Chlorine Reference Manual

7/24/2019 Chlorine Reference Manual

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THE CHLORINE REFERENCE MANUAL

GEST 06/317

1st

Edition

July 2008

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


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Euro Chlor

Euro Chlor is the European federation which represents the producers of chlorineand its primary derivatives.

Euro Chlor is working to:

improve awareness and understanding of the contribution that chlorinechemistry has made to the thousands of products, which have improved ourhealth, nutrition, standard of living and quality of life;

maintain open and timely dialogue with regulators, politicians, scientists, themedia and other interested stakeholders in the debate on chlorine;

ensure our industry contributes actively to any public, regulatory or scientificdebate and provides balanced and objective science-based information tohelp answer questions about chlorine and its derivatives;

promote the best safety, health and environmental practices in themanufacture, handling and use of chlor-alkali products in order to assist ourmembers in achieving continuous improvements (Responsible Care).

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This document has been produced by the members of Euro Chlor and should not be reproduced inwhole 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 goodfaith and was based on the best information available at the time of publication. The information is

to be relied upon at the users own risk. Euro Chlor and its members make no guarantee andassume 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 membersconvenience, it may have been translated into other EU languages by translators / Euro Chlormembers. 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 Chlors technical activities took place under the name BITC (BureauInternational Technique du Chlore). References to BITC documents may be assumed to be to Euro

Chlor documents.


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RESPONSIBLE CARE IN ACTION

Chlorine is essential in the chemical industry and consequently there is a need forchlorine to be produced, stored, transported and used. The chlorine industry has

co-operated over many years to ensure the well-being of its employees, localcommunities and the wider environment. This document is one in a series whichthe European producers, acting through Euro Chlor, have drawn up to promotecontinuous improvement in the general standards of health, safety and theenvironment associated with chlorine manufacture in the spirit of ResponsibleCare.

The voluntary recommendations, techniques and standards presented in thesedocuments are based on the experiences and best practices adopted by membercompanies of Euro Chlor at their date of issue. They can be taken into account infull or partly, whenever companies decide it individually, in the operation of existingprocesses and in the design of new installations. They are in no way intended as asubstitute for the relevant national or international regulations which should be fullycomplied with.

It has been assumed in the preparation of these publications that the users willensure that the contents are relevant to the application selected and are correctlyapplied by appropriately qualified and experienced people for whose guidance theyhave been prepared. The contents are based on the most authoritative informationavailable at the time of writing and on good engineering, medical or technicalpractice but it is essential to take account of appropriate subsequent developmentsor legislation. As a result, the text may be modified in the future to incorporateevolution of these and other factors.

This edition of the document has been drawn up by the General TechnicalCommittee to whom all suggestions concerning possible revision should beaddressed through the offices of Euro Chlor.


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TABLE OF CONTENTS

SCOPE 8

1 THE CHLORINE INDUSTRY 9

1.1 General Information 9

1.2

Economical Aspects 9

2 CHLORINE MANUFACTURE 10

2.1 Production of Chlorine 10

2.1.1 Mercury Technology 11

2.1.2 Diaphragm Technology 13

2.1.3 Membrane Technology 14

2.2 Chlorine Treatment 16

2.2.1

Cooling 16

2.2.2 Purification 16

2.2.3 Drying 16

2.2.4 Compression 17

2.2.5 Liquefaction 17

2.3 Products Usages 18

2.3.1 Chlorine 18

2.3.2 Sodium Hydroxide 18

2.3.3

Hydrogen 19

3 PROPERTIES AND HAZARDS OF CHLORINE 19

3.1 Physical Properties 19

3.2 Reactivity 19

3.3 Hazards 19

3.3.1 Chlorine and Explosion Risk 19

3.3.2 Construction Materials 20

4

PROPERTIES AND HAZARDS OF HYDROGEN 21

5 PROCESS SAFETY MANAGEMENT 21

5.1 Site Security 21

5.2 Process Safety Information 21

5.2.1 Process Design Information 22

5.2.2 Mechanical Design Information 22

5.3 Process Hazards Analysis 22

5.4 Management of Change 22

5.5

Operating Procedures 23

5.6 Safe Work Practices 23

5.7 Mechanical Integrity 23


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5.8 Pre-Start-Up Safety Review 24

5.9 Emergency Response and Control 24

5.10 Investigation of Process Related Incidents 24

5.11 Audits of Process Hazards Management Systems 25

6

TRAINING 25

6.1 Personnel of the Facility 25

6.1.1 Topics covered 25

6.1.2 Initial Training 26

6.1.3 Refresher Training 26

6.1.4 Plant Modifications 26

6.2 Training of Road Tanker Drivers 26

7 SAFETY GUIDANCE 26

7.1

Chlorine Detection and Monitoring 26

7.1.1 Purpose of Chlorine Monitors 26

7.1.2 Chlorine Monitoring Systems 26

7.1.3 Arrangement 27

7.2 Preventing Major Hazards 27

7.2.1 Nitrogen Trichloride 27

7.2.2 Moisture 28

7.2.3

Hydrogen 28

7.3 Protective Equipment 29

8 HEALTH HAZARDS, TRAINING AND FIRST AID 30

8.1 Health Hazards and Toxicity of Chlorine 30

8.2 Monitoring Chlorine Exposure to Workers 31

8.3 Treatment of Chlorine Gassing 31

8.4 Exposition of workers to mercury 32

8.5 Electromagnetic Fields (EMF) 32

9

TECHNICAL GUIDANCE FOR THE FACILITY 33

9.1 Materials 33

9.1.1 Materials for Liquid Chlorine and Dry Chlorine Gas 33

9.1.2 Materials for Wet Chlorine Gas 33

9.2 Equipments 33

9.2.1 Piping 34

9.2.2 Valves 34

9.2.3

Bolts and Gaskets 37

9.2.4 Pumps 37

9.2.5 Instruments 37


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9.2.6 Liquid Chlorine Quality 37

9.2.7 Pressure Relief Systems 38

9.2.7.1 General Policy 38

9.2.7.2 Requirements for Provision of Relief Systems 38

9.2.7.3

Design Criteria 38

9.2.7.4 Arrangement 38

9.2.7.5 Operation 39

9.2.8 Back Flow Prevention 39

9.2.9 Services 40

9.2.9.1 Instrument Air 40

9.2.9.2 Effluent Drains 40

9.3 Chlorine Transfer Compressors 40

9.4

Chlorine Storage 40

9.5 Loading and Off-loading 41

9.5.1 Introduction 41

9.5.2 Piping Connections 41

9.5.3 Padding Gas Used for the Transfer 41

9.5.4 Venting Arrangements 42

9.5.5 Choice of Flexible Connections to the Tanker 42

9.5.6

Location of the Loading or Off-loading Station 42

9.5.7 Loading and Off-loading Procedure 43

9.5.8 Emergency Planning 44

9.6 Chlorine Vaporisers 44

9.7 Absorption Systems 44

9.7.1 Chemical Principles 45

9.7.2 Disposal of Hypochlorite Solution 46

9.7.3 Technical Design of Absorption Systems 46

9.7.4

Materials of Construction 47

10 TECHNICAL GUIDANCE FOR TRANSPORT 47

10.1 DESIGN AND CONSTRUCTION OF TRANSPORT EQUIPMENT 47

10.1.1 Design and Construction of Rail Tank Wagons 48

10.1.2 Design and Construction of Road Tankers 48

10.1.3 Design and Construction of ISO Containers 48

10.1.4 Design and Construction of Drums and Cylinders 48

10.2

TRANSPORT OF CHLORINE BY RAIL 48

10.3 TRANSPORT OF CHLORINE BY ROAD 49

10.4 HANDLING OF CHLORINE IN SMALL CONTAINERS 49


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10.4.1 Cylinders 50

10.4.2 Drums 50

10.4.3 Spheres 50

10.4.4 Drums and Transport Spheres Loading and Off-loading 50

10.5

MAINTENANCE OPERATIONS 50

11 CHLORINE ACCIDENTS 51

11.1 Emergency Assistance 51

11.2 Measures for Containing Chlorine Leaks 51

11.2.1 First Measures 51

11.2.2 Limiting a Chlorine Leak 51

11.2.3 Stopping a Chlorine Leak 52

11.2.4 Sealing 52

11.2.5

Containment 52

11.3 Learning from Experience 52

12 ENVIRONMENTAL PROTECTION 52

13 SWIMMING POOLS 54

14 REFERENCES 54

15APPENDICES 57

APPENDIX 1: SAFE TRANSPORT OF LIQUID CHLORINE BY RAIL TANKERVEHICLES - HIGHLIGHTS FROM GEST 80/89 58

1. Construction Code 58

2. Operation of Rail Tankers 58

3. Transport 59

APPENDIX 2: TRAINING OF CHLORINE ROAD TANKER DRIVERS -HIGHLIGHTS FROM GEST 73/20 60

1. Driving Skills and Procedures 60

2. Properties of Chlorine 60

3.

