JP2016532243A - Cathode combustion to improve fuel cell synthesis gas production - Google Patents

Abstract

Molten carbonate fuel cells are operated with a cathode inlet stream containing a portion of a combustible gas, which may be a hydrocarbon, hydrogen, or other gas combined with oxygen, and heat is produced on the cathode catalyst surface. Form. The combustible gas may react in the stage where it is heat integrated with the cathode and / or the cathode. Using the heat generated by the combustion reaction at the cathode, for example, additional endothermic reactions (eg, reforming) may occur at the anode portion of the fuel cell while still maintaining the desired temperature gradient throughout the fuel cell. It becomes possible. Optionally, the cathode of the fuel cell can be modified to further enhance or control combustion within the cathode, for example, by introducing additional catalyst surfaces at the cathode.

Description

  In various aspects, the present invention relates to a method for operation of a molten carbonate fuel cell.

  Molten carbonate fuel cells use hydrogen and / or other fuels to generate electricity. Hydrogen may be provided upstream of the fuel cell or by reforming methane or other reformable fuel in a steam reformer within the fuel cell. The reformable fuel can include a hydrocarbon material that can react with steam and / or oxygen at elevated temperatures and / or pressures to produce a gas product comprising hydrogen. Alternatively or additionally, the fuel can be reformed in an anode cell of a molten carbonate fuel cell that can be operated to produce the proper conditions for reforming the fuel at the anode. Alternatively or additionally, reforming can occur both outside and inside the fuel cell.

  Traditionally, molten carbonate fuel cells are operated to maximize the generation of electricity per unit of fuel input, which can also be described as the electrical efficiency of the fuel cell. This maximization can be based on the fuel cell alone or in combination with another power generation system. To achieve increased electricity generation and control heat generation, fuel utilization within the fuel cell is typically maintained between 70% and 75%.

U.S. Patent No. 6,057,056 describes a system and method for operation of a fuel cell system having a substantial hydrogen content in an anode inlet stream. The technology in US Pat. No. 6,057,059 relates to providing sufficient fuel at the anode inlet so that sufficient fuel remains for the oxidation reaction when the fuel approaches the anode outlet. To ensure a suitable fuel, Patent Document 1 provides a fuel having a high concentration of H _2. H _{2 that} is not utilized in the oxidation reaction is recycled to the anode for subsequent passage. H ₂ use may be in the range of 10% to 30%, based on single pass. Patent document 1 does not describe significant reforming in the anode, but instead relies mainly on external reforming.

  U.S. Patent No. 6,057,031 describes a system and method for co-production of hydrogen and electrical energy. The co-production system comprises a fuel cell and a separation unit configured to receive the anode discharge stream and separate hydrogen. A portion of the anode discharge is recycled to the anode inlet. The operating range given in US Pat. No. 6,057,836 seems to be based on solid oxide fuel cells. A molten carbonate fuel cell is described as an alternative.

  In US Pat. No. 6,099,056, a system and method for co-production of hydrogen and power is described. Fuel cells are described as a general type of chemical conversion device for converting hydrocarbon-type fuels to oxygen. The fuel cell system also includes an external reformer and a high temperature fuel cell. An embodiment of a fuel cell system having an electrical efficiency of about 45% and a chemical production rate of about 25% is described that results in a system co-production efficiency of about 70%. U.S. Patent No. 6,099,077 does not appear to describe the electrical efficiency of a fuel cell in isolation from the system.

  U.S. Patent No. 6,057,034 describes a system for integrating a gasifier and a fuel cell so that coal gas can be used as a fuel source for the anode of the fuel cell. The hydrogen generated by the fuel cell is used as input for a gasifier used to generate methane from coal gas (or other coal) input. The methane from the gasifier is then used as at least a portion of the input fuel to the fuel cell. Thus, at least a portion of the hydrogen generated by the fuel cell is indirectly recycled to the fuel cell anode inlet in the form of methane generated in the gasifier.

Journal of Fuel Cell Science and Technology, Non-Patent Document 1, describes a power generation system that combines a combustion generator with a molten carbonate fuel cell. Various combinations of fuel cells and operating parameters are described. The combustion output from the combustion generator is used in part as an input for the cathode of the fuel cell. One goal of non-patent document 1 simulation is to use MCFC to separate CO ₂ from generator emissions. The simulation described in the paper of Non-Patent Document 1 establishes a maximum outlet temperature of 660 ° C. and indicates that the inlet temperature must be sufficiently cooled to account for the temperature increase across the fuel cell. The electrical efficiency (ie generated electricity / fuel input) for the MCFC fuel cell is 50% for the base model. The electrical efficiency in the case of a test model optimized for CO ₂ separation is also 50%.

Non-Patent Document 2 by Desideri et al. Describes a method for modeling the performance of a power generation system that uses a fuel cell for CO ₂ separation. The recirculation of the anode exhaust to the anode inlet and the cathode exhaust to the cathode inlet is used to improve the performance of the fuel cell. Model parameters describe MCFC electrical efficiency of 50.3%.

US Patent Application Publication No. 2011/0111315 US Patent Application Publication No. 2005/0123810 US Patent Application Publication No. 2003/0008183 US Pat. No. 5,084,362

G. Manzolini et. al. , J .; Fuel Cell Sci. and Tech. , Vol. 9, Feb 2012 Desideri et al. (Intl. J. of Hydrogen Energy, Vol. 37, 2012)

In one aspect, a method for producing electricity is provided. The method introduces an anode fuel stream comprising a reformable fuel into a molten carbonate fuel cell anode, an internal reforming element associated with a molten carbonate fuel cell anode, or a combination thereof. Introducing a cathode inlet stream comprising CO ₂ , O ₂ and one or more fuel compounds into the cathode of the molten carbonate fuel cell, wherein the one or more fuel compounds are H ₂ One or more hydrocarbon-like fuel compounds, CO or a combination thereof, wherein the concentration of the one or more fuel compounds in the cathode inlet stream is at least about 0.01% by volume and 1 in the cathode inlet stream. The concentration of the fuel compound of the species is lower than the autoignition concentration for the operating conditions at the cathode of the fuel cell; and a molten carbonate form A step of generating electricity in a cost battery; H _2, resulting in the anode effluent comprising CO and CO ₂ steps and, at least about 1% by volume of O ₂ and about 100vppm less of one or more fuel compounds Producing a cathode discharge comprising.

In another aspect, a method for producing electricity is provided. The method introduces an anode fuel stream comprising a reformable fuel into a molten carbonate fuel cell anode, an internal reforming element associated with a molten carbonate fuel cell anode, or a combination thereof. Introducing a cathode inlet stream comprising CO ₂ , O ₂ and one or more fuel compounds into the cathode of the molten carbonate fuel cell, wherein the one or more fuel compounds are one type At least about 0.02% by volume of the aromatic compound, one or more carbon-containing fuel compounds having at least 5 carbons, or combinations thereof, wherein the one or more fuel compounds in the cathode inlet stream. The concentration of one or more fuel compounds in the cathode inlet stream has a methylene equivalent volume percent (defined below) of Lower autoignition concentration for operating conditions at the cathode, steps and; a step resulting anode effluent comprising H _2, CO and CO _2;; and the step of generating electricity in a molten carbonate fuel cell at least about Producing a cathode discharge comprising 1% by volume of O ₂ and no more than about 0.01% by volume of methylene equivalent volume percent of one or more fuel compounds, wherein the cathode of the molten carbonate fuel cell comprises: Comprising the electrode surface and a second catalyst surface, wherein the second catalyst surface comprises at least one Group VIII metal, and producing a cathode exhaust, in the presence of the second catalyst surface 1 Oxidizing at least a portion of the one or more fuel compounds.

  In yet another aspect, a molten carbonate fuel cell system (equipment or system) is provided. The molten carbonate fuel cell system includes a molten carbonate fuel cell having an anode and a cathode, the cathode including an electrode surface and a second catalyst surface comprising at least one Group VIII metal. And the concentration of the at least one Group VIII metal on the second catalyst surface is such that the concentration of the at least one Group VIII metal in the second region of the second catalyst surface is in the first region of the second catalyst surface. Compared to the Group VIII metal concentration, the first region of the second catalyst surface is closer to the cathode inlet of the cathode of the molten carbonate fuel cell than the second region of the second catalyst surface. Optionally, the at least one Group VIII metal comprises Ni, Pt, Pd, Co, Rh, Ru, Re, Ir, Fe or combinations thereof, preferably at least Ni, Co, Fe, Pt, Including Pd or combinations thereof. Optionally, the region of the second catalyst surface comprises a continuously increasing gradient of the concentration of at least one Group VIII metal. In some embodiments, the first region of the second catalyst surface comprises at least one Group VIII metal, and the second region of the second catalyst surface is of the second catalyst surface. It comprises at least one additional Group VIII metal that is different from the at least one Group VIII metal in the first region. In other embodiments, the second region of the second catalyst surface comprises at least one Group VIII metal, and the first region of the second catalyst surface is the second region of the second catalyst surface. At least one additional Group VIII metal different from the at least one Group VIII metal in the two regions.

1 schematically illustrates an example of a molten carbonate fuel cell and associated reforming and separation stage configurations. 3 schematically illustrates another example of a molten carbonate fuel cell and associated reforming and separation stage configurations. 1 schematically shows an example of operation of a molten carbonate fuel cell.

Overview In various embodiments, a cathode inlet stream containing a non-trivial portion of a combustible gas that may be a hydrocarbon, hydrogen or other gas that forms heat at the cathode catalyst surface in combination with oxygen. Is used to operate the molten carbonate fuel cell. The combustible gas can react at the cathode and / or in the stage of being heat integrated with the cathode. Using the heat generated by the combustion reaction at the cathode, for example, additional endothermic reactions (eg, reforming) can occur at the anode portion of the fuel cell while still maintaining the desired temperature gradient throughout the fuel cell. It becomes. Optionally, the cathode of the fuel cell can be modified to further improve or control combustion within the cathode, for example, by introducing additional catalyst surfaces at the cathode.

One strategy for reducing or minimizing the amount of carbon emitted from a combustion source, such as a gas turbine, internal combustion engine, combustion boiler or other combustion source, is to fuse the combustion source with molten carbonate Integrated with a fuel cell (MCFC). Molten carbonate fuel cells can receive CO ₂ containing emissions from a combustion source as part of the cathode inlet stream to the fuel cell. As part of the cathode reaction, CO ₂ can be transported from the cathode across the fuel cell electrolyte to the anode. Thereby, molten carbonate fuel cell, it is possible to promote CO ₂ concentration in the anode output of the fuel cell, whereby, in order to avoid the discharge of CO ₂ to the atmosphere, the CO ₂ Capture / reuse can be facilitated.

  With respect to conventional molten carbonate fuel cell configurations, a major concern may be operating the molten carbonate fuel cell with high electrical efficiency while maintaining a temperature gradient within the desired range throughout the fuel cell. Some of the challenges during conventional operation may be to avoid extremely high temperature gradients throughout the fuel cell due to excessive amounts of heat or waste heat generated within the fuel cell. When operating a molten carbonate fuel cell for high efficiency, the cell is typically operated near the maximum temperature rise allowed in the fuel cell because the net operation at high efficiency is exothermic.

During conventional operation of a molten carbonate fuel cell, the amount of combustible gas present as the cathode input stream entering the cathode can typically be less than about 100 vppm, such as less than about 10 vppm. Additionally, the combustible gas can typically correspond to a compound having a relatively low fuel number per molecule, such as H ₂ or CH ₄ . Such an amount of combustibles generates an insignificant amount of heat when reacted with oxygen on the cathode as compared to the amount of heat generated in the entire fuel cell system. With respect to the portion of the cathode input stream that is derived from the emissions of the combustion source, the residual combustible material is typically previously discharged to combustion conditions optimized to achieve substantially complete combustion of the input fuel. It can reflect the fact that the object has been exposed. In some conventional configurations, a portion of the cathode input stream can also correspond to a recycled portion of the anode output stream. In such conventional configurations, the recycled portion of the anode output stream can typically be passed through a burner before entering the cathode, thereby allowing any of the anode output stream portions to be It can also result in substantially complete combustion of the fuel.

Instead of operating a molten carbonate fuel cell in a conventional manner, the molten carbonate fuel cell can be operated with a cathode input stream that includes a combustible material, such as one or more fuel compounds. The fuel compound corresponds to CO, H ₂ , CH ₄ , other hydrocarbons and / or hydrocarbon-like compounds that can be combusted, or other compounds that can be combusted (oxidized) to generate heat Can do. In some embodiments, the cathode inlet stream can contain fuel compounds corresponding to CO, H ₂ and / or CH ₄ . In other embodiments, the cathode inlet stream can contain H ₂ and / or carbon-containing fuel compounds having 4 or fewer carbon atoms. In yet other embodiments, some fuel compounds in the cathode inlet stream can correspond to aromatic compounds, or carbon-containing compounds having at least 5 carbon atoms, or combinations thereof.

  The amount of combustible material in the cathode inlet stream can be characterized in various ways. One option may be to use a volume percent of the total combustible material. Another option may be to measure the volume percent of the combustible material based on the number of carbons and / or the number of heavy atoms present in the combustible material. This latter option can account for the difference in fuel values between compounds such as hydrogen and distillation boiling range molecules. In the cathode inlet, both can exist as gases occupying a similar volume at a certain temperature, but the fuel value of the distillation boiling range molecule is significantly higher.

  For example, one option is (as a lower limit) at least about 0.01% by volume, or at least about 0.02% by volume, or at least about 0.03% by volume, or at least about 0.05% by volume, or at least about 0 1 vol%, or at least about 0.25 vol%, or at least about 0.5 vol%, or at least about 1.0 vol%, or at least about 1.5 vol%, or at least about 2.0 vol%, Or it may be to use a cathode inlet stream containing at least about 2.5% by volume, or at least 3.0% by volume of one or more fuel compounds. Additionally or alternatively, the cathode inlet stream has a (upper limit) of about 5.0% or less, or about 4.0% or less, or about 3.5% or less, or about 3.0% by volume. One or more fuel compounds may be contained in the following, or up to about 2.5% by volume. Each lower limit for the amount of one or more fuel compounds in the cathode inlet stream is explicitly considered in combination with a respective upper limit for the amount of one or more fuel compounds in the cathode inlet stream. The upper limit for the amount of combustible material can vary, but the conditions at the cathode must be below a concentration that allows the cathode inlet stream to self-ignite, typically in the range of several percent by volume, depending on the composition of the compound. Should be.

  Additionally or alternatively, another option for characterizing the amount of combustible material in the cathode inlet stream is a volume of combustible material based on the number of carbons in the combustible material, or alternatively the number of heavy atoms. It can be to measure the percentage. The fuel value of a hydrocarbon is approximately proportional to the number of carbon atoms present in the hydrocarbon. With the exception of oxygen, any additional heteroatoms present in the hydrocarbon-like material (ie, non-hydrogen atoms or heavy atoms) will contribute approximately proportionally. To account for the additional fuel value of the larger fuel component, the volume percentage of the fuel component multiplied by the number of carbon atoms in the component, or alternatively the number of non-oxygen heavy atoms in the component, modified volume Percentage can be produced. If the modified volume percent is based solely on carbon atoms in the fuel component, the modified volume percent is defined herein as the “methylene equivalent” volume percent for the fuel component. If the modified volume percent is based on non-oxygen heavy atoms in the fuel component, the modified volume percent is defined herein as the “heavy atom equivalent” volume percent for the fuel component. For purposes of defining methylene equivalent volume percent and heavy atom equivalent volume percent, a hydrogen molecule is defined as having a carbon atom or heavy atom value of 0.5. A CO molecule is similarly defined as having a carbon atom or heavy atom value of 0.5. This reflects the fact that these compounds have some fuel value, not the same fuel value as hydrocarbon-like compounds.

