United States EPA-600/8-87-034J Environmental Protection September 1987 &EPA Research and Development PREVENTION REFERENCE MANUAL: CHEMICAL SPECIFIC VOLUME 10: CONTROL OF ACCIDENTAL RELEASES OF HYDROGEN CYANIDE Prepared for Office of Air Quality Planning and Standards Prepared by Air and Energy Engineering Research Laboratory Research Triangle Park NC 27711 ------- RESEARCH REPORTING SERIES Research reports of the Office of Research and Development U.S. Environmental Protection Agency, have been grouped into nine series. These nine broad cate- gories were established to facilitate further development and application of environmental technology. Elimination of traditional grouping was consciously planned to foster technology transfer and a maximum interface in related fields. The nine series are: 1. Environmental Health Effects Research 2. Environmental Protection Technology 3. Ecological Research . 4. Environmental Monitoring 5. Socioeconomic Environmental Studies 6. Scientific and Technical Assessment Reports (STAR) 7. Interagency Energy-Environment Research and Development 8. "Special" Reports 9. Miscellaneous Reports This report has been assigned to the SPECIAL REPORTS series. This series is reserved for reports which are intended to meet the technical information needs of specifically targeted user groups. Reports in this series include Problem Orient- ed Reports. Research Application Reports, and Executive Summary Documents. Typical of these reports include state-of-the-art analyses, technology assess- ments, reports on the results of major research and development efforts, design manuals, and user manuals. EPA REVIEW NOTICE This report has been reviewed by the U.S. Environmental Protection Agency, and approved for publication. Approval does not signify that the contents necessarily reflect the views and policy of the Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. This document is available to the public through the National Technical Informa- tion Service. Springfield, Virginia 22161. ------- ------- ABSTRACT The accidental releases of a toxic chemical at Bhopal. India in 1984 was a milestone in creating an increased public awareness of toxic release problems. As a result of other, perhaps less dramatic incidents in the past. portions of the chemical industry were aware of this problem long before these events. These same portions of the industry have made advances in this area. Interest in reducing the probability and consequences of accidental toxic chemical releases that might harm workers within a process facility and people in the surrounding community prompted the preparation of this manual and a planned series of companion manuals addressing accidental releases of toxic chemicals. Hydrogen cyanide has an IDLH (Immediately Dangerous to Life and Health) concentration of 50 ppm, which makes it an acute toxic hazard. Reducing the risk associated with an accidental release of hydrogen cyanide involves identifying some of the potential causes of accidental releases that apply to the process facilities that use hydrogen cyanide. In this manual, examples of potential causes are identified as are specific measures that may be taken to reduce the accidental release risk. Such measures include recommendations on plant design practices, prevention, protection and mitigation technologies, and operation and maintenance practices. Conceptual cost estimates of example prevention, protection, and mitigation measures are provided. 11 ------- ACKNOWLEDGEMENTS This manual was prepared under the overall guidance and direction of I. Kelly Janes. Project Officer, with the active participation of Robert P. Hangebrauck. William J. Rhodes, and Jane M. Crum. all of U.S. EPA. In addition, other EPA personnel served as reviewers. Radian Corporation principal contributors involved in preparing the manual were Graham E. Harris (Program Manager). Glenn B. DeWolf (Project Director). Daniel S. Davis. • Jeffrey D. Quass. Miriam Stohs. and Sharon L. Wevill. Contributions were also provided by other staff members. Secretarial support was provided by Roberta J. Brouwer and others. Special thanks are given to the many other people. both in government and industry, who served on the Technical Advisory Group and as peer reviewers. ------- TABLE OF CONTENTS Section Page ABSTRACT ii ACKNOWLEDGEMENTS . . . ill FIGURES v TABLES vi 1.0 INTRODUCTION 1 1.1 Background 1 1.2 Purpose of This Manual 2 1.3 Sources and Uses of Hydrogen Cyanide 2 1.4 Organization of the Manual. 3 2.0 CHEMICAL CHARACTERISTICS 4 2.1 Physical Properties " 4 2.2 Chemical Properties and Reactivity 4 2.3 Tozicological and Health Effects . . 7 3.0 FACILITY DESCRIPTIONS AND PROCESS HAZARDS 10 3.1 Hydrogen Cyanide Manufacture 10 3.2 Hydrogen Cyanide Consumption 14 ' 3.2.1 Manufacture of Adiponitrile 14 3.-2.2 Manufacture of Acetone Cyanohydrin/Methyl Methacrylate 18 3.2.3 Manufacture of Cyanuric Chloride -21 3.2.4 Manufacture of Sodium Cyanide 21 3.3 Storage and Transfer 24 4.0 PROCESS HAZARDS 27 4.1 Potential Causes of Releases 27 4.1.1 Process Causes 28 4.1.2 Equipment Causes 29 4.1.3 Operational Causes 30 5.0 HAZARD PREVENTION AND CONTROL 31 5.1 General Considerations 31 5.2 Process Design 32 5.3 Physical Plant Design 34 5.3.1 Equipment 34 5.3.2 Plant Siting and Layout 45 5.3.3 Transfer and Transport Facilities 47 5.4 Protection Technologies 49 5.4.1 Enclosures 49 5.4.2 Flares 50 5.4.3 Scrubbers 54 5.5 Mitigation Technologies 5g 5.5.1 Secondary Containment Systems . 57 5.5.2 Flotation Devices and Foams §2 5.5.3 Mitigation Techniques for Hydrogen Cyanide Vapor . 64 iv ------- TABLE OF CONTENTS (Continued) Section Page 5.6 Operation and Maintenance Practices 65 5.6.1 Management Policy 66 5.6.2 Operator Training 67 5.6.3 Maintenance and Modification Practices 71 5.7 Control Effectiveness 74 5.8 Illustrative Cost Estimates for Controls 75 5.8.1 Prevention and Protection Measures 75 5.8.2 Levels of Control 79 5.8.3 Summary of Levels of Control 80 5.8.4 Equipment Specifications and Detailed Costs ... 93 5.8.5 Methodology 93 6.0 REFERENCES 116 APPENDIX A - GLOSSARY 120 APPENDIX B - METRIC (SI) CONVERSION FACTORS 124 FIGURES • Page 3*1 Hydrogen cyanide manufacturing process 11 3-2 Manufacturing process for adiponitrile 16 3-3 Manufacturing process for acetone cyanohydrin 19 3-4 Sodium cyanide manufacturing process 22 3-5 Example diagram of hydrogen cyanide tank car unloading facility . . 25 3-6 Example diagram of hydrogen cyanide storage facility 26 5-1 Computer model simulation showing the effect of diking on the vapor cloud generated from a release of refrigerated hydrogen cyanide . . 61 ------- TABLES Page 2-1 Physical Properties of Hydrogen Cyanide ,.... 5 2-2 Exposure Limits for Hydrogen Cyanide 9 2-3 Predicted Human Health Effects of Exposure to Various Concentrations of Hydrogen Cyanide 9 3-1 Typical Uses of Hydrogen Cyanide . 15 5-1 Key Process Design Considerations for Hydrogen Cyanide Processes 33 5-2 Chemical Resistance of Polymers and Elastomers to Chemical Attack by Wet Hydrogen Cyanide 36 5-3 Important Considerations for Using Flares to Prevent Accidental Chemical Releases .... 53 5-4 Aspects of Training Programs for Routine Process Operations . . 69 5-5 Examples of Major Prevention and Protection Measures for Hydrogen Cyanide Releases 76 5-6 Estimated Typical Costs of Major Prevention and Protection Measures for Hydrogen Cyanide Release 78 5-7 Summary Cost Estimates of Potential Levels of Controls for Hydrogen Cyanide Storage Tank and Sodium Cyanide Reactor ... 81 5-8 Example of Levels of Control for Hydrogen Cyanide Storage Tank. 82 5-9 Example of Levels of Control for Sodium Cyanide Manufacture . . 84 5-10 Capital and Annual Costs Associated With Baseline Hydrogen Cyanide Storage System 86 5-11 Capital and Annual Costs Associated With Level 1 Hydrogen Cyanide Storage System 87 5-12 Capital and Annual Costs Associated With Level 2 Hydrogen Cyanide Storage System 88 5-13 Capital and Annual Costs Associated With Baseline Sodium Cyanide Reactor System 39 vi ------- TABLES (Continued) Page 5-14 Capital and Annual Costs Associated With Level 1 Sodium Cyanide Reactor System 90 5*15 Capital and Annual Costs Associated With Level 2 Sodium Cyanide Reactor System 91 5-16 Equipment Specifications Associated With Hydrogen Cyanide Storage System 94 5-17 Material and Labor Costs Associated with Baseline Hydrogen Cyanide Storage System 97 5-18 Material and Labor Costs Associated with Level 1 Hydrogen Cyanide Storage System 98 5-19 Material and Labor Costs Associated With Level 2 Hydrogen Cyanide Storage System 99 5-20 Equipment Specifications Associated With Sodium Cyanide Reactor System 100 5-21 Material and Labor Costs Associated With Baseline Sodium Cyanide Reactor System 103 • 5-22 Material and Labor Costs Associated With Level 1 Sodium Cyanide Reactor System 104 5-23 Material and Labor Costs Associated With Level 2 Sodium Cyanide Reactor System 106 5-24 Format for Total Fixed Capital Cost 108 5-25 Format for Total Annual Cost 110 5-26 Format for Installation Costs 115 vii ------- SECTION 1 INTRODUCTION 1.1 BACKGROUND Increasing concern about the potentially disastrous consequences of acci- dental releases of toxic chemicals resulted from the Bhopal. India accident of December 3. 1984, which killed approximately 2,000 people and injured thou- sands more. A toxic cloud of methyl isocyanate was released. Concern about the safety of process facilities handling hazardous materials increased fur- ther after the accident at the Chernobyl nuclear power plant in the Soviet Union in April of 1986. While headlines of these incidents have created the current awareness of toxic release problems, there have been other, perhaps less dramatic incidents in the past. Interest in reducing the probability and consequences of acci- dental toxic chemical releases that might harm workers within a process facil- ity and people in the surrounding community prompted the preparation of this manual and a planned series of companion manuals. Hydrogen cyanide is a major commercial chemical and a low boiling toxic liquid or gas at typical ambient conditions. Historically, there have been few significant releases of hydrogen cyanide in the United States. However. there have been a number of deaths, mostly of chemical plant workers, that have resulted from accidental releases of hydrogen cyanide. ------- 1.2 PURPOSE OF THIS MANUAL The purpose of this manual is to provide technical information about hydrogen cyanide and specifically about prevention, protection, and mitigation. measures for accidental releases of hydrogen cyanide. The manual addresses technological and procedural prevention, protection, and mitigation measures associated with the storage, handling, and process operations involving hydrogen cyanide as it is used in the United States. This manual does not address uses of hydrogen cyanide not encountered in the United States. This manual is intended as a summary manual for persons charged with reviewing and evaluating the potential for releases of hydrogen cyanide at facilities that use. store, handle, or manufacture hydrogen cyanide. It is not intended as a specification manual, and in fact refers the reader to addi- tional technical manuals and other information sources for more complete in- formation on the topics discussed. Other information sources include manu- facturers and distributors of hydrogen cyanide, and technical literature on design, operation, and loss prevention in facilities handling toxic chemicals. 1.3 SOURCES AND USES OF HYDROGEN CYANIDE Two processes for manufacturing hydrogen cyanide (HCN) account for most of the total hydrogen cyanide produced in this country. The most widely used process produces hydrogen cyanide by reacting natural gas (methane). ammonia and air. A second widely used process (which is actually a variation of the first process) is called the DMA process and produces hydrogen cyanide by reacting methane with ammonia. In addition to direct manufacture, hydrogen cyanide is also produced as a by-product of acrylonitrile manufacture. In 1983 it was estimated that 930 million pounds of hydrogen cyanide were manu- factured. At that time, the projected demand for 1988 was 1.186 million pounds (1). ------- The major use of hydrogen cyanide in the U.S., as of 1983. was for the production of adiponitrile. Adiponitrile is used primarily as an intermediate for hexamethlyenediamine. which is a principal ingredient for nylon-6.6. Another major use of hydrogen cyanide is for the production of acetone cyano- hydrin which is used almost exclusively as an intermediate for methyl metha- crylate. Methyl methacrylate is used to manufacture polymethyl methacrylate (Plexiglas*). Hydrogen cyanide is also used in the manufacture of cyanuric chloride (an intermediate in pesticide manufacturing), miscellaneous chelating agents, sodium cyanide, and a number of other chemical products. In 1983. the uses of hydrogen cyanide in the U.S. were: adiponitrile. 38 percent; methyl methacrylate. 35 percent; cyanuric chloride. 10 percent; chelating agents 7 percent; sodium cyanide. 5 percent; other uses. 5 percent (1). In the U.S.. hydrogen cyanide is stored in small cylinders (e.g., 150 Ib), railroad tank cars, and bulk storage tanks. 1.4 ORGANIZATION OF THE MANUAL The remainder of this manual presents technical information on specific hazards and categories of hazards and their control as they relate to hydrogen cyanide. As stated previously, these are examples only and are representative of only some of the hazards that may be related to accidental releases. Section 2 discusses physical, chemical and toxicological properties of hydrogen cyanide. Section 3 describes the types of facilities which manu- facture and use hydrogen cyanide in the United States. Section 4 discusses process hazards associated with these facilities. Hazard prevention and con- trol are discussed in Section 5. Costs of example storage and process facili- ties reflecting different levels of control through alternative systems are also presented in Section 5. The examples are for illustration only and do not necessarily represent a satisfactory alternative control option in all cases. Section 6 presents a reference list. Appendix A is a glossary of key technical terms that might not be familiar to all users of the manual. Appen- dix B presents selected conversion factors between metric (SI) and English measurement units. ------- SECTION 2 CHEMICAL CHARACTERISTICS This section of the manual describes the physical, chemical, and toxico- logical properties of hydrogen cyanide as they relate to accidental release hazards. 2.1 PHYSICAL PROPERTIES Anhydrous hydrogen cyanide is a colorless or pale yellow liquid with a mild odor similar to bitter almonds. The liquid boils at 78.3°F at 1 at- mosphere of pressure and forms a colorless-, flammable, toxic gas. The physi- cal properties of anhydrous hydrogen cyanide are listed in Table 2-1. i Hydrogen cyanide is completely soluble in water. The gas is slightly less dense than air. although a mixture of hydrogen cyanide in moist air may stay near ground level. Liquid hydrogen cyanide will expand slightly with heating. As a result, liquid-full equipment can pose a hazard (although as will be seen, the potentially greater danger from trapping liquid hydrogen cyanide in equipment is the potential for polymerization). A liquid-full vessel is a vessel that is not vented and is filled with liquid hydrogen cya- nide with little or no vapor space present above the liquid. A liquid-full line is a section of pipe that is sealed off at both ends and is full of liquid hydrogen cyanide with little or no vapor space. In these situations. there is no room for thermal expansion of the liquid, and temperature increas- es can result in containment failure. 2.2 CHEMICAL PROPERTIES AND REACTIVITY Three chemical properties of hydrogen cyanide that contribute to the potential for an accidental release of the chemical are (2.3): ------- TABLE 2-1. PHYSICAL PROPERTIES OF HYDROGEN CYANIDE Reference CAS Registry Number Chemical Formula Molecular Weight Normal Boiling Point Melting Point Liquid Specific Gravity (H.0=l) Vapor Specific Gravity (air=l) Vapor Pressure Vapor Pressure Equation: log Pv = A- - 74-90-8 HCN 27.03 78.3 °F 0 1 atm 8.17 °F 0.6884 0 68 °F 0.947 0 88 °F 0.348 atm 0 32°F where: Pv = vapor pressure, mm Hg T = temperature, °C A = 7.5282. a constant B = 1329.5. a constant C = 260.4. a constant Liquid Viscosity Solubility in Water Specific Heat at Constant Pressure Latent Heat of Vaporization 0.2014 centipoise 0 68 °F Complete 16.94 Btu/(lbmole-°F) 0 62.4 °F 10.834 Btu/lbmole 0 77 °F 2 3 2 2 2 3 3 (Continued) ------- TABLE 2-1 (Continued) Reference Liquid Surface Tension Heat of Combustion Autoignition Temperature Explosive Range. Volume Z in air 9 1 atm and 68 °F min. max. Flashpoint. TCC (ASTM D-56) 17.2 dynes/cm 9 77 °F 287.000 Btu/lbmole 1.000 °F 6 41 0 °F 3 3 3 Additional properties useful in determining other properties from physical property correlations. Critical Temperature • Critical Pressure Critical Density 362.2 °F 53.2 atm 12.2 lb/ft' 3 3 3 ------- • Hydrogen cyanide is flammable in air at concentrations from 6 percent to 41 percent hydrogen cyanide. • The addition of alkaline-chemicals, water and/or heat may promote self-polymerization and decomposition of hydrogen cyanide. The self-polymerization reaction is exothermic and the heat released will promote further polymerization. The heat generation will also result in the decomposition of hydrogen cyanide into ammonia and formate. The pressure rise from polymerization/decomposition reactions can be- come explosive. Small amounts of acid such as sulfuric or phosphoric will help to stabilize the hydrogen cyanide against polymerization. • The addition of large quantities of acid (over 15? by weight of concentrated sulfuric acid) can cause rapid decomposition of hydrogen cyanide. This decomposition is highly exothermic. When sulfuric acid is involved the decomposition by-products will be sulfur dioxide and car- 4 bon dioxide. 2.3 TOXICOLOGICAL AND HEALTH EFFECTS Hydrogen cyanide is highly toxic by ingestion, inhalation and skin ad- sorption. It is a true noncumulative protoplasmic poisons (i.e.. it can be detoxified readily). Hydrogen cyanide combines with those enzymes at the blood/tissue interfaces that regulate oxygen transfer to the cellular tissues. Unless the cyanide is removed, death results through asphyxia. The warning signs of hydrogen cyanide poisoning include: dizziness, numbness, headache. rapid pulse, nausea, reddened skin, and blood shot e'yes. More prolonged expo- sure can cause vomiting and labored breathing followed by unconsciousness, cessation of breathing, rapid weak heart beat, and death. Severe exposure (by inhalation) can cause immediate unconsciousness; this rapid knockdown power ------- without any irritation or detectable odor to some people makes hydrogen cya- nide more dangerous than other materials of comparable toxicity (e.g., hydro- gen sulfide). Table 2-2 presents a summary of some of the relevant exposure limits for hydrogen cyanide. Table 2-3 presents a summary of predicted human health effects of exposure to various concentrations of hydrogen cyanide. ------- TABLE 2-2. EXPOSURE LIMITS FOR HYDROGEN CYANIDE Exposure Concentration Limit (ppm) Description Reference IDLH 50 The concentration defined as posing 5 immediate danger to life and health C.e.. causes irreversible toxic effects for a 30-minute exposure). PEL 10 A time-weighted 8-hour exposure to 6 this concentration as set by the Occupational Safety and Health Administration should result in no adverse effects for the average healthy, male worker. LCLo 178 This concentration is the lowest pub- 6 lished lethal concentration for a human over a 10-minute exposure. TABLE 2-3. PREDICTED HUMAN HEALTH EFFECTS OF EXPOSURE TO VARIOUS CONCENTRATIONS OF HYDROGEN CYANIDE ppm Predicted Effect 2-5 Odor threshold. 20 Causes slight symptoms including headache and dizziness after several hours. 50 Causes disturbances within an hour. 100 Dangerous for exposures of 30-60 minutes. 300 Rapidly fatal unless prompt, effective first aid is administered. Source: Adapted from Reference 2. ------- SECTION 3 FACILITY DESCRIPTIONS AND PROCESS HAZARDS This section provides brief descriptions of the uses of hydrogen cyanide in the United States. Major hazards of these processes as they relate to accidental releases are discussed in Section 4. Preventive measures associated with these hazards are discussed in Section 5. 3.1 HYDROGEN CYANIDE MANUFACTURE Two processes for manufacturing hydrogen cyanide account for most of the total hydrogen cyanide produced in this country. The most widely used process is one that produces hydrogen cyanide by reacting natural gas (methane), ammonia and air. A second widely used process (which is actually a variation • of the first process) is called the BMA process which produces hydrogen cyanide by reacting methane with ammonia. In addition to direct manufacture, hydrogen cyanide is also produced as a by-product of acrylonitrile manufacture. A schematic diagram of a hydrogen cyanide manufacturing process is presented in Figure 3-1. In this process ammonia, methane (or natural gas) and air are preheated to about 750 to 900°C, mixed and sent to a packed bed reactor. The reactor is typically packed with a catalytic wire gauze composed of platinum or a platinum rhodium composite (7). The exit gas from the reactor contains a mixture of hydrogen cyanide, ammonia, and water vapor (a by-product of the reaction). As illustrated in Figure 3-1, this crude product mixture is sent to an ammonia absorption column where the ammonia is absorbed in an ammonium phosphate solution (8). Most of the hydrogen cyanide exits in the gas phase where it is absorbed, washed and treated with sulfur dioxide as an inhibitor to prevent polymerization. The ammonium phosphate solution is sent through a series of processing operations where the ammonia is recovered and recycled back to the reactor. 10 ------- NH3 WASTE OASES TO FLAIR NH3 + HCN IN NH4H2PO4 SOLUTION ••m ABSORBER HCN • WATER COOLANT STEAM WASTE WATER WASTE WATER HCN WITH SO2 INHIBITOR L r HCN STRIPPER , 1 STEAM - I ^ ^ V HCN FRACTIONATOR STEAM WASTE WATER NH4PO4 SOLUTION Figure 3-1. Hydrogen cyanide manufacturing process. Adapted from References 2. 