EP4666330A1

EP4666330A1 - Module arrangement of solid oxide cell stacks

Info

Publication number: EP4666330A1
Application number: EP24756394.3A
Authority: EP
Inventors: Matti Noponen; Julius STENIUS
Original assignee: Elcogen Oy
Current assignee: Elcogen Oy
Priority date: 2023-02-14
Filing date: 2024-02-13
Publication date: 2025-12-24
Also published as: CN121039845A; KR20250149172A; WO2024170826A1; AU2024223621A1; CN219419115U; JP2026506598A

Abstract

An object of the invention is a module arrangement of solid oxide cell stacks being arranged to a 2 x N matrix, N being any natural number. The arrangement comprises a fuel inlet manifold (150) and a fuel outlet manifold (152) between the two adjacent stacks (103).The fuel inlet manifold (150) and the fuel outlet manifold (152) form a fuel manifold (171) to deliver supply fuel gas (108) to the stacks and fuel exhaust gas (177) from the stacks, and the stacks been arranged in the manifold in a parallel connection from the fuel gas supply and fuel exhaust gas connection point of view. The stacks (103) are arranged with a common oxygen side gas supply compartment (106) connecting the inlet side of the open structure of oxygen side gas delivery (105) and common oxygen side gas exhaust compartment (176) connecting the outlet side of the open structure of oxygen side gas delivery (105). The inlet manifold (150) comprises gas flow holes of controllable sizes to the stacks (103) for forming even gas flow to the stacks, and the outlet manifold (152) comprises gas flow holes of controllable sizes to the stacks (103) for forming even gas flow from the stacks. The module arrangement comprises a first gas seal (155), a first electrical insulation plate (119) and a second gas seal (156) between the manifold (171) and the stack (103). On top side (122) and on bottom side (124) of the cell stack (103) the module arrangement comprises a second electrical insulation plate (114), compression structures (116) for the stacks (103), and an air side sealing structure (169) between the stacks, and each stack end plate (170) are connected with an electrical connection (173).

Description

Module arrangement of solid oxide cell stacks

The field of the invention

Most of the energy of the world is produced by means of oil, coal, natural gas or nuclear power. All these production methods have their specific problems as far as, for example, availability and friendliness to environment are concerned. As far as the environment is concerned, especially oil and coal cause pollution when they are combusted. The problem with nuclear power is, at least, storage of used fuel.

Especially because of the environmental problems, new energy sources, more environmentally friendly and, for example, having a better efficiency than the above-mentioned energy sources, have been developed. Fuel cell’s, by means of which energy of fuel, for example biogas, is directly converted to electricity via a chemical reaction in an environmentally friendly process and electrolysers, in which electricity is converted to a fuel, are promising future energy solution devices.

Renewable energy production methods such as photovoltaic and wind power faces problems in seasonal production variations as their electricity production is limited by environmental effects. In the case of over production, hydrogen production through water electrolysis is suggested to be one of the future energy storing options. Furthermore, an electrolysis cell can also be utilized to produce high quality methane gas from renewably biogas stores.

The present invention relates to module arrangement of a Solid Oxide Fuel Cell (SOFC) stacks or a Solid Oxide Electrolyzer Cell (SOEC) stacks. A fuel cell causes input reactant fuel gas on an anode electrode and gaseous oxidizer (oxygen) on a cathode electrode to react in order to produce electricity. Electrolyzer reactions are reverse to fuel cell, i.e. electricity is used to produce fuel and oxygen. SOFC and SOEC stacks comprise stacked cell elements and separators in a sandwiched manner wherein each cell element is constituted by sandwiching an electrolyte, the anode side and the cathode side. The reactants are guided by flow field plates to the porous electrodes.

