A multi-grade waste heat grading recovery system and method for a proton exchange membrane fuel cell

Abstract

The application discloses a multi-grade waste heat grading recovery system and method of a proton exchange membrane fuel cell, and relates to the technical field of fuel cell waste heat recovery. The system not only realizes the grading and efficient recovery and storage of multi-grade waste heat of the proton exchange membrane fuel cell, but also realizes efficient and stable heat output under all working conditions of the system, and can ensure the cooling safety of the fuel cell. The system comprises a temperature zone dividing heat storage device, a first waste heat recovery unit, a second waste heat recovery unit and a third waste heat recovery unit. The temperature zone dividing heat storage device is divided into a high-temperature heat storage zone, a medium-temperature heat storage zone and a low-temperature heat storage zone. The first waste heat recovery unit is in communication with the low-temperature heat storage zone. The second waste heat recovery unit is integrated with a heat pump system. The second waste heat recovery unit is selectively in communication with the high-temperature heat storage zone, the medium-temperature heat storage zone or the low-temperature heat storage zone. The third waste heat recovery unit is in communication with the high-temperature heat storage zone. The application also discloses a recovery method based on the above recovery system.

Description

Technical Field

[0001] This application relates to the field of fuel cell waste heat recovery technology, and in particular to a multi-grade waste heat recovery system and method for proton exchange membrane fuel cells. Background Technology

[0002] When a proton exchange membrane fuel cell (PEMFC) generates electricity, its theoretical energy conversion efficiency is about 50%, with most of the remaining energy being lost as heat. Recovering and utilizing this waste heat for heating, hot water supply, or industrial processes to form a combined heat and power (CHP) system is key to increasing the primary energy utilization rate of fuel cell systems to over 80%.

[0003] While existing waste heat recovery technologies for fuel cells have achieved varying degrees of recovery from multiple sources of waste heat in fuel cell systems, they still have the following drawbacks: 1. Serious waste of thermal energy grade: Existing waste heat recovery technologies do not consider the grade level and recover all of them into a single thermal storage device. This results in the mixing of high-grade exhaust gas combustion heat and low-grade fuel cell stack cooling heat, reducing the availability of high-temperature thermal energy and limiting its application scenarios.

[0004] 2. The system integration is low and there is still room for improvement in energy efficiency: Most existing waste heat recovery technologies mainly focus on recovering waste heat from fuel cell stacks. Very few technologies consider waste heat from auxiliary components, heat pump heating, or exhaust gas. They also do not consider all heat sources in a unified manner, and they do not effectively regulate the heating performance and power of the heat pump system, resulting in low overall system energy efficiency.

[0005] 3. Potential safety hazards exist in operation: When user-side heat demand suddenly drops or disappears, current technology lacks a backup heat dissipation path independent of the heating circuit. If the heat storage device is full, the fuel cell may overheat and shut down or be damaged due to insufficient cooling. Summary of the Invention

[0006] The embodiments of this application provide a multi-grade waste heat recovery system and method for proton exchange membrane fuel cells. It not only realizes the tiered and efficient recovery and storage of multi-grade waste heat from proton exchange membrane fuel cells, but also achieves efficient and stable heat output under all operating conditions by constructing a highly integrated multi-heat source collaborative recovery system. It can also ensure the cooling safety of fuel cells and achieve decoupling and synergy between waste heat recovery and core equipment cooling.

[0007] To achieve the above objectives, in one aspect, embodiments of this application provide a multi-grade waste heat recovery system for proton exchange membrane fuel cells, including a temperature-zoned heat storage device, a first waste heat recovery unit, a second waste heat recovery unit, and a third waste heat recovery unit. The internal structure of the temperature-zoned heat storage device is divided into a high-temperature heat storage zone, a medium-temperature heat storage zone, and a low-temperature heat storage zone from top to bottom. The first waste heat recovery unit is connected to the low-temperature heat storage zone and is used to recover low-grade waste heat generated during the operation of the fuel cell system, and to transport the heat to the low-temperature heat storage zone or to perform system safety heat dissipation. The second waste heat recovery unit integrates a heat pump system. The second waste heat recovery unit can be selectively connected to the high-temperature heat storage zone, the medium-temperature heat storage zone, or the low-temperature heat storage zone, and is used to absorb heat from the air or the low-grade waste heat of the first waste heat recovery unit, and to transport the upgraded heat to the matching high-temperature heat storage zone, the medium-temperature heat storage zone, or the low-temperature heat storage zone. The third waste heat recovery unit is connected to the high-temperature heat storage zone and is used to recover high-grade waste heat generated after catalytic combustion of fuel cell exhaust gas, and to transport the heat to the high-temperature heat storage zone.

[0008] Furthermore, the temperature-divided heat storage device is a vertical hot water storage tank, which maintains temperature stratification through density differences formed by water temperature differences, and heat insulation baffles are respectively installed between the medium-temperature heat storage zone, the high-temperature heat storage zone, and the low-temperature heat storage zone.

