Hydrogen, electricity, heat and cold multi-energy coupling integrated system and variable load operation method thereof

Abstract

The invention belongs to the field of hydrogen-electricity-heat-cold multi-energy coupling, and discloses a hydrogen-electricity-heat-cold multi-energy coupling integrated system and a variable-load operation method thereof, and the integrated system comprises a PEMFC unit, a solar heat collector, a lithium bromide absorption refrigerator, a low-temperature multi-effect distillation seawater desalination device and a cooling water tank which are sequentially connected end to end to form a first circulating water path; a three-way valve is arranged on a water path of the lithium bromide absorption refrigerator and the low-temperature multi-effect distillation seawater desalination device, and the three-way valve is also connected with one inlet of the cooling water tank, so that the PEMFC unit, the solar heat collector, the lithium bromide absorption refrigerator and the cooling water tank form a second circulating water path; the PEMFC unit is used for supplying power according to user side load requirements and discharging cooling water, and the cooling water circularly participates in refrigeration and heating along the second circulating water path or is divided into two paths to participate in refrigeration and heating along the first circulating water path and the second circulating water path respectively. The fuel cell stack waste heat utilization rate and the refrigerating and heating efficiency of the integrated system can be improved.

Description

Technical Field

[0001] The present application belongs to the field of hydrogen-electricity-heat-cooling multi-energy coupling, and more specifically, relates to a hydrogen-electricity-heat-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 can convert 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 has particular advantages. PEMFC can operate at room temperature and low temperature (usually less than 80°C), has high energy density, fast dynamic response, and produces minimal pollution and noise. However, during the operation of PEMFC, the internal electrochemical reaction needs to overcome polarization and ohmic overpotential, thereby releasing a large amount of heat. Only 40% to 50% of the chemical energy of hydrogen is converted into electrical energy, which will generate a lot of waste heat.

[0003] On the user side, multi-energy coupling integrated systems with PEMFC or other fuel cells as the core are often operated in the form of combined heat and power or combined heat and power. Due to the low operating temperature of PEMFC, the waste heat brought out of the stack by cooling water is of low quality. This part of heat can be supplied to residents in the form of hot water, but there is a demand for cooling load in most usage scenarios. Low-grade waste heat refrigeration can only be carried out by adsorption refrigerators. The adsorbent of the adsorption refrigerator is solid, and the thermal conductivity is generally very small. The cooling capacity per unit heat is far less than that of the absorption refrigerator with liquid as the main heat exchanger. After the heat exchange in the adsorption refrigerator, the quality of the waste heat of the stack is further reduced, and it almost loses the value of further utilization, which has a negative impact on the heat output of the multi-energy coupling integrated system. Summary of the invention

[0004] In view of the defects of the prior art, the purpose of this application is to provide a hydrogen-electricity-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-mentioned purpose, according to one aspect of the present application, the present application provides a hydrogen-electric-heat-cold multi-energy coupling integrated system, including: an electric refrigeration / heat engine, a PEMFC unit, a solar 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 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 waterway 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 waterway;

[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 to participate in cooling and heating along the first circulating water path and the second circulating water path respectively.

[0009] Through the above technical scheme conceived in the present application, compared with the prior art, since the PEMFC stack and each unit in the hydrogen-electric-heat-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 system.

[0010] Furthermore, it also includes a cold storage tank, which is connected to the lithium bromide absorption refrigerator and is used to store the output cold energy of the lithium bromide absorption refrigerator. The purpose of this arrangement is 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 cooling.

[0012] Furthermore, the lithium bromide absorption refrigerator utilizes cooling water for heat exchange and then discharges hot water for heat exchange, and the hot water is used for external heat supply, and 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 the PEMFC unit supplies power to the refrigeration / heat 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 a part of the hot water to enter the first circulation water circuit, and another part of the hot water to enter the second circulation water circuit.

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

[0014] Furthermore, one of the water inlets of the lithium bromide absorption refrigerator is also used to introduce external seawater, and one of the water outlets is directly connected to the low-temperature multi-effect distillation desalination device, so as to input the external seawater after heat exchange and cooling into the low-temperature multi-effect distillation desalination device to participate in the preparation of fresh water. The purpose of this arrangement is to achieve the purpose of using external seawater to cool the lithium bromide absorption refrigerator, and at the same time, the seawater after heat exchange can also enter the low-temperature multi-effect distillation desalination device to prepare fresh water.

[0015] Furthermore, the low-temperature multi-effect distillation desalination device has a water inlet for introducing raw seawater for preparing fresh water, and a water outlet for discharging excess raw seawater. The purpose of this arrangement is to realize the process of using the waste heat of the cooling water of the stack after meeting the heat load to participate in the production of fresh water by the low-temperature multi-effect distillation desalination device, and further improve the efficient utilization of the waste heat of the stack.