8 and 9. ------- The reaction that produces hydrogen cyanide is endothermic. To provide the necessary heat of reaction, forty percent or more of the ammonia and methane fed to the process are intentionally oxidized in the reactor vessel. The heat input from the oxidation of the methane and ammonia balanced by the heat requirements of the hydrogen cyanide reaction will result in a normal reaction temperature of about 2000 to 2200°F (9). High hazard areas in the cyanide manufacturing process include the following: • Cyanide reactor; • Hydrogen cyanide absorber; • Hydrogen cyanide stripper; and i • Hydrogen cyanide fractionator. The cyanide reactor is critical because of the high temperatures that are involved. Overheating the reactor could result in uncontrollable combustion reactions or explosions (10). These uncontrollable combustion reactions or explosions could result in the physical breakdown of the reactor vessel by thermal fatigue or overpressure. There are three possible causes of overheat- ing. They include: • Poor heat distribution within the reactor bed, resulting in hot spots; • Overheating raw materials before they enter the cyanide reactor; or • Loss of composition or quantity control of raw material feeds. 12 ------- Hot spot formation within the reactor can result in catalyst breakdown or physical deterioration of the reactor vessel (10). If the chemical perfor- mance of the catalyst is destroyed then no reaction will occur. If the endo- thermic cyanide reaction has ceased, then the reactor is likely to overheat. In addition to the potential causes of overheating listed above, it should be noted that iron is a decomposition catalyst for hydrogen cyanide and ammonia under the conditions present in the hydrogen cyanide reactor. Exposed iron surfaces in the reactor or reactor feed system can result in uncontrolled decomposition, which could result- in an accidental release by overheating and overpressure. Only a small inventory of hydrogen cyanide will be present in the cyanide reactor. Therefore, catastrophic failure of the cyanide reactor is not likely to directly result in the release of large quantities of hydrogen cyanide. However, such failure could result in damage to other portions of the system where larger quantities of hydrogen cyanide are present. • The hydrogen cyanide absorber, stripper and fractionator are high hazard areas because they contain inventories of concentrated hydrogen cyanide., All of the associated pumps, piping and fittings for these systems are also high hazard areas. Controlling the pH of these systems is important since the vapor pressure of hydrogen cyanide is dependent upon pH. A system designed for hydrogen cyanide vapor pressure within one pH range may not be able to handle the increased cyanide vapor pressure at a lower pH. Reliable pH control is particularly important at the hydrogen cyanide fractionator where acid is intentionally added as a stabilizer to the feed stream. The quantity of acid that is added at this point is very small. However, the potential still exists for a loss of acid flow control. Large excesses of acid can result in a violent hydrogen cyanide decomposition reaction. • • • The ammonia recovery portion of the hydrogen cyanide manufacturing process does not contain large quantities of hydrogen cyanide. However. inventories of ammonia are present throughout this portion of the system. 13 ------- Therefore a potential for an accidental release of ammonia exists in this section of the process. 3.2 HYDROGEN CYANIDE CONSUMPTION The major use of hydrogen cyanide in the U.S. today is for the production of adiponitrile. Adiponitrile is used primarily as an intermediate for hexamethlyenediamine, which is a principal ingredient for nylon-6,6 (1). Another major use of hydrogen cyanide is for the production of acetone cyano- hydrin which is used almost exclusively as an intermediate for methyl metha- ciylate. Methyl methacrylate is used to manufacture polymethyl methacrylate (Plexiglas*). Hydrogen cyanide is also used in the manufacture of cyanuric chloride (an intermediate in pesticide manufacturing), miscellaneous chelating agents, sodium cyanide, and a number of other chemical products. Table 3-1 lists a variety of products that might be manufactured using hydrogen cyanide. t This subsection summarizes some of the major technical features of process facilities that might use hydrogen cyanide in the U.S. 3.2.1 Manufacture of Adiponitrile Adiponitrile is commercially manufactured by several different processes all of which begin with a different hydrocarbon raw material. Hydrogen cyanide is found only in those processes that use butadiene as a starting material. In some butadiene-based processes, sodium cyanide is used as the raw material (11). In other butadiene-based processes hydrogen cyanide is used as the raw material. Figure 3-2 illustrates a process that uses hydrogen cyanide to manufacture adiponitrile. In this process, hydrogen cyanide and a slight excess of butadiene are fed to a reactor packed with nickel catalyst. The reaction is carried out at 212°F and sufficient pressure to keep the reactants in solution (12). The product mixture contains 2-methyl-3-butenenitrile, 3-pentenenitrile, and 14 ------- TABLE 3-1. TYPICAL USES OF HYDROGEN CYANIDE Acetone cyanahydrin Adiponitrile Acrylonitrile Aminopolycarboxylic acids Barium cyanide Beta-amines Cyanuric chloride Diaminomaleonitrile Lactic acid Methionine Sodium cyanide Tertiary alkyl amines Source: Adapted from Reference 14. 15 ------- HYDROGEN CYANIDE BUTADIENE fc- HYDBOQ6N CYANIO* BUTADIENE J 2 • METHYL - 3 • BUTENENITWLE + 3-PENTENENrraiLE 3-PENTENENITBILE * 4 - PENTENENITRILE T LIGHT BY - PRODUCTS AOIPONITniLE * BY - PRODUCTS HEAVY BY - PRODUCTS AOIPONITRILE Figure 3-2. Manufacturing process for adiponitrile. 16 ------- unreacted butadiene. The unreacted butadiene is separated from the product .stream and recycled back to the reactor. The fractionated product stream from the first hydrocyanation reactor is passed through a nickel catalyst bed where an isomerization reaction converts the 2-methyl-3-butenenitrile to 3-pentenenitrile and a small amount of 2-pen- tenitrile (13). The 3-pentenenitrile is then passed through another nickel catalyst bed along with hydrogen cyanide to produce adiponitrile. Unreacted pentenenitrile is separated from the product stream by distillation and recycled back to the reactor. The crude adiponitrile is purified by distillation. The portions of the process that are of concern when considering a hydrogen cyanide release are the two hydrocyanation reactors and the hydrogen cyanide feed and storage system. The hydrocyanation reactors are run with an excess of olefin and thus the hydrogen cyanide is completely consumed by reaction. Both of these reactions are exothermic and thus there is the potential for a loss of temperature control and an accidental release by overpressure. • The hydrocyanation reactions are carried out at relatively mild condi- tions (around 212°F and 100 to 200 psia). A loss of temperature control would probably not result in high enough temperatures to structurally fatigue the reaction equipment. The major concern with a loss of temperature control would be the potential for vaporization of unreacted hydrogen cyanide within the reactor. This would result in an increase of pressure in the reactor. The consequences of such an increase would depend upon the ability of the pressure relief system to handle the vaporized hydrogen cyanide. Once the hydrogen cyanide was vaporized the hydrocyanation re.action would cease and no additional heat would be generated. The situation is. therefore, self cor- recting. There may be conditions under which loss of temperature control would result in a polymerization-decomposition of hydrogen cyanide. 17 ------- Hydrogen cyanide storage and feed systems are of concern because of the relatively large inventory of hydrogen cyanide. Leaks from valves, fittings. pumps, and storage vessels are of concern. 3.2.2 Manufacture of Acetone Cyanohydrin/Methyl Methacrylate Hydrogen cyanide can be combined with acetone to produce acetone cyano- hydrin which in turn can be combined with methanol to form methyl methacry- late. As mentioned in the introduction to this subsection, almost all of the acetone cyanohydrin produced in this country is carried on to methyl methacry- late. Methyl methacrylate is also produced by routes that do not use hydrogen cyanide (15). Figure 3-3 illustrates the acetone cyanohydrin production portion of a methyl methacrylate process that utilizes hydrogen cyanide (16). In this process, hydrogen cyanide, acetone and a catalyst are fed to a continuous stirred tank reactor to form acetone cyanohydrin. The reaction catalyst may be sodium hydroxide or some other alkaline metal salt. The reaction is run at a temperature between 70°F and 160°F. The reaction mixture is fed to a second stirred tank where sulfuric acid is added to quench the reaction. The acetone cyanohydrin is purified by first decanting off the catalyst and then distil- ling off unreacted raw materials. The purified acetone cyanohydrin is then converted to methacrylamide sulfate by the addition of sulfuric acid. Methanol in an aqueous solution is then added along with the methacrylamide sulfate to a multistaged reactor where methyl methacrylate is formed. Several purification steps complete the manufacturing process. The high hazard area of this process with regard to preventing an acci- dental release of hydrogen cyanide is the acetone cyanohydrin production portion of the process. 18 ------- ACETONE CYANOHYDRIN STRIPPER ACETONE CYANOHYOflIN REACTOR ACETONE CYANOHYORIN TO METHYL METHACRYLATE PRODUCTION PROCESS Figure 3-3. Manufacturing process for acetone cyanohydrin. 19 ------- The first potentially hazardous location is the acetone cyanohydrin reactor. The inventory of hydrogen cyanide in the reactor will be relatively small. However, if the flow of acetone to the reactor were to cease, the conditions within the vessel would promote hydrogen cyanide polymeri- zation-decomposition. The presence of excess hydrogen cyanide as well as inadequate mixing of the' hydrogen cyanide with the acetone could also lead to polymerization-decomposition of the cyanide. Polymerization-decomposition could lead to overpressure or overheating in the reactor and result in an accidental release of hydrogen cyanide. Thus, control of flow, composition. mixing and temperature are all important in this reactor. The reaction quenching vessel is a second potentially hazardous portion of this process. Failure to sufficiently quench the reaction with acid could result in a reversal of the reaction back to hydrogen cyanide and acetone. Acetone cyanohydrin will convert back to hydrocyanic acid and acetone if the pH is above a certain level. One source recommends that the pH for storage of acetone cyanohydrin not exceed 3 or 4, and the pH under more rigorous* condi- tions such as those found in a distillation operation should not exceed 2 (17). The potential hazard, therefore, is that insufficient pH adjustment will result in acetone cyanohydrin decomposition in the stripping column. This would result in a significant increase in the flow of material to the flare. This increase in flow could disrupt the performance of the flare and result in an accidental release of hydrogen cyanide. Additionally, high levels of hydrogen cyanide in the stripping column could result in polymerization- decomposition. The other major area of concern in this process is the hydrogen cyanide storage and feed system. The potential for an accidental release of hydrogen cyanide would be high because of the relatively large inventories. 20 ------- 3.2.3 Manufacture of Cyanuric Chloride Cyanuric chloride is used for the production of triazine-based herbi- cides. It is manufactured in a two-step process. In the first step chlorine and hydrogen cyanide are reacted to form cyanogen. Cyclic trimerization of the cyanogen yields cyanuric chloride (18). Another method for the production of cyanuric chloride involves a single step fluidized bed process (19). Very little hydrogen cyanide would be present in the reaction or puri- fication sections of a cyanuric chloride manufacturing facility. The initial cyanuric reaction between hydrogen cyanide and chlorine will proceed rapidly. leaving little inventory of hydrogen cyanide in the reactor. The primary area of concern from the perspective of an accidental release of hydrogen cyanide would be the initial hydrogen cyanide storage and handling facility. Pumps, valves, piping, and vessels that are dedicated to hydrogen cyanide service would be of particular concern. • 3.2.4 Manufacture of Sodium Cyanide 4 Sodium cyanide is usually produced by reacting hydrogen cyanide with a sodium hydroxide solution. Such manufacturing operations are often located directly down stream from a hydrogen cyanide manufacturing process. An example of a continuous sodium cyanide manufacturing process is presented in Figure 3-4 (20). In this process aqueous sodium hydroxide and gaseous hydrogen cyanide are fed to a vessel that functions as a reactor, evaporator and crystallizer. where they react to form sodium cyanide. The reaction vessel contains aqueous sodium cyanide with a small amount of unreacted. excess sodium hydroxide. The sodium hydroxide is fed to the top of the reaction vessel while the hydrogen cyanide is fed to a recirculation loop at the bottom of the vessel. As the two reactants mix in a countercur- rent fashion, they react to form sodium cyanide. The reactor is kept under partial vacuum. The reduced pressure lowers the boiling point of the 21 ------- VACUUM CONDENSER AQUEOUS SODIUM HYDROXIDE WASTE WATER to HYDROGEN CYANIDE AQUEOUS SODIUM CYANIDE SOLUTION RECIRCULATION LOOP CONTAINING WATER, SOLUBILIZED SODIUM CYANIDE AND SOLID SODIUM CYANIDE SEMI • DRY SODIUM CYANIDE PRODUCT SLIP STREAM Figure 3-4. Sodium cyanide manufacturing process (20), ------- solution. The heat of reaction is removed by allowing water to boil off from the solution. The temperature of the mixture is therefore kept at its boiling point. As the reaction proceeds and water is removed, some of the sodium cyanide crystallizes out of solution. A product slip stream is withdrawn from the reactor recirculation loop and the crystallized sodium cyanide crystals are filtered out and dried. The filtrate is returned to the reaction vessel. There are two issues of concern when operating a sodium cyanide manufac- turing operation. The first concern is that hydrogen cyanide will polymerize before the reaction with sodium hydroxide occurs. The conditions in the reactor are favorable for polymerization if insufficient quantities of sodium hydroxide are present or if there is incomplete mixing of the hydrogen cyanide with the sodium hyroxide. The second concern is that sodium cyanide will hydrolyze to hydrogen cyanide and sodium formate. This reaction is very dependent upon temperature and can become significant at temperatures above 160 to 180°F (20). Both of the problems listed above could be of concern from the perspec- tive of accidental release prevention. The formation of polymerized cya'nide could clog pumps and lines which could lead to an accidental release by overpressuring positive displacement pumps or overheating the contents of centrifugal pumps. Additionally, the polymerization reaction is exothermic. The heat generated by the reaction could result in excessive pressures and could contribute to additional polymer formation. Significant hydrolysis of sodium cyanide would lead to the formation of unexpected quantities of hydro- gen cyanide which could result in overpressurization of the pump or overload- ing of the vacuum system; both of which could lead to an accidental release of hydrogen cyanide. As with all processes that handle hydrogen cyanide, the hydrogen cyanide storage and feed system is of concern because of the relatively large inven- tory. A breach of containment within the hydrogen cyanide feed and storage system could result in an accidental release of the chemical. 23 ------- 3.3 STORAGE AND TRANSFER When a facility uses large quantities of hydrogen cyanide, the hydrogen cyanide is either produced on site or is unloaded from a rail car into stationary storage. Figure 3-5 shows a potential design for a hydrogen cyanide tank car unloading facility. The basic components of such a facility include nitrogen blanketing with pressure relief, grounding cables with clamps, special high-pressure piping and hoses for hookups of both hydrogen cyanide and nitrogen systems, tank level measuring device, tank car "come-along" for accurate positioning, wheel chocks, and derailers. Figure 3-6 shows a potential design for a hydrogen cyanide storage tank. The basic components of such a system are temperature and pressure recorders and alarms, pressure relief to a flare or other treatment system, sulfuric acid addition system, liquid level measuring device with alarm, cooling system and diked enclosure. • The primary hazard associated with the storage of hydrogen cyanide is the potential for self polymerization. As described in Section 2-2. self poly- merization can result in rapid temperature and pressure increases in a storage system and can result in a breach of containment. Several safety precautions concerning the prevention of polymerization will be discussed in Subsection 5.3.1. Additional hazards associated with hydrogen cyanide storage include the potential for overfilling, corrosion, and contamination caused by backflow of process materials into the storage tank. Additionally, loss of tank refriger- ation could result in overpressure due to thermal expansion of both the liquid and gaseous hydrogen cyanide. Such an overpressure would probably result in the discharge of hydrogen cyanide through the pressure relief device. The ultimate consequence of such a release will depend upon the ability, of the hydrogen cyanide containment and protection system (e.g. a flare or scrubber) to handle such a load. 24 ------- N> Ln PRESSURE INDICATOR PRESSURE RELIEF NITROGEN REGULATORS NITROGEN NITROGEN FILTER NITROGEN PRESSURE RELIEF THERMOWELL FLOW INDICATOR VALVE EXCESS FLOW VALVE MCN STORAGE TANK rr / f II i it i111 lit // I///f ///////////////// Figure 3-5. Example diagram of hydrogen cyanide tank car unloading facility. Adapted from Reference 3. ------- TO FLARE OR SCRUBBER PRESSURE - VACUUM RECORDER ALARM TEMPERATURE RECORDER ALARM ACID ADDITION TANK COOLANT COOLANT TO HCN SAMPLING SYSTEM FROM TANK CAR1 NJ \ CONTINUOUS NITROGEN PURGE BELOW VALVE OPEN VENT WITH CONDENSER HEAT EXCHANGER ON PUMP - AROUND COOLING LOOP FOR HCN TO HCN 'PROCESS SUBMERGED PUMPS PI - PRESSURE INDICATOR Tl - TEMPERATURE INDICATOR Lfi 1 — PRESSURE RELIEF VALVE VALVE Figure 3-6. Example diagram of hydrogen cyanide storage facility. Adapted from Reference 3. ------- SECTION 4 PROCESS HAZARDS Some hazards and potential causes of releases for hydrogen cyanide releases directly related to its properties and specific processes were identified in the preceding sections. This section summarizes these, and discusses more general hazards common to any facility producing or using hydrogen cyanide. Hydrogen cyanide releases can originate from many sources including ruptures in process equipment, separated flanges, actuated relief valves or rupture discs, and failed pumps or compressors. In addition, losses may occur through leaks at joints and connections such as flanges, valves, and fittings where failure of gaskets or packing might occur. The properties of hydrogen cyanide which can promote equipment failure are its ability to self polymerize, its flammability and the violent decompo- sition reaction that can occur between hydrogen cyanide and acidic solufions. Potential hydrogen cyanide releases may be in the form of either liquid or vapor. Liquid spills can occur when hydrogen cyanide is released at or below its boiling point of 78.3°F. or when a sudden release of hydrogen cyanide at temperatures above its boiling point results in vapor flashing. thus cooling at least part of the remaining material to below its boiling point. Direct releases of vapor can also occur. 4.1 POTENTIAL CAUSES OF RELEASES * Failures leading to accidental releases may be broadly classified as due to process, equipment, or operational causes. This classification is for convenience only. Causes discussed below are intended to be illustrative, not exhaustive. A more detailed discussion of possible causes of accidental re- leases is planned in other portions of the prevention reference manual series of which this present manual is a part. 27 ------- 4.1.1 Process Causes Process causes are related to the fundamentals of process chemistry* control and general operation. Examples of possible process causes of a • . • hydrogen cyanide release include: • Overheating of cyanide manufacturing reactor resulting in rapid thermal decomposition; • Loss of flow/composition control where acid stabilizer is added to a hydrogen cyanide stream resulting in excess acid. High acid levels can result in rapid decomposition and overpressure; • Loss of flow/composition control where acid stabilizer is • added to a hydrogen cyanide stream resulting in low acid levels. Low acid levels can result in polymerization- decomposition; • Loss of flow/composition control where abnormally high levels of hydrogen cyanide is fed to a reactor along with a basic catalyst or reactant. Excess hydrogen cyanide is likely to polymerize-decompose under such conditions; • Loss of adequate mixing where hydrogen cyanide is fed to a reactor along with a basic catalyst or reactant. Local- ized high concentrations of hydrogen cyanide can polyerize- decompose; • Loss of pH control where acetone cyanohydrin is present resulting in the decomposition to acetone and hydrogen cyanide. Such decomposition could result in overpressure and an accidental release; 28 ------- • Overpressure of any storage or process vessels containing hydrogen cyanide due to over heating resulting in polymerization-decomposition; • Excess hydrogen cyanide feed leading to overfilling or overpressuring equipment; • Backflow of alkaline or strongly acidic materials into hydrogen cyanide storage or process vessel resulting in polymerization-decomposition; and • Catalyst decay in hydrogen cyanide production reaction resulting in overheating of the reactor. 