United States EPA~600 /8"87-034h
Environ me ma I Protection
*«encv August 1987
SERA Research and
Development
PREVENTION REFERENCE MANUAL:
CHEMICAL SPECIFIC
VOLUME 8: CONTROL OF
ACCIDENTAL RELEASES
OF HYDROGEN FLUORIDE
Prepared for
Office of Air Quality Planning and Standards
Prepared by
Air and Energy Engineering Research
Laboratory
Research Triangle Park NC 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. SockMConomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special-Reports
9. Miscellaneous Reports
This report has been assigned to the SPECIAL REPORTS series. This series is
reserved for reports which are intended to meet the technical information needs'
of specifically targeted user groups. Reports in this series include Problem Orient-
ed Reports, Research Application Reports, and Executive Summary Documents.
Typical of these reports include state-of-the-art analyses, technology assess-
ments, reports on the results of major research and development efforts, design
manuals, and user manuals.
EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental Protection Agency, and
approved for publication. Approval does not signify that the contents necessarily
reflect the views and policy of the Agency, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service. Springfield. Virginia 22161.
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ABSTRACT
The accidental releases of a toxic chemical at Bhopal, India in 1984 was
a milestone in creating an increased public awareness of toxic release prob-
lems. 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
i
chemicals.
Anhydrous hydrogen fluoride has an IDLH (Immediately Dangerous to Life
and Health) concentration of 20 ppm. which makes it a substantial acute toxic
hazard.
Reducing the risk associated with an accidental release of hydrogen fluo-
ride involves identifying some of the potential causes of accidental releases
that apply to the process facilities that use hydrogen fluoride. 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 in-
clude recommendations on plant design practices, prevention, protection and
mitigation technologies, and operation and maintenance practices. Conceptual
cost estimates of example prevention, protection, and mitigation measures are
provided.
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ACKNOWLEDGEMENTS
This manual was prepared under the overall guidance and direction of T.
Kelly Janes. Project Officer, with the active participation of Robert P.
Hangebrauck. William J. Rhodes, and Jane M. Crum, all of U.S. EPA. In
addition, other EPA personnel served as reviewers. Radian Corporation
principal contributors involved in preparing the manual were Graham E.
Harris (Program Manager), Glenn B. DeWolf (Project Director). Daniel S. Davis.
Jeffrey D. Quass, Miriam Stohs. and Sharon L. Wevill. Contributions were also
provided by other staff members. Secretarial support was provided by Roberta
J. Brouwer and others. Special thanks are given to the many other people.
both in government and industry, who served on the Technical Advisory Group
and as peer reviewers.
111
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TABLE OF CONTENTS
Section
ABSTRACT "
FIGURES v
TABLES vi
1 INTRODUCTION 1
1.1 Background 1
1.2 Purpose of this Manual 1
1.3 Sources and Uses of Hydrogen Fluoride 2
1.4 Organization of the Manual 3
2 CHEMICAL CHARACTERISTICS 4
2.1 Physical Properties 4
2.2 Chemical Properties and Reactivity ... 7
2.3 ' lexicological and Health Effects 9
3 PROCESS FACILITY DESCRIPTIONS 12
' 3.1 Hydrogen Fluoride Manufacture . 12
3.2 Hydrogen Fluoride Consumption 16
3.2.1 Hydrogen Fluoride Alkylation 16
3.2.2 Manufacture of Chlorofluorocarbons . 21
3.2.3 Aluninum Fluoride Manufacture 24
3.2.4 Sodium Aluminum Fluoride (Cryolite) Manufacture. 25
3.2.5 Uranium Tetrafluoride Manufacture 25
3.3 Repackaging 28
3.4 Storage and Transfer 29
4 PROCESS HAZARDS 33
4.1 Potential Causes of Releases 33
4.1.1 Process Causes 34
4.1.2 Equipment Causes 35
4.1.3 Operational Causes 36
5 HAZARD PREVENTION AND CONTROL 37
5.1 General Considerations 37
5.2 Process Design . 33
5.3 Physical Plant Design 40
5.3.1 Equipment ................... 40
5.3.2 Plant Siting and Layout 53
5.3.3 Transfer and Transport Facilities 50
5.4 Protection Technologies 53.
5.4.1 Enclosures 51
5.4.2 Scrubbers 53
LV
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TABLE OF CONTENTS (Continued)
Section Page
5.5 Mitigation Technologies 67
5.5.1 Secondary Containment Systems 68
5.5.2 Flotation Devices and Foams 74
5.5.3 Mitigation Techniques for Hydrogen Fluoride
Vapor 76
5.6 Operation and Maintenance Practices .......... 78
5.6.1 Management Policy ..... 78
5.6.2 Operator Training 80
5.6.3 Maintenance and Modification Practices 84
5.7 Control Effectiveness 87
5.8 Illustrative Cost Estimates for Controls 38
5.8.1 Prevention and Protection Measures 88
5.8.2 Levels of Control 92
5.8.3 Cost Summaries 93
5.8.4 Equipment Specifications and Detailed Costs . . 107
5.8.5 Methodology 107
6 REFERENCES 129
APPENDIX A - ELECTROMOTIVE .SERIES OF METALS 134
APPENDIX B - GLOSSARY .- . 135
APPENDIX C - METRIC (SI) CONVERSION FACTORS . 138
FIGURES
Number Page
3-1 Conceptual diagram of typical hydrogen fluoride manufacturing
process 13
3-2 Conceptual diagram of typical hydrogen fluoride alkylation process 18
3-3 Conceptual diagram of typical fluorochlorocarbon process .... 22
3-4 Conceptual diagram of typical uranium tetrafluoride manufacturing
process 26
3-5 Conceptual process diagram of hydrogen fluoride rail tank car
unloading and tank storage facility . . . 30
3-6 Conceptual process diagram of hydrogen fluoride tank truck
unloading and tank storage facility ..... 31
5-1 Concept of a liquid hydrogen fluoride expansion chamber 50
5-2 Potential layouts for a neutralization basin system 71
5-3 Computer model simulation showing the effect of diking on the
vapor cloud generated from a release of refrigerated hydrogen
fluoride 73
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TABLES
Number '
2-1 Physical Properties of Hydrogen Fluoride .............. 5
2-2 Physical Properties of 70 Percent Aqueous Hydrofluoric Acid .... 7
2-3 Exposure Limits for Hydrogen Fluoride ............... 10
2-4 Predicted Human Health Effects of Exposure to Various
Concentrations of Hydrogen Fluoride ................ 11
3-1 Typical Uses of Hydrogen Fluoride ................. 17
5-1 Some Process Design Considerations for Processes Involving Hydrogen
Fluoride ........... ........... ........ 39
5-2 Characteristics of Materials of Construction in Hydrogen Fluoride
and Hydrofluoric Acid Service - - ....... .......... 41
i
5-3 Typical Hydrogen Fluoride Absorption Data . ............ 34
5-4 Example of Performance Characteristics for an Emergency Packed Bed
Scrubber for Hydrogen Fluoride ................... 66
5-5 Aspects of Training Programs for Routine Process Operations .... 32
5-6 Examples of Major Prevention and Protection Measures for
Hydrogen Fluoride Releases ..................... 89
5-7 Estimated Typical Costs of Major Prevention and Protection
Measures for Hydrogen Fluoride Releases .............. 91
5-8 Summary Cost Estimates of Potential Levels of Controls for
Hydrogen Fluoride Storage Tank and Alkylation Reactor ........ 94
5-9 Example of Levels of Control for Hydrogen Fluoride Storage Tank. . . 95
5-10 Example of Levels of Control for Hydrogen Fluoride Alkylation
Reactor. ... ........................... 97
5-11 Estimated Typical Capital and Annual Costs Associated with
Baseline Hydrogen Fluoride Storage System .............. 99
5-12 Estimated Typical Capital and Annual Costs Associated with
Level 1 Hydrogen Fluoride Storage System
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TABLES (Continued)
Number Page
5-13 Estimated Typical Capital and Annual Costs Associated with
Level 2 Hydrogen Fluoride Storage System 102
5-14 Estimated Typical Capital and Annual Costs Associated with
Baseline Hydrogen Fluoride Alkylation Reactor/Settler System .... 104
5-15 Estimated Typical Capital and Annual Costs Associated With
Level 1 Hydrogen Fluoride Alkylation Reactor/Settler System .... 105
5-16 Estimated Typical Capital and Annual Costs Associated With
Level 2 Hydrogen Fluoride Alkylation Reactor/Settler System .... 106
5-17 Equipment Specifications Associated with Hydrogen
Fluoride Storage System. ..... 108
5-18 Details of Material and Labor Costs Associated with Baseline
Hydrogen Fluoride Storage System 110
•
5-19 Details of Material and Labor Costs Associated with Level 1
Hydrogen Fluoride Storage System Ill
5-20 Details of Material and Labor Costs Associated with Level 2
Hydrogen Fluoride Storage System . 113
5-21 Equipment Specifications Associated with Hydrogen Fluoride
Alkylation Reactor/Settler 115
5-22 Details of Material and Labor Costs Associated with Baseline
Hydrogen Fluoride Alkylation Reactor/Settler System 117
5-23 Details of Material and Labor Costs Associated with Level 1
Hydrogen Fluoride Alkylation Reactor/Settler System 118
5-24 Details of Material and Labor Costs Associated with Level 2
Hydrogen Fluoride Alkylation Reactor/Settler System 119
5-25 Format for Total Fixed Capital Cost 121
5-26 Format for Total Annual Cost 123
5-27 Format for Installation Costs 128
VII
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SECTION 1
INTRODUCTION
1.1 BACKGROUND
Increasing concern about the potentially disastrous consequences of
accidental releases of toxic chemicals resulted from the Bhopal. India
accident of December 3. 1984. which killed approximately 2.000 people and
injured thousands more. A toxic cloud of methyl isocyanate was released.
Concern about the safety of process facilities handling hazardous materials
increased further after the accident at the Chernobyl nuclear power plant in
the Soviet Union in April of 1986.
While headlines of these incidents have created the current awareness of
toxic release problems, there have been other, perhaps less dramatic.
incidents in the past. Interest in reducing the probability and consequences
of 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.
Historically, major incidents in the United States involving hydrogen
fluoride do not appear to have been common, although a release of uranium
hexafluoride in Oklahoma in early 1986 decomposed to hydrogen'fluoride
resulting in at least one death and some injuries.
1.2 PURPOSE OF THIS MANUAL
The purpose of this manual is to provide technical information about
hydrogen fluoride and specifically about prevention, protection, and
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mitigation measures for accidental releases of hydrogen fluoride. The manual
addresses technological and procedural prevention, protection and mitigation
measures associated with the storage,- handling, and process operations
involving hydrogen fluoride.as it is used in the United States. This manual
does not address uses of hydrogen fluoride not encountered in the United
States.
This manual is intended as a summary for persons charged with reviewing
and evaluating the potential for releases at facilities that use. store.
handle, or manufacture hydrogen fluoride. It is not intended as a
specification manual, and in fact refers the reader to additional technical
manuals and other information sources for more complete information on the
topics discussed. Other information sources include manufacturers and
distributors of hydrogen fluoride, and technical literature on design,
operation, and loss prevention in facilities handling toxic chemicals.
i
1.3 SOURCES AND USES OF HYDROGEN FLUORIDE
•
Hydrogen Fluoride (HF) is a significant commodity chemical, produced by
sulfuric acid treatment of calcium fluoride in the natural mineral fluorspar.
In 1985, approximately 130.000 tons of hydrogen fluoride were manufactured in
the U.S. (1). Numerous references in the technical literature provide
information on both the manufacture and uses of hydrogen fluoride. In the
United States, the primary uses of hydrogen fluoride include:
• As a catalyst in petroleum refinery alkylation;
• Chlorofluorocarbon manufacture;
• Sodium aluminum fluoride manufacture;
• Uranium processing;
• Stainless steel pickling;
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• Glass etching and polishing; and
• Repackaging.
Storage systems for hydrogen fluoride include small cylinders (e.g..
150-Ib cylinder), bulk storage tanks, and railroad tank cars used for station-
ary storage.
In addition to anhydrous hydrogen fluoride (hydrogen fluoride gas).
hydrofluoric acid, an aqueous solution of hydrogen fluoride, is also used.
This manual focuses primarily on anhydrous hydrogen fluoride, but some con-
siderations also apply to hydrofluoric acid.
1.4 ORGANIZATION OF THE MANUAL
Following this introductory section, the remainder of this manual pre-
sents technical information on specific hazards and categories of hazards for
hydrogen fluoride and their control. As stated previously, these are examples
only and are representative of only some of the hazards that may be related to
accidental releases.
Section 2 discusses physical, chemical and toxicologies! properties of
hydrogen fluoride. Section 3 describes the types of facilities which manu-
facture and use hydrogen fluoride in the United States. Section 4 discusses
process hazards associates with these facilities. Hazard prevention and
control are discussed in Section 5. Costs of example storage and process
facilities reflecting different levels of control through alternative systems
are also presented in Section 5. The examples are for illustration only and
do not necessarily represent a satisfactory alternative control option in all
cases. Section 6 presents a reference list. Appendix A presents the
electromotive series of metals. Appendix B is a glossary of key technical
terms that might not be familiar to all users of the manual,- and Appendix C
presents selected conversion factors between metric (SI) and English
measurement units.
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SECTION 2
CHEMICAL CHARACTERISTICS
This section of the report describes the physical, chemical, and toxico-
logical properties of hydrogen fluoride as they relate to accidental release
hazards.
2.1 PHYSICAL PROPERTIES
Anhydrous hydrogen fluoride is a clear, colorless, corrosive liquid with
a pungent, irritating odor. With a boiling point of about 67°F, at room
temperature and atmospheric pressure, it is a colorless, corrosive, toxic gas.
Hydrogen fluoride is hygroscopic and fumes upon exposure to moist air.
t
Hydrogen fluoride in aqueous solutions is hydrofluoric acid, a highly corro-
sive liquid. Concentrated aqueous solutions also boil at relatively low
temperatures and fume upon contact with moist air. The physical properties of
anhydrous and aqueous hydrofluoric acid are listed in Tables 2-1 and 2-2,
respectively (2).
As a result of the relatively low boiling point of hydrogen fluoride.
spills and leaks of liquid can result in hazardous releases to the atmosphere
nearly as severe as direct gas or vapor releases. In addition, since the
vapor density of hydrogen fluoride is greater than that of air. releases will
remain close to the ground and could create a potentially dangerous situation
for workers and surrounding communities.
Liquid hydrogen fluoride has a large coefficient of thermal expansion.
As a result, liquid-full equipment is a special hazard. A liquid-full vessel
is a vessel that is not vented and is filled with liquid hydrogen fluoride
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TABLE 2-1. PHYSICAL PROPERTIES OF HYDROGEN FLUORIDE
Reference
CAS Registry Number
Chemical Formula
Molecular Weight
Normal Boiling Point
Melting Point
Liquid Specific Gravity (H,0=l)
Vapor Specific Gravity (air=l)
Vapor Pressure
Vapor Pressure Equation
log Pv = A - .
07664-39-3
HF
20.01
67.12 °F 8 14.7 psia
-118.4 °F
0.991 8 67.15 °F
2.4 @ 68 °F
17.8 psia 8 77 °F
where:'
Pv = vapor pressure, mm Hg
T = temperature, °C
A = 7.68098, a constant
B = 1.475.60. a constant
C = 287.88. a constant
2
2
3
4
2
5
Liquid Viscosity
Solubility in Water
Specific Heat at Constant
Volume (vapor)
0.256 centipoises ® 32 °F
Complete
0.55 Btu/(lb-8F) @ 68 «F
(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
Average Coefficient of
Thermal Expansion. 0-60 °F
2.99 Btu/(lb-°F) ® 68 °F
0.62 Btu/(lb- F) 8 68 °F
1.62 Btu/lb 9 67.15 °F
10.1 dynes/cm @ 32 °F
0.00112 °F
2
5
2
Additional properties useful in determining other properties from physical
property correlations.
Critical Temperature
Critical Pressure
Critical Density
Energy of Molecular Interaction
Effective Molecular Diameter
370 °F
940 psia
18.10 lb/ft3
355 K
3.240 Angstroms
2
2
2
7
7
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with little or no vapor space present above the liquid. A liquid-full line is
a section of pipe that is sealed off at both ends and is full of liquid
TABLE 2-2. PHYSICAL PROPERTIES OF 702 AQUEOUS HYDROFLUORIC ACID
Reference
Boiling Point 152.06°F 0 14.7 psia 6
Freezing Point -94.3°F • 6
Vapor Pressure 1.1. psia ® 32°F 6
Specific Gravity (HjO =1) 1.258 0 32-39.2°F 6
Specific Heat 0.75 Btu/lb-°F ® 64-68 °F 6
hydrogen fluoride with little or no vapor space. In these situations, there
is no room for thermal expansion of the liquid, and temperature increases can
»
result in containment failure.
2.2 CHEMICAL PROPERTIES AND REACTIVITY
Hydrogen fluoride, whether anhydrous or in aqueous solutions, is a highly
reactive chemical. The most significant chemical properties contributing to
the potential for releases are as follows (2,8):
• Anhydrous hydrogen fluoride rapidly absorbs moisture to
form highly corrosive hydrofluoric acid. Hydrofluoric
acid is corrosive to most metals and results in the
• formation of hydrogen gas in the presence of moisture.
This corrosiveness can lead to equipment failure, and the
potential buildup of hydrogen gas in confined areas
presents a fire and explosion hazard.
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Hydrogen fluoride reacts with metals listed above hydrogen
in the Electromotive Series of Metals (a ranking of metals
based on standard electrode potentials, see Appendix A.
page 109) to form fluoride salts. In addition, it reacts
with metal carbonates, oxides, and hydroxides. Accumula-
tion of these fluoride compounds can render valves and
other close-fitting moving parts inoperable in a process
system, causing possible equipment or process failures.
Such compounds also can contribute to the fouling of
critical heat transfer surfaces in process operations.
Hydrogen fluoride also attacks glass, silicate ceramics.
leather, natural rubber, and wood, but does not promote
their combustion.
Considerable heat evolves when anhydrous hydrogen fluoride
or concentrated hydrofluoric acid is diluted with water.
•Violent reactions can result from the inappropriate
addition of water or caustic solutions to these materials.
Anhydrous hydrogen fluoride and hydrofluoric acid react
with silica (SiO.) and SiO .-containing substances to form
silicon tetrafluoride (SiF.) and fluorosilicic acid.
, a colorless gas at ambient temperatures, is highly
toxic. An equilibrium mixture of SiF, in the presence of
moisture also contains hydrogen fluoride and hydrofluoric
acid.
Anhydrous hydrogen fluoride and hydrofluoric acid react
exothermally with organic and inorganic reducing agents,
but do not promote their combustion.
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• Anhydrous hydrogen fluoride reacts with cyanides and
sulfides to produce toxic hydrogen cyanide and hydrogen
sulfide. respectively. This can result in potentially
explosive mixtures in confined areas since both hydrogen
cyanide and hydrogen sulfide are flammable.
2.3 TOXICOLOGICAL AND HEALTH EFFECTS
Hydrogen fluoride is a highly toxic, and is a highly corrosive and severe
irritant to the skin. eyes, and respiratory system. The toxicology of hydro-
gen fluoride has been studied through accidental human exposure and through
animal studies (9.10.11,12,13). The acute effects of very short term exposure
to elevated concentrations of hydrogen fluoride, however, are not well docu-
mented.
The concentrations at which various acute effects occur vary significant-
ly with time of exposure and with individuals. For instance, inhalation of 50
parts per million (ppm) hydrogen fluoride for 30 to 60 minutes might be fatal,
while a concentration of 110 ppm inhaled for 1 minute might be tolerated with
only the initial onset of toxic effects. Less severe exposures cause irrita-
tion of the nose and eyes, smarting of the skin, and some degree of conjuncti-
val and respiratory irritation. More severe exposures can lead to severe
irritation of the eyes and eyelids, ulceration of the skin, inflammation and
congestion of the lungs, and eventual cardiovascular collapse and death.
Additional effects may include dyspnea, bronchopneumonia, cyanosis, shock.
muscle spasms, convulsions, parasthesias, jaundice, oliguria, albuminuria,
hematuria. nausea, vomiting, abdominal pain, diarrhea, and burns of the mouth,
esophagus, and digestive tract. A concentration of 20 ppm has been designated
as the IDLH (Immediately Dangerous to Life and Health), which is based on a 30
minute exposure. Table 2-3 presents a summary of some of the relevant expo-
sure limits for hydrogen fluoride. Table 2-4 presents a summary of predicted
human health effects of exposure to various concentrations of hydrogen fluo-
ride.
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TABLE 2-3. EXPOSURE LIMITS FOR HYDROGEN FLUORIDE
Exposure Concentration
Limit (ppm) Description Reference
IDLH 20 The concentration defined as 14
posing an immediate danger to
life and health (i.e. causes
toxic effects for a 30-minute
exposure).
PEL 3 A time-weighted 8-hour exposure 10
to this concentration, as set
by the Occupational Safety and
Health Administration (OSHA),
should result in no adverse
effects for the average worker.
i 50 This concentration is the lowest 10
published lethal concentration
for a human over a 30- minute
exposure.
110 This concentration is the lowest 10
published concentration causing
toxic effects (irritation) for
a 1-minute exposure.
10
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TABLE 2-4. PREDICTED HUMAN HEALTH EFFECTS OF EXPOSURE TO VARIOUS
CONCENTRATIONS OF HYDROGEN FLUORIDE
ppm Predicted Effect
0.5-3 ppm Odor threshold
2 ppm Repeated 6-hour exposures can result in
stinging eyes and facial skin, and nasal
irritation
>10 ppm Possible lung injury
>50 ppm Vapor is intolerably irritating and causes
damage to the lungs; inhalation may result
in serious injury
Source: Reference 11
11
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SECTION 3
PROCESS FACILITY DESCRIPTIONS
This section provides brief descriptions of the manufacture and uses of
hydrogen fluoride in the United States. Major hazards of these processes
associated with accidental releases are discussed in Section 4. Preventive
measures associates with these hazards are discussed in Section 5.
