GB997501A - Improvements in and relating to evaporators - Google Patents

Abstract

997,501. Multi-stage evaporators of the falling-film type. MACHINENFABRIK J. & H. W. VAN DER PLOEG N.V. May 3, 1963 [June 12, 1962], No. 17523/63. Heading BIB. In an evaporator comprising a plurality of tubular heaters wherein the liquid being evaporated flows in film-form down the inside surfaces of the tubes, the heaters being connected in series for the liquid, the rate of fall of the liquid-film in at least one of the heaters (other than the first) is increased by introducing into the top of the heater the vapour obtained by expansion of the liquid withdrawn from a preceding heater to the pressure prevailing in the first-mentioned heater. The apparatus shown comprises a three-stage evaporator in which milk flows through heaters 3, 14 and 6, successively. Milk at 185 ‹F. is pumped through conduit 2 to the top of heater 3 in which a temperature of 158 ‹F. prevails. Flash evaporation takes place in the top or the heater, and further evaporation takes place as the milk flows down the tubes in the form of a film. The mixture of milk and vapour is discharged into centrifugal separator 4. Part of the separated vapour is compressed in steam-jet compressor 7 and then used as heating-medium in heater 3. The remainder of the vapour removed from separator 4 is introduced, via conduit 5, as heating-medium into heater 6. The liquid withdrawn from separator 4 is pumped, together with the liquid accumulated at the bottom of heater 3, through conduit 10 into expansion vessel 11 where flash evaporation occurs, and the temperature of the milk decreases to 131 ‹F. The vapour is introduced through conduit 12 into the top of heater 6. The milk is lead from vessel 11 into the top of heater 14, which is operated at a temperature of 113 ‹F. The mixture of liquid and vapour discharged from heater 14 enters separator 15, from which the vapour passes to condenser 17. The milk withdrawn from separator 15 is pumped through conduit 19 into the top of heater 6. The conduit 19 includes a coil 20 which is heated to 158 ‹F. by the vapour in conduit 5. The temperature of the milk as it enters heater 6 is at a temperature of 131 ‹F. In the top of heater 6, the milk mixes with the vapour from expansion vessel 11, and is driven at high velocity down the internal surfaces of the tubes of the heater. A mixture of concentrated milk and vapour is discharged from the bottom of heater 6 into separator 21. The concentrated milk is withdrawn from the system via valve 23, but some of it may, if desired, be recirculated via valve 24 to heater 6. The vapour obtained in separator 21 is supplied as heating medium to heater 14. Part of the condensate of the heating-medium of heater 14 is vaporized in generator 26, and the vapour is passed through conduit 27 to expansion vessel 11. A four-stage evaporator, comprising two steam-jet compressors, is also described.