RU2647841C2 - Water electrolyser and operation method thereof - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to water electrolyzer comprising current source, control unit, sealed housing, on the external surface of which there is temperature sensor connected to control unit, device for maintaining temperature of hermetic body within predetermined limits, located in hermetic housing, porous hydrophilic membrane, two adjacent to it porous hydrophobic electrode – anode and cathode, connected to current source, two sealed partitions, one of which is connected to the end part of the anode and a sealed enclosure with the formation of an oxygen cavity between the outer surface of the anode, the partition and the inner surface of the hermetic housing, and the other – with the end part of the cathode and the hermetic case with the formation of a hydrogen cavity between the outer surface of the cathode, the partition and the inner surface of the hermetic housing, while between the partitions an electrolyte cavity is formed connected to the water supply line with the water filling valve, the hydrogen and oxygen supply lines with valves for their discharge from the respective cavities, gas differential pressure regulator connected to the discharge lines of said gases, and pressure sensor connected to the control unit. In this case, the inner surface of the hermetic body is covered with a layer of porous hydrophilic material, similar to the membrane material and having a hydraulic connection with the cavity of the electrolyte and with the membrane, and the sealed partitions are made flexible and elastic, and the elasticity of each partition is chosen such that, throughout the working range of its displacements the value of the elastic pressure on the electrolyte was lower than the capillary pressure of the membrane and a layer of a porous hydrophilic material. invention relates to a method of operating electrolysis unit.

EFFECT: technical result of the proposed invention is the simplification of the design of the water electrolyzer, as well as the deeper dehydration of gases.

5 cl, 1 dwg

Description

The invention relates to electrochemistry and can be used in installations for the decomposition of water into hydrogen and oxygen, including high pressure, mainly in zero gravity.

Electrolysis plants for work in zero gravity are known, in which, in addition to the electrolyzer itself, designed to decompose water into hydrogen and oxygen under the influence of electric current, there are electrolyte circulation circuits containing pumps for circulation, heat exchangers for removing heat from gases and electrolyte as independent units, as well as gas separators for the evolution of hydrogen and oxygen from gas-liquid mixtures. The gas separators for work in zero gravity can be of a centrifugal type with a drive (RF patent No. 2525350, publ. 08/10/2014, IPC: B64G 1/22 (2006.01), or of a static type with the movement of a gas-liquid mixture through a helical channel (space electrolysis installation "Electron- VM "," Manned space flights, No. 3 (8), 2013, p. 86). The electrolyte can be circulated inside the electrolyzer along the electrodes or along the channels in the electrodes made in the form of a coil (AS USSR No. 1840414, publ. 10.01.2007, IPC С25В 1/10 (2006.01)).

A common drawback of these installations is their structural complexity, since, for example, with an increase in gas pressure, each individual unit must be located in a separate, robust housing.

Electrolysis plants are also known in which hydrogen and / or oxygen gas separators as separate units are absent, and the gas is separated from the electrolyte inside the electrolyzer on porous hydrophobic electrodes, which are closely pressed against the hydrophilic gas shut-off diaphragm, into which the electrolyte is fed (JP 5314273 (B2), publ. October 16, 2013, IPC С25В 9/00 (2006.01), or RF patent No. 2074266, publ. 02/27/1997, IPC С25В 9/00 (2006.01)).

The same solution was used in RF patent No. 2501890, publ. 12/20/2013, С25В 9/10 (2006.01), adopted as a prototype device. The electrolyzer includes a housing with electrolysis cells installed in it, consisting of a cathode, anode, and a gas shut-off membrane, pumps for circulating an alkaline electrolyte, tanks with an alkaline electrolyte, a water supply system, oxygen and hydrogen separators from water vapor and alkali. The anode of each cell is made in the form of a tube of mesh material, and the cathode is in the form of a hollow cylinder of porous hydrophobic material. These electrodes are placed close to the gas-shut hydrophilic membrane. The cathode is connected in gas with a hydrogen cavity between the outer side of the cathode and the housing. The electrolyte is circulated through the oxygen separator and heat exchanger using a pump. A partition is installed between the end part of the cathode and the casing, which forms a hydrogen cavity together with the cathode and the casing.

