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Cryogenic re-refrigeration, or how to freeze food more economically using indirect heat exchange and turbo-expansion.

Author(s) : BARON S., TREMBLEY J.

Summary

Cryogenic refrigerants are normally used in an open cycle, in direct contact with the material to be frozen and at pressures close to atmospheric. Alternatively, it is possible to increase the available refrigeration by up to 30% by running the process with indirect cooling and by isentropically expanding the refrigerant vapour at the downstream end of the process, after which the now-colder vapour is recycled. A convenient way to do this is to run the upstream part of the process at an elevated pressure in the range 5-15 bar. The energy consumed by a liquid nitrogen pump in generating the higher pressure is small compared to the enthalpy recovered in the expander. Care is needed in the choice of turboexpander, because of the requirements for low temperatures, high flow rates, high isentropic efficiency and low shaft power. The turboexpander and closed nitrogen circuit increase capital costs compared to direct-contact freezing, but operating costs are 15-20% lower.

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Details

  • Original title: Cryogenic re-refrigeration, or how to freeze food more economically using indirect heat exchange and turbo-expansion.
  • Record ID : 2004-2280
  • Languages: English
  • Source: 21st IIR International Congress of Refrigeration: Serving the Needs of Mankind.
  • Publication date: 2003/08/17

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