Equipment and Procedures for Handling Chlorine 60

4. Examples of Operating Hazards 61

TABLE OF FIGURES

Figure 1: Flow Diagram of the Three Main Chlor-Alkali Processes 11

Figure 2: Electrolyser and Decomposer of the Mercury Technology 12

Figure 3: Electrolyser of the Diaphragm Technology 13

Figure 4: Electrolyser of the Membrane Technology 15


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SCOPE

The objective of this document is to give a brief overview of the chlorine industrycovering general information, some economical aspects, chlorine manufacture,

consumption of products, and will mainly focus on the European safety,environmental protection and health aspects, referring to the Euro Chlor guidelinesand recommendations.

Safety aspects are of much concern in the chlor-alkali industry. Production,storage, loading, transportation and use of chlorine require compliance withcertain provisions designed to minimise the possibility of incidents potentiallydangerous for operators, the public or the plant. A general policy for the preventionof and response to industrial accidents is usually based on the prevention principle:the plant is constructed and operated in such a way as to prevent any uncontrolleddevelopment and to mitigate the consequences of accidents.

In the European Union, Member States agreed in 1982 on a Directive, theSEVESO Directive (82/501/EEC), as a means of controlling major industrialhazards connected with process and storage facilities where dangeroussubstances are present. The principles of the Directive set out:

General requirements for industries which use dangerous substances totake all preventive measures to reduce the risks and to inform neighbouringpopulations of such hazards

Requirements for authorities to control the activities and prepare appropriateemergency planning in the event of major accidents.

Since then, advancing knowledge and experience have provided new insights. The

"SEVESO II" Directive (96/82/EC) represents a fundamental revision of theDirective. Storage and processes using chlorine are part of the scope of theDirective starting from 10 tonnes, along with hydrogen starting from 5 tonnes, whilethe alkali solutions are not covered.

Although chlorine is a hazardous material in terms of reactivity and toxicity, it canbe produced, distributed and handled safely provided that appropriate precautionsand measures are realised.

Since 1952, Euro Chlor, previously known as BITC, has been active in promotingthe safe handling of chlorine and has developed guidelines. This present manual isa synthesis of papers already published dealing with chlorine production, handling,loading and off loading, transportation and use. The appropriate Euro Chlorrecommendations are mentioned in each section and must be consulted for moreprecise details.

These guidelines are not intended to replace existing relevant national orinternational regulations, which must be fully complied with. They supplementthese regulations by drawing on the detailed experience of chlorine producers.Reference to existing regulations is only made where it is considered necessary forthe purpose of clarification.

Euro Chlor recommends that these guidelines should be applied by all partiesinvolved in the chlorine activity (construction, production, maintenance, distributionand use) and asks them to report all accidents and incidents in order to continue toimprove by learning from experience.


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In order to facilitate effective management of safety in the overall process oftransportation, it is recommended that chlorine producers should check periodicallythe transport arrangements.

The main goal of Health documents is to provide sufficient information tomanagers, plant engineers and local occupational physicians to enable them to

protect the health of workers against harmful effects of chlorine and mercury;electromagnetic fields is also a topic considered in a specific guideline.

Environmental protection is essentially mercury oriented. The many yearsexperience of the companies has allowed developing recommendations explainingtechniques that minimise any contamination in the final products and dischargedstreams; wherever possible, the removed mercury within the process should alsobe recycled.

1 THE CHLORINE INDUSTRY

1.1 General Inform ation

The chlor-alkali industry is the industry that produces chlorine (Cl2) and alkali,sodium hydroxide (NaOH) or potassium hydroxide (KOH), by electrolysis of a saltsolution. The main technologies applied for chlor-alkali production are mercury,diaphragm and membrane cell electrolysis, mainly using sodium chloride (NaCl) asfeed or to a lesser extent using potassium chloride (KCl) for the production ofpotassium hydroxide.

This co-production of 1 tonne of chlorine, 1.128 tonne of sodium hydroxide (or 1.58tonne of potassium hydroxide) and 28 kg of hydrogen is usually referred to as ECU

(Electrochemical unit).Other electrochemical processes in which chlorine is produced include theelectrolysis of hydrochloric acid and the electrolysis of molten alkali-metal andalkaline-earth-metal chlorides, in which the chlorine is a by-product, but theseaccount for less than 5% of the total chlorine production capacity.

In 1800, Cruickshank was the first to prepare chlorine electrochemically. Theprocess was, however, of little significance until the development of a suitablegenerator and of synthetic graphite for anodes in 1892. These two developmentsmade possible the electrolytic production of chlorine, the chlor-alkali process, onan industrial scale. About the same time, both the diaphragm cell process

(Griesheim cell, 1885) and the mercury cell process (Castner-Kellner cell, 1892)were introduced. The membrane cell process was developed much more recently(1970). Currently, 95% of world chlorine production is obtained by the chlor-alkaliprocess.

Since 1970 graphite anodes have been largely superseded by activated titaniumanodes in the diaphragm and mercury cell processes. The newer membrane cellprocess uses only activated titanium anodes.

1.2 Econom ical Asp ects

Production of chlorine was very low in the 1800s and chlorine was only used forbleaching. In 1887, annual world production was 115 tonnes. Chlorine productionsince the 1940s has risen enormously, on the back of the burgeoning demand forplastics, notably PVC, isocyanates and polycarbonates. The production of


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chloroaromatics (e.g. chlorobenzene for phenol synthesis), propylene oxide(chlorohydrin process), solvents containing chlorinated hydrocarbons, andinorganic chlorine compounds are also important factors behind the increased useof chlorine after 1940.

After a fall at the beginning of the 1990s, production in Western Europe now

seems to be stabilised at around 10 millions tonnes per year. This placed it behindthe United States, with production a bit higher, but ahead of Japan. The globaldemand for both chlorine and caustic has been forecast to increase, althoughmainly in Latin America and Asia. In the recent years, the production of chlorine inChina has boomed. In 2005, Asia became the largest chlorine producer in theworld. The total world capacity was roughly split into Europe 26%, North America23% Asia 43% and 8% for the other regions.

Euro Chlor estimates that there are 46000 employees involved in the directproduction of chlorine in the EU. When chlorine derivatives and chlorine-dependentindustry are included the number of employees is approximately two millions.

2 CHLORINE MANUFACTURE

Since 1975, the membrane cell process has been developed to a high degree ofsophistication. It has ecological advantages over the two older processes and hasbecome an economically advantageous process in recent years. Despite theseadvantages, the change of technology to membrane cells has been slow inWestern Europe because most existing chlorine plants were installed in the 1970swith a plant life of 40-60 years and there has been no need for new productioncapacity.

The reference document on best available techniques in the chlor-alkali industryreflects an information exchange carried out according to Article 16(2) of CouncilDirective 96/61/EC. (Seehttp://eippcb.jrc.es/pages/FActivities.htm).

Best available techniques for the production of chlor-alkali are considered to bemembrane or non asbestos diaphragm technologies.

During the remaining life of mercury and asbestos diaphragm cell plants, allpossible measures should be taken to protect the environment as a whole.

2.1 Produ ct ion of Chlor in e

The chlor-alkali industry produces chlorine and caustic solution (sodium orpotassium hydroxide see section1.1)simultaneously by means of electrochemicaldecomposition by direct current of a solution of salt in water. Along with thechlorine and the caustic solution, hydrogen is produced. An industrial chlor-alkaliproduction unit comprises a series of operations, structured as shown in Figure 1here below.

There are three basic processes for the electrolytic production of chlorine, thenature of the cathode reaction depending on the specific process. These threeprocesses are the diaphragm cell process, the mercury cell process, and themembrane cell process. Each process represents a different method of keepingthe chlorine produced at the anode separate from the caustic soda and hydrogenproduced, directly or indirectly, at the cathode.
http://eippcb.jrc.es/pages/FActivities.htmhttp://eippcb.jrc.es/pages/FActivities.htmhttp://eippcb.jrc.es/pages/FActivities.htmhttp://eippcb.jrc.es/pages/FActivities.htm


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Figure 1: Flow Diagram o f the Three Main Chlor-Alkal i Processes

The basic principle in the electrolysis of a sodium chloride solution is the following:

ClNaNaCl

At the anode, chloride ions are oxidised and chlorine (Cl2) is formed.

eClClgaq

22)(2)(

At the cathode:

In the mercury process a sodium/mercury amalgam is formed andtransported to another equipment, the denuder, where hydrogen (H2)and hydroxide ions (OH-) are formed by the reaction of the sodium of

the amalgam with water.

In membrane and diaphragm cells, water decomposes in a separatecompartment to form hydrogen (H2) and hydroxide ions (OH

-).

The global cathode reaction is:

)()()(22)( 22222 aqaqgaq OHNaHeOHNa

The overall reaction is:

)(2)()(22)()( 22222

gaqaqaqaq HOHNaClOHClNa

2.1.1 Mercury Technology

As shown in Figure 2 below, the mercury cell process involves two "cells".


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Figure 2: Electrolys er and Decompos er of the Mercury Techn ology

In the primary electrolyser (brine cell) purified and saturated brine flows through anelongated trough that is slightly inclined from the horizontal. In the bottom of thistrough a shallow film of mercury (Hg) flows along the brine cell co-currently withthe brine. Closely spaced above the cathode, an anode assembly is suspended.

