WO2012069693A1 - Method and control arrangement for a fuel cell device - Google Patents

Method and control arrangement for a fuel cell device Download PDF

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Publication number
WO2012069693A1
WO2012069693A1 PCT/FI2011/050913 FI2011050913W WO2012069693A1 WO 2012069693 A1 WO2012069693 A1 WO 2012069693A1 FI 2011050913 W FI2011050913 W FI 2011050913W WO 2012069693 A1 WO2012069693 A1 WO 2012069693A1
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WIPO (PCT)
Prior art keywords
fuel
species
fuel cell
cell device
information
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PCT/FI2011/050913
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French (fr)
Inventor
Tero Hottinen
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Wärtsilä Finland Oy
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Publication of WO2012069693A1 publication Critical patent/WO2012069693A1/en

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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
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0444—Concentration; Density
    • H01M8/04447—Concentration; Density of anode reactants at the inlet or inside the fuel cell
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/024—Analysing fluids by measuring propagation velocity or propagation time of acoustic waves
    • 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
    • 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
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0438—Pressure; Ambient pressure; Flow
    • H01M8/04388—Pressure; Ambient pressure; Flow of anode reactants at the inlet or inside 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
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
    • H01M8/04791—Concentration; Density
    • H01M8/04798—Concentration; Density of fuel cell 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
    • H01M8/10—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
    • 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 field of the invention Most of the energy of the world is produced by means of oil, coal, natural gas or nuclear power. All these production methods have their specific problems as far as, for example, availability and friendliness to environment are concerned. As far as the environment is concerned, especially oil and coal cause pollution when they are combusted.
  • the problem with nuclear power is, at least, storage of used fuel.
  • Fuel cell's by means of which energy of fuel, for example biogas, is directly converted to electricity via a chemical reaction in an environmentally friendly process, are promising future energy conversion devices.
  • Fuel cell as presented in fig 1, comprises an anode side 100 and a cathode side 102 and an electrolyte material 104 between them.
  • SOFCs solid oxide fuel cells
  • oxygen 106 is fed to the cathode side 102 and it is reduced to a negative oxygen ion by receiving electrons from the cathode.
  • the negative oxygen ion goes through the electrolyte material 104 to the anode side 100 where it reacts with fuel 108 producing water and also typically carbon dioxide (C02).
  • an external electric circuit 111 comprising a load 110 for the fuel cell.
  • FIG 2 is presented a SOFC device as an example of a high temperature fuel cell device.
  • SOFC device can utilize as fuel for example natural gas, bio gas, methanol or other compounds containing hydrocarbons.
  • SOFC device in figure 2 comprises more than one, typically plural of fuel cells in stack formation 103 (SOFC stack). Each fuel cell comprises anode 100 and cathode 102 structure as presented in figure 1. Part of the used fuel can be recirculated in a feedback arrangement 109 through anode sides 100.
  • SOFC device in figure 2 also comprises a fuel heat exchanger 105 and a reformer 107. Typically several heat exchangers are used for controlling thermal conditions at different locations in a fuel cell device process.
  • Reformer 107 is a device that converts the fuel such as for example natural gas to a composition suitable for fuel cells, for example to a composition containing hydrogen and methane, carbon dioxide, carbon monoxide and inert gases.
  • a reformer it is though not necessary to have a reformer.
  • measurement means 115 such as fuel flow meter, current meter and temperature meter
  • measurement means 115 such as fuel flow meter, current meter and temperature meter
  • Part of the gas used at anodes 100 may be recirculated through anodes in feedback arrangement 109 and the other part of the gas is exhausted 114.
  • a solid oxide fuel cell (SOFC) device is an electrochemical conversion device that produces electricity directly from oxidizing fuel.
  • Advantages of SOFC device include high efficiencies, long term stability, low emissions, and cost.
  • the main disadvantage is the high operating temperature which results in long start up times and both mechanical and chemical compatibility issues.
  • fuel cell device applications which utilize biogas, especially biogas based on landfill gas, the gas composition usually contains three main species with varying content values: methane CH4, carbondioxide CO2 and nitrogen N2. This causes a great challenge for process control of the fuel cell device, where both fuel utilization rate and Oxygen to Carbon (O/C) ratio have to be accurately controlled. This requires that both the volumetric flow of fuel feed and also fuel composition have to be known with adequate accuracy.
