A hydrogen-electricity-heat-cooling multi-energy coupling integrated system and its variable load operation method

Abstract

This application belongs to the field of hydrogen-electric-heat-cooling multi-energy coupling and discloses a hydrogen-electric-heat-cooling multi-energy coupling integrated system and its variable load operation method. The integrated system includes: a PEMFC unit, a solar thermal collector, a lithium bromide absorption chiller, a low-temperature multi-effect distillation seawater desalination device, and a cooling water tank, connected end-to-end to form a first circulating water circuit; a three-way valve is provided on the water circuit of the lithium bromide absorption chiller and the low-temperature multi-effect distillation seawater desalination device, and the three-way valve is also connected to an inlet of the cooling water tank, so that the PEMFC unit, solar thermal collector, lithium bromide absorption chiller, and cooling water tank form a second circulating water circuit; the PEMFC unit is used to operate according to user-side load demand to supply power and discharge cooling water. The cooling water circulates along the second circulating water circuit to participate in cooling and heating, or is divided into two paths, respectively, along the first circulating water circuit and the second circulating water circuit to participate in cooling and heating. This application can improve the utilization rate of waste heat from the fuel cell stack and the cooling and heating efficiency of the integrated system.

Description

Technical Field

[0001] The present application belongs to the field of hydrogen, electricity, heat and cooling multi-energy coupling, and more specifically, relates to a hydrogen, electricity, heat and cooling multi-energy coupling integrated system and a variable load operation method thereof. Background Art

[0002] A hydrogen fuel cell is an electrochemical device that converts the chemical energy of hydrogen into electrical energy without combustion. It is widely used in distributed power generation, microgrid integrated energy systems, electric vehicles, and other fields. Proton exchange membrane fuel cell (PEMFC) technology is mature and offers particular advantages. PEMFCs can operate at room temperature and low temperatures (typically less than 80°C), have high energy density, fast dynamic response, and generate minimal pollution and noise. However, during PEMFC operation, the internal electrochemical reaction must overcome polarization and ohmic overpotential, releasing a large amount of heat. Only 40% to 50% of the hydrogen's chemical energy is converted into electricity, generating a significant amount of waste heat.

[0003] On the user side, multi-energy coupled integrated systems with PEMFC or other fuel cells as their core often operate in the form of combined heat and power or combined cooling, heat and power. Due to the low operating temperature of PEMFC, the waste heat carried out of the stack by the cooling water is of low quality. This heat can be supplied to residents in the form of hot water, but in most usage scenarios, there is a demand for cooling load. Low-quality waste heat can only be cooled by adsorption chillers. The adsorbent of adsorption chillers is solid, and the thermal conductivity is generally very low. The cooling capacity per unit heat is far less than that of absorption chillers that use liquid as the main heat exchanger. After heat exchange in the adsorption chiller, the quality of the waste heat from the stack is further reduced, almost losing its value for further use, which has a negative impact on the heat output of the multi-energy coupled integrated system. Summary of the Invention

[0004] In response to the defects of the existing technology, the purpose of this application is to provide a hydrogen-electric-heat-cooling multi-energy coupling integrated system and its variable load operation method, aiming to solve the problem of low cooling / heat output efficiency in the multi-energy coupling system.

[0005] To achieve the above objectives, according to one aspect of the present application, a hydrogen-electric-heat-cold multi-energy coupling integrated system is provided, comprising: an electric refrigeration / heat engine, a PEMFC unit, a solar thermal collector, a lithium bromide absorption refrigerator, a low-temperature multi-effect distillation seawater desalination device, and a cooling water tank, wherein:

[0006] The PEMFC unit, solar thermal collector, lithium bromide absorption refrigerator, low-temperature multi-effect distillation seawater desalination device and cooling water tank are connected end to end in sequence to form a first circulating water circuit;

[0007] A three-way valve is provided on the water path between the lithium bromide absorption refrigerator and the low-temperature multi-effect distillation seawater desalination device, and the three-way valve is connected to an inlet of the cooling water tank, so that the PEMFC unit, the solar collector, the lithium bromide absorption refrigerator and the cooling water tank form a second circulating water path;

[0008] The PEMFC unit is used to operate and supply power according to the user-side load demand and discharge cooling water. The cooling water circulates along the second circulating water path to participate in cooling and heating, or is divided into two paths and respectively participates in cooling and heating along the first circulating water path and the second circulating water path.

