Solid Oxide Cell Arrangement

Description

[0001] The invention relates to a solid oxide cell arrangement comprising a housing, wherein the housing has a base plate, a cover and side walls, and solid oxide cell stacks, wherein the solid oxide cell stacks are located on the base plate.

[0002] Solid oxide cell (SOC) assemblies can include both high-temperature fuel cell (SOFC) assemblies and high-temperature electrolysis cell (SOEC) assemblies.

[0003] High-temperature fuel cell systems convert various liquid and gaseous hydrocarbon-based fuels (natural gas, LPG) into electricity and heat. High-temperature electrolysis cell systems convert electrical energy into chemical energy.

[0004] A solid oxide cell arrangement contains as a central unit at least one solid oxide cell stack in which, when used as a high-temperature fuel cell arrangement, gaseous hydrocarbon-based fuel or hydrogen supplied to an H2 electrode side of the solid oxide cell stack is reacted with air supplied to an O2 electrode side; when used as a high-temperature electrolysis cell arrangement, water vapor and / or carbon dioxide supplied to an H2 electrode side of the solid oxide cell stack is converted into oxygen and hydrogen or carbon monoxide.

[0005] The operating temperature of solid oxide cell arrays is typically between 700 and 900 °C, depending on the material. When heating from room temperature, heat must be transported into the solid oxide cell stacks via conduction, convection, or radiation.

[0006] From the State of the artDifferent arrangements are known for operating solid oxide fuel cells.

[0007] The cell stacks in the high-temperature fuel cell arrangements can be arranged in rows as well as in rings or circles.

[0008] A linear arrangement is known, for example, from WO 2017 / 191353 A1, which discloses a stack arrangement of a high-temperature fuel cell system or electrolysis cell system, wherein each cell in the cell system comprises an H2 electrode side, an O2 electrode side, and an electrolyte located therebetween, the cell system comprising the cells in cell stacks. The arrangement comprises the stacks arranged in series, the stacks being arranged in at least two rows adjacent to one another, and the arrangement comprising air inlet channels for supplying air to the stacks, the channels having air inlet ends that are conveyed to a sealed air inlet space formed between the stack rows with at least two sides of the air inlet space enclosed by the stacks themselves.

[0009] Cell stacks in a radial arrangement are known from the documents US 7,659,022 B2, WO 2015 / 118208 A1 and DE 42 17 892 C2.

[0010] US 7,659,022 B2 describes an integrated fuel cell unit, which includes an annular arrangement of fuel cell stacks, an annular cathode recuperator, an annular anode recuperator, a reformer and an anode exhaust gas cooler, all integrated into a common housing structure.

[0011] WO 2015 / 118208 A1 discloses an assembly of solid oxide cells in a fuel cell system or in an electrolysis cell system. The assembly comprises the cells arranged in at least four angled cell stacks and at least one substantially planar attachment side of each of the at least four angled stacks, wherein the side comprises at least one geometrically deviating attachment surface structure in the otherwise substantially planar side between at least two corners of the at least four angled stacks.The mounting arrangement further comprises at least one flow restriction structure for restricting air flows in the cell system to be mounted against the geometrically different mounting surface structure of each stack formation for securing at least one cell stack formation in the mounting arrangement, and an electrical insulation arranged for securing the flow restriction structure and the stack formation.

[0012] DE 42 17 892 C2 describes a power generation unit comprising a power supply module with a heat-insulating container that is internally divided to provide a stack chamber, a combustion chamber, and a heat exchanger chamber. The stack chamber contains at least one fuel cell stack. The individual cells are supplied accordingly, with the supplied media each being heated via the heat exchanger in the heat exchanger chamber. The direct current supplied by the fuel cells is converted into alternating current via a current regulator with a control device that regulates the entire generation of the power supply module.

[0013] Process components such as electric gas preheaters or heat exchangers are positioned on the cell stacks to control temperature. Heat transfer occurs via convection or conduction.

