Solid oxide cell temperature control system and method of use

Abstract

The object of the present invention is a temperature control system for a solid oxide cell, the cell having a fuel side (100), an oxygen-rich side (102) and an electrolyte element (104) between the fuel side and the oxygen-rich side, the system having a repeating unit structure of a solid oxide cell. The temperature control system comprises a fuel flow field plate structure (107) for the fuel, an oxidizer flow field plate structure (109) for the oxidizer, an electrical contact structure (110) for the fuel and the oxidizer, and a temperature control fluid structure (112) in the flow field plate (121) for the temperature control fluid. The temperature control fluid structure (112) is arranged in the flow field plate (121) separately between the fuel flow field plate structure (107) and the oxidizer flow field plate structure (109). The temperature control system comprises a sealing structure (114) for preventing leakage in the structures (104, 107, 109, 110, 112) and a means (116) for controlling the operating temperature in the solid oxide cell.

Description

[Technical Field]

[0001] Most of the world's energy is produced by oil, coal, natural gas or nuclear power. All these production methods have their own problems, for example, as far as availability and environmental friendliness are concerned. As far as the environment is concerned, oil and coal in particular cause pollution when they are burned. The problem with nuclear power generation is not least the storage of spent fuel.

[0002] Particularly due to environmental concerns, new energy sources are being developed that are more environmentally friendly, eg, more efficient, than traditional energy sources.

[0003] Solid oxide cells operate via chemical reactions in an environmentally friendly process and hold great promise as future energy conversion devices. The intermittency of renewable energy sources poses challenges to the stability of the power grid, calling for increased demand- and supply-side flexibility and new energy storage and conversion technologies. [Background technology]

[0004] Electrochemically active solid oxide cells can be used as fuel cells or electrolysers. Fuel cells generate electricity and heat from a variety of fuels, while electrolysers generate chemicals such as hydrogen, methane, ammonia, and carbon monoxide from steam, CO2, and nitrogen, electricity, and heat. Such cells operating in both modes, as fuel cells and electrolysers, are called solid oxide electrochemical cells (SOECs) or reversible solid oxide cells (rSOCs), or simply solid oxide cells (SOCs).

[0005] As shown in FIG. 1, a solid oxide cell (SOFC) has a fuel side 100, an oxygen-rich side 102, and an electrolyte material 104 therebetween. In a solid oxide fuel cell (SOFC), oxygen 106 is supplied to the oxygen-rich side 102 and reduced to negative oxygen ions by receiving electrons from the oxygen-rich side. The negative oxygen ions are transported through the electrolyte material 104 to the fuel side 100, where they react with fuel 108, typically producing water, carbon monoxide (CO), and carbon dioxide (CO). The fuel side 100 and the oxygen-rich side 102 are connected via an external electrical circuit 111 with a load 110 for the fuel cell operating mode, which draws electrical energy from the system. The fuel cell also generates heat in the reactant exhaust stream. In the electrolysis operating mode, the current flow is reversed, and the solid oxide cell acts as a load to which electricity is supplied. Depending on the electrolysis reaction operating conditions, cell operation can be endothermic, exothermic, or thermoneutral.

[0006] The fuel cell reactions for methane, carbon monoxide, and hydrogen fuels are shown below:

[0007] Fuel side: CH4 + H2O = CO + 3H2 CO+H2O=CO2+H2 H2+O 2- =H2O+2e -

[0008] Oxygen-rich side: O2 + 4e- = 2O 2-

[0009] Net reactions: CH4 + 2O2 = CO2 + 2H2O CO+1 / 2O2=CO2 H2+1 / 2O2=H2O

[0010] In the electrolysis mode of operation (solid oxide electrolysis cell (SOEC)), the reaction is reversed; that is, electrical energy from the power source 110 is supplied to the cell, where water, and often also carbon dioxide, is reduced on the fuel side to form oxygen ions, which migrate through the electrolyte material to the oxygen-rich side where the oxidation reaction occurs. It is possible to use the same solid oxide cell in both SOFC and SOEC modes.

[0011] Prior art solid oxide electrolyzer cells operate at temperatures that allow high temperature electrolysis reactions to occur, typically between 500-1000°C, although temperatures above 1000°C can be useful. These operating temperatures are similar to those of solid oxide fuel cells (SOFCs). The net cell reaction produces hydrogen and oxygen gases. The reaction for one mole of water is:

[0012] Fuel side: H2O+2e - --->2H2+O 2-

[0013] Oxygen-rich side: O 2- --->1 / 2O2+2e -

[0014] Net reaction: H2O ---> H2 + 1 / 2O2

[0015] In the case of co-electrolysis, carbonaceous species are fed to the cell in addition to steam, typically in a ratio favorable for subsequent purification of the resulting gas, for example, by the Fischer-Tropsch process. Carbon dioxide can be reduced directly to carbon monoxide or interact with hydrogen via the water-gas shift reaction to produce carbon monoxide and steam. Solid oxide cells can also be used to produce other types of chemicals directly via electrochemical or chemical reactions. Such chemicals can include, for example, methane and ammonia. Methane can be produced when steam and carbonaceous species are fed to a solid oxide electrolyzer, and ammonia can be produced when steam and nitrogen are fed. The reaction rate of chemical production depends on the feed current, fuel and air-side flow rates, fuel and air-side gas concentrations, fuel and air-side pressures, and fuel and air-side temperatures.

[0016] In solid oxide fuel cell (SOFC) and solid oxide electrolyte (SOE) stacks, where the flow direction of the fuel-side gas is relative to the oxygen-rich side gas within each cell and relative to the flow direction of the gas between adjacent cells, the stacks are coupled through different cell layers of the stack. Additionally, the fuel-side gas or the oxygen-rich side gas, or both, can pass through more than one cell before being exhausted, and multiple gas streams can be split or combined after passing through the primary cell and before passing through the secondary cell. These combinations help increase current density and minimize thermal gradients across the cells and stacks.

