EP4713982A1

EP4713982A1 - Stack module and method of its use

Info

Publication number: EP4713982A1
Application number: EP23723619.5A
Authority: EP
Inventors: Matti Noponen; Julius STENIUS
Original assignee: Elcogen Oy
Current assignee: Elcogen Oy
Priority date: 2023-04-28
Filing date: 2023-04-28
Publication date: 2026-03-25
Also published as: AU2023445093A1; WO2024223976A1; KR20250168611A; CN121311982A; AU2023445093B2

Abstract

An object of the invention is a stack module of solid oxide cell stacks comprising a fuel inlet manifold (150) and a fuel outlet manifold (152) between the two adjacent stacks (103). The stack module comprises at least two stack bundles, each stack bundle containing a row or a matrix of the stacks (103) together with a fuel inlet manifold (150) supplying fuel for the stacks and a fuel outlet manifold (152) collecting fuel gas from the stacks (103), which are connected to the manifolds (150, 152) parallel in terms of their fuel inlet and fuel outlet, the stack module being located inside an air tight cover (169) comprising needed interfaces into the air tight cover (169) and out from the air tight cover (169), and fuel gas flow characteristics in the manifolds (150, 152) being optimized with the size of the holes connecting the manifolds and the stack based on the pressure drop characteristics of the manifolds (150, 152) and stacks connected parallel to that, and the stacks are electrically isolated from the fuel manifold structures (150, 152) with an electrical isolation structure (172) and the other end of the stack is electrically separated from other structures, and the stack module comprises a side sealing solution (166) between the neighboring stacks (103a) in a stack bundle and between the stacks (103b) at the end of the bundle and the air tight cover (169) preventing air flowing from an inlet chamber directly to an outlet chamber without flowing through the stacks, the side sealing solution being electrically isolating, and the stack bundle comprises at least one of a unified structure of an air inlet compartment (106) and a unified structure of an air outlet compartment (176) of the adjacent parallel connected cell stack (103) bundles.

Description

Stack module and method of its use

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 conventional energy sources, have been developed.

Solid oxide cells operate via a chemical reaction in an environmentally friendly process and are very promising future energy conversion devices. The intermittency of renewable energy sources has introduced challenges for the electrical grid stability, calling for increased demand and supply side flexibility and new energy storage and conversion technologies.

The state of the art

An electrochemical active solid oxide cell can be used as a fuel cell or an electrolyser. A fuel cell produces electricity and heat from various fuels and an electrolysis cell produces chemicals such as hydrogen, methane, ammonia and carbon monoxide from steam, CO2, and nitrogen, electricity and heat. Such a cell that operates in both modes, as a fuel cell and electrolyser, is called a solid oxide electrochemical cell (SOEC) or reversible solid oxide cell (rSOC) or simply a solid oxide cell (SOC). Solid oxide cell (SOC), as presented in fig 1 , comprises a fuel side 100 and an oxygen rich side 102 and an electrolyte material 104 between them. In solid oxide fuel cells (SOFCs), oxygen 106 is fed to the oxygen rich side 102 and it is reduced to a negative oxygen ion by receiving electrons from the oxygen rich side. The negative oxygen ion is transported through the electrolyte material 104 to the fuel side 100 where it reacts with fuel 108 producing typically water and carbon monoxide (CO) and carbon dioxide (CO2). Fuel side 100 and oxygen rich side 102 are connected through an external electric circuit 111 comprising a load 110 for the fuel cell operating mode withdrawing electrical energy out of the system. The fuel cells also produce heat to the reactant exhaust streams. In electrolysis operating mode, current flow is reversed and the solid oxide cells act as a load to which electricity is supplied. Depending on electrolysis reaction operating conditions, the cell operation can be endothermic, exothermic or thermoneutral.

