A Fault Prediction Method for a Solid Oxide Fuel Cell Cogeneration System

Abstract

The invention discloses a fault prediction method for a combined heat and power system of a solid oxide fuel cell, belonging to the technical field of solid oxide fuel cells. The method includes the steps of: establishing finite element sub-models of each component according to the structural composition of the combined heat and power system of the solid fuel cell, and integrating them to form the combined heat and power system of the solid fuel cell, and simulating the system according to the normal operating conditions to obtain the output parameters under normal conditions; then establishing a fault model, simulating to obtain the output parameters of the system under different faults, comparing the output parameters under normal conditions with the output parameters under different fault conditions, and analyzing the changes generated by the system after a fault occurs; finally, predicting whether the system has a fault and the type of the fault according to the output parameters of the actual system. The invention uses a simulation method to simulate the relevant characteristics of the SOFC system after different faults occur, and can predict whether a fault occurs and the type of the fault according to the output parameters of the actual system.

Description

Technical Field

[0001] The present invention relates to the technical field of solid oxide fuel cells, and particularly to a method for predicting faults in a combined heat and power supply system of a solid oxide fuel cell. Background Art

[0002] A solid oxide fuel cell (SOFC for short) is an electrochemical power generation device that directly converts the chemical energy in fossil fuels into electrical energy under medium and high temperature conditions. Compared with traditional power generation methods based on combustion, the SOFC power generation technology eliminates the combustion process, is not restricted by the Carnot cycle and has no mechanical movement, thus greatly reducing noise pollution and environmental pollution, and improving the utilization efficiency of fossil fuels, and can achieve a fuel utilization efficiency of over 80%.

[0003] The structure of a solid oxide fuel cell is huge and its performance is complex. There are various coupling factors during the working process, and the coupling mechanism is complex. Moreover, the development cycle of SOFC is long and the cost of the stack is high, which affects the performance research of the combined heat and power supply system of a solid oxide fuel cell. During the use of the SOFC system, problems such as frequent startup and shutdown, multiple thermal cycles, and mechanical and chemical compatibility inside the SOFC stack under high temperature environment make the system inevitably tend to have faults and degradation over time, reducing the reliability and durability of the system and hindering the commercialization of the SOFC system. During the operation of the SOFC system, faults can occur at any position of the system at any time, but generally can be divided into two categories: faults of system peripheral devices and faults inside the stack, namely mainly pipeline faults, heat exchanger faults, reformer faults, electrode delamination faults, and external load faults, etc. By predicting the faults of the SOFC system, its health status can be understood in time. At present, the fault detection method of the SOFC system is usually to use machine learning methods to learn the collected historical data, build a fault prediction model, and then use this model to analyze the real-time collected status data for fault prediction. This method relies on a large amount of historical data, the acquisition time of historical data is long, and these historical data cannot cover all possible fault types, and the data is not comprehensive, resulting in the established fault prediction model being unable to predict all possible fault types. Based on this, a method for predicting faults in a combined heat and power supply system of a solid oxide fuel cell is proposed, which uses a simulation method to simulate the relevant characteristics of the SOFC system after different faults occur, saving the time and economic costs for the research of the SOFC system. Summary of the Invention

[0004] To solve the above technical problems, the present invention proposes a method for predicting faults in a combined heat and power supply system of a solid oxide fuel cell.

[0005] The present invention specifically adopts the following technical solutions:

[0006] A method for fault prediction of a solid oxide fuel cell combined heat and power supply system, comprising the steps of:

[0007] (1) According to the structural composition of the fuel cell combined heat and power supply system, finite element sub-models of the heat exchanger component, reformer component, combustion chamber component, SOFC stack component, and external load component are respectively established;

[0008] (2) According to the technological process of the fuel cell combined heat and power supply system, the finite element sub-models of each component in step (1) are used as different nodes to build a finite element model of the fuel cell combined heat and power supply system, and the model is debugged and corrected so that the difference between the output parameters of each node in the normal operating condition of the model and the output parameters of each node in the actual normal operating condition is within a preset range;

[0009] (3) Analyze the main fault types existing in the fuel cell combined heat and power supply system, and establish corresponding fault models respectively;

[0010] (4) Using the corrected finite element model of the fuel cell combined heat and power supply system in step (2), run one of the fault models in step (3) respectively to obtain the output parameters of each node under different fault types, and compare them with the output parameters of each node in the actual operating condition to analyze the influence of different fault types on the system operating state;

[0011] (5) According to the output parameters under the normal operating condition and different fault types, analyze and compare the output parameters of a fuel cell combined heat and power supply system in a certain actual operating condition to determine whether the system fails in this actual operating condition and determine the corresponding fault type.

[0012] Further, the main fault types existing in the fuel cell combined heat and power supply system in step (3) include: feed pipeline leakage fault, heat exchanger pipeline rupture fault, reformer carbon deposition fault, stack electrode delamination fault, and external load fault.

