RU2565187C1 - Method of producing pure water from sea and salt water, industrial effluent and apparatus therefor - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes heating, evaporating, removing steam from the steam space for condensation; evaporation and condensation processes are carried out in a thermostat with ambient temperature or higher; feeding a salt solution for evaporation and removing the pure water condensate and the salt solution with high salt concentration is carried out through a countercurrent heat exchanger; and an adiabatic steam compression process, which enables to return condensation heat into the cycle (regeneration), is included between processes of evaporating pure water from the aqueous salt solution and condensation thereof.

EFFECT: invention enables to carry out the process in an evaporator-condenser in a wide temperature and pressure range, including evaporation in a vacuum at a temperature close to ambient temperature, and pressure higher than 1 atmosphere and temperature higher than 100 degrees.

13 cl, 6 dwg

Description

The invention relates to the field of reversible energy cycles and can be used to create devices for separating mixtures of liquids with different boiling points that make up a multicomponent mixture. The most preferred area of the method for producing pure water from sea and mineralized waters, industrial effluents and devices for its implementation is the production of pure water from an aqueous saline solution, for example, sea and mineralized waters and industrial effluents, by distillation.

The most common method for producing pure water from aqueous salt solutions involves the process of boiling a solution to produce water vapor and then condensing it into a liquid phase.

Based on thermodynamic considerations, it is possible to build a production cycle for pure water on close to equilibrium and reversible processes, in which the work spent on the production of a unit mass of pure water, depending on the degree of salinity of the aqueous salt solution, is minimal. Such an idealized cycle will have the highest efficiency, and the technical perfection of the device in which this cycle is implemented can be taken as a sample (standard) by which other methods of obtaining pure water are verified.

In the known method for producing fresh water [1], the necessary work is obtained by using the temperature difference formed by solar heating of salt water and cooling of fresh water by underground natural sources. The maximum efficiency of such an energy generating device is possible only if the conditions of isothermal heating and cooling (Carnot cycle) are met, however, heating and cooling are carried out with fluid flows, which dramatically reduces the efficiency of this method and leads to high costs of heat and cold for producing pure water.

A known method [2] desalination of deaerated salt water, in which the evaporator and condenser of pure water are spaced in different temperature zones. The evaporator is on the sunny side, and the condenser is in the shade. Such an installation consumes the maximum amount of energy, since the supplied solar radiant energy is converted into low-grade heat and, with a slight decrease in its potential, is discharged into the environment.

A known method [3] is the distillation of homogeneous liquids and the separation of mixtures of liquids using the Peltier effect, on hot junctions which evaporate water, and on cold - its condensation.

With this method of obtaining pure water from an aqueous salt solution in a thermoelectric converter, taking into account its low efficiency, significantly more heat is generated for the evaporation of water from the salt solution compared to the resulting cold for condensing water, which reduces the efficiency of the proposed method.

In the known method [4], taken as a prototype, distillation is applied, including heating a layer of saline solution, evaporating clean water from the surface of the saline solution, removing steam from the vapor space and condensing it on the condensation surface inside the capillaries, from which there is pure water condensate It is output to the drive. In this case, each capillary passing through the mirror of the saline solution evaporation returns the heat of phase transition from the condensate of pure water flowing through the capillary channels to the mirror of the saline solution.

The main disadvantage of this method is that the proposed method of transferring (regenerating) the heat of the phase transition of the condensation of pure water to a salt solution mirror is ineffective, since it is carried out not by the shortest path in the form of - evaporation of water from a salt solution and then condensation of pure water, but using a combined ways in which an additional intermediate heat transfer process for heating the saline solution is included.

This reduces both the thermodynamic efficiency of the cycle of separation of pure water from saline, and the performance of the presented device.

The noted drawbacks are eliminated in the proposed method for implementing a cycle consisting of processes that are close to reversible and equilibrium, and an adiabatic compression of water vapor is included between the processes of evaporation of pure water from a saline solution and its condensation.

In FIG. 1 presents in an idealized formulation a device for producing pure water using processes close to reversible and equilibrium.