Fuel cell reactions in the case of methane, carbon monoxide and hydrogen fuel are shown below:

Fuel side: CF + H2O = CO + 3H2

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

Oxygen rich side: O2 + 4e^_ = 2O²’

Net reactions: CH4 + 2O2 = CO2 + 2H2O

CO + 1/202 = CO2 H₂ + 1/2O₂ = H₂O

In electrolysis operating mode (solid oxide electrolysis cells, (SOEC)) the reaction is reversed, i.e. electrical energy from a source 110 is supplied to the cell where water and often also carbon dioxide are reduced in the fuel side forming oxygen ions, which move through the electrolyte material to the oxygen rich side where oxidation reaction takes place. It is possible to use the same solid oxide cell in both SOFC and SOEC modes.

Prior art 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 even over 1000 °C temperatures may be useful. These operating temperatures are similar to those conditions of the solid oxide fuel cells (SOFCs). The net cell reaction produces hydrogen and oxygen gases. The reactions for one mole of water are shown below:

Fuel side: H₂O + 2e — > 2 H₂ + O²’

Oxygen rich side: O²’ — > 1/2O₂ + 2e~

Net Reaction: H₂O — > H₂ + 1/2O₂.

In case of co-electrolysis, a carbonaceous species is supplied to the cell in addition to steam, typically in proportions favorable for subsequent refining of the result gas according to e.g. the Fischer-Tropsch process. Carbon dioxide can be directly reduced to carbon monoxide or can interact with hydrogen through the water-gas shift reaction to form carbon monoxide and steam.

Solid oxide cell can be used also to produce other types of chemicals directly by the electrochemical reactions or through chemical reactions. Such chemicals may include e.g. methane and ammonia. Methane can be produced when steam and carbonaceous species are fed to a solid oxide electrolysis cell and ammonia when steam and nitrogen are fed. The reaction rate of the chemical production is dependent on the supplied current, fuel and air side flow rates, fuel and air side gas concentrations, fuel and air side pressures, and fuel and air side temperatures.

In Solid Oxide Fuel Cell (SOFC) and Solid Oxide Electrolyser (SOE) stacks where the flow direction of the fuel side gas are relative to the oxygen rich side gas internally in each cell as well as relative to the flow directions of the gases between adjacent cells, stacks are combined through different cell layers of the stack. Further, the fuel side gas or the oxygen rich side 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.

The high operating temperature in the SOC cells and system introduce material related challenges with respect to thermomechanical forces, material properties, chemical stability and uniformity of operating conditions. These aspects place practical constraints on feasible SOC cell, stack and module sizes. Scaling the technology for large installations, typical to SOEC application, will thus primarily rely on multiplication of cells, stacks and SOC modules. Minimizing the cost of each multiplying unit at all levels is thus crucial for reducing the overall cost.

A SOFC delivers in normal operation a voltage of approximately 0.8V and an typical operation voltage of a SOE cell is about 1.3V. In order to increase the total voltage output, the SOCs are usually assembled in stacks in which the cells are electrically connected via flow field plates (also: 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 oxidant 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 oxidant gas (i.e. air), is defined as the substantial direction from the inlet portion to the 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 of the inlet gases. When endothermic and exothermic reactions are combined in an SOFC stack, a significant temperature gradient across the stack is generated. Simultaneously flow rates are wanted to be minimized both at the fuel and oygen rich side in order to maximize overall system efficiency. Large thermal gradients induce thermal stresses in the stack which are highly undesired and they entail difference in current density and electrical resistance. The performance and lifetime of a SOC stack can be maximized when as uniform temprature profile as possible over the entire stack can be maintained. Therefore, the problem of thermal management of an SOFC stack exists in reducing thermal gradients enough to avoid unacceptable stresses and to maximize electric efficiency through homogenous current density profile.