3.1 HYDROGEN FLUORIDE MANUFACTURE
Hydrogen fluoride is manufactured by the reaction of the fluorine con-
taining mineral, fluorospar. with sulfuric acid. Figure 3-1 presents a block
diagram of a typical hydrogen fluoride manufacturing process.
l
•
Finely ground acid grade fluorospar (greater than 97 percent CaF) is
reacted in a heated rotating steel kiln with sulfuric acid to form calcium
sulfate and hydrogen fluoride. The reaction is endothermic and heat is either
supplied externally by direct fire to the rotary kiln or by the addition of
sulfur trioxide and steam to the reaction zone (15,16). The heat absorbed is
603 Btu/lb (16).
In a typical process, fluorospar and sulfuric acid are fed continuously
and concurrently to the kiln by a screw conveyor. The reaction is typically
carried out at a temperature in the range of 392-482°F (15.16). In order to
minimize energy consumption and corrosion of the reactor, the reaction is
carried out at the lowest possible temperature resulting in good yields.
Crude product gas exits the reactor at approximately 212-338PF (15,16).
It consists primarily of hydrogen fluoride saturated with sulfuric acid and a
variety of impurities which vary depending on the composition of the raw
materials used in the reaction. The gas is fed to a gas scrubber where it is
12
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nnien(
i
1 t
1
ACID DESOHPnON
""•" " COLUMN
CALCIUM
RECYCLED
TO KILN ^
h
_ COj. SOj VENT
^ OASES
1
WATER 1
* SCRUBBER 1
30-35*
ACID
ANHYDROUS
FLUORIDE
ji
2
Figure 3-1. Conceptual diagram of typical hydrogen fluoride manufacturing process.
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scrubbed with aulfuric acid to remove small particles of fluorospar and/or
calcium sulfate.
After leaving the gas scrubber, the crude hydrogen fluoride gas is cooled
and liquified. In a typical process, the gas is cooled in shell and tube heat
exchangers from 284-338°F to 41-104°F (15). The gas is then contacted with
cold liquid hydrogen fluoride at -4 to -13°F in contact condensers to produce
a liquid hydrogen fluoride product (15). The uncondensed gases are scrubbed
with sulfuric acid to recover additional hydrogen fluoride. The final
effluent gases are absorbed in water and recovered as fluorosilic acid.
Following liquefaction, the crude hydrogen fluoride is distilled to
produce anhydrous hydrogen fluoride with a purity greater than 99.9 percent.
Since this process deals with the manufacture of hydrogen fluoride,
•
hydrogen fluoride is present in high concentrations or relatively pure form in
all areas following the reactor or kiln. Thus, the possibility of a large
release of this chemical is greater than what might exist in a process where
hydrogen fluoride is consumed as a reactant.
Specific high hazard areas in the manufacturing process, excluding bulk
storage and transfer (discussed in Section 3.4). include the following:
• Reactor (kiln);
• Hydrogen fluoride scrubber;
• Hydrogen fluoride condensers;
• Desorption column; and
• Hydrogen fluoride distillation.
14
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Although the reaction between sulfuric acid and calcium fluoride
(fluorspar) is an endothermic reaction, the reactor or kiln can be considered
a high hazard area since water may be present in the sulfuric acid used in the
manufacturing process resulting in the formation of highly corrosive hydro-
fluoric acid. Additionally, the corrosiveness of hydrogen fluoride increases
with temperature. Undetected corrosion could lead to equipment failure and a
possible release of hydrogen fluoride.
In addition, other portions of the process, including the scrubbing
units, could also be affected by similar corrosion problems as a result of
hydrofluoric acid vapor being carried to other portions of the process. A
properly designed system should use materials of construction which take this
corrosion potential into account.
Shell and tube .heat exchangers present a potential hazard from tube
leakage where water is used as the cooling medium. Undetected small leaks
over time could cause corrosion and eventually a failure. Also, a cooling
system failure could result in overpressure and a resulting equipment failure.
An additional concern with cooling equipment in this process is the
buildup of sulfur deposits on cooling surfaces resulting from sulfur and
sulfur forming impurities present in the initial reaction products. These
deposits can lead to clogging of piping and heat transfer equipment and loss
of cooling efficiency.
The desorption and stripping unit operations are subject to potential
overheating and overpressure since these operations have a thermal energy
input. Loss of cooling in condensers could be a cause for overpressure. The
reboilers and bottoms pumps are potential weak points in these systems since
operating conditions are severe.
15
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3.2 HYDROGEN FLUORIDE CONSUMPTION
The primary uses for hydrogen fluoride in the United States are chloro-
fluorocarbon manufacture, aluminum fluoride manufacture, sodium aluminum
fluoride (cryolite) manufacture, petroleum alkylation. and uranium tetra-
fluoride manufacture. Additional uses are shown in Table 3-1. This sub-
section summarizes the major technical features, related to release hazards.
of typical processing facilities found in the United States.
3.2.1 Hydrogen Fluoride Alkylation
A major use of hydrogen fluoride in the petroleum refining industry is
for alkylation of olefinic hydrocarbons. In this process, anhydrous hydrogen
fluoride is used as a liquid catalyst in the production of octane improvers
for gasoline.
*
A block diagram of a typical hydrogen fluoride alkylation process is
shown in Figure 3-2. This is one of several possible configurations for a
hydrogen fluoride alkylation process. The processes differ primarily in the
configuration of the reactor/settler section and whether or not they include a
depropanizer unit (18).
Before entering the alkylation unit, the olefin-containing feed is
treated to remove sulfur compounds and water. The feed is mixed with hydro-
fluoric acid and recycled isobutane, and the combined stream is fed to the
reactor vessel. The alkylation reactor operates at a temperature in the range
of 75-100°F and at a pressure of 80-115 pounds per square inch gage (psig)
(18). Cooling water in a heat-exchange-tube bundle inside the alkylation
reactor is commonly used in hydrogen fluoride alkylation to remove the heat
generated by the exothermic reaction. The acid and organic phases of the
reactor effluent separate in the settler, and the acid recycles to the re-
actor. A small portion of the acid is sent to a regenerator column where
relatively pure hydrogen fluoride is distilled from a minor amount of heavy
16
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TABLE 3-1. TYPICAL USES OF HYDROGEN FLUORIDE
Fluorocarbon manufacture
Sodium aluminum fluoride (synthetic cryolite) manufacture
Aluminum fluoride manufacture
Gasoline alkylation catalyst
Uranium tetrafluoride manufacture
Stainless steel picking
Manufacture of specialty metals
e.g.i columbium. tantalum, beryllium, and yttrium)
Other chemical manufacture
ammonium bifluoride
ammonium fluoride
antimony pentafluoride
antimony trifluoride
barium fluroide
boron trifluoride
cadmium fluoride
cobaltous fluoride
cupric fluoride
difluorophosphoric acid
fluoboric acid
fluorine
fluasilicic acid
fluosulfonic acid
hezafluoroacetone
hexafluorophosphoric acid
lead tetrafluoride
lithium fluoride
magnesium fluoride
mercuric fluoride
monofluorophosphoric acid
perchlorofluoroacetone
potassium bifluoride
potassium fluoride
sodium bifluoride
sodium fluoride
stannous fluoride
tantalum fluoride
trifluoromethylnitrophenol
zinc fluoride
Source: Adapted from Reference 17.
17
-------
00
I BUTANE
MAKEUP
OLEFIN
FEED
COOLINO
MATER
T f
REACTOR
1
Eft
ten
•*
Ulnae n
WrrEfl
HF HECVCLE
MAKEUP HF
t ^ SATURATED BUTANES
nBUIANE
' PRODUCT
ALKVLATE
PRODUCT
POLVMiR SLUDOE TO
NEUTRALIZATION
I BUTANE
RECYCLE
DEPROPANIZER
HF
STRIPPER
PROPANE
PRODUCT
Figure 3-2. Conceptual diagram of typical hydrogen fluoride alkylation process.
-------
organic compounds and water. The settler organic phase is fed to a fraction-
ator, the isostripper, where isobutane and lighter components are separated.
The bottoms product from the isostripper is motor alkylate. A portion of the
isostripper overhead is depropanized with propane, containing some hydrogen
fluoride, taken as an overhead stream. The propane is stripped of hydrogen
fluoride and recovered as a bottoms stream.
From a hydrogen fluoride release perspective, a fundamental character-
istic of the alkylation process is the use of hydrogen fluoride as a catalyst
rather than a reactant. Only a small portion of the hydrogen fluoride cata-
lyst is consumed in the alkylation process, approximately 0.002 - 0.007 Ib/gal
of product (28), and therefore the process has a number of critical areas
where hydrogen fluoride is present in high concentrations or relatively pure
form.
High hazard areas in the alkylation process, excluding bulk storage and
transfer (discussed in Section 3.4). include the following:
• Feed treatment to remove water and sulfur compounds from
the hydrocarbon feed;
• Reactor;
• Heat exchanger tube bundle within the reactor;
• Reactor cooling system;
• Hydrogen fluoride recycle circuits, including the settler;
• -Hydrogen fluoride distillation, (the regenerator column);
and
• Hydrogen fluoride stripping (from propane).
19
-------
The feed treatment process to remove water and sulfur is a critical area
of the process because these compounds promote corrosion. Water and hydrogen
fluoride combine to form hydrofluoric acid which rapidly attacks many mater-
ials including carbon steel. A properly designed alkylation system should use
materials of construction which take this corrosion potential into account and
allow a certain feed moisture concentration to be maintained. Deficiencies or
failures in the water removal system could lead to a protracted corrosion
problem resulting eventually in equipment failure. Sulfur compounds also can
lead to corrosion with results similar to those of water.
The reactor itself operates under mild conditions with near ambient
temperatures. Since the reactor is a pressure vessel with an exothermic
reaction, the potential exists for a runaway reaction resulting in overheating
and overpressure. The normal elevated operating pressure, combined with the
adverse effects of corrosion, could cause an equipment failure even under
normal operating conditions. Proper system design must anticipate these
hazards and incorporate appropriate safeguards. These safeguards should
include highly reliable reactant feed control, pressure relief, and reactor
cooling system controls and backup.
The presence of a heat exchange tube bundle within the reactor presents a
potential hazard from tube leakage since water is used as the cooling medium.
Small leaks over time could cause corrosion and eventually a failure. Also,
since the reactor operates at pressures above typical cooling water circuit
pressures, undetected leakage of acid into the cooling system could contribute
to protracted corrosion and ultimately a cooling system failure. A cooling
system failure could lead to a runaway reaction.
Hydrogen fluoride recycle circuits are subject to corrosion, with general
vessel, piping, valve, or pump failures. Because the hydrogen fluoride is
recycled, traces of moisture may enter the system and concentrate in the
recycle stream, thus contributing to corrosion.
20
-------
The hydrogen fluoride distillation and stripping unit operations are
subject to potential overheating and overpressure since these operations have
a thermal energy input. Loss of cooling in condensers could be a cause for
overpressure. The reboile'rs and bottoms pumps are potential weak points in
these systems since operating conditions are severe.
Since the alkylation process uses and produces highly flammable mater-
ials, other potential hazards associated with the entire process are fire and
explosion. A fire or explosion is clearly a possible cause for release. An
additional consideration is that hydrogen is formed as a corrosion product in
the alkylation process. Rapid corrosion in any part of the system also
carries with it an ignition potential as a result of possible hydrogen gas
buildup.
3.2.2 Manufacture of Chlorofluorocarbons
a
A second principal use of hydrogen fluoride in the United States is in
the manufacture of Chlorofluorocarbons. One commercially important method of
I
production is the successive replacement of chlorine in chlorinated hydro-
carbon feedstocks (chlorocarbons) using hydrogen fluoride as a source of
fluorine. A block diagram of a typical liquid phase chlorofluorocarbon
manufacturing process is presented in Figure 3-3.
The liquid-phase reaction system for the manufacture of Chloro-
fluorocarbons consists of a heated reaction vessel containing catalyst dis-
solved in a mixture of chlorocarbon. and partially fluorinated intermediates
recycled to the reactor from downstream processing. Antimony pentafluoride or
a mixture of antimony trifluoride and chlorine is typically used as catalyst.
Liquid hydrogen fluoride and chlorocarbon are fed to the reactor. The reactor
typically operates at a temperature and pressure of approximately 176°F and
100 psig, respectively (18). Although the fluorination reactions are exo-
thermic, additional heat is added to the reactor because the reactor also
serves as a reboiler for an enriching column. Crude product vapors evolved
21
-------
ANHYDROUS
HCI
BYPRODUCT
NJ
SbCI3
Figure 3-3. Conceptual diagram of typical fluorochloiocarbon process.
-------
from the reactors are fed directly to the enriching column. The column is
positioned so that the liquid bottoms flow by gravity as recycle to the
reactor.
After being withdrawn from the enriching column, a stream containing
hydrogen chloride, hydrogen fluoride, and the chlorofluorocarbon products is
sent to an acid recovery column. This column typically operates at approxi-
mately 100 psig (18). Hydrogen chloride is concentrated at the top of the
column and is recovered as a by-product. The bottoms contain the product
fluorocarbons and residual hydrogen fluoride at a temperature of approximately
122°F (18). The hydrogen fluoride is removed in a hydrogen fluoride settler
and is recycled to the reactor system. The mutual solubility of hydrogen
fluoride and the fluorocarbons is temperature dependent and temperatures as
low as -22°F are often required (18).
Trace impurities are removed from the fluorocarbon products by scrubbing
with water and a dilute caustic solution. Following the scrubbing operations,
the product stream is dried and fractionated into various chlorofluorocarbon
products.
High hazard areas in the chlorocarbon manufacturing process, excluding
bulk storage and transfer (discussed in Section 3.A), include the following:
• Feed treatment to remove water from the chlorocarbon feed
streams;
• Reactor;
• Enriching and acid recovery columns;
• Hydrogen fluoride recovery unit; and
• Hydrogen fluoride recycle system.
23
-------
Concerns for moisture removal in the feed treatment process are the same
as those associated with alkylation feed treatment (Section 3.2.1).
An exothermic reaction occurs in the chlorofluorocarbon process, but
since the reactor also serves as a reboiler to an enriching column, a reactor
cooling system is not required for heat removal. In fact, additional heat is
added. A potential hazard is overheating and overpressure caused by a mal-
function in the temperature control system. Overheating and overpressure
could also be caused by a loss of cooling in the enriching column condenser.
Similar considerations apply to the other columns.
The hydrogen fluoride recycle system presents the hazards of vessel,
piping, valve, and pump failure from potential corrosion caused by a buildup
of trace quantities of water in the system.
3.2.3 Aluminum Fluoride Manufacture
Aluminum fluoride, specifically aluminum trifluoride, is manufactured
using either a "wet", aqueous hydrofluoric acid process or a "dry," anhydrous
hydrogen fluoride process.
In a typical "dry" process, alumina trihydrate is fed into the top zone
of a fluidized bed reactor. Hydrogen fluoride gas enters the bottom zone of
the reactor and receives heat from the aluminum trifluoride leaving the bottom
of the reactor. The reaction is typically carried out at a temperature of
approximately 1.100°F (2,19). Hydrogen fluoride and steam produced in the
reaction are used to fluidize the bed. The effluent gas leaving the top of
the reactor contains water vent, hydrogen fluoride, silicon tetrafluoride,
dust, and other noncondensibles. These gases are typically used in the
production of synthetic cryolite or are sent to a scrubber where they are
removed by contacting them with water to form fluorosilicic acid (2,19).
24
-------
The hazards associated with this process are the same as those presented
previously in this manual for exothermic reactors, namely overtemperature and
overpressure. In addition, this process also incorporates the potential for
equipment failure resulting from undetected corrosion since hydrogen fluoride
is extremely corrosive at the elevated temperatures found in this process.
3.2.4 Sodium Aluminum Fluoride (Cryolite) Manufacture
Synthetic cryolite (sodium aluminum fluoride) is manufactured by several
methods. Several of these are methods are based on the use of fluorine-
containing acids (e.g.. hydrofluoric acid). However, processes based on the
use of anhydrous hydrogen fluoride also exist.
In one such process, similar to that presented previously for aluminum
trifluoride, sodium carbonate and alumina are fed to the top of a fluidized
bed reactor (20). The reactor effluent gases are typically sent to a water
scrubber for removal of hydrogen fluoride and formation and recovery of
fluorosilicic acid. The solid product leaving the bottom of the reactor is
»
compressed into capsules, heated in an oven at temperatures ranging from
1.290-1.210°F for several hours, and the final product, synthetic cryolite, is
obtained (20).
The hazards associated with this process are similar to those presented
for aluminum fluoride manufacture in the preceding subsection of this manual.
3.2.5 Uranium Tetrafluoride Manufacture
Uranium tetrafluoride is typically manufactured by the hydrofluorination
of uranium dioxide with excess hydrogen fluoride. Figure 3-4 presents a flow
diagram of a typical manufacturing process for uranium tetrafluoride.
In the manufacturing process several types of reactors are used includ-
ing: stirred bed. vibrating tray, fluidized bed, and moving bed types.
25
-------
VENT
N)
ANHVOROUS
HVDROQEN
FLUORIDE
70*
HYDROFLUORIC
ACID
URANIUM
TETRAFLUORIDE
Figure 3-4. Conceptual diagram of typical uranium tetrafluoride manufacturing process.
-------
Whichever reactor is used, uranium dioxide is fed from storage hoppers by
screw conveyors to the top of a the first reactor, in a series of reactors.
Hydrogen fluoride is fed to the last reactor at approximately 200°F, after
first passing through a vaporizer and a superheater (21). The series of
reactors operate at an average temperature of approximately 1.000°F. Although
the reaction is exothermic (43.2 kcal/mole), multi-zone electrical heating is
used to maintain the required reactor temperature (21). Additionally, the
reactor operates at a low pressure of about 2 psig since the seal hoppers and
packing glands fail to function properl at higher pressures (21).
The uranium tetrafluoride product leaves through the bottom reactor and
is collected in a small seal hopper. The effluent from the top reactor
consists of hydrogen fluoride, water, and a small amount of non-condensible
gas (21). It passes through a series of carbon filters used to collect any
residual dust particles from the uranium dioxide charge. The effluent gas is
then condensed in a series of water cooled shell and tube partial condensers
which are maintained at approximately 140°F (21). The condensed liquid is
approximately 70 percent hydrofluoric acid and is sent to storage. The
resulting gases are condensed further using a shell and tube condenser operat-
ing at about -15°F (21). The condensed liquid is sent to anhydrous hydrogen
fluoride storage. A lime slurry scrubber is used to remove any residual
hydrogen fluoride from the vent gases before being released to the atmosphere.
High hazard areas in the uranium tetrafluoride manufacturing process.
excluding bulk storage and transfer (discussed in Section 3.4), include the
following:
• Reactor;
• Hydrogen fluoride vaporizing and preheating units; and
• Hydrogen fluoride condensers.
27
-------
An exothermic reaction occurs in this process, but since additional heat
is added to the systems to maintain a certain reaction temperature, a reactor
cooling system is not required for heat removal. A potential hazard is
overheating and overpressure caused by a malfunction in the temperature
control systems. In the reactor section of this process, hydrogen fluoride is
present at high temperatures and is very corrosive. Additionally, corrosive
hydrofluoric acid is present in portions of the process. A properly designed
system should use materials of construction which take this corrosion poten-
tial into account. Additionally, a level control system should be used in the
uranium dioxide feed hopper to prevent it from being completely emptied. If
such were to occur, the seal on the top reactor would be broken and hydrogen
fluoride vapor would flow into the hopper causing severe corrosion problems
and eventual equipment failure (21).
Hydrogen fluoride heating and condensing systems are affected by the same
•
potential corrosion problems as those associated with the reactor system. An
additional hazard is overheating and/or overpressure caused by a malfunction
in the temperature control system.
3.3 REPACKAGING
Anhydrous hydrogen fluoride and hydrofluoric acid are repackaged for
resale and further use. Aqueous hydrofluoric acid is typically repackaged
into drums and carboys, while anhydrous hydrogen fluoride is commonly
repackaged into cylinders. Hazards associated with this operation include
overpressure, overfilling, mechanical damage, fire exposure, and chemical
c on taminat ion.
A filling operation is usually carried out by transferring hydrogen
fluoride from a bulk storage vessel using specially designed filling systems
similar to those used for chlorine (22). Protective barriers are sometimes
used to separate the transfer storage tank from the cylinder or drum being
28
-------
filled to prevent damage from shrapnel as a result of a possible rupture of
the cylinder or drum (23).
Equipment used in repackaging operations should be constructed from
materials compatible with hydrogen fluoride or hydrofluoric acid, depending on
the operations. Relief systems are usually incorporated into the transfer
system to prevent possible equipment ruptures. In addition, care usually is
taken to prevent overfilling of drums and cylinders.
3.4 STORAGE AND TRANSFER
Anhydrous hydrogen fluoride is stored in pressure vessels because of its
relatively low boiling point and high vapor pressure. Hydrogen fluoride is
also stored in cylinders for small scale use and is shipped by tank car and
tank truck. Figures 3-5 and Figure 3-6 show typical storage and transfer
operations. These figures are only conceptual representations of storage and
transfer operations. Actual transfer system will vary in the design and
method of transfer. Moderate quantities of hydrogen fluoride may be stored as
a pressurized and liquified gas. Larger quantities are usually stored at
atmospheric pressure, as refrigerated liquids in single and double-walled
horizontal cylindrical or spherical vessels. Vendors or process licensors
should be consulted for detailed specifications on recommended storage facil-
ities (8.24.25.26.27).
