PEMFC-ORC-TEG coupling-based waste heat utilization system and coupling method

Abstract

The invention discloses a PEMFC (proton exchange membrane fuel cell)-ORC (organic Rankine cycle)-TEG (thermoelectric generator) coupling-based waste heat utilization system and a coupling method. A PEMFC module, an ORC module and a TEG module are coupled; the system comprises a fuel cell, a TEG assembly, a condenser, a delivery pump, a pressure pump, a cooling water storage tank, an evaporator, an expansion machine, a filter, a humidifier, an ejector, a compressor and an electromagnetic valve. Heat carried by cooling water in the PEMFC cooling system is used as a main energy source for waste heat recovery. As the heat taken away by the cooling water is far greater than the directly discharged waste heat, the cooling water has higher enthalpy value and excellent heat recovery potential. By constructing a reasonable heat recovery path and a heat exchange network, the waste heat gradient utilization efficiency can be remarkably improved, and the higher primary energy utilization rate is achieved. And efficient recovery and gradient utilization of the waste heat of the PEMFC are realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of waste heat utilization of proton exchange membrane fuel cells, and particularly relates to a waste heat utilization system and a coupling method based on PEMFC-ORC-TEG coupling. BACKGROUND

[0002] In recent years, with the continuous development of fuel cell technology, proton exchange membrane fuel cells are gradually widely used in distributed power generation, transportation power and standby power supply and other fields due to their rapid start, high efficiency, small pollution and other advantages. However, a large amount of waste heat is generated in the power generation process of PEMFC (proton exchange membrane fuel cell), and how to collect and utilize these waste heat has become a research hotspot today. The traditional waste heat utilization method mainly focuses on directly utilizing waste gas or cooling system waste heat for heat recovery, but due to the low temperature of the waste heat under actual working conditions and the single heat dissipation path, it is often difficult to fully tap the potential heat energy resources in the system.

[0003] Currently, there are studies that use ORC (organic Rankine cycle) technology to recover the waste heat of PEMFC. However, since the heat carried by the cooling water inside the PEMFC is significantly higher than that of other heat dissipation paths, directly utilizing the cooling water as a heat source has greater potential for heat energy recovery. At the same time, the single ORC cycle has a low energy utilization efficiency in the cross-temperature interval, and some systems attempt to combine TEG (thermoelectric generator) with ORC to realize joint work power generation, but the system has deficiencies in cooling water flow design and heat distribution, resulting in insufficient temperature difference and insufficient thermal parameter optimization between the TEG module and the ORC module, thereby affecting the overall heat recovery efficiency and causing key problems such as system parameter matching.

[0004] Therefore, it is urgent to develop a new type of coupling system to fully utilize the heat of the PEMFC cooling water, build a comprehensive waste heat recovery platform integrating ORC and TEG functions, and maximize the utilization potential of PEMFC waste heat in different temperature zones, and realize the maximization of system performance through reasonable parameter planning and sensitivity and optimization analysis. SUMMARY

[0005] The purpose of the present application is to provide a waste heat utilization system and a coupling method based on PEMFC-ORC-TEG coupling. The waste heat utilization system and the coupling method can effectively improve the utilization efficiency of PEMFC waste heat.

[0006] Technical solution: A waste heat utilization system based on PEMFC-ORC-TEG coupling, comprising a proton exchange membrane fuel cell PEMFC module, an organic Rankine cycle ORC module and a thermoelectric generator TEG module; the proton exchange membrane fuel cell PEMFC module comprises an anode gas inlet and outlet, a cathode gas inlet and outlet, a cooling water inlet and outlet, a compressor, a filter, a humidifier, an ejector and an electromagnetic valve; the organic Rankine cycle ORC module comprises a condenser, a delivery pump, a pressure pump, a cooling water tank, an evaporator and an expander; the thermoelectric generator TEG module comprises a TEG high-temperature end and a TEG low-temperature end;

[0007] The ejector and the anode gas inlet and outlet constitute an anode gas circulation loop.

[0008] The cooling water inlet and outlet, the TEG high-temperature end, the evaporator, the cooling water tank and the delivery pump constitute a cooling water circulation loop.

[0009] The two ends of the TEG low-temperature end are connected with the evaporator and the pressure pump respectively.

[0010] The proton exchange membrane fuel cell PEMFC module and the cooling water circulation loop are connected through the cooling water inlet and outlet.

[0011] The cooling water circulation loop and the organic Rankine cycle ORC module are connected through the evaporator.

[0012] The application also discloses a coupling method of the waste heat utilization system based on PEMFC-ORC-TEG coupling.

[0013] Step 1, constructing a waste heat utilization system comprising a proton exchange membrane fuel cell PEMFC, an organic Rankine cycle ORC and a thermoelectric generator TEG;

[0014] Step 2, modeling the proton exchange membrane fuel cell PEMFC based on activation loss, ohmic loss and concentration loss;

[0015] Step 3, modeling the organic Rankine cycle ORC;

[0016] Step 4, modeling the thermoelectric generator TEG;

[0017] Step 5, coupling the three models and specifying the key operating parameters of the system.