[0014] WO 2012 / 131163 A1 discloses a heating arrangement for a fuel cell device consisting of a radiant heater and a convection heater. The radiant heater is located outside a fuel cell assembly and the convection heater is located inside the fuel cell assembly. The combination of two heating types is intended to enable uniform heat distribution and rapid heating while simultaneously avoiding thermal stress.

[0015] US 2007 / 119638 A1 discloses a fuel cell system comprising at least one electrical resistance heating element. Several resistance heating elements can be distributed to ensure even heat distribution.

[0016] EP 1 271 684 A2 discloses a fuel cell system comprising a cell stack, wherein the individual cells of the cell stack have an interconnect in thermal contact with the electrochemical part of the cells, via which heat can be supplied to them. A disadvantage of using interconnects is their labor-intensive, time-consuming, and costly contacting. Interconnects also prevent stack maintenance / repair, for example, if one of the interconnects is defective and needs to be replaced. Likewise, the interconnects arranged in the stack require galvanic isolation of the electrolysis and heating elements, which also increases manufacturing costs.

[0017] EP247783 discloses radiant heating elements for an electrolysis plant for the production of fluorides.

[0018] The Problems in the state of the artThe main drawbacks are that temperatures of typically 700 to 900 °C (currently common in the state of the art) are required to operate the solid oxide cell array. Heating of solid oxide electrolysis cell arrays (SOEC and rSOC) takes place via electrical preheaters.

[0019] The media are heated convectively via electric preheaters, and these hot gases, in turn, heat the solid oxide cell stack. Heating by moving fluids inevitably leads to heat losses, even if the best possible heat recovery is achieved. The escaping gases always have a higher temperature than when they enter the respective balance chamber. This results in unnecessary energy consumption, for example, during heating.

[0020] In addition, some materials in electrical preheaters can emit contaminants in certain, mostly water vapor-containing atmospheres and in the high temperature range, which negatively affect the performance of the solid oxide cell arrays.

[0021] Electric preheaters are also relatively expensive components.

[0022] In addition, they are integrated between the cell stack and the heat exchanger, thereby lengthening the pipes, which increases heat losses.

[0023] Due to the higher media temperature, the piping must be designed larger. Furthermore, larger areas of the unit are exposed to high temperatures, which negatively impacts other functions, such as galvanic isolation, sensors, and power connections. In some design variants, heat losses are higher. For example, heat losses are increased when hot gases are routed along exterior walls.

[0024] Good accessibility to the individual components for maintenance work, such as carrying out servicing, is often not available.

[0025] The present invention is based on the Task The aim is to provide an arrangement for the efficient heating and operation of high-temperature solid oxide cell arrangements.

[0026] The complexity and number of components of an assembly largely determine the costs. For applications with few cold starts per year, a complex heating infrastructure should be avoided if possible. Ideally, only one heat-generating assembly should be used to heat both the solid oxide cell stack and the media streams on the H2 and O2 sides to the required temperature ranges.

[0027] Solved This object is achieved with a solid oxide cell arrangement according to the main claim and further advantageous embodiments according to the subclaims.

[0028] The solid oxide cell arrangement is designed with a housing, solid oxide cell stacks, and at least one radiant heating element within the housing, via which radiant heat is transferred to the solid oxide cell stacks. This eliminates the need for electrical preheaters to heat the solid oxide cell stacks. Forced convection for heating is thus eliminated, making heating significantly more efficient. Up to 90% of the electrical energy invested to raise the temperature of the cell stacks is used efficiently, compared to only approximately 40% previously. This leads to a saving of at least 50% of the electrical energy invested (kWh) during heating. Heat losses are also significantly lower, as there are significantly fewer escaping gases with a higher temperature than the ambient air.

[0029] Because the radiant heating element is designed as a heating tube or a heating plate, which can be suspended from above and / or attached to side walls and / or upright on the base plate or integrated into ceramic plates, it is possible to design and install the radiant heating element to suit the individual case in such a way that the best possible result, i.e., efficient heating, is achieved. This also allows for easy maintenance. If the radiant heating elements are integrated into a side wall, for example, access to both the radiant heating elements and the solid oxide cell stacks is possible by removing or folding away the side wall.