The disadvantage of this electrolyzer, as well as analogues, is the design complexity, which is expressed in the presence of an electrolyte circulation circuit, as well as gas separators, a heat exchanger and water vapor separators, made in the form of separate units. Another disadvantage of the prototype is the inability to work in zero gravity, since the separation of gas from liquid occurs using gravity.

Closest to the proposed technical solution - the method is an electrolysis unit for space use and the method of its operation (RF patent No. 2543048, publ. 02.27.2015, IPC: C25V 1/12 (2006/01)). In this method of operation, the goal is to dry the electrolysis gases, which is carried out in two stages - by cooling the moist gases in an evaporative refrigerator and further cooling when these gases expand in cylinders. It is proposed that the water condensed in this process be accumulated in a porous hydrophilic material inside the cylinders, and then discharged in liquid form into the electrolyzer and refrigerator using pumps.

One of the disadvantages of this method is that the condensation of water vapor both in the refrigerator and in the cylinders takes place in water in a porous hydrophilic material or in droplet water inside the cylinders, which at a temperature of about 0 ° C turn into ice in a porous material, or in hoarfrost inside the cylinder, and the pneumohydraulic lines are clogged, which greatly complicates further cooling. The second disadvantage is that in the evaporative refrigerator, water is carried away, which in space is an irreplaceable resource.

The objective of the invention is to remedy these disadvantages.

The technical result of the invention is to simplify the design of a water electrolyzer, as well as a deeper drying of gases.

The technical result is achieved in that in a water electrolyzer containing a current source, a control unit, a sealed enclosure, on the outer surface of which a temperature sensor is installed connected to the control unit, a device for maintaining the temperature of the sealed enclosure within specified limits, a porous hydrophilic membrane located in the sealed enclosure , two adjacent porous hydrophobic electrodes - anode and cathode connected to a current source, two sealed partitions, one of which is connected to the end the th part of the anode and the sealed housing with the formation of an oxygen cavity between the outer surface of the anode, the septum and the inner surface of the sealed housing, and the other with the end surface of the cathode and the sealed housing with the formation of the hydrogen cavity between the outer surface of the cathode, the partition and the inner surface of the sealed housing, an electrolyte cavity is formed between the partitions, connected to a water supply line with a water filling valve, a hydrogen and oxygen supply line from the valve and for their release from the respective cavities, a gas differential pressure regulator connected to the gas supply lines of these gases, and a pressure sensor connected to the control unit, the inner surface of the sealed housing is covered with a layer of porous hydrophilic material similar to the membrane material and having a hydraulic connection with the electrolyte cavity and with a membrane, and the sealed partitions are made flexible and elastic, and the elasticity of each partition is chosen so that in the entire working range of its movements the pressure value of the elasticity on the electrolyte was lower than the capillary pressure of the membrane and the layer of porous hydrophilic material, while the sealed partitions are made in the form of diaphragms or bellows, in addition, the electrolyzer is equipped with power limiters connected with the sealed case for maximum movement of the sealed partitions.

The technical result is also achieved by the fact that in the method of operation of the water electrolyzer, including the decomposition of water in the electrolyzer by current with the formation of hydrogen and oxygen at a temperature that provides a given performance, with control of pressure, gas temperature and electrolysis current, further accumulation, cooling and drying of the obtained gases and their subsequent delivery to the consumer, accumulation, cooling and drying of the gases is carried out inside the sealed cell body with constant contact of the gases with the electric olit, in the process of water decomposition, upon reaching a given or maximum allowable gas pressure, the sealed cell body is cooled to a temperature close to the melting temperature of the electrolyte, while the cooling rate and / or electrolysis current is maintained so that the gas pressure in the said body during cooling it did not decrease, and upon reaching the above temperature, the current is turned off and the dried gases are dispensed to the consumer.

