liquor
Condensate and Tar
*
PRIMARY COOLER [
t *
\ Gas r Condensate
^ I
EXHAUSTER HOT TAR DRAIN TANKS
1 1 1
PRECIPITATOR DECANTER Flushing -»
Liquor
,
REHEATER Tar 1 Ammonia and
Phenols
I
Gas AMMONIA STILL •*
| Acid | * *
'
| Ammonia Weak Ammonia Liquor |
*
SATURATOR PHENOL TOWER | ^
* t * *
Pyridines | Gas | Ammonia Sodium Phenolate |
* Sulfate 1
PYRIDINE ' "
PLANT ACID Further Processing
SEPARATOR
I
FINAL *• SCRUBBER -•
COOLER
GAS Benzolized
HOLDER Wash Oil
i 1
BOOSTER BENZENE
STATION PLANT
| V
Steel Plant Use Debenzolized «.
Wash Oil
Figure 7.5.2. REPRESENTATIVE BY-PRODUCT PLANT FLOW SHEET
(SOURCE: BATTELLE MEMORIAL INSTITUTE,
Reference 3)
-------
7.5.6
will serve to reduce the quantity of coke per ton of steel produced. This
source of smoke and dust is receiving very serious attention from the iron
and steel industry. Extensive investigation leading to newer more self-
contained methods of producing coke are required. Development toward this
end is now underway in Europe but turnaround methods may be 15 years away,
based on the long life of the ovens used in the United States.
C. CONTAMINANTS EMITTED
1. Coke Preparation and Oven Operations
Emissions from coking operations cover a large spectrum from smoke and
particulate matter to carbon monoxide, carbon dioxide, hydrocarbons,
hydrogen sulfide, and phenols occurring mainly during charging and
pushing and from "leaks" around the furnace doors, charging parts,
chuck doors, and any other openings. Charging of the ovens and pushing
are usually the most serious air pollution control problems in coking
operations.
Emission rates are estimated at approximately two pounds per hour of
particulate emissions for every ton of coal processed.^ Gaseous
emission rates, coal preparation losses (directly attributable to coke
operations) and airborne dust from storage piles have not been
conclusively established. The latter frequently results in numerous
complaints from areas adjacent to coke storage locations. The
regulations most commonly violated by this process are opacity or
Ringelmann number, particulate grain loading and nuisance.
In the coke preparation and blending areas the generation and emission
of dust is the principal problem. The operations found here are
size reduction and mechanical conveying. Dust is generated from the
size reduction equipment, transfer points, loading and unloading
points.
-------
7.5.7
By-Product Processing Emissions
Emissions from the primary end of the by-product processing system
usually are minor in amount due to the negative pressure in the trans-
port system. Some odor indicative of free vapor at the tar collectors
and decanters or wherever the liquor runs in lines that are not fully
enclosed may be noted. Ammonia and organic fumes are strong at the
sumps where decanted liquor and other flush liquor is collected for
recycling to the collector-mains sprays. To minimize local nuisance,
the flushing liquor sewers are usually fairly well capped and covered,
but there often is no sealing because these ducts become fouled with
tar and other "goop." Access for stream cleaning is essential, but
is not always frequently used.
Downstream of the exhausters, the detarred gas is still quite rich
in ammonia, both free and in combination. The liquor decanted from
the tar at primary cooling is also quite rich, and because of the
moisture vaporized from wet coal this liquor exceeds the requirements
of the flushing-liquor system. Both the excess liquor and the gas can
be stripped of ammonia, which is recovered usually as ammonium sulfate.
(America's largest coke plant is big enough to recover the ammonia
on a commercial basis as anhydrous ammonia.) In the conventional
sulfate process, the gas is reheated (to hold its moisture in the vapor
phase) and passed through sulfuric acid where ammonium sulfate is
precipitated. Ammonia vapor distilled from the surplus flushing liquor
is also passed through this precipitator. The residue after distillation,
known as weak liquor, may be processed further or disposed of via
sewers or to the coke quench. The residue still contains ammonia
plus a number of soluble organics such as phenols.
Emission to the air from the ammonia system generally is quite minor,
because the ducts are closed piping for the most part, and leaks usually
-------
7.5.8
are promptly detected and repaired. One activity that can cause
trouble in the older plants is the addition of strong sulfuric acid
to the precipitator tank, an operation usually accompanied by
considerable fuming of the acid.
In large coke plants, the ammonia-recovery system may be augmented
by systems for recovery of phenol (carbolic acid) from the weak
liquor after ammonia distillation and for recovery of pyridine bases
which dissolve in the ammonium sulfate precipitator tank from the gas.
In smaller coke plants, one or both of these activities may be by-
passed where volume does not justify capital investment for a recovery
system. Phenol and pyridine systems are closed except for tank vents,
and usually have no substantial problems with regard to emission
to the atmosphere.
The crude tar collected in the collector mains and in the tar
decanters is augmented by minor amounts of tar precipitating at the
secondary coolers or other points in the gas system. From this crude
tar, pitch sludge settles to the bottom of the decanter and is
mechanically raked out for disposal. Settled crude tar is sent to a
separate plant for secondary processing by distillation.
Conventional tar processing yields pitch tar, creosote, and two or
more weights of tar oil that may be used in roadbuilding. Crystals
of naphthalene are a by-product (often discarded), and in larger plants
the tar oils may be further refined to yield salable fractions.
Tars are heavily loaded with polycyclic aromatic hydrocarbons (PAH),
and are generally considered hazardous. Steelmakers have recently
taken steps to lead tar-processing tank vents and storage tank vents
through scrubbers that absorb or destroy the fumes. The work has not
-------
7.5.9
met with great success yet because tars tend to condense upon and foul
the equipment. When the scrubbers get fouled, they will discharge
unscrubbed vent vapor.
Gas leaving the ammonia precipitation tank is still warm and contains
a number of light aromatics boiling between 200 and 400 F. These
light oils are condensed from vapor by cooling the gas to about
ambient temperature in a final cooler. The condensate is then
scrubbed with a high-boiling wash oil (derived from petroleum) to
dissolve the aromatics, and the wash oil may be steam distilled to
recover the principal aromatics benzene, toluene, and xylene in
commercial form. The gas is now completely stripped and enters the
plant fuel system. It contains 3.5 to 4.5 grains of H9S per CF, which
(3)
is emitted as SO. when the gas is burned.
The vapors of the light oils are considered hazardous both because
of toxicity and because of flammability. Nevertheless, the condensers
in the distilling system and some of the process tanks are vented.
The vapors issuing from these vents often pervade a large area with
the sweet, almost pleasant smell characteristic of aromatic vapors.
Abnormalities (such as fire or major leakage) are rare in by-product
systems because the high hazard level prompts strong preventative
measures. However, in the ordinary course of pumping, straining,
dewatering, and otherwise treating coke-oven by-products, leakage
and vapor loss is inevitable. There may be as many as 40 pumps in the
liquor and still systems; usually some of these have imperfect seals.
Forced ventilation in the pumphouse is a necessity.
Identification of particulate emissions from coke-plant operations has
been limited in the past, but as a result of research carried out by
the integrated iron and steel industry since 1950, methods have
-------
7.5.10
been developed that permit the identification of particulate emissions
generated in coke-plant operation. While this research has been
directed primarily toward obtaining a better understanding of the
coking process, and toward improvements in the properties of coke
required by the advancing blast-furnace technology, it has also
provided a means of identifying air-borne particulates.
D. INSPECTION POINTS
The inspector should conduct a complete inventory of the plant, including
the by-product processing system. Charging of the coking ovens is probably
the most important single air pollution problem with which the inspector
will be concerned. The inspector should become familiar with the
equipment employed and the variety of situations that may be encountered
in charging operations.
In the interview of plant management, and subsequent inventory of equipment,
the inspector should determine with respect to charging operations:
1. Is the suction in the header or headers employed sufficient to evacuate
the emissions from the ovens with all ports and doors open? It may be
necessary to charge only through two ports at a time or one port with
the chuck door open.
2. Are sealed dust sleeves between hoppers and oven charging ports employed?
Use of good dust sleeves should choke emissions until hoppers are emptied,
greatly Educing emissions.
3. What type of feeders are employed? Use of screw feeders in place of
gravity type feeders will give better coal flow control and prevent
header stoppage thus lessening emissions.
4. How are charging port lids handled? Use of mechanical opening and
closing devices are more positive and quick acting than manual procedures
thereby reducing emissions.
-------
7.5.11
5. What operating procedures are followed to reduce emissions? Sealing of
ports and good mechanical maintenance are necessary factors in reducing
emissions.
6. What types of mechanical controls are employed, e.g., scrubbers, bag-
houses, etc., and their effectiveness.
1. Dust from Material Transfer
Inspections should be made to assure that hoods covering transfer points
are close fitting and provide sufficient draft to accommodate the dust
emitted as the coal drops from one belt to another, is dumped into a
hopper, or is transferred to other types of mechanical conveyors. Duct-
work must be visually checked to determine dust losses from belts, bucket
conveyors, screws, and other equipment. After all dust pickup points
have been observed, the inspector should check the dust collection equip-
ment to determine if the collection efficiency has degraded since the
initial installation. Dust collectors are usually located on the roof
or outside of the building housing the operation.
In the case of bag type collectors, the inspector can determine if the
bags are torn by noting the opacity or density of the discharge from the
bag house exhaust. He can also determine if the bags are not being pro-
perly shaken or cleaned by the reduced air intake at the hood due to back
pressure in the system from insufficient cleaning of the bags. Other
types of mechanical devices may be more difficult to troubleshoot; however,
the two points, pickup at the dust generating source and discharge from
the collector will give the inspector an overall idea of the effectiveness
of the control system.
The blended and sized coal is conveyed to storage bins above the ovens
and then to the oven charging device, the larry car (Figure 7.5.3).
This is another transfer point which can produce a sizeable dust
-------
[ . „._ __ j _ rtlV^v'ii.u^v-i-^j;;!;'':^";^:-!'!
L TF/ffsvitfz secr/OF
I^Tti'fftJ HtAflNG FLUCS AHO UKDLPJET GAS-DUCTS
Figure 7.5.3. TRANSVERSE AND LONGITUDINAL SECTIONS THROUGH KOPPERS-BECKER UNDERJET-
FIRED LOW-DIFFERENTIAL COMBINATION BY-PRODUCT COKE OVENS
(SOURCE: BATTELLE MEMORIAL INSTITUTE, Reference 3).
-------
7.5.13
emission. An observation of this phase of the operation should
provide the inspector with the information necessary to determine
the effectiveness of the chute enclosure which is designed to contain
dust emitted during coal transfer.
2. Charging Operations
After the larry car has received its load of coal, it will proceed to
the oven for charging. Ports on the top of the oven are either manually
or mechanically removed allowing the larry car to be placed in a position
to discharge the fresh charge into the coking oven. Highly significant
smoke and dust emissions may occur at this point in the operation.
Charging smoke is usually brown in color, in which case opacity
regulations apply.
Consideration is being given to providing quick responding mechanical
controls to open the door, insert a chute, charge the coal and re-
place the door lid as quickly as possible. Currently, however, most
of the operations still use manual labor to open and close the loading
port.
In order to reduce emissions, it is necessary that a conscientious
effort be made by the workmen to replace the doors as soon as possible
after the charge is dumped. During the operation a leveling bar is
inserted at the pushing end of the oven to level the charge (Figure
7.5.4). This causes significant smoke and dust emissions from the
push end of the oven. During the coking operation there can be
emission from the slot doors and charging ports (one at each end of the
oven) unless they are properly sealed. (Modern plants use mechanical
seals in preference to the old luting practices for door sealing.) Also,
where extensive leakage occurs from self-sealing slot oven doors, the
inspector should inspect the doors to see if they are warped, investigate
possible malfunctions in mechanical cleaners, such as blade defects and
-------
7.5.14
THf CHARGING LARRY, WITH HOOPERS CONTAINING MEASURED AMOUNTS Or C-OAL, (S IN POSI-
TION OVCP OfiA^GiNC HOi PS f-ROW WHICH COVf.RS HAVE BEEN REMGVtO. THE PUOHKR MAS
fcCTN ^'OVc.0 INTO POSITION.
15.
P. TH£ 00AC TROW THS I.A1SY HOPPERS HAS DROPPED IMTO THE OVEN OHAMHCI1. fORUIHC
PEAKED PILES.
0. T>: I.CVCLIMC- DOC'I! AT THE TOP OF THE OVf N OOOH ON THE pb'SHEn SIDE K'.C BEtH
AKD THE LEVEL INS 6iR OK THE PUSHER HAS OtEN MOVED BACK AND TOftTH ACROSS THC
PtAr.EO OO^L P'LES TO LrvCIL THLW. TKc 6AR NEXT 13 WITHL^/-WN FROM THEC OVtN.THE
U1VELINO DOOM /.NO CHARGING HOLES ARE CLOStO, AND THE CODING OPERATION BF.GIKS.
Figure 7.5.4. SCHEMATIC REPRESENTATION OF CHARGING AND
LEVELING OPERATIONS FOR A BY-PRODUCT COKE
OVEN (SOURCE: BATTELLE MEMORIAL INSTITUTE,
Reference 3.)
-------
7.5.15
make sure that maintenance crews are properly trained in manual cleaning
procedures. Table 7.5.1 shows the results of methods studied for
(3)
charging and pushing operations.
3. Condition and Operation of Oven
The condition of the oven is best indicated by emissions from doors and
ports and by green pushes. For example:
1. Green pushes - maintenance needed on oven leaks and flue, oven and
flue temperature, normal range (2000-2200°F for oven and 2800 to
3000°F for flue), proper cooking time, overfilling of ovens.
2. Excessive charging emissions - header maintenance required.
3. Emissions around doors - door leaks need correction.
A period of downtime when the ovens are open and being repaired is a
good opportunity for the inspector to examine the internal construction
of the oven. He can determine if there are cracks in the refractory
wall which would allow the products of distillation to excape through
the heating flue; he can see if the ascension pipes and headers have an
excessive accumulation of tars which would prevent the proper seating
of valves and doors, and he can see if there is a build up at the top
of the oven walls which indicates poor heating which causes green coke.
An operational point which must be considered by the operator is the
fact that some "green coal" (uncarbonized) remains near the door at the
end of the coking period. This may account for the large volumes of
smoke and dust arising from the dumped load of coke as the hot green
coal hits the air and bursts into flames. Maintenance of the right flue
temperature, oven tenperature, and proper coking time are operational
variables which can reduce green pushes. Figure 7.5.5 illustrates the
need for good control of coking time. A sharp drop in the evolution of
-------
7.5.16
Table 7.5.1. SEQUENCE OF CHARGING OPERATIONS
(SOURCE: BATTELLE MEMORIAL INSTITUTE, Reference 3)
(a)
Elapsed time ,
minutes
Operations
Potential
Emissions
0.0
2.0
2.7
2.8
4.0
5.0
Larry car is filled at blended-coal
bunker and weighed. Oven doors are
replaced. If lids of charging ports
are removed by hand, this is done now.
Larry car moves to position over the
charging ports. (Automatic lid lifters,
if provided, lift lids.) Drop sleeves
are lowered into ports.
Steam ejector in standpipe is turned on
to draft oven. Coal begins to flow
from hoppers on larry car and first
rush of gases ignites within the oven.
Dust at bunker
discharge.
Generally none.
Smoke emission
begins slowly
at ports.
Heavy rush of smoke, dust, and gas emerges Brown to black
around charging ports as steam formation smoke, with some
increases oven pressures rapidly. flashes of
Hoppers continue to discharge. flame.
Hoppers discharge more slowly as coal in
oven rises to bases of the charging
sleeves. Pusher operator goes to open
the chuck door for leveling.
Coal discharge completed, drop sleeves
raised. On signal from larryman,
leveler bar is pushed all the way across
oven, then cycled back and forth 3 to
5 feet to level the coal.
Continued smoke.
Smoke continues
from ports and
from the chuck
door.
5.7
6.5
After 5 to 7 strokes of the leveler bar,
it is withdrawn. Larryman operates lid-
replacement system, or if none, he moves
the larry car and crew begins to re-
place the lids by hand. Chuck door is
closed and ejector is turned off.
Charging completed.
Smoke continues
until chuck door
and port lids
are well seated.
Smoke via leakage
only.
(a) Attainable with mainly hand operations if coordination between larryman, top
crew, and pusherman is good. Charging of tall ovens or with sequenced dis-
charge of hoppers may take longer, and some time is generally wasted between
steps.
-------
7.5.17
Maximum
I
T3
O
en
O
O
a:
.1
Time
14
Figure 7.5.5.
15 16
Elapsed Coking Time (for Example), hours
17
APPROXIMATE CURVE ILLUSTRATING THE DECLINE IN
GAS AND VAPOR EVOLUTION AT THE END OF THE COKING
CYCLE (SOURCE: BATTELLE MEMORIAL INSTITUTE,
Reference 3.)
-------
7.5.18
volatiles occur in the last two hours of coking indicating that early
pushing will cause higher emissions.
Coke Transfer and Quench Operations
After the coke has been pushed (Figure 7.5.6) into the quench cars,
resulting in substantial smoke and dust emissions, the cars are
transferred to the quench towers where large quantities of water are
used to cool the coke. The resulting emissions are covered by a water
vapor plume; however, the plume may mask heavy grain loadings of
dust. Droplets of corrosive materials (ammonia, phenols) may be found
(2)
in the steam plumes which can cause property damage and complaints.
A. COKiWG Or TH5 COA' ORIGINALLY CrtAi^OF.M INTO THE OVSti HAS PEEK' Gf'VH PTEO (IN ASCOT
19 HOURS) AND ThC O'VTN IS Rli/Dt 10 3E "PUSHED." 1 Hi Os'fN (X>0^ Aiiri fit.'a 5VLO f-ROM
EACH END, AM) THE PLfSHtH, COKE GUIDE AND QUENGIvh'G OVf( ARf f/iOVEO IHTO PG'jIVlON.
RAM OF PUSHCR
B. tHE RAM OF THE PUSHER ADVANCES TO PUSH THE INCAMDLSCENT COKE OUT Of THIT OVEN,
THROUGH THE COKE GUIDE AND INTO THE OUENCHING CAR.
figure 7.5.6. SCHEMATIC REPRESENTATION OF PUSHING OPERATIONS
FOR A BY-PRODUCT COKE OVEN
5. Screening and Sizing
After quench, the coke is transported to the screening and sizing
plant where the unit operations are not unlike those in the coal
preparation operation and requires the same observation techniques.
-------
7.5.19
A problem which is common to all material usually stored in the open
in large piles is the dust which becomes airborne from these piles.
Heavy materials handling equipment is used to move the product,
agitating the pile and abrading the individual pieces of coke and
creating dust which can remain airborne and be transported over long
distances. This problem must be faced in all industrial activities
where material with some percentage of small particles are stored in
the open. Covering the piles, wetting and spraying with a plastic
material are some of the methods that can be used to control the dust
from storage piles.
6. Gas and Vapor Losses
The gases and vapors resulting from the distillation of the coal are
ducted to the chemical recovery plant by either a single header or a
dual header system. A steam injector in the ascension pipe provides
added energy to convey the gases to the relatively long distance to
the recovery plant. The inspector should check these headers and
the ascension pipe for leaks and check any doors or ports for
proper sealing or seating. Proper maintenance of these systems is
essential. The inspector should make sure that the frequency of cleaning
is adequate and that there is good access to all elements of the systems
that must be cleaned.
-------
7.5.20
REFERENCES
1. Control Techniques for Particulate Air Pollutants. Washington, B.C.,
DHEW, PHS, NAPCA, January 1969.
2. Schueneman, J. J., J. D. High, and W. E. Bye. Air Pollution Aspects of
the Iron and Steel Industry. DHEW, PHS, DAP. 1963.
3. Barnes, T. M. , A. D. Hoffman, and H. W. Lownie, Jr. Evaluation of Process
Alternatives to Improve Control of Air Pollution from Production of Coke.
Battelle Memorial Institute. Contract No. PH 22-68-65. January 31, 1970.
-------
7.6.1
VI. PETROLEUM INDUSTRY
A. DESCRIPTION OF SOURCE
Operations of the petroleum industry can logically be divided into
production, refining, and marketing. Production includes locating and
drilling oil wells, pumping and pretreating the crude oil, recovering gas
condensate, and shipping these raw products to the refinery or, in the
case of gas, to commercial sales outlets. Refining, which extends to the
conversion of crude to a finished salable product, includes oil refining
and the manufacture of various chemicals derived from petroleum. This
chemical manufacture is often referred to as the petrochemical industry.
Marketing involves the distribution and the actual sale of the finished
products.
As of January 1967, there were 261 United States refineries capable
of processing nearly 10 million barrels of crude oil daily
representing an investment of roughly 11.4 billion dollars and supplying
approximately 72% of the nation's fuel energy and organic chemical
requirements. Energy consumption in the United States is expected to
double between 1960 and 1975, with petroleum supplying a large share of
the increase. A domestic demand of nearly 14 million barrels per day
is projected by 1975. Nuclear power is not expected to represent a
major energy contributor until the 1980's.
B. PROCESS DESCRIPTION
1. Crude Oil Production
The air contaminants emitted from crude oil production consist chiefly
of the lighter saturated hydrocarbons. The main sources are process
equipment and storage vessels. Hydrogen sulfide gas may be an
additional contaminant in some production areas. Internal combustion
equipment, mostly natural gas-fired compressors, contributes relatively
-------
7.6.2
negligible quantities of sulfur dioxide, nitrogen oxides, and
particulate matter. Potential individual sources of air contaminants
are shown in Table 7.6.1.
Contribution of air contaminants from crude-oil production varies
widely with location and concentration of producing facilities.
Control and pretreatment facilities such as natural gasoline plants
are likely to be located in developed or highly productive areas.
Control equipment for the various air pollution sources associated
with crude-oil production are listed in Table 7.6.1.
2. Oil Refining
The oil refining process consists of rearranging hydrocarbon
molecules obtained from crude oil to produce a variety of petroleum
products, including aviation and automobile gasolines, Diesel and
industrial fuel oils, domestic heating oils, lubrication oils
and greases, kerosene, asphalt and coke, hydrocarbon gases, solvents,
and a variety of specialty products.
The air contaminants emitted from equipment associated with oil-refining
include hydrocarbons, carbon monoxide, sulfur and nitrogen compounds,
malodorous materials, particulate matter, aldehydes, organic acids,
and ammonia. The potential sources of these pollutants are of several
types, as listed in Table 7.6.2.
-------
Table 7.6.1. SOURCES AND CONTROL OF AIR CONTAMINANTS FROM CRUDE-OIL PRODUCTION FACILITIES
(SOURCE: Air Pollution Engineering Manual, Reference 2)
Phase of operation
Well drilling, pumping
Storage , shipment
Compression, absorption,
dehydrating, water treating
Source
Gas venting for production
rate test
Oil well pumping
Effluent sumps
Gas-oil separators
Storage tanks
Dehydrating tanks
Tank truck loading
Effluent sumps
Heaters, boilers
Compressors, pumps
Scrubbers, KO pots
strippers
Tank truck loading
Gas odorizing
Waste-effluent treating
Storage ves sels
Heaters , boilers
Contaminant
Methane
Light hydrocarbon vapors
Hydrocarbon vapors, H^S
Light hydrocarbon vapors
Light hydrocarbon vapors,
H2S
Hydrocarbon vapors, H^S
Hydrocarbon vapors
Hydrocarbon vapors
H2S, HC, SO2, NOX,
particulate matter
Hydrocarbon vapors, H^S
Hydrocarbon vapors, ^S
Hydrocarbon vapors
Hydrocarbon vapors, H2S
H^S mercaptans
Hydrocarbon vapors
Hydrocarbon vapors, H2$
Hydrocarbon, SO2, NOX,
particulate matter
Acceptable control
Smokeless flares, wet-gas-
gathering system
Proper maintenance
Replacement with closed vessels
Relief to wet-gas-gathering
system
Vapor recovery, floating roofs,
pressure tanks, white paint
Closed vessels, connected to
vapor recovery
vapor incineration, bottom loading
Replacement with closed vessels
connected to vapor recovery
Proper operation, use of gas fuel
Mechanical seals, packing glands
vented to vapor recovery
P Y
Vapor return, vapor recovery,
vapor incineration, bottom loading
Positive pumping, adsorption
Enclosed separators, vapor re-
Y
floating roofs
Proper operation, substitute gas
as fuel
-------
Table 7.6.2. POTENTIAL SOURCES OF EMISSIONS FROM OIL REFINING
(SOURCE: Air Pollution Engineering Manual, Reference 2)
Type of emission
Hydrocarbons
Sulfur oxides
Carbon monoxide
Nitrogen oxides
Particulate matter
Odors
Aldehydes
Ammonia
Potential source
Air blowing, barometric condensers, blind changing, blowdown systems, boilers,
catalyst regenerators, compressors, cooling towers, decoking operations, flares,
heaters, incinerators, loading facilities, processing vessels, pumps, sampling
operations, tanks, turnaround operations, vacuum jets, waste-effluent-handling
equipment
Boilers, catalyst regenerators, decoking operations, flares, heaters, incinerators,
treaters, acid sludge disposal
Catalyst regenerators, compressor engines, coking operations, incinerators
Boilers, catalyst regenerators, compressor engines, flares
Boilers, catalyst regenerators, coking operations, heaters, incinerators
Air blowing, barometric condensers, drains, process vessels, steam blowing,
tanks, treaters, waste-effluent-handling equipment
Catalyst regenerators, compressor engines
Catalyst regenerators
a\
•e-
-------
7.6.5
Refinery operations can be classified into four basic procedures:
separation, treating, conversion, and blending.
Crude oil is initially separated into its various components or fractions,
e.g., gas, gasoline, kerosine, middle distillates such as diesel fuel and
fuel oil, and heavy bottoms. Since these initial fractions seldom conform
to either the relative demand for each product or to its qualitative
requirements, the less desirable fractions are subsequently converted to
more salable products by splitting, uniting, or rearranging the original
molecular structure. Separation and conversion products are subsequently
treated for removal or inhibition of undesirable components. The refined
base stocks may then be blended with each other and with various additives
to develop the most useful products.
Individual refineries differ widely, not only as to crude oil capacity,
but also as to the degree of processing sophistication employed.
The rearrangement and modification of hydrocarbons is accomplished by
the following processes singly or in combination:
• Distillation—separation of hydrocarbon molecules according to
boiling range and type in stills and fractional distillation columns.
• Cracking—breaking down of large complicated molecules into different
compounds in catalytic cracking and hydrocracking units.
• Polymerization—joining together smaller hydrocarbon molecules to
form larger molecules in polymerization units.
• Alkylation—substituting or adding an alkyl group such as methyl or
ethyl.
• Hydrogenation and dehydrogenation—altering the hydrocarbon structure
by adding or removing hydrogen in hydrogenation and dehydrogenation
units.
-------
7.6.6
• Isomerization—rearranging molecular structure of hydrocarbon
molecules without changing chemical formula to develop new properties
in compounds.
• Reforming—cracking of hydrocarbon to increase octane rating or to
produce aromatics and paraffins from olefins in reforming. Hydroforming
or Platforming units.
Virtually all of these processes are conducted catalytically at high
temperatures and pressures in suitably designed equipment, or by thermal
processes as in distillation and some cracking processes. Petroleum
stocks are also expensively handled, treated, blended, stored and marketed.
Simple refineries may be confined to crude separation and limited
treating. Intermediate refineries may add catalytic or thermal cracking,
additional treating, and manufacture of such heavier products as lube oils
and asphalts, waxes, and gasoline upgrading processes such as catalytic
reforming, alkylation, or isomerization.
a. Separation
Crude oil is a mixture of many different hydrocarbon compounds, with
also small quantities of compounds containing sulfur, oxygen, nitrogen,
or other elements. Prior to any other processing, it is usually
separated by distillation into fractions of differing volatility. In
order of decreasing volatility (or increasing boiling point, or
increasing carbon number), resulting fractions may be known as wet gas,
gasoline, kerosene, fuel oil, middle distillate, lube distillate,
heavy bottoms. The relative quantity of such "straight-run" products
is determined by the composition of the particular crude being handled.
The products may be treated and sold as finished products, or further
processed and blended into more marketable fuels.
-------
7.6.7
Light hydrocarbons may be further fractionated by absorption processes
or other types of superfractionation. Heavy fractions may be further
fractionated by distillation with steam or in vacuum. Solvent
extraction and crystallization are other separation processes applied
to the recovery of heavier constituents such as waxes and asphalts.
b. Treating
Sulfur, in the form of compounds such as organic sulfides, mercaptans,
polysulfides and thiophenes, is the principal undesirable constituent
of most crude oil. A substantial portion of the domestic crude in
the United States contains over 0.5% sulfur, with some crudes
exceeding 2% sulfur.
Both physical and chemical procedures are available for treating
products and feedstocks for the removal of sulfur. Physical methods
include electrical coalescence, filtration, absorption, and air
blowing. Chemical methods include acid treatment, "sweetening" by
oxidation, solvent extraction, and other means. Hydrodesulfurization
processes are extensively used for treating gasolines, middle
distillates, and lubricating oils. Hydrogenation converts organic
sulfur compounds to hydrogen sulfide, which may be converted to
elemental sulfur in sulfur recovery plants.
c. Conversion
Conversion processes are employed to increase the yield of the more
desirable products such as gasoline, relative to that of less useful
fractions such as middle distillates, and also to improve the quality
of marketed products in terms of engine performance.
-------
7.6.8
Depending on refinery operations and location, between 5 and 10% of
the crude entering the refinery is consumed in processing. Refineries
producing mostly light fuels and having access to low-cost supplies
of natural gas consume less of the crude in this manner. Demands for
unleaded gasolines having adequate antiknock performance may be
expected to increase the fraction of crude that must be processed,
as well as the amount of oil and gas that must be consumed to provide
the energy for processing.
Conversion processes belong to three main categories, depending on
whether the carbon number of the product is smaller, greater, or
about the same as that of the feedstock. Processes of the first type
are referred to as cracking; the main types are thermal cracking
(which includes visbreaking and coking), catalytic cracking, and
hydrocracking. Hydrocracking is done in the presence of a high
partial pressure of hydrogen. It complements ordinary catalytic
cracking and adds flexibility in meeting seasonal products demand
fluctuations. In the second category, converting lighter hydrocarbons
to gasoline-range products, are alkylation and polymerization.
Finally, processes which improve the character of the product without
major effects on the boiling range include a variety of catalytic
reforming processes, as well as isomerization, cyclization,
hydrogenation and dehydrogenation.
d. Blending
The relative few refinery base and intermediate stocks are blended
in innumerable combinations to produce over 2,000 finished products
including liquefied gases, motor and aviation fuels, lubricating oils,
greases, waxes, and heating fuels. Rigid specifications as to vapor
pressure, viscosity, specific gravity, sulfur content, octane number,
initial boiling point, and other characteristics may be required,
depending upon the intended use of the product.
-------
7.6.9
The composition of gasoline, for example, is adjusted to be suitable
to the climate and altitude of various marketing areas. In winter,
refiners add more light hydrocarbons to increase vapor pressure and
facilitate engine starting at lower temperatures. In both winter and
summer, however, vapor pressure must be adjusted to minimize the
problem of vapor lock. Such compromises lead to constant shifting of
hydrocarbon mixtures to produce acceptable performance.
Refiners add to gasoline various chemicals such as antiknock agents
(including tetraethyl lead), detergents, polymerization inhibitors,
and others.
Types of Contaminants
Individual refineries vary greatly as to the character and quantity
of emissions. Controlling factors include crude oil capacity, type
of crude processed, type and complexity of the processing employed,
air pollution control measures in use, and the degree of maintenance
and good housekeeping procedures in force.
The major refining operations offer a guide as to the type of
releases that are likely to be encountered. In crude separation the
use of barometric condensers in vacuum distillation can release
noncondensable hydrocarbons to the atmosphere. Regeneration of
catalyst in cracking by controlled combustion can release unburned
hydrocarbons, carbon monoxide, ammonia, and sulfur oxides. Catalyst
handling systems can also be the source of discharge of catalyst
fines. The conversion processes—alkylation, reforming, polymerization,
isomerization, and their variants—are significant in that they handle
volatile hydrocarbons, and leakage from such equipment as valves and
pumps is of greater importance than in the processing of heavier
fractions.
-------
7.6.10
Air contaminants released from regeneration operations involving
combustion may include catalyst dust and other particulate matter,
oil mists, hydrocarbons, ammonia, sulfur oxides, chlorides, cyanides,
nitrogen oxides, carbon monoxide, and aerosols. The contaminants
evolved by any one type of regenerator depend on the compositions of
the catalyst and reactant, and upon operating conditions.
(3)
Table 7.6.3 presents results of a survey of hydrocarbon emissions
from refinery sources in the Los Angeles area, interpreted in terms
of emission factors related to throughput. Although these estimates
may serve to indicate the possible order of magnitude of such
emissions from various operations, they can be regarded as suggestive
only. More recent and more detailed methods of estimating effluent
(2)
rates can be found in the Air Pollution Engineering Manual.
3. Marke ting
An extensive network of pipelines, terminals, truck fleets, marine
tankers, and storage and loading equipment must be used to deliver the
finished petroleum product to the user. Hydrocarbon emissions from
the distribution of products derive principally from storage vessels
and filling operations. Additional hydrocarbon emissions may occur
from pump seals, spillage, and effluent-water separators. Table 7.6.4
lists practical methods of minimizing these emissions from this
section of the industry.
-------
Table 7.6.3. HYDROCARBON EMISSION FACTORS FOR REFINERY SOURCES
(SOURCE: Chambers, Reference 3)
SOURCE OF EMISSION
Fluid cntalv'ir cracking unit
Therniofor c.italyiic cracking unit
Crude oil storage tanks
Petroleum disiillat*1 storage tanks
Oil-water separators
Oil-water separators
Loading tank trucks & trailers (avg.)
Motor gasoline, 8-12 ibs. RVP
Aviation -,-isolnie, 4-8 Ibs. RVP
Other -Mediates, 1-4 Ibs. 1WP
Pump seals
Mechanical seals
Packed seals
Compressor seals
Compressor seals
Valves (How)
Valves (fiovv)
Relief valves
Relief valves ion process vessels'!
Cooling towers
Cooling tcweis
Treating units
Compressor exhausts
Slowdowns, turnarounds, ves;el & tank
EMISSION FACTOR
NO CUNTUOL
200
50
500
670
-100
300
150
375
170
90
125
5.0
G
8.5
23
0.5
80
2.9
10
ij
8
1
25
CONTROL
10
75(b'i
100(b)
8
I
2
5
2
1
20(c)
3.2
—
—
—
—
—
5
—
—
—
o
—
5
, ,
UNITS(a)
Lbs. per 1 .000 bbls. feed
Lbs per- 1,000 bbh feed
Lbs. per 1 000 bbls. ren'ncry crude
Lbs. per 1,000 bbls. rchriery cilldrt
Lbs. per' 1.000 hbls. refiners' crude
Lbs. pei- 1.000 bbls. waste water
Lbs. per hOi.O bbls. loaded "
Lbs. per 1.000 bbls. loaded'
Lbs. per 1 .000 bbls. loaded
f.bs. pei 1,000 bbls loaded
Lhs per 1.000 bbls. refinery crude
Lbs. per seal per day
Lbs. per seal tier day
Lbs. per 1,000 bbls. refinery crude
Lbs. pr--- s.v! per d,:y
l.bv pe; i.UOO bbls. refinery crude
Lbs. p<>r valve per day
Lbs. v>er i.0(;0 bbls. refinerv crude
Lbs. per \',dvo ]ier day
Lbs. per 1.000 bbls. refinerv crude
Lbs. per 1.000.000 pals, cooling wa
Lbs. pi'r LUi'O bbls. rcfinciv crn<'e
i -i'.s per 1 ,'!00 cubic feet gas burner
Lbs pnr 1,000 bi.ls. refinery crude
throughput
thi oughput
throughput
!
noug.ipu
throughput
t'nroughput
throughput
throughput
throughput
or
throughput
.
throughout
(a) Factor^ are e.vpt essed in uiiit-. of poucds MP: t .000 barrels of rermery cruJe throu^lipnt ^herr, in the opinion of ihc; r.Mthors, the
magnitude oi the same r-ource in dirfeicnt icli'ienc's is rc'atCLl approximate!1,' to tlvir throughputs. In some cases the factois are
expressed in a second unit which rtu^ht prove more convenient.
(b) Floating roof controls. The Lie tor uouU! theoreticr be zero for vapor recovei-y controls.
(c) Control consists of using mechanical seals in place of packed seaK for light hydn.carbon servuf.
-------
Table 7.6.4. SOURCES AND CONTROL OF HYDROCARBON
LOSSES FROM PETROLEUM MARKETING
(SOURCE: Air Pollution Engineering Manual, Reference 2)
Source
Control method
Storage vessels
Bulk-loading facilities
Service station delivery
Automotive fueling
Pumps
Separators
Spills, leaks
Floating-roof tanks; vapor recovery; vapor disposal; vapor balance;
pressure tanks; painting tanks "white
Vapor collection with recovery or incineration; submerged loading,
bottom loading
Vapor return; vapor incineration
Vapor return
Mechanical seals; maintenance
Covers; use of fixed-roof tanks
Maintenance; proper housekeeping
-------
7.6.13
C. AIR POLLUTION POTENTIAL OF PETROLEUM EQUIPMENT
Presented here are abbreviated discussions of the functions and potential
emissions associated with various types of equipment used in the petroleum
industry, especially in refining. For further detail, the reader is
referred to the Air Pollution Engineering Manual.
1. Refining Equipment
a. Flares and Slowdown Systems
Refinery process units and equipment are periodically shut down
for maintenance and repair. Losses from this source are sporadic,
occuring perhaps once in six months to two years, in most cases.
Hydrocarbons purged during shutdowns and startups may be manifolded
to blowdown systems for recovery or flaring. Vapors can be
recovered in a gas holder or compressor and discharged to the
refinery fuel gas system, or they may be vented to flares or
venturi burners. Good instrumentation and properly balanced
steam-to-hydrocarbon ratios are needed to insure smokeless flares.
b. Pressure Relief Valves
In refinery operations, process vessels are protected from
overpressure by relief valves. Corrosion or improper reseating
of the valve seat results in leakage. Proper maintenance through
routine inspections, or use of rupture discs, or manifolding the
discharge side to vapor recovery or to a flare minimizes air
contamination from this source.
-------
7.6.14
c. Storage Vessels
Tanks used to store crude oil and volatile petroleum distillates
are a large potential source of hydrocarbon emissions.
Hydrocarbons can be discharged to the atmosphere from a storage
tank as a result of diurnal temperature changes, filling
operations, and volatilization. Control efficiencies of 85 to
100 percent can be realized by vapor recovery or disposal systems,
floating-roof tanks, or pressure tanks.
d. Bulk-Loading Facilities
The filling of vessels used for transport of petroleum products
is potentially a large source of hydrocarbon emissions. As the
product is loaded, it displaces gases containing hydrocarbons to
the atmosphere. An adequate method of preventing these emissions
consists of collecting the vapors by enclosing the filling hatch
and piping the captured vapors to recovery or disposal equipment.
Submerged filling and bottom loading also reduces the amount of
displaced hydrocarbon vapors.
e. Catalyst Regenerators
In various refining processes, catalysts become contaminated with
coke during operation and must be regenerated or discarded. Thus,
for example, in catalytic cracking, regeneration of the catalyst
is a necessity and is achieved by burning off the coke under
controlled combustion conditions. The resulting flue gases may
contain catalyst dust, hydrocarbons, and other impurities
originating in the charging stock, as well as the products of
combustion.
-------
7.6.15
The dust problem encountered in regeneration of moving bed type
catalysts requires control by water scrubbers and cyclones,
cyclones and precipitators, or high-efficiency cyclones, depending
upon the type of catalyst, the process, and the regenerator
conditions. Hydrocarbons, carbon monoxide, ammonia, and organic
acids can be controlled effectively by incineration in carbon
monoxide waste-heat boilers. The waste-heat boiler offers a
secondary control feature for gases from fluid catalytic cracking
units.
f. Effluent-Waste Disposal
Waste water, spent acids, spent caustic and other waste liquid
materials are generated by refining operations and present
disposal problems. The waste water is processed through
clarification units or gravity separators. Unless adequate control
measures are taken, hydrocarbons contained in the waste water are
emitted to the atmosphere. Control may be achieved by venting the
clarifier to vapor recovery and enclosing the separator with a
floating roof or a vapor-tight cover. Spent waste materials can
be recovered or hauled to an acceptable disposal site.
g. Pumps and Compressors
Pumps and compressors required to move liquids and gases in the
refinery can leak product at the point of contact between the
moving shaft and stationary casing. Properly maintained packing
glands or mechanical seals minimize the emissions from pumps.
Compressor glands can be vented to a vapor recovery system or
smokeless flare.
-------
7.6.16
The internal combustion engines normally used to drive the
compressors are fueled by natural or refinery process gas. Even
with relatively high combustion efficiency and steady load conditions,
some fuel can pass through the engine unburned. Nitrogen oxides,
aldehydes, and sulfur oxides can also be found in the exhaust
gases.
h. Air-Blowing Operations
Venting the air used for "brightening" and agitation of petroleum
products or oxidation of asphalt results in a discharge of
entrained hydrocarbon vapors and mists, and malodorous compounds.
Mechanical agitators that replace air agitation can reduce the
volumes of these emissions. For the effluent fumes from asphalt
oxidation, incineration gives effective control of the hydrocarbons
and malodors.
i. Pipeline Valves and Flanges, Blind Changing, Process Drains
Liquid and vapor leaks can develop at valve stems as a result of
heat, pressure, corrosion, and vibration. Regular equipment
inspections followed by adequate maintenance can keep losses at a
minimum. Leaks at flange connections are negligible if the
connections are properly installed and maintained. Installation or
removal of pipeline blinds can result in spillage of some product.
A certain amount of this spilled product evaporates regardless of
drainage and flushing facilities. Special pipeline blinds have,
however, been developed to reduce the amount of spillage.
In refinery operation, condensate water and flushing water must be
drained from process equipment. These drains also remove liquid
leakage or spills and water used to cool pump glands. Modern
-------
7.6.17
designs provide waste-water-effluent systems with running-liquid-
sealed traps and liquid-sealed and covered junction boxes. These
seals keep the amount of liquid hydrocarbons exposed to the air
at a minimum and thereby reduce hydrocarbon losses.
j• Cooling Towers
The large amounts of water used for cooling are conserved by
recooling the water in wooden towers. Cooling is accomplished by
evaporating part of this water. Any hydrocarbons that might be
entrained or dissolved in the water as a result of leaking heat
exchange equipment are discharged to the atmosphere. Proper
design and maintenance of heat exchange equipment minimizes this
loss. Process water contaminated with odorous material should
not be piped to a cooling tower.
k. Vacuum Jets and Barometric Condensers
Some process equipment is operated at less than atmospheric
pressure. Steam-driven vacuum jets and barometric condensers are
used to obtain the desired vacuum. The lighter hydrocarbons that
are not condensed are discharged to the atmosphere unless
controlled. These hydrocarbons can be completely controlled by
incinerating the discharge. The barometric hot well can also be
enclosed and vented to a vapor disposal system. The water of the
hot well should not be turned to a cooling tower.
1. Effective Air Pollution Control Measures
Control of air contaminants can be accomplished by process change,
installation of control equipment, improved housekeeping, and better
equipment maintenance. Some combination of these often proves the
most effective solution. Table 7.6.5 indicates various methods of
-------
Table 7.6.5. SUGGESTED CONTROL MEASURES FOR REDUCTION OF
AIR CONTAMINANTS FROM PETROLEUM REFINING
(SOURCE: Mr Pollution Enginee~ing Manual, .Reference 2)
Source
Control method
Storage vessels
Catalyst regenerators
Accumulator vents
Slowdown systems
Pumps and compressors
Vacuum jets
Equipment valves
Pressure relief valves
Effluent-waste disposal
Bulk-loading facilities
Acid treating
Acid sludge storage and
shipping
Spent-caustic handling
Doctor treating
Sour-water treating
Mercaptan disposal
Asphalt blowing
Shutdowns, turnarounds
Vapor recovery systems; floating-roof tanks; pressure tanks; vapor balance;
painting tanks white
Cyclones - precipitator - CO boiler; cyclones - water scrubber; multiple cyclones
Vapor recovery; vapor incineration
Smokeless flares - gas recovery
Mechanical seals; vapor recovery; sealing glands by oil pressure; maintenance
Vapor incineration
Inspection and maintenance
Vapor recovery; vapor incineration; rupture discs; inspection and maintenance
Enclosing separators; covering sewer boxes and using liquid seal; liquid seals
on drains
Vapor collection with recovery or incineration; submerged or bottom loading
Continuous-type agitators with mechanical mixing; replace "with catalytic
hydrogenation units; incinerate all vented cases; stop sludge burning
Caustic scrubbing; incineration; vapor return system; disposal at sea
Incineration; scrubbing
Steam strip spent doctor solution to hydrocarbon recovery before air regen-
eration; replace treating unit with other, less objectionable units (Merox)
Use sour-water oxidizers and gas incineration; conversion to ammonium
sulfate
Conversion to disulfides; adding to catalytic cracking charge stock; incin-
eration; using material in organic synthesis
Incineration; water scrubbing (nonrecirculating type)
Depressure and purge to vapor recovery
-------
7.6.19
controlling most air pollution sources encountered in the oil
refinery. These techniques are also applicable to petrochemical
operations. Most of these controls result in some form of economic
saving.
2. Waste-Gas Disposal Systems
Large volumes of hydrocarbon gases are produced in modern refinery and
petrochemical plants. Generally, these gases are used as fuel or as
raw material for further processing. In some instances, these gases
have been considered waste gases and burned, producing large volumes of
black smoke. With modernization of processing units, this method of
waste-gas disposal, even for emergency gas releases, has become less
acceptable to the industry.
Nevertheless, refineries are still faced with the problem of safe
disposal of volatile liquids and gases resulting from scheduled
shutdowns and sudden or unexpected upsets in process units. Emergencies
that can cause the sudden venting of excessive amounts of gases and
vapors include fires, compressor failures, overpressures in process
vessels, line breaks, leaks, and power failures.
-------
7.6.20
A system for disposal of waste gases consists of a manifolded
pressure-relieving or blowdown system, and a blowdown recovery
system of flares for the combustion of the excess gases, or both.
Refinery pressure-relieving systems, commonly called blowdown systems,
are used primarily to ensure the safety of personnel and,protect
equipment in the event of emergencies. In addition, a properly
designed pressure relief system permits substantial reduction of
hydrocarbon emissions to the atmosphere.
The preferred method of disposing of the waste gases that cannot be
recovered in a blowdown recovery system is by burning in a smokeless
flare.
A blowdown or pressure-relieving system consists of relief valves,
safety valves, manual bypass valves, blowdown headers, knockout
vessels, and holding tanks. A blowdown recovery system also includes
compressors and vapor surge vessels such as gas holders or vapor
spheres.
The air pollution problem associated with the uncontrolled disposal
of waste gases is the venting of large volumes of hydrocarbons and
other odorous gases and aerosols. The preferred control method for
excess gases and vapors is to recover them in a blowdown recovery
system and, failing that, to incinerate them in an elevated-type
flare. Such flares introduce the possibility of smoke and other
objectionable gases such as carbon monoxide, sulfur dioxide, and
nitrogen oxides. Flares have been further developed to ensure that
this combustion is smokeless and in some cases nonluminous.
-------
7.6.21
Smoke is the result of incomplete combustion. Smokeless combustion
can be achieved by: (1) adequate heat values to obtain the minimum
theoretical combustion temperatures, (2) adequate combustion air,
and (3) adequate mixing of the air and fuel.
Combustion of hydrocarbons in the steam-inspirated-type elevated
flare appears to be complete. Nevertheless, the results of a field
(4)
test on a flare unit such as this indicate that the hydrocarbon
and carbon monoxide emissions from a flare can be much greater than
those from a properly operated refinery boiler or furnace.
Other combustion contaminants from a flare include nitrogen oxides.
The importance of these compounds depends upon the particular
conditions in a particular locality.
Other air contaminants that can be emitted from flares depend upon
the composition of the gases burned. The most commonly detected
emission is sulfur dioxide, resulting from the combustion of various
sulfur compounds (usually hydrogen sulfide) in the flared gas. Toxicity,
combined with low odor threshold, make venting of hydrogen sulfide to
a flare an unsuitable and sometimes dangerous method of disposal. In
addition, burning relatively small amounts of hydrogen sulfide can
create enough sulfur dioxide to cause crop damage or local nuisance.
Materials that tend to cause health hazards or nuisances should not be
disposed of in flares. Compounds such as mercaptans or chlorinated
hydrocarbons require special combustion devices with chemical
treatment of the gas or its products of combustion.
-------
7.6.22
Storage Vessels
a. Types of Storage Vessels
Storage facilities can be classified as closed-storage vessels
including fixed-roof tanks, pressure tanks, floating-roof tanks
and conservation tanks, and open-storage vessels including open
tanks, reservoirs, pits, and ponds.
Closed-storage vessels are constructed in a variety of shapes,
but most commonly as cylinders, spheres, or spheroids of steel
plate. Capacities of storage vessels range from a few gallons
up to 500,000 barrels.
Open tanks generally have cylindrical or rectangular shells of
steel, wood, or concrete. Reservoirs, pits, ponds, and sumps
are usually oval, circular, or rectangular depressions in the
ground. Any roofs or covers are usually of wood with asphalt or
tar protection. Capacities of the larger reservoirs may be as
much as 3 million barrels.
Some pressure tanks are designed to operate at pressures as high
as 200 pounds per square inch, while others may have pressure
limits of only 2 pounds per square inch. Fixed-roof tanks operate
within only a few ounces per square inch gauge pressure. The
term "gastight," often applied to welded fixed-roof tanks, is
misleading, as many such tanks have free vents open to the
atmosphere. Others are equipped with "conservation" vents opening
at very slight positive pressures. Also, such appurtenances as
hatches, relief vents and foam mixers may fail in service,
resulting in vapor leaks.
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7.6.23
Floating roof tanks are used for storing volatile materials, to
minimize fire and explosion hazards. Vaporization losses from
older types of such tanks may be high. Modern designs usually
incorporate compartmented dead-air spaces and vapor traps which
reduce this problem.
Conservation tanks are vessels of variable volume provided by
lifter-rooves, flexible diaphragms or floating blankets. Open-top
tanks and reservoirs can and should be covered, but vapor losses
remain appreciable if any volatilizable material is stored.
Loading Facilities
Gasoline and other petroleum products are distributed from the
manufacturing facility to the consumer by a network of pipelines,
tank vehicle routes, railroad tank cars, and ocean-going tankers, as
shown in Figure 7.6.1.
As integral parts of the network, intermediate storage and loading
stations receive products from refineries by either pipelines or tank
vehicles. If the intermediate station is supplied by pipeline, it
is called a bulk terminal, to distinguish it from the station supplied
by tank vehicle, which is called a bulk plant. Retail service
stations fueling motor vehicles for the public are, as a general rule,
supplied by tank vehicle from bulk terminals or bulk plants. Consumer
accounts, which are privately owned facilities operated, for example,
to fuel vehicles of a company fleet, are supplied by tank vehicles
from intermediate bulk installations or directly from refineries.
Gasoline and other petroleum products are loaded into tank trucks,
trailers, or tank cars at bulk installations and refineries by means
of loading racks. Bulk products are also delivered into tankers at
bulk marine terminals.
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7.6.24
Figure 7.6.1. REPRESENTATION OF GASOLINE DISTRIBUTION SYSTEM IN
LOS ANGELES COUNTY, SHOWING FLOW OF GASOLINE FROM
REFINERY TO CONSUMER
(SOURCE: Air Pollution Engineering Manual,
Reference 2)
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7.6.25
Loading racks (Figure 7.6.2) are facilities containing equipment to
meter and deliver the various products into tank vehicles from
storage.
Marine terminals have storage facilities for crude oil, gasoline, and
other petroleum products, and facilities for loading and unloading
these products to and from oceangoing tankers or barges. The loading
equipment is on the dock and, in modern terminals, is similar to
elevated-tank vehicle-loading facilities except for size. A pipeline
manifold with flexible hoses is used for loading at older terminals.
Marine installations are considerably larger and operate at much
greater loading rates than inland loading installations.
When a compartment of a tank vehicle or tanker is filled through
an open overhead hatch or bottom connection, the incoming liquid
displaces the vapors in the compartment to the atmosphere. Ordinarily,
but not always, when gasoline is loaded, the hydrocarbon concentration
of the vapors is from 30 to 50 percent by volume.
The volume of vapors produced during the loading operation, as well
as their composition, is greatly influenced by the type of loading
or filling employed. The types in use throughout the industry may
be classified under two general headings, overhead loading and
bottom loading.
Overhead loading, presently the most widely used method, may be
further divided into splash and submerged filling. In splash filling,
the outlet of the delivery tube is above the liquid surface during
all or most of the loading. In submerged filling the outlet of the
delivery tube is extended to within 6 inches of the bottom and is
submerged beneath the liquid during most of the loading. Splash filling
generates more turbulence and therefore more hydrocarbon vapors
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7.6.26
Figure 7.6.2. AN OVERHEAD-CONTROLLED LOADING RACK
(PHILLIPS PETROLEUM, LOS ANGELES, CA.)
(SOURCE: Air Pollution Engineering Manual,
Reference 2)
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7.6.27
than submerged filling does, other conditions being equal. On
the basis of a typical 50 percent splash filling operation, vapor
losses from the overhead filling of tank vehicles with gasoline
have been determined empirically to amount to 0.1 to 0.3% of the
volume loaded.
Bottom loading equipment is simpler than that used for overhead
loading. Loading by this method is accomplished by connecting a
swing-type loading arm or hose at ground level, to a matching fitting
on the underside of the tank vehicles. All the loading is submerged
and under a slight pressure; thus, turbulence and resultant production
of vapors are minimized.
The method employed for loading marine tankers is essentially a
bottom-loading operation. Liquid is delivered to the various
compartments through lines that discharge at the bottom of each
compartment. The vapors displaced during loading are vented through
a manifold line to the top of the ship's mast for discharge to the
atmosphere.
In addition to the emissions resulting from the displacement of
hydrocarbon vapors from the tank vehicles, additional emissions
during loading result from evaporation of spillage, drainage, and
leakage of product.
An effective system for control of vapor emissions from loading must
include a device to collect the vapors at the tank vehicle hatch
and a means for disposal of these vapors.
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7.6.28
5. Catalyst Regeneration
Modern petroleum processes of cracking, reforming, hydrotreating,
alkylation, polymerization, isomerization, and hydrocracking are
commercially feasible because of catalysts, which accelerate specific
reactions. Different catalysts vary in their effects. One might,
for example, increase oxidation rates while another might change the
rate of dehydrogenation or alkylation.
Contact between the catalyst and reactants is achieved in some
processes by passing the reactants through fixed beds or layers of
catalysts contained in a reactor vessel. Contact in other processes
involves simultaneous charging of catalyst and reactants to a
reactor vessel and withdrawal of used catalyst in one stream, and
products and unreacted materials in another stream. The first
process may be termed a fixed-bed system and the latter a moving-bed
system. Moving-bed systems may be further subclassified by the type of
catalyst and method of transporting it through the process. Examples
are the use of vaporized charge material to fluidize powdered catalyst,
as in fluid catalytic cracking units (FCC), and the use of bucket
elevators, screws, airlifts, and so forth, to move the catalyst
pellets or beads, as in Thermofor catalytic cracking units (TCC).
a. Types of Catalysts
Generally, the catalysts used are solids at process temperatures,
though some are liquids. Cracking catalysts are usually
synthetic silica-alumina compositions, including acid-treated
bentonite clay, Fuller's earth, aluminum hydrosilicates, and
bauxite. Bead or pelleted catalyst is used in TCC units while
powdered catalyst is used in FCC units.
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7.6.29
Catalysts employed in catalytic reforming include platinum-
containing catalysts used in fixed-bed reformers, and molybdena-
alumina catalysts used for fluid hydroforming. These catalysts
contain less than 1% platinum supported on a base of either
alumina or silica-alumina. Acid-type catalyst required for
reforming processes may be provided by one of the oxides as the
catalyst base. The acid may be a halogen compound added to the
catalyst, or may be directly added to the reformer charge. The
flow diagram of a platforming process is shown in Figure 7.6.3.
Commercial alkylation processes employ as catalysts either sulfuric
acid, hydrogen fluoride, or aluminum chloride with a hydrogen
chloride promoter.
Commercial polymerization catalysts consist of a thin film or
phosphoric acid on fine-mesh quartz, copper pyrophosphate, or a
calcined mixture of phosphoric acid.
Isomerization processes employ a noble metal, usually platinum,
as the catalyst in a hydrogen atmosphere. Liquid-phase
isomerization is accomplished with aluminum chloride in molten
antimony chloride with a hydrogen chloride activator.
The activity of a catalyst decreases with on-stream time. The rate
of decrease is related to composition of reactants contacted,
throughput rate, and operating conditions. Loss of activity
results from metal contamination and poisoning or from deposits
that coat the catalyst surfaces and thus reduce the catalytic
area available for contact with the reactants. Frequently carbon
from the coking of organic materials is the main deposit. The
procedure of treating the spent catalyst for removal of
-------
7.6.30
p«
CHAftQ
E IHIEBHE«IEB|
" 1
CHARGE
PREHEAT ^
-------
7.6.31
contaminants, called catalyst regeneration, is significant
from the standpoint of air pollution, since combustion is
frequently the method of regeneration.
