GB1178031A - Improvements in and relating to Multiple-Effect Falling-Film Evaporators - Google Patents

Abstract

1,178,031. Evaporators, multiple-effect type; desalination of water. STEARNS-ROGER CORP. 24 April, 1967 [29 April, 1966], No. 18708/67. Heading B1B. Liquid, e.g. sea water, is evaporated by passing it successively through a plurality of banks of falling-film evaporator tubes 50 disposed in a thermally-insulated unitary enclosure 12 divided by vertical partitions 58, 60 into a series of chambers, each maintained at a lower pressure than the preceding chamber, the arrangement being such that the vapour given off in each bank of tubes 50 acts as heating- medium for the succeeding bank of tubes. The first bank of tubes is heated by steam from a boiler. Each partition 58 extends from the bottom of the enclosure 12 up to plate 64; and each partition 60 depends from the top and terminates just above the bottom of the en closure. Each chamber contains a bank of evaporator tubes 50 and a U-tube heatexchanger 48. The openings 90, 92 in plate 64 allow the hot vapour to circulate over the tubes. The lower ends of the tubes are surrounded by a tank 56 for the condensate which flows through a pipe 80 into tank 36 which is connected to a similar tank in the next effect, where partial flashing occurs. The process vapours pass from the reservoir 18 over the top of partition 58 into the following effect. Feed liquid enters the heat-exchanger 48 through inlet 110; and the preheated feed flows through an outlet to the heat-exchanger of the preceding effect, and finally to the annular distributor 52 in the dome 54 of the first effect. Concentrated liquor is withdrawn from reservoir 18 through outlet 20 and is pumped to the dome of the next effect. In the case of the last effect, the concentrated liquor is either withdrawn from the system, or recirculated to the evaporator tubes of the last effect. Non-condensable gases are withdrawn from tank 56 through line 142. The steamcondensate withdrawn from the first effect may be used to preheat the feed liquid, before being introduced into the flash tank 36 of the second effect. Before entering the heat-exchanger 48 of the last effect, the feed liquid may be preheated by heat-exchange with the vapour withdrawn from the last effect, and with the condensate withdrawn from the flash tank 36 of the final effect. The cooled condensate is the purified product, e.g. desalinated water.