[0013] Further, the established feed pipeline leakage fault model in step (3) is:

[0014] ;

[0015] When simulating the air-side pipeline leakage fault, set: , ;

[0016] When simulating the fuel-side pipeline leakage fault, set: , ;

[0017] When simulating the simultaneous leakage faults of the fuel-side and air-side pipelines, the following are set: , ;

[0018] In the formula, is the gas flow rate at the outlet of the air-side pipeline, is the gas flow rate at the inlet of the air-side pipeline, is the gas flow rate at the outlet of the fuel-side pipeline, is the gas flow rate at the inlet of the fuel-side pipeline, is the gas leakage flow rate of the air-side pipeline, is the gas leakage flow rate of the fuel-side pipeline.

[0019] Furthermore, the heat exchanger pipeline rupture fault model established in step (3) is:

[0020] ;

[0021] In the formula, is the flow velocity of the fluid at the outlet of the heat exchanger, is the flow velocity of the fluid at the inlet of the heat exchanger, is the pressure at the outlet of the heat exchanger, is the pressure at the inlet of the heat exchanger, is the fault coefficient of the heat exchanger rupture fault, and .

[0022] Furthermore, when establishing the reformer fault model in step (3), it is modeled by reducing the reforming efficiency of the reformer.

[0023] Furthermore, when establishing the reformer fault model in step (3), the reforming efficiency of the reformer is reduced by reducing the reaction area of the reforming catalyst inside the reformer.

[0024] Furthermore, when establishing the fuel cell stack electrode delamination fault model in step (3), it is modeled by reducing the effective reaction area parameter between adjacent two layers.

[0025] Furthermore, when establishing the external load fault model in step (3), it is modeled by reducing the input current of the external load.

[0026] Furthermore, the output parameters in steps (2), (3), and (5) include temperature and / or pressure and / or flow rate.

[0027] Further, in step (4), when a leakage fault occurs in the feed pipeline, for a leakage in the fuel-side pipeline, the temperatures of the SOFC stack, reformer, and combustor decrease, and the output voltage of the SOFC stack decreases; for a leakage in the air-side pipeline, the temperatures of the SOFC stack, combustor, and reformer increase, and the output voltage of the SOFC stack increases; for simultaneous leakage in the fuel-side and air-side pipelines, it is judged according to the leakage degrees of the fuel-side and air-side pipelines. If the leakage degrees of the fuel-side and air-side pipelines are the same, the temperature of the SOFC stack will first decrease and then increase, the overall temperature will decrease, the temperature of the reformer will increase, the output voltage of the SOFC stack will first decrease and then increase, and the overall output voltage will decrease.

[0028] When a rupture fault occurs in the heat exchanger pipeline, for a rupture in the hot gas pipeline of the heat exchanger, the temperature of the SOFC stack decreases, and the output voltage of the SOFC stack decreases; for a rupture in the cold gas pipeline of the heat exchanger, the temperature of the SOFC stack continues to rise, and the output voltage of the SOFC stack increases; for simultaneous rupture of the hot gas and cold gas pipelines of the heat exchanger, local overcooling or overheating conditions occur in the heat exchanger.

[0029] When a carbon deposition fault occurs in the reformer, the output voltage of the SOFC stack decreases, the internal pressure of the reformer increases, and the local temperature of the reformer increases.

[0030] When an electrode delamination fault occurs, the output voltage of the SOFC stack decreases, and the temperatures of the SOFC stack and reformer fluctuate.

[0031] When an external load fault occurs, the input current is 0, the output voltage of the SOFC stack will rapidly rise to the open-circuit voltage, the temperature of the SOFC stack decreases, and the temperature of the reformer increases.

[0032] The present invention has the following beneficial effects:

[0033] (1) The present invention provides a method for fault prediction of a solid oxide fuel cell combined heat and power supply system. By using the simulation method to simulate the relevant characteristics of the SOFC system after different faults occur, it saves the time and economic costs for the research of the SOFC system. Moreover, based on this method, it is possible to predict whether a fault occurs and the type of fault according to the output parameters of the actual system, without the need to check and repair each component of the entire system.

[0034] (2) When establishing the finite element model of the combined heat and power supply system, the present invention first separately establishes the finite element sub-models of each component such as the heat exchanger, reformer, combustor, SOFC stack, and external load, and then integrates the finite element sub-models of each component according to the technological process to build the finite element model of the fuel cell combined heat and power supply system. The present invention adopts a modular modeling method to establish the combined heat and power supply system model. Each sub-model is independent, which not only facilitates the arbitrary addition or deletion of sub-models and the modification of the system model structure, but also the dynamic characteristics of the fluid can be observed at the inlets and outlets of each sub-model. Brief Description of the Drawings

[0035] Figure 1 is a flowchart of the present invention;

[0036] Figure 2 is a schematic structural diagram of a combined heat and power system of a solid oxide fuel cell established according to the present invention;

