CN115207415A - Fuel cell system and method for operating the same - Google Patents
Fuel cell system and method for operating the same Download PDFInfo
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- CN115207415A CN115207415A CN202210373603.0A CN202210373603A CN115207415A CN 115207415 A CN115207415 A CN 115207415A CN 202210373603 A CN202210373603 A CN 202210373603A CN 115207415 A CN115207415 A CN 115207415A
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Images
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/403—Cells and electrode assemblies
- G01N27/406—Cells and probes with solid electrolytes
- G01N27/407—Cells and probes with solid electrolytes for investigating or analysing gases
- G01N27/4073—Composition or fabrication of the solid electrolyte
- G01N27/4074—Composition or fabrication of the solid electrolyte for detection of gases other than oxygen
-
- 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
- H01M8/04537—Electric variables
- H01M8/04574—Current
-
- 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
- H01M8/04097—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with recycling of the 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
- H01M8/0444—Concentration; Density
- H01M8/04447—Concentration; Density 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
-
- 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
Abstract
The invention relates to a fuel cell system and a method of operating the fuel cell system. The invention relates to a fuel cell system (10), in particular a solid oxide fuel cell system, comprising at least one fuel cell module (26), in particular a solid oxide fuel cell module, for generating electrical and/or thermal energy. It is proposed that the fuel cell system (10) comprises at least one electrochemical gas sensor (64) which is in contact with a process gas mixture and is provided for generating a measurement current as a function of the concentration of at least one process gas of the process gas mixture.
Description
Background
Fuel cell systems have been proposed which comprise at least one fuel cell module to generate electrical and/or thermal energy.
Technical Field
The present invention relates to a fuel cell system, in particular a solid oxide fuel cell system, comprising at least one fuel cell module, in particular a solid oxide fuel cell module, for generating electrical and/or thermal energy.
Disclosure of Invention
It is proposed that the fuel cell system comprises at least one electrochemical gas sensor which is in contact with a process gas mixture and is provided for generating a measurement current depending on the concentration of at least one process gas of the process gas mixture. By the arrangement according to the invention, at least one process gas in the process gas mixture can advantageously be sensed simply and quickly. Furthermore, by means of the arrangement according to the invention, an advantageous cost-effective possible way of determining the concentration of the at least one process gas can be provided. The concentration of at least one process gas in the process gas mixture can thus advantageously be determined simply and in real time. Thereby, an advantageous efficient and safe operation of the fuel cell system according to the invention can be achieved. "fuel cell module" is preferably understood to mean a fuel cell stack. Preferably, the at least one fuel cell module is provided for converting a chemical reaction energy of a continuously supplied fuel, in particular of at least the at least one process gas and an oxidant, into electrical energy. Preferably, the at least one fuel cell module is provided for obtaining electrical energy from the process gas mixture. Preferably, the at least one fuel cell module has at least one anode which is in contact with the process gas mixture. Preferably, the at least one fuel cell module is arranged for operation at a temperature of at least 450 ℃. Preferably, the at least one fuel cell module is designed as a high-temperature fuel cell module. "provided" is preferably to be understood to mean specially programmed, designed and/or equipped. An "object is provided for a specific function" is to be understood to mean, in particular, that the object carries out and/or executes the specific function in at least one application and/or operating state. Particularly preferably, the at least one fuel cell module is designed as a solid oxide fuel cell module. Preferably, the at least one solid oxide fuel cell module comprises at least one electrolyte formed from a solid ceramic material and provided for conducting oxygen ions, wherein in particular the ceramic material is electrically insulating with respect to electrons. Preferably, the at least one electrochemical gas sensor is designed as a hydrogen sensor. Preferably, the at least one electrochemical gas sensor is designed as a galvanic cell. Particularly preferably, the at least one electrochemical gas sensor is designed as a fuel cell. Preferably, the at least one electrochemical gas sensor is arranged for sensing at least one process gas in the process gas mixture. Preferably, the at least one electrochemical gas sensor is configured for converting the reaction energy of the at least one process gas and the oxidant into electrical energy such that a measurement current is generated. Preferably, the oxidizing agent is designed as oxygen. Preferably, the at least one electrochemical gas sensor is operable independently of the at least one fuel cell module. Particularly preferably, the at least one fuel cell module and the at least one electrochemical gas sensor are designed independently of one another, in particular with regard to operability. In principle, it is conceivable for the at least one electrochemical gas sensor to be arranged at least partially in the at least one fuel cell module. A "process gas mixture" is preferably to be understood as meaning a gas mixture which comprises at least one process gas and at least one further process gas and/or impurities, in particular at a specific location of the fuel cell system. Preferably, the process gas mixture is supplied to and/or discharged from the at least one fuel cell module. "process gas" is preferably understood to mean the gaseous substances required for a chemical reaction to take place in the at least one fuel cell module. Preferably, the at least one process gas is designed as hydrogen. Preferably, the further process gas is designed as methane, in particular natural gas or carbon monoxide. "contacting" is preferably understood to mean that the process gas mixture directly adjoins and/or flows through at least a part of the at least one electrochemical gas sensor, in particular the anode or the cathode of the gas sensor.
It is also proposed that the at least one electrochemical gas sensor is arranged at the anode inlet of the fuel cell module. By means of this configuration, it is advantageously possible to determine the concentration of the at least one process gas in the process gas mixture directly before the chemical reaction in the at least one fuel cell module. Preferably, the at least one electrochemical gas sensor is integrated directly into a line system of the fuel cell system for supplying fuel, in particular the at least one process gas, to the at least one fuel cell module. An "anode inlet" is preferably understood to mean the inlet opening of at least one anode of the fuel cell module, through which the process gas mixture reaches the at least one anode of the fuel cell module during operation.