[0018] Further, step 2 is specifically:

[0019] A PEMFC theoretical model is established by a thermodynamic method, and the voltage loss is considered to be composed of activation loss, ohmic loss and concentration loss, and the single cell voltage calculation formula is as follows:

[0020] Ecell = E rev - E act - E ohm - E conc (1)

[0021] where E cell represents the PEMFC cell output voltage, E rev represents the Nernst voltage, E act represents the activation loss caused by reaction kinetics, E ohm represents the ohmic loss caused by ion and electron resistance, E conc represents the concentration loss caused by mass transport and concentration depletion;

[0022] where E rev can be calculated by the Nernst equation:

[0023]

[0024] where T is the PEMFC operating temperature, P H2 , P O2 are the partial pressures of hydrogen and oxygen, respectively.

[0025] Further, the calculation of the activation loss E act is through a semi-empirical formula:

[0026]

[0027] where ξ1 to ξ4 are empirical value coefficients, c o2,CL represents the oxygen concentration on the surface of the catalyst layer, which can be calculated by the Herry law:

[0028]

[0029] j represents the current density, which is calculated by the following formula:

[0030]

[0031] where I cell represents the cell current, A represents the effective area of the cell, N cell represents the number of cells, n H2 represents the hydrogen molar flow, β H2 represents the hydrogen excess coefficient, and F represents the Faraday constant.

[0032] Further, the ohmic loss E ohmis the voltage loss caused by charge transport, in PEMFC, the charged particles are electrons and ions, the transport of ionic charge is more difficult than that of electrons, the ionic charge not only has to overcome the transport resistance in the solution, but also has to overcome the transport resistance in the polymer electrolyte, and the conductivity of the proton membrane depends on the water content and temperature of the membrane; ohmic loss E ohm is calculated as follows:

[0033] E ohm = It m / σ m (6)

[0034]

[0035] σ 303K (λ) = 0.005193λ - 0.00326 (8)

[0036] The membrane resistance is calculated by a semi-empirical formula:

[0037]

[0038] In the formula, r m represents the specific resistivity of the hydrated proton flow, t m represents the thickness of the proton membrane, and r m can be obtained from an empirical formula:

[0039]

[0040] λ represents the water content of the proton membrane, which can be calculated by the water vapor activity a w :

[0041]

[0042] wherein P w represents the partial pressure of water, and P sat represents the saturated vapor pressure of water vapor.

[0043] Further, the concentration loss E conc is calculated based on an empirical formula:

[0044]

[0045] wherein c1 and c2 are empirical coefficients, respectively;

[0046] c2 = 2

[0047] wherein j L represents the limiting current density.

[0048] Further, step 3 is specifically: the expander does work by the push of the organic working fluid, while the pressurizing pump consumes extra electric energy to provide the energy of the pressurized organic working fluid, so

[0049] W ORC = W tur -W pump (15)

[0050] In the formula, W tur represents the work done by the expander, and W tump represents the work consumed by the pressurizing pump.

[0051] Further, step 4 is specifically: the high-temperature end and the low-temperature end of the TEG are the two ends of the TEG, and the modeling process is as follows:

[0052]

[0053] I teg = ψ (T tegh -T tegc ) / (R l + R0) (18)

[0054] R0= nγ PN L PN / A PN (19)

[0055]

[0056] In the formula, Q tegh and Q tegc are the heat absorbed by the hot side of the thermoelectric module and the heat transferred by the cold side of the thermoelectric module, respectively, W; n is the number of modules of the thermoelectric module; T tegh and T tegc are the temperatures of the hot side and the cold side of the thermoelectric module, K; I teg is the size of the thermoelectric current, A; K teg is the thermal conductivity of the thermoelectric module, W / (m·K); R0 is the internal resistance of the thermoelectric module, Ω·m; R1 is the external resistance, Ω·m; ψ is the Seebeck coefficient of the thermoelectric module, v / k; γ PN , L PN and A PN are the resistivity Ω·m, thickness m and area m 2 of the PN junction in the thermoelectric module, respectively; the internal resistance is equal to its external resistance when the thermoelectric power output is maximum.

[0057] Further, step 5 is specifically:

[0058] The PEMFC module's air circulation loop contains an air compressor, which consumes electrical energy to compress air during system operation. Therefore, in PEMFC modeling, the work done by the fuel cell is subtracted from the compressor's energy consumption, as follows:

[0059] W PEM =W cell -W comp (twenty one)

[0060] W comp The electrical energy consumed by the air compressor;

[0061] The work done by the fuel cell is:

[0062] W cell =N cell IE cell (twenty two)

[0063] E cell Where I is the single-cell voltage, N is the operating current, and N is the operating current. cell Fuel quantity;

[0064] The heat from TEG and ORC comes from the waste heat generated during the operation of the fuel cell;

[0065] Q heat =Q chem -W cell -Q flow (twenty three)

[0066] Q chem The heat generated by the chemical reaction in the fuel cell can be calculated using the following formula:

[0067] Q chem =N cell HHV (24)

[0068] In the formula, HHV represents the higher heating value of water produced by the reaction of hydrogen and oxygen;

[0069] Q flow The net heat entering and leaving the system can be calculated using the following formula:

[0070]

[0071] C H2 C O2 C H20 These represent the specific heats of hydrogen, oxygen, and water, respectively, and T represents the operating temperature. amb Indicates ambient temperature, n H2,OUT ,n H2,in ,n O2,OUT ,n O2,in n represents the inlet and outlet flow rates of hydrogen and oxygen, respectively.H2O,gen Q represents the amount of substance of the water generated.

