RU2296715C2 - Sea water distilling plant - Google Patents

Abstract

FIELD: methods of distilling sea water.

SUBSTANCE: operation of proposed distilling plant consists in forming reduced pressure above water surface, thus making it boil and causing intensive forming of steam which is condensed in special-purpose cooler. Forming the reduced pressure is based on Torricellian principle. Tank is provided with three pipe lines: delivery pipe line, drain pipe line and distilled water pipe line. It is mounted above level of distilled water at height no less than height of liquid column at given atmospheric pressure; tank is provided with funnel for fresh water and with plates onto which water being distilled is poured continuously. Cooler located near the tank has two pipe lines with cold and heated cooling agents; these pipe lines are laid inside tank. Distilled water is poured on cooling agent pipe line; part of distilled water is taken from funnel.

EFFECT: increased area of water being distilled; increased rate of condensation of steam.

1 dwg

Description

The invention relates to devices for desalination of sea water and can find application in the design and manufacture of desalination plants for fresh water for agriculture, industry and utilities.

There are several ways to obtain fresh water: evaporation, electrodialysis, and reverse osmosis [1, 2]. All these methods are quite complex and energy intensive.

The removal of salts from water to a limit close to their content in distilled water (several mg / l) is called desalination, and the removal of salts to concentrations acceptable for drinking water (up to 1 g / l) is called desalination.

Desalination of water by electrodialysis or reverse osmosis is characterized by significantly lower energy costs compared to distillation. During electrodialysis, selective, ion-exchange membranes are used.

In reverse osmosis, semipermeable membranes that allow water molecules to pass through but retain dissolved mineral and organic substances.

Electricity consumption per 1 m ^{3 of} water desalted by electrodialysis is up to 30 kWh, and reverse osmosis up to 15 kWh.

By electrodialysis, water can be desalted by 90%, reverse osmosis - by 98%.

In reverse osmosis plants, the operating pressure reaches 5-10 MPa (50-100 atmospheres).

As you can see, water desalination by electrodialysis or reverse osmosis is associated with significant energy costs, the production of quite complex and expensive desalination plants, constant monitoring of their performance, repair, replacement of membranes with a limited service life, etc.

There is also a method for distillation of sea water, based on the law of decreasing the boiling point of water with decreasing pressure above its surface [3, 6].

If you lower the pressure above the surface of the water, intensive evaporation will begin even at a temperature close to the freezing temperature. The evaporation rate depends on the temperature of the water and the pressure difference between the pressure above its surface and the pressure of saturated vapors at a given temperature. When the pressure above the surface of the water is equal to the pressure of saturated water vapor at a given temperature, evaporation will stop. If continuously formed water vapor is formed, the evaporation process will continue. This can be achieved in two ways: by pumping out the vapors with a vacuum pump followed by their condensation outside the zone of reduced pressure or by condensation of the vapor and removal of condensate from the zone of reduced pressure. As a third option, a combination of these methods is used [4, 5].

The disadvantages of these methods are the complexity and high cost of equipment, low productivity of desalination plants, high cost of water obtained.

The invention [7] is the closest prototype of the claimed method.

This method describes a device for continuous distillation under reduced pressure, having a sealed tank having a device for condensing water vapor, which is a refrigerator, the pipe with a heated refrigerant which is below the water level in the tank and gives it its heat, and the pipe with a cooled refrigerant above the water level in the tank and is used to condense water vapor, which flows into the distilled water pipe.

The first disadvantage of the device is the high energy costs of creating a vacuum above the surface of the water and, therefore, the high cost of desalinated water.

The second disadvantage of this device is the low specific productivity of the desalination plant, since the rate of water evaporation is directly proportional to the area of the water mirror in the desalination tank. To obtain acceptable performance of the desalination plant, the manufacture of a large-diameter sealed tank is required.

The third disadvantage of this device is the low rate of condensation of water vapor in the pipeline with cold refrigerant, because due to the large surface tension of the water, droplets cannot begin to slide off the pipeline until they reach a certain size. As a result, the pipeline is covered with a significant layer of water, which prevents the transfer of heat from steam to the cold pipeline.

The elimination of these disadvantages is as follows.

In order not to waste energy on creating a vacuum in the tank, the Torricelli principle is used. The sealed tank is raised to a height of approximately 10.5 meters. It has three pipelines: discharge, drain and for distilled water, the lower ends of which are below the level of desalinated water. Water under its own weight tends to fall down, but it is counteracted by atmospheric pressure, so the water level will drop to about 10 meters above sea level. Over water, a reduced pressure forms in the tank. A pump is installed on the discharge pipe, which constantly supplies fresh water to the tank, and from it the water flows by gravity back to the sea via a drain pipe. Thus, water enters the zone of reduced pressure, where it intensively evaporates.

To increase the open area of water on which evaporation occurs, metal or plastic plates are installed on the inside of the tank above the water mirror, onto which the water is irrigated from the tank. Thus, it is possible to increase the evaporated area of water by tens of times. As a result of this, with a small diameter of the tank, a large evaporation area can be obtained.

The third disadvantage is eliminated as follows. Near the tank there is a refrigerator with two pipelines with cold and heated refrigerants, which are located inside the tank. The refrigerator is designed to condense water vapor. A pipeline with a heated refrigerant is below the water level in the tank and gives it its heat, and a pipe with a cooled refrigerant is above the water level in the tank and takes heat from the steam. The steam condenses in a cold pipeline and flows through it into a pipeline for distilled water, and from it into a container for distilled water. To increase the rate of condensation, a cold refrigerant pipe is watered with desalinated water. Thus, only fresh water droplets that have begun to emerge are washed off continuously. In addition, the droplets of flowing water themselves create an additional surface for trapping water vapor.

