United States
Environmental Protection
Agency
Research and
Development
EPA--600/8- 87-0341
September 1987
PREVENTION REFERENCE MANUAL:
CHEMICAL SPECIFIC
VOLUME 12: CONTROL OF
ACCIDENTAL RELEASES
OF SULFUR DIOXIDE
Prepared for
Office of Air Quality Planning and Standards
Prepared by
Air and Energy Engineering Research
Laboratory
Research Triangle Park NC 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development. U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the SPECIAL REPORTS series. This series is
reserved for reports which are intended to meet the technical information needs
of specifically targeted user groups. Reports in this series include Problem Orient-
ed Reports, Research Application Reports, and Executive Summary Documents.
Typical of these reports include state-of-the-art analyses, technology assess-
ments, reports on the results of major research and development efforts, design
manuals, and user manuals.
EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental Protection Agency, and
approved for publication. Approval does not signify that the contents necessarily
reflect the views and policy of the Agency, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service. Springfield, Virginia 22161.
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ABSTRACT
Recent headlines of accidental releases of toxic chemicals at Bhopal and
Chernobyl have created the current public awareness of toxic release problems.
As a result of other, perhaps less dramatic incidents in the past, portions of
the chemical industry were aware of this problem long before these events.
These same portions of the industry have made advances in this area. Interest
in reducing the probability and consequences of accidental toxic chemical
releases that might harm workers within a process facility and people in the
surrounding community prompted the preparation of this manual and a planned
series of companion manuals addressing accidental releases of toxic chemicals.
Sulfur dioxide has an IDLE (Immediately Dangerous to Life and Health)
concentration of 100 ppm, which makes it an acute toxic hazard.
Reducing the risk associated with an accidental release of sulfur dioxide
involves identifying some of the potential causes of accidental releases that
apply to the processes that use sulfur dioxide. In this manual, examples of
potential causes are identified as are specific measures that may be taken to
reduce the accidental release risk. Such measures include recommendations on
plant design practices, prevention, protection and mitigation technologies,
and operation and maintenance practices. Conceptual cost estimates of possi-
ble prevention, protection, and mitigation measures are provided.
11
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ACKNOWLEDGEMENTS
This manual was prepared under the overall guidance and direction of T.
Kelly Janes. Project Officer, with the active participation of Robert P.
Hangebrauck. William J. Rhodes, and Jane M. Crum. all of U. S. EPA. In
addition, other EPA personnel served as reviewers. Radian Corporation
principal contributors involved in preparing the manual were Graham E. Harris
(Program Manager). Glenn B. DeWolf (Project Director), Daniel S. Davis,
Jeffrey D. Quass, Miriam Stohs, and Sharon L. Wevill. Contributions were also
provided by other staff members. Secretarial support was provided by Roberta
J. Brouwer and others. A special thanks is given to many other people, both
in government and industry, who served on the Technical Advisory Group and as
peer reviewers.
111
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TABLE OF CONTENTS
Section
ABSTRACT
ACKNOWLEDGEMENTS
FIGURES v
TABLES vi
1 INTRODUCTION 1
1.1 Background 1
1.2 Purpose of This Manual 2
1.3 Uses of Sulfur Dioxide 2
1.4 Contents of this Manual 3
2 CHEMICAL CHARACTERISTICS 4
2.1 Physical Properties 4
2.2 Chemical Properties and Reactivity 7
2.3 Toxicological and Health Effects 8
3 FACILITY DESCRIPTIONS AND PROCESS HAZARDS 11
3.1 Manufacture 11
3.2 Processing and Consumption 13
3.2.1 Manufacture of Sulfuric Acid 14
3.2.2 Sulfonation of Alkanes 17
3.2.3 Sulfur Dioxide in the Pulp and Paper Industry . . 21
3.2.4 Water and Wastewater Treatment 28
3.2.5 Sulfur Dioxide in the Petroleum Industry 30
3.3 Repackaging Sulfur Dioxide 35
3.4 Storage and Transfer 36
3.4.1 Storage 37
3.4.2 Transfer from Tank Cars and Trucks 38
3.4.3 Transfer from Storage Vessels 39
3.4.4 Transporting Sulfur Dioxide Storage Containers . . 41
4 POTENTIAL CAUSES OF RELEASES 42
4.1 Process Causes 42
4.2 Equipment Causes 43
4.3 Operational Causes 45
5 HAZARD PREVENTION AND CONTROL 46
5.1 General Considerations 46
5.2 Process Design 47
5.3 Physical Plant Design 48
5,3.1 Equipment 49
5.3.2 Plant Siting and Layout 65
5.3.3 Transfer and Transport Facilities 67
iv
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TABLE OF CONTENTS (Continued)
Section Page
5.4 Protection Technologies 68
5.4.1 Enclosures 68
5.4.2 Scrubbers 70
5.5 Mitigation Technologies 73
5.5.1 Secondary Containment Systems 74
5.5.2 Flotation Devices and Foams 79
5.5.3 Mitigation Techniques for Sulfur Dioxide Vapor . . 81
5.6 Operation and Maintenance Practices 82
5.6.1 Management Policy 83
5.6.2 Operator Training 85
5.6.3 Maintenance and Modification Practices 87
5.7 Control Effectiveness 91
5.8 Illustrative Cost Estimates for Controls 92
5.8.1 Prevention and Protection Measures 92
5.8.2 Levels of Control 92
5.8.3 Summary of Levels of Control 96
5.8.4 Equipment Specifications and Detailed Costs ... 96
5.8.5 Methodology 96
6 REFERENCES 137
APPENDIX A - GLOSSARY 142
APPENDIX B - METRIC (SI) CONVERSION FACTORS 145
FIGURES
Number Page
3-1 Conceptual diagram of typical sulfur dioxide extraction process . . 12
3-2 Conceptual diagram of typical double-absorption sulfuric acid
process 16
3-3 Conceptual diagram of typical sulfurization process 19
3-4 Conceptual diagram of sulfite cooking liquor preparation and sulfur
recovery process 23
3-5 Conceptual diagram of typical chlorine dioxide manufacturing
process 25
3-6 Conceptual diagram of water dechlorination with sulfur dioxide . . 27
3-7 Conceptual diagram of typical batch chromium waste treatment
process 29
3-8 Conceptual diagram of typical sulfur dioxide extraction process . . 31
5-1 Computer model simulation showing the effect of diking on the
vapor cloud generated from a release of liquified sulfur dioxide . 78
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TABLES
Number Page
2-1 Physical Properties of Sulfur Dioxide ' • 5
2-2 Exposure Limits for Sulfur Dioxide 9
2-3 Predicted Human Health Effects of Exposure to Various Concentrations
of Sulfur Dioxide 10
3-1 Sulfur Dioxide Reaction Products 15
5-1 Example Process Design Considerations for Processes Involving
Sulfur Dioxide 43
5-2 Materials of Construction for Sulfur Dioxide Service 50
5-3 Maximum Safe Volume of Liquid Sulfur Dioxide in a Storage Tank at
Various Temperatures 53
5-4 Example of Performance Characteristics for an Emergency Packed Bed
Scrubber for Sulfur Dioxide 72
5-5 Examples of Major Prevention and Protection Measures for Sulfur
Dioxide Releases 93
5-6 Estimated Typical Costs of Major Prevention and Protection Measures
for Sulfur Dioxide Releases 94
5-7 Summary Cost Estimates of Potential Levels of Controls for Sulfur
Dioxide Storage Tank and Extraction Tower 97
5-8 Example of Levels of Control for Sulfur Dioxide Storage Tank ... 98
5-9 Example of Levels of Control for Sulfur Dioxide Extraction Tower . 100
5-10 Estimated Typical Capital and Annual Costs Associated with Baseline
Sulfur Dioxide Storage System 102
5-11 Estimated Typical Capital and Annual Costs Associated with Level 1
Sulfur Dioxide Storage System 103
5-12 Estimated Typical Capital and Annual Costs Associated with Level
2 Sulfur Dioxide Storage System 105
5-13 Estimated Typical Capital and Annual Costs Associated with Baseline
Sulfur Dioxide Extraction Tower System 107
5-14 Estimated Typical Capital and Annual Costs Associated with Level 1
Sulfur Dioxide Extraction Tower System 108
vi
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TABLES (Continued)
Number Page
5-15 Estimated Typical Capital and Annual Costs Associated with Level 2
Sulfur Dioxide Extraction Tower System 110
5-16 Equipment Specifications Associated with Sulfur Dioxide Storage
System 112
5-17 Details of Material and Labor Costs Associated with Baseline
Sulfur Dioxide Storage System 115
5-18 Details of Material and Labor Costs Associated with Level 1 Sulfur
Dioxide Storage System 116
5-19 Details of Material and Labor Costs Associated with Level 2 Sulfur
Dioxide Storage System 118
5-20 Equipment Specifications Associated with Sulfur Dioxide' Extraction
Tower System 120
5-21 Details of Material and Labor Costs Associated with Baseline Sulfur
Dioxide Extraction Tower System 123
5-22 Details of Material and Labor Costs Associated with Level 1 Sulfur
Dioxide Extraction tower System 124
5-23 Details of Material and Labor Costs Associated with Level 2 Sulfur
Dioxide Extraction Tower System 126
5-24 Format for Total Fixed Capital Cost 129
5-25 Format for Total Annual Cost 131
5-26 Format for Installation Costs 136
vii
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SECTION 1
INTRODUCTION
1.1 BACKGROUND
The consequences of a large release of a toxic chemical can be
devastating. This was clearly evidenced by the release of a cloud of toxic
methyl isocyanate in Bhopal. India on December 3. 1984. which killed
approximately 2,000 people and injured thousands more. Prior to this event.
there had been other, perhaps less dramatic, releases of toxic chemicals, but
the Bhopal incident precipitated the recent public concern for the integrity
of process facilities which handle hazardous materials.
•
Recognizing the fact that no chemical plant is free of all release
hazards and risks, a number of concerned individuals and organizations have
contributed to the development of loss prevention as' a recognized specialty
area within the general realm of engineering science. Interest in reducing
the probability and consequences of an accidental release of sulfur dioxide
prompted the preparation of this manual. Furthermore, a series of manuals is
planned which will address the prevention and control of a large release of
any toxic chemical. The subjects of the other manuals planned for the series
include:
• A user's guide.
• Prevention and protection technologies,
• Mitigation technologies, and
• Other chemical specific manuals such as this one.
The manuals are based on current and historical technical literature, and they
address the design, construction, and operation of chemical process facilities
where accidental releases of toxic chemicals could occur. Specifically, the
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user's guide is intended as a general introduction to the subject of toxic
chemical releases and to the concepts which are discussed in more detail in
the other manuals. Prevention technologies are applied to the design and
operation of a process to ensure that primary containment is not breached.
Protection technologies capture or destroy a toxic chemical involved in an
incipient release after primary containment has been breached but before an
uncontrolled release occurs, while mitigation technologies reduce the
consequences of a release once it has occurred.
Historically, there do not appear to have been any significant releases
of sulfur dioxide in the United States. Major incidents elsewhere involving
sulfur dioxide also do not appear to have been common.
1.2 PURPOSE OF THIS MANUAL
The purpose of this.manual is to provide technical information about
sulfur dioxide with specific emphasis placed on the prevention of accidental
releases of this chemical. This manual addresses technological and procedural
issues, related to release prevention, associated with the storage, handling,
and process operations involving sulfur dioxide.
This manual is intended as a summary manual for persons charged with
reviewing and evaluating the potential for releases at facilities that use,
store, handle, or generate sulfur dioxide. It is not intended as a
specification manual, and the reader is often referred to additional technical
manuals and other information sources for more complete information on the
topics discussed. Other sources of information include manufacturers and
distributors of sulfur dioxide in addition to technical literature on design.
operation, and loss prevention in facilities which handle toxic chemicals.
1.3 USES OF SULFUR DIOXIDE
Sulfur dioxide is a significant commodity chemical, produced by burning
sulfur bearing ores or elemental sulfur in air, or by recovery from stack
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gases to meet clean air requirements. Numerous references in the technical
literature provide information on both the manufacture and uses of sulfur
dioxide.
The dominant use of sulfur dioxide is as a captive intermediate in the
production of sulfuric acid. Its other major uses include chemical
manufacture (primarily sulfites). food processing (primarily corn), pulp and
paper manufacture, water and waste water treatment, and metallurgical
applications. Minor uses are found in a variety of industries including the
refrigeration, food preservation, bleaching, fumigating, and petroleum
industries.
1.4 CONTENTS OF THIS MANUAL
Following this introductory section, the remainder of this manual
presents technical information on specific hazards and categories of hazards
for sulfur dioxide releases and their control. As stated previously, these
are examples only and are representative of 9nly some of the hazards that may
be related to accidental releases. The physical, chemical, and toxicological
properties of sulfur dioxide which create or enhance the hazards of an
accidental release are presented in Section 2. In Section 3. the manufacture,
consumption, and storage of sulfur dioxide are discussed, and the release
hazards associated with these operations are identified. Potential causes of
releases, including those identified in Section 3. are summarized in Section
4. Section 5 contains detailed information about hazards prevention and
control. Topics included in this section are process and physical plant
designs, protection and mitigation technologies, operating and maintenance
practices, and illustrative costs.
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SECTION 2
CHEMICAL CHARACTERISTICS
This section describes the physical, chemical, and toxicological proper-
ties of sulfur dioxide as they relate to accidental release hazards.
2.1 PHYSICAL PROPERTIES
Sulfur dioxide (SO.) is a colorless gas with a characteristic pungent
odor and taste. Although the gas is relatively inert and stable, it is toxic
and highly irritating. Its more important physical and chemical properties
are presented in Table 2-1.
The solubility of sulfur dioxide gas in water is 36 volumes per volume of
water at 68 °F. It is also very soluble (several hundred volumes per volume
of solvent) in a number of organip solvents such as acetone, other ketones.
and formic acid (1).
Because of the low boiling point, and because the gas is considerably
heavier than air. spills and leaks of liquid sulfur dioxide could result in a
vapor cloud or plume that will remain close to the ground, posing a threat to
workers and surrounding communities.
Pure liquid sulfur dioxide is a poor conductor of electricity and is only
slightly miscible with water (1). The liquid also has a high coefficient of
expansion, expanding approximately 10% when warmed from 68 °F to 140 °F (1).
Hence, an overpressurization hazard exists if storage vessels have insuffi-
cient expansion space or if liquid sulfur dioxide pipelines may be blocked in.
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TABLE 2-1. PHYSICAL PROPERTIES OF SULFUR DIOXIDE
Reference
CAS Registry Number
Chemical Formula
Molecular Weight
Normal Boiling Point
Melting Point
Liquid Specific Gravity (H 0=1)
Vapor Specific Gravity (air=l)
Vapor Pressure
Vapor Pressure Equation
where:
7446-09-5
so2
64.06
14.0 °F ® 14.7 psia
-98.9 °F
1.436 ® 32 °F
2.263 ® 32 °F
49.1 psia ® 70 °F
log Pv = A - rjp
Liquid Viscosity
Solubility in Water at 1 atm,
g/lOOg H0
1
1
2
1
2
3
Pv = vapor pressure, mm Hg
T = temperature, °C
A = 7.28228, a constant
B = 999.900, a constant
C = 237.190, a constant
0.49 centipoise @ -4 °F and 14.22 psia 4
1
32 °F
50 °F
68 "F
86 °F
104 °F
22.971
16.413
11.577
8.247
5.881
(Continued)
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TABLE 2-1 (Continued)
Reference
Specific Heat at Constant
Pressure (vapor)
Specific Heat at Constant
Pressure (liquid)
Latent Heat of Vaporization
Liquid Surface Tension
0.149 Btu/(lb-°F) @ 77 «F
0.327 Btu/(lb-°F) @ 68 °F
167.24 Btu/lb ® 14.0 °F
28.59 dynes/cm @ 14 °F
4
1
4
Additional properties useful in determining other properties from physical
property correlations:
Critical Temperature 315.7 °F
Critical Pressure 1,147 psia
3
Critical Density 0.51 Ib/ft
Energy of Molecular Interaction 252 K
Effective Molecular Diameter 4.29 Angstroms
1
1
1
5
5
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2.2 CHEMICAL'PROPERTIES AND REACTIVITY
Sulfur dioxide is extremely stable to heat, even up to 3600 °F (1). It
does not form flammable or explosive mixtures with air. It will, however,
react with water or steam to produce toxic and corrosive fumes (6). When the
gas dissolves in water it forms a weak acid solution of sulfurous acid (H-SO.)
which is corrosive and unstable when exposed to heat (7). Sulfurous acid does
not exist in the free state, dissociating to the sulfite and bisulfite ions,
S03~ and HS03~. The deleterious effect of sulfur dioxide and sulfites in
domestic water is the increased corrosivity owing to the lowered pH. However,
oxidation of sulfite to sulfate in aqueous solutions uses dissolved oxygen,
and this may retard corrosion (6). While the oxidation of sulfite and
sulfurous acid to sulfate and sulfuric acid in the atmosphere is an
environmental concern, this reaction is too slow to significantly reduce the
concentration of sulfur dioxide in a short time period in the event of a large
release.
Sulfur dioxide can be reduced by hydrogen to hydrogen sulfide. It also
reacts with chlorine to form sulfuryl chloride. Both of these gaseous pro-
ducts are toxic. The reduction of sulfur dioxide to sulfur can be accomplish-
ed with H_S, methane, carbon (coal), and CO (1). The reaction with H.S will
occur at ambient temperatures in the presence of water, but requires high
temperatures or a catalyst when sulfur dioxide is in the dry state. Sulfur
dioxide is reported to react violently with a number of compounds of which
several may be present in facilities which also use sulfur dioxide, e.g..
chlorates, Al, and Cr compounds (6,8). The reaction with chlorates produces
chlorine, and this has the potential to become an explosive reaction at
elevated temperatures (8).
Most metals are resistant to commercial dry liquid sulfur dioxide, dry
gaseous sulfur dioxide, and hot gaseous sulfur dioxide containing water vapors
above the dew point (1). These include iron, steel, copper, aluminum, and
brass. However, these materials are readily corroded by wet sulfur dioxide
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gas below the dew point. Zinc is also readily oxidized by sulfur dioxide to
form
2.3 TOXICOLOGICAL AND HEALTH EFFECTS
Sulfur dioxide is a toxic, highly irritating gas which can have immediate
effects on the eyes, throat, lungs, and skin. The toxicology of sulfur
dioxide has been studied through accidental human exposure and through animal
studies (9) . A concentration of 100 ppm has been designated as the IDLH limit
(Immediately Dangerous to Life and Health), which is based on a 30-minute
exposure (10) . Table 2-2 presents a summary of some of the relevant exposure
limits for sulfur dioxide.
The primary health effects from exposure to sulfur dioxide occur in the
upper respiratory tract and the bronchi. Chronic exposure may result in
nas ©pharyngitis, fatigue, altered sense of smell, and chronic bronchitis
symptoms such as dyspnea on exertion, cough, and increased mucous excretion
(10) . It may cause edema of the lungs or glottis and can produce respiratory
paralysis (6) . In concentrations greater than 20 ppm, sulfur dioxide is
irritating to the eye and will cause pain, tearing, inflammation, swelling of
tissue and possible destruction of the eye (7,8). Acclimation to the effects
of sulfur dioxide has been reported to develop quickly as a result of the
depression of the tracheobronchial nerve reflexes; this adjustment is not
considered to be a beneficial effect because of the possibility that the
absence of discomfort merely removes one measure of protection (9) . The
physical effects of increasing levels of gas concentrations on humans are
summarized in Table 2-3 (11).
Sulfur dioxide is not listed in the National Toxicology Program, the
International Agency for Research on Cancer, nor the Registry of Toxic Effects
of Chemical Substances (1981-82) as a carcinogen or potential carcinogen (12).
However, sulfur dioxide has been implicated as a cocarcinogen (promoter) with
arsenic (9) .
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Contact with liquid sulfur dioxide may cause cryogenic burns to the skin
in addition to conjunctivitis, corneal burns, and corneal opacity of the eye
(7.8.10). It is also reported that high concentrations of sulfite ion in
water may cause eczema (6).
TABLE 2-2. EXPOSURE LIMITS FOR SULFUR DIOXIDE
Exposure Concentration
Limit (ppm) Description Ref.
IDLH 100 The concentration defined as posing 10
an immediate danger to life and health
(i.e.. causes irreversible toxic effects
for a 30-minute exposure).
PEL 5 This concentration was determined by 10
the Occupational Safety and Health
Administration (OSHA) to be the time-
weighted 8-hour exposure limit which
should result in no adverse effects for
the average worker.
LC--. 400 This concentration is the lowest 6
published lethal concentration for a
human over a 5-minute exposure.
TCL. 4 This concentration is the lowest 6
published concentration causing toxic
effects (irritation).
*PEL stands for the "permissable exposure limit."
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TABLE 2-3. PREDICTED HUMAN HEALTH EFFECTS OF EXPOSURE TO VARIOUS
CONCENTRATIONS OF SULFUR DIOXIDE (7)
ppm Predicted Effect
0.3-1 Can be detected by taste and smell
3 Easily noticeable odor
6-12 Immediate irritation of nose and throat
20 Eye irritation - ill effects if exposure is
prolonged
50-100 Maximum permissible concentration for 30 to
60 minutes exposure
200 Severe toxic effects after one minute
>400 Immediately dangerous to life
10
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SECTION 3
FACILITY DESCRIPTIONS AND PROCESS HAZARDS
This section contains brief descriptions of the processes and facilities
for the manufacture, consumption, and storage of sulfur dioxide in the United
States. The purpose of this section is to identify major hazards associated
with these facilities which may directly or indirectly cause accidental
releases. Measures taken for the prevention of these hazards are discussed in
Section 5.
3.1 MANUFACTURE (1.2.13)
Sulfur dioxide gas is produced in the United States by several methods
which include the combustion of sulfur or pyrites, as a by-product of smelter
operations, and as a by-product of other chemical operations. For many of the
chemical process applications which require sulfur dioxide gas or sulfurous
acid, sulfur dioxide is captively produced by the burning of sulfur or pyrite,
FeS., and the gas is immediately consumed in the process. The manufacture of
liquid sulfur dioxide for commercial sale involves passing the combustion gas
into water which dissolves it and certain impurities. This liquor is then
heated to drive off the sulfur dioxide, and the liberated gas is dried and
liquefied.
Figure 3-1 is a typical flow diagram for the preparation of liquid sulfur
dioxide. The sulfur-bearing raw material is fed to the burner where it is
combusted with air. The type of burner used is primarily determined by the
rate and concentration of sulfur dioxide to be produced and the quality of
sulfur to be burned. The sulfur dioxide content of the burner gas is depen-
dent on the equilibrium adiabatic flame temperature and varies from about 6.5%
at 1470 °F to about 20% at 3180 °F when the raw material is elemental sulfur
(13). After leaving the burner, the heat of combustion is recovered in a
11
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STEAM
BOILER
FEED WATER I
I
WATER
I
SULFUR BEARING
RAW MATERIAL
BURNER
WASTE
HEAT
BOILER
ARQnnnpR
EVAPORATOR
CONDENSER
mMPRPQQnn
SCRUBBER
LIQUID SULFUR DIOXIDE
TO STORAGE
Figure 3-1. Conceptual diagram of typical sulfur dioxide manufacturing process.
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waste-heat boiler, after which the combustion gas is further cooled prior to
absorption in water. Lead pipes in flowing water are commonly used for cool-
ing the gas. The combustion gas then passes through one or more absorption
towers in which the sulfur dioxide and certain impurites are absorbed into
water. The resulting liquor is then heated to drive off sulfur dioxide gas.