Electric current flowing through the cell decomposes the brine passing through thenarrow space between the electrodes, liberating chlorine gas (Cl2) at the anodeand metallic sodium (Na) at the cathode. The chlorine gas is accumulated abovethe anode assembly and discharged to the purification process.

As it is liberated at the surface of the mercury cathode, the sodium immediatelyforms an amalgam. The liquid amalgam flows from the electrolytic cell to aseparate reactor, called decomposer or denuder, where it reacts with water in thepresence of a graphite catalyst to form sodium hydroxide and hydrogen gas. Thesodium-free mercury is fed back into the electrolyser and reused. The brine anolyteleaving the cell is saturated with chlorine and must be dechlorinated beforeresaturation with salt.

The sodium hydroxide is produced from the denuder at a concentration of about50%; decomposer may be regarded as a short-circuited electrical cell in which thegraphite catalyst is the cathode and sodium amalgam the anode.

The steel base of the electrolyser is made as smooth as possible to ensuremercury flow in an unbroken film. In the event of a break in the mercury surface,caustic soda will be formed on the bare (steel) cathode, with simultaneous releaseof hydrogen, which will mix with the chlorine. Because hydrogen and chlorine canform a highly explosive mixture, great care is necessary to prevent hydrogenformation in the cell.

The mercury process has the advantage over diaphragm and membrane cells thatit produces a chlorine gas with nearly no oxygen, and a 50% caustic soda solution(usual commercial concentration). However, mercury cells operate at a highervoltage than diaphragm and membrane cells and, therefore, use more electrical

energy (caustic soda concentration excluded). The process also requires a purebrine solution with little or no metal contaminants to avoid the risk of explosionthrough hydrogen generation in the cell. The amalgam process inherently givesrise to some environmental releases of mercury.


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2.1.2 Diaphragm Technology

The diaphragm process was the first commercial process used to produce chlorineand caustic soda from brine. In North America, diaphragm cells are still the primarytechnology. The process differs from the mercury cell process in that all reactionstake place within one cell and the cell effluent contains both salt and caustic soda.

A diaphragm is employed to separate the chlorine liberated at the anode, and thehydrogen and caustic soda produced directly at the cathode. Without thediaphragm to isolate them, the hydrogen and chlorine would spontaneouslycombine to form an explosive mixture and the caustic soda and chlorine wouldreact to form sodium hypochlorite.

The diaphragm was made of asbestos (chrysotile asbestos called "whiteasbestos") and separates the feed brine (anolyte) from the caustic-containingcatholyte. Due to the potential exposure of employees to asbestos and emissionsin the environment, replacement of asbestos by other diaphragm materials hasbeen considered.

Development of non-asbestos diaphragms started in the middle of the 1980s andperformances has improved during the last years. The basis of the material used isthe same in all diaphragms developed free of asbestos, i.e. a fluorocarbonpolymer, mainly PTFE (polytetrafluoroethylene). The differences lie in the fillersused and the way the hydrophobic PTFE fibres are treated and deposited in orderto form a permeable and hydrophilic diaphragm.

As shown in the Figure 3 purified brine enters the anode compartment andpercolates through the diaphragm into the cathode chamber. The percolation rateis controlled by maintaining a higher liquid level in the anode compartment toestablish a positive and carefully controlled hydrostatic head. The percolation rateis determined as a compromise between a low rate that would produce a desirablyhigh concentration of caustic soda in the catholyte (which provides the cell effluent)and a high rate to limit back-migration of hydroxyl ions from catholyte to anolyte,which decreases cathode current efficiency.

Figure 3: Electrolys er of the Diaphragm Techn ology

In the diaphragm cell, saturated brine (about 25% NaCl) is decomposed toapproximately 50% of its original concentration in a pass through the electrolyser.


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When graphite anodes were used, the diaphragm became rapidly inoperable dueto plugging of the diaphragm by particles of graphite. Nowadays, all plants in theEuropean Union use metal anodes.

Both diaphragm and membrane cells for the production of chlorine and sodiumhydroxide are classified as either monopolar or bipolar. The designation does rot

refer to the electrochemical reactions that take place, which of course require twopoles or electrodes for all cells, but to the electrolyser construction or assembly:

Monopolar electrolyser is assembled so that the anodes and cathodes arearranged in parallel. As a result of this configuration, all cells have the samevoltage of about three to four volts; up to 200 cells can be constructed inone circuit.

Bipolar electrolysers have unit assemblies of the anode of one cell unitdirectly connected to the cathode of the next cell unit, thus minimisingintercell voltage loss. These units are assembled in series.

Many different types of activated cathodic coating can be used in order to reduce

the energy consumption of the cell. These have to be robust because the powerfulwater jet used to remove the used diaphragm from the cathode mesh canadversely affect the cathode. This activated coating is especially interesting withlong lifetime diaphragms.

All diaphragm cells produce that contains ca. 11% caustic soda and 18% sodiumchloride. This solution is evaporated with steam to 50% NaOH by weight, at whichpoint all of the salt, except a residual 1.0-1.5% by weight, precipitates out. The saltgenerated is very pure. This high quality sodium chloride is sometimes used as araw material for an amalgam or membrane process.

Chlorine contains low concentrations of oxygen formed by electrolytic

decomposition of water; due to reaction of chlorine with water hypochlorous acid ispresent in cell liquor.

2.1.3 Membrane Technology

In the 1970s, the development of ion-exchange membranes enabled a newtechnology to produce chlorine: the membrane electrolysis process. The first ionexchange membranes were developed at the beginning of the 1970s in the UnitedStates, followed by Japan where the first industrial membrane plant was installedin 1975, due to the pressure of Japanese environmental regulations: non-chlor-alkali related mercury pollution in Minamata drove the authorities to prohibit all

mercury processes and Japan was the first country to install the membraneprocess on a massive scale in the mid-1980s.

Today, it is a promising and fast-developing state of the art technique for theproduction of chlor-alkali and it will undoubtedly replace the other two techniques intime. This can be deduced from the fact that since 1987 practically 100% of thenew chlor-alkali plants world-wide apply the membrane process. The replacementof existing mercury and diaphragm cell capacity with membrane cells is takingplace at a much lower rate because of the long lifetime of the existing plants andbecause of the high capital costs of conversion.

In this process, the anode and cathode are separated by a water-impermeable ion-

conducting membrane. Brine solution flows through the anode compartment wherechloride ions are oxidised to chlorine gas. The sodium ions migrate through themembrane to the cathode compartment which contains flowing caustic sodasolution. The demineralised water added to the catholyte circuit is hydrolysed,


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releasing hydrogen gas and hydroxide ions. The sodium and hydroxide ionscombine to produce caustic soda which is typically brought to a concentration of32-35% by recirculating the solution before it is discharged from the cell (seeFigure 4).

The membrane prevents the migration of chloride ions from the anode

compartment to the cathode compartment; therefore, the caustic soda solutionproduced does not contain salt as in the diaphragm cell process. Depleted brine isdischarged from the anode compartment and resaturated with salt. Usually, thecaustic liquor produced has to be concentrated by evaporation (using steam) toreach a concentration of 50%.

The cathode material used in membrane cells is either stainless steel (older cells)or nickel. The cathodes are often coated with a catalyst that is more stable than thesubstrate and that increases surface area and reduces over-voltage. Coatingmaterials include Ni-S, Ni-Al, and Ni-NiO mixtures, as well as mixtures of nickeland platinum group metals. The anodes used are metallic (titanium coated withtitanium/ruthenium/ oxides).

Figure 4: Electrolys er of the Membrane Techn ology

Membranes used in the Chlor-alkali industry are commonly made of perfluorinatedpolymers. They generally consist of two layers. One of these layers consists ofperfluorinated polymer with substituted carboxylic groups and is adjacent to thecathodic side. The other layer consists of perfluorinated polymer with substitutedsulphonic groups and is adjacent to the anodic side. To give the membranemechanical strength, the membrane is generally reinforced with PTFE fibres.Membranes must remain stable while being exposed to chlorine on one side and astrong caustic solution on the other.

As in the diaphragm technology membrane cells are classified as either monopolaror bipolar, the latest being the today state of the art (See section2.1.2).


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Membrane cells have the advantage of producing a pure caustic soda solution andof using less electrical electricity than the other processes. In addition, themembrane process does not use toxic materials such as mercury and asbestos.Disadvantages of the membrane process are that the caustic soda produced mayneed to be evaporated to increase concentration and, for some applications, thechlorine gas produced needs to be processed to remove the traces of oxygen.

Moreover brine entering a membrane cell must be of a very high purity, which oftenrequires costly additional purification steps prior to electrolyses.

2.2 Chlo rine Treatment

Whatever the used technology is, the chlorine produced in the electrolysis cells issaturated with water and may also contain brine mist, inert gases like nitrogen,CO2and some oxygen and traces of chlorinated hydrocarbons. Before the chlorinecan be used, it is usually cooled, dried, purified, compressed and wherenecessary, (partially) liquefied and possibly vaporised.