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

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

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

[0019] S3 The heated cooling water enters the lithium bromide absorption refrigerator for heat exchange and refrigeration, wherein 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 for heating and cooling enters the PEMFC unit through the cooling water tank to participate in the next cycle; or a part of the hot water for heating and cooling directly enters the PEMFC unit through the cooling water tank to participate in the next cycle, and another part of the hot water for heating and cooling first enters the low-temperature multi-effect distillation desalination device for heat exchange again, and then enters the PEMFC unit through the cooling water tank to participate in the next cycle.

[0021] Through the above technical solutions conceived by the present application, compared with the prior art, the variable load operation method of the hydrogen-electric-heat-cold multi-energy coupling integrated system of the present application can improve the grade of waste heat from the battery stack, so that the integrated system can use a refrigerator with a higher COP, further improving the refrigeration capacity of the system, and the integrated system can timely follow the changes in the user-side electricity / heat / cold load, and the cold output and heat output are independent of each other, which improves the overall efficiency of the integrated system. Therefore, the integrated system and variable load operation method provided by the present application are particularly suitable for applications in hydrogen-electric-heat-cold multi-energy coupling occasions 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 in the cold storage tank; when the cooling power is less than the cooling load on the user side, if there is cooling in the cold storage tank, the cold storage tank outputs cooling to supplement cooling; if there is no cooling 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 a part of the hot water to enter the PEMFC unit through the cooling water tank, and the other part of the cooling water enters the PEMFC unit through the cooling water tank after heat exchange in the first effect of the low-temperature multi-effect distillation seawater desalination device.

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

[0025] 1. In the hydrogen-electric-heat-cold multi-energy coupling integrated system provided in the present 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, simplifying the intermediate links and pipelines of the combined heat and power supply system. Specifically, on the one hand, the secondary heating of cooling water by solar collectors improves the grade of waste heat from the stack, so that the system can use lithium bromide absorption chillers with higher COP as the main cooling equipment, improving the cooling capacity of the system; on the other hand, while meeting the user-side load requirements, excess waste heat can enter the low-temperature multi-effect distillation 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-electric-heat-cold multi-energy coupling integrated system to promptly follow the changes in the user-side electricity / heat / cold load. The waste heat of the PEMFC stack is only used for heat output and fresh water production, not for refrigeration, and the heat required for refrigeration in the lithium bromide absorption chiller comes entirely from the solar collector heating the cooling water. Changes in the user-side cold load will only affect the output power of the PEMFC unit, while changes in the user-side heat load will only affect the output power and fresh water production of the PEMFC unit, ensuring that the system's cold output and heat output are independent of each other, improving the overall efficiency of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the structure of the hydrogen-electric-heat-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 of COP of a lithium bromide absorption refrigerator with the temperature of a heat source provided in Example 2 of the present application;

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

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

[0032] Figure 6 This is a schematic diagram of the change of 24-hour solar radiation and heat energy generated by a solar thermal collector provided in Example 2 of the present application;

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

[0034] Figure 8 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] Fig. 9 This is a schematic diagram of the change in PEMFC unit efficiency provided in Example 2 of the present application;

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

[0037] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

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

[0039] In addition, references throughout this specification to "one embodiment"; "one embodiment", "an example" or similar language indicate that a particular feature, structure, or characteristic described in conjunction 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] The present application provides a hydrogen-electric-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 collector, a lithium bromide absorption refrigerator, a low-temperature multi-effect distillation desalination device and a cooling water tank, wherein:

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

[0043] A three-way valve is provided on the water circuit of the lithium bromide absorption refrigerator 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, the solar collector, the lithium bromide absorption refrigerator and the cooling water tank form a second circulating water circuit;

[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 to participate in cooling and heating along the first circulating water path and the second circulating water path respectively.

[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 and generate 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 take the heat out of the stack.

[0046] In this embodiment, in order to maintain a uniform and stable temperature inside the stack, the temperature of the cooling water entering the stack is set to be 5°C lower than the temperature of the stack itself. In other embodiments, the temperature difference can also be set to be higher than 5°C or lower than 5°C, such as 3°C, 4°C, 6°C, 7°C, etc. 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 aforementioned PEMFC unit is not the focus of the invention of this application and will not be repeated 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 waste of cold.

[0048] In this embodiment, the aforementioned solar 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 minimum starting temperature of the lithium bromide absorption chiller, the lithium bromide absorption chiller starts refrigeration. The temperature difference of the cooling water in the solar collector is negatively correlated with the flow rate of the cold water. When the external solar radiation is insufficient or absent, the temperature of the cooling water entering and exiting the solar collector remains unchanged, so the lithium bromide absorption chiller cannot reach the starting temperature and will not start refrigeration.

