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EP3888165A1 - Motif de catalyseur de reformage pour pile à combustible fonctionnant avec une utilisation améliorée du co2 - Google Patents

Motif de catalyseur de reformage pour pile à combustible fonctionnant avec une utilisation améliorée du co2

Info

Publication number
EP3888165A1
EP3888165A1 EP19827929.1A EP19827929A EP3888165A1 EP 3888165 A1 EP3888165 A1 EP 3888165A1 EP 19827929 A EP19827929 A EP 19827929A EP 3888165 A1 EP3888165 A1 EP 3888165A1
Authority
EP
European Patent Office
Prior art keywords
fuel cell
anode
cathode
reforming
catalyst
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP19827929.1A
Other languages
German (de)
English (en)
Inventor
Everett J. O'NEAL
Lu Han
Carla S. Pereira
Rodrigo F. BLANCO GUTIERREZ
Timothy M. Healy
Carl A. WILLMAN
Hossein Ghezel-Ayagh
Frank J. DOBEK
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Fuelcell Energy Inc
Original Assignee
Fuelcell Energy Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Fuelcell Energy Inc filed Critical Fuelcell Energy Inc
Priority claimed from PCT/US2019/063434 external-priority patent/WO2020112895A1/fr
Publication of EP3888165A1 publication Critical patent/EP3888165A1/fr
Pending legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/06—Combination of fuel cells with means for production of reactants or for treatment of residues
    • H01M8/0606—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants
    • H01M8/0612—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants from carbon-containing material
    • H01M8/0625—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants from carbon-containing material in a modular combined reactor/fuel cell structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/8636—Inert electrodes with catalytic activity, e.g. for fuel cells with a gradient in another property than porosity
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/06—Combination of fuel cells with means for production of reactants or for treatment of residues
    • H01M8/0606—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants
    • H01M8/0612—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants from carbon-containing material
    • H01M8/0618—Reforming processes, e.g. autothermal, partial oxidation or steam reforming
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/06—Combination of fuel cells with means for production of reactants or for treatment of residues
    • H01M8/0606—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants
    • H01M8/0612—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants from carbon-containing material
    • H01M8/0625—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants from carbon-containing material in a modular combined reactor/fuel cell structure
    • H01M8/0631—Reactor construction specially adapted for combination reactor/fuel cell
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/06—Combination of fuel cells with means for production of reactants or for treatment of residues
    • H01M8/0606—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants
    • H01M8/0612—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants from carbon-containing material
    • H01M8/0637—Direct internal reforming at the anode of the fuel cell
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/14—Fuel cells with fused electrolytes
    • H01M8/144—Fuel cells with fused electrolytes characterised by the electrolyte material
    • H01M8/145—Fuel cells with fused electrolytes characterised by the electrolyte material comprising carbonates
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/14—Fuel cells with fused electrolytes
    • H01M2008/147—Fuel cells with molten carbonates
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/8605—Porous electrodes
    • H01M4/861—Porous electrodes with a gradient in the porosity
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • the fuel cell assemblies can include internal reforming assemblies with a reforming catalyst distribution that reduces or minimizes temperature gradients within the fuel cells.
  • Molten carbonate fuel cells utilize hydrogen and/or other fuels to generate electricity.
  • the hydrogen may be provided by reforming methane or other reformable fuels in a steam reformer, such as a steam reformer located upstream of the fuel cell or integrated within the fuel cell.
  • Fuel can also be reformed in the anode cell in a molten carbonate fuel cell, which can be operated to create conditions that are suitable for reforming fuels in the anode.
  • Still another option can be to perform some reforming both externally and internally to the fuel cell. Reformable fuels can encompass hydrocarbonaceous materials that can be reacted with steam and/or oxygen at elevated temperature and/or pressure to produce a gaseous product that comprises hydrogen.
  • molten carbonate fuel cells One of the attractive features of molten carbonate fuel cells is the ability to transport CO 2 from a low concentration stream (such as a cathode input stream) to a higher concentration stream (such as an anode output flow).
  • CO 2 and O 2 in an MCFC cathode are converted to a carbonate ion (CO3 2 ), which is then transported across the molten carbonate electrolyte as a charge carrier.
  • the carbonate ion reacts with H 2 in the fuel cell anode to form H 2 O and CO 2 .
  • one of the net outcomes of operating the MCFC is transport of CO 2 across the electrolyte.
  • This transport of CO 2 across the electrolyte can allow an MCFC to generate electrical power while reducing or minimizing the cost and/or challenge of sequestering carbon oxides from various COx-containing streams.
  • a combustion source such as a natural gas fired power plant
  • U.S. Patent Application Publication 2015/0093665 describes methods for operating a molten carbonate fuel cell with some combustion in the cathode to provide supplemental heat for performing additional reforming (and/or other endothermic reactions) within the fuel cell anode.
  • the publication notes that the voltage and/or power generated by a carbonate fuel cell can start to drop rapidly as the CO 2 concentration falls below about 1.0 mole%.
  • the publication further state that as the CO 2 concentration drops further, e.g., to below about 0.3 vol%, at some point the voltage across the fuel cell can become low enough that little or no further transport of carbonate may occur and the fuel cell ceases to function
  • a method for producing electricity can include passing a fuel stream comprising a reformable fuel into a fuel stack comprising a first surface.
  • the first surface can include a first portion that includes a reforming catalyst.
  • the reforming catalyst density on the first portion of the first surface can have a difference between a maximum catalyst density and a minimum catalyst density of 20% to 75%.
  • the reforming catalyst density on the first portion of the first surface can have a difference between a maximum catalyst activity and a minimum catalyst activity of 20% to 75%.
  • At least a portion of the reformable fuel can be reformed in the presence of the first surface to produce reformed hydrogen.
  • At least a portion of the reformable fuel, at least a portion of the reformed hydrogen, or a combination thereof can be introduced into an anode of a molten carbonate fuel cell.
  • the method can further include introducing a cathode input stream comprising O 2 , H 2 O, and CO 2 into a cathode of the molten carbonate fuel cell.
  • a direction of flow in the cathode of the molten carbonate fuel cell can be substantially orthogonal to a direction of flow in the anode of the molten carbonate fuel cell.
  • the molten carbonate fuel cell can be operated at a transference of 0.97 or less and an average current density of 60 mA/cm 2 or more to generate electricity, an anode exhaust comprising H 2 , CO, and CO 2 , and a cathode exhaust comprising 2.0 vol% or less CO 2 , 1.0 vol% or more O 2 , and 1.0 vol% or more H 2 O.
  • a fuel cell stack in another aspect, can include a molten carbonate fuel cell comprising an anode and a cathode.
  • the fuel cell stack can further include a reforming element associated with the anode.
  • the reforming element can include a first surface, with the first surface including a first portion comprising a reforming catalyst.
  • a reforming catalyst density on the first portion of the first surface can correspond to a monotonically decreasing catalyst density. Additionally or alternately, the reforming catalyst density on the first portion of the first surface can have a difference between a maximum catalyst density and a minimum catalyst density of 20% to 75%.
  • the fuel cell stack can further include a separator plate between the anode and the reforming element.
  • FIG. 1 shows an example of a configuration for molten carbonate fuel cells and associated reforming and separation stages.
  • FIG. 2 shows another example of a configuration for molten carbonate fuel cells and associated reforming and separation stages.
  • FIG. 3 shows an example of a portion of a molten carbonate fuel cell stack.
  • FIG. 4 shows a flow pattern example for a molten carbonate fuel cell with an anode flow direction that is aligned roughly perpendicular to a cathode flow direction.
  • FIG. 5 shows an example of a flow pattern within a reforming element.
  • FIG. 6 shows an example of a reforming catalyst density profile in a reforming element.
  • FIG. 7 shows a comparison of reforming catalyst density profiles for modeling of fuel cell behavior.
  • FIG. 8 shows a temperature profile for operation of a molten carbonate fuel cell stack with a conventional reforming catalyst pattern under conditions for elevated CO 2 utilization.
  • FIG. 9 shows a temperature profile for operation of a molten carbonate fuel cell stack with an improved reforming catalyst pattern under conditions for elevated CO 2 utilization.
  • FIG. 10 shows a comparison of reforming catalyst density profiles for modeling of fuel cell behavior.
  • FIG. 11 shows a temperature profile for operation of a molten carbonate fuel cell stack with a conventional reforming catalyst pattern under conditions for elevated CO 2 utilization.
  • FIG. 12 shows a temperature profile for operation of a molten carbonate fuel cell stack with another conventional reforming catalyst pattern under conditions for elevated CO 2 utilization.
  • FIG. 13 shows a temperature profile for operation of a molten carbonate fuel cell stack with an improved reforming catalyst pattern under conditions for elevated CO 2 utilization.
  • a reforming element for a molten carbonate fuel cell stack can reduce or minimize temperature differences within the fuel cell stack when operating the fuel cell stack with a low CO 2 content cathode feed and with enhanced CO 2 utilization.
  • the reforming element can include at least one surface with reforming catalyst deposited on the surface.
  • the difference between the minimum and maximum reforming catalyst density on a first portion of the at least one surface can be 20% to 75%, or 20% to 70%, or 25% to 65%, with the highest catalyst densities being in proximity to the side of the fuel cell stack corresponding to at least one of the anode inlet and the cathode inlet
  • the difference between the minimum and maximum reforming catalyst activity on a first portion of the at least one surface can be 20% to 75%, or 20% to 70%, or 25% to 65%, with the highest catalyst activities being in proximity to the side of the fuel cell stack corresponding to at least one of the anode inlet and the cathode inlet.
  • a maximum catalyst density and/or activity can be present at the edge of the catalyst pattern that is closest to the side of the fuel cell stack corresponding to the anode inlet (i.e., in proximity to the anode inlet).
  • the reforming catalyst density and/or activity can vary monotonically across the first portion of the at least one surface.
  • a second portion of the at least one surface in the reforming element can correspond to a portion of the surface in proximity to the cathode inlet or anode inlet side of the reforming element.
  • the second portion can be in proximity to the cathode inlet
  • the second portion can be in proximity to the anode inlet
  • the second portion of the at least one surface can have a separate catalyst profile, such as a relatively constant catalyst density profile and/or activity profile, to account for the increased fuel cell activity at the cathode inlet.
  • This reforming catalyst pattern within the reforming element can allow the fuel cell stack to operate with elevated CO 2 capture while having a temperature difference of 70°C or less, or 50°C or less, or 45°C or less, or 40°C or less across the fuel cell stack.
  • the temperature difference may be measured at the separator plate between the reforming element and the anode.