[0072] In summary, the total power of the system can be represented by the following formula:

[0073] W all = W PEM + W ORC + W TEG = W cell - W comp + W tur - W pump + W TEG (26)

[0074] The total efficiency of the system can be represented by the following formula:

[0075]

[0076] The PEMFC module power can be represented by the following formula:

[0077]

[0078] The ORC module power can be represented by the following formula:

[0079]

[0080] Wherein Q C represents the amount of fuel cell waste heat.

[0081] Further, the coupling method is carried out by Aspen Plus software.

[0082] Beneficial effects: compared with the prior art, the present application has the following remarkable advantages:

[0083] The PEMFC-ORC-TEG coupling system of the present application can make the cooling water bring the preheating of the fuel cell system to the ORC-TEG system, effectively utilize the waste heat of the PEMFC, realize the cooling water circulation, heat recovery, TEG temperature difference generation and evaporation of the organic working medium in the Rankine cycle by constructing the loop connecting the PEMFC cooling water and the high temperature end of the TEG, the Rankine cycle evaporator, the cooling water tank and the circulating pump; by constructing the loop connecting the evaporator, the expander, the condenser, the pressurizing pump and the low temperature end of the TEG, the organic working medium can be made to work through the Rankine cycle and the low temperature end of the TEG can release heat to preheat the organic working medium; by constructing the loop of the filter, the compressor and the humidifier, the thermal properties of the air required by the cathode can be realized; the electromagnetic valve can control the anode hydrogen gas inlet to realize the start and stop of the whole system.

[0084] The system mainly utilizes the heat carried by the cooling water in the PEMFC cooling system as the main energy source of waste heat recovery. Since the heat carried by the cooling water during the operation of the PEMFC is much greater than the directly discharged waste heat, the cooling water has a high enthalpy value and excellent heat recovery potential. By constructing a reasonable heat recovery path and heat exchange network, the waste heat cascade utilization efficiency can be significantly improved, and higher primary energy utilization rate can be realized.

[0085] Unlike the traditional PEMFC-ORC system, the system introduces a TEG high-temperature end module in the cooling water flow path. The cooling water first releases part of the waste heat through the TEG high-temperature side, and then enters the evaporator of the ORC system for further heat exchange, realizing multi-stage energy cascade recovery. In addition, the system innovatively designs an efficient cooling water-ORC working fluid heat exchange network. In this network, the ORC working fluid is preheated by the TEG low-temperature end heat exchanger during the pumping process, so that its temperature gradient rises. This design not only optimizes the working fluid supercooling degree, but also forms a clear temperature gradient at the TEG cold end, thereby enhancing the TEG module's Seebeck effect and improving the overall system's power generation capacity.

[0086] Through the above technical solutions, the present application can fully exploit the potential heat energy resources in the PEMFC cooling water, utilize the TEG module to realize temperature difference direct power generation, and simultaneously utilize the ORC cycle to realize energy cascade conversion in different temperature zones, thereby greatly improving the overall energy utilization efficiency of the system. In addition, the present system has good heat matching in the cooling water flow path and heat exchange network design, which can effectively reduce the irreversible heat loss and provide technical support for waste heat utilization.

[0087] The present application designs a waste heat utilization system based on a proton exchange membrane fuel cell (PEMFC)-organic Rankine cycle (ORC)-thermoelectric power generation (TEG) coupling. The system realizes efficient recovery and cascade utilization of PEMFC waste heat by reasonably configuring the cooling water circulation, ORC working fluid circulation and TEG temperature difference power generation module. Through the heat transfer mode of the cooling water passing through the TEG high-temperature end and the ORC evaporator in sequence, the overall energy utilization efficiency of the system is improved, the heat exchange network is optimized, and the irreversible loss is reduced. In addition, the present application uses Aspen Plus optimization analysis to regulate and control the key operating parameters, simulates according to the parameters designed by the present application, and obtains a series of results consistent with the actual operating conditions, thereby providing an innovative solution for fuel cell waste heat utilization. BRIEF DESCRIPTION OF DRAWINGS

[0088] Figure 1It is a structural schematic diagram of the PEMFC-ORC-TEG waste heat utilization coupling system of the application; in the diagram, hydrogen flow 1, electromagnetic valve 2, fuel cell 3, air flow 4, filter 5, compressor 6, humidifier 7, TEG high-temperature end 8, evaporator 9, cooling water storage tank 10, circulating pump 11, expander 12, condenser 13, pressurizing pump 14, TEG low-temperature end 15, ejector 16.

[0089] Figure 2 It is an Aspen Plus modeling screen of the application; in the diagram, PEMFC module 1, ORC-TEG coupling module 2, Fortran language calculator module 3.

