Module arrangement of solid oxide cell stacks

Abstract

An object of the invention is a module arrangement being arranged to a M x N matrix, N being any natural number. A fuel inlet manifold (150) and a 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 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 inlet manifold (150) comprising a connection structure (160), and a flow element (320) braking the main flow stream coming from the gas inlet connection (160), and the inlet manifold (150) comprising a gas volume (300) between the flow element braking the main flow stream and inlet manifold connection structure, and at least one of the inlet manifold and the outlet manifold comprising two layer structure comprising a gas tight cover structure (330) and inner heat insulation structure (310), and the module arrangement comprises a first gas seal (155) on the gas tight cover structure, 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) is connected with an electrical connection.

Description

[0001] Module arrangement of solid oxide cell stacks

[0002] The field of the invention

[0003] 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.

[0004] 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.

[0005] 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.

[0006] The present invention relates to module arrangement of a Solid Oxide Fuel Cell (SOFC) stacks or a Solid Oxide Electrolyzer Cell (SOEC) stacks in order to increase power output or the fuel production rate or both of them compared to a single stack arrangement. 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.

[0007] State of the art

[0008] Fuel cell, as presented in figure 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:

[0009] Anode: CH4+ H2O = CO + 3H2

[0010] CO + H2O = CO2 + H2H2+ O2- = H2O + 2e-

[0011] Cathode: O2 + 4e_= 2O2’

[0012] Net reactions: CH4+ 2O2 = CO2 + 2H2O

[0013] CO + 1 / 202 = CO2

[0014] 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.

[0015] Solid oxide electrolyser 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:

[0016] Cathode: H2O + 2e — > 2 H2+ O2’

[0017] Anode: O2-— > 1 / 202 + 2e_

[0018] Net Reaction: H2O — > H2 + 1 / 202.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] A stack power is a function of its current and voltage. If the stack current is constant, the stack power is a function of the materials, structures and solutions used inside the stack but also a function of the inlet fuel gas composition, the inlet fuel gas flow rate, the inlet fuel gas temperature, the inlet oxygen-rich gas composition, the oxygen-rich gas flow rate, the inlet oxygen-rich gas temperature, current, and heat fluxes through conduction, convection, and radiation to and from the stack. The internal stack resistances resulting from the selections of different materials, structures, solutions, and operational parameters are typically non-linear and functions of temperature, partial pressure of reactant species and overall gas pressure. In order to optimize the electrical power output in the fuel cell mode and electrical power input in the electrolyser mode, each stack connected into a system needs to have as constant operating parameters as possible. This means that the most optimal case is where each stack has equal amount of fuel input and air input resulting in equal partial pressure of reactant species in the stack inlet, and the input fuel and oxygen-rich gas have equal temperature at each stack inlet. Also, the heat flux from each stack should be the same.

[0025] Prior art fuel cell and electrolyser cell stacks module is made of a limited number of stacks each module requiring at least one of an individual piping for inlet and outlet fuel and oxygen-rich gases, structural cover and heat insulation structures around the module making the solution bulky and expensive. In addition, control of the flow and temperature for each individual stack becomes problematic with an increased number of intersecting piping all needing to have same pressure drop characteristics, and preferably no active flow control means as these would increase the cost and complexity level of a system and the individual pipe sections need to have same heat loss mechanisms or they need to have an active temperature control system also increasing the price and complexity of the overall system. Furthermore, application power requirements can be as large as hundreds of MW while a single solid oxide stack is rather small, typically in the range of 500 W to 100 kW, resulting in a large number of single stacks needed to accomplish the application. Thus, there is a need for an effective connection means of single stacks while the connection means needs to provide equal operating conditions for each stack in system.

[0026] Prior art fuel cell stacks or electrolyser 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 electrolyser stack.

[0027] High temperature solid oxide cell stacks are preferred conversion technologies due to their 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 electrolyser, 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.