[0037] Figure 3 is a comparison graph of the simulation results and actual test results of the stack and reformer temperatures when an air-side pipeline failure occurs in the combined heat and power system of the solid oxide fuel cell of the present invention at the 100th minute. Among them, (a) is the comparison graph of the simulation results and actual test results of the stack temperature, and (b) is the comparison graph of the simulation results and experimental test results of the reformer temperature;

[0038] Figure 4 is a comparison graph of the simulation results and actual test results of the stack temperature, reformer temperature, and stack output voltage when an external load failure occurs and the input current becomes 0 in the combined heat and power system of the solid oxide fuel cell of the present invention at the 626th minute. Among them, (a) is the comparison graph of the simulation results and actual test results of the stack temperature, (b) is the comparison graph of the simulation results and actual test results of the reformer temperature, and (c) is the comparison graph of the simulation results and actual test results of the stack output voltage;

[0039] Figure 5 are the simulation results of the stack and reformer when a fuel-side pipeline leak occurs in the present invention. Among them, (a) are the simulation results of the stack and reformer temperatures, and (b) is the simulation result of the stack output voltage;

[0040] Figure 6 are the simulation results of the stack and reformer when both the fuel-side pipeline and the air-side pipeline leak in the present invention. (a) are the simulation results of the stack and reformer temperatures, and (b) is the simulation result of the stack output voltage;

[0041] Figure 7 are the simulation results of the stack when a heat pipe failure occurs in the heat exchanger of the present invention. (a) are the simulation results of the stack temperature and the air temperature at the cathode inlet of the stack, and (b) is the simulation result of the stack output voltage;

[0042] Figure 8 are the simulation results of the stack when a cold pipe failure occurs in the heat exchanger of the present invention. (a) are the simulation results of the stack temperature and the air temperature at the cathode inlet of the stack, and (b) is the simulation result of the stack output voltage;

[0043] Figure 9These are the simulation results of the reformer and the stack when a carbon deposition fault occurs in the present invention. (a) shows the simulation result of the internal pressure of the reformer, and (b) shows the simulation result of the output voltage of the stack;

[0044] Figure 10 These are the simulation results of the stack and the reformer when an electrode delamination fault occurs in the present invention. (a) shows the simulation result of the temperature of the stack and the reformer, and (b) shows the simulation result of the output voltage of the stack. Specific Embodiments

[0045] The following further describes the specific embodiments of the present invention in conjunction with the accompanying drawings and specific examples.

[0046] Refer to Figure 1 , this embodiment provides a method for predicting faults in a solid oxide fuel cell combined heat and power system, including the following steps:

[0047] (1) According to the structural composition of the fuel cell combined heat and power system, finite element sub-models of each component such as heat exchangers, reformers, combustion chambers, SOFC stacks, and external loads are respectively established;

[0048] (2) According to the technological process of the fuel cell combined heat and power system, the finite element sub-models of each component in step (1) are used as different nodes to build a finite element model of the fuel cell combined heat and power system. The model is debugged and corrected so that the difference between the output parameters of each node of the model and the output parameters of each node in the actual operating conditions is within a preset range. The output parameters include temperature, pressure, flow rate, and gas composition;

[0049] (3) Analyze the main fault types existing in the fuel cell combined heat and power system, and respectively establish corresponding fault models;

[0050] (4) Using the corrected finite element model of the fuel cell combined heat and power system in step (2), at least one of the fault models in step (3) is respectively run to obtain the output parameters of each node under different fault types, and compare them with the output parameters of each node in the actual operating conditions to analyze the influence of different fault types on the system operating state;

[0051] (5) According to the output parameters under normal operating conditions and when different fault types occur, analyze and compare the output parameters of a fuel cell combined heat and power system in a certain actual operating condition to determine whether a fault occurs in the system under this actual operating condition and determine the corresponding fault type.

[0052] Specifically, the establishment process of the finite element sub-models of each component in the above step (1) is as follows:

[0053] (11) According to the specific structure of each component in the fuel cell combined heat and power system, geometric models of each component are established;

[0054] (12) Establish the fluid control unit and solid control unit of each component by analyzing the mass and energy change laws before and after the fluid flows through each component; among them, the fluid control unit mainly involves the dynamic changes of the fluid velocity, mole fraction, and temperature, and the solid control unit mainly involves the dynamic changes of the temperature of the solid material;

[0055] (13) Integrate the fluid control unit and solid control unit of each component onto the corresponding geometric model to construct the finite element sub-model of each component.

[0056] Specifically, the main fault types existing in the fuel cell combined heat and power system in step (3) above include: feed pipe leakage fault, heat exchanger pipe rupture fault, reformer carbon deposition fault, fuel cell stack electrode delamination fault, external load fault, and the fault models corresponding to different fault types are as follows.

[0057] For the feed pipe leakage fault, the established feed pipe leakage fault model is:

[0058] ;

[0059] In the formula, is the gas flow rate at the outlet of the air-side pipe, is the gas flow rate at the inlet of the air-side pipe, is the gas flow rate at the outlet of the fuel-side pipe, is the gas flow rate at the inlet of the fuel-side pipe, is the gas leakage flow rate of the air-side pipe, is the gas leakage flow rate of the fuel-side pipe, and the reduced gas flow rates at the outlets of the air-side and fuel-side pipes during the simulation are respectively equal to the air-side gas leakage flow rate and the fuel-side gas leakage flow rate .