In fixed-bed systems, catalysts are regenerated periodically in
the reactor or removed and returned to the manufacturer for
regeneration. In moving-bed systems, catalysts are continuously
removed from the reactor, regenerated in a special regenerator
vessel, and returned to the reactor.
b. Regeneration Processes
Catalysts for the catalytic cracking and reforming processes are
regenerated to restore activity by burning off the carbon (coke)
and other deposits from the catalyst surface at controlled
temperature and regeneration air rates. FCC units, all of which
have continuous catalyst regeneration, have a coke burnoff rate
of 5 to 10 times higher than TCC unit regenerators have.
Fixed-bed reformer units and desulfurizer reactors may require
regeneration only once or twice in a year.
Flue gases from catalyst regenerators for FCC units pass through
cyclone separators for removal of most of the catalyst more than
10 microns in size, through a steam generator, where process
steam is made, through a pressure-reducing chamber to air pollution
control units, and then to the atmosphere. Final dust cleanup is
accomplished by passing the effluent gases from the cyclone
separators through an electric precipitator. The gases from the
precipitator are introduced into a carbon monoxide boiler where the
sensible heat and the heat content of the CO is used to produce
steam
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7.6.32
In a TCC unit, spent catalyst (beads) from the base of the reactor
is steam purged for removal of hydrocarbons and lifted to a
hopper above the regeneration kiln. Catalyst fines at this point
in the process are separated from catalyst beads and are collected
in a cyclone separator. Spent catalyst beads drop through a
series of combustion zones, each of which contains flue gas
collectors, combustion air distributors, and cooling coils.
Regenerated catalyst from the bottom of the kiln is then
transferred to the catalyst bin for reuse in the reactor.
The largest quantities of air pollution from catalyst-regenerating
operations are experienced in fluidized cracking units. The
pollutants include carbon monoxide, hydrocarbons, catalyst fines,
dust, oxides of nitrogen and sulfur, ammonia, aldehydes, and
cyanide. Typical losses from fluid catalytic cracking regenerators,
are given by Sussman. '
An improvement made in FCC units in recent vears is a trend
toward the use of zeolite or "molecular sieve" type catalysts
replacing the older amorphous (high aluminum) catalysts. As a
result of using this type catalyst, less particulate emissions
occur from the FCC regenerator. Also, refineries are tending to
make more use of hydrogen where it is now possible to build a
"hydrogen plant." TCC units are beginning to phase out.
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7.6.33
Thermofor catalyst regeneration produces air contaminants
similar to those from fluid catalyst regeneration. Quantities
produced, however, are considerably less. The bead-type catalyst
used in TCC units does not result in the large amount of catalyst
fines that are encountered in FCC units.
Air pollution problems are not as severe from catalyst regeneration
of reforming and desulfurization reactors as those from cracking
units. These reactors are regenerated only once or twice a year
for a period of about 24 hours. The burning of the coke and
sulfur deposits yields hydrocarbons, carbon monoxide, and sulfur
dioxide.
c. Air Pollution Control Equipment
Dust from fluid cracking catalyst regenerators is collected by
centrifugal collectors and electrical precipitators. Carbon
monoxide waste-heat boilers eliminate carbon monoxide and
hydrocarbon emissions in regeneration gases. Centrifugal dust
collectors are used to collect the catalyst fines from Thermofor
regeneration gas.
The carbon monoxide and hydrocarbons in reforming and desulfuriza-
tion catalyst regeneration gases can be efficiently incinerated
by passing the regeneration gases through a heater firebox. In
some installations the sulfur dioxide is scrubbed by passing the
regeneration gases through a packed water or caustic tower.
6. Oil-Water Effluent Systems
Oil-water effluent systems are found in the three phases of the
petroleum industry—production, refining, and marketing. The systems
vary in size and complexity though their basic function remains the
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7.6.34
same, that is, to collect and separate wastes, to recover valuable
oils, and to remove undesirable contaminants before discharge of
the water to ocean, rivers, or channels.
In the production of crude oil, wastes such as oily brine, drilling
muds, tank bottoms, and free oil are generated. Of these, the oilfield
brines present the most difficult disposal problem because of the
large volume encountered.
A typical collection system includes a number of small gathering lines
or channels transmitting waste water to a pit, a sump, or a steel tank.
A pump decants waste water from these containers to water-treating
facilities. Any oil accumulating on the surface of the water is
skimmed off to storage tanks.
The effluent disposal systems found in refineries are larger and more
elaborate than those in the production phase. A typical modern
refinery gathering system usually includes gathering lines, drain
seals, junction boxes, and channels of vitrified clay or concrete for
transmitting waste water from processing units to large basins or
ponds used as oil-water separators. These may be earthen pits,
concrete-lined basins, or steel tanks.
A drawing of a typical separator is shown in Figure 7.6.4.
Factors affecting the efficiency of separation include temperature of
water, particle size, density, and amounts and characteristics of
suspended matter. Stable emulsions are not affected by gravity-type
separators and must be treated separately.
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7.6.35
TRANSVERSE OPENINGS
ELEVATION
Figure 7.6.4. A MODERN OIL-WATER SEPARATOR
(SOURCE: Air Pollution Engineering Manual,
Reference 2)
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7.6.36
The oil-water separator design must provide for efficient inlet and
outlet construction, sediment collection mechanisms, and oil skimmers.
Reinforced concrete construction has been found most desirable for
reasons of economy, maintenance, and efficiency.
The effluent water from the oil-water separator may require further
treatment before final discharge to municipal sewer systems, channels,
rivers, or streams. The methods include (1) filtration, (2) chemical
flocculation, and (3) biological treatment.
Biological treating units such as trickling filters, activated-sludge
basins, and stabilization basins are capable of reducing oil,
biological oxygen demand, and phenolic content from effluent water
streams. To prevent the release of air pollutants to the atmosphere,
certain pieces of equipment, such as clarifiers, digesters, and
filters, used in biological treatment should be covered and vented
to recovery facilities or incinerated.
In the marketing and transportation phase of the industry, waste water
containing oil may be discharged during the cleaning of ballast tanks
of ships, tank trucks, and tank cars. Leaky valves and connections and
flushing of pipelines are other sources of effluents. The methods used
for treatment and disposal of these waters are similar to those used
in the other phases of the industry.
a. The Air Pollution Problem
Among contaminants emitted from liquid waste streams are hydrocarbons,
sulfur compounds, and other malodorous materials.
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7.6.37
These contaminants can escape to the atmosphere from openings in
the sewer system, open channels, open vessels, and open oil-water
separators. The large exposed surface area of these separators
requires that effective means of control be instituted to
minimize hydrocarbon losses to the atmosphere from this source.
b. Asphalt from Crude Oil
Over 90% of all asphalt used in the United States is recovered
from crude oil. Distillation of topped crude under a high vacuum
removes oils and wax as distillate products, leaving the asphalt
as a residue. Residual asphalt can be used as paving material or it
can be further refined by airblowing. Asphalt is also produced
as a secondary product in solvent extraction processes. The
solvent, usually a light hydrocarbon such as propane or butane,
is used to remove selectively a gas-oil fraction from the asphalt
residue.
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 temperatures. 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.
Airblowing is mainly a dehydrogenation process. Oxygen in the
air combines with hydrogen in the oil molecules to form water
vapor. The progressive loss of hydrogen results in polymerization
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7.6.38
or condensation of the asphalt to the desired consistency.
Blowing is usually carried out batch-wise in horizontal or
vertical stills equipped to blanket the charge with steam, but
it may also be done continuously.
Effluents from the asphast airblowing stills include sulfur
compounds, gases, odors, and aerosols. Control of effluent
vapors from asphalt airblowing stills has been accomplished by
scrubbing and incineration. Where removal of air pollutants is
not feasible by scrubbing alone, the noncondensables must be
incinerated.
7. Valves
a. Types of Valves
Valves are employed in every phase of the petroleum industry where
petroleum or petroleum product is transferred by piping from one
point to another. There is a great variety of valve designs, but,
generally, valves may be classified by their application as flow
control or pressure relief.
Flow control valves are used to regulate the flow of fluids.
These valves are subject to product leakage from the valve stem as
a result of the action of vibration, heat, pressure, corrosion, or
improper maintenance of valve stem packing.
Pressure relief and safety valves are used to prevent excessive
pressures from developing in process vessels and lines. The
relief valve designates liquid flow while the safety valve
designates vapor or gas flow. These valves may develop leaks
because of the corrosive action of the product or because of
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7.6.39
failure of the valve to reseat properly after blowoff. Rupture
discs are sometimes used in place of pressure relief valves.
Their use is restricted to equipment in batch-type processes. The
maintenance and operational difficulties caused by the inaccessi-
bility of many pressure relief valves may allow leakage to become
substantial.
b. The Air Pollution Problem
Quantitative data as to actual extent of emissions to the
atmosphere from this leakage are somewhat limited, but available
data indicate that emissions vary over a wide range. The results
of a test program conducted to establish the magnitude of
hydrocarbon emissions from valves are presented in Table 7.6.6.
In this program, valves in a group of 11 Los Angeles County
refineries were surveyed.
An example of low leakage rate was observed in one refinery where
over 3,500 valves handling a wide variety of products under all
conditions of temperature and pressure were inspected. The
average leak rate was 0.038 pound per day per valve.
Examples of high leakage rates were found in two refineries where
all 440 valves inspected in gas service had an average leak rate
of 1.6 pounds per day per valve, and in one other refinery where
all 1,335 valves inspected in liquid service had an average leak
rate of 0.32 pound per day per valve.
These examples illustrate the wide divergence from the average
valve leak rate that can exist among refineries in a single area,
all subject to the same obligations to restrict their emissions
to the greatest possible extent. These results could not be
applied, even approximately, to refineries in other areas.
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7.6.40
Table 7.6.6. LEAKAGE OF HYDROCARBONS FROM VALVES OF
REFINERIES IN LOS ANGELES COUNTY (1958)
(SOURCE: Air Pollution Engineering Manual, Reference 2)
Total number of valves
Number of valves inspected
Small leaksa
Large leaks
Leaks measured
Total measured leakage, Ib /day
Average leak rate—large
leaks, Ib/day
Total from all large leaks,
Ib/day
Estimated total from small
leaks, lb/dayb
Total estimated leakage from
all inspected valves, Ib/day
Average leakage per inspected
valve, Ib/day
Valves in
gaseous service
31,000
2, 258
256
118
24
218
9. 1
1, 072
26
1,098
0.486
Valves in
liquid service
101, 000
7, 263
768
79
76
670
8.8
708
77
785
0. 108
All valves
132, 000
9, 521
1, 024
197
100
888
8.9
1, 780
103
1,883
0. 198
Small leaks are defined as leaks too small to be measured—those estimated to
be less than 0. 2 pound per day.
"Leaks too small to be measured were estimated to have an average rate of 0. 1
pound per day. This is one-half the smallest measured rate.
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7.6.41
These testing programs were also conducted on pressure relief
valves in the same oil refineries. Relief valves on operational
units have a slightly lower leak incidence but a much higher
average leakage rate than valves on pressure storage vessels do.
Moreover, dual-type valves (two single relief valves connected in
parallel to ensure effective release of abnormal pressures) on
pressure storage vessels have a greater leak incidence and a
larger average leakage rate than single-type valves on similar
service do. For valves on operational vessels, the average for
all refineries was 2.9 pounds of hydrocarbons per day per valve.
Average losses from specific refineries, however, varied from
0 to 9.1 pounds per day per valve. Under diverse conditions of
operation and maintenance, emissions can vary greatly from one
refinery to another.
8. Cooling Towers
Cooling towers are designed to cool, by air, the water used to cool
industrial processes. In one style the prevailing wind is used for
the required ventilation. It has become known as the natural draft
or atmospheric type of cooling tower. In contrast, the mechanical
draft cooling tower employs fans to move the air. Spray ponds, once
used extensively for cooling, have now been abandoned in favor of
towers.
The performance of an individual cooling tower is governed by the
ratio of weights of air to water and the time of contact between the
air and water. The required tower size is dependent upon: (1) cooling
range (hot water minus cold water temperature); (2) approach (cold
water minus wet bulb temperature); (3) amount of liquid to be cooled;
(4) wet bulb temperature; (5) air velocity through cell; and
(6) tower height.
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7.6.42
Cooling towers used in conjunction with equipment processing
hydrocarbons and their derivatives are potential sources of air
pollution because of possible contamination of the water. The cooling
water may be contaminated by leaks from the process side of heat-
exchange equipment, direct and intentional contact with process streams,
or improper process unit operation. As this water is passed over a
cooling tower, volatile hydrocarbons and other materials accumulated
in the water evaporate into the atmosphere. When odorous materials
are contained in the water, a nuisance is easily created.
/o \
A survey of the oil refineries operating in Los Angeles County
indicated emissions varied from 4 to 1,500 pounds per cooling tower
per day. Apparently the amount of hydrocarbon present in the water
depends upon the state of maintenance of the process equipment,
particularly the heat-exchange equipment, condensers, and coolers
through which the water is circulated. The quantity and type of
emissions should be determined by observing and testing each tower
individually.
The control of hydrocarbon discharges or of release of odoriferous
compounds at the cooling tower is not practical. Instead, the
control must be at the point where the contaminant enters the cooling
water. Hence, systems of detection of contamination in water, proper
maintenance, speedy repair of leakage from process equipment and piping,
and good housekeeping programs in general are necessary to minimize
the air pollution occurring at the cooling tower. Water that has
been used in contact with process streams, as in direct-contact
or barometric-type condensers, should be eliminated from the cooling
tower if this air pollution source is to be completely controlled.
Greater use of fin-fan coolers can also control the emissions
indirectly by reducing or eliminating the volume of cooling water to be
aerated in a cooling tower.
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7.6.43
9. Miscellaneous Sources
A number of relatively minor sources of air pollution contribute
approximately 10% of the total hydrocarbon emissions to the atmosphere
from refineries including airblowing, blind changing, equipment
turnaround, tank cleaning, use of vacuum jets, and use of compressor
engine exhausts.
a. Airblowing
In certain refining operations, air is blown through heavier
petroleum fractions for the purpose of removing moisture or
agitating the product. The exhaust air is laden with hydrocarbon
vapors and aerosols, and, if discharged directly to the atmosphere,
is a source of air pollution. Results of a survey show emissions
of less than 1/2 ton per day. These refineries operated a total
of seven airblowing units with a combined capacity of 25,000
barrels per day and a total airflow rate of 3,300 cfm. (This does
not include airblowing of asphalt, which has been disucssed
elsewhere in this chapter.) Emissions may be minimized by replacing
the airblowing equipment with mechanical agitators and incinerating
the exhaust vapors.
b. Blind Changing
Refinery operations frequently require that a pipeline be used for
more than one product. To prevent leakage and contamination of
a particular product, other product-connecting and product-feeding
lines are customarily "blinded off." "Blinding a line" is the
term commonly used for the inserting of a flat, solid plate between
two flanges of a pipe connection. In opening, or breaking, the
flanged connection to insert the blind, spillage of product in
that portion of the pipeline can occur.
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7.6.44
Emissions to the atmosphere from the changing of blinds can be
minimized by pumping out the pipeline and then flushing the line
with water before breaking the flange. In the case of highly
volatile hydrocarbons, a slight vacuum may be maintained in the
line. Spillage resulting from blind changing can also be
minimized by use of "line" blinds which do not require a complete
break of the flange connection during the changing operation.
Equipment Turnarounds
Periodic maintenance and repair of process equipment are essential
to refinery operations. A major phase of the maintenance is the
shutting down and starting up of the various units, usually
called a turnaround.
In general, shutdowns are effected by first shutting off the heat
supply to the unit and circulating the feed stock through the
unit as it cools. Gas oil may be blended into the feedstock to
prevent its solidification as the temperature drops. The cooled
liquid is then pumped out to storage facilities, leaving hydro-
carbon vapors in the unit. The pressure of the hydrocarbon vapors
in the unit is reduced by evacuating the various items of
equipment to a disposal facility such as a fuel gas system, a
vapor recovery system, a flare, or in some cases, to the
atmosphere. Discharging vapors to the atmosphere is undesirable
from the standpoint of air pollution control. The residual
hydrocarbons remaining in the unit after depressuring are purged
out with steam, nitrogen, or water. Any purged gases should be
discharged to disposal facilities. Condensed steam and water
effluent that may be contaminated with hydrocarbons or malodorous
compounds during purging should be handled by closed water-treating
systems.
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7.6.45
d. Tank Cleaning
Storage tanks in a refinery require periodic cleaning and repair.
For this purpose, the contents of a tank are removed and residual
vapors are purged until the tank is considered safe for entry by
maintenance crews. Purging can result in the release of
hydrocarbon or odorous material in the form of vapors to the
atmosphere. These vapors should be discharged to a vapor recovery
system or flare.
Steam cleaning of railroad tank cars used for transporting
petroleum products can similarly be a source of emissions if the
injected steam and entrained hydrocarbons are vented directly to
the atmosphere. Some measure of control of these emissions may
be effected by condensing the effluent steam and vapors. The
condensate can then be separated into hydrocarbon and water
phases for recovery. Noncondensable vapors should be incinerated.
e. Use of Vacuum Jets
Certain refinery processes are conducted under vacuum conditions.
The most practical way to create and maintain the necessary
vacuum is to use steam-actuated vacuum jets, singly or in series.
Barometric condensers are often used after each vacuum jet to
remove steam and condensable hydrocarbons.
The effluent stream from the last stage of the vacuum jet system
should be controlled by condensing as much of the effluent as is
practical and incinerating the noncondensables in an afterburner
or heater firebox. Condensate should be handled by a closed
treating system for recovery of hydrocarbons. The hot well that
receives water from the barometric condensers may also have to
be enclosed and any off gases incinerated.
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7.6.46
f. Use of Compressor Engine Exhausts
Gas compressors are often driven by internal combustion engines
that exhaust contaminants to the atmosphere. Although these
engines are normally fired with natural gas and operate at
essentially constant loads, some unburned fuel passes through the
engine. Oxides of nitrogen are also found in the exhaust gases
as a result of nitrogen fixation in the combustion cylinders.
D. INSPECTION POINTS AND PROCESS INVENTORIES
1. Initial Inspection Procedures
Due to the operational complexity of petroleum refineries, petrochemical
and chemical plants and other allied activities, a degree of specializa-
tion, training, and considerable experience is required on the part of
an effective refinery inspector. For such industries it is necessary
to prepare technical reports of processes in terms of both written and
graphic presentation to describe and determine the air pollution
potentials of the process units being inspected. Special inventory
forms for various types of equipment, operations, processes, or plants
are helpful at inspections to ensure coverage of specific points. This
procedure is required for these reasons:
• Because similar process vessels are used in various source activities
and are grouped in interdependent relationships, attempts to individually
itemize pieces of equipment often lead to confusion and
disorientation.
• Air pollution potentials can be better determined from an inventory
of functions of process vessels, than from itemization of equipment
units. Process inventories may also require field surveys of
product flows, throughput capacities, and emission factors.
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7.6.47
• Refinery and chemical plant inventories thus categorize,
itemize, and present data as will directly determine not only
compliance with permit regulations, but also with equipment
regulations.
To collect such information, a special inventory system is adapted to
each refinery. In order to adequately cover each of the multiple
operations of a refinery or large petrochemical plant, a system of
unitization is used in which the plant area is subdivided into
process units. (Those units with the greatest air pollution potentials
are subsequently given added emphasis by assigning higher rates of
inspection.)
Plant ownership data is recorded separately on a Plant Card. It is
most important to know who the responsible officials are and how they
can be quickly contacted either by a field inspector or by telephone.
Where accurate field data exists in the inventory files, it is
possible to make a preliminary investigation of refinery problems by
telephone.
To insure that the other refineries in the area continue to receive
surveillance when the inspector is busy at one refinery, the areas in
which the refineries are situated are sectioned and carefully checked
by patrols using a Refinery Check Sheet. On this sheet each refinery
to be checked is listed. The time of observation is noted, along with
any pertinent remarks concerning significant observations of each
refinery. Such remarks include notations of odor, visible emissions,
wind direction, etc.
-------
7.6.48
The inventory records for each refinery or petrochemical plant
consist of a group of file folders, each folder dealing with one of
the process units. One or more process units may constitute what has
been defined as the Source Activity. Hence, one inspection or
inventory is made of one or more process units programmed as a unit
for reinspection. At the head of each refinery file group is a
numbered index of all distinct source activities within the refinery.
Each number is cross-referenced to the location of the folder
containing the appropriate source activity.
Within the folder for a given source activity, the following types of
records should appear.
• A general description of the process including an analysis of its
purpose and function in the order of the flow or processing
sequence. Generally, the analysis traces the flow of materials
from introduction through various sidestreams to final effluents.
• A list of the various pieces of equipment contained in the process
unit and their function.
• The air pollution potentials of the process or the equipment
should include an analysis of any important problems. This
discussion should include, if possible, estimates of the
contaminants emitted and their chemical designations, odor quality
and intensity, opacities, or physiological effects, as well as
the potential hazards of the stocks or products released should
equipment failure occur.
• Throughput of volatile materials and estimates of emissions from
known sources. This may be determined from results of "material
balances," e.g., estimates of sulfur derivatives lost as
calculated from the differences between input and final output.
-------
7.6.49
• Results of any tests made of effluents or samples taken of fuels
or other materials.
• A process flow chart and plot plan, which can be used for reference
and verification on followup inspections and which indicate the
flow rates, pressures, temperatures, etc., in process vessels and
lines, where necessary, to estimate air pollution potentials and
to locate points of emission.
Flow charts and plot plans are systematically drawn according to
conventional engineering rules. All pertinent liquid or gas feed
lines are shown and all gas or liquid effluents indicated. Overhead
discharge and drainage from columns or vessels are generally shown by
vectors indicating method of disposal. All features not essential to
the understanding of the air pollution problem are omitted.
The flow lines are clearly labeled and vectored as to direction and
content. For example: "Refinery Gas in," "To Fuel Gas System," "To
Oil-Water Separator," etc. The process lines indicate whether the
flow originated in, or entered at the top, side, or bottom of columns
or equipment. Equipment or columns should be clearly labeled as to
function unless they can be depicted by symbols (such as heat
exchangers, condensers, etc., and by plant number as shown in
Figure 7.6.5). It is of utmost importance in a flow diagram to
clearly illustrate all sources of air pollution, including stacks,
flares, pressure relief valves, etc., and to identify the problem
areas and the contaminants which might be emitted. Process vessel and
line operating conditions recorded on pressure and temperature gauges,
manometers, continuous recorders, and relief valve pressure settings,
should be indicated wherever pertinent.
-------
PRESSURE
VACUUM VALVE
flASTE
H,0 TANK
10006
90%HZS04 J
\u
PRV
f) L.LA.
NEUTRALIZING COLUMN
C-130
SOUR WATER PUMP
to.5 TON/DAY H?S
I
111
u
FOUL AIR
IT1 RINGS
STEAM
*—
SWEET
^GAS FROM
ZDDEA
WB1IRHFB
JL
U
r/A
f\/ /
5t_X
. PLANT AIR
1950 B'D FROM
VARIOUS ACCUM.
>• FLARE
—PQ » L-P H?S ABSORBER
]so.no
TO 500,000
CF/D.
IDEGASIEIER DRUM
WASTE WATER
STRIPPER C-13!
3'. 35'H
OXIDIZING
COLUMN C-13t
-» VAPOR RECOVERY
SYSTEM
TO'Reforming
- UNIT
ABSORBER
* VAC. HEATER
TO COVERED
» WASTE WATER
SEPARATOR
COOLER
E-«9
NAME OF REFINERY _
NAME OF UNIT
DATE INSPECTED
FLOW DIAGRAM
Oil Comply, Inc. tnnRFSS »25 Court StM.t
w&ter oxidizing
10/15/59
INSPECTOR J'R
REVISIONS
DATE OF REVISION PERMIT NO - MODIFICATIONS
V3/60 031)97
C^
o
Figure 7.6.5. PROCESS FLOW DIAGRAM OF A SOUR WATER OXIDIZING UNIT FROM A FIELD DRAWING
(PAGE 4 OF THE ACTIVITY STATUS REPORT)
-------
7.6.51
A sample of an Activity Status Report covering a sour water treatment
and disposal plant, and accompanying flow charts, is shown in
Figures 7.6.5 and 7.6.6. To assist the inspector both in evaluating
and illustrating the process, symbols may be employed in chart
preparation as shown in Figure 7.6.7.
Some types of source activities are so standard that routine inventory
forms are used in describing them. Such activities include bulk
plants, truck loading facilities, oil-effluent water separators,
tanks, natural gasoline plants, and some other types of plants
operated at production facilities. Examples follow.
a. Bulk Plant Data
This inventory form (Figure 7.6.8) is used to record data obtained
from inspection of loading racks, storage tanks, pumps, vapor
controls, and associated equipment located at bulk plants. Bulk
plants are used to store and distribute various petroleum products
and may be found at airport facilities, distributing centers,
marine terminals, etc. The form is used to emphasize compliance
of equipment and operation with the applicable rules. This Bulk
Plant Data Sheet, presents a master inventory for each bulk plant.
Notice (in the sample shown in Figure 7.6.8) that by increasing
the number of spouts observed during the 7-8-57 reinspection the
permit status changed. A Permit Request was appropriately
written ("P.R.").
b. Truck Loading Inspection Data Sheet
This inspection sheet (Figure 7.6.9) is made for each truck
loading facility. It lists the number of racks and spouts, the
permit status of each rack, and throughputs of tank truck loading
racks.
-------
ACTIVITY STATUS REPORT
FIRM NAVE; Sunrise Chi Company. Inc., Unit II
ADDRESS OF PREVISFS: 1325 Court Street
RESPONSIBLE PERSCN rnMTVTFn- J. B. Hickeaon
NATURE OF BUSINESS: Petroleum refining
M.R.Ko. | 01 | 1
CITY; Onyx
TITLE;PI»
ASSIGNED INSPECTION D NEW ACTIVITY Q CHANGE OF STATUsD
DESCRIPTION - GENERAL USAGE • NAfcE OF EQUIPKENT - SYSTEM OR PROCESS
INSPECTED; Sour water oxidizing unit - Unit II
INSPECTOR'S NAIVE: J, B, Hardy
naTF- 10-15-59
INSPECTOR'S CONCLUSIONS AND RECOVMENDATIONSi The odors detected at this
time were not great enough to result in a public nuisance. This unit
remains, however, one of the greatest potential sources of odor problems
in this refinery since it comprises the processing area for sour waste
water containing malodorous components formed during the cracking
operation.
Modifications made for compliance with Rule 62 have reduced the
possibility of excessive S02 emissions from the vacuum heater. Since the
materials processed are both highly malodorous and corrosive, the
present inspection frequency of three times per year should be continued
to insure adequate maintenance.
INSPECTOR'S FINDINGS: The purpose of this unit is to deodorize the
sour water pumped from the accumulators at the crude, thermal, and cat-
alytic cracking units. This consists of the following equipment:
(1) a 10,000 barrel cone-roof tank, (2) a neutralizing column tower,
PAGE 1 OF 4
(3) a waste-water stripper, (4) an aeration column, (5) a waste-water
cooler, (6) a sour water degasifier drum, and (7) necessary pumps,
piping, and instrumentation. These are shown in the attached flow
diagram.
The sour water is pumped from the accumulators to the degasifier
drum. The gas removed from this drum flows through a back pressure reg-
ulator valve to a low pressure f>2S removal plant.
The sour water and waste caustic are collected in the 10,000 bbl.
capacity tank venting to the vapor recovery system.
The sour water is pumped from the tank to the neutralizing column
where it contacts 9856 sulfuric acid. The mereaptans released from the
water by the sulfuric acid, along with other waste gases in the over-
head line from the caustic regeneration unit, are condensed and fed
into the cracking unit for conversion to H2S and recovery. This ac-
counts for the disposal of roost of the mercaptans in the system.
The neutralized water is then pumped to the waste-water stripper,
and live steam is introduced in the column to strip out H2S and mer-
captans. Sweet gas with 7 or less grains of H2S per 100 CF from the
secondary scrubber at the H2S removal plant is introduced into the bot-
tom of the stripper at the rate of 350,000 to 500,000 CF/D- to sweep the
released gases from the water. This sour gas from the stripper goes to
the H2S absorption plant. A pressure relief valve on the stripper vents
to the flare.
The stripped water then flows to an aeration column where it is
contacted counter-currently with an air stream and caustic and is oxi-
dized to non-odorous thiosulfate. The resulting foul air from this
vessel is sent to the firebox of the vacuum unit heater for deodorizing.
PAGE 2 OF 4
-------
Inr wnier flo«s from t lie bottom of the aerater through a cooler to the
the principle sources of air pollution at this unit resulted from the
introduction uf (1) mercaptans from the neutralising tnnfc to the burn-
ers of the vacuum unit heater, and (2) the HjS from the waste-water
stripper column to the refinery fupl gas system. The APOD test team
determined that previously 0,S ton/day of f^S was contributed by this
unit to the refinery fuel g«B system. This is, equivalent to a losa of.
2f/j'". ibs dav ol SC»2 to the atmosphere. After studying data disclosed by
• aste (Tds streams throughout the refinery. Rule 62 *aa introduced to
Cfiis refinery adopted the following solutions to meet the problems
a. Enlarged ita HjS absorption facility.
b. Made provision for introduction of condensable iiercaptana into
th«! cracking plant for conversion of H2-S and its eventual recovery.
found to comply with Rule 62 during a test conducted by the APCD test
Vglieiole T*rcaptan odors **re noted in the vicinity of equip-
-*:. t at tnis '.ine. Equipment was in good condition and operating under
f-t fTi i cofiaitLons and rerjuirefnents. No visible emissions were observed
at trus tiT.e from the vacuum heater. A sample of treated water taken
fror the cooler (after oxidation) was free of noxious odors.
Figure 7.6.6. ACTIVITY STATUS REPORT FROM AN INSPECTION MADE OF A SOUR WATER OXIDIZING UNIT
AT AN OIL REFINERY (Continued)
-------
SYMBOLS USED IN PETROLEUM FLOW DIAGRAMS
Chart Number One
CENTRIFUGAL
PUIP
»/WCH SEAL Ofl
PACKED GLANDS
HEAT EXCHAKGER
STEAM 00 HOT OIL
UEQHM
VALVES
SHALL VALVES
RESSUREVACUUBVm
NATION
VEWT AND GAUGE
HATCH
HEAT EXCHANGERS
Cdinn
KcdEicUnta
Vnscl
KEOOG HEATER BORN HEATER PETROCHEH
TYPES OF FLOATING ROOFS
Chart Number Two
10
11
ft>
(b-
cfl
PAN TYPE
TRUSSED
PAN TYPE
TRUSSED WITH
SHADE OVER 50%
8 VAPOR 0AM.
DOUBLE DECK
HIGH DECK
PONTOON WITH
CENTER PONTOON
HIGH DECK
PONTOON WITHOUT
CENTER PONTOON
LOW DECK
PONTOON WITH
CENTER PONTOON
LOW DECK
PONTOON WITH
CENTER WEIGHT
PONTOON "DAY"
TYPE WITHOUT
CENTER PONTOON
CLEAR DECK
VENTILATED
PAN WITHOUT
SEAL
VENTILATED
PAN WITH
WIPER SEAL
Figure 7.6.7. SYMBOLS USED IN PETROLEUM FLOW DIAGRAMS
-------
7.6.55
SULK PLANT DATA
, WO STCRIWG GASOLINE .
00 GASOLIt U lb».
UllTS LC*DtD %Ci ISO wi Cf LADING RAOS
LENGTH OT RACKS 20 ft.
LOSS Fillin. nd brt.diiB. ol .
. NO 0* A f CONTROLS Flo.tia. roof.
TOTAL MYOftOCABaON L053S
y.. ,/t jfefVlVt^C/,
^ J
Figure 7.6.8. BULK PLANT DATA SHEET
-------
TRUCK LOADING INSPECTION DATA SHEET
COMPANY
Sunrise Oil
Company
"
••
••
-vX^X_
LOCATION
1325 Court St.
Ohyx, Calif.
* i
1 1
1 1
^~^J
RACK
NO. OR
NAME
1
2
1
2
-^
GAL/DAY GASOLINE
TO TRUCKS
AVERAGE
23,000
26,000
24,500
26,000
-"^
MAXIMUM
28,500
30,000
47,000
30,000
—~^
SPOUTS
TOTAL
5
6
5
7
-•^
OVER
4#
RVP
2
2
2
2
-1
UNDER
4#
RVP
3
4
3
5
~- ^
RULE
61
2
2
2
2
^~-_
PERMIT
STATUS
A-7432
A-4733
A- 473 2
P.R.
^
RECHECK
7-8-59
7-8-59
^^
DATE
CONTROLS
FIRST
USED
12-1-56
••
^^
INSPECTED
BY
J.R.H.
J.R.H.
J.R.H.
J.R.H.
^ ^_
Figure 7.6.9. TRUCK LOADING INSPECTION DATA SHEET
-------
7.6.57
From this form, the total losses of hydrocarbons are determined
using the following emission factors:
• Emission of hydrocarbons in gallons from uncontrolled
equipment—Approximately 1/10 of 1 percent of the average
gallon throughput per day.
• Emission of hydrocarbons in gallons from controlled equipment—
8 percent of the above.
c. Oil-Effluent Water Separator Inspection
The example shown in Figure 7.6.10 is of a single refinery
oil-effluent water separator which derives its influent from
treating vessels, south tank farm, thermal and catalytic cracking
units, and alkylation plants in the general cracking area of the
refinery. The influent waste water is traced on the flow diagram
by the inspector. The description of the controls, (i.e.,
"floating roof on primary compartments") and other information
indicates whether the equipment is in compliance with pertinent
rules.
d. Tank Inspection Report (Figure 7.6.11)
This inventory form records the type of tank, vapor control,
function, dimensions, products stored, Reid vapor pressure, storage
temperature, etc., of each tank to determine compliance with
rules.
e. Data Sheet for Natural Gasoline, Gas, and Cycle Plants
This form, illustrated in Figure 7.6.11, provides for inventory
of plants such as those named, which may be located apart from
refinery facilities, but in proximity to crude oil production
facilities. Information to be recorded includes the status of
tanks and separators subject to emission control regulations.
-------
7.6.58
OIL-EFFLUENT WATER SEPARATOR INSPECTION
OWANY Sunriii! Oii.Coapm-r DATE
1325 Court. Strwn, OnyK.Caiif.
DESIGNATION Of SEPARATOR Oil-el
D€SCRIPTtOU A_remforced cmcrcl
_ CONVERSATION WIT
iCTHOO Of SKIWING * - 2" «»m mp« Mil folded to *' '
SIZE OF INLET ft OUTLET 12" dl>. inlet md pud
LOCATION Or SEPARATOR —At »3 tretter »r«. in i
SIZE' LENGTH *7'-ll" •inn. 20'-10"
. TOff-EBATUHE—
QUANTITY ft DISPOSITION OF OIL 300 hhl./dm to oil recoTtrY ftciiltY
OISPOSITION OF WATER t ESTIMATE OF QUANTITY 15.000 bbliy
-------
7.6.59
ADDRESS HOP BU». St.
Qiv«. Califom
INFORMATION BY L. M. Black
TYPE OF PLANT: NATURAL GAaoLi
SOURCE OF MATERIAL PROCESSED WeL QB from e
THROUGHPUT: WET GAS 20 »*, sCFVi DRY_
_ TOTAL HO. OF WELLS .
_M4 SCFO
PAHE(BBL) -
BOILERS: NUMBER
_ HEATERS: NUMER .
IS FLOW DIAGRAM AVAILABLE „
STORAGE a HANDLING:
CAN IT BE OBTAINED1
OTHER (SPECIFY)
NO. CONTROLLED
OTHEHISPECIFY)
OIL_-_EFFLUENT WATER SEPARATORS
NO. OF SEPARATORS.——!
NO. QUESTIONABLE —Kant.
TYPE OF CONTROL _ Hone
FLOATING ROOF Hone
NO. UNDER RULE 59 ™°q
NO. CONTROLLED UNDER RULE 59 _
TOTALLY ENCLOSED _Mone
VAPOR RECOVERY SYSTEM
INSPECTOR'S REMARKS RE EQUIPMENT a PLANT CONDITIONS: —No lc«k»gea. Ma.1 oases noted.
Figure 7.6.11. NATURAL GASOLINE, GAS, AND CYCLE PLANT SURVEY SUMMARY
-------
7.6.60
2. Inspection Points and Reinspection Procedures
In order to maintain current information on the full extent and status
of refinery air pollution problems and potential problems, it is
desirable to conduct major resurveys on a periodic basis. Occasionally
major surveys may appropriately be conducted in cooperation with
other agencies, for joint objectives. However, for routine surveillance,
scheduled inspections of individual refinery units serve adequately.
Frequency of the inspections scheduled for any given unit will be
consistent with the expected potential of that type of unit for the
development of problems.
Most inspections of process units in refineries are arranged in
advance, as a part of the systematic programming of inspections. Such
arrangements are necessary in order to assure that the process unit is
in operation, that the appointed specialist in the plant is available,
and for safety precautions and guidance. When the process unit is
ready for reinspection, the inspector checks out the field file and
reviews the previous reports, and then proceeds to the inspection.
3. Environmental Observations
The environment in the vicinity of refineries and other petroleum
operations should be periodically surveyed for odors and for damage
to vegetation and materials. Findings should be compared with
observations of residents in neighboring communities. Soiling of
surfaces of automobiles, residences and other structures should be
noted and, where found to be severe, should be investigated. In
particular, any pattern of increasing intensity of soiling or
staining in the immediate vicinity of the subject facility should
be studied, to aid in the possible detection of previously unrecognized
emissions.
-------
7.6.61
Odors of hydrocarbon vapors and gases are likely to be particularly
prevalent near petroleum production and refining facilities. When
intense, they indicate the occurrence of high emission levels, since
odor thresholds for these compounds are relatively high and their
quality not especially offensive.
Sulfur compounds associated with crude oil production and with some
refinery operations are more readily detectable by odor. Sulfur
dioxide may be produced by combustion of fuels or waste gases, for
example in boilers, catalyst regenerators, incinerators and flares.
This gas has an acrid, suffocating odor with a threshold of about
1 ppm. Reduced sulfur compounds, including hydrogen sulfide, various
mercaptans and other sulfur-bearing organics, have characteristically
highly offensive odors and very low threshold levels, which have been
(9)
estimated at less than 1 ppb. (See, for example, Douglass. )
In reporting on occurrences of odors allegedly caused by petroleum
facilities, the inspector should note wind conditions (speed as well
as direction) at the time of his observations, and he should develop
a systematic procedure for patrolling and for characterizing odors.
Odors may be described on an intensity scale in terms of subjective
evaluation, or standardized procedure may be established, using a
scentometer or other comparison device. A community odor pannel can
help to establish the significance of day-to-day variations in odor
intensity and quality of the ambient atmosphere, as well as to alert
the inspector to the occurrence of unusual conditions.
Sulfur compounds, particularly hydrogen sulfide, can discolor and
damage lead-based paints sometimes found in residential areas. They
also accelerate tarnishing of silver and copper surfaces.
-------
7.6.62
Sulfur dioxide and trioxide may also be responsible for certain
types of damage to vegetation, causing yellow to brown blotchy spots
on many varieties, and occasionally a sort of pock-marking injury
which may be associated with sulfuric acid mist formed from the
trioxide. Diagnosis of plant damage due to air pollutants is
difficult, however, and should be confirmed by a consultant
experienced in the field.
4. The Physical Inspection
The objectives of the air pollution inspector are not only to
determine which elements of the operation are affected by the Rules and
Regulations but to determine as well the degree of compliance to them.
His inspection procedures are adapted to the specific air pollution
requirements governing the type of unit being inspected.
Safety is a prime consideration and all refineries have standard safety
procedures for employees and visitors. Accordingly, the inspector is
equipped with a hard hat, goggles, safety flash light; l^S indicator;
any other safety device the specific type of unit being inspected
calls for.
The inspector is accompanied to the unit or units to be inspected, by
the air pollution representative within the plant or by such other
informed refinery personnel as he might indicate.
General unit or plant compliance is determined through sensory
evidence, examination of current and past records, plans, recorder
charts and gauges, obtaining samples for laboratory analysis,
on-the-spot testing or calling for a mobile field test unit for more
extensive determination of suspected sources of noncompliance.
-------
7.6.63
a. Investigation of the Methods Used and the General Efficiency
Achieved in Controlling the Release of Pollutants to the Atmosphere
from Process (Basic Equipment) Units
The inspector determines plant procedures employed during start-ups,
shut-downs and equipment malfunctions, to control or eliminate
the discharge to atmosphere of noxious or malodorous emissions
through the purging or depressuring of tanks or vessels. These
include the installation of special instrumentation, e.g., high
level or high pressure alarms, liquid knock-out drums on fuel gas
systems, pressure relief or manually controlled discharge from
process equipment to blow-down vessels of either variable or fixed
capacity which are served by vapor recovery compressors, flare
systems or both, and, where emissions are a factor, fixed roof
tankage tie-in to properly sized vapor recovery or fume disposal
systems. Loading racks should be tied to vapor control systems
when the product being loaded has a significant vapor pressure.
b. Determination of Quality of Maintenance on Such Points as Manual,
Pressure Vacuum Valves, Flanges, Pump Glands, Gauge Hatches, etc.,
which May be a Source of Leakage
Such emissions are primarily recognized by sensory evidence and
their detection depends on the ability of the inspector to
recognize the odor and to trace it to its point of origin.
The inspector must also note any visible air turbulence caused by
light hydrocarbon leakage, frosting of valves or pump glands
caused by light hydrocarbon evaporation, liquid leakage, local
area discolorations caused by vapor condensate, visible emissions
or changes in flow (surging) of an emission, extinguished flare
pilot lights or detection of audible gas leaks. These may disclose
a violation or a potentially critical situation that could be
corrected in time.
-------
7.6.64
c. Procedures Used in Controlling Air Contaminants and Odors Resulting
from Disposal of Process Waste Effluents
The refinery inspector should thoroughly survey the sour water,
waste water, sour gas, spent caustic and acid sludge gathering and
processing and fume disposal systems.
Even though in a modern refinery most of these streams are "treated,"
their extremely noxious and malodorous characteristics make even
the most isolated uncontrolled streams a potential source of air
pollution problems.
Wherever possible, the inspector should point out conditions having
a high air pollution potential so that the refinery technical
staff may have the opportunity to assess the problem and arrive at
a solution. More effective use of existing control equipment is
achieved by extending its service to as many uncontrolled sources
as is possible without overloading its capacity.
The inspector may find (1) isolated streams of sour gas fuel
untreated for H-S removal and recovery; (2) sour water discharged
to open drains with live steam which has not been first
deodorized by processing in sour water oxidation or H-S stripping
facilities; (3) odors and hydrocarbons emitted to the atmosphere
from oil-water separators; (4) malodorous or noxious acid sludge,
stored in uncontrolled tanks which release fumes and odors due to
breathing and filling losses, or loaded into tank cars and trucks
with similar results.
e. Investigation of Efficiency, Operating Load and Maintenance of
Control Equipment
The effective operation of various control systems in a refinery
is of basic importance to efficient air pollution control. Such
equipment as cyclones, electrostatic precipitators, vapor recovery
-------
7.6.65
plants are subject to severe corrosion and other destructive
forces which reduce air pollution control efficiency. In addition,
a change in process feed or feed rates due to altered product
requirements may also result in overloaded or otherwise upset
operating conditions in the air pollution control system.
In the case of a vapor recovery system serving tankage, peak loads
develop in the morning hours when the heat of the sun produces
maximum volumes of hydrocarbon vapors in the space above the
liquid. Uneven loading schedules at tank truck loading facilities
tend to create a similar situation.
Since a gradual reduction in control efficiency does not always
alter the effective operation of the process unit, it may not be
noted by operating personnel until a major breakdown occurs
accompanied by a serious air pollution situation such as a public
nuisance. It is therefore essential for adequate air pollution
control that such areas be inspected regularly and frequently.
This type of inspection is sometimes more complex. Sensory
evidence such as visible discharge and odors may be disclosed by
thorough physical inspection and may be sufficient in some
situations to determine noncompliance or abnormal operation
(breakdown), i.e., Ringelmann number readings, excess hydrocarbon
vapor discharge from vapor controlled tankage, etc. However, in
other cases, sensory evidence may only be a preliminary or
corroborating step to the investigation, either because the
regulations affected call for evidence not obtainable in this
manner, (e.g., percentage sulfur in the fuel oil, H_S grain loading
in gaseous products burned and its btu value, weight of particulate
-------
7.6.66
discharge, concentration of SO- in discharge of flue gas) or
because the control equipment does not discharge a waste effluent
directly to the atmosphere. In such cases the inspector must
either rely on data indicating temperature, density, pressure,
vacuum or throughput recorded on gauges, continuous recorders,
high level or density alarms, voltmeters and ammeters, or he
must provide for special testing.
Another aid to the inspector is the information incorporated in
applications to operate the equipment. The permit status of
equipment should be routinely checked, in order to detect any
changes in equipment or process that might invalidate an existing
permit, or conflict with variance conditions.
-------
7.6.67
REFERENCES
1. Elkin, H. F. Petroleum Refinery Emissions. In: Air Pollution,
A. C. Stern (ed.). Vol. 3, New York City, Academic Press, 1968.
2. Danielson, J. A., (ed.). Air Pollution Engineering Manual, DREW,
PHS 999-AP-40, 1967. Chapter 10, Petroleum Equipment, pp. 561-677.
3. Chambers, L. A. Technical Developments Pertaining to Smog. Presented at
the Fourth Annual Waste Disposal and Stream Pollution Conference of the
Western Petroleum Refiners Association. Wichita, Kansas. October 7-8,
1959.
4. Sussman, V. H., R. K. Palmer, F. Bonamassa, B. J. Steigerwald, and
R. G. Lunche. Emissions to the Atmosphere from Eight Miscellaneous
Sources in Oil Refineries. Joint District, Federal and State Project for
the Evaluation of Refinery Emissions. Los Angeles County Air Pollution
Control District. Report No. 8. June 1958.
5. Deckert, I. S., R. G. Lunche, and R. C. Murray. Control of Vapors from
Bulk Gasoline Loading. J. Air Pollution Control Association,
8:223-233, 1958.
6. Sussman, V. H. Atmospheric Emissions from Catalytic Cracking Unit
Regenerator Stacks. Joint District, Federal and State Project for the
Evaluation of Refinery Emissions. Los Angeles County Air Pollution
Control District. Report No. 4. June 1957.
7. Kanter, C. V., R. G. Lunche, F. Bonamassa, B. J. Steigerwald, and
R. K. Palmer. Emissions to the Atmosphere from Petroleum Refineries in
Los Angeles County. Joint District, Federal and State Project for the
Evaluation of Refinery Emissions. Los Angeles County Air Pollution
Control District. Report No. 9. 1958.
8. Bonamassa, F., and Y. S. Yee. Emissions of Hydrocarbons to the Atmosphere
from Cooling Towers. Joint District, Federal and State Project for the
Evaluation of Refinery Emissions. Los Angeles County Air Pollution Control
District. Report No. 5. August 1957.
9. Douglass, I. B. The Chemistry of Pollutant Formation in Kraft Pulping.
In: Proceedings of the International Conference on Atmospheric Emissions
from Sulfate Pulping, E. R. Hendrickson (ed.). PHS, National Council for
Stream Improvement. University of Florida, April 28, 1966.
10. Brandt, C. S., and W. W. Heck. Effects of Air Pollutants on Vegetation.
In: Air Pollution, Vol. I, A. C. Stern (ed.). New York City, Academic
Press, 1968.
-------
7.7.1
VII. CHEMICAL PLANTS
A. NATURE OF SOURCE PROBLEM - UNIT PROCESSES AND UNIT OPERATIONS
The definition of what constitutes a chemical industry rests more on
accepted practice than on clearly distinguishing features. The processing
of metal ores, the manufacture of synthetic rubber and Pharmaceuticals,
and the production of synthetic fertilizers all involve significant chem-
ical reaction steps. However, in each case the industries are so large
and the end use of the products so clearly visualized that they have come
to be separately classified.
Nevertheless, the chemical industry can be broadly classified as one in
which a basic, intermediate, or end use chemical compound is produced
through one or more chemical reactions, followed by a series of separation
and purification steps. A few examples of some of the chemical products
are chlorine, sulfuric acid, nitric acid, phosphoric acid, caustic soda,
ammonia, soda ash, and synthetic organic chemicals including elastomers,
fibers, resins, plastics, pesticides, dyes, adhesives and solvents.
Both gas phase and particulate air contaminants may result from chemical
plant processes. Gaseous contaminants may be either true gases or vapors
arising from volatile liquids and solids. Contaminants may be unreacted
starting materials, unwanted by-products, or non-recovered product.
In many cases contaminants arise from the purging of inert gases that are
deliberately or inadvertantly introduced by a process. For example, if
air is used as a source of oxygen for an oxidation step in a chemical
process, the nitrogen remaining must be vented to the atmosphere. Unless
adequate controls are utilized some air contaminants may be released along
with the vented gases.
-------
7.7.2
In many cases, gaseous products of a reaction are absorbed in water (for
example, mineral acids). A small amount of gaseous material may not be
absorbed and thus lost to the atmosphere unless otherwise controlled in
what are known as tail gases.
Volatile organic liquids are a problem mainly during their storage and
transfer. Vapors of these materials may be lost as a result of filling
and breathing losses (see Section VI, Petroleum Refineries).
Liquid and solid particulates may be formed from gaseous reactions, gas-
liquid reactions, gas-solid reactions, drying operations (powders), cal-
cining, attrition losses, materials handling, and from fluidized catalyst
beds, to give only a partial list of sources.
B. PROCESS DESCRIPTION - UNIT PROCESSES AND UNIT OPERATIONS
Chemical engineers involved in the design of chemical plants have for many
years classified commonly used reactions and manufacturing steps into two
broad groups known as (1) unit processes, and (2) unit operations. Unit
processes are those procedures which involve a chemical change in one or
more reactants. Unit operations generally involve only physical changes.
The utility of the above concepts lies in the ability to use unified
design theories for most of the manufacturing steps required for even a
very complex manufacturing process. For the purposes of this section the
use of these classifications is intended to allow a broad look at the
industry without undue detail. Relatively complete individual treatment
is provided in Parts D and H of this section in the case of two large
chemical industries—sulfuric acid manufacturing and vinyl chloride produc-
tion.
-------
7.7.3
1. Unit Processes
The fundamental reactions that may be involved in a chemical manufac-
turing industry would include decomposition, double decomposition,
addition, substitution, isomerization, coupling, oxidation, reduction,
and polymerization. Specific examples of these general reactions,
which are in rather widespread use, are shown in Table 7.7.1.
Groggins presents a detailed review of most of these processes. A
brief discussion of the air pollution emission potential of several of
these processes follows.
a. Nitration
Nitration involves the formation of organic nitro compounds and is
usually accomplished by a mixture of nitric and sulfuric acids. One of
the principal potential sources of air pollution would be the
recovery by concentration of spent nitric acid. Nitrogen oxides
may be released unless specific control measures are utilized.
Figure 7.7.1 is a schematic flow diagram of a methane nitration
process for the production of nitromethane. In this process the
product nitromethane and unreacted nitric acid are condensed
following the reaction and the nitromethane recovered by distilla-
tion. The dilute (spent) nitric acid is fed to an absorption
tower through which non-condensible reaction gases containing
nitrogen oxides are passed. Following the absorber some of the
inert gases, mostly nitrogen, must be purged. Small quantities
of nitrogen oxides may also be lost.
b. Sulfonation and Sulfation
These processes use oleum and sulfuric acid to produce a great
variety of organic sulfonates and sulfates. Sulfur oxides may be
lost in small quantities.
-------
7.7.4
Table 7.7.1 COMMONLY USED UNIT PROCESSES
Unit Process
Product Examples
Nitration
Amination by Ammonolysis
Diazotization and Coupling
Halogenation
Sulfonation and Sulfation
Hydrolysis
Oxidation
Hydrogenation
Friedel-Crafts Reactions
Polymerization
Calcining
Nitromethane
Aniline
Benzenediazonium chloride
Vinyl chloride
Naphthalene sulfonic acid
Glycerol
Quinone
Methanol
Ethyl benzene
Polyethylene
Silica gel
-------
Nitric
Acid
Methane
Purge Point
For Inert Gases
Figure 7.7.1 FLOW DIAGRAM FOR NITRATION OF METHANE
-------
7.7.6
c. Halogenation
Halogens, i.e., chlorine, bromine and iodine are added to organic
compounds by this process. Either the halogen or the hydrohalogen
may be lost to the atmosphere. (See the vinyl chloride process
described later in this section.)
d. Amination by Ammonolysis
Amination by Ammonolysis describes the process of amine production
using ammonia. Tail gases may contain ammonia after the condenser
serving the purification rectifier.
e. Hydrolysis
In this process a portion of the water molecule is made to replace
another substituent. For example, phenol is produced by the hydro-
lysis of chlorobenzene. Acid vapors (hydrogen chloride in the
case of phenol production) may be lost without proper control.
f. Oxidation
Describes the process by which the oxidation state of a substance
is increased. For example, air may be used to oxidize acetaldehyde
to acetic acid. The nitrogen remaining after this process must be
vented (purged) and may contain traces of reactants or products.
A great number of oxidizing agents, including chlorine sodium
chlorite, permanganates, chlorates, chromic acid, nitric acid,
and nitrogen tetroxide may be used under this general heading.
g. Hydrogenation
Hydrogenation involves the addition of hydrogen. Examples would include
hydrogenation of vegetable oils and the production of methanol from
carbon monoxide and hydrogen. Again the purging of inert gases
-------
7.7.7
may contain reaction by-products. In the future this process may
be used on a large scale for coal gasification.
h. Friedel-Crafts Reactions
Friedel-Crafts includes a large group of reactions in which
aluminum chloride is used as a catalyst. Hydrogen chloride may
be released as a by-product.
2. Unit Operations
That sub-group of unit operations which has in common the transfer of
material from one homogeneous phase to another is described by the
(2)
term mass transfer. Except for the transfer and size classification
of dry materials in particle form, the mass transfer operations are,
from the point of view of air pollution control, the most important of
the unit operations.
That group of operations grouped under the mass transfer term is
differentiated from purely mechanical separation techniques by the
fact that they utilize differences in vapor pressure and solubility
rather than variations in particle size and density as the basis for
separation. Several of the more important mass transfer operations
together with examples of possible atmospheric emissions are given in
Table 7.7.2.
3. Control Methods
Air pollution control methods used in chemical process plants do not
differ inherently from those used in other industries. Those differ-
ences which do exist are largely a matter of degree. In general there
are probably more air pollution problems in chemical plants related to
fixed gases, volatile vapors, and liquid mists than there are those
related to solid aerosols and combustion contaminants.
-------
7.7.8
Table 7.7.2 EXAMPLES OF MASS TRANSFER OPERATIONS
AND AIR POLLUTANT POTENTIAL
Mass Transfer
Operation
Principle
Air Pollutant
Example
Absorption
Soluble gas removed from an
inert gas by absorption in
a liquid.
Residual ammonia lost along
with vented air after absorp-
tion by water.
Evaporation and
Drying
Volatile liquid removed from
non-volatile liquid or
solid by application of
heat.
Removal of solvent from
desired by-product by passage
of heated air or spray drying
of powders and flake material.
Distillation
Separates by volatilization
a mixture of miscible and
volatile substances. Vapor
must differ in composition
from boiling liquid.
Loss of alcohol vapors after
separation of alcohol and
water by distillation.
Condensation
Removal of condensible vapor
from inert gas by cooling.
Loss of odorous materials to
water used in contact (baro-
metric) condenser, and subse-
quent loss from water.
-------
7.7.9
The techniques most commonly used for air pollution control are listed
below and described more completely in Chapter 2.
Control Methods Common to the Chemical Industry
Absorption
Adsorption
Condensation
Vapor Recovery
Fume Incineration
C. INSPECTION POINTS - UNIT PROCESSES AND UNIT OPERATIONS
Perhaps the single most important factor in the inspection of a chemical
plant is the degree to which the inspector is familiar with the process(es)
involved. One of the best means of preparation is to examine a detailed
process flow diagram and accompanying descriptive text, identifying all
possible sources of pollution and the location of all vents to the atmo-
sphere. At the time of inspection this flow sheet can be much more easily
related to the plant layout plan and the equipment itself. It is nearly
inevitable to the uninitiated that continuous flow chemical plants
(as well as petroleum refineries) will resemble a jungle of vessels, pumps,
and piping.
Once on the plant site, all vents, regular and emergency, should be located
on the plot plan indicating approximate size and height. Where relatively
small quantities of inert gases (such as air) are involved the vents may
actually be quite small and easily overlooked.
The inspector should obtain an up-to-date description of all processes,
including feed rates and composition and the variations that occur in these
items. Should pollutant emissions be unusually sensitive to production
rates, this data on production should be obtained.
-------
7.7.10
The inspector should become familiar with both internal and external con-
ditions during normal operations, i.e., control instrumentation readout,
presence of visible emissions, and detectability of odors in the surround-
ing area.
One useful approach is to make inquiry as to the nature and probability of
occurrence of conditions which would necessitate the instigation of
emergency venting procedures. Of similar importance is the determination
of the effect of a rapid shut-down of all operations.
