Cryogenic Cooling Method Using a Gas-Solid Diphasic Flow of CO2

Abstract

The invention relates to a method implementing liquid CO 2 as a cryogenic fluid for transferring negative calories to products, said method being of a so-called indirect injection type wherein the liquid CO 2 is sent into a heat exchanger system where same evaporates, the method being characterized in that, prior to reaching the exchanger system, the liquid CO 2 undergoes an expansion operation, at a pressure selected to obtain a gas/solid mixture at the output of the expansion operation.

1 - 6 . (canceled) 
     
     
         7 . A process employing liquid CO 2  as cryogenic fluid, for transferring cold to products, process of the “indirect injection” type where liquid CO 2  is conveyed into a heat exchanger system where it evaporates, the transfer of cold to the products involving an exchange between the air surrounding the products and the cold walls of the heat exchanger, promoted by the involvement of ventilation means associated with the heat exchanger system, the process being characterized in that, before reaching the exchanger system, the liquid CO 2  has been subjected to an operation for reducing in pressure to a pressure chosen in order to obtain, at the outlet of the pressure-reducing operation, a solid/gas mixture. 
     
     
         8 . The process of  claim 7 , wherein before reaching the pressure-reducing operation, the liquid CO 2  exchanges heat with the cold gases obtained at the outlet of the heat exchanger system, in a means which makes possible such a heat exchange. 
     
     
         9 . The process of  claim 8 , wherein the exchange surface of the exchanger system is given dimensions so as to carry out, in the exchanger, only a partial melting of the entering gas/solid mixture, the complete melting of the mixture then taking place in said means which makes possible heat exchange. 
     
     
         10 . The process of  claim 8 , wherein said means which makes possible heat exchange is a plate exchanger. 
     
     
         11 . A plant for the transfer of cold to products using liquid CO 2 , the plant employing a process of the “indirect injection” type and comprising:
 a heat exchanger system capable of passing liquid CO 2  in transit therein; and 
 ventilation means associated with the heat exchanger system, capable of bringing the air surrounding the products into contact with the cold walls of a heat exchanger system, the plant being characterized in that it comprises a pressure-reducing system, positioned upstream of the exchanger system, thus capable of reducing the liquid CO 2  in pressure, before it arrives in the exchanger system, to a pressure chosen in order to obtain a solid/gas mixture at the outlet of the pressure, reducing operation. 
 
     
     
         12 . The plant of  claim 11 , wherein it additionally comprises a subcooling system, for example a plate exchanger, positioned in the plant according to the following arrangement:
 the subcooling system is positioned between the source of liquid CO 2  and the pressure-reducing system, in order to make it possible for the liquid CO 2  to be able to pass in transit by a first pathway of this subcooling system, before reaching the pressure-reducing system;   said arrangement is furthermore such that it makes it possible for the cold gases extracted from the heat exchanger system to pass in transit by a second pathway of the subcooling system.