A reversible solid oxide battery thermal management method and system

Abstract

The present invention discloses a reversible solid oxide battery thermal management method and system, which belongs to the field of energy (hydrogen energy) conversion and storage in renewable energy. Taking into account the consistency of the gas flow rate of the fuel electrode loop, the present invention passes the fuel side tail gas into the evaporator for a second time, and uses the internal waste heat as an ideal heat source to vaporize liquid water, thereby replacing the evaporator with a water-gas heat exchanger. The relatively low-temperature exhaust gas flowing out of the evaporator causes less thermal stress on the condenser; in the air loop, the sub-high temperature air is recovered by a heat recovery unit, and the heat recovery unit can be a thermoelectric or thermo-thermal conversion device. In order to avoid the influence of continuous high temperature on the heat recovery unit, the present invention further adopts a phase change material based on latent heat storage to store heat. Experiments have shown that the present invention effectively guarantees the premise of thermal safety and achieves high system efficiency.

Description

Technical Field

[0001] The present invention belongs to the field of energy (hydrogen energy) conversion and storage in renewable energy, and more specifically, relates to a reversible solid oxide battery thermal management method and system. Background Art

[0002] Renewable energy sources are affected by various factors, including seasonality and weather, and exhibit intermittent and unstable characteristics. These factors prevent the sufficient absorption of excess energy generated during peak energy conversion periods. Conversely, when energy conversion efficiency decreases, grid demand cannot be met. Reversible solid oxide cell (rSOC) systems can operate in either fuel cell (SOFC) or electrolyzer (SOE) mode to balance the peaks and troughs of power generated by renewable energy grids. They are primarily used as a hub for energy conversion between renewable energy grids and gas grids. High-temperature rSOC systems face numerous thermal management challenges during operation. First, the thermal properties of SOE and SOFC modes are opposite. The water vapor reduction and hydrogen oxidation reactions are highly endothermic and exothermic. This necessitates the use of auxiliary heating components to meet heat absorption requirements during SOE operation, negatively impacting system efficiency. Furthermore, the significant amount of heat released by the SOFC mode remains unutilized. The rSOC system is based on only one set of BOP components to assist the stack in bidirectional operation. It includes many power-consuming components such as evaporators, pumps, heaters, and blowers. Especially when in SOE mode, water as the main raw material causes the evaporation power consumption generated by the evaporator to be very large, resulting in an electrolysis efficiency at a non-ideal level, which limits its industrialization process. In addition, the hot exhaust gas of the stack on the air side is directly discharged into the air after heat recovery through the heat exchanger. Due to the large air flow and high temperature in the air circuit, this will cause very high heat losses. This situation is more obvious in SOFC mode. Many factors have led to the rSOC system efficiency not meeting expectations, which has put higher requirements on the thermal management level design of the system.

[0003] At present, the development of rSOC system is still in its infancy, and the research on thermal management of rSOC at home and abroad is still at the most basic stage. Figure 1, and has not been properly considered in terms of the thermal management optimization of the system. The imperfect thermal management design in the rSOC system will cause efficiency loss of the system on the one hand, and high-temperature gases will endanger the safety of system components. For example, the sub-high-temperature exhaust gas of the fuel circuit directly enters the condenser for condensation after coming out of the heat exchanger. The strong hot and cold convection will put a great test on the material and structural properties of the condenser. The exhaust gas on the air side not only maintains a high temperature, but also has a much larger flow rate than the fuel side. However, most current solutions are to discharge it directly into the atmosphere, which causes the system's efficiency level to always fall short of expectations. Therefore, designing a reasonable thermal management method is crucial to improving system performance and stabilizing system safety, and also lays the foundation for the early industrial application of the rSOC system. Summary of the Invention

[0004] In response to the above defects or improvement needs of the prior art, the present invention provides a reversible solid oxide battery thermal management method and system, the purpose of which is to avoid heat loss in the system, improve system efficiency and stabilize system safety.

[0005] To achieve the above objectives, according to one aspect of the present invention, a reversible solid oxide battery thermal management method is provided, comprising:

[0006] S1. Collecting heat at the outlet of the air-side heat exchanger in the reversible solid oxide battery system;

[0007] S2. Use the collected heat as an auxiliary heat source to heat the gas at the inlet of the fuel cell stack or convert it into electricity and feed it into the power grid.

[0008] Furthermore, heat at the outlet of the air-side heat exchanger is collected by a phase change material heat storage device based on latent heat energy storage.

