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EP-4738486-A1 - A HEAT MANAGEMENT UNIT FOR A REVERSIBLE ELECTROCHEMICAL DEVICE, AN ELECTROCHEMICAL SYSTEM WITH A HEAT MANAGEMENT UNIT AND A STACK MODULE, AND A METHOD FOR HEAT MANAGEMENT OF THE ELECTROCHEMICAL SYSTEM

EP4738486A1EP 4738486 A1EP4738486 A1EP 4738486A1EP-4738486-A1

Abstract

A heat management unit (1) for a reversible electrochemical system comprising a process air (2) flow path and a fuel (3) flow path are presented. The process air (2) flow path comprises a unit process air inlet (4), a first heat exchanger (7), an electric heater (8), a second heat exchanger (9), and a unit process air outlet (11). The fuel flow path comprises a unit fuel inlet (5), a unit fuel outlet (12), and a fuel path through the second heat exchanger (9). In the second heat exchanger (9) heat is exchangeable between process air (2) and fuel (3). The heat management unit (1) further comprises a stack connection device (10). The stack connection device (10) enables a connection to a stack module (30). The stack connection device (10) comprises the unit fuel outlet (12), the unit process air outlet (11) and additionally a stack exhaust inlet (13) and a stack fuel inlet (14). That the stack exhaust inlet (13) is connected to an afterburner (6). In the afterburner (6), stack exhaust from the stack exhaust inlet (13) is usable for the combustion of fuel (3) in the afterburner (6). The afterburner (6) is connected to the first heat exchanger (7) such that heat is exchangeable between an afterburner gas (20) from an afterburner gas outlet (53) and process air (2) from the unit process air inlet (4) in the first heat exchanger (7).

Inventors

  • Wuillemin, Zacharie
  • PERRET, Julien
  • Waeber, Florian
  • Cornu, Thierry
  • DIETHELM, STEFAN

Assignees

  • SolydEra SA

Dates

Publication Date
20260506
Application Date
20241223

Claims (17)