Transfer of the hydrofluoric acid to storage is accomplished using either
pumps or compressed gas pressure. If compressed gas is used, it should first
be dried to a moisture content equivalent to air at -22°F dew point to prevent
corrosion of the storage and transfer vessels (8). For anhydrous hydrofluoric
acid, nitrogen or hydrocarbon gas is usually used. If a hydrocarbon is used.
air must be excluded to avoid a possible flammable mixture which would be a
significant release hazard. If air is used, corrosion can occur as a result
of oxygen dissolution in the acid, since hydrogen fluoride is commonly stored
in carbon steel tanks.
29
-------
TO HYDROGEN
U)
o
1-UUUHIUt ABSl
SYSTEM
PUMP
BLEED AND SAMPLE
WITH CAP TO LIMESTONE
PACKED TILE DRAIN
PERSON IN Kl
W/ PROPER P
EQUIP*
mriHJN
. (
1
i
TENDAK
ROTECT
ENT
1
plj |~|_J PRESSURE RELIEF VALVE
S B RUPTURE T j^ PHES?Jin,ireEUEF
X T-ortJ "«• .TO K |
j t*l f 4 PROCESS^ I] m
C 6HXH T A ^
fnT ^^H r1-1! r— i X CH£CK PRESSURE
A T VALVE REGULATOR
4 BLEED
STORAGE TANK f VAIVE
L LEVEL
GAUGE
O^ 1 » PRESSURE RELIEF
A \ /^\ DEVICE
IV1 T (f\ 1 1 (Tfr, ,
PQ" r » Vf »-TJ /^t >•»
Y T II 1 1
VA^HY^OU' J, BLEEoA CHECK PRESSURE
\ANHYDROUS HFI O U»IUB 6 UAIUE REGULATOR
IvEVfO TANKCAH )~7 AWARNING
l\ J 1 l\ SIGNS
' /^ F\ 1 1 r^
1 1 lA Jl 1 | 1 | | | V JM 1 1 1 1 1 1 1 1 M
/ ^Sl WHEEL \ DE|W|,
SPILL / CHOCKS
COLLECTION-/
PAN
COMPRESSED
GAS
COMPRESSED
GAS
i
Figure 3-5. Conceptual process diagram of hydrogen fluoride rail tank car unloading and
tank storage facility.
Source: Reference 8
-------
TO HVDftOQEN
FLUORIDE ABSORPTION
SYSTEM
. COMPRESSED
' GAS
BLEED AND
SAMPLE WITH
CAP
PERSON INATTENDANCE
W/PROPER PROTECTIVE
EQUIPMENT
AWARNINQ
T-* SIGNS
CURBED AREA
W/LOW POINT DRAIN
COMPRESSED
GAS
t; 3-6. Conceptual process diagram of hydrogen fluoride tank truck unloading and tank stoiage
facility.
Source: Reference 8
-------
For safety reasons, pump transfer is commonly preferred over compressed
gas transfer. The pumps most commonly used are centrifugal, rotary, or
positive displacement, depending on the specific situation. Sealless pumps
may be required for some applications. In addition, self-priming pumps are
commonly used since they avoid the hazards that can be associated with priming
the pump.
32
-------
. SECTION 4
PROCESS HAZARDS
Both anhydrous hydrogen fluoride and hydrofluoric acid can be used safely
in appropriate processing and storage equipment. However, when exposed to the
atmosphere, hydrogen fluoride vaporizes readily and. because of its strong
affinity for water, combines with moisture in the air to form hydrofluoric
acid. This acid can be detected in air by its white fumes, pungent odor and
irritant property.
Hydrogen fluoride releases can originate from many sources including
leaks or ruptures in vessels, piping, valves, instrumentation connections, and
process machinery such as pumps and compressors.
•
Potential hydrogen fluoride releases may be liquid or vapor. Liquid
spills can occur when anhydrous fluoride is released at or below its boiling
point of 67 °F or when a sudden release of hydrogen fluoride above this temper-
ature results in vapor flashing, which cools the remainder of the chemical to
67°?. Direct releases of vapor or gas also can occur. Liquid spills of
hydrofluoric acid can release some hydrogen fluoride as well. However, the
vapor pressure resulting from the concentrated acid is considerably less than
the vapor pressure of pure hydrogen fluoride. Nonetheless, the threat fron
the acid should not be overly discounted, especially if spills occur on hot
surfaces where evaporation rates are high.
4.1 POTENTIAL CAUSES OF RELEASES
Failures leading to accidental releases may be broadly classified as due
to process, equipment, or operational causes. This classification is for
convenience only. Causes discussed below are intended to be illustrative, not
exhaustive. A more detailed discussion of possible causes of accidental
33
-------
releases is planned in other portions of the prevention reference manual
series of which this present manual is a part.
4.1.1 Process Causes
Process causes are related to the fundamentals of process chemistry.
control, and general operation. Possible process causes of a hydrogen fluo-
ride release include:
• Excess olefin feed to an alkylation reactor leading to
excessive exothermic reaction, combined with fail-are of
the cooling system;
• Backflow of process reactants to a hydrogen fluoride feed
tank;
t
.
• Inadequate water and sulfur removal from hydrocarbon feeds
to the alkylation process over a long period of time
leading to progressive corrosion;
• Excess feeds in any part of the system leading to over-
filling or overpressuring equipment;
• Loss of condenser cooling in distillation units;
• Loss of temperature control in cooling and heating units;
and
• Overpressure in hydrogen fluoride storage vessels due to
overheating or overfilling. These situations may be
caused by exothermic reactions from contamination, fire
exposure, or unrelieved overfilling.
34
-------
4.1.2 Equipment Causes
Equipment causes of accidental releases result from hardware
failures. Some possible causes include:
• Excessive stress due to improper fabrication, construc-
tion, or installation;
• Failure of vessels at normal operating conditions due to
weakening of equipment from excessive stress, external
loadings, or corrosion. Overheating is also a possi-
bility, especially for alkylation reactors and distilla-
tion columns;
• Mechanical fatigue and shock in any equipment. Mechanical
fatigue could result from age. vibration, or stress
cycling, caused by pressure cycling, for example. Shock
could occur from collisions with moving equipment such as
cranes, or other equipment in process or storage areas;
• Thermal fatigue and shock in alkylation reactors, heat
exchangers, and distillation columns;
• Brittle fracture in any equipment, but especially in
carbon steel equipment subjected to extensive corrosion
where hydrogen embrittlement from hydrogen release by
hydrogen fluoride attack may have occurred. Equipment
constructed of high alloys, especially high strength
alloys selected to reduce the weight of major process
equipment, might be especially sensitive where some
corrosion has occurred, or severe operating conditions are
encountered;
35
-------
• Creep failure in equipment subjected to extreme oper-
ational upsets, especially excess temperatures. This can
occur in equipment subjected to a fire that may have
caused damage before being brought under control; and
• All forms of corrosion. External corrosion from fugitive
emissions of hydrogen fluoride could lead to equipment
weakening. Stress corrosion cracking is also a possi-
bility since this is characteristic of certain metals
exposed to halogens.
4.1.3 Operational Causes
Operational causes of accidental releases are a result of incorrect
operating and maintenance procedures or human errors (i.e.* not following
correct procedures). These causes include:
• Overfilled storage vessels;
• Improper process system operation;
• Errors in loading and unloading procedures;
• Inadequate maintenance in general, but especially on water
removal unit operations, and pressure relief systems and
other preventive and protective systems;
• Lack of inspection and non-destructive testing of vessels
and piping to detect corrosion weakening;
• Incomplete knowledge of the properties of a specific
chemical; and
•' Incomplete knowledge of the process or chemical system.
36
-------
SECTION 5
HAZARD PREVENTION AND CONTROL
5.1 GENERAL CONSIDERATIONS
Prevention of accidental releases relies on a combination of technolog-
ical, administrative, and operational practices. These practices apply to the
design, construction, and operation of facilities where hydrogen fluoride is
stored and used. Considerations in these areas can be grouped as follows:
• Process design considerations.
• Physical plant design considerations,
• Operating and maintenance practices, and
• Protective systems. ,
In each of these areas, consideration must be given to specific factors
that could lead to a process upset or failure which could directly cause a
release of hydrogen fluoride to the environment, or result in an equipment
failure which would then cause the release. At a minimum, equipment and
procedures should be examined to ensure that they are in accordance with
applicable codes, standards, and regulations. In addition, stricter equipment
and procedural specifications should be in place if extra protection against a
release is considered appropriate.
The following subsections discuss specific considerations regarding
release prevention; more detailed discussions will be found in a manual on
control technologies, part of this manual series.
37
-------
5.2 PROCESS DESIGN
Process design considerations involve the fundamental characteristics of
the processes which use hydrogen fluoride. These considerations include an
evaluation of how deviations from expected process design conditions night
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, composi-
tion, and quantity. Additional considerations may include mixing systems,
fire protection, and process control instrumentation. Modifications to
enhance process integrity may result from review of these factors and would
involve changes in quantities of materials, process pressure and temperature
conditions, the unit operations, sequence of operations, the process control
strategies, and instrumentation used.
. Table 5-1 shows the relationship between some specific process design
considerations and individual processes described in Section 3 of this manual.
This does not mean that other factors should be ignored, nor does it mean that
proper attention to just the considerations in the table ensures a safe
system. The 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 overpressuring systems containing hydrogen fluoride. If hydrogen fluoride
is fed from a storage vessel under its own vapor pressure, the primary means
of overpressure would be from overheating. Where hydrogen fluoride might be
fed by nitrogen padding of a storage vessel, or through puaps or compressors,
overpressuring could occur without overheating. Equipment failure without
overpressure is possible if corrosion has weakened process equipment. Temper-
ature monitoring is important, not only because of a potential overpressure or
equipment weakening due to overheating, but also because hydrogen fluoride's
corrosiveness increases with temperature.
38
-------
TABLE 5-1. SOME PROCESS DESIGN CONSIDERATIONS FOR PROCESSES INVOLVING
HYDROGEN FLUORIDE
Process Design Consideration
Process or Unit Operation
Contamination (with water and
sulfur especially)
Flow control of hydrogen
fluoride feed
Temperature sensing and heating
media flow control
Temperature sensing and cooling
medium flow control
Adequate pressure relief
Mixing
Corrosion monitoring
Temperature monitoring
Level sensing and control
All
All
Hydrogen fluoride reactor, uranium
tetrafluoride reactor,
chlorofluorocarbon reactors,
distillation and stripping column
reboilers
Alkylation reactors, aluminum
fluoride reactors, distillation and
stripping column condensers
Storage tanks, reactors.
distillation and stripping columns,
heat exchangers
Alkylation reactors
»
All, but especially recycle
circuits
All reactors, alkylation. stripping
column, and distillation column
reboilers
Storage tanks, settlers in
alkylation and chlorofluorocarbon
processes
39
-------
5.3 PHYSICAL PLANT DESIGN
Physical plant design considerations include equipment, siting and
layout, and transfer/transport facilities. Vessels, piping and valves, •
process machinery, instrumentation, and factors such as location of systems
and equipment must all be considered. The following subsections cover various
aspects of physical plant design beginning with a discussion of materials of
construction.
5.3.1 Equipment
Materials of Construction—
The proper selection of materials of construction for hydrogen fluoride
service is dictated by conditions which directly and indirectly affect corro-
sion. Temperature, pressure, moisture content, flow velocity, aeration, and
impurities such as sulfur compounds are important considerations in deter-
mining the appropriate materials. Table 5-2 presents a list of possible
materials of construction for hydrogen fluoride service (24). The National
Association of Corrosion Engineers (NACE) also provides detailed information
concerning the materials of construction for hydrogen fluoride service (28).
For anhydrous hydrogen fluoride at temperatures up to 150°F, fully killed
mild steel, steel deoxidized using silicon and/or aluminum, is generally used
(e.g., ASTM A516, Grade 60 or 70). However, hydrogen blistering can occur if
plates contain lamination defects. Reducing the sulfur content to a maximum
level of 0.010% or using inclusion shaped controlled steels helps to eliminate
blistering. Another possible problem is hydrogen cracking of hardened steels.
Base metals, welds, and heat affected zones should be limited to hardness less
than HRC 22 to avoid the problem (28). This includes the use of low hardness
bolts such as ASTM A193 Grade 37M instead of B7 (28). For temperature greater
than 150°F, nickel-copper Alloy 400 and nickel-chromium-molybdenum alloys ara
often used. However, nickel-copper alloys may stress corrosion crack if humid
40
-------
TABLE 5-2. CHARACTERISTICS OF MATERIALS OF CONSTRUCTION IN HYDROGEN FLUORIDE
AND HYDROFLUORIC ACID SERVICE
KTDROQ8N FLUORIDE OR STRONG ACID (70S OR OVER)
Satiefaetery
Copper*
MOMla**
XneoiMl
Low Carbon Steel (to 150«F) Kaatelloy
Alloye B. C D Nickel Ni-reai*t Carpenter
20 Duriaet 20 Magne*ium Chlorimet 2 & 3
Karbata (70S) Polyethylene Unplaaticizad
Polyvinyl Chloride Saran-Lined Steel Pip*
(for 70S <120*f ) Fluorocarbon* (TFB. CFE
4 FEP) Platinum Molybdenum**
Un*ati«factory
Tallov
Lud
High Silicon Iron Alloy*
Cut iron
Altainini
St«ifll«H
Titanium
Zirconium
Low Silvor Bracing Alloya
Rubbtr, Natural & Synthetic
Glaai & Ceraniea
Epoxita
Aaboatoa
DILUTE ACIDS (UNDER 70S HF)
Satiafactoty
Monola**
Coppor*
Tcllov Braaa*
Nickol (over 10Z. <212*F)
Load (Choaical Grado <60Z. to b.p.)
Silvor
Carpontor 20
70-30 Coppor Niclcol Alloy
Hagnoaium (<18S°7)
lUatolloy Alloya B.C&D
Karbato
Mooprono (<30X. <140*7)
Unplaatieixod Polyvinyl Cblorido
Rubbor-Linod Stool (<60Z. <180°F)
Butyl-Rubbor-Linod Stool (<60Z. <180«F}
GR-S «60Z. <180°J)
Carbon-Fillod Sulfur Cmont
Saran-Linod Pipo
Polypropylono Vinylidono Fluoridoa
Fluoroearbona (TFE, CFE & FEP) Plajcinum
Unaatiafaetory
Stool
Stainloaa Stoola
Ni-roaiat
Caat iron
High Silicon Iron Alloya
Glaaa & Ceramics
Aluminum
Inconol «10Z. <170«F)
Wood
Tantalum
Titanium
Zirconium
Aaboatoa
*SO, and air froo.
**May bo unauitablo undor aorating conditiona.
Hotel Thia table doea not include exception* to *ati*factory cervice due to temperature.
concentration, velocity, etc. It i« given here to provide a atarting point for selecting
material*, but a given material* acceptability for a certain application *hould be confirmed
by other reference* before it ia u*ed.
41
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air is in contact with the acid or if substantial aeration in the process
stream occurs.
Hydrofluoric acid solutions of concentrations greater than 70S can also
be handled in fully-killed mild steel up to 100°F provided that the steel has
a passivation film on the surface and velocity through the equipment is less
than 1.0 foot per second (8). The passivation iron fluoride film results from
a reaction between the steel and the acid and provides a protection from
further corrosion. When velocities are in excess of 1.0 foot per second, the
passivation film is eroded (8). In addition, copper and its alloys are not
suitable where anhydrous hydrogen fluoride flows at high velocity. Materials
of greater acid resistance must be used in such service.
For anhydrous hydrogen fluoride or concentrated hydrofluoric acid solu-
tions (greater than 702) systems, carbon steel pipe is commonly used. ASTM
A53 seamless or A106, Grade A or B steel piping is often selected (3). For
piping up to one inch, the pipe should be welded steel, and for sizes of
greater diameter, the pipe should be seamless steel (24). The flanges common-
ly used are of ANSI Class3 forged steel, raised face, welding neck, and ASTM
A-105 or A-181, (24). For concentrations less than 70% hydrogen fluoride,
piping is commonly lined with polypropylene, unplasticized polyvinylchloride,
polyvinylidenechloride, polyvinylidinefluoride, or tetrafluoropolyethylene
(TFE) to prevent corrosion (2). Materials which are not recommended include
aluminum, titanium, tin. ordinary grey iron, malleable iron fittings, general
purpose valves, and porcelain valves.
Gaskets constructed of nickel-copper Alloy 400 and TFE are commonly used
for hydrogen fluoride service. These materials provide a needed resistance to
corrosion at all hydrogen fluoride concentration levels.
a
ANSI Class refers to pressure ratings at specified temperatures as set by the
American National Standards Institute (ANSI). For a carbon steel flange,
Class 150 means a 150 psig pressure rating at 500°F. and Class 300 means a 300
psig pressure rating at 850°F.
42
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Bolts with adequate resistance to hydrogen stress corrosion cracking must
b« used in holding the flanges together. Alloy steel studs with heavy hex
nuts are commonly used. Several types of bolts are often used in hydrogen
fluoride service including: ASTM A-307. Grade B, mild steel: ASTM A-193.
Grade B-7-M, alloy steel with maximum Rockwell C hardness of 22; ASTM A-193,
Grade B-8, Class 2. 304 stainless steel with a maximum Rockwell C hardness of
34 (24). If a flange begins to leak, bolts are usually replaced immediately.
Hydrofluoric acid in concentrations less than 70% must be handled and
stored in nonferrous materials. Since nickel-copper Alloy 400 is resistant to
hydrofluoric acid in almost the entire concentration range, it is commonly
used for storage of hydrogen fluoride. In addition, nickel-chromium-iron
alloys and nickel-chromium-molybdenum alloys do not show corrosion in 40-60%
hydrofluoric acid up to 206.6°F (8).
Glass and silicate ceramics should never be used with hydrogen fluoride
or hydrofluoric acid at any concentration.
*
Vessels— *
A variety of storage and process vessels are used in hydrogen fluoride
service. Examples include small storage cylinders, chemical reactors, separa-
tion columns, heat exchangers, and large storage tanks. Each type of vessel
has certain specifications under various codes and standards which are sup-
posed to be adhered to in design and fabrication.
Hydrogen fluoride storage vessels range in size from 150 Ib pressure
cylinders for small scale use up to several thousand metric ton pressurized
spherical storage tanks used by producers. Pressurized storage tanks varying
from 100-200 tons are typically used to store hydrogen fluoride for use in
chemical processes. In addition, refrigerated tanks varying in size from
100-250 tons are also used for hydrogen fluoride storage. The shell of a
refrigerated storage tank is covered by refrigeration coils and insulation.
These coverings must be removed before the tank can be inspected for signs of
43
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external corrosion or wear. The shell of a pressurized tank does not need to
be covered, and thus the exterior surface can be easily inspected. For this
reason, most producers of hydrogen fluoride prefer to use pressurized storage
in place of refrigerated storage. The hazard associated with pressurized
hydrogen fluoride is felt to be more than offset by the ability to regularly
inspect the tank. As a result of the relatively large inventories contained
in hydrogen fluoride storage vessels, they represent one of the most hazardous
parts of a hydrogen fluoride process facility.
In general, anhydrous hydrogen fluoride and hydrofluoric acid storage
tanks should be designed and built in accordance with the ASME Code for
Unfired Pressure Vessels. Special considerations may be as discussed in the
code for lethal materials, or even stricter standards may be appropriate.
As stated earlier, the usual material for hydrogen fluoride storage
vessels is mild steel. Because of the potential release of hydrogen during
corrosive attack by moist hydrogen fluoride, welding processes are usually
carefully controlled to avoid heat-affected zone hardness which can lead to
hydrogen stress cracking. Shielded arc welding with double butt-welded
longitudinal seams and single butt-welded girth seams with seal welds on the
inside is commonly used for vessels, including those in hydrogen fluoride
service.
A minimum design pressure for these storage tanks is at least 50 psig
working pressure, with a requirement that the tanks be tested at 1.5 times the
working pressure prior to use. A minimum corrosion allowance of at least a
1/8 inch on both the shell and heads is typically added to the thickness
specified by the ASME code for the specified design pressure.
Vessel nozzles are constructed of mild steel with ANSI Class 300 or
greater forged steel weld neck flanges. Except for single, flanged, bottom
clean-out drains, bottom outlet nozzles are not often used since there is a
greater risk of losing the entire tank contents as the result of valve or line
44
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failure. Where they are used, nozzles are usually double valved as a pre-
cautionary measure. The following nozzles are usually specified for mounting
on top of the tank (24): •
• One 3- or 4-inch nozzle for insertion of a dip pipe for
removal of hydrogen fluoride from the tank;
• Two 2-inch nozzles: one for filling the tank and the
other for a pressure relief device; and
• Three 1-inch nozzles: one for a dry air supply to pad the
hydrogen fluoride out, one for a vent to a caustic scrub-
ber, and the last for a pressure gauge.
Specific release prevention considerations for vessels include: over-
pressure protection, temperature control, and corrosion prevention. Relief
devices are not usually provided for 150-pound cylinders. These cylinders are
built to withstand very high pressures and must be kept from fire exposure.
contamination, and mechanical damage. Larger vessels are usually equipped
with pressure relief valves as are tank trucks and rail cars. Process vessels
are usually protected by pressure relief valves and/or rupture discs. Since
hydrogen fluoride tends to corrode pressure relief valves, they are frequently
separated from the hydrogen fluoride by a rupture disc. The pressure relief
valve is set to relieve slightly above the design working pressure of the
vessel, but well below the maximum allowable working pressure.
Pressure relief valves and rupture discs are designed to prevent explo-
sion by allowing a controlled release of overpressurized contents. These
relief systems are usually sized for flashing liquid caused by:
• Fire exposure (NFPA 30).