[0009] Through the above technical solution conceived in the present application, compared with the existing technology, since the PEMFC stack and each unit in the hydrogen, electricity, heat and cooling multi-energy coupled integrated system form the first circulating water circuit and the second circulating water circuit, the cooling water discharged from the stack circulates separately or simultaneously in the two circulating water circuits, simplifying the intermediate links and pipelines of the combined heat, cooling and power supply system.

[0010] Furthermore, the system also includes a cold storage tank connected to the lithium bromide absorption refrigerator for storing the cold output of the lithium bromide absorption refrigerator. This configuration is intended to prevent cold energy from being wasted.

[0011] Furthermore, the solar collector is used to collect external solar radiation to heat cooling water. When the cooling water is heated to a temperature higher than the minimum starting temperature of the lithium bromide absorption refrigerator, the lithium bromide absorption refrigerator starts to cool.

[0012] Furthermore, the lithium bromide absorption chiller uses cooling water for heat exchange and then discharges hot water for heat exchange. The hot water is used to supply heat to the outside. When the heat supply is less than the heat load on the user side, all the hot water enters the second circulating water circuit, and the PEMFC unit supplies power to the cooling / heating machine to supplement heating. When the heat supply is greater than the heat load on the user side, the three-way valve can allow part of the hot water to enter the first circulating water circuit and the other part to enter the second circulating water circuit.

[0013] Furthermore, the temperature of the heated water is the same as the temperature of the cooling water discharged from the PEMFC unit, and the heated water is supplied to the outside until its temperature drops to a preset temperature lower than the real-time operating temperature of the fuel cell stack before entering the cooling water tank.

[0014] Furthermore, one of the lithium bromide absorption chillers' water inlets is used to admit external seawater, and one of its outlets is directly connected to a low-temperature, multi-effect distillation desalination unit, allowing the cooled external seawater to be fed into the unit for freshwater production. This arrangement allows the external seawater to be used to cool the lithium bromide absorption chiller while simultaneously allowing the heat-exchanged seawater to flow into the unit for freshwater production.

[0015] Furthermore, the low-temperature, multi-effect distillation desalination unit has an inlet for introducing raw seawater for freshwater production, and an outlet for discharging excess raw seawater. This configuration aims to utilize the waste heat from the stack cooling water after meeting the heat load in the low-temperature, multi-effect distillation desalination unit's freshwater production process, further improving the efficient utilization of waste heat from the stack.

[0016] According to another aspect of the present application, a variable load operation method of the hydrogen-electricity-heat-cooling multi-energy coupled integrated system as described in any of the above items is also disclosed, comprising:

[0017] S1 is based on the user-side electricity load demand, and the PEMFC unit outputs the corresponding power to generate electricity and produce cooling water;

[0018] The cooling water in step S2 is input into the solar collector and heated to a preset temperature by solar radiation;

[0019] The heated cooling water in S3 enters the lithium bromide absorption refrigerator for heat exchange and refrigeration. The temperature of the heat exchange water discharged from the lithium bromide absorption refrigerator is the same as the real-time operating temperature of the fuel cell stack.

[0020] S4 adjusts the three-way valve so that all the hot water is heated and cooled before entering the PEMFC unit through the cooling water tank to participate in the next cycle; or a part of the hot water is heated and cooled before directly entering the PEMFC unit through the cooling water tank to participate in the next cycle, and the other part of the hot water is heated and cooled before first entering the low-temperature multi-effect distillation seawater desalination device for heat exchange again, and then entering the PEMFC unit through the cooling water tank to participate in the next cycle.

[0021] The above technical solutions conceived by this application, compared with the existing technology, can improve the grade of waste heat from the fuel cell stack due to the variable load operation method of the hydrogen, electric, thermal and cooling multi-energy coupling integrated system of this application, so that the integrated system can use a refrigerator with a higher COP, further improving the cooling capacity of the system. The integrated system can timely follow the changes in the user-side electric / heat / cooling load, and the cold output and heat output are independent of each other, thereby improving the overall efficiency of the integrated system. Therefore, the integrated system and variable load operation method provided by this application are particularly suitable for applications in hydrogen, electric, thermal and cooling multi-energy coupling scenarios based on low-temperature fuel cells.