[0017] High operating temperatures in SOC cells and systems pose material-related challenges in terms of thermomechanical forces, material properties, chemical stability, and uniformity of operating conditions. These aspects impose practical constraints on the feasible SOC cell, stack, and module sizes. Therefore, scaling of the technology for large-scale installations typical of SOEC applications depends primarily on the multiplication of cells, stacks, and SOC modules. Therefore, minimizing the cost of each multiplication unit at all levels is crucial to reduce the overall cost.

[0018] SOFCs deliver a voltage of approximately 0.8 V during normal operation, while the typical operating voltage for SOE cells is approximately 1.3 V. To increase the total voltage output, SOCs are usually assembled into stacks where the cells are electrically connected via flow field plates (also called interconnect plates, bipolar plates). The desired voltage level determines the number of cells required.

[0019] The bipolar plates separate the anode and cathode sides of adjacent cell units while allowing electronic conduction between the anode and cathode. The interconnect, or bipolar, plates typically contain multiple channels for passing fuel gas on one side of the 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 to the fuel outlet of the cell unit. Similarly, the flow direction of the oxidant gas (i.e., air) is defined as the substantial direction from the inlet to the outlet of the cell unit.

[0020] Traditionally, cells are stacked on top of each other with complete overlap, resulting in a stack with co-flow, for example, with all fuel and oxidant inlets on one side of the stack and all fuel and oxidant outlets on the other side. One feature that affects the temperature of the structure during operation is steam reforming of the fuel supplied to the cells. Steam reforming is an endothermic reaction, cooling the fuel inlet edge of the cell. Due to the exothermic nature of the electrochemical process, the outlet gas leaves at a higher temperature than the inlet temperature of the inlet gas. When endothermic and exothermic reactions are coupled in a SOFC stack, significant temperature gradients are created across the stack. To maximize overall system efficiency, it is desirable to simultaneously minimize flow rates on both the fuel and oxygen-rich sides. Large thermal gradients induce highly undesirable thermal stresses within the stack, which are accompanied by differences in current density and electrical resistance. The performance and lifetime of an SOFC stack can be maximized if a temperature profile as uniform as possible can be maintained across the stack. Therefore, the thermal management challenge of SOFC stacks lies in reducing thermal gradients sufficiently to avoid unacceptable stresses and maximize electrical efficiency through a uniform current density profile.

[0021] In prior art embodiments, protective coating of flow field plates is often required to slow metal corrosion. Generally, there are two corrosion mechanisms that cause aging in solid oxide fuel cells and electrolyzers. One mechanism is the formation of an oxide layer on the metal surface, which has poor electrical conductivity. The other mechanism is the precipitation of chromium compounds evaporated from the metal onto the active surface of the unit cell, which reacts with the electrochemically active material, weakening the electrochemical, chemical, electrical conductivity, and / or gas permeability of the active material. Oxide structures are commonly used as protective coatings to slow oxide diffusion onto the metal surface and, on the other hand, to slow the diffusion of alloying atoms and compounds through the oxide structure. The cost of protective coatings typically accounts for a significant portion of the total cost of a cell stack and is influenced by the manufacturing process, materials, and surfaces to be protectively coated. Furthermore, it is undesirable to extend the protective coating into areas used to seal the cell stack, as the glass, ceramic materials or minerals commonly used as sealants may react with the protective coating and cause aging effects in the cell stack structure, for example, due to increased gas leakage and / or increased undesirable electrical conductivity.

[0022] SOC modules contain dozens to hundreds of SOC stacks, support structures, thermal insulation, reactant transport and distribution structures, instrumentation, and electrical and reactant interfaces to applications or other modules. Because high-temperature interfaces are costly, space-consuming, and potentially constitute ignition sources, it is also beneficial to include heat exchange within the module to reduce the temperature of the reactant interfaces. Additionally, SOC modules require internal or external means to facilitate safe startup and shutdown.

[0023] The advantage of SOC is its high performance in the conversion process. In small-scale unit cell tests, such structures can generate power densities exceeding 2 W / cm², still demonstrating extremely high energy conversion efficiency compared to competing technologies, such as other electrochemical cell technologies based on low-temperature solutions, such as polymer electrolytes and alkaline technologies, and other conversion technologies based on the Carnot cycle, such as turbines and engines. The cell generates a thermal power density equivalent to the electrical power density in fuel cell mode. The current challenge with SOC technology to reach this high power density is that heat must be dissipated into the fuel and oxidant flows or transferred via conduction or radiation from the electrochemically active sites to avoid overheating the SOC structure. The heat transfer challenge is most pronounced at the stack level, where the primary heat transfer mechanism is convective heat transfer to the fuel and air flow. The SOC stack consists of the SOC, a flow field plate structure for the fuel, a flow field plate structure for the oxidant, electrical contact structures for the fuel and oxidant, a protective coating for the flow field plate structure, and a sealing solution to ensure reactant gases do not flow over the electrochemically active SOC region. In a SOC stack, a flow field plate supplying fuel to the opposite SOC can also supply oxidant to an adjacent SOC in the stack. Another flow field plate supplying oxidant to the same SOC can also supply fuel to a third SOC. This type of structure is called a single repeat unit (SRU) structure. Typical power densities for SOC stacks with this structure range from 0.1 to 0.4 W / cm². The heat generated, along with limited heat transfer characteristics, leads to temperature increases and large temperature gradients in the electrochemically active SOC structure. The maximum power density is typically limited by the maximum operating temperatures of not only ceramic cells but also steel-based interconnect components, coatings, and sealing solutions in stacks. Absolute temperature gradients can be detrimental to SRUs due to issues related to corrosion, chemical stability, reduced mechanical strength properties, and increased stress levels.However, unit cells can provide power densities that exceed today's stack values, with values ​​of up to 2 W / cm2 reported in the open literature. If power density can be increased, this can lower the cost per cubic meter of electricity produced or chemical species produced.