4.1.2 Equipment Causes Equipment causes of accidental releases result from hardware failure. Some possible causes include: • • Excessive stress due to improper fabrication, construc- tion, or installation; • Failure of vessels at normal operating conditions due to weakening of equipment from excessive stress, external loadings, or corrosion; • Mechanical fatigue and shock in any equipment. Mechanical fatigue could result from age. vibration, or stress cycling, caused by pressure cycling, for example. Shock could occur from collisions with moving equipment such as cranes or other equipment in process or storage areas; • Creep failure in equipment subjected to extreme operation- al upsets, especially excess temperature. This can occur 29 ------- in equipment subjected to fire that may have caused damage before being brought under control; • Failure of any equipment that is exposed to hydrogen cyanide due to stress corrosion cracking, especially equipment subject to vibration or other forms of mechani- cal stress; and • All forms of corrosion; specific type will be process and material specific. 4.1.3 Operational Causes Operational causes of accidental releases are a result of incorrect pro- cedures or human errors (i.e.. not following correct procedures). These causes include: • • Overfilled storage vessels; • Errors in loading and unloading procedures; * Inadequate maintenance in general, but especially on pressure relief systems and other preventive and protec- tive systems; and • Lack of inspection and non-destructive testing of vessels and piping to detect corrosion weakening. 30 ------- SECTION 5 HAZARD PREVENTION AND CONTROL 5.1 GENERAL CONSIDERATIONS Prevention of accidental releases relies on a combination of technologi- cal, administrative, and operational practices. These practices apply to the design, construction, and operation of facilities where hydrogen cyanide is stored and used. Considerations in these areas can be grouped as follows: • Process design; • Physical plant design; • • Operating and maintenance practices: and • Protective systems. In each of these areas, consideration must be given to specific factors that could lead to a process upset or failure which could directly cause a release of hydrogen cyanide to the environment, or result in an equipment failure which would then cause the release. At a minimum, equipment and procedures should be examined to ensure that they are in accordance with applicable codes, standards, and regulations. In addition, stricter equipment and procedural specifications should be in place if extra protection against a release is considered appropriate. Most of the large manufacturers of hydrogen cyanide provide detailed assistance as to proper storage and handling practices for their customers that use the chemical. One large company requires all of their customers to 31 ------- comply with their safety practices and will routinely inspect customer's facilities for compliance. This same company offers an annual seminar on safe storage and handling practices of hydrogen cyanide. This seminar is attended by customers as well as other producers that license technology from the sponsoring company (21). Such practices have contributed significantly toward reducing the risk of an accidental release of hydrogen cyanide. Release prevention is discussed in the following subsections. More detailed discussions will be found in a manual on control technologies, part of this manual series. 5.2 PROCESS DESIGN Process design involves the fundamental characteristics of the processes which use hydrogen cyanide. This includes an evaluation of how deviations from,expected process design conditions might initiate a series of events that could result in an accidental release. The primary focus is on how the process is controlled in terms of the basic process chemistry, and the vari- ables of flow, pressure, temperature, composition, and quantity. Additional process design issues may include mixing systems, fire protection, and process control instrumentation. Modifications to enhance process integrity may result from review of these factors and would involve changes in quantities of materials, process pressure and temperature conditions, the unit operations, sequence of operations, the process control strategies, and instrumentation used. Table 5-1 shows the relationship between some specific process design considerations and individual processes described in Section 3 of this manual. This does not mean that other factors should be ignored, nor does it mean that proper attention to just the considerations in the table ensures a safe system. The items listed, and perhaps others, must be properly addressed if a system is to be safe, however. 32 ------- TABLE 5-1. KEY PROCESS DESIGN CONSIDERATIONS FOR HYDROGEN CYANIDE PROCESSES Process Design Consideration Process or Unit Operation Flow control of hydrogen cya- nide feed Mixing Composition monitoring and control (including pH) Temperature sensing and heating/cooling media flow control Adequate pressure relief Level sensing and control Corrosion monitoring All (hydrogen cyanide is almost always used as the limiting reactant). Sodium cyanide reactor, con- tinuous stirred tank methyl methacrylate reactor, all operations where hydrogen cya- nide is mixed with alkaline or acidic materials. Hydrogen cyanide storage ves- sels, feed to hydrogen cyanide production process. Should be considered for all operations where high concentrations and/or large quantities of hydrogen cyanide are used. All operations where high con- centrations and/or large quanti- ties of hydrogen cyanide are used. Storage tanks, reactors, distil- lation and stripping columns, heat exchangers. Storage tanks, reboilers and condensers, batch or continuous stirred tank reactors All. but especially equipment exposed to hydrogen cyanide and mechanical stress at the same time. 33 ------- 5.3 PHYSICAL PLANT DESIGN Physical plant design includes equipment, siting and layout, and trans- fer/transport facilities. Vessels, piping and valves, process machinery. instrumentation, and factors such as location of systems and equipment must all be considered. The following subsections cover various aspects of physi- cal plant design beginning with a discussion of materials of construction. This section is not intended to provide detailed specifications for the design of a facility handling hydrogen cyanide. The discussion is intended to be illustrative, but not comprehensive. 5.3.1 Equipment Materials of Construction— The primary concern in selecting the appropriate materials of construc- tion* is the prevention of major hydrogen cyanide solution spills and preven- tion of contamination of the hydrogen cyanide. Anhydrous hydrogen cyanide is generally not considered corrosive. Under ambient temperatures carbon steel is an acceptable material of construction. As an example, for storage vessels, one distributor recommends ASTM A516 grade 60 steel that has been acid pickled using a 0.51 H-SO. solution for ten to twelve hours (3). However, there are conditions under which hydrogen cyanide will be corrosive to carbon steel. In general carbon steel is only appropriate for ambient storage of hydrogen cyanide. Elevated temperatures, the presence of an acid stabilizer, and the presence of water will all effect the corrosiveness of a hydrogen cyanide solution. Water solutions of hydrogen cyanide can result in transcrystalline stress- cracking of carbon steels under stress even at room temperature and in dilute solution (2). Under more severe conditions of temperature and pressure, solutions of hydrogen cyanide may also result in stress corrosion cracking of stainless steels and nickel-chromium and nickel-copper alloys 34 ------- (22). Additionally, water solutions of hydrogen cyanide containing sulfuric acid as a stabilizer severely corrode carbon steel above 100°F and stainless steels above 175°F (2). Austenitic stainless steels resist corrosion by sulfur dioxide-stabilized hydrogen cyanide and water mixtures at all concentrations and at temperatures up to the atmospheric boiling point. Types 316 and 317 stainless steels have greater corrosion resistance than stainless steels without molybdenum (23). Unstabilized stainless steels should be fully annealed to prevent intergran- ular attack (23). In higher temperature applications, nickel-chromium and nickel-copper alloys must be used. Care must be taken for correct material selection in these situations, since these materials may also be subject to stress corrosion cracking by hydrogen cyanide. A number of nonmetallic materials show good resistance to hydrogen cyanide. Table 5-2 shows a list of plastics and elastomers and their relative resistance to. chemical attack by aqueous hydrogen cyanide solutions. It is important to realize that the conditions under which these material were tested was limited to pure hydrogen cyanide and water mixtures at the temper- ature indicated on the chart. The addition of other chemical constituents could effect the corrosion resistance of the material. Higher temperatures may also effect the performance of these materials. In addition, this table says nothing about the physical characteristics of these materials. Although a material may show good chemical resistance it may not have the physical properties necessary for use in chemical equipment. Only materials that show excellent chemical resistance to hydrogen cyanide should be considered for use in a facility that handles the chemical. Actual material selection for a given application should be done in consultation with a vendor having experi- ence with hydrogen cyanide systems. Vessels— Most hydrogen cyanide is stored in refrigerated atmospheric storage vessels. Many of the design features for hydrogen cyanide storage tanks 35 ------- TABLE 5-2. CHEMICAL RESISTANCE OF POLYMERS AND ELASTOMERS TO CHEMICAL ATTACK BY WET HYDROGEN CYANIDE Material Resistance to Chemical Attack* Chlorinated Polyether Polyvinylidene Fluoride Polyamide Polyethylene Polyimides Polyphenylene oxide Polyphenyl sulfide Polypropylene Polystyrene Polysulf one Polyvinyl chloride (types I & II) Chlorinated PVC Polysulfone Vinylidene Chloride Epozy Resin Furan Resin Phenolic Resin Polyesters Vinyl ester Natural soft rubber Butadieneacrylonitrile Butyl rubber Chloroprene rubber Chlorosulfonated polyethylene Polysulfide rubber Polyurethane elastomer Excellent at 250°F Excellent at 275°F Unacceptable Good at 150°F Good at 150°F Unacceptable Good at 150°F Good at 150°F Good at 150°F Unacceptable Excellent at 150°F Fair at 150°F Unacceptable Good at 150°F Excellent at 150°F Excellent at 150°F Excellent at 150°F Good at 220°F Fair at 150°F Good at 150°F Unacceptable Good at 150°F Excellent at 150°F Excellent at 150°F Excellent at 150°F Excellent at 150°F The materials listed may or may not show similar chemical resistance at higher temperatures. 36 ------- center around the ability of the chemical to experience polymerization - decomposition. Because of this, a number of safety features should be incor- porated into the design of any hydrogen cyanide storage tank. A list of these items is presented below: e Tank cooling system; e Temperature monitoring with high temperature alarm; e Tank sampling system; • Grounding connection; • Level monitoring with alarm; e Pressure monitoring with high pressure and vacuum alarm; e Acid addition system; • Emergency pressure relief; and • Clean nitrogen supply for maintaining an inert atmosphere in the tank. In addition to these features a number of other features should be considered for a hydrogen cyanide storage tank. Examples include: e Tank vent with vapor condenser, vent discharge to flare. scrubber or equivalent treatment device; • . . • Second high level alarm; 37 ------- • Dedicated nitrogen supply (for use with hydrogen cyanide storage only); • Dike around storage tank; and • Area monitors that activate deluge system when hydrogen cyanide is detected. The cyanide polymerization - decomposition reaction is best detected by a rise in tank temperature. The second method of detection is color change. Hydrogen cyanide that has not polymerized has a "straw yellow" appearance. The color will darken as the reaction occurs until it reaches a dark brown; at this point the reaction may be proceeding at a dangerous rate. For these reasons the temperature of a hydrogen cyanide storage tank should be continu- ously monitored; any increase in temperature should be considered suspect. Samples should be withdrawn periodically from the storage tank to observe physical appearance and to test for acidity and water content. One major distributor recommends that such samples should be withdrawn at least two times per week (3). Others have suggested that sampling be carried out at least every twenty four hours (25). Cooling of a hydrogen cyanide tank can be accomplished by a recirculation loop with a heat exchanger in the loop or by cooling jackets around the outside of the vessel. Leakage of some varieties of coolant into the hydrogen cyanide storage vessel can promote polymerization. For this reason a recirculation loop may be more appropriate than a jacketed vessel, as it is easier to inspect the integrity of a single heat exchanger than the jacket on an entire vessel. Ammonia should never be used as a refrigerant as it can neutralize the acidic stabilizer in the hydrogen cyanide. An acid addition tank should be present on storage tanks so that acid can be added to stabilize a hydrogen cyanide tank where polymerization has been detected. The acid should not be added directly to the tank, as localized 38 ------- high concentrations of acid can result in violent decomposition of the hydro- gen cyanide. A system for mixing the acid, either by addition to the recircu- lation loop or by addition with nitrogen injection should be developed. Usually the acid addition is designed to be manually operated once the poly- merization reaction has been detected. However, an automated system to inject acid based on temperature rise could be developed. Usually, however, there is ample time to decide whether acid should be added. The purity of the nitrogen that is "fed to the tank is very important. Contamination brought in with the nitrogen could result in a polymerization reaction. Dryers and filters should.be present on all nitrogen supplies. Additionally, extreme care should be taken to assure that no cross contamina- tion can occur between the hydrogen cyanide storage tank and other systems using the same nitrogen supply. The best system in one where the hydrogen cyanide storage tank has a nitrogen supply that is dedicated for use by the hydrogen cyanide storage system only. When the tank is operated at atmospheric pressure extreme care must be taken to avoid contamination through the vent system. One possible solution to this is to have a vent system that is used only for the hydrogen cyanide storage tank. Another method for reducing the potential for vent contamina- tion would be to continuously feed a small amount of nitrogen into the tank and out the vent. Whenever a vented storage vessel is used it should be equipped with a vacuum alarm, as the presence of a vacuum in the tank will create a reverse flow in the vent and potentially draw air or other forms of contamination into the tank. Structurally the tank should be constructed according to a code quality design. One vendor recommends that atmospheric pressure storage vessels be designed for 25 psig minimum, with a corrosion allowance of at least 1/16 inch. The tank should be able to withstand vacuum. The tank should have no bottom outlets. Dip pipes should be of a large enough diameter to prevent high velocity impact with the bottom of the tank; such impact can result in 39 ------- erosion-corrosion (3). This same vendor provides additional specifications for tank design. Vessels such as reactors and heat exchangers that handle hydrogen cyanide must be designed with many of the same considerations in mind that were listed above for storage vessels. Protection must be provided against the potential for polymerization - decomposition. The specific precautions will depend on the process involved. Release prevention considerations for all vessels include prevention of overpressure, overfilling, overheating, and corrosion. Many of the processes that use hydrogen cyanide react the chemical with an alkaline material at elevated temperatures. In these situations precau- tions to reduce the risk of polymerization will include adequate, mixing, flow and composition control and temperature control. Therefore reaction vessels of this type must be designed with adequate monitoring and backup of one or all of these parameters. All vessels that handle hydrogen cyanide must be equipped with adequate overpressure protection. Where possible the discharge from these overpressure protection devices should be sent to a protection system such as a scrubber or flare. Care must be taken to prevent material from other process units from contaminating the hydrogen cyanide system through the vent system. Over- pressure protection systems will be discussed in a latter portion of this manual. Prevention of overfilling can be accomplished using level sensing de- vices, pressure relief devices* and adequately trained personnel. Redundant level sensing devices are often appropriate where hydrogen cyanide is used. Where a pressure relief device is used as overflow protection, the discharge from the valve should go to a catch tank. Such a valve should not be used for overpressure protection, as a valve that is sized to release vapor in the event of an overpressure will be grossly undersized if it must release liquid in the event of an overpressure. 40 ------- Because of its flammability, the contents of hydrogen cyanide vessels should be kept under an inert atmosphere unless process requirements dictate alternate conditions. This can be done using nitrogen. The inert gas that is used for such purposes should be filtered and dried. Precautions must be taken to prevent cross contamination through the nitrogen system, and in some cases it may be preferable to have a separate nitrogen supply for the hydrogen cyanide system. Piping— The characteristics of hydrogen cyanide that are most important when designing piping systems are: • The high acute toxicity of the chemical: • Its ability to cause stress corrosion cracking; and • Its ability to polymerize. The high toxicity of hydrogen cyanide is of concern because even s,mall leaks in a piping system can be dangerous to operating personnel. Hydrogen cyanide piping should be constructed with welded connections that are fully radiographed. The use of flanges should be minimized and threaded fittings should never be used. Valves should have a leak-tight gland or be leakproof such as a diaphragm or bellow-sealed valve. The valve stem seals should be externally adjustable to stop stem leakage, and the stem should not be removable while the valve is in service. Excess flow valves should be considered at the inlet and outlet of hydrogen cyanide vessels. For maintenance and emergencies, it is often useful to be able to isolate vessels and other hydrogen cyanide process equipment. Remotely operated emergency isolation valves should be considered wherever a large release could prevent access to an isolation valve. In some cases a single valve is 41 ------- insufficient to ensure complete isolation, and the use of slip plates or a double block and bleed arrangement may be necessary. Because of the potential for releasing trapped hydrogen cyanide, proper training is essential to ensure safe operation of these isolation techniques. Several precautions'must be taken in light of ability of hydrogen cyanide to cause stress corrosion cracking. Piping, valves and fittings should all be constructed of 316 stainless steel. Flange nuts and bolts should also be constructed of a material that is resistant to hydrogen cyanide attack as fugitive leaks can attack these as well (3). Gaskets should be 316 stainless steel-graphite spiral-wound or similar type, as these provide more sure leak protection than asbestos composites. These specifications may not be suffi- cient for high temperature applications. In such cases hydrogen cyanide resistant alloys such as inconel may be required. •Because of stress corrosion, piping equipment that is subject to vibra- tion, such as near a pump, are of particular concern. Piping should be ade- quately supported, as stress and vibration over a long period of time will significantly contribute to the potential for stress cracking. Tees and other similar fittings should be forged instead of welded as welds are particularly susceptible to stress cracking. Polymerization of hydrogen cyanide within a piping system will result in restricted or blocked flow and can result in an overpressured line; both of which could contribute to an accidental release. Dead ends or rarely used sections of piping should be avoided as polymerization can occur where stag- nant hydrogen cyanide is present. Piping should be well insulated from exposure to heat. Even warming by the sun on uninsulated piping can contri- bute to polymerization. Pipe runs should be pitched so that they drain when flow is stopped. Sections of pipe where liquid hydrogen cyanide could be trapped by valves should be equipped with overpressure protection. Ball and plug valves should be designed so that excess pressure in the body will relieve spontaneously toward the high pressure side. This is accomplished by 42 ------- providing a relief hole in the valve body (or the ball or plug) which bypasses the upstream seat. Modified valves such as these must indicate the flow direction on the valve body. Process Machinery — Pumps— Many of the concerns and considerations for hydrogen cyanide piping and valves also apply to pumps. To assure that a given pump is suit- able for hydrogen cyanide service, the system designer should obtain informa- tion from the pump manufacturer certifying that the pump will perform properly in this application. Wetted parts should be made of 316 stainless steel. Mechanical seals are preferred over packing for better leak protection. Double mechanical seals with a barrier fluid provide even better leak protection. In some situations the potential for a leak may be so undesirable that rotating shaft seals are not appropriate. Pumps that do not have external rotating shaft seals are, canned-motor, vertical