It is often necessary in prior art embodiments to protectively coat the flow field plates in order to slow down corrosion of the metal. Generally, there are two corrosion mechanisms that cause aging to solid oxide fuel cells and electrolyser. One mechanism is the formation of an oxide layer, that conducts electricity poorly, onto the metal surface and another mechanism is the settling of chrome compounds evaporating from metal onto the active surfaces of the unit cell and reaction with electrochemically active materials weakening the electrochemical, chemical, electrical conductivity and/or gas permeability properties of the active material. Oxide structures are generally used as protective coatings that on one hand slow down oxidant diffusion onto the surface of the metal and on the other slow down hand diffusion of alloy atoms and compounds through the oxide structure. The price of the protective coating is typically significant within the total costs of the cell stack and cost of the protective coating is influenced by the fabrication process used for the protective coating, the material and the surface to be coated protectively. Additionally it is not preferable to extend the protective coating to areas, which are used to seal the cell stack, because glass, ceramic materials or minerals generally used as sealants can react with the protective coating causing aging effects to the cell stack structures, for example because of increased gas leakages and/or increased undesired electric conductivity.

A SOC module may comprise tens up to hundreds of SOC stacks, support structures, thermal insulation, reactant conveying and distribution structures, instrumentation as well as electrical and reactant interfacing towards the application or other modules. As high temperature interfaces are costly, space-consuming and may constitute an ignition source, it is also beneficial to include heat exchanging within the module to lower the temperature of the reactant interfaces. Furthermore, the SOC module needs internal or external means to facilitate safe start-up and shutdown.

In prior art embodiments air inlet flow channels and air outlet flow channels are separated, because it has been considered as a traditional and well operating structure without noticing that a more beneficial system structure can be achieved.

Short description of the invention

The object of the present invention is to achieve a solid oxide cell system and its operation, in which energy production capacity is increased and energy production efficiency is improved. This is achieved by a stack module of solid oxide cell stacks, 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, and the stack module comprises a fuel inlet manifold to deliver supply fuel gas to the stacks and a fuel outlet manifold to collect fuel exhaust gas from the stacks. The stack module comprises at least two stack bundles, each stack bundle containing a row or a matrix of the stacks together with the fuel inlet manifold supplying fuel for the stacks and the fuel outlet manifold collecting fuel gas from the stacks, which are connected to the manifolds parallel in terms of their fuel inlet and fuel outlet, the stack module being located inside an air tight cover comprising needed interfaces into the air tight cover and out from the air tight cover, and fuel gas flow characteristics in the manifolds being optimized with the size of the holes connecting the fuel manifold and the stack based on the pressure drop characteristics of the manifolds and stacks connected parallel to that, and the stacks are electrically isolated from the manifold structures with an electrical isolation structure and the other end of the stack is electrically separated from other structures, and the stack module comprises a side sealing solution between the neighboring stacks in a stack bundle and the stacks at the end of the bundle and the air tight cover preventing air flowing from an inlet chamber directly to an outlet chamber without flowing through the stacks, the side sealing solution being electrically isolating, and the stack bundle comprises at least one of a unified structure of an air inlet compartment and a unified structure of an air outlet compartment of the adjacent parallel connected cell stack bundles.

The focus of the invention is also a method of a stack module method of solid oxide cell stacks, 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, and in the method is used in each stack flow field plates made of a material having high electrical conductivity at high temperatures, and in each stack is used a gas sealing structure made of a material that isolates electricity, and in the method is supplied fuel gas to the stacks and is exhausted fuel exhaust gas from the stacks. In the stack module method is used at least two stack bundles, each stack bundle containing a row or a matrix of the stacks, which are connected to manifolds parallel in terms of their fuel inlet and fuel outlet, and the stack module is located inside an air tight cover having needed interfaces into the air tight cover and out from the air tight cover, and in the method is optimized fuel gas flow characteristics in the manifolds with the size of the holes connecting the manifolds and the stack based on the pressure drop characteristics of the manifolds and the stacks connected parallel to that, and the stacks are electrically isolated from the manifold structures with an electrical isolation structure and the other end of the stack is electrically separated from other structures, and in method is prevented air flowing from an inlet chamber directly to an outlet chamber without flowing through the stacks with a side sealing solution between the neighboring stacks in a stack bundle and between the stacks at the end of the bundle and the air tight cover, and is formed at least one of a unified structure of an air inlet compartment and a unified structure of an air outlet compartment of the adjacent parallel connected cell stack bundles.