In various embodiments, the methylene equivalent volume percent in the cathode inlet stream is at least about 0.01 vol%, or at least about 0.02 vol%, or at least about 0.03 vol%, or at least about 0.05 vol%, Or at least about 0.1 volume%, or at least about 0.25 volume%, or at least about 0.5 volume%, or at least about 1.0 volume%, or at least about 1.5 volume%, or at least about 2. It can be 0% by volume, or at least about 2.5% by volume, or at least 3.0% by volume of one or more fuel compounds. Additionally or alternatively, the cathode inlet stream may be about 5.0% or less, or about 4.0% or less, or about 3.5% or less, or about 3.0% or less, or about One or more fuel compounds may be contained up to 2.5% by volume. Each lower limit for the methylene equivalent volume percent of one or more fuel compounds in the cathode inlet stream is explicitly considered in combination with the respective upper limit for the methylene equivalent volume percent of one or more fuel compounds in the cathode inlet stream. As an example of calculating the methylene equivalent volume percent, a hypothetical cathode inlet supply could contain 0.02% by volume of ethylene and 0.01% by volume of H ₂ fuel compound. . In such a hypothetical example, the methylene equivalent volume percent relative to the feed is 0.045% by volume. Since ethylene contains 2 carbon atoms per molecule, ethylene contributes 0.02 × 2 = 0.04 vol% to the total methylene equivalent volume percent. H ₂ is defined as being considered as 0.5 carbon atoms per molecule, thus H ₂ contributes 0.01 × 0.5 = 0.005% by volume to the total methylene equivalent volume percent. .

  Additionally or alternatively, yet another option for characterizing the amount of combustible material in the cathode inlet stream is compared to the energy value of the fuel delivered to the corresponding anode inlet of the molten carbonate fuel cell. , Based on the relative energy value of the fuel delivered to the cathode inlet. The amount of fuel in the cathode inlet stream can have no more than about 12%, or no more than about 10%, or no more than about 8% of the energy value of the anode inlet stream. For example, if the rate of fuel delivered to the anode inlet corresponds to about 1 MW of power, the rate of fuel input to the cathode in the cathode inlet stream should be about 120 kW or less, or about 100 kW or less, or about 80 kW or less. Can do. The cathode inlet stream can also contain sufficient oxygen, so even after combustion of any fuel in the cathode inlet stream, the remaining oxygen content allows for a fuel cell reaction, and still at least It is sufficient to produce a cathode outlet stream having an oxygen content of about 1% by volume, for example 2% by volume.

In some embodiments, the cathode inlet stream containing one or more fuel compounds can have a reduced or minimized sulfur content. The sulfur content of the cathode inlet stream can be about 25 wppm or less, or about 15 wppm or less, or about 10 wppm or less. Optionally, some heteroatoms different from C, H and O can be present in the oxidizable compound (ie, fuel compound) contained in the cathode inlet stream. For example, the carbon-containing fuel compound in the cathode inlet stream can optionally contain nitrogen atoms. Note that N ₂ is not a compound that is oxidizable under the conditions present in the cathode inlet, and therefore the presence of N ₂ in the cathode inlet stream does not constitute a heteroatom present in the oxidizable compound. In other embodiments, the cathode inlet stream can include no more than about 100 wppm or no more than about 10 wppm heteroatoms in the fuel compound different from C, H, and O.

The additional fuel content of the cathode inlet stream is combustible at the cathode based on the conditions at the cathode and the presence of the catalyst surface at the cathode. One suitable catalyst surface can be a nickel surface, such as a nickel surface often used as an electrode adjacent to a molten carbonate electrolyte, but any other convenience that can catalytically oxidize fuel components. Suitable catalysts such as Group VIII metals, supported catalysts, or other combustion catalysts may also be used. The cathode electrode surface can catalyze the oxidation of H ₂ and / or carbon containing fuels (including CO), and the fuel present in the cathode inlet stream is typically combusted, such as H ₂ O and CO _2. Can be converted to product.

In embodiments where the fuel in the cathode inlet stream is H ₂ , CO and / or CH ₄ , the electrode surface (typically Ni) can be sufficient to catalyze the combustion of fuel in the cathode inlet stream. . The electrode surface can also be suitable for catalyzing reactions involving lower amounts of other hydrocarbons. For example, the electrode surface may range from tens of ppm or more, such as from about 10 vppm to about 10,000 vppm, or from about 10 vppm to about 1000 vppm, or from about 10 vppm to about 200 vppm, or from about 10 vppm to about 100 vppm, or from about 50 vppm to about 10 Suitable for catalyzing the oxidation of aromatic compounds at 1,000 vppm, or about 50 vppm to about 1000 vppm, or about 50 vppm to about 200 vppm, or about 100 vppm to about 10,000 vppm, or about 100 vppm to about 1000 vppm. Can do. For aliphatic hydrocarbons or other non-aromatic hydrocarbon-like compounds, the electrode surface can be suitable for catalyzing up to about 1% by volume of the compound.

In some embodiments, the catalytic activity for oxidizing the fuel at the cathode can be improved by providing an additional catalytic surface. For example, one configuration for a conventional molten carbonate fuel cell may be to have the cathode portion of the fuel cell defined by parallel plates. One parallel plate can correspond to the electrode surface adjacent to the molten carbonate electrolyte. Traditionally, the opposite surface (the surface not near the molten carbonate electrolyte) can be a steel surface or another surface corresponding to a suitable structural material. Instead of having a steel surface (or other low-reactivity surface) opposite the electrode, the opposite surface can be coated with a catalytic material that improves the ability to catalyze fuel combustion in the cathode inlet stream. is there. One option can be to provide a surface similar to the electrolyte surface, such as a Ni surface. Another option may be to use a surface with higher activity to catalyze the combustion of aromatics and / or C ₂₊ hydrocarbon-like compounds. Examples of suitable catalyst materials can include, but are not limited to, Group VIII metals such as Ni, Fe, Co, Pt and / or Pd. Any suitable metal or metal alloy can be used directly on the steel surface or supported on a typical catalyst support. Catalyst formulations useful as combustion catalysts are well known in the art, but any formulation suitable for a fuel cell operating temperature range such as about 400 ° C. to about 800 ° C. may be used. Alloys of Group VIII metals such as alloys of multiple Group VIII metals and / or alloys of Group VIII metals with other transition metals may also be suitable. The catalyst material can be coated directly on the cathode plate surface, or the catalyst material can be supported, for example, on an oxide support.

Based on the presence of the electrode (Ni) surface and / or the additional catalyst surface, H ₂ , CO and hydrocarbon / hydrocarbon-like compounds in the cathode inlet stream can be combusted at the cathode. This will generate additional heat in the cathode. In conventional operation, this additional heat poses a problem because operations optimized for electrical efficiency are typically operated at the limits of allowable temperature rise. However, in various aspects, the additional heat generated at the cathode can be used to provide additional heat to the endothermic reaction. The endothermic reaction can correspond to reforming at the anode or another endothermic reaction that occurs in a reaction stage that is heat integrated with the cathode. For example, if the anode portion of a molten carbonate fuel cell is operated to have a low single pass fuel utilization with respect to hydrogen and / or syngas production, the additional heat generated at the cathode is in the desired range. Can be used to maintain a temperature gradient within the fuel cell.

  Although the additional heat generated at the cathode can be advantageous, it can be desirable to distribute the combustion of fuel in the cathode inlet stream throughout a larger portion of the cathode length. One way of distributing the combustion of fuel in the cathode inlet stream across a larger portion of the cathode can be to use an additional catalyst surface with a gradient of catalyst material. For example, the concentration of the catalyst material on the additional catalyst surface can be lower near the entrance to the cathode (where the concentration of combustible material and oxygen is highest) and then increases in cathode length To do. Any convenient strategy for increasing the concentration, such as a continuous gradient, a series of step increases, or other methods that allow a higher catalyst material concentration to exist at a location farther from the cathode inlet Can be used. The initial concentration of catalyst material on the additional surface at the cathode inlet can be any convenient value, with the option of starting the catalyst material at the additional surface at a position after the inlet to the cathode. including. The catalyst pattern or gradient, and subsequent exotherm, can be optimized to disperse total heat production across the cathode region and to prevent heat regions that can damage the entire fuel cell operation.

  As an example of a method for operating a molten carbonate fuel cell to take advantage of the additional heat generated at the cathode, the molten carbonate fuel cell operates with increased synthesis gas and / or hydrogen production. Can be done. This is performed in the fuel cell (and / or in the associated internal reforming stage, eg, the reforming stage of the fuel cell assembly) compared to the amount of hydrogen oxidized at the anode to generate electricity. This can be achieved by increasing the amount of modification. As defined below, this is generated in the anode by a) an electrochemical reaction combined with c) heat consumed in the fuel cell stack (or other fuel cell assembly) by an endothermic reaction. And b) operation of the fuel cell by the fuel cell heat ratio with respect to the heat generated in the cathode by the combustion of the fuel. For example, the reforming reaction within the anode and / or internal reforming stage can typically be an endothermic reaction. Thus, the endothermic reforming reaction can be balanced by an exothermic electrochemical reaction related to power generation combined with an exothermic cathode combustion reaction. Rather than attempting to transport the heat generated by an exothermic fuel cell reaction from the fuel cell, this excess amount of heat is used in situ as a heat source for reforming and / or another endothermic reaction. Can be. This can result in a more efficient utilization of thermal energy and / or reduced demands for additional external or internal heat exchange. This efficient generation and essentially in situ use of thermal energy can reduce system complexity and components while maintaining advantageous operating conditions. In some embodiments, the amount of reforming or other endothermic reaction is an amount of excess heat generated by the exothermic reaction, rather than significantly less than the thermal requirements typically described in the prior art. One can choose to have comparable or greater endothermic heat requirements.

  Additionally or alternatively, the fuel cell can be operated such that the temperature difference between the anode inlet and the anode outlet is negative rather than positive. Thus, instead of having a temperature increase between the anode inlet and the anode outlet, a sufficient amount of reforming and / or other endotherms to ensure that the output stream from the anode outlet is cooler than the anode inlet temperature. Sexual reactions can be carried out. Additionally or alternatively, the temperature difference between the anode input and the anode output is a relative value of the endothermic reaction and the combined exothermic heat generation of the anode reaction to produce the cathode combustion reaction and power. Additional fuel is supplied to the fuel cell and / or heater for the internal reforming stage (or other internal endothermic reaction stage) so that it can be smaller than expected based on the specific demand be able to. In embodiments where reforming can be used as an endothermic reaction, conventional fuels are operated while minimizing system complexity for heat exchange and reforming by operating the fuel cell to reform excess fuel. Increased synthesis gas and / or increased hydrogen production relative to battery operation may be allowed. The additional syngas and / or additional hydrogen can then be used in a variety of applications including a chemical synthesis process and / or recovery / recycling of hydrogen for use as a “clean” fuel. it can.

The amount of heat generated per mole of hydrogen oxidized by the exothermic reaction at the anode can be substantially greater than the amount of heat consumed per mole of hydrogen generated by the reforming reaction. The net reaction of hydrogen (H ₂ + 1 / 2O ₂ => H ₂ O) in a molten carbonate fuel cell can have a reaction enthalpy of about -285 kJ / mol of hydrogen molecule. At least a portion of this energy can be converted into electrical energy within the fuel cell. However, the (approximate) difference between the enthalpy of reaction and the electrical energy produced by the fuel cell can be heat in the fuel cell. This amount of energy is instead the cell current density (current per unit area) multiplied by the difference between the theoretical maximum voltage of the fuel cell and the actual voltage, or <current density> ^* Can be expressed as (Vmax-Vact). This amount of energy is defined as the “waste heat” of the fuel cell. As an example of reforming, the enthalpy of methane reforming (CH ₄ + 2H ₂ O => 4H ₂ + CO ₂ ) can be about 250 kJ / mole of methane, or about 62 kJ / mole of hydrogen molecule. From the standpoint of heat balance, each electrochemically oxidized hydrogen molecule can generate sufficient heat to generate two or more hydrogen molecules by reforming. In conventional configurations, this excessive amount of heat can result in a substantial temperature difference from the anode inlet to the anode outlet. This excess amount of heat can be dissipated by performing a compatible amount of the reforming reaction instead of being used to increase the temperature in the fuel cell. The excess heat generated at the anode can be supplemented with the excess heat generated by the combustion reaction in the fuel cell. More generally, excess heat can be dissipated by performing an endothermic reaction in an endothermic reaction stage that is heat integrated with the fuel cell anode and / or the fuel cell.

Depending on the embodiment, the amount of reforming and / or other endothermic reactions can be selected relative to the amount of hydrogen that reacts at the anode to achieve the desired heat ratio of the fuel cell. As used herein, “heat ratio” is the exothermic reaction in the fuel cell assembly divided by the endothermic heat demand of the reforming reaction occurring in the fuel cell assembly (the exothermic reaction at both the anode and cathode). Defined as the heat generated by Mathematically expressed, the heat ratio (TH) = Q _EX / Q _EN , where Q _EX is the total heat generated by the exothermic reaction, and Q _EN is consumed by the endothermic reaction occurring in the fuel cell. Is the sum of heat done. The heat generated by the exothermic reaction corresponds to any heat generated by the reforming reaction, the water gas shift reaction, the combustion reaction at the cathode (for example, oxidation of the fuel compound) and / or the electrochemical reaction in the battery. be able to. The heat generated by the electrochemical reaction can be calculated based on the ideal electrochemical potential of the fuel cell reaction across the electrolyte minus the actual output voltage of the fuel cell. For example, the ideal electrochemical potential of the MCFC reaction is believed to be about 1.04 V based on the net reaction occurring in the battery. During operation of the MCFC, the battery can typically have an output voltage of less than 1.04V due to various losses. For example, the common output / operating voltage can be about 0.7V. The heat generated can be equal to the electrochemical potential of the battery (ie about 1.04V) minus the operating voltage. For example, the heat generated by the electrochemical reaction in the cell can be about 0.34V if an output voltage of about 0.7V is achieved in the fuel cell. Thus, in this scenario, the electrochemical reaction produces about 0.7V electricity and about 0.34V thermal energy. In such an embodiment, the electrical energy of about 0.7V are _not included as part of _{Q EX.} In other words, thermal energy is not electrical energy.

  In various aspects, the heat ratio is determined by the fuel cell stack, the individual fuel cells in the fuel cell stack, the fuel cell stack having an integrated reforming stage, the fuel cell stack having an integrated endothermic reaction stage, Or for any convenient fuel cell structure, such as a combination thereof. The heat ratio may be calculated for different units within a fuel cell stack, such as a fuel cell or an assembly of fuel cell stacks. For example, the heat ratio is the fuel in the fuel cell stack with an integrated reforming stage and / or an endothermic reaction stage element that is sufficiently close to the integrated fuel cell from a thermal integration point of view. It may be calculated for a battery (or multiple fuel cells).

  From the perspective of thermal integration, the characteristic width of the fuel cell stack can be the height of the individual fuel cell stack elements. It should be noted that separate reforming stages and / or separate endothermic reaction stages could have a different stack height than the fuel cell. In such a scenario, the height of the fuel cell element can be used as a characteristic height. In the present discussion, an integrated endothermic reaction stage includes one or more fuels so that the integrated endothermic reaction stage can use heat from the fuel cell as a heat source for reforming. It can be defined as the stage that is heat integrated with the battery. Such an integrated endothermic reaction stage may be defined as one that is arranged at a height of less than 10 times the height of the laminated element from the fuel cell that provides heat to the integrated stage. it can. For example, the integrated endothermic reaction stage (e.g., reforming stage) is less than 10 times the height of the laminated element from any thermally integrated fuel cell, or less than 8 times the height of the laminated element, or It can be arranged at a height of less than 5 times the height of the laminated element or less than 3 times the height of the laminated element. In the present discussion, the integrated reforming stage and / or the integrated endothermic reaction stage representing the stack element adjacent to the fuel cell element is no more than about 1 stack element height from the adjacent fuel cell element. Define as a thing.