[0024] SOC in electrolysis mode can be connected to existing industrial processes that generate high-temperature exhaust gases, such as pulp and paper production, steel production, and energy production. These exhaust gases can be used to generate steam from liquid water and superheat it to the operating temperature of the electrolysis stack. The same exhaust gases can also be used to effectively heat the SOC stack to its operating temperature and provide heat for the endothermic electrolysis reaction. Because exhaust gases typically contain high concentrations of impurities such as sulfur and halides, these gases cannot be directly fed to the electrochemically active elements without extensive gas cleaning processes.

[0025] Temperature control in SOC stacks today is primarily governed by power density, fuel and oxygen enthalpy flow rates, and material selection, including thickness and heat transfer properties. A typical solution in polymer electrolyte fuel cells and polymer electrolyte electrolysis stack construction is to provide a third fluid used for heat transfer and balancing purposes. Typical fluids are water, alcohol, and oil. The same solution is not possible in SOC technology due to the high operating temperatures of over 800°C. At these temperatures, potential fluids in liquid form are toxic or extremely corrosive.

[0026] Prior art document CN1339181A (Patent Document 1) presents an embodiment in which air acts as an oxidant for a fuel cell stack and simultaneously acts as a cooling medium to help remove waste heat generated during operation of a high temperature fuel cell stack operating at approximately 1000°C. [Prior art documents] [Patent documents]

[0027] [Patent Document 1] CN1339181A Summary of the Invention

[0028] SUMMARY OF THE INVENTION It is an object of the present invention to provide a solid oxide cell system and its operation that increases energy production capacity, improves energy production efficiency, and extends the life of the solid oxide cells.

[0029] This is achieved by a temperature control system for a solid oxide cell, the cell having a fuel side, an oxygen-rich side, and an electrolyte element between the fuel side and the oxygen-rich side, the system having a repetitive unit structure for the solid oxide cell, the temperature control system having a fuel flow field plate structure for the fuel, an oxidizer flow field plate structure for the oxidizer, electrical contact structures for the fuel and the oxidizer, and a temperature control fluid structure within the flow field plate for a temperature control fluid, the temperature control fluid structure within the flow field plate In the flow field plate (121), separately disposed between the fuel flow field plate structure and the oxidizer flow field plate structure; In liquid form, the temperature control fluid comprises at least one of a liquid including a salt solution, a supercritical fluid, and a phase change material; and in gas form, the temperature control fluid is reacting by at least one of an endothermic reaction and an exothermic reaction; The temperature control system comprises: a sealing means for preventing leakage in the structure; Temperature control: Over 350°C by optimizing fluid temperature and flow rate and means for controlling the operating temperature within the solid oxide cell.

[0030] The present invention also focuses on a method for temperature control of a solid oxide cell, comprising flowing a fuel through a fuel flow field plate structure, flowing an oxidant through an oxidant flow field plate structure, forming electrical contact structures for the fuel and the oxidant, and flowing a temperature control fluid through a temperature control fluid structure separately disposed within the flow field plate between the fuel flow field plate structure and the oxidant flow field plate structure; In liquid form, the temperature control fluid comprises at least one of a liquid, including a salt solution, a supercritical fluid, and a phase change material, and in gas form, the gas reacts by at least one of an endothermic reaction and an exothermic reaction. , a sealing structure is formed to prevent leakage within the structure, Temperature control: Over 350°C by optimizing fluid temperature and flow rate The operating temperature within the solid oxide cell is controlled.

[0031] The present invention is based on a fuel flow field plate structure for fuel, an oxidizer flow field plate structure for oxidizer, an electrical contact structure for the fuel and the oxidizer, a temperature control fluid structure in the flow field plate for the temperature control fluid, and a sealing structure to prevent leakage within the structure, and the present invention is further based on controlling the operating temperature within the solid oxide cell.

[0032] An advantage of the present invention is that it allows for the utilization of higher power densities in the same reaction area, thereby reducing the cost of electricity and chemicals produced. [Brief explanation of the drawings]

[0033] [Figure 1] 1 shows a typical repeating cell structure.

[0034] [Figure 2] 1 illustrates an exemplary arrangement of flow field plates for a fuel cell stack.

[0035] [Figure 3] 1 illustrates an exemplary cell stack structure according to the present invention.

[0036] [Figure 4] 1 illustrates an exemplary fuel cell system according to the present invention.

[0037] [Figure 5] 1 illustrates an exemplary electrolysis cell system according to the present invention.

[0038] [Figure 6] The flow direction combinations are shown. DETAILED DESCRIPTION OF THE INVENTION

[0039] By lowering the operating temperature below 800°C, liquid fluids such as salt solutions, supercritical fluids, phase change materials, and gaseous fluids such as helium can begin to be utilized for thermal control purposes. Such a configuration requires an additional flow path structure located between the fuel and oxidant sides of the flow field plate. A temperature control fluid flow is applied between these reactant flows, separated from the oxidant and fuel flows. The temperature control fluid composition and flow rate can be optimized so that the fluid transfers heat in the range of 2 W / cm2. While the operating temperatures of systems according to the present invention are not limited to below 800°C, they can vary, for example, between 350°C and 1000°C, with lower temperatures also being utilized during startup and shutdown situations.