The device consists of a tank of the evaporator-condenser 1, filled with aqueous saline 4, coming from the pool 20 using the pump 16 in series through pipelines 15 and 13, through a regenerative heat exchanger 22 and then through pipe 10 to the tank of the evaporator-condenser 1.

The vapor space 23 of the evaporator-condenser tank 1 is connected to the steam condenser 5 by a pipe 6, on the line of which a compressor 7 is installed. From the condenser 5, clean water flows through a pipe 11 to a regenerative heat exchanger 22 and then to a clean water collector 19 through a pressure regulator 17 and a pipe 18 .

Similarly, the brine (aqueous salt solution enriched with salts) from the tank of the evaporator-condenser 1 enters through a pipe 8 into a regenerative heat exchanger 22 and then into the brine collector 21 through a pressure regulator 14 and a pipeline.

The tank of the evaporator-condenser 1 with inlet and outlet pipes and a compressor 7, as well as a regenerative heat exchanger 22 are placed in a thermostat 2 with heat-insulating material 3, to stabilize the temperature of which there is a heating element 9.

Presented idealized device operates as follows.

We take one of the options for the temperature regime of the evaporator-condenser at which the equilibrium temperature of the saline solution corresponds to the ambient pressure, that is, 1 ata. We assume that the equilibrium boiling point of the saline solution is 100 ° C.

Using a pump 15, we fill the reservoir of the evaporator-condenser 1 to the working level from the salt solution pool 20 through pipelines 15 and 13, a regenerative heat exchanger 22, and pipeline 10.

We set the temperature of the thermostat with the help of a heating element at the level of 100 ° С with a slight, by several degrees, excess over the equilibrium temperature in order to shift the process towards the evaporation of the saline solution in the tank of the evaporator-condenser 1.

We set the pressure regulators 17 and 18 to values that exceed the ambient pressure by several tenths of an atomic pressure, for each regulator.

A compressor 7 is turned on, which presses the generated water vapor from the vapor cavity 23, feeds it through a pipeline to a condenser 5, where pure water condensate forms, which through a pipe 11 enters the regenerative heat exchanger 22, whence at ambient temperature through a pressure regulator 17 and then at environmental pressure through the pipe 18 flows into the clean water collector 19.

The brine also enters through the pipeline 8 to the regenerative heat exchanger 22, wherefrom at ambient temperature through the pressure regulator 14 and then at ambient pressure through the pipeline 12 flows into the brine collector 21.

The thermodynamic efficiency of the considered method for producing pure water from an aqueous salt solution is determined only by the supplied mechanical energy supplied to the compressor 7 for compressing water vapor.

Under the condition of perfect thermal insulation 3 in thermostat 2, perfect heat transfer in the countercurrent regenerative heat exchanger 22 and the algebraic sum of the potential energy of the liquid flows entering the evaporator-condenser H and removed from it to zero, the work applied to the compressor 7 for compressing water vapor, is the minimum necessary work of separating pure water from an aqueous salt solution, and the method of producing pure water from an aqueous salt solution is from a thermodynamic point of view ershennym since it built on processes that are close to equilibrium and reversible.

The idealized cycle considered can serve as a standard by which it is possible to determine the degree of thermodynamic efficiency of other cycles for the separation of pure water from an aqueous salt solution.

A distinctive feature of a real device from an idealized one is that the cycle of isolating a unit mass of a product, in this case pure water, from an aqueous saline solution takes a specific time. Therefore, an increase in the productivity of a technical device is always associated with a decrease in cycle efficiency in comparison with an idealized one.

So, to increase the productivity of the device, it is necessary to intensify the processes of evaporation-condensation, for which it is necessary that the compressor creates an additional pressure difference with respect to the equilibrium states in the evaporation and condensing zones, in addition, to intensify the heat transfer in the heat exchanger-regenerator and return the potential energy of the liquid streams.

The following are options for devices for producing pure water from aqueous saline, the principle of operation of which is based on the above method.

In FIG. 2 presents a real device for the separation of pure water from an aqueous salt solution, the technical perfection of which implements the principles laid down in an idealized process with maximum thermodynamic efficiency.