extended-spindle submersible, magnetically coupled, and diaphragm pumps (26). • Pumps should be equipped with overpressure protection. Positive dis- placement pumps should have pressure relief that vents to a safe location. Alternately, positive displacement pumps can be equipped with pump-around loops. However, because a pump-around loop increases the complexity of the system, and the number of valves and fittings, it may increase the risk of a release. By bypassing the pump, the pump-round loop also eliminates the positive displacement pump as a back flow protection device. Deadheading a centrifugal pump can also result in a release by overheat- ing the hydrogen cyanide trapped within the pump. This can result in the initiation of a polymerization - decomposition reaction within the pump. The pump seal is very likely to fail under these conditions. One method of reducing the risk associated with such an event is to install a flammable gas detector just on the outside of the mechanical seal. The detector could be ------- connected to a deluge system that could be activated in the event of even a small release from the pump seal. Pumps handling cyanide solutions should be located within a curbed or diked area. Remotely operated shut off valves to stop the flow to a pump should be considered wherever a release of hydrogen cyanide could prevent access to the pump. Pressure Relief Devices—In most cases» emergency pressure relief should be vented to a treatment device such as a flare or scrubber. In some cases, venting can be done to a catch tank although sizing the tank in such a situa- tion may be difficult. A pressure relief valve mounted above a rupture disk is suitable for hydrogen cyanide overpressure protection. The line below the relief valve should be continually purged, with nitrogen so as to prevent plugging the relief line by the vapor phase formation of hydrogen cyanide polymer. Two valves with rupture disks in parallel are recommended so that one device can be open to the tank while the other is in service. In such situations., it is important to interlock the valves that isolate the pressure relief valves from the process so that only one relief valve can be isolated from the process at one time. A relief valve is sized so that in the event of a polymerization - decomposition reaction, the temperature of the tank contents will be control- led by the boil off rate of hydrogen -cyanide. Thus, by controlling the temperature, the rate of polymerization will be controlled at a manageable level. One vendor suggests that relief devices on hydrogen cyanide storage tanks be set at 5 psig. This will allow for sufficient heat removal in the event of a polymerization - decomposition reaction (3). It is difficult to get a device that can accurately release at this low of a pressure. In some situations, two-phase flow through the relief valve may be possible and this must be considered. A thorough understanding of the kinetics of the hydrogen cyanide polymerization - decomposition reaction is 44 ------- important for sizing the relief device. Vendors of hydrogen cyanide have this kinetic data and will provide assistance for sizing overpressure protection. One vendor has combined kinetic data with the data developed by the Design Institute for Emergency Relief Systems. (DIERS) on two-phase releases to size relief valves for their customers (27). Where possible, pressure relief vent and treatment systems on hydrogen cyanide storage and handling equipment should not be connected to any other pieces of process equipment. This will help prevent cross-contamination between systems. A flame arrester may be used in the vent line. However. such a device should be cleaned frequently to prevent plugging by hydrogen cyanide polymer. Instrumentation—Instrumentation should be constructed of materials that are compatible with hydrogen cyanide service. In many cases wetted materials can be made of 316 SS or of an elastomer of plastic with hydrogen cyanide resistance. With the exception of high temperature operations, hydrogen cyanide is not a severe environment for most instrumentation. However, one • concern when using instrumentation with hydrogen cyanide is the potential for vapor phase polymerization. Such polymer could plug measuring wells or foul sensors and isolate the instrument from the actual process environment. Example solutions for this are the use of redundant instruments, the use of instruments that may be cleaned while in service or the use of nitrogen purge streams to keep the sensing element free from hydrogen cyanide polymer forma- tion (a nitrogen purge should be used with caution, as it could adversely affect the accuracy of some instruments). 5.3.2 Plant Siting and Layout • The siting and layout of a particular facility using hydrogen cyanide requires careful consideration of numerous factors. These include: other processes in the area, the proximity of population centers, prevailing winds. local terrain, and potential natural external effects such as flooding. The 45 ------- rest of this subsection describes general considerations which might apply to siting and layout of facilities that handle hydrogen cyanide. Siting of facilities or individual equipment items should be done in a manner that reduces personnel exposure, both plant and public, in the event of a release. Since there are also other siting considerations, there may be trade-offs between this requirement and others in a process, some directly related to safety. Siting should provide ready ingress or egress in the event of an emergency and yet also take advantage of barriers, either man-made or natural which could reduce the consequences of releases. Layout refers to the placement and arrangement of equipment in the process facility. General layout considerations include: • Inventories of hydrogen cyanide should be kept away from ' sources of fire or explosion hazard; • Vehicular traffic should not go too near hydrogen cyanide process or storage areas if this can be avoided; • Where such traffic is necessary, precautions should be taken to reduce the chances for vehicular collisions with equipment, especially pipe racks carrying hydrogen cyanide across or next to roadways; • Hydrogen cyanide piping preferably should not be located adjacent to other piping which is under high pressure or temperature; • Storage facilities should be segregated from the main process unless the hazards of pipe transport are felt to outweigh the hazard of the storage tank for site-specific cases; and 46 ------- * Storage should also be situated away from control rooms. offices, utilities, storage, and laboratory areas. Various techniques are available for formally assessing a plant layout and should be considered when planning high hazard facilities handling hydro- gen cyanide (28). These techniques provide for a systematic evaluation of key siting and layout factors. Because heat increases the tendency of hydrogen cyanide to undergo polymerization - decomposition, measures should be taken to situate piping. storage vessels, and other hydrogen cyanide equipment in such a way as to minimize their exposure to heat. Hot process piping, equipment, steam lines, and other sources of direct or radiant heat should be avoided. In the event of an emergency, there should be multiple means of access to the facility for emergency vehicles and crews. Storage vessel shut off valves should be readily accessible. Containment for liquid storage tanks can be provided by diking. Flammable gas detectors and adequate fire protection must be provided for all portions of the process as hydrogen cyanide is flammable when mixed with air. 5.3.3 Transfer and Transport Facilities Transfer and transport facilities where rail tankers are loaded and unloaded are potential accident areas because of vehicle movement and the intermittent nature of the operations. Therefore, special attention should be given to the design of these facilities. Rail car unloading and loading facilities should be equipped with the following safety and release prevention features: • Grounding connections for the car and rails; ------- • A car "come-along" for accurate positioning, wheel chocks, and derailers for runaway cars; • Warning signs and lights to identify the area and restrict access during the loading or unloading; • High pressure piping and hoses, connectors on hose ends that are unique for hydrogen cyanide service and that prevent accidental attachment of the vapor hose to the liquid line on the car. or the liquid receiving line to the vapor line of the car; • Rail car temperature monitor and alarm; • Deluge system for the rail car area, or at a minimum , sufficient fire hoses or monitors to act as a deluge in the even of a spill; and • Some type of drainage control system that prevents runoff from a spill from traveling into unwanted areas. Usually a tank car will be unloaded by applying nitrogen pressure to the vapor space, thereby pushing the liquid out through the rail car dip tube. As mentioned previously, nitrogen used for -hydrogen cyanide service must be free of any contamination. Additionally, back flow protection should also be provided in the nitrogen line. In some situations, unloading a tank car will require several hours. When this is the case, the tank car should be treated as a storage tank with periodic samples withdrawn from the car to test for the formation of polymer. Whenever tank cars are loaded or unloaded, written operating procedures should be developed and enforced. 48 ------- 5.4 PROTECTION TECHNOLOGIES This subsection describes three types of protection technologies for containment, treatment and neutralization. These are: • Enclosures; • Flares; and • Scrubbers. A presentation of more detailed information on these systems is planned in other portions of the prevention reference manual series. 5.4.1 Enclosures Enclosures refer to containment structures which capture any hydrogen- cyanide spilled or vented from storage or process equipment, thereby prevent- t ing immediate discharge of the chemical to the environment. The enclosures contain the spilled liquid until it can be transferred to other containment. discharged at a controlled rate which would not be injurious to people or the environment* or transferred at a controlled rate to scrubbers for neutraliza- tion or a flare or incinerator for destruction. The use of specially designed enclosures for either hydrogen cyanide storage or process equipment does not appear to be widely practiced. The location of toxic operations in the open air has been mentioned favorably in the literature, along with the opposing idea that sometimes enclosure may be appropriate (29). The desirability of an enclosure depends partly on the frequency with which personnel must be involved with the equipment. A common • . . design rationale tor not having an enclosure where toxic materials are used is to prevent the accumulation of toxic concentrations of a chemical within a work area. However, if the issue is protecting the community from accidental releases, then total enclosure may be appropriate. Enclosures should be equipped with continuous monitoring equipment and alarms. Alarms should sound 49 ------- whenever lethal or flammable concentrations are detected. Enclosures for hydrogen cyanide should he equipped with adequate fire protection. Care must he taken when an enclosure is huilt around" pressurized equip- ment. It would not he practical to design an enclosure to withstand the pressures associated with the sudden failure of a pressurized vessel. An enclosure would probably fail as a result of the pressure created from such a release and could create an additional hazard. In these situations, it may be determined that an enclosure is not appropriate. If an enclosure is built around pressurized equipment then it should be equipped with some type of explosion protection, such as rupture plates that are designed to fail before the entire structure fails. The type of containment structures that could be suitable for hydrogen cyanide are concrete block or concrete sheet buildings, or bunkers or cor- rugated metal buildings. An enclosure would have a ventilation system de- signed to draw in air when the'building is vented to a scrubber or flare.' The bottom section of a building used for stationary storage containers should be liquid tight to retain any liquid hydrogen cyanide that might be spilled. Buildings around rail car unloading stations do not lend themselves well to effective liquid containment. However, containment could be accomplished if the floor of the building were excavated several feet below the track level while the tracks are supported at grade in the center. While the use of enclosures for secondary containment of hydrogen cyanide spills or releases is not known to be widely used, it can be considered as a possible protection technology for areas near especially sensitive receptors. 5.4.2 Flares Flares are used in the chemical process industries to dispose of inter- mittent or emergency emissions of hydrogen cyanide waste gases. The flare 50 ------- burns the waste gases, forming carbon dioxide and nitrogen oxides. Flares are capable of handling larger flow variations than are process combustion devices such as boilers. The two common styles are elevated and enclosed ground flares. The height of an elevated flare (sometimes several hundred feet) is determined by safety considerations for the surrounding areas because of the high tempera- tures and heat flux at maximum gas rates. Enclosed ground flares consist of stages of multiple burner assemblies surrounded by refractory walls and acoustical insulation. They are generally used for small to medium flow rate applications. The elevated flare is- used for larger gas flows. Often, an enclosed ground flare will be used in conjunction with an elevated flare for economical operation. A flare system may collect gases from just one source or more often it may be used to treat gases from multiple sources within a process. Because most flare systems collect gases from a variety of sources within a plant, gas compositions and flow rates vary. Many units include venting steps to the flare system during processing. Overpressurization can also cause relief valves to vent gases to the flare system. Depending on the size of the flare system, accidental releases may constitute a large or small fraction of the instantaneous gas flow. The flow rate under an emergency release from a vessel could constitute a significant or negligible portion of the total flow rate to a flare. This would depend on the time interval over which the release occurred and the flow rate of other materials going to the flare at the same time. Flare designs range up to and above 2 million pounds per hour. Several design characteristics of flare systems are important when con- sidering their use as protection against accidental, chemical releases. The design of flares is dictated by the desire to: • Operate the flare safely over a wide range of gas flow- rates; and 51 ------- • Have acceptable emissions of radiant heat, toxic and flammable materials* and noise. A fundamental flare design variable is exit velocity. At maximum flow, the flame should not leave the burner tip or be blown out. This is achieved by limiting the exit velocity. A criterion has been recommended by the EPA to ensure 98 percent destruction efficiency of flared chemicals using a steam assisted flare (30). The addition of an accidental release discharge to an existing flare must not cause this maximum flow to be exceeded. Flares can be useful protection against accidental releases of hydrogen cyanide. However, because of potentially dangerous secondary hazards, their use requires a thorough analysis for each specific application. There are two possible ways a flare system can be used to protect against accidental releases. The first is to use an existing flare system. The second is to use a dedicated "emergency" system. In essence, a flare system is a pipe transporting flammable gases to a flame at the exit. As long as the flame remains at the end of the pipe, the system operates safely. The flame can enter the pipe if air or oxygen is present above a certain concentration in the fuel. In a dedicated flare system, the entire collection network would have to be continually purged to prevent the risk of an explosion when an accidental release occurred. Since the flare collection system operates under a positive pressure (above atmospheric). release rates from an emergency relief valve will be less than the same discharge to the atmosphere. In some instances, it is conceivable that the slight delay in reducing the pressure in a vessel nay cause tank damage. This may be especially important when rupture disks blow. A sudden overpressurization of the flare collection system due to a massive accidental release could damage the pipes or potentially affect the venting of other process units. Table 5-3 summarizes the factors that need to be considered to prevent accidental chemical releases when using a flare system. 52 ------- TABLE 5-3. IMPORTANT CONSIDERATIONS FOR USING FLARES TO PREVENT ACCIDENTAL CHEMICAL RELEASES « Maximum flow rate - will it cause a flame blowout? Will it cause mechanical damage due to vibration? • Possibility of air, oxygen, or other oxidant entering system? • Is gas combustible - will it smother the flare? • Will any reactions occur in collection system? • Can liquids enter the collection system? • Will liquids flash and freeze, or overload knockout drum? • Is back pressure of collection system dangerous to releasing vessel? • Is releasing vessel gas pressure or temperature dangerous to collection system? • Will acids or salts enter collection system? • Will release go to an enclosed ground or elevated flare? • If toxic is not destroyed, what are the impacts on surrounding community? 53 ------- The rationale for using flares to protect against accidental chemical releases is that flaring reduces the effects of an atmospheric emission from a process vessel. As long as the integrity of the flare system is not compro- mised, some lessening of the overall environmental impact'would he expected. It is difficult to estimate the destruction and removal efficiency (ORE) of flares because of the many variables associated with their operation. Numer- ous studies have been conducted to determine the operational performance of flares. EPA has published a set of flare requirements to ensure 98 percent or greater destruction of the gases (30). In an emergency condition, however, these conditions might not be met. In a screening study conducted by EPA. a 100 ppm hydrogen cyanide stream was only 85 percent controlled (31). Because of the variable flow capacity, high flame temperature, capability for handling a high gas velocity, and usual remote location, using a flare to prevent accidental chemical releases of hydrogen cyanide can be an effective technique. Small or isolated vessels in a process which does not require normal venting of a flammable gas, and that employ relief valves and rupture disks which may have never been used, are examples of sources that can be connected to a flare system to prevent accidental releases. 5.4.3 Scrubbers Scrubbers are a traditional method for absorbing toxic gases from process streams. These devices can be used to control hydrogen cyanide releases from vents and pressure relief discharges from storage equipment, process equip- ment, or secondary containment enclosures. Hydrogen cyanide discharges could be contacted with an aqueous scrubbing medium in any of several types of scrubbing devices. An alkaline solution is recommended to achieve effective absorption because absorption rates with water alone would require high liquid-to-gas ratios. However, water scrubbing could be used in a make-shift scrubber in an emergency if an alkaline solution 54 ------- was not available. Typical alkaline solutions for an emergency scrubber would be calcium hydroxide derived from slaked lime or sodium hydroxide. Examples of scrubber types that might be appropriate include spray towers, packed bed scrubbers, and Venturis. Other types of special designs might be suitable. Whichever type of scrubber is selected, a key considera- tion for emergency systems is the design flow rate to be used. A conservative design would use the maximum rate that would be expected from an emergency. Whatever type of scrubber is selected, a complete system would include the scrubber itself, a liquid feed system, and reagent makeup equipment. If such a system is used as protection against emergency releases, consideration must be given to how it would be activated in time to respond to an emergency load. One approach used in some process facilities is to maintain a continu- ous circulation of scrubbing liquor through the system. For many facilities this would not be practical, and the scrubber system might be tied into a trip system to turn it on when it is needed. However, with this system, a quantity of hydrogen cyanide would be released prior to actuation of the scrubber (i.e.. starting up a blower and turning on the flow of liquid). The scrubber system must be designed so as not to present excessive resistance to the flow of an emergency discharge. The pressure drop should be only a small fraction of the total pressure drop through the emergency dis- charge system. In general, at the liquid-to-gas ratios required for effective scrubbing, spray towers have the lowest, and Venturis the highest pressure drops. While packed beds may have intermediate pressure drops at proper liquid-to-gas ratios, excessive ratios or plugging can increase the pressure drop substantially. However, packed beds have higher removal efficiencies than spray towers or Venturis. In addition, the scrubber system must be designed to handle the "shock wave" generated during the initial stages of the release. This is particu- larly important for packed bed scrubbers since there is a maximum pressure with which the gas can enter the packed section without damaging the scrubber 55 ------- internals. Design of emergency scrubbers can follow standard techniques discussed in the literature, carefully taking into account the additional considerations just discussed. Another approach is the drowning tank, where the hydrogen cyanide vent is routed to the bottom of a large tank of uncirculating caustic. The drowning tank does not have the high contact efficiency of the other scrubber types. However, it can provide substantial capacity on demand as long as the back pressure of the hydrostatic head does not create a secondary hazard, by impeding an overpressure relief discharge, for example. 