RU2778446C1 - Seawater desalination plant - Google Patents

Abstract

FIELD: water purification.

SUBSTANCE: invention relates to the desalination of salty sea and lake waters, as well as the production of concentrated solutions of various substances. The seawater desalination plant contains a chamber with two parallel diaphragms installed along and symmetrically relative to the walls of the chamber for cleaning from dissolved salts, dividing the chamber into two zones, as well as two electrodes of different polarity. The reverse osmotic membrane is located inside the second zone of the chamber bounded by two diaphragms, which is connected to a variable capacity pump for pumping permeate. The first zone of the chamber is divided into two halves united by a branch pipe: right and left relative to the direction of the seawater flow. The two outputs of the positive and negative poles of the control unit are connected to the first and second electrodes located on the outside of the chamber to the two halves of the first zone, respectively. The output of the control unit is connected to a variable capacity pump for pumping permeate, and the first and second inputs are connected, respectively, to a permeate conductivity sensor and a concentrate pH meter. The output of the first zone is the output of the concentrate.

EFFECT: efficiency and duration of operation of the device is ensured.

5 cl, 2 dwg

Description

The invention relates to the desalination of saline sea and lake waters, as well as the production of concentrated solutions of various substances.

Known methods of desalination of sea water are divided into two groups:

1 - evaporation followed by condensation of water vapor;

2 - electrochemical.

The first group of seawater desalination methods is described, for example, in the patent of the Russian Federation No. 2554720, С02F 1/04 , in the patent RU 189357, С02F 1/04 "Installation of seawater desalination and power generation", which produces seawater desalination and power generation , as well as the removal of part of the dissolved compounds and impurities from sea water and helps to reduce the deposition of salts on the heat exchange surfaces of the multistage evaporator.

The disadvantage of the devices described in the patent of the Russian Federation No. 2554720 and patent RU 189357, С02F 1/04 "Installation of sea water desalination and power generation" is the high energy costs for the evaporation and condensation of water vapor.

The second group of desalination plants is presented in RF patents 2240177, B01D 61/06 "Membrane seawater desalination plant (options)" and 2225369, C02F 9/08 "Method of natural water purification".

The membranes of this group operate on the basis of reverse osmosis. Osmosis is the penetration (diffusion) of solvent molecules into a solution through a membrane impermeable to solutes that separates the solution from a pure solvent or from a solution with a lower concentration (see Encyclopedic Dictionary, volume 2, M .: GNI "Great Soviet Encyclopedia". 1956, p. .569 Reverse osmosis is a reverse process, i.e. the penetration of a solvent from a concentrated solution through a membrane impermeable to dissolved substances.The output is a permeate, i.e. a less concentrated solution compared to the original water.

The mentioned method of purification of natural waters includes two stages of mechanical treatment, desalination by reverse osmosis and bactericidal treatment, and bactericidal treatment is carried out by chlorination before mechanical treatment of water, then after two stages of mechanical treatment, dechlorination is carried out with sodium sulfite, then the water is purified by microfiltration and an inhibitor is added, desalination by reverse osmosis carried out in two stages, after the first stage the concentrate is discarded, and an inhibitor and caustic soda are added to the permeate, increasing the pH to 10.4, then the second stage of reverse osmosis desalination is carried out, and the concentrate after the second stage of reverse osmosis is mixed into the stream at the inlet of the first stage of desalination , and acid is added to the permeate and passed through filter-conditioners with a calcium-magnesium load. In addition, part of the permeate (desalted water) after the first stage of desalination by reverse osmosis can be sent to the inlet of filter conditioners, part of the permeate after the second stage of desalination by reverse osmosis can be mixed with the output stream from filter conditioners.

The closest analogue in terms of technical essence to the proposed one is the device described in RF patent No. 2155718, С02F 1/467 "Installation for reducing salinity and disinfection of drinking water", taken as a prototype.

Figure 1 shows a diagram of a prototype device, where indicated:

1 - chamber of the electrochemical reactor;

2, 3 - first and second diaphragms;

5, 12 - the first and second anodes;

6 - cathode;

13 - insulator.