  1. A heat management unit (1) for a reversible electrochemical system comprising a process air (2) flow path and a fuel (3) flow path wherein the process air (2) flow path comprises a unit process air inlet (4), a first heat exchanger (7), an electric heater (8) and a second heat exchanger (9), and a unit process air outlet (11) and the fuel flow path comprises a unit fuel inlet (5), a unit fuel outlet (12), and a fuel path through the second heat exchanger (9), wherein in the second heat exchanger (9) heat is exchangeable between process air (2) and fuel (3), wherein the heat management unit (1) further comprises a stack connection device (10), wherein the stack connection device (10) enables a connection to a stack module (30), the stack connection device (10) comprising the unit fuel outlet (12), the unit process air outlet (11) and additionally a stack exhaust inlet (13) and a stack fuel inlet (14) characterized in that the stack exhaust inlet (13) is connected to an afterburner (6), wherein in the afterburner (6), stack exhaust from the stack exhaust inlet (13) is usable for the combustion of fuel (3) in the afterburner (6), wherein the afterburner (6) is connected to the first heat exchanger (7) such that heat is exchangeable between an afterburner gas (20) from an afterburner gas outlet (53) and process air (2) from the unit process air inlet (4) in the first heat exchanger (7).
  2. The heat management unit (1) according to claim 1, wherein the second heat exchanger (9) is located adjacent to the electric heater (8) and wherein the second heat exchanger (9) comprises at least one hollow tube through which fuel (3) from the unit fuel inlet (5) is flowable.
  3. The heat management unit (1) according to claim 1 or 2, wherein the fuel flow path comprises a third heat exchanger (41), wherein the third heat exchanger (41) is connected to the unit fuel inlet (5) and stack fuel inlet (14) such that heat is exchangeable between fuel (3) from the unit fuel inlet (5) and stack fuel from the stack fuel inlet (14) in the third heat exchanger (41).
  4. The heat management unit (1) according to any one of the previous claims, wherein the fuel flow path comprises a fuel path through a reformer (46) equipped to reform fuel (3), the fuel (3) comprising of carbonaceous gas and/or hydrogen and/or ammonia, wherein the reformer (46) is connected to the afterburner gas outlet (53) and the unit fuel inlet (5), wherein the reformer (46) comprises a reformer fuel outlet (54) for fuel (3), the reformer fuel outlet (54) being connected to the second heat exchanger (9), optionally via the third heat exchanger (41) such that heat is first exchangeable in the third heat exchanger (41) between fuel (3) from the reformer fuel outlet (54) and stack fuel from the stack fuel inlet (14), such that heat is exchangeable between fuel (3) and process air (2)in the second heat exchanger (9).
  5. The heat management unit (1) according to claim 4, wherein the heat management unit (1) comprises a flow regulator (50) to regulate the flow rate of afterburner gas (20) to the reformer (46) such as the regulate the temperature of the reformer (50).
  6. The heat management unit (1) according to one of claims 4 to 5, wherein the reformer (46) comprises a heat exchanger configured to exchange heat between afterburner gas (20) outlet (53) and fuel (3) from the unit fuel inlet (5).
  7. The heat management unit (1) according to any one of claims 4 to 6, wherein the fuel flow path comprises a third heat exchanger (41) wherein the third heat exchanger (41) is connected to the reformer fuel outlet (54) of the reformer (46) and the stack fuel inlet (14) such that heat is exchangeable between fuel (3) from the reformer fuel outlet (54) and stack fuel in the third heat exchanger (41).
  8. The heat management unit (1) according to one of claims 1 to 7, wherein the heat management unit (1) is integrated in a thermally insulated enclosure (28).
  9. The heat management unit (1) according to one of claims 1 to 8, wherein the afterburner gas outlet (53) is connected to a gas processing unit (31), the gas processing unit (31) comprising means for cooling afterburner gas (20), an outlet for exhausting afterburner gas (20) from the heat management unit (1), means for purifying fuel gas from the heat management unit (1) in case the stack module (30) is operated as an electrolyzer, means for preparing the fuel gas supplied to the fuel inlet of the heat management unit (1), means for purifying fuel gas from the heat management unit (1) in case the stack is operated as a fuel cell, means to mix external fuel and purified fuel cell fuel, and means for feeding external fuel or a mix of external fuel and purified fuel cell fuel to the afterburner (6).
  10. An electrochemical system (29) comprising the heat management unit (1) according to one of claims 1 to 8, and a stack module (30), the stack module (30) being connected to the heat management unit (1) by the stack connection device (10) .
  11. The electrochemical system (29) according to claim 9, wherein the stack module (30) comprises at least one reversible solid oxide cell.
  12. The electrochemical system according to one of claims 10 and 11, wherein the electrochemical system 29 comprises a control unit with a control logic, and controllers/sensors for controlling the electrochemical system.
  13. A method for heat management for an electrochemical system (29) according to claims 9 to 12, wherein process air (2) is conducted through the process air flow path and fuel (3) is conducted through the fuel flow path wherein the process air (2) is heated up in the first heat exchanger (7) and/or in the electric heater (8) and then exchanges heat in the second heat exchanger (9) and fed to the stack module (30) via the unit process air outlet (11) and fuel (3) is conducted through the second heat exchanger (9), wherein the fuel (3) exchanges heat with the process air (2), and enters the stack module (30) via the unit fuel outlet (12), characterized in that stack exhaust from the stack exhaust inlet (13) is conducted to the afterburner (6) and afterburner gas (20) is conducted from the afterburner (6) to the first heat exchanger (7).
  14. The method for heat management according to claim (13), wherein the fuel (3) from the unit fuel inlet (5) is first heated in the third heat exchanger (41) and then conducted through the second heat exchanger (9).
  15. The method for heat management according to one of claims 13 or 14, wherein the fuel (3) is first conducted through the reformer (46) and then conducted through the second heat exchanger (9).
  16. The method for heat management according to one of claims 13 to 15, wherein the afterburner (6) ignites the electrochemical system (29) during start-up operation by combusting fuel (3) from the unit fuel inlet (5) with stack exhaust from the stack exhaust inlet (13).
  17. The method for heat management according to one of claims 13 to 16, wherein the stack exhaust is directed from the afterburner (6) to the gas processing unit (31) outside the thermally insulated enclosure (29) for cooling and exhausting the stack exhaust gas from heat management unit (1) or purifying the stack exhaust into a fuel which is fed to the unit fuel inlet (5).