[0022] Furthermore, in step S3, when the cooling power of the lithium bromide absorption chiller is greater than the cooling load on the user side, it supplies cooling to the user side alone and stores the excess cooling capacity in the cold storage tank; when the cooling power is less than the cooling load on the user side, if there is cooling capacity in the cold storage tank, the cold storage tank outputs cooling capacity to supplement cooling; if there is no cooling capacity in the cold storage tank, the PEMFC unit increases the operating power to power the electric refrigeration / heat engine to supplement cooling.

[0023] Furthermore, in step S4, when the heat released by the cooling water discharged from the lithium bromide absorption chiller is less than the heat load on the user side, the three-way valve is used to allow all the hot water to enter the PEMFC unit through the cooling water tank; when the heat released by the cooling water discharged from the lithium bromide absorption chiller is greater than the heat load on the user side, the three-way valve is used to allow part of the hot water to enter the PEMFC unit through the cooling water tank, and the other part of the cooling water is passed through the first effect of the low-temperature multi-effect distillation seawater desalination device for heat exchange and then enters the PEMFC unit through the cooling water tank.

[0024] In general, the above technical solutions conceived by this application have the following technical advantages compared with the existing technologies:

[0025] 1. In the hydrogen-electric-heat-cool multi-energy coupled integrated system provided in this application, the PEMFC stack and each unit form the first circulating water circuit and the second circulating water circuit, so that the cooling water discharged from the stack circulates separately in the second circulating water circuit to participate in heating and cooling, or circulates in the two circulating water circuits to participate in heating, cooling and fresh water preparation, thereby simplifying the intermediate links and pipelines of the combined heat, cooling and power supply system. Specifically, on the one hand, the secondary heating of the cooling water by the solar collector improves the grade of the waste heat of the stack, allowing the system to use a lithium bromide absorption chiller with a higher COP as the main cooling equipment, thereby improving the cooling capacity of the system; on the other hand, while meeting the user-side load demand, the excess waste heat can enter the low-temperature multi-effect distillation seawater desalination device for heat exchange, providing heat for fresh water production, further improving the applicability of the integrated system in coastal scenarios.

[0026] 2. The variable load operation method provided in this application enables the hydrogen-electricity-heat-cooling multi-energy coupled integrated system to promptly adapt to changes in user-side electricity, heat, and cooling loads. PEMFC stack waste heat is used only for heat output and freshwater production, not for cooling. The heat required for cooling in the lithium bromide absorption chiller comes entirely from solar collectors heating the cooling water. Changes in user-side cooling load only affect the PEMFC unit's output power, while changes in user-side heat load only affect the unit's output power and freshwater production. This ensures the independence of the system's cooling and heat outputs, improving overall system efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the structure of the hydrogen, electricity, heat and cooling multi-energy coupling integrated system provided in Example 1 of the present application;

[0028] Figure 2 This is a flow chart of a variable load operation method of a hydrogen-electricity-heat-cooling multi-energy coupling integrated system provided in Example 2 of the present application;

[0029] Figure 3 This is a schematic diagram of the change in COP of the lithium bromide absorption chiller as a function of heat source temperature provided in Example 2 of the present application;

[0030] Figure 4 This is a schematic diagram of the dynamic changes in the user-side 24-hour electricity / heating / cooling loads provided in Example 2 of the present application;

[0031] Figure 5 This is a schematic diagram of the change in waste heat generated by the PEMFC stack when the electrical load is used as the reference output power, as provided in Example 2 of the present application;

[0032] Figure 6 This is a schematic diagram of the changes in solar radiation and heat energy generated by a solar thermal collector over 24 hours, as provided in Example 2 of the present application;

[0033] Figure 7 This is a schematic diagram of the flow rate and temperature difference of cooling water in the solar thermal collector provided in Example 2 of the present application;

[0034] Figure 8 This is a schematic diagram of energy changes of equipment related to refrigeration output in the integrated system provided in Example 2 of the present application;

[0035] Figure 9 This is a schematic diagram of the change in PEMFC unit efficiency provided in Example 2 of the present application;

[0036] Figure 10 This is a schematic diagram of the efficiency of the hydrogen, electricity, heat and cooling multi-energy coupling integrated system provided in Example 2 of the present application. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0038] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0039] Additionally, references throughout this specification to "one embodiment," "one embodiment," "an example," or similar language indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present application. Thus, appearances of the phrase "in one embodiment," "in one embodiment," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0040] Example 1