State of the art

Fuel cell, as presented in fig 1 , comprises an anode side 100 and a cathode side 102 and an electrolyte material 104 between them. Here the structure is called as the unit cell 174 (figs. 1 , 2). In solid oxide fuel cells (SOFCs) oxygen 106 is fed to the cathode side 102 and it is reduced to a negative oxygen ion by receiving electrons from the cathode. The input stream 106 is depleted from oxygen at the outlet side 176. The negative oxygen ion transfers through the electrolyte material 104 to the anode side 100 where it reacts with fuel 108 producing electrons, water, and also typically carbon monoxide (CO) and carbon dioxide (CO2), i.e. fuel exhaust gas 177. Anode 100 and cathode 102 are connected through an external electric circuit 111 comprising a load 110 for the fuel cell withdrawing electrical energy alongside heat out of the system. The fuel cell reactions in the case of methane, carbon monoxide and hydrogen fuel are shown below:

Anode: CH₄ + H2O = CO + 3H₂

CO + H2O = CO2 + H₂ H₂ + O²- = H2O + 2e-

Cathode: O2 + 4e^_ = 2O²’

Net reactions: CH₄ + 2O2 = CO2 + 2H2O

CO + 1/202 = CO2

H₂ + 1/202 = H2O

In electrolysis operating mode (solid oxide electrolysis cells (SOEC)) the reaction is reversed, i.e. heat, as well as electrical energy from a source 110, are supplied to the cell where water and often also carbon dioxide are reduced in the cathode side 100 forming oxygen ions, which move through the electrolyte 104 material to the anode side 102 where oxidation reaction takes place. It is possible to use the same solid electrolyte cell in both SOFC and SOEC modes. In such a case and in the context of this description the electrodes are typically named anode and cathode based on the fuel cell operating mode, whereas in purely SOEC applications the oxygen electrode may be named the anode, and the reactant electrode as the cathode.

Solid oxide electrolyzer cells operate at temperatures which allow high temperature electrolysis reaction to take place, said temperatures being typically between 500 - 1000 °C, but temperatures differing the said limits may be useful. These operating temperatures are similar to those conditions of the SOFCs. The net cell reaction produces hydrogen and oxygen gases. The reactions for one mole of water are shown below, with reduction of water occurring at the anode:

Cathode: H₂O + 2e — > 2 H₂ + O²’

Anode: O²’ — > 1/202 + 2e^_

Net Reaction: H2O — > H2 + 1/202.

In Solid Oxide Fuel Cell (SOFC) and Solid Oxide Electrolyzer (SOE) stacks, commonly here referred as solid oxide cell stack, where the flow direction of the cathode gas relative to the anode gas internally in each cell as well as the flow directions of the gases between adjacent cells, are combined through different cell layers of the stack. Further, the cathode gas or the anode gas or both can pass through more than one cell before it is exhausted, and a plurality of gas streams can be split or merged after passing a primary cell and before passing a secondary cell. These combinations serve to increase the current density and minimize the thermal gradients across the cells and the whole stack. A SOFC delivers in normal operation a voltage of approximately 0.8V and a SOEC 1 .3 V. To increase the total voltage output, the cells 174 are usually assembled in stacks in which the cells are electrically connected via flow field plates (also: separator plates, interconnect plates, interconnector plates, bipolar plates). The desired level of voltage determines the number of cells needed.

Bipolar plates separate the anode and cathode sides of adjacent cell units and at the same time enable electron conduction between anode and cathode. Interconnects, or bipolar plates are normally provided with a plurality of channels for the passage of fuel gas on one side of an interconnect plate and oxygen rich gas on the other side. The flow direction of the fuel gas is defined as the substantial direction from the fuel inlet portion to the fuel outlet portion of a cell unit. Likewise, the flow direction of the oxygen rich gas is defined as the substantial direction from its inlet portion to its outlet portion of a cell unit.

Conventionally, the cells are stacked one on top of each other with a complete overlap resulting in a stack with for instance co-flow having all fuel and oxidant inlets on one side of the stack and all fuel and oxidant outlets on the opposite side. One feature affecting the temperatures of the structure in operation is steam reformation of the fuel that is fed into the cell. Steam reformation is endothermic reaction and cools the fuel inlet edge of the cell.

Due to the exothermicity of the electrochemical process, the outlet gases leave at higher temperature than the inlet temperature. When endothermic and exothermic reactions are combined in an SOFC stack a significant temperature gradient across the stack is generated. Large thermal gradients induce thermal stresses in the stack which are highly undesirable and they entail difference in current density and electrical resistance. Therefore, the problem of thermal management of an SOFC stack exists: to reduce thermal gradients enough to avoid unacceptable stresses and to maximize electric efficiency through homogenous current density profile. Prior art fuel cell stacks or electrolyzer cell stacks have tolerance variations in unit cell structure thickness between the cell structures in the stacks. For example, in a cell stack structure, in which ceramic materials are used, only thickness variations in the measure of only micrometers would be convenient in the prior art embodiments. This results on differential flowing conditions between the cells causing varying cell voltage profile in the stack structure resulting in thermal gradients between the cells and decreased power density of the stack. Thus both the duty ratio of the stacks is decreased, and lifetime of the stacks is shortened, the first increasing the capital cost of the stack per produced electrical power output and the later increasing the operational cost of the stack structure as e.g. the stack replacement time is shortened in a fuel cell system and cost of electricity is increased in the electrolyzer stack.

