RU2656219C1 - Coaxial electrochemical compressor of hydrogen - Google Patents

Abstract

FIELD: electrochemistry.

SUBSTANCE: invention relates to electrochemistry, including green energy, and can be used in transport energy systems and in space. Hydrogen compressor includes a casing with inlet and outlet fittings, as well as a package of electrically insulated membrane-electrode blocks, consisting of a proton-conducting membrane installed between the gas-permeable electrodes-the cathode and the anode, contacting the surface of the membrane. Membrane-electrode blocks are located inside the housing and are divided into pneumatically isolated cavities. In each cavity, with the exception of the extreme cavities, a cathode and an anode of two adjacent blocks separated by a gas-permeable insulator are located. Package of membrane-electrode blocks is formed from nested individual blocks, made in the form of hollow cylinders. External electrode of the package is connected to the common anode power supply bus of the coaxial electrochemical hydrogen compressor, the inner electrode - the central electrode - to the common cathode supply line of the compressor. Outlet connection of the compressor communicates with the internal cathode cavity of the internal membrane-electrode block of the package located on the package axis. Inlet connection is with the external anodic cavity of the external membrane-electrode block of the package located under the compressor casing.

EFFECT: increased reliability and safety of the compressor, improved weight and size characteristics, and obtained possibility of using compressor in transport and space power plants.

1 cl, 1 dwg

Description

The invention relates to electrochemistry, including "green energy", and can be used in transport power systems and space.

The main reason for the demand for the proposed compressor in space technology is the inevitability of the future use of rocket fuel production technology in flight or at planetary stations (for example, a lunar base). The components of the fuel in this case are hydrogen and oxygen, obtained by electrolysis of water. Promising studies of such technology are being carried out both abroad and in our country. In this case, it is required to produce high-pressure hydrogen in space.

Any of the existing hydrogen compressors with a pressure of the order of 100 atm and above can serve as an analogue of this proposal (for example, www.ngpedia.ru Hydrogen compressor. A large encyclopedia of oil and gas). In such machines, gas compression is carried out in several stages by means of its piston compression, in compliance with numerous safety measures. Even with small flow characteristics, such units weigh hundreds of kilograms. Mechanical compressors of other types (screw, vibration, etc.) in this case, as a rule, are not used due to the unique properties of the gas. The specifics of hydrogen (low density, explosiveness, tendency to diffusion, etc.) are also the reason that compressors have large mass and size characteristics and a relatively low efficiency (about 40%). They require ongoing maintenance, and their reliability is poor. Due to all this, the use of mechanical hydrogen compressors in some areas, in particular in space, is problematic. In addition to mechanical, there are also compressors operating on special physicochemical principles using the special properties of hydrogen. So, to obtain a high-pressure gas, thermosorption, intermetallic alloys (used to store hydrogen in transport), hydrogen-absorbing substances or substances that react with it can be used (this method is used, for example, in nickel-hydrogen batteries). For ordinary conditions, such systems, as a rule, are not optimal, but in special conditions their use can be quite justified. "Non-mechanical" compression systems of these types do not have moving elements, which increases their reliability, but they require special thermal control systems, and the structure and composition of the hydrogen absorbing substance changes over time (for example, intermetallic alloys are saturated with hydrogen and crumble), and its "hydrogen capacity "Is declining.