[0041] This application provides a hydrogen-electricity-heat-cooling multi-energy coupling integrated system, such as Figure 1 As shown, the integrated system includes: an electric refrigeration / heat engine, a PEMFC unit, a solar thermal collector, a lithium bromide absorption chiller, a low-temperature multi-effect distillation seawater desalination device and a cooling water tank, wherein:

[0042] The PEMFC unit, solar thermal collector, lithium bromide absorption chiller, low-temperature multi-effect distillation seawater desalination device and cooling water tank are connected end to end to form the first circulating water circuit;

[0043] A three-way valve is installed in the water path of the lithium bromide absorption chiller and the low-temperature multi-effect distillation desalination device. The three-way valve is also connected to an inlet of the cooling water tank, so that the PEMFC unit, solar collector, lithium bromide absorption chiller and cooling water tank form a second circulating water path;

[0044] The PEMFC unit is used to operate and supply power and discharge cooling water according to the load demand on the user side. All cooling water circulates along the second circulating water path to participate in cooling and heating, or is divided into two paths and respectively participates in cooling and heating along the first circulating water path and the second circulating water path.

[0045] Specifically, the aforementioned PEMFC unit includes a PEMFC stack (hereinafter referred to as the stack) and auxiliary equipment such as compressors, pumps, power electronic converters, etc. required for its normal operation. Hydrogen and oxygen in the air undergo an electrochemical reaction in the stack to generate water while generating electricity to supply power to external electrical equipment. More specifically, the electrochemical reaction inside the PEMFC stack generates heat, and passing cooling water into the stack can carry the heat out of the stack.

[0046] In this embodiment, to maintain a uniform and stable temperature within the stack, the temperature of the cooling water entering the stack is set 5°C lower than the temperature of the stack itself. In other embodiments, the temperature difference can also be set above or below 5°C, such as 3°C, 4°C, 6°C, or 7°C. The temperature of the cooling water discharged from the stack is the same as the real-time operating temperature of the stack itself. The internal structure of the PEMFC unit described above is not the focus of this invention and will not be described in detail here.

[0047] The integrated system provided in this embodiment also includes a cold storage tank, the inlet of which is connected to a cold output port of the lithium bromide absorption refrigerator, and is used to store excess cold of the lithium bromide absorption refrigerator to prevent cold waste.

[0048] In this embodiment, the aforementioned solar thermal collector is used to collect external solar radiation to heat cooling water. When the cooling water temperature rises to a temperature above the minimum activation temperature of the lithium bromide absorption chiller, the lithium bromide absorption chiller starts cooling. The temperature difference of the cooling water in the solar thermal collector is negatively correlated with the flow rate of the cooling water. When external solar radiation is insufficient or absent, the cooling water temperature entering and exiting the solar thermal collector remains constant, so the lithium bromide absorption chiller does not reach the activation temperature and does not start cooling.

[0049] In this embodiment, the lithium bromide absorption chiller uses cooling water for heat exchange and then discharges hot water for heat exchange. The hot water is used for external heat supply. When the heat supply is less than the heat load on the user side, all the hot water enters the second circulation water circuit and finally enters the PEMFC unit. The PEMFC unit runs to supply power to the cooling / heating machine to supplement the heating. When the heat supply is greater than the heat load on the user side, the three-way valve can allow part of the hot water to enter the first circulation water circuit for heating and enter the PEMFC unit after cooling in the cooling water tank, and allow the other part of the hot water to enter the second circulation water circuit, enter the cooling water tank after cooling through the low-temperature multi-effect distillation seawater desalination device, and finally enter the PEMFC unit to participate in the next cycle.

[0050] Specifically, a portion of the cooling water leaving the lithium bromide absorption chiller enters the first stage of the low-temperature, multi-effect distillation desalination unit. There, it exchanges heat with the raw seawater in the first stage, cooling it to 5°C below the temperature of the fuel cell stack itself before entering the PEMFC unit through a cooling water tank. The remaining cooling water leaving the lithium bromide absorption chiller is used to supply heat to external sources based on heat load requirements until it cools to 5°C below the fuel cell stack temperature, after which it enters the PEMFC unit through a cooling water tank.