The gas is cleaned and dried with concentrated acid, cooled, compressed, and
finally condensed to pure liquid product.
The primary hazard areas in the production of liquid sulfur dioxide are
at the latter end of the process where sulfur dioxide is present in pure form.
The following potential release hazards may be identified in this portion of
the process (excluding the bulk storage system which is discussed in Section
3.4):
• The leakage of moisture into any equipment which handles a
large amount of sulfur dioxide with the consequent forma-
tion of corrosive -sulfurous acid;
• Failure of the sulfur dioxide compressor possibly
resulting from a power failure, rotor failure, or
excessive stress caused by severe vibrations; and
• A loss of cooling to the sulfur dioxide condenser which
results in a pressure buildup and possible equipment
failure.
Other release hazards, or possible causes of release, which are general to all
sulfur dioxide processing facilities are summarized in Section 4.
3.2 PROCESSING AND CONSUMPTION
The example processes discussed in this section represent many of the
primary uses of sulfur dioxide and include the production of sulfuric acid,
13
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the sulfonation of alkanes. pulp and paper manufacture, water and waste
treatment, and solvent extraction. Sulfur dioxide is also used in the
manufacture of a variety of important industrial chemicals which are too
numerous to discuss individually. Many of these products are listed in Table
3-1.
3.2.1 Manufacture of Sulfuric Acid (1)
Sulfuric acid is produced by the contact process. Different variations
of this process use a wide range of sulfur-bearing raw materials. The most
common raw material is elemental sulfur. The process produces gaseous sulfur
dioxide by sulfur combustion, followed by catalytic conversion of the sulfur
dioxide to sulfur trioxide (S0g). and absorption of the SO, into concentrated
sulfuric acid.
Regardless of the source of sulfur, the first step in the contact process
produces a continuous, contaminant-free gas stream containing appreciable
sulfur dioxide and some oxygen. A dry gas stream entering the catalytic
converters is desirable; the air used for burning elemental sulfur is general-
ly predried, while other processes dry the sulfur dioxide stream after it
leaves the combustion chamber. Sulfur trioxide is produced from the sulfur
dioxide by catalytic conversion, and it is subsequently absorbed into a
circulating stream of 98-99% H2so4 at approximately 158-176 °F.
Figure 3-2 illustrates the contact process for a double-absorption
sulfur-burning plant. Single-absorption plants used to be the industry norm,
but stricter controls on residual sulfur dioxide emissions necessitated an
intermediate absorption step to effect overall sulfur dioxide conversions of
99.5-99.8% in the newer plants. However, most existing facilities chose to
add a tail-gas unit instead of modifying the process with an additional
absorption step.
14
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TABLE 3-1. SULFUR DIOXIDE REACTION PRODUCTS (14)
sulfur dioxide
ammonium sulfite
ammonium thiosulfate
hydroxylamine sulfate
potassium bisulfite
potassium sulfate
potassium thiosulfate
sodium bisulfite
sodium persulfate
sodium sulfite
sodium bisulfate
sodium thiosulfate
sodium hydrosulfite
sulfurous acid
sulfuryl chloride
pyrosulfuryl chloride
zinc sulfide
zinc hydrosulfite
zinc formaldehyde sulfoxylate
sulfonamides:
sulfadiazine
sulfanilimide
sulfapyridine
sulfathiazole
sulfolane
15
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Molten
Sullur
i
t •
t *
Dilution Water
Boiler T
Feed 1
Water J
Sulfur
Burner
Dry
Air
Drying
Tower
SO2 Gas
(Acid)
(Acid)
Sleam
Waste
Heat
Boiler
Concentrated
Acid
1
SC
Ga
Acid
Coolers
Boiler Y
Feed 1
Water 1
Converter
And Heal
Exchange
Equipment
'3
s
Inli
Abs
Ti
urpass
orptlon
iwer
Cooled Acid
Concentrated Acid
Steam
Economizer
S03
Gas
Final
Absorption
Tower
1
Gas
lo
Slack
As Required
Product Acid
Figure 3-2. Conceptual diagram of typical double-absorption sulfuric acid process.
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The maximum concentration of sulfur dioxide present at any point in the
process is in the gas stream exiting the sulfur combustion chamber. Typical
sulfur dioxide concentrations range from 4-11 vol%. Since sulfur dioxide is
only present at this concentration between the sulfur burner and the catalytic
converters, the pieces of equipment in this part of the process are the only
potential sources of a hazardous release of sulfur dioxide under normal
operating conditions. Some general causes of equipment failure which may lead
to a large release of sulfur dioxide are discussed in Section 4.
If a process upset were to occur such that the conversion level of sulfur
dioxide to SO. was greatly reduced, the process stream beyond the catalytic
converters would contain a considerable quantity of sulfur dioxide. One
possible upset is a loss of temperature control in the converters resulting in
a significant temperature increase which would cause the equilibrium in the
oxidation reaction to become less favorable toward SO. formation.
Because of the exothermic nature of the oxidation of sulfur dioxide to
SO,, overheating resulting in overpressure is also a potential hazard in the
catalytic converters with the consequent possibility of leaks developing of,
in the worst case, equipment failure and loss of containment.
3.2.2 Sulfonation of Alkanes (15)
Sulfur dioxide is used as a reagent in several sulfation and sulfonation
processes which chemically introduce the SO, group into organic molecules.
Sulfonated and sulfated organics have many "surface-active" applications,
e.g., detergents, dyes, and medicinals, because of their unique properties of
solubility, emulsification, wetting, and foaming.
In most sulfation and sulfonation processes, the actual sulfonating agent
is either oleum, sulfuric acid, or sulfur trioxide. The use of sulfur dioxide
in these processes is not widespread in industry. However, one sulfonation
process employed in the U.S. does use significant quantities of liquid sulfur
17
-------
dioxide. The"sulfur dioxide in this process serves as a diluent for oleum
(fuming sulfuric acid) which contains 60-75% free sulfur trioxide. It is
necessary to dilute the sulfur trioxide, because acid of this strength will
severely char and degrade the alkane being sulfonated. As the reaction is
highly exothermic, cooling requirements also become very important at high
sulfur trioxide concentrations. If the sulfur dioxide is supplied in
sufficient quantities it will serve as the cooling medium for the process.
Because the sulfur dioxide does not participate as a reactant in the
sulfonation. it is separated from the reaction products and recycled to the
process.
Figure 3-3 is a flow diagram of a typical sulfonation process which uses
sulfur dioxide as a diluent and a refrigerant. The sulfur dioxide and oleum
are pumped from storage to an agitated weigh tank. The weight ratio of sulfur
dioxide to oleum is approximately 7 to 1, and the quantity of sulfur dioxide
used corresponds to a weight ratio of about 2 to 4 parts of sulfur dioxide to
one part of the alkane subsequently added. The process may be adapted for
continuous or batch-sulfonation depending on the way the reactants are fed to
the sulfonator. For batch operation, the alkane is charged to the reactor.
and the diluted oleum charge is fed to the agitated sulfonator at a controlled
rate to avoid overheating. For continuous operation, both the alkane and the
oleum are pumped continuously at controlled rates to the sulfonator, and the
sulfonated product is continuously withdrawn. The flow rates of the reactants
may be regulated by a valve which is controlled by the temperature of the
reactants in the sulfonator. This is done to maintain a reaction temperature
of about 20-65 °F. The heat of reaction is continuously removed from the
reactor by the vaporization and release of sulfur dioxide. The vented sulfur
dioxide passes through a liquid trap where any liquid materials are separated
and allowed to drain back to the sulfonator. The gas stream is then scrubbed
in a solution of 93-100% sulfuric acid before passing to one or more compres-
sors. After compression and condensation, the sulfur dioxide is returned to
storage for reuse in the process.
18
-------
Condenser
SO,
Compressors
H2 S04
Scrubber
so2
Storage
Oleum
Storage
Oleum
Weigh
Tank
Knockout
Pol
so2
gas
SO..
Liquid
Return
Sulfonator
Alkane
Weigh
Tank
Alkane
Storage
Vacuum
Distillation
Sulfonated Product
to Storage
Figure 3-3. Conceptual diagram of typical sulfonation process.
-------
There are a number of areas in this process where the sulfur dioxide is
present in high concentrations or nearly pure form. Because the sulfur
dioxide is not consumed in the sulfonation reaction, the possibility of a
large release of this chemical is greater than what might exist in a process
where the sulfur dioxide is consumed as a reactant. From a sulfur dioxide
release perspective, critical areas of the process include the sulfur dioxide
storage and feed systems, the sulfonator. and the sulfur dioxide recovery
section (including the sulfur dioxide compressors, condenser and storage
tank). Examples of possible causes of a large release include the fallowing:
• If moisture leaks into the system, equipment which handles
a large amount of sulfur dioxide may be corroded by the
sulfurous acid formed and be weakened to the point of
sudden rupture;
4 If there is a failure in the feed control system, a
runaway reaction may result which causes a buildup of
pressure exceeding the design pressure of the sulfonator;
and
• A loss of cooling to the sulfur dioxide condenser may also
result in a pressure buildup and equipment failure.
If the oleum feed is too concentrated, the exothermic sulfonation reac-
tion will proceed too quickly, resulting in a temperature rise in the reactor
and a consequent increase in pressure. Because the sulfur dioxide recovery
section involves relatively pure streams of sulfur dioxide, this section of
the process represents a potential hazard area. Overpressurization of a con-
denser may occur if the cooling system fails. Although this may not lead to
catastrophic equipment failure, leaks of sulfur dioxide into the plant cooling
water could result in the formation of corrosive levels of sulfurous acid.
20
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3.2.3 Sulfur Dioxide in the Pulp and Paper Industry
Sulfite Pulping (16.17.18)--
One of the primary uses of sulfur dioxide is in the manufacture of
chemicals (see Table 3-1) of which sulfites represent a majority of the sulfur
dioxide consumed. One major application of sulfite solutions is the sulfite
pulping process used in the manufacture of paper. There are a number of
variations of the sulfite pulping process, and there are also many other
pulping processes, encompassing both mechanical and chemical methods, which do
not require the use of sulfur dioxide.
The purpose of pulping is to separate the cellulose fibers from the
matrix of lignin which cements them together. The usual sulfite process is a
chemical method which consists of digesting the wood by "cooking" it in an
aqueous bisulfite solution (usually Ca, Mg. Na. or NH_) and an excess of
sulfur dioxide. Recently, multi-stage pulping processes have been introduced
in which the stages differ from each other in the cooking liquor used. Liquid
sulfur dioxide is used in some of these processes as the cooking liquor in the
second stage (16).
In the preparation of the sulfite solution, gaseous sulfur dioxide is
typically generated by burning molten sulfur in either rotary or spray burn-
ers. The gas exiting the burner usually contains about 17% sulfur dioxide
with the remainder of the gas consisting mostly of nitrogen and a small amount
of oxygen. This gas is cooled from a temperature of about 1800 °F to between
77 °F and 158 °F depending on the desired pH of the sulfite liquor. The
cooling process generally involves a horizontal, vertical, or pond cooler
consisting of a system of pipes surrounded by water.
The sulfite "cooking acid" is prepared by the absorption of the gaseous
sulfur dioxide in aqueous solutions containing calcium, magnesium, sodium, or
ammonium compounds. This is accomplished in a series of two or more absorp-
tion towers or acid-making tanks for Mg(HSO,)-. Sulfur dioxide solubility is
21
-------
a function of the temperature, pressure, and pH during absorption. System
absorption efficiencies for the different absorption systems used in industry
range from 97% to greater than 99% (18).
The portions of the sulfite pulping process which involve significant
quantities of sulfur dioxide include the gas exiting the sulfur burners and
the recovery of sulfur dioxide from the spent cooking liquor. Potential
hazards associated with the process gas stream involve the piping between the
sulfur burners and the absorption towers including the gas cooling section.
Because water is used as the cooling medium, a release of sulfur dioxide gas
would result in the formation of corrosive sulfurous acid. Some general
causes of equipment failure (including piping systems) are discussed in
Section 4.
A number of sulfur recovery procedures are employed in the pulping
industry. Some of these processes include a sulfur dioxide stripping opera-
tion which produces a nearly pure stream of gaseous sulfur dioxide. While the
recovered sulfur dioxide is generally fed back to the sulfur dioxide absorp-
tion towers, it may also be combined with H.S and fed to a Glaus unit or used
ft
to make liquid sulfur dioxide for use in a multi-stage pulping process (16).
This type of system is illustrated in Figure 3-4 which shows the preparation
of the cooking acid and recovery of the sulfur from the spent solution.
Potential hazards associated with the sulfur dioxide recovery section depend
on the process employed by the particular pulping operation. Some possible
causes of release general to many sulfur dioxide applications are discussed in
Section 4.
For multi-stage processes which use liquid sulfur dioxide, the storage
system constitutes one of the potential sources of a hazardous release. The
general hazards associated with the storage of sulfur dioxide are discussed in
Section 3.4.
22
-------
"Green Liquor"
Na2S + Na2C03
I w.
(from Incinerator)
SO2conlalning
flue gas
> fc
:
H2S * C02
Cartaonalkm
lower
1
Steam
*— I "2"
co2
Glaus
Unit
Sulfur
Make-up
Na2S03 Sulluf ••
Flue Gas
Scrubber
Na2S03
NaHSO3
Bisulfite
Tower
Sullur
Burner
IfTB OVf-.
N2.02
„ SOj S02
" Comprossor " Condenser
100% SO, 1 Liquid SO,
so2
Stripper _ „ ^
Abi
1
SO. containing gas
S02 + H20
so2
•nrnttVkn -*- - -- - — H O
tower
I
NaHSO3(cooklng acid) ^
Figure 3-4. Conceptual diagram of sulfite cooking liquor preparation and sulfur
recovery process.
-------
Preparation of Chlorine Dioxide (16.19.20.21)—
Chlorine dioxide is used in the pulp bleaching process, not only to
increase the brightness, but also to improve pulp strength, decrease color
reversion, and to make possible the recovery of bleach plant effluents.
Because this chemical is explosive at higher concentrations, it cannot be
transported in any concentrated form; thus, it is generally produced at the
pulp mill immediately before use.
Chlorine dioxide is manufactured from sodium chlorate in strong acid
solution, usually sulfuric. A reducing agent is required to reduce the
chlorate ion to chlorine dioxide. Three reducing agents are used for this
purpose in industry, one of which is sulfur dioxide. Figure 3-5 is a flow
diagram for a typical process which uses sulfur dioxide as the reducing agent.
The reaction is carried out in a cylindrical vessel which contains a
i
solution of sodium chlorate, sulfuric acid, and chloride ions. Sulfur dioxide
and chlorine are pumped from their respective liquid storage vessels to the
evaporators. The two gas streams are diluted with nitrogen (air is also
sometimes used) and mixed prior to entering the reactor through a sparger.
The effluent gas exiting the reactor contains chlorine dioxide, chlorine gas.
and nitrogen. Sodium chlorate and sulfuric acid are recovered from the
effluent solution and recycled back to the reactor.
The reaction of sulfur dioxide with chlorate is highly exothermic. The
temperature of the reaction must be carefully controlled to avoid a runaway
reaction. For this reason, the volume percent of sulfur dioxide in the gas
mixture must be maintained below 18% to avoid an excessive heat of reaction.
The metering of reagents and the flow of dilution gas have to be accurate.
The process hazard from an excess of sulfur dioxide in the feed or the loss of
cooling to the reactor is the production of too much chlorine dioxide. At
higher concentrations this chemical quickly decomposes to chlorine gas and
24
-------
•*• QO2, CI2. and N2 to Recovery
Recovered H2SO4 with NaOO
Nad03(dry) „
NaOH (solution) »
Neutralization
and
Crystallization
Centrifuge
by-product
Figure 3-5. Conceptual diagram of typical chlorine dioxide manufacturing process.
-------
oxygen with explosive force. Therefore, most operations incorporate a temper-
ature shutdown switch into the control system which shuts off the feed in the
event of an unacceptable rise in reaction temperature.
The prevention of an explosive concentration of chlorine dipxide gas is
the major process concern in the production of this chemical* but the release
of a large amount of sulfur dioxide is not the primary hazard of such an
explosion. This is because the release of a large quantity of chlorine
dioxide and chlorine gas would be a greater danger to workers and the sur-
rounding community. However* the ratio of sulfur dioxide to chlorine gas in
the feed may be as high as 10 to 20:1 (20). Hence, if the feed system is not
shut off at the time of a reactor explosion, the sulfur dioxide released from
a venting feed line could, in this case, pose a serious hazard in itself.
As liquid sulfur dioxide is used as the source of the gaseous sulfur
dioxide feed, potential hazards which may result in a large release of sulfur
dioxide involve the storage facilities, the evaporator, and the feed system to
the reactor. Hazards associated with the storage of liquid sulfur dioxide are
discussed in Section 3.4. Other general equipment hazards are discussed in
Section 4.
Preparation of Sodium Dithionate (18)—
Sodium dithionate is also used in the pulp bleaching process. It is
produced at the mill site by the reaction of sulfur dioxide or bisulfite with
sodium borohydride in an alkaline medium. As the sulfur dioxide is consumed
in the reaction, the hazards which may lead to a large release of sulfur
dioxide are the hazards associated with the storage and feed systems for this
chemical. General hazards pertaining to these areas are discussed in Sections
3.4 and 4.
26
-------
CHLORINATED
WATER
INJECTOR
PUMP
I—t
SULFUR
DIOXIDE
STORAGE
INJECTOR
WEAK
SULFUROUS
ACID
DECHLORINATED
WATER
Figure 3-6. Conceptual diagram of water dechlorination with sulfur dioxide.
-------
3.2.4 Water and Wastewater Treatment
Water Dechlorination (22)—
Dechlorination is a process for partially or completely removing residual
chlorine from chlorinated water. Sulfur dioxide is often used as the dechlor-
inating agent, because it reacts with residual chlorine very quickly with
little mixing, and the process is relatively simple compared to other methods
for dechlorination. The process involves absorbing gaseous sulfur dioxide
into water which results in the formation of sulfite ions. The sulfite ions
then react with the residual chlorine reducing it to chloride.
Figure 3-6 is a flow diagram of a typical dechlorination process using
sulfur dioxide. The injector prepares a weak sulfurous acid solution by
contacting sulfur dioxide gas with a small water stream. The weak sulfurous
acid is intimately mixed with the chlorinated water in the diffusor. No
further mixing is required for dechlorination with sulfur dioxide since the
reaction with the residual chlorine is virtually instantaneous. Feed forward
control is the most common method of controlling the addition of sulfur
dioxide. An effluent flow rate signal is combined with a residual chlorine
signal to produce a control signal to the sulfur dioxide metering equipment.
The sulfur dioxide injection rate will automatically increase or decrease with
changes in water flow rate and/or residual chlorine.
The release hazards associated with the dechlorination process are
associated with the sulfur dioxide feed and storage systems. These hazards,
which are general to all sulfur dioxide processes, are discussed in Sections
3.4 and 4.
Treatment of Chromium Waste (23)—
Sulfur dioxide is often used to treat industrial waste water which
contains toxic, hexavalent chromium by reducing it to the trivalent state.
Following reduction, the pH of the solution is adjusted, and the trivalent
chromium precipitates as the insoluble hydroxide.
23
-------
WASTE CHROME
LIQUOR
HYDRATED
LIME
WATER
SULFUR
DIOXIDE
STORAGE
TO SLUDGE
SEPARATOR
Figure 3-7. Conceptual diagram of typical batch chromium waste treatment process.
-------
Figure 3-7 is a flow diagram of a typical chromium reduction process.
Waste liquors are collected in storage tanks and treated in a series of
batches. Liquid sulfur dioxide is injected through an "L" shaped diffuser
located near the bottom of the reduction tank. The reduced chrome is trans-
ferred to the liming tank and treated with sufficient hydrated lime to adjust
the pH to 8.0-8.6. causing the chromium to precipitate.
As with the dechlorination process, the primary release hazards of the
chrome reduction process involve the sulfur dioxide feed and storage systems.
However, because the sulfur dioxide is fed as a liquid to the reduction tank.
there is the additional hazard of isolating liquid sulfur dioxide between
closed valves when the unit is not operational. Were this to occur, the
pressure in the piping would rapidly rise as the sulfur dioxide warms, and
overpressurization could result in pipe failure and an uncontrolled release of
sulfur dioxide.
3.2.5 Sulfur Dioxide in the Petroleum Industry
Modified Sulfur Dioxide Extraction (24,25.26) —
Liquid sulfur dioxide is used as a solvent in the Edeleanu process in
which aromatic hydrocarbons and sulfur-bearing compounds are extracted from
paraffins and naphthenic hydrocarbons. A modification of the original process
involves washing the extract with a washoil to further concentrate the aroma-
tics which are often equal in value to the paraffinic raffinate.
The washoil used in the modified process is dependent on the charge. For
the recovery of aromatics from naphtha fractions, a kerosine cut is used.
Other washoils include a gasoil cut, such as a sulfur dioxide raffinate, for
the recovery of a relatively pure aromatic stream from a petroleum fraction,
or a light paraffinic hydrocarbon, such as hexane or heptane, for use with a
gasoil feedstock.
Figure 3-8 is a typical flow diagram for the recovery of aromatics from a
naphtha refonnate. The feed is dried, deaereated, and chilled before entering
30
-------
Liquid SO,
Rafflnate
Feed
Deaeralor
Dryer
Chillers
Feed
Washoll
soa
Drying
Column
Extraction
Tower
Extract
Extract
Stripper
(Evaporators)
S02
Condensers
Washoll Recycle
Rafflnate
Stripper
(Evaporators)
Ralllnate/
Washoll
Fracllonalor
Aromatlcs to
Extract Splitter
Extract/
Washoll
Fractlonator
Figure 3-8. Conceptual diagram of typical sulfur dioxide extraction process.
-------
the extraction tower. Sulfur dioxide is used as the refrigerant to permit the
use of common condensers, collecting equipment, and pumps for the refrigerant
and the extraction solvent. The tower shown in Figure 3-8 is used for both
'the sulfur dioxide extraction and the stripping of the extract. The two
product streams go to evaporators where the sulfur dioxide is taken overhead
to be condensed in water-cooled tubular equipment. Part of the recovered
sulfur dioxide is then used to cool the charge stock and the washoil to
extraction temperature by flash vaporization, after which the vapor is com-
pressed and returned to the water-cooled condensers. The water content of the
circulating sulfur dioxide is controlled by sending a slip stream of vapor
from the extract evaporator to a sulfur dioxide drying column. Provision is
also made for removal of inert gas from the circulating sulfur dioxide.
Operating temperatures for the sulfur dioxide extraction process range
from -20 °F for naphthas and kerosines to 60 °F for high-pour-point stocks
(25) . ' To maintain the sulfur dioxide as a liquid at these temperatures,
required operating pressures range from less than 1 atm to 3 atm. The solvent
to feed ratios range from 0.5:1 to 3:1, with the heavier charge material
requiring higher solvent to oil ratios (25).
From a sulfur dioxide release perspective, a fundamental characteristic
of the extraction process is the use of sulfur dioxide as a solvent rather
than a reactant. Because recovery and recycle of the solvent involves a
number of critical areas where sulfur dioxide is present in high concentra-
tions or nearly pure form, the possibility for a release may be greater than
what might exist in a process where it is consumed as a reactant.
High hazard areas specific to this process, excluding bulk storage and
transfer (discussed in Section 3.4), include the following:
• Feed treatment to remove water from the hydrocarbon charge;
• The treating tower;
• Heat exchange equipment; and
• Sulfur dioxide drier.