  About 1.3 or less, or about 1.15 or less, or about 1.0 or less, or about 0.95 or less, or about 0.90 or less, or about 0.85 or less, or about 0.80 or less, or about A heat ratio of 0.75 or less can be lower than that typically required in the use of MCFC fuel cells. In embodiments of the present invention, the heat ratio can be reduced to increase and / or optimize synthesis gas production via an endothermic reaction, hydrogen production, production of another product, or a combination thereof.

  In various aspects of the invention, the operation of the fuel cell can be characterized based on the heat ratio. When the fuel cell is operated to have a desired heat ratio, the molten carbonate fuel cell has a temperature of about 1.5 or less, such as about 1.3 or less, or about 1.15 or less, or about 1.0 or less. Or about 0.95 or less, or about 0.90 or less, or about 0.85 or less, or about 0.80 or less, or about 0.75 or less. Additionally or alternatively, the heat ratio can be at least about 0.25, or at least about 0.35, or at least about 0.45, or at least about 0.50. Additionally or alternatively, in some embodiments, the fuel cell has a temperature increase between the anode input and anode output of about 40 ° C. or less, such as about 20 ° C. or less, or about 10 ° C. or less. Can be operated as follows. Still further, or alternatively, the fuel cell can be operated to have an anode outlet temperature from about 10 ° C. to about 10 ° C. higher than the temperature of the anode inlet. Still further, or alternatively, the fuel cell is above the anode outlet temperature, eg, at least about 5 ° C higher, or at least about 10 ° C higher, or at least about 20 ° C higher, or at least about 25 ° C. It can be operated to have a high anode inlet temperature. Still further, or alternatively, the fuel cell is from the anode outlet temperature to about 100 ° C. or lower, or to about 80 ° C. or lower, to about 60 ° C. or lower, to about 50 ° C. or lower, or to about 40 ° C. or lower. Or up to about 30 ° C. or less, or up to about 20 ° C. or less.

  Several operating parameters may be treated to generate the desired heat ratio. Some parameters are similar to those currently recommended for fuel cell operation. Parameters treated in a manner different from conventional operation include the amount of fuel provided to the anode, the composition of the fuel provided to the anode, the amount of fuel compound contained in the cathode inlet stream, and / or the input to the anode input. Separation and capture of syngas at the anode output without significant recycle, eg, without syngas or hydrogen recycle from the anode output to the anode input.

  Hydrocarbon reforming to form hydrogen and carbon oxide is an example of an endothermic reaction. Reforming is also an example of a reaction that can be performed in the anode and / or in an integrated reaction stage. In some aspects of the invention, the amount of fuel input to the anode can include more reformable fuel than the amount of reformable fuel used during conventional fuel cell operation. In such embodiments, the goal can be to generate an excess amount of synthesis gas by reforming in the associated reforming step in the anode and / or fuel cell assembly containing the anode. In one aspect, the amount of reformable fuel introduced into the anode (or their associated reforming stage, or combination) provides a fuel that provides specific fuel cell physical limitations and other selected operating parameters. The battery can be selected based on the amount of modification that is possible. For example, the anode catalyst can be donated to the reforming process. The amount of surface area on the anode catalyst can be a constraint on the amount of reforming that can occur. Similarly, the amount of reforming may be limited by the amount of heat available in the anode and the anode temperature change that occurs across the anode.

  By operating the fuel cell at a heat ratio of less than 1, a temperature drop can occur through the fuel cell. In some embodiments, the amount of reforming and / or other endothermic reaction is such that the temperature drop from the anode inlet to the anode outlet is about 100 ° C. or lower, such as about 80 ° C. or lower, or about 60 ° C. or lower, Or it may be limited to be about 50 ° C. or lower, or about 40 ° C. or lower, or about 30 ° C. or lower, or about 20 ° C. or lower. Limiting the temperature drop from the anode inlet to the anode outlet is advantageous, for example, to maintain a temperature sufficient to allow complete or substantially complete conversion of the fuel (by reforming) at the anode. Can be. In other embodiments, the anode inlet temperature is less than or equal to about 100 ° C., for example, about 80 ° C., than the anode outlet temperature due to a balance of heat consumed by the endothermic reaction and additional external heat supplied to the fuel cell. Additional heat (e.g. heat exchange or addition) such that it rises to below ℃, or about 60 ℃ or less, or about 50 ℃ or less, or about 40 ℃ or less, or about 30 ℃, Can be supplied to the fuel cell).

  The amount of reforming and / or other endothermic reactions can be additionally or alternatively limited by the operating temperature of the fuel cell. For example, in general, fuel reforming can occur more rapidly at higher temperatures. In addition, more reforming can occur if more heat is available for the reforming process. As noted above, aspects of the invention may operate within a typical range of fuel cell temperatures. The temperature range may be selected for a variety of reasons other than the considerations associated with embodiments of the present invention. For example, the cathode or anode inlet stream may already be heated to an elevated temperature because of the flow source. Such a cathode inlet stream may allow the generation of additional heat based on the combustion of the cathode inlet stream fuel at the cathode. Additionally or alternatively, the fuel cell electrolyte temperature can be maintained at a sufficient temperature so that the carbonate electrolyte remains in a molten state. Depending on which temperature is selected, the amount of reforming that can occur at the anode can be affected, and therefore the amount of reformable fuel input to the anode may need to be adjusted.

The amount of reforming may additionally or alternatively depend on the effectiveness of the reformable fuel. For example, if the fuel is contained only H _2, H ₂ is already modified, since it is not possible further modified, modified will not occur. The amount of “syngas produced” by the fuel cell can be defined as the difference between the LVH value of the synthesis gas at the anode input versus the LVH value of the synthesis gas at the anode output. The produced synthesis gas LHV (sg net) = (LHV (sg out) −LHV (sg in)), where LHV (sg in) and LHV (sg out) are the syngas LHV and anode outlet flow of the anode inlet. Or, it refers to the LHV of the synthesis gas in the flow. A fuel cell in which a fuel containing a substantial amount of H ₂ is provided is that the fuel is substantially reformed of H ₂ that has already been reformed, as opposed to containing additional reformable fuel. Because of the amount contained, the amount of potential synthesis gas production can be limited.

An example of a method of operating a fuel cell at the reduced heat ratio is to balance the generation and consumption of heat in the fuel cell and / or to consume more heat than generated. It can be a method in which excessive reforming is carried out. The reforming of the reformable fuel to form H ₂ and / or CO can be an endothermic process, while the anode electrochemical oxidation reaction and the cathode combustion reaction can be exothermic. During conventional fuel cell operation, the amount of reforming required to supply the feed components for fuel cell operation typically consumes less heat than the amount of heat generated by the anodic oxidation reaction. it can. For example, conventional operation at about 70% or about 75% fuel utilization results in a heat ratio substantially greater than 1, for example, a heat ratio of at least about 1.4 or higher, or 1.5 or higher. As a result, the output stream for the fuel cell can be hotter than the input stream. As an alternative to this type of conventional operation, the amount of fuel reformed in the reforming stage associated with the anode can be increased. For example, additional heat is generated so that the heat generated by the exothermic fuel cell reaction can be (approximately) balanced by the heat consumed in the reforming and / or consumes more heat generated. The fuel can be reformed. This can result in a substantial excess of hydrogen compared to the amount oxidized at the anode for power generation, and about 1.0 or less, or about 0.95 or less, or about 0.00. A heat ratio of 90 or less, or about 0.85 or less, or about 0.80 or less, or about 0.75 or less can be provided.

  In aspects of the invention, the heat ratio may be selected based on the desired temperature reduction through the fuel cell. Some fuel cells may have a physical aspect that can be damaged if it is greater than the threshold temperature difference that exists between the inlet and outlet. The temperature decrease may be calculated by measuring heat transfer in a bulk flow (eg, anode inlet, anode outlet, cathode inlet and cathode outlet). The decrease in temperature is the total amount of heat consumed in the endothermic reaction, the heat released in the exothermic reaction, heat loss through the fuel cell hardware, and any heat added directly to the fuel cell other than the bulk flow. It can be a function. The heat loss through the fuel cell hardware can be an estimate.

In contrast to the above operating conditions for maximum power generation, about 1.3 or less, such as about 1.0 or less, or about 0.95 or less, or about 0.90 or less, or about 0.85 or less, Alternatively, by operating the fuel cell at a heat ratio of about 0.80 or less, or about 0.75 or less, additional synthesis gas can be generated. This means that an increased amount of chemical energy generation can be arbitrarily recovered from the fuel cell output. Excess hydrogen generated by operating at a heat ratio of about 1.3 or less can be separated from, for example, the anode output flow and used as a fuel with no greenhouse gas emissions. Alternatively, a water gas shift reaction can be performed to balance the amount of hydrogen and CO present in the anode output for use as a synthesis gas having a desired synthesis gas composition, for example, a desired ratio of H ₂ to CO. Can be used.

Either hydrogen or synthesis gas can be recovered from the anode exhaust as a chemical energy output. Hydrogen can be used as a clean fuel that does not generate greenhouse gases when burned or burned. Instead, CO ₂ is “trapped” in the anode loop due to the hydrogen generated by the reforming of the hydrocarbon (or hydrocarbon compound). Additionally, hydrogen can be a useful input for various purifier processes and / or other synthetic processes. Syngas can also be a useful input for various processes. In addition to having fuel values, synthesis gas is used for the production of other higher value products, for example by using synthesis gas as an input for Fischer-Tropsch synthesis and / or methanol synthesis processes. Can be used as raw material.

Additional Fuel Cell Operation Strategies As an addition, supplement, and / or alternative to the fuel cell operation strategies described herein, reduced while having high CO ₂ utilization values, eg, at least about 60% Molten carbonate fuel cells (eg, fuel cell assemblies) can be operated at fuel utilization values, for example, less than about 50% fuel utilization. In this type of configuration, molten carbonate fuel cells, since CO ₂ utilization is possible conveniently sufficiently high, can be effective for carbon capture. Rather than attempting to maximize electrical efficiency, in this type of configuration, the overall efficiency of the fuel cell can be improved or increased based on the combined electrical and chemical efficiency. it can. Chemical efficiency may be based on drawing a hydrogen and / or syngas stream from the anode effluent as output for use in other processes. Utilizing the chemical energy output in the anode emissions can allow the desired overall efficiency for the fuel cell, even though the electrical efficiency can be reduced compared to some conventional configurations.

In various embodiments, fuel utilization at the fuel cell anode can be about 50% or less, such as about 40% or less, or about 30% or less, or about 25% or less, or about 20% or less. In various aspects, the fuel utilization in the fuel cell to generate at least some power is at least about 5%, such as at least about 10%, or at least about 15%, or at least about 20%, or at least about 25%. Or at least about 30%. Additionally or alternatively, CO ₂ utilization can be at least about 60%, such as at least about 65%, or at least about 70%, or at least about 75%.

  In some embodiments, the reformable hydrogen content of the reformable fuel in the input stream delivered to the anode and / or the reforming stage associated with the anode is at least about the net amount of hydrogen reacted at the anode. It can be 50% more, for example at least about 75% more, or at least about 100% more. Additionally or alternatively, the reformable hydrogen content of the fuel in the input stream delivered to the anode and / or the reforming stage associated with the anode is at least about 50 greater than the net amount of hydrogen reacted at the anode. %, For example, at least about 75% more, or at least about 100% more. In various embodiments, the ratio of the reformable hydrogen content of the reformable fuel in the fuel stream to the amount of hydrogen reacted at the anode is at least about 1.5: 1, or at least about 2.0: 1, Or at least about 2.5: 1, or at least about 3.0: 1. Additionally or alternatively, the ratio of the reformable hydrogen content of the reformable fuel in the fuel stream to the amount of hydrogen reacted at the anode is about 20: 1 or less, such as about 15: 1 or less, or It can be about 10: 1 or less. In one aspect, it is believed that less than 100% of the reformable hydrogen content of the anode inlet stream can be converted to hydrogen. For example, at least about 80%, eg, at least about 85%, or at least about 90% of the reformable hydrogen content of the anode inlet stream can be converted to hydrogen at the anode and / or associated reforming stages. Additionally or alternatively, the amount of reformable fuel delivered to the anode is characterized based on the lower calorific value (LHV) of the reformable fuel compared to the LHV of hydrogen oxidized at the anode. be able to. This can be called the reformable fuel excess ratio. In various embodiments, the reformable fuel excess ratio can be at least about 2.0, such as at least about 2.5, or at least about 3.0, or at least about 4.0. Additionally or alternatively, the reformable fuel excess ratio can be about 25.0 or less, such as about 20.0 or less, or about 15.0 or less, or about 10.0 or less.

  As additions, supplements, and / or alternatives to the fuel cell operating strategies described herein, conditions that can improve or optimize the combined electrical and chemical efficiency of the fuel cell A molten carbonate fuel cell (eg, a fuel cell assembly) can be operated. Instead of selecting conventional conditions for maximizing the fuel cell electrical efficiency, the operating conditions can allow for the output of excess synthesis gas and / or hydrogen in the anode discharge of the fuel cell. . Syngas and / or hydrogen can therefore be used in a variety of applications including chemical synthesis processes and hydrogen recovery for use as a “clean” fuel. In an aspect of the invention, in order to achieve a high overall efficiency, including chemical efficiency based on the chemical energy value of the synthesis gas and / or hydrogen produced compared to the energy value of the fuel input for the fuel cell. Efficiency can be reduced.

  In some embodiments, the operation of the fuel cell can be characterized based on electrical efficiency. When the fuel cell is operated to have a low electrical efficiency (EE), the molten carbonate fuel cell can have an electrical efficiency of about 40% or less, for example, an EE of about 35% or less, an EE of about 30% or less, It can be operated to have an EE of 25% or less, or an EE of about 20% or less, an EE of about 15% or less, or an EE of about 10% or less. Additionally or alternatively, the EE can be at least about 5%, or at least about 10%, or at least about 15%, or at least about 20%. Additionally or alternatively, fuel cell operation can be characterized based on total fuel cell efficiency (TFCE), such as the combined electrical and chemical efficiency of the fuel cell. When the fuel cell is operated to have high total fuel cell efficiency, the molten carbonate fuel cell is about 55% or more, such as about 60% or more, or about 65% or more, or about 70% or more, or about It can be operated to have a TFCE (and / or combined electrical and chemical efficiency) of 75% or more, or about 80% or more, or about 85% or more. It should be noted that with respect to overall fuel cell efficiency and / or combined electrical and chemical efficiency, any additional electricity generated from the use of excess heat generated by the fuel cell can be excluded from the efficiency calculation.

  In various aspects of the invention, fuel cell operation can be characterized based on a desired electrical efficiency of about 40% or less and a desired overall fuel cell efficiency of about 55% or more. When the fuel cell is operated to have the desired electrical efficiency and the desired overall fuel cell efficiency, the molten carbonate fuel cell has an electrical efficiency of about 40% or less, for example 60% with about 55% or more of TFCE. About 35% or less EE with about 35% or more, about 30% or less EE with about 65% or more TFCE, about 25% or less EE with about 70% or more TFCE, or about 20% with 75% or more TFCE It can be operated to have the following EE, about 15% or less EE with 80% or more TFCE, or about 10% or less EE with about 85% or more TFCE.