[0028] Brief description of the invention

[0029] An object of the invention is to improve the efficiency, performance, reliability and structure of the fuel cell or electrolyser cell stack modules. This is achieved by a module arrangement of solid oxide cell stacks in a fuel cell system or in an electrolyser 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 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 M x N matrix, M and N being any natural number, 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 inlet manifold comprising a connection structure, and a flow element braking the main flow stream coming from the gas inlet connection, and the inlet manifold comprising a gas volume between the flow element braking the main flow stream and inlet manifold connection structure, and at least one of the inlet manifold and the outlet manifold comprising two layer structure comprising a gas tight cover structure and inner heat insulation structure, and the module arrangement comprises a first gas seal on the gas tight cover structure, 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 is connected with an electrical connection.

[0030] The invention is based on a module arrangement of solid oxide cell stacks in a fuel cell system or in an electrolyser cell system, wherein the module arrangement comprises stacks being arranged to a M x N matrix, M and N being any natural number, the fuel inlet manifold and the fuel outlet manifold forming a fuel manifold 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 can further be 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. The invention is also based on inlet manifold comprising a connection structure, and a flow element braking the main flow stream coming from the gas inlet connection, and the inlet manifold comprising a gas volume between the flow element braking the main flow stream and inlet manifold connection structure, and at least one of the inlet manifold and the outlet manifold comprising two layer structure comprising a gas tight cover structure and inner heat insulation structure, and the module arrangement comprises a first gas seal on the gas tight cover structure.

[0031] 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. Benefit of the invention is also that temperature and flow rate conditions between the fuel gas inlet and stacks can be controlled to support optimum operation of the module arrangement of solid oxide cell stacks in a fuel cell system or in an electrolyser cell system. For example, the hot outlet flow pipe side does not disturb temperature conditions of the inlet flow side and dynamic pressure from the inlet pipe does not disturb the individual stack inlet flows.

[0032] Brief description of the drawings

[0033] Figure 1 presents a single fuel cell structure.

[0034] Figure 2 presents a repetitious sold oxide cell structure.

[0035] Figure 3 presents a first exemplary cell stack fuel arrangement according to the present invention from the the cross section top view.

[0036] Figure 4 presents a first exemplary cell stack fuel manifold arrangement according to the present invention from the first end of a fuel manifold.

[0037] Figure 5 presents a second exemplary cell stack fuel manifold arrangement according to the present invention from the cross section top view.

[0038] Figure 6 presents a third exemplary cell stack fuel manifold arrangement according to the present invention from the cross section top view.

[0039] Figure 7 presents a side view of the third exemplary cell stack bundle arrangement according to the present invention. Figure 8 presents a side view of the fourth exemplary cell stack bundle arrangement according to the present invention.

[0040] Figure 9 presents an exemplary stack module arrangement according to the present invention including an electrical connection topology for serial stack connection.

[0041] Figure 10 presents an exemplary stack module arrangement according to the present invention including stack bundles and balance of plant components from the top view.

[0042] Detailed description of the invention

[0043] According to the present invention, the fuel cell or electrolyser 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] The solid oxide electrolyser 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.

[0050] 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 electrolyser system, air is typically supplied to the anode in order to control the heat balance of the electrolyser 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 electrolyser 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 - 8 are presented a first, a second, a third, and a fourth exemplary cell stack fuel manifold arrangement according to the present invention in a fuel cell system or in an electrolyser cell system. In the fuel manifold 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 cm2and preferably below 0.01 Ohm cm2. High temperatures mean temperature values over 400 °C. Each stack can have e.g. four angled formation, and a gas sealing gasket 128 made of a material that isolates electricity. The arrangement has gas distribution structure both for the inlet 160 and outlet 162 sides of fuel gas. Oxygen side gas delivery for the stack 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.

[0051] The exemplary module arrangement according to the present invention comprises stacks 103 being arranged to a M x N matrix, N being any natural number and M being one of one and an even number. The arrangement can comprise a fuel inlet manifold 150 and a fuel outlet manifold 152 e.g. between the 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. The stacks are arranged in the manifold in a parallel connection from the fuel gas supply and fuel exhaust gas connection point of view.

