Solid oxide fuel cell system multi-modal analysis model modeling method
Technical Field
The invention belongs to the technical field of solid oxide fuel cells, and particularly relates to a solid oxide fuel cell system multi-modal analysis model modeling method.
Background
The Solid Oxide Fuel Cell (SOFC) is an all-Solid-state chemical power generation device which directly converts chemical energy stored in Fuel and oxidant into electric energy at medium and high temperature with high efficiency and environmental friendliness, has the characteristics of high efficiency, no pollution, no mechanical vibration, wide adaptability to various hydrocarbon Fuel gases and the like, and becomes one of the most attractive green power generation modes in the 21 st century.
The SOFC can be used in civil stationary power stations, airborne aerospace, thermoelectric recycling, transportation and many other fields, and research and development thereof have been vigorously developed after the 80 s. A large amount of manpower and material resources are invested in research and development of SOFC system power generation in developed countries such as the united states, germany, japan, and the like, and the ultimate goal is to realize commercialization of SOFCs. The SOFC technical levels of representative scientific research institutions and representative SOFCs of companies in SOFC international are gradually improved, and there are successful records that the SOFCs can continuously run for tens of thousands of hours without attenuation, but the data are obtained under the constant temperature condition of a test bed, when the SOFC becomes a system and goes to actual engineering application, the SOFC can generate various performance attenuation and fault mechanisms due to severe operating environment conditions, so that the performance of the system cannot be compared with that obtained by the test bed.
In the long run, only by performing targeted development mechanism analysis on each possible performance attenuation and fault situation from the perspective of the system and building a multi-mode analysis model of the SOFC system with the performance attenuation and fault evolution mechanism, corresponding attenuation and fault events can be timely identified, predicted and processed in the actual operation of the system, so that the long-term operation life of the SOFC system is effectively prolonged, and the system maintenance cost is reduced.
In addition, because the SOFC system performance and the fault evolution mechanism which are focused at present have great independence, that is, parallel logic exists among various mechanisms, a coupling relation or a causal relation is not established at present, but with continuous and deep related research, the relation between different performance attenuations and the fault evolution mechanism becomes clear gradually. Therefore, a multi-mode modeling method is adopted during modeling of the SOFC system, and switching between different fault states of the system model is realized by using event trigger logic of Stateflow, so that expansion and deletion of different fault mechanisms are facilitated, and a condition transfer space is reserved for a more complex attenuation fault evolution mechanism in the future. However, research in the field of modeling and analysis of multi-modal analysis models of SOFC systems with performance attenuation and fault evolution mechanisms is still blank at present.
Disclosure of Invention
Aiming at the defects or improvement requirements of the prior art, the invention provides a solid oxide fuel cell system multi-modal analysis model modeling method, which aims to build an initial state mechanism model of the solid oxide fuel cell system based on a Matlab/Stateflow platform, build a sub-model based on a performance attenuation and fault evolution mechanism on the basis, embed the sub-model into the initial state mechanism model, compare simulation analysis and experimental data, verify the accuracy of the model, solve the problem of multi-modal modeling of the solid oxide fuel cell system with the performance attenuation and fault evolution mechanism, and is suitable for scientific research and practical engineering application.
In order to achieve the above object, the present invention provides a method for modeling a multi-modal analytical model of a solid oxide fuel cell system, the method comprising the steps of:
(1) establishing a system initial state mechanism model according to the working mechanism of the solid oxide fuel cell system;
(2) analyzing a performance attenuation and fault evolution mechanism of the solid oxide fuel cell system, and establishing a performance attenuation model and a fault evolution mechanism model of the solid oxide fuel cell system by a mechanism analysis identification and physical equivalent method;
(3) embedding the performance attenuation model and the fault evolution mechanism model into an initial state mechanism model of the solid oxide fuel cell system to construct a multi-mode analysis model of the solid oxide fuel cell system;
(4) and importing experimental data of the solid oxide fuel cell system into the multi-modal analysis model to identify parameters of the multi-modal analysis model.