Non-routine operations, such as start-up, catalyst regeneration, scheduled
maintenance, etc., should be studied as to their effect on air pollutant
emissions.
Finally, regular surveillance of the surrounding area should be conducted
to examine for evidence of possible effects related to emissions from the
plant in question. Should complaints be received, it will be extremely
important to make a timely determination of the plant operating conditions
associated with the time of the detected effects. Meteorological data
related to the transport and diffusion of contaminants, and detectability
of effects should be obtained. These include wind speed and direction,
atmospheric stability, and relative humidity. In most cases the inspector
should make independent estimates of these parameters even though he
suspects such data may be available from weather instrumentation.
D. NATURE OF SOURCE PROBLEM - SULFURIC ACID MANUFACTURING
The manufacture of sulfuric acid, regardless of the process, results, to
some degree, in the emission of unconverted sulfur dioxide and unabsorbed
sulfuric acid mist. In plants using the lead chamber process, nitrogen
oxides may be discharged in concentrations nearly as high as the sulfur
-------
7.7.11
dioxide emitted. Of these nitrogen oxides, usually 50-60% is nitrogen
(3)
dioxide. Only traces of nitrogen oxides are normally emitted from the
contact process sulfuric acid plants, which account for over 90% of the
sulfuric acid produced in the United States.
Variable amounts of a variety of mineral dusts may be lost from plants
using smelter or ore roasting gases as a source of sulfur. Sulfuric acid
vapor as opposed to sulfuric acid mist, will be in equilibrium with the
sulfuric acid produced and will be lost in small quantities.
Other small, but possibly nuisance forming losses from sulfuric acid plants
could include wind blown raw sulfur from storage piles, odors from spent or
sludge acid storage tanks, leaks of sulfur dioxide or acid mist from
process vessels under pressure, sulfur trioxide vapor from oleum storage
and transfer.
Unless considerable care is taken there is great potential for increased
emission rates of sulfur dioxide during start-up operations.
Although sulfuric acid manufacturing accounts for only about 2% of the
total sulfur oxides emitted to the atmosphere in the United States
(approximately 600,000 tons of S09 per year out of a 28,600,000 tons per
(4) /
year total in 1966) any given sulfuric acid plant can be a significant
local source. As compared to fuel burning sources of sulfur oxides,
sulfuric acid plants are distinguished by several features which can add
to the local nuisance potential—(1) low tail gas temperatures and some-
times short stacks which in combination result in poor stack gas dispersion
and occasionally high ground level concentrations of sulfur dioxide and
acid mist, (2) presence of sulfuric acid mist as well as sulfur dioxide,
and (3) odors from raw materials and the finished product.
-------
7.7.12
E. PROCESS DESCRIPTION - SULFURIC ACID MANUFACTURING
The basic reaction in the manufacture of sulfuric acid is:
This reaction is exothermic with the higher equilibrium concentration of
SO being favored by lower temperatures. Slower reaction rates, however,
accompany the lower temperatures necessitating a careful heat balance to
achieve high SO to SO conversion at practical reaction rates. It is
obvious from the equation above that S0_ conversion is also favored by
high 0 to SO ratios.
Two processes are in use in the United States for the manufacture of sul-
furic acid. The older chamber process produces a relatively weak 60°Be
(77.7%) acid and accounts for less than 10% of the production in the
United States. Nitrogen oxides are used as a catalyst for the conversion
of sulfur dioxide to sulfur trioxide. The contact process involves the
direct conversion of sulfur dioxide to sulfur trioxide over a vanadium
pentoxide catalyst and produces concentrated sulfuric acid (98-100%) and
various strengths of oleum (concentrated sulfuric acid having additional
absorbed sulfur trioxide). All new sulfuric acid plants are of this type.
In both chamber and contact processes hydration of the sulfur trioxide
takes place during absorption operations producing the sulfuric acid. The
tail gases issuing from the final absorption tower contains excess air and
any unreacted sulfur dioxide sulfuric acid mist, sulfur trioxide, sulfuric
acid vapor, nitrogen oxides and other contaminants that might be present.
1. Chamber Process
Presently operating chamber plants in the United States use sulfur as
the raw material for the production of sulfur dioxide used in the acid
(3)
manufacturing process. ' In the chamber process, as shown in
-------
7.7.13
Figure 7.7.2, sulfur is burned to sulfur dioxide which is introduced
together with nitrogen oxides (approximately equal proportions of
nitric oxide and nitrogen dioxide) to the Glover tower. Here a
series of complex intermediate reactions are initiated between the
nitrogen oxides and the sulfur dioxide which culminate in the oxida-
tion of sulfur dioxide to sulfur trioxide and the release of the
nitrogen oxides. The nitrogen oxides which are recovered in the Gay-
Lussac towers by absorption in chamber acid are also fed to the
Glover tower for recycling in the process. Approximately 50% of the
sulfuric acid is formed in the Glover tower with the remaining con-
version taking place in large lead-lined chambers (thus the "Chamber"
process).
The range of emissions of air contaminants from chamber sulfuric acid
plants is approximately as shown below:
S02 1500-4000 ppm
Acid Mist 5-50 mg/ft3
NO ~1000 ppm
NO -500 ppm
Emission levels are affected by the concentration of sulfur dioxide
in the burner gas entering the Glover tower, the amount of nitrogen
oxides in circulation, the ratio of nitrogen dioxide to nitric oxide,
the throughput rate, and the temperature and concentration of acid
entering the final Gay-Lussac tower. All other factors being equal,
lower atmospheric temperatures generally result in somewhat reduced
sulfur dioxide emissions because of the additional cooling of the lead
chambers by ambient air.
-------
EXIT GAS AIR. SO... ACID MIST,
NO, AND NO,
78% TO ACID STORAGE
AMMONIA
OXIDATION
UNIT
OXIDES OF NITROGEN
SECONDARY AIR .
MOLTEN V"sn—
^
i
b
t'l
i
-k
1
//I'N
GAS
FAN
.
/ft. ,fi\
(One to twenty of
5,000 to 500.000
cu ft capacity each
in piants of various
capacities)
,
,fa /T-N A
ACID COLLECTING PAN
ACID COLLECTING PAN
I '
i i
78%
ACID
(60'BE)
COOLING WATER
I
i
60 - 70%
CHAMBER
ACID
TO
STACK
MUTROUS
CHAMBER
1 1
VITRIOL
A£'l _T"_
__^(__
1
•ill!
i :
AA
vm
78%
NITROUS
VITRIOL
SULFUR
BURNER
COMBUSTION
CHAMBER
SUPPLY
TANK
SUPPLY PUMP
TANK
Figure 7.7.2. SIMPLIFIED FLOW DIAGRAM OF TYPICAL LEAD-CHAMBER PROCESS FOR
SULFURIC ACID MANUFACTURE (BASED ON USE OF ELEMENTAL SULFUR
AS THE RAW MATERIAL). (SOURCE: P.H.S., DIVISION OF AIR
POLLUTION, Reference 3).
-------
7.7.15
2. Contact Process
A variety of contact processes are used in the manufacture of sulfuric
acid, differing principally in the source of sulfur and in the number
of conversion stages used in the catalytic reactor. Differences in
heat exchange equipment may occur, depending upon sources and demands
for heat in the plant complex, but these differences should have
relatively little impact on the air pollution potential of the plant.
One likely future difference in new plants is the use of the double
absorption process (see Chapter 2).
Contact plants burning elemental sulfur are sometimes known as "hot
gas" plants and utilize a drying tower for the combustion air so as
to minimize the amount of moisture entering the converter along with
the sulfur dioxide and excess air. The presence of moisture in the
converter results in the formation of sulfuric acid mist which must
be removed from the tail gas. Plants using hydrogen sulfide from
refinery operations, acid sludge, copper converter gases, and roaster
gases from other sulfide ore smelters are often described as "wet gas"
plants. In these plants reactor gases are dried and cleaned just
prior to entering the converter. Combustion air for plants burning
acid sludge and hydrogen sulfide is not dried as additional water is
formed in the burner.
Figure 7.7.3 shows a schematic flow diagram for a modern 4-stage sulfur
burning contact acid plant. In this plant atmospheric air is discharged
from a pressure type blower into a drying tower through which 93-99%
sulfuric acid is circulated as a drying agent. The dry air together
with molten sulfur is charged to the sulfur burner in such a ratio as
to produce a feed gas containing 7.5-8.5 mol% sulfur dioxide, about
13% oxygen, and a nitrogen balance. Should any hydrocarbon be present
it will be burned to carbon dioxide and water.
-------
SULFUR*
BOILER
FEED •
WATER
AIR
••STEAM
* OLEUM .
TOWER (OPTIONAL)
—
CONVERTER
WITH
INTERCOOLERS
OLEUM
r PRODljCT
TAIL
GAS
ACID
PRODUCTS
Figure 7.7.3. SCHEMATIC FLOW DIAGRAM OF SULFUR BURNING PLANT
WITH FOUR-STAGE CONVERSION. (SOURCE: CHEMICO.
Reference 5.)
-------
7.7.17
The feed gases are cooled in a waste heat boiler to a temperature of
820°-840°F and then fed to the converter. Interstage cooling is
necessary to remove the heat of reaction and to allow a satisfactory
degree of reaction to take place. Conversion of sulfur dioxide to
sulfur trioxide in this type of plant can range up to 96-98%.
The converter gas is cooled in an economizer used for heating boiler
feedwater or in some other type of heat exchanger. The converted
gases leave the economizer at about 450°F and enter the absorption .
tower where the sulfur trioxide is absorbed in a circulating stream
of 98-99% sulfuric acid. In the event that oleum is to be produced,
the converter gases first pass through the oleum tower where acid from
the 98% absorber is circulated. The gases must be cooled to a lower
temperature before entering the oleum tower than if only 98% acid were
to be produced.
Unless additional control equipment is used, the tail gases leaving
the absorption tower are discharged to the atmosphere at this point.
Typical tail gas concentrations from a 4-stage sulfur burning contact
acid plant are shown below:
so2
Acid Mist
SO,
1500-4000 ppm
2-20 mg./SCF
0.1-1.3 ppm
The "wet gas" type of contact plant using waste gases from metallurgical
operations, or acid sludge and hydrogen sulfide from refinery processing
is considerably more elaborate than the sulfur burning contact plant.
Sulfur dioxide containing gas from smelters may be contaminated by
metal fumes, dusts, acid mists, other gaseous impurities and water
vapor. These must be removed by various dust collectors, mist
-------
7.7.18
precipitators and drying towers before the feed gases enter the con-
verter. Plants based upon the use of acid sludge, spent acid or
hydrogen sulfide are usually somewhat simpler than those using waste
smelter gases in that there is less of a dust and fume contamination
problem. Figure 7.7.4 shows a simplified flow diagram of a "wet gas"
contact plant. Although the heat balance may be substantially differ-
ent for this type of plant as compared to a sulfur burning plant, the
process is essentially the same from the converter forward.
Some additional problems are encountered in plants utilizing waste
gases from metallurgical operations due to the possible variations in
sulfur dioxide content.
F. CONTROL METHODS - SULFURIC ACID MANUFACTURING
Emissions from sulfuric acid plants are in the main unconverted sulfur
dioxide (gaseous) and sulfuric acid mist (liquid aerosol). Some nitrogen
oxides may be lost from chamber plants and a small amount of unabsorbed
sulfur trioxide may reach the final discharge stack. Any sulfur trioxide
released will hydrate rapidly with atmospheric moisture and form additional
sulfuric acid aerosol.
Control methods are usually considered separately for sulfur dioxide and
acid mist but in one approach to SO tail gas scrubbing a venturi scrubbe
is proposed which would also remove some acid mist.
1. Sulfur Dioxide Control
Most existing sulfuric acid plants can reduce SO emissions to
C3\
approximately 2000 ppm by operational control methods. Reduction
to levels of 500 ppm or lower would require process changes such as
the installation of a dual absorption system, or would necessitate
tail gas treatment.
-------
BOILER
FEED
WATER
SULFUR
SOURCE
STEAM (A)
OLEUM
TOWER (OPTIONAL)
CONVERTER
WITH |
INTERCOOLERS
I qLEUM_
PRODUCT
TAIL
GAS
ACID
PRODUCTS
©INCLUDES COMBUSTION UNIT WHEN USING SLUDGE, PYRITE OR H2 S.
STEAM IS GENERATED ONLY WHEN BURNING SLUDGE OR H2 S OR
WHEN ROASTING PYRITE. NONE IS GENERATED WHEN USING A
PURIFICATION UNIT ONLY, AS WITH SMELTER GAS.
Figure 7.7.4. SCHEMATIC FLOW DIAGRAM WET GAS PLANT
WITH 4-STAGE CONVERSION. (SOURCE:
CHEMICO, Reference 5.)
-------
7.7.20
Operational methods of sulfur dioxide control basically involve
enhancement of the sulfur dioxide conversion to sulfur trioxide.
Any one or a number of the following methods might be used.
• Reduce the initial sulfur dioxide concentrations
entering the converter.
• Reduce the ratio of SO to 0 .
• Increase the number of converter stages.
• Increase the volume of catalyst.
• Change catalyst more frequently and improve
distribution.
• Improve uniformity of feed conditions.
• Reduce feed gas impurities.
• Provide additional interstage cooling in converter
and improve temperature control throughout the plant.
• Reduce throughput rate.
• Exercise additional care during plant start up.
Reductions in sulfur dioxide emissions from contact acid plants may
also be achieved by incorporating the double absorption technique in
the process. In this approach, which is mainly applicable to new
plants, conversion of SO to SO. is interrupted after two or three
stages and the gas stream is fed to the first absorption tower.
Effluent gas from this tower now having a very high 0_/SO_ ratio
is returned to the converter where the new equilibrium conditions
favor an extremely efficient conversion of SO to SO . Following an
additional one or two stages of conversion the converter gas is intro-
duced to the final absorption tower. Overall conversion of S0_ to SO
-------
7.7.21
of +99.5% is achievable with this process. Tail gas concentrations
of 500 ppm SO- are readily attainable with the double absorption modi-
fication of the contact process. For existing plants, another absorp-
tion tower and probably some additional heat exchange equipment would
be necessary.
To attain sulfur dioxide concentrations of very much less than 500 ppm,
some sort of tail gas treatment would probably be necessary. In a
recent report, prepared for the Air Pollution Control Office,
nearly 50 possible tail gas treatment schemes were listed with nine
being selected for a more detailed review. Little use of tail gas
treatment, however, is made in current practice. Two plants in the
United States have used an ammonia scrubbing process on a full scale
basis and one is engaged in pilot scale studies of the potassium
sulfite-bisulfite (Wellman-Ford) process at the present time. This
situation is likely to change over the next few years.
2. Sulfuric Acid Mist Control
As can be seen from earlier portions of this section, acid mist
emissions range from 2-20 mg/SCF (70-700 mg/M ) for most of the sul-
furic acid plants operating in the United States. Although sulfuric
acid mist accounts for a relatively small proportion of the total
sulfur losses (approximately 1-10%) from a sulfuric acid plant it is
responsible for visible plumes and is associated with material damage
and health effects at lower concentrations than is sulfur dioxide.
There are a variety of operational and process factors which affect
acid mist emissions. Among these are:
• Improper concentration and temperature of the
absorbing acid.
• Amount and concentration of oleum produced.
-------
7.7.22
• High content of organic matter in the raw materials
of a sulfur burning plant.
• High moisture content of the sulfur dioxide entering
the converter.
• Stack cooling of sulfur trioxide gases leaving the
converter, i.e., sudden cooling below the acid dew
point, resulting in condensation of very small
particles.
• Presence of nitrogen oxides, which can result from
excessive temperatures in the sulfur combustion
chamber, from nitrogen in raw materials, and from
arcing in electrical precipitators.
• Insufficient acid circulation and lack of uniformity
of acid distribution in the absorption tower.
• Improper type or dirty packing in the 98% absorber.
Many sulfuric acid plants utilize some form of collection equipment
designed specifically for acid mist. The most common type is the two-
T3
stage knitted wire or Teflon mesh pad. Such pads operate at rela-
tively low pressure drop (2-3" H_0) and are effective for acid mist
particles greater than 3 microns in size. For particles less than 3
microns in diameter, such as result from oleum producing plants, the
efficiency is much lower (15-30%). These smaller particles are
responsible for visible plumes and may be carried for considerable
distances in the atmosphere.
Venturi scrubbers operating at a pressure drop of about 35-40" H?0
have been used on acid concentrators where most of the acid mist
particles are > 3|a but recently have been proposed for combined use in
-------
7.7.23
removing both S0_ and acid mist from sulfuric acid plants. Such
units would not be expected to be effective for mist removal from
oleum plants.
The only devices capable of reducing all size ranges of acid mist to
0.1 mg/SCF are glass fiber filters and electrostatic precipitators.
Glass fiber filters presently in use operate at about 8" HO pressure
d'rop. Electrostatic precipitators operate at low pressure drops
(about 1" H_0) but are initially quite expensive. They are also
rather large because of the low gas velocities necessary for efficient
operation.
Table 7.7.3 summarizes the expected performance for the acid mist
collectors.
G. INSPECTION POINTS - SULFURIC ACID MANUFACTURING
The inspection of sulfuric acid plants must take into account the inter-
connected, continuous nature of the manufacturing process, since there is
essentially one point of emission for the major potential air contaminants.
Though there may be some wind blown sulfur and even small amounts of sul-
fur dioxide and hydrogen sulfide from sulfur storage and melting, all the
sulfur dioxide, sulfuric acid mist, and nitrogen oxides arising from the
manufacturing process will be emitted from the final absorption tower or
from the control equipment following the tower.
The emission potential of any given acid plant is dependent upon the type
of process, age of the plant, whether or not oleum is produced, nature of
the raw material, production rate, operating variables, and type of control
equipment.
-------
Table 7.7.3 EXPECTED PERFORMANCE OF ACID MIST COLLECTION SYSTEMS
System
Wire or Teflon Mesh
Glass Fiber Filter
Electrostatic Precipitator
Venturi Scrubber
Efficiency
> 3 Microns
99+%
100%
99%
98%
Efficiency
<3 Microns
15-30%
95-99%
100%
Low
Emission Level
99% Acid Plants
to 2 mg/SCF
0.1 mg/SCF
0.5 mg/SCF
3 mg/SCF
Emission Level
Oleum Plants
to 5 mg/SCF
0.1 mg/SCF
0.1 mg/SCF
Ineffective
with <. 3 micron
mist
fo
-p-
-------
7.7.25
The major tasks the inspector performs include the following: determina-
tion of the nature of the process as it affects air contaminant emission;
examination of operating conditions and relevant records; surveillance for
plume appearance (if any); determination of contaminant emission rates,
and investigation of possible property damage.
1. Environmental Surveillance
The only visual evidence of emissions from the contact process for
sulfuric acid manufacture is the white plume associated in controlled
acid mist having a particle size range generally less than three
microns. Particles larger than this do not scatter light in the
visual wave length range effectively and thus may be present but not
visible. In the case of a chamber process plant it is possible that
nitrogen oxides may be discharged from the Gay-Lussac tower in con-
centrations high enough so that the reddish-brown color of nitrogen
dioxide can be seen.
Should there be a visible plume, the inspector may use it as a guide
to locating those locations where ground level concentrations of
sulfur dioxide and acid mist are high enough to be detectable by
humans or to cause visible damage to materials and vegetation.
Regardless of whether or not there is a visible plume the behavior of
the plant effluent will be influenced by stack height, effluent gas
temperature, wind speed and direction, atmospheric stability, and
surrounding terrain. It may be desirable in some cases to utilize a
diffusion model to estimate ground-level concentrations in the
surrounding area by various averaging times and for differing atmo-
spheric conditions. The application of these diffusion models is
described in Turner's "Workbook on Atmospheric Dispersion Estimates."
-------
7.7.26
Sulfur dioxide and sulfuric acid mist can cause localized damage to
metals through corrosion and may attack a wide variety of building
materials, causing discoloration and deterioration. These contaminants
may also cause dyed fabrics of certain types to fade. Sulfur dioxide
may cause acute or chronic leaf damage to plants. The symptoms most
often observed are bleaching, yellowing, or chlorosis. Expert assis-
tance is usually necessary to confirm the cause of material or vegeta-
tion damage, but the inspector may be trained to recognize prominent
symptoms. The pattern of damage in the vicinity of a suspected source
may provide valuable circumstantial evidence as to the probable cause
of the damage.
2. Inspection of the Premises
a. Interview
In the case of a sulfuric acid plant most of the important informa-
tion obtained in a plant inspection will be from the interview
with the plant management. The continuous enclosed nature of the
manufacturing process precludes obtaining extensive information
by visual inspection alone.
The inspector will first wish to learn the specific details of the
particular process employed in a given plant, such as the nature
of the sulfur source and the range in composition and extent of
contaminants present. Even in a sulfur burning plant the latter
item can be important. The rated capacity and normal operating
rate of the plant should be obtained. Information on start-up
procedures and the frequency with which shut-downs and start-ups
occur is desirable. Operating procedures and nature of control
procedures and equipment should be secured. Some of the specific
items of importance are SO and 0 concentrations entering the
-------
7.7.27
converter, temperatures at various points in the converter and
absorption tower, and the concentration and temperature of the
absorption tower acid. In some cases the inspector may be given
the opportunity of examining operating records during the inter-
The inspector should obtain information on sulfur dioxide conver-
sion efficiency, efficiency of any collection equipment used and
data on the tail composition finally being discharged to the
atmosphere. He should inquire about maintenance procedures and
their frequency.
b. Physical Inspection
The inspector should first become familiar with the physical layout
of the plant and prepare or obtain a plot plan showing the location
of principal items of equipment.
He should inspect the sulfur storage area in the sulfur burning
plant and determine the potential for wind blown sulfur dust
losses. He should also investigate the possibility of hydrogen
sulfide formation from molten sulfur containing hydrocarbon
impurities.
Depending upon the type and age of the plant, some indicating
and/or recording instrumentation may be employed. Some of the
types which the inspector may have the opportunity of examining
include:
• Temperature (process gas entering and leaving the
several converter stages and absorption towers).
• Acid concentration (drying tower and absorption
towers).
-------
7.7.28
SO concentration (entering the converter, entering
and leaving the absorption tower or tail gas
scrubber).
Miscellaneous flow and pressure measurements.
Tests for sulfur dioxide, oxygen, acid mist concentration, and
nitrogen oxides often can be manually performed to supplement the
above instrumentation.
The inspector should determine the capability of the plant to meet
emission control regulations. These include limitations on the
discharge of (1) sulfur dioxide in the effluent in excess of 4 Ibs.
per ton of acid produced (2 kgm per metric ton), maximum 2-hour
average, (2) acid mist in the effluent in excess of 0.15 Ib. per
ton of acid produced (0.075 kgm per metric ton), maximum 2-hour
average, expressed as H.SO,, and (3) a visible emission. In
determining compliance the inspector should:
(1) Check the number of catalyst stages - older plants that have
only two stages of catalyst typically have only 90-95% conver-
sion of sulfur dioxide to sulfur trioxide. Plants with three
stages of catalyst will typically have a 96-98% conversion of
sulfur dioxide to sulfur trioxide. These conversion efficien-
cies are equivalent to emission rates of 26 to 52 Ibs. per ton
of acid produced.
-------
7.7.29
(2) Determine types of acid mist eliminators. Mesh mist elimina-
tors with double pads will collect efficiently acid spray and
mist from a properly operated 98% acid absorber, but not acid
mist from an oleum tower. Teflon mist eliminators or high
energy scrubbers are often used to collect acid mist less than
three microns in size to meet an emission limit of .15 Ib. per
ton of acid, maximum 2-hour average, expressed as H SO, or a
visible emission.
(3) Control room operating log.
(a) Check concentration of sulfur dioxide entering and leaving
the converter. Any unconverted sulfur dioxide will pass
through the absorber to atmosphere.
(b) Check temperature of 98% absorber tower acid. If the
acid temperature is considerably above 180°F, excess sulfur
trioxide and acid mist can be discharged to atmosphere.
(c) Determine operating rates from log and compare with design
capacity from permit system records. Operation at over-
capacity can result in excessive emissions of sulfur
dioxide and acid mist.
(4) Potential of the source to create a nusiance problem in terms
of:
(a) Possible effects of sulfur dioxide and acid mist on people
and property.
(b) Excessive emissions of sulfur dioxide during cold start-
ups, upset conditions or overload operations.
-------
7.7.30
(c) Excessive emissions of acid mist during oleum production
or improper operation of absorber.
The inspector should attempt to relate tail gas concentrations and
appearance to operating parameters during the time of his inspec-
tion. This information will be useful in interpreting causes of
upsets or off-normal conditions leading to excessive discharge of
air contaminants. Finally, it will be very useful for the
inspector to be present during a start-up operation to obtain
first hand information on optimum procedures for minimizing losses.
H. NATURE OF SOURCE PROBLEM - VINYL CHLORIDE MANUFACTURING
The manufacture of polyvinyl chloride plastics in the United States is
/Q \
second only to polyethylene production. As of 1967 there were nineteen
vinyl chloride monomer plants having a capacity of 2.8 billion pounds, of
which one billion pounds was based upon the use of acetylene. Predictions
at that time were that the use of acetylene as a starting chemical would
be phased out rapidly in favor of ethylene-based oxychlorination processes
which are at the present time more attractive economically. Industry
sources confirms that this indeed has occurred.
Over 80% of the chlorine production and 50% of the HC1 production in the
United States is consumed in the organic chlorination industry with a very
(9)
high proportion of this quantity being used in vinyl chloride production.
There are strong economic reasons to recover and recycle as much of the
chlorine and HC1 as possible.
1. Nature of Air Pollution Problems
The manufacture of vinyl chloride monomer (CH = CHC1) is based upon
the chlorination and hydrochlorination of acetylene and/or ethylene.
Although the air pollution potential is not great, the purging of inert
-------
7. 7.31
gases such as nitrogen from the air used in oxychlorination processes
can result in the loss of small quantities of unreacted chlorine,
hydrogen chloride, acetylene, ethylene, vinyl chloride, partially
oxidized hydrocarbons, and chlorinated side-reaction products.
These materials may be controlled by the use of caustic scrubbers,
absorption units, and waste heat boilers.
An intermittent problem may result from the burn-off of accumulated
carbon from the beds used in the cracking of ethylene dichloride to
form vinyl chloride. Normally this operation is easily controlled
but the discharge of products from incomplete combustion, including
smoke, is at least possible.
The transfer and storage of chlorine, hydrogen chloride and vinyl
chloride are usually completely closed operations, making any release
of these compounds very unlikely.
I. PROCESS DESCRIPTION - VINYL CHLORIDE MANUFACTURING
1. Basic Reactions
Vinyl chloride (CH = CHC1) is a colorless, flammable compound having
an ethereal odor. It boils at -13.81°C and is stored under slight
pressure to maintain the liquid state. Until recent years the princi
pal manufacturing process used involved the hydrochlorination of
acetylene according to the following reaction:
CH = CH + HC1 2 CH = CHC1
The reaction, which is exothermic, takes place over a mercuric chloride
catalyst. In addition to the vinyl chloride product, the reactor gases
contain small quantities of acetylene, HC1, and other organic addition
-------
7.7.32
products. Figure 7.7.5 shows a simplified schematic flow sheet of the
process. The vent gases from the absorber are composed of about 90%
inert gases and 10% acetylene. The relative quantity of these gases
is very low.
The other important basic reactions leading to the production of vinyl
chloride involve (1) the chlorination of ethylene to form ethylene
dichloride (more properly 1,2 dichloroethane) followed by (2) the
cracking of ethylene dichloride (EDO) to yield vinyl chloride and
hydrogen chloride. These reactions are seen below:
CH2 = CH2 + C12 -»~ CH2C1 - CH2C1
CH Cl - CH Cl hf^t CH = CHCL + HC1
A first step at improving the economics of the acetylene and ethylene
routes to vinyl chloride resulted in the so-called "balanced processes."
One variation of such a process is shown in Figure 7.7.6. Although
this flow sheet is considerably simplified, vent gases are similar to
the basic acetylene process.
Current Manufacturing Practice
During the past few years there has been a rapid change in industry
practice to adopt the oxychlorination process for manufacturing vinyl
chloride. ' ' In this process, ethylene, oxygen (almost always
from air), and ethylene are the starting materials.
The hydrogen chloride resulting from the cracking of ethylene dichloride
fromed by the chlorination of ethylene is fed together with oxygen and
ethylene to form additional ethylene dichloride. Thus, no acetylene is
-------
Unreacted CH=CH and CH =CHC1
Spent Caustic
Vinyl Chloride
Purification
Heavy Ends
Purified Vinyl Chloride
Heavy Ends
Figure 7.7.5 MANUFACTURE OF VINYL CHLORIDE FROM ACETYLENE AND HYDROGEN CHLORIDE
-------
CHsCH
CH=CH
Cl.,
Hydrochlorination
HC1
Chlorination
RawCH2=CHCl
EDC
Purification
Vinyl Chloride
Purification
Vinyl Chloride,
Product
CH =CHC1
HC1
EDC
Cracking
Figure 7.7.6 BALANCED PROCESS FOR VINYL CHLORIDE USING ACETYLENE AND ETHYLENE
-------
7.7.35
needed to utilize the by-product hydrogen chloride. Figure 7.7.7
shows a schematic flowsheet of one approach to this process. In the
United States pure ethylene is normally used as the starting material,
although in Japan at least one producer utilizes a relatively impure
mixed stream of ethylene and acetylene prepared from the on-stream
(14)
cracking of naphtha.
In the oxychlorination process the conversion efficiency of ethylene
to vinyl chloride is estimated to be in the range 96-98%. By-products
include unreacted feed materials, oxygenated compounds and carbon
oxides. These materials plus any inert gases must be removed from
the reactor gases prior to the ethylene dichloride cracking step. The
non-condensibles may be vented directly to atmosphere or to some form
of air pollution control equipment.
The ethylene dichloride following purification is cracked to form
vinyl chloride and hydrogen chloride with the latter being separated
and returned to the oxychlorination reactor. The cracking takes place
at 450° - 650°C at elevated pressures, and is usually done over a
catalyst. Some carbonization and tar formation takes place depositing
these materials on the catalyst. These deposits must be burned off
the cracking bed periodically in order to restore its effectiveness.
Modern practice is to use a steam-moderated air oxidation process for
the carbon burn-off. When carried out properly only carbon dioxide
should be vented.
3. Control Methods
The principal air pollution problem in the vinyl chloride manufactur-
ing process has to do with the purge gas venting taking place after
the reactor stages and before the ethylene dichloride cracking step.
Inert gases, mainly nitrogen, may be accompanied by unreacted ethylene
and chlorine, hydrogen chloride, oxygenated organics, and carbon oxides.
-------
Chlorination
EDC
EDC Purification
EDC Cracking
EDC
Oxychlorination
HC1
Vinyl Chloride
Purification
Vinyl
Chloride
Product
Figure 7.7.7 OXYCHLORINATION PROCESS FOR MANUFACTURE OF VINYL CHLORIDE
-------
7.7.37
In a well-controlled vinyl chloride plant, these vent gases are gener-
ally collected in a common manifold and treated by the following series
of air pollution control measures: (1) caustic scrubbing of reactor
vent gases; (2) combustion of oxidizable compounds in a waste heat
boiler; and (3) caustic scrubbing of boiler vent gases to remove
additional acid gases formed in the boiler.
Careful control of the waste heat boiler, usually by metering auxiliary
fuel through a steam output rate actuated controller, is necessary to
avoid smoke formation during any vent gas surges.
A lesser problem is associated with the vinyl chloride purification
steps. Here, vinyl chloride is usually liquified by refrigeration to
-20°C. Vent gases are discharged through a caustic scrubber.
Vinyl chloride is usually stored as a liquid in spherical pressurized
containers. All transfer operations are accomplished using vapor
return lines. The technology used is similar to that used for
liquified petroleum gases. Routine losses are not expected.
INSPECTION POINTS - VINYL CHLORIDE MANUFACTURING
A well operated and controlled vinyl chloride monomer plant should result
in practically no air pollution problems. However, should vent gases not
be controlled properly, the release of smoke, odorous substances and
property damaging acid gases is possible.
1. Environmental Surveillance
The greatest potential problem from a vinyl chloride plant is the
release of acid gases, principally chlorine and hydrogen chloride.
The hydrogen chloride particularly reacts with moisture in the air
to form hydrochloric acid mist and vapor which has the potential for
-------
7.7.38
accelerating corrosion in metals, damaging paint, and degrading other
surfaces and materials. When acid gas losses are suspected, the
surrounding area should be examined for evidence of the type of damage
just described. Test plates of susceptible materials may be used if
necessary. The damage pattern, if any, should be correlated with wind
direction. A wind rose (see Chapter 6, Section V, Odor Detection and
Evaluation) obtained from a representatively located wind direction
recorder is particularly useful.
Odors associated with partially oxidized organic substances and
chlorinated hydrocarbons are possible. They should be evaluated and
any complaints reviewed.
2. Plant Inspection
a. Interview
As seen from the description of the manufacturing process a wide
variety of specific plant design features may be expected in vinyl
chloride plants. Also they may be integrated with the production
of other chlorinated hydrocarbons. Therefore, it is very impor-
tant to obtain an exact description of the process used and the
starting materials.
Specific inquiry should be made as to the number and location of
process vents, the nature of vent gases, the procedure for collect-
ing vent gases, and the specific control techniques and equipment
used. The design objectives for caustic scrubbers should be
obtained.
Plant management should be asked to describe procedures for con-
trolling vent gases during upsets, including methods for preventing
or minimizing smoke from afterburners or waste heat boilers.
-------
7.7.39
b. Physical Inspection
The inspector should verify the placement of various items of
equipment in the process, paying particular importance to the
location and height of various vents. Determination should be
made of the production rate as a percent of rated capacity, the
specific materials being charged to the process, and whether
operating conditions are representative of the normal situation.
It will be useful to inspect the plant at various times to observe
start-up operations, catalyst burn-off, and raw materials and
product transfer.
Should visible emissions or odors be detected as a result of plant
operations, a specific determination of the associated operating
conditions should be made.
-------
7.7.40
REFERENCES
1. Groggins, P. H. (ed.). Unit Processes in Organic Synthesis, Third ed.
McGraw-Hill Book Co., Inc. New York, 1947.
2. McCabe, W. L., and J. C. Smith. Unit Operations of Chemical Engineering.
McGraw-Hill Book Co., Inc. New York, 1956.
3. Atmospheric Emissions from Sulfuric Acid Manufacturing Processes.
DHEW, PHS, Division of Air Pollution. PHS Publ. No. 999-AP-13, 1965.
4. Control Techniques for Sulfur Dioxide. DHEW, PHS, NAPCA, Publ. No. AP-52,
Jan., 1969.
5. Engineering Analysis of Emissions Control Technology for Sulfuric Acid
Manufacturing Processes, Final Report. CHEMICO. DHEW, PHS, NAPCA.
Contract CPA22-69-81. March 1970.
6. Tucker, W. G., and J. R. Burleigh. S02 Emission Control from Acid Plants.
Chem. Engr. Prog. 67, 57-63. May 1971.
7. Shah, I. S. Removing S02 and Acid Mist with Venturi Scrubbers.
Chem. Engr. Prog., 67, 51-56. May, 1971.
8. Sarvetnick, H. A. Polyvinyl Chloride. Reinhold Book Corp., New York.
1969.
9. Gerstle, R. R., and T. W. Devitt. Chlorine and Hydrogen Chloride
Emissions and Their Control. Paper #71-25, 64th Annual Meeting of the
APCA. Atlantic City. June 27-July 2, 1971.
10. Albright, L. F. Vinyl Chloride Processes. Chem. Engr., 74, 123-30.
November 27, 1967.
11. Buckley, J. A. Vinyl Chloride Via Direct Chlorination and Oxychlorination.
Chem. Engr., 73, 102-104. November 21, 1966.
12. Albright, L. F. Manufacture of Vinyl Chloride. Chem. Engr., 74, 219-226.
April 10, 1967.
13. Kling, H. Am. Chem. Co., (pers. comm.).
14. Vinyl Process Petrochemical, Pacesetter? Chem. Engr., 74, 48-49.
March 27, 1967.
-------
7.8.1
VIII. PRIMARY AND SECONDARY NON-FERROUS SMELTING AND REFINING
A. INTRODUCTION
The smelting and refining of non-ferrous metals are primarily concerned
with the production of copper, lead, zinc and aluminum ingots and alloys.
This activity is important from the standpoint of both the air pollutants
emitted and the extensive production of these metals in the United States.
Primary aluminum reduction is treated in Section XI of this chapter.
Copper, lead and zinc occur mainly as sulfides and are mined either in
open pits or in underground operations.
Primary smelting refers to the extraction of the virgin metal from its
original ore by crushing large quantities of ore-bearing rock, concen-
tration of the resultant feed and application of pyrometallurgical
processes such as roasting, melting and conversion. The operation may
also include dross recovery. Since the percentage of the recoverable
material is small, emissions of oxides of sulfur, fumes, dust and
participates are likely to be very great and difficult to control.
Secondary smelting and refining are concerned with the preparation and
melting of scrap metal of known and unknown analysis, dross recovery and
wire reclamation. The major metals of interest include copper-base
alloys (brass, bronze and black copper), zinc, lead and aluminum.
Emissions from melting operations include smoke, dust, fumes, oxides of
sulfur, and fluxing and degreasing agents.
Refining refers to the removal of impurities necessary to produce an
ingot or alloy of desired specification. Non-ferrous foundries,
treated in Section IX of this chapter, involve sand-casting and are oriented
-------
7.8.2
to the production of consumer and industrial products.
Primary smelters usually constitute, large, difficult to control single
sources of air pollution, are usually located outside of urban areas
and can be significant sources of visible emissions and plant damage.
Secondary smelters are commonly found in industrial and urban areas,
close to sources of scrap and other raw materials generated by population
centers. They are significant sources of pollution, as well as local
public nuisance problems. Both industries employ similar equipment,
although primary smelting involves a larger variety of processes.
B. DESCRIPTION OF SOURCE—PRIMARY SMELTING
The history of controlling emissions from non-ferrous smelters goes
back to the middle of the 19th century. Developmental projects are
still underway to find economic methods for further reducing sulfur
oxide emissions from smelters. While SO is the major contaminant of
x J
interest from this source, particulate emissions inherent in the job
of extracting any metal from its ore, is also a major problem although
air pollution control techniques and efficient equipment are currently
available.
National sulfur oxide emissions from non-ferrous smelters are estimated at
almost 3,000,000 tons, based on an annual rate for the first half of 1969
and excluding sulfur oxides or byproducts from pyrite roasting and sulfur
burning. Of this amount 852,900 tons of SO were recovered and
X (1)
1,924,400 tons were emitted to the atmosphere. Other commonalities
of non-ferrous smelting include high temperature gas emissions at
1200°F to 2400°F, heavy dust and fume loading and lean sulfur oxides
concentrations in the off-gases all of which make recovery difficult and
economically questionable.
-------
7.8.3
The Air Pollution Control Inspector, although not generally involved in
the research and development projects associated with the overall problem
of recovery of sulfur oxides, must be familiar with the basic processes,
type and magnitude of emissions, state of the art of air pollution control
methods and possible future changes in this technology.
1. Process Description
a. Copper
Before any of the pyrometallurgical processes (furnace and
related operations) can begin, the feed must be prepared into a
concentrate for economic recovery of copper. After initial
crushing, the ore is fed to wet ball or rod mills where it is
allowed to settle and is filtered. The resultant concentrate
is mixed with copper precipitates obtained from leaching mine
waste and oxidized ores. The concentrate contains between
70 and 85% copper and small quantities of direct smelting
sulfides and oxide ores which also contain four to six percent
copper.
Table 7.8.1 shows a typical analysis of a high quality concentrate.
The concentrate has a free moisture content of 10 to 12 percent while
the precipitant contains 15 to 30 percent water.
Table 7.8.1 Typical High Quality Concentrate Analysis
Constituent Percent (dry basis)
Copper, Cu 27.5
Iron, Fe 24.5
Sulfur, S 31.5
Silica, SiO 11.0
Other 5.5
(SOURCE: ARTHUR G. MCKEE & CO., Reference 1)
-------
7.8.4
The typical copper smelter in the United States uses a roaster,
reverberatory furnace and converter in the sequence shown in
Figure 7.8.1. Variations to the system shown in the flow diagram
include predrying of the feed in rotary driers or multiple
hearth dryers, or direct charging to a reverberatory furnace.
(1) Roasting
Wet concentrate is sprayed as a slurry or charged dry into
a multiple hearth, or, in more modern plants, a fluid-bed
roaster. Depending on the size of the roaster, the charge
can be 200 to 1500 tons/day of feed plus silica fluxes. The
roasting drives off the moisture and converts parts of
the sulfur to sulfur dioxide and the iron to iron oxide.
Roasting reduces the fuel requirements of the reverbatory
furnace by about half. The concentration of SO- from multiple-
hearth type roasters is about 7% while the concentration of SO.
(2)
fluid-bed roasters is about 15%. The operating temperatures
for both systems is about 1200 F. The temperature of the dust-
laden gases leaving the furnace is reduced by dilution air,
water spray or heat exchangers to 600 F. Initial dust and
fume control is achieved by use of settling chambers or
mechanical collectors followed by electrostatic precipitators.
The dust loading is between three and six percent of the feed,
most of which is captured in the flues. The roaster gas then
either goes to the stack or the sulfuric acid plant (Table
7.8.2 ). The calcine from roasting is hot and dusty and
-------
CUSTOM ORE 4
, CONCENTRATES
(S TOMSI
•^ ROAS
(ACTUAL TEMP F]
GAS (OOO SCFMl
S IN GAS TONS!
OUST TONS
S IN DUST TONS
ACTUAL TEMP F]
\
t
i
SOLIDS 1 LIQUIDS
GASES
SCPM MEASURED AT 32°F
NIL -NEGLECTFDUNSIGN
-rnn r*5~i
1 a>
I
. .ueer/^c «a, 1TA MISCELLANEOUS
LIMESTONE 5h-«-* pygj j REV£RTS
3 ryi -nri n^n-
j 'i
ISiX.f--*
1
1
1 ]
Trn , C»LC*« JRFVERBFRATORY
1*tvdS
1 1
1 FURNACE i T SLAG BLOW | '| FIN6H BLOW | » co«TS«l o.i TO-S"
1 1
-O^] [fSJi-i
IT If i *
L. .-?s^,"-«,.L. J I ! i
! ! """"'
1 ~* RECUPERATOHf""^
I2(xr 1J 100- 1 1 ior 1 1
*U«.J «„».„
j
1
f
•«
<.R
rocr
[ FLUES AND 1
PUST COLLECTION
i.
*" r 10 •TMWPHEftf' "^ TDAlMOVMC*
»o" 1 ziocr 1 iKxf 4so- ioff 1 iso- 1
** *nLUT«MUI OClrtlWiMI •*
K* COMVtHTCN | 1* «fl COWCRTa)
1- J
!
U^LEclU | STCK | | STCK |
J
1
L «— « j
•O*STf • «M> flCVt«C*5 J
OUST
NOTE
AND r.NF ATur^=uFDc °i±i' K^wf ^iXfa^e^SSf ma°^\r
F.CANT (.UANIITY NOT AFFECTING MATERIAL BALANCE) »LL FLO* QUANTITIES AOE ESTIMATED .ROASTER THE |AME OTVEBTER IS U5EO K)H SLAG
oo
On
NEC -NEGL£CTEOiMINOR CUANTITY PRESENT
N.R.-NOT R£PORIED(.CJUANTITY UNKNOWN)
AND REvERBERATORT GASES ABE SHOWN ON A
DAILY RATE BASIS. CONVERTER GASES APF AVEfl-
AGEO FOR A BLOW TIME OF n.7HR TOTAI ELAPSED
TIME. TONNAGES ARE GIVEN IN SHORT TONS FOR
IME. TONNAGES ARE
24 HOUR PERIOD
Figure 7.8.1.
FLOW DIAGRAM OF A TYPICAL COPPER SMELTER
(SOURCE: ARTHUR G. MCKEE & CO., Reference 1)
-------
7.8.6
Table 7.8.2.
(3)
handling this material, which is charged to the reverberatory
furnace, presents a dust control problem. Added to this
problem is the introduction of the material captured in the
primary dust collector to the charge of the reverbatory furnace,
EMISSIONS FROM COPPER ROASTERS, REVERBERATORY FURNACES,
AND CONVERTERS3
Roasters
Reverberatory
furnaces
Converters
Waste Gas
(m3)
1300b
2000b
10,000°
Raw Gas
Dust Content
3
(gm/m )
15
4
12
SO Content
%
2-8
-
to 8
Clean Air Guide 2101, Kommission Reinhaltung der Luft, Verein Deutscher
Ingenieure, VDI—Verlag GmbH, Dusseldorf, West Germany, January 1960
Per ton of concentrates
"Including extraneous air per ton of charge
(SOURCE: NELSON, Reference 3)
(2) Reverberatory Furnaces
The function of the reverberatory furnaces is to melt the
calcine from roasting, green ore, recycled "flue dust" or
converter slag to form matte—a mixture of cuprous and ferrous
sulfides and slag. A slightly oxidizing atmosphere is
maintained in the furnace by providing excess air above the
requirements for theoretically complete combusion. Furnace
sizes range from 22 feet x 96 feet to 38 feet x 125 feet and
hold a molten batch 24 to 48 inches deep with a feed rate
of 400 to 1100 tons/day. (See Figure 6.2.16, Fuel-Burning,
Chapter 6, Section II.) The furnace operating temperature
-------
7.8.7
reaches 2400 F. This high temperature and large volume of
the exhaust gas lends itself to heat recovery in waste-heat
boilers for generation of steam and electrical power. The
typical operating conditions from an oil or gas fired furnace
are shown in Table 7.8.3.
Table 7.8.3. TYPICAL REVERBERATORY FURNACE OPERATING CONDITIONS
Furnace bath temperature 2400 F
Excess Air 1-4 percent
Furnace pressure +0.1 in. of water
Dust load in offgas 2-5 grains per scf
Sulfur dioxide in offgas 0.5 - 3.5 percent
(SOURCE: ARTHUR G. MCKEE & CO., Reference 1)
Table 7.8.4 shows the off-gas composition at 2400 F based upon
the feed (green feed or calcined feed) to the furnace;
Table 7.8.5 gives the composition of the molten products
from the reverberatory furnace.
Table 7.8.4. REVERBERATORY FURNACE OFF-GAS COMPOSITION
Component Green Feed Calcine Feed
Carbon Dioxide 8.4% 10.2%
Nitrogen 69.3% 71.0%
Oxygen 0.25 - 1.0% 0.25 - 1.0%
Water 18.8% 17.7%
Sulfur Dioxide 1.5-3.5% .6-1.0%
(SOURCE: ARTHUR G. MCKEE & CO., Reference 1)
-------
7.8.8
Table 7.8.5. COMPOSITION OF REVERBERATORY FURNACE MOLTEN PRODUCTS
Component Matte Slag
Copper 25 - 50% 0.4 - 0.7%
Iron 29 - 35% 34 - 40%
Silica 0.8 - 1.0% 35 - 40%
Sulfur 22 - 29% 1.0 - 1.5%
(SOURCE: ARTHUR G. MCKEE & CO., Reference 1)
Dust loading in the gases leaving the furnace is heavy. Up
to 25%^- ' of the dust is recovered by gravity in the balloon
flues upstream of the waste heat boiler. This necessitates the use
of feeders (screw or gravity) from the flues and hoppers to remove
the dust for recycling. The smaller particle sizes are then
exhausted to the electrical precipitator. The particulates from
copper smelting operations are volatalized oxides, fumes of antimony
arsenic, zinc lead, bismuth, tellurium and selenium. A by-
product of non-volatilized metals include nickel, cobalt, and
precious metals which can be separately refined.
(3) Converters
Copper matte is transferred from the reverberatory furnaces
to the converters in large ladles by overhead cranes.
Converting is a batch process with three distinct phases of
operation: charging, slag skimming and pouring. Air or air
enriched with oxygen is blown into the furnace through
tuyeres for oxidation. A temperature of 2250°F is maintained
by the oxidation reaction without the requirement for additional
fuel. Most converters in use are Fierce-Smith type
cylindrical furnaces, 13 feet in diameter and 30 feet long
with an average daily production of 135 tons of copper, depend-
ing on the grade of matte charged.
-------
7.8.9
The process oxidizes and separates the iron and sulfur from
the copper in the matte. The furnaces are operated in
sequence so that the air/oxygen blowing will not occur at
the same time to allow a fairly regular flow of SO- to the
acid plant. The highest theoretical concentration of SO.
occurs after the slag has been skimmed and the "white metal"
or cuprous sulfide has been converted to copper.
Capturing the fume and off-gases from this type of furnace
requires hooding similar to the equipment used on basic
oxygen furnaces (see Section IV). The tighter the hood fits,
the less dilute are the emissions of sulfur oxides to be
controlled. The drawback is that temperatures at the hoods
remain high which may damage the hoods and accompanying
ductwork. Some experiments are being conducted with water
cooled hoods in connection with waste heat boilers to reduce
the temperature to 600 F between the converters and the
electrostatic precipitators. The product of the converter is
blister copper which is 99% pure and is either used in this
form or further refined for anode production or other shapes.
Two approaches to copper production which have received
considerable attention and which should be mentioned for
possible future interest are continuous smelting and hydro-
metallurgy. Continuous smelting will likely replace the rever-
beratory furnace and converter with a single unit while hydro-
metallurgy will likely replace all of the conventional pyro-
metallurgical processes with electrolytic processes after the
sulfide ore has been pretreated.
-------
7.8.10
(4) Contaminants Emitted
Emissions from roasting, reverberatory furnaces
and converters consist of dust, fumes and sulfur
oxides.
Typical volumetric analyses of offgases are:
Roasters SCL/SO -12%
Reverberatory furnaces S02/S03-0.6%
Converters SC>2/S03-5.0%
While perhaps not typical, some measured particulate concentrations
from these operations are roasters 18-24 GR/SCF; reverberatory
C4")
furnaces 0.55-6.0 GR/SCF; converters .55-3.0 GR/SCF.v '
A common practice among plants that recover sulfur is to
vent the gases released from the roaster and converter
gases to sulfuric acid plants and to vent the reverbera-
tory gases to the atmosphere because of the low SO
content.
Without the imposition of air pollution control standards,
economics would be the only criteria for the control of
particulates and SO . The control of dust and fumes can be
X
achieved by the use of dust control trains consisting of a
mechanical separator, gravity separators and electrostatic
precipitators. The recovery of oxides of sulfur is receiving
a great deal of attention, not only in the smelter industry
but from all processes where SO is generated. Acid plants
X
and elemental sulfur recovery operations will come into
increased use. The sulfuric acid production is discussed
in Chemical Plants, Section VII.
-------
7.8.11
b. Lead
Lead sulflde (or galena) Is prepared similarly to copper sulfide
concentrate. Lead mineral galena generally contains 55 to 70 per-
cent lead; as much as 6.5 percent zinc; 0.5 to 4.0 percent copper;
13 to 18.5 percent sulfur; as much as 5.0 percent iron and silica,
lime, cadmium, silver and gold; and arsenic in minor amounts.
Existing lead producing practices in the United States involve
fundamentally identical operations: Sintering, reduction in blast
furnaces and refining. While the processes are similar, different
types of equipment can be employed.
chart for a lead smelting operation.
types of equipment can be employed. Figure 7.8.2 shows a flow
(1) Sintering
Sintering is the agglomeration of fine particles by partial
fusion due to application of heat. Sintering is conducted
to prepare the lead sulfide concentrate and involves a
combination of roasting to remove the sulfur and sintering to
form a strong porous mass suitable for reduction of the lead
oxide in the blast furnace. Figure 7.8.3 is a flow diagran
showing material components of a typical sintering operation.
Two types of sintering machines known as Dwight-Lloyd machines
are in use. The older downdraft machine draws in large
quantities of excess air diluting the SO concentration and
requiring recirculation of the gases to bring the concentration
up to 4-7% S0_. The newer updraft machine draws in less out-
side air and does not dilute the concentration of SO . Re-
x
circulation is also used in this machine to further enrich
the effluent for recovery as H_SO,.
-------
ORE AND LEAD
CONCENTRATE
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Figure 7.8.2.
FLOW CHART FOR A LEAD SMELTING OPERATION
(SOURCE: ARTHUR G. MCKEE & CO., Reference 1)
-------
TYPICAL LEAD SINTERING PLANT MAJOR MATERIAL DISTRIBUTION
LEAD CONl
MISC. LEAD
FLUX DILUE
SINTER RtC
i
:ENTRATE 31.47
MAiERIAL 12.44
NT 19.85
YCLE 36.20
' • '
T
J Pb-37.0%
/\ S- 7.0% OFFGAS PRODUCTS
/s (SULFUR DIOXIDE 5.95
iCARBON DIOXIDE 1.60
L_
RE"Ui?tED * SINTER | TOTAL SIFTER 95.33 K SINTER PRO
OXYGEN 2.87 \ PLANT s
t £
j
RECYCLE •$
TO BLAST
DUCT 59.13 FURNACE
--.... p>
Pb-38.8%
S - 1.08%
00
(->
U)
Figure 7.8.3. TYPICAL LEAD SINTERING PLANT MAJOR MATERIAL DISTRIBUTION
(SOURCE: ARTHUR G. MCKEE & CO., Reference 1)
-------
7.8.14
Physically, the machines are conveyors made of gratebar pallets
joined together to form an endless chain. They range in size
from 3-1/2 x 22 feet to 10 x 103 feet. The wind box is
located under the pallets or the downdraft machine and above
the pallets on the updraft machine.
Both designs can be either single or two-stage operations.
About 85% of the sulfur in the feed is removed during
sintering, with 14% entering the slag and other solid by-
products. The remaining one percent is released from the
blast and dross furnaces. In a two-stage operation, 30 to 40%
of the sulfur is removed during the first stage. The
clinker is crushed and mixed with one to two percent coke and
returned to the machine. Even in single-stage machines
40 to 60 percent of the calcine is recycled.
Feed to the sintering equipment is usually pelletized for
ease in handling and ignition. Natural gas is used for
ignition but the reaction of forming lead and other oxides
maintains the necessary heat. Control to maintain temperatures
below 1400 F is essential to preclude volatilization of
metals in order to produce the proper clinker with 1 to 3-1/2%
sulfur, and to maintain the grates. Limiting the sulfur
in the feed to between 6-12% and using sulfide-free fluxes
such as silica and limestone helps to keep the temperature
within the desired limits.
As with most smelting operations the prime target of air
pollution control is SO . However, some of the operations
develop large quantities of dust and fumes, up to 20% of
the feed in some sintering operations, which will be of concern
-------
7.8.15
to the air pollution control inspector. Economics of
operation dictate that efficient dust and fume control be
exercised due to the quantity of material entrained in the
offgas. The captured material is recycled. The inspector
must make sure that capture of the dust and fume is acceptable
as well as cleaning the offgas in the air pollution control
equipment. The offgas temperature varies between 250 and
600 F depending on the amount of excess air drawn into the
system. Gas volumes are 100 to 220 SCFM per sq. ft. of bed
area. Since baghouses are often used to collect the dust and
fumes, the temperature is critical with regard to the filter
material. Gas temperature and humidity are also important
in electrostatic precipitator operations (see Section IV,
Steel Mills).
(2) Blast Furnaces
Sinter, iron and coke are charged into the blast furnace
where the lead oxide is reduced to lead. At the usual
operating temperatures of 1000 to 1200 F (gas temperature),
iron oxide and zinc oxide are not reduced to metals but,
along with most of the sulfur present, leave the furnace in
the slag. Since some zones of the furnace reach higher
temperatures there is some distillation of lead oxide and
zinc oxide. These materials along with dust and volatilized
cadmium oxide are entrained in the exhaust gases. There is
little S0_ reported in the exhaust gases. Dust from the
charge and fumes from the chemical reactions are entrained
in the air blown through the tuyeres up through the charge.
The chemical reactions are:
-------
7.8.16
PbO + CO + heat = Pb + CQ^
C + 02 = C02 + Heat
C + C02 + Heat = 2CO
Theoretical flue gas rates are 6000 to 14,000 SCFM varying
with the size of the furnace. Blast air is between 5000
and 9000 SCFM. The actual gas volume to be handled from the
furnace is 9 to 12 times the theoretical flow due primarily
to the large volume of air which leaks in at the top of the
furnace. The furnace gas, before dilution, contains 25
to 50 percent CO and may reach temperatures of 1400 F. The
high volume of dilution air aids in the combustion of CO to
CO. and serves to reduce the gas temperature to a resultant
temperature of 150 to 250°F before entering the air pollution
control equipment.
The blast furnace produces four liquids: lead bullion, matte,
speiss (metallic arsenides) and slag. The lead bullion is
separated by gravity and goes to the refining process. The
matte and speiss go to the dross furnace for further lead
recovery. The slag is removed separately and is either
transported to a dump or is moved hot to fuming furnaces for
recovery of lead and zinc.
Typical composition:
Lead Bullion: 95% to 99% lead.
Matte: 44 to 62% Copper, 10 to 20% lead and up to
13% sulfur; up to 2% zinc and small amounts
of iron and silica.
-------
7.8.17
Speiss: 55 to 64% copper; up to 18% lead and traces
of sulfur and aresenic; 1% zinc and 0.5%
iron and silica.