Description

The invention relates to a heat management unit for a reversible electrochemical device, an electrochemical system with a heat management unit and a stack module, and a method for heat management of the electrochemical system according to the preamble of the independent claims. The operating temperature of electrolysis systems with solid oxide cell stacks for power production and/or fuel production is typically in the range of 650 to 900 °C. Such operating temperatures call for measures to minimize heat losses to the environment. In addition, thermal gradients across the cell stacks are to be kept within certain limits to limit the thermomechanical stress imposed to stack components that are prone to mechanical failure, such as the ceramic cells and sealants that exist in the stacks, or that might be prone to contact loss due to uneven compression within the stacks related to imbalances in thermal expansion rates. For this reason, the feed gases are preheated to temperatures close to the operating temperature of the stacks. Finally, a temperature gradient typically exists across the stacks due to the generation of Joule heat associated with resistive losses when the stacks are in operation, and gas conversion reactions inside the stacks. Apart from lowering the electric current or modifying the enthalpy of reaction by reactant pre-processing, such temperature gradients may be controlled by tuning the mass flow of the reactants to dissipate the heat that is generated in the stacks, where, for economic reasons, it is usually the least valuable reactant that is used for stack temperature gradient control. This may be air, which in fuel cell mode provides oxygen ions to oxidize the fuel, and in electrolysis mode is used as a sweep gas for the generated oxygen gas. Previous solutions for efficient heat management and adequate gas processing within electrochemical systems involve preheating process gasses with heat exchangers or electric heaters, heat exchangers for heat recuperation, capturing radiative heat from hot components, exhaust gas recycling, reuse of condensate, the integration of burners that utilize at least one of the exhaust gases, and thermal integration of exhaust gas post-processing units, such as a water-gas shift unit. In addition, the use of start-up burners with specific gas recycling methods has been reported. For a long time, system optimization focused on employing solid oxide stacks for power production. The recent shift of using solid oxide stacks for fuel production, stimulated by the incentive to greenify today's society, have led to different views on system optimization, where the utilization of waste streams, system scaling, and safety aspects in the handling of hydrogen get more attention, whilst the availability of green electric power makes electric heating a more viable option. CN115807232A discloses a solid oxide electrolyzer system that is connected to a microgrid connected to photovoltaics, wind turbines, and batteries that, in addition to the usual solutions already addressed in the above prior art, utilizes waste heat and industrial steam for hydrogen production. CN113278993B addresses the risk of hydrogen ignition when being exposed to a heat source and suggests using a solid oxide electrolyzer arrangement where only steam is preheated, the hydrogen only being mixed in after steam preheating, just before feeding the mix to the electrolyzer. Whilst CN113278993B provides a solution to the safe operation of dedicated electrolyzers, it is less suitable for solid oxide stacks that are operated both as electrolyzer and as fuel cell. This is related to the composition of the feed gas provided to the fuel electrode. During electrolysis operation, only a small amount of reducing gas such as hydrogen, for example 10 vol% hydrogen, is mixed in with the steam to keep the fuel electrode reduced. Conversely, fuel used for power production may contain a substantially higher amount of hydrogen or other reducing gas, which complicates the gas preheating in case only the non-flammable gas constituents are preheated. Thus, it is an object of the present invention to overcome the drawbacks of the prior art. It is in particular an object to provide a solution for realizing system arrangements where equipment can be used in both operating modes, wherein the feed, including any reducing gas, can be heated both in fuel cell mode and in electrolysis mode in an efficient way. The object is solved by the subject-matter of the independent claims. Preferred embodiments are described with regard to the dependent claims. The object is in particular solved by a heat management unit for a reversible electrochemical system. The heat management unit comprises a process air flow path and a fuel flow path. The process air flow path comprises a unit process air inlet, a first heat exchanger, an electric heater, a second heat exchanger, and a unit process air outlet. The fuel flow path comprises a unit fuel in