Closer to the proposed solution is an electrochemical hydrogen compressor (ECV), the main element of which is a proton-conducting membrane of the Nafion type (the most common commercial type of membrane) installed in a membrane-electrode unit (OIE). The standard OIE is an assembly of such a membrane (with a catalyst deposited on it) and two flat gas-permeable electrodes (cathode and anode) in contact with it from different sides. The electrodes can be made, for example, of porous metal or asbestos coated with carbon. In addition to these basic parts, the OIE may also include additional gas distribution plates, membrane supports, power and sealing gaskets, etc. Such elements are important for the construction of the OIE, but do not play a fundamental role in its work. OIE membranes with Nafion membranes are widely used in modern fuel cells and solid polymer water electrolysers [Assemblies (MEA) Fuell Cell Store.www fuelcellstore.com., As well as Membrane electrode assembly - wikipedia]. OIEs were proposed for hydrogen compression about 10 years ago, and since then the principle of their operation has been studied both theoretically and experimentally [A.A. Avdienko, I.P. Zhukov. “Studies of a hydrogen compression system based on an electrochemical cell with a solid polymer electrolyte”, J.: Advances in Chemistry and Chemical Technology, Volume 23, 2009, No. 8 (101), pp. 70-75]. However, such studies were carried out using only one membrane, so the level of high pressure was limited by the strength of the latter. It is known that Nafion-type membranes in existing electrochemical cells (with an average thickness of about 100 microns and a diameter of 50-150 mm) withstand a pressure drop of 3-4 ati. A special refinement of the OIE design allows operation at pressure drops on the membrane up to 10-15 atm [A.A. Avdienko, I.P. Zhukov, “Studies of a hydrogen compression system based on an electrochemical cell with a solid polymer electrolyte”, J.: Advances in Chemistry and Chemical Technology, Volume 23, 2009, No. 8 (101), pp. 70-75; “Highly selective electrochemical concentrator / high pressure hydrogen compressor”, https // xpir.ru / project / 1648/2 SIC “Kurchatov Institute”, project 2008-2013; US patent 6361896 B1, publ. 03/26/2002, IPC: Н01М 4/86 (2006.01), СВВ 31/20 (2006.01)].

A record drop of about 50 atm for a single-membrane scheme was achieved in [R. Strobel, M. Oszcipok, M. Fasil, B. Rohland, L. Jorissen, J. Garche. The compression of hydrogen in an electrochemical cell based on a PE fuel cell design // J. of Power Sources. - 2002. - No. 105. - PP. 208-215]. This is used, for example, in the "differential" electrolysis of water. To further increase the permissible pressure drop across the membrane during electrolysis, special high-tech calipers have also been developed that allow processes to be carried out with a pressure difference of up to ~ 140 atm. [US 6916443 B2, publ. July 12, 2005, IPC: B22F 3/00 (2006.01), B22F 1/02 (2006.01); Dimensionally stable membrane - Giner Inc. www.ginerinc.com> dimensionally-stable-membrane]. Despite the fact that they significantly "obscure" the working surface of the membrane, their use in ECV in principle allows hydrogen to be compressed to such a pressure, but it is impossible to put it into practice. The reason is the back diffusion of molecular hydrogen across the membrane. In [A.A. Avdienko, I.P. Zhukov. “Studies of a hydrogen compression system based on an electrochemical cell with a solid polymer electrolyte”, J.: Advances in Chemistry and Chemical Technology, Volume 23, 2009, No. 8 (101), pp. 70-75.] It is shown that, for this reason, the pressure increase behind the membrane, it slows down even with a pressure drop of about 10 atm. With a further increase in the pressure drop, the forward and reverse hydrogen flows are compared and the pressure behind the membrane ceases to grow. Thus, ECV with a single membrane, in principle, does not allow to obtain a hydrogen pressure of more than 10-15 atm.

The prototype of this proposal is a multi-stage EEC, the main element of which is a package of OIE connected pneumatically in series, so that hydrogen, leaving each block except the last one, enters the input of the following [US 2004/0211679 A1, publ. 10/28/2004, IPC: C25D 17/00 (2006.01)]. The electrochemical hydrogen compressor includes a housing with inlet and outlet fittings, as well as a package of electrically insulated membrane-electrode blocks, consisting of a proton-conducting membrane installed between flat gas-permeable electrodes - the cathode and anode, in contact with the membrane surface, while the membrane-electrode blocks are placed inside the housing and they divide it into pneumatically isolated cavities, in each of which, with the exception of the extreme ones, there are a cathode and anode d separated by a gas-permeable insulator vuh neighboring blocks. The pressure drops on each of the blocks in the package are summed up, and at the output of the ECV, the pressure exceeds the input pressure by the sum of these drops. In the design of the prototype, standard OIEs with a Nafion membrane are used (which, generally speaking, is not important), described earlier. When a constant voltage is applied to the OIE electrodes, protons begin to diffuse through the membrane, and the current of electrons begins in the external circuit, which recombine behind the membrane with protons, again forming atomic and then molecular hydrogen. A characteristic feature of the prototype is that each OIE package has an individual power source.