[0051] In this embodiment, the temperature of the hot water is set to be the same as the temperature of the cooling water discharged from the PEMFC unit, and the hot water is supplied to the outside until its temperature drops to 5°C lower than the real-time operating temperature of the fuel cell stack before entering the cooling water tank, ensuring that the cooling water entering the PEMFC unit can take away the heat of the fuel cell stack before being discharged.

[0052] In this embodiment, one of the lithium bromide absorption chillers' water inlets is also used to receive external seawater, as indicated by the dashed line. One of its outlets is directly connected to a low-temperature, multi-effect distillation desalination unit, allowing the cooled external seawater to be fed into the unit for heat exchange and to provide heat for freshwater production. This arrangement allows the external seawater to be used to cool the lithium bromide absorption chiller while simultaneously allowing the heat exchanged seawater to flow into the unit for freshwater production.

[0053] In this embodiment, a water inlet of the low-temperature multi-effect distillation seawater desalination device is used to introduce raw seawater for preparing fresh water, and a water outlet is used to discharge excess raw seawater. Figure 1 Indicated by the dashed line. Low-temperature multi-effect distillation is a desalination technology in which the maximum evaporation temperature of the raw seawater is below 70°C. The low-temperature multi-effect distillation desalination device consists of a series of falling-film evaporators connected in series and divided into several effects. A certain amount of low-pressure steam or other heat source is input into the first effect. The water vapor evaporated by the heat of the seawater enters the second effect as the heat source, and the process continues in sequence, thereby producing distilled water through multiple evaporations and condensations of the seawater. The specific structure is not the key innovation of this application and will not be described in detail here.

[0054] Specifically, part of the raw seawater required for the low-temperature multi-effect distillation seawater desalination device comes from the cooling seawater of the lithium bromide absorption refrigerator, and part comes from natural seawater, and the excess raw seawater is discharged back to the sea.

[0055] Example 2

[0056] This embodiment provides a load-variable operation method of the integrated system disclosed in embodiment 1, such as Figure 2 As shown, the following steps are included:

[0057] S1 is based on the electricity load demand on the user side, and the PEMFC unit outputs corresponding power to generate electricity and produce cooling water.

[0058] Specifically, the PEMFC unit operates at a power output corresponding to the user-side electrical load. The temperature difference of the circulating cooling water entering and leaving the stack is preset to 5°C, and the amount of heat brought out during the flow is adjusted by changing the cooling water flow rate.

[0059] S2 inputs cooling water into the solar collector and uses solar radiation to heat it to a preset temperature.

[0060] Specifically, when there is solar radiation, the cooling water in the solar collector absorbs heat, and after the temperature rises, it enters the lithium bromide absorption refrigerator for heat exchange and cooling, outputting cooling capacity.

[0061] More specifically, when the cooling power is greater than the cooling load on the user side, the lithium bromide absorption chiller supplies cooling to the user side alone, and the excess cooling is stored in the cold storage tank; when the cooling power is less than the cooling load, if there is cooling in the cold storage tank, the cold storage tank outputs cooling to supplement it; if there is no cooling in the cold storage tank, the output power of the PEMFC unit will also increase accordingly to power the electric refrigeration / heat engine to supplement the cooling.

[0062] The heated cooling water in S3 enters the lithium bromide absorption chiller for heat exchange and refrigeration. The temperature of the heat water discharged from the lithium bromide absorption chiller is the same as the actual operating temperature of the fuel cell stack. The heat water must be cooled by at least 5°C before entering the PEMFC unit for the next cycle.

[0063] S4 adjusts the three-way valve so that all the hot water after external heat supply enters the PEMFC unit through the cooling water tank to participate in the next cycle; or a part of the hot water after external heat supply directly enters the PEMFC unit through the cooling water tank to participate in the next cycle, and the other part of the hot water first enters the low-temperature multi-effect distillation seawater desalination device for cooling, and then enters the PEMFC unit through the cooling water tank to participate in the next cycle, to prevent the cooling water flow from being too large, resulting in the temperature of the hot water being too high after heating and cooling.

[0064] Specifically, the heated water discharged from the lithium bromide absorption chiller is used to heat the outside until the temperature drops by 5°C and then enters the cooling water tank. Then, according to the output power of the PEMFC unit, the corresponding flow of cooling water in the cooling water tank is introduced into the PEMFC unit again to complete the cycle.