  • the anode of the fuel cell can include at least one surface containing reforming catalyst
  • a first portion of the at least one surface can have difference between the minimum and maximum reforming catalyst density and/or catalyst activity on a first portion of the at least one surface of 20% to 75%, or 20% to 70%, or 25% to 65%, or 40% to 75%, or 40% to 70%, or 40% to 65%.
  • the highest catalyst densities and/or activities can be in proximity to the side of tiie fuel cell stack corresponding to the anode inlet
  • the reforming catalyst density and/or activity can vary monotonically across the first portion of the at least one surface.
  • a second portion of the at least one surface in the reforming element can correspond to the cathode inlet side of the reforming element.
  • the second portion of the at least one surface can have a separate catalyst profile, such as a relatively constant catalyst density profile and/or activity profile, to account for the increased fuel cell activity at the cathode inlet.
  • catalyst activity it is noted that the nature of the catalyst pattern and the orientation of gas flows relative to the catalyst pattern can alter the resulting catalyst activity.
  • one option for providing a desired catalyst density on a surface can be to provide catalyst as a series of (substantially) parallel lines of catalyst particles. The resulting activity from such a parallel line catalyst pattern can vary depending on the orientation of the gas flow relative to the direction of the lines of catalyst particles.
  • the catalyst activity can be greater for a gas flow that is roughly aligned with (such as substantially parallel to) the lines of catalyst particles, while a skew or substantially perpendicular gas flow relative to the lines of catalyst particles could lead to varying amounts of reduction in catalyst activity.
  • molten carbonate fuel cells can be operated to have elevated CO 2 capture, such as a transference of 0.97 or less, or 0.95 or less. Operating with a transference of 0.97 or less, or 0.95 or less, can lead to a temperature distribution across the fuel cell that differs from conventional operation.
  • a portion of the current density in the fuel cell can be due to alternative ion transport.
  • alternative ion transport is typically accompanied by greater waste heat generation. If a conventional reforming catalyst pattern is used, the waste heat due to the alternative ion transport can result in significant unexpected temperature variations.
  • an alternative reforming catalyst pattern can be used so that a greater amount of reforming occurs near the anode outlet.
  • a reforming catalyst pattern with a reduced amount of variation between the maximum and minimum catalyst density.
  • the difference between the maximum and minimum in reforming catalyst density can correspond to 20% to 75% of the maximum catalyst density, or 20% to 70%, or 25% to 65%.
  • a reforming catalyst pattern can be used with a difference between the maximum and minimum reforming catalyst activity of 20% to 75% of the maximum catalyst activity, or 20% to 70%, or 25% to 65%. This can allow for increased reforming near the anode outlet, resulting in additional cooling that can mitigate the additional waste heat generated due to alternative ion transport.
  • An example of a suitable catalyst density profile and/or catalyst activity profile can be a monotonically decreasing profile.
  • the catalyst density and/or catalyst activity is at a maximum value at the anode inlet.
  • the catalyst density and/or activity then either stays roughly the same or decreases along the direction from the anode inlet to the anode outlet.
  • Examples of a monotonically decreasing profile include a catalyst density and/or activity profile with a constant slope (i.e., a constantly decreasing amount of catalyst density and/or activity); or a profile where the reforming catalyst density and/or activity corresponds to a series of steps, with the catalyst density/activity being roughly constant within each step.
  • Still other catalyst patterns can also be used, such as combinations of steps and regions of decreasing catalyst density and/or activity.
  • Using an improved reforming catalyst pattern can be beneficial when operating an MCFC to have enhanced or elevated CO 2 utilization.
  • One difficulty in operating an MCFC with elevated CO 2 utilization is that the operation of the fuel cell can potentially be kinetically limited if one or more of the reactants required for fuel cell operation is present in low quantities.
  • achieving a CO 2 utilization of 75% or more corresponds to a cathode outlet concentration of 1.0 vol% or less.
  • a cathode outlet concentration of 1.0 vol% or less does not necessarily mean that the CO 2 is evenly distributed throughout the cathode.
  • the concentration will typically vary within the cathode due to a variety of factors, such as the flow patterns in the anode and the cathode.
  • the variations in CO 2 concentration can result in portions of the cathode where CO 2 concentrations substantially below 1.0 vol% are present.
  • the amount of alternative ion transport can be quantified based on the transference for a fuel cell.
  • the transference is defined as the fraction of ions transported across the molten carbonate electrolyte that correspond to carbonate ions, as opposed to hydroxide ions and/or other ions.
  • a convenient way to determine the transference can be based on comparing a) the measured change in CO 2 concentration at the cathode inlet versus the cathode outlet with b) the amount of carbonate ion transport required to achieve the current density being produced by the fuel cell.
  • the cathode input stream and/or cathode output stream can be sampled, with the sample diverted to a gas chromatograph for determination of the CO 2 content.
  • the average current density for the fuel cell can be measured in any convenient manner.
  • the transference can be relatively close to 1.0, such as 0.98 or more and/or such as having substantially no alternative ion transport.
  • a transference of 0.98 or more means that 98% or more of the ionic charge transported across the electrolyte corresponds to carbonate ions. It is noted that hydroxide ions have a charge of -1 while carbonate ions have a charge of -2, so two hydroxide ions need to be transported across the electrolyte to result in the same charge transfer as transport of one carbonate ion.
  • regions contain additional CO 2 that would be desirable to transport across an electrolyte, such as for carbon capture.
  • the CO 2 in such regions is typically not transported across the electrolyte when operating under conventional conditions.
  • the regions with sufficient CO 2 can be used to transport additional CO 2 while the depleted regions can operate based on alternative ion transport. This can increase the practical limit for the amount of CO 2 captured from a cathode input stream.
  • One of the advantages of transport of alternative ions across the electrolyte is that the fuel cell can continue to operate, even though a sufficient number of CO 2 molecules are not kinetically available. This can allow additional CO 2 to be transferred from cathode to anode even though the amount of CO 2 present in the cathode would conventionally be considered insufficient for normal fuel cell operation. This can allow the fuel cell to operate with a measured CO 2 utilization closer to 100%, while the calculated CO 2 utilization (based on current density) can be at least 3% greater than the measured CO 2 utilization, or at least 5% greater, or at least 10% greater, or at least 20% greater. It is noted that alternative ion transport can allow a fuel cell to operate with a current density that would correspond to more than 100% calculated CO 2 utilization.
  • elevated CO 2 capture can be defined based on the amount of transference, such as a transference of 0.97 or less, or 0.95 or less, or 0.93 or less, or 0.90 or less. Maintaining an operating condition with transference of 0.97 or less can typically also result in a CO 2 concentration in the cathode output stream of 2.0 vol% or less, or 1.5 vol% or less, or 1.0 vol% or less. At higher CO 2 concentrations in the cathode output stream, there is typically not sufficient local depletion of CO 2 to result in lower transference values.
  • elevated CO 2 capture can also be indicated by other factors, although such other factors are by themselves typically not a sufficient condition to indicate elevated CO 2 capture.
  • elevated CO 2 capture can in some aspects correspond to a CO 2 utilization of 70% or more, or 75% or more, or 80% or more, such as up to 95% or possibly still higher.
  • lower concentration sources of CO 2 can correspond to CO 2 sources that result in cathode input streams containing 5.0 vol% or less of CO 2 , or 4.0 vol% or less, such as down to 1.5 vol% or possibly lower.
  • the exhaust from a natural gas turbine is an example of a CO 2 - containing stream that often has a CO 2 content of 5.0 vol% or less of CO 2 , or 4.0 vol% or less.
  • elevated CO 2 capture can correspond to operating conditions where the molten carbonate fuel cell is used to generate a substantial amount of current density, such as 60 rriA/cm 2 or more, or 80 mA/cm 2 or more, or 100 mA/cm 2 or more, or 120 mA/cm 2 or more, or 150 mA/cm 2 or more, or 200 mA/cm 2 or more, such as up to 300 mA/cm 2 or possibly still higher.
  • alternative ion transport can also be indicated by a reduced operating voltage for a fuel cell, as the reaction pathway for alternative ion transport has a lower theoretical voltage than the reaction pathway that uses carbonate ions.
  • the CO 2 concentration in the cathode exhaust of a molten carbonate fuel cell is maintained at a relatively high value, such as 5 vol% CO 2 or more, or 10 vol% CO 2 or more, or possibly still higher.
  • molten carbonate fuel cells are typically operated at CO 2 utilization values of 70% or less.
  • the dominant mechanism for transport of charge across the molten carbonate electrolyte is transport of carbonate ions. While it is possible that transport of alternative ions (such as hydroxide ions) across the electrolyte occurs under such conventional conditions, the amount of alternative ion transport is de minimis, corresponding to 2% or less of the current density (or equivalently, a transference of 0.98 or more).
  • the operating conditions can be described based on measured CO 2 utilization and“calculated” CO 2 utilization based on average current density.
  • the measured CO 2 utilization corresponds to the amount of CO 2 that is removed from the cathode input stream. This can be determined, for example, by using gas chromatography to determine the CO 2 concentration in the cathode input stream and the cathode output stream. This can also be referred to as the actual CO 2 utilization, or simply as the CO 2 utilization.
  • the calculated CO 2 utilization is defined as the CO 2 utilization that would occur if all of the current density generated by the fuel cell was generated based on transport of CO 3 2 ions across tire electrolyte (i.e., transport of ions based on CO 2 ).
  • the difference in measured CO 2 utilization and the calculated CO 2 utilization can be used individually to characterize the amount of alternative ion transport, and/or these values can be used to calculate the transference, as described above.
  • any convenient type of electrolyte suitable for operation of a molten carbonate fuel cell can be used.
  • a eutectic carbonate mixture as the carbonate electrolyte, such as a eutectic mixture of 62 mol% lithium carbonate and 38 mol% potassium carbonate (62% Li2COa/38% K 2 CO3) or a eutectic mixture of 52 mol% lithium carbonate and 48 mol% sodium carbonate (52% Li 2 C03/48% Na2CO 3 ).
  • Other eutectic mixtures are also available, such as a eutectic mixture of 40 mol% lithium carbonate and 60 mol% potassium carbonate (40% LhCO 3 /60% K 2 CO3).
  • non-eutectic mixtures of carbonate can be convenient as an electrolyte for various reasons
  • non-eutectic mixtures of carbonates can also be suitable.
  • such non-eutectic mixtures can include various combinations of lithium carbonate, sodium carbonate, and/or potassium carbonate.
