United States EPA-600/8-87-034J
Environmental Protection
September 1987
&EPA Research and
Development
PREVENTION REFERENCE MANUAL:
CHEMICAL SPECIFIC
VOLUME 10: CONTROL OF
ACCIDENTAL RELEASES
OF HYDROGEN CYANIDE
Prepared for
Office of Air Quality Planning and Standards
Prepared by
Air and Energy Engineering Research
Laboratory
Research Triangle Park NC 27711
-------
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.
-------
-------
ABSTRACT
The accidental releases of a toxic chemical at Bhopal. India in 1984 was
a milestone in creating an increased 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.
Hydrogen cyanide has an IDLH (Immediately Dangerous to Life and Health)
concentration of 50 ppm, which makes it an acute toxic hazard.
Reducing the risk associated with an accidental release of hydrogen
cyanide involves identifying some of the potential causes of accidental
releases that apply to the process facilities that use hydrogen cyanide. 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 example prevention, protection, and
mitigation measures are provided.
11
-------
ACKNOWLEDGEMENTS
This manual was prepared under the overall guidance and direction of I.
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. Special thanks are given to the many other people.
both in government and industry, who served on the Technical Advisory Group
and as peer reviewers.
-------
TABLE OF CONTENTS
Section Page
ABSTRACT ii
ACKNOWLEDGEMENTS . . . ill
FIGURES v
TABLES vi
1.0 INTRODUCTION 1
1.1 Background 1
1.2 Purpose of This Manual 2
1.3 Sources and Uses of Hydrogen Cyanide 2
1.4 Organization of the Manual. 3
2.0 CHEMICAL CHARACTERISTICS 4
2.1 Physical Properties " 4
2.2 Chemical Properties and Reactivity 4
2.3 Tozicological and Health Effects . . 7
3.0 FACILITY DESCRIPTIONS AND PROCESS HAZARDS 10
3.1 Hydrogen Cyanide Manufacture 10
3.2 Hydrogen Cyanide Consumption 14
' 3.2.1 Manufacture of Adiponitrile 14
3.-2.2 Manufacture of Acetone Cyanohydrin/Methyl
Methacrylate 18
3.2.3 Manufacture of Cyanuric Chloride -21
3.2.4 Manufacture of Sodium Cyanide 21
3.3 Storage and Transfer 24
4.0 PROCESS HAZARDS 27
4.1 Potential Causes of Releases 27
4.1.1 Process Causes 28
4.1.2 Equipment Causes 29
4.1.3 Operational Causes 30
5.0 HAZARD PREVENTION AND CONTROL 31
5.1 General Considerations 31
5.2 Process Design 32
5.3 Physical Plant Design 34
5.3.1 Equipment 34
5.3.2 Plant Siting and Layout 45
5.3.3 Transfer and Transport Facilities 47
5.4 Protection Technologies 49
5.4.1 Enclosures 49
5.4.2 Flares 50
5.4.3 Scrubbers 54
5.5 Mitigation Technologies 5g
5.5.1 Secondary Containment Systems . 57
5.5.2 Flotation Devices and Foams §2
5.5.3 Mitigation Techniques for Hydrogen Cyanide Vapor . 64
iv
-------
TABLE OF CONTENTS (Continued)
Section Page
5.6 Operation and Maintenance Practices 65
5.6.1 Management Policy 66
5.6.2 Operator Training 67
5.6.3 Maintenance and Modification Practices 71
5.7 Control Effectiveness 74
5.8 Illustrative Cost Estimates for Controls 75
5.8.1 Prevention and Protection Measures 75
5.8.2 Levels of Control 79
5.8.3 Summary of Levels of Control 80
5.8.4 Equipment Specifications and Detailed Costs ... 93
5.8.5 Methodology 93
6.0 REFERENCES 116
APPENDIX A - GLOSSARY 120
APPENDIX B - METRIC (SI) CONVERSION FACTORS 124
FIGURES
•
Page
3*1 Hydrogen cyanide manufacturing process 11
3-2 Manufacturing process for adiponitrile 16
3-3 Manufacturing process for acetone cyanohydrin 19
3-4 Sodium cyanide manufacturing process 22
3-5 Example diagram of hydrogen cyanide tank car unloading facility . . 25
3-6 Example diagram of hydrogen cyanide storage facility 26
5-1 Computer model simulation showing the effect of diking on the vapor
cloud generated from a release of refrigerated hydrogen cyanide . . 61
-------
TABLES
Page
2-1 Physical Properties of Hydrogen Cyanide ,.... 5
2-2 Exposure Limits for Hydrogen Cyanide 9
2-3 Predicted Human Health Effects of Exposure to Various
Concentrations of Hydrogen Cyanide 9
3-1 Typical Uses of Hydrogen Cyanide . 15
5-1 Key Process Design Considerations for Hydrogen Cyanide
Processes 33
5-2 Chemical Resistance of Polymers and Elastomers to Chemical
Attack by Wet Hydrogen Cyanide 36
5-3 Important Considerations for Using Flares to Prevent Accidental
Chemical Releases .... 53
5-4 Aspects of Training Programs for Routine Process Operations . . 69
5-5 Examples of Major Prevention and Protection Measures for
Hydrogen Cyanide Releases 76
5-6 Estimated Typical Costs of Major Prevention and Protection
Measures for Hydrogen Cyanide Release 78
5-7 Summary Cost Estimates of Potential Levels of Controls for
Hydrogen Cyanide Storage Tank and Sodium Cyanide Reactor ... 81
5-8 Example of Levels of Control for Hydrogen Cyanide Storage Tank. 82
5-9 Example of Levels of Control for Sodium Cyanide Manufacture . . 84
5-10 Capital and Annual Costs Associated With Baseline Hydrogen
Cyanide Storage System 86
5-11 Capital and Annual Costs Associated With Level 1 Hydrogen
Cyanide Storage System 87
5-12 Capital and Annual Costs Associated With Level 2 Hydrogen
Cyanide Storage System 88
5-13 Capital and Annual Costs Associated With Baseline Sodium
Cyanide Reactor System 39
vi
-------
TABLES (Continued)
Page
5-14 Capital and Annual Costs Associated With Level 1 Sodium
Cyanide Reactor System 90
5*15 Capital and Annual Costs Associated With Level 2 Sodium
Cyanide Reactor System 91
5-16 Equipment Specifications Associated With Hydrogen Cyanide
Storage System 94
5-17 Material and Labor Costs Associated with Baseline Hydrogen
Cyanide Storage System 97
5-18 Material and Labor Costs Associated with Level 1 Hydrogen
Cyanide Storage System 98
5-19 Material and Labor Costs Associated With Level 2 Hydrogen
Cyanide Storage System 99
5-20 Equipment Specifications Associated With Sodium Cyanide
Reactor System 100
5-21 Material and Labor Costs Associated With Baseline Sodium
Cyanide Reactor System 103
•
5-22 Material and Labor Costs Associated With Level 1 Sodium Cyanide
Reactor System 104
5-23 Material and Labor Costs Associated With Level 2 Sodium Cyanide
Reactor System 106
5-24 Format for Total Fixed Capital Cost 108
5-25 Format for Total Annual Cost 110
5-26 Format for Installation Costs 115
vii
-------
SECTION 1
INTRODUCTION
1.1 BACKGROUND
Increasing concern about the potentially disastrous consequences of acci-
dental releases of toxic chemicals resulted from the Bhopal. India accident of
December 3. 1984, which killed approximately 2,000 people and injured thou-
sands more. A toxic cloud of methyl isocyanate was released. Concern about
the safety of process facilities handling hazardous materials increased fur-
ther after the accident at the Chernobyl nuclear power plant in the Soviet
Union in April of 1986.
While headlines of these incidents have created the current awareness of
toxic release problems, there have been other, perhaps less dramatic incidents
in the past. Interest in reducing the probability and consequences of acci-
dental toxic chemical releases that might harm workers within a process facil-
ity and people in the surrounding community prompted the preparation of this
manual and a planned series of companion manuals.
Hydrogen cyanide is a major commercial chemical and a low boiling toxic
liquid or gas at typical ambient conditions. Historically, there have been
few significant releases of hydrogen cyanide in the United States. However.
there have been a number of deaths, mostly of chemical plant workers, that
have resulted from accidental releases of hydrogen cyanide.
-------
1.2 PURPOSE OF THIS MANUAL
The purpose of this manual is to provide technical information about
hydrogen cyanide and specifically about prevention, protection, and mitigation.
measures for accidental releases of hydrogen cyanide. The manual addresses
technological and procedural prevention, protection, and mitigation measures
associated with the storage, handling, and process operations involving
hydrogen cyanide as it is used in the United States. This manual does not
address uses of hydrogen cyanide not encountered in the United States.
This manual is intended as a summary manual for persons charged with
reviewing and evaluating the potential for releases of hydrogen cyanide at
facilities that use. store, handle, or manufacture hydrogen cyanide. It is
not intended as a specification manual, and in fact refers the reader to addi-
tional technical manuals and other information sources for more complete in-
formation on the topics discussed. Other information sources include manu-
facturers and distributors of hydrogen cyanide, and technical literature on
design, operation, and loss prevention in facilities handling toxic chemicals.
1.3 SOURCES AND USES OF HYDROGEN CYANIDE
Two processes for manufacturing hydrogen cyanide (HCN) account for most
of the total hydrogen cyanide produced in this country. The most widely used
process produces hydrogen cyanide by reacting natural gas (methane). ammonia
and air. A second widely used process (which is actually a variation of the
first process) is called the DMA process and produces hydrogen cyanide by
reacting methane with ammonia. In addition to direct manufacture, hydrogen
cyanide is also produced as a by-product of acrylonitrile manufacture. In
1983 it was estimated that 930 million pounds of hydrogen cyanide were manu-
factured. At that time, the projected demand for 1988 was 1.186 million
pounds (1).
-------
The major use of hydrogen cyanide in the U.S., as of 1983. was for the
production of adiponitrile. Adiponitrile is used primarily as an intermediate
for hexamethlyenediamine. which is a principal ingredient for nylon-6.6.
Another major use of hydrogen cyanide is for the production of acetone cyano-
hydrin which is used almost exclusively as an intermediate for methyl metha-
crylate. Methyl methacrylate is used to manufacture polymethyl methacrylate
(Plexiglas*). Hydrogen cyanide is also used in the manufacture of cyanuric
chloride (an intermediate in pesticide manufacturing), miscellaneous chelating
agents, sodium cyanide, and a number of other chemical products. In 1983. the
uses of hydrogen cyanide in the U.S. were: adiponitrile. 38 percent; methyl
methacrylate. 35 percent; cyanuric chloride. 10 percent; chelating agents 7
percent; sodium cyanide. 5 percent; other uses. 5 percent (1).
In the U.S.. hydrogen cyanide is stored in small cylinders (e.g., 150
Ib), railroad tank cars, and bulk storage tanks.
1.4 ORGANIZATION OF THE MANUAL
The remainder of this manual presents technical information on specific
hazards and categories of hazards and their control as they relate to hydrogen
cyanide. As stated previously, these are examples only and are representative
of only some of the hazards that may be related to accidental releases.
Section 2 discusses physical, chemical and toxicological properties of
hydrogen cyanide. Section 3 describes the types of facilities which manu-
facture and use hydrogen cyanide in the United States. Section 4 discusses
process hazards associated with these facilities. Hazard prevention and con-
trol are discussed in Section 5. Costs of example storage and process facili-
ties reflecting different levels of control through alternative systems are
also presented in Section 5. The examples are for illustration only and do
not necessarily represent a satisfactory alternative control option in all
cases. Section 6 presents a reference list. Appendix A is a glossary of key
technical terms that might not be familiar to all users of the manual. Appen-
dix B presents selected conversion factors between metric (SI) and English
measurement units.
-------
SECTION 2
CHEMICAL CHARACTERISTICS
This section of the manual describes the physical, chemical, and toxico-
logical properties of hydrogen cyanide as they relate to accidental release
hazards.
2.1 PHYSICAL PROPERTIES
Anhydrous hydrogen cyanide is a colorless or pale yellow liquid with a
mild odor similar to bitter almonds. The liquid boils at 78.3°F at 1 at-
mosphere of pressure and forms a colorless-, flammable, toxic gas. The physi-
cal properties of anhydrous hydrogen cyanide are listed in Table 2-1.
i
Hydrogen cyanide is completely soluble in water. The gas is slightly
less dense than air. although a mixture of hydrogen cyanide in moist air may
stay near ground level. Liquid hydrogen cyanide will expand slightly with
heating. As a result, liquid-full equipment can pose a hazard (although as
will be seen, the potentially greater danger from trapping liquid hydrogen
cyanide in equipment is the potential for polymerization). A liquid-full
vessel is a vessel that is not vented and is filled with liquid hydrogen cya-
nide with little or no vapor space present above the liquid. A liquid-full
line is a section of pipe that is sealed off at both ends and is full of
liquid hydrogen cyanide with little or no vapor space. In these situations.
there is no room for thermal expansion of the liquid, and temperature increas-
es can result in containment failure.
2.2 CHEMICAL PROPERTIES AND REACTIVITY
Three chemical properties of hydrogen cyanide that contribute to the
potential for an accidental release of the chemical are (2.3):
-------
TABLE 2-1. PHYSICAL PROPERTIES OF HYDROGEN CYANIDE
Reference
CAS Registry Number
Chemical Formula
Molecular Weight
Normal Boiling Point
Melting Point
Liquid Specific Gravity (H.0=l)
Vapor Specific Gravity (air=l)
Vapor Pressure
Vapor Pressure Equation:
log Pv = A- -
74-90-8
HCN
27.03
78.3 °F 0 1 atm
8.17 °F
0.6884 0 68 °F
0.947 0 88 °F
0.348 atm 0 32°F
where: Pv = vapor pressure, mm Hg
T = temperature, °C
A = 7.5282. a constant
B = 1329.5. a constant
C = 260.4. a constant
Liquid Viscosity
Solubility in Water
Specific Heat at Constant Pressure
Latent Heat of Vaporization
0.2014 centipoise
0 68 °F
Complete
16.94 Btu/(lbmole-°F)
0 62.4 °F
10.834 Btu/lbmole 0
77 °F
2
3
2
2
2
3
3
(Continued)
-------
TABLE 2-1 (Continued)
Reference
Liquid Surface Tension
Heat of Combustion
Autoignition Temperature
Explosive Range. Volume Z in
air 9 1 atm and 68 °F min.
max.
Flashpoint. TCC (ASTM D-56)
17.2 dynes/cm 9 77 °F
287.000 Btu/lbmole
1.000 °F
6
41
0 °F
3
3
3
Additional properties useful in determining other properties from physical
property correlations.
Critical Temperature
•
Critical Pressure
Critical Density
362.2 °F
53.2 atm
12.2 lb/ft'
3
3
3
-------
• Hydrogen cyanide is flammable in air at concentrations
from 6 percent to 41 percent hydrogen cyanide.
• The addition of alkaline-chemicals, water and/or heat may
promote self-polymerization and decomposition of hydrogen
cyanide. The self-polymerization reaction is exothermic
and the heat released will promote further polymerization.
The heat generation will also result in the decomposition
of hydrogen cyanide into ammonia and formate. The pressure
rise from polymerization/decomposition reactions can be-
come explosive. Small amounts of acid such as sulfuric or
phosphoric will help to stabilize the hydrogen cyanide
against polymerization.
• The addition of large quantities of acid (over 15? by
weight of concentrated sulfuric acid) can cause rapid
decomposition of hydrogen cyanide. This decomposition is
highly exothermic. When sulfuric acid is involved the
decomposition by-products will be sulfur dioxide and car-
4
bon dioxide.
2.3 TOXICOLOGICAL AND HEALTH EFFECTS
Hydrogen cyanide is highly toxic by ingestion, inhalation and skin ad-
sorption. It is a true noncumulative protoplasmic poisons (i.e.. it can be
detoxified readily). Hydrogen cyanide combines with those enzymes at the
blood/tissue interfaces that regulate oxygen transfer to the cellular tissues.
Unless the cyanide is removed, death results through asphyxia. The warning
signs of hydrogen cyanide poisoning include: dizziness, numbness, headache.
rapid pulse, nausea, reddened skin, and blood shot e'yes. More prolonged expo-
sure can cause vomiting and labored breathing followed by unconsciousness,
cessation of breathing, rapid weak heart beat, and death. Severe exposure (by
inhalation) can cause immediate unconsciousness; this rapid knockdown power
-------
without any irritation or detectable odor to some people makes hydrogen cya-
nide more dangerous than other materials of comparable toxicity (e.g., hydro-
gen sulfide). Table 2-2 presents a summary of some of the relevant exposure
limits for hydrogen cyanide. Table 2-3 presents a summary of predicted human
health effects of exposure to various concentrations of hydrogen cyanide.
-------
TABLE 2-2. EXPOSURE LIMITS FOR HYDROGEN CYANIDE
Exposure Concentration
Limit (ppm) Description Reference
IDLH 50 The concentration defined as posing 5
immediate danger to life and health
C.e.. causes irreversible toxic
effects for a 30-minute exposure).
PEL 10 A time-weighted 8-hour exposure to 6
this concentration as set by the
Occupational Safety and Health
Administration should result in no
adverse effects for the average
healthy, male worker.
LCLo 178 This concentration is the lowest pub- 6
lished lethal concentration for a human
over a 10-minute exposure.
TABLE 2-3. PREDICTED HUMAN HEALTH EFFECTS OF EXPOSURE TO VARIOUS
CONCENTRATIONS OF HYDROGEN CYANIDE
ppm Predicted Effect
2-5 Odor threshold.
20 Causes slight symptoms including headache
and dizziness after several hours.
50 Causes disturbances within an hour.
100 Dangerous for exposures of 30-60 minutes.
300 Rapidly fatal unless prompt, effective
first aid is administered.
Source: Adapted from Reference 2.
-------
SECTION 3
FACILITY DESCRIPTIONS AND PROCESS HAZARDS
This section provides brief descriptions of the uses of hydrogen cyanide
in the United States. Major hazards of these processes as they relate to
accidental releases are discussed in Section 4. Preventive measures
associated with these hazards are discussed in Section 5.