[0009] Furthermore, the low-grade waste heat includes waste heat from the fuel cell stack and waste heat from auxiliary components; the first waste heat recovery unit includes a fuel cell stack cooling branch, an auxiliary component cooling branch, a heat storage circulation branch, and a cooling branch; the fuel cell stack cooling branch includes the fuel cell stack, a first heat exchanger, and a first circulation pump; the first heat exchanger includes a low-temperature side channel and a high-temperature side channel; the inlet of the high-temperature side channel of the first heat exchanger is connected to the outlet of the fuel cell stack, and the outlet is connected to the inlet of the first circulation pump; the auxiliary component cooling branch includes auxiliary components, a second heat exchanger, and a second circulation pump; The second heat exchanger includes a low-temperature side channel and a high-temperature side channel; the inlet of the high-temperature side channel of the second heat exchanger is connected to the outlet of the auxiliary component, and the outlet is connected to the inlet of the second circulation pump; the low-temperature side channels of both the first and second heat exchangers can be selectively connected to the heat storage circulation branch or the cooling branch; the heat storage circulation branch can transfer the waste heat of the fuel cell stack and the waste heat of the auxiliary component to the low-temperature heat storage area when the low-temperature heat storage area has heat storage capacity; the cooling branch can dissipate the waste heat of the fuel cell stack and the waste heat of the auxiliary component when the low-temperature heat storage area is saturated or when it is necessary to ensure the cooling of the equipment.

[0010] Furthermore, the thermal storage circulation branch includes a sixth circulation pump; the cooling branch includes a cooling device and a seventh circulation pump; the low-temperature side channel of the first heat exchanger and the low-temperature side channel of the second heat exchanger are connected in parallel, and the inlets of the low-temperature side channels of the first and second heat exchangers can be selectively connected to the outlet of the sixth circulation pump or the outlet of the seventh circulation pump; the outlets of the low-temperature side channels of the first and second heat exchangers can be selectively connected to the inlet of the low-temperature thermal storage zone or the inlet of the cooling device; the inlet of the sixth circulation pump is connected to the outlet of the low-temperature thermal storage zone; and the outlet of the cooling device is connected to the inlet of the seventh circulation pump.

[0011] Furthermore, the first waste heat recovery unit also includes a first three-way valve, a second three-way valve, a third three-way valve, and a fourth three-way valve; the two inlets of the first three-way valve are respectively connected to the outlets of the sixth and seventh circulating pumps, and the outlet of the first three-way valve is connected to the inlet of the second three-way valve; the two outlets of the second three-way valve are respectively connected to the inlets of the low-temperature side channels of the first and second heat exchangers; the two inlets of the third three-way valve are respectively connected to the outlets of the low-temperature side channels of the first and second heat exchangers; the outlet of the third three-way valve is connected to the inlet of the fourth three-way valve, and the two outlets of the fourth three-way valve are respectively connected to the inlet of the low-temperature heat storage area or the inlet of the cooling device.

[0012] Furthermore, the second waste heat recovery unit also includes a fourth circulation pump; the heat pump system adopts a vapor compression heat pump system; the vapor compression heat pump system includes an evaporator, a compressor, a condenser, and an expansion valve that are sequentially connected and form a closed loop along the flow direction of the fluid; the evaporator can absorb heat from the ambient air or from the low-grade waste heat of the first waste heat recovery unit; the inlet of the fourth circulation pump is connected to the outlet of the low-temperature heat storage zone, and the outlet is connected to the inlet of the condenser on the condensing side; the outlet of the condenser on the condensing side can be selectively connected to the high-temperature heat storage zone, the medium-temperature heat storage zone, or the low-temperature heat storage zone through a multi-way switching valve; when the evaporator absorbs heat from the ambient air, the outlet of the low-temperature side channel of the condenser is connected to the low-temperature heat storage zone; when the evaporator absorbs heat from the low-grade waste heat of the first waste heat recovery unit, the outlet of the low-temperature side channel of the condenser is connected to the medium-temperature heat storage zone or the high-temperature heat storage zone.

[0013] Furthermore, the third waste heat recovery unit includes a fuel cell exhaust gas catalytic combustion waste heat circuit and a fifth circulation pump; the fuel cell exhaust gas catalytic combustion waste heat circuit includes a catalytic burner, a third heat exchanger, and a third circulation pump; the catalytic burner is used to treat fuel cell exhaust gas; the third heat exchanger includes a low-temperature side channel and a high-temperature side channel; the inlet of the high-temperature side channel of the third heat exchanger is connected to the outlet of the catalytic burner, and the outlet of the high-temperature side channel of the third heat exchanger is connected to the inlet of the third circulation pump; the inlet of the fifth circulation pump is connected to the outlet of the high-temperature heat storage area, and the outlet is connected to the inlet of the low-temperature side channel of the third heat exchanger, and the outlet of the low-temperature side channel of the third heat exchanger is connected to the inlet of the high-temperature heat storage area.

[0014] Furthermore, it also includes a control unit; the control unit is communicatively connected to the sixth circulating pump, the seventh circulating pump, the fourth circulating pump, the vapor compression heat pump system, the third circulating pump, and the fifth circulating pump; The control unit is configured to: start the third and fifth circulation pumps; upon receiving a switch to heat storage mode, connect the low-temperature side channels of the first and second heat exchangers to the heat storage circulation branch and start the sixth circulation pump; upon receiving a switch to safe heat dissipation mode, connect the low-temperature side channels of the first and second heat exchangers to the cooling branch and start the seventh circulation pump; upon receiving a signal to switch to ambient heat replenishment mode, start the fan or pump on the evaporator side of the heat pump system to absorb heat from the ambient air, control the heat pump system to operate at a high energy efficiency ratio, and then control the heat pump... The outlet of the condenser side in the system is connected to the inlet of the low-temperature heat storage zone, and the fourth circulation pump is started. When the signal to switch to the waste heat upgrading mode is received, the heat source of the evaporator in the heat pump system is switched to low-grade waste heat from the first waste heat recovery unit, and the heat pump system is controlled to operate at a low energy efficiency ratio. Then, according to the real-time outlet water temperature and the needs of the high-temperature / medium-temperature heat storage zone, the outlet of the condenser side in the heat pump system is connected to the inlet of the medium-temperature heat storage zone or the high-temperature heat storage zone, and the fourth circulation pump is started. When the signal to switch to the catalytic combustion waste heat utilization mode is received, the third and fifth circulation pumps are started.