High temperature solid oxide cell stacks are preferred conversion technologies due to their extreamly high efficiencies both in fuel cell and electrolysis mode. The inherent challenge related to these technologies also stems from the high temperature the challenge being corrosion of the materials causing increasing internal resistances to the structures decreasing the electricity production and hydrogen production capability of the fuel cell and the electrolyzer, respectively. Corrosion problems can exist in multiple places of the stack structure but are typically emphasized in regions containing various material systems. Such a system is the triple phase area between metallic interconnect structure, sealing structure and oxidizing gas. In such a material system e.g. the metallic interconnect material which is typically made of ferritic stainless steel grades due to its good corrosion resistance and matching thermal expansion characteristics between other stack materials can react with the sealing structure typically made from at least partly glass material by e.g. changing the crystal structure of the metal or by changing the protective oxide structure of the metal surface which eventually may lead to through plane oxidation of the steel material creating a direct path for fuel and oxygen to mix causing a catastrophic failure of the structure. Brief description of the invention

An object of the invention is to improve the reliability and structure of the fuel cell or electrolyzer cell stacks. This is achieved by a module arrangement of solid oxide cell stacks in a fuel cell system or in an electrolyzer cell system, each stack comprising of unit cells with a fuel side, an oxygen rich side, and an electrolyte material between the fuel side and the oxygen rich side, each stack comprising flow field plates made of a material having high electrical conductivity at high temperatures, each stack having four angled formation, each stack comprising gas sealing structure made of a material that isolates electricity, the arrangement having gas distribution structure both for the inlet and outlet sides of fuel gas, oxygen side gas delivery being based on an open channel structure, and the arrangement comprises end plates that are used in current collection, and the cells, flow field plates and gas sealing structures being arranged to a pile in a formation of a stack between the end plates. The module arrangement being arranged to a 2 x N matrix, N being any natural number, and the arrangement comprises a fuel inlet manifold and a fuel outlet manifold between the two adjacent stacks, the fuel inlet manifold and the fuel outlet manifold forming a fuel manifold to deliver supply fuel gas to the stacks and fuel exhaust gas from the stacks, and the stacks been arranged in the manifold in a parallel connection from the fuel gas supply and fuel exhaust gas connection point of view, and the stacks being arranged with a common oxygen side gas supply compartment connecting the inlet side of the open structure of oxygen side gas delivery and common oxygen side gas exhaust compartment connecting the outlet side of the open structure of oxygen side gas delivery, and the inlet manifold comprising gas flow holes of controllable sizes to the stacks for forming even gas flow to the stacks, and the outlet manifold comprising gas flow holes of controllable sizes to the stacks for forming even gas flow from the stacks, and the module arrangement comprises a first gas seal, a first electrical insulation plate and a second gas seal between the manifold and the cell stack, and on top side and on bottom side of the cell stack the module arrangement comprises a second electrical insulation plate, compression structures for the stacks, and an air side sealing structure between the stacks, and each stack endplate are connected with an electrical connection.

The invention is based on a module arrangement of solid oxide cell stacks in a fuel cell system or in an electrolyzer cell system, wherein the module arrangement comprises stacks being arranged to a 2 x N matrix, N being any natural number, and on a fuel manifold between the two adjacent stacks, to deliver inlet fuel gas to the stacks and exhaust gas from the stacks, and the stacks been arranged in the manifold in a parallel connection from the fuel gas supply and exhaust gas connection point of view. The invention is further based on the stacks being arranged with a common oxygen side gas compartment and common oxygen side gas exhaust compartment, and on the manifold comprising gas flow holes of controllable sizes to the stacks for forming even gas flow to and from the stacks on basis of pressure difference between an inlet pipe connection and an outlet pipe connection of the manifold.