The invention is based on that the stack module comprises at least two stack bundles, each stack bundle containing a row or a matrix of the stacks together with the fuel inlet manifold supplying fuel for the stacks and the fuel outlet manifold collecting fuel gas from the stacks, which are connected to the manifolds parallel in terms of their fuel inlet and fuel outlet. The invention is also based e.g. on that the stack module being located inside an air tight cover comprising needed interfaces into the air tight cover and out from the air tight cover, and that the stack module comprises a side sealing solution between the neighboring stacks in a stack bundle and the stacks at the end of the bundle and the air tight cover preventing air flowing from an inlet chamber directly to an outlet chamber without flowing through the stacks, and that the side sealing solution being electrically isolating structure.

Furthermore, the invention is based on that the stack bundle comprises at least one of a unified structure of an air inlet compartment and a unified structure of an air outlet compartment of the adjacent parallel connected cell stack bundles. The benefit of the invention is that costs of a produced electricity and chemicals can be reduced by enabling utilization of higher power densities on the same reaction area.

Short description of figures

Figure 1 presents exemplary repetitious cell structure.

Figure 2 presents an exemplary arrangement of flow field plates for a fuel cell stack.

Figure 3 presents an exemplary cross section perspective view of a stack module with common outlet and inlet air compartments in an air tight cover.

Figure 4 presents an exemplary cross section side view of a stack module with common outlet and inlet air compartments in an air tight cover.

Figure 5 presents an exemplary cross section side view of a stack module with common outlet and inlet air compartments and integrated balance of plant components in an air tight cover.

Detailed description of the invention

In the embodiments according to the present invention is maximized the volumetric power density of a solid oxide stack assembly by unifying the air inlet and air outlet compartments of adjacent stack assemblies.

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 cross-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 module 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 exemplary cell stack modules according to the present invention in a fuel cell system or in an electrolyzer cell system. In a stack module of solid oxide cell stacks according to the present invention, stacks 103 comprise 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. Stacks 103 further comprise flow field plates 121 made of a material having high electrical conductivity at high temperatures and a gas sealing structure 128 made of a material that isolates electricity. Preferably high electrical conductivity means area specific resistance values less than 0.1 Ohm cm² and preferably below 0.01 Ohm cm². Each stack 103 preferably comprises four angled formation. The stacks 103 can be arranged to a matrix configuration or to a row configuration together with one or multiple fuel gas manifolds supplying fuel for individual stacks and collecting exhaust fuel gas from the stacks. The stacks 103 are connected to the fuel inlet and outlet manifolds 150, 152 parallel in terms of their fuel inlet and fuel outlet.

The stack module according to the present invention comprises a fuel inlet manifold 150 to deliver supply fuel gas 108 to the stacks and a fuel outlet manifold 152 to collect fuel exhaust gas 177 from the stacks. The manifolds 150, 152 are preferably made of ferritic steel. In a preferred embodiment the manifolds 150, 152 and the cover parts of the stacks 103 are made of at least one material with the same vicinity of coefficient of thermal expansion. The stack module preferably comprises electrical connections between the stacks 103 as configurated to achieve voltage levels of 600 V -1200, i.e. objective voltage levels of the system or application. In the arrangement the cell stacks 103 are being assembled in the manifolds 150, 152 in a parallel connection from the fuel gas inlet and outletpoint of view. The cell stack module comprises unified structures of an air inlet compartment 106 and/or an air outlet compartment 176 of the adjacent parallel connected cell stack 103 assemblies. The unified structure means e.g. a shared gas volume between the adjacent stack bundles.

