xvEPA
United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
EPA/600/8-87/034k
. August 1987
Research and Development
Prevention Reference
Manual: Chemical
Specific
Volume 11. Control of
Accidental Releases of
Ammonia
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EPA/600/8-87/034k
August 1987
PREVENTION REFERENCE MANUAL:
CHEMICAL SPECIFIC:
VOLUME 11: CONTROL OF ACCIDENTAL
RELEASES OF AMMONIA
by:
D.S. Davis
G.B. DeWolf
J.D. Quass
M. Stohs
Radian Corporation
Austin, Texas 78766
Contract No. 68-02-3994
Work Assignment 94
EPA Project Officer
T. Kelly Janes
Air and Energy Engineering Research Laboratory
Research Triangle Park. North Carolina 27711
AIR AND ENERGY ENGINEERING RESEARCH LABORATORY
OFFICE Of RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NC 27711
U.S. .
Region 5, L1>vary (o:-L~j .,
230 S. Deer-born Street, &co:a ICV'O
Chicago, IL $0604
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NOTICE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
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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.
Ammonia has an IDLH (Immediately Dangerous to Life and Health) concen-
tration of 500 ppm. which makes it an acute toxic hazard. Reducing the risk
associated with an accidental release of ammonia involves identifying some of
the potential causes of accidental releases that apply to the process facil-
ities that use ammonia. 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 prac-
tices, prevention, protection and mitigation technologies, and operation and
maintenance practices. Conceptual cost estimates of example prevention,
protection, and mitigation measures are provided.
ACKNOWLEDGEMENTS
This manual was prepared under the overall guidance and direction of T.
Kelly Janes, Project Officer, with the active participation of Robert P.
Hangebrauck, William J. Rhodes, and Jane M. Crum, all of U.S. EPA. In
addition, other EPA personnel served as reviewers. Radian Corporation
principal contributors involved in preparing the manual were Graham E. Harris
(Program Manager), Glenn B. DeWolf (Project Director), Daniel S. Davis,
Jeffrey D. Quass. Miriam Stohs, and Sharon L. Wevill. Contributions were also
provided by other staff members. Secretarial support was provided by Roberta
J. Brouwer and others. A special thanks is given to many other people, both
in government and industry, who served on the Technical Advisory Group and as
peer reviewers.
Ill
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TABLE OF CONTENTS
Section Page
ABSTRACT • iii
ACKNOWLEDGEMENTS ill
FIGURES VI1
TABLES ..... . Viii
1 INTRODUCTION '.............. 1
1.1 Background ....................... 1
1.2 Purpose of this Manual 2
1.3 Uses of Anhydrous Ammonia ............... 3
1.4 Contents of this Manual ................ 3
2 CHEMICAL CHARACTERISTICS ...... . .-..-. .• .• ...... 4
2.1 Physical Properties .............. . .< . .< 4
2.2 Chemical Properties and Reactivity . . . .• . . . . ... 7
2.3 lexicological and Health Effects . . . . . . . . . ... 8
3 FACILITY DESCRIPTIONS AND PROCESS HAZARDS ........... 11
3.1 Manufacture . . . . . .• .- .- . . . .' . . . .• . . . . . . 11
3.2 Processing and Consumption .• . .- . . . . . . ..... . 17
3.2.1 Fertilizer Production 17
3.2.2 Nitric Acid Production 27
3.2.3 Recovery of Ammonia from Refinery Waste Water . . 29
3.2.4 The Use of Ammonia in the Production of Resins . 32
3.2.5 The Use of Ammonia as a Refrigerant 34
3.2.6 Neutralization of Acidic Waste Streams with
Ammonia 37
3.2.7 The Manufacture of Hydrogen Cyanide 38
3.2.8 The Manufacture of Hydrazine .......... 41
3.3 Repackaging of Anhydrous Ammonia . . . . .• .• . .• .• . . . 43
3.4 Storage and Transfer . . . . .< .' . .• . .< . .• .• .- . .• .' . 44
3.4.1 Storage ..•.......-..-..-.. 44
3.4.2 Transfer from Tank Cars and Trucks . . . . .- . . 51
3.4.3 Transfer from Storage Vessels . . . . .- .< . .• . . 52
3.4.4 Transporting Ammonia Storage Containers . . .• .• . 53
4 POTENTIAL CAUSES OF RELEASES . .... .< .• . . . .- . .- . . . 54
4.1 Process Causes .......... . . . . . . . . . . . 54
4.2 Equipment Causes 55
4.3 Operational Causes ..-..' . .• .- . .- .• .- . . . .- . .' .• .- 56
5 HAZARDS PREVENTION AND CONTROL .• .- . . . . . . .• .- . .< . . . 58
5.1 General Considerations . 58
5.2 Process Design . .• . ......'.-..•.. 59
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TABLE OF CONTENTS (Continued)
Section Page
5.3 Physical Plant Design .......... . . . . .• . . 59
5.3.1 Equipment • . • . 61
5". 3.2 Plant Siting and Layout ............ . 78
5.3.3 Transfer and Transport Facilities 80
5.4 Protection Technologies ........ . .• . . . . .• . 80
5.4.1 Enclosures . ...... 81
5.4.2 Scrubbers 82
5.5 Mitigation Technologies .... 85
5.5.1 Secondary Containment Systems .......... 86
5.5.2 Flotation Devices and Foams .• ...... 92
5.5.3 Mitigation Techniques for Ammonia Vapor ...... 93
5.6 Operation and Maintenance Practices 95
5.6.1 Management Policy ................ 95
5.6.2 Operator Training ................ 97
5.6.3 Maintenance and Modification Practices ..... 99
5.7 Control Effectiveness 103
5.8 Illustrative Cost Estimates for Controls .... . . . . 104
5.8.1 Prevention and Protection Measures ....... 104
5.8.2 Levels of Control 104
5.8.3 Cost Summaries 108
5.8.4 Equipment Specifications and Detailed Costs . . . 108
5.8.5 Methodology . . . 108
6 REFERENCES 141
APPENDIX A - GLOSSARY ........................ 146
APPENDIX B - TABLE B-l. METRIC (SI) CONVERSION FACTORS . 150
VI
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FIGURES
Number Page
3-1 Conceptual diagram of typical ammonia production process .... 13
3-2 Conceptual diagram of typical ammonium nitrate process .... 20
3-3 Conceptual diagram of typical ammonium sulfate process . . . . 22
3-4 Conceptual of diagram typical diammonium phosphate process .- . .24
3-5 Conceptual diagram of typical urea manufacturing process ... 26
3-6 Conceptual diagram of typical nitric acid production process . 28
3-7 Conceptual diagram of "WWT" waste water treatment process ... 31
3-8 Conceptual diagram of typical acrylonitrile process .• .• . .< .< . 33
3-9 Conceptual diagram of basic vapor compression refrigeration
cycle .' .- . .- .• .- .- .• . .• . ... . .1 . ...... . .• .- . .• . 35
3-10 Conceptual diagram of typical hydrogen cyanide manufacturing
process . . . . . . .• . . .- .• .• . . . 39
3.-11 Conceptual diagram of typical hydrazine manufacturing process . 42
3-12 Conceptual diagram of typical atmospheric refrigerated ammonia
storage system . . ...... .• . 46
5-1 Computer model simulation showing the effect of diking on the
vapor cloud generated from a release of liquified ammonia .- . .- 90
Vll
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TABLES
Number Page
2-1 Physical Properties of Anhydrous Ammonia 5
2-2 Exposure Limits for Anhydrous Ammonia ...... . . . . . . . . 9
2-3 Predicted Human Health Effects of Exposure to Various
Concentrations of Anhydrous Ammonia ................ 10
3-1 Anhydrous and Aqueous Ammonia Products .... . . . ........ 18
5-1 Some Process Design Considerations for Processes Involving Anhydrous
Ammonia ........... ....... 60
5-2 Maximum Safe Volume of Liquid Ammonia in Nonrefrigerated Storage
Containers at Various Temperatures .......... 68
5-3 Example of Performance Characteristics for an Emergency Packed Bed
Scrubber for Ammonia 84
5-4 Examples of Major Prevention and Protection Measures for Ammonia
Releases 105
5-5 Estimated Typical Costs of Major Prevention and Protection Measures
for Ammonia Releases ...... 106
5-6 Summary Cost Estimates of Potential Levels of Controls for Ammonia
Storage Tank and Stripper 109
5-7 Example of Levels of Control for Ammonia Storage Tank 110
5-8 Example of Levels of Control for Ammonia Stripper 112
5-9 Estimated Typical Capital and Annual Costs Associated with Baseline
Ammonia Storage System . 114
5-10 Estimated Typical Capital and Annual Costs Associated with Level 1
Ammonia Storage System 115
5-11 Estimated Typical Capital and Annual Costs Associated with Level 2
Ammonia Storage System ............... 117
5-12 Estimated Typical Capital and Annual Costs Associated with Baseline
Waste Water Treatment Ammonia Stripper . . 119
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TABLES (Continued)
Number Page
5-13 Estimated Typical Capital and Annual Costs Associated with Level 1
Waste Water Treatment Ammonia Stripper . . . . . . . . . ...... 120
5-14 Estimated Typical Capital and Annual Costs Associated with Level 2
Waste Water Treatment Ammonia Stripper . .......... . . . . 121
5-15 Equipment Specifications Associated with Ammonia Storage System . . 122
5-16 Material and Labor Costs Associated with Baseline Ammonia Storage
System .......................... . . . . 124
5-17 Material and Labor Costs Associated with Level 1 Ammonia Storage
System . -.-....• .- . . . .- .... . 125
5-18 Material and Labor Costs Associated with Level 2 Ammonia Storage
System .............. . . . . . . .• . . . . .' . .• . . 126
5-19 Equipment Specifications Associated with Waste Water Treatment
Ammonia Stripper . . . . . . . . .• .• . . .• . .• . . . . . . . . . . 127
5-20 Material and Labor Costs Associated with Baseline Waste Water
Treatment Ammonia Stripper . . . . . . . . . .• . . .• . . . . . . .• 128
5-21 Material and Labor Costs Associated with Level 1 Waste Water
Treatment Ammonia Stripper ...... . .< . .• .......... 129
5-22 Material and Labor Costs Associated with Level 2 Waste Water
Treatment Ammonia Stripper . . . . . . . . . . . . . . . . . . . . 131
5-23 Format for Total Fixed Capital Cost . . . . .• . .< . . . . . . . . 133
5-24 Format for Total Annual Cost . . . . . . . . . .... . . .... 135
5-25 Format for Installation Costs ........ 140
IX
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SECTION 1
INTRODUCTION
1.1 BACKGROUND
The consequences of a large release of a toxic chemical can be
devastating. This was clearly evidenced by the release of a cloud of toxic
methyl isocyanate in Bhopal, India on December 3, 1984, which killed
approximately 2,000 people and injured thousands more. Prior to this event.
there had been other, perhaps less dramatic, releases of toxic chemicals, but
the Bhopal incident precipitated the recent public concern for the integrity
of process facilities which handle hazardous materials.
Recognizing the fact that no chemical plant is free of all release
hazards and risks, a number of concerned individuals and organizations have
contributed to the development of loss prevention as a recognized specialty
area within the general realm of engineering science. Interest in reducing
the probability and consequences of an accidental release of anhydrous ammonia
prompted the preparation of this manual. This manual is part of a series of
manuals which addresses the prevention and control of a large release of any
toxic chemical. The subjects of the other manuals planned for the series
include
• A user's guide,
• Prevention and protection technologies,
• Mitigation technologies, and
• Other chemical specific manuals such as this one.
The manuals are based on current and historical technical literature, and they
address the design, construction, and operation of chemical process facilities
where accidental releases of toxic chemicals could occur. Specifically, the
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user's guide is intended as a general introduction to the subject of toxic
chemical releases and to the concepts which are discussed in more detail in
the other manuals. Prevention technologies are applied to the design and
operation of a process to ensure that primary containment is not breached.
Protection technologies capture or destroy a toxic chemical involved in an
incipient release after primary containment has been breached but before an
uncontrolled release occurs. Mitigation technologies reduce the consequences
of a release once it has occurred.
Historically, there have been several major releases of anhydrous ammonia
in the past fifteen years involving numerous injuries and a number of fatali-
ties. Primary sources of these releases include pressurized pipeline rup-
tures, failed storage tanks, and road tanker accidents.
1.2 PURPOSE OF THIS MANUAL
The purpose of this manual is to provide technical information about
anhydrous ammonia with specific emphasis placed on the prevention of acciden-
tal releases of this chemical. This manual addresses technological and proce-
dural issues, related to release prevention, associated with the storage,
handling, and process operations involving ammonia. (Note: Throughout this
manual, "ammonia" refers only to anhydrous ammonia and not to aqueous or
"aqua" ammonia.)
This manual is intended as a summary manual for persons charged with
reviewing and evaluating the potential for releases at facilities that use,
store, handle, or generate ammonia. It is not intended as a specification
manual, and the reader is often referred to additional technical manuals and
other information sources for more complete information on the topics dis-
cussed. Other sources of information include manufacturers and distributors
of ammonia in addition to technical literature on design, operation, and loss
prevention in facilities which handle toxic chemicals.
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1.3 USES OF ANHYDROUS AMMONIA
Anhydrous ammonia (NHg) is a significant commodity chemical, produced by
the reaction of hydrogen and nitrogen over a catalyst. The dominant use of
this chemical is in the fertilizer industry which accounts for nearly 80% of
all ammonia produced (1). The direct application of ammonia to the soil is,
in fact, the largest single use of the chemical. The primary industrial uses
of ammonia are as a raw material in the manufacture of nitric acid and as the
starting material in the production of a number of commercially important
synthetic materials.
Numerous references in the technical literature provide information on
both the manufacture and uses of anhydrous ammonia. In addition to the
primary uses mentioned above, ammonia has many other minor uses in a wide
variety of industries. Some of the more common uses include neutralization
(especially the treatment of acidic wastes), extraction, refrigeration, water
purification, the preparation of cleaners and detergents, pulp and paper
manufacture, and food and beverage treatment.
1.4 CONTENTS OF THIS MANUAL
The five sections of this manual present the relevant issues associated
with the prevention of an accidental release of anhydrous ammonia to the
atmosphere. The physical, chemical, and toxicological properties of ammonia
which create or enhance the hazards of an accidental release are presented in
Section 2. In Section 3, the manufacture, consumption, and storage of ammonia
are discussed, and the release hazards associated with these operations are
identified. Next, potential causes of releases, including those identified in
Section 3, are summarized in Section 4. Finally, Section 5 contains detailed
information about hazards prevention and control. Topics included in this
section are process and physical plant designs, protection and mitigation
technologies, operating and maintenance practices, and illustrative costs.
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SECTION 2
CHEMICAL CHARACTERISTICS
This section describes the physical, chemical and toxicological proper-
ties of anhydrous ammonia as they relate to accidental release hazards.
2.1 PHYSICAL PROPERTIES
At atmospheric temperatures and pressures, anhydrous ammonia is a pun-
gent, colorless gas. It may easily be compressed or cooled to a colorless
liquid. Its more important physical and chemical properties are presented in
Table 2-1.
Pure liquid ammonia is lighter than water, and pure gaseous ammonia is
lighter than air. Because of this latter property, a cloud of pure ammonia
gas will be buoyant and rise into the atmosphere. However, depending on the
pressure and temperature, air-ammonia mixtures which are denser than air may
also be formed. For example, air which is adiabatically saturated with
ammonia (6.1 wt%) has a density that is 1.35 times the density of air at
ambient conditions (6). Hence, a saturated air-ammonia mixture may not
disperse very readily and remain close to the ground. Water vapor may also
condense out of an air-ammonia mixture, from the cooling effect of evaporating
ammonia, causing fog. Because of the higher specific gravity of the cooled
air, this fog could spread laterally over the ground (6). Regardless of the
temperature and pressure, all air-ammonia mixtures containing more than 45 wt%
ammonia are lighter than air (6).
Liquid anhydrous ammonia has a large coefficient of expansion. Hence, an
overpressurization hazard exists if storage vessels have insufficient expan-
sion space or if pipelines full of liquid ammonia may be sealed on both ends.
In these situations, thermal expansion of the liquid with an increase in
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TABLE 2-1. PHYSICAL PROPERTIES OF ANHYDROUS AMMONIA
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
07664-41-7
17.03
-28.17 °F @ 14.7 psia
-107.93 °F
0.6815 ® -27.7 °F
0.5970 @ 32 °F
128.8 psia 9 70 °F
log
where:
Pv = A -
B
T+C
Liquid Viscosity
Solubility in Water at
1 a tin, wt. %
Specific Heat at Constant
Volume (vapor)
Pv = vapor pressure, mm Hg
T = temperature. °C
A = 7.36050, a constant
B = 926.132. a constant
C = 240.17, a constant
0.255 cp & -33.5 °C
32 °F 42.8
50 °F 33.1
68 °F 23.4
86 °F 14.1
0.38 Btu/(lb- °F) @ 32 °F
1
1
1
1
1
2
2
3
(Continued)
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TABLE 2-1 (Continued)
Reference
Specific Heat at Constant
Pressure (vapor)
Specific Heat at Constant
Pressure (liquid)
Latent Heat of Vaporization
Liquid Surface Tension
0.5 Btu/(lb-°F) @ 32 °F
1.10 Btu/(lb-°F) @ 32 °F
588.2 Btu/lb @ -27.7 °F
23.4 dynes/cm 0 52 °F
4
1
5
Additional properties useful in determining other properties from physical
property correlations:
Critical Temperature
Critical Pressure
Critical Density
270.32 °F
1639.1 psia
14.66 lb/ft-
1
1
4
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temperature can result in containment failure from the hydrostatic pressure
exerted by the liquid.
The flammahility range of ammonia in air at atmospheric pressure is from
16% to 25% ammonia by volume, while in oxygen the range is from 15% to 79% by
volume (3). Increasing the temperature and pressure of the ammonia broadens
the flammability range. Although the minimum ignition temperature for a
mixture within the flammability limits'is relatively high at 1562 °F (7), it
is possible for ammonia to burn or explode under some conditions such as a
large and intense source of ignition combined with a high concentration of
ammonia gas (8). The presence of oil or a mixture of ammonia with other
flammable substances will also increase the fire hazard. It has further been
reported that the presence of iron appreciably decreases the ignition
temperature (8).
Ammonia is readily absorbed in water to make ammonia liquor (ammonium
hydroxide or aqua ammonia). The dissolution of ammonia in water is accompa-
nied by relatively large heats of solution. Approximately 938 Btu of heat is
evolved when 2.2 Ib of ammonia gas is dissolved in water (3). The solubility
of ammonia in water at various temperatures is given in Table 2-1.
2.2 CHEMICAL PROPERTIES AND REACTIVITY
Pure ammonia is a very stable compound under normal conditions; even
slight dissociation to hydrogen and nitrogen does not occur at atmospheric
pressure until temperatures of 840-930 °F are reached (7). The products of
complete combustion of ammonia are neither toxic nor hazardous, since they are
nitrogen and water.
Ammonia is a highly reactive chemical, forming ammonium salts with
inorganic and organic acids. Ammonia reacts with chlorine in dilute solution
to give chloramines, an important reaction in water purification (3). Because
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of the alkaline characteristics of ammonia it is also used as a neutralizing
agent in a number of processes.
It has been reported that gold, silver, and mercury are each capable of
reacting with ammonia to form explosive compounds (1) . Other explosive
materials which can be formed include metal hydrazides which are produced from
the reaction of alkali metals and liquid ammonia. Acetylides, which are
highly explosive in the dry state, are formed in the presence of ammonia
solutions of copper, mercury or silver salts (1).
Most common metals do not react with dry ammonia. However, when mixed
with very small amounts of water or water vapor, ammonia will vigorously
attack copper, silver, zinc, and many alloys, especially those containing
copper (9).
2.3 TOXICOLOGICAL AND HEALTH EFFECTS
Depending on the concentration, the effects of exposure to ammonia gas
range from mild irritation to severe corrosion of sensitive membranes of the
eyes, nose, throat, and lungs (3). Because of the high solubility of ammonia
in water, it is particularly irritating to moist skin surfaces. A concentra-
tion of 500 ppm has been designated as the IDLH concentration (Immediately
Dangerous to Life and Health), which is based on a 30-minute exposure. Table
2-2 presents a summary of some of the relevant exposure limits for ammonia gas
(10).
The predicted human health effects from increasing concentrations of
ammonia gas are summarized in Table 2-3 (1,3). Because the pungent odor of
ammonia is immediately recognizable at low concentrations, it is highly
unlikely that any individual would become overexposed unknowingly. Ammonia is
not a cumulative metabolic poison; ammonium ions are actually important
constituents of living systems. However, inhalation of high levels of ammonia
gas may have fatal consequences as a result of the spasm, inflammation and
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edema of the larynx and bronchi, chemical pneumonitis and pulmonary edema
(11). Exposure of the eyes to high concentrations may result in ulceration of
the conjunctiva and cornea and destruction of all ocular tissues (11).
Contact of the skin with liquid ammonia may result in severe injury by
freezing the tissue, since liquid ammonia vaporizes rapidly when released to
the atmosphere and will absorb heat from any substance it contacts. If the
skin is moist, it may also cause severe burns from the caustic action of the
ammonium hydroxide produced.
TABLE 2-2. EXPOSURE LIMITS FOR ANHYDROUS AMMONIA
Exposure
Limit
Concentration
(ppm)
Description
Reference
IDLH
500
PEL
50
LCLO
TCLO
30,000
20
The concentration defined as posing 10
an immediate danger to life and health
(i.e., causes irreversible toxic
effects for a 30-minute exposure).
This concentration was determined by 10
the Occupational Safety and Health
Administration (OSHA) to be the
time-weighted 8-hour exposure limit
which should result in no adverse
effects for the average, healthy,
male worker.
This concentration is the lowest 10
published lethal concentration for
a human over a 5-minute exposure.
This concentration is the lowest 10
published concentration causing
toxic effects (irritation).
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TABLE 2-3. PREDICTED HUMAN HEALTH EFFECTS OF EXPOSURE TO VARIOUS
CONCENTRATIONS OF ANHYDROUS AMMONIA (1.3)
Effect
5
20-50
40
100
150-200
400
700
1700
5000-10000
10000
Least perceptible odor
Readily detectable odor
A few individuals may suffer slight eye irritation
Noticeable irritation of eyes and nasal passages after a few
minutes exposure
General discomfort and eye tearing; no lasting effect from
short exposure
Severe irritation of the throat, nasal passages, and upper
respiratory tract
Severe eye irritation; no permanent effect if the exposure
is limited to less than 1/2 hour
Serious coughing, bronchial spasms, burning and blistering
of the skin; less than 1/2 hour of exposure may be fatal
Serious edema, strangulation, asphyxia, rapidly fatal
Immediately fatal
10
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SECTION 3
FACILITY DESCRIPTIONS AND PROCESS HAZARDS
This section contains brief descriptions of the processes and facilities
for the manufacture, consumption, and, storage of anhydrous ammonia in the
United States. The purpose of this section is to identify major hazards
associated with these facilities which may directly or indirectly cause
accidental releases. Measures taken for the prevention of these hazards are
discussed in Section 5.