  • lesser amounts of other metal carbonates can be included in the electrolyte as additives, such as other alkali carbonates (rubidium carbonate, cesium carbonate), or other types of metal carbonates such as barium carbonate, bismuth carbonate, lanthanum carbonate, or tantalum carbonate.
  • a reforming element refers to a reforming stage located within a fuel cell stack.
  • a reforming element can receive a fuel feed of reformable fuel and convert at least a portion of the reformable fuel into hydrogen. After conversion of the reformable fuel to hydrogen, the hydrogen (plus optionally remaining reformable fuel) can be passed into one or more anodes associated with the reforming element.
  • the temperature uniformity within a fuel cell stack can be determined based on the temperature of a separator plate located between the anode of a fuel cell and an adjacent associated reforming element
  • reforming catalyst density is defined as the average weight of reforming catalyst per unit area on a surface.
  • the unit area for determining the reforming catalyst density at a location can be a square with a side length of 25 times a characteristic length of the particle.
  • the characteristic length for the particle can be an average diameter or an average length along the longest axis of the particle. Such a square can then be used to form a tesselation, and the catalyst density can be calculated in a discrete manner per unit square.
  • the square for defining a tesselation can have a side length of 1 mm.
  • the difference when determining a difference between the minimum reforming catalyst density and the maximum reforming catalyst density across the fuel cell (such as across a first portion of a surface in a reforming element), the difference can be determined based on normalizing the reforming catalyst density so that the maximum density corresponds to a value of 100. The difference between the maximum density and the density at a given location can then correspond to the percentage difference in reforming catalyst density between the locations.
  • the operating conditions for a molten carbonate fuel cell can be selected to correspond to a transference of 0.97 or less, thereby causing the cell to transport both carbonate ion and at least one type of alternative ion across the electrolyte.
  • operating conditions that can indicate that a molten carbonate fuel cell is operating with transport of alternative ions include, but are not limited to, CO 2 concentration for the cathode input stream, the CO 2 utilization in the cathode, the current density for the fuel cell, the voltage drop across the cathode, the voltage drop across the anode, and the O 2 concentration in the cathode input stream.
  • the anode input stream and fuel utilization in the anode can be generally selected to provide the desired current density.
  • the CO 2 concentration in at least a portion of the cathode needs to be sufficiently low while operating the fuel cell to provide a sufficiently high current density.
  • Having a sufficiently low CO 2 concentration in the cathode typically corresponds to some combination of a low CO 2 concentration in the cathode input flow, a high CO 2 utilization, and/or a high average current density.
  • such conditions alone are not sufficient to indicate a transference of 0.97 or less, or 0.95 or less.
  • a molten carbonate fuel cell with a cathode open area of roughly 33% was operated with a CO 2 cathode inlet concentration of 19 vol%, 75% CO 2 utilization, and 160 mA/cm 2 of average current density. These conditions corresponded to a difference between calculated CO 2 utilization and measured CO 2 utilization of less than 1%.
  • the presence of substantial alternative ion transport/a transference of 0.97 or less, or 0.95 or less cannot be inferred simply from the presence of a high CO 2 utilization and a high average current density.
  • a molten carbonate fuel cell with a cathode open area of between 50% and 60% was operated with a CO 2 cathode inlet concentration of 4.0 vol%, 89% CO 2 utilization, and 100 mA/cm 2 of current density. These conditions corresponded to a transference of at least 0.97. Thus, the presence of a transference of 0.95 or less/substantial alternative ion transport cannot be inferred simply from the presence of high CO 2 utilization in combination with low CO 2 concentration in the cathode input stream.
  • a molten carbonate fuel cell with a cathode open area of between 50% and 60% was operated with a CO 2 cathode inlet concentration of 13 vol%, 68% CO 2 utilization, and 100 mA/cm 2 of current density. These conditions corresponded to a transference of at least 0.98.
  • operating an MCFC to transport alternative ions across the electrolyte is defined as operating the MCFC so that more than a de minimis amount of alternative ions are transported. It is possible that minor amounts of alternative ions are transported across an MCFC electrolyte under a variety of conventional conditions. Such alternative ion transport under conventional conditions can correspond to a transference of 0.98 or more, which corresponds to transport of alternative ions corresponding to less than 2.0% of the current density for the fuel cell.
  • operating an MCFC to cause alternative ion transport is defined as operating an MCFC with a transference of 0.95 or less, so that 5.0% or more of the current density (or, 5.0% or more of the calculated CO 2 utilization) corresponds to current density based on transport of alternative ions, or 10% or more, or 20% or more, such as up to 35% or possibly still higher. It is noted that in some aspects, operating with increased open area can reduce or minimize the amount of alternative ion transport under conditions that would otherwise result in a transference of 0.95 or less. Thus, by operating with increased open area and/or reduced unblocked flow cross-section, some operating conditions with elevated CO 2 capture/substantial alternative ion transport may correspond to a transference of 0.97 or less.
  • operating an MCFC to cause substantial alternative ion transport is further defined to correspond to operating an MCFC with voltage drops across the anode and cathode that are suitable for power generation.
  • the total electrochemical potential difference for the reactions in a molten carbonate fuel cell is -1.04 V.
  • an MCFC is typically operated to generate current at a voltage near 0.7 V or about 0.8 V. This corresponds to a combined voltage drop across the cathode, electrolyte, and anode of roughly 0.34 V.
  • the combined voltage drop across the cathode, electrolyte, and anode can be less than -0.5 V, so that the resulting current generated by the fuel cell is at a voltage of 0.55 V or more, or 0.6 V or more.
  • one condition for operating with substantial alternative ion transport can be to have an H 2 concentration of 8.0 vol% or more, or 10 vol% or more in the region where the substantial alternative ion transport occurs.
  • this could correspond to a region near the anode inlet, a region near the cathode outlet, or a combination thereof.
  • the Eh concentration in a region of the anode is too low, there will be insufficient driving force to generate substantial alternative ion transport.
  • Suitable conditions for the anode can also include providing the anode with H 2 , a reformable fuel, or a combination thereof; and operating with any convenient fuel utilization that generates a desired current density, including fuel utilizations ranging from 20% to 80%. In some aspects this can correspond to a traditional fuel utilization amount, such as a fuel utilization of 60% or more, or 70% or more, such as up to 85% or possibly still higher. In other aspects, this can correspond to a fuel utilization selected to provide an anode output stream with an elevated content of H 2 and/or an elevated combined content of H 2 and CO (i.e., syngas), such as a fuel utilization of 55% or less, or 50% or less, or 40% or less, such as down to 20% or possibly still lower.
  • a fuel utilization selected to provide an anode output stream with an elevated content of H 2 and/or an elevated combined content of H 2 and CO (i.e., syngas) such as a fuel utilization of 55% or less, or 50% or less, or 40% or less, such as down to 20% or
  • the H 2 content in the anode output stream and/or the combined content of H 2 and CO in the anode output stream can be sufficient to allow generation of a desired current density.
  • the H 2 content in the anode output stream can be 3.0 vol% or more, or 5.0 vol% or more, or 8.0 vol% or more, such as up to 15 vol% or possibly still higher.
  • the combined amount of Hz and CO in the anode output stream can be 4.0 vol% or more, or 6.0 vol% or more, or 10 vol% or more, such as up to 20 vol% or possibly still higher.
  • the H 2 content in the anode output stream can be in a higher range, such as an H 2 content of 10 vol% to 25 vol%.
  • the syngas content of the anode output stream can be correspondingly higher, such as a combined H 2 and CO content of 15 vol% to 35 vol%.
  • the anode can be operated to increase the amount of electrical energy generated, to increase the amount of chemical energy generated (i.e., H 2 generated by reforming that is available in the anode output stream), or operated using any other convenient strategy that is compatible with operating the fuel cell to cause alternative ion transport.
  • one or more locations within the cathode need to have a low enough CO 2 concentration so that the more favorable pathway of carbonate ion transport is not readily available.
  • this can correspond to having a CO 2 concentration in the cathode outlet stream (i.e., cathode exhaust) of 2.0 vol% or less, or 1.0 vol% or less, or 0.8 vol% or less. It is noted that due to variations within the cathode, an average concentration of 2.0 vol% or less (or 1.0 vol% or less, or 0.8 vol% or less) in the cathode exhaust can correspond to a still lower CO 2 concentration in localized regions of the cathode.
  • the CO 2 concentration can be lower than a comer of the same fuel cell that is adjacent to the anode outlet and the cathode outlet. Similar localized variations in CO 2 concentration can also occur in fuel cells having a co-current or counter-current configuration.
  • the localized region of the cathode can also have 1.0 vol% or more of O 2 , or 2.0 vol% or more.
  • O 2 is used to form the hydroxide ion that allows for alternative ion transport. If sufficient O 2 is not present, the fuel cell will not operate as both the carbonate ion transport and alternative ion transport mechanisms are dependent on O 2 availability. With regard to O 2 in the cathode input stream, in some aspects this can correspond to an oxygen content of 4.0 vol% to 15 vol%, or 6.0 vol% to 10 vol%.
  • a fuel cell can correspond to a single cell, with an anode and a cathode separated by an electrolyte.
  • the anode and cathode can receive input gas flows to facilitate the respective anode and cathode reactions for transporting charge across the electrolyte and generating electricity.
  • a fuel cell stack can represent a plurality of 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 can function (approximately) as if they collectively represented a single fuel cell of a larger size.
  • the fuel cell stack can include flow channels for dividing the input flow between each of the cells in the stack and flow channels for combining the output flows from the individual cells.
  • a fuel cell array can be used to refer to a plurality of fuel cells (such as a plurality of fuel cell stacks) that are arranged in series, in parallel, or in any other convenient manner (e.g., in a combination of series and parallel).
  • a fuel cell array can include one or more stages of fuel cells and/or fuel cell stacks, where the anode/cathode output from a first stage may serve as the anode/cathode input for a second stage. It is noted that the anodes in a fuel cell array do not have to be connected in the same way as the cathodes in the array.
  • the input to the first anode stage of a 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 may be referred to as the cathode input to the array.
  • the output from the final anode/cathode stage may be referred to as the anode/cathode output from the array.
  • the anode input flow may first pass through a reforming element prior to entering one or more anodes associated with the reforming element.
  • a“fuel cell stack” composed of individual fuel cells, and more generally refers to the use of one or more fuel cell stacks in fluid communication.
  • Individual fuel cell elements plates
  • a“fuel cell stack” Additional types of elements can also be included in the fuel cell stack, such as reforming elements.
  • This fuel cell stack can typically take a feed stream and distribute reactants among all of the individual fuel cell elements and can then collect the products from each of these elements. When viewed as a unit, the fuel cell stack in operation can be taken as a whole even though composed of many (often tens or hundreds) of individual fuel cell elements.