2.2.1 Cooling

The gas is not cooled below 10C to avoid solid chlorine hydrate formation.Cooling is accomplished in either one or two stages. Chilled water can be used inthe second stage.

The chlorine gas can be cooled indirectly in a tubular titanium heat exchanger sothat the cooling water is not contaminated. The resultant condensate can be fedback into the brine system or into any other suitable recovery, or dechlorinated bystripping.

The chlorine gas can also be cooled directly in packed towers. This treatment

thoroughly washes the chlorine, but the cooling water must be free of ammoniumsalts traces to avoid the formation of nitrogen trichloride. The purge can berecycled in the brine or dechlorinated.

2.2.2 Purification

Two techniques are generally used:

Water droplets and impurities such as brine mist are mechanically removedby special filter elements with glass wool fillings or porous quartz granules,or in electrostatic purification (chorine gas is passed between wireelectrodes in vertical tubes collecting the charged particles). The electrodes

are maintained at a direct current potential. Particular attention must be paidto avoid too high hydrogen concentration (risk of explosion). Particles anddroplets in the chlorine become charged and are collected on the tube walls.The resultant liquid is fed back into the brine system, or chemically treatedbefore disposal.

Scrubbing with liquid chlorine reduces the content of organic impurities,carbon dioxide and bromine. Nitrogen trichloride can also be removed fromthe gaseous chlorine by this method.

2.2.3 Drying

Drying chlorine is carried out with concentrated sulphuric acid. Depending on thefinal concentration of the waste acid, drying can be a two to four stage process.Acid and chlorine flow in counter current. The final moisture content depends onthe concentration and temperature of the acid in the final stage. Chlorine is


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considered as dry when it contains less than 20 mg of water per kg. Molecularsieves can be used to get lower moisture content.

After drying, chlorine gas is passed through a demister or a packed bed to removeresidual sulphuric acid mist.

2.2.4 Compression

Several types of compressors can be used depending on the amount and thequality of chlorine to be treated, and the level of required pressure.

Wet chlorine gas can be compressed by a single-stage blower or fan with a rubber-lined steel casing or titanium turbo compressor.

Several techniques can be used to compress dry chlorine:

Liquid ring compressors: sulphuric acid is used; the heat of compression isremoved by cooling the circulating liquid; the advantages are simplicity ofconstruction, strength, reliability, ability to compress gas containing inerts,but the efficiency is low and the volume flow per equipment is limited.

Reciprocating compressors: formerly lubricated with sulphuric acid, they arenow available as dry-ring compressors (no lubrication); for high pressuresmulti-stages equipments are used; the heat of compression of each stage isremoved by chlorine heat exchangers or by liquid chlorine injection; well-purified chlorine gas is essential for trouble-free operation.

Turbo-compressors: they operate with large amount of chlorine. Labyrinthseals are used on the high-speed shafts; requirements for cooling and gaspurity are similar to those of reciprocating compressors.

To avoid chlorine-iron fires, it is recommended the chlorine temperature at the

outlet of any stage of the compressor should never exceed 120C, unless thecompressor is manufactured using special material suitable for highertemperatures.

Note: if necessary, the nitrogen trichloride present in the dry gaseous chlorine canbe destroyed by passing the compressed chlorine on active carbon bed, understrict temperature control (exothermic reaction).

2.2.5 Liquefaction

Important factors are the composition of gaseous chlorine, the desired purity ofliquid chlorine, the desired yield and the pressure level of the liquid chlorine

storage. See GEST 72/10 - Pressu re Storage of L iqu id Ch lorin e and GEST73/17 - Low Pressure Storage of Liqu id Chlorin e.

Any hydrogen is concentrated in the residual gas. To keep hydrogen concentrationbelow the explosive limit (see paragraph7.2.3), conversion of gas to liquid shouldbe limited to a level depending on the initial gas purity, or dilution dry air (ornitrogen) should be added. Continuous analysis of the content of hydrogen inresidual chlorine gas is recommended.

If the chlorine pressure is high enough, liquefaction can be achieved with water/aircooling and does not require a refrigeration unit.

In the other cases, refrigerant compatible with chlorine must be used; attentionmust be paid to the increased solubility in chlorine of other gases, especiallycarbon dioxide. The process achieved at low temperature (less than minus 40C)is advantageous when large amounts of chlorine must be liquefied as completely


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as possible. Be aware of the increased concentration of hydrogen in the residualgas, and the lower allowed water concentration in the dried chlorine gas (risk ofcorrosion).

A process achieved at temperatures between minus 10C and minus 20C isspecially useful when only a part of the chlorine has to be liquefied and the

remaining gas is to be reacted at the liquefaction pressure, e.g., with ethylene toproduce ethylene dichloride. The residual gas can be fed into the compressorsuction system, provided that the increased inert gas content does not interferewith the subsequent process (chlorine quality and explosive risk).

2.3 Produ cts Usages

The co-production of chlorine and sodium hydroxide in fixed proportions (ECU),1.128 tonnes of caustic soda (as 100% NaOH) per tonne chlorine produced, hasalways been a challenge for the chlor-alkali industry. Both products are used forvery different end uses with differing market dynamics and it is only by rare chance

that demand is balanced for the two. Depending on which demand is dominant,either can be regarded as a by-product and the price varies accordingly.

The hydrogen produced is always considered as a by-product.

2.3.1 Chlorine

Chlorine is largely used in the synthesis of chlorinated organic compounds. Vinylchloride monomer (VCM) for the synthesis of PVC still remains the driver of chlor-alkali production in most European countries (see (http://www.eurochlor.org/uses).

For safety, practical and economical reasons, chlorine is generally produced closeto the consumers. More than 90% of the chlorine produced in EU is used on the

same or adjacent sites (local pipeline transport). A general way to transportchlorine is to produce ethylene dichloride, a precursor of PVC. When required,liquid chlorine can be transported by rail, road or sometimes by ship.

The chlorine consumption can be divided into several types of uses (see alsohttp://www.eurochlor.org/applications):

Organic uses, which account for about 80% of consumption: synthesis ofVCM, chloromethanes, phosgene, organic chlorinated solvents such astrichloro-ethylene, tetrachloro-ethylene, oxygenated derivatives, precursorsor intermediates for the synthesis of pesticides or pharmaceutical products.

Inorganic uses, which account for about 15% of consumption (synthesis ofsodium hypochlorite, hydrochloric acid, metal chlorides, bromine).

Direct uses, which account for less than 4% of consumption (watertreatment, pulp and paper).

More detailed uses are also shown on the Euro Chlor website:http://www.eurochlor.org/tree.

2.3.2 Sodium Hydroxide

Sodium hydroxide is usually supplied as a 50% aqueous solution and can bestored for long periods and easily transported (rail, road and ship). The main areas

of application of sodium hydroxide are:

Chemicals: synthesis of organic or inorganic compounds

Metallurgy, alumina/aluminium
http://www.eurochlor.org/useshttp://www.eurochlor.org/useshttp://www.eurochlor.org/useshttp://www.eurochlor.org/applicationshttp://www.eurochlor.org/applicationshttp://www.eurochlor.org/treehttp://www.eurochlor.org/treehttp://www.eurochlor.org/treehttp://www.eurochlor.org/applicationshttp://www.eurochlor.org/uses


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Pulp and paper - textile

Soaps, surfactants

Water treatment.

(See alsohttp://www.eurochlor.org/causticsodaapplications).

2.3.3 Hydrogen

As sodium hydroxide, hydrogen is a co-product of the electrolysis of brine (28 kgfor 1 tonne of chlorine). Hydrogen is generally used as a combustible on integratedsites or transported via high pressure pipelines; it can be also used for certainchemical applications, in particular due to its high purity: synthesis of ammonia,methanol, hydrochloric acid, hydrogen peroxide, sulphur removal from petroleum,etc.

3 PROPERTIES AND HAZARDS OF CHLORINE

3.1 Physic al Propert ies

Density gaseous (1.013 bar, 0C) 3.21 kg/m

Relative to air (1.013 bar, 0C) 2.49

Boiling point (1.013 bar) -34.05 C

Heat of vaporisation (at34C) -101 kJ/kg

1 litre of liquid chlorine liberatesabout (25C, 1.013 bar)

463 Litre of chlorine gas

Solubility in water (25C, 1.013 bar) 6 kg/m

Liquid chlorine thermal expansion

coeff. Vt2= Vt11 + (t2-t1)= 2.10-3C-1

For a more detailed list of properties see GEST 91/168 Physical,Thermo dyn amic and Selected Chemical Propert ies of Chlorine.

3.2 Reactivity

Chlorine is not flammable but strongly oxidising; it is one of the most reactiveelements and can combine with many substances elements at ambienttemperature. With many organic and inorganic compounds the reaction can beviolent and possibly even explosive.

