Chlorine processing protective systems

Other metals that have favorable reversible Flade potentials and form passive film on their surfaces include titanium, silicon, aluminum, tantalum, and niobium. Naturally formed aluminum oxide protects the underlying aluminum metal at pH between 4 and 8. Titanium possesses very high oxidizing potentials and is used to manufacture anodes for cathodic protection systems for the chlorine-alkafi process (production of hydrogen, chlorine, and sodium hydroxide) and many other appfications. 

Returned vehicles and shipping containers frequently are emptied before reuse or to allow maintenance and revalving. Once the operators have established that the chlorine is free of dangerous contaminants, they can rework it at a rate determined by the capability of the process. While the chlorine is nearly always dry and often at or above process pressure, it is a common practice to introduce it to the inlet of the chlorine dryers. Its rate of entry into the process must be limited, and Section 11.3.2.3B describes the need for control and protective systems. 

Fine particles such as clays are normally removed by flocculation using chemicals such as aluminium sulphate. The floes can entrap bacteria and their spores protecting them from chlorination. The vast majority of floe particles are removed during processing but if one or two pass through the system the entrapped bacteria will be unaffected by the final disinfection stage. 

Cathodic protection is commonly employed in many chemical plants depending on the compatibility of the process medium with the CP system. Sacrificial anodes may produce unwanted corrosion products or permanent anodes may generate chlorine and other gases and thus affect the quality of the medium stored or transported in the vessels, piping and so forth. Cathodic protection of the most... 

Other Processes. Silver s discussion of tail-gas recovery systems [77] covered a number of other processes. Those included here are whole-stream absorption of chlorine from cell gas, absorption of chlorine from tail gas by cold water, and adsorption. As always when hydrogen is present in the gas, protective measures are necessary when the removal of chlorine can produce a hazardous mixture. 

The immediately obvious hazard in a dry air distribution system is the entry of chlorine into the air lines during pressure reversals. Some plants use non-retum valves to protect against this. The reliability of these valves is questionable, and the authors recommend the use of automatic valves that close when the differential pressure across them reverses. Figure 11.51 illustrates this technique in a different application. These valves can be used in conjunction with non-retum valves when some redundancy is desired. Section 12.7.2 reviews some of the arrangements used to connect air and other utilities to process systems. 

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