[0052] The fuel inlet manifold 150 comprises of a connection mean 160 that can be a pipe connection, a gas tight outer cell structure 330, a heat insulation structure 310 that is inside the structure 330, a structure breaking the developed inlet flow stream 320, a gas volume 300 that is between the connection mean 160, structure 320 and a structure 330 in which the main flow stream coming from the connection mean 160 and hitting the structure 320 has volume to distribute on the structure 160 before entering to the flow volume 360. The laminar flow element, which is also known as turbulence filter 320, can be made for example from a perforated or porous sheet metal structure or ceramic plate structure. The fuel inlet gas 108 flows through the turbulence filter 320 after which the flow profile is behaving like a diffusive flow. The dynamic pressure is reduced before the first fuel inlet gas flow hole 133 serving fuel flow for the first stack inlet and thus will even out the flow distribution for all stack inlet ports. The gas flow hole structure 133 is made overlaying to the heat insulation structure 310, to the gas tight outer cell structure 330, to an electrical insulation plate 119 and is parallel to the fuel inlet ports in a stack 103 bottom current collector plate 170.

[0053] There is typically a gasket structure 155 between the gas tight outer cell structure 330 and the electrical insulation plate 119, and another gasket structure 156 between the electrical insulation plate 119 and the bottom current collector plate 170 of the stack 103. Flow volume 360 serves 2 x N stacks 103 in this exemplary embodiment in a fuel manifold and each stack 103 can have one or more inlet fuel holes 133. The stack can have also one or multiple outlet fuel gas holes 137. The hole sizes 133, 137 are controlled to secure even flow distribution to each stack. The heat insulation structure 310 that is inside the structure 330 reduces heat conduction and radiation heat fluxes from the structure 330 to the fuel inlet gas flow 108. Because the heat fluxes are reduced, the inlet fuel gas heating effect is reduced when it is flowing from the flow diffuser structure 320 to the last fuel inlet port of the flow volume 360. Thus, the material that is selected to the heat insulation structure should have low thermal conductivity with below 0.1 W / m / K heat conductivity value at the operational temperature of a solid oxide stack technology. Such materials are typically microporous ceramic materials including pure and mixtures of alumina, silica, magnesium oxide and iron oxide. The heat insulation material 310 can be covered from its surface with a material that will not erode in flow conditions. These materials may include pure or mixture of materials of vermiculite, mica, steel, glass fiber and alumina felts. The gas tight outer structure 330 can be made of steel that has good corrosion and machinability properties. Such metal grades include for example ferritic steels, austenitic steels, and super alloys. The structure 330 needs further to be gas tight for the fuel gas and oxygen-rich gas as it separates these from each other. The overall structure 150 including the gas tight outer structure 330 and the heat insulation structure 310 needs to be mechanically stable enabling to withstand weight of the surrounding structures and possible external compression forces the are required to ensure gas tightness for the gasket interfaces. The structure 330 can be made leak- tight for example by welding, brazing, fusion bonding, or compressed gasket structures. An oxygen-rich gas flow restriction structure 169 is put between individual stacks 103 that ensures that air flow is guided through the stacks and not bypassing those. Two or more stacks can be located on top of each other and in this case the fuel manifold inlet 150 and outlet 152 are equipped with holes on its bottom and top structures. The outlet fuel manifold is equipped with a connection mean 162 and each stack top end has an electrical insulation structure 114.