3.1 HYDROGEN CYANIDE MANUFACTURE
Two processes for manufacturing hydrogen cyanide account for most of the
total hydrogen cyanide produced in this country. The most widely used process
is one that produces hydrogen cyanide by reacting natural gas (methane),
ammonia and air. A second widely used process (which is actually a variation
•
of the first process) is called the BMA process which produces hydrogen
cyanide by reacting methane with ammonia. In addition to direct manufacture,
hydrogen cyanide is also produced as a by-product of acrylonitrile
manufacture.
A schematic diagram of a hydrogen cyanide manufacturing process is
presented in Figure 3-1. In this process ammonia, methane (or natural gas)
and air are preheated to about 750 to 900°C, mixed and sent to a packed bed
reactor. The reactor is typically packed with a catalytic wire gauze composed
of platinum or a platinum rhodium composite (7). The exit gas from the
reactor contains a mixture of hydrogen cyanide, ammonia, and water vapor (a
by-product of the reaction). As illustrated in Figure 3-1, this crude product
mixture is sent to an ammonia absorption column where the ammonia is absorbed
in an ammonium phosphate solution (8). Most of the hydrogen cyanide exits in
the gas phase where it is absorbed, washed and treated with sulfur dioxide as
an inhibitor to prevent polymerization. The ammonium phosphate solution is
sent through a series of processing operations where the ammonia is recovered
and recycled back to the reactor.
10
-------
NH3
WASTE OASES
TO FLAIR
NH3 + HCN
IN NH4H2PO4
SOLUTION
••m
ABSORBER
HCN • WATER
COOLANT
STEAM
WASTE
WATER
WASTE
WATER
HCN WITH SO2
INHIBITOR
L
r
HCN
STRIPPER ,
1
STEAM -
I
^ ^
V
HCN
FRACTIONATOR
STEAM
WASTE
WATER
NH4PO4 SOLUTION
Figure 3-1. Hydrogen cyanide manufacturing process.
Adapted from References 2. 8 and 9.
-------
The reaction that produces hydrogen cyanide is endothermic. To provide
the necessary heat of reaction, forty percent or more of the ammonia and
methane fed to the process are intentionally oxidized in the reactor vessel.
The heat input from the oxidation of the methane and ammonia balanced by the
heat requirements of the hydrogen cyanide reaction will result in a normal
reaction temperature of about 2000 to 2200°F (9).
High hazard areas in the cyanide manufacturing process include the
following:
• Cyanide reactor;
• Hydrogen cyanide absorber;
• Hydrogen cyanide stripper; and
i
• Hydrogen cyanide fractionator.
The cyanide reactor is critical because of the high temperatures that are
involved. Overheating the reactor could result in uncontrollable combustion
reactions or explosions (10). These uncontrollable combustion reactions or
explosions could result in the physical breakdown of the reactor vessel by
thermal fatigue or overpressure. There are three possible causes of overheat-
ing. They include:
• Poor heat distribution within the reactor bed, resulting
in hot spots;
• Overheating raw materials before they enter the cyanide
reactor; or
• Loss of composition or quantity control of raw material
feeds.
12
-------
Hot spot formation within the reactor can result in catalyst breakdown or
physical deterioration of the reactor vessel (10). If the chemical perfor-
mance of the catalyst is destroyed then no reaction will occur. If the endo-
thermic cyanide reaction has ceased, then the reactor is likely to overheat.
In addition to the potential causes of overheating listed above, it should be
noted that iron is a decomposition catalyst for hydrogen cyanide and ammonia
under the conditions present in the hydrogen cyanide reactor. Exposed iron
surfaces in the reactor or reactor feed system can result in uncontrolled
decomposition, which could result- in an accidental release by overheating and
overpressure.
Only a small inventory of hydrogen cyanide will be present in the cyanide
reactor. Therefore, catastrophic failure of the cyanide reactor is not likely
to directly result in the release of large quantities of hydrogen cyanide.
However, such failure could result in damage to other portions of the system
where larger quantities of hydrogen cyanide are present.
•
The hydrogen cyanide absorber, stripper and fractionator are high hazard
areas because they contain inventories of concentrated hydrogen cyanide., All
of the associated pumps, piping and fittings for these systems are also high
hazard areas. Controlling the pH of these systems is important since the
vapor pressure of hydrogen cyanide is dependent upon pH. A system designed
for hydrogen cyanide vapor pressure within one pH range may not be able to
handle the increased cyanide vapor pressure at a lower pH. Reliable pH
control is particularly important at the hydrogen cyanide fractionator where
acid is intentionally added as a stabilizer to the feed stream. The quantity
of acid that is added at this point is very small. However, the potential
still exists for a loss of acid flow control. Large excesses of acid can
result in a violent hydrogen cyanide decomposition reaction.
• • •
The ammonia recovery portion of the hydrogen cyanide manufacturing
process does not contain large quantities of hydrogen cyanide. However.
inventories of ammonia are present throughout this portion of the system.
13
-------
Therefore a potential for an accidental release of ammonia exists in this
section of the process.
3.2 HYDROGEN CYANIDE CONSUMPTION
The major use of hydrogen cyanide in the U.S. today is for the production
of adiponitrile. Adiponitrile is used primarily as an intermediate for
hexamethlyenediamine, which is a principal ingredient for nylon-6,6 (1).
Another major use of hydrogen cyanide is for the production of acetone cyano-
hydrin which is used almost exclusively as an intermediate for methyl metha-
ciylate. Methyl methacrylate is used to manufacture polymethyl methacrylate
(Plexiglas*). Hydrogen cyanide is also used in the manufacture of cyanuric
chloride (an intermediate in pesticide manufacturing), miscellaneous chelating
agents, sodium cyanide, and a number of other chemical products. Table 3-1
lists a variety of products that might be manufactured using hydrogen cyanide.
t
This subsection summarizes some of the major technical features of
process facilities that might use hydrogen cyanide in the U.S.
3.2.1 Manufacture of Adiponitrile
Adiponitrile is commercially manufactured by several different processes
all of which begin with a different hydrocarbon raw material. Hydrogen
cyanide is found only in those processes that use butadiene as a starting
material. In some butadiene-based processes, sodium cyanide is used as the
raw material (11). In other butadiene-based processes hydrogen cyanide is
used as the raw material. Figure 3-2 illustrates a process that uses hydrogen
cyanide to manufacture adiponitrile.
In this process, hydrogen cyanide and a slight excess of butadiene are
fed to a reactor packed with nickel catalyst. The reaction is carried out at
212°F and sufficient pressure to keep the reactants in solution (12). The
product mixture contains 2-methyl-3-butenenitrile, 3-pentenenitrile, and
14
-------
TABLE 3-1. TYPICAL USES OF HYDROGEN CYANIDE
Acetone cyanahydrin
Adiponitrile
Acrylonitrile
Aminopolycarboxylic acids
Barium cyanide
Beta-amines
Cyanuric chloride
Diaminomaleonitrile
Lactic acid
Methionine
Sodium cyanide
Tertiary alkyl amines
Source: Adapted from Reference 14.
15
-------
HYDROGEN
CYANIDE
BUTADIENE fc-
HYDBOQ6N
CYANIO*
BUTADIENE
J
2 • METHYL - 3 • BUTENENITWLE
+ 3-PENTENENrraiLE
3-PENTENENITBILE
* 4 - PENTENENITRILE
T
LIGHT
BY - PRODUCTS
AOIPONITniLE
* BY - PRODUCTS HEAVY
BY - PRODUCTS
AOIPONITRILE
Figure 3-2. Manufacturing process for adiponitrile.
16
-------
unreacted butadiene. The unreacted butadiene is separated from the product
.stream and recycled back to the reactor.
The fractionated product stream from the first hydrocyanation reactor is
passed through a nickel catalyst bed where an isomerization reaction converts
the 2-methyl-3-butenenitrile to 3-pentenenitrile and a small amount of 2-pen-
tenitrile (13). The 3-pentenenitrile is then passed through another nickel
catalyst bed along with hydrogen cyanide to produce adiponitrile. Unreacted
pentenenitrile is separated from the product stream by distillation and
recycled back to the reactor. The crude adiponitrile is purified by
distillation.
The portions of the process that are of concern when considering a
hydrogen cyanide release are the two hydrocyanation reactors and the hydrogen
cyanide feed and storage system. The hydrocyanation reactors are run with an
excess of olefin and thus the hydrogen cyanide is completely consumed by
reaction. Both of these reactions are exothermic and thus there is the
potential for a loss of temperature control and an accidental release by
overpressure. •
The hydrocyanation reactions are carried out at relatively mild condi-
tions (around 212°F and 100 to 200 psia). A loss of temperature control would
probably not result in high enough temperatures to structurally fatigue the
reaction equipment. The major concern with a loss of temperature control
would be the potential for vaporization of unreacted hydrogen cyanide within
the reactor. This would result in an increase of pressure in the reactor.
The consequences of such an increase would depend upon the ability of the
pressure relief system to handle the vaporized hydrogen cyanide. Once the
hydrogen cyanide was vaporized the hydrocyanation re.action would cease and no
additional heat would be generated. The situation is. therefore, self cor-
recting. There may be conditions under which loss of temperature control
would result in a polymerization-decomposition of hydrogen cyanide.
17
-------
Hydrogen cyanide storage and feed systems are of concern because of the
relatively large inventory of hydrogen cyanide. Leaks from valves, fittings.
pumps, and storage vessels are of concern.
3.2.2 Manufacture of Acetone Cyanohydrin/Methyl Methacrylate
Hydrogen cyanide can be combined with acetone to produce acetone cyano-
hydrin which in turn can be combined with methanol to form methyl methacry-
late. As mentioned in the introduction to this subsection, almost all of the
acetone cyanohydrin produced in this country is carried on to methyl methacry-
late. Methyl methacrylate is also produced by routes that do not use hydrogen
cyanide (15).
Figure 3-3 illustrates the acetone cyanohydrin production portion of a
methyl methacrylate process that utilizes hydrogen cyanide (16). In this
process, hydrogen cyanide, acetone and a catalyst are fed to a continuous
stirred tank reactor to form acetone cyanohydrin. The reaction catalyst may
be sodium hydroxide or some other alkaline metal salt. The reaction is run at
a temperature between 70°F and 160°F. The reaction mixture is fed to a second
stirred tank where sulfuric acid is added to quench the reaction. The acetone
cyanohydrin is purified by first decanting off the catalyst and then distil-
ling off unreacted raw materials.
The purified acetone cyanohydrin is then converted to methacrylamide
sulfate by the addition of sulfuric acid. Methanol in an aqueous solution is
then added along with the methacrylamide sulfate to a multistaged reactor
where methyl methacrylate is formed. Several purification steps complete the
manufacturing process.
The high hazard area of this process with regard to preventing an acci-
dental release of hydrogen cyanide is the acetone cyanohydrin production
portion of the process.
18
-------
ACETONE
CYANOHYDRIN
STRIPPER
ACETONE
CYANOHYOflIN
REACTOR
ACETONE CYANOHYORIN
TO METHYL METHACRYLATE
PRODUCTION PROCESS
Figure 3-3. Manufacturing process for acetone cyanohydrin.
19
-------
The first potentially hazardous location is the acetone cyanohydrin
reactor. The inventory of hydrogen cyanide in the reactor will be relatively
small. However, if the flow of acetone to the reactor were to cease, the
conditions within the vessel would promote hydrogen cyanide polymeri-
zation-decomposition. The presence of excess hydrogen cyanide as well as
inadequate mixing of the' hydrogen cyanide with the acetone could also lead to
polymerization-decomposition of the cyanide. Polymerization-decomposition
could lead to overpressure or overheating in the reactor and result in an
accidental release of hydrogen cyanide. Thus, control of flow, composition.
mixing and temperature are all important in this reactor.
The reaction quenching vessel is a second potentially hazardous portion
of this process. Failure to sufficiently quench the reaction with acid could
result in a reversal of the reaction back to hydrogen cyanide and acetone.
Acetone cyanohydrin will convert back to hydrocyanic acid and acetone if the
pH is above a certain level. One source recommends that the pH for storage of
acetone cyanohydrin not exceed 3 or 4, and the pH under more rigorous* condi-
tions such as those found in a distillation operation should not exceed 2
(17). The potential hazard, therefore, is that insufficient pH adjustment
will result in acetone cyanohydrin decomposition in the stripping column.
This would result in a significant increase in the flow of material to the
flare. This increase in flow could disrupt the performance of the flare and
result in an accidental release of hydrogen cyanide. Additionally, high
levels of hydrogen cyanide in the stripping column could result in
polymerization- decomposition.
The other major area of concern in this process is the hydrogen cyanide
storage and feed system. The potential for an accidental release of hydrogen
cyanide would be high because of the relatively large inventories.
20
-------
3.2.3 Manufacture of Cyanuric Chloride
Cyanuric chloride is used for the production of triazine-based herbi-
cides. It is manufactured in a two-step process. In the first step chlorine
and hydrogen cyanide are reacted to form cyanogen. Cyclic trimerization of
the cyanogen yields cyanuric chloride (18). Another method for the production
of cyanuric chloride involves a single step fluidized bed process (19).
Very little hydrogen cyanide would be present in the reaction or puri-
fication sections of a cyanuric chloride manufacturing facility. The initial
cyanuric reaction between hydrogen cyanide and chlorine will proceed rapidly.
leaving little inventory of hydrogen cyanide in the reactor. The primary area
of concern from the perspective of an accidental release of hydrogen cyanide
would be the initial hydrogen cyanide storage and handling facility. Pumps,
valves, piping, and vessels that are dedicated to hydrogen cyanide service
would be of particular concern.
•
3.2.4 Manufacture of Sodium Cyanide
4
Sodium cyanide is usually produced by reacting hydrogen cyanide with a
sodium hydroxide solution. Such manufacturing operations are often located
directly down stream from a hydrogen cyanide manufacturing process. An
example of a continuous sodium cyanide manufacturing process is presented in
Figure 3-4 (20). In this process aqueous sodium hydroxide and gaseous
hydrogen cyanide are fed to a vessel that functions as a reactor, evaporator
and crystallizer. where they react to form sodium cyanide.
The reaction vessel contains aqueous sodium cyanide with a small amount
of unreacted. excess sodium hydroxide. The sodium hydroxide is fed to the top
of the reaction vessel while the hydrogen cyanide is fed to a recirculation
loop at the bottom of the vessel. As the two reactants mix in a countercur-
rent fashion, they react to form sodium cyanide. The reactor is kept under
partial vacuum. The reduced pressure lowers the boiling point of the
21
-------
VACUUM
CONDENSER
AQUEOUS
SODIUM HYDROXIDE
WASTE
WATER
to
HYDROGEN
CYANIDE
AQUEOUS SODIUM
CYANIDE SOLUTION
RECIRCULATION LOOP
CONTAINING WATER,
SOLUBILIZED SODIUM
CYANIDE AND SOLID
SODIUM CYANIDE
SEMI • DRY
SODIUM
CYANIDE
PRODUCT
SLIP STREAM
Figure 3-4. Sodium cyanide manufacturing process (20),
-------
solution. The heat of reaction is removed by allowing water to boil off from
the solution. The temperature of the mixture is therefore kept at its boiling
point. As the reaction proceeds and water is removed, some of the sodium
cyanide crystallizes out of solution. A product slip stream is withdrawn from
the reactor recirculation loop and the crystallized sodium cyanide crystals
are filtered out and dried. The filtrate is returned to the reaction vessel.
There are two issues of concern when operating a sodium cyanide manufac-
turing operation. The first concern is that hydrogen cyanide will polymerize
before the reaction with sodium hydroxide occurs. The conditions in the
reactor are favorable for polymerization if insufficient quantities of sodium
hydroxide are present or if there is incomplete mixing of the hydrogen cyanide
with the sodium hyroxide. The second concern is that sodium cyanide will
hydrolyze to hydrogen cyanide and sodium formate. This reaction is very
dependent upon temperature and can become significant at temperatures above
160 to 180°F (20).
Both of the problems listed above could be of concern from the perspec-
tive of accidental release prevention. The formation of polymerized cya'nide
could clog pumps and lines which could lead to an accidental release by
overpressuring positive displacement pumps or overheating the contents of
centrifugal pumps. Additionally, the polymerization reaction is exothermic.
The heat generated by the reaction could result in excessive pressures and
could contribute to additional polymer formation. Significant hydrolysis of
sodium cyanide would lead to the formation of unexpected quantities of hydro-
gen cyanide which could result in overpressurization of the pump or overload-
ing of the vacuum system; both of which could lead to an accidental release of
hydrogen cyanide.
As with all processes that handle hydrogen cyanide, the hydrogen cyanide
storage and feed system is of concern because of the relatively large inven-
tory. A breach of containment within the hydrogen cyanide feed and storage
system could result in an accidental release of the chemical.
23
-------
3.3 STORAGE AND TRANSFER
When a facility uses large quantities of hydrogen cyanide, the hydrogen
cyanide is either produced on site or is unloaded from a rail car into
stationary storage.
Figure 3-5 shows a potential design for a hydrogen cyanide tank car
unloading facility. The basic components of such a facility include nitrogen
blanketing with pressure relief, grounding cables with clamps, special
high-pressure piping and hoses for hookups of both hydrogen cyanide and
nitrogen systems, tank level measuring device, tank car "come-along" for
accurate positioning, wheel chocks, and derailers.
Figure 3-6 shows a potential design for a hydrogen cyanide storage tank.
The basic components of such a system are temperature and pressure recorders
and alarms, pressure relief to a flare or other treatment system, sulfuric
acid addition system, liquid level measuring device with alarm, cooling system
and diked enclosure.
•
The primary hazard associated with the storage of hydrogen cyanide is the
potential for self polymerization. As described in Section 2-2. self poly-
merization can result in rapid temperature and pressure increases in a storage
system and can result in a breach of containment. Several safety precautions
concerning the prevention of polymerization will be discussed in Subsection
5.3.1.