3.3 Hazards

3.3.1 Chlorine and Explosion Risk

Chlorine is an oxidising agent and can form explosive gaseous mixtures withorganic and inorganic compounds such as hydrogen, ammonia, methane andmethyl chloride. In general, the flammability and detonation limits with thesecompounds are comparable with those with oxygen. The auto ignition temperature
http://www.eurochlor.org/causticsodaapplicationshttp://www.eurochlor.org/causticsodaapplicationshttp://www.eurochlor.org/causticsodaapplicationshttp://www.eurochlor.org/causticsodaapplications


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of organic compounds in chlorine is usually around 200C lower than thecorresponding value in air, meaning that thermal ignition is easier.

Chlorine reacts with almost every organic compound containing hydrogen and/ornitrogen. The simple chlorination reaction:

HClRClClRH 2

takes place very easily and in some cases at an explosive rate even at ambienttemperature. When both the combustible and the chlorine are in the liquid phase,the explosion can be much more serious than in the case of a gaseous system.

Organic compounds which can react explosively with gaseous or liquid chlorineare, for example, alcohols, esters, oils, solvents, silicone oils and silicone rubber.This applies especially to lubricating oils, greases and cleaning solvents.Components which require to be lubricated shall be treated with chlorinecompatible chloro-fluorinated grease.

Ammonia and some other nitrogen compounds may form nitrogen trichloride, a

very unstable explosive compound detonating very easily, both in the gaseous andin the liquid phase.

Low levels of nitrogen trichloride are normally present in liquid chlorine and oneshould avoid a situation of accumulation due to vaporisation of chlorine withconcentration of the higher boiling temperature of nitrogen trichloride in the liquidphase residue. (See also section7.2.1).

This is of concern in all situations where chlorine gas is withdrawn from liquidchlorine, for example:

in a storage system, if it is being emptied by venting off gas (notrecommended by Euro Chlor),

with transport containers, if the chlorine is withdrawn from the gaseousphase (not recommended by Euro Chlor), and

in vaporisers.

Suitable precautions must be taken to ensure that the NCl3content is maintainedat a safe level (cf. GEST 76/55 - Maximum Levels o f Nitrogen Trichlor ide inL iqu id Chlor ine).

3.3.2 Construction Materials

The choice of materials depends on the state of the chlorine (wet or dry, gas orliquid, level of pressure and temperature) and must be adapted to the intendeduse.

For dry liquid or gaseous chlorine, carbon steel can normally be used. But thetemperature has to be limited to 120C to avoid any risk of iron-chlorine fire.Titanium must never be used with dry or insufficiently wet chlorine. Selected plasticmaterials may be used on low pressure gaseous systems only.

Rubber gaskets must never be used with dry gas or liquid chlorine. (See section9.2.3).

Because of safety implication of materials selection it is important to consult a

chlorine producer and to follow GEST 79/82- Materia ls of Con struc t ion for Us ein Contact wi th Chlor ine.


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4 PROPERTIES AND HAZARDS OF HYDROGEN

Due to the fact that hydrogen, generated as a co-product, is a flammable gas andmay form explosive mixtures with ambient air (or chlorine), the two ATEXDirectives (Directive 1999/92/EC of 16 December 1999 and 94/9/EC of 23 March

1994) are applicable to electrolysis units. ATEX is the French abbreviation forATmosphresEXplosives.

The Posit ion Paper X - Explosio n Protect ion Con siderat ions Regarding theCel l room of a Chlor - Alkal i Electro lys is Unitconstitutes the ATEX evaluationfor the cell room and in the low pressure hydrogen circuit downstream of the cellrooms. This document describes under which conditions electrolysis rooms mayusually be classified as non-dangerous zones according to Directive 1999/92/EC.

From the risk analysis, it can be stated that,

there is no risk of formation of an explosive atmosphere within the cell roomin normal operating conditions,

a hydrogen leak is highly unlikely - or would be detected very quickly - in allforeseeable conditions (including process deviations),

even in the case of a hydrogen leak, the consequences would be verylimited, with a risk of flame but no explosion, and there would be very little orno exposure to employees.

Taking all these items into consideration, it can be concluded that:

Cell rooms may be considered as non hazardous, with respect to the risk ofexposing employees to explosive atmospheres as defined by Directive1999/92/EC).

Based on the preceding risk analysis and on norm EN 60079-10, cell roomscan be classified as non dangerous zones according to Directive1999/92/EC.

5 PROCESS SAFETY MANAGEMENT

5.1 Site Securit y

Guidance to assist facilities producing chlorine in implementing site security

measures to reduce the facilitys vulnerability to external threats and internal actsof sabotage is described in GEST 05/316 Guidel ine for Site Securi ty ofChlor in e Produ ct ion Faci l i t ies.

5.2 Process Safety Inform at ion

Documented information should be developed and maintained. This informationwill provide the foundation for identifying and understanding the hazards involvedin the process.

The basic references are the National/International Codes and Regulations, theEuro Chlor recommendations, the Company Procedures. The information shouldinclude two parts.
http://localhost/var/www/apps/GTC%20&%20WG/R%C3%A9unions/Local%20Settings/Temporary%20Internet%20Files/OLK11/MAJ%20Septembre%202007/PROPERTIES%20AND%20HAZARDS%20OF%20HYDROGEN.doc#_Toc160463490#_Toc160463490http://localhost/var/www/apps/GTC%20&%20WG/R%C3%A9unions/Local%20Settings/Temporary%20Internet%20Files/OLK11/MAJ%20Septembre%202007/PROPERTIES%20AND%20HAZARDS%20OF%20HYDROGEN.doc#_Toc160463490#_Toc160463490


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5.2.1 Process Design Information

This information includes:

Process chemistry

Flow diagram

Maximum intended inventory Acceptable upper and lower limits for temperature, pressure, flow-rate,

concentration.

5.2.2 Mechanical Design Information

This information includes:

The materials of construction

The Piping and Instrument diagrams (P&ID)

The electrical areas classification

The design and basis of the pressure relief systems

The design of the ventilation system

The equipment and piping specifications

The description of shutdown and interlock systems

The design codes employed.

5.3 Process Hazards Analys is

A process hazards analysis must be performed for any facility. The purpose of thisanalysis is to minimise the probability and consequences of any accident.

The analysis should take account of consequences of deviation from the operatinglimits, of the steps required to correct or avoid deviation, and justify safety systemsand their functions.

5.4 Management of Change

The company should establish written procedures to review all changes in processtechnology and changes to the facility.

Such procedures should address: Technical basis for the proposed change

Safety, health and environmental considerations

Risk analysis of the modified (part of) installation

Modification to operating procedures

Proof-testing of critical instrumentation

Documentation of physical changes

Appropriate management approval

Communication and training of personnel involved

Documentation of training (and periodic retraining).


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5.5 Operat ing Procedures

Written operating procedures should specify the following information:

Clear instructions for the safe operation, that are consistent with the processsafety information

Operating conditions and steps for the following phases of operation:

Initial start-up

Normal operation

Temporary operations as the need arises

Emergency operations, including emergency shutdown

Normal shutdown

Normal start-up.

The operating limits and the steps to maintain the system within the limits or

to bring it to a safe position

Occupational safety and health considerations including the following:

The properties of and hazards presented by the materials used in theprocess

The special precautions required to prevent exposure, includingengineering controls and personal protective equipment

The control measures to be taken if physical contact or airborneexposure occurs

Any special or unique hazard.

For new and modified facilities, the operating procedures should be in place beforestart-up.

Operating procedures should be reviewed periodically, with typical review intervalsrange between 3 to 5 years.

The operating procedures should be readily accessible to operating personnel. It isalso essential to check that the procedures are well known.

5.6 Safe Work Practices

For the safe conduct of operation, maintenance and modification activities,especially including the opening of process equipment or piping, lock out and tagout of electrical and mechanical energy sources, safe work practices shouldprovide procedures that involve ignition sources, entry into confined spaces andthe use of cranes and similar equipment.

A work authorisation system must be an element of the safe work practices,including detailed written communication between the different team involved. Hotwork permits, when necessary, must be systematically used.

5.7 Mechan ical Integrity

Assuring the quality and mechanical integrity of critical equipment is addressed inthe technical guidance part of these guidelines (see section9).


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Procedures could be briefly summarised:

Written quality control procedures for critical equipment during all stages offabrication should be implemented

Appropriate checks and inspection procedures should be implementedbefore start-up

Maintenance systems that include appropriate inspection and testing shouldbe implemented to ensure ongoing mechanical integrity.

5.8 Pre-Start-Up Safety Review

The pre-start-up safety review should confirm prior to the introduction of chlorinethat:

Construction or major maintenance are in accordance with specifications

Safety, operating, maintenance and emergency procedures are in place andadequate

Process hazard analysis recommendations have been addressed andactions required for the start-up have been completed

Operating procedures are in place and training of operators has beensuccessfully completed

A physical inspection of the facilities has taken place and appropriate follow-up of findings addressed

Instrumentation has been functionally checked

Chlorine containing lines and equipment have been properly cleaned and

dried for dry chlorine service Personal and collective protective equipment are available.

5.9 Emergenc y Respons e and Contro l

The measures to be taken in the event of chlorine accidents should be carefullyprepared. Their adequateness should be regularly checked and updated.

They should include:

An alarm plan for events without consequences outside of the factory limits

An alert plan for accidents with potential consequences outside of thefactory limits. This plan has to be developed in co-operation with the local

authorities, fire brigade, etc

All personnel involved should be regularly trained in emergency response.