[0060] Specifically, during the simulation of the feed pipe leakage fault, the simulation is carried out by reducing the gas flow rates at the outlets of the air-side and fuel-side pipes, that is:

[0061] When simulating the air-side pipe leakage fault, set: , ;

[0062] When simulating the fuel-side pipe leakage fault, set: , ;

[0063] When simulating the simultaneous leakage fault of the fuel-side and air-side pipes, set: , .

[0064] For the heat exchanger pipe rupture fault, since the heat exchanger mainly uses the high-temperature exhaust gas discharged from the combustion chamber for heat exchange, the heat exchanger simulation model is designed with a multi-layer sleeve rotary structure, including a cold gas pipe and a hot gas pipe. The cold and hot fluids flow in opposite directions. The cold gas pipe is connected to the air-side pipe, and the hot gas pipe is connected to the high-temperature exhaust gas pipe. The high-temperature exhaust gas in the hot gas pipe exchanges heat with the air in the cold gas pipe. The heat exchanger fault model is divided into a cold gas pipe rupture model and a hot gas pipe rupture model. And when the heat exchanger ruptures, gas leaks, not only do the gas flow rate and velocity change, but the pressure also changes. Therefore, when establishing the heat exchanger pipe rupture fault model, two aspects of gas velocity and pressure are considered, and the occurrence of this fault is simulated by applying a fault coefficient to the velocity and pressure of the fluid at the inlet of the heat exchanger. This fault coefficient is the percentage of the leakage amount of the fluid in the total amount of the fluid at the inlet of the heat exchanger. The established heat exchanger pipe rupture fault model is as follows:

[0065] ;

[0066] In the formula, is the velocity of the fluid at the outlet of the heat exchanger, is the velocity of the fluid at the inlet of the heat exchanger, is the pressure at the outlet of the heat exchanger, is the pressure at the inlet of the heat exchanger, is the fault coefficient of the heat exchanger rupture fault, and .

[0067] Specifically, when simulating the heat exchanger pipe rupture fault, the simulation is carried out by adjusting the heat exchanger rupture fault coefficient and reducing the flow rate of the fluid at the outlet of the heat exchanger; specifically, if simulating the rupture of the cold gas pipe, the flow rate of the fluid at the outlet of the cold gas pipe is adjusted; if simulating the rupture of the hot gas pipe, the flow rate of the fluid at the outlet of the hot gas pipe is adjusted; if simulating the simultaneous rupture of the cold gas pipe and the hot gas pipe, the flow rates of the fluids at the outlets of the cold gas pipe and the hot gas pipe are adjusted simultaneously.

[0068] For the reformer fault, the performance degradation of the reformer is mainly due to the reduction of the reaction area of the reforming catalyst inside, which causes incomplete reforming reaction, resulting in the generation of carbon deposition in the reformer in addition to the normal reforming reaction to produce CO and H2, that is, occurs; for the reformer fault, the simulation is carried out by reducing the reforming efficiency of the reformer, specifically by reducing the reaction area of the reforming catalyst inside the reformer to reduce the reforming efficiency of the reformer.

[0069] For the stack electrode delamination fault, it will lead to increased activation loss and ohmic loss of the stack. The electrode is usually divided into an anode layer, an electrolyte layer, and a cathode layer. When there is a stack electrode delamination fault, the anode layer or cathode layer of the electrode separates from the electrolyte layer, resulting in a reduction in the effective conductive area. Therefore, modeling is carried out by reducing the effective reaction area parameter between adjacent layers, that is, reducing the effective reaction area parameter between the anode layer and the electrolyte layer or between the cathode layer and the electrolyte layer for simulation.

[0070] For the external load fault, simulation is carried out by reducing the input current of the external load.

[0071] By simulating each model, the following results are obtained:

[0072] When a feed pipeline leakage fault occurs, for the leakage of the fuel-side pipeline, the temperatures of the SOFC stack, reformer, and combustor decrease, and the output voltage of the SOFC stack decreases; for the leakage of the air-side pipeline, the temperatures of the SOFC stack, combustor, and reformer increase, and the output voltage of the SOFC stack increases; for the simultaneous leakage of the fuel-side and air-side pipelines, depending on the leakage degree (leakage rate) of the fuel-side and air-side pipelines, different effects will be produced for different leakage degrees. If the leakage degrees of the fuel-side and air-side pipelines are the same, the temperature of the SOFC stack will first decrease and then increase, the overall temperature will decrease, the temperature of the reformer will increase, the output voltage of the SOFC stack will first decrease and then increase, and the overall output voltage will decrease; if the air-side leakage is larger than the fuel-side leakage, the temperatures of the SOFC stack, reformer, and combustor will decrease, and the output voltage of the SOFC stack will decrease; conversely, the temperatures of the SOFC stack, combustor, and reformer will increase, and the output voltage of the SOFC stack will increase. However, in these two cases, the leakage amounts on the air-side and fuel-side are not large and the leakage degrees do not differ much. If the leakage amounts of the two are too large or the leakage degrees differ too much, obvious abnormal situations will occur;