The inlet manifold 150 according to the present invention comprises gas flow holes 133 of controllable sizes to the stacks 103 for forming even gas flow to the stacks. Also, the outlet manifold 152 comprises gas flow holes 137 of controllable sizes from the stacks 103 for forming even gas flow from the stacks. In a preferred embodiment the stack module comprises means for controlling sizes of individual gas flow holes 133, 137 based on the pressure drop characteristics of the manifold and stacks 103 connected parallel to the manifolds 150, 152 for forming even gas flows between the stacks 103. In one embodiment the manifold 150, 152 can comprise gas flow holes 133, 137 of controllable sizes of 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 150, 152. Pressure losses may require different hole sizes between the holes 133, 137.

The stack module according to the present invention is being located inside an air-tight cover 169 comprising needed interfaces into the air-tight cover 169 and out from the air-tight cover 169. In one preferred embodiment presented in figure 5 the air-tight cover 169 can cover the entire stack module including stack assemblies, balance of plant components 212 and instrumentation securing that air leakage to environment is minimized. Air- tight cover 169 includes needed interfaces for air inlet and air outlet flows, fuel inlet and outlet flows, current leads for individual stacks or stack series, measurement connections, and compression system connections. Air-tight cover 169 can be made from thermal insulation material or it can be surrounded with thermal insulation material. In the exemplary perspective cross section figure 3 is presented fuel manifold openings for fuel exhaust gas 177 from the stacks 103 to the fuel outlet manifold 152. In figure 3 is also presented fuel inlet interface 208, fuel outlet interface 204, air inlet interface 206 and air outlet interface 210. In a preferred embodiment at least two cell stacks 103 can be arranged electrically at a series connection. Benefit of the electrical series connections is to minimize need of the interfaces into the air tight cover and out from the air tight cover.

In a preferred embodiment the stack module can comprise a first gas seal 155, a first electrical insulation plate 119 and a second gas seal 156 between the manifolds 150, 152 and the stack 103. On top side 122 and on bottom side 124 of the cell stack 103 the stack module can comprise a second electrical insulation plate 114, compression structures 116 for the stacks 103, and an air side sealing solution 166 between the stacks, and each stack end plate 170 can be connected with an electrical connection 173. The stack module can comprise on at least one of the top side 122 and of the bottom side 124 of the cell stack 103 a compensating structure to compensate height tolerances between the stacks 103. In one preferred embodiment the stack module can comprise the stacks 103 as electrically isolated from the manifold 150, 152 structures with electrical isolation structure 172 made from a gas tight material. The other end of the stack 103 is electrically separated from other structures. In one preferred embodiment the stacks 103 can comprise an opening in an endplate 202 facing to the electrical isolation structure 172 for feeding gas into the fuel inlet manifold 150, 152 of the stack 103.

A stack 103 according to the present invention can be sealed to a ceramic isolation plate with a gasket made of glass, ceramic or mineral material and the isolation plate can be sealed to the fuel manifolds 150, 152 with similar materials. The other end of the stack 103 can be electrically separated from other structures with another ceramic plate. This plate does not need to be gas tight. A compression structure can be connected to said ceramic plate and compression force can be applied at least to a top part of a stack 103 including also all ceramic and gas sealing parts.

According to the present invention, a side sealing solution 166 can be applied between the neighboring stacks 103a in a stack bundle and between the stacks 103b at the end of the bundle and the air tight cover 169. The side sealing solution 166 prevents air flowing from an inlet chamber directly to an outlet chamber without flowing through the stacks. The side sealing solution 166 is electrically isolating structure and preferably follows the forms of a stack side. The side sealing solution can be made of ceramic material having compressible characteristics for its outer surface. Stacks 103 can be electrically connected to their negative endplate with a negative current lead solution and to their positive endplate with a positive current lead solution. Multiple stacks 103 in serial connection can be connected to increase the output voltage and to minimize the number of current lead-through solutions by connecting a positive current lead of a stack to the negative current lead solution of another stack. Number of stacks connected in serial connection is not limited but not all stacks in one stack assembly need to be connected in the same serial connection.