[0090] Figure 3 It is the influence of the evaporator cold flow outlet temperature, the TEG low-temperature end outlet temperature and the TEG high-temperature end outlet temperature in the system on the total output power of the system in a reasonable interval;

[0091] Figure 4 It is the influence of the evaporator cold flow outlet temperature in the system on the PEMFC efficiency, the ORC efficiency and the total efficiency of the system;

[0092] Figure 5 It is the influence of the TEG low-temperature end outlet temperature on the PEMFC efficiency, the ORC efficiency and the total efficiency of the system;

[0093] Figure 6 It is the influence of the TEG high-temperature end outlet temperature on the PEMFC efficiency, the ORC efficiency and the total efficiency of the system. DETAILED DESCRIPTION

[0094] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0095] As shown in Figure 1 the PEMFC-ORC-TEG waste heat utilization coupling system of the embodiment of the application includes hydrogen flow 1, electromagnetic valve 2, fuel cell 3, air flow 4, filter 5, compressor 6, humidifier 7, TEG high-temperature end 8, evaporator 9, cooling water storage tank 10, circulating pump 11, expander 12, condenser 13, pressurizing pump 14, TEG low-temperature end 15, ejector 16.

[0096] Wherein hydrogen stream 1, solenoid valve 2, fuel cell 3 and ejector constitute the anode hydrogen circulation loop, hydrogen stream is input into the system at a certain flow rate, temperature and pressure, and is input into the fuel cell anode through the start-stop action of the solenoid valve, and a certain amount of hydrogen will not participate in the reaction after the reaction, so a ejector is arranged to send the remaining hydrogen back to the hydrogen inlet to continue to participate in the reaction, realizing efficient circulation; wherein air stream 4, filter 5, compressor 6, humidifier 7 and fuel cell 3 constitute the cathode air circulation loop, air stream is input into the system at a certain flow rate, temperature and pressure, and the thermal physical properties of the air reach the standard of the PEMFC cathode gas after being pressurized by the compressor and humidified by the humidifier, and a certain amount of liquid water is generated after the reaction, and the liquid water is filtered out after being generated, and then is input into the PEMFC cathode gas inlet after being pressurized and humidified, realizing efficient circulation of the cathode gas; wherein TEG high-temperature end 8, evaporator 9, cooling water storage tank 10, circulating pump 11 and fuel cell 3 constitute the cooling water circulation loop, the cooling water brings the heat dissipation of the PEMFC system into the cooling water circulation system, and is preliminarily heat-exchanged with the TEG high-temperature end, the TEG high-temperature end is heated and the cooling water releases heat and is cooled, the cooling water is then heat-exchanged with the working medium of the ORC cycle through the evaporator, the working medium of the ORC cycle absorbs heat and evaporates, and the cooling water releases heat again and is cooled, and finally the cooling water without heat dissipation capacity is input into the cooling water storage tank, and is input back into the PEMFC cooling water inlet through the action of the circulating pump; wherein the evaporator 9, the expander 12, the condenser 13, the pressurizing pump 14 and the TEG low-temperature end 15 constitute the circulation loop of the ORC working medium, the ORC working medium is input from the pump inlet, is pressurized to a certain pressure by the pump, is heat-exchanged with the low-temperature end of the TEG, the low-temperature end of the TEG releases heat and is cooled, and the ORC working medium is heated and is heated, so that the temperature difference between the low-temperature end and the high-temperature end is realized to promote the TEG temperature difference power generation, effectively supplement the system power generation capacity, also realize the preheating of the ORC working medium before entering the evaporator, optimize the heat absorption process and the enthalpy rise process of the working medium, reduce the irreversible loss, then the ORC working medium is input into the evaporator and heat-exchanged with the cooling water, the ORC working medium evaporates into gas in the evaporator, then enters the expander to expand and do work, and after doing work, enters the condenser to release heat and become liquid, realizes heat recovery energy, and returns to the pressurizing pump for circulation.

[0097] According to the above system working process principle, the system modeling based on Aspen Plus is designed, and the PEMFC module, the ORC module and the TEG module are modeled respectively, and the modules are integrated to form the system.

[0098] PEMFC model

[0099] When PEMFC works, various voltage losses will inevitably occur due to the reaction kinetics, ohmic resistance of proton membrane and electrode materials, and depletion of catalyst layer concentration. Different losses have different effects on the actual output voltage of PEMFC. In this paper, a theoretical model of PEMFC is established by thermodynamic method, and the voltage loss is considered to be composed of three parts: activation loss, ohmic loss, and concentration loss. The formula for calculating the voltage of single cell is as follows:

[0100] E cell =E rev -E act -E ohm -E conc (1)

[0101] where E cell represents the output voltage of single cell, E rev represents the Nernst voltage, E act represents the activation loss caused by reaction kinetics, E ohm represents the ohmic loss caused by ion and electron resistance, and E conc represents the concentration loss caused by mass transfer and concentration depletion. Among them, E rev can be calculated by Nernst equation:

[0102]

[0103] where T is the working temperature of PEMFC, P H2 and P O2 are the partial pressures of hydrogen and oxygen, respectively.