Additional hazards associated with hydrogen cyanide storage include the
potential for overfilling, corrosion, and contamination caused by backflow of
process materials into the storage tank. Additionally, loss of tank refriger-
ation could result in overpressure due to thermal expansion of both the liquid
and gaseous hydrogen cyanide. Such an overpressure would probably result in
the discharge of hydrogen cyanide through the pressure relief device. The
ultimate consequence of such a release will depend upon the ability, of the
hydrogen cyanide containment and protection system (e.g. a flare or scrubber)
to handle such a load.
24
-------
N>
Ln
PRESSURE
INDICATOR
PRESSURE
RELIEF
NITROGEN
REGULATORS
NITROGEN
NITROGEN
FILTER
NITROGEN
PRESSURE
RELIEF
THERMOWELL
FLOW
INDICATOR VALVE
EXCESS
FLOW VALVE
MCN STORAGE
TANK
rr / f II i it i111 lit
// I///f
/////////////////
Figure 3-5. Example diagram of hydrogen cyanide tank car unloading facility.
Adapted from Reference 3.
-------
TO FLARE OR
SCRUBBER
PRESSURE - VACUUM
RECORDER ALARM
TEMPERATURE
RECORDER ALARM
ACID
ADDITION
TANK
COOLANT
COOLANT
TO HCN SAMPLING
SYSTEM
FROM
TANK CAR1
NJ
\
CONTINUOUS
NITROGEN
PURGE BELOW
VALVE
OPEN VENT WITH
CONDENSER
HEAT EXCHANGER
ON PUMP -
AROUND COOLING
LOOP FOR HCN
TO HCN
'PROCESS
SUBMERGED
PUMPS
PI - PRESSURE INDICATOR
Tl - TEMPERATURE INDICATOR
Lfi
1 — PRESSURE RELIEF VALVE
VALVE
Figure 3-6. Example diagram of hydrogen cyanide storage facility.
Adapted from Reference 3.
-------
SECTION 4
PROCESS HAZARDS
Some hazards and potential causes of releases for hydrogen cyanide
releases directly related to its properties and specific processes were
identified in the preceding sections. This section summarizes these, and
discusses more general hazards common to any facility producing or using
hydrogen cyanide. Hydrogen cyanide releases can originate from many sources
including ruptures in process equipment, separated flanges, actuated relief
valves or rupture discs, and failed pumps or compressors. In addition, losses
may occur through leaks at joints and connections such as flanges, valves, and
fittings where failure of gaskets or packing might occur.
The properties of hydrogen cyanide which can promote equipment failure
are its ability to self polymerize, its flammability and the violent decompo-
sition reaction that can occur between hydrogen cyanide and acidic solufions.
Potential hydrogen cyanide releases may be in the form of either liquid
or vapor. Liquid spills can occur when hydrogen cyanide is released at or
below its boiling point of 78.3°F. or when a sudden release of hydrogen
cyanide at temperatures above its boiling point results in vapor flashing.
thus cooling at least part of the remaining material to below its boiling
point. Direct releases of vapor can also occur.
4.1 POTENTIAL CAUSES OF RELEASES
*
Failures leading to accidental releases may be broadly classified as due
to process, equipment, or operational causes. This classification is for
convenience only. Causes discussed below are intended to be illustrative, not
exhaustive. A more detailed discussion of possible causes of accidental re-
leases is planned in other portions of the prevention reference manual series
of which this present manual is a part.
27
-------
4.1.1 Process Causes
Process causes are related to the fundamentals of process chemistry*
control and general operation. Examples of possible process causes of a
• . •
hydrogen cyanide release include:
• Overheating of cyanide manufacturing reactor resulting in
rapid thermal decomposition;
• Loss of flow/composition control where acid stabilizer is
added to a hydrogen cyanide stream resulting in excess
acid. High acid levels can result in rapid decomposition
and overpressure;
• Loss of flow/composition control where acid stabilizer is
• added to a hydrogen cyanide stream resulting in low acid
levels. Low acid levels can result in polymerization-
decomposition;
• Loss of flow/composition control where abnormally high
levels of hydrogen cyanide is fed to a reactor along with
a basic catalyst or reactant. Excess hydrogen cyanide is
likely to polymerize-decompose under such conditions;
• Loss of adequate mixing where hydrogen cyanide is fed to a
reactor along with a basic catalyst or reactant. Local-
ized high concentrations of hydrogen cyanide can polyerize-
decompose;
• Loss of pH control where acetone cyanohydrin is present
resulting in the decomposition to acetone and hydrogen
cyanide. Such decomposition could result in overpressure
and an accidental release;
28
-------
• Overpressure of any storage or process vessels containing
hydrogen cyanide due to over heating resulting in
polymerization-decomposition;
• Excess hydrogen cyanide feed leading to overfilling or
overpressuring equipment;
• Backflow of alkaline or strongly acidic materials into
hydrogen cyanide storage or process vessel resulting in
polymerization-decomposition; and
• Catalyst decay in hydrogen cyanide production reaction
resulting in overheating of the reactor.
4.1.2 Equipment Causes
Equipment causes of accidental releases result from hardware failure.
Some possible causes include:
•
• Excessive stress due to improper fabrication, construc-
tion, or installation;
• Failure of vessels at normal operating conditions due to
weakening of equipment from excessive stress, external
loadings, or corrosion;
• Mechanical fatigue and shock in any equipment. Mechanical
fatigue could result from age. vibration, or stress
cycling, caused by pressure cycling, for example. Shock
could occur from collisions with moving equipment such as
cranes or other equipment in process or storage areas;
• Creep failure in equipment subjected to extreme operation-
al upsets, especially excess temperature. This can occur
29
-------
in equipment subjected to fire that may have caused damage
before being brought under control;
• Failure of any equipment that is exposed to hydrogen
cyanide due to stress corrosion cracking, especially
equipment subject to vibration or other forms of mechani-
cal stress; and
• All forms of corrosion; specific type will be process and
material specific.
4.1.3 Operational Causes
Operational causes of accidental releases are a result of incorrect pro-
cedures or human errors (i.e.. not following correct procedures). These
causes include:
•
• Overfilled storage vessels;
• Errors in loading and unloading procedures;
* Inadequate maintenance in general, but especially on
pressure relief systems and other preventive and protec-
tive systems; and
• Lack of inspection and non-destructive testing of vessels
and piping to detect corrosion weakening.
30
-------
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 hydrogen cyanide is
stored and used. Considerations in these areas can be grouped as follows:
• Process design;
• Physical plant design;
•
• Operating and maintenance practices: and
• Protective systems.
In each of these areas, consideration must be given to specific factors
that could lead to a process upset or failure which could directly cause a
release of hydrogen cyanide to the environment, or result in an equipment
failure which would then cause the release. At a minimum, equipment and
procedures should be examined to ensure that they are in accordance with
applicable codes, standards, and regulations. In addition, stricter equipment
and procedural specifications should be in place if extra protection against a
release is considered appropriate.
Most of the large manufacturers of hydrogen cyanide provide detailed
assistance as to proper storage and handling practices for their customers
that use the chemical. One large company requires all of their customers to
31
-------
comply with their safety practices and will routinely inspect customer's
facilities for compliance. This same company offers an annual seminar on safe
storage and handling practices of hydrogen cyanide. This seminar is attended
by customers as well as other producers that license technology from the
sponsoring company (21). Such practices have contributed significantly toward
reducing the risk of an accidental release of hydrogen cyanide.
Release prevention is discussed in the following subsections. More
detailed discussions will be found in a manual on control technologies, part
of this manual series.
5.2 PROCESS DESIGN
Process design involves the fundamental characteristics of the processes
which use hydrogen cyanide. This includes an evaluation of how deviations
from,expected process design conditions might initiate a series of events that
could result in an accidental release. The primary focus is on how the
process is controlled in terms of the basic process chemistry, and the vari-
ables of flow, pressure, temperature, composition, and quantity. Additional
process design issues may include mixing systems, fire protection, and process
control instrumentation. Modifications to enhance process integrity may
result from review of these factors and would involve changes in quantities of
materials, process pressure and temperature conditions, the unit operations,
sequence of operations, the process control strategies, and instrumentation
used.
Table 5-1 shows the relationship between some specific process design
considerations and individual processes described in Section 3 of this manual.
This does not mean that other factors should be ignored, nor does it mean that
proper attention to just the considerations in the table ensures a safe
system. The items listed, and perhaps others, must be properly addressed if a
system is to be safe, however.
32
-------
TABLE 5-1. KEY PROCESS DESIGN CONSIDERATIONS FOR HYDROGEN CYANIDE PROCESSES
Process Design Consideration
Process or Unit Operation
Flow control of hydrogen cya-
nide feed
Mixing
Composition monitoring and
control (including pH)
Temperature sensing and
heating/cooling media
flow control
Adequate pressure relief
Level sensing and control
Corrosion monitoring
All (hydrogen cyanide is almost
always used as the limiting
reactant).
Sodium cyanide reactor, con-
tinuous stirred tank methyl
methacrylate reactor, all
operations where hydrogen cya-
nide is mixed with alkaline or
acidic materials.
Hydrogen cyanide storage ves-
sels, feed to hydrogen cyanide
production process. Should be
considered for all operations
where high concentrations and/or
large quantities of hydrogen
cyanide are used.
All operations where high con-
centrations and/or large quanti-
ties of hydrogen cyanide are used.
Storage tanks, reactors, distil-
lation and stripping columns,
heat exchangers.
Storage tanks, reboilers and
condensers, batch or continuous
stirred tank reactors
All. but especially equipment
exposed to hydrogen cyanide
and mechanical stress at the
same time.
33
-------
5.3 PHYSICAL PLANT DESIGN
Physical plant design includes equipment, siting and layout, and trans-
fer/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 physi-
cal plant design beginning with a discussion of materials of construction.
This section is not intended to provide detailed specifications for the design
of a facility handling hydrogen cyanide. The discussion is intended to be
illustrative, but not comprehensive.
5.3.1 Equipment
Materials of Construction—
The primary concern in selecting the appropriate materials of construc-
tion* is the prevention of major hydrogen cyanide solution spills and preven-
tion of contamination of the hydrogen cyanide.
Anhydrous hydrogen cyanide is generally not considered corrosive. Under
ambient temperatures carbon steel is an acceptable material of construction.
As an example, for storage vessels, one distributor recommends ASTM A516 grade
60 steel that has been acid pickled using a 0.51 H-SO. solution for ten to
twelve hours (3). However, there are conditions under which hydrogen cyanide
will be corrosive to carbon steel. In general carbon steel is only
appropriate for ambient storage of hydrogen cyanide.
Elevated temperatures, the presence of an acid stabilizer, and the
presence of water will all effect the corrosiveness of a hydrogen cyanide
solution. Water solutions of hydrogen cyanide can result in transcrystalline
stress- cracking of carbon steels under stress even at room temperature and in
dilute solution (2). Under more severe conditions of temperature and
pressure, solutions of hydrogen cyanide may also result in stress corrosion
cracking of stainless steels and nickel-chromium and nickel-copper alloys
34
-------
(22). Additionally, water solutions of hydrogen cyanide containing sulfuric
acid as a stabilizer severely corrode carbon steel above 100°F and stainless
steels above 175°F (2).
Austenitic stainless steels resist corrosion by sulfur dioxide-stabilized
hydrogen cyanide and water mixtures at all concentrations and at temperatures
up to the atmospheric boiling point. Types 316 and 317 stainless steels have
greater corrosion resistance than stainless steels without molybdenum (23).
Unstabilized stainless steels should be fully annealed to prevent intergran-
ular attack (23). In higher temperature applications, nickel-chromium and
nickel-copper alloys must be used. Care must be taken for correct material
selection in these situations, since these materials may also be subject to
stress corrosion cracking by hydrogen cyanide.
A number of nonmetallic materials show good resistance to hydrogen
cyanide. Table 5-2 shows a list of plastics and elastomers and their relative
resistance to. chemical attack by aqueous hydrogen cyanide solutions. It is
important to realize that the conditions under which these material were
tested was limited to pure hydrogen cyanide and water mixtures at the temper-
ature indicated on the chart. The addition of other chemical constituents
could effect the corrosion resistance of the material. Higher temperatures
may also effect the performance of these materials. In addition, this table
says nothing about the physical characteristics of these materials. Although
a material may show good chemical resistance it may not have the physical
properties necessary for use in chemical equipment. Only materials that show
excellent chemical resistance to hydrogen cyanide should be considered for use
in a facility that handles the chemical. Actual material selection for a
given application should be done in consultation with a vendor having experi-
ence with hydrogen cyanide systems.
Vessels—
Most hydrogen cyanide is stored in refrigerated atmospheric storage
vessels. Many of the design features for hydrogen cyanide storage tanks
35
-------
TABLE 5-2. CHEMICAL RESISTANCE OF POLYMERS AND ELASTOMERS TO
CHEMICAL ATTACK BY WET HYDROGEN CYANIDE
Material
Resistance to Chemical Attack*
Chlorinated Polyether
Polyvinylidene Fluoride
Polyamide
Polyethylene
Polyimides
Polyphenylene oxide
Polyphenyl sulfide
Polypropylene
Polystyrene
Polysulf one
Polyvinyl chloride (types I & II)
Chlorinated PVC
Polysulfone
Vinylidene Chloride
Epozy Resin
Furan Resin
Phenolic Resin
Polyesters
Vinyl ester
Natural soft rubber
Butadieneacrylonitrile
Butyl rubber
Chloroprene rubber
Chlorosulfonated polyethylene
Polysulfide rubber
Polyurethane elastomer
Excellent at 250°F
Excellent at 275°F
Unacceptable
Good at 150°F
Good at 150°F
Unacceptable
Good at 150°F
Good at 150°F
Good at 150°F
Unacceptable
Excellent at 150°F
Fair at 150°F
Unacceptable
Good at 150°F
Excellent at 150°F
Excellent at 150°F
Excellent at 150°F
Good at 220°F
Fair at 150°F
Good at 150°F
Unacceptable
Good at 150°F
Excellent at 150°F
Excellent at 150°F
Excellent at 150°F
Excellent at 150°F
The materials listed may or may not show similar chemical resistance at
higher temperatures.
36
-------
center around the ability of the chemical to experience polymerization -
decomposition. Because of this, a number of safety features should be incor-
porated into the design of any hydrogen cyanide storage tank. A list of these
items is presented below:
e Tank cooling system;
e Temperature monitoring with high temperature alarm;
e Tank sampling system;
• Grounding connection;
• Level monitoring with alarm;
e Pressure monitoring with high pressure and vacuum alarm;
e Acid addition system;
• Emergency pressure relief; and
• Clean nitrogen supply for maintaining an inert atmosphere
in the tank.
In addition to these features a number of other features should be
considered for a hydrogen cyanide storage tank. Examples include:
e Tank vent with vapor condenser, vent discharge to flare.
scrubber or equivalent treatment device;
• . .
• Second high level alarm;
37
-------
• Dedicated nitrogen supply (for use with hydrogen cyanide
storage only);
• Dike around storage tank; and
• Area monitors that activate deluge system when hydrogen
cyanide is detected.
The cyanide polymerization - decomposition reaction is best detected by a
rise in tank temperature. The second method of detection is color change.
Hydrogen cyanide that has not polymerized has a "straw yellow" appearance.
The color will darken as the reaction occurs until it reaches a dark brown; at
this point the reaction may be proceeding at a dangerous rate. For these
reasons the temperature of a hydrogen cyanide storage tank should be continu-
ously monitored; any increase in temperature should be considered suspect.
Samples should be withdrawn periodically from the storage tank to observe
physical appearance and to test for acidity and water content. One major
distributor recommends that such samples should be withdrawn at least two
times per week (3). Others have suggested that sampling be carried out at
least every twenty four hours (25).
Cooling of a hydrogen cyanide tank can be accomplished by a recirculation
loop with a heat exchanger in the loop or by cooling jackets around the
outside of the vessel. Leakage of some varieties of coolant into the hydrogen
cyanide storage vessel can promote polymerization. For this reason a
recirculation loop may be more appropriate than a jacketed vessel, as it is
easier to inspect the integrity of a single heat exchanger than the jacket on
an entire vessel. Ammonia should never be used as a refrigerant as it can
neutralize the acidic stabilizer in the hydrogen cyanide.
An acid addition tank should be present on storage tanks so that acid can
be added to stabilize a hydrogen cyanide tank where polymerization has been
detected. The acid should not be added directly to the tank, as localized
38
-------
high concentrations of acid can result in violent decomposition of the hydro-
gen cyanide. A system for mixing the acid, either by addition to the recircu-
lation loop or by addition with nitrogen injection should be developed.
Usually the acid addition is designed to be manually operated once the poly-
merization reaction has been detected. However, an automated system to inject
acid based on temperature rise could be developed. Usually, however, there is
ample time to decide whether acid should be added.
The purity of the nitrogen that is "fed to the tank is very important.
Contamination brought in with the nitrogen could result in a polymerization
reaction. Dryers and filters should.be present on all nitrogen supplies.
Additionally, extreme care should be taken to assure that no cross contamina-
tion can occur between the hydrogen cyanide storage tank and other systems
using the same nitrogen supply. The best system in one where the hydrogen
cyanide storage tank has a nitrogen supply that is dedicated for use by the
hydrogen cyanide storage system only.
When the tank is operated at atmospheric pressure extreme care must be
taken to avoid contamination through the vent system. One possible solution
to this is to have a vent system that is used only for the hydrogen cyanide
storage tank. Another method for reducing the potential for vent contamina-
tion would be to continuously feed a small amount of nitrogen into the tank
and out the vent. Whenever a vented storage vessel is used it should be
equipped with a vacuum alarm, as the presence of a vacuum in the tank will
create a reverse flow in the vent and potentially draw air or other forms of
contamination into the tank.
Structurally the tank should be constructed according to a code quality
design. One vendor recommends that atmospheric pressure storage vessels be
designed for 25 psig minimum, with a corrosion allowance of at least 1/16
inch. The tank should be able to withstand vacuum. The tank should have no
bottom outlets. Dip pipes should be of a large enough diameter to prevent
high velocity impact with the bottom of the tank; such impact can result in
39
-------
erosion-corrosion (3). This same vendor provides additional specifications
for tank design.
