Patent GB-834467-A (GB)
Title: A flash evaporator
IPC: B01D3/06
Filed: 1957-03-29
Abstract: <PICT:0834467/III/1> <PICT:0834467/III/2> A flash evaporator, which is particularly suitable for use in the distillation of sea water, comprises a cylindrical chamber maintained under reduced pressure, means for introducing a stream of the heated liquid along one side of the chamber so that it flows down the inner wall, a sump at the bottom of the chamber for collecting unevaporated liquid, and a cylindrical condenser disposed transversely to the evaporating chamber with the top of the chamber opening into the bottom of the condenser at their intersection.  The apparatus shown comprises a cylindrical vessel divided by partitions 14 into a plurality of chambers 20, 21, 22, 23, connected in series, above which are mounted a series of condensers 30, 31, 32, 33 respectively.  The chambers are evacuated via pipes 114 provided at the ends of each condenser. The liquid to be evaporated is introduced through inlet 42 into the tubes 40 of condenser 33 and flows in series through all the condensers wherein it acts as a cooling medium and is itself heated; the preheated liquid is further heated in a supplemental heater (not shown), such as a boiler or the cooling system of an I.C. engine; the hot liquid is then introduced into chamber 20 via inlet 52 and passes successively through each evaporating chamber. Each chamber is provided with a partition 54 which, together with partition 14 and cover 55, forms a manifold 56 communicating at opposite ends with a pair of headboxes 57 extending along opposite sides of the chamber. The lower part of each headbox has an opening over which an orifice plate 60 is bolted.  Outlets 66 are provided in the bottom of each chamber, and these outlets lead to a sump passage 68 which is divided up into separate chambers 71, 72, 73, 74 by partitions 70.  Sump chamber 71 communicates with the inlet manifold 56 of evaporating chamber 21; the second sump chamber communicates with the inlet manifold of the third evaporating chamber, and so on.  Baffles 76 enable liquid-seals to be maintained between successive evaporating chambers.  As the hot liquid passes through each evaporating chamber, a portion of it vaporizes as it flows from the orifices downwards over the wall of the evaporating chamber to outlets 66.  The last sumpchamber 74 has a pair of outlets 80, through which residual unevaporated liquid passes to waste.  The entrainment of liquid-droplets in the vapours entering the condensers is partly obviated by horizontal baffles 90 having sidewalls 92.  Entrainment is also reduced by a mass of wire-mesh or steel wool 98 supported on a perforated plate 96 below the aperture 93 of each condenser. Liquid accumulating on baffles 90 is returned to the evaporating chambers via drain-pipes 100.  The vapour is directed into the upper part of each condenser by baffles 102.  Condensate is removed from the condensers via outlets 108; the condenssate from condenser 30 passing through a U-shaped liquid-seal into condenser 31 where it unites with the condensate accumulating in the latter; the combined condensate passes to condenser 32, and from thence in condenser 33. The total combined condensate is withdrawn from condenser 33.  In an example, sea water is heated to 147 DEG  F. by passing it through the condensers.  The temperature of the water is then raised to 170 DEG F. in the supplemental heater; and it is introduced into chamber 20 which is maintained at a pressure of 8.77" Hg.  The pressure is maintained at progressively lower values in the subsequent evaporating chambers; that in the final chamber 23 being 2.70" Hg. The residual unevaporated brine is discharged at a temperature of 112 DEG  F.  The sizes of the orifices in the evaporating chambers are chosen to suit the desired operating conditions.