5.10 Invest ig at ion of Process Related Incidents

The company should investigate every incident which either resulted in or couldreasonably have resulted in an uncontrolled chlorine release.

Investigations should be initiated as promptly as possible. An investigation team

should be established and a report should be prepared, including: description of the incident and cause(s)

factors contributing to the incident


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actions foreseen or taken to avoid repetition of the incident

description of any changes in process hazard management recommendedto prevent recurrence.

The report should be reviewed by the management responsible for safetystandards in the plant.

A Euro Chlor accident report should be systematically completed and sent fordiscussion by the GEST Group, to allow improving the recommendations.

5.11 Audits of Process Hazards Management Systems

Audits should be completed periodically by a qualified audit team. A frequency ofevery three years is recommended. The team should include personsknowledgeable of the process used.

On a voluntary basis, companies may request a Euro Chlor selected audit teamconsisting of member company and/or Euro Chlor staff representatives. An audit

report should be prepared.

The company should establish a system to determine and document theappropriate response to each of the findings of the audit report and ensure actionsare completed on a timely and efficient basis.

To ensure high standards of safety are achieved, it is recommended that chlorineusers should seek the help of the chlorine producers to check their premises. SeeGEST 92/175 - A Schem e for Safety Visits to Ch lorin e Custom ers' Plants.

6 TRAINING

In all cases, it is essential that the training is carefully validated to ensure a fullunderstanding of all aspects of the job, including items which would only beexpected to occur infrequently.

Any training should be documented and include means to verify that the employeeunderstood the training.

6.1 Personnel of the Facil i ty

The health condition of employees with a potential for occupational exposure to

chlorine should be periodically checked; they should be trained to act quickly incase of emergency and should be aware at all times of the wind direction andescape routes.

In mercury plants, a special dedicated monitoring programme has to be setup.

6.1.1 Topics covered

The company should provide training for personnel responsible for operating andmaintaining the facility. The training should address the following:

Proper use and care of personal safety equipment

Proper use of emergency equipment

Operating procedures

Changes in process technology or facilities


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Training in emergency operating and emergency shutdown procedures,taking into account the local requirements of the authorities.

6.1.2 Initial Training

The company should ensure that any employee possesses the requiredknowledge, skills and abilities before operating the process.

6.1.3 Refresher Training

Periodic training should occur at fixed intervals, not bigger than three years andshould be documented.

6.1.4 Plant Modifications

Whenever a change is made, operating personnel should be informed andspecifically trained.

6.2 Training of Road Tanker Drivers

A specific training is necessary for the road tanker drivers, as their role would becrucial in case of an emergency (a rapid intervention can drastically reduce theconsequences of an accident).

Beside their driving skill, they must be informed of the properties of chlorine andmust be trained on the way to use the first intervention equipment that must beavailable in the truck.

A check list is detailed in below,and more information is available in the GEST73/20 - Code of Goo d Pract ice for Safe Transport o f Bulk Liqu id Chlorin e by

Road Tanker Vehicles.

7 SAFETY GUIDANCE

7.1 Chlor in e Detect ion and Monito r ing

7.1.1 Purpose of Chlorine Monitors

A chlorine monitoring system may be installed to warn the operators about apossible chlorine leakage in a production installation, a storage area or aloading/off-loading area, enabling them to rapidly take corrective action.

A monitoring system may also be used in a storage area or a loading/off-loadingstation for the automatic closing of valves to isolate chlorine-containing equipment.However, this integration of chlorine that monitors the protective systems of theplant should be carefully considered to ensure that automatic closure of valves,independently of the operator's judgement, will not lead to dangerous situations.

7.1.2 Chlorine Monitoring Systems

The monitoring system may consist of a single stand-alone sensor unit installed ata critical point in a plant, or a number of sensor units surrounding a productionplant, a storage area etc.

Another option is a multipoint sampling system connected to a central sensor unitmeasuring an average value at all sampling points, or measuring in sequence thevalue at the individual sampling points (scanning system).


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accumulate safely. Analytical methods to monitor this are given in Anal 2 -Determin at ion of Nitrogen Trichlor ide in Liquid Chlorin e.

However, any chlorine user, particularly if they are modifying their process orequipment, is strongly advised to seek the expert help of a chlorine producer.

7.2.2 Moisture

Chlorine is dried to less than 20 mg water content per kg of chlorine duringmanufacturing. Any subsequent equipment downstream in the producer plant, or atthe user, will normally use materials of construction appropriate for dry chlorine. Toprevent corrosion, it is vital that ingress of moisture is prevented. This can beachieved by ensuring that:

Before coming into contact with chlorine, all new equipment is thoroughlydried by heating, possibly under vacuum, by purging with dry gas, etc.

Equipment which has become wet due to washing in preparation formaintenance, or due to pressure testing, must be thoroughly dried

Any inert gas used to transfer chlorine, to purge equipment beforemaintenance of for drying after maintenance, has a dew point lower thanminus 40C

Any gasket which becomes wet during maintenance is replaced

Bellows in valves have to be dried by heating, possibly under vacuum

Precautions are taken to avoid backflow from any installation using chlorineinto a unit or equipment where water or moisture is present.

GEST 80/84 Code of Good Pract ice for the Comm ission ing of Insta l lat ions

for Dry Chlor ine Gas and Liqu id should be consulted for further details.Particular attention must be paid to flexible connections used for loading and off-loading mobile containers. To avoid corrosion due to atmospheric moisture, theseshould be purged free of chlorine after use and stored with the ends sealed. A newgasket should be used each time the flexible is connected to the mobile container.GEST 78/73 Design Princip les and Operat ional Procedures for Lo ading/Off-

Load ing Liq uid Chlo rine Road and Rai l Tankers and ISO-Containersshouldbe consulted for further details.

7.2.3 Hydrogen

Small quantities of hydrogen are present in the chlorine gas produced. Normally,

the concentration will be below 1% from the cells until the chlorine compression.The concentration will increase either as a result of chlorine liquefaction, or couldhappen due to condensation in a pipeline operating under high pressure in coldweather. If the hydrogen concentration exceeds certain limits in chlorine or air (seetable below), the gas mixture is potentially explosive. A similar problem can arise ina chlorine absorption system where explosive hydrogen in air mixtures can arisewhen the diluted chlorine is absorbed in sodium hydroxide.

The current information relating to the flammable limits of hydrogen in chlorine ispresented in the table below, with the effect of the initial temperature.


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Temp (C) H2-Air (vol % H2) H2-Oxygen (vol % H2) H2-Chlorine (vol % H2)

-60 4.0 - 69 4.0 - 96 5.0 - 90

-40 4.0 - 71 4.0 - 96 4.0 - 90.5

-20 4.0 - 72 4.0 - 96 4.0 - 91.5

0 4.0 - 73 4.0 - 96 3.5 - 92

20 - 25 4.0 - 75 4.0 - 96 3 - 92.5

50 3.7 - 76 4.0 - 96 3 - 93

100 3.0 - 80 4.0 - 97 3 - 93

The influence of the initial pressure is relatively small between 0.25 and 11.5 bara.It is recommended that experimental measurements are undertaken if operating athigher pressure.

The practical operating conditions in the production lines and equipments will bechosen to work with a suitable safety margin with respect to these limits, taking intoaccount the fact that pressure increase widens the flammability zone.

In-line analysers will be used to check that one always remains below the low limitof the table.

The possible dilution effect of water vapour will not be taken into consideration for

wet chlorine.

In very special cases, and after thorough calculations and risk assessment, it canbe acceptable to exceed the low limit by using pressure resistant equipment(possible inflammation tolerated but pressure increase contained).

Depending on the process used, chlorine producers must monitor their brine toensure adequate sodium chloride content and acceptable levels of impurities suchas calcium, magnesium and heavy metals which can promote hydrogen formation.Hydrogen in chlorine levels should be monitored continuously in the gas leavingthe cell room and after liquefaction. If a dangerous limit is approached, the gasstream should be diluted by admitting dry air or nitrogen or the plant operating rate

reduced and the gas stream sent to absorption system until the cause of theexcess hydrogen has been identified and corrected. In serious cases, it may benecessary to shut down the plant.

7.3 Protect ive Equipm ent

Information on most types of personal protective equipment used in themanufacturing and handling of chlorine is given in GEST 92/171 Person nelProtect ive Equipm ent for Use with Chlorine.

It is recommended that all persons, whether workers or visitors, entering a chlorine

plant, should be informed and provided with an escape mask.Depending on the work to be carried out or on the conditions which exist at thetime, either breathing apparatus with filter or self-contained breathing apparatusshould be used (not escape mask).


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With this type of equipment, protection is obtained only if the four followingconditions are met:

Filter or cartridge suitable for chlorine

Oxygen content at least 19% volume (make sure oxygen content issufficient)

Chlorine content under 0.5% volume

No other toxic substances (including CO) above the occupational exposurelevel.

For all other situations or for extended use, self-contained breathing apparatusshould be worn.