The technical implementation of the device allows the process in the evaporator-condenser in a wide range of temperatures and pressures, including evaporation in vacuum at a temperature close to ambient temperature and pressures of more than 1 atmosphere and a temperature of more than 100 ° C.

The device consists of a tank of the evaporator-condenser 1, filled with sea water 4, coming from the pool 20 of sea water using the pump 16 sequentially through pipelines 15 and 13, through a regenerative heat exchanger 22 and then through pipe 10 to the tank of the evaporator-condenser.

In the vapor space 30 of the tank of the evaporator-condenser 1, a screen 31 is installed to prevent the entrainment of droplets from boiling aqueous saline. The screen can be a porous heat-accumulating packing, perforated plates, typed metal strips forming labyrinth channels, a grid, etc.

To discharge the released and accumulated gases in the vapor space 30, a valve 35 is installed.

The vapor space 30 is connected to the steam condenser 5 by a pipe 6, on the line of which a compressor 7 is installed. From the steam condenser 5, clean water flows through a pipe 11 to a highly developed regenerative heat exchanger 22 and then to a clean water collector 19 through a pressure regulator 32 and a pipe 18.

Similarly, the brine from the tank of the evaporator-condenser enters through a pipe 8 to a regenerative heat exchanger 22 and then to the brine collector 21 through a pressure regulator 33 and a pipe 12.

The reservoir of the evaporator-condenser 1 with inlet and outlet pipes and a compressor 7, as well as a regenerative heat exchanger 22 are placed in a thermostat 2 with heat-insulating material 3 and a heating element 9.

The heating element 9 can use both electrical energy and the heat of the coolant in the liquid or gaseous phase.

As pressure regulators 32 and 33, for example, hydraulic motors can be used, in which the inlet pressure can be set by the liquid capacity (hydraulic motor with an inclined oblique washer).

The mechanical energy supplied to the pump 16 includes the energy discharged from the pressure regulators 32 and 33 through the communication system 34. The operation mode of the device for separating pure water from the aqueous salt solution is controlled by various sensors. So mounted in the vaporizer-condenser sensors P _{and K,} and P is measured pressure values in the cavities of the evaporation and condensation of pure water, respectively.

The temperature of the aqueous salt solution is carried out using a temperature sensor T _W.

The level of aqueous saline in the tank of the evaporator-condenser 1 is detected by the sensor h.

The temperature values of the liquid flows of the regenerative heat exchanger 22 from the environment are determined by sensors;

T _{In the} incoming stream of aqueous saline,

T _M - bleed stream of clean water,

T _P - diverted brine flow.

The presented device is characterized by three main operating modes:

Mode 1. Evaporation of pure water in a condenser-evaporator is carried out at ambient temperature in vacuum, corresponding to the pressure of saturated water vapor.

If there is a water column H equal to the distance between the liquid mirrors h in the evaporator-condenser 1 and the liquid receivers 19, 20 and 21, more than 10 meters, which corresponds to a pressure of 1 atmosphere and a pump 16 supplying the same height of the saline solution, the pressure drop across the hydraulic motor 32 also corresponds to the height of the liquid column N.

Similarly, the brine from the reservoir of the evaporator-condenser enters through the pipe 8 to the regenerative heat exchanger 22 and then to the brine collector 21 through the pressure regulator 33 and pipe 12. In this case, a hydraulic motor with a differential pressure of liquid on it also equal to N serves as a pressure regulator .

Mode 2. Evaporation of pure water in a condenser-evaporator is carried out at a temperature between the ambient temperature and a temperature equal to 100 ° C (for example 50 ° C), with a pressure corresponding to the pressure of saturated water vapor at the selected temperature of the evaporation process.

In this operating mode, the evaporation of pure water in the evaporator-condenser occurs at a shallower depth of vacuum (for example, with a pressure of saturated water vapor at 50 ° C). For a real device, the height H can be reduced taking into account this vacuum depth, therefore, the liquid heads at the pump 16 and hydraulic motors 32, 33 also decrease, down to zero at a temperature of the evaporator-condenser equal to 100 ° C.