, мм, где

- значение напряжения в вольтах на катоде и аноде первой 2 и второй 3 мембран, расположенных вдоль и симметрично относительно стенок камеры электролитического реактора 1, длина мембран равна длине стенок камеры реактора и расстояние между мембранами равно t; первого анода 5 длиной (3...5)t, расположенного между мембранами на расстоянии от второй мембраны 3, равном 0,5t; второго анода 12 длиной L=(20...30)t- (3...3)t, который расположен между первой мембраной 2 и стенкой камеры реактора 1, и расстояние от второго анода 12 до продольной оси камеры реактора вдоль этой оси (от первого анода 5) линейно увеличивается от 0,5t до 1,5t; катода 6, который расположен между второй мембраной 3 и стенкой корпуса реактора 1, расстояние от первого анода 5 до катода 6 равно t и расстояние от катода 6 до второго анода 2 вдоль оси реактора, от входа к выходу, линейно увеличивается от 1,5t до 3t.The installation for reducing mineralization and disinfection consists of a chamber of an electrochemical reactor 1 with a length L=(20...30)t, where

, mm, where

- voltage value in volts at the cathode and anode of the first 2 and second 3 membranes located along and symmetrically relative to the walls of the chamber of the electrolytic reactor 1, the length of the membranes is equal to the length of the walls of the reactor chamber and the distance between the membranes is equal to t; the first anode 5 with a length of (3...5)t, located between the membranes at a distance from the second membrane 3, equal to 0.5t; the second anode 12 with the length L=(20...30)t-(3...3)t, which is located between the first membrane 2 and the wall of the reactor chamber 1, and the distance from the second anode 12 to the longitudinal axis of the reactor chamber along this axis (from the first anode 5) increases linearly from 0.5t to 1.5t; cathode 6, which is located between the second membrane 3 and the wall of the reactor vessel 1, the distance from the first anode 5 to the cathode 6 is equal to t and the distance from the cathode 6 to the second anode 2 along the reactor axis, from inlet to outlet, increases linearly from 1.5t to 3t.

The installation works as follows.

Tap water through the inlet enters the chamber of the electrochemical reactor 1 and after filling it with water, a constant voltage source is switched on. The electrochemical chamber is functionally divided into two zones. In the first zone, two electrodes are installed: the first anode 5 and cathode 6, separated by one membrane 3. Each microvolume of water flowing in the area of the first anode 5 comes into contact with the surface of the electrodes and is exposed to an electric field, while the water is saturated with short-lived, highly active oxidizers of chlorine and oxygen. Their concentration, depending on mineralization and water flow rate, can vary from 15 to 150 mg/l, while electrolytic oxidation at the anode destroys organic and organochlorine substances in water and microorganisms of all kinds and forms are destroyed, breaking down into simple components: non-toxic and completely safe .

Near the first anode 5, water is saturated with oxygen and the decomposition products become polar, and the structural network of hydrogen bonds between water molecules is loosened and disordered, which facilitates its use by cells of living organisms and accelerates the removal of biological waste. Along the first anode 5, due to the symmetrical position of the diaphragm, the entire water flow is divided into anolyte and catholyte. In this case, the cations move to the cathode 6 due to migration and are immediately removed. In the cathode space, direct electrolytic and electrocatalytic reduction of multiply charged heavy metal cations takes place, which reduces the toxicity of water due to the presence of heavy metal ions by thousands of times.

In the second functional zone between the second anode 12 and the cathode 6, two membranes 2 and 3 are installed. In the space between the second anode 12 and the cathode 6, under the influence of an electric field, the ions and polarized decomposition products obtained in the first zone come into orderly motion. Ions of calcium, sodium, magnesium, hydrogen move to the cathode 6. In this case, hydroxyl ions OH- will prevail in the cathode space, and chloride and hydroxyl anions will move into the anode space. And therefore, water with a mixture of hydrochloric and sulfuric acids is concentrated in the anode space, salt water is concentrated in the cathode space, and purified and disinfected water remains between the first and second diaphragms. In the installation, water from the cathode and anode spaces is diverted and drained. Water, moving up along the axis of the installation due to migratory displacements of electrolysis products, gradually gets rid of harmful impurities and is saturated with oxygen.