Definition syngas: In this description, the synthesis gas is defined as a mixture of H ₂ and CO in any proportion. Optionally, H ₂ O and / or CO ₂ may be present in the synthesis gas. Optionally, inert compounds (eg, nitrogen) and residual reformable fuel compounds may be present in the syngas. When components other than H ₂ and CO are present in the synthesis gas, the combined volume percent of H ₂ and CO in the synthesis gas is at least 25% by volume, eg, at least 40% compared to the total volume of the synthesis gas. It can be vol%, or at least 50 vol%, or at least 60 vol%. Additionally or alternatively, the combined volume percent of H ₂ and CO in the syngas can be 100% or less, such as 95% or less, or 90% or less.

Reformable fuel: reformable fuel is reformable carbon in order to generate the H ₂ - is defined as a fuel containing hydrogen bonds. Like other hydrocarbon compounds such as alcohol, hydrocarbons are examples of reformable fuels. Although CO and H ₂ O may participate in the water gas shift reaction to form hydrogen, CO is not considered a reformable fuel in this definition.

Reformable hydrogen content: reformable hydrogen content of fuel, the fuel reforming, followed by completing the water gas shift reaction to maximize and H ₂ generation, be derived from a fuel Defined as the number of H ₂ molecules that can be. In the present specification, H ₂ itself is not defined as a reformable fuel, but H ₂ by definition has a reformable hydrogen content of 1. Similarly, CO has a reformable hydrogen content of 1. CO is not possible reforming strictly, but by completing the water gas shift reaction, exchange of CO is brought against H _2. As an example of the reformable hydrogen content for a reformable fuel, the reformable hydrogen content of methane is 4H ₂ molecules and the reformable hydrogen content of ethane is 7H ₂ molecules. More generally, when the fuel has the composition CxHyOz, the reformable hydrogen content of the fuel at 100% reforming and water gas shift is n (H ₂ maximum reforming) = 2x + y / 2−z. Based on this definition, fuel utilization within the cell can then be expressed as n (H ₂ ox) / n (H ₂ maximum reforming). Of course, the reformable hydrogen content of a mixture of components can be determined based on the reformable hydrogen content of the individual components. The reformable hydrogen content of compounds containing other heteroatoms such as oxygen, sulfur or nitrogen can be calculated in a similar manner.

Oxidation reaction: In the present discussion, the oxidation reaction in the anode of the fuel cell is defined as the reaction corresponding to the oxidation of H ₂ which forms H ₂ O and CO ₂ by reaction with CO ₃ ²⁻ . It should be noted that the reforming reaction in the anode where the compound containing carbon-hydrogen bonds is converted to H ₂ and CO or CO ₂ is excluded from this definition of oxidation reaction at the anode. The water gas shift reaction is similar except for this definition of oxidation reaction. Still further, reference to a combustion reaction is that H ₂ or a compound containing a carbon-hydrogen bond reacts with O _{2 in} a non-electrochemical burner such as a combustion region of a combustion generator to produce H ₂ O and carbon oxide. Is defined as a reference to the reaction that forms

  Embodiments of the invention can adjust anode fuel parameters to achieve a desired operating range for a fuel cell. The anode fuel parameters can be characterized directly and / or with respect to other fuel cell processes in the form of one or more ratios. For example, the anode fuel parameter achieves one or more ratios including fuel utilization, fuel cell heating value, fuel excess ratio, reformable fuel excess ratio, reformable hydrogen content fuel ratio, and combinations thereof. In order to be able to control.

Fuel utilization: Fuel utilization characterizes the operation of the anode based on the amount of oxidized fuel compared to the reformable hydrogen content of the input stream that can be used to define fuel utilization for the fuel cell. Is an option for. In this discussion, “fuel utilization” refers to the amount of hydrogen oxidized at the anode for electricity generation (as described above) and the reformable hydrogen content of the anode input (any associated reforming stage also Defined as a ratio. The reformable hydrogen content is H ₂ that can be derived from the fuel by reforming the fuel and then completing the water gas shift reaction to maximize H ₂ production as defined above. Defined as the number of molecules. For example, each methane introduced into the anode and exposed to steam reforming conditions results in the generation of 4H ₂ molecular equivalents at maximum production (depending on reforming and / or anode conditions, Instead, it can correspond to a non-aqueous gas shift product in which one or more of the H ₂ molecules are present in the form of CO molecules). Thus, methane is defined as having a reforming possible hydrogen content 4H ₂ molecule. As another example, in this definition, ethane has a reforming possible hydrogen content 7H ₂ molecule.

The use of fuel at the anode is associated with the lower calorific value of the hydrogen oxidized at the anode by the fuel cell anode reaction compared to the lower calorific value of all fuel delivered to the anode and / or the reforming stage associated with the anode. It can also be characterized by defining the calorific value utilization based on the ratio. As used herein, “fuel cell heating value utilization” can be calculated using the flow rate and lower heating value (LHV) of the fuel components entering and leaving the fuel cell anode. As such, the fuel cell heating value utilization can be calculated as (LHV (anode_in) −LHV (anode_out)) / LHV (anode_in). Where LHV (anode_in) and LHV (anode_out) refer to the LHV of the fuel components (eg, H ₂ , CH ₄ and / or CO) in the anode inlet and outlet streams or flows, respectively. In this definition, the flow or flow LHV may be calculated as the sum of the values of each fuel component of the input and / or output flow. The contribution of each fuel component to the sum can correspond to the fuel component flow rate (eg, mol / hour) multiplied by the fuel component's LHV (eg, joule / mol).

Lower calorific value: Lower calorific value is defined as the enthalpy of combustion of a fuel component into a gas phase, fully oxidized product (eg, gas phase CO ₂ and H ₂ O products). For example, any CO ₂ present in the anode input stream does not contribute to the fuel content of the anode input because CO ₂ is already fully oxidized. With respect to this definition, the amount of oxidation that occurs at the anode by the anode fuel cell reaction is defined as the oxidation of H ₂ at the anode as part of the electrochemical reaction of the anode, as defined above.

Note that for the case only the fuel at the anode input flow is a special and H _2, the only reaction that fuel component can occur at the anode are involved, represents the conversion of H ₂ to H _{2 O.} In such cases special, fuel utilization, _{(H 2} - Rate - In (rate-in) -H ₂ - Rate - out _{(rate-out)) / H} 2 - Rate - is simplified as in. In such a case, H ₂ is the only fuel component, and LHV of H ₂ is offset from the equation. In the more general case, the anode feed may contain, for example, CH ₄ , H ₂ and CO in various amounts. Since these species can typically be present in different amounts in the anode outlet, a summary is necessary to determine fuel utilization, as described above.

In addition to or in addition to fuel utilization, the utilization of other reactants in the fuel cell can be characterized. For example, fuel cell operation can additionally or alternatively be characterized with respect to “CO ₂ utilization” and / or “oxidant” utilization. Values for CO ₂ utilization and / or oxidant utilization can be specified in a similar manner.

Fuel excess ratio: Yet another way to characterize the reaction in molten carbonate fuel cells is a modification of the anode and / or anode associated with the lower heating value of hydrogen oxidized at the anode by the fuel cell anode reaction. By defining utilization based on the ratio of the lower heating value of all fuel delivered to the quality stage. This amount is called the fuel excess ratio. As such, the fuel excess ratio can be calculated as (LHV (anode_in) / (LHV (anode_in) −LHV (anode_out)), where LHV (anode_in) and LHV (anode_out) are respectively LHV of the fuel component (eg, H ₂ , CH ₄ and / or CO) in the anode inlet and outlet streams or flows In various aspects of the invention, the molten carbonate fuel cell is at least about 1.0. For example, at least about 1.5, or at least about 2.0, or at least about 2.5, or at least about 3.0, or at least about 4.0. Alternatively, or alternatively, the fuel excess ratio is about 25 It can be less than or equal to zero.

  Note that not all of the reformable fuel in the input stream for the anode can be reformed. Preferably, at least about 90%, such as at least about 95%, or at least about 98% of the reformable fuel in the input stream to the anode (and / or associated reforming stage) can be reformed before leaving the anode. It is. In some other embodiments, the amount of reformable fuel that is reformed can be from about 75% to about 90%, such as at least about 80%.

  The above definition for the excess fuel ratio indicates that the reforming that occurs within the reforming stage associated with the anode and / or the fuel cell as compared to the amount of fuel consumed at the fuel cell anode for power generation. Provides a way to characterize quantities.

Optionally, the fuel excess ratio can be varied to account for the condition where fuel is recycled from the anode output to the anode input. When fuel (eg, H ₂ , CO and / or unreformed or partially reformed hydrocarbons) is recycled from the anode output to the anode input, such recycled fuel components It does not represent an excess of reformable or reformed fuel that can be used for the purpose. Instead, such recycled fuel components merely indicate a desire to reduce fuel utilization in the fuel cell.

Reformable Fuel Excess Ratio: Calculating the reformable fuel excess ratio is such that such recycled fuel components contain excess fuel so that only the reformable fuel LHV is included in the input stream to the anode. It is one option that indicates limiting the definition. As used herein, “reformable fuel excess ratio” refers to the anode and / or anode associated with the anode as compared to the lower heating value of hydrogen oxidized at the anode by the fuel cell anode reaction. Defined as the lower heating value of the reformable fuel delivered to the reforming stage. In the definition for reformable fuel excess ratio, any H ₂ or CO LHV at the anode input is excluded. Such LHV for reformable fuels can still be measured by characterizing the actual composition entering the fuel cell anode, and a distinction between recycled and new components is necessary. Not. Although some unreformed or partially reformed fuels may also be recycled, in most embodiments, the majority of the fuel recycled to the anode is the reformed product (eg, H ₂ or CO). Expressed mathematically, the reformable fuel excess ratio (R _RFS ) = LHV _RF / LHV _OH , where LHV _RF is the lower calorific value (LHV) of the reformable fuel, and LHV _OH is The lower heating value (LHV) of hydrogen oxidized at the anode. The LHV of hydrogen oxidized at the anode may be calculated by subtracting the LHV of the anode outlet stream from the LHV of the anode inlet stream (eg, LHV (anode_in) −LHV (anode_out)). In various aspects of the invention, the molten carbonate fuel cell has at least about 0.25, such as at least about 0.5, or at least about 1.0, or at least about 1.5, or at least about 2.0. Or at least about 2.5, or at least about 3.0, or at least about 4.0 with a reformable fuel excess ratio. Additionally or alternatively, the reformable fuel excess ratio can be about 25.0 or less. It should be noted that such a narrower definition based on the amount of reformable fuel delivered to the anode compared to the amount of oxidation at the anode identifies two types of fuel cell operating methods with low fuel utilization. Can do. Some fuel cells achieve low fuel utilization by recycling a substantial portion from the anode output to the anode input. This recycling allows any hydrogen at the anode input to be used again as input to the anode. This can reduce the amount of reforming and at least a portion of the unused fuel is recycled in subsequent passes even if the fuel utilization is low for a single pass of the fuel cell. Thus, fuel cells with a wide variety of fuel utilization values may have the same ratio of reformable fuel delivered to the anode reforming stage to hydrogen oxidized in the anode reaction. In order to change the ratio of reformable fuel delivered to the anode reforming stage with respect to the amount of oxidation at the anode, an anode feed with the original content of non-reformable fuel needs to be identified or the anode Unused fuel at the output needs to be recovered for other uses, or both.

Reformable hydrogen excess ratio: Yet another option for characterizing the operation of a fuel cell is based on the “reformable hydrogen excess ratio”. The excess reformable fuel ratio defined above is defined based on the lower heating value of the reformable fuel component. Reformable hydrogen excess ratio is defined as the reformable hydrogen content of the reformable fuel delivered to the anode and / or the reforming stage associated with the anode as compared to the hydrogen reacted at the anode by the fuel cell anode reaction. Is done. As such, the “reformable hydrogen excess ratio” can be calculated as (RFC (reformable_anode_in) / (RFC (reformable_anode_in) −RFC (anode_out)), where (RFC (reformable_anode_in) is: Refers to the reformable hydrogen content of the reformable fuel in the anode inlet stream or flow, and RFC (anode_out) is the fuel component of the anode inlet and outlet stream or flow (eg, H ₂ , CH ₄ and / or CO) Reformable hydrogen content refers to RFC, which can be expressed in moles / second, moles / hour, etc. Fuel with a large ratio of reformable fuel to anode oxidation delivered to the anode reforming stage How to activate the battery Examples are to balance the generation and consumption of heat in the fuel cell, to reform the reformable fuel to form a can .H ₂ and CO that is excessive way modification is performed Is an endothermic process, which can be countered by the generation of current in the fuel cell, which causes the fuel cell to be in the form of heat and flow generated by the anodization and carbonate formation reactions. An excess of heat can be generated which corresponds to (roughly) the difference from the energy exited, and the excess heat per mole of hydrogen involved in the anodic oxidation / carbonate formation reaction can cause reforming to reduce the moles of hydrogen. It can be greater than the heat absorbed because it is generated, so that fuel cells operating under conventional conditions will increase in temperature from the inlet to the outlet As an alternative to this type of conventional operation, the amount of fuel reformed in the reforming step associated with the anode can be increased, for example, the heat generated by the exothermic fuel cell reaction The heat consumed by the reforming can be (approximately) balanced, or the heat consumed by the reforming can be greater than the excess heat generated by the fuel oxidation, and the temperature across the fuel cell. Additional fuel can be reformed to provide a reduction, which can result in a substantial excess of hydrogen compared to the amount required for power generation. As such, the feed to the fuel cell anode inlet or associated reforming stage may consist essentially of a reformable fuel, such as a substantially pure methane feed. Can. During conventional operation for power generation using such fuels, molten carbonate fuel cells can operate with about 75% fuel utilization. This is then about 75% (or 3/4) of the fuel content delivered to the anode to form hydrogen that reacts with carbonate ions at the anode to form H ₂ O and CO _2. Is used. In conventional operation, the remaining approximately 25% of the fuel content can be reformed to H ₂ in the fuel cell (or passing through an unreacted fuel cell for any CO or H _{2 in} the fuel). Can then be combusted outside the fuel cell to form H ₂ O and CO ₂ and provide heat for the cathode inlet to the fuel cell. The reformable hydrogen excess ratio in this state can be 4 / (4-1) = 4/3.

  Electrical efficiency: As used herein, the term “electric efficiency” (“EE”) occurs in a fuel cell divided by the rate of low heating value (“LHV”) of the fuel input to the fuel cell. Defined as electrochemical power. The fuel input to the fuel cell is delivered to the fuel delivered to the anode, the fuel delivered to the cathode, and any fuel used to maintain the temperature of the fuel cell, for example, the burner associated with the fuel cell Fuel to be included. In this description, the power generated by the fuel may be described in terms of LHV (el) fuel rate.

  Electrochemical power: As used herein, the term “electrochemical power” or LHV (el) refers to the carbonate ion passing through the fuel cell electrolyte and the circuit connecting the cathode to the anode in the fuel cell. Power generated by movement. Electrochemical power eliminates power generated from the fuel cell or consumed in upstream or downstream equipment. For example, electricity resulting from heat in a fuel cell waste stream is not considered part of the electrochemical power. Similarly, the power generated in a gas turbine or other device upstream of the fuel cell is not part of the generated electrochemical power. “Electrochemical power” does not take into account the power consumed during the operation of the fuel cell or any losses caused by the conversion from direct current to alternating current. In other words, the power used to provide fuel cell operation or otherwise to operate the fuel cell is not subtracted from the DC power generated by the fuel cell. As used herein, power density is current density multiplied by voltage. As used herein, total fuel cell power is the power density multiplied by the fuel cell area.

  Fuel Input: As used herein, the term “anode fuel input”, denoted as LHV (anode_in), is the amount of fuel in the anode inlet stream. The term “fuel input”, denoted as LHV (in), is used to maintain a) the amount of fuel in the anode inlet stream, b) the amount of fuel in the cathode inlet stream, and c) the temperature of the fuel cell. The total amount of fuel delivered to the fuel cell, including the amount of fuel that is delivered. Fuels may include reformable and non-reformable fuels based on the definition of reformable fuel provided herein. Fuel input is not the same as fuel use.