Slag: High silica 10 to 20% zinc; up to 2%
lead and 3% sulfur; some iron and calcium.
(3) Lead Refining
Lead refining produces high purity bullion (95 to 99%) as well
as matte, speiss, and dross in operations employing reverberatory
furnaces and refining kettles or pots. The products from
the lead blast furnace are fed to a gas or oil-fired
reverberatory furnace at about 1400 F with an oxidizing
atmosphere. Dross forms over the surface of the batch which
becomes a product to be processed in the dross reverberatory
along with matte and speiss. The remaining dross, matte and
speiss are skimmed from the dross reverberatory after optimum
lead removal and are shipped to copper smelters for
reclamation of copper, which may run from 44 to 62 percent.
Figure 7.8.4 describes the complete cycle of lead smelting.
Refining kettles are used to bring the bullion to desired
limits of antimony, zinc, arsenic, tin, etc. by the introduction
of sodium hydroxide, sodium nitrate or sodium salts. Table
(3)
7.8.6 describes emission rates from a lead smelting operation.
It indicates an absence of S00 emissions from reverberatory
(1)
furnaces. However, the McKee study indicates that sulfur
can be added to both the reverberatory furnaces and the
refining kettles which can cause the emission of as much as
0.2 percent of sulfur oxide for short periods after the
addition of sulfur.
-------
7.8.18
Ore
I
(1) Mine
I
(2) Crush
(3) Concentrate If low grade
I
(4) Rough roast
(5) Bins or ore beds
(6) Sinter
(7) Smelt (usually in blast furnace)
1
Slag
Waste
S
Reh
blast
" 1
Base bullion
Dressing kettle
Dross
Dross furnace
1
Base bullion
Pefinlng plant
I
ag Matte-spelsa Base bullion
rn to Ship to Return to
furnace copper smelter dressing kettle
1
Gases
Cottrell or bag house
Flue dust Cleaned
Work up
values
1
Gases
To Cottrell
or bag house
Figure 7.8.4. USUAL TREATMENT OF A SULFIDE LEAD ORE
(SOURCE: NELSON, Reference 3)
Table 7.8.6. EMISSIONS FROM LEAD SINTERING, BLAST FURNACES, AND
REVERBERATORY FURNACES3
Sintering
Blast furnaces
Reverberatory
furnaces
Waste gas
(m3)
3000'
15,000-50,000r
100-500"
Raw-
Dust content
(gm/m3)
2-15
5-15
3-20
gas
SO2 content
1.5-5
~~
" Clean Air Guide 2285, Kommission Reinlialtung der Luft, Verein
Deutscher Ingenieure, VDI—Verlag GmbH, Dusseldorf, West Germany,
September, 1961.
* Per ton of sinter.
' Per ton of coke.
d Per ton of charge.
(SOURCE: NELSON, Reference 3)
-------
7.8.19
(4) Additional Equipment and Operations
Since the by-products of lead smelting contain recoverable
amounts of cadmium and zinc oxide some plants also process
this material. Cadmium roasters, slag fuming furnaces and
deleading kilns are used in these instances. Emissions of
sulfur oxides from these processes are minor relative to the
total operation but dust and fume emissions can be significant.
The inspector should observe these operations to determine
their compliance with the appropriate regulation.
(5) Contaminants Emitted
While lead smelting operations are responsible for a smaller
volume of sulfur oxide emissions than from copper smelting
the amounts are still appreciable. In addition, a substantial
quantity of dust and fumes are generated in these operations
which may be more significant than gases or liquid aerosols.
Levels of concentration of emissions vary. Gaps in data
exist especially for dust and fume emissions.
Sintering machines will emit between 0.8 to 1.8 percent sulfur
oxides by volume and from 5 to 20 percent of the feed as
dust and fumes. Blast furnace emissions of sulfur oxides
will range between 0.01 to 0.25 percent. Dust and fume
emissions from smaller secondary smelting operation using
cupolas, sampled by the Los Angeles County Air Pollution
District, indicate a dust loading of 12.3 gr/SCF. '
Reverberatory furnaces also emit relatively small quantities
of sulfur oxides usually less than 0.05 percent, while dust
loading can be about 6 gr/SCF.
-------
7.8.20
As in copper smelting, dust and fume collection is achieved
by combinations of mechanical separators with baghouses or
precipitators.
Control of sulfur oxide emissions is variable since some of
the processes emit lean mixtures. In most instances,
emissions of SO from sintering operations are sufficiently
rich for use in H.SO. plants which act, in effect, as air
pollution control systems.
Zinc
Two principal "raw" materials are used in the production of zinc.
ZnS (sphalesite) which is separated by selective flotation to a
concentrate that contains 60% Zn and the slag from lead blast
furnaces where zinc is recovered as an impurity in fuming furnaces.
In both cases it is necessary to form dense zinc oxide for
extraction of the zinc by either pyroreduction and distillation or
electrolytic precipitation.
In the pyroreduction sequence, the concentrate is either roasted
and sintered in two separate processes or in a single process in
the sintering machine. Figure 7.8.5 shows a typical operational
sequence of a zinc retort plant. The potential air contaminants
emitted from these operations are SO and zinc oxide fume. The
latter, however, is a requirement for zinc production and will
probably be well controlled.
(1) Roasting
Roasting oxidizes about 93 to 97% of the sulfur in the concentrate
to produce zinc oxide calcines. The calcines contains 2 to 3-1/2%
sulfur as sulfide and sulfate in a completely roasted batch.
-------
MOIST CONCENTRATE
ROASTING GAS ^ TO ACID
PLANT
.f siKPFN^ioN I xT WASTE HEAT""! ,J HUMIDIFYING 1 ^
V| FJOASTfR I 1 5 BOILER 5 " \ CKAMEE_R_J
j j^l; DRYING" 1
j[ SECTION | 1 £, „*
J! COAL or PET. COKE
4- If i?
j ,,, i ii, 6 I MIXING ANP 1 ^1 SINTERING 1 .
| OHLL ...i^u Jrrvri"F'~<:T->4Va 1 COKE
]| MI3C-RECYCLE
•<> ^ ^
| R c 1 0 R ( C 1 1 ; \ r. o c?
| MIXP.'G |
F1IFL f V^ i
S S pj i je O A*5
i ^mi.^"T'.i.^
i co s z:;ic" 1
5 COMDENSERS S
-, LIQUID ZINC METM 1
7 13'.. SO2 P"
]
f F_LECTP,OSTATIC1_J
| PRtCiPliATOR J
1
f
I
DUST 1
! COLLECTOR j|
1
SINTER GAS h
O.K.S02 P T°
Figure 7.8.5. TYPICAL ZINC RETORT PLANT FLOW DIAGRAM^1)
(SOURCE: ARTHUR G. MCKEE & CO., Reference 1)
-------
7.8.22
A number of roasting methods are in use in the United States.
Table 7.8.7 gives an overview of names, operating conditions
and expected dust and SO- concentrations in the offgas. Dust
collectors usually employed in roasting operations are electro-
static precipitators. However, large quantities of dust settle
in the flues and waste heat boilers. The resultant dust free
offgas, which contains from 4.5 to 12% SO-, is usually ducted
to an H SO, acid plant for collection or to tall stacks.
Table 7.8.7- TYPICAL ZINC ROASTING OPERATIONS
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
TON/DAY
50-120
250
40-50
140-225
240-350
240
120-350
225
DUST IN
OFFGAS
% OF FEED
5-15
5-15
5
70-80
75-85
50
50
17-18
OFFGAS
so2%
4.5-6.5
4.5-6.5
0.7-1.0
7-8
10-12
9-10
8-12
11-12
TYPE OF ROASTER
Multihearth
Multihearth (2)
Ropp (3)
Fluid bed (4)
Fluid bed (2)
Fluid bed (Lurgi)
Suspension
Fluid column
(1) Dead roast except where noted otherwise (complete roasting using exothermic
heat of reaction of sulfur with 0.).
(2) First stage is a partial roast in multihearth, second stage is a dry-feed
dead roast in fluid bed.
(3) Partial roast •
(4) Slurry feed.
(SOURCE: ARTHUR G. MCKEE & CO., Reference 1)
-------
7.8.23
(2) Sintering
Where roasting is used to oxidize the sulfur in the concentrate,
sintering is employed to agglomerate the calcine. Double-pass
sintering is used in the absence of roasting operations.
Table 7.8.8 describes typical sintering operations with the
resulting dust and SO. content.
Table 7.8.8. TYPICAL ZINC SINTERING OPERATIONS
Case:
New feed material
Total charge capacity
tons cer day
Machine size, ft
Fuel added to feed, %
Total auliiir in r.ew feed, '
Recycle, % of new feed
Oust in cffgas, % of feed
Offgas SO2 content, %
(SOURCE: ARTHUR G. MCKEE & CO., Reference 1)
Downdraft machines are used in all sintering operations in
the zinc industry (as opposed to both updraft and downdraft
in lead—see description of sintering machines in
Part B,2,a). The product is a hard pourous clinker which is
mixed with coke breeze to reduce the oxide that may be
present in retorts and condensers.
1
calcine
240-300
3.5 x45
6-7
3
35-75
5
1.5-2.0
2
calcine
400-450
6x97
10-11
2
40-70
5-7
0.1
3
concentrate
550-600
12 x 16S
0-2
31
80
5-10
1.7-2.4
The dust from the process ranges from 5 to 10% of the feed
and is collected for recycling or treated for lead and calcine
recovery. The sulfur content in the offgas is low, 0.1 to 2.0%,
but can be enriched to 6.0 to 6.5% by recycling to make it
economically feasible for collection in an acid plant. How-
ever, these gases are usually vented through tall stacks.
-------
7.8.24
(3) Zinc Extraction
The steps of roasting, sintering and calcining (when performed)
are necessary for the preparation of the material for either
pyroreduction or electrolysis for extraction of zinc from
zinc oxide.
1. In pyroreduction the sinter is mixed with coke breeze and
processed in vertical retorts, horizontal retorts (the
Belgian retort process), electric arc furnaces or blast
furnaces. The vapor formed is condensed as either liquid
or solid powder. The Imperial Smelting Process, not in
use in the United States, uses a blast furnace to vaporize
zinc which is condensed by a shower of molten lead.
The zinc dissolves in the lead and floats to the top of
the container outside of the condenser where it overflows
and is cooled to produce 98% pure zinc.
2. The electrolytic zinc process produces high purity zinc
by using calcine in H.SO, solution to remove impurities
and a lead anode and aluminum cathode to accomplish
the electrolysis. The zinc is hand-stripped from the
cathode, remelted and poured into slabs for treatment.
(4) Contaminants Emitted
Tables 7.8.7 and 7.8.8 ' show typical concentrations of dust
and S02 from zinc roasting and sintering operations. Of the 15
primary zinc smelters in the United States, nine recover
sulfur from the offgases and these only from roasters. The
sulfur is recovered as sulfuric acid.
Dust and fumes which escape the process or are collected
in inefficient or undersized dust collectors are also a
-------
7.8.25
potentially serious problem from this industry. Large
quantities of dust are transmitted in the roaster and
sintering offgases and unless capture and recovery is
excellent, significant quantities of small particles can be
emitted to the atmosphere since nearly all of the particulates
are <10M-
Most dust and fume collection is achieved in baghouses and
electrostatic precipitators. The problem in these areas is
pickup of particulates at the generation points and their
handling systems.
2. Inspection Points—Primary Smelting and Refining
The emission of sulfur oxides is the major contribution to air pollution
from non-ferrous smelters. Particulates, especially specific
particulates such as lead, are receiving increasing attention.
a. Environmental Observations
When economics prohibit the capture of SO in smelters, tall
X
stacks are used to disperse the large quantities of sulfur oxides
emitted. Even with tall stacks, meteorological conditions and
topography can cause the plumes to dip into areas adjacent to the
smelters causing the classic S0« damage to plant life and
respiratory difficulties. Particulates (dust, fumes and sulfuric
acid mist) also can cause reduced visibility when meteorological
conditions are conducive to the accumulation of air pollution.
Section II, Kraft Pulp Mills, describes methods of investigating
the results of excessive emissions of sulfur oxides. The assistance
of residents and workers in adjacent areas is important since, in
effect, 24-hour surveillances can be achieved.
-------
7.8.26
b. Observations of the Exterior of Smelters
Most processes in smelters vent to one or more tall stacks which
theoretically allow the sulfur oxides to disperse to concentrations
below those which would cause damage to plants, animals or buildings.
Under some weather conditions the plume which is visible from the
stack will bend into areas adjacent to the smelter. The inspector
should observe the plume during as many changes in plant operation
as possible in order to correlate changes in opacity with differing
operations.
Dust and fume emissions from any pyrometallurigical processes
and materials handling can be spotted from outside of the facility
if the inspector is familiar with the plant layout. Specific
operations of concern include the loading and discharging of
sintering machines, charging working furnaces and pouring from
furnaces. Zinc distillation furnaces, if not properly vented
with close fitting high inlet velocity hoods, can lose fume which
can be detected from roof monitors and windows of the building
housing the processes.
Large sections of smelter property may be unpaved and material may
be stored in large piles without cover. These points, common to
many industries, should be noted and reported to plant management
as high potential dust sources.
c. In-Plant Observations
Non-ferrous smelters comprise sizeable operations usually spread over
many acres of ground and are frequently the subject of many studies
and legal actions. The inspector must present himself to plant
management with a clear picture of the air pollution control
regulations he is obligated to enforce. He must obtain cooperation
-------
7.8.27
of management in order to thoroughly understand the operations. He
should devote sufficient time to observing the basic operations to
learn the cycles, time periods of day when the various phases of the
operations occur and sequence of operations and identifying the
management personnel responsible for the various operations. The
McKee report shows a flow diagram for many of the non-ferrous
smelting operations in the United States. This is an excellent start-
ing point for an inspector, but it must be emphasized that it is only
a starting point. Also, the inspector should become very familiar
with the maintenance practices of the company. Maintaining the con-
trol equipment is probably the most important aspect of controlling
emissions and is visually given last priority.
Acid processes are treated in Section VII of this chapter. They
currently present the principal method of controlling S02 emissions
from smelters. The inspector should become familiar with the venting
system and be able to determine when the acid plant is by-passed and
the sulfur oxides are vented to atmosphere.
Dust and fume control systems are a necessary part of smelter opera-
tions. In addition to air pollution control requirements, large
quantities of dust must be separated from the process gases and
returned to the process. Smelter offgases must be cleaned before
processing in the sulfuric acid plants. The dust removal equipment
consists of cyclone and other mechanical separators for large particle
size dust, and baghouses and electrostatic precipitators for condensed
fume and small, < 10 fj. , dust particles.
C. NATURE OF SOURCE-SECONDARY SMELTERS
As a class, secondary smelters and refiners reclaim metals from scrap,
drosses and slag. Operations and equipment for brass and br.onze, lead, zinc,
and aluminum are described in this section. Smoke, dust, fumes, sulfur oxides,
fluxing and degreasing agents are typically emitted.
-------
7.8.28
Large copper secondary smelters employ many of the same operations used
in primary smelting with the exception of roasting. Precious metals are
also recovered from electrolytic refining slimes at both primary and
secondary copper smelters.
1. Process Description—General
A variety of metal alloys are produced in several basic types of
furnaces. Reverberatory furnaces are used in the secondary smelting
and refining of copper bearing alloys, aluminum and lead; blast furnaces
or cupolas are used in copper and lead production; pot furnaces,
crucibles and electrical induction furnaces are used for various
refining processes in all non-ferrous operations. Zinc production alone
has unique furnace requirements for secondary refining. This process
requires retorts and condensers and holding furnaces for some refining
processes.
a. Brass and Bronze
The basic steps in producing brass and bronze ingot in secondary
smelters are:
• Materials Preparation
• Mechanical Methods
• Hand Sorting
• Stripping
o Shredding
• ^Magnetizing
• Briquetting
-------
7.8.29
• Pyrometallurgical Methods
• Sweating
• Burning (Insulation Removal)
• Drying
• Blast furnace or Cupola (melting or oxide reduction)
• Hydrometallurgical Methods—flotation process
• Ingot Production
• Reverberatory Furnaces
• Rotary Furnaces
• Crucible Furnaces
While not all of the steps or equipment involved in the total
process emit air contaminants, the inspector should be familiar
with the total cycle. In all brass and bronze production the
primary air pollution control problem is the emission of zinc
oxide during melting and pouring to produce the ingot. This
naturally is a function of the zinc in the metal to be produced
and in the metal that makes up the charge to the furnaces.
Table 7.8.9 shows the nominal specifications of copper base
alloys commonly produced in the United States. As the zinc and
lead content increases, melting operations become more critical
relative to potential zinc oxide and lead oxide emissions. Other
likely contaminants from these processes are dust and smoke from
fuel combustion and from grease and oil present in the scrap used
as charge material.
This industry scavenges material to be refined into ingot to meet
the specification shown previously. The source of this material is
the scrap salvage industry. Table 7.8.10 describes the major types
of industrial and military scrap which become the raw material
charged to the secondary brass smelter.
-------
7.8.30
Table 7.8.9. NOMINAL CHEMICAL SPECIFICATIONS FOR BBII STANDARD ALLOYS
Alloy
No. Classification
1A Tin bronze
IB Tin bronze
2A Leaded tin bronze
2B Leaded tin bronze
2C Leaded tin bronze
3A High-lead tin bronze
3B High-lead tin bronze
3C High-lead tin bronze
3D High-lead tin bronze
3E High-lead tin bronze
4A Leaded red brass
4B Leaded red brass
5A Leaded semi-red brass
5B Leaded semi-red brass
6A Leaded yellow brass
6B Leaded yellow brass
6C Leaded yellow brass
7A Manganese bronze
8A Hi-strength mang. bronze
SB Hi-strength mang. bronze
8C Hi-strength mang. bronze
9A Aluminum bronze
9B Aluminum bronze
9C Aluminum bronze
9D Aluminum bronze
10A Leaded nickel brass
10B Leaded nickel brass
11A Leadeti nickel bronze
11 B Leaded nickel bronze
12A Silicon bronze
12B Silicon brass
Cu.%
88.0
88.0
88.0
87.0
87.0
80.0
83.0
85.0
78.0
71.0
85.0
83.0
81.0
76.0
72.0
67.0
61.0
59.0
57.5
64.0
64.0
88.0
89.0
85.0
81.0
57.0
60.0
64.0
66.5
88.0
82.0
Sn,r.
10.0
8.0
6.0
8.0
10.0
10.0
7.0
5.0
7.0
5.0
5.0
4.0
3.0
2-5
1.0
1.0
1.0
1.0
2.0
3.0
4.0
5.0
Pb, %
1.5
1.0
1.0
10.0
7.0
9.0
15.0
24.0
5.0
6.0
7.0
6.5
3.0
3.0
1.0
1,0
9.0
5.0
4.0
1.5
Zn.%
2.0
4.0
4.0
4.0
S.O
3.0
1.0
5.0
7.0
9.0
15.0
24.0
29.0
37.0
37.0
39.0
24.0
24.0
20.0
16.0
8.0
2.0
5.0
14.0
Fe, %
1.0
1.0
3.0
3.0
3.0
1.0
4.0
4.0
1.5
Al.%
0.6
1.0
5.0
5.0
9.0
10.0
11.0
11.0
Ni.%
2.0
4.0
12.0
16.0
20.0
25.0
Si,%
4.0
4-0
Mn,%
0.5
1.5
3.5
3.5
0.5
3.0
1.5
(SOURCE: CUFFE AND SCHWARTZ, Reference 5)
(1) Blast Furnaces and Cupolas
The blast furnace is an economical method of recovering copper
from low grade scrap and slag. The material is charged through
the top of the furnace with varying amounts of coke and lime-
stone. Blast air is blown through the tuyeres at the bottom of
the furnace.
By its nature, the blast furnace uses large quantities of air
for combustion which creates a significant air pollution control
-------
7.8.31
Table 7.8.10. TYPES OF COPPER-BEARING SCRAP
No.
Designation
1.
2.
S.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
No. 1 copper wire
No, 2 copper wire
No. 1 heavy copper
Mixed heavy copper
Light copper
Composition or red brass
Red bras? composition turnings
Genuine babbitt-lined brass bushings
High-grade, low-lead bronze solids
Bronze papermill wire cloth
High-lead bronze solids and borings
Machinery or hard red brass solids
TJnHncd standard red car boxes (clean journals)
Lined standard red car boxes (lined journals)
Cocks and faucets
Mixed brass screens
Yellow brass scrap
Yellow brass castings
Old rolled brass
New brass clippings
Brass shell cases without primers
Brass shell cases with primers
Brass small arms and title shells, clean fired
Brass small arms and rifle shells, clean muffled (popped)
Yellow brass primer
Brass pipe
Yellow brass rod turnings
Yellow brass rod ends
Yellow brass turnings
Mixed unsweated auto radiators
Admiralty brass condenser tubes
Aluminum brass condenser tubes
Muntz metal tubes
Plated rolled brass
Manganese bronze solids
New cupro-nickel clippings and solids
Old cupro-nickel solids
Soldered cupro-nickel solids
Cupro-nickel turnings and borings
Miscellaneous nickel copper and nickel-copper-iron scrap
New monel clippings and solids
Monel rods and forgings
Old monel sheet and solids
Soldered monel sheet and solids
Soldered monel wire, screen, and cloth
New monel wire, screen, and cloth
Monel castings
Monel turnings and borings
Mixed nickel silver clippings
New nickel silver clippings and solids
New segregated nickel silver clippings
Old nickel silver
Nickel silver castings
Nickel silver turnings
(SOURCE: CUFFE AND SCHWARTZ, Reference 5)
-------
7.8.32
problem. Depending upon local air pollution control agency
requirements, high efficiency scrubbers, baghouses and electro-
static precipitators, with primary separators for the removal
of larger size particles, are used to control emissions. The
baghouse has proven to be an excellent control device for
cupola operations, if properly sized. As important as the
dust removal system is, the design of the fume pick-up system
should include good indraft velocity at the furnace charging
door and hooding over the metal pouring spout.
The blast furnace or cupola is usually operated 24 hours per
day with continuous slag pouring and intermittent metal pouring.
Observation by the inspector should include furnace startup;
at least for one hour's operation to determine if excessive
smoke and fume escape during charging; inspection of the hoods
and ductwork to determine if they are in good repair and if
the efficiency of dust pickup has degraded. The operation of
the air pollution control equipment, depending on the type used,
must also be monitored.
The physical location of the dust and fume controls relative
to the furnace may make observations of both control systems
difficult, necessitating a two-man inspection. Efficiency
of the air pollution control equipment can only be accurately
checked by stack analysis. The inspector can, however, note
gross changes in efficiency by comparing differences in opacities
of emissions under different operating conditions.
-------
7.8.33
Other preparational operations which can cause emissions
are sweating, drying and burning. The removal of insulation
by burning is covered in the section on incineration.
Sweating to remove solder and other low melting point alloys
can cause smoke and particulate emissions, depending upon the
material being processed. The inspector should observe the
precleaning or other precautions taken to assure minimum
emissions from this operation. He should recommend the use
of incinerators or scrubbers if a large volume operation is
involved.
Drying chips require the use of afterburners or incinerators
since the removal of oil by volatalization with resultant
generation of opaque smoke and oil mists is involved. It
will be obvious from the heavy emissions of smoke and mists
that the afterburner is not in use, or is defective.
(2) Ingot Production—Reverberatory Furnaces
The basic furnace in a brass secondary smelter is the
reverberatory furnace. It is usually gas or oil fired and
can be either of the open hearth or rotary type, operating
between 2300°F to 2600°F. In the production of brass and
bronze ingot the inspector must be aware of the time periods
of the operation during which most of the fume is generated, the
condition of the material charged (oily or greasy) and the
operation of the air pollution control system. The critical
periods are charging either "raw" material or zinc slabs, to
reach the desired specification, oxygen blowing if used, and
pouring. Dense clouds of condensed fume or black smoke can
occur due to charging of oily scrap. These emissions may
be of such magnitude that the fume pickup system may not be
-------
7.8.34
able to handle the volume. The same is true during air or
oxygen blowing. Pouring, which can take 1 to 3 hours, also
generates large quantities of fume. The inspector should
observe these operations for time and opacity. It is doubtful
if any sizeable brass reverberatory furnace can meet time
and opacity standards without a well designed air pollution
control system.
The operation of other types of furnaces that may be found
in a smelter, i.e., crucible and induction furnaces are
described in Section IX of this chapter.
Quantitative and qualitative emissions from secondary brass
smelting operations are shown in the following tables.
Table 7.8.11. ROTARY FURNACE PARTICULATE EMISSIONS—TEST A
Cycle
Charge^
Refine
Pour
Total
Length, hr
6.50
6.80
1.28
14.58
Emissions, furnace2 Baghouse outletb
Ib/hr
30.05
42.75
9.54
Cycle total, Ib
195
291
12
498
Ib/hr
1.78
Total, Ib
25.9
aFmnace emission factor: 29.9 In/ton.
bCollection efficiency: 94.8 percent.
cTotal charge: 33,334 Ib. Alloy produced: BBII Alloy No. 4A; 85-5-5-5.
(SOURCE: CUFFE AND SCHWARTZ, Reference 5)
Test A
A heat of red brass 85-5-5-5 (copper, zinc, tin, lead) was made in a 17-1/2 -
ton-rated rotary furnace. A total of 33,334 pounds of scrap and 500 pounds of
flux were charged to the furnace during the 6.5-hour charging period. Air blow-
ing, slagging, and heating were performed during the 6.8-hour refining cycle.
The pouring cycle lasted 1.3 hours.
During this test, only the 17-1/2-ton rotary furnace was operating. Inlet samples
were collected during each period. A single sample was taken at the baghouse
outlet over the entire heat. The exhaust system captured an estimated 90 to
95 percent of the particulate generated at the furnace.
-------
7.8.35
Table 7.8.12. REVERBERATORY FURNACE PARTICULATE EMISSIONS—TEST C
Cycle
Charge0
Refine
Pour
Total
Length. In
6.73
9.30
3.53
19.56
Emissions, furnacea
Ib/hr
194.2
159.3
12.8
Cycle total, Ib
1.308
1.482
45
2,835
Baphouse outlet^
Ib/ht
3.32
Total, Ib
64.8
aFurnace emission factor: 53.7 Ib/ton.
^Collection efficiency; 97.7 percent.
cTotal charge: 105,500 Ib. Alloy produced: BBII Alloy No. 4A; 85-5-5-5.
Test C (SOURCE; CUFFE AID SCHWARTZ, Reference 5)
A heat of 85-5-5-5 red brass was made in <± 100-ton reverbera-
tory furnace. A total of 105, 000 pounds oi metal was charged to the
furnace over a period of 6. 7 hours. Oxygen was supplied to the
burners for 5. 3 of these hours to increase the melting rate. During
a 9. 3-hour refining period there was intermittent air blowing, and
500 pounds of fluxes were added. Pouring took 3. 5 hours.
This air pollution control system serves three 100-ton reverber-
atory furnaces. The gases pass through a common spray chamber
and then through a set of U-tube radiation coolers. From this point,
the 450° F to 650° F gases arc mixed with bleed-in air, go through
the baghouse and a 75-horsepower fan, and pass to the stack. The
16-compartment shaker-type baghouse is fitted with heat-set Orion
bags. The total filter area is 7, 360 square feet and the rated capac-
ity is 19, 000 cfm at 220° F. The design filter ratio, with one com-
partment out for cleaning, is 2,75/1.
Measured gas temperature at the baghouse inlet cycled between
•200° F and 220° F. The measured gas volume averaged 15, 000 scfm
(70° F). Baghoxise pressure drop varied from 4 to 5 inches of water.
One inlet sample was taken during each of these three furnace
period-s: charging, refining, and pouring. A continuous baghouse
outlet sample was laken over the entire heat.
-------
7.8.36
Table 7.8.13. CUPOLA PARTICULATE EMISSIONS—TEST
Sample
E-l
E-2
E-3
Average
Inlet
gr/sct
0.68
0.68
Ib/hr
216
216
Outlet
gr/scf
0.027
0.030
0.020
0.026
Ib/hr
8.38
9.25
6.38
8.00
"Charging rate: 5900 Ib/hr. Collection efficiency: 96,4 percent.
Furnace emission factor: 73.2 Ib/ton.
Test E
At the system described in Test A, samples were taken while
only the cupola was in operation. The cupola was charging at 20-
minute intervals at the rate of 5, 900 pounds per hour, including
coke and flux.
Gas temperature at the baghouse was 145° F to 200° F and the
volume was 44,000 scfm. The filter ratio was 2.11/1.
(SOURCE: CUFFE AND SCHWARTZ, Reference 5)
Lead
Secondary lead operations produce lead alloys and oxides employing
reverberatory furnaces, pot furnaces, cupolas and the Barton Process
for oxides. Sweating operations are also used to recover lead and
other low melting alloys.
(1) Reverberatory Furnaces
Battery plates, dross and slag are melted in direct gas or
oil fired reverberatory furnaces for lead reclamation (Table
7.8.14). The operation of the furnace is "tight" to allow
admission of as little air as possible in order to maintain
the furnace temperature of 2300°F. The furnace is recharged
at regular intervals as the mass of the charge becomes fluid.
About 10 to 12 pounds of metal are produced per squart foot
of hearth area. ' The furnace is tapped at regular intervals
and is kept in continuous operation.
-------
7.8.37
Table 7.8.14. CHEMICAL REQUIREMENTS FOR LEAD
(ASTM Standards, Part 2, 1958)
Silver, max %
Silver, min. %
Copper, max %
Copper, min. %
Silver and copper together,
max %
Arsenic, antimony, and
tin together, max %
Zinc, in ax %
Iron, max %
Bismuth, max %
Lead (by difference),
min. %
Cor r oding
lead
0. 0015
0. 0015
0. 0025
0. 002
0. 001
0. 002
0. 050
99. 94
Chemical
lead
0. 020
0. 002
0. 030
0. 040
0. 002
0. 00]
0. 002
0. 005
99. 90
Acid-
roppcr
lead
0. 002
0. 080
0. 040
0. 040
0. 002
0. 001
0. 002
0. 025
99. 90
Common
desilveri/.ed
lead
0. 002
0. 0025
0. 005
0. 002
0. 002
0. 150
99. 85
aCorroding lead is a designation used in the trade for many years to
describe lead refined to a high degree of purity.
Chemical lead is ,i term used in the trade to describe the undesilverized
lead produced from Southeastern Missouri ores.
Acid-copper lead is made by adding copper to fully refined lead.
Common desilverized lead is a designation used to describe fully
refined desilverized lead.
(SOURCE: NANCE, et_ al_., Reference 6)
The operation of a lead reverberatory furnace produces smoke
and fumes by the nature of the operation. It is therefore
necessary that an adequate air pollution control system be a
part of the furnace design. The inspector must observe the
charging and pouring operation to determine the collection
efficiency of the fume pickup system since these are periods
of heavy emission production. During the melting phase of the
operation some smoke and fume escaping from the doors and
other openings may occur due to the low negative pressure in
the furnace. Indrafts at the hoods over these openings
-------
7.8.38
should be high enough to prevent the escape of puffs or
continuous streams of fume. Baghouses are usually used to
collect the particulates from lead refining operations.
Table 7.8.15 describes the operating characteristics of an
exhaust system and baghouse on a lead reVerberatory furnace.
In addition to dust and fumes, emissions of sulfur oxides are
emitted. Stack analysis should be requested to determine the
extent of these emissions. The requirements of the individual
agency will govern the necessity for additional SO controls.
X
(2) Blast and Cupola Furnaces
These furnaces are similar to those used in grey iron foundries
in physical appearance. They are used to produce lead from
dross, oxide and reverberatory slags using a mixture of cast
iron and limestone to form slag and coke for heating and
reduction. The furnace is charged through a door near its
top and blast air is blown in through tuyeres near the bottom.
This is a continuous operation with the lead being discharged
in a continuous tap and the slag being tapped intermittently.
The tuyere air, as it is forced through the furnace, picks up
dust and fumes which are usually vented to a baghouse. The
furnace operates at between 1200°F and 1300°F and produces
large volumes of CO, which must be burned to CO , and
particulates. A high inlet velocity at all openings is re-
quired to prevent the escape of dust and fumes. The
inspector should observe a light off and at least an hour of
the operating cycle to determine that the air pollution control
system is functioning properly. In a properly controlled
operation, the system should be tight with no appreciable
escape of smoke or fume from the furnace during any phase of
its operation.
-------
7.8.39
Table 7.8.15. DUST AND FUME EMISSIONS FROM A
SECONDARY LEAD-SMELTING FURNACE
(6)
Test No.
Furnace data
Type of furnace
Fuel used
Material charged
Process v/eight, Ib/hr
Reverberalory
Natural gas
Battery groups
Z, 500
Sectioned tubular bagbousc'
D a c r on
16, 000
0. 98
Sectioned tubular baghousec
D a c r on
16, 000
0. 98
3, 060
10, 400
951
327
b
2, 170
13, 000h
500
175
Control equipment data
Type of control equipment
Filler material
Filter area, ft2
Filler velocity, fpm at 327 °F
Dust and fume data
Gas flow rale, scfm
Furnace outlet
Bagbouse outlet
Gas temperature, °F
Furnace outlet
Baghouse outlet
Concentration, gr/scf
Furnace outlet
Bagbouse outlet
Dust and fume emission, Ib/hr
Furnace outlet
Baghouse outlet
Baghouse efficiency, %
Baghouse catch, wt %
Particle size 0 to 1 (a.
1 to 2
2 to 3
3 to 4
4 to 16
Sulfur compounds as SO^, vol %
Baghouse outlet.
aThe same baghouse alternately serves the reverberatory furnace and the blast furnace.
Dilution air admitted to cool gas stream.
4. 98
0. 013
130. 5
1. 2
99. 1
13. 3
45. 2
19. 1
14. 0
8. 4
0. 104
Blast
Coke
Battery groups, dross, slag
2, 670
12.3
0. 035
229
3. 9
98. 3
13. 3
45. 2
19. 1
14. 0
8.4
0. 03
(SOURCE: NANCE, j^t al., Reference 6)
-------
7.8.40
(3) Pot Furnaces
(6)
Pot furnaces range in capacity from 1 to 50 tons and
are used to alloy and refine lead. These furnaces should be
hooded and vented to air pollution control equipment
to meet both air pollution regulations and industrial
hygiene requirements. Emissions can occur when drying dross
to remove as much lead as possible by introducing sawdust;
adding sulfur and agitating to reduce copper; or adding
aluminum to reduce copper, antimony and nickle. The resultant
slag is then skimmed from the pot. Hooding must be properly
designed to pickup the fume and smoke generated by these
actions. A special application is the production of lead
oxide for battery lead, red lead and paint by the Barton
Process. Lead at 700°F to 900°F is agitated by paddles
while air is drawn through the molten metal. The resultant
lead oxide is exhausted to a baghouse where the condensed
fume is captured. This process is "closed" and should not
emit appreciable fume.
Zinc
The reclamation of zinc in secondary smelting operations is performed
by vaporizing or oxidation. The products from secondary zinc
smelting are zinc, zinc oxide, and powdered zinc. Some zinc is
also recovered in sweating operations described previously in this
section.
The processes to reduce zinc oxide to metallic zinc uses powdered
dross, collected zinc oxide condensed fume and contaminated zinc
oxide from zinc plants all mixed with powdered coke and water to
form a paste. The material is then charged to retorts for treating
by the Belgian Retort Process. The retorts are arranged in banks
-------
7.8.41
and are heated externally by either gas or oil fired burners. The
operating cycle is usually 24 hours with 65 to 70% of the zinc in
the charge recovered with the remaining charge recycled.
Temperatures on the outside of the retorts reach 2,550°F. The
temperature of the charge is slowly brought up to 2,280°F. A
carbon dioxide rich atmosphere in the retorts actually reduces
the zinc where it is condensed in the cooler, 780° to 1,020°F
condenser section. Tapping of the zinc begins after about 8 hours.
Figure 7.8.6
furnace.
(6)
shows a cross section of a single Belgian retort
GROUT JOINT
CONDENSED METAL
VAPORS
METALLIC OXIDE CHARGE
KITH REDUCING MATERIALS
BURNER PORT
Figure 7.8.6. DIAGRAM SHOWING ONE BANK OF A BELGIAN RETORT FURNACE
(SOURCE: NANCE, et al., Reference 6)
-------
7.8.42
Distillation furnaces can produce zinc, zinc oxide or zinc powder
using molten zinc as the charge. The distillation type retort
furnace shown in Figure 7.8.7 is charged with molten zinc from a
pot furnace. The retort is externally heated, vaporizing the zinc.
The condenser is under positive pressure to prevent the zinc vapors
from being oxidized while they condense. If zinc oxide is to be
manufactured the zinc vapor goes through an orifice where it is
mixed with air for oxidation. When the condenser is used it is
vented through an opening called a speise hole. Here the zinc
vapor burns and must be captured by a special hood provided for
this purpose.
SPEISE HOLE .
Figure 7.8.7. DIAGRAM OF A DISTILLATION-TYPE RETORT FURNACE
(SOURCE: NANCE, et_al., Reference 6)
-------
7.8,43
A second procedure employed to produce either pure zinc (99.99%)
and pure oxide (99.95%) is conducted in a muffle furnace (Figure
7.8.8 ). This system can handle scrap metal directly in its zinc
feed well and sweating section. The furnace is heated by gas or
oil firing with the products of combustion passing over the zinc
feed well after heating the vaporizing section to 2,500 F.
Molten zinc is formed in the condenser and maintained at about
900 F. When zinc oxide is to be formed, the vapors go through an
orifice at the top of the first chamber and are mixed with air.
The resultant zinc oxide is exhausted to a baghouse where it is
collected.
DUCT FOB OKIOE
COLLECTION
RISER CONDENSER
UNI T
Figure 7.8.8. DIAGRAM OF A MUFFLE FURNACE AND CONDENSER
(SOURCE: NANCE, et_ al_. , Reference 6)
The inspector must become familiar with the operating procedure of
the particular plant and the equipment. Every operation can have
significant modifications to its equipment which can make it
unique. Capture of condensed oxide fume or smoke from any opening
in the aforementioned systems is the primary consideration. Air
pollution control field personnel must physically check all phases
-------
7.8.44
of operation of these types of furnaces to make certain that the
systems are tight and have minimal leaks.
d. Aluminum
Aluminum refining operations encompass many of the processes
described in brass and bronze refining. Principal operations are
chip drying, sweating, and pyrometallurgical refining.
Pit and crucible furnace operations are described in the section
on foundries. This subsection will emphasize reverberatory
furnaces since chip drying and sweating have been treated.
Reverberatory furnaces for aluminum refining range in capacity
from 3,000 pounds to 50 tons and over. These are usually gas or
oil fired and are continuously operated in large facilities. As
in most metallurgical processes the production is batch, that is
there is a charging phase, a working and fluxing phase and
pouring. A heat can vary in length from 4 to 72 hours.
The furnace is used to melt varied types of scrap and usually has
a well where chips and other thin section scrap is charged into
a molten bath. Figure 7.8.9 shows a 20-ton aluminum reverber
tory furnace with a fume collection hood over the well.
In order to prevent burning of thin-walled sections that may be
charged to the furnace, a heel of metal is required. This heel
is formed by melting heavy pieces of scrap or ingot prior to the
introduction of the lighter material.
The major air pollution control problem from aluminum refining
operations arises from the fluxing and degreasing necessary to bring
the melt to the specification required. Large quantities of solid
-------
Figure 7.8.9.
A 20-TON ALUMINUM-MELTING REVERBATORY FURNACE WITH CHARGING
WELL HOOD, AARON FERRER & SONS, INC., LOS ANGELES. CALIFORNIA
(SOURCE: NANCE, et_ al., Reference 6)
QO
Ui
-------
7.8.46
fluxes, as much as 1/3 the weight of the aluminum scrap charged,
may be required to prevent oxidation and gas absorption. Fluxes
that cause dense emissions are those used for degreasing and
magnesium reduction. Chlorine gas and aluminum fluride are
commonly used for magnesium reduction and cause the most extensive
emissions.
The inspector should become completely familiar with the furnace
operating cycle. He should observe the type of scrap charged to the
furnace to determine if smoke and other particulates from the melting
of dirty scrap are likely to occur. He should know the type and
quantity of fluxes used. The Air Pollution Engineering Manual can
be used as a' reference on fluxing operations.
2. Inspection Points—Secondary Smelting and Refining
Secondary smelters are usually located in areas zoned for heavy
industry so that the likelihood of nuisance complaints from these
operations may not be great. Odors also are not generally attributed
to secondary smelters but there can be significant quantities of dust
created by some of the operations. Some copper refining operations can
emit SO-, although usually below the odor threshold of 1.0-5.0 ppm.
a. Environmental Observations
Dust and particulate fallout from metal preparation may be the
most pronounced problems in areas adjacent to secondary smelters.
These include mechanical shredding and size reduction, sweating
and incineration. Relatively large dust particles and fly ash
may be emitted from these operations and settle near the company
in question.
-------
7.8.47
b. Observation of the Exterior of the Secondary Smelter
Most of the processes of concern in secondary smelting and refining
require heat to complete the operation. Usually one or more
stacks are employed to vent the products of combustion or air
pollution control system effluents. The inspector can pinpoint
the stack or roof monitor emitting excessive smoke, dust or
fumes and work backwards to the process or equipment
responsible for the emissions. The color, opacity
and length of plume can be of help in determining the source of
the problem. Incinerators used for copper wire reclamation will
emit dense black smoke if overloaded or if the auxiliary fuel is
not in use. Sweat furnaces will do the same if the afterburner
is not in operation. If a baghouse has torn bags it may appear
to be burning if it is a push-through type; if the baghouse is
a pull-through type the opacity of emissions from the stack can
be over 50% when they would otherwise be near 0%.
c. The Physical Inspection
After obtaining the necessary data from the outside of the
plant, the inspector should contact plant management to make the
inplant inspection. If the inspector is completely familiar with
the plant he can inform the operator which process caused the
problem. If he is not familiar with the operation he should
describe the color and opacity of the emissions and try to determine
their origin. Determination of the equipment responsible for
the emissions can present a problem in plants where many processes
are vented to one stack. A plant survey should be one of the first
requirements for an inspector who is new to an area.
During furnace inspections it is necessary to observe:
-------
7.8.48
• Charging operations
• Type and quantity of material charges
• Working or fluxing operations
• Type and quantity of flux added
• Pouring operations
• Fuel being used
Mechanical inspection of equipment should include:
• Repair of furnace and doors for leaks
• Repair of hoods and ductwork
• Pickup efficiency
• Effectiveness of air pollution control equipment
The inspector can make qualitative judgments of dust and fume
emissions but he may have to rely on stack tests for quantitative
results. These tests should not be limited to the stack. There
are times when emissions from charging doors, hearths or from
pouring can be very significant if not properly hooded and vented
to an air pollution control system.
Figure 7.8.1CT5' is a convenient scale showing the boiling,
pouring and melting points of metals and alloys.
-------
7.8.49
Figure 7.8.10. BOILING, POURING, AND MELTING POINTS
OF METALS AND ALLOYS (SOURCE: CUFFE
AND SCHWARTZ, Reference 5)
-------
7.8.50
REFERENCES
1. Systems Study for Control of Emissions, Primary Non-Ferrous Smelting
Industry, Volumes I, II and III. Arthur G. McKee & Co. Contract PH
86-65-85. DHEW, PHS, NAPCA. June 1969.
2. Semrav, K. T. Control of Sulfur Oxide Emissions from Primary Copper,
Lead and Zinc Smelters, A Critical Review. J. Air Pollution Control
Association. Vol. 21, No. 4. April 1971.
3. Nelson, K. W. Nonferrous Metallurgical Operations. Air Pollution,
Vol. Ill, A. C. Stern (ed.). New York City, Academic Press. 1968.
4. Konopka, A. P. Particulate Control Technology in Primary Non-Ferrous
Smelting. Presented at Third Joint Meeting, American Institute of
Chemical Engineers and Institute Mexicano De Ingenieros Quimicos.
Denver, Colorado. September 1970.
5. Cuffe, S. T., and E. S. Schwartz. Air Pollution Aspects of Brass and
Bronze Smelting and Refining Industries. DHEW, PHS, NAPCA. A.P. 58,
November 1969.
6. Nance, J. T., W. F. Hammond, and K. D. Luedtke. Lead Refining.
G. Thomas. Zinc Melting. H. Simon. Aluminum. In: Air Pollution
Engineering Manual, J. A. Danielson (ed.). Cincinnati, DHEW, PHS,
National Center for Air Pollution Control and the Los Angeles County
Air Pollution Control District. P.H.S. No. 999-AP-40. 1967.
-------
7.9.1
IX. FERROUS AND NON-FERROUS FOUNDRIES
A. DESCRIPTION OF SOURCES
The products of the ferrous and non-ferrous metallurgical industries are
oriented to consumer or industrial use while smelters and refiners, dealt
with in other sections of this chapter, provide alloys in ingot form to
be used by the foundries.
While furnaces and melting practices have long been treated as 'major
sources of air pollution from foundries, other operations also contribute.
Among these are core making, sand handling, grinding, buffing and plating.
Melting operations produce smoke and condensed fumes while the other
operations produce dust, mists, organic gases and vapors.
B. GREY IRON FOUNDRIES
Ferrous foundries depend upon the cupola for the economical production
of large quantities of grey iron. Electric furnaces and small
reverberatory furnaces are also used in some specialty shops. Grey iron
foundries have core making facilities, sand handling equipment and
shakeout systems which are described under non-ferrous foundries below.
The cupola is the oldest and still the most universally used furnace for
the production of grey iron and a large contributor to air contaminants
if not adequately controlled.
1. Process Description
A cupola is a firebrick-lined vertical cylindrical steel shell, approx-
imately 27" to 108" in diameter, supported on structural steel legs.
Air is supplied through a windbox and tuyeres (Figure 7.9.1) by either
positive displacement blowers, centrifugal blowers or fan type
blowers. As in blast furnaces, air is the largest single constituent
-------
7.9.2
BOTTOM DOOR
IN
POSITION
Figure 7.9.1. THE CUPOLA IN DETAIL (SOURCE: AIR POLLUTION
ENGINEERING MANUAL)
-------
7.9.3
of the heat, its weight being dependent on the size of the furnace and
the metal to be melted. Some foundries recycle waste heat from the
cupola to preheat the combustion air as an economy measure.
Preparation of a cupola for melting consists of preparing the bottom
by securing the bottom drop door, placing a layer of sand over the
door to prevent heat damage, closing the tap and slag holes and
charging coke for the bed. The bed is ignited and allowed to burn
through. The charges of coke, flux (limestone, fluorspar and soda
ash) and metal (pig iron, scrap and steel) are placed in alternate
layers up to the charge door which is 16' to 22' above the bottom.
The blast is then turned on and melting begins. Charging continues
until the desired tonnage has been melted after which the air is shut
off and the furnace bottom is dropped allowing the remaining charges
to fall on to the foundry floor. This material is recharged during
the next operating cycle. Table 7.9.1 is a compilation of general
operating conditions for cupolas describing capacities, physical
characteristics and air/fuel requirements for all common cupola sizes.
Grey iron cupolas emit dust, fumes, smoke, gases (including about one
pound of SO,., per ton of metal melted), and oil vapors. Combustion-
related contaminants and dust are picked up by the high velocity air
stream forced through the charge. Considerable testing has been done
by the Los Angeles County Air Pollution Control District for dust and
fumes from cupolas. Table 7.9.2 shows the results of some of these
tests. Oil mist and smoke in cupola exhaust gases are due largely
to oil and grease contamination of the scrap metal charged to the
furnace. Large volumes of CO are formed from the combustion of the
coke. A typical analyses of exhaust gases is CO -12.2%, CO-11.2%,
02-0.4% and N2-76.2%.
-------
Table 7.9.1. GENERAL RECOMMENDATIONS FOR OPERATING WHITING CUPOLAS
(SOURCE: BUREAU OF MINES, Reference 2)
(Practical Hints on Cupola Operation, No. 237-R, Whiting Corporation, Harvey, Illinois)
Cupola
llli*
0
2
Z-J/2
3
3-1/2
1
5
6
S
10
12
Shell
in.
Z7
?2
36
41
46
SI
56
63
66
76
*
108
Min.
thickness
of Ipwer
hrnr.K, in
4-1/2
4-1/2
4-1 11
7
7
f
7
9
9
9
9
12
Dum.,,,
11 • a
lining, in.
IB
23
27
27
32
37
42
45
48
60
6
84
Area
linlne. ,,,.'
2M
415
572
572
904
J.075
1, 385
1, 590
1. 809
2,827
'
A 77B !
4.778
4778
,:„
Me
6
3/4
1-3/4
1-3/4
3-J/4
4
4-1/2
5-1/2
9
Minn rat
with irn
S
1
1-1/2
2-1/1
2-1/4
4-1/4
5-1/2
6-1/4
7-1/4
1 -1/4
6 /
22-1/4
«•. tons/
10
5-1/4
7
8
9
U
2, I/,
hr.
12
10-3/4
17
B«d coke
height
9
Blono, Ib
4
7
9
9
13
17
22
26
29
4*
89
Air
through
cfm
570
940
1, 290
1.290
1, BIO
2. 420
3, 100
3,600
4, 100
6, 400
'
I2.5CO
Suggfs
sc)
cfm
640
1. 040
1. 430
1, 430
2. 000
2. 700
3.450
4.000
4, 500
1, 100
'
'
13,900
ed blower
ctionc
Discharge
g
16
16
id
16
16 to 20
20 to Z4
20 to 24
Z4 to 29
24 to 32
•
32 lo 40
bHe:gnt of bei
-------
Table 7.9.2. DUST AND FUME EMISSIONS FROM GRAY IRON CUPOLAS (SOURCE:
COUNTY AIR POLLUTION CONTROL DISTRICT, Reference 1)
LOS ANGELES
Test No.
Cupola data
Inside diameter, in.
Tuyere air, scfm
Iron - coke ratio
Process wt, Ib/hr
Stack gas data
V o 1 um e , s c f m
Temperature, °F
co2, %
02, %
CO. %
N2, %
Dust and fume data
Type of control
equipment
Concentration, gr/scf
Inlet
Outlet
Dust emission, Ib/hr
Inlet
Outlet
Control efficiency, %
Particle size, wt %
0 to 5 ji
5 to 10 ji
10 to 20 n
20 to 44 j±
> 44 H
Specific gravity
i
60
-
7/1
8, ZOO
8, 300
1, 035
-
-
-
-
None
-
0. 913
_
65-
-
18. 1
6. 8
12.8
32. 9
29. 3
3. 34
i
37
1, 950
6. 66/1
8, 380
5, 520
1, 400
12. 3
-
-
-
None
-
1. 32
-
62.4
-
17. 2
8. 5
10. 1
17. 3
46. 9
2.78
3
63
7, 500
10. 1/1
39, 100
30, 500
213
2.8
-
_
-
None
-
0.413
_
108
-
23.6
4.5
4.8
9. 5
57.9
4
56
-
6. 5/1
24, 650
17, 700
210
4. 7
12. 7
0
67. 5
Baghouse
1. 33
0. 051
197
7. 7
96
25.8
6. 3
2. 2
10. Oa
55. 7b
5
42
-
9. 2/1
14, 000
20, 300
430
5.2
11.8
0. 1
67. 3
Elec precip
aft erburner
2.973
0. 0359
184. 7
6. 24
96.6
-
-
-
_
-
6
60
-
9.6/1
36, 900
21, 000
222
-
-
_
-
Baghous e
0. 392
0. 0456
70. 6
8.2
88.4
-
_
_
_
_
7
48
-
7. 4/1
16, 800
8,430
482
-
-
_
-
Elec Precip
1. 522
0. 186
110
13. 2
87. 7
-
_
^
_
_
From 20 to 50 (i.
^Greater than 50 (i.
-------
7.9.6
The requirements for controlling the emission of air contaminants
from cupolas vary with different agencies. The criteria for control
may be emission opacity or dust and fume discharge (process weight,
see Chapter 3). Water type collectors can be used if it is necessary
to remove large particles of dust but effective dust and fume
collection requires baghouses or electrical precipitators including
CO afterburners and gas coolers. Table 7.9.3 describes pilot test
results of various air pollution control devices used on cupolas.
2. Inspection Points
Cupolas operating without air pollution control systems emit dense
grey brown smoke and fumes when the blast air is in use. Furnaces
with air pollution control systems should be inspected during the
start up, melting and pouring phases of operation. An observation
should also be made of the bottom dropping operation to make certain
that time and opacity limits are not exceeded.
In systems using a baghouse it is essential that an adequately
designed afterburner be in operation during melting to reduce the CO
content of the gas in order to minimize the explosion hazard and to
burn oil mists and vapors. Any system designed to handle cupola gases
must be sized to provide good indraft at the charging opening. Puffing
can occur frequently and the use of charging port doors plus a high
indraft will minimize losses from this area. Observation of the
effluent from the control equipment can provide qualitative readings
of the efficiency of collection. Stack tests are required to determine
if the grain loading of the exhaust gases meets compliance standards.
-------
7.9.7
Table 7.9.3. SOME COLLECTION EFFICIENCIES OF EXPERIMENTAL SMALL-SCALE CONTROL
DEVICES TESTED ON GRAY IRON CUPOLASa (SOURCE: LOS ANGELES
COUNTY AIR POLLUTION CONTROL DISTRICT, Reference 1)
Equipment tested
Controls for cupolas0
High -efficiency cyclone
Dynamic water scrubber
Venturi-type scrubber
Dynamic --impingement
wet scrubber
Baghoust — one sihcone-
JO in. dia x 10 ft length
Evaporative cooler and
redwood pipe electrical
precipitator
Other basic equipment
Natural gas-fired
Inlet
gas
volume,
scfm
330
1, 410
375
605
52.7
1. 160
"
Outlet
volume,
scfm
384
1,760
432
995
52.7
1, 330
5, 160
Inlet
dust
load.
gr/scf
1.225
1.06
1. 17
0.°5
1. 32
1.263
"
Outlet
dust
load,
gr/scl
0.826
0. 522
0.291
0. 141
0. 046
0. 0289
0.00288
Collection
effic lency,
To
22. 5
38. 2
71.3
75.6
96. 5
97.7
96. 2C
Rema'rks
cooling totalled 6 gpm
Two gpm-water introduced for cooling
gas stream; 3. 5 gpm added at venturi
throat; cyclonic scrubber operated dry
Water rate in excess of 10 gpm
Average temp, 372T; average filter-
ing velocity, 3.22gpm
precipitator, 2 gpm
Melting rate. 546 Ib/hr, gas consump-
tion rale, 4,200 cfh; melting clean
scrap and pig iron
aln all cases, equipment was installed and operated according
The six control devices were tested on the same cupola.
cThis is not an actual collection efficiency, but a percent redu
to the manufacturer's recommendations.
ction when compared with average cupola emissions.
-------
7.9.8
C. NON-FERROUS FOUNDRIES
Foundries form a part of nearly all industrial complexes and are found in
all parts of the country. These consist of small single crucible furnace
shops or large production die casting shops employing many banks of
melting furnaces. The number and types of core making equipment,
mechanical sand mullers, sand handling, grinding, buffing and plating
equipment will depend upon the size of the operation and the end-use of
the product. For example, foundries producing plumbing fixtures may have
chrome plating facilities.
Since the range of practices, equipment and alloys is extensive non-
ferrous foundries will be treated as an entity describing operations
and equipment, alloys melted, potential emissions, air pollution control
systems and inspection practices. Non-ferrous foundries can be classified
according to the metals melted: copper-base alloys (brass and bronze),
aluminum, or zinc.
1. Process Description—Copper-Ease Alloys
Brass and bronze are the common names for a group of copper base
alloys composed of 60 to 90 percent copper, zinc, lead, tin and fractional
percentages of other metals. Brasses usually contain 60-65 percent
copper; bronzes usually contain 85-90 percent. Particulate emissions
from melting operations originate from condensed metallic fume; par-
ticulates from fuel-fired furnaces originate from the products of
combustion (see Fuel-Burning Equipment, Chapter 6, Section II).
Table 7.9.4 illustrates uncontrolled emission rates from a variety of
furnaces melting copper base alloys with zinc content ranging from 5
to 38 percent. Since high copper alloys (80 to 90 percent copper)
have a fairly high boiling point the fuming rate will be low; however,
when the zinc content increases, as in alloys with 20 to 40 percent
-------
Table 7.9.4. DUST AND FUME DISCHARGE FROM BRASS FURNACES (SOURCE:
COUNTY AIR POLLUTION CONTROL DISTRICT, Reference 1)
LOS ANGELES
Type of
1 ur na c c
R ota ry
Rotary
Rotary
Elcc ind
Elcc ind
Elec ind
Cyl reverb
Cyl reverb
Cyl reverb
Cyl reverb
Crucible
Crucible
Crucible
Composition of alloy, %
Cu
85
76
85
60
71
71
87
77
80
80
65
60
77
Zn
5
14. 7
5
38
28
28
4
-
-
2
35
37
12
Pb
5
4. 7
5
2
-
-
0
18
13
10
-
1. 5
6
Sn
5
3. 4
5
-
1
1
8. 4
5
7
8
-
0. 5
3
Other
-
0. 67 Fe
-
-
-
-
0. 6
-
-
-
-
1
2
Type of
control
None
None
Slag cover
None
None
None
None
None
Slag cover
None
None
None
Slag cover
Fuel
Oil
Oil
Oil
Elect
Elect
Elect
Oil
Oil
Oil
Oil
Gas
Gas
Gas
Pouring
temp, °F
No data
No data
No data
No data
No data
No data
No data
2, 100
2, 100
1, 900 to 2, 100
2, 100
1, 800
No data
Process wt ,
Ib/hr
1, 104
3, 607
1, 165
1, 530
1, 600
1, 500
273
1, 267
1, 500
1, 250
470
108
500
Ib/hr
22. 5
25
2.73
3. 47
0. 77
0. 54
2. 42
26. 1
22.2
10. 9
8. 67
0. 05
0. 822
-------
7.9.10
zinc, the boiling point will drop considerably and increased fuming
will result. Pure zinc boils at 1663°F with the usual pouring
temperature of high zinc alloys between 1900°F and 2100°F which would
allow some zinc to form zinc oxide as it flashes from the furnace and
is released as dense white emissions. Emissions from the melting of
(2)
high lead alloys will contain as much as 56 percent lead oxide.
