A fuel cell cogeneration system based on a heat pump cycle

Abstract

This invention discloses a fuel cell cogeneration system based on a heat pump cycle, belonging to the field of fuel cell heat exchange technology. In this invention, a thermal management unit is used to output heat from the fuel cell to the user unit, achieving heat control of the fuel cell. The thermal management unit includes two circulation loops. The first circulation loop is based on a heat pump cycle, releasing a large amount of latent heat of vaporization through phase change cooling, thus significantly increasing the heat exchange capacity. The second circulation loop transfers heat to the user end through liquid water, providing heating and domestic hot water for the user. The heat exchange efficiency of this fuel cell cogeneration system is higher than that of water-cooling technology in existing systems.

Description

Technical Field

[0001] This invention belongs to the field of battery heat exchange technology, and more specifically, relates to a fuel cell cogeneration system based on a heat pump cycle. Background Technology

[0002] Fuel cell combined heat and power (CHP) systems are highly efficient energy utilization systems that can simultaneously provide users with electricity and heat. In the prior art, patent CN202011496120.7 discloses a multi-energy complementary CHP system based on fuel cells, utilizing the low-grade characteristics of waste heat from proton exchange membrane fuel cells and organically integrating it with a low-temperature air source heat pump, high-efficiency thermal storage, high-density energy storage, and a high-efficiency power supply terminal. However, the waste heat temperature utilized is the outlet temperature of the proton exchange membrane fuel cell, approximately 70°C, resulting in low waste heat grade. Patent CN202211383699.5 discloses a multi-system coupled CHP system and method, including... Solar energy systems, water electrolyzer systems, fuel cell systems, heat pump systems, and membrane distillation systems, by introducing membrane distillation systems to recover the low- and medium-temperature waste heat from fuel cell and solar energy systems to produce potable freshwater, have improved overall energy efficiency. However, their complex structures and low overall energy utilization rates remain significant challenges. Patent CN202211237485.7 discloses a fuel cell combined heat and power system that improves the relative positions of inlet and outlet water in the user unit, increasing the outlet water temperature at the user end; however, its system thermal efficiency has not been effectively improved. Therefore, a fuel cell combined heat and power system is urgently needed to address the aforementioned technical problems. Summary of the Invention

[0003] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a fuel cell cogeneration system based on heat pump cycle, the purpose of which is to improve the thermal efficiency of the existing fuel cell cogeneration system.

[0004] To achieve the above objectives, the present invention provides a fuel cell cogeneration system based on a heat pump cycle, comprising a fuel cell unit, a power unit, a user unit, and a thermal management unit. The thermal management unit is characterized in that it outputs heat from the fuel cell unit to the user unit, thereby controlling the heat output of the fuel cell unit. The thermal management unit includes a first circulation loop and a second circulation loop.

[0005] The first circulation loop includes a compressor, a first heat exchanger, and an expansion valve connected sequentially. In the first circulation loop, wet steam with a dryness fraction of x flows through the fuel cell unit, absorbs heat from the fuel cell, and its temperature remains unchanged while its dryness fraction increases. Subsequently, the wet steam flows into the compressor, undergoes adiabatic compression to become saturated steam, at which point the steam temperature increases. Then, the saturated steam flows into the hot end of the first heat exchanger, exchanges heat with the medium in the cold end of the first heat exchanger, releases heat, and becomes liquid water. Subsequently, the liquid water flows into the expansion valve, becomes wet steam with a dryness fraction of x again, and then the wet steam flows through the fuel cell unit for the next cycle. Wherein, 0.15 ≤ x ≤ 0.3.

[0006] The second circulation loop includes a first heat exchanger, a water pump, and a second heat exchanger connected end to end in sequence. In the second circulation loop, liquid water flows into the cold end of the first heat exchanger, absorbs the heat released by the phase change of the medium at the hot end of the first heat exchanger, and then rises in temperature. Subsequently, the liquid water flows into the water pump for pressurization, and then flows into the second heat exchanger. After exchanging heat with the medium at the cold end of the second heat exchanger, the temperature drops. Then, the liquid water flows into the cold end of the first heat exchanger for the next circulation.