[0040] Electrochemically active solid oxide cells can be used as fuel cells or electrolyzers. Fuel cells generate electricity and heat from a variety of fuels, while electrolyzers generate chemicals such as hydrogen, methane, ammonia, and carbon monoxide from water vapor, CO2, and nitrogen, electricity, and heat. Such cells, which operate as both fuel cells and electrolyzers, are called solid oxide electrochemical cells (SOECs), reversible solid oxide cells (rSOCs), or simply solid oxide cells (SOCs).

[0041] According to the present invention, a fuel cell or electrolyzer stack has at least two single repeat structures, as shown in FIG. 1. The single repeat structure includes at least one electrochemically active electrolyte element structure, including a fuel side, an electrolyte therebetween, and an oxygen-rich side, arranged between at least two flow field plates, one distributing oxygen-rich gas to the oxygen-rich side of the electrolyte element structure and the other distributing fuel gas to the fuel side of the electrolyte element structure, and at least one sealing means sealing the gas atmosphere in the intended enclosure. The flow field plates have at least one inlet orifice for fuel gas, temperature control fluid, and / or oxygen-rich gas, and at least one outlet orifice for fuel gas, temperature control fluid, and / or oxygen-rich gas. The oxygen-rich side can be realized in a so-called open-air structure, in which there are no inlet or outlet orifices.

[0042] The system preferably includes a repeating, i.e., single repeat unit (SRU) structure for the solid oxide cells. An example of a repeating stack 103 structure is shown in FIG. 3, in which fuel 108 flows through a fuel flow field plate structure 107, oxidant 106 flows through an oxidant flow field plate structure 109, and temperature control fluid 117 flows through a temperature control fluid structure 112. The fuel flow field plate structure 107, the oxidant flow field plate structure 109, and the temperature control fluid structure 112 within the flow field plate 121 can be arranged in a co-flow, counter-flow, or cross-flow geometry, or a combination of two or three of these flow geometries for the flow of fuel 108, oxidant 106, and temperature control fluid 117. Various examples of different combinations of flow directions are shown in the exemplary FIG. 6. In a co-flow configuration (FIG. 6a), all flows have essentially the same direction. In counterflow configurations (b, c, d), the flow directions differ from each other by essentially 180°, while in crossflow configurations (e, f, g, h, i, j), at least one flow direction differs from the other flow directions by essentially 90°.

[0043] FIG. 2 illustrates an exemplary flow field plate 121 of a SOC. A complete fuel cell stack includes several plates 121 arranged consecutively with one another in the manner shown. The plates in this exemplary embodiment are rectangular and symmetrical. An electrolyte element structure 104, which includes an electrolyte layer between the anode and cathode electrodes, is positioned between the plates 121 approximately in the center of the plates. The electrolyte element structure 104 can be any suitable electrolyte element structure and will not be described in further detail herein. The flow field plate 121 and the electrolyte element structure 104 are sealed by a sealing means 114. The purpose of the sealing means 114 is to ensure that the oxidant and fuel do not mix directly without fuel cell reaction within the electrochemically active area, that the fuel and oxidant do not leak from the electrochemical cell, that adjacent electrochemical cells do not come into electronic contact with each other, and that the oxidant and fuel are delivered to the desired flow field plate surface 121. The two opposing flow field plates 121 and the electrolyte element structure 104 therebetween form a single repeating structure. The flow field plate 121 is a planar thin plate made of a metal alloy, ceramic material, cermet material, or other material capable of withstanding the chemical, thermal, and mechanical stresses present in a fuel cell. According to the present invention, the flow field plate 121 includes inlet and outlet orifices located on the edges of the plate 121. In this example, the plate 121 is rectangular, with the flow orifices located on the slightly shorter edges. Both edges have three inlet and outlet orifices 109 for an oxygen-rich gas (in the following exemplary embodiment, air), an inlet and outlet orifice 107 for a fuel, and an inlet and outlet orifice 112 for a thermal control fluid. The oxygen-rich gas can be any gas or gas mixture that contains a measurable amount of oxygen at the outlet. In the case of an electrolysis cell configuration, there may be no supply on the oxygen-rich gas side, or the inlet gas may be a non-oxygen gas such as nitrogen, helium, or argon. On both edges 19, orifices can be arranged in the order of first fuel 107 and then thermal control fluid 112.The surfaces of the first side (top side in FIG. 2 ) and second side (below surface, not shown) around the edge of the flow field plate can be shaped to allow for an efficient seal, which confines contoured surfaces in the center of the flow field plate with specific contours for directing the fuel gas 108, air 106, and thermal control fluid 117 onto the surface of the electrolyte element 104. Note that the sealing means 114 showing the gas flow passages 106, 108, and 117 in FIG. 2 is also used to refer to the surface and contoured surface 160 of the opposite flow field plate 121 facing the sealing means 114.

[0044] The number of orifices for directing gas flow through the fuel cell stack can vary, as can how the gas flows are arranged. The basic idea is that the orifices on the superposed flow field plates 121 can be arranged so that their positions coincide and orifices in the same line form gas manifold channels through the stack. Sealing means 114 are used to prevent fuel, air, and thermal control fluid from being delivered to the wrong layer between the electrolyte element and the flow field plate. Sealing means are positioned to surround each orifice on the flow field plate 121. The flow field plate 121 and sealing elements 114 are used to form ducts (i.e., channels) through the entire fuel cell stack. The orifices in the flow field plates are overlapped to form such ducts.

[0045] The number of orifices used for gas distribution may vary depending on the fuel cell design. The minimum number is one inlet and one outlet orifice for gas. Using more orifices allows for more flow patterns, but of course the design becomes more complex. According to one embodiment, the fuel flow, air flow, and thermal control fluid can be arranged transverse to one another. This can be done, for example, by rotating every other flow field plate by 90°. The rectangular shape described above can be used to simplify the manufacturing and assembly process. However, any desired geometric shape, such as polygonal, circular, or elliptical, can be used.