Total fuel cell efficiency: As used herein, the term “total fuel cell efficiency” (“TFCE”) is the ratio of the LHV of the syngas produced by the fuel cell to the electrochemical power produced by the fuel cell. Is divided by the ratio of the LHV of the fuel input to the anode. In other words, TFCE = (LHV (el) + LHV (sg net)) / LHV (anode_in), where LHV (anode_in) is the fuel component (eg, H ₂ , CH ₄ and / or CO) at the anode LHV as delivered and LHV (sg net) refers to the rate at which synthesis gas (H ₂ , CO) is produced at the anode, which is the synthesis gas input to the anode and the synthesis gas output from the anode Is the difference between LHV (el) describes the electrochemical power generation of the fuel cell. Total fuel cell efficiency eliminates the heat generated by the fuel cell, which is advantageously used outside the fuel cell. In operation, the heat generated by the fuel cell may be advantageously used in downstream equipment. For example, heat may be used to generate additional electricity or to heat water. These applications are not part of the overall fuel cell efficiency as the terminology used in this application if they occur away from the fuel cell. Total fuel cell efficiency relates only to fuel cell operation and does not include power generation or fuel cell consumption upstream or downstream.

Chemical efficiency: As used herein, the term “chemical efficiency” refers to the lower heating value of H ₂ and CO in the anode discharge of a fuel cell divided by the fuel input or LHV (in), or LHV ( sg out).

Neither electrical efficiency nor overall system efficiency takes into account the efficiency of upstream or downstream processes. For example, it may be advantageous to use turbine emissions as a source of CO ₂ for the fuel cell cathode. In this arrangement, turbine efficiency is not considered as part of the calculation of electrical efficiency or total fuel cell efficiency. Similarly, the output from the fuel cell may be recycled as input to the fuel cell. When calculating electrical efficiency or total fuel cell efficiency in single pass mode, the recycle loop is not considered.

Steam to carbon ratio (S / C): As used herein, steam to carbon ratio (S / C) is the mole ratio of steam in a flow to the reformable carbon in the flow. Carbon in the form of CO and CO ₂ is not included as modifiable carbon in this definition. The steam to carbon ratio can be measured and / or controlled at different points in the system. For example, the composition of the anode inlet stream can be modified to achieve the appropriate S / C for modification at the anode. S / C can be given as the molar flow rate of H ₂ O divided by the product of the molar flow rate of the fuel, eg, the fuel multiplied by the number of carbon atoms in the methane. Thus, S / C = f _H2O / (f _CH4 x # C) where f _H2O is the molar flow rate of water and f _CH4 is the molar flow rate of methane (or other fuel). And #C is the number of carbons in the fuel.

  Fuel cell and fuel cell components: In this discussion, a fuel cell can correspond to a unit cell having an anode and a cathode separated by an electrolyte. The anode and cathode can receive an input gas flow to facilitate their respective anode and cathode reactions to transport charge across the electrolyte and generate electricity. A fuel cell stack can represent multiple cells in an integrated unit. Although a fuel cell stack can include multiple fuel cells, the fuel cells can typically be connected in parallel, and so that they collectively represent a single fuel cell of larger diameter (approximately ) Can function. When the input flow is delivered to the anode or cathode of the fuel cell stack, the fuel stack is a flow channel for splitting the input flow between each cell in the stack and a flow channel for combining the output flows from the individual cells Can be included. In this discussion, the fuel cell array is a plurality of fuel cells (eg, a plurality of fuel cell stacks) arranged in series, parallel, or any other convenient manner (eg, in a combination of series and parallel). Can be used to refer to. The fuel cell array includes one or more stages of fuel cells and / or fuel cell stacks, where the anode / cathode output from the first stage can serve as the anode / cathode input for the second stage. Can do. Note that the anodes of the fuel cell array need not be connected in the same manner as the cathodes of the array. For convenience, the input to the first anode stage of the fuel cell array may be referred to as the anode input for the array, and the input to the first cathode stage of the fuel cell array is the input to the array. It may be called the cathode input. Similarly, the output from the final anode / cathode stage may be referred to as the anode / cathode output from the array.

  Reference to the use of a fuel cell herein refers to a “fuel cell stack” typically comprised of individual fuel cells, and more generally refers to the use of one or more fuel cell stacks in fluid communication. That should be understood. Individual fuel cell elements (plates) can typically be “stacked” together in a rectangular array called a “fuel cell stack”. This fuel cell stack typically can provide a flow between all individual fuel cells and can distribute reactants, and then collect products from each of these elements. be able to. When viewed as a unit, an active fuel cell stack can be viewed as a single piece, even if it is composed of many (often dozens or hundreds) of individual fuel cell elements. These individual fuel cell elements can typically have similar voltages (similar reactant and product concentrations), and the total power output is when the elements are electrically connected in series, It can result from the sum of all currents of the battery element. The stacks can also be arranged in series to produce a high voltage. A parallel arrangement can increase the current. If a sufficiently large volume fuel cell stack is available to handle a given effluent flow, the systems and methods described herein should be used in a single molten carbonate fuel cell stack. Can do. In other aspects of the invention, multiple fuel cell stacks may be desirable or required for various reasons.

  For the purposes of the present invention, unless otherwise specified, the term “fuel cell” refers to one or more individual, where there is a single input and output as the manner in which the fuel cell is typically utilized in practice. Should be understood as referring to and / or including reference to it. Similarly, the term fuel cell (s) should also be understood to refer to and / or include a plurality of individual fuel cell stacks unless specifically stated otherwise. In other words, all references within the scope of this specification are interchangeably applicable to the operation of a fuel cell stack as a “fuel cell” unless specifically indicated. For example, the volume of emissions generated in commercial scale combustion generators can be too large for processing with conventional diameter fuel cells (eg, a single stack). Multiple fuel cells (ie, two or more individual fuel cells or two or more individual fuel cells) so that each fuel cell can process a (substantially) equivalent portion of the combustion exhaust in order to fully process the emissions. Fuel cell stacks) can be arranged in parallel. Although multiple fuel cells can be used, the fuel cells typically can be operated on a given (approximately) equivalent portion of the combustion emissions in a generally similar manner.

  “Internal reforming” and “external reforming”: A fuel cell or fuel cell stack may include one or more internal reforming moieties. As used herein, the term “internal reforming” refers to fuel reforming that occurs within the body of the fuel cell (fuel cell stack) or otherwise within the fuel cell assembly. External reforming is often used with fuel cells, but occurs in each of the devices located outside the fuel cell stack. In other words, the body of the external reformer is not in direct physical contact with the body of the fuel cell or fuel cell stack. In a typical preparation, the output from the external reformer can be fed to the anode inlet of the fuel cell. Unless specifically stated otherwise, the modification described in this application is an internal modification.

  Internal reforming may occur within the fuel cell anode. Internal reforming can occur additionally or alternatively within an internal reforming element that is integrated within the fuel cell assembly. Integrated reforming elements may be located between fuel cell elements in the fuel cell stack. In other words, one of the stacked trays can be a reforming part instead of a fuel cell element. In one aspect, the flow arrangement within the fuel cell stack directs fuel to the internal reforming element and then to the anode portion of the fuel cell. Thus, from a flow point of view, the internal reforming element and the fuel cell element can be arranged in series within the fuel cell stack. As used herein, “anode reforming” is fuel reforming that occurs within the anode. As used herein, the term “internal reforming” is the reforming that occurs within an integrated reforming element, not the anode portion.

  In some embodiments, the reforming stage that is internal to the fuel cell assembly can be considered as associated with the anode of the fuel cell assembly. In some alternative embodiments, for a reforming stage of a fuel cell stack that can be associated with an anode (eg, associated with multiple anodes), the output flow from the reforming stage is passed to at least one anode. As such, a flow path can be available. This can correspond to having an initial portion of the fuel cell plate that is not in contact with the electrolyte, and can instead serve as a reforming catalyst. Another option for the associated reforming stage is to return the output from the integrated reforming stage to one or more input sides of the fuel cell stack fuel cell as one of the elements of the fuel cell stack. It can be possible to have separate integrated reforming stages.

  From the viewpoint of thermal integration, the characteristic height of the fuel cell stack can be the height of the individual fuel cell stack elements. It should be noted that separate reforming stages and / or separate endothermic reaction stages could have a different stack height than the fuel cell. In such a scenario, the height of the fuel cell element can be used as a characteristic height. In some embodiments, the integrated endothermic reaction stage is one such that the integrated endothermic reaction stage can use heat from the fuel cell as a heat source for the endothermic reaction. It can be defined as a stage where heat integration with the above fuel cell is performed. Such an integrated endothermic reaction stage is defined as being placed at a height of less than 10 times the height of the laminated element from any fuel cell that provides heat to the integrated stage. be able to. For example, the integrated endothermic reaction stage (e.g., reforming stage) is less than 10 times the height of the laminated element from any thermally integrated fuel cell, or less than 8 times the height of the laminated element, or It can be arranged at a height of less than 5 times the height of the laminated element or less than 3 times the height of the laminated element. In the present discussion, the integrated reforming stage and / or the integrated endothermic reaction stage representing the stack element adjacent to the fuel cell element is no more than about 1 stack element height from the adjacent fuel cell element. Can be defined as

  In some embodiments, the separate reforming stage that is heat integrated with the fuel cell element may correspond to a reforming stage associated with the fuel cell element. In such embodiments, the integrated fuel cell element can provide at least a portion of heat to the associated reforming stage, and the associated reforming stage fuels at least a portion of the reforming stage output. The fuel cell can be provided as a stream. In other embodiments, the separate reforming stages can be integrated with the fuel cell for heat transfer without being associated with the fuel cell. In this type of situation, a separate reforming stage can receive heat from the fuel cell, but can determine that the output of the reforming stage is not used as an input to the fuel cell. Instead, the output of such reforming stages may be used for other purposes such as direct addition of output to the anode exhaust stream and / or to form a separate output stream from the fuel cell assembly. You can decide to use it.

  More generally, separate stack elements of the fuel cell stack are used to perform any convenient type of endothermic reaction that can take advantage of the waste heat provided by the integrated fuel cell stack elements. can do. Instead of a suitable plate for carrying out the reforming reaction in the hydrocarbon stream, a separate lamination element can have a suitable plate to catalyze another type of endothermic reaction. Other arrangements of manifolds or inlet conduits in the fuel cell stack can be used to provide appropriate input flow to the respective stack elements. Additionally or alternatively, other arrangements of similar manifolds or outlet conduits can be used to withdraw the output flow from each laminate element. Optionally, the output flow from the endothermic reaction stage of the stack can be recovered from the fuel cell stack without passing the output flow through the fuel cell anode. In any such embodiment, the product of the exothermic reaction can thus exit the fuel cell stack without passing through the fuel cell anode. Examples of other types of endothermic reactions that can be performed in a stack element of a fuel cell stack can include, without limitation, ethanol dehydration to form ethylene and ethane cracking.

Recycling: As defined herein, recycling of a portion of a fuel cell output to a fuel cell inlet (eg, an anode exhaust or a stream that is separated or recovered from an anode exhaust) is It can correspond to a direct or indirect recycling stream. Direct recycling of the flow to the fuel cell inlet is defined as recycling of the flow without passing through the intermediate process, and for indirect recycling, the recycling after passing the flow through one or more intermediate processes Is involved. For example, if the anode effluent passes through a CO ₂ separation stage prior to recycling, this is considered an indirect recycling of the anode effluent. If a portion of the anode exhaust recovered from the anode exhaust, for example a H ₂ stream, passes through a gasifier to convert coal into a suitable fuel for introduction into the fuel cell, this is also It is considered indirect recycling.

Anode Input and Output In various embodiments of the present invention, the MCFC array includes, for example, hydrogen and hydrocarbons, such as methane (or alternatively, hydrocarbons or A fuel received at the anode inlet comprising a hydrocarbon-like compound) can be provided. Most methane (or other hydrocarbons or hydrocarbon-like compounds) fed to the anode can typically be fresh methane. In this description, new fuel, such as new methane, refers to fuel that is not recycled from another fuel cell process. For example, methane recycled from the anode outlet stream to the anode inlet is not considered “fresh” methane and can instead be described as recovered methane. A fuel supply source that is used can be shared with other components such as a turbine which uses a portion of the fuel supply source to provide a CO ₂ containing stream to the cathode input. The fuel source input can include water in an appropriate proportion to the fuel to reform the hydrocarbon (or hydrocarbon-like) compound in the reforming section that generates hydrogen. For example, when methane is the fuel inputs for reforming to generate the H _2, the molar ratio of water to fuel is about 1: to be 1: 1 to about 10: 1, such as at least about 2 it can. A ratio of 4: 1 or higher is typical for external reforming, but lower values can be typical for internal reforming. To the extent that H ₂ is part of the fuel source, in some optional embodiments, oxidation of H _{2 at} the anode may tend to yield H ₂ O that can be used to reform the fuel. Thus, additional water may not be needed for the fuel. The fuel source may optionally contain components that are not important to the fuel source (eg, a natural gas supply may contain some content of CO ₂ as an additional component). For example, the natural gas supply can contain CO ₂ , N ₂ and / or other inert (inert) gases as additional components. Optionally, in some embodiments, the fuel source may contain CO, such as CO from the recycled portion of the anode exhaust. An additional or alternative potential source for CO in the fuel to the fuel cell assembly may be CO generated by steam reforming of hydrocarbon fuel performed on the fuel prior to entering the fuel cell assembly. it can.

  More generally, various types of fuel streams may be suitable for use as an input stream for the anode of a molten carbonate fuel cell. Some fuel streams may correspond to streams containing hydrocarbons and / or hydrocarbon-like compounds that may contain heteroatoms different from C and H. In this discussion, unless otherwise specified, references to fuel streams containing hydrocarbons for MCFC anodes are defined to include fuel streams containing such hydrocarbon-like compounds. Examples of hydrocarbon (including hydrocarbon-like) fuel streams include natural gas, streams containing C1-C4 carbon compounds (eg, methane or ethane), and heavier C5 + hydrocarbons (hydrocarbon-like compounds). Stream), as well as combinations thereof. Still other additional or alternative examples of potential fuel streams used for anode input may include biogas type streams, such as methane resulting from natural (biological) decomposition of organic materials.

In some embodiments, molten carbonate fuel cells can be used to process input streams such as natural gas and / or hydrocarbon streams with low energy content due to the presence of diluent compounds. . For example, several sources of methane and / or natural gas is the source that may include CO 2 or _nitrogen, a substantial amount of other inert molecule, such as argon or helium. Due to the presence of increased amounts of CO ₂ and / or inerts, the energy content of the fuel stream based on the source can be reduced. The use of low energy content fuels in combustion reactions (such as for powering combustion power turbines) can present problems. However, molten carbonate fuel cells can generate power based on a low energy content fuel source with little or no impact on fuel cell efficiency. The presence of an additional gas volume may require additional heat to raise the fuel temperature to the temperature for reforming and / or anodic reaction. Additionally, due to the equilibrium nature of the water gas shift reaction within the fuel cell anode, the presence of additional CO ₂ can have an effect on the relative amounts of H ₂ and CO present in the anode output. However, inert compounds can have only minimal direct impact on reforming and anodic reactions in other cases. The amount of CO ₂ and / or inert compounds in the fuel stream for the molten carbonate fuel cell, if present, is at least about 1% by volume, such as at least about 2% by volume, or at least about 5% by volume, or At least about 10%, or at least about 15%, or at least about 20%, or at least about 25%, or at least about 30%, or at least about 35%, or at least about 40%, or at least It can be about 45% by volume, or at least about 50% by volume, or at least about 75% by volume. Additionally or alternatively, the amount of CO ₂ and / or inert compounds in the fuel stream for the molten carbonate fuel cell is about 90% or less, such as about 75% or less, or about 60% by volume. Or about 50% or less, or about 40% or less, or about 35% or less.