Benefit of the invention is a practical cell stack module arrangement which can be dimensioned according to the selected fuel cell or electrolysis cell application thus saving time, economical costs and assembly space.

Brief description of the drawings

Figure 1 presents a single fuel cell structure.

Figure 2 presents a repetitious sold oxide cell structure.

Figure 3 presents a first exemplary cell stack module arrangement according to the present invention from the front side.

Figure 4 presents a second exemplary cell stack module arrangement according to the present invention from the back side.

Figure 5 presents a second exemplary cell stack module arrangement according to the present invention from the front side.

Figure 6 presents an exemplary manifold structure.

Figure 7 presents compression structures inside an air side sealing structure.

Figure 8 presents compression structures outside an air side sealing structure.

Detailed description of the invention

According to the present invention, the fuel cell or electrolyzer stack comprises at least two single repetitious structures. A single repetitious structure comprises at least of one electrochemically active unit cell structure including fuel side, electrolyte in between, and oxygen rich side, placed between at least two flow field plates the other distributing oxygen rich gas in the oxygen rich side of the unit cell structure and the other distributing fuel gas in the fuel side of the unit cell structure, and at least one sealing means sealing the gas atmosphere at its intended enclosure. The flow field plate has at least one inlet openings for fuel gas and/or oxygen rich gas and at least one outlet openings for used fuel gas and/or oxygen rich gas. The flow directions of the fuel gas and oxygen rich gas can be arranged in co-flow arrangement in which both gases are flowing essentially to the same direction on each side of the unit cell, or in counter-flow arrangement in which the flow direction is essentially the opposite between the fuel and oxygen rich gases, or in gross-flow arrangement in which the flow direction is essentially in 90° angle between the fuel and oxygen rich gas, or in their combinations.

Figure 2 presents flow field plates 121 of a fuel cell stack. A complete fuel cell stack comprises several plates 121 placed on successively each other in a shown manner. The plates in this embodiment are rectangular and symmetrical. A unit cell structure 174 comprising an electrolyte layer 104 between an anode electrode and a cathode electrode is placed between the plates 121 generally in the middle of the plate. The electrolyte element structure 174 may be any suitable electrolyte element structure and is not therefore described herein in any further detail. The flow field plates 121 and the unit cell structure 174 are sealed with a gas sealing structure 128, which is preferably made of compressible material, which is e.g. ceramic, mineral or glass material. The gas sealing structures 128 according to the present invention are compressed when the cells are assembled to a stack formation. Two opposing flow field plates 121 and the unit cell structure 174 and the gas sealing structure 128 therebetween form a single repetitious structure.

The fuel cell stack arrangement of figure 2 comprises flow restriction orifices 135, 136 opened to a flow distribution area and to a flow outlet area. The gas sealing structure 128 is compressed over the flow restriction orifices 135, 136. The flow restriction orifices 135, 136 ensures homogenous fuel flow distribution to the entire active area of the fuel cell electrode by creating an additional pressure sink to the flow path. The gas sealing structure 128 also creates similar pressure loss conditions between repetitious structures of the fuel cell ensuring homogenous flow distribution characteristics for each repetitious structure of a fuel cell. The even flow distribution in the fuel cell stack ensures also even thermal distribution conditions for the fuel cell stack, i.e. similar thermal gradients between the cells in the stack. Thus, the duty ratio of the fuel cell stack is improved, and lifetime of the fuel cell stack is made longer.

The purpose of the gas sealing structure 128 is further to ensure that oxidant and fuel are not directly mixed without the fuel cell reactions inside the electrochemically active area, that the fuel and oxidant are not leaked out from the electrochemical cells, that the adjacent electrochemical cells are not in electronic contact with each other, and that oxidant and fuel are supplied to the desired flow field plate plates 121. A flow field plate 121 is a planar thin plate that is made of metal alloy, ceramic material, cermet material or other material that can withstand chemical, thermal and mechanical stresses that are present in a fuel cell. The oxygen rich gas can be any gas or gas mixture, which comprises a measurable amount of oxygen.

The preferred manufacturing methods for forming the contoured surface of the flow field plates 121 are methods using plastic deformation such as stamping, forming, pressing and like, wherein the shape of the material is changed but no material is added or removed, or methods wherein material is added such as welding, sintering, and laser sintering or removed such as etching and machining. Other manufacturing methods can be utilized if the flow field material is brittle such as extrusion, casting, printing, molding, and like. The orifices for gases can be usually made in a same manufacturing step.