[0015] On the other hand, embodiments of this application also provide a recovery method based on the above-mentioned multi-grade waste heat recovery system for proton exchange membrane fuel cells, comprising the following steps: starting a first waste heat recovery unit to begin recovering low-grade waste heat from the fuel cell system and transferring the heat to a low-temperature heat storage area or for system safety cooling; starting a second waste heat recovery unit to begin recovering low-grade waste heat from the air recovered by the heat pump system or from the first waste heat recovery unit and transferring the upgraded heat to a matching high-temperature heat storage area, medium-temperature heat storage area, or low-temperature heat storage area; and starting a third waste heat recovery unit to begin recovering high-grade waste heat generated by the catalytic combustion of fuel cell exhaust gas and transferring the heat to a high-temperature heat storage area.

[0016] Furthermore, the first waste heat recovery unit is activated to begin recovering the low-grade waste heat from the fuel cell system and transferring the heat to the low-temperature storage area or for safe system cooling. This specifically includes the following steps: Monitor the status of the low-temperature thermal storage area; when the low-temperature thermal storage area has thermal storage capacity, control the first waste heat recovery unit to transfer heat to the low-temperature thermal storage area; when the low-temperature thermal storage area is saturated or needs to ensure equipment cooling, control the first waste heat recovery unit to perform system safety heat dissipation.

[0017] This application has the following advantages over the prior art: 1. Compared to existing technologies that use a single heat storage device or simple parallel loops to recover waste heat, which easily mix heat of different grades, leading to a decrease in overall efficiency, the multi-grade waste heat recovery system for proton exchange membrane fuel cells in this application achieves refined graded recovery and tiered utilization of waste heat of different grades from the fuel cell system through an innovative structure of temperature-zoned heat storage devices and three-stage parallel waste heat recovery units. Specifically, the first waste heat recovery unit focuses on recovering low-grade waste heat from the fuel cell stack and auxiliary components and storing it in the low-temperature zone; the second waste heat recovery unit uses a heat pump system to raise the low-grade heat source to different temperatures according to demand, flexibly supplementing the corresponding temperature zones; and the third waste heat recovery unit specifically recovers high-grade waste heat generated by the catalytic combustion of exhaust gas and stores it in the high-temperature zone. This architecture, which stores waste heat according to temperature and grade and precisely schedules it according to demand, effectively avoids the ineffective mixing of heat of different grades, allowing for more complete utilization of high-grade heat energy and a more rational destination for medium and low-grade heat energy, thereby significantly improving waste heat efficiency and overall energy utilization rate at the system level.

[0018] 2. In traditional systems, the cooling safety and waste heat recovery functions of the fuel cell stack are intertwined. Once the heat storage end becomes saturated, it directly threatens the safe operation of the fuel cell stack. This application's embodiment of a multi-grade waste heat recovery system for proton exchange membrane fuel cells deconstructs the waste heat recovery and stack cooling functions of the fuel cell system, ensuring system safety. This application establishes a forced safety cooling branch independently and in parallel within the first waste heat recovery unit. When the heat storage device becomes saturated, the control system immediately switches the stack cooling circuit to this safety branch, ensuring that the heat dissipation requirements of the fuel cell stack are unconditionally and preferentially met. This completely breaks the dangerous coupling inherent in traditional systems and ensures that the cooling safety of the fuel cell body is independently and reliably guaranteed regardless of the state of the waste heat recovery system (saturation, failure, or maintenance). Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of a multi-grade waste heat recovery system for a proton exchange membrane fuel cell according to an embodiment of this application.

[0021] Figure 2 This is a schematic diagram of multi-grade waste heat recovery and heat flow scheduling in a fuel cell system. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] In the description of this application, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0024] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation", "connection" and "joining" should be interpreted broadly, for example, they can refer to fixed connections, detachable connections, or integral connections; those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0025] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" can explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0026] Reference Figure 1 and Figure 2This application provides a multi-grade waste heat recovery system for proton exchange membrane fuel cells, including a temperature zone heat storage device 1, a first waste heat recovery unit 2, a second waste heat recovery unit 3, and a third waste heat recovery unit 4. The first waste heat recovery unit 2, the second waste heat recovery unit 3, and the third waste heat recovery unit 4 are connected in parallel.

[0027] The temperature-zoned thermal storage device 1 is a vertical hot water tank based on temperature stratification. Internally, it naturally separates and stably maintains a high-temperature thermal storage zone 11, a medium-temperature thermal storage zone 12, and a low-temperature thermal storage zone 13 along the vertical direction, relying on the density difference created by the water temperature difference. Insulating baffles with through holes can be installed between each zone to suppress convection and enhance the stratification effect. The tank has independent water distributor inlets and temperature sensors in the high, medium, and low temperature zones for low-disturbance water injection and real-time temperature monitoring.