  • the object of the invention is to accomplish a control arrangement for fuel cell device for controlling with reasonable costs and essentially accurately at least fuel utilization rate and O/C ratio of the fuel cell device.
  • a control arrangement for a fuel cell device utilizing fuel which comprises species having essentially varying content values, each fuel cell in the fuel cell device comprising an anode side, a cathode side, and an electrolyte between the anode side and the cathode side, the fuel cell device comprising the fuel cells in fuel cell stacks and means for flowing the fuel through the anode sides of the fuel cells.
  • the control arrangement comprises an acoustic measurement unit comprising transmitters for transmitting acoustic signals into the fuel flow, and receivers for receiving acoustic signals from the fuel flow to form measurement information, and the control arrangement comprises processing means for processing said measurement information at least on the basis of time differences of the received acoustic signals to determine fuel flow velocity and average acoustic speed information of the fuel, and an analyzer unit integrated with the operation of the acoustic measurement unit to provide content information of at least one species in the fuel, said content information to be utilized together with said average acoustic speed information by the processing means in determination of contents of last two species in fuel composition to determine the fuel composition for controlling at least fuel utilization rate and O/C ratio of the fuel cell device on the basis of the determined fuel composition and the determined fuel flow velocity.
  • the object of the invention is also a control method for a fuel cell device utilizing fuel, which comprises species having essentially varying content values, in which method fuel cells of the fuel cell device are arranged to fuel cell stacks, and the fuel is flown through the anode sides of the fuel cells in said stacks.
  • acoustic signals are transmitted into the fuel flow by transmitters, the transmitted acoustic signals are received from the fuel flow by receivers to form measurement information, which is processed at least on the basis of time differences of the received acoustic signals to determine fuel flow velocity and average acoustic speed
  • content information of the fuel and in a separate fuel analysis process is formed content information of at least one species in the fuel, which content information is utilized together with said average acoustic speed information in determination of contents of last two species in fuel composition to determine the fuel composition for controlling at least fuel utilization rate and O/C ratio of the fuel cell device on the basis of the determined fuel composition and the determined fuel flow velocity.
  • the invention is based on the integration of the acoustic measurement unit to form measurement information, on the basis of which is determined fuel flow velocity and average acoustic speed information of the fuel, and the analyzer unit to provide content information of at least one fuel species, said content information to be utilized together with said average acoustic speed information in determination of contents of last two species in fuel composition to determine the fuel composition.
  • the controlling of at least fuel utilization rate and O/C ratio of the fuel cell device is based on the determined fuel composition and the determined fuel flow velocity.
  • the benefit of the invention is that accurate and cost-effective controlling of fuel cell device process is achieved on the basis of the operational integration of the analyzer unit and the acoustic measurement unit.
  • both absolute volumetric flow information and fuel composition for example of a biogas can be determined.
  • Figure 1 presents a single fuel cell structure. presents an example of a SOFC device.
  • Figure 3 presents a preferred embodiment according to the present
  • Figure 4 describes principles of acoustic measurement.
  • Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound.
  • Possible method to simultaneously measure gas flows and composition with having only two main species is acoustic measurement where acoustic signals can be used to determine an absolute flow velocity and also a density of the fuel, because through acoustic measurement it is possible to obtain the ratio of the two known compounds.
  • a third species in the fuel said method is not applicable as such. This may be the case for example when the used fuel is biogas.
  • both the absolute volumetric flow information and fuel composition of a biogas can be determined for the needs of the process control of the fuel cell device.
  • FIG 3 is presented a preferred embodiment of a control arrangement for a fuel cell device according to the present invention.
  • the fuel cell device utilizes biogas as fuel, which comprises three species with essentially varying content values: methane CH4, carbondioxide C02 and nitrogen N2.
  • Fuel cells are arranged into fuel cell stack 103 formations, and the fuel is flown through the anode sides 100 of the fuel cells in said stacks 103 by means 120, which comprise for example pipes and valve structures needed for flowing the fuel.
  • the control arrangement in figure 3 comprises an acoustic measurement unit 122 comprising transmitters 124,125 for transmitting acoustic signals into the fuel flow, and receivers 126, 127 for receiving acoustic signals from the fuel flow to form measurement information.
  • the control arrangement comprises processing means 128 for processing said measurement information on the basis of time differences measured between the received acoustic signals. In said processing is determined fuel flow velocity and average acoustic speed information of the fuel.