[0046] FIG. 3 shows a solid oxide cell (SOC) temperature control system according to the present invention. The cell includes a fuel side 100, an oxygen-rich side 102, and an electrolyte element 104 between the fuel side and the oxygen-rich side. The temperature control system includes a fuel flow field plate structure 107 for the fuel, an oxidizer flow field plate structure 109 for the oxidizer, and an electrical contact structure 110 for the fuel and the oxidizer. The system according to the present invention includes a temperature control fluid structure 112 within a flow field plate 121 for the temperature control fluid. The temperature control fluid structure 112 within the flow field plate 121 can be separately positioned between the fuel flow field plate structure 107 and the oxidizer flow field plate structure 109. The system also includes a sealing structure 114 to prevent leakage within the structures 104, 107, 109, 110, and 112. The sealing structure 114 can include, for example, compressed joints including welding, soldering, metal bracing, glass bonding, and gasket materials. The temperature control system according to the present invention may further comprise means 116 for controlling the operating temperature within the solid oxide cell.

[0047] The system according to the present invention may include means 116 for controlling the operating temperature in the solid oxide cell, for example below 800°C. In one embodiment, the control may be performed by optimizing the temperature and flow rate of a temperature control fluid. The means 116 may be performed by enthalpy flow rate control, as shown in Figures 4 and 5. Figure 4 illustrates an exemplary fuel cell (SOFC) system according to the present invention, and Figure 5 illustrates an exemplary electrolysis cell (SOEC) system according to the present invention.

[0048] The sum of all enthalpy streams in the system is zero. If only one enthalpy stream is unknown, it can be calculated based on the others. In one embodiment, the enthalpy stream can be calculated based on measurements already needed for other purposes in SOC (SOFC or SOEC) unit control. Gas composition and its measurements, including methane CH content, play an important role when calculating and controlling enthalpy flow in SOFC systems. Known enthalpy feeds and utilized measurements in SOFC anode recycle type units include: A) air feed-in measurements, such as air feed-in temperature, flow rate, and humidity measurements; B) fuel 132 and start gas 144 flow-in measurements, such as incoming fuel 132 flow rate and temperature measurements; and C) exhaust feed-out information, which is preferably a combination of exhaust temperature measurement information and process calculations of composition and flow rate. Process calculations can be performed from the system inflows, for example, by assuming all fuel is combusted in the burner 142. D) power production information 110, which may be based on measured voltage and / or current; E) system heating information, which may be based, for example, on measured power consumption from at least one electric heater 128; F) fan and / or compressor heating information for the gas lines 132 and 154, which may be based, for example, on efficiency information provided by the manufacturer and / or on measured power consumption for at least one fan and / or compressor; G) heat loss information 103, which may be calculated, for example, as described later in this description; H) recycle loop gas concentration information, temperature measurements and flow measurements 148; and I) flow rates and temperatures of enthalpy flow control fluids 116, 150, 152.

[0049] The means 116 for controlling the operating temperature within the solid oxide cell is configured to minimize the energy supplied to the cell system by minimizing the amount of fuel and air used. This can be achieved by maximizing the power density per area in the SOC reaction, which maximizes heat transfer to the temperature-control fluid. The specific heat capacity of the temperature-control fluid material is thereby maximized by using at least one of a liquid fluid, a phase change material, a gas with a high specific heat capacity, and a reactive gas, such as a reformed gas. The specific heat capacity can also be increased by maximizing heat transfer from the SOC element to the temperature-control fluid by positioning the fluid near the electrochemically active reaction interface. Furthermore, to maximize the specific heat capacity, the heat transfer area can be increased, the thickness of the structure can be maximized, the size of the flow channels can be maximized, and the flow channel morphology can be optimized. Additionally, the flow characteristics can be engineered to achieve high heat capacity characteristics of the flow, for example, by creating turbulence. The flow morphology can be modified, for example, by the specific morphology of the flow channels.

[0050] A preferred exemplary method for determining the enthalpy balance of a fuel cell system that supplies fuel to the fuel cell system and provides an anode 100-side recirculation flow of reactants will now be described. Enthalpy feed-in flow information is generated from information obtained by performing one or more of the following method steps: measuring air feed-in to generate air feed-in information; measuring water flow-in to generate water flow-in information; measuring exhaust feed-out to generate exhaust feed-out information; measuring electrical power to generate electrical power production information; measuring temperature conditions to generate fuel cell system heating information; and generating fuel cell system heat loss information. The measurements can be performed, at least primarily, using common and relatively inexpensive measurement equipment without requiring high accuracy. Enthalpy feed-in flow information can be provided by obtaining information about gas lines, for example, from fans, compressors, etc. Exhaust feed-out information can be provided by calculating information from the fuel cell system inflow based on the assumption that essentially all fuel is combusted in an afterburner. Additionally, the method can measure the power consumption of at least one electric heater to generate fuel cell system heating information.

[0051] Based on the formed enthalpy feed inflow information, the enthalpy flow information is summed and it is detected that the sum of the enthalpy flow summation information is 0 or essentially close to 0, thereby achieving enthalpy flow information that provides enthalpy balance information of the fuel cell system. The methane content information of the fuel feed is determined based on the enthalpy balance information obtained by summing the enthalpy flow information. One enthalpy flow information can be determined by calculation based on the enthalpy flow summation information.