[0028] The first waste heat recovery unit 2 is connected to the cryogenic heat storage zone 13 and is used to recover low-grade waste heat generated during the operation of the fuel cell system, and to transfer the heat to the cryogenic heat storage zone 13 or to perform system safety heat dissipation. The low-grade waste heat includes waste heat from the fuel cell stack and waste heat from auxiliary components. The first waste heat recovery unit 2 includes a fuel cell stack cooling branch, an auxiliary component cooling branch, a heat storage circulation branch, and a cooling branch. The core of the first waste heat recovery unit 2 lies in its integration of the dual functions of heat recovery and system safety heat dissipation, achieving a smooth transition between the two operating modes through valve switching.

[0029] The fuel cell stack cooling branch includes a fuel cell stack 21, a first heat exchanger 22, and a first circulation pump 23.

[0030] The first heat exchanger 22 includes a low-temperature side channel and a high-temperature side channel. The fuel cell stack 21, the high-temperature side channel of the first heat exchanger 22, and the first circulation pump 23 are sequentially connected along the fluid flow direction and form a first closed loop with corresponding pipeline valves. The cooling medium is preferably an aqueous solution of ethylene glycol. The first circulation pump 23 drives the cooling medium to flow through the fuel cell stack 21, carrying away its heat and transferring it to the first heat exchanger 22. The low-temperature side channel of the first heat exchanger 22 can be selectively connected to a thermal storage circulation branch or a cooling branch. The first heat exchanger 22 transfers heat from the cooling circuit of the fuel cell stack 21 to the thermal storage circulation branch or the cooling branch.

[0031] The auxiliary component cooling branch includes auxiliary component 24, second heat exchanger 25 and second circulation pump 26.

[0032] Auxiliary components 24 include air compressors, DC / DC converters, etc.

[0033] The second heat exchanger 25 also includes a low-temperature side channel and a high-temperature side channel. The auxiliary component 24, the high-temperature side channel of the second heat exchanger 25, and the second circulation pump 26 are sequentially connected along the fluid flow direction and form a second closed loop with corresponding pipeline valves. The cooling medium is preferably an aqueous solution of ethylene glycol. The second circulation pump 26 drives the cooling medium to flow through the auxiliary component 24 of the fuel cell, carrying away its heat and transferring it to the second heat exchanger 25. The low-temperature side channel of the second heat exchanger 25 can also be selectively connected to a heat storage circulation branch or a cooling branch. The second heat exchanger 25 transfers heat from the cooling circuit of the auxiliary component 24 of the fuel cell to the heat storage circulation branch or the cooling path.

[0034] The thermal storage circulation branch includes a sixth circulation pump 27 and pipelines connecting the low-temperature thermal storage zone 13, the sixth circulation pump 27, the first three-way valve 28, the fourth three-way valve 213, and the first heat exchanger 22 and the second heat exchanger 25 respectively via the second three-way valve 29 and the third three-way valve 212. When the low-temperature thermal storage zone 13 has thermal storage capacity, the thermal storage circulation branch can transfer the waste heat from the fuel cell stack and auxiliary components to the low-temperature thermal storage zone 13.

[0035] The cooling branch and the heat storage circulation branch are connected in parallel, including a first three-way valve 28, a cooling device 211, a seventh circulation pump 210, a fourth three-way valve 213, and connecting pipelines. The cooling device 211 is either air-cooled or water-cooled. The cooling branch can dissipate waste heat from the fuel cell stack and auxiliary components when the low-temperature heat storage zone 13 is saturated or when equipment cooling is required.

[0036] Specifically, the inlet of the sixth circulating pump 27 is connected to the outlet of the low-temperature heat storage zone 13, and the outlet is connected to the first inlet of the first three-way valve 28. The outlet of the first three-way valve 28 is connected to the inlet of the second three-way valve 29. The two outlets of the second three-way valve 29 are respectively connected to the inlets of the low-temperature side channels of the first heat exchanger 22 and the second heat exchanger 25. The outlets of the low-temperature side channels of the first heat exchanger 22 and the second heat exchanger 25 are respectively connected to the two inlets of the third three-way valve 212. The outlet of the third three-way valve 212 is connected to the inlet of the fourth three-way valve 213. The first outlet of the fourth three-way valve 213 is connected to the inlet of the low-temperature heat storage zone 13, and the second outlet is connected to the inlet of the cooling device 211. The outlet of the cooling device 211 is connected to the inlet of the seventh circulating pump 210, and the outlet of the seventh circulating pump 210 is connected to the second inlet of the first three-way valve 28.

[0037] The first waste heat recovery unit 2 has two operating modes, which are switched according to the state of the low-temperature heat storage zone 13: Thermal Storage Mode: When the cryogenic thermal storage zone 13 has thermal storage capacity, the first three-way valve 28 and the fourth three-way valve 213 are controlled to open the thermal storage circulation branch and close the safety cooling branch. The sixth circulation pump 27 is started to drive the working fluid in the cryogenic thermal storage zone 13, forming two independent flow paths that flow through the cryogenic sides of the first heat exchanger 22 and the second heat exchanger 25, respectively. Inside the heat exchangers, the working fluid on the thermal storage side undergoes indirect heat exchange with the high-temperature ethylene glycol solution on the heat source side, efficiently absorbing the waste heat from the fuel cell stack and auxiliary components 24. The heated working fluid water returns to the cryogenic thermal storage zone 13 for storage, completing heat recovery. This process continuously and effectively cools the fuel cell system. At this time, the seventh circulation pump 210 and the cooling device 211 do not participate in the thermal storage process.