Further, the method is characterized in that the establishment of the system initial state mechanism model specifically includes establishing each component submodel on an MATLAB platform according to the working mechanism of each component of the solid oxide fuel cell system, and integrating each component submodel to obtain the system initial state mechanism model; each part comprises a galvanic pile, a reformer, a heat exchanger, a combustion chamber and a fan; all the sub-component submodels are built according to the mass conservation, material conservation and energy conservation laws.
Further, the solid oxide fuel cell system performance decay model comprises two parts, namely a stack performance decay mechanism modeling part and a reformer performance decay mechanism modeling part; the cell stack performance attenuation mechanism comprises cell stack anode nickel oxidation, cathode connector oxidation, physical deformation caused by thermal stress and microstructure change caused by anode nickel coarse junction and cathode particle coarse junction/diffusion.
Further, the solid oxide fuel cell system fault evolution mechanism model is divided into a stack fault evolution mechanism modeling and a peripheral auxiliary device fault evolution mechanism modeling; wherein, the failure evolution mechanism of the electric pile comprises the air leakage of the anode inlet of the electric pile and the rupture of the battery; the failure evolution mechanism of the peripheral auxiliary equipment comprises carbon deposition of a reformer, gas leakage of a smoke inlet of a heat exchanger, gas leakage of a combustion chamber and reduction of mechanical efficiency of a fan.
Further, the model formula for modeling the oxidation decay mechanism of the cathode connector in the modeling of the performance decay mechanism of the galvanic pile is as follows:
Ud(t)=0.001×exp[(5.531×10-8Ts-5.274×10-5)t]
wherein, Ud(T) is the voltage of the cell in the electric pile at the time T, exp is an exponential function, TsIs the average temperature of the stack and has the unit of K.
Further characterized in that the model formula for modeling the reformer performance decay mechanism is:
r(t)=r0(t)(1-rdrt)
wherein r (t) is the reaction rate at time t of the reformer; r is0(t) is the reaction rate in the raw state at the same input as at time t; r isdrIs the rate of decay of reformer performance; the units are%/kh, percent per thousand hours.
Further, the formula of a fuel cell stack anode inlet gas leakage model in the fuel cell stack fault evolution mechanism modeling is as follows:
fanode,fault=(1-αanode,fault)fanode,0
wherein f isanode,faultAnd fanode,0Respectively representing the fuel flow at the anode inlet of the pile in a fault state and a normal state, alphaanode,faultRepresenting the percentage of the leaked fuel flow to the total fuel flow;
the battery rupture model formula in the electric pile fault evolution mechanism modeling is as follows:
ENernst,fault=(1-αNernst,fault)ENernst,0
wherein E isNerns,t fauAnd ENernst,0Battery electromotive force, alpha, in fault and normal states, respectivelyNernst,faultIs the percentage of the cell rupture area to the total cell area.
Further, the method is characterized in that a model formula of the carbon deposit of the reformer in the peripheral auxiliary equipment fault evolution mechanism modeling is as follows:
rcf,fault=(1-αcf,fault)rcf,0
wherein r iscf,faultAnd rcf,0The reaction rates of the reformer, alpha, in the fault state and in the normal state, respectivelycf,faultRepresenting the percentage of carbon deposition covering the active catalytic area in the total active catalytic area;
the model formula of the gas leakage at the flue gas inlet of the heat exchanger in the peripheral auxiliary equipment fault evolution mechanism modeling is as follows:
fhex,fault=(1-αhex,fault)fhex,0
wherein f ishex,faultAnd fhex,0Indicating the combustion chamber exhaust gas flow, alpha, of the heat exchanger flue gas inlet in fault and normal conditions, respectivelyhex,faultRepresenting the percentage of the flow of combustor tail gas exiting the heat exchanger flue gas inlet as a percentage of the total flow of combustor tail gas to the heat exchanger flue gas inlet;
the model formula of the combustion chamber air leakage in the peripheral auxiliary equipment fault evolution mechanism modeling is as follows:
fburner,fault=(1-αburner,fault)fburner,0
wherein f isburner,faultAnd fburner,0The combustion chamber outlet exhaust gas flow, alpha, in fault and normal conditions, respectivelyburner,faultRepresenting the percentage of the exhaust flow exiting the combustor relative to the total combustor exhaust flow;
the model formula of the efficiency reduction of the fan in the peripheral auxiliary equipment fault evolution mechanism modeling is as follows:
ηblower,fault=(1-αblower,fault)ηblower,0
wherein etablower,faultAnd ηblower,0The mechanical efficiency of the fan, alpha, in fault and normal states, respectivelyblower,faultRepresents the ratio of the reduced portion of the mechanical efficiency of the fan to the initial mechanical efficiency of the fan.
