GB1241190A - Method and apparatus for evaporating a liquid containing a dissolved solid - Google Patents

Abstract

1,241,190. Evaporators; separation of salts from brine. J. B. WARD, C. B. LAKE, G. HENDERSON, F. V. LOCKMAN and M. T. RIBACK. 19 Nov., 1968, No. 54882/68. Heading BIB. Solids are separated from solution in a liquid by evaporating liquid from the solution under atmospheric pressure until a substantial amount of the dissolved solid is precipitated, and then continuing the evaporation under reduced pressure in a flashing zone wherein further precipitation of solids takes place. water is evaporated from brine, e.g. sea water, by passing it through line 16 (Fig. 3) to the upward extensions 38a of the heat-transfer walls 26a (e.g. aluminium sheets) of a vapourcompression evaporator which is provided, in the heating chambers 24a with verticallyspaced, sloping condensate-collectors 42a. The evaporation is carried out at atmospheric pressure. The sea water flows down walls 26a as films 35a, the velocity of the films, at the level where heat-transfer commences, being at least 14 feet/second. The total height of each wall 26a and its extension 38a is preferably about 22 feet. The water-vapour, evolved from the films, are withdrawn from chambers 18a through line 19a into compressor 22a. A small amount of water is injected into the compressed vapour in desuperheater 23a, and the vapour is then passed through headers 41a into chambers 24a where the compressed steam condenses. The condensate flows down walls 26a as films, but these are prevented from becoming thicker than about 0.005 inches by collectors 42a. The condensate is withdrawn from the evaporator through line 28. Some of the brine, withdrawn through lines 44a, is recycled to feed-line 16, and the remainder is passed to a second evaporator of a series of three such vapourcompression evaporators 17a .. 17c (Fig. 1). The brine withdrawn from evaporator 17c is so concentrated that a substantial amount of the calcium sulphate has been precipitated. This brine is passed through filter 46, and the filtrate is submitted to further evaporation in three flash chambers 47a .. 47c maintained under progressively increasing vacua. Steam is withdrawn from the flash chambers through lines 53a .. 53c. The brine slurry from the last flash chamber is passed to filter 56 from which the calcium sulphate cake is withdrawn to tank 51, where it is stirred with condensate water, and then separated, and washed, on filter 63. The filtrate from filter 56 passes to evaporative-crystallizer 59, which is maintained under vacuum and at a temperature of about 130‹F., wherein small crystals of sodium chloride are formed. The slurry is passed to evaporative-crystallizer 69, at a temperature of 145‹F., where the NaCl crystals grow. The slurry then passes to evaporative-crystallizer 72 at 130‹F., and finally to centrifugal separator 74 in which the NaCI crystals are separated from the concentrated liquor.