Distillation: apparatus – Apparatus – Systems
Patent
1987-03-03
1988-03-01
Bashore, S. Leon
Distillation: apparatus
Apparatus
Systems
202195, 202235, 203 2, 203 10, 203DIG4, 203DIG9, 203DIG17, 203DIG18, 159 281, 159 44, 159DIG27, 159DIG28, B01D 1300
Patent
active
047283971
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an apparatus for desalinating salt water by membrane distillation.
Apparatus utilizing membrane distillation are known to the art, inter alia from the Swedish patent specification No. 419 699. The Swedish patent specification describes an apparatus for membrane distillation comprising a plurality of first cassettes for conducting warm salt water and a plurality of second cassettes for conducting a cold liquid, such as cold sea water. Located between each pair of mutually adjacent cassettes is a separation cassette which separates one of the first cassettes from one of the second cassettes.
The separation cassette according to the aforesaid patent specification includes a hydrophobic porous membrane which constitutes one side surface of the cassette, and a thin plastics film which constitutes the other side surface of the cassette, the membrane being spaced from the plastic film so as to form an air gap between the membrane and the film. Warm salt water flows towards the membrane from the side thereof remote from the air gap and enters one of the first cassettes, whereas cold water flows into one of the second cassettes on the side of the plastic film remote from said air gap.
Distillation is effected in a manner such that the hot or warm salt water gives off water vapor which passes through the pores of the membrane and through said air gap, whereafter the water vapor condenses on the cold plastic film. The pores should be of a size which prevents liquid water from passing therethrough.
Such a distillation process affords a number of advantages; for example the process takes place at a temperature beneath the boiling point of water and approximately at atmospheric pressure, which enables a non-corrosive construction material to be used. In addition, such a process is relatively highly productive in relation to the size of the cassettes and the numbers thereof.
However, the process is encumbered with one serious disadvantage. This disadvantage is based on the fact that large quantities of energy are transported from the hot salt water on the evaporation side to the cold water on the condensation side for each product water-unit desalinated.
This energy transport results in a lowering of the temperature of the hot water flow and a corresponding increase in temperature of the cold water flow. Lowering of the temperature in the hot water flow and also the decrease in the temperature gap between the hot and the cold flow decreases the production of fresh water. In order to maintain an acceptable level of productivity, it is necessary to restrict these changes in temperature.
This can only be achieved by increasing the flows of heated salt water and cold water respectively through the desalinating unit.
This means that large quantities of salt water must be heated. In addition, large quantities of cooling water must be pumped through the distillation unit.
In order for such a process to function satisfactorily the water supplied to the process must be pre-treated by filtration and chemical treatment. Thus, the use of large quantities of water necessitates expensive heating and expensive treatment processes.
The present invention solves this problem, so that solely minor quantities of cold sea water supplied to the system need be heated and minor quantities of cold salt water need be supplied for cooling purposes, at the same time as a significant part of the energy transferred from the hot salt water to the cold salt water is recovered.
The invention also enables the process to be readily controlled.
Thus, the present invention relates to an apparatus for desalinating salt water, comprising a distillation unit which includes a porous, hydrophobic membrane which is pervious to steam or water vapor but is impervious to water, and a condensation surface arranged at a distance from the membrane, said distillation unit further comprising a first unit for heating water to be distilled and conducting said water on one side of the membrane, and a second unit arranged to conduct a liquid,
REFERENCES:
patent: 3340186 (1967-09-01), Weyl
patent: 3440146 (1969-04-01), Louw
patent: 3454470 (1969-07-01), Guarino
patent: 3454471 (1969-07-01), Kehoe
patent: 3563860 (1971-02-01), Henderckx
patent: 3878054 (1975-04-01), Rodgers
patent: 4316772 (1982-02-01), Cheng et al.
patent: 4391676 (1983-07-01), Torberger
patent: 4545862 (1985-10-01), Gore et al.
patent: 4620900 (1986-11-01), Kimura et al.
Findley, "Vaporization Through Porous Membranes", May 15-18, 1966, pp. 129-131.
Kjellander Nils
Rodesjo Bo
Bashore S. Leon
Manoharan V.
Svenska Utvecklings AB
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