  • These individual fuel cell elements can typically have similar voltages (as the reactant and product concentrations are similar), and the total power output can result from the summation of all of the electrical currents in all of the cell elements, when the elements are electrically connected in series.
  • Stacks can also be arranged in a series arrangement to produce high voltages. A parallel arrangement can boost the current. If a sufficiently large volume fuel cell stack is available to process a given exhaust flow, the systems and methods described herein can be used with a single molten carbonate fuel cell stack. In other aspects of the invention, a plurality of fuel cell stacks may be desirable or needed for a variety of reasons.
  • fuel cell should be understood to also refer to and/or is defined as including a reference to a fuel cell stack composed of a set of one or more individual fuel cell elements for which there is a single input and output, as that is the manner in which fuel cells are typically employed in practice.
  • fuel cells plural
  • fuel cells should be understood to also refer to and/or is defined as including a plurality of separate fuel cell stacks.
  • all references within this document can refer interchangeably to the operation of a fuel cell stack as a“fuel cell.”
  • a fuel cell i.e., a single stack
  • a plurality of fuel cells i.e., two or more separate fuel cells or fuel cell stacks
  • each fuel cell can process (roughly) an equal portion of the combustion exhaust.
  • each fuel cell can typically be operated in a generally similar manner, given its (roughly) equal portion of the combustion exhaust
  • FIG. 3 shows a general example of a portion of a molten carbonate fuel cell stack.
  • the portion of the stack shown in FIG. 3 corresponds to a fuel cell 301 and an associated reforming element 380.
  • the fuel cell includes separator plates 310 and 311.
  • separator plate 310 separates the fuel cell 301 from reforming element 380.
  • An additional separator plate 390 is located above reforming element 380.
  • the fuel cell 301 includes an anode 330 and a cathode 350 that are separated by an electrolyte matrix 340 that contains an electrolyte 342.
  • Anode collector 320 provides electrical contact between anode 330 and the other anodes in the fuel cell stack, while cathode collector 360 provides similar electrical contact between cathode 350 and the other cathodes in the fuel cell stack. Additionally anode collector 320 allows for introduction and exhaust of gases from anode 330, while cathode collector 360 allows for introduction and exhaust of gases from cathode 350.
  • CO 2 is passed into the cathode collector 360 along with O 2 .
  • the CO 2 and O 2 diffuse into the porous cathode 350 and travel to a cathode interface region near the boundary of cathode 350 and electrolyte matrix 340.
  • a portion of electrolyte 342 can be present in the pores of cathode 350.
  • the CO 2 and Q2 can be converted near/in the cathode interface region to a carbonate ion (CO3 2 '), which can then be transported across electrolyte 342 (and therefore across electrolyte matrix 340) to facilitate generation of electrical current.
  • CO3 2 ' carbonate ion
  • a portion of the O 2 can be converted to an alternative ion, such as a hydroxide ion or a peroxide ion, for transport in electrolyte 342.
  • an alternative ion such as a hydroxide ion or a peroxide ion
  • the carbonate ion can reach an anode interface region near the boundary of electrolyte matrix 340 and anode 330.
  • the carbonate ion can be converted back to CO 2 and H 2 O in the presence of H 2 , releasing electrons that are used to form the current generated by the fuel cell.
  • the H 2 and/or a hydrocarbon suitable for forming H 2 are introduced into anode 330 via anode collector 320.
  • Reforming element 380 can include one or more surfaces that include a reforming catalyst
  • the reforming catalyst on a first portion of at least one surface in the reforming element can correspond to reforming catalyst with a catalyst density pattern as described herein.
  • reforming catalyst can be present on a first portion of a surface within anode 330 (not shown), with the reforming catalyst in anode 330 having a catalyst density pattern as described herein.
  • the flow direction within the anode of a molten carbonate fuel cell can have any convenient orientation relative to the flow direction within a cathode.
  • One option can be to use a cross-flow configuration, so that the flow direction within the anode is roughly at a 90° angle relative to the flow direction within the cathode.
  • This type of flow configuration can have practical benefits, as using a cross-flow configuration can allow the manifolds and/or piping for the anode inlets/outlets to be located on different sides of a fuel cell stack from the manifolds and/or piping for the cathode inlets/outlets.
  • FIG. 4 schematically shows an example of a top view for a fuel cell cathode, along with arrows indicating the direction of flow within the fuel cell cathode and the corresponding fuel cell anode.
  • arrow 405 indicates the direction of flow within cathode 450
  • arrow 425 indicates the direction of flow within the anode (not shown).
  • the anode and cathode flow patterns can contribute to having different reaction conditions in various parts of the cathode.
  • the different conditions can be illustrated by considering the reaction conditions in the four comers of the cathode.
  • the reaction conditions described herein are qualitatively similar to the reaction conditions for a fuel cell operating with a CC1 ⁇ 2 utilization of 75% or more (or 80% or more).
  • Comer 482 corresponds to a portion of the fuel cell that is close to the entry point for both the cathode input flow and the anode input flow.
  • concentration of both CO 2 (in the cathode) and H 2 (in the anode) is relatively high in comer 482. Based on the high concentrations, it is expected that portions of the fuel cell near comer 482 can operate under expected conditions, with substantially no transport of ions other than carbonate ions across the electrolyte.
  • Comer 484 corresponds to a portion of the fuel cell that is close to the entry point for the cathode input flow and close to the exit point for the anode output flow. In locations near comer 484, the amount of current density may be limited due to the reduced concentration of fib in the anode, depending on the fuel utilization. However, sufficient CO 2 should be present so that any ions transported across the electrolyte substantially correspond to carbonate ions.
  • Comer 486 corresponds to a portion of the fuel cell that is close to the exit point for the anode output flow and close to the exit point for the cathode output flow. In locations near comer 486, due to the lower concentrations of both H 2 (in the anode) and CO 2 (in the cathode), little or no current would be expected due to the low driving force for the fuel cell reaction.
  • Comer 488 corresponds to a portion of the fuel cell that is close to the entry point for the anode input flow and close to the exit point for the cathode output flow.
  • the relatively high availability of hydrogen at locations near comer 488 would be expected to result in substantial current density.
  • a substantial amount of transport of hydroxide ions and/or other alternative ions can occur.
  • the substantial amount of alternative ion transport can increase the calculated CO 2 utilization by 5% or more, or 10% or more, or 15% or more, or 20% or more.
  • the transference can be 0.97 or less, or 0.95 or less, or 0.90 or less, or 0.85 or less, or 0.80 or less.
  • the anode input stream for an MCFC can include hydrogen, a hydrocarbon such as methane, a hydrocarbonaceous or hydrocarbon-like compound that may contain heteroatoms different from C and H, or a combination thereof.
  • the source of the hydrogen/hydrocaibon/hydrocarbon-like compounds can be referred to as a fuel source.
  • most of the methane (or other hydrocarbon, hydrocarbonaceous, or hydrocarbon-like compound) fed to the anode can typically be fresh methane.
  • a fresh fuel such as fresh methane refers to a fuel that is not recycled from another fuel cell process.
  • methane recycled from the anode outlet stream back to the anode inlet may not be considered“fresh” methane, and can instead be described as reclaimed methane.
  • the fuel source used can be shared with other components, such as a turbine that uses a portion of the fuel source to provide a COa-containing stream for the cathode input.
  • the fuel source input can include water in a proportion to the fuel appropriate for reforming the hydrocarbon (or hydrocarbon-like) compound in the reforming section that generates hydrogen. For example, if methane is the fuel input for reforming to generate Ha, tiie molar ratio of water to fuel can be from about one to one to about ten to one, such as at least about two to one.
  • a ratio of four to one or greater is typical for external reforming, but lower values can be typical for internal reforming.
  • Ha is a portion of the fuel source, in some optional aspects no additional water may be needed in the fuel, as the oxidation of Ha at the anode can tend to produce HaO that can be used for reforming the fuel.
  • the fuel source can also optionally contain components incidental to the fuel source (e.g., a natural gas feed can contain some content of COa as an additional component).
  • a natural gas feed can contain COa, Na, and/or other inert (noble) gases as additional components.
  • the fuel source may also contain CO, such as CO from a recycled portion of the anode exhaust
  • An additional or alternate potential source for CO in the fuel into a fuel cell assembly can be CO generated by steam reforming of a hydrocarbon fuel performed on the fuel prior to entering the fuel cell assembly.
  • a variety of types of fuel streams may be suitable for use as an anode input stream for the anode of a molten carbonate fuel cell.
  • Some fuel streams can correspond to streams containing hydrocarbons and/or hydrocarbon-like compounds that may also include heteroatoms different from C and H.
  • a reference to a fuel stream containing hydrocarbons for an MCFC anode is defined to include fuel streams containing such hydrocarbon-like compounds.
  • hydrocarbon (including hydrocarbon-like) fuel streams include natural gas, streams containing Cl - C4 carbon compounds (such as methane or ethane), and streams containing heavier C5+ hydrocarbons (including hydrocarbon-like compounds), as well as combinations thereof.
  • Still other additional or alternate examples of potential fuel streams for use in an anode input can include biogas-type streams, such as methane produced from natural (biological) decomposition of organic material.
  • a molten carbonate fuel cell can be used to process an input fuel stream, such as a natural gas and/or hydrocarbon stream, with a low energy content due to the presence of diluent compounds.
  • some sources of methane and/or natural gas are sources that can include substantial amounts of either CC1 ⁇ 2 or other inert molecules, such as nitrogen, argon, or helium. Due to the presence of elevated amounts of CO 2 and/or inerts, the energy content of a fuel stream based on the source can be reduced.
  • a low energy content fuel for a combustion reaction (such as for powering a combustion-powered turbine) can pose difficulties.
  • a molten carbonate fuel cell can generate power based on a low energy content fuel source with a reduced or minimal impact on the efficiency of the fuel cell.
  • the presence of additional gas volume can require additional heat for raising tire temperature of the fuel to the temperature for reforming and/or the anode reaction.
  • the presence of additional CO 2 can have an impact on the relative amounts of Hi and CO present in the anode output.
  • the inert compounds otherwise can have only a minimal direct impact on the reforming and anode reactions.
  • the amount of COi and/or inert compounds in a fuel stream for a molten carbonate fuel cell, when present, can be at least about 1 vol%, such as at least about 2 vol%, or at least about 5 vol%, or at least about 10 vol%, or at least about 15 vol%, or at least about 20 vol%, or at least about 25 vol%, or at least about 30 vol%, or at least about 35 vol%, or at least about 40 vol%, or at least about 45 vol%, or at least about 50 vol%, or at least about 75 vol%.
