GB794379A - Improvements in or relating to flash evaporating and condensing systems - Google Patents

Abstract

In apparatus wherein preheated liquid is introduced into a vessel maintained at reduced pressure so that flash-vaporization of part of the liquid occurs, and the vapour is condensed in another section of the same vessel, the partitions between the evaporator and the vapour-condensing sections are partly shaped to form a nozzle passage arranged so that the vapour flows from the evaporator section through the nozzle passage and then undergoes a sharp change of direction, whereby entrained liquid is separated out of the vapour, before the vapour enters the condensation section. The apparatus is suitable for distilling sea water to make boilerfeed water or drinking water. In the apparatus shown, partitions 16, 16 and 17, 17 divide the interior of shell 10 into evaporator sections 18, 18 and separator sections 20, 20; the lower parts of partitions 16 being submerged in a pool of unevaporated water in the bottom of the shell. The curved portions 25 of partitions 16 define a nozzle passage extending from one end of the shell to the other; and a vapour-deflector 30 is mounted below the outlet of the nozzle passage. The upper edges 28 of partitions 17 are disposed inwardly of, and in overlapping spaced-relationship with, the curved portions 25 of partitions 16, whereby two passages 29 are formed which lead from separator-sections 20 <PICT:0794379/III/1> <PICT:0794379/III/2> to the condensing spaces within the partitions. Passages 29 are provided with baffles 29a. The condensing spaces are provided with tubes 33, through which cooling-water is circulated in four passes from boxes 38, 39 mounted on the end-plates 12 of the shell. The apparatus is maintained at a low absolute pressure by a pump connected to conduits 32. Water, at a temperature higher than the boiling-point at the pressure in the shell, is supplied to pipes 27 which have openings through which the water is sprayed downwards into sections 18, where flash-vaporization takes place. The vapour flows down through the nozzle passage, and then undergoes a sharp reversal in direction so as to pass up passages 29 into the condensing-sections Entrained water is forced out of the vapour by centrifugal action during the change of direction; and residual droplets are removed by baffles 29a. The vapour condenses on tubes 33, and the condensate is withdrawn from the apparatus through conduits 31. Residual water is removed through outlet 22, and is pumped through heater 44 before being returned to spray-pipes 27. A periodic discharge is made by means of blow-down valve 49 in order to avoid undue concentration of salts in the spraywater. Make-up water is supplied through connection 50 having a valve 51 which is opened by float 52 when the water-level at the bottom of the shell falls below a predetermined height. In a modification (not shown) the arrangement is such that a portion of the vapour flows upwards through the condensing-sections, thereby heating the falling condensate; the hot water withdrawn from the apparatus is free from oxygen and is suitable for use as boiler feed water.