Table Of Content

Storage of Liquid Chlorine GEST 73/17 7th Edition January 2014 EURO CHLOR PUBLICATION This document can be obtained from: EURO CHLOR - Avenue E. Van Nieuwenhuyse 4, Box 2 - B-1160 BRUSSELS Telephone: 32-(0)2-676 72 65 - Telefax: 32-(0)2-676 72 41 GEST 73/17 7th Edition Euro Chlor Euro Chlor is the European federation which represents the producers of chlorine and its primary derivatives. Euro Chlor is working to:  improve awareness and understanding of the contribution that chlorine chemistry has made to the thousands of products, which have improved our health, nutrition, standard of living and quality of life;  maintain open and timely dialogue with regulators, politicians, scientists, the media and other interested stakeholders in the debate on chlorine;  ensure our industry contributes actively to any public, regulatory or scientific debate and provides balanced and objective science-based information to help answer questions about chlorine and its derivatives;  promote the best safety, health and environmental practices in the manufacture, handling and use of chlor-alkali products in order to assist our members in achieving continuous improvements (Responsible Care). *********** This document has been produced by the members of Euro Chlor and should not be reproduced in whole or in part without the prior written consent of Euro Chlor. It is intended to give only guidelines and recommendations. The information is provided in good faith and was based on the best information available at the time of publication. The information is to be relied upon at the user’s own risk. Euro Chlor and its members make no guarantee and assume no liability whatsoever for the use and the interpretation of or the reliance on any of the information provided. This document was originally prepared in English by our technical experts. For our members’ convenience, it may have been translated into other EU languages by translators / Euro Chlor members. Although every effort was made to ensure that the translations were accurate, Euro Chlor shall not be liable for any losses of accuracy or information due to the translation process. Prior to 1990, Euro Chlor’s technical activities took place under the name BITC (Bureau International Technique du Chlore). References to BITC documents may be assumed to be to Euro Chlor documents. January 2014 Page 2 of 26 GEST 73/17 7th Edition RESPONSIBLE CARE IN ACTION Chlorine is essential in the chemical industry and consequently there is a need for chlorine to be produced, stored, transported and used. The chlorine industry has co-operated over many years to ensure the well-being of its employees, local communities and the wider environment. This document is one in a series which the European producers, acting through Euro Chlor, have drawn up to promote continuous improvement in the general standards of health, safety and the environment associated with chlorine manufacture in the spirit of Responsible Care. The voluntary recommendations, techniques and standards presented in these documents are based on the experiences and best practices adopted by member companies of Euro Chlor at their date of issue. They can be taken into account in full or partly, whenever companies decide it individually, in the operation of existing processes and in the design of new installations. They are in no way intended as a substitute for the relevant national or international regulations which should be fully complied with. It has been assumed in the preparation of these publications that the users will ensure that the contents are relevant to the application selected and are correctly applied by appropriately qualified and experienced people for whose guidance they have been prepared. The contents are based on the most authoritative information available at the time of writing and on good engineering, medical or technical practice but it is essential to take account of appropriate subsequent developments or legislation. As a result, the text may be modified in the future to incorporate evolution of these and other factors. This edition of the document has been drawn up by the Equipment working group to whom all suggestions concerning possible revision should be addressed through the offices of Euro Chlor. January 2014 Page 3 of 26 GEST 73/17 7th Edition Summary of the Main Modifications in this version Section Nature All Merge with GEST 72/10 on pressure storage of liquid chlorine and adapt the terminology (refrigerated and non-refrigerated) All Clarification on double-jacketed storage tanks 3.2.5. Updated thermal insulation paragraph 3.4. Precision that stress relief is done after welding 4.2. Precision added for cases where chlorine withdraw is from the bottom of the tank 4.5.1. Removal of chlorinated fluorocarbons as example, as there is no practical experience mentioned 5.8. Added paragraph on inspection (after washing) 5.10. Addition of paragraph on fighting a big leak Table of Contents 1. GENERAL POINTS 6 1.1. The Choice between Storage with or without Refrigeration 6 1.2. Unit Capacities 6 1.3. Number of Storage Tanks 7 2. BASIC DESIGN AND LOCATION OF THE STORAGE SYSTEM 7 2.1. Design and Permits 7 2.2. Principle 8 2.3. Location 8 2.3.1. Outside or Inside Location 8 2.3.2. Protection from External Damage 8 2.3.3. Distance from Rails and Roads 8 2.3.4. Distance from Another Operating Process 8 2.3.5. Distance from the Boundary of the Factory 9 2.3.6. Distance between two Adjacent Storage Tanks 9 2.4. Bunding 9 2.5. Emergency Capacity 9 3. CONSTRUCTION OF STORAGE TANKS 10 3.1. Basis of Design 10 3.1.1. Design Pressure 10 3.1.2. Design Temperature 11 3.1.3. Corrosion Allowance 11 3.1.4. Thermal Insulation 12 