[0054] The outlet manifold structure 152 is at least made from the gas tight outer structure 330 with similar methods and materials to the inlet fuel manifold structure 150 and it can also comprise similar heat insulation material inside the structure 330 as the inlet fuel manifold includes. This will reduce the temperature gradients also at the outlet fuel gas side. The inlet fuel manifold and the outlet fuel manifold structures can be also separated with a heat insulation structure 310 that reduces the heat fluxes from the stack outlet structures to the stack inlet fuel flow 108. The heat insulation material of the structure 310 can be made from high temperature insulation material having below 0.1 W / m / K thermal conductivity value. The electrical isolation structure located between a stack and a fuel manifold structure 171 can be made of multiple parts limiting the heat transfer between the solid oxide stack outlet and inlet fuel flow 108. A stack bundle is a structure that is composed of an individual fuel manifold 171 equipped with stacks 103, gasket structures 155, 156, electrical isolation structures 114, 119, flow restriction structures 169 and current collection means for individual stacks 103. 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.

[0055] Figure 5 depicts an exemplary in which the inlet flow volume 300 is different size from the cross sectional flow area compared to the cross sectional flow area in the flow distribution area 360. The structure breaking the inlet flow stream 320 is advantageous to be sized according to the smaller flow area size of the flow volume 300 and 360. It can become advantageous to size the flow area in the flow volume 300 larger than in the flow volume 360 especially in large applications having multiple stack bundles connected as a single unit. In these applications the pressure losses in the connection sections 160 are made small by increasing the hydraulic diameter, for example a pipe diameter, that might then not fit the flow distribution area 360 requirements serving individual stacks 103. Also, the individual gas holes in the fuel manifold structure can be of different sizes enabling further stabilization of the flow between the stack inlet ports. Figure 5 presents an arrangement where the connection means for the inlet fuel gas and for the outlet fuel gas are at the opposite ends of the structure. This structure creates a z-type flow configuration between the fuel inlet and fuel outlet where the temperature distribution and flow distribution characteristics differ from a solution presented in Figure 4 where both inlet and outlet gases are fed from the same side of the fuel manifold structure.

[0056] Figure 6 depicts an arrangement in which fuel inlet gas is fed from the connection means 160 to a flow volume 300. The flow volume is preferably made of a porous or perforated material that creates controlled pressure drop over the material 320. The shape of the structure 300 can be for example a round pipe or a rectangular structure. The material is preferably having a low thermal conductivity and preferably below 0.1 W / m / K. The fuel inlet gas 108 is flowing through the structure 320 and then filling the gas volume 360 that is formed between structure 320 and gas tight structure 330. From gas volume 360 fuel gas can enter to individual stack inlet feed holes 133 made to the cover structure 330 and are not shown in the picture for clarity. Fuel gas and oxygenrich gas is flowing through the stacks 103 in which the gases are changing their temperature according to the chemical and electrochemical reactions occurring in the stacks 103 that might be either endothermic or exothermic in their nature. The fuel outlet gas is collected through the holes 137 to the outlet fuel manifold structure and collected to the connection means 162.

[0057] Figure 7 illustrates an example of a 4 x 6 stack bundle configuration. In this example fuel gas inlet connection means 160 is feeding the gas into the inlet fuel manifold structure 150. On the top and on the bottom of the of the fuel manifold structure 171 there exists two individual stacks that have a connection structure 119, 193 between them. The connection structure 119, 193 can be made of at least one of a gasket, an electrical insulation structure and a mechanical structural element and their combination. There is an oxygen-rich gas flow restriction structure 169 between each dual stack arrangement 195. The fuel gas manifold in this example has a detachable end element 331 . From this side when the end element 331 is taken away, the heat insulation structure 310 has been inserted inside to the gas tight structure 330 to together comprise the fuel inlet manifold structure 150.

[0058] Figure 8 illustrates an example of a 3 x 6 stack bundle configuration. In this example fuel gas inlet connection means 160 is feeding the gas into the inlet fuel manifold structure 150. On the top of the fuel manifold structure 171 there exists three stacks that have a connection structure 119, 193 between them. The connection structure 119, 193 can be made of at least one of a gasket, an electrical insulation structure and a mechanical structural element and their combination. There is an oxygen-rich gas flow restriction structure 169 between each stack tower arrangement 195. The fuel gas manifold in this example has a detachable element 331 . From this side when the element 331 is taken away, the heat insulation structure 310 has been inserted inside to the gas tight structure 330 to together comprise the fuel inlet manifold structure 150.