5.5 MITIGATION TECHNOLOGIES If. in spite of all precautions, a large release of hydrogen cyanide were to occur, the first priority would be to rescue workers in the immediate vicinity of the accident and evacuate persons from downwind areas. The source of the .release should be determined, and the leak should be stopped, if this is possible. The next primary concern is to reduce the consequences of the released chemical on the plant and the surrounding community. Reducing the consequences of an accidental release of a hazardous chemical is referred to as mitigation. Mitigation technologies include such measures as physical barriers, water sprays and fogs, and foams where applicable. The purpose of a mitigation technique is to divert, limit, or disperse the chemical that has been spilled or released to the atmosphere in order to reduce the atmospheric concentration and the area affected by the chemical. The mitigation tech- nology chosen for a particular chemical depends on the specific properties of the chemical including its flammability. toxicity. reactivity, and those pro- perties which determine its dispersion characteristics in the atmosphere. If a release occurs from a refrigerated, liquid hydrogen cyanide storage tank, the spilled liquid would heat up to ambient temperature. If the ambient temperature is above the boiling point of hydrogen cyanide (78.3°F). then heat transfer from the air and ground would result in rapid vaporization of the- released liquid. If the ambient temperature is below the boiling point of the 56 ------- hydrogen cyanide then vaporization would be slower but a vapor cloud is still likely to form. It is therefore desirable to minimize the area available for heat transfer to a liquid spill which in turn will minimize the rate of evaporation. Mitigation technologies which are used to reduce the rate of evaporation of a released liquid include secondary containment systems such as impounding basins and dikes. A post-release mitigation effort requires that the source of the release be accessible to trained plant personnel. Therefore, the availability of adequate personnel protection is essential. Personnel protection will typi- cally include such items as portable breathing air and chemically resistant protective clothing. 5.5.1 Secondary Containment Systems Specific types of secondary containment systems include excavated basins. natural basins, earth, steel, or concrete dikes, and high impounding walls. The type of containment system best suited for a particular storage tank or process unit will depend on the risk associated with an accidental release from that location. The inventory of hydrogen cyanide and its proximity to other portions of the plant and to the community should be considered when selecting a secondary containment system. The secondary containment system should have the ability to contain spills with a minimum of damage to the facility and its surroundings and with minimum potential for escalation of the event. Secondary containment systems for hydrogen cyanide storage facilities commonly consist of one of the following: • An adequate drainage system underlying the storage vessels which terminates in an impounding basin having a capacity as large as the largest tank served; and 57 ------- • A diked area, with a capacity as large as the largest tank served. These measures are designed to prevent the accidental discharge of liquid hydrogen cyanide from spreading to uncontrolled areas. The most common type of containment system is a low wall dike surrounding one or more storage tanks. Generally, for hydrogen cyanide, no more than one tank is enclosed within a diked area to reduce risk. Dike heights usually range from three to twelve feet depending on the area available to achieve the required volumetric capacity. The dike walls should be liquid tight and able to withstand the hydrostatic pressure and temperature of a spill. Low-wall dikes may be constructed of steel, or concrete. Earthen dikes should not be used to contain hydrogen cyanide spills, as the high acute toxicity of the chemical requires a high degree of certainty that the containment surface is impermeable to the spill. Piping should be routed over dike walls, and penetrations through the walls should be avoided if possible. Vapor fences may be situated on top of the dikes to provide additional vapor containment. If there is more than one tank in the diked area, the tanks should be situated on beams above the mflTi'nrnm liquid level attainable in the impoundment. A low-wall dike can effectively contain the liquid portion of an acci- dental release and keep the liquid from entering uncontrolled areas. By preventing the liquid from spreading, the low-wall dike can reduce the surface- area of the spill. Reducing the surface area will reduce the rate of evapora- tion. The low-wall dike will partially protect the spill from wind; this can reduce the rate of evaporation. A dike with a vapor fence will provide extra protection from wind and will be even more effective at reducing the rate of evaporation. A low-wall dike will not reduce the impact of a gaseous hydrogen cyanide release. If materials that would react violently with hydrogen cyanide are stored within the same diked area then the dike will increase the potential 58 ------- for mixing the materials in the event of a simultaneous leak. A dike also limits access to the tank during a spill. A covered, remote impounding basin is well suited to storage systems where a relatively large site is available. The flow from the hydrogen cyanide spill is directed to the basin by dikes and channels under the storage tanks which are designed to minimize contact of the liquid with other tanks and surrounding facilities. Because of the high vapor pressure of hydrogen cyanide and the high acute toxicity, the trenches that lead to the remote impounding basin as well as the basin itself should be covered to reduce the rate of evaporation. Additionally, the impounding basin should be located very near the tank area to minimize the amount of hydrogen cyanide that evaporates as it travels to the basin. The impounding basin could be filled with water to instantly dilute the liquid hydrogen cyanide as it flows into the basin. This type of system has several advantages. The spilled liquid is re- moved from the immediate tank area. This allows access to the tank during the spill and reduces the probability that the spilled liquid will damage tne tank, piping, electrical equipment, pumps or other equipment. In addition. the covered impoundment will reduce the rate of evaporation from the spill by protecting the spill from wind or heating from sunlight. High-wall impoundments may be a good secondary containment choice for selected systems. Circumstances which may warrant their use include limited storage site area, the need to minimize vapor generation rates, and/or the tank must be protected from external hazards. Maximum vapor generation rates will generally be lower for a high wall impoundment than for low wall dikes or remote impoundments because of the reduced surface .area exposed to the atmosphere. These rates can be further reduced with the use of insulation on the wall and floor in the annular space. High impounding walls may be constructed of low-temperature steel, reinforced concrete, or prestressed concrete. A weather shield may be provided between the tank and wall with the annular space remaining open to the atmosphere. The available area 59 ------- surrounding the storage tank will dictate the minimum height of the wall. For high wall impoundments, the walls may be designed with a volumetric capacity greater than that of the tank to provide vapor containment. Increasing the height of the wall also raises the elevation of any released vapor. One disadvantage of these dikes is that the high walls around a tank may hinder routine external observation. Furthermore, the closer the wall is to the tank, the more difficult it becomes to access the tank for inspection and maintenance. As with low wall dikes, piping should be routed over the wall if possible. The closeness of the wall to the tank may necessitate placement of the pump outside of the wall, in which case the outlet (suction) line will have to pass through the wall. In such a situation, a low dike encompassing the pipe penetration and pump may be provided, or a low dike may be placed around the entire wall. An example of the effect of diking as predicted by a vapor dispersion model is shown in Figure 5-1 (32). This figure shows hydrogen cyanide vapor clouds at the time when the farthest distance away from the source is exposed to concentrations above the IDLE. With diking, the model predicts that downwind distances up to 720 feet from the source of the release could be exposed to concentrations above the IDLH. Three minutes are required for the vapors to reach the maximum downwind distance. Without diking, the model predicts that downwind distances up to 2,600 feet from the source could be exposed to concentrations above the IDLE'. Thirteen minutes are required for the vapors to reach this distance. One further type of secondary containment system is one which is struc- turally integrated with the primary system and forms a vapor—tight enclosure around the primary container. Many types of arrangements are possible. A double-walled tank is an example of such an enclosure. These systems may be considered where protection of the primary container and containment of vapor for events not involving foundation or wall penetration failure are of great- est concern. Drawbacks of an integrated system are the greater complexity of 60 ------- •> BO.O •> BOO. •> a.ooo«+oa PPM O.S miles 1 mile l.S miles 2 miles Release from a tank surrounded by a 25 ft. diameter dike. Elapsed time: 3 minutes: Release from a tank with no dike. Elapsed time: 13 minutes Common Release Conditions; Storage Temperature • 40 F Storage Pressure - 14.7 psia Ambient Temperature - 85 °F Wind Speed • 10 mph Atmospheric Stability Class » C Quantity Releases = 5,000 gallons through a 2-inch hole Figure 5^1.• Computer'model simulation showing the effect of diking on the vapor cloud generated from a release of refrigerated hydrogen cyanide. 61 ------- the structure, the difficulty of access to certain components, and the fact that complete vapor containment cannot be guaranteed for all potential events. Provision should be made for drainage of rainwater from diked areas. This will involve the use of sumps and separate drainage pumps, since direct drainage to storm water sewers would presumably allow any spilled hydrogen cyanide to follow the same route. Alternately, a sloped rain hood may be used over the diked area which could also serve to direct the rising vapors to a single release point (33). The ground within the enclosure should be graded to cause the spilled liquid to accumulate at one side or in one corner. This will help to minimize the area of ground to which the liquid is exposed and from which it may gain heat. In areas where it is critical to minimize vapor generation, surface insulation may be used in the diked area to further reduce heat transfer from the environment to the spilled liquid. The floor of an impoundment should be sealed with clay or concrete to prevent the hydrogen cyanide from seeping into the ground. • 5.5.2 Flotation Devices and Foams Other possible means of reducing the surface area of spilled hydrogen cyanide include placing impermeable flotation devices on the surface or applying water-based foams. Placing an impermeable flotation device over a spilled chemical is a direct approach for containing toxic vapors with nearly 100 percent efficiency. However, being- able to use such devices requires acquisition in advance of a spill and storage until needed, and in all but small spills deployment may be difficult. The additional material and disper- sal equipment costs are a major deterrent to their use. The use of foams in vapor hazard control has been demonstrated for a broad range of volatile chemicals. Unfortunately, it is difficult to accu- rately quantify the benefits of foam systems, because the effects will vary as a function of the chemical spilled, foam type, spill size, and atmospheric conditions. With regard to liquefied gases, it has been found that with some 62 ------- materials, foams have a net positive effect, but with others, foams may tzaggerate the hazard. One approach to a hydrogen cyanide spill is dilution with water. Delug- ing a spill with water will dilute the spill and reduce the vapor generation rate. A water-based foam provides an alternative means of diluting the hydrogen cyanide. When a foam cover is first applied, an increase in the boil-off rate is generally observed which would cause a short-term increase in the downwind hydrogen cyanide concentration. The initial foam cover may be destroyed by violent boiling, in which case a second application ia necessary. Once a continuous layer is formed, a net positive effect will be achieved in the downwind area. The reduction in downwind concentration is a result of both increased dilution with air, because of a reduced vaporization rate, and the increased buoyancy of the vapor cloud. This latter effect is a result of the vapor being warmed as it rises through the blanket by heat transfer from the foam and by the heat of solution of hydrogen cyanide in water; the warmed vapor cloud will 'have greater buoyancy and will disperse in an upward direc- tion more rapidly. • The extent of the downwind reduction in concentration will depend on the type of foam used. Regardless of the type of foam used, the slower the drainage rate of the foam, the better its performance will be. A slow- draining foam will spread more evenly, show more resistance to temperature and pH effects, and collapse more slowly. The initial cost for a slow-draining foam may be higher than for other foams, but a cost effective system will be realized in superior performance. Even if the vaporization rate of hydrogen cyanide is substantially reduced within a short time after a spill, a vapor cloud will still be formed which poses a serious threat downwind. Dispersion and/or removal of the hydrogen cyanide vapor in the atmosphere is the subject of the following section. 63 ------- 5.5.3 Mitigation Techniques for Hydrogen Cyanide Vapor The extent to which the escaped hydrogen cyanide vapor can be removed or dispersed in a timely manner will be a function of the quantity of vapor re- leased, the ambient conditions, and the physical characteristics of the vapor cloud. The behavior and characteristics of the hydrogen cyanide cloud will be dependent on a number of factors. These include the physical state of the hydrogen cyanide before its release, the location of the release, and the atmospheric and environmental conditions. Many possibilities exist concerning the shape and motion of the vapor cloud, and a number of predictive models of dispersion have been developed. Large accidental releases of hydrogen cyanide may result in the formation of hydrogen cyanide-air mixtures which are denser than the surrounding atmosphere. This type of vapor cloud is especially hazardous, because it will spread laterally and remain close to the ground. One means of dispersing as well as removing toxic vapor from the air is with the use of water sprays or fogs. However, dilution of hydrogen cyanide with water results in the formation of highly toxic hydrocyanic acid which presents a health hazard to plant personnel. The spray medium is typically applied to the vapor cloud by means of hand-held hoses and/or stationary water-spray barriers. Important factors relating to the effectiveness of spray systems are the distance of the nozzles from the point of release, the spray pattern, nozzle flow rate, pressure, and nozzle rotation. Several techniques have also been developed to effectively disperse toxic vapor resulting from major leaks in piping and equipment. One such technique has been developed by Beresf ord (34). Although such a system has not been used for the mitigation of hydrogen cyanide vapor, they have been effectively used for other toxic chemicals of similar nature (34). Such techniques are not applicable to catastrophic failures of equipment, however. 64 ------- The method consists of coarse water sprays discharging upwards from flat fan sprays and wide-angled spray monitors arranged so that a vent or chimney effect is created to completely surround the toxic vapor. Results have shown that the high velocity water droplets induce large volumes of air at ground level to move upward as the water discharges upwards (34). The air is caused to move upwards through the chimney formed by the sprays. As the air moves over the ground, the heavier than air toxic gas is diluted and pushed up and out of the top of the chimney where it disperses safely. Design details are presented in Beresford (34). Both types of spray methods are incorporated into the design since the flat-fan sprays effectively stop the lateral spread of vapor and the monitors provide the -required air movement for dilution and dispersal. Another means of dispersing a vapor cloud is with the use of large fans or blowers which would direct the vapor away from populated or other sensitive areas (35). However, this method would only be feasible in very calm weather and in sheltered areas; it would not be effective in any wind and difficult to control if the release occupies a large open area. A large, mechanical blower would also be required which lowers the reliability of this mitigation tech- nique compared to water fogs and sprays. In general, techniques, used to disperse or control vapor emissions should emphasize simplicity and reliability. In addition to the mitigation tech- niques discussed above, physical barriers such as buildings and rows of trees will help to contain the vapor cloud and control its movement. 5.6 OPERATION AND MAINTENANCE PRACTICES Quality hardware, contained mechanical equipment, and protective devices all increase plant safety; however, they must be supported by the safety policies of management and by constraints on their operation and maintenance. This section describes how management policy and training, operation, and maintenance procedures relate to the prevention of accidental hydrogen cyanide releases. Within the chemical industry, these procedures and practices vary 65 ------- widely because of differences in the size and nature of the processes and because any determination of their adequacy is inherently subjective. For this reason, the following subsections focus primarily on fundamental princi- ples and do not attempt to define specific policies and procedures* 5.6.1 Management Policy Management is a key factor in the control of industrial hazards and the prevention of accidental releases. Management establishes the broad policies and procedures which influence the implementation and execution of specific hazard control measures. It is important that these management policies and procedures be designed to match the level of risk in the facilities where they will be used. Most organizations have a formal safety policy. Many make policy statements to the effect that safety must rank equally with other company functions such as production and sales. The effectiveness of any safety program, however, is determined by a company's commitment to it, as demonstrated throughout the management structure. Specific goals must be derived from the safety policy and supported by all levels of management. Safety and loss prevention should be an explicit management objective. Ideally, management should establish the specific safety performance measures, provide incentives for attaining safety goals, and commit company resources to safety and hazard control. The advantages of an explicit policy are that it sets the standard by which existing programs can be judged, and it provides evidence that safety is viewed as a significant factor in company operations. In the context of accident prevention, management is responsible for (29.36): • Ensuring worker competency; • Developing and enforcing standard operating procedures; • Adequate documentation of policy and procedures; 66 ------- • Communicating and promoting feedback regarding safety issues; • Identification, assessment, and control of hazards; and • Regular plant audits and provisions for independent checks. Additional discussion on the responsibilities of management will be found in a manual on control technologies, part of this manual series. 5.6.2 Operator Training The performance of operating personnel is a key factor in the prevention of accidental chemical releases. Many case studies documenting industrial incidents note the contribution of human error to accidental releases (29). Release•incidents may ie caused by using improper routine operating proce- dures, by insufficient knowledge of process variables and equipment, by lack of knowledge about emergency or upset procedures, by failure to recognize critical situations, and in some cases by direct physical mistake (e.g.. turning the wrong valve). A comprehensive operator training program can decrease the potential for accidents resulting from such causes. Operator training can include a wide range of activities and a broad spectrum of information. Training, however, is distinguished from education in that it is specific to particular tasks. While general education is important and beneficial, it is not a substitute for specific training. The content of a specific training program depends on the type of industry, the nature of the processes used, the operational skills required, the character- istics of the plant management system, and tradition. Some general characteristics of quality industrial training programs include: 67 ------- • Establishment of good working relations between management and personnel; • Definition of trainer responsibilities and training program goals; • Use of documentation, classroom instruction, and field training (in some cases supplemented with simulator training); • Inclusion of procedures for normal startup and shutdown. routine operations, and upsets, emergencies, and acci- dental releases; and • Frequent supplemental training and the use of up-to-date « training materials. • In many instances training is carried out jointly by plant managers and a training staff selected by management. In others, management is solely responsible for maintaining training programs. In either case, responsibili- ties should be explicitly designated to ensure that the quality and quantity of training provided is adequate. Training requirements and practices can be expected to differ between small and large companies, partly because of resource needs and availability, and partly because of differences in employee turnover. A list of the aspects typically involved in the training of process operators for routine process operations is presented in Table 5-4. Emergency training includes topics such as: • Recognition of alarm signals; 68 ------- TABLE 5-4. ASPECTS OF TRAINING PROGRAMS FOR ROUTINE PROCESS OPERATIONS Process goals, economics, constraints, and priorities Process flow diagrams Unit operations Process reactions, thermal effects Control systems Process materials quality, yields Process effluents and wastes Plant equipment and instrumentation Equipment identification Equipment manipulation Operating procedures Equipment maintenance and cleaning Use of tools Permit systems Equipment failure, services failure Fault administration Alarm monitoring Fault diagnosis Malfunction detection Communications, recordkeeping. reporting Source: Reference 29. 