[0030] Because the radiant heating element consists of several separately controllable segments with separate power connections for each radiant heating segment, it is possible to avoid thermal imbalances caused by local thermal influences. This approach is based on the physical relationship that the internal resistance of the ceramic cells decreases at higher temperatures. Furthermore, the law applies that electrical power loss (= waste heat) is influenced quadratically by the current density and linearly by the internal resistance (P Loss = RI 2< ). Furthermore, in electrical parallel circuits, higher currents are present in branches with lower internal resistance.Based on these relationships, both individual solid oxide cell series circuits of an electrical network (using radiant heating elements) and parts of a solid oxide series circuit (using radiant heating segments) can be positively influenced depending on the requirements / operating mode. It should be noted that thermal influences cannot change the prevailing material behavior (degradation), but their symptoms can be significantly mitigated.

[0031] Each solid oxide cell stack series circuit is globally controllable via the current density and switching on of the associated radiant heater.

[0032] A locally controllable solid oxide cell stack series circuit can be enhanced by locally varying the heat input. For this purpose, the entire heating conductor can be divided into segments, each with a power connection, thereby increasing the performance of the solid oxide stack. It should be noted that in a series circuit, the "weakest link" is the limiting factor. For example, if an area is subject to higher heat losses in SOEC operation, the voltage there increases up to the permissible maximum value. The current is limited for the entire series circuit, and thus the H2 production. The warmer areas are not optimally utilized. With a segmented heater, the cooler areas can be specifically reheated, thus homogenizing the temperature of the solid oxide cell stack. The current, or rather, the H2 production, can be increased because the cold cells are no longer limiting.

[0033] Since the solid oxide cell stacks can be arranged in several rows next to each other in a series connection, with each solid oxide cell stack being assigned a radiant heating element, the heating efficiency of the solid oxide stacks is further improved. The solid oxide cell stacks can thus be heated across their entire surface via the radiant heating elements. The heat emitted by the radiant heating elements is evenly distributed, as each solid oxide cell stack is heated by the radiant heating elements, and there are no unheated sections. This also contributes to an extended service life.

[0034] If, in addition to the radiant heating elements, heat exchangers for the media supply are arranged inside the housing or externally on the flanges, the process heat is retained within the system. The heat from the escaping gases is used as efficiently as possible to preheat the incoming gases. This leads to an increase in system efficiency. The previously used electrical preheaters can be eliminated. At least two heat exchangers are required, one each for the O2 and H2 electrode sides. Utilizing the enthalpy flows of the escaping gases is therefore particularly important for the profitability of a system.

[0035] In some applications, the integration of more than two heat exchangers makes sense. Depending on the application, various options are available. These include, for example: Heat exchangers with the same medium on both sides of the heat exchanger or as a mixture of H2 and O2 sides; decentralized arrangement of many small heat exchangers or the central arrangement of larger heat exchangers; parallel or series connection of several heat exchangers.

[0036] In this context, the combination of heat exchangers with radiant heating elements is relevant. A variety of variants can be derived from the above possibilities. These include, for example: Heat exchanger on the H2 side positioned directly beneath the individual towers of the cell stack series connection (decentralized arrangement on the H2 side); media line on the O2 side is cooled in two stages, first by means of a heat exchanger on the O2 side and then by means of a heat exchanger on the H2 side; media line on the O2 side is split so that part of the mass flow preheats the H2 side and another part preheats the O2 side; media supply to the O2 side from the solid oxide cell stack side facing the heater; media supply to the O2 side via separate metallic or metal-ceramic assemblies in the base support.