Furnaces used in brass foundries are either direct fired types which
include pit and tilting crucible furnaces and cylindrical reverberatory
furnaces, or indirectly heated electric induction furnaces. Of the two
types the indirectly heated furnaces will produce smaller amounts of
emissions per pound of metal melted than direct fired furnaces.
In pit type furnaces, the crucible is made of silicon carbide or other
refractory material, and is indirectly heated in a ceramic-lined pit
by either natural gas or oil. The cycle consists of melting the charge
and flux (see Table 7.9.5), removing the crucible from the pit and
pouring the metal into the molds. As in most brass melting operations
the emissions will be mostly zinc oxide or lead oxide. Where the
alloy melted has a high copper content, 85 percent to 90 percent,
emissions can be curtailed and brought within the limits of most
opacity and process weight regulations by the use of a proper slag
cover, usually molten glass, which is punctured only during pouring.
A. slag thickness of 1/4" to 3/8" is recommended. Considerable fuming
occurs when the molten metal is poured. When yellow brass is melted
(alloys with less than 80 percent copper) an air pollution control
system should be required to capture the fumes emitted during melting
and pouring.
Tilt type crucible furnaces do not vary significantly in operation
from pit type furnaces. The tilting furnace is usually larger in
capacity, is located above floor level and is fired with either gas
or oil (see Figure 7.9.2).
-------
7.9.11
Table 7.9.5. RELATIVE VOLATILITIES AND MELTING TEMPERATURES
FOR NON-FERROUS METALS (SOURCE: LOS ANGELES COUNTY
AIR POLLUTION CONTROL DISTRICT, Reference 3)
METALS
Zinc Alloys
Lead Alloys
Magnesium
Alloys
Aluminum
Alloys
Copper Alloys
(Manganese
bronze)
APPROXIMATE
MELTING TEMPS.
650°— 700'F
600'— 650°F
800°— 900 'F
1250°— 1280"F
Around 1800°F
1650°— 2000°F
RELATIVE
VOLATILITY
1
2
3
4
5
FLUXES
USED
Ammonium
chloride
Sodium Nitrate
Sal amoniac
Lump sulphur
Dow#l and #2
Flowers of
sulphur
Chlorine gas
Aluminum
chloride
Zinc chloride
Aluminum
fluoride
Silica sand
blown with air
Soda ash
Borax
In brass and bronze melting operations (copper alloys),
zinc is the first base-metal to fume because of its low melth.g
temperatures in relation to copper. Copper alloys containing
more than 5% zinc are likely to fume without proper con-
trols. In particular, the following metals must be carefully
controlled: Yellow Brass, 20% or more zinc; Manganese
Bronze, up to 45% zinc; Brazing Spelter, 40% zinc; Plumb-
ing Metals, 12% zinc. Copper alloys of less than 5% zinc
content, such as Red Brass, are not likely to fume and may
not require controls.
-------
7.9.12
Figure 7.9.2. TILTING CRUCIBLE FURNACE, LINDBERG ENGINEERING
CO., DOWNEY, CALIF. (SOURCE: LOS ANGELES
COUNTY AIR POLLUTION CONTROL DISTRICT, Reference 1)
-------
7.9.13
Induction furnaces offer by far the most rapid method of melting
metal in common use by foundries. Temperature control can be
carefully maintained, which is a prime factor in zinc oxide and lead
oxide emissions resulting from the melting of copper base allovs.
In the operation of induction furnaces, granulated charcoal has been
found to be superior as a flux to glass and borax which are destructive
to the furnace walls. Charging fluxes into a hot furnace and metal
pouring remain the critical periods in the overall operating cycle in
the emissions of dusts and fumes.
Cylindrical rotary furnaces present the greatest potential air
pollution problem of the group of furnaces commonly used in brass
foundries. These are reverberatory furnaces in which the flame from
the burners impinge on the surface of the metal. There are several
variations of this type of furnace but the operating procedures are
virtually the same (see Figure 7.9.3). The furnace rotates on its
horizontal axis and tilts for pouring and charging (Figure 7.9.4). Due
to the shape of the furnace and the large volume of gas exhausted from
the products of combustion, the velocity of the gases leaving the
furnace is very high. Therefore, tight hooding and high inlet
velocities at the hoods are required to assure acceptable fume capture.
Since the products of combustion come into contact with the metal in a
cylindrical reverberatory furnace it is desirable to have a slightly
oxidizing atmosphere to avoid smoke from combustion when oil is fired
and to prevent gas entrapment in the metal resulting from unburned
fuel and water vapor. While this is an operational problem, improper
combustion could cause smoke and fume generation which can be avoided
by good operating practice.
-------
Figure
7.9.3. ROTARY-TILTING-TYPE REVERBERATORY FURNACE VENTING TO CANOPY HOOD AND STACK VENT.
(Top) Furnace during meltdown, (Bottom) furnace during pour, VALLEY BRASS, INC.
EL MONTE, CALIF. (SOURCE: LOS ANGELES COUNTY AIR POLLUTION CONTROL DISTRICT,
Reference 1)
-------
7.9.15
TO BAGHOUSE
FURNACE
BURNER
REFRACTORY
Figure 7.9.4.
ROTARY-TILTING-TYPE BRASS-MELTING FURNACE (SOURCE: LOS ANGELES
COUNTY AIR POLLUTION CONTROL DISTRICT, Reference 1)
-------
7.9.16
The operation of these furnaces varies in melting time, method of
heating, and in the physical shape of the equipment. There is strong
similarity, however, in the air pollution potential from the common
phases of the operating cycle: charging, working and pouring.
Observations of these critical periods is mandatory in determining
compliance with ordinances governing non-ferrous foundry operations.
Inspection Points—Copper-Base Alloys
Foundries are usually a part of an integrated manufacturing facility
which includes machine shops, plating facilities, packaging and
shipping departments. It is reasonable to assume, therefore, that
metal charged to the furnace for melting will be made up of scrap
parts, gates and risers, turnings and borings, as well as ingot metal.
a. CHARGING—the condition of the metal charged should be closely
inspected to determine if there is grease or oil present. Usually,
in foundry practice, the charge will consist of rejected parts,
gates and risers, and ingot; however occasionally some other scrap
of known analysis can be used as an economy measure. Dirty and
oily material can add combustion-related contaminants to the
effluent such as smoke and particulates. Charging metals into
the furnace after the heel has formed, will break the slag cover
and allow significant quantities of fume to escape. The inspector
should time this operation for opacity violations in uncontrolled
operations and check the hood pickup efficiency in controlled
operations. Maintaining the integrity of the slag cover is essen-
tial to good operating conditions in melting brass and bronze. Any
action which breaks the cover will allow the escape of dense
emissions of metallic oxides.
-------
7.9.17
b. MELTING—prior to charging the metal the flux material (crushed
glass, borax and, in induction furnaces, granulated charcoal) is
placed in the furnace so that as melting occurs the slag will form
over the metal to inhibit contact or mixing with air. The slag
must be skimmed to remove trapped materials whenever additional
flux or metal is to be added to the furnace. This results in
heavy emissions. Properly designed air pollution control systems,
with high indraft velocities at the hoods are required to capture
these emissions. Time and opacity, and process weight regulations
are frequently violated in this phase of the operation.
c. POURING—temperatures of the metal during pouring are important
for the type of casting produced and are therefore carefully
controlled. The pouring temperature is also very important from
an air pollution control standpoint since the higher the
temperature of the alloy the more volatilization will occur. For
a given percentage of zinc an increase of 100°F increases the
rate of loss of zinc about three times.
As has been mentioned, breaking the slag cover for whatever reason
causes heavy fuming to occur. When pouring from a crucible or ladle
it is necessary to punch two holes in the slag cover; one to allow
air in and the other to pour. All transfer operations will cause
fuming by exposing the molten metal to air and allowing oxides to
form. In order to comply with process weight and opacity
regulations some foundries that melt yellow brass have found it
necessary to mechanize the pouring operation so that the molds
pass under a hood and the ladle is stationary. Various systems
are in use, some employing hoods with flexible ducting to
capture the fume produced during pouring.
-------
7.9.18
The Air Pollution Engineering Manual sets forth the factors
which cause extensive emissions of zinc fumes, and which form the
basis for understanding the operational causes of these emissions.
1. Alloy composition. The rate of loss of zinc is
approximately proportional to the zinc percentage
in the alloy.
2. Pouring temperature. For a given percentage of
zinc, an increase of 100°F increases the rate of-
loss of zinc about three times.
3. Type of furnace. Direct-fired furnaces produce
larger fume concentrations than the crucible type
does, other conditions being constant. The Los
Angeles Nonferrous Foundrymen's Committee, stated,
"It is improbable that any open-flame furnace melting
alloys containing zinc and lead can be operated
without creating excessive emissions. It is conceded
that anyone choosing to operate that type of furnace
will be required to install control equipment."
A. Poor foundry practice. Excessive emissions result
from improper combustion, overheating of the charge,
addition of zinc at maximum furnace temperature,
flame impingement upon the metal charged, heating the
metal charged, heating the metal too fast, and in-
sufficient flux cover. Excessive superheating of the
molten metal is to be avoided for metallurgical and
economic as well as pollution control reasons. From
an air pollution viewpoint, the early addition of
zinc is preferable to gross additions at maximum
furnace temperatures."
The most effective air pollution control equipment for brass
foundry melting and pouring operations are baghouses and
electrical precipitators. Of equal importance is the collection
system which includes hoods, ductwork, gas temperature reduction
mechanisms and fans.
-------
7.9.19
The design of fume pickup systems presents difficult air pollution
control problems especially when high temperature gas is to be
captured from a source where access by workmen is required and
where the source may not be stationary as in operations where
metal is poured from movable ladles. Generally if these systems
have been installed, prior approval from the air pollution control
agency is needed to assure that the design characteristics have
been thoroughly evaluated and necessary tests have been
conducted. The inspector must check these systems to determine
that the operating effectiveness has not deteriorated due to poor
maintenance or improper use; or, if prior approval was not obtained,
to determine if the system has been properly designed for the job.
3. Process Description—Aluminum Melting
Aluminum foundries that melt ingots, rejects, gates and risers in
crucible or induction furnaces are not major sources of air pollution
if fluxes are not used for cleaning, alloying, degassing or removal
of magnesium (demagging). The furnaces used in aluminum foundries are
of the pit crucible, tilt or induction type. Since indirect heating
is used there is no problem from mixing the products of combustion
with the molten aluminum.
A flux cover can be used to prevent oxidation on the surface of the
metal. The flux usually consists of mixtures of sodium chloride,
calcium chloride, calcium fluoride and borax.
Aluminum castings are made in either sand molds or in die casting
machines. There is a certain amount of off-gassing from sand casting
which is related to the type of cores used and the moisture content
of the foundry sand. (See Coremaking, this Section.) Die casting
should not be a problem if a mold release compound containing no oil
is used.
-------
7.9.20
The major air pollution control problems from melting aluminum
arises from secondary smelting and refining which is discussed in
Section XIII of this chapter.
A typical melting cycle consists of charging the metal into the
furnace after a heel has formed, fluxing and pouring. The average
fluxing temperature is 1250°F to 1280°F. In small crucibles the
metal is poured directly from the crucible into the mold. In the
larger tilt type furnaces the molten aluminum is poured into ladles
and transferred to the sand casting area of the plant for pouring
into sand molds or into smaller hand held ladles for pouring into
die casting machines.
Process Description—Zinc Melting
Foundries melting zinc alloys in pit crucibles, tilt crucible, pot
furnaces, or induction furnaces usually do not use fluxes. The metal
is melted and heated to the desired pouring temperatures which may
range from 800°F to 1100°F. At these temperatures little vaporiza-
tion and virtually no visible emissions occur. Zinc vaporizes at
1665°F. The necessity to heat zinc to temperatures approaching
this figure in non-ferrous foundries does not occur.
Many zinc foundries use die casting machines which require a mold
release compound. If a non-oily compound is used there should be no
smoking or oil mist generated from the molds after pouring.
In the zinc melting operating cycle it is not necessary to form a
heel before charging except in induction furnaces. Usually ingot and
rejects are charged before scrap and thin-walled sections to prevent
burning. If the metal charged is dirty, dross will form on the
-------
7.9.21
surface of the molten metal which must occasionally be skimmed.
Flux may be added to help float any submerged dross to the surface.
Dross is the common name applied to a mixture of oxide and impurities
which form when the white metals are melted.
If a zinc melting furnace is creating visible emissions the most
likely causes are: the vaporization of oil, grease or paint from the
metal charged; unusually high temperatures which cause the zinc to
flash to zinc oxide; or the use of a boiling flux which is intended
for melts containing less ingot in relation to scrap metal.
These operations do not require air pollution control systems and can
meet most opacity and process weight regulations if they are
controlled under the conditions described above.
5. Inspection Points—Aluminum and Zinc
In both aluminum and zinc melting operations it is necessary for the
inspector to observe a complete cycle from charge to pour to become
completely familiar with the operating procedures of the firm. The
critical phases of operation common to both are metal charging to
determine if oily material is used, fluxing and dross removal. The
pouring of zinc into ladles or molds can also be critical if the
temperature greatly exceeds 1100°F.
6. Process Description—Core Making
Core making is an integral part of foundry operations and is a
potential source of air pollution under certain operating conditions.
It is generally difficult to record opacity violations from core
ovens. The equipment can be a source of public nuisance, however.
-------
7.9.22
Cores are used to allow molten metal to flow around a given space to
form the desired cavity in a casting. The core therefore must be non-
reactive, firm and easily removed after the metal has solidified. Sand
is mixed with binders which when heated will provide the strength that
the core requires to keep it firm while the mold is being prepared and
to resist skrinking or warping when the metal is poured into the mold.
The binders when heated either change chemically, physically or both
and can emit volatiles such as aldehydes and solvent vapors.
Typical binder mixtures contain linseed oil, gum resin, cereal binder,
kerosene, and water which are proportioned according to the quantity
of sand used. As heat is applied in the core oven the light oil
fractions distill off first. As the temperature continues to
increase the heavier fractions are vaporized and polymerization of
the linseed oil occurs. As the temperature in the oven continues to
rise towards its maximum of 400°F the rosin melts, coating the sand
grains with a thin film. The remaining curing time is necessary to
reach maximum strength of the core.
A variety of ovens are used to bake cores, both gas and oil fired,
batch and continuous. Figures 7.9.5 through 7.9.8 illustrate the
types and size of ovens that can be found in foundries. The
operating cycle is dependent upon the type of binder used and ranges
from 1 to 4 hours.
Emissions from core baking are organic acids, aldehydes and smoke.
Examples of quantitative emissions are shown in Table 7.9.6.
-------
7.9.23
i
1
1
1
1
1
1
1
1
1
' ' ' '
;;;;;;'!
,,,,,, ,
'
'^r!n
'• ', ! ' "
— ., 1
• • • ' i '
;
Figure 7.9.5. SHELF OVEN, THE FOUNDRY EQUIPMENT CO., CLEVELAND,
OHIO (SOURCE: LOS ANGELES COUNTY AIR POLLUTION
CONTROL DISTRICT, Reference 1)
-------
7.9.24
Figure 7.9.6. DRAWER OVEN, DESPATCH OVEN CO.. MINNEAPOLIS, MINN. (SOURCE:
LOS ANGELES COUNTY AIR POLLUTION CONTROL DISTRICT, Reference 1)
Figure 7.9.7. RACK OVEN, DESPATCH OVEN CO.. MINNEAPOLIS. MINN. (SOURCE:
LOS ANGELES COUNTY AIR POLLUTION CONTROL DISTRICT, Reference 1)
-------
7.9.25
Figure 7.9.8. HORIZONTAL, CONTINUOUS OVEN, THE FOUNDRY EQUIPMENT
CO., CLEVELAND, OHIO (SOURCE: LOS ANGELES COUNTY
AIR POLLUTION CONTROL DISTRICT, Reference 1)
-------
Table 7.9.6. AIR CONTAMINANT EMISSIONS FROM CORE OVENS (SOURCE: LOS ANGELES
COUNTY AIR POLLUTION CONTROL DISTRICT, Reference 1)
Test No.
Oven data
Size
Type
Operating temp, °F
Core binders
Weight of cores baked, Ib
Baking time, hr
Afterburner data
Size
Type
Burner capacity, Btu/hr
Air contaminants from:
Effluent gas volume, scfm
Effluent gas temperature, °F
Particulate matter, Ib/hr
Organic acids, Ib/hr
Aldehydes, ppm
Hydrocarbons, ppm
Opacity, %
Odor
1
6 ft 2 in. W x 7 ft 11 in.
H x 1 9 f t L
Direct gas-fired
380
1 to 1/2% phenolic resin
700
11
None
Oven
100
380
0. 13
0.068
52
124
0
Slight
2
3 ft 10 in. W x 5 ft 3
in H x 18 ft L
Direct gas-fired
400
3% linseed oil
1,600
2-1/2 to 3
10 in. dia x 7 ft 6
in. H
Direct flame
200, 000
Oven
140
400
0.2
0. 008
10
-
-
-
Afterburner
260
1, 400
0.013
0.000
10
< 10
0
Slight
3
4 ft 2 in. W x 6 ft 8
in. H x 5 ft 9 in. L
Indirect electric
400
1% linseed oil
600
6
3 ft dia x 4 ft H
Direct flame
600, 000
Oven
250
400
0. 27
0. 44
377
158
-
-
Afterburner
440
1, 780
0. 02
0. 087
4
< 19
0
None
VO
N3
-------
7.9.27
Ovens which operate at 400°F or less on a batch basis can usually
meet most air pollution control regulations and should not cause a
public nuisance. Excessive emissions are likely to occur when large
quantities of cores are baked or continuous operations are employed
and curing temperatures exceed 450°F to 475°F.
The most effective air pollution control system to reduce these
emissions is an afterburner or vapor incinerator. A combustion zone
temperature of 1200°F, good mixing and at least 0.3 second retention
time are minimums for good control.
7. Inspection Points—Core Making
The inspector should observe at least the last hour of the core baking
operation to determine if odors can be detected from the oven vent or
an opacity violation occurs. If the agency has specific rules
governing the emission of organic gases and vapor it may be necessary
to request a stack test to make a quantitative and qualitative
determination of the emissions. In either case, he should learn the
trade name or specification of the binder used, the maximum oven
temperature, cure time and time of day the equipment is operated.
8. Process Description—Sand Handling
Foundry sand handling systems are usually mechanized in production
shops but are fundamentally the same regardless of the size of the
foundry. Molds are shaken to loosen the sand from the casting in the
shakeout pit. The sand, spent cores and small particles of metal
fall onto a screen which passes the proper particle size sand and
segregates the oversized material. A minimum reconditioning system
includes a crusher, conveyor and muller in which the sand is mixed
with clay and water to bring it to the proper condition to be reused
-------
7.9.28
in molds. The sand at shakeout is hot and must be cooled prior to
reconditioning. This can be accomplished by ambient air or in large
volume operations where there is a high metal-to-sand ratio in the
mold, and by mechanical air blowing equipment. Figure 7.9.9 shows a
complete sand handling and dust control system.
In addition to dust there are some smoke and organic vapor emissions
from this phase of foundry operations. After the pour into the mold
is complete some of the core binder material will break down creating
smoke and vapors. This will continue to some degree during shakeout.
Ventilation systems designed to capture fines and smoke are usually a
part of the integrated system. If a baghouse is used as control
equipment and is properly sized and maintained, emissions to the
atmosphere can be held within most emission limitations. Scrubbers
will reduce the dust emissions but have not proven effective for
eliminating smoke.
Inspection Points—Sand Handling
A survey should be made of the sand handling and conditioning system
to determine if excessive dust and smoke are emitted. If there is a
dust collection system the inspector must check all tranfer points,
the boot and discharge of the bucket elevator, and vibrating screens.
Hoods should have adequate indraft velocity to capture the dust
generated by the material handling equipment and air blowing, if used.
In foundries not using dust control systems, a qualitative estimate of
dust losses should be made to determine if a dust control system is
required. Smoking molds and sand could be a cause for complaints and
may violate opacity regulations.
-------
TO BAGHOUSE
VO
Isi
Figure 7.9.9.
TYPICAL FOUNDRY SAND-HANDLING SYSTEM (SOURCE: LOS ANGELES
COUNTY AIR POLLUTION CONTROL DISTRICT, Reference 1)
-------
7.9.30
10. Environmental Observations
Emissions of aldehydes and other organic material from foundries are
sometimes a source of nuisance complaints and can be traced to the
foundry core making operation or to the vaporization of the binder
materials after metal has been poured into the mold. These organic
materials can cause eye, nose, and throat irritation. Visible
emissions from metal melting can be easily observed from outside of
the plant and related to a particular phase of the operation after
the inspector has observed the complete melting cycle.
Dust and fines from sand handling, storage piles and unpaved areas
in a foundry are also prime causes of complaints. A survey of
nearby residents or business establishments can usually result in
isolating the offending company.
-------
7.9.31
REFERENCES
1. Hammond, W., and V. Nance. Metallurgical Equipment Iron Castings.
In: Air Pollution Engineering Manual, J. A. Danielson (ed.). Cincinnati,
DHEW, PHS, National Center for Air Pollution Control and the Los Angeles
County Air Pollution Control District. PHS No. 999-AP-40. 1967.
2. Allen, G. L., F. H. Viets, and L. C. McCabe. Control of Metallurgical and
Mineral Dust and Fumes in Los Angeles County, California. Bureau of Mines.
Information Circular 7627. 1952.
3. Weisburd, M. I. Air Pollution Control Field Operations Manual. DHEW,
PHS, DAP. Washington, D. C., 1962.
4. Handbook of Cupola Operations. American Foundryman's Association, 1949.
-------
7.10.1
X. CEMENT PLANTS
A. DESCRIPTION OF SOURCE
Portland cement takes its name from a fine building stone it resembles
when made into concrete, which is quarried on the isle of Portland, England.
Portland cement is manufactured in 180 plants in the United States. The
raw materials—limestone, cement rock, clay and iron ore—are either
blended dry or mixed with water to form a slurry and then burned into
cement clinkers. These two processes account for all of the 500,000,000
barrels of Portland cement produced in the United States.
Due to the increasing use of Portland cement, the anticipated annual growth
rate of this industry is 5% per year with a trend toward larger plants
Cement plants are located throughout the United States with the greatest
production occuring in eastern Pennsylvania; Maryland; Alabama; Missouri;
(2)
Central Texas; California and the Pacific Northwest.
B. PROCESS DESCRIPTION
The process begins with quarrying of the raw materials, transporting by
truck, rail, or barge to primary crushers for initial size reduction, and
transporting by conveyor to secondary crushers for further size reduction
and storage (Figure 7.10.1). In the wet process the raw materials are
proportioned according to the desired cement specification, and mechanically
conveyed to a grinding mill where water is added. The resulting slurry is
pumped to a vibrating screen which passes the wet mixture containing the
specified size fines to the blending tanks and diverts the oversized
material back to the grinder. The slurry is mixed and blended and is then
pumped into a final storage vessel before introduction into the kiln.
-------
7.10.2A
RAW MATERIALS CONSIST OF
COMBINATIONS OF LIMESTONE,
CEMENT ROCK, MARL OR OYSTER SHELLS,
AND SHALE, CLAY, SAND, OR IRON ORE
PRIMARY CRUSHER
EACH RAW MATERIAL
IS STORED SEPARATELY
SECONDARY CRUSHER
RAW MATERIALS CONVEYED
TO GRINDING MILLS
STONE IS FIRST REDUCED TO 5-IN. SIZE, THEN 3^-IN., AND STORED
1
DRY MIXING AND
BLENDING SILOS
GROUND RAW
MATERIAL STORAGE
RAW MATERIALS ARE GROUND TO POWDER AND BLENDED
RAW MATERIALS O
ARE PROPORTIONED
GRINDING MILL
SLURRY SLURRY IS MIXED AND BLENDED O SLURRY STORAGE BASINS
PUMPS PUMP
RAW MATERIALS ARE GROUND, MIXED WITH WATER TO FORM SLURRY, AND BLENDED
2
Figure 7.10.1. PROCESS STEPS—PORTLAND CEMENT PRODUCTION
(SOURCE: PORTLAND CEMENT ASSOCIATION, Reference 3)
-------
7.10.2B
MATERIALS ARE
STORED SEPARATELY
RAW MIX IS KILN BURNED
TO PARTIAL FUSION AT 2700° F.
COAL, OIL, OR
GAS FUEL
o
CLINKER AND GYPSUM CONVEYED
TO GRINDING MILLS
BURNING CHANGES RAW MIX CHEMICALLY INTO CEMENT CLINKER
3
GRINDING MILL
CEMENT
PUMP
BULK STORAGE
BULK BULK BOX PACKAGING TRUCK
TRUCK CAR CAR MACHINE
CLINKER WITH GYPSUM ADDED IS GROUND INTO PORTLAND CEMENT AND SHIPPED
Figure 7.10.1. PROCESS STEPS—PORTLAND CEMENT PRODUCTION (continued)
(SOURCE: PORTLAND CEMENT ASSOCIATION, Reference 3)
-------
7.10.3
In the dry process the proportioned raw materials are run through an air
separator (where drying takes place by heated air from a furnace) which
allows the proper size fines to be pneumatically pumped to the dry mixing
and blending silos and recycles the oversize material back to the grinder.
The blended mix is then pneumatically conveyed to the ground raw material
storage silos from which the material is introduced into the kiln. In
both processes, the slurry or dry mix is fed into the elevated end of the
kiln. Firing takes place at the opposite end of the kiln, giving a heat
flow counter to the material flow. The fuel can be powdered coal, oil, or
gas. The raw mix is burned to partial fusion (to produce a cement clinker)
at 2700 F, air cooled, proportioned with gypsum, ground in the same manner
as the dry mix process and stored in bulk silos for ultimate bagging or
bulk shipment.
The heart of the cement plant is the cylindrical rotary ceramic lined kiln
which is also the largest single source of dust emission in the entire
operation. Kilns range in size from 6 feet in diameter and 60 feet in
(2)
length to 25 feet in diameter and 760 feet in length. The kilns revolve
on huge roller bearings and slope from the feed end down to the discharge
and firing end at the rate of from 1/2" to 3/4" per lineal foot of kiln.
Basic operations employed in cement plants are crushing and grinding,
blending, materials handling, clinker production and cooling, and fuel
preparation for coal fired plants. Figure 7.10.1 depicts the sequence of
operations and major differences between the wet and dry processes.
C. EMISSIONS AND CONTROLS
Every operation in the cement production process, by its nature, produces
dust. Dust fall measurements made in the Lehigh Valley in Pennsylvania,
near plants using modern air pollution control equipment have recorded a
dustfall rate of 35 tons/sq. mi./month. This area has a high concentration
of plants producing 31,000,000 bbl/year of cement. Even with collection
-------
7.10.4
efficiencies of 90%, as much as 10 tons/day of dust can become airborne
from a 4000 bbl/day plant attributed to the heavy grain loading of the
kiln gas.
Test data
(4)
of dust emissions from cement kilns are:
• Wet process - dust from kilns is 1 to 33% of finished cement
(4 to 124 Ibs/bbl).
Arithmetic average of dust loadings in exhaust gases is
10.1% of the finished product.
• Dry process - dust from kilns is 1 to 25% of finished cement
(4 to 94 Ibs/bbl).
Arithmetic average of dust loadings in exhaust gases is
11.3% of the finished product.
Technological changes for processing equipment will probably be concentrated
in recycling collected kiln dust which may affect firing rates and the shape
of the kiln. Increased collection efficiency of air pollution control equip-
ment to 99.5% + is essential to reduce kiln dust emissions. Figure 7.10.2
presents the representative dust loading of kiln gases from the wet and dry
(2)
process in kiln dust in exhaust gases.
DUST LOADING CHARACTERISTICS
Kiln Type
Wet
Dry
Dust Loading
gr/ft3
1 to 13
10 to 13b
1 to 12
20 to 55b
Before collection at stack conditions (400 to 600°F)
New long kiln utilizing chains and/or lifters
Figure 7.10.2. EXAMPLE OF CHARACTERISTICS OF KILN DUST (SOURCE:
SUSSMAN, Reference 2)
-------
7.10.5
Most of the sulfur dioxide formed in cement kilns as a result of the
combustion of fuel is recovered as it combines with the alkalies. Tests
of a coal fired kiln burning 2.8% sulfur coal showed a range of 6 to 39 ppm
SO ^. There is no test data available on NOX production but its forma-
tion is a distinct possibility with kiln temperatures in excess of 2600°F.
Hydrogen sulfide and polysulfides may also be produced during drying of
slurry or in the dry process when marl, sea shells, shale or clay are the
materials processed.
Processing controls vary with the age and size of the plant. Kiln
temperatures, which have a bearing on the firing rate and the raw mix feed
rate, are indicated and usually recorded. Combustion equipment and con-
trols will also vary; however, plant operators may be able to provide
information even though data recording equipment may not be available.
A variety of dust control equipment is in use including bag type collectors,
electrical precipitators, and multiclones. Generally electrical precipitators
are used to collect the dust entrained in the kiln effluent because of the
high temperature of the exhaust gas. Baghouses using glass fabric bags
(4)
have shown efficiencies of 99.5%+ and should find increasing use in
this industry. Dusts resulting from storage (silos are under positive
pressure due to air displacement in loading or from pneumatic conveying),
grinding, cooling and materials handling are usually controlled by bag
type collectors or mechanical collectors.
Figure 7.10.3 represents a flow diagram of a cement plant which indicates
the points of dust emission. The kiln which is the primary dust source
is usually vented to an electrical precipitator or baghouse. Screens,
mills, storage bins, and packaging facilities are generally vented to
mechanical collectors and baghouses in series. Transfer points, drop
points, elevator boots and loading stations should be hooded and materials
-------
7.10.6
collected. Depending on cross drafts and physical shape, hood design inlet
velocities of 200 ft/min or more may be required.
In coal fired plants, pulverizing systems are used to prepare the coal
for burning in the kiln. While the pulverizing system is "closed" and
uses mechanical separators as part of the system, this ancillary process
can also produce large quantities of dust.
© Dust collection points
Figure 7.10.3. FLOW DIAGRAM OF CEMENT PLANT OPERATIONS
(SOURCE: SUSSMAN, Reference 2)
D. INSPECTION POINTS
The inspector should survey the plant to determine the adequacy of dust
pickup at any location where dust is generated and, if necessary, request
stack tests to determine the efficiency of the dust control equipment.
The dust emission locations shown in Figure 7.10.3, except for the kiln,
are at transfer points, size reduction equipment, classifying equipment
(screens) and bulk loading facilities. Dust pickup efficiency of the hoods
-------
7.10.7
serving these areas is indicative of air pollution control performance.
For example:
1. Good dust pickup means the system is operating at or near its design
efficiency.
2. Poor dust pickup may mean plugged lines, air bleeding in through worn
or damaged duct work, damaged fan, drive belt slippage or undersized
motor.
Equipment and methods for field checking indraft velocities at hoods are
described in Chapter 5.
The unmistakable sign of a cement plant is the plume from the kiln stack.
Visible dust can be seen in the carry-over after the steam has dissipated.
By comparison with previous observations, when the control device is known
to have been operating effectively, the inspector can make a qualitative
judgment as to the efficiency of the control equipment.
A check of the control room may provide evidence of malfunction of the
equipment if there is a recording outlet opacity indicator instrument.
The inspector will find it extremely useful to make notes of the recording
and non-recording instrumentation which can include kiln temperature,
fuel flow measurements and gas analyzers for combustion performance.
Electrical precipitators, for example, are sensitive to the temperature and
moisture content of the inlet gases. Resistivity (resistance to relinquishing
negative charge to the collection electrode) for most particles increases
sharply when the gases entering the precipitator are between 200° and 400°F
-------
7.10.8
and less than 5% moisture (see Figure 7,10.4 and Chapter 2). Collection
efficiency is adversely affected by low resistivity. The inspector thus should
become familiar with the gas conditioning requirements of the precipitator and
check the control instrumentation to see if the inlet conditions are in the
proper range. The inspector should also check the rapping or washing cycle
for removal of dust collected on the electrodes. Reentrainment of dust
can occur if this cleaning function is not precise. Dust reentrainment
can result in an increase in opacity of the effluent and a rise in the
exhaust grain loading.
Baghouses using glass fabric filters are extremely efficient air pollution
control devices for cement kilns. The major operational problem is to
maintain the temperature of the gases in the baghouse above their dew
point. Insulation of the baghouse enclosure, fan, and ducts is helpful
in maintaining the proper temperature. Good operational procedures also
require the exhaust fan to remain in operation during down time to prevent
moisture buildup in the bags.
Inspection fundamentals apply regarding observations of equipment repair,
non-use of dust collection equipment, and housekeeping. These should apply
to roads and uncovered areas where dust has collected. Since the material
is very fine, it can easily be disturbed by truck traffic and contribute to
the background count of particulates for the area, as well as creating a
public nuisance.
Dust collected from the kiln may be reinjected into the kiln, transported
dry by materials handling equipment to a waste disposal area where it is
dampened before it is dumped, or mixed with water to form a slurry and
pumped to a waste pond.
-------
7.10.10
REFERENCES
1. Control Techniques for Particulate Air Pollutants. Washington, D.C.,
DHEW, PHS, NAPCA, January 1969.
2. Sussman, V. H. Nonmetallic Mineral Products Industries. Air Pollution,
Vol. Ill, A. C. Stern (ed.). New York City, Academic Press, 1968.
3. The Making of Portland Cement. Portland Cement Association. Skokie,
Illinois.
4. Kreichhelf, T. E., D. A. Kemnitz, and S. T. Cuffe. Atmospheric Emissions
from the Manufacture of Portland Cement. DHEW, PHS. Cincinnati, Ohio.
1967.
5. Simon, H. Single-stage Electrical Precipitators. In: Air Pollution
Engineering Manual, J. A. Danielson (ed.). Cincinnati, DHEW, PHS,
National Center for Air Pollution Control and the Los Angeles County Air
Pollution Control District. PHS No. 999-AP-40. 1967.
-------
7.11.1
XI. ALUMINUM REDUCTION PLANTS
A. DESCRIPTION OF SOURCE
Aluminum production consists of four major phases: Mining of Bauxite ore;
alumina production consisting of ore refining, extraction and calcination
of alumina ore (Al.CL); smelting or reduction of alumina to produce aluminum
ingot or billet; and fabrication: processing of the ingot by casting, forging,
extrusion, machining, rolling, drawing and other production techniques.
Mining and refining of alumina is mostly conducted abroad. Domestic refining
is confined to Arkansas, Louisiana, Alabama and Texas and results in parti-
culate pollution problems similar to the cement and lime processing industries,
addressed in other sections of this Chapter. Fabrication and recycling or
reclamation of aluminum products falls under the category of secondary metals
production, treated in Section VIII. The aluminum smelting or reduction
process is most significant from a domestic air pollution standpoint and
will be treated in this section.
Approximately 30 major aluminum reduction plants are operated in the
United States. These are generally located close to relatively cheap
sources of electrical energy, particularly hydroelectric power. Additional
power may be supplied from oil or coal-fired power plants. Principal
plants are located in Alabama, Arkansas, Indiana, Kentucky, Louisiana,
Maryland, Montana, New York, North Carolina, Oregon, Tennessee, Texas,
Washington, West Virginia and Wisconsin.
The basic process consists of the extraction of (elemental) aluminum from
the refined alumina ore. Alumina is highly resistant to heat and chemicals
C2 3)
due to the strong bond holding the atoms of aluminum and oxygen together.v '
Enormous amounts of electrical energy are required to separate these chemicals
from each other. For example, the six aluminum reduction plants located in
the State of V&shington annually consume 2,000,000 kilowatts of. electrical
-------
7.11.2
energy (equivalent to the entire generating capacity of Grand Coulee Dam)
to produce 1,000,000 tons of aluminum, or 2 kilowatts for every ton of
aluminum produced, although newer plar
consuming per pound of aluminum produced.
aluminum produced, although newer plants are designed to be less power
B. PROCESS DESCRIPTION
From an air pollution standpoint the process of aluminum reduction can be
seen in three phases: (1) handling of the alumina powders; (2) preparation
of the carbon anode, and (3) aluminum reduction in pots or cells (see
Figure 7.11.1). Two types of aluminum reduction processes are employed:
prebake and Soderberg. These differ in the method of preparing the anodes
required to effect electrolytic action in the pots. Prebake refers to the
formation, pressing and baking of the carbon blocks prior to their
placement in the pots. This may be conducted in a separate plant—the
anode plant—which is usually operated within the same facility, less
commonly at a plant at a different location. In the Soderberg process an
anode paste mix of coke and pitch is added on top of the anode and is
baked in place by the heat of the pot. The two processes, although they
may be conducted at the same facility, dictate different pot and plant
designs. These are discussed in greater detail in the following parts of
this section.
1. Material Handling
Material handling involves transfer of the alumina powder in bulk
from ship or rail cars to storage bins or silos located at the
aluminum plant. Transfer is accomplished by bucket and conveyor
systems, or by the use of vacuum lifters. Storage and transfer
systems are likely to be enclosed, and in some plants exhaust systems
and bag houses are applied to recover alumina losses. The alumina is
-------
ANODE
PLANT
CATHODE
PLANT
CELL CHARGE
MATERIALS
ELECTRIC
POWER
RECEIVE
CATHODE
MATERIAL
& BUILD
CATHODE
POTROOMS
ALUMINUM PRODUCTION
CELLS (POTS)
Figure 7.11.1.
ALUMINUM REDUCTION PLANT FLOW DIAGRAM
(SOURCE: STATE OF WASHINGTON, Reference A.)
-------
7.11.4
transferred from the inplant storage facility to silos in the potroom
area, and hoppers are moved around the plant by overhead cranes or
ground dispensing vehicles (see Figure 7.11.2). The dusts generated
from the charging operation are collected by the ventilation hoods
located on the pots or by a system covering the total building (called
a secondary control system), although alumina dust will usually be
found throughout the potroom floor area.
Alumina is a fairly dense particulate and usually will pass through
a 325 mesh screen. Its white coloration makes leaks, emissions and
spills easy to detect. Since alumina is highly inert, contamination
resulting from spillage and floor deposits generally is not a problem
and the material can be swept up and fed to the reduction pots.
2. Electrode Preparation
a. Cathode Preparation
The electrolytic process of aluminum reduction depends on the
preparation and placement of the carbon anode (positive terminal)
and cathode (negative terminal) in the pot of the furnace. The
cathode consists of a pad of molten aluminum which forms over
carbon blocks located on the bottom of, and perpendicular to the
width of, the pot. The blocks are usually made from calcined
anthracite. A carbon paste is rammed between the carbon blocks
and baked in to seal the lining. During operation of the pot
alumina dissociates electrically and molten aluminum deposits
at the carbon cathode and oxygen aggregates at the anode and
combines with some of the carbon anode to form oxides of carbon.
Since the carbon cathode does not significantly deteriorate, it
-------
7.11.5
Figure 7.11.2 not available for this publication.
-------
7.11-6
may last for 2 to 4 years. Cathode operations are not significant
from an air pollution standpoint except when they are being baked
or removed. In the former, hydrocarbon emissions from binder
materials will be produced and are collected by the exhaust system.
In the latter, dust emissions may result from the process of removal
(chipping away) of the carbon from the cold pot.
b. Anode Preparation
The anode is also made from petroleum coke, reclaimed anode carbon,
and pitch or binding material. Since the carbon in the anode reacts
with the oxygen liberated from the dissociation of alumina into
oxygen and aluminum, it is gradually consumed and must be periodically
replaced in the case of prebake, or added to in the case of the
Soderberg pots.
In the prebake plant, carbon usually in the form of calcined
petroleum coke is ground, blended with melted pitch (tar) and pressed
into anode blocks, usually on a batch basis (see Figures 6.11.3,
7.11.4 and 7.11.5). Approximately 1/2 pound of carbon is required
for each pound of aluminum produced. Spent anodes are also crushed
and recycled in this operation. Wet collectors, e.g., Rotoclones,
and other conventional collection equipment are used to collect dusts
generated in this operation. Heat is supplied from a boiler plant.
The carbon anodes are block or tapered forms approximately 2 1/2 feet
cube. The green anodes are conveyed by the overhead crane system and
lowered into the ovens. The bake oven consists of a series of
trenches and compartments lined with refractory brick. A number of
trenches lie parallel to each other and run the length of the anode
plant. The ovens are indirectly fired by means of gas or oil. Flue
gas from the combustion equipment flows in chambers adjacent to the
anode blocks.
-------
COAL TAR PITCH
CALCINED
PETROLEUM COKE
BUTTS
CRUSHER
COARSE PARTICLES
HAMMER MILL VIBRATING
SCREEN
COARSE PARTICLES
HAMMER MILL
BALL MILL
TO
ELECTROLYTIC •< —
CELL
PIT E
iAKING FURNACE
f—
1 V
ii
D V V.
~rnr \"<
q cd COOLING''^
2 I_ CONVEYOR
TRAM.CAR
ra
MIXER
_WE1GH
SCALES
MOLDING F'RESS
Figure 7.11. 3. PREBAKED CARBON ANODE PRODUCTION PROCESS
(SOURCE: BLOCK AND MOMENT, Reference 1.)
-------
7.11.8
ANODE PASTE
CALCINED
PET. COKE
HAMMER
MILL
STEAM
COAL TAR
PITCH
VIBRATING
SCREEN
STEAM
ANODE
| PASTE
Figure 7.11.4. SODERBERG ANODE PASTE PRODUCTION PROCESS
(SOURCE: BLOCK AND MOMENT, Reference 1.)
-------
Figure 7.11.5. CARBON ANODES READY FOR USE IN ALUMINUM POTS (SOURCE:
INTALCO ALUMINUM COMPANY, FERNDALE, WASHINGTON)
-------
7.11.10
The ovens are preheated slowly to a maximum temperature of around
1400°F, and then cooled very slowly. The baking cycle may take
approximately 2-3 weeks. The heating cycle is intended to achieve a
durable anode with desired electrical properties, e.g., minimal
electrical resistance, in order to maximize its service in the pot.
Carbon monoxide, carbon dioxide, sulfur dioxide and particulates are
emitted from the anode plant stack. After the anodes are baked, they
are removed from the ovens, and steel pins are inserted and
copper or aluminum connectors are attached. Anode assemblies may
consist of 1-4 anodes. The anodes are conveyed to the potrooms where
they are installed in the pots.
Emissions of dust and volatiles driven off the anodes, along with the
products of combustion from the firing equipment are vented through a
single and usually tall stack. Control systems, such as, high energy
scrubbers, catalytic combustion or incineration can be employed.
Emissions include sulfur dioxide contained in the coke fuel oil used,
products of pyrolitic decomposition, including hydrocarbons, and some
fluorides.
3. Potroom Operations
a. Prebake
The potroom constitutes the major source of pollution in an aluminum
reduction plant. Smelting is performed in large rectangular pots or
cells in which alumina, and the electrolyte are charged. The
electrolyte is usually cryolite (sodium aluminum fluoride) and
fluorspar (calcium fluoride). Raw materials required in the
production of one ton °f aluminum by both the prebake and Soderberg
process are shown in Tables 7.11.1 and 7.11.2.
The cells are arranged in long pot-lines, and wired together in series
(Figure 7.11.6). Direct current flows through a buss, through the
carbon anode, the molten electrolyte and metal pad and out through
-------
7.11.11
Table 7.11.1. RAW MATERIALS FOR THE PRODUCTION
OF ONE TON OF ALUMINUM
Material Amount (tons)
Sulfur .01 = .05
Alumina (Al203> 1.9
Cryolite (NasAlFe) .03 - .05
Aluminum Fluoride (A1F3> .03 - .05
Fluorspar (CaF2) .003
Anode
Petroleum Coke .490 Prebake, .455 Soderberg
Pitch Binder .123 Prebake, .167 Soderberg
Cathode (Carbon) .02
Total: Approximately 2.6 tons raw material/ton Al
(SOURCE: HANNA, Reference 6.)
Table 7.11.2 COMPARISON OF REQUIREMENTS FOR
PREBAKED AND SODERBERG SYSTEMS
Soderberg Prebaked
Time to produce one ton 37 hours 27 hours
KWH to produce one ton 15,400 13,600
Effluent gas treated
per 100,000 amperes 4,000 CFM 23,500 CFM (no hoods)
4,000 CFM (hoods)
Scrubber water 3.3 - 4.4 Gal 10 Gal
1,000 CF 1,000 CF
(SOURCE: HANNA, Reference 6.)
-------
Figure 7.11.6. POTLINE, SHOWING ANODES SUSPENDED IN POTS, SPOKANE, WASHINGTON
(SOURCE: KAISER ALUMINUM AND CHEMICAL CORPORATION, OAKLAND,
CALIFORNIA)
-------
7.11.13
the carbon cathode linings of the cells. The current is
characterized by low voltage (around 4.5 volts) and high amperage
(about 50,000 to 200,000 amps). The temperature of the molten bath
will reach 1742°-1792°F. The molten metallic aluminum forms a layer
above the carbon lining of the pot and below the molten bath (see
Figure 7.11.7). The oxygen liberated by electrolysis reacts with
the carbon anode to form CO and CO.. Hydrogen fluoride gas from the
cryolite and particulates are also released. Emissions from the pots
are collected by removable hoods or shields and vented through
ductwork to a scrubber, an electrical precipitator, a fluidized bed,
a baghouse or limited combinations of these devices.
The alumina is charged by breaking the crust (the frozen alumina and
bath material) and laying on a fresh charge of alumina. This procedure
is necessary to minimize thermal shock and prevent the addition of
moisture. Gases, fine dust and fumes escape from the molten bath and
if not picked up by the ventilation hoods enter the workroom and
eventually the outdoor atmosphere.
b. Soderberg
In the Soderberg process, briquetted coke and pitch is charged from
hoppers on top of the anode structure by means of a crane, which
moves down over the pot line. The prebake operation is thus eliminated,
and baking emissions are captured by the ventilation hoods. The
design of control equipment, particularly electrical precipitators, in
the Soderberg process must take into account the tarry emissions, that
is, collection of wet particulates in the precipitator.
Two types of Soderberg cells are in use: side pin or horizontal stud and
verticle stud (see Figure 7.11.7). In the former, alectrical connection
is made by steel pins or studs inserted horizontally into the side of the
anode through movable steel channels. In the latter, electrical
-------
\
ALUMINA\
HOPPER
GAS COLLECTION DUCT
6AS COLLECTION
HOOOS
SOLlOiF'ED CRUST
OF ELECTROLYTE
FULLY BAKED AUOI E AND ALUMINA
Figure 7.11.7. DETAILS OF PREBAKED AND SODERBERG ALUMINUM REDUCTION CELLS
(SOURCE: ROSSANO AND PILAT, Reference 5,)
-------
7.11.15
connection is made by steel pins or studs inserted vertically into
the top of the anode. The anode is contained in a rigid casing open
at the top and bottom. The vertical stud has the advantage that the
off gases from the cell can be collected on a concentrated low volume
basis by a collecting skirt attached to the bottom of the anode
casing. The volume of off-gases is approximately 1/10 of that by
prebake or horizontal pin methods. CO and combustible gases are
passed through burners and fumes are drawn off by ducts and fans to
a control device, which may include low and high energy scrubbers,
electrical precipitators and a fluidized-bed baghouse combination.
C. CONTAMINANTS EMITTED
The obvious sources of pollution from aluminum reduction plants are the
stacks from both the anode plant (in prebake facilities) and potroom
exhaust systems and the potroom air vents and roof monitors. The tall
stacks, which may be approximately 500 feet in height, are intended to
disperse pollutants and to minimize downwind concentrations of contaminants
and resultant fluoride damage. The plumes, however, are long and
concentrated, and hence visible from many miles away. Other sources
include vents, floor operations, control equipment (particularly scrubbers
in older plants) and others.
Types of emissions related to plant operations are shown in Table 7.11.3
and fluorine and S02 emissions corresponding to various plant capacities
are shown in Tables 7.11.4 and 7.11.5.('8)
The emission of hydrogen fluoride is most significant. The fluoride ion
exhibits strong acid properties and can act as a protoplasmic poison, it
can damage foliage at .1 parts per billion, accumulate in forage to 30-50
ppm on the inside and outside of leaves and can be fatal to livestock con-
suming contaminated forage. Gaseous fluorides can be sampled by means
-------
Table 7.11.3. EMISSION SOURCES AND CONTAMINANTS
EMISSION SOURCE
OPERATION AND LOCATION
Cell operation
Emission treatment exhaust
(Soderberg only
Anode materials handling, grinding,
classifying
Building vents
Dust collector exhaust
Anode mixing
Building vents
Emission collector/treatment exhaust
Anode baking (Prebake only)
Building vents
Emission collector/treatment exhaust
Metal casting
Building vents
Emission collector/treatment exhaust
Cathode preparation
Building vents
Dust collector exhaust
Emission collector exhaust
Alumina and electrolyte materials
handling and distribution
Building vents
Dust collector exhaust
CONTAMINANT
GASEOUS
co2, co,
CF.
PARTICULATE
A1F
Na.CO-,
3,
carbon dust
Hydrocarbons Tar)
Carbon dust
Pitch dust
Hydrocarbons Carbon dust
Pitch dust
Tar
C02, CO, Carbon dust
CA TJT7
bU_, tlf
Hydrocarbons Tars
C12, HC1 A1C13, A120,
C0?, CO Cryolite
Hydrocarbons Carbon dust
Pitch dust
Tar
Cryolite, CaF ,
TYPICAL
CONTROL SYSTEMS
High energy scrubber
Electrical Precipitator
Fluidized bed
Baghouse
(Wet collectors
(Baghouse
Wet Collectors
Baghouse
(High energy scrubbers
I Catalytic combustion
(incinerators
(Operational flux
\ and temperature
1 controls
/ High energy scrubber
I Electrical precipitator
< Fluidized bed
I Baghouse
\Roof scrubber
Wet collectors
Baghouse
Fugitive Dust Sources
(SOURCE: STATE OF WASHINGTON, Reference 8.)
(Expanded)
-------
Table 7.11.4. TOTAL F EMISSION - DAILY RATE AND CONTROL EFFICIENCY
rweraoe:
ALUMINJM
PRODUCTION
-ANT TONS
i
2
3
4
5
6
per* day :
e:
480
274
575
220
720
520
:2790
465
ELECTROLYTE
CONSUMED
TONS % OF PROD.
28.5
18.0
31.6
11.5
41.9
27.6
159
26.5
5.9
6.6
5.5
5.2
5.8
5.3
5.7
5.7
POTENTIAL
F" EMISSION
TONS
14.9
9.6
16.5
5.7
22.8
14.0
83.5
13.9
% Oc PROD.
3.1
3.5
2.9
2.6
3.2
2.7
3.0
3.0
ESTIMATED
F" EMISSION
TONS
2. 16
1.82
2.94
i .52
4.56
2.Q2
15.9
2.65
% OF PROD.
0.45
0.66
0.51
0.69
0.63
0.56
0.57
0.58
F CONTROL
EFFICIENCY *
I
85
31
82
73
80
79
81
80
*Control efficiencies currently possible are in excess of 98 percent.
(SOURCE: STATE OF WASHINGTON, Reference 8.)
-------
Table 7.11.5. TOTAL SO EMISSION - DAILY RATE AND CONTROL EFFICIENCY
Average:
AlUJIINUH
PRODUCTION
.ANT TONS
1
2
3
4
5
6
>er day:
480
274
575
220
720
520
27SO
465
Af.'ODE COKE AND
PITCH CONSUMED
TONS
229
185
274
122
358
286
1454
242
% OF Pi>OD
47.7
67.6
47-5
55.5
49.8
54.9
52.2
53-8
POTENTIAL
SO., EMISSION
. lOSS
3.15
3.70
18.0*
2.44
6.72
3-56
19.6
3.92
\ OF PROD.
0.67
i-35
3.08*
1.1)
0.94
0.69
0.83
0.95
ESTIMATED
SO, EMISSION
TONS
0.88
1 .00
16.0"
0.92
1.85
0.80
5.45
1 .09
% OF PROD.
0. 18
0.36
2.8"
0.42
0.26
0.15
0.25
0.27
SO CON'iT.UL
EFFICIENCY **
-i
72
73
if
62
72
77
72
71
••Not included in total and average values
**Control efficiencies currently possible are in excess of 90 percent.
(SOURCE: STATE OF WASHINGTON, Reference 8.)
-------
7.11.19
of sampling trains using distilled water and solutions of NaOH as a
collecting medium. Particulates are collected by filtration. Forage
samples can be collected in inert containers such as a one quart glass
jar or freezer bag. Water soluble fluorine compounds collected from
ambient air are analyzed by use of ion-selective electrode methods and
others. Ambient air values can be quite low and expertise is needed
to obtain reliable data.
The application of air pollution control methods in aluminum reduction
plants will include improved basic equipment design, such as larger pot
capacities, improved operations such as automating charging; improved
hooding and collection efficiences; addition of controls to more emission
points, such as the roof monitors.
Control methods for aluminum reduction cells include the following:
Wet Scrubbers. Spray towers can remove a high percentage of hydrogen
fluoride since this contaminant is highly soluble in water. These
devices, however, have a poor collection efficiency for fine
particulates. Recent improvements include a floating-bed type of
wet scrubber on horizontal Soderberg cells. This type of scrubber
tends to overcome the problem of tar fouling that occurs in scrubbers
with stationary packings.
Electrostatic Precipitators. Wet electrostatic precipitators are
beginning to be used in controlling reduction cell emissions. These
include vertical counterflow precipitators employing plywood collection
plates which are irrigated with a falling film of water supplied from
troughs at the top of the plates. Another application utilizes
continuous spray washing of the collection plates and discharge
electrodes.
Chemisorption. This process was introduced by the Aluminum Company
of America (ALCOA) for treating gaseous and particulate fluorides.
-------
7.11.20
The method consists of the chemlsorption of hydrogen fluoride on a
fluidized bed of finely divided alumina and removal of the sorbed
fluoride by means of a fabric collector. Particulate fluorides are
also removed by simple filters. The ALCOA system (Process A-398)
requires effective local exhaust hooding on each pot (Figures 7.11.8
and 7.11.9). ' ' Particulate emissions as low as 3 pounds of HF per ton
of aluminum produced are claimed. Contamination of liquid streams and'
solid waste disposal problems are avoided. Spent alumina from the
collector system is recycled to the pots and sorbed fluoride is
added to the cryolite make-up.
Roof Collectors. In this procedure gases and dust are allowed to
enter the workroom atmosphere. Large exhaust blowers at the ceiling
(Figure 7.11.10) induce an inward flow of outside air, through
open louvres on the outside walls of the building, across the cells
and into an overhead exhaust system to the gas cleaning equipment,
usually wet scrubbing.
INSPECTION POINTS
Systems and equipment for controlling aluminum reduction emissions will
require constant upgrading in the years ahead to meet increasingly
stringent emissions standards. Emissions which may now range from 40-50
pounds/ton aluminum processed will have to be reduced to something like
15 pounds/ton and #1 Ringelmann. Bag filters and improved electrostatic
precipitators may be the only types of control systems that will help to
realize this goal. Such design improvements as larger pot capacities,
automated ore feeding, and roof scrubbers should also help to achieve
these goals.
Most of the inspector's function will be to help assure that compliance
schedules are met, that control systems are conscientously operated and
maintained, and plant facilities are operated and maintained in a manner
which takes into account air pollution control, and prevents environmental
damage in the vicinity of and downwind from the plant.
-------
HOODING
REMOVABLE
HOOD
SECTIONS
ALUMINA FEED
HOPPER
PREBAKEO
ANODE
SERVICE
ACCESS DOOR
Figure 7-11.8. SCHEMATIC OF ELECTROLYTIC CELL AS USED IN ALCOA A-398 PROCESS
(SOURCE: ROSSANO AND PILAT, Reference 5.)
-------
AIR JETS.
GAS
DISCHARGE
CONOUr
,8AG FILTERS
9999999999999/999
PERFORATED
PLATE
BED
DEPTH
CONTROL -V
ELONGATED CHAMBER
ALUMINA BED
GAS DISTRIBUTION CHAMBERS
GAS
-COLLECTING
HOODS
T7TT1
a n n n
ELECTROLYTIC CELLS
Figure 7.11.9. SCHEMATIC OF ALCOA GAS CLEANING PROCESS. (A-398)
(SOURCE: ROSSANQ AND PILAT, References.)
-------
Cleaned Air
A A A A
Air from Potroom
>
>~
Coarse sprays }
>-
>
Mist
Eliminator
Coarse sprays
Slope
Screen
Four banks of Fine Sprays
Figure 7.11.10. CROSS-SECTION OF ROOT SCRUBBER
(SOURCE: BYRNE, Reference 7.)