Each flow field plate 121 can be made similar in the stack assembly structure, thus desired amount of only one type of plate is needed to produce a fuel cell stack having desired amount of repetitious unit cell structures 174. This simplifies the structure and eases manufacturing of the fuel cells.

The solid oxide electrolyzer stack only differs from solid oxide fuel cell stack in that manner that electricity is used to produce fuel with reverse reactions to fuel cell reactions as described in the state of the art.

The single largest energy consumption device in a fuel cell system is the air blower or compressor that is used to supply air to the cathode compartment of fuel cell stack. The power consumption of the air supply devices is proportional to the pressure level they have to compress the air. Also, in solid oxide electrolyzer system, air is typically supplied to the anode in order to control the heat balance of the electrolyzer stack and to sustain well defined oxygen partial pressure on the anode compartment. One of the main pressure loss sources in the fuel cell and electrolyzer system is the stack itself. It is advantageous to design the device in such a manner that the air side of the device has open channels to the surrounding atmospheres.

In figures 3 - 5 are presented a first exemplary and a second cell stack module arrangement according to the present invention in a fuel cell system or in an electrolyzer cell system. In the module arrangement of solid oxide cell stacks each stack comprises unit cells 174 with a fuel side 100, an oxygen rich side 102, and an electrolyte element 104 between the fuel side and the oxygen rich side. Each stack 103 comprises flow field plates 121 made of a material having high electrical conductivity at high temperatures. Preferably high electrical conductivity means area specific resistance values less than 0.1 Ohm cm² and preferably below 0.01 Ohm cm². High temperatures mean temperature values over 400 °C. Each stack has four angled formation, and a gas sealing gasket 128 made of a material that isolates electricity. The arrangement has gas distribution structural 27 both for the inlet and outlet sides of fuel gas. Oxygen side gas delivery is based on an open channel structure. The arrangement comprises end plates 170 that are used in current collection, and the cells 174, flow field plates 121 and gas sealing structure 128 being arranged to a pile in a formation of a stack 103 between the end plates 170.

The exemplary module arrangement according to the present invention comprises stacks 103 being arranged to a 2 x N matrix, N being any natural number. The arrangement comprises a fuel inlet manifold 150 and a fuel outlet manifold 152 between the two adjacent stacks 103 the fuel inlet manifold 150 and the fuel outlet manifold 152 forming a fuel manifold 171 to deliver supply fuel gas 108 to the stacks and fuel exhaust gas 177 from the stacks. The stacks are arranged in the manifold in a parallel connection from the fuel gas supply and fuel exhaust gas connection point of view.

In a further embodiment the module arrangement comprises at least two cell stack 103 pairs arranged electrically at a series connection. In further embodiments the module arrangement comprises the X number of cell stacks 103 arranged in a series connection where X is natural number and fulfills 2N/X=Y, where N and Y are natural numbers. The stacks 103 are arranged with a common oxygen side gas supply compartment 106 connecting the inlet side of the open structure of oxygen side gas delivery 105 and common oxygen side gas exhaust compartment 176 connecting the outlet side of the open structure of oxygen side gas delivery 105, and common oxygen side gas exhaust compartment 176. As presented in figures 4 and 5 the manifold 171 can the inlet pipe connection 160 at a first end of the manifold and the outlet pipe connection 162 at a first end of the manifold. In another embodiment the manifold 171 can have the inlet pipe connection 160 at a first end of the manifold and the outlet pipe connection 162 at a second end of the manifold and there can be other kind of arrangements too. The manifold 171 comprises gas flow holes of controllable sizes to the stacks 103 for forming even gas flow to and from the stacks on basis of pressure difference between the inlet pipe connection 160 and the outlet pipe connection 162 of the manifold 171. In one preferred embodiment the module arrangement comprises means for controlling sizes of individual gas flow holes 133, 137 (Fig. 6) for forming even gas flows between the stacks 103. Pressure losses may require different hole sizes between the holes 133, 137.