32
-------
Removal of water from the feed is important, because sulfur dioxide
combines with water to form sulfurous acid which is corrosive to common
materials of construction such as carbon steel. The feed does not contain any
sulfur dioxide, but water introduced with the feed will mix with sulfur
dioxide downstream. While a properly designed system should use materials
which are sufficiently corrosion resistant, the materials selection will have
been based on a certain feed moisture concentration. Therefore, failure of
the water removal system to maintain the design moisture concentration may
result in a protracted corrosion problem leading eventually to an equipment
failure.
The primary concern in the treating tower is temperature control. If a
process upset were to occur which resulted in a substantial temperature
increase in the tower, significant expansion and vaporization of the liquid
sulfur dioxide may occur resulting in a number of process problems. Further-
more, the liquid phases in the column become more miscible at higher tempera-
tures, and a single liquid phase may result if the treating temperature is too
high (26) . No separation would take place in this situation, and the
raffinate recovery section could become overloaded with the excess sulfur
dioxide in the overhead product.
The use of sulfur dioxide as a refrigerant as well as the solvent means
that it will be present in a number of heat exchange vessels in pure form.
The circulating sulfur dioxide will require auxiliary equipment (pumps and
compressors) as well as a considerable amount of piping in the system. A
large amount of process equipment handling pure sulfur dioxide increases the
chances of leaks developing in the system. Some possible causes of leaks
include a loss of temperature control resulting in overpressure, corrosion, or
defective or worn-out equipment. The use of water-cooled sulfur dioxide
condensers also presents the possibility of a leak into the cooling water
system leading to the formation of sulfurous acid and the associated corrosion
hazard that this would create.
33
-------
Despite precautions taken to dry the charge oil stream, small amounts of
water enter the circulating sulfur dioxide stream from this source. This
moisture must be continuously removed to prevent accumulation in the recycle
and corrosive levels of sulfurous acid from forming. A common process used
for drying the sulfur dioxide is sending a slip stream of sulfur dioxide vapor
to a fractionating tower. Since a level of water collects in the reboiler. it
is necessary to maintain the temperature of the reboiler sufficiently low to
minimize water vaporization. The possibility of overheating the reboiler
presents a potential hazard which would result in water vapor entering the
sulfur dioxide stream and forming a corrosive mixture.
Liquid Sulfur Dioxide-Benzene Extraction (25) —
Two extraction processes which employ liquid sulfur dioxide as a
co-solvent with benzene are the removal of low-viscosity-index constituents
and the removal of wax from lube oils. These extraction processes can be
advantageously arranged in series by adjusting the solvent composition. The
solvent composition varies according to process requirements, ranging from
15-30% sulfur dioxide by volume for dewaxing to greater than 50% by volume for
lube refining. In the dewaxing process, sulfur dioxide evaporation furnishes
internal refrigeration for the precipitation of wax before its removal with
closed continuous rotary filters. The extraction temperature used in the lube
refining process is about 25 °F with a mixed solvent to oil ratio of about
2:1.
Process hazards associated with these two extraction processes are
similar to those of the modified sulfur dioxide extraction described above.
However, since the sulfur dioxide is not in pure form, the hazardous effects
of this chemical resulting from a release of solvent may be less severe.
Glaus Process—
The Glaus process is a method of treating refinery off-gases by convert-
ing hydrogen sulfide to elemental sulfur. Although appreciable amounts of
gaseous sulfur dioxide are present in the process gas stream, this stream
contains an even greater concentration of hydrogen sulfide. Hence, the
34
-------
primary hazard in the event of a process stream release is the toxicity of the
H2S. while the adverse effects of the released sulfur dioxide would be less
urgent relative to those of the released H,S.
3.3 REPACKAGING SULFUR DIOXIDE (4.27.28)
Liquid sulfur dioxide is repackaged at several locations throughout the
U.S. This process involves a number of procedures, the use of which depends
on whether the transfer is from tank cars into tank trucks, or from tank cars,
trucks, or other bulk storage containers into cylinders or one-ton steel
drums.
When a bulk quantity of liquid sulfur dioxide arrives at a repackaging
facility, filling operations may be carried out by transferring sulfur dioxide
directly from the tank car or truck to the receiving container(s). However,
most repackagers firs*t transfer the sulfur dioxide to bulk storage before
filling smaller containers. Tank cars and trucks are unloaded with the use of
a gas compressor or transfer unit; the suction side draws gas from the top of
a storage tank, while the discharge is connected to a valve on the tank car or
truck which allows flow through a dip pipe terminating in the vapor phase
within the tank. Thus, the liquid sulfur dioxide flows to the bulk storage
vessel as the pressure in this vessel is lowered and the pressure in the tank
is increased. Tank cars may alternatively be unloaded with the use of
compressed air as the padding medium in the car which causes the liquid to
flow into the bulk storage vessel. As tank trucks are equipped with self-pow-
ered compressors, they are always unloaded by the former procedure. The
potential hazards associated with the transfer of liquid sulfur dioxide from
tank cars and trucks are discussed in Section 3.4.2.
Transfer to cylinders or drums is accomplished with the use of compressed
air to pad the storage vessel, causing the liquid sulfur dioxide to flow out
of the vessel. The compressed air line should be equipped with a moisture
and/or oil separator, followed by a drier. The dew point of the dried,
compressed air should not exceed 20 °F (4). During the filling operation, the
35
-------
receiving vessels are mounted on scales to determine when they have been
filled with the correct amount of sulfur dioxide. Some repackagers reweigh
the vessels on a second scale to verify that the measurements made with the
first scale were accurate.
Equipment for the refilling process usually consists of a reciprocating
compressor, adapters for the cylinder and storage tank valves, and associated
piping. Equipment used in repackaging operations should be constructed from
materials compatible with sulfur dioxide. Suitable materials of construction
for sulfur dioxide service are discussed in Section 5.
Examples of potential hazards in repackaging operations include the
following:
• Equipment corrosion from sulfurous acid formed by moisture
'leaking into the system;
• Overpressurization of the storage vessel; and
• Overfilling of the receiving vessel.
Accidental overpressure of the storage tank could result in a release of
sulfur dioxide to the atmosphere through a relief valve (if the valve is not
vented to a closed system.) Overfilling could cause a release from a rupture
in the piping or the receiving vessel from a pressure buildup. A latent
hazard also exists in an. overfilled vessel which goes undetected and leaves
the repackaging facility. Other potential sources of release include leaks in
the connecting piping as a result of corrosion, loose joint-pipe connections.
cloggings of vapor pipes resulting in overpressure, and human error.
3.4 STORAGE AND TRANSFER
All industries which use or handle sulfur dioxide in bulk quantities must
have appropriate facilities and procedures for the safe storage and transfer
36
-------
of this material. In this section, potential hazards associated with the
storage and transfer of sulfur dioxide common to all installations are identi-
fied. Proper procedures and safety precautions for the control of these
hazards for release prevention are discussed in Section 5.
3.4.1 Storage
Large quantities of liquid sulfur dioxide are stored in pressure vessels.
because sulfur dioxide has a relatively low boiling point and a high vapor
pressure at ambient temperatures. These vessels are generally constructed of
carbon steel according to the latest edition of the American Society of
Mechanical Engineers (ASMS) Code for Unfired Pressure Vessels. Section Till,
Division I, and with the American National Standards Institute (ANSI)
Standards for Piping and Fittings (29.30.31.32). The maximum amount of sulfur
dioxide that may be stored in a container is equal to 1.25 times the water
weight capacity of the container at 60 °F (2).
The primary hazard associated with the storage of liquid sulfur dioxide
is failure of a pressurized storage vessel or its associated piping. There
are several ways this might occur:
• Overheating;
• Overfilling; and
• Failure of safety relief devices.
A liquid-full container may result from a temperature increase of the
vessel. If the vessel was overfilled to begin with, the temperature at which
it will become liquid-full is lowered. Denting or other deformations of a
storage container also effectively lowers the temperature at which it will
become liquid-full. The maximum recommended temperature to which a vessel may
be safely heated is 125 °F. Cylinders and drums are equipped with fusible
safety plugs designed to melt at 165 °F to prevent rupture of the container
because of overpressure, but the possibility also exists that the plug is
defective and will fail to melt at the correct temperature. Furthermore,
37
-------
although a fusible plug will prevent a rupture of explosive force, a melted
plug will still allow a. complete release of the contents of the container.
Larger storage vessels are generally equipped with pressure relief valves
which discharge to a pressure relief vessel or vent gas scrubber.
A potential hazard exists if sulfur dioxide is stored in an area which is
located near flammable or incompatible materials, especially if the area is
congested or not well ventilated. Cylinders or other storage vessels kept in
an area in which they are exposed to direct sunlight are also susceptible to
overheating. Storage vessels in constant contact with, dampness or standing
water are susceptible to corrosion with the consequent development of leaks.
Since the density of sulfur dioxide vapor is greater than that of air.
sub-surface storage of this material is potentially hazardous, because leaking
vapor will remain close to the ground and will not be readily dispersed in the
atmosphere.
3.4.2 Transfer from. Tank Cars and Trucks
Shipments of liquid sulfur dioxide are made in tank cars, tank trucks.
2.000-pound drums, and 150-pound cylinders. Tank cars are lagged with insula-
tion to minimize variations in pressure with ambient temperature, and they are
equipped with spring-loaded pressure-relief valves which are set to discharge
at 225 psig (4). Purchasers of tank-car quantities are required to have
adequate storage facilities to allow the prompt transfer of the sulfur dioxide
upon arrival.
Appropriate procedures must be followed when transferring sulfur dioxide
from tank cars and trucks to storage vessels to reduce the risk of a hazardous
chemical release. Tank cars are unloaded by one of the two methods described
in Section 3.3. (One method involves the use of a gas compressor, and the
other uses compressed air as a padding medium in the tank.) Tank trucks are
unloaded with the use of a self-powered compressor. Examples of potential
hazards associated with the unloading of tank cars and trucks include the
following:
38
-------
• The pressure in the tank car or truck attains the pressure
setting of its relief valve, and sulfur dioxide vapor is
vented to the atmosphere;
• Moisture enters the system with the compressed air.
because the pre-drying system is not functioning at design
conditions, resulting in the formation of sulfurous acid
which is highly corrosive to the tank car, transfer lines,
and storage tank;
• Leakage resulting from pipe corrosion or loose joint-pipe
connections; and
• Human error.
3.4.3 Transfer from Storage Vessels
Another aspect of the transfer of liquid or vapor sulfur dioxide to
consider is the discharge of sulfur dioxide from a storage container for its
designated use in the plant. This is generally accomplished by creating a
pressure differential between the container and the receiving vessel or
process to which it is flowing.
Cylinders and Drums—-
At room temperature, a 150 Ib cylinder or one-ton drum will discharge
sulfur dioxide liquid at a rate of about 5 Ibs per minute or vapor at a rate
of 0.4 Ib per minute against a discharge pressure of 10 psig (4) . When higher
rates are desired, the cylinder may be warmed to promote discharge of gaseous
or liquid sulfur dioxide. There are several safe methods of heating the
cylinder or drum including the use of a blanket type heater or electric strip.
which may be controlled with a thermostat, or use of a warm bath or heated
room not exceeding 125 °F. A potential hazard exists if an improper method of
heating a cylinder or drum is employed, such as using a blow torch or flame,
because of the danger of local overheating which may draw the temper of the
39
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steel or cause the fusible plug to melt thereby releasing the contents of the
cylinder. Small, well-insulated wooden structures may be constructed in which
one or two drums are heated with careful temperature control, but care must be
taken to protect the fusible plugs from overheating from exposure to radiant
heat.
It is possible that the evaporation of sulfur dioxide in a drum during
discharge will cause the contents of the drum to be refrigerated to a point
where there is little or no flow of gas. To avoid such a condition from
developing, drums are often manifolded together in parallel to increase the
total withdrawal rate while reducing the withdrawal rate from individual
drums. A potential hazard exists in such an arrangement if there is a gaseous
transfer between drums at different temperatures with subsequent reliquefac-
tion. If this should happen, the normal filling ratio of a drum may be
exceeded because of an increase in the ambient temperature. This condition
could result in distortion or rupture of the drum with a consequent hazardous
release of sulfur dioxide.
Another method of achieving higher flowrates of gaseous sulfur dioxide is
rapidly withdrawing and vaporizing liquid sulfur dioxide in a steam or elec-
trically heated vaporizer. A potential hazard of this process is an improper
piping arrangement which allows more than one drum to be connected to the
evaporator at a time. Transfer of liquid sulfur dioxide between two drums
connected in parallel at even slightly different temperatures takes place
rapidly and will not cease until the cooler drum is completely filled. The
hazard potential is heightened if reliance is placed on manually operated
isolation valves alone.
The use of nitrogen or air padding to promote the flow of sulfur dioxide
from cylinders or drums is also potentially hazardous, as dangerous pressures
may develop as a result of an increase in the ambient temperature, and
moisture or other forms of contamination may be introduced with the gas.
-------
Other example potential hazards include:
• The possibility of hazardous backflow into the cylinder or
into the upper valve chambers when the feed valve is shut
off at the drum;
• Contamination by moisture which could lead to a build-up
of hydrogen pressure in closed equipment and cause an
explosion of equipment with violent force;
• The possibility of isolating liquid sulfur dioxide in
piping between closed valves which could lead to bursting
of the line from a build-up in hydrostatic pressure; and
• The possible failure of piping connections from corrosion,
improper materials of construction, or work hardening or
fatigue.
t
Bulk Storage Containers—
Potential hazards associated with the transfer of sulfur dioxide from
bulk storage containers include most of those already mentioned for cylinders
and drums. The primary possibilities are overpressure as a result of over-
heating, corrosion from exposure to moisture or from moisture entering the
piping system, isolation of liquid sulfur dioxide between closed valves, and
failure to follow proper operating and maintenance procedures.
3.4.4 Transporting Sulfur Dioxide Storage Containers
Unloading containers of sulfur dioxide from a delivery vehicle or moving
them within the plant is another aspect of the storage and transfer of this
material. In general, potential hazards associated with the transport of
sulfur dioxide within a closed vessel arise from failure to follow the proper
operating procedures. Prevention of a hazardous release resulting from human
error is discussed in Section 5.
41
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SECTION 4
POTENTIAL CAUSES OF RELEASES
The potential for a hazardous release of liquid or gaseous sulfur dioxide
exists in any type of chemical plant which handles this material. The possi-
ble sources of such a release are numerous. Large-scale releases may result
from leaks or ruptures of large storage vessels (including tank cars on-site)
or failure of process machinery (e.g., pumps or compressors) which maintain a
large throughput of sulfur dioxide gas or liquid. Smaller releases may occur
as a result of ruptured lines, broken gauge glasses, or leaking valves, fit-
tings, flanges, valve packing, or gaskets.
The properties of sulfur dioxide which can promote equipment failure are
a high'coefficient of expansion and the corrosiveness of sulfurous acid which
is formed when dry sulfur dioxide comes into contact with moisture.
*
In Section 3, specific release hazards associated with the manufacture,
consumption, and storage of sulfur dioxide were identified. In addition to
those discussed, there are also numerous general hazards which, if realized,
could lead to an accidental release. Both the specific and general hazards in
sulfur dioxide facilities may be broadly classified as having process,
equipment, or operational causes. This classification is for convenience
only. Causes discussed below are intended to be illustrative, not exhaustive.
More detailed discussions of possible causes of accidental releases are
planned for other parts of the prevention reference manual series.
4.1 PROCESS CAUSES
Process causes are related to the fundamentals of process chemistry,
control, and general operation. Example process causes of a sulfur dioxide
release include:
42'
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• Excess sulfur dioxide feed to a chlorine dioxide reactor
leading to excessive exothermic reaction, combined with
failure of the cooling system;
• Backflow of process reactants to a sulfur dioxide feed
tank resulting in the formation of corrosive sulfurous
acid or explosive reactions with incompatible materials;
• Inadequate water removal from hydrocarbon feeds in a
sulfur dioxide extraction process over a long period of
time leading to progressive corrosion;
• Excess feeds in any part of a process leading to over-
filling or overpressuring equipment;
• Loss of condenser cooling to distillation units; and
•
• Overpressure in sulfur dioxide storage vessels from
overheating or overfilling.
4.2 EQUIPMENT CAUSES
Equipment causes of accidental releases result from hardware failures.
Some possible causes include:
• Excessive stress on materials of construction owing to
improper fabrication, construction, or installation;
• Failure of vessels at normal operating conditions as a
result of weakening of equipment from excessive external
loadings or thermal cycling;
43
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Mechanical fatigue and/or shock in any equipment
(mechanical fatigue could result from age, vibration, or
stress cycling, for example; shock could occur from
collisions with moving equipment such as cranes or.other
equipment in process or storage areas);
Thermal fatigue and/or shock in reaction vessels, heat
exchangers, and distillation columns;
Brittle fracture in any equipment, especially in carbon
steel equipment subjected to extensive corrosion where
hydrogen embrittlement may have occurred (equipment
constructed of high alloys, especially high strength
alloys selected to reduce the weight of major process
equipment, might be especially sensitive where some
corrosion has occurred or severe operating conditions are
encountered); . •
Creep failure in high temperature equipment subjected to
extreme operational upsets, especially excess temperatures
(this can occur in equipment subjected to a fire that may
have caused damage before being brought under control);
and
All forms of corrosion, including external corrosion from
fugitive emissions of sulfur dioxide, pipe connections
which have slowly corroded as a result of moisture
entering the tubing when cylinders are switched, and
stress corrosion cracking.
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4.3 OPERATIONAL CAUSES
Operational causes of accidental releases are a result of incorrect
procedures or human errors. Examples of these causes include the following:
• Overfilled storage vessels;
• Improper process control system operation;
• Errors in loading and unloading operations;
• Poor quality control resulting in replacement parts which
do not meet system specifications;
• Inadequate maintenance in general, but especially on water
removal unit operations, pressure relief systems, and
other preventive and protective systems; and
9
• Lack of inspection and non-destructive testing of vessels
and piping to detect corrosion weakening.
45
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SECTION 5
HAZARD PREVENTION AND CONTROL
5.1 GENERAL CONSIDERATIONS
Prevention of accidental releases relies on a combination of technologi-
cal, administrative, and operational practices. These practices apply to the
design, construction, and operation of facilities where sulfur dioxide is
stored and used. When developing a thorough release prevention and control
plan, considerations must be made in the following areas:
• Process design,
• Physical plant design,
• Protective systems, and
• Operating and maintenance practices.
Hazards prevention and control first involves identification of specific
factors in each of these areas which could directly or indirectly cause a
hazardous release of sulfur dioxide. A number of these factors or potential
causes of release were discussed in Sections 3 and 4. Equipment and proce-
dures should then be examined to ensure that they are in accordance with
applicable codes, standards, and regulations as a minimum. Further evalua-
tions should then be made to determine where extra protection against a
release is appropriate so that stricter equipment and procedural specifi-
cations may be developed.
The following subsections discuss specific measures for hazards preven-
tion and control in chemical plants which maintain a significant inventory
46
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of sulfur dioxide; more detailed discussions may be found in a manual on
control technologies, part of this manual series.
5.2 PROCESS DESIGN
Process design considerations involve the fundamental characteristics of
the processes which use sulfur dioxide. These include the hasic chemistry
involved and how this chemistry is affected by the variables of flow, pres-
sure, temperature, and composition. These characteristics are the basis for
the overall process design which includes the sequence of unit operations
along with equipment selection (process equipment, measuring systems, mixing
systems, instrumentation, emergency equipment, etc.)
Of primary concern in process design is determining how deviations from
expected conditions might initiate a series of events that could result in an
accidental release. A sensitivity analysis for the purpose of assessing the
potential hazards of a given design may result in process modifications which
would enhance the integrity of the system. Changes may involve any aspect of
the process. Possibilities include changes in the quantities of materials
used, the pressure and temperature conditions, the type and sequence of unit
operations, control strategies, and instrumentation.
In the context of the processes discussed in Section 3. primary consider-
ation should be given to the items listed in Table 5-1. For each item, the
specific process or unit operation for which the item is of greatest concern
is given. This list is not intended to be comprehensive, and there is no
guarantee that proper attention to these considerations will ensure a safe
system. However, awareness and control of these items are necessary if a safe
system is to be achieved.
The process upsets which are the most potentially hazardous with respect
to releases of sulfur dioxide from the processes discussed in Section 3 are
overheating and/or overpressuring and the leakage of moisture into the system.
-------
TABLE 5-1. EXAMPLE PROCESS DESIGN CONSIDERATIONS FOR PROCESSES INVOLVING
SULFUR DIOXIDE
Process Design Consideration
Process or Unit Operation
Contamination with water
Flow control of sulfur dioxide
feed
Temperature sensing and heating
media flow control
All
All
Distillation and stripping column
reboilers
Temperature sensing and cooling
medium flow control
Adequate pressure relief
Corrosion monitoring
Temperature monitoring
Chlorine dioxide and sulfonation
reactors, distillation and
stripping column condensers
Storage tanks, reactors,
distillation and stripping columns.
heat exchangers
All, but especially recycle
circuits
Chlorine dioxide and sulfonation
reactors, distillation and stripping
column reboilers
Level sensing and control
Storage tanks, liquid extraction
columns, reboilers and condensers
48
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Overheating is hazardous, because it may lead to overpressure which weakens
process equipment and adds to the potential for leaks at joints and valves.
Wide temperature fluctuations also significantly decrease the lifespan of many
materials of construction. Overpressure may occur without overheating if
flowrate control is not maintained of both gas and liquid streams. Careful
monitoring of the moisture content is important to prevent corrosive levels of
sulfurous acid from forming. This includes regular inspection of moisture
removal equipment along with measuring the moisture content of process streams
and monitoring the pH of cooling water used in the process.
5.3 PHYSICAL PLANT DESIGN
Physical plant design considerations include equipment, siting and
layout, and transfer/transport facilities. Vessels, piping and valves,
process machinery, instrumentation, and factors such as location of systems
and equipment must all be considered. The following subsections cover various
*
aspects of physical plant design beginning with a discussion about materials
of construction.
5.3.1 Equipment
Materials of Construction (1,4,33)—
Most common materials of construction are resistant to commercial dry
liquid sulfur dioxide, dry sulfur dioxide gas, and hot sulfur dioxide gas
containing water above its dew point. These include cast iron, carbon steel,
copper, brass, and aluminum. However, wet sulfur dioxide gas, sulfurous acid,
and sulfite solutions are all corrosive to many metals including iron, steel,
nickel, copper-nickel alloys, and nickel-chromium-iron alloys, which are
otherwise satisfactory for dry or hot sulfur dioxide service. Other suitable
materials for most sulfur dioxide service are carbon, graphite, and impreg-
nated carbon. Lead is also resistant to sulfur dioxide and sulfites under
most conditions. Zinc, however, may not be used for sulfur dioxide service.
because it is readily oxidized to ZnS-O^. Table 5-2 is a list of construction
49
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TABLE 5-2. MATERIALS OF CONSTRUCTION FOR SULFUR DIOXIDE SERVICE (4.33)
For Wet For Dry
Material or Dry S02 . S02 Only
Admirality, Antimonial x
Aluminum x
Brass x
Bronze. Commercial x
Bronze, Olympic, Type A x
Bronze, Olympic, Type B x
Bronze, Telnic x
Chlorimet 2 x
Chlorimet 3 x
Copper x
»
Copper, Tellurium x
Cupro - Nickel, 30% * x
Durco D-10 x
Durimet - 1 x
Hastelloy C x
Haveg x
Haynes Stellite 1 x
Lead x
Steel, mild x
Stainless Steel, Type 316 x
Stainless Steel, Alloy 20 x
Teflon x
containing over 1000 ppQ of water
50
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materials which have been tested and proven suitable for sulfur dioxide
service (4.33).
