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EP-4735669-A1 - ELECTROLYSER SYSTEM

EP4735669A1EP 4735669 A1EP4735669 A1EP 4735669A1EP-4735669-A1

Abstract

An electrolyser system (20) comprising an electrolyser (16) with at least one stack (10) of electrolyser cells (11), at least one fuel inlet (22) for a fuel for the at least one stack (10), at least two off-gas outlets (18, 24) for off-gases from the at least one stack (10), at least one of the at least two off-gas outlets being an anode side off-gas outlet (18) for venting an anode off-gas from the at least one stack (10) and at least one of the at least two off-gas outlets being a cathode side off-gas outlet (24) for venting a cathode off-gas from the at least one stack (10) and means (142) for exchanging heat from the cathode side off-gas to a fuel for the at least one stack (10), and means (132) for exchanging heat from the anode side off-gas to a fuel for the at least one stack (10) wherein the stack (10) is configured to output, under normal operating conditions, the anode side off-gas, wherein at least 50% by weight of the anode side off-gas is oxygen produced by the electrolyser (16). The present invention also concerns a method of operating an electrolyser system (20) comprising calculating the pressure of a fluid on one side of at least one of the electrolyser cells (11) or the at least one stack (10); and controlling the pressure of a fluid on the other side of the at least one of the electrolyser cells (11) or the at least one stack (10) so that the pressure on the cathode side of the or each of the electrolyser cells (11), or the or each if the stacks (10) is greater than the pressure on the anode side of the or each or each of the cells (11) or the or each of the stacks (10).

Inventors

  • HJALMARSSON, PER
  • RYLEY, Joshua
  • SAYERS, ROBERT

Assignees

  • Ceres Intellectual Property Company Limited

Dates

Publication Date
20260506
Application Date
20240628

Claims (20)

  1. 1 . A method of venting a substantially pure oxygen off-gas from an electrolyser of an electrolyser system, the method comprising: generating a pressure differential between the interior of the electrolyser and an inlet or outlet for the off-gas from the electrolyser; wherein the pressure differential is generated by the production of oxygen through electrolysis by the electrolyser.
  2. 2. The method of claim 1 , wherein the method operates without any external sweep gas, or with a sweep gas that is substantially pure oxygen.
  3. 3. The method of claim 1 or claim 2, wherein at least 50% by weight of the substantially pure oxygen off-gas is oxygen produced by the electrolyser.
  4. 4. The method of any preceding claim, wherein the method comprises controlling the venting of the oxygen by way of a back pressure regulator.
  5. 5. The method of any preceding claim, wherein the substantially pure oxygen off-gas is at least 85% pure by weight.
  6. 6. The method of any preceding claim, wherein the or each electrolyser comprises at least two off-gas outlets for off-gases from the at least one stack thereof, at least one of the at least two off-gas outlets being an anode side off-gas outlet for venting an anode off-gas from the at least one stack and at least one of the at least two off-gas outlets being a cathode side off-gas outlet for venting a cathode off-gas from the at least one stack, wherein the anode side off-gas outlet for venting an anode off-gas from the at least one stack is configured for connection to, or is connected to, the outlet for the substantially pure oxygen off-gas, and the anode off-gas is the substantially pure oxygen off-gas.
  7. 7. The method of any preceding claim, wherein the or each electrolyser does not comprise an inlet for sweeping the substantially pure oxygen off-gas, and the pressure differential is between the interior of the electrolyser and an outlet for the substantially pure oxygen off-gas from the electrolyser.
  8. 8. The method of any preceding claim, wherein a return loop is provided between a sweep-flow inlet of the at least one stack and the anode side off-gas outlet of that stack.
  9. 9. The method of any preceding claim, wherein the pressure of the electrolyser is 0.1 to 10 barg, preferably 0.1 to 5 barg, and more preferably 0.2 to 1 barg.
  10. 10. The method of any preceding claim, wherein the pressures on each of anode and cathode sides of electrolyser cells in the electrolyser are substantially balanced.
  11. 11. The method of any preceding claim, wherein the method comprises a start-up or transition cycle in which when the electrolyser has an internal temperature below 100 degrees C, and air, carbon dioxide or nitrogen, is fed to a cathode side of the electrolyser in place of a fuel.
  12. 12. The method of any preceding claim, wherein the method operates with no external sweep-flow, whereby no sweep-flow inlet is required for the electrolyser system.
  13. 13. The method of any preceding claim, wherein the electrolyser system further comprises a hydrogen/steam separator positioned between the cathode side off-gas outlet and the heat exchanger for exchanging heat from the cathode side off-gas.
  14. 14. The method of claim 13, wherein the hydrogen/steam separator is a membrane filter.
  15. 15. The method of claim 14, wherein the membrane filter operates with a pressure delta across the membrane.
  16. 16. The method of any preceding claim, comprising: calculating the pressure on one side of the electrolyser cell in the electrolyser; and controlling the pressure on the other side of the electrolyser cell so that the pressure on an anode side of electrolyser cells in the electrolyser is greater than the pressure on a cathode side of the electrolyser cells.
  17. 17. A method of operating an electrolyser system comprising an electrolyser with at least one stack of electrolyser cells, the cells each having an anode side and a cathode side, the method comprising: calculating the pressure of a fluid on one side of at least one of the electrolyser cells or the at least one stack; and controlling the pressure of a fluid on the other side of the at least one of the electrolyser cells or the at least one stack so that the pressure on the cathode side of the or each electrolyser cell, or the or each stack is greater than the pressure on the anode side of the or each cell or the or each stack.
  18. 18. The method of claim 16 or 17, wherein the difference in pressure between the anode and cathode sides of an electrolyser cell in the electrolyser cells or stacks is no more that 50mbar, optionally no more than 40mbar, optionally nor more than 30mbar, optionally no more than 20mbar, optionally no more than 10mbar.
  19. 19. The method of any of claims 16 to 18, wherein the pressure of the anode side of the electrolyser cells or stacks in the electrolyser is controlled by a back pressure regulator.
  20. 20. An electrolyser system configured to carry out the method according to any preceding claim.

