GB687106A - Improvements in and relating to the concentration by evaporation of heat sensitive liquors - Google Patents

Abstract

<PICT:0687106/III/1> Heat-sensitive liquids such as fruit juices, coffee extracts and milk, are concentrated by evaporation under reduced pressure in a climbing-film evaporator, by heat-exchange with a compressed gas such as ammonia or sulphur dioxide. The compressed gas is thereby liquified in the evaporator and the resulting liquid, after cooling, is used as cooling-medium in the condenser for the process-vapours. The cooling liquid vaporizes in the condenser; and the gas, after compression, is re-circulated to the evaporator. The liquid heating-cooling medium is preferably cooled, between the evaporator and the condenser, by heat-exchange with cooling water and partial flash-vaporization. Weak liquor is passed from storage-tank 1 through heater 3 wherein the temperature of the liquor is raised several degrees above its boilingpoint under the low-pressure existing in condensers 5 and 9. The heated liquor flows through valve 2 into separator 4, which is maintained under reduced pressure, so that flash-vaporization of part of the liquor occurs. The separated vapour is condensed in condenser 5, the condensate being withdrawn by pump 6. The liquor withdrawn from separator 4, is passed to climbing-film calandria-evaporator 7 wherein further evaporation takes place. The mixture of concentated liquor and vapour enters separator 8; the separated vapour passes to condenser 9 from which the condensate is removed by pump 10, and the concentrated liquor is withdrawn from the separator by pumps 11. The heating and cooling in the system is effected as follows:-Compressed gas from compressor 12 is introduced through valves 13 and 14 into the calandria of evaporator 7 and heater 3. The greater part of the compressed gas is condensed to liquid by heat-exchange with the process-liquor; and the two condensates are passed, by way of traps 15 and 16, through coil 17 which is mounted in a tank supplied with a continuous flow of coolingwater, introduced through valve 18 and withdrawn at overflow 19. The cooled liquid is then passed through expansion valve 20 whereby a part of it is flashed into vapour. This vapour is separated in receiver 21, and passed through pipe 25 to compressor 12. The cooled liquid from receiver 21 is introduced through pipes 22, 23, 24 into condensers 5 and 9 wherein it absorbs heat and evaporates, by heat-exchange with the process-vapours from separators 4 and 8 respectively. The vaporized gas is passed to the compressor through receiver 21 and pipe 25, for compression and recirculation to evaporator 7 and heater 3. Specifications 498,305 and 575,118, [Group VI], are referred to.