[0104] The semi-empirical formula is commonly used to calculate the activation loss:

[0105]

[0106] where ξ1 to ξ4 represent empirical coefficients, c o2,CL represents the oxygen concentration on the surface of catalyst layer, which can be calculated by Herry's law:

[0107]

[0108] j represents the current density, which can be calculated by the following formula:

[0109]

[0110] where I cell represents the current of single cell, A represents the effective area of single cell, N cell represents the number of cells, n H2 represents the molar flow of hydrogen, β H2 represents the excess coefficient of hydrogen, and F represents the Faraday constant.

[0111] Ohmic loss E ohm is the voltage loss caused by charge transport, in PEMFC, the charged particles are mainly electrons and ions, the transport of ionic charge is more difficult than that of electrons, the ionic charge not only has to overcome the transport resistance in the solution, but also has to overcome the transport resistance in the polymer electrolyte, and the conductivity of the proton membrane mainly depends on the water content and temperature of the membrane.

[0112] E ohm = It m / σ m (6)

[0113]

[0114] σ 303K (λ) = 0.005193λ - 0.00326 (8)

[0115] The membrane resistance can be calculated by a semi-empirical formula:

[0116]

[0117] In the formula, r m represents the specific resistivity of the hydrated proton flow, t m represents the thickness of the proton membrane. r m can be obtained by an empirical formula:

[0118]

[0119] λ represents the water content of the proton membrane, which can be calculated by the water vapor activity a w

[0120]

[0121] wherein P w represents the partial pressure of water, and P sat represents the saturated vapor pressure of water vapor.

[0122] The concentration loss of PEMFC is usually calculated based on an empirical formula:

[0123]

[0124] wherein c1 and c2 are empirical coefficients.

[0125]

[0126] wherein j L represents the limiting current density.

[0127] ORC model ​

[0128] The Figure 1 The pressurizing pump 14 and the expander 12 in the middle are the main working units and the power consuming units of the ORC. The expander works by the pushing of the organic working fluid, while the pressurizing pump needs extra electric power to provide the energy of the pressurized organic working fluid.

[0129] W ORC = W tur -W pump (15)

[0130] In the formula, W tur represents the work done by the expander, and W tump represents the work consumed by the pressurizing pump.

[0131] TEG model

[0132] TEG power generation is a technology based on the Seebeck effect that can directly convert thermal energy into electrical energy. The Figure 1 The TEG high-temperature end 8 and the TEG low-temperature end 15 are the two ends of the TEG. The modeling process is as follows:

[0133]

[0134] I teg = ψ (T tegh -T tegc ) / (R l + R0) (18)

[0135] R0= nγ PN L PN / A PN (19)

[0136]

[0137] In the formula, Q tegh and Q tegc are the heat absorbed by the hot side of the thermoelectric module and the heat transferred by the cold side of the thermoelectric module, respectively, W; n is the number of modules of the thermoelectric module; T tegh and T tegc are the temperatures of the hot side and the cold side of the thermoelectric module, K; I teg is the size of the thermoelectric current, A; K teg is the thermal conductivity of the thermoelectric module, W / (m·K); R0 is the internal resistance of the thermoelectric module, Ω·m; R1 is the external resistance, Ω·m; ψ is the Seebeck coefficient of the thermoelectric module, v / k; γ PN , L PN and A PN are the resistivity (Ω·m), thickness (m) and area (m 2 ) of the PN junction in the thermoelectric module, respectively. Generally, when the thermoelectric power output is maximum, the internal resistance is equal to its external resistance.

[0138] Model coupling

[0139] According to the accompanying Figure 1 The PEMFC module air circulation loop shown in Figure 1 has an air compressor 6, which consumes electrical energy to compress air when the system is working, so in the PEMFC modeling, the work done by the fuel cell should be subtracted by the energy consumption of the compressor, such as:

[0140] W PEM = W cell -W comp (21)

[0141] W comp is the electrical energy consumed by the air compressor 6, W

[0142] Where the work done by the fuel cell is:

[0143] W cell = N cell IE cell (22)

[0144] E cell is the single cell voltage, I is the working current, N cell is the fuel quantity.

[0145] As described in the detailed description, the heat of the TEG and ORC comes from the waste heat of the fuel cell working.

[0146] Q heat = Q chem -W cell -Q flow (23)

[0147] Where Q chem is the heat generated by the chemical reaction of the fuel cell, which can be calculated by the following formula:

[0148] Q chem = N cell HHV (24)

[0149] In the formula, HHV represents the high heat value of hydrogen and oxygen reacting to generate water.

[0150] Where Q flow represents the net heat into and out of the system, which can be calculated by the following formula:

[0151]

[0152] C H2 , C O2 , C H20 respectively represent the specific heat of hydrogen, oxygen and water, T represents the working temperature, T ambIndicates ambient temperature, n H2,OUT ,n H2,in, n O2,OUT, n O2,in n represents the inlet and outlet flow rates of hydrogen and oxygen, respectively. H2O,gen This indicates the amount of substance that produces water.