Mode 3. Evaporation of pure water in a condenser-evaporator is carried out at a temperature above 100 ° C (for example 150 ° C), with a pressure corresponding to the pressure of saturated water vapor at a selected temperature of the evaporation process.

In this mode, H = 0 is assumed, and the pressure values at the pump 16 and hydraulic motors 32, 33 are equal to the pressure of saturated water vapor, for example, at a temperature of 150 ° C.

The device shown in FIG. 2 works as follows.

We take one of the variants of the temperature regime of the evaporator-condenser, in which the equilibrium boiling point of sea water corresponds to a pressure above the environment, for example 2 ata. We assume that the equilibrium boiling point of the saline solution is 120 ° C [5].

Using a pump 15, we fill the tank of the evaporator-condenser 1 to the working level h from the brine tank 20 through pipelines 15 and 13, a regenerative heat exchanger 22, and pipeline 10.

We set the temperature of the thermostat with the help of a heating element at the level of 120 ° С and increase of steam pressure in the tank of the evaporator - condenser to 2 at. We turn on the compressor 7, which presses the steam and sends it to the condenser 5, from where the condensed clean water through the pipe 11 enters the regenerative heat exchanger 22 and, acquiring the outlet temperature T _D equal to the ambient temperature τ, enters the hydraulic motor 32 acting as a pressure regulator . In this case, the extracted mechanical power from the hydraulic motor includes the potential energy of a column with a height N of liquid.

The brine from the reservoir of the evaporator-condenser 1 enters through the pipe 8 also into the regenerative heat exchanger 22 and acquiring the outlet temperature TP equal to the ambient temperature, enters the hydraulic motor 33, which acts as a pressure regulator. In this case, the extracted mechanical power from the hydraulic motor also includes the potential energy of the column with a height N of liquid.

The mechanical energy from the hydraulic motors is consumed by the pump 16.

In a real device, due to losses in overcoming hydraulic resistance in heat exchangers other than 100% of the efficiency of hydraulic motors, there is a slight shortage of mechanical energy for pump 16. Therefore, this energy is supplied from a separate source (in Fig. 2. this energy source is not shown).

The main consumer of mechanical energy in the device is a compressor, which provides evaporation and condensation processes by creating the necessary excess of the condensation pressure of water vapor over the vaporization pressure.

By increasing the vapor condensation pressure with the help of a compressor, it is possible to intensify the processes of both condensation of pure water and boiling of an aqueous salt solution in a volume, which increases the productivity of the device for producing pure water. The droplet-vapor stream during the intensification of the processes of evaporation of an aqueous salt solution, passing through the labyrinths of the screen 31, is separated from the droplet liquid, which flows back into the tank 1.

In addition, the compressor 7 performs the function of producing additional heat to compensate for heat loss in the thermostat 2.

In FIG. Figure 3 presents a real device for the separation of pure water from an aqueous salt solution, the technical perfection of which is realized with maximum thermodynamic efficiency by using heat exchangers-regenerators with heat-accumulating packing and with reversible heat transfer.

The device consists of a unit including a left 43 and a right 44 column, consisting of identical heat exchangers-regenerators 46 and 45 with heat-accumulating packing, in the upper part of which there are screens A _l and A _p to prevent the entrainment of liquid droplets from boiling zones V _l and In _p, respectively.

To increase the boiling zones, the column in the boiling zone may have an expansion, as shown in FIG. four.

The upper parts of the columns are connected by the cavity of the vapor space of the collector 42, in the middle part of which a reversible compressor 68 is installed (for example, a compressor of the Roots type [6]). In the upper part of the collector 42, cranes 69 and 70 are installed on opposite sides of the compressor 68 to discharge the released and accumulated dissolved gases.

The lower parts of the left and right columns are connected to the pump 64 for supplying aqueous saline from the reservoir 61 by means of controlled valves 62 and 63, respectively.

Cranes 55, 53 and 51 are used to divert from the left column, respectively:

- the return part of the saline by means of a pressure regulator 57 and further along the line 60 to the pool 61,

- brine by means of a pressure regulator 58 and further along line 66 to the brine collector (brine collector not shown),

- pure water by means of a pressure regulator 59 and further along line 67 to a clean water tank (a clean water tank is not shown).