Further, the method is characterized by further comprising the steps of building a Stateflow module for integrating performance attenuation and fault evolution logic of the solid oxide fuel cell system, wherein the fault triggering condition is realized by Stateflow event triggering logic, a fault is triggered by a preset step signal, and corresponding fault parameters are transmitted to a fault point to form a new system operation state; and a parallel structure is adopted among different faults.
Further, the step (4) is specifically characterized by:
after experimental data are imported into a multi-modal analysis model of the solid oxide fuel cell system, firstly, temperature parameters are debugged, so that the error between simulation results of the average temperature of the galvanic pile and the temperature of the combustion chamber and the experimental data is not larger than a preset value, then, the average error of the voltage of the cell is reduced by adjusting the attenuation parameters of the electrical characteristics, and when the errors of the average temperature of the galvanic pile, the temperature of the combustion chamber and the average voltage of the cell are in a preset range, the parameters are the result of parameter identification of the multi-modal analysis model.
Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:
(1) compared with the prior art, the method provided by the invention has the advantages that due to the consideration of the influence of a performance attenuation and fault evolution mechanism in the actual operation of the SOFC system, the corresponding performance attenuation and fault evolution submodel is established and added into the system initial state mechanism model, so that the timely prediction, identification and processing of related attenuation and fault events in the long-term operation of the SOFC system are possible, the long-term service life of the SOFC system is effectively prolonged, and the system maintenance cost is reduced;
(2) compared with the existing model, the SOFC system multi-modal analysis model built by the method considers the performance attenuation mechanisms of cathode connector oxidation and the like in the long-term operation process of the SOFC, and establishes a corresponding attenuation mechanism model aiming at the performance attenuation mechanisms, so that the operation mechanism of the built SOFC system analysis model is more similar to the actual operation condition of the system, the error between the simulation result of the model and the experiment result is greatly reduced, the accuracy of the SOFC system analysis model is improved, and great help is provided for researching the influence of the performance attenuation mechanism of the SOFC system pile on the long-term operation of the whole system;
(3) compared with the existing model, the SOFC system multi-modal analysis model established by the method considers the performance attenuation mechanism of peripheral auxiliary equipment of the SOFC system mainly based on a reformer and establishes a corresponding attenuation mechanism model aiming at the peripheral auxiliary equipment, so that the method ensures that the operation mechanism of the established SOFC system model is closer to the actual operation condition of the system, further reduces the error of the simulation result and the experimental result of the model, improves the accuracy and the reliability of the SOFC system model and lays a foundation for further researching the influence of the performance attenuation mechanism of the peripheral auxiliary equipment on the working condition of the whole system;
(4) compared with the existing model, the SOFC system multi-modal analysis model established by the method considers the fault mechanism of the electric pile mainly based on air leakage at the anode inlet of the electric pile and battery rupture, and establishes a corresponding fault mechanism model aiming at the fault mechanism, so that the method realizes the fault mechanism which possibly occurs to the electric pile when the SOFC system actually operates, and provides great help for further researching the operation state of the system after the electric pile generates faults;
(5) compared with the existing model, the SOFC system multi-modal analysis model established by the method considers the failure mechanisms of peripheral auxiliary equipment of the SOFC system, such as reformer carbon deposition, heat exchanger flue gas inlet air leakage, combustion chamber air leakage, fan mechanical efficiency reduction and the like, and establishes a corresponding failure mechanism model aiming at the failure mechanisms, so that the method realizes the simulation of the failure mechanism of the peripheral auxiliary equipment possibly generated when the SOFC system is actually operated, and provides great help for further researching the influence of the failure generated by the peripheral auxiliary equipment on the overall operation state of the system.