[0037] In the following, embodiments of the invention are described with reference to the accompanying drawings in the Image description described in detail, which is intended to explain the invention and is not to be considered limiting:

[0038] They show: Fig. 1: A schematic representation of a solid oxide cell arrangement with one solid oxide cell stack and one lateral radiant heating element in plan view; Fig. 2: A schematic representation of a solid oxide cell arrangement with two solid oxide cell stacks and two lateral radiant heating elements in plan view; Fig. 3: A schematic representation of a solid oxide cell arrangement with two solid oxide cell stacks and three lateral and central radiant heating elements in plan view; Fig. 4: A schematic representation of a solid oxide cell arrangement with three solid oxide cell stacks and three lateral and central radiant heating elements in plan view; Fig. 5: A schematic representation of a solid oxide cell arrangement with four solid oxide cell stacks with flow through two cell stacks each and two lateral radiant heating elements in plan view; Fig.6A flow diagram of a solid oxide cell arrangement with a solid oxide cell stack and a radiant heating element in combination with two heat exchangers; Fig. 7A flow diagram of a further embodiment of a solid oxide cell arrangement with a solid oxide cell stack and a radiant heating element in combination with two heat exchangers; Fig. 8A flow diagram of a solid oxide cell arrangement with a solid oxide cell stack, a radiant heating element in combination with two heat exchangers and an additional convective, electric gas heater on the H2 media side; Fig. 9A flow diagram of a solid oxide cell arrangement with a solid oxide cell stack and a radiant heating element in combination with three heat exchangers; Fig. 10A flow diagram of a solid oxide cell arrangement with a solid oxide cell stack and a radiant heating element in combination with three heat exchangers and a split exhaust air flow; Fig.Fig. 11 shows a comparison of a solid oxide cell arrangement with a radiant heating element, centrally arranged heat exchangers, and an electric preheater with an arrangement with conventional, electric preheaters and centrally arranged heat exchangers using two flow diagrams (a, b); Fig. 12 shows a comparison of a solid oxide cell arrangement with separate radiant heating elements, decentralized heat exchangers, and an electric preheater with an arrangement with conventional, electric preheaters and decentralized heat exchangers using two flow diagrams (a, b); and Fig. 13 shows a schematic representation of a solid oxide cell arrangement with a solid oxide cell stack and a lateral radiant heating element divided into radiant heating segments in a top view.

[0039] In the following illustration descriptions, components with the same function are provided with the same reference symbols.

[0040] In Fig. 11 shows a solid oxide cell assembly 1 in a housing 2. The solid oxide cell assembly 1 consists of a solid oxide cell stack 31 with a radiant heating element 41 attached to the side of the housing 2.

[0041] The radiant heating element 41, which is attached to the side of the housing 2, serves to heat the solid oxide cell stack 31. The lateral attachment provides good accessibility to the solid oxide cell stack 31 and / or to the radiant heating element 41. The radiant heating element 41 can be designed as a heating tube or as a heating plate, which can be suspended from above and / or attached to side walls and / or upright on the base plate or integrated into ceramic plates.

[0042] Air enters the solid oxide cell stack 31 via the media supply on the O2 electrode side 71. The used air is removed via the media outlet on the O2 electrode side 81. The fuel gas is supplied via the media supply on the H2 electrode side 91. Excess fuel gas and water are removed via the media outlet on the H2 electrode side 101.

[0043] In Fig. 2 Two solid oxide cell stacks 31, 32 are arranged in a series connection. Two radiant heating elements 41, 42 are used, each mounted on the side. For each cell stack 31, 32, there is a media supply on the O2 electrode side 71, 72 and the H2 electrode side 91, 92. The media is removed from the O2 electrode side 81 in one line; the media is removed from the H2 electrode side 101, 102 separately.

[0044] Fig. 3 differs from Fig. 2in that in addition to the two laterally mounted radiant heating elements 41, 43 there is also a centrally mounted radiant heating element 42.

[0045] In Fig. 4 Three solid oxide cell stacks 31, 32, 33 are interconnected. There is a radiant heating element 41 mounted on the side of the housing 2 and two radiant heating elements 42, 43 installed centrally. Media supply and removal are provided separately for each cell stack.

[0046] In Fig. 5 The media flows through two cell stacks 3 together. Cell stacks 31, 32 and cell stacks 33, 34 each have a media supply on the O2 electrode side 71, 72 and a shared media outlet on the O2 electrode side 81. The media supply and outlet on the H2 electrode side are separate for each cell stack. There are two laterally mounted radiant heating elements 41, 42.