[0065] In this embodiment, without considering the heat exchange loss between the devices, the heat carried out of the stack by the cooling water is calculated as follows:

[0066] Q stack =C water m water ΔT stack (1)

[0067] Among them, Q stack The cooling water takes away the heat of the stack, C water is the specific heat capacity of water, m water is the cooling water flow rate, ΔT stack It is the temperature difference between the cooling water entering and leaving the fuel cell stack.

[0068] The temperature of the fuel cell stack in the PEMFC unit is stabilized at 80°C, the temperature of the cooling water entering the fuel cell stack is 75°C, and the temperature of the cooling water leaving the fuel cell stack is 80°C.

[0069] The cooling water leaving the PEMFC unit enters the solar collector. When there is no solar radiation, the temperature of the cooling water entering and leaving the solar collector is 80°C. When there is solar radiation, the cooling water absorbs solar heat energy and heats up. The temperature difference is:

[0070]

[0071] Where, ΔT STC is the temperature difference, Q STC The heat energy transferred from the solar collector to the cooling water.

[0072] like Figure 3 As shown in , in this embodiment, the COP of the lithium bromide absorption refrigerator increases with the increase of the heat source temperature within a certain temperature range. When the heat source temperature is lower than 80°C, the refrigerator does not work.

[0073] In this embodiment, when there is no solar radiation, the chiller does not operate, and the temperature of the cooling water entering and leaving the chiller is 80°C. When there is solar radiation, the cooling water heats up, and the chiller absorbs the heat from the cooling water and begins cooling. The cooling water exchanges heat with the chiller, cooling down to 80°C before leaving the chiller.

[0074] In this embodiment, since the temperature of the cooling water entering the solar collector and leaving the lithium bromide absorption chiller is the same, the output cooling capacity of the chiller can be approximately calculated as:

[0075] Q LiBr =Q STC COP LiBr (3)

[0076] Among them, Q LiBr is the cooling capacity of the refrigerator, COP LiBr is the energy efficiency ratio of the refrigerator.

[0077] In this embodiment, the dynamic changes of the user side's 24-hour electricity / heating / cooling load are as follows: Figure 4 As shown, the PEMFC unit is Figure 4 The electrical load shown is the reference output power.

[0078] The electric cooling / heating engine can consume electricity to produce cooling / heating output. Its working power is provided by the PEMFC power generation unit. The relationship between the working power and the output cooling / heating power can be expressed as:

[0079] Q c / h =W ref 2.87 (4)

[0080] Among them, Q c / h Is the output cooling and heating power, W ref is the working power.

[0081] In this embodiment, the waste heat of the stack changes as follows: Figure 5 As shown, the waste heat is greater than the heat load within 24 hours, so the electric refrigeration / heat engine does not need to generate heat in this embodiment. After meeting the heat load, the waste heat of the battery stack enters the low-temperature multi-effect distillation desalination device along with the water flow.

[0082] Solar radiation and heat generated by solar collectors vary as Figure 6 As shown, this part of solar thermal energy is all used to heat the cooling water, so that the lithium bromide absorption chiller reaches the starting temperature and outputs cooling capacity.

[0083] The flow rate and inlet and outlet temperature difference of cooling water in solar thermal collector are as follows: Figure 7As shown in the figure, when there is no solar radiation, the cooling water temperature remains unchanged as it passes through the solar collector. As the solar collector absorbs solar radiation and generates heat, the cooling water temperature begins to rise. As solar radiation gradually increases and the cooling water flow rate decreases, the heating temperature difference increases rapidly before 12:00, reaching a maximum of 11.8°C. Subsequently, as the cooling water flow rate gradually increases and solar radiation decreases, the temperature difference also decreases rapidly, returning to zero at 16:30.