It is also proposed that the at least one electrochemical gas sensor is designed as a proton-conducting ceramic fuel cell. The integration of proton-conducting ceramic fuel cells as electrochemical gas sensors makes it possible to determine, in particular, the individual gas species and thus the gas properties in an advantageous cost-effective manner. In this way, an improvement in the system regulation and performance optimization of the fuel cell system or of other apparatuses with various process gases can be advantageously achieved compared to systems which do not directly determine the gas species and regulate characteristic system parameters or which are regulated by expensive measurement methods, for example by means of flow-through and/or volume flow measurement. By this configuration, an electrochemical sensor can be incorporated into the fuel cell system, which sensor can be used particularly advantageously to determine the hydrogen proportion. Furthermore, with this configuration it is advantageously possible to realize: fossil fuels can be electrochemically oxidized directly at the anode of an electrochemical gas sensor. In this way, the otherwise necessary intermediate step of producing pure hydrogen by an expensive reforming process can advantageously be omitted. In contrast to polymer electrolyte membrane fuel cell modules, the presence of pure hydrogen is advantageously not necessary in the case of solid oxide fuel cell modules. Preferably, a reforming process takes place in the solid oxide fuel cell system to produce a hydrogen-rich process gas mixture. Further, by this configuration, it is possible to realize: no other substances enter the process gas mixture through the electrochemical gas sensor. Preferably, the at least one electrochemical gas sensor has at least one anode, at least one cathode and at least one electrolyte disposed between the anode and the cathode. Preferably, the electrolyte of the electrochemical gas sensor is formed of a ceramic electrolyte material. Preferably, the ceramic electrolyte material acts as a proton conductor between the anode and the cathode of the electrochemical gas sensor. Particularly preferably, the electrolyte of the electrochemical gas sensor allows the transition of protons from the anode to the cathode of the electrochemical gas sensor, but particularly is free of other elements. The at least one electrochemical gas sensor is provided for ionizing hydrogen molecules at an anode surface of the electrochemical gas sensor for absorption into an electrolyte of the electrochemical gas sensor, wherein they react with oxygen at a cathode of the electrochemical gas sensor after transport through the electrolyte and form water, in particular in gaseous form.
It is further proposed that the fuel cell system comprises at least one further electrochemical gas sensor, which is arranged at the anode outlet of the fuel cell module and/or in the circuit of circulation of the fuel cell system, is in contact with a further process gas mixture and is provided for generating a further measurement current as a function of the concentration of at least one process gas of the further process gas mixture. By this configuration, the concentration of the at least one process gas in the further process gas mixture can advantageously be determined directly after the chemical reaction in the at least one fuel cell module. In this way, the concentration of at least one process gas in the process gas mixture can advantageously be determined simply and in real time. Thereby, an advantageous efficient and safe operation of the fuel cell system according to the invention can be achieved. Preferably, the at least one further electrochemical gas sensor is integrated directly into a line system of the fuel cell system for discharging exhaust gases, in particular the at least one process gas, from the at least one fuel cell module. Preferably, the process gas mixture entering at the anode inlet of the at least one fuel cell module is changed by a chemical reaction in the at least one fuel cell module such that at the anode outlet of the at least one fuel cell module there is the further process gas mixture, which deviates from the process gas mixture. A "circulation path" should preferably be understood to mean a pipeline path that circulates the process gas mixture from the anode outlet of the at least one fuel cell module back to the anode inlet of the at least one fuel cell module. "anode outlet" is preferably understood to mean an outlet opening of the at least one anode of the fuel cell module, through which the further process gas mixture escapes from the at least one anode of the fuel cell module during operation. Preferably, the anode outlet is located downstream of the anode inlet in terms of flow technology.
It is also proposed that the at least one further electrochemical gas sensor is designed as a further proton-conducting ceramic fuel cell. By this configuration, an electrochemical sensor can be incorporated into the fuel cell system, which sensor can be used particularly advantageously to determine the hydrogen proportion. Preferably, the further proton-conducting ceramic fuel cell is designed at least substantially identically to the proton-conducting ceramic fuel cell, in particular with regard to function. "at least substantially" is preferably to be understood as meaning a deviation from a predetermined value of, in particular, less than 25%, preferably less than 10%, particularly preferably less than 5%, of the predetermined value.
It is also proposed that the fuel cell system comprises at least one evaluation unit which is provided to detect a measurement current generated by means of the at least one electrochemical gas sensor and a measurement current generated by means of the at least one further electrochemical gas sensor and to calculate at least one regulating value from the measurement current and the further measurement current. By this configuration, a change in the concentration of the at least one process gas between the at least one anode inlet of the at least one fuel cell module and the anode outlet of the at least one fuel cell module can be advantageously determined simply and efficiently. Thereby, the fuel cell system can be advantageously efficiently regulated. In addition, critical operating states can advantageously be avoided thereby. An "evaluation unit" is preferably to be understood to mean a unit with a processor unit and with a memory unit and with an operating program stored in the memory unit, which is provided for processing data relating to the measuring current and the further measuring current. In principle, the at least one evaluation element can be part of a control and/or regulating unit of the fuel cell system. A "control and/or regulating unit" is preferably understood to mean a unit having at least one control electronics, which unit has a processor unit and a memory unit as well as an operating program stored in the memory unit. Preferably, the at least one evaluation unit is provided for determining a fuel gas utilization of the at least one fuel cell module. "regulating value" is preferably understood to mean a value, in particular a feedback value, which is used to regulate the fuel cell system.
Furthermore, a method for operating the fuel cell system is proposed, in which a measurement current is generated in at least one method step using the at least one electrochemical gas sensor, which is designed in particular as a proton-conducting ceramic fuel cell, as a function of the concentration of at least one process gas of the process gas mixture. By this configuration, an advantageously simple and cost-effective possible way of determining the concentration of at least one process gas in the process gas mixture can be provided. In this configuration, the measuring current is generated directly by a chemical reaction, whereby a particularly advantageous sensing of the at least one process gas can be achieved. The concentration of the at least one process gas in the process gas mixture can thus advantageously be determined simply and in real time. Preferably, the measured current generated by the at least one electrochemical gas sensor is indicative of the concentration of at least one process gas in the process gas mixture. Preferably, in the at least one method step, the further measurement current is generated by means of the at least one further electrochemical gas sensor, which is designed in particular as a proton-conducting ceramic fuel cell, as a function of the concentration of at least one process gas of the further process gas mixture. Preferably, the further measured current generated by the at least one further electrochemical gas sensor characterizes the concentration of the at least one process gas in the further process gas mixture.
Furthermore, it is proposed that the fuel gas utilization and/or the oxygen/carbon ratio of the fuel cell module be calculated by an evaluation unit using the measurement current generated by the at least one electrochemical gas sensor. By this configuration, favorable efficient operation of the fuel cell system can be achieved. Preferably, the fuel gas utilization and/or the oxygen-carbon ratio of the fuel cell module is calculated by an evaluation unit using the measured current generated by the at least one electrochemical gas sensor and the further measured current generated by the at least one further electrochemical gas sensor. "fuel gas utilization" is preferably understood to mean characteristic values which describe the ratio between the reactants oxidized in the fuel cell module and the potential reaction partners of the supplied process gases, in particular natural gas, methane and/or carbon monoxide and/or hydrogen, which are supplied at the anode inlet of the fuel cell module, wherein these values are evaluated in terms of their oxygen binding. An "oxygen-carbon ratio" is preferably understood to mean a characteristic value which describes the ratio of the mass flow rates of the oxygen-carrying and carbon-carrying species, in particular hydrogen and/or methane and/or carbon monoxide and/or carbon dioxide and/or water, each evaluated according to the number of atoms. Preferably, hydrogen, methane, carbon monoxide, carbon dioxide and/or water form the gas composition common in the solid oxide fuel cell system.