Vessels such as reactors and heat exchangers that handle hydrogen cyanide
must be designed with many of the same considerations in mind that were listed
above for storage vessels. Protection must be provided against the potential
for polymerization - decomposition. The specific precautions will depend on
the process involved. Release prevention considerations for all vessels
include prevention of overpressure, overfilling, overheating, and corrosion.
Many of the processes that use hydrogen cyanide react the chemical with
an alkaline material at elevated temperatures. In these situations precau-
tions to reduce the risk of polymerization will include adequate, mixing, flow
and composition control and temperature control. Therefore reaction vessels
of this type must be designed with adequate monitoring and backup of one or
all of these parameters.
All vessels that handle hydrogen cyanide must be equipped with adequate
overpressure protection. Where possible the discharge from these overpressure
protection devices should be sent to a protection system such as a scrubber or
flare. Care must be taken to prevent material from other process units from
contaminating the hydrogen cyanide system through the vent system. Over-
pressure protection systems will be discussed in a latter portion of this
manual.
Prevention of overfilling can be accomplished using level sensing de-
vices, pressure relief devices* and adequately trained personnel. Redundant
level sensing devices are often appropriate where hydrogen cyanide is used.
Where a pressure relief device is used as overflow protection, the discharge
from the valve should go to a catch tank. Such a valve should not be used for
overpressure protection, as a valve that is sized to release vapor in the
event of an overpressure will be grossly undersized if it must release liquid
in the event of an overpressure.
40
-------
Because of its flammability, the contents of hydrogen cyanide vessels
should be kept under an inert atmosphere unless process requirements dictate
alternate conditions. This can be done using nitrogen. The inert gas that is
used for such purposes should be filtered and dried. Precautions must be
taken to prevent cross contamination through the nitrogen system, and in some
cases it may be preferable to have a separate nitrogen supply for the hydrogen
cyanide system.
Piping—
The characteristics of hydrogen cyanide that are most important when
designing piping systems are:
• The high acute toxicity of the chemical:
• Its ability to cause stress corrosion cracking; and
• Its ability to polymerize.
The high toxicity of hydrogen cyanide is of concern because even s,mall
leaks in a piping system can be dangerous to operating personnel. Hydrogen
cyanide piping should be constructed with welded connections that are fully
radiographed. The use of flanges should be minimized and threaded fittings
should never be used.
Valves should have a leak-tight gland or be leakproof such as a diaphragm
or bellow-sealed valve. The valve stem seals should be externally adjustable
to stop stem leakage, and the stem should not be removable while the valve is
in service. Excess flow valves should be considered at the inlet and outlet
of hydrogen cyanide vessels.
For maintenance and emergencies, it is often useful to be able to isolate
vessels and other hydrogen cyanide process equipment. Remotely operated
emergency isolation valves should be considered wherever a large release could
prevent access to an isolation valve. In some cases a single valve is
41
-------
insufficient to ensure complete isolation, and the use of slip plates or a
double block and bleed arrangement may be necessary. Because of the potential
for releasing trapped hydrogen cyanide, proper training is essential to ensure
safe operation of these isolation techniques.
Several precautions'must be taken in light of ability of hydrogen cyanide
to cause stress corrosion cracking. Piping, valves and fittings should all be
constructed of 316 stainless steel. Flange nuts and bolts should also be
constructed of a material that is resistant to hydrogen cyanide attack as
fugitive leaks can attack these as well (3). Gaskets should be 316 stainless
steel-graphite spiral-wound or similar type, as these provide more sure leak
protection than asbestos composites. These specifications may not be suffi-
cient for high temperature applications. In such cases hydrogen cyanide
resistant alloys such as inconel may be required.
•Because of stress corrosion, piping equipment that is subject to vibra-
tion, such as near a pump, are of particular concern. Piping should be ade-
quately supported, as stress and vibration over a long period of time will
significantly contribute to the potential for stress cracking. Tees and other
similar fittings should be forged instead of welded as welds are particularly
susceptible to stress cracking.
Polymerization of hydrogen cyanide within a piping system will result in
restricted or blocked flow and can result in an overpressured line; both of
which could contribute to an accidental release. Dead ends or rarely used
sections of piping should be avoided as polymerization can occur where stag-
nant hydrogen cyanide is present. Piping should be well insulated from
exposure to heat. Even warming by the sun on uninsulated piping can contri-
bute to polymerization. Pipe runs should be pitched so that they drain when
flow is stopped. Sections of pipe where liquid hydrogen cyanide could be
trapped by valves should be equipped with overpressure protection. Ball and
plug valves should be designed so that excess pressure in the body will
relieve spontaneously toward the high pressure side. This is accomplished by
42
-------
providing a relief hole in the valve body (or the ball or plug) which bypasses
the upstream seat. Modified valves such as these must indicate the flow
direction on the valve body.
Process Machinery —
Pumps— Many of the concerns and considerations for hydrogen cyanide
piping and valves also apply to pumps. To assure that a given pump is suit-
able for hydrogen cyanide service, the system designer should obtain informa-
tion from the pump manufacturer certifying that the pump will perform properly
in this application.
Wetted parts should be made of 316 stainless steel. Mechanical seals are
preferred over packing for better leak protection. Double mechanical seals
with a barrier fluid provide even better leak protection. In some situations
the potential for a leak may be so undesirable that rotating shaft seals are
not appropriate. Pumps that do not have external rotating shaft seals are,
canned-motor, vertical extended-spindle submersible, magnetically coupled, and
diaphragm pumps (26).
•
Pumps should be equipped with overpressure protection. Positive dis-
placement pumps should have pressure relief that vents to a safe location.
Alternately, positive displacement pumps can be equipped with pump-around
loops. However, because a pump-around loop increases the complexity of the
system, and the number of valves and fittings, it may increase the risk of a
release. By bypassing the pump, the pump-round loop also eliminates the
positive displacement pump as a back flow protection device.
Deadheading a centrifugal pump can also result in a release by overheat-
ing the hydrogen cyanide trapped within the pump. This can result in the
initiation of a polymerization - decomposition reaction within the pump. The
pump seal is very likely to fail under these conditions. One method of
reducing the risk associated with such an event is to install a flammable gas
detector just on the outside of the mechanical seal. The detector could be
-------
connected to a deluge system that could be activated in the event of even a
small release from the pump seal.
Pumps handling cyanide solutions should be located within a curbed or
diked area. Remotely operated shut off valves to stop the flow to a pump
should be considered wherever a release of hydrogen cyanide could prevent
access to the pump.
Pressure Relief Devices—In most cases» emergency pressure relief should
be vented to a treatment device such as a flare or scrubber. In some cases,
venting can be done to a catch tank although sizing the tank in such a situa-
tion may be difficult. A pressure relief valve mounted above a rupture disk
is suitable for hydrogen cyanide overpressure protection. The line below the
relief valve should be continually purged, with nitrogen so as to prevent
plugging the relief line by the vapor phase formation of hydrogen cyanide
polymer. Two valves with rupture disks in parallel are recommended so that
one device can be open to the tank while the other is in service. In such
situations., it is important to interlock the valves that isolate the pressure
relief valves from the process so that only one relief valve can be isolated
from the process at one time.
A relief valve is sized so that in the event of a polymerization -
decomposition reaction, the temperature of the tank contents will be control-
led by the boil off rate of hydrogen -cyanide. Thus, by controlling the
temperature, the rate of polymerization will be controlled at a manageable
level. One vendor suggests that relief devices on hydrogen cyanide storage
tanks be set at 5 psig. This will allow for sufficient heat removal in the
event of a polymerization - decomposition reaction (3). It is difficult to
get a device that can accurately release at this low of a pressure.
In some situations, two-phase flow through the relief valve may be
possible and this must be considered. A thorough understanding of the
kinetics of the hydrogen cyanide polymerization - decomposition reaction is
44
-------
important for sizing the relief device. Vendors of hydrogen cyanide have this
kinetic data and will provide assistance for sizing overpressure protection.
One vendor has combined kinetic data with the data developed by the Design
Institute for Emergency Relief Systems. (DIERS) on two-phase releases to size
relief valves for their customers (27).
Where possible, pressure relief vent and treatment systems on hydrogen
cyanide storage and handling equipment should not be connected to any other
pieces of process equipment. This will help prevent cross-contamination
between systems. A flame arrester may be used in the vent line. However.
such a device should be cleaned frequently to prevent plugging by hydrogen
cyanide polymer.
Instrumentation—Instrumentation should be constructed of materials that
are compatible with hydrogen cyanide service. In many cases wetted materials
can be made of 316 SS or of an elastomer of plastic with hydrogen cyanide
resistance. With the exception of high temperature operations, hydrogen
cyanide is not a severe environment for most instrumentation. However, one
•
concern when using instrumentation with hydrogen cyanide is the potential for
vapor phase polymerization. Such polymer could plug measuring wells or foul
sensors and isolate the instrument from the actual process environment.
Example solutions for this are the use of redundant instruments, the use of
instruments that may be cleaned while in service or the use of nitrogen purge
streams to keep the sensing element free from hydrogen cyanide polymer forma-
tion (a nitrogen purge should be used with caution, as it could adversely
affect the accuracy of some instruments).
5.3.2 Plant Siting and Layout
•
The siting and layout of a particular facility using hydrogen cyanide
requires careful consideration of numerous factors. These include: other
processes in the area, the proximity of population centers, prevailing winds.
local terrain, and potential natural external effects such as flooding. The
45
-------
rest of this subsection describes general considerations which might apply to
siting and layout of facilities that handle hydrogen cyanide.
Siting of facilities or individual equipment items should be done in a
manner that reduces personnel exposure, both plant and public, in the event of
a release. Since there are also other siting considerations, there may be
trade-offs between this requirement and others in a process, some directly
related to safety. Siting should provide ready ingress or egress in the event
of an emergency and yet also take advantage of barriers, either man-made or
natural which could reduce the consequences of releases.
Layout refers to the placement and arrangement of equipment in the
process facility. General layout considerations include:
• Inventories of hydrogen cyanide should be kept away from
' sources of fire or explosion hazard;
• Vehicular traffic should not go too near hydrogen cyanide
process or storage areas if this can be avoided;
• Where such traffic is necessary, precautions should be
taken to reduce the chances for vehicular collisions with
equipment, especially pipe racks carrying hydrogen cyanide
across or next to roadways;
• Hydrogen cyanide piping preferably should not be located
adjacent to other piping which is under high pressure or
temperature;
• Storage facilities should be segregated from the main
process unless the hazards of pipe transport are felt to
outweigh the hazard of the storage tank for site-specific
cases; and
46
-------
* Storage should also be situated away from control rooms.
offices, utilities, storage, and laboratory areas.
Various techniques are available for formally assessing a plant layout
and should be considered when planning high hazard facilities handling hydro-
gen cyanide (28). These techniques provide for a systematic evaluation of key
siting and layout factors.
Because heat increases the tendency of hydrogen cyanide to undergo
polymerization - decomposition, measures should be taken to situate piping.
storage vessels, and other hydrogen cyanide equipment in such a way as to
minimize their exposure to heat. Hot process piping, equipment, steam lines,
and other sources of direct or radiant heat should be avoided.
In the event of an emergency, there should be multiple means of access to
the facility for emergency vehicles and crews. Storage vessel shut off valves
should be readily accessible. Containment for liquid storage tanks can be
provided by diking. Flammable gas detectors and adequate fire protection must
be provided for all portions of the process as hydrogen cyanide is flammable
when mixed with air.
5.3.3 Transfer and Transport Facilities
Transfer and transport facilities where rail tankers are loaded and
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.
Rail car unloading and loading facilities should be equipped with the
following safety and release prevention features:
• Grounding connections for the car and rails;
-------
• A car "come-along" for accurate positioning, wheel chocks,
and derailers for runaway cars;
• Warning signs and lights to identify the area and restrict
access during the loading or unloading;
• High pressure piping and hoses, connectors on hose ends
that are unique for hydrogen cyanide service and that
prevent accidental attachment of the vapor hose to the
liquid line on the car. or the liquid receiving line to
the vapor line of the car;
• Rail car temperature monitor and alarm;
• Deluge system for the rail car area, or at a minimum
, sufficient fire hoses or monitors to act as a deluge in
the even of a spill; and
• Some type of drainage control system that prevents runoff
from a spill from traveling into unwanted areas.
Usually a tank car will be unloaded by applying nitrogen pressure to the
vapor space, thereby pushing the liquid out through the rail car dip tube. As
mentioned previously, nitrogen used for -hydrogen cyanide service must be free
of any contamination. Additionally, back flow protection should also be
provided in the nitrogen line.
In some situations, unloading a tank car will require several hours.
When this is the case, the tank car should be treated as a storage tank with
periodic samples withdrawn from the car to test for the formation of polymer.
Whenever tank cars are loaded or unloaded, written operating procedures should
be developed and enforced.
48
-------
5.4 PROTECTION TECHNOLOGIES
This subsection describes three types of protection technologies for
containment, treatment and neutralization. These are:
• Enclosures;
• Flares; and
• Scrubbers.
A presentation of more detailed information on these systems is planned in
other portions of the prevention reference manual series.
5.4.1 Enclosures
Enclosures refer to containment structures which capture any hydrogen-
cyanide spilled or vented from storage or process equipment, thereby prevent-
t
ing immediate discharge of the chemical to the environment. The enclosures
contain the spilled liquid until it can be transferred to other containment.
discharged at a controlled rate which would not be injurious to people or the
environment* or transferred at a controlled rate to scrubbers for neutraliza-
tion or a flare or incinerator for destruction.
The use of specially designed enclosures for either hydrogen cyanide
storage or process equipment does not appear to be widely practiced. The
location of toxic operations in the open air has been mentioned favorably in
the literature, along with the opposing idea that sometimes enclosure may be
appropriate (29). The desirability of an enclosure depends partly on the
frequency with which personnel must be involved with the equipment. A common
• . .
design rationale tor not having an enclosure where toxic materials are used is
to prevent the accumulation of toxic concentrations of a chemical within a
work area. However, if the issue is protecting the community from accidental
releases, then total enclosure may be appropriate. Enclosures should be
equipped with continuous monitoring equipment and alarms. Alarms should sound
49
-------
whenever lethal or flammable concentrations are detected. Enclosures for
hydrogen cyanide should he equipped with adequate fire protection.
Care must he taken when an enclosure is huilt around" pressurized equip-
ment. It would not he practical to design an enclosure to withstand the
pressures associated with the sudden failure of a pressurized vessel. An
enclosure would probably fail as a result of the pressure created from such a
release and could create an additional hazard. In these situations, it may be
determined that an enclosure is not appropriate. If an enclosure is built
around pressurized equipment then it should be equipped with some type of
explosion protection, such as rupture plates that are designed to fail before
the entire structure fails.
The type of containment structures that could be suitable for hydrogen
cyanide are concrete block or concrete sheet buildings, or bunkers or cor-
rugated metal buildings. An enclosure would have a ventilation system de-
signed to draw in air when the'building is vented to a scrubber or flare.' The
bottom section of a building used for stationary storage containers should be
liquid tight to retain any liquid hydrogen cyanide that might be spilled.
Buildings around rail car unloading stations do not lend themselves well to
effective liquid containment. However, containment could be accomplished if
the floor of the building were excavated several feet below the track level
while the tracks are supported at grade in the center.
While the use of enclosures for secondary containment of hydrogen cyanide
spills or releases is not known to be widely used, it can be considered as a
possible protection technology for areas near especially sensitive receptors.
5.4.2 Flares
Flares are used in the chemical process industries to dispose of inter-
mittent or emergency emissions of hydrogen cyanide waste gases. The flare
50
-------
burns the waste gases, forming carbon dioxide and nitrogen oxides. Flares are
capable of handling larger flow variations than are process combustion devices
such as boilers.
The two common styles are elevated and enclosed ground flares. The
height of an elevated flare (sometimes several hundred feet) is determined by
safety considerations for the surrounding areas because of the high tempera-
tures and heat flux at maximum gas rates. Enclosed ground flares consist of
stages of multiple burner assemblies surrounded by refractory walls and
acoustical insulation. They are generally used for small to medium flow rate
applications. The elevated flare is- used for larger gas flows. Often, an
enclosed ground flare will be used in conjunction with an elevated flare for
economical operation.
A flare system may collect gases from just one source or more often it
may be used to treat gases from multiple sources within a process. Because
most flare systems collect gases from a variety of sources within a plant, gas
compositions and flow rates vary. Many units include venting steps to the
flare system during processing. Overpressurization can also cause relief
valves to vent gases to the flare system. Depending on the size of the flare
system, accidental releases may constitute a large or small fraction of the
instantaneous gas flow. The flow rate under an emergency release from a
vessel could constitute a significant or negligible portion of the total flow
rate to a flare. This would depend on the time interval over which the
release occurred and the flow rate of other materials going to the flare at
the same time. Flare designs range up to and above 2 million pounds per hour.
Several design characteristics of flare systems are important when con-
sidering their use as protection against accidental, chemical releases. The
design of flares is dictated by the desire to:
• Operate the flare safely over a wide range of gas flow-
rates; and
51
-------
• Have acceptable emissions of radiant heat, toxic and
flammable materials* and noise.
A fundamental flare design variable is exit velocity. At maximum flow, the
flame should not leave the burner tip or be blown out. This is achieved by
limiting the exit velocity. A criterion has been recommended by the EPA to
ensure 98 percent destruction efficiency of flared chemicals using a steam
assisted flare (30). The addition of an accidental release discharge to an
existing flare must not cause this maximum flow to be exceeded.
Flares can be useful protection against accidental releases of hydrogen
cyanide. However, because of potentially dangerous secondary hazards, their
use requires a thorough analysis for each specific application.
There are two possible ways a flare system can be used to protect against
accidental releases. The first is to use an existing flare system. The
second is to use a dedicated "emergency" system. In essence, a flare system
is a pipe transporting flammable gases to a flame at the exit. As long as the
flame remains at the end of the pipe, the system operates safely. The flame
can enter the pipe if air or oxygen is present above a certain concentration
in the fuel. In a dedicated flare system, the entire collection network would
have to be continually purged to prevent the risk of an explosion when an
accidental release occurred.
