(BAT) Reference Document for the Production of Chlor-alkali ...
(BAT) Reference Document for the Production of Chlor-alkali ... (BAT) Reference Document for the Production of Chlor-alkali ...
Chapter 2 resaturated with salt. If needed, to reach a concentration of 50% caustic soda, the caustic liquor produced has to be concentrated by evaporation (using steam). Figure 2.8: Example flow diagram of the membrane cell process {The Figure was removed because the flow diagram is included in Figure 2.1.} Some electrolysers produce a more diluted 23 wt-% caustic soda. In this case, the caustic entering the cell has a concentration of approximately 20 – 21 wt-% and the heat of the electrolysis can be used to concentrate the 23 wt-% caustic solution to 32 – 34 wt-%. The overall energy efficiency is comparable to the aforementioned process with the 32 wt-% caustic solution but more equipment for the caustic evaporation is required. On the other hand, simpler and cheaper construction materials can be used in the caustic circuit around the membrane cells [ 3, Euro Chlor 2011 ]. Generally, the caustic produced in a concentration of 30 – 33 wt-% is concentrated to the usual commercial standard concentration of 50 wt-% by evaporation (using steam). Another possibility is to use the caustic produced in the membrane cells as feed to the decomposers of mercury cells. A flow diagram of a possible integrated plant is shown in Figure 2.8. Salt Depleted brine Salt Depleted brine Brine saturation Brine purge Brine saturation Brine purification Dechlorination Brine purification Dechlorination H 2 H 2 WORKING DRAFT IN PROGRESS 32 December 2011 TB/EIPPCB/CAK_Draft_1 Cl 2 Membrane cells Cl 2 Mercury cells Depleted brine Depleted Brine 30 – 33 wt-% NaOH Amalgam Mercury Water Decomposer 50 wt-% NaOH Figure 2.8: Flow diagram of the integration of the membrane and mercury cell techniques The concentration of sodium chlorate in the produced caustic soda typically ranges from Q 10 – 50 mg/kg [ 28, EIPPCB 2011 ]. The level depends on the membrane characteristics, the operational current density and the chlorate levels in the brine [ 3, Euro Chlor 2011 ]. The chlorine produced in membrane cells contains low concentrations of oxygen (0.5 – 2.0 vol-%). The formation of oxygen and chlorate can be depressed by selecting an anode coating with suitable characteristics and/or by decreasing the pH in the anode compartment [ 1, Ullmann's 2006 ], [ 10, Kirk-Othmer 2002 ]. The brine depletion in membrane cells is two or three times greater than in mercury cells which allows the brine system to be smaller, resulting in significantly lower recycling rates and less equipment needed compared to mercury cell plants of the same capacity [ 1, Ullmann's 2006 ], [ 22, Uhde 2009 ]. Membrane cells have The membrane cell technique has the advantage of producing a very pure caustic soda solution and of using less energy electricity than the other techniques processes. In addition, the membrane cell technique uses neither process does not use highly toxic materials such as mercury, which is classified as very toxic nor and asbestos which is classified as toxic
Chapter 2 (carcinogenic) [ 76, Regulation EC/1272/2008 2008 ]. Disadvantages of the membrane cell technique process are that the caustic soda produced may need to be evaporated to increase concentration and, for some applications, the chlorine gas produced needs to be processed to remove oxygen, usually by liquefaction and evaporation. Furthermore, the brine entering a membrane cell must be of a very high purity, which often requires costly additional purification steps prior to electrolysis (see Section 2.5.3.3 paragraph on brine purification) [ 1, Ullmann's 2006 ], [ 10, Kirk-Othmer 2002 ]. 2.4.2 The cell Various designs of membrane cells have been developed and used in commercial operations. Figure 2.9 shows a sectional drawing of a typical bipolar membrane electrolysis cell, Figure 2.10 shows a bipolar membrane cell room example and Figure 2.11 shows a monopolar membrane cell room example. Source: [ 136, Asahi Kasei 2008 ] [Source: De Nora] {The figure was replaced.} WORKING DRAFT IN PROGRESS Figure 2.9: Exploded view of a monopolar membrane electrolyser Sectional drawing of a typical bipolar membrane electrolysis cell TB/EIPPCB/CAK_Draft_1 December 2011 33
- Page 1 and 2: EUROPEAN COMMISSION JOINT RESEARCH
- Page 3 and 4: PREFACE 1. Status of this document
- Page 5 and 6: Reference Document on Best Availabl
- Page 7 and 8: 3.4.7 Emissions of noise ..........
- Page 9 and 10: 4.3.6.3.3 Chemical reduction ......
