RU2393995C1 - Method of desalinating sea water and installation for desalinating sea water - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to desalination of sea water and can be used to desalinate salty, sea and ocean water in warm climatic regions. Method involves feeding water to be desalinated under pressure into an evaporation zone, evaporation at low pressure while tapping the vapour-gas mixture formed into a condensation zone, condensation of vapour through contact with the cooled circulating fresh water, outlet of the released gases and desalinated water and salt water. The evaporation and condensation process is carried out in corresponding zones lying higher than the barometric height of the column of desalinated water above the free surface of sea water. The vapour-gas mixture formed is tapped into the condensation zone through a convergent channel with increase of the speed of the mixture to 0.6-1.0 of the speed of sound. Pressure of the circulating fresh water at the input of the condensation zone is kept at a level sufficient for supersonic flow of the vapour-gas mixture in the condensation zone. Released gases are output continuously. The installation has a water evaporation zone, a vapour condensation zone formed by the mixing chamber of a supersonic ejector and connected by a fresh water circulation main pipe, fitted with a pump and a heat exchanger, a steam pipe which narrows along the direction of movement of the vapour and connects the evaporation and condensation zones.

EFFECT: reduced material and energy consumption.

10 cl, 3 dwg

Description

The invention relates to the field of desalination of sea waters and can be used for desalination of salt, sea and ocean waters in warm climatic regions, as well as in areas of the coastal location of nuclear power plants having a discharge of warm waters.

Widely used industrial desalination methods based on the distillation method, as a rule, use the principle of flash evaporation (“flash”). In traditional methods, which are currently most widely used, multi-case evaporators equipped with heat exchangers are used. The energy consumption required for the implementation of the distillation method of desalination of sea water is 14-50 kW · h / m ³ . In addition, such installations are distinguished by large dimensions, metal consumption and high operating costs.

There is a method of desalination of deaerated sea water, which is carried out at relatively low temperatures and pressure created by hydrostatic evacuation of a column of source water and brine (RF Patent No. 2335459, 10.10.2008). The advantage of this method is that the evaporation process is carried out at low temperatures, thereby eliminating the problem of scale formation. The desalination device according to this method contains two vertically mounted circuits, while the upper parts of the evaporation and condensation circuit are located at a barometric height relative to sea level and both are connected by a steam line.

However, for the effective use of the known method, preliminary deaeration of salt water is necessary, which is a rather complicated and energy-consuming operation.

The known technology of degassing, purification and condensation of water using an installation containing a supersonic liquid ejector (RF Patent No. 2271999, 03.20.2006).

However, the known solution is not intended for desalination of salt water, since it involves the removal of the vapor-gas phase from the circuit of the treated water at a supply pressure that ensures an uninterrupted flow of the two-phase mixture in the mixing chamber of the ejector. To realize such a flow, it is necessary to supply water at a pressure of at least 2.5 bar to the nozzle blocks of both ejectors, which will lead to high energy costs. Conducting desalination of water with a salinity of 30-36 g / l according to this patent will require energy consumption at the level of 100-120 kW · h / m ³ .

Closest to the proposed invention is a method and installation for desalination of sea water, described in RF patent No. 2309125, 05.20.2007.

The known method includes the supply of water under pressure to the evaporation zone, evaporation under reduced pressure, the removal of the resulting vapor-gas mixture into the condensation zone, condensation of steam by contacting it with cooled circulating water, the removal of gases and desalinated water and the discharge of brine. According to the method, the evaporation and condensation processes are carried out in an area located at a height exceeding the barometric height of the water column above the surface of desalinated sea water.

The seawater desalination plant described in the well-known patent contains locking and control devices, a water evaporation chamber connected to a seawater supply line equipped with a pump, and a brine discharge line, a steam condensation chamber connected to a fresh water circulation line equipped with a pump , a heat exchange device and a desalination water outlet pipe, and a steam line connecting the evaporation chamber and the condensation chamber, wherein the evaporation chamber, the steam pipe and the condensation chamber mescheny at a height greater than the barometric height of the water column above the free surface of the desalination of sea water.

The disadvantages of the known technical solutions adopted for the prototype are as follows. Conducting periodic removal of gases simultaneously emitted from the water, for which it is necessary to stop the process, condensation is carried out due to the natural contact of the falling flow of atomized water droplets with a fixed volume of low-pressure steam, which together does not allow for high process performance.