The disadvantages of the prototype include:

- the need to calculate the housing for maximum output pressure, which may be an order of magnitude higher than its input value. The consequence of this uneven load on the housing is the "overload" of the compressor as a whole. In the proposed design, the housing has a minimum inlet pressure;

- contact of the output part of the casing with high-pressure hydrogen, accelerating the diffusion of hydrogen into the casing material, which changes the properties of the material (for example, the metal becomes brittle). As a result, the housing resource and compressor safety are reduced, the use of more expensive materials is required. In the proposed design, the ECV casing is isolated from high pressure hydrogen, and the “hydrogen disturbance” of the casing material is much less;

- the shape of the membrane: if it is round, then in order to increase the efficiency of the ECV (i.e., the operating current) it is necessary to increase its diameter and the diameter of the housing. At high pressures, this increases the likelihood of depressurization of the OIE and requires strengthening the body. If the membrane is the lateral surface of the cylinder, its area (and, consequently, the operating current and ECV performance) can be made significantly larger at the same current density without significantly increasing the mass and size characteristics of the compressor.

In addition, the cylindrical surface (membranes) is, in principle, more resistant to internal pressure (which is used in pipelines and cylinders), and the allowable working pressure for such a membrane will generally be greater.

The objective of this proposal is to develop a safe and easy high-pressure ECV with an increased service life and productivity.

The technical result of the invention is to increase the reliability and safety of ECV, to improve its weight and size and flow characteristics, allowing the use of such compressors in transport and space systems.

The technical result is achieved by the fact that in a coaxial electrochemical hydrogen compressor, comprising a housing with inlet and outlet fittings, as well as a package of electrically insulated membrane-electrode blocks consisting of a proton-conducting membrane installed between gas-permeable electrodes - the cathode and anode in contact with the membrane surface, while membrane-electrode blocks are placed inside the housing and divide it into pneumatically isolated cavities, in each of which, with the exception of the extreme, there are p the cathode and anode of two adjacent blocks separated by a gas-permeable insulator, the membrane-electrode block package is formed of separate blocks made in the form of hollow cylinders, the external electrode of the package being connected to a common anode power supply bus of a coaxial hydrogen electrochemical compressor, and the inner one, the central electrode - to the common cathode power supply bus of said compressor, the output fitting of which communicates with the internal cathode cavity of the internal the membrane-electrode block of the package, and the inlet fitting with the external anode cavity located under the casing of the said compressor of the external membrane-electrode block of the package.

The essence of the proposal is in the overall architecture of the OIE, which allows cardinally improving the safety of high-pressure ECB, reducing the strength characteristics of the casing and the overall dimensions of the compressor. The possibility of manufacturing a flexible OIE is confirmed in the patents for inventions: US 8846267 B2, 09/30/2014, IPC: Н01М 4/88 (2006.01), Н01М 8/10 (2006.01); US 8410747 B2, 04/02/2013, IPC: Н01М 2/08 (2006.01), Н01М 8/02 (2006.01); US 8920998 B2, 12/30/2014, IPC: Н01М 8/04 (2006.01), Н01М 8/24 (2006.01).

In FIG. 1 shows a cross section of the proposed coaxial ECV. It includes the OIE package (three blocks are shown in the diagram), formed from separate blocks inserted into each other, made in the form of hollow cylinders and placed in a common housing (1), having inlet (2) and output (3) fittings located at the ends housing (1).