Since the flare collection system operates under a positive pressure
(above atmospheric). release rates from an emergency relief valve will be less
than the same discharge to the atmosphere. In some instances, it is
conceivable that the slight delay in reducing the pressure in a vessel nay
cause tank damage. This may be especially important when rupture disks blow.
A sudden overpressurization of the flare collection system due to a massive
accidental release could damage the pipes or potentially affect the venting of
other process units. Table 5-3 summarizes the factors that need to be
considered to prevent accidental chemical releases when using a flare system.
52
-------
TABLE 5-3. IMPORTANT CONSIDERATIONS FOR USING FLARES TO PREVENT
ACCIDENTAL CHEMICAL RELEASES
« Maximum flow rate - will it cause a flame blowout? Will it cause
mechanical damage due to vibration?
• Possibility of air, oxygen, or other oxidant entering system?
• Is gas combustible - will it smother the flare?
• Will any reactions occur in collection system?
• Can liquids enter the collection system?
• Will liquids flash and freeze, or overload knockout drum?
• Is back pressure of collection system dangerous to releasing vessel?
• Is releasing vessel gas pressure or temperature dangerous to
collection system?
• Will acids or salts enter collection system?
• Will release go to an enclosed ground or elevated flare?
• If toxic is not destroyed, what are the impacts on surrounding
community?
53
-------
The rationale for using flares to protect against accidental chemical
releases is that flaring reduces the effects of an atmospheric emission from a
process vessel. As long as the integrity of the flare system is not compro-
mised, some lessening of the overall environmental impact'would he expected.
It is difficult to estimate the destruction and removal efficiency (ORE) of
flares because of the many variables associated with their operation. Numer-
ous studies have been conducted to determine the operational performance of
flares. EPA has published a set of flare requirements to ensure 98 percent or
greater destruction of the gases (30). In an emergency condition, however,
these conditions might not be met. In a screening study conducted by EPA. a
100 ppm hydrogen cyanide stream was only 85 percent controlled (31).
Because of the variable flow capacity, high flame temperature, capability
for handling a high gas velocity, and usual remote location, using a flare to
prevent accidental chemical releases of hydrogen cyanide can be an effective
technique. Small or isolated vessels in a process which does not require
normal venting of a flammable gas, and that employ relief valves and rupture
disks which may have never been used, are examples of sources that can be
connected to a flare system to prevent accidental releases.
5.4.3 Scrubbers
Scrubbers are a traditional method for absorbing toxic gases from process
streams. These devices can be used to control hydrogen cyanide releases from
vents and pressure relief discharges from storage equipment, process equip-
ment, or secondary containment enclosures.
Hydrogen cyanide discharges could be contacted with an aqueous scrubbing
medium in any of several types of scrubbing devices. An alkaline solution is
recommended to achieve effective absorption because absorption rates with
water alone would require high liquid-to-gas ratios. However, water scrubbing
could be used in a make-shift scrubber in an emergency if an alkaline solution
54
-------
was not available. Typical alkaline solutions for an emergency scrubber would
be calcium hydroxide derived from slaked lime or sodium hydroxide.
Examples of scrubber types that might be appropriate include spray
towers, packed bed scrubbers, and Venturis. Other types of special designs
might be suitable. Whichever type of scrubber is selected, a key considera-
tion for emergency systems is the design flow rate to be used. A conservative
design would use the maximum rate that would be expected from an emergency.
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 continu-
ous 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 hydrogen cyanide 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 dis-
charge 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 particu-
larly important for packed bed scrubbers since there is a maximum pressure
with which the gas can enter the packed section without damaging the scrubber
55
-------
internals. Design of emergency scrubbers can follow standard techniques
discussed in the literature, carefully taking into account the additional
considerations just discussed.
Another approach is the drowning tank, where the hydrogen cyanide vent is
routed to the bottom of a large tank of uncirculating caustic. The drowning
tank does not have the high contact efficiency of the other scrubber types.
However, it can provide substantial capacity on demand as long as the back
pressure of the hydrostatic head does not create a secondary hazard, by
impeding an overpressure relief discharge, for example.
5.5 MITIGATION TECHNOLOGIES
If. in spite of all precautions, a large release of hydrogen cyanide 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 stopped, if this
is possible. The next primary concern is to reduce the consequences of the
released chemical on 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 tech-
nology chosen for a particular chemical depends on the specific properties of
the chemical including its flammability. toxicity. reactivity, and those pro-
perties which determine its dispersion characteristics in the atmosphere.
If a release occurs from a refrigerated, liquid hydrogen cyanide storage
tank, the spilled liquid would heat up to ambient temperature. If the ambient
temperature is above the boiling point of hydrogen cyanide (78.3°F). then heat
transfer from the air and ground would result in rapid vaporization of the-
released liquid. If the ambient temperature is below the boiling point of the
56
-------
hydrogen cyanide then vaporization would be slower but a vapor cloud is still
likely to form. It is 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 liquid include secondary containment systems such as
impounding basins and dikes.
A post-release mitigation effort requires that the source of the release
be accessible to trained plant personnel. Therefore, the availability of
adequate personnel protection is essential. Personnel protection will typi-
cally include such items as portable breathing air and chemically resistant
protective clothing.
5.5.1 Secondary Containment Systems
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 hydrogen cyanide 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 hydrogen cyanide storage facilities
commonly 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; and
57
-------
• A diked area, with a capacity as large as the largest tank
served.
These measures are designed to prevent the accidental discharge of liquid
hydrogen cyanide from spreading to uncontrolled areas.
The most common type of containment system is a low wall dike surrounding
one or more storage tanks. Generally, for hydrogen cyanide, no more than one
tank is enclosed within a diked area to reduce risk. Dike heights usually
range from three to twelve feet depending on the area available to achieve the
required 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, or concrete. Earthen dikes should not be
used to contain hydrogen cyanide spills, as the high acute toxicity of the
chemical requires a high degree of certainty that the containment surface is
impermeable to the spill. Piping should be routed over dike walls, and
penetrations through the walls should be avoided if possible. Vapor fences
may be situated on top of the dikes to provide additional vapor containment.
If there is more than one tank in the diked area, the tanks should be situated
on beams above the mflTi'nrnm liquid level attainable in the impoundment.
A low-wall dike can effectively contain the liquid portion of an acci-
dental release and keep the liquid from entering uncontrolled areas. By
preventing 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 evapora-
tion. 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
protection from wind and will be even more effective at reducing the rate of
evaporation.
A low-wall dike will not reduce the impact of a gaseous hydrogen cyanide
release. If materials that would react violently with hydrogen cyanide are
stored within the same diked area then the dike will increase the potential
58
-------
for mixing the materials in the event of a simultaneous leak. A dike also
limits access to the tank during a spill.
A covered, remote impounding basin is well suited to storage systems
where a relatively large site is available. The flow from the hydrogen
cyanide spill is directed to the basin by dikes and channels under the storage
tanks which are designed to minimize contact of the liquid with other tanks
and surrounding facilities. Because of the high vapor pressure of hydrogen
cyanide and the high acute toxicity, 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
very near the tank area to minimize the amount of hydrogen cyanide that
evaporates as it travels to the basin. The impounding basin could be filled
with water to instantly dilute the liquid hydrogen cyanide as it flows into
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 tne
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.
High-wall impoundments may be a good secondary containment choice for
selected systems. 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 generally be lower for a high wall impoundment than for low wall dikes or
remote impoundments because of the reduced surface .area exposed to the
atmosphere. These rates can be further reduced with the use of insulation on
the wall and floor in the annular space. High impounding walls may be
constructed of low-temperature steel, reinforced concrete, or prestressed
concrete. A weather shield may be provided between the tank and wall with the
annular space remaining open to the atmosphere. The available area
59
-------
surrounding the storage tank will dictate the minimum height of the wall. For
high wall impoundments, the walls may be designed with a volumetric capacity
greater than that of the tank to provide vapor 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 outlet (suction) line will
have to pass through the wall. In such a situation, a low dike encompassing
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 (32). This figure shows hydrogen cyanide vapor
clouds at the time when the farthest distance away from the source is exposed
to concentrations above the IDLE. With diking, the model predicts that
downwind distances up to 720 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 downwind distance. Without diking, the model
predicts that downwind distances up to 2,600 feet from the source could be
exposed to concentrations above the IDLE'. Thirteen 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 may 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
60
-------
•> BO.O
•> BOO.
•> a.ooo«+oa PPM
O.S
miles
1
mile
l.S
miles
2
miles
Release from a tank surrounded by a 25 ft. diameter dike.
Elapsed time: 3 minutes:
Release from a tank with no dike.
Elapsed time: 13 minutes
Common Release Conditions;
Storage Temperature • 40 F
Storage Pressure - 14.7 psia
Ambient Temperature - 85 °F
Wind Speed • 10 mph
Atmospheric Stability Class » C
Quantity Releases = 5,000 gallons
through a 2-inch hole
Figure 5^1.• Computer'model simulation showing the effect of diking on the
vapor cloud generated from a release of refrigerated hydrogen
cyanide.
61
-------
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 storm water sewers would presumably allow any spilled hydrogen
cyanide 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 (33). 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 clay or concrete to prevent the hydrogen
cyanide from seeping into the ground.
•
5.5.2 Flotation Devices and Foams
Other possible means of reducing the surface area of spilled hydrogen
cyanide include placing impermeable flotation devices on the surface or
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. The additional material and disper-
sal equipment costs are a major deterrent to their use.
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 the effects will vary as
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
62
-------
materials, foams have a net positive effect, but with others, foams may
tzaggerate the hazard.
One approach to a hydrogen cyanide spill is dilution with water. Delug-
ing a spill with water will dilute the spill and reduce the vapor generation
rate. A water-based foam provides an alternative means of diluting the
hydrogen cyanide. When a foam cover is first applied, an increase in the
boil-off rate is generally observed which would cause a short-term increase in
the downwind hydrogen cyanide concentration. The initial foam cover may be
destroyed by violent boiling, in which case a second application ia necessary.
Once a continuous 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 vaporization 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 heat transfer from
the foam and by the heat of solution of hydrogen cyanide in water; the warmed
vapor cloud will 'have greater buoyancy and will disperse in an upward direc-
tion more rapidly.
•
The extent of the downwind reduction in concentration will depend on the
type of foam used. Regardless of the type of foam used, the slower the
drainage rate of the foam, the better its performance will be. A slow-
draining foam will spread more evenly, show more resistance to temperature and
pH effects, and collapse more slowly. The initial cost for a slow-draining
foam may be higher than for other foams, but a cost effective system will be
realized in superior performance.
Even if the vaporization rate of hydrogen cyanide is substantially
reduced within a short time after a spill, a vapor cloud will still be formed
which poses a serious threat downwind. Dispersion and/or removal of the
hydrogen cyanide vapor in the atmosphere is the subject of the following
section.
63
-------
5.5.3 Mitigation Techniques for Hydrogen Cyanide Vapor
The extent to which the escaped hydrogen cyanide 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 hydrogen cyanide cloud will be
dependent on a number of factors. These include the physical state of the
hydrogen cyanide 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. Large accidental releases of hydrogen cyanide
may result in the formation of hydrogen cyanide-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 hydrogen cyanide
with water results in the formation of highly toxic hydrocyanic acid which
presents a health hazard to plant personnel.
The spray medium is typically applied to the vapor cloud by means of
hand-held hoses and/or stationary water-spray barriers. Important factors
relating to the effectiveness of spray systems are the distance of the nozzles
from the point of release, the spray pattern, nozzle flow rate, pressure, and
nozzle rotation.
Several techniques have also been developed to effectively disperse toxic
vapor resulting from major leaks in piping and equipment. One such technique
has been developed by Beresf ord (34). Although such a system has not been
used for the mitigation of hydrogen cyanide vapor, they have been effectively
used for other toxic chemicals of similar nature (34). Such techniques are
not applicable to catastrophic failures of equipment, however.
64
-------
The method consists of coarse water sprays discharging upwards from flat
fan sprays and wide-angled spray monitors arranged so that a vent or chimney
effect is created to completely surround the toxic vapor. Results have shown
that the high velocity water droplets induce large volumes of air at ground
level to move upward as the water discharges upwards (34). The air is caused
to move upwards through the chimney formed by the sprays. As the air moves
over the ground, the heavier than air toxic gas is diluted and pushed up and
out of the top of the chimney where it disperses safely. Design details are
presented in Beresford (34). Both types of spray methods are incorporated
into the design since the flat-fan sprays effectively stop the lateral spread
of vapor and the monitors provide the -required air movement for dilution and
dispersal.
Another means of dispersing a vapor cloud is with the use of large fans
or blowers which would direct the vapor away from populated or other sensitive
areas (35). However, this method would only be feasible in very calm weather
and in sheltered areas; it would not be effective in any wind and difficult to
control if the release occupies a large open area. A large, mechanical blower
would also be required which lowers the reliability of this mitigation tech-
nique compared to water fogs and sprays.
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.
5.6 OPERATION AND MAINTENANCE PRACTICES
Quality hardware, contained mechanical equipment, and protective devices
all increase plant safety; however, they must be supported by the safety
policies of management and by constraints on their operation and maintenance.
This section describes how management policy and training, operation, and
maintenance procedures relate to the prevention of accidental hydrogen cyanide
releases. Within the chemical industry, these procedures and practices vary
65
-------
widely because of differences in the size and nature of the processes and
because any determination of their adequacy is inherently subjective. For
this reason, the following subsections focus primarily on fundamental princi-
ples and do not attempt to define specific policies and procedures*
5.6.1 Management Policy
Management is a key factor in the control of industrial hazards and the
prevention of accidental releases. Management establishes the broad policies
and procedures which influence the implementation and execution of specific
hazard control measures. It is important that these management policies and
procedures be designed to match the level of risk in the facilities where they
will be used. Most organizations have a formal safety policy. Many make
policy statements to the effect that safety must rank equally with other
company functions such as production and sales. The effectiveness of any
safety program, however, is determined by a company's commitment to it, as
demonstrated throughout the management structure. Specific goals must be
derived from the safety policy and supported by all levels of management.
Safety and loss prevention should be an explicit management objective.
Ideally, management should establish the specific safety performance measures,
provide incentives for attaining safety goals, and commit company resources to
safety and hazard control. The advantages of an explicit policy are that it
sets the standard by which existing programs can be judged, and it provides
evidence that safety is viewed as a significant factor in company operations.
In the context of accident prevention, management is responsible for
(29.36):
• Ensuring worker competency;
• Developing and enforcing standard operating procedures;
• Adequate documentation of policy and procedures;
66
-------
• Communicating and promoting feedback regarding safety
issues;
• Identification, assessment, and control of hazards; and
• Regular plant audits and provisions for independent
checks.
Additional discussion on the responsibilities of management will be found
in a manual on control technologies, part of this manual series.
5.6.2 Operator Training
The performance of operating personnel is a key factor in the prevention
of accidental chemical releases. Many case studies documenting industrial
incidents note the contribution of human error to accidental releases (29).
Release•incidents may ie caused by using improper routine operating proce-
dures, by insufficient knowledge of process variables and equipment, by lack
of knowledge about emergency or upset procedures, by failure to recognize
critical situations, and in some cases by direct physical mistake (e.g..
turning the wrong valve). A comprehensive operator training program can
decrease the potential for accidents resulting from such causes.
Operator training can include a wide range of activities and a broad
spectrum of information. Training, however, is distinguished from education
in that it is specific to particular tasks. While general education is
important and beneficial, it is not a substitute for specific training. The
content of a specific training program depends on the type of industry, the
nature of the processes used, the operational skills required, the character-
istics of the plant management system, and tradition.
Some general characteristics of quality industrial training programs
include:
67
-------
• 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 upsets, emergencies, and acci-
dental releases; and
• Frequent supplemental training and the use of up-to-date
« training materials.
•
In many instances training is carried out jointly by plant managers and a
training staff selected by management. In others, management is solely
responsible for maintaining training programs. In either case, responsibili-
ties should be explicitly designated to ensure that the quality and quantity
of training provided is adequate. Training requirements and practices can be
expected to differ between small and large companies, partly because of
resource needs and availability, and partly because of differences in employee
turnover.
A list of the aspects typically involved in the training of process
operators for routine process operations is presented in Table 5-4.
Emergency training includes topics such as:
• Recognition of alarm signals;
68
-------
TABLE 5-4. ASPECTS OF TRAINING PROGRAMS FOR ROUTINE PROCESS OPERATIONS
Process goals, economics, constraints, and priorities
Process flow diagrams
Unit operations
Process reactions, thermal effects
Control systems
Process materials quality, yields
Process effluents and wastes
Plant equipment and instrumentation
Equipment identification
Equipment manipulation
Operating procedures
Equipment maintenance and cleaning
Use of tools
Permit systems
Equipment failure, services failure
Fault administration
Alarm monitoring
Fault diagnosis
Malfunction detection
Communications, recordkeeping. reporting
Source: Reference 29.
69
-------
• Performance of specific functions (e.g., shutdown switch-
es);
• Use of specific equipment;
• Actions to be taken on instruction to evacuate;
• Fire fighting; and
• Rehearsal of emergency situations.
Aspects specifically addressed in safety training include (29,36}:
• Hazard recognition and communication,
• Actions to be taken in particular situations.
• Available safety equipment and locations,
• When and how to use safety equipment,
• Use and familiarity with documentation such as,
- plant design and operating manuals,
- company safety rules and procedures,
- procedures relevant to fire, explosion, accident, and
health hazards,
- chemical property and handling information, and
• First aid and CPR.
Although emergency and safety programs typically focus on incidents such
as fires, explosions, and personnel safety, it is important that prevention of
accidental chemical releases and release responses be addressed as part of
these programs.
70
-------
Much of the type of training discussed above is also important for
management personnel. Safety training gives management the perspective
necessary to formulate good policies and procedures, and to make changes that
will improve the quality of plant safety programs. Lees suggests that train-
ing programs applied to managers include or define (29):
• Overview of technical aspects of safety and loss preven-
tion approach.