- Page 11 and 12: List of Tables Table 2.1: Main char
- Page 13 and 14: List of Figures Figure 1.1: Share p
- Page 15 and 16: SCOPE WORKING DRAFT IN PROGRESS Sco
- Page 17 and 18: 1 GENERAL INFORMATION 1.1 Industria
- Page 19 and 20: Chlorine production in Mt/yr 12 11
- Page 21 and 22: Chapter 1 Figure 1.4 shows the annu
- Page 23 and 24: Share of total capacity in % 70 70%
- Page 25 and 26: 1.4 Chlor-alkali products and their
- Page 27 and 28: Total consumption: 9 801 kt Miscell
- Page 29 and 30: 1.4.5 Consumption of hydrogen Chapt
- Page 31 and 32: Chapter 1 and hazardous waste incin
- Page 33 and 34: 2 APPLIED PROCESSES AND TECHNIQUES
- Page 35 and 36: Chapter 2 WORKING DRAFT IN PROGRESS
- Page 37 and 38: Chapter 2 The main characteristics
- Page 39 and 40: 2.2 The mercury cell technique proc
- Page 41 and 42: Chapter 2 Characteristics of the ca
- Page 43 and 44: 2.3 The diaphragm cell technique pr
- Page 45 and 46: Source: [ 2, Le Chlore 2002 ] [USEP
- Page 47: 2.4 The membrane cell technique pro
- Page 51 and 52: Chapter 2 The membranes used in the
- Page 53 and 54: Table 2.2: Typical configurations o
- Page 55 and 56: 2.5 Brine supply 2.5.1 Sources, qua
- Page 57 and 58: Chapter 2 centrifuges before dispos
- Page 59 and 60: Source: [ 29, Asahi Glass 1998 ] (p
- Page 61 and 62: Impurity Source Upper limit of brin
- Page 63 and 64: Chapter 2 No such dechlorination tr
- Page 65 and 66: Chapter 2 The cooling water is gene
- Page 67 and 68: Chapter 2 composition of the chlori
- Page 69 and 70: 2.6.11 Dealing with impurities 2.6.
- Page 71 and 72: Chapter 2 amount of chlorine, and t
- Page 73 and 74: 2.6.12.2 Chemical reactions Chapter
- Page 75 and 76: 2.7 Caustic processing production,
- Page 77 and 78: Chapter 2 2.8 Hydrogen processing p
- Page 79 and 80: 3 CURRENT PRESENT EMISSION AND CONS
- Page 81 and 82: Chapter 3 Table 3.1: Overview of em
- Page 83 and 84: 3.3 Consumption levels of all cell
- Page 85 and 86: 3.3.3 Ancillary materials Ancillary
- Page 87 and 88: Further materials and/or further us
- Page 89 and 90: Chapter 3 current) and the efficien
- Page 91 and 92: Chapter 3 distance means a higher f
- Page 93 and 94: 3.3.4.3.6 Production of caustic pot
- Page 95 and 96: Chapter 3 hydrogen at low pressure
- Page 97 and 98: 28 kg of hydrogen is produced {Thes
Chapter 2<br />
(carcinogenic) [ 76, Regulation EC/1272/2008 2008 ]. Disadvantages <strong>of</strong> <strong>the</strong> membrane cell<br />
technique process are that <strong>the</strong> caustic soda produced may need to be evaporated to increase<br />
concentration and, <strong>for</strong> some applications, <strong>the</strong> chlorine gas produced needs to be processed to<br />
remove oxygen, usually by liquefaction and evaporation. Fur<strong>the</strong>rmore, <strong>the</strong> brine entering a<br />
membrane cell must be <strong>of</strong> a very high purity, which <strong>of</strong>ten requires costly additional purification<br />
steps prior to electrolysis (see Section 2.5.3.3 paragraph on brine purification) [ 1, Ullmann's<br />
2006 ], [ 10, Kirk-Othmer 2002 ].<br />
2.4.2 The cell<br />
Various designs <strong>of</strong> membrane cells have been developed and used in commercial operations.<br />
Figure 2.9 shows a sectional drawing <strong>of</strong> a typical bipolar membrane electrolysis cell, Figure<br />
2.10 shows a bipolar membrane cell room example and Figure 2.11 shows a monopolar<br />
membrane cell room example.<br />
Source: [ 136, Asahi Kasei 2008 ] [Source: De Nora] {The figure was replaced.}<br />
WORKING DRAFT IN PROGRESS<br />
Figure 2.9: Exploded view <strong>of</strong> a monopolar membrane electrolyser Sectional drawing <strong>of</strong> a<br />
typical bipolar membrane electrolysis cell<br />
TB/EIPPCB/CAK_Draft_1 December 2011 33
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