Sea water evaporating and distilling plant

摘要

An evaporator of the vapour-compression type for use in the distillation of sea water is provided with a standpipe which is connected to the brine-outlet of the evaporator; the sea-water feed is supplied to this standpipe, and part of the hot mixture of brine and fresh sea water is continuously pumped from the standpipe for introduction into the evaporator. The standpipe is preferably vented to the atmosphere so that the sea water is deaerated. The apparatus has the advantage that a sea water/brine mixture can be evaporated with less scale formation than occurs in the evaporation of an equal body of sea water. The apparatus shown comprises heat exchanger 36, standpipe 41, evaporator 10, and auxiliary boiler 24 which is heated by electric elements. In the evaporator is a boiler chamber 11 having a corrugated heater 14 which is supplied with steam though conduit 16. The brine outlet of the boiler chamber is connected to the standpipe by conduit 47. Above the boiler chamber is a water-reservoir 13 which supplies feed to the boiler chamber via pipe 12. When the brine in the boiler chamber covers the end of the pipe 12, the body of water in the reservoir is balanced, via conduit 47, by the column of brine in standpipe 41. Below the boiler chamber is a chest 25 which receives, via annular opening 15, condensate from the interior of the heater 14. This condensate, i.e. the distilled water product, collects in sump 17. The bulk of this hot distilled water is pumped via line 58 to heat exchanger 36; and the cooled product is withdrawn from the system through line 60. Above the reservoir 13 are a centrifugal separator 18 and a steam-dome 19, the latter leading via conduit 20 to compressor 21 which is driven by motor 22. A small quantity of the water in sump 17 is pumped via line 61 to the upstream side of the compressor. Sump 17 is connected to auxiliary boiler 24 by pipe 63, so that boiler 24 contains a body of distilled water at the same level as the distilled water in the sump. The steam-inlet conduit 16 of heater 14 extends into the vapour space of the boiler 24 by a slotted extension 16a; the vapour space of the boiler is also connected to the compressor 21 by slotted conduit 23. The slots in conduits 23 and 16a eliminate pulsations from the system. Chest 25 is connected to steam-dome 19 by line 64; valve 65 being open when the evaporator is being started-up. The sea water is introduced into the system through line 30 and is pumped through valve 34 (controlled by float 35 in reservoir 13) and line 32 to tube 38 of heat exchanger 36. While flowing up tube 38, the sea water is preheated by hot brine, from standpipe 41, flowing down tube 37, and by hot distillate, from sump 17, flowing down tube 39. The preheated water flows through line 40 and is discharged tangentially into the dome 44 of standpipe 41. The water spills down over pans 45 and then mixes with the hot brine in the lower part of the standpipe. Steam and air are vented from chest 25 into standpipe via line 48. Air is vented from the system via valve 46 at the top of the standpipe. The mixture of brine and de-aerated feed, which is at a temperature near the boiling point, is withdrawn from the standpipe through line 50; part of the mixture is pumped via line 52 to reservoir 13 and the remainder is pumped through line 53 to heat exchanger 36, the proportions being controlled by valves 54 and 55. The mixture is pumped from the standpipe to the reservoir at a rate in excess of the evaporation rate (in chamber 11) so as to induce evaporator-to-stand-pipe flow in pipe 47. Standpipe 41 is fitted with a pair of sight-glasses g and g1 which contain electrical probes p and p1, respectively, to actuate relays for energizing the heating elements in boiler 24. If the liquid column in the standpipe is below a desirable level, the level in the evaporator will also be low so that the immersed area of heater 14 will be small and steam-generation will be low. When however the liquid column falls below a preselected level, the probes actuate the relays to energize the heating elements of heater 24. Conversely, if the level rises above a preselected level, the probes will open the relays to de-energize the heating elements. Specifications 642,845 and 674,385 are referred to.