Similarly, controlled taps 56, 54 and 52 respectively serve to divert the return portion of saline, brine and clean water from the right column.

The heat-accumulating packing of heat exchangers-regenerators can be porous bodies, granite chips, mesh, etc.

The columns are placed thermostat 40 with thermal insulation 41 and heating elements 49 and 50.

The temperature conditions of the left and right columns are controlled by the upper temperature sensors T _VL and T _VP and lower T _NL and T _NP, respectively. Pressure sensors for monitoring the pressure at the inlet and outlet of the compressor 68, pressure regulators 57, 58, 59 and pump 64 are not shown in the drawing.

The device shown in FIG. 3 works as follows.

Let us take one of the variants of the temperature regime of the columns at which the equilibrium boiling point of the aqueous saline solution corresponds to a pressure above the environment, for example, 2 ata. We assume that the equilibrium boiling point of water is 120 ° C [5].

The columns work in antiphase - if the process of vaporization is carried out in one, then condensation occurs in the other. So at the end of time τ equal to half the cycle τ _{(1/2) процесс the} process of vaporization changes to the opposite, that is, to the condensation process. Therefore, we consider the operation of one column, for example, the right 44.

To reach the steady state, it is necessary to start the device, for which the following operations are carried out:

- The value of 2 ata is set on the pressure regulators 57, 58 and 59;

- The pump 64 is turned on, the taps 63 and 62 open and the taps 69 and 70 open.

- They are filled with aqueous saline from the pool 61 of the columns 44 and 43 to the level h, after which the pump 64 is turned off and the taps 63 and 62, as well as 69 and 70, are closed;

- Using heaters 49, 50, the temperature of thermostating is set to 120 ° C;

- After the start of the boiling water of a saline solution in the boiling zones B _L and B _{P, the} steam together with the air in the vapor space 42 are discharged into the atmosphere through taps 69 and 70, for which the latter open for a short time, for example, by 0.5-1 , 0 seconds.

From this moment on, the thermal state of the installation and the vapor pressure in the vapor space of the collector 42 allows reaching a steady state and performing a cycle to separate clean water from an aqueous salt solution.

It should be noted that the accepted values of the equilibrium values of pressures and temperatures are taken for an idealized case without taking into account water salinity, atmospheric pressure, as well as operating and structural characteristics embedded in a real device, which increase the losses attributable to both internal and external irreversibility of the allocation cycle water from an aqueous saline solution.

This includes heat losses in the thermal insulation of the thermostat and heat losses in heat exchangers-regenerators with heat-accumulating packing, which are compensated by the excess power supplied to the compressor 68.

In addition, the work supplied to the compressor should provide an additional degree of compression to ensure the necessary intensification of the processes of evaporation and condensation.

Consider the work of the main cycle processes carried out in the right column.

1 - During the first half of the cycle τ _{(1/2) C} , the liquid moves upward.

To do this, turn on the pump 64, open the taps 63, 55 and turn on the compressor 68, which creates a vacuum in the vapor space of the right column, which leads to the beginning of the boiling of an aqueous salt solution in the boiling zone of B _P columns 44.

The water vapor is distilled by the compressor into the left column, and the aqueous saline is fed to the boiling zone from the bottom of the column.

In FIG. 5. A stationary heat wave is shown, which is formed from the upward movement of an aqueous salt solution at time instants τ ₀ , τ ₂ , τ ₂ , τ ₃ . For the entire time the heat wave moves upward, steam is generated in the boiling zone, and a brine is formed in the boiling zone itself.

Legend T ₀ and T _H correspond to the ambient temperature and the thermostat respectively.

Boiling is stopped at time τ _{(1/2) n,} when the boiling zone _VP thermal wave crest (T = T _H).

The second half of the cycle begins when the heat wave moves down, for which the reverse movement of liquid in the column and the reverse of compressor 68 are turned on. To do this, the valve 63 closes, the valve 62 opens and the generated steam in the left column, following the model of steam generation in the right column, enters the right the column. The rotation of the rotors of compressor 68 (what is possible for a compressor of the Roots type) is reversed.