[0073] When a heat exchanger pipeline rupture fault occurs, for the rupture of the hot gas pipeline of the heat exchanger, the temperature of the SOFC stack decreases and the output voltage decreases because the rupture of the hot gas pipeline of the heat exchanger will lead to insufficient heating of the cathode air and reduce the system energy utilization rate; for the rupture of the cold gas pipeline, the intake air volume of the cathode air decreases, the temperature of the stack continues to rise, the output voltage increases, and if it lasts for a long time, it will lead to the degradation of the stack performance and the instability of the output voltage; the simultaneous rupture of the hot gas and cold gas pipelines of the heat exchanger will cause the temperature control of the SOFC system to completely fail and the performance to decline sharply, and local overcooling or overheating conditions will occur in the heat exchanger;

[0074] When a reformer carbon deposition fault occurs, the reforming efficiency decreases, resulting in insufficient hydrogen supply, affecting the electrochemical reaction of the stack, and the output voltage decreases. It will also block the flow channels of the reformer, causing too high internal pressure and local overheating of the reformer;

[0075] When an electrode delamination fault occurs, the performance of the SOFC stack decreases, the output voltage decreases, and the temperatures of the SOFC stack and the reformer fluctuate.

[0076] When an external load fault occurs, the input current is 0, the output voltage of the stack will rapidly rise to the open-circuit voltage, the stack temperature drops, and the reformer temperature rises.

[0077] Referring to Figure 2 , in this embodiment, a typical solid oxide fuel cell combined heat and power system is constructed, which includes: a heat exchanger, a reformer, a combustion chamber, an SOFC stack, and an external load connected to the power output terminal of the SOFC. The fuel side pipeline and the deionized water pipeline are respectively connected to the fuel inlet and the steam inlet of the reformer, and the fuel and deionized water are preheated by a heater before entering the reformer. In the reformer, the mixed steam of fuel and deionized water undergoes a reforming reaction to generate reformed gas H2 and CO2; the reformed gas outlet of the reformer is connected to the anode gas inlet of the SOFC stack, and the air side pipeline is connected to the cathode gas inlet of the SOFC stack after passing through the heat exchanger. In the SOFC stack, the anode gas and the cathode gas react to output electrical energy, and at the same time, the unreacted gas (H2 and CO2) is discharged as tail gas; the stack tail gas outlet of the SOFC stack is connected to the combustion chamber and burns in the combustion chamber to generate high-temperature flue gas. A part of the high-temperature flue gas discharged from the combustion chamber is connected to the heat exchanger through a pipeline and is used to preheat the air transported by the air pipeline, and another part of the high-temperature flue gas is connected to the reformer through a pipeline and is used to provide heat for the reforming reaction of the reformer, and can also provide heat for heating the fuel and deionized water.

[0078] Based on the above solid oxide fuel cell combined heat and power system, in this embodiment, a finite element model of the SOFC system under normal operating conditions is first established and its accuracy is verified. Specifically:

[0079] In MATLAB / Simulink, finite element sub-models of components such as heat exchangers, reformers, combustion chambers, SOFC stacks, and external loads are established. According to the technological process of the fuel cell combined heat and power generation system, the finite element sub-models of each component are used as different nodes to build a finite element model of the fuel cell combined heat and power generation system. Then, the input parameter data under normal operating conditions are imported into this system finite element model, that is, the input natural gas flow rate is 8.2 L / min, the cathode air flow rate is 115 L / min, and the deionized water flow rate is 25 L / min. The actual output data under this normal operating condition are: the temperature of the SOFC stack is about 750 °C, the temperature of the reformer is 820 - 860 °C (the temperature fluctuates greatly during the actual operation of the reformer. In this embodiment, its temperature is set to 850 °C and simulated at this temperature), and the actual output voltage under a constant output current of 25 A is 60.4 V. Based on the imported input parameter data, the cathode air intake, fuel intake, and the exhaust speed of the tail gas of each component of the SOFC are adjusted so that the error between the simulated output data and the actual output data of this system finite element model is within the preset range, that is, to ensure that the error range of the temperature of each component, especially the temperature of the SOFC stack and the reformer, is within ±5 °C, more preferably within ±2 °C, and the error of the output voltage of the SOFC stack is within 0.5%. At this time, the established model is considered reasonable and accurate.