At the same time, the outlet fitting (3) communicates with the internal (cathode) cavity of the internal OIE, which is located on the axis of the packet, where the pressure is maximum. The inlet fitting (2) communicates with the external (anode) cavity of the external OIE located directly below the compressor housing (1) and the pressure here is minimal. The main elements of a cylindrical OIE, as well as its usual “flat” version, are a membrane (6) and gas-permeable electrodes - a cathode (5) and an anode (4) that come into contact with it along its lateral cylindrical surface. The external electrode of the packet is connected to a common anode power bus (not shown in Fig. 1) of the compressor, the inner - central electrode - to a common cathode power bus (not shown in Fig. 1) of a coaxial electrochemical hydrogen compressor. Minor design elements of the OIE that do not play a fundamental role in its operation (mandrel parts, sealing gaskets, fasteners, etc.) in FIG. 1 are not shown. OIE are separated from each other by gas permeable insulators (7), also made in the form of cylindrical gaskets. Thus, the cathode cavity (i.e., the cavity in which the OIE cathode is placed) of each block is pneumatically connected to the anode cavity (cavity in which the anode is placed) of the next block (the exception is, of course, the outermost blocks of the packet). Electric power supply of electric energy supply is carried out according to a monopolar scheme, i.e. all electrodes of the same name are electrically connected to each other (cathodes with cathodes, anodes - with anodes). Thus, in this scheme, the OIE are electrically connected in parallel, and pneumatically in series.

Coaxial EQ works the same as its "flat" prototype. Through the fitting (2), hydrogen is directed into the housing (1) and fills the anode cavity of the first (in this case, the outer) OIE package. On the catalyst covering the surface of the membrane (6) and the anode (4), the gas molecules first dissociate, then ionize, and the protons thus obtained diffuse through the membrane (6) to the cathode (5). The electrons flow between the electrodes in an external circuit. At the cathode (5), protons recombine with electrons, forming first atomic and then molecular hydrogen. The latter through a gas-permeable insulator (7) falls on the anode (4) of the second MEA, and the process repeats. Moreover, due to the voltage between the OIE electrodes, a certain pressure drop across its membrane is maintained.

The pressure difference at the inlet fitting (2) in the anode cavity of the first block (i.e., under the ECV housing) and at the outlet nozzle (3), in the cathode cavity of the internal OIE (i.e., in the cavity on the axis of the packet) is equal to the sum of the pressure drops on all blocks of the package. Thus, in principle, a coaxial EEC works the same as a prototype, however, unlike an EEC with a flat membrane, where the working pressure drop of all blocks is the same, the allowable pressure drop of cylindrical OIEs can vary significantly, despite the same strength parameters of the film, from which their membrane is made. The latter is explained by the fact that the permissible pressure of the cylindrical shell substantially depends on its diameter; therefore, the working differential for internal OIEs can be noticeably greater than for external ones (approximately inversely proportional to the radius of the block). The latter can also be attributed to the advantages of the cylindrical architecture of coaxial EQ, since this allows the use of fewer blocks to achieve a given pressure.

In general, the foregoing allows us to conclude that the compactness and relatively small mass of this ECV, along with its ability to generate high pressure hydrogen, make it advisable to use it on board small spacecraft, the propulsion system of which includes a water electrolyzer.

Claims (1)

A coaxial electrochemical hydrogen compressor including a housing with inlet and outlet fittings, as well as a package of electrically insulated membrane-electrode blocks consisting of a proton-conducting membrane installed between gas-permeable electrodes - the cathode and anode in contact with the membrane surface, while the membrane-electrode blocks are placed inside the housing and divide it into pneumatically isolated cavities, in each of which, with the exception of the extreme, are the cathode separated by a gas-permeable insulator the anode of two adjacent blocks, characterized in that the membrane-electrode block package is formed of individual blocks embedded in each other made in the form of hollow cylinders, the external electrode of the package being connected to a common anode power supply bus of a coaxial electrochemical hydrogen compressor, the inner one - the central electrode - to the common cathode power supply bus of the said compressor, the output fitting of which communicates with the inner cathode cavity of the inner membrane-electrode cavity located on the axis of the stack block of the package, and the inlet fitting with the external anode cavity located under the casing of the mentioned compressor of the external membrane-electrode block of the package.

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