GB812210A - Preservation of food and other perishable materials - Google Patents

Abstract

812,210. Preserving perishable materials. BRITISH OXYGEN CO. Ltd. Oct. 10, 1957 [Nov. 21, 1956], No. 35655/56. Class 49. [Also in Group XIII] Food and other perishable materials, e.g. corpses, are preserved by cooling with liquid air or nitrogen in a thermally-insulated container to below - 50‹ C., e.g. to about - 190‹ C., the liquid air or nitrogen having been liquefied by using liquid methane as refrigerant. In one form of the invention, air or nitrogen is compressed to 15 or 20 atmospheres, cooled to about - 160‹ C. by heat exchange with cold gaseous methane, liquefied by heat exchange with evaporating liquid methane, passed to a storage tank and thence to a thermally-insulated vessel containing food or other perishable material (preferably pre-chilled to about - 5‹ C.) until the desired low temperature is reached. In the form of the invention shown, risk of forming explosive mixtures of air with methane is avoided by cooling air with methane-cooled cooled nitrogen. Air at about 32 atmospheres leaves a compressor 10, is cooled and purified in heat exchanger 11 by a countercurrent stream of cold nitrogen and also any waste gaseous oxygen deriving from column 16, and is liquefied in heat exchanger 12 by heat exchange with liquid nitrogen evaporating at about 5.7 atmospheres. The liquid air may be fed directly through valve 13 into a thermallyinsulated container 14 containing perishable material, or it may be fed through valve 15 to rectification column 16 in which it is separated into fractions of liquid nitrogen and gaseous oxygen, these fractions being used respectively for cooling purposes in container 14 (after storage in vessel 19 if desired) and to assist in cooling air in heat exchangers 11 and 12. Nitrogen leaving exchanger 11 is compressed and cooled and passed through heat exchanger 22 and heating coil 23 by means of which heat is exchanged with evaporated methane in exchanger 22 and heat is supplied to evaporate liquid methane in storage vessel 24, thereby liquefying the nitrogen which is passed to heat exchanger 12. Nitrogen not required for heat exchanger 11 passes via line 26 to a heat exchanger 28 where it serves to cool nitrogen by-passing heat exchanger 22 through line 29. When liquid air is used for cooling purposes in container 14, enrichment of oxygen occurring in the container due to preferential vaporization of nitrogen during the cooling of the food &c. may require that the container after cooling be flushed out with a small amount of gaseous nitrogen to reduce the oxygen content therein. Specification 804,944, [Group XXVIII], is referred to.