The objective of the invention is the creation of a high-performance economical method of desalination of sea or ocean water, using natural conditions, in particular, the temperature difference between the warm and cold layers of water.

The problem is solved by the described method of desalination of sea water, which includes the supply of desalinated water under pressure to the evaporation zone, evaporation at reduced pressure with the removal of the resulting vapor-gas mixture into the condensation zone, condensation of steam by contact with cooled circulating fresh water, the output of the released gases and desalinated water and drain the brine, while the processes of evaporation and condensation are carried out in the corresponding zones located at a height exceeding the barometric height of the column water above the free surface of sea water, the resulting vapor-gas mixture is discharged to the condensation zone along a tapering channel with increasing the mixture speed to a speed equal to 0.6-1.0 of the speed of sound, the pressure of the circulating fresh water at the entrance to the condensation zone is maintained at sufficient to implement the regime of supersonic flow of vapor-gas mixture in the condensation zone, and the evacuation of gases is carried out continuously.

Preferably, the vapor-gas mixture is condensed in a condensation zone formed by the mixing chamber of the supersonic ejector.

Preferably, the desalination water is supplied to the evaporation zone through a nozzle nozzle under pressure to prevent boiling of water inside the nozzle.

Preferably, desalinated water is taken from a layer of sea water with a temperature of more than 20 ° C, cooling of the circulating fresh water is carried out in a heat exchanger immersed in a layer of sea water with a temperature of not more than 10 ° C.

If necessary, before supplying desalinated water to the evaporation zone, it can be heated from an external heat source to 30-60 ° C, while circulating fresh water can be cooled with sea water from the surface layer.

The problem is also solved by the described installation for desalination of sea water, which contains a water evaporation zone associated with a seawater supply line equipped with a pump and a brine drain line, a steam condensation zone associated with a fresh water circulation line equipped with a pump, heat exchange device and the desalinated water outlet pipe, a steam pipe connecting the evaporation zone and the condensation zone, wherein the evaporation zone, steam pipe and condensation zone are located at a height exceeding the barome the height of the desalinated water column above the free surface of sea water, shut-off and control valves, instrumentation, and the condensation zone is formed by a mixing chamber of a supersonic ejector installed at the outlet of the steam pipe and equipped with a nozzle block at the entrance to the mixing chamber, a diffuser at the exit of the chamber mixing and a vacuum pump, the steam line is made tapering along the direction of steam into the mixing chamber of a supersonic ejector.

Preferably, the evaporation zone, the steam line and the condensation zone are arranged sequentially, horizontally and coaxially in the installation.

It is possible to carry out an installation in which the seawater supply line at the outlet is equipped with a nozzle nozzle, said nozzle being placed in the evaporation zone and installed with a turn to the direction of steam movement, preferably at an angle of 135-180 degrees.

It is possible to carry out an installation in which, at the outlet of the seawater supply line, a drip removal prevention device is installed between the evaporation zone and the steam line.

The seawater supply line may be further provided with a heat exchanger connected to an external heat source.

The claimed installation is schematically represented in figures 1, 2 and 3.

The installation contains the following components and parts:

1 - seawater supply line equipped with a pump;

2 - nozzle nozzle (a variant with a nozzle nozzle arrangement at an angle of 180 ° to the direction of steam movement is presented);

3 - evaporation zone;

4 - line drain brine;

5 - steam line;

6 - nozzle block of a supersonic ejector;

7 - mixing chamber of a supersonic ejector;

8 - diffuser;

9 - a vacuum pump;

10 - circulation line of fresh water;

11 - pump;

12 - heat exchanger;

13 - outlet pipeline of desalinated water;

14 - device to prevent drip entrainment;

15 is a heat exchanger associated with an external heat source.

Figure 1 presents the installation in which the desalination process is carried out without the use of additional heating of sea water from an external heat source. Such a process is best carried out in areas where there is a natural temperature difference of 10-20 degrees between the layers of warm and cold sea water. The line for supplying desalinated water in the installation shown in figure 1, is equipped with a nozzle nozzle.

Figure 2 presents the installation for operation in the same climatic conditions. Its difference is the absence of a nozzle nozzle at the outlet of the desalinated water supply line. In this case, the evaporation process takes place directly in the upper part of the supply line 1, and to prevent drip entrainment in front of the steam pipe installed device to prevent drip entrainment 14.