Drawings
FIG. 1 is a schematic flow diagram of the process of the present invention;
FIG. 2 is a block diagram of a steam externally reforming SOFC system;
FIG. 3 is a specific structural diagram of a steam externally reforming SOFC in accordance with a preferred embodiment of the present invention;
fig. 4 is a verification graph of the model simulation result and the experimental result of the average voltage of the SOFC system cell;
FIG. 5 is a verification graph of model simulation results and experimental results of the SOFC system stack average temperature;
fig. 6 is a verification graph of model simulation results and experimental results of SOFC system combustor temperature.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention provides a solid oxide fuel cell system multi-modal analysis model modeling method based on performance attenuation and fault evolution mechanisms, which specifically comprises the following steps as shown in figure 1:
(1) establishing a system initial state mechanism model according to the working mechanism of the solid oxide fuel cell system;
(2) analyzing a performance attenuation and fault evolution mechanism of the solid oxide fuel cell system, and establishing a performance attenuation model and a fault evolution mechanism model of the solid oxide fuel cell system by a mechanism analysis identification and physical equivalent method;
(3) embedding the performance attenuation model and the fault evolution mechanism model into an initial state mechanism model of the solid oxide fuel cell system to construct a multi-mode analysis model of the solid oxide fuel cell system;
(4) and importing experimental data of the solid oxide fuel cell system into the multi-modal analysis model to identify parameters of the multi-modal analysis model.
Fig. 2 is a block diagram of a typical steam externally reforming solid oxide fuel cell standalone power generation system, which is a typical solid oxide fuel cell system, wherein:
the steam external reforming SOFC mainly comprises an SOFC galvanic pile, a reformer (with a heat exchange function), an air heat exchanger, a combustion chamber, a fan, a power converter and other parts. On the fuel side, deionized water is mixed with preheated methane after heat exchange and evaporation and enters a reformer to generate a reforming reaction (SR) and a water-gas displacement reaction (WGS);
SR:CH4+H2O→3H2+CO,Δh0=+206kJ/mol
WGS:CO+H2O→H2+CO2,Δh1=-41kJ/mol
the fuel is changed into reformed gas rich in hydrogen and carbon monoxide after passing through the reformer, and the reformed gas enters the anode of the pile; on the air side, cold air is preheated in the air heat exchanger through another path of high-temperature tail gas of the combustion chamber and then is led to the cathode of the electric pile.
Reformed gas and hot air respectively enter the galvanic pile and then generate electrochemical reaction to generate electric energy, and finally tail gas generated by the SOFC galvanic pile is led to a combustion chamber to supply heat for cold methane, deionized water and cold air. In addition, two bypass valves in the system supply additional methane and air to the combustor to better control the combustor temperature and meet actual system test requirements. The power converter converts the electric energy generated by the SOFC pile so that the load and the fan can work normally.
Fig. 2 is a specific structural diagram of a steam external reforming SOFC independent power generation system implementing an embodiment of the method of the present invention.
The initial state mechanism model of the SOFC system with the steam externally reformed is obtained by integrating main components (comprising an SOFC electric stack, a reformer, a heat exchanger, a combustion chamber, a fan and the like) according to the process flow of the system. The SOFC electric pile is a core component of the SOFC system, the electric pile and the heat exchanger model are one-dimensional submodels, and other subcomponents adopt lumped parameter models.