3.1 MANUFACTURE (3.12)
Anhydrous ammonia is prepared by the reaction of hydrogen and nitrogen
(the "synthesis" or "syn" gas) in the presence of a catalyst at elevated
temperatures and pressures. The manufacturing process consists of three basic
steps: synthesis gas preparation, purification, and ammonia synthesis. The
first step involves the production of hydrogen and the introduction of the
stoichiometric amount of nitrogen. In the second step, catalyst poisons
(carbon dioxide, carbon monoxide, and water) are removed from the synthesis
gas. The third step includes the catalytic fixation of nitrogen at high
temperatures and pressures and recovery of the ammonia. The specific
processes used by the numerous producers of ammonia primarily differ in the
source of hydrogen for synthesis gas and the temperature and pressure of the
ammonia synthesis loop.
The main sources of hydrogen in modern ammonia plants are coal, petroleum
fractions, and natural gas, with the latter being the principal source in
commercial practice. In general, the most economic feedstock has the highest
hydrogen to carbon ratio. The two hydrogen generation techniques used for
processing these raw materials are partial oxidation (reaction with oxygen)
and steam reforming (reaction with steam). Of these, steam reforming is the
11
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more widely used process; partial oxidation processes are employed where
steam-reformable feeds are not available or in special situations where
favorable economic conditions exist.
Figure 3-1 is a typical process diagram for the production of ammonia by
steam reforming. The first step in the preparation of the synthesis gas is
desulfurization of the hydrocarbon feed. This is necessary, because sulfur
poisons the nickel catalyst (albeit, reversibly) in the reformers, even at
very low concentrations. Steam reforming of hydrocarbon feedstock is carried
out in the primary and secondary reformers. The primary reformer is a
refractory-lined furnace which contains vertically suspended tubes filled with
a nickel-based catalyst. In the primary reformer, the feed reacts with steam
to produce hydrogen gas and carbon monoxide. Some of the carbon monoxide also
reacts with steam in the "shift conversion" reaction to produce carbon dioxide
and hydrogen. The secondary reformer is a refractory-lined pressure vessel
which contains additional reforming catalyst. Primary reformer effluent gas
is mixed with air prior to entering the secondary reformer. This serves a
two-fold purpose; it supplies the stoichiometric amount of nitrogen, and
it supplies oxygen for combustion which supplies the heat required for the
reforming reaction.
After passing through waste heat boilers, the syn gas enters the purifi-
cation stage. Regardless of the hydrogen generation technique used, the
unpurified syn gas contains carbon oxides which deactivate the ammonia
synthesis catalyst and must be removed. In the shift converters, carbon
monoxide is catalyticaliy converted to carbon dioxide, which is removed more
easily than CO, and hydrogen gas. The next purification step is the removal
of carbon dioxide. Commercial processes generally involve absorbing the gas
into a solvent under pressure and then recovering the solvent in a stripping
column. The final purification step involves removal of the residual carbon
monoxide and carbon dioxide in a methanator and, in some plants, cryogenic
purification. In the methanator, CO and CO are catalyticaliy converted to
methane which passes through the ammonia synthesis loop as an inert. The
12
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STEAM AIR
NATURAL >
GAS(CH4)C w
DESULrURIZER
AMMONIA
CONDENSER
1
*
LIQUID
NH3
PRIMARY AND
REFORMERS
AMMONIA
CONVERTER
RECYCLE
CO. C02 _ SHIFT
W CONVERTERS W
N2.H2
co2
REMOVAL
1
METHANATOR
& CRYOGENIC
PURIFICATION
Figure 3-1. Conceptual diagram of typical ammonia production process.
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purpose of cryogenic purification is to remove the excess nitrogen added to
the secondary reformer. This is done to avoid excessive loss of hydrogen and
excessive compression costs in the ammonia synthesis loop.
The purified syn gas next flows to the final production stage which is
ammonia synthesis and recovery. The first step is compression of the syn gas.
Synthesis pressures range from 2,000 to 10,000 psi depending on the quality of
the syn gas and certain other conditions, such as production requirements per
converter (12). Almost without exception, all modern large-scale ammonia
plants employ steam-driven centrifugal compressors for synthesis service. One
of the advantages of centrifugal compressors is that a minimal amount of
lubricating oil is required, as this material causes problems in the synthesis
loop. For smaller plants, under 600 tons/day, reciprocating compressors are
still used.
Basically, there are two classes of ammonia converters, tubular and
multiple bed. The tubular bed reactor is limited in capacity to a maximum of
about 544 tons/day (3). In most reactor designs, the cold inlet synthesis gas
flows through an annular space between the converter shell and the catalyst
cartridge. This maintains the shell at a low temperature, minimizing the
possibility of hydrogen embrittlement which can occur at normal synthesis
pressures. The inlet gas is then preheated to synthesis temperature by the
exit gas in an internal heat exchanger, after which it enters the interior of
the ammonia converter which contains the promoted iron catalyst.
Gas recirculation in the ammonia synthesis section is necessary, because
only 9-30 percent conversion is obtained per pass over the catalyst (12). The
synthesis loops are generally of two types. One type recovers ammonia product
after makeup gas-recycle compression and the other recovers ammonia product
before recycle compression. Inerts entering with the makeup gas are removed
with a purge stream. The ammonia is recovered by condensation which requires
refrigeration. Since anhydrous ammonia is readily available, it is normally
used as the refrigerant.
14
-------
Ammonia release hazards in the production process described above occur
in the latter part of the process, specifically in the ammonia synthesis loop,
where ammonia is present in relatively pure form. The types of equipment in
the synthesis loop include large compressors, the ammonia converter, the
ammonia condenser (plus ammonia refrigeration equipment), and the associated
piping and instrumentation. Some previously reported and other possible
causes of equipment failure in this section include the following (13,14):
• Compressors
- severe vibrations on compressor and/or turbine,
- rotor failed,
- compressor thrust collar broke,
- coupling bolts failed,
- compressor seal failed,
- broken blades on turbine,
- reduction gear bearing failed, and
- compressor 0-ring failed.
• Ammonia Converter
- cracking induced by thermal shock,
- hydrogen-induced cracking,
- loss of feed control, and
- overheating of the catalyst bed.
• Heat exchangers (including condensors)
- tube failures, and
- loss of cooling resulting in overpressure.
• Piping and instrumentation
- relief valve did not reseat,
- valve packing was blown,
- improper materials of construction, and
- rupture due to corrosion/erosion effects.
15
-------
Of the four major compressors in ammonia production, the service
performed by the synthesis gas compressor is the most demanding (13). It
discharges at the highest' pressure, requires the most horsepower, has an
intricate seal oil system, has the most compressor/turbine bodies, and
operates at a relatively high speed. If the ammonia is condensed from the
synthesis loop prior to compression of the syn gas, the ammonia content in the
compressor will be relatively low. However, if the ammonia is compressed with
the syn gas prior to recovery, a failure in the syn gas compressor is a
significant release hazard.
Ammonia plants are subjected to a thermal cycle with each shutdown and
start-up. During planned shutdowns, the plant comes down at a slow, control-
led rate. However, other shutdowns are unplanned, and some plants tend to
come down rather quickly in these situations. The effect of rapidly reducing
the process gas temperature in the ammonia converter is the creation of high
thermal stresses. This thermal cycle is a primary cause of surface cracks in
the walls and outlet of the converter (14). A second effect of cooling a
thick-wall component in high-temperature, high-pressure hydrogen service is to
supersaturate the metal with respect to hydrogen. The excess- hydrogen is
trapped in the metal and collects in discontinuities, such as small cracks or
non-metallic inclusion, and exerts pressures high enough to initiate cracks.
Hydrogen-induced cracking may therefore magnify the effect of thermal stress
to produce hazardous internal cracks.
Overheating the ammonia converter could result in uncontrollable
combustion reactions or explosions with the consequent physical breakdown of
the reactor vessel by thermal fatigue or overpressure. Possible causes of
overheating include the following:
• Poor heat distribution within the reactor bed, resulting in hot
spots;
• Overheating raw materials before they enter the ammonia converter;
and
16
-------
• Loss of composition or quantity control of raw material feeds.
The condenser, piping, and instrumentation hazards listed above are not
specific to the ammonia production process. Other possible causes of release
from these components are covered in Section 4. The hazards associated with
the use of ammonia as a refrigerant are discussed in Section 3.2.5.
3.2 PROCESSING AND CONSUMPTION
Because the uses of ammonia in the U.S. are many and diverse, the
processes discussed in this section are limited to those which 1) represent
the primary consumers of anhydrous ammonia. 2) are widespread but not large
consumers of ammonia, or 3) are especially hazardous. Some of the numerous
minor uses of ammonia which are not discussed include the following processes:
manufacture of rubber, water purification, food and beverage treatment, the
production of pulp and paper, the preparation of cleaners and detergents, and
leather and textile treatment.
Ammonia is also used in the manufacture of many important industrial
chemicals which are too numerous to discuss individually. Table 3-1 lists
many of the industrial chemicals produced directly from anhydrous or aqueous
ammonia (15). In many cases, the primary release hazards in the production
processes are associated with the ammonia storage, feed, and recovery systems,
The processes discussed in the following subsections provide specific examples
of the general hazards of ammonia processing, while the specific hazards of
ammonia storage are discussed in Section 3.4.
3.2.1 Fertilizer Production (16.17,18)
The fertilizer industry is, by far, the largest consumer of anhydrous
ammonia in the United States, accounting for 70-80 percent of all ammonia
17
-------
TABLE 3-1. ANHYDROUS AND AQUEOUS AMMONIA PRODUCTS (15)
ammonium acetate
ammonium adipate
ammonium benzoate
ammonium bicarbonate
ammonium bifluoride
ammonium binoxalate
ammonium bisulfate
ammonium bitartrate
ammonium tetraborate
ammonium bromide
ammonium carbonate
ammonium chloride
ammonium citrate
ammonium dichrornate
ammonium fluoride
ammonium fluorosilicate
ammonium gluconate
ammonium iodide
ammonium molybdate
ammonium nitrate
ammonium oxalate
ammonium perchlorate
ammonium picrate
ammonium polysulfide
ammonium salicylate
ammonium stearate
ammonium Slllfate
ammonium sulfide (hydrosulfide)
ammonium tartrate
ammonium thiocyanate
ammonium thiosulfate
ammonium paratungstate
urea
monoammonium phosphate
diammonium phosphate
nitric oxide
acrylonitrile
caprolactam
monomethylamine
dimethylamine
hexamethylenetetramine
trimethylamine
monoethanolamine
diethanolamine
triethanolamine
hydrogen cyanide
fatty nitrogen compounds
(nitriles, amines, quaternary
ammonium compounds)
boron nitride
calcium carbonate (precipitated
from calcium chloride)
hydrazine
hydrogen (high purity)
lead hydroxide
lithium amide
methyl ethyl pyridine
sodamide
sodium cyanide
nitrogen dioxide
nitric acid
18
-------
produced in the past decade. In fact, the largest single use of ammonia is
its direct application as a fertilizer. The ammonia-based fertilizers
produced in the greatest quantity include ammonium nitrate, ammonium sulfate.
ammonium phosphates (mono- and di-). and urea. In addition, nitrogen
solutions and mixed fertilizers are prepared which consist of combinations of
the various products mentioned above along with fertilizers derived from
elements other than nitrogen, e.g., phosphorus.
In the following paragraphs, the processes for the manufacture of the
three ammonium salts and urea are briefly discussed, and the primary process
hazards within the fertilizer industry are identified. In many cases, plants
for the production of ammonia-based fertilizers are integrated with ammonia
plants at the same facility, such that the hazards of ammonia production
presented in the Section 3.1 would also exist at this type of installation.
Ammonium Nitrate—
Ammonium nitrate is produced by the neutralization of nitric acid with
anhydrous ammonia in an atmospheric or pressurized reactor. Figure 3-2 is a
flow diagram of a typical manufacturing process. The reaction of ammonia with
nitric acid is strongly exothermic. The high heat of reaction causes flash
vaporization of water with some ammonia and nitrate going overhead. The
temperature of the solution in the neutralizer is controlled by regulated
addition of the reactants and by removal of the heat. The reactor effluent is
approximately 83 wt% ammonium nitrate. This product can be sold without
further processing, or additional water can be evaporated to produce the salt
in dry form.
The parts of the ammonium nitrate production process which present
ammonia release hazards are between the ammonia feed (storage) tank and the
reaction tank or neutralizer. Release hazards of ammonia storage are
discussed in Section 3.4. The neutralizer is a high hazard area because it
operates at elevated temperatures and pressures, and the neutralization
reaction is extremely exothermic. Potential causes of a release include
loss of feed control and loss of cooling.
19
-------
1
AMMONIA
STORAGE
AMMONIA
VAPORIZER
NEUTRALIZER
N>
O
I
1
EVAPORATOR
PRILL TOWER
OR
CRYSTALLIZER
( AMMONIUM NITRATE
(PRILLS OR CRYSTALS)
NITRIC ACID
Figure 3-2. Conceptual diagram of typical ammonium nitrate process.
-------
Both a loss of feed control and a loss of cooling would result in
overheating of the reactor contents. Overheating may lead to overpressure if
the vessel does not have adequate pressure relief devices, or if they fail to
operate in the correct manner. In addition to causing excessive heat
generation, a loss of feed control may also cause overpressure if the relief
devices fail to activate. Reactor failure (rupture) could result from the
development of temperatures or pressures which exceed design conditions.
Solid and molten NH^NOg can be hazardous under certain conditions, e.g.,
when detonated and/or in the presence of an oxidizable substance. However,
this property does not create a significant ammonia release hazard in the
ammonium nitrate production process, because it is highly unlikely that these
conditions will exist (especially prior to evaporation) in the parts of the
process where ammonia is present. The explosive property of ammonium nitrate
would, however, create a hazard with respect to an ammonia release if the
storage facilities for the dry ammonium nitrate were located in close
proximity to the ammonia storage tank.
Ammonium Sulfate—
Ammonium sulfate is produced by the reaction of by-product ammonia from
various processes with sulfuric acid. Because of the limited number of by-
product ammonia sources, ammonium sulfate is also produced by the neutraliza-
tion of sulfuric acid with synthetic ammonia. (The same principles and
practices are involved in the two procedures, but the synthetic raw materials
give a purer product.) A typical process diagram for the production of
ammonium sulfate from synthetic ammonia is shown in Figure 3-3. Anhydrous
ammonia is dissolved in water and pumped to the neutralizer where it meets a
stream of concentrated sulfuric acid (92-98% H.SO.). The solution of ammonium
sulfate that forms is pumped into double-effect crystallizers. The ammonium
sulfate crystals from the crystallizer are separated by centrifuging or
filtering and are dried.
21
-------
WATER
SULFURIC
ACID
f AQUEOUS f
AMMONIA
STORAGE
AMMONIA
VAPORIZER
AMMONIA
ABSORBER
AMMUIMIA
18-26% __
ta
CENTRIFUGES
AMMONIUM
> SULFATE
CRYSTALS
N)
K>
Figure 3-3. Conceptual diagram of typical ammonium sulfate process.
-------
The ammonia release hazards in this process are only present between the
storage/feed systems and the point where ammonia is absorbed in water to form
the aqueous solution which is fed to the neutralizer. These hazards are not
specific to the ammonium sulfate process and are discussed in other parts of
this manual.
Ammonium Phosphate—
Although ammonium phosphate fertilizers are produced by several methods,
the simultaneous ammoniation and granulation process is, by far, the
predominant method. In this process, a rolling bed of recycled undersized
ammonium phosphate particles is acidified by a spray of phosphoric acid which
is immediately neutralized by ammonia injected beneath the surface of the bed
through fixed spargers. Alternatively, the granulation process can be
combined with a preneutralizer unit in which the phosphoric acid is first
partially neutralized with ammonia in an agitated vessel. This process is
shown in Figure 3-4. The heat of reaction results in a preneutralizer vessel
temperature of about 240 °F and the evaporation of about 20% of the water
present. The hot slurry is sufficiently fluid to be distributed over the
rolling bed in the ammoniator-granulator. In either case, an excess of
ammonia is required in the ammoniator to reach the required N:P.O,- ratio
required. This excess is recovered by scrubbing the ammoniator-granulator
off-gases with the incoming acid.
As in the production of the other two ammonium salts, the ammonia release
hazards are present between the ammonia storage/feed systems and the preneu-
tralizer. The hazards of ammonia storage and handling general to all ammonia
processes (including heat exchangers, piping, and instrumentation) are
discussed in other parts of this manual. As with the ammonium nitrate
process, the neutralization of phosphoric acid is accompanied by a large heat
of reaction, and thus a loss of feed control or reactor cooling could lead to
overheating and/or overpressure, possibly resulting in reactor failure with a
loss of containment of the contents.
23
-------
PHOSPHORIC
ACID
NJ
FINES RECYCLE
Figure 3-4. Conceptual of diagram typical diammonium phosphate process.
-------
Urea—
Urea is indirectly produced by the exothermic reaction of anhydrous
liquid ammonia and gaseous carbon dioxide at elevated temperatures and
pressures. The initial reaction product is ammonium carbamate, which
subsequently decomposes to produce urea and water. Urea plants are always
built in conjunction with ammonia plants, so that both reactants are obtained
from the ammonia synthesis operation.
Figure 3-5 is a typical flow diagram for the production of urea. The
reaction is carried out with an excess (50-100%) of liquid anhydrous ammonia
in a stainless steel- or lead-lined reactor at pressures ranging from
2000-5000 psig and temperatures of 250-380 °F. As the reaction does not go to
completion, the unreacted gases must be separated from the reactor effluent by
heating and decompression, after which they are either recycled to the reactor
or utilized in another process. Total recycle of the reactants is the most
common practice. In this process, the ammonia, carbon dioxide, and ammonium
carbamate are separated from the reactor effluent in the low- and high-pres-
sure decomposers. The low-pressure off-gas is condensed in the low-pressure
absorber, and the liquid is pumped into the high-pressure absorber for
absorption of the high-pressure decomposer gas. Unabsorbed excess ammonia
from the high-pressure absorber is condensed in the ammonia condenser and
recycled to the reactor, as is the concentrated carbamate solution recovered
in the high-pressure absorber. The product stream leaving the decomposers is
about 70% to 80% urea. This product can be used as is, or it can be further
concentrated to a solid product.
In the urea manufacturing process, ammonia is present in relatively pure
form in the ammonia recovery section (condenser and receiver), the feed system
(storage, receiver, pump, and preheater), and the carbamate reactor. Of
these, the reactor presents the only release hazards which are specific to the
urea manufacturing process. Release hazards are significant because of the
25
-------
MAKE - UP NH3
FROM STORAGE
AMMONIA
RECEIVER
AMMONIA
CONDENSER
PUMP AND
PREHEATER
ro
l—*
NH3 -i
C02
HIGH AND LOW
PRESSURE
ABSORBERS
i
REACTOR
UREA
HYDROLYZER
STRIPPER
HIGH AND LOW
PRESSURE
DECOMPOSERS
RECYCLE
CONCENTRATION
EQUIPMENT
UREA MELTER
AND PRILL
TOWER
UREA
PRILLS
Figure 3-5. Conceptual diagram of typical urea manufacturing process.
-------
high temperatures and pressures in the reactor, and because the reaction is
highly exothermic. Therefore, a loss of cooling or feed control could result
in overheating or overpressure with subsequent reactor fracture and the loss
of containment of the reactants. Another hazard arises from the possibility
that there will be an upset in the ammonia process resulting in unacceptable
levels of impurities in the reactants. If, for example, the CO. were to
contain more than about 2% (volume) nitrogen and hydrogen and was somehow
mixed with air. an explosive gaseous mixture may result (19). High tensile
steel is also susceptible to stress corrosion cracking by steam, hot water
chlorides, sulfur compounds, and nitrates.
3.2.2 Nitric Acid Production (17,20)
Nitric acid, a major industrial chemical, is prepared by the oxidation of
ammonia. Although its primary consumption is in the fertilizer industry.
nitric acid is also the starting material for most of the nitrogen compounds
used in the manufacture of explosives, which account for about 4-5 percent of
all ammonia produced, in addition to being a raw material in the production of
a large number of commercially important organic chemicals.
Although the specific operating details vary among the plants which
produce nitric acid, they have in common the following three steps: oxidation
of ammonia to nitric oxide (NO), oxidation of the nitric oxide to the dioxide
(NC^), and absorption of nitrogen oxides in water to produce nitric acid.
Figure 3-6 is a diagram of a typical nitric acid production process.
Ammonia is evaporated and superheated before being mixed with preheated air.
Since the explosive limit of ammonia is approached at concentrations greater
than 12 mol% (at the conditions of this process). the ratio of ammonia to air
in the feed is controlled in the range 9.5-10.5 mol% ammonia. This mixture
flows to the ammonia converter where it is reacted on a platinum-rhodium gauze
pad operating in the ranges of 1472-1760 °F and 0-120 psig. The reaction,
which produces NO and H20. is extremely rapid and goes almost to completion.
27
-------
STACK
AIRl
ro
Qt>
Figure 3-6. Conceptual diagram of typical nitric acid production process.
-------
The NO thus produced undergoes a slow homogeneous reaction with oxygen to
yield nitrogen dioxide. The production of NO. is favored by relatively lower
temperatures (below 300 °F). The hot effluent gas is therefore cooled by heat
exchange with the feed gas and passes through low pressure boilers before
entering the absorption towers. The pressure of the gas and the residence
time in route to the absorption towers can be adjusted to effect the desired
percentage oxidation of the NO. In the absorption towers, which may be spray
towers, packed columns, or plate columns, the gas is scrubbed with weak acid
and water (steam condensate). The normal grades of 45-65% HNO, are produced
directly in the plant; these may be concentrated to 86-99% HNO., (fuming) by
distillation under various conditions.
Ammonia release hazards specific to the nitric acid process are a loss of
cooling or a loss of feed control to the ammonia converter. The realization
of these hazards may result in overheating and/or overpressure of the reactor
causing failure and release of the reactor contents. A loss of feed control
is especially hazardous, because an explosive mixture which exceeds the
flammability limits of ammonia may result.
3.2.3 Recovery of Ammonia from Refinery Waste Water (21,22)
In the petroleum industry ammonia is used as a solvent, a refrigerant, a
corrosion inhibitor, and as a neutralizer of the acidic constituents of oil.
Additionally, in some refineries, it is recovered as a salable product from
sour water. This process is described below; refrigeration and neutralization
processes are discussed in Sections 3.2.5 and 3.2.6, respectively.
Waste waters from several petroleum refining processes contain
appreciable quantities of ammonia. Typical concentrations reported in the
literature range from 3% to 10% by weight. The "WWT Process" is a patented
process for treating these refinery wastes. The process recovers high-purity
ammonia along with hydrogen sulfide and clean water suitable for reuse or for
discharge. The larger WWT units produce more than 50 tons of anhydrous
ammonia per day (21).