The compressor presses the steam in the manifold 42 from the side of the right column and causes it to condense in the zone B _P , and the pure water generated in this case moves downward, pushing the brine volume in front of it.

This process of pushing out a volume with an increased concentration of salts is similar to the operation of gas analyzer columns with carrier gas.

Simultaneously with the movement of the brine volume, a heat wave moves from τ _{(1/2) q} , τ ₄ , τ ₅ , τ ₆ to τ _1c , FIG. 6.

Due to the fact that the speed of movement of the brine volume can exceed the speed of advancement of the heat wave in 2; 3 or more times depending on the characteristics of the applied structure, this allows during the second half of the cycle (τ _{(1/2) c} - τ _1c ) to withdraw from the column the volume of aqueous saline solution in the column, the volume of brine and the volume of part of pure water which condenses and is transported down the column during the second half of the cycle. At the moments of the appearance of an aqueous salt solution at the outlet of the column, the valve 56 opens, brine is discharged when the valve 54 is turned on, and clean water when the valve 52 is turned on.

Next, the cycle repeats.

Information sources

1. Patent RU No. 2184592.

2. Patent RU No. 2335459.

3. Patent RU No. 2408539.

4. Patent RU No. 2362606.

5. N.B. Vargaftik. Handbook of thermophysical properties of gases and liquids. M .: Publishing house "Science", 1972.

6. A.K. Mikhailov, V.P. Voroshilov. Compressor machines. Textbook for high schools. - M: Energoatomizdat, 1989.

Claims (13)

1. A method of obtaining pure water from an aqueous salt solution, for example, sea and mineralized waters and industrial effluents, including heating, evaporation, steam removal from the steam space for condensation, characterized in that the evaporation-condensation processes are carried out in a thermostat with an ambient temperature and above, the supply of the saline solution to the evaporation and removal of the condensate of pure water and the saline solution with a high salt concentration is carried out by means of a counterflow heat exchanger, and between the processes of evaporation ode from an aqueous saline solution and its condensation included adiabatic compression process steam, allowing to return the loop (regenerate) the condensation heat. 2. The method according to p. 1, characterized in that the evaporation of pure water is carried out with intensive boiling in the volume of an aqueous salt solution in which the heat exchange surface of the condensation of steam of pure water is located. 3. The method according to p. 1, characterized in that to prevent the entrainment of the spray of the aqueous salt solution during boiling over its surface, screens are installed in the form of perforated plates of various shapes or a layer of porous material. 4. The method according to p. 1, characterized in that the intensity of the evaporation-condensation processes is set by the degree of compression of pure water vapor in the compressor. 5. The method according to p. 4, characterized in that periodically discharge the released and accumulated gases in the vapor space. 6. The method according to p. 1, characterized in that, provided that the pressure values are different from atmospheric in the countercurrent heat exchanger lines, the role of pressure regulators is performed by liquid pumps and hydraulic motors. 7. The method according to p. 6, characterized in that the hydraulic motors and the liquid pump have a common connection with a single shaft of rotation. 8. The method according to p. 7, characterized in that the supply of saline to evaporate and drain the condensate of pure water and saline with a high concentration of salts is carried out by means of heat regenerators with heat-accumulating packing. 9. The method according to p. 8, characterized in that the heat recovery is carried out using a heat wave during the reverse movement of heat carriers in a heat storage pad. 10. The method according to p. 9, characterized in that the heat regenerators are built into the columns, in the upper part of which there are screens to prevent the entrainment of droplets of liquid from the boiling zone of the aqueous salt solution. 11. The method according to p. 10, characterized in that the boiling zone may have an extension. 12. The method according to p. 9, characterized in that the upper parts of the columns are connected by the cavity of the vapor space of the collector, in the middle part of which is installed a reversible compressor for compressing clean water steam. 13. The method according to p. 4, characterized in that periodically discharge into the atmosphere the released and accumulated gases in the vapor space.

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