-------
7.11.24
1. Environmental Observations
In the conduct of the inspection, the inspector should patrol, and
tour on foot, the exterior of the plant looking for possible damage
to forage and foliage. The type of damage that may occur varies with
the species of vegetation. Any appearance of damage, particularly
on margins and tips of leaves should be suspect and sampled. It may
also be desirable to sample foliage that appears undamaged for
analysis whenever there is reason to suspect that damage may be
occurring. Samples should be taken in forage areas to ascertain the
possibility of damage to livestock. Visual observations of livestock
could also be made. In any event, if an inspector found something to
suspect, a person with expertise in fluoride vegetation or animal
effects should be consulted.
In selecting sampling points, prevailing winds and distances from
the stacks should be taken into account. The following procedures
should be used in forage sampling:
• Cut the forage with a sharp knife or shears about 2 inches
above the ground to avoid contamination by soil particles.
Collect about 200 grams of sample; cut it into 1/4" to 1/2"
pieces and store it in an appropriate container.
Samples may be stored for up to 5 days before analysis, at
refrigerator temperatures (5°C). Store the samples at 0°C or
lower if they are to be kept for longer than 5 days.
Care must be taken to assure that the sample represents the
intake of the animal using the forage. In general, the
sample should include the main species of forage vegetation
in about the same proportion as they grow in the field.
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7.11.25
• Do not take samples within 100 feet of any road unless it
can be shown that road dust contamination is not a factor.
The following information must be included as part of the sample
identification:
• Date of sample
• Time of day
• Location of sample
• Types and approximate proportions of vegetation in the sample,
• Weather conditions
• Any abnormal factor such as heavy traffic, construction in
the area, harvesting nearby, etc.
• Original source of sample—is it stacked hay, baled hay, etc.
• Name of person who took the sample.
Exterior of Plant
The inspector should observe the exterior of the plant noting all
emission points and the character of the emissions including
the tall stacks, roof monitor emissions, scrubber outlets and other
parts of the plant structure. In some locations, reading visible
emissions from monitors may be approved procedure. Also, in some
localities, background humidity readings, with the use of a sling
psychrometer may be required (see Chapter 4). Scrubber outlets
may have a tendency to contain a significant portion of dry fume in
the emissions.
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7.11.26
3. Interior of Plant
In the interior of the plant, the inspection should be organized
around the initial alumina handling procedures, the anode plant and
control systems (some plants may conduct both prebake and Soderberg
operations), the potrooms, potroom control systems, and cast houses
and other secondary metal operations. The inspector should note the
following:
a. Firing system and fuels used in anode ovens, such as gas or oil,
and the effectiveness and status of control systems.
b. General potroom emissions. The inspector should view down the
potline for general inplant emissions, the degree to which
emissions are expelled through the monitors and side vents, and
handling of tapping and pot maintenance operations. The extent
of emissions within the potrooms will give some idea of the
general operational efficiency. HF is an eye and nose irritant,
therefore, evidence of HF emissions could be detected by eye
irritation or odor.
c. Collection efficiency of hooding in potrooms. When pots are opened
to replace anodes, charge materials or to tap furnaces hooding ef-
ficiencies can be greatly reduced. The inspector should note how
long the pots are open, and whether the hoods are damaged due to
handling. Sometimes shields are pulled on 4-5 pots at a time. Auto-
matic ore feeding employed in new plants may greatly reduce oper-
ational emissions.
d. Operational schedule of potroom. The inspector should become
familiar with this schedule. The anode replacement schedule is
usually equivalent to the anode baking schedule, in prebake
plants. Cathodes are replaced less frequently, every 2 to 4 years
depending on pot life.
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7.11.27
e. Voltage readings on guages located atop each furnace. Voltages
are relative to initial plant design, production schedules, etc.
Generally, 4 to 6 volts is normal.
f• Pot performance. An anode effect is caused by the depletion of
alumina and results in increased temperature, vapor pressure and
fluoride and other emissions. If caught in time, the condition
can be corrected by adding alumina, agitating the pot and/or
adding more air. A sick pot results from too much alumina and
causes a cold spot to form in the pot, a decrease in resistance,
and an impairment of the electrolytic process. A light and a bell
usually signal an anode effect and a sick pot respectively. The
inspector could inquire about the rate at which these malfunctions
occur per potline per day.
§• Performance characteristics and maintenance practices of scrubbers
and other control equipment serving the pot ventilation system.
The plant should also have the capability to by-pass to an
alternative system, when it is necessary to shut down one of the
control systems. The inspector should note capacities of
scrubbers, special design features, such as mist eliminators and
straightening baffles. The inspector should note the disposal
of waste water from the scrubbers. High fluoride water should not
be sent to rivers and lakes. United States Public Health Service
standards require fluorine below 1 ppm if river is used for
drinking supply. The inspector should also determine if pH
adjustment of water is made in the scrubber.
h. Emissions from holding furnaces. The inspector should physically
inspect all plant operations including cast houses and fabrication.
Aluminum holding furnaces (see Chapter 7.8, part Old) are used to remove
air, organic matter and traces of metal as magnesium. The control
of chlorine emissions from fluxing agents is poor or nonexistent
at most primary aluminum smelters. Chlorine odor has a sweet,
sickly odor and is easily noted when touring an aluminum plant.
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7.11.28
REFERENCES
1. Block, I., and S. Moment. Pacific Northwest Economic Base Study for Power
Markets, Vol. II, Part 7B. U.S. Department of the Interior, Bonneville
Power Administration. Portland, Oregon. 1967.
2. The Aluminum Association. The Story of Aluminum. 420 Lexington Avenue,
New York, New York 10017.
3. Nelson, K. W. Nonferrous Metallurgical Operations. In: Air Pollution,
Vol. Ill, A. C. Stern (ed.). New York City, Academic Press, 1968.
4. Background Report in Support of Regulations and Standards for Primary
Aluminum Plants. State of Washington, Department of Ecology. April 1970.
5. Rossano, A. T., and M. J. Pilat. Recent Developments in the Control of
Air Pollution from Primary Aluminum Smelters in the United States.
Second International Clean Air Congress of the International Union of the
Air Pollution Prevention Association. Washington, D.C.
6. Hanna, T. Air Emissions from Primary Aluminum Industry. Term Paper,
Air Resource Program, Department of Civil Engineering. University of
Washington. March 10, 1970.
7. Byrne, J. L. Fume Control at Harvey Aluminum. Presented at Annual
Meeting, Pacific Northwest International Section, Air Pollution Control
Association. Spokane, Washington. November 16-18, 1970.
8. Background Report in Support of Regulations and Standards for Primary
Aluminum Plants. State of Washington, Department of Ecology. April 1970.
9. Thomas, M. D. Effects of Air Pollution on Plants. E. 0. Catcott. Effects
of Air Pollution on Animals. World Health Organization. Geneva, 1961.
10. Methods of Sampling and Analysis for Fluoride in Ambient Air and Forage.
Washington State Department of Ecology, Air Quality Control Branch.
Appendix 1 to Chapters 18-48 EAC. September 1970.
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7.12.1
XII. MINING
A. NATURE OF SOURCE PROBLEM
Mining is the process of extracting mineral wealth from the earth, sea, or
atmosphere. Since these mineral assets are not self-replenishing, it is
important that they be collected in an efficient and non-wasteful manner.
The air pollution problem from mining operations involves primarily par-
ticulates from surface operations and combustion contaminants from fires.
Additional pollutants are emitted into the ambient atmosphere via the
ventilation systems of underground mines.
Mining often results in other forms of environmental pollution as well.
Water contamination may occur as runoff passes through surface mining
regions and into nearby bodies of water. This may have a very detrimental
effect on the water supplies of downstream communities.
The condition of the land after mining is completed is becoming a major
issue to conservationists. They are particularly critical of its ravaged
appearance and apparent uselessness as a resource.
B. PROCESS DESCRIPTION
In order to remove natural resources from the ground, either underground
methods and/or surface techniques may be employed. The character of the
mineral deposits and the state of technology have important bearing on the
procedure selected. In actual practice, it is more desirable to employ
surface procedures for the following reasons:
• It is possible to recover deposits which often could not
be retrieved by underground means.
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7.12.2
Safer and more healthful working conditions are provided
• A more complete retrieval of the resource is accomplished.
• The cost per unit of production is less than with below
ground methods.
Generally, surface mining is only possible if the thickness of the covering
material (overburden) is small as compared to the size of the mineral
deposit.
The utilization of below ground techniques requires extensive planning and
consideration of a number of significant factors. Some of these include
digging and supporting the mine, removing the resource, keeping the
mine atmosphere healthful and free from the possibility of explosion,
and other safety factors. Although proper planning is necessary for
surface mining as well, the number of factors involved overall are
far fewer and less critical.
1. Surface Mining
The surface mining methods producing the greatest air pollution
effects are strip mining and open-pit mining. Strip mining is
of primary importance in connection with coal. Open-pit mines are
normally constructed in order to recover copper, iron and gypsum.
Regardless of the equipment or technique used, surface mining consists
of the following steps:
• Site preparation—constructing access roads, designating
dump sites, and clearing vegetation and other obstructions.
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7.12.3
• Removal and disposal of overburden.
• Excavation and collection of the deposit.
• Transportation of the mined resource for processing.
Strip Mining
Strip mining is usually applied to recover coal deposits that
are located near the surface of the earth. It consists of
removing the overburden covering the mineral bed, and then
loading the uncovered material.
Strip mining techniques are utilized on both flat and hilly terrain.
On flat areas, a series of parallel cuts 40' to 150' wide are made
in the surface. The overburden from the first cut is deposited in
an area where no deposit exists (if possible). Thereafter, the
overburden from one cut is deposited in the trench made by the
previous cut. This process may be carried on systematically
throughout the mining site.
If the area is hilly, the deposit may outcrop at the surface.
In this case, the first cut is made at just above the exposed
deposit with the overburden dumped further down the hill.
As additional cuts are made, the overburden to be removed
becomes thicker. It is piled next to the previous overburden
in waste banks or spoil piles. These series of cuts continue
until the overburden gets too thick as compared to the amount
of deposit to be retrieved. Equipment utilized in strip mining
consists mainly of bulldozers, draglines, and large power shovels.
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7.12.4
The most serious air pollution problem in strip mining involves
the extremely high combustibility of coal spoil piles. The spoil
is stored in an area where the useful mineral is not being
developed. Waste from coal cleaning and washing operations (see
Section XIII) is frequently added to the piles. They are commonly
ignited spontaneously or by burning rubbish close by or in strip
pits. Once ignited, these waste banks may burn for decades emit-
ting smoke and gases into the atmosphere and are very difficult,
if not impossible, to extinguish.
A 1964 survey^' counted 495 burning refuse piles in the United
States. Often the burning piles are covered with some inert
material to try to cutoff the oxygen supply. This practice only
proves to be a temporary measure and the fire usually picks up
again.
In the past, many methods to control fires, such as flooding,
blanketing, slurry injection, and compacting have been attempted.
However, a potential fire hazard will continue to exist unless the
temperature within the spoil bank is maintained below the kindling
point. Active burning is usually visible on the sides and bottoms
of the spoil piles, where the large blocks of refuse generally tend
to accumulate during dumping. Air is able to penetrate through the
crevices formed by these blocks, is heated, and rises as if in a
chimney. Changes in barometric pressure cause considerable air
flows into and out of the pile.
The Bureau of Mines conducted a research program designed to aid
the coal-mining industry in the control of burning refuse, and its
disposal in a safe and economical manner. The Bureau studied the
permeability of refuse, its spontaneous ignition tendency, and
methods of extinguishing a burning pile of coal.
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7.12.5
In field tests, the Bureau extinguished a five acre burning refuse
pile in fifteen months. The technique involved decreasing the
slope of the flank to approximately 30° and compressing the surface
with a bulldozer. The pile was then covered with a three to five
foot layer of minus 1/4-inch refuse material. A dike was constructed
above the flank to prevent erosion. When the fire was determined to
be out, the temperature of the pile three feet below the surface was
less than 100°F.
In other experiments it was judged that minus 1/4-inch mesh refuse has
little tendency to ignite spontaneously. In addition, under labora-
tory conditions it was found that four times as much air passed through
3 1/2-inch mesh refuse than through 1/4-inch mesh refuse.
Field investigations have shown that reducing airflow into the pile
decreases the possibility of spontaneous combustion. Since most of
the air enters the refuse pile through the flank, a dumping technique
that reduces the flank area is preferred.
Although this technique has proved successful in testing, there is
at present no indication how widespread its use is in practice, or
how successful it has been.
Strip mining methods also often tend to liberate explosive gases such
as methane, hydrogen sulfide, and acetylene. However, if allowed
to be diffused into the atmosphere, the hazards due to possible
explosion are eliminated. If the gases are trapped in any manner,
the situation must be considered dangerous. The presence of hydro-
gen sulfide gas is easily detected by a strong odor of rotten eggs.
b. Open-Pit Mining
Open-pit mining is a common method used to extract consolidated ore
deposits that are located at or near the earth's surface. These
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7.12.6
mines are generally cut into and around a hill or mountain, or are
forged into the ground. They necessitate the removal of large
amounts of overburden before actual deposit recovery may begin.
Loose overburden is easily done away with, but all other rock must
be excavated by combinations of the four principal operations of
mining—rock drilling, blasting, loading, and haulage.
Drilling operations are employed to form blast holes. The type and
amount of explosives used are governed by the character of the rock.
Generally dynamite or ammonium nitrates are utilized. Loading is
done by very large capacity power shovels and draglines.
Haulage systems may utilize railroad cars, trucks, inclined skip
hoists, or belt conveyors.
The system employed is determined by the depth of the pit, the pro-
duction required, and the distance to the crusher or waste pile.
\
Open-pit mines are generally structured in benches or terraces. Each
bench must be wide enough to carry trucks or railcars on tracks and
not be buried in blasting operations. Sufficient space must also be
available for large power shovels. Benches are usually between 20
and 76 feet in width. Fifty feet may be considered an average figure,
with 30 feet regarded as a practical minimum. When the height of a
face or bank exceeds a safe and practical limit, another bench must
be created.
The general slope of the entire mine is measured by a line connecting
the outer edge of the top and bottom benches. The height of each face
and width of each bank must be such that the general slope of the mine
considering all terraces is between 22° and 60°. However, since
open-pit mines vary a great deal, slope criteria is extremely diffi-
cult to fix.
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7.12.7
Open-pit mining methods are used to produce iron, copper, sand and
gravel, gypsum, limestone and marble. The amount of overburden
removed is small as compared to the amount of product recovered. In
many cases, deposits are very thick resulting in a continuous mining
activity for decades.
Some open-pit mines are difficult to distinguish from strip mines.
This is especially true with certain brown iron ore and clay mines.
Iron ore pits are generally quite large and quite deep. Lean, low-
grade ore is often piled near the mine but is not responsible for
very much environmental pollution.
Copper pits consist also of large openings. They are few in number
and located in arid or semi-arid regions. Overburden and waste piles
occupy large surface areas as well. Care must be taken to prevent
their location above future ore reserves, yet close to the mine to
reduce transportation costs. The waste piles may become a source of
sedimentation and dust if preventive measures are not taken.
Frequently the waste pile contains small quantities of ore which is
recovered by leaching. Leaching is the extraction of a mineral from
an ore by selectively dissolving it into a suitable solvent as water
or acified water. It is therefore desirable that the ground under
the piles be impervious to leach water. Leaching is responsible for
approximately 12% of recovered copper ore in the United States.
Sand and gravel pits are generally more disturbing to the general
public than iron and copper mines. They are often located in or near
urban centers where blowing dust, unsightly appearance, and noise are
annoying problems, and steep banks are subject to dangerous slides.
Other sand and gravel operations may be in the vicinity of streams.
In these cases, significant amounts of sediment may be drained into
the waterways.
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7.12.8
2. Underground Mining
Distinctly subsurface deposits of minerals and ores are extracted by
underground mining methods. Metal mining practices are similar to those
used in coal mining except that the former are more diverse because of
the more numerous variations in ore deposits.
The primary mine plans of operation are stoping and caving. In stop-
ing, the ore-body is broken by drilling and blasting. There are
various stoping techniques but the method selected is dependent upon
the physical characteristics of the deposit in the mine, and economic
and safety factors. Caving is often applied to large ore deposits
with lower mineral content. A void is created below the ore-body, and
then support is withdrawn from below. Possibly with the aid of blast-
ing, the ore-body is collapsed allowing the ore to be drawn off.
Another technique involves the caving-in of covering waste matter
followed by the mining of the ore deposit from above.
In underground mines, special attention must be paid to the maintenance
of safe and healthful working conditions for workers. Among the factors
to be considered are mine support, explosives, air quality, and fires.
Except if included under state law, normal air quality requirements
require the absence of smoke and dust with moderate air temperatures.
In addition, coal mines require the elimination of methane. Good
quality air does not contain harmful amounts of physiological or
explosive contaminants.
The following gases are common to underground mines and should be
expelled as contaminants.
(1) Carbon dioxide is produced by the combustion and oxidation of
organic compounds. It is usually found in low, poorly ventilated
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7.12.9
(2) Carbon monoxide is not normally found in mine air. It is
formed as a result of mine fires, or from gas or dust explosions,
and the incomplete combustion of carbonaceous matter.
(3) Hydrogen sulfide is found near pools of stagnant water in poorly
ventilated mine sections, and is the product of the decomposition
of sulfur compounds.
(4) Methane is a natural constituent of all coals and may be found
in metal mines as well. This highly explosive gas is often
found in high, poorly ventilated cavities.
(5) Sulfur dioxide is commonly found only in sulfur mines. It is
usually present after fires in rich sulfur ore mines.
(6) Black damp is a term used to describe oxygen deficient mine
atmospheres that may contain many gases. It is produced by
oxidation and processes that use oxygen and give off carbon
dioxide.
In order to maintain mine safety, equipment is available to deter-
mine the presence of these contaminants in mines.
Dust in mines may be both a physiological and an explosive hazard.
The incidence of various forms of pneumoconiosis (dust-related
respiratory diseases) are common among miners, while coal dust
presents an extreme explosive danger. Preventive measures include
suppressing the dust with water, sprays, foam, or other agents.
Effective ventilation systems are required in mines in order to
dilute mine gases and render them harmless, and to extract or
collect dust particles from the mine. Various quantities of gas
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7.12.10
or dust may be expelled Into the ambient atmosphere, but no data
are presently available that will permit estimations of emission
rates. Investigations should be conducted on this emission source.
C. INSPECTION POINTS
Because mining operations present health hazards to workers and are the
basis of conservation issues, they are extensively supervised and inspected
by other Federal and state agencies such as the Bureau of Mines and state
divisions of mines. The purpose of this supervision is to minimize hazards
related to physical injury and to occupational exposures to air contaminants
within the mines (especially from CO, C02, S02> H2S, methane, etc.).
The field enforcement officer is interested in mining activities from a
number of standpoints:
1. Mines may be subject to equipment or activity inventory or source
registration inspections. The enforcement officer therefore must
become familiar with mine operations. All discrete surface and
internal mine operations should be inventoried and described.
2. Dusts, smoke and organic emissions will occur from surface operations
such as amassing spoil piles, loading and dumping, transportation
activities and coal preparation (see Section XIII). The emissions
and their sources should be surveyed, and notices written where
indicated. Mine owners should prepare and submit source reduction
plans.
3. Some mines will have greater emission potentials than others, due to
the type of mine and nature of the deposits (e.g., sulfur deposits).
Mine operational methods, products and capacities should be care-
fully shown on reports.
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7.12.11
A. Ventilation systems should be checked and evaluated both from the
standpoint of mine safety and emissions to the atmosphere from surface
outlets. If necessary, air samples should be taken for analysis, or
source tests conducted.
5. The enforcement officer should be aware of the hazards that may be
present to himself and others.
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7.12.12
REFERENCES
1. Stahl, R. W. Survey of Burning Coal-Mine Refuse Banks. Bureau of Mines.
Information Circular, No. 8209. 1964.
2. Myers, J. W., J. J. Pfeiffer, E. M. Murphy, and F. E. Griffith. Ignition
and Control of Burning of Coal Mine Refuse. Bureau of Mines. Report of
Investigations No. 6758. 1966.
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7.13.1
XIII. COAL PREPARATION PLANTS
A. DESCRIPTION OF SOURCE
Coal preparation plants clean, blend, size, dry and store raw coal which when
mined contains 20 to 50% refuse material of undetermined size. Materials
handling, sizing, drying and storage procedures and associated air pollution
control problems are similar to those of many industries where large
quantities of rock-like material are processed. Coal preparation plants
also will play an increasing role in providing low sulfur coal in the
future.
Air pollution control problems from coal preparation plants are sizeable.
Among them are dust from the many drop points, conveyors and open storage
piles; smoke, H S, sulfur oxides and other odors from burning refuse
piles; particulate emissions from thermal dryers, de-dusters and other
cmmbustion related processes.
B. PROCESS DESCRIPTION
The preparation of coal for use by utilities or the metallurgical industry
divides into two major air pollution control problems: (1) dust and
particulate matter from the many mechanical and thermal processes in the
plant and (2) gas, odors and particulates emitted from burning refuse piles.
Coal preparation plants vary in capacity and preparation methods. Common
processes which create dust and particulates are cleaning processes, sizing,
drying, refuse and storage.
1. Cleaning Processes
The principal reason for cleaning coal is to reduce ash content and
some amount of surface sulfur. Sulfur, in the form of pyritic sulfur,
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7.13.2
(sulfur combined with iron), organic sulfur (sulfur combined with coal)
or sulfate (calcium sulfate) and mineral matter are present in raw
coal. Ash-forming mineral matter can be removed by common cleaning
methods but the inherent impurities—finely divided pyrite, organic
sulfur and inherent mineral matter—cannot be removed.
(2)
The general cleaning methods in use in the United States are:
• Cleaning at the mine face
• Separating impurities manually or mechanically
• Froth flotation
• Gravity concentration
a. wet
b. dry or pneumatic
Mechanical, strip and auger mining account for most of the coal mined
in the United States. Manual cutting and loading in which the
impurities in the coal are reduced at the source by selective cutting
is still performed. This process is known as cleaning at the mine
face. Increasing use of mechanical devices, however, has greatly re-
duced the need for this procedure.
The earliest method of cleaning coal, hand picking, is still practiced
along with mechanical assistance from shake tables. After the initial
screening operation, oversized coals, 4 inches and larger, are sent
to the picking table where the impurities are manually removed from
the stream coal. Picking facilities include belt and apron conveyors,
shaking tables and occasionally chain conveyers. Since hand picking
can leave as much as 50 to 60% coal in the refuse, it is economical to
crush the refuse to reclaim the coal by mechanical means. An example
of a mechanical device for removing flat impurities from coal such as
slate and shale, which can be installed on shaker screens, is shown in
Figure 7.13.1.
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7.13.3
COAL
SLATE AND SHALE
Figure 7.13.1. REJECTION OF FLAT REFUSE BY SLOT SHAKER
(SOURCE: THE BABCOCK AND WILCOX CO., Reference 2.)
Froth flotation supplements other cleaning processes by recovering
coal fines from coarse coal cleaning. Flotation media may consist of
alcohols and an added frothing agent. This process is most effective
for 48 mesh and smaller material. The mixture is agitated by air
injection with the coal particles adhering to the bubbles and the slate
and shale sinking to the bottom of the vessel and removed as waste.
The principles of gravity concentration apply to wet and pneumatic
systems for removal of impurities based upon differences in specific
gravity (see Table 7.13.1). Wet systems in use in the United
(2)
States include:
• Launders
• Jigs
• Classifiers
• Dense-media method
Table 7.13.1. SPECIFIC GRAVITIES OF COAL AND IMPURITIES
Material Specific Gravity
Bilumiiious ^o.tl 1.12 - 1.35
Bono coal 1.3.3-1.7
Carbonac'coiH ilutle 1.6 -2.2
Shale 2.0 -2.6
Clay J.8 -2.2
Pyritc 4.8 -5.2
(SOUJICE: THE BABCOCK AND WILCOX CO., Reference 2.)
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7.13.4
a. Launders
In launders, shown diagramatically in Figure 7.13.2, coal is fed
into a trough where high velocity water is introduced. The stratification
of coal, middlings and slate occur in the steep section of the device.
As the slope decreases the velocity of the mixture decreases allowing
the heavier particles to settle and the cleaned coal to be removed.
,-RAW.COAL FEED
SLATE AND
HIGH % ASH
MIDDLINGS
SOME SLATE AND MIXTURE OF
HIGH AND LOW % ASH MIDDLINGS
(REV/ASHED OR FOR REWASHING)
Figure 7.13.2. DIAGRAM OF RHEOLAVEUR COAL LAUNDER WITH TWO RHEOBOXES
(SOURCE! THE BABCOCK AND WILCOX CO., Reference 2.)
b. Jigs
Coal on screen plates is subjected to pulsating streams of water in
a device known as a jig. The Baum jig, which uses air and water to
produce pulsation can operate over a wide range of coal sizes while
some types of jigs depend upon careful control of coal size in the feed
for good classification results. An example of a Baum jig is shown in
Figure 7.13.3. This system operates in two stages. Primary
separation takes place at the feed end, while quality coal and middlings
go to a second compartment where the quality coal is separated and the
middlings are recycled.
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7.13.5
Figure 7.13.3. McNALLY NORTON STANDARD WASHER
(SOURCE: MC NALLY, Reference 3.)
Dense-media
The dense-media process uses a mixture of water and sand or magnetite,
Fe.,0, , proportioned to give the desired specific gravity to float coal
and allow the waste material to sink. Figure 7.13.4 is a cross-
section of a McNally Tromp Bath using the laminar flow principal to
provide strata of equal density medium for uniform settling. Machines
that provide more than one stage of settling, when required, may also
be used.
d. Classifiers
Pneumatic classification systems process coal that has already been
screened and is preferably low in moisture. Jigs and tables are used
with air as the fluid instead of water. Air, blown up through the
table suspends the lighter coal while the heavier waste material is
caught in grooves between the rifles on the table bottom. The table
is tilted and agitated so that the waste settles and the coal and
middlings remain on top. The air used in this process is passed
through cyclones and baghouses for fine dust collection.
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7.13.6
Figure 7.13.4. CROSS SECTION McNALLY TROMP BATH
(SOURCE: MC NALLY, Reference 3.)
De-dusting usually occurs after the raw coal has been screened. Coal
dust rather than refuse is removed in this process. The dust clinging
to the lumps falls free as the coal drops into the de-duster. A
stream of air with a velocity high enough to entrain the dust—48
mesh—is forced counter to the flow of coal. The resultant air and
coal dust mixture is run through cyclones and baghouses to remove the
fines which can be loaded with the product or burned in any of the
furnaces used in coal drying.
2.
Run-of-the-mine coal must be broken, sized and screened before cleaning
or washing. These processes, along with handling, loading, storage
and general housekeeping, account for most of the dust emissions from
coal cleaning plants. Screen sizes generally conform to ASTM Standard
D431, designating the size of coal from its analysis, but Bituminous
coal sizes have not been well standardized. The following are common
(2)
designations.
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7.13.7
• Run-of-Mine. Run-of-mine is shipped without screening. It is
used for both domestic heating and steam production.
• Run-of-Mine (8 in.). This is run-of-mine with oversize lumps
broken up.
• Lump (5 in.). This size will not go through a 5-in. round hole.
It is used for hand firing and domestic purposes.
• Egg (5 in. x 2 in.). This size goes through 5-in. and is retained
on 2-in. round-hole screens. It is used for hand firing, gas
producers, and domestic firing.
• Nut (2 in. x 1-1/4 in.). This size is used for small industrial
stokers, gas producers, and hand firing.
• Stoker Coal (1-1/4 in. x 3/4 in.). This size is used largely for
small industrial stokers and domestic firing.
• Slack (3/4 in. and under). Used for pulverizers, cyclone furnaces,
and industrial stokers.
• Several other sizes of bituminous coal are prepared by different
producers, especially for domestic-stoker requirements.
Definite sizes of anthracite coal are standardized and shown in Table
7.13.2.
Table 7.13.2. COMMERCIAL SIZES OF ANTHRACITE
(Graded on Round-Hole Screens)
(SOURCE: The Babcock and Wilcox Co., Reference 2)
Diameter of Holes, Inches
Trade Name
Broken
Egg
Stove
Nut
Pea
Buckwheat
No. 1
No. 2 (Rice)
No. 3 (Barley)
No. 4
Through
4^
3M to 3
2A
IK
«
A
A
A
A
Retained On
3li to 3
2A
}%
iJ
A
A
A
A
3
0 -f
-------
7.13.!
The broken, egg, stove, nut, and pea sizes are largely used for hand-
fired domestic units and gas producers.
Buckwheat Nos. 1 and 2 are used in domestic stokers and hand-fired
steam boilers. Buckwheat Nos. 3 and 4 are used for traveling-grate
stokers, and No. 4 is also burned in pulverized form.
a. Breakers and Crusher
Size reduction is usually accomplished in two stages—breaking and
crushing. Breaking the run-of-the-mine coal, removing rock and
tramp iron is accomplished by a rotary equipment, such as the
Bradford Breaker, shown in Figure 7.13.5. As the coal enters
the perforated drum it is raised by the rotary motion (about 20 RPM)
and falls breaking the lumps into smaller sizes that pass through
the perforations. This process does not produce large quantities
of fines.
RECEIVING
RING
DISCHARGE
REMOVABIP
DISCHARGE
rTf
Figure 7.13.5. BRADFORD BREAKER, FOR USE AT MINE AND PLANT
(SOURCE: The Babcock and Wilcox Co., Reference 2)
The next class of equipment is crushers which, by mechanical action,
further reduces the size of the coal. They are:
• Single Roll crushers which produce large quantities of fines—
Figure 7.13.6.
• Double Roll crushers which produce small quantities of fines—
Figure 7.13.7.
-------
7.13.9
Hammer-mill crushers which produce large quantities of fines-
Figure 7.13.8.
Ring coal crushers which produce large quantities of fines—
Figure 7.13.9.
ADJUSTABLE
PLATE
Figure 7.13.6. SINGLE-ROLL COAL CRUSHER—DIAGRAMMATIC SECTION
(SOURCE: The Babcock and Wilcox Co., Reference 2)
Figure 7.13.7. DOUBLE-ROLL COAL CRUSHER—DIAGRAMMATIC.SECTION
(SOURCE: The Babcock and Wilcox Co., Reference 2)
-------
7.13.10
Figure 7.13.8. HAMMER-MILL COAL CRUSHER—DIAGRAMMATIC SECTION
(SOURCE: The Babcock and Wilcox Co., Reference 2)
ACCESS
DOOR
Figure 7.13.9. RING COAL CRUSHER—DIAGRAMMATIC SECTION
(SOURCE: The Babcock and Wilcox Co., Reference 2)
-------
7.13.11
b. Screening
Screens provide another method of sizing. The bar screen or
grizzly is used at the mines to size coal by gravity. The bars
are sloped to allow the larger size lumps to traverse the screen
while the smaller sizes fall through the openings.
Revolving screens are similar to rotating breakers except that
they are inclined. Since the coal has a tendency to break in this
type of action it is not customary to use coal sizes larger than
3 inches.
Shaker screens are usually sloped downward from the feed end to
the discharge end. Again the oversize coal rides down the shaker
and the desired size falls through the holes in the screen. This
process is also used for dewatering washed coal.
Vibrating screens are also sloped from feed to discharge end.
The high frequency vibration continually loosens the feed from
the openings which aids in dewatering.
These processes produce significant quantities of fine dust. In
addition to the use of local exhaust systems to capture dust, water
sprays with wetting agents help to control emissions from these
sources.
Mechanical drying or dewatering devices have been described above. The
greatest single source impact on air pollution in coal preparation
plants is thermal drying. Thermal drying is a process of accelerated
evaporation. Unless the dry product can be kept below its critical
-------
7.13.12
ignition temperature of 130 to 150°F, fires will result in transit
from spontaneous combustion. Coal dryers all use direct heat transfer
where the combustion gases plus tempering incoming air come in direct
contact with the material.
Five principal methods for drying coal used in the United States
include :^
• Rotary dryers
• Screen type dryers
• Cascade dryers
• Suspension type dryers
• Fluid bed dryers
a. Rotary Dryers
The rotary dryers resemble kilns and may be parallel or counterflow
(air and coal), single or double shell and louvre types. These are
the older kind and better known to the trade. These cylindrical drums
are pitched longitudinally about 3/8 inch per foot, causing the
material to travel slowly from the feed to the discharge end. The
drums may be 8 to 10 feet in diameter and 65 to 80 feet long.
Lifting vanes drop the coal through the hot gases. The inner shell
of the double shell type carries the hot gases to the discharge end
of the dryer where they turn and reverse their direction in direct
contact with the counter flow of the solids.
b . Screen Type Dryers
The screen type dryers carry the coal on reciprocating screens which
accomplish evaporation by passing hot gases through the bed. These
can be down-draft or up-draft; the down-draft type affords the
opportunity of some mechanical drainage. These are designed
for coal with top sizes up to 2 inches and a bottom size of 1/2 mm.
On one model, an induced draft fan draws the hot gases down through
-------
7.13.13
the screen decks and the flow is automatically alternated so as to
transfer the suction from the first to the second screen sections
every second. This arrangement causes the full force of the gas
pressure to squeeze the bed, thus accelerating mechanical drainage
c. Cascade Dryers
Cascade dryers (Figure 7.13.10) accomplish their heat transfer by
introducing hot gases through louvers which are arranged to cause
the coal to cascade. The coal forms a curtain of flowing coal and
hot gases are passed through it to impart heat for evaporation.
This type is most widely used for fine coal (3/8 x 0) but coals up
to 1-1/2 x 0 have been dried successfully.
Figure 7.13.10 not available for this publication.
-------
7.13.14
d. Suspension Type Dryers
Suspension-type systems (Figure 7.13.11) introduce the wet coal
into a moving hot stream of gases which pneumatically convey and dry
the material in transit to the dust collector where the coal is
separated from the moisture-laden spent gases. This class of dryers
is ideal for extremely fine coal with the top size not over 3/8 inch.
1
10 AIMOttHtll CK
Figure 7.13.11. SUSPENSION-TYPE FLUSH DRYING SYSTEM (THERMAL DRYER)
(SOURCE: RAYMOND DIVISION, COMBUSTION ENGINEERING,
CHICAGO, ILLINOIS)
-------
7.13.15
e. Fluid Bed Dryers
In fluidized bed dryers (Figure 7.13.12) the wet coal is fed onto
a perforated or bar type retention plate where hot gases are blown
or drawn through the bed. Fluidized beds are characterized by a
loose pulsating mass which is kept porous by the action of the gas
stream.
-—~
Figure 7.13.12. McNALLY FLOWDRYER
(SOURCE: McNally, Reference 3)
The air pollution control problem from coal drying does not differ from
most drying operations where the hot products of combustion pass
through wet material which contain fine particles of product.
Coal is the primary fuel used to produce the hot gases which evaporate
the moisture from the product (see Chapter 6, Section II). Fuel oil
-------
7.13.16
is used at some installations especially during startup operations.
Primary dust collectors are cyclones followed by wet collectors and
demisters. Conventional scrubbers have not proven effective on thermal
dryers but high energy venturi scrubbers with demisters have reduced the
grain loading in several installations from a high of 5.5 grains per
standard cubic foot to 0.04 grains per standard cubic foot. Bag-
houses are not used in these systems because of fire hazards.
4. Refuse
Coal refuse piles are a constant source of combustion and dust related
air pollution control problems. Some of these piles cover acres of
ground and contain hundreds of tons of material. Spontaneous
combustion, carelessness or deliberate action are the general causes
of refuse pile fires. Often trash not resulting from coal preparation
contributes to the potential fire hazard at the refuse dump site. A
survey made in 1964 indicates that there are approximately 500
burning piles in 15 states; approximately 150 in Pennsylvania and 200
in West Virginia. Emissions, in addition to blowing dust from the
piles are H S, S0_ and smoke. Other noxious gases which result from
burning piles include CO, ammonia and carbon disulfide.
Air pollution control and safety measures include proper construction
of the pile by compaction and sealing to prevent air circulation and
ignition. Some methods of controlling a burning coal refuse dump
are:(1)
a. Digging out the fire or isolating the fire area by trenching.
b. Pumping water onto the fire areas and immediate vicinity.
c. Applying a blanket or cover of incombustible material such as
limestone dust, shale dust, or slag dust over the fire area.
-------
7.13.17
d. Injecting a slurry of rock dust or other incombustible material
into the fire area through drill holes. Grouting with cement is
also practiced.
e. Spraying water over the area.
5. Coal Storage
Coal is stored in huge open piles and in silos or underground
facilities. As in refuse storage there are two primary air pollution
control problems, blowing dust and combustion products. Anthracite
coal is very safe to store in large piles. These piles should be
(2)
capped with larger sizes to prevent loss of fines due to wind.
Bituminous coal should be packed and sealed as a fire prevention
technique. Promising tests have been made using water soluble
organic polymer as a spray on outdoor piles of crushed coal to form a
hard surface to reduce wind blown dust. Test piles have withstood
winds as high as 60 MPH and numerous freeze thaw cycles.
C. EMISSIONS AND CONTROLS
The largest single source of dust, smoke and particulates in coal
preparation plants are the thermal dryers. Dust loading of the effluent
from a dryer operating at 150°F, 180 to 120,000 cfm with the feed 1/4"
centrifugal coal and filter coke, can be in excess of 2.5 grains per cubic
foot with a particle size distribution of:
0 to 2M 55% by weight
2 to 5M 33% by weight
5 to 10M 11% by weight
10 +M 1% by weight
Cyclone separators can eliminate high percentages of the larger particle
sizes and serve as the first stage in a particulate recovery train. Dark
-------
7.13.18
brown emissions of 100% opacity are visible from plants using cyclones
and low resistance scrubbers. Effective emission reduction from thermal
drying requires, in addition to cyclones, pack towers or venturi scrubbers
with demisters.
D. INSPECTION POINTS
1. Screening, Crushing and Breaking
Fines escaping from ventilation systems serving the equipment from these
processes constitute a major air pollution control problem. The inspector
can readily determine the effectiveness of sprays to suppress dust
and hooding and local exhaust systems to pick up the dust generated.
Exhaust systems and cyclones can become plugged by caking of fine
coal which will add to the system back pressure thus reducing hood
indraft velocity and reducing the cyclone collection efficiency.
2. Conveyors and Elevators
Long open conveyor belts carrying dry material or appreciable
quantities of fines can be a significant source of dust. All drop
points onto or off of open belt conveyors should be evaluated for
dust emissions. Special attention should be paid to railroad car
loading and dry coal storage activities.
3. Pneumatic Classifying and Dedusting
These processes use high velocity air streams which entrain sizeable
quantities of fines which are collected by cyclones and a baghouse
in series. An increase in resistance to flow caused by plugging the
exhaust lines and dust collectors will cause a decrease in pickup from
the ventilation system resulting in dust emissions or poor pickup
of dust at the source. Since the material collected is a useable
product the operator will make certain that the dust control equipment
is properly maintained.
-------
7.13.19
4. Thermal Drying
In order to determine the effectiveness of air pollution control
equipment on thermal dryers, stack tests should be required. The
inspector can determine if fine material, e.g., 48 mesh, is being used
as furnace fuel which experience has shown contributes to the particulate
emissions. Because of this, some operators intend to go to oil-fired
furnaces full time.
E. ENVIRONMENTAL OBSERVATIONS
Dust and particulate matter will be found in areas adjacent to coal
preparation plants when rigid air pollution control programs are not
mandatory. Meteorological conditions will determine how far and in what
direction fine dust particles will travel. If burning refuse is a
problem, the probability of odor complaints will be high.
The inspector should determine the direction of the prevailing wind so
that he may station himself properly to make readings from the dryer
exhaust stacks. This will also help to establish a gross dust fallout
pattern and a probable pattern for nuisance complaints. One method
of making these determinations is to place dust fall jars at the plant
property lines. In-plant observations should focus on housekeeping since
there usually is an abundance of fine coal particles which can be disturbed
and become air borne by the large volume of truck traffic in and out of
the plant.
-------
7.13.20
REFERENCES
1. Sussman, V. H. Nonmetallic Mineral Products Industries. In: Air Pollution,
Vol. Ill, A. C. Stern (ed.). New York City, Academic Press, 1968.
2. Steam its Generation and Use. The Babcock and Wilcox Co., 37th Edition.
3. Coal Preparation Manual. McNally Pittsburg Mfg. Corp., #570.
4. Spicer, T. S. Thermal Drying Enhances Coal Value. Coal Utilization.
Aug. 1958.
5. Journal of Environmental Health. Vol. 33, No. 4. March and April, 1971.
p. 523.
6. Gleason, T. Wet Scrubbing of Coal Dust from Thermal Dryers with Peabody
Scrubber. Transactions. Society of Mining Engineers. March 1963.
-------
7.14.1
XIV. FERTILIZER INDUSTRY
A. NATURE OF SOURCE PROBLEM
For the purposes of this chapter we will define the fertilizer industry as
being limited to the chemical fertilizers. Only very limited amounts of
fertilizer are derived from natural waste products at the present time in
the United States and most of this originates from activated sludge plants
operated in connection with municipal sanitary sewage treatment plants.
The practice of using fertilizers dates back to antiquity. As early as
200 B.C. the Carthaginians were said to have used bird dung on soil as a
source of phosphatic materials. ' Over the centuries replenishment in the
soil of this essential element was aided by the use of bones, fish and bat
and sea bird guano. In the nineteenth century a number of individuals
experimented with methods increasing the solubility of the phosphate sources
and in 1842 a British patent was issued to John B. Lowes on the process of
treating bone ash with sulfuric acid.
The other two major constituents of fertilizers—nitrogen and potash—were
also first used as natural waste products. Nitrogen sources included oil
seed meals, fish by-products, tankage, and dried blood. Since the advent
of chemical fertilizers these natural materials are more valuable as direct
animal feed supplements. Potash was probably first utilized in the form of
wood ash.
Present day compounds used as sources of phosphates, nitrogen, and potash
result from the processing of minerals or from direct chemical synthesis.
These manufacturing processes can produce a variety of gaseous and particu-
late air contaminants generally associated with the chemical fertilizer
industry.
-------
7.14.2
Two major sub-groupings of the chemical fertilizer industry are of particu-
lar importance as air pollutant sources and will be considered in more
detail in this chapter. These are (1) the phosphatic compounds produced
from phosphate rock and (2) ammonium nitrate produced by the reaction of
ammonia with nitric acid.
1. Phosphate Fertilizers
The air pollutants emanating from the phosphate fertilizer industry are
of two distinct classes: the first being particulates originating from
the crushing, grinding, drying, and bulk handling of rock ore, benefici-
ated rock and product materials; the second being gaseous contaminants
evolved during the acidulation and curing of phosphate rock to produce
phosphoric acid, superphosphate and triple superphosphate. Other
gaseous compounds may be released from the secondary treatment of super-
phosphates such as in the combined ammoniating and granulation operation.
While the particulate losses may result in visible plumes and settleable
dusts, the principal air pollution problem associated with the phosphate
fertilizer industry is that related to the evolution of gaseous fluorine
compounds during the acidulation of phosphate rock. As will' be described
in more detail later, fluorine compounds are also present in most phos-
phate bearing mineral formations used commercially. The gaseous com-
pounds thought to be most predominant in the reaction products of the
acidulation process are hydrogen fluoride (HF) and silicon tetrafluoride
(SiF4).
These gaseous fluoride compounds damage citrus, gladioli and truck
( 2}
crops, and can deposit fluorine compounds on cattle forage. Should
cattle ingest excessive quantities of fluorides from this feed source,
they may develop tooth mottling and decay (fluorosis), skeletal defects
such as lameness (exotosis), loss of appetite and emaciation.
-------
7.14.3
Gaseous sulfur oxides and nitrogen oxides may also be lost from phos-
phate fertilizer processes particularly during the use of sulfuric and
nitric acids where there is a significant organic content to the
material being treated. Ammonia and ammonium chloride may also be
(3)
evolved during the ammoniation of phosphate fertilizers.
2. Ammonium Nitrate
The possible air contaminants arising from the manufacture of ammonium
nitrate from the reaction between ammonia and nitric acid are: ammonia,
nitric oxide, and ammonium nitrate fume and dust. The principle problem
has been the objectionable haze formed as the result of water condensing
on finely divided ammonium nitrate fume lost during prilling operations
(production of pellets by counter-current flow of air against falling
spray of molten ammonium nitrate).
(4)
Payne and Glikin state that at relative humidities above 60% at a
temperature of 30°C water will condense on ammonium nitrate nuclei,
causing a growth in particle size so as to result in a visible haze.
Scorer has also evaluated the environmental impact of a proposed
British ammonium nitrate plant and predicted a fallout rate of 400
2
tons/mi /mo within 2/3 mile of the prilling operation.
B. PRODUCTS DESCRIPTION
1. Phosphate Fertilizers
The various types of phosphate fertilizers are produced commercially
from mineral deposits of phosphate rock. Although major deposits are
found at numerous locations throughout the world a significant propor-
tion of commercially recoverable rock is found in the United States.
At the present time the world's center of phosphate production lies in
2 (2 3)
500 mi area of central Florida. ' The deposits are of the sedi-
mentary pebble type and largely consist of phosphate in the form of
-------
7.14.4
fluorapatite—3 [Ca (PO ) ] • CaF2< This form of phosphate is rather
insoluble, thus accounting for the stability of the deposits.
Commercial deposits of phosphate rock are also found in Tennessee,
North Carolina, Idaho, Montana, Wyoming and Utah. These deposits
are also of the sedimentary type, but vary in depth, phosphorous assay,
and amount of organic content.
Phosphate rock is usually mined using open strip-mining techniques, with
the rock being sluiced into pipes carrying the rock slurry to beneficia-
tion plants. Here the ore is upgraded by separating undesired sand,
clay and other non-phosphate minerals by a variety of physical and
flotation processes. Up to this point, the air pollution problems are
minor in nature.
The beneficiated rock must be dried and pulverized before further treat-
ment. These operations may result in major atmospheric losses of dust
unless adequate controls are used. In some cases calcination is used
to reduce the content of organic mattei
largely outside of the Florida region.
to reduce the content of organic matter. This applies to deposits
Phosphate in the form of fluorapatite is very insoluble, thus reducing
its availability to the soil if used directly. The success of the
phosphate fertilizer industry depended upon the development of technology
to produce a form of readily available phosphate. That process which has
been longest in use is that which involves the acidulation of phosphate
rock (fluorapatite) with sulfuric acid to produce normal superphosphate
(acid phosphate). This process in one form or another has been in use
-------
7.14.5
for over a century. The simplified reaction involved is shown below:
+2HF
The hydrogen fluoride evolved may react with silica present to form
silicon tetrafluoride:
4HF+SiO. -»- SiF.+2H00
2 42
Fluosilicic acid may also be formed as a result of reactions with
water:
3SiF.+4H_0-^2HnSiF.+Si(OH).
42 26 4
A great deal has been written about these reactions and there is not
(1 3)
total agreement about them or the order in which they occur. '
However, it is a fact that gaseous fluorine compounds are emitted as a
result of the acidulation process, thus giving rise to a significant air
pollution problem. Figure 7.14.1 shows a simplified flow sheet for the
production of normal superphosphate.
Depending upon the specific process, the reactions in the acidulation
step do not take place immediately, but are completed in the curing
operation which may take a number of weeks or months. During the
curing operation, fluorine compounds continue to be evolved and in the
past have not been usually controlled. In fact, in a study conducted by
Cross and Ross , fluoride emissions \
quantities from gypsum settling ponds.
Cross and Ross , fluoride emissions were shown to arise in significant
Under the stimulus of the demand for more concentrated forms of ferti-
lizer, a process for,the acidulation of phosphate rock with phosphoric
acid was developed. This process results in a product known as triple
-------
7.14.6
Figure 7.14.1 PRODUCTION OF NORMAL SUPERPHOSPHATE
(SOURCE: HELLER, etal., Reference 6)
-------
7.14.7
superphosphate. The assay for available phosphorous is about 2-1/2
times that of normal superphosphate because the active ingredient is
not admixed with calcium sulfate. This process is shown in Figure
7.14.2. Many of the air pollution problems in the manufacture of triple
superphosphate are very similar to those of normal superphosphate pro-
duction, including the evolution of gaseous fluorides.
Although not discussed in this chapter the integrated production of
sulfuric acid and phosphoric acid (particularly by the wet process) are
unalterably bound up with the phosphate fertilizer industry. Sulfuric
acid manufacturing is, however, discussed in Section VII and the wet
process for the production of phosphoric acid essentially involves the
more complete acidulation of phosphate rock with sulfuric acid with the
accompanying filtration of calcium sulfate from the phosphoric acid
formed.
A variety of product mixes are prepared following the actual production
of superphosphate or triple superphosphate. In many cases the super-
phosphate is sold as "run of the pile" (as it will not attempt to meet
a guaranteed assay) or is ground and bogged to specifications. Increas-
ingly, however, granulated product is produced which sometimes has been
ammoniated or had other forms of nitrogen, such as urea, added. The
granulation processes involve the use of other mixing and drying steps
thus increasing the opportunity for dust and fume production. On the
other hand, if combined ammoniation is used, the acidulation reaction
is terminated and gaseous fluoride emissions are not evolved after the
acidulation process itself. On the other hand, ammonia and ammonium
chloride may be lost from the ammoniation process.
-------
7.14.8
[AMMONIA.FLUORIDE AND PAHTICULATE)
PHOSPHORIC ACID
EXIT
PflRTICUt-ATE,FL(JOR!DEjWD SULFUR OXIDE
(PflRTICULATE)
PHOSPHATE ROCK
Figure 7.14.2 PHOSPHORIC ACID ACIDULATION PROCESS
(SOURCE: HELLER, etal., Reference 6)
-------
7.14.9
2. Ammonium Nitrate
This important source of nitrogen in fertilizer is produced by the
reaction between ammonia and nitric acid to form ammonium nitrate in
solution:
NH.+HNO,-*-NH.NO,
33 43
After concentration of this solution by heating and evaporation, solid
ammonium nitrate is produced by "prilling," or vacuum crystallization.
Another process known as the Stengel process mixes preheated ammonia
and nitric acid in a packed reactor where the heat of reaction is
sufficient to vaporize the water in nitric acid feed, thus directly
producing molten ammonium nitrate which is separated from the unreacted
materials and water vapor by a centrifugal separator. This molten
nitrate is ultimately distributed on an endless stainless steel water
cooled belt where it solidifies. Vapors from the separator are recov-
ered by condensation and scrubbing.
The "prilling" process is the more common in the United States and is
shown in Figure 7.14.3. As mentioned earlier, the prilling process
involves the spraying of concentrated ammonium nitrate solution down
through the top of a tower through a rising stream of air. The droplets
solidify and harden during their fall resulting in spherical pellets
called prills which may be bagged after drying futher on a conveyor to
less than 0.5% moisture. Product in this form may be kept in moisture
proof bags for more than a year without caking.
The loss of fines in this process is very low but some ammonium nitrate
fume may be discharged. If ammonia is added in excess, the possibility
of nitric oxide loss is nearly eliminated and the ammonia may be recov-
ered by scrubbing.
-------
Nitrogen Oxides, NH.NO , NH
Ammonia
Nitric Acid
Neutralizer
Evaporator
Off Gases
Water
Scrubber
•Air
Product Ammonium Nitrate
Prilling Tower
Figure 7.14.3 FLOW DIAGRAM FOR THE MANUFACTURE OF AMMONIUM NITRATE
-------
7.14.11
The damages of fire or explosion can exist with ammonium nitrate so
that great care must be taken in bulk handling. One approach has been
the use of urea as an admixture to inhibit oxidation of ammonium
(4)
nitrate. Urea has been increasingly utilized by itself or as urea-
forms as a fertilizer substance. Ureaforms are reaction products of
urea and formaldehyde which release nitrogen very slowly.
3. Control Methods
The control of emissions from chemical fertilizer production basically
involves the control of soluble gases, principally fluorine compounds,
and finely divided particulate matter. Fluorine compounds are usually
removed by water scrubbers which have been stated to range in efficiency
from 92-97%. This scrubber water may go to waste or be reclaimed for
value of the fluorine contained. This latter approach is increasingly
being used.
Particulate matter may be recovered by cyclones, cloth filters and high
efficiency scrubbers. Because of great numbers of possible emission
points from both phosphate and ammonium nitrate production, Table 7.14.1
has been prepared which lists emission sources, types of emissions, and
possible means of control.
In general, a number of principles should be applied when considering
control approaches for fertilizer plants. For the proper control of
dusts, all conveyors, feeders, hoppers, bins, and size reduction
equipment should be closed and properly vented to the dust abatement
equipment. Adequate ventilation velocities should be based upon
accurate knowledge of the particulate size distribution involved.
Gaseous fluoride emissions should be collected properly and a determina-
tion made of all possible emission points. Where curing operations are
-------
Table 7.14.1 CONTROL OF EMISSIONS FROM FERTILIZER MANUFACTURING
Source
Nature of Emissions
Control Method(s)
Phosphate Fertilizers
Rock Drying
Rock Crushing and Grinding
Acidulation
Curing (denning)
Granulation
Ammoniation
Nitric Acid Acidulation
Superphosphate Storage and
Shipping
Ammonium Nitrate
Reactor
Prilling Tower
Rock Dust
Rock Dust
HF, SiF
HF, SiF
Product Dust
NH NH Cl,SiF ,HF
NO , Gaseous F Cpds.
Product Dust
NHn, NO
3 x
NH4NO Fume
Cyclones and Wet Scrubber
Baghouses
Water Scrubber
Water Scrubber
Cyclones and Wet Scrubbers
or Cloth Filters
Cyclone, Elect. Precip.,
Cloth Filters, Highest
Scrubber
Scrubbers, Addition of Urea
Cyclones, Cloth Filters
Scrubbers
Reduce Formation by Control
of Conditions
-------
7.14.13
used, they should be conducted inside enclosures through which air can
be recirculated and passed through a scrubber. Consideration should be
given to the reduction of losses from gypsum ponds.
C. INSPECTION POINTS
General
The chemical fertilizer industry has been shown to be a variety of
separate industries ranging greatly in complexity, types of operations,
and nature of potential environmental impact. A "fertilizer plant1' may
range from one engaged in the relatively simple process of blending and
packaging bulk dry ingredients to a large scale integrated operation
involved in mining raw materials; crushing, grinding, and drying these
materials; conduct of chemical processing; and finally blending and
packaging of finished product.
Because of the seasonal demand for fertilizer, plant operation often
follows a similar cyclic pattern with maximum production just prior to
peak demand. Nearly every type of air pollution control equipment may
be found in use in the fertilizer industry, ranging from inertial
collectors through fabric filters, water scrubbers and electric precipi-
tators.
The factors listed above require a varied approach to the overall field in-
spection and abatement operations. In relatively simple cases, straight-
forward inspection procedures involving primarily an inspection of the
source premises may be adequate. In the case of very large integrated
plants where there are potential toxic emissions a team approach may be
desirable. In addition to the regular field abatement personnel
specialists in chemistry, process and control engineers, meteorologists,
and plant and animal scientists may be called upon.
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7.14.14
2. Environmental Surveillance
The most significant efforts in environmental surveillance will be con-
cerned with the phosphate fertilizer industry as a result of the poten-
tial for the emission of gaseous fluoride compounds and in some cases
sulfur dioxide, hydrogen sulfide, and nitrogen oxides. Other candidates
for special surveillance activities would include the evaluation of the
deposition of particulates from many of the fertilizer processes, and
plume formation from ammonium nitrate plants.
In the case of fluoride emissions from phosphate fertilizer production
two types of surveillance activities may be employed. The first involves
the determination of possible damage to susceptible receptors, i.e..,
citrus, row crops, ornamentals and grazing animals (through fluorides
deposited on forage). This type of activity will require extensive
training of field personnel and the cooperation of land users sustaining
damage at the minimum. Desirably, other resource individuals such as
farm advisors, veterinarians, and university personnel will be utilized
(2)
as well. Techniques such as this have been described by Hendrickson.
Environmental surveillance may also be conducted by sampling for sus-
pected emissions in the ambient atmosphere. Most surveys for atmospheric
fluorides have been conducted by the use of static sampling utilizing
lime or calcium formate impregnated papers, but continuous analyzers have
(2 7)
been used as well. '
3. Plant Inspection
a. Interview
As in the case of any complex pollution source, the interview of
plant management should include the obtaining or verification of
process descriptions, flow sheets, equipment lists and management's
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7.14.15
estimate of emission inventories. Information on process variations
and production scheduling should be obtained. Should source test
data be available it should be secured and examined. Statements
from plant management on plant operations, their assessment of
pollution problems and plans for control should be requested.
b. Physical Inspection
The inspector should obtain and/or verify the plant layout and equip-
ment location. He should observe each process step. Several visits
may be necessary before a representative set of operating conditions,
production rates and meteorological conditions have been covered.
In the case where much process and control equipment is used in the
fertilizer industry, corrosion, erosion and other forms of mechan-
ical wear and tear are a major problem. It will be important, there-
fore, to make careful observations as to the condition and maintenance
level for important items of equipment.
Another significant factor in terms of overall emission rates from
a plant, process or operation is the effectiveness of emission
pickup and retention in the exhaust and control system. This is
especially important to examine in the fertilizer industry where so
much bulk transfer of material in particulate or granulated form
takes place.