The invention is illustrated in the drawing, which shows a diagram of the proposed water electrolyzer.

It includes a sealed housing 1, internally coated with a layer of porous hydrophilic material 2 and having on the outside a temperature sensor 21 connected to a control unit (not shown). The power limiters for the maximum movement of the partitions 3 and 14 are connected with the said casing. A hydrophilic porous membrane 7, two adjacent porous hydrophobic electrodes - anode 6 and cathode 12 connected to a current source (not shown), two flexible elastic sealed partitions are located in the sealed casing. 4 and 15, made, for example, in the form of diaphragms, one of which is connected to the end part of the anode 6 and the housing 1 with the formation of an oxygen cavity 5 between the outer surface of the anode 6, the partition 4 and the inner surface of the sealed housing 1, and the other with the end part of the cathode 12 and the housing 1 with the formation of a hydrogen cavity 13 between the outer side of the cathode 12, the partition 14 and the inner surface of the sealed housing 1. At the same time, an electrolyte cavity 16 hydraulically connected between the partitions 3 and 14 is also formed with a hydrophilic membrane 7 and a layer of porous hydrophilic material 2. In addition, the electrolyte cavity 16 is connected to the water supply pipe 18, which includes a water filling valve 17. The cell also includes a master l the release of hydrogen 19 with a valve for the release of hydrogen 10, the line for the release of oxygen 20 with the valve for the release of oxygen 9, a differential pressure regulator 8 connected to the lines for the delivery of these gases, as well as a pressure sensor 11 connected to any of the lines 19 or 20 and connected to the block management. The composition of the electrolyzer also includes (not shown) a current source connected to the anode 6 and cathode 12, a control unit connected to all sensors, valves and a current source, and a device for maintaining the temperature of the sealed enclosure within specified limits.

Sealed housing 1 is designed to accommodate the equipment of the electrolyzer, counteracting the internal pressure of gases and heat dissipation. It has devices for maintaining its temperature within predetermined limits (not shown). It can be a gas or liquid heat exchanger, or a radiation emitter.

The differential pressure controller 8 is designed to equalize the pressures in the cavities 5 and 13 and can be any of the known types, for example, a membrane one, in which the membrane, moving under the action of the differential pressure of hydrogen and oxygen, opens the gas outlet valve, the pressure of which is higher by a predetermined amount. This predetermined value should be such that the pressure drop does not exceed the capillary pressure of the membrane 7 and the hydrophilic layer 2. In this case, the liquid filling the membrane 7 will not be squeezed out under the pressure drop between the cavities. The differential pressure controller 8 is set so that its inputs and outputs are connected to the oxygen supply line 20 and the hydrogen supply line 19 before and after the exhaust valves 9 and 10.

The cell operates as follows.

Before the next cycle of operation, the electrolyte cavity 16 is filled with electrolyte that was not consumed in the previous cycle, for example, KOH alkali solution, the partitions 4 and 15 are close to each other, the volume of the cavity 16 is minimal, and the electrolyte concentration is maximum. The hydrophilic membrane 7 and the hydrophilic layer 2 are soaked with electrolyte, impervious to gases and communicate with each other and with the electrolyte in the cavity 16. Valves 9, 10 and 17 are closed. In the cavities 5 and 13 are oxygen and hydrogen, respectively, with residual (low) pressure, as well as water vapor with a partial pressure corresponding to the temperature of the cell.

The cycle of operation of the electrolyzer begins with the fact that power is supplied to the control unit (not shown), the pressure sensors 11 and temperature 21, include a differential pressure controller 8 (if it is of an electrical type).