  • the amount of COi and/or inert compounds in a fuel stream for a molten carbonate fuel cell can be about 90 vol% or less, such as about 75 vol% or less, or about 60 vol% or less, or about 50 vol% or less, or about 40 vol% or less, or about 35 vol% or less.
  • anode input stream can correspond to refinery and/or other industrial process output streams.
  • coking is a common process in many refineries for converting heavier compounds to lower boiling ranges. Coking typically produces an off-gas containing a variety of compounds that are gases at room temperature, including CO and various Ci - CU hydrocarbons. This off-gas can be used as at least a portion of an anode input stream.
  • Other refinery off-gas streams can additionally or alternately be suitable for inclusion in an anode input stream, such as light ends (Ci - C4) generated during cracking or other refinery processes.
  • Still other suitable refinery streams can additionally or alternately include refinery streams containing CO or COi that also contain Hi and/or reformable fuel compounds.
  • Still other potential sources for an anode input can additionally or alternately include streams with increased water content.
  • an ethanol output stream from an ethanol plant (or another type of fermentation process) can include a substantial portion of HiO prior to final distillation.
  • HiO can typically cause only minimal impact on the operation of a fuel cell.
  • a fermentation mixture of alcohol (or other fermentation product) and water can be used as at least a portion of an anode input stream.
  • Biogas or digester gas
  • Biogas may primarily comprise methane and CO 2 and is typically produced by the breakdown or digestion of organic matter. Anaerobic bacteria may be used to digest tiie organic matter and produce the biogas. Impurities, such as sulfur-containing compounds, may be removed from the biogas prior to use as an anode input.
  • the output stream from an MCFC anode can include H 2 O, CO 2 , CO, and H 2 .
  • the anode output stream could also have unreacted fuel (such as H 2 or CH 2 ) or inert compounds in the feed as additional output components.
  • this output stream can be used as a fuel source to provide heat for a reforming reaction or as a combustion fuel for heating the cell.
  • one or more separations can be performed on the anode output stream to separate the CO 2 from the components with potential value as inputs to another process, such as H 2 or CO.
  • the H 2 and/or CO can be used as a syngas for chemical synthesis, as a source of hydrogen for chemical reaction, and/or as a fuel with reduced greenhouse gas emissions.
  • the anode exhaust can be subjected to a variety of gas processing options, including water-gas shift and separation of the components from each other. Two general anode processing schemes are shown in FIGS. 1 and 2.
  • FIG. 1 schematically shows an example of a reaction system for operating a fuel cell array of molten carbonate fuel cells in conjunction with a chemical synthesis process.
  • a fuel stream 105 is provided to a reforming stage (or stages) 110 associated with the anode 127 of a fuel cell 120, such as a fuel cell that is part of a fuel cell stack in a fuel cell array.
  • the reforming stage 110 associated with fuel cell 120 can be internal to a fuel cell assembly.
  • an external reforming stage (not shown) can also be used to reform a portion of the refomnable fuel in an input stream prior to passing the input stream into a fuel cell assembly.
  • 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. Fuel stream 105 can also optionally contain Hi and/or CO, such as Hi and/or CO provided by optional anode recycle stream 185. It is noted that anode recycle stream 185 is optional, and that in many aspects no recycle stream is provided from the anode exhaust 125 back to anode 127, either directly or indirectly via combination with fuel stream 105 or reformed fuel stream 115. After reforming, the reformed fuel stream 115 can be passed into anode 127 of fuel cell 120. A CO 2 and Ch-containing stream 119 can also be passed into cathode 129.
  • a reformable fuel such as methane, other hydrocarbons, and/or other hydrocarbon-like compounds such as organic compounds containing carbon-hydrogen bonds.
  • Fuel stream 105 can also optionally contain Hi and/or CO, such as Hi and/or CO provided by optional an
  • a flow of carbonate ions 122, CO3 2 , from the cathode portion 129 of the fuel cell can provide the remaining reactant needed for the anode fuel cell reactions.
  • the resulting anode exhaust 125 can include H 2 O, CO 2 , one or more components corresponding to incompletely reacted fuel (H 2 , CO, CH*, or other components corresponding to a reformable fuel), and optionally one or more additional nonreactive components, such as Na and/or other contaminants that are part of fuel stream 105.
  • the anode exhaust 125 can then be passed into one or more separation stages.
  • a CO 2 removal stage 140 can correspond to a cryogenic CO 2 removal system, an amine wash stage for removal of acid gases such as CO 2 , or another suitable type of CO 2 separation stage for separating a CO 2 output stream 143 from the anode exhaust.
  • the anode exhaust can first be passed through a water gas shift reactor 130 to convert any CO present in the anode exhaust (along with some H 2 O) into CO 2 and H 2 in an optionally water gas shifted anode exhaust 135.
  • a water condensation or removal stage 150 may be desirable to remove a water output stream 153 from the anode exhaust Though shown in FIG. 1 after the CO 2 separation stage 140, it may optionally be located before the CO 2 separation stage 140 instead.
  • an optional membrane separation stage 160 for separation of H 2 can be used to generate a high purity permeate stream 163 of H 2 .
  • the resulting retentate stream 166 can then be used as an input to a chemical synthesis process.
  • Stream 166 could additionally or alternately be shifted in a second water-gas shift reactor 131 to adjust the H 2 , CO, and CO 2 content to a different ratio, producing an output stream 168 for further use in a chemical synthesis process.
  • anode recycle stream 185 is shown as being withdrawn from the retentate stream 166, but the anode recycle stream 185 could additionally or alternately be withdrawn from other convenient locations in or between the various separation stages.
  • the separation stages and shift reactor(s) could additionally or alternately be configured in different orders, and/or in a parallel configuration.
  • a stream with a reduced content of CO 2 139 can be generated as an output from cathode 129.
  • various stages of compression and heat addition/removal that might be useful in the process, as well as steam addition or removal, are not shown.
  • FIG. 2 shows an example of an alternative order for performing separations on an anode exhaust
  • anode exhaust 125 can be initially passed into separation stage 260 for removing a portion 263 of the hydrogen content from the anode exhaust 125. This can allow, for example, reduction of the H 2 content of the anode exhaust to provide a retentate 266 with a ratio of H 2 to CO closer to 2 : 1. The ratio of H 2 to CO can then be further adjusted to achieve a desired value in a water gas shift stage 230.
  • the water gas shifted output 235 can then pass through CO 2 separation stage 240 and water removal stage 250 to produce an output stream 275 suitable for use as an input to a desired chemical synthesis process.
  • output stream 275 could be exposed to an additional water gas shift stage (not shown).
  • a portion of output stream 275 can optionally be recycled (not shown) to the anode input.
  • still other combinations and sequencing of separation stages can be used to generate a stream based on the anode output that has a desired composition. For the sake of simplicity, various stages of compression and heat addition/removal that might be useful in the process, as well as steam addition or removal, are not shown.
  • a molten carbonate fuel cell 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 voltage of the fuel cell can then be determined by the load, fuel input to the anode, air and CO 2 provided to the cathode, and the internal resistances of the fuel cell.
  • the CO 2 to the cathode can be conventionally provided in part by using the anode exhaust as at least a part of the cathode input stream.
  • the present invention can use separate/different sources for the anode input and cathode input.
  • an MCFC can be operated to cause alternative ion transport across tire electrolyte for the fuel cell.
  • the CO 2 content of the cathode input stream can be 5.0 vol% or less, or 4.0 vol% or less, such as 1.5 vol% to 5.0 vol%, or 1.5 vol% to 4.0 vol%, or 2.0 vol% to 5.0 vol%, or 2.0 vol% to 4.0 vol%.
  • 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). Additional or alternate sources can include other types of boilers, fired heaters, furnaces, and/or other types of devices that bum carbon-containing fuels in order to heat another substance (such as water or air).
  • Other potential sources for a cathode input stream can additionally or alternately include sources of bio-produced CO 2 .
  • This can include, for example, CO 2 generated during processing of bio-derived compounds, such as CO 2 generated during ethanol production.
  • An additional or alternate example can include CO 2 generated by combustion of a bio-produced fuel, such as combustion of lignocellulose.
  • Still other additional or alternate potential CO 2 sources can correspond to output or exhaust streams from various industrial processes, such as COi-containing streams generated by plants for manufacture of steel, cement, and/or paper.
  • CO 2 - containing streams from a fuel cell can correspond to a cathode output stream from a different fuel cell, an anode output stream from a different fuel cell, a recycle stream from the cathode output to the cathode input of a fuel cell, and/or a recycle stream from an anode output to a cathode input of a fuel cell.
  • an MCFC operated in standalone mode under conventional conditions can generate a cathode exhaust with a CO 2 concentration of at least about 5 vol%.
  • Such a CO 2 -containing cathode exhaust could be used as a cathode input for an MCFC operated according to an aspect of the invention. More generally, other types of fuel cells that generate a CO 2 output from the cathode exhaust can additionally or alternately be used, as well as other types of CCh-containing streams not generated by a“combustion” reaction and/or by a combustion- powered generator. Optionally but preferably, a C0 2 -containing stream from another fuel cell can be from another molten carbonate fuel cell.
  • the output from the cathode for a first molten carbonate fuel cell can be used as the input to the cathode for a second molten carbonate fuel cell.
  • a cathode input stream can include O 2 to provide the components necessary for the cathode reaction.
  • Some cathode input streams can be based on having air as a component
  • a combustion exhaust stream can be formed by combusting a hydrocarbon fuel in the presence of air.
  • Such a combustion exhaust stream, or another type of cathode input stream having an oxygen content based on inclusion of air can have an oxygen content of about 20 vol% or less, such as about 15 vol% or less, or about 10 vol% or less.
  • the oxygen content of the cathode input stream can be at least about 4 vol%, such as at least about 6 vol%, or at least about 8 vol%.
  • a cathode input stream can have a suitable content of oxygen for performing the cathode reaction. In some aspects, this can correspond to an oxygen content of about 5 vol% to about 15 vol%, such as from about 7 vol% to about 9 vol%.
  • the combined amount of CO 2 and O 2 can correspond to less than about 21 vol% of the input stream, such as less than about 15 vol% of the stream or less than about 10 vol% of the stream.
  • An air stream containing oxygen can be combined with a CO 2 source that has low oxygen content.
  • 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.
  • a 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.
  • inert/non-reactive species such as N 2 , H 2 O, and other typical oxidant (air) components.
  • the exhaust gas can include typical components of air such as N 2 , H 2 O, and other compounds in minor amounts that are present in air.