  • the processing means 128 are analog and/or digital processor based means, for example a computer to store the measurement information and to perform the processing of the measurement information through calculations and other determinations.
  • the acoustic measurement unit comprises of two transducer units, the first transducer unit 124, 127 comprising the first transmitter 124 and the second receiver 127, and the second transducer unit 125, 126 comprising the second transmitter 125 and the first receiver 126.
  • the first transmitter 124 transmits acoustic signals downstream into the fuel flow
  • the second transmitter 125 transmits acoustic signals upstream into the fuel flow.
  • the first receiver 126 receives the acoustic signals transmitted from the first transmitter 124
  • the second receiver 127 receives the acoustic signals transmitted from the second transmitter 125.
  • tl represents measured travel time of acoustic signals between the first transmitter 124 and the first receiver 126 transmitted downstream into the fuel flow from the first transmitter 124 and received by the first receiver 126
  • t2 represents measured travel time of acoustic signals between the second transmitter 125 and the second receiver 127 transmitted upstream into the fuel flow from the second transmitter 125 and received by the second receiver 127:
  • s is the known (i.e. measured) distance between the first transducer unit 124, 127 and the second transducer unit 125, 126
  • v' is speed of the acoustic signal in the fuel
  • v is fuel flow velocity.
  • t2 measurements and distance s measurement only v' and v are unknown factors, but because we have said two equations, it is easy to calculate both v' and v by the processing means 128.
  • Said factor v' is named also as average acoustic speed information of the fuel, and v' is utilized in determination of contents of fuel species by the processing means 128.
  • Locations of transmitters 124, 125 and receivers 126, 127 described in figure 4 are exemplary ones.
  • the transmitter and the receiver do not need to locate in the same transducer unit.
  • the transmitters and/or the receivers can also locate separately and for example on different sides of the fuel flow.
  • an analyzer unit 130 with the operation of the acoustic measurement unit 122 to provide content information of one species in the fuel.
  • the analyzer unit 130 is preferably a single gas analyzer 130 to determine percentual amount of one species in the fuel as the content information, which is utilized by the processing means 128 in the determination of percentual amounts of the last two species in fuel composition.
  • said single gas analyzer 130 is an infrared radiation (IR) sensor, which is accurate to provide methane (CH4) content information or carbondioxide (C02) content information.
  • IR infrared radiation
  • the content information of a single gas means methane (CH4) content information or carbondioxide (C02) content information, which is utilized together with the average acoustic speed information in the processing means 128 for determining contents of last two species in fuel composition to determine the fuel composition.
  • CH4 methane
  • C02 carbondioxide
  • fuel utilization rate and O/C ratio of the fuel cell device are controlled on the basis of the determined fuel composition and the determined fuel flow velocity. Said controlling is performed by the processing means 128 or by a separate control processor unit.
  • the preferred embodiment only presents one exemplary embodiment of the invention.
  • Embodiments according to the invention may comprise many variations.
  • the determined fuel flow velocity can be utilized together with diameter information of the means 120, for example with diameter information of the pipe 120 for flowing fuel to calculate absolute volumetric fuel flow information by the processing means 128.
  • an embodiment according to the invention may comprise two single gas analyzers 130, which each determines percentual amount of one dedicated species in the fuel as the content information.
  • the first single gas analyzer determines CH4 content information
  • the second single gas analyzer which is a lambda- transducer, determines 02 content information
  • both CH4 and 02 content information is utilized together with the average acoustic speed information by the processing means 128 in the determination of percentual amounts of the last two species in fuel composition.
  • Other possible species to be determined by a single gas analyzer 130 are for example carbonmonoxide (CO), Hydrogen (H2) and water (H2O).

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Abstract

The focus of the invention is a control method for a fuel cell device utilizing fuel, which comprises essentially varying species content values, in which method fuel cells of the fuel cell device are arranged to fuel cell stacks (103), and the fuel is flown through the anode sides (100) of the fuel cells in said stacks. In the control method acoustic signals are transmitted into the fuel flow by transmitters (124, 125), and the transmitted acoustic signals are received from the fuel flow by receivers (126, 127) to form measurement information, which is processed at least on the basis of time differences of the received acoustic signals to determine fuel flow velocity and average acoustic speed information of the fuel. In a separate fuel analysis process is formed content information of at least one species in the fuel, which content information is utilized together with said average acoustic speed information for determination of contents of last two species in fuel composition to determine the fuel composition for controlling at least fuel utilization rate and O/C ratio of the fuel cell device on the basis of the determined fuel composition and the determined fuel flow velocity.