Next, the valve 17 is opened and, using an external metering device (not shown), a predetermined amount of distilled water is supplied through the water supply line 18 to the electrolyte cavity 16. This amount of water can be determined in various ways, for example, as much water (by weight) can be supplied as the number of electrolysis gases produced in the previous cycle. You can also calculate water refueling based on the number of ampere hours accumulated in the previous cycle. In the process of filling with water, the partitions 4 and 15 are opened, the pressure of oxygen, hydrogen, electrolyte in the cavities 5, 13, 16 increases. After filling, the valve 17 is closed. Under the action of diffusion, distilled water dilutes the electrolyte remaining in the electrolyzer in cavity 16, membrane 7 and hydrophilic layer 2 to a minimum working concentration.

Then a DC voltage from an external current source (not shown) is supplied to the hydrophobic electrodes 6 (anode) and 12 (cathode), respectively, of positive and negative polarity. A current flows through the membrane 7, impregnated with the electrolyte, while oxygen is released at the boundary between the electrode 6 and the membrane 7, and hydrogen is released at the boundary between the electrode 12 and the membrane 7. Gases cannot penetrate the membrane 7 due to the surface tension of the liquid, therefore they pass through the porous electrodes 6 and 12, respectively, oxygen into the cavity 5, and hydrogen into the cavity 13. The hydrophobicity of the electrodes 6 and 12 prevents them from wetting with liquid electrolyte therefore, the porous channels in the electrodes are always dry and gas permeable.

During the passage of current through the electrolyte, the membrane 7 heats up and the process of evaporation of water from the electrolyte is enhanced. Water vapor from the surface of the membrane 7 freely passes through hydrophobic electrodes in cavities 5 and 13. In these cavities, the vapor partially condenses on the colder hydrophilic layer 2, and the resulting water is absorbed into the hydrophilic layer 2 under the action of capillary forces. In this case, the heat from condensation of water vapor is transferred to the housing 1 and then removed from it by external means. The described mechanism of heat transfer from the membrane to the housing, and the circulation of water in the electrolyzer, is similar to the mechanism of action of the heat pipe. Non-condensed vapor remains in cavities 5 and 13, its partial pressure is equal to the saturated vapor pressure above the alkali at a temperature equal to the average temperature in cavities 5 and 13.

Excess water in the hydrophilic layer 2 under the action of capillary pressure moves into the cavity 16 and into the membrane 7, with which the hydrophilic layer 2 is hydraulically connected. The movement of fluid from the hydrophilic layer 2 to the cavity 16 occurs because the capillary pressure in the hydrophilic layer 2 and the membrane 7 is higher than the elastic pressure of the walls 4 and 15 on the electrolyte in the entire working range of movement of the walls. Capillary pressure in a hydrophilic material occurs at the interface between liquid and gas and is due to the fact that due to the wettability of the material, the interface of the liquid consists of convex menisci on which surface tension forces create excess pressure in the liquid. This capillary pressure is proportional to the wettability of the hydrophilic material and inversely proportional to the radius of the capillaries.

Flexible partitions 4 and 15 are used to form an electrolyte cavity 16 of variable volume, to equalize the electrolyte pressure with gas pressures, to reduce the differential pressure of gases in cavities 5 and 13. In addition, the partitions create additional pressure on the electrolyte due to its elasticity. This additional pressure creates the condition for constant forced soaking of the membrane 7. Without this pressure, when working in zero gravity, a situation may arise when the liquid in the cavity 16 collects in a ball drop and comes off from the membrane 7, and the liquid in the membrane 7 is used up for electrolysis. The additional pressure from the partitions should not exceed capillary pressure so as not to transfer electrolyte from the membrane 7 and the hydrophilic layer 2 to the gas cavities 5 and 13. For example, if the capillary pressure in the membrane and in the hydrophilic layer is 10 kPa, then the elastic pressure of the elastic partitions at the electrolyte, even with their greatest possible extension, should not exceed 10 kPa.