  • additional species present after combustion based on the fuel source may include one or more of H 2 O, oxides of nitrogen (NOx) and/or sulfur (SOx), and other compounds either present in the fuel and/or that are partial or complete combustion products of compounds present in the fuel, such as CO.
  • These species may be present in amounts that do not poison the cathode catalyst surfaces though they may reduce the overall cathode activity. Such reductions in performance may be acceptable, or species that interact with the cathode catalyst may be reduced to acceptable levels by known pollutant removal technologies.
  • the amount of O 2 present in a cathode input stream can advantageously be sufficient to provide the oxygen needed for the cathode reaction in the fuel cell.
  • the volume percentage of O 2 can advantageously be at least 0.5 times the amount of CO 2 in the exhaust.
  • additional air can be added to the cathode input to provide a sufficient oxidant for the cathode reaction.
  • the amount of N 2 in the cathode exhaust can be at least about 78 vol%, e.g., at least about 88 vol%, and/or about 95 vol% or less.
  • the cathode input stream can additionally or alternately contain compounds that are generally viewed as contaminants, such as H 2 S or NH3.
  • tiie cathode input stream can be cleaned to reduce or minimize the content of such contaminants.
  • a suitable temperature for operation of an MCFC can be between about 450°C and about 750°C, such as at least about 500°C, e.g., with an inlet temperature of about 550°C and an outlet temperature of about 625°C.
  • heat Prior to entering the cathode, heat can be added to or removed from the cathode input stream, if desired, e.g., to provide heat for other processes, such as reforming the fuel input for the anode.
  • the combustion exhaust stream may have a temperature greater than a desired temperature for the cathode inlet.
  • heat can be removed from the combustion exhaust prior to use as the cathode input stream.
  • the combustion exhaust could be at a very low temperature, for example after a wet gas scrubber on a coal-fired boiler, in which case the combustion exhaust can be below about 100°C.
  • the combustion exhaust could be from the exhaust of a gas turbine operated in combined cycle mode, in which the gas can be cooled by raising steam to run a steam turbine for additional power generation. In this case, the gas can be below about 50°C. Heat can be added to a combustion exhaust that is cooler than desired.
  • the anode of the fuel cell when operating an MCFC to cause alternative ion transport, can be operated at a traditional fuel utilization value of roughly 60% to 80%.
  • operating the anode of the fuel cell at a relatively high fuel utilization can be beneficial for improving electrical efficiency (i.e., electrical energy generated per unit of chemical energy consumed by the fuel cell).
  • This can be beneficial, for example, if it is desirable to consume excess heat generated in the fuel cell (or fuel cell stack) by performing additional reforming and/or performing another endothermic reaction.
  • a molten carbonate fuel cell can be operated to provide increased production of syngas and/or hydrogen.
  • the heat required for performing the endothermic reforming reaction can be provided by the exothermic electrochemical reaction in the anode for electricity generation.
  • this excess heat can be used in situ as a heat source for reforming and/or another endothermic reaction. This can result in more efficient use of the heat energy and/or a reduced need for additional external or internal heat exchange. This efficient production and use of heat energy, essentially in-situ, can reduce system complexity and components while maintaining advantageous operating conditions.
  • the amount of reforming or other endothermic reaction can be selected to have an endothermic heat requirement comparable to, or even greater than, the amount of excess heat generated by the exothermic reaction(s) rather than significantly less than the heat requirement typically described in the prior art
  • the fuel cell can be operated so that the temperature differential between the anode inlet and the anode outlet can be negative rather than positive.
  • a sufficient amount of reforming and/or other endothermic reaction can be performed to cause the output stream from the anode outlet to be cooler than the anode inlet temperature.
  • additional fuel can be supplied to a heater for the fuel cell and/or an internal reforming stage (or other internal endothermic reaction stage) so that tiie temperature differential between the anode input and the anode output can be smaller than the expected difference based on the relative demand of the endothermic reaction(s) and the combined exothermic heat generation of the cathode combustion reaction and the anode reaction for generating electrical power.
  • reforming is used as the endothermic reaction
  • operating a fuel cell to reform excess fuel can allow for production of increased synthesis gas and/or increased hydrogen relative to conventional fuel cell operation while minimizing the system complexity for heat exchange and reforming.
  • the additional synthesis gas and/or additional hydrogen can then be used in a variety of applications, including chemical synthesis processes and/or collection/repuiposing of hydrogen for use as a“clean” fuel.
  • the amount of heat generated per mole of hydrogen oxidized by the exothermic reaction at the anode can be substantially larger than the amount of heat consumed per mole of hydrogen generated by the reforming reaction.
  • This quantity of energy can alternatively be expressed as the current density (current per unit area) for the cell multiplied by the difference between the theoretical maximum voltage of the fuel cell and the actual voltage, or ⁇ current density>*(Vmax - Vact).
  • This quantity of energy is defined as the“waste heat” for a fuel cell.
  • this excess heat can result in a substantial temperature difference from anode inlet to anode outlet
  • the excess heat can be consumed by performing a matching amount of the reforming reaction.
  • the excess heat generated in the anode can be supplemented with the excess heat generated by the combustion reaction in the fuel cell. More generally, the excess heat can be consumed by performing an endothermic reaction in the fuel cell anode and/or in an endothermic reaction stage heat integrated with the fuel cell.
  • the amount of reforming and/or other endothermic reaction can be selected relative to the amount of hydrogen reacted in the anode in order to achieve a desired thermal ratio for the fuel cell.
  • the“thermal ratio” is defined as the heat produced by exothermic reactions in a fuel cell assembly (including exothermic reactions in both the anode and cathode) divided by the endothermic heat demand of reforming reactions occurring within the fuel cell assembly.
  • the thermal ratio (TH) QEX/QEN, where QEX is the sum of heat produced by exothermic reactions and QEN is the sum of heat consumed by the endothermic reactions occurring within tiie fuel cell.
  • the heat produced by the exothermic reactions can correspond to any heat due to reforming reactions, water gas shift reactions, combustion reactions (i.e., oxidation of fuel compounds) in the cathode, and/or the electrochemical reactions in the cell.
  • the heat generated by the electrochemical reactions 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.
  • the ideal electrochemical potential of the reaction in an MCFC is believed to be about 1.04 V based on the net reaction that occurs in the cell.
  • the cell can typically have an output voltage less than 1.04 V due to various losses.
  • a common output/operating voltage can be about 0.7 V.
  • the heat generated can be equal to the electrochemical potential of the cell (i.e. -1.04 V) minus the operating voltage.
  • the heat produced by the electrochemical reactions in the cell can be -0.34 V when the output voltage of -0.7 V is attained in the fuel cell.
  • the electrochemical reactions would produce -0.7 V of electricity and -0.34 V of heat energy.
  • the -0.7 V of electrical energy is not included as part of Q EX . In other words, heat energy is not electrical energy.
  • a thermal ratio can be determined for any convenient fuel cell structure, such as a fuel cell stack, an individual fuel cell within a fuel cell stack, a fuel cell stack with an integrated reforming stage, a fuel cell stack with an integrated endothermic reaction stage, or a combination thereof.
  • the thermal ratio may also be calculated for different units within a fuel cell stack, such as an assembly of fuel cells or fuel cell stacks.
  • the thermal ratio may be calculated for a fuel cell (or a plurality of fuel cells) within a fuel cell stack along with integrated reforming stages and/or integrated endothermic reaction stage elements in sufficiently close proximity to the fuel cell(s) to be integrated from a heat integration standpoint.
  • a characteristic width in a fuel cell stack can be the height of an individual fuel cell stack element. It is noted that the separate reforming stage and/or a separate endothermic reaction stage could have a different height in the stack than a fuel cell. In such a scenario, the height of a fuel cell element can be used as the characteristic height
  • an integrated endothermic reaction stage can be defined as a stage heat integrated with one or more fuel cells, so that the integrated endothermic reaction stage can use the heat from the fuel cells as a heat source for reforming. Such an integrated endothermic reaction stage can be defined as being positioned less than 10 times the height of a stack element from fuel cells providing heat to the integrated stage.
  • an integrated endothermic reaction stage (such as a reforming stage) can be positioned less than 10 times the height of a stack element from any fuel cells that are heat integrated, or less than 8 times the height of a stack element, or less than 5 times tire height of a stack element, or less than 3 times the height of a stack element.
  • an integrated reforming stage and/or integrated endothermic reaction stage that represents an adjacent stack element to a fuel cell element is defined as being about one stack element height or less away from the adjacent fuel cell element.
  • a thermal ratio of 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 of less, can be lower than the thermal ratio typically sought in use of MCFC fuel cells.
  • the thermal ratio can be reduced to increase and/or optimize syngas generation, hydrogen generation, generation of another product via an endothermic reaction, or a combination thereof.
  • the operation of the fuel cells can be characterized based on a thermal ratio.
  • a molten carbonate fuel cell can be operated to have a thermal ratio of about 1.5 or less, for example 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 alternately, the thermal 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. Further additionally or alternately, in some aspects the fuel cell can be operated to have a temperature rise between anode input and anode output of about 40°C or less, such as about 20°C or less, or about 10°C or less.
  • the fuel cell can be operated to have an anode outlet temperature that is from about 10°C lower to about 10°C higher than the temperature of the anode inlet
  • the fuel cell can be operated to have an anode inlet temperature greater than the anode outlet temperature, such as at least about 5°C greater, or at least about 10°C greater, or at least about 20°C greater, or at least about 25°C greater.
  • the fuel cell can be operated to have an anode inlet temperature greater than the anode outlet temperature by about 100°C or less, or about 80°C or less, or about 60°C or less, or about 50°C or less, or about 40°C or less, or about 30°C or less, or about 20°C or less.
  • a temperature drop across the fuel cell can cause a temperature drop across the fuel cell.
  • the amount of reforming and/or other endothermic reaction may be limited so that a temperature drop from the anode inlet to the anode outlet can be about 100°C or less, such as about 80°C or less, or about 60°C or less, or about 50°C or less, or about 40°C or less, or about 30°C or less, or about 20°C or less. Limiting the temperature drop from the anode inlet to the anode outlet can be beneficial, for example, for maintaining a sufficient temperature to allow complete or substantially complete conversion of fuels (by reforming) in the anode.
  • additional heat can be supplied to the fuel cell (such as by heat exchange or combustion of additional fuel) so that the anode inlet temperature is greater than the anode outlet temperature by less than about 100°C or less, such as about 80°C or less, or about 60°C or less, or about 50°C or less, or about 40°C or less, or about 30°C or less, or about 20°C or less, due to a balancing of the heat consumed by the endothermic reaction and the additional external heat supplied to the fuel cell.