[0007] Furthermore, the medium in the first and second circulation loops is deionized water. When the deionized water flows through the first heat exchanger, expansion valve, fuel cell, compressor and the first heat exchanger in sequence, it undergoes phase change heat cycles of liquid, two-phase, two-phase, gaseous and liquid states in sequence. In the second circulation loop, the deionized water is in the liquid state.

[0008] Furthermore, the power unit converts the power generated by the fuel cell unit into AC / DC power and voltage power before supplying it to the power grid, the compressor, the water pump, and the user unit.

[0009] Furthermore, the feature is that, in the user unit, tap water flows into the cold end of the second heat exchanger, exchanges heat with the hot end of the second heat exchanger and is heated up, and the heated tap water meets the user's heating and water needs, and the water consumed by the user is replenished by an external tap water source.

[0010] Furthermore, the fuel cell stack in the fuel cell unit operates in a temperature range of 60°C to 90°C.

[0011] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0012] (1) The fuel cell cogeneration system of the present invention is based on heat pump cycle and adopts phase change cooling in the first cycle loop. It utilizes the large amount of latent heat of vaporization released by phase change to achieve a significant increase in heat exchange, which is more efficient than the water cooling technology in the existing system.

[0013] (2) The present invention utilizes the adiabatic compression of the compressor to achieve the temperature rise of the cooling working fluid in the first circulation loop, thereby improving the heat energy grade and heat exchange, and thus improving the output thermal efficiency of the system.

[0014] (3) The present invention absorbs the heat of the fuel cell through the phase change of the cooling medium, which not only improves the heat exchange efficiency but also effectively ensures the temperature uniformity of the fuel cell. Attached Figure Description

[0015] Figure 1 This is a structural schematic diagram of an embodiment of the system of the present invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be 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 illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0017] Figure 1 This is a structural schematic diagram of an embodiment of the system of the present invention, as shown below. Figure 1 As shown, it includes: a fuel cell unit, a thermal management unit, a power unit, and a user thermal unit.

[0018] The fuel cell unit includes a fuel cell stack (101), an air source and air inlet (106), and a hydrogen source and air inlet (107);

[0019] The thermal management unit includes a first circulation loop and a second circulation loop.

[0020] The first circulation loop includes a compressor (102), a first heat exchanger (103), and an expansion valve (105).

[0021] The second circulation loop includes a first heat exchanger (103), a first water pump (201), and a second heat exchanger (202);

[0022] The power unit includes a fuel cell, a DC / DC converter (301), and a DC / AC converter (302);

[0023] The user heating unit includes a second heat exchanger (202), a third heat exchanger (401), a hot water storage tank (402), and a second water pump (403).

[0024] In the first loop of the thermal management unit, the fluid is deionized water. Low-dryness wet steam located in the two-phase region flows through the fuel cell, absorbs heat from the fuel cell, increases dryness, and the wet steam temperature remains unchanged. The wet steam flows through the compressor and is adiabatically compressed into saturated steam. At this time, the compressor operates, and the gas temperature increases significantly. The saturated steam flows through the first heat exchanger, exchanges heat with the fluid in the cold end of the first heat exchanger, releases a large amount of heat, and becomes liquid water. The liquid water flows through the expansion valve and becomes low-dryness wet steam again for the next cycle.

[0025] In the second circulation loop of the thermal management unit, the fluid is deionized water. The liquid water flows through the cold end of the first heat exchanger and absorbs a large amount of heat released by the phase change of the medium at the hot end of the first heat exchanger, causing the temperature to rise. After being pressurized by the water pump, the heated liquid water flows through the second heat exchanger and exchanges heat with the fluid at the cold end of the second heat exchanger, causing the temperature to drop. The low-temperature fluid then re-enters the cold end of the first heat exchanger for cooling circulation.

[0026] In the user's heating unit, the fluid is tap water. The low-temperature tap water flows through the second heat exchanger for heat exchange, and the water temperature rises. It then flows through the water pump, the hot water storage tank, and the third heat exchanger in sequence. In the third heat exchanger, it exchanges heat with the user's space, raising the indoor temperature of the user. The hot water is then supplied to the outside for domestic hot water through the hot water storage tank, and water is replenished.