[0059] In a further embodiment the module arrangement comprises at least two cell stack 103 pairs arranged electrically at a series connection as shown in Figure 9. In further embodiments the module arrangement comprises the X number of cell stacks 103 arranged in an electrical series connection where X is natural number and fulfills M*N / X=Y, where X, N and Y are natural numbers and M is either one or an even number. In this example six stacks 103 are connected to an electrical series where the first stack 103 is connected with a current collector rod 401 to its negative current collector plate 170. The other end of the first stack 103 is connected from its positive current collector 170 with a current collector rod 402 to a negative current collector plate 170 of the second stack in the electrical series. The electrical series is continued with by connecting a positive current collector 170 of a previous stack 103 to the negative current collector 107 of the next stack 103 with a current collector rod 402. The last stack in the electrical series connection is connected with the current collector rod 403 to the current collector 170 of the last stack 103 in the series. The overall voltage between the current collector rod 401 and 403 in this example is 6 times the stack voltage 103. The increased voltage level of the serial connected individual stacks increase the overall system efficiency as the power connection to an electrical grid will become energetically and economically more efficient. 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. Figure 10 shows an example of an arrangement of a connection mean of multiple stack bundles. In this example an individual stack bundle has 9 stack rows and one stack is connected on the manifold top and one on manifold bottom making the bundle structure as 2x9 configuration, and the inlet fuel manifold 150 has the structures described to unify the flow and temperature. The fuel inlet connection means 160 are connected to a common fuel distribution structure 215. The fuel outlet connection means 162 are connected to a common fuel distribution structure 216. The fuel distribution structures can include thermal compensation structures such as bellows. The oxygen-rich gas inlet side 106 can supply gas to two adjacent stack bundles and the oxygen-rich gas outlet side 176 can be connected with two adjacent stack bundles. The outlet side 176 can contain also some balance of plan components like a prereformer, a fuel gas ejector, an in-line electrical heater and an in-line gas heater components. The balance of plant components can be located also at the gas inlet side 106 in other examples of the invention.

[0060] 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.

[0061] 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

Claims1 . Module arrangement of solid oxide cell stacks in a fuel cell system or in an electrolyser 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) 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 M x N matrix, M and N being any natural number, 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 respect to N 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 inlet manifold (150) comprising a connection structure (160), and a flow element (320) braking the main flow stream coming from the gas inlet connection (160),and the inlet manifold (150) comprising a gas volume (300) between the flow element braking the main flow stream and inlet manifold connection structure, and at least one of the inlet manifold and the outlet manifold comprising two layer structure comprising a gas tight cover structure (330) and inner heat insulation structure (310) , and the module arrangement comprises a first gas seal (155) on the gas tight cover structure, 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 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) is connected with an electrical connection.2 . Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that in the module arrangement the inner heat insulation structure (310) comprises at least one of the heat insulation material and a support material to keep the insulation material mechanically stable in the gas tight cover structure.

3. Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the heat insulation structure (310) is made of a material having thermal conductivity smaller than 0.1 W / m / K.

4. Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the module arrangement comprises at least one detachable panel (331 ) for fuel inlet manifold (150) and for fuel outlet manifold (152) to install the heat insulation structure (310).

5. Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the gas tight cover structure (330) of the manifold (171 ) and the stack (103) are made of at least one material with thesame vicinity of coefficient of thermal expansion.

6. Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the gas tight cover structure (330) of the manifold (171 ) is made of ferritic steel .

7. Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the flow element (320) is made of perforated structure.

8. Module arrangement of solid oxide cell stacks according to claim 1 , characterized in that the flow element (320) is made of porous ceramic material.

9. 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 M x N / X = Y, where M, N and Y are natural numbers.

10. 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 inlet manifold structure (150), the fuel outlet manifold structure (152), 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).11 . 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.

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