[0084] Energy changes of equipment related to cooling output in the integrated system are as follows: Figure 8 As shown in the figure, at 0:00, the net cooling capacity of the cold storage tank is zero. From 0:00 to 7:10, due to the lack of solar radiation at night, the solar collector cannot reheat the cooling water, and the lithium bromide absorption chiller is not operating. The cooling load is entirely provided by the electric cooling / heating engine. Therefore, during this period, the output of the PEMFC unit exceeds the electrical load. Subsequently, solar radiation increases rapidly, and the cooling output of the lithium bromide absorption chiller increases rapidly, while the electric cooling / heating engine gradually shuts down. When the cooling output exceeds the cooling load, the excess cooling capacity is stored in the cold storage tank. At 1:30 pm, the cold storage tank reaches a peak of 26.2 kWh. Thereafter, solar radiation decreases, and the cooling output of the lithium bromide absorption chiller is insufficient to meet the cooling load, and the cold storage tank gradually releases the stored cooling capacity. At 4:20 pm, the lithium bromide absorption chiller shuts down. At 5:30 pm, the cold storage tank's stored cooling capacity is exhausted, and the electric cooling / heating engine restarts cooling, and the output of the PEMFC unit once again exceeds the electrical load.

[0085] In this embodiment, the energy efficiency of the PEMFC unit is as follows: Figure 9 When the PEMFC unit operates at low power, some waste heat is dissipated into the environment, resulting in a low percentage of recoverable heat and a significant decrease in thermal efficiency. As operating power increases, thermal efficiency rapidly improves, and in the mid-to-high power range, it complements electrical efficiency, resulting in a stable energy efficiency of around 82%.

[0086] In this embodiment, the energy efficiency of the hydrogen-electric-heat-cooling multi-energy coupling integrated system is as follows: Figure 10 As shown in the figure, the COP of the lithium bromide absorption chiller is lower than the energy efficiency of the PEMFC power generation system. The system's energy efficiency decreases significantly while the solar collector and lithium bromide absorption chiller are operating. When the solar collector and lithium bromide absorption chiller are stopped, the system's energy efficiency is the same as that of the PEMFC power generation system. This indicates that the heat generated by the lithium bromide absorption chiller comes entirely from the solar collector, and the system's cooling and heating outputs are independent of each other.

[0087] The hydrogen, electricity, heat, and cooling multi-energy coupling integrated system and its variable load operation method provided in this application can improve the quality of waste heat from the fuel cell stack, allowing the system to use a refrigerator with a higher COP, thereby improving the system's cooling capacity. The integrated system can promptly follow changes in the user-side electricity, heat, and cooling loads, and the cooling output and heat output are independent of each other, improving the overall efficiency of the integrated system. Therefore, this integrated system and method are particularly suitable for applications in hydrogen, electricity, heat, and cooling multi-energy coupling scenarios based on low-temperature fuel cells.

[0088] The above technical solutions conceived by this application, compared with the existing technology, can improve the grade of waste heat from the fuel cell stack due to the variable load operation method of the hydrogen, electric, thermal and cooling multi-energy coupling integrated system of this application, so that the integrated system can use a refrigerator with a higher COP, further improving the cooling capacity of the system. The integrated system can timely follow the changes in the user-side electric / heat / cooling load, and the cold output and heat output are independent of each other, thereby improving the overall efficiency of the integrated system. Therefore, the integrated system and variable load operation method provided by this application are particularly suitable for applications in hydrogen, electric, thermal and cooling multi-energy coupling scenarios based on low-temperature fuel cells.

[0089] It is easy for those skilled in the art to understand that the above is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A hydrogen, electricity, heat and cooling multi-energy coupling integrated system, characterized in that: It includes: electric refrigeration / heat engine, PEMFC unit, solar thermal collector, lithium bromide absorption chiller, low-temperature multi-effect distillation desalination device and cooling water tank, among which: The PEMFC unit, solar thermal collector, lithium bromide absorption refrigerator, low-temperature multi-effect distillation seawater desalination device and cooling water tank are connected end to end in sequence to form a first circulating water circuit; A three-way valve is provided on the water path between the lithium bromide absorption refrigerator and the low-temperature multi-effect distillation seawater desalination device, and the three-way valve is connected to an inlet of the cooling water tank, so that the PEMFC unit, the solar collector, the lithium bromide absorption refrigerator and the cooling water tank form a second circulating water path; The PEMFC unit is used to operate and supply power according to the user-side load demand and discharge cooling water. The cooling water circulates along the second circulating water path to participate in cooling and heating, or is divided into two paths and respectively participates in cooling and heating along the first circulating water path and the second circulating water path.

2. The hydrogen-electricity-heat-cooling multi-energy coupling integrated system according to claim 1, characterized in that: The device also includes a cold storage tank, which is connected to the lithium bromide absorption refrigerator and is used to store the output cold capacity of the lithium bromide absorption refrigerator.