3.2. Materials of Construction 12 3.2.1. Steel 12 3.2.2. Branches, Flanges, Nuts and Bolts 13 January 2014 Page 4 of 26 GEST 73/17 7th Edition 3.2.3. Pipework 13 3.2.4. Quality of Jointing Materials 13 3.2.5. Thermal Insulation 13 3.3. Foundations and Supports 14 3.3.1. Foundations 14 3.3.2. Supports 14 3.4. Stress Relief 14 3.5. Inspection and Testing 14 3.5.1. Inspection of Construction Materials 14 3.5.2. Inspection during Fabrication 15 4. ACCESSORIES 15 4.1. Branches 15 4.2. Valves and Isolation 16 4.3. Pipework 16 4.4. Measuring Equipment 17 4.5. Safety Equipment 17 4.5.1. Over and Under-Pressure 17 4.5.2. Protection of the External Shell 18 4.6. Filling Ratio 18 4.7. Thermal Expansion Bellows for Double-Jacketed Tanks 18 4.8. Filling, Emptying and Venting Equipment 19 4.8.1. Filling 19 4.8.2. Emptying 19 4.8.3. Venting 19 5. OPERATION 19 5.1. Cleaning and Drying before Chlorine can be Admitted 19 5.2. Leak Testing 19 5.3. Commissioning 20 5.4. Total Emptying 20 5.5. Reactive Materials 21 5.6. Filling and Emptying in Normal Operation 21 5.6.1. Quality of Chlorine Introduced 21 5.6.2. Temperature and Pressure of the Liquid Chlorine Introduced 21 5.6.3. Emptying the Tank 21 5.7. Venting and Isolated Systems (Cold Chlorine Storage) 22 5.8. Periodic Inspection and Testing 22 5.8.1. External inspection 22 5.8.2. Internal inspection 23 5.9. Methods of Protection and Alarm 23 5.10. Response to a significant loss of primary containment - Methods and Equipment 24 6. REFERENCES 25 January 2014 Page 5 of 26 GEST 73/17 7th Edition DEFINITIONS This recommendation concerns storage systems provided by fixed liquid chlorine storage tanks constructed to operate with or without refrigeration. 1. GENERAL POINTS 1.1. The Choice between Storage with or without Refrigeration Ambient temperature chlorine storage means storage at high pressure. The advantages of ambient temperature storage are:  Simplicity of operation  Easy visual external inspection (no thermal insulation)  Lower investment cost Refrigerated chlorine storage means storage at lower pressure, in some cases at atmospheric pressure. The advantages of refrigerated storage are:  Lower initial emission in case of loss of containment if at atmospheric pressure (lower initial flash of chlorine gas due to the fact that liquid chlorine is at lower temperatures compared to pressurized storage) The complexities of refrigerated storage and its associated systems mean it is unsuitable for small chlorine users. 1.2. Unit Capacities In order to minimise hazard, the inventory should be limited to the minimum strictly necessary. The unit capacity is chosen taking into account:  The process requirements (operation continuity, maintenance/inspections works),  The loading/off-loading requirements; the tank must normally be larger than the contents of one mobile tanker. Based on practical long term field experience, the probability of a total tank failure can be assumed as negligible. The most important safety feature depends primarily on the design, operation and inspection of the storage system. January 2014 Page 6 of 26 GEST 73/17 7th Edition 1.3. Number of Storage Tanks In order to provide the desired storage capacity and the continuity of the supply, a compromise may be required between the individual unit capacities and the number of storage tanks. It should be noted that increasing the number of tanks leads to a proportional increase in the number of accessories, with the related various risks of mal- operation and mal-functioning. It is therefore desirable to limit the number of tanks, without forgetting the necessity of an available safety capacity (see point 2.5.). 2. BASIC DESIGN AND LOCATION OF THE STORAGE SYSTEM 2.1. Design and Permits A careful risk assessment study, periodically updated, is necessary to ensure that the required level of safety is attained. The methods used should be agreed with the relevant national/local authorities. In some countries scenarios and models are required. Some consideration is given below to the choice of the worst case scenario (see paragraph 2.2. Principles). Simple models are usually sufficient to evaluate the physical effects. However, relevant expertise is always needed to define the scenarios, to use and to interpret the results of such models correctly. To assess the effect on people (workers and neighbouring population) recognised toxicity “probit function”1 will be used. The study must show that the risk is acceptable and that adequate measures have been taken to protect people and the environment. In some cases, storage tanks may be designed with double jacket; Usually, double jacket means that the outer wall is designed to resist a lower pressure than the inner wall as it is primarily used to monitor possible small leaks of the chlorine inner storage tank (for example PN 10). The space inside the double jacket should be monitored, e.g. by a permanent flow of dry air or nitrogen with a chlorine detector at the outlet of the flushing gas with alarm; alternatively the space can be kept under nitrogen pressure with alarm. 1 The probit function is a statistical function describing the range of susceptibility in a population to a harmful consequence; it uses a criterion in the form of an equation which expresses the percentage of a defined population which will suffer a defined level of harm (normally death) when exposed to a specified dangerous load (time and intensity/concentration).. January 2014 Page 7 of 26 GEST 73/17 7th Edition In some cases, the outer wall is also used as bunding and its design conditions will then be identical to those of the inner wall. 2.2. Principle Liquid chlorine bulk storage could be the potential source of the worst case of loss of primary containment. However, a chlorine storage system can be designed and operated safely so that the risk of complete tank failure and release of much of its contents can be assumed negligible. The principles which must be followed to achieve this are discussed in the following chapters. It is also recommended to use GEST 87/130 - Hazard Analysis for Chlorine Plant' for the design of the storage system. 