• Thermal expansion,
45
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• Internal reaction/decomposition, and
• Excess supply rates.
Relief piping must be sized for adequate flow. To avoid direct discharge to
the atmosphere, an overflow tank might be provided for overpressured liquid.
If there is a possibility that overpressuring may occur due to causes other
than liquid thermal expansion, or where there is no overflow receiver, the
vessels should be relieved to either a point in the process which can handle
the discharge flow, or to a gas absorption system.
The foundations and supports for vessels are important design consider-
ations, especially for large storage vessels and tall equipment such as
distillation columns. Supports for storage tanks containing hydrogen fluoride
are usually concrete saddles. Tubular support legs are usually avoided. The
supports must be protected from possible hydrofluoric acid contact since rapid
corrosion can result from dilution of the acid with moisture in the air.
Fugitive emissions of hydrogen fluoride can lead to significant external
corrosion of supports and bolting. These supports should be protected by
fugitive emissions control and regular maintenance of structural members.
Surface coatings of mastics or polymers may also help retard external corro-
sion.
Cylinder storage of hydrogen fluoride is common where small to moderate
quantities are required. A hood with forced ventilation is commonly used with
hydrogen fluoride cylinders. Cylinder storage temperatures should not exceed
130°F and cylinders should be located away from sources of heat (25). Trap or
check-valves are commonly inserted in transfer lines to prevent hazardous
backflow into the cylinder. In addition, pressure-reducing regulators are
used when connecting cylinders to lower pressure piping systems to prevent
overpressure with leaks or rupture of downstream line (25). Air pressure is
usually not used to transfer hydrogen fluoride from cylinders since corrosion
resulting in the generation of hydrogen gas can occur. When pressure transfer
46
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(above the vapor pressure of hydrogen fluoride) is needed, nitrogen or other
inert gases are usually used. Cylinders also may be slightly heated using hot
water. However, care must be taken to guard against overpressure. Cylinders
are usually examined periodically for signs of valve or other leakage and
external deterioration. Cylinders which have been stored for long periods of
time are usually safely vented prior to use. since they may contain hydrogen
gas. Complete details on cylinder storage are provided in hydrogen fluoride
manufacturer's literature (25.26).
The reactors used in hydrogen fluoride related processes represent
possible sources of major releases since they contain a large portion of the
anhydrous hydrofluoric acid used in their respective processes. These re-
actors must, therefore, be properly constructed of appropriate materials of
construction.
The feed to the reactors must be dry since moisture accelerates the
corrosion rate of materials used in construction (e.g.. carbon steel).
Provisions should be made for exclusion of moisture during any process shut-
downs, or purging of the reactors at shutdown and before startups.
Since the alkylation reaction is exothermic, a heat-exchange-tube bundle
is commonly used to cool the alkylation reactor contents. Water is the
cooling medium. This equipment must be designed to prevent water leakage into
the acid section of the reactor. Provisions must be made for corrective
action to be taken if such leakage should occur. Common precautions include
ensuring that the water pressure is lower than the process fluid pressure, and
monitoring the cooling water for pH. If leakage should then occur, the acid
would enter the water system and be detected by the pH monitoring.
A pressure relief system along with a means of gas purging is also
sometimes incorporated into the reactor designs since hydrogen gas may build
up as a result of corrosion. All vents should be routed to a caustic scrub-
ber.
47
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Distillation and stripping columns present significant release hazards
because they contain large amounts of hydrogen fluoride in pure form and have
a heat input. The conditions under which this equipment operates (especially
the column reboilers and bottoms pumps) are severe and as a result these areas
are potential sites for a release.
If cooling in a condenser is lost, overpressure may occur. Thus, it is
necessary to use pressure relief valves to protect against leaks and ruptures
which can result from overpressure. Relief protection is also necessary in
the event of a fire to protect from overpressure. Likewise, loss of steam to
the reboilers can result in underpressure in the column.
Columns used in hydrogen fluoride service must be constructed from the
suitable materials mentioned in Section 5.3.1. The columns should be properly
supported, taking into consideration expansion and contraction as a result of
temperature changes, corrosion, and possible wind loadings.
Piping—
As with hydrogen fluoride vessels, hydrogen fluoride pipework design must
reflect the pressure, temperature, and corrosion concerns associated with use
of the chemical. Careful attention must be paid to pipework and associated
fittings since failures of this type of equipment are major contributors to
accidental releases of chemicals. Regardless of the physical state of the
hydrogen fluoride, there are some general guidelines for hydrogen fluoride
piping systems. The first is simplicity of design: the number of joints and
connections should be minimized. In addition to being securely supported.
pipes should be sloped, with drainage at the low points. Piping should be
constructed so as to allow room for thermal expansion of the pipe and should
be protected from exposure to fire and high temperatures. Placement of valves
should ensure isolation of leaking pipes and equipment.
A chief concern in liquid hydrogen fluoride lines is overpressure due to
thermal expansion of the chemical or pressure pulses caused by rapid valve
48
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closure. These pressures can be sufficient to rupture the pipe. Where
applicable, an expansion chamber, such as the one shown in Figure 5-1. may be
installed to prevent such a rupture. An expansion chamber device typically
consists of a rupture disc and a receiver chamber which can hold about 20-30%
of the protected line's capacity. The chamber is equipped with a pressure
indicator or alarm switch set to function upon disk rupture. The chamber
should be constructed in accordance with Section VIII of the ASME Code for
Unfired Pressure Vessels (29).
Another concern in liquid hydrogen fluoride systems is low temperature
toughness. Material selection must take this into, account and should be
resistant to brittle fracture over the entire range of process conditions.
The correct design and use of pipe supports is essential to reduce
overstress and vibration which could lead to piping failure. The supports
should be designed to handle the load associated with the pipe, operating and
testing medium, insulation, and other equipment. Factors which must be
considered include thermal expansion and contraction, vibrations caused by
pumping and fluid flow, bending moments as a result of overpressure in the
pipe, and external loads such as winds or ice accumulation.
Piping networks are usually pressure tested at a minimum, to meet the
requirements specified by ANSI code B31.3 (32). If a gas is used, it must be
dry to prevent corrosion and resulting hydrogen gas formation. If water is
used, the piping must.be drained and blown dry before use.
As a result of the possible buildup of hydrogen gas from corrosive
effects and the relatively low boiling point of hydrogen fluoride, rupture due
to hydrostatic pressure is possible. Protection against this is commonly
provided by installing a pressure relief valve, rupture disk, or a suitably
designed, operated, and maintained expansion chamber (23).
49
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a-3/4-
hydrogen
fluoride
line
expansion
chamber
pressure switch with
protective diaphragm
reducing ell
pture disk
Figure 5-1. Concept of a liquid hydrogen fluoride expansion chamber.
Source: Reference 29
50
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All piping should be situated away from fire and fire hazards since the
presence of hydrogen gas could trigger an explosion. If possible, piping
carrying hydrogen fluoride should not be routed near other processes or piping
networks which might present an external threat (e.g.. piping carrying highly
corrosive materials, high pressure processes). Pipe flanges should be situ-
ated so as to minimize potential hazards from drips and small leaks since
these could cause rapid external corrosion. In addition, the piping network
should be protected from possible impact and other structural damage.
Valves in hydrogen fluoride service are discussed in a number of refer-
ences (8.23,24.30). Several types of valves including gate, globe, ball.
relief, excess flow, and check configurations are used in hydrogen
fluoride-containing systems. Valves of all sizes and for all pressure ranges
used in hydrogen fluoride alkylation processes must be approved by one of the
major hydrofluoric acid alkylation process licensers (i.e.. U.O.F.. Phillips
Petroleum and Chevron) before being used (30).
Nickel-copper Alloy 400 is commonly used for all valve trim parts (i.e.,
»
seats, disks and stems) because of its resistance to the corrosive properties
of hydrofluoric acid. A problem with valve trim materials is that they have
thermal expansion coefficients which exceed those of cast or forged carbon
steel and as a result often become distorted, causing leaks. Often this is
solved by either closing the valve more tightly or inserting an acid compati-
ble ring either in or alongside the trim material in the seat or disk. For
anhydrous hydrogen fluoride, the valve bodies can be cast steel. For hydro-
fluoric acid (<70% concentration) nickel-copper Alloy 400 valve bodies are
often used.
Hydrofluoric acid will react with carbon steel and to a lesser extent
with copper-nickel alloys that contain small amounts of iron to form ferric
fluoride. Thus, hydrogen fluoride valves must have appropriate clearances at
critical interfaces such as wedge/body guides and stem back-seat bushings to
prevent the valves from becoming inoperable from ferric fluoride deposits.
51
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Check valves are a primary means of preventing undesired back or reverse
flows. They are typically mounted vertically on hydrogen fluoride storage
tanks so that forward flow is required to lift and open them. Such valves can
prevent undesired materials from entering hydrogen fluoride-containing equip-
ment and also prevent possible explosions as a result of backups into tanks.
Check valves are also used widely on the pump discharges to prevent undesired
backflow which could render a pump inoperable and eventually result in a
hazardous release. Nickel-copper alloy ball check valves are commonly used in
hydrogen fluoride service. Dual check valves in series are commonly used in
sensitive/severe service areas. A power operated control valve with suitable
instrumentation may be used as a substitute for a check valve.
Pressure relief devices should be installed on all hydrogen fluoride-
containing vessels where the chemical can be blocked in. • Such devices are set
to relieve at a pressure approximately equal to the design pressure (which is
greater than the normal operating pressure) for each specific piece of equip-
ment. Where fires are likely, in alkylation units for example, the relief
system should also be designed for fire relief, which tends to require a
larger pressure relief capacity.
Process Machinery-
Process machinery refers to rotating or reciprocating equipment that may
be used in the transfer or processing of hydrogen fluoride or hydrofluoric
acid. This includes pumps and compressors which may be used to move liquid or
gaseous hydrogen fluoride where gas pressure padding is insufficient or
inappropriate.
Pumjjs—Many of the concerns and considerations for hydrogen fluoride
piping and valves also apply to pumps. To assure that a given pump is suit-
able for a hydrogen fluoride service application, the system designer should
obtain information from the pump manufacturer certifying that the pump will
perform properly in this application.
52
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Pumps should be constructed with materials which are resistant to hydro-
gen fluoride at operating temperatures and pressures. They should be in-
stalled dry and oil-free. It is especially important that their design not
•How hydrogen fluoride or lubricating oil to enter seal chambers where they
may contact one other. Net positive suction head (NPSH) considerations are
especially important for hydrogen fluoride since pumping the liquid near its
boiling point may be common (hydrogen fluoride boils at near ambient condi-
tions). The pump's supply tank should have high and low level alarms; the
pump should be interlocked to shut off at low supply level or low discharge
pressure. External pumps should be situated inside a diked area, and should
be accessible in the event of a tank leak.
The type of pump selected depends on pumping requirements and operating
conditions. Centrifugal, rotary, and positive displacement are used to pump
hydrogen fluoride. Sealless pumps are used for some applications. The pumps
used should be constructed of suitable materials such as carbon steel, nickel-
chromium-molybdenum and nickel-copper alloys which are resistant to hydrogen
fluoride corrosion. These pumps are subject to shaft seal leakage, so real
*
rings made of polyvinylidenefluoride. nickel-chromium-molybdenum alloy and
nickel-copper Alloy 400 are often used to eliminate this problem. Close-
fitting moving parts should not be constructed of steel since the ferric
fluoride film produced by the corrosion of steel can cause the parts to freeze
up. In addition. Type 400 stainless steels, cast iron, and hardened steels
should never be used.
In some situations, the potential for seal leakage rules out the use of
standard rotating shaft seals. One solution is to use pump types which
isolate the seals from the process stream. The seals are typically cartridge
canister double type (31). The buffer fluid between the mechanical seals is
commonly light oil. Another solution is to use pump types which eliminate
shaft seals altogether such as canned-motor pumps, vertical submersible pumps,
magnetically coupled pumps and diaphragm pumps (4,23).
53
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Canned motor pumps are centrifugal units in which the motor housing is
interconnected with the pump casing.. Here, the process liquid actually serves
as the bearing lubricant. An alternative concept is the vertical pump often
used on storage tanks. These pumps consist of a submerged impeller housing
connected by an extended drive shaft to the motor. The advantages of this
arrangement are that the shaft seal is above the maximum liquid level (and is
therefore not wetted by the pumped liquid) and the pump is self priming
because the liquid level is above the impeller.
Pumps using stuffing boxes and packing should be provided with
double-packed seal chambers designed to prevent hydrogen fluoride from con-
tacting any reactive material. These chambers can be purged with an appro-
priate inert fluid such as dry and oil-free nitrogen, or a suitable seal
liquid. The seal gas pressure should exceed the tank pressure by an appro-
priate margin. A seal fluid back-up system should be considered (31).
Magnetically-coupled pumps replace the drive shaft with a rotating
magnetic field as the pump-motor coupling device. Diaphragm pumps are posi-
tive displacement units in which a reciprocating flexible diaphragm drives the
fluid. This arrangement eliminates exposure of packing and seals to the
pumped liquid.
For metering service, diaphragm pumps -are commonly used. The r.ain
advantage of this'type of pump is none of the packing and seals are exposed to
the pumped liquid. However, a major consideration in the application of such
pumps is that at some point, diaphragm failure will probably occur. Such a
failure could lead to a release. These pumps may have a pressure relief valve
on the outlet, bypassing to the suction.
Improper operation of pumps as a result of cavitation,. running dry, and
deadheading can cause damage and failure of pumps. Cavitation can be a
problem in pumping because of low boiling point of hydrogen fluoride and
tendency to vaporize easily. If cavitation is allowed to occur, pitting and
54
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eventual serious damage to the impeller can result. Running a pump dry as a
result of loss of head in a feed tank, for example, can seriously damage a
pump. Finally, pumping against a closed valve can have serious ramifications.
A pump bypass or kick-back are useful in avoiding such an occurrence. Failure
of a pump, for whatever reason, can eventually lead to a hazardous release.
Centrifugal pumps often have a recycle loop back to the feed container
which prevents overheating if the pump is deadheaded. This is an important
consideration in hydrogen fluoride systems since hydrogen fluoride corrosive-
ness increases rapidly with increasing temperature. Deadheading is also a
concern with positive displacement pumps. To prevent rupture, positive
displacement pumps commonly have a pressure relief valve which bypasses to the
pump suction. Because of the probability of eventual diaphragm failure, the
use of diaphragm pumps should be carefully considered in view of this hazard
potential.
Pumps are not always necessary; in many circumstances, liquid hydrogen
fluoride is moved by pressure padding. With hydrogen fluoride cylinders and
ton-containers, the liquid may be displaced from the vessel by the force of
hydrogen fluoride vapor pressure. As discussed earlier, this process is
temperature dependent. With other types of vessels, an inert gas such as dry
nitrogen may be used to force liquid from the tank. Padding system designs
must reflect the operating conditions and limitations (e.g., required flow
rate) and therefore must be custom designed for a process.
Compressors—Reciprocating, centrifugal, liquid-ring rotary, and
non-lubricated screw compressors are used with hydrogen fluoride. Details of
such compressors used with hydrogen fluoride are discussed in the technical
literature (4,31).
Like pumps, compressors have the potential for heat buildup and shaft
seal leakage. Heat sources in a compressor include the heat of compression as
well as the heat generated through mechanical friction. Heat buildup in
55
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hydrogen fluoride compressors is a particular concern because hydrogen fluor-
ide's corrosion increases with increasing temperature. Most multistaged
compressors can be equipped with intercoolers which limit heat buildup and
increase compressor efficiency by reducing the volume of gas going to the next
compression stage. Both air and water cooling are used, but water systems
must be designed to prevent leakage and contact of water with hydrogen fluo-
ride.
While it is often possible to avoid using rotary shaft seals with hydro-
gen fluoride pumps, compressors in hydrogen fluoride service usually require
special seals such as double labyrinth seals. These seals have a series of
interlocking touch points which, by creating many incremental pressure drops,
reduce total leakage. Also, to further reduce leakage, dry air is injected
into the seal. In the event of deadheading, a compressor discharge can have a
pressure relief mechanism which vents to the compressor inlet or to a scrubber
system. The former appears to be satisfactory for a short term downstream
flow interruption. Where a sustained interruption might occur, relief to a
scrubber system-would be safer. Positive displacement compressors and pumps
must always be equipped with overpressure relief as close to the discharge as
possible (non-isolatable).
Miscellaneous Equipment—
Pressure Relief Devices—Information on specific relief valve types for
hydrogen fluoride service is not readily available. Some characteristics for
chlorine service seem to apply for hydrogen fluoride, however. For vessels,
an acceptable relief valve is of angle body construction with a closed bonnet
and a screwed cap over the adjusting screw. These valves are normally used in
combination with a rupture disc or a breaking pin assembly. Typical valve
construction materials include a cast carbon steel body; a nickel plated steel
spring; and nickel-copper or nickel-chromium-molybdenum alloy nozzle, disc
adjusting ring, nozzle ring, and spindle guide. The inlet flange should be
ANSI Class 300 or greater and the outlet flange should be ANSI Class 150 or
56
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greater. Valves of this construction which also have Viton® "0" ring seat
seals need not have a rupture disc or breaking pin. Other types of pressure
relief devices are acceptable as long as they are constructed of materials
suitable for hydrogen fluoride service and meet the general requirements of
the ASME boiler and Pressure Vessel Code. Section VIII. Division 1 (26).
Rupture discs are constructed of appropriate hydrogen fluoride-resistant
materials. Impervious graphite rupture discs fragment upon overpressure, and
therefore, should not be used in conjunction with relief valves. Connections
can be screwed, flanged or socket-welded for connections smaller than two
inches. However, connections two inches or larger should be flanged or butt-
welded. The flanges should be constructed of forged carbon steel and be rated
in accordance with the associated piping system. Because operating pressures
exceeding 70% of a disc's burst pressure may induce premature failure, a
considerable margin should be allowed when sizing rupture discs. When it is
possible to draw a vacuum on the disc, supports should be provided (23).
Instrumentation—Process instrumentation in hydrogen fluoride service
often uses isolating diaphragms for corrosion protection. Pressure gauges,
switches, or sensors commonly use a nickel-chromium-molybdenum alloy dia-
phragm, and may be filled with an inert fluid, such as chlorofluorocarbon
specialty lubricants (24).. Bourdon tube pressure gauges are not commonly
used, but if they are would require a corrosion resistant alloy for the tube.
The pressure range for both types of pressure measurement devices is commonly
twice the operating pressure (29).
Similar materials considerations apply to other instrumentation such as
temperature, flow, and level measurement devices. An additional consideration
for all instruments is that they should be protected from external corrosion
as well as direct process corrosion.
Periodic source by source fugitive emission monitoring can help identify
hydrogen fluoride leaks which, if left unrepaired, might promote corrosion and
57
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increase the likelihood of a. larger release. Continuous area monitoring can
help detect the presence of large leaks.
The use of level gauges or weight systems can be used to monitor tank
contents.
5.3.2 Plant Siting and Layout
The siting and layout of a particular hydrogen fluoride facility is a
complex issue which requires careful consideration of numerous factors. These
include: other processes in the area, the proximity of population centers.
prevailing winds, local terrain, and potential natural external effects such
as flooding. The rest of this subsection describes general considerations
which might apply to siting and layout of hydrogen fluoride facilities.
, 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.
Layout refers to the placement and arrangement of equipment in the
process facility. All anhydrous hydrogen fluoride and aqueous hydrofluoric
acid storage and handling equipment should be located away from other poten-
tially hazardous storage and handling facilities. Such equipment is usually
located in concrete enclosures or pits surrounded by curbing or walls to
prevent acid spills from contaminating surrounding areas and also to serve as
a boundary for the restricted acid area. Concrete containment areas are often
treated with polymeric sealers to increase the containment efficiency. The
drain system from the containment area should be designed to cause storm water
58
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to be routed to wastewater treating. The system should be capable of direct-
ing spilled hydrogen fluoride to a high capacity neutralization facility.
Containment of hydrogen fluoride by berms of lime-containing rock has been
suggested as a means of combined containment and passive neutralization. The
effectiveness of these systems has not been determined.
Various techniques are available for formally assessing a plant layout
and should be considered when planning high hazard facilities (23).
General layout considerations 'include:
• Large inventories of hydrogen fluoride should be kept away
from sources of fire or explosion hazard;
• Vehicular traffic should not go too near hydrogen fluoride
process or storage areas if this can be avoided;
• Where such traffic is necessary, precautions should be
taken to reduce the chances for vehicular collisions with •
equipment, especially pipe racks carrying hydrogen fluo-
ride across or next to roadways;
• Hydrofluoric acid piping preferably should not be located
adjacent to other piping which is under high pressure or
temperature, or which carries flammable materials; and
• Storage facilities should be segregated from the main
process unless the hazards of pipe transport are felt to
outweigh the hazard of the storage tank for site-specific
cases.
Because heat increases the corrosiveness of hydrogen fluoride and causes
thermal expansion of liquid hydrogen fluoride, measures should be taken to
59
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situate piping, storage vessels, and other hydrogen fluoride equipment so that
they are less exposed to heat sources. Hot process piping, equipment, steam
lines, and other sources of direct or radiant heat should be avoided or
systems should be designed for heat induced corrosion and pressure increases.
Storage should also be situated away from control rooms, offices, utilities,
other hazardous storage, and laboratory areas by distances similar to those
specified for flammable materials (23). Special precautions should be taken
to keep hydrogen fluoride storage vessels away from potential fire or explo-
sion sources.
