GB869848A - Multiple effect vacuum evaporator - Google Patents

Abstract

<PICT:0869848/III/1> A multiple effect vacuum evaporator comprises a plurality of separating stages each having a separating vessel and external heating means, the final separating vessel 18 containing a vapour condensing member 23 and each of the preceding separating vessels 1 containing a vapour scrubbing member 6. In Fig. 1 only one such preceding separating vessel is shown. Air is first evacuated from the apparatus through a pipe 29 and the liquid to be treated, e.g. a spent coagulating bath employed in rayon manufacture, is introduced by pipe 5 into the first stage heater 2 where it is heated by steam from a booster 17. Heated liquid passes into vessel 1 from pipe 3 and returns by pipe 4 to the heater 2. It is then passed by pipe 22, level controller 21, and pipe 22a into the second stage heater 15 where it is further heated by vapour generated in vessel 1, this vapour having passed through an entrainment separating member 7, a vapour scrubbing member 6, and a pipe 16. Part of the vapour from the first separating vessel may be returned to the first stage heater 2 by conduit 16a. Liquid from heater 15 passes into the second stage separating vessel 18 from pipe 19 and is recirculated to the heater by pipe 20 until liquid of the required density is obtained, when it is removed by an outlet 30. During evaporation a dilute solution of sodium hydroxide is showered into the vapour scrubbing member 6 equipped with perforated trays 6a from a nozzle 14a to remove acidic elements from the vapour. The sodium hydroxide solution is recirculated through pipes 8 and 14 by a pump 13 and is maintained at the temperature of the vapour generated in vessel 1 by a heating member 11. Cooling water is showered into the condensing member 23 from a nozzle 26 and the vapour generated in the vessel 18, after passage through an entrainment separating member 25, is thereby condensed. The member 23, which is equipped with perforated trays 23a, is heat-insulated on its inside 24, thereby preventing condensation of vapour before its entry into the member 23.