The temperature resistance of a material must be taken into account for
use with hot sulfur dioxide gas or solutions, especially if plastics or resins
are used. Materials such as ceramic, glass, and stone should also be evalua-
ted for their ability to withstand thermal shock. These latter materials are
suitable for use with wet gas. sulfurous acid, or sulfite solutions.
The metals which are best suited for a wide variety of wet, dry, and hot
sulfur dioxide, sulfurous acid, and sulfite service include nickel-chromium
alloys such as Worthite and Durimet 20, and several of the austenitic stain-
less steels. While type 304 stainless steel may be satisfactory for mild
conditions, types 316 and 317 are usually required for high temperatures or
other severe applications. In processes which also involve the presence of
sulfuric acid, the use of a 20-grade stainless steel may be warranted. Inconel
is another material which is especially resistant to very hot sulfur dioxide
gas.
Corrosion is a very serious hazard, and it is important to use appropri-
ate materials for applications which may involve some exposure of the sulfur
dioxide to small amounts of moisture. At approximately 300 ppm moisture.
liquid sulfur dioxide discolors iron, copper, and brass. As the moisture
content increases, light scale is produced at approximately 0.1 wt%. with
serious corrosion occurring at 0.2 wt% and higher. For low moisture contents
or where some corrosion can be tolerated, copper or brass can be used. The
use of wooden tanks is common for the preparation, handling, and storage of
sulfurous acid, while sulfite pulp digesters are commonly made of steel lined
with acid-resistant brick. Organic coatings may be used to protect metals
from corrosion unless gas diffusion through the organic film is appreciable.
Organic materials used for sulfur dioxide and sulfurous acid service include
hard rubber at moderate temperatures and butyl rubber which performs similar-
ly.
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For all processes involving the use of sulfur dioxide or other hazardous
materials, special care should be taken to ensure that all replacement parts
or new equipment are made of materials which are compatible with the chemicals
involved in the process. Materials of construction suitable for specific
pieces of equipment will be discussed in the following subsections which
address the equipment used in sulfur dioxide storage and processing.
Storage Vessels—
Storage vessels for sulfur dioxide range in size from 150-pound cylinders
to multi-ton tanks. As stated in Section 3.4.1. these containers are general-
ly constructed of carbon steel according to the ASME Code for Unfired Pressure
Vessels, Section VIII, Division I (29). The vessels are also typically con-
structed with provisions for keeping process solutions and gases out of the
tank. The maximum allowable weight of sulfur dioxide which may be stored is
1.25 times the water weight capacity of the container measured at 60 °F (2).
This 4uantity is expressed as a percent of the maximum volume of the container
for various temperatures in Table 5-3 (4).
A large inventory of sulfur dioxide contained in storage vessels on site
represents one of the most hazardous components of a chemical plant which uses
this material. The most probable causes of a hazardous release from a storage
vessel include overpressurization from a temperature increase and/or acciden-
tal overfilling, and corrosion resulting from contaminants entering the
storage system or associated piping. This section discusses the protection
devices and safety procedures associated with the storage of sulfur dioxide
which are designed for the prevention of a hazardous release of this material.
Several methods for preventing overpressurization of sulfur dioxide
storage vessels are employed depending on the size of the container. Cylin-
ders and one-ton drums are manufactured with one or more fusible safety plugs
which are designed to melt at a temperature of 165 °F. This safeguard, while
preventing the container from a potentially explosive rupture, will still
result in the complete release of the sulfur dioxide if a plug becomes hot
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TABLE 5-3. MAXIMUM SAFE VOLUME OF LIQUID SULFUR DIOXIDE IN
A STORAGE TANK AT VARIOUS TEMPERATURES (A)
Maximum Safe Volume
Temperature of Liquid Liquid Sulfur Dioxide in
Sulfur Dioxide in Tank % of Full Volume
2l at 125% Filling Density
30 86
40 87
50 88
60 89
70 90
80 91
90 92
100 93
53
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enough to melt. For this reason, it is important to never allow the tempera-
ture of cylinders or drums to exceed 125 °F or to expose the fusible plugs to
a source of radiant heat.
Larger storage vessels are generally equipped with a pressure relief
valve which is protected by one or more rupture disks. These valves allow a
controlled release of overpressurized contents. To prevent releases of sulfur
dioxide to the atmosphere when a vessel is overpressured, the relief valve may
discharge to an overflow tank in a closed system which in turn is relief
vented to a scrubber system. To accommodate flashing liquid, relief piping
must be sized for adequate flow. Tank cars and trucks are equipped with
spring-loaded pressure relief valves which are tested to be vapor tight at 180
psig and set to discharge at 225 psig (4). For large containers, including
tank cars, it may be feasible to construct a scalable housing around the
container which would be vented to a scrubber system.
t
Overfilling of storage vessels may occur during sulfur dioxide transfer
as a result of a malfunctioning measuring device, operator error, or the use
of a damaged container with a reduced filling capacity which has gone unno-
ticed. The immediate danger of overfilling during transfer operations is an
unexpected overflow and release of liquid or gaseous sulfur dioxide. The
latent hazard is overpressurization and possible rupture of the container with
an increase in temperature, because the temperature at which it will become
liquid-full is lower than it should be.
If it is possible for a vessel to be overfilled, it should be fitted with
a relief device which discharges to an overflow tank or other suitable receiv-
er. To reduce the risk of overfilling during transfer, the storage vessel may
be mounted on a scale which will indicate the weight of fluid in the container
at all times. All storage vessels should also be equipped with a liquid level
gauging device. The Compressed Gas Association makes the following recommen-
dations for the design and use of these gauges (2):
54
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The gauge should be designed to permit reading the liquid
level within plus or minus 1% of the capacity of the tank
from full tank level down to at least 20% below full tank.
(Readings below this level may be useful for other pur-
poses but are not required to avoid overfilling.)
Certain precautions must be observed if gauge glasses are
used as liquid level devices. They should be protected by
solid, transparent shields and guards. Gauge cocks should
be provided with ball checks which will shut off the flow
if the glass accidentally breaks. The ball checks will
also allow the gauge cock to remain open at all times
which minimizes the possibility that the glass will break
by liquid expansion. The gauge should be located such
that the glass and its contents do not differ greatly in
temperature from the container and the sulfur dioxide
inside.
Gauges should be situated to allow ready determination of
the maximum level to which the container may be filled.
It is recommended that the information in Table 5-2 be
attached to the tank near the gauge.
Gauging devices which require bleeding of sulfur dioxide
to the atmosphere, such as a rotary tube, fixed tube or
slip tube, should be designed so that the bleed valve
maximum opening is no greater than a No. 54 drill size.
unless provided with an excess flow valve.
Gauging devices should be designed for a working pressure
of at least 200 pounds gauge.
55
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A short, vented dip pipe can provide protection from overfilling in the
event of failure of the volume or weight measuring device. However, this
device will not always prevent an overflow of sulfur dioxide liquid. Further-
more, it will only work if there is no other outlet from the vapor space and
if the line to the vent system has enough capacity.
In addition to venting provisions, storage vessels should have valve
arrangements which allow the vessel to be isolated from the process to which
the sulfur dioxide is being fed. Backflow of material into the upper valve
chambers when the feed valve is shut off at the storage tank must be prevented
because of the possibility of a corrosive solution of sulfurous acid being
formed. This may be accomplished with a vented feed line or a barometric leg.
Moisture must also be excluded from the storage system to prevent corrosion by
sulfurous acid. For this reason, storage containers should not be in contact
with standing water or exposed to continual dampness. These conditions must
also be avoided to prevent external rusting of the vessel.
Process and Reaction Vessels-
General considerations for hazard control for storage vessels also apply
to the design and use of process and reaction vessels. In the latter type of
vessels, however, there is a greater degree of risk, as these containers are
often exposed to more severe conditions of temperature and/or pressure than a
regular storage vessel.
Primary considerations for process and reaction vessels include:
• Materials of construction,
• Pressure relief devices.
• Temperature control.
• Overflow protection (including high-level alarms). and
• Foundations and supports.
56
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The foundations and supports for vessels are important design considera-
tions, especially for large storage vessels and tall equipment such as distil-
lation columns. The choice of construction materials is also an important
consideration particularly where low-temperature conditions are encountered.
If cooling to a condenser is lost, overpressure may occur. Thus, it is
necessary to use pressure relief valves to protect against leaks and ruptures
which can result from overpressure. Relief protection is also necessary in
the event of a fire to protect from overpressure.
Distillation and stripping columns present significant release hazards.
because they contain large amounts of sulfur dioxide in pure form and have a
heat input. As they are often located outdoors, external factors such as
ambient temperature fluctuations and wind loadings must be properly accounted
for in their design and construction, especially for the support structure.
Piping-
Schedule 80 steel pipe, butt welded and/or flanged with butt welded
and/or flanged fittings, is normally used to transport pure, dry sulfur
dioxide, since dry sulfur dioxide is virtually non-corrosive (4). Flanges can
be slip-on and flat face and should be fitted carefully to prevent leaks.
Flanges used for connecting a storage tank and the valves adjacent to it
should be especially well fitted, because a leak before the first valve would
necessitate unloading the tank for repair.
Because of the corrosive nature of sulfurous acid, sulfur dioxide con-
taining moisture should be transported with 316 SS piping or other example
materials listed in Table 5-2. Zinc-coated pipe should not be used, because
sulfur dioxide readily oxidizes zinc in the presence of very small quantities
of water.
57
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Flexible pipe, tubing or hose is usually required somewhere in a sulfur
dioxide piping system, such as when connecting to a cylinder. A commonly used
material is 500 psig copper tubing with a standard yoke and adapter at the
cylinder end, or a series of reverse bends may be put into the line. Since
copper is prone to work hardening, the connection should be inspected each
time the cylinder is changed and replaced as necessary. When making connec-
tions to a cylinder, a new 3% antimony lead or graphitized gasket should be
used (34). Flexible pipe or hose should never be used where straight piping
is adequate, because it does not have comparable physical strength and can
fail more easily. Where a flexible connection is required, flexible metal
hose designed for service with corrosive acids under pressure provides an
extra measure of safety if used for carrying undiluted sulfur dioxide.
Piping connections to a tank car during transfer may be constructed out
of steel, brass, copper, or stainless steel, but never out of galvanized
material (4). A one-inch air line should be connected to the "GAS" valve on
the tank car with a pressure gauge installed near the car. A two-inch liquid
unloading line is usually sufficient (4). Ordinary ground joint or flanged
unions can be used in making the various connections.
Special material considerations may be required for high or low tempera-
ture applications or other unusual or severe conditions.
Because liquid sulfur dioxide expands with temperature, bursting of lines
due to hydrostatic pressure must be prevented. This may be accomplished with
expansion chambers which should be located at the highest point of each
section that may be .closed, trapping liquid sulfur dioxide. Construction of
these chambers should be in accordance with the ASME Code for Unfired Pressure
Vessels. Section VIII (29). The size of the vapor chamber should provide
approximately 20% excess volume for expansion (4) .
The following is a list of general guidelines for the safe transport of
sulfur dioxide in piping systems:
58
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• All pipes, valves, and instrumentation should be installed
and maintained in a dry. greaseless condition.
• Piping systems should have as simple a design as possible
with a minimum number of joints and connections.
• A pressure reducing regulator should be installed when
connecting to lower pressure piping or systems from
storage vessels.
• In addition to being securely supported, pipes should be
sloped with drainage provisions at the low points.
• Clips or hangers should not fit too tightly to allow for
thermal expansion of the pipe.
• Piping should be protected from exposure to fire and
high temperatures.
• Pressure testing should be done with dry. oil-free air;
hydraulic testing must not be used because of the diffi-
culties of drying out the system after the test is com-
pleted.
• Pipelines should always be emptied when sulfur dioxide
flow is not required to prevent the possible isolation of
liquid sulfur dioxide between closed valves.
Valves (35) —
Under normal conditions of flow, ball, gate or plug valves constructed of
Type 316 stainless steel are used for sulfur dioxide service. In the case of
gate valves, the use of the rising stem type will prevent rotation of the stem
on the valve seat. Teflon packing should be used for the seats of ball or
gate valves, and diaphragm valves should have teflon-faced diaphragms.
59
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Valves in sulfur dioxide service must be carefully selected in certain
circumstances. For service where water may mix with the sulfur dioxide in
contact with the valve it must be corrosion resistant. Valves for such
service may be constructed of or lined with materials listed in Table 5-2.
Diaphragm valves with inner lining of the diaphragm constructed of type 316
stainless steel are suitable for service under corrosive conditions. For more
severe conditions valves should be constructed of "20-alloys" which minimize
the tendency of a valve to "freeze". Teflon packing is suitable for wet or
dry sulfur dioxide service.
Check valves must be installed in the line between the sulfur dioxide
feed vessel and the process to prevent hazardous backflow into the sulfur
dioxide feed line when the shutoff valve is closed, or when the container
supplying sulfur dioxide is empty. It is important to keep sulfur dioxide
from mixing with moisture in closed equipment* because hydrogen pressure may
be generated leading to an explosion with violent force. A swing check valve
made of type 316 stainless steel* or Alloy 20 for longer life, should be used.
A needle valve is often used for accurate flow control at low flow rates.
For high flow rates, a globe valve with V-ports should be used. These should
also be constructed of type 316 stainless steel, or Alloy 20 for longer life.
Gate valves are better than globe valves for use as a shutoff valve because of
the lower pressure drop in a gate valve.
Excess flow valves should be considered for sulfur dioxide in vessels,
tank cars, and other places where unintentional high liquid discharge rates
need to be prevented. In the event that a liquid discharge line is broken,
the resulting high flow rate would cause the valve to close off, restricting
the escape of sulfur dioxide.
Process Machinery—
Process machinery refers to rotating or reciprocating equipment that may
be used in the transfer or processing of sulfur dioxide. Included in this
classification are pumps and compressors which may be used to move liquid or
60
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gaseous sulfur dioxide where gas pressure padding is insufficient or inappro-
priate.
Pumps—Many of the considerations for sulfur dioxide piping and valves
also apply to pumps. To assure that a given pump is suitable for a sulfur
dioxide service application, the design engineer should obtain information
from the pump manufacturer certifying that the pump will perform properly in
this application.
Pumps should be constructed with materials which are resistant to sulfur
dioxide at operating temperatures and pressures. They should be installed dry
and oil-free. Lubricating oil should be resistant to breakdown as a result of
contact with sulfur dioxide. Highly refined mineral oil may be suitable for
many applications (36). Even with the use of special lubricants, it is
important that pump design not allow sulfur dioxide or lubricating oil to
enter seal chambers where they may contact one another. Net positive suction
head (NFSH) considerations are especially important for sulfur dioxide, since
pumping the liquid near its boiling point may be common. (Sulfur dioxide is a
gas at typical ambient conditions.) The pump's supply tank should have high
and low level alarms; the pump should be interlocked to shut off at low supply
level or low discharge pressure. External pumps should be situated inside a
diked area and should be accessible in the event of a tank leak.
In some cases, the potential for seal leakage may rule out the use of
rotating shaft seals. Some pump types which either isolate the seals from the
process stream or eliminate them altogether include canned-motor, vertical
extended-spindle submersible, magnetically-coupled, and diaphragm (37).
Canned motor pumps are centrifugal units in which the motor housing is
interconnected with the pump casing. Here, the process liquid actually serves
as the bearing lubricant. An alternative concept is the vertical pump often
used on storage tanks. Vertical pumps consist of a submerged impeller housing
connected by an extended drive shaft to the motor. The advantages of this
arrangement are that the shaft seal is above the maximum liquid level (and is
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therefore not made wet by the pumped liquid). and the pump is self-priming.
because the liquid level is above the impeller.
Vertical pumps should be provided with double-packed seal chambers which
are designed to prevent contact of sulfur dioxide and any reactive material.
Seal gas should be dry. oil-free, and inert to sulfur dioxide. The seal gas
pressure should be greater than tank pressure, and a seal gas backup system
should be considered.
Magnetically-coupled pumps replace the drive shaft with a rotating
magnetic field as the pump-motor coupling device. Diaphragm pumps are posi-
tive displacement units in which a reciprocating flexible diaphragm drives the
fluid. This arrangement eliminates exposure of packing and seals to the
pumped liquid.
Centrifugal pumps often have a recycle loop back to the feed container
which prevents overheating in the event that the pump is deadheaded (i.e.. the
discharge valves close.) Deadheading also is a concern with positive dis-
placement pumps. To prevent rupture, positive displacement pumps commonly
have a pressure relief valve which bypasses to the pump suction. Because of
the probability of eventual diaphragm failure, the use of diaphragm pumps
should be carefully considered in view of this hazard potential.
Pumps are not always necessary; in some circumstances, liquid sulfur
dioxide is moved by pressure padding. With sulfur dioxide cylinders and ton
containers, the liquid may be displaced from the vessel by the force of sulfur
dioxide's vapor pressure. With other types of vessels, an inert gas such as
dry nitrogen may be used to force liquid from the tank. Padding system
designs reflect the operating conditions and limitations (e.g., required flow
rate) and therefore must be custom designed for a process.
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Compressors—Sulfur dioxide compressors include reciprocating,
centrifugal, liquid-ring rotary, and non-lubricated screw compressors.
Detailed descriptions of these compressors may be found in the technical
literature (37).
While it is often possible to avoid using rotary shaft seals with sulfur
dioxide pumps, compressors in sulfur dioxide service usually require special
seals such as double labyrinth seals. These seals have a series of interlock-
ing touch points which, by creating many incremental pressure drops, reduce
total leakage. To further reduce leakage, dry air is injected into the seal.
For reciprocating compressors, a two-compartment distance piece with purge gas
may be used to prevent shaft exposure to sulfur dioxide. In the event of
deadheading, a compressor discharge can have a pressure relief mechanism which
vents to the compressor inlet or to a scrubber system. The former appears to
be satisfactory for a short-term downstream flow interruption. Where a
sustained interruption might occur, relief to a scrubber system would be
safer. As with pumps, compressors for sulfur dioxide service may require the
use of lubricating oils that are resistant to breakdown by sulfur dioxide.
Miscellaneous Equipment—
Pressure Relief Devices—Pressure relief devices for sulfur dioxide
service should be constructed in accordance with CGA S-1.3 - "Pressure Relief
Device Standards - Part 3 - Compressed Gas Storage Containers" (38). All
wetted parts of relief valves and rupture disks should be constructed from
materials compatible with sulfur dioxide at the operating temperature and
pressure. For balanced relief valves, the balance seals must also be made of
a corrosion resistant material. For most applications, 316 stainless steel is
an appropriate material of construction.
Fugitive emissions of sulfur dioxide can result in external corrosion of
a relief valve. For this reason it may be appropriate to construct the entire
relief device of a material that is resistant to wet sulfur dioxide.
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Measures should be taken to ensure that process equipment is not isolated
from its relief system. To provide continuous pressure relief protection when
a device is out of service for maintenance, equipment may be provided with
dual relief systems, each sized to provide the total required flow capacity.
Piping and valves should be arranged so that one of the systems always
provides protection. Stop valves installed between a vessel and its relief
device should have a full port area that is at least equal to that of the
pressure relief device inlet. These valves should be locked open or have
handles removed when the protected vessel is in use. If the discharge is to
be piped to a closed disposal system, such as a scrubber, the pressure drop
caused by the additional piping must be considered and the relief device sized
accordingly.
Rupture disks may be used to protect pressure relief valves from constant
contact with the contents of the storage vessel. Rupture disks should not be
used in sulfur dioxide service where the ruptured disk discharges directly
into the atmosphere. If the disk relieves the contents of the container
through a spring-loaded pressure relief valve, a small vent should be provided
in the chamber between the disk and the valve to prevent any back pressure on
the rupture disk. Because operating pressures exceeding 70% of a disk
bursting pressure may induce premature failure, a considerable margin should
be allowed when sizing rupture disks.
Instrumentation—Rotameters may be used for measuring the rate of flow of
sulfur dioxide gas or liquid. If liquid sulfur dioxide is being measured
through a meter in which the liquid takes a pressure drop, the sulfur dioxide
liquid must be cooled well below its boiling point to prevent bubbling which
will destroy the accuracy of the measurement (4). For high pressure work the
glass tube should be enclosed in a vented shield or, preferably, a steel-
armored type.
Instrumentation must be constructed of materials suitable for sulfur
dioxide service, and special attention should be paid to materials used for
wet sulfur dioxide. Thermocouples may be enclosed in glass sleeves for
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corrosion protection in some processes. An additional consideration for all
instruments is that they should be protected from external corrosion which may
be caused by fugitive emissions of sulfur dioxide or other process chemicals.
Gaskets—Gaskets should be graphited or Teflon impregnated asbestos.
l/16th-inch thick (4). Gaskets should have smooth faces. Compensation for
flaws in gasket faces must not be made by the use of thicker gaskets (4).
5.3.2 Plant Siting and Layout
The siting and layout of a particular sulfur dioxide facility is a
complex issue which requires careful consideration of numerous factors. These
include the other processes in the area, the proximity of population centers.
prevailing winds, local terrain, and potential natural external effects such
as flooding.
The objective in siting and layout should be to avoid fires, explosions.
releases of toxic gases and other dangerous incidents, rather than to protect
people from their consequences after the fact. However, while prevention is
always the first priority, complete prevention may be impossible. For this
reason, siting and layout of facilities or individual equipment items should
be done in a manner that reduces exposure to persons, both in and out of the
plant, in the event of a release. Protection for people, control equipment.
and records can be had by locating them in specially designed buildings.
Siting should further provide ready access in the event of an emergency for
both evacuation purposes and the use of emergency equipment. However, advan-
tage should also be taken of barriers, either man-made or natural which could
reduce the hazards of releases.
Various techniques are available for formally assessing a plant layout
and should be considered when planning high hazard facilities (39).
The siting and layout of any facility handling sulfur dioxide should
adhere to the following general guidelines:
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• Areas in which sulfur dioxide hazards exist should have an
adequate number of well marked exits through which person-
nel can escape quickly if necessary; doors should open
' outward and lead to unobstructed passageways:
• The plant is laid out so that, whenever possible, there
are no confined spaces between equipment; large distances
between large inventories and sensitive receptors is
desirable;
• Access to platforms above ground level should be by
stairway in preference to cat ladders, and work areas
above ground level should have alternative means of
escape;
\
• Large inventories of sulfur dioxide should be kept away
from possible sources of fire or explosion; special
consideration should be given to the location of furnaces
and other permanent sources of ignition in the plant; and
• Storage facilities should be located in cool. dry. well-
ventilated areas, away from heavily trafficked areas and
emergency exits.
An existing facility may not be able to conform to all of these criteria.
When this is true, other prevention measures must be taken to compensate for
deficiencies in plant layout.
Because heat causes thermal expansion of liquid sulfur dioxide, measures
should be taken to situate piping, storage vessels, and other sulfur dioxide
equipment so that they are not adjacent to piping which carries flammable
materials, hot process piping, equipment, steam lines, and other sources of
direct or radiant heat. Storage should also be situated away from control
rooms, offices, utilities, and laboratory areas.
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In the event of an emergency, there should be more than one entrance to
the facility which is accessible to emergency vehicles and crews. Storage
vessel shutoff valves should be readily accessible. Containment for liquid
storage tanks can be provided by diking. Dikes reduce evaporation while
containing the liquid. It is also possible to equip a diked area to allow
drainage to an underground containment sump. This sump would be vented to a
scrubber system for safe discharge. A full containment system using a speci-
ally constructed building vented to a scrubber is another possible option.