3. The hydrogen-electricity-heat-cooling multi-energy coupling integrated system according to claim 1, characterized in that: The solar thermal collector is used to collect external solar radiation to heat the cooling water. When the cooling water is heated to a temperature higher than the lowest starting temperature of the lithium bromide absorption refrigerator, the lithium bromide absorption refrigerator starts to cool.

4. The hydrogen, electricity, heat and cooling multi-energy coupling integrated system according to claim 1, characterized in that: The lithium bromide absorption chiller uses cooling water for heat exchange and then discharges hot water for heat exchange. The hot water is used to supply heat to the outside. When the heat supply is less than the heat load on the user side, all the hot water enters the second circulating water circuit, and the PEMFC unit supplies power to the cooling / heating machine to supplement heating. When the heat supply is greater than the heat load on the user side, the three-way valve can allow part of the hot water to enter the first circulating water circuit and the other part to enter the second circulating water circuit.

5. The hydrogen-electricity-heat-cooling multi-energy coupling integrated system according to claim 4, characterized in that: The temperature of the heated water is the same as that of the cooling water discharged from the PEMFC unit, and the heated water is supplied to the outside until its temperature drops to a preset temperature lower than the real-time operating temperature of the fuel cell stack before entering the cooling water tank.

6. The hydrogen-electricity-heat-cooling multi-energy coupling integrated system according to claim 1, characterized in that: One water inlet of the lithium bromide absorption refrigerator is also used to introduce external seawater, and one water outlet is directly connected to the low-temperature multi-effect distillation seawater desalination device, so as to input the external seawater after heat exchange and cooling into the low-temperature multi-effect distillation seawater desalination device to participate in fresh water preparation.

7. The hydrogen-electricity-heat-cooling multi-energy coupling integrated system according to claim 6, characterized in that: The low-temperature multi-effect distillation seawater desalination device has a water inlet for introducing raw seawater for preparing fresh water, and a water outlet for discharging excess raw seawater.

8. The variable load operation method of the hydrogen-electricity-heat-cooling multi-energy coupling integrated system according to any one of claims 1 to 7, characterized in that: include: S1 is based on the user-side electricity load demand, and the PEMFC unit outputs the corresponding power to generate electricity and produce cooling water; The cooling water in step S2 is input into the solar collector and heated to a preset temperature by solar radiation; The heated cooling water in S3 enters the lithium bromide absorption refrigerator for heat exchange and refrigeration. The temperature of the heat exchange water discharged from the lithium bromide absorption refrigerator is the same as the real-time operating temperature of the fuel cell stack. S4 adjusts the three-way valve so that all the hot water is heated and cooled before entering the PEMFC unit through the cooling water tank to participate in the next cycle; or a part of the hot water is heated and cooled before directly entering the PEMFC unit through the cooling water tank to participate in the next cycle, and the other part of the hot water is heated and cooled before first entering the low-temperature multi-effect distillation seawater desalination device for heat exchange again, and then entering the PEMFC unit through the cooling water tank to participate in the next cycle.

9. The variable load operation method of the hydrogen-electricity-heat-cooling multi-energy coupling integrated system according to claim 8, characterized in that: In step S3, when the cooling power of the lithium bromide absorption chiller is greater than the cooling load on the user side, it supplies cooling to the user side alone and stores the excess cooling capacity in the cold storage tank; when the cooling power is less than the cooling load on the user side, if there is cooling capacity in the cold storage tank, the cold storage tank outputs cooling capacity to supplement cooling; if there is no cooling capacity in the cold storage tank, the PEMFC unit increases the operating power to power the electric refrigeration / heat engine to supplement cooling.

10. The variable load operation method of the hydrogen-electricity-heat-cooling multi-energy coupling integrated system according to claim 8, characterized in that: In step S4, when the heat released by the cooling water discharged from the lithium bromide absorption chiller is less than the heat load on the user side, the three-way valve is used to allow all the hot water to enter the PEMFC unit through the cooling water tank; when the heat released by the cooling water discharged from the lithium bromide absorption chiller is greater than the heat load on the user side, the three-way valve is used to allow part of the hot water to enter the PEMFC unit through the cooling water tank, and the other part of the cooling water is passed through the first effect of the low-temperature multi-effect distillation seawater desalination device for heat exchange and then enters the PEMFC unit through the cooling water tank.

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