• Company systems and procedures.
• Division of labor between safety personnel and managers in
with respect to training, and
• Familiarity with documented materials used by workers.
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 a primary
source of accidental release incidents, proper maintenance and modification
practices are an important part of accidental release prevention. Use of a
formal system of controls is perhaps the most effective way of ensuring that
maintenance and modification are conducted safely. In many cases, control
systems have had a marked effect on the level of failures experienced (29).
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.
71
-------
Maintenance permits originate with the operating staff. Permits may be
issued in one or two stages. In one-stage systems, the operations supervisor
issues permits to the maintenance supervisor* who is then responsible for his
staff. Two-stage systems involves a second permit issued by the maintenance
supervisor to his workforce (29).
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, including identification and quantification of failures responsible for
hazardous conditions, failures responsible for downtime, and failures respon-
sible for direct repair costs.
Accidental releases are frequently the result of some aspect of plant
modification. 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. In
these situations, it is important that careful assessment of the modification
results has a priority equal to that of getting the plant on-line.
For effective modification control, there must be established procedures
for authorization, work activities, inspection, and assessment, complete
documentation of changes, including the updating of manuals, and additional
training to familiarize operators with new equipment and procedures (29,34).
Formal procedures, and checks on maintenance and modification practices
must be established to ensure that such practices enhance rather than adverse-
ly affect plant safety. As with other plant practices, procedure development
and complete documentation are necessary. However, training, attitude, and
the degree to which the procedures are followed also significantly influence
plant safety and release prevention.
72"
-------
The use and availability of clearly defined procedures collected in
naintenance and operating manuals is crucial for the prevention of accidental
releases. Well written instructions should give enough information about a
process that the worker with hands on responsibility for operating or main- •
taining the process can do so safely, effectively, and economically. These
instructions not only document the path to the desired results, but also are
the basis for most industrial training programs (37.38). In the chemical
industry, operating and maintenance manuals vary in content and detail. To
some extent, this variation is a function of process type and complexity;
however, in many cases it is a function of management policy. Because of
their importance to the safe operation- of a chemical process, these manuals
must be as clear, straightforward, and complete as possible. In addition.
standard procedures should be developed and documented before plant startup.
and appropriate revisions should be made throughout plant operations.
Operation and maintenance may be combined or documented separately.
Procedures should include startup, shutdown, hazard identification, upset
conditions, emergency situations, inspection and testing, and modifications
(29). Several authors think industrial plant operating manuals should include
(29.36.37.38):
• Process descriptions;
• A comprehensive safety and occupational health section;
• Information regarding environmental controls;
• Detailed operating instructions, including startup and
shutdown procedures;
• Upset and'emergency procedures;
• Sampling instructions;
73
-------
• Operating documents (e.g.. logs, standard calculations);
• Procedures related to hazard identification;
• Information regarding safety equipment;
• Descriptions of job responsibilities; and
• Reference materials.
Plant maintenance manuals typically contain procedures not only for
routine maintenance, but also for inspection and testing, preventive mainte-
nance, and plant or process modifications. These procedures include specific
items such as codes and supporting documentation for maintenance and modifi-
cations (e.g., permits to work, clearance certificates), equipment identifi-
cation and location guides, inspection and lubrication schedules, information
on lubricants, gaskets, valve packings and seals, maintenance stock require-
ments, standard repair times, equipment turnaround schedules, and specific
inspection codes (e.g.. for vessels and pressure systems) (29). Full documen-
tation of the maintenance required for protective devices is a particularly
important aspect of formal maintenance systems.
The preparation of operating and maintenance manuals, their availability.
and the familiarity of workers with their contents are all important to safe
plant operations. The objective, however, is to maintain this safe practice
throughout the life of the plant. Therefore, as processes and conditions are
modified, documented procedures must also be modified.
5.7 CONTROL 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 nay involve numerous combinations of
process design, equipment design, and operational measures, are especially
74
-------
difficult to quantify because they reduce the probability of a release rather
than a physical quantity of chemical. Protective measures are more analogous
to traditional pollution control technologies. Thus they may be easier to
quantify in terms of their efficiency in reducing a quantity of chemical that
could be released.
Preventive measures reduce the probability of an accidental release by
increasing the reliability of process systems operations and equipment.
Control effectiveness can thus be expressed for both of the qualitative
improvements achieved and quantitative improvements as probabilities. Table
5-5 summarizes what appear to be major design, equipment, and operational
measures applicable to the primary hazards identified for the hydrogen cyanide
applications in the U.S. The items listed in Table 5-5 are for illustration
only and do not necessarily represent a satisfactory control option for all
cases. These control options appear to reduce the risk associated with an
accidental release when viewed from a broad perspective. However, there are
undoubtedly specific cases where these control options will not be appropri-
ate. Each case must be evaluated individually. A presentation of more
information about reliability in terms of probabilities is planned in other
volumes of the prevention reference manual series.
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 hydrogen cyanide
storage and process facilities that might be 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 storag'e 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
75
-------
TABLE 5-5. EXAMPLES OF MAJOR PREVENTION AND PROTECTION MEASURES FOR
HYDROGEN CYANIDE RELEASES
Hazard Area
Prevention/Protection
Temperature control of
cyanide manufacturing
reactor
Flov control where acid
stabilizer is added to
hydrogen cyanide.
Flow/composition control
to continuous reactor
using hydrogen cyanide.
Overpressure
Corrosion
Reactor and reboiler
temperatures
Overfilling
Atmosphere releases frc
relief discharges
Storage tank or line
rupture
Redundant temperature sensors;
interlock feed flow to high
temperature signal. Interlock
preheater heating fluid flow to
high temp signal. Pressure relief
valve discharge sent to flare.
Redundant flow control loops; acid
addition line sized to restrict
maximum possible flow.
Redundant flow control loops;
composition monitoring; level
monitoring.
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.
(continued)
76
-------
TABLE 5-5 (Continued)
Hazard Area Prevention/Protection
Human error Increased training and
supervision; use of checklists;
use of automatic systems.
External fire Water sprays to cool exposed
hydrogen cyanide storage vessels;
siting away from other flammables;
storage tank refrigeration systems.
77
-------
TABLE 5-6. ESTIMATED TYPICAL COSTS OF MAJOR PREVENTION AND
PROTECTION MEASURES FOR HYDROGEN CYANIDE RELEASES
Prevention/Protection Measure
Continuous moisture monitoring
Flow control loop
Temperature sensor
Pressure relief
- relief valve
- rupture disk
Interlock system for flow shut-off
pH monitoring
Alarm system
Level sensor
- liquid level gauge
- load cell
Diking (based on a 10.000 gal. tank)
- 3 ft. high
- top of tank height (10 ft.)
Increased corrosion inspection
Capital Cost
(1986 $)
7.500-10.000
4.000-6.000
250-400
1.000-2,000
1,000-1,200
1.500-2.000
7.500-10.000
250-500
1.500-2.000
10,000-15,000
1,200-1,500
7,000-7.500
Annual Cost
(1986 $/yr)
900-1.300
500-750
30-50
120-250
120-150
17*5-250
900-1.300
30-75
175-250
1.300-1.900
150-175
850-900
200-400
Costs shown are for pressure relief device only and do not include other
equipment items such as piping to scrubbers or flares.
78
-------
presents costs for some of the major design, equipment, and operational
measures applicable to the primary hazards identified in Table 5-5 for the
hydrogen cyanide applications in the United States.
5.8.2 Levels of Control
Prevention of accidental releases relies on a combination of techno-
logical, 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 pro-
cedures should be in accordance with applicable codes, standards, and regu-
lations. However, additional measures can be taken to provide extra pro-
tection against an accidental 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.
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.
79
-------
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.
These estimates are for illustrative purposes only. It is doubtful that
any specific installation would find all of the control options listed in
these 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 here. The purpose of these estimates is to illus-
trate the relationship between cost and control, and is not to provide an
equipment check list.
Levels of control cost estimates were prepared for a 29 ton fixed hydro-
gen cyanide storage tank system with a 10.000 gallon capacity and a 2.000 gal.
sodium cyanide reactor system. These systems are representative of storage
and process facilities that might be found in the United States.
5.8.3 Summary 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 hydrogen cyanide storage system
and the sodium cyanide reaction 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 informa-
tion and breakdown for each level of control for both the storage and process
facilities are presented in Tables 5-10 through 5-15.
80
-------
TABLE 5-7. SUMMARY COST ESTIMATES OF POTENTIAL LEVELS OF CONTROLS
FOR HYDROGEN CYANIDE STORAGE TANK AND SODIUM CYANIDE
REACTOR
Systt
Level of
Control
Total Total
Capital Cost Annual Cost
(1986 $) (1986 $/yr)
Hydrogen Cyanide Storage Tank;
29 ton Fixed Storage Tank with
10•000 Gallon Capacity.
Baseline
Level No. 1
Level No. 2
100.000 12,000
141.000 17.000
360.000 43.000
Sodium Cyanide Reactor System
2.000 Gallon Continuous Reactor
Baseline
Level No. 1
Level No. 2
147.000 18.000
221.000 28.000
417.000 51.000
81
-------
TABLE 5-8. EXAMPLE OF LEVELS OF CONTROL FOR HYDROGEN CYANIDE STORAGE TANK
Process: 29 Ton Fixed Hydrogen Cyanj.de Storage Tank - 10.000 gallon
Controls
Baseline
Level No. 1
Level No. 2
Flow:
00
to
Temperature:
Pressure:
Quantity:
Location:
Materials of
Construction:
Single check valve on
tank process feed line.
Temperature indicator and
alarm.
Single pressure relief
valve, vent to flare.
Pressure vacuum recorder
alarm.
Local level indicators and
alarms.
Away from traffic.
flammables. and other
hazardous processes.
Carbon steel.
Add second check valve.
Add remote indicator.
Add second relief valve.
secure non-isolatable.
Vent to flare.
Add remote indicator.
Same
Carbon steel with
increased corrosion
allowance (1/16 inch).
Add a reduced - pressure
device with internal air
gap and relief vent to con-
tainment tank or scrubber.
Add redundant sensors and
alarms.
Add redundant alarms. Add
rupture disks under relief
valves.
Add redundant alarms and
high-low level interlock
shut-off for both inlet
and outlet lines.
Same
Stainless steel. Type 316.
(continued)
-------
TABLE 5-8 (Continued)
Controls
Baseline
Level No. 1
Level No. 2
oo
Vessel:
Piping:'
Process
Machinery:
Enclosures:
Diking:
Release
Protection:
Tank pressure specification: Same
25 psig
Tank pressure Specifica-
tion: 50 psig.
Schedule 40. stainless steel Schedule 80. stainless Schedule 80 Honel*
steel
Type 316 stainless steel Same
submerged pumps.
Same
None
3 ft. high dike
Shared flare system.
None Steel Building
Top of tank height. 10 ft.
Same Dedicated flare system.
Mitigation: None
Foam system.
Same
-------
TABLE 5-9. EXAMPLE OF LEVELS OF CONTROL FOR SODIUM CYANIDE MANUFACTURE
Process: Continuous sodium cyanide reactor
Typical Operating Conditions: - Temperature: 1AO°F
- Pressure: 100 mm Hg
Controls
Baseline
Level No. 1
Level No. 2
Process:
Temperature:
Pressure:
oo
Flow:
Corrosion:
Use of acid stabilizing
system.
Provide temperature control
with remote temperature
indication and alarms.
Provide remote control on
vacuum system with remote
pressure sensing. Single
pressure relief valve to a
shared flare system.
Provide remote flow control
on NaOH and HCN feed
streams and on heating
medium flow control.
Provide periodic visual
inspection.
Composition: None
Operate reactor at a lower
temperature.
Add redundant temperature
sensors and alarms.
Automatic switch to a
cooling system.
Add redundant remote
pressure sensing and
control with alarms. Add
second relief valve. Vent
to shared flare system.
Add redundant flow control
loops.
Add increased monitoring
with periodic ultronsonic
inspection.
Provide periodic testing
for HCN polymer formation
in reactor vessel.
Use of interlocks and
backup cooling systems.
Add backup cooling system.
Add rupture disks under
relief valves. Vent to
dedicated flare.
Add automatic shut-off of
feeds and automatic switch
from heating to cooling
medium.
Add increased monitoring
with more frequent
testing.
Periodic testing for HCN
polymer formation in
reactor vessel and in HCN
feed.
(Continued)
-------
TABLE 5-9 (Continued)
Controls
Baseline
Level No. 1
Level No. 2
OD
Ol
Material of Type 316 stainless
Construction: steel-clad carbon steel.
Vessel: Pressure specification:
Full vacuum. 50 psig
pressure.
Piping: Schedule 40 Type 316
stainless steel.
Process Centrifugal pump. Type 316
Machinery: stainless steel, double
mechanical seal.
Protective Curbing around reactor.
Barrier:
Enclosure: None.
Flare: Shared flare system.
Type 316 stainless
steel-clad carbon steel
with increase corrosion
allowance.
Pressure specification:
Full vacuum. 100 psig
pressure.
Schedule 80 Type 316
stainless steel.
Same.
3 ft. high retaining wall.
None.
Same.
Monel* - clad carbon
steel.
Pressure specification:
Full vacuum. 150 psig
pressure.
Schedule 80 Monel®
Centrifugal pump. Monel*
construction, double
mechanical seal.
Steel building.
Dedicated flare system.
-------
TABLE 5-10. CAPITAL AND ANNUAL COSTS ASSOCIATED WITH BASELINE
HYDROGEN CYANIDE STORAGE SYSTEM
Capital Cost Annual Cost
(1986 $) (1986 $/yr)
Vessels:
Storage Tank 33.000 3.806
Piping and Valves:
Pipework 10.000 1.100
Check Valve* 530 60
Globe Valves (20) 8.100 950
Relief Valve 1.600 190
Process Machinery:
Submergihle Pumps (2) 13.000 1.500
Refrigeration System 22.000 2.500
Instrumentation:
Local Temperature Indicator 1.900 220
Temperature Alarm 380 45
Pressure Gauges (2) 1.485 170
Pressure Alarm . 380 .45
Liquid Level Indicator 1.900 220
Level Alarm .380 45
Flare System: 4.500 520
Diking:
Three-Foot High Concrete Dike 1.300 160
Procedures and Practices:
Visual Tank Inspection (external)
Visual Tank Inspection (internal)
Relief Valve Inspection
Piping Inspection
Piping Maintenance
Valve Inspection
Valve Maintenance
TOTAL COSTS 100.000 12.000
86
-------
TABLE 5-11. CAPITAL AND ANNUAL COSTS ASSOCIATED WITH LEVEL 1
HYDROGEN CYANIDE STORAGE SYSTEM
Capital Cost Annual Cost
(1986 $) (1986 $/yr)
Vessels:
Storage Tank 54.000 6.200
Piping and Valves:
Pipework 15.000 1.800
Check Valves (2) 1.000 120
Globe Valves (20) 8.100 950
Relief Valve (2) 3.900 450
Process Machinery:
Subnergible Pumps (2) 13.000 1.500
Refrigeration System 22,000 2,500
Instrumentation:
Local Temperature Indicator 1.900 220
Remote Temperature Indicator 2.200 260
Temperature Alarm 380 45
Temperature Sensor 380 .45
Pressure Gauges (2) 1.485 170
Pressure Alarm 380 45
Liquid Level Indicator 1.900 220
Remote Level Indicator 2.200 260
Level Alarm 380 45
Flare System: 5.100 590
Diking:
Ten-Foot High Concrete Dike 7.600 880
Procedures and Practices:
Visual Tank Inspection (external)
Visual Tank Inspection (internal)
Relief Valve Inspection
Piping Inspection
Piping Maintenance
Valve Inspection
Valve Maintenance
TOTAL COSTS . 141.000 17.000
87
-------
TABLE 5-12. CAPITAL AND ANNUAL COSTS ASSOCIATED WITH LEVEL 2
HYDROGEN CYANIDE STORAGE SYSTEM
Capital Cost Annual Cost
(1986 $) (1986 $/yr)
Vessels:
Storage Tank ' 240.000 28.000
Piping and Valves:
Pipework 20.000 2.400
Check Valves (2) 1.000 120
Globe Valves (20) 8.100 - 950
Relief Valve (2) 3.900 450
Rupture Disks (2) 1.100 130
Process Machinery:
Subotergible Pumps (2) 13.000 1.500
Refrigeration System 22.000 2.500
Instrumentation:
Local Temperature Indicator 1.900 220
Remote Temperature Indicator 2.200 260
Temperature Alarms (2) 760 90
Temperature Sensor 380 . 45
Pressure Gauges (2) 1.485 170
Pressure Alarms (2) 760 90
Liquid Level Indicator 1.900 220
Remote Level Indicator 2.200 260
Level Alarms (2) 760 90
High-low Level Shutoff 1.900 220
Flare System: 22.000 2.600
Diking:
Three-Foot High Concrete Dike 1.400 160
Enclosures:
Steel Building 10.000 1.200
Procedures and Practices:
Visual Tank Inspection (external)
Visual Tank Inspection (internal)
Relief Valve Inspection
Piping Inspection
Piping Maintenance
Valve Inspection
Valve Maintenance
TOTAL COSTS 360.000 43.000
88
-------
TABLE 5-13. CAPITAL AND ANNUAL COSTS ASSOCIATED WITH
BASELINE SODIUM CYANIDE REACTOR SYSTEM
Capital Cost Annual Cost
(1986 $) (1986 $/yr)
Vessels:
Reactor 84.000 10.000
Heat Exchanger 800 95
Piping and Valves:
Pipework 10.000 1.100
Glove Valves (20) 8.100 950
Relief Valve 1.600 190
Process Machinery:
Centrifugal Pump 6.300 760
Instrumentation:
Remote Temperature Indicator 2.200 260
Temperature Alarm 380 45
Temperature Control:
Controller 1.800 220
Sensor . 380 45
Control Valve 2.700 320
Remote Pressure Indicator 2.200 260
Pressure Alarm 380 45
Flow Control Loops (3):
Controller 5.400 650
Flowmeter 6.800 850
Control Valve 8,400 1.000
Flare System: 4.500 520
Diking:
Curbing Around Reactor 910 110
Procedures and Practices:
Visual Tank Inspection (external)
Visual Tank Inspection (internal)
Relief Valve Inspection
Piping Inspection
Piping Maintenance
Valve Inspection
Valve Maintenance
TOTAL COSTS 147.000 18,000
89
-------
TABLE 5-14. CAPITAL AND ANNUAL COSTS ASSOCIATED WITH
LEVEL 1 SODIUM CYANIDE REACTOR SYSTEM
Vessels:
Reactor
Heat Exchanger
Piping and Valves:
Pipework
Glove Valves (20)
Relief Valves (2)
Process Machinery:
Centrifugal Pump
Instrumentation:
Remote Temperature Indicator
Temperature Alarms (2)
Temperature Sensor
Temperature Control:
Controller
Censor
Control Valve
Temperature Switch
'Remote Pressure Indicators (2)
Pressure Control:
Controller
Sensor
Control Valve
Pressure Alarms (2)
Flow Control Loops (3) :
Controller
Flowmeter
Control Valve
Flare System:
Diking:
Three-Foot High Retaining Wall
Procedures and Practices:
Visual Tank Inspection (external)
Visual Tank Inspection (internal)
Relief Valve Inspection
Piping Inspection
Piping Maintenance
Valve Inspection
Valve Maintenance
TOTAL COSTS
Capital Cost
(1986 $)
153.000
800
10.000
8.100
3.200
6.300
2,200
760
380
1.800
380
2.700
540
4.300
1.800
380
2.700
760
5.400
1.400
8.400
4,500
1.300
221.000
Annual Cost
(1986 $/yr)
18.000
95
1,100
950
380
760
260
90
45
220
45
320
65
520
220
45
320
90
650
850
1.000
520
200
15
60
15
300
120
30
350
28,000
90
-------
TABLE 5-15. CAPITAL AND ANNUAL COSTS ASSOCIATED WITH LEVEL 2
SODIUM CYANIDE REACTOR SYSTEM
Capital Cost
(1986 $)
Annual Cost
(1986 $/yr)
Vessels:
Reactor
Heat Exchanger
Piping and Valves:
Pipework
Glove Valves (20)
Relief Valves (2)
Rupture Disks (2)
Process Machinery:
Centrifugal Pump
Instrumentation:
Remote Temperature Indicator
Temperature Alarms (2)
Temperature Sensor
Temperature Control:
Controller
Sensor
Control Valve
Temperature Switch
Remote Pressure Indicators (2)
Pressure Control:
Controller
Sensor
Control Valve
Pressure Alarms (2)
Flow Control Loops (3):
Controller
Flowmeter
Control Valve
Flow Interlock Systems (2)
Flare System:
Diking:
Three-Foot High Retaining Wall
300.000
790
18.700
8.500
3,400
1.100
9.300
2.200
780
350
1.800
390
2.800
SAO
4.300
1.800
390
2.800
780
5.400
7,000
8.400
3.900
22.000
1.600
36.000
95
2,200
950
380
130
1.100
260
90
45
220
45
3,20
65
520
220
45
320
90
650
850
1.000
430
2.600
200
(Continued)
91
-------
TABLE 5-15 (Continued)
Capital Cost Annual Cost
(1986 $) (1986 $/yr)
Enclosure:
Steel Building - 8.400 1.000
Procedures and Practices:
Visual Tank Inspection (external)
Visual Tank Inspection (internal)
Relief Valve Inspection
Piping Inspection
Piping Maintenance
Valve Inspection
Valve Maintenance
TOTAL COSTS 417,000 51.000
92
-------
5.8.4 Equipment Specifications and Detailed Costs
Equipment specifications and details of the capital cost estimates for
the hydrogen cyanide storage and the sodium cyanide reactor systems are
presented in Tables 5-16 through 5-23.