[0038] Safe heat dissipation mode: When the low-temperature heat storage zone 13 reaches its heat storage limit, the first three-way valve 28 and the fourth three-way valve 213 are controlled to close the heat storage circulation branch and open the cooling branch. At this time, the seventh circulation pump 210 is started, driving the cooling working fluid to flow through the low-temperature side of the first heat exchanger 22 and the second heat exchanger 25 and the cooling device 211 to dissipate heat to the environment, so as to independently and continuously provide cooling protection for the fuel cell stack 21 and auxiliary components 24, ensuring the safe operation of the system. The cooling branch of the fuel cell stack 21 and the cooling branch of the auxiliary components 24 continue to operate in this mode. At this time, the sixth circulation pump 27 and the heat storage device do not participate in the cooling process.

[0039] The second waste heat recovery unit 3 serves as the core of the system's adjustable-grade active heating. It is mainly used to circulate the energy from the ambient air or the low-grade waste heat of the first waste heat recovery unit 2 to a usable temperature through a heat pump, and intelligently distribute it to the corresponding temperature zone of the temperature-divided heat storage device 1 according to the system's needs.

[0040] The second waste heat recovery unit 3 includes a heat pump system, a fourth circulation pump 35, and a multi-way switching valve 36.

[0041] The heat pump system employs a complete vapor compression heat pump system. The vapor compression heat pump system includes an evaporator 31, a compressor 32, a condenser 33, and an expansion valve 34, which are sequentially connected along the fluid flow direction to form a closed loop, along with corresponding control components. The refrigerant used is preferably environmentally friendly refrigerants such as R134a or R290.

[0042] In the heat pump circuit, low-temperature, low-pressure liquid refrigerant flows through evaporator 31, exchanging heat with ambient heat sources or other low-grade heat sources. The refrigerant boils and evaporates at a relatively low temperature, absorbing a large amount of heat from the environment or other low-grade heat sources, and transforms into a low-temperature, low-pressure gaseous refrigerant. Subsequently, compressor 32 adiabatically compresses it, transforming the refrigerant into a high-temperature, high-pressure gaseous state. It then flows through condenser 33, exchanging heat with the heat storage circulating medium flowing outside condenser 33. During this process, the refrigerant condenses and liquefies, releasing a large amount of heat. The high-temperature, high-pressure liquid refrigerant then flows through expansion valve 34, undergoing adiabatic throttling expansion, causing its pressure and temperature to drop sharply, forming a low-temperature, low-pressure gas-liquid mixture, which then flows into evaporator 31 to enter the next cycle.

[0043] Specifically, the evaporator 31 can absorb heat from the ambient air or from the low-grade waste heat of the first waste heat recovery unit 2; the inlet of the fourth circulation pump 35 is connected to the outlet of the low-temperature heat storage zone 13, and the outlet is connected to the inlet of the condenser side of the condenser 33; the outlet of the condenser side of the condenser 33 can be selectively connected to the high-temperature heat storage zone 11, the medium-temperature heat storage zone 12, or the low-temperature heat storage zone 13 through the multi-way switching valve 36; when the evaporator 31 absorbs heat from the ambient air, the outlet of the low-temperature side channel of the condenser 33 is connected to the low-temperature heat storage zone 13; when the evaporator 31 absorbs heat from the low-grade waste heat of the first waste heat recovery unit 2, the outlet of the low-temperature side channel of the condenser 33 is connected to the medium-temperature heat storage zone 12 or the high-temperature heat storage zone 11.

[0044] For the second waste heat recovery unit 3, the fourth circulating pump 35 drives the working fluid in the heat storage device to first flow through the connected condenser 33 to recover heat from the heat pump circuit, and then return to the heat storage device. The heat generated by the heat pump can be input into different temperature-layer heat storage devices according to the grade characteristics and requirements.

[0045] Based on the system's heating demand, the temperature of each heat storage zone, and the operating status of the heat pump, the second waste heat recovery unit 3 is dynamically adjusted, mainly including the following two basic modes: Ambient Heating Mode: This mode is activated when the system's primary demand is to supplement the basic heat load (such as building heating) and environmental conditions are suitable. The fan or pump on the evaporator 31 side is controlled to extract heat from the ambient air. The heat pump is controlled to operate at a high energy efficiency ratio, with its condenser 33 outlet water temperature typically set in the medium-low temperature range of 35°C to 55°C. The outlet water is guided to the low-temperature heat storage zone 13 of the temperature-zoned heat storage device 1 for storage as a basic heat source.

[0046] Waste Heat Enhancement Mode: This mode is activated when high-temperature hot water needs to be produced or low-grade waste heat needs to be upgraded. The heat source of evaporator 31 is switched to low-temperature waste heat from the first waste heat recovery unit 2 (e.g., cooling water at 40-50°C). This heat source temperature is higher than that of ambient air, which can significantly improve the coefficient of performance and output temperature of the heat pump. The heat pump is controlled to achieve a condenser 33 outlet water temperature of 60°C to 85°C or even higher in the medium-high temperature range. Based on the real-time outlet water temperature and the demand of the high-temperature / medium-temperature heat storage zone 12, hot water is precisely allocated to the medium-temperature heat storage zone 12 or the high-temperature heat storage zone 11. For example, when 75°C hot water is produced and the high-temperature zone has an urgent need, it is injected into the high-temperature zone; when 65°C hot water is produced and is mainly used for preheating domestic hot water, it is injected into the medium-temperature zone. It should be noted that the temperature of the hot water can be measured by the thermometer built into the heat pump system, and the urgency of the high-temperature zone demand is determined by the water level gauge of the high-temperature heat storage zone 11 or by feedback from the client.