Description

Method and control arrangement for a fuel cell device
The field of the invention Most of the energy of the world is produced by means of oil, coal, natural gas or nuclear power. All these production methods have their specific problems as far as, for example, availability and friendliness to environment are concerned. As far as the environment is concerned, especially oil and coal cause pollution when they are combusted. The problem with nuclear power is, at least, storage of used fuel.
Especially because of the environmental problems, new energy sources, more environmentally friendly and, for example, having a better efficiency than the above-mentioned energy sources, have been developed.
Fuel cell's, by means of which energy of fuel, for example biogas, is directly converted to electricity via a chemical reaction in an environmentally friendly process, are promising future energy conversion devices.
The state of the art
Fuel cell, as presented in fig 1, comprises an anode side 100 and a cathode side 102 and an electrolyte material 104 between them. In solid oxide fuel cells (SOFCs) oxygen 106 is fed to the cathode side 102 and it is reduced to a negative oxygen ion by receiving electrons from the cathode. The negative oxygen ion goes through the electrolyte material 104 to the anode side 100 where it reacts with fuel 108 producing water and also typically carbon dioxide (C02). Between anode 100 and cathode 102 is an external electric circuit 111 comprising a load 110 for the fuel cell. In figure 2 is presented a SOFC device as an example of a high temperature fuel cell device. SOFC device can utilize as fuel for example natural gas, bio gas, methanol or other compounds containing hydrocarbons. SOFC device in figure 2 comprises more than one, typically plural of fuel cells in stack formation 103 (SOFC stack). Each fuel cell comprises anode 100 and cathode 102 structure as presented in figure 1. Part of the used fuel can be recirculated in a feedback arrangement 109 through anode sides 100. SOFC device in figure 2 also comprises a fuel heat exchanger 105 and a reformer 107. Typically several heat exchangers are used for controlling thermal conditions at different locations in a fuel cell device process. Reformer 107 is a device that converts the fuel such as for example natural gas to a composition suitable for fuel cells, for example to a composition containing hydrogen and methane, carbon dioxide, carbon monoxide and inert gases. Anyway in each SOFC device it is though not necessary to have a reformer.
By using measurement means 115 (such as fuel flow meter, current meter and temperature meter) necessary measurements are carried out for the operation of the SOFC device. Part of the gas used at anodes 100 may be recirculated through anodes in feedback arrangement 109 and the other part of the gas is exhausted 114.
A solid oxide fuel cell (SOFC) device is an electrochemical conversion device that produces electricity directly from oxidizing fuel. Advantages of SOFC device include high efficiencies, long term stability, low emissions, and cost. The main disadvantage is the high operating temperature which results in long start up times and both mechanical and chemical compatibility issues. In fuel cell device applications, which utilize biogas, especially biogas based on landfill gas, the gas composition usually contains three main species with varying content values: methane CH4, carbondioxide CO2 and nitrogen N2. This causes a great challenge for process control of the fuel cell device, where both fuel utilization rate and Oxygen to Carbon (O/C) ratio have to be accurately controlled. This requires that both the volumetric flow of fuel feed and also fuel composition have to be known with adequate accuracy. With prior art methods it is very difficult to achieve said object in cost effective manner, because fuel composition has to be measured e.g. by using a gas chromatograph which is very expensive. A problem is also that volumetric flow velocity measurements are typically very sensitive to composition variations without yielding any result on the composition measurements as such.