[0052] In the exemplary fuel cell system according to the present invention shown in FIG. 4, a temperature control fluid 117 (FIG. 1) is delivered to the temperature control fluid structure 112. The chemistry of the temperature control fluid 117 is described in more detail in the next section. The fluid 117 can be controlled by a means 116 for controlling temperature, pressure, and flow rate. An external control fluid 150 can be delivered to the means 116. The external control fluid 150 has the chemistry and temperature necessary to achieve the target chemistry and temperature of the temperature control fluid 117 and thus the target operating temperature of the fuel cell system. A controlled desired outlet fluid 152 can also be delivered from the means 116, as needed. The means 116 optimizes the temperature of the temperature control fluid 117. In addition, the means 116 can optimize the flow rate, as this also affects the operating temperature of the fuel cell system. The outlet stream 152 can be further connected to any external or internal system that utilizes heat. The internal system can include a temperature control unit, such as a heat exchanger for heating a process gas. The external system may include a thermodynamic cycle such as a district heating network, a power cycle or a heat pump cycle.

[0053] FIG. 4 shows the electrical load 110 in the stack 103 configuration. A fuel supply and control 132 supplies fuel to the fuel cell system. A startup control 144 performs startup operations for the system. The fuel is supplied to a recycler 148 for fuel recycling operations. The gas recycling function can be performed by a mechanical pump, a compressor-type solution, or an ejector solution. A reformer 146 receives fuel and performs a reforming reaction on the fuel to reform it into a suitable form for supply to the fuel side 107 (anode side) of the fuel cell system. The reforming reaction is typically in an equilibrium state defined by the inlet flow rate, concentration, pressure, temperature, and catalyst type used. In another embodiment, for example, if ammonia (NH4) is used as fuel, the reaction is a decomposition reaction rather than a reforming reaction, so a reformer is illustrated in FIG. 4.

[0054] An air supply control 154 supplies oxygen to the fuel cell system via a temperature control 128 to the oxygen side 109. The outlet stream has a burner that performs an afterburning reaction on the exhaust gases that are discharged to an outlet 156 via the temperature control 128.

[0055] In addition to the described means 116 and associated fluids 117, 150, 152, other fuel system pressure and temperature conditions may also be controlled with the aid of the means 116 and associated fluids 117, 150, 152 so that target operating temperatures are more effectively achieved.

[0056] FIG. 5 illustrates an exemplary SOEC system according to the present invention, in which the temperature flows and associated fluids 117, 150, and 152 operate similarly as described in connection with FIG. 5, but the temperatures are controlled based on electrolysis mode conditions to achieve the target operating temperature of the electrolysis system. A power unit 140 provides power to the stack 103. Gases (e.g., air, oxygen (O), carbon dioxide (CO), and nitrogen (N)) are supplied to the oxygen side 109 from the gas control unit 126 via temperature control 128. A reactant (i.e., water (H), carbon dioxide (CO)) supply control 132 receives water or a water and carbon dioxide mixture from the reactant cleaning unit 134 and supplies it to a steam generator 136 to generate steam. The generated steam is supplied to the fuel side 107 via temperature control unit 138. From the fuel side, steam is circulated via the temperature control unit 138 and further routed to the product gas outlet 122 via a possible pressure control unit 120. The product gas may be, for example, hydrogen H, ammonia, methane, and / or carbon monoxide. In one embodiment, the water vapor may be recycled to the reactant supply control unit 132 or the steam generator 136. From the oxygen side 109, oxygen is supplied via a temperature control unit 128 and possibly a pressure control unit 120 to an oxygen outlet 124.

[0057] The pressure and temperature conditions of the described means 116 and associated fluids 117, 150, 152, as well as other electrolysis system conditions, can be controlled with the aid of the means 116 and associated fluids 117, 150, 152 such that the target operating temperature is more effectively achieved.

[0058] Temperature control fluids can be in liquid form, including, for example, salt solutions and molten metals. Molten salts based on fluoride (e.g., FLiNaK), chloride (e.g., MgCl-KCl), carbonate (e.g., 60% LiCO and 40% KCO or NaCO), and nitrate (e.g., NaNO-KNO [40-60 wt%], LiNO-NaNO-KNO [30-52-18 wt%]) compounds and molten metals such as Wood's metal and lead-bismuth eutectic alloys are examples of heat transfer fluids that can be used at temperatures above 350°C. Heat transfer fluids can also be gaseous compounds, which can be inert gases such as argon, helium, or nitrogen. The heat transfer fluid may be a reactive compound or mixture of gaseous solutions composed of binary, ternary, or more complex gas mixtures capable of chemically reacting in the temperature range between ambient and 900°C, a typical operating temperature range for solid oxide cell processes, including electrochemically active cells as well as afterburner reactors that convert unused chemical energy into heat. Such gas mixtures may include diatomic systems, such as nitrogen (N), hydrogen (H), and combinations thereof (in the form of molecular nitrogen (N), molecular hydrogen (H), and ammonia (NH)), triatomic systems, such as carbon (C), hydrogen (H), and oxygen (O), and combinations thereof (in the form of methane (CH), carbon monoxide (CO), carbon dioxide (CO), water (H), and hydrogen (H)). The temperature control fluid may also be a phase change material that undergoes a phase change from solid to molten or liquid phase, from molten or liquid phase to gas phase, or from solid to gas phase. The solid-liquid phase change material can include various salt solutions containing stabilizers, such as eutectic K2CO3-Na2CO3 salt with MgO as a morphological stabilizer, and encapsulation and microencapsulation materials, such as potassium nitrate and Al-Si alloys. The temperature-control fluid can also be a phase change fluid in a critical, supercritical, or ultra-supercritical state. Examples of such fluids that can be used include carbon dioxide, water, and hydrocarbons, such as alkanes, cycloalkanes, benzene, and mixtures thereof.In principle, an effective heat transfer fluid is a gas, liquid, solid, or combination thereof that participates in the heat transfer for cooling, transporting and storing thermal energy on one side of the process, and heating on the other side of the process.