It is also proposed that the current of the fuel cell system, in particular of the gas supply, the circulation and/or the fuel cell module, is regulated as a function of the measured current generated by the at least one electrochemical gas sensor and of a further measured current generated by the at least one further electrochemical gas sensor. Thereby, an advantageous efficient and safe operation of the fuel cell system according to the invention can be achieved. In addition, critical operating states can advantageously be avoided thereby. "gas supply" is preferably understood to mean the supply of fresh fuel, in particular natural gas, methane and/or hydrogen, into the fuel cell system. Preferably, the cycle rate, the oxygen-carbon ratio and/or the fuel gas utilization rate are determined and/or influenced, in particular controlled and/or regulated, by means of information about the composition of the process gas mixture at the anode inlet and the composition of the further process gas mixture at the anode outlet of the at least one fuel cell module.
It is furthermore proposed that, in addition to the concentration of the at least one process gas, at least one further concentration of at least one further process gas, in particular methane and/or water, of the process gas mixture is determined by means of the at least one electrochemical gas sensor. With this configuration, the process gas mixture can advantageously be analyzed diversely by the electrochemical gas sensor. Preferably, the concentration of the at least one further process gas may be determined by selecting a further potential of the electrochemical gas sensor. In principle, it is conceivable here to determine the at least one further process gas of the process gas mixture by means of closed conditions (Schlie beta besidinging) and/or by assuming thermodynamic equilibrium under the existing temperature measurement.
The fuel cell system according to the invention and/or the method according to the invention should not be limited to the above-described applications and embodiments here. In particular, the fuel cell system according to the invention and/or the method according to the invention may have a different number than the number mentioned here of the individual elements, components and units and method steps in order to satisfy the operating principle described here. Furthermore, in the case of the value ranges shown in the disclosure, values within the mentioned limits should also be regarded as disclosed and can be used arbitrarily.
Drawings
Further advantages result from the following description of the figures. Embodiments of the invention are shown in the drawings. The figures, description and claims contain many of the features in combination. Those skilled in the art suitably also consider these features individually and combine them into other meaningful combinations.
In which is shown:
figure 1 schematically shows a fuel cell system according to the invention,
figure 2 schematically shows an electrochemical gas sensor of a fuel cell system according to the invention,
figure 3 schematically illustrates the regulation of a fuel cell system according to the invention,
FIG. 4 is a diagram in schematic form with U-i-characteristic lines, and
fig. 5 shows a method according to the invention for operating a fuel cell system according to the invention in the form of a schematic diagram.
Detailed Description
A fuel cell system 10 is shown in fig. 1. The fuel cell system 10 is used to convert chemically combined energy directly, in particular without a combustion process, into electrical energy. In the present case, the fuel cell system 10 is designed as a solid oxide fuel cell System (SOFC).
The fuel cell system 10 comprises a first supply line 12 arranged for conducting natural gas into the fuel cell system 10. The fuel cell system 10 includes a desulfurization unit 14 integrated into the first supply line 12. The fuel cell system 10 comprises a second supply line 16 arranged for leading water into the fuel cell system 10. The fuel cell system 10 has an evaporator 18 integrated into the second supply line 16, which is provided for converting water into a gaseous state of matter. A second supply line 16 is coupled to the first supply line 12 at a location downstream of the desulfurization unit 14 and the evaporator 18. The fuel cell system 10 includes a preheater 20 downstream of the first supply line 12.
The fuel cell system 10 includes a third supply line 22 downstream of the preheater 20. The fuel cell system 10 includes a reformer 24 configured to convert longer chain hydrocarbons (C) through at least one reforming process n H 2n+2 ) To hydrogen, methane and carbon monoxide. After the at least one reforming process, methane is also present in the process gas mixture in a small proportion. A reformer 24 is downstream of the third supply line 22.
The fuel cell system 10 includes a fuel cell module 26. The fuel cell module 26 is configured to generate electrical and/or thermal energy. In the present case, the fuel cell module 26 is designed as a solid oxide fuel cell module.
The fuel cell system 10 includes a fourth supply line 28 upstream of the fuel cell module 26. A fourth supply line 28 is downstream of the reformer 24.
The fuel cell module 26 has an anode 30. The fuel cell module 26, and particularly the anode 30, has an anode inlet 32. Fourth supply line 28 is coupled to an anode inlet 32 of fuel cell module 26. At an anode inlet 32 of the fuel cell module 26, the process gas mixture is directed to an anode 30 of the fuel cell module 26. The process gas mixture reacts electrochemically in the fuel cell module 26. The fuel cell module 26, and particularly the anode 30, has an anode outlet 34. At the anode outlet 34 of the fuel cell module 26, additional process gas mixture is discharged from the anode 30 of the fuel cell module 26. The fuel cell module 26 has a cathode 36. The fuel cell module 26, and particularly the cathode 36, has a cathode inlet 38. The fuel cell module 26, and particularly the cathode 36, has a cathode outlet 40. The fuel cell module 26 has an electrolyte 42. The electrolyte 42 of the fuel cell module 26 is disposed between the anode 30 and the cathode 36 of the fuel cell module 26. The anode space and the cathode space of the fuel cell module 26 are separated from each other at least by the electrolyte 42 of the fuel cell module 26. The anode 30, the electrolyte 42 and the cathode 36 of the fuel cell module 26 are each designed as a layer. The electrolyte 42 of the fuel cell module 26 is formed of a solid ceramic material. The electrolyte 42 of the fuel cell module 26 is composed of a solid oxide. The electrolyte 42 of the fuel cell module 26 is provided for conducting oxygen ions, wherein in particular the ceramic material is electrically insulating with respect to electrons. When oxygen ion (O) 2- ) The fuel cell module 26 provides electrical energy when transported through the electrolyte 42 due to the chemical potential difference. The conductivity of the electrolyte material depends to a large extent on the operating temperature and values such that the losses become acceptably low are only achieved at temperatures above 450 ℃.
In a solid oxide fuel cell module, hydrogen and carbon monoxide react. The anodic reaction occurs according to equations (1) and (2), and the cathodic reaction occurs according to equation (3).