In case of higher exposition risk, full protective clothing will protect the skin; thedecision to wear them will be taken by the intervention team leader, based on hisassessment of the situation.

Important remark: the filter mask must never be used inside vessels, reservoirs orconfined space without very careful testing of the oxygen content and the level ofcontamination of the atmosphere, which should be very low (much lower than 0.5% volume).

8 HEALTH HAZARDS, TRAINING AND FIRST AID

8.1 Health Hazards and Toxici ty of Chlor ine

The injurious effects of chlorine gas are due to its strongly oxidative properties. It

mainly causes damage to the mucous membranes of the larger airways, becauseof the action of hydrochloric acid and hydrochlorous acid which are formed, andchlorine itself.

Symptoms appear immediately after the start of the exposure. After cessation ofexposure the process stops and thus shortly after exposure, the level of severity ofthe effects is evident.

The general effects of various levels of chlorine inhalation (depending on thephysical condition of the person involved and also on the duration of the exposure)are as follows:

Exposure level Effects

Less than 1 ppm Threshold of odour perception for the average person

130 ppm Symptoms in increasing order of severity: immediateirritation of eyes, nose and upper airways, intense cough,shortness of breath, chest pain, choking and vomiting

Above 30 ppm Development of chemical tracheo-bronchitis, severebronchospasm, bronchial oedema or oedema of the glottis.Prolonged exposure time at high concentration will cause

unconsciousness and finally death.

Determination of Chlorine in Workplace Air is described in the document An al 8 -Determin at ion of Chlorin e in Workp lace Air.


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Individuals suffering from asthma or chronic bronchitis and also heavy smokers areparticularly susceptible.

A study of chlorine toxicity carried out by the Dutch TNO-CIVO Toxicology andNutrition Institute at the request of Euro Chlor, has been published in Journal ofHazardous Materials, 19 (1988) 195-208.

Toxicity of chlorine under emergency conditions has been published inHEALTH7 - Code of Pract ice: Contro l o f Workers Expo sure to Chlorine in the Chlor -

Alkal i Indu stry.

8.2 Monito r ing Chlor ine Expos ure to Workers

A code of practice (HEALTH 7 - Code of Pract ice: Contro l of WorkersExpos ure to Chlorine in the Chlor-Alkal i Indu stry) defines:

a monitoring strategy

advice about monitoring equipment

insight into the costs of the proposed monitoring strategy.

The purpose of the document HEALTH 5 - Aud it Quest ionnaire Chlorine is toproduce a self-assessment guideline to evaluate the health risk managementperformance of a Chlor-Alkali plant with regard to chlorine.

8.3 Treatment of Chlor ine Gassing

Warning: rescuers should always take care of avoiding intoxicating themselves.

ACTIONS TO BE TAKEN BY FIRST AIDERS

Use individual protective equipment to rescue casualties Remove casualty to fresh air, in quiet area, in a half seated position

Remove contaminated clothing

If breathing has ceased, let the patient sit in a half seated position or liecomfortably, start artificial respiration, avoiding contamination

Administer oxygen as soon as possible. Let the patient sit in a half seatedposition or lie comfortably

In case of skin and/or eye contamination irrigate with water for at least 15minutes

Avoid unnecessary exercise

Keep the casualty warm

Transport the casualty to the factory medical centre

All cases of chlorine gassing should be referred to the factory medicaldepartment.

Euro Chlor has developed a document on this subject: HEALTH 7 - Code ofPract ice: Contro l of Workers Exposure to Chlorine in the Chlor-Alkal i

Industry.


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8.4 Exposi t ion of workers to mercury

In electrolysis units based on the mercury technology, workers are potentiallyexposed to mercury and the toxicity of this product imposes to proactively takeprotective measures.

HEALTH 2 - Code of Pract ice: Contro l of Wo rker Expos ure to Mercury in theChlor-Alkal i Indu stry provides information on the health hazards of mercury andadvices for the personal hygiene of the workers to reduce the risk of exposure tomercury The document gives also recommendations for the bio-monitoring of theworkers. The document Analyt ical 6 - Determin at ion of Mercury in Gassesindicates the recommended methods for sampling and analysing mercury in thecell room air.

The guideline An alyt ical 11 - Determ inat ion of mercury and c reat in ine in urin erecommends the methods for analysis of workers urine to determine their level ofexposition to mercury.

The purpose of HEALTH 6 - Au dit Quest ion naire Mercury is to produce a self-assessment guideline to evaluate the health risk management performance of aChlor-Alkali plant with regard to mercury. This paper can be also used for externalaudits.

In case of plant dismantling, the risk of exposure can be higher and the specificaspects are treated in a dedicated chapter of the guideline Env Prot 3 -Decommiss ion ing of Mercury Chlor A lka li Plants .

8.5 Electromagnetic Fields (EMF)

Referring to the Directive 2004/40/EC published on this subject, the Euro Chlor

documentHEALTH 3 - Electromagn et ic Fields in the Chlorine Electro lyses:Ef fects on Heal th and Recommended Limi ts describes the electromagneticfields present in a chlorine cell-room and examines the medical evidence for directand indirect effects to human health. The document also provides guidance onmeasurement and practical solutions to consider in electrolysis units.

The two main issues of concern are:

The direct effect of static magnetic fields greater than 0.5 mT onpacemakers and other medical implants.

This effect has been known for many years and requires control over the access of

personnel fitted with pacemakers and others medical implants to plant areas wherethe static field exceeds 0.5 mT. This field, which can extend beyond the boundaryof the cell-room building, is usually marked with signs and hazard warnings.

The estimation of multi-frequencies time-varying magnetic fields effect inelectrolysis units that needs to take into account the phase coherence, as asimple summation formula on the different frequencies will lead tooverestimation of the exposure.

Euro Chlor has proposed to the Cenelec (the European Committee forElectrotechnical Standardisation that has been charged by the EuropeanCommission to prepare the measurement standards for applying the Directive) an

measurement standard to apply in our particular case.It must be pointed out that the application of the directive has been postponed fortill 2012 for further analysis of its socio-economical implications and to taken intoaccount a scientific update of the proposed limits.


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9 TECHNICAL GUIDANCE FOR THE FACILITY

9.1 Materials

Materials of constructions must be chosen to suit the conditions under which

chlorine is being handled: Wet or dry

Gaseous or liquid

Temperature

Pressure.

Plastic materials must also be chosen taking account of their resistance to ageingand to external factors. A basic principle in chlorine safety is to learn from previousexperience. Caution is therefore necessary before any new materials areintroduced. This may require extensive testing before any equipment is built.

General advice on the suitability of various materials for use with dry and wetchlorine is given in Euro Chlor publication GEST 79/82 - Materials ofConst ruct ion for Use in Contact wi th Chlor ine .

The principal materials are summarised below.

9.1.1 Materials for Liquid Chlorine and Dry Chlorine Gas

For dry chlorine gas, carbon steel is the usual material. For liquid chlorine and colddry chlorine gas, fine grain carbon steel, showing low temperature impact strengthshould be used, to take account of low temperature (till minus 40C) arising when

depressurising the system.In view of the reactivity of chlorine with carbon steel at elevated temperatures, achlorine temperature of 120C should not be exceeded. If higher temperatures areunavoidable for process reasons, special materials (e.g. nickel, nickel alloys orstainless steel) must always be used.

Under no circumstances may zinc, tin, aluminium, titanium and alloys based onthese be used for dry chlorine gas and liquid chlorine, as these metals reactspontaneously with dry chlorine.

9.1.2 Materials for Wet Chlorine Gas

Wet chlorine gas reacts with virtually all metals, with the exception of titanium andtantalum that are successfully used. Attention has to be paid to the use of titaniumwith wet chlorine gas that requires the respect of a minimum water content (seeGEST 79/82 Materia ls of Construc t ion for Use in Contact with Chlorin e).Other suitable materials are carbon steel lined with rubber, enamel or chlorine-resistant plastics, e.g. GRP (Glass Reinforced Polyester), PVC-GRP or PVDF.

9.2 Equipments

All equipment should be robust and protected against mechanical damage andexternal corrosion. All precautions must be taken to avoid the entry of moisture into

the chlorine system, especially in the loading/off-loading connections.


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9.2.1 Piping

Chlorine can be transported safely by pipeline either in the gaseous or liquidphase. The design of the pipeline must take account of the problems associatedwith the chosen phase. Piping must be carefully specified to ensure it meets thespecific requirements of each situation. All precautions should be taken to prevent

the accidental formation of liquid in a pipeline designed for chlorine gas.The material used should be suitable for operations at minus 40C. Euro Chlor hastherefore drawn up two recommendations, which specify the criteria to be used inthe design, construction and operation of piping systems for a nominal pressure of25/40 bars, or equivalent ASA classification.. One deals with inside plants pipingsystems: GEST 79/81 Liqu id and Dry Gaseous Chlor ine Pip ing SystemsLocated Inside Producer 's or Consumer's Plants. Detailed informationconcerning the transport of chlorine by pipeline (often longer than 1000 m) passingoutside the limits of the factory producing or using chlorine, is given in GEST 73/25- Transport of Chlor ine by Pipel ine outs ide Site Boun daries.