[0153] In summary, the total power of the system can be expressed by the following formula:

[0154] W all =W PEM +W ORC +W TEG =W cell -W comp +W tur -W pump +W TEG (26)

[0155] The overall system efficiency can be expressed by the following formula:

[0156]

[0157] The power of the PEMFC module can be expressed by the following formula:

[0158]

[0159] The power of the ORC module can be expressed by the following formula:

[0160]

[0161] Q C This indicates the waste heat of the fuel cell.

[0162] Based on the above model, this invention combines the calculator function in Aspen Plus and compiles the model using the Fortran language, successfully establishing the system model. A diagram of the Aspen Plus interface modeling system is attached. Figure 2 As shown. Figure 2As shown in the middle, the system is divided into three parts, PEMFC feed and reaction zone, ORC-TEG coupling module and calculator. The function of PEMFC feed and reaction zone is to simulate the process of hydrogen and air entering the fuel cell for reaction, the ORC-TEG coupling module simulates the heat exchange process of organic working medium, TEG module and fuel cell cooling water, and the calculator is to specify the mathematical logic relationship in the system, such as specifying the fuel cell waste heat as the heat absorbed by the cooling water in the cooler, realizing the module function which Aspen Plus itself does not have. The invention combines Aspen Plus optimization module and thermodynamic theory analysis to develop key operating parameters such as evaporation temperature, condensation temperature, working medium pressure and heat exchange end temperature difference. Ensure that the system can realize stable and efficient energy conversion under different working conditions. The parameters are shown in Table 1.

[0163] Table 1

[0164]

[0165]

[0166] The net output power of the system constructed according to the above parameters is 54.5018kw.

[0167] In order to explore the influence of TEG low temperature end, TEG high temperature end and evaporator cold end outlet temperature on the overall system power, the invention uses Aspen Plus software to carry out sensitivity analysis and multi-parameter optimization on the system. By constructing a steady-state thermodynamic model, the influence of the above factors on the system power output and system efficiency is analyzed. The analysis results are shown in Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 .

[0168] As Figure 3 shown, the three curves respectively represent the change curves of the total power of the system with the outlet temperature of the TEG high temperature end, the outlet temperature of the TEG low temperature end and the outlet temperature of the evaporator cold stream. Among them, since the reasonable working temperature range of each needs to be considered, the three curves do not cover the same coordinates on the x-axis. The specific explanation is shown in Table 2. When each curve takes the respective horizontal coordinate as the independent variable, the other two variables are based on the description in Table 1. It can be seen that when the outlet temperature of the evaporator cold stream is above 62℃, the total power of the system remains at a certain value; when the outlet temperature of the TEG low temperature end is above 50℃, the total power of the system always shows an upward trend, and the change trend is more drastic before 51℃; when the outlet temperature of the TEG high temperature end is 67℃, the total power of the system reaches a maximum value, and before and after 67℃, the total power of the system will become smaller.

[0169] Table 2

[0170]

[0171] As Figure 4 shown, three curves are the PEMFC efficiency, ORC efficiency and total efficiency in the system with the evaporator cold stream outlet temperature variation curve. The system total efficiency is stable at about 42% between 62.5℃ and 69℃, the PEMFC efficiency is stable at about 38% between 62℃ and 69℃, and the ORC module efficiency is relatively low, stable at about 17% between 62℃ and 69℃; and the three maintain an upward trend before the temperature changes.

[0172] As Figure 5 shown, three curves are the PEMFC efficiency, ORC efficiency and total efficiency in the system with the TEG low temperature end outlet temperature variation curve. The total efficiency shows an upward trend between 50℃ and 51.5℃ and between 51.5℃ and 59℃, but the latter rises slowly; the PEMFC efficiency shows an upward trend between 50℃ and 51℃, and is stable at about 38% between 51℃ and 59℃; the ORC efficiency shows an upward trend between 50℃ and 51℃, and is stable at about 17% between 51℃ and 59℃.

[0173] As Figure 6 shown, three curves are the PEMFC efficiency, ORC efficiency and total efficiency in the system with the TEG high temperature end outlet temperature variation curve. The total efficiency shows an upward trend between 65.5℃ and 66.5℃, and a downward trend between 66.5℃ and 70℃, and the highest efficiency is about 46%; the PEMFC efficiency shows an upward trend between 65.5℃ and 66.5℃, and is stable at about 38% between 66.5℃ and 70℃; the ORC efficiency shows an upward trend between 65.5℃ and 66.5℃, and is stable at about 17% between 66.5℃ and 70℃.

[0174] In summary, the application designs a waste heat utilization system based on a proton exchange membrane fuel cell (PEMFC)-organic Rankine cycle (ORC)-thermoelectric power generation (TEG) coupling. The system realizes efficient recovery and cascade utilization of PEMFC waste heat by reasonably configuring cooling water circulation, ORC working fluid circulation and TEG thermoelectric power generation module. Through the heat transfer mode of cooling water through the TEG high temperature end and the ORC evaporator in turn, the overall energy utilization efficiency of the system is improved, the heat exchange network is optimized, and the irreversible loss is reduced. In addition, the application uses Aspen Plus optimization analysis to control the key operating parameters, simulates according to the parameters designed by the application, and obtains a series of results consistent with the actual operating conditions, providing an innovative solution for fuel cell waste heat utilization.