[0047] The third waste heat recovery unit 4 is connected to the high-temperature heat storage zone 11 and is used to recover the high-grade waste heat generated after the fuel cell exhaust gas is catalytically combusted, and to transport the heat to the high-temperature heat storage zone 11.

[0048] The third waste heat recovery unit 4 includes a waste heat circuit for catalytic combustion of fuel cell exhaust gas and a fifth circulation pump 44.

[0049] The waste heat circuit of fuel cell exhaust catalytic combustion includes a catalytic burner 41, a third heat exchanger 42, and a third circulation pump 43.

[0050] The waste heat recovery circuit for fuel cell exhaust gas catalytic combustion is an important component of the third waste heat recovery unit 4. After the fuel cell exhaust gas is mixed with supplemental air, it enters the catalytic burner 41, where a flameless combustion reaction occurs under the action of a catalyst, releasing chemical energy and converting it into heat energy.

[0051] The third heat exchanger 42 includes a low-temperature side channel and a high-temperature side channel. The inlet of the high-temperature side channel of the third heat exchanger 42 is connected to the outlet of the catalytic burner 41, and the outlet of the high-temperature side channel of the third heat exchanger 42 is connected to the inlet of the third circulating pump 43. The inlet of the fifth circulating pump 44 is connected to the outlet of the high-temperature heat storage zone 11, and the outlet is connected to the inlet of the low-temperature side channel of the third heat exchanger 42. The outlet of the low-temperature side channel of the third heat exchanger 42 is connected to the inlet of the high-temperature heat storage zone 11.

[0052] In this way, the working fluid in the third circulation pump 43 drives the heat away from the catalytic burner 41 and transfers the heat to the third heat exchanger 42, where it exchanges heat with the heat storage circulating working fluid flowing outside the third heat exchanger 42. The fifth circulation pump 44 drives the working fluid in the heat storage device, which flows through the third heat exchanger 42 and is connected to the high-temperature heat storage zone 11 to recover high-grade waste heat from the catalytic combustion process. The third circulation pump 43 and the fifth circulation pump 44 are activated in real time.

[0053] Figure 2 This is a schematic diagram of multi-grade waste heat recovery and heat flow scheduling in a fuel cell system provided in the embodiments of this application.

[0054] The diagram clearly illustrates the connection between heat sources of different grades and their corresponding thermal storage areas, as well as the path and direction of heat flow. The waste heat recovery system in this embodiment also includes a control unit (not shown in the figure). The control unit can control the working status and heat distribution of the first waste heat recovery unit 2, the second waste heat recovery unit 3 and the third waste heat recovery unit 4 based on the temperature of each zone of the temperature-divided heat storage device 1.

[0055] Specifically, the control unit is communicatively connected to the first three-way valve 28, the fourth three-way valve 213, the multi-way switching valve 36, the sixth circulating pump 27, the seventh circulating pump 210, the fourth circulating pump 35, the vapor compression heat pump system, the third circulating pump 43, and the fifth circulating pump 44.

[0056] The control unit is configured as follows: Upon receiving the switch to thermal storage mode, the system controls the low-temperature side channels of the first heat exchanger 22 and the second heat exchanger 25 to connect with the thermal storage circulation branch (i.e., controls the first three-way valve 28 to switch to the first inlet connected and the second inlet closed; and the fourth three-way valve 213 to switch to the first outlet connected and the second outlet closed), and starts the sixth circulation pump 27.

[0057] Upon receiving the switch to safe heat dissipation mode, the low-temperature side channels of the first heat exchanger 22 and the second heat exchanger 25 are connected to the cooling branch (i.e., the first three-way valve 28 is switched to the second inlet and the first inlet is closed; the fourth three-way valve 213 is switched to the second outlet and the first outlet is closed), and the seventh circulation pump 210 is started.

[0058] Upon receiving a signal to switch to ambient heating mode, the system controls the start of the fan or pump on the evaporator 31 side of the heat pump system to absorb heat from the ambient air and controls the heat pump system to operate at a high energy efficiency ratio. Then, the system controls the outlet of the condenser 33 side of the heat pump system to connect with the inlet of the low-temperature heat storage zone 13 and starts the fourth circulation pump 35.

[0059] Upon receiving the signal to switch to waste heat enhancement mode, the heat source of the evaporator 31 in the heat pump system is switched to low-grade waste heat from the first waste heat recovery unit 2, and the heat pump system is controlled to operate at a low energy efficiency ratio. Then, based on the real-time outlet water temperature and the requirements of the high-temperature / medium-temperature heat storage zone 12, the outlet of the condenser 33 in the heat pump system is connected to the inlet of the medium-temperature heat storage zone 12 or the high-temperature heat storage zone 11 (the multi-way switching valve 36 is switched to connect the outlet to the medium-temperature heat storage zone 12 or the high-temperature heat storage zone 11), and the fourth circulation pump 35 is started.

[0060] It should be noted that: high energy efficiency ratio refers to 3.5-4.5; low energy efficiency ratio refers to 2.5-3.5.

[0061] In addition, to improve energy efficiency, the recovery system in this application embodiment is equipped with temperature sensors on the first heat exchanger 22, the second heat exchanger 25, the heat pump system, and the third heat exchanger 42. Based on a comparison between the actual detection values ​​of each temperature sensor and a preset suitable ambient temperature value, the operating power of each circulation pump is controlled to ensure that each device operates within a suitable temperature range and recovers all heat with minimal power consumption. Furthermore, embodiments of this application also provide a recovery method based on the above-described multi-grade waste heat recovery system for proton exchange membrane fuel cells, comprising the following steps: S1. Activate the first waste heat recovery unit 2 to begin recovering low-grade waste heat from the fuel cell system and transfer the heat to the low-temperature storage area 13 or for safe system cooling. Specifically, this includes the following steps: Monitor the status of low-temperature thermal storage area 13; When the low-temperature heat storage zone 13 has heat storage capacity, the first waste heat recovery unit 2 is controlled to transfer heat to the low-temperature heat storage zone 13; when the low-temperature heat storage zone 13 is saturated or needs to ensure equipment cooling, the first waste heat recovery unit 2 is controlled to perform system safety heat dissipation.