Short description of the invention
The object of the invention is to accomplish a control arrangement for fuel cell device for controlling with reasonable costs and essentially accurately at least fuel utilization rate and O/C ratio of the fuel cell device. This is achieved by a control arrangement for a fuel cell device utilizing fuel, which comprises species having essentially varying content values, each fuel cell in the fuel cell device comprising an anode side, a cathode side, and an electrolyte between the anode side and the cathode side, the fuel cell device comprising the fuel cells in fuel cell stacks and means for flowing the fuel through the anode sides of the fuel cells. The control arrangement comprises an acoustic measurement unit comprising transmitters for transmitting acoustic signals into the fuel flow, and receivers for receiving acoustic signals from the fuel flow to form measurement information, and the control arrangement comprises processing means for processing said measurement information at least on the basis of time differences of the received acoustic signals to determine fuel flow velocity and average acoustic speed information of the fuel, and an analyzer unit integrated with the operation of the acoustic measurement unit to provide content information of at least one species in the fuel, said content information to be utilized together with said average acoustic speed information by the processing means in determination of contents of last two species in fuel composition to determine the fuel composition for controlling at least fuel utilization rate and O/C ratio of the fuel cell device on the basis of the determined fuel composition and the determined fuel flow velocity. The object of the invention is also a control method for a fuel cell device utilizing fuel, which comprises species having essentially varying content values, in which method fuel cells of the fuel cell device are arranged to fuel cell stacks, and the fuel is flown through the anode sides of the fuel cells in said stacks. In the control method acoustic signals are transmitted into the fuel flow by transmitters, the transmitted acoustic signals are received from the fuel flow by receivers to form measurement information, which is processed at least on the basis of time differences of the received acoustic signals to determine fuel flow velocity and average acoustic speed
information of the fuel, and in a separate fuel analysis process is formed content information of at least one species in the fuel, which content information is utilized together with said average acoustic speed information in determination of contents of last two species in fuel composition to determine the fuel composition for controlling at least fuel utilization rate and O/C ratio of the fuel cell device on the basis of the determined fuel composition and the determined fuel flow velocity.
The invention is based on the integration of the acoustic measurement unit to form measurement information, on the basis of which is determined fuel flow velocity and average acoustic speed information of the fuel, and the analyzer unit to provide content information of at least one fuel species, said content information to be utilized together with said average acoustic speed information in determination of contents of last two species in fuel composition to determine the fuel composition. The controlling of at least fuel utilization rate and O/C ratio of the fuel cell device is based on the determined fuel composition and the determined fuel flow velocity.
The benefit of the invention is that accurate and cost-effective controlling of fuel cell device process is achieved on the basis of the operational integration of the analyzer unit and the acoustic measurement unit. Through combining only partial fuel composition measurement together with optional acoustic measurements, both absolute volumetric flow information and fuel composition for example of a biogas can be determined.
Short description of figures
Figure 1 presents a single fuel cell structure. presents an example of a SOFC device. Figure 3 presents a preferred embodiment according to the present
invention.
Figure 4 describes principles of acoustic measurement.
Detailed description of the invention
Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. Possible method to simultaneously measure gas flows and composition with having only two main species is acoustic measurement where acoustic signals can be used to determine an absolute flow velocity and also a density of the fuel, because through acoustic measurement it is possible to obtain the ratio of the two known compounds. However, when there exists a third species in the fuel, said method is not applicable as such. This may be the case for example when the used fuel is biogas.
In a solution according to the present invention is utilized an integration of both acoustic measurements and fuel composition analyzing measurements to achieve a reliable controlling of at least fuel utilization rate and O/C ratio of the fuel cell device process. In the fuel composition analyzing
measurement can be fixed the percentual amount of a single species of the fuel, which percentual amount is utilized in determination of percentual amounts of two remaining, i.e. last species. Through said integration of only partial fuel composition measurement together with the acoustic
measurement, both the absolute volumetric flow information and fuel composition of a biogas can be determined for the needs of the process control of the fuel cell device.
In figure 3 is presented a preferred embodiment of a control arrangement for a fuel cell device according to the present invention. The fuel cell device utilizes biogas as fuel, which comprises three species with essentially varying content values: methane CH4, carbondioxide C02 and nitrogen N2. Fuel cells are arranged into fuel cell stack 103 formations, and the fuel is flown through the anode sides 100 of the fuel cells in said stacks 103 by means 120, which comprise for example pipes and valve structures needed for flowing the fuel.
The control arrangement in figure 3 comprises an acoustic measurement unit 122 comprising transmitters 124,125 for transmitting acoustic signals into the fuel flow, and receivers 126, 127 for receiving acoustic signals from the fuel flow to form measurement information. The control arrangement comprises processing means 128 for processing said measurement information on the basis of time differences measured between the received acoustic signals. In said processing is determined fuel flow velocity and average acoustic speed information of the fuel. The processing means 128 are analog and/or digital processor based means, for example a computer to store the measurement information and to perform the processing of the measurement information through calculations and other determinations.