The disadvantages of the prototype device are the complexity of the design, high operational power losses and low reliability.

The objective of the proposed technical solution is to reduce operating costs for obtaining desalinated water and increase the life of the plant.

To solve the problem, in a seawater desalination plant containing a chamber with two parallel diaphragms installed along and symmetrically relative to the chamber walls, dividing the chamber into two zones, as well as two electrodes of different polarity, according to the invention , a reverse osmosis membrane is introduced, placed inside limited by two diaphragms the second zone of the chamber, which is connected to a pump of variable capacity for pumping out the permeate, while the first zone of the chamber is divided into two, united by a pipe halves - right and left with respect to the direction of sea water flow, as well as a control unit, two outputs of the positive and negative poles of which are connected to the first and second electrodes located on the outer side of the chamber to the two halves of the first zone, respectively; the output of the control unit is connected to a variable displacement pump for pumping out the permeate, and the first and second inputs of the control unit are connected respectively to the permeate electrical conductivity sensor and the concentrate pH meter; the output of the first zone is the output of the concentrate.

The scheme of the proposed device is shown in figure 2, where it is indicated:

1 - camera;

2, 3 - first and second diaphragms;

4 - branch pipe;

5, 6 - first and second electrodes;

7 - reverse osmosis membrane;

8 - control unit;

9 - pump for pumping out permeate;

10 - concentrate pH meter;

11 - permeate electrical conductivity sensor;

"MW" - sea water;

"K" - concentrate;

"P" - permeate.

The inventive seawater desalination plant contains a chamber 1, functionally divided into two zones. Moreover, the two halves of the first zone (right and left relative to the direction of the flow of sea water by analogy with the definition of the banks of the river) are united by a branch pipe 4. The second zone is limited by the first 2 and second 3 diaphragms and is separated by them from the first zone.

Two electrodes 5 and 6 are connected to the right and left halves of the first zone from the outside, connected to the corresponding positive ("+") and negative ("-") poles of the DC source of the control unit 8.

In addition, inside the second zone of chamber 1, at the outlet, a reverse osmosis membrane 7 is placed. At the same time, the outlet of the second zone of chamber 1 is equipped with a variable capacity pump for pumping out permeate 9, connected to the output of control unit 8, the inputs of which are connected respectively to the outputs of the permeate electrical conductivity sensor 11 and concentrate pH meter 10.

The proposed seawater desalination plant operates as follows.

The permeate pump 9 is switched on. As a result, flowing sea water "MV" enters the second zone of chamber 1. A constant voltage is applied to electrodes 5 and 6, which creates a high tension inside the chamber 1. During the operation of the permeate pump 9 and the presence of high voltage on the electrodes 5 and 6, the movement of ions dissolved in the “MW” occurs. Cations move towards the negative electrode and anions move towards the positive electrode. As a result, they penetrate through diaphragms 2 and 3. The right and left halves of the first zone of chamber 1 are connected by branch pipe 4, so that at the outlet of the first zone, a concentrate "K" with neutral acidity (pH=7) is obtained. Control over the acidity of the concentrate is carried out using a concentrate pH meter 10. The length of the diaphragms is chosen such that during the advancement of the MW flow inside the second zone of the chamber, all ions that caused the salinity of sea water crossed the diaphragms 2 and 3. At the outlet of the second zone of the chamber 1, a solution is obtained, purified from ions, which is pumped out through the reverse osmosis membrane 7 by the pump 9. Assuming that sea water is practically cleared of ions of dissolved salts, the osmotic pressure on the reverse osmosis membrane 7 will be relatively small, which significantly reduces the load on the permeate pump 9. Controlling the operation of the desalination plant sea water is carried out by the control unit 8, the inputs of which receive data from the concentrate pH meter 10 and the permeate electrical conductivity sensor 11, respectively. Based on the data obtained, the operating mode of the pump for pumping out permeate 9 and the value and polarity of the direct voltage on the electrodes 5 and 6 are determined. The result of the operation of the seawater desalination plant is the production of permeate - purified water from dissolved salts and concentrate - a solution more concentrated for disposal.

