Liquefaction chlorine

Chlor-verbindung,/. chlorine compound, -ver-i fliissigung, /. chlorine liquefaction, -wasser, n. chlorine water. 

On this basis a demonstration plant having a capacity of 10 000 tonnes a-1 of chlorine was built in the Bayer production plant at Leverkusen. The plant was successfully commissioned on 4 January 2000. Figure 4.8 illustrates the electrolyser section of the plant, with the peripheral apparatus arranged mostly outside this building. The 76-element electrolyser was found to behave very smoothly and could be immediately operated up to 5 kA m-2 without any problems. Permanent operation is performed at 4 kA m-2. The power consumption was found to be about 1080 kWh tonne-1 CI2 with a typical current efficiency of nearly 100%. Chlorine purity is found to be 99.9%, which obviates the need for a chlorine liquefaction purification and therefore simplifies the plant drastically. 

The chlorine liquefaction plant comprises a bromine-removal column, a compression-condensation unit and a Tetra absorption/distillation unit (Fig. 14.2). Waste streams of chlorine are absorbed in diluted cell-liquor in the chlorine destruction area. As a result, the destruction liquid contains sodium chloride and less sodium hydroxide than is usual. Bromine from the bromine-removal column is also added to the chlorine destruction unit. The hypochlorite solution that is formed contains a reasonable amount of bromine and salts. However, it is a hypochlorite of non-marketable quality. 

An additional advantage is the oxidation of all organic and nitrogen-containing components of the brine in the brine degassing tanks. These impurities are not fed to the electrolysis cells, but the products removed to the chlorine destruction unit and incinerator. Control of NCI3 concentrations in chlorine liquefaction has become easier. 

Whilst there are many other factors that would have to be taken into consideration, the four major components of cost savings developed in this chapter add up to a total annual saving of US 2.7 million, as shown in Table 21.3, which is equivalent to US 13 per tonne of chlorine. As can be seen, the economic incentive to delete the chlorine liquefaction is truly large. The question is how to do this in the most reasonable manner. 

In the first step the chlorine from the tail gas and chlorine feed reacts with the caustic in the jet-loop reactor. The advantage of the jet-loop reactor is that it also acts as a suction device for the gas stream. The residence time of the liquid in step one is dependent on the capacity of the hypochlorite production and liquid level in the tank and varies between 1 and 4 h. A heat exchanger in the loop controls the temperatures in steps one and two. The amount of caustic in the feed-tank of step two is the back-up for failure of chlorine liquefaction. 

Hydrochloric acid may be purchased or produced internally. It is a widely available commodity, easily obtained in good quality. HCl is available in the anhydrous form as well as in the form of aqueous acid (up to 23° Be or about 37% HCl). The use of aqueous acid is standard in the chlor-alkali industry, and we do not discuss anhydrous HCl here. Byproduct acids are available, sometimes at lower prices, and may be suitable for use in the chlor-alkali process. Their quality should be checked carefully, and testing may be advisable before use. When HCl is produced from chlorine liquefaction tail gas, the absorbing water is the most likely source of impurities. Demineralized water is the standard source when producing acid for use in a membrane-cell chlorine plant. A certain amount of chlorine tends to be present in burner acid. This can be minimized by process control, and a small bed packed with activated carbon (Section 7.5.9.3B) is a useful safeguard. Usually only the acid intended for use in the ion-exchange system need be treated in this way. 

The first seven considerations account for the long dominance of chlorofluoro-carbons (CFCs) in chlorine liquefaction systems. These refrigerants are outstanding in the first four points listed. The fourth is especially important in our particular case. Accidental mixing of chlorine and the refrigerant should not create a hazard. Also, generally CFCs have low specific heat ratios. This property equates to low eneigy consumption in compression (point 5). 

Condensing chlorine washes hydrate from the tubes as it forms. Since it is lighter than chlorine (density of 1.23 vs 1.5-1-), hydrate floats on the liquid accumulating in the shell. Unless it is removed, it can eventually restrict flow or even plug the equipment. Because the quantities involved are small, it is not rare for a chlorine liquefaction plant to operate for long periods with occasional shutdowns for cleanout. 

S. Hieger, Retrofitting a Chlorine Liquefaction System to R-134a, 39th Chlorine Institute Plant Managers Seminar, Washington, DC (1996). 

Chlorine Liquefaction. One or more liquefier units can be fed through the liquefier feed valve (Fig. 11.27). Each liqueiier unit will have its own manual isolation valve. A liquefier unit comprises a complete refrigeration system, a chlorine liquefaction exchanger, and a knockout pot for vapor-liquid separation. 

Air systems include compressed air as a plant utility and refined versions for more specialized uses. These include instrument air and breathing air. Of particular significance in a chlor-alkali plant is a supply of dry air for use in the chlorine processing section. An alternative to dry air is nitrogen, which also serves as an inert gas in the hydrogen plant and sometimes in chlorine liquefaction and tail-gas handling. For convenience, we include the discussion of nitrogen in the section on air systems. 

Section 9.1.7.1 on chlorine liquefaction briefly describes the typical mechanical refrigeration cycle. Several different types of compressor appear in water chillers. They include reciprocating, screw, and centrifugal machines. The best choice depends very much on the suitability of a manufacturer s package details. The choice of refrigerant is not constrained by reactivity, as in the case of chlorine compression. 

Figures. Explosive limits of chlorine-hydrogen-other gas mixture Horizontally hatched area = Explosive region with residue gas from chlorine liquefaction (O2, Nj, CO2)...

Figure 80. Multistage reciprocating compressor for chlorine liquefaction at i MPa with cooling water at 15 C with liquid chlorine scrubbing...

Chlorine boiled off in the stripper passes upward through a packed top section of the column where it is scrubbed and purified by liquid chlorine from the discharge knock-out drum. The stripper overhead stream, a mixture of chlorine and a small amount of inerts, is sent to the chlorine liquefaction system or recycled to the suction knock-out drum to maintain the stripper reflux [223], [224]. 

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