H 2 + O 2- = H 2 O + 2 e - (1)
CO + O 2- = CO 2 + 2 e - (2)
0.5 O 2 + 2 e - = O 2- (3)。
At the anode inlet 32 of the fuel cell module 26, CH is typically present 4 、H 2 、CO、CO 2 And H 2 O as a species of the process gas mixture. After the electrochemical reaction, there is typically H present at the anode outlet 34 of the fuel cell module 26 2 、CO、CO 2 And H 2 O as a species of the further process gas mixture. Thus, H 2 And CO is the only combustible gas component left at the anode outlet 34 of the fuel cell module 26. At the anode outlet 34 of the fuel cell module 26, CO are discharged 2 、H 2 And H 2 A mixture of O. When air is supplied, the air with reduced oxygen content is exhausted at the cathode outlet 40 of the fuel cell module 26.
The fuel cell system 10 comprises a fifth supply line 44, which is provided for supplying air, in particular oxygen, into the fuel cell system 10. The fuel cell system 10 comprises a further preheater 46 integrated into the fifth supply line 44. The fifth supply line 44 is upstream of the fuel cell module 26. A fifth supply line 44 is coupled to the cathode inlet 38 of the fuel cell module 26.
The fuel cell system 10 includes an inverter 48 configured to convert the direct current generated by the fuel cell module 26 to alternating current. The inverter 48 is electrically connected to the fuel cell module 26. The converter 48 is provided for delivering electrical power to a power grid, not shown in detail.
The fuel cell system 10 includes a drain line 50. A drain line 50 is downstream of the fuel cell module 26. A drain line 50 is coupled to anode outlet 34. A discharge line 50 is provided for discharging the further process gas mixture from the anode 30 of the fuel cell module 26.
The fuel cell system 10 includes a circulation path 52. A circulation path 52 is provided for leading the further process gas mixture from the exhaust line 50 to the third supply line 22 for circulation. The circulation path 52 is coupled with the discharge line 50. The circulation path 52 is coupled with the third supply line 22. The anode off-gas circulation is performed through the circulation path 52. Through the circulation path 52, a portion of the anode exhaust gas, in particular a portion of the further process gas mixture, is circulated and mixed with fresh natural gas. Thereby, the unused fuel gas component is circulated, whereby an increase in the system efficiency is advantageously achieved, and the steam required for steam reforming can be advantageously efficiently supplied. Instead of recycling the anode off-gas, in particular the further process gas mixture, an external steam supply for steam reforming may also be provided. In principle, it is also possible to reform natural gas with oxygen. Instead of a circulating anode off-gas, in particular the further process gas mixture or an external steam supply for steam reforming, a supply, not shown in detail, of oxygen-containing air from the fifth supply line 44 to the reformer 24 for oxygen reforming in the sense of catalytic partial oxidation can also be provided. To characterize the cyclic operation, a parameter cycle rate r is introduced, which can be determined by equation (4).
The fuel cell system 10 includes an additional discharge line 54. The further discharge line 54 is downstream of the fuel cell module 26. The additional exhaust line 54 is coupled to the cathode outlet 40 of the fuel cell module 26.
The fuel cell system 10 includes a combustor 56. The burner 56 is provided for generating thermal energy, in particular by burning combustible components of the further process gas mixture. A combustor 56 is downstream of the discharge line 50. A burner 56 is downstream of the further discharge line 54. The discharge line 50 and the further discharge line 54 are coupled with a burner 56.
The fuel cell system 10 includes an exhaust line 58. An exhaust line 58 is downstream of the burner 56. The fuel cell system 10 includes a heat exchanger 60. A heat exchanger 60 is provided for extracting heat from the exhaust gas in the exhaust line 58. The fuel cell system 10 includes internal and external heat utilization 62 by which waste heat from the heat exchanger 60 can be used in the preheater 20, the evaporator 18, and/or the additional preheater 46.
The fuel cell system 10 includes an electrochemical gas sensor 64. The electrochemical gas sensor 64 is schematically shown in fig. 2. The electrochemical gas sensor 64 is in contact with the process gas mixture. The electrochemical gas sensor 64 is provided for generating a measurement current depending on the concentration of the process gas mixture. The electrochemical gas sensor 64 is designed as a hydrogen sensor. The electrochemical gas sensor 64 is designed as a galvanic cell. The electrochemical gas sensor 64 is designed as a fuel cell. An electrochemical gas sensor 64 is provided for sensing at least one process gas in the process gas mixture. The electrochemical gas sensor 64 is configured to convert the energy of the chemical reaction of the at least one process gas and the oxidant into electrical energy, thereby generating a measurement current. The oxidant is designed as oxygen. The electrochemical gas sensor 64 may operate independently of the fuel cell module 26. The fuel cell module 26 and the electrochemical gas sensor 64 are designed independently of one another, in particular with regard to operability. An electrochemical gas sensor 64 is disposed at the anode inlet 32 of the fuel cell module 26. In principle, it is conceivable for the electrochemical gas sensor 64 to be arranged at least partially in the fuel cell module 26, in particular in the anode inlet 32 of the fuel cell module 26. The electrochemical gas sensor 64 is integrated directly into a line system of the fuel cell system 10 for supplying fuel, in particular the at least one process gas, to the fuel cell module 26. An electrochemical gas sensor 64 is integrated into the fourth supply line 28. The process gas mixture flows in the fourth supply line 28. The electrochemical gas sensor 64 is designed as a proton conducting ceramic fuel cell (PCFC). An alternative name is proton ceramic fuel cells. The electrochemical gas sensor 64 includes an anode 66, a cathode 68, and an electrolyte 70 disposed between the anode 66 and the cathode 68. The electrolyte 70 of the electrochemical gas sensor 64 is formed of a ceramic electrolyte material. The ceramic electrolyte material serves as a proton conductor between the anode 66 and the cathode 68 of the electrochemical gas sensor 64. The electrolyte 70 of the electrochemical gas sensor 64 allows protons to be transferred from the anode 66 to the cathode 68 of the electrochemical gas sensor 68, but in particular without other elements. Ceramic electrolyte material inHas high proton conductivity at high temperature. Proton conducting ceramic fuel cells offer the thermal and kinetic advantages of high temperature operation of 400 ℃ to 700 ℃ and the inherent advantages of proton conduction. High operating temperatures are necessary to achieve very high electrical conversion efficiencies with hydrocarbon fuels. Proton conducting ceramic fuel cells can be operated at high temperatures and fossil fuels are electrochemically oxidized directly at the anode 66. This eliminates the intermediate step of producing pure hydrogen by an expensive reforming process. The electrochemical gas sensor 64 is provided for ionizing hydrogen molecules at the surface of the anode 66 of the electrochemical gas sensor 64 in order to absorb them into the electrolyte 70 of the electrochemical gas sensor 64, wherein they react with oxygen at the cathode 68 of the electrochemical gas sensor 64 after transport through the electrolyte 70 and form water in a particularly gaseous state. At low anode overvoltage, the measured current occurring between the anode 66 and the cathode 68 of the electrochemical gas sensor 64 comes only from the sum of H 2 The electrolyte 70, which permeates the proton conducting membrane, in particular the electrochemical gas sensor, is pumped to the air side, in particular the cathode 68 of the electrochemical gas sensor 64. CO can only be pumped together at a higher anode potential. It is possible to ensure that for a single H, for example, an advantageous ratio between the electrochemically active electrode area and the diffusion limitation of the supplied anode fuel gas 2 Sufficiently low anode potential for oxidation. In principle, a diffusion barrier with specific properties can be applied to the measurement gas side of the electrochemical gas sensor 64, in particular to the anode 66, such that only H 2 To the anode 66 of the electrochemical gas sensor 64, so that H in the occurring diffusion-limited current can then be measured 2 。
In principle, in particular, lambda sensors for motor vehicles can serve as the basis for the construction of proton-conducting ceramic fuel cells. Alternatively, a jump probe (sprungsunde) can be used, for example, as a construction basis, wherein in principle only the electrolyte needs to be replaced by a proton-conducting electrolyte. The electrical contact of the skip probe originally used to measure the open circuit termination voltage may now act as an electronic conductor between the anode and cathode of the electrochemical gas sensor.
