Compression chlorine

The evening shift loaders first task was to return the repaired chlorine line to service. The loader quickly pressured the section of piping with 100 psig (690 kPa gage) compressed air and determined the repairs were leak-free. He next opened a valve connecting the 2-inch (5 cm) pipeline to 160 psig (1100 kPa gage) compressed chlorine gas. 

Introduction. The object of this experiment is to illustrate the method used for the chlorination of organic compounds in the liquid phase. The use of the macro method is restricted to advanced students, since it involves the use of compressed chlorine. Although it is possible to generate chlorine in the laboratory for the preparation of 25-30 g of material, the time required for the completion of the experiment is rather long. The semimicro method permits chlorination of 5-10 g of a substance within one or two hours. 

Calcium or sodium hypochlorite (e.g., household bleach) is also effective for disinfection of water supplies, and is a convenient choice for smaller volumes when required, such as for a single household, a hamlet, or for small campsites [7, 8]. Hypochlorite solutions are somewhat more expensive to buy than compressed chlorine gas, but the equipment required for metering it into the supply is simpler. With hypochlorite salts, similar equilibria operate to rapidly establish a concentration of hypochlorous acid, which corresponds to the amount of hypochlorite salt added (Eq. 5.7, Table 5.2). 

C. Formation of Chlorine Hydrate. Because of the presence of traces of water in compressed chlorine, the chlorine hydrate discussed in Section 9.1.3.5 again becomes a problem. As chlorine condenses, some of the water accompanies it. Depending on the temperature, a certain amount of water is soluble in the chlorine. So long as this solubility is not exceeded, the condensate remains homogeneous and solid hydrate does not form. Below we develop an estimate of the solubility of water in liquid chlorine and show that, because of its very low solubility in chlorine and therefore its very high activity coefficient in solution, it behaves as a volatile component. The practical effect of this is that water tends to concentrate in the gas phase in most first-stage liquefiers. 

There may be more oxygen in membrane cell chlorine than in the gas from the other processes. This can be a problem if the compressed chlorine is fed directly to chlorination processes. An offsetting advantage is that there is essentially no hydrogen in the chlorine gas. 

The suction pressure control system shown in Fig. 11.24 uses a fail-open recycle valve to return compressed chlorine from discharge to suction. In the common situation with multiple compressors, there is one control system, and the chlorine is piped from the common discharge header to the suction header. The control valve should have an equal percentage characteristic and should be sized to handle the total capacity of the compressors when 90% open. It should have excellent turndown in order to control small recycle flows and should be aided by a valve positioner. 

Direct feed of compressed chlorine to another process is possible only when the quality of the chlorine meets the user s needs. The receiving process determines and controls how much chlorine is taken from the header, but another control valve is necessary at the compressor discharge header in case the user attempts to take more chlorine than is available. The liquefiers normally handle the chlorine not taken by the direct user. It has been common practice to design the liquefaction plant for full cell output, so that the cells can operate at full rate during short upsets in the user s process. This approach may be modified to suit restrictions on maximum chlorine inventory. In any case, the liquefiers should always have some chlorine gas fed to them to keep them operational and ready to handle full chlorine production should the direct user suddenly stop taking gas. In addition, a supply of liquid chlorine may be needed for a suction chiller. A bypass line around the control with a restricting orifice sized for about 10% of full capacity at the control valve drop can meet this requirement. Any chlorine not taken... 

Liquid-Ring Pumps. Many smaller plants, in particular, compress chlorine with liquid-ring pumps. Section 9.1.6.2C discusses the mechanism of their operation, and Fig. 9.23 is a typical flowsheet. Here, we consider them as sources of vacuum. 

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