[0009] Furthermore, the method further includes:

[0010] Collect the stack exhaust gas discharged from the fuel side heat exchanger in the reversible solid oxide battery system;

[0011] The collected fuel cell tail gas is used as a heat source and passed into the evaporator to vaporize liquid water.

[0012] According to another aspect of the present invention, a reversible solid oxide battery thermal management system is provided, comprising: an air-side heat exchanger, a fuel-side heat exchanger, a heat recovery device, an evaporator, and a condenser;

[0013] The air-side heat exchanger inlet is connected to one side of the fuel cell stack and is used to collect the high-temperature exhaust gas generated by the fuel cell stack;

[0014] The heat recovery device is connected to the outlet of the air side heat exchanger and is used to collect heat at the outlet of the air side heat exchanger;

[0015] The inlet of the fuel-side heat exchanger is connected to the other side of the fuel cell stack, and is used to receive the heat output by the heat recovery device and the high-temperature gas generated by the fuel cell stack to heat the gas at the inlet of the fuel cell stack;

[0016] The evaporator inlet is connected to the outlet of the fuel side heat exchanger, and is used to vaporize liquid water using the heat of the fuel stack tail gas output by the fuel side heat exchanger;

[0017] The condenser is connected to the outlet of the evaporator and is used to discharge the low-temperature exhaust gas flowing out of the evaporator.

[0018] Furthermore, the heat recovery device adopts a phase change material based on latent heat energy storage.

[0019] The present invention also provides a reversible solid oxide battery thermal management system, comprising: an air-side heat exchanger, a fuel-side heat exchanger, a heat recovery device, an evaporator, a condenser, and a thermoelectric conversion unit;

[0020] The air-side heat exchanger inlet is connected to one side of the fuel cell stack and is used to collect the high-temperature exhaust gas generated by the fuel cell stack;

[0021] The inlet of the heat recovery device is connected to the outlet of the air side heat exchanger, and is used to collect heat at the outlet of the air side heat exchanger;

[0022] The thermoelectric conversion unit is connected to the outlet of the heat recovery device and is used to convert the heat output by the heat recovery device into electricity and incorporate it into the power grid;

[0023] The inlet of the fuel side heat exchanger is connected to the other side of the fuel cell stack, and is used to receive the high-temperature gas generated by the fuel cell stack and heat the gas at the inlet of the fuel cell stack;

[0024] The evaporator inlet is connected to the outlet of the fuel side heat exchanger, and is used to vaporize liquid water using the heat of the fuel stack tail gas output by the fuel side heat exchanger;

[0025] The condenser is connected to the outlet of the evaporator and is used to discharge the low-temperature exhaust gas flowing out of the evaporator.

[0026] Furthermore, the heat recovery device adopts a phase change material based on latent heat energy storage.

[0027] The present invention also provides a reversible solid oxide battery thermal management system, comprising: an air-side heat exchanger, a fuel-side heat exchanger, a heat recovery device, an evaporator, a condenser, and a thermoelectric conversion unit;

[0028] The air-side heat exchanger inlet is connected to one side of the fuel cell stack and is used to collect the high-temperature exhaust gas generated by the fuel cell stack;

[0029] The inlet of the heat recovery device is connected to the outlet of the air side heat exchanger, and is used to collect heat at the outlet of the air side heat exchanger;

[0030] The thermoelectric conversion unit is connected to the outlet of the heat recovery device and is used to convert the heat output by the heat recovery device into electricity and incorporate it into the power grid;

[0031] The inlet of the fuel-side heat exchanger is connected to the other side of the fuel cell stack, and is used to receive the heat output by the heat recovery device and the high-temperature gas generated by the fuel cell stack to heat the gas at the inlet of the fuel cell stack;

[0032] The evaporator inlet is connected to the outlet of the fuel side heat exchanger, and is used to vaporize liquid water using the heat of the fuel stack tail gas output by the fuel side heat exchanger;

[0033] The condenser is connected to the outlet of the evaporator and is used to discharge the low-temperature exhaust gas flowing out of the evaporator.

[0034] Furthermore, the heat recovery device adopts a phase change material based on latent heat energy storage.

[0035] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art.