In fig. 3, the fuel cell system 10 is shown based in part on the regulator 72 of the fuel cell system 10.
The fuel cell system 10 includes an additional electrochemical gas sensor 74. The further electrochemical gas sensor 74 is arranged at the anode outlet 34 of the fuel cell module 26. In principle, the further electrochemical gas sensor 74 can also be arranged in the circulation path 52 of the fuel cell system 10. The further electrochemical gas sensor 74 is in contact with the further process gas mixture. The further electrochemical gas sensor 74 is provided for generating a further measurement current depending on the concentration of at least one process gas of the further process gas mixture. The further electrochemical gas sensor 74 is integrated directly into a line system of the fuel cell system 10 for discharging anode exhaust gas, in particular the at least one process gas, from the fuel cell module 26. The process gas mixture entering at the anode inlet 32 of the fuel cell module 26 is changed by a chemical reaction in the fuel cell module 26 such that the additional process gas mixture is present at the anode outlet 34 of the fuel cell module 26. The further process gas mixture deviates from the process gas mixture. The further electrochemical gas sensor 74 is designed as a further proton-conducting ceramic fuel cell. The further proton-conducting ceramic fuel cell is designed at least substantially identically to the proton-conducting ceramic fuel cell, in particular with regard to function.
Alternatively, it is also conceivable for the electrochemical gas sensor 64 and/or the further electrochemical gas sensor 74 to each be designed as an electrochemical pump cell (Pumpzelle). Instead of fuel cells, in particular instead of using air-flushed cathodes, simple electrochemical pump cells can in principle also be used for the exhaust gas of the solid oxide fuel cell module. In this case, the two electrodes of the electrochemical pump cell will be in the process gas mixture of the solid oxide fuel cell module and the transport through the proton-conducting membrane is effected only by applying an external pump voltage.
Proton conducting ceramic fuel cells are provided for determining gas composition and/or gas properties. The proton conducting ceramic fuel cells are arranged directly in the process gas mixture at the anode inlet 32 of the fuel cell module 26. The further proton-conducting ceramic fuel cells are arranged directly in the further process gas mixture at the anode outlet 34 of the fuel cell module 26. The proton-conducting ceramic fuel cells are integrated as electrochemical gas sensors 64 in the particularly combustible process gas mixture at the anode inlet 32 of the fuel cell module 26 in the immediate vicinity and directly, and the further proton-conducting ceramic fuel cells are integrated as further electrochemical gas sensors 74 in the further process gas mixture at the anode outlet 34 of the fuel cell module 26 in the immediate vicinity and directly, in order to determine the individual gas components and/or gas properties and to enable a targeted adjustment of the system.
In principle, it is conceivable to integrate additional electrochemical gas sensors into the fuel cell system 10, in particular in the case of larger plants, in each case at subsections, in particular about 2kW, in order to be able to detect and compensate for unequalities in the gas distribution or the current strength.
The fuel cell system 10 includes an evaluation unit 76. The evaluation unit 76 is provided to detect the measurement current generated by means of the electrochemical gas sensor 64 and a further measurement current generated by means of the further electrochemical gas sensor 74 and to calculate at least one control value from the measurement current and the further measurement current.
The fuel cell system 10 includes a regulator 72. The regulator 72 obtains a target value 78 FU for the fuel gas utilization of the fuel cell module 26 Heap, target . The regulator 72 obtains from the evaluation unit 76 the actual value 80 FU of the fuel gas utilization of the fuel cell module 26 Heap of reality . The regulator 72 is provided for regulating a gas supply 82, a circulation 84, in particular a circulation rate, of the natural gas and/or the current I of the fuel cell module 26 Stack 86 and/or voltage U of fuel cell module 26 Stack 86. The electrochemical gas sensor 64 supplies the evaluation unit 76 with the measured current I H2, anode inlet . The further electrochemical gas sensor 74 isThe evaluation unit 76 provides the further measurement current I H2, outlet of anode 。
An important parameter for the operation of a fuel cell module 26 designed as a solid oxide fuel cell module is the fuel gas utilization FU (fuel utilization). Fuel gas utilization is a characteristic system parameter. Fuel gas utilization generally describes the ratio between the reactants oxidized in the fuel cell module 26 and the potential reaction partners supplied at a particular location, where these elements are evaluated in terms of their oxygen binding capacity. In the present case of a fuel cell system 10 with anode exhaust gas recirculation, the fuel gas utilization FU at the fuel cell system 10 System (taking into account conditions at the system inlet and system outlet) and the fuel gas utilization FU of the fuel cell module 26 Stack (taking into account the conditions of the anode inlet 32 and the anode outlet 34 of the fuel cell module 26).
Fuel gas utilization FU Stack The ratio between the reactants oxidized in the fuel cell module 26 and the potential reaction partner supplied at the anode inlet 32 of the fuel cell module 26 is described, where these elements are evaluated in terms of their oxygen binding capacity. When hydrogen, methane and carbon monoxide are used as common combustible gases at the anode inlet 32, FU is calculated for fuel gas utilization Stack Thus, equation (5) is obtained.
To avoid damage, fuel gas utilization FU Stack There must be essentially an upper limit in operation. According to an embodiment, this limit is about 60-75%. Exceeding this limit may result in permanent damage to the fuel cell module 26 due to fuel gas depletion.
Fuel gas utilization FU System The ratio between the reactants oxidized in the fuel cell module 26 and the potential reaction partners supplied at the system inlet of the supplied natural gas, pure methane or hydrogen is described, wherein these elements are evaluated according to their oxygen binding capacity.
