GB965750A - Improvements in flash evaporators for distilling sea or other brackish water - Google Patents

Abstract

965,750. Evaporators ; distilling sea-water. AMF INTERNATIONAL Ltd. Dec. 15, 1960 [Dec. 30, 1959], No. 44173/59. Heading BIB. In an evaporator, particularly for use in the distillation of sea water, wherein the sea water is heated and then passed successively through a series of flash chambers A<SP>1</SP> . . . A<SP>6</SP>, Fig. 1, via channels 1 which extend below the chambers, entrainment of saline droplets in the flashedsteam is minimized by providing plates 2, each having a horizontal upper edge, which constrain the water to flow in the form of a thin layer over the horizontal base of each flash chamber. The flash chambers, which are maintained under reduced pressure, are so arranged that the water follows a zig-zag course in passing through them. Tubular condensers B<SP>1</SP> ... B<SP>6</SP> are mounted above the flash chambers, each condenser being twice the length and half the width of a flash chamber, so that each condenser extends lengthwise over two flash chambers, and two condensers extend laterally over each flash chamber. The sea water to be distilled is pumped as cooling- medium through the condensers in the order B<SP>6</SP> ... B<SP>1</SP>, and is thereby preheated. An external heater for the water is provided between the last condenser and the first flash chamber. In order to minimize the formation of scale, the temperature of the water entering chamber A<SP>1</SP> is kept below 190 ‹C. by a valve which automatically controls the supply of the heating-medium, e.g. hot combustion gases, steam or hot water, to the external heater. The external heater may comprise a fuel-burner immersed in the sea water so that the combustion gases are in direct contact with the water. The temperature of the feed-water entering the first condenser is kept above a predetermined value, e.g. 70 ‹F., by mixing some of the warm unflashed brine (withdrawn from the last flash chamber) with the feed water. In an alternative embodiment, illustrated in Fig. 4 for use in an evaporator having four flash chambers, the warm brine from the last chamber A<SP>4</SP> is pumped through one pass of a heat-exchanger D<SP>1</SP>, and the feed water is pumped through the other pass. The condensing spaces are arranged in series so that the condensate (i.e. distilled water) flows from the first condenser B<SP>1</SP> through the succeeding condensers to the outlet. Automatic devices are described for shutting-down the plant in the event of a fault.