In the event of an emergency, there should be multiple means of access to
the facility for emergency vehicles and crews. Storage vessel shut off valves
should be readily accessible. Containment for liquid storage tanks can be
provided by diking. Dikes reduce evaporation while containing the liquid. It
is also possible to equip a diked area to allow drainage to an underground
containment sump. This sump should be vented to a scrubber system for safe
discharge. A full containment system using a specially constructed building
vented to a scrubber is another possible option. This type of secondary
containment could be considered for large volume, liquid hydrogen fluoride
storage tanks.
5.3.3 Transfer and Transport Facilities
Transfer and transport facilities where both road 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.
As mentioned in the previous section, tank car and tank truck facilities
should be located away from sources of heat, fire, and explosion. Equipment
in these areas should also be protected from impact by vehicles and other
moving equipment. These tank vehicles should be securely moored during
transfer operations; an interlocked barrier system is commonly used.
60
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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.
When possible, the transfer of hydrogen fluoride should be made using
fixed rigid piping. In situations which require flexible hoses or tubes.
precautions must be taken to ensure sound connections. Avoiding cross contam-
ination of chemical materials is also a key concern.
5.4 PROTECTION TECHNOLOGIES
This subsection describes two types of protection technologies for
containment and neutralization. These are:
• Enclosures; and
•
• Scrubbers.
A presentation of more detailed information on these systems is planned in
other volumes of the prevention reference manual series.
S.A.I Enclosures
Enclosures refer to containment structures which capture any hydrogen
fluoride spilled or vented from storage or process equipment, thereby prevent-
ing immediate discharge of the chemical to the environment. The enclosures
contain the spilled liquid or gas until it can be transferred to other con-
tainment, discharged at a controlled rate which would not be injurious to
people or the environment, or transferred at a controlled rate to scrubbers
for neutralization.
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The use of specially designed enclosures for hydrogen fluoride storage or
process equipment does not appear to be widely practiced. The location of
toxic operations in the open air has been mentioned in the literature (23),
along with the opposing idea that sometimes enclosure may be appropriate. The
desirability of using an 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 protecting the community from accidental releases, then total enclo-
sure may be appropriate. Enclosures should be equipped with continuous
monitoring equipment and alarms. Alarms should sound whenever lethal or
flammable concentrations are detected. Enclosures for hydrogen fluoride
should be equipped with adequatge fire protection.
Care must be taken when an enclosure is built around pressurized equip-
ment. ' It would not be practical to design an enclosure to withstand the
pressures associated with the sudden failure of a pressurized vessel. An
enclosure would probably fail as a result of the pressure created from such a
release and could create an additional hazard. In these situations, it may be
determined that an enclosure is not appropriate. If an enclosure is built
around pressurized equipment, then it should be equipped with some type of
explosion protection, such as rupture plates that are designed to fail before
the entire structure fails.
The type of structures that appear to be suitable for hydrogen fluoride
are concrete blocks, or concrete sheet buildings or bunkers. While hydrogen
fluoride would attack these structures, they would serve long enough to
contain any spilled or leaked material until it could be discharged through a
scrubber. An enclosure building would have a ventilation system designed to
draw in air when-the building was vented to a scrubber. The bottom section of
the building used for stationary storage containers should be liquid tight to
retain any liquid hydrogen fluoride that might be spilled. Buildings around
rail tank cars used for storage do not normally lend themselves easily to
effective liquid containment. However, containment could be accomplished if
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the floor of the building 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 hydrofluoric
acid 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 hydrogen fluoride
releases from vents and pressure relief discharges, from process equipment, or
from secondary containment enclosures.
Hydrogen fluoride discharges could be contacted with an aqueous scrubbing
medium in any of several types of scrubbing devices. An alkaline solution is
required to achieve effective absorption because absorption rates with water
alone might require unreasonably high liquid-to-gas ratios. However, water
»
scrubbing could be used if an alkaline solution were not available. A sodium
hydroxide solution would be a typical alkaline solution for an emergency
scrubber.
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.
Some typical absorption data for the various types of scrubbers used for
hydrogen fluoride are presented in Table 5-3.
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
aust be given to how it would be activated in time to respond to an emergency
load. One approach used in some process facilities is to maintain a continu-
ous circulation of scrubbing liquor through the system. For many facilities
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TABLE 5-3. TYPICAL HYDROGEN FLUORIDE ABSORPTION DATA
cr>
Type of Scrubbing
Equipment
Crossflow Spray
Crosfiflow Spray
Crossflow Spray
Crossflow Spray
Crossflow Spray
Crossflow Spray
Counterflow Spray
Parallel Flow Spray
Counterflow Spray
Venturi:
Venturi:
Venturi:
Venturi:
Venturi
Venturi:
Venturi:
Scrubbing
Medium
Water
Water
Water
Water
Water
Lime Water
Water
Lime Water
Water
Water
Water
Water
Water
Water
Water
Water
Gas Rate.
(lb/hr/ft^)
2.110
1.880
2.080
1.830
1.400
2.050
2.000
13.800
2.000
76.000s
7 0.000s
70.000s
70.000s
70.000s
70.000s
70.000s
Overall Mass
Transfer Coeffi-
cient. K a Number of
Liquid Rate (lb/mole/ Transfer
(Ib/hr/ft ) hr-ft -atm) Unit. N..,
tXj
72
72
103
84
92
105
800
3.800
380
42.000S
40. 000-65. 000s
40.000-65.000°
40.000-65.000°
40. 000-65. 000s
40. 000-65. 000s
40. 000-65. 000s
11
12
12
15
25
35
9
51
4.3
_
_
—
_
—
"
0.33
0.38
0.25
0.62
1.09
1.50
5.85
2.58
2.5
2.9
2.0
2.3
3.0
3.9
2.3
Efficiency
(%)
28
32
22
46
66
77
99+
92
92
94
86
90
95
98
90
a
Based on throat cross-section.
Source: Reference 33
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this would not be practical, and the scrubber system might be tied into a trip
system to turn it on when it is needed. However, with this system a quantity
of hydrogen fluoride would be released prior to actuation of the scrubber
(i.e.. starting up a blower and turning on the flow of liquid).
The scrubber system must be designed so as not to present excessive
resistance to the flow of an emergency discharge. The pressure drop should be
only a small fraction of the total pressure drop through the emergency
discharge system. In general, at the liquid-to-gas ratios required for
effective scrubbing, spray towers have the lowest, and Venturis the highest
pressure drops. While packed beds may have intermediate pressure drops at
proper liquid-to-gas ratios, excessive ratios or plugging can increase the
pressure drop substantially. However, packed beds have higher removal
efficiencies than spray towers or Venturis.
In addition, the scrubber system must be designed to handle the "shock
wave" generated during the initial stages of the release. This is
particularly important for packed bed scrubbers since there is a maximum
pressure with which the gas can enter the packed section without damaging the
scrubber internals.
Design of emergency scrubbers can follow standard techniques discussed in
the literature, carefully taking into account the additional considerations
just discussed. An example of the sizing of an emergency packed bed scrubber
is presented in Table 5-4. This example provides some idea of the size of a
typical emergency scrubber for various flow rates. This is an example only
and should not be used as the basis for an actual system which might differ
based on site specific requirements.
Another approach is the drowning tank, where the hydrogen fluoride vent
is routed to the bottom of a large tank of uncirculating caustic. The drown-
ing tank does not have the high contact efficiency of the other scrubber
types, but can provide substantial capacity on demand. However, the static
head associated with the drowning tank must be less than the required relief
pressure in order for the system to operate.
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TABLE 5-4. EXAMPLE OF PERFORMANCE CHARACTERISTICS FOR AN EMERGENCY
PACKED BED SCRUBBER FOR HYDROGEN FLUORIDE
Basis: Inlet stream of 50Z HF in 50% air. Constant gas flow per unit
cross-sectional area of 455 acfm/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 140 140
— operating 70 70
Packed Height, ft. 5.2 18.3
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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5.5 MITIGATION TECHNOLOGIES
If, in spite of all precautions, a large release of anhydrous hydrogen
fluoride 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 community. Reducing the consequences of an accidental release of
a hazardous chemical is referred to as mitigation. Mitigation technologies
include such measures as physical barriers, water sprays and fogs, and foams
where applicable. The purpose of a mitigation technique is to divert, limit.
or disperse the chemical that has been spilled or released to the atmosphere
in order to reduce the atmospheric concentration and the area affected by the
chemical. The mitigation technology chosen for a particular chemical depends
on the specific properties of the chemical including its flammability, tozic-
ity. reactivity, and those properties which determine its dispersion charac-
teristics in the atmosphere. »
If a release occurs from a pressurized liquid hydrogen fluoride storage
tank above the boiling point, a quantity of liquid will immediately flash off
as vapor, while the remaining liquid will be cooled to the normal boiling
point of 67.1°F. Heat transfer from the air and ground will result in further
vaporization of the released liquid. Since the hydrogen fluoride accidentally
released from a refrigerated storage tank is already at or below its normal
boiling point, a comparable quantity of vapor will not flash off. as with the
pressurized release discussed above, but heat transfer from the environment
will cause evaporation and the formation of a vapor cloud. It is 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.
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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
Specific types of secondary containment systems include excavated basins,
natural basins, earth, steel.- or concrete dikes, and high impounding walls.
The type of containment system best suited for a particular storage tank or
process unit will depend on the risk associated with an accidental release
from that location. The inventory of hydrogen fluoride and its proximity to
other portions of the plant and to the community should be considered when
selecting a secondary containment system. The secondary containment system
t
should have the ability to contain spills with a minimum of damage to the
facility and its surroundings and with minimum potential for escalation of the
event.
Secondary containment systems for hydrogen fluoride storage facilities
commonly consist of one of the following:
• An adequate drainage system underlying the storage vessels
which terminates in a lime containing neutralization basin
having a capacity as large as the largest tank served;
• A diked area with a capacity as large as the largest tank
served.
These measures are designed to prevent the accidental discharge of liquid
hydrogen fluoride from spreading to uncontrolled areas.
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The most common type of containment system is a low wall dike surrounding
one or more storage tanks. Generally, no more than three tanks are enclosed
within one diked area to reduce risk. Dike heights usually range from three
to twelve feet depending on the area available to achieve the required volu-
metric capacity. The dike walls should be liquid tight and able to withstand
the hydrostatic pressure and temperature of a spill. Low wall dikes may be
constructed of steel, concrete or earth. If earthen dikes are used, the dike
wall must be constructed and maintained to prevent leakage through the dike.
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.
A low wall dike can effectively contain the liquid portion of an acciden-
tal release and keep the liquid from entering uncontrolled areas. By prevent-
ing the liquid from spreading, the low wall dike can reduce the surface area
of the spill. Reducing the surface area will reduce the rate of evaporation.
•
The low wall dike will partially protect the 'spill from wind; this can reduce
the rate of evaporation. A dike with a vapor fence will provide extra protec-
tion from wind and will be even more effective at reducing the rate of evapo-
ration.
A dike also creates the potential for hydrogen fluoride and trapped water
to mix in the dike, which may accelerate the rate of evaporation and form
highly corrosive hydrofluoric acid. If materials that would react violently
with hydrogen fluoride are stored within the same diked area then the dike
will increase the potential for mixing the materials in the event of a simul-
taneous leak. A dike also limits access to the tank during a spill.
A neutralization basin is well suited to storage systems where more than
one tank is served and a relatively large site is available. The flow from a
hydrogen fluoride spill is directed to the basin by dikes and channels under
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the storage tanks which are designed to minimize exposure of the liquid to
other tanks and surrounding facilities. In the basin, the hydrogen fluoride
is mixed with lime to form an insoluble fluoride sludge which can be hauled
away for1 disposal (34). The lime could be stored in the basin either as a
premized slurry or as solid limestone. Figure 5-2 illustrates two potential
layouts for a remote neutralization basin. Because of hydrogen fluoride's
high vapor pressure, the trenches that lead to the neutralization basin should
be covered to reduce the rate of evaporation. Additionally, the neutraliza-
tion basin should be located near the tank area to minimize the amount of
hydrogen fluoride that evaporates as it travels to the basin.
This type of system has several advantages. The spilled liquid is re-
moved from the immediate tank area. This allows access to the tank during the
spill and reduces the probability that the spilled liquid will damage the
tank,- piping, electrical equipment, pumps or other equipment. In addition, a
t
lime containing basin will immediately neutralize the hydrogen fluoride and
prevent its release to the atmosphere.
A limitation of a neutralization basin is that they do not completely
reduce the impact of a gaseous release. Additionally, the reaction of lime
with hydrogen fluoride is exothermic. The heat generated by the neutraliza-
tion could result in an increase in the rate of evaporation of the liquid.
An alternative to a lime filled basin would be to allow the spilled
liquid to flow into a covered, empty basin. The vapor from the basin could be
directed to a scrubbing system. The advantage of this system is that the
scrubber could be sized to accommodate the vapor generated from the spilled
liquid. The disadvantages are the same as those mentioned in Section 5.4.2
where scrubbers as a protection technology are discussed.
Although few authorities for hydrogen fluoride facilities require them,
high wall impoundments may be a good secondary containment choice for selected
systems. Circumstances which may warrant their use include limited storage
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CONCRETE DIKES AND PAD PARTIAL!*
FILLED WITH LIMESTONE UNDER
HYDROGEN FLUORIDE STORAGE TANK
LIMESTONE FILLED REMOTE
NEUTRALIZATION BASIN
(COULD BE COVERED)
DRAIN LINE
LIMESTONE NEUTRALIZATION BASIN
CONCRETE DIKES AND PAD
UNDER HYDROGEN FLUORIDE
STORAGE TANK
LIME-WATER SLURRY FILLED
REMOTE NEUTRALIZATION BASIN
(COULD BE COVERED)
DRAIN LINE
LIME WATER NEUTRALIZATION SYSTEM
Figure 5-2. Potential layouts for a neutralization basin system.
Source: Adapted from Reference 34.
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site area, the need to minimize vapor generation rates, and/or the tank must
be protected from external hazards. Maximum vapor generation rates will gen-
erally be lower for a high wall impoundment than for low wall dikes or remote
impoundments because of the reduced surface contact area. These rate* can be
further reduced with the use of insulation on the wall and floor in the annu-
lar space. High impounding walls may be constructed of low temperature steel.
reinforced concrete, or prestressed concrete. A weather shield may be pro-
vided between the tank and wall with the annular space remaining open to the
atmosphere. The available area surrounding the storage tank will dictate the
minimum height of the wall. For high wall impoundments, the walls may be da-
signed with a volumetric capacity greater than that of the tank to provide va-
por containment. Increasing the height of the wall also raises the elevation
of any released vapor.
.One disadvantage of these dikes is that the high walls around a tank may
hinder routine- external observation. Furthermore, the closer the wall is to
the tank, the more difficult it becomes to access the tank for inspection and
maintenance. As with low wall dikes, piping should be routed over the wall if
possible. The closeness of the wall to the tank may necessitate placement of
the pump outside of the wall, in which case the 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 placad
around the entire wall.
An example of the effect of diking as predicted by one vapor dispersion
model is shown in Figure 5-3 (35). With diking the predicted maximum IDLH
exposure occurs at a distance of 2,100 feet downwind from the release source
at 3 minutes after release.. Without diking the predicted maximum IDLH
exposure occurs at a distance of 9,400 feet at 13 minutes after exposure.
One further type of secondary containment system is one which is struc-
turally integrated with the primary system and forms a vapor tight enclosure
around the primary container. Many types of arrangements are possible. A
72
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o.s
nilaa
1
mile
1.9
mllea
Release from a tank surrounded by a 25 ft. diameter dike.
Elapsed Time: 3 minutes
1
mile
1.5
miles
2
mi las
Release from a tank with no dike.
Elapsed Time: 13 minutes
Common Release Conditions;
Storage Temperature = 40°F
Storage Pressure = 14.7 psia
Ambient Temperature = 85°F
Wind Speed =10 mph
Atmospheric Stability Class = C
Quantity Released = 5000 gallons
through a 2-inch hole
Figure 5-3. Computer model simulation showing the effect of diking on
the vapor cloud generated from a release of refrigerated
hydrogen fluoride.
73
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double walled tank is an example of such an enclosure. These systems may be
considered where protection of the primary container and containment of vapor
for events not involving foundation or wall penetration failure are of great-
est concern. Drawbacks of an integrated system are the greater complexity of
the structure, the difficulty of access to certain components, and the fact
that complete vapor containment cannot be guaranteed for all potential events.
Provision should be made for drainage of rainwater from diked areas.
This will involve the use of sumps and separate drainage pumps, since direct
drainage to stormwater sewers would presumably allow any spilled hydrogen
fluoride 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 (36). 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
t
from which it may gain heat. In areas where it is critical to minimize vapor
generation, surface insulation may be used in the diked area to further reduce
heat transfer from the environment to the spilled liquid.. The floor of an
impoundment should be sealed with a clay blanket to prevent the hydrogen
fluoride from seeping into the ground; percolation into the ground causes the
ground to cool more quickly, increasing the vapor generation rate. Absorption
of the hydrogen fluoride into water in the soil would also release additional
heat.
5.5.2 Flotation Devices and Foams
Other possible means of reducing the surface area of spilled hazardous
chemicals include placing impermeable flotation devices on the surface,
dilution with water, and applying water-based foam. However, where hydrogen
fluoride releases are concerned, neither of these are satisfactory.
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efficiency. However, being able to use such devices requires acquisition in
advance of a spill and storage until needed. In addition, deployment may be
difficult in all but small spills.
Although such devices are potentially effective, no systems are currently
available for use in mitigating hydrogen fluoride spills. The primary deter-
ent to their use is the cost associated with material and disposal equipment.
Such a system would require the dispersal of a minimum of 280 particles per
square foot of spill material (37). Based on 1986 prices, material costs
would be approximately $100 per square foot, with dispersal equipment costs
running 100 times the cost (37).
The use of foams in vapor hazard control has been demonstrated for a
broad range of volatile chemicals. However, no foam systems are currently
available for use with hydrogen fluoride. Results of a laboratory test
program conducted by the Mine Safety Appliance (MSA) Research Corporation (37)
to evaluate the applicability and effectiveness of various foams for various
hazardous chemicals including hydrogen fluoride showed that because of,the
extremely high heat of solution, hydrogen fluoride boils and fumes violently
upon application of foam.
Finally, the dilution of a hydrogen fluoride spill with water will result
in highly corrosive hydrofluoric acid. In addition, because of the high heat
of solution, the addition of pure water results in violent boil-off of hydro-
gen fluoride and a dispersal of corrosive acid. Thus, water should not be
used on a pool of hydrogen fluoride.
One alternative for hydrogen fluoride spills is to spread soda ash on.the
spill or use a strong soda ash solution to act as a neutralizing agent and
prevent the release of toxic hydrogen fluoride vapors.
Another alternative for retarding evaporation of liquid hydrogen fluoride
is to use a paraffin-base oil. A test program using several agents including
75
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an oil with a viscosity of 675 Saybolt seconds at 100°F was conducted by Union
Carbide Corporation (39). The results showed that this type of oil spread
over the surface and effectively sealed the vapors without being destroyed.
Any oil used must have a high enough flash point to prevent a secondary fire
hazard from resulting.
5.5.3 Mitigation Techniques for Hydrogen Fluoride Vapor
The extent to which the escaped hydrogen fluoride 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 hydrogen fluoride cloud
will be dependent on a number of factors. These include the physical stats of
the hydrogen fluoride before its release, the location of the release, and the
atmospheric and environmental conditions. Many possibilities exist concerning
•
the shape and motion of the vapor cloud, and a number of predictive models of
dispersion have been developed. As a result of the higher specific gravity of
pure hydrogen fluoride, large accidental releases of hydrogen fluoride will •
often result in the formation of hydrogen fluoride-air mixtures which are
denser than the surrounding atmosphere. This type of vapor cloud is espec-
ially hazardous, because it will spread laterally and remain close to the
ground. At this writing, research data from tests on hydrogen fluoride
releases is being analyzed (40). When these results ara published much more
will be known on the behavior of hydrogen fluoride under actual release
conditions.
One possible means of dispersing as well as removing toxic vapor from the
air is with the use of water sprays or fogs. However, dilution of hydrogen
fluoride with water results in the formation of highly corrosive hydrofluoric
acid and presents an additional health hazard to plant personnel as well as
corrosion problems for machinery and equipment. In addition, to be effective,
an impractically large volume of water might have to be used, although it may
be beneficial in controlling relatively small releases where principal hazard
76
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is to plant personnel (41). An alternative is to use a mild aqueous alkaline
spray system such as an ammonia-injected water spray system which would act as
a neutralizing agent for the acid. Although such systems do not appear to be
widely used for the mitigation of hydrogen fluoride vapors, they are used for
other toxic chemicals of similar nature (42).
The spray medium is typically applied to the vapor cloud by means of
hand-held hoses and/or stationary water-spray barriers. Important factors
relating to the effectiveness of spray systems are the distance of the nozzles
from the point of release, the fog pattern, nozzle flow rate, pressure, and
nozzle rotation. If spray systems are used to mitigate hydrogen fluoride
vapors from a diked area containing spilled liquid hydrogen fluoride, great
care must be taken not to direct water into the liquid hydrogen fluoride
itself.
Several techniques have also been developed to effectively disperse toxic
vapor resulting from major leaks in piping and equipment. One such technique
has been developed by Beresford (43). Although such a system has not been
used for the mitigation of hydrogen fluoride vapor, they have been effectively
used for other toxic chemicals of similar nature (43).
The method consists of coarse water sprays discharging upwards from flat
fan sprays and wide-angled spray monitors arranged so that a vent or chimney
effect is created to completely surround the toxic vapor. Results have shown
that the high velocity water droplets induce large volumes of air at ground
level as the water discharges upwards (43). The air is caused to move upwards
through the chimney formed by the sprays. As the air moves over the ground,
the heavier than air toxic gas is diluted and pushed up and out of the top of
the chimney where it dispenses safely. Design details are presented in
Beresford (43). Both types of spray methods are incorporated into the design
since the flat-fan sprays effectively stop the lateral spread of vapor and the
monitors provide the required air movement for dilution and dispersal.