  • the amount of reforming can additionally or alternately be dependent on the availability of a reformable fuel. For example, if the fuel only comprised H 2 , no reformation would occur because f1 ⁇ 2 is already reformed and is not further reformable.
  • the amount of “syngas produced” by a fuel cell can be defined as a difference in the lower heating value (LHV) value of syngas in the anode input versus an LHV value of syngas in the anode output.
  • Syngas produced LHV (sg net) (LHV(sg out) - LHV(sg in)), where LHV(sg in) and LHV(sg out) refer to the LHV of the syngas in the anode inlet and syngas in the anode outlet streams or flows, respectively.
  • a fuel cell provided with a fuel containing substantial amounts of H 2 can be limited in the amount of potential syngas production, since the fuel contains substantial amounts of already reformed H 2 , as opposed to containing additional reformable fuel.
  • the lower heating value is defined as the enthalpy of combustion of a fuel component to vapor phase, fully oxidized products (i.e., vapor phase CO 2 and H 2 O product).
  • any CO 2 present in an anode input stream does not contribute to the fuel content of the anode input, since CO 2 is already fully oxidized.
  • the amount of oxidation occurring in the anode due to the anode fuel cell reaction is defined as oxidation of H 2 in the anode as part of the electrochemical reaction in the anode.
  • An example of a method for operating a fuel cell with a reduced thermal ratio can be a method where excess reforming of fuel is performed in order to balance the generation and consumption of heat in the fuel cell and/or consume more heat than is generated. Reforming a 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(s) can be exothermic. During conventional fuel cell operation, the amount of reforming needed to supply the feed components for fuel cell operation can typically consume less heat than the amount of heat generated by the anode oxidation reaction.
  • conventional operation at a fuel utilization of about 70% or about 75% produces a thermal ratio substantially greater than 1, such as a thermal ratio of at least about 1.4 or greater, or 1.5 or greater.
  • the output streams for the fuel cell can be hotter than the input streams.
  • the amount of fuel reformed in the reforming stages associated with the anode can be increased.
  • additional fuel can be reformed so that the heat generated by the exothermic fuel cell reactions can either be (roughly) balanced by the heat consumed in reforming and/or consume more heat than is generated.
  • Either hydrogen or syngas can be withdrawn from the anode exhaust as a chemical energy output.
  • Hydrogen can be used as a clean fuel without generating greenhouse gases when it is burned or combusted. Instead, for hydrogen generated by reforming of hydrocarbons (or hydrocarbonaceous compounds), the CO 2 will have already been “captured” in the anode loop. Additionally, hydrogen can be a valuable input for a variety of refinery processes and/or other synthesis processes. Syngas can also be a valuable input for a variety of processes. In addition to having fuel value, syngas can be used as a feedstock for producing other higher value products, such as by using syngas as an input for Fischer- Tropsch synthesis and/or methanol synthesis processes.
  • the reformable hydrogen content of reformable fuel in the input stream delivered to the anode and/or to a reforming stage associated with the anode can be at least about 50% greater than the net amount of hydrogen reacted at the anode, such as at least about 75% greater or at least about 100% greater. Additionally or alternately, the reformable hydrogen content of fuel in the input stream delivered to the anode and/or to a reforming stage associated with the anode can be at least about 50% greater than the net amount of hydrogen reacted at the anode, such as at least about 75% greater or at least about 100% greater.
  • a ratio of the reformable hydrogen content of the reformable fuel in the fuel stream relative to an amount of hydrogen reacted in the anode can be 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 alternately, the ratio of reformable hydrogen content of the reformable fuel in the fuel stream relative to the amount of hydrogen reacted in the anode can be about 20 : 1 or less, such as about 15 : 1 or less or about 10 : 1 or less. In one aspect, it is contemplated that less than 100% of the reformable hydrogen content in the anode inlet stream can be converted to hydrogen.
  • the amount of reformable fuel delivered to the anode can be characterized based on the Lower Heating Value (LHV) of the reformable fuel relative to the LHV of the hydrogen oxidized in the anode.
  • LHV Lower Heating Value
  • the reformable fuel surplus 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.
  • the reformable fuel surplus 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.
  • the cathode is typically operated with a CO 2 concentration in the cathode input feed of 8 vol% or more and/or a CO 2 utilization of 70% or less. Such operation typically corresponds to a cathode exhaust that includes 5.0 vol% or more CO 2 .
  • the anode is operated with an excess of fuel at a fuel utilization of 60% or more.
  • reforming catalyst patterns have been developed in order to improve fuel cell operation. These catalyst patterns are based on an expected temperature profile during conventional fuel cell operation. The expected temperature profile is based on a corresponding expectation of where the reaction will occur within a fuel cell.
  • FIG. 5 shows an example of a flow pattern within a reforming element
  • the reformable fuel 521 is initially passed through a channel 530 on the side of the reforming element 510.
  • the channel 530 is in proximity to the cathode inlet of the fuel cell stack.
  • the channel 530 is separated from a remaining or first portion of reforming element 510 by a barrier 535.
  • the catalyst density in channel 530 can be relatively uniform, such as due to having no reforming catalyst in channel 530.
  • channel 530 can have a non-zero reforming catalyst density, such as reforming catalyst density corresponding to the average reforming catalyst density in the first portion 540, the minimum catalyst density in first portion 540, or any other convenient catalyst density.
  • the reformable fuel 521 is passed 545 from channel 530 to first portion 540 of reforming element 510, where it flows through first portion 540 in the direction of arrow 508.
  • the hydrogen produced by reforming and/or remaining portions of unreformed fuel can then exit the reforming element (not shown) and be passed into one or more anodes (via anode collectors) by any convenient method, such as via one or more manifolds or conduits.
  • Arrow 550 shows the direction of flow within an anode associated with the reforming element 510
  • arrow 560 shows the direction of flow within a cathode associated with the reforming element 510.
  • FIG. 6 shows an example of a reforming catalyst pattern suitable for use on a surface that includes reforming catalyst.
  • the catalyst pattern is formed based on parallel lines of catalyst particles, with the direction of flow being substantially parallel the lines of catalyst particles during most portions of the flow path.
  • the pattern shown in FIG. 6 corresponds to a pattern suitable either for the reforming catalyst in the entire reforming element, or alternatively for a portion such as first portion 510 in a reforming element.
  • the reforming catalyst density is highest at the left end, and decreases to no catalyst density at the right end.
  • the maximum amount of endothermic reforming occurs near the maximum amount of exothermic oxidation in the anode. It is noted that if an average catalyst density is used in an initial channel in proximity to the cathode inlet, such as the initial channel 510 in FIG. 5, the catalyst pattern in FIG. 6 can provide substantial reforming in proximity to both the anode inlet and the cathode inlet
  • U.S. Patent 8,822,090 describes another type of reforming catalyst pattern.
  • two separate catalyst density variations are present, with one being aligned with the cathode flow and the other being aligned with the anode flow.
  • the fuel enters the reforming element on a side that is in proximity to the cathode outlet side of the fuel cell stack.
  • the catalyst density increases as the fuel moves from the cathode outlet side of the reforming element toward the cathode outlet side.
  • An example of a catalyst pattern is shown with variations in reforming catalyst density based on placement of reforming catalyst particles.
  • the maximum catalyst density corresponds to placement of particles with a frequency of one particle per two potential placement sites and a minimum catalyst density of one particle per sixty-four potential placement sites. This corresponds to a variation from maximum to minimum of over 90%, under the definitions provided herein. It is noted that in addition to the variation along the direction of cathode flow, there is a second gradient along the direction of anode flow in the anode associated with the reforming element
  • a molten carbonate fuel cell model that included aspects to represent fluid flows and heat transfer within the fuel cell was used to determine the impact of catalyst pattern on temperature differences within the fuel cell.
  • the model was constructed using a commercially available process modeling platform.
  • the model represented a system with a reforming element, an associated fuel cell having an anode and a cathode, and a separator plate between the reforming element and the associated fuel cell.
  • the flow pattern in the reforming element corresponds to the flow pattern shown in FIG. 5.
  • the reforming element included an initial channel in proximity to the cathode inlet with a constant catalyst density (corresponding to the average in the first portion), and a first portion with a catalyst pattern that was aligned with the flow pattern in the anode.
  • modeling results are provided for molten carbonate fuel cells with two different types of catalyst patterns for a first portion of the reforming element
  • One type of catalyst pattern corresponds to the catalyst pattern shown in FIG. 5.
  • a second type of catalyst pattern corresponds to a catalyst pattern with a difference between maximum and minimum catalyst density of roughly 63%.
  • FIG. 7 shows three types of catalyst density profiles for a first portion of a reforming element
  • the x-axis corresponds to the flow axis in the anode, with 0 corresponding to the anode inlet and 1 corresponding to the anode outlet
  • Line 910 corresponds to the conventional catalyst profile shown in FIG. 5.
  • Line 920 corresponds to the catalyst profile used for the second fuel cell that was modeled.
  • line 920 has a ratio of minimum to maximum catalyst density of 60/160, or 3/8. This corresponds to a difference between maximum and minimum of 62.5%.
  • the difference between maximum and minimum for line 910 is effectively 100%, as the catalyst density drops to zero at the anode outlet in line 910.
  • FIG. 7 also shows line 930, which is similar to the profile in line 920, but with a continuous monotonic decrease in catalyst density, as opposed to the step-wise monotonic decrease in catalyst density shown in line 920.
  • FIG. 8 shows the temperature variation at the separator plate for the fuel cell that was modeled with the comparative reforming catalyst density corresponding to line 910 of FIG. 7.
  • the x-axis corresponds to the anode flow direction, while the y-axis corresponds to the cathode flow direction.
  • the temperature gradient across the fuel cell is greater than 80°K, or greater than 80°C.
  • FIG. 9 shows the temperature variation at the separator plate for the fuel cell that was modeled with the reforming catalyst density corresponding to line 920 of FIG. 7.
  • a molten carbonate fuel cell model that included aspects to represent fluid flows and heat transfer within the fuel cell was used to determine the impact of catalyst pattern on temperature differences within the fuel cell.
  • the model was constructed using a commercially available process modeling platform.
  • the model represented a system with a reforming element, an associated fuel cell having an anode and a cathode, and a separator plate between the reforming element and the associated fuel cell.
  • the flow pattern in the reforming element corresponds to the flow pattern shown in FIG. 5.
  • the reforming element included an initial channel in proximity to the cathode inlet with a constant catalyst density (corresponding to the average in the first portion), and a first portion with a catalyst pattern that was aligned with the flow pattern in the anode.