This type of secondary containment could be considered for large volume,
liquid sulfur dioxide storage tanks.
5.3.3 Transfer and Transport Facilities
Transfer and transport facilities where both road vehicles and rail
tankers are loaded or unloaded are potential accident areas because of vehicle
movement and the intermittent nature of the operations. Therefore, special
attention should be given to the design of these facilities.
As mentioned in the previous section, tank car and tank truck facilities
should be located away from sources of heat, fire and explosion. Before
unloading, tank vehicles should be securely moored; an interlocked barrier
system is commonly used. Tank cars should also be protected on both ends by
derailers or on the switch end if located on a dead end siding. Sufficient
space should be available to avoid congestion of vehicles or personnel during
loading and unloading operations. Vehicles, especially trucks, should be able
to move into and out of the area without reversing. High curbs around trans-
fer areas and barriers around equipment should be provided to protect equip-
ment from vehicle collisions.
Correct procedures must be followed when unloading and handling small
sulfur dioxide storage vessels such as cylinders and drums. Dragging, slid-
ing, or rolling cylinders, even for short distances, is not acceptable.
Lifting magnets, slings of rope or chain, or any other device in which the
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cylinders themselves form a part of the carrier should never be used for
transporting cylinders. Drums may be moved over short distances with the use
of hooks which are connected to a chain sling or a lifting beam supported by a
hoist or monorail (4). It is important to instruct operating personnel in the
proper use of such equipment, since additional stresses are imposed on slings
through angles -developed, which the operators may not be aware of, thus
creating an overload on the system. Suppliers' vehicles specially equipped so
that drums lie in cradles cannot be safely loaded or unloaded with convention-
al fork lift trucks. A system of runway beams in the drum storage area is the
preferred method.
5.4 PROTECTION TECHNOLOGIES
This subsection describes two types of protection technologies for
containment and neutralization. These are:
• Enclosures, and
• Scrubbers.
More detailed discussions on these systems are planned for other parts of the
prevention reference manual series.
5.4.1 Enclosures
Enclosures refer to containment structures which capture any sulfur
dioxide spilled or vented from storage or process equipment, thereby prevent-
ing immediate discharge of the chemical to the environment. The enclosures
contain the spilled liquid or gas until it can be transferred to other con-
tainment and discharged at a controlled rate which would not be injurious to
people or the environment, or transferred at a controlled rate to scrubbers
for neutralization.
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Specially designed enclosures for sulfur dioxide storage or process
equipment do not appear to be in widespread use. The principle that it may be
preferable to locate toxic operations in the open air has been mentioned in
the literature (39)., along with the opposing idea that sometimes enclosure may
be appropriate. The desirability of enclosure depends partly on the frequency
with which personnel must be involved with the equipment.- A common design
rationale for not having an enclosure where toxic materials are used is to
prevent the accumulation of toxic concentrations within enclosed areas. How-
ever, if the issue is providing for secondary containment, total enclosure may
be appropriate.
If an enclosure is deemed appropriate for a given installation, it should
be equipped with continuous monitoring equipment and adequate fire protection.
Alarms should sound whenever lethal or flammable concentrations are detected.
Care must be taken when an enclosure is built around pressurized
equipment. From an economic standpoint, it would.not be practical to design
an enclosure to withstand the pressures associated with the sudden failure of
a pressurized vessel. Therefore, if an enclosure is built around pressurized
equipment, it should be equipped with some type of explosion protection, such
as rupture plates. These components are designed to fail at a pressure lower
than the design pressure of the enclosure, thus preventing the entire
structure from failing.
The type of structures that appear to be suitable for sulfur dioxide are
concrete blocks, or concrete sheet buildings or bunkers. An enclosure would
have a ventilation system designed to draw in air when it is vented to a
scrubber or the atmosphere. The bottom section of an enclosure which is used
for stationary storage containers should be liquid tight to retain any liquid
sulfur dioxide that might be spilled. Enclosures around rail cank cars which
are used for storage 'do not normally lend themselves easily to effective
liquid containment. However, containment can be accomplished if the floor of
the enclosure is excavated several feet below the track level while the tracks
are supported at grade in the center.
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While the use of enclosures for secondary containment of sulfur dioxide
spills or releases is not known to be widely used, it might be considered for
areas near sensitive receptors.
5.4.2 Scrubbers
Scrubbers are a traditional method for absorbing toxic gases from process
streams. These devices can be used for the control of sulfur dioxide releases
from vents and pressure relief discharges, from process equipment, or from
secondary containment enclosures.
Sulfur dioxide discharges could be contacted with an aqueous scrubbing
medium in any of several types of scrubbing devices. An alkaline solution is
required to achieve effective absorption, because absorption rates with water
alone might require unreasonably high liquid-to-gas ratios. However, water
scrubbing could be used if an alkaline solution were not available. Typical
alkaline solutions for an emergency scrubber could be calcium hydroxide,
derived from slaked lime, or sodium hydroxide or sodium carbonate.
Types of scrubbers that might be appropriate include spray towers, packed
bed scrubbers, and Venturis. Other types of special designs might be suit-
able, but complex internals subject to corrosion do not seem to be advisable.
Whatever type of scrubber is selected, a complete system would include
the scrubber itself, a liquid feed system, and reagent makeup equipment. If
such a system is used as protection against emergency releases, consideration
must be given to how it would be activated in time to respond to an emergency
load. One approach used in some process facilities is to maintain a
continuous circulation of scrubbing liquor through the system. For many
facilities this would not be practical, and the scrubber system might be tied
into a trip system to turn it on when it is needed. However, with this system
a quantity of sulfur dioxide would be released prior to actuation of the
scrubber (i.e., starting up a blower and turning on the flow of liquid).
-------
The scrubber system must be designed so as not to present excessive
resistance to the flow of an emergency discharge. The pressure drop should be
only a small fraction of the total pressure drop through the emergency
discharge system. In general, at the liquid-to-gas ratios required for
effective scrubbing, spray towers have the lowest, and Venturis the highest
pressure drops. While packed beds may have intermediate pressure drops at
proper liquid-to-gas ratios, excessive ratios or plugging can increase the
pressure drop substantially. However, packed beds have higher removal
efficiencies than spray towers or Venturis.
In addition, the scrubber system must be designed to handle the "shock
wave" generated during the initial stages of the release. This is
particularly important for packed bed scrubbers since there is a maximum
pressure with which the gas can enter the packed section without damaging the
scrubber internals.
Design of emergency scrubbers can follow standard techniques discussed in
the literature, carefully taking into account the additional considerations
just discussed. An example of the sizing of an emergency packed bed scrubber
is presented in Table 5-4. This example provides some idea of the size of a
typical emergency scrubber for various flow rates. This is an example only
and should not be used as the basis for an actual system which might differ
based on site specific requirements.
Another approach is the drowning tower where the sulfur dioxide vent is
routed to the bottom of a large tank of uncirculating caustic. The drowning
tower does not have the high contact efficiency of the other scrubber types,
but can provide substantial capacity on demand.
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TABLE 5-4. EXAMPLE OF PERFORMANCE CHARACTERISTICS FOR AN EMERGENCY
PACKED BED SCRUBBER FOR SULFUR DIOXIDE
Basis: Inlet stream of 50% SO. in 50% air.. Constant gas flow per unit
cross-sectional area of 290 scfm/ft .
Packing: 2-inch plastic Intalox* saddles.
Pressure Drop: 0.5 inch water column
Scrubbing Medium: 8% (wt) NaOH solution
Removal Efficiency, % 50 90
Liquid to Gas Ratio
(gal/thousand scf)
— at flooding 220 220
— operating 130 130
Packed Height, ft. 4.6 15.3
Column "Diameter and Corresponding Gas Flow Rates for Both Removal Efficiencies
Column
Diameter Flow Rate
(ft) (scfm)
0.5 60
1.0 240
2.0 960
6.6 10,000
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5.5 MITIGATION TECHNOLOGIES
If, in spite of all precautions, a large release of sulfur dioxide were
to occur, the first priority would be to rescue workers in the immediate
vicinity of the accident and evacuate persons from downwind areas. The source
of the release should be determined, and the leak should be plugged to stop
the flow if this is possible. This post release mitigation effort requires
that the source of the release is accessible to trained plant personnel, and
adequate personnel protection is readily available.- Personnel protection
includes such items as portable breathing air and chemically resistant
protective clothing.
The next primary concern becomes reducing the consequences of the
released chemical to the plant and the surrounding community. Reducing the
consequences of an accidental release of a hazardous chemical is referred to
as mitigation. Mitigation technologies include such measures as physical
barriers, water sprays and fogs, and foams where applicable. The purpose of a
mitigation technique is to divert, limit, or disperse the chemical that has
been spilled or released to the atmosphere in order to reduce the atmospheric
concentration and the area affected by the chemical. The mitigation technol-
ogy chosen for a particular chemical depends on the specific properties of the
chemical including its flammability, toxicity, reactivity, and those proper-
ties which determine its dispersion characteristics in the atmosphere.
If a release occurs from a pressurized sulfur dioxide storage tank above
the boiling point, a gas cloud or a quantity of liquid will immediately flash
off as vapor, while the remaining liquid will be cooled to the normal boiling
point of 14.0 °F. Heat transfer from the air and ground will result in fur-
ther vaporization of the released liquid. Since the sulfur dioxide accident-
ally released from a refrigerated storage tank is already at or below its
normal boiling point, a comparable quantity of vapor will not flash off, as
with the pressurized release discussed above, but heat transfer from the
environment will cause evaporation and the formation of a vapor cloud. It is
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therefore desirable to minimize the area available for heat transfer to a
liquid spill which in turn will minimize the rate of evaporation. Mitigation
technologies which are used to reduce the rate of evaporation of a released
liquified gas include secondary containment systems such as impounding basins
and dikes.
5.5.1 Secondary Containment Systems (40)
Specific types of secondary containment systems include excavated basins.
natural basins, earth, steel, or concrete dikes, and high impounding walls.
The type of containment system best suited for a particular storage tank or
process unit will depend on the risk associated with an accidental release
from that location. The inventory of sulfur dioxide and its proximity to
other portions of the plant and to the community should be considered when
selecting a secondary containment system. The secondary containment system
should have the ability to contain spills with a minimum of damage to the
facility and its surroundings and with minimum potential for escalation of the
event.
Secondary containment systems for sulfur dioxide storage facilities may
consist of one of the following:
• An adequate drainage system underlying the storage vessels
which terminates in an impounding basin having a capacity
as large as the largest tank served; or
• A dike surrounding the storage area with a capacity as
large as the largest tank served.
These measures ara designed to prevent the accidental discharge of liquid
sulfur dioxide from spreading to uncontrolled areas.
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The most common type of containment system is a low wall dike sur-
rounding one or more storage tanks.- Generally, no more than three tanks are
enclosed within one diked area to reduce risk. Dike heights usually range
from three to twelve feet depending on the area available to achieve the re-
quired volumetric capacity. The dike walls should be liquid tight and able to
withstand the hydrostatic pressure and temperature of a spill. Low wall dikes
may be constructed of steel, concrete, or earth. If earthen dikes are used,
dike walls must be constructed and maintained to prevent leakage through the
dike. Piping should be routed over dike wails, and penetrations through the
walls should be avoided if possible. Vapor fences may be situated on top of
the dikes to provide additional vapor storage capacity. If there are more
than one tank in the diked area, the tanks should be situated on beams above
the maximum liquid level attainable in the impoundment.
A low wall dike can effectively contain the liquid portion of an acciden-
tal release and keep the liquid from entering uncontrolled areas. By prevent-
ing the liquid from spreading, the low wall dike can reduce the surface area
of the spill. Reducing the surface area will reduce the rate of evaporation.
The low wall dike will partially protect the spill from wind; this can reduce
the rate of evaporation. A dike with a vapor fence will provide extra protec-
tion from wind and will be even more effective at reducing the rate of evapo-
ration.-
A low wall dike will not reduce the impact of a gaseous sulfur dioxide
release. A dike also creates the potential for sulfur dioxide and trapped
water to mi* in the dike, which may accelerate the rats of evaporation and
form highly corrosive sulfurous acid. If materials that would react violently
with sulfur dioxide are stored within the same diked area then the dike will
increase the potential for mixing the materials in the event of a simultaneous
leak. A dike also limits access to the tank during a spill.
A remote impounding basin is well suited to storage systems where more
than one tank are served and a relatively large site is available. The flow
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from a sulfur dioxide spill is directed to the basin by dikes and channels
under the storage tanks which are designed to minimize exposure of the liquid
to other tanks and surrounding facilities. Because of sulfur dioxide's high
vapor pressure the trenches that lead to the remote impounding basin as well
as the basin itself should be covered to reduce the rate of evaporation.
Additionally, the impounding basin should be located near the tank area to
minimize the amount of sulfur dioxide that evaporates as it travels to the
basin.
This type of system has several advantages. The spilled liquid is re-
moved from the immediate tank area. This allows access to the tank during the
spill and reduces the probability that the spilled liquid will damage the
tank, piping, electrical equipment, pumps or other equipment. In addition,
the covered impoundment will reduce the rate of evaporation from the spill by
protecting the spill from wind or heating from sunlight.
»
A limitation of a remote impounding basin is that there is still the
potential for water or other incompatible materials to be trapped in the
impoundment and mix with the incoming sulfur dioxide. Remote impounding
basins do not reduce the impact of a gaseous sulfur dioxide release.
Although few authorities for sulfur dioxide facilities require them, high
wall impoundments may be a good secondary containment choice for selected sys-
tems. Circumstances which may warrant their use include limited storage site
area, the need to minimize vapor generation rates, and/or the tank must be
protected from external hazards. Maximum vapor generation rates will gen-
erally be lower for a high wall impoundment than for low wall dikes or remote
impoundments because of the reduced surface contact area. These rates can be
further reduced with the use of insulation on the wall and floor in the annu-
lar space. High impounding walls may be constructed of low temperature steel,
reinforced concrete, or prestressed concrete. A wea.ther shield may be pro-
vided between the tank and wall with the annular space remaining open to the
atmosphere. The available area surrounding the storage tank will dictate the
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minimum height of the wall. For high wall, impoundments, the walls may be de-
signed with a volumetric capacity greater than that of the tank to provide va-
por containment. Increasing the height of the wall also raises the elevation
of any released vapor.
One disadvantage of these dikes is that the high walls around a tank may
hinder routine external observation. Furthermore, the closer the wall is to
the tank, the more difficult it becomes to access the tank for inspection and
maintenance. As with low wall dikes, piping should be routed over the wall if
possible.- The closeness of the wall to the tank may necessitate placement of
the pump outside of the wall, in which case the tank outlet (suction) line
will have to pass through the wall. In such a situation, a low dike encompas-
sing the pipe penetration and pump may be provided, or a low dike may be
placed around the entire wall.
An example of the effect of diking as predicted by a vapor dispersion
model is shown in Figure 5-1 (41). This figure shows sulfur dioxide vapor
clouds at the time when the farthest distance away from the source is exposed
to concentrations above the IDLH. With diking, the model predicts that
downwind distances up to 3000 feet from the source of the release could be
exposed to concentrations above the IDLH. Three minutes are required for the
vapors to reach the maximum down wind distance. Without diking, the model
predicts that downwind distances up to 5800 feet from the source could be
exposed to concentrations above the IDLH. Seven minutes are required for the
vapors to reach this distance.
One further type of secondary containment system is one which is struc-
turally integrated with the primary system and forms a vapor tight enclosure
around the primary container. Many types of arrangements are possible. A
double walled tank is an example of such an enclosure. These systems jiay be
considered where protection of the primary container and containment of vapor
for events not involving foundation or wall penetration failure are of great-
est concern. Drawbacks of an integrated system are the greater complexity of
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LE8BNO:
> 100.
---> aoo.
> 40O.
PPM
PPM
PPM
•0.2S
miles
Release fro;a a tank
Elapsed Time: 3
0.5 0.75 i
miles miles mile
.s-jrr.3-i.iJed b/ a 25 Et. diameter dike.
Release from a tank with ao dike.
Elapsed Time: 7 minutes
Common Release Conditions
Storage Temperature = 85°F
Storage Pressure =51 psig
Ambient Temperature = 85°F
Wind Speed = 10 mph
Atmospheric Stability Class = C
Quantity Released = 5000 gallons
through a 2-inch hole
Figure 5-1. Computer aodel simulation showing the effect of diking on
the vapor cloud generated from a release of liquified
sulfur dioxide.
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the structure, the difficulty of access to certain components, and the fact
that complete vapor containment cannot be guaranteed for all potential events.
Provision should be made for drainage of rainwater from diked areas.
This will involve the use of sumps and separate drainage pumps, since direct
drainage to stormwater sewers would presumably allow any spilled sulfur
dioxide to follow the same route. Alternately, a sloped rain hood may be used
over the diked area which could also serve to direct the rising vapors to a
single release point (40). The ground within the enclosure should be graded
to cause the spilled liquid to accumulate at one side or in one corner. This
will help to minimize the area of ground to which the liquid is exposed and
from which it may gain heat. In areas where it is critical to minimize vapor
generation, surface insulation may be used in the diked area to further reduce
heat transfer from the environment to the spilled liquid. The floor of an
impoundment should be sealed with a clay blanket to prevent the sulfur dioxide
from seeping into the ground; percolation into the ground causes the ground to
cool more quickly, increasing the vapor generation rate. Absorption of the
sulfur dioxide into water in the soil would also release additional heat.
5.5.2 Flotation Devices and Foams (42.43)
Other possible means of reducing the surface area of spilled sulfur
dioxide include placing impermeable flotation devices on the surface, and
applying water-based foams. Placing an impermeable flotation device over a
spilled chemical is a direct approach for containing toxic vapors with nearly
100 percent efficiency. However, being able to use such devices requires
acquisition in advance of a spill and storage until needed, and in all but
small spills deployment may be difficult. In addition, material and dispersal
equipment costs are a major deterrent to their use (42).
• • •
The use of foams' in vapor hazard control has been demonstrated for a
broad range of volatile chemicals. Unfortunately, it is difficult to accu-
rately quantify the benefits of foam systems, because tne affects will vary as
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a function of the chemical spilled, foam type, spill size, and atmospheric
conditions. With regard to liquefied gases, it has been found that with some
materials, foams have a net positive effect, but with others, foams may
exaggerate the hazard.
One approach to a sulfur dioxide spill is dilution with water. However,
dilution of sulfur dioxide with water results in the formation of highly
corrosive sulfurous acid.- A water-based foam cover provides an alternative
means of diluting the sulfur dioxide. When a foam cover is first applied, an
increase in the boil off rate is generally observed which causes a short-term
increase in the downwind sulfur dioxide concentration. The initial foam cover
may be destroyed by violent boiling, in which case a second application is
necessary. Once a continuous foam layer is formed, a net positive effect will
be achieved in the downwind area. The reduction in downwind concentration is
a result of both increased dilution with air, because of a reduced vaporiza-
tion rate, and the increased buoyancy of the vapor cloud.- This latter effect
is a result of the vapor being warmed as it rises through the blanket by tteat
transfer from the foam and by the heat of solution of sulfur dioxide in water;
the warmed vapor cloud will have greater buoyancy and will disperse in an
upward direction more rapidly.
The extent of the downwind reduction in concentration will depend on the
type of foam used. Research in this area has indicated that medium to high
expansion foams (300 to 350:1) give significantly better results than do lov
expansion foams (6 to 8:1) (43). Furthermore, a. high expansion foam will
cause a smaller initial increase in boil off than a low expansion foam.
Regardless of the type of foam used, the slower the foam's drainage rate,
the better its performance will be. A slow draining foam will spread more
evenly, show more resistance to tamperature and pH effects, and collapse more
slowly. The initial cost for a slow draining roam may be higher than for
other foams, but a cost effective systam. vill be realized in superior perfor-
aance.
80
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5.5.3 Mitigation Techniques for Sulfur Dioxide Vapor (44.45.46)
The extent to which the escaped sulfur dioxide vapor can be removed or
dispersed in a timely manner will be a function of the quantity of vapor re-
leased, the ambient conditions, and the physical characteristics of the vapor
cloud. The behavior and characteristics of the sulfur dioxide cloud will be
dependent on a number of factors. These include the physical state of the
sulfur dioxide before its release, the location of the release, and the
atmospheric and environmental conditions. Many possibilities exist concerning
the shape and motion of the vapor cloud, and a number of predictive models of
dispersion have been developed. As a result of the higher specific gravity of
pure sulfur dioxide, large accidental releases of sulfur dioxide will often
result in the formation of sulfur dioxide-air mixtures which are denser than
the surrounding atmosphere. This type of vapor cloud is especially hazardous.
because it will spread laterally and remain close to the ground.
One means of dispersing as well as removing toxic vapor from*the air is
with the use of water sprays or fogs. However, dilution of sulfur dioxide
with water results in the formation of highly corrosive sulfurous acid and
presents an additional health hazard to plant personnel as well as corrosion
problems for machinery and equipment. In addition, to be effective, an
impractically large volume of water would have to be used, although it may be
beneficial in controlling relatively small releases whose principal hazard is
to plant personnel (44). An alternative is to use a mild aqueous alkaline
spray system which would act as a neutralizing agent for the acid.
The dispersing medium is commonly applied to the vapor cloud by means of
hand-held hoses and/or stationary spray barriers. For effective absorption.
it is important to direct fog or spray nozzles from a downwind direction to
avoid driving the vapors downwind more quickly. Other important factors
relating to the effectiveness of alkaline sprays are the distance of the
nozzles from the point of release, the fog pattern, nozzle flow rate, pres-
sure, and nozzle rotation. If the right strategy is followed, a "capture
81
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zone" can be created downwind of the release into which the sulfur dioxide
vapor will drift and be absorbed. In low wind conditions, two fog nozzles
should be placed upwind of the release to ensure that the sulfur dioxide cloud
keeps moving downwind against the fog nozzle pressures.- If an alkaline fog is
used to absorb sulfur dioxide vapors from a diked area containing spilled
liquid sulfur dioxide, great care must be taken not to direct alkaline solu-
tion into the liquid sulfur dioxide itself.
Spray barriers consist of a series of nozzles which can be directed
either up or down. If placed directly downwind from the point of sulfur
dioxide release, these barriers will absorb some of the sulfur dioxide vapors
passing through without significant distortion of the sulfur dioxide cloud
(45). Several fog nozzles may be situated farther downwind to absorb some of
the remainder of the vapors getting through.
In general, techniques used to disperse or control vapor emissions should
emphasize simplicity and reliability. In addition to 'the mitigation tech-
niques discussed above, physical barriers such as buildings and rows of trees
will help to contain the vapor cloud and control its movement. Hence, reduc-
ing the consequences of a hazardous vapor cloud can actually begin with a
carefully planned layout of facilities and the use of imaginative landscaping
around major hazard sites.
5.6 OPERATION AND MAINTENANCE PRACTICES
Accidental releases of toxic materials result not only from deficiencies
of design but also from deficiencies of operation. Unfortunately, human error
is often responsible for the realization of hazards with potentially damaging
consequences. The human error hazard manifests itself in numerous ways, both
indirectly and directly. For example, a lax management policy which does not
enforce safety standards might be indirectly responsible for an unnecessary
injury or fatality, or an operator may take the wrong action at a control
panel which would directly lead to a hazardous release. Aspects of plant
82
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operation which impact the magnitude of the risk of human error include
management policy, operator training, and maintenance and modification
procedures. These topics are.discussed in the following subsections.