Depending on the operating conditions, in particular the temperature, the pressure and/or the gas composition at the system inlet, chemical reactions can take place in the fuel cell system 10, which is designed as a solid oxide fuel cell system, in which carbon deposits occur. The result is coking. Upon coking, the active layers of the anode 30 of the fuel cell module 26 and the active layers of the reformer 24 become clogged (zugesetzt), which can lead to increased pressure losses and, due to clogging of the reaction surfaces, to a loss of performance and a reduction in service life to complete functional failure. In operation, this must be avoided as much as possible by adjusting the gas composition and temperature. A sufficient supply of water vapor for preventing coking at the time of steam reforming in the reformer 24 and at the anode 30 of the fuel cell module 26 and is shown by the oxygen-carbon-ratio O/C. In the case of catalytic partial oxidation as the reforming process, sufficient oxygen must be supplied. Thus, the oxygen-to-carbon ratio at the reformer outlet or at the anode inlet 32 of the fuel cell module 26 is another important characteristic system parameter for operational management and regulation of the fuel cell module 26 designed as a solid oxide fuel cell module and/or the fuel cell system 10 designed as a solid oxide fuel cell system. The oxygen-carbon ratio is formed from the mass flow rates of oxygen-carrying and carbon-carrying species, such as water vapor and methane, each evaluated according to the atomic number, according to equation (6).
A minimum oxygen-carbon-ratio occurs in the reformer 24 because the oxygen-carbon-ratio in the anode channels of the fuel cell module 26 increases due to the transport of cations in the fuel cell module 26, and the reformer 24 is therefore a critical component of coking. A common oxygen-carbon ratio is 1.5 to 3. In the case of a fuel cell system 10 designed as a solid oxide fuel cell system without anode off-gas circulation, in particular in the case of an external water supply via the second supply line 16, the water vapor-carbon ratio S/C is often used as an alternative.
According to the prior art, the characteristic system parameters fuel gas utilization FU and oxygen-carbon-ratio O/C cannot be measured directly during operation of the plant. These two system parameters can be calculated by means of concentration measurements of the gas components only. However, due to the time consumption of the concentration measurement, the values thus determined cannot be used for an adjustment in the form of a closed adjustment loop with a high time resolution. Furthermore, the measurement techniques required for concentration measurement are associated with high costs. This is therefore not a viable solution for serial operation in the sense of reducing costs for the competitiveness of SOFC technology. Alternatively, although it is possible in principle to physically model the fuel gas utilization FU and the oxygen-carbon-ratio O/C, physical-based models are unsuitable for use in actual operation according to the prior art due to their complexity and the computation time associated therewith. Therefore, in prior art fuel cell systems, an open loop regulation strategy is usually implemented, wherein target values of these two system parameters are predetermined as a pilot control. However, the values occurring in the actual fuel cell system are not checked with a sufficiently high time resolution, in particular in real time, so that no information is available about the actual values of the operating system parameters and the accuracy of the pilot control. In addition, in the case of sometimes dynamic operation of operating point variants, information about these two system parameters is essential. When the operating point changes, for example when a higher current is drawn from the fuel cell module, the two system parameters may briefly have values which exceed their respective limits for optimum operation. In addition to the additional losses, exceeding the respective limits can also lead to damage to the solid oxide fuel cell module. However, in the event that the values of the system parameters are not determined during operation of the system, exceeding these limits cannot be detected and the effect cannot be effected in the form of a closed control loop.
The gas composition of natural gas varies greatly in volatility and regional differences. In Germany, the fluctuations over time at the connection points are expected to be. + -. 5% (Wobbe index). The fluctuations are within an allowable fluctuation range. The wobbe index is not exactly proportional to the fluctuations in the number of electrons, but gives an inference about volatility. The regional differences may also be greater depending on the gas used, and produce more than 10% fluctuation and/or difference in the number of electrons. Since the fuel cell systems which are designed as solid oxide fuel cell systems are controlled in a pilot manner as a function of the gas composition of the natural gas, these severe differences result in the solid oxide fuel cell systems having to be set such that the feared maximum deviation does not lead to exceeding the fuel gas utilization FU and/or to falling below the oxygen-carbon ratio O/C, since otherwise damage, in particular deterioration, may occur. This in turn means that the fuel cell system cannot be operated with maximum efficiency if the variation in the gas composition of the natural gas is unknown and therefore the mass flow cannot be adapted accordingly.
By using a proton conducting ceramic fuel cell, the sensing system in a solid oxide fuel cell system can be advantageously simplified. By using proton-conducting ceramic fuel cells, it is advantageously possible to comply with predetermined limits for maximum fuel gas utilization, and in particular a minimum oxygen-carbon ratio, independently of the gas composition. By using proton-conducting ceramic fuel cells, the possible fuel gas utilization can be advantageously utilized with fluctuating gas compositions. Furthermore, an advantageously low oxygen-carbon ratio can be set by using proton-conducting ceramic fuel cells. This therefore means that the dynamic behavior of the fuel cell system 10 is improved. By using the proton-conducting ceramic fuel cell, even when the gas composition changes, favorable and optimized operation management can be performed, thereby achieving an improvement in efficiency and a reduction in deterioration.
A graph 88 with a U-i-profile 90 is shown in fig. 4. Graph 88 has an abscissa 92 and an ordinate 94. The current density j and/or the current density i are plotted on the abscissa 92. The voltage E and/or the voltage U are plotted on the ordinate 94. U-i-characteristic line 90 describes the battery voltage E z Distribution of (2). In graph 88, an activation loss 96, an ohmic loss 98, and a diffusion loss 100 are indicated based on a U-i-characteristic line 90. Furthermore, the reversible cell voltage E is plotted in the diagram 88 rev 102, and an open terminal voltage OCV 104. Reversible cell voltage E rev The difference between 102 and the open circuit termination voltage OCV 104 is the steady state voltage loss 106. The diffusion limited current density of the fuel cell module 26 is depicted at the three-phase boundary,the state in particular when no species are present anymore at the fuel cell module 26 or at the anode 30 of the electrochemical gas sensor 64, in particular when no hydrogen is present anymore at the anode 66 of the electrochemical gas sensor 64, and is decisively dependent on the diffusion coefficient D eff Electrode thickness delta and initial concentration of reactant x R,0 . After reaching the diffusion limit current, the load current cannot be increased by further overvoltages. This diffusion-limited current density is shown in the characteristic U-i characteristic line 90 in the region of the diffusion losses 100 at high current densities, where the cell voltage E z Rapidly falls and at the battery voltage E z A limited diffusion limited current is achieved at 0V.