29
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A typical WWT Process arrangement is shown in Figure 3-7. The feed
consists of sour water from a degassing unit in which dissolved hydrogen,
methane* and other light hydrocarbons are removed. The feed is pumped through
a feed heater into a reboiler stripper column. In this column, the hydrogen
sulfide is stripped overhead while the ammonia and water are removed as the
bottoms product. The overhead product is high purity hydrogen sulfide which
contains negligible ammonia. The bottoms product goes directly to a second
reboiler stripper column. The bottoms from this column is "clean" water
(typically <50 ppm NH3 and <5 ppm l^S) suitable for many in-plant reuse needs.
while the overhead product is ammonia with small amounts of hydrogen sulfide
and water. These constituents are removed in the ammonia purification section
which consists of one or more scrubbing stages depending on the desired
purity. The ammonia product is then compressed and condensed to salable
anhydrous liquid ammonia. Alternatively, the ammonia product can be produced
as high-purity aqueous ammonia solution which eliminates the need for an
ammonia compressor. Because the ammonia is handled in solution, the
production of aqueous ammonia may be less hazardous than the production of
anhydrous ammonia. If there is no immediate use or sale for the ammonia
recovered from the second stripper, it can be incinerated in a process furnace
or special incinerator.
The potential hazards which may result in a large release of ammonia
liquid or gas involve the latter portion of the process where ammonia is
present in relatively pure form. This section of the process begins with the
overhead product from the second stripper and ends with the final ammonia
product storage. Included are the ammonia stripper and condenser; one or more
#2$ scrubbers; product compressors, condensers and storage facilities; and
associated piping and instrumentation. Process upsets specific to the WWT
Process which may lead to a large release of anhydrous ammonia include:
• Overheating of the ammonia stripper from excess heat to
the ammonia stripper reboiler or a sudden decrease in
ammonia feed; and
30
-------
Hydrogen
Sulfkte
By-Product
Recycle
Deaeraled
Condensate
Degassed »
Sour Water t
Anhydrous
Ammonia to
By-Product
Storage
Stripped
Water
Figure 3-7. Conceptual diagram of "WWT" waste water treatment process.
-------
• Overheating of the ammonia condensers from a loss of
cooling water.
These process upsets could potentially result in equipment failure from
overpressurization. Additional hazards which are associated with the storage
and transfer of anhydrous ammonia are discussed in Section 3.4, while general
causes of equipment failure are discussed in Section 4.0.
3.2.4 The Use of Ammonia in the Production of Resins (16,17,23)
Anhydrous ammonia and ammonia derivatives (e.g., aqueous ammonia, nitric
acid) are used in the production of a variety of resins and fibers. These
resins are subsequently used in the manufacture of many commercially important
products in the synthetic plastics, adhesives, coatings, and textiles
industries. This market consumes between 8 and 10 percent of all ammonia
produced in the U.S. By far, the greatest amounts go to the production of
amino, acrylic, and polyamide (nylon) resins, polyurethanes, and linear
polyesters (17).
The production of acrylonitrile (an acrylic resin) is one process which
uses anhydrous ammonia directly as a reactant. The process, shown schematic-
ally in Figure 3-8, involves reacting a gaseous mixture of propylene, ammonia,
and air in a ratio of 1.4:1.4:10 in the presence of a catalyst. The three
reactants are fed to a fluidized bed reactor operating at a temperature of
750-950 °F and 5-30 psig pressure. The reactor effluent is scrubbed in a
countercurrent absorber, and the organic materials are recovered from the
absorber water by distillation. Hydrogen cyanide, water, light ends, and high
boiling impurities are removed from the crude acrylonitrile by fractionation
to produce specification acrylonitrile product. Because the conversion
obtained on a once-through basis is high, no separation or recycling of
unreacted raw materials is necessary. However, in another commercial process
which does not have a high conversion, the unreacted ammonia is absorbed by a
countercurrent flow of aqueous sulfuric acid to produce ammonium sulfate as a
by-product (16).
32
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Water Off Gas
Water
Crude
HCN
Air
Ammonia
Propytone
Product
Acrytonitrite
Bo
Fe
WB
Reacta
\
rier 1
ed Pri
Her S
r
i
I
i
Absorber
*gh
assure
team
!
Acrytonitrit
Recovery
Column
!
AcetonMrita
Recovery
Column
i
e
uruoe
AcrylonHrile
fc LJohts
Column
f Product
Column
(Recycle)
Crude
' Acetonitrile
Ha
knpu
i
ivy
rities
Figure 3-8. Conceptual diagram of typical acrylonitrile process.
-------
Hazards which may lead to a large release of anhydrous ammonia in the
acrylonitrile production process involve the portions of the process where
ammonia is present in relatively pure form. Because no ammonia recovery is
required, this only includes the section between the storage (feed) tank and
the catalytic reactor. This section contains the storage tank, the ammonia
vaporizer (usually a solenoid valve), feed preheater, piping to the reactor, a
flow controller, and various other instrumentation. Possible causes of a
hazardous release from any of these components are discussed in Sections 3.4
and 4.0. Process upsets, e.g., overheating from a loss of cooling water, are
unlikely to lead to a large release of ammonia unless coupled with another
event such as the loss of ammonia feed control. In the event of a reactor
failure, this situation would allow excess ammonia to vent to the atmosphere.
3.2.5 The Use of Ammonia as a Refrigerant (14,24)
One of the predominant minor uses of ammonia (generally less than 2% of
annual production) is as a refrigerant. Because of its toxic properties,
ammonia is primarily suitable for industrial applications where a refrigerant
leak will not cause occupant discomfort. For this reason also, it is
extremely important that ammonia equipment and piping are arranged so that
components may be easily isolated for repair, replacement, or overhaul.
Anhydrous ammonia is used in vapor compression systems. These systems
vary from simple single-stage refrigeration cycles to complex multistage
compound or cascade cycles depending on the application.
Figure 3-9 shows the basic refrigeration cycle for a single-stage system.
The four basic components are the compressor, condenser, expansion valve, and
evaporator. High pressure liquid ammonia flows from the condenser receiver
through an expansion valve to the evaporator. Here, heat is absorbed from the
fluid to be cooled, and the ammonia boils. The gaseous ammonia is then
34
-------
u>
Ln
Expansion
Valve
Cooling
Medium
Condenser
Evaporator
Product
Cooled
Compressor
Figure 3-9. Conceptual diagram of basic vapor compression refrigeration cycle.
-------
compressed to a temperature and pressure at which the superheated vapor can be
condensed by the cooling media available for use in the condenser. The
refrigeration cycle thus involves two pressures, high and low. to enable a
continuous process which produces the desired cooling effect.
Possible causes of a hazardous release from an ammonia refrigeration
system include the following:
• Overpressurization, and
• Equipment damage.
Failure of the refrigeration compressor stops circulation of refrigerant
through the evaporator. If the flow of the fluid being cooled is not stopped,
the pressure in the evaporator will rapidly rise causing the relief valves to
open. If these valves are not vented to a closed system, ammonia will be
released to the atmosphere. A similar situation can occur if cooling water to
the condenser is lost. Again, relief valves on the condenser would open as
the pressure exceeds the limit.
Catastrophic equipment failure could result in a large release of ammonia
liquid and/or gas. Because refrigeration systems operate at greater than
atmospheric pressure, ammonia will quickly escape from the source of a re-
lease.
The primary cause of refrigeration equipment problems is lack of adequate
precautions during the design, construction and installation of the system
(24). The components of the refrigeration system which are especially vulner-
able to damage from start-up procedures and process upsets include machinery
with moving parts such as pumps and compressors. Abnormally high process
temperatures may occur either during start-up or process upsets. Provision
must be made for this possibility, for it can cause damaging thermal stresses
on refrigeration components and excessive boiling rates in evaporators,
causing liquid to carry over and damage the compressor.
36
-------
It is also important that the system is kept internally clean during
installation. This is because ammonia is a powerful solvent, and dirt, scale,
sand, or moisture remaining in the pipes, valves and fittings will be swept
along with the suction gas to the compressor, where it is potentially harmful
to the bearings, pistons, cylinder walls, valves and lubricating oil. When a
compressor is run for the first time, moving parts are often scratched (24).
Although damage is only minor in the beginning, scratches may progress until
they seriously affect the operation of the compressor or render it inoperative
(24).
3.2.6 Neutralization of Acidic Waste Streams with Ammonia (25)
A variety of industrial processes generate waste streams which are acidic
in nature. For example, sulfuric acid is used in lead-acid battery manufac-
turing processes resulting in waste streams with a pH of around 2 (25).
Regardless of the source, acidic wastes must usually be neutralized prior to
further treatment or discharge. Owing to its alkaline properties, anhydrous
ammonia is often used as the neutralizing agent for these wastes.
The neutralization process itself is relatively simple. In most process-
es, anhydrous ammonia is vaporized through a solenoid valve as it leaves a
pressurized storage tank. The gaseous ammonia flows through carbon steel
piping to a neutralization drum, pit, or tank where it is sparged into the
waste solution. The ammonia may be piped directly into the bottom of the tank
or sent through a vertical feed pipe which is immersed in the solution. The
quantity of ammonia fed is automatically controlled by either wastewater
flowrate or pH.
The hazards associated with the neutralization process primarily involve
the ammonia storage system. These hazards are general to all ammonia facili-
ties and are discussed in Section 3.4. The only other part of the process
where ammonia is present in nearly pure form is the feed system. However, a
failure in this system which causes too much or too little ammonia to be fed
would probably not result in a large release of anhydrous ammonia. A slight
37
-------
overpressurization potential would exist if the neutralization tank were a
closed system without a pressure relief device or had insufficient relief
piping volume to handle any excess gas which is not absorbed in solution.
However, because ammonia is so soluble in water, it would take a rather large
quantity to saturate an aqueous waste stream.
One other consideration in neutralization systems is the use of suitable
materials of construction for the tank and any ammonia piping which comes into
contact with the waste solution. Improper materials of construction may lead
to corrosion and possible equipment failure. The type of container used as
well as the materials of construction will depend on the characteristics of
the waste. A corrosion hazard also exists if precautions are not taken to
prevent backflow of the waste into the carbon steel ammonia piping.
3.2.7 The Manufacture of Hydrogen Cyanide (17)
Anhydrous ammonia is a raw material in the manufacture of hydrogen
cyanide (HCN). This chemical is a colorless, volatile liquid that is highly
flammable and very toxic. All production of HCN in the United States is based
on the continuous catalytic reaction of air, ammonia, and methane.
Figure 3-10 is a block diagram of a typical hydrogen cyanide manufactur-
ing process. In this process, ammonia, methane, and air are preheated to
about 750-950 °F, mixed, and sent to a packed bed reactor. The reactor is
typically packed with a catalytic wire gauze composed of platinum, and a
normal reaction temperature of about 2000-2200 °F is maintained. The gaseous
effluent consists of a mixture of HCN, ammonia, and water vapor. The crude
product mixture flows through an ammonia absorption column where the ammonia
is removed by an ammonium phosphate solution. (Dilute sulfuric acid or
ammonium sulfate may also be used.) The product stream (mostly gaseous HCN)
passes to the product recovery section where it is absorbed in water,
distilled, and treated with sulfur dioxide as an inhibitor to prevent
polymerization. The ammonium phosphate solution is first stripped of HCN,
38
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CO
VO
Figure 3-10. Conceptual diagram of typical hydrogen cyanide manufacturing process.
-------
after which it passes to the ammonia recovery columns. The recovered ammonia
is condensed and recycled as feed to the process.
Hazardous areas of this process with respect to the potential for a large
release of ammonia to the atmosphere (other than the ammonia storage and feed
systems) include the feed gas mixer, the HCN reactor, and the ammonia recovery
columns. Specifically, the following upsets may occur which could lead to
equipment failure and the loss of containment of the reactants:
• Loss of feed gas composition or quantity control;
• Overheating of the reactor; and
• Loss of cooling or heating in the ammonia recovery section.
A loss of feed gas composition is hazardous, because a flammable mixture
of ammonia and air may form which would be especially hazardous in the
presence of methane. In addition to posing an explosion hazard, an incorrect
feed composition or quantity could result in overheating of the reactor,
creating the potential for reactor failure from thermal fatigue or
overpressure. Other possible causes of overheating in the reactor include
poor heat distribution within the reactor bed, resulting in hot spots, and
overheating the raw materials before they enter the reactor. Hot spot
formation within the reactor can result in catalyst breakdown or physical
deterioration of the reactor vessel.
Because the ammonia recovery section involves both stripping columns
(heat input) and an ammonia condenser (heat removal), a loss of flow control
or other failure affecting the heating or cooling medium could potentially
result in overheating and/or overpressure of equipment with subsequent
equipment failure and loss of containment of the process streams.
40
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3.2.8 The Manufacture of Hydrazine (17.26)
Hydrazine is produced by the partial oxidation of ammonia with chlorine,
hypochlorite, or hydrogen peroxide. Its many uses result from a variety of
advantageous properties. It has a high heat of combustion (hence, its use as
rocket fuel), is a strong reducing agent, an oxidizing agent under suitable
conditions, and a good completing ligand. However, hydrazine is also a highly
reactive chemical and great care must be taken in its manufacture, handling.
and storage.
Although there are several processes for the manufacture of hydrazine.
the predominant method is based on the oxidation of ammonia with alkaline
hypochlorite. A typical flow diagram for this process is presented in Figure
3-11. Liquid chlorine is first absorbed in dilute sodium hydroxide to form
sodium hypochlorite. This chemical is then mixed with about a threefold
excess of aqueous ammonia to produce chloramine; the reaction is almost
instantaneous at a temperature of about 40 °F. Next, a 20-30 molar excess of
anhydrous ammonia under pressure is added to the process stream, and the heat
of dilution raises the temperature to about 266 °F. The reactor effluent
contains hydrazine, ammonia, ammonium chloride, sodium chloride, water, and
nitrogen. The nitrogen is scrubbed with water to remove ammonia and is then
used as an inert pad to prevent decomposition of hydrazine during the
concentration steps. The liquid effluent is preheated and sent to the ammonia
recovery section, which consists of two columns. In the first column, ammonia
is taken overhead under pressure and recycled to the anhydrous ammonia storage
tank. In the second column, some water and final traces of ammonia are
removed overhead. The bottom stream from this column, consisting of water,
sodium chloride, and hydrazine. is sent on to the hydrazine recovery portion
of the process.
Ammonia release hazards are present in this process, because ammonia is
recovered in relatively pure form and the product is hydrazine which is not
easily handled because of its highly corrosive nature and its hazardous
reactivity. For the latter two reasons, hydrazine process equipment is
41
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-P-
NJ
NaOHJ
(ANHYDROUS
HYDRAZINE
NH3 + N2TO
SCRUBBER
Figure 3-11. Conceptual diagram of typical hydrazine manufacturing process.
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stainless steel, and all vessels containing high concentrations of hydrazine
in solution are blanketed with nitrogen to prevent ignition. Ammonia release
hazards in the ammonia recovery section are a loss of cooling to the ammonia
condenser, or overheating of the recovery columns. Both of these failures
could lead to dangerous overheating and/or overpressure of equipment.
3.3 REPACKAGING OF ANHYDROUS AMMONIA (27)
In addition to its use in various chemical processes, anhydrous ammonia
is also repackaged for resale and further use. Repackaging involves a number
of procedures, the use of which depends on whether the liquid ammonia is being
transferred from tank cars into tank trucks, or from tank cars, trucks, or
bulk storage into cylinders or other portable containers.
Filling operations may be carried out by transferring ammonia directly
from the tank car or truck to the receiving container. However, since
demurrage begins to accrue after a short period of time, most repackagers
first transfer the ammonia to bulk (pressurized) storage before filling the
smaller containers. Filling can be accomplished with a compressor or vapor
pump by reducing the pressure within the container being filled and at the
same time increasing the pressure within the storage tank being emptied.
Filling can also be accomplished with the use of a liquid pump. Compressed
air should never be used to cause a flow of liquid ammonia, because oxygen
contamination in a storage vessel causes stress corrosion cracking in certain
carbon steels. During the filling operation the receiving vessels are mounted
on scales to determine when they have been filled with the correct amount of
ammonia. Some repackagers reweigh the vessels on a second scale to verify
that the measurements made with the first scale were accurate.
Potential hazards in repackaging operations include the following:
• Contamination, such as with oxygen (latent hazard);
• Overpressurization of the storage vessel; and
43
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• Overfilling of the receiving vessel.
Stress corrosion cracking of certain carbon steels is caused by oxygen
contamination. This hazard is discussed in more detail in Section 3.4.
Contamination with other materials could result in potentially violent
reactions. Accidental overpressure of the storage tank could result in a
release of ammonia from the pressure relief valve if it is not vented to a
closed system. Overfilling could cause a release from a rupture in the piping
or the receiving vessel from a pressure buildup. A latent hazard also exists
in an overfilled vessel which goes undetected and leaves the repackaging
facility.
Equipment used in repackaging operations should be constructed from
materials compatible with ammonia. Suitable materials of construction for
ammonia service are discussed in Section 5. Other potential causes of a
release include leaks in the connecting piping as a result of corrosion or
loose joint-pipe connections, cloggings of vapor or liquid pipes leading to
overpressure, and human error.
3.4 STORAGE AND TRANSFER
All industries which use or handle ammonia in bulk quantities must have
appropriate facilities and procedures for the safe storage and transfer of
this material. In this section, the potential hazards associated with the
storage and transfer of anhydrous ammonia common to all installations are
identified. Proper procedures and safety precautions for the control of these
hazards for release prevention are discussed in Section 5.
3.4.1 Storage
Liquid anhydrous ammonia is stored in either refrigerated vessels at
atmospheric pressure or in pressure vessels at ambient temperatures. The type
of vessel used at a particular installation generally depends on the relative
costs of the two systems. However, materials and fabrication constraints
-------
place an upper limit on the size of pressure vessels* such that no more than
50.000 gallons of ammonia should be stored in an unrefrigerated tank (3). The
maximum amount of ammonia that may be stored in a particular vessel, the
"filling density", depends on the type of container and ranges from 0.56 to
0.58 times the water weight capacity of the container at 60 °F (7).
Refrigerated Storage—
The predominant use of ammonia in the fertilizer industry has made
refrigerated storage economically attractive to producers. This is because
the fertilizer season is relatively short, and large single-train plants which
produce ammonia year-round require large storage terminals during the off
season. The quantities of ammonia involved make pressurized storage prohibi-
tively expensive.
Normally, flat-bottomed, insulated, cylindrical tanks are used for
refrigerated storage of anhydrous ammonia at atmospheric pressure. In
general, these storage tanks have design pressures of less than 15 psig and
are constructed in accordance with Appendix R of the American Petroleum
Institute (API) Standard 620 (28). Because of the toxicity of ammonia,
however, this standard is considered as a minimum requirement, and many
installations are designed to meet stricter standards. Although refrigerated
tanks are insulated, heat is still added to the system from the surroundings,
and thus vapor is continually generated within the tank. It is therefore
necessary to collect, reliquify, and return the vapor to the tank. A closed
vapor return system is necessary, not only to prevent the release of ammonia
to the atmosphere but also to prevent contamination of the stored ammonia with
oxygen. A typical refrigerated storage system is shown schematically in
Figure 3-12. The system in this figure extracts unwanted heat from the stored
liquid by drawing low-pressure ammonia vapor from the tank, compressing it,
and delivering it at a sufficiently high pressure for the condenser cooling
medium to reliquify it.
45
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NH3
VAPOR
VERTICAL
CYLINDRICAL
STORAGE TANK
FIRST - STAGE
COMPRESSOR
LIQUID
RETURN LINE
FLASH
DRUM
SECOND - STAGE
COMPRESSOR
CONDENSER
LIQUID
NH3
AMMONIA
PUMP
VAPORIZER
OR HEATER
TO
^ PROCESS
Figure 3-12. Conceptual diagram of typical atmospheric refrigerated ammonia storage system.
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There are basically two types of refrigerated storage tanks, single- and
double-wall. A single-wall tank consists of a single shell with a domed roof.
The roof and side walls are clad with insulation; the materials usually used
for insulating single-wall tanks are foamed polyurethane or polyisocyanurate,
expanded polystyrene, and foamed glass (17). These materials all require a
vapor seal over the entire outer surface in order to prevent moisture from
entering the insulation or the space between the insulation and the tank. A
double-wall tank consists of an inner tank designed to store ammonia under the
required conditions, surrounded by a carbon steel outer tank. The gap between
the shells is usually not less than 18" and is filled with a powdered insulant
(Perlite) or wool fiber. A third type of tank is sometimes used which is a
variation of the double-wall tank. This type of tank is called a "double-
integrity" system whereby the outer shell is designed to hold all of the
liquid in the event of a total failure of the main tank.
Regardless of the type, all storage tanks must be supported on suitable
foundations with a layer of load-bearing insulation placed between the tank
bottom and the base. With certain foundation designs, it is also necessary to
install a foundation heating system to prevent the temperature of the subgrade
from falling below 32 °F. This is because the continuous formation of ice
lenses on some soils will cause the ground to heave (commonly referred to as
"frost heave11) with the resultant risk of damage to the underside of the tank.
Pressurized Storage—
In general, pressurized storage containers are used in conjunction with
processes which require relatively small quantities of ammonia (less than
40,000 gallons stored). Pressurized storage tanks are generally constructed
of carbon steel according to the American Society of Mechanical Engineers
(ASME) Code for Unfired Pressure Vessels. Section VIII, Division I, and with
the American National Standards Institute (ANSI) Standards for Piping and
Fittings (29,30,31,32). Stationary pressurized storage vessels are usually
cylindrical in shape with formed ends and may be installed with the axis
either vertical or horizontal. Transportable cylinders are a special type of
47
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pressurized storage which are used when only small quantities (usually no more
than 150 Ibs) of ammonia are required.
Storage System Hazards—
A large release of anhydrous ammonia from a refrigerated or pressurized
storage system would result from failure of the storage vessel or its associa-
ted piping. The failure might occur as a result of over- or underpressure of
the vessel, or as a result of weakened areas' of the vessel walls which
ruptured as a result of a very small applied stress. Possible causes of
vessel failure include the following:
• Improper materials of construction,
• Corrosion,
• Overheating,
• Overfilling,
• External damage, and
• Failure of safety relief devices.
The importance of using the proper materials of construction for ammonia
storage, especially refrigerated systems, cannot be overstressed. Refrigera-
ted storage equipment is frequently subjected to subzero temperatures which
may be as low as -28 °F. The significant difference between vessels working
at ambient temperature and refrigeration temperatures of this order is that
carbon steel vessels working at subzero temperatures are more liable to
brittle fracture under stress. The "transition temperature" for various casts
and types of steel ranges from -58 °F to 50 °F (17). For brittle fracture to
occur, the steel must be below its transition temperature, there must be a
notch or crack generally in association with a weld, and there must be
sufficient stress to cause plastic strain in the region where the stress is
48
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concentrated by the notch. Once a fracture is initiated at the notch, it may
propagate at high speed under the influence of quite low applied stresses.
