WO2010081936A1 - A method in a fuel cell arrangement - Google Patents

A method in a fuel cell arrangement Download PDF

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Publication number
WO2010081936A1
WO2010081936A1 PCT/FI2010/050010 FI2010050010W WO2010081936A1 WO 2010081936 A1 WO2010081936 A1 WO 2010081936A1 FI 2010050010 W FI2010050010 W FI 2010050010W WO 2010081936 A1 WO2010081936 A1 WO 2010081936A1
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Prior art keywords
water
fuel gas
fuel
gas
fuel cell
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PCT/FI2010/050010
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French (fr)
Inventor
Timo Mahlanen
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Wärtsilä Finland Oy
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Publication of WO2010081936A1 publication Critical patent/WO2010081936A1/en

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    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01B—BOILING; BOILING APPARATUS ; EVAPORATION; EVAPORATION APPARATUS
    • B01B1/00—Boiling; Boiling apparatus for physical or chemical purposes ; Evaporation in general
    • B01B1/005—Evaporation for physical or chemical purposes; Evaporation apparatus therefor, e.g. evaporation of liquids for gas phase reactions
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/32—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
    • C01B3/34—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents
    • C01B3/38—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents using catalysts
    • 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
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04007—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids related to heat exchange
    • H01M8/04014—Heat exchange using gaseous fluids; Heat exchange by combustion of reactants
    • 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
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
    • H01M8/04089—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants
    • H01M8/04119—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with simultaneous supply or evacuation of electrolyte; Humidifying or dehumidifying
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02—Processes for making hydrogen or synthesis gas
    • C01B2203/0205—Processes for making hydrogen or synthesis gas containing a reforming step
    • C01B2203/0227—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
    • C01B2203/0233—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step the reforming step being a steam reforming step
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/06—Integration with other chemical processes
    • C01B2203/066—Integration with other chemical processes with fuel cells
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/08—Methods of heating or cooling
    • C01B2203/0805—Methods of heating the process for making hydrogen or synthesis gas
    • C01B2203/0811—Methods of heating the process for making hydrogen or synthesis gas by combustion of fuel
    • C01B2203/0822—Methods of heating the process for making hydrogen or synthesis gas by combustion of fuel the fuel containing hydrogen
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/12—Feeding the process for making hydrogen or synthesis gas
    • C01B2203/1258—Pre-treatment of the feed
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/14—Details of the flowsheet
    • C01B2203/148—Details of the flowsheet involving a recycle stream to the feed of the process for making hydrogen or synthesis gas
    • 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
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/12—Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte
    • H01M2008/1293—Fuel cells with solid oxide electrolytes
    • 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
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/06—Combination of fuel cells with means for production of reactants or for treatment of residues
    • H01M8/0662—Treatment of gaseous reactants or gaseous residues, e.g. cleaning
    • H01M8/0675—Removal of sulfur
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency

Definitions

  • the present invention relates to the method in a fuel cell arrangement according to the preamble of patent claim 1 , according to which method fuel gas is fed to the anode side of the fuel cell arrangement, and according to which method water is supplied to the fuel gas before the fuel gas is fed to the anode side of the fuel cell arrangement.
  • a fuel cell suitable for this purpose is a solid oxide fuel cell, SOFC.
  • SOFC solid oxide fuel cell
  • a solid oxide fuel cell is efficient and the heat produced by it may be used as heat source for various purposes, such as for heating of buildings or for steam production.
  • a solid oxide fuel cell poses limitations to the fuel that may be used. Especially a fuel containing heavy hydrocarbons is not as such suitable for introduction to the anode of a fuels cell. The risk of formation of carbon on the anode is high which impairs the operation of a fuel cell. Thus, many fuels require some kind of a pretreatment before they are fed to a fuel cell.
  • the pretreatment may include, among other things, desulfurization and/or modifying the fuel by catalytic cracking.
  • the reactions produce mainly methane which is a particularly favorable fuel for a solid oxide fuel cell or a molten-carbonate cell, as using it provides cooling of the cell through internal reforming and thus it is possible to influence the required volume of gas flowing through the cell.
  • Steam reforming thus requires steam which can be produces, as is known, for example in a separate steam generator. Normally it is heated for example with electricity.
  • the steam generator may utilize also heat from the main process via a heat exchanger.
  • a separate steam generator of this kind is disadvantageous as it requires quite a large space, a connecting pipeline of its own, and also a relatively complex control system.
  • Publication DE 19956378A1 describes an apparatus and a method in which air is heated and hydrocarbon in liquid form is introduced to the heated gas.
  • the heat of the gas vaporizes the hydrocarbon and this mixture is further heated to a higher temperature and subsequently water is brought to the mixture.
  • the heat of the gas vaporizes water and after this the mixture is further heated.
  • the heating stages have been described to be carried out by means of separate heat exchangers.
  • the size of the heat exchangers is remarkably large and thus this kind of a solution is unfavorable.
  • the object of the invention is to provide a method in a fuel cell arrangement according to which method fuel gas is fed to the anode side of a fuel cell arrangement, and according to which method water in liquid form is brought to the fuel gas before the fuel gas is fed to the anode side, and which method provides a fuel cell arrangement having a more compact structure than before.
  • the objects of the invention are achieved with a method in a fuel cell arrangement according to which method fuel gas is led to the anode side of the fuel cell arrangement, and according to which method water in liquid form is brought to the fuel gas before the fuel gas is fed to the anode side, and according to which method the pressure of the water is raised before it is introduced to the fuel gas.
  • the temperature of the liquid water is raised after its pressure has been raised, by means of a heating device arranged in the feeding apparatus, heat from the exhaust gas of fuel cell arrangement being transferred to the water in said heating device, and that water is vaporized in to the fuel gas by means of the enthalpy of the water.
  • a method of this kind can be carried out with a very simple and reliable apparatus. Further, the apparatus is advantageous also in that respect that it can be carried out with very compact equipment. The method is also very economical.
  • the fuel gas is preferably introduced to a fuel reformer prior to feeding of the fuel gas to the anode side, in order to modify the composition of the fuel gas in the reformer, and prior to feeding of the fuel gas to the reformer, liquid water is brought to the fuel gas, the water being vaporized to the fuel gas by means of the enthalpy of the water. Then, steam is present already in the reformer thus minimizing the formation of carbon onto the surfaces of the reformer catalyst.