During the accumulation of gases in cavities 5 and 13, the pressure in them increases. To ensure approximately the same pressure growth in cavities 5 and 13, the volumes of these cavities are structurally performed in a ratio of 1: 2, in accordance with the molarity of the gases produced. The maximum allowable gas pressure is determined by the strength of the sealed housing 1, valves 9, 10, 17, differential pressure controller 8 and pressure sensor 11. Temperature is controlled by temperature sensor 21, pressure is controlled by pressure sensor 11, pressure equalization in cavities 5 and 13 - with the help of a constantly working differential pressure controller 8. The additional regulation of the differential pressure is carried out by flexible partitions 4 and 15, which, under the action of the uncompensated differential pressure in the cavities 5 and 13, are possible NOSTA moved left or right within its free stroke until the force limiters 3 and 14.

Typically, the consumer requires the issuance of dried gases. For example, in space technology, gases with a dew point of the order of minus (50-60) ° C are used.

The essence of the proposed method of operation of a water electrolyzer is as follows.

The accumulation of electrolysis gases is carried out inside the sealed housing 1 of the electrolyzer, in cavities 5 and 13 with closed valves 9 and 10. The electrolysis process is accompanied by heat generation during the passage of current through the electrolyte. This heat is removed from the sealed housing 1 using an external heat exchanger, and the working temperature of the electrolysis can be selected over a wide range. In the proposed electrolyzer, as in most others, the temperature of the electrolysis during gas production is maintained within the range of 50-70 ° C. This temperature is optimal to ensure both small current losses due to the low resistance of the electrolyte, and relatively small evaporation of water.

As water is consumed for electrolysis, the volume of the cavity 16 decreases, the volumes of the cavities 5 and 13 increase, the concentration of the electrolyte increases, and the pressure in all cavities also increases.

When the pressure sensor 11 reaches the specified or maximum permissible gas pressure, without turning off the electrolysis current, an additional, more intensive cooling of the sealed housing 1 is carried out and its temperature is gradually brought to a temperature close to the melting temperature of the electrolyte. At the same time, the cooling rate and the electrolysis current are maintained such that the gas pressure in the housing during cooling does not decrease. Temperature control is carried out by temperature sensor 21, and upon reaching the specified temperature, the current should be turned off and gas should be dispensed to the consumer by opening valves 9 and 10.

The melting point of an electrolyte, for example, a 30% KOH solution is minus 60 ° C. When cooled to this temperature (but before freezing), the electrolyzer is fully operational, although its electrical efficiency is reduced by about half. These data were obtained in experimental work at RSC Energia.

When cooled to minus (55-60) ° C, saturated water vapor in cavities 5 and 13 condenses on the surface of hydrophilic layer 2, combining with a saturated alkali solution and diluting it, it is absorbed in liquid form into hydrophilic layer 2, then it is collected in the electrolyte cavity 16 and hereinafter used in the next cycle of work. In this case, unlike the prototype, water does not leave the cell with steam.

Essentially important in this method is also the fact that the condensation of the vapor does not occur over water, as in the prototype, but over the electrolyte. It is known that the pressure of saturated vapor above the electrolyte at any temperature is more than half that of water. For example, at a temperature of 20 ° C, the vapor pressure above a 30% NaOH solution is 8 mm Hg, and above water it is 17.5 mm Hg. (Yakimenko L.M., Water Electrolysis, 1970, p. 28). This feature allows you to get dried gases in the electrolyzer with a dew point lower than minus 60 ° C.

To produce accumulated gases to the consumer, valves 9 and 10 are opened and hydrogen is supplied via line 19, and oxygen is supplied via line 20. After the dried gases are dispensed to the consumer, valves 9 and 10 are closed, and the cell operation cycle is completed.