Figure 3 presents the installation, similar to that shown in figure 2, but equipped with a heat exchanger 15 for additional heating of sea water from an external heat source.

It should be noted that the energy cost of supplying water in the absence of a nozzle nozzle when supplying water to the evaporation zone will be slightly lower than when feeding through the nozzle nozzle, however, in any case, they will be lower than in the prototype method, and the design of the installation allows her continuous work.

The claimed method is as follows.

Before the installation starts, its main units (evaporation zone 3, steam pipe 5 and condensation zone 7) are placed at a barometric height, and pre-desalinated water is poured into its circulation line 10 (water can be with a given salt composition that meets regulatory requirements, it is not necessary to distill ) The amount of filled water corresponds to the sum of the volumes of the circulation line and the heat exchanger. The required barometric elevation of sea water (h1) above the sea surface is calculated preliminarily based on the temperature at which it is supposed to evaporate warm sea water and atmospheric pressure. So, for example, given the conditions of boiling water at 25 ° C and atmospheric pressure at sea level equal to 101.3 kPa, the height of the hydrostatic column of water required to ensure a vacuum in the evaporation zone corresponding to boiling sea water at 25 ° C will be 10.032 m This is for these conditions and will be a barometric height h1. For the practical implementation of the desalination process, the supply of warm desalinated water to a height of h h _. , which will slightly exceed the barometric height h1 of the column of the source sea water. h _{log huts} with the central location of the nozzle nozzle in the evaporation zone will be set constructively. It is about half the height of the evaporation zone, which in industrial installations will be 0.5-1 m. If the nozzle nozzle is located in the lower part of the evaporation chamber or if there is no nozzle nozzle in the supply line, h _huts. will be determined by the location of the supply line relative to the brine drain line. In practice, this height will be no more than 0.3 m. To realize the evaporation process at low temperatures corresponding to the temperature of warm sea layers 20-30 ° C, a vacuum is created in the installation corresponding to the saturation pressure of desalinated sea water, for which it is subjected to start-up evacuation using a vacuum pump installed in the condensation zone 9. During operation, the vacuum is maintained by removing dissolved gases released from the water.

To supply the required amount of desalinated water, a low-pressure pump installed in the seawater supply line is used. Desalination of water having a temperature of 20-30 ° C is carried out from the surface warm sea layer. Reaching the evaporation zone with reduced pressure, the water instantly boils. If there is a nozzle nozzle in the sea water supply line, the flow of the supplied water should be carried out at a pressure that excludes its boiling in the nozzle nozzle. During evaporation, together with the steam, the smallest droplets of the source water are carried away, the so-called drip entrainment. The problem of separating water droplets from steam is solved by turning the nozzle nozzle 135-180 degrees with respect to the movement of the vapor-gas mixture (Fig. 1 shows a nozzle with a rotation angle of 180 degrees from the direction of steam movement). If the installation does not contain a nozzle nozzle (see Fig. 2), then a drip removal prevention device 14 is used to prevent droplet entrainment. Water vapor and dissolved gases released in the evaporation zone enter the narrowing channel of the vapor-gas vapor pipeline connecting the evaporation zone to the condensation zone, and with a mixing chamber of a supersonic ejector. Fresh water cooled in the heat exchanger is continuously circulated through a nozzle block of a supersonic ejector through a circulation line using a pump. In the mixing chamber of the ejector, there is an intensive contact of cold water with steam, its condensation with simultaneous heating of the circulating water due to the latent heat of vaporization. The gases simultaneously released into the contact condensation zone together with the steam do not condense, therefore during the installation they are continuously discharged using the vacuum pump installed in the upper part of the diffuser, due to which the specified vacuum in the system is automatically maintained. Under normal conditions, the dissolved gas content in water is about 0.012 g / l, i.e. in relation to the resulting pair, their amount is about 0.001 mass fraction, which allows us to neglect the energy losses for their pumping. To completely condense the resulting steam, 50-150 kg of water per 1 kg of steam obtained in the evaporation zone is passed through an ejector. Since water will heat up during steam condensation, a heat exchanger is installed in the lower part of the circulation line to cool it. In the installation shown in FIG. 1, the heat exchanger is placed in a layer of water having a temperature of not more than 10 ° C, and in the installation shown in FIG. 3, the heat exchanger is placed in the surface layer of water. Due to steam condensation, the accumulation of fresh water occurs, the amount of which is equivalent to the amount of condensate formed. Desalinated water is supplied to the consumer through a pipeline. The brine formed in the evaporation zone has a temperature lower than the temperature of the source water, while the density of the brine is higher, so the brine falls under the layers of warm water. The following are specific examples of the method.