[0059] Different heat transfer fluids can be coupled to different thermal processes. For example, molten salts, molten metals, and phase change materials have been used and developed for photovoltaic applications, where radiant heat from the sun is used to heat the molten substance or phase change material. In such processes, a solid oxide electrolyzer, along with a temperature control fluid, can be coupled to a concentrated solar power plant (CSP) enthalpy control unit 116, and an electrochemical process takes place in an endothermic reaction zone, enabling greater than 100% conversion efficiency for hydrogen production from water vapor. In such applications, the heat transfer fluid is heated in the CSP 116 by concentrated solar radiation and releases heat for the electrochemical reaction in the TCF 112 for the fuel side 107 and oxygen-rich side 109 fluid streams. A photovoltaic application operating as the CSP 116 can also be coupled to a fuel cell via a heat transfer fluid. In this case, the molten solution or phase change fluid in the CSP 109 enhances heat transfer compared to a typical solid oxide fuel cell configuration without a temperature control fluid circuit, allowing the fuel cell to operate at a higher power density. As an example, the specific heat capacities of KNO3 and air are the same order of magnitude (~1 kJ / kg.K) at 750 K, but the density difference at the same temperature is about four orders of magnitude greater for the molten solution (~1700 kg / m3) than for air (0.5 kg / m3). Therefore, the ability to transfer heat for the same volume of material in a salt solution is also about four orders of magnitude greater than for air. Typical phase change materials (mixed chloride salts of anhydrous calcium chloride and sodium chloride) have latent heats in the range of 90 kJ / kg, dramatically enhancing heat transfer.

[0060] An example of a process in which an inert gas or critical fluid can be coupled with a solid oxide cell stack is a high-temperature nuclear reactor. In such a reactor, helium or carbon dioxide can be used as a heat transfer fluid, either indirectly via a heat exchanger or directly coupled to an electrolyzer or fuel cell process via the TCF 112, respectively, in the enthalpy control unit 116, to provide either a heating or thermal stabilization function for the electrochemical device. When such a process is performed with the aid of a liquid-to-gas phase change fluid, the process is called a Rankine cycle. Other phase change fluid cycles include the Kalina cycle, the hygroscopic cycle, and regenerative cooling. In addition, refrigeration cycles can be coupled with a solid oxide cell stack structure via a temperature control fluid, with or without a phase change fluid.

[0061] An example of a process in which a chemical reaction can be used for heat balancing purposes may include the Haber process. In this loop, the enthalpy control unit 116 is used to produce ammonia from nitrogen and hydrogen. This process requires heat generated by the fuel cell reaction. In the TCF 112, ammonia is converted to nitrogen and hydrogen. This reaction is endothermic and therefore consumes heat, thus helping to balance the heat of the fuel cell reaction. When the enthalpy flow diagram is modified, heat can be generated for the electrolysis reaction and dissipated in the ammonia decomposition reaction. Other similar chemical reaction loops, such as a steam reforming-methanation reaction loop for methane or a water gas shift reaction loop for carbon monoxide, carbon dioxide, and water, can also be utilized. The advantage of using chemical reactions for heat transfer purposes is related to the high reaction enthalpy of these reactions. For example, the enthalpies of the Haber process (-90 kJ / mol), water gas shift reaction (-40 kJ / mol), and methanation reaction (-206 kJ / mol) are all exothermic and therefore generate heat for the electrochemical processes, and their counter-endothermic reactions can balance the exothermic electrochemical reactions in the TCF 112. In such configurations, catalytically active materials within the TCF 112 may be advantageous. Such catalysts may be applied to the structure by a coating deposited on the surface of the channels 112 or as separate catalyst particles inserted into the gas channels 112.

[0062] The system according to the present invention can include a protective coating 115 for the flow field plate structure on the metallic interconnect structure, for example, a flow field plate structure made from a steel structure. The protective coating can be applied to the air side 108, the fuel side 107, and the temperature control fluid side 117. The coating can preferably be selected according to at least one property of the fuel, the oxidant, the temperature control fluid, and the metallic interconnect structure and material. In some embodiments, the protective coating 115 has catalytic properties.

[0063] The greatest potential for the protective coating 115 on the air side of the solid-state cell structure is a ceramic material with the general formula spinel (A,B)3O4, where A and B are metal cations. Current interest in SOFC use is in Mn 2-x Co 1+x The focus has been on O4-based spinels (x=0...1), which provide better Cr barrier properties against migrating Cr species and the formation of more chemically stable (Mn,Co,Cr)3O4 spinels with enhanced electrical conductivity compared to the Cr oxide layer that forms on steel structures without a protective coating structure. Mn-Co-O spinels are characterized by the Mn 1+x Co 2-x In the O4 system, when the stoichiometric coefficient x is between 0.3 and 0.9, it has cubic and tetragonal crystal structures. 2-x Co 1+x O4 spinel, in relation to its chemical composition, has acceptable electrical properties with electrical conductivity varying from 15 to 68 S / cm in the temperature range of 700...800°C. MnCo 2-x Fe x Small amounts of iron doping likely enhance the electronic conductivity by obtaining O4. Co cations have a stronger tendency to occupy tetrahedral sites than Mn cations, and Fe cations have a weaker tendency to occupy tetrahedral sites than Co and Mn cations, so doping is likely to enhance the electronic conductivity of the (Co 2+ , Mn 2+ , Fe 3+ )(Co 2+ , Co 3+ , Mn 3+ , Mn 4+ , Fe 2+ , Fe 3+ )2O4 cation distribution. The existence of mixed valence states at the octahedral sites in the (A,B)3O4 spinel system leads to the formation of MnCo 1.9 Fe 0.1 Activation energy of O4 (E a ) is 0.38 eV, i.e., the E of MnCo2O4 is 0.44 eV a As a result, MnCo 1.9 Fe 0.1 O4 at 38...72 S / cm and MnCo at 800°C1.8 Fe 0.15 Electronic conductivities of 85 S / cm can be achieved with O4. Several other spinels, such as CuFe2O4 and CuMn2O4, have also shown great interest in achieving high electrical conductivity. Spinel materials can be further doped with rare earth metals, such as Ce and Y, which have been shown to further stabilize the coating structure by increasing the bond strength between the coating and the steel and to reduce chromium mobility in the coating structure. The same materials can also be used to protect the fuel side of the solid oxide structure to prevent oxide scale growth and nickel diffusion from the active fuel electrode into the metal structure.