[0036] The present invention fully targets the gas characteristics of the fuel and air circuits and proposes a thermal management solution that combines the fuel-side branch and the air-side heat recovery, thus avoiding the interference of complex working conditions on the system. Taking into account the consistency of the gas flow in the fuel electrode circuit, the present invention passes the fuel-side exhaust gas into the evaporator for a second time, and uses the internal waste heat as an ideal heat source to vaporize liquid water, thereby replacing the evaporator with a water-gas heat exchanger. The relatively low-temperature exhaust gas flowing out of the evaporator causes less thermal stress on the condenser; in the air circuit, the sub-high-temperature air is recovered by a heat recovery unit, which can be a heat-to-electricity or heat-to-heat conversion device. In order to avoid the impact of continuous high temperature on the heat recovery unit, the present invention further uses a phase change material based on latent heat storage to store heat. Experiments have shown that this solution effectively guarantees the premise of thermal safety and achieves high system efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a basic rSOC system flow chart;

[0038] Figure 2 This is a flow chart of the rSOC system for secondary utilization of tail gas according to the present invention;

[0039] Figure 3 The experimental data and simulation model verification results are shown in Figure 2. (a) is the single cell voltage at different current densities, and (b) is the power density at different current densities.

[0040] Figure 4 is the result of SOE mode control analysis; where (a) is the current density (Current density) versus electrolysis efficiency (η SOE) influence analysis, (b) is the air excess ratio (ε air ) for η SOE The impact analysis, (c) is the fuel utilization rate (U f ) for η SOE The influence of (d) is the water vapor mole fraction For η SOE Impact analysis; FE&AE indicates that improvements to the thermal management of both the fuel and air circuits exist simultaneously; FE indicates that only the fuel circuit heat recovery branch exists; AE indicates that only the air-side heat recovery device exists; and Basic indicates the basic rSOC system structure.

[0041] Figure 5 is the result of the SOFC model comparison analysis; where (a) is the relationship between current density and discharge efficiency (η SOFC ), (b) is the impact analysis of ε air For η SOFC The impact analysis of U f For η SOFC The influence of (d) is the hydrogen mole fraction. For η SOFC Impact analysis;

[0042] Figure 6 is the result of the reversible efficiency comparison analysis. DETAILED DESCRIPTION

[0043] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0044] The basic rSOC system consists of the rSOC stack. Other BOP components include power-consuming components such as heaters, pumps, blowers, evaporators, and non-power-consuming components such as HEX (heat exchange) and condensers to keep the stack running in a good environment. The rSOC system is a normal pressure system without compressors and pressure relief valves. These two components are considered to be hydrogen pipeline components. Since the hydrogen consumed or produced by the rSOC system is directly connected to the hydrogen pipeline, there is only one mass flow controller (MFC) to control the flow of hydrogen into the system.

[0045] In SOFC mode, hydrogen is delivered to the rSOC system and water is vaporized in the fuel circuit. Next, the gas mixed in the mixer enters the preheater and is heated. The HEX plays a role in the preheater, not the heater, and the heater remains off. The mixed gas enters the fuel cell stack after being fully preheated and then reacts. At the same time, a certain amount of air that has been fully preheated in the HEX enters the fuel cell stack to provide oxygen for the redox reaction in the TPB (three-phase boundary), releasing electrical energy and generating a large amount of heat, which is used to preheat the fuel mixture or air in the HEX. The diverted mixture is then recycled to the water tank and the hydrogen network. However, the sub-high temperature air is directly discharged into the atmosphere.

[0046] In SOE mode, liquid water, the raw material, is converted into steam in an electric evaporator. The steam is mixed with hydrogen to prevent electrode oxidation prior to preheating. Unlike SOFC mode, the heater operates continuously to ensure the required heat for electrolysis. Air serves as a purge gas to prevent high oxygen concentrations from corroding the stack materials. Similarly, hydrogen, the primary product, is separated in a condenser, and the oxygen-rich exhaust gas is released to the atmosphere.

[0047] Reversible solid oxide cell (rSOC) systems are oriented towards thermal safety and high-efficiency thermal management methods. Current research can be divided into three major aspects:

[0048] The first and most common method is to combine the rSOC system with a heat storage medium / heat storage component. Since the stack releases heat when operating in SOFC mode and absorbs heat in SOE mode, this solution uses a heat storage medium to collect the heat released in SOFC mode and release it in SOE mode to reduce the power consumption of electric heating in SOE mode, thereby improving efficiency. The limitation of this method is that it is constrained by the duration of the two modes. When the SOE mode operates longer than the SOFC mode, it is difficult to meet the heat absorption requirements in SOE mode.