Yet another example of a potential source for the anode input stream may correspond to a refiner and / or other industrial process output stream. For example, coking is a common process in many refiners to convert heavier compounds to a lower boiling range. Coking typically produces off-gas containing various compounds that are gases at room temperature, including CO and various C1-C4 hydrocarbons. This off-gas can be used as at least part of the anode input stream. Other refiner off-gas streams can be additionally or alternatively suitable for inclusion in the anode input stream, e.g., light fractions generated during cracking or other refiner processes ( C1-C4). Still other suitable refiner streams can additionally or alternatively include a refiner stream containing CO or CO ₂ that also contains H ₂ and / or reformable fuel compounds.

Still other potential sources for anode input can additionally or alternatively include streams having increased water content. For example, an ethanol output stream from an ethanol plant (or another type of fermentation process) contains a substantial portion of H ₂ O prior to final distillation. Such H ₂ O can typically have only minimal impact on the operation of the fuel cell. Thus, a fermentation mixture of alcohol (or other fermentation product) and water can be used as at least a portion of the anode input stream.

Biogas or digester gas is another additional or alternative potential source for the anode input. Biogas may consist primarily of methane and CO ₂ and is typically generated by decomposition or digestion of organic substances. Anaerobic bacteria may be used to digest organic material and produce biogas. Prior to use as an anode input, impurities (eg, sulfur-containing compounds) may be removed from the biogas.

The output stream from the MCFC anode can include H ₂ O, CO ₂ , CO, and H ₂ . Optionally, the anode output stream could have unreacted fuel (eg, H ₂ or CH ₄ ) or inert compounds in the feed as an additional output component. Instead of using this output stream as a fuel source to provide heat for the reforming reaction or as a combustion fuel to heat the cell, it has a potential value as an input to another process One or more separations can be performed in the anode output stream to separate CO ₂ from the components (eg, H ₂ or CO). H ₂ and / or CO can be used as a synthesis gas for chemical synthesis, as a source of hydrogen for chemical reactions, and / or as a fuel with reduced greenhouse gas emissions.

  Anode emissions can be subject to various gas treatment options, including water gas shift and separation of components from each other. Two general anodization schemes are shown in FIGS.

FIG. 1 schematically illustrates an example of a reaction system for operating a fuel cell array of a molten carbonate fuel cell in connection with a chemical synthesis process. In FIG. 1, a fuel stream 105 is provided to a reforming stage 110 associated with a fuel cell 120, eg, a fuel cell anode 127 that is part of a fuel cell stack of a fuel cell array. The reforming stage 110 associated with the fuel cell 120 can be internal to the fuel cell assembly. In some optional embodiments, an external reforming stage (not shown) may also be used to reform a portion of the reformable fuel in the input stream before passing the input stream through the fuel cell assembly. it can. The fuel stream 105 can preferably include a reformable fuel, such as methane, other hydrocarbons, and / or other hydrocarbon-like compounds, such as organic compounds containing carbon-hydrogen bonds. The fuel stream 105 can optionally contain H ₂ and / or CO, eg, H ₂ and / or CO provided by the optional anode recycle stream 185. Note that the anode recycle stream 185 is optional, and in many embodiments, the recycle stream is directly from the anode exhaust 125 through the anode stream 125 or in combination with the fuel stream 105 or the modified fuel stream 115. Return to 127 and not provided. After reforming, the reformed fuel stream 115 can be passed through the anode 127 of the fuel cell 120. A CO ₂ and O ₂ containing stream 119 can also be passed to the cathode 129. The flow of carbonate ions 122, CO ₃ ²⁻ from the cathode portion 129 of the fuel cell can provide the remaining reactants required for the anode fuel cell reaction. The anode exhaust 125 obtained based on the reaction at the anode 127 is H ₂ O, CO ₂ , a component corresponding to one or more incompletely reacted fuels (H ₂ , CO, CH ₄ , or reformable fuel). As well as one or more additional non-reactive components, such as N ₂ , and / or other contaminants that are part of the fuel stream 105. The anode exhaust 125 can then be passed through one or more separation stages. For example, CO ₂ removal stage 140, the low-temperature CO ₂ removal system, the acidic amine washing step for the removal of gas or CO ₂ output stream 143 for separating from the anode effluent CO ₂ separation stage, such as CO ₂ Can correspond to another appropriate kind of. Optionally, anode discharge is first passed through water gas shift reactor 130 so that any CO present in the anode discharge (in addition to any H ₂ O) is optionally water gas shifted anode discharge 135. Can be converted to CO ₂ and H ₂ . Depending on the nature of the CO ₂ removal stage, the water condensation or removal stage 150 may be desirable to remove the water output stream 153 from the anode effluent. Although shown in FIG. 1 after the CO ₂ separation stage 140, it may instead be optionally located before the CO ₂ separation stage 140. Additionally, in order to generate the high purity permeate stream 163 of H _2, can use any membrane separation stage 160 for H ₂ separation. The resulting retained stream 166 can then be used as an input to the chemical synthesis process. Stream 166 can be additionally or alternatively shifted in the second water gas shift reactor 131 to adjust the H ₂ , CO and CO ₂ content to different ratios, in a chemical synthesis process This produces an output stream 168 for further use. Although the anode recycle stream 185 is shown in FIG. 1 as being recovered from the retentate stream 166, the anode recycle stream 185 may additionally or alternatively be placed at various separation stages or other convenient locations therebetween. Can be recovered from. The separation stages and shift reactors can be configured additionally or alternatively in different orders and / or in a parallel configuration. Eventually, a stream 139 having a reduced content of CO ₂ can be generated as output from the cathode 129. For simplicity, the various stages of compression and heat addition / removal and steam addition or removal that may be useful in the process are not shown.

As described above, the various types of separations performed in the anode discharge can be performed in any convenient order. FIG. 2 shows another sequence of examples for performing separation in the anode discharge. In FIG. 2, the anode effluent 125 can first pass through a separation stage 260 to remove a portion 263 of the hydrogen content from the anode effluent 125. This can allow for a reduction in the H ₂ content of the anode effluent, for example, to provide retentate 266 at a H ₂ : CO ratio closer to 2: 1. The ratio of H ₂ to CO can then be further adjusted to achieve the desired value in the water gas shift stage 230. The water gas shifted output 235 can then be passed through a CO ₂ separation stage 240 and a water removal stage 250 to produce an output stream 275 suitable for use as an input to the desired chemical synthesis process. . Optionally, the output stream 275 can be exposed to an additional water gas shift stage (not shown). A portion of the output stream 275 can optionally be recycled to the anode input (not shown). Of course, still other combinations and arrangements of separation steps can be used to generate a stream based on the anode output having the desired composition. For simplicity, the various stages of compression and heat addition / removal, and steam addition or removal that may be useful in the process are not shown.

Cathode Inlet and Output Conventionally, molten carbonate fuel cells can be operated based on drawing a desired load while consuming some portion of the fuel in the fuel stream delivered to the anode. The fuel cell voltage can then be determined by the load, the fuel input to the anode, the air and CO ₂ provided to the cathode, and the internal resistance of the fuel cell. CO ₂ to the cathode can conventionally be provided in part by using anode emissions as at least a portion of the cathode input stream. In contrast, the present invention can use separate / different sources for the anode and cathode inputs. By removing any direct association between the anode input flow and cathode input flow compositions, additional options become available to operate the fuel cell, for example, generating excess amounts of synthesis gas. To improve carbon dioxide capture and / or in particular improve the overall efficiency (electrical and chemical power) of the fuel cell.

In a molten carbonate fuel cell, the transport of carbonate ions through the electrolyte in the fuel cell transports CO ₂ from the first flow path to the second flow path, with a lower concentration (cathode) to a higher concentration (anode). enabling transport to, therefore, it is possible to provide a method which can facilitate the capture of CO _2. Selection of a portion of the fuel cell for the CO ₂ separation can be based on an electrochemical reaction which allows the battery to generate electricity. For non-reactive species (eg, N ₂ ) that do not participate effectively in electrochemical reactions within the fuel cell, there can be an amount that is not critical to the reaction and transport from the cathode to the anode. In contrast, the potential (voltage) difference between the cathode and anode can provide a strong driving force for the transport of carbonate ions through the fuel cell. As a result, the transport of carbonate ions in molten carbonate fuel cells is relatively highly selective, with CO ₂ being transported from the cathode (lower CO ₂ concentration) to the anode (higher CO ₂ concentration). Make it possible. However, a challenge in using a molten carbonate fuel cell for carbon dioxide removal may be that the fuel cell has a limited ability to remove carbon dioxide from a relatively lean cathode supply. . When the CO ₂ concentration is reduced to less than about 1.0 mol%, the voltage and / or power generated by the carbonate fuel cell can begin to decline rapidly. Further, when the CO ₂ concentration is reduced to, for example, less than about 0.3% by volume, at some point the fuel cell voltage causes little or no longer carbonate transport and the fuel cell stops functioning. Can be low enough. Thus, at least some CO ₂ is optionally present in the exhaust gas from the cathode stage of the fuel cell at commercially viable operating conditions.

The amount of carbon dioxide delivered to the fuel cell cathode can be determined based on the source CO ₂ content for the cathode inlet and / or the amount of carbon-containing fuel in the cathode inlet stream. For a cathode inlet stream containing a carbon-containing fuel, that is, an amount of CO ₂ proportional to the volume percent of fuel in the cathode inlet stream multiplied by the average number of carbons in the fuel compound can occur in situ at the cathode. . For example, H ₂ has no carbon, CO and CH ₄ have 1 carbon, ethane has 2 carbons, and so on. As a result, the amount of CO ₂ provided to the cathode by fuel combustion ranges from about 0.25% to about 10% by volume from the range where there is no CO ₂ (when all of the fuel at the cathode is H ₂ ). Can be up to range. The upper limit of the range of CO ₂ derived from the burned fuel represents a state in which a substantial portion of the fuel corresponds to aromatic compounds having multiple carbons and / or other fuels. The CO ₂ content of the cathode inlet stream derived from fuel combustion can be added to any CO ₂ present in the cathode inlet stream as the stream enters the cathode.

An example of a suitable CO ₂ containing stream for use as a cathode input flow may be an output or effluent flows from the combustion source. Examples of combustion sources include, but are not limited to, sources based on combustion of natural gas, combustion of coal, and / or combustion of other hydrocarbon type fuels (including biologically derived fuels). It is. Additional or alternative sources include burning carbon-containing fuels to heat other types of boilers, burned heaters, furnaces, and / or other materials (eg, water or air) Other types of devices can be included. For the first approximation, the CO ₂ content of the output flow from the combustion source can be a fractional part of the flow. For higher CO ₂ content effluent flows, eg, output from coal combustion sources, the CO ₂ content from most commercial coal-fired power plants can be up to about 15% by volume. More generally, the CO ₂ content of the output or exhaust flow from the combustion source is at least about 1.5% by volume, or at least about 1.6% by volume, or at least about 1.7% by volume, or at least about 1 .8% by volume, or at least about 1.9% by volume, or at least 2% by volume, or at least about 4% by volume, or at least about 5% by volume, or at least about 6% by volume, or at least about 8% by volume. Can do. Additionally or alternatively, the CO ₂ content of the output or emissions flow from the combustion source is about 20% or less, such as about 15% or less, or about 12% or less, or about 10%. % Or less, or about 9% or less, or about 8% or less, or about 7% or less, or about 6.5% or less, or about 6% or less, or about 5.5% or less, or It can be about 5% by volume or less, or about 4.5% by volume or less. The concentrations indicated above are on a dry basis. It should be noted that lower CO ₂ content values are derived from some natural gas or methane combustion sources, such as generators that are part of a power generation system that may or may not include an exhaust gas recycling loop. Can be present in the effluent.

Another potential source for the cathode input stream may comprise a source of CO ₂ produced in biologically additionally or alternatively. This, for example, CO 2 generated during the processing of bio derived _compounds, for example, can contain CO ₂ that occurs during ethanol production. Additional or alternative examples can include CO ₂ generated by biologically produced fuel combustion, eg, lignocellulose combustion. Yet another additional or alternative potential CO ₂ source is the output from various industrial processes or the exhaust stream, eg the CO ₂ content generated by the plant for the production of steel, cement and / or paper. Can correspond to a stream.

Additional yet another CO ₂ or potential sources of alternative may be a CO ₂ containing stream from the fuel cell. CO ₂ containing stream from the fuel cell is different cathode output stream from the fuel cell, different anode output stream from the fuel cell, the recycle stream from the cathode output to the cathode input of the fuel cell, and / or the anode output Can correspond to a recycle stream from the fuel cell cathode input. For example, an MCFC operated in stand-alone mode under conventional conditions can generate cathode emissions having a CO ₂ concentration of at least about 5% by volume. Such CO ₂ containing cathode effluent can be used as a cathode input for the MCFC is operated by embodiments of the present invention. More generally, other types of fuel cells that generate CO ₂ output from cathode emissions can be used in addition or as an alternative, as well as other types of CO ₂ -containing streams that are “combustion” reactions. And / or by a combustion generator. Optionally, but preferably, CO ₂ containing stream from another fuel cell may be from another molten carbonate fuel cell. For example, for a molten carbonate fuel cell connected in series with respect to the cathode, the output from the cathode of the first molten carbonate fuel cell is used as the input to the cathode of the second molten carbonate fuel cell. can do.

With regard to various types of CO ₂ containing stream from a source other than the combustion source, CO ₂ content of the stream may vary widely. The CO ₂ content of the input stream to the cathode is at least about 2% by volume, such as at least about 4% by volume, or at least about 5% by volume, or at least about 6% by volume, or at least about 8% by volume CO ₂ . Can be contained. Additionally or alternatively, the CO ₂ content of the input stream to the cathode is about 30% or less, such as about 25% or less, or about 20% or less, or about 15% or less, or about It can be 10% or less, or about 8% or less, or about 6% or less, or about 4% or less. For some even higher CO ₂ content streams, the CO ₂ content can be higher than about 30% by volume, for example, the stream is substantially from only CO ₂ and other non-critical amounts of other compounds. Configured. As an example, a gas-fired turbine without exhaust gas recycling can produce an exhaust stream having a CO ₂ content of about 4.2% by volume. By exhaust gas recycling, gas-fired turbines can produce an exhaust stream having a CO ₂ content of about 6-8% by volume. Stoichiometric combustion of methane can produce an exhaust stream having a CO ₂ content of about 11% by volume. Coal combustion can result in reject flow with CO ₂ content of about 15 to 20 vol%. Combustion heaters that use purifier off-gas can produce an exhaust stream having a CO ₂ content of about 12-15% by volume. A gas turbine operating at low BTU gas without using any exhaust gas recycling can produce an exhaust stream having a CO ₂ content of about 12% by volume.

In addition to CO ₂ , the cathode input stream must contain O ₂ to provide the necessary components for the cathode reaction. Some cathode input streams can be based on having air as a component. For example, a combustion exhaust stream can be formed by burning hydrocarbon fuel in the presence of air. A cathode input stream having an oxygen content based on the inclusion of such a combustion exhaust stream, or another type of air, has an oxygen content of about 20% or less, such as about 15% or less, or about 10% or less. Can have. Additionally or alternatively, the oxygen content of the cathode input stream can be at least about 4% by volume, such as at least about 6% by volume, or at least about 8% by volume. More generally, the cathode input stream can have a suitable oxygen content to carry out the cathode reaction. In some embodiments, this can correspond to an oxygen content of about 5% to about 15% by volume, such as about 7% to about 9% by volume. For many types of cathode input streams, the combined amount of CO ₂ and O ₂ represents less than about 21% by volume of the input stream, eg, less than about 15% by volume of the stream or less than about 10% by volume of the stream. be able to. An oxygen containing air stream can be combined with a CO ₂ source having a low oxygen content. For example, the exhaust stream generated by burning coal may include a low oxygen content that can be mixed with air to form a cathode inlet stream.