5.6.-1 Management Policy
Competent and effective management plays a vital role in the prevention
of accidental releases as a result of human error. The primary responsibili-
ties of managers at chemical plants with large inventories of hazardous
chemicals include the following (39):
• Ensuring worker competency;
• Developing, documenting, and enforcing standard operating
procedures and safety policies;
• Communicating and promoting feedback regarding safety
issues;
• Identification, assessment, and control of hazards; and
• Regular plant audits and provisions for independent
checks.
Management is ultimately responsible for the competency of workers hired
at facilities which handle hazardous materials. Because of the serious
consequences that may result from operator error at these installations, the
qualifications and capabilities of prospective personnel for high hazard areas
should be carefully assessed to ensure that worker skills are matched to job
responsibilities. In addition, the skills of competent operators should be
maintained by regular training, safety meetings, and .employee reviews.
83
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In the chemical industry, documentation is generally produced which sets
forth standard procedures for equipment operation, maintenance, inspection,
hazard identification, and emergencies. The enforcement of standard
procedures is therefore one of management's most fundamental responsibilities
in the area of plant safety and accident prevention. However, before proce-
dures can be enforced, they must be communicated to plant personnel in a
clear, concise style so that they are thoroughly understood. Emphasis should
be placed on worker safety and the serious consequences of operator error in
processes involving hazardous materials.
Unfortunately, requiring workers to read documents which contain safety
policies is often not enough to ensure that they are fully understood and
followed. For this reason, verbal communication should be practiced and
encouraged which emphasizes plant safety and promotes feedback. When manage-
ment demonstrates a willingness to respond to initiatives from below and
*
participates directly with workers in improving safety, worker morale in-
creases, influencing the degree to which standard procedures are followed.
Hazard identification, assessment, and control is another area that
should be addressed by management to minimize the potential for accidental
chemical releases. The establishment of formal hazard assessment techniques
would provide management with a mechanism for obtaining information which can
be used to rank potential problems and decide how best to allocate hazard
control resources.
The plant safety audit is one of the most frequently used methods for
obtaining safety related information. A total plant safety audit involves a
thorough evaluation of a plant's design, layout, and procedures, and is
specifically aimed at identifying and correcting potentially unsafe
conditions. The objectives of these audits include alerting operating
personnel to process hazards, determining if safety procedures need to be
modified, screening for equipment or process changes that may have introduced
new hazards, assessing the feasibility of applying new hazard control
84
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technologies, identifying additional hazards, and reviewing inspection and
maintenance programs (47). In-house safety audits can be performed by
appointed safety review committees, or qualified consultants or insurers aiay
be brought in to provide a more objective assessment.
5.6.2 Operator Training
Accidental chemical releases may result from numerous types of operator
errors including following incorrect operating procedures, failing to
recognize critical situations, or by direct physical mistakes, e.g.. by
turning the wrong valve. For all of these errors, the fundamental problem may
be the operator's lack of knowledge or understanding of process variables,
equipment operation, or emergency procedures. It is important for management
to recognize the extent to which a comprehensive operator training program can
decrease the potential for accidental releases resulting from human error.
Some general characteristics of quality industrial training programs include
the following: •
• Establishment of good working relations between management
and personnel;
• Definition of trainer responsibilities and training
program goals;
• Use of documentation, classroom instruction, and field
training (in some cases supplemented with simulator
training);
• Inclusion of procedures for normal startup and shutdown,
routine operations, and emergencies; and
• Frequent supplemental training and the use of up-to-date
training materials.
85
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Employees in plants which manufacture, process, or store sulfur dioxide
should be thoroughly educated about the important aspects of handling this
chemical. These include the proper means of handling and storing, potential
consequences of improper use and handling, prevention of spills, cleanup
procedures, maintenance procedures, and emergency procedures. It is the job
of the trainer to ensure that the right type and amount of information is
supplied at the right time. To do this he must not only understand the
technical content of a job, but also those aspects of Che job where operators
may have difficulty. It is therefore advantageous for trainers to spend time
observing and analyzing the tasks and skills they will be teaching.
Two types of training which are especially important cover emergencies
and safety procedures. Emergency training includes topics such as:
• Recognition of alarm signals;
•>
• Performance of specific functions (e.g., shutdown
switches);
• Use of emergency equipment;
• Evacuation procedures;
• Fire fighting; and
• Rehearsal of emergency situations.
Safety training includes not only responses to emergency situations, but also
accident prevention measures. Aspects addressed in safety training sessions
include (39):
• Hazard recognition and communication;
• Actions to be taken in particular situations;
86
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• Available safety equipment and locations;
• When and how to use safety equipment;
• Use and familiarity with relevant documentation; and
• First aid and CPR.
The frequency of training and the frequency with which training materials
are updated are important in maintaining strong training programs. Chemical
processes may be modified to the extent that equipment changes require opera-
tional change, and operators must be made aware of the changes and safety
considerations that accompany them in a timely manner. In addition to opera-
tor training programs, organized management training is also beneficial as it
provides managers with the perspective necessary to formulate good policies
and procedures and to make changes that will improve the quality of the
overall plant safety program.
5.6.3 Maintenance and Modification Practices
Plant maintenance is necessary to ensure the structural integrity of
chemical processing equipment; modifications are often necessary to allow more
effective production. However, since these activities are also potential
causes of accidental chemical releases, proper maintenance and modification
practices are important to the prevention of accidents.
Maintenance refers to a wide range of activities, including preventive
maintenance, production assistance (e.g., adjustment of settings), servicing
(e.g., lubrication and replacement of consumables), running maintenance.
scheduled repairs during shutdown, and breakdown maintenance. These activi-
ties in turn require specific operations such as emptying, purging, and
cleaning vessels, breaking pipelines, tank repair or demolition, welding, hot
87
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tapping (attaching a branch to an in-service line), and equipment removal
(39).
Proper maintenance and modification programs should be a normal part of
plant operation and design procedures, respectively, to reduce the chances for
an accidental release.- Maintenance should be based on a priority system to
ensure that the most critical equipment is taken care of first. Strict
procedures should apply to process modifications to ensure that modifications
do not create unintended hazards. Inspections and nondestructive testing of
vessels, piping, and machinery should be conducted periodically to detect
small flaws that could eventually lead to a major release.
Two of the more common maintenance problems are equipment identification
and equipment isolation (39). Work performed on the wrong piece of equipment
can have disastrous effects, as can failure to completely isolate equipment
from process materials and electrical connections. Other potential sources of
maintenance accidents are improper venting to relieve pressure, insufficient
draining, and not cleaning or purging systems before maintenance activities
begin.
Permit systems and up-to-date maintenance procedures minimize the poten-
tial for accidents during maintenance operations. Permit-to-work systems
control maintenance activities by specifying the work to be done, defining
individual responsibilities, eliminating or protecting against hazards, and
ensuring that appropriate inspection and testing procedures are followed.
Such permits generally include specific information such as (39) :
• The type of maintenance operations to be conducted,
• Descriptions and identifying codes of the equipment to be
worked on,
• Classification of the area in which work will be
conducted.
88
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• Documentation of special hazards and control measures.
• Listing of the maintenance equipment to be used, and
• The date and time when maintenance work will be performed.
Permit-to-work systems offer many advantages.- They explain the work to
be done to both operating and maintenance workers. In terms of equipment
identification and hazard identification, they provide a level of detail that
significantly reduces the potential for errors that could lead to accidents or
releases. They also serve as historical records of maintenance activities.
Another form of maintenance control is the maintenance information
system. Ideally, these systems should log the entire maintenance history of
equipment, including preventative maintenance, inspection and testing, routine
servicing, and breakdown or failure maintenance.- This type of system is also
used to track incidents caused by factors such as human error, leaks, and
fires which resulted in hazardous conditions, downtime, or direct repair
costs.
One important maintenance practice is repairing or replacing equipment
that appears to be headed for failure. A number of testing methods are
available for examining the condition of equipment.- Some of the most common
types of tests are listed below.
• Metal thickness and integrity testing
• Vibration testing and monitoring
• Relief valve testing
89
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All of the above testing procedures are nondestructive, i.e.. they do not
damage the material or equipment that they test.
Accidental releases are frequently the result of some aspect of plant
modification. To avoid confusion with maintenance activities, a modification
is defined as an intentional change in process materials, equipment, operating
procedures, or operating conditions (39). Accidents result when equipment
integrity and operation are not properly assessed following modification, or
when modifications are made without updating corresponding operation and
maintenance instructions. Frequently, hazards created by modifications do not
appear in the exact location of the change. For example, equipment modifica-
tions can invalidate the arrangements for system pressure relief and blowdown
or they can invalidate the function of instrumentation systems.- Several
factors should be considered in reviewing modification -plans before author-
izing work. According to Lees, these include (39):
• Sufficient number and size of relief valves,
• Appropriate electrical area classification,
• Elimination of effects which could reduce safety
standards,
• Use of appropriate engineering standards,
• Proper materials of construction and fabrication
standards,
• Existing equipment not stressed beyond design limits,
• Necessary changes in operating conditions, and
90
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• Adequate instruction and training of operation and
maintenance teams.
5.7 CONTRX EFFECTIVENESS
It is difficult to quantify the control effectiveness of preventive and
protective measures to reduce the probability and magnitude of accidental
releases. Preventive measures, which may involve numerous combinations of
process design, equipment design, and operational measures, are especially
difficult to quantify because they reduce a probability rather than a physical
quantity of a chemical release. Protective measures are more analogous to
traditional pollution control technologies. Thus, they may be easier to
quantify in terms of their efficiency in minimizing the adverse effects of a
chemical that could be released.
Preventive measures reduce the probability of an accidental release by
increasing the reliability of both process systems operations and the equip-
ment. Control effectiveness can thus be expressed for both the qualitative
improvements and the quantitative improvements through probabilities. Table
5-5 summarizes what appear to be some of the major design, equipment, and
operational measures applicable to the primary hazards identified for the
sulfur dioxide processes in the U.S.- The items listed in this table are for
illustration only and do not necessarily represent a satisfactory control
option for all cases.- These control options appear to reduce the risk associ-
ated with an accidental release when viewed from a broad perspective. How-
ever, there are undoubtedly specific cases where these control options will
not be appropriate. Each case must therefore be evaluated individually. A
discussion of reliability in terms of probabilities is planned for other parts
of the prevention reference manual series.
91
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5.8 ILLUSTRATIVE COST ESTIMATES FOR CONTROLS
This section presents cost estimates for different levels of control and
for specific release prevention and protection measures for sulfur dioxide
storage and process facilities found in the United States.-
5.8.1 Prevention and Protection Measures
Preventive measures reduce the probability of' an accidental release from
a process or storage facility by increasing the reliability of both process
systems operations and equipment. Along with an increase in the reliability
of a system is an increase in the capital and annual costs associated with
incorporating prevention and protection measures into a system. Table 5-6
presents costs for some of the major design, equipment, and operational
measures applicable to the primary hazards identified in Table 5-5 for the
sulfur dioxide applications discussed in Section 3.
5.8.2 Levels of Control
Prevention of accidental releases relies on a combination of technologi-
cal, administrative, and operational practices as they apply to the design,
construction, and operation of facilities where hazardous chemicals are used
and stored. Inherent in determining the degree to which these practices are
carried out is their costs. At a minimum, equipment and procedures should be
in accordance with applicable codes, standards, and regulations. However,
additional measures can be taken to provide extra protection against an acci-
dental release.
The levels of control concept provides a means of assigning costs to
increased levels of prevention and protection. At the lower end of the tier
is the "Baseline" system. This system consists of the elements required for
normal safe operation and basic prevention of an accidental release of hazard-
ous material.
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TABLE 5-5. EXAMPLES OF MAJOR PREVENTION AND PROTECTION MEASURES
FOR SULFUR DIOXIDE RELEASES
Hazard Area
Prevention/Protection
Water contamination
in hydrocarbon feeds
to extraction tower
Sulfur dioxide flow
control
Temperature sensing
and cooling medium
flow control
Temperature sensing
and heating medium
flow control
Overpressure
Corrosion
Reactor and reboiler
temperatures
Overfilling
Atmosphere releases .
from relief discharges
Storage tank or line
rupture
Continuous moisture monitoring;
Backflow prevention
Redundant flow control loops; Minimal
overdesign of. feed systems
Redundant temperature sensors;
Interlock flow switch to shut off
SO. feed on loss of cooling, with
relief venting to emergency scrubber
system
Redundant temperature sensors;
Interlock flow switch to shut off
SO. feed on loss of heating, with
relief venting to emergency scrubber
system
Redundant pressure relief; not
isolatable; adequate size; discharge
not restricted
Increased monitoring with more
frequent inspections; use of pH
sensing on cooling water and steam
condensate loops; use of corrosion
coupons; visual inspections;
non-destructive testing
Redundant temperature sensing and
alarms
Redundant level sensing, alarms
and interlocks; training of
operators
Emergency vent scrubber system
Enclosure vented to emergency
scrubber system; diking; foams;
dilution; neutralization; water
sprays
93
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TABLE 5-6. ESTIMATED TYPICAL COSTS OF MAJOR PREVENTION AND PROTECTION
MEASURES FOR SULFUR DIOXIDE RELEASE*
=^==============
Prevention/Protection Measure
Continuous moisture inonitoring
Flow control loop
Temperature sensor
Capital Cost
(1986 $)
7500-10000
4000-6000
250-400
Annual Cost
(1986 $/yr)
900-1300
500-750
30-50
Pressure relief
- relief valve
- rupture disk
Interlock-system for flow shut-off
pH monitoring of cooling water
Alarm system
Level sensor
- liquid level gauge
- load cell
Diking
- 3 ft high
- top of tank height, 10 ft.
Increased corrosion inspection
1000-2000
1000-1200
1500-2000
7500-10000
250-500
1500-2000
10000-15000
1200-1500
7000-7500
120-250
120-150
175-250
900-1300
30-75
175-250
1300-1900
150-175
850-900
200-400
a3ased on a 10,000 gallon fixed sulfur dioxide storage tank system and a
200.000 gallon/day hydrocarbon extraction system.
b3ased on 10-20 hr @ $20/hr.
94
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The second level of control is "Level 1." "Level 1" includes the base-
line system with added modifications such as improved materials of construc-
tion, additional controls, and generally more extensive release prevention
measures. The costs associated with this level are higher than the baseline
system costs.
The third level of control is "Level 2." This system incorporates both
the "Baseline" and "Level 1" systems with additional modifications designed
specifically for the prevention of an accidental release such as alarm and
interlock systems. The extra accidental release prevention measures incorpo-
rated into "Level 2" are reflected in its cost, which is much higher than that
of the baseline system.
When comparing the costs of the various levels of control.- it is impor-
tant to realize that higher costs do not necessarily imply improved safety.
The measures applied must be applied correctly. Inappropriate modifications
or add-ons may not make a system safer. Each added control option increases
the complexity of a system. In some cases the hazards associated with the
increased complexity may outweigh the benefits derived from the particular
control option. Proper design and construction along with proper operational
practices are needed to assure safe operation.
Example "levels of control" cost estimates were prepared for a 42 ton
fixed sulfur dioxide storage tank system with a 10,000 gal capacity and a
sulfur dioxide extraction tower system for a 200.000 gal/day hydrocarbon
extraction facility.- These cost estimates are presented for illustrative
purposes only. It is doubtful that any specific installation would find all
of the control options listed in the following tables appropriate for their
purposes. An actual system is likely to incorporate some items from each of
the levels of control and also some control options not listed. The purpose
of these estimates is to illustrate the relationship between cost and control,
and not to provide an equipment check list.
95
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5.8.3 Simmary of Levels of Control
Table 5-7 presents a summary of the total capital and annual costs for
each of the three levels of controls for the sulfur dioxide storage system and
the sulfur dioxide extraction tower system. The costs presented correspond to
the systems described in Table 5-8 and Table 5-9. Each of the level costs
include the cost of the basic system plus any added controls. Specific cost
information and breakdown for each level of control for both the storage and
process facilities are presented in Tables 5-10 through 5-15.-
5.8.4 Equipment Specifications and Detailed Costs
Equipment specifications and details of the capital cost estimates for
the sulfur dioxide storage and the sulfur dioxide extraction tower systems are
presented in Tables 5-16 through 5-23.
»
5.8.5 Methodology
Format for Presenting Cost Estimates—
Tables are provided for control schemes associated with storage and pro-
cess facilities for sulfur dioxide showing capital, operating, and total
annual costs. The tables are broken down into subsections comprising vessels,
piping and valves, process machinery,- instrumentation, and procedures and
practice. The presentation of the costs in this manner allows for easy com-
parison of costs for specific items, different levels, and different systems.
Capital Cost—All capital costs presented in this report are shown as
total fixed capital costs. Table 5-24 defines the cost elements comprising
total fixed capital as it is used here.
The computation of total fixed capital as shown in Table 5-24 begins with
the total direct cost for the system under consideration. This total direct
cost is the total direct installed cost of all capital equipment comprising
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TABLE 5-7. SUMMARY COST ESTIMATES OF POTENTIAL LEVELS OF CONTROLS
FOR SULFUR. DIOXIDE STORAGE TANK AMD EXTRACTION TOWER
Level of
Control
Total
Capital Cost
(19S6 $)
Total
Annual Cost
(1986 $/yr)
Sulfur Dioxide Tank
63 ton Fixed S02 Tait^ witn
10.000 gal Capacity
Baseline
Level #1
Level #2
186.000
549.000
1.360,000
22.000
65.000
160.000
Sulfur Dioxide Extraction
Tower System with
5 ft x 20 ft Packed Tower
Baseline
Level #1
Level #2
189.000
548.000
780,000
24.000
68.000
95.000
97
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TABLE 5-8." EXAMPLE OF LEVELS OF CONTROL FOR SULFUR DIOXIDE STORAGE TANK
Process: 63 ton fixed sulfur dioxide storage tank
10.000 gal
Controls
Baseline
Level No. 1
Level No. 2
Process:
Flow:
None
None
Temperature:
Pressure:
Quantity:
Location:
Materials of
Construction:
Vessel:
Single check- Add second check
valve on tank- valve.
process feed line.
None
Single pressure
relief valve,
vent to atmos-
phere.
Local level
indicator.
Away from traffic.
Carbon steel
Tank pressure
specification
150 psig.
None
Add second relief
valve, secure
non-is datable.
Vent to limited
scrubber. Provide
local pressure
indicator.
Add remote level
indicator.
Away from traffic
and flamznables.
Carbon steel with
increased corrosion
allowances. (1/3
inch)
Tank pressure
specification
225 psig.
None
Add a reduced-pressure
device3 with internal
air gap and relief
vent to containment
tank or scrubber.
Add temperature
indicator.
Add rupture disks
under relief valves.
Provide local pressure
indication on space
between disk and
valve.
Add level alarm. Add
high-low level inter-
lock shut-off for both
inlet and outlet
lines.
Away from traffic,
flammables, and other
hazardous processes.
Stainless steel. Type
316.
Tank pressure
specification
375 ,psig.
A reduced pressure device is a modified double check valve.
(Continued)
98
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TABLE 5-8 (Continued)
Process: 63 ton fixed sulfur dioxide storage tank
10.000 gal
Controls
Baseline
Level No. 1
Level No. 2
Piping:
Process
Machinery:
Enclosures:
Diking:
Scrubbers:
Mitigation:
Sch. 80 carbon
steel.
Sch. 80 316 SS
Centrifugal pump. Centrifugal pump.
carbon steel. 316 SS construc-
stuffing box tion. double cap-
seal, acity mechanical
seal.
None
None
None
None
Steel building.
3 ft. high.
Water scrubber.
Water sprays.
Sch. 80 Alloy 20 SS
Magnetically-couple
centrifugal pump. 316
SS, construction.
Concrete building.
Top of tank height.
Alkaline scrubber.
Alkaline water sprays
and barriers.
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TABLE 5-9. EXAMPLE OF LEVELS OF CONTROL FOR SULFUR DIOXIDE EXTRACTION TOWER
Controls
Baseline
Level
Level 1/2
o
o
Process:
Temperature:
Pressure:
Flow:
Quantity:
Corrosion:
Composition:
Material of
Construction:
Vessel
Dryers on feed
lines.
Local temperature
indicator.
None
Flow control of
sulfur dioxide
feed.
Local level control.
Visual inspection
and monitoring.
Dryers on hydrocar-
bon charge and S0?
feed lines.
Carbon-steel
Tank pressure speci-
fication 50 psig.
Enchanced flow control.
Add redundant sensors
and alarm.
None
Redundant flow control
loop.
Add level alarm.
Increased monitoring
with increased inspec-
tions.
Occasional moisture
monitoring. Add mois-
ture alarms on S0? and
hydrocarbon feed.
Acid brick lined carbon
steel.
Tank pressure specifi-
cation 100 psig.
Operate tower at lower
temperature.
Add remote indicator.
None
Add interlock system
to shutoff sulfur
dioxide feed upon
reaching a temperature
above a set point.
Same
Same
Continuous moisture
monitoring
Type 316 stainless-
steel.
Tank pressure speci-
fication 150 psig.
(Continued)
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TABLE 5-9 (Continued)
Controls
Baseline
Level
Level
Piping:
Process
Machinery:
Protective
Barrier:
Enclosures
Scrubbers:
Mitigation:
Sch. 80 carbon steel.
Centrifugal pump
with stuffing box.
carbon steel
construction.
None
None
None
None
Sch. 80 Type 316 stain-
less steel.
Centrigual pump, double
mechanical seal. Type
316 stainless steel
construction.
Curbing around tower.
Steel building.
Water scrubber.
Water sprays.
Sch. 80 Alloy 20
stainless steel.
Magnetically-coupled
centrifugal pump.
Type 316 stainless
steel construction.
3 ft. high retaining
wall.
Concrete building.
Alkaline scrubber.
Alkaline water sprays.
-------
TABLE 5-10. ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED WITH
BASELINE SULFUR DIOXIDE STORAGE SYSTEM
Capital Cost
(1986 $)
Annual Cost
(1986 $/yr)
Vessels:
Storage tank
Expansion tanks (3}
Piping and Valves:
Pipework
Check valve
Ball valves (5)
Excess flow valves (2)
Angle valves (2.)