Example 1

The method used the installation depicted in figure 1, with a capacity of 1 kg / s condensate. The method is carried out under the following conditions: evaporated sea water has T = 30 ° C, and the layer of water used for cooling is 10 ° C. This temperature difference is sufficient to realize the flow of steam at the entrance to the condensation chamber with the speed of sound in this pair. Thus, salt water is supplied to the evaporation zone from the sea surface in the amount of 116.23 kg / s with a temperature of 30 ° C and a pressure of 0.01 MPa. After the evaporation of part of the water (1 kg / s), its temperature decreases by 5 ° C and is 25 ° C. The resulting steam through a tapering steam line is sent to a supersonic ejector for condensation. Moreover, the inlet section of the steam pipeline is 2.23 m ² and the outlet section is 0.179 m ² . The steam velocity at the end of the narrowing steam line is WC3 = 376 m / s, which is close to the speed of sound in this pair and _sv = 382 m / s (WC3 / a _sv ≈1). To condense the released steam, 50 kg / s of water with t = 10 ° C is continuously supplied to the ejector mixing chamber, which is the condensation zone. The supply pressure of this water circulating through the circulation line to the nozzle block of the ejector is 0.05 MPa. After steam condensation, the water temperature at the outlet of the ejector is no longer 10, but 21.8 ° C. To ensure the possibility of multiple use of this water at a depth in the layer of cold water, a heat exchanger is installed in which it is again cooled from 21.8 ° C to 10 ° C, etc. T.O. in the water recirculation circuit, the amount of desalinated water increases by 1 kg / s all the time, and part of the water from this circuit is continuously discharged to the consumer.

The energy costs of obtaining a given amount (1 kg / s) of condensate will be composed of three components:

- the cost of supplying water for evaporation (116.23 kg / s of water with an injection pressure of 0.01 MPa);

- the cost of supplying the water necessary for steam condensation (50 kg / s water with an injection pressure of 0.05 MPa);

- the cost of the vacuum pump for pumping incidentally released gases from the water.

The total energy consumption for desalination in this example is 2.4 kWh / m ^{3 of} desalinated water.

Example 2

The method is carried out at the installation with the same performance as in example 1, but in the design shown in figure 2. In this case, by reducing the elevation of desalinated water, the energy consumption for supplying water for evaporation is significantly reduced and, accordingly, the total cost will be about 1.9 kW · h / m ^{3 of} desalinated water.

Example 3

The method is carried out at the installation with the same performance as in example 1, but at the same time in the design shown in figure 3. The method is carried out under the following conditions: the source surface water has t = 15 ° C, it is heated to 25 ° C in the heat exchanger 15, and the same surface water with t = 15 ° C is used for cooling. In this case, the amount of water supplied to the evaporation is 116.85 kg / s, after evaporation (1 kg / s) the water temperature is 20 ° C. The resulting steam through a tapering steam line is sent to the ejector for condensation. The area of the inlet section of the steam pipeline is 3.05 m ² and the outlet section is 0.274 m ² . The steam velocity at the end of the narrowing steam line is WC3 = 230 m / s, which is 0.6 of the speed of sound in this pair (a _sound = 382 m / s). The vapor pressure in front of the ejector is in this case 1779.8 n / m ² . Under these conditions, a condensation water flow rate of 150 kg / s is ensured. As a result, the water temperature at the outlet of the ejector is 18.9 ° C. For cooling and reuse of desalinated water, a heat exchanger is placed in the surface layer of water through which water is passed after steam is condensed in it. Water cools from 18.9 ° C to 15 ° C, etc. In the condensation circuit, an increase in the amount of desalinated water by 1 kg / s occurs, and part of the water from the circuit is continuously withdrawn.

The total energy cost of obtaining a given amount (1 kg / s) of condensate will in this case be 4.9 kW · h / m ^{3 of} desalinated water, which is two times higher than in example 1.