The inspector should determine what design factors are used for
control equipment such as volumetric flow rates, entrance velocities
to centrifugal collectors, water flow rates for scrubbers, pressure
drop across scrubbers, etc. Adherence to design rates should be
evaluated. Secondary sources of pollution such as waste water
treatment facilities, settling ponds and fluoride recovery systems
should be examined.
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7.14.16
An increasing use of process control instrumentation in the
fertilizer industry provides another potential source of informa-
tion useful to inspection personnel. Of particular importance
would be any instrumentation used to control feed rates and that
used to monitor effluents.
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7.14.17
REFERENCES
1. Waggaman, W. H. Phosphoric Acid, Phosphates, and Phosphatic Fertilizers,
second ed. New York, Reinhold Publishing Corp., 1952.
2. Hendrickson, E. R. Dispersion and Effects of Air Borne Fluorides in
Central Florida. Air Pollution Control Assoc., 11. pp. 220-5, 232.
May, 1961.
3. Savchelli, V. (ed.). Chemistry and Technology of Fertilizers. New York,
Reinhold Publishing Corp., 1960.
4. Payne, A. J. and P. G. Glikin. Ammonium Nitrate - Process Survey.
Chem. & Proc. Eng. 49. April, 1968. pp. 65-9.
5. Scorer, R. S. Air Pollution Problems at a Proposed Merseyside Chemical
Fertilizer Plant: A Case Study. Atmos. Env., 2. January, 1968. pp. 35-48
6. Heller, A. N., S. T. Cuffe, and D. R. Goodwin. Inorganic Chemical
Industry. In: Air Pollution, Vol. Ill, A. C. Stern (ed.). New York City,
Academic Press. 1968.
7. Cross, Jr., F. L., and R. W. Ross. New Developments in Fluoride Emissions
from Phosphate Processing Plants. J. Air Pollution Control Assoc., 19,
January, 1969. pp. 15-17.
8. English, M. Fluorine Recovery from Phosphatic Fertilizer Manufacture.
Chem. & Proc. Eng., 48:43-7. December, 1967.
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7.15.1
XV. PAINT AND VARNISH MANUFACTURING
A. NATURE OF SOURCE PROBLEM
The paint and varnish manufacturing industry in a fairly broad context
could be said to include synthetic resin manufacturing, varnish cooking,
and paint blending processes. Of these, the first two present the
greatest air pollution control problems.
The major air pollutants from synthetic resin manufacturing would include
emissions of monomers and other raw materials from storage and reaction
vessels, sublimed phthalic anhydride and oil bodying odors from
alkyd resin manufacturing, and possible solvent losses during thinning
operations and storage of thinned resins.
Varnish cooking presents the greater of the air pollution problems in
this industry because of the wide variety of odorous substances released
during the polymerization and other chemical reactions that the natural
drying oils enter into during the cooking process. These range from
acrolein and other partially oxidized organic compounds to sulfur
derivatives, some of which are detectable in the parts per billion range.
Some varnish cooking is still carried out in open vessels which complicates
the design and operation of control equipment.
Solvent losses may also occur in the thinning of varnish and in paint
blending operations.
B. PROCESS DESCRIPTION
Two of the principal ingredients in protective coatings are resins and
drying oils. When organic solvents and driers (soaps of heavy metals)
are added to the heat processed blend of the resin and oil the product
is known as varnish. The addition of pigments to varnish results in
enamel type paints. The manufacture of water-based paints bears little
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7.15.2
relationship to oil-based paints and varnishes from an air pollution point
of view and will not be considered here. The resins used in water-based
paints are usually produced in chemical process plants using continuous
processes.
Resins used in varnish production may be either natural or synthetic.
Natural resins include Rosin, Congo, Batu, Dammar and Lac. These natural
resins in dry form are added at some point during the heat processing of
natural drying oils known as varnish cooking. Oleoresinous (oil plus
resin) varnishes result. This process will be described later in this
section.
A number of synthetic resins are also used in the preparation of
protective surface coatings. A partial list would include modified
phenolic, alkyd, coal tar, urethane and petroleum-based resins. Most of
these are produced in closed reaction vessels and are more properly
considered under the chemical process industries. However, the alkyd
resins are sufficiently different and are in such widespread use as to
justify a description of the manufacturing process.
1. Alkyd Resin Manufacturing
Alkyd resins are a special class of polyesters modified by additions
of fatty, monobasic acids. As a general class a polyester resin is
defined as the product of a condensation reaction between a polyhydric
alcohol and a polybasic acid. Thus, an alkyd resin might contain as
base ingredients phthalic anhydride, glycerol and a fatty acid
formed from a natural oil such as linseed.
Other natural oils used as modifiers include cottonseed, soya, tung,
and sometimes, fish oil. Other base ingredients used include maleic
and formic acids, and alcohols such as ethylene glycol, mannitol,
pentaerythritol and sorbitol.
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7.15 . 3
The production of alkyd resins is usually carried out in an enclosed,
indirectly heated reaction vessel equipped with a stirring mechanism,
a condenser, and usually a scrubber. All ingredients may be cooked
simultaneously, or the oil and a portion of the alcohol component
(such as glycerol) may be added first to convert the naturally
occurring triglycerides in the oil to a more reactive monoglyceride
form. The resin is formed by reacting this monoglyceride with the
acid (such as phthalic anhydride) at a temperature slightly below
500°F, using agitation and sparging with inert gas. The reaction is
carried out until the desired viscosity is attained.
Because of the use of natural drying oils as modifiers, a variety of
odorous, noncondensible gases are given off during alkyd resin
manufacturing which are similar to those emitted from the production
of oleoresinous varnishes. These include acrolein, other aldehydes,
fatty acids, etc. This class of air contaminants is generally
controlled by fume burners. Addition of phthalic anhydride to the
heated drying oils may cause the emission of visible plumes of the
sub1imed anhyd ride.
2. Varnish Cooking
Varnish cooking generally refers to the manufacture of oleoresinous
varnishes. Four groups of materials are used in preparation of the
final form used for protective or decorative coating. These include
antioxidants, resins, drying oils, driers, and solvents. While there
is a good deal of variety in all four groups, an almost endless number
of resins and drying oils are used. To a considerable extent the nature
of these materials influences the possible air pollution problem.
-------
7.15.4
The principal reactions taking place in the manufacture of varnish
involve the addition of heat. Reactions include:
a. Polymerization of the drying oils. Some, such as tung oil, are
easily polymerized and are added early in the processing while
with a slower bodying (polymerizing) oil such as linseed oil
a certain amount of prebodying may be carried out before the
resin is added.
b. Depolymerization. Certain natural fossil resins are of such high
molecular weight that heat-assisted cracking (depolymerization)
is necessary before the resin is ready soluble in the oil.
c. Melting and solution.
d. Esterification. Natural rosin or tall is modified for use in
some varnishes by esterification with a polyhydic alcohol such as
glycerol or pentaerythritol. The product, ester gum, is almost
always used in conjunction with other resins.
e. Gas checking. Certain of the faster reacting conjugated oils, such as
Chinawood oil, tend to form crystalline films giving a frosted or
"gas checked" effect. This effect can usually be prevented by
heating to top temperatures of 575-585°F during the cooking.
f. Distillation and Evaporation. Used to remove volatile constituents,
particularly such as those present or formed during esterification
of tall oil or rosin.
The air pollution problem in oleoresinous varnish cooking largely is
a result of the breakdown products of resin depolymerization, the
thermal decomposition and oxidation products of oil bodying, the
-------
7.15.5
volatile portion of the raw materials, and the by-products of gum
running (esterification). These might include fatty acids, formic
acids, acetic acid, glycerine, acrolein, other aldehydes, phenols, and
terpenes.*- ' In the case of tall oil esterification, hydrogen sulfide,
alkyl sulfide, butyl mercaptan, and thiophene may also be emitted.
These sulfur compounds are present in unpurified tall oil as a result
of the sulfides used in the kraft wood pulping process from which the
tall oil by-product is produced.
A significant amount of solvent may be lost to the atmosphere if
added to hot cooked varnishes where proper solvent recovery equipment
or controls are not used. This is most likely when the solvent
cut-back or thinning operation takes place in open varnish kettles.
The type of vessel used for varnish cooking can have a significant
effect on the air pollution problem. The old, open movable kettle
(Figure 7.15.1) having a capacity ranging from about 150 to 500 gallons
is heated over a fire pit making close temperature control somewhat
(2)
difficult. Because odorous fume evolution is temperature dependent,
excessive temperatures or local hot spots can increase fume loss and
even change the nature of the effluent. Further, the installation of
a close fitting effective fume hood and at the same time allowing the
flexibility necessary for use over a movable kettle is more difficult
than hooding a fixed fume source.
Much of the varnish cooking is now carried out by chemical companies
and large paint plants in closed reactor kettles having an external
(3)
source of heat supplied by a heat transfer medium such as Dowtherm.
Some are directly heated with gas, oil or electric resistance heaters.
Internal cooling coils may also be provided. Temperature can be con-
trolled much more closely than in open kettles. Liquid raw materials
are pumped with solids being added through a scalable port. These
closed systems are often equipped with vapor recovery condensers. The
-------
Figure 7.15.1. UNCONTROLLED OPEN KETTLE FOR VARNISH COOKING (SOURCE:
AIR POLLUTION ENGINEERING MANUAL, Reference 4)
-------
7.15.7
product is withdrawn by pumping and is transferred to solvent thinning
tanks usually equipped with agitators and integral reflux condensers
to reduce solvent losses.
Solvent loss control has become of more concern since the adoption of
regulations such as Rule 66 of the Los Angeles County Air Pollution
Control District and Regulation 3 of the Bay Area Air Pollution Control
District (California). From the standpoint of total volume and
photochemical air pollution potential, the control of certain types
of solvents such as olefins, branched chain aromatics and ketones may
be of more importance in the general air pollution picture than is
the control of varnish cooking fumes. However, the localized nuisance
and visible plume aspect of varnish cooking fumes cannot be neglected.
Air Pollution Control Techniques
The application of the best technology in the paint and varnish
industry would call for the use of fume burners wherever varnishes
are cooked or drying oils are heat processed. In some cases pre-
collection devices such as water scrubbers for the control of
phthalic anhydride fumes are in order. Generally speaking, other
means of control such as activated carbon adsorption units are not
satisfactory for use with odorous fumes containing tacky particulate
matter such as is contained in typical varnish cooking fume.
Solvents may be controlled by use of closed thinning vessels,
temperature control, condensers, and in some cases, fume burners.
Fume or afterburners should be designed to accomplish three objectives:
(1) eliminate visible plumes, (2) eliminate odor, and (3) oxidize
all organic substances to carbon dioxide and water.
-------
7.15.8
These objectives can only be met by good mixing of the plume in
the combustion zone, application of sufficient heat to reach some
acceptable minimum temperature, and provision of sufficient
residence time at these conditions to permit quantitative oxidation
of the organic material in the fume. Both direct flame and
catalytic afterburners have been applied to varnish cooking operations.
In general, sufficient auxiliary fuel (usually gas) must be supplied
in direct flame afterburners to heat the exhaust air containing the
process effluent to a range of 1200°-1500°F. Maximum flame contact time
is desirable. A minimum residence time of the effluent stream in the
(4)
combustion zone of 0.3-0.5 seconds is suggested, although longer
times may be desirable in cases of materials resistant to oxidation.
Good mixing can be achieved by proper combustion chamber design. One
type of fume burner design which has often been used successfully
involves the use of tangentially fixed burners (Figure 7.15.2). A
number of other proprietary designs have been developed with the
objectives of maximizing flame contact and promoting good mixing.
Figure 7.15.3 is a schematic diagram of a burner in which the
process effluent is forced to travel through the flame. An overall
schematic view of a varnish cooking fume burner control system is
shown in Figure 7.15.4.
Catalytic afterburners have also been used to control varnish cooking
fumes and odors. The principle advantage of such an approach
according to theory is that the use of a catalyst allows the
oxidation reactions to take place at a lower temperature thus
reducing the use and cost of auxiliary fuel. Mixed success has been
achieved in the use of catalytic afterburners for organic emissions.
Some apparently are successful while in other cases, odors not
-------
7.15.9
^REFRACTORY RING BAFFLE
INLET FOR CONTAMINATED
AIRSTREAM
Figure 7.15.2.
TYPICAL DIRECT-FIRED AFTERBURNER WITH
TANGENTIAL ENTRIES FOR BOTH THE FUEL
AND CONTAMINATED GASES. (SOURCE: AIR
POLLUTION ENGINEERING MANUAL, Reference 4)
-------
7.15.10
PROFILE PLATE
COMBUSTIFUME"
LINE BURNER
CAS SUPPLY LIN!
INSULATED SHELL
Figure 7.15.3.
DIAGRAM OF COMBUSTIFUME BURNER IN VERTICAL STACK
(SOURCE: JOURNAL OF THE AMERICAN INDUSTRIAL
HYGIENE ASSOCIATION, Reference 5)
-------
RECIRCULATING KftTER BASIN
Figure 7.15.4. SCHEMATIC PLAN FOR VARNISH-COOKING CONTROL SYSTEM
(SOURCE; AIR POLLUTION ENGINEERING MANUAL, Reference 4)
-------
7.15.12
originally present in the effluent can result. Specific test
information is desirable before the performance of catalytic units
can be predicted with confidence. Selheimer and Lance, for
example, report that a laboratory scale test of a catalytic
combustion process was successful on a given varnish cooking
effluent at a temperature of 700°F.
C. INSPECTION POINTS
With the exception of opacity regulations there are relatively few
specific prohibitory regulations dealing with the paint and varnish
industry. In most cases, prohibitions of odorous organic fumes such as
those arising from uncontrolled varnish cooking are based upon nuisance
law. There are a few agencies such as the San Francisco Bay Area Air
Pollution Control District (Regulation 3) which have mass or concentration
standards for certain organic compounds, and there is increasing interest
in quantified odor measurement standards, but these are the exception at
the present time. Consequently the inspector should become familiar with
the conduct of an odor survey (see Chapter 6, Section VI).
Solvent losses from thinning operations in some cases may be governed
by specific regulations (see Rule 66, L.A. County APCD), but this class
of regulation is far from universal.
Control of solvent losses is based quite often on best technology either
with or without the aid of a permit system.
The inspector will have several main tasks in relationship to the
inspection of paint and varnish related industries. These would include:
• General surveillance for odors and possible visible plumes
• Investigation of odor complaints.
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7.15.13
• Determination of nature of processes carried out, including the
range of materials processed.
• Inspection of production and control equipment and the
determination of operating practices.
• Determining whether source testing is desirable.
1. Environmental Observations
The major obvious environmental effects which can possibly be observed
would include the broad spectrum of odors possible from varnish
cooking and alkyd resin manufacturing, odors from aromatic and
unsaturated solvents such as dicyclopentadiene, surface contamination
from oil mists, and visible plumes from cooking operations or from
the uncontrolled emission of phthalic anhydride.
Odors originating from varnish cooking operations are quite varied
depending upon the raw materials and stage of the process. Some are
characteristic of vegetable drying oils such as linseed, oiticica,
and castor oils. Fish oils would be easily recognized by their
characteristic odor. Other pungent and sometimes irritating odors
are formed by the partial oxidation and polymerization reactions
taking place during the cooking process. Terpene or pine oil odors
together with sulfur compound odors could possibly originate from
the use of tall oil. Most of these odors are rather pervasive and
ill smelling. Some are slightly nauseous in higher concentrations.
The inspector must be careful to note wind speed and direction,
relative humidity, atmospheric stability and other possible odor
sources when tracking odors or investigating odor complaints. Tracking
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7.15.14
of odors should be done systematically noting times, locations,
and odor type and intensity during the investigation. Should
regular complaint patterns develop, a community odor panel may be
utilized to obtain more objective evidence on time, location, quality
and intensity of odors.
Plume sources should be carefully identified and observations should
be made consistent with good opacity observation practices (see
Chapter 5). Complaints of damage from oil droplets should be
plotted on a map and identification of materials made by collecting
samples of glass plates for laboratory examination in case of
materials of doubtful origin.
2. Observations of Plant Exterior
Points of emission visible from the exterior of paint and varnish
plants are process vent stacks serving resin kettles and varnish
cooking operations, condenser vents from storage of heated liquid
phthalic anhydride and solvent thinning tank vents. Visible plumes
may or may not be associated with varnish cooking operations. In
general there should be no readily visible plume from a varnish
cooking operation served by a fume burner.
Intermittent visible emissions may result from the addition of
resins to hot oils and from thinning operations when the cooked
varnish has not been cooled sufficiently. Visible emissions may
also result from filling operations in liquified phthalic anhydride
storage tanks.
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7.15.15
3. Interior Plant Inspection
a. The Interview
The interview with plant management should be directed towards
obtaining information about the process operations as they affect
the air pollution potential, to determine operating and maintenance
procedures, and to examine applicable records such as fume burner
temperature recorder charts (if used). Examples of specific
types of information to be obtained by interview are:
• Nature of raw materials used and finished product
manufactured. It is particularly important to determine the
type of natural drying oils used in varnish cooking or in
modifying alkyd resins as the odor potential may be quite
different for each. A list of solvents used should also be
obtained.
• Process descriptions should be obtained such as sequence of
materials added to cooking vessels, temperatures used, length
of cook, technique used for solvent thinning operations, and
equipment used for various operations.
Operation and maintenance schedules should be determined
particularly as to time of day that varnish cooking operations
are carried out. Maintenance of exhaust systems serving
varnish cooking operations is important because of the great
potential for lines being partially obstructed with fume
deposits. Obstructed lines may reduce exhaust flow rates and
thus result in less effective fume pickup at hoods over open
varnish cooking kettles.
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7.15.16
• Production data is important in determining emission inventory
data by the application of general or specific emission
factors.
• Exhaust and control system data. Plant management should be
asked to provide data on exhaust flow rates used, amount of
fuel used in afterburners, water rates in any water scrubbers
used, and on any internal guidelines or procedures used to
determine the effectiveness of the control equipment.
b. The Physical Inspection
The physical inspection should concentrate on equipment which is
a potential source of air contaminants or designed to control
them. It is important that some inspections be made during the
conduct of operations having the greatest air pollution potential.
Safety procedures instituted by plant management particularly
near hot and flammable materials should be respected. Important
items to observe are:
• Specific equipment used for each relevant operation, where
and how used.
• Condition of fume exhaust equipment including fans, drive
belts, hooding, ducts and control equipment. Examination
should be made for leaks, clogged ducts and general level of
maintenance.
• Functioning of exhaust and control equipment including hooding
effectiveness, hood in-draft velocities, evidence of fume
burner fuel-use rates, afterburner temperatures and
relationship of these parameters to evidence of visible plumes
and odors.
-------
7,15.17
• Data obtained in the interview should be verified wherever
possible during the inspection. This is particularly
important with respect to operational procedures.
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7.15.18
REFERENCES
1. Maltiello, J. J. (ed.). Protective and Decorative Coatings, Vol. III.
New York, John Wiley and Sons, Inc., 1943.
2. Maltiello, J. J. (ed.). Protective and Decorative Coatings, Vol. I.
New York, John Wiley and Sons, Inc., 1941.
3. Payne, H. F. Organic Coating Technology, Vol. I. New York, John Wiley
and Sons, Inc., 1954.
4. Danielson, J. A. (ed.). Air Pollution Engineering Manual. Cincinnati,
DHEW, PHS, National Center for Air Pollution Control and the Los Angeles
County Air Pollution Control District. P.H.S. No. 999-AP-40, 1967.
5. Waid, D. E. Incineration of Organic Materials by Direct Gas Flame for
Air Pollution Control. Am. Ind. Hyg. Assoc. J 30, 291-297. 1969.
6. Selheimer, E. W., and R. Lance. Analysis of Fumes Leaving Resin Kettles
and Fume Abatement Equipment. Off. Dig. Fed. Paint and Varnish Prod.
Clubs, 27, 711-68. August, 1954.
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7.16.1
XVI. GALVANIZING OPERATIONSv '
A. DESCRIPTION OF SOURCE
The coating of iron and steel materials (sheet metal, structural shapes
and wire) with zinc to prevent oxidation is an industrial practice
commonly found in most industrialized communities. The primary source
of air contaminants is the galvanizing kettle containing molten zinc.
Galvanizing operations can be conducted on a batch basis, as in
the coating of nuts and bolts, or as a continuously fed operation
as in the coating of wire or chain link fencing. This process may be
found in job shops or as a captive operation in a large plant.
B. PROCESS DESCRIPTION
Since the surface of the material to be coated must be free of rust and
oil so that the zinc can adhere to it, the product must go through
cleaning and degreasing processes prior to the hot zinc dip. The
cleaning process has air pollution control impact as well as a quality
control consideration. If the metal to be coated is not clean, oil mists
can be generated and an increased use of flux for proper coating action
will be required with resultant increases in fume emissions.
The process flow shown in Figure 7.16.1 is usually independent of batch
or continuous operations. Variations occur in the physical design of the
galvanizing kettle and its ventilation system, depending upon whether
batch or continuous operations are employed. For example, galvanizing
chain link fencing will require kettle configurations which differ sub-
stantially from kettles used for structural shapes and fasteners.
-------
DUSTING WITH
SAiAfMPNIAC
CLEAR TOP N
FLUX COVER ^
GALVANIZED
,
,
k
<
DECREASING
TANK
HOT ALKALINE
SOLUTION
: t It it 1 T r±i
WATER
RINSE
ACID
PICKLING
TANK
WATER
RINSE
PREFLUX
ZINC
CHLORIDE
SOLUTION
V
\\ PRODUCT
Sfl '
GALVANIZING
TANK/ KETTLE
Figure 7.16.1. SIMPLIFIED FLOW CHART OF GALVANIZING PROCESS
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7.16.3
In the galvanizing step, zinc is maintained in the molten state at a
maximum temperature of 860°F. The kettle is heated externally so that
the products of combustion do not enter the process and are separately
vented. A flux cover is maintained on the surface of the molten metal
bath primarily to remove oxide formations from the metal to be coated
(some small amount of oxide may be formed between cleaning and the hot
dip) and to exclude air from the part as it enters the zinc bath. The
secondary functions of the flux cover are to reduce heat losses from the
bath, reduce spattering of molten zinc and to keep the molten zinc surface
free of oxides thus assuring a bright coating on the product.
While a flux cover is necessary in the galvanizing process it is also the
major cause of the emission of air contaminants. The two fluxes in
common use are ammonium chloride and zinc ammonium chloride plus a foaming
agent such as glycerine, wood flour or sawdust to provide a deeper flux
layer and to extend the life of the flux. Visible emissions occur when
this cover is disturbed by piercing it with the product to be coated,
adding new flux, or in dusting the product with ammonium chloride as it
is removed from the bath to assure an even flow of zinc on the plated
surface. Emissions are usually grey with the opacity varying according
to the mechanical agitation of the flux cover resulting from any of the
above conditions and especially from dusting when nearly all of the flux
is converted to dense ammonium chloride fumes.
As the configuration of the galvanizing kettle varies it is necessary to
vary the air pollution control system to capture the effluent caused by
this process. Figure 7.16.2 shows a galvanizing batch operation. The flux
may be noted on the surface of the bath in the foreground. The parts are
dusted with ammonium chloride to form a bright finish. Figure 7.16.3
shows the same tank with a room type hood covering the kettle. This
hooding design allows for overhead materials handling equipment
to be used and gives the operators unimpaired access to the kettle.
-------
7.16 . 4
Figure 7.16.2.
REMOVING WORK THROUGH A CLEAN ZINC SURFACE. FLUX COVER IN
FOREGROUND, LOS ANGELES GALVANIZING CO., HUNTINGTON PARK,
CA. (SOURCE: THOMAS, Reference 1) " ~ ~~'~"
-------
7.16. 5
Figure 7.16.3.
OPEN TO A ROOM-TYPE HOOD OVER A GALVANIZING KETTLEf
LOS ANGELES GALVANIZING CO., HUNTINGTON PARK, CA.
(SOURCE: THOMAS, Reference 1) '' """"
-------
7.16.6
Figure 7.16.4 illustrates a slot hood (high inlet velocity) used
in a continuous operation for galvanizing chain link fences. As in most
open processes the design of the ventilation system is critical. Good
engineering practices, outlined in Chapter III of the Air Pollution
Control Engineering Manual, describe inlet velocities, materials of
construction, fan requirements, and other factors of interest to the
inspector.
Fume arresting equipment commonly used to capture the effluent from this
process include scrubbers which produce the least satisfactory results;
precipitators, where oil mists are a significant part of the air
contaminants to be captured, and baghouses where there is little or no
oil mist entering the exhaust system. Recent experience has shown that
precipitators are more sensitive and require more maintenance than do
baghouses for this application. While a baghouse requires less maintenance,
the temperature inside must be kept above the dew point, even when not
in use, to prevent condensation on the bags. Also consideration has been
given to using a mechanical separator upstream of the baghouse to remove
oil mists from the effluent in cases where oil mists present a problem.
The requirement for high efficiency air pollution control equipment in
galvanizing operations is necessitated by the small particle sizes of the
fumes generated. The average particle size is 2u as illustrated in
Figure 7.16.5 of a photomicrograph of fume collected from a galvanizing
kettle. Table 7.16.1 shows the chemical analysis of materials collected
from galvanizing kettles in a baghouse and in an electrical precipitator.
C. INSPECTION POINTS
Galvanizing operations, whether in large integrated plants or in job shops
would be cited under opacity vs. time, process weight vs. allowable
emissions, or public nuisance regulations. Usually in job shops there
-------
7.16.7
Figure 7.16.4.
SLOT-TYPE HOOD SERVING A CHAIN LINK FENCE-GALVANIZING
FLUX BOX, ANCHOR POST PRODUCTS, INC., OF CALIFORNIA,
WHITTIER, CALIF. (SOURCE: THOMAS, Reference 1)
-------
7.16.8
Figure 7.16.5. PHOTOMICROGRAPH OF FUMES DISCHARGED FROM A
GALVANIZING KETTLE (SOURCE: THOMAS, Reference 1)
-------
7.16.9
Table 7.16.1.
CHEMICAL ANALYSES OF THE FUMES COLLECTED BY A BAGHOUSE
AND BY AN ELECTRIC PRECIPITATOR FROM ZINC-GALVANIZING
KETTLES
Component
NH4C1
ZnO
ZnCl2
Zn
NH3
Oil
H2°
C
Not identified
Fumes collected
in a baghouse
(job shop kettle),
wt %
68.0
15.8
3.6
4.9
1. 0
1. 4
2.5
2.8
Fumes collected
in a precipitator
(chain link galvanizing),
wt|%
23. 5
6.5
15.2
3. 0
41. 4
1. 2
9.2
(SOURCE: THOMAS, Reference 1)
-------
7.16.10
will be a one or at most two-shift operation (7:00 a.m. to 11 p.m.) while
three-shift operations are not uncommon in large integrated plants. At
best, opacity readings are very difficult outside of daylight hours so
it may be necessary for the inspector to determine if there is any
difference in operating procedures during the various shifts.
The inspector will find it nececessary to observe the metal precleaning
operations, determine the type and quantity of flux and foaming agents
used, the normal hours of operation, and to isolate the location of the
galvanizing kettles within the plant relative to windows and roof
monitors, and the location of the air pollution control equipment serving
the kettles.
1. Environmental Observation
Due to the density and opacity of possible emissions from galvanizing
plants public attention can be drawn to these operations. Often
nuisance complaints will arise from "dense white.smoke" which can
result from galvanizing operations. Complainants may be helpful in
gathering information regarding excessive emissions during hours when
the inspector is usually not in the area, allowing him to modify his
hours of patrol to observe and record any variations in operations.
2. Observations of the Exterior of the Plant
An initial inspection of galvanizing operations may arise from the
observation of dense clouds of grayish emissions from the roof
monitors and windows of the building housing the operation or from the
air pollution control equipment which serves the kettle. In job shops
this operation will be easy to pinpoint from outside the plant but in
a large industrial complex only a systematic inventory of equipment
and processes may spot the location of the operation.
-------
7.16.11
Uncontrolled galvanizing operations are characterized by intermittent
dense clouds of fume and oil mists and continuous light grey emissions
Plants with air pollution control systems may still emit noticable
quantities of fumes during dusting, as a result of adding flux or
agitation of the bath, depending on the ventilation system design and
its state of repair.
3. Inspection of the Interior of the Plant
Upon entering the plant the inspector should discuss with the plant
operator the observations made outside of the plant, including a
description of the emission and whether or not violations of any
regulations were recorded. The interview may continue during the
inspection and include:
a. A detailed explanation of operating procedures and any
variations from these procedures that may have occurred
immediately preceding the inspection.
b. The type and quantity of flux used, frequency of addition of new
flux and the quantities added.
c. Description of the material to be galvanized and the normal
process weight in pounds per hour. (Material to be plated, flux,
and quantity of zinc added as makeup).
d. Normal operating periods, hours of the day and days of the week.
e. Any experimental work done with fluxes or foaming agents.
-------
7.16.12
The observations should include:
1. At initial inspection:
a. Overall dimensions of the tank.
b. Sketch of the air pollution control system.
c. Make and model number of the air pollution control equipment
(if not a catalog item, details of design such as water rate
for scrubbers, filter area for baghouses and fan capacity and
motor horsepower should be noted).
d. Make and model number of burners, type and quantity of fuel
used. If oil is used there is a possibility of smoke emissions,
especially during startup. Depending on the sulfur content of
the oil, SOx emissions in excess of that allowed may occur.
2. After the initial inspection any changes to the equipment and
operating procedures should be noted since permit action may be
required.
3. Observe one or more operating cycles including fluxing and dusting.
The inspector should determine the varieties of materials galvanized
to observe the worst operating conditions.
4. Check for the condition of repair of the ventilation system and
estimate fume-pickup efficiency during the periods of worst fuming.
5. Check for repair of fume suppression equipment, i.e., are there
leaks, visible emissions from points other than the equipment
exhaust duct; have the bags been shaken or do they appear to be
clogged; is there full water pressure to the scrubber.
-------
7.16.13
Any items that vary from normal operating conditions should be
challenged by the inspector to determine if there has been negligence
in the operation, equipment breakdown or a change in operation.
For plants that have no air pollution control systems, suppression of
emissions will depend solely on the use of a flux cover. At least one
hour of operation should be observed to record time and opacity of
emissions.
-------
7.16.14
REFERENCE
1. Thomas, G. Zinc Galvanizing Equipment. In: Air Pollution Engineering
Manual, J. A. Danielson (ed.). Cincinnati, DHEW, PHS, National Center for
Air Pollution Control and the Los Angeles County Air Pollution Control
District. PHS No. 999-AP-40. 1967.
-------
7.17.1
XVII. ROOFING PLANTS — ASPHALT SATURATORS
A. DESCRIPTION OF SOURCE ^
Asphalt impregnated paper and felt, which is used extensively in the build-
ing trades, is manufactured by means of asphalt roofing saturators. These
are high speed continuous processes using still bottoms from petroleum
crude oil. The saturators are a major source of vapors, liquid particulates
and steam emissions. Total emissions may range from 50 to 100% opacity
where air pollution control systems are inadequate. Unless properly
controlled, these operations can be a major nuisance, particularly if
located within a metropolitan area.
B. PROCESS DESCRIPTION
Felt used in this process is derived from vegetable fibers and contains 5 to
10% moisture. It is continuously fed through a machine known as a saturator
(Figure 7.17.1) where it is impregnated with asphalt at 400 to 450°F. The
felt enters the machine through a series of dry loops (to preclude binding)
where one side of the felt is sprayed with asphalt. The spray serves to drive
the moisture from the felt to assure smooth coating in the saturator tank.
After leaving the tank the felt is once again looped to cool the product.
Crushed rock or mica is applied with bituminous material to produce
roofing shingles .
C. EMISSIONS AND CONTROLS
Figure 7.17.2 shows the points of emissions from asphalt saturators. The
emissions are a mixture of asphalt vapors, liquid particulates and water
vapors. The machines are large and require hoods with indraft velocities
of 200 ft/min or more to capture the vapors and mists. Figure 7.12.2
illustrates the extent of hooding required to achieve positive control of
ventilation.
The crushed rock feeder may emit dust and should be hooded and vented to a
cyclone or scrubber.
-------
DRY
LOOPER
SPRAY
SECTIONV
WET
LOOPERY
TO ASPHALT
^~
HEATER
TO ROLL PRODUCT
OR SHINGLE
PRODUCT OPERATIONS
T POINTS OF EMISSIONS
Figure 7.17.1. SCHEMATIC DRAWING OF AN ASPHALT ROOFING FELT SATURATOR
(SOURCE: WEISS, Reference 1).
-------
Figure 7.17.2. ASPHALT SATURATOR HOOD AT FELT FEED
(Lloyd A. Fry Roofing Co., Los Angeles, Calif.)
(SOURCE: WEISS, Reference 1)
-------
7.17 .4
Due to the physical shape and size of the machines and high indraft
velocities at the hoods, large volumes of air are required to capture the
air contaminants. Collection devices commonly used are spray scrubbers,
baghouses and two-stage low voltage electrical precipitators in combination
with spray scrubbers.
The Los Angeles County Air Pollution Control District in tests conducted
on three types of air pollution control systems mentioned above report
the results shown in Tables 7.17.1, 7.17.2, and 7.17.3.
Table 7.17.1. EMISSIONS FROM A WATER SCRUBBER AND LOW-VOLTAGE,
TWO-STAGE ELECTRICAL PRECIPITATOR VENTING AN
ASPHALT SATURATOR
Volume, scfm
Temperature, °F
Emission rate,
gr/scf
Ih/hr
Water vapor, %
Collection efficiency
Scrubber inlet
20, 000
139
0.416
71.4
3.7
Scrubber, 71%
Precipitator inlet
20, 234
85
0. 115
20
4.9
Precipitator, 50%
Precipitator outlet
20, 116
82
0. 058
10
4.8
Overall, 86%
(SOURCE; WEISS, Reference 1.)
Table 7.17-2. EMISSIONS FROM A BAG FILTER AND CYCLONE SEPARATOR
VENTING AN ASPHALT SATURATOR
Volume, scfm
Temperature, "F
Emission rate,
gr/scf
Ib/hr
Water vapor, %
Collection efficiency, %
Control equipment
inlet
10. 500
217
0.768
67.7
6.4
Control equipment
discharge
10, 300
I8S
0. 2S9
25. 5
6.8
62. 3
(SOURCE: WEISS, Reference 1.)
-------
7.17.5
Table 7.17.3. EMISSIONS FROM A WATER SCRUBBER VENTING
AN ASPHALT SATURATOR
Volume, scfm
Temperature, ' F
Emission rale,
gr/scf
Ih/hr
Water, %
Collection efficient, y, %
Scrubber
inlet
12,000
138
0. 535
55.0
2. 7
Scrubber
discharge
12, 196
82
0.0737
7.7
4.2a
86
aAt 3. 7 volume % of water, vapor is saturated air.
Other qualitative tests run simultaneously showed
no particulaU- water.
(SOURCE; WEISS, Reference 1.)
While electrical precipitators show greater collection efficiencies than bag-
houses, critical maintenance problems must be considered. Due to oil deposits
on the precipitator components, regular cleaning is mandatory to maintain
collection efficiency. Regular checks are also necessary to assure timely
replacement of cracked wires and insulators. Oil particles may build
up in baghouses and blind the filter bags to cause increase in pressure
drop and decrease in vapor pickup at the hoods. Baghouses can be used
in series with a cyclone separator downstream to collect reentrained oil
droplets.
The use of spray scrubbers may not be desirable in areas where air pollution
control agency regulations prohibit excessive opacities of emissions. Due
to greatly reduced collection efficiency in the one micron particle size
range the opacity of the effluent from spray scrubbers can exceed 50%.
Tests have shown fairly good efficiencies on a weight basis.
D. INSPECTION POINTS
Plant inspections should be directed at (1) the saturator to determine
the effectiveness of the ventilation system which captures the vapors and
particulates from the application of the asphalt and (2) the collection
-------
7.17.6
device to determine if it is operating efficiently, as indicated
by the opacity of emissions. Air Pollution control equipment operating
characteristics and maintenance recommendations are described in Chapter 2.
The inspector will observe poor pick up at the hood serving the saturator
if there are excessive air leakages through holes in the duct work, plugged
lines or other maintenance problems which can hinder the gas flow in the
system. Methods of quantitatively determining hood indraft velocities
are discussed in Chapter 5.
Observations from outside the plant should be directed at windows and roof
monitors which will emit opaque vapors if the air pollution control system
is not in use.
|!
Asphalt saturators can be a source of nuisance complaints as well as
violations of opacity regulations.
-------
7.17.7
REFERENCE
1. Weiss, S. M. Asphalt Roofing Felt-Saturators. In: Air Pollution
Engineering Manual, J. A. Danielson (ed.). Cincinnati, DREW, PHS, National
Center for Air Pollution Control and the Los Angeles County Air Pollution
Control District. PHS No. 999-AP-40. 1967.
-------
7.18.1
XVIII. ASPHALTIC CONCRETE BATCHING OPERATIONS
A. DESCRIPTION OF SOURCE
Asphaltic concrete is produced by combining asphalt cement with sized, dry
aggregate and fines to form a workable mixture for use in a variety of paving
applications. At ambient temperatures asphalt cement is a solid tarlike
petroleum product. It is heated to between 275° and 325°F until it flows
sufficiently to thoroughly permeate the aggregate to form the mix
specification desired. Aggregate is the name applied to crushed rock, sand,
gravel and fines which provide the properties of compressive strength and
wear desired in concrete. Batching plants are common to many construction
sites and are portable to some degree. Since large quantities of rock,
sand and gravel are used in the batching operation, batching plants are
found near quarries and gravel beds.
The batching plant consists of a rotary drier, aggregate bins, materials
handling equipment, screens, asphaltic cement storage and heating equipment,
weigh boxes, and fuel storage. Some form of air pollution control
equipment is used ranging from cyclone separators and scrubbers to baghouses.
Losses from uncontrolled rotary driers average about 5 pounds of dust per
ton of material processed. Tests conducted by the Los Angeles County
Air Pollution Control District have shown dust loadings in dryer effluent
C2)
as high as 6,700 pounds/hour prior to entering the primary separator.
Dust loadings can often reach 1,000 pounds/hour or more from equipment
controlled only by cyclones.
B. PROCESS DESCRIPTION
A typical equipment train for hot asphalt batching plants consists of sand
and aggregate storage bins feeding into a bucket elevator or cold elevator
which discharges into a rotary dryer, which may be either gas or oil
-------
7.18.2
fired. Depending on the proportions of the different sizes of aggregate
the dryer temperature will range from 250° to 350°F. The dried aggregate
discharges to the hot elevator which feeds into vibrating screens for size
classification (Figure 7.18.1) and interim storage. Varying amounts of rock,
sand and fines are then weighed and dropped into the pug mill where the asphalt
cement is added. Finally, after thorough mixing the batch is dropped into
trucks for transport to the job site. In a continuous-type plant the aggregate
and asphalt are introduced into the mixer and the mix discharges continuously.
Exhaust systems usually serve the hot and cold elevators, the dryer and the
weigh hopper-storage bin combination. Figure 7.18.2 illustrates a typical
system.
The Asphalt Institute classifies paving mixes according to the relative
amounts of coarse aggregate, fine aggregate and mineral dust used for
various desired specifications. By definition, coarse aggregate is
retained on a No. 8 sieve (up to 2 1/2"); fine aggregate will pass a
No. 8 sieve; mineral dust will pass a No. 200 sieve. Table 7.18.1
describes the standard U.S. and Taylor Sieve Series. The
difference is that the U.S. Sieve is identified by millimeters or microns
while the Taylor Sieves are identified by the nominal meshes per linear
inch. Table 7.18.2 is a summary of mixes recommended by the Institute. The
numbers represent the amount of material that will pass a given sieve
opening. For example, 100 percent of MIX Type la will pass through a
2 1/2 inch opening.
Asphalt cement is a thermoplastic material which decreases in viscosity
as it is heated. A range of specifications for describing the quality of
the asphalt is shown in Table 7.18.3. These include: penetration tests to
determine relative hardness at ambient temperature (77°F or 25°C);
viscosity tests, conducted at temperatures of 275°F (135°C), to establish
ease of flow; flash point to determine safe heating limits; thin film test
to determine the degree of hardening which may occur during the plant
-------
GRADATION CONTROL UNIT
ASPHALT BATCH MIX PLANT
COLD AGGREGATE STORAGE
AND FEED
00
U>
Figure 7.18.1. ASPHALT BATCH PLANT WITH A CYCLONE
TYPE DUST COLLECTOR
(SOURCE: The Asphalt Institute,
Reference 3)
-------
7.18.4
HOT AGGREGATE-
BUCKET ELEVATOR
(a) Primary Collector
(b) Secondary Collector
(c) Mineral Filler & Asphalt Cement Added at Mixer
A Emission Points
Figure 7.18.2. FLOW DIAGRAM OF A TYPICAL HOT-MIX ASPHALT PAVING BATCH PLANT
(SOURCE: Danielson, Reference 2)
-------
7.18.5
Table 7.18.1.
STANDARD U.S. AND TYLER SCREEN SCALES
(SOURCE: Public Health Service, Reference 4)
Nominal
Aperture width
microns
1
2.5
5
10
20
37
43
44
53
61
62
74
88
89
104
105
124
125
147
149
175
177
208
210
246
250
295
297
350
351
417
inches*
.00004
.0001
.0002
.0004
.0008
.0014
.0017
.0017
.0021
.0024
.0024
.0029
.0035
.0035
.0041
.0041
.0049
.0049
.0058
.0059
.0069
.0070
.0082
.0083
.0097
.0098
.0116
.0117
.0138
.0138
.0164 (1/64)
U.S.
Standard
12500
5000
2500
1250
625
400
325
270
230
200
170
140
120
100
80
70
60
50
45
Tyler
325
270
250
200
170
150
115
100
80
65
60
48
42
35
Nominal
Aperture width
microns
420
495
500
589
590
701
710
833
840
991
1000
1168
1190
1397
1410
1651
1680
1981
2000
2362
2380
2794
2830
3327
3360
3962
4000
4699
4760
6680
inches*
.0165
.0195
.0197
.0232
.0232
.0276
.0280
.0328 (1/32)
.0331
.0390
.0394
.0460 (3/64)
.0469
.0550
.0555
.0650 (1/16)
.0661
.0780 (5/64)
.0787
.093 (3/32)
.0937
.110 (7/64)
. Ill
.131 (1/8)
.132
.156 (5/32)
. 157
. 185 (3/16)
. 187
.263 (1/4)
U.S.
Standard
40
35
30
25
20
18
16
14
12
10
8
7
6
5
4
Tyler
32
28
24
20
16
14
12
10
9
8
7
6
5
4
3
*NUmbers in parentheses indicate approximate fractions of an inch.
-------
7.18.6
(SOURCE:
Table 7.18.2. MIX COMPOSITIONS
Air Pollution Engineering Manual, Reference 2)
-------
7.18.7
Table 7.18.3. ASPHALT TEST SPECIFICATIONS
TEST NAME
1. Penetration
2. Viscosity
3. Flash Point
4. Thin Film Test
5. Ductility Test
6. Soluability Test
7. Specific Gravity
8. Softening Point
TEST METHOD
AASHO* Test
T 49
T 201
T 48
T 179
T 51
T ff
T 43
T 53
ASTM** Test
D 5
D 2170
D 92
D 1754
D 113
D 4
D 70
D 36
* American Association of State Highway Officials
** American Society for Testing Materials
-------
7.18.8
mixing operation; ductility tests to indicate the adhesive quality of
asphalt and temperature susceptibility; solubility tests to determine
the active cementing constituents of the asphalt by establishing the
bitumen content; specific gravity, the ratio of weight of a volume of
water at the indicated temperature, to make volume corrections at
elevated temperatures and to determine voids in asphalt paving mixes;
softening point tests, for asphalt grades harder than those used for
paving , to indicate the temperatures at which they reach an arbitrary
degree of softening.
C. CONTAMINANTS EMITTED
As in all operations employing rotating kilns or dryers, entrainment of
dust in the products of combustion due to product drying is the primary
source of contaminants. Secondary sources are materials handling equip-
ment and sizing equipment. In the typical plant shown in Figure 7.18.2,
dust pickup points served by local exhaust systems are indicated.
Table 7.18.4 shows the results of tests taken from plants with oil-fired
dryers indicating the high dust loading in the exhaust gas and in the vent
lines which capture dust from elevators and shakers. The materials handling
equipment accounts for as much as 2,000 pounds/hour exclusive of dust
from the rotary dryer.
Particle size distribution of the dust generated is an important factor in the
selection of adequate air pollution control equipment. Results of investi-
gations made of the distribution of particle size versus percent by weight
from drier exhaust and vent lines are shown in Figure 7.18.3. This study
indicated that as much as 89 percent of the particles may fall below 10
microns. The design of the mix which specifies the aggregate and
fines required will affect the particle size distribution and the total
dust loading of the exhaust.
-------
Table 7.18.4.
DUST AND FUME DISCHARGE FROM ASPHALT BATCH PLANTS
(SOURCE: Sheehy et. al., Reference 4)
Test No.
Batch plant data
Mixer capacity, Ib
Process weight, Ib/hr
Drier fuel
Type of mix
Aggregate feed to drier, wt %
+10 mesh
-10 to +100 mesh
-100 to +200 mesh
-200 mesh
Dust and furne data
Gas volume, scfm
Gas temperature, °F
Dust loading, Ib/hr
Dust loading, grains/scf
Sieve analysis of dust, wt %
+100 mesh
-100 to +200 mesh
-200 mesh
Particle size of -200 rnesh
0 to 5 p., wt %
5 to 10 n, wt %
10 to 20 p., wt %
20 to 50 u, wt %
> 50 |i, wt %
C-426
6, 000
364, 000
Oil, PS300
City street, surface
70. 8
24.7
1. 7
2.8
Vent linea
2, 800
215
2, 000
81.8
4. 3
6.5
89.2
19.3
20. 4
21. 0
25. 1
14.2
Drier
21, 000
180
6, 700
37. 2
17. 0
25. 2
57.8
10. 1
11. 0
11.0
21. 4
46. 5
C-537
6, 000
346, 000
Oil, PS300
Highway, surface
68.
28.
1.
1.
Vent linea
3, 715
200
740
23. 29
0. 5
4. 6
94. 9
18. 8
27. 6
40. 4
12. 1
1. 1
1
9
4
6
Drier
22,
4,
050
430
720
24. 98
18.9
32. 2
48. 9
9.2
12.3
22. 7
49.3
6.5
^J
M
00
aVent line serves hot elevator, screens, bin, weigh hopper, and mixer.
-------
7.18.10
12 5 10 20 30 50 70 80 90 95 98 99.5 99 9 99.99
Per cent by weight less than indicated size
Figure 7.18.3.
COMPOSITE ASPHALT PLANT DUST PARTICLE
SIZE DISTRIBUTION
(SOURCE: JAPCA, Reference 5)
-------
7.18.11
Collection and control systems for batch or continuous plants usually have
primary and secondary dust collection devices and in some instances a
tertiary device is added to the collection train. The air pollution
control system is usually comprised of cyclone separators (singly or in
multiple units) and scrubbers or baghouses in series. In addition to
collecting dust to meet air pollution control regulations, the dust
collected can be recycled to the process.
Cyclones have a reasonable efficiency for larger particle sizes (>20
microns) with a 2 to 3 inches water pressure drop. Since as much
as 89 percent of the dust can be < 10 microns, additional high efficiency
collection is required. High efficiency mechanical collectors such as
multiclones, which can reach 90 percent efficiency in the 5 to 10 micron
particle size range with a pressure drop of 4 to 6 inches water gauge, are
available. These devices may not meet the requirements of many agencies
having process weight or exhaust grain loading regulations.
The next higher order of efficiency of air pollution control equipment is
wet collectors. A wide range of configurations, spray pattern designs
and gas path designs are available with efficiencies for the low particle
size range reaching greater than 99 percent (see Table 7.18.5). Water
requirements range from 4 to 10 GPM/1,000 ft. of gas entering the
scrubber and the water pressure varies from 50 to 100 psi. A wide range
of pressure drops from 3 to 10 inches water may occur..
As new regulations which decrease maximum allowable dust emissions are
enacted, baghouses will come into greater use as the final collector in
the dust removal train. Efficiencies of overall dust collection with this
equipment is 99+ percent at a pressure drop of 4 to 5 inches water. Air-
3 2
to-cloth ratios of 2/1 to 6.25/1 (2 ft. of air per ft. of cloth to 6.25
3 2
ft. of air per ft. of cloth) are required depending on the fabric used
as the filter media and bag cleaning procedures.
-------
Table 7.18.5. TEST DATA FROM HOT-MIX ASPHALT PAVING PLANTS CONTROLLED BY SCRUBBERS
(SOURCE: Danielson, Reference 2)
Test No.
C-357
C-82
C-379
C-355
C-372B
C-372A
C-369
C-393
C-354
C-185
C-173
1
C-379
C-337
2
C-234
C-426
C-417
C-425
3
C-385
C-433
C-422(l)
C-422(2)
C-418
Averages
Scrubber
inlet dust
loading,
Ib/hr
940
427
4, 110
2, 170
121
76
352
4, 260
--
1,640
__
.-
3, 850
305
--
372
2,620
560
485
--
212
266
--
--
3,400
Stack
emission,
Ib/hr
20.7
35.6
37. 1
47.0
19.2
10.0
24.4
26.9
27.8
21. 3
31.0
33.5
30.3
13.6
21. 1
21.2
25.5
39.9
32.9
25.5
17. 5
11.0
26.6
37.0
30.8
26.7
Aggregate
fines rate, a
Ib/hr
9, 550
4, 460
8, 350
14, 000
2, 290
2,840
4,750
4,050
6,370
5,220
8, 850
7,520
6, 500
2, 510
3, 730
2, 530
10,200
3,050
2,890
6,590
4, 890
5, 960
7, 140
3, 340
9,350
5, 900
Water-gas
ratio,
gal/1, 000 scf
6.62
3. 94
6.38
6. 81
10.99
11. 11
5.41
12. 01
6. 10
19.40
20. 40
11. 01
5.92
11. 11
7.28
5.70
7.75
2. 94
4.26
6.60
4.56
8. 12
4. 90
3.02
8. 90
Overall
scrubber
efficiency,
wt %
97.8
91.6
99. 1
97. 8
84.2
86. 8
93. 0
99.3
--
98. 7
--
--
99.2
95.5
--
94.3
99.0
92.8
93.2
--
91.7
95.8
--
--
99. 1
94.9
Type
of
scrubber
C
c
C
c
c
c
c
T
T
T
T
T
C
C
T
T
C
C
C
c
c
c
c
c
T
Type
of
drier
fuel
Oil
Oil
Oil
Oil
Oil
Gas
Oil
Oil
Oil
Oil
Oil
Oil
Gas
Oil
Gas
Gas
Oil
Oil
Oil
Gas
Oil
Gas
Oil
Oil
Oil
Production
rate,
tons/hr
183.9
96.9
174. 0
209. 1
142.9
158. 0
113. 0
92.3
118.4
137.8
184.2
144.6
191.3
114. 6
124.4
42.0
182.0
138.9
131. 4
131.7
174. 3
114.5
198.0
152.0
116.5
Gas
effluent
volume,
scfm
23, 100
19,800
26,200
25, 700
18,200
18,000
16, 100
19,500
7,720
18,700
17,000
23,700
28, 300
24, 300
15,900
17,200
22,000
24,600
18,000
18,200
20,000
19,600
21,000
22,200
17, 100
aQuantity of fines (minus 200 mesh) in dryer feed.
°C = Multiple centrifugal-type spray chamber.
T = Baffled tower scrubber.
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7.18.13
D. INSPECTION POINTS
Asphaltic concrete batching plants that operate in industrial or mixed
industrial/residential areas can be the subject of nuisance complaints. The
large quantities of small particle size dust emitted from plants with only
cyclones or inadequately sized wet collectors can carry relatively long
distances under certain meteorological conditions.
While the dust emitted from the batching plant is not toxic or potentially
destructive to vegetation or finished surfaces, the potential health hazard
that may occur from any finely divided material and possible soiling effects
must be considered. One hot asphalt plant with only a primary separator can
emit 200 to 2,000 pounds of fine dust per hour. Dust from asphalt plants
settling on automobiles and other stationary items indicates that the
air pollution control equipment is either not in use or is not operating
properly.
Inspection of a batching plant should determine the capability of existing
equipment to meet emission control regulations. The enforcement officer
should:
(1) Check type of air pollution control equipment installed and
observe emissions.
(2) Check basic equipment, suction points, duct work, etc., for leaks.
(3) Check ancillary equipment (boilers, mixers, etc.) for emissions
and odors.
(4) Check plant area for potential sources of fugitive dust (storage
areas, yard area, etc.).
(5) Check equipment capacity, operating schedule and plant throughput.
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7.18.14
The enforcement officer should determine whether equipment which has been
accepted as capable of meeting an emission limit is operating properly and
complying with that limit, assuming a cyclone-scrubber control system is
used. He should:
(1) Check water pressure and flow rate.
(2) Check for leaks in duct work.
(3) Check loading area for dust or odors.
(4) Check methods used to minimize fugitive dust emissions in the yard.
(5) Check type of fuel utilized in dryer and boiler.
(6) Check temperature of asphalt cement (assuming a cyclone-baghouse
system is used).
(7) Check condition of bags for tears and blinding.
(8) Check pressure drop across baghouse to determine if it is higher
than design specifications.
The enforcement officer should determine the potential of the batching
plant to create a nuisance problem:
(1) Discuss with plant management dust and odors caused by
overload, plugging or upset conditions.
(2) Discuss odors that may result from mixing operations.
(3) Discuss dust problems that may result from trucks in yard area,
storage piles, etc.
Visual observation can provide a qualitative measure of the dust emitted
from a batch plant but only stack tests will give quantitative results.
Most batch plants should be tested if specific regulations regarding
process weight or allowable grain loading of exhaust gases are in effect.
The enforcement officer can. then make comparative readings of the dust
emissions to determine if the plant is in compliance.
-------
7.18.15
REFERENCES
1. Control Techniques for Particulate Air Pollutants. Washington, D.C. ,
DREW, PHS, NAPCA, January 1969.
2. Danielson, J. A., and R. S. Brown, Jr. Hot Asphalt-Mix Paving Batch Plants.
In: Air Pollution Engineering Manual, J. A. Danielson (ed.). Cincinnati,
DREW, PHS, National Center for Air Pollution Control and the Los Angeles
County Air Pollution Control District. pyg NO. 999-AP-40. 1967.
3. The Asphalt Plant Manual. The Asphalt Institute. Series No. 3 (MS-3).
March 1967.
4. Sheeny, J. P., W. C. Achinger, and R. A. Simon. Handbook of Air Pollution,
DHEW, PHS, NCADC No. 999-AP-44. (No date).
5. Air Pollution Control Practices for Hot Mix Asphalt Paving Batch Plants.
J. Air Pollution Control Assoc. , Vol. 19, No. 12, December 1969.
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G.I
GLOSSARY
ABSORBER: A device utilized to extract selectively cne or more elements of a
gas stream from others by absorption in a liquid medium. Usually the
process is performed in cylindrical towers packed with an inert material
thus providing a large surface area for intimate 'contact between the rising
gas and the falling liquid. (The process may also be carried out in a
tower containing perforated trays in which the rising gas bubbles through
the layer of liquid on the trays.)
ABSORPTION: A process in which one or more constituents are removed from a
gas stream by dissolving them in a selective liquid solvent. This may
or may not involve a chemical change.
ACCUMULATOR: A vessel for the temporary storage of a gas or liquid; usually
used for collecting sufficient material for a continuous charge to a
refining process.
ACID SLUDGE: The residue left after treating petroleum oil with sulfuric acid
for the removal of impurities. It is a black, viscous substance contain-
ing the spent acid and impurities which have been separated from the oil.
ACID TREATMENT: An oil-refining process in which unfinished petroleum pro-
ducts, such as gasoline, kerosene, diesel fuel, and lubricating stocks,
are contacted with sulfuric acid to improve color, odor, and other
properties.
ACIDULATE: To make acid, especially slightly acid; to treat with acid.
ADDITION REACTION: Direct chemical combination of two or more substances to
form a single product, such as the union of ethylene and chlorine to form
ethylene dichloride:
C2H4 + C12 ~* C2H4C12
ADIABATIC LAPSE RATE: The rate at which a given mass of air lifted adiabatical-
ly (without loss or gain of heat) cools due to the decrease of pressure
with increasing height, 5.4°F/1000 ft C9.7°C/km).
ADIABATIC PROCESS: A thermodynamic change of state of a system in which there
is no transfer of heat or mass across the boundaries of the system.
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G.2
ADIABATIC TEMPERATURE: (Combustion) The theoretical temperature that would
be attained by products of combustion provided the entire chemical energy
of the fuel, the sensible heat content of the fuel, and combustion air
above the ambient temperature were transferred to the products of combus-
tion. This assumes (1) that combustion is complete, (2) that there is no
heat loss, (3) that there is no dissociation of the gaseous compounds
formed, and (4) that inert gases play no part in the reaction.
ADSORPTION: A reaction in which one or more constituents (adsorbates) are re-
moved from a gas stream by contacting and adhering to the surface of a
solid (adsorbent). Periodically the adsorbent must be regenerated to re-
move the adsorbate.