  • the heat required for vaporizing the water is transferred to the liquid water and, as heat transfer to water is clearly more efficient than to gas or steam, the apparatus according to the invention among other things also allows using apparatus of a relatively small size.
  • the temperature of the mixture of water and fuel gas is adjusted to the desired level substantially simultaneously as water is introduced to the fuel gas and vaporized.
  • the temperature adjustment is preferably carried out so that in the location of the water injection point or immediately following it, there is a device influencing the temperature of the mixture by means of which device additional heat may be brought to the mixture of water and fuel gas.
  • the temperature of the mixture of water and fuel gas is adjusted by bringing additional heat to the mixture of water and fuel gas from the anode side exhaust gas.
  • the injection pressure of the liquid water being brought to the fuel gas is at least 20-fold in the injection point, compared with the pressure of the fuel gas. This ensures that the vaporizing of the water is efficient among other things in view of droplet formation.
  • the injection pressure is 5 - 12 MPa.
  • a large portion of the water is vaporized as so-called flash steam, thus consuming less energy from the fuel gas to vaporization.
  • the fuel gas in order to reform hydrocarbon-containing fuel gas by means of a catalyst in the presence of steam, the fuel gas is fed to a fuel reformer before the fuel gas is taken to the anode side of the fuel cell, to modify the composition of the fuel gas in the reformer, and prior to feeding the fuel gas to the reformer, water in liquid form in introduced at injection pressure, which is 5 -12 MPa, and mainly as saturated water, into the fuel gas.
  • injection pressure which is 5 -12 MPa
  • saturated water water in liquid form in introduced at injection pressure, which is 5 -12 MPa, and mainly as saturated water, into the fuel gas.
  • injection pressure which is 5 -12 MPa
  • steam is generated in a simple way and with equipment requiring only very little space.
  • Steam is present already in the reformer, minimizing the formation of carbon on the surfaces of the catalyst.
  • Preferably all the liquid water is brought to the fuel gas before the gas is introduced into the fuel reformer.
  • the approach according to the invention provides several advantages.
  • the formation of carbon is minimized and the size of the apparatus is relatively small.
  • An advantage is the possibility to omit the complex steam generator with its superheater, which require much space, and to simplify and speed up the adjustment of the method.
  • the saving of space is remarkable but the solution is applicable also in other installations to protect the catalyst.
  • FIG. 1 illustrates an embodiment of the method according to the invention.
  • FIG 1 illustrates in a simplified manner a schematic presentation of a typical solid oxide fuel cell arrangement applying the method of the invention.
  • the reference number 6 signifies a fuel cell apparatus.
  • the fuel cell arrangement comprises a fuel cell apparatus 6 operating at a high temperature, typically > 500 0 C and formed by stacks of fuel cells operating at a high temperature.
  • the fuel cells stacks may be formed for example of solid oxide fuel cells (SOFC) or molten-carbonate fuel cells (MCFC) or fuel cells of other suitable types.
  • SOFC solid oxide fuel cells
  • MCFC molten-carbonate fuel cells
  • natural gas is used as fuel.
  • the natural gas in fed into the apparatus as pressurized fuel gas in feed duct 1 and through a heat exchanger 2, in which the fuel gas is heater with the heat of the exhaust gases from the fuel cell arrangement.
  • a desulfurization unit 3 removing sulfur form the fuel.
  • the fuel gas is, depending on the apparatus assembly, taken either to a pre-reformer or a reformer 4, in which among other things hydrogen is formed of the fuel gas, for example natural gas.
  • Water brought to the fuel gas in feed duct 16 is used to assist in the reforming of the fuel, in other words among other things in the production of hydrogen.
  • the hydrocarbons of the natural gas are converted with steam into hydrogen, methane or carbon oxides.