A predominant internal corrosion hazard of ammonia storage tanks is
stress corrosion cracking (SCC) which occurs in certain carbon steels and has
been the subject of extensive research over the last thirty years. The
effects of SCC are several hundred or more fine cracks invisible to the naked
eye which vary in depth from less than a millimeter to the full thickness of
the plate (17). The cracks always occur in zones of high stress, usually the
weld deposit. Cracking susceptibility increases with the strength of the
steel and with temperature. It is generally agreed that the primary cause of
SCC is contamination with oxygen; it is postulated that cracking may be
induced in some vessels with an oxygen concentration as low as 1 ppm (33).
The addition of 0.1 to 0.2 wt% of water has been found to inhibit cracking in
the liquid phase, but this practice does not prevent cracking in the vapor
phase (34). No SCC has been reported in refrigerated storage vessels; it is
assumed that the reason for this is that any oxygen present is removed in the
recompression cycle and not because of the low temperature and pressure (33).
As pressurized vessels are often associated with frequent transfer operations,
contamination of the ammonia with air is a definite risk. If prompt detection
of SCC is not made, a serious corrosion hazard exists which may ultimately
lead to complete failure of the vessel.
In addition to stress corrosion cracking, an external corrosion hazard
exists if storage vessels are in constant contact with dampness or standing
water. Furthermore, if corrosive materials are stored near ammonia storage
vessels, fugitive emissions of these materials would enhance the possibility
of external corrosion of an ammonia storage tank.
An uninsulated storage vessel filled with ammonia at the maximum filling
density will become liquid full at a temperature of 130 °F (7). Thus, an
overheating hazard exists if ammonia is stored in an area which is located
near flammable or incompatible materials, especially if the area is not well
ventilated or heavily trafficked, or if storage vessels are exposed to direct
49
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sunlight. An overheating hazard exists in refrigerated storage systems
because of the dependence on the components of the refrigeration system to
maintain the low temperature of the system by removing and recompressing the
vapor phase. If this system were to fail, the temperature in the vessel would
increase, and the pressure would eventually exceed the design pressure of the
vessel.
Overfilling of storage vessels may occur as a result of a malfunctioning
scale, level gaging device or operator error. An overfilled ammonia storage
tank presents a hazard, because the temperature at which the vessel will
become liquid full is lowered. This creates the possibility of a liquid full
container with an otherwise insignificant increase in temperature. The
resulting hydrostatic pressure would cause the pressure relief device to vent
ammonia to the atmosphere; if the pressure relief device failed to activate, a
catastrophic release could result from vessel rupture.
Single-wall refrigerated storage vessels are especially vulnerable to
external damage due to the ingress of moisture which will subsequently freeze
and damage the installation. Poor vapor sealing, which allows moisture to
enter the insulation or the space between the insulation and the tank, is
often directly responsible for insulation failures (17). Another potential
cause of external damage is failure of the tank base heating system with the
subsequent formation of ice on the subgrade. resulting in "frost heave" which
was discussed previously. insulation or other forms of external damage may
also result from high winds or other severe weather conditions. Hence,
storage vessels located in regions with a high frequency of violent storms,
earthquakes, or high winds present a greater risk of external vessel damage
than those located in areas with mild weather conditions.
In the event of an overpressure of a storage vessel, the safety relief
valve(s) would open, allowing the pressure to be relieved by venting ammonia
to the atmosphere. Likewise, if a partial vacuum were to occur in a
refrigerated storage vessel, the vacuum relief valves would open and allow
50
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material (such as air) from the discharge side of the relief valve to enter
the vessel. If the relief valve in either of these situations failed to open,
the structural design conditions of the tank could be exceeded, potentially
resulting in the catastrophic failure of the container.
3.4.2 Transfer from Tank Cars and Trucks
Appropriate procedures must be followed when transferring ammonia from
tank cars and trucks to storage vessels to reduce the risk of a hazardous
chemical release. Tank cars are generally unloaded by using a gas compressor
or transfer unit to create a pressure differential between the storage vessel
and the tank car. Tank cars may also be unloaded with the use of a liquid
pump (1,7). Examples of hazards associated with the unloading of tank cars
and trucks include the following:
• The pressure in the tank car or truck attains the pressure
setting of its relief valve, and ammonia vapor is vented
to the atmosphere;
• The pressure in the tank car is lowered to the extent that
the tank is subjected to an internal vacuum condition,
possibly caused by a subsequent reduction of ambient
temperature;
• The vapor or liquid transfer line becomes clogged or
control valve fails in the closed position resulting in an
overpressure of the storage vessel;
• Leakage resulting from pipe corrosion or poor pipe-joint
connections;
51
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• Incompatible contamination in the receiving vessel which
could result in an uncontrolled reaction with
overpressure, or corrosion of the receiving vessel;
• A malfunctioning level indicating device on the receiving
vessel resulting in an overflow of the receiving vessel;
and
• Human error.
3.4.3 Transfer from Storage Vessels
Another aspect of the transfer of liquid or vapor ammonia is its transfer
from a storage container to its designated use in the plant. This is general-
ly accomplished with the pressure differential between the container and the
receiving vessel or process to which it is flowing.
One hazardous transfer practice is manifolding to withdraw liquid ammonia
from two or more cylinders simultaneously. This is because under certain
temperature conditions it is possible for liquid to flow from one cylinder
into another cylinder until it is completely filled (1). If the valve of this
completely filled cylinder were subsequently closed, any rise in temperature
would result in a build—up of hydrostatic pressure and could result in the
rupture of the cylinder. Because evaporation within a cylinder may cause the
ammonia to be refrigerated to a point where there is little or no flow of
ammonia vapor to a process, cylinders are often manifolded together to
increase the total vapor withdrawal rate. Gaseous transfer between cylinders
at different temperatures in such an arrangement is likewise potentially
hazardous if there is subsequent reliquefaction and isolation of an overfilled
container.
Nitrogen or air padding should never be used to promote the flow of
ammonia from cylinders or other storage vessels. Hazards include dangerous
52
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high pressures as a result of an increase in the ambient temperature and
oxygen contamination which causes stress corrosion cracking. Furthermore, a
cylinder should never be warmed with a flame to increase the vapor discharge
rate because of possible pressure buildup sufficient to rupture the container.
Warming by other methods such as a water bath should be done with caution so
as to prevent accidental overpressure of the cylinder.
Other transfer hazards include:
• Potential backflow of foreign material into the cylinder
or into the upper valve chambers of the ammonia storage
vessel;
• Isolation of liquid ammonia in piping between closed
valves which could lead to bursting of the line from a
build-up in hydrostatic pressure with a temperature
increase; and
• Failure of piping connections from corrosion, improper
materials of construction, or work hardening or fatigue.
3.4.4 Transporting Ammonia Storage Containers
Unloading containers of ammonia from the delivery vehicle or moving them
within the plant is another aspect of the storage and transfer of this materi-
al. In general, hazards associated with the transport of ammonia within a
closed vessel arise from failure to follow the proper transport procedures in
a safe manner. Prevention of a hazardous release resulting from human error
is discussed in Section 5.6.
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SECTION 4
POTENTIAL CAUSES OF RELEASES
The potential for a hazardous release of liquid or gaseous ammonia exists
in any type of facility which handles this material. The possible sources of
such a release are numerous. Large amounts of ammonia may be released from
leaks or ruptures of large storage vessels (including tank cars on-site) or
failure of process machinery (e.g., pumps or compressors) which maintain a
large throughput of ammonia gas or liquid. Smaller releases may occur as a
result of ruptured lines, broken gauge glasses, or leaking valves, fittings,
flanges, valve packing, or gaskets.
In Section 3, specific release hazards associated with the manufacture,
consumption, and storage of anhydrous ammonia were identified. In addition to
those discussed in the preceding section, there are also numerous general
hazards which, if realized, could lead to an accidental release. Both
specific and general hazards in ammonia facilities may be broadly classified
as process, equipment, or operational causes. This classification is for con-
venience only. Causes discussed below are intended to be illustrative, not
exhaustive. More detailed discussions of possible causes of accidental re-
leases are planned for other parts of the prevention reference manual series.
4.1 PROCESS CAUSES
Process causes are related to the fundamentals of process chemistry,
control, and general operation. Possible process causes of an ammonia release
include:
• Loss of feed composition control resulting in the
formation of ammonia-air mixtures within the flammability
limits;
54
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• Backflow of process reactants to an ammonia feed tank;
• Excess feeds in any part of a process leading to
overfilling or overpressuring equipment or excess feed to
a reactor;
• Loss of condenser cooling to distillation units;
• Overheating of reaction vessels and distillation columns;
and
• Overpressure in ammonia storage vessels from overheating
as a result of fire exposure or unrelieved overfilling.
4.2 EQUIPMENT CAUSES
Equipment causes of accidental releases result from hardware failures.
Some possible causes include:
• Failure of feed control systems from a loss of power,
clogged lines, jammed valves, or instrument failure;
• Excessive stress on materials of construction due to
improper fabrication, construction, or installation;
• Failure of pressure relief systems;
• Mechanical fatigue and shock in any equipment (mechanical
fatigue could result from age, vibration, excessive
external loadings, or stress cycling; shock could occur
from collisions with moving equipment such as cranes or
other equipment in process or storage areas);
55
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• Thermal fatigue and shock in reaction vessels, heat
exchangers, and distillation columns;
• Equipment constructed of high alloys, especially high
strength alloys selected to reduce the weight of major
process equipment, which might be especially sensitive to
corrosion or severe operating conditions;
• Brittle fracture in low temperature equipment subjected to
large temperature swings or creep failure which might
occur in equipment previously subjected to a fire that may
have caused undetected damage; and
• All forms of corrosion including stress corrosion cracking
from oxygen contamination, pipe connections which have
slowly corroded as a result of contaminants entering the
system when cylinders are switched, and external corrosion
from exposure to precipitation or constant dampness.
4.3 OPERATIONAL CAUSES
Operational causes of accidental releases are a result of incorrect
procedures or human errors. These causes include:
• Overfilled storage vessels;
• Improper process control system operation;
• Errors in loading and unloading procedures;
• Poor quality control resulting in replacement parts which
do not meet system specifications;
56
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Inadequate maintenance in general* but especially on
pressure relief systems and other preventive and
protective devices; and
Lack of inspection and non-destructive testing of vessels
and piping to detect corrosion weakening.
57
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SECTION 5
HAZARDS 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 ammonia is stored and
used. When developing a thorough release prevention and control plan, consid-
erations must he made in the following areas:
• Process design,
• Physical plant design,
• Operating and maintenance practices, and
4 Protective systems.
In each of these areas, consideration must he given to specific factors
that could lead to a process upset or failure which could directly or
indirectly cause a hazardous release of ammonia to the environment. At a
minimum, equipment and procedures should be examined to ensure that they are
in accordance with applicable codes, standards, and regulations. Further
evaluations should then be made to determine where extra protection against a
release is appropriate so that stricter equipment and procedural specifica-
tions may be developed.
The following subsections discuss specific considerations regarding
release prevention; more detailed discussions may be found in a manual on
control technologies, part of this manual series.
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5.2 PROCESS DESIGN
Process design considerations involve the fundamental characteristics of
the processes which use ammonia. These considerations include 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 variables of flow, pressure* temperature, composition, and
quantity. Specific considerations may include mixing systems, fire protec-
tion, and process control instrumentation. Modifications to enhance process
integrity may result from review of these factors and might 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 considerations listed, and perhaps others, must be properly
addressed if a system is to be safe, however.
The most significant considerations are aimed at preventing overheating
and/or overpressurizing systems containing ammonia. Overheating is hazardous
because it may lead to overpressure which weakens process equipment and adds
to the potential for leaks at joints and valves. Wide temperature fluctua-
tions also significantly decrease the lifespan of many materials of construc-
tion, uverpressure may occur without overheating if flowrate control of both
gas and liquid streams is not maintained.
5.3 PHYSICAL PLANT DESIGN
Physical plant design considerations include equipment, siting and
layout, and transfer/transport facilities. Vessels, piping and valves,
process machinery, instrumentation, and factors such as location of systems
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TABLE 5-1. SOME PROCESS DESIGN CONSIDERATIONS FOR PROCESSES INVOLVING
ANHYDROUS AMMONIA
Process Design Consideration
Process or Unit Operation
Contamination (with air especially)
Flow control of ammonia feed
Temperature sensing and heating
medium flow control
Temperature sensing and cooling
medium flow control
Adequate pressure relief
Corrosion monitoring
Temperature monitoring
Level sensing and control
Feed systems, storage tanks,
SCR catalyst
All
Distillation and stripping column
reboilers, feed preheaters.
reactors
Distillation and stripping column
condensers, reactors
Storage tanks, reactors, refrigera-
tion condensers, distillation and
stripping columns, heat exchangers
Pressurized storage tanks,
neutralization equipment
Distillation and stripping column
reboilers, storage tanks, catalytic
converters
Storage tanks, reboilers and
condensers
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and equipment must all be considered. The following subsections discuss
specific design aspects of facilities which handle anhydrous ammonia.
5.3.1 Equipment
The design of equipment for anhydrous ammonia calls for special and
up-to-date knowledge, particularly where low-temperature conditions are
encountered. The following paragraphs are intended to familiarize the reader
with the kinds of equipment which are used in ammonia service with specific
reference to materials of construction, safety devices, and safe operation.
The discussions herein are not intended as specifications; the appropriate
standards should be consulted and expert advice should always be sought in the
design and procurement of equipment for liquid ammonia duty.
Materials of Construction—
Dry ammonia is noncorrosive to most common metals. However, moist
ammonia corrodes copper, tin, zinc, and many alloys, particularly copper
alloys. Therefore, only iron or steel, despite the fact they decrease the
minimum ignition temperature, or other nonreactive material should be used in
contact with ammonia (8).
Carbon and carbon-manganese steels are commonly used for various types of
equipment in ammonia service. As discussed in Section 3.4.1, one of the
primary concerns with ammonia storage is the susceptibility of certain carbon
steels to stress corrosion cracking in the presence of small amounts of oxygen
contamination. Although it is not possible to specify a particular type of
carbon or carbon-manganese steel which will definitely not succumb to stress
corrosion cracking, it has been found that low-strength steels (yield less
2
than 350 N/mm ) are less susceptible to cracking than high-strength steels,
and thermal stress relief seems to completely eliminate the mechanism (17).
Piping for ammonia service should be constructed of rigid steel (11).
Copper, brass or galvanized fittings should not be used. Unions, valves.
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gauges, pressure regulators and relief devices having copper, brass or bronze
parts are not suitable for ammonia service. Certain aluminum alloys may be
used for various components in ammonia systems. Mercury thermometers in
ammonia service should be avoided (3)-.
Metallic and nonmetallic gasket materials, such as compressed asbestos,
graphited asbestos, carbon steel or stainless steel spiral-wound asbestos
filled, and aluminum are suitable for ammonia service. Ferfluorinated plastic
materials and neoprene have also been found suitable if they are fully con-
fined so as to prevent creep or blow out in the event of elevated temperatures
(1).
Storage Vessels—
A large inventory of ammonia contained in storage vessels on site repre-
sents one of the most hazardous components of a facility which uses or
produces this material. This fact has manifested itself in the number of
accidental releases from storage tanks over the years. In this section, the
different types of ammonia storage vessels are briefly discussed along with
the associated protection devices and safety procedures which are designed for
the prevention of a hazardous release of this material. For detailed
specifications of ammonia storage systems the reader is advised to consult
references (1) and (7).
Anhydrous liquid ammonia is stored commercially at full pressure, par-
tially refrigerated, and fully refrigerated in vessels ranging from two pound
cylinders to multi-ton tanks. In general, the quantity of ammonia determines
the choice of container, which in turn influences the maximum storage pres-
sure. Storage at ambient temperature (full pressure) is restricted to rela-
tively small vessels, usually uninsulated and cylindrical in shape with
rounded ends. The most frequent sizes range from 500 to 45,000 gallons (1).
These containers must >be designed for pressures of at least 250 psig and
constructed in accordance with the American Society of Mechanical Engineers
(ASME), Boiler and Pressure Vessel Code, Section VIII, Division 1 (29). If
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the pressure is only partially reduced, the vessel is usually spherical in
shape and insulated. The pressure in a "semi-pressure11 storage vessel is
selected to suit the individual requirements of the site process. This type
of storage is not as prevalent today as in the past due to the increasing
amount of ammonia which is being stored and transported in the fully
refrigerated state.
Full refrigeration of the liquified gas at -27.4 °F reduces the pressure
essentially to atmospheric. However* a slight positive pressure is necessary
to accommodate minor pressure fluctuations and to avoid negative pressure on
the tank, since air must be excluded. Normally, refrigerated vessels are
flat-bottomed, insulated, cylindrical tanks which are mounted vertically.
Tanks with design pressures of 15 psig or less should be constructed in
accordance with American Petroleum Institute (API) Standard 620 (28) as a
minimum, while those with higher design pressure should conform to the ASME
Code cited above.
The most probable causes of failure of an ammonia storage vessel were
discussed in Section 3.4 and include corrosion and the buildup of hydrostatic
pressure in a liquid-full container caused by overfilling or overheating.
Other possible causes of storage tank failure include brittle fracture from
overstressing, the use of improper materials of construction, and external
damage. This section discusses the safety devices and precautions designed to
minimize the chances of an accidental release as a result of one of these
causes.
Precautions should be taken to prevent both internal and external corro-
sion of ammonia storage vessels. Stress corrosion cracking in ammonia storage
vessels is caused by the contamination of the ammonia with air (oxygen). The
primary means of preventing this type of corrosion is by the addition of at
least 0.2% water. This is not an absolute safeguard, however, because
cracking can still occur in the areas of the vessel which are exposed to the
vapor phase. Preventive measures which may be taken to reduce the risk of
stress corrosion cracking include the following (33):
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• Reduce the tensile stress by thermal stress relief of the
entire vessel;
• Decrease the residual welding stresses by shotpeening or
stress relieving crown plates* leg column plates, and
bottom plates in a furnace prior to commissioning;
• Careful purging when commissioning; and
• Purge the vapor space with an oxygen free inert gas on a
regular basis.
Prevention of external corrosion involves good housekeeping and
maintenance practices which assure that containers are never in contact with
standing water or exposed to continual dampness.
Brittle fracture of steel is another potential cause of vessel failure.
It generally occurs in the vicinity of a notch or crack when the material is
below its transition temperature. To lower the susceptibility of carbon steel
to brittle fracture, vessels should either be built of a steel having a
transition temperature not higher than the design temperature, or steps should
be taken to eliminate plastic strain of the notches, since it is not possible
to be certain that all surface imperfections have been eliminated (17). This
may be achieved by thermal stress relieving the vessel after fabrication.
Pressure relief valves and rupture discs are designed to allow a con-
trolled release of overpressurized contents. According to American National
Standard (ANSI) K61.1, ammonia storage containers (with the exception of small
cylinders) should be provided with one or more pressure relief valves of the
spring-loaded type which are set to discharge at a pressure not exceeding the
design pressure of the container. The Compressed Gas Association (CGA)
specifies that the maximum discharge rate of the valve should be such that the
pressure in the container will not exceed 120% of the design pressure (1).
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Further provisions recommended by the CGA and ANSI K61.1 include the following
(1.7):
• The discharge from pressure relief valves should be
directed away from the container upward and unobstructed
to the open air.
• Vent pipes should not be restrictive nor smaller in size
than the pressure relief valve outlet connection.
• Vent pipes should have loose-fitting caps to exclude water
and debris but not restrict free discharge of vapor. In
addition, suitable provision should be made for draining
condensate which may accumulate.
• Shut-off valves should not be installed between the
pressure relief valves and the container unless the
arrangement is such that full flow is possible through at
least one nonisolated pressure relief valve at the re-
quired capacity. (Dual relief valves are usually fitted
which can be isolated individually and are interlocked so
that a relief valve can be removed for servicing without
losing protection of the vessel (17).)
Furthermore, it is important to ensure that if the relief valve lifts, the
ammonia vapor can be vented harmlessly. This may mean leading the vent to a
stack, the height and position of which is related to work areas in the
vicinity.
A cylinder containing less than 165 pounds of ammonia is not required to
have a pressure relief device (1). Instead, cylinders are designed to with-
stand very high pressures, as these containers are generally used indoors
where product containment is paramount. Regardless of the higher design
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pressure, these containers should be protected from fire and direct exposure
to the sun, because they are still susceptible to becoming liquid-full from an
increase in temperature. Without a pressure relief device, overpressure would
result in a sudden rupture and complete discharge of the cylinder contents.
Protection from overheating of larger pressurized storage vessels may be
provided by a shield to prevent direct exposure to the sun and by painting the
vessel with some reflective paint.
Atmospheric and semipressure storage tanks should be equipped with
instrumentation to ensure that the design pressure is not exceeded. This is
often done by having a pressure controller which will stop and start the
refrigeration system as required to maintain tank pressure. Provision should
also be made to reduce or stop any incoming ammonia once the refrigeration
system is fully loaded. In the event of a total failure of the refrigeration
plant, the pressure in the storage vessel will rise until it reaches the
design pressure of the relief valve, at which time it will begin to vent to
the atmosphere. Therefore, a standby diesel generator should be provided in
case it is not possible to restore the power before the design pressure of the
relief valve is attained.
Refrigerated storage vessels operating at atmospheric pressure, in
addition to having relief valves for overpressure, must also be protected from
underpressure, since these vessels can only withstand a few inches water gauge
of vacuum. Negative pressure (vacuum) relief valves are therefore provided
which allow warm ammonia gas to flow from the refrigeration system back into
the vessel in the event that pressures below atmospheric develop in the
vessel.
In addition to venting provisions, storage vessels should have valve
arrangements which allow the vessel to be isolated from the process to which
the ammonia is being fed. Backflow of material into the upper valve chambers
when the feed valve is shut off at the storage tank must be prevented because
of the possibility of corrosion in the feed pipe. Other valve specifications
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found in ANSI K61.1 require storage tank filling connections to be provided
with an approved combination back-pressure check valve and excess flow valve;
one double or two single back-pressure check valves; or a positive shut-off
valve, in conjunction with either an internal back-pressure valve or an
internal excess flow valve (7). Each container should also be equipped with a
vapor return valve. Furthermore, it is good practice to place a valve in the
liquid outlet pipe as close to the tank as possible which is capable of remote
closure in the event of a pipe failure during a transfer operation.
To reduce the risk of overfilling during transfer operations, smaller
storage vessels are often mounted on a scale which will indicate the weight of
fluid in the container at all times. All bulk storage vessels should also be
equipped with a reliable liquid level gauge which allows for quick and
accurate readings. The design and installation of an ammonia liquid level
gauge should adhere to the requirements given in ANSI K61.1 (7). Most ammonia
storage tanks have float-type gauges whereby a float mechanism is magnetically
coupled to a pointer which indicates percent of capacity on a volume basis
(1). Although this is an accurate method of measuring the level, the
equipment is vulnerable to mechanical damage and is often supplemented with an
additional measuring device. A differential pressure gauge which measures the
static head of the liquid is one possible back-up (17). Each nonrefrigerated
storage container nameplate should include markings which indicate the maximum
level to which the container may be filled with liquid ammonia between 20 °F
and 100 °F. The percent of the maximum volume of the container which may be
filled with liquid ammonia for various temperatures is given in Table 5-2.