[0049] The second approach combines specific reaction properties and operating conditions. Some studies have attempted to achieve system thermal management through pressurization (20 bar) and methanation exotherm. However, this approach imposes strict requirements on system sealing, and carbonaceous gases can easily cause stack degradation (carbon deposits).

[0050] The third is variable bypass, which fully utilizes the waste heat in the system. Existing research has ignored the gas properties in the fuel electrode loop and the air electrode loop. In fact, the air loop gas flow is much greater than the fuel side.

[0051] The present invention fully targets the gas characteristics of the fuel and air circuits and proposes a thermal management solution that combines the fuel-side branch and the air-side heat recovery. It effectively absorbs the advantages of the above-mentioned solutions and avoids the interference of complex working conditions on the system. This solution introduces the fuel-side exhaust gas into the evaporator for a second time and replaces the evaporator with a water-gas heat exchanger because the gas flow rate of the fuel electrode circuit is consistent; in the air circuit, the heat of the sub-high temperature air is recovered by a heat recovery unit, which can be a heat-to-electric or heat-to-heat conversion device. In order to avoid the impact of continuous high temperature on the heat recovery unit, this solution further uses phase change materials based on latent heat energy storage to store heat. The results show that this solution effectively guarantees the premise of thermal safety and achieves high system efficiency.

[0052] like Figure 2 In the fuel circuit, the present invention extracts the exhaust gas of the fuel cell stack coming out of the preheating unit (heat exchanger), and uses the high-temperature exhaust gas as a heat source to pass into the evaporator through a heat bypass to vaporize liquid water. In this way, the evaporator no longer adopts electric heating but is similar to a water-air heat exchanger. In the air circuit, the air flow is much larger than that on the fuel side, but the temperature is maintained at a similar level. A heat recovery device is added at the outlet of the air side heat exchanger, which can be a heat storage unit or a steam turbine. The recovered heat can be used as an auxiliary heat source for heating, or it can be used in the form of combined heat and power. Regardless of the specific form of heat recovery, the heat recovery power of the heat recovery device depends on the flow rate and temperature of the fluid.

[0053] In order to verify the effectiveness of the method of the present invention, the following examples are used to model and verify the rSOC system; the rSOC system model consists of the SOC stack and the remaining BOP components.

[0054]

[0055]

[0056] Stack model:

[0057] 1. Electrical characteristics

[0058] U Cell (i,T,p)=U Nernst -(U ohm +U act +U con ) (1)

[0059] 2. Heat and mass transfer process

[0060]

[0061]

[0062] Heat exchanger:

[0063]

[0064] Evaporator:

[0065]

[0066] mixer:

[0067]

[0068] Blower:

[0069]

[0070] Water pump:

[0071]

[0072] Heat recovery device:

[0073]

[0074] The results of model validation are as follows Figure 3 As shown in (a)-(b), when CD is from 0.25A cm -2 Change to 0.25A cm -2 When |CD| increases, the deviation between the experimental and simulated voltages is relatively large. As |CD| increases, the experimental data and the simulated results are in good agreement (similar trends and close values). Figure 3 The maximum deviation of the measured stack voltage observed in (a) is only 0.032 V. It results in a stack power density of about 0.0106 Wcm -2 The deviation is within the acceptable range. The high consistency between the experimental and simulation results shows that the model is reasonable and effective.

[0075] Set steady-state performance indicators:

[0076] 1. Input parameters

[0077] The main parameters to be set are fuel utilization rate, air excess ratio, fuel mole fraction, and operating current.

[0078]

[0079]

[0080]

[0081]

[0082]

[0083] 2. Efficiency indicators

[0084]

[0085]

[0086]

[0087] Control analysis experimental results

[0088] Control group setting:

[0089] They are FE&AE, AE, FE and Basic, indicating the presence of thermal management devices for both fuel and air circuits, heat recovery units on the air side only, evaporator bypass on the fuel side only, and basic system structure.

[0090] The results show:

[0091] 1) SOE model efficiency

[0092] refer to Figure 4 In Figures (a)-(d), the efficiency gain for the AE configuration, calculated from the average deviations between the curves FE&AE and FE, and between AE and Basic, is (a) 8.21%, (b) 10%, (c) 8.09%, and (d) 8.2%, respectively. The overall average efficiency gain is 8.625%. This means that with the air-side heat recovery unit, the average electrolysis efficiency gain for the rSOC system is 8.625%. The efficiency gain for the FE configuration, calculated from the average deviations between FE&AE and AE, and between FE and Basic, is (a) 1.28%, (b) 1.075%, (c) 1.52%, and (d) 1.24%, respectively. The overall average efficiency gain is 1.28%, and the average electrolysis efficiency gain is 1.28% when only the fuel circuit evaporator bypass is present.