By means of the diffusion limiting current I measured by the evaluation unit 76 lim,H2 As characteristic parameters of the hydrogen mass flow or hydrogen concentration in the process gas mixture at the anode inlet 32 and the further process gas mixture at the anode outlet 34, a fuel gas utilization H can be established 2 For the definition of specificity, see equation (7).
This is particularly interesting because hydrogen is the main conversion component in the solid oxide fuel cell module and can therefore be used decisively as a measure for the fuel utilisation or to avoid fuel gas depletion as an undesirable critical operating state. Thus, such hydrogen-specific fuel gas utilization FU can be determined and regulated in the fuel cell system 10 Stack 。
A method 108 of operating the fuel cell system 10 is shown in fig. 5. In the present case, the method 108 has a method step 110 and a further method step 112. In method 108, in particular in method step 110, the hydrogen-specific fuel gas utilization FU is determined with the aid of the proton-conducting ceramic fuel cell at the anode inlet 32 of the fuel cell module 26 and the further proton-conducting ceramic fuel cell at the anode outlet 34 of the fuel cell module 26 Stack 。
In method step 110, a measurement current is generated by means of the electrochemical gas sensor 64 of the ceramic fuel cell, which is designed to conduct protons, as a function of the concentration of at least one process gas of the process gas mixture. The measured current generated by the electrochemical gas sensor 64 is indicative of the concentration of at least one process gas in the process gas mixture. In a method step 110, the further measurement current is generated by means of the further electrochemical gas sensor 74, which is designed as a proton-conducting ceramic fuel cell, as a function of the concentration of at least one process gas of the further process gas mixture. The further measurement current generated by the further electrochemical gas sensor 74 characterizes the concentration of the at least one process gas in the further process gas mixture. The fuel gas utilization and/or the oxygen-carbon ratio of the fuel cell module 26 is calculated by the evaluation unit 76 using the measured current generated by the electrochemical gas sensor 64. With the aid of the measured current generated by the electrochemical gas sensor 64 and the further measured current generated by the further electrochemical gas sensor 74, the fuel gas utilization and/or the oxygen-carbon ratio of the fuel cell module 26 is calculated by the evaluation unit 76. The evaluation unit 76 is provided for determining the gas composition and/or the gas properties and for using and adjusting to the hydrogen-specific value and/or the fuel utilization of the fuel cell module 26.
In a further method step 112, the current 86 and/or the voltage 86 of the fuel cell system 10, in particular of the gas supply 82, the circuit 84 and/or the fuel cell module 26, is/are regulated as a function of the measured current generated by the electrochemical gas sensor 64 and the further measured current generated by the further electrochemical gas sensor 74. Determining and/or influencing, in particular controlling and/or regulating, the circulation rate, the oxygen-carbon ratio and/or the fuel gas utilization FU by means of information about the composition of the process gas mixture at the anode inlet 32 of the fuel cell module 26 and the composition of the further process gas mixture at the anode outlet 34 of the fuel cell module 26 Stack 。
In addition to the concentration of the at least one process gas, in particular hydrogen, the electrochemical gas sensor 64 is used, in particular, in method step 110, at least one concentration of at least one further process gas, in particular methane and/or water, of the process gas mixture is determined. The concentration of the at least one additional process gas may be determined by selecting other potentials of the electrochemical gas sensor 64. The proton-conducting ceramic fuel cell is arranged directly in the combustible process gas, in particular even at high temperatures, as is the case for the anode inlet 32 and the anode outlet 34 of the fuel cell module 26, primarily as a hydrogen sensor. In addition to the hydrogen concentration, the CH can also be determined by proton-conducting ceramic fuel cells 4 Or the concentration of water. In principle, it is conceivable here to determine the at least one further process gas of the process gas mixture by closed conditions and/or by assuming thermodynamic equilibrium under the existing temperature measurement.
In principle, there is no H mentioned before 2 In the case of a specific diffusion barrier, CH present in the process gas mixture 4 And H 2 O can also release its H and thus contribute to current flow. However, empirically, this is only at the ratio H 2 At a higher potential, so that an operating state can be selected in which only H is taken into account 2 Or H 2 +CH 4 And/or H 2 And O. In particular, at the anode outlet 34 of the fuel cell module 26, except for H 2 In addition, essentially only H is present 2 O as a hydrogen-bearing gaseous species. Thereby passing through with H 2 The water concentration at the anode outlet 34 of the fuel cell module 26 can be determined by means of the further proton-conducting ceramic fuel cells compared to the increased potential. Conversely, at the anode inlet 32 of the fuel cell module 26, H may be determined at a higher potential 2 O and CH 4 And respectively determine H at different higher potentials 2 O and CH 4 。
Therefore, ultimately only CO and CO are still present at the anode inlet 32 and the anode outlet 34 of the fuel cell module 26 2 As unknown parameters. These parameters can be determined by closed conditions, by experience with other measurable system parameters, in particular volume flow, temperature, pressureThe equations are formulated and/or determined by assuming thermodynamic equilibrium at the existing temperature measurement. In this case, all gas components, in particular process gases, of the process gas mixture at the anode inlet 32 and of the further process gas mixture at the anode outlet 34 of the fuel cell module 26 are known. Thus, in this case, the universally applicable fuel gas utilization FU can be determined according to equation (5) Stack . Furthermore, the oxygen-carbon-ratio O/C at the reformer outlet or at the anode inlet 32 of the fuel cell module 26 can be determined in this case according to equation (6). Thus, the adjustment 72 thereof can be effected in real time by means of the determination of these system parameters.
By determining these two system parameters, and by determining the hydrogen-specific fuel gas utilization, the sensing system in a solid oxide fuel cell system can be advantageously simplified. By determining these two system parameters, and by determining the hydrogen-specific fuel gas utilization, it is advantageously possible to comply with predetermined limits for the maximum fuel gas utilization, and in particular the minimum oxygen-carbon ratio, independently of the gas composition. By determining these two system parameters, and by determining the hydrogen-specific fuel gas utilization, the possible fuel gas utilization can be advantageously utilized in the case of fluctuating gas compositions. Furthermore, by determining these two system parameters, and by determining the hydrogen-specific fuel gas utilization, an advantageously low oxygen-carbon ratio can be set. This therefore means that the dynamic behavior of the fuel cell system 10 is improved. By determining these two system parameters, and by determining the hydrogen-specific fuel gas utilization rate, it is possible to perform favorable optimized operation management even when the gas composition changes, thereby achieving an improvement in efficiency and a reduction in deterioration.