5.8.5 Methodology
Format for Presenting Costs Estimates—
Tables are provided for control schemes associated with storage and
process facilities for hydrogen cyanide 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
comparison of costs for specific items, different levels, and different
systc
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
the system. Depending on the specific equipment item involved, the direct
capital cost was available or was derived from uninstailed 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
93
-------
TABLE 5-16. EQUIPMENT SPECIFICATIONS ASSOCIATED WITH
HYDROGEN CYANIDE STORAGE SYSTEM
Equipment Itc
Equipment Specification
Reference
VESSEL:
Storage tank
PIPING & VALVES
Pipework
Check Valve
Globe Valve
Relief Valve
Reduced
Pressure Device
Rupture Disk
PROCESS
MACHINERY:
Submerged Pump
Baseline: 10.000 gal. ASTM AS16 grade 60
carbon steel* 25 psig rating
Level #1: 10.000 gal. carbon steel with
1/8 inch corrosion protection.
25 psig pressure rating
Level #2: 10.000 gal.. Type 316
stainless steel. 50 psig
pressure rating
Baseline: 100 ft. of 2 in. Schedule 40
Type 316 stainless steel
Level II: 100 ft. of 2 in. Schedule 80
Type 316 stainless steel
Level #2: 100 ft. of 2 in. Schedule 80
Monel»
2 in. vertical lift check valve.
stainless steel construction
2 in. ANSI Class 300. Type 316 stainless
steel body
1 in. z 2 in., ANSI Class 300 inlet and
outlet flange, angle body, closed bonnet
with screwed cap. Type 316 stainless
steel body and trim
Double check valve type device with
internal air gap and relief valve
1 in. Type 316 stainless steel and carbon
steel holder
Type 316 stainless steel, submergible
pump. 100 gpm capacity
39. 40.
41. 42
43
40. 44
39. 40.
44
40
39
39. 41.
45
39, 46
(Continued)
94
-------
TABLE 5-16 (Continued)
Equipment Item
Equipment Specification
Reference
INSTRUMENTATION
Local Tempera-
ture Indicator
Remote Tempera-
ture Indicator
Temperature
Sensor
Temperature
Alarm
Pressure Gauge
Pressure Alarm
Level Alarm
Level Indicator
High-Low Level
Shut-off
Thermocouple, thermowell. and electronic
indicator /recorder
Transmitter and associated electronic
indicator/recorder
Thermocouple and associated thermowell
Indicating and audible alarm
Diaphragm sealed. Type 316 stainless
steel diaphragm. 0-100 psig rating
Indicating and audible alarm
Indicating and audible alarm
Electrical differential pressure type
indicator
Solenoid valve, switch and relay system
39. 40.
47
39. 47
39. 40.
47
40. 46.
48
39. 40.
47
40. 46.
48
40. 46.
48
39. 46
39. 40.
46. 47
ENCLOSURE:
Building
DIKING:
Level #2: 26-gauge steel walls and roof,
door, ventilation system
Baseline: 6 in. concrete walls, 3 ft.
high
Level #1: 10 in. concrete walls, top of
tank height (10 ft.)
46
46
(Continued)
95
-------
TABLE 5-16 (Continued)
Equipment Item Equipment Specification Reference
FLARE: Baseline and Level #1: Elevated flare' 49
system based on a release rate
of 4,600 Ib/hr and a shared
system with a total of five
units
Level #2: Elevated flare system based on
above flow-rate and a
dedicated unit for only this
storage facility
96
-------
TABLE 5-17. MATERIAL AND LABOR COSTS ASSOCIATED WITH BASELINE HYDROGEN CYANIDE STORAGE SYSTEM
vO
1986 Dollars
•
Vessels:
Storage Tank
Piping and Valves:
Pipework
Check Valve
Globe Valves (20)
Relief Valve
Process Machinery:
Submergible Pumps (2)
Refrigeration System
Instrumentation:
Local Temperature Indicator
Temperature Alarm
Pressure Gauges (2)
Pressure Alarm
Liquid Level Indicator
Level Alarm
Flare System:
Diking:
Three-foot High Concrete Dike
TOTAL COSTS
Materials
Cost
15,000
3.800
300
5.000
1.000
6.000
10.000
1.000
200
800
200
1.000
200
2.000
390
47.000
Labor
Cost
•
6.800
2.600
50
500
50
2.600
4.500
250
50
200
50
250
50
1.000
510
20.000
Direct
Costs
22.000
6.400
350
5.500
1.100
8.600
14.500
1.250
250
1.000
250
1.250
250
3.000
900
97.000
Indirect
Costs
7.700
2.200
130
1.900
380
3.000
5.000
440
90
350
90
440
90
1.100
320
23.000
Capital
Cost
33.000
10.000
530
8.100
1.600
13,000
22.000
1.900
380
1.485
380
1.900
380
4.500
1.300
100.000
-------
TABLE 5-18. MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 1 HYDROGEN CYANIDE STORAGE SYSTEM
vO
00
1986 Dollars
Vessels:
Storage Tank
Piping and Valves:
Pipework
Check Valves (2)
Globe Valves (20)
Relief Valves (2)
Process Machinery:
Submergible Pumps (2)
Refrigeration System
Instrumentation:
Local Temperature Indicator
Remote Temperature Indicator
Temperature Alarm
Temperature Sensor
Pressure Gauges (2)
Pressure Alarm
Liquid Level Indicator
Remote Level Indicator
Level Alarm
Flare System:
Diking:
Ten-foot High Concrete Dike
TOTAL COSTS
Materials
Cost
25.000
5.000
600
500
2.500
6.000
10.000
1.000
1.200
200
200
800
200
1.000
1.200
200
3.000
2.200
65.000
Labor
Cost
11.000
5.200
100
500
100
2.600
4.500
250
300
50
50
200
50
250
300
50
1.400
2.900
30.000
Direct
Costs
36.000
10.200
700
5.500
2.600
8.600
14.500
1.250
1.500
250
250
1.000
250
1.250
1.500
250
3.400
5.100
95.000
Indirect
Costs
13.000
3.600 -
250
1.900
900
3.000
5.000
440
530
90
90
350
90
440
530
90
1.200
1.800
33.000
Capital
Cost
54.000
15.000
1.000
8.100
3.900
13.000
22.000
1.900
2.200
380
380
1.485
380
1.900
k 2.200
380
5.100
7.600
141. OOO
-------
TABLE 5-19. MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 2 HYDROGEN CYANIDE STORAGE SYSTEM
vO
vO
1986 Dollars
Vessels:
Storage Tank
Piping and Valves:
Pipework
Check Valves (2)
Globe Valves (20)
Relief Valves (2)
Rupture Disks (2)
Process Machinery:
Submergible Pumps (2)
Refrigeration System
Instrumentation:
Local Temperature Indicator
Remote Temperature Indicator
Temperature Alarms (2)
Temperature Sensor
Pressure Gauges (2)
Pressure Alarms (2)
Liquid Level Indicator
Remote Level Indicator
Level Alarm (s)
High-Low Level Shutoff
Flare System:
Diking:
Three-Foot High Concrete Dike
Enclosures:
Steel Building
TOTAL COSTS
Materials
Cost
110.000
8.000
600
5.000
2.500
650
6.000
10.000
1.000
1.200
400
200
800
400
1.000
1.200
400
1.000
10.000
390
4.600
165.000
Labor
Cost
50.000
5.000
100
500
100
75
2.600
4.500
250
300
100
50
200
100
250
300
100
250
5.000
520
2.300
73.000
Direct
Costs
160.000
14.000
700
5.500
2.600
725
8.600
14.500
1.250
1.500
500
250
1.000
500
1.250
1.500
500
1.250
15.000
910
6.900
238.000
Indirect
Costs
56.000
5.000
250
1.900
900
260
3.000
5,000
440
530
180
90
350
180
440
530
180
440
5.300
320
2.400
84.000
Capital
Cost
24.000
20.000
1.000
8.100
3.900
1.100
13.000
22.000
1.900
2.200
760
380
1.485
760
1.900
2.200
760
1.900
22.000
1.400
10.000
360.000
-------
TABLE 5-20. EQUIPMENT SPECIFICATIONS ASSOCIATED WITH
SODIUM CYANIDE REACTOR SYSTEM
Equipment Item
Equipment Specification
Heat Exchanger
PIPING AND VALVES:
Pipework
Globe Valve
Relief Valve
Rupture Dish
PROCESS MACHINERY:
Centrifugal Pump
carbon steel, full vacuum -
50 psig rating
Level #1: Same as baseline with added
corrosion allowance and full
vacuum - 100 psig rating
Level #2: 2.000 gal. Monel* clad carbon
steel, full vacuum - 150 psig
rating
Type 316 stainless steel construction.
20 ft. of surface area, shell and tube
type
Baseline: 100 ft. of 2 inch Schedule
Type 316 stainless steel
Level #1: 100 ft. of 2 inch Schedule 80
Type 316 stainless steel
Level #2: 100 ft. of 2 inch Schedule 80
Monel*
2 in. ANSI class 300. Type 316 stainless
steel body
1 in. z 2 in. ANSI class 300 inlet and
outlet flange, angle body, closed bonnet
with screwed cap. Type 316 stainless
steel body and trim
1 in. Type 316 stainless steel and carbon
steel holder
Baseline and Level #1: Single stage.
100 gpm capacity. Type 316 stainless
steel construction, double mechanical
seal
Level #2: Same as above except Monel«
construction
Reference
VESSEL:
Reactor
Baseline: 2.000 gal.
stainless
Type 316
steel-clad
•
39.
41.
40.
42
39
43
39. 40.
44
40
39. 41.
45
40. 50
(Continued)
100
-------
TABLE 5-20 (Continued)
Equipment Item
Equipment Specification
Reference
INSTRUMENTATION:
Local Temperature
Indicator
Remote Temperature
Indicator
Temperature Sensor
Temperature Alarm
Temperature
Control Loop
Temperature Switch
Pressure Control
Loop
Remote Pressure
Indicator
Flow Control Loop
Flow Interlock
System
DIKING:
Thermocouple, thermowell. and electronic 39* 40, 47
indicator
Transmitter and associated electronic 39, 47
indicator
Thermocouple and associated thermowell 39. 40, 47
Indicating and audible alarm 34, 46, 48
PID controller, 2 in. globe control valve 39. 47
of stainless steel construction, and
temperature sensor
Two-stage switch with independently set 39. 47
actuation
PID controller. 2 in. globe control valve 39, 47
of stainless steel construction, pressure
sensor
*
Transducer, transmitter, and electronic 39. 47
indicator
PID controller. 2 in. globe control valve 39, 47
of stainless steel construction.
flowmeter
Solenoid valve, switch, and relay system 39, 40, 46
Baseline: 0.5 ft. high concrete curbing 46
Level II & 2: 3 ft. high concrete
retaining wall
(Continued)
101
-------
TABLE 5-20 (Continued)
Equipment Item Equipment Specification Reference
ENCLOSURE: Level f2: 26 gauge steel walls and roof, 46
door, ventilation system
Flare: Baseline and Level fl: Elevated flare 49
system based on a total release rated
5.000 Ib/hr and a shared system with
a total of five units.
Level #2: Same as above except that
system is dedicated only to this
system
102
-------
TABLE 5-21. MATERIAL AND LABOR COSTS ASSOCIATED WITH BASELINE SODIUM CYANIDE REACTOR SYSTEM
o
OJ
1986 Dollars
Vessels:
Reactor
Heat Exchanger
Piping and Valves:
Pipework
Globe Valves (20)
Relief Valve
Process Machinery:
Centrifugal Pump
Instrumentation:
Remote Temperature Indicator
Temperature Alarm
Temperature Control:
Controller
Sensor
Control Valve
Remote Pressure Indicator
Pressure Alarm
Flow Control Loops (3):
Controller
Flowmeter
Control Valve
Flare System:
Diking:
Curbing Around Reactor
TOTAL COSTS
Materials
Cost
40.000
500
3.800
5.000
1.000
3.000
1.200
200
1.000
200
1.500
1.200
200
3.000
3,900
4,500
2.000
500
73.000
Labor
Cost
18.000
250
2.600
500
50
1.400
300
50
250
50
375
300
50
750
1.000
1.300
1.000
*
130
28.000
Direct
Costs
58.000
550
6.400
5.500
1.100
4.400
1.500
250
1.250
250
1.875
1.500
250
3.750
4.900
5.800
3.000
630
101,000
Indirect
Costs
15.000
140
2.200
1.900
380
1.100
380
90
320
90
470
380
90
940
1.200
1.500
1.100
160
27.000
Capital
Cost
84.000
800
10,000
8.100
1.600
6.300
2.200
380
1.800
380
2.700
2.200
380
5.400
6.800
8.400
4.500
910
'147,000
-------
TABLE 5-22. MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 1 SODIUM CYANIDE REACTOR SYSTEM
1986 Dollars
Vessels:
Reactor
Heat Exchanger
Piping and Valves:
Pipework
Globe Valves (20)
Relief Valves (2)
Process Machinery:
Centrifugal Pump
Instrumentation:
Remote Temperature Indicator
Temperature Alarms (2)
Temperature Sensor
Temperature Control:
Controller
Sensor
Control Valve
Temperature Switch
Remote Pressure Indicators (2)
Pressure Control:
Controller
Sensor
Control Valve
Pressure Alarms (2)
Materials
Cost
73,000
500
3.800
5.000
2.000
3.000
1.200
400
200
1.000
200
1.500
300
2.400
1.000
200
1.500
400
Labor
Cost
33.000
250
2.600
500
100
1.400
300
100
50
250
50
375
75
600
250
50
375
100
Direct
Costs
106.000
550
6.400
5.500
2.200
4.400
1.500
500
250
1.250
250
1.875
375
3.000
1.250
250
1.875
500
Indirect
Costs
27,000
140
•
2.200
1.900
760
1.100
380
180
90
320
90
470
95
760
320
90
470
180
Capital
Cost
153.000
800
10.000
8.100
3.200
6.300
2.200
760
380
1.800
380
. 2.700
540
' 4.300
1.800
380
2.700
760
(Continued)
-------
TABLE 5-22 (Continued)
o
en
1986 Dollars
Flow Control Loops (3):
Controller
Flowmeter
Control Valve
Flare System:
Diking:
Three-Foot High Retaining
TOTAL COSTS
Materials
Cost
3.000
3.900
A.500
2.000
Wall 900
112.000
Labor
Cost
750
1.000
1.300
1.000
230
45.000
Direct
Costs
3.750
4.900
5.800
3.000
1.130
157.000
Indirect
Costs
940
1.200
1.500
1.100
290
42.000
Capital
Cost
5.400
1.400
8.400
4.500
1.300
221.000
-------
TABLE 5-23. MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 2 SODIUM CYANIDE REACTOR SYSTEM
o
cr>
1986 Dollars
Materials
Cost
Vessels:
Reactor 146.000
Heat Exchanger
Piping and Valves:
Pipework
Globe Valves (20)
Relief Valves (2)
Rupture Disks (2)
Process Machinery:
Centrifugal Pump
Instrumentation:
Remote Temperature Indicator
Temperature Alarms (2)
Temperature Sensor
Temperature Control:
Controller
Sensor
Control Valve
Temperature Switch
Remote Pressure Indicators (2)
Pressure Control:
Controller
Sensor
Control Valve
Pressure Alarms (2)
500
8.000
5.000
2.000
650
4.500
1.200
400
200
1.000
200
1.500
300
2.400
1.000
200
1.500
400
Labor
Cost
66.000
250
5.000
500
100
75
2.000
300
100
50
250
50
375
75
600
250
50
375
100
Direct
Costs
210.000
550
13.000
5.500
2.200
725
6.500
1.500
500
250
1.250
250
1.875
375
3.000
1.250
250
1.875
500
Indirect
Costs
53.000
140
.