360 л/ч пермеата, что составляет 0,1 л/с. Площадь поперечного сечения второй зоны камеры 1 определим как

дм². Скорость движения морской воды будет

0,67 дм/с, что равно 6,7 см/с.Assuming that the width and thickness of the diaphragms are predetermined, we determine the length of the diaphragm 2 (or 3), provided that it is possible to obtain desalinated sea water with the output

360 l/h of permeate, which is 0.1 l/s. The cross-sectional area of the second zone of chamber 1 is defined as

dm ² . The speed of sea water will be

0.67 dm/s, which is equal to 6.7 cm/s.

см²/В·с. Примем напряжение между металлическими электродами 12 кВ при расстоянии между ними

см. Тогда напряженность электрического поля будет

В/см. Используя формулу (6) на С. 426 этой книги, получим поперечную скорость ионов Na ⁺ :In the book G. Jos. Course of theoretical physics. Part 1. Mechanics and electrodynamics, M.: GUPIMP RSFSR, 1963, p. 427 it is indicated that the mobility of Na ⁺ ions is

cm ² /V s. Let's take the voltage between the metal electrodes 12 kV with a distance between them

see Then the electric field strength will be

W/cm Using formula (6) on page 426 of this book, we obtain the transverse velocity of Na ⁺ ions:

, (1)

, (one)

- напряжённость электрического поля внутри камеры (В/см); where

- electric field strength inside the chamber (V/cm);

- подвижность иона (см²/В·с).

- ion mobility (cm ² /V·s).

0,92 (см/с). Учитывая расстояние, равное 5 см, которое необходимо пройти иону

, получим время пролёта иона

до встречи с диафрагмой 2

=5,435 (с). Длина диафрагмы 2 должна быть

(см).Substituting the known values into formula (1), we find

0.92 (cm/s). Considering the distance equal to 5 cm that the ion needs to travel

, we obtain the time of flight of the ion

before meeting aperture 2

=5.435 (s). Diaphragm length 2 should be

(cm).

We generalize the calculations made by the following formula:

, (2)

, (2)

- выход пермеата (л/с);

- ширина диафрагмы;

- подвижность иона;

- напряжённость электрического поля внутри камеры (В/см);

- площадь поперечного сечения второй зоны камеры(cм²).where

- permeate output (l/s);

- aperture width;

- ion mobility;

- electric field strength inside the chamber (V/cm);

- cross-sectional area of the second zone of the chamber (cm ² ).

To estimate the pore radius of diaphragm capillaries, we use the formula given in the Physical Encyclopedia, volume 2, M: "Soviet Encyclopedia", 1990, p. 240:

. (3)

. (3)

диафрагм (мкм):Equating the right parts of formulas (1) and (3), then transforming the resulting expression, we find the pore radius of the capillaries

f-stop (µm):

, (4)

, (four)

- напряжённость электрического поля внутри камеры (В/см); where

- electric field strength inside the chamber (V/cm);

- подвижность иона (см²/В⋅с);

- коэффициент вязкости жидкости (морской воды) (Пас⋅с);

- толщина диафрагмы (см);

- межфазное поверхностное натяжение (н/м);

- краевой угол, образуемый поверхностью жидкости со стенками капилляра (рад).

- ion mobility (cm ² /V⋅s);

- coefficient of viscosity of the liquid (sea water) (Pas⋅s);

- diaphragm thickness (cm);

- interfacial surface tension (n/m);

- the contact angle formed by the surface of the liquid with the walls of the capillary (rad).

Let us determine the smallest thickness of the diaphragms, which ensures their strength in the operation of the desalination plant.

определяется по следующей формуле:For diaphragm pores with a radius of less than 25 µm, allowable tension

is determined by the following formula:

, (5)

, (5)

- давление жидкости на пору диафрагмы (н/м²);

- модуль Юнга материала диафрагмы (н/м²). where

- fluid pressure on the pore of the diaphragm (n/m ² );

- Young's modulus of the diaphragm material (n/m ² ).