  • a part of the exhaust gases of the fuel cell anode side 7 is taken via a heat exchanger 5 and a fan or a compressor 13 to the feed side of the reformer 4 whereby also carbon dioxide and the steam from the exhaust gas of the anode side 7 is mixed into the feed flow.
  • Fuel gas is heater in the heat exchanger 5 with the exhaust gas of the anode side 7.
  • the fuel is fed via said heat exchanger 5 to the anode side 7 of the fuel cell unit 6 formed of stacks of fuel cells.
  • the fuel cell stacks of the fuel cell unit 6 are formed of a plurality of fuel cells pressed against each other, each having an anode side 7, a cathode side 8 and an electrolyte 9 between these.
  • the fuel cell stacks and their feasible combinations are illustrated schematically as one entity.
  • the part of the anode side 7 exhaust gases which is not recycled is fed to an afterburner 14, where the residual fuel is combusted and subsequently the exhaust gases are discharged from the apparatus through heat exchangers 17, 2.
  • oxygen is fed to the cathode side 8 along with air with a fan or a compressor 10, from which air is taken via a feed duct 11 to a heat exchanger 12, where the air to be fed to the cathode side 8 is preheated with the exhaust gases of the cathode side, itself.
  • the majority of the heat of the cathode side exhaust gases is used in the heat exchanger 12 in the preheating of the air to be fed to the cathode side.
  • a smaller part of the heat is taken further with the exhaust gases to the afterburner 14 and via it out from the apparatus, or directly out from the apparatus for example via a heat exchanger (not illustrated).
  • Water used in the reforming of the fuel is brought to the fuel gas in liquid form in a duct 16 which is a part of the water feed system, prior to the feed of the fuel gas to the reformer 4.
  • a pressure increasing device 19 for example a pump, the suction side of which has a flow communication with a liquid water source 18.
  • the pump 19 has been provided in the feed duct 16 to raise the pressure of the liquid water.
  • the pump 19 has been equipped for example with a control system 22, controlling its rotation speed, for adjusting the water flow to be fed to the desired level.
  • the rotation velocity is preferably adjusted based on the power of the fuel cell unit.
  • the heater 20 is also a heater 20 provided in the feed duct. It is located in the feed duct between the pressure side of the pump 19 and the water feed member 21 , whereby the temperature of the water is raised after the pressure increase.
  • the heater 20 may be electric, or it may also be a heat exchanger connected at one side for example to the anode side exhaust gas flow.
  • the water feed member 21 preferably comprises several nozzles which may be opened and closed independently, whereby the volume and/or feed pressure of the water being fed may be controlled by opening and closing the nozzles, in addition to or as an alternatively for controlling the rotation speed of the pump 19.
  • a device 23 influencing the temperature of the mixture functioning as the regulator of the temperature of the water and fuel gas fed.
  • the device 23 is preferably a heater, by means of which the temperature of the water and the fuel gas are adjusted suitable for the reformer 4.
  • the heater is electric.
  • the heater is a heat exchanger utilizing the heat of the exhaust gas from the fuel cell (not illustrated in the Figure).
  • Fuel gas pressure 150 - 300 kPa
  • Fuel gas temperature 400 - 500 0 C
  • water is supplied in a pressurized state directly via nozzle/s to the gas feed duct 1 , where small droplets are immediately vaporized and thus the required steam is produced.
  • a suitable and accurately adjusted steam volume for the catalyst of the reformer 4 may be obtained at different partial load ranges.
  • the volume of the flash steam formed this way depends on the enthalpy difference of the water under different conditions.
  • the pressure difference of the water feed pressure and the fuel gas pressure has a significant influence on the amount of the so-called flash steam. Therefore, the injection pressure of the liquid water at the injection point is kept at least 20-fold compared with the prevailing fuel gas pressure.
  • the fuel may, instead of the natural gas mentioned, be any other hydrocarbon-containing fuel suitable for use.