All subcomponent models are built according to the laws of mass conservation, material conservation and energy conservation, with some important modeling assumptions as follows: (1) all gases are ideal; (2) all cells in the stack are identical; (3) the steam reforming reaction and the water gas shift reaction proceed to an equilibrium state because the reaction reaches equilibrium conditions very quickly.
Further, a model of a performance attenuation mechanism of the SOFC system with steam external reforming is built. The performance decay mechanism modeling comprises two parts of stack performance decay mechanism modeling and reformer performance decay mechanism modeling.
The specific technical scheme of the modeling of the pile performance attenuation mechanism is as follows:
and (3) taking the experimental data of the SOFC system long-term test as the data support deduced by the galvanic pile performance attenuation mechanism, and processing and analyzing the long-term test data to obtain a modeling formula of the galvanic pile performance attenuation mechanism.
The SOFC pile performance attenuation mechanism mainly comprises pile cathode connector oxidation, anode nickel oxidation, physical deformation caused by thermal stress, anode nickel coarse knot, cathode particle coarse knot, microstructure change caused by diffusion and the like.
Here, only the modeling formula for the stack cathode interconnect oxidation decay mechanism is shown:
Ud(t)=0.001×exp(λt)=0.001×exp[(5.531×10-8Ts-5.274×10-5)t]
wherein the time unit is second, Ud(T) is the voltage of the cell stack at the time T, exp is an exponential function, lambda is a decay time constant, TsIs the average temperature of the stack and has the unit of K.
Next, reformer performance decay mechanism modeling is performed.
The reformer performance decay is reflected in that (at a fixed input) the reformer reaction rate decreases as it accumulates over time, so the reformer reaction rate can be constructed as a function of time, which is a gradual process similar to the stack performance decay, requiring long-term system test data as support, but the decay law is not identified by sufficient experimental data, where it is assumed that the reformer reaction rate is a linear function of time, and the expression is:
r(t)=r0(t)(1-rdrt)
where r (t) is the reaction rate at time t of the reformer, r0(t) is the reaction rate in the raw state at the same input as at time t, rdrIs the rate of decay of the reformer performance in%/kh (percent per thousand hours).
Further, the specific technical scheme for modeling the fault evolution mechanism of the steam external reforming SOFC system is as follows:
the SOFC system fault evolution mechanism modeling is divided into electric pile fault evolution mechanism modeling and peripheral auxiliary equipment fault evolution mechanism modeling.
The fault evolution mechanism of the electric pile comprises two types of air leakage at an anode inlet of the electric pile and battery rupture.
The stack anode inlet leak is represented in the system model by a portion of the fuel gas entering the stack leaking out of the stack, and the fuel gas entering the stack anode in the fault condition needs to be multiplied by a constant between 0 and 1, which can be expressed by the mathematical formula:
fanode,fault=(1-αanode,fault)fanode,0
wherein f isanode,faultAnd fanode,0Respectively representing the fuel flow at the anode inlet of the pile in a fault state and a normal state, alphaanode,faultRepresenting the percentage of the fuel flow that leaks out of the total fuel flow.
Cell rupture refers to the partial loss of the cell's ability to generate electromotive force, so the nernst voltage of the cell in a fault condition needs to be multiplied by a factor between 0 and 1:
ENernst,fault=(1-αNernst,fault)ENernst,0
wherein ENerns,t faulAnd ENernst,0Battery electromotive force, alpha, in fault and normal states, respectivelyNernst,faultIs the percentage of the cell rupture area to the total cell area.
And the peripheral auxiliary equipment fault evolution mechanism modeling considers four types of reformer carbon deposition, heat exchanger flue gas inlet air leakage, combustion chamber air leakage and fan mechanical efficiency reduction.