[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 heating. When the heating amount 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, and the PEMFC unit runs to supply power to the refrigeration / heat machine to supplement the heating. When the heating amount is greater than the heat load on the user side, the three-way valve can allow a 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 the cooling water finally enters 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 effect of the low-temperature multi-effect distillation desalination device, where the cooling water exchanges heat with the raw seawater in the first effect, and enters the PEMFC unit through the cooling water tank when the temperature drops to 5°C lower than the temperature of the fuel cell itself. The other portion of the cooling water leaving the lithium bromide absorption chiller supplies heat to the outside according to the demand for heat load, until the temperature drops to 5°C lower than the fuel cell temperature, and then enters the PEMFC unit through the 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 water inlets of the lithium bromide absorption refrigerator is also used to introduce external seawater, as shown by the dotted line, and one of its water outlets is directly connected to the low-temperature multi-effect distillation desalination device, and is used to input the external seawater after heat exchange and cooling into the low-temperature multi-effect distillation desalination device for heat exchange, so as to provide heat for fresh water preparation. The purpose of this setting is to achieve the purpose of using external seawater to cool the lithium bromide absorption refrigerator, and at the same time, the seawater after heat exchange can also enter the low-temperature multi-effect distillation desalination device for fresh water preparation.

[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 As shown by the dashed line. Low-temperature multi-effect distillation is a seawater desalination technology with a maximum evaporation temperature of raw seawater below 70°C. The low-temperature multi-effect distillation seawater desalination device is composed 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, and the water vapor evaporated by the seawater enters the second effect as a heat source, and the process is carried out in sequence, thereby obtaining distilled water through multiple evaporation and condensation of seawater. Its specific structure is not the key innovative content of this application and will not be repeated 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 variable load operation method of the integrated system disclosed in Embodiment 1, such as Figure 2 As shown, the following steps are included:

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

[0058] Specifically, the PEMFC unit works at a power corresponding to the user-side electrical load as a reference output. 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 refrigeration, and outputs cold 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 also increases 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 exchange water discharged by the lithium bromide absorption chiller is the same as the real-time operating temperature of the fuel cell stack. The heat exchange water must be cooled by at least 5°C before it can enter the PEMFC unit to participate in 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 cooling down.

[0064] Specifically, the hot water discharged from the lithium bromide absorption chiller is used for external heat supply 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 cooling water of the corresponding flow rate 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 calculation formula of the cooling water out of the stack is:

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

[0067] Among them, Q stack The cooling water takes away the heat from the battery 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 of 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 refrigerator does not work, and the temperature of the cooling water entering and leaving the refrigerator is 80°C. When there is solar radiation, the cooling water heats up, and the refrigerator absorbs the heat of the cooling water and starts cooling. The cooling water cools down after heat exchange with the refrigerator, and the temperature leaving the refrigerator is 80°C.

[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 electricity / heating / cooling load on the user side for 24 hours are as follows: Figure 4 As shown, the PEMFC unit is Figure 4 The electrical loads shown are reference output powers.

[0078] The electric refrigeration / heating machine can consume electric energy to output cooling / heating. 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 output in this embodiment. After meeting the heat load, the waste heat of the stack enters the low-temperature multi-effect distillation seawater desalination device along with the water flow.

[0082] Solar radiation and the heat generated by solar collectors vary as Figure 6 As shown, this part of solar thermal energy is all used to heat 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 temperature of the cooling water does not change when it passes through the solar collector. When the solar collector absorbs solar radiation to generate heat, the cooling water begins to heat up. As the 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; then, the cooling water flow rate gradually increases, the solar radiation decreases, and the temperature difference also decreases rapidly, becoming 0 again at 16:30.

[0084] Energy changes of equipment related to cooling output in the integrated system Figure 8 As shown, it is assumed that at 0:00, the net cooling capacity of the cold storage tank is 0. From 0:00 to 7:10, due to the lack of solar radiation at night, the solar collector cannot reheat the cooling water, the lithium bromide absorption chiller does not operate, and the cooling load is completely provided by the electric refrigeration / heat engine alone. Therefore, during this period, the output power of the PEMFC unit is higher than the electrical load. Subsequently, the solar radiation increases rapidly, the cooling output of the lithium bromide absorption chiller increases rapidly, and the electric refrigeration / heat engine gradually shuts down. When the cooling output is greater than the cooling load, the excess cooling capacity is stored in the cold storage tank. At 13:30, the cold storage capacity of the cold storage tank reaches a peak of 26.2kWh. Thereafter, the solar radiation decreases, 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 16:20, the lithium bromide absorption chiller is shut down. At 17:30, the cold capacity stored in the cold storage tank is used up, the electric refrigeration / heat engine starts cooling again, and the output power of the PEMFC unit is higher than the electrical load again.