Abstract

The invention relates to a method in a fuel cell arrangement, according to which method fuel gas is led to the anode side (7) of the fuel cell arrangement, and according to which method water in liquid form is brought (21 ) to the fuel gas before the gas is taken to the anode side, and according to which method the pressure of water is raised before it is brought to the fuel gas. The temperature of the liquid water is raised, after its pressure has been raised, by means of a heating means (17, 20) disposed in the feed apparatus, in which heating means heat from the exhaust gas of the fuel cell arrangement is transferred to the water, and that the water is vaporized to the fuel gas (1 ) by means of the enthalpy contained in the water.

Description

A METHOD IN A FUEL CELL ARRANGEMENT
The present invention relates to the method in a fuel cell arrangement according to the preamble of patent claim 1 , according to which method fuel gas is fed to the anode side of the fuel cell arrangement, and according to which method water is supplied to the fuel gas before the fuel gas is fed to the anode side of the fuel cell arrangement.
It is known in the prior art to produce electricity and heat in a fuel cell operating at a high temperature. A fuel cell suitable for this purpose is a solid oxide fuel cell, SOFC. A solid oxide fuel cell is efficient and the heat produced by it may be used as heat source for various purposes, such as for heating of buildings or for steam production.
A solid oxide fuel cell, however, poses limitations to the fuel that may be used. Especially a fuel containing heavy hydrocarbons is not as such suitable for introduction to the anode of a fuels cell. The risk of formation of carbon on the anode is high which impairs the operation of a fuel cell. Thus, many fuels require some kind of a pretreatment before they are fed to a fuel cell. The pretreatment may include, among other things, desulfurization and/or modifying the fuel by catalytic cracking.
In order to minimize the risk of carbon being deposited onto the surface of the fuel cell, it is known to pretreat the fuel with a catalyst in the presence of steam at a high temperature, typically at 400 - 550 C°. It is known to use for example noble meal or nickel as the catalyst. The so-called steam reforming of this kind decomposes the fuel of the fuel cell, for example the heavier hydrocarbons of natural gas to hydrogen, methane, carbon oxides. Also when cracking the fuel by means of a catalyst, steam is needed to protect the catalyst from becoming carbonized when carbon C is released from the long carbon chains. Then the steam H2O binds the carbon to form CO2 and at the same time hydrogen H2 is released. With suitable control, the reactions produce mainly methane which is a particularly favorable fuel for a solid oxide fuel cell or a molten-carbonate cell, as using it provides cooling of the cell through internal reforming and thus it is possible to influence the required volume of gas flowing through the cell. Steam reforming thus requires steam which can be produces, as is known, for example in a separate steam generator. Normally it is heated for example with electricity. The steam generator may utilize also heat from the main process via a heat exchanger.
Especially in a fuel cell apparatus a separate steam generator of this kind is disadvantageous as it requires quite a large space, a connecting pipeline of its own, and also a relatively complex control system.
An alternative for reducing the steam demand is recycling of the anode gas of the fuel cell. Steam is obtained with this gas but the drawback is among other things that during the start-up of the apparatus there is no produced recycled steam available although it is required in any case.
Publication DE 19956378A1 describes an apparatus and a method in which air is heated and hydrocarbon in liquid form is introduced to the heated gas. The heat of the gas vaporizes the hydrocarbon and this mixture is further heated to a higher temperature and subsequently water is brought to the mixture. The heat of the gas vaporizes water and after this the mixture is further heated. The heating stages have been described to be carried out by means of separate heat exchangers. The size of the heat exchangers is remarkably large and thus this kind of a solution is unfavorable.
The object of the invention is to provide a method in a fuel cell arrangement according to which method fuel gas is fed to the anode side of a fuel cell arrangement, and according to which method water in liquid form is brought to the fuel gas before the fuel gas is fed to the anode side, and which method provides a fuel cell arrangement having a more compact structure than before. The objects of the invention are achieved with a method in a fuel cell arrangement according to which method fuel gas is led to the anode side of the fuel cell arrangement, and according to which method water in liquid form is brought to the fuel gas before the fuel gas is fed to the anode side, and according to which method the pressure of the water is raised before it is introduced to the fuel gas. It is characteristic to the invention that the temperature of the liquid water is raised after its pressure has been raised, by means of a heating device arranged in the feeding apparatus, heat from the exhaust gas of fuel cell arrangement being transferred to the water in said heating device, and that water is vaporized in to the fuel gas by means of the enthalpy of the water.
A method of this kind can be carried out with a very simple and reliable apparatus. Further, the apparatus is advantageous also in that respect that it can be carried out with very compact equipment. The method is also very economical.