As a direct determination of fuel gas utilization FU Stack Alternatively, indirect adjustment thereof may be performed. By means of the method shown, the hydrogen concentration at the anode outlet 34 of the fuel cell module 26 can be determined and provision is made in the regulator 72 for the hydrogen concentration to be regulated to a specific value. The reason for this is that hydrogen is a solid oxideA variant of the main conversion in a fuel cell module. In order to avoid fuel gas depletion and the cell damage associated therewith, a critical minimum value for the hydrogen concentration may also be specified, which is not allowed to fall below. Without an accurate knowledge of the gas composition of the process gas mixture or of the additional process gas mixture, an optimum fuel gas utilization can be set at this point, wherein no fuel gas depletion occurs and an advantageously high efficiency is achieved due to the sufficient hydrogen present at the anode outlet 34 of the fuel cell module 26.
In addition to being used in solid oxide fuel cell systems, the sensor concept according to the invention with the electrochemical gas sensor 64 and the further electrochemical gas sensor 74 can in principle also be used in other devices with different process gases. The described method 108 can also be applied to other systems with in particular different process gases (which contain hydrogen) in order to determine the individual gas components and/or gas properties and to enable targeted adjustment of the system.
In order to improve the method 108 with the aim of higher accuracy in determining the gas composition and/or the gas properties, the method 108 can be combined with at least one machine learning method in the sense of a hybrid system. The machine learning method can be used here to estimate the actual value h s (e.g. hydrogen concentration) and the value h measured by the sensor concept shown s, sensor In particular already small errors, and thus improve the latter values. For example, equation (8) may be used to determine the actual value h s 。
For this reason, the algorithm of the machine learning method only needs to be trained with training data in a preparation phase to estimate the error of each operating point. The machine learning method may be established based on measured parameters of the proton conducting ceramic fuel cell(s) (e.g., pump current, pump voltage, and/or temperature) and other parameters (e.g., temperature, pressure, and/or volumetric flow, among others) of fuel cell system 10 (where proton conducting ceramic fuel cells are used). At this time, the sensor error is an initial parameter. For example, the calculation can be performed by equation (9). In addition to the multiple linear regression, the use of neural networks, in particular the use of the gaussian method, is a suitable method here.
𝜀 𝑀𝐿 = f( 𝐼 𝑝 , 𝐼 𝑠 , 𝑈 𝑠 ) (9)。
This can be used in physics-based methods and for correcting gas composition (CO, CO) 2 Possibly also CH 4 And/or H 2 O), the gas composition being determined by means of closed conditions, empirical equations and/or simplifying the thermodynamic equilibrium at the anode inlet 32 or the anode outlet 34 and the equilibrium composition of the process gas mixture or of the further process gas mixture associated therewith.
Alternatively or additionally, in a further advantageous embodiment of the invention, the use of a proton-conducting ceramic fuel cell as electrochemical gas sensor 64, 74 can be combined with the use of an oxygen ion-conducting cell as a gas sensor in a solid oxide fuel cell system. Evaluation of two different measurement principles may enable an improvement of the accuracy of the gas composition information. It is also contemplated that the electrochemical gas sensors 64, 74, which are designed as proton conducting ceramic fuel cells, are used to quantify H-containing molecules (H) 2 、CH 4 、H 2 O) and reacting O 2 Ion conductors are similarly used to quantify O-containing molecules (CO) 2 、H 2 O). This can be done, for example, by applying an external pump voltage to ionize all O-containing reactants. Since the water concentration participates in the material balance in both cases, the carbon dioxide concentration can be calculated when the hydrogen concentration and the methane concentration are measured separately in advance.
Claims (10)
1. Fuel cell system (10), in particular solid oxide fuel cell system, comprising at least one fuel cell module (26), in particular solid oxide fuel cell module, for generating electrical and/or thermal energy, characterized by at least one electrochemical gas sensor (64) which is in contact with a process gas mixture and is provided for generating a measurement current depending on the concentration of at least one process gas of the process gas mixture.
2. A fuel cell system (10) according to claim 1, characterized in that said at least one electrochemical gas sensor (64) is arranged at the anode inlet (32) of the fuel cell module (26).
3. Fuel cell system (10) according to claim 1 or 2, characterized in that the at least one electrochemical gas sensor (64) is designed as a proton-conducting ceramic fuel cell.
4. Fuel cell system (10) according to one of the preceding claims, characterized by at least one further electrochemical gas sensor (74) which is arranged at the anode outlet (34) of the fuel cell module (26) and/or in the circulation path (52) of the fuel cell system (10) and is in contact with a further process gas mixture and is provided for generating a further measurement current depending on the concentration of at least one process gas of the further process gas mixture.
5. Fuel cell system (10) according to claim 4, characterized in that the at least one further electrochemical gas sensor (74) is designed as a further proton-conducting ceramic fuel cell.
6. The fuel cell system (10) as claimed in claim 4 or 5, characterized by at least one evaluation unit (76) which is provided for acquiring a measurement current generated by means of the at least one electrochemical gas sensor (64) and a measurement current generated by means of the at least one further electrochemical gas sensor (74) and for calculating at least one regulating value from the measurement current and the further measurement current.
7. Method (108) for operating a fuel cell system (10) according to one of the preceding claims, characterized in that a measurement current is generated in at least one method step (110) by means of the at least one electrochemical gas sensor (64) depending on the concentration of at least one process gas of the process gas mixture, the electrochemical gas sensor being designed in particular as a proton-conducting ceramic fuel cell.
8. The method (108) according to claim 7, characterized in that the fuel gas utilization and/or the oxygen-carbon ratio of the fuel cell module (26) is calculated by means of a measuring current generated by the at least one electrochemical gas sensor (64) by means of an evaluation unit (76).
9. The method (108) according to claim 7 or 8, characterized in that the current (86) of the fuel cell system (10), in particular of the gas supply (82), the circulation (84) and/or the fuel cell module (26), is regulated depending on the measured current generated by the at least one electrochemical gas sensor (64) and the further measured current generated by the at least one further electrochemical gas sensor (74).
10. The method (108) according to any one of claims 7 to 9, characterized in that, in addition to the concentration of the at least one process gas, at least one concentration of at least one further process gas, in particular methane and/or water, of the process gas mixture is determined by means of the at least one electrochemical gas sensor (64).
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE102021203538.8A DE102021203538A1 (en) | 2021-04-09 | 2021-04-09 | Fuel cell system and method for operating the fuel cell system |
| DE102021203538.8 | 2021-04-09 |
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| CN115207415A true CN115207415A (en) | 2022-10-18 |
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| JP3680232B2 (en) | 1997-03-31 | 2005-08-10 | トヨタ自動車株式会社 | Solid electrolyte and fuel cell, hydrogen pump, oxygen concentration sensor and water vapor concentration sensor using the same |
| JP2002179404A (en) | 2000-12-08 | 2002-06-26 | Toho Gas Co Ltd | Operation control system for fuel reformer |
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