69 ------- • Performance of specific functions (e.g., shutdown switch- es); • Use of specific equipment; • Actions to be taken on instruction to evacuate; • Fire fighting; and • Rehearsal of emergency situations. Aspects specifically addressed in safety training include (29,36}: • Hazard recognition and communication, • Actions to be taken in particular situations. • Available safety equipment and locations, • When and how to use safety equipment, • Use and familiarity with documentation such as, - plant design and operating manuals, - company safety rules and procedures, - procedures relevant to fire, explosion, accident, and health hazards, - chemical property and handling information, and • First aid and CPR. Although emergency and safety programs typically focus on incidents such as fires, explosions, and personnel safety, it is important that prevention of accidental chemical releases and release responses be addressed as part of these programs. 70 ------- Much of the type of training discussed above is also important for management personnel. Safety training gives management the perspective necessary to formulate good policies and procedures, and to make changes that will improve the quality of plant safety programs. Lees suggests that train- ing programs applied to managers include or define (29): • Overview of technical aspects of safety and loss preven- tion approach. • Company systems and procedures. • Division of labor between safety personnel and managers in with respect to training, and • Familiarity with documented materials used by workers. 5.6.3 Maintenance and Modification Practices Plant maintenance is necessary to ensure the structural integrity 'of chemical processing equipment; modifications are often necessary to allow more effective production. However, since these activities are also a primary source of accidental release incidents, proper maintenance and modification practices are an important part of accidental release prevention. Use of a formal system of controls is perhaps the most effective way of ensuring that maintenance and modification are conducted safely. In many cases, control systems have had a marked effect on the level of failures experienced (29). Permit systems and up-to-date maintenance procedures minimize the poten- tial for accidents during maintenance operations. Permit-to-work systems control maintenance activities by specifying the work to be done, defining individual responsibilities, eliminating or protecting against hazards, and ensuring that appropriate inspection and testing procedures are followed. 71 ------- Maintenance permits originate with the operating staff. Permits may be issued in one or two stages. In one-stage systems, the operations supervisor issues permits to the maintenance supervisor* who is then responsible for his staff. Two-stage systems involves a second permit issued by the maintenance supervisor to his workforce (29). Another form of maintenance control is the maintenance information system. Ideally, these systems should log the entire maintenance history of equipment, including preventative maintenance, inspection and testing, routine servicing, and breakdown or failure maintenance. This type of system is also used to track incidents caused by factors such as human error, leaks, and fires, including identification and quantification of failures responsible for hazardous conditions, failures responsible for downtime, and failures respon- sible for direct repair costs. Accidental releases are frequently the result of some aspect of plant modification. Accidents result when equipment integrity and operation are not properly assessed following modification, or when modifications are made without updating corresponding operation and maintenance instructions. In these situations, it is important that careful assessment of the modification results has a priority equal to that of getting the plant on-line. For effective modification control, there must be established procedures for authorization, work activities, inspection, and assessment, complete documentation of changes, including the updating of manuals, and additional training to familiarize operators with new equipment and procedures (29,34). Formal procedures, and checks on maintenance and modification practices must be established to ensure that such practices enhance rather than adverse- ly affect plant safety. As with other plant practices, procedure development and complete documentation are necessary. However, training, attitude, and the degree to which the procedures are followed also significantly influence plant safety and release prevention. 72" ------- The use and availability of clearly defined procedures collected in naintenance and operating manuals is crucial for the prevention of accidental releases. Well written instructions should give enough information about a process that the worker with hands on responsibility for operating or main- • taining the process can do so safely, effectively, and economically. These instructions not only document the path to the desired results, but also are the basis for most industrial training programs (37.38). In the chemical industry, operating and maintenance manuals vary in content and detail. To some extent, this variation is a function of process type and complexity; however, in many cases it is a function of management policy. Because of their importance to the safe operation- of a chemical process, these manuals must be as clear, straightforward, and complete as possible. In addition. standard procedures should be developed and documented before plant startup. and appropriate revisions should be made throughout plant operations. Operation and maintenance may be combined or documented separately. Procedures should include startup, shutdown, hazard identification, upset conditions, emergency situations, inspection and testing, and modifications (29). Several authors think industrial plant operating manuals should include (29.36.37.38): • Process descriptions; • A comprehensive safety and occupational health section; • Information regarding environmental controls; • Detailed operating instructions, including startup and shutdown procedures; • Upset and'emergency procedures; • Sampling instructions; 73 ------- • Operating documents (e.g.. logs, standard calculations); • Procedures related to hazard identification; • Information regarding safety equipment; • Descriptions of job responsibilities; and • Reference materials. Plant maintenance manuals typically contain procedures not only for routine maintenance, but also for inspection and testing, preventive mainte- nance, and plant or process modifications. These procedures include specific items such as codes and supporting documentation for maintenance and modifi- cations (e.g., permits to work, clearance certificates), equipment identifi- cation and location guides, inspection and lubrication schedules, information on lubricants, gaskets, valve packings and seals, maintenance stock require- ments, standard repair times, equipment turnaround schedules, and specific inspection codes (e.g.. for vessels and pressure systems) (29). Full documen- tation of the maintenance required for protective devices is a particularly important aspect of formal maintenance systems. The preparation of operating and maintenance manuals, their availability. and the familiarity of workers with their contents are all important to safe plant operations. The objective, however, is to maintain this safe practice throughout the life of the plant. Therefore, as processes and conditions are modified, documented procedures must also be modified. 5.7 CONTROL EFFECTIVENESS It is difficult to quantify the control effectiveness of preventive and protective measures to reduce the probability and magnitude of accidental releases. Preventive measures, which nay involve numerous combinations of process design, equipment design, and operational measures, are especially 74 ------- difficult to quantify because they reduce the probability of a release rather than a physical quantity of chemical. Protective measures are more analogous to traditional pollution control technologies. Thus they may be easier to quantify in terms of their efficiency in reducing a quantity of chemical that could be released. Preventive measures reduce the probability of an accidental release by increasing the reliability of process systems operations and equipment. Control effectiveness can thus be expressed for both of the qualitative improvements achieved and quantitative improvements as probabilities. Table 5-5 summarizes what appear to be major design, equipment, and operational measures applicable to the primary hazards identified for the hydrogen cyanide applications in the U.S. The items listed in Table 5-5 are for illustration only and do not necessarily represent a satisfactory control option for all cases. These control options appear to reduce the risk associated with an accidental release when viewed from a broad perspective. However, there are undoubtedly specific cases where these control options will not be appropri- ate. Each case must be evaluated individually. A presentation of more information about reliability in terms of probabilities is planned in other volumes of the prevention reference manual series. 5.8 ILLUSTRATIVE COST ESTIMATES FOR CONTROLS This section presents cost estimates for different levels of control and for specific release prevention and protection measures for hydrogen cyanide storage and process facilities that might be found in the United States. 5.8.1 Prevention and Protection Measures Preventive measures reduce the probability of an accidental release from a process or storag'e facility by increasing the reliability of both process systems operations and equipment. Along with an increase in the reliability of a system is an increase in the capital and annual costs associated with incorporating prevention and protection measures into a system. Table 5-6 75 ------- TABLE 5-5. EXAMPLES OF MAJOR PREVENTION AND PROTECTION MEASURES FOR HYDROGEN CYANIDE RELEASES Hazard Area Prevention/Protection Temperature control of cyanide manufacturing reactor Flov control where acid stabilizer is added to hydrogen cyanide. Flow/composition control to continuous reactor using hydrogen cyanide. Overpressure Corrosion Reactor and reboiler temperatures Overfilling Atmosphere releases frc relief discharges Storage tank or line rupture Redundant temperature sensors; interlock feed flow to high temperature signal. Interlock preheater heating fluid flow to high temp signal. Pressure relief valve discharge sent to flare. Redundant flow control loops; acid addition line sized to restrict maximum possible flow. Redundant flow control loops; composition monitoring; level monitoring. Redundant pressure relief; not isolatable; adequate size; discharge not restricted. Increased monitoring with more frequent inspections; use of pH sensing on cooling water and steam condensate loops; use of corrosion coupons; visual inspections; non-destructive testing. Redundant temperature sensing and alarms. Redundant level sensing, alarms and interlocks; training of operators. Emergency vent scrubber system. Enclosure vented to emergency scrubber system; diking: foams; dilution; neutralization; water sprays. (continued) 76 ------- TABLE 5-5 (Continued) Hazard Area Prevention/Protection Human error Increased training and supervision; use of checklists; use of automatic systems. External fire Water sprays to cool exposed hydrogen cyanide storage vessels; siting away from other flammables; storage tank refrigeration systems. 77 ------- TABLE 5-6. ESTIMATED TYPICAL COSTS OF MAJOR PREVENTION AND PROTECTION MEASURES FOR HYDROGEN CYANIDE RELEASES Prevention/Protection Measure Continuous moisture monitoring Flow control loop Temperature sensor Pressure relief - relief valve - rupture disk Interlock system for flow shut-off pH monitoring Alarm system Level sensor - liquid level gauge - load cell Diking (based on a 10.000 gal. tank) - 3 ft. high - top of tank height (10 ft.) Increased corrosion inspection Capital Cost (1986 $) 7.500-10.000 4.000-6.000 250-400 1.000-2,000 1,000-1,200 1.500-2.000 7.500-10.000 250-500 1.500-2.000 10,000-15,000 1,200-1,500 7,000-7.500 Annual Cost (1986 $/yr) 900-1.300 500-750 30-50 120-250 120-150 17*5-250 900-1.300 30-75 175-250 1.300-1.900 150-175 850-900 200-400 Costs shown are for pressure relief device only and do not include other equipment items such as piping to scrubbers or flares. 78 ------- presents costs for some of the major design, equipment, and operational measures applicable to the primary hazards identified in Table 5-5 for the hydrogen cyanide applications in the United States. 5.8.2 Levels of Control Prevention of accidental releases relies on a combination of techno- logical, administrative, and operational practices as they apply to the design, construction, and operation of facilities where hazardous chemicals are used and stored. Inherent in determining the degree to which these practices are carried out is their costs. At a minimum, equipment and pro- cedures should be in accordance with applicable codes, standards, and regu- lations. However, additional measures can be taken to provide extra pro- tection against an accidental release. The levels of control concept provides a means of assigning costs to increased levels of prevention and protection. At the lower end of the tier is the "Baseline" system. This system consists of the elements -required for normal safe operation and basic prevention of an accidental release of hazard- ous material. The second level of control is "Level 1". "Level 1" includes the base- line system with added modifications such as improved materials of construc- tion, additional controls, and generally more extensive release prevention measures. The costs associated with this level are higher than the baseline system costs. The third level of control is "Level 2". This system incorporates both the "Baseline" and "Level 1" systems with additional modifications designed specifically for the prevention of an accidental release such as alarm and interlock systems. - The extra accidental release prevention measures incorpo- rated into "Level 2" are reflected in its cost, which is much higher than that of the baseline system. 79 ------- When comparing the costs of the various levels of control, it is impor- tant to realize that higher costs do not necessarily imply improved safety. The measures applied must be applied correctly. Inappropriate modifications or add-ons may not make a system safer. Each added control option increases the complexity of a system. In some cases the hazards associated with the * increased complexity may outweigh the benefits derived from the particular control option. Proper design and construction along with proper operational practices are needed to assure safe operation. These estimates are for illustrative purposes only. It is doubtful that any specific installation would find all of the control options listed in these tables appropriate for their purposes. An actual system is likely to incorporate some items from each of the levels of control and also some control options not listed here. The purpose of these estimates is to illus- trate the relationship between cost and control, and is not to provide an equipment check list. Levels of control cost estimates were prepared for a 29 ton fixed hydro- gen cyanide storage tank system with a 10.000 gallon capacity and a 2.000 gal. sodium cyanide reactor system. These systems are representative of storage and process facilities that might be found in the United States. 5.8.3 Summary of Levels of Control Table 5-7 presents a summary of the total capital and annual costs for each of the three levels of controls for the hydrogen cyanide storage system and the sodium cyanide reaction system. The costs presented correspond to the systems described in Table 5-8 and Table 5-9. Each of the level costs include the cost of the basic system plus any added controls. Specific cost informa- tion and breakdown for each level of control for both the storage and process facilities are presented in Tables 5-10 through 5-15. 80 ------- TABLE 5-7. SUMMARY COST ESTIMATES OF POTENTIAL LEVELS OF CONTROLS FOR HYDROGEN CYANIDE STORAGE TANK AND SODIUM CYANIDE REACTOR Systt Level of Control Total Total Capital Cost Annual Cost (1986 $) (1986 $/yr) Hydrogen Cyanide Storage Tank; 29 ton Fixed Storage Tank with 10•000 Gallon Capacity. Baseline Level No. 1 Level No. 2 100.000 12,000 141.000 17.000 360.000 43.000 Sodium Cyanide Reactor System 2.000 Gallon Continuous Reactor Baseline Level No. 1 Level No. 2 147.000 18.000 221.000 28.000 417.000 51.000 81 ------- TABLE 5-8. EXAMPLE OF LEVELS OF CONTROL FOR HYDROGEN CYANIDE STORAGE TANK Process: 29 Ton Fixed Hydrogen Cyanj.de Storage Tank - 10.000 gallon Controls Baseline Level No. 1 Level No. 2 Flow: 00 to Temperature: Pressure: Quantity: Location: Materials of Construction: Single check valve on tank process feed line. Temperature indicator and alarm. Single pressure relief valve, vent to flare. Pressure vacuum recorder alarm. Local level indicators and alarms. Away from traffic. flammables. and other hazardous processes. Carbon steel. Add second check valve. Add remote indicator. Add second relief valve. secure non-isolatable. Vent to flare. Add remote indicator. Same Carbon steel with increased corrosion allowance (1/16 inch). Add a reduced - pressure device with internal air gap and relief vent to con- tainment tank or scrubber. Add redundant sensors and alarms. Add redundant alarms. Add rupture disks under relief valves. Add redundant alarms and high-low level interlock shut-off for both inlet and outlet lines. Same Stainless steel. Type 316. (continued) ------- TABLE 5-8 (Continued) Controls Baseline Level No. 1 Level No. 2 oo Vessel: Piping:' Process Machinery: Enclosures: Diking: Release Protection: Tank pressure specification: Same 25 psig Tank pressure Specifica- tion: 50 psig. Schedule 40. stainless steel Schedule 80. stainless Schedule 80 Honel* steel Type 316 stainless steel Same submerged pumps. Same None 3 ft. high dike Shared flare system. None Steel Building Top of tank height. 10 ft. Same Dedicated flare system. Mitigation: None Foam system. Same ------- TABLE 5-9. EXAMPLE OF LEVELS OF CONTROL FOR SODIUM CYANIDE MANUFACTURE Process: Continuous sodium cyanide reactor Typical Operating Conditions: - Temperature: 1AO°F - Pressure: 100 mm Hg Controls Baseline Level No. 1 Level No. 2 Process: Temperature: Pressure: oo Flow: Corrosion: Use of acid stabilizing system. Provide temperature control with remote temperature indication and alarms. Provide remote control on vacuum system with remote pressure sensing. Single pressure relief valve to a shared flare system. Provide remote flow control on NaOH and HCN feed streams and on heating medium flow control. Provide periodic visual inspection. Composition: None Operate reactor at a lower temperature. Add redundant temperature sensors and alarms. Automatic switch to a cooling system. Add redundant remote pressure sensing and control with alarms. Add second relief valve. Vent to shared flare system. Add redundant flow control loops. Add increased monitoring with periodic ultronsonic inspection. Provide periodic testing for HCN polymer formation in reactor vessel. Use of interlocks and backup cooling systems. Add backup cooling system. Add rupture disks under relief valves. Vent to dedicated flare. Add automatic shut-off of feeds and automatic switch from heating to cooling medium. Add increased monitoring with more frequent testing. Periodic testing for HCN polymer formation in reactor vessel and in HCN feed. (Continued) ------- TABLE 5-9 (Continued) Controls Baseline Level No. 1 Level No. 2 OD Ol Material of Type 316 stainless Construction: steel-clad carbon steel. Vessel: Pressure specification: Full vacuum. 50 psig pressure. Piping: Schedule 40 Type 316 stainless steel. Process Centrifugal pump. Type 316 Machinery: stainless steel, double mechanical seal. Protective Curbing around reactor. Barrier: Enclosure: None. Flare: Shared flare system. Type 316 stainless steel-clad carbon steel with increase corrosion allowance. Pressure specification: Full vacuum. 100 psig pressure. Schedule 80 Type 316 stainless steel. Same. 3 ft. high retaining wall. None. Same. Monel* - clad carbon steel. Pressure specification: Full vacuum. 150 psig pressure. Schedule 80 Monel® Centrifugal pump. Monel* construction, double mechanical seal. Steel building. Dedicated flare system. ------- TABLE 5-10. CAPITAL AND ANNUAL COSTS ASSOCIATED WITH BASELINE HYDROGEN CYANIDE STORAGE SYSTEM Capital Cost Annual Cost (1986 $) (1986 $/yr) Vessels: Storage Tank 33.000 3.806 Piping and Valves: Pipework 10.000 1.100 Check Valve* 530 60 Globe Valves (20) 8.100 950 Relief Valve 1.600 190 Process Machinery: Submergihle Pumps (2) 13.000 1.500 Refrigeration System 22.000 2.500 Instrumentation: Local Temperature Indicator 1.900 220 Temperature Alarm 380 45 Pressure Gauges (2) 1.485 170 Pressure Alarm . 