In figure 4 is described principles of acoustic measurement utilized in the preferred embodiment of the invention. The acoustic measurement unit comprises of two transducer units, the first transducer unit 124, 127 comprising the first transmitter 124 and the second receiver 127, and the second transducer unit 125, 126 comprising the second transmitter 125 and the first receiver 126. The first transmitter 124 transmits acoustic signals downstream into the fuel flow, and the second transmitter 125 transmits acoustic signals upstream into the fuel flow. The first receiver 126 receives the acoustic signals transmitted from the first transmitter 124, and the second receiver 127 receives the acoustic signals transmitted from the second transmitter 125. In the following equations tl represents measured travel time of acoustic signals between the first transmitter 124 and the first receiver 126 transmitted downstream into the fuel flow from the first transmitter 124 and received by the first receiver 126, and t2 represents measured travel time of acoustic signals between the second transmitter 125 and the second receiver 127 transmitted upstream into the fuel flow from the second transmitter 125 and received by the second receiver 127: tl = s/v'-s/v t2= s/v'+s/v
, in which s is the known (i.e. measured) distance between the first transducer unit 124, 127 and the second transducer unit 125, 126, v' is speed of the acoustic signal in the fuel, and v is fuel flow velocity. After said travel time tl, t2 measurements and distance s measurement only v' and v are unknown factors, but because we have said two equations, it is easy to calculate both v' and v by the processing means 128. Said factor v' is named also as average acoustic speed information of the fuel, and v' is utilized in determination of contents of fuel species by the processing means 128. Locations of transmitters 124, 125 and receivers 126, 127 described in figure 4 are exemplary ones. For example the transmitter and the receiver do not need to locate in the same transducer unit. The transmitters and/or the receivers can also locate separately and for example on different sides of the fuel flow. In the preferred control arrangement of figure 3 is integrated an analyzer unit 130 with the operation of the acoustic measurement unit 122 to provide content information of one species in the fuel. The analyzer unit 130 is preferably a single gas analyzer 130 to determine percentual amount of one species in the fuel as the content information, which is utilized by the processing means 128 in the determination of percentual amounts of the last two species in fuel composition. In the preferred embodiment said single gas analyzer 130 is an infrared radiation (IR) sensor, which is accurate to provide methane (CH4) content information or carbondioxide (C02) content information. There is also achieved as a benefit a need for only one gas analyzer channel, because only one gas analyzer 130 is used in the preferred embodiment.
As described, in the preferred embodiment the content information of a single gas means methane (CH4) content information or carbondioxide (C02) content information, which is utilized together with the average acoustic speed information in the processing means 128 for determining contents of last two species in fuel composition to determine the fuel composition. As a result of these determinations fuel utilization rate and O/C ratio of the fuel cell device are controlled on the basis of the determined fuel composition and the determined fuel flow velocity. Said controlling is performed by the processing means 128 or by a separate control processor unit.
The preferred embodiment only presents one exemplary embodiment of the invention. Embodiments according to the invention may comprise many variations. For example the determined fuel flow velocity can be utilized together with diameter information of the means 120, for example with diameter information of the pipe 120 for flowing fuel to calculate absolute volumetric fuel flow information by the processing means 128. The
controlling of fuel utilization rate and O/C ratio of the fuel cell device is then performed on the basis of the determined fuel composition and the determined fuel flow velocity. When the fuel is for example biogas, which comprises at least methane (CH4), carbon dioxide (CO2), Nitrogen (N2) and Oxygen (02) as said species with essentially varying content values, an embodiment according to the invention may comprise two single gas analyzers 130, which each determines percentual amount of one dedicated species in the fuel as the content information. For example the first single gas analyzer determines CH4 content information, and the second single gas analyzer, which is a lambda- transducer, determines 02 content information, and both CH4 and 02 content information is utilized together with the average acoustic speed information by the processing means 128 in the determination of percentual amounts of the last two species in fuel composition. Other possible species to be determined by a single gas analyzer 130 are for example carbonmonoxide (CO), Hydrogen (H2) and water (H2O). Although the invention has been presented in reference to the attached figures and specification, the invention is by no means limited to those as the invention is subject to variations within the scope allowed for by the claims.