77
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Another means of dispersing a vapor cloud is with the use of large fans
or blowers which would direct the vapor away from populated or other sensitive
areas (44). However, this method would only be feasible in very calm weather
and in sheltered areas; it would not be effective in any wind and would be
difficult to control if the release occupies a large open area. A large.
mechanical blower would also be required which lowers the reliability of this
mitigation technique compared to water fogs and sprays.
In general, techniques used to disperse or control vapor emissions should
emphasize simplicity and reliability. In addition to the mitigation tech-
niques discussed above, physical barriers such as buildings and rows of trees
may help to contain the vapor cloud and control its movement. Additional
discussions concerning mitigation technologies will be found in a manual on
control technologies, part of this manual series.
5.6 'OPERATION AND MAINTENANCE PRACTICES
• Quality hardware, contained mechanical equipment, and protective devices
all increase plant safety; however, they must be supported by the safety
policies of management and by constraints on their operation and maintenance.
This section describes how management policy and training, operation, and
maintenance procedures relate to the prevention of accidental chlorine re-
leases. Within the hydrogen fluoride industry, these procedures and practices
vary widely because of differences in the size and nature of the processes and
because any determination of their adequacy is inherently subjective. For
this reason, the following subsections focus primarily on fundamental princi-
ples and do not attempt to define specific policies and procedures.
5.6.1 Management Policy
Management is a key factor in the control of industrial hazards and the
prevention of accidental releases. Management establishes the broad policies
and procedures which influence the implementation and execution of specific
78
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hazard control measures. It is important that these management policies and
procedures be designed to match the level of risk in the facilities where they
will be used. Most organizations have a formal safety policy. Many make
policy statements to the effect that safety must rank equally with other
company functions such as production and sales. The effectiveness of any
safety program, however, is determined by a company's commitment to it. as
demonstrated throughout the management structure. Specific goals must be
derived from the safety policy and supported by all levels of management.
Safety and loss prevention should be an explicit management objective.
Ideally, management should establish the specific safety performance measures.
provide incentives for attaining safety goals, and commit company resources to
safety and hazard control. The advantages of an explicit policy are that it
sets the standard by which existing programs can be judged, and it provides
evidence that safety is viewed as a significant factor in company operations.
In the context of accident prevention, management is responsible for
(23,45):
•
•
• Ensuring worker competency.
• Developing and enforcing standard operating procedures.
• Adequate documentation of policy and procedures.
• Communicating and promoting feedback regarding safety
issues,
• Identification, assessment, and control of hazards, and
• Regular plant audits and provisions for independent
checks.
79
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Additional discussion on the responsibilities of management will be found
in a manual on control technologies, part of this manual series.
5.6.2 Operator Training
The performance of operating personnel is also a key factor in the
prevention of accidental hydrogen fluoride releases. Many case studies
documenting industrial incidents note the contribution of human error to
accidental releases (23). Release incidents may be caused by using improper
routine operating procedures, by insufficient knowledge of process variables
and equipment, by lack of knowledge about emergency or upset procedures, by
failure to recognize critical situations, and in some cases by direct physical
mistake (e.g.. turning the wrong valve). A comprehensive operator training
program can decrease the potential for accidents resulting from such causes.
'Operator training can include a wide range of activities and a broad
spectrum of information. Training, however, is distinguished from education
in that it is specific to particular tasks. While' general education is
important and beneficial, it is not a substitute for specific training. The
content of a specific training program depends on the type of industry, the
nature of the processes used, the operational skills required, the character-
istics of the plant management system, and tradition.
Some general characteristics of quality industrial training programs
include:
• Establishment of good working relations between management
and personnel.
• Definition of trainer responsibilities and training
program goals.
80
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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 upsets, emergencies, and acci-
dental releases, and
• Frequent supplemental training and the use of up-to-date
training materials.
In many instances training is carried out jointly by plant managers and a
training staff selected by management. In others, management is solely
responsible for maintaining training programs. In either case, responsibili-
ties should be explicitly designated to ensure that the quality and quantity
of training provided is adequate. Training requirements and practices can be
expected to differ between small and large companies,- partly because of
resource needs and availability, and partly because of differences in employee
»
turnover.
A list of the aspects typically involved in the training of process
operators for routine process operations is presented in Table 5-5.
Emergency training includes topics such as:
• Recognition of alarm signals,
• Performance of specific functions (e.g., shutdown
switches),
• Use of specific equipment.
• .Actions to be taken on instruction to evacuate.
81
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TABLE 5-5. ASPECTS OF TRAINING PROGRAMS FOR ROUTINE PROCESS OPERATIONS
Process goals, economics, constraints, and priorities
Process flow diagrams
Unit Operations
Process reactions, thermal effects
Control systems
Process materials quality, yields
Process effluents and wastes
Plant equipment and instrumentation
Equipment identification
Equipment manipulation
Operating procedures
Equipment maintenance and cleaning
Use of tools
Permit systems
Equipment failure, services failure
Fault administration
Alarm monitoring
Fault diagnosis
Malfunction detection
Communications, recordkeeping, reporting
Source: Reference 23
32
-------
• Fire fighting, and
• Rehearsal of emergency situations.
Aspects specifically addressed in safety training include (23.43):
• Hazard recognition and communication.
• Actions to be taken in particular situations.
• Available safety equipment and locations,
• When and how to use safety equipment.
• Use and familiarity with documentation such as.
- plant design and operating manuals,
- company safety rules and procedures.
- procedures relevant to fire, explosion, accident, and
health hazards.
- chemical property and handling information, and
• First aid and CPU.
Although emergency and safety programs typically focus on incidents such
as fires, explosions, and personnel safety, it is important that prevention of
accidental chemical releases and release responses be addressed as part of
these programs.
Much of the type of training discussed above is also important for
management personnel. Safety training gives management the perspective
necessary to formulate good policies and procedures, and to make changes that
will improve the quality of plant safety programs. Lees suggests that train-
ing programs applied to managers include or define (23):
83
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• Overview of technical aspects of safety and loss preven-
tion approach,
• Company systems and procedures.
• Division of labor between safety personnel and managers in
with respect to training, and
• Familiarity with documented materials used by workers.
5.6.3 Maintenance and Modification Practices
Plant maintenance is necessary to ensure the structural integrity of
chemical processing equipment; modifications are often necessary to allow more
effective production. However, since these activities are also a primary
•
source of accidental release incidents,- proper maintenance and modification
practices are an important part of accidental release prevention. Use of a
*
formal system of controls is perhaps the most effective way of ensuring that
maintenance and modification are conducted safely. In many cases, control
systems have had a marked effect on the level of failures experienced (23).
Permit systems and up-to-date maintenance procedures minimize the poten-
tial for accidents during maintenance operations. Permit-co-work systems
control maintenance activities by specifying the work to be done, defining
individual responsibilities, eliminating or protecting against hazards, and
ensuring that appropriate inspection and testing procedures are followed.
Maintenance permits originate with the operating staff. Permits may be
issued in one or two stages. In one-stage systems,- the operations supervisor
issues permits to the maintenance supervisor, who is then responsible for his
staff. Two-stage systems involves a second permit issued by the maintenance
supervisor to his workforce (23).
84
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Another form of maintenance control is the maintenance information
system. Ideally, these systems should log the entire maintenance history of
equipment, including preventative maintenance, inspection and testing, routine
servicing, and breakdown or failure maintenance. This type of system is also
used to track incidents caused by factors such as human error, leaks, and
fires, including identification and quantification of failures responsible for
hazardous conditions, failures responsible for downtime, and failures respon-
sible for direct repair costs.
Accidental releases are frequently the result of some aspect of plant
modification. Accidents result when equipment integrity and operation are not
properly assessed following modification, or when modifications are made
without updating corresponding operation and maintenance instructions. In
these situations, it is important that careful assessment of the modification
results has a priority equal to that of getting the plant on-line.
•
For effective modification control, there must be established procedures
for authorization, work activities, inspection, and assessment, complete
•
documentation of changes, including the updating of manuals, and additional
training to familiarize operators with new equipment and procedures (23.45).
Formal procedures and checks on maintenance and modification practices
must be established to ensure that such practices enhance rather than adverse-
ly affect plant safety. As with other plant practices, procedure development
end complete documentation are necessary. However, training, attitude, and
the degree to which the procedures are followed also significantly influence
plant safety and release prevention.
The use and availability of clearly defined procedures collected in
maintenance and operating manuals is crucial for the prevention of accidental
releases. Well-written instructions should give enough information about a
process that the worker with hands-on responsibility for operating or main-
taining the process can do so safely, effectively, and economically. These
85
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instructions not only document the path to the desired results, but also are
the basis for most industrial training programs (46.47). In the chemical
industry, operating and maintenance manuals vary in content and detail. To
some extent, this variation is a function of process type and complexity;
however, in many cases it is a function of management policy. Because of
their importance to the safe operation of a chemical process, these manuals
must be as clear, straightforward, and complete as possible. In addition,
standard procedures should be developed and documented before plant startup,
and appropriate revisions should be made throughout plant operations.
Operation and maintenance may be combined or documented separately.
Procedures should include startup, shutdown, hazard identification, upset
conditions, emergency situations, inspection and testing, and modifications
(23). Several authors think industrial plant operating manuals should include
(23.45,46.47):
•
•
• Process descriptions,
• A comprehensive safety and occupational health section,
• Information regarding environmental controls,
• Detailed operating instructions, including startup and shut-
down procedures,
• Upset and emergency procedures,
• Sampling instructions,
• Operating documents (e.g., logs, standard calculations),
• Procedures related to hazard identification.
86
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• Information regarding safety equipment,
• Descriptions of job responsibilities, and
• Reference materials.
Plant maintenance manuals typically contain procedures not only for
routine maintenance, but also for inspection and testing, preventive mainte-
nance, and plant or process modifications. These procedures include specific
items such as codes and.supporting documentation for maintenance and modifica-
tions (e.g., permits-to-work, clearance certificates), equipment identifica-
tion and location guides, inspection and lubrication schedules, information on
lubricants, gaskets, valve packings and seals, maintenance stock requirements,
standard repair times, equipment turnaround schedules, and specific inspection
codes (e.g., for vessels and pressure systems) (23). Full documentation of
the maintenance required for protective devices is a particularly important
aspect of formal maintenance systems.
»
The preparation of operating and maintenance manuals, their availability,
and the familiarity of workers with their contents are all important to safe
plant operations. The objective, however, is to maintain this safe practice
throughout the life of the plant. Therefore, as processes and conditions are
modified, documented procedures must also be modified.
5.7 CONTROL EFFECTIVENESS
It is difficult to quantify the control effectiveness of preventive and
protective measures to reduce the probability and magnitude of accidental
releases. Preventive measures, which 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
87
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quantify in terms of their efficiency in reducing a quantity of chemical that
could be released.
Preventive measures reduce the probability of an accidental release by
increasing the reliability of 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
5-6 summarizes what appear to be some of the major design.- equipment, and
operational measures applicable to the primary hazards identified for the
hydrogen fluoride applications in the United States. The items listed in
Table 5-6 are for illustration only and do not necessarily represent satis-
factory control options 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 be evaluated indi-
vidually. A presentation of more information about reliability in terms of
probabilities is planned in other volumes of the prevention reference manual
series.
5.8 ILLUSTRATIVE COST ESTIMATES FOR CONTROLS
This section presents cost estimates for different levels of control and
for specific release prevention and protection measures for hydrogen fluoride
storage and process facilities that might be found in the United States.
5.8.1 Prevention and Protection Measures
Preventive measures reduce the probability of an accidental release from
a process or 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 5-7
presents costs for some of the major design, equipment, and operational
38
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TABLE 5-6. EXAMPLES OF MAJOR PREVENTION AND PROTECTION MEASURES
TOR HYDROGEN FLUORIDE RELEASES
Hazard Area
Prevention/Protection
Water contamination
in hydrocarbon feeds
to alkylation
Sulfur contamination
in hydrocarbon feeds
to alkylation
Hydrogen fluoride
flow control
Temperature sensing
and cooling medium
flow control
Temperature sensing
and heating medium
flow control
Overpressure
Mixing in alkylation
reactors
Corrosion
Continuous moisture monitoring;
Backflow prevention
Continuous sulfur monitoring
Redundant flow control loops;
Minimal overdesign of feed systems
Redundant temperature sensors;
Interlock flow switch to shut off
HF feed on loss of cooling, with
relief venting to emergency scrubber
system
Redundant temperature sensors;
Interlock flow switch to shut off.
HF feed on loss of heating, with
relief venting to emergency scrubber
system
Redundant pressure relief; adequate
size; discharge not restricted
Interlock HF and olefin feed shutoff
with loss of mixing
Increased monitoring with more
frequent inspections; use of pH
sensing on cooling water and steam
condensate loops; use of corrosion
coupons3; visual inspections;
non-destructive testing
(Continued)
89
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TABLE 5-6 (Continued)
Hazard Area Prevention/Protection
Reactor and reboiler Redundant temperature sensing and
temperatures alarms
Overfilling Redundant independent level sensing.
alarms and interlocks; training of
operators
Atmosphere releases Emergency vent scrubber system
from relief discharges
Storage tank or line Enclosure vented to emergency
rupture scrubber system; diking; foams;
dilution; neutralization; water
sprays
A piece of metal of known composition which is used to monitor corrosion
rates by allowing it to reside in the corrosive environment and measuring
the amount of corrosion as a function of time.
90
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TABLE 5-7. ESTIMATED TYPICAL COSTS OF MAJOR PREVENTION AND
PROTECTION MEASURES FOR HYDROGEN FLUORIDE RELEASES*
Prevention/Protection Measure
Capital Cost
(1986 $)
Annual Cost
(1986 $/yr)
Continuous moisture monitoring
Flow control loop
Temperature sensor
Pressure relief
- relief valve
- rupture disk
Interlock system for flow shut-off
pH monitoring of cooling water
Alarm system
Level sensor
- liquid level gauge
- load cell
Diking (based on a 10,000 gal. tank)
- 3 ft. high
- top of tank height. 10 ft.
Increased corrosion inspection
7.500-10.000
4,000-6,000
250-400
1.000-2.000
1.000-1.200
1.500-2.000
7.500-10.000
250-500
1.500-2.000
10,000-15,000
1.200-1.500
7.000-7.500
900-1.300
500-750
30-50
120-250
120-150
175-250
900-1.300
30-75
175-250
1.300-1.900
150-175
850-900
200-400
on a 10.000 gallon fixed hydrogen fluoride storage tank system and a
147.000 gallon/day alkylation reactor system.
Based on 10-20 hours ® $20/hour.
91
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measures applicable to the primary hazards identified in Table 5-6 for the
hydrogen fluoride applications in the United States.
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
to aa 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 che 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.
92
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When comparing the costs of the various levels of control, it is impor-
tant to realize that higher costs do not necessarily imply improved safety.
The measures applied must be applied correctly. Inappropriate modifications
or add-ons may not make a system safer. Each added control option increases
the complexity of a system. In some cases, the hazards associated with the
increased complexity may outweigh the benefits derived from the particular
control option. Proper design and construction along with proper operational
practices are needed to assure safe operation.
These estimates are for illustrative purposes only. It is doubtful that
any specific installation would find all of the control options listed in
these tables appropriate for their purposes. An actual system is likely to
incorporate some items from each of the levels of control and also some
control options not listed here. The purpose of these estimates is to illu-
strate the relationship between cost and control, and is not to provide an
equipment check list.
Two sets of cost estimates were prepared; one for a 42 ton fixed hydrogen
fluoride storage tank system with 10.000 gal capacity and the other for a
hydrogen fluoride alkylation reactor system for a 147,000 gal/day alkylate
capacity plant. These systems are representative of storage and process
facilities that might be found in the United States.
5.8.3 Cost Summaries
Table 5-8 presents a summary of the total capital and annual costs for
each of the three levels of control for the hydrogen fluoride storage system
and the hydrogen fluoride alkylation reactor system. The costs presented
correspond to the systems described in Table 5-9 and Table 5-10. 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 Table 5-11 through 5-16.
93
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TABLE 5-8. SUMMARY COST ESTIMATES OF POTENTIAL LEVELS OF CONTROLS FOR
HYDROGEN FLUORIDE STORAGE TANK AND ALKYLATION REACTOR
System
HF Storage Tank;
42 ton
Fixed HF Tank
with 10.000 gal
Capacity
HF Alkylation Reactor
at Typical Operating
Conditions of 75-100°F
and 80-115 psig with a
147.000 gal/day alkylate
capacity
Level of
Control
Baseline
Level No. 1
Level No. 2
Baseline
Level No. 1
Level No. 2
Total
Capital Cost
(1986 $)
147.000
471.000
1.312.000
2.425.000
4.172.000
4.453.000
Total
Annual Cost
(1986 $/yr)
18.000
56.000
154,000
332.000
544.000
579.000
94
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TABLE 5-9: EXAMPLE OF LEVELS OF CONTROL FOR HYDROGEN FLUORIDE STORAGE TANKa
Process: 42 ton fixed hydrogen fluoride storage tank
10.000 gal
Controls
Baseline
Level No. 1
Level No. 2
Flow:
Single check- Add second check
valve on tank- valve.
process feed line.
Temperature:
Pressure:
None
Single pressure
relief valve.
vent to atmos-
phere.
None
Add second relief
valve. Vent to
limited scrubber.
Provide local
pressure indicator.
Add a reduced-pressure
device with internal
air gap and relief
vent to containment
tank or scrubber.
Add temperature
indicator.
Add rupture disks
under relief valves.
Provide local pressure
indication on space
between disk and
valve.
Quantity:
Location:
Materials of
Construction:
Vessel:
Local level
indicator.
Away from traf-
fic, and flam-
mables, and other
hazardous pro-
cesses.
Carbon steel.
Tank pressure
specification
150 psig.
Add independent
remote level
indicator.
Away from traffic.
flammables. and
other hazardous
processes.
Carbon steel with
increased corrosion
allowances. 1/8
inch
Tank pressure
specification
psigc.
Add level alarm. Add
high-low level inter-
lock shut-off for both
inlet and outlet
lines.
Away from traffic.
flammables. and other
hazardous processes.
Monel*.
Tank pressure
specification 375
psigc.
(continued)
95
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TABLE 5-9 (Continued)
Process: 42 ton fixed hydrogen fluoride storage tank
10,000 gal
Controls
Baseline
Level No. 1
Level No. 2
Piping:
Prooess
Machinery:
Enclosures :
Diking<
Scrubbers :
Mitigation:
Sen. 80 carbon
steel.
Centrifugal pump.
carbon steel,
stuffing box.
None
None
None
None
Sch. 80 Saran*-
lined carbon
steel.
Centrifugal pump.
Monel* construc-
tion, double
capacity mechanical
seal.
Steel building.
3 ft high.
Hater scrubber.
Hater sprays.
Sch 80 Monel*.
Magnetically-coupled
centrifugal pump,
Monel* construction.
Concrete building.
Top of tank height. 10
ft.
Alkaline scrubber.
Alkaline water sprays
and barriers.
a The examples in this table are appropriate for many, but not all applica-
tions. This is only an exemplary system. Design must be suited to fit the
service.
A reduced pressure device is a modified double check valve.
c Note that tank pressure specification will be a function of mayi apm operat-
ing pressure. These values are chosen only as representative examples.
96
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TABLE 5-10: EXAMPLE OF LEVELS OF CONTROL FOR HYDROGEN FLUORIDE ALKYLATION
REACTOR*
Process: HF alkylation
Typical Operating Conditions: - Temperature: 75-100°F
- Pressure: 80-115 psig
Controls
Baseline
Level No. 1
Level No. 2
Process:
Temperature:
Pressure:
Flow:
Quantity:
Mixing:
Corrosion:
Dryers on feed
lines.
Provide local
temperature
control.
Provide local
pressure control.
Single pressure
relief valve.
Vent to
atmosphere.
Provide local
flow control on
HF feed and
cooling medium to
reactor.
None.
Improved reactor
design.
Add redundant
temperature sensors
and alarms. Add
remote temperature
indicator.
Add redundant
pressure sensors.
Add second relief
valve. Vent to
limited scrubber.
Add remote pressure
indicator.
Add redundant flow
control loops.
None.
Provide adequate Add agitation
nixing. detection system.
Visual inspection
and pH monitoring
of cooling
medium.
Increased
monitoring with
increased
inspections.
Use of interlock
systems.
Add temperature switch
and back-up cooling
system.
Add rupture disks
under relief valves
and provide local and
remote pressure
indicator on space
between disk and
valve.
Add interlock flow
switch to shut off HF
feed on loss of
cooling medium.
None.
Interlock HF and
olefin feed shut off
with loss of mixing.
Add pH sensing on
reactor cooling
medium. Add corrosion
coupons.
(Continued)
97
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TABLE 5-10 (Continued)
Process: H? alkylation
Typical Operating Conditions: - Temperature: 75-100°F
- Pressure: 80-115 psig
Controls
Baseline
Level No. 1
Level No. 2
Composition:
Material of
Construction:
Vessel:
Dryers on feed
lines.
Carbon-steel
Pressure
specification:
150 psig.
Occasional Continuous moisture
moisture monitoring monitoring of feed.
of feed.
Carbon steel with
added corrosion
allowance.
Pressure
specification:
200 psig.
Monel*.
Pressure
specification:
200 psig.
Piping:
Process
Machinery:
Sch 80 carbon
steel.
Centrifugal pump,
carbon steel
construction,
stuffing box.
Sch 80 Saran* lined
carbon steel.
Centrifugal pump,
Monel*
construction,
double capacity
mechanical seal.
Sch 80 Monel*.
Magnetically-coupled
centrifugal pump.
Monel* construction.
Protective
Barrier:
Enclosures:
Scrubbers:
Mitigation:
None.