2.3. Location 2.3.1. Outside or Inside Location Storage system can be located in the open air or in a closed building. The decision on this matter must be based on a careful risk assessment taking into account the advantages and disadvantages of each alternative listed in the Position paper XII - Memorandum on Confinement of Liquid Chlorine Plants. 2.3.2. Protection from External Damage Chlorine storage must be located in an area with protective barriers so that it is fully protected from external damage from vehicle impact. The location and design of a storage tank has to be chosen to minimise the possible effects resulting from traffic (see 2.3.3), flooding, subsidence, earthquake, fire or explosion in a neighbouring plant. 2.3.3. Distance from Rails and Roads Installations should be located at least 25 m from public roads and railway lines to minimise the risk of damage to the storage in the event of an accident. This distance has to be defined taking into account the local conditions, rules and regulations. 2.3.4. Distance from Another Operating Process If a neighbouring unit does not present risk of fire or explosion, the minimum recommended separation is 10 m taking into account the local situation. January 2014 Page 8 of 26 GEST 73/17 7th Edition If a fire or explosion risk exists, greater distances or means of protection will be required. These must be established for each individual case, based on a risk assessment and taking any national and local rules and regulations into account. 2.3.5. Distance from the Boundary of the Factory The minimum recommended separation is 10 m taking into account the local situation and the size of the storage. In all cases, suitable fences, together with adequate security supervision, should be provided to prevent unauthorised access (see also GEST 05/316 – Guideline for site security of chlorine production facilities). 2.3.6. Distance between two Adjacent Storage Tanks It is recommended that sufficient distance should be provided between adjacent storage tanks, to give good access to the tanks for operation, maintenance and inspection, and to permit the passage of personnel equipped with self-contained breathing apparatus in case of incident. 2.4. Bunding All above ground storage tanks should be placed in a liquid tight bund. The volume of the bund should be calculated to receive at least the full contents of the worst realistic case scenario. A retention capacity of one storage tank is generally considered adequate. As a single bund may contain more than one storage tank, its capacity shall be based on the largest tank contained. The bund should be designed to limit the surface area in order to reduce the rate of evaporation of liquid chlorine in the event of a leakage, but without restricting access (see sections 5.9 and 5.10. The bund shall never be directly connected to a drain. Collected water (rain …) shall be removed by a pump or an ejector which shall be manually operated only after checks on the bund contents. In case of double-jacketed tank, the outer wall can be designed to provide such a bunding facility. 2.5. Emergency Capacity It is essential that a damaged storage tank can be emptied rapidly into a spare capacity, preferably a spare tank. If the emergency capacity is in the form of an empty tank, there should be a means to maintain it at low pressure, e.g. a system of degassing to an January 2014 Page 9 of 26 GEST 73/17 7th Edition absorption system or a chlorine consuming unit, or a large liquefaction set, the reliable operation of which should be assured. The use of a double-jacketed storage tank with the external wall designed as bunding facility means that any chlorine leakage will be contained and will not affect the external environment. In this case it is therefore not necessary to provide spare capacity to which the contents of a leaking tank can be immediately transferred. 3. CONSTRUCTION OF STORAGE TANKS 3.1. Basis of Design 3.1.1. Design Pressure The design pressure should be chosen on the basis of detailed consideration of all circumstances which will arise during operation of the storage system. The principal factor to be taken into account is the vapour pressure of chlorine at the maximum temperature to which the storage system can be subjected. Allowance must also be made for the maximum pressure resulting from the presence of any padding gas. Once the design pressure has been chosen, all reasonable measures must be taken to ensure that it is not exceeded in the course of subsequent operations. It is also necessary to consider a minimum design pressure. In case of double-jacketed tank, these minimum and maximum design pressures have to be determined both for the internal and the external shells. Storage tank (inner shell in case of double-jacketed tank) The minimum design pressure should be calculated taking into account:  the minimum temperature of the chlorine introduced  the means of emptying and venting chlorine (connection to absorption unit or suction of a compressor)  the maximum venting rate, even under accidental circumstances  the pressure from any purge gas between the two walls of double- jacketed tanks  the possible accidental presence of some chlorine between the two walls of double-jacketed tanks. January 2014 Page 10 of 26