[0062] S2. Start the second waste heat recovery unit 3 to start recovering the low-grade waste heat from the air recovered by the heat pump system or the first waste heat recovery unit 2, and transport the upgraded heat to the matching high-temperature heat storage zone 11, medium-temperature heat storage zone 12 or low-temperature heat storage zone 13.

[0063] S3. Start the third waste heat recovery unit 4 to start recovering the high-grade waste heat generated by the catalytic combustion of fuel cell exhaust gas and transport the heat to the high-temperature heat storage area 11.

[0064] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A multi-grade waste heat recovery system for proton exchange membrane fuel cells, characterized in that, It includes a temperature-zoned thermal storage device, a first waste heat recovery unit, a second waste heat recovery unit, and a third waste heat recovery unit; The internal structure of the temperature-zoned thermal storage device is divided into a high-temperature thermal storage zone, a medium-temperature thermal storage zone, and a low-temperature thermal storage zone from top to bottom. The first waste heat recovery unit is connected to the low-temperature thermal storage zone and is used to recover the low-grade waste heat generated during the operation of the fuel cell system, and to transfer the heat to the low-temperature thermal storage zone or to perform system safety heat dissipation. The second waste heat recovery unit integrates a heat pump system. The second waste heat recovery unit can be selectively connected to the high-temperature thermal storage zone, the medium-temperature thermal storage zone, or the low-temperature thermal storage zone, and is used to absorb heat from the air or the low-grade waste heat of the first waste heat recovery unit, and to transfer the upgraded heat to the matching high-temperature thermal storage zone, the medium-temperature thermal storage zone, or the low-temperature thermal storage zone. The third waste heat recovery unit is connected to the high-temperature thermal storage zone and is used to recover the high-grade waste heat generated after the fuel cell exhaust gas is catalytically combusted, and to transfer the heat to the high-temperature thermal storage zone.

2. The multi-grade waste heat recovery system for proton exchange membrane fuel cells according to claim 1, characterized in that, The temperature-divided heat storage device is a vertical hot water storage tank. The internal temperature is maintained by the density difference formed by the difference in water temperature. Insulation baffles are respectively installed between the medium-temperature heat storage zone, the high-temperature heat storage zone, and the low-temperature heat storage zone.

3. The multi-grade waste heat recovery system for proton exchange membrane fuel cells according to claim 1, characterized in that, The low-grade waste heat includes waste heat from the fuel cell stack and waste heat from auxiliary components; the first waste heat recovery unit includes a fuel cell stack cooling branch, an auxiliary component cooling branch, a heat storage circulation branch, and a cooling branch; The fuel cell stack cooling branch includes the fuel cell stack, a first heat exchanger, and a first circulation pump; the first heat exchanger includes a low-temperature side channel and a high-temperature side channel; the inlet of the high-temperature side channel of the first heat exchanger is connected to the outlet of the fuel cell stack, and the outlet is connected to the inlet of the first circulation pump. The auxiliary component cooling branch includes the auxiliary component, the second heat exchanger, and the second circulation pump; The second heat exchanger includes a low-temperature side channel and a high-temperature side channel; the inlet of the high-temperature side channel of the second heat exchanger is connected to the outlet of the auxiliary component, and the outlet is connected to the inlet of the second circulating pump. The low-temperature side channels of both the first and second heat exchangers can be selectively connected to the heat storage circulation branch or the cooling branch. The thermal storage circulation branch can transfer the waste heat of the fuel cell stack and auxiliary components to the low-temperature thermal storage area when the low-temperature thermal storage area has thermal storage capacity. The cooling branch can dissipate the waste heat of the fuel cell stack and auxiliary components when the low-temperature heat storage area is saturated or when the equipment needs to be cooled.

4. The multi-grade waste heat recovery system for proton exchange membrane fuel cells according to claim 3, characterized in that, The thermal storage circulation branch includes a sixth circulation pump; the cooling branch includes a cooling device and a seventh circulation pump. The low-temperature side channels of the first heat exchanger and the second heat exchanger are connected in parallel, and the inlets of the low-temperature side channels of the first heat exchanger and the second heat exchanger can be selectively connected to the outlet of the sixth circulating pump or the outlet of the seventh circulating pump; the outlets of the low-temperature side channels of the first heat exchanger and the second heat exchanger can be selectively connected to the inlet of the low-temperature heat storage zone or the inlet of the cooling device; the inlet of the sixth circulating pump is connected to the outlet of the low-temperature heat storage zone; and the outlet of the cooling device is connected to the inlet of the seventh circulating pump.