Reformer fouling is expressed in a system model as the catalyst active surface area being covered and losing catalytic ability, and the reformer reaction rate under a fault condition is multiplied by a coefficient between 0 and 1 on the original basis:
rcf,fault=(1-αcf,fault)rcf,0
wherein r iscf,faultAnd rcf,0The reaction rates of the reformer, alpha, in the fault state and in the normal state, respectivelycf,faultRepresenting the percentage of carbon deposit coverage over the active catalytic area over the total active catalytic area.
The gas leakage at the flue gas inlet of the heat exchanger is represented in a system model that a part of the tail gas of the combustion chamber entering the flue gas inlet of the heat exchanger leaks out of the heat exchanger, so that the tail gas of the combustion chamber entering the flue gas inlet of the heat exchanger in a fault state is multiplied by a coefficient between 0 and 1 on the original basis:
fhex,fault=(1-αhex,fault)fhex,0
wherein f ishex,faultAnd fhex,0Indicating the combustion chamber exhaust gas flow, alpha, of the heat exchanger flue gas inlet in fault and normal conditions, respectivelyhex,faultRepresenting the percentage of the flow of combustor tail gas exiting the heat exchanger flue gas inlet as a percentage of the total flow of combustor tail gas to the heat exchanger flue gas inlet.
The leakage of the combustion chamber is expressed in a system model that a part of the tail gas after the combustion chamber is fully combusted leaks out of the combustion chamber, so that the flow of the outlet tail gas of the combustion chamber in a fault state is multiplied by a coefficient between 0 and 1 on the original basis:
fburner,fault=(1-αburner,fault)fburner,0
wherein f isburner,faultAnd fburner,0The combustion chamber outlet exhaust gas flow, alpha, in fault and normal conditions, respectivelyburner,faultIndicating the percentage of exhaust flow exiting the combustor as a percentage of the total combustor exhaust flow.
The drop in fan efficiency is expressed in the system as a drop in efficiency of its electrical power to mechanical power, so the fan mechanical efficiency constant in the fault state is multiplied by a factor between 0 and 1 on an as-needed basis:
ηblower,fault=(1-αblower,fault)ηblower,0
wherein etablower,faultAnd ηblower,0The mechanical efficiency of the fan, alpha, in fault and normal states, respectivelyblower,faultRepresents the ratio of the reduced portion of the mechanical efficiency of the fan to the initial mechanical efficiency of the fan.
After the establishment of the Stateflow basic frame and the performance attenuation and fault evolution mechanism sub-model is completed, the two parts are embedded into the steam external reforming SOFC system initial state mechanism model.
Further, a multi-mode analysis model of the SOFC system based on performance attenuation and fault evolution mechanisms is established.
And finally, verifying the model by using the SOFC system long-term test data again, wherein the test duration of the SOFC system is 500 hours, and comparing and verifying the experimental results of three system key parameters of the cell average voltage, the cell stack average temperature and the combustion chamber temperature of the SOFC system with the model simulation result:
as shown in fig. 4, the results of the model simulation and the experimental results of the average voltage of the SOFC system cell are verified, and the results of the analysis by using the multi-modal analysis model of the present application conform to the actual voltage;
as shown in fig. 5, the results of the multi-modal analysis model analysis according to the present application are in accordance with the actual average temperature of the cell stack by verifying the model simulation results and the experimental results of the average temperature of the cell stack of the SOFC system;
as shown in fig. 6, the results of the model simulation and the experimental results of the SOFC system combustion chamber temperature are verified, and the results of the analysis by using the multi-modal analysis model of the present application conform to the actual combustion chamber temperature;
the experimental verification results show that the model output of three important state parameters, namely the average voltage of the battery, the average temperature of the galvanic pile and the temperature of the combustion chamber, in the multi-modal analysis model can be basically consistent with experimental data, so that the built SOFC system multi-modal analysis model based on the performance attenuation and fault evolution mechanism is reliable.
It will be appreciated by those skilled in the art that the foregoing is only a preferred embodiment of the invention, and is not intended to limit the invention, such that various modifications, equivalents and improvements may be made without departing from the spirit and scope of the invention.