380 .45 Liquid Level Indicator 1.900 220 Level Alarm .380 45 Flare System: 4.500 520 Diking: Three-Foot High Concrete Dike 1.300 160 Procedures and Practices: Visual Tank Inspection (external) Visual Tank Inspection (internal) Relief Valve Inspection Piping Inspection Piping Maintenance Valve Inspection Valve Maintenance TOTAL COSTS 100.000 12.000 86 ------- TABLE 5-11. CAPITAL AND ANNUAL COSTS ASSOCIATED WITH LEVEL 1 HYDROGEN CYANIDE STORAGE SYSTEM Capital Cost Annual Cost (1986 $) (1986 $/yr) Vessels: Storage Tank 54.000 6.200 Piping and Valves: Pipework 15.000 1.800 Check Valves (2) 1.000 120 Globe Valves (20) 8.100 950 Relief Valve (2) 3.900 450 Process Machinery: Subnergible Pumps (2) 13.000 1.500 Refrigeration System 22,000 2,500 Instrumentation: Local Temperature Indicator 1.900 220 Remote Temperature Indicator 2.200 260 Temperature Alarm 380 45 Temperature Sensor 380 .45 Pressure Gauges (2) 1.485 170 Pressure Alarm 380 45 Liquid Level Indicator 1.900 220 Remote Level Indicator 2.200 260 Level Alarm 380 45 Flare System: 5.100 590 Diking: Ten-Foot High Concrete Dike 7.600 880 Procedures and Practices: Visual Tank Inspection (external) Visual Tank Inspection (internal) Relief Valve Inspection Piping Inspection Piping Maintenance Valve Inspection Valve Maintenance TOTAL COSTS . 141.000 17.000 87 ------- TABLE 5-12. CAPITAL AND ANNUAL COSTS ASSOCIATED WITH LEVEL 2 HYDROGEN CYANIDE STORAGE SYSTEM Capital Cost Annual Cost (1986 $) (1986 $/yr) Vessels: Storage Tank ' 240.000 28.000 Piping and Valves: Pipework 20.000 2.400 Check Valves (2) 1.000 120 Globe Valves (20) 8.100 - 950 Relief Valve (2) 3.900 450 Rupture Disks (2) 1.100 130 Process Machinery: Subotergible Pumps (2) 13.000 1.500 Refrigeration System 22.000 2.500 Instrumentation: Local Temperature Indicator 1.900 220 Remote Temperature Indicator 2.200 260 Temperature Alarms (2) 760 90 Temperature Sensor 380 . 45 Pressure Gauges (2) 1.485 170 Pressure Alarms (2) 760 90 Liquid Level Indicator 1.900 220 Remote Level Indicator 2.200 260 Level Alarms (2) 760 90 High-low Level Shutoff 1.900 220 Flare System: 22.000 2.600 Diking: Three-Foot High Concrete Dike 1.400 160 Enclosures: Steel Building 10.000 1.200 Procedures and Practices: Visual Tank Inspection (external) Visual Tank Inspection (internal) Relief Valve Inspection Piping Inspection Piping Maintenance Valve Inspection Valve Maintenance TOTAL COSTS 360.000 43.000 88 ------- TABLE 5-13. CAPITAL AND ANNUAL COSTS ASSOCIATED WITH BASELINE SODIUM CYANIDE REACTOR SYSTEM Capital Cost Annual Cost (1986 $) (1986 $/yr) Vessels: Reactor 84.000 10.000 Heat Exchanger 800 95 Piping and Valves: Pipework 10.000 1.100 Glove Valves (20) 8.100 950 Relief Valve 1.600 190 Process Machinery: Centrifugal Pump 6.300 760 Instrumentation: Remote Temperature Indicator 2.200 260 Temperature Alarm 380 45 Temperature Control: Controller 1.800 220 Sensor . 380 45 Control Valve 2.700 320 Remote Pressure Indicator 2.200 260 Pressure Alarm 380 45 Flow Control Loops (3): Controller 5.400 650 Flowmeter 6.800 850 Control Valve 8,400 1.000 Flare System: 4.500 520 Diking: Curbing Around Reactor 910 110 Procedures and Practices: Visual Tank Inspection (external) Visual Tank Inspection (internal) Relief Valve Inspection Piping Inspection Piping Maintenance Valve Inspection Valve Maintenance TOTAL COSTS 147.000 18,000 89 ------- TABLE 5-14. CAPITAL AND ANNUAL COSTS ASSOCIATED WITH LEVEL 1 SODIUM CYANIDE REACTOR SYSTEM Vessels: Reactor Heat Exchanger Piping and Valves: Pipework Glove Valves (20) Relief Valves (2) Process Machinery: Centrifugal Pump Instrumentation: Remote Temperature Indicator Temperature Alarms (2) Temperature Sensor Temperature Control: Controller Censor Control Valve Temperature Switch 'Remote Pressure Indicators (2) Pressure Control: Controller Sensor Control Valve Pressure Alarms (2) Flow Control Loops (3) : Controller Flowmeter Control Valve Flare System: Diking: Three-Foot High Retaining Wall Procedures and Practices: Visual Tank Inspection (external) Visual Tank Inspection (internal) Relief Valve Inspection Piping Inspection Piping Maintenance Valve Inspection Valve Maintenance TOTAL COSTS Capital Cost (1986 $) 153.000 800 10.000 8.100 3.200 6.300 2,200 760 380 1.800 380 2.700 540 4.300 1.800 380 2.700 760 5.400 1.400 8.400 4,500 1.300 221.000 Annual Cost (1986 $/yr) 18.000 95 1,100 950 380 760 260 90 45 220 45 320 65 520 220 45 320 90 650 850 1.000 520 200 15 60 15 300 120 30 350 28,000 90 ------- TABLE 5-15. CAPITAL AND ANNUAL COSTS ASSOCIATED WITH LEVEL 2 SODIUM CYANIDE REACTOR SYSTEM Capital Cost (1986 $) Annual Cost (1986 $/yr) Vessels: Reactor Heat Exchanger Piping and Valves: Pipework Glove Valves (20) Relief Valves (2) Rupture Disks (2) Process Machinery: Centrifugal Pump Instrumentation: Remote Temperature Indicator Temperature Alarms (2) Temperature Sensor Temperature Control: Controller Sensor Control Valve Temperature Switch Remote Pressure Indicators (2) Pressure Control: Controller Sensor Control Valve Pressure Alarms (2) Flow Control Loops (3): Controller Flowmeter Control Valve Flow Interlock Systems (2) Flare System: Diking: Three-Foot High Retaining Wall 300.000 790 18.700 8.500 3,400 1.100 9.300 2.200 780 350 1.800 390 2.800 SAO 4.300 1.800 390 2.800 780 5.400 7,000 8.400 3.900 22.000 1.600 36.000 95 2,200 950 380 130 1.100 260 90 45 220 45 3,20 65 520 220 45 320 90 650 850 1.000 430 2.600 200 (Continued) 91 ------- TABLE 5-15 (Continued) Capital Cost Annual Cost (1986 $) (1986 $/yr) Enclosure: Steel Building - 8.400 1.000 Procedures and Practices: Visual Tank Inspection (external) Visual Tank Inspection (internal) Relief Valve Inspection Piping Inspection Piping Maintenance Valve Inspection Valve Maintenance TOTAL COSTS 417,000 51.000 92 ------- 5.8.4 Equipment Specifications and Detailed Costs Equipment specifications and details of the capital cost estimates for the hydrogen cyanide storage and the sodium cyanide reactor systems are presented in Tables 5-16 through 5-23. 5.8.5 Methodology Format for Presenting Costs Estimates— Tables are provided for control schemes associated with storage and process facilities for hydrogen cyanide showing capital, operating, and total annual costs. The tables are broken down into subsections comprising vessels. piping and valves, process machinery, instrumentation, and procedures and practice. The presentation of the costs in this manner allows for easy comparison of costs for specific items, different levels, and different systc Capital Cost—All capital costs presented in this report are shown as total fixed capital costs. Table 5-24 defines the cost elements comprising total fixed capital as it is used here. The computation of total fixed capital as shown in Table 5-24 begins with the total direct cost for the system under consideration. This total direct cost is the total direct installed cost of all capital equipment comprising the system. Depending on the specific equipment item involved, the direct capital cost was available or was derived from uninstailed equipment costs by computing costs of installation separately. To obtain the total fixed capital cost, other costs obtained by utilizing factors are added to the total direct costs. The first group of other cost elements is indirect costs. These include engineering and supervision, construction expenses, and various other expenses such as administration expenses, for example. These costs are computed by multiplying total direct costs by a factor shown in Table 5-24. The factor is 93 ------- TABLE 5-16. EQUIPMENT SPECIFICATIONS ASSOCIATED WITH HYDROGEN CYANIDE STORAGE SYSTEM Equipment Itc Equipment Specification Reference VESSEL: Storage tank PIPING & VALVES Pipework Check Valve Globe Valve Relief Valve Reduced Pressure Device Rupture Disk PROCESS MACHINERY: Submerged Pump Baseline: 10.000 gal. ASTM AS16 grade 60 carbon steel* 25 psig rating Level #1: 10.000 gal. carbon steel with 1/8 inch corrosion protection. 25 psig pressure rating Level #2: 10.000 gal.. Type 316 stainless steel. 50 psig pressure rating Baseline: 100 ft. of 2 in. Schedule 40 Type 316 stainless steel Level II: 100 ft. of 2 in. Schedule 80 Type 316 stainless steel Level #2: 100 ft. of 2 in. Schedule 80 Monel» 2 in. vertical lift check valve. stainless steel construction 2 in. ANSI Class 300. Type 316 stainless steel body 1 in. z 2 in., ANSI Class 300 inlet and outlet flange, angle body, closed bonnet with screwed cap. Type 316 stainless steel body and trim Double check valve type device with internal air gap and relief valve 1 in. Type 316 stainless steel and carbon steel holder Type 316 stainless steel, submergible pump. 100 gpm capacity 39. 40. 41. 42 43 40. 44 39. 40. 44 40 39 39. 41. 45 39, 46 (Continued) 94 ------- TABLE 5-16 (Continued) Equipment Item Equipment Specification Reference INSTRUMENTATION Local Tempera- ture Indicator Remote Tempera- ture Indicator Temperature Sensor Temperature Alarm Pressure Gauge Pressure Alarm Level Alarm Level Indicator High-Low Level Shut-off Thermocouple, thermowell. and electronic indicator /recorder Transmitter and associated electronic indicator/recorder Thermocouple and associated thermowell Indicating and audible alarm Diaphragm sealed. Type 316 stainless steel diaphragm. 0-100 psig rating Indicating and audible alarm Indicating and audible alarm Electrical differential pressure type indicator Solenoid valve, switch and relay system 39. 40. 47 39. 47 39. 40. 47 40. 46. 48 39. 40. 47 40. 46. 48 40. 46. 48 39. 46 39. 40. 46. 47 ENCLOSURE: Building DIKING: Level #2: 26-gauge steel walls and roof, door, ventilation system Baseline: 6 in. concrete walls, 3 ft. high Level #1: 10 in. concrete walls, top of tank height (10 ft.) 46 46 (Continued) 95 ------- TABLE 5-16 (Continued) Equipment Item Equipment Specification Reference FLARE: Baseline and Level #1: Elevated flare' 49 system based on a release rate of 4,600 Ib/hr and a shared system with a total of five units Level #2: Elevated flare system based on above flow-rate and a dedicated unit for only this storage facility 96 ------- TABLE 5-17. MATERIAL AND LABOR COSTS ASSOCIATED WITH BASELINE HYDROGEN CYANIDE STORAGE SYSTEM vO 1986 Dollars • Vessels: Storage Tank Piping and Valves: Pipework Check Valve Globe Valves (20) Relief Valve Process Machinery: Submergible Pumps (2) Refrigeration System Instrumentation: Local Temperature Indicator Temperature Alarm Pressure Gauges (2) Pressure Alarm Liquid Level Indicator Level Alarm Flare System: Diking: Three-foot High Concrete Dike TOTAL COSTS Materials Cost 15,000 3.800 300 5.000 1.000 6.000 10.000 1.000 200 800 200 1.000 200 2.000 390 47.000 Labor Cost • 6.800 2.600 50 500 50 2.600 4.500 250 50 200 50 250 50 1.000 510 20.000 Direct Costs 22.000 6.400 350 5.500 1.100 8.600 14.500 1.250 250 1.000 250 1.250 250 3.000 900 97.000 Indirect Costs 7.700 2.200 130 1.900 380 3.000 5.000 440 90 350 90 440 90 1.100 320 23.000 Capital Cost 33.000 10.000 530 8.100 1.600 13,000 22.000 1.900 380 1.485 380 1.900 380 4.500 1.300 100.000 ------- TABLE 5-18. MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 1 HYDROGEN CYANIDE STORAGE SYSTEM vO 00 1986 Dollars Vessels: Storage Tank Piping and Valves: Pipework Check Valves (2) Globe Valves (20) Relief Valves (2) Process Machinery: Submergible Pumps (2) Refrigeration System Instrumentation: Local Temperature Indicator Remote Temperature Indicator Temperature Alarm Temperature Sensor Pressure Gauges (2) Pressure Alarm Liquid Level Indicator Remote Level Indicator Level Alarm Flare System: Diking: Ten-foot High Concrete Dike TOTAL COSTS Materials Cost 25.000 5.000 600 500 2.500 6.000 10.000 1.000 1.200 200 200 800 200 1.000 1.200 200 3.000 2.200 65.000 Labor Cost 11.000 5.200 100 500 100 2.600 4.500 250 300 50 50 200 50 250 300 50 1.400 2.900 30.000 Direct Costs 36.000 10.200 700 5.500 2.600 8.600 14.500 1.250 1.500 250 250 1.000 250 1.250 1.500 250 3.400 5.100 95.000 Indirect Costs 13.000 3.600 - 250 1.900 900 3.000 5.000 440 530 90 90 350 90 440 530 90 1.200 1.800 33.000 Capital Cost 54.000 15.000 1.000 8.100 3.900 13.000 22.000 1.900 2.200 380 380 1.485 380 1.900 k 2.200 380 5.100 7.600 141. OOO ------- TABLE 5-19. MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 2 HYDROGEN CYANIDE STORAGE SYSTEM vO vO 1986 Dollars Vessels: Storage Tank Piping and Valves: Pipework Check Valves (2) Globe Valves (20) Relief Valves (2) Rupture Disks (2) Process Machinery: Submergible Pumps (2) Refrigeration System Instrumentation: Local Temperature Indicator Remote Temperature Indicator Temperature Alarms (2) Temperature Sensor Pressure Gauges (2) Pressure Alarms (2) Liquid Level Indicator Remote Level Indicator Level Alarm (s) High-Low Level Shutoff Flare System: Diking: Three-Foot High Concrete Dike Enclosures: Steel Building TOTAL COSTS Materials Cost 110.000 8.000 600 5.000 2.500 650 6.000 10.000 1.000 1.200 400 200 800 400 1.000 1.200 400 1.000 10.000 390 4.600 165.000 Labor Cost 50.000 5.000 100 500 100 75 2.600 4.500 250 300 100 50 200 100 250 300 100 250 5.000 520 2.300 73.000 Direct Costs 160.000 14.000 700 5.500 2.600 725 8.600 14.500 1.250 1.500 500 250 1.000 500 1.250 1.500 500 1.250 15.000 910 6.900 238.000 Indirect Costs 56.000 5.000 250 1.900 900 260 3.000 5,000 440 530 180 90 350 180 440 530 180 440 5.300 320 2.400 84.000 Capital Cost 24.000 20.000 1.000 8.100 3.900 1.100 13.000 22.000 1.900 2.200 760 380 1.485 760 1.900 2.200 760 1.900 22.000 1.400 10.000 360.000 ------- TABLE 5-20. EQUIPMENT SPECIFICATIONS ASSOCIATED WITH SODIUM CYANIDE REACTOR SYSTEM Equipment Item Equipment Specification Heat Exchanger PIPING AND VALVES: Pipework Globe Valve Relief Valve Rupture Dish PROCESS MACHINERY: Centrifugal Pump carbon steel, full vacuum - 50 psig rating Level #1: Same as baseline with added corrosion allowance and full vacuum - 100 psig rating Level #2: 2.000 gal. Monel* clad carbon steel, full vacuum - 150 psig rating Type 316 stainless steel construction. 20 ft. of surface area, shell and tube type Baseline: 100 ft. of 2 inch Schedule Type 316 stainless steel Level #1: 100 ft. of 2 inch Schedule 80 Type 316 stainless steel Level #2: 100 ft. of 2 inch Schedule 80 Monel* 2 in. ANSI class 300. Type 316 stainless steel body 1 in. z 2 in. ANSI class 300 inlet and outlet flange, angle body, closed bonnet with screwed cap. Type 316 stainless steel body and trim 1 in. Type 316 stainless steel and carbon steel holder Baseline and Level #1: Single stage. 100 gpm capacity. Type 316 stainless steel construction, double mechanical seal Level #2: Same as above except Monel« construction Reference VESSEL: Reactor Baseline: 2.000 gal. stainless Type 316 steel-clad • 39. 41. 40. 42 39 43 39. 40. 44 40 39. 41. 45 40. 50 (Continued) 100 ------- TABLE 5-20 (Continued) Equipment Item Equipment Specification Reference INSTRUMENTATION: Local Temperature Indicator Remote Temperature Indicator Temperature Sensor Temperature Alarm Temperature Control Loop Temperature Switch Pressure Control Loop Remote Pressure Indicator Flow Control Loop Flow Interlock System DIKING: Thermocouple, thermowell. and electronic 39* 40, 47 indicator Transmitter and associated electronic 39, 47 indicator Thermocouple and associated thermowell 39. 40, 47 Indicating and audible alarm 34, 46, 48 PID controller, 2 in. globe control valve 39. 47 of stainless steel construction, and temperature sensor Two-stage switch with independently set 39. 47 actuation PID controller. 2 in. globe control valve 39, 47 of stainless steel construction, pressure sensor * Transducer, transmitter, and electronic 39. 47 indicator PID controller. 2 in. globe control valve 39, 47 of stainless steel construction. flowmeter Solenoid valve, switch, and relay system 39, 40, 46 Baseline: 0.5 ft. high concrete curbing 46 Level II & 2: 3 ft. high concrete retaining wall (Continued) 101 ------- TABLE 5-20 (Continued) Equipment Item Equipment Specification Reference ENCLOSURE: Level f2: 26 gauge steel walls and roof, 46 door, ventilation system Flare: Baseline and Level fl: Elevated flare 49 system based on a total release rated 5.000 Ib/hr and a shared system with a total of five units. Level #2: Same as above except that system is dedicated only to this system 102 ------- TABLE 5-21. MATERIAL AND LABOR COSTS ASSOCIATED WITH BASELINE SODIUM CYANIDE REACTOR SYSTEM o OJ 1986 Dollars Vessels: Reactor Heat Exchanger Piping and Valves: Pipework Globe Valves (20) Relief Valve Process Machinery: Centrifugal Pump Instrumentation: Remote Temperature Indicator Temperature Alarm Temperature Control: Controller Sensor Control Valve Remote Pressure Indicator Pressure Alarm Flow Control Loops (3): Controller Flowmeter Control Valve Flare System: Diking: Curbing Around Reactor TOTAL COSTS Materials Cost 40.000 500 3.800 5.000 1.000 3.000 1.200 200 1.000 200 1.500 1.200 200 3.000 3,900 4,500 2.000 500 73.000 Labor Cost 18.000 250 2.600 500 50 1.400 300 50 250 50 375 300 50 750 1.000 1.300 1.000 * 130 28.000 Direct Costs 58.000 550 6.400 5.500 1.100 4.400 1.500 250 1.250 250 1.875 1.500 250 3.750 4.900 5.800 3.000 630 101,000 Indirect Costs 15.000 140 2.200 1.900 380 1.100 380 90 320 90 470 380 90 940 1.200 1.500 1.100 160 27.000 Capital Cost 84.000 800 10,000 8.100 1.600 6.300 2.200 380 1.800 380 2.700 2.200 380 5.400 6.800 8.400 4.500 910 '147,000 ------- TABLE 5-22. MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 1 SODIUM CYANIDE REACTOR SYSTEM 1986 Dollars Vessels: Reactor Heat Exchanger Piping and Valves: Pipework Globe Valves (20) Relief Valves (2) Process Machinery: Centrifugal Pump Instrumentation: Remote Temperature Indicator Temperature Alarms (2) Temperature Sensor Temperature Control: Controller Sensor Control Valve Temperature Switch Remote Pressure Indicators (2) Pressure Control: Controller Sensor Control Valve Pressure Alarms (2) Materials Cost 73,000 500 3.800 5.000 2.000 3.000 1.200 400 200 1.000 200 1.500 300 2.400 1.000 200 1.500 400 Labor Cost 33.000 250 2.600 500 100 1.400 300 100 50 250 50 375 75 600 250 50 375 100 Direct Costs 106.000 550 6.400 5.500 2.200 4.400 1.500 500 250 1.250 250 1.875 375 3.000 1.250 250 1.875 500 Indirect Costs 27,000 140 • 2.200 1.900 760 1.100 380 180 90 320 90 470 95 760 320 90 470 180 Capital Cost 153.000 800 10.000 8.100 3.200 6.300 2.200 760 380 1.800 380 . 2.700 540 ' 4.300 1.800 380 2.700 760 (Continued) ------- TABLE 5-22 (Continued) o en 1986 Dollars Flow Control Loops (3): Controller Flowmeter Control Valve Flare System: Diking: Three-Foot High Retaining TOTAL COSTS Materials Cost 3.000 3.900 A.500 2.000 Wall 900 112.000 Labor Cost 750 1.000 1.300 1.000 230 45.000 Direct Costs 3.750 4.900 5.800 3.000 1.130 157.000 Indirect Costs 940 1.200 1.500 1.100 290 42.000 Capital Cost 5.400 1.400 8.400 4.500 1.300 221.000 ------- TABLE 5-23. MATERIAL AND LABOR COSTS ASSOCIATED WITH LEVEL 2 SODIUM CYANIDE REACTOR SYSTEM o cr> 1986 Dollars Materials Cost Vessels: Reactor 146.000 Heat Exchanger Piping and Valves: Pipework Globe Valves (20) Relief Valves (2) Rupture Disks (2) Process Machinery: Centrifugal Pump Instrumentation: Remote Temperature Indicator Temperature Alarms (2) Temperature Sensor Temperature Control: Controller Sensor Control Valve Temperature Switch Remote Pressure Indicators (2) Pressure Control: Controller Sensor Control Valve Pressure Alarms (2) 500 8.000 5.000 2.000 650 4.500 1.200 400 200 1.000 200 1.500 300 2.400 1.000 200 1.500 400 Labor Cost 66.000 250 5.000 500 100 75 2.000 300 100 50 250 50 375 75 600 250 50 375 100 Direct Costs 210.000 550 13.000 5.500 2.200 725 6.500 1.500 500 250 1.250 250 1.875 375 3.000 1.250 250 1.875 500 Indirect Costs 53.000 140 . 3.300 1.900 760 260 1.600 380 180 90 320 90 470 95 760 320 90 470 180 Capital Cost 300.000 790 18.700 8.500 3.400 1.100 9.300 2.200 780 350 1.800 390 2.800 • 540 4.300 1.800 390 2.800 780 (Continued) ------- TABLE 5-23 (Continued) 1986 Dollars Flow Control Loops (3): Controller Flowmeter Control Valve Flow Interlock Systems (2) Flare System: Diking: Three-Foot High Retaining Wall Enclosure: Steel Building TOTAL COSTS Materials Cost 3.000 3.900 4.500 2.000 10.000 900 4.600 206.000 Labor Cost 750 1.000 1.300 500 5.000 230 1.200 86.000 Direct Costs 3.750 4.900 5.800 2.500 15.000 1.130 5.800 292.000 Indirect Costs 940 1.200 1.500 880 3.800 290 1.500 75.000 Capital Cost 5.400 7.000 8.400 3.900 22.000 1.600 8.400 417.000 ------- TABLE 5-24. FORMAT FOR TOTAL FIXED CAPITAL COST Item No. Item Cost 1 Total Material Coat 2 Total Labor Cost — 3 Total Direct Cost Items 1+2 4 Indirect Cost Items (Engi- neering & Construction Expenses) 0.35 x Item 3a 5 Total Bare Module Cost Items (3 + 4) 6 Contingency (0.05 x Item 5)b 7 Contractor's Fee 0.05 x Item 5 B Total Fixed Capital Cost Items (5 + 6 + 7), aFor storage facilities, the indirect cost factor is 0.35. For process facilities, the indirect cost factor is 0.25. bFor storage facilities, the contingency cost factor is 0.05. For process facilities, the contingency cost factor is 0.10. 108 ------- approximate, is obtained from the cost literature, and is based on previous experience with capital projects of a similar nature. Factors can have a range of values and vary according to technology area and for individual technologies within an area. Appropriate factors were selected for use in this report based on judgement and experience. When the indirect costs are added to the total direct costs, total bare module cost is obtained. Some additional cost elements, such as contractor's fee and contingency are calculated by applying and adding appropriate factors to the total bare module cost as shown in Table 5-24 to obtain the total fixed capital cost. Annual Cost—Annual costs are obtained for each of the equipment items by applying a factor for both capital recovery and for maintenance expenses to the direct cost of each equipment item. Table 5-25 defines the cost elements and appropriate factors comprising these costs. Additional annual costs are incurred for procedural items such as valve and vessel inspections, for example. When all of these individual costs are added, the total annual cost is obtained. Sources of Information— The costs presented in this report are derived from cost information in existing published sources and also from recent vendor information. It was the objective of this effort to present cost levels for hydrogen cyanide process and storage facilities using the best costs for available sources. The primary sources of cost information are Peters and Timmerhaus (39). Chemical Engineering (51). and Valle-Riestra (52) supplemented by other sources and references where necessary. Adjustments were made to update all costs to a June 1986 dollar basis. In addition, for some equipment items. well documented costs were not available and they had to be developed from component costs. 