[0047] As described in the above exemplary embodiments for the arrangement of radiant heating elements 4 in solid oxide cell arrangements 1, each solid oxide cell stack 3 can be assigned a radiant heating element 4. In such a case, individual radiant heating elements 4 can be installed either centrally between the individual rows of solid oxide cell stacks 3 and / or attached laterally as previously described. The solid oxide cell stacks 3 can thus be heated across their entire surface via the radiant heating elements 4. Since the radiant heating elements 4 can consist of several separately controllable segments with separate power connections for the respective radiant heating segments, thermal imbalances can be avoided.

[0048] In the Fig. 6-10Flow diagrams of a solid oxide cell arrangement 1 are shown. The flow diagrams show various possibilities for combining the radiant heating element 4 with the heat exchanger 6.

[0049] In Fig. 6 A radiant heating element 41 is combined with two heat exchangers 61, 62 in a solid oxide cell arrangement 1. A solid oxide cell stack 31 is heated by the radiant heating element 41. Heat exchangers are installed on the O2 electrode side 61 and a heat exchanger on the H2 electrode side 62. Air enters the solid oxide cell stack 31 via the media supply on the O2 electrode side 71. The used air is removed via the media outlet on the O2 electrode side 81. The fuel gas is supplied via the media supply on the H2 electrode side 91. Excess fuel gas and water are removed via the media outlet on the H2 electrode side 101.

[0050] The heat exchanger on the O2 electrode side 61 heats the media supply on the O2 electrode side 71 via the media outlet on the O2 electrode side 81. Accordingly, the heat exchanger on the H2 electrode side 62 heats the media supply on the H2 electrode side 91 via the media outlet on the H2 electrode side 101. This increases the system efficiency.

[0051] The heat exchangers 61, 62 can be mounted either directly in the housing 2 beneath the solid oxide cell stack 31 or flanged to the sides of the housing 2's inlets and outlets. By locating the heat exchangers 61, 62 directly in the housing 2, heat losses are minimized. The pipes are kept as short as possible, and all elements are housed in a single assembly within the thermally insulated housing 2.

[0052] In Fig. 7 is like in Fig. 6A radiant heating element 41 is combined with two heat exchangers 61, 62 in a solid oxide cell arrangement 1. A solid oxide cell stack 31 is heated by the radiant heating element 41. Only the flow of the media through the heat exchangers 61, 62 was varied.

[0053] In Fig. 8 There is a solid oxide cell arrangement 1 in which an additional convective, electric gas heater 51 has been installed on the media supply side on the H2 electrode side 91.

[0054] The installation of such a convective, electric gas heater 5 is possible in all variants of the combination of radiant heating elements 4 with heat exchangers 3, but should no longer be absolutely necessary according to the novel solid oxide cell arrangement 1.

[0055] In Fig. 9A radiant heating element 41 is combined with three heat exchangers 61, 62, 63. The media discharge from the O2 electrode side 81 passes through two heat exchangers 61, 62 and thus heats both the media supply on the O2 electrode side 71 and the media supply on the H2 electrode side 91.

[0056] In Fig. 10 is like in Fig. 9 A radiant heating element 41 is combined with three heat exchangers 61, 62, 63. In addition, the O2 exhaust air stream leading out of the solid oxide cell stack 31 is divided into two substreams.

[0057] When combining radiant heating elements 4 with heat exchangers 6 in solid oxide cell arrangements 1, a multitude of further variants are possible. Both the number and position of radiant heating elements 4 for heating the solid oxide cell stacks 3, as well as the number and position of heat exchangers 6, and additionally the media supply and removal on the electrode sides can be varied, for example, split in the case of the media supply and removal.

[0058] Fig. 11 consists of a flow diagram a) of a solid oxide cell arrangement with a radiant heating element 41, heat exchangers 61, 62 arranged centrally in the gas processing unit 11 and an electric preheater 51 and a flow diagram b) of an arrangement with only conventional, electric preheaters 51, 52 and heat exchangers 61, 62 arranged centrally in the gas processing unit 11.

[0059] The two flow diagrams show how the technical system structure for the operation of solid oxide cells changes when using radiant heating elements 4 with a central arrangement of the heat exchangers 6.