Formula (5) is taken from the Journal of The Franklin Institute, May 1976, p. 425, Table II.

не превосходит 0,4366 (н/м²). Учитывая, что

, где

- плотность воды (жидкости), (кг/м³),

- ширина диафрагмы (м),

9,78 (м/с²) – ускорение свободного падения, толщина диафрагмы

должна быть больше, чемFor polymer materials (such as rubber) from which the diaphragm is made, the allowable tension

does not exceed 0.4366 (n/ ^m2 ). Given that

, where

- density of water (liquid), (kg / m ³ ),

- aperture width (m),

9.78 (m / s ² ) - free fall acceleration, diaphragm thickness

should be more than

, (6)

, (6)

- ширина диафрагмы;

- модуль Юнга материала диафрагмы; where

- aperture width;

- Young's modulus of the diaphragm material;

- радиус пор капилляров диафрагмы (система единиц СИ).

is the pore radius of the diaphragm capillaries (SI units).

Over time, diaphragms 2 and 3 become clogged with salt ions dissolved in sea water. Therefore, they need to be cleaned periodically. This cleaning can be done without stopping the permeate pump 9 by changing the polarity of the voltage on the electrodes 5 and 6.

The proposed design of the seawater desalination plant does not require large amounts of energy, since no direct current flows through electrodes 5 and 6, which indicates the absence of power losses. The design of the seawater desalination device does not contain moving elements, which indicates its reliability and durability. The prototype device works with a stop to purify sea water, and in the proposed installation, the purification process occurs continuously, which ensures its higher performance.

The control unit 8 can be implemented, for example, as described in the book Yu.I. Dytnersky "Reverse osmosis and ultrafiltration", pp. 102-108, fig. II-24; reverse osmosis membrane 7 can be selected from tables II.3 and II.4, pages 59-60 of the same book.

Claims (12)

1. Seawater desalination plant, containing a chamber with two parallel diaphragms installed along and symmetrically relative to the chamber walls, dividing the chamber into two zones, as well as two electrodes of different polarity, characterized in that a reverse osmosis membrane is inserted, placed inside the second zone limited by two diaphragms chamber, which is connected to a pump of variable capacity for pumping out permeate, while the first zone of the chamber is divided into two halves united by a branch pipe - right and left with respect to the direction of sea water flow, as well as a control unit, two outputs of the positive and negative poles of which are connected to the first and second electrodes located on the outer side of the chamber to the two halves of the first zone, respectively; the output of the control unit is connected to a variable displacement pump for pumping out the permeate, and the first and second inputs of the control unit are connected respectively to the permeate electrical conductivity sensor and the concentrate pH meter; the output of the first zone is the output of the concentrate. 2. Installation according to claim 1, characterized in that the diaphragms are cleaned without stopping the desalination process by changing the polarity on the electrodes. 3. Installation according to claim 1, characterized in that the length of the diaphragm

(cm) is determined based on the formula:

, where

- permeate output (l/s);

- aperture width (cm);

- ion mobility (cm ² /V⋅s);

- electric field strength inside the chamber (V/cm);

- cross section of the second zone of the chamber (cm ² ). 4. Installation according to claim 1, characterized in that the radius of the capillaries of the diaphragm is determined by the following formula

(µm):

, where

- electric field strength inside the chamber (V/cm);

- ion mobility (cm ² /V⋅s);

- coefficient of viscosity of the liquid (sea water) (Pas s);

- diaphragm thickness (cm);

- interfacial surface tension (N/m);

- the contact angle formed by the surface of the liquid with the walls of the capillary (rad). 5. Installation according to claim 1, characterized in that the wall thickness of the diaphragm

(cm), made of polymeric materials, is determined by the formula - the SI system of units:

, where

- aperture width (cm);

- Young's modulus of the diaphragm material (N/m ² );

- pore radius of diaphragm capillaries (µm).

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