In addition to CO ₂ and O ₂ , the cathode input stream can also be composed of inert / non-reactive species such as N ₂ , H ₂ O and other typical oxidant (air) components. For example, for cathode input derived from emissions from combustion reactions, when air is used as part of the oxidant source for combustion reactions, the exhaust gas is a typical component of air, for example, N ₂ , H ₂ O and small amounts of other compounds present in air can be included. Depending on the nature of the fuel source for the combustion reaction, additional species present after combustion based on the fuel source include oxides of H ₂ O, nitrogen (NO _x ) and / or sulfur (SO _x ) , And / or one or more of the other compounds that are present in the fuel and / or partially or completely burned products present in the fuel, eg, CO. These species can be present in an amount that can reduce overall cathode activity, but does not impair the cathode catalyst surface. Such performance degradation can be acceptable, or the species interacting with the cathode catalyst can be reduced to an acceptable concentration by known contaminant removal techniques.

The amount of O ₂ present in the cathode input stream (eg, the input cathode stream based on combustion emissions) is conveniently sufficient to provide the oxygen required for the cathode reaction in the fuel cell. be able to. Thus, the volume percent of O ₂ can conveniently be at least 0.5 times the amount of CO _{2 in} the effluent. Optionally, if necessary, additional air can be added to the cathode input to provide sufficient oxidant for the cathode reaction. If some form of air is used as the oxidant, the amount of N ₂ in the cathode exhaust should be at least about 78% by volume, such as at least about 88% by volume, and / or not more than about 95% by volume. Can do. In some embodiments, the cathode input stream can additionally or alternatively contain compounds commonly found as contaminants, such as H ₂ S or NH ₃ . In other embodiments, the cathode input stream can be cleaned to reduce or minimize the content of such contaminants.

In addition to the reaction of forming carbonate ions for transport through the electrolyte, the conditions at the cathode can also be appropriate for the conversion of nitric oxide to nitrate and / or nitrate ions. Hereinafter, only nitrate ions are described for convenience. The resulting nitrate ions can also be transported through the electrolyte for reaction at the anode. Concentration of NO _x cathode input flow, since typically can be in the order of ppm, the nitrate transport reaction, to have a minimal impact on the amount of carbonate which are transported through the electrolyte it can. However, this method of NO _x removal can be advantageous with respect to cathode input streams based on combustion emissions from gas turbines because it can provide a mechanism to reduce NO _x emissions. Conditions at the cathode are additionally or alternatively for the conversion of unburned hydrocarbons (in combination with cathode input stream O ₂ ) to typical combustion products such as CO ₂ and H ₂ O. Can be appropriate.

  Suitable temperatures for operation of the MCFC can be about 450 ° C. to about 750 ° C., such as an inlet temperature of at least about 500 ° C., eg, about 550 ° C. and an outlet temperature of about 625 ° C. Prior to entering the cathode, heat is added to or removed from the combustion exhaust as needed, for example, to provide heat to other processes, such as the process of reforming the fuel input for the anode. can do. For example, if the source for the cathode input stream is a combustion exhaust stream, the combustion exhaust stream may have a temperature that is higher than the desired temperature for the cathode inlet. In such embodiments, heat can be removed from the combustion exhaust prior to use as the cathode input stream. Alternatively, the combustion emissions can be very cold, for example after a wet gas scrubber of a coal combustion boiler, in which case the combustion emissions can be less than about 100 ° C. Alternatively, the combustion emissions may be from the emissions of a gas turbine operated in a combined cycle mode that can cool the gas by increasing steam to operate the steam turbine for additional power generation. It will be possible. In this case, the gas can be below about 50 ° C. This heat can be added to the combustion emissions at a lower temperature than desired.

Operation of Molten Carbonate Fuel Cell In some embodiments, the fuel cell may be operated in a single pass or once-through mode. In single pass mode, the modified product of the anode exhaust is not returned to the anode inlet. Thus, recycling syngas, hydrogen or some other product directly from the anode output to the anode inlet is not done in a single pass operation. More generally, in single-pass operation, the modified product of the anode exhaust is, for example, by using the modified product to treat the fuel stream subsequently introduced into the anode inlet. Is not returned indirectly. Optionally, CO ₂ from the anode outlet can be recycled to the cathode inlet during single pass mode MCFC operation. More generally, in some other embodiments, recycling from the anode outlet to the cathode inlet may occur for MCFCs operating in a single pass mode. Heat from the anode exhaust or output may be recycled additionally or alternatively in a single pass mode. For example, the anode output flow may pass through a heat exchanger where the anode output is cooled and the input stream for another stream, such as the anode and / or cathode, is warmed. Recycling heat from the anode to the fuel cell is consistent with use in single pass or once-through mode operation. Optionally, but not preferred, the components of the anode output may be combusted to provide heat to the fuel cell during the single pass mode.

FIG. 3 shows a schematic embodiment of the operation of the MCFC for power generation. In FIG. 3, the anode portion of the fuel cell can receive fuel and steam (H ₂ O) as inputs, water, CO ₂ , and optionally an excess of H ₂ , CH ₄ (or other hydrocarbon). And / or CO is the output. The cathode portion of the fuel cell can receive CO ₂ and some oxidant (eg, air / O ₂ ) as input, and the output is to a reduced amount of CO ₂ in O ₂ deficient oxidant (air). Equivalent to. The cathode portion can also receive one or more fuel compounds as part of an inlet stream that can be combusted to produce heat, CO ₂ and H ₂ O. Within the fuel cell, the CO ₃ ²⁻ ions formed on the cathode side can be transported through the electrolyte and provide the carbonate ions required for the reaction occurring at the anode.

Several reactions can occur within a molten carbonate fuel cell, such as the example fuel cell shown in FIG. Reforming reaction can be any, if sufficient H ₂ is provided directly to the anode, it is possible to reduce or, or eliminated. The following reactions are based on CH ₄ , but similar reactions can occur when other fuels are used in the fuel cell.
(1) <Anode reforming> CH ₄ + H ₂ O => 3H ₂ + CO
(2) <Water gas shift> CO + H ₂ O => H ₂ + CO ₂
(3) <combined reforming and water gas shift> CH ₄ + 2H ₂ O => 4H ₂ + CO ₂
(4) <Anode H ₂ oxidation> H ₂ + CO ₃ ²⁻ => H ₂ O + CO ₂ + 2e ⁻
(5) <Cathode> 1 / 2O ₂ + CO ₂ + 2e ⁻ => CO ₃ ²⁻

Reaction (1) represents a basic hydrocarbon reforming reaction to generate H ₂ for use in a fuel cell anode. The CO formed in reaction (1) can be converted to H ₂ by the water gas shift reaction (2). The combination of reactions (1) and (2) is shown as reaction (3). Reactions (1) and (2) can occur outside the fuel cell and / or reforming can be carried out inside the anode.

Reactions (4) and (5) represent reactions that can cause power generation in the fuel cell at the anode and cathode, respectively. Reaction (4) is formed of electrons or present in the feed, or reaction (1) and / or _{H 2} generated arbitrarily by (2) in combination with the carbonate _ions, H 2 O, the CO ₂ and circuitry To do. Reaction (5) combines O ₂ , CO ₂ and electrons from the circuit to form carbonate ions. The carbonate ions generated by reaction (5) can be transported through the fuel cell electrolyte to provide the carbonate ions required for reaction (4). In combination with the transport of carbonate ions through the electrolyte, a closed current loop can then be formed by providing an electrical connection between the anode and the cathode.

In various embodiments, the goal of operating the fuel cell may be to improve the overall efficiency of the fuel cell and / or the overall efficiency of the fuel cell and the integrated chemical synthesis process. This is typically in contrast to conventional fuel cell operation, where the goal may be to operate a fuel cell with high electrical efficiency to use the fuel provided to the cell for power generation. Is. As defined above, the overall fuel cell efficiency may be determined by dividing the fuel cell electrical output and the lower heating value of the fuel cell output by the lower heating value of the input component for the fuel cell. . In other words, TFCE = (LHV (el) + LHV (sg out)) / LHV (in), where LHV (in) and LHV (sg out) are the fuel components delivered to the fuel cell (eg, H ₂ , CH ₄ and / or CO) and the LHV of the synthesis gas (H ₂ , CO and / or CO ₂ ) in the anode outlet stream or flow. This can provide a measure of the electrical and chemical energy generated by the fuel cell and / or the integrated chemical process. It should be noted that under this definition of total efficiency, the thermal energy used in the fuel cell and / or used in the integrated fuel cell / chemical synthesis system can contribute to the total efficiency. However, any excess heat that is exchanged or otherwise recovered from the fuel cell or integrated fuel cell / chemical synthesis system is excluded from this definition. Thus, if an excessive amount of heat from the fuel cell is used, for example, to generate steam for power generation by a steam turbine, such excessive amount of heat is excluded from the definition of total efficiency.

Integration Example: Application for Integration with a Combustion Turbine In some embodiments of the present invention, a combustion source for power generation and emission of CO ₂ containing emissions is used to operate a molten carbonate fuel cell. It can be integrated. An example of a suitable combustion source is a gas turbine. Preferably, the gas turbine is capable of burning natural gas, methane gas or other hydrocarbon gas in a combined cycle mode integrated with steam generation and heat recovery for additional efficiency. Modern natural gas combined cycle efficiency is about 60% for maximum and modern designs. Resulting CO ₂ containing effluent gas stream high temperature compatible with the MCFC operating, for example, 300 ° C. to 700 ° C., preferably it can be produced at 500 ° C. to 650 ° C.. The gas source is optional, but is preferably capable of cleaning contaminants such as sulfur that may adversely affect the MCFC before entering the turbine. Alternatively, the gas source can be a coal fired generator where the exhaust gas is typically cleaned after combustion due to the higher concentration of exhaust gas pollutants. In such an alternative, some heat exchange to / from the gas may be required to allow for lower temperature cleanup. In additional or alternative embodiments, CO ₂ sources containing effluent gases, boiler, can combustion chamber, or the output from the heat source for burning a rich fuel carbon. In other additional or alternative embodiments, CO ₂ sources containing effluent gas may be biologically generated CO ₂ in combination with other sources.

In some embodiments, the operation of the combustion source can be modified to take advantage of the cathode's ability to burn fuel in the cathode inlet stream. For conventional combustion reactions, a typical goal is to burn substantially all of the fuel delivered to the combustion reaction zone. This simplifies the treatment of emissions since little or no fuel remains in the combustion emissions. However, operating the combustion reaction zone to achieve substantially complete combustion does not necessarily represent the most efficient way to operate the combustion zone. Instead, it may be desirable to operate the combustion zone to have a residual fuel content after combustion in order to improve the overall efficiency of the combustion reaction. In the past, such residual fuel would probably have been wasted due to the low concentration of fuel in the combustion emissions. Additionally, the wasted fuel would have become a pollutant or required a pollution control device to eliminate. However, if a molten carbonate fuel cell is used to treat such emissions, can residual fuel be used to produce additional CO ₂ while acting as a pollution control device, Additional heat can be generated for the fuel cell, or a combination thereof. The amount of fuel remaining in the combustion exhaust that is then at least partially used as part of the cathode inlet stream for the fuel cell is at least about 0.5% by volume, as described above for the fuel content of the cathode inlet stream. Or at least about 1.0% by volume and up to about 5.0% by volume or less.

Several other configurations for the treatment of fuel cell anodes may be desirable for integration with combustion sources. For example, another configuration may be to recycle at least a portion of the emissions from the fuel cell anode to the fuel cell anode input. In the output stream from the MCFC anode, the main output components are H ₂ O, CO ₂ , optionally CO, and optionally, but typically unreacted fuel (eg, H ₂ or CH ₄ ). Can be included. Instead of using this output stream as an external fuel stream and / or input stream for integration with another process, one or more separations can be performed with components having potential fuel values, such as H ₂ or It can be carried out in the anode output stream to separate CO ₂ from CO. The fuel value component can then be recycled to the anode input.

This type of configuration can provide one or more advantages. First, CO ₂ can be separated from the anode output, such as by using a low temperature CO ₂ separator. Some of the components of the anode output (H ₂ , CO, CH ₄ ) are not easily condensable components, but CO ₂ and H ₂ O can be separated individually as condensed phases. Depending on the embodiment, at least about 90% by volume of the CO ₂ of the anode output can be separated, and a relatively pure CO ₂ output stream can be formed. Alternatively, in some embodiments, less CO ₂ can be removed from the anode output, about 50 vol% to about 90% by volume of the anode output of CO _2, such as about 80 vol%, or about 70 A volume% or less can be separated. After separation, the remaining portion of the anode output can correspond to a component having primarily a fuel number and a reduced amount of CO ₂ and / or H ₂ O. This portion of the anode output after separation can be recycled for use as part of the anode input in addition to additional fuel. In this type of configuration, even though the single pass fuel utilization through the MCFC is low, the unused fuel can be conveniently recycled for another pass through the anode. As a result, single pass fuel utilization can be at a reduced level, while loss of unburned fuel to the environment (emission) can be avoided.

In addition to, or instead of recycling a portion of the anode emissions to the anode input, another configuration option is the combustion reaction of a turbine or other combustion device such as a boiler, furnace and / or combustion heater It can be to use a portion of the anode discharge as input for. The relative amount of anode emissions recycled to the anode input and / or as input to the combustion device can be any convenient or desirable amount. If the anode emissions are recycled to only one of the anode input and combustion device, the amount of recycling can be any convenient amount, for example, removing CO ₂ and / or H ₂ O. Up to 100% of the anode discharge remaining after any separation. When a portion of the anode emissions is recycled to the anode input and combustion device, the total recycled amount by definition can be no more than 100% of the remaining portion of the anode emissions. In other cases, any convenient division of the anode discharge can be used. In various embodiments of the invention, the amount of recycle to the anode input is at least about 10% of the anode emissions remaining after separation, such as at least about 25%, at least about 40%, at least about 50%, at least about It can be 60%, at least about 75%, or at least about 90%. Additionally or alternatively, in those embodiments, the amount recycled to the anode input is no more than about 90% of the anode emissions remaining after separation, such as no more than about 75%, no more than about 60%, no more than about 50%. % Or less, about 40% or less, about 25% or less, or about 10% or less. Additionally or alternatively, in various embodiments of the invention, the amount recycled to the combustion device is at least about 10% of the anode emissions remaining after separation, such as at least about 25%, at least about 40. %, At least about 50%, at least about 60%, at least about 75%, or at least about 90%. Additionally or alternatively, in those embodiments, the amount of recycle to the combustion device is about 90% or less of the anode emissions remaining after separation, for example about 75% or less, about 60% or less, about 50 % Or less, about 40% or less, about 25% or less, or about 10% or less.

In yet another aspect of the invention, the fuel for the combustion device is additionally or alternatively inactive and / or otherwise enhanced in components that act as a diluent in the fuel. A fuel having a specified amount. CO ₂ and N ₂ are examples of components of a natural gas supply that can be relatively inert during the combustion reaction. If the amount of inert components in the fuel supply reaches a sufficient level, the performance of the turbine or other combustion source can be affected. This effect can be due in part to the ability of the inert component to absorb heat that may tend to quench the combustion reaction. Examples of fuel feeds having sufficient levels of inert components include fuel feeds containing at least about 20% by volume CO ₂ , or fuel feeds containing at least about 40% by volume N ₂ , or similar quench capability A fuel supply containing a combination of CO ₂ and N ₂ having a sufficient inert heat capacity to provide (Note that CO ₂ has a greater heat capacity than N ₂ , so lower concentrations of CO ₂ can have similar effects as higher concentrations of N _2. CO ₂ is easier than N _2. It can also participate in the combustion reaction, removing H ₂ from the combustion, such consumption of H ₂ by reducing the flame speed and limiting the flammability range of the air and fuel mixture. And more generally, with respect to a fuel supply containing an inert component that affects the flammability of the fuel supply, the inert component of the fuel supply is at least about 20% by volume, For example, it can be at least about 40% by volume, or at least about 50% by volume, or at least about 60% by volume. Preferably, the amount of inert components in the fuel supply can be up to about 80% by volume.