The fuel gas is preferably introduced to a fuel reformer prior to feeding of the fuel gas to the anode side, in order to modify the composition of the fuel gas in the reformer, and prior to feeding of the fuel gas to the reformer, liquid water is brought to the fuel gas, the water being vaporized to the fuel gas by means of the enthalpy of the water. Then, steam is present already in the reformer thus minimizing the formation of carbon onto the surfaces of the reformer catalyst. In the solution according to the invention, the heat required for vaporizing the water is transferred to the liquid water and, as heat transfer to water is clearly more efficient than to gas or steam, the apparatus according to the invention among other things also allows using apparatus of a relatively small size.
Preferably all the water in liquid form is brought to the fuel gas before the fuel gas is fed to the fuel reformer. According to an embodiment of the invention, the temperature of the mixture of water and fuel gas is adjusted to the desired level substantially simultaneously as water is introduced to the fuel gas and vaporized. The temperature adjustment is preferably carried out so that in the location of the water injection point or immediately following it, there is a device influencing the temperature of the mixture by means of which device additional heat may be brought to the mixture of water and fuel gas.
According to an embodiment of the invention, the temperature of the mixture of water and fuel gas is adjusted by bringing additional heat to the mixture of water and fuel gas from the anode side exhaust gas.
According to an embodiment of the invention, the injection pressure of the liquid water being brought to the fuel gas is at least 20-fold in the injection point, compared with the pressure of the fuel gas. This ensures that the vaporizing of the water is efficient among other things in view of droplet formation. Preferably the injection pressure is 5 - 12 MPa. Further, due to the great pressure difference, a large portion of the water is vaporized as so-called flash steam, thus consuming less energy from the fuel gas to vaporization.
In a method according to an embodiment of the invention, in order to reform hydrocarbon-containing fuel gas by means of a catalyst in the presence of steam, the fuel gas is fed to a fuel reformer before the fuel gas is taken to the anode side of the fuel cell, to modify the composition of the fuel gas in the reformer, and prior to feeding the fuel gas to the reformer, water in liquid form in introduced at injection pressure, which is 5 -12 MPa, and mainly as saturated water, into the fuel gas. Thus, steam is generated in a simple way and with equipment requiring only very little space. Steam is present already in the reformer, minimizing the formation of carbon on the surfaces of the catalyst. Preferably all the liquid water is brought to the fuel gas before the gas is introduced into the fuel reformer. The other patent claims present solutions according to various embodiments of the invention.
The approach according to the invention provides several advantages. In the reforming of the fuel, the formation of carbon is minimized and the size of the apparatus is relatively small. An advantage is the possibility to omit the complex steam generator with its superheater, which require much space, and to simplify and speed up the adjustment of the method. In particular in fuel cell modules the saving of space is remarkable but the solution is applicable also in other installations to protect the catalyst.
The invention is described below with reference to the accompanying schematic drawing, in which Fig. 1 illustrates an embodiment of the method according to the invention.
Figure 1 illustrates in a simplified manner a schematic presentation of a typical solid oxide fuel cell arrangement applying the method of the invention. In Figure 1 , the reference number 6 signifies a fuel cell apparatus. The fuel cell arrangement comprises a fuel cell apparatus 6 operating at a high temperature, typically > 500 0C and formed by stacks of fuel cells operating at a high temperature. The fuel cells stacks may be formed for example of solid oxide fuel cells (SOFC) or molten-carbonate fuel cells (MCFC) or fuel cells of other suitable types.
In the apparatus of Figure 1 , for example natural gas is used as fuel. The natural gas in fed into the apparatus as pressurized fuel gas in feed duct 1 and through a heat exchanger 2, in which the fuel gas is heater with the heat of the exhaust gases from the fuel cell arrangement. Subsequent to the heat exchanger 2, there is in the feed duct 1 a desulfurization unit 3 removing sulfur form the fuel. After the desulfurization unit 3, the fuel gas is, depending on the apparatus assembly, taken either to a pre-reformer or a reformer 4, in which among other things hydrogen is formed of the fuel gas, for example natural gas. Water brought to the fuel gas in feed duct 16 is used to assist in the reforming of the fuel, in other words among other things in the production of hydrogen.
In the reformer 4, the hydrocarbons of the natural gas are converted with steam into hydrogen, methane or carbon oxides. In order to intensify the operation of the apparatus, a part of the exhaust gases of the fuel cell anode side 7 is taken via a heat exchanger 5 and a fan or a compressor 13 to the feed side of the reformer 4 whereby also carbon dioxide and the steam from the exhaust gas of the anode side 7 is mixed into the feed flow. Fuel gas is heater in the heat exchanger 5 with the exhaust gas of the anode side 7.