Relief valve
131.000
6.500
9.200
1.000
6.200
1.900
7.500
2.000
15,000
760
1.100
120
720
220
870
230
Process Machinery:
Centrifugal pump
Instrumentation:
Pressure gauges (4)
Liquid level gauge
Procedures and Practices:
Visual tank inspection (external)
Visual tank inspection (internal)
Relief valve inspection
Piping inspection
Piping maintenance
Valve inspection
Valve maintenance
18.000 ' 2.100
1.500 180
1.500 180
15
60
15
300
120
30
350
Total Costs
186.000
22.000
102
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TABLE 5-11. ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED WITH
LEVEL 1 SULFUR DIOXIDE STORAGE SYSTEM
Capital Cost
(1986 $)
Annual Cost
(1986 $/yr)
Vessels:
Storage tank
Expansion tanks (3)
Piping and Valves:
Pipework
Check valve
Ball valves (5)
Excess flow valves (2)
Angle valves (2)
Relief valve
Process Machinery:
Centrifugal pump
Instrumentation:
Pressure gauges (4)
Flow indicator
Load cell
Remote level indicator
Enclosures:
Steel building
Scrubbers:
Water scrubber
Diking:
3 ft high concrete diking
190.000
6,500
30,000
2.000
6.200
1,900
7.500
4,000
35.000
1.500
3.700
1.500
1.900
10.000
249.000
1.400
22.000
760
3.500
240
720
220
870
460
4.000
180
430
180
220
1.200
29.000
160
(Continued)
103
-------
TABLE 5-11 (Continued)
Capital Cost
(1986 $)
Annual Cost
(1986 $/yr)
Procedures and Practices:
Visual tank inspection (external)
Visual tank inspection (internal)
Relief valve inspection
Piping inspection
Piping maintenance
Valve inspection
Valve maintenance
15
60
30
300
120
35
400
Total Costs
549.000
65.000
104
-------
TABLE 5-12. ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED WITH
LEVEL 2 SULFUR DIOXIDE STORAGE SYSTEM
Capital Cost
(1986 $)
Annual Cost
(1986 $/yr)
Vessels:
Storage tank
Expansion tanks (3)
Piping and Valves:
Pipework
Reduced pressure device
Ball valves (5)
Excess flow valves (2)
Angle valves (2)
Relief valve
Rupture disks (2)
Process Machinery:
Centrifugal pump
Instrumentation:
Temperature indicator
Pressure gauges (6)
Flow indicator
Load cell
Remote level indicator
Level alarm
High-low level shutoff
Enclosures:
Concrete building
Scrubbers:
Alkaline scrubber
Diking:
10 ft. high diking
879.000
6,500
49,000
5.000
6.200
1.900
7.500
4.000
1.100
43.000
2.200
2.200
3.700
16.000
1.900
750
1.900
19,000
302.000
7.500
102.000
760
5.700
590
720
220
870
460
130
5.000
260
260
440
1.800
220
90
220
2.200
35,000
370
(Continued)
105
-------
TABLE 5-12 (Continued)
Capital Cost Annual Cost
(1986 $) (1986 $/yr)
Procedures and Practices:
Visual tank inspection (external) 15
Visual tank inspection (internal) 60
Relief valve inspection 50
Piping inspection 300
Piping maintenance 120
Valve inspection 35
Valve maintenance 400
Total Costs 1.360.000 160.000
106
-------
TABLE 5-13. ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED WITH
BASELINE SULFUR DIOXIDE EXTRACTION TOWER SYSTEM
Capital Cost
(1986 $)
Annual Cost
(1986 $/yr)
Equipment:
Extraction tower
Tower packing
Expansion tank
Piping and Valves:
Pipework
Ball valves (8)
Process Machinery:
Centrifugal pumps (2)
Instrumentation:
P. res sure gauges (3)
Liquid level control
56,000
35.000
2.500
27,000
13.000
35.000
1.100
6.800
4.200
300
3.200
1.600
4.200
130
- Controller
- Sensor
- Control valve
Local temp, indicator
Flow control
- Controller
- Flowmeter
- Control valve
Maintenance and Inspections:
Visual tower inspection (external)
Visual tower inspection (internal)
Piping inspection
Piping maintenance
Valve inspection
Valve maintenance
1.800
2.200
4.500
2.200
1.800
2.300
4.500
220
260
540
260
220
280
540
15
60
900
360
30
350
Total Costs
189.000
24.000
107
-------
TABLE 5-14. ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED WITH
LEVEL 1 SULFUR DIOXIDE EXTRACTION TOWER SYSTEM
Equipment :
Extraction tower
Tower packing
Expansion tank
Piping and Valves:
Pipework
Ball valves (8)
Process Machinery:
Centrifugal pumps (2)
Instrumentation:
Pressure gauges (3)
Level alarm
Liquid level control
- Controller
- Sensor
- Control valve
Local temp, indicator
Temperature sensor
Temperature alarm
Flow control
- Controller
- Flowmeter
- Control valve
Addition flow control loop
Moisture alarm
Capital Cost
(1986 $)
65,000
35.000
2,500
85,000
13.000
66.000
1.100
360
1.800
2.200
4.500
2.200
360
360
1.800
2.300
4.500
9.000
360
Annual Cost
(1986 $/yr)
7,800
4.100
300
10. 000
1.600
8,000
130
45
220
260
540
260
45
45
220
280
540
1.100
45
(Continued)
108
-------
TABLE 5-14 (Continued)
Capital Cost Annual Cost
(1986 S) (1986 S/yr)
Diking:
Curbing around tower 1,200 150
Enclosure:
Steel building 10.000 1.200
Scrubber:
Water scrubber 240.000 29,000
Maintenance and Inspections:
Visual tower inspection (external) 15
Visual tower inspection (internal) 60
Piping inspection 900
Piping maintenance ' 360
Valve inspection 30
Valve maintenance 350
Total Costs 548.000 68,000
109
-------
TABLE 5-15. ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED WITH
LEVEL 2 SULFUR DIOXIDE EXTRACTION TOWER SYSTEM
Vessels:
Extraction tower
Tower packing
Expansion tank
Piping and Valves:
Pipework
Ball valves (8)
Process Machinery:
Centrifugal pumps (2)
Instrumentation :
Pressure gauges (3)
Level alarm
Liquid level control
- Controller
- Sensor
- Control valve
Local temp, indicator
Remote temp, indicator
Temperature sensor
Temperature alarm
Flow interlock system
Flow control
- Controller
- Flowaietar
- Control valve
Capital Cost
(1986 $)
205.000
35,000
2,500
85.000
13.000
83,000
1.100
360
1.800
2.200
4.500
2.200
1.800
360
360
1.800
1.300
2.300
4.500
Annual Cost
(1986 $/yr)
25,000
4,100
300
10.000
1.600
10, 000
130
45
220
260
540
260
220
45
45
220
220
230
540
(Continued)
110
-------
TABLE 5-15 (Continued)
Capital Cost Annual Cost
(1986 $) (1986 $/yr)
Additional flow control loop 9,000 1,100
Moisture alarm 360 45
Moisture monitoring system 9,000 1,100
Diking:
3 ft. high retaining wall 3.100 370
Enclosure:
Concrete building 18.000 2,200
Scrubber:
Alkaline scrubber 292,000 35.000
Maintenance and Inspections:
Visual tower inspection (external)
Visual tower inspection (internal)
Piping inspection
Piping maintenance
Valve inspection
Valve maintenance
15
60
900
360
30
350
Total Costs 780.000 95,000
111
-------
TABLE 5-16. EQUIPMENT SPECIFICATIONS ASSOCIATED WITH SULFUR DIOXIDE STORAGE SYSTEM
Equipment Item
Equipment Specification
Reference
Vessels:
Storage tank
Expansion tank
Baseline: 10,000 gal. carbon steel storage tank 150
psig rating
Level 1: 10,000 gal. carbon steel with 1/8 in.
corrosion protection. 225 psig. rating
Level 2: 10.000 gal. Type 316 stainless steel
375 psig rating
Standard carbon steel pressure vessel with rupture disk
and pressure gauge
Piping and Valves: Baseline: 100 ft. of 4 in. schedule 80 carbon steel
Pipework Level 1: 100 ft. of 4 in. schedule 80 Type 316
stainless steel
Level 2: 100 ft. of 4 in. schedule 80 Alloy 20
Ball valve
Check valve
4 in., Class 300. flanged. Type 316 stainless
steel construction
4 in.. Class 300. vertical lift. Type 316 stainless
steel
Excess flow valve 4 in. standard valve
Angle valve 4 in.. Type 316 stainless steel
48. 49
50. 51
48. 49
51
49. 53
49. 53
49
54
(Continued)
-------
TABLE 5-16 (Continued)
Equipment Item
Equipment Specification
Reference
Relief valve
Reduced pressure
device
Rupture disk
Process Machinery:
Centrifugal pump
Instrumentation:
Temperature
indicator
Pressure gauge
Liquid level
gauge
1 in. x. 2 in.. Class 300 inlet and outlet flange.
angle body, closed bonnet with screwed cap. Type
316 stainless steel body and trim 49
Double check valve type device with internal air gap 48
and relief valve
1 in. Type 316 stainless steel and carbon steel holder 50, 55, 56
Baseline: single stage, carbon steel construction,
stuffing box
Level 1: single stage. Type 316 stainless steel 49, 57
construction, double mechanical seal
Level 2: Type 316 stainless steel construction. 48, 49. 52
magnetically-coupled
Thermocouple, thermowell, electronic indicator 48. 49. 52
Diaphragm sealed. Type 316 stainless steel diaphragm. 58, 52
0-1.000 psig
Differential pressure type level gauge
(Continued)
-------
TABLE 5-16 (Continued)
Equipment Item
Equipment Specification
Reference
Flow indicator
Level indicator
Load ceil
Level alarm
High-low/ level
shutoff
Enclosures:
Building
Scrubbers:
Diking:
Differential pressure cell, transmitter, and associated
flowmeter
Electronic differential pressure type indicator
Electronic load cell
Indicating and audible alarm
Solenoid valve, switch, and relay system
Level 1: 26 gauge steel walls and roof. door.
ventilation system
Level 2: 10 in. concrete walls. 26 gauge steel
roof
Level 1: Spray tower. Type 3*16 stainless steel
construction, water sprays. 3 ft. x 24 ft.
Level 2: Spray tower. Type 316 stainless steel
construction, alkaline sprays
Level 1: 6 in. concrete walls. 3 ft. high
Level 2: 10 in. concrete walls, top of tank
height
48. 52
48, 49, 52
48. 52, 58
49, 54. 59
48. 49. 52
54
54
60
54
-------
TABLE 5-17. DETAILS OF MATERIAL AND LABOR COSTS ASSOCIATED WITH BASELINE SULFUR DIOXIDE
STORAGE SYSTEM
•
Vessels:
Storage tank
Expansion tanks (3)
Piping and Valves:
Pipework
Check valves
Ball valves (5)
Excess flow valves (2)
Angle valves (2)
Relief valve
Process Machinery :
Centrifugal pump
Instrumentation:
Pressure gauges (4)
Liquid level gauge
Total Costs
Materials
Cost
61.000
3.500
2.300
640
4.000
1.200
5.000
1.300
8.500
800
800
89.000
Labor
Cost
27.000
880
3.900
30
150
40
40
50
3.600
200
200
36.000
Direct
Costs
(1986 $)
88.000
4.380
6.200
670
4.150
1.240
5.040
1.350
12. 100
1.000
1.000
125.000
Indirect
Costs
31.000
1.500
2.200
230
1.500
440
1.800
470
4.200
350
350
44.000
Capital
Cost
131.000
6.500
9.200
1.000
6.200
1.900
7.500
2.000
18.000
1.500
1.500
186.000
-------
TABLE 5-18. DETAILS OF MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 1 SULFUR DIOXIDE
STORAGE SYSTEM
Vessels:
Storage tank
Expansion tanks (3)
Piping and Valves:
Pipework
Check valves (2)
Ball valves (5)
Excels flow valves (2)
Angle valves (2)
Relief valves (2)
Process Machinery:
Centrifugal pump
Instrumentation:
Pressure gauges (4)
Flow indicator
Liquid level gauge
Remote level indicator
Enclosures:
Steel building
Materials
Cost
88.000
3.500
15.000
1.300
4,000
1.200
5.000
2.600
16.000
800
2.000
800
1.000
4.600
Labor
Cost
40. 000
880
5.000
60
150
40
40
100
7.000
200
500
200
250
2.300
Direct
Costs
(1986 $)
128.000
4.380
20.000
1.360
4.150
1.240
5.040
2,700
23.000
1.000
2.500
1.000
1.250
6.900
Indirect
Costs
45,000
1.500
7.000
480
1.500
440
1.800
940
8.100
350
880
350
440
2.400
Capital
Cost
190. 000
6.500
30.000
2.000
6.200
1,900
7.500
4.000
35.000
1.500-
3.700
1.500
1.900
•
10.000
(Continued)
-------
TABLE 5-18 (Continued)
Materials Labor Direct Indirect Capital
Coat Cost Costa Costs Cost
(1986 $)
Scrubbers:
*
Water scrubber 115.000 52.000 167.000 59.000 249.000
Diking:
3 ft. high concrete 390 520 910 320 1.400
diking
Total Costa 261.000 109.000 370,000 130.000 549.000
-------
TABLE 5-19. DETAILS OF MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 2 SULFUR DIOXIDE
STORAGE SYSTEM
Materials
Cost
Labor
Cost
Direct
Costs
Indirect
Costs
(1986 $)
Capital
Cost
co
Vessels:
Storage tank 408.000
Expansion tanks (3) 3.500
Piping and Valves:
Pipework 28.000
Reduced pressure device 3.200
Ball valves (5) 4.000
Excess flow valves (2) 1,200
Angle valves (2) 5.000
Relief valve 2.600
Rupture disks (2) 650
Process Machinery:
Centrifugal Pump 20.000
Instrumentation:
184.000
880
5.000
200
150
40
40
100
75
9.000
592.000
4.380
33.000
3.400
4.150
1.240
5.040
2.700
725
29.000
207.000
1.500
12.000
1.200
1.500
440
1.800
940
260
10.000
879.000
6.500
49.000
5.000
6.200
1.900
7.500
4.000
1.100
43.000
Temperature indicator
Pressure gauges (6)
Flow indicator
Load cell
Remote level indicator
Level alarm
High-low level shutoff
1.200
1.200
2.000
8.400
1.000
400
1.000
300
300
500
2.100
250
100
250
1.500
1.500
2.500
10.500
1.250
500
1.250
530
530
880
3.700
440
180
440
2.200
2.200
3.700
16.000
1.900
750
1.900
(Continued)
-------
TABLE 5-19 (Continued)
Materials Labor Direct Indirect Capital
Coat Cost Costs Costs Cost
(1986 $)
Enclosures:
Concrete building
Scrubbers:
Alkaline scrubber
Diking:
10 ft. high diking
6.100 6.600 12.700 4.500 19.000
140.000 63.000 203.000 71.000 302,000
2.200 2.900 5.100
1.800
7.500
Total Costs
640.000 276.000 916.000 321.000 1.360.000
-------
TABLE 5-20. EQUIPMENT SPECIFICATIONS ASSOCIATED WITH SULFUR DIOXIDE EXTRACTION TOWER
SYSTEM
Equipment Item
Equipment Specification
Reference
Vessels:
Extraction tower
Tower packing
Expansion tank
Piping and Valves:
Pipework
Ball valves
Process Machinery:
Centrifugal pump
Baseline: 5 ft. x 20 ft. packed tower, carbon steel
construction, 50 psig rating
Level 1: Acid brick lined carbon steel construction.
100 psig rating
Level 2: Type 316 stainless steel construction. 48
150 psig rating
1-3/4 in. Type 316 stainless steel Raschig 48
rings at a depth of 10 ft.
Standard carbon steel pressure vessel with rupture disk 48.49
and pressure gauge
Baseline: 300 ft. of 4" schedule 80 carbon steel
Level 1: 4in. schedule 80 Type 316 stainless
steel
Level 2: 4 in. schedule 80 alloy 20 stainless 52
steel
4 in.. Class 300. flanged. Type 316 stainless 49. 53
steel construction
Baseline: single stage, carbon steel construction.
stuffing box
Level 1: single stage. Type 316 stainless steel
construction, double mechanical seal 49, 57
(Continued)
-------
TABLE 5-20 (Continued)
Equipment Item
Equipment Specification
Reference
Centrifugal
Pump
Instrumentation:
Pressure gauge
Level alarm
Liquid level
control loop
Local tempera-
ture indicator
Remote tempera-
ture indicator
Temperature
sensor
Temperature
alarm
Flow interlock
system
Flow control
loop
Level 2: Type 316 stainless steel construction,
magnetically-coupled
Diaphragm sealed. Type 316 stainless steel diaphragm,
0-1,000 psig rating
Indicating and audible alarm
PID controller, 4 in. globe control valve of
stainless steel construction, gravity differential
sensor system
Thermocouple, therraowell, and electronic indicator
Transmitter and associated electronic indicator
Thermocouple and associated thermowell
Indicating and audible alarm
Solenoid valve, switch, and relay system
PID controller, 4" globe control valve of stainless
steel construction, flowmeter
Moisture alarm Moisture sensor and indicating and audible alarm
49. 57
48. 49. 52
48. 52
48. 49. 52
48. 52
48. 49. 52
49. 54. 59
48, 49. 52
54
48. 52
58
(Continued)
-------
TABLE 5-20 (Continued)
Equipment Item
Equipment Specification
Reference
Moisture Moni-
toring System
Diking:
Enclosure:
Scrubber:
Capacitance or Infrared absorption system
Level 1: 0.5 ft. high concrete curbing
Level 2: 3 ft. high concrete retaining wall
Level 1: 26 gauge steel walls and roof. door.
ventilation system
Level 2: 0.8 ft. concrete walls. 26 gauge steel
roof
Level 1: Spray tower. Type 316 stainless steel construc-
tion, water sprays. 8 ft. x 24 ft.
Level 2: Spray tower. Type 316 stainless steel construc-
tion, alkaline sprays
-------
TABLE 5-21. DETAILS OF MATERIAL AND LABOR COSTS ASSOCIATED WITH BASELINE SULFUR
DIOXIDE EXTRACTION TOWER SYSTEM
Equipment :
Extraction tower
Tower packing
Expansion tank
Piping and Valves:
Pipework
Ball valves (8)
Materials
Cost
27.000
17.000
1.200
6.800
8.000
Labor
Cost
•
12,000
7,400
540
12,000
1.200
Direct
Costs
(1986 $)
39.000
24, 400
1.740
18.800
9.200
Indirect
Costs
9.800
6.100
440
4.700
2,300
Capital
Cost
56. 000
35.000
2,500
27,000
13.000
Process Machinery:
Centrifugal pumps (2)
Instrumentation:
Pressure gauges (3)
Liquid level control
17.000
600
7.200
150
24,200
750
6.100
190
35.000
1.100
- Controller
- Sensor
- Control valve
Local temp, indicator
Flow control
- Controller
- Flowmeter
- Control valve
Total CoiUu
1.000
1.200
2.500
1.200
1.000
1,300
2.500
88.000
250
300
630
300
250
330
630
43.000
1.250
1.500
3.130
1.500
1.250
1.630
3,130
131.000
320
380
780
380
320
410
780
33.000
1.800
2.200
4.500
2.200
1.800
2.300
4.500
189.000
-------
TABLE 5-22. DETAILS OF MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 1 SULFUR
DIOXIDE EXTRACTION TOWER SYSTEM
Equipment::
Extraction tower
Tower packing
Expansion tank
Piping and Valves:
Pipework
Bail valves (8)
Process Machinery:
Centrifugal pumps (2)
Instrumentation:
Pressure gauges (3)
Level alarm
Liquid level control
- Controller
- Sensor
- Control valve
Local temperature indicator
Materials
Cost
31.000
17.000
1.200
44. 000
8.000
32.000
600
200
1.000
1.200
2.500
1.200
Labor
Cost
14.000
7.400
540
15.000
1. 200
14.000
150
50
250
300
630
300
Direct
Costs
(1986 $)
45.000
24. 400
1.740
59.000
9.200
46.000
750
250
1.250
1.500
3.130
1.500
Indirect
Costs
11.000
6.100
440
15.000
2.300
12.000
190
65
320
380
780
380
Capital
Cost
65.000
35.000
2.500
85.000
13.000
66.000
1.100
360
1.800
2.200
4.500
2.200
(Continued)
-------
TABLE 5-22 (Continued)
Materials
Cost
Labor
Cost
Direct
Costs
Indirect
Costs
Capital
Cost
(1986 $)
Temperature sensor
Temperature alarm
Flow control
- Controller
- Flowmeter
- Control valve
Additional flow control loop
Moisture alarm
200
200
1.000
1.300
2.500
4.800
200
50
50
250
330
630
1.210
50
250
250
1.250
1,630
3.130
6.010
250
65
65
320
410
780
1,600
65
360
360
1.800
2.300
4.500
9,000
360
Diking:
•
Curbing around tower 500 350 850 220 1.200
Enclosure:
Steel building 4.600 2.300 6,900 1.700 10.000
Scrubber:
Water scrubber 115.000 52,000 167,000 42,000 240.000
Total Costs 270.000 111.000 381.000 96.000 548.000
-------
TABLE 5-23. DETAILS OF MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 2
SULFUR DIOXIDE EXTRACTION TOWER SYSTEM
NJ
CT>
Equipment: :
Extraction tower
Tower packing
Expansion tank
Piping and Valves:
Pipework
Ball valves (8)
Process Machinery ;
Centrifugal pumps (2)
Instrumentation:
Pressure gauges (3)
Level alarm
Liquid level control
- Controller
- Sensor
- Control valve
Materials
Cost
98.000
17.000
1.200
44.000
8.000
40.000
600
200
1.000
1.200
2.500
Labor
Cost
44.000
7.400
540
15.000
1.200
18. 000
. 150
50
250
300
630
Direct
Costs
(1986 $)
142. 000
24. 400
1.740
59.000
9.200
58.000
750
250
1.250
1.500
3.130
Indirect
Costs
36. 000
6.100
440
15. 000
2.300
15. 000
190
65
320
380
780
Capital
Cost
205.000
35.000
2.500
85. 000
13.000
83.000
1.100
360
1.800
2.200
4.500
(Continued)
-------
TABLE 5-23 (Continued)
Materials
Cost
Labor
Cost
Direct
Costs
Indirect
Costs
Capital
Cost
(1986 $)
Local temp, indicator
Remote temp, indicator
Temperature sensor
Temperature alarm
Flow interlock sytem
Flow control
- Controller
- Flowmeter
- Control valve
Additional flow control .loop
Moisture alarm
Moisture monitoring system
Diking:
3 ft. high retaining wall
Enclosure:
Concrete building
1.200
1.000
200
200
1.000
1,000
1.300
2.500
4.800
200
5.000
900
6.000
300
250
50
50
250
250
325
625
1,210
50
1.250
1.200
6.600
1.500
1.250
250
250
1.250
1.250
1.625
3.125
6.010
250
6.250
2.100
12.600
380
320
65
65
320
320
410
780
1.600
65
1.600
530
3.200
2.200
1.800
360
360
1.800
1.800
2.300
4.500
9.000
360
9.000
3.100
18. 000
(Continued) .
-------
TABLE 5-23 (Continued)
Materials Labor Direct Indirect Capital
Cost Cost Costs Costa Cost
(1986 $)
Scrubber:
Alkaline scrubber 140.000 63.000 203.000 51.000 292.000
Total Costs 379.000 163.000 542.000 135.000 780.000
-------
TABLE 5-24. FORMAT FOR TOTAL FIXED CAPITAL COST
Item No. Item Cost
1 Total Material Cost
2 Total Labor Cost
3 Total Direct Cost Items 1+2
4 Indirect Cost Items (Engi-
neering & Construction
Expenses) 0.35 x Item 3a
5 Total Bare Module Cost Items (3 + 4)
6 Contingency (0.05 x Item 5)b
7 Contractor's Fee 0.05 x Item 5
8 Total Fixed Capital Cost Items (5+6+7)
For storage facilities, the indirect cost factor is 0.35. For process
facilities, the indirect cost factor is 0.25.
For storage facilities, the contingency cost factor is 0.05. For process
facilities, the contingency cost factor is 0.10.
129
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the system. Depending on the specific equipment item involved, the direct
capital cost was available or was derived from uninstalled equipment costs by
computing costs of installation separately. To obtain the total fixed capital
cost, other costs obtained by utilizing factors are added to'the total direct
costs.
The first group of other cost elements is indirect costs. These include
engineering and supervision, construction expenses, and various other expenses
such as administration expenses, for example. These costs are computed by
multiplying total direct costs by a factor shown in Table 5-24. The factor is
approximate, is obtained from the cost literature, and is based on previous
experience with capital projects of a similar nature. Factors can have a
range of values and vary according to technology area and for individual
technologies within an area. Appropriate factors were selected for use in
this report based on judgement and experience.