The piping system must be designed to meet the most severe condition of internalor external pressure and temperature variations to which it can be subjected duringservice. The most severe condition is that which results in the greatest componentthickness and the highest component rating.

The design pressure for liquid chlorine service should be based on the vapourpressure of chlorine at the chosen maximum design temperature and allowing forany pressure surge conditions which may arise as a result of abnormalcircumstances, e.g. pump start-up.

It is also recommended that a 20% safety margin be allowed between themaximum operating pressure of the system and its design pressure, i.e.:

PN 25 for 20 barg

PN 40 for 32 barg

PN 64 for 52 barg.

PN 25 should be the minimum design pressure.

Small branches on vessels and in piping are potential weak points in the system.For liquid chlorine a minimum wall thickness should be selected to ensureresistance to mechanical impact. Thus, for example, for the frequently used pipe of2 inches or 50 mm diameter, the wall thickness should be 4 mm instead of 1 or2 mm as indicated by calculation.

The corrosion resistance of steel in contact with liquid chlorine is due to a thin layerof ferric chloride formed on the internal surface. In order to avoid destruction of thisprotective layer by erosion, the linear velocity of chlorine at the wall should belimited. The normal practice for pipework is to limit liquid chlorine velocities to2m/s; for gas-piping the practical experience shows that a maximum velocity of 20m/s is acceptable when liquid entrainment is excluded.

9.2.2 Valves

To ensure safe handling of liquid chlorine it is essential that suitable valves areused.

Euro Chlor has published specifications or recommendations which define therequirements for each type of valve.


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Criteria for design, construction, testing and inspection on dispatch or receipt ofvalves for use with liquid chlorine are explained in following Euro Chlor documents:

For flanged globe valves see GEST 90/150 Specif icat ion for FlangedSteel Globe Valves -Packed Gland- for Use on L iquid Chlorine.

For quarter turn, self lubricating straight through ball valves, see GEST

93/180Specif icat ion fo r Flanged Steel Bal l Valves -Packed Gland- for

Use on Liqu id Chlor ine.

For control valves (either with double packed gland or with bellows andpacked gland) see GEST 98/245 - Specif ication for Process ControlValves -Bel lows Sealed- for Use on L iquid Chlorine.

For remotely operable globe shut off valves (including quick-closing valves),it is recommended that the criteria given in GEST 89/140 Specif icat ionfor Flanged Steel Globe Valves -Bel lows Sealed- for Use on Liqu id

Chlor ine and GEST 90/150 Specif icat ion for Flang ed Steel GlobeValves -Packed Gland- for Use on L iquid Chlorineare followed.

Manual valves should be in accordance with GEST 89/140 - Specif icatio nfor Flanged Steel Globe Valves -Bel lows Sealed- for Use on Liqu id

Chlor ineor GEST 90/150 - Specif ic ation for Flang ed Steel Globe Valves-Packed Gland- for Use on L iquid Chlorine.

A remotely operated valve is recommended in the fixed liquid chlorine pipeworkconnected to the loading or off-loading point. This valve should be sufficiently closeto the flexible connection to limit the emission in the event of an accident.

The operation of this valve and of the automatic valves on the transport tankershould be linked. These valves should be fail-closed.

Opening of the pneumatic valves should be linked to the interlock system.Provision should be made for operation from at least two alternative locations.

GEST 98/247 - Specif ic ation fo r Remo tely Operable Shut -Off Valves Bellow s

Sealed for Use on L iquid Chlorinegives requirements for this type of forged andcast steel flanged valves used at temperatures between minus 40C and plus120C.

The same valves are recommended for use with dry gas under pressure (morethan 4 barg).

It should be noted that valves are available from several suppliers with the

designation Euro Chlor approval.This is issued by Euro Chlor to confirm that the concerned valves have beenapproved according to GEST 86/128 - Procedure fo r Ap prov al of Valves for Useon Liqu id and Dry Gaseous Chlor ine, tested according to GEST 86/129 -Procedure for an Independent Assessment of Valves for Use on L iqu id and

Dry Gaseous Chlo rine, Prior to Considerat ion for Euro Chlor App roval andrespect the specifications defined in the corresponding Euro Chlorrecommendation.

The purchase of suitable valves by itself will not guarantee a high safety standard.It is also necessary to ensure correct installation, operation and maintenance, as

outlined in Code of good practice GEST 80/84

Code of Good Pract ice for theComm iss ion ing of Instal lat ions for Dry Chlor ine Gas and Liqu id.

The content of the previous paragraph is also applicable for tanker valves.


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Practical experience has shown that the installation of dry gaseous and liquidchlorine valves necessitates specific precautions to avoid their deterioration andconsequent loss of gas tightness. GEST 80/85 - Code of Goo d Practic e forInsta l lat ion Removal and Maintenance of Manu al ly Operated Chlo rine Valveshas been written to provide a number of simple rules that will help avoiddeterioration of such valves; the guidance is applicable:

During initial installation or following replacement on an operatinginstallation.

In the course of maintenance to or inspection of the installation.

During repairs to or overhaul of such types of valve.

Pneumatically operated valves for use on storage tanks for liquid chlorine need tosatisfy a number of basic functions and technical characteristics different fromother types of valves. The functions and characteristics necessary to satisfy theEuro Chlor safety criteria are described in GEST 94/204 - PneumaticallyOperated Valves for Use on Storage Tanks fo r Liqu id Chlorin ewhich covers

design, manufacture, materials, examination, testing and verification.

GEST 94/201 - Proced ure for Verif icatio n of Pneum atically Operated Valves

for Use on Rai l and Road Tankers and ISO-Containers for L iquid Chlorinegives a procedure that relates to the Euro Chlor verification of pneumaticallyoperated valves for use on rail and road tankers and ISO containers for liquidchlorine. The procedure, whose objective is to promote the safe transport of liquidchlorine, covers the assessment of the valve's design, which needs to satisfy anumber of basic functions and technical characteristics unique to the particulartype of valve, the valve's manufacture and its performance. The valves to whichthis procedure applies are covered by GEST 75/46 - Pneumatically Op erated

Valves for Use on Rai l and Ro ad Tankers and ISO-Containers for Liqu idChlor ine, a document which is based on a limited number of valve provendesigns, manufacture and development.

GEST 76/53 Code of Good Pract ice for Insta l lat ion, Removal and

Maintenance of Pneumat ic Valves on Road and Rai l Tankers and ISO-

Conta iners for L iqu id Chlor ine provides simple rules that will minimise anydeterioration of pneumatic valves; it is applicable:

For the first installation on a new vessel (road and rail tankers, ISO-containers)

For the inspection and testing of the vessel.

Repair weld procedures shall be in accordance with European Regulation.Production weld repairs refers to the repair by welding of valves to be used for drygaseous or liquid chlorine duty, during the casting, and subsequent machiningprocedures, prior to assembling of the finished product. GEST 96/220 -Specif icat ion for Weld Repairs during Manufactur ing of Cast Valves for

L iqu id and Dry Gaseous Chlor ine relates to the weld repairs referenced inrelevant Euro Chlor valve standards. The specification includes the requirementsfor the welding methods, standards to be followed, locations on the valve whichmay be repaired, and inspection procedures to be employed to ensure defect freeweld repairs. The individual valve specifications define the acceptable defects for

that type of valve.


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9.2.3 Bolts and Gaskets

For liquid chlorine service stud bolts (threaded studs with nuts) or hexagonal headsbolts with nuts should be used. See GEST 88/134 Stud Bo lts, Hexagon HeadBol ts and Nuts for L iqu id Chlor ine.

The jointing material should be suitable for the style and rating of the flanges.

Experience with these materials is given in GEST 94/216Experience of Non -

Asb estos Gaskets on Liquid and Dry Chlorin e Gas Service.

Procedures must ensure that gaskets are never used twice.

9.2.4 Pumps

For continuous or semi-continuous processes, pumps may be used to transferliquid chlorine. Canned pumps or submerged pumps are recommended.

For canned pumps, the pump and motor are built together as one unit, in which alllubrication is made by liquid chlorine recycled from the delivery side to the pump

suction side through the space between the stator and rotor.For safety and design principles, materials of construction and other particulars ofthe pumping system, see GEST 83/119 Canned Pump for Use wi th L iqu idChlor ine.

For submerged pumps, special measures have to be taken to ensure no leakagetakes place along the shaft even in case of mechanical seal failure.

9.2.5 Instruments

The purpose of the code GEST 94/210 - Code of Practic e for the Installat io n o fFlow Measur ing Devices on Dry Gaseous and Liqu id Chlor ine App l icat ionsis

to provide advice on the installation of flow measuring instruments used on drygaseous and liquid chlorine applications. This code does not advise the selectionof equipment; however, installation related selection criteria are mentioned.

Advice on the installation of pressure measuring and detection instrumentation ondry compressed gaseous and liquid chlorine applications are described in GEST94/207 - Code of Pract ice for the Insta l lat ion o f Pressure Sensing Devices on

Dry Gaseous and L iqu id Chlor ine A ppl ica t ions

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