Example 4

The method is carried out in a plant with the same capacity as in example 1, but under the following conditions: the initial surface water has t = 25 ° C, water with t = 20 ° C is used for cooling. In this case, the steam velocity at the end of the narrowing steam line will be WC3 = 130 m / s, which is 0.34 of the speed of sound in this pair (and _sv = 382 m / s). Under such conditions, the total energy cost of obtaining a given amount (1 kg / s) of condensate will be about 10 kWh / m ^{3 of} desalinated water, which makes such a method inefficient.

As can be seen from the above examples, the proposed invention allows the desalination of salt, in particular, sea waters with minimal material and energy costs. The energy consumption of the present invention is significantly lower than in the prototype method. At the same time, the proposed installation has practically no performance restrictions, since the main unit of the installation that determines its performance is a supersonic ejector. When implementing the claimed invention, it becomes possible to use the natural temperature difference between the surface and deeper (at depths of 20-100 m) layers of water. The warm surface layer of water in oceans with temperatures above 20 ° covers 53% of the entire surface of the oceans. The highest temperature of the water surface in the ocean is near the equator: 28 ° С. In this region, temperature fluctuations during the year are minimal and amount to 2.2-2.4 ° С. In closed seas and low latitudes, the temperature of the surface layer can reach 32 ° C, and this layer has a small thickness, not more than 100-150 m, and below is a huge volume of water with a lower temperature, which allows us to conclude that the invention is promising in these areas.

Claims (10)

1. The method of desalination of sea water, including the supply of desalinated water under pressure to the evaporation zone, evaporation under reduced pressure with the removal of the resulting vapor-gas mixture into the condensation zone, condensation of steam by contact with the cooled circulating fresh water, the discharge of released gases and desalinated water and the discharge of brine, moreover, the processes of evaporation and condensation are carried out in the corresponding zones located at a height exceeding the barometric height of the column of desalinated water above the free surface of sea water, about characterized in that the resulting vapor-gas mixture is discharged to the condensation zone along a narrowing channel with an increase in the mixture velocity to a speed equal to 0.6-1.0 of the speed of sound, the pressure of the circulating fresh water at the entrance to the condensation zone is maintained at a level sufficient to realize the supersonic flow regime of the vapor-gas mixture in the condensation zone, while the evacuation of gases is carried out continuously. 2. The method according to claim 1, characterized in that the condensation of the vapor-gas mixture is carried out in the condensation zone formed by the mixing chamber of the supersonic ejector. 3. The method according to claim 1, characterized in that the supply of desalinated water to the evaporation zone is carried out through a nozzle nozzle under pressure, excluding boiling of water inside the nozzle. 4. The method according to claim 1, characterized in that the intake of desalinated water is carried out from the surface layer of sea water with a temperature of more than 20 ° C, cooling of the circulating fresh water is carried out in a heat exchanger immersed in a layer of sea water with a temperature of not more than 10 ° C. 5. The method according to claim 1, characterized in that before supplying the desalinated water to the evaporation zone, it is heated from an external heat source to 30-60 ° C, while circulating fresh water is cooled with sea water from the surface layer. 6. Installation for desalination of sea water, containing a water evaporation zone associated with a seawater supply line equipped with a pump and a brine drain line, a steam condensation zone associated with a fresh water circulation line equipped with a pump, a heat exchange device and a desalinated water outlet pipe , a steam line connecting the evaporation zone and the condensation zone, and the evaporation zone, steam pipe and condensation zone are located at a height exceeding the barometric height of the desalinated water column above freely the surface of the sea water, shut-off and control valves and instrumentation, characterized in that the condensation zone is formed by a mixing chamber of a supersonic ejector installed at the outlet of the steam pipe and equipped with a nozzle block at the entrance to the mixing chamber, expanding diffuser at the exit of the mixing chamber and vacuum pump, and the steam line is made tapering along the direction of steam into the mixing chamber of the supersonic ejector. 7. Installation according to claim 6, characterized in that the evaporation zone, the steam pipe and the condensation zone are arranged sequentially, horizontally and coaxially. 8. Installation according to claim 6, characterized in that the seawater supply line at the outlet is equipped with a nozzle nozzle, said nozzle being placed in the evaporation zone and installed with a turn to the direction of steam movement, preferably at an angle of 135-180 °. 9. Installation according to claim 6, characterized in that at the outlet of the seawater supply line between the evaporation zone and the steam line, a drip removal prevention device is installed. 10. Installation according to claim 6, characterized in that the seawater supply line is additionally equipped with a heat exchanger associated with an external heat source.

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