109 ------- TABLE 5-25. FORMAT FOR TOTAL ANNUAL COST Item No. Item Cost 1 Total Direct Cost — 2 Capital Recovery on Equip- 0.163 x Item 1 merit Items* 3 Maintenance Expense on 0.01 x Item 1 Equipment Items 4 Total Procedural It* 5 Total Annual Cost Items (2-1-3 +4) a8ased on a plant life of ten years and an interest rate of ten percent. 110 ------- Costs in this document reflect the "typical" or "average" representation for specific equipment items. This restricts the use of data in this report to: • Preliminary estimates used for policy planning, • Comparison of relative costs of different levels or systems, and • Approximations of costs that might be incurred for a specific application. The costs in this report are considered to be "order of magnitude" with a +50 percent margin. This is because the costs are based on preliminary esti- mates and many are updated from literature sources. Large departures from the design basis of a particular system presented in this manual or the advent of a different technology might cause the system cost to vary by a greater extent than this. If used as intended, however, this document will provide a reason- able source of preliminary cost information for the facilities covered. * When comparing costs in this manual to costs from other references, the user should be sure the design bases are comparable and that the capital and annual costs as defined here are the same as the costs being compared. Cost Updating— All costs in this report are expressed in June 1986 dollars. Costs re- ported in the literature were updated using cost indices for materials and labor. Costs expressed in base year dollars may be adjusted to dollars for another year by applying costs indices as shown in the following equation: 111 ------- , , ^ new base year index new base year cost = old base year cost x . old base year index The Chemical Engineering (CE) Plant Cost Index was used in .updating cost for this report. For June 1986, the index is 316.3. Equipment Costs- Most of the equipment costs presented in this manual were obtained directly from literature sources of vendor information and correspond to a specific design standard. Special cost estimating techniques, however, were used in determining the costs associated with'vessels, piping systems, scrub- bers, diking, and enclosures. The techniques used are presented in the following subsections of this manual. Vessels—The total purchased cost for a vessel, as dollars per pound of weight of fabricated unit f.o.b. with carbon steel as the basis (January 1979 • dollars) were determined using the following equation from Peters and Timmerhaus (39): Cost = [50(Weight of Vessel in Pounds)~°*34] The vessel weight is determined using appropriate design equations as given by Peters and Timmerhaus (39) which allow for wall thickness adjustments for cor- rosion allowances, for example. The vessel weight is increased by a factor of 0.15 for horizontal vessels and 0.20 for vertical vessels to account for the added weight due to nozzles, manholes, and skirts or saddles. Appropriate factors are applied for different materials of construction as given in Peters and Timmerhaus (39). The vessel costs are updated using cost factors. Final- ly a shipping cost amounting to 10 percent of the purchased cost is added to obtain the delivered equipment cost. Piping—Piping costs were obtained using cost information and data presented by Yamartino (43). A simplified approach is used in which it is assumed that a certain length of piping containing a given number of valves. .112 ------- flanges, and fittings is contained in the storage or process facility. The data presented by Tamartino (43) permit cost determinations for various lengths, sizes, and types of piping systems. Using these factors, a repre- sentative estimate can b.e obtained for each of the storage and process facili- ties. Diking—Diking costs were estimated using Mean's manual (46) for re- inforced concrete walls. The following assumptions were made in determining the costs. The dike contains the entire contents of a tank in the event of a leak or release. Two dike sizes are possible: A three-foot high dike, six inches thick; and a top-of-tank height dike ten inches thick. The tanks are raised off the ground and are volumetrically included in the volume enclosed by the diking. These assumptions facilitate cost determination for any size diking system. Enclosures—Enclosure costs were estimated using Mean's Manual (46) for both reinforced concrete and steel-walled buildings. The buildings are assumed to enclose the same area and volume as the top-of-tank height dikes. The concrete building is ten inches thick with a 26-gauge steel roof an'd a metal door. The steel building has 26-gauge roofing and siding and metal door. The cost of a ventilation system was determined using a typical 1.000 scfm unit and doubling the cost to account for duct work and requirements for the safe enclosure of hazardous chemicals. Flares—Flare costs were estimated using the following equation from Vatavuk (49) based on the use of an elevated flare system for a high Btu gas system. Costs = 288 [Mass flow rate of gas]0*398 . A release rate of '4.600 Ib/hr was assumed for the storage vessel and an appropriate rate was determined for the process system based on the quantity of hazardous chemical present in the system at any one time. For the sodium 113 ------- cyanide reactor system, a release rate of 1.000 Ib/hr was assumed. In ad- dition* the shared systems were based on a combined discharge for five identi- cal units. The dedicated system was based on a single unit. The costs pre- sented are updated to June 1986 dollars. Installation Factors— Installation costs were developed for all equipment items included in both the process and storage systems. The costs include both the material and labor costs for installation of a particular piece of equipment. The costs were obtained directly from literature sources and vendor information or indirectly by assuming a certain percentage of the purchased equipment cost through the use of estimating factors obtained from Peters and Timmerhaus (39) and Valle-Riestra (52). Table 5-26 lists the cost factors used or the refer- ence from which the cost was obtained directly. Many of the costs obtained from the literature were updated to June 1986 dollars using a 10 percent per year .rate of increase for labor and cost indices for materials associated with installation. 114 ------- TABLE 5-26. FORMAT FOR INSTALLATION COSTS Equipment Item Factor or Reference VESSELS: Storage Tank 0.45 Expansion Tank 0.25 PIPING AND VALVES: Pipework Ref. 41 Reduced Pressure Device Ref. 38 Check Valves Ref. 38 Globe Valves Ref. 38 Relief Valves Ref. 38 Rupture Disks Ref. 38 • PROCESS MACHINERY: Centrifugal Pump 0.43 Gear Pump 0.43 INSTRUMENTATION: All Instrumentation Items 0.25 ENCLOSURES: Ref. 44 DIKING: Ref. 44 SCRUBBERS: 0.45 115 ------- SECTION 6 REFERENCES 1. Chemical Profile. Hydrogen Cyanide. Chemical Marketing Reporter. Schnell Publishing Company Inc., June 4, 1984. 2. Mark, Herman F.. Othmer, Donald F.. Overberger, Charles G., Seaborg. Glenn T. Kirk-Othmer Encyclopedia of Chemical Technology. 3rd edition. Volume 7. John Wiley & Sons, 1983. 3. Hydrogen Cyanide Storage and Handling. E.I. du Pont de Nemours & Company, Incorporated. Wilmington. OE. 1983. 4. Dean, J. (ed.). Lange's Handbook of Chemistry. Twelfth Edition. McGraw-Hill Book Company. New York, NY. 1979. 5. Chemical Emergency Preparedness Program Interim Guidance. Chemical Pro- files. 2 volumes. U.S. Environmental Protection Agency. Washington, DC, December 1985. 6. Tatken, R.L. and Lewis. R.J. (ed.). Registry of Toxic Effects of Chemical Substances. (RTECS). 1981-82 edition. 3 volumes. NIOSH Contract No. 210-81-8101. DHHS (NIOSH) Publication No. 83-107. June 1983. 7. U.S. Patent No. 3.360.335. 8. U.S. Patent No. 3.718.731. 9. U.S. Patent No. 3,104.945. 10. U.S. Patent No. 3.215.495. 11. U.S. Patent No. 2.680.761. 12. U.S. Patent No. 3.496.215. 13. U.S. Patent No. 3,536.748. 14. Lawler, G.M. (ed.). Chemical Origins and Markets. Fifth Edition. Chemical Information Services, Stanford Research Institute. 1977. 15. Methyl Methacrylate. 1983 Petrochemical Handbook Issue. Hydrocarbon Processing, Gulf Publishing Company. Houston. TX. November 1983. 16. Methyl Methacrylate. 1979 Petrochemical Handbook Issue. Hydrocarbon Processing, Gulf Publishing Company, Houston. TX, November 1979. 116- ------- 17. U.S. Patent No. 2.537.814. 18. Strong Outlook for Cyanuric Chloride. Chemical and Engineering News. July 26. 1976. 19. U.S. Patent No. 2.762.798. 20. U.S. Patent No. 2.993.754. 21. HCN Safety Symposium. E.I. DuPont DeNemours and Company. Memphis, TN. 22. McNaughton. K.J. (ed.). Materials Engineering I: Selecting Materials for Process Equipment. McGraw-Hill Publications Company, New York. NY, 1980. 23. Metals Handbook Ninth Edition. Volume 3. American Society for Metals. Metals Park. OH. 1980. 24. Harper. C.A. (ed.). Handbook of Plastics and Elastromers. McGraw-Hill Book Company. New York. NY. 1975. 25. Telephone conversation between D.S. Davis of Radian Corporation and a representative of Monsanto Corporation. St. Louis. MO. January 1987. 26. Green. D.W. (ed.). Perry's Chemical Engineer's Handbook. 6th edition, McGraw-Hill Book Company. New York. NY. 1984. • . 27. Telephone conversation between D.S. Davis of Radian Corporation and a representative of E.I. DuPont DeNemours and Company. Memphis. TN. January 1987. 28. Lewis. D.J. The Mond Fire, Explosion and TozLcity Index Applied to Plant Layout and Spacing. Loss Prevention, Volume 13. American Institute of Chemical Engineers, 1980. 29. Lees, Frank P. Loss Prevention in the Process Industries. Volumes 1 & 2. Butterworths. London. England, 1983. 30. Federal Register. Volume 50. April 16, 1985. pp. 14.941-14.945. 31. Pool. J.H. and Soelberg, N.R. Evaluation of the Efficiency of Industrial Flares: Flare Head Design and Gas Composition. EPA-600/2-85-106 (NTIS PB86-100559). Energy and Environmental Research Corporation, September 1985. 32. Radian Notebook No. 215. EPA Contract 68-02-3994. Work Assignment 94, Page 5. 1986. 33. Darts. J.J. and D.M. Morrison. Refrigerated Storage Tank Retainment Walls. Chemical Engineering Progress Technical Manual. Volume 23. Ameri- can Institute of Chemical Engineers. New York, NY, 1981. 117 ------- 34. Beresford. T.C. The Use of Water Spray Monitors and Fan Sprays for Dis- persing Gas Leakage. I. Chen. E. Symposium Proceeding. The Containment and Dispersion of Gases by Water Sprays, Manchester. England. 1981. 35. McQuaid. J. and A. P. Roberts. Loss of Containment - Its Effect and Con- trol, in Developments '82 (I. Chem. E. Jubilee Symposium). London. Eng- land. April 1982. 36. Chemical Manufacturers Association. Process Safety Management (Control of Acute Hazards). Washington. DC. May 1985. 37. Stus. T.F. On Writing Operating Instructions. Chemical Engineering. November 26. 1984. 38. Burk. A.F. Operating Procedures and Review. Presented at the Chemical Manufacturers Association Process Safety Management Workshop. Arlington. VA, May 7-8, 1985. 39. Peters. M.S. and K.D. Timmerhaus. Plant Design and Economics for Chemi- cal Engineers. McGraw-Hill Book Company. New York. NY. 1983. 40. Richardson Engineering Services. Inc. The Richardson Rapid Construction Cost Estimating System, Volume 1-4, San Marcos. CA. 1986. • 41. Pikulic. A. and H.E. Diaz. Cost Estimating for Major Process Equipment. Chemical Engineering. October 10, 1977. 42. Hall, R.S., J. Mat ley, and K.J. McNaughton. Cost of Process Equipment. Chemical Engineering. April 5. 1982. 43. Yarmartino. J. Installed Cost of Corrosion - Resistant Piping. Chemical Engineering. November 20, 1978. 44. Telephone conversation between J.D. Quass of Radian Corporation and a representative of Mark Controls Corporation. Houston, TX, August 1986. 45. Telephone conversation between J.D. Quass of Radian Corporation and a representative of Fike Corporation. Houston. TX. August 1986. 46. R.S. Means Company, Inc. Building Construction Cost Data, (44th Ed.) Kingston, MA. 1986. 47. Liptak, B.C. Cost of Process Instruments. Chemical Engineering. Seotem- ber 7, 1970. * 48. Liptak, B.C. Control - Panel Costs, Process Instruments. Chemical Engi- neering, October 5, 1970. 49. Vatavuk. W.M. and R.B. Neveril. Cost of Flares. Chemical Engineering February 21. 1983. 118 ------- 50. Green. D.W. (ed.). Perry's Chemical Engineers' Handbook (Sixth Edition). McGraw-Hill Book Company. New York. NY. 1984. 51. Coat indices obtained from Chemical Engineering. McGraw-Hill Publishing Company. New York. NY. June 1984, December 1985. and August 1986. 52. Valle-Riestra. J.F. Project Evaluation in the Chemical Process Indus- tries. McGraw-Hill Book Company. New York. NY. 1983. 119 ------- APPENDIX A GLOSSARY This glossary defines selected terms used in the text of this manual which might be unfamiliar to some users or which might be used differently by different authors. Accidental release; The unintentional spilling, leaking, pumping, purging, emitting, emptying, discharging, escaping, dumping, or disposing of a toxic material into the environment in a manner that is not in compliance with a plant's federal, state, or local environmental permits and results in toxic concentrations in the air that are a potential health threat to the surrounding community. Assessment; The process whereby the hazards which have been identified, are evaluated in order to provide an estimate for the level of risk. Containment/control; A system to which toxic emissions from safety relief discharges are routed to be controlled. A caustic scrubber and/or flare can be containment/control devices. These systems may serve the dual function of destrueting continuous process exhaust gas emissions. Enthalpy; A thermodynamic property of a chemical related to its energy content at a given condition of temperature, pressure and physical state. Enthalpy is the internal energy added to the product of pressure times volume. Numerical values of enthalpy for various chemicals are always based on the change in enthalpy from an arbitrary reference pressure and temperature, and physical state, since the absolute value cannot be measured. 120 ------- Facility: A location at which a process or set of processes are used to produce, refine or repackage chemicals, or a location where a large enough inventory of chemicals are stored so that a significant accidental release of a toxic chemical is possible. Hazard; A source of danger. The potential for death, injury or other forms of damage to life and property. Identification; The recognition of a situation, its causes and consequences relating to a defined potential, e.g. Hazard Identification. Mild steel; Carbon steel containing a maximum of about 0.25Z carbon. Mild steel is satisfactory for use where severe corrodants are not encountered or where protective coatings can be used to prevent or reduce corrosion rates to acceptable levels. Mitigation; Any measure taken to reduce the severity of the adverse effects associated with the accidental release of a hazardous chemical. > Passivation film; A layer of oxide or other chemical compound of a metal on its surface that acts as a protective barrier against corrosion or further chemical reaction. Plant; A location at which a process or set of processes are used to produce. refine, or repackage, chemicals. Prevention; Design and operating measures applied to a process to ensure that primary containment of toxic chemicals is maintained. Primary containment means confinement of toxic chemicals within the equipment intended for normal operating*conditions. Primary Containment; The containment provided by the piping, vessels and machinery used in a facility for handling chemicals under normal operating conditions. 121 ------- Probability/potential; A measure* either qualitative or quantitative, that an event will occur within some unit of time. Process; The sequence of physical and chemical operations for the production. refining, repackaging or.storage of chemicals. Process machinery; Process equipment, such as pumps, compressors, heaters, or agitators, that would not be categorized as piping and vessels. Protection; Measures taken to capture or destroy a toxic chemical that has breached primary containment, but before an uncontrolled release to the environment has occurred. Qualitative Evaluation; Assessing the risk of an accidental release at a facility in relative terms; the end result of the assessment being a verbal • description of the risk. Quantitative Evaluation; Assessing the risk of an accidental release at a facility in numerical terms; the end result of the assessment being some type of number reflects risk, such as faults per year or mean time between failure. Reactivity; The ability of one chemical to undergo a chemical reaction with another chemical. Reactivity of one chemical is always measured in reference to the potential for reaction with itself or with another chemical. A chemical is sometimes said to be "reactive", or have high "reactivity", without reference to another chemical. Usually this means that the chemical has the ability to react with common materials such as water, or common materials of construction such as carbon steel. Redundancy; For control systems, redundancy is the presence of a second piece of control equipment where only one would be required. The second piece of equipment is installed to act as a backup in the event that the primary piece of equipment fails. Redundant equipment can be installed to backup all or selected portions of a control system. 122 ------- Risk; The probability that a hazard may be realized at any specified level in a given span of time. Secondary Containment; Process equipment specifically designed to contain material that has breached primary containment before the material is released to the environment and becomes an accidental release. A vent duct and scrubber that are attached to the outlet of a pressure relief device are examples of secondary containment. Toxicity; A measure of the adverse health effects of exposure to a chemical. 123 ------- APPENDIX B TABLE B-l. METRIC (SI) CONVERSION FACTORS Quantity Length: Area: Volume: Mass (weight): Pressure: • Temperature Caloric Value; Enthalpy : Specific-Heat Capacity : Density : Concentration: Flowrate: Velocity: Viscosity: To Convert From in ft in2 *t? *3 ft3 gal Ib short ton (ton) short ton (ton) atm mm Hg . psia psig OJ °C Btu/lb Btu/lbmol kcal/gmol Btu/lb-9F lb/ft3 Ib/gal oz/gal quarts /gal gal /min ga^/day ft /min ft /min ft/sec centipoise (CP) To cm 9 cm* »5 cm3 m3 m3 kg Mg metric ton (t) kPa kPa kPa kPa* «c* K* kJ/kg kJ/kgmol kJ/kgmol kJ/kg-°C kg/»3 kg/< kg/m3 cm3/*3 m./min m3/day m /min m/min m/sec kg/m-s Multiply By 2.54 0.3048 6.4516 0.0929 16.39 0.0283 0.0038 0.4536 0.9072 0.9072 101.3 0.133 6.895 [(psig)+14.696] i(6.895) (5/9)x(«F-32) 8C+273. 15 2.326 2.326 4.184 4. 1868 16.02 119.8 7.490 25.000 0.0038 0.0038 0.0283 0.3048 0.3048 0.001 ^Calculate as indicated. 124 ------- TECHNICAL REPORT DATA (Please read Instructions on the reverse before completing) . REPORT NO. EPA-6007 8-87-034J 2. 3. RECIPIENT'S ACCESSION NO. 4. TITLE AND SUBTITLE Prevention Reference Manual: Chemical Specific, Volume 10: Control of Accidental Releases of Hydrogen Cyanide B. REPORT DATE September 1987 6. PERFORMING ORGANIZATION CODE '. AUTHOR(S) D. S. Davis, G. B. DeWolf. and J. D. Quass B. PERFORMING ORGANIZATION REPORT NO. DCN 87-203-024-98-35 I. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT NO. Radian Corporation 8501 Mo-Pac Boulevard Austin. Texas 78766 11. CONTRACT/GRANT NO. 68-02-3994. Task 94 12. SPONSORING AGENCY NAME AND ADDRESS EPA, Office of Research and Development Air and Energy Engineering Research Laboratory Research Triangle Park, NC 27711 13. TYPE OF REPORT AND PERIOD COVERED Task Final; 11/86 - 6/87 14. SPONSORING AGENCY CODE EPA/600/13 is.SUPPLEMENTARY NOTES AEERL project officer is T. Kelly Janes. Mail Drop 62B, 919/541 2852. i*. ABSTRACT repOrt discusses the control of accidental releases of hydrogen cya- nide (HCN) to the atmosphere. HCN has an IDLH (immediately dangerous to life and health) concentration of 50 ppm. making it an acute toxic hazard. Reducing the risk associated with an accidental release of HCN involves identifying some of the poten- tial causes of accidental releases that apply to the process facilities that use HCN. The manual identifies examples of potential causes and measures that may »be taken to reduce the accidental release risk. Such measures include recommendations on: plant design practices; prevention, protection, and mitigation technologies; and operation and maintenance practices. Conceptual cost estimates of example preven- tion, protection, and mitigation measures are provided. The accidental release of a toxic chemical at Bhopal, India, in 1984 was a milestone in creating an increased public awareness of toxic release problems. As a result of other, perhaps less dramatic, incidents in the past, portions of the chemical industry were aware of this problem long before Bhopal. These same portions of the industry have made ad- vances in this area. Interest in reducing the probability and consequences of acciden- tal toxic chemical releases that might harm workers within a process facility and people in the surrounding community prompted this and other similar manuals. KEY WORDS AND DOCUMENT ANALYSIS DESCRIPTORS b.lOENTIPIERS/OPEN ENDED TERMS c. COSATI Field/Group Pollution _ Maintenance Hydrogen Cyanide Cost Estimates Accidents Emission Toxicity Design Pollution Control Stationary Sources Accidental Releases 13 B 07B 13 L 14G 06T 05E 05 A, 14 A 8. DISTRIBUTION STATEMENT Release to Public 19. SECURITY CLASS (Thit Report) Unclassified 21. NO. OF PAGES 132 20. SECURITY CLASS (Thispage) Unclassified 22. PBICE Form 2230-1 (».731 125 ------- |