[0080] In the process of establishing the finite element sub-models of the above components, the finite element sub-models of each component are also dynamically simulated according to the normal operating conditions of the system, and the accuracy of each component model is verified, that is, to ensure that the error between the simulation results of the finite element sub-models of each component and the output data of each component under actual operating conditions is within the preset range, especially the error range of the temperature of the SOFC stack and the reformer is within ±5 °C, more preferably within ±2 °C, and the error of the output voltage of the SOFC stack is within 0.5%. If the output results of each component model have a large difference from the actual error when verifying the accuracy of each component, the structure of the corresponding component sub-model needs to be adjusted; after the finite element sub-models of each component are verified to be accurate, according to the technological process of the fuel cell combined heat and power generation system, the finite element sub-models of each component are used as different nodes to build a finite element model of the fuel cell combined heat and power generation system under normal operating conditions.

[0081] In addition, in the establishment of the finite element sub-model of the SOFC stack above, the edge effect of the SOFC stack is ignored. All single cells have exactly the same dynamic behavior, there is no influence between each single cell sheet, and the voltages output by each single cell sheet are accumulated to the total output voltage of the stack. The SOFC stack model is equivalent to a single cell model, and the electrical characteristic relationship of each node of the stack (i.e., the stack inlet, the stack outlet, and the inside of the stack) adopts a quasi-static electrochemical model; at the same time, it is set that the voltages of each node of the stack are equal, and the working voltage of a single cell is calculated using the Nernst equation, that is:

[0082] ;

[0083] Wherein, is the output voltage of the SOFC stack, is the Nernst voltage, , and are the ohmic loss, activation loss and concentration loss respectively. By comparing and debugging with the actual data, the error between it and the output value of the actual combined heat and power system is within the set value.

[0084] In this embodiment, the flow rate of the natural gas input is adjusted to 8.5 L / min, the flow rate of the cathode air is 115 L / min, the flow rate of the deionized water is 24.8 L / min, and the current set value is 25 A. The finite element model of the SOFC system built is run, and the output parameters under normal conditions are basically the same as those of the actual system. The output voltage is 60.40 V, the stack temperature is 749.80 °C, and the reformer temperature is 852.20 °C, indicating that the finite element model of the SOFC system established can accurately simulate the actual operating state. On this basis, according to the established fault models, the output parameters of each node of the system when different faults occur are simulated, and then combined with the output parameters under normal conditions and when each fault occurs and the actual operating results, the faults generated by the actual system can be quickly predicted.

[0085] In addition, when simulating the faults occurring in the actual system, since the output parameters of each node are also different during the actual operation of different systems, the model needs to be adjusted according to the actual operating conditions of the system, so as to better simulate the fault situation.

[0086] Taking the actual occurrence of an air-side pipeline fault in a certain system as an example, at the 100th minute, an air-side pipeline fault occurs. Before the fault, the air flow rate of the air-side pipeline is 119 L / min. At the 100th minute, the air flow rate drops to 113 L / min, and the air leakage rate is 6 L / min. After the leakage is discovered and processed in time, no great influence is produced. For this fault, when simulating on the Matlab / Simulink platform, the air flow rate is adjusted from 119 L / min to 113 L / min for simulation. As Figure 3 shown is the comparison diagram of the simulation results and the actual test results of the SOFC stack temperature and reformer temperature when an air-side pipeline fault occurs in the solid oxide fuel cell combined heat and power system at the 100th minute. From Figure 3It can be seen that when a fault occurs in the air-side pipeline, the temperature of the stack and the reformer increases, and the change trend of the simulation results is basically consistent with the actual results. In addition, for the simulation of air leakage in the air-side pipeline, during the actual simulation, the air leakage volume can be increased arbitrarily, and even completely leaked. However, when the leakage volume reaches a certain level, the system cannot operate normally. When the air flow rate is reduced to 100 L / min during the simulation, the temperature of the stack has reached about 850 °C after stabilization, which is 100 °C higher than the normal operating temperature. However, when the system actually operates, it will not wait until the temperature of the stack rises to 850 °C to detect problems and perform repairs.

[0087] Taking the actual occurrence of an external load fault in a certain system as an example, the input current suddenly changes to 0 A at the 626th minute of the external load, and recovers to 25 A at the 643rd minute. As Figure 4 shown is the comparison chart of the simulation results and the actual test results of the stack temperature, reformer temperature, and stack output voltage of the solid oxide fuel cell combined heat and power system when the external load fails and the input current becomes 0 at the 626th minute. From Figure 4 it can be seen that when an external load fault occurs, the temperature of the SOFC stack decreases, the temperature of the reformer increases, and the output voltage of the SOFC stack will quickly rise to the open-circuit voltage, and the change trend of the simulation results is basically consistent with the actual results.

[0088] The above comparison shows that when an air pipeline fault or an external load fault occurs during the operation of the solid oxide fuel cell combined heat and power system, it causes abnormal changes in the reformer temperature, stack temperature, or output voltage of the system. The simulation results of the solid oxide fuel cell combined heat and power system fault model built are basically consistent with the test data, which also shows that the solid oxide fuel cell combined heat and power system fault model built can accurately simulate various faults.