[0027] In the power unit, the fuel cell stack is connected to a DC / DC converter, and voltage conversion is achieved through a DC / DC converter. When there is a power surplus, the excess power is supplied to the grid. The DC power is converted into AC power through a DC / AC converter to supply users with electricity for lighting, appliances and other daily life.

[0028] The experimental process and conclusions of the system of the present invention, based on simulation experiments, are as follows:

[0029] Wet steam with a dryness fraction of 0.153 and a temperature of 358.15 K flows through a fuel cell operating at 358.15 K. The dryness fraction of the wet steam increases to 0.95 while the temperature remains constant. After being adiabatically compressed by a compressor, it becomes saturated steam with a temperature of 416.76 K. The saturated steam flows through the first heat exchanger for heat exchange, liquefying the steam and lowering the working fluid temperature to 352.07 K. The liquid working fluid flows through an expansion valve for isentropic expansion, becoming wet steam with a dryness fraction of 0.153 and a temperature of 358.15 K, for the next cycle.

[0030] At an operating temperature of 358.15 K, the system achieves a power output of 1 MW with an electrical efficiency of 39.2%, a thermal output of 1.3 MW with a thermal efficiency of 57.3%, and a total system efficiency of 96.5%. Compared to a water-cooled method under the same operating conditions (electrical efficiency of 44.1%, thermal efficiency of 48.5%, and total system efficiency of 92.6%), the proposed system efficiency is improved by 3.9%.

[0031] It is evident that the thermal efficiency of the fuel cell cogeneration system of this invention is higher than that of existing systems.

[0032] The above content is readily understood by those skilled in the art. 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 within the protection scope of the present invention.

Claims

1. A fuel cell cogeneration system based on a heat pump cycle, comprising a fuel cell unit, a power unit, a user unit, and a thermal management unit, characterized in that, The thermal management unit is used to output heat from the fuel cell unit to the user unit, thereby achieving heat control of the fuel cell unit. The thermal management unit includes a first circulation loop and a second circulation loop. The first circulation loop includes a compressor, a first heat exchanger, and an expansion valve connected sequentially. In the first circulation loop, wet steam with a dryness fraction of x flows through the fuel cell unit, absorbs heat from the fuel cell, and its temperature remains unchanged while its dryness fraction increases. Subsequently, the wet steam flows into the compressor, undergoes adiabatic compression to become saturated steam, at which point the steam temperature increases. Then, the saturated steam flows into the hot end of the first heat exchanger, exchanges heat with the medium in the cold end of the first heat exchanger, releases heat, and becomes liquid water. Subsequently, the liquid water flows into the expansion valve, becomes wet steam with a dryness fraction of x again, and then the wet steam flows through the fuel cell unit for the next cycle. Wherein, 0.15 ≤ x ≤ 0.

3. The second circulation loop includes a first heat exchanger, a water pump, and a second heat exchanger connected end to end in sequence. In the second circulation loop, liquid water flows into the cold end of the first heat exchanger, absorbs the heat released by the phase change of the medium at the hot end of the first heat exchanger, and then rises in temperature. Subsequently, the liquid water flows into the water pump for pressurization, and then flows into the second heat exchanger. After exchanging heat with the medium at the cold end of the second heat exchanger, the temperature drops. Then, the liquid water flows into the cold end of the first heat exchanger for the next circulation.

2. The system according to claim 1, characterized in that, The medium in the first and second circulation loops is deionized water. When the deionized water flows through the first heat exchanger, expansion valve, fuel cell, compressor and the first heat exchanger in sequence, it undergoes phase change heat cycles of liquid, two-phase, two-phase, gas and liquid in sequence. In the second circulation loop, the deionized water is in liquid state.

3. The system according to claim 1, characterized in that, The power unit converts the power generated by the fuel cell unit into AC / DC power and voltage power, and then supplies it to the power grid, the compressor, the water pump, and the user unit.

4. The system according to claim 1, characterized in that, In the user unit, tap water flows into the cold end of the second heat exchanger, exchanges heat with the hot end of the second heat exchanger and is heated up. The heated tap water meets the user's heating and water needs, and the water consumed by the user is replenished by an external tap water source.

5. The system according to claim 1, characterized in that, The fuel cell stack in the fuel cell unit operates in a temperature range of 60°C to 90°C.

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