[0175] In the description of the application, the terms "first", "second", "third", etc. are used only for the purpose of description, and are not to be interpreted as indicating or implying relative importance or a specific order of the technical features indicated. Thus, features defined with "first", "second" or "third" can explicitly or implicitly include one or more of the features. The meaning of "a plurality" is two or more, unless otherwise explicitly specified and limited.

[0176] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting", "fixing" and the like should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrated; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0177] In the present application, unless otherwise explicitly specified and limited, the first feature is "on" or "under" the second feature, which can be direct contact between the first and second features, or indirect contact between the first and second features through intermediate medium. Moreover, the first feature "above", "over" and "on" the second feature can be directly above or obliquely above the first feature, or only indicate that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "under" and "under" the second feature can be directly below or obliquely below the first feature, or only indicate that the horizontal height of the first feature is less than that of the second feature.

[0178] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms is not necessarily for the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in the present application and the features of different embodiments or examples without contradiction.

[0179] It should be understood that parts of the present application can be implemented in hardware, software, firmware or a combination thereof. In the above embodiments, a plurality of steps or methods can be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, and as in another embodiment, it can be implemented using any or a combination of the following technologies, which are known in the art: discrete logic circuitry having logic gates for implementing logic functions on data signals, application specific integrated circuits having appropriate combinational logic gates, programmable gate arrays (PGA), field programmable gate arrays (FPGA), etc.

[0180] Those skilled in the art can understand that all or part of the steps carried out by the above-mentioned embodiment methods can be completed by programs instructing relevant hardware, and the programs can be stored in a computer readable storage medium, and when the programs are executed, one or a combination of the steps of the method embodiments is included.

[0181] In addition, each functional unit in each embodiment of the present application can be integrated into one processing module, or each unit can exist physically, or two or more units can be integrated into one module. The integrated module can be realized in the form of hardware or in the form of a software functional module. The integrated module, if realized in the form of a software functional module and sold or used as an independent product, can also be stored in a computer readable storage medium.

[0182] Although the embodiments of the present application have been shown and described above, it should be understood that the above-mentioned embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-mentioned embodiments within the scope of the present application.

Claims

1. A waste heat utilization system based on PEMFC-ORC-TEG coupling, characterized in that, The waste heat utilization system comprises a proton exchange membrane fuel cell (PEMFC) module, an organic Rankine cycle (ORC) module and a thermoelectric generator (TEG) module; the PEMFC module comprises an anode gas inlet and outlet, a cathode gas inlet and outlet, a cooling water inlet and outlet, a compressor, a filter, a humidifier, an ejector and an electromagnetic valve; the ORC module comprises a condenser, a delivery pump, a pressurizing pump, a cooling water tank, an evaporator and an expander; the TEG module comprises a TEG high-temperature end and a TEG low-temperature end; the ejector and the anode gas inlet and outlet constitute an anode gas circulation loop; the cooling water inlet and outlet, the TEG high-temperature end, the evaporator, the cooling water tank and the delivery pump constitute a cooling water circulation loop; two ends of the TEG low-temperature end are connected with the evaporator and the pressurizing pump respectively; the PEMFC module and the cooling water circulation loop are connected through the cooling water inlet and outlet; the cooling water circulation loop and the ORC module are connected through the evaporator.

2. A coupling method of a waste heat utilization system based on a PEMFC-ORC-TEG coupling, characterized in that, The waste heat utilization system comprises the following steps: Step 1, constructing a waste heat utilization system comprising a proton exchange membrane fuel cell (PEMFC), an organic Rankine cycle (ORC) and a thermoelectric generator (TEG); Step 2, modeling the PEMFC based on activation loss, ohmic loss and concentration loss; Step 3, modeling the ORC; Step 4, modeling the TEG; Step 5, coupling the three models and specifying key operating parameters of the system.

3. The coupling method of a waste heat utilization system based on a PEMFC-ORC-TEG coupling according to claim 1, characterized in that, Step 2 is specifically as follows: A theoretical model of the PEMFC is established by a thermodynamic method, and voltage loss is considered to be composed of activation loss, ohmic loss and concentration loss, and a calculation formula of single-cell voltage is as follows: E cell = E rev - E act - E ohm - E conc (1) where E cell represents the PEMFC cell output voltage, E rev represents the Nernst voltage, E act represents the activation loss due to reaction kinetics, E ohm represents the ohmic loss due to ion and electron resistance, E conc represents the concentration loss due to mass transport and concentration depletion; where E rev This can be calculated from the Nernst equation: where T is the PEMFC operating temperature, P H2 , P O2 are the partial pressures of hydrogen and oxygen, respectively.

4. The coupling method of a waste heat utilization system based on a PEMFC-ORC-TEG coupling according to claim 3, characterized in that, The activation loss E act is calculated by the semi-empirical formula: wherein ξ1to ξ4represent empirical value coefficients, c o2,CL represents the oxygen concentration at the surface of the catalytic layer, calculated from the Herry law: j represents current density, which is calculated by the following formula: In the formula, I cell represents the single cell current, A represents the single cell effective area, N cell represents the number of cells, n H2 represents the hydrogen molar flow, β H2 represents the hydrogen excess coefficient, F represents the Faraday constant.