[0089] On this basis, other fault types are simulated, the output parameter changes of each node are analyzed and summarized. Specifically, for the fuel-side pipeline leakage, in this embodiment during the simulation, the fuel flow rate of 8.2 L / min during normal operation is adjusted to 7.3 L / min, and the simulation results are obtained as Figure 5 shown, Figure 5 which are the simulation results of the stack and the reformer when a fuel-side pipeline leakage occurs. From Figure 5It can be seen that when a fuel-side pipeline leakage fault occurs, the temperature of the fuel cell stack and the reformer decreases, and the output voltage of the fuel cell stack decreases; similar to the air-side pipeline leakage, during the actual simulation process, the fuel leakage amount can be increased arbitrarily, and even can be completely leaked, but when the leakage amount reaches a certain level, the system cannot operate normally. When the fuel amount is reduced to 6.3 L / min during the simulation process, the temperature of the reformer has dropped to about 780 °C, but in actual operation of the system, it will not wait until the temperature of the reformer drops to 780 °C to detect problems and perform maintenance;

[0090] For the simultaneous leakage of the fuel-side pipeline and the air-side pipeline, in this embodiment, during the simulation, the leakage amounts of the fuel-side pipeline and the air-side pipeline are set to 10% of the normal amount for simulation, and the simulation results are obtained as Figure 6 shown below. Figure 6 The simulation results of the fuel cell stack and the reformer when the fuel-side pipeline and the air-side pipeline leak simultaneously are shown in Figure 6 It can be seen that when simultaneous leakage occurs, the temperature of the SOFC fuel cell stack will first decrease and then increase, but the overall temperature decreases, while the temperature of the reformer increases. The output voltage of the SOFC fuel cell stack first decreases and then increases, but the overall output voltage decreases;

[0091] For the heat exchanger rupture fault, in this embodiment, during the simulation, the simulation is carried out by adjusting the fault coefficient of the heat exchanger fault, and the fault coefficient can take values from 0 to 1. However, in the actual simulation process, for the heat pipe fault of the heat exchanger, when the fault coefficient is 0.3, the output voltage of the SOFC fuel cell stack has dropped to about 20 V, and at this time the system can no longer operate normally; for the cold pipe fault of the heat exchanger, when the fault coefficient is 0.35, the temperature of the SOFC fuel cell stack has exceeded 1000 °C, and at this time the system can no longer operate normally; therefore, during the simulation process, it is preferably set that the fault coefficient of the heat exchanger fault takes values in the range of 0 - 0.3. In this embodiment, the fault coefficient when the heat pipe fault of the heat exchanger occurs is set to 0.15, and the fault coefficient when the cold pipe fault of the heat exchanger occurs is set to 0.2, and the simulation results are obtained as Figure 7 and Figure 8 shown below. Figure 7 The simulation results of the fuel cell stack when the heat pipe fault of the heat exchanger occurs are shown in Figure 7 It can be seen that both the temperature of the fuel cell stack and the air temperature at the cathode inlet of the fuel cell stack decrease, and the output voltage of the fuel cell stack decreases; Figure 8 The simulation results of the fuel cell stack when the cold pipe fault of the heat exchanger occurs are shown in Figure 8 It can be seen that both the temperature of the fuel cell stack and the air temperature at the cathode inlet of the fuel cell stack increase, and the output voltage of the fuel cell stack increases;

[0092] For the carbon deposition fault of the reformer, it is found in the simulation process that the carbon deposition fault of the reformer occurs slowly and gradually with the increase of the system operation time. It may take hundreds or even thousands of hours for carbon deposition to occur during actual operation. To study the reaction of the system after carbon deposition, the speed of carbon deposition of the reformer is accelerated in this embodiment. At the 2000s of the simulation, the reaction area of the reforming catalyst is reduced by 20% to cause carbon deposition in the reformer. The simulation results are obtained as shown in Figure 9 the following simulation results. Figure 9 The simulation results of the reformer and the stack when the carbon deposition fault of the reformer occurs. It can be seen from Figure 9 it that: the gas pressure at the reformer outlet increases, and the output voltage of the stack decreases;

[0093] For the electrode delamination fault of the stack, this embodiment simulates by reducing the effective reaction area between the anode layer and the electrolyte layer or the cathode layer and the electrolyte layer by 10%, and obtains the simulation results as shown in Figure 10 the following simulation results. Figure 10 The simulation results of the stack and the reformer when the electrode delamination fault occurs. It can be seen from Figure 10 it that: when the electrode delamination fault occurs, the temperatures of the stack and the reformer fluctuate, the temperature of the stack decreases, the temperature of the reformer increases, and the output voltage of the stack decreases.

[0094] By simulating different fault types, the variation rules of the output parameters of each component when different fault types occur can be summarized. During the actual operation of the solid oxide fuel cell combined heat and power system, the actual output parameters can be compared with those under normal operation conditions and different faults to determine whether the actual solid oxide fuel cell combined heat and power system has a fault and the type of the fault.

[0095] It should be noted that the parts not described in this embodiment are obtained by using the existing technology.