None.
None.
None.
Curbing around
reactor/settler.
Steel building.
Water scrubbers.
Water sprays.
3 ft high retaining
wall.
Concrete building.
Alkaline scrubbers.
Alkaline water sprays.
The examples in this table are appropriate for many, but not all applica-
tions. This is only an exemplary system. Design must be suited to fit the
specific service.
98
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TABLE 5-11. ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED WITH
BASELINE HYDROGEN FLUORIDE STORAGE SYSTEM
Capital Cost
(1986 $)
Annual Cost
(1986 $/yr)
VESSELS:
Storage Tank
131.000
15,000
PIPING AND VALVES:
Pipework
Check Valve
Gate Valves (5)
Excess Flow Valves (2)
Angle Valves (2)
Relief Valve
2,300
280
1.700
500
2.100
2.000
270
30
200
60
250
240
PROCESS MACHINERY:
Centrifugal Pump
4.000
460
INSTRUMENTATION:
Pressure Gauges (4) 1.500
Liquid Level Gauge 1.500
PROCEDURES AND PRACTICES:
Visual Tank Inspection (external)
Visual Tank Inspection (internal)
Relief Valve Inspection
Piping Inspection
Piping Maintenance
Valve Inspection
Valve Maintenance
170
170
15
60
15
300
120
30
350
TOTAL COSTS
147.000
18.000
99
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TABLE 5-12. ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED
WITH LEVEL 1 HYDROGEN FLUORIDE STORAGE SYSTEM
Capital Cost
(1986 $)
Annual Cost
(1986 $/yr)
VESSELS:
Storage Tank
Expansion Tanks (3)
187.000
6.500
22.000
760
PIPING AND VALVES:
Pipework
Check Valve
Gate Valves (5)
Excess Flow Valves (2)
Angle Valves (2)
Relief Valves (2)
6.200
560
1,700
500
2.100
4.000
720
65
200
60
250
470
PROCESS MACHINERY:
Centrifugal Pump
16,000
1.900
INSTRUMENTATION:
Pressure Gauges (4)
Flow Indicator
Liquid Level Gauge
Remote Level Indicator
1.500
3.700
1.500
1.900
175
430
175
220
ENCLOSURES:
Steel Building
10,000
1.200
SCRUBBERS:
Water Scrubber
226.000
26,000
(Continued)
100
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TABLE 5-12 (Continued)
Capital Cost Annual Cost
(1986 $) (1986 $/yr)
DIKING:
3 ft High Concrete Diking 1.400 160
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 471,000 56.000
101
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TABLE 5-13. ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED
WITH LEVEL 2 HYDROGEN FLUORIDE STORAGE SYSTEM
VESSELS:
Storage Tank
Expansion Tanks (3)
PIPING AND VALVES:
Pipework
Reduced Pressure Device
Gate 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 Shut-off
ENCLOSURES:
Concrete Building
Capital Cost
(1986 $)
932,000
6.500
9.200
1.500
1,700
500
2.100
4.000
1.100
19.000
2.200
2.200
3.700
16.000
1.900
380
1.900
19.000
Annual Cost
(1986 $/yr)
109,000
760
1.100
170
200
60
250
470
130
2.200
260
260
430
1.900
220
45
220
2.300
(Continued)
102
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TABLE 5-13 (Continued)
Capital Cost Annual Cost
(1986 $) (1986 $/yr)
SCRUBBERS:
Alkaline Scrubber 280.000 33,000
DIKING:
10 ft High Concrete Diking 7.600 500
PROCEDURES AND PRACTICES:
External Tank Inspection 15
Internal Tank Inspection . 60
Relief Valve Inspection 50
Piping Inspection 300
Piping Maintenance 120
Valve Inspection 35
Valve Maintenance 400
I
TOTAL COSTS 1.312.000 154,000
103
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TABLE 5-14. ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED WITH
BASELINE HYDROGEN FLUORIDE ALKYLATION REACTOR/SETTLER SYSTEM
EQUIPMENT:
Vessels and Machinery:
Reactor/Settler
Feed Dryers (2)
Centrifugal Pumps (3)
Capital Cost Annual Cost
(1986 $) (1986 S/yr)
Total Vessels and Machinery
Piping and Valves:
INSTRUMENTATION:4
Maintenance and Inspections :a
TOTAL COSTS
1.459.000
664. 000
302,000
2.425.000
175.000
79,000
36.000
42.000
332,000
Costs are based on using cost factors from Peters and Tioimerhaus (48) and a
total fixed capital cost of $10.06 million (1986 basis) (49) for a 147,OOQ
gal/day alkylate capacity plant.
104
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TABLE 5-15. ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED WITH
LEVEL 1 HYDROGEN FLUORIDE ALKYLATION REACTOR/SETTLER SYSTEM
Capital Cost Annual Cost
(1986 $) (1986 $/yr)
EQUIPMENT:
Vessels and Machinery:
Reactor/Settier
Feed Dryers (2)
Centrifugal Pumps (3)
Total Vessels and Machinery3 2.646.000 318.000
Piping and Valves:3 943.000 114.000
Relief Valve 2.000 230
INSTRUMENTATION:3 302.000 36.000
Temperature Sensor 360 45
Temperature Alarm 360 45
Remote Temperature Indicator 1.800 220
Remote Pressure Indicator 1.800 220
•
Flow Control Loops (2) ll.-OOO 1.300
Agitation Detection System and Alarm 1.800 220
DIKING:
Curbing Around Reactor 1.200 150
SCRUBBER:
Water Scrubber 260.000 31.000
MAINTENANCE AND INSPECTIONS:3 42.000
Relief Valve Inspection 15
TOTAL COSTS
4.172.000 544.000
3Costs are based on using cost factors from Peters and Timaerhaus (4831 and a
total fixed capital cost of $10.06 million (1986 basis) (49) for a 147.000
gal/day alkylate capacity plant.
105
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TABLE 5-16 ESTIMATED TYPICAL CAPITAL AND ANNUAL COSTS ASSOCIATED WITH
LEVEL 2 HYDROGEN FLUORIDE ALKYLATION REACTOR/SETTLER SYSTEM
Capital Cost Annual Cost
(1986 $) (1986 $/yr)
EQUIPMENT:
Vessels and Machinery:
Reactor/Settler
Feed Dryers (2)
Centrifugal Pumps (3)
Total Vessels and Machinery 2.646.000 319.000
Piping and Valves:a 943.000 114,000
Relief Valves (2) 4.000 470
Rupture Disk 2.300 280
INSTRUMENTATION:* 302.000 36.000
Temperature Sensor 360 45
Temperature Alarm 360 45
Temperature Switch 540 65
Remote Temperature Indicator 1,300 220
Remote Pressure Indicator 1.800 220
Flow Control Loops (2) 11.000 1.300
Flow Interlock System 1.800 220
Agitation Detection System and Alarm 1,300 220
Mixing Interlock System 1.300 220
pH Monitoring System 9.000 1,100
Moisture Monitoring System 9,000 1,100
All Loops on Computer Control 201,000 24.000
DIKING:
3 ft High Retaining Wall 3.000 360
SCRUBBER:
Alkaline Scrubber 312.000 38.000
MAINTENANCE AND INSPECTIONS:* 42.000
Relief Valve Inspection 25
TOTAL COSTS 4.453.000 579,000
Costs are based on using cost factors from Peters and Tiamerhaus (48) and a
total fixed capital cost of $10.06 million (1986 basis) (49) for a 147,000
gal/day alkylate capacity plant.
Computer Control costs are determined using cost estimating factors from
Valle-Riestra (50).
106
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5.3.4 Squipment Specifications and Detailed Costs
Equipment specifications and details of the capital cost estimates for
the hydrogen fluoride storage and the hydrogen fluoride alkylation reactor
systems are presented in Tables 5-17 through 5-24.
5.8.5 Methodology
Format for Presenting Cost Estimates—
Tables are provided for control schemes associated with storage and pro-
cess facilities for hydrogen fluoride showing capital, operating, and total
annual costs. The tables are broken down into subsections comprising vessels,
piping and valves, process machinery, instrumentation, and procedures and
practice. The presentation of the costs in this manner allows for easy com-
parison of costs for specific items, different levels, and different systems.
•
Capital Cost—All capital costs presented in this report are shown as
total fixed capital costs. Table 5-25 defines the cost elements comprising
total fixed capital as it is used here.
The computation of total fixed capital as shown in Table 5-25 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-5-25. The factor is
107
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TABLE 5-17. EQUIPMENT SPECIFICATIONS ASSOCIATED WITH HYDROGEN
FLUORIDE STORAGE SYSTEM
Equipment Item
Equipment Specification
Reference
7ESSELS:
Storage Tank
Expansion Tank
PIPING AND VALVES:
Pipework
Check Valve
Gate Valve
Excess Flow
Angle Valves
Relief Valves
Reduced Pressure Device
Rupture Disk
PROCESS MACHINERY:
Centrifugal Pump
Baseline: 10,000 gal. Carbon Steel
Storage Tank. 150 psig
Level #1; 10.000 gal. Carbon Steel
With 1/8 in. Corrosion Protec-
tion. 225 psig
Level #2: 10,000 gal. Monel* 43.51.52
375 psig 53
Standard Carbon Steel Pressure
Vessel With Rupture Disk and
Pressure Gauge 48*51
Baseline: 1 in. Schedule 30 Carbon
Steel
Level #1: 1 in. Schedule 30 Saran*-
lined Carbon Steel
Level $2: 1 in. Schedule 30 Monel® 54
•
1 in. Vertical Lift Check Valve.
Monel* Trim 51.-55
1 in. Screwed. Monel* Trim. Bolted
Bonnet 43.51,55
1 in. Standard Valve 51
1 in. Carbon Steel. Monel* Trim 56
1 in. x 2 in.. Class 300 Inlet
and Outlet Flange. Angle Body.
Closed Bonnet With Screwed Cap,
Carbon Steel Body, Monel* Trim 51
Double Check Valve Type Device With
Internal Air Gap and Relief Valve 48
1 in. Monel* Disk and Carbon Steel
Holder 52.57,58
Baseline: Single Stage. Carbon Steel
Construction,- Stuffing Box
Level #1: Single Stage. Monel* Con-
struction. Double Mech. Seal 51,59;
Level #2: Magnetically-coupled, Monel®
Construction,
51,59
(Continued)
108
-------
TABLE 5-17 (Continued)
Equipment Item
Equipment Specification
Reference
INSTRUMENTATION:
Pressure Gauge
Liquid Level Gauge
Temperature Indicator
Flow Indicator
Level Indicator
Load Cell
Level Alarm
High-low Level Shutoff
ENCLOSURES:
Building
SCRUBBERS:
DIKING:
Diaphragm Sealed. Hastelloy C Dia-
phragm, 0-1.000 psi 48,51.54
Differential Pressure Type 48.54
Thermocouple. Thermowall. Elec-
tronic Indicator 43.51.54
Differential Pressure Cell and
Transmitter and Associated Flow-
meter 48.54
Differential Pressure Type Indicator 43.51.54
Electrical Load Cell 48.54,60
Indicating and Audible Alarm 51.56.61
Solenoid Valve, Switch, and Relay 48.51.54
System . 56
Level #1: 26-Gauge Steel Walls and
Roof, Door. Ventilation System
Level #2: 10 in. Concrete Walls,
26-Gauge Steel Roof 56
Level #1: Spray Tower, Monel* Con-
struction, Water Sprays.
6 ft. x 18 ft.
Level #2: Spray Tower. Monel* Con-
struction. Alkaline Sprays 62
Level #1: 6 in. Concrete Walls.
3 ft. High
Level #2: 10 in. Concrete Walls,
Top of Tank Height (10 ft.) 56
109
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TABLE 5-18. DETAILS OF MATERIAL AND LABOR COSTS ASSOCIATED WITH BASELINE
HYDROGEN FLUORIDE STORAGE SYSTEM
VESSELS:
Storage Tank
PIPING AND VALVES s
Pipework
deck Valve
Gate Valves (5)
Excess Flow Valves (2)
Angle Valves (2)
Relief Valve
Materials
Cost
61.000
550
160
1.000
300
1.400
1.300
Labor
Cost
27.000
1.000
30
150
40
40
50
Direct
Costs
(1986 $)
38.000
1.550
190 '
1.-150
340
1.440
1.350
Indirect
Costs
31.000
540
60
400
120
500
470
Capital
Cost
131.000
2.300
280
1.700
500
2.100
2.000
PROCESS MACHINERY:
Centrifugal Pump
1,900
300 2.700
940
4.000
INSTRUMENTATION:
Pressure Gauges (4)
Liquid Level Gauge
TOTAL COSTS
800
800
69.000
200
200
30.000
1.000
1.000
99.000
350
350
35.000
1.500
1.500
147.000
110
-------
TABLE 5-19. DETAILS OF MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 1
HYDROGEN FLUORIDE STORAGE SYSTEM
VESSELS :
Storage Tank
Expansion Tanks (3)
FIFING AND VALVES:
Fipework
Check Valves
Gate Valves (5)
Excess Flow Valves (2)
Angle Valves (2)
Relief Valves (2)
Materials
Cost
87 .-000
3.500
3.300
320
1.000
300
1.400
2,600
Labor
Cost
39.000
880
860
60
150
40
40
100
Direct
Costs
(1986 $)
126.000
4.380
4.160
380
1.150
340
1.440
2.700
Indirect
Costs
44. 000
1.500
1,500
130
400
120
500
950
Capital
Cost
187.000
6.500
6.200
560
1,700
500
2.100
4.-000
PROCESS MACHINERY:
Centrifugal Pump
7.900
3.400 11.300
3.900
16.-000
INSTRUMENTATION:
Pressure Gauges (4)
Flow Indicator
Liquid Level Gauge
Remote Level Indicator
800
2.000
800
l.-OOO
200
500
200
250
1,000
2.500
1.000
1.250
350
380
350
440
1.500
3.700
1.-500
1.900
ENCLOSURES:
Steel Building
4.600
2.300 6.900 2.400 10.000
SCRUBBERS:
Water Scrubber
105.000 47.000 152.000 53.000 226.000
(Continued)
111
-------
TABLE 5-19 (Continued)
Materials Labor Direct Indirect Capital
Cost Coat Costs Costs Cost
(1986 $)
DIKING:
3 ft High Con- 390 520 910 320 1.400
crete Diking
TOTAL COSTS 222.000 95,000 317,000 111.000 471.-000
112
-------
TABLE 5-20. DETAILS OF MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 2
HYDROGEN FLUORIDE STORAGE SYSTEM
Materials Labor
Cost Cost
Direct Indirect
Costs Costs
Capital
Cost
(1986 $)
VESSELS :
Storage Tank
Expansion Tanks (3)
PIPING AND VALVES:
Pipework
Reduced Pressure Device
Gate 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 Shu toff
ENCLOSURES :
Concrete Building
432.000 195.000
3.500
4.800
800
1.000
300
1.400
2,600
650 '
9.000
1.200
1.200
2.000
8.400
1.000
200
1.000
6.100
880
1.400
200
150
40
40
100
80
3.900
300
300
500
2.100
250
50
250
6.600
627.000 220.000
4.380
6.200
1.000
1.-150
340
1.440
2.700
730
12.900
1.500
1.500
2.500
10.500
1.250
250
1.250
12.700
1.500
2.200
350
400
120
500
950
260
4.500
530
530
880
3.700
440
. 90
440
4.500
932.000
6.500
9.200
1.500
1.700
500
2.100
4.000
1.100
t
19,000
2.220
2.200
3.700
16.000
1.900
380
1.900
19.000
(Continued)
113
-------
TABLE 5-20 (Continued)
Materials Labor Direct Indirect Capital
Cost Cost Costs Costs Cost
(1986 $)
SCRUBBERS:
Alkaline Scrubber
130.000 59.000 189.000 66.000 280.000
DIKING:
10 ft High Con-
crete Dike
2.200
2.900 5.100 1.800 7.600
TOTAL COSTS
609.000 274.000 884.000 310.000 1.312.000
114
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TABLE 5-21. EQUIPMENT SPECIFICATIONS ASSOCIATED WITH HYDROGEN
FLUORIDE ALXYLATION REACTOR/SETTLER
Equipment Item
Equipment Specification
Reference
VESSELS AND MACHINERY:
Reactor/Settler
Feed Dryers
PIPING AND VALVES:
Relief Valve
Rupture Disk
INSTRUMENTATION:
Temperature Sensor
Temperature Alarm
Temperature Switch
Remote Temp. Indicator
Remote Press. Indicator
Flow Control Loop
Flow Interlock System
Agitation Detection
System and Alarm
Mixing Interlock Syste
pH Monitoring System
Moisture Monitoring
System
Gravity Flow Reactor/Settler System
Sieve Dryers or Equivalent on Reac-
tor Feed Streams
2 in. x 3 in. Class 300 Inlet and
Outlet Flange, Angle Body. Closed
Bonnet With Screwed Cap. Carbon
Steel Body. Monel* Trim
2 in. Monel* Disk and Carbon
Steel Holder
Thermocouple and Associated Thermo-
well
Indicating and Audible Alarm
Two-Stage Switch with Independently
Set Actuation
Transmitter and Associated Elec-
tronics Indicator
Transducer. Transmitter and Elec-
tronic Indicator
2 in. Globe Control Valve. Monel9
Trim, Flowmeter and PID
Controller
Solenoid Valve, Switch, and Relay
System
Temperature Sensor Indicator and
Alarm System for Phillips Reactor/
Settler Design. Mechanical Agita-
tion Detector for Others
Solenoid Valve. Switch, and Relay
System
Electrode. Electrode Chamber, Ampli-
fier-Transducer and Indicator
Capacitance or Infrared Absorption
System
49
49
51
52.57.53
48.51.54
51.56.61
43,54
48,54
48.54
48.5*
43.51.54
56
48,54
48.51.54
56
48.60
60
(Continued)
115
-------
TABLE 5-21 (Continued)
Equipment Item
Equipment Specification
Reference
DIKING:
SCRUBBER:
Level #1: 6 in. High Concrete
Curbing
Level #2: 3 ft High Concrete
Retaining
Level #1 Spray Tower, Monel* Con-
struction. Water Sprays,
8 ft. x 24 ft.
Level #2 Spray Tower, Monel* Con-
struction. Alkaline Sprays
56
62
116
-------
TABLE 5-22. DETAILS OF MATERIAL AND LABOR COSTS ASSOCIATED WITH BASELINE
HYDROGEN FLUORIDE ALKYLATION REACTOR/SETTLER SYSTEM
Materials Labor Direct Indirect Capital
Cost Cost Costs Costs Cost
(1986 $)
EQUIPMENT:
Vessels and Machinery:
Reactor/Settier
Feed Dryers (2)
Centrifugal Pumps (3)
Total Vessels and 700,000 315.000 1.015.000 254.000 1.459.000
Machinery3 ,
Piping and Valves:3 252.000 210,000 462,000 115,000 664,000
INSTRUMENTATION:3 153,000 52,000 210.000 52.000 302.000
TOTAL COSTS 1.110.000 577.000 1.687.000 421.000 2.425.000
a Costs are based on using cost factors from Peters and Timmerhaus (48) and a
total fixed capital cost of $10.06 million (1986 basis) (49) for a 147.000
gal/day alkylate capacity plant.
117
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TABLE 5-23. DETAILS OF MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 1
HYDROGEN FLUORIDE ALKYLATION REACTOR/SETTLER SYSTEM
Materials
Cost
EQUIPMENT:
Vessels and Machinery:
Reactor/ Settler
Feed Dryers (2)
Centrifugal Pumps (3)
Total Vessels and 1.
Machine rya
Piping and Valves :a
Relief Valve
INSTRUMENTATION:*
Temperature Sensor
Temperature Alarm
Remote Temperature
Indicator
Remote Pressure Indicator
Flow Control Loops (2)
Agitation Detection System
and Alarm
DIKING:
Curbing Around Reactor
SCRUBBER:
Water Scrubber
TOTAL COSTS 2.
270,000
492.000
1.300
158.000
. 200
200
1.000
1.000
6.000
1.000
500
125.000
056.000
Labor
'Cost
571.000
164.000
50
52.000
50
50
250
250
1.500
250
350
56.000
846. 000
Direct Indirect
Costs Costs
(1986 $)
1.841.000
656.000
1.350
210,000
250
250
1.250
1.250
7.500
1.250
850
181.000
2.902.000
460,000
164.000
340
52.000
60
60
310
310
1.900
310
210
45.000
725, 000
Capital
Cost
2.646.000
943.000
2.000
302.000
360
360
1,800
1.800
11.000
1.800
1.200
260.000
4,172.000
Costs are based on using cost factors from Peters and Tiameraaus (43) and a
total fixed capital cost of $10.06 million (1986 basis) (49) for a 147.000
gal/day alkylate capacity plant.