3.300
1.900
760
260
1.600
380
180
90
320
90
470
95
760
320
90
470
180
Capital
Cost
300.000
790
18.700
8.500
3.400
1.100
9.300
2.200
780
350
1.800
390
2.800
• 540
4.300
1.800
390
2.800
780
(Continued)
-------
TABLE 5-23 (Continued)
1986 Dollars
Flow Control Loops (3):
Controller
Flowmeter
Control Valve
Flow Interlock Systems (2)
Flare System:
Diking:
Three-Foot High Retaining Wall
Enclosure:
Steel Building
TOTAL COSTS
Materials
Cost
3.000
3.900
4.500
2.000
10.000
900
4.600
206.000
Labor
Cost
750
1.000
1.300
500
5.000
230
1.200
86.000
Direct
Costs
3.750
4.900
5.800
2.500
15.000
1.130
5.800
292.000
Indirect
Costs
940
1.200
1.500
880
3.800
290
1.500
75.000
Capital
Cost
5.400
7.000
8.400
3.900
22.000
1.600
8.400
417.000
-------
TABLE 5-24. FORMAT FOR TOTAL FIXED CAPITAL COST
Item No. Item Cost
1 Total Material Coat
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
B Total Fixed Capital Cost Items (5 + 6 + 7),
aFor storage facilities, the indirect cost factor is 0.35. For process
facilities, the indirect cost factor is 0.25.
bFor storage facilities, the contingency cost factor is 0.05. For process
facilities, the contingency cost factor is 0.10.
108
-------
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.
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 hydrogen cyanide
process and storage facilities using the best costs for available sources.
The primary sources of cost information are Peters and Timmerhaus (39).
Chemical Engineering (51). and Valle-Riestra (52) 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
component costs.
109
-------
TABLE 5-25. FORMAT FOR TOTAL ANNUAL COST
Item No. Item Cost
1 Total Direct Cost —
2 Capital Recovery on Equip- 0.163 x Item 1
merit Items*
3 Maintenance Expense on 0.01 x Item 1
Equipment Items
4 Total Procedural It*
5 Total Annual Cost Items (2-1-3 +4)
a8ased on a plant life of ten years and an interest rate of ten percent.
110
-------
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 esti-
mates 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 reason-
able source of preliminary cost information for the facilities covered. *
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 re-
ported 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 costs indices as shown in the following equation:
111
-------
, , ^ new base year index
new base year cost = old base year cost x .
old base year index
The Chemical Engineering (CE) Plant Cost Index was used in .updating cost for
this 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) were determined using the following equation from Peters and
Timmerhaus (39):
Cost = [50(Weight of Vessel in Pounds)~°*34]
The vessel weight is determined using appropriate design equations as given by
Peters and Timmerhaus (39) which allow for wall thickness adjustments for cor-
rosion 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 (39). The vessel costs are updated using cost factors. Final-
ly 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 (43). A simplified approach is used in which it is
assumed that a certain length of piping containing a given number of valves.
.112
-------
flanges, and fittings is contained in the storage or process facility. The
data presented by Tamartino (43) permit cost determinations for various
lengths, sizes, and types of piping systems. Using these factors, a repre-
sentative estimate can b.e obtained for each of the storage and process facili-
ties.
Diking—Diking costs were estimated using Mean's manual (46) for re-
inforced 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 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 (46) for
both reinforced concrete and steel-walled buildings. The buildings are
assumed to 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 an'd a
metal door. The steel building has 26-gauge roofing and siding and metal
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.
Flares—Flare costs were estimated using the following equation from
Vatavuk (49) based on the use of an elevated flare system for a high Btu gas
system.
Costs = 288 [Mass flow rate of gas]0*398 .
A release rate of '4.600 Ib/hr was assumed for the storage vessel and an
appropriate rate was determined for the process system based on the quantity
of hazardous chemical present in the system at any one time. For the sodium
113
-------
cyanide reactor system, a release rate of 1.000 Ib/hr was assumed. In ad-
dition* the shared systems were based on a combined discharge for five identi-
cal units. The dedicated system was based on a single unit. The costs pre-
sented 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 (39)
and Valle-Riestra (52). 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.
114
-------
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. 41
Reduced Pressure Device Ref. 38
Check Valves Ref. 38
Globe Valves Ref. 38
Relief Valves Ref. 38
Rupture Disks Ref. 38
•
PROCESS MACHINERY:
Centrifugal Pump 0.43
Gear Pump 0.43
INSTRUMENTATION:
All Instrumentation Items 0.25
ENCLOSURES: Ref. 44
DIKING: Ref. 44
SCRUBBERS: 0.45
115
-------
SECTION 6
REFERENCES
1. Chemical Profile. Hydrogen Cyanide. Chemical Marketing Reporter.
Schnell Publishing Company Inc., June 4, 1984.
2. Mark, Herman F.. Othmer, Donald F.. Overberger, Charles G., Seaborg.
Glenn T. Kirk-Othmer Encyclopedia of Chemical Technology. 3rd edition.
Volume 7. John Wiley & Sons, 1983.
3. Hydrogen Cyanide Storage and Handling. E.I. du Pont de Nemours &
Company, Incorporated. Wilmington. OE. 1983.
4. Dean, J. (ed.). Lange's Handbook of Chemistry. Twelfth Edition.
McGraw-Hill Book Company. New York, NY. 1979.
5. Chemical Emergency Preparedness Program Interim Guidance. Chemical Pro-
files. 2 volumes. U.S. Environmental Protection Agency. Washington, DC,
December 1985.
6. Tatken, R.L. and Lewis. R.J. (ed.). Registry of Toxic Effects of
Chemical Substances. (RTECS). 1981-82 edition. 3 volumes. NIOSH Contract
No. 210-81-8101. DHHS (NIOSH) Publication No. 83-107. June 1983.
7. U.S. Patent No. 3.360.335.
8. U.S. Patent No. 3.718.731.
9. U.S. Patent No. 3,104.945.
10. U.S. Patent No. 3.215.495.
11. U.S. Patent No. 2.680.761.
12. U.S. Patent No. 3.496.215.
13. U.S. Patent No. 3,536.748.
14. Lawler, G.M. (ed.). Chemical Origins and Markets. Fifth Edition.
Chemical Information Services, Stanford Research Institute. 1977.
15. Methyl Methacrylate. 1983 Petrochemical Handbook Issue. Hydrocarbon
Processing, Gulf Publishing Company. Houston. TX. November 1983.
16. Methyl Methacrylate. 1979 Petrochemical Handbook Issue. Hydrocarbon
Processing, Gulf Publishing Company, Houston. TX, November 1979.
116-
-------
17. U.S. Patent No. 2.537.814.
18. Strong Outlook for Cyanuric Chloride. Chemical and Engineering News.
July 26. 1976.
19. U.S. Patent No. 2.762.798.
20. U.S. Patent No. 2.993.754.
21. HCN Safety Symposium. E.I. DuPont DeNemours and Company. Memphis, TN.
22. McNaughton. K.J. (ed.). Materials Engineering I: Selecting Materials
for Process Equipment. McGraw-Hill Publications Company, New York. NY,
1980.
23. Metals Handbook Ninth Edition. Volume 3. American Society for Metals.
Metals Park. OH. 1980.
24. Harper. C.A. (ed.). Handbook of Plastics and Elastromers. McGraw-Hill
Book Company. New York. NY. 1975.
25. Telephone conversation between D.S. Davis of Radian Corporation and a
representative of Monsanto Corporation. St. Louis. MO. January 1987.
26. Green. D.W. (ed.). Perry's Chemical Engineer's Handbook. 6th edition,
McGraw-Hill Book Company. New York. NY. 1984. • .
27. Telephone conversation between D.S. Davis of Radian Corporation and a
representative of E.I. DuPont DeNemours and Company. Memphis. TN.
January 1987.
28. Lewis. D.J. The Mond Fire, Explosion and TozLcity Index Applied to Plant
Layout and Spacing. Loss Prevention, Volume 13. American Institute of
Chemical Engineers, 1980.
29. Lees, Frank P. Loss Prevention in the Process Industries. Volumes 1 & 2.
Butterworths. London. England, 1983.
30. Federal Register. Volume 50. April 16, 1985. pp. 14.941-14.945.
31. Pool. J.H. and Soelberg, N.R. Evaluation of the Efficiency of Industrial
Flares: Flare Head Design and Gas Composition. EPA-600/2-85-106 (NTIS
PB86-100559). Energy and Environmental Research Corporation, September
1985.
32. Radian Notebook No. 215. EPA Contract 68-02-3994. Work Assignment 94,
Page 5. 1986.
33. Darts. J.J. and D.M. Morrison. Refrigerated Storage Tank Retainment
Walls. Chemical Engineering Progress Technical Manual. Volume 23. Ameri-
can Institute of Chemical Engineers. New York, NY, 1981.
117
-------
34. Beresford. T.C. The Use of Water Spray Monitors and Fan Sprays for Dis-
persing Gas Leakage. I. Chen. E. Symposium Proceeding. The Containment
and Dispersion of Gases by Water Sprays, Manchester. England. 1981.
35. McQuaid. J. and A. P. Roberts. Loss of Containment - Its Effect and Con-
trol, in Developments '82 (I. Chem. E. Jubilee Symposium). London. Eng-
land. April 1982.
36. Chemical Manufacturers Association. Process Safety Management (Control
of Acute Hazards). Washington. DC. May 1985.
37. Stus. T.F. On Writing Operating Instructions. Chemical Engineering.
November 26. 1984.
38. Burk. A.F. Operating Procedures and Review. Presented at the Chemical
Manufacturers Association Process Safety Management Workshop. Arlington.
VA, May 7-8, 1985.
39. Peters. M.S. and K.D. Timmerhaus. Plant Design and Economics for Chemi-
cal Engineers. McGraw-Hill Book Company. New York. NY. 1983.
40. Richardson Engineering Services. Inc. The Richardson Rapid Construction
Cost Estimating System, Volume 1-4, San Marcos. CA. 1986.
•
41. Pikulic. A. and H.E. Diaz. Cost Estimating for Major Process Equipment.
Chemical Engineering. October 10, 1977.
42. Hall, R.S., J. Mat ley, and K.J. McNaughton. Cost of Process Equipment.
Chemical Engineering. April 5. 1982.
43. Yarmartino. J. Installed Cost of Corrosion - Resistant Piping. Chemical
Engineering. November 20, 1978.
44. Telephone conversation between J.D. Quass of Radian Corporation and a
representative of Mark Controls Corporation. Houston, TX, August 1986.
45. Telephone conversation between J.D. Quass of Radian Corporation and a
representative of Fike Corporation. Houston. TX. August 1986.
46. R.S. Means Company, Inc. Building Construction Cost Data, (44th Ed.)
Kingston, MA. 1986.
47. Liptak, B.C. Cost of Process Instruments. Chemical Engineering. Seotem-
ber 7, 1970. *
48. Liptak, B.C. Control - Panel Costs, Process Instruments. Chemical Engi-
neering, October 5, 1970.
49. Vatavuk. W.M. and R.B. Neveril. Cost of Flares. Chemical Engineering
February 21. 1983.
118
-------
50. Green. D.W. (ed.). Perry's Chemical Engineers' Handbook (Sixth Edition).
McGraw-Hill Book Company. New York. NY. 1984.
51. Coat indices obtained from Chemical Engineering. McGraw-Hill Publishing
Company. New York. NY. June 1984, December 1985. and August 1986.
52. Valle-Riestra. J.F. Project Evaluation in the Chemical Process Indus-
tries. McGraw-Hill Book Company. New York. NY. 1983.
119
-------
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.
Assessment; The process whereby the hazards which have been identified, are
evaluated in order to provide an estimate for the level of risk.
Containment/control; A system to which toxic emissions from safety relief
discharges are routed to be controlled. A caustic scrubber and/or flare can
be containment/control devices. These systems may serve the dual function of
destrueting continuous process exhaust gas emissions.
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.
120
-------
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.
Identification; The recognition of a situation, its causes and consequences
relating to a defined potential, e.g. Hazard Identification.
Mild steel; Carbon steel containing a maximum of about 0.25Z carbon. Mild
steel is satisfactory for use where severe corrodants 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.
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.
Primary Containment; The containment provided by the piping, vessels and
machinery used in a facility for handling chemicals under normal operating
conditions.
121
-------
Probability/potential; A measure* either qualitative or quantitative, that an
event will occur within some unit of time.
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.
Qualitative Evaluation; Assessing the risk of an accidental release at a
facility in relative terms; the end result of the assessment being a verbal
•
description of the risk.
Quantitative Evaluation; Assessing the risk of an accidental release at a
facility in numerical terms; the end result of the assessment being some type
of number reflects risk, such as faults per year or mean time between failure.
Reactivity; The ability of one chemical to undergo a chemical reaction with
another chemical. Reactivity of one chemical is always measured in reference
to the potential for reaction with itself or with another chemical. A chemical
is sometimes said to be "reactive", or have high "reactivity", without
reference to another chemical. Usually this means that the chemical has the
ability to react with common materials such as water, or common materials of
construction such as carbon steel.
Redundancy; For control systems, redundancy is the presence of a second piece
of control equipment where only one would be required. The second piece of
equipment is installed to act as a backup in the event that the primary piece
of equipment fails. Redundant equipment can be installed to backup all or
selected portions of a control system.
122
-------
Risk; The probability that a hazard may be realized at any specified level in
a given span of time.
Secondary Containment; Process equipment specifically designed to contain
material that has breached primary containment before the material is released
to the environment and becomes an accidental release. A vent duct and
scrubber that are attached to the outlet of a pressure relief device are
examples of secondary containment.
Toxicity; A measure of the adverse health effects of exposure to a chemical.
123
-------
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:
Velocity:
Viscosity:
To Convert From
in
ft
in2
*t?
*3
ft3
gal
Ib
short ton (ton)
short ton (ton)
atm
mm Hg
. psia
psig
OJ
°C
Btu/lb
Btu/lbmol
kcal/gmol
Btu/lb-9F
lb/ft3
Ib/gal
oz/gal
quarts /gal
gal /min
ga^/day
ft /min
ft /min
ft/sec
centipoise (CP)
To
cm
9
cm*
»5
cm3
m3
m3
kg
Mg
metric ton (t)
kPa
kPa
kPa
kPa*
«c*
K*
kJ/kg
kJ/kgmol
kJ/kgmol
kJ/kg-°C
kg/»3
kg/<
kg/m3
cm3/*3
m./min
m3/day
m /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)+14.696]
i(6.895)
(5/9)x(«F-32)
8C+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.
124
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
. REPORT NO.
EPA-6007 8-87-034J
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Prevention Reference Manual: Chemical Specific,
Volume 10: Control of Accidental Releases of
Hydrogen Cyanide
B. REPORT DATE
September 1987
6. PERFORMING ORGANIZATION CODE
'. AUTHOR(S)
D. S. Davis, G. B. DeWolf. and J. D. Quass
B. PERFORMING ORGANIZATION REPORT NO.
DCN 87-203-024-98-35
I. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
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; 11/86 - 6/87
14. SPONSORING AGENCY CODE
EPA/600/13
is.SUPPLEMENTARY NOTES AEERL project officer is T. Kelly Janes. Mail Drop 62B, 919/541
2852.
i*. ABSTRACT
repOrt discusses the control of accidental releases of hydrogen cya-
nide (HCN) to the atmosphere. HCN has an IDLH (immediately dangerous to life and
health) concentration of 50 ppm. making it an acute toxic hazard. Reducing the risk
associated with an accidental release of HCN involves identifying some of the poten-
tial causes of accidental releases that apply to the process facilities that use HCN.
The 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 example preven-
tion, protection, and mitigation measures are provided. The accidental release of a
toxic chemical at Bhopal, India, in 1984 was a milestone in creating an increased
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 Bhopal. These same portions of the industry have made ad-
vances in this area. Interest in reducing the probability and consequences of acciden-
tal toxic chemical releases that might harm workers within a process facility and
people in the surrounding community prompted this and other similar manuals.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lOENTIPIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution _ Maintenance
Hydrogen Cyanide Cost Estimates
Accidents
Emission
Toxicity
Design
Pollution Control
Stationary Sources
Accidental Releases
13 B
07B
13 L
14G
06T
05E
05 A, 14 A
8. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (Thit Report)
Unclassified
21. NO. OF PAGES
132
20. SECURITY CLASS (Thispage)
Unclassified
22. PBICE
Form 2230-1 (».731
125
------- |