Distillation: apparatus – Apparatus – Systems
Patent
1990-04-16
1992-04-28
Manoharan, Virginia
Distillation: apparatus
Apparatus
Systems
159 242, 159DIG16, 159DIG40, 2021856, 202262, 202205, 203 11, 203 26, 203 91, 203DIG4, 203DIG8, B01D 310
Patent
active
051085488
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to low pressure distillation apparatus, that is distillation apparatus in which evaporation takes place at sub-atmospheric pressures. Although the invention will be described with particular reference to the desalination of water it is not limited to that use.
BACKGROUND ART
Much attention has been given to methods of improving the efficiency of distillation systems, especially those used in water desalination, with a view to reducing the costs of production of purified water.
It is usual practice in distillation to condense the distillate in a condenser section of the evaporation chamber. Vapor enters the condenser section, is cooled and condensed by a cooling water coil, and gives up heat including latent heat of condensation. Cooling water enters this coil from a separate circuit, takes up the "recovered heat", and emerges at a higher temperature. The "recovered heat" is often utilized to heat feed liquid entering the evaporation chamber by using the feed as coolant in the cooling water coil.
In order to improve efficiency, it is common to use a mechanical vapor compression system in which vapor is withdrawn from the evaporation chamber and condensed by means of a centrifugal compressor. The compressor is typically the most expensive component of the plant, requiring vapor seals, bearings, oil seals and rotating parts. It is also the most easily damaged component.
There are many advantages in operating stills at sub-atmospheric pressures. Such systems operate at low temperatures for example in the range 30.degree. to 50.degree. C. At these temperatures, problems associated with the formation of scale are greatly reduced and plastics construction materials may be used. However, the difficulties in using vapor compression in sub-atmospheric systems are greater in comparison with stills operating at or above atmospheric pressure, since the compressor must extract vapor at a lower pressure.
An object of the present invention is to provide an efficient apparatus for distillation which is operable at sub-atmospheric pressures and which alleviates at least some of the disadvantages of the prior art.
DISCLOSURE OF THE INVENTION
According to the invention there is provided a low pressure distillation apparatus comprising:
a sealed evaporation chamber having a feed liquid inlet port, a concentrated liquid outlet port, and a vapor outlet port; the vapor outlet port being in communication with a vapor entrainment device situated within a distillate tank, wherein, in use of the apparatus vapor condenses in the entrainment device releasing latent heat of condensation to the distillate.
For preference the vapor entrainment device may comprise a rotating impeller pump which is wholly immersed in liquid distillate and which generates a stream of liquid distillate into which the vapor is entrained and condensed such that the latent heat of condensation of the vapor is recovered directly by the distillate. This heat may subsequently be used to assist in vaporization of the liquid in the evaporation chamber by use of a heat-pump system.
Advantageously there is a shear tube in the inlet of the impeller to prevent pre-swirl of the distillate and entrained gas and vapor.
Preferably there is a heating coil in the evaporation chamber and a first heat exchange coil in the distillate tank, the heating coil being arranged in series and upstream of the first heat exchange coil in a heat-pump circuit The concentrated liquid is drawn off and sometimes referred to as "residue", "bottoms" or "blow-down". The concentrated liquid outlet port may be in communication with a blow-down entrainment device situated within a blow-down tank. The blow-down entrainment device may incorporate a second rotating impeller pump which is wholly immersed in its delivery medium.
In one embodiment a second heat exchange coil is situated in the blow-down tank and is connected in series in the heat-pump circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the invention will now be described by
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Keane Brian H.
Shafaghi Farhad
Spencer Colin W.
Manoharan Virginia
Valuepace Limited
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