Distillation: apparatus – Apparatus – Systems
Reexamination Certificate
2000-08-17
2004-12-21
Manoharan, Virginia (Department: 1764)
Distillation: apparatus
Apparatus
Systems
C159S044000, C159SDIG001, C202S172000, C202S176000, C202S185100, C202S205000, C203S011000, C203S071000, C203SDIG008, C203SDIG001, C203SDIG001, C203SDIG001, C203SDIG002
Reexamination Certificate
active
06833056
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a desalination method and a desalination apparatus that are used for desalinating raw water (e.g. saline water, sea water) by utilizing a local unused waste heat source, or relates to a desalination method and a desalination apparatus that produce fresh water or suitable water, drinking water or demineralized water by softening hard water, for example.
BACKGROUND ART
In various facilities, e.g. plants and marine structures, agricultural land, in inland areas, islands and desert regions, it is difficult to obtain suitable water for industrial use, drinking water or agricultural water, and in many cases, it is necessary to transport water by ship or truck or to lay pipelines. In other cases, these facilities use, a membrane or other types of desalination apparatus that necessarily consume a large amount of electric energy.
While thermal or nuclear power plants and so forth reuse high-temperature waste heat to generate electricity from steam turbines, low-pressure steam and its potential heat energy is discharged as waste. In fact, various kinds of low-temperature heat exist, for example, local (regional) temperature differences, terrestrial heat, and fermentation heat.
Many plants or other facilities having a waste heat source as stated above require demineralized water or water having a low impurity content to operate. The technique of transporting such water by ship, truck or pipelines as stated above suffers from the problem that the cost of transportation, the construction costs and maintenance and management costs are high. Membranes or other types of desalination apparatus consume a large amount of electric energy, and this also contributes to high operation costs.
In order to efficiently desalinate saline or hard water, vacuum evaporation type desalination apparatuses have been proposed.
As conventional vacuum evaporation type desalination apparatuses in particular, those which use a flash system or a multiple-effect can system have been proposed.
However, conventional flash or multiple-effect desalination apparatuses suffer from the disadvantage that the amount of water used for cooling in condensers is large, and the amount of water discharged is correspondingly large, resulting in the need for a great amount of pump power.
In a flash system, if the difference in temperature between a heat source used and cooling water is small, efficiency becomes low, and it is difficult to realize an efficient multiple-effect system. Similarly, the conventional multiple-effect can system suffers from the disadvantage that if a temperature difference between a heat source used and cooling water is small, it is impossible to increase the number of cans used to form a multiple-effect desalination apparatus. Accordingly, it is difficult to improve efficiency. Consequently, in a case where a temperature difference between a heat source used and cooling water is small, it is necessary to increase the heat transfer surface area of the apparatus. This causes a rise in installation costs and necessitates the use of a large installation area.
Furthermore, because both the systems use a continuous operation mode, it is necessary to run a fluid transfer pump, a vacuum pump, etc. at all times. Consequently, the amount of power consumed in the whole system is large, and efficiency is low. Regarding a vacuum pump in particular, because a high degree of vacuum is produced in a low-temperature condition, a large amount of water vapor is entrained in the extracted gas. Therefore, a large capacity vacuum pump which consumes a large amount of power is required.
The present invention was made in view of the above-described circumstances, and it is an object of the present invention to provide a desalination method and a desalination apparatus capable of producing fresh water stably at reduced cost by making cascade use of low-temperature waste heat as an energy source, which has heretofore been disposed of without being used.
DISCLOSURE OF INVENTION
To solve the above-described problems, according to a first aspect of the invention, a desalination method for raw water comprising the steps of: (1) supplying raw water into a confined space means; (2) evacuating the confined space means and depressurizing an inside thereof; (3) supplying low-temperature waste heat into the confined space means so as to subject the low-temperature waste heat and the raw water in the confined space means to heat exchange and generate water vapor in the confined space means; and (4) cooling the water vapor to obtain a distilled water.
The confined space means may comprise a single evaporation can.
Instead, the confined space means may comprise a plurality of evaporation cans which are connected in series, wherein the low-temperature waste heat is supplied into a first evaporation can, and wherein in each pair of adjacent evaporation cans, the downstream-side evaporation can receives water vapor from an upstream-side evaporation can, cools the water vapor with raw water in the downstream-side evaporation can and thereby produces distilled water, and also heats the raw water in the downstream-side evaporation can and generates water vapor.
The confined space means may comprises a plurality of evaporation cans which are connected in parallel rows, wherein the steps of (1) to (4) above are switched over from one evaporation can to another to thereby enable a continuous desalinating operation.
In the method described above, the step of evacuating may be effected intermittently or at optional time, for example, for a predetermined period during the time of starting the desalinating operation.
The step of supplying raw water into the confined space means could be effected by evacuating the confined space means while opening the confined space means to a raw water source. The method further may comprise a step of discharging concentrated raw water out of the confined space means and this step may be effected, after opening the confined space means to the atmosphere, by opening the confined space means and allowing flowing down of the concentrated raw water therefrom.
According to a second aspect of the invention, a desalination apparatus includes a heat exchanger cooperating with an evaporation can so as to subject low-temperature waste heat and raw water in the evaporation can to heat exchange and generate water vapor in the evaporation can; a condenser cooperating with a raw water tank to receive the water vapor from the evaporation can, cool the water vapor by subjecting the water vapor and raw water in the raw water tank to heat exchange and obtain distilled water; a distilled water tank for storing the distilled water; vacuum means for evacuating the evaporation can and depressurizing the inside thereof so as to promote generation of water vapor in the evaporation can; and raw water supply means for supplying raw water to the evaporation can.
According to a further aspect of the invention, a desalination apparatus includes a heat exchanger cooperating with an evaporation can so as to subject low-temperature waste heat and raw water in the evaporation can to heat exchange and generate water vapor in the evaporation can; a condenser adapted to receive the water vapor from the evaporation can, cool the water vapor by subjecting the water vapor and cooling water to heat exchange and obtain distilled water; a distilled water tank for storing the distilled water; vacuum means for evacuating the evaporation can and depressurizing the inside thereof so as to promote generation of water vapor in the evaporation can; and raw water supply means for supplying raw water to the evaporation can.
In the desalination apparatus described above, the low-temperature waste heat may consist of the potential heat of exhaust steam from a steam turbine for electric power generation in a plant.
The desalination apparatus may be incorporated in series and/or parallel with a condenser of the steam turbine for electric power generation, or can be used in place of the condenser. In a case where the desalination
Kamiya Ichiro
Kuroda Tetsuo
Narasaki Yuzo
Ebara Corporation
Manoharan Virginia
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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