Because refrigerated, atmospheric storage tanks are maintained at a fairly
constant temperature, they may be filled to within a few inches of the
roof/wall seam.
As an overfilled storage vessel is a serious hazard, it is normal for
level indicators to be fitted with high-level alarms to warn the operator when
the maximum filling level has been reached (17). Important level alarms
should be connected to the vessel separately from the level controller in case
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TABLE 5-2. MAXIMUM SAFE VOLUME OF LIQUID AMMONIA IN NONREFRIGERATED
STORAGE CONTAINERS AT VARIOUS TEMPERATURES (1)
Maximum Safe Volume
Temperature of Liquid Liquid Ammonia as a % of
Ammonia in Tank Container Water Volume
30 87.3
40 88.3
50 89.5
60 90.7
70 91.8
80 93.0
90 94.4
100 95.7
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the bottom lead line of the level controller inadvertently becomes blocked by
oil and/or dirt. As a further precaution, a short, vented dip pipe can
provide protection from overfilling in the event of failure of the volume or
weight measuring device. However, this device will not prevent an overflow of
ammonia liquid. Furthermore, it will only work if there is no other outlet
from the vapor space and if the line to the vent system has enough capacity.
It is therefore recommended that a vessel be fitted with a relief device which
discharges to an overflow tank or other suitable receiver if the possibility
of overfilling exists.
Process and Reaction Vessels—
General considerations for hazard control for storage vessels also apply
to the design and use of process and reaction vessels. In the latter type of
vessels, however, there is a greater degree of risk, as these containers are
often exposed to more severe conditions of temperature and/or pressure than a
regular storage vessel.
Primary considerations for process and reaction vessels include:
• Materials of construction,
• Pressure relief devices,
• Temperature control,
• Overflow protection (in addition to high level alarms), and
• Foundations and supports.
The foundations and supports for vessels are important design considera-
tions, especially for large storage vessels and tall equipment such as distil-
lation columns. The choice of construction materials is also an important
consideration particularly where low-temperature conditions are encountered.
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Expert advice should always be sought in the design and procurement of equip-
ment for liquid ammonia duty.
If cooling to a condenser is lost, overpressure may occur. Thus, it is
necessary to use pressure relief valves to protect against leaks and ruptures
which can result from overpressure. Pressure relief protection is also
necessary in the event of a fire.
Distillation and stripping columns present significant release hazards
because they may contain large amounts of ammonia in pure form and have a heat
input. As they are often located outdoors, external factors such as ambient
temperature fluctuations and wind loadings must be properly accounted for in
their design and construction, especially for the support structure.
Piping-
All ammonia piping should be extra heavy (schedule 80) steel when thread-
ed joints are used (1). However, schedule 40 piping may be used when joints
are either welded or joined by flanges. All refrigeration system piping
should conform to ANSI B31.5 - American National Standard for Refrigeration
Piping (35). Iron and steel piping, fittings, and valves are suitable for
ammonia gas and liquid. Nonmalleable metals, such as cast iron, must not be
used for fittings (1). As low temperature embrittlement is a concern in
ammonia systems, material selection must take this into account. In general,
if a material is not notch-tough at the operating temperature, the welds
should be subjected to post-weld heat treatment.
Because liquid NH expands with temperature, bursting of lines due to
hydrostatic pressure must be prevented. This may be accomplished with expan-
sion chambers which should be located at the highest point of each section
that may be closed, trapping liquid NH . Construction of these chambers
should be in accordance with the ASME Code for Unfired Pressure Vessels,
Section VIII (29). An expansion chamber device typically consists of a
rupture disk and a receiver chamber which can hold 20—30% of the protected
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line's capacity. The chamber is equipped with a pressure indicator or alarm
switch set to function upon disk rupture. Alternatively, a hydrostatic relief
valve may be installed in each section of piping in which liquid ammonia can
be isolated between shut-off valves.
The following is a list of general guidelines for the safe transport of
liquid ammonia in piping systems:
• Piping systems should have as simple a design as possible
with a minimum number of joints and connections; flow
should not be restricted by an excessive number of elbows
and bends.
• Piping should be at least 7.5 feet above the floor if
possible; provision should be made to protect all exposed
piping from physical damage that might result from moving
machinery, the presence of automobiles or trucks, or any
other undue strain that may be placed on the piping.
• In addition to being securely supported, pipes should be
sloped with drainage provisions at the low points.
• Clips or hangars should not fit too tightly to allow for
thermal expansion of the pipe.
• Piping should be protected from exposure to fire and high
temperatures.
• A pressure reducing regulator should be installed when
connecting to lower pressure piping or systems from
storage vessels.
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• Low points should be avoided in inlet lines to relief
valves for ammonia vapors* because liquid can condense in
these lines under ambient conditions.
• Pipelines should always be emptied when ammonia flow is
not required to prevent the possible isolation of liquid
NHn between closed valves.
Valves—
Valves in ammonia service are discussed in a number of references
(1,7,24). Several types of valves including gate, globe, ball, and check
configurations are used in ammonia systems. Construction may be of iron or
steel. Copper and copper-bearing materials must not be used for the valve or
trim parts, because these materials are attacked by ammonia (when moisture is
present.)
It is good practice to locate stop valves in the inlet and outlet lines
to all condensers, vessels, evaporators, and long lengths of pipe so they can
be isolated in case of leaks and to facilitate pumping out. If globe-type
valves are used they should be installed with the valve stem horizontal to
lessen the chance for dirt or scale to lodge on the valve seat or disk (24).
Pressure regulators, solenoid valves, and thermal expansion valves should
be flanged for easy assembly and removal. A strainer should be used in front
of self-contained control valves to protect them from pipe construction
material and dirt (24). Solenoid valves should be located upright and pro-
tected from moisture. A manual opening stem is useful for emergencies.
When ammonia flow is shut off at the feed tank, the piping system between
that point and the point of application is filled with vapor. Gradual absorp-
tion of the vapor in the process fluid leaves a vacuum which draws ammoniated
fluid back into the piping system. This may cause serious problems, especial-
ly if the shut-off point is upstream from instruments and other items of
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equipment. A diaphragm-operated check valve held in a closed position by
ammonia pressure may be used to prevent undesired back or reverse flows. If
the ammonia pressure falls and pressure on the diaphragm becomes subatmos-
pheric, the valve opens and allows air to flow into the piping system, thus
breaking the vacuum which would otherwise cause backflow of the process fluid.
Excess flow valves should be considered for ammonia in vessels, tank
cars, and other places where unintentional high liquid discharge rates need to
be prevented. In the event that a liquid discharge line is broken, the
resulting high flow rate would cause the valve to close off, restricting the
escape of ammonia.
The pressure of ammonia gas can be controlled by a pressure reducing and
regulating valve of steel construction. The valve should be designed for the
range of conditions under which it will be required to operate, taking into
account the maximum and minimum flow of ammonia gas, its average temperature,
and the average upstream and downstream pressures (1).
Process Machinery—
Process machinery refers to rotating or reciprocating equipment that may
be used in the transfer or processing of ammonia. Included in this classifi-
cation are pumps and compressors which may be used to move liquid or gaseous
ammonia where gas pressure padding is insufficient or inappropriate.
Pumps— Any pump used in ammonia service must conform to ANSI/DL 51 -
American National Standard for Power-Operated Pumps for Anhydrous Ammonia and
LP Gas (36). To assure that a given pump is suitable for an ammonia service
application, the design engineer should obtain information from the pump
manufacturer certifying that the pump will perform properly in this applica-
tion.
Centrifugal pumps are normally used for pumping liquefied ammonia in a
fully refrigerated condition (17). Glandless, canned type or conventional
pumps fitted with either a single mechanical seal together with a soft packed
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auxiliary gland or a double mechanical seal may be used. Canned pumps are
generally used indoors or in congested areas. When a glanded pump is used a
mechanical seal is advisable followed by a soft packed gland (17). The seal
pressure should not exceed the manufacturer's recommendations, and the inter-
space should be vented in a safe manner.
Pumps should be constructed with materials which are resistant to ammonia
at operating temperatures and pressures. Lubricating oil should be resistant
to breakdown as a result of contact with ammonia. In some cases, the poten-
tial for seal leakage may rule out the use of rotating shaft seals. Some pump
types which either isolate the seals from the process stream or eliminate them
altogether include canned motor, vertical extended spindle submersible.
magnetically-coupled, and diaphragm (4).
Net positive suction head (NPSH) considerations are especially important
for ammonia, since the liquid may be pumped near its boiling point. Long
suction lines reduce the effective NPSH available, and if the suction lines
are very long in relation to the NPSH available, a vapor release vessel should
be fitted in the suction line as close to the pump as possible (17). The pump
supply tank should have high and low level alarms, and the pump should be
interlocked to shut off at low supply level or low discharge pressure.
Centrifugal pumps often have a recycle loop back to the feed container
which prevents overheating in the event that the pump is deadheaded (i.e., the
discharge valves close). Positive displacement pumps can be equipped with a
constant differential relief valve capable of discharging the entire capacity
of the pump into the suction port of the pump to prevent rupture in the event
of deadheading. When a positive displacement pump is used to reduce the
chance of backflow, such a relief valve could defeat this purpose if the back
pressure were high enough. In such a case, the relief valve discharge should
be routed somewhere other than the suction part of the pump. Pumps can also
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be protected by a differential pressure switch fitted across the pump to trip
the motor should a low-pressure condition arise. This could be caused by
inadequate priming, by vaporizing in the pump, or by too low a suction head.
Compressors— Ammonia compressors include reciprocating, centrifugal,
liquid-ring rotary, and non-lubricated screw compressors. Usually two-stage
reciprocating compressors are used for ammonia service, although rotary
compressors are also common and may be preferable if it is necessary to avoid
oil contamination (17). Detailed descriptions of the different types of
compressors may be found in the technical literature (4).
As with pumps, materials of construction must be selected which are
compatible with ammonia at the operating conditions. Copper and
copper-bearing alloys must be avoided and particular attention paid to the
gland arrangement (17). Any ammonia compressor must be designed for at least
250 psig working pressure except those used for refrigeration service.
A pressure relief valve large enough to discharge the full capacity of
the compressor should be installed between the discharge of the compressor and
the high pressure shut-off valve. If the crank case is not designed to
withstand system pressure, it should also be protected with a suitable pres-
sure relief valve. In addition, a liquid trap should be installed before the
compressor suction to prevent entry of liquid into the compressor.
Miscellaneous Equipment—
Pressure Relief Devices— Pressure relief devices for ammonia service
should be constructed in accordance with CGA S-1.3 - "Pressure Relief Device
Standards - Part 3 - Compressed Gas Storage Containers" (37) . All wetted
parts of relief valves and rupture disks should be constructed from materials
compatible with ammonia at the operating temperature and pressure. For
balanced relief valves, the balance seals must also be made of appropriate
materials.
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Measures should be taken to ensure that process equipment is not isolated
from its relief system. To provide continuous pressure relief protection when
a device requires maintenance, equipment may be provided with dual relief
systems, each sized to provide the total required flow capacity. Stop valves
installed between a vessel and its relief device should have a full port area
that is at least equal to that of the pressure relief device inlet. These
valves should be locked open or have handles removed when the protected vessel
is in use. If the discharge is to be piped to a closed disposal system, the
pressure drop caused by the additional piping must be considered and the
relief device sized accordingly.
Some aspects of the proper placement and use of pressure relief valves
have been discussed earlier in this section in conjunction with storage
vessels. Additional guidelines for the correct use of pressure relief valves
include the following (7):
• Arrangement should be such as to minimize the possibility
of tampering with the pressure setting adjustment;
• They should have direct communication with the vapor space
of the container;
• When relief valves are put in series, the downstream
valves must be large enough to accept the total potential
relief capacity;
• Discharge lines of liquid relief valves should not be run
to a high point;
• The set-point of a relief valve in the discharge of a pump
should be checked to ensure that it is higher than the
maximum shut-off pressure of the pump;
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• The flow capacity should not be restricted by any connec-
tion to it on either the upstream or downstream side; and
• Discharge from pressure relief valves should not terminate
in or beneath any building.
Rupture disks may be used to protect pressure relief valves from constant
contact with the contents of the storage vessel. Rupture disks should not be
used in ammonia service where the ruptured disk discharges directly into the
atmosphere. If the disk relieves the contents of the container through a
spring-loaded pressure relief valve, a small vent should be provided in the
chamber between the disk and the valve to prevent any back pressure on the
rupture disk. Because operating pressures exceeding 70% of a disk bursting
pressure may induce premature failure, a considerable margin should be allowed
when sizing rupture disks.
Instrumentation— For normal applications, all steel pressure, gauges
graduated from 0-400 psig are recommended for ammonia service (1). For low
pressure work, the range for the gauge should be one and one-half times the
maximum service pressure.
The most commonly used flowmeter for ammonia gas is the tapered tube,
float type (1). For high pressure work the glass tube should be enclosed in a
vented shield or, preferably, a steel-armored type. Orifice meters with
differential pressure cells may also be used. Mercury manometers should not
be used in ammonia service. The quantity of liquid ammonia transferred from
one system to another may be measured with positive displacement or turbine
meters.
Magnetic or rotary gauges are preferred to gauge glasses (3). Ammonia
should never be closed into a gauge glass, as an increase in pressure may
break the glass. Glasses should be equipped with excess flow valves to stop
the flow of ammonia if breakage occurs, and they should have automatic
self-closing shutoff valves which must be held open to take a reading (3).
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Instrument component failures cause about 0.6 plant shutdowns each year
(38). It is projected that this can be reduced by 36% by making all single
pressure, temperature, flow, and level switches redundant.
5.3.2 Plant Siting and Layout
The siting and layout of a particular ammonia facility is a complex issue
which requires careful consideration of numerous factors. These include the
other processes in the area, the proximity of population centers, prevailing
winds, local terrain, and potential natural external effects such as flooding.
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
safety related. 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 hazards of releases. Large distances between
large inventories and sensitive receptors is desirable.
Various techniques are available for formally assessing a plant layout
and should be considered when planning high hazard facilities (39).
The siting and layout of any facility handling ammonia should adhere to
the following general guidelines:
• Areas in which ammonia hazards exist should have an
adequate number of well marked exits through which person-
nel can escape quickly if necessary; doors should open
outward and lead to unobstructed passageways;
• The plant is laid out so that, whenever possible, there
are no confined spaces between equipment; large distances
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between large inventories and sensitive receptors is
desirable;
• Access to platforms above ground level should be by
stairway in preference to cat ladders, and work areas
above ground level should have alternative means of
escape;
• xhe ground under process equipment and storage vessels
should be sloped so that fire water and liquid spillages
flow away from equipment and then into drains, avoiding
pools underneath equipment;
.• Storage facilities should be located in cool, dry, well-
ventilated areas, away from heavily trafficked areas and
emergency exits; and
• Tank car, tank truck and storage facilities should be
located away from sources of heat, fire and explosion.
Because heat causes thermal expansion of liquid ammonia, measures should
be taken to situate piping, storage vessels, and other ammonia equipment so
that they are not located adjacent to piping containing flammable materials,
hot process piping, equipment, steam lines, and other sources of direct or
radiant heat. Special consideration should be given to the location of
furnaces and other permanent sources of ignition in the plant. Storage should
also be situated away from control rooms, offices, utilities, and laboratory
areas.
In the event of an emergency, there should be more than one entry to the
facility which is accessible to emergency vehicles and crews. Storage vessel
shut-off valves should be readily accessible. Containment for liquid storage
tanks can be provided by diking. Dikes reduce evaporation rates while
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containing the liquid. It is also possible to equip a diked area to allow
drainage to an underground containment sump. This sump would be vented to
either a recovery or scrubber system for safe removal. A full containment
system using a specially constructed building is another possible option.
This type of secondary containment could be considered for large volume.
liquid ammonia storage tanks.
5.3.3 Transfer and Transport Facilities
Transfer and transport facilities where both road vehicles and rail
tankers are loaded or unloaded are likely 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.
Before unloading, tank vehicles should be securely moored; an interlocked
barrier system is commonly used. Tank cars must also be protected on both
ends by derailers or on the switch end if located on a dead end siding-.
Sufficient space should be available to avoid congestion of vehicles or
personnel during loading and unloading operations. Vehicles, especially
trucks, should be able to move into and out of the area without reversing.
High curbs around transfer areas and barriers around equipment should be
provided to protect equipment from vehicle collisions.
Correct procedures must be followed when unloading and handling small
ammonia storage vessels. Dragging, sliding, or rolling cylinders, even for
short distances, is not acceptable. Lifting magnets, slings of rope or chain,
or any other device in which the cylinders themselves form a part of the
carrier should never be used for transporting cylinders.
5.4 PROTECTION TECHNOLOGIES
This subsection describes two types of protection technologies for
containment and neutralization. These are:
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• Enclosures; and
• Scrubbers.
A presentation of more detailed information on these systems is planned in
other volumes of the prevention reference manual series.
5.4.1 Enclosures
Enclosures refer to containment structures which capture any ammonia
spilled or vented from storage or process equipment, thereby preventing
immediate discharge of the chemical to the environment. The enclosures
contain the spilled liquid or gas until it can be transferred to other con-
tainment and discharged at a controlled rate which would not be injurious to
people or the environment, or transferred at a controlled rate to water
scrubbers for absorption.
Specially designed enclosures for ammonia storage or process equipment do
not appear to be in widespread use. The principle that it may be preferable
to locate toxic operations in the open air has been mentioned in the
literature (39), along with the opposing idea that sometimes enclosure may be
appropriate. The desirability of enclosure depends partly on the frequency
with which personnel must be involved with the equipment. A common design
rationale for not having an enclosure where toxic materials are used is to
prevent the accumulation of toxic concentrations within enclosed areas.
However, if the issue is providing for secondary containment, total enclosure
may be appropriate.
If total enclosure is deemed appropriate for a given installation, it
should be equipped with continuous monitoring equipment and adequate fire
protection. Alarm's should sound whenever lethal or flammable concentrations
are detected. Care must be taken when an enclosure is built around
pressurized equipment. From an economic standpoint, it would not be practical
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to design an enclosure to withstand the pressures associated with the sudden
failure of a pressurized vessel. Therefore, if an enclosure is built around
pressurized equipment, it should be equipped with some type of explosion
protection, such as rupture plates. These components are designed to fail at
a pressure lower than the design pressure of the enclosure, thus preventing
the entire structure from failing.
An enclosure would have a ventilation system designed to draw in air when
the enclosure was vented. The bottom section of an enclosure which is used
for stationary storage containers should be liquid tight to retain any liquid
ammonia that might be spilled. Enclosures around rail tank cars which are
used for storage do not normally lend themselves easily to effective liquid
containment. However, containment can be accomplished if the floor of the
enclosure is excavated several feet below the track level while the tracks are
supported at grade in the center.
While the use of enclosures for secondary containment of ammonia spills
or releases is not known to be widely used, it might be considered for areas
near sensitive receptors.
5.4.2 Scrubbers
Scrubbers are a traditional method for absorbing toxic gases from process
streams. These devices can be used for the control of ammonia releases from
vents and pressure relief discharges, from process equipment, or from secon-
dary containment enclosures.
Because of its high solubility, ammonia discharges could be absorbed in
water in any of several types of scrubbing devices. Types of scrubbers that
might be appropriate include spray towers, packed bed scrubbers, and Venturis.
Other types of special designs might be suitable but complex internals subject
to corrosion do not seem to be advisable.
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Whatever type of scrubber is selected, a complete system would include
the scrubber itself, a liquid feed system, and reagent makeup equipment. If
such a system is used as protection against emergency releases, consideration
must be given to how it would be activated in time to respond to an emergency
load. One approach used in some process facilities is to maintain a
continuous circulation of scrubbing liquor through the system. For many
facilities this would not be practical, and the scrubber system might be tied
into a trip system to turn it on when it is needed. However, with this system
a quantity of ammonia would be released prior to actuation of the scrubber
(i.e., starting up a blower and turning on the flow of liquid).
The scrubber system must be designed so as not to present excessive
resistance to the flow of an emergency discharge. The pressure drop should be
only a small fraction of the total pressure drop through the emergency
discharge system. In general, at the liquid-to-gas ratios required for
effective scrubbing, spray towers have the lowest, and Venturis the highest
pressure drops. While packed beds may have intermediate pressure drops at
proper liquid-to-gas ratios, excessive ratios or plugging can increase the
pressure drop substantially. However, packed beds have higher removal
efficiencies than spray towers or Venturis.
In addition, the scrubber system must be designed to handle the "shock
wave" generated during the initial stages of the release. This is
particularly important for packed bed scrubbers since there is a maximum
pressure with which the gas can enter the packed section without damaging the
scrubber internals.
Design of emergency scrubbers can follow standard techniques discussed in
the literature, carefully taking into account the additional considerations
just discussed. An example of the the sizing of an emergency packed bed
scrubber is presented in Table 5-3. This example provides some idea of the
size of a typical emergency scrubber for various flow rates. This is an
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TABLE 5-3. EXAMPLE OF PERFORMANCE CHARACTERISTICS FOR AN EMERGENCY
PACKED BED SCRUBBER FOR AMMONIA
Basis: Inlet stream of 50% NH in 50% air. Constant gas flow per unit
cross-sectional area of 455 scfm/ft .
Packing: 2-inch plastic Intalox® saddles.
Pressure Drop: 0.5 inch water column
Removal Efficiency, % 50 90
Liquid to Gas Ratio
(gal/thousand scf)
— at flooding 160 160
— operating 80 80
Packed Height, ft. 3.1 11.4
Column Diameter and Corresponding Gas Flow Rates for Both Removal Efficiencies
Column
Diameter Flow Rate
(ft) (scfm)
0.5 90
1.0 360
2.0 1,400
6.3 14,000
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example only and should not be used as the basis for an actual system which
might differ based on site specific requirements.
Another approach is the drowning tower where the ammonia vent is routed
to the bottom of a large tank of uncirculating wfter. The drowning tower 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 overpres-
sure relief discharge, for example.
5.5 MITIGATION TECHNOLOGIES
If, in spite of all precautions, a large release of anhydrous ammonia
were to occur, the first priority would be to rescue workers in the immediate
vicinity of the accident and evacuate persons from downwind areas. The source
of the release should be determined, and the leak should be plugged to stop
the flow if this is possible. The next primary concern becomes reducing the
consequences of the released chemical to the plant and the surrounding commu-
nity. Reducing the consequences of an accidental release of a hazardous
chemical is referred to as mitigation. Mitigation techniques include such
measures as physical barriers, water sprays and fogs, and foams. The purpose
of a mitigation technique is to divert, limit, or disperse the chemical that
has been released to the atmosphere. The mitigation technology chosen for a
particular chemical will depend on the specific properties of the chemical
including its flammability, toxicity, reactivity, and those properties which
determine its dispersion characteristics in the atmosphere.