118
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TABLE 5-24. DETAILS OF MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 2
HYDROGEN FLUORIDE ALKYLATION REACTOR/SETTLER SYSTEM
Materials
Cost
Labor
Cost
Direct Indirect
Costs Costs
Capital
Cost
(1986 $)
EQUIPMENT:
Vessels and Machinery:
React or/ Set tier
Feed Dryers (2)
Centrifugal Pimps (3)
Total Vessels and 1,
Machinery3
Piping and Valves:
Relief Valves (2)
Rupture Disk
INSTRUMENTATION:*
Temperature Sensor
Temperature Alarm
Temperature Switch
Remote Temperature
Indicator
Remote Pressure Indicator
Flow Control Loops (2)
Flow Interlock System
Agitation Detection System
and Alarm
Mixing Interlock System
pH Monitoring System
270,000
492.000
2.600
1.-500
158.000
200
200
300
1.000
1.000
6.000
1.000
1.000
1.000
5.000
571.000
164.-000
100
100
52.000
50
50
75
250
250
1.500
250
250
250
1.-300
1.841.000
656.000
2.700
1.600
210.000
250
250
375
1.-250
1.250
7.500
1.250
1.-250
1.-250
6.300
460,000
164.000
680
400
52.000
60
60
95
310
310
1.900
310
310
310
1.-600
2. 646. 000
943.000
4,000
2.300
301.000
360
t
360
540
1,800
1.800
11.000
1.-800
1.800
1.800
9.000
(Continued)
119
-------
TABLE 5-24 (Continued)
Materials Labor Direct Indirect Capital
Cost Cost Costs Costs Cost
(1986 $)
Moisture Monitoring
System
All Loops on Computer
Control
DIKING:
Retaining Wall
SCRUBBER:
Alkaline Scrubber
5.000 1.300 6.300 1.600
900 1.200
2.100
530
9.000
105.000 35.000 140.000 35.000 201.000
3.000
150,000 67.000 217.000 54.000 312.000
TOTAll COSTS
2.202.000 896.000 3,098.000 775.000 4.453.000
Costs are based on using cost factors from Peters and Timmerhaus (48) and a
total fixed capital cost of $10.06 million (1986 basis) (49) for a 147.000
gal/day alkylate capacity plant.
Computer Control costs ara determined using cost estimating factors from
Valle-Riestra (50).
120
-------
TABLE 5-25. FORMAT FOR TOTAL FIXED CAPITAL COST
Item No. Item Cost
1 Total Material Cost
2 Total Labor Cost
3 Total Direct Cost Items 1+2
4 Indirect Cost Items (Engi-
neering & Construction
Expenses) 0.35 x Item 3a
5 Total Bare Module Cost Items (3 + 4)
6 Contingency (0.05 x Item 5)
7 Contractor's Fee 0.05 x Item 5
8 Total Fixed Capital Cost Items (5+6+7)
a For storage facilities, the indirect cost factor is 0.35. For process
facilities, the indirect cost factor is 0.25.
b For storage facilities, the contingency cost factor is 0.05. For process
facilities, the contingency cost factor is 0.10.
121
-------
TABLE 5-26. FORMAT ¥OR TOTAL ANNUAL COST
Item No. Item Cost
1 Total Direct Cost
2 Capital Recovery on Equip-
ment Items 0.163 z Item 1
3 Maintenance Expense on
Equipment Items 0.01 z Item 1
4 Total Procedural Items -
5 Total Annual Cost Items (2+3+4)
*Based on a capital recovery factor at 10% cost of capital for 10 years.
123
-------
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.
When comparing costs in this manual to costs from other references, the
user should be sure the design bases are comparable and that the capital and
annual costs as defined here are the same as the costs being compared.
Cost Updating—
All costs in this report are expressed in June 1936 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:
124
-------
new
base year cost = old base year cost x new base year index
old base year index
The Chemical Engineering (CE) Plant Cost Index was used in updating cost for
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 free on board (f.o.b.) with carbon steel as the
basis (January 1979 dollars) were determined using the following equation from
Peters and Timmerhaus (48):
•
Cost = [50(Weight of Vessel in Pounds)'0*34]
The vessel weight is determined using appropriate design equations as given by
Peters and Timmerhaus (48) which allow for wall thickness adjustments for
corrosion allowances, for example. The vessel weight is increased by a factor
of 0.15 for horizontal vessels and 0.20 for vertical vessels to account for
the added weight due to nozzles, manholes, and skirts or saddles. Appropriate
factors are applied for different materials of construction as given in Peters
and Timmerhaus (48). The vessel costs are updated using cost factors.
Finally a shipping cost amounting to 10 percent of the purchased cost is added
to obtain the delivered equipment cost.
Piping—Piping costs were obtained using cost information and data
presented by Yamartino (64). A simplified approach is used in which it is
125
-------
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 (64) 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 (56) 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.
t
Enclosures—Enclosure costs were estimated using Mean's Manual (56) 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
aetal door. The steel building has 26 gauge roofing and siding and metal
door. The cost of a ventilation system was determined using a typical 1,000
scfm unit and doubling the cost to account for duct work and requirements for
the safe enclosure of hazardous chemicals.
Scrubbers—Scrubber costs were estimated using the following equation
from the Card (62) 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 * (ACFM + 43,000)
A release rate of 10,000 ft3/minute was assumed for the storage vessel systems
and an appropriate rate was determined for process system based on the
126
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quantity of hazardous chemicals present in the system at any one time. For
the hydrogen fluoride alkylation system, a release rate of 36,000 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 (48)
and Valle-Riestra (50). Table 5-27 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.
127
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TABLE 5-27. FORMAT FOR INSTALLATION COSTS
Equipment Item Factor or Reference
Vessels:
Storage Tank 0.45
Expansion Tank 0.25
Piping and Valves:
Pipework Ref. 64
Expansion Loop Ref. 51
Reduced Pressure Device Ref. 51
Check Valves Ref. 51
Gate Valves Ref. 51
Ball Valves Ref. 51
Excess Flow Valves Ref. 51
Angle Valves Ref. 56
Relief Valves Ref. 51
Rupture Disks Ref. 51
Process Machinery:
Centrifugal Pump 0.43
Gear Pump 0.43
Instrumentation:
All Instrumentation Items 0.25
Enclosures: Ref. 56
Diking: Ref. 55
Scrubbers: 0.45
128
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SECTION 6
REFERENCES
1. U.S. Bureau of the Census. Statistical Abstract of the United States:
1986. 106th Edition. Washington. D.C.. 1985.
2. Kirk. R.E. and D.F. Othmer. Encyclopedia of Chemical Technology. 3rd
Edition. Volume 10. John Wiley & Sons, Incorporated. 1980.
3. Weast. R.C. (ed.). CRC Handbook of Chemistry and Physics. 63rd Edition.
CRC Press. Incorporated. Boca Raton. FL. 1982.
4. Green. D.W. (ed.). Perry's Chemical Engineers' Handbook. Sixth Edition.
McGraw-Hill Book Company. New York. NY. 1984.
5. Dean, J. (ed.). Lange's Handbook of Chemistry. Twelfth Edition,
McGraw-Hill Book Company. New York. NY. 1979.
6. Hydrogen Fluoride Product Data Brochure. Pennwalt Chemical Corporation.
Philadelphia. FA. July 1979.
7. Bird. R.B., W.E. Stewart, and E.N. Lightfoot. Transport Phenomena. John
Wiley & Sons. 1960.
8. Hydrofluoric Acid - Properties. Uses. Storage and Handling. E.I. duPont
de Nemours & Co. (Inc.). Wilmington. DE. September 1984.
9. Chemical Emergency Preparedness Program Interim Guidance, Chemical
Profiles. Volumes 1 & 2. U.S. Environmental Protection Agency,
Washington. DC. December 1985.
10. Tatken, R.L. and R.J. Lewis, (eds.). Registry of Toxic Effects of
Chemical Substances, (RTECS). 1981-82 edition. 3 volumes. NIOSH Contract
No. 210-81-8101, DHHS (NIOSH) Publication No. 83-107, June 1983.
11. Patty, F.A. Industrial Hygiene and Toxicology. 2nd edition, Volumes
1 & 2. Wiley - Interscience, New York. NY. 1962.
12. Toxic and Hazardous Industrial Chemicals Safety Manual. The
International Technical Information Institute of Japan. Tokyo, Japan,
1976.
13. Effects of Exposure to Toxic Gases - First Aid and Medical Treatment.
Matheson Gas Products, Secaucus, NJ, 1984.
14. NIOSH/OSHA Pocket Guide to Chemical Hazards. DHEW (NIOSH) Publication
No. 78-210, September 1985.
129
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15. Burris. H.O. U.S. Patent # 4,031.191. June 21. 1977.
16. U.S. Environmental Protection Agency. Industrial Process Profiles For
Environmental Use: Chapter 16. The Fluorocarbon - Hydrogen Fluoride
Industry. Cincinnati. OH, Publication No. 600/2-77-023p. February 1977.
17. Lawler. G.M. (ed.). Chemical Origins and Markets. Fifth Edition.
Chemical Information Services, Stanford Research Institute. 1977.
18. McKetta, J. Encyclopedia of Chemical Processing and Design. Marcel
Dekker Publishing Company. NT, 249-259. 1985.
19. Fluorine - Chemical Complex Getting A Big Boost. Chemical Engineering.
January 18, 1965.
20. Saccardo. P. and F. Gozzo. U.S. Patent # 3,104,156, September 17, 1963.
21. Harrington, C.D. and A.E. Ruekle (ed.). Uranium Production Technology.
Van Nostrand Company. Incorporated, 1959.
22. Pamphlet 8: Chlorine Packaging Manual. The Chlorine Institute. NT,
1985.
23. Lees, F.P. Loss Prevention in the Process Industries - Hazard
Identification, Assessment and Control. Butterworth & Company Ltd..
London. England. Volumes 1 & 2. 1980.
24. Hydrofluoric Acid Storage and Handling Equipment Bulletin. Pennwalt
Chemicals Corporation, Philadelphia. PA. August 1984.
25. Specialty Gas Material Safety Data Sheet: Air Products and Chemicals,
Incorporated. Allentown, PA, June 1983.
26. Material Safety Data Sheet: Matheson Gas Products, Incorporated.
Secaucus, NJ, October 1985.
27. Licensors of Hydrogen Fluoride Alkylation Process Technology are:
Chevron U.S.A. Inc.. San Francisco, CA; Phillips Petroleum Company,
Bartlesville. OK; U.O.P. Inc.. Des Plaines, IL.
28. Materials for Receiving, Handling and Storing Hydrofluoric Acid.
National Association of Corrosion Engineers (NACE). Publication No.
5A171, 1974.
29. The Chlorine Institute: Chlorine Manual and Associated Pamphlets New
Tork, NT.
30. Erfft, R. and K. Kramer. Monel Valves Reliable in Hazardous Hydrogen
Fluoride Service. Chemical Processing 43 (7), 32, (June 1980).
130
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31. Ferry. R.H.. and C.H. Chilton. Chemical Engineers' Handbook. Fifth
Edition. McGraw-Hill Book Company. New York. NY. 1973.
32. ASME Boiler and Pressure Vessel Code. ANSI/ASME BPV-VIII-1. The American
Society of Mechanical Engineers. New York. NY. 1983.
33. Kohl. A.L.. and F.C. Riesenfeld. Gas Purification. Third Edition. Gulf
Publishing Company. 1979.
34. Benson. R. Hydrogen Fluoride Exposure - Prevention, in the Operation of
HF Alkylation Plants; Industrial Medicine 13(1), 113-117, 1944.
35. Radian notebook number 215. For EPA Contract 68-02-3994. Work
Assignment 94, Page 5. 1986.
36. Aarts, J. J. and D. M. Morrison. Refrigerated Storage Tank Retainment
Walls. CEP Technical Manual, Volume 23, American Institute of Chemical
Engineers. New York, NY. 1981.
37. Bennett. G. F.. F. S. Feates. and I. Wilder. Hazardous Materials Spills
Handbook. McGraw-Hill Book Company. New York, NY, 1982.
38. Gross, S.S., and R.H. Hiltz (MSH Company). Evaluation of Foams for
Mitigating Air Pollution From Hazardous Spills. EPA-600/2-82-029 (NTIS
PB82-227-117). March 1982.
39. Small. F.H.. and G.E. Snyder. Controlling In-PI ant Toxic Spills. Loss.
Prevention, Volume 8, American Institute of Chemical Engineers. 1974.
40. Telephone conversation between D.S. Davis of Radian Corporation and a
representative of Amoco Corporation, Chicago, IL, June 18, 1987.
41. Canvey: A Second Report. Health and Safety Executive (U.K.). London,
England, 1981.
42. Private communication with an industry consultant. Name withheld by
request. February 1987.
43. Beresford, T.C. The Use of Water Spray Monitors and Fan Sprays for
Dispersing Gas Leakage. Institute of Chemical Engineers Symposium
Proceedings on the Containment and Dispersion of Gases by Water Sprays,
Manchester. England. 1981.
44. 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.
45. Chemical Manufacturers Association. Process Safety Management (Control
of Acute Hazards). Washington, DC, May 1985.
131
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46. Stus, T.F. On Writing Operating Instructions. Chemical Engineering.
November 26. 1984.
47. Burk, A.F. Operating Procedures and Reviews. Presented at the Chemical
Manufacturers Association Process Safety Management Workshop. Arlington,
VA. May 7-8. 1985.
48. Peters, M.S. and K.D. Timmerhaus. Plant Design and Economics for
Chemical Engineers. McGraw-Hill Book Company, New York, NY. 1980.
49. Meyer, D.W., L.E. Chapin, and R.F. Muir. Cost Benefits of Sulfuric Acid
Alkylation. Chemical Engineering Progress, August 1983.
50. Valle-Riestra, J.F. Project Evaluation in the Chemical Process Indus-
tries. McGraw-Hill Book Company, New York, NY, 1983.
51. Richardson Engineering Services. Inc. The Richardson Rapid Construction
Cost Estimating System, Volumes 1-4, San Marcos, CA, 1986.
52. Pikulik, A. and H.E. Diaz. Cost Estimating for Major Process Equipment.
Chemical Engineering. October 10, 1977.
t
53. Hall, R.S., J. Matley. and K.J. McNaughton. Cost of Process Equipment.
Chemical Engineering. April 5. 1982.
«
54. Liptak, B.G. Costs of Process Instruments. Chemical Engineering.
September 7, 1970.
55. Telephone conversation between J.D. Quass of Radian Corporation and a
representative of Mark Controls Corporation. Houston. TX, August 1986.
56. R. S. Means Company, Inc. Building Construction Cost Data 1986 (44th
Edition), Kingston. MA.
57. Telephone conversation between J.D. Quass of Radian Corporation and a
representative of Zook Enterprises, Chagrin Falls, OH, August 1986.
58. Telephone conversation between J.D. Quass of Radian Corporation and a
representative of Fike Corporation, Houston. TX, August 1986.
59. Green, D.W. (ed.). Perry's Chemical Engineer's Handbook (Sixth Edition).
McGraw-Hill Book Company, New York, NY, 1984.
60. Liptak, B.G. Costs of Viscosity, Weight, Analytical Instruments.
Chemical Engineering. September 21. 1970.
61. Liptak, B.G. Control-Panel Costs, Process Instruments. Chemical
Engineering. October 5, 1970.
132
-------
62. Capital and Operating Costs of Selected Air Pollution Control Systems.
EPA-450/5-80-002. U.S. Environmental Protection Agency. 1980.
63. Cost indices obtained from Chemical Engineering. McGraw-Hill Publishing
Company. New York. NY, June 1974. December 1985. and August 1986.
64. Yamartimo. J. Installed Cost of Corrosion-Resistant Piping-1978.
Chemical Engineering.- November 20.- 1978.
65. Baumeister. T. (ed). Mark's Standard Handbook for Mechanical Engineers.
Eighth Edition. McGraw-Hill Book Company. New York. NY. 1978.
133
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APPENDIX A
ELECTROMOTIVE SERIES OF METALS
TABLE A-l. ELECTROMOTIVE SERIES OF METALS
Lithium
Potassium
Rubidium
Calcium
Sodium
Magnesium
Plutonium
Beryllium
Uranium
Aluminum
Titanium
Zirconium
Manganese
Tantalum
Zinc
Iron
Nickel
Molybdenum
Tin
Lead
Tungsten
HYDROGEN
copper
Mercury
Silver
Gold
Platinum
Palladium
Least noble
Most noble
Source: Reference 65
134
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APPENDIX B
GLOSSARY
This glossary defines selected terms used in the text of this manual
which might he 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 that creates toxic
concentrations in the air that are a potential health threat to the surround-
ing community.
Cavitation; The formation and collapse of vapor bubbles in a flowing liquid.
Specifically, the formation and.collapse of vapor cavities in a pump or com-
pressor when there is sufficient resistance to flow at the inlet side. ,
Chlorofluorocarbons; Organic compounds containing chlorine and/cr fluorine
atoms within the molecule. l
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 pro-
tracted failure.
Deadheading; Closing or nearly closing or blocking the discharge outlet or
piping of an operating pump or compressor.
135
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Electromotive Series of Metals; A list of metals and alloys arranged accord-
ing to their standard electrode potential which also reflects their relative
corrosion potential.
Enthalpy; A thermodynamic property of a chemical related to its energy con-
tent 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, temperature and phys-
ical state, since the absolute value cannot be measured.
Facility; A location at which a process or set of processes are used to pro-
duce, refine or repackage chenicals, or a location where a large enough inven-
tory of chemicals are stored so that a significant accidental release of a
toxic chemical is possible.
t
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.
Killed steel; Steel that is deoxidized with a strong deoxidizing agent such a
silicon or aluminum in order to reduce the oxygen content to such a level that
no reaction occurs between carbon and oxygen during solidification. Such a
steel will have a smaller grain size than a steel that is not killed. The
grain size affects the physical and chemical properties of the steel. Fully-
killed steel is fully deoxidized and has a smaller grain size than semi-killed
steel which is partially deoxidized and has a smaller grain size than steel
that is not killed.
Mild steel; Carbon steel containing a maximum of about 0.25% carbon. Mild
steel is satisfactory for use where severe corrodants are not encountered or
136
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where protective coatings can be used to prevent or reduce corrosion rates to
acceptable levels.
Mitigation; Any measure taken to reduce the severity of the adverse effects
associated with the accidental release of a hazardous chemical.
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. Aliphatic hydrocarbons are hydrocarbons
with a basic straight or branched chain structure in contrast with ring struc-
tured compounds.
Passivation film; A layer of oxide or other chemical compound of a metal on
its surface that acts as a protective barrier against corrosion or further
chemical reaction.
Plant; A location at which a process or set of processes are used to produce,
refine or repackage chemicals.
I
Prevention; Design and operating measures applied to a process to ensure that
primary containment of toxic chemicals is maintained. Primary containment
means confinement of toxic chemicals within the equipment intended for normal
operating conditions.
Process; The sequence of physical and chemical states and operations for the
production, refining, or repackaging of chemicals.
Process machinery; Process equipment such as pumps, compressors, or agitators
that would not be categorized as piping and vessels.
Protection; Measures taken to capture or destroy a toxic chemical that has
breached primary containment, but before an uncontrolled release to the envi-
ronment has occurred.
Toxicity; A measure of the adverse health effects of exposure to a chemical.
137
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TABLE 0-1.
APPENDIX C
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
fs
in?
ft?
in3
ft3
gal
Ib
short ton (ton)
short ton (ton)
atm
mm Hg
psia
psig
°F
°C
Btu/lb
Btu/lbmol
kcal/gmol
Btu/lb-°F
lb/ft3
Ib/gal
oz /gal
quarts/gal
gal/min
gal/day
ffYmin
ft/min
ft/sec
centipoise (CP)
To
cm
2
cm;
•3
cm.
m3
m3
kg
Mg
metric ton (t)
kPa
kPa
kPa
kPa*
OG*
K*
kJ/kg
kJ/kgmol
kj/kgmol
kJ/kg-°C
kg/»!
kg/a3
kg/m3
cm^/m3
m./min
m3/day
m /min
m/min
m/sec
kg/m-s
BS^ ^ ^-_
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)c(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
138
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TECHNICAL REPORT DATA
(fltae rmd buaucnont on the rerene btfort computing)
1. REPORT NO.
EPA-600/8-87-034h
3. RECIPIENT'S ACCESSION-NO.
4. TITLI AND SUBTITLE
Prevention Reference Manual: Chemical Specific.
Volume 8: Control of Accidental Releases of
Hydrogen Fluoride
I. REPORT DATE
August 1987
I. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
D. S. Davis, G. B. DeWolf, and J. D. Quass
B. PERFORMING OROANIZATION REPORT NO.
DCN 87-203-023-94-13
I. PERFORMING OROANIZATION NAME AND ADDRESS
1O. PROGRAM ELEMENT NO.
Radian Corporation
8501 Mo-Pac Boulevard
Austin. Texas 78766
11. CONTRACT/GRANT NO.
68-02-3994, Task 94
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air and Energy Engineering Research Laboratory
Research Triangle Park, NC 27711
13. TYPE Of REPORT AND PERIOD COVERED
Task Final; 1-7/87
14. SPONSORING AGENCY CODE
xxcaviwu ifuuugiic r*u.A.t xv\+ *« «AA tirA/DUU/lO
is. SUPPLEMENTARY NOTES AEERL project officer is T. Kelly Janes. Mail Drop 62B. 919/541-
2852.
18. ABSTRACT
The report is a chemical specific manual for hydrogen fluoride (HF). It
summarizes information to aid regulators and industry personnel in identifying and
controlling release hazards associated with HF. Reducing the risk associated with
accidental release of HF involves identifying some of the potential causes of acciden-
tal releases that apply to the process facilities that handle and store HF. It identi-
fies examples of potential causes and measures that may be taken to reduce the acci-
dental release risk. Such measures include recommendations on plant design prac-
tices; prevention, protection, and mitigation technologies; and operation and main-
tenance practices. Conceptual cost estimates of example prevention, protection,
and mitigation measures are provided. Interest in reducing the probability and con-
sequences of accidental toxic chemical releases that might harm workers within a
process facility and people in the surrounding community prompted the preparation
of a series of technical manuals addressing accidental releases of toxic chemicals.
7.
KEY WORDS'AND DOCUMENT ANALYSIS
DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution
Hydrogen Fluoride
Emission
Toxicity
Accidents
Materials Handling
Storage
Design
Maintenance
Cost Estimates
Pollution Control
Stationary Sources
Accidental Releases
13B
07B
14G
06T 05 A. 14A
13L
15E. 13H
8. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (THu Rtport)
21. NO. OF PAGES
Unclassified
146
20. SECURITY
Unclassified
22. PRICE
139
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