Patent GB-1252981-A (GB)
IPC: F28C3/00
Filed: 1969-02-05
Abstract: 1,252,981. Cooling conveyed materials. E.I. DU PONT DE NEMOURS & CO. 5 Feb., 1969 [6 Feb., 1968; 19 April, 1968; 30 Jan., 1969 (3)], No. 6232/69. Heading F4H. Articles or materials are cooled by direct contact with a boiling liquid freezant in a vessel which is open at its top to the atmosphere and which contains a freezant vapour condenser to avoid the escape of freezant vapour and to maintain in the lower part of the vessel a layer of gas which comprises only freezant vapour. The articles or materials are passed into and out of the freezant vapour layer either through a passage which terminates within the layer or on slow moving conveyers so that the layer is disrupted as little as possible. As illustrated in Fig. 1, articles are passed by a conveyer 4 into a sluice pan 9 containing freezant. A pump 10 maintains a fast moving surface current in the sluice pan to carry the articles to an output conveyer 13. Freezant vapour generated by contact with the articles forms a layer of 100% freezant vapour whose top is indicated at 5. Above the level 5 is a freezant vapour/air mixture whose freezant concentration decreases to the top of the vessel. The level 5 is maintained between the limits 18 and 19 by a condenser 17 which avoids the escape of substantial amounts of freezant from the vessel. Liquid freezant from the condenser falls into the sluice pan and into a sump 16. The depth of the sluice pan is such that articles falling from the conveyer 4 do not touch the bottom of the pan. For servicing purposes, the freezant may be withdrawn into a tank 24, and after servicing may be returned to the vessel leaving any sludge to be removed through a valve 26. Make up freezant may be supplied from a store 20. As illustrated in Fig. 2, articles are passed down an entrance passage 36 into a sluice pan 41 after which they are further cooled on a conveyer 47 by films of liquid freezant formed by running the freezant over plates 51. A baffle 44 prevents liquid freezant from the condenser 43 from contacting articles on the conveyer 47. The upper limit of the 100% freezant vapour layer is indicated at 40 and the maintainance of quiescent conditions is aided by a baffle 45 and by a honeycomb structure 69. The latter is surmounted by a dust cover 70. Freezant vapour produced by a heater 58 may be passed to distributers 60 and 59 on the conveyer 47 and the output conveyer 52 in order to evaporate any liquid freezant remaining on the articles. Secondary vapour condensers 62 and 63 may be located in the outlet passage 53 to aid the conservation of freezant. In a modification, Fig. 6 (not shown), the sluice pan is omitted and a single conveyer carries the articles through the entrance passage, the cooling zone and the outlet passage. The freezant may be a single polyfluorinated hydrocarbon having a boiling point between 5‹ C. and - 50‹ C. or may be an azeotropic mixture of such hydrocarbons. Hydrate formation is minimized when wet articles are being cooled since the articles contact the liquid freezant early in the cooling process and are therefore passed quickly through the hydrate forming temperature range. The process of the invention may be used to freeze solid or liquid foods and to cool metal parts which require shrink fitting. The Specification lists foods to which the process is applicable and also discloses preferred freezants, operating conditions and dimensions.