[0064] A contact coating 115 is applied between the active electrode 100, 102 structure and the cell structure plate 121 to reduce contact losses between the interfaces and increase the lateral conductivity of the coating solution 115. The contact coating material is typically the same as the active electrode material, i.e., on the air side, the coating material is typically (La,Sr)MnO 3-δ , (La,Sr)(Co,Fe)O 3-δ , (La,Sr)CoO 3-δ or La(Ni,Fe)O 3-δ , Sr(Ti,Fe)O 3-δ On the fuel side, the most commonly used contact material is nickel deposited in the form of NiO, although other materials such as titanates can also be used for the purpose. To be effective, the electrical conductivity needs to be higher for the contact material used compared to the protective coating material. For example, (La,Sr)CoO 3-δ is >1000 S / cm over the typical solid oxide cell operating temperature range, La(Ni,Fe)O 3-δNi has an electrical conductivity of approximately 300 S / cm and Ni>>1000 S / cm, both of which are approximately an order of magnitude higher than typically used protective coating spinel materials. Typical layer thicknesses of the contact coating 162 are a few micrometers to tens of micrometers. The microstructural and surface properties of the contact coating 115 layer can be varied according to the active electrode surface structure to maximize contact points and bonding between the contact layer 115 and one of the active electrode 100, 102 structures.

[0065] The temperature-control fluid structure can be coated with standard industrial oxide metal coatings, including, for example, aluminum oxide, titanium oxide, zirconium oxide, yttrium oxide, cobalt oxide, copper oxide, manganese oxide, iron oxide, chromium oxide, silicon oxide, nickel oxide, and their compounds. If the coating is made of aluminum oxide and Li2CO3, they react with the temperature-control fluid solution to produce, for example, LiAlO2. The temperature-control fluid structure can also include catalytically reactive compounds and structures that can be selective for different chemical processes. The coating can be applied to the metal interconnect surface by any application method, including, for example, slurry methods, physical and chemical deposition processes, and high-temperature deposition processes with or without reactive subprocesses. In the case of catalytically active structures, the catalyst can be in the form of discrete particles within the gas-fluid channels 112.

Claims

1. A temperature control system for a solid oxide cell, the cell having a fuel side, an oxygen rich side, and an electrolyte element between the fuel side and the oxygen rich side, the temperature control system having a repeating unit structure of the solid oxide cell, the temperature control system having a fuel flow field plate structure for a fuel, an oxidant flow field plate structure for an oxygen rich gas, electrical contact structures for the fuel and the oxidant, and a temperature control fluid structure in the flow field plate for a temperature control fluid, the temperature control fluid structure in the flow field plate being configured to include a fuel flow field plate structure and an oxidant flow field plate structure in the flow field plate. and a temperature control fluid in liquid form comprising at least one of a liquid including a molten salt, a supercritical fluid, and a phase change material, and in gas form, the temperature control fluid gas is reacting by at least one of an endothermic reaction and an exothermic reaction, the temperature control system comprising: a sealing structure for preventing leakage in the fuel flow field plate structure, the oxidant flow field plate structure, the electrical contact structure, and the temperature control fluid structure; and a means for controlling an operating temperature in the solid oxide cell above 350°C by optimizing a temperature control fluid temperature and flow rate. Solid oxide cell temperature control system.

2. The temperature control fluid is in gas form.

10. The solid oxide cell temperature control system of claim 1.

3. the thermal control system having a protective coating for the fuel flow field plate structure and the oxidizer flow field plate structure made of steel construction, the protective coating being selected according to the properties of the fuel, the oxidizer and the thermal control fluid; 10. The solid oxide cell temperature control system of claim 1.

4. 1. A method of temperature control of a solid oxide cell, comprising: flowing a fuel in a fuel flow field plate structure, flowing an oxidant in an oxidant flow field plate structure, forming electrical contact structures for the fuel and the oxidant, flowing a temperature control fluid in a temperature control fluid structure disposed separately between the fuel flow field plate structure and the oxidant flow field plate structure in a flow field plate, the temperature control fluid in liquid form comprising at least one of a liquid including a molten salt, a supercritical fluid, and a phase change material, and in gas form, the temperature control fluid gas reacts by at least one of an endothermic reaction and an exothermic reaction, forming sealing structures to prevent leakage in the fuel flow field plate structure, the oxidant flow field plate structure, the electrical contact structures, and the temperature control fluid structure, and optimizing the temperature control fluid temperature and flow rate, thereby controlling an operating temperature in the solid oxide cell above 350°C. A method for controlling the temperature of a solid oxide cell.

5. The temperature control fluid is in gas form.

5. A method for controlling the temperature of a solid oxide cell according to claim 4.

6. the fuel flow field plate structure and the oxidizer flow field plate structure made of steel structure are protected by a protective coating selected according to the properties of the fuel, oxidizer and thermal control fluid; 5. A method for controlling the temperature of a solid oxide cell according to claim 4.

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