If a release occurs from a pressurized ammonia storage tank, a quantity
of liquid will immediately flash to its atmospheric boiling point producing a
vapor/aerosol cloud of ammonia. The remaining liquid will cool to the normal
boiling point of -28 °F. Heat transfer from the air and ground will result in
further vaporization of the released liquid. Since the ammonia accidentally
released from a refrigerated storage tank is already at or below its normal
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boiling point, a comparable quantity of vapor will not flash off. as with a
pressurized release, but heat transfer from the environment will still quickly
cause the formation of a vapor cloud. 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 liquified gas include secondary
containment systems such as impounding basins, dikes, and enclosures.
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
typically include such items as portable breathing air and chemically
resistant protective clothing.
5.5.1 Secondary Containment Systems (7.40,41)
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 facility will
depend on the risk associated with an accidental release from that location.
The inventory of ammonia and its proximity to other portions of the plant and
to the community are primary considerations in the selection. 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.
While it is common practice to provide ammonia storage tank installations
with an earth or concrete dike to contain the liquid into a manageable pool
should a total failure of the main tank occur, the efficacy of a dike in the
event of a release from pressurized storage has been questioned. This is
because a sudden loss of pressurized containment tends to result in ejection
of all the contents in the form of vapor, or spray, leaving no residual liquid
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(17). There may, however, be situations where a dike would be appropriate for
a pressurized ammonia storage vessel.
A conventional dike is of use when refrigerated storage is involved. The
liquid is already at atmospheric pressure, and it is assumed that most of the
contents of the tank will be contained within the confines of the dike in the
event of a release from the tank. ANSI K61.1 requires that one of the
following should be provided with any primary refrigerated storage system; it
has no similar provisions for pressurized storage (7):
• An adequate drainage system underlying the storage vessels
which terminates in an impounding basin having a capacity
as large as the largest tank served; or
• A diked area with the capacity as large as the largest
tank served.
These measures are designed to prevent accidental discharge of liquid ammonia
from spreading to uncontrolled areas.
The most common type of containment system is a low wall earth dike
surrounding one or more storage tanks. Generally, no more than three tanks
are enclosed within one diked area because of increased risk. 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 storage capacity. If there is more than one tank in
the diked area, the tanks should be situated on berms above the maximum liquid
level attainable in the impoundment.
Dike heights usually range from 3 to 12 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. It may be necessary to construct low wall dikes of low
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temperature steel or concrete because of adverse soil conditions or other
specific requirements. In addition, some experiments have led to the conclu-
sion that earth dikes should be covered with a layer of clay, asphalt, plastic
film, or a similar material that is impermeable to liquid ammonia (42).
Otherwise, the ammonia will percolate into the ground, and the loss of ammonia
by evaporation will be greater in the absence of an impermeable layer over the
dike.
A low wall dike can effectively contain the liquid portion of an acciden-
tal release and keep the liquid from entering uncontrolled areas. However, a
dike also limits access to the tank during a spill. Therefore, a remote
impounding basin may be considered if a relatively large site is available
within a reasonable distance of the storage system. With such a system, the
flow is directed to the basin by dikes and channels under the storage tanks
which are designed to minimize exposure of the liquid to other tanks and
surrounding facilities. The advantages of this type of system are
• The spilled liquid is removed from the immediate tank
area;
• The probability of the spilled liquid causing further
damage to the tank, piping, electrical facilities, pumps,
and other equipment is reduced;
• The tank area is accessible during the spill; and
• Access to the tank pumps or related piping for regular
operation, inspection, or maintenance is not restricted by
the impoundment.
The impounding basin may be located to use the natural topography of the area
thus minimizing additional excavation and diking. A sump can also be provided
within the main impounding basin to limit the liquid surface and ground
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contact areas. Furthermore, the depth of the basin can be increased to
provide vapor containment.
Although few authorities for ammonia facilities require them, high wall
impoundments may be the best secondary containment choice for selected sys-
tems. Circumstances which may warrant their use include limited storage site
area, the need to minimize vapor generation rates, and/or the tank must be
protected from external hazards. Maximum vapor generation rates will general-
ly be lower for a high wall impoundment than for low wall dikes or remote
impoundments because of the reduced surface contact area. These rates can be
further reduced with the use of insulation on the wall and floor in the
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 surrounding the storage tank will dictate
the minimum height of the wall. The walls may be designed with a volumetric
capacity greater than that of the tank to provide vapor containment. Increas-
ing the height of the wall also raises the elevation of any released vapor.
One disadvantage of these dikes is that high walls around a tank may
hinder routine external observation. Furthermore, the closer the wall is to
the tank, the more difficult it becomes to access the tank for inspection and
maintenance. As with low wall dikes, piping should be routed over the wall if
possible. The closeness of the wall to the tank may necessitate placement of
the pump outside of the wall, in which case the tank outlet (suction) line
will have to pass through the wall. In such a situation, a low dike
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 (43). This figure shows ammonia vapor clouds at
the time when the farthest distance away from the source is exposed to
concentrations above the IDLH. With diking, the model predicts that downwind
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>> BOO.
• > i.oooe+oa PPM
> > 1.00OB+O4 PPM
o.as
O.B
O.7B
1.88
Release from a tank surrounded by a 25 ft. diameter dike.
Elapsed Time: 2 minutes
> 500.
X - MAX CONCeNTRATXON
• BO9.4B PPM
0.20
O.B
0.78
1.88
Release from a tank with no dike.
Elapsed Time: 8 minutes
Common Release Conditions
Storage Temperature = 85°F
Storage Pressure = 148 psig
Ambient Temperature = 85°F
Wind Speed = 10 mph
Atmospheric Stability Class = C
Quantity Released = 5000 gallons
through a 2-inch hole
Figure 5-1. Computer model simulation showing the effect of diking on
the vapor cloud generated from a release of liquified
ammonia.
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distances up to 1400 feet from, the source of the release could be exposed to
concentrations above the IDLH. Two minutes are required for the vapors to
reach the maximum down wind distance. Without diking, the model predicts that
downwind distances up to 6600 feet from the source could be exposed to
concentrations above the IDLH. Eight 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. 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 greatest concern. Drawbacks of an integrated system are the
greater complexity of 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 both impounding
basins and diked areas. This will involve the use of sumps and separate
drainage pumps, since direct drainage to stormwater sewers would presumably
allow any spilled ammonia 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 (41). 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 or
impoundment to further reduce heat transfer from the environment to the
spilled liquid. The floor of an impoundment should be sealed with a clay
blanket to prevent the ammonia from seeping into the ground; percolation into
the ground causes the ground to cool more quickly, increasing the vapor
generation rate. Absorption of the ammonia into water in the soil would also
release additional heat.
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5.5.2 Flotation Devices and Foams (42,44.45,46)
Other possible means of reducing the surface area of spilled liquid
ammonia include placing impermeable flotation devices on the surface, dilution
with water, and applying water-based foams.
Placing a lid over a spilled chemical is a direct approach for containing
the toxic vapors with nearly 100 percent efficiency. The floating cover may
be continuous or a distribution of light particulates. However, being able to
use these techniques requires acquisition in advance of the spill and storage
until needed, and in all but small spills deployment may be difficult.
Furthermore, although particulate covers are potentially effective, cost is a
deterrent to their use. Determination of appropriate materials for applica-
tion to an ammonia spill has been the subject of some research (42), but the
use of mechanical barriers on an actual spill has not been reported in the
literature.
One approach to an ammonia spill is dilution with water, but, because of
the high heat of solution, the addition of pure water would result in a
violent boil-off of ammonia. A water-based foam cover provides a means of
diluting the ammonia with a minimum heat of solution, because water is added
at a slow rate. While the use of foams in vapor hazard control has been
demonstrated for a broad range of volatile chemicals, it is difficult to
accurately quantify the benefits of foam systems, because the effects will
vary as a function of the chemical spilled, foam type, spill size, and atmo-
spheric conditions. With regard to liquified gases, it has been found that
with some materials, foams have a net positive effect, but with others, foams
may exaggerate the hazard.
When a foam cover is first applied, an increase in the boil off rate is
generally observed which causes a short-term increase in the downwind ammonia
concentration. The initial foam cover may be destroyed by violent boiling, in
which case a second application is necessary. Once a continuous layer is
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formed, a net positive effect will be achieved in the downwind area (44). 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 wanned
as it rises through the blanket by heat transfer from the foam and by the heat
of solution of ammonia in water; the warmed vapor cloud will have greater
buoyancy and will disperse in an upward direction more rapidly.
The extent of the downwind reduction in concentration will depend on the
type of foam used. Research in this area has indicated that medium to high
expansion foams (75 to 350:1) give significantly better results than do low
expansion foams (6 to 8:1) (44,45). Furthermore, a high expansion foam will
cause a smaller initial increase in boil off than a low expansion foam.
Regardless of the type of foam used, the slower the 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 slowly draining foam may be higher than
for other foams, but a cost effective system will be realized in superior
performance.
5.5.3 Mitigation Techniques for Ammonia Vapor (47,48)
The extent to which the escaped ammonia vapor can be removed or dispersed
in a timely manner will be a function of the quantity of vapor released, the
ambient conditions, and the physical characteristics of the vapor cloud. The
behavior and characteristics of the ammonia cloud will be dependent on a
number of factors. These include the physical state of the ammonia 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 devel-
oped. In spite of the lower specific gravity of pure ammonia vapor, large
accidental releases of ammonia have often resulted in the formation of
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ammonia-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.
The primary means of dispersing as well as removing ammonia vapor from
the air is with the use of water sprays or fogs. The water is applied to the
vapor cloud by means of hand-held hoses and/or stationary water-spray barri-
ers. For effective absorption, it is important to direct waterfog or spray
nozzles from a downwind direction to avoid driving the vapors downwind more
quickly. Other important factors relating to the effectiveness of water
sprays are the distance of the nozzles from the point of release, the fog
pattern, nozzle flow rate, pressure, and nozzle rotation. If the right
strategy is followed, a "capture zone" can be created downwind of the release
into which the ammonia vapor will drift and be absorbed. In low wind condi-
tions, two fog nozzles should be placed upwind of the release to ensure that
the ammonia cloud keeps moving downwind against the water fog nozzle pres-
sures. If water fog is used to absorb ammonia vapors from a diked area
containing spilled liquid ammonia, great care must be taken not to direct
water into the liquid ammonia itself.
Water-spray barriers consist of a series of spray nozzles which can be
directed either up or down. If placed 30-40 feet from the point of ammonia
release, these barriers are very effective in absorbing the ammonia vapors
passing through without distortion of the ammonia cloud (47). Several fog
nozzles may be situated farther downwind to absorb the remainder of the vapors
getting through.
In general, techniques used to disperse or control vapor emissions should
emphasize simplicity and reliability. In addition to the mitigation tech-
niques discussed above, physical barriers such as buildings and rows of trees
will help to contain the vapor cloud and control its movement. Hence, reduc-
ing the consequences of a hazardous vapor cloud can actually begin with a
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carefully planned layout of facilities and the use of imaginative landscaping
around major hazard sites.
5.6 OPERATION AND MAINTENANCE PRACTICES
Accidental releases of toxic materials result not only from deficiencies
of design but also from deficiencies of operation. Unfortunately, human error
is often responsible for the realization of hazards with potentially damaging
consequences. The human error hazard manifests itself in numerous ways, both
indirectly and directly. For example, a lax management policy which does not
enforce safety standards might be indirectly responsible for an unnecessary
injury or fatality, or an operator may take the wrong action at a control
panel which would directly lead to a hazardous release. Aspects of plant
operation which impact the magnitude of the risk of human error include
management policy, operator training, and maintenance and modification
procedures. These topics are discussed in the following subsections.
5.6.1 Management Policy
Competent and effective management plays a vital role in the prevention
of accidental releases as a result of human error. The primary responsibili-
ties of managers at chemical plants with large inventories of hazardous
chemicals include the following (39):
• Ensuring worker competency;
• Developing, documenting, and enforcing standard operating
procedures and safety policies;
• Communicating and promoting feedback regarding safety issues;
• Identification, assessment, and control of hazards; and
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• Regular plant audits and provisions for independent checks.
Management is ultimately responsible for the competency of workers hired
at facilities which handle hazardous materials. Because of the serious
consequences that may result from operator error at these installations, the
qualifications and capabilities of prospective personnel for high hazard areas
should be carefully assessed to ensure that worker skills are matched to job
responsibilities. In addition, the skills of competent operators should be
maintained by regular training, safety meetings, and employee reviews.
In the chemical industry, documentation is generally produced which sets
forth standard procedures for equipment operation, maintenance, inspection,
hazard identification, and emergencies. The enforcement of standard proce-
dures is therefore one of management's most fundamental responsibilities in
the area of plant safety and accident prevention. However, before procedures
can be enforced, they must be communicated to plant personnel in a clear,
concise style so that they are thoroughly understood. Emphasis should be
placed on worker safety and the serious consequences of operator error in
processes involving hazardous materials.
Unfortunately, requiring workers to read documents which contain safety
policies is often not enough to ensure that they are fully understood and
followed. For this reason, verbal communication should be practiced and
encouraged which emphasizes plant safety and promotes feedback. When
management demonstrates a willingness to respond to initiatives from below and
participates directly with workers in improving safety, worker morale
increases, influencing the degree to which standard procedures are followed.
Hazard identification, assessment, and control is another area that
should be addressed by management to minimize the potential for accidental
chemical releases. The establishment of formal hazard assessment techniques
would provide management with a mechanism for obtaining information which can
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be used to rank potential problems and decide how best to allocate hazard
control resources.
The plant safety audit is one of the most frequently used methods for
obtaining safety related information. A total plant safety audit involves a
thorough evaluation of a plant's design, layout, and procedures, and is
specifically aimed at identifying and correcting potentially unsafe
conditions. The objectives of these audits include alerting operating
personnel to process hazards, determining if safety procedures need to be
modified, screening for equipment or process changes that may have introduced
new hazards, assessing the feasibility of applying new hazard control
technologies, identifying additional hazards, and reviewing inspection and
maintenance programs (49). In-house safety audits can be performed by
appointed safety review committees, or qualified consultants or insurers may
be brought in to provide a more objective assessment.
5.6.2 Operator Training
Accidental chemical releases may result from numerous types of operator
errors including following incorrect operating procedures, failing to
recognize critical situations, or by direct physical mistakes, e.g., by
turning the wrong valve. For all of these errors, the fundamental problem may
be the operator's lack of knowledge or understanding of process variables,
equipment operation, or emergency procedures. It is important for management
to recognize the extent to which a comprehensive operator training program can
decrease the potential for accidental releases resulting from human error.
Some general characteristics of quality industrial training programs include
the following:
• Establishment of good working relations between management and
personnel;
• Definition of trainer responsibilities and training program goals;
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• Use of documentation, classroom instruction, and field training (in
some cases supplemented with simulator training);
• Inclusion of procedures for normal startup and shutdown, routine
operations, and emergencies; and
• Frequent supplemental training and the use of up-to-date training
materials.
Employees in plants which manufacture, process, or store anhydrous
ammonia should be thoroughly educated about the important aspects of handling
this chemical. These include the proper means of handling and storing,
potential consequences of improper use and handling, prevention of spills,
cleanup procedures, maintenance procedures, and emergency procedures. It is
the job of the trainer to ensure that the right type and amount of information
is supplied at the right time. To do this he must not only understand the
technical content of a job, but also those aspects of the job where operators
may have difficulty. It is therefore advantageous for trainers to spend time
observing and analyzing the tasks and skills they will be teaching.
Two types of training which are especially important cover emergencies
and safety procedures. Emergency training includes topics such as:
• Recognition of alarm signals;
• Performance of specific functions (e.g., shutdown switches);
• Use of emergency equipment;
• Evacuation procedures;
• Fire fighting; and
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• Rehearsal of emergency situations.
Safety training includes not only responses to emergency situations, but also
accident prevention measures. Aspects addressed in safety training sessions
include (39):
• Hazard recognition and communication;
• Actions to be taken in particular situations;
• Available safety equipment and locations;
• When and how to use safety equipment;
• Use and familiarity with relevant documentation; and
• First aid and CPR.
The frequency of training and the frequency with which training materials
are updated are important in maintaining strong training programs. Chemical
processes may be modified to the extent that equipment changes require
operational change, and operators must be made aware of the changes and safety
considerations that accompany them in a timely manner. In addition to
operator training programs, organized management training is also beneficial
as it provides managers with the perspective necessary to formulate good
policies and procedures and to make changes that will improve the quality of
the overall plant safety program.
5.6.3 Maintenance and Modification Practices
Plant maintenance is necessary to ensure the structural integrity of
chemical processing equipment; modifications are often necessary to allow more
effective production. However, since these activities are also potential
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causes of accidental chemical releases, proper maintenance and modification
practices are important to the prevention of accidents.
Maintenance refers to a wide range of activities, including preventive
maintenance, production assistance (e.g., adjustment of settings), servicing
(e.g., lubrication and replacement of consumables), running maintenance,
scheduled repairs during shutdown, and breakdown maintenance. These
activities in turn require specific operations such as emptying, purging, and
cleaning vessels, breaking pipelines, tank repair or demolition, welding, hot
tapping (attaching a branch to an in-service line), and equipment removal
(39).
Proper maintenance and modification programs should be a normal part of
plant operation and design procedures, respectively, to reduce the chances for
an accidental release. Maintenance should be based on a priority system to
ensure that the most critical equipment is taken care of first. Strict
procedures should apply to process modifications to ensure that modifications
do not create unintended hazards. Inspections and nondestructive testing of
vessels, piping, and machinery should be conducted periodically to detect
small flaws that could eventually lead to a major release.
Two of the more common maintenance problems are equipment identification
and equipment isolation (39). Work performed on the wrong piece of equipment
can have disastrous effects, as can failure to completely isolate equipment
from process materials and electrical connections. Other potential sources of
maintenance accidents are improper venting to relieve pressure, insufficient
draining, and not cleaning or purging systems before maintenance activities
begin.
Permit systems and up-to-date maintenance procedures minimize the
potential 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
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ensuring that appropriate inspection and testing procedures are followed.
Such permits generally include specific information such as (39):
• The type of maintenance operations to be conducted,
• Descriptions and identifying codes of the equipment to be
worked on,
« Classification of the area in which work will be conducted,
• Documentation of special hazards and control measures,
• Listing of the maintenance equipment to be used, and
• The date and time when maintenance work will be performed.
Permit-to-work systems offer many advantages. They explain the work to
be done to both operating and maintenance workers. In terms of equipment
identification and hazard identification, they provide a level of detail that
significantly reduces the potential for errors that could lead to accidents or
releases. They also serve as historical records of maintenance activities.
Another form of maintenance control is the maintenance information
system. Ideally, these systems should log the entire maintenance history of
equipment, including preventative maintenance, inspection and testing, routine
servicing, and breakdown or failure maintenance. This type of system is also
used to track incidents caused by factors such as human error, leaks, and
fires which resulted in hazardous conditions, downtime, or direct repair
costs.
One important maintenance practice is repairing or replacing equipment
that appears to be headed for failure. A number of testing methods are
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available for examining the condition of equipment. Some of the most common
types of tests are listed below:
• Metal thickness and integrity testing,
• Vibration testing and monitoring, and
• Relief valve testing.
All of the above testing procedures are nondestructive, i.e., they do not
damage the material or equipment that they test.
Accidental releases are frequently the result of some aspect of plant
modification. To avoid confusion with maintenance activities, a modification
is defined as an intentional change in process materials, equipment, operating
procedures, or operating conditions (39). Accidents result when equipment
integrity and operation are not properly assessed following modification, or
when modifications are made without updating corresponding operation and
maintenance instructions. Frequently, hazards created by modifications do not
appear in the exact location of the change. For example, equipment
modifications can invalidate the arrangements for system pressure relief and
blowdown or they can invalidate the function of instrumentation systems.
Several factors should be considered in reviewing modification plans before
authorizing work. According to Lees, these include (39):
• Sufficient number and size of relief valves,
• Appropriate electrical area classification,
• Elimination of effects which could reduce safety standards,
• Use of appropriate engineering standards.
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• Proper materials of construction and fabrication standards.
• Existing equipment not stressed beyond design limits,
• Necessary changes in operating conditions, and
• Adequate instruction and training of operation and
maintenance teams.
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 may involve numerous combinations of
process design, equipment design, and operational measures, are especially
difficult to quantify because they reduce a probability rather than a physical
quantity of a chemical release. Protective measures are more analogous to
traditional pollution control technologies. Thus, they may be easier to
quantify in terms of their efficiency in minimizing the adverse effects of a
chemical that could be released.
Preventive measures reduce the probability of an accidental release by
increasing the reliability of both process systems operations and the equip-
ment. Control effectiveness can thus be expressed for both the qualitative
improvements and the quantitative improvements through probabilities. Table
5-4 summarizes what appear to be some of the major design, equipment, and
operational measures applicable to the primary hazards identified for the
ammonia applications in the U.S. The items listed in this table are for
illustration purposes 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 appropriate. Each case must therefore be evaluated individually. A
103
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presentation of more information about reliability in terms of probabilities
is planned for 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 ammonia storage
and process facilities found in the United States.
5.-8.1 Prevention and Protection Measures
Preventive measures reduce the probability of an accidental release from
a process or storage facility by increasing the reliability of both process
systems operations and equipment. Along with an increase in the reliability
of a system is an increase in the capital and annual costs associated with
incorporating prevention and protection measures into a system. Table 5-5
presents costs for some of the major design, equipment, and operational
measures applicable to the primary hazards identified in Table 5-4 for the
ammonia applications discussed in Section 3.
5.8.2 Levels of Control
Prevention of accidental releases relies on a combination of technologi-
cal, administrative, and operational practices as they apply to the design,
construction, and operation of facilities where hazardous chemicals are used
and stored. Inherent in determining the degree to which these practices are
carried out is their costs. At a minimum, equipment and procedures should be
in accordance with applicable codes, standards, and regulations. However.
additional measures can be taken to provide extra protection against an acci-
dental release.
The levels of control concept provides a means of assigning costs to
increased levels of prevention and protection. The minimum level is referred
104
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TABLE 5-4. EXAMPLES OF MAJOR PREVENTION AND PROTECTION MEASURES
FOR AMMONIA RELEASES
Hazard Area
Prevention/Protection
Ammonia flow
control
Temperature sensing
and cooling medium
flow control
Temperature sensing
and heating medium
flow control
Overpressure
Corrosion
Reactor and reboiler
temperatures
Overfilling
Atmospheric releases
from relief discharges
Storage tank or line
rupture
Redundant flow control loops;
Minimal overdesign of feed systems
Redundant temperature sensors;
Interlock flow switch to shut off
NH- feed on loss of cooling, with
relief venting to emergency scrubber
system
Redundant temperature sensors;
Interlock flow switch to shut off
NH. feed on loss of heating, with
relief venting to emergency scrubber
system
Redundant pressure relief; not
isolatable; adequate size; discharge
not restricted
Increased monitoring with more
frequent inspections; use of 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
Diking; foams; dilution;
neutralization; water sprays;
enclosure vented to emergency
scrubber system
105
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TABLE 5-5. ESTIMATED TYPICAL COSTS OF MAJOR PREVENTION AND
PROTECTION MEASURES FOR AMMONIA RELEASE3
Prevention/Protection Measure
Capital Cost
(1986 $)
Annual Cost
(1986 $/yr)
Flow control loop
Temperature sensor
Pressure relief
- relief valve
- rupture disk
Interlock system for flow shut-off
Alarm system
Level sensor
- liquid level gauge
- load cell
Physical barriers
- curbing
- 3 ft. retaining wall
Diking (based on a 10,000 gal. tank)
- 3 ft. high
- top of tank height. 10 ft.