[0060] Fig. 12 consists of a flow diagram a) of a solid oxide cell arrangement 1 with two separate radiant heating elements 41, 42, heat exchangers 61, 62 arranged decentrally in the cell stack module 12 and an electric preheater 51 and a flow diagram b) of an arrangement only with conventional, electric preheaters 51, 52 and heat exchangers 61, 62 arranged decentrally in the cell stack module 12.

[0061] The two flow diagrams show how the technical system structure for the operation of solid oxide cells changes when using radiant heating elements 4 with a decentralized arrangement of the heat exchangers 6.

[0062] A comparison of Figures 11 and 12 shows the differences in the technical system design for the operation of solid oxide cells with central and decentralized arrangement of the heat exchangers 6.

[0063] In Fig. 13 is a solid oxide cell arrangement 1 according to Figure 1 The radiant heating element 41 consists of several radiant heating segments 411, 412, 413, 414, 415. List of reference symbols

[0064] 1 Solid oxide cell arrangement 71 Media supply O2 electrode side 1 72 Media supply O2 electrode side 2 2 Housing 73 Media supply O2 electrode side 3 3 Solid oxide cell stack 81 Media discharge O2 electrode side 1 31 Solid oxide cell stack 1 82 Media discharge O2 electrode side 2 32 Solid oxide cell stack 2 83 Media discharge O2 electrode side 3 33 Solid oxide cell stack 3 34 Solid oxide cell stack 4 91 Media supply H2 electrode side 1 92 Media supply H2 electrode side 2 4 Radiant heating element 93 Media supply H2 electrode side 3 41 Radiant heating element 1 411 Segment 1 of radiant heating element 1 101 Media removal H2 electrode side 1 102 Media removal H2 electrode side 2 412 Segment 2 of radiant heating element 1 103 Media removal H2 electrode side 3 413 Segment 3 of radiant heating element 1 11 Gas processing unit 414 Segment 4 of radiant heating element 1 12 Cell stack module 415 Segment 5 of radiant heating element 1 42 Radiant heating element 2 43 Radiant heating element 3 5 convective, electric gas heater 51 convective electric gas heater 1 52 convective, electric gas heater 2 6 heat exchanger 61 Heat exchanger 1 62 Heat exchanger 2 63 Heat exchanger 3

Claims

1. A solid oxide cell assembly (1) comprising: - a housing (2), wherein the housing (2) comprises a bottom plate, a cover and side walls; - solid oxide cell stacks (3), wherein the solid oxide cell stacks (3) are located on the bottom plate; characterised in that - at least one radiant heating element (4) is arranged inside the housing (2) and radiating heat onto the solid oxide cell stacks (3), and - the radiant heating element (4) is designed as a heating tube or as a heating plate, and - the radiant heating element (4) consists of a plurality of separately controllable segments with separate power connections for the respective radiant heating segments and that the solid oxide cell arrangement is designed as a high-temperature electrolytic cell arrangement (SOEC).

2. Solid oxide cell arrangement (1) according to claim 1, characterised in that the solid oxide cell stacks (3) are present in a plurality of rows next to one another as a solid oxide cell stack row arrangement, a radiation heating element (4) being assigned for each solid oxide cell stack (3).

3. Solid oxide cell arrangement (1) according to one of the preceding claims, characterised in that in addition to the radiant heating elements (4), heat exchangers (6) are arranged in the housing (2) or outside directly on the flanges.

4. Solid oxide cell arrangement (1) according to claim 3, characterised in that the system efficiency is increased by the combination of radiant heating element (4) with heat exchanger (6).

5. Solid oxide cell arrangement (1) according to one of claims 1 to 4, characterised in that the radiant heating element (4) is integrated as a heating tube or as a heating plate in one of the side walls.

6. Solid oxide cell arrangement (1) according to claim 1 to 4, characterised in that the radiant heating element (4) is attached as a heating tube or as a heating plate suspended from above, on side walls or upright on the base plate.

7. Solid oxide cell arrangement (1) according to claim 1 to 4, characterised in that the radiant heating element (4) is integrated as a heating tube or as a heating plate in one or more ceramic plates.