From the reformer 4 the fuel is fed via said heat exchanger 5 to the anode side 7 of the fuel cell unit 6 formed of stacks of fuel cells. The fuel cell stacks of the fuel cell unit 6 are formed of a plurality of fuel cells pressed against each other, each having an anode side 7, a cathode side 8 and an electrolyte 9 between these. In the Figure, the fuel cell stacks and their feasible combinations are illustrated schematically as one entity. The part of the anode side 7 exhaust gases which is not recycled is fed to an afterburner 14, where the residual fuel is combusted and subsequently the exhaust gases are discharged from the apparatus through heat exchangers 17, 2.
In a corresponding way, oxygen is fed to the cathode side 8 along with air with a fan or a compressor 10, from which air is taken via a feed duct 11 to a heat exchanger 12, where the air to be fed to the cathode side 8 is preheated with the exhaust gases of the cathode side, itself. The majority of the heat of the cathode side exhaust gases is used in the heat exchanger 12 in the preheating of the air to be fed to the cathode side. A smaller part of the heat is taken further with the exhaust gases to the afterburner 14 and via it out from the apparatus, or directly out from the apparatus for example via a heat exchanger (not illustrated). Water used in the reforming of the fuel, in other words among other things in the production of hydrogen, is brought to the fuel gas in liquid form in a duct 16 which is a part of the water feed system, prior to the feed of the fuel gas to the reformer 4. In the feed system 16, there is a pressure increasing device 19, for example a pump, the suction side of which has a flow communication with a liquid water source 18. The pump 19 has been provided in the feed duct 16 to raise the pressure of the liquid water. The pump 19 has been equipped for example with a control system 22, controlling its rotation speed, for adjusting the water flow to be fed to the desired level. The rotation velocity is preferably adjusted based on the power of the fuel cell unit. Some of the indicators of the power of the apparatus available for use in the adjustment are among other things the flow volume and/or pressure of the fuel gas prior to the reformer 4.
There is also a heater 20 provided in the feed duct. It is located in the feed duct between the pressure side of the pump 19 and the water feed member 21 , whereby the temperature of the water is raised after the pressure increase. The heater 20 may be electric, or it may also be a heat exchanger connected at one side for example to the anode side exhaust gas flow.
The water feed member 21 preferably comprises several nozzles which may be opened and closed independently, whereby the volume and/or feed pressure of the water being fed may be controlled by opening and closing the nozzles, in addition to or as an alternatively for controlling the rotation speed of the pump 19. In connection with the water feed members 21 in the feed duct 1 , there is also provided a device 23 influencing the temperature of the mixture, functioning as the regulator of the temperature of the water and fuel gas fed. The device 23 is preferably a heater, by means of which the temperature of the water and the fuel gas are adjusted suitable for the reformer 4. According to an embodiment, the heater is electric. According to another embodiment, the heater is a heat exchanger utilizing the heat of the exhaust gas from the fuel cell (not illustrated in the Figure). When applying the invention in a fuel cell arrangement with solid oxide fuel cells, with natural gas as the fuel, the state of the fuel gas at the feed point of water is typically the following.
Fuel gas pressure = 150 - 300 kPa
Fuel gas temperature = 400 - 500 0C
According to the method water is supplied in a pressurized state directly via nozzle/s to the gas feed duct 1 , where small droplets are immediately vaporized and thus the required steam is produced.
By means of adjusting the number of revolutions of the high-pressure pump and/or employing a suitable number of nozzles, a suitable and accurately adjusted steam volume for the catalyst of the reformer 4 may be obtained at different partial load ranges.
The enthalpy available while the pressure drops at the water feed to the fuel gas vaporizes a remarkable part of the liquid water, forming so-called flash steam. The volume of the flash steam formed this way depends on the enthalpy difference of the water under different conditions. Thus, the pressure difference of the water feed pressure and the fuel gas pressure has a significant influence on the amount of the so-called flash steam. Therefore, the injection pressure of the liquid water at the injection point is kept at least 20-fold compared with the prevailing fuel gas pressure.
It is obvious to a person skilled in the art that the invention is not limited to the embodiment example described above but it may be modified within the scope of the patent claims presented below. Thus, for example the apparatus and the structural components used may differ from what has been presented above. Thus it is clear to a person skilled in the art that circulation of the materials, such as fuel, exhaust gas and air, led in the apparatus need not necessarily be identical with what has been described above but the circulation may be effected in several different ways and with different apparatus assemblies.
It is clear to a person skilled in the art that the solution according to the invention is not limited to be used only in connection with solid oxide fuel cells (SOFC), only, but I may be applied in connection with all fuel cells operating essentially at a high temperature.
Further, it is clear to a person skilled in the art that the fuel may, instead of the natural gas mentioned, be any other hydrocarbon-containing fuel suitable for use.