Claims

Claims
1. A control arrangement for a fuel cell device utilizing fuel, which comprises species having essentially varying content values, each fuel cell in the fuel cell device comprising an anode side (100), a cathode side (102), and an electrolyte (104) between the anode side and the cathode side, the fuel cell device comprising the fuel cells in fuel cell stacks (103) and means (120) for flowing the fuel through the anode sides (100) of the fuel cells,
characterized by, that the control arrangement comprises an acoustic measurement unit (122) comprising transmitters (124, 125) for transmitting acoustic signals into the fuel flow, and receivers (126, 127) for receiving acoustic signals from the fuel flow to form measurement information, and the control arrangement comprises processing means (128) for processing said measurement information at least on the basis of time differences of the received acoustic signals to determine fuel flow velocity and average acoustic speed information of the fuel, and an analyzer unit (130) integrated with the operation of the acoustic measurement unit (122) to provide content information of at least one species in the fuel, said content information to be utilized together with said average acoustic speed information by the processing means (128) in determination of contents of last two species in fuel composition to determine the fuel composition for controlling at least fuel utilization rate and O/C ratio of the fuel cell device on the basis of the determined fuel composition and the determined fuel flow velocity.
2. A control arrangement for a fuel cell device in accordance with claim 1, characterized by, that the fuel is biogas, which comprises at least methane (CH4), carbon dioxide (C02) and nitrogen (N2) as said species with essentially varying content values
3. A control arrangement for a fuel cell device in accordance with claim 1, characterized by, that the fuel is biogas, which comprises at least methane (CH4), carbon dioxide (CO2), nitrogen (N2) and oxygen (02) as said species with essentially varying content values.
4. A control arrangement for a fuel cell device in accordance with claim 1, characterized by, that the analyzer unit (130) is a single gas analyzer to determine percentual amount of one species in the fuel as said content information to be utilized by the processing means (128) in the
determination of percentual amounts of the last two species in fuel composition.
5. A control arrangement for a fuel cell device in accordance with claim 1, characterized by, that the analyzer unit (130) is an infrared radiation (IR) sensor.
6. A control arrangement for a fuel cell device in accordance with claim 1, characterized by, that the control arrangement comprises the processing means (128) for utilizing the determined fuel flow velocity and diameter information of the means (120) for flowing fuel to calculate the absolute volumetric fuel flow information.
7. A control method for a fuel cell device utilizing fuel, which comprises species having essentially varying content values, in which method fuel cells of the fuel cell device are arranged to fuel cell stacks (103), and the fuel is flown through the anode sides (100) of the fuel cells in said stacks,
characterized by, that in the control method acoustic signals are transmitted into the fuel flow by transmitters (124, 125), the transmitted acoustic signals are received from the fuel flow by receivers (126, 127) to form measurement information, which is processed at least on the basis of time differences of the received acoustic signals to determine fuel flow velocity and average acoustic speed information of the fuel, and in a separate fuel analysis process is formed content information of at least one species in the fuel, which content information is utilized together with said average acoustic speed information in determination of contents of last two species in fuel composition to determine the fuel composition for controlling at least fuel utilization rate and O/C ratio of the fuel cell device on the basis of the determined fuel composition and the determined fuel flow velocity.
8. A control method in accordance with claim 7, characterized by, that in the method the fuel is biogas, which comprises at least methane (CH4), carbon dioxide (C02) and nitrogen (N2) as said species with essentially varying content values.
9. A control method in accordance with claim 7, characterized by, that in the method the fuel is biogas, which comprises at least methane (CH4), carbon dioxide (C02), nitrogen (N2) and oxygen (02) as said species with essentially varying content values.
10. A control method in accordance with claim 7, characterized by, that in the method the separate fuel analysis process is performed by a single gas analyzer (130) to determine percentual amount of one species in the fuel as said content information, which is utilized in the determination of percentual amounts of the last two species in fuel composition.
11. A control method in accordance with claim 7, characterized by, that in the method the separate fuel analysis process is performed by an infrared radiation (IR) sensor (130).
12. A control method in accordance with claim 7, characterized by, that in the method the determined fuel flow velocity and diameter information of the means (120) for flowing fuel are utilized to calculate the absolute volumetric fuel flow information.
PCT/FI2011/050913 2010-11-24 2011-10-19 Method and control arrangement for a fuel cell device WO2012069693A1 (en)

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