• • b
Increased corrosion inspection
4,000-6.000
250-400
1.000-2.000
1.000-1,200
1,500-2.000
250-500
1.500-2.000
10.000-15.000
750-1.000
1.500-2.000
1.200-1,500
7,000-7,500
500-750
30-50
120-250
120-150
175-250
30-75
175-250
1,300-1,900
120-150
175-250
150-175
850-900
200-400
on a 10,000 gallon fixed ammonia storage tank system and a 10 tons/day
ammonia stripper system.
Based on 10-20 hours 0 $20/hr.
106
-------
to as the "Baseline" system. This system consists of the elements required
for normal safe operation and basic prevention of an accidental release of
hazardous 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.
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.
Levels of control cost estimates were prepared for a 25 ton fixed ammonia
storage tank system with a 10,000 gal capacity and a waste water treatment
ammonia stripper system with a 10 tons/day ammonia recovery rate. The reader
should be aware that the cost estimates presented in this section are for
illustrative purposes only, i.e., it is doubtful that any specific instal-
lation would find all of the control options listed in these tables appro-
priate for their purposes. An actual system is likely to incorporate some
107
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items from each of the levels of control and also some control options not
listed here. The purpose of these estimates is to illustrate the relationship
between cost and control, not to provide an equipment check list.
5.8.3 Cost Summaries
Table 5-6 presents a summary of the total capital and annual costs for
each of the three levels of controls for the ammonia storage system and the
ammonia stripper system. The costs presented correspond to the systems
described in Table 5-7 and Table 5-8. Each of the level costs include the
cost of the basic system plus any added controls. Specific cost information
and breakdown for each level of control for both the storage and process
facilities are .presented in Tables 5-9 through 5-14.
5.8.4 Equipment Specifications and Detailed Costs
Equipment specifications and details of the capital cost estimates for
the ammonia storage and the ammonia stripper systems are presented in Tables
5-15 through 5-22.
5.8.5 Methodology
Format for Presenting Cost Estimates—
Tables are provided for control schemes associated with storage and pro-
cess facilities for ammonia 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 systems.
Capital Cost—All capital costs presented in this report are shown as
total fixed capital costs. Table 5-23 defines the cost elements comprising
total fixed capital as it is used here.
108
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TABLE 5-6. SUMMARY COST ESTIMATES OF POTENTIAL LEVELS OF CONTROLS
FOR AMMONIA STORAGE TANK AND STRIPPER
System
Level of
Control
Total
Capital Cost
(1986 $)
Total
Annual Cost
(1986 $/yr)
Ammonia Storage Tank;
25 Ton Fixed Ammonia
Tank with 10,000
Gallon Capacity
Baseline 215.000
Level #1 553,000
Level #2 1,254,000
26,000
65.000
146.000
Waste Water Treatment
Ammonia Stripper
with 10 Tons/Day
Ammonia Recovery
Baseline 430,000
Level #1 948,000
Level #2 1.760,000
59.000
120,000
197.000
109
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TABLE 5-7. EXAMPLE OF LEVELS OF CONTROL FOR AMMONIA STORAGE TANK
Process: 25 ton fixed ammonia storage tank
10.000 gal
Controls
Baseline
Level No. 1
Level No. 2
Process:
Flow:
None
None
Single check- Add second check.
valve on tank— valve.
process feed line.
None
Add a reduced-pressure
device with internal
air gap and relief
vent to containment
tank or scrubber.
Temperature:
None
None
Add temperature
indicator.
Pressure:
Single pressure
relief valve,
vent to atmos-
phere. Provide
local pressure
indicator.
Add second relief
valve, secure
non-is datable.
Vent to limited
scrubber.
Add rupture disks
under relief valves.
Provide local pressure
indication on space
between disk and
valve.
Quantity:
Local level
indicator.
Add remote level
indicator.
Add level alarm. Add
high-low level inter-
lock shut-off for both
inlet and outlet
lines.
Location:
Materials of
Construction:
Vessel:
Away from traffic. Away from traffic
and flammables.
Carbon steel
Tank pressure
specification:
250 psig.
Carbon steel with
increased corrosion
allowances. (1/8
inch)
Tank pressure
specification:
300 psig.
Away from traffic,
flammables, and other
hazardous processes.
Type 316 SS.
Tank pressure
specification:
375 psig
(Continued)
A reduced pressure device is a modified double check valve
110
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TABLE 5-7 (Continued)
Process: 25 ton fixed ammonia storage tank
10,000 gal
Controls
Baseline
Level No. 1
Level No. 2
Piping:
Process
Machinery:
Enclosures;
Diking:.
Scrubbers:
Mitigation:
Schedule 40
carbon steel.
Schedule 80
carbon steel.
Centrifugal pump. Centrifugal pump,
carbon steel, 316 SS construc-
stuffing box tion, double cap-
seal, acity mechanical
seal.
None
None
None
None
Steel building.
3 ft high.
Water scrubber.
Water sprays.
Schedule 80 Type 316
stainless steel.
Magnetically-coupled
centrifugal pump, 316
SS, construction.
Concrete building.
Top of tank height,
10 ft.
Same.
Same.
Ill
-------
TABLE 5-8. EXAMPLE OF LEVELS OF CONTROL FOR AMMONIA STRIPPER
Process: Waste water Treatment
Basis: 10 tons/day ammonia recovery plant
Controls
Baseline
Level No. 1
Level No. 2
Process:
Temperature:
Pressure:
Flow:
Quantity:
Mixing:
Corrosion:
Composition:
Materials of
Construction:
Provide local
temperature
control.
Provide local
pressure control.
Single pressure
relief valve.
Vent to atmos-
phere.
Provide local
flow control on
stripper feed
and heating
medium to re-
boiler.
None.
None.
Visual inspec-
tions.
None.
Carbon steel.
Enhanced tempera-
ture and flow
control.
Add redundant
temperature sensors
and alarms. Add
remote tempera-
ture indicator.
Add redundant
pressure sensors.
Add second relief
valve. Vent to
limited scrubber.
Add redundant flow
control loops.
None.
None.
Same.
None.
Carbon steel with
added corrosion
allowance.
Computer control of
process. Use of
interlock systems.
Add computer control.
Add temperature switch
and back-up cooling
system.
Add computer control.
Add rupture disks
under relief valves
and provide local and
remote pressure indi-
cator on space between
disk and valve.
Add computer control.
Add interlock flow
switch to shut off
feed on loss of cool-
ing medium.
None.
None.
Same.
None.
Type 316 stainless
steel.
(Continued)
112
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TABLE 5-8 (Continued)
Process: Waste water Treatment
Basis: 10 tons/day ammonia Recovery Plant
Controls
Baseline
Level No. 1
Level No. 2
Vessel:
Piping:
Process
Machinery:
Pressure speci-
fication: 250
psig.
Schedule 40
carbon steel.
Centrifugal
pump, carbon
steel construc-
tion, stuffing
box.
Protective
Barriers:
Scrubbers :
Mitigation:
None.
None.
None.
Pressure specifi-
cation: 300 psig.
Schedule 80 car-
bon steel.
Centrifugal pump.
Type 316 stainless
steel construction.
double capacity
mechanical seal.
Curbing around
stripper.
Water scrubber.
Water sprays.
Pressure specifica-
tion: 375 psig.
Schedule 80 Type
316 stainless
steel.
Magnetically-coupled
centrifugal pump. Type
316 stainless steel
construction.
3 ft. high retain- ing
wall.
Same.
Same.
113
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TABLE 5-9. ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED
WITH BASELINE AMMONIA STORAGE SYSTEM
Capital Cost Annual Cost
(1986 $) (1986 $/yr)
Vessels:
Storage Tank 186,000 22.000
Piping and Valves:
Pipework 4.500 520
Check Valve 520 60
Ball Valves (5) 3.200 370
Excess Flow Valves (2) 950 110
Angle Valves (2) 3,600 420
Relief Valve 2.000 230
Process Machinery:
Centrifugal Pump 10,000 1.200
Instrumentation:
Pressure Gauges (4) 1,500 170
Liquid Level Gauge 1.500 170
Procedures and Practices:
Visual Tank Inspection (external) 15
Visual Tank Inspection (internal) 60
Relief Valve Inspection 15
Piping Inspection 300
Piping Maintenance 120
Valve Inspection 30
Valve Maintenance 350
Total Costs 215.000 26.000
114
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TABLE 5-10. ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED
WITH LEVEL 1 AMMONIA STORAGE SYSTEM
Capital Cost
(1986 $)
Annual Cost
(1986 $/yr)
Vessels:
Storage Tank
Piping and Valves:
Pipework
Check Valve
Ball Valves (5)
Excess Flow Valves (2)
Angle Valves (2)
Relief Valves (2)
Process Machinery:
Centrifugal Pump
Instrumentation:
Pressure Gauges (4)
Flow Indicator
Load Cell
Remote Level Indicator
Enclosures:
Steel Building
Scrubbers:
Water Scrubber
Diking:
3 ft
220,000
12.000
1,100
3.200
950
3.600
4.000
20.000
1.500
3.700
1,500
1,900
10.000
268.000
1.300
26.000
1.300
120
370
110
420
460
2.300
170
430
170
220
1.200
31.000
160
(Continued)
115
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TABLE 5-10 (Continued)
Capital Cost Annual Cost
(1986 $) (1986 $/yr)
Procedures and Practices:
Visual Tank Inspection (external) 15
Visual Tank Inspection (internal) 60
Relief Valve Inspection 30
Piping Inspection 300
Piping Maintenance 120
Valve Inspection 35
Valve Maintenance 400
Total Costs 553.000 65.000
116
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TABLE 5-11. ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED
WITH LEVEL 2 AMMONIA STORAGE SYSTEM
Capital Cost
(1986 $)
Annual Cost
(1986 $/yr)
Vessels:
Storage Tank
Piping and Valves:
Pipework
Reduced Pressure Device
Ball Valves (5)
Excess Flow Valves (2)
Angle Valves (2)
Relief Valves (2)
Rupture Disks (2)
Process Machinery:
Centrifugal Pump
Instrumentation:
Temperature Indicator
Pressure Gauges (6)
Flow Indicator
Load Cell
Remote Level Indicator
Level Alarm
High-Low Level Shutoff
Enclosures:
Concrete Building
Scrubbers:
Alkaline Scrubber
Diking:
10 ft High Concrete Dike
877.000
6.000
2,700
3.200
950
3.600
4.000
1.100
32.000
2.200
2,200
3.700
16.000
1.900
740
1.900
19.000
268,000
7.400
102.000
680
310
370
110
420
460
130
3.700
260
260
430
1.800
220
90
220
2,200
31,000
870
(Continued)
117
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TABLE 5-11 (Continued)
Capital Cost
(1986 $)
Annual Cost
(1986 $/yr)
Procedures and Practices:
Visual Tank Inspection (external)
Visual Tank Inspection (internal)
Relief Valve Inspection
Piping Inspection
Piping Maintenance
Valve Inspection
Valve Maintenance
15
60
50
300
120
35
400
Total Costs
1.254.000
146.000
118
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TABLE 5-12. ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED WITH
BASELINE WASTE WATER TREATMENT AMMONIA STRIPPER
Capital Cost Annual Cost
(1986 $) (1986 $/yr)
Equipment:
Vessels and Machinery:
Stripping Column
Reboiler and Condenser
Centrifugal Pumps (3)
Total Vessels and Machinery
Piping and Valves:
a
Instrumentation:
Q
Maintenance and Inspections:
Total Costs
260,000
117,000
53.000
430,000
31,000
14,000
6,000
8,000
59.000
o
Costs are based on using cost factors from Peters and Timmerhaus (50) and a
total fixed capital cost of $1.8 million (1986 basis) (21) for a 10 tons/day
ammonia recovery plant.
119
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TABLE 5-13. ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED WITH
LEVEL 1 WASTE WATER TREATMENT AMMONIA STRIPPER
Capital Cost Annual Cost
(1986 $) (1986 $/yr)
Equipment:
Vessels and Machinery:
Stripping Column
Reboiler and Condenser
Centrifugal Pumps (3)
Total Vessels and Machinery3 470,000 56.000
Piping and Valves:3 147,000 17,000
Relief Valve 2,000 240
Instrumentation:3 53,000 6,000
Temperature Sensor 360 45
Temperature Alarm 360 45
Remote Temp. Indicator 1,800 220
Remote Press. Indicator 1,800 220
Flow Control Loops (2) 11,000 1,300
Diking:
Curbing Around Reactor 1,200 150
Scrubber:
Water Scrubber 260,000 31,000
a
Maintenance and Inspections: 8,000
Relief Valve Inspection 15
Total Costs 948,000 120,000
Q
Costs are based on using cost factors from Peters and Timmerhaus (50) and a
total fixed capital cost of $1.8 million (1986 basis) (21) for a 10 tons/day)
ammonia recovery plant.
120
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TABLE 5-14. ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED WITH
LEVEL 2 WASTE WATER TREATMENT AMMONIA STRIPPER
Capital Cost Annual Cost
(1986 $) (1986 $/yr)
Equipment:
Vessels and Machinery:
Stripping Column
Reboiler and Condenser
Centrifugal Pumps (3)
Total Vessels and Machinerya 1.049,000 126,000
Piping and Valves*: 167,000 20,000
Relief Valve (2) 7,400 880
Rupture Disk (2) 2.300 280
Instrumentation8: 53.000 6,400
Temperature Sensor 360 45
Temperature Alarm 360 45
Temperature Switch 540 65
Remote Temp. Indicator 1,800 220
Remote Press. Indicator 1.800 220
Flow Control Loops (2) 11,000 1,300
Flow Interlock System 1,800 220
All Loops on Computer Control 201,000 2,400
Diking:
3 ft High Retaining Wall 3,000 360
Scrubber:
Water Scrubber 260,000 31,000
Maintenance and Inspections3: 8,000
Relief Valve Inspection 25
Total Costs 1,760.000 197,000
a Costs are based on using cost factors from Peters and Timmerhaus (50) and a
total fixed capital cost of $1.8 million (1986 basis) (21) for a 10 tons/day
ammonia recovery plant.
Computer control costs are determined using cost estimating factors from
Va1 1 e*—Ri e>fi1-ra fS11.
Valle-Riestra (51).
121
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TABLE 5-15. EQUIPMENT SPECIFICATIONS ASSOCIATED WITH AMMONIA STORAGE SYSTEM
Equipment Item
Equipment Specifications
Reference
VESSELS:
Storage Tank
PIPING AND VALVES:
Pipework
Check Valve
Ball Valve
Excess Flow
Angle Valve
Relief Valve
Reduced Pres-
sure Valve
Rupture Disk
Baseline: 10,000 gal Carbon Steel
Storage Tank, 250 psig rating
Level #1: 10,000 gal Carbon Steel with
1/8 in. Corrosion Protection
300 psig
Level #2: 10,000 gal Type 316 Stainless
Steel, 375 psig rating
Baseline: 4 in. Schedule 40 Carbon Steel
Level #1: 4 in. Schedule 80 Carbon Steel
Level #2: 4 in. Schedule 80 Type 316
Stainless Steel, 100 ft. in
Length
4 in. Vertical Lift Check Valve, Carbon
Steel Construction
4 in. Class 300, Carbon Steel Body, Monel®
Ball and Trim
4 in. Standard Valve
4 in. Carbon Steel Construction
2 in. x 3 in. Class 300 Inlet and Outlet
Flange, Angle Body, Closed Bonnet with
Screwed Cap, Carbon Steel Body
Double Check Valve Type Service with
Internal Air Gap and Relief Valve
2 in. Monel® Disk and Carbon
Steel Holder
PROCESS MACHINERY:
Centrifugal Pump Baseline:
Level 1:
Level 2:
Single Stage, Carbon Steel
Construction, Stuffing Box
Single Stage, Type 316 Stainless
Steel Construction, Double
Mechanical Seal
Type 316 Stainless Steel Con-
struction, Magnetically-Coupled
50.52.53.54
55
52,56
50,52,56
52
57
52
50
53,58,59
52,60
52.60
52,60
(Continued)
122
-------
TABLE 5-15 (Continued)
Equipment Item
Equipment Specifications
Reference
INSTRUMENTATION:
Pressure Gauge
Liquid Level
Gauge
Temperature
Indicator
Flow Indicator
Level Indicator
Load Cell
High-low Level
Shutoff
ENCLOSURE:
Building
SCRUBBER:
DIKING:
Diaphragm Sealed, Hastelloy C Diaphragm,
0-1,000 psi
Differential Pressure Type 50,61
Thermocouple, Thermowell, Electronic
Indicator 50,52,61
Differential Pressure Cell and Transmitter
and Associated Flowmeter 50,61
Differential Pressure Type Indicator 50,52,61
Electronic Load Cell 50,61,62
Solenoid Valve, Switch, and Relay System 50,52,61
Level #1: 26-Gauge Steel Walls and Roof,
Door, Ventillation System 57
Level #2: 10 in. Concrete Walls,
26-Gauge Steel Roof 64
Level #1 and 2: Spray Tower, Monel® Con-
struction, 4 ft. x 12 ft..
Water Sprays
Level #1: 6 in. Concrete Walls,
3 ft. high 57
Level #2: 10 in. Concrete Walls, Top
of Tank Height
123
-------
TABLE 5-16. MATERIAL AND LABOR COSTS ASSOCIATED WITH BASELINE AMMONIA STORAGE SYSTEM
ts>
Vessels:
Storage Tank
Piping and Valves:
Pipework
Check Valves
Ball Valves (5)
Excess Flow Valves (2)
Angle Valves (2)
Relief Valve
Process Machinery:
Centrifugal Pump
Instrumentation:
Pressure Gauges (4)
Liquid Level Gauge
Total Costs
Materials
Cost
86.000
900
320
2,000
600
2.400
1.300
4,900
800
800
100.000
Labor
Cost
39,000
2.100
30
150
40
40
50
2,100
200
200
44.000
Direct
Costs
(1986 $)
125.000
3.000
350
2.150
640
2.440
1.330
7,000
1.000
1.000
144. 000
Indirect
Costs
44. 000
1.100
120
750
220
860
460
2.500
350
350
50.000
Capital
Cost
186.000
4.500
520
3.200
950
3.600
2,000
11.000
1,500
1,500
215.000
-------
TABLE 5-17. MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 1 AMMONIA STORAGE SYSTEM
NJ
Ln
Vessels:
Storage Tank
Piping and Valves :
Pipework
Check Valves
Ball Valves (5)
Excess Flow Valves (2)
Angle Valves (2)
Relief Valve (2)
Process Machinery:
Centrifugal Pump
Instrumentation:
Pressure Gauges (4)
Flow Indicator
Liquid Level Gauge
Remote Level Indicator
Enclosures:
Steel Building
Scrubbers:
Water Scrubber
Diking:
3 ft. High Concrete
Diking
Total Costs
Materials
Cost
102.000
5.300
640
2.000
600
2.400
2.600
9.300
800
2.000
800
1,000
4.600
125.000
390
259.000
Labor
Cost
46, 000
2,500
60
150
40
40
100
4.000
200
500
200
250
2,300
56.000
520
113.000
Direct
Costs
(1986 $)
148.000
7.800
700
2.150
640
2.440
2.660
13.300
1.000
2.500
1.000
1.250
6.900
181.000
900
372.000
Indirect
Costs
52.000
2.700
250
750
220
860
920
4.700
350
880
350
440
2.400
63,000
320
130.000
Capital
Cost
220, 000
12.000
1,100
3.200
950
3.600
4.000
20. 000
1.500
3.700
1.500
1,900
10. 000
268.000
1.300
553,000
-------
TABLE 5-18. MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 2 AMMONIA STORAGE SYSTEM
N5
(f*
Vessels:
Storage Tank
Piping and Valves:
Pipework
Reduced Pres. Device
Ball Valves (5)
Excess Flow Valves (2)
Angle Valves (2)
Relief Valve (2)
Rupture Disks (2)
Process Machinery:
Centrifugal Pump
Instrumentation:
Temperature Indicator
Pressure Gauges (6)
Flow Indicator
Load Cell
Remote Level Indicator
Level Alarm
High-Low Level Shut off
Enclosures:
Concrete Building
Scrubbers:
Water Scrubber
Diking:
10 ft. High
Concrete Dike
Total Costs
Materials
Cost
407.000
1.400
1.600
2.000
600
2.400
2,600
650
15.000
1.200
1.200
2.000
8.400
1.000
400
1.000
6.100
125,000
2.200
582.000
Labor
Cost
183,000
2.600
200
150
40
40
100
75
6.400
300
300
500
2.100
250
100
250
6.600
56.000
2.850
262,000
Direct
Costs
(1986 $)
590,000
4.000
1,800
2.150
640
2.440
2,660
725
21.400
1.500
1.500
2.500
10.500
1.250
500
1,250
12.700
181,000
5,000
844, 000
Indirect
Costs
207.000
1.400
630
750
220
860
920
250
7,500
530
530
880
3,700
440
180
440
4.500
63,000
1.800
295,000
Capital
Cost
877,000
6.000
2.700
3.200
950
3,600
4.000
1.100
32.000
2.200
2.200
3.700
16.000
1.900
740
1,900
19.000
268.000
7.400
1,254.000
-------
TABLE 5-19. EQUIPMENT SPECIFICATIONS ASSOCIATED WITH WASTE WATER
TREATMENT AMMONIA STRIPPING PROCESS
Equipment Item
Equipment Specification
Reference
VESSELS AND MACHINERY:
PIPING AND VALVES:
Pipework
Relief Valve
Rupture Disk
INSTRUMENTATION:
Temp. Sensor
Temp. Alarm
Temp. Switch
Remote Temp.
Indicator
Remote Press.