  • modeling results are provided for molten carbonate fuel cells with three different types of catalyst patterns for a first portion of the reforming element
  • One type of catalyst pattern corresponds to the catalyst pattern shown in FIG. 5.
  • a second type of catalyst pattern corresponds to a catalysts pattern with a difference between maximum and minimum catalyst density of roughly 100 %, like the first type of catalyst pattern in this example.
  • a third type of catalyst pattern corresponds to a catalyst pattern with a difference between maximum and minimum catalyst density of roughly 43%.
  • FIG. 10 shows four types of catalyst density profiles for a first portion of a reforming element.
  • the x-axis corresponds to the flow axis in the anode, with 0 corresponding to the anode inlet and 1 corresponding to the anode outlet
  • Line 910 corresponds to the conventional catalyst profile shown in FIG. 5 and in FIG. 7 from Example 2 above.
  • the difference between maximum and minimum catalyst density for this catalyst profile is effectively 100%, as the catalyst density drops to zero at the anode outlet in line 910.
  • line 1010 corresponds to another catalyst profile having a difference between maximum and minimum catalyst density as effectively 100%, since here too, the catalyst density drops to zero at the anode outlet in line 1010.
  • FIG. 10 shows four types of catalyst density profiles for a first portion of a reforming element.
  • the x-axis corresponds to the flow axis in the anode, with 0 corresponding to the anode inlet and 1 corresponding to the anode outlet
  • Line 910 corresponds to the conventional catalyst profile shown
  • line 1020 has a ratio of minimum to maximum catalyst density of approximately 80 / 160, or 1 / 2. This corresponds to a difference between maximum and minimum of approximately 50%.
  • FIG. 10 also shows line 1030, which is similar to the profile in line 1020, but with a continuous monotonic decrease in catalyst density, as opposed to the step-wise monotonic decrease in catalyst density shown in line 1020.
  • fuel cells using the catalyst profiles described by line 1010 for the first portion of the surface in the reforming element were modeled under conditions that resulted in elevated CO 2 utilization.
  • the model conditions were a cathode inlet CO 2 concentration of 4.3 vol%, a fuel utilization of 50%, an actual CO 2 utilization of ⁇ 85%, an average cathode temperature of roughly 903.15°K (630°C), and a current density of 110 mA/cm 2 .
  • the input stream into the reformer included 7 vol% H 2 , 2 vol% C O 2, 60 vol% H 2 O, and 30 vol% CHt, with the balance corresponding to nitrogen.
  • fuel cells using the catalyst profiles described by line 1020 for the first portion of the surface in the reforming element were modeled under conditions that resulted in elevated CO 2 utilization.
  • the model conditions were a cathode inlet CO 2 concentration of 4.4 vol%, a fuel utilization of 50%, an actual CO 2 utilization of ⁇ 85%, an average cathode temperature of roughly 903.15°K (630°C), and a current density of 150 mA/cm 2 .
  • the input stream into the reformer included 10 vol% H 2 , 3 vol% CO 2 , 58% H 2 O, and 29 vol% CHt with the balance corresponding to nitrogen.
  • FIG. 11 shows the temperature variation at the separator plate for the fuel cell that was modeled with the comparative reforming catalyst density corresponding to line 910 of FIG. 10.
  • the x-axis corresponds to the anode flow direction
  • the y-axis corresponds to the cathode flow direction.
  • the temperature gradient across the fuel cell is greater than 100°K, or greater than 100°C. This is due to the excess waste heat generated by alternative ion transport in the comer of the fuel cell corresponding to the cathode outlet and the anode outlet.
  • the catalyst density is close to zero near the comer corresponding to the cathode outlet and anode outlet
  • FIG. 12 shows the temperature variation of the separator plate for the fuel cell that was modeled with the reforming catalyst density corresponding to line 1010 of FIG. 10.
  • the temperature gradient across the fuel cell is approximately 70°K or 70°C, which is due to the excess waste heat generated by alternative ion transport in the comer of the fuel cell corresponding to the cathode outlet and the anode outlet.
  • the catalyst density is close to zero near the comer corresponding to the cathode outlet and anode outlet.
  • FIG. 13 shows the temperature variation at the separator plate for the fuel cell that was modeled with the reforming catalyst density corresponding to line 1030 of FIG. 10.
  • Embodiment 1 A method for producing electricity, the method comprising: passing a fuel stream comprising a reformable fuel into a fuel stack comprising a first surface, the first surface comprising a first portion comprising a reforming catalyst, a reforming catalyst density on the first portion of the first surface having a difference between a maximum catalyst density and a minimum catalyst density of 20% to 75%; reforming at least a portion of the reformable fuel in the presence of the first surface to produce reformed hydrogen; introducing at least a portion of the reformable fuel, at least a portion of the reformed hydrogen, or a combination thereof into an anode of a molten carbonate fuel cell; introducing a cathode input stream comprising O 2 and CO 2 into a cathode of the molten carbonate fuel cell, a direction of flow in the cathode of the molten carbonate fuel cell being substantially orthogonal to a direction of flow in the anode of the molten carbonate fuel cell; and operating the molten carbonate fuel
  • Embodiment 2 The method of Embodiment 1, wherein the cathode input stream comprises 5.0 vol% or less of CO 2 , or wherein the cathode exhaust comprises 1.0 vol% or less of CO 2 , or a combination thereof.
  • Embodiment 3 A method for producing electricity, the method comprising: passing a fuel stream comprising a reformable fuel into a fuel stack comprising a first surface, the first surface comprising a first portion comprising a reforming catalyst, a reforming catalyst density on the first portion of the first surface having a difference between a maximum catalyst activity and a minimum catalyst activity of 20% to 75%; reforming at least a portion of the reformable fuel in the presence of the first surface to produce reformed hydrogen; introducing at least a portion of the reformable fuel, at least a portion of the reformed hydrogen, or a combination thereof into an anode of a molten carbonate fuel cell; introducing a cathode input stream comprising O 2 and CO 2 into a cathode of the molten carbonate fuel cell, a direction of flow in the cathode of the molten carbonate fuel cell being substantially orthogonal to a direction of flow in the anode of the molten carbonate fuel cell; and operating the molten carbonate fuel
  • Embodiment 4 The method of any of the above embodiments, wherein the transference is 0.95 or less, or 0.90 or less.
  • Embodiment 5 The method of any of the above embodiments, wherein the reforming catalyst on the first portion of the first surface comprises a monotonic catalyst density variation.
  • Embodiment 6 The method of any of the above embodiments, wherein the maximum catalyst density is in proximity to the anode inlet, or wherein the maximum catalyst density is in proximity to the cathode inlet
  • Embodiment 7 The method of any of the above embodiments, wherein the minimum catalyst density is in proximity to the anode outlet, or wherein the minimum catalyst density is in proximity to the cathode outlet.
  • Embodiment 8 The method of any of the above embodiments, wherein the fuel cell stack comprises a reforming element associated with the anode, wherein the first surface comprises an interior surface of the reforming element, and wherein a temperature variation within the fuel cell stack at a separator plate between the reforming element and the anode is optionally 70°C or less (or 40°C or less).
  • Embodiment 9 The method of any of Embodiments 1 - 7, wherein the first surface comprises an interior surface of the anode, and wherein a temperature variation within the fuel cell stack at a separator plate between the anode and another element is optionally 70°C or less (or 40°C or less).
  • Embodiment 10 The method of any of the above embodiments, wherein the first surface further comprises a second portion, the second portion optionally comprising at least one of a constant catalyst density and a constant catalyst activity, and wherein the second portion is in proximity to the cathode inlet, or wherein the second portion is in proximity to the anode inlet
  • Embodiment 11 The method of any of the above embodiments, wherein the reforming catalyst comprises a plurality of lines of catalyst particles, and wherein reforming the at least a portion of the reformable fuel comprises flowing the at least a portion of the reformable fuel over the catalyst particles in a direction that is substantially parallel to the lines of catalyst particles.
  • a fuel cell stack comprising: a molten carbonate fuel cell comprising an anode and a cathode; a reforming element associated with the anode, the reforming element comprising a first surface, the first surface comprising a first portion comprising a reforming catalyst, a reforming catalyst density on the first portion of the first surface comprising a monotonically decreasing catalyst density, the reforming catalyst density on the first portion of the first surface having a difference between a maximum catalyst density and a minimum catalyst density of 20% to 75% (or 25% to 70%, or 25% to 65%); and a separator plate between the anode and the reforming element, wherein the first surface optionally further comprises a second portion, the optional second portion being in proximity to the cathode inlet or in proximity to the anode inlet, the optional second portion comprising a constant catalyst density.
  • Embodiment 13 The fuel cell stack of Embodiment 12, wherein the maximum catalyst density is in proximity to the anode inlet, or wherein the maximum catalyst density is in proximity to the cathode inlet.
  • Embodiment 14 The fuel cell stack of Embodiment 12 or 13, wherein the minimum catalyst density is in proximity to the anode outlet, or wherein the minimum catalyst density is in proximity to the cathode outlet
  • Embodiment 15 The fuel cell stack of any of Embedments 12 to 14, wherein tiie reforming catalyst comprises substantially parallel lines of catalyst particles.

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Abstract

L'invention concerne un élément de reformage pour un empilement de piles à combustible à carbonate fondu et des procédés correspondants qui peuvent réduire ou réduire au minimum les différences de température à l'intérieur de l'empilement de piles à combustible lors du fonctionnement de l'empilement de piles à combustible avec une utilisation améliorée du CO2. L'élément de reformage peut comprendre au moins une surface sur laquelle est déposée un catalyseur de reformage. Une différence entre la densité et/ou l'activité du catalyseur de reformage minimale et maximale sur une première portion de ladite surface peut être de 20 % à 75 %, les densités et/ou activités de catalyseur les plus élevées se trouvant à proximité du côté de l'empilement de piles à combustible correspondant à au moins l'une parmi l'entrée d'anode et l'entrée de cathode.
EP19827929.1A 2018-11-30 2019-11-26 Motif de catalyseur de reformage pour pile à combustible fonctionnant avec une utilisation améliorée du co2 Pending EP3888165A1 (fr)

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US201862773485P 2018-11-30 2018-11-30
PCT/US2019/063434 WO2020112895A1 (fr) 2018-11-30 2019-11-26 Motif de catalyseur de reformage pour pile à combustible fonctionnant avec une utilisation améliorée du co2

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CN113261133B (zh) 2023-09-01
CN113261133A (zh) 2021-08-13

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