AEROSOL: A colloidal system in which particles of solid or liquid are sus-
pended in a gas. There is no clear-cut upper limit to the particle size
of the dispersed phase in an aerosol, but as in all other collodial sys-
tems, it is commonly set at 1 micro-meter. Haze, most smoke, and some fogs
and clouds may be regarded as aerosols.
AFTERBURNER: A burner located so that combustion gases are made to pass through
its flame in order to remove smoke and odors.
AGGLOMERATION: Groups of fine particles clinging together to form a larger
particle.
AIR ATOMIZING OIL BURNER: A burner in which oil is atomized by compressed air
which is forced into and through one or more streams of oil thus breaking
it into a fine spray.
AIR CURTAIN DESTRUCTOR: A device employing an air blower with pit incinerator.
Excess oxygen and turbulence result in apparent complete combustion, leaving
no residue unburned carbon (smoke) nor odorous hydrocarbons. The device
has been satisfactorily demonstrated for disposal of low-ash, high-Btu
waste, such as trees, tree trunks, brush (but not leaves), and wooden
crating material. Excessive pollution results when materials such as
automobile tires, cushions, and other non-wood wastes are burned.
AIR HEATER OR AIR PREHEATER: Heat transfer apparatus through which combustion
air is heated by a medium of higher temperature, such as the products of
combustion or steam.
ALKYLATION: In petroleum refining, usually the union of an olefin (ethylene
through pentene) with isobutane to yield high-octane, branched-chain paraf-
finic hydrocarbons. Alkylation may be accomplished by thermal and catalytic
reactions. Alkylation of benzene and other aromatics with olefins yields
alkyl aromatics.
ALUMINA: Aluminum oxide (Al^O-), an intermediate product in the production of
aluminum. This oxide also occurs widely in nature as corundum.
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G.3
AMBIENT AIR: That portion of the atmosphere, external to buildings, to which
the general public has access.
ANODE: In aluminum production, the positively charged carbon terminal in the
reduction cell or pot. Oxygen is attracted to the anode where it combines
with carbon plus any impurities, such as sulfur, which may be present. The
anode is consumed by this process and must be replaced periodically.
ANTHRACITE COAL: A hard, black, lustrous coal containing a high percentage of
fixed carbon and a low percentage of volatile matter. Commonly referred
to as "hard coal," it is mined in the United States, mainly in eastern
Pennsylvania, as well as in small quantities in other states.
AREA SOURCE: Any small residential, governmental, institutional, commercial,
or industrial fuel combustion operations, as well as on-site waste disposal
and transportation sources (see point source).
ASH: The noncombustible solid matter in fuel.
ASH-FREE BASIS: The method of reporting fuel analysis whereby ash is deducted
and other constituents are recalculated to total 100 percent.
ASME: The American Society of Mechanical Engineers.
ASPIRATING BURNER: A burner in which the fuel in a gaseous or finely divided
form is burned in suspension. The air of combustion is supplied by drawing
it through one or more openings by the lower static pressure created by
the velocity of the fuel stream.
ASTM: The American Society for Testing and Materials.
ATOMIZER: A device by means of which a liquid is reduced to a very fine spray.
ATMOSPERIC PRESSURE: The pressure due to the weight of the atmosphere. Normal
atmospheric pressure at sea level is approximately 14.7 p.s.i. or 29.92
inches of mercury.
AVAILABLE HEAT: The quantity of useful heat per unit of fuel available from
complete combustion after deducting dry flue gas and water vapor losses.
B
BAGASSE: Sugar cane from which the juice has been essentially extracted.
BAG FILTER: A device containing one or more cloth bags for recovering particles
from the dust-laden gas which is blown through it.
-------
G.4
BAGHOUSE: Structures containing several bag filters (see bag filters).
BAG-TYPE COLLECTOR: A filter wherein the cloth filtering medium is made in the
form of cylindrical bags.
BANKING: Burning solid fuels on a grate at rates sufficient to maintain igni-
tion only.
BARK BOILER: A combustion unit designed to burn mainly bark and wood residues,
used to produce steam for process or electrical energy.
BAROMETRIC CONDENSER: An inexpensive direct contact condenser used when con-
densate recovery is not a factor. In this type of condenser, steam rises
into a rain of cooling water, and both condensed steam and water flow out
of the bottom of the condenser, maintaining a partial vacuum in the con-
denser.
BASE STOCK: A sheet, usually produced from unbleached kraft pulp, formed into
linerboard on a fourdrinier machine.
BATCH FED INCINERATOR: An incinerator that is charged with refuse periodically,
the charge being allowed to burn down or burn out before another charge is
added.
BINDER: See core binder.
BITUMINOUS COAL: Soft coal, dark brown to black in color, having a relatively
high proportion of gaseous constituents and usually burning with a smoky
luminous flame.
BLACK LIQUOR: Spent chemical solution which is formed during the cooking of
wood pulp in the digester. The black liquor is burned as a fuel in the
recovery furnace.
BLAST FURNACE: A shaft furnace in which solid fuel is burned with an air blast
to smelt ore.
BLEEDER: A bypass or relief valve used to relieve excess pressure.
BLISTER COPPER: An impure intermediate product in the refining of copper, pro-
duced by blowing copper bearing material in a converter; the name is
derived from the large blisters on the cast surface that result from the
liberation of SO and other gases.
BLOWBACK: The difference between the pressure at which a safety valve opens
and at which it closes, usually about three percent of the pressure at
which the valve opens.
BLOWDOWN: Hydrocarbons purged during refinery shutdowns and startups which are
-------
G.5
manifolded for recovery, safe venting, or flaring.
BOILER: A closed pressure vessel in which the liquid, usually water, is vapor-
ized by the application of heat.
BOILER HORSEPOWER: A unit of rate of water evaporation. One boiler horsepower
equals the evaporation of 34.5 Ib. of water per hour from a temperature of
212°F into dry saturated steam at the same temperature (equivalent to
33,472 Btu per hour).
BRASSESS: Copper-based alloy of 60-65% copper. Alloying material is usually
zinc.
BREAKER: In anthracite mining, the structure in which the coal is broken, sized,
and cleaned for market. Also known as a coal breaker. A machine used for
the primary reduction of coal, ore, or rock.
BREECHING: A sheet-iron or sheet-metal casing at the end of boilers for
conveying the smoke from the flues to the smokestack.
BRIGHTENING: The process of producing bright stock (see bright stock).
BRIGHT STOCK: Refined high viscosity lubricating oils usually made from resi-
dual stocks by suitable treatment, such as a combination of acid treatment
or solvent extraction with dewaxing or clay finishing.
BRITISH THERMAL UNIT (Btu): The mean British thermal unit is 1/180 of the heat
required to raise the temperature of one pound of water from 32 °F to 212°F
at a constant atmospheric pressure. It is about equal to the quantity of
heat required to raise one pound of water 1°F. A Btu is essentially 252
calories.
BRONZES: Copper based alloy of 85-90% copper. Alloying material is usually tin.
BUNKER C OIL: Residual fuel oil of high viscosity commonly used in marine and
stationary power plants (No. 6 fuel oil).
BURNER: A device for the introduction of fuel and air into a furnace at the
desired velocities, turbulence, and concentration to establish and main-
tain proper ignition and combustion of the fuel.
BUSS (BUSBAR): A heavy metal conductor, usually copper, for high amperage
electricity.
BUSTLE PIPE: In steel making, a metal tube of large diameter which surrounds
a blast furnace at a level a little above the tuyeres; it is lined with
refractory material and distributes the hot air from the blast stoves to
the pipes (goosenecks) which carry the air to the tuyeres.
-------
G.6
CALCINE: Ore or concentrate which has been treated by calcination or roasting
and which is ready for smelting.
CALCINING: Roasting of ore in an oxidizing atmosphere usually to expel sulfur
or carbon dioxide. If sulfur removal is carried to practical completion,
the operation is termed "sweet roasting"; if all C02 is removed, the opera-
tion is termed "dead roasting."
CALORIE: The mean calorie is 1/1000 of the heat required to raise the tempera-
ture of one gram of water from 0°C to 100°C at a constant atmospheric
pressure. It is about equal to the quantity of heat required to raise one
gram of water 1°C.
CARBONIZATION: The process of converting coal to carbon in the absence of air
by using intense heat to remove volative ingredients.
CARBON LOSS: The loss representing the unliberated thermal energy caused by
failure to oxidize some of the carbon in the fuel.
CARCINOGENIC: Producing or tending to produce cancer.
CARRYOVER: The chemical solids and liquid entrained in the steam from a boiler
or effluent from a fractionating column, absorber, or reaction vessel.
CATALYST: A substance capable of changing the rate of a reaction without itself
undergoing any net change.
CATALYTIC CRACKING: The conversion of high boiling hydrocarbons into lower
boiling substances by means of a. catalyst which may be used in a fixed
bed, moving bed, or fluid bed. Natural or synthetic catalysts are employed
in bead, pellet, or powder form. Feedstocks may range from naphtha cuts
to reduced crude oils.
CATHODE: In aluminum production, the negatively charged terminal of the reduc-
tion cell to which the aluminum migrates. The terminal consists of the
carbon lining that makes up the bottom of the cell.
CAVING: In metal mining, caving implies the dropping of the over-burden as
part of the system of mining.
CHARGING: Feeding raw material into an apparatus, for example, into a furnace,
for treatment or conversion.
CHLOROSIS: A diseased condition in green plants marked by yellowing or blanch-
ing of the leaves.
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G.7
CINDERS: Particles not ordinarily considered as fly ash or dust because of
their greater size; these particles consist essentially of fused ash and/
or unburned matter.
CLEANING FIRES: The act of removing ashes from the fuel bed or furnace.
CLINKERS, CEMENT: The glassy, stony, lump-like product of fusing together clay
and limestone as the first stage in the manufacture of portland cement.
COAL DESULFURIZATION: See desulfurization.
COAL GAS: Gas formed by the destructive distillation of coal.
COAL TAR: A black viscous liquid formed as a by-product from the distillation
of coal.
COKE: Bituminous coal from which the volatile constituents have been driven
off by heat so that the fixed carbon and the ash are fused together.
COKE BREEZE: Fine coke particles leaving the coke quencher with the quenched
coke by conveyor. The particles are very fine and may be blown away.
COKE, PETROLEUM: The solid carbonaceous residue remaining as the final product
of the condensation processes in cracking. It consists of highly poly-
cyclic aromatic hydrocarbons very poor in hydrogen. It is used extensive-
ly in metallurgical processes. Calcination of petroleum coke can yield
almost pure carbon or artificial graphite suitable for production of
electrodes, motor brushes, dry cells, etc.
COKING: 1. Carbonization of coal by destructive distillation. 2. In petro-
leum refining: any cracking process in which the time of cracking is so
long that coke is produced as the bottom product; thermal cracking for
conversion of heavy, low-grade oils into lighter products and a residue
of coke; or the undesirable building up of coke or carbon deposits on
refinery equipment.
COLLECTION EFFICIENCY: The ratio of the weight of pollutant collected to the
total weight of pollutant entering the collector.
COLLOID: 1. A substance composed of extremely small particles, ranging from
0.005 micro—meters to 0.2 micro-meters, which when mixed with a liquid
will not settle, but will remain suspended. The colloidal suspension thus
formed has properties that are quite different from the simple solution of
the two substances. 2. In fuel burning, a finely divided organic sub-
stance which tends to inhibit the formation of dense scale and results in
the deposition of sludge, or causes it to remain in suspension, so that it
may be blown from the boiler.
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G.8
COLLOIDAL FUEL: Mixture of fuel oil and powdered solid fuel.
COMBINATION BOILER: A combustion unit used to produce steam for process or
electrical energy which is designed to burn bark and at least one other
fuel.
COMBUSTION CONTAMINANTS: Particulate matter discharged into the atmosphere from
the burning of any kind of material containing carbon.
COMBUSTION TOWER: Refractory graphite-lined or water-jacketed stainless steel
tower in which phosphorus is burned to phosphorus pentoxide.
CONDENSED FUMES: Minute solid particles generated by the condensation of vapors
from solid matter after volatilization from the molten state, or generated
by sublimation, distillation, calcination, or chemical reaction when these
processes create airborne particles.
CONDENSER BOILER: A boiler in which steam is generated by the condensation of
a vapor.
CONTACT CONDENSER: A condenser in which coolant, vapors, and condensate are
mixed.
CONTINUOUS-FEED INCINERATOR: An incinerator into which refuse is charged in a
nearly continuous manner in order to maintain a steady rate of burning.
CONTROL STRATEGY: A combination of measures designed to achieve the aggregate
reduction of emissions necessary for attainment and maintenance of a
national ambient air quality standard.
CONVECTION: The transmission of heat by circulation of a liquid or a gas. Con-
vection may be natural or forced.
CONVERTER: 1. A furnace in which air is blown through a bath of molten metal
or matte, oxidizing the impurities and maintaining the temperature through
the heat produced by the oxidation reaction. 2. In nitric acid produc-
tion, the chamber in which ammonia is converted to nitric oxide and water
by reacting it with air over a platinum-rhodium catalyst.
CONVERTING: The process of removing impurities from molten metal or metallic
compounds by blowing air through the liquid. The impurities are changed
either to gaseous compounds, which are removed by volatilization, or to
liquids or solids which are removed as slags.
CORE: The central part of a sand mold as used in foundries. The device placed
in a mold to make a cavity in a casting.
CORE BINDER: Organic material added to foundry sand to aid in formation of a
-------
G.9
strong core for casting. Flour, linseed oil, starch, and resins are among
materials used.
CRACKING: Chemical reaction by which large oil molecules: are decomposed into
smaller, lower—Boiling -molecules. At the same time, certain of these
molecules, which are reactive, comBine with, one another to give even larger
molecules than those in the original stock.. The-more stable molecules
leave the system as cracked gasoline, But the reactive ones polymerize,
forming tar and even coke. Cracking -may Be in either the liquid or vapor
phase. When a catalyst is used to Bring aBout the desired chemical reac-
tion, this is called "catalytic cracking"; otherwise, it is assumed to Be
"thermal cracking" Csee catalytic cracking!.
CRACKLINGS: The crisp residue left after the fat has Been separated from the
fiBrous tissue in rendering lard or frying or roasting the skin of pork,
turkey, duck, or goose.
CRUSHER: A machine for crushing rock, or other materials. Among the various
types of crushers are the ball mill, gyratory crusher, Hadsel mill, ham-
mer mill, jaw crusher, red mill, rolls, and stamp mill.
CRYOLITE: Sodium aluminum fluoride (Na A1F ) used as an electrolyte in smelting
of alumina to provide aluminum.
CULM: The fine refuse from anthracite coal production.
CUPOLA: A vertical shaft furnace used for melting metals, especially grey
iron, by having the charge come in contact with the hot fuel, usually
metallurgical coke. Metal, coke, and flux are charged from the top of the
furnace onto a bed of hot coke through which air is blown.
CURTAIN WALL: A partition wall between chambers in an incinerator under which
combustion gases pass.
CYCLONE: A structure without moving parts in which the velocity of an inlet
gas stream is transformed into a confined vortex from which centrifugal
forces tend to drive the suspended particles to the wall of the cyclone
body. The particles then slide down the cyclone wall and are collected
at the bottom.
CYCLONE SCRUBBERS: Devices ranging from simple dry cyclones with spray nozzles
to multistage devices. All feature a tangential inlet to a cylindrical
body.
CYCLONIC SPRAY TOWER: Liquid scrubbing apparatus where sprays are introduced
countercurrent to gases for removal of contaminants.
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G.10
D
DEHYDROGENATION; The removal of hydrogen from a chemical compound; for example,
the removal of two hydrogen atoms from Butane to make Butylene, and the
further removal of hydrogen to make Butadiene.
DEMISTER (COLLECTOR): 1. A mechanical device used to eliminate finely divided
liquid particles from process streams- by Impaction and agglomeration.
2. Apparatus made of wire mesh, or glass- fiBer and -used to eliminate acid
mist as in the manufacture of sulfurlc acid.
DESTRUCTIVE DISTILLATION: 1. A process of distillation in which an organic
compound or mixture Is heated to a temperature high, enough to cause de-
composition. 2. The heating of organic matter when air is not present,
resulting in the evolution of -volatile matter and leaving char consisting
of fixed carbon and ash..
DESULFURIZATION: 1. In coal processing, the removal of sulfur from the coal,
often by mechanical cleaning processes. 2. Hi petroleum refining, remov-
ing sulfur or sulfur compounds from a charge stock Coil that Is to be
treated in a particular unit].
DIFFUSION: The spreading or scattering of a gaseous or liquid material.
1. Eddy diffusion: diffusion caused by turbulent activity in a fluid
system. 2. Molecular diffusion: a process of spontaneous intermixing
of different substances, attributed to molecular motion and tending to
produce uniformity of concentration.
DIRECT-FIRED BOILER: Commonly used to denote a boiler and furnace fired by
pulverized coal.
DISPERSION: The dilution of a pollutant by diffusion, or turbulent action, etc.
Technically, a two-phase system of two substances, one of which (the dis-
persed phase) is uniformly distributed in a finely divided state through
the second substance (the dispersion medium). Either phase may be a gas,
liquid, or solid.
DISTILLATE: The product of distillation obtained by condensing the vapors from
a still.
DISTILLATE FUELS: Liquid fuels distilled usually from crude petroleum, except
residuals such as No. 5 and No. 6 fuel oil.
DISTILLATE OILS: The lighter oils produced by distilling crude oil.
DISTILLATION: The process of heating a substance to the temperature at which
it is converted to a vapor, then cooling the vapor, and thus restoring it
to the liquid state.
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G.ll
DOCTOR TREATMENT: Treatment of gasoline with sodium-plumbite solution and sul-
fur to improve Its odor.
DOPES FOR GASOLINES': Materials added in small amounts to gasoline to increase
the octane number and thus help to prevent knocking.
DOUBLE DECOMPOSITION: A chemical reaction between two compounds in which, part
of the first compound becomes united with the remainder of the second, as:
AK + CD = AD + KC.
DRAFT: A gas flow-resulting from the pressure difference between the incinera-
tor, or any component part, and the atmoshpere, which.moves the products
of combustion from the incinerator to the atmosphere. 1. Natural draft:
the negative pressure created By the difference in density Between the hot
flue gases and the atmosphere. 2. Induced draft: the negative pressure
created by the vacuum action of a fan or blower located Between the in-
cinerator and the stack. 3. Forced draft: the positive pressure created
by the action of a fan or blower, which, supplies the primary or secondary
air.
DROP ARCH: A refractory construction or baffle which serves to deflect gases
in a downward direction.
DROSS: 1. Impurity formed in melted metal. A zinc-and-iron alloy forming in
a bath of molten zinc, in galvanizing iron. 2. The scum that forms on
the surface of molten metals usually due to oxidation, But occasionally
due to the rising of impurities to the surface.
DRUM, FLASH COR FLASH TOWER): A drum or tower into which the heated outlet
products of a preheater or exchanger system are conducted, often with some
release in pressure. The purpose of the drum is to allow vaporization and
separation of the volatile portions for fractionation elsewhere.
DRY BOTTOM FURNACE: A furnace designed to burn pulverized coal at temperatures
low enough to prevent the ash from fusing or slagging.
DUST: Generally particles from 1 to 100 micro-meters in size that become air-
borne by natural or mechanical means. These particles do not diffuse but
will settle under the influence of gravity Csee also particle].
DUST COLLECTING FAN: A centrifugal fan which concentrates dust and skims it
into a cyclone or hopper.
DUSTLESS LOADING: The amount of dust in a gas, usually expressed in grains per
cubic foot or in pounds per thousand pounds of gas Csee also grain load-
ing) .
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G.12
ECONOMIZER: A heat recovery device designed to transfer heat from the products
of combustion to a fluid, usually feedwater for a steam boiler. The water
flows through a bank of tubes placed across the flue gases and is heated by
these gases prior to entering the boiler.
EFFICIENCY: The ratio of output to input. The efficiency of a steam generating
unit is the ratio of the heat absorbed by the water or steam to the heat in
the fuel fired, expressed in percent.
EFFLUENT: Any waste material (solid, liquid, gas) emitted by a process.
EFFLUENT WATER SEPARATOR: A container designed to separate volatile organic
compounds from waste water prior to discharge or reuse.
ELECTROLYSIS: 1. Chemical change resulting from the passage of an electric
current through an electrolyte. 2. Transfer or transport of matter
through a medium by means of conducting ions (positively or negatively
charged particles). The medium may consist of fused salts or conducting
solutions which permit free movement of ions toward the countercharged
electrodes immersed in the system.
ELECTROSTATIC PRECIPITATOR: Devices that separate particles from a gas stream
by passing the carrier gas between two electrodes across which a unidirec-
tional, high-voltage electrical charge is placed. The particles pass
through this field, become charged and migrate to the oppositely charged
electrode. Single-stage precipitators are those in which gas ionization
and particulate collection are combined into a single step. In the two-
stage unit, ionization is achieved by one element of the unit and the col-
lection by the other. Electrostatic precipitators are highly efficient
collectors for minute particles.
ELUTRIATOR: A vertical tube through which a gas or fluid passes upward at a
specific velocity while a solid mixture whose separation is desired is fed
into the top of the column. The large particles which settle at a veloci-
ty higher than that of the rising fluid are collected at the bottom of the
column, and the smaller particles are carried out of the top of the column
with the fluid.
EMISSION: The total amount of a solid, liquid, or gaseous pollutant emitted
into the atmosphere from a given source in a given time, and indicated in
grams per cubic meter of gas, pounds per hour, or other quantitative
measurement.
ENDOTHERMIC REACTION: A reaction which requires the addition of heat for its
continuation.
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G.13
ENTRAINMENT: The process of particulates or other materials being carried
along by a gas stream.
EVAPORATOR: Usually a vessel which receives the hot discharge from a heating
coil and, by a reduction in pressure, flashes off overhead the light pro-
ducts and allows the heavy residue to collect in the bottom (see flash
tower) .
EXCESS AIR: Air supplied for combustion in excess of that theoretically re-
quired for complete combustion, usually expressed as a percentage of
theoretical air, such as "130 percent excess air."
EXOTHERMIC REACTION: A reaction which produces heat.
FABRIC FILTER: See bag filter.
FIXED CARBON: That part of the carbon which remains when coal is heated in a
closed vessel until the volatile matter is driven off. It is the nonvola-
tile matter minus the ash.
FEEDSTOCK: Starting material used in a process. This may be raw material or
an intermediate product that will undergo additional processing.
FLOATING ROOF: A special tank roof which floats upon the oil in a storage tank.
FLUE: Any duct, passage, or conduit through which the products of combustion
are carried to a stack or chimney Csee also breeching) .
FLUE GAS: The gaseous products of combustion passing from the furnace into the
stack.
FLUIDIZED ROASTING: Oxidation of finely ground pyritic minerals by means of
upward currents of air, blown through a reaction vessel (fluid bed roaster)
with sufficient force to cause the bed of material to expand (boil) . Re-
action between mineral and air is maintained at a desired exothermic level
by control of oxygen entry, by admission of cooling water, or by addition
of fuel .
FLUOROSIS: A chronic poisoning resulting from the presence of 0.9 milligrams
or more per liter of fluorine in drinking water. Teeth became brittle and
opaque white with a mottled enamel.
FLUOROSPAR: A natural calcium fluoride (CaH^) used as a flux in open hearth steel
furnaces and in gold, silver, copper, and lead smelting.
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G.14
FLUX: 1. In chemistry and metallurgy, a substance that promotes the fusing
of minerals or metals or prevents the formation of oxides. 2. A substance
added to a solid to increase its fusibility. 3. A substance to reduce
melting temperature. 4. Any chemical or rock added to an ore to assist
in its reduction by heat, such as limestone with iron ore in a blast fur-
nace.
FLY ASH: In incineration, suspended incombustible particles, charred paper,
dust, soot, or other partially incinerated matter, carried in the gaseous
products of combustion.
FOOD-GRADE ACID: Phosphoric acid that has been treated for removal of heavy
metals and is suitable for -use in food products.
FORCED DRAFT: See draft.
FRACTIONAL DISTILLATION: The separation of the components of a liquid mixture
by vaporizing and collecting the fractions which condense in different
temperature ranges.
FUEL: Any form of combustible matter—solid, liquid, vapor, or gas, excluding
combustible refuse.
FUEL-BURNING EQUIPMENT: Any furnace, boiler, apparatus, stack, and all appur-
tenances thereto, used in the process of burning fuel for the primary pur-
pose of producing heat or power by indirect heat transfer.
FUGITIVE DUST: Solid airborne particulate matter emitted from any source other
than a flue or stack.
FUME: Fine solid particles predominately less than 1 micro-meter in diameter
suspended in a gas. Usually formed from high-temperature volatilization
of metals, or by chemical reaction.
FUMIGATION: Fumigation is an atmospheric phenomenon in which pollution, which
has been retained by an inversion layer near its level of emission, is
brought rapidly to ground level when the inversion breaks up. High con-
centrations of pollutant can thus be produced at ground level.
FUMING NITRIC ACID: A mixture of 98 percent nitric acid and an equilibrium
mixture of nitrogen tetroxide Q$20iJ and nitrogen dioxide CNO,).
FURNACE OIL: A distillate fuel primarily intended for domestic heating use.
No. 1 commercial standard grade is Intended for "vaporizing" burners re-
quiring a volatile fuel, whereas No. 2 and No. 3 commercial standard
grades are less volatile, and are thus usable in the "atomizing" type of
burners.
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G.15
G
GAGE PRESSURE: The pressure above atmospheric pressure, expressed as pounds
per square inch, gage (psig).
GOB. PILES: Large piles of low-combustilble refuse from coalmine preparation
plants. Fires may develop in these waste material piles by liberation of
heat through slow oxidation, until ignition temperature is reached Csee
also culm).
GRAIN LOADING: Concentration of particulates in exhaust gas, expressed as
grains per standard cubic foot (7000 grains = 1 pound) Csee also dust
loading).
GRAVITATIONAL SETTLING: Removal of material from the atmosphere due to the ac-
tion of gravity.
GREEN COKE: Coke that has not been fully cooked. Green coke produces exces-
sive emissions when pushed from a coke oven.
GREEN FEED (CALCINED FEED): Not fully processed or treated feed.
GROUT (GROUTING): A pumpable slurry of portland cement or a mixture of port-
land cement and fine sand commonly forced into a borehole to seal crevices
in a rock to prevent ground water from seeping or flowing into an excava-
tion or for extinguishing underground fires.
H
HEAT ISLAND EFFECTS: Meteorological characteristics of an urban area or large
industrial complex which differentiates it from its surroundings. Gener-
ally, the urban area has (1) higher temperatures, C2) a less stable noc-
tournal lapse rate immediately above the surface, (3) lower relative
humidities, (4) greater cloudiness, (5) more frequent fogs, (6) less in-
coming radiation, (7) lower wind speeds, and (8) greater precipitation.
HEAT RELEASE RATE: The amount of heat liberated during the process of combus-
tion and expressed in Btu per hour per cubic foot of internal furnace vol-
ume in which the combustion takes place.
HOG FUEL BOILER: See bark boiler.
HOT BLAST MAIN: A duct lined with refractory material, through which hot air
passes from a hot blast stove to the bustle pipe of a blast furnace.
HOT WELL: A reservoir for receiving warm condensed steam drawn from a con-
denser.
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G.16
HYDRATOR-ABSORBER: A single or double tower in which phosphorus pentoxide is
hydrated to phosphoric acid and the resulting acid mist is absorbed.
HYDRAULIC FLY ASH HANDLING: A system using water-filled pipes or troughs in
which fly ash is conveyed by means of gravity, water jets, or centrifugal
pumps.
HYDROCARBONS: Organic compounds which- consist solely of carbon and hydrogen
and occur in petroleum, natural gas and coal.
HYDROCRACKING: A low-temperature catalytic method of converting crude oil,
residual oil, petroleum tar, and asphalt to high-octane gasoline, jet fuel,
and/or high-grade fuel oil. The process combines cracking, hydrogenation,
and isomerization.
HYDRODESULFURIZATION: A desulfurization process in which the oil is heated
with hydrogen.
HYDROGENATION: The chemical addition of hydrogen to a material at high pres-
sure in the presence of a catalyst.
HYDROMETALLURGY: The treatment of ores, concentrates, and other metal-bearing
materials by wet processes, usually involving the solution of some compo-
nent, and its subsequent recovery from the solution.
HYDROTREATING: A treating process using hydrogen for the desulfurization of
cracked distillates.
IMPINGEMENT: In air sampling, impingement refers to a process for the collec-
tion of particulate matter in which, the gas being sampled is directed
forcibly against a surface. 1. Dry impingement: the process of impinge-
ment in the gas stream where particulate matter is retained upon the sur-
face against which the stream is directed. The collecting surface may
be treated with a film of adhesive. 2. Wet impingement: the process of
impingement in a liquid which retains the particulate matter.
IMPINGEMENT SEPARATORS: Devices using the principle that when a gas stream
carrying particulate matter impinges on a body, the gas is deflected
around the body, while the particles, because of their greater inertia,
tend to strike the body and be collected on its surface. The bodies may
be in the form of plates, cylinders, ribbons, or spheres.
INCINERATION: The process of burning solid, semi-solid, or gaseous combustible
waste.
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G.17
INCINERATOR: An apparatus designed to burn solid, semi-solid, or gaseous waste
leaving little or no combustible material Csee multiple chamber incinera-
tor) .
INERTIAL SEPARATOR: The most widely used device for collecting medium and
coarse sized particles. Inertial separators operate by the principle of
imparting centrifugal force to the particle to be removed from the car-
rier gas stream.
INTERRUPTIBLE GAS: Gas sold whereby the seller may curtail or stop delivery,
generally at his option. The gas customer under these conditions is ex-
pected to have standby equipment capable of taking over 100% of his needs
by an alternate fuel.
INVERSION: A stratum in the atmosphere through which the temperature increases
with height. The layer is thermally stable and vertical motion within the
layer is suppressed.
INVERSION BASE: The lowest height in the atmosphere at which the temperature
ceases to decrease with height.
ISOMERIZATION: A reaction which alters the fundamental arrangement of the
atoms in a molecule without adding or removing anything from the original
material. In the petroleum industry, straight-chain hydrocarbons are con-
verted catalytically to branched-chain hydrocarbons of substantially high-
er octane number by isomerization.
JIG: A device which separates coal from foreign matter by means of their dif-
ference in specific gravity in a water medium. The water pulsates up and
down causing the heavy material to work to the bottom.
K
KETTLE: 1. An open-top vessel used in carrying out metallurgical operations
on low-melting-point metals; for example, in dressing and desilverizing
lead. 2. An open or (usually) closed vessel for preparing paints, var-
nishes, and resins.
KILN: A furnace in which the heating operations do not involve fusion. Kilns
are most frequently used for calcining, and free access of air is permit-
ted. The raw materials may be heated by the combustion of solid fuel with
which they are mixed, but more usually they are heated by gas or the waste
heat from other furnaces.
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G.18
KILN GAS: Hot effluent gases from a kiln. Unless controlled, these gases can
be the largest source of partlculates In a plant.
KNOCKOUT DRUM: A drum or vessel constructed with baffles through which a mix-
ture of gas and liquid is passed to disengage one from the other. As the
mixture comes in contact with the Baffles, the impact frees the gases and
allows them to pass overhead; the heavier substance falls to the bottom of
the drum.
LAPSE RATE: The decrease of temperature with altitude.
LAUNDER: A trough, channel, or gutter usually of wood, by which water is con-
veyed. Specifically, in mining, a chute or trough for conveying powered
ore, or for carrying water to or from the crushing apparatus.
LEACHING: Extracting a soluble metallic compound from an ore by selectively
dissolving it in a suitable solvent, such as water, sulfuric acid, hydro-
chloric acid, etc.
LIGNITE COAL (BROWN COAL): A brownish-black variety of coal, usually high in
moisture and low in Btu's. Lignite is one of the earlier stages in the
formation of bituminous coal.
M
MANIFOLD: A pipe or header for collecting a fluid or gas from, or distributing
a fluid or gas to, a number of pipes or tubes.
MANUFACTURED GAS: Fuel gas manufactured from coal, oil, etc., as differenti-
ated from natural gas.
MATERIAL BALANCE: An accounting of the weights of material entering and leav-
ing a process.
MATTE: A metallic sulfide mixture formed in smelting sulfide ores of copper,
lead, and nickel.
MECHANICAL, CENTRIFUGAL SEPARATORS: A device for separating particulates. A
rotating fan blade exerts a large centrifugal force on the particulates,
ejecting them from the tips of the blades to a skimmer bypass leading into
a dust hopper.
MECHANICAL SCRUBBER: A scrubber in which the water spray is generated by a ro-
tating element or disk {see also scrubber).
MECHANICAL TURBULENCE: In meteorology, the induced eddy structure of the at-
mosphere due to the roughness of the surface over which the air is passing
The height and spacing of the elements causing the roughness will affect
the turbulence.
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G.19
MERCAPTANS: Organic compounds having the general formula R-SH (where R repre-
sents any hydrocarbon radical) which are analogous to the alcohols and
phenols but which contain sulfur in place of oxygen. The simpler mercap-
tans have strong, repulsive odors.
MESH: The number of holes per linear unit in a sieve or gauze, or the space
between the wires of the sieve expressed in inches or millimeters.
METRIC TON: 2204.6 pounds or 1000 kilograms.
MIST: A suspension of any finely divided liquid in a gas.
MODIFIED COAL: Coal of a stoker size containing a controlled percentage of
fines.
MULTICYCLONE CALSO MULTIPLE CYCLONE OR MULTICLONE): A dust collector consisting
of a number of cyclones, operating in parallel, through, which the volume
and velocity of gas can be regulated by means of dampers to maintain dust-
collector efficiency over the load range.
MULTIPLE-CHAMBER INCINERATOR: Any incinerator consisting of a primary combus-
tion chamber, mixing chamber, and secondary combustion chamber in series.
The chambers are separated by refractory walls, and interconnected by gas
passage ports.
MULTIPLE-HEARTH TYPE ROASTER: See roasting furnace.
MUNICIPAL INCINERATOR: An incinerator owned or operated by government or by a
person who provides incinerator service to government or others; a device
designed for and used to burn waste materials of any and all types.
N
NATURAL GAS: Gaseous forms of petroleum occurring in nature and used directly
as a fuel. Natural gas consists of mixtures of hydrocarbon gases and va-
pors, the more important of which are methane, ethane, propane, and butane.
NET TON: 2000 pounds (sometimes known as a "short ton").
NITROGEN OXIDES: A general term pertaining to a mixture of nitric oxide (NO)
and nitrogen dioxide (NO.).
0
ODORANT: A gaseous nuisance that is offensive or objectionable to the smell.
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G.20
ODOR INTENSITY: The numerical or verbal indication of the strength of an odor.
ODOR PERVASIVENESS: The ability of an odor to diffuse into a large volume of
air and still continue to possess a detectable intensity. A pervasive odor
is one whose odor intensity changes very little on dilution.
ODOR QUALITY: A verbal description of an odor. The quality -may be described
in terms of such familiar odorants as coffee, onions, lemons, or by asso-
ciating an unfamiliar odor with a familiar odor.
ODOR THRESHOLD: The lowest concentration of an odor in air that can be detected
by a human.
ODOR UNITS: That quantity of odor necessary to contaminate one cubic foot of
air to threshold or barely perceptible level. The number of odor units
is equal to the volumes C.scf) of air necessary to dilute the concentration
of odorant in one volume Cscf) of air to the threshold concentration.
OIL BURNER: Any device for the introduction of vaporized or atomized fuel oil
into a furnace.
OIL-EFFLUENT WATER SEPARATOR: Any tank, box, sump, or other container in which
any petroleum product entrained in water is physically separated and re-
moved prior to out-fall, drainage, or recovery of the water.
OITICICA COIL): A drying oil obtained from the kernels of the fruit of the
oiticica tree that is similar to tung oil in many properties and is used
chiefly in varnishes, paints, and printing inks.
OLEORESIN: A varnish or paint vehicle, made of plant oils and resins, usually
cooked.
OLEUM (FUMING SULFURIC ACID): A heavy, oily, strongly corrosive liquid that
consists of a solution of sulfur trioxide in anhydrous sulfuric acid. It
fumes in moist air and reacts violently with water.
ONSTREAM TIME: The length of time a unit is in actual production.
OPACITY: The degree to which emissions reduce the transmission of light and
obscure the view of a distant object.
OPEN BURNING: The burning of any matter in such a manner that the products of
combustion are emitted directly into the ambient air without passing
through a stack, duct, or chimney.
OPEN HEARTH FURNACE: Reverberatory furnace, containing a basin-shaped hearth,
for melting and refining suitable types of pig iron, iron ore, and scrap
for steel production.
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G.21
ORE AND LIME BOIL: Reactions which occur in an open hearth furnace when carbon
monoxide is produced by the oxidation of carbon. Ore boil is a violent
agitation of the metal as it escapes during this process; lime boil occurs
when the limestone decomposes and the carbon dioxide gas escapes. The
second reaction begins before the first is completed.
ORGANIC SULFUR: The difference between the total sulfur in coal and the sum of
the pyritic sulfur and sulfate sulfur.
ORGANOLEPTIC: Affecting or making an impression upon one or more of the sense
organs.
ORIFICE SCRUBBERS: Devices for the removal of particulates from gas streams in
which the flow of air through a restricted passage partially filled with
water causes the dispersion of the water and consequent wetting and col-
lection of the particulates.
ORSAT: An apparatus used for analyzing flue gases volumetrically.
OVERBURDEN: Material of any nature, consolidated or unconsolidated, that over-
lies a deposit of useful material, ores, or coal, especially those deposits
that are mined from the surface by open cuts.
OVERFIRE: Air for combustion admitted into the furnace at a point above the
fuel bed.
OXIDATION: The act or process of combining oxygen with a substance, with or
without the production of a flame.
OXYGEN LANCING: In steel making, a procedure in which oxygen is injected into
the bath of molten metal through a water cooled lance. The oxygen oxidizes
carbon, silicon, manganese, and some iron in exothermic reactions. The
procedure materially shortens the time needed to tap the furnace.
PACKED COLUMN (PACKED SCRUBBER OR PACKED TOWER): A vertical column used for
distillation, absorption, and extraction, containing packing; e.g., Raschig
rings, Berl saddles, or crushed rock, which provide a large contacting
surface area between phases. Normally, gas flow is countercurrent to
liquid flow.
PAN: Peroxyacyl nitrates. Secondary pollutants formed in photochemical oxida-
tion and major eye irritants of photochemical smog.
PARTICLE CONCENTRATION: Concentration expressed in terms of number of particles
per unit volume of air or other gas.
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G.22
PARTICULATE MATTER: Any dispersed matter, solid or liquid, in which, the indi-
vidual aggregates are larger than single small -molecules CO.0002 -micro-
meters) but smaller than 500 micro-meters.
PERCOLATOR: A device used in rendering plants for the separation of dry pro-
teinaceous crackling from the clear moisture-free tallow. They are gener-
ally perforated pans which, allow- the tallow to drain away from the crack-
lings.
PERFORMANCE TEST: Measurements of emissions used for the purpose of determin-
ing compliance with a standard of performance.
PETROCHEMICAL INDUSTRY: A branch of the petroleum industry in which refined
crude oil is manufactured into various chemicals.
PETROLEUM COKE: See coke, petroleum.
PHOTOCHEMICAL REACTION: A chemical reaction which involves either the absorp-
tion or emission of radiation in the form of light energy.
PLUME: The path taken by the continuous discharges of products from a chimney
or stack. The shape of the path and the concentration distribution of
gas plumes is dependent on turbulence of the atmosphere.
POINT SOURCE: Any stationary emitting point or plant/facility whose summation
of emitting points totals 100 tons (or some other fixed amount) per year
of any pollutant in a given region.
POLYCYCLIC MOLECULE: A molecule containing two or more fused rings (as in
anthracine).
POLYMERIZATION: 1. A reaction combining two or more molecules to form a
single molecule having the same elements in the same proportions as in the
original molecules. 2. The union of light olefins to form hydrocarbons
of higher molecular weight. The process may be thermal or catalytic.
POLYNUCLEAR AROMATIC HYDROCARBONS: Compounds consisting of two or more aro-
matic rings which share a pair of carbon atoms. The simplest and most
important is naphthalene (C H ; also polycyclic).
10 o
PRECLEANERS: Collectors of limited efficiency used ahead of the final cleaner.
If the gas contains an appreciable amount of hard, coarse particles, a
precleaner can materially reduce erosive wear of the more efficient final
collector.
PRECURSORS: Gaseous air pollutants which react with other substances in the
atmosphere to produce different pollutants; e.g., photochemical reactions
of NO and NO with the oxygen of the air which produce ozone.
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G.23
PRILLING: A combination spray drying and crystallization technique used in the
production of ammonium nitrate. A hot ammonium nitrate solution is sprayed
in the top of a tower, and air is blown in at the bottom. The liquid is
converted into spherical pellets.
PRIMARY AIR: In incineration, air which is introduced with the refuse into
the primary chamber.
PRIMARY EMISSION: Pollutants emitted directly into the air from identifiable
sources.
PRIMARY STANDARD: The national primary ambient air quality standard which de-
fines levels of air quality which, are necessary to protect public health.
PROCESS WEIGHT: The total weight of all materials introduced into a source
operation, including solid fuels, but excluding liquids and gases used
solely as fuels, and excluding air introduced for purposes of combustion.
PUG MILL: A machine for mixing water and clay which consists of a long hori-
zontal barrel within which is a long longitudinal shaft fitted with knives
which slice through the clay, Tailing it with water which is added by
sprayers from the top. The knives are canted to give some screw action,
forcing the clay along the barrel and out one end.
PUMP, RECIPROCATING: A positive-displacement type of pump consisting of a
plunger or a piston moving back and forth within a cylinder. With each
stroke of the plunger or piston, a definite volume of liquid is pushed
out through the discharge valves.
PYRITIC SULFUR: Sulfur combined with iron, found in coal.
PYROLYSIS: Chemical change brought about by the action of heat upon a sub-
stance.
PYROMETER: An instrument for measuring temperatures beyond the range of thermo-
meters.
RECOVERY BOILER: In wood pulping, a combustion unit designed to recover the
spent chemicals from the cooking liquor and to produce steam for pulping
and recovery operations.
REDUCTION: 1. The addition of hydrogen or the abstraction of oxygen from a
substance. 2. The extraction of any metal from its ore.
REFINERY GAS: Any form or mixture of still gas gathered in a refinery from the
various stills.
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G.24
REFINING: In metallurgy, the removal of impurities necessary to produce an
ingot or alloy of desired specification. In petroleum, toe process of
separating, combining, or rearranging petroleum oil constituents- to pro-
duce salable products.
REFORMING: The thermal or catalytic conversion of naphtha into more volatile
products of higher octane rmmBer. It represents the total effect of nu-
merous reactions, such as cracking, polymerization, dehydrogenation, and
isomerization, taking place simultaneously.
REFRACTORY: A ceramic material of a very high melting point with properties
that make it suitable for such uses; as furnace and kiln linings.
RERUN OIL: Oil which has been redistilled.
RESIDUAL: Heavy oil left in the still after gasoline and other distillates
have been distilled off, or residue from the crude oil after distilling
off all but the heaviest components.
RESISTIVITY: The property of a body whereby it opposes and limits the passage
of electricity through it. Resistivity of dust is an important factor in
the performance of electrostatic precipitators. If the resistivity of the
collected dust is higher than about 2 x 10 ohm-cm, excessive arcing or
reverse corona can occur, thereby limiting precipitator performance.
REVERBERATORY FURNACE: A furnace with a shallow hearth; having a roof that de-
flects the flame and radiates heat toward the surface of the charge. Fir-
ing may be with coal, pulverized coal, oil, or gas.
RINGELMANN CHART: A standardized chart giving shades of gray by which the
densities of columns of smoke rising from stacks may be compared.
ROAST: To heat to a point somewhat short of fusing, with access to air, so as
to expel volatile matter or effect oxidation. In copper metallurgy, ap-
plied specifically to the final heating which causes self-reduction to oc-
cur by the reaction between the sulfide and the oxide.
ROASTER: 1. A contrivance for roasting, or a furnace for drying salt cake.
2. A reverberatory furnace or a muffle used in roasting ore.
ROASTING: 1. Heating an ore to effect some chemical change that will facili-
tate smelting. 2. The heating of solids, frequently to promote a reac-
tion with a gaseous constituent in the furnace atmosphere.
ROASTING FURNACE: A furnace in which finely ground ores and concentrates are
roasted to eliminate sulfur; heat is provided by the burning sulfur.
RUN OF MINE COAL: Unscreened bituminous coal as It comes from the mine.
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G.25
SALAMANDER: A small portable incinerator, or a small portable heater burning
coke or oil.
SCRUBBER: A device used to remove entrained liquids and solids from a gas
stream by passing the gas through, wetted "packing" or spray Csee absorber).
SECONDARY AIR: Air introduced into a combustion chamber beyond the point of
fuel and primary air introduction for the purpose of achieving -more com-
plete oxidation.
SECONDARY STANDARD: The national secondary ambient air quality which defines
levels of air quality judged necessary to protect the public welfare from
any known or anticipated adverse effects of a pollutant.
SINTERING: A heat treatment that causes adjacent particles of material to
cohere or agglomerate at a temperature below- that of complete melting.
SKIMMING PLANT: An oil refinery designed to remove and finish only the lighter
constituents from the crude oil, such as gasoline and kerosene. In such a
plant the portion of the crude remaining after the above products are re-
moved is usually sold as fuel oil.
SKIP HOIST, INCLINED: A bucket or can operating up and down, receiving, ele-
vating, and discharging bulk materials.
SLAG: The non-metallic top layer which separates from the metallic products in
smelting of ores.
SLOP OR SLOP OIL: A term rather loosely used to denote odds and ends of oil
produced at various places in a plant, which must be rerun or further pro-
cessed in order to get in suitable condition for use. When good for noth-
ing else, such oil usually goes into pressure-still charging stock, or to
coke stills.
SMELT: In wood pulping, the molten chemicals from the kraft recovery furnace
consisting mostly of sodium sulfide and sodium carbonate.
SMELTING: Any metallurgical operation in which metal is separated by fusion
from impurities with which it may be chemically combined or physically
mixed, such as in ores.
SMOKE: Small gas—borne particles resulting from incomplete combustion, con-
sisting predominantly but not exclusively of carbon, ash, and other com-
bustible material, and present in sufficient quantity to be observable.
SMOKE CANDLE(S): Apparatus used in collecting acid mists. Tubes or candles
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G.26
made from glass or plastic fibers are pressed into pads with thicknesses
up to 2 inches and mounted in Banks. Efficiency is much increased when
the glass is treated with silicone oil.to repel water, or when normally
water-repellent plastic is -used.
SMOKE UNIT: The number of "smoke units" is obtained by multiplying the smoke
density in Ringelmann numbers by the time of occurrence in minutes. For
the purpose of this calculation, a Ringelmann density- reading is made at
least once per minute during the period of oBservation. The sum of the
Ringelmann density readings (made once per minutej during the period of
observations would equal the number of smoke units.
SOILING: Visible damage to materials by deposition of air pollutants.
SOOT: Agglomerated particles consisting mainly of carbonaceous material.
SOUR: Gasolines, naphthas, and refined oils are said to be "sour" if they show
a positive "doctor test"; i.e., if they contain hydrogen sulfide and/or
mercaptans. Sourness is directly connected with odor, while a "sweet"
gasoline has a good odor.
SOURCE: Any property, real or personal, or person contributing to air pollution.
SOURCE SAMPLE: A sample of the emission from an air contamination source, col-
lected for analysis from within a stack.
SPARK ARRESTOR: A screenlike device to prevent sparks, embers, and other ig-
nited materials larger than a given size from being expelled to the atmos-
phere.
SPEISS: Metallic arsenides and antimonides smelted from cobalt and lead ores.
SPRAY CHAMBER: The simplest type of scrubber consisting of a chamber in which
spray nozzles are placed. They are used extensively as gas coolers be-
cause they have a low collection efficiency for anything but coarse particles,
STABILITY CSTATIC STABILITY): The state of the atmosphere when it is stable
relative to vertical displacements.
STACK OR CHIMNEY: Any flue, conduit, or duct arranged to conduct an effluent
to the open air.
STACK SPRAY: A nozzle or series of nozzles installed in a stack above the
breeching, used to inject wetting agents at high pressure to suppress the
discharge of particulate matter from the stack.
STANDARD CONDITIONS: For source testing, 70°F C21.1°CI and 29.22" Hg (760mm
Hg) ; for aix quality measurements,' 77°F C25°C) and 29^.92" Hg (760mm Hg) ;
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G.27
for chemistry, 273. 1°K (0°C) and one atmosphere (760ram Hg] ; for petroleum
refining, 60°F C15.55°C) and 14.7 psi (760mm Hg) .
STATIONARY SOURCE: Any non-mobile building, structure, facility, or installa-
tion which emits or may emit any- air pollutant.
STEAM DISTILLATION: Introduction of "open" steam into the liquid during dis-
tillation to assist in vaporizing the volatiles at a lower temperature.
STILL: A closed chamber, usually cylindrical, in which heat is applied to a
substance to change it into vapor, with or without chemical decomposition.
The substance, in its -vapor form, is conducted to some cooling apparatus
where it is condensed, liquefied, and collected in another part of the unit,
STOCK: In general, any oil which is to receive further treatment before going
into finished products.
STOKER: A machine for feeding coal into a furnace, and supporting it there
during the period of combustion. It may also perform other functions,
such as supply air, control combustion, or distill volatile matter. Modern
stokers may be classified as overfeed, underfeed, and conveyor. Any mech-
anical device that feeds fuel uniformly onto a grate or hearth within a
furnace may be termed a "stoker."
STOPING: In mining, any process of excavating ore which has been made acces-
sible by shafts and drifts.
STRAIGHT-RUN DISTILLATION: Continuous distillation which separates the products
of petroleum in the order of their boiling points without cracking.
STRIPPER: Equipment in which the lightest fractions are removed from a mixture.
In a natural-gasoline plant, gasoline fractions are stripped from rich oil.
In the distillation of crude petroleum, light fractions are stripped from
the various products.
SUBSTITUTION: A chemical reaction in which one or more atoms or groups of a
molecule are replaced by equivalent atoms or groups to form at least two
products, especially the replacement of hydrogen In an organic compound by
another element or group.
SULFIDITY: An expression of the percentage makeup of chemical kraft cooking
liquor obtained by the formula
, 100
Na2S + NaOtt
where the sodium compounds are expressed as
SUPERPHOSPHATE: Products obtained by mixing phosphate rock with either sul-
furic or phosphoric acid, or both.
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SURFACE CONDENSERS: A condenser in which the coolant does not contact the
vapors or condensate. Most are of the tube and shell type. W/ater flows
inside the tubes and -vapors condense on the shell side.
SURGE TANK: A storage reservoir at the downstream end of a feeder pipe to ab-
sorb sudden rises of pressure and to furnish, liquid quickly during a drop
in pressure.
SWEETENING: The process by which petroleum products are improved in odor and
color by oxidizing or removing the sulfur—containing and -unsaturated com-
pounds.
SYNERGISM: Cooperative action of discrete agents such that the total effect is
greater than the sum of the two effects taken Independently.
SYNTHETIC CRUDE: The total liquid, multi-component mixture resulting from a
process involving molecular rearrangement of charge stock. Term commonly
applied to the product from cracking, reforming, -wisbreaklng, etc.
TAIL OIL: That portion of an oil which vaporizes near the end of the distil-
lation; the heavy end.
TAIL GAS: The exhaust or waste gas from a process.
TALLOW: The rendered fat of animals that is white and almost tasteless when
pure, composed of glycerides of fatty acids containing a large proportion
of palmitic acid and stearic acid, and that is used chiefly in making
soap, glycerol, margarine, candles, and lubricants.
TAPPING: Removing molten metal from a furnace.
TEMPERATURE INVERSION: An atmospheric layer in which temperature increases
with altitude. The principal characteristic of a temperature inversion is
its marked static stability, so that very little turbulent exchange can
occur within it (see also Inversion).
THEORETICAL AIR: The exact amount of air (stoichiometric air) required to sup-
ply the oxygen necessary for the complete combustion of a given quantity
of a specific fuel or refuse.
THERMAL TURBULENCE: Air movement and mixing caused by temperature differences.
TOPPED CRUDE PETROLEUM: A residual product remaining after the removal, by
distillation, of an appreciable quantity of the more volatile components
of crude petroleum.
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G.29
TOPPING: The distillation of crude oil to remove light fractions only.
TOTAL REDUCED SULFUR COMPOUNDS (TRS): Malodorous gases produced in the wood
pulping industry exclusive of sulfur oxides. TRS usually includes hydro-
gen sulfide (H S), methyl mercaptan CCtLSH), dimethyl sulfide (CH_SCH ),
and dimethyl dlsulfide (CR-jSSCK,) . The concentration of TRS is usually
expressed as H^S regardless of the constituent compounds.
TURBULENCE: Atmospheric motions which produce a thorough horizontal and verti-
cal mixing of the air.
TURNAROUND: The time between shutting down and starting up of process equip-
ment for repair or maintenance.
TUYERES: Openings or nozzles in a metallurgical furnace through which air is
blown as part of the extraction or refining process.
TWADDELL DEGREES (°TW): A measure of acid density and strength:
°TW = sp. gr. (60°/60°F)
0.005
Each twaddell degree corresponds to a specific gravity interval of 0.005.
ULTIMATE ANALYSIS (OF COAL): Contains the following, expressed in percent by
weight:
Carbon
Hydrogen
Sulfur
Oxygen
Nitrogen
Moisture
Ash
CC) %
CH2) %
(S) %
(02) %
(N2) %
(H20) %
(H00) %
100.0%
UNDERFEED STOKER: A stoker consisting of a trough or pot-shaped report into
which coal is forced by an endless screw or ram. Coal is fed to the fire
zone by being pushed up from underneath.
UNIT OPERATION: 1. Methods by which raw materials may be altered into states,
such as vapor, liquid, or solid without being changed into new substances
with different properties and composition. 2. Recognition, study, appli-
cation and control of the principles and factors utilized in a distinct
and self-contained process (for example, filtration). This avoids the
duplication of effort which attends the study of similar processes as
though each process involved a unique set of principles.
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G.30
UNIT PROCESS: 1. Reactions where raw materials undergo chemical change. 2.
See unit operation C2)•
UREA FORMS: A urea-formaldehyde reaction product that contains more than one
molecule of urea per molecule of formaldehyde.
VACUUM JET (STEAM JET EJECTOR): A fluid nozzle that discharges a high velocity
jet stream across a section chamber that is connected to the equipment to
be evacuated. The gas in the chamber is entrained by the jet stream.
VAPOR: The gaseous phase of a substance that generally exists as a liquid or
solid at room temperature.
VAPOR PLUME: The stack effluent consisting of flue gas made visible by con-
densed water droplets or mist.
VAPOR RECOVERY SYSTEM: System used in petroleum refining for separating a
mixed charge of miscellaneous gases and gasolines into desired intermedi-
ates for further processing.
VENTURI SCRUBBER: A type of high energy scrubber in which the waste gases pass
through a tapered restriction (venturi) and impact with low-pressure water.
Gas velocities at the restriction are from 15,000 to 20,000 fpm and pres-
sure drops from 10 to 70 inches water gage.
VISBREAKING: Viscosity breaking; lowering or "breaking" the viscosity of resi-
dual oil by cracking at relatively low temperatures.
VISIBILITY: In United States weather observing practice, the greatest distance
in a given direction at which it is just possible to see and identify with
the unaided eye (a) in the daytime, a prominent dark object against the
sky at the horizon, and (b) at night, a known, preferably unfocused,
moderately intense light source. After visibilities have been determined
around the entire horizon circle, they are resolved into a single value
of prevailing visibility for reporting purpose.
VISIBLE EMISSION: An emission of air pollutants greater than 5 percent opacity
or 1/4 Ringelmann.
VOLATILE OR VOLATILE MATTER: 1. The gasoline constituents that can be driven
off liquids and solids by the application of heat. 2. Specifically for
coal, that portion which is driven off in gas or vapor form when coal is
subjected to a standardized temperature test.
VOLATILE ORGANIC COMPOUNDS: Any compound containing carbon and hydrogen or
containing carbon and hydrogen in combination with any other element which
has a vapor pressure of 1.5 pounds per square inch absolute or greater
under actual storage conditions.
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G.31
tf-X-Y-Z
WASTE HEAT BOILERS: Boilers which utilize the heat of exhaust gas or process
gas to generate steam or to heat water.
WEAK WASH: In wood pulping, a liquid stream in the kraft process which results
from washing of the lime mud.
WET COLLECTORS: Devices which use a variety of methods to wet the contaminant
particles in order to remove them from the gas stream Csee scrubbers) .
WET FILTERS: A spray chamber with filter pads composed of glass fibers, knit-
ted wire mesh, or other fibrous materials. The dust is collected on the
filter pads.
WHITE LIQUOR: Cooking liquid used in the wood pulping industry. Kraft process:
consists of approximately 1/3 sodium sulfide (Na S) and 2/3 sodium hydroxide
(NaOK) . Sulfite process: consists of sulfurous acid plus one of the fol-
lowing: calcium bisulfite, sodium bisulfite, magnesium bisulfite, or
ammonium bisulfite.
U. S. GOVERNMENT PRINTING OFFICE: 1972 746763/^111
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