In figure 5 is presented an exemplary preferred embodiment according to the present invention, in which the stack module comprises balance of plant components 212 as integrated inside the unified structure. The air inlet 106 and air outlet 176 compartments forming the unified structure can host balance of plant components 212 in order to facilitate e.g. system safety, heat management and increased volumetric energy density. These balance of plant components 212 can include e.g. reforming or cracking reactors, heat exchangers, (catalytic) burners and gas recycling equipment including ejectors, pump heads and compressor heads. The air compartments 106, 176 can host also current lead solutions, instrumentation wiring e.g. for voltage measurements and temperature measurements, and instrumentation piping for pressure measurements and gas composition measurements.

One exemplary stack module 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 to deliver supply fuel gas 108 to the stacks and a fuel outlet manifold 152 to collect 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 one further exemplary embodiment the stack module can comprise at least two cell stack 103 pairs arranged electrically at a series connection. In further embodiments the module arrangement can comprise 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.

In the embodiments according to the present invention the stack module can comprise the compression structures 116 inside the air tight structure 169. In other embodiments according to the present invention the module arrangement can comprise the compression structures 116 outside the air tight structure 169. The stack module can preferably comprise such a gas flow structure in the manifold 150, 152 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 150, 152 can comprise connection to the inlet pipe and outlet pipe and gas flow holes to the stacks and gas flow holes 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.

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 module 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.

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 . Stack module of solid oxide cell stacks, 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 a gas sealing structure (128) made of a material that isolates electricity, and the stack module comprises a fuel inlet manifold (150) to deliver supply fuel gas (108) to the stacks and a fuel outlet manifold (152) to collect fuel exhaust gas (177) from the stacks, characterized in that the stack module comprises at least two stack bundles, each stack bundle containing a row or a matrix of the stacks (103) together with the fuel inlet manifold (150) supplying fuel for the stacks and the fuel outlet manifold (152) collecting fuel gas from the stacks (103), which are connected to the manifolds (150, 152) parallel in terms of their fuel inlet and fuel outlet, the stack module being located inside an air tight cover (169) comprising needed interfaces into the air tight cover (169) and out from the air tight cover (169), and fuel gas flow characteristics in the manifolds (150, 152) being optimized with the size of the holes connecting the fuel manifold and the stack based on the pressure drop characteristics of the manifolds (150, 152) and stacks connected parallel to that, and the stacks are electrically isolated from the manifold (150, 152) structures with an electrical isolation structure (172) and the other end of the stack is electrically separated from other structures, and the stack module comprises a side sealing solution (166) between the neighboring stacks (103a) in a stack bundle and between the stacks (103b) at the end of the bundle and the air tight cover (169) preventing air flowing from an inlet chamber directly to an outlet chamber without flowing through the stacks, the side sealing solution being electrically isolating, and the stack bundle comprises at least one of a unified structure of an air inlet compartment (106) and a unified structure of an air outlet compartment (176) of the adjacent parallel connected cell stack (103) bundles.

2. Stack module of solid oxide cell stacks according to claim 1 , characterized in that the at least one manifold (150, 152) and the cover parts of the stacks (103) are made of at least one material with the same vicinity of coefficient of thermal expansion.

3. Stack module of solid oxide cell stacks according to claim 1 , characterized in that the stack module comprises balance of plant components (212) as integrated inside the at least one unified structure.

4. Stack module of solid oxide cell stacks according to claim 1 , characterized in that the stack module comprises a first gas seal

(155), a first electrical insulation plate (119) and a second gas seal

(156) between the manifold (150, 152) and the stack (103), and on top side (122) and on bottom side (124) of the cell stack (103) the stack module comprises a second electrical insulation plate (114) and compression structures (116) for the stacks (103), and an air side sealing structure (166) being located between the stacks, and each stack end plate (170) are connected with an electrical connection (173).