5. The coupling method of a waste heat utilization system based on a PEMFC-ORC-TEG coupling according to claim 3, characterized in that, The ohmic loss E ohm is the voltage loss caused by charge transport, in PEMFC, the charged particles are electrons and ions, the transport of ionic charge is more difficult than that of electrons, the ionic charge not only has to overcome the transport resistance in the solution, but also has to overcome the transport resistance in the polymer electrolyte, and the conductivity of the proton membrane depends on the water content and temperature of the membrane; The ohmic loss E ohm is calculated as follows: E ohm = It m / σ m (6) σ 303K (λ) = 0.005193 λ - 0.00326 (8) membrane resistance is calculated by a semi-empirical formula: where r m represents the specific membrane resistance of the water-hydrated proton flow, t m represents the proton membrane thickness, r m may be obtained from an empirical formula: λ represents the proton membrane water content, which can be derived from the water vapor activity a w Calculation: where P w represents the partial pressure of water, P sat represents the saturated vapor pressure of water vapor.

6. The coupling method of a waste heat utilization system based on a PEMFC-ORC-TEG coupling according to claim 3, characterized in that, The concentration loss E conc The calculation is based on an empirical formula: wherein c1 and c2 are empirical coefficients; where j L represents the limiting current density.

7. The coupling method of a waste heat utilization system based on a PEMFC-ORC-TEG coupling according to claim 2, characterized in that, Step 3 is specifically as follows: the expander does work by driving the organic working medium, and the pressurizing pump consumes additional electric energy to provide energy of the pressurized organic working medium, so W ORC = W tur - W pump (15) where W tur represents work done by the expander, W tump represents work done by the expander, W 8. The coupling method of a waste heat utilization system based on a PEMFC-ORC-TEG coupling according to claim 2, characterized in that, Step 4 is specifically as follows: the TEG high-temperature end and the TEG low-temperature end are two ends of the TEG, and the modeling process is as follows: I teg = ψ(T tegh -T tegc ) / (R l + R0) (18) R0 = ny PN L PN / A PN (19) wherein Q tegh and Q tegc are the heat absorbed by the hot side and the heat transferred by the cold side of the thermoelectric module, respectively, W; n is the number of modules of the thermoelectric module; T tegh and T tegc are the temperatures of the hot side and the cold side of the thermoelectric module, K; I teg is the thermoelectric current, A; K teg is the thermal conductivity of the thermoelectric module, W / (m K); R0 is the internal resistance of the thermoelectric module, Ω m; R1 is the external resistance, Ω m; ψ is the Seebeck coefficient of the thermoelectric module, v / k; γ PN , L PN and A PN are the resistivity, thickness and area of the PN junction in the thermoelectric module, respectively, Ω m, m and m 2 ; the internal resistance is equal to its external resistance when the thermoelectric power output is maximum.

9. The coupling method of a waste heat utilization system based on a PEMFC-ORC-TEG coupling according to claim 2, characterized in that, Step 5 is specifically as follows: An air compressor exists in the air circulation loop of the PEMFC module, which consumes electric energy to compress air when the system works, so in the modeling of the PEMFC, work done by the fuel cell is reduced by the energy consumption of the compressor, i.e. W PEM = W cell - W comp (21) W comp for the electric energy consumed by the air compressor; wherein work done by the fuel cell is: W cell = N cell IE cell (22) E cell Vcell is the single cell voltage, I is the operating current, N cell is the fuel quantity; Heat of the TEG and the ORC is derived from waste heat of the fuel cell; Q heat = Q chem -W cell -Q flow (23) where Q chem is the heat generated by the chemical reaction of the fuel cell and can be calculated by the following equation: Q chem = N cell HHV (24) wherein HHV represents high heating value of hydrogen and oxygen reacting to generate water; where Q flow represents the net heat into or out of the system and can be calculated by the equation: C H2 , C O2 , C H20 represent the specific heat of hydrogen, oxygen and water, respectively, T represents the operating temperature, T amb represents the ambient temperature, n H2,OUT , n H2,in, n O2,OUT, n O2,in represent the hydrogen inlet and outlet flow rates and the oxygen inlet and outlet flow rates, respectively, n H2O,gen represents the amount of substance of the generated water; Work done by the ORC is represented as follows: W ORC = +W tur -W pump where W tur represents the work done by the expander, W pump represents the electrical energy consumed by the booster pump; The work done by the TEG module is the electrical energy produced by the TEG assembly, expressed in W TEG . In summary, total power of the system can be represented by the following formula: W all = W PEM + W ORC + W TEG = W cell - W comp + W tur - W pump + W TEG (26) Total efficiency of the system can be represented by the following formula: Power of the PEMFC module can be represented by the following formula: Power of the ORC module can be represented by the following formula: where Q C represents the amount of waste heat of the fuel cell.

10. The coupling method of a waste heat utilization system based on a PEMFC-ORC-TEG coupling according to claim 2, characterized in that, The coupling method is performed by Aspen Plus software.

Images