*
When the indirect costs are added to the total direct costs, total bare
module cost is obtained. Some additional cost elements such as contractor's
fee and contingency are calculated by applying and adding appropriate factors
to the total bare module cost as shown in Table 5-24 to obtain the total fixed
capital cost.
Annual Cost—Annual costs are obtained for each of the equipment items by
applying a factor for both capital recovery and for maintenance expenses to
the direct cost of each equipment item. Table 5-25 defines the cost elements
and appropriate factors comprising these costs. Additional annual costs are
incurred for procedural items such as valve and vessel inspections, for
example. When all of these individual costs are added, the total annual cost
is obtained.
130
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TABLE 5-25-. FORMAT FOR TOTAL ANNUAL COST
Item No. Item Cost
1 Total Direct Cost
2 Capital Recovery on Equip-
ment Items 0.163 x Item 1
3 Maintenance Expense on
Equipment Items 0.01 x Item 1
4 Total Procedural Items
5 Total Annual Cost Items (2+3+4)
131
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Sources of Information—
The costs presented in this report are derived from cost information in
existing published sources and also from recent vendor information. It was
the objective of this effort to present cost levels for sulfur dioxide process
and storage facilities using the best costs for available sources. The
primary sources of cost information are Peters and Timmerhaus (48), Chemical
Engineering (61), and Valle-Riestra (62) supplemented by other sources and
references where necessary. Adjustments were made to update all costs to a
June 1986 dollar basis. In addition, for some equipment items, well-
documented costs were not available and they had to be developed from compo-
nent costs.-
Costs in this document reflect the "typical" or "average" representation
for specific equipment items. This restricts the use of data in this report
to:
>
•
• Preliminary estimates used for policy planning.
• Comparison of relative costs of different levels or
systems, and
• Approximations of costs that might be incurred for a specific
application.
The costs in this report are considered to be "order of magnitude" with a
+50 percent margin. This is because the costs are based on preliminary
estimates and many are updated from literature sources. Large departures from
the design basis of a particular system presented in this manual or the advent
of a different technology might cause the system cost to vary by a greater
extent than this. If used as intended, however,- this document will provide a
reasonable source of preliminary cost information for the facilities covered.
132
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When comparing costs in this manual to costs from other references, the
user should be sure the design bases are comparable and that the capital and
annual costs as defined here are the same as the costs being compared.
Cost Updating—
All costs in this report are expressed in June 1986 dollars.- Costs
reported in the literature were updated using cost indices for materials and
labor.
Costs expressed in base year dollars may be adjusted to dollars for
another year by applying cost indices as shown in the following equation:
new base year cost = old base year cost x new base year index
old base year index
The Chemical Engineering (CE) Plant Cost Index was used in updating cost for
t.his report. For June 1986. the index is 316.3.
Equipment Costs—
Most of the equipment costs presented in this manual were obtained
directly from literature sources of vendor information and correspond to a
specific design standard.- Special cost estimating techniques, however, were
used in determining the costs associated with vessels, piping systems, scrub-
bers, diking, and enclosures. The techniques used are presented in the
following subsections of this manual.
Vessels—The total purchased cost for a vessel, as dollars per pound of
weight of fabricated unit f.o.b. with carbon steel as the basis (January 1979
dollars) was determined using the following equation from Peters and Timmer-
haus (48):
Cost = [50(Weight of Vessel in Pounds)"0'34]
133
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The vessel weight is determined using appropriate design equations as given by
Peters and Timmerhaus (48) which allow for wall thickness adjustments for
corrosion allowances, for example. The vessel weight is increased by a factor
of 0.15 for horizontal vessels and 0.20 for vertical vessels to account for
the added weight due to nozzles, manholes,- and skirts or saddles. Appropriate
factors are applied for different materials of construction as given in Peters
and Timmerhaus (48). The vessel costs are updated using cost factors.
Finally a shipping cost amounting to 10 percent of the purchased cost is added
to obtain the delivered equipment cost.
Piping—Piping costs were obtained using cost information and data
presented by Yamartino (63). A simplified approach is used in which it is
assumed that a certain length of piping containing a given number of valves.
flanges, and fittings is contained in the storage or process facility, the
data presented by Yamartino (63) permit cost determinations for various
lengths*, sizes, and types of piping systems. Using these factors, a represen-
tative estimate can be obtained for each of the storage and process facili-
ties.-
Diking—Diking costs were estimated using Mean's Manual (54) for rein-
forced concrete walls.- The following assumptions were made in determining the
costs. The dike contains the entire contents of a tank in the event of a leak
or release. Two dike sizes are possible: a three-foot high dike, six-inches
thick and a top-of-tank height dike ten inches thick. The tanks are raised
off the ground and are not volumetrically included in the volume enclosed by
the diking. These assumptions facilitate cost determination for any size
diking system.
Enclosures—Enclosure costs were estimated using Mean's Manual (54) for
both reinforced concrete and steel-walled buildings. The buildings are
assumed co enclose the same area and volume as the top-of-tank height dikes.
The concrete building is ten inches thick with a 26-gauge steel roof and a
metal door. The steel building has 26 gauge roofing and siding and metal
134
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door. The cost of a ventilation system was determined using a typical 1,000
scfm unit and doubling the cost to account for duct work and requirements for
the safe enclosure of hazardous chemicals.
Scrubbers—Scrubber costs were estimated using the following equation
from the Gard (60) manual for spray towers based on the actual cubic feet per
minute of flow at a chamber velocity of 600 feet/min.
Costs = 0.235 x (ACFM + 43.000)
A release rate of 10.-000 ft /min was assumed for the storage vessel systems
and an appropriate rate was determined for the process system based on the
quantity of hazardous chemicals present in the system at any one time. For
3
the sulfur dioxide extraction tower system, a release rate of 10.000 ft /min
was assumed. In addition to the spray tower, the costs also include pumps and
a storage tank for the scrubbing medium. The.costs presented are updated to
June 1986 dollars.
Installation Factors—
Installation costs were developed for all equipment items included in
both the process and storage systems. The costs include both the material and
labor costs for installation of a particular piece of equipment.- The costs
were obtained directly from literature sources and vendor information or
indirectly by assuming a certain percentage of the purchased equipment cost
through the use of estimating factors obtained from Peters and Timmerhaus (48)
and Valle-Riestra (62). Table 5-26 lists the cost factors used or the refer-
ence from which the cost was obtained directly. Many of the costs obtained
from the literature were updated to June 1986 dollars using a 10 percent per
year rate of increase for labor and cost indices for materials associated with
installation.
135
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TABLE 5-26. FORMAT FOR INSTALLATION COSTS
Equipment Item Factor or Reference
Vessels:
Storage Tank 0.45
Expansion Tank 0.25
Piping and Valves:
Pipework ' Ref. 63
Expansion Loop Ref. 49
Reduced Pressure Device Ref. 49
Check Valves Ref. 49
Gate Valves Ref. 49
Ball Valves Ref. 49
Excess Flow Valves Ref. 49
Angle Valves Ref. 54
Relief Valves Ref. 49
Rupture Disks Ref. 49
Process Machinery:
Centrifugal Pump ^ 0.43
Gear Pump ' 0.43
Instrumentation:
All Instrumentation Items 0.25
Enclosures: Ref.- 54
Diking: Ref. 54
Scrubbers: 0.45
136
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SECTION 6
REFERENCES
1. Mark. Herman E.. Othmer. Donald F., Overberger. Charles G., Seaborg.
Glenn T.. Kirk-Othmer Encyclopedia of Chemical Technology. 3rd ed.. vol.
22. John Wiley & Sons. 1983.
2. Sulfur Dioxide. Compressed Gas Association. Inc., Pamphlet G-3, 3rd
edition. 1964.
3. Dean. J.A.. (ed.). Lange's Handbook of Chemistry. 12th ed. McGraw-Hill
Book Company. 1979.
4. Tennessee Chemical Company. Atlanta, GA. Sulfur Dioxide Technical
Handbook. 5th ed.. 1979.
5. Bird. R.B., et al. Transport Phenomena. John Wiley & Sons. Inc.. 1960.
6. Sulfur Dioxide. Dangerous Properties of Industrial Materials Report.
Volume 1. No. 3. Jan/Feb 1981.
7. Air Products and Chemicals, Inc.. Allentown. PA. Speciality Gas Material
Safety Data Sheet. Revised March 1985.
8. Liquid Air Corporation, Alphagaz Division, Walnut Creek, CA. Material
Safety Data Sheet. October 1985.
9. U.S. Dept. of Health. Education, and Welfare. Criteria for a Recommended
Standard...Occupational Exposure to Sulfur Dioxide. HEW(NIOSH)
Publication No. 74-111. NTIS Order No. PB-228152. 1974.
10. Sittig. Marshall. Handbook of Toxic & Hazardous Chemicals and Carcin-
ogens. 2nd edition. Noyes Publications, 1985.
11. National Joint Health and Safety Committee for the Water Service. Safety
Aspects of Storage, Handling and Use of Chlorine and Sulphur Dioxide.
London, England, April 1982.
12. Tennessee Chemical Company, Atlanta, GA. Material Safety Data Sheet.
Revised June 1984.
13. Schroeter. L.C. Sulfur Dioxide. Pergamon Press, New York 1966.
14. Lawler, G.M. (ed.). Chemical Origins and Markets, Fifth Edition.
Stanford Research Institute, 1977.
137
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15. U.S. Patent No. 2,703.788.
16. Britt. Kenneth W. Handbook of Pulp and Paper Technology, 2nd ed. van
Nostrand Reinhold Company, 1970.
17. Austin, George T. Shreve's Chemical Process Industries, 5th ed.
McGraw-Hill, 1984, pp. 621-625.
18. Casey, James P. (ed.). Pulp and Paper Chemistry and Chemical Technology.
3rd ed.. Volume 1. John Wiley & Sons, 1980.
19. Telephone conversation between M. Stohs of Radian Corporation and a
representative of Champion Paper Company, Pasadena, TX, September 1986.
20. U.S. Patent No. 3,864,457.
21. U.S. Patent No. 3,950,500.
22. Sulfur Dioxide in Water Dechlorination. Technical Information Bulletin,
Stsuffer Chemical Co.. Industrial Chemical Division, Westport. CT.
January 1977.
23. Treatment of Chromium Waste with Sulfur Dioxide. Bulletin 514, Virginia
Chemicals, Inc., Portsmouth. VA.
24. Stone & Webster Engineering Corporation. Modified Edeleanu Process for
Recovery of Aromatics. Pet. Ref., 30(9), 237-238, 1951.
25. Bland, Wm. F. and Davidson, R.L. (eds.). Petroleum Processing Handbook.
McGraw-Hill, 1967.
26. Dickey, S. W. Diesel Fuel of 50-Cetane Value Produced in New Sulfur
Dioxide Extraction Plant. Pet. Proc. 3(6), 538-542, 1948.
27. Telephone conversation between M. Stohs of Radian Corporation and a
representative of Tennessee Chemical Company, Atlanta, GA. September
1986. -
28. Telephone conversation between M. Stohs of Radian Corporation and a
representative of PB&S Chemical Company, Henderson, KY, August 1986.
29. ASME Boiler and Pressure Vessel Code. ANSI/ASME BPV-VIII-1, American
Society of Mechanical Engineers, New York, NY, 1983.
30. Chemical Plant and Petroleum Refinery Piping. ANSI/ASME B31.3, American
National Standards Institute, Incorporated, New York, NY, 1980.
138
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31. Steel Valves. ANSI/ASME B16.34. American National Standards Institute,
Incorporated, New York, NY, 1977.
32. Steel Pipe Flanges and Flanged Fittings. ANSI/ASME B16.S. American
National Standards Institute, Incorporated, New York. NY, 1977.
33. Construction Materials for SO. Service. Technical Data Sheet, Tennessee
Chemical Company. Atlanta. GA; revised June 1983.
34. Handling of Sulfur Dioxide Containers. Technical Data Sheet. Tennessee
Chemical Company. Atlanta, GA.
35, Valves for SO. Service. Technical Data Sheet. Tennessee Chemical
Company. Atlanta, GA.
36. Telephone conversation between M. Stohs of Radian Corporation and a
representative of Ingersoil-Rand, Houston. TX, September 1986.
37. Green, D. W., (ed.). Ferry's Chemical Engineer's Handbook. 6th ed.
McGraw-Hill, New York. NY. 1984.
38. Pressure Relief Device Standards - Part 3 - Compressed Gas Storage
Containers. Pamphlet S-1.3. Compressed Gas Association, Inc.. Arlington,
• VA, 1984.
39. Lees, F. P. Loss Prevention in the Process Industries-Hazard
Identification, Assessment, and Control, Vol. 1 & 2. Butterworths.
London, England, 1983.
40. Aarts, J. J. and D. M. Morrison. Refrigerated Storage Tank Retainment
Walls. CEP Technical Manual, Volume 23, American Institute of Chemical
Engineers. New York. NY, 1981.
41. Radian Notebook Number 215. for EPA Contract 68-02-3994. Work Assignment
94. Page 5. 1986.
42. Bennett. G. F., F. S. Feates. and I. Wilder. Hazardous Materials Spills
Handbook. McGraw-Hill Book Company. New York. NY. 1982.
43. Hiltz. R.H. and Gross S.S. The Use of Foams to Control the Vapor Hazard
From Liquified Gas Spills in Control of Hazardous Materials Spills -
Proceedings 1980. National Conference on Control of Hazardous Material
Spills, Louisville, KY, May 1980.
44. Canvey:' A Second Report. Health and Safety Executive (U.K.). London,
England, 1981.
139
-------
45. Greiner. M. L. Emergency Response Procedures for Anhydrous Ammonia Vapor
Release. CEP Technical Manual. Volume 24, American Institute of Chemical
Engineers, New York, NY, 1984.
46. McQuaid, J. and A. F. Roberts. Loss of Containment - Its Effects and
Control, in Developments '82 (Institution of Chemical Engineers Jubilee
Symposium). London, England, April 1982.
47. Kubias, F.O. Technical Safety Audit. Presented at the Chemical
Manufacturer's Association Process Safety Management Workshop, Arlington,
Va.. May 7-8, 1985.
48. Peters, M.S. and K.D. Timmerhaus. Plant Design and Economics for
Chemical Engineers. McGraw-Hill Book Company, New York, NY, 1980.
49. Richardson Engineering Services, Inc. The Richardson Rapid Construction
Cost Estimating System, Volume 1-4, San Marcos, CA, 1986.
50. Pikulik, A. and H.E. Diaz. Cost Estimating for Major Process Equipment.
Chemical Engineering. October 10, 1977-
51. Hall, R.S., J. Matley, and K.J. McNaughton. Cost of Process Equipment.
Chemical Engineering, April 5, 1982.
52. Liptak, B.G. Costs of Process Instruments. Chemical Engineering,
September 7, 1970.
53. Telephone conversation between J.D. Quass of Radian Corporation and a
representative of Mark Controls Corporation. Houston. TX. August 1986.
54. R. S. Means Company, Inc. Building Construction Cost Data 1986 (44th
Edition). Kingston, MA.
55. Telephone conversation between J.D. Quass of Radian Corporation and a
representative of Zook Enterprises. Chagrin Falls, OH, August 1986.
56. Telephone conversation between J.D. Quass of Radian Corporation and a
representative of Fike Corporation. Houston, TX. August 1986.
57. Green, D.W., ed. Perry's Chemical Engineer's Handbook (Sixth Edition).
McGraw-Hill Book Company. New York, NY. 1984.
58. Liptak, B.G. Costs of Viscosity, Weight. Analytical Instruments.
Chemical Engineering. September 21, 1970.
59. Liptak, B.G. Control-Panel Costs, Process Instruments. Chemical
Engineering. October 5, 1970.
60. Capital and Operating Costs of Selected Air Pollution Control Systems.
EPA-450/5-80-002, U.S. Environmental Protection Agency. 1980.
140
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61. Cost indices obtained from Chemical Engineering. McGraw-Hill Publishing
Company. New York, NY. June 1974. December 1985. and August 1986.
62. Valle-Riestra, J.F. Froj.ect Evaluation in the Chemical Process Indus-
tries. McGraw-Hill Book Company, New York, NY, 1983.
63. Yamartimo. J. Installed Cost of Corrosion-Resistant Piping-1978.
Chemical Engineering. November 20. 1978.
141
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APPENDIX A
GLOSSARY
This glossary defines selected terms used in the text of this manual
which might be unfamiliar to some users or which might be used differently by
different authors.
Accidental release; The unintentional spilling, leaking, pumping, purging,
emitting, emptying, discharging, escaping, dumping, or disposing of a toxic
material into the environment in a manner that is not in compliance with a
plant's federal, state, or local environmental permits and results in toxic
concentrations in the air that are a potential health threat to the
surrounding community.
Cavitation; The formation and collapse of vapor bubbles in a flowing liquid.
Specifically the formation and collapse of vapor cavities in a pump when there
is sufficient resistance to flow at the inlet side.
Creep failure; Failure of a piece of metal as a result of creep. Creep is
time dependent deformation as a result of stress. Metals will deform when
exposed to stress. High levels of stress can result in rapid deformation and
rapid failure. Lower levels of stress can result in slow deformation and
protracted failure.
Deadheading; Closing or nearly closing or blocking the discharge outlet or
piping of an operating pump or compressor.
Electromotive Series of Metals; A List of metals and alloys arranged
according to their standard electrode potentials; which also reflects their
relative corrosion potential.
142
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Enthalpy; A thermodynamic property of a. chemical related to its energy
content at a given condition of temperature, pressure and physical state.
Enthalpy is the internal energy added to the product of pressure times volume.
Numerical values of enthalpy for various chemicals are always based on the
change in enthalpy from an arbitrary reference pressure and temperature, and
physical state, since the absolute value cannot be measured.
Facility; A location at which a process or set of processes are used to
produce, refine or repackage chemicals, or a location where a large enough
inventory of chemicals are stored so that a significant accidental release of
a toxic chemical is possible.
Hazard; A source of danger. The potential for death, injury or other forms
of damage to life and property.
Hygroscopic; Readily absorbing and retaining moisture, usually in reference
to readily absorbing moisture from the air.
Mild steel; Carbon steel containing a maximum of about 0.25% carbon. Mild
steel is satisfactory for use where severe corrodents are not encountered or
where protective coatings can be used to prevent or reduce corrosion rates to
acceptable levels.
Mitigation; Any measure taken to reduce the severity of the adverse effects
associated with the accidental release of a hazardous chemical.
Passivation film; A layer of oxide or other chemical compound of a metal on
its surface that acts as a protective barrier against corrosion or further
chemical reaction.
Plant; A location at which a process or set of processes are used to produce,
refine, or repackage, chemicals.
143
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Prevention; Design and operating measures applied to a process to ensure that
primary containment of toxic chemicals is maintained. Primary containment
means confinement of toxic chemicals within the equipment intended for normal
operating conditions.
Process; The sequence of physical and chemical operations for the production,
refining, repackaging or storage of chemicals.
Process machinery; Process equipment, such as pumps, compressors, heaters, or
agitators, that would not be categorized as piping and vessels.
Protection; Measures taken to capture or destroy a toxic chemical that has
breached primary containment, but before an uncontrolled release to the
environment has occurred.
Toxicicy; A measure of the adverse health effects of exposure to a chemical.
L44
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APPENDIX B
TABLE B-l. METRIC (SI) CONVERSION FACTORS
Quantity
Length :
Area:
Volume:
Mass (weight) :
Pressure:
Temperature:
Caloric Value:
Enthalpy:
Specific-Heat
Capacity:
Density:
Concentration:
Flowrate:
Velocipy:
Viscosity:
To Convert From
in
ft
in2
ft2
in3
ft3
gal
Ib
short ton (ton)
short ton (ton)
a tin
mm Hg
psia
psig
op
°C •
Btu/lb
Btu/lbmol
kcal/gmol
Btu/lb-°F
lb/ft3
Ib/gal
oz/gal
quarts/gal
gal/min
gal /day
ft3/min
ft/min
ft/sec
centipoise (CP)
To
cm
m
cm2
a.2
cm3
m3
m3
kg
Mg
metric ton (t)
kPa
kPa
kPa
kPa*
"C* *
K*
kJ/kg
kJ/kgmol
kJ/kgmol
kJ/kg-°C
kg/m3
kg/m3
kg/m3
cm3/m3
m3 /min
m3/day
m3/min
m/min
m/sec
kg/m-s
Multiply By
2.54
0.3048
6.4516
0.0929
16.39
0.0283
0.0038
0.4536
0.9072
0.9072
101.3
0.133
6.895
(psig+!4.696)x(6.-895)
(5/9)x(°F-32)
"C+273.15
2.326
2.326
4.184
4. 1868
16.02
119.8
7.490
25.000
0.0038
0.0038
0.0283
0.3048
0.3048
0.001
^Calculate as indicated
145
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TECHNICAL REPORT DATA .
(Please read Inunctions on the reverse before completing)
. REPORT NO.
EPA-600/8-87-0341
2.
3. RECIPIENT'S ACCESSIOF
.. TITLE AND SUBTITLE
Prevention Reference Manual: Chemical Specific,
Volume 12: Control of Accidental Releases of Sulfur
Dioxide
8. REPORT DATE
September 1987
6. PERFORMING ORGANIZATION CODE
'. AUTHOHIS)
D. S. Davis. G. B. DeWolf, J. D. Quass, and
M. Stohs
8. PERFORMING ORGANIZATION REPORT NO
DCN 87-203-023-94-16
10. PROGRAM ELEMENT NO. : ~~
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Radian Corporation
8501 Mo-Pac Boulevard
Austin, Texas 78766
11. CONTRACT/GRANT NO.
68-02-3994, Task 94
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air and Energy Engineering Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Task Final; 10/86-6/87
14. SPONSORING AGENCY CODE
EPA/600/13
15.SUPPLEMENTARY NOTES AEERL projec t officer is T. Kelly Janes, Mail Drop 62B, 919/541
2852.
is. ABSTRACT Tlie report discusses the control of accidental releases of sulfur dioxide
(SO2) to the atmosphere. SO2 has an IDLH (immediately dangerous to life and health)
concentration of 100 ppm, making it an acute toxic hazard. Reducing the risk asso-
ciated with an accidental release of SO2 involves identifying some of the potential
causes of accidental releases that apply to the processes that use SO2. This manual
identifies examples of potential causes and measures that may be taken to reduce the
accidental release risk. Such measures include recommendations on: plant design
practices; prevention, protection, and mitigation technologies; and operation and
maintenance practices. Conceptual cost estimates of possible prevention, protection,
and mitigation measures are provided. Headlines of accidental releases of toxic
chemicals at Bhopal and Chernobyl have added to the current public awareness of
toxic release problems. As a result of other, perhaps less dramatic, incidents in
the past, portions of the chemical industry were aware of this problem long before
these events. These same portions of the industry have made advances in this area.
Interest in reducing the probability and consequences of accidental toxic chemical
releases that might harm workers within a process facility and people in the sur-
rounding community prompted the preparation of this series of manuals.
17.
KEY WORDS AND DOCUMENT ANALYSIS
a.
DESCRIPTORS
b.lOENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution
Sulfur Dioxide
Emission
Accidents
Toxicity
Design
Maintenance
Cost Estimates
Pollution Control
Stationary Sources
Accidental Releases
13B
07 B
14G
13 L
06T
15E
05A.14A
3. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report}
Unclassified
20. SECURITY CLASS (Thispage)
Unclassified
21. NO. OF PAGES
153
22. PRICE
cPA Form 2220-1 (9-73)
146
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