The module arrangement further comprises a first gas seal 155, a first electrical insulation plate 119 and a second gas seal 156 between the manifold 171 and the cell stack 103 as presented in figure 7. On top side 122 and on bottom side 124 of the cell stack 103 the module arrangement comprises a second electrical insulation plate 114, compression structures 116 for the stacks 103, and an air tight structure 169 between the stacks. Each stack endplate 170 is connected with an electrical connection 173. The module arrangement can comprise an air tight structure 200 in which the fuel manifold structure 171 , stacks 103, sealing structures 155, 156, and electrical insulation plates 119, 114 are located. The air side sealing structure 169 has been sealed against the air tight structure 200.

In the embodiments according to the present invention the module arrangement can comprise the compression structures 116 inside (Figure 7) the air tight structure 169. In other embodiments according to the present invention the module arrangement can comprise the compression structures 116 outside (Figure 8) the air tight structure 169. In a preferred embodiment the module arrangement can comprise a centering structure in the top side 122 and bottom side 124. The centering structure can comprise a threaded hole and a sealing part. In one preferred embodiment the module arrangement can comprise on top side 122 of the cell stack 103 a compensating plate to compensate height tolerances between the stacks 103. The module arrangement can preferably comprise such a gas flow structure in the manifold 171 to form pressure conditions in which pressure losses in the inlet manifold 150 and outlet manifold 152 are smaller than pressure losses in a single cell 174. An exemplary manifold 171 presented in figure 6 comprises connection to the inlet pipe 160 and outlet pipe 162 and gas flow holes 133 to the stacks and gas flow holes 137 from the stacks. In a preferred embodiment the fuel inlet manifold 150 and fuel outlet manifold 152 can be connected together by welding to increase the structural stiffness and strength.

The manifold 171 and the cover parts of the stack 103 are preferably made of material with the same vicinity of coefficient of thermal expansion. The air side sealing structure 169 preferably comprises in a middle part hard ceramic and in an edge part soft ceramic. The manifold 171 is preferably made of ferritic steel. The first electrical insulating plates 119 are preferably made of at least one dense material. The second electrical insulating plates 114 are preferably made of at least one of porous material. Said dense or porous materials are preferably ceramic materials and/or minerals. The gas sealing structure 128 and first and second gas seals 155, 156 are preferably manufactured by screen printing technology, and they are at least partly of glass material, of glass-ceramic material, or of brazing alloy material. The module arrangement preferably comprises ceramic and/or glass paste to bind the cells and the gas seals 155, 156 together.

In one embodiment (e.g. fig. 2) heights of the flow orifices can be determined by a distance from at least one of a bottom of the flow distribution area and of the flow outlet area to a bottom of the gasket structure to stabilize flow distribution in the repetitious structures of the stack, which has tolerance variations in electrolyte element structure thickness. Similar pressure loss conditions between the cells are accomplished by utilizing the gasket structure which can be compressed and also pre-compressed at least from the flow parts in order to accomplish even thermal distribution, i.e. similar thermal gradients between the cells in the stack. Thus, the duty ratio of the solid oxide cell stack is improved, and also lifetime of the stack is made longer.

A cell stack arrangement according to the present invention can comprise flow restriction orifices opened to a flow distribution area and to the flow outlet area. In one embodiment means can be used for guiding fuel feed flow to the flow distribution area from sides of the fuel cell. A gasket structure is compressed over the flow restriction orifices. The flow restriction orifices ensure homogenous fuel flow distribution to the entire active area of the fuel cell electrode by creating an additional pressure sink to the flow path. The gasket structure also creates similar pressure loss conditions between repetitious structures of the fuel cell ensuring homogenous flow distribution characteristics for each repetitious structure of a fuel cell. The even flow distribution in the fuel cell stack ensures also even thermal distribution conditions for the fuel cell stack, i.e. similar thermal gradients between the cells in the stack. Thus, the duty ratio of the fuel cell stack is improved, and lifetime of the fuel cell stack is made longer.