[0096] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for predicting faults in a solid oxide fuel cell cogeneration system, characterized in that: Includes steps: (1) According to the structural composition of the fuel cell cogeneration system, finite element sub-models of the heat exchanger components, reformer components, combustion chamber components, SOFC stack components, and external load components are established respectively; (2) According to the process flow of the fuel cell cogeneration system, the finite element sub-models of the components in step (1) are used as different nodes to build a finite element model of the fuel cell cogeneration system, and the model is debugged and corrected so that the difference between the output parameters of each node of the model under normal operating conditions and the output parameters of each node under actual normal operating conditions is within a preset range; (3) Analyze the main fault types existing in the fuel cell cogeneration system and establish corresponding fault models; (4) Using the finite element model of the fuel cell cogeneration system corrected in step (2), respectively running one of the fault models in step (3) to obtain output parameters of each node under different fault types, and comparing them with the output parameters of each node under actual operating conditions to analyze the impact of different fault types on the system operating state; (5) Analyze and compare the output parameters of a fuel cell cogeneration system under an actual operating condition based on the output parameters under normal operating conditions and when different fault types occur, determine whether a fault occurs in the system under the actual operating condition, and determine the corresponding fault type; The main types of faults in the fuel cell cogeneration system in step (3) include: feed pipeline leakage fault, heat exchanger pipeline rupture fault, reformer carbon deposition fault, stack electrode stratification fault, and external load fault; The feed pipeline leakage fault model established in step (3) is: ； When simulating the air side pipe leakage fault, set: , ; When simulating the fuel side pipeline leakage fault, set: , ; When simulating the simultaneous leakage of fuel and air side pipelines, set: , ; In the formula, is the gas flow rate at the air side pipeline outlet, is the gas flow rate at the air side pipeline inlet, is the gas flow rate at the outlet of the fuel side pipeline, is the gas flow rate at the fuel side pipeline inlet, is the gas leakage flow rate in the air side pipeline, is the gas leakage flow rate of the fuel side pipeline; The heat exchanger pipe rupture fault model established in step (3) is: ； In the formula, is the flow rate of the fluid at the heat exchanger outlet, is the flow rate of the fluid at the heat exchanger inlet, is the pressure at the heat exchanger outlet, is the pressure at the heat exchanger inlet, is the failure coefficient of heat exchanger rupture failure, and .

2. A method for predicting faults in a solid oxide fuel cell cogeneration system according to claim 1, characterized in that: When establishing the reformer fault model in step (3), the model is built by reducing the reforming efficiency of the reformer.

3. A method for predicting faults in a solid oxide fuel cell cogeneration system according to claim 2, characterized in that: When establishing the reformer fault model in step (3), the reforming efficiency of the reformer is reduced by reducing the reaction area of ​​the reforming catalyst inside the reformer.

4. A method for predicting faults in a solid oxide fuel cell combined heat and power system according to claim 1, characterized in that: When establishing the stack electrode delamination failure model in step (3), the model is built by reducing the effective reaction area parameter between two adjacent layers.

5. A method for predicting faults in a solid oxide fuel cell combined heat and power system according to claim 1, characterized in that: When establishing the external load fault model in step (3), the model is built by reducing the input current of the external load.

6. A method for predicting faults in a solid oxide fuel cell combined heat and power system according to claim 1, characterized in that: The output parameters in steps (2), (3) and (5) include temperature and / or pressure and / or flow.

7. A method for predicting faults in a solid oxide fuel cell combined heat and power system according to claim 1, characterized in that: In the step (4), when a feed pipeline leakage fault occurs, if the fuel side pipeline leaks, the temperature of the SOFC stack, the reformer, and the combustion chamber decreases, and the output voltage of the SOFC stack decreases; if the air side pipeline leaks, the temperature of the SOFC stack, the combustion chamber, and the reformer increases, and the output voltage of the SOFC stack increases; if the fuel side and air side pipelines leak at the same time, according to the leakage degree of the fuel side and air side pipelines, if the leakage degree of the fuel side and air side pipelines is the same, the SOFC stack will first decrease and then increase, the overall temperature will decrease, the reformer temperature will increase, the SOFC stack output voltage will first decrease and then increase, and the overall output voltage will decrease; When a heat exchanger pipe rupture occurs, if the heat exchanger hot gas pipe ruptures, the SOFC stack temperature drops and the SOFC stack output voltage decreases; if the heat exchanger cold gas pipe ruptures, the SOFC stack temperature continues to rise and the SOFC stack output voltage increases; if the heat exchanger hot gas and cold gas pipes rupture at the same time, the heat exchanger will produce local overcooling or overheating conditions; When a reformer carbon deposition failure occurs, the SOFC stack output voltage decreases, the internal pressure of the reformer increases, and the local temperature of the reformer increases; When a stack electrode stratification failure occurs, the SOFC stack output voltage decreases, and the SOFC stack temperature and reformer temperature fluctuate; When an external load fault occurs, the input current is 0, the output voltage of the SOFC stack will quickly rise to the open circuit voltage, the temperature of the SOFC stack will drop, and the temperature of the reformer will rise.

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