The invention is illustrated in the drawing.

The desalination plant device for implementing the proposed method is a sealed tank 1 mounted on a stand 2. The upper end of the tank is above the level of the water column 3 in the tube (the level of the water column in the Torricelli barometer at a given atmospheric pressure), the upper end of which is sealed and the lower end is lowered into the water 4.

The tank has three pipelines: injection 5 for sea water, drain 6 for brine and distilled water 7. The lower ends of all pipelines are located below the level of desalinated water. The discharge pipe 5 is equipped with a water intake with a filter 8 and a pump 9.

The lower end of the drain pipe 6 is equipped with a locking device (valve) 10, opening or closing it.

For condensation of steam and heating of desalinated water, a refrigerator 11 is located next to the tank 1.

From the refrigerator 11 to the tank 1 there are two pipelines with heated refrigerant 12, which is located below the water level in the tank, and a pipeline with cooled refrigerant 13, which is located above the water level in the tank. The pipeline with refrigerated refrigerant 13 is used to condense water vapor, which flows from it into the pipeline for distilled water 7, and from it into the tank for distilled water 14.

The pipeline for distilled water 7 contains a locking device (valve) 15.

The tank has a check valve 16 at the top, which opens when the pressure in it increases and closes when the pressure drops below atmospheric pressure, and the tank is full. This sensor signals that the tank is full with water. Inside the tank there is a sensor for the lower limit level of water 18. The height of the lower limit level of water 19 is selected from the condition that the pipeline with heated refrigerant 12 should always be below the water level in the tank, that is, it is completely closed by water.

Plates 20 are mounted above the water mirror, onto which water flows from the sprayer 21 on both sides of the plates. Water is taken from the same tank and pump 22 is supplied to the sprayer 21.

A pump 24 is installed in the funnel for collecting fresh water 23, which supplies fresh water to the atomizer 25, which is poured onto the pipeline with cold refrigerant 13.

The principle of operation of the desalination plant is to create a reduced pressure above the surface of the water, which leads to its boiling, intense vaporization and subsequent condensation of water vapor in a special receiver. Water vapor condenses and merges into the receiver 14.

In order not to waste energy on creating a vacuum in the tank, the Torricelli principle is used. Desalinated water is pumped into tank 1 with closed taps of drain 10 and pumping out 15 pipelines. Air from the tank exits through a check valve 16 located at the top of the tank. When the tank 1 is filled and water begins to pour out of it through the check valve, at the signal from the tank fullness sensor 17, the taps 10 of the drain pipe and 15 of the pipe for distilled water open.

Water under its own weight tends to fall down, but it is counteracted by atmospheric pressure, so the water level will drop to about 10 meters above sea level. The exact height of the water level depends on the atmospheric pressure at a given moment, at a given geographical point on the earth.

A reduced pressure forms above the surface of the water. Water will begin to evaporate intensely.

Turns on the refrigerator 11, designed to condense water vapor. The pipeline with heated refrigerant 12 is below the water level in the tank and gives off its heat, and the pipeline with cooled refrigerant 13 is above the water level in the tank and is used to condense water vapor that flows into the distilled water pipeline 7. Condensed water flows by gravity into a pipeline for distilled water 7 and through it to a container for distilled water 14.

Since dissolved air is always present in water, it will come out of the water and accumulate above the surface in the tank. This is especially intense under reduced pressure. As the air escapes, the water level in the tank will drop. When the water level drops to the pipeline with heated refrigerant 12, the installation capacity will begin to decrease, since the heat transfer of desalinated water will begin to decrease, and part of the heat will be transferred to the steam, reducing the efficiency of the refrigerator.

To prevent stopping the distillation, periodically remove accumulated air.

This is achieved by the fact that when lowering the water level in the tank to the maximum set level 18, the taps in the drain pipe 10 and the distilled water pipe 15 are closed. Water continues to fill the tank 1 with water through the discharge pipe 5 and the air that has accumulated above the surface of the water is squeezed out through the return valve to the atmosphere.

At the moment when water begins to pour out of the tank through the non-return valve 16, the tank fullness sensor 17 generates a signal that opens the taps on the drain pipe 10 and the distilled water pipe 15. The non-return valve of the tank 16 closes, the water level drops, again above the water surface reduced pressure is created and the distillation process resumes.

Information sources.

1. Chemical encyclopedia. In 5 volumes - M .: Soviet Encyclopedia, 1988.

2. Physical encyclopedia. In 5 volumes - M .: Soviet Encyclopedia, 1988.

3. Matveev A.N. Molecular Physics: Textbook. manual for universities. - M .: Higher school, 1981. - 400 p., Ill.

4. Russian patent No. 2142912, class C 02 F 1/04.

5. Patent of Russia No. 2206510, class C 02 F 1/04.

6. Patent of Russia No. 2087421, class C 02 F 1/14.

7. US patent No. 4985122, 01 D 3/10, 01/15/1991.

Claims (1)

A device for desalination of sea water, containing a sealed tank, a discharge pipe, on which there is a pump for continuous supply of desalinated water into the tank, two pipelines: drain and for distilled water having shut-off valves, while the tank has a device for heating and condensing water vapor, which is a refrigerator, the pipeline with a heated refrigerant which is below the water level in the tank and gives off its heat, and the pipeline with the cooled refrigerant is above the water level in the tank and serves for condensation water vapor that flows into the distilled water pipeline and then into the distilled water tank, characterized in that the tank is installed above the level of desalinated water at a height not less than the maximum height of the liquid column at a given atmospheric pressure and equipped with a funnel for collecting fresh water, above plates are placed on the surface of the water in the tank, onto which desalinated water is continuously poured, and desalinated water is poured onto the pipeline with cold refrigerant, part of which is taken from the funnel to collect fresh water.