Process for the concentration by evaporation in several stages of depositing of the salts

摘要

PICT:0748572/III/1 In a process for the evaporation of solutions containing salts, e.g. ammonium sulphate solution or cellulose waste liquor, wherein the solution is heated and partially evaporated in an initial evaporator 1, then subjected to reduced pressure in a series of zones 6, 8, 10, 11, 12, in which the solution evaporates with simultaneous cooling and separation of salt which forms a suspension in the residual-liquor, and the latter, after removal of the salt, is circulated back to zone 10 through a series of heat-exchangers 14 to 25 which are supplied with part of the steam evolved in zones 10 and 11, at least part of the fresh feed, introduced through pipe 35, is supplied to the initial evaporator 1 through a series of preheaters 36 to 47 which are disposed in parallel to heatexchangers 14 to 25 and are heated by the remainder of the steam from zones 10 and 11. The external heaters 2 of evaporator 1 are operated with fresh steam or backpressure steam from pipe 4. The process affords a saving of steam and obviates the formation of salt-incrustations on the surfaces of the apparatus. Each of the evaporators 10, 11, 12 is divided into a number of stages by partitions 13. The suspension of salt and residual-liquor is pumped from evaporator 12 through pipe 85 to separator 52, wherein the salt is deposited and withdrawn through pipe 53, while the residual-liquor flows through pipe 32 to heat-exchanger 14. After leaving heat-exchanger 25 the liquor passes through heater 33, wherein it is heated by heat-exchange with steam supplied through pipe 34 from evaporator 1, and is then introduced through pipe 76 into evaporator 10. The fresh feed after leaving preheater 47 is further heated in heaters 48 and 49, which are supplied with steam from evaporators 8 and 6 respectively, before it is introduced through pipe 3 into evaporator 1. A part of the fresh liquid may be introduced from pipe 35 through pipe 50 into the liquor circulating through heat-exchangers 14 to 25 and evaporators 10, 11 and 12. The three stages of evaporator 12 are connected to condensers 28, 29 and 30 which are connected in series with respect to the cooling water supplied through pipe 79.