The purpose of the gasket structure is further to ensure that oxidant and fuel are not directly mixed without the fuel cell reactions inside the electrochemically active area, that the fuel and oxidant are not leaked out from the electrochemical cells, that the adjacent electrochemical cells are not in electronic contact with each other, and that oxidant and fuel are supplied to the desired flow field plate planes. A flow field plate is a planar thin plate that is made of metal alloy, ceramic material, cermet material or other material that can withstand chemical, thermal and mechanical stresses that are present in a fuel cell. The oxygen rich gas can be any gas or gas mixture, which comprises a measurable amount of oxygen. Thus, while there have been shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the invention may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements which perform substantially the same results are within the scope of the invention. Substitutions of the elements from one described embodiment to another are also fully intended and contemplated. It is also to be understood that the drawings are not necessarily drawn to scale but they are merely conceptual in nature. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Claims

1 . Module arrangement of solid oxide cell stacks in a fuel cell system or in an electrolyzer cell system, each stack comprising of unit cells (174) with a fuel side (100), an oxygen rich side (102), and an electrolyte material

(104) between the fuel side and the oxygen rich side, each stack (103) comprising flow field plates (121 ) made of a material having high electrical conductivity at high temperatures, each stack (103) having four angled formation, each stack (103) comprising gas sealing structure (128) made of a material that isolates electricity, the arrangement having internal gas distribution structure (127) both for the inlet and outlet sides of fuel gas, oxygen side gas delivery being based on an open structure

(105), and the arrangement comprises end plates (170) that are used in current collection, and the cells (174), flow field plates (121 ) and gas sealing structures (128) being arranged to a pile in a formation of a stack (103) between the end plates (170), characterized in that the module arrangement being arranged to a 2 x N matrix, N being any natural number, and the arrangement comprises a fuel inlet manifold (150) and a fuel outlet manifold (152) between the two adjacent stacks (103), the fuel inlet manifold (150) and the fuel outlet manifold (152) forming a fuel manifold (171 ) to deliver supply fuel gas (108) to the stacks and fuel exhaust gas (177) from the stacks, and the stacks been arranged in the manifold in a parallel connection from the fuel gas supply and fuel exhaust gas connection point of view, and the stacks (103) being arranged with a common oxygen side gas supply compartment (106) connecting the inlet side of the open structure of oxygen side gas delivery (105) and common oxygen side gas exhaust compartment (176) connecting the outlet side of the open structure of oxygen side gas delivery (105), and the inlet manifold (150) comprising gas flow holes of controllable sizes to the stacks (103) for forming even gas flow to the stacks, and the outlet manifold (152) comprising gas flow holes of controllable sizes to the stacks (103) for forming even gas flow from the stacks, and the module arrangement comprises a first gas seal (155), a first electrical insulation plate (119) and a second gas seal (156) between the manifold (171 ) and the stack (103), and on top side (122) and on bottom side (124) of the cell stack (103) the module arrangement comprises a second electrical insulation plate (114), compression structures (116) for the stacks (103), and an air side sealing structure (169) between the stacks, and each stack end plate (170) are connected with an electrical connection (173).

2 . Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the module arrangement comprises means for controlling sizes of individual gas flow holes (133, 137) for forming even gas flows between the stacks (103).

3 . Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the manifold (171 ) has the inlet pipe connection (160) at a first end of the manifold and the outlet pipe connection (162) at a first end of the manifold.

4 . Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the air side sealing structure (169) comprises in a middle part hard ceramic and in an edge part soft ceramic.

5 . Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the manifold (171 ) and the cover parts of the stack (103) are made of at least one material with the same vicinity of coefficient of thermal expansion.

6 . Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the first electrical insulating plates (119) are made of at least one dense material. 7 . Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the second electrical insulating plates (114) are made of at least one porous material.

8 . Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the manifold (171 ) is made of ferritic steel.

9 . Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the module arrangement comprises at least two cell stack (103) pairs arranged electrically at a series connection.

10 . Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the module arrangement comprises the X number of cell stacks (103) arranged in a series connection where X is natural number and fulfills 2N/X=Y, where N and Y are natural numbers.

11 . Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the module arrangement comprises on top side (122) or on bottom side (124) of the cell stack (103) a compensating structure to compensate height tolerances between the stacks (103).

12 . Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the module arrangement comprises an air tight structure (200) in which the fuel manifold structure (171 ), stacks (103), sealing structures (155, 156), and electrical insulation plates (119, 114) are located, and the air side sealing structure (169) sealed against the air tight structure (200).

13 . Module arrangement of solid oxide cell stacks according to claim 12, characterized in that the module arrangement comprises the compression structures (116) inside the air tight structure (200). 14 . Module arrangement of solid oxide cell stacks according to claim 12, characterized in that the module arrangement comprises the compression structures (116) outside the air tight structure (200).

15 . Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the module arrangement comprises the fuel inlet manifold (150) and fuel outlet manifold (152) connected together by welding to increase the structural stiffness and strength.