5. Stack module of solid oxide cell stacks according to claim 1 , characterized in that the stack module comprises on at least one of the top side (122) and of the bottom side (124) of the cell stack (103) a compensating structure to compensate height tolerances between the stacks (103).

6. Stack module of solid oxide cell stacks according to claim 1 , characterized in that the stack module comprises the stacks (103) as electrically isolated from the manifold (150, 152) structures (150, 152) with electrical isolation structure (172) made from a gas tight material.

7. Stack module of solid oxide cell stacks according to claim 1 , characterized in that the stacks (103) comprise an opening in an endplate (202) facing to the electrical isolation structure (172) for feeding gas into the manifold (150, 152) of the stacks (103).

8. Stack module of solid oxide cell stacks according to claim 1 , characterized in that the stack module comprises connections between the stacks (103) as configurated to achieve voltage levels of 600 V -1200.

9. A stack module method of solid oxide cell stacks, 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, and in the method is used in each stack (103) flow field plates (121 ) made of a material having high electrical conductivity at high temperatures, and in each stack (103) is used a gas sealing structure (128) made of a material that isolates electricity, and in the method is supplied fuel gas (108) to the stacks and is exhausted fuel exhaust gas (177) from the stacks, characterized in that in the stack module method is used at least two stack bundles, each stack bundle containing a row or a matrix of the stacks (103) which are connected to fuel inlet and outlet manifolds (150, 152) parallel in terms of their fuel inlet and fuel outlet, and the stack module is located inside an air tight cover (169) having needed interfaces into the air tight cover (169) and out from the air tight cover (169), and in the method is optimized fuel gas flow characteristics in the manifold

(150, 152) with the size of the holes connecting the fuel manifold and the stack based on the pressure drop characteristics of the manifold (150, 152) and the stacks connected parallel to that, and the stacks are electrically isolated from the manifold structures (150, 152) with an electrical isolation structure (172) and the other end of the stack is electrically separated from other structures, and in method is prevented air flowing from an inlet chamber directly to an outlet chamber without flowing through the stacks with a side sealing solution (166) between the neighboring stacks (103a) in a stack bundle and between the stacks (103b) at the end of the bundle and the air tight cover (169), and is formed at least one of a unified structure of an air inlet compartment (106) and a unified structure of an air outlet compartment (176) of the adjacent parallel connected cell stack (103) bundles.

10. A stack module method of solid oxide cell stacks according to claim 9, characterized in that the at least one manifold (150, 152) and the cover parts of the stacks (103) are made of at least one material with the same vicinity of coefficient of thermal expansion.

11 . A stack module method of solid oxide cell stacks according to claim 9, characterized in that balance of plant components (212) are integrated inside the at least one unified structure.

12. A stack module method of solid oxide cell stacks according to claim 9, characterized in that in the method is located a first gas seal (155), a first electrical insulation plate (119) and a second gas seal (156) between the manifold (150, 152) and the stack (103), and on top side (122) and on bottom side (124) of the cell stack (103) is located a second electrical insulation plate (114), compression structures (116) for the stacks (103), and an air side sealing solution (166) is located between the stacks, and each stack end plate (170) are connected with an electrical connection (173).

13. A stack module method of solid oxide cell stacks according to claim 9, characterized in that in the method is located a compensating structure on at least one of the top side (122) and of the bottom side (124) of the cell stack (103) to compensate height tolerances between the stacks (103).

14. A stack module method of solid oxide cell stacks according to claim 9, characterized in that in the method is electrically isolated the stacks (103) from the manifold (150, 152) structures (150, 152) with electrical isolation structure (172) made from a gas tight material.

15. A stack module method of solid oxide cell stacks according to claim 9, characterized in that in the method is fed gas into the manifold (150, 152) of the stacks (103) through an opening in an endplate (202) facing to the electrical isolation structure (172).

16. A stack module method of solid oxide cell stacks according to claim 9, characterized in that in the method is the connections between the stacks (103) are configurated to achieve voltage levels of 600 V -1200.