[0093] 2) SOFC mode efficiency

[0094] refer to Figure 5 In (a)-(d), the average efficiency gains for the AE configuration are (a) 19.79%, (b) 17.21%, (c) 15.9%, and (d) 16.37%, respectively. The average efficiency gain with the air-side heat recovery unit is 17.32%. The average efficiency gains for the AE configuration are (a) 0.79%, (b) 0.73%, (c) 0.82%, and (d) 1.42%, respectively. The average efficiency gain for the FE configuration is 0.94%.

[0095] 3) Round-trip performance (round-trip efficiency)

[0096] refer to Figure 6The average deviations between the FE&AE curve and the FE curve, and between the AE and Basic curves, are 17% and 16.7%, respectively. The average deviations between the FE&AE curve and the AE curve, and between the FE and Basic curves, are 1.17% and 0.84%, respectively. The combined average efficiency gains for AE and FE are 16.85% and 1%, respectively. The AE configuration maintains a significant increase, far exceeding the FE configuration.

[0097] 4) Parameter impact study

[0098] Different operating parameters will affect the flow rate and temperature of the exhaust gas at the stack outlet, and these two parameters determine the effect of the exhaust gas secondary utilization, that is, directly affect the efficiency gain, especially on the air circuit side. By comparing the efficiency impact under the four configurations, combined with Figure 4-6 It can be seen that the efficiency of FE&AE configuration (i.e., equipped with both air-side and fuel-side thermal management devices / branches) is much higher than that of Basic configuration (i.e., Figure 1 The basic rSOC system structure shown in FIG3 is shown), so it can be fully proved that the method of the present invention can effectively improve the economic performance of the system.

[0099] The parameter studies mainly include the operating current, air excess ratio, fuel utilization and fuel mole fraction in SOE and SOFC modes, respectively. Figure 4 and 5 shown.

[0100] Key conclusions:

[0101] In both modes, the two input parameters that have the greatest impact on mode efficiency are current density and air excess ratio. Both electrolysis efficiency and discharge efficiency decrease with increasing current density and with increasing air excess ratio. In SOE mode, the air excess ratio has a more significant impact on electrolysis efficiency, while in SOFC mode, current has the most significant impact on discharge efficiency. For fuel utilization and mole fraction, although efficiency increases with both, the rate of change in the corresponding efficiency is minimal, indicating a minimal impact on efficiency.

[0102] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A reversible solid oxide battery thermal management system, characterized in that: include: Air-side heat exchanger, fuel-side heat exchanger, heat recovery device, evaporator, condenser and thermoelectric conversion unit; The air-side heat exchanger inlet is connected to one side of the fuel cell stack and is used to collect the high-temperature exhaust gas generated by the fuel cell stack; The inlet of the heat recovery device is connected to the outlet of the air side heat exchanger, and is used to collect heat at the outlet of the air side heat exchanger; The thermoelectric conversion unit is connected to the outlet of the heat recovery device and is used to convert the heat output by the heat recovery device into electricity and incorporate it into the power grid; The inlet of the fuel-side heat exchanger is connected to the other side of the fuel cell stack, and is used to receive the heat output by the heat recovery device and the high-temperature gas generated by the fuel cell stack to heat the gas at the inlet of the fuel cell stack; The evaporator inlet is connected to the outlet of the fuel side heat exchanger, and is used to vaporize liquid water using the heat of the fuel stack tail gas output by the fuel side heat exchanger; The condenser is connected to the outlet of the evaporator and is used to discharge the low-temperature exhaust gas flowing out of the evaporator; The working state equation of the evaporator is: Where N is the amount of fuel, C V is the constant volume specific heat capacity, T is the temperature, is the enthalpy at the evaporator inlet, is the enthalpy output from the evaporator, represents the heat consumed by convection, The heat consumed in converting electrical energy, The heat consumed by evaporation; The working state equation of the heat recovery device is: Where, P rec is the heat recovery power of the heat recovery device, T in is the inlet temperature of the heat recovery device, T out is the outlet temperature of the heat recovery device, is the flow rate in the heat recovery device.

2. A reversible solid oxide battery thermal management system according to claim 1, characterized in that: The heat recovery device adopts a phase change material based on latent heat energy storage.

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