Description

Electrolyser System The present invention relates to an electrolyser system, and in particular an electrolyser system in which high energy efficiencies are achievable. An electrolyser system will have one or more electrolysers, each of which may comprise one or more stacks of electrolyser cells - also known as regenerative fuel cells. The electrolysers are used to split a source fluid (the “fuel”) - usually steam or carbon dioxide - into its constituent parts and for that purpose it requires a source of electricity for supplying an electric current and voltage across/through the at least one stack of electrolyser cells. As an example, electrolysers can be used to produce hydrogen and oxygen from water, or carbon monoxide and oxygen from carbon dioxide, each by way of electrolysis. The collection or use of the produced oxygen is important as it can be utilised in industry and medical applications, amongst many other uses. The collection and the subsequent storage and/or distribution of carbon monoxide is also important as it is useful for numerous chemical processes. The collection and the subsequent storage and/or distribution of hydrogen is also important as it is a fuel commodity that can help in the race for decarbonisation and for achieving net zero targets. The produced hydrogen can be utilised as a fuel for combustion, or as a fuel for a use in a fuel cell system for achieving an electrolytic reaction in the fuel cell to recombine the hydrogen with oxygen, with resultant electrical and heat outputs. The hydrogen can also have many other uses. Combining electrolysers with green energy sources is also important as that can greatly contribute towards the green credentials of electrolysers, and particularly in their use in hydrogen capture, thus accelerating the achievement of net zero and decarbonisation targets. Given the importance of electrolysers for meeting net zero and decarbonisation targets, and in industry in general, any improvement in the efficiency or service life of an electrolyser is considered important and valuable. In typical electrolyser systems, oxygen is produced at the anode side of the electrolyser, and it is a product of the electrolysis of both water and carbon dioxide. In typical electrolysers, this oxygen is forced out of the electrolyser by way of a ‘sweep gas’. The sweep gas is typically pumped through the electrolyser via a fan, but the energy required to power the fan reduces the overall efficiency of the system. It can be termed a ‘parasitic load’. It is also advantageous to bring the sweep gas up to the operational temperature of the stack before passing it through the anode side of the electrolyser. This is to avoid dropping the temperature of the stack, and diminishing its operational efficiency. Most electrolyser stacks have a narrow optimum operational temperature range at which they have an optimum efficiency, and thus they typically are desired to operate at a substantially constant temperature within that temperature range. Furthermore, temperature deltas (variations/differences) across the stack or across an electrolyser cell, can create thermal stresses within the stack or cell, which in turn can lead to premature failure of the stack or cell, or leaks in the stack due to thermal expansion characteristics of the materials involved. The provision of such heating for the sweep gas, however, also increases the energy load on the electrolyser system - a further “parasitic load”. Additionally, the sweep gas can introduce contaminants into the stack, or otherwise cause degradation to the stack through the interaction of the sweep-flow gas with the materials of the system, especially in the case of intermediate or high temperature electrolysers - i.e. those with an operational temperature in excess of 400 degrees C. These contaminants or degradations/interactions can reduce the operational service life of the stack through damage to the anode, or through the manifolds or pipework of the sweep-flow pipelines. Indeed, any system with such a sweep-flow will always encounter a gradual degradation of the anode or the manifolds or pipework of the sweep-flow pipelines during use of the electrolyser, but contaminants such as dirt particulates or trace elements of other toxic or reactive substances can worsen that rate of degradation. The present invention therefore seeks to provide an electrolyser system with a longer service life, and preferably one where the parasitic loads associated with the sweep gas are reduced, removed, or avoided. Statements of Invention According to a first aspect of the present invention there is provided an electrolyser system comprising an electrolyser with at least one stack of electrolyser cells, the electrolyser comprising: at least one fuel inlet for a fuel for the at least one stack; at least two off-gas outlets for off-gases from the at least one stack, at least one of the at least two off-gas outlets being an anode side off-gas outlet for ve