The processes described above relate to the normal operation of the electrolyzer. In the event of an emergency, in the event of a failure of the differential pressure regulator 8 or a failure of one of the valves 9 or 10, the pressure difference acts on the partitions 4 and 15, which is significantly higher than the permissible one, up to the full pressure of one of the gases. For example, when the cavity 5 is depressurized, the partition 4 is completely adjacent to the power limiter 3 and transfers to it the full force of the gas pressure in the cavity 13. The pressure differential between the cavities 16 and 5 becomes higher than the capillary one, and the liquid from the electrolyte cavity 16, as well as from the membrane 7 and the hydrophilic layer 2 is pressed into the cavity 5, after which the septum 15 is also adjacent to the limiter 3. Thus, the destruction of the membranes, as the least durable structural elements, does not occur. In the event of an emergency and pressure equalization in all cavities, the partitions return to their working position, the electrolyte from the cavity 5 is absorbed into the hydrophilic layer 2 and then into the membrane 7 and fills the electrolyte cavity 16. After that, the electrolyzer is again ready for operation.

Structurally, the internal surface of the sealed housing 1 can be used as limiters 3 and 14. Partitions 4 and 15 can be made, for example, of alkali-resistant rubber or polysulfone. Hydrophilic layers 2 and membrane 7 can be made of alkali-resistant synthetic filter materials (for example, PP-100, MPS-020, MMK-010 manufactured by NPP Tekhnofiltr, Vladimir). Hydrophobic electrodes can be made of nickel nets or sintered nickel powder with a fluoroplastic coating (with the exception of the outer electrically conductive layer adjacent to the membrane). Cooling the electrolyzer body to minus 60 ° C in space can be achieved by shading it from sunlight and opening to the side of open space, without using the spacecraft thermal control loop.

In addition to the proposed method, the electrolyzer can work in the traditional mode, at a constant pressure and temperature, with the continuous release of gases to the consumer. In this case, the valves 9 and 10 must be open, and the departure of gases to the consumer is compensated by their running hours.

Claims (5)

1. A water electrolyzer containing a current source, a control unit, a sealed enclosure, on the outer surface of which a temperature sensor is mounted connected to the control unit, a device for maintaining the temperature of the sealed enclosure within specified limits, a porous hydrophilic membrane located in the sealed enclosure, two adjacent to it porous hydrophobic electrode - anode and cathode connected to a current source, two sealed partitions, one of which is connected to the end part of the anode and a sealed housing with a the formation of an oxygen cavity between the outer surface of the anode, the septum and the inner surface of the sealed housing, and the other with the end part of the cathode and the sealed housing with the formation of a hydrogen cavity between the outer surface of the cathode, the septum and the inner surface of the sealed housing, while an electrolyte cavity is connected between the walls, connected with a water supply line with a water filling valve, a hydrogen and oxygen supply line with valves for their release from the respective cavities, a gas differential pressure regulator connected to the gas supply lines and a pressure sensor connected to the control unit, the inner surface of the sealed housing being covered with a layer of porous hydrophilic material similar to the membrane material and having a hydraulic connection with the electrolyte cavity and the membrane, and the sealed partitions are made flexible and elastic, and the elasticity of each septum is chosen so that in the entire working range of its movements, the pressure of elasticity on the electrolyte is ilk capillary pressure of the membrane layer and a porous hydrophilic material. 2. A water electrolyzer according to claim 1, wherein the sealed partitions are made in the form of diaphragms. 3. The water electrolyzer according to claim 1, wherein the sealed partitions are made in the form of bellows. 4. The water electrolyzer according to claim 1, wherein it is equipped with power limiters associated with the sealed enclosure for maximum movement of the sealed partitions. 5. A method of operating a water electrolyzer according to claim 1, including the decomposition of water in the electrolyzer by current with the formation of hydrogen and oxygen at a temperature that provides a given performance, with control of pressure, gas temperature and electrolysis current, further accumulation, cooling and drying of the obtained gases and subsequent delivery their consumer, moreover, the accumulation, cooling and drying of gases is carried out inside a sealed cell housing with constant contact of gases with the electrolyte, in the process of decomposition of water, etc. and reaching a predetermined or maximum allowable gas pressure, the sealed cell body is cooled to a temperature close to the melting temperature of the electrolyte, while the cooling rate and / or electrolysis current is maintained so that the gas pressure in the said cell does not decrease during cooling, but upon reaching the above temperatures turn off the current and produce dried gases to the consumer.

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