Indicator
Flow Control Loop
Flow Interlock
System
DIKING:
Ammonia Stripper and Associated Re- 21
boiler and Condenser as Defined in
Reference
Baseline: 4 in. Schedule 40
Carbon Steel, 360 ft. 55
Level #1: Schedule 80 Carbon Steel
Level #2: Schedule 80 Type 316
Stainless Steel
2 in. x 3 in. Class 300 Inlet and
Outlet Flanges, Angle Body, Closed
Bonnet with Screwed Cap, Carbon Steel
Body
2 in. Monel® Disk and Carbon
Steel Holder
Thermocouple and Associated Thermowell
Indicating and Audible Alarm
Two-Stage Switch with Independently
Set Actuation
Transmitter and Associated Electronic
Indicator
Transducer, Transmitter and Electronic
Indicator
4 in. Globe Control Valve, Flowmeter
and PID Controller
Solenoid Valve, Switch, and Relay
System
Level #1: 6 in. High Concrete Curbing
Level #2: 3 ft. High Concrete Retain-
ing Wall
52
53,58,59
50,52,61
51,58,63
50,61
50,61
50,61
50,61
50.52.57,61
57
SCRUBBER:
Level #1 and #2: Spray Tower, Monel*
Construction 4 ft. x 12 ft.,
Water Sprays 64
127
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TABLE 5-20. MATERIAL AND LABOR COSTS ASSOCIATED WITH BASELINE WASTE WATER
TREATMENT AMMONIA STRIPPER
NJ
oo
Materials Labor Direct Indirect
Cost Cost Costs Costs
Capital
Cost
(1986 $)
Equipment :
Vessels and Machinery:
Stripping column
Reboiler and Condenser
Centrifugal Pumps (3)
Total Ves. and Mach. a 125,000 56,000 181,000 45,000
Piping and Valves:3 45.000 37,000 82,000 20,000
Instrumentation:3 28,000 9,000 37,000 9,000
Total Costs 198,000 102,000 300,000 74,000
260,000
117,000
53,000
430.000
Costs are based on using cost factors from Peters and Timmerhaus (50) and a total fixed
capital cost of $1.8 million (1986 basis) (21) for a 10 tons/day ammonia recovery plant.
-------
TABLE 5-21. MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 1 WASTE WATER
TREATMENT AMMONIA STRIPPER
VO
Materials Labor
Cost Cost
Direct Indirect
Costs Costs
Capital
Cost
(1986 $)
Equipment:
Vessels and Machinery:
Stripping column
Reboiler and Condenser
Centrifugal Pumps (3)
Total Ves. and Mach. a 226.000 101.000
Piping and Valves:3 77,000 25.000
Relief Valve 1,300 50
Instrumentation:3 28.000 9,000
Temperature Sensor 200 50
Temperature Alarm 200 50
Remote Temp. Indicator 1,000 250
327.000 82.000
102.000 25.000
1.350 340
37.000 9.000
250 60
250 60
1.250 310
470, 000
146. 000
2,000
53,000
360
360
1.800
(Continued)
Costs are based on using cost factors from Peters and Timmerhaus (50) and a total fixed
capital cost of $1.8 million (1986 basis) (21) for a 10 tons/day ammonia recovery plant.
-------
TABLE 5-21 (Continued)
Remote Press. Indicator
Flow Control Loops (2)
Diking:
Curbing Around Reactor
Scrubber:
Water Scrubber
Total Costs
Materials
Cost
1,000
6,000
500
125,000
466.000
Labor
Cost
250
1,500
350
56.000
194.000
Direct
Costs
(1986 $)
1.250
7.500
850
181.000
660.000
Indirect
Costs
310
1.900
210
45.000
164,000
Capital
Cost
1,800
11.000
1.200
260.000
948.000
-------
TABLE 5-22. MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 2 WASTE WATER
TREATMENT AMMONIA STRIPPER
Materials Labor
Cost Cost
Direct
Costs
Indirect Capital
Costs Cost
(1986 $)
Equipment :
Vessels and Machinery:
Stripping column
Reboiler and Condenser
Centrifugal Pumps (3)
Total Ves. and Mach.a 504.000 226.000
Piping and Valves:3 87.000 29.000
Relief Valve (2) 5.000 100
Rupture Disk (2) 1.500 100
Instrumentation:3 28,000 9.000
Temperature Sensor 200 50
Temperature Alarm 200 50
730. 000
116.000
5.100
1,600
37. 000
250
250
182.000 1.049,000
29.000 167.000
1.300 7.400
400 2. 300
9,000 53.000
60 360
60 360
(Continued)
Costs are based on using cost factors from Peters and Timmerhaus (50) and a total fixed
capital cost of $1.8 million (1986 basis) (21) for a 10 tons/day ammonia recovery plant.
-------
TABLE 5-22 (Continued)
Co
N>
Materials Labor Direct
Cost Cost Costs
Indirect Capital
Costs Cost
(1986 $)
Temperature Switch 300 75 375
Remote Temp. Indicator 1,000 250 1.250
Remote Press. Indicator 1.000 250 1,250
Flow control Loops (2) 6.000 1.500 7.500
Flow Interlock System 1,000 250 1,250
All Loops on Computer 105.000 35.000 140.000
Control
Diking:
3 ft. high retaining wall 900 1. 200 2, 100
Scrubber:
Water Scrubber 125,000 56.000 181,000
Total Costs 866,000 359.000 1.225.000
95 540
310 1.800
310 1,800
1.900 11,000
310 1,800
35.000 201.000
530 3.000
45,000 260.000
305.000 1.760.000
Computer control costs are determined using cost estimating factors from Valle-Riestra
/ c- -t ^
(51).
-------
TABLE 5-23. FORMAT FOR TOTAL FIXED CAPITAL COST
Item No. Item Cost
1 Total Material Cost
2 Total Labor Cost
3 Total Direct Cost Items 1+2
4 Indirect Cost Items (Engineering
& Construction Expenses) 0.35 x Item 3a
5 Total Bare Module Cost Items (3 + 4)
6 Contingency (0.05 x Item 5)
7 Contractor's Fee 0.05 x Item 5
8 Total Fixed Capital Cost Items (5+6+7)
For storage facilities, the indirect cost factor is 0.35. For process
facilities, the indirect cost factor is 0.25.
For storage facilities, the contingency cost factor is 0.05. For process
facilities, the contingency cost factor is 0.10.
133
-------
The computation of total fixed capital as shown in Table 5-23 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 uninstalled equipment costs by
computing costs of installation separately. To obtain the total fixed capital
cost, other costs obtained by utilizing factors are added to the total direct
costs.
The first group of other cost elements is indirect costs. These include
engineering and supervision, construction expenses, and various other expenses
such as administration expenses, for example. These costs are computed by
multiplying total direct costs by a factor shown in Table 5-23. The factor is
approximate, is obtained from the cost literature, and is based on previous
experience with capital projects of a similar nature. Factors can have a
range of values and vary according to technology area and for individual
technologies within an area. Appropriate factors were selected for use in
this report based on judgement and experience.
When the indirect costs are added to the total direct costs, total bare
module cost is obtained. Some additional cost elements such as contractor's
fee and contingency are calculated by applying and adding appropriate factors
to the total bare module cost as shown in Table 5-23 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 5-24 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.
134
-------
TABLE 5-24. FORMAT FOR TOTAL ANNUAL COST
Item No. Item Cost
1 Total Direct Cost
2 Capital Recovery on Equipment 0.163 x Item 1
Items
3 Maintenance Expense on Equipment 0.01 x Item 1
Items
4 Total Procedural Items
5 Total Annual Cost Items (2+3+4)
135
-------
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 ammonia process and
storage facilities using the best costs for available sources. The primary
sources of cost information are Peters and Timmerhaus (50). Chemical Engineer-
ing (65). and Valle-Riestra (51) 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.
Costs in this document reflect the "typical" or "average" representation
for specific equipment items. This restricts the use of data in this report
to:
• Preliminary estimates used for policy planning,
• Comparison of relative costs of different levels or systems.
and
• Approximations of costs that might be incurred for a specific
application.
The costs in this report are considered to be "order of magnitude" with a
+50 percent margin. This is because the costs are based on preliminary
estimates and many are updated from literature sources. Large departures from
the design basis of a particular system presented in this manual or the advent
of a different technology might cause the system cost to vary by a greater
extent than this. If used as intended, however, this document will provide a
reasonable source of preliminary cost information for the facilities covered.
136
-------
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—
A1.1 costs in this report are expressed in June 1986 dollars. Costs
reported in the literature were updated using cost indices for materials and
labor.
Costs expressed in base year dollars may be adjusted to dollars for
another year by applying cost indices as shown in the following equation:
, , , , .. new base year index
new base year cost = old base year cost x -,-. v * r—:—
J 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 Timmer-
haus (50):
—0 34
Cost = [50(Weight of Vessel in Pounds) u'-1^]
137
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The vessel weight is determined using appropriate design equations as given by
Peters and Timmerhaus (50) which allow for wall thickness adjustments for
corrosion allowances, for example. The vessel weight is increased by a factor
of 0.15 for horizontal vessels and 0.20 for vertical vessels to account for
the added weight due to nozzles, manholes, and skirts or saddles. Appropriate
factors are applied for different materials of construction as given in Peters
and Timmerhaus (50). The vessel costs are updated using cost factors.
Finally a shipping cost amounting to 10 percent of the purchased cost is added
to obtain the delivered equipment cost.
Piping—Piping costs were obtained using cost information and data
presented by Yamartino (55). A simplified approach is used in which it is
assumed that a certain length of piping containing a given number of valves,
flanges, and fittings is contained in the storage or process facility, the
data presented by Yamartino (55) permit cost determinations for various
lengths, sizes, and types of piping systems. Using these factors, a represen-
tative estimate can be obtained for each of the storage and process facili-
ties.
Diking—Diking costs were estimated using Mean's Manual (57) for rein-
forced concrete walls. The following assumptions were made in determining the
costs. The dike contains the entire contents of a tank in the event of a leak
or release. Two dike sizes are possible: a three-foot high dike, six-inches
thick and a top-of-tank height dike ten inches thick. The tanks are raised
off the ground and are not volumetrically included in the volume enclosed by
the diking. These assumptions facilitate cost determination for any size
diking system.
Enclosures—Enclosure costs were estimated using Mean's Manual (57) 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 and a
metal door. The steel building has 26 gauge roofing and siding and metal
138
-------
door. The cost of a ventilation system was determined using a typical 1.000
scfm unit and doubling the cost to account for duct work and requirements for
the safe enclosure of hazardous chemicals.
Scrubbers—Scrubber costs were estimated using the following equation
from the Gard (64) manual for spray towers based on the actual cubic feet per
minute of flow at a chamber velocity of 600 feet/minute.
Costs = 0.235 x (ACFM + 43.000)
3
A release rate of 10,000 ft /minute was assumed for the storage vessel systems
and an appropriate rate was determined for process system based on the
quantity of hazardous chemicals present in the system at any one time. For
the ammonia stripper system, a release rate of 10,000 ft /minute was assumed.
In addition to the spray tower, the costs also include pumps and a storage
tank for the scrubbing medium. The costs presented are updated to June 1986
dollars.
Installation Factors—
Installation costs were developed for all equipment items included in
both the process and storage systems. The costs include both the material and
labor costs for installation of a particular piece of equipment. The costs
were obtained directly from literature sources and vendor information or
indirectly by assuming a certain percentage of the purchased equipment cost
through the use of estimating factors obtained from Peters and Timmerhaus (50)
and Valle-Riestra (51). Table 5-25 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.
139
-------
TABLE 5-25. FORMAT FOR INSTALLATION COSTS
Equipment Item Factor or Reference
Vessels:
Storage Tank 0.45
Expansion Tank 0.25
Piping and Valves:
Pipework Ref. 55
Expansion Loop Ref. 52
Reduced Pressure Device Ref. 52
Check Valves Ref. 52
Gates Valves Ref. 52
Ball Valves Ref. 52
Excess Flow Valves Ref. 52
Angle Valves Ref. 57
Relief Valves Ref. 52
Rupture Disks Ref. 52
Process Machinery:
Centrifugal Pump 0.43
Gear Pump 0.43
Instrumentation:
All Instrumentation Items 0.25
Enclosures: Ref. 57
Diking: Ref. 57
Scrubbers: 0.45
140
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SECTION 6
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Inc.. Arlington. VA, 1984.
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3. Mark, H.F.; Othmer. D.F.; Overberger, C.G.; and Seaborg, G.T.,
Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed., Volume 2, John
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6. Blanken, J.M., Behavior of Ammonia in the Event of a Spillage. CEP
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7. Safety Requirements for the Storage and Handling of Anhydrous Ammonia.
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New York, NY, 1981.
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14. Prescott, G.R., and F.W. Badger. Cracking Problems in Ammonia
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15. Lawler, G.M.. (ed.). Chemical Origins and Markets, Fifth Edition.
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16. Considine, D.M., (ed.). Chemical and Process Technology Encyclopedia,
McGraw-Hill. 1974.
17. Slack, A.V., and James, G.R., (eds.). Ammonia, Part IV, Marcel Dekker,
Inc.. New York and Basel, 1979.
18. Lowenheim, F.A., and M.K. Moran. Faith, Keyes, and Clark's Industrial
Chemicals, Fourth Ed., John Wiley & Sons, 1975.
19. Jojima, T. Urea Reactor Failure. CEP Technical Manual, Ammonia Plant
Safety and Related Facilities, Volume 21, AIChE, 1979.
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Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed.. Volume 15, John
Wiley & Sons, 1983.
21. Chevron Waste Water Treating Process - WWT Process. Chevron Research
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22. Klett, R.J. Treat Sour Water for Profit. Hydrocarbon Processing,
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Processing, November 1981.
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Conditioning Engineers, Inc., Atlanta, GA. 1986.
25. Conversation between M. Stohs of Radian Corporation and a representative
of General Battery Corporation, Reading, PA, August 1986.
26. Mark. H.F.; Othmer, D.F.; Overberger. C.G.; and Seaborg, G.T.,
Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed., Volume 12, John
Wiley & Sons, 1983.
27. Conversation between M. Stohs of Radian Corporation and a representative
of PB&S Chemical Company, Henderson. KY, August 1986.
28. Recommended Rules for Design and Construction of Large Welded
Low-Pressure Storage Tanks. API Standard 620, American Petroleum
Institute. Washington, D.C., 1970.
142
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29. ASME Boiler and Pressure Vessel Code. ANSI/ASME BPV-VIII-1, American
Society of Mechanical Engineers, New York. NY. 1983.
30. Chemical Plant and Petroleum Refinery Piping. ANSI/ASME B31.3, American
National Standards Institute. Inc. New York. NY. 1980.
31. Steel Valves. ANSI/ASME B16.5, American National Standards Institute.
Inc., New York, NY, 1977.
32. Steel Pipe Flanges and Flanged Fittings. ANSI/ASME B16.5, American
National Standards Institute, Inc., New York, NY, 1977.
33. Blanken, J.M. Stress Corrosion Cracking of Ammonia Storage Spheres:
Survey and Panel Discussion. CEP Technical Manual, Ammonia Plant Safety
and Related Facilities, Volume 24, AIChE, 1984.
34. Lunde, L. Stress Corrosion Cracking of Steels in Ammonia: Specially
Vapor-Phase Cracking. CEP Technical Manual, Ammonia Plant Safety and
Related Facilities, Volume 24, AIChE, 1984.
35. American National Standard for Refrigeration Piping. ANSI B31.5,
American National Standards Institute, Inc., New York, NY, 1974.
36. American National Standard for Power-Operated Pumps for Anhydrous
Ammonia and LP Gas. ANSI/UL 51, American National Standards Institute,
Inc., New York. NY, 1981.
37. Pressure Relief Device Standards - Part 3 - Compressed Gas Storage
Containers. Pamphlet S-1.3, Compressed Gas Association, Inc., Arlington,
VA, 1984.
38. Prijatel, J. Failure Analysis of Ammonia Plant Shutdown Instrumentation
and Control. CEP Technical Manual. Ammonia Plant Safety and Related
Facilities. Volume 24, AIChE, 1984.
39. Lees, F.P. Loss Prevention in the Process Industries - Hazard
Identification, Assessment, and Control, Volumes 1 & 2, Butterworths,
London, 1983.
40. Aarts, J.J. and D.M. Morrison. Refrigerated Storage Tank Retainment
Walls. CEP Technical Manual, Ammonia Plant Safety and Related
Facilities, Volume 23, American Institute of Chemical Engineers, New
York, NY, 1981.
41. Roberts, R.H. and S.E. Handman. Minimize Ammonia Releases, Hydrocarbon
Processing, March 1986.
42. Feind, K. Reducing Vapor Loss in Ammonia Tank Spills. CEP Technical
Manual, Ammonia Plant Safety and Related Facilities, Volume 17, American
Institute of Chemical Engineers, New York', NY, 1975.
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43. Radian Laboratory Notebook Number 215. for EPA Contract 68-02-3994. Work
Assignnment 94, Page 5, 1986.
44. Hiltz, R.H. and S.S. Gross. The Use of Foams to Control the Vapor Hazard
from Liquified Gas Spills. In Control of Hazardous Material Spills -
Proc. 1980 National Conference on Control of Hazardous Material Spills.
Louisville. KY. May 1980.
45. Clark, W.D. Using Fire Foam on Ammonia Spills. CEP Technical Manual,
Ammonia Plant Safety and Related Facilities, Volume 18, American
Institute of Chemical Engineers, New York, NY, 1976.
46. Hiltz, R. Part 3 - Vapor Hazard Control. In Bennett, G.F., Feates,
F.S., and Wilder, I. Hazardous Materials Spills Handbook, McGraw-Hill,
1982.
47. Greiner, M.L. Emergency Response Procedures for Anhydrous Ammonia Vapor
Release. CEP Technical Manual, Ammonia Plant Safety and Related
Facilities, Volume 24, American Institute of Chemical Engineers, New
York, NY, 1984.
48. McQuaid, J. and A.F. Roberts. Loss of Containment - Its Effects and
Control. In Developments '82 (Institution of Chemical Engineers Jubilee
Symposium), London, England, April 1982.
49. Kubias, F. 0. Technical Safety Audit. Presented at the Chemical
Manufacturers Association Process Safety Management Workshop. Arlington,
VA, May 7-8. 1985.
50. Peters, M.S. and K.D. Timmerhaus. Plant Design and Economics for
Chemical Engineers. McGraw-Hill Book Company, New York, NY, 1980.
51. Valle-Riestra, J.F. Project Evaluation in the Chemical Process Irius-
tries. McGraw-Hill Book Company, New York, NY, 1983.
52. Richardson Engineering Services, Inc. The Richardson Rapid Construction
Cost Estimating System, Volume 1-4, San Marcos, CA, 1986.
53. Pikulik, A. and H.E. Diaz. Cost Estimating for Major Process Equipment.
Chemical Engineering, October 10, 1977.
54. Hall, R.S., J. Matley, and K.J. McNaughton. Cost of Process Equipment.
Chemical Engineering, April 5, 1982.
55. Yamartimo, J. Installed Cost of Corrosion-Resistant Piping-1978.
Chemical Engineering, November 20, 1978.
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representative of Mark Controls Corporation. Houston, TX, August 1986.
144
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57. R.S. Means Company. Inc. Building Construction Cost Data 1986 (44th
Edition). Kingston, MA.
58. Telephone conversation between J.D. Quass of Radian Corporation and a
representative of Zook Enterprises. Chagrin Falls, OH, August 1986.
59. Telephone conversation between J.D. Quass of Radian Corporation and a
representative of Fike Corporation. Houston, TX, August 1986.
60. Green, D.W. (ed.). Perry's Chemical Engineers' Handbook (Sixth Edition).
McGraw-Hill Book Company, New York, NY, 1984.
61. Liptak, B.C. Costs of Process Instruments. Chemical Engineering,
September 7, 1970.
62. Liptak, B.C. Costs of Viscosity, Weight, Analytical Instruments.
Chemical Engineering, September 21, 1970.
63. Liptak, E.G. Control-Panel Costs, Process Instruments. Chemical
Engineering, October 5. 1970.
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Company, New York, NY, June 1974, December 1985, and August 1986.
145
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APPENDIX A
GLOSSARY
This glossary defines selected terms used in the text of this manual
which might be unfamiliar to some users or which might be used differently by
different authors.
Accidental release; The unintentional spilling, leaking, pumping, purging,
emitting, emptying, discharging, escaping, dumping, or disposing of a toxic
material into the environment in a manner that is not in compliance with a
plant's federal, state, or local environmental permits and results in toxic
concentrations in the air that are a potential health threat to the
surrounding community.
Assessment; The process whereby the hazards which have been identified are
evaluated in order to provide an estimate for the level of risk.
Cavitation; The formation and collapse of vapor bubbles in a flowing liquid.
Specifically the formation and collapse of vapor cavities in a pump when there
is sufficient resistance to flow at the inlet side.-
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
destructing continuous process exhaust gas emissions.
Creep failure; Failure of a piece of metal as a result of creep. Creep is
time dependent deformation as a result of stress. Metals will deform when
exposed to stress. High levels of stress can result in rapid deformation and
rapid failure. Lower levels of stress can result in slow deformation and
protracted failure.
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Deadheading; Closing or nearly closing or blocking the discharge outlet or
piping of an operating pump or compressor.
Electromotive Series of Metals; A list of metals and alloys arranged
according to their standard electrode potentials; which also reflects their
relative corrosion potential.
Enthalpy; A thermodynamic property of a chemical related to its energy
content at a given condition of temperature, pressure and physical state.
Enthalpy is the internal energy added to the product of pressure times volume.
Numerical values of enthalpy for various chemicals are always based on the
change in enthalpy from an arbitrary reference pressure and temperature, and
physical state, since the absolute value cannot be measured.
Facility; A location at which a process or set of processes are used to
produce, refine or repackage chemicals, or a location where a large enough
inventory of chemicals are stored so that a significant accidental release of
a toxic chemical is possible.
Hazard; A source of danger. The potential for death, injury or other forms
of damage to life and property.
Hygroscopic; Readily absorbing and retaining moisture, usually in reference
to readily absorbing moisture from the air.
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 0.25% carbon. Mild
steel is satisfactory for use where severe corrodents are not encountered or
where protective coatings can be used to prevent or reduce corrosion rates to
acceptable levels.
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Mitigation; Any measure taken to reduce the severity of the adverse effects
associated with the accidental release of a hazardous chemical.
Olefinic hydrocarbons; A specific subgroup of aliphatic hydrocarbons sharing
the common characteristic of at least one unsaturated carbon-to-carbon atomic
bond in the hydrocarbon molecule, and with straight or branched chain
structure.
Passivation film; A layer of oxide or other chemical compound of a metal on
its surface that acts as a protective harrier 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.
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.
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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.
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.
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TABLE B-l.
APPENDIX B
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
in*
ft*
in3
ft3
gal
Ib
short ton (ton)
short ton (ton)
atm
mm Hg
psia
psig
°C
Btu/lb
Btu/lbmol
kcal/gmol
Btu/lb-°F
Ib/ft3
Ib/gal
oz/gal
quarts/gal
gal/min
gal /day
ft3/min
f t/min
ft/sec
centipoise (CP)
To
cm
m
cm*
m*
cm3
m3
m3
kg
Mg
metric ton (t)
kPa
kPa
kPa
kPa*
°c*
K*
kJ/kg
kJ/kgmol
kJ/kgmol
kJ/kg-°C
kg/m3
kg/m3
kg/m3
5 / 3
G^I / m
on / QLIU
m3/day
m3/min
m/min
m/sec
kg/m-s
Multiply By
2.54
0.3048
6.4516
0.0929
16.39
0.0283
0.0038
0.4536
0.9072
0.9072
101.3
0.133
6.895
((psig)+14.696)x(6.895)
(5/9)x(°F-32)
°C+273.15
2.326
2.326
4.184
4. 1868
16.02
119.8
7.490
25. 000
0.0038
0. 0038
0.0283
0.3048
0.3048
0.001
^Calculate as indicated
OUS GOVERNMENT PRINTING OFFICE:! 9 87 -7it8-121/ 670314
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