[0085] In this embodiment, the energy efficiency of the PEMFC unit is as follows: Fig. 9 When the PEMFC unit operates at low power, some waste heat is dissipated to the environment, resulting in a low percentage of recoverable heat and a significant reduction in thermal efficiency. As the operating power increases, the thermal efficiency increases rapidly, and in the medium and high power range it is complementary to the electrical efficiency, so the energy efficiency is stabilized at around 82%.

[0086] In this embodiment, the energy efficiency of the hydrogen-electric-heat-cooling multi-energy coupling integrated system is as follows: Fig.10 As shown. Since the COP of the lithium bromide absorption chiller is lower than the energy efficiency of the PEMFC power generation system, the energy efficiency of the system decreases significantly during the operation of the solar collector and the lithium bromide absorption chiller. When the solar collector and the lithium bromide absorption chiller stop running, the energy efficiency of the system is the same as that of the PEMFC power generation system. This shows that the heat of the lithium bromide absorption chiller comes entirely from the solar collector, and the cold output and heat output of the system are independent of each other and do not affect each other.

[0087] The hydrogen-electric-heat-cold multi-energy coupling integrated system and its variable load operation method provided by the present application can improve the grade of waste heat from the fuel cell stack, so that the system can use a refrigerator with a higher COP, thereby improving the cooling capacity of the system. The integrated system can timely follow the changes in the user-side electricity / heat / cold 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 method are particularly suitable for applications in hydrogen-electric-heat-cold multi-energy coupling scenarios based on low-temperature fuel cells.

[0088] Through the above technical solutions conceived by the present application, compared with the prior art, the variable load operation method of the hydrogen-electric-heat-cold multi-energy coupling integrated system of the present application can improve the grade of waste heat from the battery stack, so that the integrated system can use a refrigerator with a higher COP, further improving the refrigeration capacity of the system, and the integrated system can timely follow the changes in the user-side electricity / heat / cold load, and the cold output and heat output are independent of each other, which improves the overall efficiency of the integrated system. Therefore, the integrated system and variable load operation method provided by the present application are particularly suitable for applications in hydrogen-electric-heat-cold multi-energy coupling occasions based on low-temperature fuel cells.

[0089] It will be easily understood by those skilled in the art that the above description 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 shall be included in the scope of protection of the present application.

Claims

1. A hydrogen-electricity-heat-cooling multi-energy coupling integrated system, characterized in that: It includes: electric refrigeration / heat engine, PEMFC unit, solar collector, lithium bromide absorption refrigerator, low temperature multi-effect distillation desalination device and cooling water tank, among which: The PEMFC unit, solar 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 waterway 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 waterway; 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 to participate in cooling and heating along the first circulating water path and the second circulating water path respectively.

2. A hydrogen-electricity-heat-cooling multi-energy coupling integrated system as claimed in claim 1, characterized in that: It 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 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 refrigeration.

4. The hydrogen-electricity-heat-cooling multi-energy coupling integrated system according to claim 1, characterized in that: The lithium bromide absorption refrigerator utilizes 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 circulating water circuit, and the PEMFC unit supplies power to the refrigeration / heating machine to supplement the heating. When the heat supply is greater than the heat load on the user side, the three-way valve allows a portion of the hot water to enter the first circulating water circuit and another portion of the hot water to enter the second circulating water circuit.

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

6. The hydrogen-electricity-heat-cooling multi-energy coupling integrated system according to claim 1, characterized in that: A water inlet of the lithium bromide absorption refrigerator is also used to introduce external seawater, and a water outlet is directly connected to the low-temperature multi-effect distillation seawater desalination device 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. A hydrogen-electricity-heat-cooling multi-energy coupling integrated system as claimed in 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 Based on the electricity load demand on the user side, the PEMFC unit outputs the corresponding power to generate electricity and produce cooling water; S2 The cooling water is input into the solar collector and heated to a preset temperature by solar radiation; S3 The heated cooling water enters the lithium bromide absorption refrigerator for heat exchange and refrigeration, wherein 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 for heating and cooling enters the PEMFC unit through the cooling water tank to participate in the next cycle; or a part of the hot water for heating and cooling directly enters the PEMFC unit through the cooling water tank to participate in the next cycle, and another part of the hot water for heating and cooling first enters the low-temperature multi-effect distillation desalination device for heat exchange again, and then enters 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-cold 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 in the cold storage tank; when the cooling power is less than the cooling load on the user side, if there is cooling in the cold storage tank, the cold storage tank outputs cooling to supplement cooling; if there is no cooling 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-cold 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 enters the PEMFC unit through the cooling water tank after heat exchange in the first effect of the low-temperature multi-effect distillation seawater desalination device.

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