If a sufficient amount of inert component is present in the fuel supply, the resulting fuel supply can be outside the combustible region for the fuel component of the supply. In this type of condition, the addition of H ₂ from the recycled portion of the anode emissions to the combustion zone for the generator can extend the flammability zone for the fuel supply and H ₂ combination, thereby For example, a fuel supply containing at least about 20% by volume CO ₂ or at least about 40% by volume N ₂ (or other combinations of CO ₂ and N ₂ ) can be successfully combusted.

Compared to the total volume of the fuel supply and H ₂ is delivered to the combustion zone, the amount of H ₂ for expanding the combustible region is at least about 5% by volume of the total volume of the fuel supply and H _2, for example, It can be at least about 10% by volume and / or not more than about 25% by volume. Another option for characterizing the amount of H ₂ added to extend the flammable region can be based on the amount of fuel component present in the fuel supply into H ₂ before addition. The fuel component may correspond to methane, natural gas, other hydrocarbons, and / or other components conventionally considered as fuel for combustion power turbines or other generators. The amount of H ₂ added to the fuel supply is at least about one third of the volume of the fuel component (1: 3 H ₂ : fuel component ratio) in the fuel supply, eg, at least about half the volume of the fuel component. (1: 2 ratio). Additionally or alternatively, the amount of H ₂ added to the fuel supply is less than or equal to the volume of fuel components in the fuel supply (1: 1 ratio) or less. For example, to achieve a ratio of H ₂ to CH ₄ of about 1: 2 for a feed containing about 30% by volume CH ₄ , about 10% by volume N ₂ and about 60% by volume CO ₂ , A sufficient amount of emissions can be added to the fuel supply. Regard the ideal anode effluent containing only H _2, 1: by the addition of _{H 2} for achieving the 2 ratio of about 26% by volume of _CH 4, 13 vol% of _H 2, 9% by volume of N A feed containing ₂ and 52% by volume of CO ₂ can be provided.

Additional Embodiments The present invention can include one or more of the embodiments described below in addition or as an alternative.

Embodiment 1. FIG. A method for producing electricity, wherein an anode fuel stream comprising a reformable fuel is converted into an anode of a molten carbonate fuel cell, an internal reforming element associated with an anode of a molten carbonate fuel cell, or Introducing a cathode inlet stream comprising CO ₂ , O ₂ and one or more fuel compounds into the cathode of the molten carbonate fuel cell, wherein the one or more fuels The compound comprises H ₂ , one or more carbon-containing fuel compounds, or combinations thereof, wherein the concentration of the one or more fuel compounds in the cathode inlet stream is at least about 0.01% by volume, and the cathode inlet stream The concentration of the one or more fuel compounds in is lower than the autoignition concentration for operating conditions at the cathode of the fuel cell; A step of generating electricity in the salt form the fuel _cell; H 2, resulting in the anode effluent comprising CO and CO ₂ steps and, at least about 1% by volume of _{O 2} and about 100vppm less of one or more Producing a cathode effluent comprising a fuel compound.

  Embodiment 2.1 The method of Embodiment 1 wherein the methylene equivalent volume percent of the one or more fuel compounds is at least about 0.02% by volume.

  Embodiment 3. FIG. The step of the molten carbonate fuel cell cathode comprising an electrode surface and a second catalyst surface, the second catalyst surface comprising at least one Group VIII metal to produce cathode emissions; The method of embodiment 1 or 2, comprising oxidizing at least a portion of the one or more fuel compounds in the presence of the second catalyst surface.

Embodiment 4 FIG. A method for producing electricity, wherein an anode fuel stream comprising a reformable fuel is converted into an anode of a molten carbonate fuel cell, an internal reforming element associated with an anode of a molten carbonate fuel cell, or Introducing a cathode inlet stream comprising CO ₂ , O ₂ and one or more fuel compounds into the cathode of the molten carbonate fuel cell, wherein the one or more fuels The compound comprises one or more aromatic compounds, one or more carbon-containing fuel compounds having at least 5 carbons, or combinations thereof, wherein the one or more fuel compounds in the cathode inlet stream is at least about A concentration of one or more fuel compounds in the cathode inlet stream having a methylene equivalent volume percent of 0.02% by volume; Lower autoignition concentration for operating conditions in the over-de, steps and; a step of generating electricity in a molten carbonate fuel cell; a step to produce H _2, anode effluent comprising CO and CO _2; at least A cathode exhaust comprising about 1% by volume O ₂ , wherein the one or more fuel compounds have a methylene equivalent volume percent that is at least about 50% lower than a methylene equivalent volume percent of the cathode inlet stream. The methylene equivalent volume percent of the cathode discharge is optionally less than or equal to about 0.01% by volume, wherein the cathode of the molten carbonate fuel cell is connected to the electrode surface and the second A second catalyst surface comprising at least one Group VIII metal and a cathode Produce distillate step, comprising the step of oxidizing at least a portion of the presence in one or more fuel compound of the second catalyst surface, method.

  Embodiment 5. FIG. The at least one Group VIII metal comprises Ni, Pt, Pd, Co, Rh, Ru, Re, Ir, Fe or combinations thereof, for example, at least Ni, Co, Fe, Pt, Pd or combinations thereof The method of embodiment 3 or 4, comprising a combination of:

  Embodiment 6. FIG. The method of any one of the preceding embodiments, wherein the sulfur content of the cathode inlet stream is about 25 wppm or less, such as about 15 wppm or less.

  Embodiment 7. FIG. The one or more fuel compounds in the cathode inlet stream contain heteroatoms different from C, H and O, and the concentration of heteroatoms different from C, H and O is relative to the weight of the one or more fuel compounds The method of any one of the preceding embodiments, wherein the method is about 100 wppm or less.

  Embodiment 8. FIG. The cathode inlet stream comprises at least a portion of the combustion exhaust, and at least a portion of the combustion exhaust optionally comprises at least about 0.02 vol% methylene equivalent volume percent of one or more carbon-containing fuel compounds. The method of any one of the preceding embodiments, wherein at least a portion of the combustion emissions is optionally at least a portion of the emissions from the gas turbine.

  Embodiment 9. FIG. Embodiments above, wherein the molten carbonate fuel cell is operated at a heat ratio of about 0.25 to about 1.3, such as about 0.25 to about 1.0 or about 0.4 to about 1.0. Any one method.

  Embodiment 10 FIG. The amount of reformable fuel introduced into the anode of the molten carbonate fuel cell, the reforming stage (optionally internal reforming element) associated with the anode of the molten carbonate fuel cell, or a combination thereof, The method of any one of the preceding embodiments, wherein the amount is at least about 75% greater than the amount of hydrogen reacted in the molten carbonate fuel cell to generate.

Embodiment 11. FIG. Fuel utilization at the anode of a molten carbonate fuel cell is no more than about 50%, and CO ₂ utilization at the cathode of the molten carbonate fuel cell is at least about 60%, The method of any one of the above-described embodiment .

  Embodiment 12 FIG. The method of any one of the preceding embodiments, wherein the electrical efficiency of the molten carbonate fuel cell is about 10% to about 40% and the total fuel cell efficiency of the molten carbonate fuel cell is at least about 55%.

  Embodiment 13 FIG. A molten carbonate fuel cell system comprising a molten carbonate fuel cell having an anode and a cathode, the cathode comprising an electrode surface and a second catalyst surface comprising at least one Group VIII metal And the concentration of the at least one Group VIII metal on the second catalyst surface is at least 1 in the second region of the second catalyst surface, in the first region of the second catalyst surface. The first region of the second catalyst surface is lower in the cathode inlet of the molten carbonate fuel cell cathode than the second region of the second catalyst surface, compared to the concentration of the seed Group VIII metal. Close, system.

  Embodiment 14 FIG. The at least one Group VIII metal comprises Ni, Pt, Pd, Co, Rh, Ru, Re, Ir, Fe or combinations thereof, for example, at least Ni, Co, Fe, Pt, Pd or combinations thereof Embodiment 14. The system of embodiment 13 comprising a combination of:

  Embodiment 15. FIG. The system of embodiment 13 or 14, wherein the region of the second catalyst surface comprises a continuously increasing gradient of the concentration of at least one Group VIII metal.

  Embodiment 16. FIG. The first region of the second catalyst surface comprises at least one Group VIII metal, and the second region of the second catalyst surface is at least one of the first regions of the second catalyst surface. Embodiment 16. The system of any of embodiments 13-15, comprising at least one additional Group VIII metal that is different from one Group VIII metal.

  Embodiment 17. FIG. The second region of the second catalyst surface comprises at least one Group VIII metal and the first region of the second catalyst surface is at least of the second region of the second catalyst surface. Embodiment 16. The system of any of embodiments 13-15, comprising at least one additional Group VIII metal that is different from one Group VIII metal.

  Although the invention has been described with reference to particular embodiments, it is not necessarily so limited. Appropriate variations / modifications for operation under specific conditions will be apparent to those skilled in the art. Accordingly, it is intended that the following claims be interpreted as encompassing all such variations / modifications falling within the true spirit / range of the present invention.

Claims (17)

A method for producing electricity,
Introducing an anode fuel stream comprising a reformable fuel into an anode of a molten carbonate fuel cell, an internal reforming element associated with the anode of the molten carbonate fuel cell, or a combination thereof; ;
Introducing a cathode inlet stream comprising CO ₂ , O ₂ and one or more fuel compounds into the cathode of the molten carbonate fuel cell, wherein the one or more fuel compounds are H ₂ , Comprising one or more carbon-containing fuel compounds or combinations thereof, wherein the concentration of the one or more fuel compounds in the cathode inlet stream is at least about 0.01% by volume, and the 1 in the cathode inlet stream. The concentration of the fuel compound of more than one species is lower than the autoignition concentration for operating conditions at the cathode of the fuel cell;
Generating electricity in the molten carbonate fuel cell;
Producing an anode exhaust comprising H ₂ , CO and CO ₂ ;
Producing a cathode effluent comprising at least about 1% by volume O ₂ and no more than about 100 vppm of said one or more fuel compounds.   The method of claim 1, wherein the one or more fuel compounds have a methylene equivalent volume percent of at least about 0.02% by volume.   The cathode of the molten carbonate fuel cell comprises an electrode surface and a second catalyst surface, the second catalyst surface comprises at least one Group VIII metal, and the cathode discharge The method of claim 1, wherein the resulting step comprises oxidizing at least a portion of the one or more fuel compounds in the presence of the second catalyst surface. A method for producing electricity,
Introducing an anode fuel stream comprising a reformable fuel into an anode of a molten carbonate fuel cell, an internal reforming element associated with the anode of the molten carbonate fuel cell, or a combination thereof; ;
Introducing a cathode inlet stream comprising CO ₂ , O ₂ and one or more fuel compounds into the cathode of the molten carbonate fuel cell, wherein the one or more fuel compounds are one or more; Of the aromatic compound, one or more carbon-containing fuel compounds having at least 5 carbons, or combinations thereof, wherein the one or more fuel compounds in the cathode inlet stream is at least about 0.02 volume. And the concentration of the one or more fuel compounds in the cathode inlet stream is lower than the autoignition concentration for operating conditions at the cathode of the fuel cell;
Generating electricity in the molten carbonate fuel cell;
Producing an anode exhaust comprising H ₂ , CO and CO ₂ ;
A cathode effluent comprising at least about 1% by volume of O _2, methylene equivalents volume percent of the one or more fuel compound is at least about 50% lower than the methylene equivalents volume percent of said cathode inlet stream, Producing a cathode discharge, wherein the methylene equivalent volume percent of the cathode discharge is optionally less than or equal to about 0.01 vol%, the cathode of the molten carbonate fuel cell Comprising an electrode surface and a second catalyst surface, wherein the second catalyst surface comprises at least one Group VIII metal, and the step of producing the cathode exhaust comprises the second catalyst Oxidizing the at least a portion of the one or more fuel compounds in the presence of a surface.   The at least one Group VIII metal comprises Ni, Pt, Pd, Co, Rh, Ru, Re, Ir, Fe or combinations thereof, for example, at least Ni, Co, Fe, Pt, Pd or The method according to claim 3 or 4, comprising a combination thereof.   6. A method according to any one of the preceding claims, wherein the sulfur content of the cathode inlet stream is about 25 wppm or less, for example about 15 wppm or less.   The one or more fuel compounds in the cathode inlet stream contain a heteroatom different from C, H and O, and the concentration of the heteroatom different from C, H and O is that of the one or more fuel compounds. The method according to any one of claims 1 to 6, which is about 100 wppm or less based on weight.   The cathode inlet stream comprises at least a portion of a combustion exhaust, and the at least a portion of the combustion exhaust optionally includes at least about 0.02 volume percent methylene equivalent volume percent of one or more carbon-containing fuel compounds. 8. The method of any one of claims 1-7, wherein the at least a portion of the combustion emissions is optionally at least a portion of the emissions from the gas turbine.   The molten carbonate fuel cell is operated at a heat ratio of about 0.25 to about 1.3, such as about 0.25 to about 1.0 or about 0.4 to about 1.0. The method as described in any one of 1-8.   The reformability introduced into the anode of the molten carbonate fuel cell, the reforming step (optionally the internal reforming element) associated with the anode of the molten carbonate fuel cell, or a combination thereof 10. The method of any one of claims 1-9, wherein the amount of fresh fuel is at least about 75% greater than the amount of hydrogen that reacts in the molten carbonate fuel cell to generate electricity. Fuel utilization in the anode of the molten carbonate fuel cell is no more than about 50%, and CO ₂ utilization in the cathode of the molten carbonate fuel cell is at least about 60%, claims 1 to 10 The method as described in any one of.   12. The electrical efficiency of the molten carbonate fuel cell is about 10% to about 40%, and the total fuel cell efficiency of the molten carbonate fuel cell is at least about 55%. The method according to one item.   A molten carbonate fuel cell system comprising a molten carbonate fuel cell having an anode and a cathode, wherein the cathode comprises an electrode surface and at least one Group VIII metal. A concentration of the at least one Group VIII metal on the second catalyst surface is a second region of the second catalyst surface in a first region of the second catalyst surface. The first region of the second catalyst surface is less than the second region of the second catalyst surface than the concentration of the at least one Group VIII metal in the region. A system close to the cathode inlet of the cathode of a carbonate fuel cell.   The at least one Group VIII metal comprises Ni, Pt, Pd, Co, Rh, Ru, Re, Ir, Fe or combinations thereof, for example, at least Ni, Co, Fe, Pt, Pd or The system of claim 13 comprising a combination thereof.   15. A system according to claim 13 or 14, wherein the region of the second catalyst surface comprises a continuously increasing gradient of the concentration of the at least one Group VIII metal.   The first region of the second catalyst surface comprises at least one Group VIII metal, and the second region of the second catalyst surface is the second region of the second catalyst surface. 16. The system according to any one of claims 13 to 15, comprising at least one additional Group VIII metal that is different from the at least one Group VIII metal in a first region.   The second region of the second catalyst surface comprises at least one Group VIII metal, and the first region of the second catalyst surface is the second region of the second catalyst surface. 16. The system according to any one of claims 13 to 15, comprising at least one additional Group VIII metal that is different from the at least one Group VIII metal in a second region.

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