5. The multi-grade waste heat recovery system for proton exchange membrane fuel cells according to claim 4, characterized in that, The first waste heat recovery unit further includes a first three-way valve, a second three-way valve, a third three-way valve, and a fourth three-way valve; the two inlets of the first three-way valve are respectively connected to the outlets of the sixth and seventh circulating pumps, and the outlet of the first three-way valve is connected to the inlet of the second three-way valve; the two outlets of the second three-way valve are respectively connected to the inlets of the low-temperature side channels of the first and second heat exchangers; the two inlets of the third three-way valve are respectively connected to the outlets of the low-temperature side channels of the first and second heat exchangers; the outlet of the third three-way valve is connected to the inlet of the fourth three-way valve, and the two outlets of the fourth three-way valve are respectively connected to the inlet of the low-temperature heat storage area or the inlet of the cooling device.

6. The multi-grade waste heat recovery system for proton exchange membrane fuel cells according to claim 5, characterized in that, The second waste heat recovery unit also includes a fourth circulating pump; the heat pump system adopts a vapor compression heat pump system; A vapor compression heat pump system includes an evaporator, a compressor, a condenser, and an expansion valve that are connected sequentially along the direction of fluid flow and form a closed loop; the evaporator is capable of absorbing heat from ambient air or from low-grade waste heat in the first waste heat recovery unit. The inlet of the fourth circulation pump is connected to the outlet of the low-temperature thermal storage area, and the outlet is connected to the inlet of the condenser on the condensing side. The outlet of the condenser on the condensing side can be selectively connected to the high-temperature thermal storage area, the medium-temperature thermal storage area, or the low-temperature thermal storage area through a multi-way switching valve. When the evaporator absorbs heat from the ambient air, the outlet of the low-temperature side channel of the condenser is connected to the low-temperature heat storage area. When the evaporator absorbs heat from the low-grade waste heat of the first waste heat recovery unit, the outlet of the low-temperature side channel of the condenser is connected to the medium-temperature heat storage zone or the high-temperature heat storage zone.

7. The multi-grade waste heat recovery system for proton exchange membrane fuel cells according to claim 6, characterized in that, The third waste heat recovery unit includes a fuel cell exhaust gas catalytic combustion waste heat circuit and a fifth circulation pump; the fuel cell exhaust gas catalytic combustion waste heat circuit includes a catalytic burner, a third heat exchanger, and a third circulation pump; the catalytic burner is used to treat fuel cell exhaust gas; the third heat exchanger includes a low-temperature side channel and a high-temperature side channel; the inlet of the high-temperature side channel of the third heat exchanger is connected to the outlet of the catalytic burner, and the outlet of the high-temperature side channel of the third heat exchanger is connected to the inlet of the third circulation pump; the inlet of the fifth circulation pump is connected to the outlet of the high-temperature heat storage area, and the outlet is connected to the inlet of the low-temperature side channel of the third heat exchanger, and the outlet of the low-temperature side channel of the third heat exchanger is connected to the inlet of the high-temperature heat storage area.

8. The multi-grade waste heat recovery system for proton exchange membrane fuel cells according to claim 7, characterized in that, It also includes a control unit; the control unit is communicatively connected to the sixth circulating pump, the seventh circulating pump, the fourth circulating pump, the vapor compression heat pump system, the third circulating pump, and the fifth circulating pump; The control unit is configured as follows: Start the third and fifth circulation pumps; Upon receiving the switch to thermal storage mode, the system connects the low-temperature side channels of the first and second heat exchangers to the thermal storage circulation branch and starts the sixth circulation pump. Upon receiving the switch to safe heat dissipation mode, the system connects the low-temperature side channels of the first and second heat exchangers to the cooling branch and starts the seventh circulation pump. Upon receiving a signal to switch to ambient heating mode, the system controls the start of the fan or pump on the evaporator side of the heat pump system to absorb heat from the ambient air, and controls the heat pump system to operate at a high energy efficiency ratio. Then, the system controls the outlet of the condenser side of the heat pump system to connect with the inlet of the low-temperature heat storage area, and starts the fourth circulation pump. Upon receiving the signal to switch to waste heat enhancement mode, the heat source of the evaporator in the heat pump system is switched to low-grade waste heat from the first waste heat recovery unit, and the heat pump system is controlled to operate at a low energy efficiency ratio. Then, based on the real-time outlet water temperature and the needs of the high-temperature / medium-temperature heat storage zone, the outlet of the condenser side in the heat pump system is connected to the inlet of the medium-temperature heat storage zone or the high-temperature heat storage zone, and the fourth circulation pump is started.

9. A method for recovering waste heat from a multi-grade waste heat recovery system based on any one of claims 1 to 8 of a proton exchange membrane fuel cell, characterized in that, Includes the following steps: The first waste heat recovery unit is activated to begin recovering the low-grade waste heat from the fuel cell system and transferring the heat to the low-temperature heat storage area or for safe system heat dissipation. The second waste heat recovery unit is started to recover the low-grade waste heat from the air recovered by the heat pump system or the first waste heat recovery unit, and the upgraded heat is delivered to the matching high-temperature heat storage area, medium-temperature heat storage area or low-temperature heat storage area. The third waste heat recovery unit is activated to recover the high-grade waste heat generated by the catalytic combustion of fuel cell exhaust gas and transfer the heat to the high-temperature heat storage area.

10. The recycling method according to claim 9, characterized in that, The first waste heat recovery unit is activated to begin recovering low-grade waste heat from the fuel cell system and transferring the heat to the low-temperature storage area or for safe system cooling. This includes the following steps: Monitor the status of the low-temperature thermal storage area; When the low-temperature thermal storage area has thermal storage capacity, the first waste heat recovery unit is controlled to transfer heat to the low-temperature thermal storage area. When the low-temperature thermal storage area is saturated or when it is necessary to ensure equipment cooling, the first waste heat recovery unit is controlled to perform system safety heat dissipation.

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