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Optimising chlorine compression design with vapour phase nitrogen trichloride destruction

Authors

  • K. Maka,

    1. Engineering Services—Imperial Oil Canada, 237 4th Ave. SW, Calgary, Alberta, Canada, T2P 3M9
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  • Graeme W. Norval

    Corresponding author
    1. Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, Ontario, Canada, M5S 3E5
    • Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, Ontario, Canada, M5S 3E5
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Abstract

Nitrogen trichloride (NCl3) is a by-product of electrolytic chlorine manufacture, produced when the brine is contaminated with ammonia. A common treatment method is a thermal destruction process in which the NCl3 is absorbed in a solvent (CHCl3) using a distillation column with no liquid bottoms product. The chlorine gas is cooled through direct contact with liquid chlorine, which flashes and condenses the solvent and NCl3 vapours. The condensate drains through trays to a reboiler in which the NCl3 decomposes while the chlorine, solvent, NCl3 solution boils. This process is well-known and widely practiced but is known to experience catastrophic detonations. A vapour phase thermal decomposition of NCl3 does occur, particularly when the heat added through compression is considered. The known data on this decomposition reaction have been collected and converted in a rate expression that allows for integration within an ASPENPLUS process model. Different options for the compressor, precooler, intercooler and liquefier operations are considered, and their impact on the compressor and liquefier duties is reported. A different approach to the design and operation for a chlorine compression/liquefaction train is presented and discussed. © 2013 Canadian Society for Chemical Engineering

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