Claims

We claim:
1. A method in a fuel cell arrangement, according to which method fuel gas is led to the anode side (7) of a fuel cell arrangement, and according to which method water in liquid form is brought (21 ) to the fuel gas before the gas is taken to the anode side, and according to which method the pressure of water is raised before it is supplied to the fuel gas, characterized in that the temperature of the liquid water is raised, after its pressure has been raised, by means of a heating means (17, 20) arranged in the feeding apparatus, in which heating means heat from the exhaust gas of the fuel cell arrangement is transferred to the water, and that water is vaporized to the fuel gas (1 ) by means of the enthalpy contained in the water.
2. A method according to patent claim 1 , characterized in that essentially at the same time (21 , 23) as water is brought to the fuel gas and vaporized, the temperature of the mixture of water and fuel gas is adjusted (23) to the desired level by introducing additional heat to the mixture of water and fuel gas.
3. A method according to patent claim 1 , characterized in that the water introduced in liquid form is vaporized by means of the enthalpy contained in the water and the fuel gas.
4. A method according to patent claim 1 , characterized in that the fuel gas (1 ) is transported to a fuel reformer (4) in order to modify the composition of the fuel gas in the reformer before the fuel gas is taken to the anode side (7) of the fuel cell arrangement, and that liquid water is brought (21 ) to the fuel gas prior to taking the fuel gas to the reformer (4).
5. A method according to patent claim 2, characterized in that the temperature of the mixture of water and fuel gas is adjusted by bringing additional heat to the mixture of water and fuel gas from the exhaust gas of the anode side,
6. A method according to patent claim 4, characterized in that all the liquid water is introduced (21 ) into the fuel gas before the gas is taken to the fuel reformer.
7. A method according to any of the preceding patent claims, characterized in that the fuel gas to be fed into the reformer (4) is a hydrocarbon-containing gas.
8. A method according to patent claim 1 , 2 or 3, characterized in that the injection pressure of the water introduced to the fuel gas is at least 20-fold compared with the prevailing fuel gas pressure at the injection point.
9. A method according to patent claim 1 , characterized in that the temperature of the liquid water is raised so that during the injection the water is mainly saturated water.
10. A method according to patent claim 1 , characterized in that heat obtained from combustion (14) of the exhaust gas from the anode side of the fuel cell arrangement is transferred to the water in a heating device (17).
PCT/FI2010/050010 2009-01-15 2010-01-12 A method in a fuel cell arrangement WO2010081936A1 (en)

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EP2919310A1 (en) * 2014-03-14 2015-09-16 Panasonic Corporation Fuel cell system
JP2015201297A (en) * 2014-04-07 2015-11-12 日産自動車株式会社 Fuel cell system and operation method thereof

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US6120923A (en) * 1998-12-23 2000-09-19 International Fuel Cells, Llc Steam producing hydrocarbon fueled power plant employing a PEM fuel cell
DE19956378A1 (en) 1999-11-24 2001-06-13 Daimler Chrysler Ag Introduction of liquids into gas fed to diesel reformer, e.g. for SOFC avoiding solids deposition, takes place in alternating stages of heating and liquid addition
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Publication number Priority date Publication date Assignee Title
US5401589A (en) * 1990-11-23 1995-03-28 Vickers Shipbuilding And Engineering Limited Application of fuel cells to power generation systems
US6120923A (en) * 1998-12-23 2000-09-19 International Fuel Cells, Llc Steam producing hydrocarbon fueled power plant employing a PEM fuel cell
DE19956378A1 (en) 1999-11-24 2001-06-13 Daimler Chrysler Ag Introduction of liquids into gas fed to diesel reformer, e.g. for SOFC avoiding solids deposition, takes place in alternating stages of heating and liquid addition
US20060137350A1 (en) * 2004-12-29 2006-06-29 Utc Fuel Cells, Llc Fuel cell in combined heat and electric power system

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Publication number Priority date Publication date Assignee Title
EP2919310A1 (en) * 2014-03-14 2015-09-16 Panasonic Corporation Fuel cell system
US9647287B2 (en) 2014-03-14 2017-05-09 Panasonic Corporation Fuel cell system
JP2015201297A (en) * 2014-04-07 2015-11-12 日産自動車株式会社 Fuel cell system and operation method thereof

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FI20095034A0 (en) 2009-01-15

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